Tham khảo tài liệu 'surface engineering of metals - principles, equipment and technologies part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. Microhardness profile in superficial layer a 1045 grade steel laser beam hardened with overlapping of hardened zones b gray pearlitic cast iron 1 - after remelt laser hardening 2 - after transformation laser hardening and tempering at 450YC for 1 h. Fig. b - from Straus J. and Burakowski T. 51 . With permission. - surface layer of non-metallic phases composed mainly of metal oxides and compounds formed as the result of chemical interaction of the atmosphere and thermal reaction of the laser beam with the steel with gases dissolved in it and with components of the absorption coating its layer usually does not exceed several micrometers - remelted and hardened from the melt surface layer dendritic with a martensitic structure carbides present in the steel underwent total or partial melting within the area adhering to the intermetallic phase layer the melted zone has a diminished carbon content - hardened from the solid phase subsurface layer with a non-uniform structure martensitic with retained austenite and carbides in the vicinity of the remelted zone and martensitic with elements of initial structure near the core. These elements are ferrite in hypoeutectoid steels and cementite in hypereutectoid steels. Throughout the layer a dispersion of martensite occurs to times greater than after conventional hardening 1999 by CRC Press LLC - tempered core zone also called intermediate with a structure of tempered martensite or sorbite. Remelt hardening by laser beam causes similar effects as experienced in electron beam hardening deterioration of surface roughness the surface after remelting has the appearance of a weld or overlay and an enhancement of service properties such as tribological fatigue and anticorrosion. The microhardness profile along the laser beam path is approximately uniform with clearly lowered hardness due to the tempering effect of beam overlap Fig. . In the remelted zone of martensitic stainless steels and tool steels residual
