JP3370649B2 - Horizontal continuous casting of hypoeutectic cast iron - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting hypoeutectic cast iron having a wide range of liquidus temperature and solidus temperature. The material of this hypoeutectic cast iron has recently been subjected to machining, cold forging, high temperature forging, and the like, and its demand is increasing as various machine parts.

[0002]

2. Description of the Related Art As a material for hypoeutectic cast iron, carbon eutectic (CE = C + Si / 3) is 1.9 to 3.9% (in the present specification,% is% by weight). Cast iron is preferred. However, when hypoeutectic cast iron is cast by the continuous casting method,
The wide solid-liquid coexistence temperature range is a factor that impedes the castability in continuous casting. That is, since there is almost no material strength in the solid-liquid coexistence state in the mold, when the slab is drawn out, the slab breaks in the mold and cannot be drawn out, which makes industrial production difficult.

As a prior art example, a continuous casting method of low carbon white cast iron having a carbon content of 2 to 3% is disclosed in JP-A-57-91851. This low carbon white cast iron also has a wide solidification temperature range (100 to 200 ° C.), so that the casting conditions are controlled within a predetermined narrow operating condition range to enable continuous casting.

However, although the casting temperature is controlled at 1400 ± 20 ° C., the solidification temperature of hypoeutectic cast iron originally varies depending on the carbon equivalent and is in a wide range of 1130 to 1400 ° C. It cannot be said that the temperature can be applied.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to stably cast hypoeutectic cast iron by horizontal continuous casting. Here, the hypoeutectic cast iron targeted by the present invention is hypoeutectic cast iron having a carbon equivalent (CE = C + Si / 3) of 1.9 to 3.9%. Other component composition is M
n is 1.0% or less, other alloy elements such as Cr, Ni, and V can be contained in an amount of 1% or less, and inevitable impurities such as P and S are contained.

[0006]

A first aspect of the present invention is a continuous casting method in a horizontal continuous casting apparatus equipped with a tundish, a mold connected to the tundish, a secondary cooling zone, and a drawing apparatus, which has a carbon equivalent (CE). = C + Si / 3) is 3.9% or less, when casting hypoeutectic cast iron, the carbon equivalent of the predetermined amount of molten metal component to be poured first in the tundish at the start of casting is 3.5 to 4.4%. The horizontal continuous casting method is characterized by increasing the carbon equivalent of the hypoeutectic cast iron in the range.

At the start of casting, the solidification temperature range, that is,
The liquidus temperature and the solidus temperature are small in width, and both of these temperatures are around 1130 ° C. Carbon equivalent is 3.5 to 4.4%.
When cast iron is cast, the molten metal in the mold is wholly solidified at a substantially constant temperature, so that the slab does not break at the start of drawing.

A second aspect of the invention is a horizontal continuous casting method, wherein the predetermined amount of the molten metal initially poured is at least substantially the amount of molten metal that is filled in the mold. If the amount of eutectic cast iron that fills the mold at the start of casting is in the tundish, the inside of the mold can be uniformly solidified, so that smooth casting can be started.

A third aspect of the invention is, in the casting,
The horizontal continuous casting method according to claim 1 or 2, wherein the generation position (L1) of the tip of the solidified shell (fs = 0, fs: solid phase ratio) from the mold inlet is controlled within the range of the following formula. 0.5 × L0 ≧ L1 ≧ L3 However, L0: mold length, L1: distance from the mold inlet to the position where the solidification shell is generated, L3: drawing stroke Under these conditions, the molten metal solidifies during steady casting. The distance L1 up to the start defines the amount of one withdrawal, that is, the stroke L3 or less, and L1 is 1/2 or less of the length of the mold, so that the solidified shell is sufficiently developed in the mold. It is a condition for.

A fourth aspect of the invention is, in the casting,
It is a horizontal continuous casting method characterized in that the temperature of the molten metal in the tundish (Tt: ° C) is set in the range of the following formula. Tl + 80 ≦ Tt ≦ Tl + 160 (° C.) Here, Tl: liquidus temperature of hypoeutectic cast iron to be cast This condition is an operating condition for more specifically implementing the condition in the third aspect.

