KR101286213B1 - Twin roll strip casting process of martensitic stainless strip and twin roll strip casting apparatus of martensitic stainless strip - Google Patents

Abstract

The present invention relates to a method for casting a martensitic stainless steel sheet by a twin roll thin plate casting method, injecting molten steel between two casting rolls rotating in a opposite direction from a tundish to cast a martensitic stainless steel sheet, The molten steel temperature of the tundish is 1520 ~ 1560 ℃, provides a casting method of martensitic stainless steel sheet is suppressed plate generation occurs, characterized in that the rolling reduction is maintained at 2 to 10 tons.
According to the present invention, the martensitic stainless steel sheet is cast by a twin roll type sheet casting process, and the molten steel temperature of the tundish and the rolling force of the casting roll are controlled under optimum conditions, thereby preventing center segregation, cracking, and plate breaking during casting. By securing the casting stability and greatly reducing the variation in the casting thickness can produce a product with high hardness and high quality when producing ceramics or tools.

Description

Casting method of martensitic stainless steel sheet and casting apparatus of martensitic stainless steel sheet {TWIN ROLL STRIP CASTING PROCESS OF MARTENSITIC STAINLESS STRIP AND TWIN ROLL STRIP CASTING APPARATUS OF MARTENSITIC STAINLESS STRIP}

The present invention relates to a method for producing martensitic stainless steel sheet by twin roll type sheet casting process, and more particularly, to prevent the center segregation, cracks and plate breakage during casting to ensure casting stability, high hardness and high quality The present invention relates to a method for casting martensitic stainless steel sheets in which plate breaking generation, which enables excellent product manufacturing, is suppressed.

In general, martensitic stainless steel is used for manufacturing various tools and ceramics because of its excellent corrosion resistance, hardness, and abrasion resistance.The slab is manufactured by continuous casting process or ingot, and then reheated and hot rolled. In the rolled state, the steel structure is present in a mixture of martensite phase, tempered martensite phase, ferrite phase and residual austenite phase. The hot rolled steel sheet is transformed into ferrite and carbide through a batch annealing process, softened, and subjected to a pickling process to remove scale, and then the soft material is cold rolled or processed into a product, followed by a heat treatment process of final demand. Through the transformation to martensitic stainless steel.

Here, in the case of manufacturing martensitic stainless steel by the continuous casting process, the higher the amount of carbon added, the more coarse central segregation is formed in the center of the slab, and the solid-liquid coexistence area is wider. After the slab is manufactured, it is reheated and hot rolled to produce a hot rolled coil, followed by an annealing process, and then cold rolled to produce martensitic stainless steel.

However, in the case of using the above-described ingot casting method, coarse center segregation is formed in the slab due to the slow cooling rate, and the center segregation is not easily removed in the subsequent heat treatment process, and thus the lamination defect is generated during the cutting of the strip. Accompanying, coarse primary chromium carbide (chromium carbide) is precipitated at the grain boundary and cracks or plate breakages 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 crystal structure at the center of cast steel and form solidification layer quickly, reducing central segregation. There is a problem that productivity is lowered.

Therefore, there has been a demand for development of high quality martensitic stainless steel and a method of manufacturing the same, in which the center segregation is suppressed during casting and cracking and sheet breaking are prevented to ensure casting stability.

The present invention has been made to solve the above problems, by casting a martensitic stainless steel sheet by a twin-roll thin plate casting process, by controlling the molten steel temperature of the tundish and the rolling force of the casting roll to the optimum conditions, Marten, which ensures casting stability by preventing center segregation, cracks, and plate breakage, and greatly reduces the variation in casting thickness, thereby suppressing plate breakage, which enables the production of high hardness and high-quality products in the manufacture of ceramics and tools. An object of the present invention is to provide a casting method of a sight-based stainless steel sheet.

