KR102255910B1 - Ferritic stainless steel, martensitic stainless steel with high corrosion resistance and high hardness using the same, and manufacturing method thereof - Google Patents

Abstract

In the present specification, a ferritic stainless steel, a high corrosion resistance and high hardness martensitic stainless steel using the same, and a manufacturing method thereof are disclosed. According to an embodiment of the disclosed high corrosion resistance high hardness martensitic stainless steel, the high corrosion resistance high hardness martensitic stainless steel is in wt%, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si: 0.1 to 0.6 %, Mn: 0.2 to 1.0%, Cr: 13 to 17%, C+N: 0.5% or less, the remaining Fe and inevitable impurities are included, and 5/100 μm ² or less chromium carbides are distributed in the microstructure, The hardness is 53 HRC or more, and the value of the following formula (1) is 16.5 or more.
(1) Cr + 16*N
In the above formula (1), Cr and N mean the content (% by weight) of each alloy element.

Description

Ferritic stainless steel, martensitic stainless steel with high corrosion resistance and high hardness using the same, and manufacturing method thereof

The present invention relates to a ferritic stainless steel, a high corrosion resistance high hardness martensitic stainless steel using the same, and a manufacturing method thereof, and in more detail, a high corrosion resistance high hardness martensitic stainless steel that can be used as a material for ceramics and the same It relates to a manufacturing method.

Materials for paint, such as the esophagus, scissors, razors, and scalpels, which are generally widely used, require high hardness to maintain machinability and abrasion resistance, and because they are easily in contact with moisture or stored in a humid atmosphere, excellent corrosion resistance is required. Accordingly, high hardness martensitic stainless steel is mainly used as a material for ceramics.

The material for ceramics is very brittle because it requires high hardness. Accordingly, it is necessary to soften the ceramic material to a certain level or higher to facilitate processing. To this end, the brittle material is manufactured including a batch annealing (BAF) process that facilitates heat treatment workability.

During this phase annealing, the material reacts with carbon and chromium in the ferrite matrix structure, resulting in dispersion and precipitation of fine particles in the form of chromium carbide, which lowers the solid solution carbon content in the matrix structure, thus applying the manufacturing process of stainless steel such as rolling and pickling. This becomes easier.

In addition, the fine chromium carbide uniformly distributed within the ferrite matrix enables rapid re-use of chromium and carbon into the high-temperature austenite phase in the reinforcement heat treatment process performed by the ceramics manufacturer, and the hardness of the martensite structure after quenching. And corrosion resistance can be improved.

Therefore, in order to provide high corrosion resistance and high hardness martensitic stainless steel, it is required to establish a steel material and an annealing pattern capable of uniformly distributing fine chromium carbide in a microstructure.

Korean Patent Application Publication No. 10-2005-0054058 (Publication date: June 10, 2005)

In order to solve the above problems, the present invention is to provide a ferritic stainless steel, a high corrosion resistance and high hardness martensitic stainless steel using the same, and a method of manufacturing the same.

As a means for achieving the above object, the ferritic stainless steel according to an example of the present invention is in wt%, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si: 0.1 to 0.6%, Mn: 0.2 to 1.0%, Cr: 13 to 17%, C+N: 0.5% or less, containing the remaining Fe and inevitable impurities, 25 /100㎛ ² or more chromium carbides are distributed in the microstructure, the value of the following formula (1) This is 16.5 or higher.

(1) Cr + 16*N

In the above formula (1), Cr and N mean the content (% by weight) of each alloy element.

In each ferritic stainless steel of the present invention, the particle diameter of the chromium carbide may be 3 μm or less.

In each ferritic stainless steel of the present invention, the elongation may be 20% or more.

In addition, as another means for achieving the above object, the high corrosion resistance and high hardness martensitic stainless steel according to an example of the present invention is in wt%, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si: 0.1 To 0.6%, Mn: 0.2 to 1.0%, Cr: 13 to 17%, C+N: 0.5% or less, the remaining Fe and inevitable impurities are included, and 5/100 μm ² or less chromium carbides are distributed in the microstructure. And, the hardness is 53 HRC or more, and the value of the following formula (1) is 16.5 or more.

(1) Cr + 16*N

In the above formula (1), Cr and N mean the content (% by weight) of each alloy element.

In each of the high corrosion resistance and high hardness martensitic stainless steels of the present invention, the particle diameter of the chromium carbide may be 1 μm or less.

