KR20220068004A - Stainless steel and mathod of manufacturing the same - Google Patents

Abstract

Disclosed are stainless steel with excellent corrosion resistance and formability and a manufacturing method thereof. The stainless steel according to the present invention contains, by wt%: 0.02 % or less of C; 0.8 % or less of Si; 1.0 % or less of Mn; 18.0-21.0 % of Cr; 15.0-25.0 % of Ni; 6.0-7.0 % of Mo; 0.5-1.0 % of Cu; 0.15-0.25 % of N; and the balance of Fe and unavoidable impurities, wherein (Mn + Cu + Ni) + 10 × (C + N) satisfies 20 or more. In addition, the stainless steel according to the present invention shows that a sigma (σ) phase fraction (area %) of a central portion in the thickness direction is 1 % or less through alloy components and process control.

Description

Stainless steel and its manufacturing method

The present invention relates to stainless steel manufacturing technology. More specifically, the present invention relates to an austenitic stainless steel having excellent corrosion resistance and formability.

Further, the present invention relates to a method for manufacturing an austenitic stainless steel having excellent corrosion resistance and formability.

Stainless steel is classified into ferritic stainless steel, austenitic stainless steel, and duplex stainless steel according to the main microstructure. Among them, austenitic stainless steel is used in various fields such as kitchens, home appliances, and industrial facilities due to its excellent corrosion resistance, workability and weldability. Commonly used austenitic stainless steels include 304 stainless steel and 316 stainless steel. Recently, many studies have been conducted on highly corrosion-resistant austenitic stainless steel so that it can be used under severe corrosive environments such as seawater or acid atmosphere.

In general, corrosion resistance of austenitic stainless steel is obtained by alloying elements such as Cr, Mo, and N with Fe, and a higher content of Cr, Mo, and N is required to improve corrosion resistance. However, when the content of these elements is increased, intermetallic compounds represented by the sigma (σ) phase are inevitably precipitated in the matrix structure, and there is a problem in that corrosion resistance and formability are rather deteriorated.

Patent Document 1 and Patent Document 2 disclose suppressing the sigma (σ) phase formation by adding W instead of Mo. However, adding a large amount of W instead of Mo may cause precipitation of another intermetallic compound such as a chi (χ) phase.

In addition, in Patent Document 3, by controlling the component so that the value of the sigma (σ) equivalent defined by the formula: Cr + 2Mo - 40N + 0.5Mn - 2Cu is 18 or less, the content of Si to control the sigma (σ) phase is initiating However, in Patent Document 3, only limited elements such as Cr, Mo, N, and Mn Cu are considered as alloying elements affecting the control of the sigma (σ) phase.

Laid-open Patent Publication No. 10-2001-0026770 (2001.04.06) Laid-open Patent Publication No. 10-2000-0056551 (2000.09.15) US Patent Application Publication No. US2015/0050180 (2015.02.19)

An object of the present invention is to provide a stainless steel excellent in corrosion resistance and formability.

Another object to be solved by the present invention is to provide a method for manufacturing stainless steel having excellent corrosion resistance and formability.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention not mentioned may be understood by the following description, and will be more clearly understood by the examples of the present invention. It will also be readily apparent that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the appended claims.

Stainless steel according to an embodiment of the present invention for solving the above problems is C: 0.02% or less, Si: 0.8% or less, Mn: 1.0% or less, Cr: 18.0-21.0%, Ni: 15.0-25.0% by weight % , Mo: 6.0~7.0%, Cu: 0.5~1.0%, N: 0.15~0.25% and the remaining Fe and unavoidable impurities, (Mn+Cu+Ni)+10×(C+N) is 20 or more .

The stainless steel according to the present invention has a sigma (σ) phase fraction (area %) of 1% in the thickness direction center through process control such as hot rolling annealing as well as control of alloy components such as Mn, Cu, and Ni, which are austenite stabilizing elements. is below. Through such a low sigma (σ) phase fraction in the center of the thickness direction, excellent corrosion resistance can be obtained, and moldability can be improved.

The stainless steel according to the present invention may have a pitting resistance equivalent number (PREN) of 40 to 50 expressed by the following formula.

