KR101368502B1 - Martensitic stainless steel with enhanced anti-corrosion performance and method for manufacturing the same - Google Patents

Abstract

The present invention is a method for producing martensitic stainless steel containing C: 0.5 to 0.7%, Cr: 12 to 15% by weight, the first surface to form a surface relief on the martensitic stainless steel by mixed acid Reforming step; And a second surface modification step of forming a micro pit on the surface of the martensitic stainless steel by cold rolling the martensitic stainless steel passed through the first surface modification step. It relates to a process for producing martensitic stainless steels and martensitic stainless steels.

Description

Martensitic stainless steel with enhanced anti-corrosion performance and method for manufacturing the same

The present invention relates to martensitic stainless steel and a method of manufacturing the same, and more particularly, to a martensitic stainless steel and a method of manufacturing the martensitic stainless steel with improved rust resistance.

The present invention relates to martensitic stainless steels, and more particularly to martensitic stainless steels used as razor blade material. Martensitic stainless steel has a microstructure composed of fine chromium carbide uniformly distributed in a ferrite matrix having a chromium concentration of about 7%. In order to produce the final product using such a material, it is processed into a material having a final thickness of 0.1 ~ 0.075mm through cold rolling and annealing several times.

If the thickness of 0.1 ~ 0.075mm martensite stainless steel is supplied for the production of the razor blade, a burr may occur during high-speed punching to the final razor blade shape. Therefore, in order to prevent burr of the martensitic stainless steel to ensure excellent cut surface quality, the martensitic stainless steel is required to have a predetermined hardness of about 280 ~ 330Hv level. The martensitic stainless steel is manufactured in the form of a coil after cold rolling so that the coil-shaped material is precisely slitted at a narrow blade size. At this time, the martensitic stainless steel is rewound in a coil form narrowly after forming an oil protective film on the surface by using an oil such as antirust oil to prevent rust on the surface of the martensitic stainless steel.

Using the rewound narrow coils, the blade manufacturer processes the martensitic stainless steel to the final shape of the blade through high speed punching, and then the martensitic stainless steel is subjected to a reinforcement heat treatment process. The fine chromium carbide uniformly distributed in the matrix structure of the martensitic stainless steel by the reinforcing heat treatment process is reclaimed to increase carbon, thereby securing the high hardness of the martensitic stainless steel. In addition, the martensitic stainless steel is increased in corrosion resistance due to the increased chromium in the matrix of the martensitic stainless steel.

Martensitic stainless steel must be narrowly wound and stored and transported for a long time before the high speed punching and reinforcing heat treatment process is performed. On the other hand, since the martensitic stainless steel has about 7% of chromium, corrosion resistance and the like are poor, which is a problem. Therefore, it is essential that the martensitic stainless steel is coated with oil to prevent contact with oxygen and moisture in the air.

The martensitic stainless steel is subjected to several cold rolling and annealing in order to make it suitable for the razor blade. Thus, the martensitic stainless steel has a beautiful surface when the surface glossiness has a predetermined level. On the other hand, the martensitic stainless steel having too high surface glossiness easily evaporates the oil because there are few trapping sites on the surface thereof. Therefore, martensitic stainless steel is easily corroded by contact with moisture and oxygen in the air. Therefore, the martensitic stainless steel for razor blades with improved oil adsorption property has been studied in various aspects in order to maintain predetermined rust resistance even after long time movement and storage.

An object of the present invention devised to solve the above problems is to provide a method for producing martensitic stainless steel with improved corrosion resistance not easily corroded in air.

In addition, another object of the present invention is to provide a martensitic stainless steel having a predetermined strength and at the same time increase the oil adsorption property to improve the rust resistance.

According to a feature of the present invention for achieving the above object, the present invention is a method for producing martensitic stainless steel containing C: 0.5 to 0.7%, Cr: 12 to 15% by weight, in a mixed acid A first surface modification step of forming surface relief on the martensitic stainless steel; And a second surface modification step of forming a micro pit on the surface of the martensitic stainless steel by cold rolling the martensitic stainless steel passed through the first surface modification step. An excellent method for producing martensitic stainless steels.

In the second surface modification step, the martensitic stainless steel may be cold rolled at a reduction ratio of 20% to 30%.

