Microalloyed steel

About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.

On the Influence of Surface Hardening Treatments on Microstructure Evolution and Residual Stress in Microalloyed Medium Carbon Steel

Abstract: Tailoring surface properties is a key to superior performance of components subjected to fatigue loadings in application. Process–microstructure–property relationships have to be established to allow for optimization of techniques employed for surface treatments such as deep rolling and induction hardening. Although both techniques are employed widely in industrial application, studies examining microstructure evolution and residual stress states for a single material in a comparative manner are missing. Amongst others, this is related to the labor-intensive characterization techniques to be employed for this purpose. In order to establish pathways toward more efficient characterization approaches, the present work evaluates relations between microstructure evolution, hardness and results obtained by x-ray diffraction for a medium carbon steel treated by established surface hardening techniques. In this context, a strong correlation between hardness values and integral width distributions obtained by x-ray diffraction can be seen, while only weak correlations between hardness and residual stress measurements are existing. For in-depth microstructure analysis, high-resolution electron optical microscopy has proven to be very effective in resolving microstructural features down to the nanoscale substantiating elementary relationships. The study focuses on highly stressed fillet regions of real components, i.e., crankshaft sections. A 44MnSiVS6 microalloyed steel grade was used for measurements, representing a current standard for the crankshaft production in the automotive sector.

Effect of coiling temperature on microstructure and mechanical properties of a Nb-V microalloyed steel

Abstract: The effect of coiling temperature on the microstructure and mechanical properties of a Nb-V microalloyed steel was investigated. Controlled rolling followed by accelerated cooling and coiling was simulated by means of both, uniaxial compression, using a quenching and deformation dilatometer, and torsion. Specimens were reheated at 1250o for 5-10 min, then deformed at 1150°C, =0.3, and subsequently at 900°C, =0.4, followed by rapid cooling to a temperature between 450 and 700°C where coiling was simulated by holding the specimen for one hour at the selected temperature followed by a slow cooling to room temperature. Mechanical characterization was performed by means of hardness measurements and tensile tests, using tubular specimens machined from the torsion samples. It was found that decreasing the coiling temperature the ferrite-pearlite microstructure changed to ferrite-bainite, with a hardness peak reached for coiling at 600°C-650°C.

Microstructural development in a low carbon Ti-microalloyed steel during deformation within the ferrite region

Abstract: Microstructural evolution of ferrite in a low carbon Ti-microalloyed steel, during deformation within the ferrite region, was investigated by using torsion testing. Warm deformation characteristics of ferrite were studied by analyzing of its flow curves, optical microstructures and electron back-scattered diffraction maps. The results show that an unstable sub-boundaries network forms and then these transform into high angle boundaries, with further straining. It was found that the occurrence of continuous dynamic recrystallization is responsible for the development of very fine ferrite grains with high angle boundaries.

Effect of Ti(C, N) Particle on the Impact Toughness of B-Microalloyed Steel

Abstract: Simultaneously improving the toughness and strength of B-microalloyed steel by adding microalloying elements (Nb, V, Ti) has been an extensively usedmethod for researchers. However, coarse Ti(C, N) particle will precipitate during solidification with inappropriate Ti content addition, resulting in poor impact toughness. The effect of the size, number density, and location of Ti(C, N) particle on the impact toughness of B-microalloyed steel with various Ti/N ratios was investigated. Coarse Ti(C, N) particles were investigated to act as the cleavage fracture initiation sites, by using scanning electron microscopy (SEM) analysis. When more coarse Ti(C, N) inclusions were located in ferrite instead of pearlite, the impact toughness of steel with ferrite–pearlite microstructure was lower. Meanwhile, when the size or the number density of Ti(C, N) inclusions was larger, the impact toughness was adversely affected. Normalizing treatment helps to improve the impact property of B-microalloyed steel, owing to the location of Ti(C, N) particles being partly changed from ferrite to pearlite. The formation mechanism of coarse Ti(C, N) particles was calculated by the thermodynamic software Factsage 7.1 and Thermo-Calc. The Ti(C, N) particles formed during the solidification of molten steel, and the N-rich Ti(C, N) phase precipitated first and, then, followed by the C-rich Ti(C, N) phase. Decreasing the Ti and N content is an effective way to inhibit the formation of coarse Ti(C, N) inclusions.