Cold Worked 204Cu SS vs conventional heat treated SS 4

[slashragnarok]

While researching some high strength steels I came across 204Cu which apparently offers quite high tensile strength values depending on how much cold reduction it's subjected to. What difference would there be between heat treated stainless steels and cold worked 204Cu? I am looking at 150 ksi - 180 ksi UTS. Also it seems that 204Cu is a lot cheaper than other SS.

Thanks

 

[EdStainless]

All austenitic SS alloys will work harden.
They fall into two broad groups, some just strain harden and other also harden by transformation. In the transformation martensite is formed and the alloy becomes noticeably magnetic.
If you want examples of properties look at ASTM A666. This lists as cold worked properties for many stainless grades, at various cold work levels.
You will notice that some alloys loose ductility much faster than others as they get cold worked.
204Cu is one option, but it has fairly marginal corrosion resistance.
There are also some other options, the new Outokumpu FDX25 lean duplex will work also.
Almost all aurt SS will reach this strength, you need to think about what level of ductility and corrosion resistance you need.

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P.E. Metallurgy, Plymouth Tube

 

[slashragnarok]

I am trying to steer clear of Duplex and PH stainless steels. Cost and availability is a big factor here. What I intend to know is would 204Cu work the same as any other high strength steel while offering moderate corrosion resistance?

If you may recall I had posted a thread about selecting a steel for a weightlifting application. Now the roadblock I've hit is that no heat treater is willing to heat treat a small quantity for my prototype. Which is why I've turned to cold drawn steels which have similar strength properties as heat treated alloy steels. At least close to that. Corrosion resistance is a value added feature as I could always electroplate the shaft. It's a 2.2 m long shaft, 28.5mm in diameter which would mainly be subjected to bending stresses. Moderately high impact toughness is also desirable.

If not 204Cu, which other cold drawn steel, stainless or otherwise do you suggest I could use which would still allow me to have strength close enough to heat treated steels?

Thanks

 

[EdStainless]

I am afraid that if you want cold drawn bar you will have the same availability issues.
A PH grade would get you around that, since it all comes annealed and is simple to age.
The advantage is that you could machine (and knurl) the softer material and then age harden.
I would suggest that you look at 13-8PH, it is sold under a variety of trade names such as SuperTough.
The H1100 condition will have 150ksi min UTS and lots of ductility.

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P.E. Metallurgy, Plymouth Tube

 

[slashragnarok]

Wouldn't the cost be prohibitive? A local dealer has confirmed that he has 204Cu in stock and could get it cold drawn to whatever percentage specified.

 

[EdStainless]

If you can get the 204 custom drawn for less then go for it.
Just make sure that they don't over do it.

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P.E. Metallurgy, Plymouth Tube

 

[slashragnarok]

Thanks Ed.

Does the material knurl the same as any other steel hardened and tempered to a similar hardness? I am asking this because I've come across data (link:

http://www.ulbrich.com/204cu-stainless-steel/)

which suggests that cold rolled 204Cu has higher elongation stats than, say, QT chrome-moly steel at the same strength (subsequently similar hardness?) levels. Does elongation mean anything as far as knurling is concerned? Also how does this material machine in the cold worked state?

 

[EdStainless]

The hardness will be similar to a Q&T steel at the same strength.
It will be hard to knurl, but it should work. Use lots of lube.
The elongation only means that the material will bend before it breaks, it will have more damage tolerance.

It will take 35% reduction cold drawn get 150kis min UTS this material. You should end up with about 20% elong at that strength.

It will machine like any metal with 40-45Rc hardness. Stainless often machines better when hard because it does not stick to the tools as badly.

Do you know the source of the material?

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P.E. Metallurgy, Plymouth Tube

 

[slashragnarok]

Thanks Ed,

The data I pulled suggests 175 ksi UTS at 50% cold draw with 27% elongation. Is this too deviating from experience? I don't know for sure the actual source of the material. I'm getting it from a local stainless steel dealer, who himself had suggested this alloy when I told him I was having a hard time finding a heat treater. What questions should I ask him?