The martensitic stainless steel is in weight%, C: 0.5 to 0.7%, N: 0.02 to 0.08%, Si: more than 0 to 1.0%, Mn: more than 0 to 1.0%, Cr: 12 to 15%, and Mo It may have an alloy component composed of at least one of: 0.1-2% and W: 0.1-2%, the balance Fe and other unavoidable impurities.

In the first surface modification step, the mixed acid may contain 5% to 20% nitric acid, 0.5% to 3% hydrofluoric acid, but the temperature is 40 ° C. to 70 ° C., and the time may be performed for 30 seconds to 180 seconds. Can be.

The hardness of the martensitic stainless steel passed through the second surface modification step may be 280 Hv to 330 Hv.

In another aspect of the present invention, the present invention is by weight, C: 0.5-0.7%, Cr: 12-15%, Si: more than 0%-1.0%, Mn: 0%-1.0%, Ni: more than 0% 1.0% Or less than N: 0.1% or less, S: greater than 0 or less 0.04% or less, P: greater than or equal to 0.05% or less, containing residual amounts of iron and other unavoidable impurities, and having a micropit ), But the hardness relates to martensitic stainless steel having excellent rust resistance, characterized in that 280Hv to 330Hv.

The martensitic stainless steel is provided with a surface relief by a mixed acid, the surface relief may be formed into a micro pit by cold rolling the martensite stainless steel.

The martensitic stainless steel may have a surface glossiness of 230 to 400.

According to the present invention as described above, it is possible to provide a method for producing martensitic stainless steel with improved corrosion resistance not easily corroded in the air.

In addition, according to the present invention, it is possible to provide martensitic stainless steel having a predetermined strength and improving oil adsorption, thereby improving rust resistance.

1 is a view schematically showing a method of manufacturing martensitic stainless steel with improved rust resistance according to a preferred embodiment of the present invention.
Figure 2 is a graph showing the hardness of martensitic stainless steel after cold rolling by varying the reduction ratio in the second surface modification step of the martensitic stainless steel for blades.
3 is an optical microscope picture of Comparative Example 5.
4 is an optical microscope picture of Comparative Example 6.
5 is an optical micrograph of Example 2.

The details of other embodiments are included in the detailed description and drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with 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.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

According to a preferred embodiment of the present invention, a method of manufacturing martensitic stainless steel having excellent rust resistance is a method of preparing martensitic stainless steel containing C: 0.5 to 0.7% and Cr: 12 to 15% by weight, A first surface modification step of forming surface relief on the martensitic stainless steel; And a second surface modification step of forming a micro pit on the surface of the martensitic stainless steel by cold rolling the martensitic stainless steel passed through the first surface modification step. In addition, in the second surface modification step, the martensitic stainless steel may be cold rolled at a reduction ratio of 20% to 30%.

1 is a view schematically showing a method of manufacturing martensitic stainless steel with improved rust resistance according to a preferred embodiment of the present invention.

Referring to FIG. 1, the martensitic stainless steel 100 wound by the winding roll 400 may be passed through a pickling apparatus 200 and a cold rolling mill 300 to perform first and second surface modification steps. have. In the second surface modification step, the martensitic stainless steel 100 having a relief on the surface of the martensitic stainless steel 100 through a cold rolling mill 300 is micro-pitted on the surface of the martensitic stainless steel 100 through the pickling device 200. It may include forming a.

In general, martensitic stainless steels used for razor blades are hot rolled and repeatedly cold rolled and annealed several times using a hot rolled coil provided in a coil state to produce a final thickness of 0.1 to 0.075 mm. As described above, the martensitic stainless steel has a surface glossiness more than a predetermined level by cold rolling and annealing repeated several times, thereby ensuring beautiful surface quality. On the other hand, martensitic stainless steel having such a surface quality may be a problem when the precision blade grinding process is performed by the blade manufacturer. Specifically, a large amount of light is specularly reflected by the beautiful material surface of the martensitic stainless steel, which hinders the precision grinding process of the blade tip, making it difficult to secure the blade tip quality. In addition, in order to prevent rust during storage and movement of martensitic stainless steel, an oil such as rust-preventive oil may be provided on the surface of the martensitic stainless steel. It does not exist. Therefore, the oil easily evaporates on the surface of the martensitic stainless steel, and therefore, the martensitic stainless steel reacts with moisture and oxygen in the air to easily cause rust on the surface.

