KR101834996B1 - High hardness martensitic stainless steel with excellent hardenability and method of manufacturing the same - Google Patents

Abstract

Disclosed are a high hardness martensitic stainless steel with excellent hardenability, and a manufacturing method thereof. The disclosed martensitic stainless steel with excellent hardenability comprises: 0.60-0.80 wt% of C; 0.07-0.15 wt% of N; 0.1-0.6 wt% of Si; 0.5-1.0 wt% of Mn; 12-14 wt% of Cr; 0.90 wt% or less of C+N; and the remaining including Fe and other inevitable impurities, wherein 50/100 μm^2 or greater of chrome nitrides are distributed within a microstructure of a cold rolled steel.

Description

TECHNICAL FIELD [0001] The present invention relates to a high hardness martensitic stainless steel having excellent hardenability and a method for manufacturing the same. BACKGROUND ART [0002]

More particularly, the present invention relates to a high-hardness martensitic stainless steel having excellent hardenability and a method for producing the same.

In general, widely used materials such as esophagus, scissors, razors, and scalpels such as scalpels, which are medical instruments, require high hardness in order to maintain cutting and abrasion resistance, and are required to have excellent corrosion resistance because they are easily contacted with moisture or stored in a humid atmosphere. Accordingly, a high-hardness martensitic stainless steel having a high hardness is mainly used as a raw material for plumbing.

These high-carbon martensitic stainless steels contain 0.45 to 0.80% by weight of carbon, up to 1.0% of manganese, up to 1.0% of silicon, and 12.0 to 15.0% of chromium, of which about 0.60 to 0.80% 12.0 ~ 15.0% A chromium-based component system is widely used as a water-based material requiring high hardness.

High hardness materials for water require very hardness, so they are very brittle. Therefore, it is necessary to soften the material for the water to a predetermined level so as to facilitate the processing. For this purpose, a BAF (Batch Annealing Furnace) process which can easily perform the heat treatment of the brittle material is included.

During the calcination process, the material reacts with chromium in the ferrite matrix to disperse fine particles of chromium carbide in the ferrite matrix, which lowers the solid carbon content in the matrix and facilitates the application of the stainless steel manufacturing process such as rolling and pickling.

In addition, the distribution of fine chromium carbide uniformly distributed in the structure of the ferrite matrix enables rapid reutilization of chromium and carbon to a high temperature austenite phase in a strengthening heat treatment process performed by the logistics manufacturer, and the hardness of the martensite structure And an important factor for improving the corrosion resistance.

In order to secure a martensite structure of high hardness with excellent corrosion resistance, it is essential to form a fine chromium carbide in the annealed ferrite structure.

However, in the case of the conventional 420-type martensitic stainless steel, chromium carbides locally precipitate in the grain boundaries due to grain-size preferential precipitation and growth of chromium carbide when 0.5% or more of high carbon is added, and the stockability ratio to the austenite phase Resulting in lowering of hardness and corrosion resistance.

On the other hand, nitrogen in the ferrite matrix also reacts with chromium to disperse fine particles of chromium nitride in the ferrite matrix, and this chromium nitride is also known to improve the hardness and corrosion resistance of the martensite structure after quenching through the strengthening heat treatment process have.

Therefore, in order to secure a material having high hardness and corrosion resistance of a high-carbon martensitic stainless steel for use as a tool, it is necessary to develop a new steel material capable of uniformly distributing fine chromium nitride in a microstructure as well as fine chromium carbide, do.

Korean Patent Publication No. 10-2016-0062988 (2016.06.03)

Embodiments of the present invention are to provide a high hardness martensitic stainless steel which is capable of uniformly distributing fine chromium carbide as well as fine chromium carbide in a ferrite matrix structure of martensitic stainless steel to improve hardness and corrosion resistance.

In addition, the embodiments of the present invention are also applicable to a high-hardness martensite-based martensitic stainless steel having excellent hardenability and capable of improving the hardness and corrosion resistance of a martensite structure by uniformly distributing chromium carbide and chromium nitride by newly setting annealing heat treatment conditions of martensitic stainless steels To provide a method of manufacturing stainless steel.

