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

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.