On the other hand, the martensitic stainless steel according to the present invention can provide a trapping site having a predetermined strength and at the same time fixing oil such as antirust oil. Specifically, the first marchite-based stainless steel may have surface relief through a first surface modification step, and the micropit may be formed on the martensite-based stainless steel through a second surface modification step. Since the micropits may improve the adsorption property of oils such as rust-preventing oils, it is possible to prevent the oils from evaporating from the surface of the martensitic stainless steel. Therefore, the martensitic stainless steel can prevent contact between the surface of the martensitic stainless steel and moisture and oxygen in the air even during long time storage and movement, thereby improving rust resistance.

The first surface modification step may include a pickling process of chemically etching the surface of the martensitic stainless steel 100 by impregnating the martensitic stainless steel 100 in a mixed acid. In the first surface modification step, the mixed acid may contain 5% to 20% nitric acid, 0.5% to 3% hydrofluoric acid, but the temperature is 40 ° C. to 70 ° C., and the time may be performed for 30 seconds to 180 seconds. Can be.

The martensitic stainless steel includes a microstructure composed of a ferrite base and fine carbides uniformly distributed in the ferrite base. When the martensitic stainless steel is chemically polished by using a mixed acid in the first surface modification step, the ferrite base is eroded by the mixed acid, while the fine carbides in the ferrite base are not eroded. . Therefore, the surface of the martensitic stainless steel may be mixed with the eroded portion and the eroded portion, and surface relief may be formed on the surface of the martensitic stainless steel by the fine carbides.

Mixed acid may be used by adjusting the concentration of nitric acid and hydrofluoric acid using distilled water, wherein the mixed acid is preferably in the concentration of%, nitric acid 5% to 20%, hydrofluoric acid 0.5% to 3%. The hydrofluoric acid provides free hydrofluoric acid, and the free hydrofluoric acid may remove an oxide layer on the surface of martensitic stainless steel. Therefore, it is preferable to maintain the effective free hydrofluoric acid concentration in the mixed acid above a certain acidity.

As in the present invention, the martensitic stainless steel having a Cr content of 12 to 15% by weight is high in corrosion resistance to mixed acids. Therefore, when the% concentration of hydrofluoric acid is less than 0.5%, the concentration of free hydrofluoric acid in the mixed acid is small, so that there is insufficient solubility in oxides such as scale formed on the surface of martensitic stainless steel, and the problem of surface fine washing May occur. In addition, when the% concentration of hydrofluoric acid exceeds 3%, the erosion rate of the martensitic stainless steel is increased, and the surface of the martensitic stainless steel after the pickling process becomes rough, and the surface relief of the martensitic stainless steel is not formed. Therefore, it is preferable that the% concentration of hydrofluoric acid is 0.5% to 3%.

If the% concentration of nitric acid is less than 5%, the concentration of the effective free hydrofluoric acid provided by the hydrofluoric acid is not maintained, so that hydrofluoric acid may dissociate. Therefore, the concentration of the effective free hydrofluoric acid is lowered, making it difficult to remove the surface scale of martensitic stainless steel and the like, and the surface undulation of the martensitic stainless steel may not be formed. Also. When the concentration of nitric acid is more than 20%, a large amount of NO ₂ is generated in the first surface modification step, which may react with distilled water to lower the concentration of hydrofluoric acid. Therefore, in the first surface modification step, the concentrations of nitric acid and hydrofluoric acid in the mixed acid have a related effect, and therefore, the concentration of nitric acid is preferably 5% to 20% and 0.5% to 3% hydrofluoric acid.

The temperature in the first surface modification step is 40 ℃ ~ 70 ℃, time is preferably carried out for 30 seconds to 180 seconds. When the temperature is less than 40 ° C, the movement of ions in the mixed acid may not be active, thereby reducing the efficiency of the first surface modification step. Therefore, a predetermined surface relief may not be formed on the surface of the martensitic stainless steel. In addition, when the temperature is higher than 70 ℃ because the acid constituting the mixed acid is a strong acid may be a safety problem. Therefore, it may be desirable to maintain the temperature of the pickling solution at 40 ° C to 70 ° C.

