Seznam abstraktů 2016: POSTEROVÁ SEKCE C
Datum: 26.5.2016
Most cryogenic systems failures are generally caused by incorrect choice of construction materials or neglect change of some physical property from the atmosphere to low temperatures. For example, the property of ductility of the material requires careful consideration since the low temperature has the effect of making some structural materials brittle or less malleable.
The aim of our work is to study the behavior of two metals at low temperatures: austenitic stainless steel A790 and Carbon Steel A333, especially their behavior in the hardness and resilience tests.
The samples (14 for each metal) are cut in pipes formed by two pieces welded steel and subjected to hardness tests which are applied in 45 points distributed in three areas of the sample : the base metal; the heat affected zone and the molten zone representing the welding metal. Other samples (also 14 for each) were subjected to Charpy tests and the absorbed energy were recorded.
The tests were conducted on the prepared samples from ambient (25°C) to low temperature of ( -150 ° C). In total seven different temperatures were used in this study (25, 0, -30, -60, -90, -120 and -150 ° C). Results of the resilience and hardness tests for each temperature were analyzed.
It was confirmed that at low temperatures the behavior of the austenitic stainless steel A790 is more adequate than Carbon Steel A333.
This paper analyzes, by comparison, the cavitation erosion resistance of the samples treated through softening annealing at 710 ±10°C with the purpose of partial spheroidization of pearlite and decomposition of free cementite traces from the microstructure, respectively the samples treated through normalizing at 860 ±10°C with the purpose of the pearlite proportion increasing and the cavitation erosion resistance improving. Cavitation tests were conducted on a vibrating device with piezoceramic crystals, following standard rules ASTM G32-2010.
The microstructure characterisation of the heat treated and eroded by cavitation was made by optic microscopy, and scan electronic microscopy.
The obtained results show an improvement of cavitation erosion resistance after the application of the heat treatment for normalizing as a follow-up of the structure finishing and growthing of the pearlite proportion in the base matrix.
Additive technologies provide engineers with an innovative approach for design and manufacture of parts. Additive manufacturing technologies, such as selective laser melting, allows making metal products by melting the powder and obtaining a solid-phase structure. The paper presents results of study of selective laser melting process of 316L steel powder. Morphology and particle size distribution of the initial powder was studied. The chemical composition, microstructure and phase composition of compact samples obtained by selective laser melting technology before and after heat treatment was investigated. The results show that the density of the samples was close to 100%. Analysis of microstructure of samples before heat treatment shows a high crystallization speed, leading to the formation of the fine structure. Mechanical tensile properties of samples before and after heat treatment were measured.
Today, advanced steels which are used in the automotive industry are required to possess high strength and ductility. Two heat treatment methods capable of meeting these requirements were tried in the present experimental programme that involved selected types of steels. These methods were the Q-P process (Quenching and Partitioning) and intercritical bainitic annealing. Favourable elongation levels combined with high ultimate strengths were obtained by stabilizing the retained austenite in the microstructure.
The Q-P process, which can produce mixtures of martensite and a certain amount of retained austenite, led to strengths above 2000 MPa and elongation levels of 10-15 %. The intercritical annealing, which results in combinations of bainite, ferrite and retained austenite, provided strengths of up to 2000 MPa and elongation levels up to 25 %.
Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the required shape. Basic parameters of mechanical, electrical, and magnetic properties of the sheets are usually obtained from the producer but the magnetic properties are changing in dependence on additional machining processes. The aim of this study is to describe changes in parameters of magnetic behavior after punching, laser and spark cutting of the original sheets. The basic information of structure was obtained by optical and scanning electron microscopy. The magnetic parameters were acquired from the measuring of magnetic hysteresis loops in dependence on saturation fields and frequencies. The results are discussed from the point of view of applied cutting technology with the aim to obtain the best magnetic parameters and consequently a higher efficiency of the final product. Results can be used as input parameters in simulation of the electrical machine.
Assessment of remaining lifetime represents a very complicated problem, which needs the knowledge of degradation processes in the material of a component, and also the service conditions of the compo-nents, e.g. way of loading and the influence of the surrounding environment. There is a common interest to operate the produced components as effectively as possible and thus as long as possible without reducing their safety and reliability, what could cause economic and human losses. This is a problem of safe operation and its prolongation in justifiable cases.
As a result of new modern and more resistant materials development, the general interest is to be able to evaluate the extent and rate of degradation processes at various service conditions, mainly to prevent the components from brittle fracture. The goal even in the stage of a component design is to guarantee their long-time operation. At present, the assessment of component material microstructure is one of the methods that makes it possible to evaluate its remaining lifetime.
It is thus important to be able to evaluate the extent of material mechanical properties degradation as a result of various service factors and the elaboration of methods for its assessment.
Nowadays, the evaluation of component material microstructure represents one of the possible meth-ods for remaining lifetime assessment.