In each of the high corrosion resistance and high hardness martensitic stainless steels of the present invention, in 25° C., 3.5% NaCl aqueous solution, the pitting potential may be 200 mV or more.

In addition, as another means for achieving the above object, the method of manufacturing a high corrosion resistant, high hardness martensitic stainless steel according to an example of the present invention is in weight %, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si : 0.1 to 0.6%, Mn: 0.2 to 1.0%, Cr: 13 to 17%, C + N: 0.5% or less, including the step of hot rolling a cast steel containing the remaining Fe and inevitable impurities and phase annealing heat treatment And, the phase annealing heat treatment includes a step of first cracking treatment for 15 to 25 hours at a temperature range of 800 to 900°C and a second cracking treatment for 5 to 15 hours at a temperature range of 500 to 750°C, and , The microstructure after the phase annealing heat treatment is characterized in that ferrite is the main structure, and chromium carbides having a particle diameter of 3 µm or less are distributed in ^{25 parts/100 µm 2 or more.}

In the method of manufacturing each high corrosion resistance and high hardness martensitic stainless steel of the present invention, it may further include pre-cracking treatment at a temperature range of 400 to 600°C for 5 to 15 hours before the first cracking treatment step. have.

In the method of manufacturing each high corrosion resistance and high hardness martensitic stainless steel of the present invention, the step of raising the temperature at a rate of 40 to 200°C/h from the pre-cracking step to the first cracking treatment step is further performed. Can include.

In the method of manufacturing each high corrosion resistance, high hardness martensitic stainless steel of the present invention, further comprising the step of cooling at a rate of 10°C/h or higher from the step of the first cracking treatment to the step of the second cracking treatment can do.

In each method of manufacturing a martensitic stainless steel having high corrosion resistance and high hardness of the present invention, after the step of performing the second cracking treatment, the step of air cooling may be further included.

In the method for manufacturing each high corrosion resistance high hardness martensitic stainless steel of the present invention, further comprising a step of strengthening heat treatment, wherein the strengthening heat treatment is performed by austenizing for 10 seconds to 5 minutes at a temperature of 1,000 to 1,200°C. The step, quenching to room temperature, dip freezing at a temperature of -50 to -150°C for 10 seconds to 5 minutes, and tempering at a temperature of 400 to 600°C for 30 minutes to 2 hours may be included. .

In each manufacturing high corrosion-resistant high-hardness martensitic stainless steel, the method of the present invention, since the microstructure of the heat-treating and the sharpening is martensite as primary tissue, particle size less than or equal to this 1㎛ chromium carbides 5 / 100㎛ ² It can be characterized by being distributed below.

The ferritic stainless steel according to the present invention can improve workability by controlling the chromium carbide to be finely and uniformly distributed in the microstructure.

According to the present invention, a high corrosion resistance and high hardness martensitic stainless steel can be provided.

According to the present invention, a high hardness characteristic can be ensured by finally controlling the main structure into a martensite phase. In addition, by controlling the chromium carbide to be finely and uniformly distributed in the ferrite matrix structure, the chromium carbide is re-used as chromium and carbon in the subsequent reinforcement heat treatment, so that a desired high hardness characteristic can be secured.

According to the present invention, high corrosion resistance can be ensured by controlling the value of Equation (1) to 16.5 or more. In addition, the chromium carbide is controlled to be finely and uniformly distributed in the ferrite matrix structure, so that the chromium carbide is re-dissolved in the subsequent strengthening heat treatment to increase the chromium concentration of the matrix structure to about 12%. As a result, it is possible to obtain a desired high corrosion resistance property by densely generating a thin chromium oxide on the steel surface.

1 is a schematic diagram of a phase annealing heat treatment step according to the present invention.
2 is a photograph of observing the microstructure of Inventive Example 1.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the technical idea of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided in order to more completely explain the present invention to those with average knowledge in the art.

The terms used in the present application are only used to describe specific examples. So, for example, a singular expression includes a plural expression unless the context clearly has to be singular. In addition, terms such as "include" or "include" used in the present application are used to clearly refer to the existence of features, steps, functions, components or combinations thereof described in the specification, but other features It should be noted that it is not used to preliminarily exclude the presence of elements, steps, functions, components, or combinations thereof.

