Columnar grain development in C-Mn-Ni low-alloy weld metals and the influence of nickel

This paper discusses the development of columnar grains in as-deposited C-Mn-Ni(-Mo) low-carbon low-alloy weld metals and the influence of the alloying elements, particularly nickel. It was found that the austenite columnar grain size prior to the gamma - alpha transformation of the weld metals was mainly controlled by the alloying contents rather than HAZ grains adjacent to the fusion boundaries, although the latter determined the size of the initial columnar grain size. The addition of nickel initially depressed the prior austenite grain size and subsequently dramatically coarsened it. This was related to the nickel equivalent (Ni sub eq ) of the weld metals and the peritectic reaction during the solidification process. Small columnar grains were associated with a Ni sub eq between 3.4 and 6.2% which resulted in a peritectic reaction when the weld melt solidified, while a Ni sub eq higher than 6.2% produced very large columnar grains because the weld pool would directly solidify into austenite and have a subsequent continuous growth.