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The concept of digital twinning is essential for smart manufacturing and cyber-physical systems to be connected to the Metaverse. These digital representations of physical objects can be used for real-time analysis, simulations, and predictive maintenance. A combination of smart manufacturing, Industry 4.0, and the Metaverse can lead to sustainable productivity in industries. This paper presents a practical approach to implementing digital twins of a magnetic forging holder that was designed and manufactured in this project. Thus, this paper makes two important contributions: the first contribution is the manufacturing of the holder, and the second significant contribution is the creation of its digital twin. The holder benefits from a special design and implementation, making it a user-friendly and powerful tool in materials research. More specifically, it can be employed for the thermomechanical influencing of the structure and, hence, the final properties of the materials under development. In addition, this mechanism allows us to produce a new type of creep-resistant composite material based on Fe, Al, and Y. The magnetic forging holder consolidates the powder material to form a solid state after mechanical alloying. We produce bars from the powder components using a suitable forging process in which extreme grain coarsening occurs after the final heat treatment. This is one of the conditions for achieving very high resistance to creep at high temperatures.

Mechanical alloying (MA) of powders represents the first processing step in the production of oxide dispersion-strengthened (ODS) alloys. MA is a time and energy-consuming process also in the production of Fe-10Al-4Cr-4Y

The use of asphaltic concrete cores for sealing embankments and rockfill dams is very important. The self-healing properties of bitumen, simple construction in cold and rainy conditions compared to clay cores, good flexibility and connection with embankment materials are the essential characteristics of asphaltic concrete. The main concern regarding the use of asphaltic concrete cores in Iran is mainly the performance of these dams under seismic loads. The evaluations of the performance of these types of dams in other countries show that asphaltic concrete cores perform satisfactorily in the static state, but in earthquake conditions, the situation may be different. In this paper, the static and seismic behavior of the Meijaran dam in Iran, Mazandaran, is evaluated for three core angles of 90°, 60° and 45°. This evaluation was conducted at the end of the impounding stage and after applying seismic loads using FLAC 2D software and Mohr–Coulomb consitutive models. The results were matched with the ICOLD recommendation to use angled cores in dams with asphaltic cores and showed that the dam performs better with angled cores. Finally, for the Meijaran dam, the results from the dynamic analysis are compared with the results from the centrifuge test.

Oxide-dispersion-strengthened (ODS) Fe-Al-Y2O3-based alloys (denoted as FeAlOY) containing 5 vol. % of nano-oxides have a potential to become top oxidation and creep-resistant alloys for applications at temperatures of 1100–1300 °C. Oxide dispersoids cause nearly perfect strengthening of grains; thus, grain boundaries with limited cohesive strength become the weak link in FeAlOY in this temperature range. One of the possibilities for significantly improving the strength of FeAlOY is alloying with appropriate elements and increasing the cohesive strength of grain boundaries. Nearly 20 metallic elements have been tested with the aim to increase cohesive strength in the frame of preliminary tests. A positive influence is revealed for Al, Cr, and Y, whereby the influence of Y is enormous (addition of 1% of metallic Y increases strength by a factor of 2), as it is presented in this paper.

Excellent creep strength of the ODS steels is associated with an attractive interaction between dislocations and oxides. The aim of this study is to explore the Fe-Al-O and Fe-Al-Cr-Y-O systems with high oxygen content (up to 1.5 wt %) represented by alumina or yttria oxides (up to 5 vol. %) to identify the potentials of the new generation of ODS alloys. The basic material is prepared from Fe and 10 or 11 wt. % of Al. Theoretical models showed stability of Al oxides even above 1000°C, while practical results show coarsening with time at these temperatures. Stability of Y oxides is about 200°C higher, so there is a potential to have stable creep resistant alloy in range of 1000-1200°C.

An experimental steel 42SiCr was heat treated with a quenching and partitioning treatment in order to achieve high strength and at the same time acceptable ductility. This crucial combination requires the formation of a martensitic microstructure with a small volume fraction of retained austenite embedded on a microscopic scale. The objective of this work was to investigate the evolution of microstructure and hardness in the heat affected zone (HAZ) of welds in this 42SiCr and its major influence factors. Thermo-physical simulations with a dilatometer yielded samples of each zone in the HAZ and allowed a detailed investigation of HAZ microstructures and properties. A decrease in hardness from 580 HV in the quenched and partitioned base material to the HAZ, with minimum hardness values of 370 HV in a region exposed to temperatures close to the Ac3 temperature, was revealed. Simulation showed that the experienced peak temperature is predominantly determining the HAZ properties. The microstructure after quenching and partitioning treatment consisted of fine martensite with presumed retained austenite. The HAZ regions that were heated above Ac3 temperature can be characterized to have a fine bainitic/martensitic microstructure, while the regions heated to more than 1100 °C show coarser grain, with bainitic/martensitic features. To support the HAZ simulation results sheets of this steel were rolled and resistance spot welds were produced. The welds were characterised with respect to the microstructure in the heat affected zone, as well as the mechanical properties of the joint. Results proved that the data obtained by thermo-physical simulation is in very good agreement with the spot welding results. On a macroscopic scale the welding results indicate very good joint formation but very brittle fracture behaviour using a conventional resistance spot welding process for the quenching and partitioning steel. However, despite the relatively high carbon equivalent of the material, also ductile aspects of fracture were observed.

