KR20140010248A

KR20140010248A - Martensitic stainless steel and the method of manufacturing the same

Info

Publication number: KR20140010248A
Application number: KR1020120077141A
Authority: KR
Inventors: 채동철; 이재화; 정성인; 이일구
Original assignee: 주식회사 포스코
Priority date: 2012-07-16
Filing date: 2012-07-16
Publication date: 2014-01-24
Also published as: KR101423826B1; CN104471095B; WO2014014246A1; CN104471095A

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to martensitic stainless steel and its manufacturing method for esophagus such as kitchen knives, and in particular, in martensitic stainless steel produced by strip casting, C: 0.4 to 0.5% by weight. , N: 0.1 to 0.2%, Cr: 13 to 15%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Ni: more than 1.0% or less, C + N: 0.5% or more, and N / C is 0.2 It is controlled by more than%, the remainder includes Fe and other unavoidable impurities, the size of the residual carbide of the martensitic stainless steel is 10㎛ or less and hardness of 55HRC or more to provide a martensitic stainless steel and its manufacturing method. .
In the martensitic stainless steel according to the present invention, steel is manufactured by using a strip casting method. In performing a tempering heat treatment on a hot-rolled and annealed sheet having a thickness of 1 mm or more and manufactured by strip casting, By reducing the length of the carbide to 10 탆 or less, it is possible to obtain a martensitic stainless steel excellent in sharpness quality and excellent in hardness and corrosion resistance for use for cooking in a kitchen knife.

Description

Description: TECHNICAL FIELD The present invention relates to a martensitic stainless steel and a method for manufacturing the same,

The present invention relates to a martensitic stainless steel and a method of manufacturing the same, and more particularly, to a martensitic stainless steel utilizing a rapid cooling casting method for use in high-grade steaming and the like, and a manufacturing method thereof.

Martensitic stainless steels are steels consisting essentially of iron (Fe) - chromium (Cr) - carbon (C), containing about 12-18% Cr by weight and containing about 1% It is a river containing. This martensitic stainless steel is produced by a manufacturing process of an alloy manufacturer to produce a hot-rolled and annealed sheet composed of a ferrite phase and a Cr carbonitride. After the pickling of the hot-rolled and annealed sheet, Rolled and supplied. Finally, the final demand for steel is transformed into a hard martensite structure, which is made of a ferrite phase and a carbide, by means of a tempering heat treatment process on the stainless steel.

The requirements for martensitic stainless steel to be used for transient and esophageal applications are largely divided into three categories: corrosion resistance, hardness and toughness. In the transient and esophageal diseases of general use, 420J2 series steel (0.3% C-13% Cr) which is 0.3% C and 13% Cr by weight is mainly used and generally hardened to a hardness level of about 52 ~ 54 HRC, do. 420J2 has a relatively low carbon content, excellent corrosion resistance of the product, and excellent toughness. However, since the carbon content is low, the hardness is somewhat low.

As a high-grade esophagus material with a hardness higher than 420J2, 1.4116 steel added with a small amount of Mo is mainly used based on 0.5% C and 14% Cr by weight%. Advanced esophagus based on the 1.4116 family of ingredients is primarily used for enhanced heat treatment with a hardness of about 55 HRC or higher. This steel increases the carbon content compared to 420J2 and can secure high hardness by heat treatment, and has high resistance to deformation and excellent wear resistance during use. However, since the coarse carbide remains in the reinforced heat-treated material with a high carbon content, the carbide is detached from the edge of the blade during edge processing, thereby deteriorating the sharpness quality, and the local corrosion resistance is deteriorated due to the coarse residual carbide . In order to minimize such adverse effects on the quality, the size of the carbide remaining in the microstructure should be small, and the carbide observed in a conventional commercial stainless steel kitchen knife has a size of 10 μm or less.

