KR20120072492A - Casting roll of twin roll strip caster for casting martensitic stainless steel strip and method for casitng martensitic stainless steel strip by twin roll strip caster - Google Patents

Abstract

PURPOSE: A casting roll of a twin roll strip caster for casting martensitic stainless steel strip and a method for casting martensitic stainless steel strip by a twin roll strip caster including the casting roll are provided to solidify molten steel uniformly in a lateral direction by optimally controlling casting variables, including the crown value of casting rolls, the temperature of molten steel, and the amount of cooling water. CONSTITUTION: A casting roll(3) of a twin roll strip caster for casting martensitic stainless steel strip is formed with a crown where C50/E50 is 1.2-1.5. As to C50/E50, E50 is a crown value from an edge to 50mm of the casting roll in the lateral direction and C50 is a crown value from the center to the 50mm point. Molten steel(4) for casting comprises C of 0.1-1.5weight%, Cr of 12-15weight%, Ni of 1weight% or less, and Fe and inevitable impurities of the remaining amount.

Description

MASTENSIONIC STAINLESS STEEL STRIP MARTENSITIC STAINLESS STEEL STRIP AND METHOD FOR CASITNG MARTENSITIC STAINLESS STEEL STRIP BY TWIN ROLL STRIP CASTER}

The present invention relates to a casting roll of a twin roll thin sheet casting machine and a method of casting a thin sheet by a twin roll sheet casting machine including the casting roll, and more particularly to casting a martensitic stainless steel sheet by a twin roll sheet casting machine. The present invention relates to a casting roll, and a method of casting a martensitic stainless steel sheet by a twin roll thin sheet casting machine including the casting roll.

In general, martensitic stainless steel is used in the manufacture of various tools and ceramics because of its excellent corrosion resistance, hardness and abrasion resistance.

In the case of manufacturing such martensitic stainless steel by the continuous casting process, the higher the carbon content, the more severe coarse central segregation is formed in the center of the slab, and the solid-liquid coexistence area is wider, which is weak to castability. After the manufacture of re-heated and hot rolled to produce a hot rolled coil, after the pickling process through the annealing process is cold rolled to produce martensitic stainless steel.

However, even when the ingot casting method is used, coarse central segregation is formed in the slab due to the slow cooling rate, and the central segregation is hardly removed in a subsequent heat treatment process and remains in the hot-rolled steel sheet so that the lamination is performed during the cutting of the strip. It is accompanied by defects, and coarse chromium carbide (chromium carbide) is precipitated at grain boundaries, so that cracks or plate breakage, such as edge cracks, occur in the steel sheet during the post-treatment process.

In order to solve the above problems, techniques for increasing the annealing temperature and maintaining the annealing time for a long time in a batch annealing process (BAF) after hot rolling to employ carbide are known, There is a problem that the production cost is increased, the productivity decreases sharply.

In addition, low-temperature casting and low-speed casting methods have been proposed, but these methods form granular equiaxed structure at the center of cast steel and rapidly form cast solidification layer to reduce central segregation, but the nozzle is clogged during casting and operation is unstable and productivity is reduced. There is a problem.

In addition, there is a problem in that the solidification ability is not uniform in the width direction of the thin plate and bulging occurs in the center of the thin plate surface, and the shape of the cast thin plate is poor because the temperature of the molten steel is kept low.

Therefore, the center segregation and cracks are suppressed during casting, the chromium carbide is finely deposited at the grain boundary, and the casting stability is secured due to the excellent crack resistance, and the technology development for the production of high quality martensitic stainless steel sheet with excellent sheet shape is achieved. This has been requested.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and applies a twin roll thin sheet casting process to martensitic stainless steel sheet casting, and optimally controls casting parameters such as crown value, molten steel temperature and amount of cooling water of the casting roll. Therefore, it is possible to manufacture a thin plate having excellent product shape due to the uniform coagulation ability in the width direction, and to secure casting stability by preventing center segregation and plate breakage during casting, and to form a uniformly distributed microstructure. Martensitic stainless steel sheet by casting roll of twin roll thin sheet casting machine for martensitic stainless steel sheet casting, and twin roll type sheet casting machine including the casting roll, which can produce products with high hardness and high edge quality in the manufacture of tools and tools. The object of the present invention is to provide a method of casting.

