Technology And Properties Of 17-4PH Stainless Steel By Laser Solid Solution And Alloying Hybrid Strengthening

17-4PH stainless steel is widely used in large capacity turbine parts,components in nuclear reactors and other important equipment for its high strength and toughness,corrosion resistance and simplicity of adjusting intensity level.But for the natural limitation of the material,it is not ability to be hardened by ordinary quenching.In the light of the deformation problem by conventional solid solution and aging treatments,small thickness and weak adhesion with substrate by carburizing,nitriding and spraying,laser synchronous hybrid strengthening is proposed to make a certain thickness of laser compound hardened layer on the surface of 17-4PH stainless steel.The microstructure,elements distribution and phase of laser compound hardened layer by different processes are discussed.Microhardness of hardened layers,wear resistance and cavitation resistance of the surface have also been tested.The results show that laser hybrid strengthening treatments can result in a compound hardened layer on the surface of 17-4PH stainless steel.A deep hardened layer combined with alloyed zone,transition zone,heat affected zone,solid solution zone and substrate from top to inner is obtained.The depth of the hardened layer is more than 1.4mm,with the highest microhardness 600HV0.2 and average microhardness over 435HV0.2,which is 32%higher than that of the substrate.The microhardness of alloyed zone slightly decreases after aging because of part-decomposition of the intermetallic(Al0.28Co0.4Cr0.24W0.08),while the deposition of precipitation hardening phases(M23C6,?-Cu,etc.)leads to increase of microhardness of solid solution zone.Surface performances of the hardened layer have been improved.The wearing capacity and cavitation loss of strengthened layer are respectively only 1/6 and 46%of that of substrate after a period time testing.The contrast experiment of hybrid strengthening processes shows the feasibility of laser synchronous hybrid treatment with laser alloying going first.It is also proved that small area of facula can make a certain depth of hardened layer with high surface quality.It assures technical support to the industrialization of dual beam laser synchronous hybrid strengthening.