KR101223107B1 - Apparatus for manufacturing martensitic stainless hot rolled steel strip and method for manufacturing martensitic stainless hot rolled steel strip - Google Patents

Abstract

The present invention relates to a rolling roll used in a twin-roll thin sheet casting process and a method for producing a martensitic stainless steel hot rolled sheet using the rolling roll, wherein a molten steel is injected between a pair of casting rolls rotating in opposite directions. In a rolling roll of a hot-rolled inline rolling mill, an initial crown having a shape in which the diameter of the roll end portion is larger than the diameter of the center portion of the roll is processed, and crack-resistant martensitic stainless steel hot rolled by a twin roll type sheet casting process. Injecting molten steel between a rolling roll for thin plate production and a pair of casting rolls rotating in the opposite direction to cast a martensitic stainless steel sheet, and when the cast sheet is rolled in an in-line rolling mill, the diameter of the roll end is equal to that of the roll center portion. The thin plate by using a rolling roll machined initial crown having a shape larger than the diameter Provides a crack resistance martensite-based stainless steel hot-rolled steel sheet manufacturing method of the site including the step of hot rolling to a reduction ratio becomes higher, the edge portion.
According to the present invention, a thin-rolled sheet casting process is applied to the production of a martensitic stainless steel hot rolled sheet, and the rolling ratio of the inline rolling mill is applied to give an initial crown having a heavy double concave to increase the reduction ratio of the sheet edge. By minimizing the concentrated tensile stress, the occurrence frequency and size of edge cracks generated during hot rolling after thin plate casting are greatly reduced to prevent plate breakage, thereby securing casting stability, and forming a uniformly distributed microstructure in the steel. It is possible to manufacture products with high hardness and edge quality when manufacturing fabrics and tools.

Description

Apparatus for manufacturing martensitic stainless steel hot rolled sheet and manufacturing method of martensitic stainless steel hot rolled sheet

The present invention relates to a rolling roll used in a twin roll thin plate casting process and a method for producing a martensitic stainless steel hot rolled sheet using the roll roll, and more particularly, to a crack resistant martensite stainless steel using a twin roll thin plate casting process. A rolling roll for producing a hot rolled sheet and a method for producing a crack resistant martensitic stainless steel rolled sheet using the rolled 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.

Therefore, the development of high quality martensitic stainless steel hot rolled sheet and its manufacturing method have been demanded in which the center segregation and edge cracks are suppressed during casting, and the chromium carbide is finely deposited at the grain boundaries to ensure casting stability due to excellent crack resistance. come.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and applies a twin roll thin plate casting process to the production of martensitic stainless steel hot rolled sheet, and gives an initial crown with heavy concave to the rolling roll of an inline rolling mill to reduce the sheet edge portion. By increasing the rate, the occurrence frequency and size of edge cracks are greatly reduced to prevent sheet breakage, thereby securing casting stability, and forming a uniformly distributed microstructure in the steel, resulting in high hardness when producing ceramics or tools. It is an object of the present invention to provide a rolling roll used in a twin roll thin sheet casting process capable of producing a product having excellent edge quality, and a method for producing a martensitic stainless steel hot rolled sheet using the rolling roll.

In order to achieve the above object, the present invention, in the rolling roll of the in-line rolling mill for hot-rolling the cast sheet by injecting molten steel between a pair of casting rolls rotating in the opposite direction, the diameter of the roll end portion is larger than the diameter of the roll center portion Provided is a rolling roll for producing a crack-resistant martensitic stainless steel hot rolled sheet by a twin roll thin plate casting process, wherein an initial crown having a shape is processed.

At this time, the value of the initial crown is also characterized in that the 80 ~ 150㎛.

In addition, the molten steel is injected between a pair of casting rolls rotating in the opposite direction to cast martensitic stainless steel sheet, and when the cast sheet is rolled in an in-line rolling mill, the diameter of the roll end portion is larger than the diameter of the roll center portion. It provides a method of producing a crack-resistant martensitic stainless steel hot-rolled thin sheet comprising the step of hot rolling to increase the reduction ratio of the edge portion of the thin plate by using a rolling roll processed the initial crown.

Here, the value of the initial crown is also characterized in that the 80 ~ 150㎛.

According to the present invention, a thin-rolled sheet casting process is applied to the production of a martensitic stainless steel hot rolled sheet, and the rolling ratio of the inline rolling mill is applied to give an initial crown having a heavy double concave to increase the reduction ratio of the sheet edge. By minimizing the concentrated tensile stress, the occurrence frequency and size of edge cracks generated during hot rolling after thin plate casting are greatly reduced to prevent plate breakage, thereby securing casting stability, and forming a uniformly distributed microstructure in the steel. It is possible to manufacture products with high hardness and edge quality when manufacturing fabrics and tools.

