Effect of preheating and post heating in reducing diffusible hydrogen content and hydrogen assisted cracking susceptibility of modified 9Cr-1Mo steel

The hydrogen assisted cracking susceptibility of Modified 9Cr-1Mo steel weld is evaluated by implant test by determining lower critical stress for different preheating and combination of pre, post heating conditions. The diffusible hydrogen present in the implant specimens for different test conditions is estimated. Residual stress distribution in the weld for different heating condition is estimated using SYSWELD software. For a combination of pre + post heating at 200 degrees C, the diffusible hydrogen content of the weld comes down to 1.17 from 4.7 mL/100g and the lower critical stress of the implant specimen increases from 250 to 370 MPa. Preheating + post heating also brings down the peak tensile residual stress level in the weld joints and lowers the cracking susceptibility.