JP5770743B2 - High carbon martensitic stainless steel and method for producing the same - Google Patents

Description

  The present invention relates to a high carbon martensitic stainless steel and a method for producing the same, and more particularly, strips a high carbon martensitic stainless steel containing 0.4 to 0.8% carbon and 11 to 16% chromium. The present invention relates to a high-carbon martensitic stainless steel manufactured using a casting process and having a reduced primary carbide size, and a method for manufacturing the same.

  Generally, a high carbon martensitic steel containing 0.40% or more of carbon by weight is excellent in corrosion resistance, hardness, and wear resistance, and is used for razor blades, swords, and the like. Thus, when using a razor blade manufactured using a high carbon martensitic stainless steel used for a razor blade or the like, the razor blade comes into contact with moisture during a shaving process.

  In addition, such a razor blade is required to have corrosion resistance because it is stored in a moist atmosphere. Thus, since the environment is too harsh for high carbon steel to be used, usually martensitic stainless steel containing about 13% chromium is mainly used. In the razor blade manufactured using such martensitic stainless steel, the martensite of the base structure contains chromium of about 12% or more by weight, and as a result, a thin chromium oxide is formed on the surface of the razor blade. Is precisely produced and plays a role in suppressing corrosion of the base structure of the razor blade from moisture.

  On the other hand, shaving is a process in which a razor blade is brought into close contact with a material to cut the beard, and in order to cut a high-strength beard, higher hardness is required. The high hardness level required by razor blades is achieved by the martensitic base structure of steel. The martensite structure is a very hard microstructure produced when rapidly cooling high-temperature austenite. The higher the content of carbon dissolved in the high-temperature austenite phase, the more carbon dissolved in martensite and the higher the hardness of martensite. Therefore, in order to produce a razor blade steel having a high hardness, it must be possible to add as much carbon as possible to the steel.

  In general, 420 series martensitic stainless steel is mainly used as a razor blade material that satisfies the above requirements in terms of corrosion resistance and hardness. These steels are steels containing 0.45 to 0.70% carbon by weight, up to 1% manganese, up to 1% silicon, and 12 to 15% chromium, especially about 0. Component systems based on 65% and about 13% chromium are commonly used.

  On the other hand, the thickness of the razor blade is generally 0.2 mm or less. Therefore, in order to manufacture a razor blade, a very thin high carbon martensitic stainless steel having a thickness of 0.2 mm or less is used as an initial material. This initial material has a microstructure composed of a ferrite matrix and a fine chromium carbide uniformly distributed. At this time, the distribution of fine chromium carbide enables rapid re-solidification of carbon in the high temperature austenite phase in the subsequent hardening process, and martensite transformed by cooling is used as a razor blade. Is a main factor for adjusting to have sufficient hardness.

And the size of the chromium carbide of the initial material can be defined as the number of chromium carbide per unit area, and when observed at a high magnification of 10,000 times, the chromium carbide having a size of 0.1 μm or more is obtained. There must be 50 or more per 100 μm ² area. After slitting the initial material to an appropriate width and coiling, a razor blade is manufactured through a plurality of subsequent steps. Subsequent processes provide a tempering heat treatment process that heats and holds the hot austenite region and then cools it to impart high hardness, a process that sharpens the razor blade, wear resistance and lubricity. A coating process for the razor, and a welding process for mounting the razor blade on the razor.

  In addition, the initial material of a thin object (thickness of 0.2 mm or less) used for manufacturing a razor blade must be free of coarse chromium carbide in the microstructure, for the following reason. When coarse chromium carbide is present, the fall of the coarse chromium carbide occurs at the edge of the razor blade during the subsequent process of sharpening the razor blade, and the sharpness of the edge of the razor blade becomes dull. The phenomenon occurs. This phenomenon is called edge tear-out, which is the main factor that hurts the skin while shaving. In addition to coarse chromium carbide, coarse inclusions also act as factors causing edge dropout. The maximum size of chromium carbide allowed in view of edge dropout is 10 μm. Crude chromium carbide having a size of 10 μm or more, which exists in the initial material and acts as a main cause of occurrence of edge dropout, is coarse primary carbide produced during casting of the alloy. This rough primary carbide is distinguished from fine secondary carbides that are generated during hot working or heat treatment of the alloy. Coarse primary carbide is produced by segregation that occurs between dendrite arms during the solidification process of high carbon martensitic stainless steel. Carbon and chromium segregation is a natural phenomenon that occurs during solidification, so primary carbide formation cannot be avoided, but its size must be minimized during the solidification process to prevent edge shedding. There is.

