Fe-30Ni-15Cr-0.6Nb-3Al-2Mo-3.5Cu奥氏体耐热钢高温蠕变行为

High temperature creep behavior of Fe-30Ni-15Cr-0.6Nb-3Al-2Mo-3.5Cu austenitic heat-resistant steel

研究了一种含铝奥氏体耐热钢在温度为750℃,蠕变应力为120、170、210和250 MPa下的高温蠕变行为,运用扫描电子显微镜、电子背散射衍射技术研究了蠕变试样的微观结构演变。结果表明,蠕变后第二相主要是B2-NiAl相与σ-FeCr相,没有发现Laves-Fe_(2)Nb相的析出;随着蠕变应力从250 MPa下降到120 MPa,最小蠕变速率从5.72×10^(-6)s^(-1)下降到3.11×10^(-7) s^(-1)。在蠕变过程中,B2-NiAl相初期在晶界析出,随后逐渐在晶内析出并有轻微长大现象,B2-NiAl相的析出有助于提高材料的抗蠕变性能。通过包含双曲正弦函数的方程计算得到应力指数n=3.01,确定相关的蠕变变形机制是位错滑移。根据蠕变断口微观形貌与蠕变损伤容限因子表明,确定蠕变失效是由析出相粗化导致的显微组织退化引起的。

The high temperature creep behaviors of an aluminum forming austenitic(AFA)heat-resistant steel at 750℃and creep stress of 120,170,210 and 250 MPa were studied.The microstructure evolution of creep specimens was investigated by scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD).The results show that the second phase after creep is mainly B2-NiAl phase and σ-FeCr phase,and no precipitation of Laves-Fe_(2)Nb phase is found.As the creep stress decreases from 250 MPa to 120 MPa,the minimum creep rate decreases from 5.72×10^(-6) s^(-1) to 3.11×10^(-7) s^(-1).During the creep process,the B2-NiAl phase precipitates at the grain boundary at the initial stage,and then gradually precipitates in the grain and grows slightly.The precipitation of B2-NiAl phase helps to improve the creep-resistance performance of material.The stress exponent n=3.01 is calculated by equation including the hyperbolic sine function,and it is determined that the relevant creep deformation mechanism is dislocation slip.According to the creep fracture micro morphologies and the creep damage tolerance factor,it is determined that the creep failure is resulted from the microstructure degradation caused by the coarsening of the precipitated phase.