Improved laser surface hardening of AISI 4130 low alloy steel with electrophoretically deposited carbon coating

In the present study, the laser surface hardening of AISI 4130 was conducted using a continues wave diode laser with a maximum power of 1600 W. To improve the laser surface hardening process, carbon powder is deposited on the sample surface by electrophoretic method. By conducting laser surface hardening at the same input parameters and same heat input, the quality of the hardening is compared; cross sectional geometry of the hardened area (width, depth and entry angle of hardened), micro-hardness and the ferrite phase percentage of hardened layer. Microstructure evaluation of the laser hardened area was performed using optical microscopy. Results indicate that because of increasing the laser absorption in carbon coated samples, hardened area is larger (deeper and wider) and the value of the hardness is more than laser hardening of bare samples. Microstructure analysis indicates that transformation of the retained austenite into martensite due to the fast quenching, lead to the lower ferrite phase in martensitic structure in laser hardened layer and causes higher microhardness. Observations reveal that depth, width, and maximum hardness of laser hardening carbon coated sample without surface melting are 1.150 mm, 9.980 mm, and 762 Vickers, respectively, while for bare sample these values are 0.957 mm, 9.451 mm, and 707 Vickers, respectively. Comparing the results with the furnace hardening heat treatment show that the laser hardening process especially with carbon coated, is more effective and precise than conventional processes.