In this video I show you how to cryogenically case harden your low carbon steel parts with the induction heater. What you end up with is a material that has a ductile inner core with a hard outer shell. Parts that require impact resistance as well as abrasion resistance are great candidates for case hardening. Low carbon steel does not harden well on its own. When heating the part up and submerging it in a carbon compound, carbon gets impregnated into the surface of the material. This results in a hard outer surface.

Gears, Firing pins, Engine Camshafts, Lock Shackles, Security Fasteners, and Self Drilling Screws are all commonly case hardened. The method of case hardening used in the video is also known as carburizing with a cryogenic treatment. Liquid nitrogen is usually used but I used a isopropyl alcohol dry ice bath. Liquid nitrogen would provide even more benefits by converting even more retained austenite to martensite. Also, if you don't mind the darkness of the part after the hardening process, it's best not to polish it for even more rust protection. The method used in the video can be repeated multiple times until the desired hardness is achieved.

Induction is particularly good at case hardening. This is because of the skin effect discussed in the next step. The same high frequency skin depth that is seen in the working coil is also seen in the part being heated. The higher the frequency, the more the current is flowing on the outside of the material. For steel in this case, the current is only flowing about 6 thousandths of an inch deep. This is perfect for case hardening.

This process should only be used with low carbon steel so I'll show you a way to determine what type of steel you have.

In this video, I'll show you an easy way to determine the carbon content of your steel parts by observing the spark profiles. You can use this technique to find which of your parts would benefit from the case hardening method used in my last video. This is not the most accurate way of determining the composition of the steel, but many welders use this technique when welding unknown materials and is a good test for most non-critical jobs. This technique is known as spark testing.