PREN: Cr + 3.3Mo + 16N

The stainless steel according to another embodiment of the present invention has a thickness of 5 to 6 mm, and the sigma (σ) phase fraction (area %) of the central portion in the thickness direction may be 0.7% or less. By controlling the material temperature of the primary hot-rolling annealing as well as the material temperature and line speed control of the primary hot-rolling annealing and the secondary hot-rolling annealing, the fraction of the sigma (σ) phase in the center of the thickness direction can be lowered.

Stainless steel according to another embodiment of the present invention has a thickness of 1 mm or less, a sigma (σ) phase fraction (area %) of the central portion in the thickness direction satisfies 0.15% or less, and an Ericsson height is 10.2 mm or more, and is rolled The elongation (%) in a direction orthogonal to the direction may be 40% or more. This can be obtained by controlling the temperature of cold rolling annealing in addition to controlling alloy components and hot rolling annealing. Accordingly, the fraction of the sigma (σ) phase of the central portion in the thickness direction can be reduced as much as possible, and stainless steel having high formability can be provided.

In the stainless steel according to another embodiment of the present invention, the concentration of Cr at a depth of 1 μm from the surface may be 18% by weight or more. Also, according to some embodiments, the concentration of Cr at a depth of 0.5 μm from the surface may be higher than that of Ni. In general, stainless steel containing 21 wt% or less of Cr has a lower Cr concentration as it approaches the surface, and even if a polishing process is added, the Cr concentration hardly reaches 18 wt% at a depth of 1 μm from the steel surface. However, the stainless steel according to the present invention can increase the Cr concentration in the portion adjacent to the surface through the above-described alloy composition and process control, and an additional polishing process.

In a method for manufacturing stainless steel according to an embodiment of the present invention for solving the above problems, C: 0.02% or less, Si: 0.8% or less, Mn: 1.0% or less, Cr: 18.0-21.0%, Ni: 15.0% by weight 25.0%, Mo: 6.0~7.0%, Cu: 0.5~1.0%, N: 0.15~0.25% and the remaining Fe and unavoidable impurities, (Mn+Cu+Ni)+10×(C+N) is 20 Hot rolling a material satisfying the above; and performing primary hot rolling annealing of the hot-rolled material, wherein the primary hot rolling annealing is performed at 1200° C. or higher.

In the stainless steel manufacturing method according to an embodiment of the present invention, the primary hot-rolling annealing is performed at 1200 °C or higher, preferably at 1200 to 1250 °C. This corresponds to a temperature somewhat higher than the normal hot rolling annealing temperature. As a result of performing the primary hot rolling annealing at 1200° C. or higher for the material having the above alloy composition, it was possible to lower the sigma (σ) phase fraction (area %) at the center in the thickness direction to 1% or less.

The stainless steel manufacturing method according to another embodiment of the present invention may include additionally rolling and secondary hot-rolling annealing of the first hot-rolled annealed material. In this case, the primary hot rolling annealing may satisfy the following formula (1), and the secondary hot rolling annealing may satisfy the following formula (2).

[Equation 1]

1st hot rolling annealing material temperature (℃)]/[1st hot rolling annealing line speed (mpm)] > 150

[Equation 2]

Secondary hot rolling annealing material temperature (℃)]/[Secondary hot rolling annealing line speed (mpm)] > 105

When Equations 1 and 2 were satisfied, the fraction of the sigma (σ) phase at the center of the thickness direction could be further reduced.

A stainless steel manufacturing method according to another embodiment of the present invention comprises the steps of: cold rolling the secondary hot annealed material; and cold rolling annealing the cold-rolled material, further comprising, wherein the cold rolling annealing is performed at 1175° C. or higher, and more preferably at 1175 to 1200° C.

Through the control of the cold rolling process as described above, it was possible to further lower the fraction of the sigma (σ) phase in the central portion in the thickness direction.

A method for manufacturing stainless steel according to another embodiment of the present invention further performs a polishing treatment.

Through the additional polishing treatment, the concentration of Cr at a depth of 1 μm from the surface after the secondary cold rolling annealing can be made to be 18% or more.

ADVANTAGE OF THE INVENTION According to this invention, the fraction of sigma (σ) phase in the center part in thickness direction is reduced, and it can provide the austenitic stainless steel excellent in corrosion resistance and formability.

