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17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment
14

17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
I have a question about 17-7 PH, condition TH 1050 that has been troubling me for some time.

We manufacture wire products, so any 17-7 we use is in wire form that we coil into shape. When using 17-7 PH, we usually (99.9% of the time) use Condition CH900 which works well for us, but every now and again we get a request for Condition TH 1050 that we just cannot seem to get to work. The problem is that the AMS 5528 specification states the tensile strength should be 180 - 210 ksi after heat treatment and we can barely get over 150 ksi.

I know we are meeting the specification exactly in regards to the heat treat process and I even have the furnace charts that show our vendor is cooling to the 60°F within one hour to ensure proper formation of Martensite (they go down to -150°F for get the proper cooling rate). I would think that if we meet the heat treat process exactly, we should be able to duplicate the physical properties, but that just isn't happening.

I have heard from several sources that chemistry can play a role in how the material responds. Does anyone have insight on what could be happening to make the TH 1050 come out with a lower than desired tensile strength? Also, does anyone have any insight on the chemical elements that could affect the response to heat treatment and what are the optimal ranges for those elements?

Thanks,
-Ben Moskalik

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

heat treat a sample of the rod before you draw to wire.
Your original mill certs should have data for both the annealed rod and a heat treated sample showing that it is capable of meeting properties, and that is usually TH1050.

You draw, anneal (1950), cool, austenite condition (1400), cool, then age at 1050, right?
There is no reason to cool this alloy below RT. We never do and it always comes out correct.
We cold draw a lot of tubing in this grade with very reliable properties.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Thank you for the reply, Ed.

That is an interesting concept to test the rod direct from the mill, but I am not sure that the results are going to be any different. You are correct in the process that we follow for the anneal, conditioning and transformation. More specifically, every step that we do is as follows:
- Receive rod as Condition A, Direct Cooled ("D" Cooled)
- Draw rod into round wire
- Round wire is Cold Rolled into flat wire (the physical properties at this point is about 220 ksi because of all the cold work)
- The flat wire is annealed (1925°F) and cooled (tensile: 120 ksi)
- The Flat wire is conditioned (1400° for 90 minutes) and cooled (transformed) to "60°F". As I stated, to get the proper cooling rate within the 1 hour for a batch coil of wire, our vendor needs to cool to a lower temperature so it properly transforms, so they drop it to -150°F to assure the 60°F within an hour. (Tensile: 150 ksi)
- The wire is then aged (1050°F for 90 minutes) and the physical properties do not respond (Tensile 150 ksi)

We have even tried this process WITHOUT the anneal to try to retain the deformation martensite with the same results: the conditioning and transformation drops the tensile to 150 ksi and the age doesn't increase the physical properties as one would think it should.

Which brings me to my original question: is there a possible chemical difference? I wonder if there is something different between the rod/wire that we use and the tube that you use that is causing the wire we use to not respond but the tube you use to work just fine?

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

No, they are doing something wrong in the heat treat.
You need to lab heat treat some rod samples.
I would do some solution anneal and well as working from the process annealed condition (which may suck).

If you want try retaining the cold work then you go from C to AC at 1550F, then 0F for at least 4 hours, and then age at 1050.

I have worked with a hundred different heats from three different mills, we have never fails to achieve properties.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
You are right, I should have an actual lab do it to see if we get the same results. Heat treatment vendors are ... well .... interesting to work with.

The chemistry question that I have is based on what I have been told by wire/rod suppliers, but then they won't elaborate on the chemistry that affects the heat treatment. I was hoping someone else knew that answer.

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Has the material been verified against the certs?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Yes, if you mean the chemistry. The chemistry is well within the AMS and UNS chemical content. I just heard that certain elements could be skewed one way or another to improve results, I just don't know what those elements are. As far as I know, there may even be an unrecorded element that is affecting this...

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Ben, Do you have a copy of the old Armco 17-7/15-7 handbook?
If not drop me an email at eblessmanatplymouthdotcom and I'll send you the pdf.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Ed, Yes, I think I have it. Are you just talking about the Armco technical data sheet that is maybe 10 pages long? I have several: one from 1991 and one from some time before that (S-30a). I know it lists the different conditions and heat treats and things like that. Is there something is particular to focus on in that document?

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Exactly how is the wire being quenched? What method is being implemented to achieve the required cooling rate? Nitrogen? Oil? Forced air? What is the manner in which the wire is being held in place (i.e. how is it coiled geometrically) during the thermal treatment cycle? And where are you cutting your test sample from on the coil to determine the tensile strength? Or are you cutting a test sample beforehand and running it through the thermal treatment cycle separate from the coil?

Maui

www.EngineeringMetallurgy.com

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
From what I know, the quenching is achieved by back purging the furnace with Nitrogen. Typically the wire we have is bundled in a coil that is about 26 inched in diameter and then we just take an end piece for physical property testing.

