New Developments and Future Trends in Low-Temperature Hot Stamping Technologies: A Review

Abstract

Improvement of the hot stamping process is important for reducing processing costs and improving the productivity and tensile properties of final components. One major approach to this has been to conduct all or part of the process at lower temperatures. The present paper reviews the state of the art of hot stamping techniques and their applications, considering the following aspects: (1) conventional hot stamping and its advanced developments; (2) warm stamping approaches in which complete austenitisation is not attained during heating; (3) hot stamping with a lower forming temperature, i.e., low-temperature hot stamping (LTHS); (4) advanced medium-Mn steels with lower austenitisation temperatures and their applicability in LTHS. Prospects for the further development of LTHS technology and the work required to achieve this are discussed.

Influence of Quenching and Partitioning Parameters on Phase Transformations and Mechanical Properties of Medium Manganese Steel for Press-Hardening Application

“…Consequently, this allows a more robust process control and, in addition, a significantly lower austenitization temperature. In comparison to manganese boron steels, the austenitization temperature of medium manganese steels can be lowered by 100-200 °C [15], which is associated with considerably reduced energy consumption [16]. Furthermore, the lower austenitization temperature leads to a comparatively finer microstructure, which positively influences both the strength and the ductility of the material, respectively [17].…”

Recent Progress of Low and Medium-Carbon Advanced Martensitic Steels

“…The hot-stamping process considerably reduces the spring back of the products, differing from the cold-stamping process [120]. As the process suppresses the hydrogen embrittlement due to lowering the residual stress, hot-stamping steels such as DIN-22MnB5 and 30MnB5 steels are applied to automotive center pillars with the tensile strength of 1.5 to 1.8 GPa [120,122]. The matrix structure after die-quenching is almost martensite.…”

“…Recently, warm-stamping at temperatures above M s are developed to improve productivity and reduce manufacturing costs [122][123][124][125] (Figure 16). In the warm-stamping, the blank is austenitized at temperatures above Ac 3 , in the same way as the conventional hot-stamping process.…”

“…By this warm-stamping, the blank is strain-hardened along with the improvement of the drawability and formability. In addition, productivity can also be increased by shortening the cooling cycle time and decreasing the oxidation [122]. At present, the warm-stamping at 450 to 500 • C is applied to the B-pillar of (0.08-0.2)%C-(4.0-7.0)%Mn D-MMn steels, not M-MMn steel [125].…”

Investigation of austenitising behaviour of medium-Mn steel in the hot-stamping heating process

“…In particular, the addition of Mn (3-10 wt.%) to the material decreases both the lower (Ae1) and upper (Ae3) temperatures of the austenite transformation under equilibrium conditions with respect to those of boron steels, allowing the blanks to be austenitised at lower temperatures. This enables the use of low-temperature hot stamping (LTHS), which is defined as a hot stamping process whereby full austenitisation is attained in the soaking stage while stamping takes place at a lower temperature than in the conventional case (Tong et al, 2020).…”