In order to achieve the above object, the present invention, in the casting roll of the twin-roll thin plate casting machine for cooling the injected molten steel while the pair rotates in the opposite direction, 50mm in the casting roll width direction from the edge of the casting roll Of double roll type sheet casting machine for casting martensitic stainless steel sheet casting in which the crown is formed so that C50 / E50, which is the ratio of crown value (C50) from the center of the casting roll to the edge of 50 mm to the crown value (E50), is 1.2 to 1.5. Provide a casting roll.

In this case, the molten steel is characterized by being composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, balance Fe and other inevitable impurities added.

Moreover, the said casting roll has the characteristics that the inclination of 50 mm-300 mm point from the edge to the casting roll width direction is 0.00027-0.00032.

In addition, the casting roll is characterized in that the total crown value is 175 ~ 180㎛.

In addition, the molten steel is injected between a pair of casting rolls rotating in the opposite direction while being cooled by the coolant through the immersion nozzle of the tundish to cast martensitic stainless steel sheet, and 50 mm in the casting roll width direction from the edge of the casting roll. Using a casting roll formed with a crown so that C50 / E50, which is the ratio of the crown value (C50) from the center portion of the casting roll to the edge 50mm point to the crown value (E50), is 1.2 to 1.5, the temperature of the molten steel is 1,500 Maintaining at ~ 1,600, the cooling water provides a method for casting martensitic stainless steel sheet by a twin-roll thin plate casting machine characterized in that it is supplied to the casting roll in the range of 12,000 ~ 14,000 lpm.

In this case, the molten steel is characterized by being composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, balance Fe and other inevitable impurities added.

Moreover, the said casting roll has the characteristics that the inclination of 50 mm-300 mm point from the edge to the casting roll width direction is 0.00027-0.00032.

Further, the cast roll is also characterized in that the total crown value is 175 ~ 180㎛.

According to the present invention, a molten steel sheet casting process is applied to martensitic stainless steel sheet casting, and optimally controlling casting parameters such as crown value, molten steel temperature and amount of cooling water of the casting roll, the molten steel is uniform in the width direction. It is possible to manufacture thin plate with excellent product shape by solidifying, to secure casting stability by preventing center segregation and plate break during casting, and to form fine structure evenly distributed in steel to make ceramics and tools. It is possible to manufacture products with high hardness and edge quality at the time of manufacture.

1 is a configuration diagram of a twin roll thin plate casting process.
Figure 2 is a photograph of the crack generation of the martensitic stainless steel sheet during the twin roll sheet metal casting process.
3 is a photo of chromium carbide deposited on the grain boundaries of martensitic stainless steel hot rolled sheet;
Figure 4 is a schematic diagram showing the crown value of the thin plate.
5 is a graph showing the change in thermal expansion of the casting roll according to the casting thickness of the thin plate.
Figure 6 is a photo contrasting the edge microstructure of the austenitic and martensite system.

Hereinafter, the configuration of the present invention with reference to the drawings will be described in detail with reference to the drawings.

In the present invention, the martensitic stainless steel sheet is cast using a twin roll sheet casting machine, and as shown in FIG. 1, a tundish 1 between a pair of casting rolls 3 rotating in the opposite direction while being cooled by a coolant. It is a facility that supplies molten steel (4) through the immersion nozzle (2) of the) and continuously casts a thin product of several mm thickness directly from the molten steel.

That is, the molten steel 4 having a predetermined component injected through the immersion nozzle 2 between the casting rolls 3 cooled while rotating in the opposite direction is solidified to form a solidification shell, which is pressed in the roll and pressed into the thin plate 7. Casting. The thin plate 7 thus cast is guided by a pinch roll 10 and hot rolled by a rolling roll in an inline rolling mill (IRM) 11 and wound by a winder 12 to produce a martensitic stainless steel sheet. Will be.

In the case of manufacturing martensitic stainless steel sheet by conventional continuous casting process or ingot casting method, central segregation is formed to cause linear defects or plate separation, and coarse chromium carbide is precipitated at grain boundaries, as shown in FIG. In the processing process, there was a problem that cracks or plate breaks occurred in the steel sheet. However, when the martensitic stainless steel sheet is cast by the twin roll type sheet casting machine, a squeezing flow is generated while the molten steel near the roll nip is pressed. As the molten steel is extruded (squeezing out) in the section in which solute concentration occurs, not only the central segregation is removed, but also the cooling rate at which the molten steel solidifies is fastened, as shown in the photograph of FIG. Since this is reduced, it is possible to secure casting stability by suppressing center segregation and cracking during casting.

