The Influence of High Vanadium and Phosphorus Contents on the Risk of Transverse Cracking during the Continuous Casting of Austenitic TWIP Steels
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abstract
There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation strengthening and grain refinement. However, the effect on slab quality during continuous casting has not been determined. In this study, the hot ductility of two twinning-induced plasticity (TWIP) steels, Fe-0.6C-22Mn and Fe-0.6C-22Mn-0.2V, was examined over the temperature range 650–1200 °C. Tensile samples were taken from continuous cast 225 mm slabs and from 36 mm transfer bars. The addition of V caused the ductility trough in the temperature range 650–900 °C to deepen and widen and the lowest reduction in area (RA) recorded in the as-cast condition was 30%. This deterioration of hot ductility was due to V(C,N) precipitation. Even though the minimum RA was below the value often accepted to avoid cracking, no transverse cracking was observed in industrial trials and the surface quality was acceptable. The RA values of Fe-0.6C-22Mn were found to be very sensitive to the P level. However, this sensitivity was less evident when V was added, possibly due to P trapping by VC at austenite boundaries. No transverse cracking was observed in industrially produced slabs with P in the range examined (0.02 to 0.04 wt.% P).
