Seznam abstraktů 2015: POSTEROVÁ SEKCE C

The corrosion behaviour of four grades of valves steels i.e.; X33CrNiMn23-8, X50CrMnNiNbN21-9, X33CrNiMnN23-8, X50CrMnNiNbN21-8, X53CrMnNiN20-8 and X55CrMnNiN20-8 in combustion gases of fuel oil with different quantities of FAME (Fatty Acid Methyl Esters) has been studied.
In this work, the results of kinetic oxidation of above mentioned valve steels in combustion gases from diesel engine with 5, 10, 20% [v/v] of FAME are presented. It has been found that increase of FAME up to 20% volume percentage to the fuel oil decreases corrosion resistance of tested steels.
The corrosion tests have been performed gravimetrically under thermal shock conditions by heating of specimens from room temperature up to 1173 K. After heating at 1173 K for two hours, specimens were quenching at room temperature for 20 minutes and again heated. This experiment simulated valves work conditions of highly thermal loaded combustion engines.

This paper summarizes the most important results of research dealing with the use of magnetic spot-pole method and measurement of ultrasonic wave velocity for process control of castings made of austempered ductile, grey and vermicular-graphite irons. It describes the most important dependencies of measured physical quantities on the specific structure of these materials, especially the content of retained austenite. Suggests other possible developments of this control methodology.

Steel, which was designated to process as high-grade and hardening of surface was investigated from the point of views of magnetic and transport properties. The aim of this study is to describe the magnetic behavior, electrical resistivity and thermal conductivity of this material in case that it is applied for the components of magnetic circuits or some parts in an electrical equipment. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction and Mössbauer Spectroscopy. The temperature stability of the material was proved by measurements of temperature dependences of magnetic moment and electrical resistivity. The magnetic parameters were obtained by measuring of magnetic hysteresis loops in dependence on saturation fields and their frequencies. The parameters are discussed from the point of view of possible applications as a magnetic material, which can be stressed by enormous mechanical forces.

The macroscopic mechanical properties of steel are highly dependent upon microstructure, crystallographic orientation of grains and distribution of each phase present etc... Nanomechanical testing using depth sensing indentation (DSI) provides a straightforward solution for quantitatively characterizing each of phases in microstructure because it is very powerful technique for characterization of materials in small volumes. Measuring the local properties (indentation hardness HIT, Young’s modulus EIT, indentation energy: total W, elastic Wel, plastic Wpl) of each microstructure component separately in multiphase materials gives information that is valuable for the development of new materials and for modeling.
In this work, depth sensing indentation has been used to reveal mechanical properties of individual grains with various crystallographic orientations in steel sheets with various microstructure. An Electron Backscatter Diffraction (EBSD) analysis was used to determine the grain orientations, in which were made the nanohardness measurements.

The paper refers to the research on low-cycle fatigue of the selected wrought light-metal alloys, applied, inter alia, in the aviation technology. The material for the research consisted of hot-worked rods made of AZ31 magnesium alloy, Ti-6Al-4V two-phase titanium alloy and 2017A (T451) aluminium alloy. Low-cycle fatigue tests were performed using the MTS-810 machine in an oscillatory cycle (R=-1) for two ranges of total strain (1 and 1.2%). Based on the results obtained, characteristics of cyclic deformation of the tested materials were developed, as well as characteristics of their low-cycle durability. It was found that the titanium alloy had the highest fatigue durability expressed by the number of cycles until failure of the sample. The magnesium alloy showed much lower durability (by ca. 3 times), while the aluminium alloy had the lowest durability (by ca. 10 times).

The paper deals with the study of phase transformations temperatures of real steel grade. Phase transformations temperatures were obtained using Differential Thermal Analysis (DTA) and Setaram Setsys 18TM laboratory system. There are presented results from the low temperature region (below 1000 °C) and high temperature region (above 1000 °C). The extrapolation of obtained phase transformation temperatures to zero mass and heating rate is performed. The obtained phase transformations temperatures are discussed. Phase transformations temperatures are calculated using thermodynamic and kinetic software Thermocalc and IDS also. Experimentally obtained data of phase transformations temperatures are compared and discussed with calculated data. Experimentally obtained data are essential for thermodynamic calculations and they are used also as input data for numerical mathematical and physical models.

In work the presented numerical models of steel hardening processes take into account thermal, mechanical phenomena and phase transformations. In the model of phase transformations, in simulations heating process continuous heating was applied, whereas in cooling process continuous cooling of the steel at issue. The phase fraction transformed (austenite) during heating and fractions during cooling of ferrite, pearlite or bainite are determined by Johnson-Mehl-Avrami formulas. The theoretical model of phase transformations was then verified by experiments. The nescent fraction of martensite is determined by Koistinen and Marburger formula or modified Koistinen and Marburger formula. The stress and strain fields are obtained using the solution of the Finite Elements Method of the equilibrium equation in rate form. The thermophysical constants occurring in constitutive relation depend on temperature and phase composite. For determination of plastic strain the Huber-Misses condition with isotropic strengthening was applied whereas for determination of transformation plasticity a modified Leblond model was used. A satisfactory agreement was found.

Monitoring the mechanical properties changes is very important to assure structural integrity of NPP components, especially within the context of their operational life extension. Determination of current mechanical properties of several structural materials of NPP components, especially reactor internals, is not possible using the standard testing methods, in connection with the material volume necessary for the testing. In comparison with reactor pressure vessel, reactor internals are usually not covered by the system of surveillance samples as well as other hardly replaceable components of the primary circuit, e.g. primary piping, steam generator etc. Sampling of the optimal material volume usually brings adverse consequences of affecting the integrity of component or in several cases destruction of the whole evaluated component. For standard size specimens, it is also necessary to take into account the high activity of the material, with influence on the collective dose of hot cell facilities personnel. Aim of this work is to present the advantages of the semi-destructive testing method (instrumented hardness test method) in the process current mechanical properties evaluation of the hardly replaceable long-term operated NPP components. Semi-destructive testing techniques (instrumented hardness test method) use technological processes and equipment enabling the direct determination of mechanical properties from the component surface without affecting its integrity. Advantage of semi-destructive degradation mechanisms quantification could be very promising for use in the field of nuclear energy for components of NPP as well as in other industrial sectors, e.g. chemical and petrochemical industry.

In this study, cryogenic treatment is applied to compacted graphite cast iron which is used for clutch pressure plate in automobile. After cryogenic treatment, microstructural investigations, macro and micro hardness test and wear tests were carried out. Cryogenic treatment is applied which the cooling rate of 2 °C per minute to -196 °C and had stood at this temperature at specified times. Optical microscope and SEM techniques were used to examine the changes in the microstructure and worn surface. Rocwell B and Vickers were drawn on in determining the macrohardness and microhardness changes. Wear tests were carried out dry conditions by using ball-on-disc method for each times of cryogenic treated and untreated samples with 5 N normal load, 2,5 mm radius, 100 meters sliding distance and 10 cm/s sliding velocity. Specific wear rates of cryogenic treated and
untreated samples compared each other. Result of the comparisons, both wear rates of cryogenic treated samples decrease according to untreated samples. Test with 5 N normal load, wear resistance of the sample which cryogenic treated at 12 hours was improved %68,7.