The fatigue crack propagation (FCP) behavior of a quenched and partitioned (Q&P), low-alloyed CSiCrMn steel containing 12% of retained austenite is investigated in ΔK-controlled tests at different R-ratios and compared with its quenched and tempered (QT) counterpart, containing 4% of retained austenite. Characteristic features of the crack wake and FCP surfaces are examined by scanning electron microscopy and related to the presence or absence of martensitic transformation. Comparing the FCP behavior of the Q&P condition with its QT counterpart, the fatigue threshold ΔKth is higher, and fatigue crack growth rates in the Paris-regime are lower, for Q&P. With an increase of ΔK, Paris-lines intersect and, at high ΔK, the fatigue crack growth resistance of the Q&P condition becomes inferior. Such FCG behavior is attributed to the amount and stability of retained austenite: at low ΔK, contributions of the martensitic transformation are negligible, and thus a higher fraction of retained austenite accounts for an increased FCG resistance. With increasing ΔK, an increasing percentage of retained austenite in the cyclic plastic zone at the crack tip is transformed, providing brittle pathways for fast crack propagation and thus lowering FCG resistance. Analysing the crack surface, cleavage-like intergranular crack propagation can be directly related to martensitic transformation: in the threshold region, FCP occurs predominantly in a transgranular mode and the percentage of cleavage planes increases as ΔK increases. This study is the first one that examines the FCP behavior in a Q&P-processed steel and one of very few which deal with the near-threshold FCP behavior in TRIP steels.

Nowadays the waste rubber problems are concerned due to the environmental issues, storage, and recycling difficulty. However, the rubber base equipment has been widely used to protect structures for vibrations - that has been generated by the structure or induced from the vicinity area or the bedrock into the structure - due to the notable capability of absorbing energy. In this study, the repeated-loading behaviour of the Sand Rubber Mixture (SRM) has been investigated and the remarkable energy absorption properties of the mixture have been illustrated. The test soil material that has been used in this study was a well-graded sand (SW) with a mean grain size of 2 mm. The test martial rubber that has been used was grain particles with a uniform size of 4.76 mm. The sand rubber mixture (SRM) was prepared by using 7.5% rubber inclusion because it was found as the optimum rubber content. A series of force control repeated-loading CBR tests have been arranged. The effect of mixing rubber particles with the well-graded sand (SW test material) has been investigated. This shows the remarkable energy absorption capability of Sand Rubber Mixture (SRM) to protect the bed of a machine’s footing that is generating repeated loads. The SRM usage could be extended to be employed as a part of an energy absorption unit and dampers facilities beneath a machine footing or structures that are sensitive to the vibration to prevent destructive deformation and resonance phenomenon.

A new generation of Oxide Dispersion Strengthened (ODS) alloys called Oxide Precipitation Hardened (OPH) alloys, has recently been developed by the authors. The excellent mechanical properties can be improved by optimizing the chemical composition in combination with heat treatment. However, the behavior of such materials requires the consideration of a large number of variables, nonlinearities, and uncertainties in the analyses, and the modeling of such alloys by analytical methods is not accurate enough. Therefore, artificial intelligence (AI) methods, such as machine learning (ML), can be beneficial to alleviate the problems associated with the complexity of these alloys. In this work, three different hybrid ML techniques have been employed to estimate the ultimate tensile strength (UTS) and elongation in these special alloys. The proposed methods include a feedforward artificial neural network (FF-ANN) trained using particle swarm optimization (PSO) and two adaptive neuro-fuzzy inference system (ANFIS) methods trained using both fuzzy C-means (FCM) clustering and subtractive clustering (SC). Since OPH alloys are mainly produced via mechanical alloying (MA) of a mixture of powder components followed by consolidation and hot rolling, a series of standard tensile tests were performed on the different variants of the OPH alloy. In this way, some critical parameters such as UTS and elongation could be extracted from the experimental results. The main contribution of the present study is to estimate these important parameters based on some material properties including Aluminum (Al), Molybdenum (Mo), Iron (Fe), Chromium (Cr), Tantalum (Ta), Yttrium (Y) and Oxygen (O), MA and the heat treatment conditions. The results show that the proposed strategies are not only able to accurately determine the complex behavior of OPH alloy with an accuracy of about 95%, but they can also help the designer to benefit from these powerful tools to design new versions of such materials without analytical calculations.