  Such an edge drop-off problem is an important quality factor that determines the quality of the cutting edge not only for razor blades but also for general blade applications. As described above, in order to produce a razor blade having high hardness, it is necessary to add as much carbon as possible to the steel. However, the higher the carbon content, the rougher the primary carbide is formed during solidification. This makes it difficult to manufacture high quality razor blades.

  For this reason, in Japanese Patent No. 6103161, which is conventionally known, an alloy component system in which the carbon content is reduced to 0.40 to 0.55% in order to minimize edge dropout due to primary carbide. Presents. In particular, the ingot casting method generally used for the production of razor blade steel material has a drawback that segregation occurs seriously and primary carbides are formed coarsely. Because of this drawback, in order to re-dissolve the primary carbide or reduce its size, additional heat treatment such as heat treatment or forging is applied to the ingot.

  Therefore, in order to manufacture a high-quality razor blade, a method for suppressing the formation of coarse primary carbide during casting is required. In particular, compared to ordinary razor blade steel, it has become necessary to develop an economical casting method that can effectively reduce the size of the primary carbide within the microstructure without reducing the carbon content. .

  The present invention has been made in response to the above-mentioned demand, and a strip casting method is newly used for the purpose of replacing the ingot casting method mainly used for the production of existing high carbon martensitic steels. It is. According to the present invention, a martensitic stainless steel containing high carbon is economically produced while dramatically suppressing the primary primary carbide generated during solidification, which was the biggest drawback of the existing ingot casting method. The purpose is to present a method that can be.

  In order to achieve the above object, the present invention provides a pair of rolls rotating in opposite directions, an edge dam provided so as to form a molten steel pool on both side surfaces thereof, and an inert nitrogen gas on the upper surface of the molten steel pool A strip casting apparatus including a meniscus shield for supplying a molten stainless steel containing C: 0.40 to 0.80% and Cr: 11 to 16% in weight% from a tundish through a nozzle to the molten steel pool To produce a hot-rolled annealed strip at a rolling reduction of 5 to 40% using an in-line roller immediately after casting, and within the microstructure of the hot-rolled annealed strip. A method for producing a high carbon martensitic stainless steel in which the primary carbide is 10 μm or less is provided.

  Moreover, in this invention, the said martensitic stainless steel is a weight%, Si: 0.1-1.0, Mn: 0.1-1.0, Ni: 0 excess 1.0 or less, N: 0 Provided is a method for producing a high-carbon martensitic stainless steel, wherein the excess is 0.1 or less, S is 0 or more and 0.04 or less, P is 0 or more and 0.05 or less, and the balance is Fe and other inevitable impurities .

  Furthermore, in the present invention, the hot-rolled annealed strip is subjected to batch annealing in a reducing gas atmosphere at a temperature range of 700 to 950 ° C. to produce a hot-rolled annealed plate, and a high carbon martensite system Stainless steel can be manufactured.

  Moreover, in this invention, it is preferable to implement the said batch annealing in the range of 1-3 times.

  Furthermore, in the present invention, the hot-rolled annealed strip that has been subjected to the batch annealing treatment can be pickled after shot blasting.

  In the present invention, in the hot-rolled annealing strip before the pickling treatment, the depth of the decarburized layer can be 20 μm or less immediately below the surface scale.

  Further, in the present invention, the hot-rolled annealed strip can be subjected to subsequent cold rolling, and at this time, it is preferable that a single cold rolling reduction is 70% at maximum.

