Hydrogen has a critical effect on the quality of weld deposits in steels. Under certain conditions, the presence of hydrogen results in cracking. Hydrogen induced cracking is also called underbead cracking, cold cracking, or delayed cracking. Cracking generally occurs at a temperature below 93°C (200°F) immediately on cooling or after a period of several hours. The time depends on the type of steel, the magnitude of welding stresses, and the hydrogen content of the steel weld and heat-affected zones (HAZ). Diffusion of hydrogen into the heat-affected zone from the weld metal during welding contributes to cracking in the HAZ.
To eliminate this problem, a low-hydrogen electrode was developed for shielded metal arc welding.
The main source of hydrogen in welding is from moisture, either from the base metal, the electrode coating, or from the shielding gases used in gas tungsten arc welding, gas metal arc welding, and flux cored arc welding. The elimination of moisture from
these sources is necessary to prevent the formation of underbead or delayed cracking. See LOW-HYDROGEN ELECTRODES.