Effect of nitrogen on supersolidus sintering of modified M35M high speed steel

Water atomised high vanadium M35M high speed steel powders with different carbon contents were cold compacted at 700 MPa and sintered under an N2 rich atmosphere. Full density specimens were obtained at temperatures between 1140 and 1105°C for carbon contents between 1.8 and 2.5 wt-% respectively. The sintering behaviour of these powder mixtures was correlated with dilatometric curves and phase diagram calculations made by Thermo-Calc software. It is demonstrated that densification takes place above the solidus temperature, within the austenite + carbide + liquid phase field, and that nitrogen widens this region, which is responsible for increased sinterability with regards to vacuum sintered high speed steel.