JPH01313165A - Continuous casting method partially containing semi-molten metal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting method that partially includes semi-molten metal in a solid-liquid coexistence state.

[Prior Art] Recently, with the aim of saving energy and resources, a semi-molten processing process for producing a primary product from molten metal in one process has been developed and put into practical use. The semi-molten processing process uses semi-molten molten metal with a fine solid phase, and directly molds the molten metal into a shape close to the product. refers to technology that increases
The application of this to casting is called the so-called rheocasting technology. That is, the temperature of the molten metal is appropriately adjusted to a temperature range between the liquidus line and the solidus line, and the molten metal is poured into the mold in a solid-liquid coexistence state immediately before solidification. If such a semi-melt processing process is used, solidification of the molten metal will be completed before the dendrites become coarse, so the equiaxed quality of the product will be improved and the structure will be uniform and fine.

[Issue to be solved by the invention, 11 Generally, slabs manufactured by continuous casting method tend to have center porosity in the center due to segregation of alloy components such as carbon and delay in solidification, and center porosity tends to occur in the center compared to the surrounding area. The quality of the center is significantly inferior. It is usually difficult to remove casting defects in the center in a post-process, or even if it can be removed, it requires a lot of effort. For this reason, in conventional continuous casting technology, solidification in the final solidification zone (so-called crater end) is controlled by light reduction casting, electromagnetic stirring, or a combination of these methods to improve the internal quality of the slab. We aim to

However, in the light reduction casting method, the effect of preventing center segregation is observed for low carbon steel with a carbon content of about 0.2% by weight or less, but the effect is not noticeable for high carbon steel. I can't do it.

In addition, even in the electromagnetic stirring method, the effect of preventing segregation is limited to a carbon content of approximately 0.5% by weight, and in the case of steel with a high alloy content, it is hardly effective. is not recognized.

Therefore, when continuously casting high carbon high alloy steel, it is necessary to promote solidification in the center before the alloy components are concentrated at the crater end. Therefore, a technique has been proposed to prevent center segregation by continuously introducing solid material into a molten pool in a mold to promote solidification in the center.

However, in the technique of adding a solid material to the molten metal during casting, it is not possible to make the molten steel component and the solid material component the same composition system. Further, there is a problem in that impurities are mixed in from the solid material and impair the integrity of the slab structure.

This invention was made in view of the above circumstances, and when continuously casting steel such as high carbon high alloy steel,
It is an object of the present invention to provide a continuous casting method that includes semi-molten metal in a part, which can effectively prevent the occurrence of casting defects in the center of a slab.

[Means for Solving the Problems] The continuous casting method according to the present invention, which includes semi-molten metal as a part, continuously injects completely molten metal into a mold to form a solidified shell, and then casts a solidified shell into the solidified shell. It is characterized by supplying semi-molten metal in a solid-liquid coexisting state to the enclosed unsolidified area.

[Function] In the continuous casting method of the present invention, which partially includes semi-molten metal, completely molten molten metal is cast into a mold, a solidified shell is formed around the periphery, and an unfinished metal surrounded by the solidified shell is cast into a mold. Semi-molten metal is supplied to the solidification region, ie, the center. For this reason, the equiaxed crystallinity of the region that should become the center of the slab increases, and its solidification is promoted, and solidification is completed before center segregation occurs.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

As shown in FIG. 1, a tundish 2 is disposed above a mold 20 of a continuous casting machine, and molten steel 3a in the tundish is continuously injected into the mold 20 through an immersion nozzle 4. The molten metal discharge port of the immersion nozzle 4 branches,
Molten steel is discharged from side to side. A semi-molten metal manufacturing apparatus 10 is provided on the side of the tundish 2, and the two are communicated with each other through a passage 6. The container of the semi-molten metal manufacturing apparatus IO is equipped with a heating/cooling means (not shown), and the molten steel is adjusted to an appropriate temperature within the solid-liquid coexistence region between the liquidus line and the solidus line. . Further, a stirring rotor 12 is inserted into the container of the apparatus 10 from above, and the rotation of the rotor 12 divides and refines the crystallized solid phase. Note that the upper end of the rotor 12 is connected to a rotating device (not shown) and a lifting device (not shown). A nozzle 14 is provided at the bottom of the device 10, the lower end of which is immersed in the molten pool within the mold 20, so that semi-molten metal within the container is supplied to the mold 20. That is, the water-cooled pipe 16 is wound around the nozzle 14,
After the semi-molten metal 3b is further cooled and adjusted to a predetermined solid phase ratio, it is supplied into the mold. The area inside the mold is covered with powder 7 to prevent oxidation of the molten steel and to provide lubrication between the mold and the slab. Note that the containers of the tundish 2 and the semi-molten metal manufacturing apparatus 10 are each covered with a lid (not shown) so that the inside of the container is replaced with an inert gas. Some nozzles 22 continue below the mold 20, and the solidified shell 8a cooled by the mold is guided downward. Pinch rolls (not shown) are installed below the continuous casting machine,
The completely solidified slab 8 is pulled downward at a predetermined speed.

Next, the operation of the embodiment will be explained.

