改进型热连轧精轧机组后段高镍铬工作辊表面剥落的原因

Surface Spalling Causes of Working Roll with High Cr and Ni in Rear Unit of Hot Rolling Finishing Mill

某热轧厂精轧机组后段改进型高镍铬工作辊表面接连发生剥落事故,经过对剥落工作辊进行现场调查和剥落断口、显微组织、夹杂物、微观断裂特征等分析,查找工作辊剥落的原因。结果表明:一方面,轧钢过程中F7机架易发生甩尾事故,造成工作辊辊面易产生微裂纹,如果不能及时换辊或者修磨彻底,该微裂纹就会成为疲劳源,引起剥落;另一方面,剥落工作辊中碳化物尺寸较大,起到类似夹杂物的作用,而由于微裂纹沿碳化物边界或者穿过碳化物内部扩展的速度较快,故形成剥落;改善工作辊基体组织、碳化物形态和使用与维护条件,提高工作辊抗疲劳和热冲击能力,并杜绝残留裂纹,是防止工作辊出现剥落事故的有效途径。

The spalling on the surface of improved high Ni and Cr working rolls happened continuously in the rear unit of a hot roiling finishing. The causes of spalling were found out by site investigation, and analyes of fracture, microstructure, inclusion and fracture characteristics. The results .show that the tail-out accident easily happed on F7 stand to result in microcracks on the surface of working roll, and the microcracks would be crack source to cause spalling if the roll was not changed or was poor ground. The carbides in working roll was fairly big in size and acted as inclusions, and the mierocracks propagation rate along carbide boundaries or across carbides was fairly fast to cause spalling. The effective ways to prevent accidental spalling were improving the working roll matrix structure, carbide morphology, use and maintenance conditions, increasing the fatigue and thermal-shock resistance ability, and completely eradicating the remained cracks.