Abstract
A small series of ring compression tests were performed on BS970:708M40 alloy steel. The samples were tested using a 2-factor temperature variable, and a 4-factor lubricant variable, as the design parameters. Two differing soak temperatures were used, namely 1030 °C and 1300 °C respectively. The lubricants applied at the billet to tooling interface were synthetic water–based, graphite water–based, graphite and molybdenum disulphide viscous grease, and finally, unlubricated samples were tested. The ring compression tests were performed using a traditional drop forging hammer and induction heating to minimise any unintentional process variability. The impact that the two varying process parameters have upon the compression sample was then assessed by measuring each sample’s surface hardness and surface roughness prior to and post forging with fully calibrated equipment. It was demonstrated that the higher soak temperature of 1300 °C yielded a lower surface hardness value and higher surface roughness than the lower soak temperature, 1030 °C. The two water-based lubricants offered negligible change in results compared with the unlubricated forging, strongly suggesting that the lubricants were evaporated off the surface prior to forging. However, the results from the graphite–molybdenum disulphate grease do indicate in particular higher surface roughness than other lubricants, and a non-symmetric distortion pattern.
Highlights
Closed die forging operations have been studied comprehensively over many years, to better understand the material flow and deformation in order to optimise processing routes
There were no visible difference in surface hardness, it is thought that the bottom die, upon which the sample was placed for a few seconds before the hammer blow was struck, could have been acting as a heat sink on the sample, delivering a non-symmetric temperature field across the part and facilitating differing amounts of plastic deformation
This effect would in theory have been observed on the other forged rings with different lubricants as well, unless the graphite molybdenum disulphide grease acted as a thermal conductor
Summary
Closed die forging operations have been studied comprehensively over many years, to better understand the material flow and deformation in order to optimise processing routes. These parameters dictate how a material deforms and the final surface properties observed [21] The processing conditions such as heat, lubrication and tooling play a major role in this particular area, demonstrated by Groche et al [11]. The intention of this work is to experimentally measure the impact that the variation of two process parameters, namely the billet temperature and the lubricant used at the tooling to billet interface, has on the surface hardness and surface roughness properties of the as-forged BS970:708M40 alloy steel
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