Titanium Modulated the Occurrence States and Strain Aging Resistance of Residual Element Nitrogen in Scrap-Based Low-Alloy Steels

TL;DR

Adding titanium to steel made from recycled scrap reduces nitrogen-related issues, improving sustainability and material properties.

Contribution

Titanium microalloying is shown to effectively fix nitrogen and reduce strain aging in scrap-based steels.

Findings

Titanium reduces mobile nitrogen atoms by 60–70%, lowering strain aging effects.

Fine TiN precipitates (5–20 nm) enable nitrogen fixation without harmful inclusions.

Titanium microalloying improves ductility and allows sustainable steel production.

Abstract

The steel industry is responsible for 7–9% of global CO2 emissions. Shifting from primary iron ore to recycled scrap in electric arc furnace (EAF) steelmaking offers significant decarbonization potential, reducing carbon intensity by 60–70%. However, increased scrap use in EAF operations leads to higher nitrogen absorption, which can degrade mechanical properties. Nitrogen dissolves into molten steel, where it forms Cottrell atmospheres at dislocations in the following processing steps, intensifying strain aging and reducing ductility. This study establishes a precipitation criterion based on the TiN solubility product to prevent harmful liquid TiN formation, enabling effective nitrogen fixation via fine TiN precipitates (5–20 nm). Multiscale characterization techniques, such as TEM and EBSD, show that Ti reduces the number of mobile N atoms by 60–70%, evidenced by a 50–65% decrease in Snoek/SKK peak intensities. Excessive titanium can refine ferrite grain size and prevents harmful TiN inclusions. Titanium microalloying presents a cost-effective, sustainable strategy to reduce strain aging in scrap-rich EAF steels, enabling more sustainable steel production without sacrificing material properties.

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