vacuum carburizing VS surface carbon content

[MATTHEWZHI]

Hello every expert:

We had one issue when we vacuum carburized 9310 gears.The case depth required is .019-.022" from customer. The surface carbon content required is 0.70-0.90wt%. We used 0.5"DIAx6" carbon gradient sample to check surface carbon content. The result was 0.64wt% when using combustion method.But case hardness and microstructure etc all met acquirements. This issue always happens when the case depth is lower than .020".

Can I ask you how we can resolve this issue?

Many thanks in advance!!!

Matthew

 

[redpicker]

It seems as if your carburizing temperature is too high, particularly if this is a common problem.

With higher carburizing temperatures, the carbon diffuses from the surface at a faster rate, reducing the surface carbon content. You could try increasing the carbon potential in the furnace, but then you run the risk of having too high a carbon content, leading to retained austenite (low case hardness) and/or a carbide network in the case. With a shallow case like this, I'd lower the carburizing temperature, if you can.

rp

 

[mfgenggear]

is there any stock to be removed from the gear teeth?

what is the carbon content below .003?

as red picker said there may be decarb at the surface.
it could also be cause from the carbon potential from
hardening operation. not enough methane\propane.

 

[MATTHEWZHI]

Hi Mfgenggear:

Norminal .006" material will be removed from gear teeth surface. We sent carbon gradient bar out for surface carbon check. Actually this surface does not mean real surface. Lab has to machine .002-.005" off before they get chips from sample.

We used vacuum carburizing method at our facility. I think one thing caused this issue is the low pulse/diffusion time ratio. At the same time, I am checking how much deep materials the lab removed when they get chips.

Thanks,


Matthew

 

[mfgenggear]

see the thread below

http://www.eng-tips.com/viewthread.cfm?qid=219403&page=1