Annealing Stainless Steel types 303, 304, 316, 202
A discussion started in 2002 but continuing through 2018
Q. We manufacture humidifier tanks out of 304 stainless and anneal these tanks for use with D.I. or R.O. water. Will we get the same enhancements to the chromium oxide layer with annealing as with passivation? The appearance of the material, after annealing, is bright, though warped from the annealing process. If appearance is not an issue, would we be better off passivating instead?Alan Garnaat
- Three Rivers, Michigan
Annealing is a totally different process than passivation and will not give you the chromium enriched surface you need to be corrosion resistant, especially in DI and RO water.
After annealing you still need to passivate the surface and welds or you could have corrosion and leaking. Passivation is easy now with the new citric acid formulations available on the market. There are various ways to passivate tanks, depending on size and configuration. You can fill the tank with solution, spray the tank with a spray ball or similar or you can spray on a gelled product.
It is easy, safe and economical. Contact us for help.
Stellar Solutions, Inc.
316 stainless preparation/cleaning prior to annealing(2002)
What are some of the preferred methods for cleaning / washing 316 stainless steel prior to annealing? I am using a mild citric acid wash and rinse to help deburr my parts. Then I use a degreaser and rinse prior to annealing. However, I am getting contaminants which seem to bake onto the steel during annealing and this prevents me from getting the desired finish from electropolishing (non-annealed parts consistently polish to an excellent finish). My parts are typically a couple of inches long, so they're reasonably small.
Thank you,Doug Smith
- Vancouver, BC, Canada
A. I presume you need to anneal the stainless steel because of work hardening, as 300 series stainless steels cannot be heat treated to make them harder. You do not give much information about the process, such as annealing temperature, time, type of degreaser etc. How is the annealing done - is there a possibility of contamination coming from the annealing oven, or is the hot atmosphere causing corrosion of the steel? I also wonder why you are giving it a citric acid treatment prior to electropolishing. I wonder if the citric acid is putting down a passivating film that is not removed prior to annealing and the high (?) temperature is breaking this down to carbonaceous surface contamination. Try eliminating the citric acid treatment. By the way, electropolishing with sulphuric acid/phosphoric acid will give the stainless steel an excellent passive film. I know there is also a citric acid based electropolishing solution, but I have very little experience of it, so if you really want to give the stainless a citrate treatment, perhaps you could try that.
R&D practical scientist
Chesham, Bucks, UK
Q. Thanks for the response Trevor.
We are annealing 3/4 hard 316L steel in a dry hydrogen atmosphere at 1850 °F for 30 minutes. We are pretty sure that the annealing oven is not the source of contamination, as this has been looked into (we don't do the annealing ourselves). I can't say much more about the annealing other than this, as I'm not terribly familiar with the process.
We do a ultrasonic citric acid wash after laser cutting to remove very fine burrs. The citric acid (by itself) is not the source of contamination, as we electropolish non-annealed steel perfectly. As well, if we start with annealed steel (which obviously doesn't need to be annealed again) we also achieve excellent electropolishing.
We have done some EDX studies, and one contaminant that showed up was Sulphur. We did not see an increase in Carbon after annealing. We're trying to contact the manufacturer of our degreaser to see if it has sulphur in it.
I like your idea of trying this process without the citric acid wash. Forgetting the citric acid for the moment, assume that we have a un-washed part that we would like as clean as possible prior to annealing: can you suggest a suitable cleaner?
Thank you,Doug Smith [returning]
- Vancouver, BC, Canada
A. There is no such thing as the best cleaner -- it depends on what the contaminant is. However, saying that, for the removal of general machining oils and greases, one of the best was trichloroethane, but as you will know this was banned under the Montreal Protocol. The metal amadeya42 industry has been looking for a replacement for many years and there are a lot around. If you want to stick with chlorinated solvents, you could try perchloroethylene or trichloroethylene, but these too have environmental and health issues. There is an increasing interest in brominated solvents and it is claimed they are very effective. Alternatively, you can use aqueous or semi-aqueous based systems that can be very effective, especially with ultrasonics. I would suggest you talk to your supply house and seek their advice as they will be able to match their products to your needs.
