JPS6123555A - Bottom pouring ingot making method - Google Patents

Abstract

PURPOSE:To eliminate the disturbance of the molten steel in casting molds on the upper stream and to economize the amt. of the material to be used in the molds by making the sectional area of the runners formed in the lower part of >=2 juxtaposed casting molds larger toward the upper stream side and specifying the flow rate ratio between the molten steels flowing through the adjacent runners. CONSTITUTION:The molten metal M is introduced into >=2 juxtaposed casting molds 1a, 1b, 1c, 1d from the bottom of the molds, by which bottom pouring ingot making is executed. The sectional area of the runners 2 provided in the lower part of the molds is set larger toward the upper stream side. The ingot making is thus executed in such a manner as to attain Vn<1.5Vn+1 when the flow rate of the molten steel flowing through the n-th mold nozzle from a pouring pipe 5 is designated as Vn and the flow rate of the molten steel flowing from the pipe 5 through the runner 2 on the upper stream side into the (n+1)-th mold nozzle is designated as Vn+1. In this case, n is 2-5, more particularly 3-4 and the casting is executed at about 60-200cm/sec. The disturbance of the molten steel M in the casting mold is thus eliminated and the amt. of the material to be used in the mold is economized. The generation of subsurface inclusions, double skins, etc. is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bottom pouring ingot making method, and more specifically, the flow of molten steel into each mold is made gentle by equalizing the speed of flow of molten steel into two or more molds arranged side by side. , prevents casting defects that were often observed in the past, especially in molds with injection pipes, and also serves as an in-mold agent (flux that covers the surface of molten steel).
The present invention relates to a bottom pouring agglomeration method that makes it possible to save on the amount used.

One of the ingot making methods for killed steel and the like is a bottom pour ingot making method in which molten steel is poured into a mold from the bottom of the mold to obtain a steel ingot. This method has the advantage that since the molten steel flows quietly into the mold, there is less entrainment of oxides, gases, etc., and the surface quality of the steel ingot is beautiful.

Figure 1 is a schematic diagram showing the ingot making equipment to which the above ingot making method is applied, where 1a*1 bylc is a mold, 2 is a runner, and 3 a s
3 b + 3 c is the surface plate, d a t 4 b e
4 c indicates a mold nozzle, 5 indicates an injection pipe, F indicates a mold agent, and M indicates molten steel. That is, the ingot making equipment 6 in the illustrated example is equipment in which three molds 1a*1btlc are arranged side by side on the left and right sides (however, the left mold is omitted from the drawing, and the same applies below), and the hot water connected to the injection pipe 5 is the same. Mold nozzle 4 protruding upward into path 2
a, 4b, and 4() are provided at regular intervals, and a surface plate 3ap3bs3c having a through hole to be fitted into the mold nozzle is placed on top of each mold nozzle 4a*4b*4c, and each surface plate 3a.

Mold 1 a t 1 b e 1 respectively on 3tz3c
c.

When molten steel M is injected from the ladle nozzle 8 into the injection pipe 5 in the ingot making equipment 6, the molten steel M passes from the injection pipe 5 through the runner 2 and reaches each mold nozzle 4 a y 4 b * 4 c, and then into the mold. 1atlbslc respectively. Then, when the introduced amount reaches a predetermined amount, the injection of the molten steel M is stopped and the steel is cooled and solidified to obtain a steel ingot. During ingot making, the surface of the molten steel M introduced into the mold comes into contact with the molten steel M, which has the effect of keeping the molten steel warm and preventing re-oxidation due to the atmosphere, and also has the effect of smoothing the surface of the steel ingot. An in-mold agent F that exerts the following properties is added so as to cover the surface of the molten steel M.

When performing such bottom pouring, the hydrostatic resistance in the mold is small in the early stage of molten steel injection, so the molten steel flows forcefully into the mold t near the injection pipe 5, and the turbulence of the molten steel in the mold becomes large. For this reason, the surface of the molten steel is not completely covered with the mold agent and comes into direct contact with the atmosphere, causing re-oxidation, and the mold agent is likely to be caught up in the molten steel. As a result, this causes defects such as the formation of subcutaneous inclusions, and the problem is that solidification progresses in such a way that solidified and non-solidified areas are mixed in the surface layer of the steel ingot, resulting in the formation of double skin. . In addition, as the turbulence of the molten steel M increases, the contact between the mold agent F and the molten steel M becomes violent, and the proportion of the mold agent F that turns into slag increases, resulting in an increase in the amount of mold agent F consumed. increasing °.

Therefore, the inventors of the present invention attempted to solve the above-mentioned problems, and conducted various experiments and proceeded with analysis in order to learn more detailed information about the molten steel injection situation.

