Experimental Investigation on Partition Induction Heating of High‐Strength Boron Alloyed Steel Blanks

Abstract

To manufacture B pillars with tailored properties of car body‐in‐white, a new partition induction heating process for 22MnB5 blanks is proposed. After 30 s of heating, different temperature zones are formed on the blanks under the impact of two magnetizer shapes. The low‐temperature zone exists in the two‐phase zone, whereas the high‐temperature zone reaches the austenitic temperature. Different microstructures are formed in different temperature zones after the water quenching, as the mixed microstructures (F + M) appear in the low‐temperature zones, and 100% martensite is formed in the high‐temperature zones. As for mechanical properties, the ultimate tensile strengths in the low‐temperature zones with the presence of magnetic rings and sheets are 896 and 1038 MPa, corresponding to elongation rates of 18.6% and 17.4%, respectively. The tensile strengths in the high‐temperature zones are 1665 and 1654 MPa, corresponding to elongation rates of 16% and 16.4%, respectively. In contrast with the mechanical properties obtained in a conventional heat treatment, the new partition induction heating improves the tensile strength in the high‐temperature zones by more than 100 MPa as well as the ductility. These experimental results well underlie the subsequent experiments on randomly tailoring the low strength with higher ductility zones and shapes.