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我们用光学显微镜、电子显微镜和冲击-疲劳试验机研究了高强度马氏体钢30CrMnSiNi2A的组织、塑性变形、微裂纹形成和疲劳无裂纹寿命。实验结果表明,30CrMnSiNi2A钢经油淬和马氏体区等温淬火,其组织主要是板条状马氏体。在疲劳裂纹顶端塑性区内观察到所谓的“形变浮凸”;形变浮凸的位向和尺寸与马氏体板条的位向和尺寸有着严格的对应关系。据此,可以认为,形变浮凸的形成是马氏体板条相互滑动的结果;马氏体板条的相对滑动是板条状马氏体组织塑性变形的一种重要模型。当马氏体板条间的滑动量超过某一极限值时,将沿马氏体板条间界开裂而形成微裂纹。残留奥氏体的薄层夹在马氏体板条之间,会使马氏体板条易于滑动,因而降低钢的屈服强度,促使微裂纹形成,缩短疲劳无裂纹寿命。切口根部的局部予应变对疲劳无裂纹寿命有巨大的影响;反向予应变缩短疲劳无裂纹寿命。正向予应变则大大延长疲劳无裂纹寿命。
We studied the microstructure, plastic deformation, micro-crack formation and fatigue crack-free life of high-strength martensitic steel 30CrMnSiNi2A using optical microscope, electron microscope and impact-fatigue testing machine. The experimental results show that 30CrMnSiNi2A steel is austempered by oil quenching and martensite, and its structure is mainly lath martensite. The so-called “deformation relief” is observed in the plastic zone at the top of the fatigue crack; the orientation and size of the deformation relief are in strict correspondence with the orientation and size of the martensite lath. Accordingly, it can be considered that the formation of deformation and embossment is the result of the mutual sliding of the martensite laths; and the relative sliding of the martensite laths is an important model for the plastic deformation of the lath martensite. When the amount of sliding between martensite laths exceeds a certain limit, cracks will form along the martensite laths to form microcracks. The thin layer of retained austenite sandwiched between the martensite lath makes the lamella of martensite easy to slide, thereby reducing the yield strength of the steel, promoting the formation of micro-cracks and shortening the fatigue-free crack-free life. Local pre-strain at the incision root has a huge effect on fatigue-free crack life; reverse pre-strain shortens fatigue-free crack-free life. Forward to strain is greatly extended fatigue-free crack life.