  Furthermore, in the present invention, the cold-rolled strip can be annealed in a reducing gas atmosphere with a total of 5 times or less.

  In the present invention, the cold-rolled strip can be subjected to cold rolling annealing at a temperature of 650 to 800 ° C.

  According to another aspect of the present invention, a pair of rolls rotating in opposite directions, an edge dam provided to form a molten steel pool on both side surfaces thereof, and inert nitrogen gas on the upper surface of the molten steel pool are provided. In a strip casting apparatus including a meniscus shield to be fed, a molten stainless steel containing C: 0.40 to 0.80% and Cr: 11 to 16% by weight is transferred from a tundish to the molten steel pool through a nozzle. A stainless steel sheet is cast to supply a hot rolled annealed strip at a rolling reduction rate of 5 to 40% using an in-line roller immediately after casting. A high carbon martensitic stainless steel having a primary carbide of 10 μm or less can be provided.

  As described above, the present invention is characterized by applying a strip casting method for manufacturing a hot-rolled coil directly from molten steel manufactured in a steelmaking process. Strip casting can innovatively reduce the size of the primary carbide formed of the solidified tissue and is very usefully applicable to the production of high quality razor blades. In particular, not only the quality of razor blades but also the production of hot-rolled coils directly from molten steel, the advantages of a simpler hot-rolled coil manufacturing process and a much lower manufacturing cost than existing ingot casting methods. There is.

It is a figure which shows the schematic of a general strip casting process. It is a structure | tissue photograph figure which shows that the rough primary carbide is produced | generated in the crystal grain boundary by the cross-sectional microstructure of the ingot cast by the ingot casting method. This is a microstructure photograph of an ingot cast by the ingot casting method that has been hot-rolled and then water-cooled, and shows that the primary carbide that existed at the grain boundaries of the ingot also remains in the microstructure of the hot rolled sheet. is there. A low-magnification cross-sectional microstructure of a hot-rolled sheet material cast by the strip casting method and continuously in-line rolled at a high temperature immediately after casting, an equiaxed crystal structure formed in the center of the thickness, and the surface layer It is a structure photograph figure which shows the columnar crystal (columnar crystals) structure | tissue formed in the part. It is the structure | tissue photograph figure which expanded the columnar crystal area | region of FIG. It is the structure | tissue photograph figure which expanded the equiaxed crystal area | region of FIG. It is a structure | tissue photograph figure which shows the cross-sectional microstructure of the low magnification of the thin cold-rolling raw material manufactured to 0.075 mm thickness. It is a structure | tissue photograph figure which shows the cross-sectional microstructure of the high magnification of the thin cold-rolling raw material manufactured to 0.075 mm thickness.

  Hereinafter, embodiments of the present invention and other matters necessary for those skilled in the art to easily understand the contents of the present invention will be described in detail with reference to the accompanying drawings. However, since the present invention can be realized in various different forms within the scope of the claims, the embodiment described below is merely an example regardless of the expression.

  In describing this embodiment, if it is determined that a specific description related to the known function or configuration may obscure the gist of the present invention, the detailed description thereof will be omitted. In the drawings, it should be noted that the same components are denoted by the same reference numerals and symbols as much as possible even if they are displayed on other drawings. In the drawings, the thickness and size of each layer may be exaggerated for convenience of explanation and clarity, and may differ from the actual thickness and size of the layer.

  FIG. 1 is a schematic view of a conventionally known strip casting equipment. This strip casting process is a process for producing thin hot-rolled annealed strips directly from molten steel, omitting the hot-rolling process, and pioneering manufacturing costs, capital investment costs, energy consumption, pollution gas emissions, etc. It is a new steel process that can be reduced. As shown in FIG. 1, a twin roll type thin plate casting machine used in a general strip casting process takes molten steel in a ladle 1 and flows into the tundish 2 along the nozzle and into the tundish 2. Molten steel 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 is started. At this time, the molten metal surface between the rolls is protected by the meniscus shield 4 to prevent oxidation, and an appropriate gas is injected to adjust the atmosphere appropriately. The thin plate 8 is manufactured while passing through the roll nip 7 where both rolls meet, and after being rolled through the rolling mill 9 while being drawn, it is wound by the winding equipment 10 through a cooling process.

