Investigation of Causes for Hot-extrusion Cracking of UNS S32760 Seamless Steel Tube and Relevant Control Measures

Investigated are the causes for cracking of the UNS S32760 super duplex stainless steel bar as occurring during the hot-extrusion process.Also analyzed is the reason for development of the σ inter-metallic compound by means of specific chemical reagent for inter-metallic compound, and SEM-EDS as well as the super duplex stainless steel thermodynamic phase equilibrium diagram, and the TTT isothermal transformation curve, which further leads to the conclusion that the σ inter-metallic compound is the key factor responsible for development of the said cracking.Accordingly, the hot extrusion test is conducted again after adjusting the melting, hot extrusion and heat treatment processes.As a result, the hot-extruded UNS S32760 super duplex stainless steel tube possesses smooth inner and outer surfaces, and is free of defects like crack and folding, etc., having its comprehensive performance up to requirements as specified by applicable specification and the customer as well.