Seznam abstraktů 2017: POSTEROVÁ SEKCE C
Datum: 25.5.2017
Austenitic Stainless Steel is known as responsible for the largest manufacturing share of stainless steel. Different processes, as well as the addition of alloying elements, by the wide action in its microstructure, provide specific properties to each steel grade. One of the mechanisms most studied in austenitic stainless steels is the formation of intermetallic phases, especially the sigma phase. Its presence and distribution in the microstructure, may influence in a negative way in several characteristics of the alloy, as for example the reduction of the tenacity and ductility, generating important discussions on engineering. The present paper aims to overview the effects of the presence of the sigma phase in 317L grade austenitic stainless steel, welded, without and with heat treatment at 850°C and 1080°C with different exposure times. The effect of the heat treatments was followed by the mechanical tests of hardness and tensile strength. The investigation of the evolution of the microstructure was accompanied by metallographic analysis in samples with and without treatment. After the polishing the microstructure was revealed by means of electrolytic etching (NaOH), with subsequent analysis by optical microscopy, scanning electron and EDS microanalysis techniques. The presence of stabilizing elements of ferrite, chromium and molybdenum tend to accelerate the precipitation of the sigma phase at 850°C, even at small exposure intervals at this temperature. It was observed a greater hardening in the region welded by the precipitation of the sigma phase, emphasizing also that its presence is related to the decrease of the resistance and ductility.
Mining support profiles are produced by forging from hot rolled steel. The profiles are subjected to quenching followed by tempering. Mechanical properties can be improved with the dual-phase structure obtained by partial austenitization of 31Mn4 steel used as mining support profile. The purpose of this work is to compare the mechanical properties of the tempered martensite steel with the dual-phase steel for mining applications. Different heat treatment cycles are used in the production of dual phase steels, namely intercritical annealing and intermediate quenching. In intercritical annealing method, ferrite and perlite initial structure is obtained at first step followed by quenching in air, as martensitic initial structure is obtained by water quenching in intermediate method. These different initial microstructures before to partial austenitization step changes the final microstructure. Microstructural characterization was examined for two different microstructures of dual-phase steel. It was seen that finer microstructure occurred when the initial structure is martensite. Charpy impact toughness tests were performed to investigate the effect of the change in microstructure on the mechanical properties.
This article discusses experimental results obtained for elements made of a wear- and abrasion-resistant steel, Hardox400, finished using a non-conventional method. The analysis focused on the relationship between of the tumbling time and the radius of rounding. The effect of the angle of the cut was also taken into consideration. The surface of the finished items was examined with a Nikon MA200 microscope equipped with a NIS-elements viewer (version 4.20). The study also involved determining the influence of the tumbling time on the relative mass loss and the basic surface texture parameters. The surface texture of the finished elements was examined using a Taylor Hobson Talysurf CCI Lite optical 3D profiler.
The ODS (oxide dispersion strengthened) steels are promising materials for high temperature applications due to their strength and creep resistance at high temperatures. The new generation of 9Cr1W ferritic (ODS) steels with yttrium and aluminum oxides have been developed at IPM. The oxide particles are introduced into microstructure by direct adding and by internal oxidation. The Small Punch Test method is used for mechanical properties evaluation as it needs only small amount of material. The typical specimen is a disc with 8 mm diameter and 0.5 mm thickness. The disc is penetrated by a punch with hemispherical tip and force-deflection-time dependencies are measured. The results of small punch tests have been compared to the results of the tensile tests performed on the same materials. The tests have been performed at the room temperature and 600°C. The values of yield stress and ultimate strength are correlated and compared with derived theoretical relations. The comparison shows good correlation between the results of both techniques which confirms that small punch test can be the useful method for obtaining mechanical properties from a limited amount of material.
Samples made of nodular cast iron FGN 400-15 have been heat treated by oil quenching from 850 °C followed by tempering at 450 °C. The objective of the paper aimed the microstructure modification and improvement of the mechanical properties and wear resistance by cavitation. The results showed that the cavitation erosion resistance of heat treated cast iron is 1,8 times higher than that of the thermal stress relieved cast iron.
Examination of surface topography and microstructure of the cross section samples after the cavitation attack showed that the wear of heat-treated samples occurs by fatigue cracking mechanism, while by the thermal stress relieved cast iron a severe plastic deformation and a combined micro-cutting and micro-ploughing of the ferritic matrix appeared.
Improving of the cavitation resistance after the quenching-tempering heat treatment is explained by the fine structure, a relatively high hardness and yield strength, associated with an acceptable toughness.
In this work we show that the kinetic model of JMA, applied to isothermal decomposition of ferrite delta in duplex stainless steel in the range of temperatures between 750 and 850 °C is not applicable to later stages of processing. Corrections to this model mainly concern the impingement which should reflect the competition between crystal growths. We also show that the corrected model fits better the transformation kinetics.
Fracture toughness (KIC) is the one of the most important parameters for evaluating the fracture resistance of the machine elements or structural parts subjected to cyclic loading. These cyclic stresses can cause damage or premature failure. For these reasons, prior knowledge of the fracture toughness is critical. Some institutions have proposed the standards for determination of fracture toughness values. But these procedures of the standards are difficult to manufacture the specimens and cost a high price in terms of instrumentation. The objective of this work is determining fracture toughness with alternative methods which uses round bar specimens with and without fatigue precracking. In this way, fracture toughness can be evaluated rapid and inexpensive test methods. Two different approaches are investigated for S355 and Domex 700MC in experimentally. The values can be comparable with the values reported in the literature which are obtained by standard test specimens.
Surface coating of electrical steel sheets is very important due to minimizing eddy current losses in electrical machines. The quality of coating can differ according to the composition. The coating layer has limited heat stability and after crossing of the guaranteed temperature it can be significantly degraded and its insulation properties may change importantly. Colour of insulation after annealing is changing and it is the first indicator that something is wrong. The aim of this study is to describe changes in parameters of magnetic behavior due to heat degradation of the coating. The parameters were acquired from the measuring of magnetic hysteresis loops on two types of samples with different excitation. The basic information of structure was obtained by scanning electron microscopy. Acquired data are compared between samples with the damaged coating layer by annealing and the original coating layer. The results are discussed from the point of view of the possibility of using sheets with damaged insulation in electrical machines.
