Nitrogen alloying element

Alloying elements either enlarge the austenite field or reduce it. The former include manganese, nickel, cobalt, copper, carbon, and nitrogen and are referred to as austenite stabilizers. 

The basic steel types arc undergoing gradual modifications to adapt the steels to the continuous casting process. This has led to changes in the minor constituents of steel such as boron, nitrogen, titanium, and other alloying elements. 

Other common alloying elements are molybdenum up to 5% and copper up to 3%. Nitrogen, which is usually present at residual levels of about 0,03—0,06%, can also be used as an alloying addition of up to 0,2%. 

K. OsozawaandN. Okato, Effect of Alloying Elements, Especially Nitrogen, on Initiation of Pitting in Stainless Steel, Passivity and Its Breakdown in Iron and Iron-Base Alloys, R.W. Staehle and H. Okada, Ed., National Association of Corrosion Engineers, 1976, p 135-139... 

There are four main classes of stainless steel (austenitic, ferritic, ferritic-austenitic (duplex) and martensitic), and within these, a variety of different grades. The names ferritic and austenitic follow from their structures ferrite (P-Fe) and austenite (y-Fe) lattices hosting the alloying elements. The presence of Cr promotes the formation of the ferrite structure, while the austenite lattice forms when Ni is introduced. While ferritic and martensitic stainless steels are magnetic, austenitic stainless steel is non-magnetic. Further additives to some stainless steels are molybdenum (which improves corrosion resistance) and nitrogen (which adds strength and improves corrosion resistance). 

Ers] Ershov, G.S., Kasatkin, A.A., Influenee of Alloying Elements on the Diffusion of Nitrogen in Liquid Iron , Russ. Metall, (3), 24-27 (1981) (Experimental, Thermodyn., 13)... 

To improve their resistance to pitting corrosion, molybdenum is often added to stainless steel. Figure 7.52 illustrates the effect of molybdenum on the pitting potential of two stainless steels in NaCl [27]. Certain other alloying elements, in particular nitrogen and tungsten, also are beneficial whereas others, such as copper and sulfur, reduce the resistance to pitting corrosion. 

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