The high hardness martensitic stainless steel according to one embodiment of the present invention contains 0.60 to 0.80% of C, 0.07 to 0.15% of N, 0.1 to 0.6% of Si, 0.5 to 1.0% of Mn, 12 to 14% of Cr, and 0.90% or less of C + N, the remainder being Fe and unavoidable impurities, and chromium nitrides of 50/100 μm ² or more are distributed in the microstructure of the cold rolled annealed material.

Also, according to an embodiment of the present invention, at least 80/100 μm ² of chromium carbide may be distributed in the microstructure of the cold-rolled annealed material.

According to an embodiment of the present invention, the cold-rolled annealed material may have a Vickers hardness of 700 Hv or more at the time of tempering treatment at a temperature of 1,100 ° C or more for 12 seconds or more.

According to an embodiment of the present invention, the martensitic stainless steel may have an elongation of 18% or more.

A method for producing a high hardness martensitic stainless steel having excellent curability according to an embodiment of the present invention comprises: 0.60 to 0.80% of C; 0.07 to 0.15% of N; 0.1 to 0.6% of Si; 0.5 to 0.6% of Mn; By weight of Cr and 12 to 14% of Cr, and 0.90% or less of C + N, the balance being Fe and unavoidable impurities, and a step of subjecting the hot-rolled steel sheet to a heat- .

The preliminary heat treatment includes a first cracking step of uniformly distributing chromium carbide and chromium nitride in the microstructure of the hot-rolled steel sheet, and a second cracking step of spheroidizing the chromium carbide and the fine particles of chromium nitride.

Also, according to an embodiment of the present invention, the first cracking step may be performed at 800 to 900 ° C, and the second cracking step may be performed at 600 to 750 ° C.

Also, according to an embodiment of the present invention, the first cracking step may be performed for 15 to 25 hours, and the second cracking step may be performed for 5 to 15 hours.

According to an embodiment of the present invention, there is provided a method of manufacturing a hot-rolled steel sheet, comprising the steps of raising the hot-rolled steel sheet at a rate of 40 to 200 ° C / hour until reaching the first cracking step, Lt; RTI ID = 0.0 > 10 C / hr. ≪ / RTI >

Further, according to an embodiment of the present invention, the method may further include the step of air-cooling after the second cracking step is completed.

According to an embodiment of the present invention, the step of cold-rolling and annealing the heat-treated hot-rolled steel sheet may be included.

Further, according to one embodiment of the present invention, it can be a 50 / 100㎛ ² or more chromium nitride distributed in the microstructure of the cold-rolled bovine dunjae.

Further, according to an embodiment of the present invention, at least 80/100 mu m ² of chromium carbide may be distributed in the microstructure of the cold-rolled annealed material.

According to the embodiments of the present invention, it is possible to control the components of the high-carbon martensitic stainless steel and uniformly distribute the fine chromium carbide and chromium nitride in the matrix through the hot-rolling treatment of the hot-rolled steel sheet to obtain the high hardness, high corrosion resistance, This excellent material can be produced.

1 is a graph for explaining a method of manufacturing a high-hardness martensitic stainless steel according to an embodiment of the present invention.
2 and 3 are photographs for explaining the microstructure of the high-hardness martensitic stainless steel according to one embodiment of the present invention.
FIGS. 4 and 5 are views for explaining the change in hardness of the high-hardness martensitic stainless steel according to the reinforcing heat treatment condition according to an embodiment of the present invention.
6 is a view for explaining a change in hardness according to a change in time when a hardened martensitic stainless steel according to an embodiment of the present invention is subjected to a tempering heat treatment at a temperature of 1,100 ° C.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

The high hardness martensitic stainless steel according to one embodiment of the present invention contains 0.60 to 0.80% of C, 0.07 to 0.15% of N, 0.1 to 0.6% of Si, 0.5 to 1.0% of Mn, %, Cr: 12 to 14%, C + N: 0.90% or less, and the balance includes Fe and unavoidable impurities.

The role of each alloy component in the high-hardness martensitic stainless steel according to one embodiment of the present invention and the reason for limiting the alloy composition range will be described below. In addition, the percentages described below are all% by weight.

C: 0.60 to 0.80%

When the content of C is low, the hardness of the martensitic stainless steel after the tempering treatment is lowered and the machinability and the wear resistance can not be secured. On the other hand, if the content is excessively large, the chromium carbide is excessively formed and the corrosion resistance of the material itself is deteriorated. In addition, there is a risk of formation of coarse carbides in the annealed structure due to carbon segregation, so the upper limit is set at 0.80% Limit.