In order to produce martensitic steel for high carbon steel, a continuous casting process or an ingot casting process is generally used. However, in the conventional casting method, since the cooling rate is slow during casting, a coarse carbide center segregation portion is formed at the center of the thickness, and the carbide center segregation portion thus generated remains in the microstructure even after the subsequent preliminary casting process, It is a major cause of residual carbides in the product. Therefore, the rapid cooling casting method can be exemplified as a step of drastically removing the carbide center segregation instead of the conventional continuous casting and ingot casting in the martensite steel ingot producing process for water. The rapid cooling casting process includes a strip casting process as a process capable of producing a hot rolled steel sheet directly from a molten steel without passing through a conventional casting process. However, even if the rapid cooling casting method is used, even if the coarse carbides aggregate in the grain boundaries in the structure subjected to the final strengthening heat treatment, it may be inapplicable to use for water.

The present invention is based on the finding that even if a component steel in which corrosion resistance is enhanced by adding Mo or W alone or in combination to a steel product by rapid cooling casting is used in a product having a residual carbide length of 10 m or less in the microstructure of the product after the final strengthening heat treatment, And to provide a method for manufacturing the same.

Further, the present invention provides a martensitic stainless steel having a thickness of at least 1 mm, which is used for cooking, and which is excellent in quality of edge after tempering heat treatment.

The present invention relates to a martensitic stainless steel produced by a rapid cooling casting method and a method for producing the same. The rapid cooling casting process may include a strip casting process. The strip casting process includes a pair of rolls rotating in opposite directions, an edge dam installed on both sides of the roll, and a maniskus shield for supplying inert nitrogen gas to the upper surface of the spooling coil A strip casting device is used.

In one embodiment of the present invention in the martensitic stainless steel produced by the rapid cooling casting method, in the weight% C: 0.4 ~ 0.5%, N: 0.1 ~ 0.2%, Cr: 13 ~ 15%, Si: 0.1 ~ 1.0%, Mn: 0.1 ~ 1.0%, Ni: more than 1.0% or less, C + N: 0.5% or more and N / C is controlled to 0.2% or more, the rest containing Fe and other unavoidable impurities, the martens It provides a martensitic stainless steel characterized in that the residual carbide of the site-based stainless steel is 10 µm or less in size and 55HRC or more in hardness.

Further, in the present invention, 0.1 to 2% of W and 0.1 to 2% of Mo are added singly or in combination in weight percent.

Further, in the present invention, the size of the residual carbide is preferably 3 mu m or less.

In the present invention, the stainless steel exhibits a hardness of 55 HRC or more after the tempering heat treatment.

Further, in another embodiment of the present invention by weight% C: 0.4-0.5%, N: 0.1-0.2%, Cr: 13-15%, Si: 0.1-1.0%, Mn: 0.1-1.0%, Ni: 1.0% or less than 0, C + N: 0.5% or more, and N / C is controlled to 0.2% or more, the remainder is cast into a thin sheet of stainless steel molten steel including Fe and other unavoidable impurities by a rapid cooling casting method, the casting Provided is a method for producing martensitic stainless steel for producing a hot rolled strip at a reduction ratio of 5 to 40% by using an inline roller.

In the present invention, the rapid cooling casting method is a pair of rolls that rotate in opposite directions to each other and 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 pool. And a strip casting process of supplying the molten stainless steel of the composition from the tundish to the molten steel pool through a nozzle to cast a stainless steel sheet.

In the present invention, the hot-rolled strip is subjected to batch annealing in a temperature range of 700 to 950 ° C under a reducing gas atmosphere to produce a hot-rolled and annealed sheet.

In the present invention, the hot-rolled and annealed sheet is maintained at a temperature of 1000 to 1100 占 폚 and then quenched so that the size of the residual carbide in the microstructure is 10 占 퐉 or less.

Also, in the present invention, the quenched material is subjected to a tempering heat treatment at 150 to 250 ° C.

Further, in the present invention, the martensitic stainless steel exhibits a hardness of 55 HRC or more after the tempering heat treatment.

Further, in the present invention, the quenched martensitic stainless steel is subjected to a deep freezing heat treatment at a temperature of -50 to 150 캜 before the tempering heat treatment.

As described above, a martensitic stainless steel having a high quality finish and a high corrosion resistance for a kitchen knife can be obtained by using the rapid cooling casting method based on the alloy design according to the present invention, while satisfying the hardness characteristics of 55 HRC or more.

Further, according to the present invention, it is possible to obtain a martensitic stainless steel having a residual carbide length of 10 탆 or less in the microstructure of the final product, and having excellent microstructure and having a high endurance.

