17-4 and condition A 4

[musashi99]

I use a lot of 17-4 bar in condition A. I have been told and have observed indications of the following:

The bar (1" in dia.)is annealed to condition A while in coil form then it is straighted. It is delivered with all that cold working stresses in the material.

Is this a true story?

Thanks

 

[EdStainless]

It could be, it depends on who makes it.
Are you having straightness issues with finished parts?
If not, then don't worry.
It isn't really that much strain to coil 1" bar. The yield strength in the A condition is pretty low.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[musashi99]

I'm not having straightness issue. We are making pressure transducers (of course stress sensative).
I am trying to convince my team that there is more stress induced into the bar by straightening process than there is in the machining process. I am propossing that we solution anneal the bars before machining.

 

[israelkk]

Here is a quote from MIL-HDBK-5J

"MIL-HDBK-5J
31 January 2003
2-195
2.6.9 17-4PH
2.6.9.0 Comments and Properties — Alloy 17-4PH is a precipitation-hardening, martensitic
stainless steel used for parts requiring high strength and good corrosion and oxidation resistance up to 600EF.
The alloy is available in all product forms.
Manufacturing Considerations — 17-4PH is readily forged, machined, welded, and brazed. Machining
requires the same precautions as the austenitic stainless steels except that work-hardening is not a problem.
Best machinability is exhibited by Conditions H1150 and H1150M. A dimensional contraction of 0.0004 to
0.0006 and 0.0008 to 0.0010 in./in. occurs upon hardening to the H900 and H1150 conditions, respectively.
This fact should be considered before finish machining prior to aging treatment.
When permanent deformation is performed, such as cold straightening of hardened parts, reaging is
recommended to minimize internal stresses.
Alloy 17-4PH can be fusion welded with any of the normal processes using 17-4PH filler metal without
preheat. For details up to ½-inch thickness, Condition A is satisfactory prior to welding, but for heavy sections,
an overaged condition (H1150) is recommended to preclude cracking...."

As I undeRstand it is better to use aged to condition H1150 prior to machining than using condition A. It will also stress relieve all prior induced stresses.

 

[EdStainless]

musashi99, aren't you aging after machining? If so you should be re-annealing as a first heat treatment step. The reall stresses that you end up with will be related to the transformation and cooling from the aging treatment.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[monkeydog]

From israelkk response, I would suspect he is speaking from experience on that one. 17-4PH is one of the "funny" stanless steels that does not react to heat treatment in the classical sense of metals. You need to check a good metals handbook to understand the heat treat response of 17-4PH. For example, looking at hardness, annealed will yield about 35 HRc, H900 gives you about 45 HRc, and H1150 about 33 HRc. Note that H1150 actually gives you a lower hardness then annealed.

 

[EdStainless]

The mechanicals are whacked too.
On 17-7 we get cond A 35ksi yield 130ksi UTS
That is why we never use hardness as an indicator for PH materials. Tensile testing is the only indication that works.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[musashi99]

This how I have been doing it.

17-4 condition A

solution anneal

machine

age to H900

One of the advantages of pre-machining annealing is you get less dimension change on your machined dimensions

 

[unclesyd]

Why do you solution treat 17-4 Cond A? This is the solution treated condition as received. Why not take Cond A and age to H-925 then machine.
The beauty of 17-4 was never having to use a furnace, just use an oven.

We have used 17-4 from its introduction in all forms and conditions and have never had to solution anneal any component.

The above comments about hardness and strength levels certainly apply. The best way we found to use the material is to select the condition required and heat treat to accomplish this taking the physical values as such and then machining the component.

 

[israelkk]

musashi99

How do you get rid of the surface discoloration after H900?
If you use chemicals you risk hydrogen embrittlement and uncontrolled dimension change due to unpredictable chemical removal of metal

My experience with vaccum furnace heat treatment is not so good and many times we still needed to use chemical etching to clean the surface before passivation.

However, the chemical cleaning always resulted in unpredictable metal removal and sometimes up to 0.05mm where the diameteral tolerance was +/- 0.01mm resulting in rejected parts.

