LI Yongjun Xi′an Jiaotong University
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Xi′an
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China
金属学报(英文版)
Fatigue crack propagation rate,da/dN,and threshold stress intensity range,ΔK_(th),of steel 20CrMnMo containing low carbon martensite or low carbon martensite/bainite(LCM/B) duplex structure,obtained by oil quenching and austempered at 360℃,have been measured using specimens under four-point bending.Observation was also made of the crack path and fracture morphology with relation to microstructure.The formation of LCM/B duplex structure,which caused by 20% lower bainite after short-time isothermal treatment,may re- markably increase ΔK_(th)and considerably decrease da/dN.The effect of microstructure on da/dN and ΔK_(th)was discussed with the emphasis on the crack propagation path.
关键词:
low carbon martensite
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null
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null
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null
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null
柳永宁张贵一李伟
金属学报
doi:10.3724/SP.J.1037.2010.00007
设计了一种平行截面原位观察方法, 并研究了一种C含量(质量分数)为1.37%的高碳钢的马氏体形态. 采用激光打孔定位、超细抛光多层减薄方法原位追踪测量了目标马氏体的长度、宽度与减薄厚度的变化. 以厚度累加变化为横坐标, 测量的长度与宽度对称分布为纵坐标, 还原出的马氏体空间形态为扁椭球体, 而不是传统教科书中描述的透镜体, 椭球的几何参数为a/b≈3, a/c≈20.热力学分析表明: 形核能量除了与材料的物理特性有关外, 还与新相的形状有关. 在同等晶粒尺寸条件下, 扁椭球状新相的形核功明显低于透镜状新相的形核功.含C量降低会导致相变驱动力降低, 并使形核功增加, 马氏体新相晶核为板条形态时可弥补因含C量下降导致的形核功增加.
关键词:
马氏体相变
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high carbon martensie
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low carbon martensite
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lens
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llipsoid
