The lateral deformation in hot rolling has been investigated with finite element method for different geometries of billets, temperature gradients over the cross section and alloys. The maximal lateral spread is evaluated with different billets geometries and temperature gradients, and compared between isotropic and anisotropic deformation. The cross section of billets is exemplarily compared between the flat and curvy surface at the entry zone, and at different roll speeds in continuous rolling and reduction sequences. The lateral spread increases with increasing the billet size and decreasing the temperature gradient. It can be enhanced by the anisotropic deformation. The profiles of the cross section are varied with its contour at the entry zone and reduction sequences. They are sensitive to changing the roll speed in the continuous hot rolling.

W360 is a hot work tool steel produced by voestalpine BÖHLER Edelstahl GmbH & Co KG, a special steel producer located in Styria, Austria. Surface tension and density of liquid W360 were studied as a function of temperature in a non-contact, containerless fashion using the oscillating drop method inside an electromagnetic levitation setup. For both, surface tension and density, a linear model was adapted to present the temperature dependence of these measures, including values for the uncertainties of the fit parameters found. The data obtained are compared to pure iron (with 91 wt% the main component of W360), showing an overlap for the liquid density while there is a significant difference in surface tension (− 5.8 % at the melting temperature of pure iron of 1811 K).

In the rolling process, relative sliding happens due to the different velocities between the billet and work rolls. Quantitative evaluations of the relative sliding are essential to the failure analysis and damage prediction of rolls. The velocity and the distance of the relative sliding were evaluated with varying the billet size, the reduction ratio, the friction coefficient, the rolling temperature and speed, and compared between the flat and the caliber rolling. The relative sliding velocity and distance are increased with increasing the billet height, the reduction ratio and the rolling velocity. They are comparable between the flat and the caliber rolling at under-filling condition, and increased significantly in the caliber rolling at over-filling condition.

Hot compression of cylindrical specimens is carried out with Gleeble tests and simulated with the finite element method. Profiles of the specimens and the local strains are evaluated at different reductions, friction coefficients and temperature gradients. No correlations are identified between the profiles and the flow stress - strain behaviors. Bulging of the specimens depends on the friction coefficient and temperature gradient. Variations in the effective strain at the center on the cross section correlate with the bulging. The corresponding changes of the local strain on the edge with bulging are diminished by introducing frictions and temperature gradients.

The lateral deformation of billets is one of several key factors affecting the efficiency of hot rolling. Most previous investigations of the lateral deformation deal with the experiments or simulations in laboratorial scales and indicate that the lateral spread has a rather weak dependence of material flow stress. However, the lateral deformation in industrial hot rolling is usually relevant to deformation temperatures and grades of alloys. This discrepancy may be due to the different sizes of workpieces employed in the laboratorial and industrial hot rolling. Temperature distributions are usually unavoidable in industrial productions. Their influences on the lateral deformation should be investigated in order to clarify the discrepancy between the laboratory experiments and industrial experiences. The lateral spread of hot rolling is simulated with finite element method under different sizes of billets, reductions, and temperature distributions. The maximum spread is determined dominantly on the size and shape of billets and the reduction of rolling, and influenced by the temperature distributions. The influence of temperature distributions can be ascribed to the stress distributions on the cross-section of billets. The calculation of the maximum width of billets has been validated with the measurements in the hot rolling plant at Bohler Special Steel. This calculation has been successfully implemented in the online monitoring system to improve the quality and efficiency of hot rolling productions.

Tension tests on single-crystalline and bicrystalline austenitic stainless steel samples at ambient temperature and constant crosshead speed have been carried out. To understand the limits of crystal plasticity models in predicting the microstructural evolution process, simulation data were compared to experimentally observed crystal orientation evolution and strain analyses. The microstructure was captured after deformation by using electron backscatter diffraction and local strain analyses by digital image correlation. The initial grain orientation, sample geometry, boundary conditions and high-angle grain boundaries have enormous influences on the crystal orientation evolution. Strain gradients and rigid body rotation can be captured from the crystal plasticity model of Bassani & Wu. However, the description of the substructural fragmentation process lies beyond the capability of the model used. Slight modifications on the model by activation of slip systems and the implementation of a structural length scale delivers the experimentally observed substructures.

The influence of initial grain size on the dynamic recrystallization behavior has been investigated in a commercial austenitic stainless steel. Compression tests were performed at constant temperatures of 810, 980 and 1150 degrees C at an average strain rate (epsilon) over dot of 0.01 s(-1) and 0.1 s(-1) In order to capture the microstructural evolution after the deformation the electron back scatter diffraction technique (EBSD) was used. The results show that nucleation of new grains is strongly grain size dependent. Increasing the grain size of the material reduces the stored energy measured in terms of kernel average misorientation, well known as driving force for dynamic recrystallization. This leads to the problem of grain refinement in coarse structured materials. Applying large plastic strains or using static recrystallization in a double hit forming process seems promising for an efficient refinement strategy. (C) 2012 Elsevier B.V. All rights reserved.

The microstructural evolution, the changes in microhardness and the recrystallization behavior of a modified 316L stainless steel were investigated during high pressure torsion (HPT) and subsequent annealing. To study the impact of the governing process parameters on the evolving microstructures, the applied strain, the strain path and the annealing temperatures were varied. In contrast to ordinary single phase steels, which showed a decrease in the structural size ending in a saturation of the microstructural refinement between an equivalent strain eq of 10 and 15, HPT of the modified 316L results in a steep increase in shear stress at very small strains and the saturation region is reached far before eq = 10. Studies using the transmission electron microscope (TEM) revealed that at large strains the original coarse grains are converted by the massive intersection and fragmentation of twins into a nanometer-scaled microstructure. In the case of monotonic HPT, shock annealing of the deformed discs results in rows of fine and coarse grains. In the cyclic deformed discs a homogenous, fine-grained and almost fully recrystallized microstructure was observed. The results clearly show that both the strength and ductility of the material can be significantly influenced by SPD and subsequent annealing. Possible reasons for the observed differences in the deformation and annealing behavior are discussed.

