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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.

Semi-solid processing is complicated by various inherent technical problems. However, once these problems are solved, thixoforming allows intricately shaped components to be manufactured very effectively – often with microstructures that cannot be produced by any other techniques. The recently introduced mini-thixoforming method is an example of such a novel technique for semi-solid processing of steel. The wall thicknesses of resulting parts are about 1 mm. Microstructures of semi-solid-processed steels typically consist of a high proportion of globular particles of metastable austenite embedded in a carbide network, the latter being much harder and more brittle. This paper illustrates that mini-thixoforming allows inverting that microstructural configuration. As an experimental material, powder steel with increased content of vanadium and chromium was used. The post-thixoforming microstructure consisted of a dispersion of carbides and high-vanadium and high-chromium eutectic in an austenitic matrix. Applying optimised processing parameters, complex-shaped parts could be produced. According to the high hardness of resulting microstructural components, the new materials are likely to exhibit extraordinary strength and wear resistance.

Thixoforming is an alternative forming method, by which intricate and complex-shaped products can be manufactured using a single production step. This technology allows a material’s microstructure to be altered profoundly. Typical microstructure of steels processed in this manner consists of quasi-polyhedral austenite grains embedded in a ledeburite-carbide network. This type of microstructure was produced by processing the experimental material in this study: the X210Cr12 steel. Since austenite is a metastable component depending on oversaturation with a number of elements, its thermal and mechanical stability needs to be known. This information is required for further modification and enhancment efforts. In previous experiments, the thermal stability was tested by thermal exposure. In the present work, the behaviour of austenite was explored under mechanical load at room temperature in a micro-compression test. A single block of austenitic material was used for making a test specimen with the dimensions of 2.4×2.2×4.9 µm. Its mechanical properties were measured and deformation stability was investigated using compressive deformation.

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.

This article deals with an alternative method of joining advanced steels for frame structures. These steels cannot be joined by a conventional process due to the impact of temperature on the base material. Therefore, a simple and cost-effective method of forming a high-strength joint, intended for advanced high-strength materials, was designed using explosive forming. One of its key advantages is that it preserves the microstructure of the high-strength material being joined. At the same time, the design of the joint allows it to undergo further plastic deformation if the yield stress is exceeded, thus preventing the step change in load-carrying capacity and the instability of the structure. The alternative joint was intended for materials with yield stress above 1000 MPa and elongation of 10%, under quasi-static conditions. However, the design is also suitable for materials with ultimate tensile strength higher than 2000 MPa. Testing of the load-carrying capacity of the joint in a mechanical testing shop showed that the larger the flow stress of the material, the higher the load-carrying capacity of the joint. The selected joint designs with good load-bearing capacity values were manufactured by forming using products of detonation of the SEMTEX industrial blasting explosive. In a compression test, the demonstration joints showed the axial load-bearing capacity of 200 kN with up to 20-mm displacement to failure.

The use of the combined influence of retained austenite and bainitic ferrite to improve strength and ductility has been known for many years from the treatment of multiphase steels. Recently, the very fine films of retained austenite along the martensitic laths have also become the centre of attention. This treatment is called the Q-P process (quenching and partitioning). In this experimental program the quenching temperature and the isothermal holding temperature for diffusion carbon distribution for three advanced high strength steels with carbon content of 0.43 % was examined. The alloying strategies have a different content of manganese and silicon, which leads to various martensite start and finish temperatures. The model treatment was carried out using a thermomechanical simulator. Tested regimes resulted in a tensile strength of over 2000MPa with a ductility of above 14 %. The increase of the partitioning temperature influenced the intensity of martensite tempering and caused the decrease of tensile strength by 400MPa down to 1600MPa and at the same time more than 10 % growth of ductility occurred, increasing it to more than 20%.

