Problems with Heat Treating of P/M Parts (Abstract)

By Chaman Lall, Ph.D., MPP VP-Mfg. & Technology

Components manufactured by powder metallurgy are being used in increasingly demanding applications and environments, which dictates that the optimum performance be obtained from these materials. One aid in the achievement of this goal is the appropriate utilization of high temperature sintering. In this review, the fundamentals and thermodynamic principles of high temperature sintering are described, followed by specific examples for stainless steels, soft magnetic materials, and selected additional alloys. A brief overview of the metallurgical characteristics of these materials is given. In ferrous-based materials, sintering well above the traditional 1120C (about 2050F) temperature minimizes the absorption of nitrogen and, hence, the subsequent formation of nitrides during cooling. High temperature sintering also promotes the reduction of any oxides that inhibit the metal-to-metal bonding of particles. In addition, the significant changes in diffusion rate with increasing temperature result in notable increases in the rate of grain growth, the homogenization of alloys, and the attainment of spheroidal pore morphology. Marked improvements in the corrosion resistance of stainless steels and the performance of soft magnetic alloys result from the use of high temperature sintering.

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