Improvement of Hardenability of Steel Containing Aluminum and Boron by Double Quenching

Hardenability increasing effect due to B was studied for low alloy steels treated with Al-B (0.06-0.08%Al-0.0010%B). The quench hardenability was found to be markedly improved by double quench. The mechanism of the increased quench hardenability by the double quench was studied by means of a fission track etching technique. It was shown, in the double quench, that a quenching from 1 000°C for 1hr prior to the 2nd quench gave rise to excellent hardenability which could not be attained by a single quench. The role of the 1st quench is to obtain the optimum amount of soluble B in matrix. A combination of the Al-B treatment and the double quench is a reliable method to maximize the hardenability increasing effect of B in low alloy steels.