Microstructure and mechanical properties of multi-pass forged and annealed 42CrMo steel

Abstract In this work, we investigate the effects of multi-pass forging and annealing treatment on the microstructure and mechanical properties of 42CrMo steel. The homogenized specimens were firstly multi-pass forged at 1100 °C followed by air cooling, and then were annealed for 1 h at 400 °C, 500 °C, 600 °C, and 700 °C, respectively. It is found that the average prior austenite grain size of the homogenized material is refined from 273 ± 78 μm to 12 ± 1 μm accompanied by an increased dislocation density from 6.09 × 1014 m−2 to 2.35 × 1015 m−2 after multi-pass forging. As a result, the yield stress of the as-forged specimen is 1.7 times that of the homogenized counterparts. Annealed at different temperatures ranging from 400 °C to 700 °C after forging, the yield stress of the forged specimen reduces from 798 MPa to 522 MPa with an enhancement of elongation from 8% to 16%. The corresponding fracture features experience brittle-ductile transition. The results are attributed to gradually spheroidized pearlite and reduced dislocation density with increasing annealing temperature.