Seznam abstraktů 2017: POSTEROVÁ SEKCE B

The article presents the results of tests of plastic shaping of magnesium alloys Mg-Li-Ca. This is a new group of ultra-light construction materials. Alloys for extrusion process were achieved with the method of vacuum smelting and casting to graphite moulds. The materials for tests were cast slabs from magnesium alloys with symbols LX41, which include Mg, Li, Ca in their chemical composition as their basis chemical elements but also modifiers such as TiB, Sr and RE (mischmetal). Those introduced modifiers positively influence the casting properties and strength properties as well as creep resistance and refinement of the structure. Before the process of deformation the castings were subject to homogenization. Tests of classic extrusion were also performed. An assessment was performed of the influence of deformation process parameters on the structure and properties of tested alloys. Results of the mechanical tests were presented both for static compression test in room and in elevated temperature. An analysis of microstructure was conducted both in initial condition and condition after plastic deformation with the use of techniques of light and scanning microscopy.

The results of the numerical calculations for two aluminum alloys 2014, 2024, representing the 2XXX series (aluminum alloy with copper) are presented. The three-stage study was designed to determine the most effective ECAP process parameters (tool speed, friction factor and channel radius). In all three stages, the determination of the most favorable parameters was based on the analysis of distributions of temperature, mean stress, effective stress, plastic deformation and load. In the first stage, the effect of the press ram speed on the analyzed parameters was verified in a wide range of speed values from 0.01 to 100 mm/s. In the second stage, the influence of the applied lubricant on the analyzed parameters was examined in detail, friction coefficient values from 0 to1. The last step was a comprehensive examination of the effect of the radius of channel rounding.

The hot deformation behaviour of Ni55Cr45 alloy was investigated by isothermal compression test on the GLEEBLE 3800 thermo-mechanical simulator in the wide range of temperatures (750 – 1150 °C ) and strain rates (1 – 100 s-1). The experimental stress-strain data were employed to develop the constitutive equation and activation energy of the investigated Ni-Cr alloy. The correlation between the flow stress, temperature and strain rate at high temperatures was expressed by an Arrhenius type equation. The effects of temperature and strain rate on deformation behaviour were represented by Zener-Hollomon parameter in an exponent-type equation. Activation energy was calculated using a sine-hyperbolic type equation. The processing maps based on the Murty’s approach were developed. The processing window and the flow instability areas were determined. Furthermore the experimental rolling test was conducted according to delineated processing parameters. The results of numerical simulation and experimental rolling test showed good agreement with the optimum hot deformation condition.

Indefinite chill cast iron rolls are commonly used in the finishing stands in hot strip rolling mills. Due to characteristic rolling conditions in these stands and due to a hypoeutectic ledeburitic microstructure with graphite inclusions in the working layer, the mechanism of thermo-mechanical wear is different compared to earlier stands. Some research has been done on thermal fatigue crack formation and propagation in various alloys used for working layers in rolls. This research focuses on the impact of formation and propagation of extremely long cracks in some enhanced grades along with a possible influence of the amount of added special carbide forming elements in these grades. These long cracks propagate from the surface of the roll inwards and may lead to bigger problems during rolling campaigns when not dealt with properly.
Previous work also suggests that the ledeburitic network microstructure is indicative of the formation of thermal fatigue cracking on the surface of the roll. We analyzed the as-is microstructure of the roll’s surface after a campaign using silicon replicas to assess the crack mesh created on the surface during rolling. The results of this work highlight the combined influence of microstructure and thermo-mechanical fatigue in work roll degradation.

The influence of two variants of initial soaking at 1120°C/2 h and 1180°C/2 h and parameters of hot plastic deformation on the deformability of an IN-718 type superalloy have been presented. The hot deformation characteristics of alloy were investigated by hot torsion tests using Setaram torsion plastometer. The tests were executed at constant strain rates of 0.1 s-1 and 1.0 s-1, and testing temperature in the range of 900°C to 1150°C and were conducted until total fracture of the samples. Plastic properties of the alloy were characterized by worked out flow curves and the temperature relationships of maximum yield stresses (σpp) and strain limits (εf). It was found that optimal values of flow stresses and strain limits were obtained for the alloy after its initial soaking at 1120°C/2 h and deformation in the temperature range of 1100÷1050°C at strain rate 0.1 s-1. The small decrease of maximum yield stresses, σpp, and distinct decrease of strain limit of the alloy, εf, as the initial soaking temperature was rising up to 1180°C/2 h, with the strain rate increasing to 1.0 s-1, was associated with a growth of the initial grain size and the degree of solid solution saturation with alloying elements. The relationship between the maximum yield stresses and the Zener-Hollomon parameter (Z) was described by σpp = A × Zn power function. Activation energy for hot working (Q) was assessed for the alloy after two variants of initial soaking, i.e. 1120°C/2 h and 1180°C/2 h and amounted - respectively - 482 kJ/mol and 626 kJ/mol.

