Tailored properties of hot stamping steel by resistance heating with local temperature control

Local austenization by local heating temperature control of blanks is one of the methods to obtain hot stamping parts with tailored properties. Resistance heating is a novel heating technology with high efficiency and rapid heating rate. In this paper, a heat transfer model was firstly developed to describe the steady temperature distribution of the blank during resistance heating. Then two resistance heating schemes to achieve tailored properties of hot stamping steel were investigated by experiments. One scheme is local resistance heating by adjusting the electrode position. And the other scheme is resistance heating with middle insulation. The results showed that the developed model could provide adequate accuracy in calculating the blank temperature field. For the local resistance heating, the percentage of high temperature region in heating zone was about 70 %. From the non-heating region to the middle heating region, hardness increased from 200 to 515 HV10. And the length ratio between high and low hardness regions could he controlled by adjusting electrode positions. For the resistance heating with middle insulation, a 340360 HV10 medium hardness region with the length of 80mm was observed. The total length of transition hardness regions was about 60 mm. In summary, the local resistance heating scheme showed more advantages including shorter transition region and significant hardness difference. (C) 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 17th International Conference on Metal Forming.