In the paper there were presented possibilities of combining metal sheet with metallic foams using a sintering powder mixture in dissociated ammonia. The research were carried out over the properties of sintering powder iron foam, with superalloy HASTELLOY® X, by diffusion joint. The results indicated that there’s a possibility to obtain the satisfying quality joint between the Fe foam and superalloy HASTELLOY® X.
The studies were focused on the properties of microstructure and some mechanical characteristics. Example of structural applications for metallic foams, utilizing benefits in weight, stiffness, energy dissipation, mechanical damping, and vibration frequency were summarized already by many authors. That’s why, the author chose to study selected properties of fusion of Fe foam and superalloy sheet metal with new approach.
The studies used to determine basic quality parameters of the sintered joint. Using EDS analysis, there were identified a types of alloying elements and the extent of diffusion from superalloy HASTELLOY® X in the course of Fe foam.
In the paper the method of predicting the structural composition and mechanical properties of heat affected zone (HAZ) welded joints using the analytical methods was presented. On the basis of presented phenomenological formulas the computational CCT diagram and corresponding with it phase composition according to cooling rates of S355 steel was created. These values were used to predict the structural composition and mechanical properties of HAZ welded joint. The mechanical properties of HAZ through arising structure in this area and mechanical properties of individual phase components were determined.
The predicting of phase composition and mechanical properties of the SWC was performed for the front of the weld joint carried out with the laser technology. The ABAQUS FEA engineering software was used in order to determine the temperature field. In the calculations, the mathematical model of the volume source welding, based on the distribution of power described by Goldak distribution was applied. On the basis of the temperature distributions in the welded joint, the phase composition and mechanical properties of the SWC were determined. For the purpose of verification of the results, the experimental studies of the base material investigated steel were performed.
The article presents the research results on the mechanical properties of aluminum alloy 5083 – the most currently used in shipbuilding aluminium alloy and its friction stir welded (FSW) joints. Influence of different welding parameters and kinds of welding tools used for the connection of the sheets made of 5083 alloy on quality of the joint were presented. During the study used two types of tools: with cylindrical pin and with conical pin. Metallographic analysis of chosen joints showed the correct construction of structural bonded joints.
Friction Stir Welding (FSW) – a new technology can be successfully used for butt welding of different types of aluminum alloy sheets. FSW method can be an alternative to traditional arc welding methods i.e. MIG or TIG. The research was carried out using a static tensile test in accordance with the requirements of the Standards PN-EN ISO 4136:2011 and PN-EN ISO 6892-1:2010. Flat samples cut perpendicular to the direction of rolling were used. The research was conducted at the temperature of + 20ºC.
The shape of the welding tool pin does not affect the strength properties of the FSW welded joint. In the case of joints welded by FSW method, achieved reduction of ultimate tensile strength (UTS) approx. 7% and yield strength (YS) approx. 12% compared to the native material. When considering plastic properties of FSW welded joint observed almost 2 times lower elongation comparing to the native material, but with reserves meet the requirements of classification societies, including the PRS (Polish Register of Shipping).
The work deals with two types of high entropy alloys (HEAs) of Fe4CrCuMnNi and Fe4CrCuMnNi type, which were laboratory synthesized by vacuum arc-melting method. Much cheaper Fe of higher portion replaced cobalt in high entropy alloy of CoCuCrMnNi type. Tensile tests and micro-hardness for both HEAs and a susceptibility to hydrogen induced cracking for Fe4CrCuMnNi were carried. Reached results in as cast state of both HEAs were compared each other. Mechanical properties were more favourable in case of Fe4CrCuMnNi. In average, yield stress was by 29 % higher, strength insignificantly lover by 14 MPa, while ductility by 2 % higher. Micro-hardness HV0.5 showed higher level in case of alloy with higher Fe content. Regarding hydrogen induced cracking of Fe4CrCuMnNi alloy under conditions in accord with NACE Standard TM0284-2013, Item No. 21215 the exposed samples were without any defects, even when length of sample was approx. 15 mm and diameter 3 mm only. Using Ni and Cr equivalents FCC+ BCC and/or BCC solid solution structures were found out. Microstructure, segregation and micro-fracture investigations were part of solution.
IIn the terms of nuclear power plant operational life management, current trend of components lifetime extension requires precise and credible information of structural material degradation. Present-day standard conventional methods of mechanical testing are usually based on the use of large specimens and higher consumption of testing material, whose availability and volume is often limited. For determination of material properties, sampling of the necessary volume of material is in most cases connected with affecting the integrity or even destruction of the assessed component. Moreover, several components are not usually covered surveillance programs, e.g. reactor pressure vessel internals.
Innovative testing method of Instrumented Hardness Test Method (ABIT) is based on the determination of material properties from miniaturized testing specimens and the semi-destructive approach is very promising for the possibility of present data base of irradiated materials testing results enlargement.
Aim of this work is to present the advantages of the semi-destructive testing method (instrumented hardness test method) in the process current mechanical properties evaluation of the hardly replaceable long-term operated NPP components. Instrumented hardness test method is a semi-destructive testing method for direct measurement of mechanical and fracture properties of materials including yield strength, ultimate tensile strength (UTS), strain hardening exponent, and fracture toughness.
