It has been half a century since aluminum was used to refine the grain size of steel and improve its strength and toughness. In a broad sense, there are seven or eight types of microalloying elements, but titanium, vanadium, and niobium are the most extensively studied and used.
The application of boron in composite alloying in individual high-strength steel 4140. Phosphorus can affect the evolution of texture and is therefore used for stamping steel plates.
Zirconium and titanium can change the morphology of sulfides, but there are currently more economical and effective methods for controlling the morphology of inclusions, so they have not been applied in practice. As for calcium and rare earth elements, due to the lack of clear regulations on their content in the final product, they are generally not considered alloy elements. Microalloying elements form various compounds with carbon, hydrogen, oxygen, and sulfur in steel, which have various effects on performance.
Titanium is the most active microalloying element, with strong affinity for oxygen, sulfur, carbon, and nitrogen. However, only titanium, vanadium, and niobium can generate carbon and nitrogen compounds and have precipitation strengthening effects.
The parameters that can affect the main microstructure of microalloyed elements are:
(1) Grain size and shape;
(2) Precipitates of various sizes;
(3) Matrix structure (ferrite, bainite, martensite);
(4) Dislocation density.
Link to this article：Reasons for implementing microalloying in steel bar production
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