In order to achieve the above object, the present invention injects molten steel between two casting rolls rotating in the opposite direction from the tundish to cast martensitic stainless steel sheets, and the molten steel temperature of the tundish is 1520 to 1560 ° C., the casting roll. It provides a casting method of martensitic stainless steel sheet is suppressed plate generation occurs, characterized in that the reduction force of 2 to 10 tons.

At this time, the molten steel in the weight% C: 0.1 ~ 1.5%, Cr: 12 ~ 15%, Ni: 1% or less, Ti: 0.005 ~ 0.1%, the balance Fe and other unavoidable impurities also There is a characteristic.

In addition, the molten steel is also characterized in that Mo: 0.005 to 0.1%, V: 0.005 to 1.0% is further added alone or in combination to the molten steel.

In addition, the cast thin plate is characterized in that the number of mixing of the skull per 100 ton coil is 40 or less.

Furthermore, there is a feature in that the variation in the casting thickness of the cast thin plate is 70 μm or less.

According to the present invention, the martensitic stainless steel sheet is cast by a twin roll type sheet casting process, and the molten steel temperature of the tundish and the rolling force of the casting roll are controlled under optimum conditions, thereby preventing center segregation, cracking, and plate breaking during casting. By securing the casting stability and greatly reducing the variation in the casting thickness can produce a product with high hardness and high quality when producing ceramics or tools.

1 is a schematic diagram of a twin roll sheet metal casting process;
Figure 2 is a plate breaking picture by the skull of the martensitic stainless steel sheet during casting.
Figure 3 is a plate breaking picture generated along the horizontal pattern of the martensitic stainless steel sheet during casting.
4 is a photograph of primary chromium carbide deposited on the grain boundaries of martensitic stainless steel sheet;
5 is a graph showing the relationship between the tundish molten steel temperature and the skull mixing and large cracks in the present invention.
6 is a graph showing an example of casting data relating to variation in casting thickness variation in the rolling force of the casting roll in the present invention.
Figure 7 is a graph showing the variation of the thickness of the casting according to the rolling force of the casting roll in the present invention.

Hereinafter, a method of casting a martensitic stainless steel sheet according to the present invention will be described in detail with reference to the accompanying drawings.

The present invention casts martensitic stainless steel sheet by a twin roll type sheet casting process, and by controlling the molten steel temperature of the tundish and the rolling force of the casting roll to the optimum conditions, to prevent the center segregation, cracks and plate breakage during casting It is characterized by ensuring stability and greatly reducing the variation in casting thickness to produce ceramics and tools having high hardness and excellent quality.

The method of casting martensitic stainless steel sheet in which plate breakage is suppressed according to the present invention is manufactured by using the twin roll thin plate casting process of FIG. 1, and the twin roll thin plate casting process is a molten steel housed in the tundish 1. (4) is supplied to a pair of casting rolls (3) rotating in the opposite direction through the lower immersion nozzle (2) and is a facility for continuously producing a sheet product of several mm thickness directly from the molten steel.

That is, molten steel having a predetermined component injected through the immersion nozzle 2 is solidified between the pair of casting rolls 3 cooled while rotating in the opposite direction to form a solidification shell, which is pressed in the roll and pressed into the thin plate 7. Is generated. The thin plate 7 thus produced is guided by the pinch roll 10 and rolled by the rolling roll of the in-line rolling mill 11 to produce a martensitic stainless steel sheet.

When martensitic stainless steel sheet is cast by a conventional continuous casting process or ingot casting method, central segregation may be formed and linear defects or plate-like separation may occur, and coarse primary chromium carbide is deposited at the grain boundary to post-treatment process. There was a problem that cracks or plate breaks occurred in the steel sheet, but when casting the martensitic stainless steel sheet by the twin roll type sheet casting process, a squeezing flow occurs when the molten steel near the roll nip is pressed. The molten steel in the section where solute concentration occurs is extruded (squeezing out) to remove the center segregation, and the cooling rate at which the molten steel solidifies is fast, so that the grain size of the grain boundary is refined and the precipitate of primary chromium carbide is reduced. Segregation and cracks can be suppressed to ensure casting stability.

