JPH0422538A - Method for continuously casting beam blank - 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 method for continuously casting steel containing 0.005 wt.% or more of SoQ and AR into beam blank slabs.

[Conventional technology]

Beam blank slabs, which are mainly made of H-section steel, are continuously cast by semi-open casting using an apparatus whose main part is shown in FIG. 5(a).

In FIG. 5, 1 is a tundish, 2 is molten steel, 3 is a mold with an H-shaped cross section, and 4 is two semi-immersion nozzles (semi-immersion nozzles) with open tops fixed to the mold 3. Molten steel 2, which is released into the outside air from two holes (metering nozzles) la formed in the bottom wall of the tundish 1, is injected into the mold 3 through two semi-immersed nozzles 4. FIG. 5(b) shows molten steel injection points a in the mold 3 by two semi-immersed nozzles 4.

On the other hand, when an H-section steel made of low-temperature steel designated as aluminum killed steel is cast by the above-mentioned semi-open casting, the metering nozzle 1a and the semi-immersed nozzle 4 are clogged. Furthermore, in the case of semi-open casting, when the molten steel comes into contact with the atmosphere, Aρ203 inclusions are generated, which significantly impairs the cleanliness of the molten steel. Therefore, in the case of such H-beam steel, as shown in FIG. Seal casting is performed using a porous nozzle 6 with an inner diameter of 11 to 20 mm. How to adjust the level of molten steel 2 in mold 3.

This is done by controlling the speed at which the slab is pulled out by pinch rolls. However, SoQ.

In the case of molten steel with a l content of 0.005υt0% or more, nozzle clogging occurs in the early stages of casting, and casting often has to be stopped.Furthermore, due to fluctuations in casting speed, casting A problem arises in which the surface texture and meat quality of the pieces become unstable.

The apparatus shown in FIG. 7 consists of a tandish 1 and a mold 3.
Although this device is equipped with an inert gas sealing means 7 such as Ar between the two, it is difficult to ensure the sealing on an industrial scale. Furthermore, in both of the apparatuses shown in FIGS. 6 and 7, inert gas is flowed through the porous nozzle 6 on the bottom wall of the tundish 1, and AQ, 0. Although methods have been taken to prevent nozzle clogging, it is difficult to reliably prevent nozzle clogging.

Furthermore, as shown in FIG. 8, in a device in which a stopper 8 is attached to each of the two porous nozzles 6 on the bottom wall of the tundish 1, if the distance Q between the injection points is short, there is no space for attaching the stopper 8. There is no margin for this and the stopper opening is small, resulting in uncontrollable or nozzle clogging. Workability is poor because there are two stoppers to operate.

Furthermore, in Japanese Patent Application Laid-Open No. 49-123125, Fig. 9 (
As shown in a) and (b), the flange portions 3b at both ends of the mold 3, which has an H-shaped cross section, consist of a central web portion 3a and flange portions 3b and 3c at both ends of the web portion 3a. and 3c, a first discharge hole 9a facing the web portion 3a, and a second discharge hole 9b and a third discharge hole 9c facing the inner wall surface of the inner cavity of the flange portions 3b and 3c.
The immersion nozzle 9 having the following is arranged, and from each of the three discharge holes 9a, 9b, 9c of such two immersion nozzles 9,
An apparatus for supplying molten steel into an H-shaped mold 3 is disclosed.

However, the following problems are expected with the above-mentioned device.

(1) Since two immersion nozzles 9 are used, even if we try to control the casting speed in order to stabilize the quality of the slab, the distance between the injection points is short (1111 m), similar to the device shown in Fig. 8. In some cases, there is no space to install a stopper or a sliding nozzle, and therefore it is difficult to control the casting speed as described above.

(2) As shown in FIG. 9(b), the molten steel is discharged from the first discharge hole 9a of each of the two immersion nozzles 9 toward the web portion 3a, so that the discharged molten steel flow flows into the web portion. Ria
They collide within each other, and an upward upward flow and a downward downward flow occur violently. Because of this upward and downward flow,
As a result of large fluctuations in the melt level in the web portion 3a of the mold 3, the powder 24 is rolled into the molten steel 2 and the 10th
As shown in the figure, vertical cracks 11 are formed in the web portion 10a of the cast beam blank slab 1o, and inclusions brought into the mold 3 are pushed downward into the mold 3 due to the downward flow. , the flotation and separation properties of inclusions deteriorate.