Quenching and partitioning (Q&P) treatments result in promising mechanical properties of advanced high-strength steels. However, recent studies indicate that Q&P steels are very susceptible to hydrogen embrittlement (HE). Using slow strain-rate tests, the effects of hydrogen charging in different media without and with recombination poison were investigated for Fe-0.38C-1.92Si-0.66Mn-1.39Cr in quenched and tempered as well as Q&P conditions. In addition, corrosion tests and Zn electroplating of tensile specimens were performed. In both heat-treatment states, it was found that the intensified hydrogen-charging conditions using a recombination poison strongly impact the result of HE investigations: HE only occurs when a recombination poison is present. In addition, the negative influence of hydrogen formed during Zn electroplating can be limited by using proper electrolytes and electrical parameters. This allows keeping the HE susceptibility of the Q&P steel low in practical applications when recombination poisons are absent.

The aim is to realize a Q&P (Quenching and Partitioning) process for a hot forged component made of low-alloyed advanced high-strength steel (AHSS) 42MnSiCr. One advantage of this steel is the low alloy concept which is cost-effective. After forging, the component is cooled down to room temperature with a subsequent heat treatment to achieve the characteristic microstructure with martensite and retained austenite. The material is annealed and then quenched to just above the martensite finish temperature (MF-temperature). Hence, in the martensitic matrix about 10 to 15% retained austenite is included. Finally, the Q&Ped material is artificially aged at 250 °C to support the diffusion process of carbon from the over-saturated martensite into the austenite. Thereby, mechanical properties of 2000 MPa for tensile strength with fracture strains of 10% can be achieved. This paper provides details of the process and material behavior for a reduction of the process chain. The goal is to develop a technology for the quenching and partitioning treatment of forged components by using the thermal energy from forging. Ideally, the quenching step should be performed in the forming dies just above the MF-temperature with additional holding on the temperature level. The majority of forged parts have different cross sections. Therefore, the cooling conditions are inhomogeneous in each cross section of the components. This cooling behavior was analyzed in laboratory tests with a forged part. Furthermore, the heat transfer coefficients were determined for different cooling media (water, air). The cooling technology was experimentally and numerically simulated in a first step for the conventional process chain (forging, cooling to room temperature, austenitisation, quenching, artificial ageing) and correlated with the microstructural evolution in combination with the component’s mechanical properties.

Oxide Precipitation-Hardened (OPH) alloys are a new generation of Oxide Dispersion-Strengthened (ODS) alloys recently developed by the authors. The mechanical properties of this group of alloys are significantly influenced by the chemical composition and appropriate heat treatment (HT). The main steps in producing OPH alloys consist of mechanical alloying (MA) and consolidation, followed by hot rolling. Toughness was obtained from standard tensile test results for different variants of OPH alloy to understand their mechanical properties. Three machine learning techniques were developed using experimental data to simulate different outcomes. The effectivity of the impact of each parameter on the toughness of OPH alloys is discussed. By using the experimental results performed by the authors, the composition of OPH alloys (Al, Mo, Fe, Cr, Ta, Y, and O), HT conditions, and mechanical alloying (MA) were used to train the models as inputs and toughness was set as the output. The results demonstrated that all three models are suitable for predicting the toughness of OPH alloys, and the models fulfilled all the desired requirements. However, several criteria validated the fact that the adaptive neuro-fuzzy inference systems (ANFIS) model results in better conditions and has a better ability to simulate. The mean square error (MSE) for artificial neural networks (ANN), ANFIS, and support vector regression (SVR) models was 459.22, 0.0418, and 651.68 respectively. After performing the sensitivity analysis (SA) an optimized ANFIS model was achieved with a MSE value of 0.003 and demonstrated that HT temperature is the most significant of these parameters, and this acts as a critical rule in training the data sets.

