Abstract
The toughness of SUS 316L MIG weld metal was investigated in relation to the oxygen content, pass sequence, δ ferrite content and PWHT conditions, and also the effect of δ ferrite content on the hot crack susceptibility of the weld metal was discussed. (1) The toughness is greatly improved by decreasing oxygen content in the weld metal to about 50 ppm. The value of VE-269 reaches to as high as 15.2 kgf·m. (2) Welds with low oxygen contents can be attained by using rare-earths-bearing welding wires in a pure argon shield. (3) For preventing reheat embrittleness, decreasing δ ferrite content to about 1% and using narrow-gap MIG arc welding with 1 pass/1 layer are effective. (4) When the δ ferrite content is too high, the toughness of weld metal is deteriorated. This is because cracks propagate along the δ ferrite where precipitates of M23C6 produced by multiple welding thermal cycles are existing. (5) Decreasing δ ferrite content to about 1% is not so harmful to the hot crack resistivity of the weld metal so far as the contents of silicon, phosphorus and sulfur are sufficiently low. (6) Since PWHT deteriorates the weld metal toughness, it is desirable to be avoided. In the case that PWHT is required, the one at a relatively low temperature (about 600°C) is recommended.
