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Electromechanical Engineer Anthony “Proto G” Garofalo has been busy. Not only did he build an induction heater and explain how to make one of your own, but in the same article he goes over several uses for one. Making an electric cooker and loosening stuck hardware are two such interesting use cases, but his most exotic technique is a process called “cryogenic case hardening.” Case hardened metals are more resistant to rust, impacts, and scratches.

As seen in the video below, Garofalo hardens four low carbon steel bolts. One he simply heats then quenches, one he uses a case hardening compound when he heats then quenches, and finally two others are hardened cryogenically. In this final process, he heats the bolt, melts the case hardening compound onto it, heats it further, then quenches it in warm water. Finally it is cooled to a sub-zero temperature in a dry ice and alcohol bath. As you might suspect, it’s an interesting process to watch, starting at just before 3:00.

After hardening, Garofalo then tests the bolts with a set of hardness files to see what the results were. As you might suspect, all the bolts were harder, but those that were treated with a carburizing compound were harder to scratch. Bolts that are cryogenically hardened are reportedly not any harder than those hardened with a normal case hardening process, but the result is a deeper casing.

As a final test, the bolts were doused with salt water and left outside for a few days. The carburized bolts were definitely less susceptible to rust than the one that was not treated with a carburizing compound. Those that were cryogenically treated appeared to have even less rust.

As a bonus, he also goes over how to determine the carbon content of steel using a grinder in the video below. I had never heard of this technique before, but it looks quite useful!

Finally, for more from “Proto G,” why not check out how an oscilloscope looks in slow motion?