Ce元素对316LN奥氏体不锈钢高温蠕变性能的影响

Influence of Cerium on Creep Properties of 316LN Austenitic Stainless Steel

采用蠕变持久试验机、扫描电子显微镜和透射电子显微镜等实验手段,系统研究了Ce元素添加对316LN奥氏体不锈钢(316LN钢)高温蠕变行为和微观组织的影响。结果表明,添加0.032%的Ce元素使316LN钢的蠕变断裂寿命显著提高。在温度为700℃、载荷为150 MPa的条件下,添加0.032%Ce元素的316LN钢蠕变寿命为555.5 h,比不添加Ce元素时的蠕变寿命312.6 h提高了78%。在温度为600~700℃、载荷为150~200 MPa的条件下,未添加Ce元素和添加0.032%Ce元素的316LN钢对应的蠕变应力指数分别为7.64和9.07,蠕变激活能分别为415.3 kJ/mol和454.8 kJ/mol,蠕变门槛应力分别为61.7 MPa和76.6 MPa。蠕变断裂后的微观组织表明,添加0.032%的Ce元素显著促进了蠕变过程中316LN钢晶内Laves相的析出。晶内细小弥散分布的Laves相,在蠕变过程中能够阻碍位错移动,提高基体的蠕变抗力,从而有效改善蠕变性能。

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 temperature 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 promising 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 600oC to 700oC 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 addition of 0.032%Ce could significantly improve the creep rupture life of 316LN steel.For instance,at 700oC/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.Furthermore,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 movement 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 intragranular Laves precipitation strengthening.