The cold formability of ferritic-pearlitic steels is one of the base parameters for material choice for different forming parts. One of the key factors is the pearlite morphology, which is strongly dependent on chemical composition and previous treatment history. The carbides in pearlite occur mainly in the lamellar form. One of the ways of improving the ductility along with formability is the change of lamellar carbides to globular carbides. This can be conventionally done by soft annealing, which is characterised by long processing times and high energy costs. This paper presents a new processing modification which can lead on the one hand to significant shortening of carbide spheroidization times and on the other hand to intensive refinement of grain size even for low-carbon steels. Low temperature thermomechanical treatment with variation of the heating temperature around Ac1 and incremental deformation was examined on low carbon plain RSt-32 steel. After the thermomechanical treatment conditions were optimized, the refinement of the ferritic grains from an initial 30 μm to circa 5 μm took place, and the time necessary for carbide spheroidization was shortened from several hours to several seconds.

Material processing in a semi-solid state with rapid solidification is an innovative technology, which enables us to produce complex-shaped semi products in one operation. Unconventional properties and microstructures can be obtained in this way. Material processing in a semi-solid state has been used for materials with lower melting temperatures, particularly for Al alloys. This paper concentrates on the development of new technologies for production of miniature thin-walled steel components with complicated shapes. Ledeburitic steel with 1.8% of carbon and 11% of chromium was chosen for this experimental study. This material was used to produce very small thin-walled semi products. From the initial structure consisting of primary and secondary carbides distributed in a ferrite matrix was obtained a microstructure with over 90% of metastable austenite after cooling from the semi-solid state. The main aim of this experimental program was to describe the effect of two different methods of heating to the semi-solid state. The first method used unique heating equipment, combining high frequency and resistance heating. The second method consisted of conventional heating in a furnace. The influence of the cooling rate on the development of the microstructure was investigated. If was found that both heating and cooling rates influence grain size and the size and the morphology of carbide network placed between the globular austenite grains. Structure analysis was performed with the help of light microscopy, laser scanning confocal microscopy and scanning electron microscopy. EDX analysis was applied to determine chemical profiles of phases and X-ray diffraction phase analysis was used to establish volume fraction of austenite in the final microstructure. Characterisation of individual structural components was further completed by hardness measurements.

Semi-solid forming processes belong to the progressive technologies which can be exploited for the manufacturing products with complicated shapes and special material and utility properties. Semi-solid metal forming takes place at temperatures between solidus and liquidus combining the advantages of metal forging and metal casting processes. The paper is focused on the analysis of microstructures and phase composition of the X210Cr12 steel identified in the thin-walled products after forming in semi-solid state. Microstructure of the X210Cr12 steel after rapid cooling and solidification from semi-solid state is formed by quasi-globular grains of metastable austenite surrounded by carbides and fine eutectics. The fraction of metastable austenite in structure was found to be 96 % exhibiting the thermal stability up to the temperature of 500 °C. Along with experimental study, the numerical analysis of the material flow during a die cavity filling was carried out using developed 2D simulation model taking into account one-phase non-newtonian flow.

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.

The concepts new types of materials are, for economic reasons, focused mainly on low alloyed steels with a good combination of strength and ductility. Suitable heat and thermo-mechanical treatments play an important role for the utilization of these materials. Different alloying strategies are used to influence phase transformations. The quenching and partitioning process (Q-P Process) is one of the heat treatment methods which can result in a high ultimate strength as well as a good ductility. However, these good properties can be obtained only if a sufficient amount of retained austenite is stabilized. The influence of different contents of manganese, silicon and chromium on microstructural development and mechanical properties were experimentally tested. Alloying elements were used to stabilize the retained austenite in the final microstructure and also to strengthen the solid solution. Ultimate strengths of over 2000MPa with ductility over 10% were reached after the optimization of the Q-P Process. The microstructures were analyzed using several microscopic methods; mechanical properties were determined by a tensile test and the volume fraction of the retained austenite was established by X-ray diffraction phase analysis.

Higher demands are currently being made on material properties and their combinations, for example, high strength steel with good cold formability. With increasing strength, material formability generally worsens, but with some kinds of steels, for example, with TRIP steel, it is possible to obtain an excellent combination of strength and ductility. However, these materials are interesting not only for use as sheets but also for other applications. Semi-products with thin walls represent the best way of further extending TRIP steels into the bulk forming area. This trend supposes that suitable technological conditions will be found and the process for a chosen production procedure will be optimized. The model optimization of the process for TMT with incremental deformations was experimentally carried out on a thermomechanical simulating machine. Microstructures obtained by the model treatment were analyzed by means of optical and electron microscopy.

