Effect of Prior Austenite Grain Size on Hole Expansion Ratio of Quenching and Partitioning Processed Medium-Mn Steel

The effect of the prior austenite grain size (PAGS) on the tensile properties and hole expansion ratio (HER) has been investigated. Starting from different PAGS values (4.7 μ m and 15.2 μ m) obtained by controlling the austenitizing temperature, microstructure consisting of martensite and austenite ( V γ of 0.09–0.18) was produced by the quenching and partitioning process. Increasing V γ had a beneficial influence on the tensile elongation regardless of the PAGS, but deteriorated the HER. However, larger PGAS alleviated the degradation of the HER. The major influence of a larger PAGS on the HER results from the decreased population of interface between neighboring martensite in the shear-affected zone, because that interface is revealed to be a major site for void formation during hole expansion testing.