Electrodes of any class used for welding quenched and tempered steels shall have a diffusible hydrogen content not exceeding what?

• A. H4 (4 ml of diffusible hydrogen per 100 g weld metal)
• B. H2 (2 ml per 100 g weld metal)
• C. H6 (6 ml per 100 g weld metal)
• D. H8 (8 ml per 100 g weld metal)

Answer: (A)

The key idea is preventing hydrogen-induced cracking in quenched and tempered steels. These high-strength steels are especially sensitive to diffusible hydrogen in the weld metal, which can migrate and cause delayed cracking in the heat-affected zone. To minimize this risk, welding electrodes used on quenched and tempered steels must supply very low diffusible hydrogen. The acceptable limit is 4 ml of diffusible hydrogen per 100 g of weld metal, which corresponds to a low-hydrogen electrode category. Using electrodes with higher hydrogen content raises the risk of cracking, even with good welding practice and post-weld cooling. Keeping hydrogen down also goes hand in hand with proper electrode drying, storage, and appropriate preheat/interpass temperatures. So, the required limit is 4 ml per 100 g weld metal.