Meanwhile, unless otherwise defined, all terms used in the present specification should be viewed as having the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Therefore, unless clearly defined in the specification, a specific term should not be interpreted as an excessively ideal or formal meaning. For example, in the present specification, expressions in the singular include plural expressions unless the context clearly has exceptions.

In addition, "about", "substantially" and the like in the present specification are used in or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid understanding of the present invention. Or absolute figures are used to prevent unreasonable use of the stated disclosure by unconscionable infringers.

The ferritic stainless steel according to an embodiment of the present invention or the high corrosion resistance and high hardness martensitic stainless steel using the same is weight %, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si: 0.1 to 0.6%, Mn : 0.2 to 1.0%, Cr: 13 to 17%, C+N: 0.5% or less, the remaining Fe and inevitable impurities are included.

Hereinafter, the reasons for limiting the alloy composition will be described in detail. All of the following component compositions refer to% by weight unless otherwise specified.

Carbon (C): 0.2 to 0.3% by weight

When the content of C is low, the hardness decreases after the reinforcement heat treatment, so it may be difficult to secure machinability and abrasion resistance, so in the present invention, C may be added in an amount of 0.2% by weight or more. However, if the C content is excessive, chromium carbide is excessively formed and corrosion resistance is deteriorated, and there is a concern that coarse carbides in the annealing structure may be formed due to carbon segregation. Accordingly, the upper limit of the C content in the present invention is preferably limited to 0.3% by weight.

Nitrogen (N): 0.05 to 0.15% by weight

N is an element added to improve corrosion resistance and hardness at the same time, and even if added instead of C, it does not cause local fine segregation, and thus has the advantage of not forming coarse precipitates. For this effect, N may be added in an amount of 0.05% by weight or more in the present invention. However, if the N content is excessive, it may be difficult to control the component system as the melting limit in molten steel is exceeded during casting, and it may appear as a pinhole defect on the surface. Accordingly, in the present invention, the upper limit of the N content is preferably limited to 0.15% by weight.

Silicon (Si): 0.1 to 0.6% by weight

Si is an element that is essentially added for deoxidation. In consideration of this, in the present invention, Si may be added in an amount of 0.1% by weight or more. However, if the Si content is excessive, there is a problem of increasing brittleness by lowering the pickling property. Accordingly, the upper limit of the Si content in the present invention is preferably limited to 0.6% by weight.

Manganese (Mn): 0.2 to 1.0% by weight

Manganese (Mn) is an element essential for deoxidation. In consideration of this, in the present invention, Mn may be added in an amount of 0.2% by weight or more. However, if the Mn content is excessive, the surface quality of the steel may be impaired, and it may be difficult to secure hardness through the formation of residual austenite in the final heat treated material. Accordingly, in the present invention, the upper limit of the Mn content is preferably limited to 1.0% by weight.

Chromium (Cr): 13 to 17% by weight

Cr is a typical element for improving corrosion resistance of stainless steel, and in the present invention, in order to secure sufficient corrosion resistance, Cr may be added in an amount of 13% by weight or more. However, if the Cr content is excessive, manufacturing costs increase, and micro-segregation of chromium components in the structure increases, causing local coarsening of chromium carbides, thereby lowering the corrosion resistance and hardness of the reinforced heat treated steel. Accordingly, the upper limit of the Cr content in the present invention is preferably limited to 17% by weight.

Content of carbon (C) + nitrogen (N): 0.5% by weight or less

C and N are elements necessary to secure the hardness of steel after reinforcing heat treatment. However, if the C and N content is excessive, there is a problem in that the proportion of chromium carbide distributed during phase annealing of the hot-rolled steel sheet increases and the elongation decreases. Accordingly, in the present invention, the upper limit of the C+N content is preferably limited to 0.5% by weight.

The remaining component of the present invention is iron (Fe). However, since unintended impurities may inevitably be mixed in the raw material or the surrounding environment in a typical manufacturing process, this cannot be excluded. Since the impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

In addition, in addition to limiting the content of each alloy element to the above-described conditions, the relationship between them can be further limited as follows.

Value of equation (1): 16.5 or more

According to the present invention, in order to secure corrosion resistance, a PREN (Pitting Resistance Equivalent Number) value can be controlled.

According to the present invention, Mo is added to the extent of impurities. In addition, since Mn is considered as an alloying element for deriving the pitting resistance index in the case of 200-based stainless steel or when the content of Mn exceeds 1.0%, in the present invention, which is not applicable in both cases, It can be excluded from alloying elements. In consideration of the above, in the present invention, Mo and Mn may be excluded from the alloying element for deriving the pitting resistance index.

