Effect of Phosphorus on Microstructure and Mechanical Properties of Iron-Based Alloys Processed Through Powder Forging

In sintered as well as cast steels presence of phosphorus is a problem as it induces brittleness in the steels and deteriorates the mechanical properties. The present research work describes a P/M route to produce ductile iron phosphorous alloys. Alloys with phosphorus contents 0, 0.35, 0.65, 1.3, 2, and 3 wt.% were developed by a powder forging route. Care was taken to ensure that no liquid-phase formation takes place during processing. First, a master alloy powder containing 5 wt.% phosphorus was produced by reacting water-atomized iron (Fe) powder with orthophosphoric acid. The iron phosphate (master alloy) particles were then blended with the iron powder. The blended powders were placed in a mild steel can and hot forged at 1323 K in a flowing hydrogen atmosphere. Hot-forged slabs were re-forged to final density and then homogenized at 1373 K for 2 h. Increasing the phosphorus content led to an increase in strength and hardness of forged alloys. Alloys with phosphorus contents < 1 wt.% exhibited significant ductility, suggesting that the presence of phosphorus did not cause the expected embrittlement. The solid-state processing used may lead to development of ductile phosphorus-containing alloys with attractive properties.