'multi-track laser surface hardening of low carbon cold rolled closely annealed (crca) grades of steels'

摘要

The invention relates to a multi-track laser beam process of surface hardening of steel sheet with low-carbon and low manganese steel. The resulting steel shows improved mechanical strength and can be used for manufacturing of automotive components. The process comprises the steps of: providing CRCA steel grades of ( low carbon and low manganese) in the form of flat sheet having a chemical composition range by weight percentage, C: 0.03-0.07, Mn: 0.15-0.25 and 1.4, S: 0.005-0.009, P: 0.009-0.014, Si: 0.005-0.02, Al: 0.04, V: 0.001, Nb: 0.001,and Ti:0.002 ; optimizing laser processing variables to reach austenizing temperature capable for phase transformation of the initial microstructure to harder dual phase structure of the steel sheet; selecting a laser track pattern for surface hardening of the steel sheet; applying the selected laser processing variables in the form of laser power (2.5-3.5 KW) and scanning speed (150-250 mm/s) combinations on the surface of the steel sheet; selecting and adapting associated laser optics to operate the laser beam such that an impingement laser spot size on the sheet is of square shape, wherein a 6-axis robot employed to carry the laser through a fiber fixed on 6th axis enabling an movement of the laser beam under the specimen along the axis of the square beam controlling the surface temperature of the specimen to eliminate any possibility of melting the sheet based on on-line surface temperature effect and comparing with pre-stored data representing surface temperature effect; and periodically reviewing the development of desired microstructure of the sample, including measuring hardness level and fraction of different phases.