engleski

The susceptibility to sulphide stress cracking of low alloy steels

The susceptibility to sulphide stress cracking (SSC) of low alloy Mn-V and Cr-Mo-Nb steels in standard NACE solution was determined. The critical stress (Sc) and threshold stress of steels were determined in both as-received and heat treated condition. In the as-received state the steel shows a highly susceptibility to SSC domimantly due to its microstructure. By quenching and tempering of steels at high temperature the SSC resistance was increased. It was found that susceptibility to SSC for Cr-Mo-Nb steel is lower than that of Mn-V steel at a comparable yield strength. It was explained by the presence of different second phases in the ferrite matrix and spheroidized carbide particles resulting from the higher tempering temperature. In addition to Fe3C, the presence of Cr2C3, Mo2C and NbC in the ferrite matrix of Cr-Mo-Nb steel play an important role in their resistance to SSC. In all cases tested was Sc>threshold stress which suggests of the importance of plastic deformation during the test. The microfractographic analysis of specimens before and after SSC testing have been done. Occurence of cracks in the near outer surface of non-failed tensile specimens during 720 hours test suggested that SSC could be explained as a combination of hydrogen-induced cracking (HIC) and stress corrosion cracking (SCC).

Mechanical properties; microstructure; low alloy steels; sulphide stress cracking

nije evidentirano