Role of microstructure and testing conditions in sulphide stress cracking of X52 and X60 API steels

The resistance of X52 and X60 API steels to sulphide stress cracking (SSC) was tested by tensile tests at a constant load and also by slow strain rate tensile (SSRT) tests. Both steels were tested after hot-rolling, when they had a microstructure which consisted predominantly of ferrite and pearlite. They were then tested after laboratory quenching and tempering, when their microstructure was predominantly of tempered bainite or martensite. The results showed that the resistance of the steel to SSC depended strongly on the microstructure when it was tested under a constant load. In this case, the quenching and tempering considerably increased the resistance of the steel to SSC. The results of SSRT tests were similar regardless of the heat treatment used. Non-metallic inclusions seemed to play an important role as crack initiation sites during the SSRT tests; this may be due to the hydrogen-deformation interaction. The resistance to SSC varied as a function of the specimen's orientation during the SSRT tests. This may be related to the geometric characteristics of the non-metallic inclusions.