How Does Heat Treatment Contribute to the Strength of Sintered Powdered Metal Parts?

16 November 2018

Sintered components are produced when fine metallic powders are compacted inside special cavities. As high pressures cause densification, heat is added. Therefore, as a process precursor, this operation employs a finite amount of heat treatment toughening right at the end of the product forming procedure. However, if the tightly packed, materially diffused particles still don’t exhibit sufficient tensile strength and pure hardenability, additional heat treatment work may be deemed necessary.

Powder Metallurgy: Post-Processing Heat Treatment 

The atomized powder has its binding agents and lubricants. A slightly porous metal construct has taken shape inside the cavity compaction mechanism, and the presence of material diffusing heat has even introduced a measure of heat treated hardness. Still, the project engineer knows where this product batch is heading. He knows the present fatigue resistance and hardness rating ingrained within each part just won’t cut-the-grade. To maximize hardness, to really address this hardenability issue, the components require the services of a heat treatment furnace.

Unlike Other Product Structures 

Let’s say this is a batch of bushings or bearings. They’re heading for a shafting mechanism, where they’ll be placed under great stress. Loaded with their self-lubricating abilities and capillary action, the bushings address their duties with unmitigated ease. But the loads are heavy, the dynamic forces extreme, and the porous metal is under pressure. Using in-house precipitation hardening technology, the friction-mitigating components gain cross-sectional strength and uniform mass hardness. Alternatively, there are all the usual surface hardening techniques, which include nitrocarbonizing, carbonizing, and plasma nitriding. Internal stresses are less likely here, probably because the bearings avoid the machine shop. Unless the parts are taken through a post-production shape refinement phase, there’s not likely to be any tool-produced stress in sintered parts, after all. If cold work stress does rear its ugly head, however, the P/M processed parts can be annealed until those stresses are removed.

Two complex issues hamper heat treatment work, as carried out on sintered components. First of all, several soft materials are used in this sector, including bronze. Powder metallurgy work is also used to control structural porosity. The heat treatment process must account for such unique variables. There could also be a lubricating fluid stored inside those metal pores, which is common enough when the components incorporate a self-lubricating property. So, to answer the title’s question, yes, sintered components should be subjected to heat treatment if their structures lack strength and hardness. For those bearings and bushings alone, the service does supplement and optimize the metal, leaving the friction-handling components ready for the most challenging rotational duties.

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