Non-seismically designed existing reinforced concrete (RC) structures are susceptible to any thermal effect. Indeed, difficulties arise even more in understanding the performance of buildings in fire due to the inherent complexity in the behavior of composite materials at elevated temperature. This paper deals with determination of mechanical properties of hot rolled structural steel under thermal effect. A focus on the influence of the passive fire to the structural steel is thus provided. The specimens were firstly heated up to a certain level (i.e. in a range of 300-700 °C) and then cooled down up to room temperature. Then, the dog-bone shape steel tensile test samples were taken from reinforcing bar of RC bond-slip specimens complying with RILEM test method. Dependence of the heating and cooling rate on mechanical properties of S275 type smooth reinforcing steel was identified by either destructive or nondestructive testing methods. Two different techniques including their pros&cons and difficulties in implementing the tests were therefore closely compared. Moreover, the major parameters characterizing the behavior of the steel samples exposed to the aggressive fire were compared with the control ones. It is found that the ductility in the fire exposed specimens was essentially different from the ones at ambient temperature while the deterioration in yield and ultimate strength was not considerably affected.
In this study the effect of notch angle on fracture toughness (Kıc) of AISI 4340 steel is investigated by using circumferentially notched bar method. The specimens have three different notch angles 45°, 60°, 75° and specimen diameters (D) – notch diameters (d) ratio (D/d) keep constant as 1.2. The purpose of the study is determining the effect of notch angle on fracture toughness. Moreover, it shows the advantages of using circumferentially notched bar specimen for fracture toughness determination of metallic materials. The obtained fracture toughness values for different notch diameter are compared with the literature. The result shows that the notch angle has significant effect on the value of fracture toughness (Kıc).
The forging industry seeks ways to improve mechanical properties of forged parts without using costly alloyed steels or complicated and time-consuming post-forge heat treatment. One of the available options is Q&P processing (Quenching and Partitioning) of advanced high-strength martensitic steels. The Q&P process is characterized by rapid cooling from the soaking temperature to a quenching temperature which is between the Ms and the Mf, and subsequent reheating to and holding at a partitioning temperature. Strength levels of more than 2000 MPa and elongation above 10 % can be obtained. Since the quench needs to be interrupted between the Ms and the Mf, new alloying strategies are being developed in order to depress the Mf below 100 °C. With such steels, plain quenchants could be used, including boiling water.
Using material-technological modelling, several heat treatment routes involving various cooling profiles were tested on three high-strength 2.5 % Mn steels with different Ni and Mo levels. The data for constructing the first model were acquired from a real-world treatment of a forged part. Quenching a forged part in boiling water and subsequent partitioning led to a strength of 2130 MPa and elongation of 12 %. Metallographic examination and measurement of mechanical properties were carried out on the experimental steels after the treatments.
The effect of the strain rate on master curve of the martensitic chromium steel was examined in the work. The tests were performed in both quasi-static and dynamic conditions. The pre-cracked standard Charpy V specimens were used in the test to allow Master Curve determination in dynamic conditions using standard Charpy pendulum. Based on the research, the effect of the strain rate on master curve was found. The increasing of strain rate from quasi-static to dynamic conditions in tested steel caused the significant decrease of KJc and consequently an increase of the reference temperature (T0).
Description of the procedure and results are given for computer simulations of small punch test (SPT) performed on P92 structural steel. The maximum force calculated using the SPT simulation is about 5% higher than the measured value. The punch displacement at the maximum calculated force is 2% less than the measured punch displacement. Effects of several factors were analysed using the SPT simulation, such as friction between the test device and the test specimen, the geometry of the test device, and the clamping force. It was found that SPT results depend strongly on the amount of friction and on imperfections of the test device dimensions and geometry.
Cold drawing of steel tubes is the manufacturing process characterized by anisotropic material flow during drawing. In this paper, the microstructural and mechanical properties of the E235 hot rolled steel tube after normalizing and cold drawing were characterized by optical microscopy, EBSD (Electron Backscatter Diffraction) analysis performed on scanning electron microscope, and also by standard mechanical tests. The input feedstock with dimensions of Ø 31.8 mm × 2.6 mm (O.D × W.T.) was cold drawn in two drawing passes with fixed plug to the final dimensions of Ø 25 mm × 1.5 mm (O.D × W.T.). The development of grain texture in 3 different regions was analyzed on a longitudinal section of the tube. The stress state in the tube material during drawing was calculated by finite element software and the development of the texture depending on the stress state in three different directions using cylindrical coordinates with respect to the drawing direction was evaluated.
Reactor pressure vessel (RPV) of light water reactor and its internals are the most important components of any nuclear power plant. RPV and its internals are exposed to high temperatures, pressures and intensive neutron flux during the operation. These conditions lead up to material degradation – especially radiation hardening and embrittlement.
Poster presents the annealing treatment as one of the possible solutions to provide and re establish sufficient mechanical properties of RPV internals during the operation. The first part of the poster is dedicated to the description of equipment which is used for the annealing of unirradiated and irradiated materials at the UJV Rez hot cell facility. Following part shows selection of unirradiated material for definition of original mechanical properties. Next part is an overview of selected annealing regimes. The main section is focused on definition of mechanical properties (especially hardness) of original and annealed material of WWER 440 type reactor internals as well as on methods and analyses employed to study of mechanical properties changes.
The final part discusses the next planned steps in the solution of the research project TH02020565: “Assurance of Safe and Long Term Operation of Nuclear Reactor Pressure Vessel Internals” which is realized in the period from 2016 to 2020 with the support of Technology Agency of the Czech Republic.
An in-situ tensile tests with high strength steel were performed in SEM to observe microstructural changes. In the main focus were both deformation of grains in the material and initiation and propagation of the crack. For this, different specimen shapes were designed. Material used for testing were low alloyed high strength TRIP steels.
