Theoretical Study On The Effects Of Alloying Elements On The Structural Stability And Mechanical Properties Of Sanicro 25 Steel

As a highly efficient and clean power generation technology,ultrasupercritical technology is the key development direction of coal-fired thermal power stations.In order to further reduce coal consumption and carbon dioxide emissions,thermal power generation technology is rapidly developing to higher parameters.The increase of steam parameters will accelerate the aging rate of core components such as superheaters and reheaters in thermal power unit,and shorten its service life.Austenitic heat-resistant steels such as HR3 C and Super304 H,which are used in 600? ultra-supercritical units,are subjected to carbide precipitation and coarsening when operating under higher steam parameters.The structural thermal stability is deteriorated.The high-temperature mechanical properties and its service life will also be seriously affected.The Sanicro 25 austenitic heat-resistant steel has higher thermal stability and high-temperature mechanical properties than HR3 C,and is expected to be used in key materials of 630?650? grade ultra-supercritical thermal power units.By comparing the chemical composition and mechanical properties of HR3 C and Sanicro 25 steel,it can be found that alloying elements Co,W,Cu,Nb play an important role in thermal stability and mechanical properties.In order to further analyze the effects of these elements on the structure and properties of Sanicro 25 steel,we use first principles calculations to explain the effects of alloying elements such as Co,W,Cu and Nb on the structural stability and mechanical properties of Sanicro 25 steel.According to the main chemical compositions of Sanicro 25 steel,we have built different systems containing alloying elements such as Co,W,Cu and Nb based on Fe-Cr-Ni system.The effects of solid solution strengthening elements Co and W on the structural stability and mechanical properties of Sanicro 25 steel are first analyzed.In this paper,the effects of Co and W on the structural stability,thermodynamic stability and mechanical properties of Sanicro 25 steel are analyzed by structural optimization,elastic constant calculation,Peierls stress calculation and generalized stacking fault energy calculation with first-principles calculation method.The conclusions are as follows: Co and W dissolved in FeCr-Ni system have good structural stability,and the structural stability of the systems are better at 630?650?.W and a small amount of Co can improve the mechanical properties such as strength and ductility.When Co and W are far from the stacking fault region,the possibility of twinning in the system is increased,thereby improving their plastic deformation ability.Then,the effects of Cu and Nb on the structural stability,thermodynamic stability and mechanical properties of Sanicro 25 steel are also analyzed by structural optimization,elastic constant calculation,Peierls stress calculation and generalized stacking fault energy calculation,and the following conclusions were obtained: Cu and Nb dissolved in Fe-Cr-Ni system can improve the structural stability,and the structural stability of the systems are better at 630?650?.Cu will reduce the strength and ductility of the system,while Nb will reduce the strength and improve the ductility.Cu will reduce the tendency of twinning in the system,resulting in the decrease of its plastic deformation ability.When Nb is far from the stacking fault region,it will increase the possibility of twinning in the system,thereby improving its plastic deformation ability.