Seznam abstraktů 2017: SEKCE C - VÝROBKY Z OCELI A JEJICH VLASTNOSTI

This new surface induction hardening technology for railway wheel axles is the first technology of its type designed in Europe by the BONATRANS GROUP. Tests carried out on surface induction hardened EA4T and EA1N steel axles confirmed the benefits of this process for increasing fatigue resistance and lifespan in railway wheel sets. However, the substantial increase in the fatigue strength of induction hardened railway axles is accompanied by a lesser increase in notch sensitivity. The benefits of surface induction hardening were also reflected in the results of fatigue tests performed on an actual-size wheel press-fitted to an axle which suffered from fretting fatigue. The positive effect of axle induction hardening is also evident in relation to a range of other aspects, including surface and subsurface residual stresses, hardness profile in dependence on depth below the surface, and seizure resistance during the assembly or disassembly of railway wheel sets. The fatigue crack propagation behavior at the surface of the induction hardened axle is also studied from the perspective of fracture mechanics. The results of these observations were used in order to estimate intervals for service inspections of newly designed railway wheel sets. All the results obtained from the application of the new technology are compared with the results obtained from the standard heat treatment of railway axles; the comparison clearly demonstrates the effectiveness of this new technology.

The present paper deals with an experimental determination of fatigue crack growth rate (FCGR) of high strength low alloy (HSLA), steel also called microalloyed steel (38MnVS6) to study the crack propagation in forged automobile crankshafts. The criterion based on crack tip opening displacement range (∆CTOD) is used to investigate the fatigue crack growth rate. In the current work use of 2D-digital image correlation (DIC) technique for the measurement of crack tip opening displacement (CTOD) and crack length (a) is proposed. Digital Image Correlation (DIC) is a full field displacement and strain measurement technique. It is easier to measure the crack tip opening displacement (CTOD) and crack length (a) with this technique than other. Fatigue crack growth curve based on crack tip opening displacement (CTOD) criteria of 38MnVS6 steel is presented using DIC. The SEM fractographic analysis has been carried out on FCGR sample to observe fatigue crack growth region.

Mechanical testing and cyclic fatigue testing belong to the important material examinations. Standard fatigue testing is mostly time-consuming and needs a number of identical samples that makes the testing expensive. Infrared thermography as a noncontact method of temperature measurement is used in many industrial applications. As the mechanical energy is changed to thermal energy during the cyclic loading, the infrared thermography can be used for fatigue testing. Most of the research regarding fatigue limit evaluation by infrared thermography has been focused to a measured data post-processing. An online evaluation of infrared thermography measurement during a sample cyclic loading is introduced in this contribution.

Fracture surfaces of X70 steel DWTT broken samples are analysed using new surface evaluation concept. The presented approach is an alternative to expert determining a ratio between the ductile and the brittle fracture area. The analysed data source, i.e. x, y, and z coordinates of fracture surface points, comes from 3D scan using Limess Measurement Technique. Beside formerly used fractal geometry approach new concept based on normal vector characteristics is used. The fracture surface net is generated by triangulation of fracture surface points. For every triangle, the normal vector is computed. Thereafter, normal vector characteristics are analysed by various Lloyd type clustering algorithms. Applications of clustering algorithms improve correct detection of the brittle and ductile fractures significantly, so that achieved clusters highly correspond to real distribution of ductile and brittle fracture areas on DWTT surface. Furthermore, applied methods are computationally very fast, so that it is possible to apply them for scans with considerably higher magnitude. The correctness of the final cluster results are evaluated comparing with the real displacement of brittle and ductile fracture, and by using various theoretical approaches. Presented methods are proved to be useful tools for objective evaluation of ductile fracture percentage.

Paper deals with the martensitic stainless steel after reversed extrusion, quenching into polymer from austenitzation temperature of 1130 °C and subsequently tempered at 480 °C with final cooling in the air. Wall thickness of cylinders corresponded to 5 mm. Subsequently some cylinders were cyclically loaded. Basic mechanical properties and microstructure features of cylinders before and after cyclic loading were compared.

