| Martensitic stainless steels are mainly applied to the manufacture of key components such as steam turbine blades due to their excellent characteristics.However,these parts often cause corrosion fatigue failure because of the influence of various external factors such as alternating stress,corrosive and moist environments,etc.Corrosion fatigue fracture often occurs because of the initiation of micro-cracks on the surface of components.Therefore,it is necessary to strengthen the surface of the component to suppress cracks initiation.Laser Shock Peening(LSP)is a new surface modification technology that can improve the surface properties and corrosion fatigue properties of materials,but there is no systematic research on the effect of LSP on corrosion fatigue crack initiation of stainless steel at present.In view of the above-mentioned problems,the effects of LSP with different coverage layers on surface properties and corrosion fatigue crack initiation(CFCI)of 2Cr13 stainless steel were investigated in this study.The main research work is listed as follows:(1)The effects of LSP with different coverage layers and double-sided impact strategy on residual stress yield of 2Cr13 stainless steel were investigated combined with the methods of numerical simulation and experimental tests.The results showed that LSP can induce high compressive residual stress on the specimen surface.The surface compressive residual stress value and the influence depth of compressive residual stress were also increased with the increase of LSP coverage layers.The compressive residual stress value and influence depth of the top surface were greater than the bottom surface after LSP with the double-sided impact strategy for the same specimen,but the difference of the two surfaces in compressive residual stress value and influence depth was getting weak with the increase of coverage layers.(2)The effects of LSP with different coverage layers on the surface microstructure and mechanical properties of 2Cr13 stainless steel were studied.The results showed that the surface microhardness and surface roughness of 2Cr13 stainless steel specimens were significantly improved after LSP,and further increased with increasing LSP coverage layers,but the increase range was reduced.A large number of dislocation structures appeared on the specimen surface and the grain size was obviously refined after LSP.The dislocation density of the specimen surface continued to increase and the grain size further decreased with the increase of LSP coverages layers.(3)Corrosion fatigue tests were carried out to investigate the effects of LSP with different coverage layers on the corrosion fatigue crack initiation of 2Cr13 stainless steel in air and 3.5% NaCl solution,respectively.The results showed that LSP can effectively improve the CFCI life and the total life of 2Cr13 stainless steel.With the increase of LSP coverage layers,the ratio of CFCI life to total fatigue life was also increase.The CFCI life of the specimen with one layer and two layer in 3.5% NaCl solution was increased by 35.9 % and 52.8%,respectively.The the increase of CFCI life of LSP specimens in air is better than compared with that in 3.5% NaCl solution due to the corrosion effect of NaCl solution.(4)The characteristics of corrosion fracture of 2Cr13 stainless steel were analyzed and the microscopic morphology of the crack initiation region was studied in depth.The corrosion fatigue crack initiation model of was obtained,and the influence mechanism of LSP with different coverage layers on the corrosion fatigue crack initiation of 2Cr13 stainless steel was revealed.The results showed that the grains of the surface layer were refined and high compressive residual stresses were induced after LSP.The refined grain layer can enhance the resistance of sliding deformation and pitting corrosion,inhibit the corrosion effect of NaCl solution,restrain the initiation of corrosion fatigue crack.At the same time,the compressive residual stress can balance the external cyclic load and delay the initiation of the crack.As a result,the resistance of CFCI of 2Cr13 stainless steel was improved under the combined action of grain refinement layer and compressive residual stress,and the resistance of CFCI was further improved with the increase of LSP coverage layers.In summary,the research of this paper provides the theoretical and experimental basis for the influence of LSP with different coverages layers on the resistance of corrosion fatigue crack initiation of 2Cr13 stianless steel. |
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