Strengthening behaviour and failure analysis of hot-rolled Nb+V microalloyed steel processed at various coiling temperatures

High-carbon hardline steels are primarily used for the manufacture of tire beads for both automobiles and aircraft, and vanadium (V) microalloying is an important means of adjusting the microstructure of high-carbon hardline steels. Using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the microstructure and precipitation phases of continuous cooled high-carbon steels were characterized, and the vanadium content, carbon diffusion coefficient, and critical precipitation temperature were calculated. The results showed that as the V content increased to 0.06 wt.%, the interlamellar spacing (ILS) of the pearlite in the experimental steel decreased to 0.110 μm, and the carbon diffusion coefficient in the experimental steel decreased to 0.98 × 10−3 cm2·s−1. The pearlite content in the experimental steel with 0.02 wt.% V reached its maximum at a cooling rate of 5 °C·s−1, and a small amount of bainite was observed in the experimental steel at a cooling rate of 10 °C·s−1. The precipitated phase was VC with a diameter of ~24.73 nm, and the misfit between ferrite and VC was 5.02%, forming a semi-coherent interface between the two. Atoms gradually adjust their positions to allow the growth of VC along the ferrite direction. As the V content increased to 0.06 wt.%, the precipitation-temperature-time curve (PTT) shifted to the left, and the critical nucleation temperature for homogeneous nucleation, grain boundary nucleation, and dislocation line nucleation increased from 570.6, 676.9, and 692.4 °C to 634.6, 748.5, and 755.5 °C, respectively.

Section: Resultsmentioning

confidence: 99%

“…V refines grains primarily by precipitation but also by its presence in a solid solution, enhancing the mechanical properties of steel [ 4 , 5 ]. When V exists in a solid solution within the austenite, it can inhibit the recrystallization of austenite grains [ 6 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of V on the Microstructure and Precipitation Behavior of High-Carbon Hardline Steel during Continuous Cooling

Zhang,

Gu,

Wang

et al. 2024

“…where σ 0 is the friction stress, which has a value of 53.9 MPa [7]. The calculation formulas of the four strengthening effects are as follows [10,24,25]:…”

Section: Strengthening Mechanismsmentioning

confidence: 99%

Effect of Controlling Nb Content and Cooling Rate on the Microstructure, Precipitation Phases, and Mechanical Properties of Rebar

Shen,

Gu,

Wang

et al. 2024

Seismic anti-seismic rebar, as materials for supporting structures in large buildings, need to have excellent mechanical properties. By increasing the Nb content and controlling the cooling rate, the microstructure and precipitation behavior of the steel are adjusted to develop seismic anti-seismic rebar with excellent mechanical properties. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and a universal tensile testing machine were used to characterize the microstructure, precipitation phases, and mechanical properties of the experimental steels. The results show that the ferrite grain size, pearlite lamellae layer (ILS), and small-angle grain boundaries (LAGB) content of the high-Nb steels decreased to 6.39 μm, 0.12 μm, and 48.7%, respectively, as the Nb content was increased from 0.017 to 0.023 wt.% and the cooling rate was increased from 1 to 3 °C·s−1. The strength of the {332}<113>α texture is the highest in the high-Nb steels. The precipitated phase is (Nb, Ti, V)C with a diameter of ~50 nm, distributed on ferrite, and the matrix/precipitated phase mismatch is 8.16%, forming a semicommon-lattice interface between the two. The carbon diffusion coefficient model shows that increasing the Nb content can inhibit the diffusion of carbon atoms and reduce the ILS. The yield strength of the high-Nb steel is 556 MPa, and the tensile strength is 764 MPa.

“…With the development of the economy and society, improving the strength of steel components and reducing the weight of steel products have become key indicators for the iron and steel industry’s development. Consequently, the industry has been focusing on the development of new high-strength steel [ 1 , 2 , 3 ]. Microalloyed steel, characterized by high yield strength, high toughness, and high durability, is achieved by incorporating small amounts of alloying elements (such as Nb, Ti, and V) into the chemical composition of ordinary mild steel and ordinary high-strength low-alloy steel matrices, thereby enhancing the mechanical and corrosion resistance properties of the steel [ 4 ].…”

Section: Introductionmentioning

confidence: 99%

Effect of Nb-Ti Microalloyed Steel Precipitation Behavior on Hot Rolling Strip Shape and FEM Simulation

Li,

Shao,

Yao

et al. 2024

Strip shape control is a hotspot and challenge in strip rolling, where the development trend of rolling technology is towards high strength, high toughness, and a large width-to-thickness ratio. The influence of material microstructure evolution on strip shape control is being increasingly emphasized. In this paper, a Nb-Ti microalloyed steel is taken as the research object. Thermodynamic and kinetic models focusing on the precipitation of the austenite phase are established to quantify the precipitation process. A coupled model of rolls and strips is built using ABAQUS 2022 software, where the precipitation strengthening model and high-temperature constitutive model are embedded into the finite element model (FEM) through subroutines. A two-dimensional alternating differential model is employed to acquire real-time temperature differences in the width direction of the strip. The effects of precipitation inclusion and exclusion on the strip crown under different operating conditions are compared and analyzed. The results indicate that as the temperature decreases, the strengthening effect increases, reaching around 40 MPa at temperatures above 1000 °C and 96.6 MPa at 800 °C. Furthermore, the inclusion of crown in the precipitation consideration is more sensitive to overall temperature changes, but as the strip width decreases, the sensitivity of crown to temperature decreases. The research findings of this paper provide guidance for improving strip shape control and reducing abnormalities during the rolling process.