N: 0.07 to 0.15%

N is an element added to improve corrosion resistance and hardness at the same time. Even when added in place of C, it does not cause local fine segregation, and thus it is advantageous not to form a coarse precipitate on the product. Add 0.07% or more to achieve this effect. However, when it is added excessively, pore due to nitrogen is formed during casting, and the hot workability and elongation rate are lowered. As a result, a large amount of cracks may occur on the surface and the edge portion of the material after hot rolling. .

Si : 0.1 to 0.6%

Since Si is an essential element added for deoxidation, 0.1% or more is added. However, since excessive Si addition decreases the acidity and increases the brittleness of the material, its upper limit is limited to 0.6%.

Mn: 0.5 to 1.0%

Since Mn is an element added for deoxidation, 0.5% or more is added. However, if it is added excessively, the surface quality of the steel is inhibited and the upper limit is limited to 1.0% because the retained austenite of the final heat treatment material is inhibited from securing high hardness properties.

Cr : 12 to 14%

Cr is a basic element for ensuring corrosion resistance, so add 12% or more. However, if it is added excessively, the manufacturing cost is increased, the fine segregation of the chromium component in the tissue is increased, and the corrosion resistance and hardness of the reinforcing heat treatment material may be lowered by locally causing chromium carbide coarsening, .

C + N: 0.90% or less

C and N contents are satisfied, the surface and edge portions are good in quality even when the C + N content exceeds 0.90%. However, since the fractions of chromium carbide and chromium nitride distributed in the hot rolled steel sheet are increased, There is a problem of deterioration. The C + N content is limited to 0.90% or less in order to secure a good elongation.

For example, the high hardness martensitic stainless steel excellent in curability according to an embodiment of the present invention may further include Ni, Mo, W, V, and the like.

Ni : 0.1 to 0.5%

Ni is an austenite stabilizing element, which is inevitably brought in from steel scrap in the steelmaking process and is added in an amount of 0.1% or more. However, when a high content of Ni is contained, it is difficult to secure high hardness properties by increasing the amount of retained austenite in the final heat-treated material. Therefore, the upper limit is limited to 0.5%.

Mo : 0.1 to 2.0%

Mo has an excellent effect on improving the corrosion resistance, so that it is possible to add 0.1% or more. However, excessive addition limits the upper limit to 2.0% because it leads to an increase in the manufacturing cost.

W: 0.1 to 2.0%

W may be added in an amount of 0.1% or more to improve the corrosion resistance. However, since the excessive addition causes an increase in manufacturing cost and operability, the upper limit is limited to 2.0%.

V: 0.1 to 0.3%

V may optionally be added in an amount of 0.1% or more for the refinement of the carbide. However, since V is a carbide-forming element, the upper limit is limited to 0.3% in order to prevent the loss of the base metal alloy component.

It is essential to form fine chromium carbide and chromium nitride in the annealed ferrite structure in order to secure a high-hardness martensite structure excellent in corrosion resistance.

Generally, in the case of the martensitic stainless steel material, the steel sheet is processed into a final shape and then subjected to a hardening process to secure corrosion resistance and hardness. In the strengthening heat treatment process, the material is maintained at a high temperature of about 1,000 to 1,200 ° C for a short time, and then quenched to room temperature. The chromium carbide or chromium nitride is reutilized on the high-temperature austenite to raise the concentration of the known chromium to about 12% , Resulting in dense generation of thin chromium oxide on the surface of the material to improve the corrosion resistance of the material.

Further, the quenching results in an increase in hardness as the austenite phase containing the reused carbon or nitrogen is transformed into a martensite phase. At this time, when the size of the spheroidized chromium carbide or chromium nitride distributed in the matrix is large, it is difficult to reuse chromium carbide or chromium nitride on the high temperature austenite, so that the concentration of chromium, carbon and nitrogen existing in the matrix is decreased As a result, corrosion resistance and hardness are lowered. On the other hand, when fine chromium carbide and chromium nitride are distributed, it is easy to reuse, and the concentration of chromium, carbon and nitrogen in the matrix increases, thereby improving corrosion resistance and hardness. Therefore, in order to ensure corrosion resistance and hardness of the high carbon martensitic stainless steel, it is required to distribute fine chromium carbide and chromium nitride in the material before the tempering heat treatment process.

