Originally shared May 5, 2023
In this letter we’d like to share highlights from the article Sintering Atmospheres authored by TAT Technologies President, Harb Nayar. It was first published in Volume 4 of the ASM Handbook (1981), and again in Volume 7, Powder Metallurgy (2015), editors P. Samal & J. Newkirk.
Copies of Sintering Atmospheres will be freely given by request. Please contact This email address is being protected from spambots. You need JavaScript enabled to view it. for a PDF copy.
The article covers production, use, and chemistry of both generated natural gas-based atmospheres like Endo, Exo, and dissociated ammonia as well as nitrogen-based atmospheres now primarily used in the sintering of ferrous PM parts. I suggest that anyone who wants to optimize their sintering operation, especially for ferrous PM parts, should read this article. It will help you take a “walk” through a typical sintering furnace to better understand it. You will find a road map of desired atmosphere composition as parts enter the furnace, travel through many temperature zones, and finally the furnace.
Here are a few notable highlights from the article:
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(1) Atmosphere REQUIREMENTS in individual sections (Figure 8):
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Preheat (Preparation) - Very oxidizing to lubricants during delubing and highly reducing to metals during ixide reduction.
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Sintering - Reducing to metals and neutral to carbon.
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Initial Cooling - Reducing to metals and neutral to carburizing to carbon.
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Final cooling - Mildly reducing to neutral to metals.
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(2) Pros and cons of different types of atmospheres used in the PM Industry.
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(3) Physical properties and compositions of different atmospheres used.
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(4) “Reactive” vs “neutral to carbon” concept.
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(5) You need a little more admixed graphite to iron-carbon alloy mixes when using N2-base atmosphere compared to Endo.
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(6) Furnace Zoning Concept to improve delubing and to increase throughput in existing furnaces.
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(7) N2-H2 atmospheres and different sources of H2
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(8) Long list of references related to yhe use of sintering atmospheres during the last century.