Molten steel 3a adjusted to a predetermined composition and temperature is transferred from a ladle (not shown) to a tundish 2, and when the liquid level reaches a predetermined height, the immersion nozzle 4 is opened and the mold 20
Molten steel 3a is injected into the mold, and casting is started while a dummy bar (not shown) is pulled out at a predetermined speed. The injected molten steel 3a contacts the casting wall and is cooled, forming a solidified shell 8a. On the other hand, the valve (not shown) of the passage 6 is opened, and the molten steel 3a is supplied from the tundish 2 to the semi-molten metal manufacturing apparatus 10, and then the rotor 12 is rotated to stir the molten steel and transfer it to a predetermined location in the solid-liquid coexistence region. Adjust to temperature. As a result, a solid phase crystallizes in the molten steel at a predetermined ratio and grows and develops, but the coarsened dendrites are fragmented by stirring and become finer. When the molten steel is adjusted to a predetermined semi-molten state, the nozzle 14 is opened to supply the molten steel 3b to the mold 20. When the molten MA 3b passes through the nozzle 14, it is further cooled by the water-cooled pipe 16, and is adjusted to a state with a high solid phase ratio, that is, a molten metal just before solidification. In this case, it is preferable to control the solid phase ratio between 0.2 and 0.8, and in the case of steel, it is more preferable to control the solid phase ratio between 0.5 and 0.8. The internal pressure of the device 10 is increased by a pumping means (not shown), and the highly viscous semi-molten metal molten steel 3 is
b is extruded from the nozzle 14. At this time, the pressure of the pumping means is appropriately controlled so that the amount of molten steel 3b supplied is a predetermined ratio to the fully molten molten steel 3a. Extruded molten steel 3
Since b has a higher density than the molten steel 3a in a completely molten state,
After leaving the nozzle 14, it settles. Semi-molten metal molten steel 3
When b reaches the final solidification region below, it fuses together with the solidified shell 8a, absorbs heat from the solidified shell 8a, and immediately solidifies.

As a result, the solidification of the center portion is completed quickly, and a slab 8 with a high equiaxed product ratio is manufactured.

Next, the effects of the embodiment will be explained with reference to various data obtained by the conventional continuous casting method shown in FIGS. 2 to 4.

Figure 2 is a graph showing the relationship between the carbon content m [C] of molten steel on the horizontal axis and the equiaxed crystallinity on the vertical axis, when molten steel is continuously cast while being stirred by the electromagnetic stirring method. It is a diagram. The results show some variation within the shaded area in the figure, but the effect of electromagnetic stirring is most noticeable in [C]
When the amount is in the range of 0.2 to 0.4% by weight, [C]
When ffi exceeds 0.5% by weight, substantially no stirring effect is observed.

Moreover, the equiaxed crystallinity obtained is also up to 40%.

FIG. 3 is a graph showing the carbon content [C] of molten steel on the horizontal axis and the center porosity occurrence rate on the vertical axis, and investigating the relationship between the two by electromagnetic stirring under the same conditions as above. Although the results show some variation within the shaded area in the figure, the effect of electromagnetic stirring is noticeable when the amount of [C] is in the range of 0.2 to 0.4% by weight, as in the case above. When the amount of [C] exceeds 0.5% by weight, the stirring effect is not substantially observed. Further, no effect is observed even in the range where the amount of [C] is less than 0.2% by weight.

FIG. 4 is a graph showing the relationship between the center porosity occurrence rate on the horizontal axis and the degree of carbon segregation on the vertical axis. As is clear from the figure, both the carbon segregation degree and the center porosity occurrence rate tend to increase as one increases. This shows that when the center porosity occurrence rate is reduced, the degree of carbon segregation can also be reduced.

Therefore, according to the conventional continuous casting method, when casting high carbon steel, it is not possible to increase the equiaxed product ratio, and it is also difficult to reduce casting defects such as center segregation.

On the other hand, according to the embodiment of the present invention, semi-molten molten steel is supplied to the final solidification region and is immediately solidified, so that the equiaxed crystallinity of the slab can be greatly increased. Casting defects such as center segregation and center porosity can be significantly reduced.

In addition, in the above example, the semi-molten metal molten steel and the normal molten steel were injected into the mold using separate nozzles, but the invention is not limited to this, and it is also possible to inject both through one nozzle. It is.

[Effects of the Invention] According to the present invention, casting defects such as center segregation and center porosity can be reduced regardless of the composition system, and the equiaxed product rate of slabs can be increased, thereby improving the quality of high alloy steel slabs. You can improve your performance. In particular, when high carbon steel is continuously cast, the occurrence of significant center segregation, which has conventionally been unavoidable, can be effectively eliminated. Also,
It is easy to make the semi-molten metal molten metal and the completely molten molten metal have the same composition, and it is also possible to avoid contamination with impurities.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an apparatus used in a continuous casting method including semi-molten metal as a part according to an embodiment of the present invention, and FIGS. 2 to 4 respectively show castings manufactured by a conventional casting method. It is a graph figure showing the result of investigation about a piece. 2: Tundish, 3a: Molten metal, 3b: Semi-molten metal,
4, 14; Nozzle, 8; Slab, 8a; Solidified shell, 10; Semi-molten metal manufacturing device, 12; Rotor, 16; Water-cooled pipe, 20
;template. Applicant's representative Patent attorney Takehiko Suzue [C] ('/,) Fig. 3 Fig. 4 □□Yu-"+69- #"Atypical Kakemeku 1, Indication of case Patent application No. 144813-1988 2, Name of the invention Continuous casting method 3 containing semi-molten metal as a part, relationship with the case of the person making the amendment Patent applicant (412) Nippon Kokan Co., Ltd. 4, Agent 3-7-2 Kasumigaseki, Chiyoda-ku, Tokyo UBE building 7,
In the statement of contents of the amendment, page 6, lines 12 and 13, it is stated that “Nozzle 2
2" should be corrected to "Roll 22."

Claims (1)

[Claims] A semi-molten metal characterized by continuously injecting completely molten metal into a mold to form a solidified shell, and supplying semi-molten metal in a solid-liquid coexisting state to an unsolidified region surrounded by the solidified shell. A continuous casting method that includes