The Effect of Deposition Thickness on the Microstructure and Hardness of Laser Forming Repaired 300M Steel
F-G. Liu, X. Lin, H-O. Yang and W-D. Huang
Microstructure and hardness evolution of laser forming repaired 300M steel with different deposition thickness were investigated. The as-deposited microstructure of laser forming repaired 300M steel changed significantly along the deposition direction. Microstructure in the repaired zone was composed of lath martensite and a small amount of bainite. With increase of the deposited layers, the microstructure at the bottom of the repaired zone changed little, but the amount of bainite at the top increased gradually. The microstructure in the substrate zone and heat affected zone (HAZ) was tempered sorbite and tempered martensite, respectively. After heat treatment, the microstructure of laser forming repaired 300M steel tended to be uniform, which consisted of tempered martensite, bainite and a small amount of retained austenite. Hardness of as-deposited laser forming repaired 300M steel gradually increased from the substrate zone to the repaired zone; however, the hardness of heat treated laser forming repaired 300M steel became uniform and fluctuated in the range of 450 to 500 HV.
Keywords: CO2 laser, 300M steel, laser forming repairing, heat treatment, deposition, hardness microstructure