Seznam abstraktů 2019: POSTEROVÁ SEKCE C

Microstructure of dissimilar weld joint of steels COST FB2 and COST F after creep test to the rupture was investigated by advanced scanning electron microscopy (SEM) techniques. The microstructure was imaged using a concentric back-scatter (CBS) detector, which enables us angular filtering of the signal electrons in the SEM. The filtered SEM micrographs offer precise and accurate information about the Laves phase presence in the matrix. Energy-Dispersive X-Ray spectroscopy (EDS) analysis was used for precise element distribution mapping and the high resolution EDS maps were collected. Information about the crystallography was acquired by an electron back-scattered diffraction (EBSD) technique. The SEM, EDS and EBSD results provide comprehensive information about the creep induced microstructural changes in dissimilar weld joint of COST FB and COST F steels. A relationship between the microstructure and creep behavior will be discussed in detail.

Recently, it is possible to observe a very fast development of the optical 3D scanning methods. It is caused by the development of computer technology and optical systems whose accuracy is becoming more and more competitive in comparison to other measuring methods. Companies offer a lot of kinds of 3D scanners prepared to different applications. Scanners are different in the aspect of size of measurement area and accuracy. The most important in aviation industry is quality because all the parts installed in airplane must meet dimensional requirement. 3D scanning allows very accurate measurements of manufactured parts with accuracy up to several hundredths of a millimetre. Additionally, it is possible to identify in a full way the measured elements thanks to the fact that they are saved in the form of a three-dimensional model. This is a huge advantage from the point of view of the aviation industry because it significantly reduces the risk of making a mistake and allows conducting virtual measurements of parts even when it is already mounted on the aircraft. This method also has many applications which are supporting the production process. Examples of such applications are measurements of tools and workshop aids, digitalization of tools that were made by hand or those for which there is no dimensional documentation in the form of a 3D model, scanning of entire aircraft, virtual assembly of elements, dimensional inspection of assemblies and checking their completeness.

This paper presents the results of the effect of temperature on stability of the structure of metallic glass. The iron-based metallic glass was subjected to annealing in the temperature range from 450oC to 650oC during 5 hours. The study found that the increase in the annealing temperature causes an increase in the percentage of the crystalline phase in the amorphous matrix. The examinations included X-ray measurements (phase composition, degree of crystallinity, crystallite sizes), the microscopic observations, and hardness measurement. The X-ray measurements were performed using a Seifert XRD 3003 X-ray diffractometer with the radiation generated by a tube with a cobalt anode.

The paper deals with the effect of high-pressure hydrogen on fatigue crack growth rate of low alloy 34CrMo4 steel used for hydrogen cylinders production. Testing was performed on pre-cracked 1/2 C(T) specimens, which were dynamically loaded both in the air and in pure hydrogen environment at pressure 15 MPa. Fatigue crack growth was measured using potential method measuring system. Hydrogen effect was assessed from different curves fatigue crack growth rate in both environments. Fracture surface analysis subsequently confirmed significant effect of hydrogen on fatigue properties of this material.

The effect of tempforming temperature on the microstructure and mechanical properties, especially impact toughness, of the S700MC-type high-strength low-carbon steel was investigated. Tempforming at temperatures of 923 and 973 K was characterized by the development of ultrafine-grained layered microstructure consisting of grains highly elongated in the rolling direction with the transverse grain size of 530 and 920 nm, respectively. This microstructure improved significant the mechanical properties including the toughness in a wide range of test temperatures. The steel tempformed at 923K exhibited the ultimate tensile strength of 1110 MPa and the impact toughness, KCV, above 450 J/cm2 at a temperature of 293 K, and KCV of 109 J/cm2 at a liquid nitrogen temperature for the impact direction perpendicular to the rolling plane. An increase in the toughness was achieved by absorbing the impact energy during the separation of steel in the direction perpendicular to the direction of impact.

The present work is focused on studying the effect of multiple forging at room temperature and subsequent annealing on the microstructure and mechanical properties of a promising austenitic stainless steel with increased nitrogen content. An austenitic stainless steel, Fe-0.03C-22Cr-10Ni-0.36N-6.2Mn-0.34Si-1.9Mo (all in wt%), with an average grain size of about 11 µm was used as the initial material in the present study. The multiple forging was carried out by means of multi-pass compressions at room temperature to a total true strain of 2. The multiple forging was accompanied by deformation twinning and resulted in significant strengthening. Upon reaching the total strain of 2, the yield strength increased by 690 MPa, and the hardness increased by 210 HV. The steel samples subjected to multiple forging to a total strain of 2 were annealed for 30 minutes at temperatures of 773, 873 and 973 K. Annealing at temperatures of 773 and 873 K resulted in further strengthening, i.e., the yield strength increased to 1990 MPa and 1940 MPa, the hardness increased to 614 HV and 588 HV, respectively. Annealing at a temperature of 973 K led to the formation of an equiaxial ultrafine-grained microstructure and a decrease in the yield strength and hardness to 1300 MPa and 407 HV, respectively. The microstructural evolution during multiple forging and subsequent annealing and the structure-property relationship are discussed in some detail.