1 is a configuration diagram of a twin roll thin plate casting process.
2 is a chromium carbide photograph deposited at the grain boundaries of martensitic stainless steel hot rolled sheet;
Figure 3 is a photograph of the crack generation of the martensitic stainless steel sheet during the twin roll sheet metal casting process.
Figure 4 is a photo of crack generation of the edge of the thin plate during hot rolling by the rolling roll of the in-line rolling mill of the twin-roll thin plate casting process
5 is a schematic view showing a rolling state according to the initial shape of the rolling roll when martensitic stainless steel sheet rolling.
Figure 6 is a graph showing the relationship between the initial shape of the rolling roll and the size of the edge cracks according to the present invention.
7 is a graph showing the frequency and frequency of edge crack generation of martensitic stainless steel sheet according to the initial shape of the rolling roll, (a) is the case of Comparative steel 1, the initial crown is not applied, (b) is in the present invention In the case of invention steel 1 to which the initial crown accordingly was applied.

Hereinafter, the martensitic stainless steel hot rolled sheet of the present invention and a method of manufacturing the same will be described in detail with reference to the drawings.

The martensitic stainless steel hot rolled sheet according to the present invention is manufactured using a twin roll thin sheet casting process. As shown in FIG. 1, the twin roll thin sheet casting process is performed between a molten steel 4 between a pair of rotating casting rolls 3. ) Is a facility to continuously manufacture sheet products of several mm thickness directly from the molten steel.

That is, the molten steel 4 having a predetermined component injected through the nozzle 2 between the casting rolls 3 cooled while rotating in the opposite direction is solidified to form a solidification shell, which is pressed down on the roll chuck to form the thin plate 7. Cast. 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.

When manufacturing martensitic stainless steel hot rolled sheet by conventional continuous casting process or ingot casting method, central segregation is formed, linear defects and plate separation occur, coarse chromium carbide precipitates at grain boundary, There was a problem that cracks or plate breakage occurred, but in the case of manufacturing the martensitic stainless steel hot rolled sheet by the twin roll type sheet casting process, a squeezing flow is generated while the molten steel near the roll nip is pressed, so that As the molten steel in the section where the concentration occurs is squeezed out, not only the central segregation is removed but also the cooling speed of solidifying the molten steel is faster, so that the grain size of the grain boundary is reduced and the precipitates of chromium carbide are reduced. By suppressing the casting stability can be secured.

As such, the martensitic stainless steel hot rolled sheet produced by the twin-roll thin plate casting process is removed from the center segregation as compared with the conventional casting method, and as shown in FIG. And plate break is suppressed, but as shown in the photo of Figure 3, the chromium carbide may act as a cause of cracks and plate break during casting should be suppressed as much as possible.

That is, the martensitic stainless steel contains high carbon and has low cracking sensitivity due to low temperature toughness due to the chromium carbide formed at the grain boundary. In particular, as shown in the photograph of FIG. Edge cracks are easily generated at the thin edge of the sheet during hot rolling. This occurs because excessive tensile stress acts on the thin edge of the sheet rather than the center of the thin plate. Therefore, it is necessary to minimize excessive tensile stress on the thin edge of the sheet. It is possible to improve the error rate by preventing cracks by reducing cracks.

To this end, the present invention first performs the step of casting the martensitic stainless steel sheet by injecting molten steel between a pair of casting rolls rotating in the opposite direction.

The cast thin plate 7 performs the step S20 of hot rolling in the in-line rolling mill 11, that is, the cast thin plate 7 is guided by the pinch roll 10 to the in-line rolling mill 11. It is hot rolled by the rolling rolls inside, and it is manufactured from a martensitic stainless steel hot rolled sheet. At this time, when the hot rolling is not applied, since the elongation is not secured and is so brittle that it is difficult to perform the post-process, the hot rolling is essentially performed in the manufacturing method according to the present invention.

At this time, as shown in Figure 5 (b), when rolling the cast thin plate with the rolling roll of the in-line rolling mill 11, the rolling roll has an initial crown having a shape where the diameter of the end of the roll is larger than the diameter of the center of the roll It is characterized by being processed. Here, the initial crown means a crown formed on the rolling roll before rolling.

Martensitic stainless steel sheet containing 0.1 to 1.5% by weight of high carbon has high crack sensitivity due to precipitation of chromium carbide at grain boundaries and high crack sensitivity, and thin edge at hot rolling due to overcoagulation. Edge cracking easily occurs in the part, and since the shape defects of the edge crack and the edge part cannot be controlled only by the control of the rolling conditions of the in-line rolling mill, it is necessary to determine the shape of the rolling roll in advance.