A fifth aspect of the invention is a horizontal continuous casting method, wherein the temperature of the molten metal in the tundish is controlled by an induction heating device provided in the tundish. This is because the induction heating device can easily control the temperature of the molten metal.

In a sixth aspect of the invention, in the temperature control, a thermocouple is set in the vicinity of the mold inlet to detect the temperature of the molten metal, the amount of electricity supplied to the induction heating device is controlled, and the temperature of the molten metal is automatically controlled. It is a horizontal continuous casting method.

In a seventh aspect of the invention, during the continuous casting, the length L2 (fs = 0 to
1, fs: solid phase ratio) is controlled within the range of the following formula, which is a horizontal continuous casting method. L2 ≧ L3 where L3: length of drawing stroke solid-liquid coexistence region L2 (fs = 0 to 1, fs: solid phase ratio)
This is because if the temperature is not controlled within the above range, the unsolidified molten metal comes into contact with the mold wall in one stroke, and a sound shell does not develop. Further, it is because the shells do not fuse and repair when broken in the solid-liquid coexisting region.

In an eighth aspect of the invention, in the continuous casting, the drawing stroke L3 is 10 to 45 mm, and the stop time is 5 to 1
It is a horizontal continuous casting method characterized in that it is carried out within a range of 5 seconds. The casting conditions are conditions that specifically define the casting conditions.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An outline of a horizontal continuous casting apparatus for carrying out the present invention is shown in FIG. The tundish 2 holds the molten metal 4 and supplies the molten metal to the mold 8. The temperature control of the molten metal 4 is performed by, for example, a channel type induction heating device 6 as shown in the figure. The induction heating device may be a ring-shaped coil type provided on the side wall instead of the channel type. For example, 6000 kg of molten metal can be stored in the tundish.

The mold 8 is composed of a die 80 having an inner wall approximately equal to the size of a cast piece and a water-cooled jacket 82 for cooling the outer side thereof. As for the material of the die, since the molten metal to be cast is hypoeutectic cast iron, graphite die is not desirable, and ceramics containing nitride is desirable. Examples of ceramics containing nitride include boron nitride (BN), and hexagonal boron nitride (h-BN) is preferable. In the case of a graphite die, the inner wall is coated with a ceramic containing thick nitride.

A so-called secondary cooling zone 10 composed of a water cooling nozzle is provided between the mold outlet and the drawing device. Drawing device 1
Reference numeral 2 includes a pinch roll that controls the drawing speed of the slab 14 and a control device that controls the pinch roll.

The present invention discloses a casting method in the above horizontal continuous casting apparatus. As described above, the molten metal cast in the present invention is intended for hypoeutectic cast iron. Here, hypoeutectic cast iron is
The carbon equivalent (CE = C + Si / 3) is 1.9 to 3.9%, and the other component compositions include Mn of 1.0% or less and the balance Fe and unavoidable. In addition, alloy elements such as Cr, Ni and V may be contained in an amount of 1% or less.

When casting hypoeutectic cast iron, eutectic cast iron having a carbon equivalent (CE) of 3.5 to 4.4% is preferable as the predetermined amount of molten metal component to be initially poured into the tundish at the start of casting. . At the beginning of casting after pouring, the temperature in the mold is in an indefinite state and the temperature distribution is unstable, so the molten liquid with a composition close to that of eutectic cast iron with a narrow range between liquidus temperature and solidus temperature Is desirable.

With such a molten metal, when the temperature falls below a substantially constant temperature, the slab in the mold is wholly solidified, and a slab that withstands the drawing stress is formed at the start of drawing the slab. This is because. The carbon equivalent of the component composition of the molten metal to be poured first is preferably larger than the carbon equivalent of the intended product. For example, when the carbon equivalent of the product is 3.5% or less, the carbon equivalent of the first molten metal to be poured is preferably 3.5 to 4.4%.

When hypoeutectic cast iron is poured from the beginning, a wide solid-liquid coexistence region occurs as is apparent from the iron-carbon binary system phase diagram, and the slab is likely to break at the start of drawing. Therefore, as a countermeasure, when casting is started from cast iron of eutectic composition with a low melting point and an extremely narrow solidification temperature range, and the temperature of the vicinity of the mold reaches a steady state and then transition to casting of the hypoeutectic component, it becomes stable. Can start casting.