Accordingly, in the present invention, the equation for deriving the pitting index was modified, and according to an example of the present invention, the value of the following equation (1) may be 16.5 or more.

(1) Cr + 16*N

Here, Cr and N mean the content (% by weight) of each alloy element.

According to an example, in the present invention, in addition to limiting the content of the alloying element to the above-described conditions, excellent corrosion resistance can be secured by controlling the content of each alloying element so that the value of Equation (1) is 16.5 or more.

According to the present invention, the ferritic stainless steel having the alloy composition as described above is produced as a cast steel by continuous casting or ingot casting, and then hot-rolled to produce a hot-rolled steel sheet capable of processing. The hot-rolled steel sheet manufactured after that is subjected to phase annealing heat treatment to secure good workability before proceeding with processing such as precision rolling to a thickness that can be used for coating materials. The microstructure after the phase annealing heat treatment is made of ferrite as the main structure, and fine chromium carbide may be uniformly distributed. Ferritic stainless steel is made of martensitic stainless steel by a subsequent strengthening heat treatment step.

First, the phase annealing heat treatment will be described.

As shown in FIG. 1, the phase annealing heat treatment according to an example of the present invention includes a first crack treatment step 200 and a second crack treatment step 300. In addition, it may further include a step (100) of pre-cracking treatment prior to the step (200) of selectively first cracking treatment.

The pre-cracking step 100 is a step of performing cracking prior to the first cracking step, and is a pretreatment step for a uniform increase in temperature throughout the material. According to an example, it is preferable that the pre-cracking step 100 is heated to a constant temperature for 5 to 15 hours in a temperature range of 400 to 600°C.

If the heating temperature is less than 400 or exceeds 600°C, the temperature cannot be uniformly increased throughout the material. In addition, if the heating time is less than 5 hours or exceeds 15 hours, the temperature cannot be uniformly increased throughout the material.

The first cracking treatment step 200 is a step of uniformly distributing chromium carbide in the microstructure of the hot-rolled steel sheet. According to an example, it is preferable to heat the first cracking treatment step 200 at a constant temperature at 800 to 900° C. for 15 to 25 hours.

When the heating temperature is less than 800°C, localized chromium carbide aggregates may be formed at the grain boundaries, and when the heating temperature exceeds 900°C, coarse chromium carbides are formed at the grain boundaries.

In addition, if the heating time is less than 15 hours, the size of the chromium carbide can be refined, but chromium carbide may be concentrated and distributed in a part, and if the heating time exceeds 25 hours, chromium carbides adjacent to each other may be combined to form locally coarse. have.

Agglomerated or coarse chromium carbide causes material imbalance, resulting in lower ductility, and may deteriorate the stiffness, ductility, and corrosion resistance of the final product. In order to prevent this, the present invention limits the heating temperature to 800 to 900° C. and the heating time to 15 to 25 hours in the first cracking treatment step 200.

The second cracking treatment step 300 is a step of spheroidizing chromium carbide. By spheroidizing chromium carbide, it is possible to improve workability in a subsequent processing step. According to an example, the second cracking treatment step 300 is preferably heated to a constant temperature for 5 to 15 hours in a temperature range of 500 to 750°C.

In order for chromium carbide to spheroidize, a heating temperature of at least 500°C is required. On the other hand, when the heating temperature exceeds 750° C., spheroidized chromium carbides grow excessively and the number of chromium carbides decreases, resulting in decreased ductility. In addition, when the heating time is less than 5 hours, the chromium carbide does not spheroidize, and when the heating time exceeds 15 hours, the chromium carbide grows excessively and the ductility decreases.

A step 150 of raising the temperature at a rate of 40 to 200° C./h from the pre-cracking step 100 to the first cracking treatment step 200 may be further included.

If the heating rate is less than 40°C/h, the time passing through 700 to 750°C, which is a temperature range in which chromium carbide becomes coarse, may increase, and accordingly, the size of the chromium carbide becomes coarse and the chromium carbide distributed in the microstructure. The ductility may decrease due to a decrease in the number. On the other hand, when the temperature increase rate exceeds 200°C/h, the time passing through the temperature section in which the chromium carbide is coarsened decreases, and thus fine chromium carbide can be secured. However, there is a disadvantage in that the chromium carbide is distributed unevenly due to insufficient time to diffuse.