Today’s advanced steels are required to possess high strength and ductility. This can be accomplished by producing appropriate microstructures with a certain volume fraction of retained austenite. The resulting microstructure depends on material’s heat treatment and alloying. High ultimate strengths and sufficient elongation levels can be obtained by various methods, including quenching and partitioning (Q&P process). The present paper introduces new procedures aimed at simplifying this process with the use of material-technological modelling. Three experimental steels have been made and cast for this investigation, whose main alloying additions were manganese, silicon, chromium, molybdenum and nickel. The purpose of manganese addition was to depress the Ms and Mf temperatures. The Q&P process was carried out in a thermomechanical simulator for better and easier control. The heat treatment parameters were varied between the sequences and their effect on microstructure evolution was evaluated. They included the cooling rate, partitioning temperature and time at partitioning temperature. Microstructures including martensite with strength levels of more than 2000 MPa and elongation of 10–15 % were obtained.

A nearly abrupt coarsening of grains is observed in a newly developed Fe–Al–O ultra-fine-grained nanocomposite with a significant volume fraction (4%) of alumina nano-precipitates. The micr...

An important factor in enhancing the mechanical properties of high-strength steels is the stabilization of an appropriate amount of metastable retained austenite in martensitic matrix. Various novel heat treatment and thermomechanical processing routes have been developed recently which benefit from the effects of retained austenite in terms of achieving better elongation at still high ultimate strength levels. One of these procedures is the Q&P process (Quenching and Partitioning). It produces martensite and retained austenite to obtain strengths of more than 2000 MPa and elongation levels of about 10%. For this investigation, four steels with low Ms temperatures have been selected. Their chemistries contained manganese, silicon, molybdenum and chromium.The development of heat treatment sequences involved trials with various austenitizing temperatures, cooling rates, quenching temperatures, and carbon partitioning temperatures for the stage in which austenite becomes stabilized. The experimental heat treatment led to microstructures consisting of martensite with retained austenite in all the steels. Their strengths were in the range of 1750-2400 MPa and their A5mm elongation was 10-15 %. The largest fraction of retained austenite, according to X-ray diffraction, was 10 %. Specimens with the largest fraction of retained austenite obtained from one schedule were used for studying the stability of retained austenite under cold and hot.

Three low alloyed transformation induced plasticity (TRIP) steels with 0.2%C were used in this work. The first one was based on the most common and popular 0.2%C - 1.5%Mn - 1.8%Si concept and was used as a reference material. The second steel was further micro-alloyed by 0.06% of Niobium. The third steel was designed with lower manganese content of 0.6% and additional alloying by 0.8% of Chromium. Thermo-mechanical processing with incorporated incremental deformation was applied to each steel. Various cooling rates and numbers of deformation steps were tested with regard to final microstructure and properties. After this optimization, microstructures with the potential to utilize TRIP effect were achieved for all steels. Very good mechanical properties were obtained with ductility typically in the interval of 30-40% and the tensile strengths in the range of 680-835 MPa.

This paper describes selected capabilities of unconventional processing of steels in semi-solid state under various process conditions and with the use of various steel chemistries for obtaining unusual structures formed by rapid solidification in combination with other procedures. This investigation involves the use of severe plastic deformation techniques (SPD) and in-situ observation of the transformation of microstructure from solid state to semi-solid state at temperatures above 1200°C using a high-temperature microscope.

In the forging industry, as in other sectors, opportunities are sought for a continuous improvement in the manufacturing productivity. The solution can be found predominantly in optimizing the existing manufacturing processes or developing new ones. However, suspending the production in order to verify optimization proposals often results in substantial financial losses to the company. The present paper describes a design of a comprehensive material/technological model of a production sequence of real-world forging, including the heat treatment in continuous furnaces. A forging used in automotive applications is made of the C45 steel by closed-die forging. A material/technological model of this forging was developed using data gathered in the real-world forging production and with the aid of a FEM simulation. Good agreement between the specimen processed according to the model and the real-world forging was confirmed with a metallographic observation and tension testing. In both cases, the microstructure consisted of ferrite and pearlite. The ultimate strength of the forging was 676 MPa and its elongation reached 28 %. In the material processed according to the model, the ultimate strength was 655 MPa and the elongation level was 32 %. The results will be used as the basis for the material/technological modelling in an effort to develop and optimize a controlled cooling sequence to replace the existing heat-treatment process.

With the prices of raw materials as well as final products growing a significant tendency to search for weight reduction of the machine components through improving their quality can be observed at present. To achieve as good mechanical properties as possible, efforts are made to reach the finest microstructure possible in steels. Besides the fine grain microstructure the required phase volume fraction must also be obtained in case of AHS steels to ensure the possibility of utilizing the TRIP effect during the final cold deformation. Their structure usually consists of ferrite, bainite and retained austenite, which transforms to deformation induced martensite during final cold deformation. With an appropriate volume fraction of these phases the materials show good combination of strength and ductility. In the experiment eight and twenty step incremental deformation was applied within identical thermomechanical sequences in the deformation temperature range of 900 – 720°C. At the same time the influence of twenty step incremental deformation on the development of microstructure was examined down to 600°C. Comparison of the results was carried out by means of light and electron microscopy. The volume fraction of structural phases including the fraction of retained austenite was determined by image analysis.

