Urgent question, Residual stress 5

[akhb76]

Hi,
I'm R&D manager of a bone implant manufacturing company,
We recently produced 1000 screws using Thread rolling method but they didn't get approved and we recalled them,
The reason was 'Residual stress' how to release the stress by non-thermal method.

Thanks

 

[Maui]

We are talking about 316 stainless steel.

Maui

 

[Maui]

Maybe you should take the book that I wrote off the shelf and read it:

http://www.asminternational.org/home/-/journal_content/56/10192/05306G/PUBLICATION

Maui

 

[Frederick]

I've read your book. I have also bought it for my employees. Maybe you should take ASM Handbook Volume 4A off the shelf and read pages 382 to 386. I wrote that.

 

[Maui]

Good for you. Can you provide a single objective and unbiased peer reviewed article that demonstrates unambiguously that 316 stainless steel which does not contain any significant amounts of ferrite or martensite is altered or impacted in any significant way by a cryogenic treatment? If so, please reference it.

Maui

 

[Frederick]

Here is one. It was on the web and took about 3 minuets to find. I will submit it to the CSA database for inclusion.

International Journal of Engineering Research and Reviews ISSN 2348-697X (Online)
Vol. 2, Issue 4, pp: (18-23), Month: October - December 2014, Available at:

http://www.researchpublish.com

Page | 18
Research Publish Journals
A Review Paper on Methods of Improvement of
Wear, Corrosion and Hardness Properties of
Austenitic Stainless steel 316L
P.Elango
PG Student, Department of mechanical Engineering, Bharath University, Chennai –India

My own experience with the use of 319 stainless has shown a huge increase in life over 319 with a hard coating. The use was a screen used in the manufacture of highly abrasive plastics. DCT replaced a hard coating that was many times more expensive and many times less effective. We are now specified on the print for DCT to be done because it saves the plastics company so much money. That in my eyes is better than a research paper.

We have to rethink wear resistance in light of what DCT is showing us. I see huge increases in fatigue life on almost all metals. Top drag racers are using DCT to give them six times the life on valve springs. They do not take this lightly as a broken valve spring can cause an engine to detonate and kill the driver.

You have to look at the crystal lattice structure for the benefits, not the microstructure. To relate to this thread, the release of residual stresses DCT can create and the refining of the crystal structure may be what is needed in the referenced screw. DCT is MUCH more than conversion of retained austenite.

 

[tbuelna]

Maui-

The significant amount of mechanical working applied to the 316L material during the thread rolling process might result in some strain-induced martensite formation. Here is a tech paper that discusses the issue. Don't know if cryo stress-relief would be of any benefit though.

 

[Maui]

Tbuelna, thank you for referencing a peer reviewed article. Yes, that is a possibility. Martensite can form in 316 during cold working if the resulting deformation is severe enough. But this is usually only a concern if the cold working is done at a relatively low temperature. Unless the material has been processed to induce it, when cold worked at room temperature the formation of martensite is usually minimal in this stainless grade. This is discussed, for example, in the following article,

http://www.sciencedirect.com/science/article/pii/S1877705811004012

Fred, what you provided is a review by a college student of several different investigations, one of which is entitled "A study on wear and corrosion characteristics of marine propeller shaft material - AISI 316L stainless steel subject to cryogenic treatment" by J. Suresh and S. Suthagar. This is not a peer reviewed investigation - it is a conference proceeding from the 2nd international conference on science, engineering and management. And the summarized results that are claimed raise several questions. The author claims that by cryogenically treating 316L material he improved the wear characteristics according to his pin test results, dramatically improved the corrosion resistance, and the material was 16% harder (whatever that means). This is all supposed to be accomplished by inducing a martensitic transformation in the 316L by cryogenically treating it at -186 C which is referred to by P. Elango as the liquid nitrogen temperature. At atmospheric pressure nitrogen boils at -195.79 C (77 K, or -320 F), not -186 C. The formation of martensite would be expected to reduce, not enhance, the corrosion resistance of the material. And since I am not able to locate a copy of the paper by J. Suresh I am unable to review the details of his investigation beyond what was summarized by P. Elango.

And none of this suggests that the residual stress that was the original topic of discussion by the OP would be relieved by a cryogenic treatment.

Maui

 

[FennLane]

Frederick,

I just don't believe you comments concerning the movement if voids and other crystal structure changes due to DCT and I have never seen a paper which was based on good science to explain these phenomena.

Most diffusion processes are thermally activated so how can very low temperatures and allow alloy diffusion this to me is counter intuitive - Re-visit Fick's Laws if you disagree and explain to my mistake.

 

[Frederick]

Maui:
The scientific community generally accepts the beginning of the cryogenic temperature zone to be -244F, so the research you are criticizing was done well under cryogenic conditions. As a practical matter it takes a lot of liquid nitrogen to get a chamber down to -320F so a lot if not most research in the field is done at -300F or slightly lower. There is nothing sacred about the boiling point of liquid nitrogen.