In the paper are presented the calculations of temperature field, volume fractions of structural components and strains during multipass GMAW surfacing of a prismatic element made of S235 steel. In the description of temperature field is used the bimodal heat source model. The solution takes into consideration heating caused by the welding heat source during overlaying subsequent weld beads and self-cooling of already padded areas. Highest temperatures enable to determine characteristic heat-affected zones. Critical temperatures A1 and A3 are used to determine partial and full austenitic transformation zones, while the temperature of solidus to determine the fusion line. Kinetics of phase changes during heating is limited by temperature values at the beginning (A1) and at the end (A3) of austenitic transformation. In order to quantitatively describe the dependence of structure and material quality on temperature and transformation time of over-cooled austenite during surfacing, time-temperature-transformation at continuous cooling (TTT) welding diagram is used. The structural and thermal expansion coefficient values are determined on the basis of authors’ own dilatometric research. For calculations are used authors’ programs made in Borland Delphi. The results are presented in the form of temperature and volume phase fraction distributions in the element’s cross section as well as thermal cycles of volume phase fractions and strains at a selected points.

This paper analyzes the effect of work hardening on the behavior to cavitation erosion for the low alloyed steel 16MnCr5.
Cavitation tests were conducted on a vibrator device with piezoceramic crystals, which fully complies with the requirements imposed by the ASTM G32 – 2010.
The evaluation of behavior at cavitation erosion was made based on curves gradient of hardness on the section of layer hardened by cold plastic deformation, as well as the variation curves of cavitation parameters MDE (depth of penetration of erosion) and MDER (penetration rate of erosion) with the duration of test. The topography of surfaces damaged by cavitation and the structural changes resulting in marginal layer were analyzed with light microscopy and scanning electron microscope, they justified the significant increases of resistance to cavitation erosion.

It was revealed that it is possible to form a ferritic - bainitic microstructure with retained austenite in the 35CrSiMn5-5-4 structural steel. This microstructure was produced during intercritical annealing which allowed the determined volume fractions of austenite and ferrite to be obtained. The subsequent austempering performed in the temperature range of bainitic transformation led to obtaining a microstructure composed of carbide-free bainite with retained austenite and of the ferrite grains with carbides. After the aforementioned treatment, this steel may be classified as one of the multiphase steels (TRIP - Transformation induced plasticity) which belong to the broader group of Advanced High Strength Steels (AHSS).
The preliminary heat treatment conducted before isothermal quenching from the incomplete austenitisation led to the greater refinement of the microstructure, in which the width of ferritic areas was in the range of 200-700nm. The thickness of bainite plates was about 100-200 nm in both cases, while the average thickness of the austenite layers was about 100 nm. Due to this preliminary step of heat treatment, 35CrSiMn5-5-4 steel gains higher strength and plasticity parameters in comparison to the steel after the treatment without the preliminary heat treatment step.

Pitting is a type of fatigue wear of the material subjected to cyclic loading, especially occurring in the gears or bearings. Si-DLC coatings are currently used due to their excellent properties such as low friction coefficient, high hardness and wear resistance. Tribological studies of 30CrMoV9 steel samples with Si-DLC coating wereperformed using four ball testing machine T03 used for surface fatigue resistant test condition. Analysis of pitting cracks was made using a profilometer, light microscopy and scanning electron microscopy. The experimental results were compared with the theoretical model.

This article deals with the new results from measurement of mechanical properties of P92 welded joints. Tested specimens (welded joints of P92 steel) were prepared using GTAW technology (141). After the welding the different modes of Post Weld Heat Treatment (PWHT) were made and the values of hardness, tensile strength and impact toughness of weld metal and heat-affected zone (HAZ) were measured. The aim of the research is to find the dependence between the mode of PWHT and the mechanical properties of weld metal and heat-affected zone. This study contains mechanical properties of P92 welded joints obtained in the years 2011-2014.
Because P92 is modern heat-resistant high-alloy steel used in thermal power plants with supercritical parameters (600°C/30 MPa), it is necessary to find out the mode of Post Weld Heat Treatment where the advantageous combination of mechanical properties will be achieved.

Effects of weld path curvature on microstructure and mechanical properties of structured sheet arc welded joints are studied. Solution of the direct heat conduction problem is obtained by the Green's function method. Optimisation problem for obtaining a constant weld or heat affected zone width is formulated and solved numerically. By way of example the optimum power distribution along the curved weld path in arc welding of a 0.7 mm thick steel panel is presented.

The quality and efficiency of the reheating process has a profound effect on the austenite grain size and uniformity of grain size along the entire length of the slab or billet. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size. This reheating step in the steelmaking process often receives low priority in the evaluation of product quality and mechanical property performance. In laboratory studies, the furnace heating step is typically quite uniform resulting in a homogeneous and fine prior austenite grain size. Unfortunately, in industrial operations, it is much more difficult to control the uniformity of heating along the entire length and through the thickness of the work piece. Such inhomogeneity and efficiency of heating is highly influenced by several combustion process variables such as the air to gas ratio, furnace burner condition, furnace pressure and refractory condition. The optimum air to gas ratio of 1.10 yields the highest adiabatic flame temperature. However, often in actual operations, cracked burner orifice plates, poor burner tuning and inefficient combustion fan performance contribute to variations in the air to gas ratio. These situations have a huge effect on the optimal adiabatic flame temperature performance which translates into inhomogeneous austenite grain size and variations in mechanical properties in the hot rolled product. Corrective actions and operational practice recommendations to minimize inhomogeneous heating effects on product quality are presented.

The corrosion behaviour of four grades of valves steels i.e. X33CrNiMn23-8, X50CrMnNiNbN21-9, X33CrNiMnN23-8, X50CrMnNiNbN21-8, X53CrMnNiN20-8 and X55CrMnNiN20-8 in combustion gases of petrol with different of ethanol volume percentage has been studied. In this work, the results of kinetic oxidation of above mentioned valve steels in combustion gases of petrol-ethanol mix with 5, 10, 50% [v/v] of ethanol are presented. It has been found that increase of ethanol in a petrol-ethanol mix up to 50% ethanol volume percentage decreases corrosion resistance of tested steels.
The corrosion tests have been performed gravimetrically under thermal shock conditions by heating
of specimens from room temperature up to 1173 K. After heating at 1173 K for two hours, specimens were quenching at room temperature for 20 minutes and again heated. This experiment simulated valves work conditions of highly thermal loaded combustion engines.

Since most of the test stands for tensile test are computer controlled today, measured test data are also evaluated by automatic software tools. The article focuses on comparative study of different algorithms used for automatic evaluation tensile test results. Four different algorithms were applied on real data obtained from fifteen specimens. The specimens were made of various materials and therefore with different strain-stress curves.
Discussion of deviations in results (ultimate stress, yield stress, ductility and Young’s modulus of elasticity) is provided.