Detailed comparison between the results of standard conventional testing techniques and ABIT for both, initial unirradiated and irradiated state, for the experimental material is included for determination of suitability of used method for testing of materials within the surveillance programs of WWER type reactors.
Many laboratories conduct fracture toughness tests on Compact Tension (CT) metallic specimens.
Since there was expected to be a very high volume of specimens (hundreds per month), Exova Plzeň identified the key operations and their time requirements. The main processes where time savings could be realised were inspection of the specimens before the test and measurement of the pre-crack length. The laboratory identified the opportunity to reduce the time of these processes as well to eliminate operator errors and transcription mistakes.
Each Exova laboratory, has a different process of measurement, which takes approximately between 10 to 20 minutes per specimen. Exova Plzeň required a system, which would be able to measure the specimen before and after the test and would reduce the time for required for these processes. Exova Plzeň asked for a quotation from many suppliers. The delivery time and price were up to € 100,000 and 3 years. In the end Exova in cooperation with one Ph.Dr. student from West Bohemia University developed the software and assembled the hardware in 1.5 moths for an equivalent of £ 8,700.
The system is able to save thousands of hours of working time as well as financial resources. Another positive point is that quality should increase, because the software will eliminate typing mistakes and operators errors. In the future the system can be further developed for the inspection of other shapes and dimensions.
Some surface treatments that apply to the hydraulic equipment components, which operated at high hydrodynamic loads, in which appear the phenomenon of erosion by cavitation, shall be listed and laser nitriding. Before laser nitriding, the steel was undergone thermal annealing treatments for improving machinability cutting, followed by a volumic martensitic quenching and a tempering to high temperature. By changing the laser beam power are changes the layer thickness enriched in nitrogen and thus the resistance to erosion by cavitation. The cavitation tests , carried out in accordance with the requirements of ASTM G32-2010 standards, followed by hardness measurements with microsarcini HV0.3 and optical and electronic metallographic investigations, justifies the increasing resistances to erosion by cavitation of nitrided layer, compared with the volume heat treatment.
The paper presents the numerical-analytical method to estimate parameters that control the cracking process in elastic-plastic materials – J-integral and crack tip opening displacement. These parameters may be considered as material constants, while different conditions are satisfied [1]. An evaluation of load line displacement as a function of external loads and verification of the limit loads were also done [2].
The aim of the work is to develop a new method for yield strength determination of chosen corrosion resistant steels using the micro-indentation measurements. The main advantage of such method is a demand for minimal amount of analyzed material.
In the frame of the experiment, the elastic-plastic behavior of special corrosion-resistant – ferritic, martensitic and austenitic – steels was investigated. These steel types are partly suitable for nuclear energetics and also for other fields with high demands on steel quality.
The experiment is focused on discovering and defining of such surface quality which would be optimal for maximal yield strength evaluation accuracy determined by micro-indentation measurements, and along with on finding the strengthening trend of the steel types investigated.
As the main tool for the evaluation, of the elastic-plastic response, the methodology based on the instrumented penetration test by means of 0,7 mm indenter diameter was chosen. The basic principle of the experiment was comparing evaluated yield strength with help of micro-indenter and those determined by classical tensile test.
This paper also deals with FEM simulation of indentation by a flat-ended cylindrical punch into elastic-plastic material with assumed rough contact surfaces. This work shows one of the ways how to include the influence of rough surface into numerical calculation without requiring all asperities of contacting rough surfaces modelled by the finite elements in detail.
The influence of the rough surface in combination with the elastic-plastic materials behavior on the shape of the loading curve is subject of this study.
Martensitic heat-resistant steel P92 belongs to very progressive group of 9-12% Cr steels modified with vanadium and niobium, with controlled boron and nitrogen content. P92 has got excellent creep properties and it is used very often to build the most exposed parts of supercritical units in steam power plants.
The goal of this article is to compare the real welded joints with the simulated samples and optimize the heat treatment and welding process of P92 steel. To allow that, the analysis of the microstructure with transmission electron microscopy was made. The measurement of trend of hardness along the welded joint was carried out, as well. The good accordance between the simulated samples and real welded joints were found.
The paper deals with the change of the structure and mechanical properties of the austenitic steels after the exposure at the critical temperature. The effect of the bend radius of tubes on the mechanical properties and the structure was studied. The effect of solution annealing was studied too. The grades TP347 HFG, Super 304H and HR3C were chosen in the study. The bend radius R60, R80 and R100 were on the matter. The mechanical properties were studied using small punch test and miniaturized tensile tests. From the results can be concluded that the mechanical properties and the structure have been influenced due to one year exposure at the working temperature significantly. Various amounts of σ-phase were found in the pulled part of the bend side of the tubes even after only thermal exposure without any loading.
Hadfield steel has been widely used for railway switch, frogs because of its desirable mechanical behavior under high load applications . Austenitic Hadfield´s steel containing about % 1.2 mass C and % 12 mass Mn is known for a high resistance to impact wear caused by rapid cold work hardening.
