UNS S32760无缝钢管热挤压裂纹原因分析及控制

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

分析超级双相不锈钢UNS S32760棒材在热挤压时产生裂纹的原因;采用金属间化合物特定的化学试剂、扫描电镜能谱分析,并结合超级双相不锈钢热力学相平衡图和TTT等温转变曲线等,分析产生σ金属间化合物的原因,进一步得出σ金属间化合物是超级双相不锈钢UNS S32760棒材在热挤压时产生裂纹的主要原因。调整冶炼、热挤压和热处理工艺后再次进行热挤压试验,发现超级双相不锈钢UNS S32760管体内外表面光滑,无裂纹、褶皮等缺陷,钢管综合性能达到标准和客户要求。

Investigated are the causes for cracking of the UNS S32760 super duplex stainless steel bar as occurr- ing 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 re- quirements as specified by applicable specification and the customer as well.