That is, in the twin-roll thin plate casting process, once the casting rolls are used for casting of a plurality of orders, the casting rolls are replaced for repair if a problem occurs on the surface of the casting rolls. Rolling rolls are replaced with new rolling rolls for every casting. If rolling rolls are damaged during casting, they are used online during casting. Therefore, the shape of the casting roll and the shape of the initially formed thin plate is checked at every casting, the shape of the rolling roll to be applied at the next casting is determined, and the appropriate initial crown value predicted for the rolling roll is given to the value. It can be processed and polished to be used for casting, and can be finely processed by using an online processing device (ORG, Online Roll Grinding).

However, since the rolling roll is different from the shape before use because of thermal expansion, wear, etc. during casting, in the present invention, the initial crown is given based on the initial shape of the rolling roll, which is the shape of the rolling roll before rolling. Here, the value of the initial crown means the height from the concave valley of the roll center portion to the roll end portion as shown in FIG. 5 (b).

At this time, as shown in Figure 6, the value of the initial crown is formed in the range of 80 ~ 150㎛ bar frequency of occurrence of edge cracks of the hot rolled sheet is greatly reduced, the size of the edge crack is preferably 60mm or less, If the initial crown value is less than 80 μm, there is a problem that the occurrence rate and size of the edge crack are increased by the tensile stress on the edge portion of the thin plate due to the reduction in the rolling reduction of the edge portion of the thin plate, and the initial crown value is 150 μm. This is because when the excess is exceeded, the flatness of the thin plate becomes poor and its shape becomes poor.

[Example]

The molten steel component injected between the two rolls contains C: 0.67% and Cr: 13.2% by weight, and an appropriate amount of Si and Mn is included therein, and the P and S components were managed to minimize segregation. Then, the molten steel was cast by 100 ton by a twin roll thin plate casting machine with a casting width of 1,300 mm to prepare a thin plate having a martensitic stainless steel thickness of 2.86 mm, and the thin plate was shown in Table 1 below by an inline rolling mill immediately after casting. By rolling under the shape conditions of the rolling roll, a hot rolled sheet having a thickness of 2 mm was continuously manufactured. As a result, the occurrence frequency and average size of the edge cracks shown in the rolled sheet were again shown in Table 1.

[Table 1]

As shown in Table 1, in the case of Comparative Steel 1, in which the initial crown was not processed and rolled into a flat rolling roll, as shown in FIG. 7 (a), the rolling ratio of the thin plate edge was low, and thus the frequency and magnitude of edge cracks. In the case of the invention steel 1 rolled with a rolling roll processed the initial crown according to the present invention, as shown in Figure 7 (b) increased the rolling ratio of the thin plate edge portion is reduced the frequency of the edge crack, the size of the edge crack In addition, the results were reduced to less than 60mm maximum.

In addition, more preferably, in the case of the inventive steels 2 to 4 rolled with a rolling roll having an initial crown value in the range of 80 to 150 μm, the occurrence frequency of the edge cracks and the maximum size of the cracks were further reduced.

However, in the case of the invention steel 5 rolled with a rolling roll applied with an initial crown value of 170 μm, the frequency of occurrence of edge cracks and the maximum size of the cracks were excellent, but the flatness of the hot rolled sheet was worsened due to excessive crown application. There was a rather bad problem.

Thus, the present invention has a high hardness by the microstructure uniformly distributed in the steel by manufacturing a high carbon martensitic stainless steel hot rolled sheet through a twin-roll thin plate casting process, and excellent edge quality when manufacturing tools or ceramics, By giving an initial crown with heavy concave to the rolling roll of the in-line rolling mill to increase the reduction ratio of the thin plate edge part, the tensile stress concentrated on the thin plate edge part is minimized, which greatly increases the occurrence frequency and size of edge cracks generated during hot rolling after sheet casting. It can be reduced to prevent plate breakage and ensure casting stability.

1: tundish 2: 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 (4)

A twin roll type sheet casting machine having a pair of casting rolls rotating in opposite directions, and casting a thin plate from molten steel for martensitic stainless steel production injected between the casting rolls; And
Including an in-line rolling mill having a rolling roll for hot rolling the thin plate,
The rolling roll has martensitic stainless steel sheet, characterized in that the diameter of the end has an initial crown having a shape larger than the diameter of the center portion to secure the reduction ratio of the edge portion of the thin plate. The method of claim 1,
Martensitic stainless steel hot-rolled sheet manufacturing apparatus, characterized in that the value of the initial crown is 80 ~ 150㎛. Casting molten steel between a pair of casting rolls rotating in opposite directions to cast martensitic stainless steel sheets; And
When the cast sheet is rolled in an in-line rolling mill, hot rolling is performed to increase the rolling reduction ratio of the edge portion of the sheet by using a rolling roll having an initial crown having a diameter of an end portion larger than a diameter of a central portion. Method for producing a stainless steel hot rolled sheet. The method of claim 3,
The value of the initial crown is a method for producing a martensitic stainless steel hot rolled sheet, characterized in that 80 ~ 150㎛.

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