Low-carbon aluminum killed steel slag washing and straightening process technology

Aluminium-killed steel is directly subjected to slag washing in the tapping process of the steel converter, and then argon is refined after the furnace to promote the floating of the inclusions. The LF refining is not carried out, and casting is continued on the continuous casting.

When many plants produce low-carbon aluminum killed steels such as SPHC, they often need to be refined by LF after tapping, which not only has a long process path, but also facilitates carbon addition and silicon addition in the refining process, and the cost is high. This paper briefly introduces a direct slag washing and blowing argon straightening process, ie slag washing in the steelmaking process of the converter, and then argon refining after the furnace to promote the floating of inclusions. It can directly cast on the continuous casting without LF refining.

The main operation of this process is to add slag washing material during the tapping process of the converter, add 3~10kg/t steel (depending on the end condition of the molten steel and the amount of slag to determine the amount), the bottom of the tapping process is stirred with argon at the end of the tapping process. The blowing of argon is carried out for more than 8 minutes, and if the process is controlled well, the calcium can be directly casted without continuous casting. The process is stable and can guarantee the number of continuous casting furnaces.

The key technologies of this process are as follows:

(1) Slag washing material: its composition and status are of vital importance, and it is the key to whether it can cause nodulation and guarantee continuous pouring;

(2) Timing of joining: adding during tapping;

(3) Addition amount: It is determined based on the end point of the converter and the amount of slag and the amount of deoxidizer added;

(4) soft blowing: guarantee soft blowing effect (soft blowing intensity and time);

(5) Heating capacity: The slag washing material must have a self-heating ability to prevent the cooling after joining.

The following is a factory's production practice for reference:

(1) The production process is simplified and the process is shortened

The original production process for steel grades represented by SPHC is “converter-LF-calcium treatment-soft blow-continuous casting”. Now it is changed to “converter-smelting steel slag washing-soft blowing-continuous casting” process. The new process is not With LF refining and calcium treatment, the process flow is significantly simplified and the process is significantly shortened.

(2) The pourability of molten steel is greatly improved, no water nozzle nodules appear, and the number of continuous furnaces is significantly increased

Before the slag washing process is used, whether the LF refining or calcium treatment, the liquidity of the molten steel is poor, there are 20% or more of the heat flow is poor or no flow phenomenon, resulting in the continuous casting of 6 to 8 packets of molten steel generally burned Oxygen 3 to 5 times, the steel pouring time 6 ~ 8h. After the slag washing process is adopted, no LF and no calcium treatment are needed. During the period of about 16 h in the continuous bag, oxygen is not required and no nodules occur.

(3) Reduced material consumption and significant cost reduction

Before the slag washing process was used, the Al consumption was greater than 2.2 kg/t steel, the Ca wire was >200 m/kiln, and the slag consumption was greater than 12 kg/t steel. The new process at least saves aluminum 0.2kg/t steel, no Ca treatment, slag material 5 ~ 10kg/t steel, ladle use process does not require minor repair slag line. Compared with LF, the cost per ton of steel is reduced by 10 yuan/t steel to 40 yuan/t steel (there is a certain difference between steel grades).

(4) Obvious reduction in user quality objections, significant increase in the number of orders

Before the slag washing process was not used, the monthly contract volume was about 40,000 tons, and the quality objection payment amount was 5.6 to 204,000 yuan/month; after the slag washing process was adopted, the monthly contract volume increased to 8 to 11 million tons, and the quality objections were made. The compensation is less than 0.5 yuan/month.