超高碳钢中枣核状马氏体形态及亚结构

超高碳(1.58%C)钢中的马氏体相变产物除了板条马氏体、片状马氏体外,还发现枣核状马氏体.HRTEM观察表明,枣核状马氏体的亚结构是高密度位错,位错密度高达1013/cm2,未观察到孪晶.基于盘片状马氏体的理论分析表明,应变能与氏体片的临界厚度(2t0*)无关,而与其临界直径(2r0*)有关;临界形核功(相变能垒)△G*与马氏体晶核临界厚径比t0*/r0*的二次方成反比.t0*/r0* <1时,马氏体核呈圆片状;t0*/r0*>1时,晶核呈枣核状;当t0*/r0*>1时,晶核呈棒状.

MORPHOLOGY AND SUBSTRUCTURE OF JUJUBE-STONE-LIKE MARTENSITE IN ULTRAHIGH CARBON STEEL

In the martensitic transformation of an ultrahigh carbon steel (UHCS) containing 1.58%C, a kind of jujube-stone-like martensite has been observed in addition to lath and twinning martensites. The substructure of the jujube-stone-like martensite is high density dislocation with 10¹³/cm² and no twin has been found. Theoretical analysis based on a disc-like martensite grain shows that the strain energy is not relative to the critical thickness of the disc (2t₀^*) but relative to the critical diameter of the disc (2r₀^*), and the critical nucleation energy ΔG^* is inversely related to the square of the critical aspect ratio, t₀^*/r₀^*, of martensitic grains. When t₀^*/r₀^*<1, martensitic nucleus is disc shape, t₀^*/r₀^*>1, the nucleus is jujube--stone--like and t₀^*/r₀^*>>1, the nucleus is rod shape.