Heat Treatment Spec 1

[skudwoofer]

I have a part (see attached). It is currently made out of 4140 Steel and I want to spec. a post heat treatment process after machining. Questions:

1.) Do I need to be concerned about warping due to the part being pretty thin.

2.) What hardness will I be able to achive (this part has a rubber seal that runs against it)?

3.) Should I consider 4340 or 4150 instead?

 

[TVP]

Can you post an image file (.jpg, .tif, etc.) instead of an image from a modeling program? Very few of us can open this type of attachment.

 

[Wrenchbender]

Skudwoofer,
I could not view the attachment, but in attempt to response to your numbered items:
[1] I would always be concerned about warpage, even on a thick part. Generally some warping occurs anytime there are phase transformations (e.g., austenite to martensite during the quench, carbides during tempering, etc.) or thermal effects that have taken place. Thin parts could slump in the furnace if not well supported. For these reasons, finish machining, esp. close tolerance features and threading are almost always done after HT (as you are already doing).

Ref ASM Handbook, Vol I, 10th Ed.:
[2] Untempered 4140 steel should go about 55-60 HRC. (Caution on low toughness with anything left untempered.)
[3] Hardenability curves for 4140 look pretty good for parts < 1 inch crossection. Therefore based on hardenability, there is no great advantage in using 4340 or 4150 or other. (Also, no reason that I know of to expect less warpage or better machinability.) You may even want to consider a medium carbon steel such as 1040.

Lastly, for spec’ing out a HT process (mentioned in your first paragraph), a good source would be AMS (formerly MIL)-H-6875.

 

[skudwoofer]

here is a pdf

 

[skudwoofer]

3d pdf

 

[redpicker]

Not to be glib, but you really haven't given enough information.

1.) Do I need to be concerned about warping due to the part being pretty thin.
This all depends on how flat and round you need the part to be after heat treatment. That is, you only need to worry about if you need to worry about it.

2.) What hardness will I be able to achive (this part has a rubber seal that runs against it)?
With 4140, this will depend on the actual dimensions of the part and you processing. If the thin part of web is 8 inches thick, with a normalize and temper process, I'd expect around 200 Brinell, maybe less. If the thin part of the web is only 1/16" thick, well, you are going to have a bunch of problems, not the least would be machining it in the first place.

3.) Should I consider 4340 or 4150 instead?
You can consider these, but they will have the same problems as the 4140. The effective differences between these materials have to do with hardenability and impact strength, properties you haven't indicated are important.

You need to first decide what hardness you need (or, better yet, define what combination of properties you need). From that, you can form a list of canidate materials. From those, you can determine the processing needed to meet your requriements. Then, you can run a cost analysis to find which is the most cost effective.

From the looks of your model, my guess is you would be best to machine after heat treatment as any of the materials you listed will distort badly with that geometry during a quench and temper operation. If surface wear is critical, but service stresses will be low, you might consider a plating or even a plastic coating.

rp

 

[CoryPad]

1) Yes
2) 60 HRC on the surface, less than that in the core (this is a function of the part dimensions, which you have not provided)
3) Yes, if you need hardenability (this is a function of the part dimensions, which you have not provided)

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[skudwoofer]

sorry guys for being so vague, the conical surface has a thickness of 4mm and the wall thickness of the face with the smallest hole is 1mm thick the diameter of the part is 25.4mm. It is a washer type part to hold wheel grease in. The customer is looking for a material that will have a service life of 60,000 miles and 1008 rotations per mile for a total service life of 60504343 rotations... I am not sure that last bit is important, I am just wondering if the "customer picked" 4140 hardened before final machining to 60-65 HRc would be "adequate". Impact strength is non-existent and all of the design revolves around surface wear... For all I care it could be 7075 T6 with some sort of coating, it just needs to stand up to stationary wear where the seal contacts the surface of the part in one radial area, think hub seals on a car hub / spindle combo.
HTH,
Eric

 

[redpicker]

With this information, we can be a lot more specific.

As has been noted above, 4140 will not achieve 60-65 HRC without a surface treatment. It will distort severely during heat treatment with those dimensions, and at that hardness, will be nearly impossible to straighten without cracking. Even machining 4140 at a reasonable hardness to those dimensions would be very tricky.

While this is not my area of expertise, I think I'd try to find a way to stamp it from mild steel. If a surface hardness in excess of 60 HRC was needed, I'd look into nitriding.

rp

 

[unclesyd]

As stated above 4140 will not achieve the desired hardness of 60-65 Rc even in the as quenched condition, neither will 4340. 4150 will get to 50-63 as quenched but generally be used in this condition.
Oil Quenching the part made from 4140 distortion will not be the only problem as the thin section will probably break where it changes in section.

I would certainly look at nitriding the part.

Are you talking about a large production run?

Where did you get your hardness requirements as we run lubricated lip seals against 4140 heat treated to 30-32 Rc all the time?

 

[skudwoofer]

I really appreciate all the expertise from you fine fellows. I was not sure on the hardness requirements, as I am not a materials engineer, and I just want to offer a qualified solution to the customer.

unclesyd - thanks for the information, I suggested nitriding, and now I will go back to the customer with some more informed suggestions. Does any one know what the "standard hardness is for 4140? This part is obviously being machined out of bar stock. The run for this year would be 500ish. Next year 1000, and the following 2500 with a level production after that of 2500 a year.

 

[unclesyd]

You can get 4140 to around 55 RC but it is extremely brittle at this hardness. As the hardness decreases the toughness goes up and most 4140 is used in the range of 28-32 Rc if any ductility is required.


I certainly would look at something like the Crucible 135 to make the part. You should be able to get these materials in hollow bar. Also you may have to leave the "flange" a little thicker until you get the production ironed out.

http://crucibleservice.com/eselector/prodbyapp/carbon/nit135c.html