The layered metallic materials are widely used due to their beneficial property combination providing high strength, corrosion resistance, thermal conductivity, heat resistance, wear resistance, and etc. Such materials consist of two or more metallic layers. Designated combination of mechanical and functional properties in the layered metals and alloys can be attained by appropriate thermo-mechanical treatments.
Two steels, a S700MC-type of high strength low-carbon steel and a 316L-type of austenitic stainless steel, were used as the layer materials for bimetallic semi-product, which was produced by electro-slag cladding. The both steels were subjected to warm rolling as a method of thermo-mechanical treatment. The effect of processing conditions on the microstructure and mechanical properties of the 316L and S700MC steels was clarified. The ultrafine-grained microstructures with average transverse grain sizes of 530 nm and 950 nm were developed in the S700MC and 316L steels, respectively, during warm rolling at 923 K. The developed ultrafine-grained microstructures provided similar strength levels with ultimate tensile strengths of 980 MPa and 945 MPa in the S700MC and 316L steels, respectively. Moreover, the warm rolled bimetallic semi-product was characterized by the improved combination of high strength and high impact toughness ranging from 130 J/cm2 to 540 J/cm2 depending on the impact test direction.
The subject of the work is to present the possibility of using a non-contact optical system for measuring strains. Dantec's multi-unit Q-400 3D image correlation system was used. The aim of the work was to determine the distribution of displacements and deformations on the surface of samples with different cross-sections and made of different materials during the bending test. The measurement was used basically to estimate the deflection line of the bending beams and at different points of the cross-section. Measurement was carried out by tracing the displacement of the prepared surface of the bending sample. In the paper, the results of the studies show the displacement and deformation fields for different bending steps of flat samples. A numerical model of the bending process was also developed to compare the results with experimental studies.
Modern inorganic materials, especially geosilicates, offer many waste storage applications their use for new processes and properties of these materials. This article deals with the use of chips from unalloyed steel ČSN 11 373. Process fluids used in machining were chemically removed and the chips were subsequently mixed into a composite based on geosilicate. The mechanical properties of composites after thermal exposure have been verified.
Mechanical alloying is a powder metallurgy processing technique involving cold welding, fracturing, and rewilding of powder particle in a high energy. It has been used to obtain nanocrystalline alloy. Fe 53%atm. Si 28%atm B19% atm. alloys were synthesized using a planetary ball mill (Retsch PM400). X-ray diffraction was used to identify and characterise various phase during the milling process. We used the Mössbauer and the electromagnetic methods, to characterize the variation of structure and their influence. The shape of hyperfine field distributions used to describe the Mössbauer spectra is discussed. It is shown that the FeSi solid solution was formed after 4 hours milling. The study state grain size is about 13 nm.
9%Cr martensitic steels are perspective candidates for elements of boilers, steam pipes and tubes for novel fossil fuel power plants which are able to work at ultra-supercritical parameters of steam (T=600-620 °C, P=25-30 MPa). Crept structure of 0.1C-9Cr-3Co-3W-VNbBN steel after creep tests at 650 °C under the applied stresses ranging from 80 to 220 MPa with a step of 20 MPa was studied. During first 5 000 h, the Laves phase particles were essentially stable, their sizes remained unchanged, while after 5 000 h the extensive coarsening of these phases started to occur. The coarsening behavior of the Laves phase particles was also calculated using the Prisma software. The results of the calculations are corroborated by experimental observations. There are three features of microstructural evolution of the Laves phase particles during creep in the steel studied. First, volume fraction of Laves phase increases with time. Second, there is a well-defined peak in size distribution of the Laves phase particles. Third, interfacial energy of Laves phase changes when transition from short-term creep to long-term creep occurs.
Resistance spot welds (RSW) are one of the main joining technology of thin plates in automotive industry. Key factors affecting the strength of the RSW joint is the nugget diameter, assymetricity, expulsions, intended surfaces, and presence of cracks. Despite its broad use, the weld quality verification is limited only to destructive testing and small number of NDT methods. Most of the testing is done destructively by sampling, which assesses only systematic defects. Ultrasonic Testing is the most used NDT method to detect nonsystematic defects in the RSW joints, however the probability of defect detection (POD) of conventional testing technique is not fully satisfactory. Other approaches were invented to deal with this situation. The article compares the currently most used NDT approach with other options and discusses its usability and mutual interchangeability.
Resistance welding process is one of the most common method used to bond different kinds of metals. One of the kinds of resistance welding process is a spot welding method which is used in different kinds of industry, especially in automotive and airline sectors. One of the most important problems present in general during the spot welding process is a fast damage of welding tips, especially when welding metals are zinc layered. Typical welding tips used in spot welding process are made of copper alloys with high electrical conductivity, high mechanical properties and high thermal resistance. However due to the constant impact of high temperature during the welding process, mechanical properties of welding tips are being degraded, which is a direct cause of their graduate wear. Within this article research results of mechanical, electrical and structural properties of welding tips used in resistance welding of galvanized steel sheets are being presented. Obtained data showed that impact of high temperature in welding tips working area (approx. 40 µm) causes structural transformation which is a direct cause of mechanical properties loss. Additionally on the working area of electrode a brass is being created during the process, lowering electrical properties of the tip and reducing its operating time.
ACKNOWLEDGEMENTS: The project was financed by the National Centre for Research and Development in the Applied Research Programme granted on the basis of the decision number No. TECHMATSTRATEG G1/347960/6/NCBR/2017
The paper presents results of studies on the crystallite sizes of oxide layer formed during a long-term operation on 13CrMo4-5 steel at an elevated temperature (T=470oC, t=190,000h). This value was determined by a method based on analysis of the diffraction line profile, according to a Scherrer formula. The oxide layer was studied on a surface and a cross-section at the outer and inner site on the pipe. X-ray studies were carried out on the surface of a tube, then the layer’s surface was polished and the diffraction measurements repeated to reveal differences in the originated oxides layer.