1 is a schematic view of a strip casting process, which is an example of a rapid cooling casting process,
Fig. 2 is a tissue photograph showing an example in which tip corrosion is caused by coarse carbide according to the prior art. Fig.
3 is a micrograph of a carbide microstructure of a material produced by a conventional ingot casting process and quenching heat treated after 1050 < 0 > C austenitizing heat treatment.
FIG. 4 is a micrograph of a carbide microstructure of a material manufactured by a strip casting method, which is one example of a conventional rapid cooling casting method, and quenched and heat-treated after a 1050 ° C. austenitizing heat treatment.
FIG. 5 is a micrograph of a carbide microstructure of a material produced by strip casting, which is one example of the rapid cooling casting method according to the present invention, and quenched and heat-treated after 1050 ° C. austenitizing heat treatment.
6A and 6B are graphs comparing softening resistance after quenching and tempering of Comparative Example and Inventive Steel,
7 is a graph showing the corrosion resistance of the steel of the present invention and the comparative example in comparison with weight loss during immersion in sulfuric acid.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described more fully hereinafter with reference to the drawings, in which advantages and features of the present invention, and how to accomplish them, will be apparent by referring to the embodiments described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. In the following description, it is assumed that a part is connected to another part, But also includes a case in which other elements are electrically connected to each other in the middle thereof. In the drawings, parts not relating to the present invention are omitted for clarity of description, and like parts are denoted by the same reference numerals throughout the specification.

As an example of a rapid cooling casting method for producing martensitic stainless steels for water, a strip casting process in which carbide center segregation has been drastically removed is known. Korean Patent Publication No. 2011-0071517 discloses a martensitic stainless steel containing 0.10 to 0.50% by weight and 11 to 16% by weight Cr, and a method for producing the same. The martensitic stainless steel includes a pair of rolls rotating in opposite directions, The strip casting apparatus according to any one of claims 1 to 3, wherein the strip casting apparatus comprises an edge dam installed on both sides and a maniscus shield for supplying inert nitrogen gas to the upper surface of the spool, 16% of the molten steel is supplied from the tundish through the nozzle to the molten metal pool to cast a stainless steel thin plate, and the cast stainless steel thin plate is manufactured with an inline roller at a reduction ratio of 5 to 40% And a martensitic stainless steel produced by the method for producing the martensitic stainless steel. The above-mentioned patent shows that when the strip casting method is used, the carbide center segregation is largely alleviated due to the rapid casting speed, and microstructure having uniform hardness can be realized in the thickness of the produced hot-rolled annealed sheet.

The present inventors have further studied from the improvement of the texture characteristics of the hot-rolled and annealed sheet in which the carbide center segregation is largely reduced in the above-mentioned strip casting process, and further the structure of the final hardened material subjected to the final heat treatment process. Namely, by using the strip casting process disclosed in Korean Patent Publication (KR 2011-0071517), Mo or W of 0% to 2% by weight or more and 0.5% or more of C by weight%, alone or in combination, A study on stainless steel materials for various reinforced ceramics showed that even after the final strengthening heat treatment process was carried out even though there was no carbon center segregation in the microstructure of the hot-rolled annealed material, Or more) of the carbides aggregated at grain boundaries. It has been confirmed that there is a disadvantage in that when the corrosion resistance test is performed after manufacturing the esophagus with such a material, the sharpness of the nose tip becomes fast.

FIG. 2 is a photograph of a tissue showing an example where tip corrosion is caused by coarse carbides. As shown in the drawing, it can be seen that coarse carbide aggregates in the grain boundaries.

The present invention proposes a method of manufacturing the alloy based on the alloy design and the alloy design to solve such a problem.

1. Alloy design

First, in one embodiment of the present invention in the martensitic stainless steel produced by the rapid cooling casting method, in weight% C: 0.4 ~ 0.5%, N: 0.1 ~ 0.2%, Cr: 13 ~ 15%, Si: 0.1 ~ 1.0%, Mn: 0.1 ~ 1.0%, Ni: more than 1.0% or less, C + N: 0.5% or more and N / C is controlled to 0.2% or more, the rest containing Fe and other unavoidable impurities, the martens A martensitic stainless steel having a size of residual carbide of the sight-based stainless steel of 10 µm or less and a hardness of 55 HRC or more is provided. In the present invention, 0.1 to 2% of W, and 0.1 to 2% of Mo may be added alone or in combination, and preferably, the size of the residual carbide is 3 m or less. The martensitic stainless steel has a thickness of 1 mm or more and exhibits a hardness of 55 HRC or more after the tempering heat treatment.

