减震器吊环扩口开裂的原因分析

Analysis on flared crack reason of damper rings

20钢冷拔管经退火后进行喷丸、扩口成型,扩口时出现局部纵向开裂问题。采用体视显微镜、光学显微镜、SEM、EDS、显微硬度计等设备对20钢减震器吊环的断口形貌、非金属夹杂、显微组织、裂纹缺陷内部成分以及显微硬度进行分析与测试。结果表明:由于炼钢炉内壁保护渣剥落,在穿孔时心部组织形成裂纹缺陷,且在裂纹缺陷处存在增碳现象致使吊环的力学性能存在差异,加之管体退火后残余应力与扩口应力相互叠加致使裂纹发生扩展,减震器吊环外壁存在浅表层折迭缺陷,非金属夹杂与带状组织较为严重,也进一步促使钢管开裂。通过对减震器吊环失效原因的研究分析,不仅对其失效进行了有效预防,而且对这类性质的失效问题的研究具有指导和推广意义。

A partial longitudinal cracking phenomenon occurred after 20 steel cold drawn tubes were annealed,and then put through shot peening and flaring.By equipments of stereoscopic microscope、SEM、EDS、optical microscope and micro-hardness meter etc,the 20 steel damper rings were analyzed and tested on their fracture morphology,non-metallic inclusions,microstructure,cracks＇ internal components and micro-hardness.Results showed that due to the peeling of slag powder of inner wall in steelmaking furnace,cracks were formed in heart tissue during the perforation,and there were differences in the mechanical properties of rings resulting from the carburizing phenomenon.Besides,the mutual superposition of residual stress after quenching and flared stress eventually led to extended crack.There were shallow outer fold presences in damper rings,and the non-metallic inclusions and the banded structure were serious,which played a catalytic role on flared cracks.The research and analysis of the reason for the damper rings＇ failure can not only prevent its failure,but also are beneficial for providing guidance for this kind of failure problem.