Since the stainless steel according to the present invention has excellent corrosion resistance and formability, it can be applied as a material for industrial facilities such as desulfurization facilities, heat exchangers, desalination facilities, and food and beverage facilities.

In addition to the above-described effects, the specific effects of the present invention will be described together while describing specific details for carrying out the invention below.

1 shows the fraction of the sigma phase in the thickness direction of the stainless steel according to the alloy component and the primary hot-rolling annealing temperature.
2 shows the fraction of the sigma (σ) phase of the thickness direction center of the stainless steel according to the primary and secondary hot rolling annealing temperatures.
Figure 3a shows the Cr concentration distribution of the polar surface layer of the specimen according to Comparative Example 9.
Figure 3b shows the Cr concentration distribution of the polar surface layer of the specimen according to Inventive Example 7.

Hereinafter, with reference to the drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification. Further, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to components of each drawing, the same components may have the same reference numerals as much as possible even though they are indicated in different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description may be omitted.

In describing the components of the present invention, terms such as first and second may be used. These terms are only for distinguishing the elements from other elements, and the nature, order, order, or number of the elements are not limited by the terms. When it is described that a component is “connected”, “coupled” or “connected” to another component, the component may be directly connected or connected to the other component, but other components may be interposed between each component. It should be understood that each component may be “interposed” or “connected”, “coupled” or “connected” through another component.

In addition, in implementing the present invention, components may be subdivided for convenience of description, but these components may be implemented in one device or module, or one component may include a plurality of devices or modules. It may be implemented by being divided into .

Hereinafter, a stainless steel and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.

The stainless steel according to the present invention is C: 0.02% or less, Si: 0.8% or less, Mn: 1.0% or less, Cr: 18.0 to 21.0%, Ni: 15.0 to 25.0%, Mo: 6.0 to 7.0%, Cu in weight % : 0.5~1.0%, N: 0.15~0.25% and the remaining Fe and unavoidable impurities. At this time, in the stainless steel according to the present invention, (Mn+Cu+Ni)+10×(C+N) satisfies 20 or more.

In addition, the stainless steel according to the present invention has a sigma (σ) phase fraction (area %) of 1% or less in the thickness direction center through process control such as hot rolling annealing and cold rolling annealing, which will be described later along with the control of alloy components as described above. can indicate Corrosion resistance and formability can be secured at the same time through such a low cisma phase fraction.

In general, the corrosion resistance of austenitic stainless steels is expressed by the Pitting Resistance Equivalent Number (PREN), and is expressed as Cr + 3.3Mo + 16N in terms of Cr, Mo, and N components. In addition, in order to maintain the material in an environment containing a large amount of salt such as seawater or an extremely corrosive environment containing acidic substances, the PREN value should be 40 or more. If it has a corrosion resistance of less than that, it cannot withstand a corrosive environment for a long time, and if it has a value of 50 or more, a large amount of Cr, Mo, and W content is included, so there is concern about corrosion resistance deterioration due to intermetallic compound precipitation.

The stainless steel according to the present invention has a PREN of 40 to 50, and (Mn+Cu+Ni)+10×(C+) so that the fraction (area %) of the sigma (σ) phase of the center in the thickness direction can be satisfied by 1% or less. N) has an alloy composition of 20 or more. Hereinafter, alloy components included in the stainless steel according to the present invention and their content ranges will be described. The content of each component means % by weight.

C: C is a strong austenite phase stabilizing element, and is an effective element for increasing material strength by solid solution strengthening. However, when the content is excessive, the content of C is limited to 0.02% or less because it is easily combined with carbide-forming elements such as Cr, which are effective for corrosion resistance at the austenite phase boundary, and lowers the Cr content around the grain boundaries to reduce corrosion resistance.

Si; Si, which also acts as a ferrite phase stabilizing element, is effective in improving corrosion resistance and is an element that plays a role as a major deoxidizer. However, when excessive, it promotes the precipitation of intermetallic compounds such as sigma (σ) phase, resulting in mechanical properties related to impact toughness and corrosion resistance and cracks during hot rolling, so it is limited to 0.8% or less.

Mn; Mn is an austenite phase stabilizing element such as C and Ni, and may improve the N solid solubility. However, since the increase of the Mn content is not preferable when corrosion resistance is required due to the formation of inclusions such as MnS, it is preferable to limit the Mn content to 1.0% or less in order to secure corrosion resistance.

