Effect of Heating Rate on Martensite to Austenite Transformation Kinetics in Supermartensitic Stainless Steel Weld Deposit

Abstract

The supermartensitic stainless steels (SMSS) have a better combination of weldability, toughness and corrosion resistance than conventional martensitic and duplex stainless steels. Nevertheless, for both base material and weld deposit, heat treatments (inter-and sub-critical tempering) are required to control the resultant microstructure. A tempered martensite microstructure with a high content of reformed austenite, obtained after a post-weld heat treatment, improves the properties of SMSS weld deposits. The comprehension of austenite formation during post-weld heat treatment in weld metal deposits is a key aspect to predict the final properties. In the present work, the transformation kinetics of martensite into austenite in SMSS all-weld metal deposit was studied by dilatometry, considering the effect of the heating rate (1, 10 and 100 °C/s). In addition, the austenitic transformation kinetic was modeled by a sigmoidal equation. The increase of the heating rate increases Ac1 and Ac3 and reduces the range of the transformation (Ac3–Ac1) from 120 to 80 °C. The maximum transformation rate reached values of 0.023, 0.018 and 0.019 1/°C for 1, 10 and 100 °C/s, respectively. Thus, the maximum transformation rate was reached for the slowest heating rate. Nevertheless, the average transformation rate increased as a function of the heating rate. This could be associated with a change in the transformation mechanism.