The Danish coal-fired Ultra Super Critical (USC) plant, Nordjyllandsværket, was commissioned in 1998 with 290 bar and 580°C/580°C steam data. The boiler was designed as an USC once-through Benson tower type boiler with double reheat. The challenging steam conditions required the use of state of the art materials, such as P91 or TP347HFG for the construction of the boiler. The plant has now reached 100.000 hours of operation. Taking advantage of the boiler maintenance programme, tube sections were removed from more than 20 different locations in the boiler during the 2012 summer shutdown to assess the materials conditions of the boiler. The tubes have been investigated to document wall thickness, fireside corrosion and steamside oxidation rates
and morphology and microstructure evolution after 100,000 hours exposure. The mechanical and fracture properties were obtained using small punch test technique (SPT) as well as using miniaturized tensile test specimens. This data together with the temperature data of the plant will serve to give a lifetime evaluation of the boiler components. The present paper focuses on investigations and modelling of the influence of sigma phase precipitation on mechanical and thermal stability of the austenitic alloy TP347H that was used as a construction material for superheaters and re-heaters. Obtained results show that even very small amounts of sigma phase affects fracture behaviour significantly. Drop in fracture properties can be clearly identified using miniaturized test specimens or SPT.

The high carbon steel rods are designed for the manufacture of wire on the rope and steel cords. They are produced in a continuous rolling mills with accelerated cooling device. High carbon wire rods should have a uniform pearlitic structure at cross section and a longitudinal which guarantees high tensile strength and relatively good plasticity. In practice rolled high carbon steel rods (0.40 ÷ 0.94% C) should have a uniform pearlite structure with uniformly distributed cementite plates having a thickness of 0.02 ÷ 0,04μm and the distances between the plates at 0.1 ÷ 0.2μm. That type of pearlitic structure ensures good plasticity.
The paper presents results of research on the influence of cooling conditions of high carbon wire rods (C70D and C46D) on the morphology of pearlite. For thermo-plastic treatment a deformation dilatometer DIL 805A / D was used. The samples after deformations were cooled to temperature to obtain pearlitic structure. The metallographic analyze of samples were done and morphologies perlite were determined. As a result of the research was to describe the dependence of the distance inter plates (Lm) as a function of the cooling rate after deformation. It will be used to the design high carbon wire rods cooling technology with high level of plasticity after rolling processes.

Formed parts of the car-body represent cyclic loaded products. For the proper design of these parts is very important not only knowledge of deformation and stress material behavior at production by forming technologies but important is also knowledge of other factors which influence subsequent product utility properties at the car operation. It´s obvious that truly important parameter for the proper car-body part proposal is the fatigue strength of the given material. Regarding fact that formed parts from steel sheets are during production cut by several different technologies is submitted paper focuses on the determination of material cutting influence on the fatigue strength. For experiment there was chosen ultra-high strength TRIP steel and the most commonly used material cutting technologies (shearing, abrasive water jet and laser). For samples prepared as mentioned was on the six stress levels observed material cutting influence on the achieve number of cycles up to fracture. Results of experiments were compared with the reference samples which were machined. Results from measurements are presented mainly graphically as stress versus number of cycles and fracture surfaces images.

The residual lifetime assessment and the risk of a possible service components failure are critical issues in the safety and reliability analyses of industrial plants. The residual lifetime can be evaluated by the standard mechanical test techniques, such as the tensile test, uniaxial creep test, the Charpy or the fracture toughness test. Fracture mechanics in particular has attained high significance in establishing ultimate load limitations and assessing the integrity for a large number of engineering structures of multifarious types.
Standard mechanical tests used to determine the fracture toughness involve extraction of large blocks of material and therefore are not applicable to in-service components. The development and in-service application of essentially non-destructive, miniature material sample removal systems (e. g. the surface sampling systems, such as Electric Discharge Sampling Equipment - EDSE) provided the practical incentive for development of small specimen test methods to evaluate material properties, e. g. fracture toughness. The EDSE can cut out small slices (‘boat sampling’) about 3 mm thick and approximately 20 mm wide x 25 mm long from thick-section components leaving behind cavities with round edges that usually do not require repair.
In this study, two different methods will be used for fracture toughness determination: Small Punch Test and multiple-specimen method using subsize Charpy specimens (3x4x27 mm). Both methods require very little experimental material and specimens can be made directly from the removed ‘boat sample’ by the EDSE. The applicability and reliability of both methods will be discussed.

The paper below presents the results of studies of the flexible SuperCor SC-57S structure built by Polish manufacturer ‘ViaCon Polska Sp. z o.o.’ at their test site in Rydzyna. The tests aimed to examine the behaviour of the steel shell and soil structure in the construction phase. The measured quantities included the displacement, determined through geodetic surveys, and stress, recorded with a set of strain gauges. Values of internal forces that occur in the structure were determined. The conclusions based on these results, may be helpful in understanding the behaviour of flexible steel shell and soil structures in the construction phase.

In this study, the effect of different traverse speed on abrasive water-jet (AWJ) of hardox 400 steel was experimentally investigated. In the experiment five different traverse speeds of 20, 40, 60, 80 and 100 mm/min were used. After the cutting the qualitative aspects, especially surface roughness, and the analysis of 3D surface topography were measured. The experiment was carried out on the water-jet machine with pump power of 18.5 kW generating working pressure 280 MPa. Few well known relations have been proven. First of all, the highly growing surface roughness parameters with increasing traverse speed. Another relation is that the smallest values of surface roughness parameters are obtained for profile close to the upper edge cutting surface. Contrary, the profile close to the bottom edge is characterized by a significant increase of surface roughness with increasing traverse speed. The smallest declination angle was obtained for the slowest traverse speed. The good cutting quality is associated with a slower traverse speed but longer time of cutting brings higher costs, since the process consumes a greater quantity of water, electricity and abrasive. Therefore, some optimization is suggested to make process sufficiently precise and economic.

Phase composition of the steel P91 during annealing was studied with the aim to reveal the evolution of new phases. In this paper, the precipitation was characterized using energy-dispersive X-ray spectroscopy (EDS) and electron diffraction in transmission microscopy (TEM). Only Nb-rich particles were found in the studied samples austenitized at 1423°C for 20h and water cooled. After tempering at 673°C for 2h, the formation mainly M3C type carbides and after tempering at 873°C for 2h, the formation of M7C3 and M23C6 was observed. These structure changes play an important role for stability and also carbon diffusion.

Deformations occurring during welding are one of the major problems in the design of welded constructions. The character and size of deformations depends on the physical properties of the material, rigidity of a construction and the welding method. The proper selection of the welding technology can reduce deformations in a large extent. Unquestionable advantages of laser welding contribute to the very intense development of this technology and wide application in industry. However, the proper use of this joining method requires a quantitative analysis and control of occurring deformations in welded joints for assumed various process parameters. At the time the computer simulations by mathematical and numerical modelling of physical phenomena occurring in the process becomes a helpful tool.
This work concerns numerical simulations of thermomechanical phenomena in laser butt-welding of sheets made of X5CrNi18-10 steel. Abaqus FEA software is used in calculations taking into account phase transformations during material’s state changes and temperature dependent thermomechanical properties of analyzed steel. Additional numerical subroutines are implemented into Abaqus solver in order to describe the movable heat source power intensity distribution.
The shape and size of melted zone is predicted as well as residual stress and deformations. Real butt-welded joints are executed in order to verify the results of numerical simulations. Numerically predicted deflection of the joint is compared to real displacement, measured using profilographometer New Form Talysurf 2D/3D 120. Melted zone of the cross section of the joint is compared to numerically predicted geometry of the fusion zone.