A step 250 of cooling at a rate of 10° C./h or more may be further included from the first cracking treatment step 200 to the second crack treatment step 300.

If the cooling rate is less than 10°C/h, the time passing through the temperature section in which the chromium carbide is coarsened increases, and accordingly, the chromium carbide in the microstructure becomes coarse, making it difficult to secure high corrosion resistance and high hardness.

In addition, after the step 300 of the second cracking treatment, a step 350 of air cooling is performed.

In the above-described phase annealing heat treatment step, carbon and chromium in the microstructure react to form chromium carbide. As a result, the amount of carbon dissolved in the structure is reduced, so that the workability is improved, and the subsequent application of the manufacturing process of stainless steel is easy, so that it can be processed into a desired final shape. The ferritic stainless steel according to an example of the present invention may have an elongation of 20% or more.

In addition, the chromium carbide uniformly and finely distributed in the microstructure by the phase annealing heat treatment step described above enables rapid re-use of chromium and carbon into the high temperature austenite phase in the subsequent reinforcement heat treatment step, and the martensitic structure after quenching. It can improve the hardness and corrosion resistance.

According to the present invention, the chromium carbide in the microstructure of the ferritic stainless steel can be refined and uniformly distributed through the above-described phase annealing heat treatment step.

According to an example of ferritic stainless steel, ^{chromium carbides of 25 /100 μm 2} or more may be distributed in a microstructure. 25 in microstructure/100㎛ ² When the chromium carbide is distributed less than that, the number of chromium carbides is small and the size is coarse, so that the ductility decreases, and it is difficult to re-use chromium and carbon in the subsequent reinforcing heat treatment step, so that the desired hardness cannot be secured.

According to an example of ferritic stainless steel, the particle diameter of chromium carbide may be 3 μm or less. When the particle diameter of the chromium carbide in the microstructure exceeds 3 μm, the ductility decreases, and it is difficult to re-use chromium and carbon in the subsequent reinforcing heat treatment step, so that the desired hardness cannot be secured.

The microstructure of the steel material after the phase annealing heat treatment step according to the present invention is made of ferrite as the main structure, and chromium carbides having a particle diameter of 3 μm or less may be distributed in ^{25/100 μm 2 or more.}

According to the present invention, the above-described phase-annealed and heat-treated ferritic stainless steel can be quenched to produce a high corrosion resistance and high hardness martensitic stainless steel. For example, ferritic stainless steel can be manufactured into a high corrosion resistance and high hardness martensitic stainless steel through a step of reinforcing heat treatment after being processed into a final shape.

The strengthening heat treatment may include austenizing, quenching, deep freezing, and tempering.

The step of austenizing treatment is a step of transforming the matrix structure of the steel material from ferrite to austenite.

In this step, the chromium carbide is re-used as a matrix structure in the form of chromium and carbon, so that the hardness of martensitic stainless steel can be increased after the subsequent quenching or deep freezing step. In addition, as a result of the re-dissolution of chromium carbide, the chromium concentration in the matrix structure is increased to about 12%, and as a result, thin chromium oxide is densely produced on the steel surface, thereby improving the corrosion resistance of the steel.

According to an example, the austenizing process may be heat-treated at a temperature of 1,000 to 1,200°C for 10 seconds to 5 minutes. When the temperature is less than 1,000°C, the desired high hardness cannot be secured, and when the temperature exceeds 1,200°C, the hardness may decrease due to excessive formation of residual austenite due to an increase in the carbide inventory capacity.

In addition, if the austenizing treatment time is less than 10 seconds, the desired high hardness cannot be secured, and if it exceeds 5 minutes, the crystal grains grow excessively and residual austenite may occur.

The step of quenching is a step of transforming the austenite structure into martensite having high hardness through rapid cooling to room temperature after austenizing treatment.

The step of deep freezing is a step of additionally cooling the steel material quenched to room temperature at cryogenic temperatures to additionally transform the residual austenite structure into a martensite structure, and in this step, the hardness of the steel material further increases. According to an example, in the deep freezing step, a subzero heat treatment may be performed at a temperature of -50 to -150°C for 10 seconds to 5 minutes.

The tempering step is a step for imparting toughness to a martensitic structure with high hardness and strong brittleness after the deep freezing step. According to an example, heat treatment may be performed at a temperature of 400 to 600° C. for 30 minutes to 2 hours.

