Austempering/marquenching powder metal parts

Abstract

A powder metal part is made by compaction at room temperature or an elevated temperature followed by sintering, a secondary densification, heat treating, and optional secondary operations. The particulate materials preferably include iron, 0-2.0 wt % copper, 0.15-0.9 wt % carbon, 0.5-2.0 wt % molybdenum, 0.5-4.5 wt % nickel, 0-4.0 wt % chromium, and 0-1.5 wt % silicon. At least one secondary densification is applied to the part after compaction and pre-sinter/sinters steps to achieve medium to high density. The secondary densification is part of a double-press double-sinter (DPDS) or is a mechanical working depending on the application requirements. The powder metal is heat treated by austempering or marquenching followed by tempering. A unique composite microstructure is achieved from austempering by controlling the powder chemistry and the holding time at an elevated temperature. The combination of a secondary densification and austempering or marquenching produces a high performance powder metal part for demanding applications.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention pertains to the field of powder metallurgy. More particularly, the invention pertains to the formation of a high-performance powder metal part using a manufacturing process including a secondary densification and austempering or marquenching as a heat treatment. [0003] 2. Description of Related Art [0004] Powder metallurgy manufacturing processes have been successfully used to produce powder metal parts while providing various advantages. Such powder metal parts can be made into a variety of complex shapes with minimal steps, and with little or no finishing machining. Powder metallurgy also enables a high-volume of metal parts to be produced in an economic fashion. Powder metallurgy processes have been found to be more energy efficient than other processes involving forging and outright machining. [0005] Secondary densifications of powder metals followed by heat treatment are known in the art. [0006] U...

AI Technical Summary

Benefits of technology

[0012] A powder metal part is made by compaction at room temperature or an elevated temperature followed by sintering, a secondary densification, heat treating, and optional secondary operations. The particulate materials preferably include iron, 0-2.0 wt % copper, 0.15-0.9 wt % carbon, 0.5-2.0 wt % molybdenum, 0.5-4.5 wt % nickel, 0-4.0 wt % chromium, and 0-1.5 wt % silicon. At least one secondary densification is applied to the part after compaction and pre-sinter / sinters steps to achieve medium to high density. The secondary densification is part of a double press double sinter (DPDS) or is a mechanical working depending on the application requirements. The powder metal is heat treated by austempering or marquenching followed by tempering. A unique composite microstructure is achieved from austempering by controlling the powder chemistry and the holding time at an elevated temperature. The combination of a secondary densification and austempering or marquenching produces a high performance powder metal part for demanding applications.

Problems solved by technology

Powder metal parts may be used in a variety of applications, but have found only limited use in high-performance applications, such as within an automobile transmission, due to the fact that many powder metal parts suffer from reduced bending fatigue strength and lowered wear resistance.

Images