How to Case Harden Steel
Pure steel is somewhat soft and malleable. In many situations it is important that the steel have a tough, hard coating. Adding that hard coating to steel is what case hardening is all about.In order to case harden steel you will need to heat the steal in the presence of carbon. It is the infusion of carbon into the outer layer of the steel which hardens it.
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Things You'll Need
- Steel
- Forge or furnace
- Carbon (powdered charcoal)
- Metal container
- Tongs
- Heavy gloves
- Protective clothing
- Eye protection
Instructions
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1
Crush several dozen charcoal briquettes, enough to more than cover the item you wish to case harden.
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2
Prepare a metal container with a metal lid. The container should be slightly larger than the item you wish to case harden. Place a 2-inch layer of crushed charcoal into the bottom of the container.
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3
Heat the steel you wish to case harden until it glows red hot. This can be done in a furnace or it can be done using a torch with a rich fuel mixture.
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4
Using tongs remove the red hot steel and place it in the metal container on the bed of crushed charcoal. Immediately pour additional crushed charcoal over the red hot steel until it is completely covered. Put the lid on the metal container and leave your steel to cool for at least 1 hour.
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Remove your steel from the charcoal and reheat it until it glows red hot. Using tongs dump it into a container of room-temperature water. Your item is now case hardened.
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Tips & Warnings
If you want to add a second layer a carbon to your steel in order to increase the depth of the hardening, reheat the item to red hot and place it back into the crush charcoal and leave it covered for another hour. Then reheat to red hot and plunge into water.
Use extreme caution when handling red hot steel. When you cover your steel with the crush charcoal it is likely the charcoal will catch fire. Simply place the metal cover on the box and allow the fire to extinguish itself.
Always wear heavy gloves when working with hot steel.
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Comments
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Complete nonsense: this is no casehardening, even a lousy explanation of normal (carbon) steel hardening, first: you need to know if it’s even possible to harden the steel you have at hand: only steel with a large enough carbon content can be hardened the way it’s described above, if not, there is sometimes (not with all steels) the possibility to perform a casehardening. So first find out what kind of steel(alloy) you have before attempting any hardening. Casehardening is something completely different then described here above, most commonly casehardening is performed by placing the object in a canister completely packed by carbon rich material (traditionally charcoal, very fine crushed animal bones and such) and airtight sealed so no oxygen can get in. This is placed into a oven that can reach high temperatures (let’s say minimum 800 to 1100 degrees C), the heated steel will absorb a small amount of carbon that will make the outer layer suitable for hardening. The longer you will leave the object at absorbing temperatures, the thicker this layer will become (we are talking about 100ths of mm!). After removing the object out of it’s canister you may then perform the actual hardening: heat the object to hardening temperature and quench it in oil, after this the internal crystal-structure in the new outer layer of carbon rich steel will be modified from a soft structure to a hard structure (austenite to martensite) In contrast to normal hardened steel: with casehardening it’s common NOT to temper the steel by heating it again tot a (much lower) temperature (say about 200 to 280 degrees C) and leave it to rest to cool down. This tempering is mostly common practice with normal hardened steel, this to relieve stresses in the steel that are build up by the rapid down cooling caused by quenching the steel in oil Casehardened steel only has stresses in that thin outer layer. That’s often something very useful: the outer layer is extremely hard, but the core of the steel is still soft: you’ve got a very strong outside, resistant to wear and a soft and elastic core that can resist to shock and pressure. This all is a very brief and certainly incomplete story about steel hardening. There are numerous kinds of steels, alloys, numerous method’s of hardening, there isn’t one easy way in this field. The only thing you can do is: find out what kind of steel you have, look on the internet for the datasheet for this steel, read the manufactures advices about the recommended hardening method: temperature ranges for heating and quenching and so forth. Novoltny, The Netherlands
