Experimental investigation on partition controllable induction heating-hot stamping process of high-strength boron alloyed steel plates with designable temperature patterns

Abstract

For the purpose of manufacturing the automotive B-pillars with tailored properties, based on the proposed partition induction heating-quenching process, the partition controllable induction heating-stamping process of high-strength boron alloyed steel plates with designable temperature patterns is experimentally investigated. The temperature distribution of the various low temperature region patterns on the steel plates can be arbitrarily customized after heating for 30 s by properly arranging the magnetizer groups. Furthermore, the temperature field of the test B-pillar is customized. The temperature in the low temperature region of the heated B-pillar is 600 °C, which is lower than the start temperature of austenite transformation (AC1 = 750 °C), while the temperature in the high temperature region is 950 °C, which realizes fully austenization. After stamping and quenching, different microstructures are generated in the test B-pillar corresponding to the different temperature regions. The microstructures of the stamped test B-pillar in the low temperature region are mixture microstructures of ferrite + pearlite, while the fine lath martensite microstructures are transformed in the high temperature region. In terms of mechanical properties, the tensile strengths according to the low temperature region and high temperature regions are 438 and 1610 MPa, while the uniform elongation is 14.8% and 6.5% respectively, which meets the design requirements of the B-pillars with tailored properties. The specimens with a tensile strength difference ratio greater than 1: 3.5 and an elongation difference ratio greater than 1: 2.2 are obtained, which indicates the partition controllable induction heating-stamping process provides a new way to achieve automobile lightweight and significantly increasing the safety.