In this study, several methods have been performed to detail mechanical properties of Hadfield. Dislocations and white etching layers are observed as expected during metallographic analysis. Beside this, Indentation method applied to evaluate elastic-plastic response of the surface. In addition to our previous studies, spherical indentation method have been introduced to get better results even rough(uneven) surface. Force-Indentation depth graphs are examined by specific method. Real rail sample, with or without explosive hardening samples are compared by means of new method.
Resistive weldability of high-strength steel 22MnB5 is very important for automotive industry. Coatedsteel is galvanized. Al-Sicoating protects the steel against oxidation during forming. At the interface of Al-Si coating and base material the diffusion layer is created. The layer thickness depends on temperature and holding time of heat treatment. The contribution deals with chemical composition of coating (includingdiffusion layer) and its mechanical properties (indentation hardness H and elastic modulus E)
Increasing demand on materials characterization together with improvements in apparatus testing lead to the development of new testing procedures such as sub-size specimens testing. Miniaturized specimens allow reliable properties determination while using very small amount of material.
These methods are widely used for local material properties determination. Basically, there are two main applications in industry: firstly, the determination of the distribution of mechanical properties in heterogeneous materials (e.g. heterogeneous weldments or weld deposits) and secondly the characterisation of stamping parts which are usually too thin for the production of standard testing samples.
Other applications are also important, e.g. anisotropy determination on thin components, residual service life evaluation, or new materials development when there is a lack of material (e.g. severe plastic deformation).
In the last few years, a new methodology using small samples for tensile properties determination at RT has been developed. The newly proposed specimen is derived from the SPT specimen which has a diameter of 8 mm and a thickness of 0.5 mm. Therefore, the newly proposed specimen size is very small in comparison to standard size specimens and thus the new methodology is named a Micro-Tensile Test (M-TT). For precise strain measurement the ARAMIS system using the Digital Image Correlation method (DIC) is used.
Moreover, as many components are operated at elevated temperature, it was necessary to develop a Hot Micro-Tensile Test for tensile properties determination at elevated temperature. This paper presents the possibilities of performing the M-TT at elevated temperatures while maintaining high measurement precision.
High alloyed materials are required by certain industrial sectors as is power, chemical and nuclear industry, etc. These materials have superior mechanical properties and are resistant to chemically aggressive environment in which it must accommodate the long term mechanical stresses at high temperatures. However, in the course of operating loading reduces their service life. Steels are losing their specific characteristics and in particular the toughness and corrosion resistance.
This paper deals with the influence of the structure stay on electrochemical properties of steel, mainly the behaviour in the passivity area. The experiment was effected on the bearing body made from the high alloyed steel 440C. Specimens were treated to a different mode of heat treatment - quenching 930°C to 1080°C/ 0,75h / oil; consequently tempering 200°C to 750 °C/ 2 h /air; or freezing (-80 °C, 0.5h). Microstructure was observed in two directions – on outside round surface and cross section. In addition to the optical microscopy have been used SEM and the EDX analysis. The volume of residual austenite was determined by XRD analysis. The changes of mechanical properties are verified by measurement of microhardness HV 0,01. Corrosion tests are proceeded out in hydrochloric and boric acid environment. Corrosion potential has been measured and corrosion loss (corrosion rate). The results showed that in the first environment corrosion occurs in the active area, in the second case in the passive. Also interesting connections were observed between corrosion rate and the development of hardness for each of the samples.
Operating life and reliability of steam boiler and piping systems are considerably determined by long-term creep rupture strength of welded joints of boiler tubes and pipes. Consequently, the appreciable research effort has been focused to reveal the most important factors affecting the creep properties of weldments. The presented work deals with the evaluation of creep rupture strength of welded joints in steam boiler piping system made from low-alloy and chromium modified steels. Cross-weld creep rupture tests and, at the same time, comparative creep tests of parent material are considered as the optimum approach how to evaluate the decreasing of creep resistance of weldment towards the base metal and how to quantify this effect e.g. by using strength reduction factor (SRF) and lifetime reduction factor (LRF) of welded joints. The necessary condition for such an approach is that the mechanism of creep damage (type IV cracking) in laboratory tests must be the same that acts in in-plant welded joints of the mentioned steels. The obtained results confirmed that the precipitation strengthened steels (mainly Cr-Mo-V type) show more pronounced decreasing of creep rupture strength of the critical locality of welded joint – intercritical part of heat affected zone when compared to Cr-Mo steels and that they are, therefore, much more prone to the premature failure.
