as aluminum, chromium, molybdenum and titanium. In 2015, nitriding was used to generate a unique duplex microstructure in an iron-manganese alloy (martensite-austenite, austenite-ferrite), known to be associated with strongly enhanced mechanical properties. History Systematic investigation into the effect of nitrogen on the surface properties of steel began in the 1920s. Investigation into gas nitriding began independently in both Germany and America. The process was greeted with enthusiasm in Germany and several steel grades were developed with nitriding in mind: the so-called nitriding steels. The reception in America was less impressive. With so little demand the process was largely forgotten in the US. After WWII the process was reintroduced from Europe. Much research has taken place in recent decades to understand the thermodynamics and kinetics of the reactions involved. See also Boriding Carburization Carbonitriding Ferritic nitrocarburizing Surface finishing References Further reading External links An Introduction to Nitriding Metal heat treatments Plasma processing Nitrogen et:Nitriitimine