Help selecting proper in-house HT procedure for 8620

[bob1111]

We are wanting to bring a case hardening process in house for some parts we are making. We are primarily looking at 8620 as the material. These are auto transmission parts. We would like to buy the material in the pre-hard condition (125ksi), machine the parts, then apply a surface hardening technique with a kiln. We are primarily looking at nitriding with Ammonia gas because it seems the safest and most practical but wondering if that process is ideal for 8620 with it's Chromium and Moly content to acheive our target hardness of HRC 60-62 with .010" thickness.

Also, would it be typical to apply a tempering technique after the surface hardening?

If nitriding is not idea for this material, are there other materials that work better with gas nitriding or possibly other surface hardening techniques that would work for a small in-house situation? ie, Cyanide gas, Methane gas in a hot oven, etc do not sound safe enough for some rookie heat treaters like us.

I have not checked as of yet but wondering if Ammonia gas is even available without special licensing.

 

[metengr]

viper6383;
What is the intended service or application of the part(s) that would exclude other surface treatment options, like carburizing?

 

[bob1111]

The part is an automotive shift fork. We are not opposed at all to carburizing but the techniques involve using a carbon rich gas (Methane) that is highly flammable thus my reluctance to use it. Obviously it would be the cheapest route by far.

gas nitriding was also appealing because it does not require a quench. I am certainly open to other ideas though.

We have pretty much wrote off nickel or chrome plating due to cost and our materials are more than capable of obtaining our target hardness on their own.

 

[metengr]

viper6383;
You may need to look closer at the differences between nitriding and carburizing in terms of case performance, and not just cost. This is a well researched subject area with information to guide you on the advantages and disadvantages of both surface treatment options based on intended service conditions.

 

[bob1111]

I will admit that our documentation here is limited but in our research, the nitriding will create a thinner surface layer but with our targeted .010" thickness, it should not be an issue for nitriding our 1 in3 part. maybe I am missing something on the subject.

 

[swall]

Viper6383--since you were concerned about the hazards of methane for carburizing, you should be equally concerned about the hazards of ammonia for nitriding. Ammonia-air mixtures are exposive at certain concentration ranges and ammonia by itself is a hazardous substance, requiring proper handling and emergency procedures. Venting of ammonia to atmosphere, even at permitted levels, may draw complaints from your neighbors. You also need to control the dissociation reaction in order to mitigate white layer formation. I looked at bringing nitriding in house at my plant and was looking at a $100K investment and I already had a suitable bell furnace. The cost and the environmental/safety issues led us to a "farm out" decision.

 

[CoryPad]

8620 is a strange alloy selection if you choose to use nitriding - the Ni and Mo are for through hardening, and the low C is for carburizing. Are you sure you can obtain pre-hardened material in the strength and size you need?

 

[dbooker630]

Methane (natural gas) can be used to impart carburization but is very inefficient not to mention sooty. A carbon monoxide source whether it is an endo- or exo-thermic mixture, or a nitrogen-methanol mix would be what you need.

Based on your case depth requirement I would go with carbonitriding or cyaniding. I would also recommend contacting the Metal Treating Institute for a capable experienced heat treater because of the safety requirements and furnace and atmosphere controls required.

 

[bob1111]

Our original material selection was 4340 but learned that it is prone to through hardening which would cause problems in this application. Our material selection is being driven by the structural properties. Quite honestly, we are very open to other material selections but it seems that we can live with the 8620 properties and it case hardens well so that is where I am at.

I guess we can get Ammonia but still not sure if that procedure is right for this shop. The last thing I need is a safety concern in the shop..

 

[unclesyd]

You might want to also look at liquid carbonitriding from Kolene/Nitromet. I've had excellent results on parts with wear problems.

http://www.nitromet.com/

 

[CoryPad]

8620 may be great for case carburizing, but you are asking about nitriding, so you should consider a different alloy that should perform as well or better and be less expensive to boot. If you don't need through hardening, then use 4130 or 1030 or 1020 or 1010, whatever has the strength you need and then use the nitriding (or other surface treatment) for wear resistance.

 

[mfgenggear]

Viper

besides all the good sugestions

Nitraloy 135(Best) or 4340M or 4330M Steel for Gas/Ion Nitriding
4340M induction harden to 50-55 Hrc

9310 or 8620 for Edothermic/Vacuum Carburize.

it is better farm this job out."for testing"
there would have to be a million parts to justify
up starting a dedicated heat treat shop.
plus the experience to run it.

for minimal distortion Nitride is best bet.

 

[mfgenggear]

oops spelling should be endothermic