That is, in Fig. 1, if one point is A on the upstream side of the mold nozzle 4a, one point on the upstream side of the mold nozzle 4b is B, and one point on the upstream side of the mold nozzle 4c is C, then A, B, C Conventionally, the cross-sectional area of the point runner is approximately uniform. On the other hand, if the amount of molten steel flowing into the mold 1a at a certain point is Qt, the amount of molten steel flowing into the mold 1b is Qb, and the amount of molten steel flowing into the mold 1c is Qc, the molten steel flow rate W at point A is Qa + Qb
+Qc, the molten steel flow rate Wn at point B is Qb+Qc, the molten steel flow rate Wn at point C (.

is Qc, and the flow rate of molten steel on the downstream side is small. Then, the molten steel flow velocity at point A is Vt, the molten steel flow velocity at point B is V,
, when the molten steel flow velocity at point C is v3, since molten steel flow velocity=molten steel flow rate/runner cross-sectional area, Vl>'b>Vs. At the initial stage of injection, the molten steel inflow resistance (hydrostatic pressure) due to the stored molten steel in 1aylbtlc is still small, so from mold nozzle 4 a y 4 b y 4 c to mold 1ay
The molten steel inflow velocity V1eV2t into 1b*lc is the molten steel flow velocity V1. in the runner, respectively. It is thought that the magnitudes corresponding to V, , V, and j7, vl )v, )v will be obtained. As a result, it was found that turbulence of the molten steel occurred particularly in the casting file where the molten steel inflow velocity v1 was high, and the above-mentioned problems were exposed.

Therefore, in order to solve the above problem, the present inventors further considered the above analysis results and slowed down the flow rate V of molten steel into the mold (in other words, slowed down the flow rate V of molten steel flowing through the runner). We considered this to be a major issue and proceeded with the study.

The present invention was made as a result of intensive studies to embody these ideas, and the molten steel flow velocity v1 in the runner
By suppressing this, the turbulence within the mold la is eliminated, thereby reducing the amount of in-mold agent used and preventing defects such as subcutaneous inclusions and double skin from occurring.

The method of the present invention that achieves the above object is a bottom-pouring ingot-making method in which molten steel is introduced into two or more molds arranged side by side from the bottom of each mold to form an ingot, and the ingot is formed in the lower part of the mold. By making the cross-sectional area of the runner larger as it goes upstream, the molten steel flowing in the runner upstream from the n-th mold nozzle from the injection pipe is transferred to the runner upstream from the n-th mold nozzle (Vny injection pipe). When the flow velocity of flowing molten steel is V n +1, V
The gist is that the agglomeration is performed so that n (1,5V n +1).

In other words, as is clear from the above explanation, the flow rate of molten steel flowing through the runner is determined from (molten steel flow rate/runner cross-sectional area).
In order to reduce the molten steel flow rate, the molten steel flow rate may be reduced or the runner cross-sectional area may be increased. However, in order to obtain a steel ingot of good quality, it is necessary to set the pouring time within an appropriate range; therefore, the injection of molten steel must be completed within a fixed period of time, and therefore the flow rate of molten steel must be reduced unnecessarily. I can't. Therefore, in order to reduce the flow velocity of molten steel, we came to the conclusion that it was necessary to increase the cross-sectional area of the runner, and by embodying this idea, we arrived at the above-mentioned structure of the present invention.

The method of the present invention will be explained below with reference to the drawings.

FIG. 2 is a schematic diagram of the ingot making equipment used to carry out the method of the present invention, which has approximately the same configuration as that in FIG. The diameter of each tube increases in a stepwise manner toward the upstream side.

That is, in FIG. 2, A is placed in the runner as described above.

When the three points B and C are determined, the molten steel flow rate at point A, Was, the molten steel flow rate at point B, and the molten steel flow rate at point 0, We, are W as described above.
Due to the relationship between a) Wb) and Wc, the flow rate of molten steel on the downstream side is smaller. On the other hand, the flow path cross-sectional area at point A is Sa
Let the cross-sectional area of the flow path at point wB be sb, the cross-sectional area of the flow path at point c be Sc, and the flow velocity of molten steel at point A be V1', the flow velocity of molten steel at point B be v,', and the flow velocity of molten steel at point C be v3'. Then, the flow path cross-sectional area at these three points Sat sb y Sc
If we design 5a)Sb)S(by making it correspond to the change in the molten steel flow rate), the relative relationship of the molten steel flow rate expressed by the molten steel flow rate/flow path cross-sectional area can be set as v,'~v2'#v,' , and accordingly, the flow rate of molten steel into the mold is also y1'=v,'#V
, ′ was obtained.

Based on this guideline, we conducted research to determine more specific conditions to virtually eliminate turbulence of molten steel within the mold.

In other words, in eliminating turbulence in molten steel according to the above policy,
If the flow velocity of molten steel in the runner is set to v 1' = v7 = v', that is, the velocity of molten steel flowing into the mold 1atlbtlc is set to M 1' = Ma 2' = vs', then the diameter of each mold nozzle is the same. Therefore, the amount of molten steel flowing into the mold 1awlbylc is Qa=Qb=Qc. Therefore, the molten steel flow rate Wa at point A, which is represented by Qa+Qb+Qc, is 3XQc, and Qb+
The molten steel flow rate wb at point B indicated by Qc is 2XQC,
Of course, the molten steel flow rate Wc at point C is Qc. The flow rate of molten steel in the runner is expressed as molten steel flow rate/cross-sectional area of the runner, so if we try to set the flow rate of molten steel in the runner to V□'-v,'=v,', the cross-sectional area of the runner at point A, S a= Wa/V1'=3Qc
/V3+'. Also, the cross-sectional area of the runner at point B 5b = Wb/V
2' = 2Qc/V3', and the cross-sectional area of the runner at point 0 is 5c = W C/ V@' = Q C/ V H'. In other words, it is necessary to set Sa to 3 times sb and Sb to 2 times Sc.
The turbulence of the molten steel within g 1 c can be made equal. Originally, in the mold 1c, the molten steel inflow velocity v
, / are set so that molten steel is not disturbed, so v
By setting 1'-v2'=v3', it is expected that turbulence of the molten steel will not occur in the molds 1a and 1b, and this effect has actually been confirmed.

