基于屈服平台理论开发的600MPa级高强塑性螺纹钢的研究

600 MPa GRADE REBAR WITH HIGH DUCTILITY DEVELOPED BASED ON THEORY OF YIELD PLATEAU

采用冷轧与热处理相结合的方式研究了铁素体晶粒尺寸对力学性能的影响．将C含量为0．1％（质量分数）的板材经不同道次的冷轧，随后在600℃进行再结晶退火5-300min，获得晶粒直径在5．2-40．4μm之间的铁素体．室温拉伸实验结果表明，细化铁素体晶粒不仅提高了强度，还有效增加了屈服平台延伸率．SEM观察表明，细化晶粒促进了塑性形变在不同晶粒间的均匀性，宏观上累积成了较长的屈服平台．结合Hollomon和Hall-Petch公式导出屈服平台延伸率五与晶粒尺寸巩之间存在的定量关系，并确定了公式的适用范围．采用狭缝喷水实现快速冷却的新方法对HRB400钢筋进行热处理，不仅获得细晶铁素体，而且得到高比例的非平衡珠光体，使材料在获得高强度的同时还具有相当的塑性，由此开发出具有明显的屈服平台的600MPa级高强塑性螺纹钢，该商业用钢的成功开发进一步印证了理论分析的正确性．

Development of high strength and high ductility rebar with obvious yield plateau is a tendency for anti-seismic requirement in building steels. In this work, the basic relationship between ferrite grain size and mechanical property, especially the elongation of yield plateau, was investigated by the combination of cold-rolling and heat treatment. After several passes of cold rolling followed by recrystallization annealing for 5-300 min at 600 ℃, ferrite with grain size between 5.2-40.4 μm was obtained in plain steel plates with a carbon content of 0.1% （mass fraction）. Mechanical properties were studied by tensile test. With the decrease of ferrite grain size, not only the strength but also the elongation of yield plateau increases. Base on the scanning electron microscopy observa- tion, the deformation becomes more homogeneous with the decrease of grain size, resulting in a higher elongation of yield plateau. A quantitative relationship between grain size da and the elongation of yield plateau δL was derived from the combination of Hollomon and Hall-Petch equations. The application range of dα-δL equation was also determined, which is well consistent with the experimental results. The narrow-slit spraying equipment was used to treat the HRB400 rebar, and refined ferrite and a considerable non-equilibrium pearlite were obtained due to high cooling rate in treatment. A novel rebar with yield strength of 600 MPa grade was manufactured successfully in commerce, which also verified the above theoretical analysis.