Friction stir welding of thick section reduced activation ferritic-martensitic steel.

Full penetration friction stir welding was conducted on 12 mm thick reduced activation ferritic-martensitic steel at tool rotational speeds of 500 and 900 rev min⁻¹. Comparator welds at 500 rev min⁻¹ were also produced in 6 mm thick reduced activation ferritic-martensitic steel plate to evaluate section thickness effects. Increase in section thickness led to an increase in heat input, which strongly influenced the microstructure evolution in stir zone (SZ), thermo-mechanical affected zone and the overall hardness in the SZ of this steel. In the as-welded condition, the base metal microstructure was significantly altered and resulted in carbide-free grain boundaries. The desirable microstructure and mechanical properties were achieved by subjecting the as-welded joints to appropriate post-weld heat treatments. [ABSTRACT FROM AUTHOR]