KR101647209B1 - Method for manufacturing thin martensitic stainless steel sheet using strip caster with twin roll and thin martensitic stainless steel sheet produced uising the same - Google Patents

Abstract

The present invention relates to a method for producing a martensitic stainless steel sheet using a twin roll type thin sheet casting machine and a martensitic stainless steel sheet produced by the method.
An embodiment of the present invention is a method for producing a martensitic stainless steel thin plate by casting a thin piece of cast steel using a thin plate casting machine including a pair of rotating thin casting rolls and hot rolling the cast piece, A method of manufacturing a martensitic stainless steel sheet using the twin roll type sheet metal casting machine and a martensitic stainless steel sheet produced by the method are provided .
(a) Bender volume of rolling roll: 30 to 500 kN
(b) Crown size of rolling roll: 50 to 250 탆

Description

TECHNICAL FIELD The present invention relates to a method for producing a martensitic stainless steel thin plate using a twin roll type thin plate casting machine and a martensitic stainless steel thin plate produced by the method and a martensitic stainless steel thin plate produced by the method. SAME}

The present invention relates to a method for producing a martensitic stainless steel sheet using a twin roll type thin sheet casting machine and a martensitic stainless steel sheet produced by the method.

Martensitic stainless steel has excellent corrosion resistance, hardness and abrasion resistance, and is used for various kinds of materials such as razor blades, medical knives, general esophagus and scissors. In general martensitic stainless steels, molten steel is continuously cast or slabs are prepared by ingot, and then reheated and hot-rolled. In the hot-rolled state, the steel structure is martensite phase, tempered martensite phase, ferrite phase, retained austenite And so on. The hot-rolled coil is transformed into a ferrite and a carbide by a batch annealing process for the purpose of annealing the hot-rolled sheet and softened. The soft material by hot-rolling annealing is subjected to a pickling process for removing scale formed during hot- After pickling, the soft material is transformed into martensitic steel after cold rolling or product processing and the final demand is subjected to heat treatment process.

The higher the degree of hardness is, the higher the hardness is required. The higher hardness level is realized by the martensite base structure of the steel. The martensite structure is a very light microstructure that is produced when the hot austenite is rapidly cooled. The higher the content of carbon solved in the austenite phase at high temperature, the more carbon atoms are dissolved in the martensite and the higher the martensite hardness. Therefore, in order to produce a martensitic stainless steel having high hardness, it is necessary to add as much carbon as possible to steel.

However, in order to produce such a martensitic steel, the carbon content must be increased, but in this case, segregation occurs severely, and the high-coexistence region becomes high. In addition, as in Patent Documents 1 and 2, ingot casting is mainly used for casting martensitic steels. However, in the case of the ingot casting method, coarse precipitates formed at the grain boundaries due to a slow cooling rate, Which causes a lot of difficulties. In order to solve this problem, a strip casting process is used instead of the above-mentioned ingot casting process. In this case, center segregation is suppressed and chromium carbide precipitation is reduced in the initial grain boundaries, thereby achieving quality improvement.

In general, in the thin plate casting method, molten steel 1 subjected to a refining process is received in a ladle 2, the molten steel 1 is introduced into a tundish 3, and the molten steel 1 is introduced through the immersion nozzle 4 1 is fed into a sump which is a space formed by the thin sheet casting roll 5 and the edge dam 6 and then the molten steel is passed between the thin sheet casting rolls 5 to manufacture the thin piece 7. At this time, a meniscus shield (8) is provided on the upper part of the thin casting roll (5) to prevent oxidation of the molten steel, and a suitable gas is injected into the sump to maintain a proper atmosphere. The thin strip piece 7 which is manufactured while exiting the roll nip 9 where the thin strip casting roll 5 meets is rolled through the rolling roll 10 and then cooled and wound in the winding equipment 11 And is manufactured as a thin steel plate.

At this time, an important technique in the twin roll type thin sheet casting process for directly manufacturing thin steel plates having a thickness of 10 mm or less from molten steel is to supply molten steel through an immersion nozzle between inner water-cooled twin rolls rotating at a high speed in the opposite direction, So that the thin plate is free from cracks and the rate of water loss is improved.

