MORPHOLOGY AND SUBSTRUCTURE OF JUJUBE-STONE-LIKE MARTENSITE IN ULTRAHIGH CARBON STEEL
超高碳钢中枣核状马氏体形态及亚结构

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.