KR101312776B1 - Martensitic stainless steel and method of the manufacture the same containing 0.1~0.5% carbon - Google Patents

Abstract

The present invention relates to martensitic stainless steel containing 0.10 to 0.50% carbon, 11 to 16% chromium, and a method of manufacturing the same, by a weight% used in aquaculture machines, knives and scissors, and a pair of rolls rotating in opposite directions to each other. And a strip casting device including an edge dam installed to form molten steel on both sides thereof and a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel, the weight% of which is C: 0.10 to 0.50%, Cr: A molten stainless steel containing 11 to 16% is supplied from a tundish to the molten steel pool through a nozzle to cast a stainless steel sheet, and the cast stainless steel sheet is hot-rolled and annealed at a reduction ratio of 5 to 40% using an inline roller. It characterized by the manufacturing method of the medium-carbon martensitic stainless steel for producing and the martensitic stainless steel produced by the method. According to the present invention, by reducing carbide central segregation, lamination defects can be suppressed, and the hardness difference between the carbide segregation portion and the uneven segregation portion is small, and thus the martensitic stainless steel with uniform hardness as a whole can be obtained.

Stainless steel, martensite, strip casting, for painting

Description

Martensitic stainless steel and method of the manufacture the same containing 0.1 ~ 0.5% carbon}

The present invention relates to martensitic stainless steels and a method for manufacturing the same. More specifically, the lamination is made of a medium-carbon martensitic stainless steel containing 0.10 to 0.50% carbon and 11 to 16% chromium by using a strip casting method. The present invention relates to a medium-carbon martensitic stainless steel with reduced hardness and uniformity, and a method of manufacturing the same.

In general, martensitic stainless steel is manufactured through the following manufacturing process. In other words, molten steel is cast to manufacture a performance slab, and then reheated and hot rolled. In the hot rolled state, the steel is present in a mixture of martensite phase, tempered martensite phase, and residual austenite phase. The hot rolled coil is transformed into ferrite and carbide through a batch annealing process for the purpose of hot rolled sheet annealing, and softened. The soft material by the hot rolled annealing undergoes a pickling process to remove the scale formed. After pickling, the soft material is transformed into martensitic steel after cold rolling or product processing through final heat treatment.

Typical martensitic stainless steels include 420 series steels, which form coarse carbide center segregation in the casting slab manufacturing process due to the high carbon content of the steel. Carbide central segregation is a phenomenon that occurs as a result of suction and accumulation into the bulk molten steel as the fine segregated molten steel existing between dendrite solidifies. The central segregation formed in the slab is hardly removed in the reheating or annealing heat treatment process, and thus remains in the hot rolled or cold rolled sheet, which causes lamination defects during shearing of the strip. do.

In the case of producing a slab of the conventional 200 ~ 250mm, in order to minimize the center segregation in the casting process to reduce the casting speed to 70 ~ 80% compared to the conventional material, there is a problem that the performance is significantly reduced. In addition, in order to employ the coarse carbide in the center formed during casting, the annealing temperature and the holding time of the batch annealing after hot rolling must be excessively increased, which leads to a sharp decrease in productivity. Since the central segregation generated during continuous casting is generated by the thickened steel due to the accumulation of carbon as the solidification progresses, a method of reducing the segregation has been reported. That is, methods for reducing central segregation include electromagnetic stirring, mechanical soft reduction, and thermal soft reduction.

Accordingly, the present inventors have been devised in accordance with the above requirements, by reducing the central segregation of carbide by producing martensitic stainless steel by using a strip casting method of producing a non-existing continuous casting method by direct twin roll, It is an object of the present invention to provide a high-carbon martensitic stainless steel having a uniform hardness and suppressing lamination defects, which is a major disadvantage of conventional continuous casting.

In order to achieve the above object, the present invention provides a pair of rolls rotating in opposite directions and an edge dam installed to form molten steel pools on both sides thereof, and a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel pool. In the strip casting device comprising a, by supplying a molten stainless steel containing C: 0.10 to 0.50%, Cr: 11 to 16% by weight from a tundish to the molten steel pool through a nozzle to cast a stainless steel sheet, the casting Provided is a method for producing a medium-carbon martensitic stainless steel for producing a hot-rolled annealing strip with a reduced stainless steel sheet of 5 to 40% using an inline roller.

Further, in the present invention, the martensitic stainless steel is Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: more than 0 and less than 1.0, N: more than 0.1 and less, S: more than 0 and less than 0.04, P: Above 0 and below 0.05 and the balance include Fe and other unavoidable impurities.

