Novel Method for Predicting Hardness Distribution of Hot-Stamped Part Using FE-Simulation Coupled with Quench Factor Analysis

Abstract

In the hot stamping of boron-alloyed steel, the mechanical properties of hot-stamped parts have been predicted by many empirical models based on Kirkaldy’s equation. Although these models are skillfully developed, there is still a need to precisely and easily predict the mechanical properties in the hot stamping process. Therefore, this study aims to suggest a novel method for the accurate prediction of the hardness distribution of hot-stamped parts by the use of finite element (FE)-simulations coupled with quench factor analysis (QFA). First, dilatometry of boron steel was performed at various cooling rates from 0.5 to 70 K/s using a dilatometer with a forced-air cooling system. The dilatometry test provided hardness data according to the cooling rates, which were used to determine the material constants (K 1 to K 5) of the QFA and the time–temperature–property diagram of boron steel. Then, FE-simulation of hot stamping was conducted to obtain the cooling curves for blanks with thicknesses of 1.2 and 1.6 mm. The extracted results from the FE-simulation were used to predict the hardness distribution of the hot-stamped parts using QFA. Finally, a hot stamping experiment was performed to verify the predicted results and to examine the effect of the blank thickness on the cooling rates of a hot-stamped part. The predicted hardnesses for the parts were in good agreement with the measured values, within a maximum error of 4.96 pct.