The paper deals with the use of small samples for fatigue tests of two types of steels used for power plant components (P92 and 15CH2NMFA). The main advantage of small fatigue samples is their use in cases, where sufficient amount of material is not available for standard test specimens. This problem can occur in cases of power plant components, e.g. steam turbine rotors or pressure vessels. The results of the small sample tests are afterwards correlated with the results of standard fatigue test specimens. In addition, different ways of sample manufacturing are compared. The small samples are produced either by machining, or waterjet cutting. The stress concentration which occurs in the small fatigue samples was determined by finite element method. The performed tests proved an acceptable correlation of small and standard test specimen results.
In research was tested modified alloy 80 A. The tests were performed on the material in the different deformation state with help of micro-hardness measurement, methalography and micro-tensile test. The aim was to find the relation between micro-hardness measurement and yield strength and ultimate strength. Experiment was done on the nickel alloy (modified alloy 80 A). In the case of relation between micro-hardness and mechanical properties, would be possible, to use this method in the future, for non destruct tests on the supplied products or on the running component. The benefit of evaluating the mechanical properties from the micro-hardness is, that the measurement can be used evaluation or for verification of real mechanical properties each part in the final size. That all, without need of destruction of tested part and with possibility to use the tested part for the commerce supplies. Together it is possible to make the indicative estimation of residual life time of component with FEM methods with re-counted mechanical properties. Except of mechanical properties from the micro-hardness were the microstructure observed, with aim to define the grain size and it potential influence on the measured values.
In archaeology, the Iron Age is the period when the iron usage and the technological processes of its obtaining were the most important for society. The Iron Age is the last period from the system of the three ages of classifying the prehistoric societies, preceded by the Bronze Age. The influences on the large areas in Europe were remarkable. Many legend says that responsible for this result were the ancient gods, but it can be also another cause: some people used for the tools and weapons better materials from the first Iron Age, while the inhabitants from other areas used poor quality steel or bronze. It is very important to research the ancient epopees using the "engineering glasses", to discover the origin of the materials and also the secrets that wrote the history of the world. At the beginning, human believed that everything must remain hidden in the basement, so there were few ones in charge of mines and iron processing. Later, humanity began to understand the iron importance, and starts to use iron for more and more activities. The present paper limits only to some milestones regarding the evolution of the usage of the new material but also to some specific technologies for the epoch.
The compression endurance strength is well characterized by the ability to transfer compressive stresses through porous materials. It can be determined by examining the material on the endurance machine in a single-axis compression test. The test was made on a strength machine Zwick/Roell Z100. Cylindrical specimens, made from Fe powder (ASC 100.29 and DISTALOY SE) and Fe powder with carbon addiction, about dimensions H = 14 [mm], d = 16 [mm], have been subjected to compression. The initial force was 100 [N], while the displacement was 1 [mm/min]. The graphs of strain dependence on deformation were presented in the study. Based on each graph, the yield strength was determined. Direct compressive strength (Rm) was obtained by examining the maximum value of compressive force of data range for deformation stress function. The diversity in the microstructure and porous structures properties can lead to fluctuations in the results during the endurance tests. The divergence of the Young's modulus of the aluminum porous material can vary from 5 to 30%, and a compressive strength from 5 to 15%. The Young's modulus was calculated on the basis of the range of 0.25 - 0.75 stresses in the linear range by dividing the stress tension by the deformation.
The subject of the work is to present the possibility of using a non-contact optical system for measuring strains. Dantec's multi-unit Q-400 3D image correlation system was used. The aim of the study was to determine the distribution of displacements and strains on the surface of hybrid welded samples during the tensile test. The measurement was mainly used to estimate the mechanical properties of the welded joint, taking into account the change in the properties of the various joint zones. Measurement was carried out by tracing the displacement of the prepared surface of the tensile sample. In the paper, the results of the studies show the displacement and deformation fields for different tensile steps of flat samples to compare the effect of the process parameters selection on the mechanical properties of welded joints. The results was compared with the results of tensile test of the base material to determine the impact of the welding process change the mechanical properties of the investigated steel.
Electrochemical noise analysis (ENA) was used for the evaluation of corrosion protective properties of patina rust layer formed on weathering steel S355J23W after 8 years of exposure test in Berlin atmosphere. Electrochemical parameters derived from shot noise theory were obtained and related with changes or degradation in tested rust film during 456 h exposure in SO42- and Cl- containing aqueous solution. The electrochemical data was compared with other standard corrosion data.
Effect of creep on distribution of Laves phase was examined in a 0.1С-9Сr-3Co-3W-VNbBN steel under creep tests at 650°C and applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was shown that three stages of evolution of Laves phase could be distinguished under creep condition. First, precipitation of Laves phase occurs during 1000 h. These Laves phase particles retain their dimensions unchanged up to 5000 h, at which the onset of extensive coarsening appears. The coarsening of Laves phase particles at third stage at > 5000 h led to the formation of micron scale boundary particles. Strain accelerates these processes. Theoretical consideration of coarsening behavior using the Prisma software showed three main features. First, volume fraction of Laves phase increases with time. Second, there is a well-defined peak in size distribution of the Laves phase particles, which tends to shift to higher dimensions with time. Third, interfacial energy of Laves phase changes with transition from short-term creep to long-term creep. Under short-term creep condition, interfaces of Laves phase remain semi-coherent, while under long-term creep conditions these interfaces are incoherent that promotes coarsening of Laves phase.
The paper presents experimental results of the changes of strength and fracture toughness characteristics of high-strength steel Hardox-400 in brittle-to-ductile temperature range from -100 °C to +20 °C. It was shown that the values of strength properties has increased linearly with lowering the test temperature. The changes of fracture toughness characteristics with temperature are more complex and they will be described by exponential type function.
New wear-resistant special cast iron CHMN-35M was produced to be used for parts which are operated under the conditions of intense friction loads. Based on obtained results, technical requirements by chemical compounds and mechanical properties were determined. Wear resistant properties of experimental material in friction couples with a different type of steel were investigated. Experimental samples were tested by static and dynamic bendings to evaluate strength and crack resistance of the material. Fractography investigations of samples after mechanical test were carried out. Influence of nickel and molybdenum on structure and mechanical properties of special cast iron CHMN-35M are presented in this work.
The authors of the article analyzed the performed laser welding process tests of 1.4462 duplex steel in terms of the selection of the appropriate parameters. Welding was carried out using Nd:YAG laser type without the use of the filler material. To assess the correctness of the joint the following tests of welded joint were selected: macro structure and micro structure, strength and hardness and the content of the ferrite in the weld zone, heat affected zone and base metal. During the implementation of individual process tests the following variables were adopted as parameters: laser light beam power (kW), and the focus distance from the joint surface (mm). The studies were carried out to determine the impact of laser welding parameters on the selected properties of the joint prepared using different welding parameters.