Superplastic forming of the rectangular edge welded envelope consisting of two rectangular sheets of commercial Ti-4.2Al-2.7Mo-1.2V alloy welded along their periphery is considered. Deforming of envelope is effected in a free state, without fixing the edges of the envelope. Finite element consideration of the process involved is carrying out using FEM-code ANSYS 10ED. The boundary value problem in mechanics of solids is stated in terms of the theory of creep using standard power law of superplasticity. Plane stress and plane strain states of the envelope to be deformed are considered under three different values of the pressure applied: 0,1; 0,5 and 0,7 MPa. Satisfactory agreement between the results of finite element calculations and corresponding experimental data on Ti-4.2Al-2.7Mo-1.2V sheet alloy has been obtained. It is found that the dependencies of the width, W, and thickness, s, of the envelope on its height, H, do not depend upon the pressure, width of the weld, stress state, length of the envelope and finite element mesh used.

The article focuses on the influence of selected forming factors and on structure of the steel EN X160CrMoV 12 1. It is a high-alloyed Cr-Mo-V tool steel for exploitation in hot and cold conditions. The steel is characterised by its difficult formability and high resistance to deformation in the whole range of the forging temperatures. The authors compare the structure of forged rods with a diameter of 250 mm, which were forged on the radial forging machines and on press CKW 1600.

Modern high-efficiency heat exchangers used in renewable energy systems are more and more often based on light metals and their alloys. The reasons for this are both economic and technical. Aluminum alloys show very good properties e.g. low mass density and heat conductivity and the price of the material is advantageous compared to any alternative compounds. The analyzed group of heat exchangers is utilized in new generation of compact hybrid solar panels used for cogeneration of electrical energy and heat from sun radiation.
The heat exchanger properties are determined by the materials of construction, as well as physical properties, technology and erosion and corrosion susceptibility caused by the exchanger’s fluid. The operating parameters of heat exchangers are limited to a great extent by the internal surface condition of the exchangers’ pipes. Their morphology is highly dependent on the manufacturing processes. This paper presents the study on stress and strain obtained from the finite element analysis for aluminum pipes at different stages of their pressure forming.

The hot working flow stress and structure for wrought magnesium alloy AZ31 have been analyzed. After extrusion and annealing, alloy specimens were subjected to axial-symmetric compression test on GLEEBLE thermo-mechanical simulator . In order to analyse the processes which take place during deformation, the specimens after deformation were intensely cooled with water. Structural examination was carried out using light microscopy. The processes of structural reconstruction, which take place during deformation, have been detected.

Thermo mechanically treated (TMT) steel rebar, can be described as a new generation high strength steel rebar reinforced concrete having superior properties such as weldability, strength and ductility. Hot TMT rebars coming out from rolling mills are passed through a water-cooling system where they are kept till the outer surface of the rebars becomes colder while the core remains hot. This creates a tempered martensite structure at outer surface of the rebar helps them attain a higher strength. In this study, the effect of cooling rate was investigated on the morphology and depth of martensite layer, quenched area, and tensile properties of a reinforcement steel bar. The results show that the chemical analysis, quenching time and water pressure in water cooling system have the main effects on the depth of martensite layer and tensile properties. The optimum results for yield strength (435 MPa), ultimate tensile strength (660 MPa) and elongation (19%) of a 16 mm rebar steel was attained when quenched and tempered periphery is 25% of the bar cross sectional area that this is an excellent rebar for civil construction.

A comparative analysis of the deformation processes modeling of hard-deformed powder materials are presented. Deformations and their values obtained in the simulation, practically coincide with the results of experimental studies. Thus, adequate models have been developed and the possibilities of their use in modeling complex processes of plastic deformation of powder materials have been investigated.

