Elementary question about 17-4 / 17-4PH / 17-4 Double Aged H1150 2

[tr1ntx]

I recently started a new job with a company where the engineering has not been "by the book". There are varying material specifications for different sized parts (same function in different sized assemblies). One that is tripping me up because I have never encountered it before is the 17-4 Stainless Steel. We have some parts spec'd as "17-4 H1150", some as "17-4 Double Aged H1150", others as "17-4 Double H1150", also "17-4 HH1150", a few as "17-4PHH1150" or "17-4PH H1150", and a few as "17-4PH Double H1150".

I searched for information on these material conditions and I think I'm right in saying that "17-4 H1150" is not the same as "17-4 Double Aged H1150" (double aged having an extra soak). I assume that "17-4 Double H1150" means the same thing as "17-4 Double Aged H1150" but whoever typed it left out the word "Aged". (or maybe including "Aged" is redundant in the first place)

What I can't find an answer definite enought to suit me for regards the "PH" designation. I know that it means either "precipitation hardened" (that it has been hardened by molecular precipitation) or "precipitation hardening" (that it is capable of being hardened by molecular precipitation). Another question is whether "17-4" and "17-4PH" mean the same thing, i.e., is there such a thing as plain, non-PH 17-4 stainless steel?

I saw on thread, maybe on here, which I understood to say that there is a difference. I can't find it now, but nevertheless, it didn't spell out the case in elementary enough terms for me. My take was that 17-4 Double Aged H1150 is material that was put through the H1150 age hardening process twice, whereas 17-4PH H1150 is material that was first precipitation hardened, then went through the H1150 age hardening process once. I may be wrong, "age hardening" and "precipitation hardening" may be the same thing.

On that note, even if the 2 processes are different, how different are the 2 end products. I can't find that spelled out either.

 

[EdStainless]

Most of us don't care what PH really stands for, but you are correct.
While there could be a 17-4 (non-PH) it would be a duplex grade.
The correct name for the heat treatment condition is H1150.
(other letters are used for aging heat treatments that involve prior cold work or cryogenic temps)
As for the double aging, it will give you a bit less strength and a bit more toughness.
How to write it out is a matter of taste.
17-4PH double aged H1150 might be the easiest to read.

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

 

[mcguire]

Age-hardening is precipitation hardening which is done at low temperature on aluminum alloys. PH was coined by stainless metallurgists. There weren't any language cops around.



Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[MikeMet]

I think it is a misnomer to say that "double aged" is the same as H1150M, but I have seen it writen that way. H1150M is an intermediate soft condition where the alloy is given a subcritical anneal prior to final aging treatment to obtain the softer properties. The 1400F treatment after the 1900F solution anneal is the sub-critical anneal. So more correctly it is double annealed, not double aged.

There is not heat treatment in the ASTM or AMS Specs that calls for a double age at a standard aging temperature, such as H1150 at 4 hrs done twice. You can age at the materials at a specific aging temperature for well over 4 hrs and not greatly effect the properties, which may be necessary for very thickn parts that have a bore and the heat is not able to circulate in the bore.

I recommend you get a copy of AMS27593E at look at the heat treating information contained therein. Very good stuff.

 

[tr1ntx]

Reviving this old thread, I stumbled across information I couldn't find earlier. From Specialty Steel Supply:

"Stainless steel 17-4 H1150 is stainless steel grade 17-4, also known as 630 alloy, that has been heat treated at a temperature between 1140° F and 1160° F for 3.75 hours to 4.25 hours. The steel will become softer than it is in the annealed condition after being treated at such a high temperature. On the Rockwell C scale, 17-4 H1150 Stainless Steel has a hardness of 28.

Stainless steel 17-4 HH1150 is stainless steel grade 17-4, also known as 630 alloy, that has been heat treated twice at a temperature between 1140° F and 1160° F for 3.75 hours to 4.25 hours. The steel will become softer than it is in the annealed condition after being treated at such a high temperature."


So there IS a difference between 17-4 H1150 and 17-4 HH1150, that being that it gets the heat treatment twice and is thus "double-aged".

 

[mighoser]

AMS 2759/3 covers the heat treatment cycles for PH stainless including 17-4PH aka type 630. You would have to buy the spec of course. If you don't want to spend the money MIL-H-6875 has almost the same info. You'll have to spend a little more time sorting through it since it covers heat treatment of multiple classes of steels.

"Condition H1150" is two step aging treatment. Heat to 1150F hold, cool to RT, heat to 1150F hold cool to RT.

