JP3152276B2 - Continuous casting method of SUS304 stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for continuously casting SUS304 stainless steel.
The present invention relates to a continuous casting method of SUS304 stainless steel, which is improved by electromagnetic stirring of SUS304 stainless steel molten steel in a mold.

[0002]

2. Description of the Related Art Continuous casting of a slab is carried out by cooling molten steel poured into a mold from a tundish through a dip nozzle, cooling from the surroundings by a mold wall, and drawing the molten steel while forming and developing a solidified shell. At this time, in the mold, the molten steel injected from the tundish flows out from the discharge hole of the immersion nozzle in the width direction of the slab, and the molten steel flow collides with the narrow surface portion of the mold to generate a downward flow. And penetrates deeply into molten steel. According to such a continuous casting method,
It is known that inclusions and bubbles such as argon gas entrained in the downward flow are trapped at the interface of the solidified shell, become inclusion inclusion zones, and are exposed as defects during rolling, causing a problem.

[0003] In particular, recently, the continuous casting speed has been increased and the continuous casting and the rolling process have been directly linked to each other. However, the occurrence of the casting defects has been a major obstacle in implementing them. . The barbed flaws caused by inclusions and pinholes in the stainless steel slab are steelmaking defects generated by trapping them at the solidified shell interface in the mold. As shown in FIG. 6, the degree of superheat ΔT of the molten steel in the mold (mold It tends to decrease as the (internal molten steel temperature−liquidus temperature) increases. In order to increase the degree of superheat ΔT of the molten steel in the mold, it is known to use exothermic mold powder as shown in FIG. 7 or to raise the discharge angle of the immersion nozzle as shown in FIG.

[0004] On the other hand, in order to eliminate the burrs on the rolled product, as shown in FIG.
It is necessary to maintain a temperature of ℃ ° C., and the use of the exothermic mold powder or the increase in the temperature of the upper molten steel due to the upward discharge angle of the immersion nozzle alone is not sufficient because of variations in operation. In the case of an immersion nozzle having a discharge angle upward of 30 °, the molten powder is entrained, which causes surface flaws.

[0005] Even under the condition of superheat ΔT <10 ° C of the molten steel in the mold, electromagnetic stirring of the molten steel in the mold is effective to suppress the occurrence rate of scabs. In other words, if the molten steel in the mold is subjected to electromagnetic stirring to properly apply the molten steel flow to the solidified shell interface growing in the mold, pinholes generated in the surface layer of the slab or interposition captured by the surface layer of the slab Objects are known to be washed away and reduced by the flow of molten steel. However, electromagnetic stirring of the molten steel in the mold has the effect of cleaning the interface of the solidified shell, but there is a problem that if the stirring is too strong, entrainment of the molten powder is likely to occur.

Many proposals have been made for improving the quality of slabs by electromagnetic stirring. For example, two electromagnetic stirring devices are installed facing each other in the vicinity of the meniscus on at least one long side of the mold, and a flow toward the center in the width direction is given to the molten steel in the mold by electromagnetic stirring, and the molten steel flow from the immersion nozzle (Japanese Patent Application Laid-Open No. 57-75270) by reducing the depth of penetration of molten steel into the molten steel in a mold (Japanese Unexamined Patent Publication No. 57-75270). A method of producing a slab of excellent quality by imparting a vertical rotating flow to the inner molten steel to sufficiently generate an isotropic crystal axis (Japanese Patent Application Laid-Open No. 57-75272), at a set position in the height direction. Using a mold equipped with a variable electromagnetic stirrer, the distance h from the meniscus to the center of the motor core of the device was determined such that the relationship of the following equation (1) was substantially satisfied: Of molten steel in mold at position As the flow rate is in the range of 15~40cm / sec, a method of imparting horizontal swirling flow in the molten steel in the mold by the electromagnetic stirring apparatus (JP-A-63-60056). h = １ ／ · V · (D / K) ² (1) where h: distance (m) from the meniscus to the center of the motor core in the casting direction. K: coagulation constant (mm / min ^1/2 ). D: Solidified shell thickness (mm) at a distance of 2 h from the meniscus, and a numerical value in the range of 10 to 30 mm.