The ferritic martensitic steel T91 is among the candidate materials for internal structural components of future Heavy Liquid Metal cooled reactors. The position of T91 on the list of the candidate materials is now being questioned due to the evidence of its sensitivity to liquid metal embrittlement (LME), mainly in PbBi eutectic. Therefore, a renewed interest is placed on austenitic steels, in particular the 1.4970, due to the lack of evidence of LME for austenitic steels.
The main goal of this work was to provide an inside view into crack initiation phenomena in Liquid Metals for the two different steels and evaluation of possible mechanisms initiating and propagating the cracks.
Slow Strain Rate Tensile (SSRT) tests were carried out with flat specimens in PbBi at 300°C with low oxygen content (about 10-8 wt.%) and, for comparison in air, up to the Ultimate Tensile Stress, UTS, point. Tests were performed on flat tapered specimens, which were meant to create a variation of stress along the gauge length, with the maximum stress concentrated in the smallest area. This specimen geometry can be used for threshold stress determination of crack initiation.
The behaviour of the two materials was affected by the environment, as their cracking mode changed when compared to testing in air. Post-tests examinations were carried out with SEM and FIB milling. The role of oxides formation and microstructure is discussed and correlated to the initiation of cracks.
The 1.4970 steel, in this experimental conditions, was not affected by the environment, as small plastic cracks were observed around the Ti-rich precipitates in both air and PbBi.
The T91 showed a market tendency to crack initiation and rapid growth in PbBi.

Paper presents the analyses of high strength steels type of MnB5, widely used for autobody passive safety parts. Different surface treatment towards to weldability optimization was subjects of performed experiments. Diffusion processes in surface layer due to variable heat treatment were observed as a substantial influence on strength of welding joints; prospective influence on microstructure and dynamic response outside heat affected zone was also examined.
Current development trends in this area lead to limitations for standard mechanical tests. Variable mechanical response of a particular constructional parts is required for energy flow during crash, so the local dynamic response including energy consumption during deformation and destruction needs to be analysed. The rate-dependent behavior was examined at strain rates approaching operational relevant strain-rates, i.e. at strain rates ranging from quasistatic to 1000 s-1. Behavior of steels in the sub-Hopkinson regime revealed the most influential strengthening effects, and also the higher sensitivity to phase heterogeneities. The present study employed servohydraulic tensile testing machine and the hammer loading system to obtain precise uniaxial loading and also decisive information about energy consumption.

Heat treatment is the most widespread treatment of metal products. The modes of heat treatment are developed for most existing metals. However, in the case of processing new types of gradient metals based on iron, the typical modes are not suitable. The article describes a method for producing gradient materials based on iron with a nonequilibrium structure. The results of experiments on the development of heat treatment regimes, as well as studies of micro structures, the dependence of mechanical properties on the species and the mode of heat treatment are presented.

Design and semi-industrial verification of thermomechanical processing conditions designed for microalloy steel is presented. Based on assumption of utilization of the heat attained in the forged part after hot deformation, austempering cycles were investigated so as to meet the microstructure-property combination required by special applications. The presented study is focused on elaboration of the processing conditions of forging and controlled cooling for medium-carbon steel alloyed with micro additions, so as to meet the requirements of special civil engineering applications. The plan of the study is consisted of two parts: 1) laboratory investigation of the kinetics and effects of strain-induced precipitation and microstructure evolution during multistage hot deformation and subsequent continuous cooling in controlled temperature regime, and 2) semi-industrial verification of the processing cycle, with application of the selected process parameters into industrial forging conditions, dictated by energy saving aspects. The laboratory investigation was based on the numerical analysis of evolution of strain and temperature in the real forging process, which provided data for theoretical prediction of the processing conditions. Wide range of microstructure-property combination achieved for the same alloy, produced strength properties ranging from 620 to 1340 MPa and elongation-at-fracture 8 to 22%. The conditions, which were found the most proper for the concerned application, were the basis for definition of process conditions of semi-industrial verification while the thermomechanical processing of a complex shape forged part. Thus, in addition to dependence of the material response on austempering conditions, transferability and reproducibility of laboratory tests' results into industrial conditions was considered.