Strength and ductility in FCC alloys can raised by twinning induced plasticity. Due Low stacking fault energy in these FCC alloys, the stain hardening exponent can be increased due to increase of slip - twin interaction and increase of additional slip system due to twin formation.
The paper contains results of fractal analysis of oxide layers formed on steels used in the power industry. The studies were carried out on elements taken from three steel grades: 13CrMo4-5 (T=470 °C, t=190 000 h), X10CrMoVNb9-1 (T=535 °C, t=75 000 h), 10CrMo9-10 (T=575 °C, t=100 000 h). The oxide layer was studied at the inner and outer surface of the tube wall. The obtained results of studies have shown that the fractal analysis results are affected by operational parameters and by the type of formed oxide layers.
Steel construction needs to present high plastic properties especially during dynamic load. It is necessary for impact conditions. The way to improve of plastic prop-erties of welds is welding with micro-jet cooling. It is a innovative method of welding. After welding with micro-jet cooling the microstructure of weld presents the high content of acicular ferrite in weld metal deposit. It allow to obtain a high values of the plastic properties. In this paper influence of the micro-jet streams number and the kind of cooling gas on plastic deformation of welds was presented.
TRIP steels are modern structural materials which are currently mainly used in an automotive industry. The processing of these steels utilize an effect of transformation induced plasticity resulting in good mechanical properties – high strength (up to 1200 MPa) and formability (around 35 %). TRIP effect is based on stabilisation of sufficient amount of retained austenite and its transformation into strain induced martensite in consequence of applied plastic deformation at low temperature. The properties of this steel are based on a multiphase microstructure, which consists of ferrite, bainite and retained austenite.
In this work, CMnSiAl steel was heat treated using various processing parameters. Three different temperature of austenitization (850 – 900 – 950 °C) were applied and the samples were subsequently cooled by cooling rates in the range of 26 – 32 °C/s to different bainitic hold temperatures ranging 410 – 460 °C. The resulting microstructures were evaluated with use of optical and scanning electron microscopy and volume fraction of retained austenite was determined using X-ray diffraction phase analysis. Mechanical properties of this steel were established by HV10 hardness measurement, which reached the values 260 – 301 HV10.
Sharp-edged carbides in high-alloy tool steels reduce their toughness appreciably. Since they form during solidification, they are virtually impossible to remove by conventional routes. One of the techniques available to meet this purpose involves thermomechanical treatment with transition through the semi-solid state. It relies on using temperatures above the solidus, thereby redissolving the carbides in the austenitic matrix. The resulting structure consists of polyhedral austenite grains embedded in lamellar austenite-carbide network. Using appropriate forming parameters, this network can be removed by thermomechanical treatment.
An experiment was carried out on X210Cr12 steel, combining semi-solid processing and subsequent thermomechanical treatment in a press. Hot plastic deformation led to redissolution of carbides from the eutectic network to the matrix. The rate of cooling after deformation played a major role in the evolution of the resulting microstructure. It was found that by varying the cooling rate one can obtain a broad range of hardness values. Water quenching led to fine-grained structures consisting of the M-A constituent and fine chromium carbides whose hardness exceeded 860 HV10. By contrast, very slow cooling caused pearlite to form, producing structures with a hardness of 230 HV10. The process represents an alternative to known and well-established treatment routes which are normally used for tool steels with chromium carbides.
The purpose of the paper was to analyse the effect of diverse heat treatment parameters (normalising and tempering) on mechanical characteristics of 508x20x90° tube bends made of the 10CrMo9-10 steel manufactured by bending with local induction heating. The research conducted included tests of basic mechanical properties and creep at the temperature of 500°C. With reference to the results thus obtained, it has been established that there is a relationship between mechanical properties of samples and individual features of their microstructure. Heat treatment parameters triggered changes in the bends microstructure, compared to in-delivery state. This effects included change of strength characteristics (Rm, Rp0,2) and material creep-lifetime, compared to the tube. Heat treatment in lower temperature and shorter tempering time assured the longest creep lifetime. It was found that main structural factor determining creep lifetime of bends was a grain size.
A use of selected steels in the industrial practice is very important and frequent and this is the reason why it is necessary to know their qualities not only from the standpoint of material, but also regarding its machinability with the aim to gain a product of a fine quality in optimal economic conditions. Machinability was compared in cases of steel 100Cr6 and steel C56E2 directly in the production process by means of experimental verification of deterioration of cutting materials, measurements of dynamics of a cutting process, eveluation of macrostructure and quality of surface layers.
Paper deals with evaluation of effect of high pressure hydrogen environment with actual pressure of hydrogen up to 30 MPa on fatigue crack growth rate properties of structural steel used for cylinders production. 34CrNiMo6 grade steel was used for experimental programme. A unique new testing equipment (hydrogen autoclave) was build in MATERIAL & METALLURGICAL RESEARCH, Ltd. to study degradation mechanism of high pressure hydrogen environment on mechanical properties including fracture mechanics properties of structural materials. There is comparison of results of crack growth rate in the air and high pressure hydrogen presented In the paper. Potential method was used for crack growth monitoring in the hydrogen autoclave due to cycling. Effect of hydrogen is presented on fractography examination, change in fracture morphology was found on fracture surfaces of tested specimens due to presence of high pressure hydrogen.
Mould powders significantly influence the correct course of steel continuous casting process, the surface quality and subsurface structure of cast strands. For many users of continuous casting equipments the choice of proper mould powder for the local condition of casting process is still the essential problem. The solution of such problem could be empirical equations (worked out in the last years), which with more and more accuracy enable to determine the values of physicochemical parameters of mould powders for the parameters of casting process of specific steel grade. The article presents the way of using the empiric equations to determine the physicochemical properties of mould powders dedicated for casting the round cast strands (Ø 170 mm) from C45 steel and their verification in industry.
This paper presents the results of research on manufacturing technology and the application of composite iron-zeolite. The composite was made by powder metallurgical technology using compression hydraulic press by pressure 400 MPa and sintering temperature at 1100 °C. The tested zeolite was provided by the company VSK PRO-ZEO from the quarry in Kucin located in eastern Slovakia. Before the production of sinter, the study of zeolite's morphology and chemical composition was performed. The rock was grounded and separated for further study by a fraction of 0.0-0.2 mm.
The produced sinters were subjected to the following tests: measurement of density, hardness, porosity and compression test. Observations of the microstructure and chemical composition analysis of EDS metallographic specimen sinters were also carried out using a scanning electron microscope.