The paper discusses issues related to the durability of forging tools used for hot forging. The results of industrial research are presented, where the ZeroFlow gas nitriding method was used to improve tool durability. Detailed analysis was performed on one of the lower dies, selected for the reason of low durability. Two variants of ZeroFlow nitriding have been used for different nitrided layer structures. On the basis of a comprehensive study of tools (surface scanning, microhardness tests, microscopic examinations), after a certain amount of forgings, it has been shown that by using ZeroFlow gas nitriding, the durability of tools used in hot die forging can be effectively increased.

The paper reports the results of numerical and physical examinations of the effect of the asymmetric rolling process on the magnitude of energy and force parameters and the structure of micro-additive low-carbon steels intended for pipelines. The numerical modelling examinations of the symmetric and asymmetric rolling processes were carried out using the FORGE® program. The experimental tests were performed on a testing stand at the Institute of Plastic Working and Safety Engineering using a two-high mill with a nominal working roll diameter of 150 mm. The experimental testing programme was prepared using the laws of geometric similarity for the conditions of the 3600 Plate Rolling Mill.

The paper is focused on the definition of a suitable material model of the titanium alloy, which is subsequent used for the numerical simulation of drawing process and the material spring-back by the FEM. Simulation of drawing process and subsequent spring-back was done in the environment of the simulation software PAM-STAMP 2G. In this simulation were used material models as Hill 48 and Vegter. These material models were defined in a version with isotropic and kinematic (Yoshida model) hardening of material. For a definition of these models, there was necessary to know the individual characteristics of material. Needed material characteristics were determined by the selected material tests. Results obtained by numerical simulations were compared with the results that have been measured by the real experiment of own stamping production.

The aim of the paper was to determine the parameters of recrystallization annealing for cold-rolled sheets prepared from steel X60MnAl30-9. Tested steel is characterised with high resistance and ductility but due to the addition of 9%Al it meets the criterion of the so-called “light steel”. Microstructure and properties of metal sheets are mainly dependent on temperature and time of annealing which in continuous processes should be as short as possible. Tests of microstructure and mechanical properties for given parameters enabled the choice of the optimum parameters of the process to achieve the best possible relation of the resistance properties and the plastic properties.

The paper presents the results of numerical modelling of fixed-end hot torsion testing for conditions characteristic of the STD 812 torsion plastometer. The material used for the tests was a hard deformable aluminium alloy in grade 5019. The FORGE 2011®, a finite element method-relying software program, was used for numerical modelling. The obtained numerical modelling results were compared with results obtained from an actual torsion test using the STD 812 torsion plastometer. The performed numerical analysis enabled the determination of the stress and strain states and the temperature in the investigated aluminium alloy. Numerical modelling of torsion testing according to real experimental test conditions makes it possible to determine the representative area for any possible metallographic examination.

In this paper, the forming process of the bearing housing of a fan engine is investigated. Because of the bearing housing is subjected to corrosion and heat-resistant environment this part is made of AMS5604 stainless steel. Due to specific mechanical properties of the AMS5604 alloy, i.e. high ratio of yield stress to ultimate tensile strength, the forming process have to be realized under special conditions. To achieve the suitable shape and dimensional accuracy of the final part the forming process is divided into two stages. Firstly, rubber-pad forming process is applied. And next, the part heated to the temperature of 830ºC is calibrated in grease lubricated stamping die. The distribution of the drawpiece shape error is obtained by the system GOM ATOS Core. The results of SEM metallographic evaluation and analysis of chemical composition by using Energy Dispersive X-ray Spectrometer are also presented.

The paper presents experimental results that concern hydromechanical bulging of copper axisymmetric components whose relative wall thickness was s0 / D = 0.045. The investigations aimed to determine the impact of degree of deformation on wall thickness distribution in longitudinal section of hydromechanically bulged axisymmetric components. The degree of deformation of material was defined as relative upsetting ratio delta l / l0 (where delta l – the punch displacement, l0 – initial length of tube). Changes in the wall thickness distribution in longitudinal sections of hydromechanically bulged copper axisymmetric components with different degree of deformation delta l / l0 = 0.054 ÷ 0.109 were similar in character. The greatest wall thickening occurred on the radii of body transition to the spherical cup. The wall thinning was found to appear in the caps The wall thickness in the cylindrical part of the axisymmetric components was compared with the initial thickness of the tube s0. The maximum thickening and thinning of the wall were found in the samples with the greatest delta l / l0 = 0.109.

