DENSIFICATION BEHAVIOUR OF IRON AND IRON BASED ALLOY POWDER PREFORMS DURING HOT FORGING

Abstract

The present investigation deals with hot upsetting, partially open die forgings and closed die forgings of sintered iron, iron-carbon alloys (carbon varying from 0.35 to 1.36 %) and 0.45 % phosphorus steel powder preforms which were sintered at 112000 for a period of one hour. Forging temperature was variod in the range of 800--11200C for hot upsetting of iron and iron-carbon preforms with varying initial aspect ratio (0.57 to 1.17) whereas, iron-phosphorus alloy powder preforms were upset forged at 9600C at the initial aspect ratio of 0.59. Height strains at which fine to heavy cracking at the circumference of the forged component occurred were employed in the design of partially open and closed dies. Partially open (step down cylindrical and hemi- spherical) dies were designed with an aim to study the characteristics of pore flow. This study has helped to understand metal flow, existence of dead metal zone (hydrostatic zone) and mechanism by which pore closure takes place. Design of closed dies was based on introduction of circumferential constraints such that the preform experiences these constraints after varying degree of deformation under upset forged condition. Different height strain values were set such that a preform experiences limited degree of upset forging condition before being subjected to circumferential die constraints. One of the height strain was corresponding to a limit of cracking. Partially open and closed die forgings were performed on sintered preforms (H/D = 1.18) of iron and iron—carbon alloys at 1120 °C while 0.45 % phosphorus steel preforms (H/D = 1.18) were forged at 960°C at various density levels.