The zeolite was introduced into the matrix in an amount of 5, 10 and 15 % by weight.
The aim of the study was to observe the changes in properties of the zeolite constituting the strengthening phase under the influence of heating.
This work deals with the proposal for the new evaluation system of calibration data in the VÍTKOVICE STEEL Testing laboratories. The main purpose of this work is the best possible use of the information obtained during regular calibrations of Charpy impact machine performed according to standard ČSN EN ISO 148-2:2010 - Metallic materials – Charpy pendulum impact test – Part 2: Verification of testing machines, and ASTM E23 – 16 Standard test methods for notched bar impact testing of metallic materials. The results of a direct calibration of geometric properties of Charpy impact machine, as well as the results of indirect calibration obtained by testing of prepared etalons will be taken into consideration.
The contribution deals with research on the influence of welding parameters at the size of the thermal field and heat affected zones at a resistance spot welding. Joints were weld at the unalloyed deep-drawing steel DC06, used in the automotive industry for car body. There is a quality evaluation of spot welds using thermography measurement and comparisons with conventional nondestructive testing.
In the automotive industry, the sheets are coated for protection against oxidation during forming. This coating may deteriorate the weldability of steel sheets and shorten the life of welding electrodes. Currently, new tips of coatings are used, e.g. coatings based on Al-Si or NIT (New Inorganic Treatment). The contribution deals with the influence of the NIT layer on weldability and electrode lifetime.
The crucial role in the case of any FEM simulation play input data. There is significantly increasing demand on material data measurement for FEM simulation and on their accuracy. The paper deals with the simulation of heterogeneous weld bending determination with the use of local mechanical properties measurements using micro tensile samples. Newly developed Micro-Tensile test technique (M-TT) is employed here. M-TT specimen dimensions are: thickness of 0.5 mm, width of 1.5 mm and parallel length of 3 mm. ARAMIS system using Digital Image Correlation method (DIC) enables precise strain measurement in the course of M-TT.
In the current paper, comparison of heterogeneous weld simulation using “standard material data” such as base metal and weld metal with local material properties determined with the use of M-TT measured from the first base metal, across heat affected zone, weld to the other heat affected zone and second base metal. The simulation is compared to experimental bending of heterogeneous weld. In order to be able to perform a detailed comparison of the results obtained by the experiment and simulation, next to standard load displacement measurement in the course of tests, also local strain measurements were carried out using digital image correlation systems. A final comparison confirmed significantly better agreement of the simulation using local data measurements in both investigated fields, load-displacement record and the local strain distribution in the course of bending.
The article describes the state of the art computer simulation in the field of metal forming processes, the main problem points of traditional methods were identified. The method, that allows predict the deformation distribution in the volume of deformable metal with taking into account of microstructure behavioral characteristics in deformation load conditions, was described. The article compares the results of modelling allowing for the TRIP effect and overlooking it. The comparison shows that martensite, which forms in the microstructure, causes a significant rise of equivalent stresses across the entire representative volume, which is extremely critical in the drawing process engineering. The method applied also gave a better understanding of how the microstructural elements interact in TRIP steel under strain, which helped explain more intense (2 or 3 times as high compared with the average values) radial strains in the plastic phases close to bigger grain clusters of stronger bainite and martensite phases. To save computing time, statistical representation of the microstructure was applied. Statistically Similar Representative Volume Element (SSRVE), representing metastable steel microstructure, was developed. Applying the SSRVE concept dramatically decreased the calculation time of the model while maintaining the overall accuracy. The study helped obtain initial data that can be used to design the drawing processes for TRIP steels. This will enable advanced and technically flexible materials to be used in the conventional drawing process, thus expanding the range of applicable steels.
This paper discusses results of wear of the turning tool bit after face turning. The results obtained under wet conditions, i.e. when the cutting fluid containing mineral oil was present, were compared with the data collected under dry conditions. The experiments were carried out using CTX 310 ECO Numerical Control lathe. The tool wear after face turning was analysed by means of an SX80 stereo zoom microscope. The workpiece surface texture was studied using a Talysurf CCI Lite non-contact 3D profiler. A JSM 7100F scanning electron microscope equipped with an EDS microanalysis system was employed to identify the elements on the surface of the tool tips. The tribological tests were performed with a T-01 M tribometer for a ball-on-disc configuration in the sliding contact. The cutting fluid used during the experiments was responsible for a decrease in the selected tool wear factors, which directly transferred to the smaller wear tracks.
The use of hybrid welding technique, involving a laser beam and electric arc, reduces a number of drawbacks of both methods used separately. The proper use and optimization of hybrid welding requires the knowledge about complex thermal phenomena accompanying this process and a number of technological parameters that need to be correctly set to ensure the process stability and proper quality of the joint.
In addition to the parameters associated with separate arc welding and laser beam welding methods there are new technological parameters that have to be taken into account in the development of this welding process. The most important role plays here the relative arrangement of heat sources (a system with leading laser beam in the tandem or system with leading electric arc in the tandem) and the relative distance of heat sources that directly influence the shape and size of the welding pool.
This paper concerns the mathematical and numerical modeling of thermal phenomena in the laser-arc hybrid welding process with the motion of liquid steel in the welding pool taken into considerations. Developed models are used in computer simulations of hybrid welding process with assumed different relative arrangement of heat sources in the process. The shape and size of the welding pool is numerically estimated. Numerical predicted hybrid welded joints are compared to macroscopic pictures of cross sections of experimentally obtained welds.
The newly developed grades of austenitic heat resistant steels (Super 304H, HR3C, TP 347 HFG) exhibit superior corrosion resistance in steam as well as creep strength thanks to their fine-grained microstructure, especially in case of Super 304H and TP 347 HFG. They are worldwide used in USC power plant boilers and substitute steels AISI 316, AISI 321 and/or AISI 347 formerly used in superheater and reheater tubes. On the other hand, the structural stability of these new steels is under examination, especially form the viewpoint of sigma phase precipitation, which is known for its embrittlement effect.
The precipitation of sigma phase was already found in the mentioned steels after long-term annealing at working temperature in the base material of tubes as well as in the tube bends. However, it seems that the presence of applied stress (and/or deformation) significantly promotes the precipitation of this phase. Therefore, much more and coarser particles of sigma phase were detected in the weldments after creep exposure.
The paper presents the results of stress rupture tests of welded tubes made of steels Super 304H and HR3C, the assessment and prediction of long-term creep life and describes also the structural changes that appeared in these steels, especially precipitation of sigma phase, when significant difference in the amount of sigma phase between the both steels was revealed.
