Effect of Thermal Simulation Process on Microstructure of Seismic Steel Bars

Abstract

Thermal deformation has a significant influence on the microstructure of high-strength antiseismic steel. The effect of hot deformation on the microstructure of experimental steel was studied by the Gleeble-3800 thermal simulator. The microstructure of the steel was characterized by the metallographic microscope, microhardness, tensile test, field emission scanning electron microscope, electron backscatter diffraction, and high-resolution transmission electron microscope. The results show that the core microstructure of the test steel is composed of polygonal ferrite and lamellar pearlite. The test steel is mainly ductile fracture. Tensile strength and hardness increase with the decrease of temperature. At 650 °C isothermal temperature, the ferrite distribution was uniform, the average grain size was 7.78 μm, the grain size grade reached 11, the pearlite lamellar spacing was 0.208 μm, and the tensile fracture was distributed with uniform equiaxed dimples. Polygonal ferrite grain boundaries have high density dislocations that can effectively block the initiation and propagation of cracks. However, there are some low dislocation boundaries and subgrain boundaries in ferrite grains. Precipitation strengthening is mainly provided by fine precipitates of V-rich carbonitride in experimental steel. The precipitates are round or narrow strips, about 70–100 nm in size, distributed along ferrite grain boundaries and matrix.

Effect of Cold and Hot Compounds Forming on Microstructures and Mechanical Properties in the Deformation Zone of Sharp-Edged High-Strength Steel Sections

“…Similarly, a forming temperature of 850 • C and 100% deformation yielded a tensile strength of 448.52 MPa and an elongation after break of 23.64%, comparable to the original material. The results demonstrate that the material is austenitized at 850 • C, shifting from flattened grains to an equiaxed state and forming smaller polygonal ferrite [52]. After 70% deformation, the crystal size homogenizes, thus improving the material properties.…”

Optimizing Seismic Steel for Earthquake-Resistant Structures: The Role of Alloy Chemistry and Thermo-mechanical Processing

“…In the aerospace industry, it is employed in aircraft structures and components, where its high strength-to-weight ratio contributes to weight reduction, increased payload capacity, and overall performance improvements. [5], [6], [11] In the construction industry, the high strength and toughness of S700 steel make it an attractive option for structural applications such as bridges, buildings, and other largescale infrastructure projects. In the energy sector, S700 steel is used in producing wind turbine towers, oil and gas pipelines, and other energy-related infrastructures, where it is high strength and resistance to fatigue are crucial.…”

“…By using advanced numerical methods and models, engineers can simulate the behavior of S700 steel structures under different loading scenarios and optimize their design to ensure their performance during earthquakes. [6], [14] The use of numerical simulation with S700 steel structures has several benefits. Firstly, it reduces the cost and time required for physical testing, as simulations can provide accurate predictions of the behavior of steel structures under different seismic loads.…”

“…The hightemperature steel microstructure, called austenite, is deformed, recrystallized, and grainrefined during the multi-stage rolling process. [1], [6], [7] The hot rolled products are then rapidly cooled, such as quenching in water or by water sprays, to transform the austenite into a mixture of ferrite and martensite, providing strength and toughness. The cooling rate is carefully controlled to achieve the desired phase balance, with slower cooling yielding more ferrite and quicker quenching resulting in a higher amount of martensite.…”