Impact forging of sintered steel preforms

The results of a fifteen year research and development programme on the application of forge hammers to the impact powder forging of 46xx steel preforms are reviewed and assessed. The main topics are suitability of forge hammers to powder forging; effects of forging strain and forging pressure on core residual porosity; importance of pressure dwell or contact time in determining residual porosity near the surfaces and comers of powder forgings; dependence of tensile ductility, toughness, and fatigue strength on high strength, impact powder forged 46xx steel on lateral strain, residual porosity, oxygen, and sulphur contents; and inclusion volume fraction and spacing. It is shown that impact forged steels can achieve mechanical property parity at very high strength levels with high quality wrought steels. State of the art forge hammers have significant technical and economic advantages over presses in powder forging applications and are best suited to powder forging processes for which the forging strains and energy requirements are small.