Pitting corrosion of laser welded stainless offshore steels

Laser weldability and pitting corrosion properties of four stainless steels were investigated. Three of them were austenitic stainless steels with varying molybdenym contents, (2.6 - 6 % Mo) and one is autenitic-femtic steel. The welds were made both autogenously and with the filler wire. For comparison, austenitic stainless steel with molybdenum level 2.6 % was plasma welded. Microstructure and microsegregation in the welds were analysed and compared. Pitting corrosion resistance was measured by pitting corrosions potentials in 1.0 N NaCl. The results show that pitting corrosion resistance in the welds studied is very much dependent on the composition, especially on the molybdenum content, as shown earlier in many references. The new results is that in laser welds the resistance to pitting corrosion is as good as the resistance of the base metal. Earlier it has been shown that in arc welding, like TIG or MIG welding, autogenous welds give worse resistance to pitting corrosion than base metal, especially in high-molybdenum welds. Now, mainly because of milder micro segregation, the resistance to pitting corrosion does not decrease, even if filler metal is not used.