The influence of alloying elements on the rate of pearlite formation influences whether martensite will be formed when austenite is quenched because martensite can form only from austenite. If the formation of pearlite is delayed, more austenite will be available at the Ms temperature to transform to martensite. The term hardenability is used to describe this effect. We say that alloying elements increase the hardenability of steel, making it possible to harden them to greater depths.
Jominy End-Quench Test
Hardenability may be quantitatively described several ways. One of the simplest is the Jominy end-quench test in which a 4-in.-long, one-inch-diameter bar of the steel is austenitized and then placed in a fixture and cooled from one end with a specified water spray (Figure 13.1). The hardness is then measured as a function of distance from the quenched end. Figures 13.2 and 13.3 show the resulting curves for several steels.