Electron beam (EB) welding of thick materials is not an easy task and finding the correct welding parameters and conditions is one of the crucial factors especially when the quality of weld root is required. The undesirable features of an electron beam weld can lead to premature failure or reduces the effectiveness of the resulting components (e. g. impellers). In attempts to understand how these defects are formed, the formation of EB cavity is primary importance. The greatest significance is attributed to the cavity oscillation in size and shape due to the rapid pressure and temperature changes which occurs during formation of EB cavity. These dynamic behaviors of molten metal during EBW enable creation of liquid metal protrusions in cavity instabilities – spiking. In the preset paper the initial results of several steel and titanium plates with different thickness welded without filler metal are presented. During the welding various approaches have been verified to eliminating the spiking. For spiking elimination was tested the modification of weld joint configuration, using of solder, using of background material and modification of EB welding process parameters. The obtained results are complemented by microstructure analysis and by evaluation of the quality and appearance of the weld root.
One method for evaluating the mechanical properties of components in operation is the use of methods that focus on the use of miniaturized test specimens. Basic properties used mostly for the service life evaluation are tensile strength, impact notch toughness or impact notch toughness transition curve, fracture toughness, creep and high cycle fatigue.
This research explores high cycle fatigue and tensile tests with the use of on standard test bars and sub sized samples obtained by semi destructive sampling. The first part of the testing was focused on the micro-tensile tests. The tensile tests were carried out to find out the initial stress level. In this research were studied the mechanical properties on steel X1CrNiMoAlTi 12-11-2 and 16 343. The results from micro-tensile tests and high cycle properties show excellent agreement with each other. Therefore, this fact leads us to conclusion that the miniature specimen tests can replace the fatigue testing under certain circumstances. The use of miniature specimen brings many advantages such as cost reduction, non-invasive affection of the material, time saving.
High strength multiphase TRIP steels are very often used as structural materials, especially in the automotive industry. Due to their ability to absorb energy during the impact, they are used as safety components of the car body. These parts can be produced by a hot stamping process, which has the advantage of using lower forming forces and a smaller spring back effect. The problem during heat treatment of TRIP steels is the holding time in the area of bainitic transformation, which serves for bainite formation and stabilization of retained austenite.
In the present study, two low-alloyed TRIP steels with and without niobium content were chosen. The method of material-technological modeling was used to test the possibility to remove the isothermal holding time during cooling and the processing of these steels by hot stamping process. Different continuous cooling profiles from the tool temperature were tested. The results were then compared with the isothermal processing in the area of bainitic transformation. Mixed structures consisted of bainite, martensite, ferrite and retained austenite were obtained for both steels. The ultimate strength reached over 1000 MPa with the elongation A5mm = 14%.
This paper summarizes results of experimental work and numerical simulations carried out 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”. This project deals with the utilization of the small punch test for evaluation of material degradation of critical components of a power station in the company ČEZ. The main goal of the WP8 activities is an improvement of empirical correlation of selected materials used in power industry for manufacturing of the critical components (rotors, steam-pipes, etc.). Moreover, WP8 activities are also focused on utilization of FE method and neural networks (NN) for evaluation of mechanical properties (yield stress, tensile strength, and fracture toughness) at a room temperature, based on SPT results. Neural networks are computing systems inspired by the biological neural networks that constitute animal brains. Such systems learn to perform tasks by considering examples, generally without task-specific programming. They have found most use in applications difficult to express in a traditional computer algorithm using rule-based programming. The aim of the experimental work presented in this paper is to develop a software for prediction of mechanical properties (yield stress, tensile strength and fracture behaviour in the term of J0,2) of the new materials used in the power industry. Such investigation is based only on built database and SPT results. Additional tests, such as tensile and fracture toughness, requiring large volume of material taken from components, are not desirable here.
The results of the structure and phase composition investigation 316L stainless steel of samples formed by selective laser melting on Mlab cusing R (Concept Laser) equipment are presented. The physical and mechanical properties investigation conducted by X-ray diffraction analysis, scanning electron microscopy, and microhardness measurements. It was found that 316L steel powder after selective laser method has the austenitic structure. The structure of the samples is characterized by cross sections of tracks left by the laser. A thin cell-dendritic substructure has been identified, there are pits inside which droplets with a diameter of about 50 μm are observed, which is typical for objects obtained by laser melting of powder material. Samples are characterized as the structure with high degree of homogeneity.
The paper deals with the influence of the main welding parameters of resistance spot welding on the quality of the joint. Effect parameters were studied in the range of welding, which are expected joints without defects (as recommended by EN ISO 14373). DOE analysis was used as an analytical tool. The DC06 deep-drawing steel, with thickness 0.7 mm, used in the automotive industry, was used as the base material. Quality was judged by visual inspection, ultrasonic examination, macroscopic and mechanized shearing tests. The results show that a significant impact on the quality of weld and weld size of the lens is particularly well set welding current. The results can be used to predict the size of the welding lens depending on the set welding parameters.
Austenitic stainless steel with higher chromium and nickel contain are often used as popular material in the energetics, chemical, food processing and medical applications. That material has a suitable combination of strength and corrosion properties for a given purpose. Their processing technology are also not above-sophisticated. For these materials are typical some of the following degradation processes. In case of corrosion some types of localized corrosion attack types, such as. intergranular, corrosion cracking, etc. It is also necessary to monitor fatigue processes and influences.
This article discusses the causes of damage of the sieve of the vibratory separator of MgCl2.6h2o. The sieve is made of Steel AISI 304. Damage manifested itself with the cracking of certain strand (wires), mostly in the area of the outer circular frame. The damage started to occur after change of the vibration (frequency) parameters. The possible influences of chemical damage by environment or corrosion attack were observed, mechanical stress, fatigue, etc.