In addition, when the time is performed in less than 30 seconds in the first surface modification step, the surface relief of the martensitic stainless steel may not be sufficiently formed, when the time is greater than 180 seconds, the martensitic stainless steel This can be a problem because it can corrode not only the steel surface but also the interior.

Since the martensitic stainless steel having the surface relief formed by the mixed acid in the first surface modification step has a low hardness, burrs may be generated during high-speed punching in order to be used for razor blades, thereby reducing product quality. Can be. Therefore, a predetermined hardness may be required in order to be suitable for the high speed punching, and the martensitic stainless steel may have a predetermined hardness through the second surface modification step. The second surface modification step may include forming a micro pit on the surface of the martensitic stainless steel by cold rolling martensitic stainless steel having a relief on the surface at a reduction ratio of 20% to 30%. In this case, in the second surface modification step, the martensitic stainless steel may be cold rolled to increase internal stress, thereby increasing the hardness of the martensitic stainless steel.

For example, the hardness of the martensitic stainless steel passed through the second surface modification step may be 280 Hv to 330 Hv. When the hardness of the martensitic stainless steel is less than 280Hv, the hardness of the martensitic stainless steel may not be sufficient, and a burr may be generated during high speed punching to use the blade. In addition, when the hardness of the martensitic stainless steel is more than 330Hv, the hardness of the martensitic stainless steel is so high that it is difficult to high-speed punching processing, and thus it may be difficult to process the martensitic stainless steel in a desired shape.

It is preferable that the rolling reduction rate at the time of cold rolling in a 2nd surface modification step is 20%-30%. When the reduction ratio is less than 20%, the pressure applied to the martensitic stainless steel is not sufficient, which indicates that the martensitic stainless steel is suitable for use in the razor blade even by the internal stress of the martensitic stainless steel, such as 280 Hv or more. Hardness can be difficult. When the reduction ratio is more than 30%, while the increase rate of the hardness of the martensitic stainless steel is insignificant, the energy applied to rolling the martensitic stainless steel may increase to increase the production cost.

In addition, in the second surface modification step, microfit may be provided on the surface of the martensitic stainless steel. The surface relief of the martensitic stainless steel formed by the mixed acid in the first surface modification step may be cold rolled in the second surface modification step to form microfit. The micropit may be formed at the interface between the ferrite substrate and the fine carbide to act as a trapping site for fixing the oil, thereby improving the adsorption of the oil. The micropits can suppress the evaporation of the oil applied to the surface of the martensitic stainless steel to maintain the protective film by the oil for a long time, thereby improving the rust resistance of the martensitic stainless steel.

The martensitic stainless steel 100 is in weight%, C: 0.5 to 0.7%, N: 0.02 to 0.08%, Si: more than 0% to 1.0%, Mn: more than 0% to 1.0%, Cr: 12 to 15% And an alloy component composed of at least one of Mo: 0.1-2% and W: 0.1-2%, the balance Fe and other unavoidable impurities.

Hereinafter, the role of each alloy component and the reason for limitation of the composition range of the alloy component will be described. In addition, all the percentages described below are% by weight.

If the content of C is low, the hardness of martensitic stainless steel is lowered, so that it is impossible to secure machinability, so 0.5% or more is added. However, if the content is excessively high, the corrosion resistance of the material is reduced through carbide formation, and the upper limit is limited to 0.7% because there is a fear of coarse cast carbide formation due to carbon segregation during casting.

N contributes to strength and corrosion resistance, so 0.02% or more is added. However, when excessively added, pore due to nitrogen may be generated during casting, so the upper limit is limited to 0.08%.

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.

Cr is a basic element to ensure corrosion resistance, so 12% or more is added. However, when the excessive addition, the manufacturing cost increases, and the upper limit is limited to 15% because carbides can lower the solid solution carbon of the final heat treatment material.

Mo has an excellent effect on improving the corrosion resistance, so 0.1% or more is added. However, the excessive addition limits the upper limit to 2% because it leads to an increase in the manufacturing cost.

W is added at least 0.1% to improve the corrosion resistance. However, excessive addition inhibits the increase in manufacturing cost and operability, so the upper limit is limited to 2%.

