Tailoring the surface microstructure of starch consolidated vanadium-rich high speed steel powder

The nitrogen sintering of vanadium rich high speed steel has been applied for tailoring of surface microstructure. The approach has been facilitated by thermodynamics modelling of phase equilibria, novel shaping methods like starch consolidation and various manipulations of the sintering atmosphere. It is demonstrated that elevated nitrogen sintering densification occurs when an open pore structure interacts with nitrogen slightly below the nitrogen-reduced solidus temperature. The compact can then first be pre-sintered to around 85% relative density in vacuum, and thereafter be infiltrated with nitrogen at the nitrogen-reduced solidus temperature and finally be sintered to near full density at a temperature of 10% liquid phase formation in nitrogen. The end result is a microstructure with an elevated MX transformation in the surface, whose depth depends on the carbon balance of the material