| 2.25Cr1 Mo steel is widely used in the hydrogenation reaction due to its high mechanical strength as well as good resistance against creep and hydrogen corrosion at elevated temperature.Hydrogenation reactor is under high temperature and high pressure working condition for a long period.It is necessary to investigate the cyclic mechanical property of 2.25Cr1 Mo steel at 455 oC.In this study,uniaxial tensile test was conducted at room temperature and 455 oC.Low cycle fatigue and creep-fatigue interaction tests were conducted under strain control.Racheting fatigue and creep-racheting-fatigue tests were conducted under stress control.The main factors influencing the fatigue life and the damage mechanism of different experimental conditions were explored.A modified plastic strain energy approach is proposed to predict the creep-fatigue life.The high temperature behavior of 2.25Cr1 Mo and 2.25Cr1 MoV steel were compared.The experimental results showed that:(1)Elastic modulus,yield strength,tensile strength and elongation of 2.25Cr1 Mo steel decreased significantly with the rise of temperature.(2)S-N curve can be fitted well by combined Basquin and Coffin-Manson equation.Material exhibits cyclic softening.No matter tensile hold or compressive hold time is induced,softening becomes more pronounced.A modified plastic strain energy approach is proposed to predict the creep-fatigue life.(3)It is concluded that average stress and stress amplitude will increase material ratcheting strain accumulation rate in racheting fatigue tests.Initiation and connection of toughness cavity is the major cause for material failure.(4)When peak hold and double hold are induced,fatigue life will decreases.Double hold is more damaging than peak hold.The higher the stress level,the greater the damage of material while hold time is induced.(5)The uniaxial tensile properties of 2.25Cr1 MoV steel are slightly better than that of 2.25Cr1 Mo steel.When strain amplitude is high,the fatigue resistance of 2.25Cr1 Mo is better than that of 2.25Cr1 MoV steel.When strain amplitude is low,the fatigue resistance of 2.25Cr1 MoV steel is better.No matter high strain amplitude or low strain amplitude,it is obvious that softening degree of 2.25Cr1 Mo is greater than that of 2.25Cr1 Mo steel. |
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