The low temperature superplastic characteristics of commercial 40Cr steel, which was subjected to water quenching three times and subsequent high temperature tempering, were investigated. The results show that the 40Cr steel has a grain size of 5-10 μm, and exhibits an elongation of 254 %, a flow stress of 108.1 MPa, a strain rate sensitivity m-value of 0.221 at the temperature of 650 ℃ and the initial strain rate of 3.16×10-4 s-1.
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