Dynamic yield stress values predicted within the structural-temporal approach based on the incubation time concept and those found from the popular empirical Johnson–Cook and Cowper-Symonds formulas and its known modification are compared with the examples of high strength steels and nickel alloy subjected to high-rate plastic deformation. It is shown that the structural–temporal approach is an efficient and convenient tool for calculations in a much wider range of deformation rates. An advantage of the yield stress calculations based on the incubation time criterion is the minimal number of parameters, which do not require further modifications at high strain rates, in contrast to the empirical Johnson–Cook model and Cowper-Symonds formulas.
Experimental curves of the static and dynamic deformation (stress-strain curves) for two high strength steels are analyzed on the basis of the relaxation model of plasticity [1] with a constant characteristic relaxation time definable from the structural-temporal approach. It is shown that the relaxation model for one material is predicted an existence of the yield drop effect on high-rate deformation for advanced high strength steel and absence of this effect for high strength 2.3Ni-1.3Cr steel in a wide range of strain rates.

Nanocrystalline stainless steels with solute additions were synthesized using high energy mechanical alloying. Microstructural evolutions as a function of alloy compositions and annealing temperatures were investigated using focused ion beam microscopy, transmission electron microscopy and in-situ and ex-situ x-ray diffraction techniques. The dependence of hardness on the microstructure was utilized to study the mechanical changes. The relative importance of composition and solute additions in various temperature ranges up to 1200 ºC were discussed with respect to grain growth, hardness and phase stability. The research reported in this work was supported by TUBITAK under Grant number 114M214. The authors wish to thank TUBITAK for the support.

The key characteristic of austenitic Hadfield´s steel is high resistance to the abrasion wear. Different applications mean various operating conditions and different types of abrasive wear.
This paper describes the most common faults on rolled sheets and their influence on abrasion resistance. As base for samples selection were chosen sheets of standard production on which were identified following defects: decarburized layer on surface, carbides on the grain boundaries, and martensitic structure in delivered condition before any mechanical loading. For the comparison of abrasive resistance was used test in shot blasting machine and impact test on laboratory equipment. Weight difference was evaluated on each sample.

The direct quenching of low-carbon steel has been shown to be an effective way of producing ultrahigh-strength, tough structural steels in the as-quenched state without tempering. However, in the present study, the influence of tempering at 600 °C has been studied in order to evaluate the possibilities of widening the range of strengths that can be produced from a single base composition.
Microstructural studies of direct quenched (DQ) and direct quenched and tempered (DQT) steels showed that, in both cases, the microstructure consisted of mainly auto-tempered lath martensite and bainite formed from highly pancaked prior austenite grains, the main difference being a larger carbide size in the tempered condition.
Mechanical properties were determined by tensile testing and Charpy-V impact testing. Bendability, in turn, was estimated by three-point bending to a 90° angle with various bending radii. The yield strength was 940 MPa in the DQ state and 900 MPa in the DQT state. Impact toughness at -40 °C and -60°C were 230 J/cm2 and 213 J/cm2, respectively in the DQ state, and after tempering impact toughness was slightly better. The minimum bending radius in DQ material was 2.4 times the sheet thickness (2.4t) in with the bend axis in the longitudinal direction and 1.5t transverse to the rolling direction. After tempering bendability was even better.
The results show that steels with minimum specified yield stresses of 900 MPa with good impact toughness and bendability properties can be produced from a single composition by employing respectively DQ and DQT processing.

The novel quenching and partitioning (Q&P) heat-treatment process was first introduced in 2003 by Speer et al. based on the fact that carbon can diffuse from supersaturated martensite into untransformed austenite. The initial partial or full austenitization that is followed by an interrupted quench to a temperature between the martensite start and martensite finish temperatures results in untransformed austenite, which is stable at room temperature. The main objective of this heat-treatment process is to generate a microstructure with martensite/austenite combinations giving attractive properties.
API steel grade was subjected to the Q&P heat-treatment using physical simulation on Gleeble 3500 to control the cooling rates, quench stop temperature, partitioning temperature and partitioning times. Specimens were partially austenitized then followed by interrupted quenching and then step partitioning at 420 ⁰C. Different partitioning times were followed to study the effect of partitioning time on the resulting microstructure and mechanical properties.

