Hardening a 4140 cold Chisel

[@crakilldurmom]

I generally use a magnet for bringing carbon steels to critical temp.

[@Stubbornnut]

please explain

[@benbos6625]

​@@StubbornnutThe way I understood the essence is: the iron atoms are much larger than the carbon atoms. The goal is to get enough carbon atoms evenly between those of iron so that there is no more regular structure and therefore no large "sliding planes" can arise. Magnetism is that the iron atoms rotate synchronously to the left or right. Very strong heating makes them no longer rotate synchronously but "in all directions" due to the energy introduced; the 'shaking' iron atoms. When the iron is no longer magnetic, thats the moment all mutual synchronicity has actually disappeared: it is about to become liquid when even more energy is introduced. In it are also the carbon atoms, now evenly spread. By cooling quickly you force that carbon into the chaotic structure that is there at that moment. No regular stucture, less change on sliding fractions. You force some carbon outwards (blackening of the surface) and further inwards (where the iron then becomes weaker again instead of hard due to a surplus). It is all about applying THE right temperature to THE right material. And that is called craftsmanship (what you saw here).

[@garyvanbreda3022]

Great video. I think you meant temper it (to the straw colour) after hardening, not annealing it.

[@Stubbornnut]

you are 100% correct. nice catch!

[@melgross]

I agree with everything other than using motor oil. That’s somewhat dangerous as the flash point is below the flame point which means that it will sustain a fire even after the hot part is removed if it’s large enough to start one when it’s plunged in. I know a lot of people don’t use, or even know about quenching oil, but it should be used because it’s just the opposite and will not sustain a fire. It’s also pure. Used oils can contain noxious substances that are bad for the health and sometimes for the metals being hardened. That’s particularly true for motor oils which can contain chemicals that you shouldn’t breathe when they get that hot.

[@Stubbornnut]

you’re right! i will get some quenching oil for the next class.

[@rfisher79]

Make a Vid aboot your Forge Furnace.. Two pieces of C Channel.

[@Stubbornnut]

sure. i’ll make a video on shop furnaces for heat treatment. we have a couple electric furnaces and a few types of bearing heaters too. great idea !

[@stickermigtigger]

@@Stubbornnut When is this video coming? 🙂 Really interested in that gas forge design.