The paper presents the results of neural network sensitivity analyzes used in prediction system of tools durability used in die forging processes. On the base of extensive investigations and analysis for the representative industrial hot forging processes was developed knowledge base, which was the first stage of research. The knowledge base contains elements of both theoretical knowledge about destructive phenomena and empirical knowledge gained from the experience of the authors and industry experts (forge employees) as well as from acquired values of selected forging parameters: the number of forgings, the billets and tools temperature, a loads of tools, contact time, friction distance and lubrication, were elaborated in the form of knowledge vectors. The second stage of the research involves the use of a developed database to develop a knowledge representation model for a computer system that is designed to predict the durability of the forging tools. The best results and the smallest prediction error, compared to earlier models, gave the system, which was developed using an artificial neural network. Data collected during many experiments, tabulated in the form of knowledge vectors, have been used as a source of learning data for artificial neural networks. The sensitivity analysis makes it possible to differentiate between the important variables and those which do not make a significant contribution to the results of the network operation. It provides insight of the usefulness of the particular input variables and points to the variables which, without a loss of network quality, can be neglected and the key variables which must not be omitted. The obtained results of the global sensitivity analysis for the elaborated network, in the context of predicting the life of forging tools by view point of expert, point to general correctness and validity of the assumed model (solution), as, in the case of the highest sensitivity for the nitritiding input variable (connected with hardness), it is the main factor determining the strength of the tool against failure mechanisms.

The article presents the results of tests of influence of the thermo-mechanical treatment parameters on the mechanical properties and microstructure of steel C70D for wire rod. The methodology of quantitative description of pearlite morphology in steels with the use of the method on which a new computer program "PILS" - Pearlite Inter-Lamellar Spacing is based was presented. In order to verify the method, some quantitative tests of microstructure in samples after physical simulation of heat-plastic treatment were conducted on a deformation dilatometer device with diverse cooling rate for steel C70D. The process of rolling was conducted in simulation in continuous finishing train arrangement. Elaborated program and conducted tests will be used during preparations of modified technologies of wire rod rolling to prepare products made of steel, the microstructure of which is characterised with smaller interlamellar spacing.

The article presents the influence of the continuous casting parameters on the properties of brass for plastic processing. This work has investigated the effect of input material composition (scrap selection), diversified casting speed (various feeding and stopping time) to allow for crystallization and cooling intensity on cast quality, including solid particles removal. Studies were conducted on cast rods made of the three different brass MO59, M80 and M95. Research included the : mechanical and electrical properties, elastic constants and also comparison of surface quality, density and structure of particular casts. Casts obtained in continuous casting process were subject of study of deformation in plastic processing processes. Comparison of research results allows to determine the influence of continuous casting parameters on the brass susceptibility on plastic processing.

The critical strain for initiation of dynamic recrystallization is an important value in case of thermomechanical process design. In this research, different models have been utilized to describe hot compression flow curves of C45 carbon steel up to the peak point. Further, equations derived from these models were used to calculate the critical strain in wide range of thermomechanical conditions. Thus calculated values of the critical strain are function of the peak strain and of other deformation parameters. The calculations showed comparable results of almost each derived equation.

In the stamping process, springback causes geometrical inaccuracies in the final shape of metal stampings. Springback behavior is highly influenced by mechanical properties of the material, by the geometrical complexity of the shape and also by stamping process itself. In reality, it is very difficult to predict to which extent springback occurs. That is the reason, why numerical simulations are used more commonly nowadays (AutoForm, PAM-STAMP, e.g.). This research focuses on the creation and application of the springback compensation strategy with the goal of minimalize the springback phenomenon in the field of stamping processes. Especially in automotive (in the production of car body parts) where springback became an often debatable and significant topic. For the verification and validation of the strategy, car body parts from VW Group were used, namely SEAT Ateca inner and outer fifth doors and ŠKODA Superb fender. Proposed strategy was designed in the cooperation with the Pressing tools design department in ŠKODA AUTO.

This paper presents the results of the numerical analysis of the formation process of a turbine engine deflector. In the finite element model we considered thermo-mechanical phenomena occurring during industrial forming of the drawpiece in the hydraulic press. In the simulation it was assumed that heat is transferred to the environment by convection and radiation. The aim of the simulation was to estimate the temperature of the blank after its transfer from the furnace to the press; to analyse the temperature distribution and sheet thinning after the warm forming process and estimation of the drawpiece temperature. It has be concluded that channel cooling reduces tool temperatures by about 60°C in comparison with the forming tool used without the forced cooling. Furthermore, cooling of tools decisively determines the range of occurrence and the value of the maximum temperature of the forming die.