The presented paper is devoted to the comparison of hydrogen diffusion characteristics in three different kinds of TRIP steels (with higher phosphorus content, higher aluminium content and higher silicon content). The steels were tested in as-received state after standard heat treatment including two step annealing – an intercritical annealing and an annealing in the range of bainitic transformation and in states after 5 % and 10 % tensile deformation. Steel microstructures were analyzed by light microscopy, scanning electron microscopy and X - ray diffraction. Hydrogen diffusion characteristics were electrochemically measured by Devanathan-Stachurski method with a double cell separated by steel in the form of a thin membrane. Exit sides of the steel membrane were palladium coated to prevent from hydrogen atom recombination during permeation experiments. Hydrogen diffusion coefficients were calculated using the „time lag“ method. The lowest values of hydrogen diffusion coefficients were recorded in the TRIP steel with higher aluminium content, while the highest values were observed in the TRIP with higher phosphorus content. Phosphorus probably enhances hydrogen diffusion in steel. Very high sub-surface hydrogen concentrations were observed also in the TRIP steel with higher phosphorus content.
This paper addresses the FEM numerical analysis of thermal field distribution in a thin-walled aluminum alloy pipe subjected to circumferential welding with a laser beam as a source of heat. The paper presents constitutive equations describing the studied phenomenon. Computation results were compared to the experimental welding results. Welding process was performed on the TRUMPF CO2 laser, model TruFlow6000. The temperature ahead of the moving laser beam front was measured by the optical pyrometer. Pyrometer indications confirm that there is a sufficient level of correspondence between the numerical analysis and the actual results.
Implementation of controlled thermomechanical processing for new references of forgings call for prediction the expected effects of the processing conditions on microstructure and properties. It is especially important in the light of wide variety of geometries and sequence of forging to obtained the required geometry. Thus, alongside with the deformation history, dynamic response of the material changes between locations, producing varied conditions for the evolution of microstructure, which in controlled thermomechanical processing has a crucial bearing on final properties.
The presented study combines numerical simulation with theoretical modeling for analysis of the microstructure development in progressive stages of the forging sequence and prediction of the parameters of austenite in as-forged condition, prior to and after direct cooling. Based on numerical modeling of the multi-stage forging process with incremental forging of a preform, temperature, strain and strain-rate was calculated in selected locations in the bulk, dynamic recrystallization kinetics was analysed with use of JMAK model, and the transformed grain size was calculated on the basis of Hodgson-Gibbs and Sellars-Beynon models. After validation in a simple upsetting, the results have been verified and evaluated in semi-industrial forging process, which forms a basis for comparative assessment of applicability of the applied theoretical models for the microstructure prediction, as well as effectiveness of the controlled processing technology in reference to hammer-forged parts considered in the study.
The effect of hydrogen on the growth of short cracks in martensitic-bainitic microalloyed steel subjected to a rapid cooling cycle was studied. Cylindrical specimens were heated at 1300°C for 10 minutes and then quenched into stirred water. The short crack growth tests were performed in a rotating bending fatigue machine. Tests were performed employing modified specimen designed for short cracks tests. The crack growth as a function of the number of cycles (N) applied during the fatigue test was monitored on specimens in three different conditions: a) as heat treated (HT); b) HT with hydrogen charging and c) HT with hydrogen charged/hydrogen discharged by baking treatment. The hydrogen charging was performed electrochemically with a density current of 40 mA/cm2 during 60 minutes. After testing, all samples showed persistent slip marks (PSMs), and the initial crack growth and propagated along high shear stress. Without hydrogen presence, the crack grows perpendicular to the applied stress and the PSMs observed and are located far-off to the crack tip area and crack path. In the presence of hydrogen, the crack growth is affected by the microstructural defects induced by hydrogen; additionally, the PSMs are developed in the region near the crack tip area and around the crack path at lower N values. This indicates that the plasticity was increased, that is, damage that occurs in the presence of hydrogen come into the hydrogen enhanced local plasticity mechanism (HELP).
Proposition of a Cellular Automata (CA) model of carbonitride precipitation to simulate image of microstructure in microalloyed niobium steels is presented in the paper. Cellular Automata model proved to be very efficient in modelling various phenomena in materials science. Numerical modelling played important role in development of new processing technologies taking advantage of precipitation. By modelling we mean a mathematical description of the relation between the main process variables and the resulting material properties, based on sound physical principles. In microalloyed steels the microalloying elements: Ti, Nb, V are added in order to control their microstructure and mechanical properties. High chemical affinity of these elements for interstitials (N, C) results in precipitation of binary compound, nitrides and carbides and products of their mutual solubility – carbonitrides. The model accounts for an increase of dislocation density due to plastic deformation and predicts kinetics of precipitation as well as shape of precipitates.
The dilatometry measurements are very important part of material science, especially for alloys where phase transformation leads to change in volume, like well-known transformation of austenite to martensite in steels. For dilatometric measurement, two push rod materials were used for measurements of length change on dilatometer TA Instruments 805A: fused silica (SiO2) and alumina (Al2O3). In this study different sample materials were used to study the influence of push rod material on the results. The results were also compared to platinum sample material at the same heating cycle. For W600 steel, the results showed difference in value of length change when heating to an annealing temperature as well as during cooling from annealing temperature. At constant temperature, the change in length for alumina push rods was increasing, while for fused silica push rods the change in length was minimal.
Simulation of iron alloy corrosion is used widespread to predict corrosion resistance. The simulation using corrosion chambers or climatic chambers does provide reasonable information on corrosion resistance, the corrosion rate however must be compared to real exposition as the corrosion in simulated environment is accelerated compared to real situation. However the composition of corrosion products and its structure is different question. The corrosion products composition is dependant on corrosion process. The phases present are mos likely the same; most voluminous hydrated oxides and oxi-hydroxides on the outside where the less voluminous oxides are present in the lower layers. However this macroscopic phase structure may not fully describe the layered structure of corrosion products, thickness of corrosion products or mechanical properties. In the vicinity of crack in corrosion products the structure is more likely to be similar to the structure near the surface.
