Nitriding processes are most widely used on low – alloy steels or low – carbon steels; however they are also used on intermediate and high – carbon content steels, aluminum, molybdenum and titanium. General applications of Nitriding include plastic – mold tools, cam followers, camshafts, extruder screws, crankshafts, valve parts, die – casting tools, firearm components, forging dies, extrusion dies, injectors and gears. Nitriding alloys are steel alloys with nitride – forming elements like titanium, molybdenum, aluminum and chromium. Systematic investigation in the light of nitrogen’s effect on the surface of metal (particularly, metal alloy – steel) started in the 1920s. Investigation of gas nitriding began independently in both America and Germany. The process met with great enthusiasm in Germany and many steel grades were made keeping nitriding in mind: they are the so – called nitriding steels. This process is named after the medium which is used to donate. The three general methods used are: gas nitriding, salt bath nitriding, and plasma nitriding and so – named are its types.
Examples of simply nitridable steels include the SAE 9800, 9300, 8700, 8600, 6100, 5100, 4300 and 4100 series, UK’s aircraft quality steel grades are some tool steels (For example, P20 and H13), stainless steel, 905M39 (EN41B),BS 4S 106, BS 3S 132, and some cast irons. Ideally, steels for nitriding should be in a hardened and tempered condition which requires nitriding to take place at a lower temperature than the last tempering temperature. A fine – turned or earth surface finish is the finest. Minimum amounts of material should be removed after nitriding in order to preserve the surface from hardness.