High‐Temperature Properties of High Mn Steel with Al, Si, and C

Abstract

In the automotive industry, greenhouse gas emission reduction and improvement of vehicle safety are the main goals. New materials are considered to contribute significantly to this aim. [1] In this respect steels combining both high strength and high ductility offer considerable benefits. Due to high strength, the sheet thickness can be reduced without loss of stability, thereby, a weight reduction is achieved. High ductility enlarges the degrees of freedom in the design of components. Furthermore, it yields high energy absorbing ability in a crash. A unique combination of high strength and ductility is provided by high manganese steel.The properties of high manganese steels result from different mechanisms, such as crystallographic slip, the transformation of metastable austenite to martensite (TRIP), [2] twinning (TWIP), [3,4] and nano size κ-carbide formation (TRIPLEX). [5] High Mn steel containing about 13 wt.-% Mn and up to 1.4 wt.-% C, first made by Sir Robert Abbott Hadfield in the 1880s, is famous for its high impact strength and resistance to abrasion. [6] By variation of the Mncontent from 5 to 30 wt.-% (medium to high Mn steels) and by alloying with Al, Si, and C the excellent mechanical properties of Mn steel can be further optimized and adjusted. The addition of Al and Si improves roomtemperature properties by adjusting stacking fault energy and it also reduces density. [5,7,8] Increasing C-content in a suitable range was found to increase both strength and ductility. [9] Microalloying with Ti, Nb, and V can be used to increase yield strength by precipitation hardening. [10] Thermomechanical treatment, e.g., by warm rolling at about 200 °C and subsequent annealing at 520-550 °C, adjusts deformation mechanisms and in this way the resulting properties. [11] Furthermore, properties can be adjusted by annealing, e.g., to control the carbide morphology. [12] Apart from the mechanical properties, various further aspects of high Mn steel properties have been investigated like crack formation mechanisms and the influence of hydrogen. [13][14][15][16] Hydrogen embrittlement and delayed fracture is a serious problem for certain highmanganese steels. Micro-segregation in high Mn steels can have a significant effect on the mechanical properties at ambient temperature. [17][18][19] Compared to fundamental aspects and the properties under application conditions, the behavior of high and medium Mn steels during production and processing has not found so much attention. The behavior during cold rolling has been investigated by Ofei et al. [20] The strain rate effect on the mechanical properties is important to adjust forming processes to the specific material and it is furthermore important for the crash performance in automotive applications. [21] For casting, [22][23][24][25][26] hot rolling, [27] and welding, [28,29] the hightemperature properties are of crucial importance and it is essential to ensure a sufficient quality in these process steps. High-temperature brittleness restricts the applicability of the con...