Cr: Cr is a basic element that contains the most of the corrosion resistance improvement elements of stainless steel, and in the present invention, the PREN value of 40 or more should be included in at least 18% or more for the expression of corrosion resistance. However, Cr is a ferrite stabilizing element, and when the Cr content is increased, the ferrite fraction increases to deteriorate the hot workability of the steel, and the formation of the shigame (σ) phase is promoted, which causes deterioration of mechanical properties and corrosion resistance. Therefore, it is preferable to limit the Cr content to 21% or less.

Ni: Ni is the strongest element among the austenite phase stabilizing elements, and should be contained in an amount of 15% or more in order to maintain the austenite phase. However, since an increase in the Ni content is directly related to an increase in the raw material price, it is preferable to limit it to 25% or less.

Mo: Mo is a ferrite stabilizing element. When added to austenitic stainless steel, it acts as an element to improve the corrosion resistance of steel. Therefore, it is necessary to add 6% or more in order to secure high corrosion resistance of PREN 40 or higher. However, although useful in terms of mechanical properties and corrosion resistance in the annealed state, it is preferable to limit the content to 7% or less because it is a representative element that generates a sigma (σ) phase during processes such as aging heat treatment, hot rolling, or welding.

Cu; Cu is an austenite stabilizing element, and has the advantage of suppressing phase transformation to martensite during cold deformation and improving corrosion resistance in a sulfuric acid atmosphere. However, in a chlorine atmosphere, there is a disadvantage of reducing pitting resistance and also reducing hot workability, so that the Cu content is limited to 0.5 to 1.0%.

N; N is an element useful for stabilizing the austenite phase as well as improving corrosion resistance in a chlorine atmosphere. Therefore, it is necessary to add 0.15% or more to secure corrosion resistance of steel. However, when a large amount is added, it is preferable to limit it to 0.25% or less, since it reduces the hot workability and lowers the yield rate of steel.

On the other hand, the stainless steel according to the present invention does not contain phosphorus (P) or sulfur (S) that deteriorates the hot workability of the steel, or even if it is unavoidably included, the content thereof is P: 0.02% or less and S: 0.005% or less.

Formula A: (Mn+Cu+Ni)+10×(C+N)

Mn, Cu, Ni, C, and N are each useful element for stabilizing austenite, and the inventors of the present invention found that it is effective in reducing the fraction of sigma (σ) phase in the thickness direction center when Formula A is 20 or more.

1 shows the fraction of the sigma (σ) phase of a steel stainless steel having a thickness of about 5 mm according to the value of Equation A.

Referring to FIG. 1 , when the value of Equation A is very low, for example, about 18, it can be seen that the fraction of the sigma (σ) phase in the center of the thickness direction is relatively high regardless of the hot rolling annealing temperature. However, when the value of Equation A is 20 or more, the sigma (σ) phase fraction in the center of the thickness direction is relatively low, and in particular, in conjunction with the primary hot rolling annealing condition of 1200 ° C or higher, the sigma (σ) phase fraction in the thickness direction center is It can be seen that the decrease is below 1%.

Therefore, in order to lower the sigma (σ) phase fraction in the center of the thickness direction by 1%, Equation A related to the content of austenite stabilizing elements needs to represent 20 or more, and the primary hot rolling annealing conditions also need to be performed at 1200° C. or more. there is

ASTM G48-A (10%FeCl ₃ .6H ₂ O, 50) when the sigma (σ) phase is precipitated at the center of the thickness direction at less than 1.0% in hot-rolled products with a thickness of 5-6 mm (for example, parts for desulfurization equipment for ships) ℃, weight loss after immersion for 24 hours 4.0g/m ² or less) standards can be satisfied. In addition, in a cold-rolled product (for example, a plate heat exchanger component) with a thickness of about 1 mm, when the sigma (σ) phase is precipitated at the center of the thickness direction at less than 0.15%, the Ericsson height is 10.2 mm or more, and the 90 degree tensile elongation ( %) was confirmed to have a characteristic of 40% or more.