In the high-hardness martensitic stainless steel excellent in hardenability according to the embodiment of the present invention, chromium nitride of 50/100 μm ² or more is distributed in the microstructure of the cold-rolled annealed material.

The distribution of the chromium nitride can be obtained by adjusting the content of N. As the content of N increases, the number of chromium nitrides also increases. When the chromium nitride is contained in the microstructure of the cold-rolled annealed material at less than 50/100 μm ² , the corrosion resistance and the hardness are lowered, There is a problem that the capacity is lowered.

In addition, the 80 / 100㎛ ² or more chromium carbides in the microstructure of the cold rolling is small dunjae distribution.

The distribution of the chromium carbide can be obtained by controlling the content of C. As the content of C increases, the number of chromium carbides also increases. When the chromium carbide is contained in the microstructure of the cold-rolled annealed material at less than 80/100 μm ² , the hardness is lowered.

For example, the cold-rolled annealed material may have a Vickers hardness of 700 Hv or more at a tempering temperature of 1,100 ° C or more for a tempering treatment for 12 seconds or more. More preferably, the cold-rolled annealed material is heat-treated at a temperature of 1,100 DEG C or higher for 12 to 15 seconds to have a Vickers hardness of 700 Hv or more.

Generally, it is necessary to secure an elongation of about 18% or more in the martensitic stainless steel in order to secure a good quality cold rolling property. When a large amount of N is added to secure the chromium nitride, pores are formed by nitrogen, and the elongation is decreased.

Accordingly, in the high hardness martensitic stainless steel having excellent hardenability according to an embodiment of the present invention, the martensitic stainless steel may have an elongation of 18% or more.

The martensitic stainless steel according to the present invention is produced as a hot-rolled steel sheet by which a cast steel is produced by continuous casting or ingot casting and subjected to hot rolling treatment.

The produced hot-rolled steel sheet has a thickness that can be used for rolling, and softening work is carried out through heat treatment to ensure good workability before proceeding with the process such as precision rolling.

1 is a graph for explaining a method of manufacturing a high-hardness martensitic stainless steel according to an embodiment of the present invention.

Referring to FIG. 1, a method for producing a high hardness martensitic stainless steel having excellent hardenability according to an embodiment of the present invention comprises: 0.60 to 0.80% of C, 0.07 to 0.15% of N, 0.1 to 0.15% of Si, Hot rolling a martensitic stainless steel slab containing 0.6 to 0.6% Mn, 0.5 to 1.0% Cr, 12 to 14% Cr and 0.90% or less C + N and the balance Fe and unavoidable impurities, And a step of subjecting the steel sheet to a heat treatment.

The preliminary heat treatment includes a first cracking step of uniformly distributing chromium carbide and chromium nitride in the microstructure of the hot-rolled steel sheet, and a second cracking step of spheroidizing the chromium carbide and the fine particles of chromium nitride.

Further, the method includes a step of raising the hot-rolled steel sheet to the first cracking step and a cooling step at a rate of 10 ° C / hour or more to reach the second cracking step after the first cracking step is completed. Thereafter, the method further includes air cooling after the second cracking step is completed.

For example, the step of raising the hot-rolled steel sheet may be performed at a rate of 40 to 200 ° C / hour until reaching the first cracking step, that is, 800 to 900 ° C.

The heating step is a step of raising the hot-rolled steel sheet at a rate of 40 to 200 ° C / hour until reaching the first cracking step.

When the heating rate is lower than 40 ° C / hour in the temperature rising step, the time period over which the chromium carbide and the chromium nitride are coarsened, for example, 700 to 750 ° C, increases and the sizes of chromium carbide and chromium nitride are coarse And the density of chromium carbide and chromium nitride distributed in the microstructure can be reduced. On the other hand, if the heating rate is higher than 200 ° C / hour, the durability of the chromium carbide and chromium nitride during the temperature interval in which the chromium carbide and the chromium nitride are coarsened is reduced to secure fine chromium carbide and chromium nitride. However, Chromium carbide and chromium nitride are unevenly distributed.

