| In this paper, with HL-1500 helium-free transverse flow CO2 laser processing machine,on normalized 40Cr steel substrate,modified layers are formed by laser beam obliquely incident scaning, large acreage and staggered mesh scanning. The microstructure and properties of modified layers by laser transformation hardening and the effects of process parameters on them were studied. Results indicate that the microstructure from the outside to the inside of samples is respectively phase hardened region, transition region and substrate region. The phase hardened region are fine acicular martensites and retained austenites, the transition region are tempered martensites, retained austenites, ferrites and carbides. The substrate region remains unchanged. When the laser incidents with different angle, the depth of hardened layer decreases with the increase of incident angle. The microhardness and wear resistance alse reduces accordingly. When the incident angle is below 40°, the microhardness and wear resistance are high, when over 40°, they decrease remarkably, so not good for surface modified, the maintaining passivity current density increases obviously and the passivation region minishes in some degree. Properties change as scaning space changes. When the scaning space is 12mm, the average hardness gets the highest, of which the value is 61.1HRC; the wear resistance is the best as 2.9 times as the substrate; the salt corrosion resistance is alse the best. When the scaning space is 16mm, the acid corrosion resistance gets the best with the smallest maintaining and critical passive current density and a passivation region, of which the value is 1200mV. When staggered mesh scaning, the average hardness reaches 59.6~60.7HRC, which is 2~3 times as the substrate; the wear resistance is 1.6~1.9 times more than the substrate; the acid corrosion resistance is obviously better than the substrate. When the staggered mesh space is 12mm, the wear and corrosion resistance is the best.
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