A creep damaged area was found during the routine control of the steampipe bend of 200 MW fossil-fuelled power plant boiler close to the outer fiber and near the top of the bend. The damaged area with identified creep cracks was about 250 x 600 mm in size and the maximum depth of the cracks was 7 mm. Metallographic analysis carried out in this area confirmed the non-homogeneous cavitation damage. Density of cavities continuously decreased throughout the affected area from the outer to the inner surface of the pipe, around the pipe circumference and also in the axial direction along the length of the bend.
The actual extent of degradation of material properties was then evaluated by testing the mechanical properties, notch and fracture toughness and the results were used to calculate the residual life of the bend. The results of these analyses showed that although the creep damage extent was probably one of the worst, which had been ever detected in the boiler of this type, cracks would propagate through the bend by stable growth until the mid-wall thickness and only then would the final rapid failure occur. This result confirms the possibility of extending the life of the steampipe bends far beyond the limits of the currently used criteria.

This article presents a method for software assessing the level of axial segregation of wire rod. This so-called center segregation is routinely determined visually as dark spots on the etched cross-section wire, which classifies comparison to a etalon. The result is a class of characterizing the degree of segregation in the axial wire. The disadvantage of the visual evaluation is considerable subjectivity in evaluating particularly borderline levels of segregation and mere categorical variable characterizing the degree of segregation. Software evaluation eliminates these drawbacks. The evaluation algorithm still works in the same way and the output is a quantitative variable, which can be further processed statistically. Measurement is faster, more accurate and more objective. The paper gives an example of a software evaluation of the level of segregation in the rolled wire before and after modernization of wire rod mill in Trinec Ironworks, Inc.

Steel is the most popular structural material. The properties and practical applications of all constructional materials, including steel, are determined mostly by their structure. Non-metallic inclusions are one of the factors that influence the fatigue strength of steel. The physical and chemical reactions that occur in the process of steel melting and solidification produce non-metallic compounds and phases, referred to as inclusions. The quantity of non-metallic inclusions is correlated with the content of dopants in the alloy, while their phase composition and structure, in particular shape, dimensions and dispersion, are determined by the course of metallurgical processes.
The experimental material consisted of semi-finished products of high-grade, medium-carbon structural steel. The production process involved two melting technologies: steel melting in a 140-ton basic arc furnace with desulfurization and argon refining variants and in a 100-ton oxygen converter and next subjected to vacuum circulation degassing. Billet samples were collected to analyze the content of non-metallic inclusions with the use of an optical microscope and a video inspection microscope. The application of various heat treatment parameters led to the formation of different microstructures responsible for steel hardness values. Examination was realized on calling out to rotatory curving machine about frequency 6000 periods on minute. The objective of this study was to determine the influence of size proportions and distances between the fine non-metallic inclusions (up to 2 µm in size) on bending fatigue strength of high plasticity constructional steel. The results revealed that fatigue strength is determined by the analyzed parameters and tempering temperature.

Managing instrumentation and control obsolescence, improving the safety, and extending the lifetime of older nuclear reactors (such as VVER-440) are the primary objectives of nuclear power plants in Central and Eastern Europe. Extending reactor life to 60 years and beyond will likely increase susceptibility and severity of known forms of degradation. Additionally, new mechanisms of materials degradation are also possible. Therefore, it is necessary to examine on a regular basis structures, systems and components of the reactor facility using specific techniques such as those based on non-destructive testing to conduct special inspections with varied objectives. The main purpose of this paper is to present the advanced procedures for monitoring degradation processes under static and dynamic loading (simulation of operational loading of pressure equipment) using acoustic emission technique. It is one of the most powerful non-destructive methods for assessing active processes occurring in the loaded material. Experiments have been performed on specimens made of Cr–Ni–Mo–V nuclear ferritic steel (known as 15Ch2NMFA) at room temperature. The acoustic emission results showed a clear response to loaded specimens with and without a crack.

From the economic reasons many products originally made from austenite stainless steel are nowadays made from ferritic stainless steel. Ferritic steels have relatively low yield strength and the work hardening is limited. They cannot be hardened by heat treatment and only moderately hardened by cold working. Commercially made stainless steel tubes from ferritic steel, used for industrial plumbing was examined on presence of cracks. The cracking was present on the inner side of the convoluted tube shape. The tube manufacturing process consisted of continual bending of the sheet to tube shape, weld the tube, then of cold shaping by pulling through rib-forming frames, which is done in several steps. Then thermal treatment applies to the nearly finished product to remove stress remaining in the structure. Prime suspect was deformation beyond the ductility of used material. However the stress-strain tensile testing does not approved this hypothesis. Several samples of failed material were taken together with reference, and were examined by optical microscopy, and X-Ray Diffraction structure analysis. The structure of the cracked tubes does not show the signs of deformation over the limit, except the location near to the crack itself. Interestingly enough the failed material showed more homogenous structure than the original one. Needle like structures were found when the material is “over-etched”, on these structures concentration of stress under bending occur. This structure was identified as δ-ferrite, however its presence in α-ferrite matrix is unclear.

Ferritic-martensitic P91 grade steel is widely used for manufacture pipes and boilers of thermal and nuclear power plants due to its high strength and creep behaviour at high temperatures and the advantage of small thermal stress in cyclic operations. During the long-term operation of power plant components under elevated temperatures and steam pressure the changes of steel structure occur, on which those mechanical features and remnant service life depend. Due to diffusion processes at elevated temperatures, alloying elements replace iron within carbides, leading to more thermodynamically favoured alloy carbides precipitate and coarsening as well as lattices parameters of those changing.
To obtain necessary structural information for evaluation of the operational state of P91 steel the investigation of thermal ageing effect on the changes of crystal structure parameters of M23C6 carbide during long term thermal exposure at 600, 650 and 700 °C temperatures have been performed. The identification of alloy carbides and calculation of their lattice parameter changes have been accomplished by XRD analysis using crystal structure parameters evaluation and Rietveld refining programs.
X-ray diffraction study revealed that carbide M23C6 crystal lattice parameter a changes from a = 1.0635 nm to a = 1.0655 nm as a function of heat exposure in the laboratory conditions. Johnson-Mehl-Avrami low was applied for the calculation of carbide M23C6 crystal lattice parameters.

