This paper presents a method for calculating quench severity based on hardness profile matching. The new method has the potential to eliminate the need for Jominy end-quench testing as required in the traditional Kern approach. To assess the accuracy of the proposed method, a test bar and Jominy bar were machined from 2-in. bar stock and heat treated in accordance with ASTM A255. The test bar was quenched in a draft-tube system with a water velocity of 6 ft/s. An excel workbook was programmed to calculate the quenched hardness profile based on prior austenite grain size and steel chemistry. The calculations were in good agreement with measured Jominy hardness as were the quench severities determined by the Kern method and the proposed hardness profile matching technique.

A method of predicting tempered hardness of mixed microstructures has been formulated, which uses the quenched hardness and steel chemistry as independent variables. This calculation is based upon a method first proposed in 1947 by Crafts and Lamont for mixed microstructures and modified using the 1977 chemistry-based, tempered martensite hardness calculation of Grange, Hribal, and Porter. Tempered hardness predictions were examined using Jominy end-quench bars tempered between 204°C (400°F) and 649°C (1200°F). The measured Jominy hardness after tempering was used to make adjustments to the Crafts and Lamont parameters used in the hybrid model. Both plain carbon (SAE 1045) and low alloy (SAE grades 8620, 4130, 4142, and 5160) were used to evaluate the chemistry-based hardness prediction. In combination with a ASTM A255 Jominy hardenability calculation, the proposed calculation can be used to predict the quenched and tempered hardness profile of a round bar based upon chemistry, quench severity, and tempering temperature.