Newly developed methods for heat treatments and any necessary thermomechanical working have led to the achievement of excellent properties for new types of multiphase structures. One of these new methods is the Q-P (Quenching and Partitioning) process. The result is usually martensitic structure with a defined proportion of retained austenite. This process can be used for different kinds of steels with a tensile strength about 2000 MPa with retention of good ductility of more than 10%. The Q-P process was applied to experimental steel whose main alloying elements were silicon, manganese and chrome. The resulting specimens were evaluated metallographically, the proportion of retained austenite was ascertained by X – ray analysis and mechanical properties were found using tension tests.

Convenient structure adjustment and thereby the achievement of suitable material and technological properties is one of the very important areas of technological as well as material research. In general, this issue includes a great number of parameters and variables. To find suitable technological conditions, it is possible to use various kinds of modeling processes. One of them is the utilization of thermomechanical simulators, which allow simulating the conditions of the real processes to be simulated with sufficient accuracy. It is then possible to perform the optimization on smaller specimens, while monitoring the real conditions with higher accuracy. This method was used for the optimization of unconventional technological processes for selected alloying strategies of low-alloyed multiphase steels. These strategies are designed to be applied to technologies, which combine anisothermal forming and thermomechanical treatment of quasimassive components using intensive plastic deformation. Incremental deformations allow a high amount of deformation to be reached. It is also possible to obtain very fine grained structures by a suitable choice of temperature. By a suitable choice of temperature it is also possible to obtain structures with very fine grain. At the same time, the morphology of the structure and thus also its final mechanical properties can be significantly influenced this way.

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.

Kurzfassung Die thermomechanische Behandlung der Stähle ermöglicht es, bei geeigneter Wahl der Strategie hervorragende mechanische Eigenschaften zu erzielen. Dabei können auch klassische Stähle ohne spezielles und kostenintensives Legierungskonzept eingesetzt werden. Diese Tatsache wurde hier am Beispiel des Stahls C45 dokumentiert. Bei dem ausgewählten Konzept der thermomechanischen Behandlung konzentrierte man sich vor allem auf den Kornfeinungsprozess, durch den hohe Streckgrenzen, Festigkeiten und Kerbschlagzähigkeiten im ferritisch-perlitischen Zustand bei gleichzeitig guter Dehnung erreicht wurden.

The influence of thermo-mechanical processing (TMP) on the microstructure and mechanical properties of 0.22%C–0.87%Mn–0.73Cr–0.40Mo steel was investigated. The transformation CCT diagram and CCCT diagram were determined by dilatometric measurements. Hot deformation before austenite decomposition slightly accelerates ferritic transformation, retards bainitic reactions and decreases the bainite start temperature. Special methods of TMP were performed consisting of hot and/or warm compression deformations and dwell at an elevated temperature. The microstructure was studied using metallography and transmission electron microscopy. The compression deformation results in a remarkable refinement of the microstructure and an improvement of mechanical properties. Warm deformation followed by dwell at 470 °C was found to be suitable for an increase of tensile strength and notch toughness; the corresponding microstructure is a fine lath-like bainitic microstructure with a relatively homogeneous distribution of carbide particles.

The constant evolution of industry brings demands for components of ever-higher quality, complex shapes and excellent mechanical properties, with reduced operating costs and with improved reliability in service. Such demands can be met by processing high-strength, low-alloyed steels using novel heat-treatment methods. One of such methods is the quenching and partitioning (Q&P) process, which can lead to high strengths of about 2000 MPa at elongation levels of more than 10 %. The Q&P process can be combined with unconventional procedures for making complex-shaped parts to manufacture components with excellent mechanical properties and an intricate shape. This paper describes the sequence of internal high-pressure forming, hot stamping and the Q&P process used for making a functional product with good mechanical properties and a complex shape. The purpose of the experimental programme was to employ a production chain for processing hollow, thin-walled stock. Using a step-by-step optimization, commercially usable products were obtained. The microstructure of the products consisted primarily of martensite and a small fraction of bainite. Such a microstructure guarantees a high ultimate strength. The strength level throughout the part was not less than 1950 MPa, combined with an excellent elongation of approximately 15 %.

