Study On Microstructure And Dynamic Properties Of Martensite Laser Cladding Layer

Based on 40 CrNiMo quenched and tempered steel as substrate material,the use of laser cladding technology preparation of martensite laser cladding layer on the surface,with 210?low temperature tempering can improve the performance of the cladding layer,mainly studies the original state and heat treatment microstructure of cladding layer and the dynamic change of mechanical properties is analyzed the direction of laser forming of cladding layer fatigue and impact toughness.The results are as follows:(1)The surface quality of the cladding layer prepared by high purity nitrogen is good,without pores and slag inclusion.After 210?tempering heat treatment,the microstructure of the cladding layer is changed.The original microstructure of the cladding layer is martensite and M₂₃C₆,but after heat treatment,martensite is transformed into tempered martensite,and austenite is produced in the microstructure.After heat treatment,the tensile strength and plasticity are significantly improved,the tensile strength is increased from 1485MPa to 1700MPa,the elongation after fracture is increased from 1.3%to 14.5%,and the microhardness is slightly decreased from 498.6HV_0.2to 478.1HV_0.2.(2)the cladding layer samples after the heat treatment of low coefficient of friction and wear,stable wear after the friction coefficient from 0.40 to 0.42,the friction coefficient of the original state,respectively,compared with the cladding layer and substrate was reduced by 5.75%and 17.2%,the wear quantity is 0.8 mg,erosion rate of cladding layer respectively,53.33%,66.67%of the original state and matrix wear form is adhesive wear,oxidation wear and slight abrasive wear.(3)under the maximum stress is 680 MPa fatigue experiment,the cladding layer heat treatment state sample break cycles before an average of 225170 times,is about 3.03 times as much as 40CrNiMo substrate,5.33 times that of the original state sample,the original state and heat treatment state sample fatigue crack initiation in the surface of the sample,but the fracture mode is different,the original state of cleavage fracture,heat treatment state shall prevail cleavage fracture;After heat treatment,the impact toughness of the cladding layer reaches 82.50J/cm²,which is16.7%higher than that of the matrix and 67.8%higher than that of the original sample.After heat treatment,the fracture form is ductile fracture,and there are a lot of equiaxial dimples in the fracture.(4)Different laser scanning directions have great influence on the fatigue property of the cladding layer,but little influence on the impact toughness.The fatigue property of the cladding layer parallel to the laser scanning direction is the best,which is 23.65%and 28.57%higher than that of the vertical laser scanning direction and the 45°laser scanning direction,respectively.The impact toughness of the cladding layer is slightly better in the parallel laser forming direction,while the impact toughness of the cladding layer in the vertical laser forming direction is basically the same as that in the 45°laser forming sample(5)The impact toughness of the cladding layer will be seriously reduced when there are defects in the cladding layer.The impact toughness of the cladding layer with defects is only 41.5%-45.5%of the impact toughness of the cladding layer without defects.However,when the cladding layer has defects,the impact toughness of the samples with different laser scanning directions is basically the same.