A method for improving the cleanliness of steel containing nb and ti

Abstract

The invention provides a method for improving cleanness of Nb-Ti containing steel. The method comprises the following steps of: smelting in a top-bottom combined blowing converter under the condition of argon gas bottom-blowing in the whole process; adding small-grain limes and fluorite in a steel tapping process; adding slow-release deoxidizing agent to the top of the slag after the steel tapping; carrying out secondary refining onto molten steel; feeding the refined molten steel to a continuous casting process for carrying out full-protection casting. According to the invention, low-nitrogen molten steel is obtained by adopting an argon gas bottom-blowing mode in the whole converter smelting process, calcium treatment and soft blowing are performed after LF (Low Frequency) furnace refining desulfuration and heating up, Nb-Ti alloying is carried out and the alloy melting is promoted by carrying out soft blowing again. Moreover, oxide impurities can be reduced by calcium pre-treatment and a soft-blowing process, the Nb-Ti alloy is promoted to melt by the soft blowing, impurities are removed by RH (Ruhrstahl Heraeus) vacuum refining and degassing, impurities are further removed by carrying out soft blowing after breaking the vacuum, and casting blank segregation can be weakened by continuous casting and low-superheat-degree casting, so that the purpose of controlling the oxide impurities and the nitride impurities in the steel is achieved.

Description

technical field [0001] The invention relates to the field of steelmaking and refining control, in particular to a method for reducing non-metallic inclusions in Nb and Ti-containing steel. Background technique [0002] At present, most of the domestic production of high-grade pipeline steel and high-strength steel adopts the process of LF refining + RH vacuum refining. The LF furnace mainly realizes heating and deep desulfurization, and the RH realizes degassing and removing inclusions. Combined with the full protection casting process, high-quality pipeline steel and high strength steel. High-strength steel and high-grade pipeline steel basically adopt Nb and Ti strengthening to improve performance. Nb and Ti are easy to segregate elements, and can be combined with N to form NbN and TiN in the high temperature process. Morphology exists. When the degree of superheat is high, the content of N is high, and there are many oxide inclusions, a large number of oxide and nitride...

AI Technical Summary

Problems solved by technology

The addition of Nb and Ti will inevitably generate NbN and TiN. There are more oxide inclusions in the steel during and immediately after the LF furnace treatment. The NbN and TiN formed during this process will be combined with oxide inclusions as the core. Composite inclusions are formed, which are difficult to remove from the molten steel after they are formed, and will remain in the slab until the rating of D-type inclusions in the hot-rolled plate is high

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