CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 2
2. 3 Effect of alloying elements on the properties of austenitic stainless steel
Apart from major alloying elements such as chromium and nickel, certain minor alloying
elements such as nitrogen, molybdenum, manganese etc also influences the physical, mechanical
and chemical properties of austenitic stainless steel. The combined effect of the alloying elements
and heat treatment procedures gives enormous varieties, microstructure and properties of different
types of austenitic stainless steel (Fig. 2.4). Residual elements which are inherently present in raw
materials, and entering during steel making practices also profoundly affect the properties of steel.
General effects of the alloying elements commonly found in austenitic stainless steel are as
summarized below [15,34,35].
2.3.1 Carbon
Carbon is one of the extremely powerful austenite stabilizers, and the solubility of carbon
decreases as the temperature decreases giving chromium rich precipitates. Austenitic stainless
steels in general contain carbon from 0.02 wt % to 0.15 wt %. Carbon is the key alloying element
which controls maximum attainable hardness, and increasing the carbon content is the least
expansive way for increasing hardness. High carbon content increases the tensile strength but
decreases the ductility. Moreover, with high carbon content chromium carbide precipitates at the
grain boundaries leading to depletion of chromium which increase the susceptibility to
intergranular corrosion.
2.3.2 Nitrogen
Nitrogen is one of the important elements for stabilizing -field similar to carbon. It can
expand and stabilize the austenite phase. It is used as an alloying element in austenitic stainless
steel for precipitation or solid solution strengthening for increasing the yield strength. Nitrogen in
solid solution makes austenitic stainless steel more wear and fatigue resistance. Apart from this,
nitrogen provides beneficial effects to avoid localized corrosion.