The presented paper deals with hydrogen diffusion and hydrogen provoked degradation in the TRIP 800 Mn-Si-Al steel with increased aluminium content. The steel was studied after standard heat treatment including two step annealing – an intercritical annealing and an annealing in the range of bainitic transformation. A part of specimens was submitted to a plastic deformation in tension (5 and 10 %) in order to modify both structure and mechanical properties. Microstructure of the steel consisted predominantly of ferrite, bainite and retained austenite, the amount of which decreased with increasing extent of the plastic deformation. Hydrogen diffusion was studied by electrochemical permeation method. Hydrogen diffusion coefficients were calculated using “time lag” method. The lowest values of hydrogen diffusion coefficients were always observed for the first build-up transient, while the highest values were recorded for the second build-up transient due to the less intense hydrogen trapping. As to the impact of deformation, the highest hydrogen diffusion coefficients were observed after 5 % tensile deformation. Subsurface hydrogen concentration reached values about 14 mass ppm. Hydrogen embrittlement of the steel was studied using tensile tests after previous electrolytic charging in diluted sulphuric acid solution. Hydrogen embrittlement manifested itself mainly by a drop of elongation at fracture. As to fracture morphology, hydrogen embrittlement resulted in a change of fracture mode from transgranular ductile fracture to transgranular cleavage fracture with an appearance of “fish eyes” nucleated on aluminium rich non-metallic inclusions.
One of the greatest problems of modern production techniques is the achievement of an appropriate quality at minimal costs and accompanied by the production efficiency increase. Therefore while designing the production process, the technology used should have a considerable influence on the durability and reliability of machine parts to be produced. During finish treatment the final dimensions as well as functional properties are imparted to a given element by application of proper treatment type. The engineer has a range of production techniques to choose for the proper surface layer formation. It is crucial to find a suitable solution which will meet the requirements as well as the work conditions of a given machine part.
The article presents the research results referring to the analysis of the influence of burnishing process on surface topography of marine pump shaft. The research was performed on a shaft made of X5CrNi18-10 (AISI 304 L) stainless steel. The preliminary turning process was carried out by means of a WNMG 080408 WF Sandvik Coromant cutting tool with replaceable inserts. The process of burnishing was done by Yamato SRMD burnisher. The goal of the paper was to define the influence of burnishing tool passes number on surface roughness parameter. The surface topography was measured by MicroXAM-800 optical surface profiler.
Amorphous alloys are characterized by high values of hardness and tensile strength, great corrosion stability and also favorable soft magnetic properties. Industrially, they are produced as ribbons with thicknesses below 60 µm; many technical applications require the joint of the ribbons from such alloys by welding or soldering processes. Due to their low thermal stability, the welding process becomes a critical issue because of the need to avoid the crystallization of the welded joint. One of the welding methods where the temperature of the components remains under the solidification scale point is the welding with stored energy in capacitors. The characteristic of this method is that energy absorbed by the AC network is not used directly in the welding process but is converted by the power circuit in a current pulse. This paper aims the mechanical and structural characterization of welded joints through scanning electron microscopy, static tensile test and hardness test.
This paper deals with the impact of solution annealing on properties of X2CrNiMoN2253 duplex steel. Experimental specimens were 100×100×150 mm forged and air-cooled pieces, which were solution-annealed at several temperatures changed in 20 °C steps between 1020 and 1120 °C.
Mechanical tests conducted on these processed specimens included a tension test and Charpy impact tests at room temperature and at -46 °C. The results were compared with data stipulated in EN 10088-3 standard and with minimum requirements for X2CrNiMoN2253 forgings for onshore oil and gas extraction according to technical delivery specifications
Microstructure of the specimens was explored using optical and electron microscopes and EBSD analysis. Fracture surfaces of impact specimens were examined as well.
EBSD measurement showed significant ferrite texture in some specimens, whereas no signs of texture were detected in austenite in any samples. The causes of the ferrite texture were investigated and its impact on properties of the duplex steel was explored.
In high strength low alloyed steels (HSLA) the microalloying elements: Ti, Nb, V are added in order to control their microstructure and mechanical properties. These elements show high chemical affinity for interstitial elements, C and N and form precipitates of carbides and nitrides. Because of similar structure these compounds form carbonitrides. The stereological parameters of compounds, volume fraction and dispersion affect the microstructure of steel and its mechanical properties. These parameters can be predicted using different mathematical model. One of them is Cellular Automata (CA) model. Cellular Automata model proves to be very efficient in modelling various phenomena in materials science. In this paper CA model for carbonitride precipitation process in microalloyed steels is presented. It enables to calculate the volume fraction of carbonitrides as well as size distribution of precipitates. Examples of practical application of it model are presented.
The work deals with chosen properties of bimetal weld and its neighbourhood of Ti-clad Cr/Ni steel after one or double heat treatment (at 600 °C / 1.5 h / air) applied after explosive bonding. Notch impact strength values were compared with bimetal weld of C-Mn steel bonded with Ti after the same heat treatments. After double annealing, stainless steel Ti-clad showed the best transition temperature level (-60 °C at 310 J / cm2) unlike the Ti-clad C-Mn steel (-38 °C at 140 J / cm2). One annealing applied after explosive bonding resulted in worse parameters (decrease by 33 % and/or 87 % for stainless steel and/or C-Mn steel). Next part of work was target on sulphide stress cracking under tensile test and bent-beam test for Cr/Ni steel joined with Ti only after double heat treatment. Threshold level (for tensile) corresponded to 40 MPa and maximal deflection at 160 MPa to 0.609 mm without any defect. Results have been confronted with by now found facts.
