6150 vs 4340 vs 4140 vs ?

[purpledrillmonkey]

Hi,

I'm having some issue selecting material and I wondered if anyone had any suggestions. The application is essentially a large snap/latch ring which gets squeezed down in diameter somewhat agressively, and needs to spring back to it's intial state. Say ring size OD ~ 4.25, ID ~ 3.625, 2" long.

My initial knee jerk reaction to material was an oil-quenched and tempered 6150 to about 45-50 HRc range (~ 190-210 ksi yield if I'm not mistaken) I have some experience with this material and it seems to behave quite well for these applications, but it is proving to be tough to source the material for these sizes. It's not impossible, but it isn't ideal.

Thus, I have been looking into trying out something we can get ahold of easier like a 4140, or possibly 4340. I've estimated a stress state around 160 ksi, and I'd like a bit of breathing room so I was targeting the 190 ksi yield...

I'm concerned about embrittlement in the 4140 as it looks like I need a temperature around 800°F which is right on the verge of temper embrittlement (as I understand it), but it is easier for me to get. Conversely the 4340 seems like a better choice due to inherent resistance to TE, but I don't know about availability here.

Is my thinking at all correct? Are there some materials I am unaware of or overlooking for good spring tempering properties?

Thanks for any help!

 

[swall]

As you are discovering, availability is everything these days, and it's tougher to find stuff, especially small quantities. What sort of starting stock are you contemplating? Kind of hard to provide further advice without knowing that.

 

[purpledrillmonkey]

This is going to be small quantity, say 10 or so at the start. Price isn't much of a problem here as long as it works - we're used to spending the money for low volume prototypes, but the time it takes to get 6150 tends to be long (in a 5+ inch OD), and that's what isn't good for me. I could make these things out of 4140 tomorrow for next to nothing were it not for the spring-like yield requirements.

 

[TVP]

PDM,

Can you upload a sketch of the part geometry? I'm having difficulty understanding what form the raw material would be in, meaning sheet, plate, bar, tube, etc. In general, you're thinking is along the right lines, spring steels instead of 4140 that is tempered at too low a temperature.

 

[EdStainless]

you are thinking of turning these out of bar?
Could you work with pieces cut from plate? That might help availability.
You might want to look at some of the higher ductility tool steels. that might get the properties that you need.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[purpledrillmonkey]

Sorry yeah, these would be turned from bar/tube stock. Think of a 2" wide ring, 4.25 OD, 3.675 ID, then a ~1" cut through it to split it into a "C" shape.

I've considered making it from flat/strip stock, but it's outside the scope of what we deal with typically, and this is pretty thick stuff. I'm sure it's doable, but we turn and mill for the most part.

 

[TVP]

EMJ Metals stocks 6150 in 5" OD bars.

http://www.emjmetals.com/products/S...mGrpCode=001&FamDesc=Round&MatDesc=Commercial

Alloy&SupDesc=Bar&pGrade=6150

 

[purpledrillmonkey]

Thanks for the link TVP,

It's not that 6150 is unattainable, my question is more regarding whether I can 'get away with' 4140 or 4340.

I'm up in Canada, so unless I expedite the shipping, we typically end up with many weeks for delivery of material when we order stuff like this from the states.

That being said, if you folks think that 6150 is the proper material for such a part, then it's worth waiting or paying the $$. It's the only 'spring steel' I've ever worked with for a machined part and it's served me well in the past.

However, if I can get similar properties out of a 4140 or 4340 without too much trouble or worry, that is considerably easier and quicker for me.

By the way, thanks to all for all the input!

 

[swall]

Purpledrillmonkey--I think you just answered your own question. Stay with what you know has worked in the past, since you indicate you have the time to wait for the material.

 

[TVP]

Agreed. This sounds like a tricky application, and I wouldn't risk 4140 or 4340 tempered at low temperatures.

 

[unclesyd]

In addition to the link posted above here is Castle Metals. We used them a lot for our alloy steel.
You might check with Scot Forge as to availability of rings or blanks in your size. I would always go with a rolled ring if possible though we use a lot of forged blanks.

http://www.amcastle.com/castlemetals/products.aspx#alloy

http://www.scotforge.com/sf_products.htm

 

[purpledrillmonkey]

Thanks for the links and advice guys. I'll push to use 6150 then as it is my initial gut feeling, it's familiar, and it's appropriate for the application.

If nothing else, I have a few more places to source the material from if need be.

Thanks!

 

[TemperedMartensite]

I used to use 6150 and 4140M (.43%C) interchangably. 4340 is a step-up in price and is likely overkill. You may want to look into 4145 - which should be readily available.

 

[unclesyd]

You might want to look at Flexor from Pennsylvania Steel. We used this as well as others as a substitute for many other alloy steels. I've had very good success with this material especially when a part was evaluated for higher loads, which always happens.

http://www.pennsylvaniasteel.com/flexor.php