It is desirable that the amount of the molten metal initially poured into the tundish be sufficient to fill the mold in which the dami bar is inserted. This amount is of course for filling the mold, for filling the channels in the induction heating device, and for filling the bottom of the tundish.

When performing steady drawing, it is basically important to control the generation position (L1) of the solidified shell tip (fs = 0, fs: solid phase ratio) from the mold inlet within the range of the following formula. is there. 0.5 × L0 ≧ L1 ≧ L3 where L0: mold length, L1: distance from mold inlet to position where solidification shell is generated, L3: drawing stroke

This point will be described with reference to FIGS. Figure 2
Is a die with an inner diameter of 70 mm, carbon equivalent 3.2%, temperature 1
It is the result of heat transfer calculation of the development state of the solidified shell in the case of pouring a molten metal at 410 ° C. and performing steady casting. The solidification start line (fs = 0) and the solidification end line (fs = 1) have a large distance at the center, indicating that the width of the solid-liquid coexisting phase of hypoeutectic cast iron is large. In particular, the die wall has a length of the solid-liquid coexisting phase of about 30 mm, which corresponds to L2.

FIG. 3 schematically shows FIG. 2. A solidified shell is generated in the die 80. The tip of the shell has a solidification rate fs = 0, and the completely solidified portion has fs = 1. is there. In order for a healthy shell to be generated in the mold, the distance L1 from the mold inlet to the position where the solidified shell is generated needs to be constantly in the mold.

If the stroke is short, the tip of the shell may project into the tundish, and the slab will break when pulled out. The condition for avoiding this is L1 ≧ L
It is 3. Further, it is empirically preferable that the position of the tip of the shell is forward of 1/2 in the mold. Therefore,
0.5 × L0 ≧ L1.

More specifically, the above conditions are embodied by controlling the temperature of the molten metal. That is, at the time of casting, it is carried out by setting the temperature of the molten metal in the tundish (Tt: ° C) within the range of the following formula. Tl + 80 ≦ Tt ≦ Tl + 160 (° C.) where Tl: liquidus temperature of the hypoeutectic cast iron to be cast (varies depending on CE value)

In the above temperature control, it is desirable that the temperature of the molten metal is detected by the thermocouple 16 set near the inlet of the mold, the amount of electricity supplied to the induction heating device is controlled, and the heating condition is automatically set. The above liquidus temperature and the above-mentioned solidus temperature can be calculated from the phase diagram of the metal given the component composition of the molten metal.

In order to control the temperature in the tundish as described above, it is desirable to use an induction heating device provided in the tundish (hereinafter abbreviated as TD). This is because the induction heating device can easily control the temperature of the molten metal. The temperature control of the molten metal 4 can be performed by, for example, a channel-type induction heating device 6 as illustrated. The induction heating device may be a ring-shaped coil provided on the side wall instead of the channel type. The capacity of the tundish can accommodate, for example, 6000 kg of molten metal.

Furthermore, in order to continue stable casting, the length L2 (f
It is desirable to control s = 0 to 1, fs: solid phase ratio within the range of the following formula. L2 ≧ L3 where L3: drawing stroke

This point will be described with reference to FIG. FIG. 4 schematically shows the shell formed by pulling out the first formed shell for one stroke. The length of the solidified shell or the length of the solid-liquid coexistence region is L2 (fs = 0 to 1, fs: solid phase ratio). Assuming that the length of one stroke is L3, if the control is not controlled to L2 ≧ L3, the unsolidified molten metal will contact the mold wall and a new shell will develop in one stroke. Otherwise, the development of a healthy shell will be hindered. Further, when a fracture occurs in the solid-liquid coexistence region, it becomes difficult to fuse and repair the slab, which hinders the development of a shell having strength enough to withstand redrawing.

More specifically, in the casting of hypoeutectic cast iron, the drawing stroke L3 is 10 to 45 mm and the stop time is 5 to 1
It is desirable to perform the intermittent drawing in the range of 5 seconds.
The casting conditions embody the above casting conditions.
If the drawing stroke is less than 10 mm, the solidified shell becomes thick within the above stop time, the temperature of the molten metal at the mold inlet is lowered, the fluidity is decreased, and the porosity and the like easily occur in the slab.

