POST WELD HEAT TREATMENT OF MARTENSITIC STAINLESS STEEL

摘要

Submerged arc welding of martensitic stainless steel layer has become a common practice to improve the in-service behaviour of continuous caster rolls. The combination of good corrosion and wear resistance provides excellent performance. The welding process and following post weld heat treatment affect the final microstructure, particularly secondary Cr carbides precipitation which causes a general loss of corrosion resistance. This effect is particularly striking in overlap weld regions where thermal cycling and long term exposition to aggressive environment promote a faster degradation by corrosion and thermal fatigue. The selection of the proper stainless steel grade is a decisive factor looking at improved service life. Special grades were developed in order to reduce the risk of sensitization. On the other side, the heat treatment strategy may also play an important role. In this paper the possibility to redissolve carbides precipitating during welding is evaluated. The efficacy of solubilization is evaluated by relatively short induction treatment carried out in a dilatometer. Samples were rapidly heated up to 1065°C and quenched at 1, 5 and 10°C/s. Microstructural analysis after suited electrolytic etching with oxalic acid revealed different extent of precipitation. The largest part of carbides precipitated at the δ ferrite-martensite interface where corrosion was clearly localized. The influence of tempering was also evaluated, carrying out treatments at different temperatures (420-620°C) and for different times.