Martensitic stainless steel according to the present invention is by weight%, C: 0.5 ~ 0.7%, Cr: 12 ~ 15%, Si: more than 0 ~ 1.0%, Mn: more than 0 ~ 1.0%, Ni: more than 0 1.0% Or less than N: 0.1% or less, S: greater than 0 or less 0.04% or less, P: greater than or equal to 0.05% or less, containing residual amounts of iron and other unavoidable impurities, and having a micropit ), But the hardness may be from 280Hv to 330Hv. In addition, the martensitic stainless steel is provided with a surface relief by a mixed acid, the surface relief may be formed into a micro pit by cold rolling the martensitic stainless steel.

On the surface of the martensitic stainless steel, it may be preferable to have micropits of 10 μm or less, and the micropits may be more preferably 5 μm or less.

When the micropits provided on the surface of the martensitic stainless steel exceed 10 μm, the size of the micropits is too large, which may cause a problem in that the surface glossiness of the martensitic stainless steel is reduced. In addition, when the micropit is controlled to 5 μm or less, the size variation between the micropits provided on the surface of the martensitic stainless steel is reduced, so that the surface glossiness is good and the quality of the martensitic stainless steel is reduced. Can be kept more uniform.

In addition, the martensitic stainless steel may have a surface glossiness of 230 to 400 for a razor blade. When the surface glossiness of the martensitic stainless steel is less than 230, the surface glossiness is poor, which is not suitable for use for a razor blade, and may cause poor appearance when used for the razor blade. When the surface glossiness is greater than 400, a large amount of light may be specularly reflected while polishing the martensitic stainless steel, thereby hindering the precision polishing process, thereby degrading the quality.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the scope of the present invention is not limited by the following examples.

Table 1 below is a composition component (% by weight) constituting the martensitic stainless steel used in Comparative Examples and Examples.

ingredient C Si Mn P S Cr Ni N Fe and impurities weight(%) 0.5 to 0.7 0.42 0.64 0.023 0.004 13.4 0.12 0.04 Remainder

The martensitic stainless steel having the composition shown in Table 1 was hot rolled to a thickness of 0.25 mm, and manufactured in the form of a coil. The martensitic stainless steel was manufactured by Comparative Example 1 to Comparative Example 5 by varying the reduction ratio only through the second surface modification step without passing through the first surface modification step, and the first surface modification step was performed through the second surface. Comparative Example 6 was produced without undergoing a modification step. In addition, Comparative Examples 7 to 11 and Examples 1 and 2 were prepared by varying the reduction ratio in the second surface modification step after the first and second surface modification steps.

In the first surface modification step, mixed acid was used by diluting nitric acid and hydrofluoric acid in distilled water, and the mixed solution was prepared with 5% nitric acid and 0.5% hydrofluoric acid at a% concentration. At this time, Comparative Examples and Examples were impregnated in the mixed solution, but the first surface modification step was performed for 30 seconds at a temperature of 60 ℃. In the second surface modification step, the comparative examples and the examples were cold-rolled by varying the reduction ratio, and the comparative examples 1 to 11 and the examples 1 and 2 in which rolling was completed were measured using a hardness tester. It was shown in FIG. In addition, the Comparative Examples and Examples measure the surface glossiness by using a surface gloss meter, and after observing the micro-pit formed on the surface of the martensitic stainless steel using an optical microscope, the oil on the surface of the martensitic stainless steel Was applied to check oil adsorption. Oil adsorption confirms the degree of oil evaporation after a certain amount of time at room temperature. Table 2 shows good, normal and poor.

2 is a graph showing the hardness of martensitic stainless steel after cold rolling by varying the reduction ratio in the second surface modification step of the martensitic stainless steel for razor blades.

