The phase transformation law is analyzed through determining the transformation kinetics curve of supercooled austenite for U71Mn steel. The effects of cooling rate and finish cooling temperature on microstructure and hardness are studied with the thermal simulation tests of sectional type cooling strengthening based on the heat treatment process of rails on site. The results showed that the critical cooling rate of perlitic transformation for U71Mn steel was 7 ℃/s and temperature range allowing perlitic transformation was 500~600 ℃. The reasonable process parameters of sectional type cooling for U71Mn steel were that the starting cooling temperature was 850 ℃, cooling rates was 6~12 ℃/s and finish cooling temperature was 570 ℃. The perlite structrure could be obtained with this process parameter and it could meet the hardness requirements of rails.

U71Mn steel  /  sectional type cooling strengthening  /  thermal simulation  /  microstructure  /  hardness