| Martensite stainless steel is a stainless steel whose mechanical properties can be adjusted by heat treatment. Martensite stainless steel have favorable comprehensive performance and the steel have broad application prospects in aviation, aerospace and other fields. But higher requirements have been asked to the martensite stainless steel’s surface performance for its severe working environment. So it’s full of practical significance to improve the surface performance of martensite stainless steel with laser shock peening(LSP) and warm laser shock peening(WLSP) technique.In this artical, the research object is the aviation materials heat resistant martensite stainless steel ЭП866. In order to improve the surface microstructure and residual stress distribution of target material of martensite stainless steel and then improve its surface properties. WLSP and different number of LSP had been operated on the steel. After the LSP and WLSP. the surface residual stress, microhardness and microstructure of target material of martensite stainless steel are analyzed and simulated. The results show that:After WLSP, high amplitude of compressive residual stress are formed on the surface of martensite stainless steel. Compared with room temperature LSP, only under the condition of 250 ℃ and 300 ℃ WLSP induce a higher amplitude of the compressive residual stress. Hardness test results has the same trend with the test results of residual stress. For different number of LSP: the surface roughness of target material increased with the increase of impact times, but when the impact number exceed 3 times, the surface roughness have few change; Multiple laser shock introduced higher amplitude of the compressive residual stress on the surface of target material and more uniform distribution are formed for compressive residual stress of the lap zone. Though it’s not obvious for the influence of surface hardness with the increasement of the impact time, a larger depth of hardening layer will be obtained; It is not stable for a high amplitude of the residual stress area and will greatly released after heat treatment, but large values still can be keeped.Microstructure analysis shows that after the LSP, high density of tangled dislocation are formed within the impact area of stainless steel; In addition, under the 250 ℃ WLSP, dislocation multiply and tangle with each other and form the dislocation core which is considered to be nucleation points for precipitation, besides, the dynamic strain aging and heat assisted dynamic precipitation induced larger precipitation and more tangled dislocation structure than the LSP and 150℃ WLSP, precipitation interacted with dislocation to form stable "cottrell atmosphere". The pinning effect on the movement of mobile dislocation by cottrell atmosphere result in more stable microstructure and thus improve the mechanical properties and fatigue life. Multiple laser shock peening could induce higher density dislocations and precipitation. The dislocation structure are more tangled. High density dislocations accumulate in the martensite lath to form lath-shaped dislocation boundaries. The dislocation structure still has high density and tangled organizational structure after 500℃ and 1 hour high-temperature heat treatment, which indicate that the structure has good thermal stability.In addition, the residual stress of multiple impact samples are simulated. The simulation results show that the laser shock induce high amplitude of the compressive residual stress on the material surface, the residual tensile stress into the subsurface and the residual compressive stress on the back of material; With the increasement of impact times, compressive residual stress amplitude will increase. The simulation results have a good match with the experimental results. |
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