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Structural components which are loaded in cyclic load mostly fail due to fatigue. The fatigue strength of metals as well as weld joint regions in metals depends on mechanical properties especially hardness, the size of defect and the size of grains. Resistivity of the fine grain HAZ prepared against fatigue crack initiation will be explained in this article. Samples of material with martensitic fine grain microstructure were prepared by laboratory furnace by proper thermal treatment. Mechanical properties of fine grain heat affected zone and its microstructure were investigated. Special attention was given to behavior of fine grain during the cycle loading under stress concentration. Stress concentration was similar to the one in real welds. The S-N curve and the fatigue limit were determined. The Paris curve and the threshold for crack propagating were also determined. [ABSTRACT FROM AUTHOR]

This presented paper deals with the mechanical properties of diffusion alloyed Cu–Ni–Mo sintered steel. The material’s response to static and dynamic loading is summarized from previous work and referenced, while the testing methods and results for the fracture mechanics’ parameters are discussed in greater detail. It was observed that despite being more brittle, additionally quenched and tempered sintered steel has a lower crack growth rate than basic sintered steel. However, fracture and impact toughness are reduced after quenching and tempering. The crack growth threshold was found to be very similar and slightly higher after additional heat treatment. [ABSTRACT FROM AUTHOR]

This paper presents research experience related to implementation of vibrations on residual stress relief with the equipment for treatment by vibration method. The paper provides explanation of effects achieved by vibration method when implemented during welding, and elaborates advantages and disadvantages of that method applied after welding process. In order to present effects of vibration on solid structures, there was experimental analysis performed and compared with heat treatment. [ABSTRACT FROM AUTHOR]

This paper presents weld thermal cycle simulation of high strength steel S960QL, and describes influence of cooling time t8/5 on hardness and impact toughness of weld thermal cycle simulated specimens. Furthermore, it presents analysis of characteristic fractions done by electron scanning microscope which can contribute to determination of welding parameters for S960QL steel. [ABSTRACT FROM AUTHOR]

The paper presents impact energy results of thermal cycle simulated specimens of quenched and tempered fine grain structural steel S960QL. These results are obtained by examining notched Charpy specimens. Upon performed metallographic analysis and measured hardness, total impact energy is separated into ductile and brittle components. [ABSTRACT FROM AUTHOR]

Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material is presented in this paper. The research is done on a hot strip mill working roll where High Chromium Steel is used for roll's shell material. To obtain corresponding parameters, a rectangular single edge notched bend specimens - SENB, according to standard BS 7448, were used. The fatigue crack growth analysis was done on a resonant testing machine with use of special crack gauges, while for fracture mechanics parameters the electro-mechanical testing machine was used. [ABSTRACT FROM AUTHOR]

The paper presents research of weldability of microalloyed high strength steels TStE 420 and S960QL after weld thermal cycle simulation. Beside mechanical properties hardness and impact strength, the microstructures of characteristic weld thermal cycled structures for both steels are given. The results will contribure to determination of weakest points in Heat Af ected Zone of both steels. [ABSTRACT FROM AUTHOR]

The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the material in the connection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT. [ABSTRACT FROM AUTHOR]

In the process of testing real components exposed to elevated temperature, it is not possible to neglect cracks. The most significant cracks can be induced by welding, which is applied for joining of structural components. Pressure equipment in service is also exposed to high pressure and high stresses. Materials for their manufacturing are designed to resist high stress at elevated temperature, and to meet requirements regarding creep resistance. The objective of this study is to investigate microstructure of different regions of the heat affected zone in T/P91 steels by using thermal simulation instead of welding. [ABSTRACT FROM AUTHOR]

Abstract: The subject of this paper is the microstructural and mechanical characterisation of regions of the heat-affected zone (HAZ) in steels containing 9–12% Cr that are used for operation at elevated temperatures. Tests were performed on regions in the HAZ, which was created by physical simulation using a thermal welding simulator. Half of the simulated samples (SSs) were tested at room temperature (RT) and at an operating temperature (OT) of 600°C immediately after simulation/welding, while the rest of the simulated samples were tested at RT and at the OT after heat treatment following the welding, i.e., post-weld heat treatment (PWHT). In addition to the results from mechanical testing, the results from microstructural analysis using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are also presented. The manner in which PWHT contributes to the creep resistance of the HAZ in P91 steel is demonstrated. [Copyright &y& Elsevier]

Abstract: The article deals with the comprehensive research of temperature influence upon fracture energy of operational 12Cr1MoV steel of steam superheater collector of TP-100 type boiler. The authors found out that heating from 20°С to 200°С results in an increase of Charpy toughness and eventual reaching of plateau. There were also spotted the main dependencies of changes of steel microhardness along the thickness of collector considering on the distance from the hole. [Copyright &y& Elsevier]

