Effects of post-weld heat treatments in microstructure, mechanical properties, and corrosion resistance of simulated heat-affected zone of supermartensitic steel UNS S41426

Abstract

Supermartensitic stainless steel (SMSS) UNS S41426 is an extra-low carbon steel with 12–13%Cr-5%Ni-2%Mo (%wt.) and microadditions of Ti and V. This material offers an interesting combination of mechanical and corrosion resistance. Although the weldability was improved in relation to conventional martensitic steels, due to the drastic reduction of carbon content, post-weld heat treatments are still necessary to decrease the hardness of the heat affected zone (HAZ). The UNS S41426 is used to manufacture mandrels for chemical products or gas injection in the well in the oil and gas off-shore production. Those mandrels are constructed with forged parts and hot rolled seamless pipes joined by welding. The microstructure, hardness, toughness, and sensitization of simulated HAZ of SMSS UNS S41426 forged and hot rolled were investigated. The effect of single tempering at 650 °C for 5 min and at 620 °C for 1 h, as well as double tempering (670 °C/2 h + 600 °C/2 h), was analyzed. The short duration tempering treatments did not change considerably the microstructure, but provoked an undesirable decrease of toughness. The single tempering for 1 h and the double tempering promoted more important microstructural changes, accompanied by the decrease of hardness and the increase of the degree of sensitization.