[Problem to be solved by the invention]

As a means to solve the above-mentioned problem,
Publication No. 4050 discloses a method proposed by the present inventors, in which a single immersion nozzle having a plurality of asymmetrical discharge holes is attached to the bottom wall of a tundish, in a mold with an H-shaped cross section.
A method for continuous casting of a beam blank is disclosed, which comprises supplying molten steel into the mold from a plurality of asymmetrical discharge holes of the submerged nozzle, which are arranged in the bore of one of the flange parts.

However, with the method described above, C: 0.05 to 0.
50vt,%,Si: 0.05~0.5(ht,%
, Mn: 0.15-2.00wt,%, SoQ
, AQ: 0.005 to 0.20 (ht, %, remainder: having a component composition consisting of Fe and inevitable impurities,
It has been found that when steel containing 0.005% or more of SoQ and AQ is cast into beam blank slabs with excellent surface and wall quality, the following problems occur.

That is, when casting by placing one immersion nozzle in the inner cavity of one flange part of a mold having an H-shaped cross section,
The direction, diameter, etc. of the molten steel discharge hole provided in the immersion nozzle greatly affect the surface texture and wall quality of the cast H-section steel. In particular, the beam blank slab 1 shown in FIG.
Corner crack 12 occurring in the flange tip portion 10b of 0
This is likely to occur when casting is performed using a single immersion nozzle.

Regarding the causes of such corner cracks 12,
As a result of investigation by the present inventors, the following was found. One immersion nozzle arranged in the flange part inner cavity of the mold has at least a discharge hole facing the inner wall surface of the arranged flange part inner cavity, and a nozzle part inner cavity between the web part and the other flange part. A discharge hole is provided. When the above-mentioned molten steel flow from the discharge hole toward the inner wall surface of the flange part inner cavity is directed toward a part of the corner of the flange tip, the molten steel flow in the vicinity of the part of the flange tip corner in the mold The water level fluctuates. As a result, the molten powder flows unevenly between the mold and the shell, causing the corner cracks 12 described above.
occurs.

Furthermore, the molten steel flow from the discharge hole toward the inner wall surface of the inner cavity of the flange portion and the molten steel flow from the discharge hole toward the inner cavity of the joint between the web portion and the other flange portion, as described above, cause the molten steel flow in the mold. Due to uneven flow of molten powder between the mold and shell due to fluctuations in the molten steel level, vertical cracks 11 occur in the web portion 10a and fillet portion 10c of the beam blank slab 10, as shown in FIG.
occurs.

Therefore, the object of the present invention is to provide a 5of1. The purpose of the present invention is to provide a method for casting steel containing AQ into beam blank slabs that are free from defects such as longitudinal cracks, corner cracks, and slag scratches and have excellent surface and wall quality.

[Means to solve the problem]

The present inventors investigated the relationship between the nozzle shape and the fluctuation of the molten metal level within the mold through a water model test. Figure 3 (
a) to (d) are explanatory diagrams showing the nozzles used in the test and their arrangement in the mold, and FIG.
) is a graph showing the fluctuation of the melt level in the mold when using the nozzle.

FIG. 3(a) shows the inner cavity of the web part and the knots of the flange parts on both sides of a mold with an H-shaped cross section.

2, each having a first discharge hole facing the web part, second and third discharge holes facing the inner wall surface of the lumen of the flange part, and a fourth discharge hole facing downward of the mold, on the lower circumferential surface thereof. This is a case where a book immersion nozzle is arranged.

FIG. 3(b) shows a first discharge hole in the inner cavity of the joint between one of the flange parts and the web part of the mold, and a first discharge hole facing the web part on the lower peripheral surface and a first discharge hole facing the inner wall surface of the flange tip part. the second and third discharge holes, and the fourth discharge hole facing downward of the mold.
This is a case where one immersion nozzle having a discharge hole is arranged. FIG. 3(C) shows a case in which the same immersion nozzle as in FIG. 3(b) is arranged except that it does not have a discharge hole directed toward the bottom of the mold.

FIG. 3(d) shows a case where the same immersion nozzle as FIG. 3(b) is arranged except that it does not have a discharge hole facing the flange tip.

FIG. 4 shows the melt level fluctuations of each of the left flange, web, and right flange when the four types of immersion nozzles described above are used, using an evaluation index of 0 to 4. An evaluation index of 0 indicates a good condition with the least fluctuation in the hot water level, and an evaluation index of 4 indicates a poor condition with the most fluctuation in the hot water level.

As is clear from FIG. 4, in the case of method (a) using two immersion nozzles, there is a large fluctuation in the melt level in the web portion, and the penetration depth of inclusions is also large. Even if one immersion nozzle is used, in the case of (c) in which the lower end face is not provided with a discharge hole directed downward of the mold, the liquid level fluctuates significantly at the left and right flange portions. Even if one immersion nozzle is used, if the flange part does not have a discharge hole facing the inner wall surface of the lumen (cl), the fluid level fluctuation in the right flange part is extremely large. .

