The structure and mechanical properties o£ test steel (/% : 0. 22C
1. 46 ~ 1. 66Mn
0. 45 ~0. 58Si
0. 011 ~ 0. 013S
0. 010 ~0. 012P
0. 014 ~ 0. 047V
0. 040 ~0. 044N) melted by vacuum induction furnace cast to 10 kg ingot
forged to 25 mm x 25 mm billet
heat-treated at 870 °C for 40 min
air cooling and natural aged for 180 days are observed and tested. Results show that after natural ageing the grains in high nitrogen steel 20MnSi is fined with grain diameter 0. 8 ~ 6 μm and banded structure disappearing
due to V ( CN) precipitation its yield strength increases by 25 ~ 93 MPa
tensile strength increases by 17 ~ 157 MPa
elongation increases from original 9% ~ 15% to 26. 0% ~31. 5% ; and after natural ageing the brittlement zone in test steel disappears.