All sectors of industry experience high demand for shaped products with as good mechanical properties as possible at low costs. Automotive industry, in addition, requires that the parts are of lightweight construction. Consequently, new types of materials and processes have to be combined to design new production chains capable to meet this demand. For instance, there are high-strength low-alloyed steels, whose final properties are attained by advanced heat treating techniques. One of such techniques is the Q&P process which can deliver excellent ultimate strengths exceeding 2000 MPa at a sufficient elongation level of 10 %. When combined with an unconventional forming method, it allows complex-shaped parts with outstanding mechanical properties to be made. One example of such combined procedure is the sequence of internal high pressure forming, hot stamping and Q&P processing. In the present study, thin-walled hollow stock was processed using such a combined procedure. After stepwise optimization of processing parameters, products with martensitic structure and a small amount of bainite were obtained. In all locations of the product which were tested, the ultimate strength exceeded 1950 MPa and elongation reached 15 %

Changing the lamellar morphology of pearlite to a globular morphology significantly enhances the formability of pearlite-ferrite steels. This change is conventionally achieved by soft annealing. Annealed structures possess low yield strength and excellent ductility and this ensures their good cold formability. The problems of these technologies lie not only in long processing times, but also in high energy consumption which makes the final product quite expensive. The time necessary for cementite spheroidization can be shortened by unconventional heat treatment around Ac1 temperature combined with deformation applied at various processing stages. Several processing methods were utilized for spring steel 54SiCr with ferrite-pearlite original microstructure and lamellar pearlite morphology. The hardness of this structure reached 290 HV10. Three main strategies were tested in this work, using either tensile and compression deformation with following hold applied at heating temperature, temperature cycling around AC1 temperature, or deformation cycles applied at heating temperature. First of all, various heating temperatures in the region of 680-740°C were tested to determine the most suitable heating temperature for this steel. Subsequently, the influence of the character and intensity of applied deformations on cementite spheroidization and ferrite grain refinement were investigated. Carbide morphology and distribution were determined by the means of light and scanning electron microscopy and mechanical properties were determined by hardness measurement. Spheroidized carbides evenly distributed in fine ferrite matrix were obtained after the optimization of processing parameters.

Deformation-induced martensitic transformation is used for improving mechanical properties of AHS steels which contain metastable retained austenite. TRIP steels are one of the categories that fall into this group. Their microstructures consist of proeutectoid ferrite, bainite, and metastable retained austenite. Cold working causes retained austenite in these steels to transform to deformation-induced martensite. A technical complication to their treatment routes is the isothermal holding stage. At this stage, bainite forms and retained austenite becomes stabilized which is the key aspect of the process. A CMnSi-type low-alloy steel with 0.2 % carbon was subjected to various experimental cooling sequences which represented press hardening operations at tool temperatures ranging from 500 °C to the room temperature, followed by isothermal holding in the bainitic transformation region. By varying the cooling parameters, one can obtain a broad range of mixed martensitic-bainitic structures containing retained austenite, with strengths in the vicinity of 1300 MPa, and A20 elongation levels of 10 %.

In order to achieve specific mechanical properties and structures of a material, a combination of new technologies together with an unconventional use of different types of materials could be an asset. Powder metallurgy, involving a metal matrix and dispersed stable particles, in combination with mechanical alloying and hot consolidation could be a solution. This paper describes the thermomechanical characteristics of new oxide-dispersion-strengthened (ODS) alloys with a Fe-Al matrix in terms of changes in the grain-size distribution. Recrystallization and grain growth were investigated over a range of temperatures and deformations. The results show that the grain-growing process in the new ODS alloys is significantly affected by the thermomechanical treatment, leading to the maximum grain size within 20-h annealing at 1200 °C. They are analysed using different methods, including optical microscopy.

Existing oxide dispersion strengthened (ODS) alloys are, besides Ni-based superalloy single crystals, the most creep-resistant materials. The creep resistance of the ODS alloys may, moreover, be significantly improved thanks to increasing the volume fraction of the nano oxides by more than one order of magnitude so that the oxides play a decisive role in strengthening. The present experimental study deals with two systems of such a high-volume fraction of nano oxides, namely, the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems prepared by mechanical alloying and hot rolling leading to a rather stable fine-grained microstructure. This microstructure undergoes static recrystallization at high temperatures. The kinetics of static recrystallization and coarsening of nano oxides in recrystallized grains is determined for both systems. The difference in kinetics of coarsening of Al-based and Y-based oxides in the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems is expressive and predetermines the Fe-17Cr-7Al-4Y2O3 system or similar ones to become the new leading system among creep- and oxidation-resistant materials for applications up to 1200 &deg, C.

