| The American cast martensite stainless steel CA6 NM,the Chinese brand is 0Cr13Ni4 Mo,has been widely used in the field of nuclear power,because of its excellent properties,such as good corrosion resistance and cavitation resistance,etc.It is necessary to research the fatigue fracture of the nuclear power materials,because the nuclear power materials always failed in fatigue mode in the using process.The fatigue properties of most nuclear materials are studied by ASTM standard bulk specimens.Since structural components in the nuclear power plant are unable to be disassembled during their in service process,it is an urgent and key problem how to quickly and non-destructively evaluate fatigue reliability of these key structural components by using small-scale specimens.Fatigue properties of small specimens of CA6 NM martensite stainless steel for impellers in the nuclear pump were obtained by using symmetrically bending fatigue loading and uniaxial tension-tension fatigue loading,respectively.A comparison of fatigue properties between the small specimens and bulk specimens was conducted to examine feasibility for the evaluation of fatigue reliability of the CA6 NM steel using small specimens.The results show that tensile strength of the 40 ?m-thick CA6 NM specimens is slightly higher than that of the bulk specimens,but elongation of the 40 ?m-thick specimens is lower than that of the bulk counterparts.In low cycle fatigue regime,fatigue strength of the 40 ?m-thick specimens subjected to uniaxial tension-tension fatigue loading is lower than that of the standard bulk counterparts.With decreasing the applied stress amplitude,the difference in fatigue properties gradually decreases,and the fatigue limit of the small specimen is close to that of the bulk counterparts.Fatigue strength of the 40 ?m-thick specimens subjected to bending fatigue loading is much higher than that subjected to uniaxial tension-tension fatigue loading,and also higher than that of the bulk counterparts.Fatigue strength of the small specimens is related to the loading mode.The difference in the fatigue mechanism between the small specimens and the bulk counterparts is discussed,and the feasibility to evaluate fatigue reliability of the steel using small specimens is addressed.The tensile tests and uniaxial tension-tension fatigue tests were carried out to study the size effects of tensile and fatigue of CA6 NM steel.The sample is designed to be 40 ?m,100 ?m,230 ?m,600 ?m,1 mm and 2.5 mm.It is found that with the decrease of thickness,the tensile strength of CA6 NM steel specimens first decreases and then increases,and the plasticity decreases continuously.As the thickness decreases,the fatigue performance of the sample increases first and then decreases:From the 2.5 mm thick to the 230 ?m thick sample,there is no obvious size effect except the fatigue limit;The fatigue property of the 100 ?m thick specimen is obviously improved,and it is better than that of the bulk specimen;The fatigue property of the 40 ?m thick specimen is obviously reduced.The mechanism of the size effect on tensile and fatigue specimens with different thicknesses is discussed,and the feasibility to evaluate fatigue reliability of the steel using different thick sample under uniaxial tensile-tension fatigue loading is addressed. |
PDF Full Text Request