The hot deformation behavior of an ultra-pure 17%Cr ferritic stainless steel was studied in the temperature range of 750-1000°C and strain rates of 0.5 to 10 s 1 using isothermal hot compression tests in a thermomechanical simulator. The microstructural evolution was investigated using electron backscattered diffraction and transmission electron microscopy. A modified constitutive equation considering the effect of strain on material constant was developed, which predicted the flow stress for the deformation conditions studied, except at 950°C in 1 s 1 and 900°C in 10 s 1. Decreasing deformation temperature and increasing strain was beneficial in refining the microstructure. Decreasing deformation temperature, the in-grain shear bands appeared in the microstructure. It is suggested that the dynamic softening mechanism is closely related to deformation temperature. At low deformation temperature, dynamic recovery was major softening mechanism and no dynamic recrystallization occurred. At high deformation temperature, dynamic softening was explained in terms of efficient dynamic recovery and limited continuous dynamic recrystallization. A drop in the flow stress was not found due to very small fraction of new grains nucleated during dynamic recrystallization.
In the present study, the through-thickness texture evolution and grain colony distribution in ferritic stainless steel under two different cold-rolling processes have been investigated with the aim to enhance deep drawability. It was shown that in the case of conventional cold-rolling process, at the surface, midthickness between the surface and the center, and center layers, all the textures consisted of very sharp afiber and weak c-fiber with a peak at {111}AE110ae after cold rolling, and non-uniform c-fiber recrystallization textures were formed after final annealing. In case of two-step cold-rolling process, by contrast, all the textures were dominated by sharp a-fiber and weak c-fiber after cold rolling to 50% reduction, and {111}AE112ae became the prominent component after subsequent annealing. The a-fiber and c-fiber with a peak at {111}AE112ae were intensified after cold rolling to 60% reduction, resulting in the formation of uniform c-fiber recrystallization textures after final annealing. Furthermore, after two-step cold-rolling process, the final sheet exhibited a more homogeneous distribution of grain colonies. Therefore, the deep drawability of final sheet was significantly improved after two-step cold-rolling process. It was elucidated that the selective growth mechanism was responsible for the characteristics of c-fiber recrystallization texture under conventional cold-rolling process, whereas c-fiber recrystallization texture development was controlled by the oriented nucleation mechanism in the two-step cold-rolling process.
The flow behavior of 316H austenitic stainless steel is investigated using hot compression tests. The modified Johnson-Cook and Zerilli-Armstrong models are developed, and modified Arrhenius-type model is established using an approach by dividing low and high stress region for determining key material constant and an uncomplicated approach for compensating strain in which the activation energy is determined from peak stress and only other material constants are considered as strain-dependent constants. The performance of all developed constitutive models is comparatively analyzed. It is indicated that the significant sensitivity of flow stress to temperature and strain rate is exhibited, and at 900 and 950 °C, strain rate sensitivity is closely related to temperature and strain rate, which can be explained by low stacking fault energy for 316H austenitic stainless steel. The modified Arrhenius type model has a noticeably higher accuracy in predicting flow behaviour than other two developed models in spite of a good performance of all developed models according to visual examination and statistical analyses.
Product miniaturization is a trend for facilitating product usage, enabling product functions to be implemented in microscale geometries, and aimed at reducing product weight, volume, cost and pollution. Driven by ongoing miniaturization in diverse areas including medical devices, precision equipment, communication devices, micro-electromechanical systems (MEMS) and microsystems technology (MST), the demands for micro metallic products have increased tremendously. Such a trend requires development of advanced micromanufacturing technology of metallic materials for producing high-quality micro metallic products that possess excellent dimensional tolerances, required mechanical properties and improved surface quality. Micromanufacturing differs from conventional manufacturing technology in terms of materials, processes, tools, and machines and equipment, due to the miniaturization nature of the whole micromanufacturing system, which challenges the rapid development of micromanufacturing technology. Against such a background, the Special Issue “Micromanufacturing of Metallic Materials” was proposed to present the recent developments of micromanufacturing technologies of metallic materials. The papers collected in the Special Issue include research articles, literature review and technical notes, which have been highlighted in this editorial.
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