finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics

World's most popular finishing site / Internet's friendliest corner

topic 45435

Removing magnetism from 304 Stainless Steel


A discussion started in 2007 but continuing through 2019

2007

Q. Hello,

I need to know how to remove any magnetism from 304 Stainless Steel. I've machined a 304 stainless steel disk that is 6" in diameter. I put it into a lathe and removed a 3" hole in the center and drilled four 1/2" holes on the solid ring that was remaining. This was for a vacuum system with cryogenic feeds. Once I powered up the electromagnet in the lab to 0.8 Tesla (the Earth's magnetic field is about 0.00005 Tesla) the part was very strongly attracted to the magnet.

Here is the issue, I need to create a hole in a 304 stainless steel disk. This disk will be the vacuum seal for the sample mount in a cryogenic chamber that can produce a field of 10 Tesla. The field is created with a superconducting electromagnet. If there is anything magnetic with in 1.5 meters of the magnetic it will quench (very bad).

So how do I remove the magnetism from machined/welded 304 stainless steel? I know a lot of articles on here say that 304 is barely magnetic when machined, but I'm working with very high fields, and yes machines stainless is very magnetic.

Thank you.

Dustin Kreft
Student - Mad, Wisconsin


2007

? Why are you concerned about removing the magnetism? Wouldn't it be better to change material? If your steel is magnetic, will it not magnetize again in service under such high fields?

Guillermo Marrufo
Monterrey, NL, Mexico


2007

Q. It is standard to use 304 Stainless Steel when developing high vacuum system, I need to go to 10^-7 Torr. Flanges and other machined parts(304 SS) can be purchased with out being attracted by a magnetic field. I want to know the process to remove magnetism. I've read that 304 SS may need to be heat treated to turn BCC into FCC. If this is what's done then what are the details. 304 SS is machinable and initially non-magnetic.

Dustin Kreft [returning]
- Madison, Wisconsin


2007

A. Dustin, when you machine the 304 stainless steel, you can work harden it. The change in structure that the material experiences can make it ferromagnetic, such that it'll be unsuitable for your applications. I think you're on the right track trying to anneal it.

We generally use 1950 F for about 20 minutes of soak time. We also figure it takes about an hour for a one inch thick part to heat up, maybe two hours for a two inch thick section to heat up, etc. So the general, rule of thumb is to heat it for one hour per inch of thickness.

Cooling is another question. We commonly use a water quench, and then take steps to deal with the distortion. The reason you want to cool fast is that 304 MIGHT be susceptible to sensitization, wherein the carbon in the stainless steel combines with chromium, and this takes place primarily at the grain boundaries. With the grain boundaries depleted of chromium, the corrosion resistance is decreased, and you can get significant corrosive attack of a sensitized part, since the corrosion is concentrated along the grains. Cooling fast through the sensitization range keeps the carbon and chromium separate.

If you use 304L, you won't have that problem, since it has low carbon to start with.

1950 °F is fairly hot, so if you heat your part to that temperature, you'll get scaling and discoloration if you do it in air. Vacuum of 10 to the minus 3 Torr works well, as do protective atmospheres of argon, hydrogen, and others.

If you send your parts to a heat treater, I'd recommend using one that will certify the work in accordance with AMS 2759/4, a specification used in the aerospace industry for heat treating of austenitic stainless steel.

lee gearhart Lee Gearhart
metallurgist - E. Aurora, New York



September 3, 2008

Q. Hi,

I'm doing machining of SS 304 grade materials and some parts are magnetic after machining and some are not. I would like to know whether It will stick to magnet after machining or not. Could you please clarify my doubt?

Shanmugam Chandrasekar
Product Engineer - Coimbatore, India


September , 2008

A. Hi, Shanmugam. Sorry but I don't know how to further clarify this :-)

You have proven to yourself through experience that machining can render SS 304 parts slightly magnetic, and you are reading here that it can do so as well. The practical answer is that SS 304 is not strongly magnetic, but machining and cold working can make it somewhat magnetic. If you need a quantitative relationship between degree of magnetism vs. type & degree of machining, sorry, it's beyond my knowledge. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


May 14, 2012

Q. Hi,

I just tried two ss 316L plates for welding, but after the welding the material shows magnetism (only for welded space) what is the reason? How will I prevent it? Is it possible or not? Welding rods used are ss 316L.