Currently, quality control in modern enterprises is one of the factors creating the principles of organization and functioning of enterprises. The paper presents one of the techniques of non-destructive testing - ultrasonic testing in quality control of casting of the base of an industrial robot. Ultrasonic testing is used for inspection due to the possibility of detecting internal, surface and sub-surface discontinuities in the entire volume of the tested material. The aim of the study was to determine, using traditional quality management tools (Pareto-Lorenza and Ishikawa diagrams), the most significant incompatibilities of castings detected in ultrasonic testing and to reduce or eliminate the number of non-compliant products. The survey concerned a batch of products manufactured in the 3rd quarter of 2018 in one of the companies in the southern part of Poland. The results of the ultrasound examination revealed the presence of discontinuities (emptiness) in the casting. Tests carried out using the Pareto-Lorenz diagram have shown the most important discontinuity in the products - material voids. The use of the presented tools may allow for precise reaching the source of quality problems in the casting process. Further research directions will be related to the application of the presented research methodology in the quality control of the remaining products offered by the enterprise, and then its implications in enterprises of similar specificity.

9-12% Cr martensitic steels are used as materials for fossil power plants with steam temperature more than 600 °C. Superior creep strength of these steels is attributed to a dispersion of nanoscale boundary M23C6 carbides and Laves phase particles. The aim of present work is to reveal the mechanisms of grain boundary pinning by precipitates and their effect on the thermal stability of lath martensitic structure of a Re-containing (in wt %) 10Cr, 3Co, 3W steel. The structural evolution in a Re-containing (in wt %) 10Cr, 3Co, 3W steel with a low N content (0.002 wt %) and high B content (0.01 wt%) after creep at temperature of 650 °C under the stresses of 200 - 140 MPa was investigated. The time to rupture after creep test at 650 °C/140 MPa was about 11,000 h. Tis steel was solution treated at 1050 °C and tempered at 770 °C, formerly. The structure in the grip portion of the crept specimen changed scarcely after creep exposure for ~11,000 h. In contrast, the structural changes in the gauge portion were characterized by transformation of the tempered martensite lath structure into relatively coarse subgrain structure. The formation of a well-defined subgrain structure in the gauge section was accompanied by the coarsening of M23C6 carbides and precipitations of Laves phase during creep.

Resistance spot welding is one of the most used welding technologies for joining of thin, deep drawn steel sheets in automotive industry. The condition of electrodes may have significant impact on the resulting weld quality, therefore it is necessary to check the electrodes´ wear that otherwise may cause creation of specific defects in the weld joints. One of the possibilities is utilization of infrared thermography. In order to perform the testing correctly it is essential to know the expected emissivity of the electrodes. This article deals with the changes in emissivity due to wear. It demonstrates that the emissivity of new electrodes is significantly different in comparison with worn electrodes. The biggest change is observed between the first and 25th weld. With increasing number of performed welds the emissivity drops slightly with increasing number of welds. The increased temperature caused significant drops when temperature is elevated up to 40 °C, but it is virtually constant for temperatures above 40 °C. It concludes that a mean „operational emisivity of the electrodes operated at higher temperatures (i.e. 40 °C +) is a suitably accurate factor to be used during the weld inspection on defects.

In its pure form, aluminum is relatively soft, with poor mechanical strength and weak cavitation erosion characteristics. The alloys series 6xxx have as main elements alloying silicon and magnesium, which improve their mechanical properties, making them competitive for many structural applications. The present paper establishes the correlation between the heat treatment, the microstructure and the mechanism of cavitation erosion damage of a deformable alloy, aluminum base. Cavitation tests were conducted on a vibrator with piezo-ceramic crystals that meet ASTM G32 - 2010 requirements. The metallographic examinations by optical microscopy and scanning electron microscopy, coupled with the hardness tests, highlighted the microstructural changes in a cavitationally affected material and the cracks propagation mode.

The paper contains results of studies on the formation of oxide layers on 13CrMo4-5 steels long-term operated at an elevated temperature. The studied steels were operated at the temperature of 380 °C for 130,000 h (steel 1) and 535 °C for 230,000 h (steel 2). X-ray structural examinations (studying the phase composition and crystallite sizes) were carried out and microscope observations using an optical and scanning microscope were performed. The native material chemical composition was analysed by means of emission spark spectroscopy, while that of oxide layers on a scanning microscope (EDS). The obtained test results showed that the steel exploited at a higher temperature and longer time was significantly degraded.

