Deformation behaviour of chromium sheets in mechanical and laser bending

Chromium is known to have limited room-temperature ductility but to exhibit apparent ductile-to-brittle transition behaviour at temperatures ranging from 150 to 300°C. In this paper, the deformation behaviour of a chromium sheet was investigated in roll-compression and laser bending. Tensile tests and three-point bending tests were performed also to determine the basic mechanical properties of the chromium sheet. The ductile-to-brittle transition temperature of the chromium determined by the tensile test was found to be 180°C. While the sheet could be bent to 90° at a temperature of 130°C in three-point bending, it was possible to bend the sheet to the same bending angle at a lower temperature (100°C) in roll-compression bending, the presence of compressive stress in roll-compression bending being considered to be the reason for the difference in the temperatures. A finite element stress analysis was also conducted to reveal the stress distribution of the chromium sheet in roll-compression bending. Laser bending was demonstrated to be a possible process to deform chromium sheets. A threshold laser power of 40W is observed, below which bending is unlikely to occur. The bending angle was found to increase with increasing laser power and number of irradiations, and decreasing scanning velocity.