Furthermore, in order to manufacture a high-martensitic stainless steel having high brittleness by applying such a twin roll thin sheet casting process, casting technology is important, but it is more important to reduce edge cracks generated in hot rolling, It is necessary to develop an economical casting method capable of improving the edge quality by minimizing the tensile stress that induces the tensile stress.

EP 1238118 EP 1739199

The present invention relates to a method for producing a martensitic stainless steel thin plate by using a twin roll type thin plate casting machine and a hot rolling roll, To provide a martensitic stainless steel thin plate produced by the method.

An embodiment of the present invention is a method for producing a martensitic stainless steel thin plate by casting a thin piece of cast steel using a thin plate casting machine including a pair of rotating thin casting rolls and hot rolling the cast piece, The method of manufacturing a martensitic stainless steel sheet using the twin roll type sheet metal casting machine is characterized in that at least one of the conditions (a) and (b) is satisfied.

(a) Bender volume of rolling roll: 30 to 500 kN

(b) Crown size of rolling roll: 50 to 250 탆

In another embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: 0.3 to 0.8% of C, 12.0 to 16.0% of Cr, 0.2 to 1.0% of Si, 0.2 to 1.0% of Mn, 0.2 to 1.0% 0.1%, P: not more than 0.03%, and S: not more than 0.03%, the balance being Fe and other unavoidable impurities, and having an edge crack of 30 mm or less.

According to the present invention, in producing a martensitic stainless steel sheet by using a thin sheet casting machine, it is possible to effectively reduce the occurrence of edge cracks which are likely to occur during hot rolling, and thus a martensitic stainless steel sheet having excellent edge quality can be manufactured.

1 is a schematic view schematically showing a twin roll type thin plate casting method.
Fig. 2 schematically shows a state in which a hoop piece is rolled.
FIG. 3 is a photograph of Example 3 of the present invention. FIG.
4 is a photograph of Comparative Example 3 which is outside the scope of the present invention.

An embodiment of the present invention is a method for producing a martensitic stainless steel thin plate by casting a thin piece of cast steel using a thin plate casting machine including a pair of rotating thin casting rolls and hot rolling the cast piece, The method of manufacturing a martensitic stainless steel sheet using the twin roll type sheet metal casting machine is characterized in that at least one of the conditions (a) and (b) is satisfied.

(a) Bender volume of rolling roll: 30 to 500 kN

(b) Crown size of rolling roll: 50 to 250 탆

1, a molten steel 1 subjected to a refining process is received in a ladle 2, and the molten steel 1 is placed in a tundish (not shown) 3 and then the molten steel 1 is supplied through the immersion nozzle 4 to the sump which is a space formed by the thin plate casting roll 5 and the edge dam 6, The thin strip piece 7 thus produced is hot-rolled by a rolling roll 10 and then subjected to a cooling process and wound around the winding equipment 11 to form a thin steel strip 7, .

One of the main reasons for increasing the defective ratio in the casting of the martensitic stainless steel using the twin roll type thin plate casting method is edge quality deterioration due to edge cracks. The martensitic steel has a disadvantage that cracking sensitivity is high due to low temperature toughness due to generation of intergranular carbides by high carbon. Therefore, an edge crack easily occurs in the process of rolling a cast product produced by the thin sheet casting method, and when the shape of the cast steel is controlled or when it is wound in a coil form, the crack is enlarged due to the tension applied between the rolling mill and the take- .

The cause of the edge cracks is the discrepancy of the shape of the foil strip, the skull due to the subcooling now locally before rolling, and the rolling conditions. . Usually, the rolling roll used for hot rolling includes a bender for controlling the amount of bending change of the rolling roll. In general, when the bender amount of the bender is reduced, the edge reduction rate of the thin strip is increased, and when the bender amount is increased, the reduction ratio of the edge is decreased.

