Low Cycle Fatigue Properties And Laser Shock Peening Treatment On FV520B Steel

With the continuous improvement of modern science and technology,The energy that humans need puts forward a new test to modern industry,the production of large-scale,complicated,equipment efficiency accelerates the high performance steel is widely used.However,in the high-intensity working conditions,especially the resonance,peak operation and the start-stop stage of the unit,many high performance steel also faces the danger of fatigue failure.FV520 B is widely used in gear,shaft,wheel disk,blade,rotor,pump and so on because of its high strength,good impact toughness,corrosion resistance and welding property.In this paper,The low cycle fatigue cycle performance of FV520 B stainless steel was studied by experiment and ANSYS finite element simulation,and the laser shock peening technology is applied to strengthen the steel.The main contents are as follows:First,A series of low cycle fatigue tests were carried for FV520 B steel.The cyclic properties of different strain amplitudes were compared from the peak stress-cyclic times curve and hysteresis curve,and analyzed the circulation characteristics in theory from microstructure.The results show that the slight cyclic hardening is observed for the initial cycles and the stable hysteresis loop is gained under small strain amplitude.The cyclic softening phenomenon is not significant for all strain amplitudes before failure.The plastic deformation increases with the increase of the total strain amplitude.Secondly,based on the fatigue test data,fitting and paint stress-strain curve of the material,using multilinear kinematic hardening model,the Von Mises yield criterion and uniaxial cyclic stress-strain curve describing material properties when applied to ANSYS software simulation calculation the stress-strain history at half-life.The results show that the simulation results and experimental results are in good agreement,the average stress error was 2%.Then,according to the fitting parameters to predict fatigue life using three kinds of methods of Masson-Coffin equation,the energy approach and the SWT approach.Several statistical parameters are employed to evaluate the prediction ability for quantitative evaluation of life prediction results.The results showed that the SWT method had the best effect on life prediction,followed by Manson-Coffin equation,and the worst prediction method was energy method.Finally,the FV520 B stainless steel was strengthened by the laser shock peening technique,and the cyclic deformation of the material was studied by the same fatigue test method.Compared the material fatigue fracture results of SEM before and after the strength,and the mechanism was analyzed.The test results show that the hardening rate is greater than the smooth specimen for the initial cycles under small strain amplitude due to the dislocation density increased,and the cyclic softening rate is greater than the smooth specimen under large strain amplitude due to stress relaxation.The plastic deformation in the cyclic process decreases,and the fatigue life of the material is improved significantly.The results of SEM show that the crack initiation under the small strain amplitude of the strengthened sample is transferred from the surface to the inside and the crack initiation under the large strain amplitude is small.In conclusion,the improvement of the fatigue properties is attributed to the refinement of the microstructure and the generation of residual compressive stress on surface of the material.