Studies on Hydrogen Assisted Cracking Susceptibility of 2.25Cr-1Mo Steel Weldments

Abstract

Hydrogen Assisted Cracking Susceptibility of 2.25Cr-1Mo steel was studied using UT-Modified Hydrogen Sensitivity Test (UT-Mod. HST). Welding was carried out using GTAW process and hydrogen was introduced into the weld metal by mixing it with argon shielding gas. Autogenous bead-on-plates were made on specimens fixed on a copper fixture and the specimens were strained for 4% strain immediately after welding for 24 hrs and checked for cracks. Preheating during welding was achieved by heating the copper fixture and the minimum preheat temperature required to prevent cracking for known vol.% of hydrogen in the shielding gas found out. Diffusible hydrogen content (H₀,) in the specimen prepared under identical conditions employed for testing was measured using Gas Chromatograph Weld cooling cun/es were obtained by plunging a thermocouple into the molten weld pool and cooling time (t_8/5)was estimated from the curves. Variation in weld metal hardness and microstructure was also studied. The results showed that both minimum preheat temperature and (H₀) content increased with hydrogen in the shielding gas. Preheating results in reduction in (H₀) content but does not affect the hardness indicating that cracking is prevented due to reduction in (H₀) content in the weld prepared with preheating. The results show that it is possible to choose an optimum preheat temperature to prevent cracking if (H₀) level in the weld is known.