If the drawing stroke exceeds 45 mm, the drawing resistance becomes large, the solidified shell does not develop sufficiently in the mold, and the slab tends to break during drawing. On the other hand, if the stop time is less than 5 seconds, the thickness of the shell is thin in the stroke range, and breakout easily occurs.
If the stop time exceeds 15 seconds, the productivity will be poor.

The slab drawn from the mold is water-cooled in the secondary cooling zone to complete solidification. To control the length of the solid-liquid coexisting layer in the mold as short as possible, it is necessary to desirably increase the temperature gradient in the mold longitudinal direction.
It is effective to forcibly cool the slab at the mold outlet to lower the temperature. This has the effect of further increasing the temperature gradient by the combination with the molten metal heating by the induction heating.

Further, in the mold, it also has an effect of promptly forming a shell of a completely solid phase (fs = 1) having high strength,
Great effect. It is most effective to use water as the cooling medium for the secondary cooling. The effect of using a gas having a low cooling capacity such as air as a cooling medium is small.

In order to stably and continuously draw out a slab having a small strength, it is necessary to form a stable solidified shell in the mold to obtain a cast body having at least a strength capable of withstanding the drawing. In the mold, the solidification proceeds steadily,
It is important to control the residence time of the slab in the mold for stable casting.
It is desirable to set 0 to 45 mm and stop time in the range of 5 to 15 seconds.

When the drawing mode is out of this range, for example, when the residence time of the cast slab in the mold is shorter than this, a solidified shell having strength sufficient for drawing cannot be obtained. On the contrary, when the residence time is excessive, a crack is generated and propagates on the surface of the slab to break the slab, or the solidification abnormally progresses, so that the slab cannot be drawn.

As the die of the mold, a mold that does not react with the molten metal, and in this embodiment, boron nitride (BN) is used.

[0039]

EXAMPLES Casting Example 1 Casting was performed under the following conditions.   Slab size: 100 mm diameter   Total casting time: 240 minutes   Total casting amount: 2800 kg, total casting length: 50 m   First molten metal composition: C: 2.6%, Si: 3.3%, CE: 3.7%   First ladle temperature: 1465 ° C   steady state     Composition of molten metal in TD: C: 2.5%, Si: 2.0%, CE: 3.2%     Molten metal temperature in TD: Initial 1350 ℃ (Tl + 135 ℃)                     Terminal 1300 ℃ (Tl + 30 ℃)   Casting result summary: The temperature of the molten metal in the TD is low, and after casting for 240 minutes   The slab broke and the casting was interrupted.

Casting Example 2 Casting was performed under the following conditions.   Slab size: 70 mm diameter   Total casting time: 345 minutes   Total casting amount: 2800 kg, total casting length: 90 m   First molten metal composition: C: 2.6%, Si: 2.6%, CE: 3.5%   First ladle temperature: 1486 ° C   steady state     Composition of molten metal in TD: C: 2.5%, Si: 2.0%, CE: 3.2%     Temperature of molten metal in TD: Initial 1406 ℃ (Tl + 160 ℃)                     Terminal stage 1410 ℃ (Tl + 140 ℃)   Casting result summary: The temperature of the molten metal in the TD is sufficient, and casting is completed as planned until the end.   Finished.

Casting Example 3: Casting was performed under the following conditions.   Slab size: 70 mm diameter   Total casting time: 420 minutes   Total casting amount: 4000 kg, total casting length: 120 m   First molten metal composition: C: 2.7%, Si: 2.5%, CE: 3.5%   First ladle temperature: 1486 ° C   steady state     Composition of molten metal in TD: C: 2.5%, Si: 2.0%, CE: 3.2%     Molten metal temperature in TD: Initial 1410 ℃ (Tl + 160 ℃)                     Terminal stage 1410 ℃ (Tl + 145 ℃)   Casting result summary: Casting was completed as planned until the end.

Other casting conditions Stroke: 20 mm, stop time: 10 seconds Induction heating in TD: 45 ~ 140KW Number of strands: 3 strands Secondary cooling water 540l / Hr / strand

[0043]

As apparent from the above-mentioned embodiment, the present invention can continuously cast hypoeutectic cast iron, which has been difficult to cast continuously in the past. Therefore, it is possible to supply materials for various machine parts at a high yield and at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a horizontal continuous casting apparatus for carrying out the present invention.

