Duplex and super duplex stainless steels are applied in a variety of industries. It has been demonstrated in practice that hydrogen cracking in duplex stainless steel weldments may occur where hydrogen potential and ferrite level are relatively high and sufficient stress is applied. It remains however process and consumable dependent.

Apart from hydrogen in the consumables or base materials, potential sources for weldmetal hydrogen are moisture in the shielding gas, the gas supply system and the welding environment.

In addition, the weldmetal hydrogen level is affected by welding parameters.

By means of this investigation, an attempt is offered to contribute to the understanding of factors influencing the hydrogen content in duplex stainless steel GTAW and GMAW weldments as well as to what extend it affects the hydrogen induced cracking susceptibility.

Hydrogen content in GTA and GMA welds have been determined using standard 22%Cr duplex and 25%Cr super-duplex wires. GTA wires in diameter 2.4mm were welded with Argon and Argon + 30%Helium shielding gas with heat-input (HI) varying from 0.9 to 2.6 kJ/mm.

For 1.2mm GMA wires, Argon + 2%Oxygen and Argon + 2%Carbon dioxide shielding gases were used and welding was performed with HI ranging from 0.8 through 1.3 kJ/mm.

The applied shielding gas moisture level has been varied from 'as supplied' up to 1000 ppm.

Hydrogen determinations were performed using the encapsulation technique in an evacuated quartz glass capsule. After heating the capsule for 72 hours at 400°C, the hydrogen content has been determined at ambient temperature using a gas chromatograph. As a recent Group Sponsored project at TWI indicated that significant levels of hydrogen might remain in the sample after applying the encapsulation technique, all samples were re-analysed at 900°C.

The effect of welding parameters, type of shielding gas and shielding gas moisture level on hydrogen content in weldmetal has been identified for duplex and super duplex GTA and GMA welds.

Susceptibility to hydrogen cracking has been determined using a 3-point bend test for 24 hours, maintaining a 12% strain in the weld on specimen welded with conditions rated as most critical: being high ferrite, high shielding gas moisture (1000 ppm), low heat-input, high hydrogen level and an increased restrain level.

Results indicated that susceptibility for hydrogen cracking, using the GTA or GMA process appears to be limited. In practice, a guaranteed moisture level of max 10 ppm in the shielding gas is of less importance than applied welding parameters. Even a moisture level of 1000 ppm in shielding gas in combination with correct welding parameters will result in a sufficient low hydrogen content in the weld, which questions the 10 ppm moisture requirement to the gas supplier. A maximum of 10 ppm moisture in shielding gas however, does not necessarily result in low weldmetal hydrogen contents. Although very high ferrite levels were combined with high restrain and high hydrogen content, none of the GMA and GTA welds cracked.

Susceptibility to hydrogen cracking is concluded to be limited.