For research, has been applied methods of optical microscopy and SEM analysis. Fractographical analysis of fracture surfaces, evaluation of mechanical properties (hardness) and verification of chemical composition was carried out. The results show the majority influence of fatigue damage.
The mechanical and corrosion properties of weathering steel had been deeply studied in 70 and 80 ties of last century. In this period a lot of structure was built in the Czech Republic. As the corrosivity of atmosphere significantly changed during 1995-2005 the corrosion rate was reduced. Paper performed a new data of corrosion rate and comparison of change. The effect of steel structure design was studied too.
The intended operation time prolongation of the key components of fossil-fuelled power plants working in the creep conditions over 200,000 or even 250,000 hours (far beyond their original design lifetime) must be accompanied by thorough and extensive monitoring of the current material state and particularly creep damage. The extent of cavitation damage is routinely tested in-situ by using replica method and its quantification is based on a practice stated in VGB-TW 507, NORDTEST NT TR 170 or NORDTEST NT TR 302 that further develop the original Neubauer's classification. Although the evaluation of cavitation damage based on the measurement of the number of cavities and/or creep micro-cracks is a routine activity, what is still in question is the depth of the damaged area and the corresponding material properties through the wall thickness.
Mutual correspondence between the creep damage evaluation performed in accordance with NORDTEST NT TR 302 and VGB TW 507 was carried out in a pipe bend made of a low-alloy 0.5Cr-0.5Mo-0.3V steel creep exposed at 525-540 °C for more than 225,000 hours and the relation between creep damage at the outer surface of the pipe bend (as a typical result of replica testing) and mechanical properties of the whole pipe bend are discussed in the paper with reference to the residual life assessment.
Powders are nowadays used as an input material not only for conventional powder metallurgy technologies, but increasingly also for additive technologies. Powder producers usually limit their description to an average chemical composition and typical grain size. However, the real grain size distribution might be much more complex than the one declared by producers and chemical composition of an individual grain also does not have to be homogeneous. Additive technologies often claim to be waste-less production technologies meaning that powder which was not melted could be freely re-used. In this case, it is important to know if that re-used powder is really the same as the original virgin powder and how can potential differences influence the properties of produced parts.
New powders and powders left in the chamber after selective laser melting were compared for three materials, 1.2709 maraging steel, stainless steel 316L and Inconel 718. Metallographic cross sections of powders were prepared for subsequent microstructure analysis by light and scanning electron microscopy (SEM). Local chemical composition of new and used powders was checked by energy dispersive X-ray spectroscopy. An average grain size and grain size distribution were established by image analysis of SEM images of randomly chosen samples of new powders.
42SiCr steel is a middle carbon, low alloyed steel with 0.4%C, 1.3%Cr, 0.6%Mn and 2%Si (in weight %). In this work, the steel was used in the forged and annealed state, possessing ferritic-pearlitic-bainitic microstructure. In development and optimization of heat and thermo-mechanical treatments, small volumes of materials are commonly processed in various simulators or dilatometers. This means that smaller samples for mechanical testing are also necessary and question arise how exactly various sample geometries affects measured mechanical properties, particularly ductility. Four types of samples for tensile test were used for the comparison. Three of them were flat, with various cross sections and active lengths of 15, 20 and 50 mm. The thickness of all three types of samples was kept the same, 1.2 mm. For a reference, a sample with circular cross section with 5 mm diameter and 25 mm active length was tested as well. Zwick Roell Z250 was used to perform tensile tests, according to ČSN EN ISO 6892-1. Six samples of each geometry were tested and used for calculation of average values of tensile properties. Following intervals of tensile properties were obtained: yield strengths of 721-766 MPa, ultimate tensile strengths of 1205 - 1335 MPa and total elongation of 15-19 %. The highest elongation was measured for circular samples, while the highest ultimate tensile strength was achieved in the flat sample with active length of 20 mm.
This paper deals with fatigue tests performed on miniature specimens and subsequent correlation of the results with the standard samples. The small specimens can find application especially in cases where, for various reasons, it is not possible to remove sufficient volume of material to produce specimens of standard size.
Due to the small volume of material, the small test specimens are suitable for the evaluation of the residual lifetime of components such as e.g. pressure vessels, steam pipes, turbine covers and rotors and other power plants components.
In this study, the miniature test specimens were made of the 15CH2NMFA steel CT/50 test specimens after fracture toughness tests. The paper discusses the shape of miniature test specimens, clamping system and the subsequent correlation of the obtained results.
Phase identification of corroded objects might be problematic; present corrosion products are complex mixture of different phases each of different amount. Furthermore some of present phases may be either semi-crystalline or amorphous. The most suitable procedure is to use the XRD for analysing crystalline structure of phases in bulk; then use Raman spectroscopy to obtain information on smaller scale and given location. Raman spectroscopy identifies crystalline and semi-crystalline phases. The last step is to apply the Mossbauer spectroscopy to find amorphous phases. If Mossbauer spectroscopy is not available and it is reasonable to assume the contained phases are not strictly amorphous; the XRD and Raman should be sufficient. Should using FTIR in addition to Raman give a suitable advantage? The methods may be interchangeable to some point. But is it safe to assume all phases present can be detected?
This paper deals with corrosion behavior of steels with reduced effective chromium content in the matrix. The intent is to estimate long-term behavior of these steels in environments with low corrosion aggressiveness. Materials for this research were steels with varying character of influencing of the effective chromium content, by precipitation of chromium carbides or by spinodal decomposition of chromium / martensitic steels, or by the formation of other types of chromium-rich phases, e.g. borides in austenitic steels. Binding chromium into these compounds reduces the amount of effective chromium in the solid solution (up to several wt. %), which may be the cause of the reduced overall passivation ability of the steel, or to sensitivity to intergranular corrosion.
