Hydrogen-Induced Cracking of Steels Under Wet Hydrogen Sulfide Environment

The hydrogen induced cracking (HIC) of as-rolled steels has been investigated. The specimens were immersed into the synthetic sea water saturated with H₂S. Since the cracks initiated at the elongated MnS particles, the HIC susceptibility decreased with decreasing sulfur content. It was, however, often observed that the HIC occurred even in the steels containing extremely low sulfur. These cracks propagated along an anomalous structure, which consisted of low temperature transformation products. Such an anomalous structure arose from the segregation of manganese and phosphorus during the solidification of steels. As to the controlled-rolled steels, the effects of texture, residual strain, and the shape of inclusions on the HIC were examined. It was revealed that the rolling at lower temperature did affect the HIC susceptibility with elongating the sulfide inclusions, while little effect of controlled rolling was recognized in the extremely low sulfur steels. It was also demonstrated that the addition of small amount of copper markedly reduced the amount of hydrogen absorbed. This could be due to the interface reaction between steel and wet H₂S environment. As the application of the foregoing results, the steel highly resistant to the HIC under the present experimental environment has been developed.