In addition, the present invention provides a method for producing a hot-rolled annealing plate by performing annealing (batch annealing) of the hot-combustion strip in a temperature range of 700 ~ 950 ℃ under a reducing gas atmosphere.

Further, in the present invention, the hot-rolled annealing strip can obtain a medium-carbon martensitic stainless steel having a hardness difference of 90 Hv or less in the cross section of the thickness when measured with a Vickers hardness of 100g.

In addition, another aspect of the present invention includes a pair of rolls that rotate in opposite directions, an edge dam installed to form a molten steel pool on both sides thereof and a meniscus shield for supplying inert nitrogen gas to the molten steel upper surface. In a stripcasting apparatus, a molten stainless steel containing C: 0.10 to 0.50% and Cr: 11 to 16% by weight is supplied from a tundish to the molten steel pool through a nozzle to cast a stainless steel sheet, and the cast stainless steel sheet It is to provide a medium-carbon martensitic stainless steel that is pressed using a inline roller at a reduction ratio of 5 to 40%.

Further, in the present invention, the martensitic stainless steel is Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: more than 0 and less than 1.0, N: more than 0.1 and less, S: more than 0 and less than 0.04, P: Above 0 and below 0.05 and the balance include medium carbon martensitic stainless steel made of Fe and other unavoidable impurities.

In the present invention, the stainless steel is obtained in the carbonaceous martensitic stainless steel passed through the annealing (batch annealing) in a temperature range of 700 ~ 950 ℃ under a reducing gas atmosphere.

In addition, in the present invention, the stainless steel may obtain martensite stainless steel having a hardness difference of 90 Hv or less in the cross section of the carbide when measured at Vickers hardness of 100g.

In addition, the stainless steel produced by the above method in the present invention includes a thickness of 1 ~ 5mm thin plate.

As described above, the present invention has the effect of producing martensitic stainless steel using the strip casting method to reduce the center segregation and to suppress the lamination defects. The obtained martensitic stainless steel has the effect that the hardness is uniform throughout the structure.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention and other matters required by those skilled in the art will be described in detail with reference to the accompanying drawings. However, the present invention may be embodied in various different forms within the scope of the claims, and thus the embodiments described below are merely exemplary, regardless of expression.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. Note that the same components in the drawings are represented by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In addition, the thickness and size of each layer in the drawings may be exaggerated for convenience and clarity, and may differ from actual layer thicknesses and sizes.

1 is a schematic diagram of a conventionally known stripcasting installation. This strip casting process produces hot-rolled annealing strips of thin metal directly from molten steel, eliminating the hot rolling process, and is a new steel processing process that can drastically reduce manufacturing costs, equipment investment costs, energy consumption, and pollution gas emissions. A twin roll type thin plate casting machine used in a general strip casting process is a casting machine in which a molten steel is received in a ladle 1 as shown in Fig. 1, flows into a tundish 2 along a nozzle, Is supplied through the molten steel injection nozzle 3 between the edge dams 5 provided at both ends of the casting roll 6, that is, between the casting rolls 6, and solidification starts. At this time, in order to prevent oxidation, the melt surface between the rolls is protected with a meniscus shield (4) and an appropriate gas is injected to appropriately control the atmosphere. The thin plate 8 is manufactured while being pulled out from the roll nip 7 where both rolls meet, rolled through the rolling machine 9 while being drawn, and then cooled and wound in the winding machine 10 through the cooling process.

In this case, an important technique in a twin roll thin plate casting process for directly producing a thin plate having a thickness of 10 mm or less from molten steel is to supply molten steel through an injection nozzle between inner water-cooled twin rolls rotating at a high speed in the opposite direction, So that cracks are not generated and the rate of water loss is improved.

The inventors of the present invention have found that the core segregation problem, which is difficult to remove by the existing playing method, can be innovatively reduced by manufacturing the strip casting method. As a result, it was confirmed that the lamination (dual plate) defects are alleviated during shearing of strips and the uniformity in hardness in the sheet thickness direction is confirmed.

(Example)

Hereinafter, the present invention will be described by way of examples.

The base material used in this invention uses the range of C: 0.10 to 0.50% and Cr: 11 to 16% by weight as martensitic stainless steel. In the present invention, if the range of C is 0.1% or less, the center segregation will not be severely generated, but it is not preferable in hardness. If the range of C is 0.5% or more, the residual austenite is excessively contained in the microstructure during the quenching heat treatment. May remain. Therefore, the present invention proposes C: 0.1 to 0.5% and Cr: 11 to 16% as an optimum range.