Based on the basic techniques of material identification, the causes of different behavior of both types of steels after sensitization or tempering were estimated. Described are situations risky in terms of heterogeneity in the chromium content, which may create sites with reduced corrosion resistance during exposition in aggressive corrosive environments (e.g. decontamination processes or intergranular corrosion tests). However, these sites in a real operating environment with low aggressiveness should not show.
Microalloying elements Ti, Nb, V, entered into steel they influence their microstructure and mechanical properties, because formation of carbonitrides, M (C, N), which in the high temperature inhibit the austenite grains growth and during the cooling of the austenite form fine precipitates giving the dispersion precipitation effect in ferrite.
Influence of carbonitrides to the microstructure and mechanical properties depends on their basic stereological parameters: volume fraction, VV, and their size, r.
In this work the model of the kinetics of the carbonitrides precipitation which enable to predict the chemical composition of austenite as well as the size distribution of carbonitrides formed during isothermal annealing of supersaturated steel is presented. The model is based on the Kampmann and Wagner model developed using the classical theory of nucleation.
Work is aimed at three laboratory manufactured high strength manganese steels after cast, rolling and aging process (at 500 °C after 6, 12, 30 and/or 60 minutes of dwell). Micro-hardness (HV0.2) after all modes of treatment are mutually compared and also from point of view of potential k-carbides formation of µm - and/or nano-size and character of microstructures. Revealed disproportions are also explained by chemical composition and by cooling from high finishing rolling temperature leading to undesirable µm-size k-carbides formation. Simultaneously, changes in selected thermos-physical parameters after hot rolling and aging (560 °C / 6 minutes) were studied. Between micro-hardness and those thermos-physical parameters some proportionality was observed.
Induction quenching can be used for hardening the outer surface of large parts, achieving superior mechanical properties, with the advantage that heating is not required to the whole part. Induction heating is a complex combination of electromagnetic, heat transfer, and metallurgical phenomena involving factors such as: current, voltage, frequency, applied power, scanning speed, heating period, and many more. The influence of some of these factors on the material properties will be shown, for an induction-quenched steel large bearing ring (50CrMo4/Saarstahl). It was observed that increasing the induction heating working frequency results in a decrease in the quenched depth in the sample, but also in an increase in sample surface temperature. It was possible to obtain the same desired thickness of the hardened layer using different combinations of power and frequency density. For example, when it would be necessary to obtain a hardened shallow superficial layer, the same result could be obtained with a lower frequency than the optimum in combination with a higher power density applied for a shorter time. On the other hand, if a thicker layer is desired, with an existing system using a higher frequency than the optimum value, the use of a lower power density in combination with a higher heating time would be beneficial. Choosing the optimal parameters is critical, in terms of lower number of defects, such as cracks and uneven depths for the hardened material.
The article deals with the evaluation of the functional surfaces of the ball valve body. It deals with the finishing methods when machining parts of the ball valve assembly. Above all, it is good practice to achieve a reduced roughness of the machined seating surfaces and areas where a special sealing element will be used. From the offered variants of surface finish machining methods, emphasis is placed on turning technology, so called fine turning. Experimental machining attempts to achieve the required surface roughness (parameter Ra less than 0.2μm) directly after the finishing operation.
The effect of heat treatment on the microstructure and mechanical properties of the 10 wt % Cr-3 % Co-3 % W-0.2 % Re martensitic steel was investigated. The microstructure and the mechanical properties of this steel subjected to the normalizing at 1050 °C were studied after tempering under different conditions. After normalizing at 1050 °C, the average size of prior austenite grains was 55 μm and no evidence of δ-ferrite was observed. The tempering temperature has a strong effect on tempered martensitic/ferritic lath structure: lath width increases from 280 to 710 nm and dislocation density decreases with increasing tempering temperature from 750 to 800 °C. Boundary M23C6 and M6C carbides and randomly distributed within matrix Nb-rich MX carbonitrides were detected. Increasing tempering temperature led to significant growth of all secondary phase particles. No depletion of Re from the solid solution during any tempering conditions was revealed. Impact toughness of the steel studied is independent of tempering temperature, whereas tensile properties and hardness decrease with increasing tempering temperature. This steel subjected to the tempering at 770 °C was carried out the short-term creep tests at 650 °C under the applied stresses ranging from 200 to 140 MPa with a step of 20 MPa. High creep resistance of this steel under shot-term creep testing is provided by the stability of tempered martensitic/ferritic lath microstructure.
The subject of the paper is finding optimal setting of the laser power for the utility properties of the surface roughness parameter in the Additive technology by SLM method for differently large overhangs. The overhangs created on the sides, which are not supported by a supporting structure and are not designed in any way for printing by Additive technology. The samples were printed from stainless steel 316L (1.4404) under constant building parameters with change only of laser power. In total three laser power sizes were tested on differently large overhangs. The surface roughness parameters were measured and evaluated on the lower side of the overhang. The quality of the surface roughness parameter shows the suitability of overhangs in cases where it is not possible to add supporting construction. In conclusion, the most appropriate laser power was determined in relation to the size of the overhang and its surface roughness parameter.
The paper presents the problems of the basic parameters of the ASWJ cutting process, such as abrasive flow rate, diameter and length of the nozzle forming the hydro-abrasive jet with a pressure reduced to the order of 30 MPa. The efficiency of such a process is similar to a conventional 400 MPa Abrasive water Jet cutting. Achieving such a high efficiency in the processing mild steel results from the use of circular motion of the liquid to create a stream. This has become possible due to the replacement of a low-efficiency injector mixer with a new mixer in which the hydro-abrasive mixture is generated directly under high pressure. The conducted research allowed to determine the abrasive flow rate and best geometric dimensions of the working nozzle, thanks to which the best machining effects were achieved.
