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 6