| Super austenitic stainless steel has been used in various fields,such as energy and environmental protection,marine development,petrochemical industry,pulp and paper bleaching equipment because of superior resistance to pitting corrosion,grain boundary?GB?corrosion and stress corrosion.Super austenitic stainless steel contains more Mo elements than traditional austenitic stainless steel.Mo can promote the formation of passivation film Cr2O3 on the surface of stainless steel and can significantly improve the corrosion resistance of stainless steel.However,the brittle?phase is easily formed in the grain boundary due to the segregation of Mo,which directly affects the hot working property and corrosion resistance of super austenitic stainless steel.Therefore,reducing the segregation of Mo at grain boundary and restraining precipitation of?phase is the key to improve the quality of super austenitic stainless steel.The experimental results show that the addition of B in super austenitic stainless steel can obviously reduce the precipitation tendency of?phase at grain boundary,thus improving the phenomenon of hot forging cracking of super austenitic stainless steel in our research group.Combining with the experimental results,we study the effect of B,Mo on the precipitation behavior of?5?210?grain boundary?phase in super austenitic stainless steel by using the first-principle theoretical calculation method,and explained the electron origin behind the experimental phenomenon from the atomic level.Based on the composition ratio of main element Fe,Cr and Ni in super austenitic stainless steel,the construction of Fe-Cr-Ni?5?210?GB was the basis of face centered cubic Fe.Firstly,we study the effect of Mo on segregation behavior of Cr at Fe-Cr-Ni?5?210?GB in order to reconstruct formation process of?phase from the angle of simulation.The calculated results show that Mo at grain boundary sites can attract the segregation of Cr from other sites to grain boundary sites and improve the strength of grain boundary.The calculated results also show that the recombination of Mo and Cr will reduce the bonding ability of grain boundary,which explains the reason why?phase is easy to crack in hot working.Next,we study the occupation and the segregation of B and Mo elements at Fe-Cr-Ni?5?210?GB.The results show B and Mo elements tend to segregate toward the grain boundary sites and B is easier segregation than Mo.In addition,high content of B can improve the strength of grain boundary,low content of B and different content of Mo have little effect on the strength of grain boundary when B and Mo tend to converge to grain boundary sites.The experimental results of tensile simulation show that the high content of Mo is not beneficial to the adhesion of grain boundary and the high content of B is beneficial to the adhesion of grain boundary when B and Mo tend to converge to grain boundary sites.Finally,we study the effect of B on segregation behavior of Mo at Fe-Cr-Ni?5?210?GB and B at the sites of grain boundary can inhibit the segregation of Mo to sites of grain boundary and it can also improve the strength of grain boundary.The result explains that the decrease of the aggregation tendency of?phase in super austenitic stainless steel with B in the experiments.The calculated results also show that the stability of grain boundary is the best when B is located at the grain boundary sites and the low content of Mo tend to segregate toward the transition sites. |
PDF Full Text Request