The Influence of Rolling Temperature on Mechanical Properties of Weathering Resistant Hot-Rolled H-Section Steel

According to the deformation characteristics of hot-rolled H-section steel that flange thickness deformation concentrated in the universal rolling stage, the opening rolling temperature of universal stage was set at 800-1 000 ℃, and the other main technological parameters remained unchanged. Through the mechanical property test and microstructure comparison analysis of hot-ralled H-section steel, The result indicated the grain size and shape of ferrite have a significant effect on the mechanical properties of hot-rolled Hsection steel, and the opening rolling temperature of universal stage has a significant effect on the grain size and shape of ferrite. For 1 000-950 ℃ opening rolling temperature, dynamic recrystallization of austenite could be completed, but the initial air cooling after rolling was 900-850 ℃ and recrystallization grain growth was rapid and also easy to grow abnormally. For 1 000 ℃ opening rolling temperature, ferrite grain size was differ and there was an obvious mixed crystal. When the temperature decreased to 950 ℃, mixed crystal situation has improved, but it still cannot eliminate. When the temperature decreased to 900 ℃, austenite dynamic recrystallization could be completed and the initial air cooling temperature decreased to 800 ℃. The growth of recrystallized grains was inhibited, and the small and uniform initial austenite structure was formed. At this time, the ferrite grains were 10-30 μm at equiaxial shape. When the temperature further reduced to 850-800 ℃, the thermal activation energy required to promote dynamic recrystallization of austenite cannot be met, so the deformation only appeared in the unrecrystallized zone, and flat ferrite grain was formed with the ratio of the long axis to the short axis being nearly 2 ∶1. The size of the long axis was not significantly reduced, but the size of the short axis was further reduced. Because of this, as the open rolling temperature decreased from 1 000 ℃ to 900 ℃, the ferrite grain boundary area was increased with the decrease of grain size, reduced the stress concentration degree, and increased the ability of distribution with the instantaneous deformation. The product yield strength increased from 369 MPa to 415 MPa. The tensile strength increased from 508 MPa to 546 MPa, the percentage elongation after fracture increased from 30. 0% to 31. 5%, the impact energy at low temperature increased from 36 J to 99 J. When the temperature decreased to 850-800 ℃, flat ferrite grain further increased the grain boundary area, made the product yield strength and tensile strength further to 468 MPa and 567 MPa respectively. When the distortion increased due to coordinate rotation between different size grains in plastic deformation, the percentage elongation after fracture decreased to 27. 0%, the impact energy at low temperature increased to 109 J, and the yield to tensile ratio reached 0. 83. In view of the fact that the lower rolling temperature affects the production output, and considering the universal mill load, energy consumption and economic factors, 900-850 ℃ is an ideal open rolling temperature range. At this time, not only the strength and plasticity indicators of the product are maintained at a relatively high level, but also the toughness index has been greatly improved. The comprehensive mechanical properties of weathering resistant hot-rolled H-section steel have been significantly improved.