STILL TRYING TO SELECT MATERIAL FOR TRANS. SHIFT FORK 1

[bob1111]

Here is the deal. We had pretty much settled on 8620 and then carburize it. Then we found out that 8620 is pretty much non-existent in flats. So now we are back to the drawing board... The part needs to be through hardened to around HRC 35 depending on alloy. The fork tips need to achieve around HRC60-65. I have looked again at 4340 and induction harden the fork tips but not sure how hard I can get with 4340 and also how it might work to try and surface harden a cross section of only .200". I am concerned that is the whole thing goes to HRC60, we would have a reduced fatigue life.

I do not want to get into nitriding and trying tokeep the process in house. We were going to pack carburize the parts until we learned we cannot get 8620.

So I guess we are either looking for a good structural material that will work with carburizing, or an induction hardenable alloy with similar properties. Both commonly available in flats or rectangle bar, not cut from plate.

 

[CoryPad]

How big is this part? A thickness of 0.2" is far from plate and bar - that is sheet territory.

For wear resistance on thin parts, you may want to consider ferritic nitrocarburizing. Use a simple 1XXX or 51XX or 41XX or 43XX steel that meets your strength needs and then put it in the pit/furnace for the surface treatment.

 

[bob1111]

The part varies greatly in cross section. We would start with a 1x2x3 block and machine 65% of it away. Fork tips are thin but the back of the part remains 1" wide x .75" squared. This should keep the bulk of the part from trying to through harden but I am worried that trying to case harden a .200" CS will not happen.

Again, we are looking to keep all processes in house. We have an oven and willing to setup for induction heating but some of the case harden methods are too dangerous for us to mess with. We planned to use pack carburization if we were to use 8620. Very open to ideas on this one. 300K psi ultimate, HRC59+ surface....

 

[CoryPad]

8620 is available in flat bar in 1" to 2" sizes. Alro is one source:

http://www.alro.com/DATACatalog/UpdatedCatalogSections02-24-09/008-Alloys.pdf#page=23

 

[bob1111]

Ironically, last time I quotes with Alro, they could only offer cut plate which would cost much more than bar. I will chech with them again.

If we cannot get 8620, we were looking at pack carburizing something like a 4320 or maybe 4340. We planned to slow cool so as not to harden the part at that stage. Then follow up with a harden process and temper..

Any thoughts on pack carb on 4000 class alloys?

 

[arunmrao]

4340 and pack carburizing incompatible. Be a little more flexible in your choice of process and many more solutions can come up.

If you can discuss with any heat treater in your area,he can provie a boquet of solutions. But, I gues you want to stay fixed with pack carburizing.!

Learn the rules,so you know how to break them properly.
Dalai Lama

_____________________________________

 

[bob1111]

No at all. We are open to ideas here but carburizing seemed the best solution at the time..

If we could find something that would induction harden to our specs, that could work too. No one locally does nitriding. We were pretty fixed on just using 8620 and taking them in to be carburized but the lack of material selection is killing this project. Cutting from rounds simply is not cost effective.

 

[DAVIDSTECKER]

If you are looking for low friction and high wear characteristics, maybe you should take a look at the grey and ductile irons.
You can get it in variety of bar and flat shapes as well as casting to near net shape.
Since your gears are already hardened steel the dissimular metals concept is in your best interest also. Works real well in engine cyclinders.

 

[swall]

Bob1111, I have followed this thread from its inception and have to tell you your approach is all wrong. Your desire to keep all of the processing in house is at odds with producing a serviceable part in a cost effective manner. You are severely limiting yourself here and you need to go back to square one. Start with a sound design, which it sounds like you already have. Then work with a metallurgical consultant to flesh out the material and processing details, both in house and out sourced. Gather the costs and determine if you have a viable program.

 

[tbuelna]

Bob1111,

Your shift fork is basically a semi-circular finished shape. I'd suggest trying this:

Call a local forging house and see about rolling a ring segment shape from 8620 rectangular bar. There should be no tooling costs, it will minimize material scrap, you'll get a fairly close net shape, and you'll get forged properties to boot.

I think you'll be surprised how inexpensive those rolled rings might be. The lower ram material cost also might be enough to offset the rolling charges.

Good luck.
Terry