High Temperature Oxidation of T91 Alloy

Ferritic-martensitic steels are extensively used in thermal and nuclear power plants due to their higher thermal conductivity and lesser thermal expansion coefficient. T91 alloy (Ferritic-martensitic steel) is proposed as material of clad for metal fuel fast breeder reactors. The choice is based on characteristics viz. Low swelling (BCC structure) and minimum DBTT (Ductile Brittle Transition Temperature) shift. The possibility of oxidation of this alloy under the influence of high temperature and exposure time cannot be ruled out. The studies on high temperature oxidation of T91will be useful in understanding the underlying mechanism of oxidation and for further improvement in the oxidation resistance of T91. In the present work the high temperature oxidation of T91 alloy was studied using thermogravimetry technique. Both isothermal and non-isothermal methods were used. A multistep oxidation reaction was observed. Change in slope of the curve in temperature interval (1073–1673 K) showed the simultaneous oxidation of constituent elements of alloy T91 which is due to difference in the tendency of constituent elements to form respective oxides and is governed by the standard Gibbs energy of formation of respective oxide and kinetics of the reaction.