The 4140 alloy steel head now undergoes a ferritic nitrocarburizing treatment that both hardens the surface and improves its corrosion resistance, while also blackening it.

General Motors has a solution, and has applied for patents for its Ferritic Nitro-Carburizing (FNC) process, first used on the 2008 Cadillac DTS. 0:00 / 0:00.