  At this time, an important technique in the twin roll type thin plate casting process in which a thin plate having a thickness of 10 μm or less is directly manufactured from molten steel is to introduce the molten steel through an injection nozzle between internal water-cooled twin rolls rotating in the opposite direction at a high speed. Supplying and manufacturing the thin plate of desired thickness without a crack and improving a real yield.

  The present invention relates to a method for producing a high carbon martensitic stainless steel using a strip casting process, and in particular, the main component is 0.40 to 0.80% carbon and 11 to 16% chromium by weight%. Razor blade with excellent cutting edge quality by reducing the size of primary carbide formed in the cast structure to 10 μm or less in order to manufacture high carbon martensitic stainless steel including It is characterized by producing high carbon martensitic stainless steel.

  The strip casting process, which is a feature of the present invention, is a production method in which liquid steel is directly cast on a plate material having a thickness of 1 to 5 mm, and a very fast cooling rate is applied to the cast plate to minimize segregation occurring during casting. It is. In the present invention, a hot-rolled coil is manufactured using a twin roll type strip caster. Twin roll strip casters supply molten steel between twin-drum rolls and side dams that rotate in opposite directions, and release a large amount of heat through the water-cooled roll surface. It is characterized by casting. At this time, a solidified cell is formed on the roll surface at a high cooling rate, and a thin hot-rolled sheet having a thickness of 1 to 5 mm is produced by in-line rolling performed continuously after casting.

(Example)
Hereinafter, the present invention will be described using examples.

  The base material used in the present invention is a high carbon martensitic stainless steel, and uses C: 0.4 to 0.8% and Cr: 11 to 16%. In the present invention, when the C content is 0.4% or less, a large amount of primary carbide is not generated in the strip or ingot, but the hardness is not preferable. Moreover, when it is 0.8% or more, even if it is manufactured by strip casting, it may be difficult to suppress generation of coarse primary carbide. Therefore, in this invention, C: 0.4-0.8% and Cr: 11-16% are proposed as an optimal range.

  Further, the martensitic stainless steel according to the embodiment of the present invention is, by weight, Si: 0.1 to 1.0, Mn: 0.1 to 1.0, Ni: 0 to 1.0 or less, N: 0 excess 0.1 or less, S: 0 excess 0.04 or less, P: 0 excess 0.05 or less, and the balance are intended for alloys related to component systems composed of Fe and other inevitable impurities.

  In the examples, the microstructural characteristics of the steel manufactured by applying the hot-rolled annealing strip manufactured through the existing ingot casting method and the strip casting method were compared. Table 1 shows the components of steel produced by the ingot casting method and the strip casting method. First, in order to compare the microstructure of the material cast by the strip casting method with the material manufactured by the ingot casting method, ordinary razor blade steel is manufactured by an ingot, and the components are shown as comparative examples in Table 1 ( # 1) Shown. The ingot was produced with a weight of 50 kg by vacuum induction melting method. The ingot was re-heated at a temperature of 1200 ° C., hot-rolled to a 3.5 mm-thick plate, and water-cooled immediately after hot-rolling. And steel of various components was manufactured as a hot-rolled sheet using a twin roll type strip caster. 100 tons of each were cast, and the components are shown in Table 2. 100 tons of material cast between water-cooled rolls using the strip casting method is hot-rolled immediately after casting with an in-line roller at a high temperature to produce a 1-5 mm thick heat. It was continuously manufactured with hot rolled coils.