Material-technological modelling is based on thermo-mechanical treatment of a small amount of real material using a thermomechanical simulator. This is a procedure allowing quick and accurate changes to selected parameters of the thermomechanical treatment. Due to the high dynamics of the process, material-technological models and forming technologies with high strain rates and with steep gradients in temperature changes can be designed using this method. The current state of technology also allows the use of this method for die forging. The paper is focused on the issues of material-technological modelling of die forgings made from C45 and the possibility of its application to designing changes and optimization of forming and heat treatment technology. The first phase of the solution is the creation of a material-technological model for a real forging. The objective of this phase was to achieve the desired agreement between the model and the real forging. In the second phase, this model was used to replace the conventionally processed material C45 by thermomechanical micro-alloyed steel 30MnVS6. The aim of the controlled cooling from the forging temperature was to achieve structures without heat treatment, which is currently a necessary part of the manufacturing process. Replacing conventional technology with controlled cooling results in a significant saving of production costs.

The article describes the effect of input material structure on the structure development during the subsequent processing by mini-thixoforming technology. Two different initial states were prepared from X210Cr12 tool steel for the experiment. The first semi-product was used in the soft-annealed state with ferritic-carbidic microstructure and coarse primary chromium carbides. Ferritic grain size 13,7 μm and the hardness was 210 HV30. The second state was prepared by high temperature annealing at 1200 °C for 1 hour. The microstructure then consisted of austenite and carbides. The grain size was in the range of cca 37 to 50 μm, hardness was 300 HV30. Treatment consisted of heating to a semi-solid state at the temperature 1265 °C in 9 s. That was followed by direct cooling to room temperature in 2 s. The grain size and distribution of eutectic in the volume of the processed material were selected as the attributes for microstructure evaluation after mini-thixoforming. The structure after processing in a semi-solid state consists of polyhedral austenite with a grain size of 43-59 μm, compared to the initial range 37-50 μm. This compares to the soft annealed state when, after semi-solid processing, the grain size was only 10 to 13 microns.

Martensitic microstructures with a controlled fraction of retained austenite have the potential to reach high tensile strength above 1900-2000 MPa with ductility higher than 10 %. These microstructures can be obtained by using the Q&P process. The Q&P process with integrated incremental deformation was tested and optimized for two high-strength steels 42SiCr and 42SiMn with 0.43 % C. The 42SiCr steel contained an additional 1.3 % of Cr. A suitable austenitization temperature was determined in the first step and then quenching and partitioning temperatures and cooling rate after deformation were optimized. The results suggest that the addition of Cr has a significant influence on the mechanical properties. Tensile strength of 1367 MPa with ductility A 5mm = 7 % were obtained in 42SiMn without Cr (sample geometry: 2x1.5 mm, 5 mm active length). However, the Cr content of 1.33 % in the 42SiCr steel was responsible for the increase in its strength up to 1965 MPa and for the very good ductility A 5mm =21 %.

New strategy of thermo-mechanical treatment with continuous cooling was proposed and optimised for high strength low alloyed TRIP (transformation induced plasticity) steel with 0.2% C, 1.8% Si, 1.5% Mn. Basically all methods of TRIP steels processing that have been investigated in the last fifteen years incorporated the hold in bainite region as the irreplaceable part of the processing. This hold should ensure convenient bainite content in the final microstructure and also sufficient carbon enrichment of austenitic areas. New strategy described in this article was designed according to the conventional rolling mill processing of steels with similar chemical composition. All processing schedules contained the same heating to 1050 °C and 10 incremental deformation steps during the cooling to 830 °C. After the deformations, the cooling was carried out either by constant cooling rates or by quicker cooling to 425 °C with subsequent slower cooling to room temperature. Cooling parameters were optimized with respect to final microstructures and properties. The microstructures with good potential to utilize TRIP effect were obtained, with about 10% of retained austenite, tensile strengths in the range of 800 – 900 MP and ductility about 25- 31%.

