Microstructure Analysis of High-Manganese TWIP Steels Produced via Strip Casting

Abstract

Steels with manganese contents of more than 20% offer a new and favourable combination of material properties like high strength and high ductility. These extraordinary mechanical properties are based on the TWIP effect, which depends on the Stacking Fault Energy (SFE). But there are still problems in the conventional production of high-manganese steels, which prevents their widespread use. Both in casting and subsequent hot rolling difficulties occur, with the consequence that the production is very expensive. One alternative production process of high-manganese steels is strip casting, which basic feasibility was shown in earlier work. Strip casting allows the casting and rolling of hot strip in one combined process. In this way hot strip with a thickness of less than 3 mm could be produced. Characteristic for the strip cast material is the as-cast structure with a fine dendritic structure, which shows pronounced microsegregations with a short wavelength. The pronounced microsegregations can have an impact on the local chemical composition and thus on the dominating forming mechanisms that occur. In this work therefore the microsegregations of strip cast material are investigated by means of electron probe microanalysis (EPMA) measurement. Besides the local element distribution, also the presence and composition of non-metallic inclusions are analysed. Especially oxides from the casting process and sulfides from the raw material are expected. Furthermore, different annealing processes for the elimination of the dendritic as-cast structure are examined. In these experiments the temperatures were varied in the range from 900 to 1150°C at annealing times from several minutes to a few hours.