Effects of carbon and chromium on block size of acicular ferrite in low carbon steel weld metals

The effects of carbon and chromium on the block size of acicular ferrite (AF) were investigated, focusing on cementite formation. Block size of the AF refined with increasing carbon content and coarsened with increasing chromium content. The effects of carbon and chromium on cementite size were inverse. The block size did not necessarily become finer with increasing yield stress of the γ-phase and driving force of the γ→α phase transformation. On the other hand, the block size became finer regardless of the carbon and the chromium content when the sympathetic/ autocatalytic nucleation frequency increased and the cementite size increased. This suggests that carbon depleted zone increased with cementite formation and promoted the sympathetic/ autocatalytic nucleation. The effect of the cementite formation on the number of the sympathetic/ autocatalytic nucleation sites were quantified. © 2022 Japan Welding Society. All rights reserved.