The reason for limiting the specific composition range of the martensitic stainless steel according to the present invention will be described in detail below. First, the base material used in the present invention is martensitic stainless steel in which the content of C is 0.4 to 0.5% by weight, the content of N is 0.1 to 0.2%, and the content of Cr is 13 to 15% by weight. The C + N is 0.5% or more while the N / C is controlled to 0.2% or more.

When C is 0.4% or more, it is possible to secure a hardness of 55HRC or more after the tempering heat treatment, and when it exceeds 0.5%, it is defined by the austenitization treatment due to the increase of local carbon segregation in the strip casting casting structure Coarse carbide exceeding 10 탆 may be generated after the strengthening heat treatment at 1000 to 1100 캜.

N is an element to be added for the purpose of simultaneously improving the corrosion resistance and hardness. Particularly, when N is added in the range of 0.1% to 0.2% or less in place of C, it does not cause local fine segregation like C, There is an advantage that no carbide is formed. However, when it exceeds 0.2%, fine pores may occur in the microstructure, thus limiting the upper limit to 0.2%. When N is less than 0.1%, the tempering resistance is not improved and the hardness is easily lowered after tempering, so that the lower limit is set to 0.1%.

On the other hand, in the present invention, it is preferable to control the C + N, which is the sum of the carbon and nitrogen content, to be 0.5% or more, and to control the N / C, which is the ratio of nitrogen and carbon content, to 0.2% or more. This is due to the increase of local carbon segregation in the strip casting casting structure as described above when the C content exceeds 0.5%, and after the 1000 ~ 1100 ° C strengthening heat treatment specified by the austenitization treatment, , But it is preferable to control the range of C to 0.5% or less and to add N of 0.1% or more so that the sum of the C + N ranges is 0.5% or more so that the coarse carbide It is possible to suppress the occurrence and simultaneously improve the tempering resistance. It is preferable to control the range of C and N so that the range of C + N is 0.5% or more while the range of N / C is 0.2% or more.

The content of Cr should be 13% or more. The corrosion resistance of the base material of the coated product after the tempering treatment is a stainless steel property. If the content exceeds 15%, the fine segregation of the Cr component in the casting casting structure increases and austenitization Austenitization treatment, the Cr content remains in the microstructure after the tempering heat treatment at 1000 ~ 1100 ℃. Therefore, the Cr content is limited to 15% or less.

W and Mo can be added alone or in combination for the purpose of enhancing corrosion resistance, but in case of excess, austenitization delays the re-use of carbide during heat treatment and promotes the formation of coarse residual carbide, %.

The martensitic stainless steel according to an embodiment of the present invention may further contain 0.1 to 1.0% by weight of Si, 0.1 to 1.0% by weight of Mn, 0.1 to 1.0% by weight of Ni, 0 to 0.04 or less of S, And the remainder is an alloy relating to a constituent system comprising Fe and other unavoidable impurities.

Si is an essential element for deoxidation, whereas high Si content decreases the acidity and limits the upper limit to 1.0% because it increases the brittleness of the material.

Mn is an element to be added for deoxidation, whereas when it is added excessively, the surface quality of the steel is inhibited and the upper limit is limited to 1.0% because the increase of hardness is suppressed through formation of retained austenite of the final heat treatment material.

Ni is an element that improves corrosion resistance, but it is a very expensive element and its content is limited to 1.0% or less.

S easily forms an inclusion as an element inevitably contained in the main element alloy, so its content is limited to 0 to 0.04% as low as possible.

P is an element which is easy to segregate in the grain boundaries and causes a processing crack in the production of the alloy, so that the content is limited to 0 to 0.05% as low as possible.

2. Rapid cooling casting method

The present invention relates to a martensitic stainless steel based on the above alloy design by a rapid cooling casting method. The rapid cooling casting process may include a strip casting process.