This paper presents the results of studies of X37CrMoV5-1 steel subjected to a nanostructuring process consisting on one- and two-step isothermal quenching. The Transmission Electron Microscopy (TEM) observations showed that steel after one-step quenching consisted of carbide-free bainite plates of nanometric width separated by thin layers of austenite. The microstructure contained also austenite blocks partially transformed into martensite during final quenching to room temperature. The high content of austenite led to high plasticity and moderate strength of steel. In order to improve the strength parameters, it was necessary to reduce the content of austenite. To achieve this goal an innovative heat treatment consisting on two-step isothermal quenching was proposed. The parameters of this process were designed basing on the results of dilatometric tests. The second step of the isothermal quenching was set below the initial Ms temperature. No martensitic transformation was recorded during the dilatometric tests, because of gradual carbon-enrichment of austenite during the first step of bainitic transformation. By use of magnetic tests and TEM observations it was shown, that the two-step heat treatment led to an increase in the bainitic ferrite content, which resulted in an improvement of strength with no decrease of the plasticity of steel.

The work deals with hydrogen susceptibility of joint of explosively welded anticorrosion steel of 18Cr/10Ni type with titanium of commercial purity. Studied welds were after twice heat treatment and those were tested in corrosive solution in accord with NACE Standard TM0177-2003 (sulphide stress cracking under stress), representing dynamic test. Threshold level layed close to 40 MPa, approximately. The sources of failure were intermetallic phases of the Fe2Ti type detected using EBDS. Results were confronted with former results and accessible literature.

In this paper is analyzed, through comparison, the cavitation erosion resistance of Duplex stainless steel, with a microstructure of aprox. 50% austenite and 50% ferrite, solution annealed from 1060oC with water cooling and finally nitrited at 520oC for 40 hours in an ammonia environment.
The cavitation test results were expressed by variation of cumulated mass loss with the attack time and through the correlation between the attacked surface roughness and the erosion resistance.
The microstructure investigations, with an optical microscope and electronic scanning microscope, explains the erosion mechanism of the surface layer, by starting and propagation of microcracks.

The article presents preliminary results of microwelding thin sheet occurred of superalloy H 230®. There were shown the possibilities of combining thin metal sheet using resistive pulse microwelding. The joints were made using a device to microwelding SST WS 7000s. For characterizing of the obtained weld tests properties there were examined mechanical properties like: measuring the microhardness, tensile tests and microstructure observation. Microhardness measurements of the joints and base material where taken using Matsuzawa Vickers MX 100 type with applied load 100G (0.98 N). Tensile test where made on Zwick/Roell Z100 machine with applied load 100N. To observe mentioned joints, metallographic microscope Nikon Eclipse MA200 was used. The studies determined the basic parameters of microwelding thin sheet of joint made and the quality of the weld. The results showed that there is a possibility of obtaining the satisfying quality joint using microwelding between the thin sheet from superalloy H 230®.

Nanostructured chalcopyrite CuAlxGa1-xTe2 (x =0.25, 0.50 and 0.75) has been prepared by ball milling of Cu, Al, Ga and Te precursors. Preliminary ab initio calculations of the main properties have been performed on the prototype chalcopyrite semiconductor CuAlGaTe2. The simulation method used is based on the density functional theory within the framework of pseudo-potentials and plane waves. Band structure calculation suggest that CuAlxGa1-xTe2 is a direct bandgap semiconductor having band gap = 1.35 eV. In the experimental part, X-ray diffraction analysis revealed the presence of (112), (220)/(204), (312)/(116) and (400) reflections for all the milled powders characteristic of the chalcopyrite structure. Shift in peaks towards higher value of 2 is observed with the increase in Al composition. Lattice constants a and c are found to decrease with the increase in concentration of aluminium. With increasing Al content, it is found that the average crystallite size decreases and the bandgap energy increases from 1.34 eV to 1.51 eV. Compared with experimental data, calculated results by GGA–mBJ functional quantitatively agree with experimental data.

The paper presents the results of microstructure for ductile iron with the addition of Ni, Cu and Mo and presented graphs: TTT - illustrating the range of phase stability depending on the time of isothermal heating at a given temperature, CCT diagram - illustrating the range phase stability during continuous cooling at a predetermined rate.

Paper analyzes the influence of the surface properties on the ultrasonic cavitation erosion of the complex alloyed bronze AMPCO M4 in two states: extruded and heat treated (quenched + tempered) and afterward work hardened through mechanical percussion. The cavitation erosion was realized in a laboratory facility which respects integrally the indication of the ASTM G-32 Standard. Aditional hardness measurments of the cavitation-affected surface layer have been performed, as well as roughness measurements. All the same, by scan microscopy SEM, evidence was made of the destruction, that are an effect of the treatment of mechanical percution.

The methods of intensive plastic deformation SPD (Severe Plastic Deformation) belong to a group of very attractive means of increasing utility properties of metallic materials (strength and structural characteristics). The paper is focused on experimental verification of weldability of high-carbon steel C55E processed by the SPD DRECE (Dual Rolling Equal Channel Extrusion) process. Within experimental works, test welded joints were made from the C55E steel with the use of 15-PAW single or double thermal cycle. A test of basic mechanical properties, metallographic examination and an analysis of residual stresses were performed on these joints. Acquired results show that the choice of an appropriate technology and the optimization of welding parameters and thermal cycles allow to achieve solid welds even in the case of materials rather difficult to weld. The optimized welding process does not significantly degrade the properties acquired by SPD.

Process of heat treatment of cast ductile iron involves two stages: austenitising at temperatures in the range 850-950 oC with following austempering of alloy in the temperature range of 250-380 oC. Resulting microstructure contains ferrite saturated in carbon in a matrix of reacted high carbon austenite with a spherical graphite, typical of ductile iron. This microstructure offers high mechanical properties of the alloy. The microstructure and mechanical properties of ADI depends on the kinetic of phase transformation during austempering.
Kinetic model of phase transformation during austempering of undercooled austenite of ADI iron was developed. The model is based on Fick’s diffusion laws. The solution of the differential equations is carried out using Finite Difference Method, explicit scheme, under the boundary conditions adequate for the austempering temperature. In calculations the effect of carbon content in austenite on its diffusion coefficient was considered. The model and developed computer program enable to trace the process of ausferrite growth. Using developed computer program the effect of isothermal annealing temperature on growth rate of ferritic phase was investigated. The results of calculation were compared with experimental data and good agreement was observed.

It is generally recognized that the high content of non-metallic inclusions in structural steels alter their physical and mechanical properties. Formation of non-metallic inclusions is a complex phenomenon that depends on the composition, pressure and temperature of the working media. By use of different surface analysis techniques we analysed an austenitic stainless steel pipe that has been contaminated by petroleum products as a result of diffusion and concluded that the liquid medium penetrates relatively far into the metal by adsorptive migration, resulting in formation of chemically active sites that promote the formation of intermetallic compounds. It is important to understand this mechanism as it directly influences corrosion and further failure of the steel, leading to problems that translate into human and economic losses.

The formation of austenite above A1 temperature plays very important role in the heat treatment of hypoeutectoid steels, especially automotive DP steels. It is widely accepted that the formation of austenite during intercritical annealing takes place in three stages: 1 – very rapid pearlite to austenite transformation, 2 – slower growth of austenite into ferrite, 3 – slow final equilibration of ferrite and austenite. According to the literature data, important factors that influence the phase transformation kinetics are the cementite morphology, the grain size and the heating rate.
In this work, experimental results of dilatometric examinations of low alloy normalized hypoeutectoid steels show that during heating at the same rate, temperature range of pearlite to austenite transformation strongly depends on the amount of alloying elements. ThermoCalc and DICTRA computational tools were also used to calculate the eutectoid regions of the equilibrium phase diagrams for some low alloy hypoeutectoid steels.