FIG. 2 is a view schematically showing a state in which a foil strip is rolled. In the present invention, the foil is uniformly rolled in the width direction according to the crown of the foil strip as shown in FIG. 2 through control of the bender amount. More specifically, the amount of bend of the rolling roll during hot rolling is controlled to 30 to 500 kN. If the bender amount is less than 30 kN, the reduction rate applied to the edge portion becomes excessively high to cause an edge wave or warp to cause unstable rolling control. When the bender amount exceeds 500 kN, a small reduction rate is applied to the edge portion, Since the length of the edge portion is less than that of the center portion, tensile stress is generated in the edge portion at the time of rolling, and an edge crack is easily generated. Therefore, the bender amount of the rolling roll suggested in the present invention is preferably in the range of 30 to 500 kN, and more preferably in the range of 30 to 300 kN in order to realize good edge quality through reduction of the edge crack. Even more preferably, it is advantageous to have a range of 30 to 150 kN, and most preferably to have a range of 30 to 100 kN. On the other hand, the above-mentioned edge wave means that the edge portion has a longer wave shape as a result of a high reduction rate applied to the edge portion, as compared with the center portion. The difference in the reduction rate applied between the two edges means that there is a difference in the rolling speed between both edge portions.

Alternatively, it is preferable to control the crown size of the rolling roll to be in the range of 50 to 250 mu m in order to secure a good edge quality by causing a uniform reduction rate to be applied to the center portion and the edge portion of the thin stripper. If the crown size of the rolling roll is less than 50 탆, edge cracks may easily occur, which may cause a decrease in the yield rate. If the crown size exceeds 250 탆, problems such as casting stoppage may occur due to edge wave or twist. Lt; / RTI > The crown size of the above-mentioned rolling roll means the height difference (h) between the edge of the thin strip and the center (see Fig. 2). Therefore, the crown size of the rolling roll suggested in the present invention is preferably in the range of 50 to 250 mu m, and more preferably in the range of 50 to 200 mu m in order to realize good edge quality. Even more preferably, it is advantageous to have a range of 50 to 150 mu m, and most advantageously to have a range of 50 to 100 mu m.

On the other hand, the present invention is not particularly limited as far as the alloy composition of the stainless steel thin plate has a martensitic microstructure. However, in order to realize a more preferable effect, it is preferable that 0.3 to 0.8% of C, 12.0 to 16.0 0.2 to 1.0% of Si, 0.2 to 1.0% of Mn, 0.2 to 1.0% of Ni, 0.01 to 0.1% of N, 0.03% or less of P and 0.03% or less of S and the balance Fe and other inevitable It is preferable that it is made of an impurity. Hereinafter, the alloy composition proposed by the present invention will be described.

C: 0.3 to 0.8%

Carbon (C) is an element which increases the hardness of martensitic stainless steel. It is preferable that carbon (C) is contained in an amount of 0.3% or more to secure a hardness of 600 Hv or more required for razor blade steel. As the content of the carbon increases, the hardness of the martensite generated by the heat treatment increases, but the amount of the carbide precipitates increases, and the corrosion resistance and the cold workability decrease, so that the carbon content is preferably 0.8% or less.

Cr: 12.0 to 16.0%

Chromium (Cr) is an element added for improving the corrosion resistance in the martensitic stainless steel. When the chromium content of the matrix is 12% or more, the chromium oxide film is densely formed to improve the corrosion resistance. In addition, it is more preferable that the Cr is added in an amount of 12.5% or more in order to improve the corrosion resistance due to the formation of the chromium oxide film by preventing a large amount of carbides from being formed to lower the known chromium content. However, when it exceeds 16%, the corrosion resistance is improved, but the hardness of the martensite produced by the heat treatment is lowered, so that it is preferable that the range is 16% or less.

Si: 0.2 to 1.0%

Silicon (Si) is an element to be added for deoxidation. When it is 0.2% or less, it is difficult to sufficiently obtain the deoxidation effect. However, when it exceeds 1.0%, the cold workability is remarkably lowered, and therefore, it is preferable that the range is 1.0% or less.

Mn: 0.2 to 1.0%

Manganese (Mn) is an element added for the purpose of deoxidation and nitrogen solubility. When the Mn content is 0.2% or less, the deoxidation effect is not sufficient. Therefore, the Mn content is preferably 0.2% or more. However, when it exceeds 1.0%, the corrosion resistance is deteriorated, and therefore, it is preferable that the range is 1.0% or less.

