Implant Weldability Testing for Steels in Underwater Wet Welding

Abstract

For the purpose of estimating susceptibility of steels to cold cracking in underwater wet welding, implant weldability tests (Test piece: 8 mmφ, 0.5 mm (40°, 0.10 mmR) helical V-notch) for underwater welds were conducted, while diffusible hydrogen evolved from weld metal was measured according to the method specified in JIS Z 3113-1975.
The test welding (Bead welding in flat position) was carried out at a depth of 20 cm in fresh water by using a plasma arc as a source of heat. No filler metal was supplied.
Theresultsaresummarizedasfollows:
1) The under water weld just after solidification was estimated to contain diffusible hydrogen of the level of some 9.4ml/100g of weld metal (Collecting medium: Glycerin).
2)For the lower critical stress (σcr)imp (below which cracking does not lead to complete rupture of the implant) to exceed the yield point σY of the base metal, it was required that cooling time from peak temperature to 100°C, S(P-100°C), during undcrwater welding was over
2-1) 23 sec for a JIS-SM41A steel (PCM specified in WES-3002A-1973: 0.21%, C: 0.15% and σY: 31 kgf/mm²),
2-2) 35 sec for SM41A steel (PcM: 0.28%, C: 0.24% and σY: 30kgf/mm²) and
2-3) 100 sec for a SM50B steel (PCM: 0.24%, C: 0.16% and σY: 38kgf/mm²).
3) At a fixed time of S(P-100°C), (σcr)imp's of steels under water were higher tha n those in air because of lower hardness in coarse-grained regions of underwater welds.