[0007]

Problems to be Solved by the Invention
The methods disclosed in Japanese Patent Publication No. 270 and Japanese Patent Application Laid-Open No. 57-75272 are intended to favorably form equiaxed axes in a slab, and do not improve the surface properties of the slab. Further, the method disclosed in Japanese Patent Application Laid-Open No. 63-60056 discloses a method in which the magnetic stirrer is used so that the horizontal flow rate of molten steel in a mold at a position 2 × h from the meniscus is in a range of 15 to 40 cm / sec. A horizontal swirling flow is to be applied to the molten steel in the mold. However, the output of the electromagnetic stirrer is generally represented by a current value. However, even at the same current value, the flow speed varies depending on the mold width, and it is difficult to control the flow speed within the above range.

An object of the present invention is to solve the drawbacks of the prior art, to prevent the surface portion defect of slab in the continuous casting of SUS304 stainless molten steel, it can be completely eliminated the scab flaw occurrence of SUS304 stainless steel plate after rolling SUS304
It is to provide a continuous casting method of stainless steel.

[0009]

Means for Solving the Problems The present inventors have intensively studied and studied to achieve the above object. As a result, the output of electromagnetic stirring in continuous casting is generally represented by a current value. However, even with the same current value, the wider the slab width, the faster the slab is accelerated and the higher the stirring intensity. Therefore, the flow velocity of the horizontal swirling flow of the molten steel in the mold was measured for each slab width, the relationship with the occurrence of scabs was investigated, and it was determined that an appropriate flow velocity range exists for each slab width. did.

[0010] That is, the present invention relates to SUS304 in a mold.
In the method of continuously casting molten stainless steel with electromagnetic stirring, the product V · W of the flow velocity V (cm / sec) of the horizontal swirling flow of the SUS304 stainless molten steel in the mold and the wide surface width W (cm) of the mold is 10 ³ or more and 10 ³ or more. Adjust the applied current to the electromagnetic stirrer so that it is ⁴ (cm ² / sec) or less, and
A continuous casting method of SUS304 stainless steel and controlling the flow rate V of SUS304 stainless molten steel.

[0011]

According to the present invention, the product V · W of the flow velocity V (cm / sec) of the horizontal swirling flow of the SUS304 stainless steel molten steel in the mold and the wide surface width W (cm) of the mold is 10 ³ or more.
^{By controlling the} current applied to the electromagnetic stirrer so as to be ⁴ (cm ² / sec) or less and controlling the flow velocity V of the horizontal swirling flow of the SUS304 stainless steel melt in the mold, the solidified shell interface due to the flow of the molten steel in the mold is formed. The effect of washing and removing trapped inclusions and air bubbles is sufficiently exhibited, and the incorporation of molten powder can be prevented, and there is no occurrence of barbed flaws due to accumulation of inclusions and pinholes on the surface layer of the slab. It can be.

SUS3 in the mold used in the present invention
04 Stainless steel molten steel horizontal swirl flow velocity V (cm / sec)
c) is 200 mm from the narrow surface of the mold, as shown in FIG.
A brick piece was floated at a position near the center and 20 mm away from the wide surface and at the highest flow velocity, and an image obtained by photographing with a high-speed camera was used. In the present invention, the wide surface width W of the mold
(Cm) and the product W of the molten steel flow velocity V (cm / sec) in the mold.
The reason why V was set to 10 ³ or more and 10 ⁴ (cm ² / sec) or less was that the wide surface width W (cm) of the mold and the flow velocity V (cm
/ Sec) is less than 10 ³ (cm ² / sec), the stirring power of the electromagnetic stirrer is too weak to sufficiently remove and remove inclusions and air bubbles from the solidified shell interface, resulting in scorching. On the other hand, if it exceeds 10 ⁴ (cm ² / sec), the stirring power of the electromagnetic stirrer is too strong, and scabs are generated due to the entrainment of the molten powder.

