UNS N08810无缝钢管冷扩(拔)裂纹的形成原因分析及控制

Analysis of Causes for Crack of UNS N08810 Seamless Steel Tube as Occurring during Cold-expansion(drawing) Process and Relevant Control Measures

介绍了UNS N08810管冷扩外径的工艺路线及主要工艺参数,通过光学显微镜、扫描电子显微镜、能谱分析仪并结合热力学曲线分析冷扩裂纹产生的原因.分析认为:管坯固溶温度较高,晶粒度级差大,非正常混晶,降低了钢的机械性能;脆性TiC在晶界形成大尺寸的TiC薄膜,给裂纹提供了一个低能扩展的通道,增加了裂纹产生的倾向.采用多道次大变形量冷轧,以及控制热处理工艺和冷却方式,可以有效地细化组织晶粒,减少扩拔裂纹的产生.

Described in the paper are the process path and major technological parameters of the cold-(OD) expansion process for the UNS N08810 seamless steel tube. Analyzed are the causes for cracks of the said tube as occurring during the cold-expansion process by means of optical metallographic microscopy, SEM , EDS and the thermodynamic curve. The analysis result reveals the facts as follows. The mechanical properties of the tube are weakened due to such factors as rather high solid solution temperature of the mother tube, big grain size differential, and abnormal mixed grain, etc. Large-sized TiC films are formed by brittle TiC particles in the grain boundary, which provides a channel for low-energy expansion, and thus increases the tendency of the cracking Accordingly taking such measures as multi-pass/large deformation cold-rolling, and well-controlled heat treatment process, and proper cooling method will get the microstructure grains refined so as to reduce the occurrence of the crack during the cold-expansion (drawing) process.