Which are the stabilzed grades 2

[bmoorthy]

Dear All

I know SS 321 is stabilsed grade.

1)Is SS 316 a stablised grade.
2)Is Inconel 625 a stabilsed grade
3)Is Incoloy 825 a stabilsed grade?

4)How does one know whether the grade is stablised or not?

There is a client specification that pose restriction on heat treatment of non stablised grade SS and clad Steel where the high alloy material is non stablised grade.

5) Is stablised grade (In the context of corrossion resistance for stainless steel)unique to Austenitic stainless steel? or does it spread to even non ferrous grades such as inconel and incoloy?

6) Should on extend the above concepts (Of restricting the Heat treatment soaking time and temperature) to non ferrous grades as well.

 

[metengr]

The stabilized grades of stainless steel are ones designed for welded applications, high temperature service and contain alloy additions of Titanium, or Niobium (plus Tantalum). These alloying elements are strong carbide formers (designed to be stronger than chromium) that tie up the carbon and avoid harmful precipitation at grain boundaries upon prolonged exposure to elevated temperature service.

1). No, 316SS is not a stabilized grade

2). Yes. However, between 1200 deg F - 1300 deg F, it has been reported that the ductility of the alloy decreases. Above 1300 deg F, the ductility increases.

3). Yes

Nickel-base alloys, like certain grades of high temperature austenitic stainless steels, also contain Ti and Nb alloy additions to stabilize the alloy. These alloy additions reduce susceptibility to the harmful formation of sigma phase or other precipitates in elevated temperature service.

To assure proper stabilization of Ni-base or certain grades of austenitic stainless steel, a stabilization anneal heat treatment is often specified. This heat treatment is specified to assure complete dissolution of carbides for maximum corrosion resistance, and elevated temperature performance.

 

[bmoorthy]

Thanks Metengr.

What is the rule of thumb or where is the guideline, to find which are stabilsed grades and which are not?

If i see ti or Ta or Nb in an austenitic material do i say they are stabilized?

 

[metengr]

If you visit some of the stainless steel producer web sites like Allegheny Ludlum or Outokumpu they have information on their grades of stainless steel for high temperature service, and indicate which are stabilized. This would apply to austenitic grades and ferritic grade (AISI Type 439). Yes, the presence of Ti, Nb or Nb(Ta) would indicate a stabilized grade of stainless.

 

[arunmrao]

How about the L grades? The carbon levels being very low addition of stabilizers is redundant.

 

[metengr]

arunmrao;
The L grades are not generally suitable for exposure to elevated temperature service because of the low carbon content. The L grades were formulated to improve weldability, for moderate to ambient temperature service.

The stabilized grades of stainless (321, 347, 348) were originally developed to reduce susceptibility to sensitization upon exposure to elevated service temperatures, while maintaining higher carbon content for creep strength.

 

[heaterguy]

How about the H grades? Is 316H a stabilized grade?

 

[metengr]

316H is a higher carbon version of 316 SS for creep strength, and is not stabilized. The stabilized grade of 316 SS contains Ti.

This information will help you;

http://www.azom.com/details.asp?ArticleID=2868#_316Ti_and_316H

 

[arunmrao]

I always thought that 316L is a substitute for 316+Ti.

 

[EdStainless]

It can be, but it depends on why you need stablization.
If you want it for weldability, then an "L" grade will work fine. If you want it for long term high temp exposure, then maybe not.
The stab grades have no different strength or creap or stress rupture properties. They will resist sensitisation which can increase sensitivity to stress cracking, intergranular corrosion, and also reduce your ductility.
Many Ni alloys designed for high temp service are not stabalized in the same way that 321 is, but the chemistry is balanced to maintian properties at high temp.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[arunmrao]

Last week a customer brought a pattern and asked me to cast a few pieces in 316+Ti grade alloy. As the pattern was his and the end application not known I processed it as a regular engineering casting and supplied. This week he comes back with the machined casting the wall thickness of which is reduced to 4mm. He complained of hydro leakage.

The pattern was a cylindrical with one flat base and a shoulder ring. If I was to know about leak tightness requirement,pattern making needed to be changed. Also the greatest shock to me was it is a mixer drum for mixing 5kgs RDX with a oil jacket of 304 welded all around. .

I collected the casting back and repaid the customer .How come for such a severe requirement a casting was recommended. If an accident was to occur who would be responsible? Foundry,designer,or fabricator?

 

[metengr]

arunmrao;
Most likely, the individual or organization asking for the casting had little or no experience in dealing with procurement of high quality castings. Maybe it was cost or other factors in addition to lack of experience. Consider yourself and the company you own fortunate and learn from this event.

Regarding your second question - unfortunately, the answer is it depends on your location and the extent of collateral damage to equipment and injury to human life.

I suppose that with any product, you can attempt to craft a waiver that reduces your extent of liability. It seems as though people and organizations like to point fingers today, and as a result, lawyers will go after the ones with the deepest pockets.

 

[arunmrao]

Thanks Metengr 1 My pockets have big holes , My whole life has become a learning process when will I make money and reapay my debts?