| In order to meet the needs of repairing and remanufacturing of large-scale equipment,an intensive nitrogen-bearing duplex stainless steel powder has been designed.It can be used for repairing those large-scale bearing components of Q345,Q460,EQ56 and 18-8 austenitic stainless steel.The laser formed layers were prepared on Q345?1Cr18Ni9Ti and AH420 substrates under the protection of 99.999%high-purity nitrogen.X-ray diffractometer,metallographic microscope and scanning electron microscope were used to observe and analyze the phase and microstructure of the formed layer,the morphology and element change of the interface between the layer and the substrate;The mechanical properties of the formed layer were tested and analyzed by microhardness tester,tensile tester and friction and wear tester;The corrosion resistance of the layer was tested by electrochemical workstation,and the residual stress of the layer was calculated.The results are as follows:(1)The laser formed layer of nitrogen-bearing duplex stainless steel can be prepared under the protection of high-purity nitrogen.The N content of the alloy powder used to prepare the formed layer should be controlled below 0.3%.Too much N content will lead to a large number of pores in the formed layer.At the same time,comparing the N content before and after laser forming,it is found that the N content in the formed layer is approximately 45%lower than that in the powder.(2)Ferrite and austenite are the main structures in the powder.In the formed layer,austenite and ferrite have existed as two-phase matrix,and the peak strength of austenite is obviously increased.There are no pores and cracks in the layer,and there are obvious austenite and ferrite phases.The distribution of austenite and ferrite grains is uniform,and the grain boundary is clear.(3)The formed layers are well combined with three different substrates,and the metallurgical bonding is realized.Near the bonding interface with Q345 and AH420,from the substrate to the formed layer,the C and Fe elements show a downward trend,the N and Cr elements show an upward trend,the Ni element basically remains unchanged,and there is a white substance CrN;Near the bonding interface with1Cr18Ni9Ti,from the substrate to the formed layer,the content of each element has little change,the element diffusion is uniform,and the structure near the formed interface is stable.(4)The tensile strength,yield strength,elongation and microhardness of the layer are in the range of 940-1040 MPa,800-910MPa,21.1%-25.7%,and 275-310 HV,respectively.Under the testing condition with an alternating load of 20 HZ and loading coefficient of 0.6,the average cycles of the formed layer are about 7-9 times of Q345,1Cr18Ni9Ti and AH420,the wear amount is about 0.3-0.5 times of Q345,1Cr18Ni9Ti and AH420,and the formed layer on each substrate is residual tensile stress,163?147and 125 MPa respectively;The corrosion potential of the formed layer is 0.574 V,the corrosion current density is2.78×10~-77 A/cm~2.The formed layer has good comprehensive properties. |
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