Some observations on the effect of heat treatment on stress corrosion cracking of Hardenable Steel

Martensitic stainless steels when heat treated to very high strength level have been known to be susceptible to stress corrosion cracking under substantially milder corrosive conditions, such as marine or semi-industrial atmosphere. The heat treatment, type of corrosive environments, etc. have been found to have a great influence on the cracking time. In the present paper the authors discuss the effect of tempering temperature and hardness level on the stress corrosion behaviour of 12% chromium stainless steel on the basis of tests carried out by them and the results reported in literature. Tests were conducted in acidic chloride solution containing H2S, which promotes entry of hydrogen into the steel. In such media tempering temperature was found to be very important as regards the susceptibility to cracking. Steels tempered above 600°C was found to be immune to cracking. Maximum susceptibility was found for steels tempered at temperatures between 400 and 500°C. The results have been discussed on the basis of changes in physical properties, the type of precipitated carbides and hydrogen embrittlement. (Dr. A.K. Lahiri, Scientist; Dr. T. Banerjee, Scientist; Dr. B.R. Nijhawan, Director; National Metallurgical Laboratory, Jamshedpur)