Investigation of the forming limit behavior of martensitic chromium steels for hot sheet metal forming

Abstract

A possible alternative to the established press hardening steel Usibor 1500 (22MnB5) are hot formed martensitic chromium steels. The combination of strength and ductility of the martensitic chromium steels can be adjusted to an extreme level. By this means conventional lightweight solutions can be enhanced and this leads to a more economical use of resources. Furthermore, the extreme strength combined with the higher ductility provides an extreme crash safety of the produced car body parts. Forming limit curves (FLC) are used to identify the forming capacity of the sheet material, so the production process can be designed to the limiting range. Conventional FLC recorded at room temperature do not adequately describe the forming capacity for hot forming as it strongly depends on temperature. Therefore, in this paper an experimental-numerical method for determining quasi-isothermal FLC at high forming temperatures is introduced, applied to the steel AISI 420C (X46Cr13) at 900 {\textdegree}C and compared to literature values of Usibor 1500.