| 摘要 |
<p>The invention relates to a process to increase surface hardness of low-carbon steel sheets, the process comprising the steps of providing a low-carbon steel sheet, the steel strip having a composition, C: 0.09 (max), Mn: 0.6 (max) Si: 0.006 (max), S: 0.009 (max), P: .016 (max) A1:0.06(max), N: 35 ppm(max), with thickness in the range up to 1.2 mm including a microstructure of ferrite with hardness of 120 VHN; covering the surface of the strip at least with one layer of carbon soot and its derivatives; causing a laser beam to sweep across the steel strip in different configurations at an optimized intensity such that a width and depth of the processed zone being restricted up to 3 mm and 200 micron respectively; and allowing the molten surface of the steel sheet comprising a plurality of tracks each consisting of several spots with different degree of overlapping to solidify which increases the surface hardness and refine the microstructure, wherein the velocity of the laser beam is maintained in a range of 0.6 to 0.8 mm/sec, and wherein the frequency, current and residence period of the laser beam are respectively maintained between 2.5 to 3.0 Hz, 130- 200 amp, and 6 to 8 milliseconds.</p> |