According to the present invention, the ferrite structure may be finally transformed into a martensite structure by the above-described reinforcing heat treatment step, and desired high corrosion resistance characteristics and high hardness characteristics may be obtained.

On the other hand, the chromium carbide formed finely and uniformly by the phase annealing heat treatment is re-used as a matrix structure in the form of chromium and carbon through the step of reinforcing heat treatment of the present invention. In order to secure high corrosion resistance and high hardness properties of the martensitic stainless steel manufactured by the step of reinforcing heat treatment, it is preferable that chromium carbide is not included in the final secured structure as much as possible.

The high corrosion resistance and high hardness martensitic stainless steel according to an example of the present invention may contain chromium carbide of 5/100 ^{μm 2 or less in a microstructure.} When chromium carbide is ^{contained in excess of 5/100㎛ 2} , there is a concern that high corrosion resistance and high hardness characteristics may not be secured.

At this time, the particle diameter of the chromium carbide may be 1 μm or less. When the particle diameter of chromium carbide exceeds 1 μm, there is a concern that high corrosion resistance and high hardness characteristics may not be secured.

The microstructure of the steel material after the step of reinforcing heat treatment according to the present invention has martensite as the main structure, and chromium carbides having a particle diameter of 1 μm or less may be distributed in ^{5/100 μm 2 or less.}

The high corrosion resistance and high hardness martensitic stainless steel according to an example of the present invention may have a hardness of 53 HRC or more. In the present invention, high hardness characteristics can be obtained by controlling the main structure in a martensite phase. In addition, by controlling the chromium carbide to be finely and uniformly distributed in the ferrite matrix structure, the chromium carbide is re-used as chromium and carbon in the subsequent reinforcement heat treatment, so that a desired high hardness characteristic can be secured.

The high corrosion resistance and high hardness martensitic stainless steel according to an example of the present invention may have a pitting potential of 200 mV or more at 25° C. and 3.5% NaCl aqueous solution. In the present invention, high corrosion resistance can be obtained by controlling the value of Equation (1) to 16.5 or more. In addition, the chromium carbide is controlled to be finely and uniformly distributed in the ferrite matrix structure, so that the chromium carbide is re-dissolved in the subsequent strengthening heat treatment to increase the chromium concentration of the matrix structure to about 12%. As a result, it is possible to obtain a desired high corrosion resistance property by densely generating a thin chromium oxide on the steel surface.

Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.

{Example}

Table 1 below shows the alloy components and pinholes corresponding to each invention example and comparative example.

Alloy composition (% by weight) Pinhole
Occur
Whether
(O/X) C Si Mn Cr N C+N Comparative Example 1 0.6500 0.29 0.69 13.12 0.146 0.8060 X Comparative Example 2 0.1500 0.50 0.45 13.50 0.009 0.1590 X Comparative Example 3 0.1460 0.51 0.48 13.45 0.081 0.2270 X Comparative Example 4 0.2530 0.42 0.45 15.36 0.195 0.4480 O Invention Example 1 0.2445 0.47 0.46 15.35 0.114 0.3585 X

Referring to Table 1, in Comparative Example 4, in which nitrogen more than a solid solution of nitrogen was added, surface pinholes were generated by nitrogen gas on the surface.

^{Table 2 below shows the distribution of chromium carbides (pcs/100㎛ 2} ) and elongation (%) of each Inventive Example and Comparative Example of the ferritic stainless steel after the phase annealing heat treatment step.

Chromium carbide
(Pcs/100㎛ ² ) Elongation
(%) Comparative Example 1 63 17.6 Comparative Example 2 19 28.1 Comparative Example 3 17 32.4 Comparative Example 4 21 19.6 Invention Example 1 32 29.3

Referring to Table 2, Inventive Example 1 had a ^{distribution of 32 chromium carbides/100㎛ 2} , and an elongation of 29.3% was good. On the other hand, the attached Figure 2 is a photograph of observing the microstructure of Inventive Example 1. Referring to FIG. 2, the distribution of chromium carbide of Inventive Example 1 can be visually confirmed.

On the other hand, in Comparative Example 1 containing 0.6% by weight or more of high carbon, the C+N content exceeded 0.5% by weight, so that the fraction of chromium carbide was excessively increased. As a result, the chromium carbide was ^{distributed in 63 pieces/100㎛ 2} , but the elongation was inferior to 17.6%.

