Transformation behavior of heat-affected zone during underwater wet welding was investigated by comparing with that of welding in air.
Welding was carried out at a depth of 20 cm in fresh water by using a plasma arc as a source of heat and 19 mm thick plates of steel (JIS-SM41A and SM50B) as base metals, while synthetic heat-affected zone tests were conducted.
The attention was focussed on coarse-grained regions near the center of bond.
The results are summarized as follows:
1) For both of SM41A and SM50B, Fs temperature during cooling of underwater wet welding is lower by about 20°C and Ms temperature is higher within the limit of some 25°C than those of welding in air.
2) In order to equalize the amount of Martensite in an underwater wet weld with that in air, it is required for both of SM41A and SM50B that cooling time from A₃ to 500°C during underwater wet welding is longer within the limit of some 50 % than that during welding in air.
3) In case an underwater wet weld and a weld in air contain the same amount of Martensite, no significant difference in their hardness is found for SM41A and SM50B.
4) In the same case as above, however, cooling of underwater wet welding makes 50 % shear transition temperature of SM50B higher by about 10°C than that of welding in air.

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