利用Gleeble-2000型热模拟试验机在两种冷却方式下对Q500q桥梁钢的冷却转变行为进行研究，一种冷却方式为以恒定的冷却速率（1，4，8，16，32℃·s^-1）从900℃冷却至300℃（恒速冷却），另一种方式为以一定的冷却速率（同前）从900℃冷却至650℃后再冷却速率减半冷却至300℃（分段冷却）。结果表明：在恒速冷却条件下，当冷却速率在1～4℃·s^-1时，试验钢得到多边形铁素体+珠光体组织，当冷却速率在8～16℃·s^-1时得到贝氏体组织，冷却速率增至32℃·s^-1时得到马氏体组织；在分段冷却条件下，当中温区（650～300℃）冷却速率在0.5～4℃·s^-1时试验钢发生铁素体和珠光体转变，多边形铁素体数量较多，当中温区冷却速率在8～16℃·s^-1范围内发生贝氏体转变；与恒速冷却方式下的相比，贝氏体转变的终了温度升高，贝氏体转变区间缩小，贝氏体晶粒的细化程度降低。

Cooling transformation behaviors of Q500q bridge steel by two cooling modes were studied with Gleeble-2000 thermal simulation machine. One cooling mode method (constant cooling) was cooling from 900℃ to 300℃ at constant cooling rates (1, 4, 8, 16, 32℃·s^-1) and the other cooling mode (subsection cooling) was cooling from 900℃ to 650℃ at constant cooling rates (ditto) and then to 300℃ at halving cooling rates. The results show that under constant cooling conditions, the steel had a structure of polygonal ferrite+pearlite at the cooling rates of 1-4℃·s^-1, a structure of bainite at the cooling rates of 8-16℃·s^-1, and a structure of martensite at the cooling rates of 32℃·s^-1. Under subsection cooling conditions, the ferrite and pearlite transformation occurred at the cooling rates in the intermediate temperature range (650-300℃) of 0.5-4℃·s^-1, and the amount of polygonal ferrite was relatively large; the bainite transformation occurred at the cooling rates in the intermediate temperature range (650-300℃) of 8-16℃·s^-1. Compared with those by constant cooling method, the bainite transformation end temperature increased, the transformation region was reduced, and the grain refinement degree of bainite decreased.