Core Hardenability Calculations for Carburizing Steels

Abstract

Analytical expressions are presented which allow the calculation of an ideal critical diameter (D₁) and a Jominy end-quench hardenability curve for a steel from its chemical composition and prior austenite grain size. The expressions are based on alloy hardenability factors in the literature and on the previously unpublished “hardness drop” method of determiningD, from end-quench hardenability curves. Relationships defining Jominy curve shape as a function ofD _I are developed. These differ from similar relationships previously published by recognizing that, for steels of low to medium hardenability, the microstructure contains significant amounts of non-martensitic transformation products even at the prescribed first position of hardness measurement on the end-quench hardenability bar, 1.59 mm (1/16 inch) from the quenched end. The analytical expressions presented are particularly well suited for the calculation ofD _I and end-quench hardenability curves for boron-free carburizing steels containing 0.15 to 0.25 pct carbon.