Innovation opens new opportunities in the field of processing hollow semi-products, as it offers the potential for manufacturing complex-shaped structural parts with enhanced properties. This introduces a manufacturing route comprising the following steps: internal high pressure forming, hot stamping and thermomechanical Q&P processing. In this manufacturing route, the demonstration product, a tube–shaped stock, is first austenitized. It is then expanded in a closed die by internal pressure of nitrogen until the material touches the die wall. As a result, it cools down quickly and martensite begins to form. At a temperature above the M f , the cooling is interrupted and the workpiece is transferred to a furnace and tempered. The furnace temperature is below the M s temperature. Within several minutes, a mixed microstructure forms, consisting of martensite and stabilized retained austenite. Thanks to this microstructure, the material exhibits a favourable combination of high strength and adequate ductility. Martensite imparts sufficient strength to the material whereas the retained austenite provides ductility. At a carbon level of approximately 0.4 % and with a simple Si-Mn-Cr-based chemistry, strengths of 2000 MPa and A 5 mm elongations of 15% can be achieved.

This paper describes the results of laboratory tests conducted on flexible PVC pipes with diameter of 160 mm, buried in unreinforced and reinforced trench with geogrid layer and expanded polystyrene (EPS) geofoam block. The repeated load with amplitude of 450 kPa and frequency of 0.33 Hz was applied on the trench surface, using plate loading at a diameter of 150 mm to simulate the vehicle loads. Vertical diameter strain (VDS), strain at pipe's crown and transferred pressure on the pipe's crown were recorded throughout the test for up to 500 cycles of loading. The variables examined in the testing program include thickness of EPS block (30, 60 and 100 mm) and its density (10, 20 and 30 kg/cm3). The pipes were embedded at depths 1.5 times their diameter and the width of EPS block was kept constant at 2.0 times the pipe diameter in all tests. The results show that the values of VDS and pipe strain increased rapidly during the initial loading cycles, thereafter the rate of deformation and strain reduced significantly as the number of load cycles increased. According to the results, the minimum VDS and pipe's crown strain were provided by 100 mm thickness and 30 kg/cm3 of EPS block placed over the pipe with a geogrid layer giving values of, respectively, 0.15 and 0.10 times those obtained in the reinforced trench with a geogrid layer.

With increase in cities' population and development of urbane life, passing buried pipelines near ground's surface is inevitable in urban areas, roads, subways and highways. This paper presents the results of three-dimensional full scale model tests on high-density polyethylene (HDPE) pipe with diameter of 250 mm in geocell reinforced soil, subjected to repeated loading to simulate the vehicle loads. The effect of geocell's pocket size (55*55 mm and 110*110 mm) and embedment depth of buried pipe (1.5 and 2 times pipe diameter) in improving the behaviour of buried pipes was investigated. The geocell's height of 100 mm was used in all tests. The repeated load of 800 kPa was applied on circular loading plate with diameter of 250 mm. The results show that the pipe displacement, soil surface settlement and transferred pressure on the pipe's crown has been influenced significantly upon the use of geocells. For example, the vertical diametric strain (VDS) and soil surface settlement (SSS), in a way that using a geocell with pocket size of 110*110 mm reduces by 27% and 43%, respectively, compared with the unreinforced one. Meanwhile, by increasing buried depth of pipe from 1.5D to 2D, the use of geocell of 110*110 mm delivers about 50% reduction in SSS and VDS, compared with the unreinforced soil.

Evolution of microstructure during heat treatment plays a fundamental role in the resulting mechanical properties of steel. Today, mechanical properties in conjunction with technological properties, such as weldability, formability, and machinability, and their optimum combinations, are widely discussed in a number of mechanical engineering disciplines. In this manner, requirements arise for developing steels which could offer high strength and good formability, and which could be used for making parts with high resistance to failure and with a long life. One present-day example of such steels involves Q&P-processed martensitic steels. Their properties are dictated by their treatment, as well as their alloying, particularly by the silicon content. Silicon fundamentally affects microstructure evolution during Q&P processing and, as a result, mechanical properties. With this way it is possible to receive microstructures consinsting of martensite and retained austenite with an ultimate tensile stress of more than 1600 MPa and a uniform elongation of more than 12 %.

