Hardening steel

Viewing 6 posts - 1 through 6 (of 6 total)
  • Author
  • #134775

    Any metallurgists out there?

    I’ve seen O1 tool steel hardened in two ways, one with an intense heat source like a mapp gas torch, and the other, as Paul does it, with charcoal briquettes. The torch heats very quickly. The charcoal heats more slowly. Assuming you go to the same temperature, does it matter whether you heat to your target temperature quickly vs. more slowly?

    Salko Safic

    Same thing no difference between the two methods. Ones a faster method over the other.

    The Lost Scrolls of HANDWORK
    (Hand tool only woodworking magazine)


    Hi Ed – I have a blacksmith setup with a forge/anvil etc but for this job either the torch or briquettes would work fine and speed of heating is not an issue. I would use the torch personally as I have one and it would be much quicker than firing up the forge.
    Remember you are only trying to harden the sharp end. When I make blades of any sort the aim is to have the cutting edge hard enough to keep an edge and the rest of the steel softer to absorb shock and be less brittle and likely to break. Tempering the edge to a straw colour and the rest to a blue/purple colour is the aim, don’t stress if you get it wrong steel can be re-hardened and tempered many times.
    For the record different types of steel harden by quenching in different liquids ie some steels need oil to quench and if you were to use water it will become so hard it will shatter like glass. So use a steel like 01, 1085 etc that you can find out the best way to harden and temper.
    I hope that helps, have fun


    Thanks. Good to know that the two ways are equivalent. I’ve used a torch before and just wondered if the charcoal would be equivalent. In some ways, it seems more convenient.

    Matt McGrane

    @ed – Ed, I read once about the use of charcoal actually infusing (doubt that is proper terminology) the steel with carbon. So there may be a difference in the two methods. I think they did that a century or two ago, but now the steels are made “high carbon”, so the two methods are probably more equivalent with current steels.

    Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/


    Hi Ed,
    If you are just doing one blade at a time in the torch then the torch will be the best way to harden the O1. Just don’t linger too long – get it to temperature all the way through and quench quickly. Matt is right about the role of carbon – a charcoal furnace is a much better option if you have a few pieces to harden at the same time. If you keep steel at austenitising temperature for too long in an oxidising (oxygen rich)environment, then carbon will be lost to the atmosphere (as carbon dioxide) from the surface layers of the steel – called decarburisation. If it goes on for too long it reduces the carbon in the surface sufficiently to lower the surface hardness – sometimes significantly. Then you basically have to grind the surface away to remove the decarburised layer. You can’t get carbon back into a high carbon steel.
    Matt’s comments about carbon infusing in a charcoal furnace is called “case hardening” but you can only do it to steel that is very low carbon in the first place (0.1% Carbon) – it puts a hard “case” on the surface of the component that you are making when you quench. No difference between modern steels and old steels in this treatment – it was used where you needed machineability in one part of the component and hardenability in another! Manufacturing brake pins and bushes is where this technique was often used.

    If I can be of further help – please contact me.
    Mark Heady

Viewing 6 posts - 1 through 6 (of 6 total)
  • You must be logged in to reply to this topic.