In addition, the martensitic stainless steel according to the embodiment of the present invention is Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: more than 1.0 or less, N: more than 0.1 or less, S: more than 0.04 in weight% Below, P: greater than 0.05 and the remainder are for alloys related to the component system composed of Fe and other unavoidable impurities.

In the embodiment, the microstructure characteristics of the hot-rolled annealing plate manufactured by the conventional continuous casting method and the steel produced by the strip casting method were compared.

Table 1 shows the components of the steel produced by the continuous casting method and the strip casting method. Using a conventional continuous casting method, 100 tons of a 200m-thick playing slab was manufactured using 420J2. This is shown as a comparative example as # 1 of Table 1. Then, the slab was reheated in a heating furnace for hot rolling, and hot rolled to a thickness of final 3mm. A component similar to # 1 of Table 1, which is a component steel prepared by continuous casting, was prepared in the form of a hot rolled coil using a twin roll strip caster as the inventive steel of Table 1. The twin roll strip casters are characterized in that they supply molten steel between twin-drum rolls and side dams rotating in mutually opposite directions and cast a large amount of heat through the surface of the water-cooled roll. At this time. A solidification cell is formed at a high cooling rate on the surface of the roll, and a thin hot rolled sheet of about 1 to 5 mm is finally produced by in-line rolling, which is continuously performed at a high temperature after casting. In this example, a 420J2 component was cast to 3.0mmt, and a hot rolled coil having a thickness of 2mm was prepared by performing in-line rolling after the main structure. Batch annealing was performed under the same conditions for a 3 mm thick hot rolled sheet manufactured by using the continuous casting method and a 2 mm thick hot rolled coil manufactured by using strip casting.

Steel components produced by continuous casting and strip casting ID C Si Mn P S Cr Ni N ΔHv Remarks #One 0.29 0.43 0.45 0.021 0.004 13.2 0.1 0.03 98 Continuous casting (comparative example) #2 0.13 0.43 0.50 0.023 0.001 12.3 0.25 0.02 4 Strip Casting (Invention) # 3 0.30 0.45 0.49 0.021 0.001 13.3 0.1 0.03 6 Strip Casting (Invention) #4 0.32 0.46 0.50 0.019 0.001 13.4 0.4 0.03 9 Strip Casting (Invention) # 5 0.45 0.35 0.40 0.018 0.002 14.0 0.15 0.02 8 Strip Casting (Invention) # 6 0.48 0.52 0.45 0.018 0.002 14.8 0.3 0.02 10 Strip Casting (Invention)

FIG. 2 is a 200 mm-thick slab cross-sectional structure photograph of Comparative Example # 1 as a component steel manufactured by a conventional playing method. A black etched carbide center segregation is present in the center of the slab. On the contrary, as a 2 mm thick hot rolled sheet cast by strip casting, the inventive steel # 3 of Table 1 only confirmed the presence of equiaxed crystals in the center of the thickness, and traces of segregation were found in the center on the optical microscope. It wasn't. This can be seen in more detail with reference to FIG. 3.

4 and 5 are microstructures taken at the magnifications of x50 and x1000, respectively, of the central section of the comparative example # 1 of the comparative example # 1 of the 3mm thick material manufactured by the conventional casting method and softened through annealing. It can be seen that the central segregation portion in which the carbide is densely formed in the form of a band having a thickness of about 20 μm is formed at the center of the thickness section. However, such carbide central segregation is not observed in the central section of the steel # 3 of the invention steel of Table 1, which is made by strip casting and softened by annealing. This can be confirmed through the organizational pictures of FIGS. 6 and 7.

FIG. 8 is a result of measuring the hardness of the carbide central segregation unit and the unsegregated unit identified in FIG. 5. Vickers hardness value (Hv) was measured, each measured 10 times with a load of 100. The results are shown in the box form of FIG. The average hardness of the central segregation of carbides was 288 Hv, and the uneven segregation was 193, resulting in a difference of about 95 Hv. Table 1 shows the cross-sectional hardness measurement results of martensitic stainless steel hot-rolled annealing materials of various components prepared by strip casting. Vickers hardness difference (ΔHv) shown in Table 1 is a result of measuring the difference in hardness of the central segregation portion and the unsegregated portion of the carbide as described above, except for the comparative example # 1 of Table 1, a steel manufactured by continuous casting In all the invention examples, the variation in the cross-sectional hardness was measured to be 10 Hv or less. This result means that the uniformity of hardness is improved when the carbide core segregation is removed by the strip casting method.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

The scope of the present invention is defined by the following claims. The scope of the present invention is not limited to the description of the specification, and all variations and modifications falling within the scope of the claims are included in the scope of the present invention.

