1989-09-01

A Non-Distorting Heat Treatment Which Provides Both Wear and Corrosion Resistance 891787

For structural components that require improved fatigue and wear resistance, shallow case carbonitriding has traditionally been specified by the automotive industry.
A typical specification might call for .003 to .010 inch case depth consisting of clear martensite and a surface file hardness of Rc 58 file hardness.
A problem with this treatment has been excessive distortion in precision components such as fine blanked stampings, screw machine parts, and powder metal parts. In many cases, these parts have to be finish ground or sized in some manner to return the parts to print tolerances.
Another problem has been a severe loss of fatigue strength because of over-casing. This embrittles parts with thin cross sectional thicknesses.
Lindberg Corporation has developed the Lindure process to provide an alternative to carbonitriding. Lindure is a gaseous nitrocarburizing treatment which takes place at temperatures below the lower critical (AC1) where the austenite transformation begins.
The process provides improved wear and fatigue resistance, as well as good tolerance control and can maintain surface finishes down to approximately 25 microinches.
This treatment is usually applied as the last operation to the part prior to assembly and has eliminated the need for calibration in many applications.
The objective of this paper is to discuss the processing parameters of the Lindure treatment, properties obtained by applying the process, and to show successful applications of the process.

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