In this way, the martensitic stainless steel sheet produced by the twin roll type sheet casting process is removed from the center segregation compared to the conventional casting method, and finely precipitated primary chromium carbide at the grain boundary as shown in FIG. However, even if a twin-roll thin sheet casting process is applied, as shown in the photographs of FIGS. 2 and 3, the current generated in the molten metal or the lower portion of the edge dam 5 during casting is mixed in the slab and overcoagulated in the thin plate edge portion. As a result, an edge skull is formed, and when a horizontal pattern is formed on a thin plate, plate breaking occurs.

This edge skull is closely related to the molten steel temperature of the tundish 1, which will be described in detail with reference to the following Examples.

The molten steel component of the tundish contains C: 0.65% and Cr: 13.2% by weight, and an appropriate amount of Si and Mn components is included therein, and the P and S components are managed to minimize segregation. Then, the cast width of 1,300mm, casting thickness of 2.86mm, the molten steel was cast by 100 ton by twin roll type sheet casting machine to produce martensitic stainless steel sheet, the sheet was rolled by an in-line rolling mill after the main structure about 2mm It was continuously produced with a hot rolled coil of thickness.

As a result, as shown in FIG. 5, the higher the molten steel temperature of the tundish is, the more the number of edge skulls and the number of large cracks having a size of 20 mm or more decrease, so that the molten steel temperature of the tundish is preferably maintained at 1,520 ° C. or more. Do. However, when the molten steel temperature of the tundish exceeds 1,560 ° C., the number of mixed edges of the skull decreases but not only the number of large cracks increases, but also the high temperature toughness lowers the crack sensitivity during casting, thereby decreasing casting stability. , The molten steel temperature of the tundish in the present invention is preferably maintained at 1,520 ~ 1,560 ℃. Of course, if the edge skull is reduced according to the operating conditions of the edge dam 5, the molten steel temperature of the tundish may be kept lower.

In addition, Figure 6 is a graph showing the change in the roll thickness (RSF, Roll Separation Force) and the casting thickness (mm) of the thin plate according to the casting time (seconds) of the horizontal axis in the 20 tons section and the 8 tons section In the graphs related to RSF, red and blue are the reduction forces of the drive side (DS) and the work side (WS), respectively, and in the graphs related to the casting thickness of the sheet, red and blue are the reduction rates as the thickness hunting. When rolling at 30%, the thickness before rolling and the thickness after rolling are respectively shown.

In general, 304 stainless steel is less likely to break due to the change in the rolling force of the casting roll. However, in the case of martensitic stainless steel, the brittleness is very strong due to the high carbon. As shown in FIG. 6, the variation in the reduction force (variation of the reduction force) is large in the reduction force of 20 tons, and the deviation of the reduction force in the reduction force of 8 tons, as shown in FIG. 6. It can be seen that is small, according to the variation in casting thickness (red and blue deviations in each graph of red and blue) is also reduced to less than 70㎛ within 200㎛, thus reducing the rolling force of the casting roll It can be seen that as the thickness of the casting thickness of the thin plate decreases.

As such, when the rolling force of the casting roll is reduced, the variation of the casting roll pressing force is reduced, and thus the variation of the casting thickness is also reduced, so that the generated horizontal pattern is blurred, thereby reducing the possibility of cracks or plate breakage. do.

And, Figure 7 is a graph showing the deviation of the casting thickness according to the pressing force of the casting roll, when the rolling pressure of the casting roll exceeds 10 tons, the deviation of the casting thickness is large, so that the horizontal pattern is severely generated, accordingly The occurrence of plate breakage is increased, and the horizontal pattern generated when the pressing force is 20 tons, and the photo of the plate breakage are shown in FIG. 3.

