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 采用光学金相显微镜、超声波探伤和力学性能测试等方法对Cr5支承辊大面积剥落的原因进行了分析。宏观断口和探伤结果表明，该轧辊的剥落面经过了一段疲劳延伸过程，裂纹由硬化层底部起源，沿轧辊圆周，逆轧制方向发展。剥离块为辊身的硬化层，硬化层外表为马氏体，中部为索氏体，硬化层的底部组织为屈氏体。轧辊辊身传动侧存在的轧辊制造问题和热处理工艺不当是该次剥落的原因。

Cracking Failure Analysis of Back-up Roll of Cr5

Analysis of the surface spalling of back-up roll Cr5 was carried out using optical microscope,ultrasonic probing and mechanical property testing.The macroscopical fracture analysis and probing results show that the roll underwent a fatigue extending process.The crack began at the bottom of the hardening layer,followed the roll's circumference,and reversed its rolling direction.The fragment fell from the roll is the hardening layer,and the micrograph of its surface,its middle area and its bottom are martensite,sorbite,and troostite respectively.The reasons of the failure are the manufacturing defect in the wok side of the roll,as well as its improper heat treatment process.