Currently, one of the modern techniques for improving the surface properties of the stainless steel is the nitriding thermochemical treatment. Research conducted in this paper aims at forming coatings with high surface hardness evidence on Duplex stainless steel X2CrNiMoN22-5-3 subjected to nitriding with laser beam using three pulse power regimes (240 W, 180 W, 120 W). To highlight the effect of the behavior of the thermochemical treatment on parts functioning in cavitation, for comparison, there were used the results on the same steel, solution treated. Surface degradation was highlighted by tracing specific erosion curves, expressing their variation of the mass loss and their speed duration of exposure to cavitation and by macro - and micrographic images of layer – substrate system. The results showed that the change in the pulse power of the laser beam from 120 W to 240 W, will lead to an increase in the depth of the nitrogen-enriched layer from 0.14 to 0.20 mm, at the same time increasing the resistance to cavitation with about 42% if it is referred to the cumulative mass loss, by 35% respectively when referring to speeds of erosion.
The article presents the results of computer quantitative analysis of the microstructure of ductile cast iron heat treated with isothermal transformation. To determine the relative volume fraction of austenite and the geometric parameters of ferrite needles the methods of image analysis were used.
Analysis of the effect of temperature and time of austempering on the volume fraction of austenite and the dimensions of the ferrite needles was carried out.
Valve-seats are the most thermally and mechanically stressed structural components of a two and four-stroke internal combustion engines. These loads increase rapidly with the use of LPG and CNG gaseous fuels. The valve seats are usually made of high-alloyed sintered powders. Attempts of application of same valve seats to the engines fuelled by CNG as to engines fuelled by LPG gas were finished unsuccessfully. After approximately of 40 hours of these valve seats operating at temperature reaching about 950oC it was stated the simultaneous permanent deformation of valve seat and thus the reduction of tested engine durability.
The aim of the study was to investigate the effect of molybdenum disulfide and open porosity saturated with Cu on the durability of the valve seats faces in the operating conditions of two-cylinder engine type 0.9 SGE TC80 CNG fuelled by natural gas. Durability test was conducted according to the methodology
of BOSMAL procedure, measuring among others the power, torque and rotation speed, also the exhaust gases temperature and the hourly fuel consumption. Studies had shown a strong effect of molybdenum disulfide and open porosity on the durability of tested valve seats in combustion engine fuelled by compressed natural gas (CNG).
The methods of intensive plastic deformation SPD (Severe Plastic Deformation) belong to a group of very attractive means of increasing utility properties of metallic materials (strength and structural characteristics). The paper is focused on numerical simulation forming of high-carbon steel C55E processed by the SPD DRECE (Dual Rolling Equal Channel Extrusion) and GTAW-141 welding process by Simufact software. Numerical simulation of welding and forming process benefits allows much wider perform verification of the influence of individual technological parameters on the final properties. On the test welds were verified and compared results of numerical simulation. Last but not least, acquired information about the weldability, mechanical properties, structure, distribution of residual stresses allow an effective deployment of given materials in real industrial applications.
In paper the results of the X-ray diffraction analysis of the perlitic - ferritic spheroidal cast iron with the addition of Ni are presented. The cast iron was heat treated using austenitization followed by austempering in different conditions. Investigations of the crystal structure parameters as well as volume fractions of austenite and ferrite were carried out. The effect of heat treatment parameters, temperature and time of austempering, on volume fraction of austenite and carbon content in austenite was investigated.
The article deals with the evaluation of residual stress after machining of surfaces using effective milling strategies programmed by CAM systems. Milling of the shaped parts containing pockets and grooves, the cutting tool must be driven into corners with lower feed rate, because angle of entry, cutting depth increase and then a chip is tamped and leaving from the place of cut is very difficult. Application of standard strategies affects the beginning of tool wear, decreased durability and tool life, raised roughness parameters of the machined surface and increased residual stress. Aspects of efficient milling strategies programmed by CAM systems allow to machine with the entire cutting length of the tool with a constant angle of entry for the entire machining time. These strategies have a positive effect on residual stress in the material. It was confirmed by the machining test of an experimental piece from material Toolox44. The residual stress was measured by non-destructive method with using the device Proto iXRD operating on the principle of X-Ray diffraction. This measurement was realized in cooperation with the Department of Machining and Manufacturing Technology at University of Žilina in Žilina.
A new method of simulation of evolution of polydisperse ensemble of carbonitride particles in steels has been elaborated. The method takes into account the multi-component type of a system, diffusion interaction of elements in solid state, final volume fraction of precipitates and describes precipitates evolution at all stages: nucleation, growth, dissolution and coarsening. Its main differences are that, firstly, it describes the behavior of complex precipitates and, secondly, it enables to simulate evolution of several ensembles of particles of different compositions (taking into account the formation of new nucleation centers).