"Condition H1150M" is a modification to the two step "H1150" treatment. The first step is 1400F instead of 1150F.

Keep in mind that the intent of using this condition callouts (ie. "H1150") is to hit a set of mechanical properties. Specifically hardness and elongation are bounded and the heater is allowed to vary the heat treatment a few degrees to hit the specified property range.

NASA Tech Reports has a good reference for effect of varying heat treatments on the properties of PH Stainless. It is: NASA-SP-5089 "Thermal and Mechanical Treatment for Precipitation Hardening Stainless Steels"

 

[blacksmith37]

A footnote of caution : be sure it has been aged. In the annealed condition the hardness is about the same as H 1150, but the toughness and ductility are not good. I have seen a couple failures where annealed was used instead of H1150.

 

[tr1ntx]

mighoser,

So are you saying that the info from Specialty Steel Supply is wrong?

You said Condition H1150 is a 2 step treatment.

They said Condition HH1150 has been heat treated twice, i.e., it could have received the 2 step treatment process twice.

These 2 statements are not necessarily mutually exclusive. Is that what you meant?

 

[unclesyd]

Checkout the 17-4 PH Data Sheet from AK Steel. They were the developers of the alloy.

http://www.aksteel.com/markets_products/stainless_precipitation.aspx

We use tons of the material and only use H150m when we have do some fine work on a part. Usually the HH150 treatment will be satisfactory for most repairs that call for machining.

 

[Metalguy]

tr1ntx,

Be happy that whoever in your company didn't specify the H900 heat treatment for 17-4PH!

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[boo1]

here is a helpfull link on 17-4

http://www.hightempmetals.com/techdata/hitemp17-4PHdata.php#6

 

[redpicker]

In my experience:

H1150 refers to a single aging treatment at 1150 for 4 hours and air cool.

HH1150 refers to a a double aging. The H1150 treatment performed twice, with cooling to <100 F between treatments

H1150M is a modified two step treatment (as stated above) with one treatment at 1400 F and one at 1150F.

I bleieve both HH1150 and H1150M are both acceptable for sour service while the single H1150 condition is not. For this reason, nearly all 17-4 material processed at 1150 F is given the HH1150 treatment (the mechanical properties overlap and nearly always will meet both) so it will be suitable to a wider range of applications.

rp

 

[prdave00]

Metalguy,

I had to ask. What's wrong with the H900 condition - if that's what the application calls for (i.e. high hardness, low ductility)?

 

[Metalguy]

SCC, unless it's in dry argon or equiv!

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[prdave00]

Metalguy,

So if SCC is not a concern then H900 is adequate? Our company specifies H900 all the time for the surgical instruments we design since hardness is the attribute we are primarily concerned with for our application. I just found your comment odd and a bit out of context since the OP was about clarification about 17-4PH in the H1150 without mentioning the application or questioning if that was the right condition to specify. That's all.

 

[Metalguy]

The H900 treatment will only harden 17-4 to ~Rc44-45, so it usually isn't used for cutting instruments--440C or a newer alloy is the stainless of choice there.

But H900 has had numerous SCC failures in highly stressed parts that get wet, esp. with salt water. Way back in 1960 when I started my metallurgical career, one of the things I discovered was that the US Navy forbade its use for certain aircraft parts.

It has its uses, but for nuclear power bolting, etc. the H1150 treatment is used. There was one major AE firm that used it with the 1025 treatment IIRC, then they switched to the 1075 for a LOT of years.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[tr1ntx]

Thanks unclesyd & redpicker. So now I've got 3 sources that say the same thing about H1150 and HH1150, i.e., the way redpicker explained it.

And it's comforting to know that nearly all 17-4 processed at 1150F is given the HH1150 double treatment, since as I stated originally, our material specifications are worded in several different ways. I had checked some MTR's and found that they specified it as the double-aged treatment, so our suppliers were getting it right anyway.

 

[unclesyd]

One little bit of information about 17/4 PH steel is you will probably get range of hardness, even in thee same lot.

One other point to make is don't crowd n oven, like stacking, making a floor any thing that increases the mass.

Make sure no one uses an oven that has exposed radiant heating elements.

If you want a shinny surface that requires pickling make sure you retreat with alkaline/permanganate. Stay as low as possible with the HF.

addenda:
I as talking on the phone with ARMCO's chief metallurgist of the Baltimore plant when his boss walked in and told him they were pulling the plug at 11:00 AM.