Anomalous distribution in atom map of solute carbon in steel.

The distribution of carbon in atom probe tomography maps was investigated in various phases of steel. Carbon atoms in 3D atom maps of martensite and cementite phases showed an almost uniform distribution. On the other hand, carbon atoms in ferrite were consistently enriched along the zone line joining the (0 0 2) and the (2 2 2) poles, and in the depth direction of analysis, which was different from the actual distribution. The width and concentration of the enriched regions remained unchanged at a specimen temperature ranging from 90 to 30K. Moreover, the ratio of molecular carbon ions to total carbon ions decreased with decreasing temperature, but did not change between the enriched and diluted regions. Based on the results, the reason for the anomalous distribution of solute carbon atoms in atom maps is discussed.