Tempering behavior of iron-carbon sputter deposits with 0 to 5 wt pct C

Iron-carbon sputter deposits with 0.06, 0.18, 0.66, 2, 3, and 5 wt pct C were tempered at temperatures from 100° to 550°C. The 0.06, 0.18, and 0.66 wt pct C sputter deposits were similar to severely cold-worked martensite, both as-deposited and in tempering response. Specifically, these three deposits were much harder than water quenched steels of the same composition, and the deposit hardnesses decreased less than martensite hardnesses on tempering below 400°C. The hardnesses of the 2 and 3 wt pct C deposits increased 40 to 50 Dph units upon tempering at low temperatures (150° to 250°C) and decreased for higher tempering temperatures. The hardness of the 5 wt pct C deposit remained constant (920 Dph) after tempering at 150°C, but increased to 1170 Dph upon tempering at 250°C when monoclinic Hägg carbide (Fe₅C₂) formed. Cementite (Fe₃C) was the only other carbide detected in the tempered deposits, and it formed only at 475°C and above. The columnar grains of the sputter deposits transformed to equiaxed grains upon tempering above 250°C. This change in grain structure was due to recovery and not recrystallization. Some grain growth occurred in the 0.06, 0.18, 0.66, and 2 wt pct C deposits above 300°C, but the grain size of the 3 and 5 wt pct C deposits remained submicron. The hardnesses of the deposits after tempering at 550°C increased with carbon content, the 5 wt pct C deposit having the highest hardness (960 Dph) and the 0.06 wt pct C deposit the lowest (360 Dph).