Laboratory experiments were conducted on steels with different chemical compositions to simulate the hot rolling process of high strength low alloy steels (HSLA). Several finish rolling temperatures were selected for three different steel alloys for the investigation. The microstructure and hardness were evaluated as a function of both microalloying elements and finish rolling temperature. Electron backscattered diffraction (EBSD) was used to further characterize the microstructure and crystallographic texture of the studied alloys. The objective of the present paper is to provide some perspective on the effects of varying the finish rolling temperature on the microstructure and texture evolution of different microalloyed low carbon steels.

Cold-drawn high-carbon steel wire with pearlite microstructure is one of the most popular raw materials for modern reinforcing ropes. Lamellae thinning, changes in interlamellar interface and metallographic texture, strain localization are the main property-forming phenomena in the wire drawing process. However, the experimental study of these phenomena dynamics is difficult and time-consuming. Drawing process of pearlitic steel wire was investigated. Behavior of pearlite colonies on the surface and the central layer of the wire were researched based on the multiscale computer simulation. Cementite lamellae orientation in relation to the drawing axis, interlamellar spacing and shape of cementite inclusions were key factors. Regularities of the pearlite colonies reorientation, changing the shape and size of cementite lamellae and strain localization in the ferrite were established on the basis of FEM. It was established that the cementite lamellae, that are parallel to the drawing axis, had the maximum thinning. Interlamellar distance in pearlite colonies with such lamellae changed most intensively. Cementite lamellae, that are perpendicular to the drawing axis, are the most susceptible to fracture. It found that for certain values interlamellar distance this effect can be reduced. Intensive reorientation of pearlite colonies in relation to the drawing axis was observed in the case of their location at an angle to the drawing direction. At the same time there were a significant bending of cementite lamellae and their susceptibility to fragmentation. Estimated values of the wire mechanical properties were compared with a real experiment. The simulation results were verified by metallographic analysis.

Favourable impact of sub-zero treatment on variety of important properties of tools is known over a long period. Alternatively, metallurgical principles responsible for elevated hardness, improved wear performance, changes in the tempering response and toughness, and better dimensional stability are known only over the last few years, and they have never been presented in all their complexity. The topic of the current paper is to make an overview of the most important properties of ledeburitic cold work die steels, their improvements by application of sub-zero treatments, and to explain these improvements upon the basis of the latest elaborated theory explaining the metallurgical background of this kind of treatment.

The microstructure, the phase constitution and hardness of Cr-V ledeburitic tool steel Vanadis 6 subjected to sub-zero treatment with several soaking time in nitrogen vapors have been investigated. The metallurgical aspects include reducing the amount of retained austenite and increasing carbide count, so wear resistant and dimensional stability are better as compared to conventionally heat treated material. The matrix is martensitic with certain amount of retained austenite, irrespectively to the time of sub-zero treatment. The amount of retained austenite has been significantly decreased from 20.2 vol. % to minimum 3.2 vol. % at 48 h soaking time. The microstructures have been characterized using the light microscopy, scanning electron microscopy and X-ray diffraction. The microstructure of sub-zero treated steel contains eutectic, secondary and increased amount of small globular carbides. The amount of small globular carbides for conventionally heat treated samples was around 48 x 103 / mm2 and for sub-zero treated samples was increased more than four times with maximum 209 x 103 / mm2 at 24 h soaking time. These particles have size of up 500 nm but 100 nm in most cases. The hardness has been increased as compared to no sub-zero treated samples from 875 ± 16 HV 10 up to 954.6 ± 14 HV 10 at holding time 48 h.