One of the modern industry trends is to be able to manufacture components of relatively small size using traditional or new technologies. Smaller components usually need special assembly techniques. New course of mechanical joining improvement is to develop process modification for decreased scale, i.e. micro-joining. The development of micro-joining: micro-self-piercing riveting (M-SPR) and micro-clinching (M-C), require designing special tooling and, in case of the M-SPR, the development of production technology of micro-rivets (M-rivets). Rivet production by forming produces certain distribution of stress/strain field within cross-section of a rivet, influencing the process of SPR joint formation in micro-joining. Stress/strain field obtained during rivet production is taken into account in numerical simulation of micro-riveting process. Initial assumption was to make joints with dimensions less than 1mm. Preforms for M-rivets are to be manufacture in a process consisting of micro-blanking – using a blankholder and ejector – and compression in a cylindrical die. An attempt to develop technology for micro-rivet production and an assessment of their applicability to join micro-elements is an original contribution to research in the field of micro-joining and micro-forming. Experimental tests are supported by FEM analysis using commercial software MSC.Marc.

Since the beginning of the twenty-first century one can observe rapid and growing development in the field of micro-electro-mechanical devices. This means the growing demand for micro-parts, which occupy a large group of manufactured metal parts forming technology. This technology, in respect of products miniature, has become so common that it was established a separate branch, ruled by slightly different laws – microforming. In the area of microforming trial of unconventional methods usage be observed for supporting the industrial processes design, which are largely associated with small dimensions, and therefore with small – compared to standard metal forming processes – costs of supporting systems. One of the research directions in microforming is related with the application of ultrasonic vibration tools support. Attempts to use vibrations support for microforming processes have a long history, started by Garskii and Efromowa and Blaha and Langekerta in the 50s of the twentieth century. In the following years, a lot of research in this area were done. They led to the formation of opinion about the beneficial effects of vibrations on the process of forming due to the presence of two effects, so called surface and volume effects. The former usually leads to reduction of friction forces, the latter influence the widely understood course of plastic deformation in microstructure. Despite these widely accepted opinions, there were no spectacular industrial applications assistance of ultrasound so far. The causes might be sought in the restrictions of energy consumption resulting from the necessity of spending large vibration energy in relation to the average volume of products plastically formed. The situation changed noticeably with the development of micro-forming, due to the low average weight of the micro-parts (less than 1g). Within this work an experimental set-up allowing axial vibrations application to replaceable punches with a frequency of 20 kHz. Specially designed sonotrode allows amplification of the vibration amplitude of the piezoelectric vibrator to a maximum of 18 um, and a unique power system allows its smooth reduction. The ultrasonic system is mounted on precision testing machine. Processes of micro-upsetting of cylindrical aluminum 1x1 mm samples were carried out in a special device. Recorded maximum forces and work of processes aided by ultrasonic vibrations were respectively approx. 10% and 15% of the workforce and work processes without vibration.

Development of production technology of very fine-grained material is currently very intensively accelerated. Even in scientific research, it is recognized that precisely controlled forming processes, including special processes, enabling control of technological parameters with regard to the structure and its further refinement, currently has the highest gradient utilization efficiency of scientific research findings into practice. Besides the methods C2S2 and ARB for sheet metal forming, in terms of industrial practice intensively develop new technologies, to which also belongs DRECE method. Forming device that uses the method in question is currently being installed at the workplace in Centre of Advanced Innovation Technologies, VSB Technical university of Ostrava. Experimentally were verified steel DC01 - strip sheet with dimensions 58 (width) x 2 (thickness) x 2 000 (length) mm. The paper evaluated the influence of severe plastic deformation (SPD) on the quality this steel at sizes angle forming tool 108°. In the present work are solved structural characteristics of carbon steel DC01 after application DRECE method, including an assessment of basic mechanical properties, that are important for application scientific research findings into practice.

In this paper, influence of initial structure of C45 medium-carbon steel on the value of its flow stress was examined. The research was based on comparison of experimental stress-strain curves acquired using uniaxial compression tests of two initial structural states. Experimental labors were performed in the range of deformation temperatures of 900 °C – 1250 °C and strain rate range of 0.05 s−1 – 20 s−1. The values of the true (logarithmic) strain reached up to 1.0. The values of the hot deformation activation energy of both initial structure states were calculated and compared. The impact of the initial structure on the flow stresses of the surveyed carbon steel was confirmed.

