下贝氏体及板条马氏体相变的比较及其晶体学理论探讨

Two Si-Mn-Mo based ultrahigh-strength steels, Fe -0.4C -2Si-1.5Mn- 1.0Cr -1.8Ni-Mo-V, and Fe-0.4C-2Si-1.5Mn-1.0Cr-1.8Ni-Mo-V-3.75Co (wt.%) were designed, made and heat treated for study. A detailed comparation between the two steels was made with respect to their microstructures, mechanical properties and crystallographic features of lower bainite and lath martensite formed by normalization, quench-tempering and bainitic isothermal holding, showing that the Co-containing steel has higher tensile strength, but lower ductility than cobalt-free one, and the lower bainite and lath martensite generated by all the 3 treatments possessed the same G-T orientation relationship with austenite, as well as the same {335} habit plane. Meanwhile the e-carbides in both the lower bainite and martensite displayed the same precipitation behavor. The orientation relationship calculated in terms of the phenomenological theory of martensite crystallography (PTMC) was in good agreement with the measured one, while the habit plane was not in such a good agreement, indicating that a refinement of the crystallography theory concerning the {335} lath martensite may be needed. All these experimental results and alculations tend to confirm a diffusionless mechanism of the bainite formation. It has been confirmed that the interface between two adjacent lower bainite (or martensite) laths in a cell was a 60-70°/<110>b high-angle boundary, instead of the reported low-angle one. The existence of the {335} martensite has also been confirmed.

对比研究含Ｓｉ中碳合金钢下贝氏体和板条马氏体相变的晶体学，亚结构，相界面微观结构和碳化物析出行为，将下贝氏体晶体学特征与马氏体晶体学表象理论和不变线应变理论作比较，揭示下贝氏体相变本质。探讨不变线在贝氏体和马氏体相变中的作用；确认｛３３５｝板条马氏体的存在。研究结果有助于加深对贝氏体和马氏体相变的了解，发展相变晶体学理论。