Centrum výzkumu Řež will carry out fatigue and fracture toughness tests in the frame of project Research for Sustainable Energy, in support of the European effort for the development of the Lead-cooled Fast Reactor as one of possible cooling systems of the Generation IV primary circuits. In order to progress material development for the future nuclear systems, an insight into the material properties at cycle fatigue loading and fracture toughness of candidate materials in Heavy Liquid Metals is required. The testing equipment has greater demands on precise measurement by comparison with Constant Extension Rate Tensile test previously performed in Centrum výzkumu Řež. Thus an extensometer for the liquid metal environment was developed to improve the accuracy of the measured results. The approach to testing conditions was upgraded with pumping circulation loop and possibility for sampling of liquid medium during the pretreatment. The progress in solving an issue of precise measurement is summarized and the adjustments of testing equipment are presented and justified.

Residual lifetime estimation and early detection of possible risks of mechanical equipment failure and structures is a key question for reliable operation of industrial plants. Currently, this issue is particularly critical in power stations that are approaching their designed lifetime. Residual lifetime of operating device can be evaluated using standard tests, but these usually cannot be performed due to limited material amount that can be extracted from the components. It is possible to use in these cases a semi destructive sampling of materials and testing methods employing miniature specimens. This article deals with comparison of the creep results obtained with the use of on standard test bars and sub sized samples that are axially loaded. The experiment was performed on steam line steel CSN 15 128 after operation and G17CrMoV510. Emphasis was put to practical use of the test results and therefore residual life was assessed with the use of standard and new mini specimens. The results obtained for standard and mini samples exhibit very good agreement without necessity of any correlation.

All metal products that operate under high loading conditions are subject to wear over time. Therefore, there is a need to restore the geometric shape of the working parts after the consumption of the product life. For each material from which the product is made, special repair conditions are needed. There are many defects that can appear during the repair process, for example: cold and hot cracks, delamination and cavities. This article explores the possibility of repair using the DED process of the working part of the stamp from high carbon steel grade SKD11. Restoration of the worn area was carried out by surfacing the powder die tool steel H13. The results of the study of the structure and hardness in the repair zone are presented. It is shown that the obtained values are sufficient for this type of product, which indicates the successful restoration of a worn section of a high carbon steel product using the DED method.

Press hardening is a modern forming technology for the production of shaped sheet parts. Its use has been growing in recent years because of its high production accuracy, reduced spring back effect and lower forming forces. This technology is also suitable for high strength TRIP steels (transformation induced plasticity). However, with dies at room temperature, undesirably high cooling rates are obtained, leading to the formation of martensitic structures with a low ferrite content. These structures possess high strength but low ductility. It is therefore important to interrupt the press hardening operation at the right time or even carry out additional heat treatment in a furnace. Two low-alloy TRIP steels with a carbon content of 0.2 % and different niobium levels were selected for this experiment. At the first stage, the sheets were press-hardened between dies of a hydraulic press. The holding time was varied from 0 to 10 s and the sheet temperature after removal from the dies was measured with a thermal imaging camera. At the second stage, press hardening in a flat press hardening tool was followed by isothermal holding in a furnace. Mixed structures of martensite, bainite, proeutectoid ferrite and retained austenite were obtained when parameters were chosen properly.

This paper deals with effect of long-term exploitation on structure and mechanical and fracture properties of X20CrMoV11-1 grade steel. Mechanical properties were evaluated both using standard test specimens and small punch test (SPT). Obtained results were compared with received state conditions. Creep properties, crack growth rate as well as fracture toughness tests were carried out too.

This work summarizes results and progress in new method development for identification of material properties of steel. This work deals with application of the small punch test for evaluation of material degradation of power station in the Czech Republic within the project TE01020068 “Centre of research and experimental development of reliable energy production, work package 8: Research and development of new testing methods for evaluation of material properties”. The main effort is here an improvement of empirical correlation of selected steel materials used in power industry for the manufacturing of critical components (rotors, steam-pipes, etc.). The effort here is on the utilization of the finite element method (FEM) and the neural network (NN) for evaluation of mechanical properties (Young modulus of elasticity, yield stress, tensile strength) of the selected material, based on SPT results only. Paper contains results of experimental work carried out over past 7 years. After modification of actual neural network and increasing of the number of results interesting results of mechanical properties prediction have been obtained. Increasing data of points in common up to 300, leads to significantly lower deviation that varies about 3-5 %.