Semi-solid processing is an unconventional technique, which can be used to produce intricate components by forming and also to remove the sharp-edged carbides. However, the resulting microstructure after semi-solid processing consists of polyhedral austenite grains and lamellar ledeburite network. The network can be fragmented by applying an appropriate deformation sequence during cooling. X210Cr12 tool was experimentally processed by a combination of semi-solid processing and subsequent thermomechanical treatment. The heating temperature was varied from 1200°C to 1280°C. The obtained microstructures consisted of recrystallized grains of the M-A constituent and fine chromium precipitates without sharp-edged carbides with hardness higher than 800 HV10.

By stabilising metastable austenite with a suitable morphology in a martensitic structure, it is possible to impart to multi-phase steels high ductility combined with tensile strengths exceeding 2000 MPa. One way to achieve such mixed structures consisting of martensite and retained austenite (RA) is the Q&P (quenching and partitioning) process. The resulting structure contains metastable austenite in the form of thin foils located between martensite laths or plates. The stability of austenite under mechanical loading is the essential factor contributing to the extraordinary plasticity of such materials during cold deformation. A steel with 0.43% of carbon, alloyed with manganese, silicon and chromium was chosen for the experiment described in the present paper. Using the Q&P process, a martensitic structure with 20% of retained austenite was obtained. As cold plastic deformation causes the austenite to transform, 10% cold deformation was applied after the Q&P process. This deformation reduced the RA fraction to 11%. Materials prepared by this method were examined using micro-pillar compression experiments. Using the focused ion beam (FIB) method, pillars of 3 × 3 μm cross-section and 8 μm length were fabricated. These were afterwards mechanically tested in situ in an electron microscope in quasi-static compression at a true strain rate of 3 × 10−4 s−1 to different amounts of plastic strain. The experiment showed that mechanical properties of the two conditions of material differ in terms of yield strength and the strain hardening exponent. An additional metallographic analysis of structures, including the exploration of the influence of decomposition of retained austenite, was performed.

Quenching and partitioning process with incorporated incremental deformation was optimized for six high strength steels with various contents of carbon (0.4-0.6%), manganese (0.6-1.2), silicon (2-2.6%) and chromium (0.8-1.3%). The optimization was gradually done for each steel with respect to the final microstructures and properties. The effect of cooling rate, quenching and partitioning temperature on microstructure development was further investigated. Interesting combinations of mechanical properties were obtained, with tensile strength in the region of 1600-2400 MPa and ductility of 6-20%.

Mechanical properties of all metals depend predominantly on the type and morphology of their microstructure. Microstructure attributes can be altered by various heat treating and thermomechanical treatment procedures. One of the advanced techniques profoundly affecting the microstructure evolution is semi-solid processing. It can produce unconventional microstructures even in conventional steel types. Moreover, subsequent heat treatment can also deliver a wide range of microstructures and correspondingly varied mechanical properties. In the present experimental programme, the X210Cr12 ledeburitic tool steel was studied. Its initial annealed microstructure consisted of ferritic matrix, chromium carbides and globular cementite particles. The semi-solid processed structure, on the other hand, contained polyhedral austenite grains embedded in carbide-austenite network. The austenite volume fraction exceeded 95 %. This microstructure was then altered by subsequent heat treatment or thermomechanical treatment. The experimental programme comprised three stages. At the first stage, the effects of the rate of cooling from the semi-solid region to the ambient temperature on the nature and morphology of the ledeburitic network and the austenitic grain size were explored. The second stage was aimed at the impact of tensile and compressive deformation applied after transition through semi-solid state on the microstructure evolution and, in particular, on grain size. Once suitable processing conditions and parameters were identified, the treatment led to a recrystallized austenitic microstructure with an average grain size of less than 3 μm. As high volume fractions of austenite were obtained, the third stage involved exploring the effects of thermal exposure. The stability of austenite and the decomposition of austenite into other microstructure constituents were mapped. Metallographic observation revealed a resulting wide range of microstructures from fine pearlite to martensite, depending on the heat treating schedule.

By processing steels in the semi-solid state it is possible to achieve unconventional structures even with commonly used steels. This can be demonstrated on X210Cr12 tool steel. After semi-solid state processing, 96% of the microstructure can consist of metastable austenite. In the microstructure, there are polyhedral grains embedded in a ledeburitic network. A combination of semi-solid state processing and rapid solidification is a new method for modifying the microstructure more substantially. In the present experiment, two tool steels, CPM 15V and CPM S30V, were processed by an unconventional method. Since the steels are made by powder metallurgy, their initial structure contains globular carbides in ferritic matrix. Both materials have high levels of carbon and alloying elements, namely vanadium and chromium. The unconventional processing was carried out by mini-thixoforming which enables the use of a small amount of metal. After heating into the semi-solid region, the material was rapidly forced by lateral extrusion into a cavity of a metal die where rapid solidification and rapid cooling took place. Two cooling schedules were employed. In the first case, the die was at room temperature, whereas in the second one it was pre-cooled to-196°C using liquid nitrogen. Since the test sample was cooled from both sides and its thickness was 3 mm, immensely high cooling rates were achieved. The influence of the cooling rate was also noticeable in the microstructures containing high fractions of metastable austenite, martensite and carbides.