[0013]

EXAMPLES Example 1 Thickness 20 cm, width 100 cm, 125 cm, 150 cm
Using a curved slab continuous casting machine with a curved radius of 15 m having a slab mold, an electromagnetic stirrer was installed on the wide surface of this mold, and a heating powder was used as a mold powder. ΔT <10
Upon continuous casting by injecting SUS30 4 stainless molten steel ° C., by adjusting the applied current to the electromagnetic stirring device in the mold
The flow velocity V of the horizontal swirling flow of SUS304 stainless steel molten steel is 2
SUS304 obtained by continuous casting at a drawing speed of 0.8 m / min while changing in the range of ~ 250 cm / sec.
Hot rolled and cold rolled stainless steel SUS304
A stainless steel plate was used, and the occurrence rate of bark flaws was investigated. The results are shown in FIGS.

As shown in FIG. 1, when the mold width is 100 cm, if the flow velocity V is less than 10 cm / sec and the stirring power is weak, the stirring effect is too weak to wash and remove inclusions and bubbles from the solidified shell interface. Not enough, and scabs are generated. When the flow velocity V exceeds 100 cm / sec,
The agitation force is too strong, and the swarf flaw is generated by the entrainment of the molten powder. On the other hand, when the flow velocity V is 10 to 100 c
In the case of m / sec, there is no generation of barbed flaws in all cases, the agitation effect sufficiently removes inclusions and air bubbles from the interface of the solidified shell, and furthermore, there is no entrainment of molten powder, and the mold width is reduced. Is an appropriate area at 100 cm.

As shown in FIG. 2, when the mold width is 125 cm, the flow velocity V is less than 7 cm / sec. When the stirring power is weak, the stirring effect is too weak to wash out and remove inclusions and bubbles from the solidified shell interface. Is not enough, and scabs are generated. When the flow velocity V exceeds 70 cm / sec,
The agitation force is too strong, and the swarf flaw is generated by the entrainment of the molten powder. On the other hand, the flow velocity V is 7 to 70 cm /
In the case of sec, there is no occurrence of barbed flaws in any case,
It can be said that the agitation effect sufficiently removes inclusions and bubbles from the interface of the solidified shell, removes entrainment of the molten powder, and is an appropriate region with a mold width of 125 cm.

As shown in FIG. 3, when the mold width is 150 cm, when the flow velocity V is less than 6 cm / sec, when the stirring power is weak, the stirring effect is too weak to remove inclusions and bubbles from the solidified shell interface. Is not enough, and scabs are generated. When the flow velocity V exceeds 55 cm / sec,
The agitation force is too strong, and the swarf flaw is generated by the entrainment of the molten powder. On the other hand, the flow velocity V is 6 to 55 cm /
In the case of sec, there is no occurrence of barbed flaws in any case,
It can be said that the agitation effect is sufficient to wash and remove inclusions and air bubbles from the solidified shell interface, and that there is no entrainment of the molten powder, and that the mold width is an appropriate region at 150 cm.

1 to 3, the product W · V (cm ² ) of the mold width W (cm) and the flow velocity V (cm / sec) of the horizontal swirling flow of the SUS304 stainless steel melt in the mold.
/ Sec) and the relationship between the occurrence of barbed flaws are summarized and shown as follows:
As shown in FIG. That is, as shown in FIG. 4, the product W · V of the mold width W (cm) and the flow velocity V (cm / sec) of the horizontal swirling flow of the SUS304 stainless steel melt in the mold.
By controlling the current applied to the electromagnetic stirrer so that the flow rate becomes 10 ³ to 10 ⁴ (cm ² / sec), and controlling the flow velocity V of the horizontal swirling flow of the SUS304 stainless steel molten steel in the mold, the occurrence of barbed flaws is reduced. It can be said that it is possible to have none.