  FIG. 2 shows a cross-sectional structure of an ingot of a comparative example (# 1) in Table 1 which is a normal component steel cast by vacuum induction melting. And FIG. 3 showed the microstructure which water-cooled after the hot rolling of the component steel regarding the said comparative example (# 1). As is clearly observed from the microstructure of the ingot of FIG. 2, it is shown that the primary carbide shown as primary carbide is irregularly formed between the grains. Such coarse primary carbide does not completely re-solidify as a base structure even during reheating performed at a temperature of 1200 ° C., and therefore remains in the microstructure after hot rolling and is arranged in the rolling direction. Observed at. This can be confirmed from FIG.

  FIG. 4 shows a 2.1 mm thick hot-rolled coil (Table 2, # 6) having a similar composition to the component steel of the present invention (Table 1, # 1) manufactured by strip casting and cast by an ingot. A low-magnification cross-sectional structure. In a coil manufactured by strip casting, a microstructure of columnar crystals shown as (columnar crystal) developed in the surface layer part and a fine structure of equiaxed crystals shown as (equiaxed crystal) developed in the central part of the thickness. The tissues are shown in FIGS. 5 and 6, respectively. The primary carbide size can be compared from the ingot structure shown in FIGS. 2 and 3 and the strip casting structure shown in FIGS. 5 and 6. That is, when manufactured by the existing ingot casting method, it can be clearly observed that coarse primary carbide is formed at a magnification of 1000 times. However, in the hot rolled coil manufactured by applying the strip casting method shown in FIGS. 5 and 6, the coarse primary carbide observable from the solidified structure of FIG. 2 and the hot rolled plate of FIG. 3 manufactured by the ingot casting method. Is not observed in a fine structure having a magnification of 1000 times. This is the result of highlighting the technical effect of the present invention that when forming a martensitic stainless steel containing high carbon, the formation of coarse primary carbide can be innovatively suppressed when casting using the strip casting method. is there. On the other hand, in the hot-rolled sheet, the size of primary carbide observable with an optical microscope with a magnification of 1000 times was examined, and the results are summarized in Tables 1 and 2.

  When casting a high carbon martensitic stainless steel, another advantage of applying the strip casting method is that the process is reduced and the manufacturing cost is lower than that of the existing ingot casting method. In order to produce a high carbon martensitic hot rolled coil by the ingot casting method, subsequent hot working processes such as slabbing and hot rolling are essential after ingot forming. This is the main factor that increases the manufacturing cost of the ingot casting method. In addition, the heat treatment process, including material cooling and temperature increase, which are essential in subsequent hot working processes such as ingots and hot rolling, are concerned with the occurrence of cracks due to thermal shock. This is very disadvantageous in terms of productivity because it must be performed very slowly and work for transferring materials between processes must be performed carefully at high temperatures. The strip casting method has a great advantage in that a high-carbon martensitic stainless steel can be manufactured at a low cost because a hot-rolled coil is directly manufactured without going through another hot working step including the above-mentioned block.

  As a 2.1 mm-thick hot-rolled coil manufactured in the strip casting process, the inventive steel 6 (# 6) in Table 2 was subjected to batch annealing for a long time in a batch-type heat treatment furnace. At this time, the hot-rolled coil was gradually heated to an annealing temperature of 700 to 950 ° C. in a reducing atmosphere, kept at that temperature for a long time, and then gradually cooled again in the furnace. This annealing heat treatment can be performed at least once and at most three times. Of course, the higher the number of batch annealing treatments, the more homogeneous the material can be, but this can lead to additional manufacturing costs. The heat treatment in this process serves to change the martensite and retained austenite constituting the microstructure of the hot rolled coil into ferrite and chromium carbide. The hardness of the hot-rolled annealed structure after this process was about 220 Hv. The annealed hot-rolled coil is shot blasted, and the surface scale and decarburized layer are removed with a pickling solution composed of sulfuric acid and sulfuric acid / nitric acid mixed acid at a temperature of about 70 ° C. did. At this time, the depth of the decarburized layer was formed to be about 20 μm or less just below the surface scale, and could be easily removed by pickling. Generally, ingots manufactured by the ingot casting method are indispensable to heat treatment of ingots at high temperatures to alleviate segregation of alloying elements generated during casting, but decarburization occurs seriously in this process. In addition, additional work for removing the decarburized layer may be required after manufacturing the hot-rolled coil. Although a decarburized layer may be present in a coil manufactured by strip casting, the time for exposure to a high temperature of 1000 ° C. or higher is as short as 5 minutes or less until it is cooled after casting, and a slight decarburized layer is generated. Accordingly, since the decarburized layer can be easily removed by pickling in the hot rolled coil manufactured by the strip casting process, additional coil grinding can be omitted to remove the decarburized layer. It is.