However, as shown in FIG. 7, the austenitic stainless steel sheet has a high carbon as compared with the edge bulging phenomenon in which the surface of the sheet is swelled due to liquid phase remaining in the solidification shell due to insufficient solidification of the edge portion. The martensitic stainless steel sheet containing is cast due to excessive solidification of the edge portion, resulting in excessive solidification, resulting in edge drop rather than edge bulging, and a high heat flux acting on the casting roll during solidification of the high carbon martensitic stainless steel sheet. Since a lot of thermal expansion of the roll occurs, there is a problem that the flatness of the cast thin plate is bad, the shape is poor.

In addition, the demand is required to have a crown value of 30 ± 10㎛ in the final rolled sheet, in order to satisfy this, the crown value of the thin sheet before rolling should be cast to 55㎛ or less in consideration of the rolling rate.

To this end, the casting roll according to the present invention is a high-carbon martensite composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, balance Fe and other unavoidable impurities. The crown value is given in consideration of thermal expansion of the casting roll and oversolidification of the edge part due to the characteristics of the stainless steel sheet. As shown in Figure 5, the crown value in the present invention is the total crown value, C50, E50 will be described later, first, the total crown value is expressed in micrometer (㎛) the depth of the center portion of the roll recessed concave from the horizontal plane C50 is a value representing the length of the concave to the point 50mm away from the center and the edge of the casting roll, E50 is a value representing the length of the concave up to the point 50mm from the edge and the edge of the casting roll.

At this time, the ratio (C50 / E50) of the crown value C50 from the center of the casting roll to the edge 50mm point to the crown value E50 from the edge of the casting roll to the 50mm point in the casting roll width direction is 1.2 to 1.5. If the C50 / E50 is less than 1.2, there is a problem in that the edge solidification of the thin plate edge portion is reduced and the edge portion is formed thick, and if the C50 / E50 exceeds 1.5, the edge drop occurs to enable product release This is because there is a problem that the range of 30 ± 10 μm, which is the crown value of the thin plate, cannot be satisfied.

In addition, the casting roll preferably has a slope of 0.00027 to 0.00032 in the casting roll width direction from the edge of 0.00027 ~ 0.00032, 50mm ~ 300mm away from the edge of the casting roll is a portion of the thermal expansion of the casting roll, the shape of the thin plate This is a position that greatly influences the bar, because if the inclination is lower or higher than the above range to fall outside the proper range, the overall shape of the thin plate to be cast becomes poor.

On the other hand, the martensitic stainless steel sheet containing high carbon has excessive coagulation at the edge, thereby increasing the temperature of the molten steel supplied through the immersion nozzle 2 of the tundish 1 to maintain the coagulation performance in the width direction. Preferably, for this purpose, the temperature of the molten steel supplied through the immersion nozzle 2 of the tundish (1) is to be maintained at 1,500 ~ 1,600 ℃. If the molten steel temperature is less than 1,500 ° C, there is a problem that the number of mixed edges and large cracks of the edge skull increases due to overcoagulation of the edge part. This is because there is a problem in that the casting stability is lowered and the crack sensitivity is increased during casting.

In addition, since the value of the crown of the casting roll depends on the amount of thermal expansion of the casting roll, if the thermal expansion of the casting roll is large, an excessive crown value should be given, so that the amount of cooling water flowing through the inside of the casting roll to cool the water is controlled. There is a need.

As shown in FIG. 6, the lower the casting thickness, the higher the endothermic amount of the casting roll increases as the casting thickness decreases during the casting of the martensitic stainless steel sheet containing high carbon, and thus the thermal expansion of the casting roll is increased. In order not to excessively cast the crown, it is desirable to reduce the thermal expansion of the casting roll by supplying it to the casting roll in the range of 12,000 to 14,000 lpm (liter per minute) corresponding to about 1.5 times the amount of cooling water supplied. Do.