1 is a schematic view of a facility for explaining a strip casting process, which is an example of a rapid cooling casting process. This strip casting process is a new steel process process which can reduce the manufacturing cost, facility investment cost, energy consumption, pollutant gas emissions, etc. by omitting the hot rolling process, which is a process of producing hot strips of steel products directly from molten steel. 1, a molten steel is received in the ladle 1, is introduced into the tundish 2 along the nozzle, and the molten steel is introduced into the tundish 2, 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 molten steel is rolled through the rolling mill 9 while the thin plate 8 is produced while being pulled out of the roll nip 7 where both rolls meet, and is then cooled and wound in the winding facility 10 through a cooling process. 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.

In one embodiment of the present invention by weight% C: 0.4-0.5%, N: 0.1-0.2%, Cr: 13-15%, Si: 0.1-1.0%, Mn: 0.1-1.0%, Ni: greater than 1.0 % Or less, C + N: 0.5% or more and N / C is controlled to 0.2% or more, the rest of the molten stainless steel containing Fe and other unavoidable impurities by casting a thin plate by the rapid cooling casting method, the cast stainless steel Provided is a method for producing martensitic stainless steel in which a thin sheet is produced using a inline roller to produce a hot rolled strip at a reduction ratio of 5 to 40%. In the present invention, 0.1 to 2% of W and 0.1 to 2% of Mo may be added alone or in combination as a weight% of the stainless steel.

The rapid cooling casting method includes a strip casting process, wherein the strip casting process includes a pair of rolls rotating in opposite directions and an edge dam installed to form molten steel on both sides thereof, and an inert nitrogen gas into an upper surface of the molten steel pool. In the apparatus including a supplying meniscus shield, the molten stainless steel of the composition may be supplied from a tundish to the molten steel pool through a nozzle to cast a stainless steel sheet.

When producing a product for use in a kitchen knife, transient, or the like of the present invention, the reinforcement heat treatment is performed in the following order.

The first heat treatment process that is performed first is the austenitization process.

The austenitization process is a heat treatment in which the material is exposed to a high temperature of about 1000 to 1100 ° C. During this process, chromium carbide or chromium carbonitride is reused as the base structure, and the base structure is transformed from ferrite to austenite. Next, quenching is carried out. Quenching is a heat treatment process for transforming austenite structure into martensite having high hardness through rapid cooling from a high temperature to room temperature. And a tempering heat treatment process is finally performed to impart toughness to the brittle martensite structure with high hardness. However, if the hardness is not sufficiently high even after quenching, a Deep Freezing process is additionally performed between the quenching and the tempering heat treatment. The Deep Freezing process is a process of further cooling the material quenched at room temperature to a cryogenic temperature of about -50 to -150 ° C. Through this process, austenite remaining in the microstructure of the quenching material The structure is further transformed into a martensite structure to further increase the hardness.

In the present invention, the hot-rolled and annealed sheet is maintained at a temperature of 1000 to 1100 占 폚 and then quenched so that the residual carbide in the microstructure has a size of 10 占 퐉 or less.

The quenched material is subjected to a tempering heat treatment at 150 to 250 DEG C

Allow the hardness to be above 55 HRC after tempering heat treatment.

In the present invention, the quenched martensitic stainless steel can be subjected to a deep freezing heat treatment at a temperature of -50 to 150 ° C before the tempering treatment.

(Example)

Hereinafter, embodiments of the present invention will be described. In the examples of the present invention, the microstructural characteristics of the steel produced through the strip casting method, which is one example of the rapid cooling casting method, were compared with the hot-rolled annealed sheet produced through the conventional continuous casting method.

Table 1 shows the components of the steel produced by the ingot casting method and the strip casting method. In the comparative example of the present invention, 40 kg of a vacuum induction melting ingot having a thickness of 140 mm was manufactured by using the conventional ingot casting method. This is shown in Comparative Example 1 in Table 1. Thereafter, the ingot was reheated to 1250 占 폚 in an inert atmosphere furnace for hot rolling, maintained at that temperature for 3 hours, and then hot-rolled to a final thickness of 2 mm. On the other hand, steels of various compositions were prepared in the form of hot-rolled coils using a twin-roll type strip casters, including components similar to those of Table 1 in component steels produced by continuous casting. The results are shown in Tables 2 to 5.

