Deformation behavior and microstructural changes of a hardened high carbon alloy steel in laser bending

In this article, the deformation behavior and microstructure of a hardened high carbon steel in laser bending were examined. A CO2 laser unit (TEM00) was used to bend the samples at different laser powers, scanning velocities, and number of scans. A relatively linear relationship between bending angle and number of scans was obtained at laser powers of 150 and 200 W and at a scanning velocity of 30 mm/s. A threshold heat input of about 3.25 J/mm was observed, below which bending was unlikely to occur. The bending angle was also found to increase linearly with increasing line energy and was sensitive to specimen width. The microstructure and microhardness profile of the sheets deformed at both low- and high-energy inputs were examined. For accumulated energy density (AED) of 193 J/mm2, melting was observed at the scanning surface and the microstructure was different significantly across the thickness of the bent region. A microstructure of coarse martensite with retained austenite was observed near the top surface, whereas martensite with retained carbide and banite was found near the bottom surface. For AED of 97 J/mm2, no melting was observed, and tempered martensite could be found at the bottom surface of the bent region.