Work deals with phase formation of eight high entropy alloys of FeCuxCr1-xMnNi type and of three alloys of FexCuCrMnNi system with high entropy effect. Predicted compositions of phases using Ni and Cr equivalents and by use of valence electron concentration are compared with real finding of presented phases in all aforesaid systems. Types of phases were detected by hard X-ray synchrotron micro-diffraction. With increasing Cr content in FeCuxCr1-xMnNi system double FCC phases changed into double FCC with BCC phases under simultaneously increase of yield stress. In FexCuCrMnNi system with atypical higher Fe contents double FCC phases were detected with their different volume fractions. With increasing Fe content as a BCC stabilizer a rise of yield stress was detected. In both investigated systems, some predicted results of formed phases partially differed from founded phases using synchrotron.
Steels in the cooling water circuits are most vulnerable to localized corrosion problems, crevice corrosion or deposit corrosion, intergranular corrosion. Austenitic steels excel in their resistance to corrosive environments. In case of use of the tubes in the cooling circuits is necessary to connect them by welding. Welding of austenitic steel is not the easy process in the field of welding. Place of weld joint then becomes a critical place for mechanical properties, but also for corrosion resistance. For application of invoking of stress corrosion cracking have been selected tubular bodies of the most commonly used steels EN 1.4541 and 1.4571. On these transverse welded tubes were manufactured artificial defects by EDM method. For the tests were used modified welds with artificial defect and without it. These defects were intended to localize of future damage. The thus prepared samples were exposed in corrosive environments. To induce stress corrosion cracking for tubular bodies from austenitic steels was used method of exposure in the melt MgCl2.6H2O. It is known that method for austenitic high alloy steels, is very sensitive to the presence of local areas and under the influence of tensile stress (and residual stress). Modeling of conditions for crack initiation corrosive damage help to determine how the weld joint behaves in aggressive environment exposure. These knowledge help to prevent accidents. Of course is possible take into account the resulting knowledge in the design and life prediction of cooling water circuits.
Using pulsed current at manual metal arc welding represents a new research idea perspective and provocative for major manufacturers of welding equipment. The concept is based on the ability to control the volume of welding pool at low frequencies of the pulses, below 5Hz.
Experimental research underline the beneficial influence of pulsed current welding on weld geometry for butt joints. Also the technological particularities of the process are highlighted and the use of two welding techniques depending on the frequency of pulses in terms of how the welding of the root layer is done compared with standard welding:
- at low frequencies below 2Hz welding is performed intermittently, electrode oscillation frequency has the frequency of the pulses, during the pulse time the welding arc is of the flanks on the joint, and during the basic time of the pulsed the welding arc moving from one flank on the joint to other; This technique ensures safe melting of the flanks on one side, and on the other side avoid penetration root layer;
- at frequencies above 2 Hz welding root is done without oscillation electrode, with support the electrode on the flanks of the joint, root is safe and uniform without excessive penetration; but it requires the right choice of the opening joint.
The results confirm that manual metal arc welding with pulsed current is feasible and technological beneficial effects can be obtained. It requires the expansion and diversification of research for a more complete assessment.
This paper deals with the correlation of the fatigue tests results obtained on standard and miniature test samples. The aim was to compare the fatigue properties (Woehler curves) of the samples of 15CH2NMFA steel of different cut off CT/50 test specimens after fracture toughness tests. The advantage of the use of these miniature samples is the minimum volume of removed material necessary for the production of test samples. This makes it possible to check the components in service, e.g. pressure vessels, steam turbine casings and rotors, steam pipelines, and other components of power plants after some time of operation in order that the residual lifetime could be determined. The article discusses the design of tests samples and clamping fixtures, test conditions and resulting correlation of test results.
This research is concerned with the effect of titanium in the range 0.01 to 0.13 wt.% on the base plate and weldability properties of laboratory hot-rolled cold-formable steels with yield strengths in the range 500 – 900 MPa (S500MC - S900MC). Different strength levels were achieved by varying the contents of boron, chromium, vanadium and molybdenum. For the base metal, titanium had a small strengthening effect and it also raised the impact transition temperature. In MAG-welding (t8/5 = 5 s), titanium had a strengthening effect probably due to precipitation strengthening which was seen both in the strength of the welded steels and in the lower hardness difference between the base metal and the HAZ. Titanium, especially with higher concentrations, had a clear negative effect on the impact toughness of the fusion line and a somewhat smaller negative effect on the impact toughness of the fusion line + 1 mm position. This was probably due to the presence of large angular TiN inclusions promoting cleavage crack nucleation. Also unlike TiN precipitates, these inclusions are ineffective in preventing austenite grain coarsening in the coarse-grained HAZ.
Overall, high titanium contents have been shown to have a detrimental effect on HAZ properties: although titanium reduces the softening of the HAZ experienced in these types of steels, it has a clear negative effect on the HAZ impact toughness with low heat input.
The effect of a strain rate varying from 10-3 to 10-5 s-1 at a strain amplitude ranging from 0.25% to 0.6% on the low cycle fatigue (LCF) behavior and the microstructure of a 10%Cr-2%W-0.7%Mo-3%Co-NbV steel with 0.008 wt.% B and 0.003 wt.% N additions was studied at room temperature. The number of cycles to failure tends to slightly increase with decreasing the strain rate. The fatigue life time curves at all tested strain rates and strain amplitudes could be described using the Basquin-Manson-Coffin relationship. The transition life of 2Nt, when plastic and elastic strain components are equal, shifted to higher reversals with a decrease in the strain rate from 10-3 to 10-4 and 10-5 s-1, whereas the transition total strain amplitude, when plastic and elastic strain components are equal, remained unchanged. At cyclic deformation with low strain amplitude of 0.25%, strain softening is attributed to decreasing dislocation density and lath coarsening, whereas at Eac =0.6%, the knitting reaction between dislocations comprising lath boundaries and trapped lattice dislocation leads to the transformation of lath boundaries to subboundaries and strain softening. At Eac=0.25%, decreasing the strain rate leads to insignificant acceleration of recovery processes, whereas at Eac=0.6%, decreasing the strain rate slows down the knitting reaction, that leads to an increase in density of low-angle boundaries and kernal average misorientation.
The microstructural evolution of 304L and 316L steels during plate warm rolling to a strain of 3 and subsequent annealing as well as the structural effect on the mechanical properties were investigated. The warm rolled microstructures consisted of flattened wavy austenitic grains with transverse grain sizes of about 220 nm and 160 nm in 304L and 316L steels, respectively. The formation of the wavy austenite structures was facilitated by high density of microshear bands. The subsequent annealing was accompanied by the development of static recrystallization and grain growth. The 304L steel samples were characterized by a lower stability against recrystallization and grain growth as compared to the 316L ones. The grain coarsening during annealing was accompanied by gradual softening. The hardness decreased by 50% in both steels after annealing at 1073 K. The grain coarsening was accompanied by strength degradation, although the tensile strength of above 900 MPa and 1000 MPa remained in the 304L and 316L steel samples, respectively, after annealing at 700°C.