Example 2 Thickness 20 cm, width 100 cm, 125 cm, 150 cm
Using a curved slab continuous casting machine with a curved radius of 15 m having a slab mold, an electromagnetic stirrer was installed on the wide surface of this mold, and a heating powder was used as a mold powder. ΔT <10
Upon continuous casting by injecting SUS30 4 stainless molten steel ° C., by adjusting the applied current to the electromagnetic stirring device in the mold
By controlling the flow velocity V of the horizontal swirling flow of the SUS304 stainless steel molten steel, the product W · V of the mold width W and the flow velocity V should be 10 ³ or more and 10 ⁴ or more.
(Cm ² / sec) or less and the drawing speed is 0.8 m
/ Min, and the obtained SUS304 stainless steel slab was hot-rolled and cold-rolled to form a SUS304 stainless steel plate, and the occurrence of barge defects was investigated. As a result, no burrs were generated on the SUS304 stainless steel sheet after cold rolling.

[0019]

As described above, according to the method of the present invention, the current applied to the electromagnetic stirring device is adjusted according to the width of the mold, and the flow velocity V of the horizontal swirling flow of the SUS304 stainless steel molten steel in the mold and the width W of the mold width W are adjusted. The product V · W should be 10 ³ or more and 10 ⁴ (cm ²
/ Sec) by controlling SUS304
Defects in the surface layer of the stainless steel slab can be prevented, and there is no occurrence of barbed flaws, so that the product yield can be improved.

[Brief description of the drawings]

FIG. 1 is a semilogarithmic graph showing the relationship between the flow velocity V in a mold and the occurrence rate of barbed flaws when the width of a mold is 100 cm in Example 1;

FIG. 2 is a semilogarithmic graph showing the relationship between the flow velocity V (cm / sec) in the mold and the occurrence rate of barbed flaws when the wide surface width of the mold is 125 cm in Example 1.

FIG. 3 is a semilogarithmic graph showing the relationship between the flow velocity in the mold V (cm / sec) and the rate of occurrence of barbed flaws when the wide surface width of the mold is 150 cm in Example 1.

FIG. 4 is a semilogarithmic graph showing the relationship between the wide surface width of the mold, the product W · V (cm ² / sec) of the wide surface width of the mold and the flow velocity in the mold, and the occurrence rate of barbed flaws.

FIG. 5 is an explanatory diagram of a measurement position of a flow velocity V (cm / sec) in a mold according to the present invention.

FIG. 6 is a graph showing the relationship between the degree of superheat ΔT of molten steel in a mold and the rate of occurrence of barbed flaws.

Fig. 7 Powder type and degree of superheat Δ of molten steel in tundish
4 is a graph showing the relationship between T and the degree of superheat ΔT of molten steel in a mold.

FIG. 8 is a graph showing a relationship between a discharge angle of a submerged nozzle, a superheat degree ΔT of molten steel in a tundish, and a superheat degree ΔT of molten steel in a mold.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-60056 (JP, A) JP-A-59-33060 (JP, A) JP-A-8-52545 (JP, A) JP-A-59-525 104258 (JP, A) JP-A-57-75272 (JP, A) JP-A-57-75270 (JP, A) JP-A-7-290214 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) B22D 11/115 B22D 11/00 B22D 11/04 311

Claims (1)

(57) [Claims] 1. A template in SUS304 stainless molten steel in a method of continuous casting with electromagnetic stirring in the mold SUS
Flow velocity V (cm / s) of horizontal swirling flow of 304 stainless molten steel
ec) and the wide surface width W (cm) of the mold, V · W, is 10 ³
SUS3 characterized in that the current applied to the electromagnetic stirrer is adjusted so as to be 10 ⁴ (cm ² / sec) or less and the flow velocity V of the SUS304 stainless steel molten steel in the mold is controlled.
04 Stainless steel continuous casting method.