The method is based on joint solution of a system of diffusion and thermodynamic equations along with balance equations at interfaces. A quasi-stationary approach and mean field model are used for the solution of diffusion equations. Particle size distributions are given by several histograms corresponding to precipitates of different composition. A new parameter of a histogram – a fraction of precipitates of a given composition among the precipitates of all compositions – is inserted for calculation of average concentration of diffusing elements in a matrix.
The algorithm suggested has been realized in form of a program for simulation of precipitates evolution in steels doped with V, Nb and Ti.
The work was carried out within the state assignment of FASO of Russia (theme “Spin” No. 01201463330) and supported in part by the Program of Fundamental Research of UB RAS (project No. 15-9-2-44) and RFBR (project No. 16-38-00164).
The paper presents results of corrosion resistance of heat treated and plastically deformed aluminized steel strips. For tests were chosen strips made of DX52D + AS120 with both sides hot dip coating of Al-10%Si with a thickness of approximately 20 µm. Strips were heat-treated at a temperature of 250-700°C for 30, 180 and 1440 minutes, and then plastically deformed by stamping. In the next step, burr periodically immersed in vessels containing snow mud. The study was divided into three twelve days stages, after which the inspection, measurements and photographic documentation of the corrosion progress was carried out. Determined elementary corrosion weight loss (Km) by weight, and visually determined changes on the surface of the burrs, with particular emphasis on the size of the damage, the type and quantity of the products and uniformity of the corrosion.
Creep resistance of austenitic steels can be improved by small additions of strong carbide and nitride forming elements. Additions of such elements to steels have to be followed by detailed investigations on microstructural stability and surveys of creep failure mechanisms.
This paper deals with creep behaviour and microstructure evolution in the AISI 316LN + 0.1 wt.% Nb steel during long-term creep exposure at 600 and 625°C. Creep tests with a constant tensile load were carried out in air up to times to rupture of 200 000 hours. Microstructure evolution during long-term creep exposure was studied using light microscopy, scanning and transmission electron microscopy. A small addition of niobium resulted in a reduction of the minimum creep rate and shortening of the tertiary creep stage. Investigations on microstructure evolution in creep ruptured specimens revealed the following minor phases: Z-phase (NbCrN), M23C6, M6X (Cr3Ni2SiX type), η-Laves and δ-phase. M6X gradually replaced M23C6 carbides. Primary Z-phase particles were present in the matrix after solution annealing, while secondary Z-phase particles formed during creep. Precipitation of Z-phase was more intensive at 625°C. The dimensional stability of Z-phase particles was excellent and these particles had a positive effect on the minimum creep rate. However, niobium also accelerated the formation and coarsening of δ-phase, η-Laves and M6X. Coarse particles, especially of δ-phase, facilitated the development of creep damage, which resulted in poor long-term creep ductility.
The presentation poster describes procedures and methods used to conduct long term material tests at high temperatures of up to 1200°C and utilize creep frames to perform non-standard tests. These methods allow to perform material testing within a timespan of min. 15000hours, under conditions that are not usually available to other laboratories. Therefore an added value is established by using creep frames to do stress rupture tests, cold dwell fatigue, stress relaxation tests and composite testing for significant duration of time. Exova developed and built automatic frames for these various types of tests. Subsequently, more complex tests are feasible providing fast loading rates ( ̴̴ 5s), light weight extensometry readings and high temperature rates with no noise showing on the final test curve. Consequently, complying to higher standards.
To perform a creep test we are able to establish testing methods and create test matrix if required based on isothermal data using Larson Miller Parameter (LMP).
We have started with six frames in 2007 and currently utilize three hundred test frames. We have been successful at providing extremely efficient way of testing of alloys under tight conditions supplying data to airspace industry.
The harmful effect of cavitation is the erosion of the material. Although there are many studies on improving the mechanical properties of the material in order to increase resistance to cavitation, so far none has defined the optimal solution for complete protection from this type of wear. New methods aimed at increasing resistance to cavitation erosion using surface hardening techniques of parts. One of them is the gas nitriding, which ensures a significant increase of the surface layer hardness by the cavitation attack. In this sense, this paper highlights the behavior and the resistance that acquires X5CrNi18-10 austenitic stainless steel, nitrided in gas. Research of this steel is determined by application to the manufacture and repair parts required intense cavitation, as are hydromechanical equipment. Highlighting resistance to cavitation is done through images structure eroded obtained by optical and electronic microscopy, and by comparing the specific characteristics curves of the same steel subjected to solution treatment at 1050°C with cooling water and the steel standard OH12NDL, which is known for its resistance to cavitation attack.
Numerical prediction of thermal loads in laser welded joints is important at the stage of construction design. Appropriate positioning of the heat source to joined elements is important during execution of T-joints using a laser beam.
