Abstract: The deformation resistance test of a new type of longitudinal variable section weather-resistant bridge steel with different Nb content was carried out by Gleeble 3800 thermal simulation tester. The deformation stress curves of the steel were measured at different deformation parameters， such as deformation rate of 1， 5， 10 s^-1， deformation temperature of 750-1 000 ℃ and deformation amount of 50%. The microstructure changes of the test steel under different thermal deformation parameters were studied by means of metallographic microscope， scanning electron microscope and transmission electron microscope. According to the test results， the influence principle and main reason of deformation parameters and Nb content on the deformation resistance and microstructure of longitudinal variable section were analyzed. The results show that when the content of Nb ≥0.03%， the deformation resistance of steel plate increases significantly， and the microstructure is obviously refined. The addition of certain Nb element can increase the recrystallization temperature of steel plate above 50 ℃， so that LP weather-resistant bridge steel can be rolled in the high temperature range of deformation temperature between 850 ℃ and 950 ℃， so as to better guarantee the profile and comprehensive properties of LP steel plate. It provides a theoretical basis for the trial production of LP steel plate.

Key words: Weather-resistant Bridge Steel, Longitudinal Variable Cross-section, Nb Content, Deformation Parameter, Deformation Resistance, Microstructure

摘要： 通过Gleeble 3800热模拟试验机，对一种新型不同Nb含量纵向变截面耐候桥梁钢进行变形抗力试验，测定了试验钢在变形速率为1、5、10 s^-1，变形温度为750～1 000 ℃，变形量为50%等不同变形参数下的变形-应力曲线。并通过金相显微镜、扫描电镜和透射电镜等手段，研究了试验钢在不同热变形参数下的显微组织变化。根据试验结果，分析了变形参数和Nb含量对纵向变截面耐候桥梁钢的变形抗力和显微组织的影响。结果表明：当Nb含量≥0.03%时，钢板的变形抗力显著增大，组织明显细化，添加一定量的Nb元素可提高钢板再结晶温度50 ℃以上，使LP耐候桥梁钢能够在变形温度为850～950 ℃的高温区轧制，以更好的保证LP钢板的板型和综合性能，为LP钢板产品的试制提供了理论依据。

关键词: 耐候桥梁钢, 纵向变截面, Nb含量, 变形参数, 变形抗力, 显微组织