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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.

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 %

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.

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.

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.

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.

The purpose of this article is to demonstrate the potential of hydroforming process combined with the Engineering Design Science (EDS) in single piece production of a technical product. The chosen demonstration product for this integrated approach is a ski riser for extreme carving. Its load-bearing base is an intricate-shape part that is well suited for modified hydroforming process in an isostatic press. In order to reduce production costs, rapid prototyping and rapid tooling methods were used.

Mechanical properties of metallic materials depend on their chemical composition and on microstructure, which can be altered by various heat treatment or thermomechanical treatment processes. Semi-solid processing is one of unconventional methods, which can be used for altering the microstructure and as well as for the manufacturing components with intricate shapes. The purpose of this experimental programme was to investigate the influence of transition of the X210Cr12 steel through semi-solid state on their hot deformation behaviour. The typical microstructure of this steel after semi-solid processing consisted of more than 95% of austenite located in quasi-globular austenitic grains and the austenite-carbide eutectics placed in the area among the austenitic grains. During experimental regimes, the specimens were heated into the semi-solid state. Immediately after the transition through semi-solid state, the material was cooled down to hot forming temperature, deformed and then cooled down in a controlled manner. The deformation was performed in three steps in the temperature interval from 1100 °C to 870 °C and the cooling rate after deformation from 1.2 K/s to 500 K/s. Reducing the deformation temperature led to the considerable grain refinement. The hardness of the microstructure was influenced by temperature interval of deformation as well as by the cooling rate reaching the values from 370 to 465 HV10.

We report on mini-thixoforming of a hard and wear-resistant crucible particle metallurgy tool steel. Significant microstructural modifications associated with the special semisolid forming process are characterized in detail by scanning electron microscopy and X-ray diffraction. The mechanical performance of the material is assessed both pre-thixoforming and post-thixoforming by nanoindentation of the constituent phases. The novel microstructural changes that result from mini-thixoforming, which are discussed in this article for the first time, are beneficial in further improving the hardness of the steel.

In connection with increasing needs of different branches of industry for steels with excellent mechanical properties, like high strength combined with high ductility on one hand and low or at least moderate costs on the other hand, an experimental low alloy 42SiCr steel has been developed. If a conventional heat treatment is applied to this material, a very high strength can be reached, however with an unacceptable low ductility. Well balanced properties, i.e. strength about 2000 MPa and ductility more than 10 – 15%, can be achieved by an application of advanced heat treatment methods like Q-P (quenching and partitioning) process, consisting in quenching at intervals between martensite start and martensite finish temperatures resulting in stabilization of untransformed austenite by partitioning carbon. In service, numerous engineering components are exposed to variable, fatigue loading, whereas resistance to fatigue is usually particularly affected by different heat treatment methods or parameters and fatigue damage mechanisms have strong connections to material type, strength and microstructure. The aim of this study was to investigate fatigue properties of the 42SiCr steel treated using the Q-P process. Results of fatigue experiments are presented with respect to the basic material state and after traditional heat treatment – quenching and tempering. Fatigue damage initiation mechanisms, analysed particularly from fracture surfaces, and connections between fatigue properties and microstructure are discussed.

To obtain new unconventional structures with specific mechanical and physical properties is possible not only by the development of new types of materials but also by treatment of conventional materials using unconventional innovative technological procedures. One of these technologies is the forming in semi-solid state involving rapid solidification of miniature components from steels. Production of such components is complicated by a number of technical problems. To explain phenomena of the process and structure development, the production of miniature components from the tool steel X210Cr12 difficult to form was experimentally tested. The structure of this originally ledeburite steel consisted of 95 % of metastable austenite after the treatment. Metastable austenite was located particularly in globular and polygonal grains while the remaining interspaces were filled by lamellar network. The detected high stability of extremely high fraction of metastable austenite was tested under different conditions of thermal exposition and mechanical loading.

Semi-solid processing can lead to microstructures with a high proportion of metastable austenite embedded in carbide–austenite network even in ordinary steels. This type of microstructure is a result of non-uniform distribution of alloying elements in a partially melted material. The paper deals with semi-solid processing and heat treatment of the ledeburitic steel with 1.8% carbon and 11% chromium. Its initial microstructure typically consists of ferrite matrix with primary chromium carbides and globular cementite particles. Upon semi-solid processing, the material comprised 95% metastable austenite, predominantly in the form of polyhedral grains with the size of 19 μm. Previous research has demonstrated the grain refinement effect of plastic deformation applied immediately after solidification. In follow-up experiments, the influence of thermomechanical treatment upon subsequent evolution of microstructure was studied. In this experiment, particular attention was devoted to the decomposition of metastable austenite and its contribution to microstructure refinement. Upon the transition through the semi-solid state, the material was cooled down below its solidus temperature and subjected to deformation. This was followed by several cooling schedules. Some of the schedules included a dwell at 600 °C to allow metastable austenite to decompose. Cooling schedules were immediately followed by heating to austenitizing temperature and cooling to room temperature at an equal rate. These procedures produced various types of microstructures. The treatment with the dwell produced mixed-type microstructures with an exceptional form of martensite and partially decomposed carbide network. Processing without the dwell led to the development of microstructures with polyhedral retained austenite grains embedded in the original carbide network. Their hardness ranged from 445 to 850 HV30.

