Study On Microstructure And Properties Of Martensitic Laser Forming Layer On 300M Steel

Aiming at the problem of repairing 300M steel and the manufacturing and remanufacturing of high strength steel,a low carbon martensitic forming layer with high strength and toughness at tempering temperature 500?and below was designed and prepared on 300M steel substrate using laser cladding technology which is based on the principle of fast cooling induced martensitic phase transition.The microstructure and mechanical properties of the forming layer and the heat-affected area were studied by means of SEM,XRD and microhardness tester,and stoney formula was used to calculate the average residual stress of the laser forming layer.The results show that the microstructure of the original laser-shaped layer is a mixture of martensite and bainsite and a small amount of residual austenite at the top,the microstructure of the bottom is thick martensite,and the microstructure of the heat-affected area is short martensite with uneven ferrite distribution.The tensile strength and elongation of the original sample is in the range of 1715±35MPa,10%±1%,respectively;The formed layer samples were treated by tempering,.When the tempering temperature was 500?or below,the formed layer samples could maintain martensite morphology and maintain good mechanical properties.The 300?heat treatment sample is in the range of1615±35MPa,15%±1%,respectively;The 500?heat treatment sample is in the range of 1565±35MPa,13%±1%,respectively.Electrochemical corrosion performance is not lower than 1Cr13 profiles.At the interface of 300M steel and martensite cladding layer,the substrate and the cladding layer were taken and 1mm respectively to prepare tensile samples in the bonding zone and measure their mechanical properties.Through the measurement of microhardness,it is found that the microhardness of the substrate and cladding layer is about 550HV_0.2,but the microhardness with the thermal influence of the width around0.2mm drops sharply,and the lowest microhardness is only about400HV_0.2.The tensile strength and yield strength of the samples in the bonding zone are 1600±30MPa and 1300±50MPa respectively.Under the influence of heat affected area,it still has high strength and toughness.