Effect Of Transition Layer On Microstructure And Properties Of Laser-Formed M/F Duplex Stainless Steelspecimen Bonding Zone

Quenched and tempered steel is widely used in the field of construction machinery because of its good comprehensive mechanical properties.Due to special working conditions,corrosion and wear will occur on the surface of tempered steel,which will lead to equipment failure.Therefore,the research on laser repair and remanufacturing of tempered steel surface is of great significance.At present,most of the existing literatures on laser cladding technology focus on the characteristics of laser cladding coating on the surface of structural steel,but few studies have been conducted on its bonding state.In this paper,based on the actual situation,the microstructure and properties of the bonding interface are studied and analyzed with 40CrMo of commonly used quenched and tempered steel as the substrate.the main contents are as follows:in the substrate and laser cladding interface of duplex stainless steel in combination with cladding layer thickness of 0.1 mm or so of 304stainless steel transition layer,comparison and analysis of 304 stainless steel transition layer on the microstructure and mechanical properties of laser forming sample combined interface.The microstructure,cross section morphology and mechanical properties of the samples in the laser rapid prototyping area are characterized by X-ray diffractometer,electron microscope,microhardness tester and tensile fatigue tester,and the residual stress of the formed parts are calculated.Combined with schaeffler organization chart.The results are as follows:（1）The substrate/forming layer interface of the specimen without transition layer is pure martensite structure.The substrate/transition layer bonding interface of the sample with transition layer is M/A biphasic structure,and the forming layer/transition layer bonding interface is M/A/F three-phase structure.At the bonding interface of the specimen without transition layer,the plasticity is relatively poor compared with the substrate and the formed layer,and it is easy to form stress concentration in the bonding area.（2）Within 100μm of the bonding interface,the substrate/forming layer without transition layer shows a downward trend of C and Fe elements in the bonding zone from thebase material to the forming layer;Cr element is on the rise.In the transition layer/transition layer bonding zone,C and Fe elements show a downward trend,while Cr and Ni elements show an upward trend.The hard phases M₂₃C₆ and M₇C₃ are precipitated at the bonding interface.（3）The average tensile strength of the samples in the zone without transition layer bonding is 1385MPa and the samples are brittle fracture.The average tensile strength and elongation are 1389MPa and6.35%respectively.After adding austenite transition layer,the elongation is improved without affecting the tensile strength of the specimens in the bonding zone.（4）When the loading coefficient is 0.4 and the frequency is 20Hz,the low cycle fatigue life of the specimens with transition layer is 105times,while the average low cycle fatigue life of the specimens without transition layer is 31,651 times.The residual compressive stress of the specimens with transition layer is 16.3%lower than that without transition layer.