2 shows that the martensitic stainless steels subjected to the first surface modification step are cold-rolled by varying the reduction ratio in the second surface modification step, and then the hardness of the martensitic stainless steels is confirmed. As shown in FIG. 2, when only the first surface modification step was performed and the reduction ratio in the second surface modification step was 0%, the hardness of the martensitic stainless steel was 220 Hv. In other words, the martensitic stainless steel without undergoing the second surface modification step is low in hardness and is not suitable for use in razor blades, and thus, burrs are generated during high speed punching. In addition, it was confirmed that the hardness of the martensitic stainless steel increases as the reduction ratio is increased. In order for the martensitic stainless steel to have a hardness of 280 Hv to 330 Hv suitable for use in the blade, it was confirmed that it is preferable to roll the martensitic stainless steel at a reduction ratio of 20% to 30% during cold rolling.

division First surface modification step
Whether or not Second surface modification step
(% Reduction) Hardness
(Hv) Surface gloss Oil adsorption Comparative Example 1 radish 3 232 155 usually Comparative Example 2 radish 6 243 180 usually Comparative Example 3 radish 10 256 207 usually Comparative Example 4 radish 20 287 380 Bad Comparative Example 5 radish 30 322 410 Bad Comparative Example 6 U 0 220 10 Good Comparative Example 7 U 4 238 21 Good Comparative Example 8 U 8 252 87 Good Comparative Example 9 U 10 261 127 Good Comparative Example 10 U 40 332 347 usually Comparative Example 11 U 50 334 412 usually Example 1 U 20 286 257 Good Example 2 U 30 319 280 Good

3 is an optical microscope picture of Comparative Example 5, Figure 4 is an optical microscope picture of Comparative Example 6, Figure 5 is an optical microscope picture of Example 2.

Referring to Table 2 and FIGS. 3 to 5, when the second surface modification step is performed without undergoing the first surface modification step as in Comparative Examples 1 to 5, the reduction in the second surface modification step is performed. Only in Comparative Example 4 and Comparative Example 5 having a rate of 20% and 30%, the hardness was 287Hv and 322Hv, respectively, it could be confirmed that the hardness suitable for the blade. On the other hand, Comparative Examples 1 to 3 except for Comparative Example 4 and Comparative Example 5 was confirmed that the hardness is less than 280Hv. In addition, Comparative Examples 1 to 3 was confirmed that the surface glossiness is not suitable for the blade. On the other hand, in Comparative Example 4 and Comparative Example 5 it was confirmed that the reduction ratio in the second surface modification step is 20% and 30%, respectively, the hardness is 287Hv and 322Hv. On the other hand, Comparative Example 4 and Comparative Example 5 did not go through the first surface modification step was confirmed that the oil adsorption is poor. Referring to FIG. 3, in the optical micrograph of Comparative Example 5, it was confirmed that sufficient micropits were not formed on the surface and had a smooth surface. That is, when considering the Comparative Examples 1 to 5, when the rolling rate is 20% to 30% in the second surface modification step, it can be obtained that the hardness is 280Hv to 330Hv, but not subjected to the first surface modification step In this case, sufficient micro feet were not formed on the surface, and thus oil adsorbability was poor.

In addition, Comparative Example 6 confirmed the hardness, surface gloss, and oil adsorption when only the first surface modification step was performed and the rolling reduction ratio without the second surface modification step was 0%. As shown in Table 2, it was confirmed that the oil adsorption is good, but the cold rolling is not carried out in the second surface modification step was confirmed that the hardness is 220Hv and the surface gloss is 10. Referring to FIG. 4, when only the first surface modification step was performed as in Comparative Example 6, the surface ups and downs were severely formed so that oil adsorption was good but surface glossiness was poor and hardness was low.

Comparative Examples 7 to 11 and Example 1 and Example 2 were performed both the first surface modification step, and the hardness, surface glossiness, oil adsorption was confirmed by varying the reduction ratio in the second surface modification step. First, in Comparative Example 7 to Comparative Example 9 in which the reduction ratio is less than 20% in the second surface modification step, the hardness was 238Hv, 252Hv and 261Hv, respectively, it was confirmed that the hardness of less than 280Hv which is not suitable for the blade. In addition, in Comparative Example 10 and Comparative Example 11, it was confirmed that the reduction ratio in the first surface modification step is 40% and 50%, respectively, and the hardness is 332Hv and 334Hv, respectively. In the case of Comparative Example 10 and Comparative Example 11, the oil adsorption is normal, and the hardness of each of the 332Hv and 334Hv was confirmed that both exceeded 330Hv.

