Influence of Cerium on Creep Properties of 316LN Austenitic Stainless Steel
316LN austenitic stainless steel(316LN steel)is widely used as structural components in nuclear industries for their excellent corrosion resistance and high temperature mechanical properties.With the development of next-generation nuclear reactors,it is imperative to improve the high tempera-ture creep properties of 316LN steel to warrant the corresponding components being subjected to higher temperatures.Alloying with rare earth(RE)elements,such as Cerium(Ce),are considered as a promis-ing approach to enhance creep properties of the austenitic stainless steels.However,the effect of Ce on the microstructure evolution and creep performance of 316LN steel have not been reported.In this study,the effect of Ce on creep behavior and microstructure of 316LN steel in the temperature range 600℃ to 700℃ and stresses range150 MPa to 200 MPa was investigated by electronic creep tester,scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that the addi-tion of 0.032％Ce could significantly improve the creep rupture life of 316LN steel.For instance,at 700℃/150 MPa,the creep life of 316LN steel with 0.032％Ce prominently increased from 313 h to 556 h.The creep stress exponent,activation energy and threshold stress of 316LN steel without Ce were found to be 7.64,415.3 kJ/mol and 61.7 MPa,respectively,whereas those of 316LN steel with 0.032％Ce addition were corresponding to 9.07,454.8 kJ/mol and 76.6 MPa.The creep mechanism of those two 316LN steels were also controlled by dislocation climbing.The addition of 0.032％Ce has not changed the creep mechanism of 316LN steel but clearly raised the creep activation energy and threshold stress.Further-more,microstructural analysis demonstrates that the addition of 0.032％Ce may obviously promote the precipitation of Laves phase within the matrix.These intragranular Laves phases could inhibit the move-ment of dislocations during creep deformation,notably enhancing the creep resistance of the matrix.Therefore,the addition of 0.032％Ce remarkably improved the creep properties of 316LN steel by intra-granular Laves precipitation strengthening.
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