The continuous casting behavior of medium manganese steels

Abstract

The continuous casting behavior of medium manganese steels (MMnS: 6Mn, 6Mn–1Si, 6Mn–1Si–1Al, 10Mn–1Si and 10Mn–1Si–1Al) have been investigated and compared with unalloyed carbon steel C30. A series of in-situ melting/re-solidification hot tensile tests were conducted in the temperature range 800–1450 °C. The corresponding tensile forces and ductility parameters were monitored. Differential thermal analysis (DTA) was applied to determine the liquidus temperatures. The solidified zones and fracture surfaces of the tested specimens were analyzed using scanning electron microscopy (SEM). Scheil-solidification and equilibrium thermodynamic calculations were performed to explore the solidification and precipitation behavior. The processability of MMnS using thin slab casting technology has been discussed in light of their hot ductility behavior. The findings indicate the prime role of precipitation, phase transformation and extension/shift of solidification intervals induced by the alloying concepts in controlling the hot ductility of MMnS. It turns out that the formation of MnS, complex AlN and MnS precipitates and δ-ferritic solidification deteriorates the high temperature ductility. A shift of the second hot ductility drop to higher temperatures was identified for the Al-containing and high-Mn content MMnS when compared to the reference steel C30. This study demonstrates the adequate hot ductility (>30%) of MMnS 6Mn and 6Mn–1Si as well as reference steel C30 for thin slab casting technology, while higher Al-containing MMnS undergo a ductility drop in the straightening temperature range (900–1080 °C), which impairs their castability. An optimization of their alloying concepts, especially Al-content, is recommended to tune their continuous casting behavior.