Abstract
In a narrow gap arc welding process with one run per layer technique, the weld metal toughness greatly depends on that of as-dendritic structure, because of the reduced reheated zone compared with the central part of conventional multipass weld metal. With an emphasis on the improvement of asdendritic structure weld metal toughness, the effects of micro-alloying elements such as C, V, Ti, Nb on 2 1/4%Cr-1%Mo SA-weld metal toughness are investigated and the following results are obtained:
1) The increase of carbon content and V-addition are effective to improve the as-dendritic structure toughness by refinning the bainitic lath sub-structure from the higher hardenability and increasing carbon-nitrides precipitated uniformly within the grains after PWHT.
2) In 0.12%C-0.07%V bearing weld metal, the difference in toughness between as-dendritic structure and reheated zone is greatly reduced, resulting in homogeneous weld metal.
3) The addition of Nb and Ti is effective to increase the strength but deteriorates the weld metal toughness due to precipitation hardening.
4) The optimum chemistry of 2 1/4%Cr-1%Mo weld metal for a narrow gap SAW process is decided to be
C : 0.12% Cr : 2.25%
Si : 0.20% Mo : 1.0%
Mn : 0.70% V : 0.07%
P : ≤0.010% x : ≤15ppm
S : ≤0.010%
