Residual Stresses from Quenching

[KSor]

We just had some 316 SS parts solution heat treated after welding, and instead of quenching from 1650°F to 1000°F then air cooling to room temperature as per our procedure, the heat treaters quenched it from 1650°F to room temperature. Would re-running the solution heat treat procedure (properly this time) remove the residual stresses caused by the rapid cooling? Are there any other issues I need to be aware of, distortion, etc...?

 

[EdStainless]

i don't think that your cooling method will do anything to reduce stresses.
You would get the same result reheating to 1000 and then slow cooling.

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Plymouth Tube

 

[metengr]

We just had some 316 SS parts solution heat treated after welding, and instead of quenching from 1650°F to 1000°F then air cooling to room temperature as per our procedure, the heat treaters quenched it from 1650°F to room temperature.

Why are you even step cooling 316 stainless steel? For a proper solution anneal you should be rapidly cooling to ambient temperature, step cooling will result in lower corrosion resistance.

 

[stanweld]

The 1650 F temp is not a solution treating temperature. It is a carbide stabilization jeat treatment temp. Did you mean 1950 F?

 

[KSor]

The heat treatment procedure was developed for us by our materials consultants. I am not a materials guy, so I need to defer to other experts on this matter. What would be the point of the step cooling if it doesn't reduce the stresses?

Stanweld, you are right. It is a stabilization heat treat, not solution.

 

[metengr]

KSor
Precisely. Step cooling of this material will achieve little benefit in terms of residual stresses. In fact, step cooling will undo what you have attempted to achieve with a stabilization heat treatment.

 

[EdStainless]

If you really did use 1650 ( I assumed that you meant 1950) then this is not 316, but rather a stabilized version, right?
If not then you have about the corrosion resistance of 410.

If you actually plan to heat to this temp then there is really no reason to rapidly cool at all since you will probably not be able to avoid formation of sigma and carbides.

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Plymouth Tube

 

[arunmrao]

If your carbon in SS is low,then perhaps you could do away with the heat treatment process. No benfit by step cooling,you need to fast cool to RT by water quenching. Vibratory stress relief is not an option for stainless steels.

Learn the rules,so you know how to break them properly.
Dalai Lama

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[unclesyd]

Aide from the Powerhouse our plant is over 90% stainless steel. In the time before the ready availability of the stabilized grades we solution annealed nearly everything. The treatment was 2200F water quench or if small rapid air cool.
We would seldom attempt to stress relieve SS, especially weldments, as there were no measurable benefits.

 

[bklauba]

Addressing arunmrao's statement:

"Vibratory stress relief is not an option for stainless steels."

Vibratory stress relief is very commonly applied to stainless steel fabrications, due to the problems associated with using PWHT on such components. The options are to use what is called a "low-temperature" stress relief, which many manufacturing engineers feel has little benefit to issues involving dimensional stability, or to use a higher temperature heat treatment, and quench, as described above.

On large and/or complex components the quenching option is either not possible, or can re-establish a new set of stresses, having little to do with the original pattern of HAZ's, but much to do with the quenching method and cooling details. This new stress pattern might well threaten dimensional integrity more than the as-welded component, so typically PWHT is not performed on such parts.

There are reports showing examples of vibratory stress relief applied to stainless steel components at:

http://www.vsrtechnology.net/resources/job-stories-reports/stainless-steel/

One of the entries does not involve stainless steel, but rather, pure titanium, but was included since this material machines very much like 300-series stainless (tough, gummy, heat not carried away by chips very well). This report also shows the effectiveness of the VSR Process, in that dimensional accuracies of a few 0.001" were maintained on a population of ~ 80, 144 inch long parts, despite having extremely asymmetrical machining performed that removed more than 30% of the material during rough machining alone.

These reasons explain why the use of vibratory stress relief is one of its MOST COMMON areas of application.

 

[EdStainless]

If you quench, whether from solution them or stabalization temp you will end up with residual stresses equal to the yield strength of the material. Period.

I presume that this is 316Ti. The best thing to do is verify that you have stablization. If you do then leave it alone.

VSR does not remove stresses, it helps equalize them and make them more uniform. If your part has uniform high residual stress then VSR will not change anything. If the stresses vary a lot then it helps a lot.

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Plymouth Tube

 

[stanweld]

The 1650F stabilization heat treatment was developed in the 1960's by one of the US Oil Refiners. Its purpose was/is to aglomerize carbide formation in the grain structure away from the grain boundaries. It was used in specific refining applications where 316 SS was to be placed in service at temperatures above the senitization temperature. There was not an original requirement to step cool; slow cooling was all that was required. Carbide aglomerization ocurred at longish hold times at the 1650F temp.

 

[bklauba]

To EdStainless: Perhaps we are talking semantics here, perhaps not. Below is a link to one of the most sited research papers on vibratory stress relief, authored by Dawson and Moffat. Doug Moffat sent a high-quality original to me several years back, so it could be scanned and included in the VSR On-Line Research Library.

It can be seen at:

http://www.vsrtechnology.net/wp-content/uploads/dawson-moffat.pdf

In this work the authors claim to have relieved an average of 90% of stresses in multiple samples of 3 different alloys. This paper has stood up very well to peer review for more than 25 years. I have yet to find a single work that questions the validity of these conclusions. I would be very glad to receive such; please submit such work to the library for consideration of inclusion. We would welcome any work that refines our understanding of this technology.

BK

 

[unclesyd]

Before I get into one of those contests a sited paper with all it's acquirement's carries no meaning except for those particular parts with their mechanical and thermal history.
I speak from having for many years of work in attempting to straighten and stress relieve metal parts. There is essentially no problem with CS weldment or not, but working with SS it's a new ball game. As far as straightening I go with the sage advice given me many years ago when I asked about straightening as stress relieving a 22 ft long SS screw looking device with a 22 in dia central hollow shaft. The answer I received was repeat after me "Our father wh........ " We spent several thousands' of dollars attempting to use VSR on this part on two occasions in an effort to keep this component from squirming, worming, or snaking when put into operation. Our goal was to kept the 22" dia packing journal from running on an orbit in the packing gland. Our solution was to rough machine and heat this component to the maximum temperature it will see during it's service life. We tried VSR at this point in time with no success. Then using flame to correct the shaft runout on both both ends to 0.010". The component will then be final machined and run out brought to 0.005" or less. During operation we let the center section act like a crankshaft.
As far as solution annealing I have solution annealed, water quench, many pump housings after weld repair of the casting. It might require a skin cut on the back plate landing area. Normally the nozzles are withing OEM tolerance, feet to nozzle center-line and gasket plane.
Our development group tried VSR much to my chagrin on several machine bases and frames and much to their surprise it didn't work.
A much better method is how the Swiss and Henry Ford did it. park it outside for a couple of winters.

My final test was a couple of SS U-bends, the VSR coupons broke in the same time frame or a little faster that he untreated ones.

 

[metman]

EdStainless

Quote: There are reports showing examples of vibratory stress relief applied to stainless steel components at:

http://www.vsrtechnology.net/resources/job-stories-reports/stainless-steel/

With all due respect, is it possible that in the examples of attempted VSR on SS you were associated with that the required resonant frequency was incorrectly established or maybe the amplitude was insufficient? Is there some explanation why SS is not susceptible to VSR?

I do not understand your contention because in one place you say, "There is essentially no problem with CS weldment or not, but working with SS it's a new ball game." But in another place you say, "If the stresses vary a lot then it helps a lot." This last comment you made wr2 SS.