Compacted graphite iron (CGI) is an important engineering material, studied first in 1948, with special morphology of graphite particles often resulting in a good combination of thermal and mechanical properties [1, 2]. So, CGI is considered as an important potential material in modern industries, with many investigations dedicated to its thermomechanical behaviour, especially under extreme working conditions [3]. However, few studies of its fracture and strengthening mechanisms were implemented for CGI. Therefore, more systematic and comprehensive analysis should be carried out to gain a better understanding of underpinning deformation processes.
The aim of this research is to establish relationships between the manufacturing (casting) process, resulting local microstructures and thermo-mechanical properties employing advanced thermomechanical tests. In this study, the influence of thermal conditions on microstructure evolution and thermo-mechanical properties including tension, compression, creep and relaxation was investigated. Additionally, micro-mechanisms of deformation and failure in CGIs were studied at various temperatures and loading conditions by using scanning electron microscopy.
REFERENCES:[1] M. Gorny, M. Kawalec, J. Mater. Effect of titanium addition on microstructure and mechanical properties of thin-walled compacted graphite iron castings, J. Mater. Eng. Perform. 22 (2013), 1519-1524; [2] V.D. Cocco, F. Locoviello, M. Cavallini, Damaging micromechanisms characterization of a ferritic ductile cast iron. Eng. Fract. Mech. 77 (2010), 2016-2023; [3] M. Konig, M. Wessen. Influence of alloying elements on microstructure and mechanical properties of CGI. Int. J. Cast Met. Res. 18, 2005, 321-330.

Steel S235JR is one of the most popular structural material using on welding constructions. The microstructure of this steel consists of two phases: ferrite and perlite. This is the reason for this steel's low resistance to a number of aggressive environments. Despite this weakness, this steel is widely used in industry. The reason for its popularity is relatively low price and ease of joining in the process of manufacturing welded constructions. St3S steel is often used in construction works in the NaCl environment. The corrosive processes occurring in the sodium chloride environment depend on the concentration and the state of the environment. A lot of papers showing corrosion processes in this environment use NaCl as an aerosol. Industry also needs information on the corrosion resistance of this steel in aqueous solution of NaCl.
The aim of the research was to present the corrosion resistance of S235JR steel in 20% aqueous NaCl solution at 3oC.
The experiment was performed with low carbon S235JR (1.0038) steel designation according to EN 10025-2:2004, plate - thickness t = 5 mm. Steel was held in aqueous solution for 432 hours testing its wear every 48 hours. Corrosion tests show that tested steel in both corrosive environments are characterized through a continue corrosion. Roughness parameters for every one of research times are determine the size of steel corrosion. Loss of weight during the steel retention process in NaCl was determined measured in g/m2 and mm/year. The dependence of corrosion time on steel surface quality was determined.

Assessment of the remaining life of high temperature service exposed components is necessary for effective utilization of these expensive items beyond the design life. Knowledge of residual life also allows time for replacement of the components and avoids accident of such type of components used at high temperature. Amongst the various methods used to predict the remaining service life of a component, metallographic technique is an important one since this method can be considered as non-destructive, very small sample is needed and this method can directly measures the damage micro mechanism. The present paper reviews the microstructural changes of ferritic steels due to long term service exposure and describes the remaining life of service exposed components used in thermal power plant.

Dissimilar welds are widely used in tubular systems of power plant boilers to compensate for different operating conditions. Redistribution of interstitial elements across the fusion line is regarded to be the most dangerous degradation mechanism in heterogeneous welds. Carbon and nitrogen move along the gradient of their chemical potential, in our case from P23 steel towards P91 steel. The paper deals with a TEM characterization of precipitation processes in fusion zones of two variants of heterogeneous P23/P91 welds after creep tests at 550°C with times to rupture up to ca 80 000 hours. Both carbon extraction replicas and thin foils were studied. In carburized areas of welds heavy precipitation of carbides was observed, most of them corresponded to M23C6 carbides. The Cr/Fe ratio in these carbides continuously and systematically changed from the onset of carburized areas towards WM91 or P91 base material. This proved that carburization started in fusion zones, characterized by a continuous gradient of chemical composition. Furthermore, a low fraction of M6X particles occurred in carburized areas. In adjacent partly decarburized areas of WM23 or P23 steel M23C6 and M7C3 particles dissolved during creep at 550 °C. Furthermore, SAED investigations revealed precipitation of Laves phase of Fe2W type in partly decarburized areas of both variants of P23/P91 welds. Precipitation of Laves phase has not been reported in P23 steel yet. Thermodynamic calculations proved that a reduction of carbon content in partly decarburized areas of WM23 or P23 steel made it possible to stabilize this minor phase.

