Removing magnetism from 304 Stainless Steel

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 AMS2759/4, a specification used in the aerospace industry for heat treating of austenitic stainless steel.

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,

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.

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!!

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,

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,

  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,

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,

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

Regards,