In the paper, the results of statistical control of complex metal products have been presented. The statistical process control (SPC) is indicated as a solution developed to collect and analyse data, which allow to process performance monitoring. The process has been validated based on the evaluation of the process repeatability - repeatability in terms of meeting the criteria approving the product as compatible. As the basis for assessing the stability of the assembly processes the measurements of tensile strength (statistical tensile test) of metal hitch shaped by cold forming have been indicated. A set of the strength tests from 5 production days (in period 1 and 2) has been presented. The changes on histograms and frame-mustache charts have been highlighted as a first sign of deregulation of the forming machine - a threat to process stability in terms of efficiency and quality.

Welding technology is not currently merely a technology for joining materials. With the development of additive manufacturing, welding can also be used as a technology to produce complex components. WAAM together with 3D metal printing are the basic technologies used for additive production. WAAM (Wire and Arc Additive Manufacturing) technology is characterized by cladding weld passes into final shape of mechanical part. The WAAM process is characterized by several variables, among others the MIG/MAG protective gas shield effects. The aim of this paper is to evaluate the influence of individual components of protective gases used for welding the whole structure. Especially it regards of Argon, Carbon dioxide, Oxygen and Helium according to the resulting component geometry and to the efficiency of the welding process. Thanks to the results obtained, a suitable shielding gas can be better determined by reducing the heat input to the material during welding especially reducing or eliminating content of carbon dioxide or helium.

At present time is increasingly applying 3D printing methods in the area of production of metallic materials also. 3D printing is use for serial and individual unit production in the aerospace, automotive and medical applications (prosthetics, implants, etc.). 3D printing methods are chosen especially for the production of dimensionally complicated products, where is difficult or impossible to achieve a result by classical methods of production. In the case of steels, the austenitic stainless materials with high nickel and chromium contain shall be applied in this area. Due to fact, that by this way manufactured material has diametrically different microstructure, it is necessary to verify its properties. This article deals with, in particular, mechanical and microstructural properties of products (test specimens) from Steel AISI 316L produced by 3D printing (SLM method). Assessments of the strength parameters in the tensile test, the impact energy and hardness are studied. For the assessment of basic microstructure, porosity and fracture surfaces evaluation the light microscopy is used. Obtained results are compared with the properties of identical test specimens made by “conventional” ways. The results show promising and homogenous mechanical properties.

The steel wires are used as strand core for phase conductors in electrical distribution network. The mechanical properties of these wires are tested by tensile strength, twist and winding tests before production of conductors. The new wires failed in winding test. The analysis of failure reasons was performed. The results show the negative effects of various impurities in steel.

Small punch creep test (SPC) is an alternative method for obtaining information about the material properties of steels and alloys when only a limited amount of test material is available that does not make it possible to perform conventional creep and/or stress rupture tests. SPCT testing can also be used for determination of the residual life of critical components of a fossil fuelled power plant. SPCT method is a part of the CWA 15627 "Small Punch Test Method for Metallic Materials" published in 2007 and this method will be a part of a prepared proposal of a standard of Small Punch Testing. Similar activities are also within ASTM (ASTM WK47431 “New Practice for Small Punch Test Method for Metallic Materials”), and in Japan they have an approved SPCT test standard. Although the complex stress state of the SPCT tests differs considerably from the uniaxial tension in case of creep test and further changes during the test, it was shown that the same stress-temperature dependence and relationships are valid in SPCT tests as in creep tests, and by using a simple load-based conversion factor between the SPCT test and the creep test with the same time to rupture, the results of both test types can be integrated. This is demonstrated by an example of modified chromium steel of F-type where a comparison of creep and SPCT tests results was presented, as well as the conversion factor that allows comparison of these two methods.

Low carbon low alloyed TRIP steel with partial substitution of silicon by aluminium was thermo-mechanically treated to obtain a multiphase microstructure typical for TRIP steels. The processing consisted of soaking at 900 °C and two compressive deformations applied during the cooling to the isothermal hold temperature of 425 °C. The microstructure was predominantly bainitic with about 17 % of retained austenite and little proeutectoid ferrite. Bainite consisted of the mixture of bainitic ferrite and retained austenite laths. The samples underwent tensile test with five different strain rates, 0.003, 0.3, 1, 10, 100 s-1. Mechanical properties show some dependency on strain rate, tensile strengths of 832-925 MPa were achieved together with total elongation of 30-38 %. Significantly higher strain rates of 380, 470 and 520 s-1 were produced by impact test with various initial positions of the pendulum (90°, 120°, 150°). In these cases, only the impact energy was evaluated, showing the increasing values with increasing deformation rate. The effect of increasing strain rate on the stability of retained austenite was also evaluated by the means of X-ray diffraction phase analyses. The microstructure after the straining was documented by scanning electron microscopy, as well as fracture surfaces.

