Structure formation at high rates of heating during welding of steels

Abstract

This paper deals with structure formation in weld joints of quenching steels 15Cr5Мo and 12Cr1МoV as made by “short cycle” argon-shielded welding as well as with the possibility of control of transformation and quality for weld joints by the thermodynamic cycle of welding. It is demonstrated that where the developed technology is applied, the weld metal is sound, defect-free, of martensitic-ferritic structure. In the weld-affected zone of steels at high heating rates and with short time of metal exposure to temperatures exceeding critical transformation temperatures in heating, non-uniform austenite of low homogeneity is formed, in which the carbide phase containing alloy elements undergoes partial dissolution. As a result, the austenite breakdown in cooling (in spite of high rates) takes place in the bainitic range as well as in the martensitic range. In the weld-affected zone of steel 12Cr1МoV, the bainitic structure predominates while the weld-affected zone of steel 15Cr5Мo shows the bainitic-martensitic structure mainly. During weld joint inspection by shock loading testing, the metal having the above structure experiences bending or ductile fracture. The process parameters were determined, with which structures of high brittle fracture resistance are formed. The technology developed was implemented in tube studding for manufacture and repairs of cooling panels; it is recommended for common use in industrial applications. Keywords: welding, quenching, thermodynamic cycle, argon, bainite, quality, application.