For example, the first cracking step may be performed at 800 to 900 DEG C for 15 to 25 hours.

The first cracking step is a step of uniformly depositing chromium carbide and chromium nitride in the structure of the hot-rolled steel sheet.

The first cracking step may be followed by a heating step to uniformly distribute chromium carbide and chromium nitride in the hot-rolled steel sheet, wherein the hot-rolled steel sheet is uniformly heated for 15 to 25 hours in a constant-temperature atmosphere at 800 to 900 ° C Process. In this process, chromium carbide and chromium nitride are uniformly distributed in the tissue.

When the cracking temperature is less than 800 ° C, aggregated portions may be formed due to chromium carbide and chromium nitride locally precipitated at the grain boundary during the cracking treatment. When the temperature exceeds 900 ° C, coarse chromium carbide and chromium nitride Such chromium carbide and chromium nitride agglomerates, coarse chromium carbides and chromium nitrides cause local material imbalance of the material, making it difficult to secure ductility and causing material deterioration in the final heat treatment.

In addition, when the cracking time in the first cracking step is less than 15 hours, chromium carbide and chromium nitride are advantageously used for formation of fine chromium carbide and chromium nitride but not uniformly distributed, can be clustered and distributed, , The chromium carbide and chromium nitride adjacent to each other, the local chromium carbide and the chromium nitride coarsening, and the heat treatment time increase, the process efficiency decreases, and the manufacturing cost increases.

For example, the hot-rolled steel sheet may be cooled to the second cracking stage after the completion of the first cracking step, that is, at a temperature of 600 to 750 ° C at a rate of 10 ° C / hour or more.

The cooling step is a step of cooling the hot-rolled steel sheet after the first cracking step to the second cracking step.

In the cooling step, when the cooling rate is less than 10 캜 / h, the time for the size of the chromium carbide and the chromium nitride microstructure to pass through the coarse temperature range is increased, which causes the chromium carbide and chromium There is a problem that it is difficult to secure corrosion resistance and hardness at the time of strengthening heat treatment because the nitride microstructure is coarsened.

For example, the second cracking step may be performed at 600 to 750 ° C for 5 to 15 hours.

The second cracking step is followed by the cooling step to solidify the fine particles of chromium carbide and chromium nitride in the hot-rolled steel sheet at low temperature. The hot-rolled coil is maintained at a constant temperature for 5 to 15 hours at 600 to 750 ° C, . The minimum temperature condition for spheroidizing chromium carbide and chromium nitride is 600 ° C. When the cracking temperature exceeds 750 ° C., spheroidized chromium carbide and chromium nitride are excessively grown to decrease the number of chromium carbide and chromium nitride and decrease ductility There is a problem.

Also, if the holding time of the second cracking process is less than 5 hours, the progress of spheroidization of chromium carbide and chromium nitride is insufficient, and if it is more than 15 hours, the spheroidized carbide and nitride are excessively grown to form coarse microstructure.

For example, the hot-rolled steel sheet may be air-cooled after the second cracking step is completed.

After the second cracking step, the hot-rolled steel sheet is air-cooled in the atmosphere to complete the annealing process.

For example, the heat-treated hot-rolled steel sheet may be subjected to a step of cold-rolling and annealing to produce a final product.

Hereinafter, the present invention will be described in more detail with reference to Examples.

The composition of the high-carbon martensitic stainless steel according to one embodiment of the present invention is shown in Table 1 below.

C Si Mn Cr N Inventive Steel 1 0.67 0.30 0.65 13.09 0.072 Invention river 2 0.67 0.30 0.65 13.06 0.093 Invention steel 3 0.55 0.295 0.68 13.40 0.130 Inventive Steel 4 0.71 0.30 0.68 13.05 0.119 Comparative River 1 0.68 0.31 0.65 13.00 0.023 Comparative River 2 0.69 0.31 0.70 13.35 0.045 Comparative Steel 3 0.65 0.29 0.69 13.12 0.156 Comparative Steel 4 0.78 0.31 0.72 12.94 0.138

A cast steel having the composition shown in Table 1 was prepared, and hot-rolled steel sheets having a thickness of 3 mm were produced through hot rolling. Then, the quality of the surface portion and the edge portion of each hot-rolled steel sheet was confirmed and shown in Table 2 below.

