Hot Re-pressing of Powder Made from Mild Steel Machining Swarf

Abstract

Since economic studies indicate that powder produced from mild steel machining swarf in a cryogenic hammer mill is significantly cheaper than that made by any other method, it was decided to investigate whether powder-metallurgy products of acceptable properties could be obtained from such powder by a number of alternative methods. The powder was first isostatically compacted, either with or without prior heat-treatment, at room temperature at pressures of up to 1·38 GN/m2 (200000 Ibf/in2). The cylindrical preforms were then used to produce specimens by the alternative routes of sintering, or hot forging, or sintering followed by hot forging at small strains. The density and tensile properties of the .swarf powder metal were determined as a function of the process variables. By using certain processing routes the density closely approached that of the parent metal while elongation and ultimate tensile strength remained relatively lower, partly because the limited capacity of the forging machine restricted the plastic strain and hence bonding of the particles, partly owing to contamination of the swarfpowder. The presence of non-metallic inclusions caused considerable scatter in the results.