The purpose of the present study was to develop the optimum processing condition to improve sulfide stress corrosion cracking (SSCC) resistance for line pipe steels. The effects of alloying, slab
reheating temperature, water cooling pattern and coiling temperature on microstructure, hydrogen induced cracking (HIC) and SSCC sensitivities, and mechanical properties were analyzed. The mechanism of SSCC was studied by a dead weight tensile test as well as a constant elongation rate test method. The maximum contents of Mn and P showed the best relationship with the HIC sensitivity, and the mean contents of P and S were the secondary factor. The HIC and SSCC sensitivity of Nb-V-Ti added steels were better than those of Nb-V added steel. However, the addition of Cu and Ni that has been used to HIC resistant steels in the weak acidic solution (pH=4.8-5.4) was not helpful in the strong acidic
solution (pH=2.5-3.8). The HIC sensitivity was increased as
slab-reheating temperature (SRT) was decreased from 1250°C to 1150°C. The HIC sensitivity was increased due to the formation of coarse
ferrite grains as the cooling rate was reduced. Anodic or cathodic polarization at about +-100mV resulted in reducing the SSCC resistance, which was explained by a model related to anodic dissolution and
hydrogen embrittlement. The SSCC mode could be classified into stress corrosion cracking (SCC) and stress oriented hydrogen induced cracking (SOHIC) and the former that was formed in the lower strength steels showed lesser threshold strength level. The reason of SCC formation was attributed to the mixed grain structure and grain boundary film cementite. The SSCC resistance was superior when the acicular ferrite structure was formed. Key Words; HSLA steel, Line pipe steel, Hot strips, H2S gas, HIC, SSCC, CLT, SSRT, Hot rolling conditions