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 advanced steels are required to possess high strength and ductility. It can be achieved by choosing an appropriate steel chemistry which has a substantial effect on the properties obtained by heat treatment. Mechanical properties influenced the presence of retained austenite in the final structure. Steels of this group typically require complicated heat treatment which places great demands on the equipment used. The present paper introduces new procedures aimed at simplifying the heat treatment of high-strength steels with the use of material-technological modelling. Four experimental steels were made and cast, whose main alloying additions were manganese, silicon, chromium, molybdenum and nickel. The steels were treated using the Q-P process with subsequent interrupted quenching. The resulting structure was a mixture of martensite and retained austenite. Strength levels of more than 2000 MPa combined with 10-15 % elongation were obtained. These properties thus offer potential for the manufacture of intricate closed-die forgings with a reduced weight. Intercritical annealing was obtained structure not only on the basis of martensite, but also with certain proportion of bainitic ferrite and retained austenite.

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.

Today, new types of materials and procedures are sought continuously in order to achieve lower manufacturing costs, reduced energy consumption, shorter production times and other savings. In terms of the materials, TRIP steels are an attractive choice, as they provide an excellent combination of strength and ductility. They also offer good energy absorption in crash scenarios. Their main use is in the production of automotive body parts. One can expect that well-chosen processing parameters and unconventional forming routes would enable a wider range of thin-walled products to be made of these steels. Those could include thin-walled hollow products with excellent mechanical properties imparted by effective manufacturing routes at relatively low costs. If these materials are to be employed in real-world forming processes, an appropriate forming route must be chosen, integrated into an appropriate production chain and then optimized in terms of its parameters. This article describes a study of a rotary spin extrusion process. In the first stage, the impact of strain magnitude on microstructural evolution was studied in CMnSi steel using physical modelling of thermomechanical treatment. Subsequently, trials of a real-life technology chain, which efficiently combined incremental forming and heat treatment, were carried out on low-alloy CMnSi and CMnSiNb steels. The resulting products were stepped hollow parts of various diameters. Their strength was close to 1000 MPa and their elongation level exceeded 20%.

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.

The contemporary development of technological processes for the production of modern multiphase steels can be characterized by the need for precise control of their technological parameters. The design of modern technological processes that allow sophisticated microstructures to be obtained usually cannot be carried out on real production equipment for technical as well as economical reasons. Therefore, new processes and test devices are continuously being developed to make it possible to simulate and model thermomechanical treatments on small specimens with precise control and monitoring of process parameters. A simulator for experimental modelling of thermomechanical processes has been developed at the University of West Bohemia. In this paper, to demonstrate the feasibility of simulating thermomechanical treatments with this setup on a lab scale, we discuss the thermomechanical treatment of TRIP steels without isothermal holding - a processing route that is difficult to handle and thus poses several technological as well as economic problems. The realistic processing of wire rolling with different cooling strategies is tested on the TRIP CMnSiNb steel. Our results show that the processing route without isothermal holding allows to obtain multiphase microstructures with a tensile strength of up to 835 MPa and a ductility A5mm = 25%.

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.

Testing device and testing method for determination of material properties of very thin metal foils (up to 0.05 mm of thickness) using modified bulge test method were introduces in previous works. The paper describes recent development of both the device and the methodology which further improve given concept. The design of the whole device was all remade, pressure measurement was significantly improved, new control and evaluation software was introduced. The method for laser measurement on glossy surfaces is presented. The method is an outcome of problems we faced during measurement using a laser system on glossy surfaces as it is almost impossible to obtain proper data on highly glossy surfaces for further post-processing. Our measurement outcomes are presented and discussed on specimens made of several different materials - Al, Cu, FeNi alloy. Finally we recognize specific limitations of the presented methodology.

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.