 

[mcguire]

204Cu..., really? Why screw around with an alloy no one has produced in a decade? 301 or 201 will do the job quite well. 301 is very available. 201 less so. A 301 composition close to 17.0 Cr 7.0Ni with 0.05 to 0.12 C should do the trick without excessive cold reduction. If you have a dealer with left over 204Cu and the price is right, then buy it. It will require more cold reduction to attain properties than 301 or 201, but it will work just fine.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[slashragnarok]

You're in the USA I believe? Where I live 204Cu is available abundantly. But thanks for the 301 tip. I'll take a look at it. Cost is also a major factor here.

 

[slashragnarok]

How does the diameter of the round change how much cold reduction is required to achieve a particular UTS?

 

[EdStainless]

I would ask them a couple of things.
Tell than that you need a minimum yield strength of 150ksi, and a minimum elongation of 20%.
Then ask what cold reduction they will use.
If you need 28.5mm finished size they will start larger. If they use 38mm (1134sq mm) and draw to 28.5mm (638) the reduction is (1134-638)/1134 = 44%
This looks to be in the right range.

McG, in 2013 there was as much 200 stainless produced world wide as 300 series. This is big change from just 10 years ago. Driven largely by Ni prices, and the use of more SS in Asia. There is almost no houseware item made in Asia today that is not a 200 alloy.

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P.E. Metallurgy, Plymouth Tube

 

[mcguire]

I always promoted the use of 201 for food service in the US in the 1990's. J&L got a lot of very profitable business that way. The main obstacle was the service center industry which refused to stock another grade. So we sold direct to big end users, who really appreciated the savings. It is just plain dumb to use 304 in situations where 201 is fully adequate. That comprises about 90% of the flat rolled market. The main exception being you tubing guys.

Michael McGuire

 

[slashragnarok]

Bang on Ed! In fact after the nickel price surge in the 1980s, my country (India) became a huge producer of the 200 series.

Also thanks for the data. I'll pass it on to my supplier. Doubt that he would know anything about elongation.

While we are on the subject of austenitic stainless steels; this application I'm talking about entails the 204Cu shaft which I mentioned here and two sleeves which would be restricted in axial movement but rotate on the shaft supported on two cast bronze bushings on either end (one each end). I have contemplated making these out of 304SS tubing (I've attached the assembly pic sans retaining rings, end cap, spacers and the flange which would be press/shrunk fit on the interior end of the sleeve to restrict the weight plates). This tube would be internally bored to cut a couple of shoulders and also have internal retaining ring grooves machined. Apart from this I'll have to turn down the OD from 60.3mm to 50mm thanks to the next standard OD size being 48.3mm. If legend is true about the work hardening potential of 304, how difficult on a scale of 10, do you think machining the stuff would be?

 

[EdStainless]

You need to get the right size of 304 so that you only do a short counter bore in each end. You do not what to machine the whole ID.
You may end up using steel tube for these, just because of availability.

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P.E. Metallurgy, Plymouth Tube

 

[EdStainless]

Most of the 200 stainless in the world is total junk with very poor corrosion resistance.
Unless you keep the Cr over 17%, and the N above 0.25%, and the S below 0.015% you have trouble.
You need the high Cr and N to get corrosion resistance.
And you need low S because of the MnS that forms and acts as corrosion initiation sites.
I have seen a lot of Asian 2xx samples that were no better than 409 in corrosion testing, nowhere near decent 304 levels.

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P.E. Metallurgy, Plymouth Tube

 

[slashragnarok]

Thanks Ed. The OD is what would be turned down from 60.3mm to 50mm; roughly a 5mm or 0.197" total depth of cut. The ID would be counter bored as you mentioned along with snap ring grooves. The nearest tube size available for my design has an OD of 60.3mm and wall thickness of 11.1mm (Schedule XXS). I actually changed my design to accommodate a standard size to avoid extensive boring operations. Custom sizes are available but only if I order in large quantities.

204 does have 17.5% as the upper limit of its Cr content.

 

[tbuelna]

I can't believe you can purchase any stainless steel bar for less than you can purchase a comparable alloy steel bar and plate it to get the corrosion protection needed.

 

[slashragnarok]

@tbuelna - The key factor here is Volume. It means I'll be charged at an exorbitant rate to plate a couple of feet of material. Which I presume would run me the same cost of using SS. Also since heat treatment is no longer an option, I need some work hardening variant of steel.