Effect of Normalizing Temperature on Hardness and Microstructure of Rail Joints with Narrow-Gap Automatic Arc Welding

PD3 rails were welded by narrow-gap automatic arc welding, then simulated normalization was performed for the joints in the temperature range of 800-975 ℃. The effects of the normalization temperature on the hardness and microstructure of the joints were investigated by microstructure observation and microhardness testing. The results show that the welding seam microstructure without normalizing was lower bainite with coarse grains. And the grains near the bond area were coarser with lots of retained austenite. With the increase of the normalization temperature, the welding grains were refined, the martenite proportion increased gradually. Meanwhile the microstructure of the welding at 925 ℃ was refined bainite and martenite. And the hardness of the softening region of the joint annealed at the temperature was equivalent to that of the base material.