The work concerns the modeling and numerical analysis of thermal phenomena in laser welded T-joints. The effect of laser beam slope relative to welded elements on the temperature distribution is analyzed. The shape and size of fusion zone is predicted on the basis of obtained results. Temperature field in welded T-joint is modelled in Abaqus/FEA engineering software as three dimensional task. Numerical analysis takes into account thermomechanical properties changing with temperature for welded plates made of austenitic steel. Additional author’s numerical subroutine DFLUX is implemented into Abaqus/FEA in order to solve issues concerning mathematical description of movable laser welding heat source. Formulas for coordinate system transformations in terms of the rotation of coordinate system about selected angle are used for the proper positioning of the heat source regard to joined edge of T-joint.
Temperature distribution in welded joints is obtained on the basis of numerical simulations, which allowed determining the geometry of the fusion zone. The influence of the laser beam slope on the shape and size of the fusion zone is estimated.
Article is about the process of machining titanium alloy Ti6Al4V DIN W. Nr 3.7164 and choosing the appropriate cutting tool. For machining alloys have been under predetermined conditions used cutting inserts labeled according to the standard ISO - 120408 CNMG with different geometry chip breaker. The experimental part was carried out to determine the effect on the course of chip breaker geometry and size of the dynamic load of the external longitudinal turning of titanium alloy Ti 6Al 4V. For the load measuring and determining the size of the individual components of force was cut in the course turning used the three-component piezoelectric dynamometer KISTLER 9257B. Based on the measured and processed values was determined minimum and maximum force acting on the surface of the machined material and the load of edge of the cutting tool when machining titanium alloy Ti6Al4V.
The paper deals with degradation of the structural and mechanical parameters of DOMEX 700MC steel due to welding process. It is focused on evaluation of the mechanical heterogeneities influence at higher strain rate. DOMEX 700MC presents the microalloyed steel with the increasing utilization mainly for the lightweight construction of the transportation means. The precise characterization of material behavior at high strain rate is of great importance for reliable prediction of welded parts in that application.
Evaluation of the local mechanical parameters of experimental welding joints was performed. The three-point instrumented dynamic fracture analyses and instrumented indentation tests were employed to study the elastic-plastic response of critical weldments sublayers. The static vs. dynamic yield strength and energy consumption to fracture was compared in different stages of temper influence. Structural analyses brought the information about the conducted structural changes in tempered zone. Fractography analyses were focused on evaluation of local differences in fracture behaviour influenced by real metallurgy quality. Based on the experimental results, the used combination of loading method is suitable to determine the local mechanical properties and enable the estimation of temper sensitivity of analyzed steel.
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes due to effects of severe plastic deformation together with thermal shocks by friction process were expected. The information about structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction, Mössbauer Spectroscopy and Glow Discharge Emission Spectroscopy (GDOES) and this was completed by microhardness measurements. The results show that the surface layer in comparison with the original material exhibits important changes in grain structure, an increase in microhardness and high content of iron oxide and hydrooxides. According to the depth profile of the chemical composition measured by GDOES there is an increase in carbon content in the surface layer which can be effect of up-hill diffusion.
The paper sets out a synergic program by MAG pulsed welding of Duplex stainless steel plates with thickness of 12 mm. The selected filler material was a E2209-16 wire with a diameter of 1.2 mm and as shielding gas Cronigon 2 was used.
The root layer was obtained at lower linear energy, of 6.9 kJ/cm, and for the filling layers the heat input was different namely: 10 kJ/cm, 15 kJ/cm and 20.7 kJ/cm. Macro- and micrographic analysis showed that variation of linear energy for obtaining the filling layers, by reducing the welding speed or increasing the welding current, permitted the obtaining of welded joints without continuous metallic defects and of a free defects surface such as marginal notches.
During heat treatment of carburized steel parts the transformation of austenite to martensite occurs and a certain amount of retained austenite remains in the carburized layers. The higher content of retained austenite in the carburized layer adversely influences hardness and frictional characteristics and increases susceptibility to fatigue damage. Furthermore, retained austenite can transform into deformation induced martensite during service, which provokes changes in properties of the carburized layers. From the technological viewpoint, the content of retained austenite is nearly always monitored but obtained results can be different depending on experimental methods.
In this work, the amount of retained austenite in carburized layers of manganese-chromium steels was evaluated by image analysis method, by X-ray diffraction and also by EBSD. The largest amount of retained austenite was measured using the technique of X-ray diffraction, i.e. 25 to 28%. The amount of retained austenite measured by image analysis of metallographic images varied from 14 to 16%. However, the results of image analysis greatly depend on the metallographic preparation of samples, digital image processing and the grayscale level settings for the calculation of the retained austenite content. The lowest amount of retained austenite was determined by EBSD, i.e. 4.1 to 6.5%. Even in this case the values depended on the method of scanned data processing. No method used to determine the amount of retained austenite in the carburized layer is universal and largely depends on the sample preparation and partial steps performed in individual measurement methods.
The paper deals with use of small samples for fatigue tests. The main advantage of the small fatigue samples is in use in cases, where sufficient amount of material is not available. For example at power plant parts. Results of small sample tests are afterwards correlated with the results of standard fatigue test specimens. Further different ways of sample manufacturing are compared. The small samples are produced either by machining, or cutting with waterjet. The stress concentration of the small fatigue sample is detected using finite element method.