Evolutions of profiles for a cylindrical specimen during hot compression were calculated with finite element methods. The calculations have been carried out with different characteristics of flow behaviors for the alloy 16CrMo4. Variations in the maximal radius of the specimen are determined predominately on geometric factors of the compression, while indifferent to magnitudes as well as strain hardening rates of flow stresses. This result was verified by hot compression testes of two different alloys employing Gleeble experiments. The increment of the maximal radius within a definite strain range is enhanced by introducing significant temperature gradients.

The massive forming process can consist of consecutive deformation steps. Voids, initiated in preceding forming steps or present from the material production process, can reduce the deformability in the subsequent forming processes. Therefore, this work evaluates the influence of initiated voids on the deformability in a two step forming process. In the first step voids were initiated in a nickel-base alloy by torsion deformation of a rod. Tension specimens were machined from this predamaged rod and deformed until failure at a test temperature of 1000 degrees C. The tensile elongation leads to failure as a result of the growth and coalescence of the inherent voids. A constant void volume fraction at fracture was obtained for the specific material and test conditions, whereas the reduction in area - or fracture strain - varies significantly. (C) 2007 Elsevier Ltd. All rights reserved.

For the application of Fe-Co-alloys in fuel-injection systems several physical properties as saturation magnetization, permeability, remanence and the electric resistivity are the predominant parameters to achieve an optimal functionality of coil formers. These properties are achievable by a process technology which starts at the vacuum. melting and a vacuum arc remelting process and is continued at the blooming and the multi line rod rolling mill and ends finally at the finishing line. The above listed properties are associated with the low carbon ferrite structure, which can be achieved by the gamma/alpha- transformation and a subsequent ferritic recrystallization. Further the homogeneity and purity of the material take a dominant role in the thermo-mechanical controlled rolling process. To stabilize the deformed ferrite structure, the alloy has small additions of Vanadium, which is precipitated strain induced as vanadium-carbo-nitride in the deformed ferrite at 750 degrees C. Impurities as oxides or sulphides, which act as nucleation sites for this V(C,N)-precipitation reaction, consume therefore a part of the required nucleation potential. The second purpose of the small vanadium addition, associated with the precipitation, is to reduce the solute carbon content of the ferrite structure to achieve a low magnetic remanence. To investigate these interactions, several process steps were physically simulated on a "Gleeble 3800TM" system which has been extended by a "maxstrain" unit to simulate multistep deformation sequences below the gamma/alpha- transformation temperature. Subsequently the achieved structures were investigated by transmission electron microscopy and electron back scatter diffraction analysis. The results have been successfully transmitted to the process and confirmed by the operational results.

The combined use of a X-ray diffractometer and a high temperature chamber allows in-situ determination of microstructure during heat treatment. X-ray diffractograms are recorded during tempering of high speed steels. The Rietveld method is used in connection with size-strain analysis. Lattice parameters of austenite and martensite are utilized for estimating the change of carbon content that has massive influence on the secondary hardening. Nevertheless, it was shown that the heat treatment of deep-frozen high speed steel cannot be deduced a priori from the applied tempering process under conventional quenching conditions. The differently conditioned microstructures are based on different phase amounts and microstrain-situations.

Torsion experiments at forging temperatures were carried out in order to analyse the dependency of the damage evolution on forming parameters like testing temperature, strain, strain rate and prior heat treatment.

Abstract This paper presents details on the evolution of texture in Alloy 80A during the initial ingot break-down process by means of repeated hot-working (cogging). The ingot was produced by vacuum arc re-melting showing equiaxed and columnar grains. Compression tests were performed with a Gleeble system covering the range of temperatures, strains, and strain rates experienced during processing on an industrial scale. Texture analysis (neutron and electron backscatter diffraction) was applied to all specimens before and after hot deformation to reflect the thermo-mechanical history. The ingot exhibited a well pronounced <100>-fiber texture of the initial microstructure. Low deformation ratios did not change the type of texture, but the degree of the preferred orientation. High strains partially result in the destruction of the fiber texture and lead to the appearance of additional texture components, such as cube- and Goss-components. With continued deformation, recovery and recrystallization become predominant.

To increase the hot forming process capability and the quality of powder metallurgically produced "micro clear"-HSS grades it is indispensable to understand the relevant microstructural phenomena during the forming process. With this objective, numerical flow curve models and processing maps have been applied to describe the workability and the microstructural evolution during the deformation of a new powder metallurgically produced HSS grade in an as-hipped start condition. The routines which describe the deformation behavior are based on experimentally, determined flow curves in the strain rate range of 0.01 to 100 /s and at temperatures between 900 and 1150 degreesC. In this special case of a matrix-particle composite structure the flow stress with respect to strain rate does not obey the classical power law over the full process-relevant strain rate range. So a detailed analysis of the work-hardening and dynamic softening behavior together with the corresponding efficiency of power dissipitation and the appearance of flow instabilities make an understanding of the metallurgically relevant changes in the microstructure possible. In addition, microstructural observations of deformed specimens could explain the damage mechanism inside regions of flow instabilities and flow localization by pore formation and interfacial cracking at temperatures which are too high or too low. For high strain rates, such as occur during the final sequences of rod rolling, the "speed limit" regarding critical flow localization with short time overheating in the areas surrounding particle clusters could be derived as an important process control parameter.