Ni: 0.2 to 1.0%

Nickel (Ni) is an element which is added to martensitic stainless steel to improve the corrosion resistance of the base material without forming carbide. In order to sufficiently obtain the above-mentioned corrosion resistance, it is preferable to add at least 0.2%. However, if it exceeds 1.0%, the formation of retained austenite becomes excessive after the tempering heat treatment, and high hardness can not be obtained. The conventional martensitic stainless steel has a disadvantage in that the corrosion resistance of the martensite structure after the strengthening heat treatment largely changes depending on the austenitization temperature and time conditions during the strengthening heat treatment. However, the 0.2 to 1.0% The addition of Ni in this formulation complements these drawbacks and has the effect of improving local corrosion, especially pitting and crevice corrosion.

N: 0.01 to 0.1%

Nitrogen (N) is an element added to increase hardness by strengthening heat treatment and improve resistance to pitting and crevice corrosion. In order to obtain the above effect, it is preferable to add at least 0.01%. When it exceeds 0.1%, nitrogen bubbles are generated at the time of casting to generate pores and pinholes, so that the content of N is preferably 0.01 to 0.1% .

P: not more than 0.03%

Phosphorus (P) is an element existing as an impurity in steel. When the content thereof is excessive, it is unevenly distributed in crystal grain boundaries to deteriorate hot workability, so that the upper limit is limited to 0.03% or less.

S: not more than 0.03%

S, like P, is an element existing as an impurity in steel. If it is excessive, S is unevenly distributed in crystal grain boundaries or sulfide is formed to lower hot workability, so that the upper limit is limited to 0.03%.

According to the method for producing a martensitic stainless steel sheet of the present invention provided as described above, the difference in reduction ratio between the center portion and the edge portion of the thin lap piece at the time of hot rolling is 0.8% or less and a very uniform reduction rate can be given. The edge cracks occur at less than 30 mm or do not occur at all, thereby achieving a remarkably excellent edge quality. Edge cracks occur in the range of 60 mm or less in the production of the martensitic stainless steel. Thus, when trimming the edge portion of the thin steel sheet by about 60 mm, it is considered that the method of the present invention has excellent edge quality .

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only illustrative of the present invention in more detail and do not limit the scope of the present invention.

(Example 1)

And the balance Fe and other unavoidable impurities are contained in an amount of 0.65% of C, 13.5% of Cr, 0.3% of Si, 0.65% of Mn, 0.2% of Ni, 0.03% of N, 0.02% Was obtained by using a twin roll type thin plate casting method. The width of the strip was 1300 mm and the thickness was 3.0 mm. The strip was hot-rolled and rolled into a thin steel sheet having a thickness of 2 mm. On the other hand, the bender amount of the rolling roll during the hot rolling was controlled as shown in Table 1 below, and the crown size of the rolling roll was 30 탆. The thin steel sheet thus produced was observed for edge cracks, edge waves and warpage exceeding 30 mm, and the difference in the reduction ratio between the center portion and the edge portion of the thin steel sheet, and the results are shown in Table 1 below.

division Bender volume
(kN) Edge cracking (more than 30mm) Edge wave
Occurrence Twist
Occurrence Reduction ratio difference
(%) Comparative Example 1 10 × ○ ○ 0.1 Comparative Example 2 20 × ○ ○ 0.1 Inventory 1 30 × × × 0.2 Inventory 2 50 × × × 0.3 Inventory 3 100 × × × 0.4 Honorable 4 300 × × × 0.6 Inventory 5 500 × × × 0.8 Comparative Example 3 600 ○ × × 1.0 Comparative Example 4 800 ○ - - 1.1

As can be seen from Table 1, in the case of Inventive Examples 1 to 5 satisfying the bender amount condition proposed by the present invention, a uniform reduction rate is given and edge cracks exceeding 30 mm are not generated, In addition, edge wave or distortion does not occur, and it can be seen that excellent shape quality is ensured.