The hot-rolled steel sheet thus prepared was subjected to heat treatment using the following annealing conditions and then air-cooled to observe the microstructure and evaluate the elongation. The results are shown in Table 2 below.

[Condition for heat treatment]

- Heating step: Heating rate 100 캜 / hour

- First crack stage: 20 hours at 850 ° C

- Cooling step: Temperature lowering rate 10 ° C / hour

- Second crack stage: 7 hours at 650 ° C

C N C + N Hot-rolled steel sheet quality Microstructure Elongation (%) Surface portion Edge portion Number of carbides (pieces / 100 탆 ² ) Number of nitrides (number / 100 탆 ² ) Example 1 0.67 0.072 0.742 Good Good 93 59 20.1 Example 2 0.67 0.093 0.763 Good Good 87 78 18.9 Example 3 0.55 0.130 0.680 Good Good 82 93 19.2 Example 4 0.71 0.119 0.829 Good Good 106 81 20.4 Comparative Example 1 0.68 0.023 0.703 Good Good 97 18 19.3 Comparative Example 2 0.69 0.045 0.735 Good Good 91 37 19.2 Comparative Example 3 0.65 0.156 0.806 crack crack 97 121 17.6 Comparative Example 4 0.78 0.138 0.918 Good Good 121 101 16.4

When the N content in the hot-rolled steel sheet was less than 0.15%, the quality of the surface and edge of the material was favorably observed after hot rolling. On the other hand, in the case of Comparative Example 3 in which the N content is 0.15% or more, a large amount of cracks occurred on the surface and the edge portion of the material after hot rolling, and the elongation after annealing was less than 18%.

In the case of Comparative Example 4 in which the C + N content in the hot-rolled steel sheet exceeded 0.90%, the quality of the surface and the edge portion was good, while the elongation after the application was less than 18%.

2 and 3 are photographs for explaining the microstructure of the high-hardness martensitic stainless steel according to one embodiment of the present invention.

2 and 3, FIG. 2 is a photograph of a surface of a martensitic stainless steel hot-rolled steel sheet according to Comparative Example 1, FIG. 3 is a photograph of the surface of a martensitic stainless steel hot- It is the photograph of the surface.

The black particles in the photographs of the precipitates of FIGS. 2 and 3 represent chromium carbide, and the red particles represent chromium nitride. As a result of observation of the precipitates, the number of chromium nitrides distributed in the martensitic stainless steel hot-rolled steel sheet according to Example 2 in which a large amount of N was added compared to the martensitic stainless steel hot-rolled steel sheet according to Comparative Example 1 in which a small amount of N was added You can see relatively many things.

In order to quantitatively analyze the change of the density of chromium nitride according to the N content, a 3 mm thick material was subjected to cold rolling and annealing several times and rolled to a cold-rolled annealed sheet of 0.2 mm, The results are shown in Table 2 above.

Evaluation N content is less than 0.07% indicating when chromium nitride number of about ^50/2 100㎛ less than the other hand, if containing more than 0.07% N is the number of chromium nitride about 50 to ^120/2 of the distribution of 100㎛ .

These results indicate that the fraction of chromium nitride formed during the first cracking process performed at a temperature of 800 to 900 캜 as described above means that the density of the precipitate increases as the N content in the alloy component increases.

FIGS. 4 and 5 are views for explaining the change in hardness of the high-hardness martensitic stainless steel according to the reinforcing heat treatment condition according to an embodiment of the present invention.

4 and 5 are graphs showing changes in hardness of the martensitic stainless steel cold rolled annealed material according to Comparative Example 1 with respect to the tempering heat treatment temperature and time, and the graphs of the hardening of the martensitic stainless steel cold rolled annealed material according to Example 1 Graphs showing changes in hardness with heat treatment temperature and time.

In general, as the heat treatment time increases and the heat treatment temperature increases, the hardness of the material increases after the tempering treatment. Particularly, in the case of Example 1, as the N content increases, the 700Hv Or more of the hardness can be secured.

6 is a view for explaining a change in hardness according to a change in time when a hardened martensitic stainless steel according to an embodiment of the present invention is subjected to a tempering heat treatment at a temperature of 1,100 ° C.

