Stress corrosion cracking of laser-welded stainless steels

Abstract

Autogenous welded specimens of austenitic (S30400 and S31603), duplex (S31803) and super duplex (S32760) stainless steels were fabricated by laser penetration welding (LPW) with a 2.5-kW CW Nd:YAG laser in an Ar atmosphere. The phases present in the welded zone of the laser-welded specimens were analyzed by X-ray diffractometry. The pitting corrosion and stress corrosion cracking (SCC) of the stainless steels in the laser-welded and unwelded conditions in 6% FeCl3 solution at 25 ◦C was studied by immersion test and spring-load SCC test. From the results of immersion test, corrosion rate of the laser-welded specimens are higher than that of the unwelded specimens. It is not only due to the pre-cracks and δ-ferrite in the weld zone which act as the active sites for corrosion, but also the large area ratio of anode and cathode resulting in strong galvanic effect. The SCC resistance of the laser-welded stainless steels in 6%FeCl3 solution is also lower than that of the unwelded specimens. The SCC susceptibility of the unwelded specimens is consistent with the pitting resistance ranking of stainless steels, i.e. super duplex and duplex stainless steels are more resistant than the austenitic stainless steels. However, laser-welded S31803 has lower SCC resistance than the laser-welded austenitic stainless steels because the highest ferrite content in the former is the most sensitive to SCC.