Fabrication strain rate-stress corrosion property correlations of thermomechanically treated 15Cr-15Ni-2-2Mo titanium modified austenitic stainless steel

Abstract

A 15Cr-15Ni-2.2Mo titanium modified austenitic stainless steel was thermomechanically worked to a strain of 30% in a single stage at temperatures between 873 and 1473 K and at strain rates of 0.15, 1.0, and 100S^-l. These strain rates were obtained by working the alloy in a hydraulic press, a rolling mill, and aforge hammer, respectively. At all strain rates, the yield strength (YS) increased while ductility and stress corrosion cracking (SCC) resistance significantly decreased on thermomechanically working the solution annealed alloy at temperatures below 1173 K. Thereafter, the YS decreased and ductility along with SCC resistance increased substantially towards valuesfor the solution annealed alloy on thermomechanical treatment at and above 1273 K. The highest ductility was obtained on working the alloy at a strain rate of less than 1.0 S^-l. However, the best SCC resistance was obtained on working the material at the highest strain rate of l00 S^-l. The improvement in SCC resistance has been attributed to the finer grain size obtained on working the alloy at higher strain rates. Fractographic examination indicated failure by transgranular SCC. The size ofthefan shaped patterns increased with increasing temperature of working, and decreased with increasing strain rate offabrication.