Case hardning
- Thread starter therevjay
- Start date
Register to hide this ad
DeathGrip
US Veteran
Its Krispy on the ootside and soft on the inside
gregintenn
Member
I understand that it hardens the outside of the steel, perhaps a few thousandths deep, while leaving the inside softer. I'm sure I will be corrected shortly if I am wrong.
That's what it does. Certain steels are case hardenable,,others not. Those that are not generally have too much carbon content to start with and the process ends up hardening the piece all the way through because of the quench. Other hi-tech alloys just don't respond to the process and need special heat treatments to obtain hardness.
The colors that result from some forms of the process are an after effect and actually have nothing to do with the hardness or lack or it. Case hardening can/is done w/o colors. Also, colors can be obtained w/o hardening ,,if everything is done right.
scooter123
Member
In addition, case depth can be varied to a certain extent by how the steel is processed. For low carbon steel in the 1008 to 1020 range, normal case depth is usually in the range of 1/64 to 1/32 inch. However, deeper case depths can be achieved by double carburizing but doing this does entail a significant risk of the case cracking due to dimensional changes in the hard case.
With low carbon steels, the common practice is to pack the steel in powdered charcoal, heat it to a specific temperature, hold it at that temperature for a specific period of time, and then cool it slowly. After the caruburizing treatment the steel is still fully anealed so it then has to be hardened by re-heating it to the hardening temperature and then quenching it, usually in oil.
After hardening, the part is then normally tempered to relieve stresses induce in the hardened steel by quenching. This is done be re-heating the steel to somewhere in the range of 850 to 1050 degrees F and then slowly bringing it back to room temperature. The tempering temperature is what will determine the final hardness of the case hardened layer.
Benefits of case hardening are twofold. One is that you get a hardened surface in the desired final shape. The second is that the strength of the part is actually increased due to that hard skin. However a case hardened part that is exposed to cyclic loading at a high level will tend to develop cracks in the case, which then can lead to failure due to crack propogation through the soft core.
With low carbon steels, the common practice is to pack the steel in powdered charcoal, heat it to a specific temperature, hold it at that temperature for a specific period of time, and then cool it slowly. After the caruburizing treatment the steel is still fully anealed so it then has to be hardened by re-heating it to the hardening temperature and then quenching it, usually in oil.
After hardening, the part is then normally tempered to relieve stresses induce in the hardened steel by quenching. This is done be re-heating the steel to somewhere in the range of 850 to 1050 degrees F and then slowly bringing it back to room temperature. The tempering temperature is what will determine the final hardness of the case hardened layer.
Benefits of case hardening are twofold. One is that you get a hardened surface in the desired final shape. The second is that the strength of the part is actually increased due to that hard skin. However a case hardened part that is exposed to cyclic loading at a high level will tend to develop cracks in the case, which then can lead to failure due to crack propogation through the soft core.
