The effect of sigma phase formation on the corrosion and mechanical properties of Nb-stabilized stainless steel cladding

The formation of sigma phase in Nb-stabilized austenitic stainless cladding containing 9-10 % delta ferrite has been studied. The delta ferrite was found to decompose during stress relief heat treatments (10-600 h at 670 °C) forming sigma phase and secondary austenite. The effect of sigma phase on mechanical properties was evaluated by using tensile, impact and COD-tests. Corrosion properties were studied with the aid of anodic polarization measurements and EPR-tests. Slow strain-rate tests in 1N HCl and 0.58N H3BO3 solutions were used to study stress corrosion cracking. Hydrogen embrittlement tests were performed by charging thin tensile specimens with hydrogen through cathodic polarization