On the other hand, only in the inner cavity of the joint between one of the flange parts and the web part of the mold, there is a first spout hole facing the web part on the lower side, and a second spout hole facing the inner wall surface of the flange tip part. ．． In the case of (b) in which one immersion nozzle having a third spout hole and a fourth discharge hole facing downward of the mold is arranged, the evaluation index of the left flange and the right flange is 2,
In addition, it was found that the evaluation index of the web portion was 0, that there was extremely little fluctuation in the hot water level, and that there was almost no intrusion of inclusions.

This invention was made based on the above findings, and
The bottom wall of the tundish and the inside of the mold are formed only in the inner cavity of the joint between one flange part and the web part of a mold having an H-shaped cross section and consisting of a central web part and flange parts at both ends of the web part. A single immersion nozzle that connects the molten steel without a gap is placed apart from each inner wall surface of the bore, and a lower surface of the immersion nozzle is provided with a immersion nozzle that connects the molten steel with the other flange part and the web part. A first discharge hole facing the cavity, and a second discharge hole and a third discharge hole facing the inner wall surface of each flange tip of the one flange portion, and the lower end surface of the immersion nozzle is provided with the A fourth discharge hole is provided facing downward in the mold, and the ratio of the cross-sectional area of the first discharge hole, the cross-sectional area of the second and third discharge holes, and the cross-sectional area of the fourth discharge hole is ( 3-5): Limited to (1-2)=1.

By discharging molten steel into the mold from the four discharge holes of one immersion nozzle, 0.005w
This method is characterized in that steel containing SoQ and AQ of t,% or more is continuously cast into beam blank slabs.

[Effect]

In this invention, as described above, the mold having an H-shaped cross section has a first discharge hole directed toward the web portion only in the inner cavity of the knot between one flange portion and the web portion, and on the lower circumferential surface thereof. , the second and third points facing the inner wall surface of each flange tip.
One immersion nozzle having a discharge hole and a fourth discharge hole facing downward from the mold is arranged, and molten steel is discharged into the mold from the four discharge holes.

Therefore, no upward flow or downward flow of the discharged molten steel occurs in the web portion, so that there are extremely few variations in the situation in the flange portion and the web portion. As a result, there is almost no entry of inclusions, and vertical cracks and slags that occur in the beam blank slab are prevented.
vt, SoQ of % or more.

AQ-containing steel can be continuously cast into beam blank slabs with clean surfaces and walls.

In this invention, the cross-sectional area of the first discharge hole, the cross-sectional area of the second and third discharge holes, and the fourth discharge hole of the immersion nozzle are
The ratio to the cross-sectional area of the discharge hole is (3-5): (1-2)
It is necessary to limit it to =1. When the ratio of the cross-sectional area of the first discharge hole to the fourth discharge hole is less than 3, the flow rate of molten steel discharged from the first discharge hole decreases, and the molten steel near the flange tip on the side where the immersion nozzle is not provided decreases. As the surface temperature decreases, the molten powder layer may solidify, resulting in the problem of slag formation in the beam blank slab. On the other hand, if the ratio of the above-mentioned cross-sectional areas exceeds 5, the flow rate of the molten steel discharged from the first discharge hole becomes too large, and the scene of the molten steel changes at the flange part and the flange tip part on the side where the immersion nozzle is not provided. As a result, problems such as vertical cracks and slag scratches occur.

If the ratio of the cross-sectional area of the second and third discharge holes to the fourth discharge hole is less than 1, the flow rate of molten steel discharged from the second and third discharge holes will be too large, and the side where the immersion nozzle is provided will A problem arises in which corner cracks occur at some corners. On the other hand, when the ratio of the cross-sectional areas exceeds 2, the flow rate of molten steel discharged from the fourth discharge hole becomes too large, and the downward flow of molten steel becomes deep. As a result, the floatability of inclusions such as AQ203 deteriorates, and inclusions come to exist inside the slab, resulting in a problem of deterioration of the quality of the beam blank.

Next, the present invention will be explained with reference to the drawings.

FIG. 1(a) is a sectional view showing the main parts of an apparatus for carrying out the method of the present invention, and FIG. 1(b) is a diagram showing a molten steel injection point in a mold of the same apparatus. As shown in the drawing, the porous nozzle 6 provided on the bottom wall of the tundish 1 has a first discharge hole 15a and a second discharge hole 15a at its lower part.
Spout hole 15b, third discharge hole 15c, and fourth discharge hole 15
One immersion nozzle 14 having four discharge holes d,
It is attached by immersing its lower part into the molten steel 2 in the mold 3.