FIG. 2 is a diagram showing a development state of a liquidus line and a solidus line by heat transfer calculation when hypoeutectic cast iron is solidified in a mold.

FIG. 3 is a diagram illustrating a position in a mold of a liquidus line generation position L1 when hypoeutectic cast iron is solidified in the mold.

FIG. 4 is a diagram illustrating a relationship between a liquidus line, a solidus line, and a stroke when hypoeutectic cast iron is solidified in a mold.

[Explanation of symbols]

2 Tundish (TD) 4 molten metal 6 induction heating device 8 molds 80 dice 82 Water cooling jacket 10 Secondary cooling zone 12 Drawing device 14 Slab 16 thermocouple

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI B22D 11/128 B22D 11/128 Z 11/16 11/16 B 104 104S 11/20 11/20 A // C22C 37/00 C22C 37/00 Z (72) Inventor Toru Niinuma 2-1, Shiraishi-cho, Kawasaki-ku, Kawasaki, Kanagawa Nippon Foundry Co., Ltd. (72) Masayuki Tsuchiya 1-4-1, Chuo, Wako-shi, Saitama Honda R & D Center (72) Inventor Hiroaki Ueno 1-4-1, Chuo, Wako-shi, Saitama Honda R & D Lab. (72) Inventor Hiroshi Awajitani 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Steel Tube (72) Invention Person Masayuki Nakata 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) Reference JP 2001-276958 (JP, A) JP 2000-280048 (JP, A) JP 63-20140 (J P, A) JP 5-285599 (JP, A) JP 57-91851 (JP, A) JP 62-282752 (JP, A) JP 58-193308 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) B22D 11/04 114 B22D 11/00 B22D 11/045 B22D 11/10 310 B22D 11/11 B22D 11/128 B22D 11/16 B22D 11/16 104 B22D 11/20 C22C 37/00

Claims (8)

(57) [Claims] 1. A tundish, a mold connected thereto,
A method for continuously casting hypoeutectic cast iron in a horizontal continuous casting device equipped with a secondary cooling zone and a drawing device, which casts hypoeutectic cast iron having a carbon equivalent (CE = C + Si / 3) of 3.9% or less. At this time, the carbon equivalent of a predetermined amount of molten metal component to be poured first in the tundish at the start of casting is set in the range of 3.5 to 4.4% to be larger than the carbon equivalent of the hypoeutectic cast iron. Horizontal continuous casting method. 2. The horizontal continuous casting method according to claim 1, wherein the predetermined amount of molten metal initially poured is at least substantially the amount of molten metal that is filled in the mold. 3. In the continuous casting, the generation position (L1) of the solidified shell tip (fs = 0, fs: solid phase ratio) from the mold inlet is controlled within the range of the following formula. The horizontal continuous casting method described in 2. 0.5 × L0 ≧ L1 ≧ L3 However, L0: mold length, L1: distance from the mold inlet to the position of the tip of the solidification shell, L3: drawing stroke 4. The horizontal continuous casting method according to claim 1, wherein the temperature of the molten metal in the tundish (Tt: ° C.) is controlled within the range of the following formula during the continuous casting. Tl + 80 ≦ Tt ≦ Tl + 160 (° C.) where Tl: liquidus temperature of hypoeutectic cast iron to be cast 5. The horizontal continuous casting method according to claim 4, wherein the molten metal temperature in the tundish is controlled by an induction heating device provided in the tundish during the continuous casting. 6. The molten metal temperature in the tundish is controlled by detecting the molten metal temperature with a thermocouple provided in the vicinity of the mold inlet, controlling the energizing amount of the induction heating device, and automatically controlling the molten metal temperature. The horizontal continuous casting method according to claim 4 or 5, characterized in that: 7. The length L2 (fs = 0 to 1, fs: solid phase ratio) of the solid-liquid coexisting region in the mold wall portion is controlled within the range of the following formula during the continuous casting. Three
The horizontal continuous casting method according to any one of 1 to 6. L2 ≧ L3 where L3: drawing stroke 8. The horizontal continuous casting according to any one of claims 1 to 7, wherein the continuous casting is performed with a drawing stroke L3 of 10 to 45 mm and a stop time of 5 to 15 seconds. Method.