Abstract
During the development of the popular ultrahigh strength AF1410 steel, Machmeier, et.al., observed that a small variation in the chromium content had a significant improvement on the toughness of the steel in the quenched and tempered condition. The present TEM study was directed at examining the microstructural basis for this toughness enhancement.The following samples of AF1410 type steels with two levels of chromium were examined: Steel A: 0.16%C, 10.02%Ni, 2.97%Cr, 1.21 %Mo, 13.74%Co and bal. Fe Steel B: 0.16%C, 10.15%Ni, 1.95%Cr, 0.98%Mo, 13.8% Co and bal. Fe. Steel A represents the composition of AF1410 while steel B had the same base composition except for 1% higher chromium.Figure 1 shows the strength and toughness of steels A and B when tempered in the range of 400-600°C. The yield strengths of the two steels were comparable over most of the tempering range; however, the toughness of steel B, measured by Charpy V notch impact test, was superior in the range of 482 - 538°C.
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