The objective of this research is to investigate the effect of extension rate on tensile properties of AISI 4140 steel. The steel was supplied by local vendor in Thailand and its use for some military product. The primary material testing was needed to be done in order to obtain mechanical properties. The extension rate testing was performed on tensile testing machine ranged from 300 to 500 min/min. The results were shown that when higher extension rate was applied, the tensile stress of 4140 steel was increased. In contrast with elongation, the trend was decreased according to extension rate advancement. Moreover, extension rate is not affect to deformation mode of 4140 because ductile failure remains in the same as quasi-static tensile test.
The development of Generation IV nuclear reactors and accelerator driven systems (ADS) is supporting a wide range of work on the compatibility of stainless steels with heavy liquid metals (HLM).
The austenitic steel DIN 1.4970 (also known as 15-15Ti) is being qualified for use in heavy liquid metals because of its lack of sensitivity to Liquid Metal Embrittlement. The aim of this study is to look into cracking modes in air and in PbBi and their main characteristics in order to reach a clear idea of mechanisms.
Flat tensile, tapered specimens were slow monotonic loaded in PbBi at 300°C with low oxygen content and, for comparison in air, up to the maximum load and rupture. The specimens had one ground and one polished surface, to highlight also the effect of the surface finish. Post-test examinations were carried out with SEM and EBSD. The role of microstructure towards crack initiation and propagation is here described. The behaviour of the steel was not notably affected by the environment, when compared to testing in air. In both cases, the cracking mode was mainly ductile and affected only by the presence of large Ti-rich precipitates in the steel matrix.
Steel MLX 17 (X1CrNiMoAlTi 02.11.12) belongs to martensitic precipitation-hardened steels for use in demanding applications in aviation, offshore oil and gas industry. The unique combination of high strength, toughness, fatigue strength and corrosion resistance is obtained after ageing of low carbon martensite above 500 °C.
Due to its chromium content, steel MLX 17 represents materials prone to embrittlement at 475 °C induced by decomposition of oversatured solid solution into two solid solutions alpha + alpha´ and/or embrittlement caused by precipitation of chromium-rich brittle sigma phase.
Although this steel is not typically exploited at higher temperatures, it is interesting to know the effect of long-term ageing on material properties, microstructure and substructure. Therefore, ageing at 475 °C for 1 000, 2 000 and 3 000 hours was performed and material properties and microstructure were evaluated. Analysis of substructure confirmed the additional precipitation of Laves phase, one of the main sources of precipitation hardening in MLX 17 steel, decomposition of the solid solution and formation of chromium-rich particles (alpha´) of nanometric size, but very small amount without any effect in precipitation hardening. The same was true for particles of Laves phase, which quickly grew up to the size of about 100 nm. Ageing at 475 °C was also accompanied by doubling the reverse austenite content in comparison with the as-received state. Long-term annealing at 475 °C was accompanied by a slow decline of strength and impact energy. The effect of the stabilization of the reverse austenite overcame the contribution of additional precipitation.
In modern world probably no one can imagine traveling without airplanes. But the engines and especially their components had to walk a long way for today’s efficiency and safety. This paper deals with the original idea of testing not just cut specimens as stress rupture tests, but whole blades for increasing the authenticity of the simulated environment and the the nature of the test itself. The object of the project was to prepare whole testing setup from beginning. That includes an attachment of the blade, special furnace which can simulate heating process in the body of the blade, but not in shroud and fir tree and monitoring of the temperature. The combination of all these factors can be an appreciated solution for all aircraft engines suppliers over the world.
Modern blocks of fossil fuel power plants designed for steam temperatures above 600 °C require advanced stainless steels in super heater or reheated systems. Great attention is paid to the usability of new steel grades with higher utility properties. In the area of austenitic steels, the perspective grade is undoubtedly HR3C steel (X6CrNiNbN 25-20). In terms of the use of similar weld joints made of HR3C steel in fossil fuel power plants, detailed knowledge on creep resistance and microstructural stability of these weld joints is necessary.
Similar weld joints made of HR3C steel were manufactured using a combination of GTAW and SMAW welding technologies. Weld joints were studied both in the as-welded state, and after post weld heat treatment (PWHT). The paper presents the results of creep rupture tests on cross-weld samples at temperatures of 650 and 700 °C. There are discussed results of detailed metallographic analysis on longitudinal sections of ruptured creep samples and results of microhardness profile HV 0.5 evaluation over individual regions of cross-weld samples. The paper analyses the priority failure locations of the HR3C similar weld joints in dependence on the temperature of creep exposure and applied stress.
Numerical studies are increasingly carried out, at the initial stage of manufacturing of welded joints, which allows determining the most appropriate process parameters and accepting the appropriate parts fixing method during welding. The aim of this is to reduce stress concentrations and prevent the formation of welding deformation.
The paper concerns numerical modeling of single-side T-joint welding using the laser beam. The purpose of performed analysis is the determination of the temperature field in the welded joint, stress state and the estimation of welding deformation. Numerical analysis of laser welding phenomena is carried out in Abaqus/FEA software. The position of the beam in relation to the connected edges of the T-joint is selected in the developed three-dimensional discrete model to ensure full melting of the contact area of joined surfaces. The calculation model has been extended with additional subroutines that allow perform a full analysis of thermomechanical phenomena. The power distribution of a moving welding source is modeled in subroutines by the use of mathematical formulas based on transformational equations for relative positioning of the heat source to the joined elements. Changing with temperature thermomechanical properties of welded elements made of austenitic steel are taken into account in the material module of Abaqus/CAE software.
Temperature distribution in analyzed joint, stress state and welding deformations are determined on the basis of numerical simulations. The experimental research available in domestic and foreign literature is used to verify obtained simulation results.
