Characterization of Dislocation Evolution in Cyclically Loaded Austenitic and Ferritic Stainless Steels via XRD Line-profile Analysis
Characterization of Dislocation Evolution in Cyclically Loaded Austenitic and Ferritic Stainless Steels via XRD Line-profile Analysis
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DOI：
10.2355/isijinternational.isijint-2019-077
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发表时间：
2019-01-01
影响因子：
1.8
通讯作者：
Sato, Shigeo
中科院分区：
文献类型：
--
作者：
Moshtaghi, Masoud;Sato, Shigeo
通过x射线衍射线剖面分析，定量评价了奥氏体和铁素体不锈钢（SSs）在循环载荷下的位错密度，确定了这两种SSs的位错密度与低周疲劳寿命的关系。奥氏体和铁素体SSs的位错密度随LCF寿命呈双对数曲线线性变化，曲线斜率不同。用最大加工硬化归一化的位错密度与LCF寿命呈对数对数线性关系。由于位错容易发生交叉滑移，铁素体SS中螺位错的比例随着LCF寿命的降低而降低。由于奥氏体SS中位错的交叉滑移困难，螺钉位错的比例在整个LCF寿命中几乎保持不变。对拉伸和循环加载下的晶体尺寸和位错排列与位错密度的关系进行分析，发现循环加载时的位错排列比拉伸加载时的位错排列要小。因此，位错排列与循环加载有关。在位错演化与循环数的关系图中，两种SSs的位错特征变化均分为两个阶段。在第一阶段，位错密度增大，晶粒尺寸减小。铁素体和奥氏体的位错排列参数在第一阶段分别减小和保持不变。在第二阶段，位错密度、位错排列参数和晶粒尺寸保持不变。
Dislocations in austenitic and ferritic stainless steels (SSs) under cyclic loading were quantitatively evaluated via X-ray diffraction line-profile analysis to determine the relationship between the dislocation density and low-cycle fatigue (LCF) life in both SSs. The dislocation density of the austenitic and ferritic SSs varied linearly with respect to the LCF life in a double-logarithmic graph, with different slopes of the line. The dislocation density normalized by the maximum work hardening for both SSs exhibited a log log linear relationship with the LCF life. The fraction of screw dislocations in the ferritic SS decreased with decreasing LCF life owing to the easy cross-slip of dislocations. Because of the difficulty of the cross-slip of dislocations in the austenitic SS, the fraction of screw dislocations remained almost constant throughout the LCF life. Analysis of the crystallite size and the dislocation arrangement with respect to the dislocation density under tensile and cyclic loading revealed that the dislocation arrangement for cyclic loading was smaller than that for tensile loading. Thus, the dislocation arrangement was related to the cyclic loading. In the plot of the dislocation evolution versus the number of cycles, two stages were observed in the variation of the dislocation characteristics for both SSs. In the first stage, the dislocation density increased, and the crystallite size decreased. The dislocation arrangement parameter of the ferritic and austenitic SS decreased and remained the same, respectively, in the first stage. In the second stage, the dislocation density, dislocation arrangement parameter, and crystallite size remained constant.