However, this last test I did only used test strips as an experiment. I only sent out 12 inch strips and the heat treater pulled out 3 strips for every step of the heat treatment so we could verify what was happening. Everything looked fine until the last step as I mentioned before. Because I was only using test strips and not a whole thermal load, I was hoping I could at least get some kind of favorable result, but no dice.

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Sounds like we need to look at some micros.
If the material will work as CH900 then it should work fine as TH1050.
Heck, I might have you mail me some sample to HT and test here.

The file is an 18MB .zip
Ed

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
An 18 MB .zip should work. Can you Email that to me?

As for sending you samples, I may take you up on that offer :)

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
I got the file open. Worked like a charm. Thanks, Ed!

Now I have some light reading for the rest of the morning.

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
The 17-7 Handbook was a very good read and enlightening in what freedom we have with the Austenite conditioning and Transformation. Since I only had the technical bulletins before now, the information was limited to the optimal temperatures and times, but they never mentioned the reasons behind the times and temperatures. The fact that the Handbook mentions there is a modified AC that can be used if there is some residual Cold Work was a real eye opener in that I can do different things to try and make this work.

My next step is to proceed with testing different times and temperatures for the Austenite Conditioning and the Transformation. The final age will obviously have to remain at 1050°F. Hopefully I can get something that responds much better than what I have been able to do up to this point.

On the point of chemistry, this still seems to be a variable as well. The handbook does mention some chemical elements that affects the process and how it can affect the austenite conditioning, but it doesn't explain it well. I still appeal to this forum that if anyone has insight on the effects from the slight differences with the chemistry for 17-7 would be appreciated.

Other than that, I really do appreciate the hand book, Ed. I have some work cut out for me!

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

The handbook does mention that excessive carbon pickup can render the material incapable of age hardening. If in-process annealing is part of your manufacturing sequence, check that the material is being adequately cleaned/degreased before going in the annealing oven, and that the oven atmosphere is neutral.

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

BT, good point, Nitrogen can also have a negative influence.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

EdStainless- Thanks for the Armco handbook, it's great reference material.

Moskalik- I noticed you are with Smalley. A couple years back I ordered 3 or 4 custom wave springs in AMS 5529 (17-7PH/C CH900) from Smalley. The wave springs were manufactured based on SCD's I provided. The parts were delivered with material & HT certs and an AS9102 FAI record for each p/n. I was especially impressed with how smoothly things went with these custom parts. They were delivered on time and on budget, 100% of the parts were accepted by our QA, and Smalley did not submit a single DR on any of the parts in the order. When I was preparing the SCD's I got quite a bit of assistance/feedback from an engineer at Smalley, but unfortunately I cannot recall her name.

To make a long story short, based on my personal experience it seemed that Smalley had a pretty good understanding of manufacturing very high quality wire products, including those using 17-7 stainless. Has something changed recently at the company? I have worked with a large number of aerospace component suppliers over the past 25+ years, and I would rate Smalley as being in the top 5% of them. I would hate to hear that Smalley is not the first-class operation it was just a few short years ago.

Regards,
Terry

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Terry,

Thank you for the positive feedback on Smalley and sharing the good experience you had with us. We have many engineers (about 20) that work on the sales side of things and they do a good jobs giving the technical assistance that our customers need. I am glad to hear that you have a good impression of Smalley. What company do you work for? It is always nice to pass along positive feedback.

To get back to your question about why I am asking these questions about 17-7 PH, Condition TH1050, I want to direct your attention back to my very first post on this thread. We currently manufacture many 17-7 products that are made out of 17-7 PH Stainless Steel, Condition CH900 flat wire and we do not have a problem with the condition CH900 of material. We have our own rolling mills in-house and we can tightly control the geometric dimensions and physical properties (amount of cold work) of the wire. Again, we have no problem with Conditions CH900 similar to the parts we supplied to your company in the past. We pride ourselves on being able to roll our own raw material (flat wire) and being about to tightly control the parameters that are important to make quality product.

However, we have never been able to successfully make 17-7 PH, Condition TH1050 material that meets industry specification for physical properties, and it frustrates us that we cannot doso. This means we cannot bid on these requests. TH1050 is different than CH900 because it relies on thermal heat treatment to achieve final physical properties, and that requires a heat treat vendor to perform the heat treatment correctly and the original material to have correct chemistry to respond to that heat treatment. Both of these parameters are out of Smalley's control unlike CH900 which mostly relies on the cold work which Smalley does control.

I have approaching wire suppliers, rod suppliers, heat treaters ... anybody who may know something about why the 17-7 wire doesn't respond to the heat treatment of TH1050 and I have received a wide range of answers from "I don't know" to "the chemistry of the rod changed 30 years ago and TH1050 can no longer be achieved". Since I am an R&D Engineer, you can imagine those are not answers that are acceptable and I want to know exactly why we cannot do something, so this is why I am here :)

So I appeal that you still consider Smalley as a first-class operation. Nothing has changed at our organization or the knowledge base we possess and we still pride ourselves on quality product and the technical assistance we supply. Smalley is just trying pursue something that we have not been able to do previously so we can continue to be world leaders in coiled flat wire products.