This paper presents results of a study on martensitic coarse grain heat affected zone that can appear in welded joints. Mechanical properties of martensitic coarse grain heat affected zone and its microstructure were investigated. Special attention was given to its behaviour during the cycle loading under stress concentration. Stress concentration was similar to the one in real welds. The S-N curve and the fatigue limit were determined. The Paris curve and the threshold for crack propagating were also determined. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical comparison calibration of gauge blocks with dissimilar materials at the highest level is not wide spread because bigger national laboratories tend to calibrate non-steel gauge blocks with reference gauge block of like material. For smaller laboratories this is not viable economically due to the high costs of reference gauge block sets. Therefore, steel reference sets are used for calibrating gauge blocks from other materials. Lack of knowledge about material properties is causing a significant rise in calibration uncertainty. In order to improve best measurement capabilities, we have performed extensive research on gauge block material behaviour. For this purpose we have bought sample gauge blocks from all leading producers and evaluated their influences on the uncertainty budget, based on experimental measurements. The uncertainty budget of gauge blocks with dissimilar materials mechanical calibration, as well as the results of analytical and experimental research, is presented in this paper in detail. Significantly smaller uncertainty of gauge block calibration of dissimilar materials is achieved. [Copyright &y& Elsevier]

Abstract: In this investigation we look at the influence of the local residual stresses caused by Vickers-pyramid indenting on the initiation and early propagation of small cracks from indentations in coarse-grain martensitic steel. The size of these indentations is comparable to the grain size. Specimens with and without a local residual stress field were tested on a rotary bending machine. A focused ion beam and a scanning electron microscope were used to reveal the influence of those stresses on the location of the cracks’ initiation and the mechanism of the small-crack propagation. The existing local residual stresses assist in the initiation of two cracks at a level lower than the fatigue limit. The early small-crack propagation is gradually obstructed by the residual stress-field configuration until the cracks become non-propagating cracks. At levels higher than the fatigue limit, both cracks succeed in breaking through the compressive stressed domain and link together. From that moment the crack begins to behave as a long crack, penetrating outside the indentation into the tensile-stressed domains. [Copyright &y& Elsevier]

The fracture toughness of some areas in the multi-pass heat affected zone (HAZ) of a high strength low alloy (HSLA) structural steel was analysed in a straightforward way using precracked, cylindrical specimens tested on a conventional tensile machine. The specimens were made from samples with a simulated HAZ microstructure; however, the size of the samples was restricted by the limitations of the Gleeble machine. The brittleness of the samples was an indication of the detrimental effect of welding on their toughness. The specimens were not large enough for a direct KIc measurement over a wide testing temperature range; it was necessary to modify the results. The low fracture toughness and the substantial shift of fracture transition temperatures suggest that welding of the investigated steel could be a delicate procedure. [ABSTRACT FROM AUTHOR]

• Fatigue and fracture behaviour of FSW AA2024-T351-joints was investigated experimentally. • The fatigue and fracture behaviour regarding typical welding parameters is presented. • The highest value of the threshold stress intensity range was obtained for the welding speed v = 116 mm/min. • The highest value of the fracture toughness was obtained for the welding speed v = 116 mm/min. • The welding speed v = 116 mm/min was found favourable in regard to the fatigue and fracture behaviour. The presented paper deals with the mechanical properties of Friction Stir Welded (FSW) AA2024-T351-joints. The material's response to the static and fatigue strength (S – N curve) is summarised from previous work and referenced, while the testing methods and results for the fatigue and fracture mechanics' parameters regarding to the fatigue crack growth and occurrence of final fracture are discussed in the greater details and represent the main contribution of this work. The evaluation of the obtained experimental results was performed for three different welding speeds (v = 73, 116 and 150 mm/min), which enabled the determination of the most appropriate welding speed in regard to the fatigue and fracture behaviour of the analysed FSW-joint. The highest value of the threshold stress intensity factor range, Δ K th , and, consequently, the highest resistance against crack extension, was obtained for the welding speed v = 116 mm/min. A similar conclusion was observed when determining the fracture toughness K JIc , where the highest value was obtained for the same welding speed. On the other hand, not significant differences in the slope m were obtained between the considered welding speeds when analysing the fatigue behaviour in the modified Paris diagram. In that respect, it can be concluded that the welding speed v = 116 mm/min is favourable in regard to the fatigue and fracture behaviour of the analysed FSW-joint. [ABSTRACT FROM AUTHOR]

In the current paper, the main regularities in fracture of the railway axle steel have been found. It is established that the energy intensity of the steel fracture is connected with the deformational manifestations at the meso and macrolevels. As a part of the methodology of mesomechanics, the deformation behavior of the locomotive axis material has been described, taking into account the interaction between the processes that take place at different scale levels under the impact loading of Charpy specimens. A special role is given to the investigation of the local response of the material at the mesolevel, where the stress-strain state is characterized by a significant nonuniformity, and leads to the formation of shear lips. The shear lip parameters are found to be linearly and depend on the energy intensity of the impact deformation and fracture of the material. The additional evaluation parameters of the energy intensity of deformation and fracture of Charpy specimens can be tore out on the surface and micromechanisms of fracture. [ABSTRACT FROM AUTHOR]

