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The effects of Mn (0.5 to 1.1 pct), Mo (0.0 to 0.5 pct), Ni (0.0 to 1.5 pct) and Cr (0.0 to 1.0 pct) on retarding the formation of bainite in carburized steels were studied using 81 different alloy compositions. Jominy bars for all the alloys were carburized at 925 °C (1700 °F), cooled to 845 °C (1550 °F) and end quenched. Flats were ground on the bars to a depth corresponding to 0.9 pct case carbon content, hardness profiles were determined and the flats were metallographically examined to determine the distance from the quenched end of the bar at which bainite first forms, the so-called distance to first bainite (DFB). Multiple regression analysis was applied to the data to yield an empirical relation for DFB vs alloy content. An analysis of variance was also applied to the DFB data and revealed that those elements which have a statistically significant effect on retarding bainite formation are molybdenum (strongest effect), chromium (strong effect) and manganese (moderate effect). The effect of nickel is of borderline statistical significance and the weakest of all the elements. |
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