Analytical models used for the analysis of phase transformations as well as the prediction of structural composition of welded elements are the subject of research for many years. Models are still developed and upgraded. Despite of certain simplifications they are invaluable in assessing the weldability and welding conditions. Results obtained by analytical methods are often used for the initial analysis of the material properties prior to the experimental studies and used before developing of mathematical models. The use of analytical methods in the analysis largely eliminates the expensive and labor-intensive technological research, which contributes to the speed up and reduction of costs of the development of welding technology.
The paper presents an analysis of phase transformations in solid state during welding of S460 steel. Empirical relations are given with the cooling rates taken into consideration, on which start and finish temperatures of bainite, ferrite, pearlite, and martensite transformation are determined. Obtained data allowed predicting different start and finishing temperatures of phase transformations for various cooling rates v8/5 (t8/5). Analytical diagram CCT for steel is determined as well as volume fractions of phases in a function of cooling rates. Analytically obtained results are compared with experimental data obtained by dilatometric tests.

Development of advanced materials requires knowledge of relationship between microstructure and mechanical properties. Traditional high voltage scanning electron microscopy (SEM) can become insufficient for advanced materials exhibiting complex micro- and nano-structure.
Benefits of using slow electrons have been known for more than two decades [e.g. 1,2]. Experiments reported here have been done with a XHR SEM Magellan 400L (FEI Company) equipped with two detectors for secondary electrons (SE), an Everhart Thornley detector and an in-lens TLD detector, and with a solid state BSE detector bellow the pole piece of the objective lens. The microscope is equipped also with the beam deceleration (BD) mode with negatively biased specimen [3]. In this mode, the electric field around the specimen not only retards the primary electrons but also accelerates the emitted signal electrons towards detectors. Furthermore, high angle backscattered electrons (BSE) are collimated towards the optical axis and detected. These electrons carry mainly the crystal orientation contrast. SE and low angle BSE are detected by the TLD detector.
Examined material was X210Cr12 steel subjected to the high-pressure torsion (HPT) process at elevated temperature, leaving material heavily strained. Commercial EBSD device was found unable of resolving grains due to their small size and lattice distortion.
The sample was also observed using the BD mode. These micrographs reveal elongated grains sized about 70 x 1000 nm. Imaging time for the BD mode is comparable with the standard SEM speed and hence much shorter than that of the EBSD mode, providing moreover higher lateral resolution.

In this article, the pearlitic and ferritic transformations during isothermal heat treatment were studied for ductile cast iron and Cu containing ductile iron under different holding times. The austentising time and temperature were selected to be 120 min and 920 ⁰C, respectively, referring to previous studies. The isothermal heat treatments were performed at 486 ⁰C and 586 ⁰C for different durations. Microstructures have been examined by optical microscopy and scanning electron microscopy. The microstructure of treated ductile cast iron consists of spheroidal graphite which is randomly dispersed in a matrix consisting of bainitic-ferrite, pearlite and carbon enriched retained austenite. It has been shown that the former austenite grain boundaries are the preferred sites for pearlite and ferrite nucleation.

Oxide-dispersion-strengthened steels MA957 and ferritic-martensitic EUROFER97 alloy have been selected as a candidate materials for Tritium Breeding Blanket (TBB) for fusion reactors. TBB is a key component for production and recovery of tritium where a radiation damage at high neutron fluence and temperature range 250–650 °C are expected. It limits the choice of structural material and leads to the choice of helium (He) as the blanket coolant.
This work presents results of the study where the oxidation behaviour of two selected materials (MA957; EUROFER97) under high temperature helium is compared. Microstructure of those materials and the interaction with He and He effects on both types of steel were investigated. The average exposure temperature was held at 720 °C. Subsequently, the weight changes were determined. Impact testing and material surfaces were studied in detail by means of SEM and TEM microscopy. It is essential to understand the He effect on microstructure and mechanical properties of structural materials since the He embrittlement in TBB may be significant.

The cavitation erosion resistance of the stainless steel was studied with ultrasonic vibration equipment, at a frequency of 20 kHz and oscillation amplitude of 50 μm. Varying the holding duration in the annealing solution at a constant temperature, causes changes in both, in the terms of the undissolved austenite chemical compounds (carbides, inter-metallic phases) phases proportion, as well as in the size of the crystal grains.
The cavitation test results were compared with those obtained by standard OH12NDL steel used in the manufacturing of hydraulic turbine blades Kaplan of the Iron Gates I, Romania. Optical and electronic metallographic examinations and hardness tests have shown, that by heat treatment, obtaining a fine and homogeneous microstructure with a high resistance to plastic deformation, provides an improvement in the cavitation behavior .

Fe-Cr-Nb ternary alloys with different concentrations of iron (60-95 at. %) are arc melted and characterized systematically by means of differential thermal analysis, optical and scanning electron microscopy coupled to an energy dispersive X-Ray microprobe analysis and X-Ray diffraction.
In the present paper, solidification sequences are proposed in relation to the observed microstructures for Fe-Cr-Nb synthesis alloys. Correlations have been established leading to the conclusion that different eutectic structures (lamellar, globular, acicular…) are involved.
Microstructures of alloy studied can be divided into three family of competition eutectic structure. For the first family, one eutectic phase are obtained for the 75 at.%Fe alloy , it takes place at 1234°C in form of Chinese script. The second type of eutectic has appeared for the 65 at.% Fe alloy in form of Chinese script, this phase is detected by DTA to 1390°C with the another eutectic at 1340°C. The last phase eutectic is obtained for the 65 at.%Fe alloy in regular form located in interdendritic space at 1382°C.

The process of dynamic strengthening of Hadfield steel, currently widely used for cast railway frogs, was studied. Continual dislocation hardening up to the depletion of plasticity and creation of surface microcracks presents the specific limited state under rolling contact in this application. The narrow affected zone and intensive mechanical and structural heterogeneity on the loaded surface are restrictive for standard mechanical testing.
To study the different states of this process, instrumented indentation tests were performed. The results showed the possibility of comparative evaluation of the elastic-plastic behavior of this steel, which is typical with high dynamic durability, but also with the significant sensibility to the ratio of normal impact loading vs. tangential slip. Because of this, an important parameter of fatigue life is the primary state of dynamic strengthening. The influence of explosion hardening, as a prospective way to improve the wear resistance of Hadfield steel, was included in the test. Each step of the degradation process was simulated using the special rolling contact stand at a defined loading condition. The measured hardness gradient of loaded surface layers displayed the depth and intensity of the induced changes. Martens hardness was measured in thus identified layers for each representative state of material. The elastic-plastic capacity of the surface layer was evaluated as a ratio elastic to the global energy of indentation. The metallography evaluation, focused on the contact surface, documented an increase of elastic response as a result of the dislocation hardening process.

