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The microstructures have been investigated in steel plates with different rolling processes to find the reasons of yield ratio overseted standard in few high strength building steel plates produced in Echeng Iron and Steel Corporation. The effects of rolling path, rolling path depress ratio on microstructure and properties. Some reasons of yield ratio overseted standard have been analyzed. The results show that decreasing rolling paths and increasing depress ratio refined grains but unchanged area ratio and interlamellar spacing of pearlite. Yield strength excessively increased but tensile strength unchanged increased yield ratio. So, excellent properties can be obtained by applying the optimization process.

The effects of controlled rolling and controlled cooling parameters on the microstructure and mechanical properties of 550MPa grade engineering mechanism steel were investigated in the industrial trial conditions. The results show that the mechanical properties of 550MPa grade engineering mechanism steel are obviously improved by controlling finishing rolling temperature ranged from 780°Cto 850°C, and by using accelerate cooling after rolling, ferrite grains are refined markedly of the steel which possess excellent strength and toughness behaviors.