PLEASE REPLY

Solbin Thomas
- Doha, Qatar


January 8, 2013

A. Hi,

Welding consumables for 316L materials are designed to produce a small amount of ferrite in the deposited weld to avoid weld hot cracking, this is why the weld shows some magnetism i.e. the deposited weld metal does not contain a 100% austenite phase. It is normal to check the ferrite level of completed 316L welds to ensure the ferrite % is in the range 3% to 8% in order to give adequate protection from hot cracking and required properties at low temperature.

Mark Thomas
- UK



October 12, 2017

Q. I'm a forger in India and I have a little question to ask. I had forged 304L round bar and made a sheet ring from it.
But now I'm a little tense: the material is lightly catching magnet and I don't know how to remove magnetism from it.
Can you please help me out of it

mahendra mehta
- india


October 13, 2017

A. Hi Mahendra!

As our partner Lee Gearhart says, you can heat treat AISI 304 steel to regain its austenite structure. This parameters work (1950 °F = 1065 °C, 20 minutes, then quench in water), and you can rotofinish later with some brighteners to reach something aesthethically "correct" finish for SS304.

Be aware that this WILL lower the part hardness (for SS304 I think final value will be like 80 HRB) and could modify the part dimensions, so please make some tests before treating the whole batch.

Best regards!!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina


December 16, 2018

A. Dear friends,

Here we are talking about the magnetism of austenitic stainless steel,in order to remove the magnetism of SS steel there are 2 steps we can follow the same .
1.To maintain the chemistry of Stainless steel in such a way so that metal get high amount of austenite in steel there mostly two elements are widely used a strong stabilizer of austenite like Ni & Mn. so we have to properly maintain the ratio between Ni & Cr.

2. we can remove the magnetism of steel by following the heat treatment cycle,Heated to 1065-1080 °C soaked for 1 hr per inch as per thumb rule and follow the quenching in water.

Regards,

Ilyas varaiya, Metallurgist
R.K Consultancy. - Rajkot, Gujarat, India



July 13, 2019

Q. We are using SS304 grade material to make a 2 inch long tube. But when the tube is manufactured it becomes magnetic and sticks with magnet. But I want to know is there any kind of stainless steel material which will not become magnetic if we draw the part.

Amit Panchal
Aditya Engineering Works - Delhi, India


July 2019

A. Hi Amit. If you can't anneal the tubing as suggested by Lee Gearhart and others, switching to 316SS will give you a tube with a lessened tendency to turn magnetic.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



August 9, 2019

Q. Hi,
How to remove magnetism permanently from a drawn SS 304 part, as my component should have 0% towards magnetic.

K Sasi Kumar
- Chennai, Tamilnadu, India


August 2019

thumbs up sign  Hi K Sasi. I am not a metallurgist, but it seems that people have suggested that annealing to change the crystal structure is the only way to do it, but that this may soften your part and be a problem (depending on what it is), that 316SS would be better than 304SS, and finally that stainless may not be an appropriate material if true 0% magnetism is required.

Another issue is the question of whether you mean it must not be magnetic in the sense of attracting an iron nail (which can probably be simply addressed with degaussing, but not "permanently"), or whether you mean it must not be attracted to a magnet like an iron nail is, which is the more difficult problem discussed here.

Please try to engage in the conversation by asking for clarification on the assertions and methods proposed, explaining your unique component & application, etc. Re-introducing an abstract question 14 postings later may not lead to much progress, but good luck. Thanks!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


August 11, 2019

Q. Sir, thanks for your information, my question is part should not attract to magnet, since my part is not attract with iron.

Thanks & Regards,

K Sasikumar
- CHENNAI,TAMILNADU, INDIA


August 2019

A. Okay cousin. We seem to be having a language difficulty, but your question was answered. Good luck with it.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental Compliance


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.