The aim of this study was to examine the frictional wear resistance of X37CrMoV5-1 steel with nanobainitic structure before and after cathodic hydrogen charging process. The nanobainitic structure was obtained by use of austempering treatment at the temperature of bainitic transformation. Detailed information on the nanobainitic structure is given in a separate paper [1]. The results obtained for the nanobainitic steel samples were compared to the wear resistance of the same steel with tempered martensite obtained by use of conventional quenching and high tempering treatment. The samples were investigated before and after hydrogen charging.
Nanobainitic steel sample before hydrogen charging displays better wear resistance, as compared to the steel sample with tempered martensite. After cathodic hydrogen charging the frictional wear resistance of the X37CrMoV5-1 steel significantly decrease, regardless of its microstructure. However, the decrease of the wear resistance of steel with nanobainitic structure is greater than this of steel with tempered martensite. This may be related to the nature and course of the cracks formed in the material as a result of cathodic hydrogen charging.
REFERENCES
[1] E. Skołek, S. Marciniak, P. Skoczylas, J. Kamiński, W. A. Świątnicki, Nanocrystalline steels' resistance to hydrogen embrittlement, Archives of Metallurgy and Materials, 60, (2015)

Many structural components of nuclear power plant systems are made of austenitic stainless steels. These structures undergo degradation by thermo-mechanical fatigue (TMF) caused by simultaneous cyclic straining and temperature cycling, particularly during start-up, shut down and transient operations. The present work reports the cyclic deformation behavior and fatigue damage of austenitic stainless steel AISI 316L during TMF and isothermal fatigue (IF) testing in air. Total strain controlled in-phase TMF loading in the temperature range of 200-600 °C and isothermal fatigue (IF) cycling at 600 °C were performed. Hardening/softening curves, cyclic stress-strain response and fatigue life diagrams were obtained both for TMF and IF tests. Fatigue damage was documented using surface relief and fracture surface observations. Mean stress evolution and fatigue degradation data are employed to discuss the fatigue behavior of 316L steel both in TMF and IF regimes.

The article summarizes the results obtained within a project PRAMEK. The project is focused on corrosion behavior of structural materials for fossil – power – plant – steam - generator systems in water environment with supercritical parameters. Three types of steels were evaluated: ferritic - martensitic steels P91, P92 and VM12SHC; austenitic stainless steels 17 341, Super 304H and HR3C; and bainitic – martensitic steel T24. Materials were exposed in water environment under supercritical parameters (600°C, 25 MPa) for 1000 hours. For basic comparisons were steels tested in demineralized water without further chemical modifications. Then, selected steels were tested in alkaline demineralized water in oxygen and oxygen-free regime. The effect of the start-ups and shutdowns of the power plant is also studied. Furthermore, the effect of the chemical composition of the working fluid on steel resistance and service life was tested. Steel resistance is given mainly by the quality of the oxide layers which are formed on the surface in contact with the supercritical water environment. High quality oxide layer serves as a barrier against further oxidation of the steel. Evaluation of oxide layers and steel structural stability was performed by light and scanning electron microscopy equipped with wave and energy spectroscopy.
Multi – layered oxide was formed on ferritic-martensitic and bainitic – martensitic materials sample surface. Double layered oxide was formed on austenitic steels Super 304H and 17 341. Very thin oxide layer was created on HR3C surface, which means that steel exhibit very good corrosion resistance under the SCW conditions.

Computer simulation of hardness distribution in quenched steel specimens can be consisted of computer simulations of specimen cooling, specimen hardening and respectively of prediction of mechanical properties. The objective of design of quenching is to estimate the results of quenching, concerning mostly with the estimation of mechanical properties. For the simulation of specimen cooling which is thermodynamical problem, it is necessary to establish the appropriate algorithm which describes cooling process, and to accept appropriate input data.
The accuracy of applied numerical simulation of quenching directly depends on the applied input variables. In numerical simulation calibrated data will be used. Calibrated data are not as precise as experimentally acquired data but they are useful for large spectra of specimen dimensions.
Microstructure composition and hardness will be defined by kinetic equations of prior microstructure decomposition, based on time of cooling from 800 to 500 °C, which is relevant to microstructure transformation. Semiempirical methods are derived from kinetic equations of microstructure transformation to predict microstructure composition of quenched steel.
If the cooling time t8/5 is equal for two different specimens, i.e. quenched workpiece and Jominy specimen, the hardness of these two specimens could be equal to each other. To accept the assumption that the equal cooling time t8/5 of several samples indicates their equal hardness. The history of cooling of these samples will be taken in account in simulation of as quenched hardness. Other mechanical properties will be predicted based on hardness and microstructure composition.

The paper presents a brief study of micro electrical spark deposition with an tungsten electrode. The anti-wear coatings were applied on carbon steel C45 with using microerosion. These coatings could be applied to increase the abrasive wear resistance of tools and machine parts.
The surface roughness of the machined job was measured by using optical profilometer Talysurf CCI Lite-Taylor Hobson. Using high-resolution optical microscope Nikon Eclipse MA2000 the visible trace of the discharges were observed.
There were measured microhardness of the superficial layer and based material. For investigation was used Matsuzawa Vickers microhardness MX 100 type. There were applied load 100 G (0.98 N).
The superficial layer was investigated with metallographic methods and EDS analyses. SEM examination was performed using a JEOL JSM 7100F microscope with field emission (Schottky). The results showed that there is a possibility of obtaining the satisfying quality joint between the carbon steel C45 and tungsten electrode.

Existing models of microstructure evolution are based on the classical formulas which include the principles of thermodynamics and physics of metals. The accuracy of the theoretical solutions are closely dependent on the proper selection the coefficients of the equations describing the changes in the microstructure. To ensure the proper determination of the factors used in the mathematical models is necessary to set the effect of temperature - deformation occurring during the plastic forming processes to the austenite microstructure. The paper present the concept of a mathematical model for predicting changes in the microstructure of the austenite steel for cold upsetting, the research was carried for 30MnB4 23MnB4 steel grade. Microstructure evolution model is based on the classic Sellars model developed by taking into account the the parameters of plastic forming processes and their impact on the processes occurring in the deformed steel. The coefficients of mathematical equations describing the evolution of deformed austenite microstructure were calculated based on the results of experimental studies carried out in the Czestochowa University of Technology. For the verification of the accuracy developed model laboratory studies were conducted using a metallurgical processes simulator Gleeble 3800. Comparison of the results obtained in the theoretical and experimental studies have confirmed good agreement developed model of the microstructure evolution for the steel with boron for a cold upsetting.