  On the other hand, cold rolling was performed on the invention steel (# 6) in Table 2 as a hot-rolled coil after pickling. As described above, since the initial material for manufacturing a razor blade has a thickness of 0.2 mm or less, in order to reduce the thickness of the initial material from a 2.1 mm thick hot-rolled annealing coil to a target thickness. Significant cold reduction is required. In particular, razor blade steel materials are caused by fine carbides present in the microstructure, and work hardening is fast during cold rolling, and the ductility is greatly reduced. In order to perform cold rolling to a target thickness while preventing sheet breakage due to the occurrence of edge cracks during cold rolling, a maximum of 70% or less of cold rolling was performed during one cold rolling. Thereafter, edge trimming and intermediate annealing were performed. At this time, the intermediate annealing was performed at a temperature of about 750 ° C. for a time within 5 minutes. In order to roll to the final target thickness, cold rolling and intermediate annealing were repeated several times. In this manner, a cold rolled thin coil having a thickness of 0.075 mm was manufactured. At this time, it is economical to limit the total number of annealing steps for obtaining the cold-rolled sheet within 5 times including the number of annealing steps performed on the hot-rolled annealing strip. In the present invention, it is possible to further improve the economy with the same quality by using the number of annealing times within 5 times. Moreover, the cold-rolled strip can be cold-rolled annealed at a temperature of 650 to 800 ° C.

7 and 8 showed the microstructure of the coil cold rolled to a thickness of 0.075 mm. In the manufactured coil, there is no carbide having a size of 10 μm or more, and most of the carbide is uniformly distributed in a size of 0.1 to 1.5 μm. That is, it can be seen from FIG. 8 that a fine structure advantageous for preventing edge dropout is formed. Further, the number of carbides having a size of 0.1 μm or more observed in FIG. 8 is about 120 EA / 100 μm ² , and it can be seen that it was manufactured as a fine structure suitable for manufacturing a razor blade.

  As described above, the present invention uses the strip casting method to innovatively suppress the formation of coarse primary carbide compared to razor blade steel manufactured by the ingot casting method, and economically produces a high-quality razor blade. It can be manufactured automatically. Although the present invention has been described in terms of particular embodiments of razor blade applications, the scope of the present invention is not limited to razor blade applications, but includes the scope recited in the claims.

  Although the technical idea of the present invention has been specifically described by the above preferred embodiments, it should be noted that the above embodiments are for the purpose of explanation and not for limitation. There must be. Further, those who have ordinary knowledge in the technical field of the present invention can understand that various modifications are possible within the scope of the technical idea of the present invention. The scope of the right to the invention described above is defined by the following claims, and is not restricted by the description of the specification, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention. Belongs.

Claims (14)

