Study On The Performance Of Angle Iron Specially Used For The Power Tower

In this study, the performance and microstructure of Q420,Q460 angle irons used for the power tower had been studied by micro-alloying technology and controlled rolling process, etc. Besides possessing higher strength of the prepared Q420> Q460 angle irons, they are also have an excellent low-temperature toughness. It can improve the loading intensity of power tower and prolong its life time, which will have a great significance to the construction of the power tower.Based on the domestic and overseas experience and mechanism of alloying, the chemical composition of special applications angle iron used for power tower was initially designed. During experiment, the composition was adjusted continuously to achieve the best composition range. The optimal technological parameters of the controlled rolling process were obtained according to optimize the rolling process on the basis of test results. At the same time, the influence of heat treatment process on the performance of the Q420 angle iron was also studied in this paper.The results show that the alloying elements had a great influence on the performance of the angle iron. Increasing the carbon content could improve the strength of the angle iron, however, the low-temperature toughness of the sample will be reduced. The test results indicated that the carbon content should be controlled within a certain range, it should be controlled at the range of 0.15%～0.18%for the Q460 angle iron of∠8～12.5, however, for∠5～7.5, the carbon content is 0.15%～0.18%, for∠8～12.5, it is 0.15%～0.18%, for∠5～7.5, it is 0.12%～0.18%. The study also shown that the addition of vanadium is benefit to improve the strength and toughness of the angle iron, so its content in angle iron should be controlled, for Q460 of∠8～12.5 angle iron, within the range of 0.09%～0.13%; for Q460 of∠5～7.5 angle iron, within the range of 0.05%～0.08%; for Q420 of∠8～12.5 angle iron, within the range of 0.05%～0.08%; for Q420 of∠5～7.5 angle iron; within the range of 0.04%～0.07%. Meanwhile, Aluminum, as a strong deoxidizing agent in the steel, could play a role of grain refinement, and the best content of aluminum in Q420 and Q460 angle iron should be slightly larger than 0.03%. The impact test to angle iron at different temperatures showed that the impact energy reduced with the temperature decreased and the rolling process affected the low-temperature toughness greatly in addition to the composition of alloying elements. In this study, the conventional rolling process and trial rolling process were contrasted in the experiment to study systematically the influence of the finishing temperature on the micro structure and properties of angles. It is shown that the grain refinement could effectively improve the strength and toughness of the angle iron. By controlling the rolling process of the angle iron samples and combining with the tensile test and impact test, the results showed that when the heat temperature was controlled within the range of 1050～1100℃, the starting rolling temperature was within the range of 1000～1050℃, and we performed a multi-pass rolling before the recrystallizing of austenite to make the cumulative deformation of steel more than 45%, controlled finishing rolling temperature of steel within the range of 850～900℃, then cooled the steel in air. All above processes could make the microstructure of steel fully refined and get the best mechanical properties.The heating treatment process affected the performance of angle greatly. In the study, the influence of different heating treatment process on the performance and microstructure of Q420 angle irons was investigated then the changes of its low temperature performance was analyzed in detail. The grain size will be refined under the normalizing treatment of 910℃, which can improved the strength and toughness of Q420 angle iron. The experiment results showed that 40 minutes'heat treatment at 900～920℃and then keeping warm for 50 minutes at 550℃could make the Q420 angle iron own better mechanical properties. It was also found that the heat treatment at 900～920℃could effectively prevent the grain growth of austenite and at the same time, the hardness of the sample could reach the maximum. A 50 minutes tempering at 550℃after the quenching could obtain the sorbite, which was pretty abundant in Q420 angle iron when the sample had strong strength and toughness.