The Q&P process (Quenching and Partitioning) is a heat treating method for high-strength low-alloyed steels. It delivers the desired combinations of high strength and adequate ductility. These properties are achieved thanks to the unique martensitic microstructure with a certain volume fraction of stable retained austenite. Retained austenite imparts plasticity to the otherwise brittle martensitic structure. Optimum mechanical properties are achieved by using correct processing parameters and chemistry of the material. The experimental material was a steel with 0.47 % carbon alloyed with silicon, manganese and chromium. The purpose of the effort was to optimise the heat treating parameters in order to obtain a strength level above 2000 MPa and an elongation of no less than 10%. In the first step, the appropriate austenitizing temperature was identified. In the second, effects of various quenching temperatures and cooling rates on the microstructure evolution were explored. In the third, the impact of raising the partitioning temperature on stabilization of retained austenite was examined. Adjustment of the parameters led to a strength of more than 2300 MPa and an elongation of 8 %.

Processing in the semi-solid state allows the benefits of the process of forming and casting to be combined. In addition to obtaining complicated shapes, unusual forms of structures with exceptional properties can also be formed. A special processing procedure in the semi-solid state for very small parts has been developed, which is called mini-thixoforming, is able to handle CPM15V steel powder. From the original ferrite matrix with primary chromium–vanadium carbides – a mixed structure was obtained by processing consisting of metastable austenite, rod-shaped chromium–vanadium carbides and the original chromium–vanadium carbides. Compared to the initial state (micro hardness approx. HV10 330), this structure achieved, as a result of the relatively high rate of cooling in the form, a hardness of approx. 730 HV10. Due to the fact that this is a metastable structure, experimental heating to temperatures 400, 500, 600, 700, 800 °C for 1 h was performed. With exposure at temperatures 400 and 500 °C there was a slight decrease in hardness of approx. 20 points, heat treatment at 600 °C achieved hardness of 960 HV10. This state corresponds to an equivalent value of compressive strength of approx. 2880 MPa, Further increase in temperature leads to a continuous decrease in hardness due to decomposition of the metastable matrix. Thermal exposure at 700 °C, resulted in hardness of 585 HV10. After exposure to 800 °C there was a significant decrease of hardness to 425 HV10.

A fast, cost effective and simple methodology and testing apparatus was developed for testing basic material properties of thin (up to 0.05 mm) metal sheets during production. The method is based on the bulge test method. Air is used as a pressurizing medium and specimen deformations are measured using a 2D laser scanner. Test control and software for evaluating results was programmed in MATLAB using the GUI feature. The testing procedure and test assembly were developed with the accent on simplicity and obtaining fast results, which are both necessary for fast product testing during the manufacturing process.

Progress in materials science is inseparably connected with development of new analytical methods which make possible to observe the materials microstructure with high sensitivity. The aim of the present study is shown that scanning low energy electron microscopy (SLEEM) has a significant impact in advance of a fundamental understanding of the evolution of microstructure upon semi-solid processing. This paper deals with the application of the ultra high vacuum scanning low energy electron microscopy (UHV SLEEM) to the study of microstructure of X210Cr12 steel after the formation in semi-solid state and the study of the annealing of deformed metastable austenite. Examples from these specimens show that the contrast between differently oriented grains in polycrystalline materials is very sensitive to the parameters such as energy of the primary beam, working distance and detection of high angle backscattered electrons.

ODS steels are used for their very good mechanical properties at high temperature and low-cost production in comparison with other super alloys (ex. nickel super alloys). The paper describes a new group of Fe-Al Oxide Dispersion Strengthened (ODS) alloys with fine Al2O3 precipitates. ODS ferritic steels are high temperature creep resistant materials, which are intended to be applied more in the future industry. The steel was prepared by powder metallurgy under mechanical alloying and hot consolidation. To describe the stability of this material, annealing with different temperatures and holding times were carried out. The results show that the fine-grained microstructure is stable during long-term annealing up to 800 °C. At temperatures over 1000 °C, the grain structure coarsens by abnormal grain growth by keeping the size of oxides unchanged. Besides, the grain structure of the material is improved by differing the annealing time and temperature. The obtained structures were analyzed by optical and scanning electron microscopy. The mechanical properties and hardness were measured by tensile test at different temperatures.