The resistance to stress corrosion of austenitic stainless steel alloyed with nitrogen (ASS N25) was determined in comparison with AISI 316L steel. The research into stress corrosion cracking was performed by using corrosion elongation curves in a 50% CaCl2 solution, at 100°C, under axial tensile loadings defined as various percentages of Rp0,2, and with anodic polarization at a current density of 1.0 mA/cm2. The increased resistance of the nitrogen‐alloyed steel to stress corrosion is based on the occurrence of NH4+ ions, and the repulsive action of the negatively charged nitrogen atoms towards the Cl− ions on the interface between the passive layer and the corrosion medium. Additionally, the interstitially dissolved nitrogen is able to accelerate the local deformation hardening of the material at the crack tip, for which reason the critical stress needed for stress corrosion to occur, or for further growth of the crack if it has already occurred, is increased.

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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 (σth) 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 dominantly due to its microstucture. By quenching and tempering of steels at high temperature the SSC resistance was increased. It was found that the 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 Cr3C2, 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>σth which suggests of the importance of plastic deformation during the test. The microfractographic analysis of specimens before and after SSC testing have been done. Occurrence 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).

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