Ductile iron with 1.56% Ni was subjected to various cycles of the austempering treatment. For all variants, the austenitization temperature was 920oC and the time of holding was 2 hours. Austempering was carried out at temperatures of 260, 300, 330, 360, 380, 400oC with the time of 15, 30, 60, 90, 120 and 150 seconds. After each variant, the microstructure of the metal matrix was examined. Measurements covered hardness of the matrix and microhardness of "acicular" ferrite, austenite and martensite.
This paper deals with a comparison between the standard spring steel grade 0.54C-1.45Si-0.7Mn-0.7Cr and a spring steel grade micro-alloyed with 0.12%V in terms of microstructure, grain refinements, strength and ductile properties. The micro-alloyed steel is supposed to provide a better performance as it had been proved for hot-rolled and heat treated wires. The vanadium micro-alloyed steel grades are quenched in oil typically, and high strengths and high ductility can be expected. It has been confirmed especially for induction heat treatment and quenching temperatures 810-910°C, and the tempering temperatures 430°C and 450°C. That phenomenon explains the strengthening effect of vanadium carbides precipitation and effective suppression of the grain growth. The mechanism has been confirmed with electron scanning and transmission electron microscopy.
The article deals with the evaluation of chosen parameters of surface roughness on the square section samples from stainless steel 316L (1.4404), manufactured by the additive technology with using Selective Laser Melting method (SLM). As part of the experiment was measured (scanned) and compared of chosen parameters of surface roughness on plane area of the samples printed in the same process parameters with a difference of power of the laser. One set of samples was printed during half power machine (200W), the second during maximum power (400 W). The samples were oriented in the building chamber in the same way. The plane areas of blocks were parallel with plane XZ and YZ of coordinate system of 3D printer Renishaw AM400. The measuring of parameters of surface roughness was evaluated by optical microscope Alicona Infinite Focus5.
The article deals with the study of verification and evaluation of selected mechanical properties of stainless steel 316L (1.4404) after the production of additive technologies (3D printing) by Selective Laser Melting (SLM). For the purpose of the experimental testing were printed two sets of samples from the powder metal by the laser-sintering process at different process parameters. The main difference was in the power of laser for first set was determined half power 200 W and for second set maximum power of 400 W. The machine printed samples were further divided into two sets, one of which has been heat treated by annealing, the second set was not thermally affected. Making the test samples were realized on Renishaw AM 400. The investigated parameters were the results of mechanical tests of specimens after the tensile test according to EN ISO 527-1 and impact bending test by Charpy according to ISO 148-1.
This paper deals with the influence of various austenitizing temperatures on microstructure and kinetics growth of austenite grain in 9 CrNB steel. High austenitizing temperatures (1070 °C, 1150 °C, 1170 °C, 1190 °C, 1210 °C and 1230 °C) with a holding time 120 min were used. The microstructure was formed by martensite after austenitization. The occurrence of delta ferrite was observed in microstructure at temperature higher than 1190 °C. Delta ferrite was located at the grain boundaries and its amount was about 3 % at the austenitization temperatures of 1190 °C and 1210 °C and up to 5,5 % at the temperature of 1230 °C. In terms of the kinetics of austenite grain growth, it can be concluded, that up to temperature of 1170 °C there is an increase in grain size. At the higher austenitization temperature (over 1190 ° C) we observed the decrease of grain size.
Twinning Induced Plasticity steel, or TWIP steel, has had increased interest in recent years from various industry sectors. This is due to it being light weight, strong, and ductile; which are all properties that are useful in the automotive and aerospace industries. These steels potentially can offer lighter weight vehicles and parts with increased strength and other mechanical properties. This combination could offer greater fuel efficiency and performance while at the same time improving the safety features of the vehicle. This paper deals with the description of the behaviour of high manganese steel after cold rolling and subsequent annealing. Impacts on microstructure, phase composition, yield strength and tensile strength are described.
The Selective Laser Melting (SLM) is an advanced technology of producing three-dimensional solid objects (3D printing) from a digital file. The 3D object is created by laying down successive layers of material. The article deals with fatigue testing of SLM samples to determine the dependence of fatigue characteristics on the orientation of laser melted layers to the loading axis and on the quality of the surface of 3D printed objects. The results revealed that the transverse orientation of layers exhibits the distinctly lower fatigue life than both the longitudinal and inclined (45o) ones. The specimens with machined and polished surfaces exhibit much higher fatigue life than those as-received with significantly higher surface roughness.
The most negative effect of cavitation is the destruction of the solid surface by microjets impact or shock waves generated by implosion or explosion of cavitation bubbles.It is present in all hydro-mechanical equipment where the pressures fluctuate which lead to the appeareance and development of these bubbles, as a result of the flow section changing.
The paper analyzes the behavior and resistance to vibrating cavitation of grey cast iron with pearlite microstructure, used for manufacturing of components and shutters valves with metal-metal sealing. The experiment is performed on a standard vibrator device, and the evaluation is made based on microstructural images of eroded surfaces and by comparing the curves and specific parameters with those of quality carbon steel C45, which has in annealed state mechanical properties close of this grey cast iron.
The steels with high chromium content are known to suffer embrittlement at elevated temperature induced either by decomposition of the microstructure into two arranged solid solutions α + α´ (embrittlement at 475 °C) or by precipitation of chromium-rich brittle phase sigma. Martensitic precipitation hardening steels belong among materials having chromium content close to the minimum embrittlement concentration and in some circumstances there could be possibility of prolonged exposure of these steels at elevated temperatures. The effect of long-term ageing (1 000, 2 000 and 3 000 hours at 475 °C) on the material properties, microstructure and substructure of precipitation hardening martensitic stainless steel Custom 465 was analysed and the additional precipitation of very fine particles of intermetallic phases and also decomposition of solid solution α into chromium-rich particles of nanometric size of the phase α´ was found. Despite expectations a slight decrease of strength and impact energy was detected after ageing at 475 °C as a result of stabilization and of reverted austenite, which completely compensated the effect of the additional precipitation hardening of martensite. The total content of reverted austenite even doubled after ageing in comparison with the as-received state, although the ageing temperature (was significantly lower than the temperature Ac1 of the steel.
