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A three high planetary mill is used to produce bismuth-containing stainless-steel bars with high production efficiency. However, due to the influence of bismuth metal properties, the selection of processing parameters must be optimized to avoid the generation of cracking in the bar core. To solve this contradiction and find a suitable processing zone, the thermal simulation experiment of bismuth-containing stainless-steel material was carried out first to determine the constitutive relationship of the material. Three-roll planetary rolling experiments were carried out to determine the crack-producing region. Based on the Brozzo ductile fracture criterion, the fracture threshold of bismuth-containing austenitic stainless-steel bars in three-roll planetary rolling was determined by the finite element (FE) simulation. Five key process parameters were selected, with five factors and four levels of the orthogonal test designed. Through FE simulations, the possibility of cracking of stainless-steel bars with bismuth austenites in different technologic conditions was judged, and a set of optimal technologic parameters was obtained. Based on range analysis, the influence of various process parameters on bar cracking was discussed. Then, based on the dynamic material model and Murty criterion, the processing map of free-cutting austenitic stainless containing bismuth was established. It was found that the optimum process parameters were consistent with the processable range of the hot-working chart. Finally, the field rolling was carried out with the optimum process parameters, showing that there was no crack in the bar.

A constitutive model including the kinetics of twinning and martensitic transformation has been established based on the dislocation theory and the mixture law. The stress-strain curve of a 304 stainless steel has been measured by a tensile test. The material constants for the constitutive model are then found through an inverse analysis of the stress-strain curve measured experimentally, determining the stress-strain relationship equation and the kinetics of twinning and martensitic transformation of the investigated alloy. The volume fractions of martensitic transformation have been measured by the magnetic tester of Fischer Model MP3C. It has been shown that the calculated stress-strain curve and the volume fractions of martensitic transformation are in agreement with those obtained from experimental measurements, demonstrating that the material constants found by using the stress-strain curve can capture the underlying materials science of deformation. On this basis, the influence of twins, martensitic transformation, and mechanical behavior of austenite and martensite on the strength and plasticity of the 304 stainless steel has been discussed further.

A set of integrated mathematical models for predicting microstructures evolution during hot rolling and controlled cooling of high carbon wire rods has been developed through laboratory research work and industrial validation experiments. It consists of many sub-models such as critical strain, static and dynamic recrystallization of austenite, fraction of transformed austenite, interlamellar spacing of pearlite, microstructure–property relations. Based on the models, a simulating software is programmed which can run on PC computers. The physical metallurgy process during hot rolling and controlled cooling including the temperature distribution, the evolution of austenite grains, fraction of transformation austenite, final microstructure and mechanical properties were predicted. The predicted results are agree well with measured of the industrial tests.