Mossbauer Spectrometry Study of Aging Deterioration in Duplex Stainless Steel

铸造双相不锈钢作为核电站冷却系统中的泵壳和阀壳，在长期使用后机械性能下降。钢的寿命可以通过在高于工作温度的温度下进行加速试验所获得的激活能来评估。本文研究了商品CF3M铸造双相不锈钢在623-723K时效时的退化原因，并测量了其激活能。穆斯堡尔谱测量了铁素体中Fe的平均内磁场随时效时间的延长而增大。~lt；H&gt；的变化对应于平均铬含量的降低，这表明铁素体的相分解。得到了&lt；H&gt；变化的激活能约为180kJ/mol.铁素体硬度随时效时间的延长而增加。由硬度变化得到的激活能为160-17…更多的0kJ/mol，这与上面提到的一致。这些结果表明，硬度的变化归因于铁氧体中铬或铁原子的体积扩散控制的相分解。在273K下测得的V型缺口冲击能CE随时效时间的延长而减小。这主要归因于铁素体的相分解。然而，得到的CE变化的活化能为63kJ/mol，与上述结果不一致。假设CE变化用tanh函数表示：Ce(t，T)=A-B{1+tanh[(logt-C-(Q loge/RT))/D]}，其中未知参数由最小二乘拟合法确定。根据上述结果计算了压水堆和沸水堆在工作温度下的夏比能量曲线，如果假设30J的值保证区域合理的延性，压水堆和沸水堆的寿命预期为50年，内部平均磁场变化与夏比冲击减小量之间有很好的相关性。穆斯堡尔谱可用于时效脆化的非破坏性评价。较少

Cast duplex stainless steels which are used as the pump casings and valve casings in the cooling system of atomic power plants are degraded in the mechanical properties after avery long term use. The life time of the steel may be evaluated by the activation energy obtained by the accelerated test performed at temperatures higher than the operation temperature. The present study aims to investigate the origin of the degradation and to measure the activation energy for the commercial CF3M cast duplex stainless steel aged at 623-723K.The average intemal magnetic filed of Fe, <H>, in the ferrite measured by Mossbauer spectroscopy increases with agin time. The change in <H> corresponds to a decrease in the mean Cr content that in dicates the phase decompositon of ferrite. The activation energy for the <H> change is obtained to be about 180kJ/mol.The ferrite hardness increases with aging time corresponding with the <H> change. The activation energy obtaine from the hardness change are 160-17 … More 0kJ/mol which is consistent with one mentioned above. These results suggest that the hardness change is ascribed to the phase decomposition which is controlled by the volume diffusion of Cr or Fe atom in ferrite.V-notch Charpy impact energy, CE,measured at 273K decreases with aging time. The decrease is mainly ascribed to the phase decomposition of ferrite. However the activation energy of 63kJ/mol obtained for the CE Change is unconsistent with those mentioned above. The CE change is assumed to be expressed by a tanh function : CE (t, T) =A-B {1+tanh [(logt-C- (Q loge/RT)) /D]}, in which unknown parameters are detemined experimentally by a least square fit. Charpy energy curves at the operation temperature of PWR and BWR are calculated from the above result.if a 30J value is assumed to guarantee areasonable ductility, 50years of life time will be expected for the PWR and BWR application.There is a good corelation between the average intemal magnetic field change and the Charpy impact decrease. Mossbauer spectroscopy may be useful for anondestructive evaluation of the aging embrittlement. Less