The paper presents the results of investigation into the effect of structure banding on the mechanical and technological properties of finished wire rod. It describes also the causes of the formation of banding and the possibility of reducing it by changing the thermoplastic working parameters. Tests were carried out for a low-carbon ferritic-pearlitic steel intended for further cold plastic working. The test results have shown that the occurring banding adversely affects the mechanical and technological properties of the steel grade under study. Within the study, the rolling end temperature and cooling rate that reduce the banding and improve the finished product properties have been determined.

Bainite based quenching and partitioning process (BQ&P) has been treated as an optimizing heat treatment method to improve the mechanical properties of advanced high strength steel(AHSS). This is because it has been confirmed that the low toughness of martensitic steel is improved by the formation of a bainite phase, which has been known to form at above the Ms temperature, in the matrix. However, it has also been reported that lower bainite can be formed even below the Ms temperature. In this study, the method of isothermal heat treatment at below the Ms temperature(Quenching and Isothermal Bainite Transformation, Q&IBT) was proposed and the changes of the mechanical properties of medium carbon (0.27C) steel were investigated. By carrying out isothermal heat treatment below the Ms temperature, a complex phase steel consisting of auto tempered martensite, lower bainite and a small fraction of retained austenite could be obtained. And it was confirmed that Q& IBT steel has excellent impact toughness while having tensile properties comparable to AHSS steel.

16Cr - 2Ni - Mn- Mo - xN (wt.%) stainless steel powders were synthesized by mechanical alloying (MA) of elemental powders and nitrogen-containing ferrochrome (FeCrN) powders alloy. Compaction of resulting powders was carried out using spark plasma sintering (SPS) technology.
The microstructural and phase evolution of the powders at different times of alloying, microstructure, phase composition and mechanical properties after SPS were studied. The X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis showed that increasing alloying time up to 30 ks improves chemical homogeneity of the powders and promotes the formation of α-phase solid solution for the sample without nitrogen source and incomplete dissolution of FeCrN on the α-phase solid solution for the sample with a nitrogen source. The XRD and SEM analysis of sintering samples showed the formation of α and γ-phase solid solution. Tensile and microhardness tests showed increasing of tensile stress and increasing hardness for the sample with a nitrogen source.

During the spheroidization process of the heat-resistant alloy powder 3X11H2B2MF nanoparticles appears on its surface which can lead the influence on the microstructure and mechanical properties when manufacturing the parts. The paper presents the results of the microstructure study and mechanical tests of the specimens manufactured by directed energy deposition technology from the heat-resistant alloy powder with and without nanoparticles the recommendation of the further usage of the powder material obtained by plasma spheroidization are given.

Work is aimed at tool steel of 55NiCrMoV7 after four different heat treatment types. One part of material was after nitridation, other was quenched using laser, the third part was quenched by laser and subsequently nitrided and one part of steel 55NiCrMoV7 was in basic state after conventional quenching and tempering. Results of surface hardening using micro-hardness of all heat treated modes were compared mutually to find the most effective heat treatment. Micro-hardness was investigated from surface into the 2 mm depth of material. Micro-structure investigation completes the study and includes both purity evaluation and structure using light and SEM microscopy. The given steel type is suitable material for different applications, e.g. for cutting tools.

Cooling in the continuous steel casting process starts within the primary cooling zone. Controlling the amount of water flowing through the mould cooling system allows the shell thickness growth to be directly controlled. Depending on the continuous casting machine type, the secondary cooling zone is divided into a few spray sub-zones. The cooling intensity monitoring within the secondary cooling zone is more and more often related to the strand surface temperature measurement in the cooling chamber. This measurement is performed on the basis of modern systems using optical pyrometers. In this paper, the authors present the method of strand surface temperature measurement in the cooling chamber using optical pyrometers. In addition, the solidifying strand surface temperature was monitored with a thermovision camera, and direct measurements were performed with a contact thermocouple - immediately after the strand had left the secondary cooling chamber. The experiments were carried out in industrial conditions at ArcelorMittal Poland S.A. Unit in Dąbrowa Górnicza, on a six-strand machine for casting billets. The measurements covered a sequence comprising five heats of a high carbon steel grade, dimensions 160x160 mm. The authors used a proprietary measurement method presented in the awarded patent: PL 225107 B1 „Method of a continuous temperature measurement at any point of a wide area of the strand after falling off the solidified mould slag in the secondary cooling chamber of a machine for the continuous casting of flat ingots during the entire casting sequence”.

The cobalt based alloy, Stellite, was deposited through the TIG welding process on the surface of a Duplex stainless steel to improve cavitation erosion resistance of engineering components that work in aggressive environments. Cavitation tests were performed using ultrasonic vibratory equipment which complies with requirements of the ASTM G32 - 2010 standard. The microstructure of the deposited layers consisted of complex carbides in a Co-Cr solid solution strengthened alloyed matrix with a dendritic structure which ensures high hardness and a significant increase in cavitation erosion resistance compared to the base metal.