Did that somewhat answer your question or at least ease your mind? :)

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Maui,

That link was very useful. I had seen this NASA document before but needlessly blew it off. Since you focused my attention to it, I sat down and read it yesterday and it is very good compliment to the 17-7 handbook that Ed posted a few days ago. Thanks again!

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

We used to make 17-7 PH at J&L. It was a very early PH grade and extremely sensitive to minor changes in chemistry within the specification. Aluminum is the crucial precipitate former. To the extent it has formed oxides or nitrides, it will show up in the analysis, yet not be useful. Too little carbon will cause a too high MS temperature, the same as an incomplete austenitizing. The as-received condition may be difficult to re-homogenize from prior heat treat making large carbides. And, if the ferrite balance is slightly off, but within spec, you get delta ferrite that you can't eliminate.

It is a nasty, ill-designed grade of stainless. I would ask ATI or Carpenter for their recommendation on a substitute. 17-7PH really is trouble.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Yes Mike, it has issues, but it is fully austenitic when annealed which means that those of us that cold draw tube and wire need it.
In order to do heavy cold work with 17-4 it would have be in the overaged condition (to get enough ductility) and the be re-annealed and re-overaged between each draw cycle.
I do like the 17-7 alloy, but that said I would never try to go over about 0.125" thick with it. And we never run strip without first heat treating a sample to verify properties.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Dr. McGuire,

Thank you for the feedback and the insight on which chemical elements may be affecting the material. Like Ed said, 17-7 may have its issues, but for us making edge coiled wave springs out of flat wire, it works really well in the Condition CH900 and is one of the most stable and predictable materials we use.
I looked at the chemical content in regards to the Aluminum and Carbon content for the 17-7 PH material I used to test the TH1050 process, and they both appear to be OK. AMS 5528 lists the Aluminum content to be 0.75 - 1.50 and the material was actually 0.97 . The Carbon is to be 0.09 maximum and the material was actually 0.080 . I think you stated that a low carbon content would be bad, but this seems fairly high on the allowable range. The Aluminum content is right in the middle of the range, so that appears OK too.

I wonder if the chemistry has been OK all along and it is something to do with improper solution that is not erasing the cold working we are doing. I really hope it doesn;t have anything to do with the chemistry since that is not something we can easily control. Definitely some testing is in order.

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

2
At the risk of being criticized for guessing, I have to follow the reasoning that the age hardening response is inadequate. This relies on Al and Ni combining. Since there is plenty of Ni, I have to guess that the AL may not be available. It could be in the form of aluminum nitride and unavailable for precipitation as Ni3Al. Nitrogen is more reactive with Al and you may have some pick-up in it via heat treat atmosphere. Just a suggestion. This wouldn't show up on mill certs and it is more possible in your light gauges.

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

moskalik-

Thanks for the response. And don't worry, I still have a high regard for the Smalley Company and its excellent products.

This thread is very interesting to me, and the responses were quite informative. I did some reading on the subject and it seems that what btrueblood noted above about carbon pickup from surface contamination hindering the age hardening process may be one potential source of your problem. I've attached the relevant pages from a technical bulletin from AK Steel discussing issues like surface contamination and furnace atmospheres on heat treatment of 17-7.

Hope it helps.
Terry

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

(OP)
Terry - For my testing, I will make sure I vapor degrease the samples before I start. That way I can eliminate the carbon pickup as a variable. Definitely a good suggestion.

Dr. McGuire - You will never be accused of guessing by me :) We are all guessing at this point what is the issue. I appreciate all the input and insight.

I just got all my test strips placed on my desk a few minutes ago. I have my work cut out for me next week heating these and testing the response. :)

===========================
Ben Moskalik
Smalley Steel Ring Company

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

OK Guys

I'm retired now and my help is always free to real people with real questions.

Mike McGuire

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Ed,

Can you expound on why you wouldn't use 17-7 in thicknesses over 1/8"? Is it due to the difficulty in getting the right degree of cold work into the material? I ask out of curiousity, and because our spring winding vendor has typically steered us away from 17-7 for our heavier springs.

Mike, is there a way to deduce what degree of oxidation/nitriding of the Al has occurred?

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

I know that they say that you can go a lot thicker, but given how sensitive the material is to the annealing and austenite conditioning treatments I would be cautious. Especially if the parts have varying thickness, getting uniform properties could be very difficult. The thicker areas may not get strong enough, and they may also have poor toughness.

If you look at 17-4 you will see that as sections get heavier people move to 15-5.
These alloys as a class are sensitive to heat treatment and can be tricky.

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Plymouth Tube

RE: 17-7 PH Stainless Steel, Condition TH 1050 not responding to Heat Treatment

Thanks Ed.

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