Hydrogen embrittlement is a form of environmentally-assisted failure, which caused by the action of hydrogen, often in combination with residual or applied stress that result in a reduction in the load-bearing capacity of a component. The objectives of this work include: a) examine the mechanisms of hydrogen embrittlement in steels exposed to different deformation rates, and b) the role of the second phases on the susceptibility to hydrogen.
The susceptibility of materials to hydrogen embrittlement is directly related to the interaction between steels' defects (traps) and hydrogen. Since trapping affects the metal diffusivity, it has a major influence on the hydrogen embrittlement phenomenon. Hydrogen trapping states were explored using thermal desorption spectrometry (TDS) and were supported using post-microstructural observations.
In this research we review mechanisms proposed for hydrogen embrittlement and present an analytical model for hydrogen trapping in steels. We will discuss the hydrogen's physical trapping in order to better understand hydrogen embrittlement mechanisms.

The CMT/CMTP braze - welding process is characterized by interruption of a short-arc at low welding current values, which is controlled by an invertor source. Thereby, the used energy is lowered by short time (about 1 μs) before reignition of the electric arc. Because of the offered benefits (joining of thin materials, the possibility of using large diameter wire electrode by low welding current, low heat input values, etc.) is facilitated the achievement of butt, corner and overlap welded joints, between dissimilar materials that have a low welding metallurgical behavior. In this paper is analyzed the opportunity to produce heterogeneous braze-welded joints (galvanized steel – aluminum alloy) starting from a factorial experiment which considers three sets of technological parameters. Welded joints quality is evaluated by metallographic examinations and mechanical testing.

Two welding schemes of single and double pulse were used for the resistance spot welding of DP1000 dual phase steel. The changes in the mechanical performance and variant pairing of martensite under two different welding conditions were scrutinized. It is demonstrated that, although both welds fail in pull-out failure mode, double pulse welding enhances cross-tension strength and energy absorption capability of the weld compared to single pulse welding process. Double pulse welding effectively changes the microstructure of the fusion zone. While the fusion zone of single pulse welds has a typical microstructure of columnar grains, the initial fusion zone of double pulse welds is subdivided into two zones: the outer recrystallized layer composing of martensitic microstructure formed within the equiaxed prior austenite grains, and the inner part of columnar grains resulted from the rapid solidification process of resistance spot welding. Orientation imaging microscopy results show that the recrystallized layer of double pulse welds exhibits a lower fraction of high angle grain boundaries and coarse structure of Bain groups. The coarse grained heat affected zone of double pulse welds has a higher fraction of high angle grain boundaries and finer structure of prior austenite grains and Bain groups compared to that of the single pulse welds.

Failure mode of resistance spot welds is a qualitative measure of the weld performance. Two major types of spot weld failure are pull-out and interfacial fracture. Interfacial failure, which typically results in reduced energy absorption capability, is considered unsatisfactory and industry standards are often designed to avoid this occurrence. In this paper, in the light of failure mechanism, a simple analytical model is presented to estimate the critical fusion zone size to prevent interfacial fracture. According to this model, the hardness ratio of fusion zone to pull-out failure location and the volume fraction of voids in fusion zone are the key metallurgical factors governing type of failure mode of advanced high strength spot welds during the tensile–shear test.