The stainless steel according to the present invention may have a microstructure of a single austenite phase through the alloy components as described above and process control described later, and may contain a sigma (σ) phase of 1% or less. More specifically, for example, for a hot rolled material having a thickness of 5 to 6 mm, 0.7% or less of sigma (σ) phase may be included, and, for example, 0.15% or less of sigma (σ) phase may be included for cold rolled material having a thickness of 1 mm or less. can

The stainless steel manufacturing method according to an embodiment of the present invention includes hot rolling a material having the above alloy composition and performing primary hot annealing of the hot rolled material. If necessary, the secondary rolling and secondary hot rolling annealing of the primary hot annealed material may be performed. For example, in hot rolling, the material may be rolled to a thickness of 7 to 8 mm, and in secondary rolling, the hot rolled material may be rolled to a thickness of 5 to 6 mm. The secondary rolling may be performed, for example, by cold rolling, and the secondary hot rolling annealing temperature may be performed, for example, at 1180 to 1230°C. Hot rolling annealing and cold rolling annealing to be described later may be performed in an annealing furnace, which is a heating furnace for recrystallization growth of stainless steel.

In the stainless steel manufacturing method according to the present invention, as previously described in FIG. 1 , the primary hot rolling annealing is performed at 1200° C. or higher, and preferably at 1200 to 1250° C. The primary hot-rolling annealing temperature applied in the stainless steel manufacturing method according to the present invention corresponds to a slightly higher temperature than a typical hot-rolling annealing temperature. As a result of performing the primary hot rolling annealing at 1200° C. or higher for the material having the above alloy composition, it was possible to lower the sigma (σ) phase fraction (area %) at the center in the thickness direction to 1% or less. Referring to FIG. 2 , when the primary hot rolling annealing temperature is 1200° C. or higher, even if the secondary hot rolling annealing temperature is lower than 1200° C., there is a possibility that the fraction of the sigma (σ) phase in the thickness direction center becomes 1% or less. This means that the range of the secondary hot annealing temperature that can lower the sigma (σ) phase fraction is very wide. From these results, the effect of the primary hot-rolling annealing temperature is very large, and it can be seen as a result of decomposition of the sigma (σ) phase formed in the center of the thickness direction by performing the primary hot-rolling annealing at a relatively high temperature. On the other hand, if the primary hot-rolling annealing temperature does not reach 1200 ℃, the width of the secondary hot-rolling annealing temperature that can lower the sigma (σ) phase fraction as can be seen in FIG. 2 is very narrow. Therefore, it is preferable that the primary hot rolling annealing temperature is 1200°C or higher.

After primary hot-rolling annealing or secondary hot-rolling annealing is performed, cooling may be performed by air cooling or water cooling.

On the other hand, the primary hot rolling annealing may satisfy the following formula (1), and the secondary hot rolling annealing may satisfy the following formula (2).

[Equation 1]

1st hot rolling annealing material temperature (℃)]/[1st hot rolling annealing line speed (mpm)] > 150

[Equation 2]

Secondary hot rolling annealing material temperature (℃)]/[Secondary hot rolling annealing line speed (mpm)] > 105

For example, if the line speed of the first hot rolling annealing is 8.1mpm, the annealing temperature may be 1215℃ or higher to satisfy Equation (1), and if the line speed of the second hot rolling annealing is 11.3mpm, 2 Primary hot rolling annealing can be performed at about 1180 ℃ or higher . When the primary hot-rolling annealing and the secondary hot-rolling annealing are performed under conditions that satisfy the following Equations 1 and 2, the fraction of the sigma (σ) phase in the center of the thickness direction may be lowered.

In addition, the stainless steel manufacturing method according to another embodiment of the present invention may further include a cold rolling process. More specifically, the method may further include cold-rolling the primary and secondary hot-rolled annealed material, and cold-rolling the cold-rolled material. After cold rolling annealing, cooling such as air cooling or water cooling may be performed. In this case, the cold rolling annealing is preferably performed at 1175° C. or higher, and more specifically, it may be suggested that the cold rolling annealing is performed at 1175 to 1200° C. Through the control of the cold rolling process, the fraction of the sigma (σ) phase in the central portion in the thickness direction could be further reduced.

