JPS6160125B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing continuously cast slabs, particularly continuous cast slabs such as small cross-section billets and blooms.

When manufacturing small cross-section billets, blooms, etc. by continuous casting, it is difficult to use an immersion nozzle in the mold or add powder additives, so it is necessary to use an open nozzle or add oil such as rapeseed oil to the mold. A casting method is used.

However, when using this casting method,
A large number of air bubbles occur in the slab, especially on the top side, forcing it to be discarded, accounting for approximately 20% of the monthly production volume. Therefore, as a measure to reduce air bubbles, aluminum is added into the mold during casting and non-oxidized casting is performed, but when these methods are used, there are many unstable factors at the start of casting, which severely restricts operations and still prevents casting. Defects such as frequent occurrence of bubbles in one head and deterioration of the surface properties of the slab occur, and in order to eliminate these defects, it is essential to further strengthen the deoxidation in the mold at the early stage of casting.

To this end, the present invention aims to strengthen the initial deoxidation in the mold and reduce the bubbles in the slab head by charging Al evenly into the mold, for example on the dummy par head, before casting. Before starting casting,
This method is characterized by charging 100 gr or more of Al per ton of molten steel into the mold and pouring the molten steel, and after pouring the molten steel, continuous casting is carried out while adding Al in a conventional manner.

In this case, continuously cast slabs with small cross-sections are billets of 50□ to 200□, blooms of 200□ to 400□, and it is preferable to use metal Al or Fe-Al as the Al to be added, and it is preferable to use metal Al or Fe-Al. It is necessary to add 100 gr or more of Al per ton; if it is less than 100 gr, it will not be effective in preventing the generation of bubbles, and if it is more than 300 g, Al and diffusion will be poor, resulting in undesirable uneven distribution of SolAl.

According to this method, Al diffuses after complete dissolution, and
The range of SolAl variation also accumulates within the dummy bar head crop, making it possible to eliminate air bubbles without impairing the effective length of the slab, and the effect extends approximately 1.5 to 2.0 m from the slab head side, cutting off harmful parts. It has the advantage of being able to prevent quality deterioration such as waste and debris falling, as well as improving the surface quality and making it possible to upgrade the quality of slabs.

Next, examples of the present invention will be shown.

C: 0.60%, Si: 0.18%, Mn: 0.55%, balance
When continuously casting carbon steel made of Fe in a billet size 116, casting was started after placing 200 g of Al/t of molten steel on the top of the dummy bar head in the mold, and during casting, the steel was poured into the mold as usual.
After adding 300 g of Al/t of molten steel using an addition device,
The results were as shown in FIG. Figure 1 shows the position of the slab from the dummy bar head side.
This shows the variation in SolAl.The results of SolAl analysis at 100mm pitch from the head side of the slab show variation up to 300mm from the dummy bar head, but this variation range is within the normal cutoff amount. It's settled down, there's no particular problem. That is, in the case where the conventional Al filling was not performed, the billet scraping rate of the slab after the above-mentioned cutting was as high as 20 to 45%. The cause of this was a large number of bubbles due to insufficient deoxidation on the early casting side of the billet, but in the case of the billet in which Al was placed as shown in Fig. 2, the number of bubbles was significantly reduced and the billet The scraping rate has been significantly reduced to less than 1%. The standard for the number of bubbles shown in FIG. 2 is determined by visual judgment of the billet surface after scarfing and classification according to the bubble diameter.

As described above, the present invention is an industrially useful invention that can greatly improve the yield of slabs produced in continuous casting.

[Brief explanation of the drawing]

In the attached drawings, Figure 1 shows the
Figure 2 is a chart showing the number of bubbles by bubble diameter in the slab head, comparing the cases with and without Al.

Claims (1)

[Claims] 1. When producing continuously cast slabs, before starting casting, 100 gr or more of Al per ton of molten steel is charged into the mold, and the molten steel is injected. A method for producing continuously cast slabs, characterized in that continuous casting is carried out while adding.