1 is a schematic diagram of a typical strip casting process,

Figure 2 is a tissue photograph showing that the carbide segregation is present in the center of the thickness of the slab cross-sectional microstructure of the thickness of 200mm cast by the continuous casting method, black etched;

3 is a low magnification cross-sectional microstructure of a hot rolled sheet material which is cast by strip casting and continuously in-line rolled at high temperature after a main structure, with equiaxed crystals formed at the center of thickness and columnar crystals formed at the surface layer. Organization chart showing the organization,

FIG. 4 is a texture photograph showing that the carbides are formed in the form of black bands as a low magnification microstructure of the hot-rolled annealing plate which is cast and batch annealed by the continuous casting method. FIG.

FIG. 5 is a tissue photograph showing a band of carbide segregation having a thickness of about 20 μm with a microstructure in which the black band portion shown in FIG. 4 is enlarged;

FIG. 6 is a tissue photograph showing that the formation of a strip-shaped central segregation portion shown in FIG. 4 was suppressed by a low magnification microstructure of a hot-rolled annealing plate cast and batch annealed by strip casting; FIG.

Figure 7 is a tissue photograph showing that the formation of the central segregation into the microstructure enlarged in Figure 6 is suppressed,

8 is a graph comparing the Vickers hardness values measured at the carbide central segregation section and the unsegregation section.

(Explanation of main reference numerals)

1: ladle 2: tundish

3: injection nozzle 4: meniscus shield

5: edge dam 6: casting roll

7: roll nib 8: cast

9: IRM (Roller) 10: Coil Winding Equipment

Claims (11)

In a strip casting apparatus comprising a pair of rolls rotating in opposite directions and an edge dam installed on both sides thereof to form a molten steel pool and a meniscus shield for supplying inert nitrogen gas to the molten steel upper surface. A stainless molten steel containing C: 0.10 to 0.50% and Cr: 11 to 16% by weight is supplied from a tundish to the molten steel pool through a nozzle so that the stainless molten steel passes directly between the pair of rolls and directly into the stainless steel sheet. After the cast, the cast stainless steel sheet is produced by using a in-line roller continuously at high temperature after casting to produce a hot-rolled annealing strip at a reduction ratio of 5 to 40%, The hot-rolled annealing strip is subjected to annealing (batch annealing) in a temperature range of 700 ~ 950 ℃ under a reducing gas atmosphere to produce a hot-rolled annealing plate martensitic stainless steel. The method of claim 1, The martensitic stainless steel has a weight percent of Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: greater than 0 and less than 1.0, N: greater than 0.1 and less, S: greater than 0 and less than 0.04, P: greater than 0 and less than 0.05 and The balance is a method for producing martensitic stainless steel consisting of Fe and other unavoidable impurities. delete The method of claim 1, The hot-rolled annealing strip is a manufacturing method of martensitic stainless steel having a hardness difference of less than 90 Hv of carbide segregation and unsegregation in the thickness section when measured by Vickers hardness of 100g load. The method of claim 1, A method for producing martensitic stainless steel having a thickness of the carbide segregation layer at a thickness end surface of the hot-rolled annealing strip having a thickness of 20 µm or less. In a strip casting apparatus comprising a pair of rolls rotating in opposite directions and an edge dam installed on both sides thereof to form a molten steel pool and a meniscus shield for supplying inert nitrogen gas to the molten steel upper surface. A stainless molten steel containing C: 0.10 to 0.50% by weight and Cr: 11 to 16% by weight is supplied from a tundish to the molten steel pool through a nozzle, and the stainless molten steel passes directly between the pair of rolls and directly into the stainless steel sheet. After casting, the cast stainless steel sheet is cast at a high reduction ratio of 5 to 40% using an inline roller continuously at high temperature after casting to manufacture stainless steel. The stainless steel is passed through a batch annealing in a temperature range of 700 ~ 950 ℃ under a reducing gas atmosphere, The stainless steel is a martensitic stainless steel having a hardness difference of less than 90 Hv between the carbide segregation and the unsegregation in the thickness section when measured by Vickers hardness of 100g load. The method according to claim 6, The martensitic stainless steel has a weight percent of Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: greater than 0 and less than 1.0, N: greater than 0.1 and less, S: greater than 0 and less than 0.04, P: greater than 0 and less than 0.05 and The balance is martensitic stainless steel composed of Fe and other unavoidable impurities. delete delete The method according to claim 6, Martensitic stainless steel having a thickness of the carbide segregation layer in the thickness cross section of the stainless steel having 20㎛ or less. The method according to any one of claims 6, 7, and 10, The stainless steel is martensitic stainless steel having a thickness of 1 to 5mm.

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