Surface hardening while maintaining close dimensional tolerance…
Gas nitriding is a surface hardening process that involves the diffusion of nitrogen (via ammonia) into the surface of a metal to improve its wear and corrosion resistance. The process is typically carried out at relatively low temperatures (typically 925 – 1050°F) which is beneficial in reducing the amount of distortion that occurs with other surface hardening processes. Parts are first cleaned to remove any residual contaminants, then heated to the desired temperature and exposed to the ammonia gas. The ammonia splits into constituent nitrogen and hydrogen atoms with the nitrogen diffusing into the surface of the metal, creating a depth of hardness according to the time and temperature of the cycle used.
Advantages
- High surface hardness, low dimensional movement process.
- Can eliminate the need for a final grinding operation due to low dimensional movement.
- No oil quenching required.
- A clean process. Parts will finish with a consistent, matte gray appearance.
Disadvantages
- Low temperature processing dictates longer cycle times to achieve specified case depth (compared to carburizing), which can be costly.
- Incoming part cleanliness can affect the ability to form a case depth via nitriding.
- Potential for longer turnaround times due to longer furnace cycles (anywhere from 12 to 100 hours is possible).
- Reduces corrosion resistance (stainless steel only).
Equipment Used
- Sealed retort positive pressure furnace.
- Working dimensions 42″ diameter x 68″ height.
- Weight capacity up to 10,000 lbs.
Materials (Alloys) Treated
SAE series 41, 43, 51, 61, 86, 87, 93 and 9800. Stainless steels, and some tool steels can also be nitrided. Parts should be in the hardened and tempered condition with the last received tempering temperature to be higher than the nitriding temperature.
Applications
Gears, crankshafts, camshafts, cam followers, valve parts, springs, extrusion screws, die-cast tooling, forging dies, aluminum-extrusion dies, injectors and plastic injection molds.
Industries
Automotive, aerospace, defense, construction, diesel engine manufacturing, tool and die.
Specifications
- AMS2759/6 & AMS2759/10 (DMT’s furnace is not yet qualified for these specs).
- OEMs and Tier 1 suppliers generally create their own specifications for nitriding.
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