Stress relaxation of the prestressed steel wire ropes is quite important parameter not just for builders all over the world. A few steel strands twisted into a helix became very popular since its invention and today, they are used to transmit power through various distance. New materials bring new possibilities but they subject to the strict criteria. This poster describes the development and application for the prediction of prestress loss in seven wired steel ropes. It deals with a testing methods, calibration of relevant testing equipment, preparation of the test, test progress and conclusions of the measurement. Significant importance is also dedicated to the possible usage and extrapolation in accordance of relevant ASTM and EN standards, which can reveal possible behavior and lead to decreased lifetime of the material.
Extending the application area of Duplex stainless steels has led to the necessity of creating componenets or structures made of dissimilar materials. Due to the differences in the microstructure, the welding of the dissimilar steels is more difficult than that of similar steels.
The research carried out in the current paper focuses on the particularities of completing the heterogeneous welded joints between a Duplex stainless steel and a Cr-Mo low alloy steel using as additional material an electrode wrapped in E 309MoL - 16, which contains approx. 23 % Cr, 12 % Ni and 2%Mo. The implementation of this welding technology focuses on eliminating the technological operations of preheating and post welding thermal treatment, which is mandatory for welding low alloy steels sensitive to hardening through martensitic transformation and cold cracking respectively. Based on the Schäffler model a prediction of the metal microstructure laid by welding is carried out and the quality of the joints made is carried out by metalographical investigations.
Knowledge of the stress state induced in welding processes is important in construction design in terms of static as well as dynamic loads. Experimental research on physical phenomena accompanying welding processes are often reduced due to financial and time consumption reasons in favor of mathematical and numerical modeling of physical, structural and operational properties of welded joints.
This paper concerns computer analysis of stress states and numerical prediction of the formation of deformations in T-joint welded by a laser beam technique. Numerical analysis of thermomechanical phenomena are carried out in Abaqus/FEA commercial engineering software, which is based on finite element method (FEM). Three dimensional discrete model is created in the design module of Abaqus/CAE. Different inclinations of welding source are assumed with respect to the edges of joined elements. Numerical analysis takes into account changing with temperature thermomechanical properties of welded plate made of austenitic steel. Simulations of complex thermomechanical phenomena in welding process required the implementation of additional numerical subroutine written in Fortran programming language.
Mathematical modells of the power distribution of a moving welding source and the position of the source relative to the edges are implemented into numerical subroutine DFLUX. Temperature distribution, stress state and welding deformations are analysed on the basis of numerical simulations of thermomechanical phenomena.
The article presents a review of the most new structure materials that currently are being applied to production of different the vehicle elements. The main purpose of the article is to draw attention to the materials applied to fabricate this kind of elements.
The authors have made a comparison of the basic physical and chemical properties of these materials. Furtemore, they have considered the influence of those properties on the operation of the vehicle chassis elements.
The paper deals with the development of new clamping jaws which are designed for static tensile tests of miniature test specimens. The jaws are used to hold specimen of dimensions 2 x 1-20mm. During the static tensile tests, there were problems with the measurement of longitudinal deformation by laser extensometer what caused unreliable stress vs. elongation curve. For the deformation measurement, an extensometer Zwick/Roell laserXtens was used. In the paper, three development levels of mechanical grips that were designed at Mechanical testing laboratory of the Regional Technological Institute (Faculty of mechanical engineering, University of West Bohemia) are described.
The microstructures of complex phase 780C steel and TRIP 690T steel joints with thickness of 1.5 mm welded using fibre laser process were evaluated. The microstructures and microhardness of butt joints were characterized in the fusion zones and heat affected zones. The microstructure in the fusion zone was predominantly built of lower bainite and martensite. In both heat affected zones near 780C and 690T grain coarsening of dominantly martensitic microstructure with small portion of lower bainite and retained austenite was observed. The microhardness increased in the fusion zone and both heat affected zones of joints. The highest microhardness of 485 HV0.1 was measured in HAZ near 780C steel region of joint. The average tensile strength of all joints was 750MPa and it achieved the strength of the 690T steel, because the failures during the tests occurred in this steel base material.
Kinetics of austenite phase transformation in previously deformed steels of different alloy systems during continuous cooling are studied. It is shown that at basic chemical composition of steel of C-Mn-Ni-Cu-Nb-Ti with chromium addition (0.19%) results in formation after cooling practically of identical microstructure from the standpoint of fineness and hardness, as with molybdenum (0.14%) additive. An optimum steel alloy system is suggested from an economic point of view that provides the required set of properties for rolled sheet more than 30 mm thick of strength category X65 produced under conditions of the VMZ (Vyksa) sheet rolling complex (5000 mill).
The susceptibility to the hydrogen embrittlement of commercial melt of TRIP 780 steel of the type C-Mn-Si was studied on previously hydrogenated hydrogenated samples by a slow strain rate tensile tests (SSRT) in the initial state and in the state after 5% deformation in the longitudinal and transverse directions relative to the rolling direction. Samples were hydrogenated in 0.1N sulfuric acid solution with the addition of KSCN. Due to the transformation of retained austenite to deformation-induced martensite after 5% deformation, an increase of yield strength of 230 MPa, a tensile strength of 30 MPa and elongation at fracture decrease by 6.5 % occurred in the contrast with the initial state without hydrogen. The presence of hydrogen in the steel in the initial state caused a decrease of steel strength from 900 MPa to 753 MPa, and a significant reduction in elongation at fracture from 34 % to 6 %. Hydrogen present in the samples after the 5% deformation had an effect on the increase of the yield strength by 60 MPa, a decrease in the tensile strength by 100 MPa, while the elongation at fracture reached only 2.5 %. There were no differences found in the mechanical properties of the samples taken in the longitudinal and transverse direction relative to the rolling direction. Fracture surfaces of the tensile test bars were subjected to fractographic analysis. For hydrogenated samples, the proportion of brittle fracture and quasi-cleavage fracture increased.
This project is concerned to improve design, preparation of the adaptor and realization of the fatigue test on the Roller Finger Follower in the oil bath at frequency 40 Hz. This piece is produced by precision casting method and used in automotive industry as a part of the engine. Fatigue testing is conducted only in pressure load on several stress levels.
This paper attempts to study safety and exploitation conditions of long weld steel structures. To study the effects of the long structure flexibility and resistance, the structue been welded by steel electrodes with varied amount of Mo. The most significant of factors influencing that conditions are connected with material choice, welding technology, state of stress and temperature. Because of that a good selection of steel and welding method is crucial to obtain proper steel structure. Shielded metal arc welding (SMAW) is a very popular method of welding used for structure reparation. Very often SMAW could be also treated as main montage process.