Nanoporous ceramic products from pure aluminum oxide were fabricated by plasma spraying method. The deposition process consists of passing of sprayed material particles with high velocity through plasma flow and subsequent coating of these particles on the surface of rotating metal forming mandrel. The products manufactured by standard techniques of plasma spraying have low thermal conductivity and selectively high gas permeability. The material of these products has a heterogeneous phase composition which is formed during the high speed cycle of heating and cooling when aluminum oxide particles passing through a stream of air plasma. Aluminum oxide particles in the composition of the material of products are in the alpha state and also in the beta- and gamma states. Reduction in porosity of products to nanoscale values (100-250 nm) and translation of material of plasma sprayed oxide product into single-phase alpha-state leads to a sharp increase in its thermal conductivity. By varying the sintering modes it is possible to fabricate nanoporous products with desired values of thermal conductivity.
Products of this material may be efficiently used in special electrometallurgy as containers for growing single crystals, in chemical industry, in mechanical engineering, instrumentation and special equipment, as well as in medicine and biotechnology.

Compatibility of structural materials with coolant, in conditions relevant to power plant operation, is a field of research of primary importance to nuclear safety. The current work describes the behaviour of T91 steels, under such conditions. Three-point-bend specimens were pre-stressed up to yield strength and subsequently exposed to lead-bismuth eutectic (LBE) in static conditions for 2000 hours. The aim was to identify the susceptibility to crack initiation in the selected experimental conditions. Post-test examination by means SEM equipped with EDX, demonstrated the formation of oxide scales without any trace of crack initiation. The oxide was characterised by a 3 layers structure. By FIB cutting, lamellas were produced and analysed in HRTEM. EELS technique was used for elemental evaluation of the oxides. Characteristics of oxide and its interphase with the steel were thoroughly characterised.

Bearing steels are used for parts requiring high hardness and wear resistance. Conventional hardening of the bearing steel is carried out at 840-870 °C after reheating of an initial structure consists of ferrite and carbides. At this temperature range, the hardening occurs without dissolving all carbides in order to prevent coarsening of austenite grains and formation of cracks in martensite plates following the quenching step. In this study, it is aimed to obtain a fine-grained initial microstructure by full austenitization before the hardening. For this purpose, the full austenitization followed by quenching to obtain the initial microstructure of martensite. Finer and well distributed carbides reprecipitate at the hardening step. The effects of initial microstructure on phase transformations have been investigated by hardening of different initial microstructures namely martensite, martensite and carbide or ferrite and carbide, followed by the hardening treatment at 840 °C. Accordingly, different heat treatment cycles also helped to understand the effect of different austenitizing temperature before the hardening step. Dilatometer tests were carried out to determine to critical transformation temperatures. Microstructural characterization and image analysis performed to change of the carbide size and distribution depends on the initial structure. It was found that phase transformations and final carbide size and distribution is sensitive to the initial microstructure.

Since thermomechanical treatments favors increased mechanical resistance characteristics of steels, their degree of alloying is lower than that of any found in normalized steel with the same strength.
This is extremely beneficial for the weldability of steel.
To prevent the emergence of unwanted micro-structural transformations in welded joint areas (softening HAZ, excessive growth of grain, cold cracking), the present paper aims to implement the narrow gap MAG welding of steel X65M intended for the fabrication of pipeline used for the transportation of natural gases and liquid hydrocarbons.
Root and hot layers have been welded using MAG spray arc and the fill layers in pulsed current.
The equipment used is composed by an internal welding machine for the root pass and external one with two welding torches for the fill layers, where the pipe is fix and the welding equipment make an downward vertical orbital movement around the pipe.
Assessments of the quality of the welds are done through macro- and micrographic analyzes in conjunction with sclerometer examinations.