At this time, if the amount of the cooling water is less than 12,000 lpm, it is difficult to control the thermal expansion of the casting rolls, there is a problem that can increase the crown value of the thin plate, if the amount of the cooling water exceeds 14,000 lpm supply excessive cooling water compared to the thermal expansion of the casting rolls This is because the casting quality of the thin plate can be reduced.

Hereinafter, embodiments of the present invention will be described in detail.

Using the casting roll having a crown value shown in Table 1 below, the edge quality was confirmed by the experiment according to the molten steel temperature and the amount of cooling water.

Casting roll D and casting roll E corresponding to the scope of the present invention was confirmed that the edge state is excellent without edge bulging or edge drop, but in the case of casting roll C edge bulging, casting roll F edge drop occurs It was confirmed that the shape of the thin plate was poor.

In addition, in the case of the casting roll A, the edge quality is poor due to the over-solidification of the edge part because the molten steel temperature is low, and in the case of the casting roll G, there is a problem that cracks are generated in the thin plate during casting.

In addition, in the case of the casting roll B, the amount of cooling water was insufficient, and the shape of the cast thin plate was poor due to thermal expansion of the casting roll, and thus the value of the product was very low.

[Table 1]

As a result, the present invention by optimally controlling the casting parameters such as the crown value of the casting roll, the molten steel temperature and the amount of cooling water, so that the molten steel is uniformly solidified in the width direction, it is possible to manufacture a thin plate excellent in product shape, twin roll type By manufacturing in a thin plate casting process, the microstructure uniformly distributed in the steel has high hardness, and excellent edge quality can be secured when manufacturing tools or ceramics.

1: tundish 2: immersion nozzle
3: casting roll 4: molten steel
5: edge dam 6: brush roll
7: thin sheet 8: loop fit
9: meniscus shield 10: pinch roll
11: in-line rolling mill (IRM) 12: winding machine

Claims (8)

In the casting roll of a twin-roll type sheet casting machine for cooling the injected molten steel while the pair rotates in the opposite direction, casting the thin plate,
The crown is set so that C50 / E50 is 1.2 to 1.5, which is the ratio of the crown value C50 from the center of the casting roll to the edge 50mm point to the crown value E50 from the edge of the casting roll to the 50mm point in the casting roll width direction. A cast roll of a double roll type sheet casting machine for forming martensitic stainless steel sheet casting. The method of claim 1,
The molten steel is a martensitic stainless steel sheet casting pair, characterized in that the composition is composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, balance Fe and other inevitable impurities. Casting roll of roll type sheet casting machine. The method according to claim 1 or 2,
The casting roll is a casting roll of a martensitic stainless steel sheet casting twin roll type sheet casting machine, characterized in that the inclination of the 50mm ~ 300mm point in the casting roll width direction from the edge is 0.00027 ~ 0.00032. The method according to claim 1 or 2,
The casting roll is a casting roll of a twin roll thin plate casting machine for martensitic stainless steel sheet casting, characterized in that the total crown value is 175 ~ 180㎛. The molten steel is cast between a pair of casting rolls rotating in the opposite direction while being cooled by the coolant through the immersion nozzle of the tundish to cast martensitic stainless steel sheet,
The crown is set so that C50 / E50 is 1.2 to 1.5, which is the ratio of the crown value C50 from the center of the casting roll to the edge 50mm point to the crown value E50 from the edge of the casting roll to the 50mm point in the casting roll width direction. Using the formed casting roll,
The temperature of the molten steel is maintained at 1,500 ~ 1,600,
The cooling water is cast to the cast roll in the range of 12,000 ~ 14,000 lpm method for casting martensitic stainless steel sheet by a twin roll type sheet casting machine. The method of claim 5,
The molten steel is martensite by twin roll type sheet casting machine, characterized in that it is composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, balance Fe and other unavoidable impurities. How to cast a stainless steel sheet. The method according to claim 5 or 6,
The casting roll is a method for casting a martensitic stainless steel sheet by a twin roll thin plate casting machine, characterized in that the inclination of the 50mm ~ 300mm point in the casting roll width direction from the edge is 0.00027 ~ 0.00032. The method according to claim 5 or 6,
The casting roll is a method of casting a martensitic stainless steel thin plate by a twin roll thin plate casting machine, characterized in that the total crown value is 175 ~ 180㎛.

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