The purpose of this paper is to investigate the influence of hybride heat source on the properties of welded joints produced by the Plasma+MAG method of S700 MC (high strength Re = 700 MPa). Due
to the verification of the quality and properties of the obtained joints, destructive tests, hardness measurements mean dimention of grains and mechanical properties of joints were performed.
The paper presents the results of mechanical properties tests at reduced and elevated temperature after a four-stage hot-rolling and cooling in water, microstructure tests and fractographic studies of breakthroughs of high-strength high-manganese steel X98MnAlSiNbTi24-11 and X105MnAlSi24-11 TRIPLEX type. In order to determine the mechanical properties of the steels tested, microhardness tests and a static tensile test were performed, on the basis of which the conventional yield strength, tensile strength and elongation were determined. Structural investigations using light microscopy and scanning electron microscopy enabled the identification of austenitic-ferritic structure in steels with the participation of carbides and numerous deformation twins in austenite grains. Diffraction in SEM was also used to analyze the structure. The obtained test results allow to assess the influence of reduced and increased test temperature on the strength properties of the analyzed steels in correlation with their structure.
The Inconel 617 alloy is used in the construction of boiler pressure elements with ultra-supercritical performance parameters. The paper presents the results of microstructure testing after 10,000 h of ageing at a temperature of 750 °C. Microstructure research was performed using scanning electron microscopy. Identification of occurring precipitates was carried out using X-ray phase composition analysis. The influence of ageing time on the changes of microstructure and the precipitation process in the native material, heat influence zone and weld, which were referred to the changes of basic mechanical properties was described. The presented research results are an element of the material characteristics of the new generation alloys, which are used in the design work of pressure devices of steam boilers and diagnostic work during operation.
The paper deals with the possibility of using the SPT-(small punch tests method) for evaluation of material properties of the individual areas of welded joints. The homogeneous and heterogeneous welds for USC power plants were assessed. The selected combination of welded joints made of austenitic creep resistant steels of the TP347 HFG, HR3C, Super304H and P92 grades in as-received state and after exposure in the real boiler conditions for one year were studied. The mechanical and fracture properties were assessed using small punch test of welds under investigation. The mechanical properties and fracture properties were studied using miniaturized tests, too. From the results it can be concluded that especially fracture properties were influenced significantly due to one-year exposure, which can be demonstrated on the Charpy impact tests, where the impact energy dropped down to only 1/3 of the original value.
he continuous increase in the demand for electricity, the need to increase the power and of power units efficiency causes the development and researches of dedicated materials. These materials work in extremely harsh conditions, they must be resistant to high temperatures, sudden changes of temperature and deformation. They are also exposed to fatigue damage both mechanical and thermal. The steel grade presented in this paper is a boiler steel working in temperature ranges 500-600 degC. Important parameters for steels of this type are high temperature mechanical properties. It is also important that a high level of properties is achieved at both elevated and room temperatures. Elements working in such conditions, including the steam turbine armor, are exposed to thermal shock what will be presented in this paper.
The article deals with the design of a vehicle dismantling component. It is the front axle of the SUV, with a 4x4 drive produced by Brembo. The main part of the article describes the design of the dismantling product, which you allows a reliable removal of the scrap assembly by a hydraulic press. Subsequently, the design of the individual parts of the product and the process of disassembling the scraper knuckle from the whole assembly to the individual parts is described. For components of the product, the material is designed with respect to the safety and maximum load of the hydraulic press. Finally, a technical and economic evaluation is carried out for the dismantle product, which calculates the financial savings associated with the practical use of the disassembly tool.
Pressure to increase manufacturing production capacity altogether with the economic aspects of production can lead in the incorrect technological practice that does not bear in mind specific material properties and inevitable parameters of its treatment.
The paper deals with the effect of heat treatment parameters on mechanical properties and microstructure of low alloy high-strength steel 55Cr3. The material standard of this steel defines the hardening temperature interval from 830 to 850 °C, which brings about the question of minimum soaking time in order to dissolve carbide particles and to homogenize austenite before quenching. The higher is the heating rate the higher is also the temperature that ensures perfect transformation of the initial microstructure into austenite and makes optimum conditions for desired final microstructure and properties of the steel. The dilatometric analysis performed on the samples simulating different conditions of austenitization confirmed that the incomplete austenitic transformation moved the curves of pearlitic and/or bainitic transformation in CCT diagram of the steel to the left, i.e. towards shorter times. After cooling the mixed microstructure containing not only the desired phases (bainite and/or martensite) but also a significant proportion of pearlite, including the original undissolved pearlite, was detected.
The development scope is cast and hot deformed bulk industrial products made of conventional low alloy structural steels. Chemical and microstructure homogenization, grain size refinement (up to 12 ASTM G) and over twice impact resistance increase were revealed in semi-industrial conditions for as cast 34CrMo4 and as hot rolled E36 steels, due to developed cooling regime application after a high temperature austenitizing. Solid grounds of the regime industrial application at conventional casting, hot deformation and heat treatment are emphasized. Future applications of the proposed regime are discussed for elimination of the hot deformation, to regenerate microstructures of weld, deposited, 3-D printed, recycled and renovated low alloy steel products.
Compression helical springs operate frequently under varying loads and deflections. High strength steels are typically used by the manufacturers, but high UTS value should not degrade toughness and fatigue resistance, which can be achieved by control of steel composition and proper heat treatment. In this paper was investigated failure of helical compression springs used on a train coach. Analysis included assessment of mechanical properties and observation of microstructure and fracture surfaces. Provided springs were made from 51CrV4 steel from different heat numbers. Results of tensile test showed high ultimate tensile strength, well above declared material properties but lower elongation. Nominal energies of Charpy impact tests were less than 20 % of required values. Chemical composition of steel complied with specification. Fractography analysis in SEM revealed brittle fracture on the whole surface without any striations otherwise indicating fatigue failure. Observation of microstructure revealed tempered martensite in whole cross-section without distinctive segregations, but prior austenite grain size was larger than specified almost by the factor of two. It was concluded that cause of failure was synergic effect of larger grain size, quenched microstructure and high UTS resulting in low fracture toughness and resistance to impact loadings.