Modern low-carbon micro-alloyed steel for tubes must have high strength, ductility, weldability and special properties (toughness at low temperatures and resistance to hydrogen induced cracking (HIC)). Hardening of steels can be achieved in various ways.
One of the types of hardening is nitride hardening, in which the metal is especially micro-alloyed by nitrogen. Nitrogen adversely affects the toughness and resistance to brittle fracture of low-alloy steels by dissolving it in a solid solution or the formation of iron nitride, causing the phenomenon of deformation aging. When using it as a micro-alloying element in the metal, a nitride hardening mechanism is implemented, which leads to an increase in strength without reducing the plastic and viscous properties (in the case of simultaneous grinding of grain)
The concept of micro-alloying of steel with vanadium and nitrogen for production in casting and rolling complex is follows. A single-phase ferritic matrix, strengthened by dispersed precipitates of vanadium nitrides/carbonitrides, should be formed in the flat-rolled. In this case, nitrogen should be bound in the particles, so as not to embrittle the metal and not cause degradation of mechanical properties in the process of long-term operation of the pipe. This structure provides a combination of high strength and ductility. It is characterized by uniformity of mechanical properties in the longitudinal and transverse direction, has resistance to HIC. ACKNOWLEDGEMENTS: The paper presents the results of laboratory and industrial experiments of low-carbon V-N micro-alloyed steels.

The application of new materials in the power units of new generation, which are able to work at ultra-supercritical parameters of steam (T ≥ 620-650 °С, Р = 25 - 35 MPa), can increase their efficiency up to 41-44 % and decrease the amount of harmful emissions. The aim of the present research was to investigate the major structural changes in new Re-containing steel during ageing at temperature of 650 °C. Structural changes in martensitic 10%Сr-3 %Co-3 %W-0.2 %Re steel during long-term ageing at 650 °C for about 13,600 h were investigated. This steel was solution treated at 1050 °C for 1 h, cooled in air, and subsequently tempered at 770 °C for 3 h. High thermal stability of tempered martensitic/ferritic lath structure is provided by a dispersion of fine M23C6 carbides precipitated during tempering and the Laves phase particles precipitated after 110 h of 650 °C aging. The precipitation of the Laves phase particles is accompanied with depletion of W atoms from the ferritic matrix. Moreover, decreasing W content in the ferritic matrix have a good correlation with increasing volume fraction of the Laves phase particles in the structure of the 10 %Сr-3 %Co-3%W-0.2 %Re steel during long-term ageing at 650 °C. The effect of Re addition on the kinetic of depletion of W from the solid solution and kinetic of precipitation Laves phase will be discussed.

Thermal annealing is a proven material treatment method applicable to WWER type reactor pressure vessels with the aim of prolonging their operational lifetime. However, reactor pressure vessel internals of nuclear power plants are exposed to more severe operating conditions (high pressure and temperatures, higher neutron flux, corrosion environment), which cause gradual degradation of their mechanical properties. Thermal annealing can be one of the possible solutions to re-establish initial mechanical properties of reactor pressure vessel internals materials and thus can contribute to long term operation of nuclear power plants. This paper presents results of mechanical properties evaluation (especially hardness) of non-annealed and annealed state of material of WWER 440 - type reactor internals in initial un-irradiated conditions. Within the project an extensive program of experimental activities realized on un-irradiated materials in initial, work hardened, and annealed state was performed to create basis for further analyses on irradiated structural materials. As an integral part of experimental activities microstructural analyses were also incorporated to study of structural changes of non-annealed and annealed material. This paper includes results obtained within the project TH02020565 “Assurance of Safe and Long-Term Operation of Nuclear Pressure Vessel Internals” which is realized by ÚJV Řež, a. s. in cooperation with Czech Technical University in Prague, FNSPE, in the period from 2017 to 2020 with the support of Technology Agency of the Czech Republic.

TWIP steels are steels with a good combination of strength and plasticity. Their application should be relevant in case of critical parts of car bodies. The paper describes the development of a particular type of high carbon manganese steel with low carbon content from the design of the heat to final evaluation of microstructural and mechanical properties of rolled steel sheets. The heat treatment of cold rolled sheets ensured a high elongation in combination with a good yield and tensile strength together with a favorable phase composition of experimental steel.

16Cr - 2Ni - Mn - Mo - xN (wt%) stainless steel powders were synthesized by mechanical alloying (MA) of elemental powders, metal nitride (MeN) powders and nitrogen-containing ferroalloy (FeMeN) powders at argon atmosphere. The microstructural and phase evolution of the powders at different times of alloying and microstructure were studied. The X-Ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis showed that chemical homogeneity improves with increasing alloying time and decreasing nitrides powder content. The phase composition changes during the MA up to 30 ks processing time showed dissolving of alloying elements and formation of α-phase solid solution for the sample with low nitrogen contents. Samples with high nitrogen contents have a nitrides inclusion, which partially dissolves with increasing processing time.

