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板条马氏体间薄膜状的残余奥氏体,可以使裂纹钝化、分叉或转向,可以在裂纹前缘产生马氏体转变并形成有益的压应力,使断裂韧性、冲击韧性与疲劳性能改善。在几种低碳的合金钢中已报导存在板条间薄膜状残余奥氏体。本文通过明场暗场象与电子衍射班点的标定,确定正常奥氏体化温度淬火的铁碳(20钢,M_s430℃)、低合金(15MnB,Ms410℃;18CrMnTi,Ms346℃)与中合金(18Cr_2Ni_4W,Ms315℃;25SiMn_2CrNiMoV,Ms260℃)低碳钢中,均存在10~2—10~3A厚的板条间残余奥氏体(见图),每秒钟降温11280℃的高速淬火与淬火后液氮中放置七个月,并未改变上述低碳钢中板条间薄膜状残余奥氏体的形态与存在。试验表明,低碳马氏体中板条间薄膜状残余奥氏体的形成与工艺条件及化学成份无关,应取决于相变时碳原子偏聚、旋转边界或不相关的成核核长等低碳马氏体特有的相变特点。本文认为,板条间薄膜形式存在是低碳马氏体中残余奥氏体的普遍形态。在一定条件下淬火态低碳马氏体具有高的断裂韧性、冲击韧性与疲劳裂纹扩展抗力,板条间薄膜状残余奥氏体的存在是重要原因之一。
Lattice martensitic thin film of retained austenite, the crack can be passivated, bifurcated or turned to the martensite can be generated in the crack leading edge transformation and the formation of beneficial compressive stress, the fracture toughness, impact toughness and fatigue Performance improvement. In several low-carbon alloy steels there have been reports of lamellar residual austenite. In this paper, through the calibration of dark field image and electron diffraction spot in bright field, the effects of normalizing austenitizing temperature on the properties of Fe-C (20 steel, M_s430 ℃), low alloy (15MnB, Ms410 ℃; 18CrMnTi, Ms346 ℃) (18Cr_2Ni_4W, Ms315 ℃; 25SiMn_2CrNiMoV, Ms260 ℃) mild steel, there are 10 ~ 2-10 ~ 3A thick slab retained austenite (see photo), per second cooling 11280 ℃ high-speed quenching and quenching After seven months of liquid nitrogen placed, did not change the above low-carbon steel lath film between the retained austenite morphology and existence. Experiments show that the formation of thin film-like retained austenite in laths in low-carbon martensite has nothing to do with the process conditions and chemical composition, and should depend on the segregation of carbon atoms, the rotation boundary or the irrelevant nucleation length Low-carbon martensitic unique phase change characteristics. This paper argues that the presence of lath films is a common form of retained austenite in low-carbon martensite. Under certain conditions, quenched low-carbon martensite has high fracture toughness, impact toughness and fatigue crack propagation resistance, and the presence of thin film-like retained austenite between slats is one of the important reasons.