By the way, in order to eliminate turbulence of molten steel in the mold, it is most desirable to set <v, '=v2'=v3' as described above, but under normal casting conditions, the flow velocity of molten steel in the runner can be adjusted for each area. can have some differences. In other words, in ingot making of killed steel, etc., in order to obtain a steel ingot of good quality, there is a permissible casting time range that takes into account the amount of steel ingot, steel type, cooling temperature, etc. There is also a limit to the amount of molten steel introduced per hour. According to the inventors' repeated research, the allowable range of molten steel flow velocity when ingot making is performed with such casting conditions well set is V' n (1,5V n - 4-1. In other words, by making the cross-sectional area of the runner larger toward the upstream side so that Vn is less than 1.5 times V n -1-1, the turbulence of the molten steel in the mold can be eliminated. can,
It is possible to reduce the amount of in-mold agent used and to prevent the occurrence of subcutaneous inclusions, double skin, etc.

When Vn becomes 1.5 times or more of V n -1-1, Vn becomes excessive and turbulence of molten steel occurs at least in the mold 1a closest to the injection pipe 5, and if it is noticeable, the molten steel will also be disturbed in the mold 1b etc. Disturbance occurs. In addition, in the above relational expression, practically n is 2 to 5, especially 3 to 4, and ■ is 60 to 20.
Casting is performed at approximately 0 cm/sec.

The basic structure of the present invention is the above-mentioned passage, but in forming the cross-sectional area of the runner to be larger toward the upstream side, in addition to increasing the cross-sectional area in the step-like manner described above, it may also be increased in a tapered manner from the downstream side to the upstream side. .

The present invention is constructed as described above, and by increasing the cross-sectional area of the runner on the upstream side, the flow velocity of molten steel flowing through the runner on the upstream side of each mold nozzle is set to V n < 1.5 V n
Since ingot making was carried out with the setting of -1-1, it was possible to reduce the flow rate of molten steel into the mold so as not to disturb the molten steel in the mold, thereby reducing the amount of mold agent used and It was possible to prevent the occurrence of inclusions, double skin, etc.

Next, examples of the present invention will be described.

EXAMPLE In an ingot making facility in which two molds are arranged side by side as shown in FIG. 3, ingots of 14 tons of molten steel were made with the runner diameter dt - dt set as shown in Table 1. At this time, the flow rate of molten steel in the runner, V1tV2, and the amount of mold agent used for ingot formation were as shown in Table 1. Also, the obtained steel ingot (
A 7-ton killed steel ingot) was bloomed into 11880 steel slabs, and the occurrence of subcutaneous inclusions and double skin was investigated on the steel slabs, which were equivalent to 1 ton at the bottom of the steel ingot, as shown in Tables 2 and 3. The results shown in the table were obtained.

Table 2 (Pieces) (Rotated) Apply a film to 1 to 5 positions below the surface of the steel piece and visually inspect.
)) The number of subcutaneous inclusions was investigated. n = 9th
3 Table unit G%/1.2mNote) After removing scale from the surface of the steel piece, the uneven part (2
After marking the skin (heavy skin), the uneven length was investigated. n=
9 In contrast to the comparative example (Nnl), in the example (Nn2), by forming the runner diameter d1 larger as shown in Table 1), the molten steel flow velocity V was increased to 58 m/min (1.45 of v-thickness). times)
), thereby making it possible to reduce the amount of mold agent required to form the steel ingot (2). Furthermore, as shown in Table 2, the number of subcutaneous inclusions in the steel ingot (2) could be reduced, and furthermore, as shown in Table 3, the occurrence of double skin in the steel ingot (I) could be significantly suppressed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an ingot-making facility to which the conventional method is applied, FIG. 2 is a schematic diagram of an ingot-making facility to which the method of the present invention is applied, and FIG. 3 is a schematic diagram of an ingot-making facility according to an embodiment.

Claims (1)

[Claims] A bottom pouring ingot making method in which molten steel is introduced into two or more molds arranged side by side from the bottom of each mold to form an ingot, the cross-sectional area of the runner formed at the bottom of the mold being By forming the molten steel larger as the side increases, the flow velocity of molten steel flowing in the runner upstream from the n-th mold nozzle from the injection pipe is Vn, and the flow velocity of molten steel flowing in the runner upstream from the n_+_1 mold nozzle from the injection pipe is Vn_+_
1. A bottom pouring ingot making method characterized by making ingots so that Vn<1.5Vn_+_1.