Metallurgical Change of SM-type Steels during Underwater Wet Welding

Abstract

Transformation behavior of coarse-grained regions during underwater wet welding and some resulting characteristics were investigated by comparing with those of welding in air.
JIS-SM type steels between SM41A and SM58Q were used as the base metal.
The results are summarized as follows:
1) Starting temperature of ferritic transformation during cooling of underwater wet welding is lower by about 20-25°C over the range of Ceq (JIS G 3106) from 0.33 to 0.41% and slightly lower for the Ceq of 0.44% than that during cooling of welding in air.
On the contrary, Ms is higher within the limit of some 30°C for the Ceq of 0.33%. The difference is gradually reduced as Ceq becomes still higher and hardly found for the Ceq of 0.44%.
2) For the amount of martensite between 50% and 10%, cooling time from 800 to 500°C during underwater wet welding is longer within the limit of nearly 90% than that during welding in air.
3) In case that the "coarse-grained regions near the center of bond" of an underwater wet weld and a weld in air contain the same amount of martensite, the "coarse-grained regions near the toe" of both the welds also contain almost the same amount of martensite.
4) In case that the coarse-grained regions of an underwater wet weld and a weld in air contain the same amount of martensite, no significant difference is found in their hardness.
5) In the same case as above, no significant difference is found in their elongation at crack initiation, too.