However, in the case of Comparative Examples 1 and 2 which did not meet the conditions of the bender amount proposed by the present invention, it was found that edge wrinkles and warpage occurred due to an excessive amount of reduction, .

On the other hand, in the case of Comparative Examples 3 and 4 exceeding the amount of the benders proposed by the present invention, it was found that an edge crack occurred due to a low reduction in the edge portion compared to the center portion, and in particular, Edge cracks were generated severely and plate breakage occurred.

Figs. 3 and 4 are photographs of the thin steel sheets of Inventive Example 3 and Comparative Example 3, respectively. As can be seen from FIGS. 3 and 4, in the case of Inventive Example 3 that satisfies the conditions of the present invention, edge cracking does not occur and the quality of the edge portion is excellent. On the contrary, in Comparative Example 3, excessive bender amount is given It can be confirmed that an edge crack has occurred.

(Example 2)

The bending amount was 600 kN and the crown of the rolling roll was controlled as shown in Table 2 to produce a thin steel sheet under the same conditions as in Example 1. The thus obtained thin steel sheet was subjected to an edge crack exceeding 30 mm, After observing the occurrence of wave and distortion, the results are shown in Table 2 below.

division Crown size
(탆) Edge cracking (more than 30mm) Edge wave
Occurrence Twist
Occurrence Comparative Example 5 0 ○ × × Comparative Example 6 30 ○ × × Inventory 6 50 × × × Honorable 7 80 × × × Honors 8 100 × × × Proposition 9 150 × × × Inventory 10 200 × × × Exhibit 11 250 × × × Comparative Example 8 300 × ○ ○

As can be seen from Table 2, in the case of Examples 6 to 11 satisfying the crown size condition of the rolling roll proposed by the present invention, a uniform reduction rate is given and edge cracks exceeding 30 mm are not generated, Not only edge wave or distortion is generated, but also excellent quality of shape is ensured.

However, in the case of Comparative Examples 5 and 6 which do not meet the crown size condition of the rolling roll proposed by the present invention, edge cracks are generated due to a low reduction ratio at the edge portion as compared with the center portion, In the case of Comparative Example 8, which exceeded the crown size of the proposed rolling roll, a high rolling reduction was given to the edge portion, so that an edge crack did not occur but an edge wave and a twist occurred due to an excessive rolling reduction.

1: molten steel
2: ladle
3: Tundish
4: immersion nozzle
5: Sheet metal casting roll
6: Edge dam
7:
8: Meniscus shield
9: Roll nip
10: rolling roll
11: Coiling equipment

Claims (6)

A method for producing a martensitic stainless steel thin plate by casting a thin piece of cast steel using a thin plate casting machine including a pair of rotating thin casting rolls and hot rolling the cast piece,
Wherein at least one of the following conditions (a) and (b) is satisfied in the hot rolling,
Wherein the difference in the reduction ratio between the center portion and the edge portion of the thin lap piece during the hot rolling is 0.8% or less.
(a) Bender volume of rolling roll: 30 to 500 kN
(b) Crown size of rolling roll: 50 to 250 탆
The method according to claim 1,
Wherein the bending amount of the rolling roll is 30 to 300 kN. ≪ RTI ID = 0.0 > 21. < / RTI >
The method according to claim 1,
Wherein the crown of the rolling roll has a size of 50 to 200 mu m. ≪ RTI ID = 0.0 > 20. < / RTI >
The method according to claim 1,
Wherein the steel sheet comprises 0.3 to 0.8% of C, 12.0 to 16.0% of Cr, 0.2 to 1.0% of Si, 0.2 to 1.0% of Mn, 0.2 to 1.0% of Ni, 0.01 to 0.1% of N, 0.03% or less of P and 0.03% or less of S, and the balance Fe and other unavoidable impurities. The method for producing a martensitic stainless steel sheet according to claim 1,
delete The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.3 to 0.8% of C, 12.0 to 16.0% of Cr, 0.2 to 1.0% of Si, 0.2 to 1.0% of Mn, 0.2 to 1.0% of Ni, 0.01 to 0.1% Or less and S: 0.03% or less, the balance being Fe and other unavoidable impurities, and having an edge crack of 30 mm or less.

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