Warm hooker extrusions of sintered powder metallurgical preforms of steel were investigated at different temperatures ranging from room temperature to 773 K in steps of 100 K for strains of 0·87, 1·0, 1·14 and 1·3. The resident densities for extrusion were chosen from the formability limit diagrams generated at different temperatures, which demarcates the safe zone from fail zone. Microstructure characterisations vide pore closure revealed the possibility of deformation and warm working assisted sintering of preforms extruded at warm working temperatures. The rate of force/stroke (dF/dS) and ratio of actual force to theoretical force called correction factor Φ for different temperatures were evaluated to substantiate the deformation and warm working assisted sintering. Hardness data of the extruded samples were measured to determine the densification. The extruded samples were analysed for the surface roughness along their length and the optimum temperature for extruding steel preforms for better properties were identified. © 2011 Institute of Materials, Minerals and Mining.

Chakkingal Uday

Department of Metallurgical and Materials Engineering

P. Venugopal

Correction factors

EXTRUDES

Optimum temperature

Pore closure

Room temperature

SAFE ZONES

SINTERED POWDERS

STROKE RATES

WARM EXTRUSION

Warm working

Deformation

extrusion

Preforming

Steel metallurgy

Surface roughness

Sintering

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IIT Madras

Deformation and temperature aided sintering during hooker extrusion of sintered PM preforms of steel

Powder Metallurgy

The current paper deals with the generation of formability limit diagrams (FLD) for sintered preforms of steel from room to warm working temperatures. Steel compacts of different resident densities have been prepared by applying recommended pressures. Stage wise upsetting has been carried out to obtain the densification curves from room temperature (27 °C) to 600 °C in steps of 100 °C to explore the possibility of in situ sintering. Compression tests were performed and the critical transition densities vide formability limit diagrams were found to be 6.28 g cm-3 at room temperature, 6.21 g cm-3 at 100 °C, 6.08 g cm-3 at 200 °C, 5.95 g cm-3 at 300 °C, 5.72 g cm-3at 400 °C and 5.5 g cm-3 at 500 °C. The decreasing trend in critical transition density addresses the energy conservation and cost effectiveness during secondary processing of sintered preforms of steel. © 2007 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Influence of temperature on the forming limit diagrams of sintered P/M preforms of steel

Mathematical expressions have been derived for relating the values of apparent strength coefficient Ka (in N/mm2) and strain hardening exponent na to preform density ρ{variant}0, based on axial ring compression tests. These equations are consulted for prediction of cold hooker extrusion forces for P/M preforms of various starting preform densities, ρ{variant}0. Experimental values of extrusion forces are compared with those predicted. Such analysis demonstrates the usefulness of the generated Ka, na against ρ{variant}0 equations to avoid elaborate experimentation on the extrusion. Besides, the analysis suggests that the void closure is persistent till the theoretical density and if corrections are applied for force, theory and experiment agree well. © 1988.

Journal of Mechanical Working Technology

Some uses of na and Ka in the prediction of cold extrusion forces of sintered powder metallurgical preforms

Cold Hooker extruded iron compacts have been evaluated for density, mechanical and metallurgical properties, in the as-extruded, annealed and re-sintered conditions and the results compared with those for an equivalent wrought composition. The extent of densification occurring due to cold deformation of the P/M compacts has also been examined. The commercial viability of the process of cold extruding a P/M preform has been analysed by considering the manufacture of a suitable component by the above process and comparing it with manufacture by the existing conventional process. This evaluation gives an indication of the economics of the Hooker extrusion process of P/M preforms for the manufacture of a similar family of products. © 1988.

On the properties and economics of sintered iron powder metallurgical extrudes

This paper highlights some typical circumferential and longitudinal cracking encountered during the Hooker extrusion of sintered iron preforms. Studies carried out indicate that the preform shape, the preform sintered density, the die included angle and the extrusion reduction (deformation ratio) have a strong influence in the arresting of such cracks. © 1988.

Some failure studies in the Hooker extrusion of sintered iron powder metallurgical preforms

The advantages gained by the forging of a powder metallurgical preform are well known. Cold extrusion of a P/M preform combines the advantages inherent in the cold extrusion process with the forging of a preform, but for successful deformation of a P/M preform, the inherent brittleness has to be overcome. In this paper various cold extrusion methods are examined, based on the state of stress, from which the Hooker extrusion process is chosen as the deformation method due to its favourable (compressive) state of stress. The paper then goes on to deal with the experimental tooling evolved for the Hooker extrusion of sintered iron preforms. Compacts made under different compacting pressures (loads) and therefore of different preform densities have been Hooker extruded at different extrusion ratios. The forces and energies have been evaluated and the results compared with values calculated for the equivalent wrought steel. An empirical relationship has been obtained for the estimation of force during the Hooker extrusion of iron preforms, making use of force equations for the cold Hooker extrusion of wrought steel. © 1987.

Force and energy during the cold hooker extrusion of sintered iron preforms

Journal	Powder Metallurgy
ISSN	00325899
Open Access	No