Here is some research done to 316 which is focused on residual stress.
Relief of tensile residual stress in girth joint of AISI 316 steel
by deep cryogenic treatment
Qiongqi Wang, Weize Wang, Fu-Zhen
Xuan, Zhengdong Wang, Shan-Tung Tu
*
School of Mechanical and Power Engineering, East China Un
iversity of science and tec
hnology, Shanghai 200237,

Abstract
Although it has been reported that deep cryogenic treatment can improve the wear and fatigue resistance of some metals and alloys, less work was done to investigate the effect of such processing on weld joint of austenitic stainless steels. In this study, phase trans-formation of 316 austenitic stainless steels was studied by the magnetic measurement before and after deep cryogenic treatment, and residual stress in fusion zone and heat-affected zone of girth joint of AISI 316 stainless steel was measured by the electric discharge cutting and static state strain gauge after deep cryogenic treatment. The results indicated that the deep cryogenic treatment can greatly alleviate tensile residual stress of girth joint of austenitic stainless steels greatly.

I did not have time to read the entire paper, but you can see that cold can be used to reduce residual stress. Also the work of Victor Sloan at Victor Aviation has indicated that most metals will have residual stresses relieved at cryogenic temperatures. This is why very sensitive satellite components are treated to -400F so that they do not move in use.

Fennlane


Collins (Cryogenic Treatment of Tool Steels
Collins, D. N.
Advanced Materials and Processes
December 1998, pp. H23-H29)

Collins concludes that the formation of fine carbides are initiated during the hold at -300F and they actually form as the temperature comes up. The diffusion of carbon atoms is happening at cold temperatures. The longer you hold, the more carbides are formed. As to research,you have to realize that the diffusion of point defects is taught in Metallurgy 101. The colder you go the fewer point defects will be in equilibrium. (See Structure-Property Relations in Nonferrous Metals, Alan M. Russell, Wiley, 2005. pages 18-19. The trick is to lower the temperature slowly as not to "freeze in" the point defects.

Something that I don't believe is how supposedly astute metallurgists can make blanket statements without looking into the claims being made. More and more research is being done in the world on this process that can save industry huge amounts of money, and it is not being done here in the USA. Yet my company has shown auto parts makers six to nine time life on their carbide tooling. Those are their numbers, not mine. Why does DCT work on carbide when there is no retained austenite in it? Why did a recent paper show that plastics respond to DCT? Something is happening. Go to the CSA

http://www.Cryogenictreatmentdatabase.org

and read before you tell me you "don't believe." This is not a religion.

 

[Maui]

Fred,

In the first paper you referenced I pointed out that the student referred to -184 C as the temperature of liquid nitrogen. This very basic statement is incorrect. At atmospheric pressure nitrogen boils at -195.79 C. If the author gets something this fundamental wrong, then it leads the reader to question what else in the paper might be in error. This is the main reason why I mentioned it.

In the other paper you listed above entitled, "Relief of tensile residual stress in girth joint of AISI 316 steel
by deep cryogenic treatment" the author discusses the benefits of using cryogenic treatment to relieve the residual tensile stresses produced in welding 316 stainless steel. But the component that the OP described was not welded. It was cold rolled. And the residual stresses produced during cold rolling are completely different from the residual stresses produced by welding 316. This study simply does not appear to be relevant to the problem at hand. I am not inferring or suggesting that cryogenic treatment cannot be beneficial [bold]when used correctly in the appropriate application[/bold]. My point is that for this particular problem it would not be beneficial in resolving the issue that the OP described.

Maui

 

[Frederick]

The paper I noted states:

" In a Deep Cryogenic treatment the material is first allowed to cool from room temperature
to a temperature of -186 C by introducing the test piece in Liquid Nitrogen (LN2) controlled flow chamber up to 2-3
hours duration to take, then maintained in a cooling chamber with the above temperature up to 24 hrs and retain back to
room temperature, it takes 6 hrs. "

Nowhere does it state a boiling point for liquid nitrogen. What he is saying is that the part was put into a chamber where a controlled flow of liquid nitrogen slowly reduced the temperature to -186 C. He then maintained the temperature at -186 for up to 24 hours and brought it back to room temperature in 6 hours. So he did not get anything fundamentally wrong. You are probably assuming the piece was immersed in LN2 which is a common (but usually wrong) assumption that people make about DCT.

Regarding the stresses from welding being different from the stresses of cold rolling, you have a point. But that doesn't mean that DCT would not help the screw in question. DCT has been shown to relieve residual stresses in many materials. Savvy die makers use it to reduce time on EDM machining because it reduces the movement in plates being machined. The suggestion to try DCT on the subject screw would be an inexpensive process to try out that did not involve high temperatures. DCT is a valid process that can be used on almost all metals and some plastics. It can do a lot of things and can save this country considerable time and money if we can get it passed the uninformed naysayers. I know it is not intuitive that you can modify something with cold and we have been using heat to modify metals for over 8000 years. But we have only had industrial quantities of cold for a little over 100 years and we are just scratching the surface.

 

[Guest102023]

Has composition been consistent batch to batch?
Heavily worked 300 stainless steels are sensitive to composition, particularly nickel.
Long ago I encountered an unlisted Cu grade (4% Cu IIRC) intended just for fasteners, to withstand the severe strain.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[CoryPad]

Brimstoner,

Even listed grades can have high copper. ISO 3506-1 A4 allows up to 4 % copper, and 302HQ (UNS 30430) is another example.