Surface hardening or case hardening is a process that creates a harder outer layer on a metal object. Only the surface is hardened, while the metal underneath is left mostly untouched. This process allows for a hybrid type of metal where the outside is resistant to wear and the inside is still ductile enough to absorb the wear without breaking.
Surface hardening, or case hardening, has many benefits and allows metallurgists to create hybrid types of metal that are hard enough to last but not so hard that the metal becomes brittle and prone to fracturing.
Here are 10 benefits of case hardening.
Increases surface strength of metal parts
We touched on this above, but case hardening provides a special metal layer on the outside of metal parts that can make them stronger and, thus, more resilient to potential damage. This unique process is often superior to through hardening, where the whole piece is hardened all the way through.
Offers interior flexibility of metal parts
If a metal part was through-hardened, it would likely become tougher. It would also become more brittle. This defeats the purpose of strengthening the part in the first place. Surface hardening allows metal parts to maintain their flexibility below the surface, increasing their overall durability.
Increases durability
The hybrid composition of case-hardened metal parts makes them more durable on both the interior and exterior. It provides increased longevity for the respective part.
Increases weldability
One of the top case hardening benefits is that it makes metal parts easier to weld.
Increases customizability
Despite the name, case hardening doesn’t have to be performed uniformly across an entire metal surface. Certain gun parts and automotive engine parts, for example, only have certain portions of the surface case hardened, as those will be receiving the most wear.
Nitriding causes little distortion
With nitriding, a metal part is subjected to superheated gas, and the subsequent reaction forms an outer layer of metal. This process doesn’t deform the object, so nitriding can be performed after it’s already been machined, quenched or tampered.
Nitriding guards against corrosion
Using nitriding in concert with martensitic hardening can offer exceptional resistance to both abrasion and corrosion. This process is commonly used for bearings.
Cyaniding is a quick process for small parts
Screws, nuts and bolts are often case hardened through a process known as cyaniding; this involves submerging superheated steel into a liquid bath of a cyanide salt solution. Cyaniding offers a firm shell on the outside and can be conducted in 20 or 30 minutes.
Carburizing is a dynamic process for automotive parts
Carburizing is a process that involves introducing carbon to superheated steel and quenching it at the end to seal the carbon in. It’s used for car parts like shafts, gears, piston pins, clutch plates and bearings.
Flame hardening is simple and effective
Using an oxyacetylene torch, you can take parts like sprocket teeth, crankshafts or axles and heat them up. You can then use water to quench the part, and the process is complete. It’s that simple.
Call for case hardening today
Understanding the benefits of case hardening can help you decide if it’s something you need. For case hardening and many other metallurgical processes, call our experts at J.F. Heat Treating Inc. Our labs have all the latest tools, and our technicians have decades of metalworking experience.