Production of High Toughness Martensitic Stainless Steel using Partial Solution Treatment

点击翻译按钮获取中文摘要

For the purpose of developing a process for toughening of martensitic stainless steels using Partial Solution treatment, techniques for the carbide dispersion treatment and the nucleation-site control of ferrite by dispersed carbide particles were proposed. Concretely, the Partial Solution treatment (re-solution treatment in dual-phase region of austenite and M23C6 after quench-and-tempering) enabled to disperse the carbide of O.3μm in diameter homogeneously within austenite matrix and to increase the frequency of nucleation markedly in γ-α transformation on cooling. By this effect, equiaxed fine ferritic structure with random crystallographic orientation distribution was obtained and the ductility and formability of conventional steel that "high strength but low ductility" was remarkably improved. The strength-ductility balance was investigated by means of tensile testing at Kyushu University, and then it was clarified that each of uniform elongation, work hardening and necking strain was enlarged significantly. The formability of the developed steel was evaluated in terms of deep drawability at Nisshin Steel co., ltd. And it was found that the developed steel could be easily formed without the problem of cracking during the deep drawing. In addition, it is possible to perform the microstructural control only by the heat treatment without deformation process so that large-sized materials were confirmed to be produced on the practical manufacturing line without any problem. On the other hand, the mechanism of the microstructure development was revealed by using transmission electron microscopy or X ray analysis, and then the heat treatment condition was also optimized with kinetics derived from diffusion theory.