On the other hand, the molten steel injected from the tundish between a pair of casting rolls in weight% C: 0.1 ~ 1.5%, Cr: 12 ~ 15%, Ni: 1% or less, Ti: 0.005 ~ 0.1%, balance Fe and other unavoidable It is preferable to be composed of impurities to be added. At this time, Mo: 0.005 ~ 0.1%, V: 0.005 ~ 1.0% by weight may be further added alone or in combination.

The reason for limiting the composition range of the above-mentioned components is as follows.

The C is a very effective element for improving the hardness of stainless steel, when the content of C is less than 0.1% by weight, the hardness required for the martensitic stainless steel sheet cannot be secured, and when the content of C exceeds 1.5% by weight, it is relatively coarse. Since the formation of primary chromium carbide increases the crack sensitivity and reduces the corrosion resistance, the content of C is limited to 0.1 to 1.5% by weight.

The Cr is added to improve the corrosion resistance, when the content of Cr is less than 12% by weight, the effect of improving the corrosion resistance is insignificant, and when the content of Cr is more than 15% by weight, the corrosion resistance is improved, but the strength is high and the elongation is low, the workability is reduced. And because the cost is relatively high, the Cr content is limited to 12 to 15% by weight.

When Ni is added as a gamma (γ) phase generating element, the γ phase increases, and when the coil is air-cooled after hot rolling, martensite phase is promoted to increase strength and hardness, while elongation decreases. It is preferable to limit it to 1 weight% or less.

As Ti is a grain boundary strengthening element, the primary chromium carbide of the grain boundary is segmented or finely precipitated to suppress cracking and delamination. When the Ti content is less than 0.005% by weight, the effect of inhibiting cracking and delamination of the steel sheet is insignificant. If the content of Ti exceeds 0.1% by weight, the clogging phenomenon of clogging of the stopper of the tundish due to the Ti-based oxide occurs, which causes problems in casting. Therefore, the content of Ti is 0.005 to 0.1% by weight. It is limited.

The Mo and V may be contained alone or in combination, and the content of Mo and V is preferably 0.005% by weight or more for strengthening the grain boundary and improving the corrosion resistance. However, since the toughness is lowered when the content exceeds 0.1% by weight, the content of Mo and V is 0.005. It is limited to 0.1 weight%.

As described above, the present invention utilizes a twin roll thin plate casting process, controls the molten steel temperature of the tundish and the rolling force of the casting roll to an optimum condition to cast the martensitic stainless steel sheet, and rolls the thin plate in the in-line rolling mill 11. To produce martensitic stainless steel hot rolled steel sheet, and in some cases, the annealing of the hot rolled steel sheet followed by cold rolling to form martensitic stainless steel cold rolled steel sheet to form fine structure uniformly distributed in steel It is possible to manufacture products with high hardness and edge quality when manufacturing articles or tools.

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: Inline Rolling Mill (IRM)

Claims (5)

The molten steel contained in the tundish is injected between two casting rolls rotating in opposite directions to cast martensitic stainless steel sheets,
The molten steel is composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, Ti: 0.005 to 0.1%, balance Fe, and other unavoidable impurities.
The temperature of the molten steel is 1520 ~ 1560 ℃, the casting method of the martensitic stainless steel sheet, characterized in that the rolling reduction is maintained at 2 to 10 tons. delete The method of claim 1,
Mo: 0.005 ~ 0.1%, V: 0.005 ~ 1.0% by weight or added to the molten steel, the casting method of martensitic stainless steel sheet, characterized in that it is further added alone or in combination. A tundish for receiving molten steel and a pair of casting rolls rotating in the opposite direction, and an immersion nozzle for supplying the molten steel between the casting rolls,
The molten steel is composed of C: 0.1 to 1.5% by weight, Cr: 12 to 15%, Ni: 1% or less, Ti: 0.005 to 0.1%, balance Fe, and other unavoidable impurities.
The temperature of the molten steel is 1520 ~ 1560 ℃, the casting device of the martensitic stainless steel sheet, characterized in that the rolling reduction force is 2 to 10 tons. delete

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