One of the main concern in the development of the Gen IV lead-cooled fast reactors (LFRs) is the compatibility of the candidate structural steels and cladding materials with the heavy liquid metal (HLM). Structural materials compatibility in conditions relevant to plant operation is of primary importance to safety. The work describes performance of austenitic stainless steel AISI 321 with various surface pre-treatment exposed to liquid lead. The cylindrical specimens were pre-treated by using electro-polishing, pre-oxidation, and their combination as well as non-treated ones. Pre-oxidation was performed in argon with 30-50 Pa O2 at 450-500 °C for 14 days. Then the specimens were exposed to lead at 480 °C, flow velocity ~3 m/s and oxygen concentration 10-7 wt. % in corrosion loop MatLoo for 500 hr. The concentration of dissolved oxygen in liquid lead was controlled by mass exchange between flowing metal and argon cover gas with variable Ar ÷ 5 % H2-Ar or 10 % 02-Ar ratio. Oxygen concentration was continuously monitored using electrochemical oxygen sensors with Bi/Bi2O3 reference electrode. The Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS) was used for post-test examination of the surfaces and cross sections of the specimens. The SEM observation demonstrated significant differences in the behaviour and in the formation of thin oxide layers of the specimens. From tested specimens the best performance showed that specimen in as-received condition while pre-oxidized specimen formed non homogeneous and non-protective oxide layer and electro-polished specimen showed vulnerability to intergranular corrosion attack.

There are high demands placed on ensuring the integrity when building blocks of fossil power plants with USC steam parameters. Weld joints are critical parts of fossil power units. At present, the behaviour of the new austenitic steels such as HR3C (X6CrNiNbN 25-20) is not sufficiently studied. The aim of this paper is to study the microstructure and creep behaviour of the homogeneous HR3C weld joints in two states: in the as-welded state (AW) and after the post-weld heat treatment (PWHT). The PWHT was carried out at the temperature of 1230 °C for 15 min. Stress rupture tests were performed on the cross-weld joints of tubes ø 38 x 6.3 mm at 700 °C with times to rupture up to nearly 22,000 hours. The structural changes after long-term creep exposure were studied on longitudinal sections by various microscopic techniques. The stress rupture test results of welds after PWHT indicate slightly better long-term creep strength when compared to the AW state. The calculated creep rupture strengths at 700 °C/100,000 hours for the base material (BM) and the homogeneous weld joints after PWHT are almost the same. The AW specimens as opposed to the PWHT specimens did not show a noticeable growth of austenitic grains in the heat-affected zone (HAZ). In specimens after PWHT the average grain size in HAZ was more than twice that of the BM.

Using X-ray diffraction analysis, scanning electron microscopy and magnetic properties analysis the Sm2Fe17 compound nitrides after severe plastic deformation by torsion at a temperature of 77K were studied. It was shown that severe plastic deformation led to the structure refinement without the formation of new phases. A decrease in grain size led to coercivity increase up to 235.2 kA/m/2.94 kOe and a residual magnetization increase up to 53 A×m2/kg.

The main methods of cooling of hot-rolled strip at continuous mills and casting and rolling complexes are considered. Based on the data of the influence of the cooling conditions on mechanical properties of strip, the actuality of the existing equipment and automation modernization is shown (within the boundaries of the runout-table layout). An assessment of the effect of the cooling rate and the placement of water cooling equipment on the microstructure and mechanical characteristics is made. The paper summarizes the research and practical experience of accelerated and intensified water cooling at laboratory equipment and industrial rolling mill. During the production at industrial rolling mill, it has been established that for different thicknesses and initial chemical compositions, it’s possible to increase strength properties and cold-resistance of final strip. The transformation of the microstructure of steel by varying the conditions of post-deformation cooling contributes to obtaining rolled products of various strength classes from steel of the same chemical composition.

The article analyses the state of the production process of the friction bearings into the NT compressor. The basis of this article is the production process of the friction bearing, where it was necessary to suggest a fundamental change for the intensification of the production. Significant change mainly concerns production technology, and consequently the design of material and semi-finished product from which the new friction bearing will be produced. An important part of the process is the design of the bearing, the technological process and the following testing and comparison by simulation of strength analyses of the model of the present and the designed bearing. The article compares production costs of the current and designed process also it evaluates investment and returns on the designed technology of production.