The solution was to always "machine" all dimensions after heat treatment (even the H900). This way there is no problem of dimension shrinkage. This is quite simple when the heat treatment is up to H1025 where it is quite easy to machine the parts at this heat treatment.

When the heat treatment is H900, H925, H950 we sometimes use two stage machining. First we machine all non accurate dimensions leaving enough material to machine the accurate dimensions later. Then we heat treat to H900, H925, H950 and then use low pressure high mesh sand blast to render a clean surface and then finally machine/grind the accurate dimensions. Finally we passivate the parts.

 

[metman]

I should think (don't really know) that dimensional control would not be as critical as residual stress in a pressure transducer. However it seems like H1150 achieves the best of both effects if aged to this condition both before and after machining. H1150 Before machining in this instance to minimize residual stresses induced by straightening and H1150 after machining to minimize residual stresses induced by machining. If you machine without ageing, the internal stress from straightening prior to machining is still resident and could produce distortion during ageing.

The only question I have is what is the M in H1150M? Below encased in double quotes ("") are excerpts from the posts in this thread that seem most salient and upon which I arrived at the above conclusion:

""When permanent deformation is performed, such as cold straightening of hardened parts, reaging is
recommended to minimize internal stresses.

Best machinability is exhibited by Conditions H1150 and H1150M.

As I undeRstand it is better to use aged to condition H1150 prior to machining than using condition A. It will also stress relieve all prior induced stresses.

Note that H1150 actually gives you a lower hardness then annealed.

For example, looking at hardness, annealed will yield about 35 HRc, H900 gives you about 45 HRc, and H1150 about 33 HRc.""

 

[metman]

OK,
If anyone is interested, the answer to the "M" question is at:

H1150M
thread1135-113274

Thanks to unclesyd and mcguire.

 

[EdStainless]

Unclesyd, we re-anneal PH grades before aging because we get a lot more variation in final properties if rely on the mill anneal (even when it is our own). This is very critical if you are going for high properties. A reanneal is simple and helps uniformity a lot.
(my favorite is 17-7 in the RH950 at 200ksi +)

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

There is nothing wrong with reannealing the PH materials we were just happy to get out of the furnace and into the oven. Our big Lindbergs would dim the lights.

Though we never push the physical limits of the PH alloys in design where we used them, mainly 17/4, as replacements for Chromized Tool Steels and Carp 7Mo due to the ease of having a corrosion resistant materials with good mechanical properties and simple heat treatment. We stayed mainly with H1125 treatment for all our components which allowed us to do most anything with the components without substantial metallurgical problems cropping up. As I mention before we thermal cycle, operate at 550°F short excursion to 900°F, our components on short time basis and the result is we get a considerable increase in hardness over time. As the hardness approaches Rc 48/49 we will overage the part, do any repairs, and start the cycle over again.

 

[BobUXL]

musashi99 - Solution annealed materials up to about 1-1/4" is diameter are first hot rolled in coil form, solution annealed and can be processed in one of 2 ways - (1) straighten/cut/ground or cold drawn/straighten/cut. Depending on the mill, changing from a cold drawn operation to a straighten/cut operation can range from 3/4" to 1". These materials are not solution annealed after cold processing. So yes, there will be some residual stresses.

As far as the stresses in the material you are concerned with, you should be aging the parts after machining, so the aging operation should releave any of the residual stresses in the material. If you are having dimensional control problems when making the sensors, you may need to stress relieve the material first. But whether the material was cold drawn or straightened, the stresses on the outside of the material should not be much of an issue. I know of several companies making sensors for critical applications with the materials discribed above.

There were statements also made about machining thie grade in the H1150 and H1150M condition. My opinion is that this is old thinking. This condition is, of course, the softest condition and will minimize cutting forces, but you will then struggle with chip control. it would be better to machine either the solution annealed condition (Rc 28/32) or in the final aged condition. The H1150M was developed when all the tools available were tool steel. With today's carbides and coatings, this is a thing of the past. And you can be more productive in the long run.