The strip casting apparatus includes a pair of rolls rotating in opposite directions, an edge dam provided so as to form a molten steel pool on both sides thereof, and a meniscus shield for supplying an inert nitrogen gas to the upper surface of the molten steel pool. In the method for producing carbon martensitic stainless steel,
By weight, C: 0.40 to 0.80%, Cr: 11 to 16% , Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Ni: more than 0 Martensitic stainless steel consisting of 0 or less%, N: more than 0, 0.1% or less, S: more than 0, 0.04% or less, P: more than 0, 0.05% or less, and the balance being Fe and other inevitable impurities the molten steel is supplied to the molten steel pool through a nozzle from the tundish to cast the stainless steel sheet, the cast stainless steel sheet, with 5-40% of reduction ratio by using the inline roller immediately after casting, 1 When producing a hot-rolled annealed strip that is ˜5 mm thick and has a primary carbide in the microstructure of 10 μm or less,
The pre SL hot rolled annealed strips, a reducing gas atmosphere, carried out batch annealing in the temperature range of 700 to 950 ° C., to produce a hot-rolled annealed sheets,
The said batch annealing is implemented in the range of 1-3 times, The manufacturing method of the high carbon martensitic stainless steel characterized by the above-mentioned. The batch annealing is performed such that in the cross-sectional microstructure of the hot-rolled annealing strip, batch annealing is performed so that 50 or more chromium carbides having a size of 0.1 μm or more per 100 μm ² area. The manufacturing method of the high carbon martensitic stainless steel of description.   The method for producing a high-carbon martensitic stainless steel according to claim 1, wherein the hot-rolled annealed strip subjected to the batch annealing treatment is pickled after shot blasting.   The method for producing a high-carbon martensitic stainless steel according to claim 3, wherein in the hot-rolled annealing strip before the pickling treatment, the depth of the decarburized layer is 20 µm or less just below the surface layer scale.   5. The high-carbon martensten according to claim 1, wherein the hot-rolled annealed strip is cold-rolled and has a maximum cold reduction ratio of one time of 70%. Method for producing site-based stainless steel.   The method for producing high-carbon martensitic stainless steel according to claim 5, wherein the cold-rolled strip is annealed in a reducing gas atmosphere at a total of 5 times or less.   The method for producing a high carbon martensitic stainless steel according to claim 5, wherein the cold-rolled strip is subjected to cold rolling annealing at a temperature of 650 to 800 ° C. Manufactured by a strip casting apparatus including a pair of rolls rotating in opposite directions, an edge dam provided so as to form a molten steel pool on both side surfaces thereof, and a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel pool High carbon martensitic stainless steel
By weight, C: 0.40 to 0.80%, Cr: 11 to 16% , Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Ni: more than 0 Martensitic stainless steel consisting of 0 or less%, N: more than 0, 0.1% or less, S: more than 0, 0.04% or less, P: more than 0, 0.05% or less, and the balance being Fe and other inevitable impurities the molten steel is supplied to the molten steel pool through a nozzle from the tundish to cast the stainless steel sheet, the cast stainless steel sheet, with 5-40% of reduction ratio by using the inline roller immediately after casting, 1 When producing a hot-rolled annealed strip that is ˜5 mm thick and has a primary carbide in the microstructure of 10 μm or less,
Before SL hot rolled annealed strips, atmosphere a reducing gas, a hot-rolled annealed sheet produced by carrying out the batch annealing in the temperature range of 700 to 950 ° C.,
The said batch annealing is implemented in the range of 1-3 times, The high carbon martensitic stainless steel characterized by the above-mentioned. The batch annealing may be performed so that the number of chromium carbides having a size of 0.1 µm or more is 50 or more per 100 µm ² in the cross-sectional microstructure of the hot-rolled annealing strip. The high carbon martensitic stainless steel described.   The high-carbon martensitic stainless steel according to claim 9, wherein the hot-rolled annealed strip subjected to batch annealing is subjected to pickling after shot blasting.   11. The high carbon martensitic stainless steel according to claim 10, wherein a depth of the decarburized layer is 20 μm or less just below the surface scale in the hot-rolled annealing strip before the pickling treatment.   12. The high carbon martensten according to claim 8, wherein the hot-rolled annealed strip is cold-rolled and has a maximum cold reduction of 70% at one time. 13. Site-based stainless steel.   The high-carbon martensitic stainless steel according to claim 12, wherein the cold-rolled strip is annealed in a reducing gas atmosphere at a total of 5 times or less.   The high-carbon martensitic stainless steel according to claim 12, wherein the cold-rolled strip is subjected to cold rolling annealing at a temperature of 650 to 800 ° C.

Images