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topic 55257

Can I anneal mild steel

June 24, 2010

Q. Hey guys,
I've been looking into making some electromagnets and have had a lot of difficulty finding iron or ductile iron anywhere to make my cores.

Can mild steel be heated to a cherry red glow and slow cooled to make it "softer"? I read that somewhere and wondered if it was true.

Thanks for any responses

Shaun Heatly
- Perth West Australia

October 13, 2012

Q. How do you anneal mild steel?

I understand you are supposed to heat it above a critical temperature, I do not know what that is. This is for the experiment to make it handle more magnetism aka Gauss.

I also understand that the rate of cooling is important as well...

So what is the BEST?

Also how does this change for thickness of the mild steel?

Thank you,


Richard Raynault
- Surrey, BC, Canada

October 13, 2012

A. Hi Shaun; hi Richard.

Yes, optimum annealing conditions do depend on the thickness of the steel (because the cooling rate does), but also upon the composition of the steel, including percentage of carbon. There is a short but outstanding introduction to heat treatment including annealing and tempering, with nice tables and graphs, at:

That page should answer your immediate heat treatment / annealing questions. On the other hand, heat treatment is a subject that fills shelves (if not aisles), of technical libraries, so you can take it as deep as you want. Sorry, I don't know the magnetic properties.

For a school science project it may be enough to know that you need to get the steel red hot (about 1400 °F) and then slowly cool it to soften it, or rapidly cool it to harden it.

On a few occasions I've needed curved sewing needles to repair car upholstery, etc., and made them from straight needles very simply. Just put the needle on a burner on an electric kitchen stove until it's red hot then turn the burner off. After it slowly cools, it's soft and you can bend it as you wish. Then put the curved needle back on the burner until red hot, pick it up with pliers and drop it into a shallow dish of oil for rapid cooling, and it's good enough for one-time use. Wear googles though because you haven't tempered it for toughness and it could shatter like glass :-)

P.S.: I'm not sure that the term "mild steel" is a good one for this instance because a lot of people consider mild steel to be low carbon steel that can't be hardened by heat treatment this way. If you try the same kitchen science project I mentioned on a shirt pin it doesn't work; you can't get it hard because it doesn't have enough carbon.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Bending old barbells

January 15, 2017

Q. I want to repurpose my broken barbells. They have snapped and are brittle. What do I need to do to be able to bend into a 15 inch radius? Is annealing with a torch going to be sufficient? Open to any suggestions!

Stephanie Retz
Maker with a degree in industrial design - Fairhaven Massachusetts USA

January 2017

A. Hi Stephanie. I don't know much about heat treatment but until somebody reads this who does, I'm going to say "no". I don't think you can get enough of it hot, and make it cool down slow enough, with a torch. I think you need to make a blacksmith's forge :-)

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

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