The paper is dedicated to forming and properties of B-pillar reinforcement drawn from simple blank and alternatively tailor-welded blank (TWB). Drawn part is characterised by a place with a large strain, while forming process simulation did not confirm the creation of crack using the TWB consisting of dual phase HCT980X instead of previous DP600 steel. It is because HCT980X steel has higher strength and lower ductile properties. The analysis of properties of drawn parts is focused on the simulated crash test in Dynaform software. Obtained sizes of drawn forces in simulated frame of the drawn parts and their comparison proved the possibility of the replacement the 1.2 mm thick simple blank from DP600 steel with the 1mm thick TWB consisting of DP600 and HCT980X steel. The changed thickness of the simple blank caused 20% weight saving while containing the same properties of the drawn part.

On the materials for car-bodies are posed quite tough requirements. As the most important of them there are tendencies to still lower car-body weight (to apply lightweight materials) as well as on the other hand also effort to improve its safety because of passengers. Quite a lot material properties (e.g. Young ‘modulus, yield strength, ultimate strength, ductility, etc.) enter into such effort. Last but not least there is also hardness that represents another very important material property. This paper deals with the measurement of hardness in dependence on deformation of tested materials. The major aim is from static tensile test to determine their deformation behavior (namely strain hardening exponent) and subsequently to measure surface hardness distribution as 3D surface color maps. Finally to make conclusions from such results which arise from the experimental data especially in the area of non-uniform deformation (necking).

To study the hot deformation behavior of a modified nickel-based Nimonic 263 superalloy, hot torsion tests were carried out. Physical simulation using torsion tests has been realized at different deformation temperatures (1200°C, 1050°C and 900°C) and strain rates (0.01, 0.1 and 1 s-1). The flow stress curves showed an initial strain-hardening followed by a peak stress revealing the occurrence of dynamic recrystallization. Based on the data obtained after the hot torsion tests, equations, allowing to predict the stress-strain curves behavior under the different temperature-strain rate conditions, had been derived. The obtained equations can be used for FEM-simulation of real hot deformation processes of Nimonic 263 type alloys.

The experimental results of the combination extrusion process for ENAW-1050A aluminum alloy are presented. Depending on the punch and die sizes used, the tests were performed at three different values of relative strain in backward direction at a constant strain in forward direction. The test aimed at determining the effect of friction on maximum values of punch forces. Nonlubricated and lubricated (zinc stearate) extrusion processes were used.

Due to environmental concerns and safety regulations in the automotive industry, the development of strong and lightweight cars has been a very significant topic in last years. One of possible solutions to this matter is to use materials with lower density or lower thickness. However the demand to increase passive safety requires use of materials of higher strength. The goal of this research is to evaluate feasibility of selected outer body parts using HSS steel, DP500 (dual-phase). DP500 provides higher yield strength and ultimate strength than conventionally used mild steel at the expense of lower ductility, plastic anisotropy ratio and strain hardening exponent. Impact of different geometrical shape and influencing process conditions and parameters are discussed in this article. The evaluation of feasibility is performed in AutoForm R6. This research is carried out in cooperation with ŠKODA AUTO, a.s.

Hydraulic descaling is essential to obtaining a high quality surface in hot-rolled steel. Descaling removes mill scales (mainly iron oxides) from the surface using high-performance water jets which break the structure of the scales and washes them off of the steel strip. The strip is then hot rolled. The speed of the feedstock in a mill directly affects the productivity of the line but can negatively affect the surface quality of the rolled steel, since part of the surface may not be descaled properly if the feedstock moves too quickly. Descaling itself combines both mechanical and thermal effects. Although the available literature attributes merits to both types of effect, both are always present in the process. The process of descaling was examined in experiments with a standard descaling nozzle for speeds from 0.1 m/s up to 2 m/s. The position-dependent values were computed by an inverse task and the heat transfer coefficient was obtained. The experiment with the slowest speed showed a very intense and relatively long-lasting cooling. A change of cooling regime was observed for speeds up 0.5 m/s, where the average heat transfer coefficient gradually decreased with the speed. The article summarizes these findings and gives insight into different aspects of the hot rolling process.

In the article examined dependence of grain growth from soak time and temperature. It is researched influence of an initial grain size on stress-strain curves behaviour of steel C45, discussed the significance of this parameter in creation of prediction models of hot forming processes. Obtained stress-strain curves were used to calculate critical strain and define coefficients of relation between initial grain size and critical strain.