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 was formed at a rapid cooling rate on the roll surface. In-line rolling was performed immediately after casting to produce a 2 mm thick hot-rolled coil.

A 2 mm thick hot-rolled sheet manufactured by using the ingot casting method and a 2 mm thick hot-rolled coil produced by strip casting were subjected to batch annealing under the same conditions. The hot rolled strip was subjected to heat treatment at 700 to 950 캜 in a reducing atmosphere. Then, the hot-rolled annealed material was subjected to tempering heat treatment. The strengthening heat treatment is carried out at a temperature of 1000 ~ 1100 ℃. Preferably austenitization heat treatment is performed at a temperature of 1050 DEG C and maintained for 0.5 to 2 hours, preferably at least 1 hour. After the austenitization heat treatment, the material is subjected to quenching ). The microstructure of the quenched material was investigated using a scanning electron microscope and the size of the residual carbide in the microstructure was investigated to find out if the carbide was 10 μm or less in the presence of "fine" And "Coarse", and the results are shown in Table 1.

Further, the quenched material is subjected to a deep freezing heat treatment at a temperature of -50 to -150 DEG C, preferably -70 DEG C for at least 1 hour and then at 150 to 250 DEG C, And tempering heat treatment was performed at 200 占 폚 for at least 2 hours to measure the hardness of the material.

division C Si Mn P S Cr Ni Mo W N Carbide
size Remarks One 0.54 0.44 0.36 0.018 0.002 14.5 0.37 0.60 1.20 0.03 minuteness Ingot casting
(Comparative Example) 2 0.54 0.31 0.49 0.019 0.003 14.5 0.25 0.62 1.24 0.03 clay pipe Strip casting
(Comparative Example) 3 0.47 0.31 0.49 0.021 0.002 14.5 0.25 0.61 1.31 0.12 minuteness Strip casting
(Honorable Mention) 4 0.45 0.43 0.61 0.019 0.002 14.2 0.31 0.51 1.57 0.13 minuteness Strip casting
(Honorable Mention) 5 0.42 0.38 0.55 0.020 0.003 13.8 0.26 1.53 1.02 0.1 minuteness Strip casting
(Honorable Mention) 6 0.43 0.51 0.71 0.018 0.002 13.2 0.15 0.5 - 0.11 minuteness Strip casting
(Honorable Mention) 7 0.43 0.6 0.44 0.019 0.002 14.7 0.22 - 0.5 0.1 minuteness Strip casting
(Honorable Mention) 8 0.41 0.7 0.4 0.018 0.002 14.9 0.12 - - 0.18 minuteness Strip casting
(Honorable Mention) 9 0.45 0.32 0.5 0.019 0.002 14.2 0.22 0.6 One 0.08 minuteness Strip casting
(Comparative Example) 10 0.48 0.33 0.46 0.018 0.002 14.3 0.3 0.5 1.3 0.05 minuteness Strip casting
(Comparative Example) 11 0.46 0.33 0.46 0.018 0.002 14.3 0.3 - - 0.05 minuteness Strip casting
(Comparative Example)

3 is a micrograph of a carbide microstructure of a material produced by the ingot casting method and quenching heat treated after 1050 占 폚 austenitizing heat treatment (1 in Table 1, comparative example), Fig. 4 is a graph showing the microstructure of carbide produced by strip casting method, (2 in Table 1, comparative example) after the austenitizing heat treatment. 5 is a micrograph of carbide microstructure of a material (4 of Table 1) manufactured by the strip casting method according to the present invention and subjected to a quenching heat treatment after a 1050 ° C austenitizing heat treatment.

3, a large number of residual carbides and minor coarse carbides within about 2 탆 are observed, but the size of coarse carbides is less than 10 탆.

The following are the carbide microstructures observed in steel casting and quenching heat treated (2 in Table 1) with strip casting having components similar to those of the ingot casting and quenching heat treated steel (1 in Table 1).