The immersion nozzle 14 consists of a central web part 3a and flange parts 3b and 3c on both sides of the web part 3a, and a negative flange part 3 of a mold 3 having an H-shaped cross section.
It is arranged only in the inner lumen of the node between b and the web portion 3a, and away from each inner wall surface of the lumen.

The first discharge hole 15a of the immersion nozzle 14 is directed toward the inner cavity of the joint between the other flange portion 3c and the web portion 3a. The second discharge hole 15b and the third discharge hole 15c are directed toward the inner wall surface of the flange chip 3b' of one flange portion 3b of the mold 3.

The fourth discharge hole 15d is provided on the lower end surface of the immersion nozzle 14, facing downward from the mold 3.

The first discharge hole 15a of the immersion nozzle 14 and the second discharge hole 15
b, the third discharge hole 15c, and the fourth discharge hole 15
The ratio of cross-sectional area to d is (3-5):(1-2):1.

The porous nozzle 6 on the bottom wall of the tanditshu 1 has Ar
A stopper 8 capable of injecting an inert gas such as the like is attached. In addition, since the molten steel 2 is injected into the mold 3 by one porous nozzle 6 and one immersion nozzle 14, the inner diameter of the porous nozzle 6 and the inner diameter of the immersion nozzle 14 are larger than those of the conventional method. Therefore, nozzle clogging is less likely to occur than in the past, and since the stopper opening can be larger than in the past, as shown in Figure 1(a), nozzle clogging is also less likely to occur.

With the above configuration, four of one immersion nozzle 14
The molten steel 2 in the tundish 1 is supplied into the mold 3 from the three discharge holes 15a, 15b, 15c, and 15d.

As a result, the molten steel 2 supplied into the mold 3 is discharged through the first discharge hole 15a toward the inner cavity of the joint between the other flange portion 3C and the web portion 3a, and is discharged through the first discharge hole 15a.
b and the third discharge hole 15c toward the flange tip 3b' of one flange portion 3b, and then through the fourth discharge hole 15d toward the lower part of the mold 3.

Such discharge from the first discharge hole 15a toward the inner cavity of the knot between the other flange portion 3c and the web portion 3a, the second
Discharge toward the flange chip 3b' from the discharge hole 15b and the third discharge hole 15c, and the fourth discharge hole 15d
By discharging downward from the mold, violent upward and downward flows of molten steel do not occur in the web section 3a, and there is no fluctuation in the molten metal level, so powder entrainment is reduced, and the web section of the cast slab is No vertical cracks or slag scratches will occur.

Furthermore, since the stopper 8 can be operated stably, from this point of view as well, fluctuations in the liquid level in the web portion 3a of the mold 3 and powder entrainment can be reduced.

Next, the present invention will be explained with reference to examples.

[Example 1] Using the immersion nozzle shown in FIGS. 2(a) to (e), the first
As shown in Figures (a) and (b), the tundish 1 was installed so as to isolate the space between the bottom wall of the tundish 1 and the molten steel 2 in the mold 3 from the outside air. 1,530 to 1,550 with the component composition shown in Table 1 below, housed in Tanditsh 1.
Molten steel at a temperature of
0 kg/m” beam blank.

Table 1 (needle 1%) The width a of the mold 3 shown in FIG. 1(b) is 480 m.

The depth is 400+w+.

As shown in FIGS. 2(a) to 2(e), the immersion nozzle 14 used had gas for blowing argon gas surrounding the molten steel through hole 16 and on the outside of the through hole 16. Tamari 17
．． 18 are formed. 19°2o is gas reservoir 17
．． A supply hole 21 for blowing argon gas into 18,
This is a through hole through which argon gas is ejected into the through hole 16. The lower outer periphery of the immersion nozzle 14, which is in contact with the slag, is formed of a refractory material 22 having excellent erosion resistance against the slag. 23 is a reinforcing iron plate.

The dimensions of each part of the immersion nozzle 5 used are as follows.

(a) External diameter of immersion part: 100 m + (b) External diameter of base: 130 mn (c) Inner diameter: 40 to 55 mm (d) First discharge hole 15a: Oval shape of 35 x 45 mm (angle: horizontal) (e) Second discharge hole Hole 15b: 25mnφ circular (angle: 10 degrees downward) (f) Third discharge hole 15c: 25m+nφ circular (angle:
(g) Fourth discharge hole 15d: 20 plates φD circular shape. The distance Q between the upper end of the discharge hole and the molten steel surface shown in FIG. 2(a) was set in the range of 100 to 140 am.

