The possibility of using new, high-strength steels with an attractive forming behaviour (e.g. induced plasticity steels) in automotive manufacturing, offers a significant potential for improvement in the area of reducing the weight while simultaneously increasing crash safety. Induced plasticity steels not only possess high strength but also excellent elongation properties and high energy absorption capacities due to the TRIP and TWIP effects, Table 1. [1±4] This profile of mechanical properties is of great interest for crash-relevant automotive components.Common TWIP steel concepts are based on high Mn and Al contents, which are known to cause various problems during steelmaking. The search for suitable primary and secondary steelmaking processes, and the feasibility of casting these steel grades on conventional continuous casting machines, is the focus of ongoing research. The aim of the work presented here is to provide a basis for decisions on the subsequent development of the industrial production of high-Mn and -Al steels.At the very beginning, the following potential difficulties for the continuous casting of high-Mn, high-Al steels were identified: [5] ± high-temperature strength: is expected to be extremely high for these steels, and thus may be a problem for the strand guiding and soft reduction system in casting machines;± hot tearing: the wide brittle-temperature range during the solidification of high-Mn and -Al steels indicates a high crack susceptibility;± segregation at the micro-and macroscopic levels: possible formation of banded structures, resulting in difficulties during further processing;± non-metallic inclusions: the possible interaction between precipitates and mechanical properties means that steel cleanliness levels (secondary metallurgy) should be defined;± scale formation: partial oxidation plays a role in the formation of surface cracks in the casting and rolling process.This list does not consider necessary process adjustments, such as the development of suitable mold powders for highAl steels.The work presented here is concerned with the high-temperature mechanical properties of an high strength structural steel (HSSS) steel and the high-Mn, high-Al steel X50MnAl 25 1 in comparison to common ultra low carbon (ULC) and electrical sheet (ES) steels, the latter both known not to cause many problems during the continuous casting process.
MethodologyThe high-temperature mechanical properties and the crack susceptibility were analyzed using the SSCT (submerged split-chill tensile) method. The principle of this testing method is described in detail elsewhere. [6±8] The SSCT test was developed to simulate the shell straining during the continuous casting process. A steel cylinder, split in two halves, is submerged in a liquid steel melt inside an induction fur-
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