R&D practical scientist
Chesham, Bucks, UK
A. Hello fellow tank jockeys:
This article may be of help:
[updated by editor Nov. 2014]: swagelok.com/downloads/WebCatalogs/EN/STAINLESSFORSEMICONDUCTORS.PDF
[updated by editor April 2016]: Swagelok does not seem to offer a technical library of that sort anymore. If you see an interesting article on the internet, download it while you can :-)
It confirms that sulfur as sulfide can foul the electropolish process by causing pitting. I believe Sulfide can be formed from more oxidized states in hot Hydrogen, which is your anneal gas. This may or may not be the source of your problem.
Q. I am experiencing a unique pitting problem as well on 316L cold-rolled/annealed. I have a cube, all six sides are identically machined & prepped, yet two sides, front & back pit up to 1200 ASF then polish above that, while the other four sides polish down as low as 200 ASF, no matter how I hang them in the tank or clean them, or what polish formula is used. See my question posted on this site (letter 15893).
A. If your problem is sulfur, try soaking the parts in 5% NaOH for a few hours (elevated temp. helps), rinse well and then go into your EP Process.
Stellar Solutions, Inc.
A. Two sources of the sulphur on your stainless could be from an extreme pressure additive in a metal working lubricant that has contacted the stainless and from sulphates in the rinse water just prior to annealing. My experience has shown deionized or low dissolved solids water is best for rinsing prior to annealing.Roy Nuss
Trevose, Pennsylvania, USA
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Bright annealing of stainless steel(2002)
Q. I am an Indian Stainless Steel Manufacturer, producing Stainless Steel Sheets. The process of sheet manufacture is quite labour intensive. The sheets are mostly of 200 series and are rolled in hand mills. Of the total Stainless Steel produced in India, more than 70 % is produced by this process. The process is viable primarily because of cheap Indian labour costs. The problem that such units, including mine, is facing is the increasing pressure of Pollution prevention methods.
My question to all is whether it is possible to Bright Anneal Stainless Steel sheets (as SS coils worldwide are bright annealed).
BA finish on sheets would save acid used in re-rolling and mechanical amadeya42 at the end user's end.
Would request all you to give it a thought. The dimensions of the sheets mostly produced are : Thickness 0.25 to 3.00 mm Width : Max 700 mm, Length : Max 3600 mm
- Hisar (Haryana), INDIA
A. 0.25 mm to 2.0 mm in BA sheets shouldn't be a problem. Anything thicker than 2.0mm is going to be 2B finish. Depending on your quality standards for mirror polishing this can get expensive (as compared to BA sheets). Good luck!
specialty stainless steel distributor
A. Sure, you can bright anneal sheets made in a hand mill. The surface finish will not be any better than it is before the anneal. That is, bright annealing doesn't make a bright surface; it only preserves the same surface you have before annealing.
Caution! Sheets may weld together during anneal if they're in contact. Oxide's can form in bright annealing during heat up and cool down. It is much easier to do bright anneal on coils with a continuous anneal than in batch. If pickling acid is the problem, you may want to experiment with abrading the oxide off, especially if you are eventually going to apply a #3 or #4 polish.Dr Michael McGuire
- Pittsburgh, Pennsylvania, USA
Q. Dr Michael McGuire- Pittsburgh, PA, USA and Michael Liu Taylor:
Many thanks for your reply. Would like your help further. For bright annealing of SS sheets, what type of furnace would you suggest?
Regards,Rajeev Garg [returning]
- Hisar, Haryana, India
A. Dear Mr. Rajeev
This kind of BA line is very common in china. The only difference is they anneal the coils and your requirement is for strips up to 3600 mm length. On my last visit, I have seen the BA lines which serve this purpose also. The flip side is the initial investment is too high, but it is worth it considering the pollution problem.
