In the present study, the high temperature workability of high manganese austenitic steel has been examined to prevent the grain boundary embrittlement cracking problems in the continuous casting process. As-cast Fe-22Mn-0.4C steel exhibited poor hot ductility behaviors at 900°C tensile test. Phosphorus segregation and BN precipitation at grain boundaries were mainly responsible for this deterioration. In order to enhance the hot ductility, titanium was added to this steel, and high temperature workability was compared in view of reduction of area in tensile test at 900°C. BN precipitation at grain boundaries was effectively suppressed by the formation of interior Ti(C,N) precipitates. Furthermore, phosphorus atoms, a grain boundary embrittlement element, were observed to segregate at Ti(C,N) interfaces in Auger electron spectroscopy and atom probe tomography. These results show that titanium addition in Fe-22Mn-0.4C steel can effectively improve the high temperature workability by decreasing the segregation of phosphorus at grain boundary.KEY WORDS: high manganese austenite steel; high temperature workability; grain boundary segregation; Ti(C,N) precipitate; atom probe tomography.
A study has been made on the effects of Mn content and addition of Al on the microstructure and mechanical properties of (4-6)Mn steels, with the aim of developing ferritic Mn steels having good combination of tensile properties and impact toughness. It has been shown that the reduction of Mn content to 6 wt% and lower from 8-12 wt% of conventional steels can effectively prevent the occurrence of intergranular fracture, which has been a major problem of (8-12)Mn steels with poor toughness at cryogenic temperature. While increasing Mn content in the binary (4-6)Mn steels results in an increase in strength and a decrease in impact toughness, the addition of 1Al to (4-6)Mn steels results in improvements in both strength and impact toughness as compared to those of the binary (4-6)Mn steels and the best impact toughness has been obtained in the as-rolled 1Al added 4Mn steel, whose microstructure consists of fine acicular ferrite grains.
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