Re-Nitrding Gearing
Re-Nitrding Gearing
(OP)
We currently have a Gear with a tire made from NiCrMoV steel that we had gas nitrided. The company performing the nitriding stacked two gears on top of each other in a pit furnace. There was plenty of space between the gears and gear teeth for gas flow. The pit furnacve is heated from the bottom and the ammonia gas is pushed in from the bottom with a fan that pulls it up the furnace. The gas is measured every hour for potential and showed no irregularities. The diameter of the gear is about 40 inches. The bottom gear nitrided perfectly. The top gear only sporatically nitrided and has a surface hardness range varying from 43 to 51HRC, with a minimum requirement of 50 HRC. The core hardness prior to entering the furnace was 40HRC. Metallurgical test coupons were run with the gear, and they show perfuect hardness and case depth. So, the question is, what are my possible issues as to why the top gear did not fully nitride?





RE: Re-Nitrding Gearing
RE: Re-Nitrding Gearing
Another question is whether I can have this gear renitrided without fear of over nitriding at this point. I know we will have to blast the gears prior to renitriding.
RE: Re-Nitrding Gearing
There are two stage gas nitriding processes (AMS 2759/6 CL 1). The minimum second stage temperature limit is about 35degF higher than the first stage, but otherwise the procedure for each stage is similar.
Also, check for decarburization in your parts.
Good luck.
Terry
RE: Re-Nitrding Gearing
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RE: Re-Nitrding Gearing