DEVELOPMENT OF IRON-PHOSPHORUS BASED ALLOYS AS HSLA STEELS BY P/M ROUTE

Abstract

Iron-Phosphorus based alloys are known for excellent combination of mechanical properties. The present work involves the development of new alloys formed from powders in the form of thin sheets and wires based on Fe-P-Al-Si-C and Fe-P-Al-Si-Cu systems, which have an optimal combination of strength and ductility. The mechanical properties of the alloys developed in the present investigation are comparable with the mechanical properties of some of the grades of high strength low alloy steels. High density alloys were made using powder forging technique. In this process powders (blend of Iron powder, Ferro-Phosphorus powder, Ferro-Silicon powder, Copperpowder and Aluminum powder, with/without Carbon powder or Copper powder) were forged into slabs. The slabs were hot rolled to get highly densified sheets and wires. These highly densified products were annealed to relieve the residual stresses. Use of fine powder and high temperature processing facilitate densification. These alloys were characterized in terms of microstructure, porosity content / densification, hardness and tensile properties. Densification as high as 98% has been realize by adopting powder forging technique. Microstructures of these alloys consist of single phase ferrite only.Fe-0.2P-0.5A1-0.3Si showed very high elongation (23%) in annealing state. Fe-0.3P-0.5A1-0.3Si-1.5Cu alloys showed higher strength (as high as 550 MPa) and higher hardness (as high as 367Hv/10kgf). Fe-0.3P-0.SAl-0.3Si-0.3Calloy showed high strength (as high as 558.63MPa) with higher hardness(369Hv/1 Okgf). It was found that as Phosphorus content increased (0.2wt% to 0.3wt %) strength and hardness increased by expenseof totalelongation. Addition of Carbon and, Copper in Fe-P-Al-Si alloys improved proof strength and ultimate tensile strength of thealloys. The all alloys were capable of hot working to very thin gauge of sheet and wire.