形成Al_(2)O_(3)表层的奥氏体不锈钢加速蠕变实验研究

Investigations on the Accelerated Creep Testing of Alumina-Forming Austenitic Stainless Steel

利用Gleeble热力模拟试验机对一种形成Al_(2)O_(3)表层的奥氏体(alumina-forming austenitic,AFA)不锈钢在循环载荷条件下进行加速蠕变实验,评估材料的高温蠕变性能,同时获得该合金在高温加速蠕变过程中的组织演化规律。结果表明,采用加速蠕变实验在较短时间内加速完成了常规蠕变实验过程中析出相、位错、孪晶等微观结构的组织演变;但加速蠕变实验过程中AFA合金内大量位错的反复产生与湮灭为难析出第二相提供形核点,降低Laves等难析出第二相的形核驱动力;同时加速蠕变实验所施加的循环应变逐步削弱新型AFA合金中纳米级形变孪晶强化效果,导致评价效果的差异。加速蠕变实验有助于高效评估材料的蠕变性能,但有关实验参数的最佳区间还需要更加深入的研究。

The heat transfer component is a major component of a nuclear power plant,the safety and service life of which are determined based on the long-term creep performance of the heat-transfer pipe material.Several long-term creep tests are usually required to determine the creep life of the heattransfer pipe materials,which considerably restrict the evaluation efficiency of the material service performance.The objective of this study is to investigate the feasibility of accelerated creep test(ACT)to reduce the time required for evaluating the creep properties of materials.A alumina-forming austenitic(AFA)stainless steel was prepared,and the ACT was performed on a Gleeble thermal simulator.Based on the ACT developed and realized on the Gleeble thermal simulator,damage accumulation was realized by applying elastic-plastic tensile and compressive strains on the ACT specimen to simulate the accelerated changes in the microstructure of the alloy that can be usually observed during a conventional creep test(CT).The average stress with respect to all the cyclic stress relaxation stages in the ACT was considered to be the initial stress of the conventional CT,and a creep fracture test was conducted on the alloy sample.Results revealed that the ACT accelerated the microstructure evolution of the precipitated phases,dislocations,twins,and so on in a short time.Nevertheless,the repeated generation and annihilation of a large number of dislocations in the AFA alloy during the ACT provided the nucleation point and reduced the driving force associated with the nucleation of the precipitated second phase,including the Laves phase.In addition,the cyclic strain applied during the ACT will reduce the strengthening effect of the nanoscale deformation twins in the AFA alloy,resulting in differences in the evaluation effect.Thus,ACT is useful for the efficient evaluation of the creep properties of materials;however,the optimal range of test parameters must be further investigated.