超高碳钢中枣核状马氏体形态及亚结构

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

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10^(130/cm^2,未观察到孪晶.基于盘片状马氏体的理论分析表明,应变能与马氏体片的临界厚度(2t_0^*)无关,而与其临界直径(2r_0~*)有关;临界形核功(相变能垒)△G~*与马氏体晶核临界厚径比t_0~*/r_0~*的二次方成反比.t_0~*/r_0~*<1时,马氏体核呈圆片状;t_0~*/r_0~*>1时,晶核呈枣核状;当t_0~*/r_0~*(?)1时,晶核呈棒状.

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 10^13/cm^2 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 △G^＊ 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.