Product Code: ICAL07_P523

Laser Surface Melting of Tool Steels H13, O1 and D6
C.T. Kwok, University of Macau; Macau Peoples Republic of China
H.C. Man, Hong Kong Polytechnic University; Kowloon Hong Kong
F.T. Cheng, The Hong Kong Polytechnic University; kowloon Hong Kong
Presented at ICALEO 2007

The surfaces of three hot / cold working steels (WSs),H13, O1 and D6, were laser surface melted by a CW 2.5-kW Nd:YAG laser at a power density of 71.9 W/mm2. Their microstructures were investigated by optical microscopy, SEM and X-ray diffractometry and their corrosion behavior in 3.5 wt% NaCl solution at 25oC was studied by potentiodynamic polarization technique. After LSM, the ferritic matrix with fine spheriodal carbides of annealed H13 and O1 was transformed to martensite as the main phase with submicron-size carbides. For D6, with high Cr and C contents, the pearlitic matrix with large carbide particles of annealed D6 was converted to mainly austenite with some submicron-size carbides. The maximum hardness of the melt zones of laser-melted H13, O1 and D6 was increased by LSM to 490, 625 and 410 Hv, respectively. Compared with the conventionally hardened working steels, the corrosion resistance of the laser-melted WSs was improved, as evidenced by the decrease in the corrosion current density by at least an order of magnitude. The enhancement in corrosion resistance is attributed to the combined effects of the refinement of large alloy carbides and the enrichment of the passivating alloying elements such as Cr, Mo and W in the solid solution.

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