This work deals with the influence of hydrogen on the mechanical properties of TRIP 780 type C-Mn-Si steel. Tensile test bars were hydrogenated in 0.1N sulfuric acid solution with the addition of KSCN during the slow strain rate tensile tests (SSRT). Due to the presence of hydrogen in the steel microstructure, there was a significant decrease of elongation at fracture from 33 % to 3 % and a decrease of tensile strength from 868 MPa to 634 MPa, respectively 658 MPa at current density 5 or 1 mA/cm2. The yield strength slightly increased from 507 MPa to approximately 520 MPa after hydrogenation. The relative change of elongation at fracture due to hydrogen was expressed by the index of hydrogen embrittlement F, which exceeded 90 %. The fracture surfaces of the tensile test bars were subjected to fractographic analysis. The presence of hydrogen during the tensile test influenced the failure mechanism and manifested itself by the occurrence of the quasi-cleavage fracture at the fracture surface.
In this paper we present a mathematical model for evaluating the Lankford coefficient (LC) in automotive sheet steels as a function of the ferrite grain size after hot rolling, the degree of cold rolling reduction, the chemical composition, and the volume fractions of perlite and bainite in the final structure. Empirical parameters values of the model were determined using the experimental data base on average LC in 138 strips of 13 steel grades, produced at PJSC Severstal, with a significant range of chemical composition variation. Complementary, databases on calculated steel microstructure parameters after hot rolling, and after heat treatment of cold-rolled strips on a continuous annealing line were used when creating the model. There is a satisfactory agreement between the results of LC calculations made by the developed model and the experimental data. The mean absolute value of relative error in the calculations for considered steels is 7.1%.
The article presents the results of corrosion resistance tests of multi-groove pads made with the MAG method on a steel substrate. The process of hardfacing the multi-grooves was carried out with constant parameters of the welding process, i.e. current intensity, arc voltage, welding speed). Two gases were used to apply the additional material: CO2 and korgon. The results of previously performed tests allowed to determine the optimal process parameters at which we obtain the smallest share of the base material in the padding. The samples were subjected to corrosion tests in two environments (3.5% sodium chloride solution and 0.01 sulfuric acid solution). The assessment of corrosive properties was made on the basis of constant current measurements (potentio-dynamic method). On the basis of the research, the influence of the chemical composition of pads on corrosion properties was demonstrated.
Speciation and speciation analysis is currently the subject of research in various domains of science and technology, such as chemistry, metallurgy, materials engineering, medicine and environmental protection, being an important factor in the material and environmental analytics development. Speciation is the occurrence of various physical and chemical forms of a given chemical element, the existence of species in tested material. Speciation analysis helps in identification of those forms and their quantitative marking in a given object. Therefore, assuming with a certain degree of simplification that speciation is the presence of various chemical forms of an element in a sample and the speciation analysis allows for quantitative determination of these forms, similarly in reference to metallurgical samples the notion of phase identification and phase analysis is used including chemical analysis as well. The rule, possibilities and limitations of chemical and electro-chemical phase isolation were also described. Chemical analysis of isolated phases in reference to metallurgy almost always meets the quantitative requirements of speciation analysis. Taking into account the numerous advantages of atomic absorption spectrometry (AAS), the role of the method was underlined as significant in research pointing out particularly the applications in determination of chemical composition of intermetallic phases type γ’ in multi-component nickel alloys and carbide phases in tool alloys. The determination of aluminium in steel is also presented with division into aluminium soluble in acids and total aluminium as a classic example of speciation analysis in metallurgy. Additional application possibilities of own solutions and technical modifications were also shown.
The formation of bimodal microstructure in 316L austenitic steel subjected to large strain cold rolling and subsequent annealing and its effect on the mechanical properties were studied. The cold rolling was accompanied by a strain-induced martensitic transformation and grain refinement. The strain-induced martensite comprised 25 % after rolling to a total strain of 3. The deformation microstructures consisted of flattened austenite / martensite grains with the transverse grain sizes of about 130 nm. The steel with nanocrystalline structure exhibited high yield strength (σ0.2= 1680 MPa), but low total elongation (δ = 5 %). The subsequent annealing was accompanied by austenite reversal, static recrystallization and grain growth. The annealing at a temperature of 700 °C (2 hours) led to a fully austenitic structure with bimodal grain size distribution. This bimodal microstructure consisted of individual micrometer-sized grains surrounded by the nanocrystalline matrix. The development of bimodal microstructure resulted in an increase of the total elongation above 15 % while maintaining high strength (σ0.2 = 960 MPa).
The microstructure of dual-phase steels (DP) consists of two phases with completely different mechanical properties. One group of DP steels are made up of a ferrite matrix with a martensite fraction, yielding a good combination of strength, ductility, toughness and strain hardening. In some cases, the percentage of bainite, perlite, or residual austenite is also found in these steels. The overall mechanical properties of these DP steels are controlled by the ratio of martensite to ferrite, martensite carbon content, grain size and strength of each contributing phase. In this paper, the effect of different variables such as intercritical holding temperature, time, initial microstructure and quenching media on the mechanical properties of an industrial grade SAPH440 low carbon steel sheet containing ~0.2 wt.% carbon was studied. The main objective was to simultaneously increase the ultimate tensile strength and elongation of the sheet samples to improve the overall mechanical properties. An L9 orthogonal array was selected based on Taguchi’s robust design and optimization approach. The microstructure and mechanical properties obtained from tensile tests were discussed using analysis of variance.