| The ultra-high-strength stainless steel with high strength and toughness, highspecific strength, high inherent fatigue strength and good corrosion resistance can beused in some load-carrying components, such as aircraft, carrier aircraft that workingunder corrosion environment.The material composed of Fe-Cr-Co-Ni-Mo was studied in this paper by measuringthe mechanical properties of tensile, impact, KIC, fatigue and other test, the influence ofdifferent heat treatment process on mechanism properties. By means of metallographicmicroscope, scanning electron microscope, energy dispersive analysis, transmissionelectron microscope, X-ray diffractometry and other microscopic analytical methods,the relationship between microstructure and heat treatment parameters were studied.And the fracture characteristics of the ultra-high-strength stainless steel under differentconditions were analysed, the fracture mechanism was studied.The results achieved in this paper were the best heat treatment parameters of theultra-high-strength stainless steel is solution treatment at1080℃for1h and agingtreatment at540℃for4h. Under this heat treatment state, the ultra-high-strengthstainless steel can be achieved good strength and toughness, the tensile strength is1902MPa and yield strength is1544MPa, and elongation and reduction of area are14.2%and67.2%separately, and impact toughness can reach130.7J/cm2. The microscopestructure of the ultra-high-strength stainless steel is high density of dislocations of lathmartensite structure and small quantity residual austenites after best heat treatmentprocess. In a specific range of solution temperature, solution temperature has relativelyminor impact on the pattern of martensitic laths. But the grain size obviously grows upwith solution temperature increases, and solution temperature has little influence onstrength and hardness of the material. In under-aged state, small amount of cementitephase in the ultra-high-strength stainless steel result in the strength of the material is nothigh. In over-aged state, the increasing of reverted austenites and the growth ofprecipitates in the ultra-high-strength stainless steel leads to the decrease of the strengthand toughness of the material. The fracture mechanism of the ultra-high-strengthstainless steel is ductile fracture. The fatigue resistance of the ultra-high-strengthstainless steel is good after best heat treatment process. The main reasons thatultra-high-strength stainless steel with high strength and toughness are the high density of dislocations of lath martensite structure, the large amount of precipitates and theresidual austenites between martensitic laths.The research results of the paper can be applied to other environments whichrequire high strength and corrosion resistance. It has important scientific significancefor the development of new materials and the exploration of microscopic field, and itlays the foundation for our national defense industrial materials. |
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