Hot ductility of Nb and Al microalloyed steels follovving high-temperature solution treatment

Abstract

AbstractC–Mn–Al, C–Mn–Nb, and C–Mn–Nb–Al steels are known to exhibit troughs in their hot ductility behaviour. This paper attempts to explain the high-temperature brittleness of these steels by examining their hot deformation behaviour. Slow strain-rate, hot tensile testing of laboratory-melted and commercial C–Mn steels containing niobium and/or soluble aluminium following solution treatment at 1300°C for 1·5 h has been performed. The occurrence (or otherwise) of dynamic recrystallization, hot strength, and elongation to fracture were noted as a function of deformation temperature, and the austenite-ferrite equilibrium transformation temperature determined by slow-heating dilatometry. The addition of niobium and/or soluble aluminium to C–Mn–N steel produced a hot ductility trough, failure being intergranular when ductility was poor and by dimpled rupture and tensile necking when ductility was good. Poor ductility was associated with a fully austenitic microstructure. Small amounts of ferrite did not appe...