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

[moskalik]

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

 

[EdStainless]

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

 

[moskalik]

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

 

[EdStainless]

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

 

[moskalik]

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

 

[ornerynorsk]

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.

 

[moskalik]

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

 

[EdStainless]

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

 

[moskalik]

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

 

[Maui]

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

http://www.EngineeringMetallurgy.com

 

[moskalik]

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

 

[EdStainless]

Ben,
Let's see if I can use the file hosting to get the handbook to you.
Ed

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Plymouth Tube

 

[EdStainless]

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

 

[moskalik]

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

 

[moskalik]

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

 

[moskalik]

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

 

[Maui]

Ben, the following paper should help:

http://articles.adsabs.harvard.edu//full/1967NASSP5089.....S/0000001.000.html

Maui

http://www.EngineeringMetallurgy.com

 

[btrueblood]

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.

 

[EdStainless]

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

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Plymouth Tube

 

[tbuelna]

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