The main features of crack initiation in main gas pipeline steel after forty years of operation with impact loading are studied. The energy capacity of gas pipeline material breakdown is studied for different directions of specimen cutting. Each stage of the impact loading diagram is specified by self-organization of deformation levels, and the shape of the diagram makes it possible to describe the stages of breakdown. [ABSTRACT FROM AUTHOR]

This paper elaborates results of hardness and impact energy of thermal cycle simulated specimens of high-alloy steel P 91 and their dependence on cooling time from 800 to 500 °C. Results were obtained by measuring hardness HV 1 and by experimental testing of Charpy notched specimens. Metallographic analysis of samples was performed on scanning electronic microscope. [ABSTRACT FROM AUTHOR]

The paper deals with research into dependence of hardness and impact energy of thermal cycle simulated specimens of fine-grained structural steel S960QL on cooling time from 800 to 500 °C and on tested temperature. Results were obtained by measuring hardness of HV 10 and by experimental testing of Charpy notched tubes on instrumented Charpy hammer. Total impact energy, initiation energy and fracture propagation energy needed for occurrence of fracture is also elaborated. [ABSTRACT FROM AUTHOR]

We study the impact toughness of three batches of Charpy specimens cut out from the rollers of continuous-casting machines. We determine the stages of dynamic deformation and fracture of bimetallic and monometallic specimens on the micro-, meso-, and macrolevels. With the help of scanning and transmission microscopies, we study the specific features of the micromechanisms of plastic deformation and fracture for steels with ferrite-pearlite (35G2) and ferrite-martensite (18Kh11MNFB) structures. In addition, we analyze their impact toughness with regard for these features. [ABSTRACT FROM AUTHOR]

A study was made of the impact toughness of three series of Charpy specimens that were cut from a continuous-caster roller and contained stress concentrators having different orientations relative to the hard-facing on the roller. Tests were performed on an automated impact tester. The steel with a ferrite-pearlite structure (steel 35G2) was found to have a higher impact toughness than steel with a ferrite-martensite structure (steel 18Kh11MNFB). The effect of microstructure on crack growth in the bimetal was studied experimentally for different types of steels. The results that were obtained can be used to check the impact toughness of hard-facings. [ABSTRACT FROM AUTHOR]

The analysis of the energy of fracture of specimens from steel OSL, which is widely used for the manufacture of railway axles under shock loading, is performed. The nature and quantitative parameters of the typical stages of the processes of plastic and brittle fracture, depending on the test temperature and stiffness of the stress state at the tip of the crack-like defect, are established. It is shown that impact loading at 20 °C leads to the formation of the local zone of plasticity and ductile-brittle fracture of the material. An increased stiffness of the stress state at the tip of the defect at −40 °C causes brittle fracture. An approach is developed, which is based on using the size of shear lips as a quantitative parameter of fracture under normal and low temperatures, similar in its physical essence to deformation approaches of nonlinear fracture mechanics. Based on this approach and the quantitative analysis of specimen fracture zones, the physical and mechanical scheme of specimen fracture is proposed in the presence of localized plasticity and in its absence near the tip of the concentrator. [ABSTRACT FROM AUTHOR]

We study the mechanical and corrosion-mechanical properties and the behavior of hydrogen in X52 steel in the intact state and after operation for 30 yr. It is shown that the long-term operation of gas mains made of this steel is accompanied by the degradation of the metal in the bulk of the pipe wall. This is manifested, first of all, in the decrease in impact toughness, relative narrowing ψ, fracture toughness, and corrosion-cracking resistance. It is shown that the in-service embrittlement of the metal is characterized by the presence of two anomalies in its mechanical behavior, namely, its brittle fracture resistance decreases parallel with the drop of hardness and the decrease in ψ is accompanied by the increase in relative elongation. The characteristics of crack growth resistance are especially sensitive to the in-service degradation of the material. The detection of degradation is more efficient under the action of embrittling factors, such as the severe stress-strain states, low testing temperatures, and the presence of corrosive media. In general, the degradation is more pronounced for the bottom part of the operating pipes, which is explained by the negative effect of hydrogen penetrating into the metal from the transported media. A hypothesis is advanced concerning the microdamage of operating steel as the principal factor of degradation of pipes as a result of long-term operation. Note that the results of investigation of hydrogen permeability and the temperature dependences of the extraction of hydrogen from the metals in different states are in good agreement with the proposed hypothesis. [ABSTRACT FROM AUTHOR]

This paper presents the results of investigation of a nuclear reactor pressure vessel steel 15Kh2MFA of two strength levels under cyclic loading. The mechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found. [ABSTRACT FROM AUTHOR]