High Temperature Gear

[whorley]

Hi,
What is the best material and heat-treatment for high temperature gears.

I am looking at making a small planetray gearbox that must operate in 450F environment.

I can buy some of the gears off of the shelf but they are carburized... I think they will temper at this temperature.. can I nitride carburized gears and get better high temp hardness from them?

Thanks in advance for any responses.

 

[Carburize]

Carburized gears are typically tempered in the range 325- 375F. You are correct that operating such gears at 450F will soften the carburized surfaces and reduce the rating of the gears. Nitriding is performed at around 950F so a 450F service environment should not reduce the rating of the gears - I have never heard of anybody nitriding a carburized gear! Nitriding is usually performed on quenched and tempered materials.

 

[sacem1]

Carburizing works in low C steels like 1020 or 1018 or even 8620 and 3215 which are low carbon low alloy steels.
Nitriding is used in alloy steels usually with Cr and V like 4140 or 4340 usually the processes are not interchangeable for a given steel quality.

If the gears are not going to be subjected to shocks I would recomend going the full hardening way and at that temp (450ºF) you would get a very light tempering effect that still would leave you with a hard enough gear.

i.e. with 4340 you harden at 1560ºF temper at 1100ºF so the 450ºF of your working temp will not affect the gear hardness. if with the same alloy steel you nitride it would be done at 1100ºF and the tempering at 800ºF or less and then you will have a decrease in strenght.

I think you should worry more about your lubrication problems as you are near the flash point of several oils.

Check that out with your oil supplier and keep an eye on the seals which have to be high temp resistant.

Cheers

SACEM1