In the case of FIG. 4, similarly to the case of FIG. 3, a large number of residual carbides of about 2 μm or less are observed, but in the case of coarse carbides, the shape and size are obviously different. 3), roughly spherical coarse carbides having a size of about 5 탆 are observed, while in the case of a material produced by strip casting (Fig. 4), irregular shapes Of carbide having a size of 10 mu m or more is observed. Therefore, it can be seen that the size and shape of the residual carbide are different when the manufacturing method of the alloy is different even though they are similar components. Particularly, in the case of producing the esophagus by strip casting, the carbide having an irregular shape and having an irregular shape as shown in Fig. 4 is a micro-histological factor which can deteriorate the sharpness of the nib.

Fig. 5 shows the microstructure after quenching of the component steel in which carbon is reduced and the nitrogen is adjusted upward compared with the component 2 in Table 1 in order to control the size of the coarse carbide observed in Fig. 4 to 10 탆 or less.

Fig. 5 shows the microstructure after quenching of the No. 4 steel of Table 1, which shows very fine microstructure in which the irregular shaped coarse carbide aggregates shown in Fig. 4 are removed. This is because, even if it is produced by a strip casting process, when the carbon content is limited to minimize the micro segregation of carbon and the hardness of the martensite steel decreases with the decrease of carbon by adding nitrogen, It is possible to produce a microstructural steel for a water-based material having a better performance.

Next, after the austenitizing heat treatment in which the martensitic stainless steel hot-rolled annealed material according to the present invention is heated to 1050 占 폚 and held for one hour, quenching is performed in the oil. The quenched material was subjected to a deep freezing heat treatment at a temperature of -70 DEG C for at least 1 hour and then subjected to a tempering treatment at 200 DEG C for at least 2 hours, .

As shown in Table 2, in Examples 3 to 8 of the present invention, when the range of C + N is 0.5% or more and the range of N / C is 0.2% or more, the hardness is 55HRC or more. Can be. However, in Comparative Example 1, it was manufactured by the ingot casting method, and the hardness shows 55HRC or more when the N / C range is 0.06, respectively. However, in the case of Comparative Example 1, there is a problem in that carbide center segregation occurs in the hot rolled sheet because it is manufactured by the ingot casting method. In the case of Comparative Example 2 is produced by a strip casting process, but the N / C range is less than 0.2%, the hardness is 55HRC or more, there is a problem that coarse carbide is produced. On the other hand, in the case of Comparative Examples 9 to 11 it can be seen that the hardness of less than 55HRC is obtained when the range of N / C is controlled to less than 0.2%.

The above results, by weight% C 0.4 ~ 0.5% and N 0.1% ~ 0.2%, Cr content of 13 ~ 15%, C + N more than 0.5%, N / C 0.2 Controlling more than% and using the strip casting process to produce steel of 1 mm or more, it has been shown that it is possible to produce high hardness steel with excellent blade tip quality with hardness of 55 HRC or more suitable for advanced esophagus.

division One 2 3 4 5 6 7 8 9 10 11 C + N 0.57 0.57 0.59 0.58 0.52 0.54 0.53 0.59 0.53 0.53 0.51 N / C 0.06 0.06 0.26 0.29 0.24 0.26 0.23 0.44 0.18 0.10 0.11 Hardness (HRC) 55.2 55.9 57.6 56.5 56.1 55.3 55.1 58.1 53.9 53.5 53.1

6A and 6B are graphs showing the softening resistance of the tempering of the comparative steel and the inventive steel in the present invention. 6A shows a case where the value of the existing nitrogen (N) is 0.03 wt% as a comparative example. However, when the nitrogen (N) value is low as described above, the hardness is greatly lowered by tempering, which is disadvantageous in securing the hardness in the final product. On the other hand, FIG. 6B shows a case in which the value of C is reduced to 0.5 wt% or less to reduce the segregation of carbide and increase the value of N to 0.1 wt% or more, thereby minimizing the segregation of C, And the hardness value due to N can be obtained. As shown in FIG. 6B, when the value of N is increased to 0.10 wt% and the value of C is controlled to less than 0.5 wt% in the embodiment of the present invention, softening resistance by tempering is large, .

In the reinforcing heat treatment in the embodiment of the present invention, after the austenitizing heat treatment in which the martensitic stainless steel hot-rolled annealed material is heated to 1000 to 1100 ° C, preferably 1050 ° C and held for 1 hour, quenching is performed in the oil And the heat treatment is carried out at a temperature of 150 to 250 ° C, preferably 200 ° C for at least 2 hours.