On the other hand, referring to Examples 1 and 2, when both the first and second surface modification steps are performed, and the reduction ratios in the second surface modification step are 20% and 30%, respectively, the hardness is 286Hv. And 319Hv was confirmed to be included in the range of 280Hv to 330Hv hardness that is suitable for the blade. In addition, it was confirmed that the oil adsorption property is also good. Referring to Figure 5, in the case of Example 2 was formed with a suitable micropit on the surface, it was confirmed that the oil adsorption property is good and rust resistance is improved.

As described above, in order to have a predetermined strength and oil adsorption property, it is required to perform both the first and second surface modification steps, and in the second surface modification step, the reduction ratio is required to be 20% to 30%. In the case where only the second surface modification step is performed, no surface undulation in the first surface modification step is formed and no micropits are cold rolled to fix the oil. In addition, the surface glossiness of the steel sheet is excessively high, and oil adsorption is poor, and burrs and the like are formed during processing for the blade, resulting in deterioration of quality.

That is, when the reduction ratio in the second surface modification step is less than 20%, it may be a problem when processing the blade for having a hardness of less than 280Hv. On the other hand, when the reduction ratio is more than 30% has a hardness of more than 320Hv, brittleness due to work hardening increases not only to reduce the workability, but also micropits are reduced due to excessive reduction ratio to reduce the oil adsorption.

On the other hand, when the first and second surface modification steps are performed, but the reduction ratio is 20% to 30% in the second surface modification step, the hardness of 280Hv to 330Hv is shown in FIG. As described above, it was confirmed that the micropit was mainly generated at the interface between the ferrite base and the fine carbide to have an appropriate surface glossiness and to exhibit excellent oil adsorption.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalents thereof are included in the scope of the present invention Should be interpreted.

100: martensitic stainless steel
200: pickling device
300: cold rolling mill
400: winding roll

Claims (8)

By weight% C: 0.5-0.7%, Cr: 12-15%, Si: 0-1.0%, Mn: 0-1.0%, Ni: 0-1.0% or less, N: 0-0.1% or less, S : A method for producing martensitic stainless steel containing more than 0 and less than 0.04%, more than P: 0 and less than 0.05%, residual iron and other unavoidable impurities,
A first surface modification step of forming a surface relief on the martensitic stainless steel by a mixed acid; And
And a second surface modification step of forming a micro pit on the surface of the martensitic stainless steel by cold rolling the martensitic stainless steel passed through the first surface modification step. Method for producing martensitic stainless steel. The method of claim 1,
In the second surface modification step, the martensitic stainless steel is cold rolled at a reduction ratio of 20% to 30%. The method of claim 1,
The martensitic stainless steel is, in weight%, at least N: 0.02 to 0.08%, Si: more than 0 to 1.0%, Mn: more than 0 to 1.0%, and Mo: 0.1 to 2% and W: 0.1 to 2%. 1 type, remainder Fe and the manufacturing method of the martensitic stainless steel excellent in the rust prevention property containing another unavoidable impurity. The method of claim 1,
In the first surface modification step, the mixed acid may contain 5% to 20% nitric acid and 0.5% to 3% hydrofluoric acid at a concentration of 40 ° C. to 70 ° C., and the time may be performed for 30 seconds to 180 seconds. Method for producing martensitic stainless steel excellent in rust resistance. The method of claim 1,
The hardness of the martensitic stainless steels subjected to the second surface modification step is 280 Hv to 330 Hv. In weight%, C: 0.5 to 0.7%, Cr: 12 to 15%, Si: more than 0 to 1.0%, Mn: more than 0 to 1.0%, Ni: more than 0 to 1.0%, N: more than 0 to 0.1%, S: more than 0 and less than 0.04%, more than P: 0 and less than 0.05%, containing residual amount of iron and other unavoidable impurities, and having a micro pit of 10 μm or less on the surface, the hardness being 280 Hv to 330 Hv Martensitic stainless steel excellent in corrosion resistance. The method according to claim 6,
The martensitic stainless steel is provided with a surface relief by a mixed acid, the surface relief is martensite-based excellent rust resistance, characterized in that the martensitic stainless steel is cold rolled to form a micro pit (micro pit) Stainless steel. The method according to claim 6,
The martensitic stainless steel is martensitic stainless steel excellent in rust resistance, characterized in that the surface glossiness of 230 to 400.

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