This paper is focused on the modelling of the heat-affected zone of steel P92 during one layer TIG (141) welding. Simulation of the heat-affected zone (HAZ) was performed on the thermal cycle simulator of its own design. The test results of mechanical properties of the modelled HAZ are compared with the results obtained on real welded joints. Critical parts of ultra-supercritical (USC) boilers are welded joints. This significantly affects the operational reliability and service life of components in USC blocks. Therefore, this work is focused just on the research of the properties of HAZ of P92 steel. The thermal cycle simulator allows transferring the properties of very small HAZ to the sufficiently large sample where the tests of the mechanical properties can be performed. Satisfactory accordance was found when comparing the microstructure and mechanical properties of real welds and simulated samples.

The susceptibility to hydrogen embrittlement of a dual-phase steel DP600 with ferritic-martensitic microstructure was studied on previously hydrogenated samples by slow strain rate tensile tests (SSRT). The samples were subjected to electrolytic hydrogen charging in 0.05M sulfuric acid solution with the addition of KSCN at a current density of 1 and 5 mAcm-2 during 4, 8 and 24 hours. Due to the presence of hydrogen in the steel microstructure, a decrease of elongation at fracture from 24 % to 15 % was observed. Index of hydrogen embrittlement describing the relative change of elongation at fracture due to hydrogen was calculated as 38 % for the following hydrogen charging conditions: current density 1 mAcm-2 and time 8 hours. The index of hydrogen embrittlement decreased with increasing the hydrogenation time and the current density likely due to the formation of a corrosion layer that prevented further penetration of hydrogen into the steel. Changes of yield strength and tensile strength at a low current density were not observed, but at higher current densities, the yield strength increased by more than 40 MPa. Fracture surfaces of the tensile test bars were subjected to fractographic analysis. Transgranular ductile fracture was a predominant kind of fracture for all testing conditions, even for hydrogenated tensile bars. The proportion of quasi-cleavage fracture typical of hydrogen embrittlement was very low.

This article describes the practical application of hot extrusion for compaction of magnesium shavings in semi-finished products and the study of the influence of process parameters on the mechanical properties of the obtained MA5 (AZ80) magnesium alloy bars. Production of bars was carried out at different heating temperatures and plastic deformation degree to find technology provide the best combination of tensile and compressive properties. The resulting bars are somewhat higher in strength characteristics than the strength of deformed cast bars made from MA5 alloy, however, they are significantly lower in ductility.

Creep is one of the main phenomena responsible for degradation of material on in-service equipment operated at high temperatures and pressures e.g. steam pipings and superheaters. Process is accompanied by microstructure changes as well as plastic deformation of the equipment that is difficult to measure via conventional NDT. Ultrasonic waves velocity is able to react on changes created due to microstructure changes and due to change of stress-strain conditions. Measurements performed as a part of this article monitors deformation on a cross-section of a steam piping from heat-resistant steel via area scan of ultrasonic waves velocity ratio. Experiments also confirmed that the trend of the velocity ratio along the part´s circumference corresponds to the cross-section measurements and is in correlation with hardness development.

Welding is one of the so-called special processes that require verification to ensure correct execution in sufficient quality. Low-quality weld is not satisfying the requirements for in-service operation, either due to presence of defects (e.g. cracks, lack of fusion, porosity), or due to undesirable microstructure changes in heat-affected zone, that causes degradation of the weld joint. Welds are the main topic of NDT that searches for defects. The main method for detection of internal defects is the ultrasonic testing, that recently saw many new applications. This article shows how to use Phased Array probes to detect microstructure changes due to failure to follow the welding procedure. It was experimentally confirmed that the technique is able to identify microstructure changes in heat-affected zone created by change of welding parameters or by poor restart. The technique may be in principle performed in parallel with ultrasonic testing for defects, so it is possible to be used one instrument to perform complex assessment of weld joint quality.

Each metal is characterized by its typical stacking-fault energy (SFE). The higher this energy is, the less often are stacking errors in the crystal lattice. The stacking-fault energy has a large influence on the behavior of the metal during plastic deformation, which is mainly related to the relationship between SFE and the dislocation ability for climbing and lateral slip. The measurement of deformations is usually performed in a uniaxial tension test. In order to determine the deformations in real time, GAMA's ARAMIS system is used, which is non-contact and is independent of the tested material. Its operation involves the use of digital image correlation. An interesting solution seems to be the use of thermovision to measure deformation by analyzing thermographic images during stretching of materials. The aim of the study was a comparative analysis of the results obtained by measuring strains using the ARAMIS system and temperature using a FLIR thermal imaging camera. Samples cut from sheets of aluminium, copper and steel alloys were designated for testing. In the first frame, the most favorable way of preparing the surface of the plates was determined in order to obtain reliable temperature measurements by increasing the emissivity factor. The samples were then stretched. Then a correlation was made between the temperature and the deformation for a given material. The results allow us state that thermovision can be successfully used in the future to measure material deformations.