Microstucture And Properties Of Fine Grains For High Strength Hot Rolled Bars

Reinforced bar is an important building steel, and the requirement quantity is rapid growth with the development of China’s national economy. But China’s steel product structure is behind, and HRB335which is steel grade Ⅱ still occupy around60%market share, not only result in wasting a large number of resources, but also affect the quality of construction. Therefore, fine grain high strength steel is produced by controlled rolling and controlled cooling technology. And it will improve the performance of various aspects of properties, and promote the upgrading of steel bars.Based on the different intensity levels including HRB400, HRB500and different diameters including the Φ16, Φ20,Φ25of fine grain high strength steel bar, the research and analysis for ultra-fine grain twisted steel production of new standards provide technical support for experimental research data.Reinforced by the organization, composition and its application performance compared to study the morphology and reinforced reasonable composition, determine a reasonable technical requirement and the final performance. Experimental results show that reinforced the organization of ferrite+pearlite as the best organization, not only to ensure good mechanical properties, but also has good weldability.Through the twisted steel of different specifications for tensile, bending tests to study the fine grain high strength steel bars’yield strength, tensile strength, elongation, ratio of intensity and yield strength, elastic modulus and the other properties, and to determine the fine grain high strength steel bars’bending performance. Experimental results show that fine grain high strength steel bars can not only meet the national standard requirements, and the mechanical properties are far exceeding the national standard.Through the twisted steel’s aging tests and impact tests to study the mechanical properties of twisted steel’s effect change at any time trend, and get the twisted steel’s ductile-brittle transition temperature. Experimental results show that the mechanical properties of twisted steel at any time the trend of efficiency and stability, and most twisted steel’s ductile-brittle transition temperature are-60℃in the following.Through the twisted steel of low-temperature and high-temperature tensile tests, we get twisted steel in the low and high temperature mechanical properties of the context, and determine the use area of fine grain high strength steel. In the low temperature case, with the temperature decreased, the twisted steel’s yield strength, tensile strength is increased, and it can maintain good elongation. In the high temperature case, the elongation will reach a minimum between200℃and300℃, then it will increase with the increasing temperature. The tensile strength will get the maximum about300℃and then it will drop drastically with increasing temperature. The yield platform began to disappear about400℃.Through the twisted steel fatigue tests show that the fine grain high strength steel bars have good fatigue resistance.