| Cr-Ni series duplex stainless steel is a new type of stainless steel in which both ferrite and austenite coexist.It has both the characteristics of ferritic stainless steel and austenitic stainless steel,and has excellent comprehensive properties.It is mainly used in nuclear power,marine engineering,tidal power stations and other fields that require good corrosion resistance and mechanical properties.Ferritic-austenitic duplex stainless steel is mainly used in the preparation of complex structural parts such as turbine blades and propellers in offshore engineering equipment.The traditional casting method has a long processing cycle and low dimensional accuracy,which requires post-processing to ensure the surface quality,which limits the use of duplex stainless steel in parts.The laser direct deposition technology is a new technology that uses laser as the energy source to deposit metal powder layer by layer through rapid coaxial powder feeding.It is mainly used to directly manufacture parts with complex shapes and structures.The manufacturing cycle is short and excellent performance can be obtained.In this paper,a YLS-1000W fiber laser is used to prepare a Cr-Ni duplex stainless steel sample by direct laser deposition technology.The composition design is changed by adding Ni,Cr,and N elements,and the dual comparison examples are adjusted to achieve mechanical and corrosion properties.The optimized parameters for laser direct deposition obtained through experiments are:laser power of 650 W,laser scanning speed of 4 mm/s,and overlap rate of 30%.Under the optimized parameters,25Cr-xNi-4Mo(x=7.0 wt.%,8.0 wt.%,9.0 wt.%,10.0 wt.%),and xCr-7Ni-4Mo(x=25.0 wt.%,26.0 wt.%,27.0 wt.%,28.0 wt.%,29.0 wt.%)and 25Cr-7Ni-4Mo-xN(x=0.2 wt.%,0.3 wt.%,0.4 wt.%,0.5 wt.%)Multiple component laser directly deposited samples.Use OM,SEM,EBSD,TEM,EPMA,etc.to analyze the composition,microstructure,and material of the deposited sample.Use microhardness testers,universal testing machines,friction and wear testing machines,and electrochemical workstations to study the mechanics of the deposited materials.The experimental results show that by optimizing the process parameters,a duplex stainless steel sample without defects such as cracks and porosity was successfully prepared.The deposited sample is dense and has good formability.The microstructure of the direct ferrite-austenite stainless steel samples deposited by laser is mainly ferrite dendritic structure and austenite.Ferrite primary dendrite arms are longer and secondary dendrites are underdeveloped.Between 5 ?m and 10?m.Laser direct deposition of 25Cr-xNi-4Mo(x=7.0 wt.%,8.0 wt.%,9.0 wt.%,10.0 wt.%)duplex stainless steel using elemental mixed powder for laser deposition.As the content of Ni increases,the austenite phase increases,but the maximum was only 9%,which was caused by the insufficient content of Ni element due to the selective sending of powder particle size during the experiment.And the alloy powder is added with a small amount of Cr for laser direct deposition of xCr-7Ni-4Mo(x=25.0 wt.%,26.0 wt.%,27.0 wt.%,28.0 wt.%,29.0 wt.%)Duplex stainless steel.As the element content increases,the ferrite phase region gradually expands.When the Cr content is 27.0 wt.%,The ferrite volume fraction is 54.9%and the austenite volume fraction is 45.1%.At this time,the double-comparison is the closest.25Cr-7Ni-4Mo-xN(x=0.2 wt.%,0.3 wt.%,0.4 wt.%,0.5 wt.%)Duplex stainless steel is directly deposited by laser deposition using alloy powder with a small amount of N element.With the increase,the austenite phase content gradually increases.When the N element mass fraction is added in the range of 0.2%to 0.5%,the austenite phase volume fraction in the laser direct deposition duplex stainless steel ranges from 65.2%to 76.4%.The increase of Cr element improves the tensile properties and corrosion resistance of laser direct deposition duplex stainless steel.When the Cr content is increased to 27 wt.%,The comprehensive performance reaches the best,its microhardness reaches 457 HV0.2,and the minimum amount of wear is only 3.03496 ×10-5 mm3/Nm;the yield strength and tensile strength of the tensile sample The strength and elongation are:889 MPa,1286 MPa,7.8%.Its corrosion resistance is good,self-corrosion potential:-0.059 V,self-corrosion current density:5.154 × 10-8 A/cm2.The addition of the N element replaced the role of the Ni element in stabilizing the austenite phase in the duplex stainless steel,which greatly saved costs.When the mass percentage of element N is increased to 0.5 wt.%,Its microhardness reaches 440 HV0.2,the minimum wear is only 8.20448 × 10-5 mm3/Nm,the self-corrosion potential is-0.074 V,and the self-corrosion current density is 1.112 × 10-8 A/cm2.The comprehensive tensile properties are excellent.The yield strength,tensile strength,and elongation of the tensile samples respectively:732 MPa,1093 MPa,and 5.5%. |
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