For example, if the cold rolling process is performed in the order of primary cold rolling, primary cold rolling annealing, secondary cold rolling and secondary cold rolling annealing, both primary cold rolling annealing and secondary cold rolling annealing are preferably performed at 1175° C. or higher do. When both the primary cold rolling annealing and the secondary cold rolling annealing are performed at 1175°C or higher, the target Ericsson height of 10.2mm or more and the transverse elongation of 40% or more can be obtained, and the primary cold rolling annealing or secondary cold rolling annealing is performed at less than 1175°C. When performed, at least one of Ericsson height and elongation did not meet the target values. This can also be confirmed in Table 3 of Examples to be described later.

A method for manufacturing stainless steel according to another embodiment of the present invention further performs a polishing treatment.

Through the additional polishing treatment, the concentration of Cr at a depth of 1 μm from the surface after the secondary cold rolling annealing can be made to be 18% or more. Furthermore, the concentration of Cr at a depth of 0.5 μm from the surface may be higher than that of Ni.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention in any sense.

Content not described here will be omitted because it can be technically inferred sufficiently by a person skilled in the art.

1. Preparation of specimens

The alloy compositions of the specimens used in the Inventive Examples and Comparative Examples are shown in Table 1. Except for the components listed in Table 1, Fe and unavoidable impurities.

[Table 1] (Unit: % by weight)

After melting steel having the chemical composition shown in Table 1 in a vacuum induction melting furnace, hot rolling was performed to prepare a material with a thickness of 8 mm. After performing annealing while changing the material temperature (°C) of the primary hot rolling annealing for each material, secondary rolling (cold rolling) was performed to prepare a material with a thickness of about 5 mm. Thereafter, for each material, the change in the sigma (σ) phase fraction (%) of the thickness direction center of the material subjected to secondary hot rolling annealing at 1180°C was investigated.

Table 2 shows the sigma (σ) phase fraction according to the alloy components and the primary hot rolling annealing material temperature of the specimens with a thickness of about 5 mm manufactured through the hot rolling process as described above.

[Table 2]

Referring to Table 2, for the hot-rolled specimens according to Invention Examples 1 to 6, (Mn+Cu+Ni)+10Х(C+N) satisfies 20 or more, and the material temperature (°C) of the primary hot rolling annealing is Manufactured at 1200℃ or higher, the fraction (area%) of the sigma (σ) phase in the center of the thickness direction is 1% or less, ASTM G48-A (10%FeCl ₃ 6H ₂ O, 50℃, weight loss after immersion for 24 hours) 4.0 g/m ² or less) standards were satisfied. For the hot-rolled specimens according to Comparative Examples 1 to 8, (Mn+Cu+Ni)+10Х(C+N) is less than 20 or the material temperature (°C) of the primary hot-rolling annealing is less than 1200°C, the thickness The fraction (area %) of the sigma (σ) phase at the center of the direction was 1.1% or more, indicating that it did not meet the ASTM G48-A standard.

Table 3 shows the mechanical properties of the cold-rolled specimen obtained by performing a cold rolling process using the specimen according to Invention Example 1 of Tables 1 and 2. For this, cold-rolled specimens with a thickness of about 1 mm were prepared by performing primary cold rolling, primary cold-rolling annealing, secondary cold-rolling and secondary cold-rolling.

[Table 3]

Referring to Table 3, the manufactured cold-rolled specimens did not show a significant difference in tensile strength and yield strength. However, the values of the Erickson height and the elongation in the direction perpendicular to the rolling direction (C direction) showed a large difference according to the temperature of the primary cold rolling annealing and the secondary cold rolling annealing. Even if the same alloy component and the same hot rolling process were performed, the sigma (σ) phase fraction in the center of the thickness direction when the cold rolling process was performed under the conditions suggested in the present invention, that is, when the temperature of the primary cold rolling annealing and the secondary cold rolling annealing was 1175° C. or higher It can be seen that (area %) satisfies 0.15% or less, the Ericsson height is 10.2mm or more, and the elongation (%) in a direction orthogonal to the rolling direction represents 40% or more.

On the other hand, when any one of the primary cold rolling annealing and the secondary cold rolling annealing is performed at 1175° C. or less, the Ericsson height is less than 10.2 mm, or the elongation (%) in the direction orthogonal to the rolling direction was 40% or less. .

When looking at the results of Table 3, it can be seen that each of the primary cold rolling annealing and the piece secondary cold rolling annealing is preferably performed at 1175° C. or higher.