Treatment of high-alloy tool steels that involves transition to the semi-solid state can transform the sharp-edged primary carbides which usually form during solidification. These carbides severely impair toughness and are virtually impossible to eliminate by conventional treatment routes. Upon classical semi-solid processing which dissolves these carbides, the resulting microstructure consists of polyhedral and super-saturated austenite embedded in lamellar austenite-carbide network. This type of microstructure reflects in the mechanical properties, predominantly in material behaviour under tensile loading. Such a network, however, can be removed by appropriate thermomechanical treatment. In the present experiment, various procedures involving heating to the semi-solid state were tested on X210Cr12 tool steel. The feedstock was heated to the temperature range of 1220 – 1280 °C. The heating was followed by procedures involving either water quenching to the forming temperature, room temperature or temperature from the range from 500 °C to 1000 °C followed by reheating to the forming temperature. It was found that the development of the lamellar network strongly depends on the temperature of heating to semi-solid state. Thermomechanical treatment produced microstructures in which the matrix consisted of a mixture of polyhedral austenite grains and the M-A constituent. In addition, the initial lamellar eutectic network was partially or even completely melted and substituted with a mixture of very fine recrystallized austenite grains and precipitates of chromium carbides. Some fine M7C3 carbides were present in the austenitic-martensitic matrix as well. When appropriate processing parameters were chosen, very good mechanical properties were obtained, among them a hardness of 860 HV10.

Today's requirements for the design of functional parts and components demand low weight and, at the same time, high strength. There are several heat treatment methods which can satisfy such requirements. These include TRIP heat treatment, long-time low-temperature austempering, and Q&P processing. It is the Q&P processing which delivers excellent results in terms of mechanical properties and light weight. It relies on stabilising retained austenite through partitioning of carbon between martensite and austenite. The carbon-enriched austenite then becomes a ductile constituent in the otherwise brittle martensitic matrix. A precondition for successful Q&P processing consists in sufficient silicon content in the steel, which precludes precipitation of undesirable cementite. Cementite would otherwise form as a result of enrichment of retained austenite with carbon. To ascertain the usefulness of higher silicon level in steel for Q&P processing, one can compare Q&P processes in steels with various levels of this element

In order to investigate the effect of embedment depth on settlement of footing supported by geocell-reinforced bed, a series of cyclic plate loading at a diameter of 300 mm supported by layers of geocell in a test pit of 2000*2000 mm in plane and 700 mm in depth, were performed. The results show that installation of the geocell layers in the foundation bed toward embedded footing supported by one layer geocell has more effect on increasing the resilient behaviour in addition to reduction of accumulated plastic and total settlement of system. The study also compares the embedment depth ratio of one layer geocell reinforcement with two and three layer geocell reinforcement bed with no embedment depth.

Thanks to the available advanced control technology, manufacturing processes which have been described in the past but their hidden potential remained untapped are now continuing to be developed. As a result, even conventional materials which have been around for years can be manipulated to obtain unusual microstructures with specific mechanical and physical properties. Semi-solid processing belongs to the above-described group: it had been studied in the past but, due to complicated process control, it gradually lost its appeal. However, advanced techniques of temperature field control enable engineers to control this complex process accurately. One of the innovative methods of semi-solid processing is mini- thixoforming. As it focuses on very small-size products, it offers very steep heating curves and extremely high solidification and cooling rates, when compared to conventional thixoforming. The capabilities of this process were tested on X210Cr12 ledeburitic tool steel. After the optimum processing conditions were found, additional materials were tried, ranging from low- carbon microalloyed steels through medium-alloy steels to high-alloy tool steels. The microstructure evolution upon the mini-thixoforming process is an issue of its own. The final microstructure of X210Cr12 consisted of more than 90% of austenite and chromium carbides. Semi-solid processing of a steel with a high vanadium content led to a microstructure comprising MA matrix and globular vanadium carbides. In a low-alloy steel, martensitic microstructure was obtained.

Steel is a traditional material which has been used by mankind for more than five thousand years. We may therefore be tempted to believe that we know practically everything about steel and its forms and variants which offer an extraordinary and broad range of properties. It is this diversity of properties which makes steel such a popular and widely used material. And yet, in recent years new opportunities have emerged for processing steel by unconventional techniques and producing novel, as yet unknown or unusual microstructures. This paper describes several examples of how microstructure evolution can be modified and how new and unconventional processing routes can be developed. These examples present several results of projects carried out in recent years by FORTECH Research Centre of Forming Technology and the University of West Bohemia in collaboration with their research partners.

Material behaviour in a corroding medium varies depending on its properties. These properties are affected by the treatment, alloy elements and last but not least its surface condition. The sensitivity of a material to iron scale formation and decarburisation limits some technological processes, especially those where materials are exposed to a corroding medium at high temperatures for a very long time. A typical example is the heating of semi-products to forming temperature. Considering that similar materials can react differently under the same heating conditions, it is important to know the characteristic behaviour of a material in certain production processes. A comparison of two kinds of steels during model treatment was carried out in order to be able to determine the influence of different heating parameters. The model treatment consisted of three different heating temperatures at three different time durations. The intensity of the oxidation process was analysed by means of mass increments and the thickness of the oxide layer was detected via metallography. The depth and intensity of the surface layer decarburisation was evaluated from the profile of the microhardness change curve.