Of course, in the present invention, it is also possible to further perform a deep freezing process between the quenching and the tempering heat treatment. In this case, the material quenched at room temperature in the Deep Freezing process is further cooled to a cryogenic temperature of about -50 to -150 ° C to remove the austenite structure remaining in the microstructure of the quenching material, It can be further transformed into a tissue to further increase the hardness.

Meanwhile, FIG. 7 is a graph showing that corrosion resistance is improved in comparison with the existing steel by adding C / N to a corrosion resistant element Mo / W in the embodiment of the present invention. This is compared with the results of weight loss of immersion corrosion resistance in a 0.1% sulfuric acid solution (Comparative Example) and 0.1% sulfuric acid solution of the invention steel, and the weight loss of the present invention steel is less than that of the comparative example. In this graph, the comparative example is a steel grade including the conventional 0.5C-0.03N-14Cr, which is compared with the steel grade including 0.45C-0.1N-14Cr relating to the steel of the present invention.

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.

1: Ladle 2: Tundish 3: Injection nozzle
4: Meniscus shield 5: Edge dam 6: Casting roll
7: Roll nip 8: Casting 9: Rolling machine
10: Coil winding equipment

Claims

In martensitic stainless steel produced by strip casting, in weight%, C: 0.4 to 0.5%, N: 0.1 to 0.2%, Cr: 13 to 15%, Si: 0.1 to 1.0%, Mn: 0.1 ~ 1.0%, Ni: more than 1.0% or less, C + N: 0.5% or more and N / C is controlled to 0.2% or more, the rest containing Fe and other unavoidable impurities, the martensitic stainless steel Martensitic stainless steel, characterized in that the size of the residual carbide of the steel is 10㎛ or less and the hardness is 55HRC or more.

The method of claim 1,
Martensitic stainless steel in which the weight%, W: 0.1-2%, Mo: 0.1-2% is added alone or in combination.

3. The method according to claim 1 or 2,
Wherein the residual carbide has a size of 3 mu m or less.

3. The method according to claim 1 or 2,
Wherein the stainless steel has a hardness of 55 HRC or more after the tempering heat treatment.

3. The method according to claim 1 or 2,
The stainless steel is martensitic stainless steel is a thin plate material of 1mm or more thickness.

By weight% C: 0.4-0.5%, N: 0.1-0.2%, Cr: 13-15%, Si: 0.1-1.0%, Mn: 0.1-1.0%, Ni: more than 0 and 1.0% or less, C + N: 0.5% or more and N / C is controlled to 0.2% or more, the remainder of the molten stainless steel containing Fe and other unavoidable impurities by thin casting by strip casting, the cast stainless steel sheet inline A method for producing martensitic stainless steel that produces a hot rolled strip at a rolling reduction of 5 to 40% using a roller.

The method according to claim 6,
0.1 to 2% of W, and 0.1 to 2% of Mo are added singly or in combination, in terms of% by weight, of the martensitic stainless steel.

8. The method according to claim 6 or 7,
The strip casting includes a pair of rolls rotating in opposite directions, 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 pool. A method for producing martensitic stainless steel in which a molten stainless steel sheet is cast by supplying molten steel of the composition from a tundish to a molten steel pool through a nozzle.

8. The method according to claim 6 or 7,
And subjecting the hot-rolled strip to batch annealing in a temperature range of 700 to 950 占 폚 in a reducing gas atmosphere to produce a hot-rolled and annealed sheet.

10. The method of claim 9,
Wherein the hot-rolled and annealed sheet is maintained at a temperature of 1000 to 1100 占 폚 and quenched to have a residual carbide size of 10 占 퐉 or less in a microstructure.

The method of claim 10,
Wherein the quenched material is subjected to a tempering heat treatment at 150 to 250 占 폚.

12. The method of claim 11,
Wherein the martensitic stainless steel exhibits a hardness of 55 HRC or more after the tempering heat treatment.

12. The method of claim 11,
Wherein the quenched martensitic stainless steel is subjected to a deep freezing heat treatment at a temperature of -50 to 150 占 폚 before the tempering heat treatment.