Influence of process conditions during Ruhrstahl–Hereaeus refining process and effect of vacuum degassing on carbon removal to ultra-low levels

Abstract

The effect of the time taken to add the alloy and the gas injection mode are significant factors for fast decarburisation. Industrial experiments and thermodynamic calculations are adopted to show the transition of the main factors and reaction sites with time. The results indicate that adding steel scrap and alloy are not recommended in the first 7 min in order to keep good thermodynamic and dynamic conditions. The gas injection mode is more critical for reducing the chamber pressure to 67 Pa in 8.5 min and the gas volume should be less than 10 m 3 in the first 4 min after the reaction begins. This method is effective in improving the decarburisation rate and decreasing the carbon content at the end of decarburisation. For 69% of the site tests the final carbon content was kept to about 10 ppm within 15 min.

Characteristic Transformation of Manganese-containing Inclusions during Al-killed Process in Ultra-low Carbon Interstitial-free Steel

“…During the Al-killed process, different types of inclusions were formed by reactions (1) and (2). The spherical FM inclusions are transformed to be FA or AO based on reaction (1) by heterogeneous nucleation.…”

“…In IF steel the interstitial atoms, such as carbon and nitrogen etc., are controlled in a very low level during the smelting process by a series of manufacturing techniques, especially RH decarburization and nitrogen removal. [1][2][3][4][5] Meanwhile, the titanium or niobium is used to stabilize the residual carbon and nitrogen to make interstitial atoms free in the final matrix. 6) As mentioned in references, [7][8][9] most of defects on surfaces in cold-rolled sheet were relevant with the inclusions especially the macro-inclusions.…”