Dynamic CCT Diagram of Automobile Beam Steel With High Strength Produced by FTSR Technology

The dynamic continuous cooling transformation (CCT) diagram and phase transformation rules of 510 MPa automobile beam steel, which is produced by a continuous casting of thin slab of FTSR technology in Tangshan Iron and Steel Co. Ltd., are researched by thermal simulation experiment. The microstructure characteristics of the beam steel under different test conditions are studied by means of optical microscope and scanning electron microscope. The test results show that the critical temperatures of phase transformation Ar3 and Ar1 will all decrease with the increase of the cooling rate. When the cooling rate is lower than 20 °C · s−1, the ferrite and pearlite phase transformations are the main parts: when the cooling rate is higher than 20 °C · s−1, the bainite phase appears. Moreover, the microstructures of 510 MPa automobile beam steel produced by FTSR technology are also studied, and the results are basically in accordance with the CCT diagram gained from the test.