New Empirical Formula for Estimation of Hardenability from Chemical Compositions

The accuracy of GROSSMANN'S equation, which has been widely used for calculation of the hardenability of a steel, is not always satisfactory in paticular in the case of B-added steels. We found out that this problem arose from the fact that the GROSSMANN'S equation was not always formulated rationally. In this work, an investigation has been made to obtain the new empirical formula for estimating the hardenability in place of GROSSMANN'S equation.The results are as follows :The hardenability of a steel can be predicted acculately by the following equations.(1) In the case of a B-added steel (free-B≥5 ppm)log Vc-90=2.94-0.75ββ(%)=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo where, Vc-90 is the critical cooling velocity (°C/s) at which 90% martensite structure can be obtained.(2) In the case of a B-free steel.log Vc-90=3.69-0.75β'β'(%)=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+MoThose results show that the effect of Mo in B-free steels is a half of that in B-added steels and the effect of B itself is equivalent to 1%Mn addition.