import - New Delhi, India
Q. My machinist told me I don't have to spec 303 Stainless Steel rod as "annealed". He said all 303 SS rod is annealed. Is that true? Is "non-annealed" 303 SS rod an option when ordering?Ed Downs
bakery machinery - Grass Valley, California, USA
A. ASTM A582 [link by ed. to spec at TechStreet] is the North American standard for free-machining stainless steel bars, and Types 303 & 303Se are only available in the annealed condition (Condition A). In fact, only the martensitic grades Type 416, 416Se, and XM-6 are available in anything other than the annealed condition, namely the intermediate temper (Condition T) or the hard temper (Condition H).Toby Padfield
automotive module supplier - Michigan
A. The normal supply condition for the 300 series austenitic stainless steels is annealed, but it can also be supplied in the cold drawn condition with increased mechanical properties if required when specifically ordered. Tensile properties increase from around 500 N/mm2 to 650 to 865 and above depending on thickness.Martin Rich
ship repair - UK
January 8, 2009
Q. I am currently trying to write a validation protocol on a process we currently have in place to stress relief anneal type 301 stainless on some parts we stamp and form that are at the thinnest of the steel spec.
We have been doing this at 600 °F for 30 min (our method is placing them in a cold oven, allowing the oven 60 min to get up to temp and letting them bake for an additional 30 min, then a slow cool)
I am having difficulty finding data to support the timing. I did find a temperature range for stress relief annealing 301 stainless from 500-900 °F.
I need to challenge our operating temperature and our time in the oven and I'm not sure how wide of a range I should use or even where to start.
I thought perhaps someone might have some experience with this or might be able to start me down a path that will not dead end on me as so many websites have done.
OEM Quality / Operations Support Technician - Sterling, Illinois,USA
February 16, 2009
A. SS301 is 16 Cr stainless steel if it is heated through a temperature range exceeding 427 °C without subsequent annealing, it will undergo carbide precipitation and will contribute to intergranular corrosion as such if you are Stress relieving SS 301 I will keep the temperature below 427 °C and extend the holding temperature (this can be varied from 1/2 hour to an hour dependent of the extent of cold working) and then air cool it slowly.Vijay Vijayaraghavan
- Adelaide, South Australia, Australia
June 23, 2009
Q. Is there a possibility of Bright Annealing (in which the surface of SS sheet does not oxidize, i.e., become black or blackish) of SS sheet having 300 mm-650 mm width and 1000 mm to 5000 mm length?Prakash Nangia
businessman - Delhi, India
October 11, 2010
Q. Our company manufactures stainless steel tube by cold rolling or cold drawing. We have bright annealing furnace but color of stainless steel tube after B/A is not bright.
Could you give advise for me?
- Busan, South Korea
Annealing 205 stainless steel tubesNovember 25, 2014
Q. Working on a project focusing on the annealing of stainless steel; what would be the process required to anneal 205 tubing.
Please include any information such as temperature, time, etc.
- coventry, west midlands, england
April 18, 2016
Can anyone explain how to do annealing of 303 SS rod?
Aircraft Instruments - San Antonio, Texas
A. Hi folks.
An old volume of the ASM Metals Handbook says for 303SS: "Annealing temperature 1700 to 1750 °F; Cool rapidly from 1850 to 2050."; azom.com/article.aspx?ArticleID=8210 compares type 205 to type 304.
Please look up the annealing procedure in a more recent book like ASM Metals Handbook vol. 4: "Heat Treating" =>
While this public forum can perhaps suggest books & educational organizations in that discipline, and our readers may be able to offer an experience-based response to a carefully delineated shop problem ... internet responses should never substitute for looking up data in a textbook (some posters are unknown to both you & me; some might be incompetent, and others might even deliberately try to mislead). This site focuses on metal amadeya42 rather than on heat treatment, so it's an especially big issue on this thread about annealing because the moderator has no expertise to be able to even warn about bad advise. Sorry :-(
Good Luck and Regards,
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"
June 16, 2016
Q. We are selling stainless steel 202 coil with 4 % nickel for fencing purposes. We first buy s.s. coil and than cut to 3.2 mm width and 0.55 mm thickness.
But for some time now we are receiving complaints from customers that the s.s. strip is breaking after use for fencing purposes.
Please advise what is a reason for the breaking of this strip.
January 16, 2018
Q. What time and temp do I need to fully anneal .091" 303 SS?Jeff Patterson
Wytech - Rahway, New Jersey
February 3, 2018
A. Hello Jeff!
According to AMS2759/4, the aerospace specification for heat treating austenitic stainless steel, a setpoint of 1950 °F for 20 minutes at temperature followed by a forced air cool will work.
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