3a and 3b show the concentration distribution of Cr according to the depth from the surface when the additional polishing process is performed on the cold-rolled specimens according to Comparative Example 9 and Inventive Example 7 of Table 3;

Referring to FIG. 3A , when grinding was performed with the cold rolled specimen according to Comparative Example 9, it can be seen that the Cr concentration did not reach 18% by weight at a thickness of 1 μm from the surface. On the other hand, referring to FIG. 3B , when the cold-rolled specimen according to Inventive Example 7 was polished, it can be seen that the Cr concentration was 18 wt % or more at a thickness of 1 μm from the surface.

In addition, referring to FIG. 3A , when polishing was performed with the cold-rolled specimen according to Comparative Example 9, the Cr concentration was lower than the Ni concentration at a thickness of 0.5 μm from the surface. It can be seen that the Cr concentration is higher than the Ni concentration at a thickness of 0.5 μm from the surface.

As described above, the present invention has been described with reference to the illustrated drawings, but the present invention is not limited by the embodiments and drawings disclosed in this specification, and a variety of It is obvious that variations can be made. In addition, although the effects according to the configuration of the present invention are not explicitly described and described while describing the embodiments of the present invention, it is natural that the effects predictable by the configuration should also be recognized.

Claims (10)

C: 0.02% or less by weight, Si: 0.8% or less, Mn: 1.0% or less, Cr: 18.0-21.0%, Ni: 15.0-25.0%, Mo: 6.0-7.0%, Cu: 0.5-1.0%, N : Consists of 0.15~0.25% and the remaining Fe and unavoidable impurities,
(Mn+Cu+Ni)+10×(C+N) satisfies 20 or more, and the sigma (σ) phase fraction (area%) of the center in the thickness direction is 1% or less.
According to claim 1,
The stainless steel is Cr + 3.3Mo + 16N stainless steel, characterized in that 40-50.
According to claim 1,
The stainless steel has a thickness of 5 to 6 mm, and the sigma (σ) phase fraction (area%) of the central portion in the thickness direction is 0.7% or less.
According to claim 1,
The stainless steel has a thickness of 1 mm or less, the sigma (σ) phase fraction (area%) of the central portion in the thickness direction satisfies 0.15% or less, the Ericsson height is 10.2 mm or more, and the elongation in the direction orthogonal to the rolling direction ( %) is 40% or more.
5. The method of claim 4,
Stainless steel, characterized in that the concentration of Cr at a depth of 1 μm from the surface is 18% or more.
5. The method of claim 4,
Stainless steel, characterized in that the concentration of Cr at a depth of 0.5 μm from the surface is higher than that of Ni.
C: 0.02% or less by weight, Si: 0.8% or less, Mn: 1.0% or less, Cr: 18.0-21.0%, Ni: 15.0-25.0%, Mo: 6.0-7.0%, Cu: 0.5-1.0%, N : Hot rolling a material consisting of 0.15 to 0.25% and the remaining Fe and unavoidable impurities, (Mn+Cu+Ni)+10×(C+N) satisfying 20 or more; and
Including; primary hot annealing of the hot-rolled material;
The first hot rolling annealing is a stainless steel manufacturing method, characterized in that performed at 1200 ℃ or higher.
8. The method of claim 7,
The stainless steel manufacturing method comprises the steps of additionally rolling and secondary hot-rolling annealing of the primary hot-rolling annealed material,
The first hot rolling annealing satisfies the following formula (1), and the secondary hot rolling annealing satisfies the following formula (2).
[Equation 1]
1st hot rolling annealing temperature (℃)]/[1st hot rolling annealing line speed (mpm)] > 150
[Equation 2]
Secondary hot rolling annealing temperature (℃)]/[Secondary hot rolling annealing line speed (mpm)] > 105
9. The method of claim 8,
The stainless steel manufacturing method is
Cold rolling the secondary hot annealed material; and
Further comprising; cold rolling annealing the cold rolled material;
The cold rolling annealing is a stainless steel manufacturing method, characterized in that performed at 1175 ℃ or higher.
10. The method of claim 9,
Stainless steel manufacturing method, characterized in that after the cold rolling annealing, further performing a polishing treatment so that the concentration of Cr at a depth of 1 μm from the surface is 18% or more.

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