The alumina-forming ODS-steels combine good creep strength of the ODS steel and excellent oxidation resistance of aluminium containing heat-resistant steels. The steels develop dense α-alumina scale upon high temperature oxidation. The alumina-forming ODS steels are candidate high-temperature structural materials for highly corrosive environments.
In the present study, the microstructural changes and consequent mechanical behaviour of 19Cr-4.5Al-0.3Ti-0.5Y2O3 ferritic alumina-forming ODS steel subjected to the liquid lead-bismuth environment were studied. It was found that dense oxide layer of thickness about 5μm develops onto a surface of the ODS steel after oxidation at 1100 °C for 120 hours. The tensile and bending specimens made from the ODS steel with the outer α-alumina scale was subjected to liquid lead-bismuth at 500 °C for 1000 hours.
The complex influence of liquid lead-bismuth corrosion to mechanical properties and microstructure was divided into three processes studied separately: i) influence of annealing at Pb-Bi corrosion temperature, ii) influence of long-term annealing at α-alumina scale forming temperature and iii) influence of corrosion in liquid lead-bismuth. The controlling sets of tensile and bending specimens were machined from the ODS steel bulk isothermally aged in an air atmosphere at 650 °C for 1000 hours and at 1100 °C for 120 hours to eliminate an influence of surface scale development.
The microstructure and fracture surfaces after tensile and impact test were analysed by the SEM and TEM. The synergy effect of microstructural and surface changes was revealed. The long-term high-temperature annealing caused grain coarsening and subsequent change of mechanical properties.

Martensitic stainless steels are broadly used in industrial applications where demands for higher strength, hardness and wear resistance are high. Tempering treatment plays a crucial role on performance of such steels. The present work is focusing on the effect of tempering on carbide precipitations and properties of AISI 410SS. Samples were austenitized at 980 °C for 30 min and tempered over the range of 300-732 °C. During tempering the carbides precipitated in the form of M23C6 and Fe2C in varying amount. During tempering at 300 °C, the ultimate tensile strength (UTS) increased to 1100 MPa from 741 MPa (as-received). Tempering in the range of 500-550 °C yields segregation of carbides at the grain boundaries; which causes precipitation strengthening with ductility. The coarsening and spheroidization of carbides at higher tempering temperature (732 °C) reduces hardness and strength. UTS was found to be reduced gradually from 944 MPa to 641 MPa when tempering temperature increased from 550 to 732 °C, respectively. Fracture strain increased from 6% to 12% and microhardness decreases from 498 Hv to 238 Hv when tempering temperature increased from 300 to 732 °C respectively. The optimized tempering condition was found out to be 550 °C for enhanced strength-ductility ratio with UTS (944 MPa), significant elongation (11 %) and hardening effect (515 Hv).

Electro-slag remelting is one of the ways to produce high-strength metal. For this reason, the machining of electro-slag metal is difficult. It is especially difficult to obtain a cylindrical billet from such a metal. The article proposes a new, high-tech method for producing a hollow ingot with electro-slag remelting. The production of a hollow ingot is obtained by introducing the melting point during melting. Due to the difference in the melting point between the base metal and the phase introduced, the low-melting material is forced into the center of the ingot that is being formed. The course of the experiment, the investigation of the macro- and microstructure, and the mechanical properties of the resulting hollow ingot are described.

One solution to overcoming these challenges is to optimize by tailoring microstructures of the copper plates used in the new tundish plate’s critical components. An approach that has proven effective in improving the thermal resistance of material to intergranular degradation is grain boundary junction in copper (GBJC). The results showed that the triple line tension has a considerable effect on grain growth, particle–boundary interactions and void shape, especially for nanocrystalline materials. Copper has been and will continue to be vital to thermal transmission and heat transfer applications. The copper plates of a tundish thin slab caster coated by electrodeposited Ni (Co) coating presented cracks and small Ni detachments on the meniscus area after some charge sequence (7 heats cast). We have observed on the copper plates more cracks and detachments of the Ni (Co) coating below the meniscus area. The cracks have mainly longitudinal direction and lead to the detachment of the coating. The remaining coating on the area below the meniscus has a dark grey color while where the coating was completely detached the copper substrate presented a yellow color due to the formation of brass alloy. Moreover on the bottom part of the plate some scars are present due to the wear between the solidifying metal and the protective coating. The presence of the wear scars on this area is normal for the mold plates. Nevertheless, on the same area the protective coating is cracked even if in a less intense mode compared to the meniscus area.