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Surface Engineering of Metals - Principles, Equipment and Technologies Part 4

Tham khảo tài liệu 'surface engineering of metals - principles, equipment and technologies part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 2.26 Comparison of microhardness a and wear resistance b of different steels heat treated by traditional methods with those enhanced by the electron beam N -normalized H - hardened T - tempered A - annealed E - electron beam hardened. From Zenker R. 83 86 and Zenker R. et al. 89 91 92 . With permission. Fig. 2.25 shows the distribution of microhardness of electron beam hardened surface layers with different initial heat treatment while Fig. 2.26 shows maximum achievable microhardness values and wear resistance for similar layers. Fig. 2.27 shows a comparison of microhardness values for different materials after different versions of thermo-chemical treatment with and without subsequent electron beam hardening. The thickness of the hardened layer is within the range of several pm to as much as several mm. The electron beam method may be used to harden low carbon and alloyed structural bearing and tool steels as well as white and gray cast irons 4295 . All techniques are used utilizing all types of beams. Besides a higher hardness than that achieved by conventional hardening the electron beam allows the precise heating of selected spots even of very small dimensions while maintaining very close tolerances of hardened layer thickness and lower quench stresses occurring only in small zones or even microzones of the treated material. This method enables 1999 by CRC Press LLC Fig. 2.28 Micrographs of the surface of N135M steel after electron beam treatment a transformation hardened b surface remelted c remelted d intensive remelted e with non-homogenous structure f with traces of electron beam path. From Zielecki w 26 . With permission. - Intensive remelting resulting in a clearly deteriorated three-dimensional structure of the surface primarily due to the formation of runs of remelted material. - Very intensive remelting resulting in a very clear deterioration of surface structure increase of waviness and unevenness with clearly visible electron paths. It is also .