FIG. 6 is a graph showing the change in hardness with the heat treatment time at 1,100 ° C., which is the test temperature condition with the highest hardness in the tempering heat treatment, based on the results of FIGS. 4 and 5.

Referring to FIG. 6, in the case of the martensitic stainless steel cold-rolled annealed material according to Comparative Example 1 having an N content of 0.023%, it is necessary to maintain about 18 seconds at the tempering heat treatment temperature of 1,100 ° C to secure a hardness of about 700 Hv or more . On the contrary, it can be seen that a hardness of 700 Hv or more can be secured when the martensitic stainless steel cold rolled annealed material according to Example 1 having an N content of 0.072% is maintained at 1,100 ° C for about 12 seconds.

As the N content increases, the hardenability is improved at the same tempering temperature. As the number of finely dispersed chromium nitrides increases, the proportion of recycled chromium nitride increases And as a result, the hardness is increased.

From the above results, it is found that when the content of C is 0.60 to 0.80%, 0.07 to 0.15% of N, 0.1 to 0.6% of Si, 0.5 to 1.0% of Mn, 12 to 14% includes, and the rest Fe and unavoidable to apply a heat treatment based appeal of the conditions presented in this invention with respect to the martensitic stainless steel according to the present invention contain impurities in the microstructures 50 / 100㎛ ² than the chromium nitride and a 80 / 100㎛ ² or more chromium carbide distribution, excellent hardness capability hardening elongation is more than 18% it may be seen that manufacturing martensitic stainless steel are possible.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited thereto. Those skilled in the art will readily obviate modifications and variations within the spirit and scope of the appended claims. It will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

Claims (12)

Wherein the steel contains 0.60 to 0.80% of C, 0.07 to 0.15% of N, 0.1 to 0.6% of Si, 0.5 to 1.0% of Mn, 12 to 14% of Cr and 0.90% or less of C + N, The remainder being Fe and inevitable impurities, in martensitic stainless steels,
A hardness martensitic stainless steel excellent in curability with chromium nitride of 50/100 μm ² or more and chromium carbide of 80/100 μm ² or more distributed in the microstructure of the cold-rolled annealed material. delete The method according to claim 1,
Hardened martensitic stainless steel excellent in hardenability having a Vickers hardness of 700 Hv or more at the time of tempering at a temperature of 1,100 DEG C or higher for 12 seconds or more. The method according to claim 1,
The martensitic stainless steel is a high-hardness martensitic stainless steel having an elongation of 18% or more and excellent curing ability. Wherein the steel contains 0.60 to 0.80% of C, 0.07 to 0.15% of N, 0.1 to 0.6% of Si, 0.5 to 1.0% of Mn, 12 to 14% of Cr and 0.90% or less of C + N, Hot rolling the martensitic stainless steel slab containing Fe and unavoidable impurities; And
Heat treating the hot-rolled steel sheet,
The above-
A first cracking step of uniformly distributing chromium carbide and chromium nitride in the microstructure of the hot-rolled steel sheet; And
And a second cracking step of spheroidizing the fine particles of the chromium carbide and the chromium nitride. The method of producing a high hardness martensitic stainless steel having excellent hardenability. 6. The method of claim 5,
The first cracking step is performed at 800 to 900 < 0 > C,
Wherein the second cracking step is performed at a temperature of 600 to 750 占 폚. 6. The method of claim 5,
The first cracking step is performed for 15 to 25 hours,
Wherein the second cracking step is performed for 5 to 15 hours. 6. The method of claim 5,
Heating the hot-rolled steel sheet at a rate of 40 to 200 ° C / hour until reaching the first cracking step; And
And cooling the steel sheet at a rate of 10 ° C / hour or more from the completion of the first cracking step to the second cracking step. 9. The method of claim 8,
Further comprising the step of air-cooling after completion of the second cracking step. 6. The method of claim 5,
And heat-treating the heat-treated hot-rolled steel sheet by cold rolling and annealing. 11. The method of claim 10,
^50/2 100㎛ excellent hardness capability of at least chromium nitride is distributed hardening method for producing martensitic stainless steel in the microstructure of the cold-rolled bovine dunjae. 11. The method of claim 10,
^80/2 100㎛ excellent hardness capability of at least chromium carbide distribution hardening method for producing martensitic stainless steel in the microstructure of the cold-rolled bovine dunjae.

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