Effects of Laser Energy Density on the Microstructure and Properties of 304 Stainless Steel
Y-L. Chen, X. LI, Y-C. Zhang1, J-Y. Liu and X-H. Chen
To investigate the effects of laser energy density on the microstructure and properties of the 304 stainless steel remelted layer, a nanosecond pulsed fibre laser was used to remelt the surface of 304 stainless steel. Based on heat transfer theory, a three-dimensional (3-D) unsteady temperature field finite element (FE) model of nanosecond pulsed laser surface remelting stainless steel was established to analyse the temperature distribution. The laser energy density was changed to analyse the structure, micromorphology, composition, microhardness and corrosion resistance of the remelted layer. The simulation and experimental results show that the maximum temperature of the stainless steel surface is proportional to the pulse energy density. The surface temperature of stainless steel increases with the laser power density and the Gaussian distribution of the laser causes the temperature field distribution to obey the law of high in the middle and low in the surrounding area. The intensity of the newly generated phase diffraction peaks increases with the laser energy density; however, the surface microhardness first increased and then decreased, the phase distribution of the remelted layer was more uniform when the laser energy density was 0.0318 J/mm2. The laser surface remelting technology can refine the grains and basically eliminate grain boundaries and intragranular carbide inclusions, which improves the intergranular corrosion resistance of the remelted layer. The self-corrosion current density of stainless steel after remelting is lower than that before remelting. Laser surface remelting technology improves the surface mechanical properties and corrosion resistance of 304 stainless steel.
Keywords: Fibre laser, 304 stainless steel, laser surface remelting, nanosecond pulse, laser energy density, microstructure, microhardness, corrosion resistance