| Pressure vessel components and structures are often subjected to high temperature, high pressure, and corrosion medium. It must be a disaster once accident occurs. As to 16MnR steel used extensively in pressure vessel and piping, a series of fatigue experiments under stress control at elevated temperature and SCC experiments in nitrate solution were conducted to investigate its low-cycle fatigue behaviors at elevated temperature, effects of temperature on fatigue performance and SCC performance in nitrate solution. Life prediction methods, design curves and damage evaluation models of low-cycle fatigue are obtained. All studies can be concluded as follows.Stress fatigue behaviors of 16MnR at 300℃ and 420℃ are analyzed carefully. Laws of cyclic hardening and softening, transformation laws of strain amplitude, plastic amplitude, laws of cyclic creep caused by mean stress under stress control, Masing behavior of material, etc, are examined in detail. Experimental datum and analytical results are given in order to further investigate life prediction methods, design curves and damage evaluation models of low-cycle fatigue.Simple tensile tests and low-cycle fatigue tests under stress control at different temperature were conducted to investigate the effects of temperature on fatigue behavior and fatigue strength. It is found that when temperature lies between 250℃ and 375℃, "blue brittle" phenomenon happens, fatigue strength of material is enhanced greatly which can be rationalized by dynamic strain aging effect, and material exhibits lower velocities of cyclic creep and cyclic hardening character. When temperature exceeds this range, material exhibits higher velocities of cyclic creep and cyclic softening character.Life prediction methods of low-cycle fatigue, which consider effect of mean stress, are summarized, and a previously proposed energy-based life prediction criterion is modified in order to promote its convenience. Life prediction models of 16MnR at 300℃ and 420℃ are also given. Comparison between theoretical predictions with test results is found to be quite satisfactory.S-N curves of 16MnR steel at 300℃ and420℃ are obtained. After amendment of mean stress and considering effects of various factors on fatigue life, experimental datum are compared with the ASME Code, and low-cycle fatigue design curves of16MnR steel at 300℃ and 420℃ are established. Due to existence of "blue brittle" phenomenon, 250℃ and 375℃ can be regarded as critical temperatures of fatigue strength of 16MnR steel, and low-cycle fatigue design curves with temperature that ranged from 250℃ to375℃ and from 375℃ to420℃ are also established.Models of exhaustion potential of X. H. Yang and Y. Wang are ameliorated to consider effects of maximum stresses and temperature on low-cycle fatigue damage evolution. Equivalent modulus is selected to define damage variable, which has a definite physical meaning and can be measured by a simple procedure. Models of low-cycle fatigue damage evolution under various loading conditions with different maximum stresses and temperature are derived based on several hypotheses when temperature exceeds the "blue brittle" range. These are elementary explorations for the application of damage mechanics to fatigue analysis and life prediction of pressure vessel.SEM analyses of fracture surfaces were conducted, and preliminary understanding of fracture surfaces under various loading conditions with same maximum stresses and different temperature is obtained.SCC performance of 16MnR steel and welded joints are studied by the method of stress corrosion test for pro-cracked wedge-open loading WOL specimen in nitrate solution. Critical stress intensity factors and spreading rates of SCC of the parent material and welded joints were measured. Meanwhile, effects of rust inhibition, microscopic organization of metal, temperature, and solution concentration on SCC performance of 16MnR steel and welded joints are also investigated.In conclusion, detailed understanding of low-cycl...
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