HSLA钢连续冷却过程的相变与组织研究

在Gleeble—1500热模拟试验机上研究了20SiMn3NiA钢在不同连续冷却条件下相和组织变化，用热膨胀法测定了该钢的连续冷却转变曲线（动态CCT曲线）。研究结果表明，20SiMn3NiA钢中的Mn、Ni、Si等合金元素能有效地阻止铁素体和珠光体的形成，故20SiMn3NiA钢的过冷奥氏体连续冷却转变曲线只有马氏体和贝氏体相变区。当临界冷却速度大于1℃／s时，20SiMn3NiA钢就可以获得板条状马氏体组织，且随着冷却速度的增大，马氏体组织变得越来越细。与静态CCT曲线相比，形变使动态CCT曲线的Ms点升高，奥氏体稳定性降低，形变细化了马氏体和贝氏体组织，使20SiMn3NiA钢在1℃／s的冷却速率下产生较高的强度。

Investigation on Phase Transformation and Microstructure of HSLA Steel during Continuous Cooling

The phase transformation and microstructure of 20SiMn3NiA steel during continuous cooling were studied using Gleeble-1500 thermal mechanical simulator and the continuous-cooling-transformation diagram of the steel was drawn（dynamic CCT diagram） by thermal dilatometer test. The results show that there are only martensitic and bainite phase transformation zones in the diagram of over-cooling austenite continuous cooling curve, because the formations of ferrite and pearlite can be effectively deterred by adding Mn, Ni,Si alloying agents in the tested steel. When the critical cooling rate is more than 1℃/s, the lath martensitie microstructure is obtained and with increasing cooling rate the microstructure is thinner and thinner. The deformation makes austenite more unstable and Ms temperature of dynamic CCT diagram higher than the static CCT curve. Also 20SiMn3NiA steel achieved high strength at very low cooling rate（1℃/s）, for the deformation making microstructure of martensite and bainite refine