Can I anneal mild steel

A. Hi Ron. Hopefully a metallurgist will reply because my knowledge of this is very limited.

All I can offer is my understanding that the general route to softening steel {although that's not the only reason for annealing, I don't think nuance can be read into your 5-word question :-) } is to make it red hot, then allow it to cool very slowly.

But my understanding is also that mild steel isn't hardenable & annealable, and that's one of the reasons it's called mild.

Luck & Regards,

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:
threeplanes.net/toolsteel.html

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.

Regards,

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. Further, are you sure they're steel, not cast iron? You'll never make cast iron soft :-)




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