A relatively high viscosity powder 24 (1300° C., 3.0 poise or more) was added to the surface of the molten steel 2 in the mold 3 in order to prevent oxidation of the molten steel, keep it warm, collect inclusions, and lubricate it.

Table 2 shows the number of defects in slabs during continuous casting for 15 heats (3 months) as described above, and Table 3 shows problems with beam blanks.

Table 2 Note: Inspection was conducted visually after shot blasting.

As is clear from Tables 2 and 3, there are no troubles during casting, stable operation is possible, and no slag, vertical cracks, corner cracks, etc.1
We were able to continuously cast beam blanks with excellent surface texture and wall quality.

[Example 2] Molten steel having the composition and temperature shown in Table 4 below was cast into a beam blank using the same method as in Example 1 at a casting speed of 0.9 m/min and a casting length of 2 heats/TD. .

As a result, as in Example 1, stable operation was possible, and beam blanks with excellent surface texture and wall quality without slag, vertical cracks, corner cracks, etc. could be continuously cast.

〔Effect of the invention〕

As stated above, according to this invention, 0.005v
Steel containing SoQ, AQ of t,% or more can be cast into beam blank slabs with excellent surface texture and wall quality without defects such as longitudinal cracks, corner cracks, and slag scratches, and therefore, Many industrially useful effects are brought about, such as the ability to manufacture high-quality H-section steel from beam blank slabs.

[Brief explanation of drawings]

FIG. 1(a) is a sectional view showing the main parts of an apparatus for carrying out the method of the present invention, FIG. 1(b) is a view showing the molten steel injection point in the apparatus, and FIG. 2(a) is A vertical cross-sectional view showing an example of a submerged nozzle used in the method of the present invention, FIG. 2(b) is a cross-sectional view taken along line A-A in FIG. 2(a), and FIG.
-B sectional view, Figure 2(d) is an explanatory diagram showing the same nozzle and its arrangement in the mold, and Figure 4 is the hot water in the mold when the nozzles in Figures 3(a) to (d) are used. Graphs showing surface fluctuations, FIGS. 5 to 9 are explanatory diagrams showing the conventional method, and FIG. 10 is an explanatory diagram showing the flow generation state of the beam blank slab. In the drawings, 1... Tandish, 2... Molten steel, 3... Mold, 6... Porous nozzle, 8... Stopper, 10... Beam blank, 11... Vertical crack, 12... ... Corner crack, 13... Slag bite,
14... Immersion nozzle, 15a... First discharge hole,
15b...second discharge hole, 15c...third discharge hole,
15d... Fourth discharge hole, 16... Through hole,
17.18... Gas reservoir, 19.20... Supply hole,
21...Through hole. 22...Refractories with excellent erosion resistance, 23...Reinforcing iron plates, 24...Powder diagrams (a) (b) wa+ 慾图(b) (c) 1shi] Figure (a) ) (b) (c) (d) Fig. 7 Fig. Fig. Nest Fig. (a) (b) Fig.

Claims (1)

[Scope of Claims] 1. In a mold having an H-shaped cross section and consisting of a central web part and flange parts at both ends of the web part, only within the inner cavity of the joint between one flange part and the web part, One immersion nozzle that connects the bottom wall of the tundish and the molten steel in the mold without a gap is arranged apart from each inner wall surface of the bore, and the lower circumferential surface of the immersion nozzle is provided with the other one. A first discharge hole facing the inner cavity of the node of the flange portion and the web portion, and a second discharge hole and a third discharge hole facing the inner wall surface of each flange tip of the one flange portion, and
A fourth discharge hole facing downward of the mold is provided in the lower end surface of the immersion nozzle, and the cross-sectional area of the first discharge hole, the cross-sectional area of the second and third discharge holes, and the fourth discharge hole The ratio to the cross-sectional area of the holes is limited to (3-5):(1-2):1, and the molten steel is discharged into the mold from the four discharge holes of one immersion nozzle. Accordingly, 0.005
wt. % or more of Sol. A method for continuous casting of beam blanks, characterized in that steel containing Al is continuously cast into beam blank slabs. 2 Carbon: 0.05 to 0 using the one immersion nozzle
．． 50wt. %, silicon: 0.05-0.50wt. %,
Manganese: 0.15-2.00wt. %, Sol. Al
:0.005~0.200wt. %, the remainder, Fe and unavoidable impurities, and the temperature in the tundish is 1,510 to 1,570 ° C.
The method according to claim 1, characterized in that continuous casting is carried out into a beam blank slab having a clean surface and texture.