Effect of Preform Geometry on the Material Behaviour and the Densification Mechanism during Hot Upset Forging of Sintered AISI 9840 P/M Steel Produced Using Elemental Powders
Journal Title: International Journal of Modern Engineering Research (IJMER) - Year 2014, Vol 4, Issue 11
Abstract
The present investigation pertains to generate experimental data in order to establish the influence of initial preform geometries on the material behaviour and the operative densification mechanism/s during hot upsetforging of sintered AISI 9840 P/M Steel composition prepared from the elemental powders. Powder blend corresponding to AISI 9840= C(0.4%), Mn(0.8%), Si(0.3%), Ni(1.0%),Cr(0.8%), Mo(0.25%) and Fe(96.4%) composition was prepared on a pot mill and the blending was carried out for a period' of 16hrs. while maintaining the powder to ball ratio 1.1: I by weight. Compacts of 27.5mm diameter and 12 - 24mm heights were prepared from the aforesaid blend in the density range of 84±1 percent of theoretical density by applying accurately controlled pressures in the range of 460±10 MPa and by taking pre-weighed powders. Indigenously developed ceramic coating was applied all over the compact surfaces and dried under an ambient conditions for a period of 10- 12 hrs. These ceramic coated compacts were recoated 90° to the previous coating and re- dried under the aforesaid conditions. These ceramic coated preforms were sintered in an electric muffle furnace for a period of 90 minutes at 11500±10°C. Immediately after the completion of the sintering schedule, the preforms corresponding to 0.45, 0.68 and 0.92 initial aspect ratios were axially hot forged to different height strains. Analysis of the experimental data has revealed that the lower aspect ratio preforms densified rapidly compared to higher aspect ratios and the densification curves corresponded to a third order polynomial of the form:(ρf/ρth) = ao +al €h + a2€h2 +a3€h3; where, €h= ln (Ho/Hf) and a0, al, a2 anda3 are empirically determined constants. Further analysis has established that the Poisson's ratio would always remain less than one half and will have the tendency to approach to a limiting value of 0.5 in the near vicinity of the theoretical density. Influence of the preform geometry is established to be quite pronounced and has affected the densification curves and Poisson's ratio with density.
Authors and Affiliations
Manoj Kumar , Dr. (Mrs. ) Shashi Krishna Pandey , Dr. (Mrs. ) R. Nagalakshmi , Dr. K. S. Pandey
Keywords
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