Formability of Cold Rolled Medium Manganese Steel

The intercritical annealing time effects on the microstructure,mechanical properties and hole expansion capacity of the cold rolled medium manganese steel(0.1C-5Mn) was studied.The microstructure evolution during annealing was examined by SEM and EBSD.The strength,ductility and hole expansion were measured by tensile and hole expansion test.It was found that an equiaxed ultrafine ferrite and austenite structure was developed due to the austenite-reverted transformation in the annealing process(ART-annealing) at 650 ℃,product of strength to ductility attained over 30 GPa·%.The austenite volume fraction increased with increasing of the annealing time,but over-increased austenite fraction was detrimental to the hole expansion capacity.