In Comparative Example 4 including high nitrogen, the fraction of chromium carbide was smaller than that of the present invention, and the elongation was also inferior.

In Comparative Examples 2 and 3, the elongation was 28% or more, but chromium carbides were ^{distributed in 25 parts/100µm 2} or less.

The ferritic stainless steels of each of the invention examples and comparative examples of Table 2 were reinforced and heat treated to prepare martensitic stainless steels. After measuring the values of formula (1), pitting potential (mV), and hardness (HRC) of the prepared martensitic stainless steel, the results are shown in Table 3.

In Table 3, the value of Equation (1) of each Inventive Example and Comparative Example was derived by substituting the content (% by weight) of each alloy element in Equation (1) below.

(1) Cr + 16*N

In Table 3, the formula potential of each Inventive Example and Comparative Example was measured at 25° C. and 3.5% NaCl aqueous solution.

Value of Equation (1) Official potential (mV) Hardness (HRC) Comparative Example 1 15.46 15 61 Comparative Example 2 13.64 97 51.2 Comparative Example 3 14.75 93 51.9 Comparative Example 4 18.48 240 52.6 Invention Example 1 17.17 212 54.7

Referring to Table 3, in Inventive Example 1, the value of Equation (1) was 16.5 or more, and the formula potential was 200 mV or more, thereby securing high corrosion resistance. In addition, the hardness was 54.7 HRC to secure high hardness characteristics.

On the other hand, Comparative Example 1 containing 0.6% by weight or more of high carbon had a value of less than 16.5 in Equation (1), and as a result of excessive increase in the fraction of chromium carbide, sensitization due to lack of chromium in the steel was promoted. It showed the lowest official potential.

In Comparative Examples 2 and 3, the value of Equation (1) was less than 16.5, and ^{as a result of the distribution of chromium carbides to 25 /100㎛ 2} or less, the re-use rate decreased by reinforcement heat treatment, a sensitization phenomenon due to lack of chromium in steel This was promoted to show the lowest official potential among the examples.

Comparative Example 4 exhibited the highest pitting potential due to the influence of nitrogen, but was inappropriate as a final product due to the occurrence of surface pinholes.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and those of ordinary skill in the art are within the scope of not departing from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (13)

delete delete delete delete delete delete In% by weight, C: 0.2 to 0.3%, N: 0.05 to 0.15%, Si: 0.1 to 0.6%, Mn: 0.2 to 1.0%, Cr: 13 to 17%, C+N: 0.5% or less, the remainder of Fe and Hot rolling a cast steel containing inevitable impurities;
Phase annealing heat treatment; And
Including; strengthening heat treatment
The phase annealing heat treatment,
Pre-cracking treatment;
Raising the temperature at a rate of 40 to 200° C./h from the pre-cracking step to the first cracking treatment step;
Performing a first crack treatment for 15 to 25 hours at a temperature range of 800 to 900°C;
Cooling at a rate of 10° C./h or higher from the step of treating the first crack to the step of treating the second cracking; And
Including the step of performing a second cracking treatment for 5 to 15 hours at a temperature range of 500 to 750°C, and the microstructure after the phase annealing heat treatment step is made of ferrite as a main structure, and a chromium carbide having a particle diameter of 3 μm or less is 25 A method for producing a high corrosion resistance, high hardness martensitic stainless steel, characterized in that distributed in the number / 100㎛ ^{2 or more.} The method of claim 7,
The pre-cracking step is a method for producing a high corrosion resistance, high hardness martensitic stainless steel, characterized in that the cracking treatment for 5 to 15 hours at a temperature range of 400 to 600 ℃. delete delete The method of claim 7,
After the step of the second cracking treatment, the step of air-cooling; a method of manufacturing a high corrosion resistance high hardness martensitic stainless steel further comprising The method of claim 7,
The reinforcing heat treatment is performed by austenizing treatment at a temperature of 1,000 to 1,200°C for 10 seconds to 5 minutes, quenching to room temperature, and deep freezing for 10 seconds to 5 minutes at a temperature of -50 to -150°C. Step, a method for producing a high corrosion resistance and high hardness martensitic stainless steel comprising the step of baking for 30 minutes to 2 hours at a temperature of 400 to 600 ℃. The method of claim 12,
The microstructure after the step of reinforcing heat treatment is made of martensite as the main structure, and the chromium carbide having a particle diameter of 1 μm or less is distributed in ^{5/100 μm 2 or less.} Way.

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