Among the steel and cast steel resistant to corrosion most modern and dynamically developing group are ferritic-austenitic alloys, commonly known as duplex. Higher than austenitic steels, mechanical properties and good corrosion resistance in both overall and pitting make duplex steels irreplaceable material in the petrochemical industry, power, pulp and paper, food. Duplex steels and cast steels characterized by multiphase microstructure have a complex plasticity due the fact of deforming two different phase austenite and ferrite. The chemical composition of a steel containing about 0.02% C, 26% Cr, 6.5% Ni, 3% Mo, 1.4% Mn, 0.2% N guarantees that already, in the raw state, immediately after casting is obtained ferritic - austenitic structure. Because Due to the fact that a substantial part of the problems associated with the production of duplex steels appears in the as cast state this state was taken as initial condition for the deformation process. In the paper [1] were resented discussed problems of the discussed steel plasticity. As the microstructure of the final product is affected, but three last deformation [2] in this paper are presented results of applied from one to three deformation. In this article are presented results of microstructure changes and physical simulation of the rolling process carried out with the simulator Gleeble 3800.

Heat treatment is one of methods to improve material properties. Heat treated tubes are used in petrochemical industry when high strength, low cost and low weight are needed. Spray cooling could be used for heat treatment because very high cooling intensity is required. This paper deals with influence of spray cooling parameters on the material hardness.
Special device was developed by Heat transfer and fluid flow laboratory for quenching of small samples. Four different materials were tested. The main object of these tests was to find the influence of cooling distance, material and two-side cooling on material hardness. Device Innovatests Nexus 4303 (Vickers) was used to measure hardness in various depths from the cooled surface. Results showed that the hardness was improved for all of four materials. The influence of the spray cooling distance was not so significant. Hardness of material also depends on the cooling intensity in the inner side of the tube. If the cooling intensity in the inner side of the tube is much lower than external, it has negligible effect on the final hardness. If the inner and external cooling intensity is the same it causes increase of the hardness.

Our research is focused on the changes in thin surface layer of the brake disc due to the impact of severe plastic deformation and heating by friction process. The aim of this study is to compare structure, chemical and phase compositions of the surface layer in depth up to several hundreds of nanometers in the no affected central part of brake disk and the part which was in contact with brake pads by braking. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction and Mössbauer Spectroscopy. The thin surface layer was studied using Conversion Electron Mössbauer Spectroscopy and X-ray Photoelectron Spectroscopy. We explain the observed changes with the knowledge on effects of plastic deformation and/or diffusion of alloying elements in the material of the brake disc.

Austempered ductile cast iron is part of a family of heat-treated cast irons. Isothermal hardening transforms ductile cast iron into ausferritic cast iron (ADI), which has the appropriate characteristics of strength, the impact strength and fatigue resistance. ADI is more resistant per unit weight than aluminum and so resistant to wear as steel. The values of tensile strength and yield point are twice as high as values of the standard cast iron. The article presents the results of fatigue tests of the ADI cast iron with the use of load high frequency in the area of ultra high cycle.

The paper analyzes the structural modifications occurred in the welded joints from a Duplex stainless steel, delivered in solution annealed state in form of sheet with 1.2 mm thickness. As the filler material it has been selected an electrode wire E 2209-16 with a diameter of 1.2 mm, which has a higher Ni content (8-10%) compared to the base material (4.5-6.5%) in order to promote the formation of austenite and to induce in the weld approximately equal proportions of ferrite and austenite.
Also are capitalized the benefits of the pulsed current arc-welding regarding the precipitation reactions limitation of the intermetallic phase and of the nitrides in weld and heat affected zone (HAZ) which can affect both corrosion resistance and toughness.

The paper is dealing with microstructural characterisation and mechanical properties of thermally simulated parts of the heat affected zone in homogeneous weldments of T24 steel. The study has been targeted on the blunt peripheral weld joints of steel T24 between two tubes, which are an integral part of the production of membrane walls. Investigations on thermally simulated HAZ samples were performed in two states: after welding and after PWHT 740 °C / 1 hour. Thermal cycles for simulation of individual parts of HAZ in homogeneous welds of T24 steel were obtained by real measurements with subsequent corrections based on numerical simulations of welding using the Sysweld software. Thermal simulations were carried out on samples of Vallourec & Mannesmann tubes using a simulator TCS 1405. On the thermally simulated samples hardness and impact energy were evaluated. Microstructural characterisation was carried out using both light microscopy and transmission electron microscopy. Extraction replicas were used for identification minor phases. Results were validated on a real weldment. Results on thermally simulated samples essentially complied with results obtained on the real homogeneous weldment of T24 steel.

The carbide-free microstructures in steel which contains retained austenite have good wear resistance and tensile strenght while maintaining high ductility. Ensuring desired ductility is the role of the retained austenite in the form of nanometric layers of a chemical composition required for a martensitic transformation induced by plasticity (TRIP effect). This phenomenon improves mechanical and tribological properties. The heat treatment that allows obtaining microstructure consisting of carbon-depleted martensitic matrix and carbon-enriched retained austenite is called quenching and partitioning (Q&P). These Q&P processes are suitable for steels containing alloying additions of silicon and aluminum, that suppress formation of iron carbides.
The paper presents results of microstructure characteristic, mechanical and tribological tests of 35CrSiMn5-5-4 steel after Q&P processes. The parameters of the Q&P processes were chosen on the basis of computer simulations and dilatometric measurements.

The paper presents models of temperature field, phase transformation kinetics, thermal and structural strain calculations in a steel element during multi-pass Gas Metal Arc Weld surfacing. The temperature field is described analytically assuming a bimodal volumetric model of heat source and a semi-infinite body model of the surfaced (rebuilt) workpiece. The electric arc is treated physically as one heat source. Part of the heat is transferred by the direct impact of the electric arc, while another part of the heat is transferred to the weld by the melted material of the electrode. In the description are considered temperature increments caused by overlaying consecutive welding sequences and self-cooling of areas previously heated. Kinetics of phase transformations during heating is limited by temperature values at the beginning and at the end of austenitic transformation, while the progress of phase transformations during cooling is determined on the basis of TTT-welding diagram and Johnson-Mehl-Avrami and Kolomogorov law for diffusive transformations and Koistinen-Marburger for martensitic transformation. Total strains result from strain history in subsequent cycles of heating and cooling (as a result of the passage of the welding head) and are equal to the sum of thermal and structural strains induced by phase transformations in these cycles.

It has been recently shown that an increase in the magnetostriction of Fe occurs when small amounts of Ga or Al are added, which is linked to the formation of D03 sort range order (SRO) in the disordered Fe structure. The structural transitions due to different cooling rates from high temperature and the effect of substitution of Ga with Al on the ordering processes were investigated in this work. Two iron-based alloys Fe-13 at. % Ga and Fe-8 at. % Al-3 at. % Ga are studied. Dilatometric and calorimetric tests were carried out to check ordering in these alloys after different heat treatments. They have revealed that the cooling rate after annealing plays an important role for the formation of D03 ordered phase. Moreover, ordering in the studied alloys leads to the increase of microhardness. The values of activation energy for the two alloys calculated from DSC curves show that ordering in Fe-8 at. % Al-3 at. % Ga alloy requisite more energy than in Fe-13 at. % Ga alloy.

In the paper is shown the device how carrying capacity of steel columns can be increasing by enhancement inflexibility of extent. Inclusion extent to cooperation with columns increases load resistance of steel columns of the halls. The conclusion is that the carrying capacity of columns in steel halls can be increasing and how reliability of columns grows by simple construction measure. The theoretical speculation was affirmed by an example.