Stainless steel sheet for brazing and manufacturing method therefor

Abstract

The present invention may provide a stainless steel sheet for brazing, comprising: a base material including, in wt%, more than 0.00% but not more than 0.10% of C, more than 0.00% but not more than 1.50% of Si, more than 0.00% but not more than 5.00% of Mn, 11.00-25.00% of Cr, 5.00-14.00% of Ni, more than 0.00% but not more than 0.40% of N, and the remainder of Fe and impurities; and a surface depletion layer positioned on the base material, wherein the surface depletion layer is composed of 50% or more of Cu, less than 50% of formula (1) of [Fe]+[Cr]+[Mn]+[Si], and unavoidable impurities.

Description

Stainless steel plate for brazing joints and method of manufacturing the same

[0001] The present invention relates to a stainless steel plate for brazing joints capable of joining stainless steels without a metal bonding agent, and a method for manufacturing the same.

[0002] Plate heat exchangers are widely used in various industrial fields and are manufactured by forming stainless steel sheets and then stacking and joining dozens to hundreds of them. Among the methods used for joining stainless steel in these plate heat exchangers, brazing is a process in which a metal bonding agent is inserted between stainless steel plates and then heat-treated at the melting temperature of the agent; the molten metal bonding agent then flows between the plates via capillary action to create a bond.

[0003] In the brazing of stainless steel for plate heat exchangers, copper (Cu) with a low melting point is primarily used as the metal bonding agent. Stainless steel plates with formed fluid channels and thin copper sheets are alternately laminated, and the copper bonding agent is melted and joined using heat treatment equipment in a vacuum atmosphere. This process ensures the airtightness of the heat exchanger.

[0004] However, copper sheets, which are essential metal bonding agents used in the manufacture of plate heat exchangers, are more expensive than stainless steel sheets. Furthermore, the additional process of laminating them alternately with stainless steel sheets is required, which is one of the causes of increased heat exchanger manufacturing costs.

[0005] In order to solve the aforementioned problems, the present invention aims to provide a stainless steel plate for brazing that can be joined without using a metal bonding agent, and a method for manufacturing the same.

[0006] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0007] As a means to achieve the above-mentioned purpose, a stainless steel sheet for brazing joint according to one embodiment of the present invention comprises, in weight %, a base material including C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities, and a surface depletion layer located on top of the base material, wherein the surface depletion layer may include, in composition, a Cu content of 50% or more, less than 50% of the following formula (1), and unavoidable impurities.

[0008] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0009] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0010] In a stainless steel sheet for brazing according to one embodiment of the present invention, the surface of the surface deficiency layer may have an area fraction of metal Cu of 50% or more.

[0011] In a stainless steel plate for brazing according to one embodiment of the present invention, the surface depletion layer may have a thickness of 1.0 μm to 10.0 μm.

[0012] In a stainless steel plate for brazing according to one embodiment of the present invention, the surface deficiency layer may be formed on both sides of the base material.

[0013] In a stainless steel plate for brazing according to one embodiment of the present invention, the surface deficiency layer can be formed entirely on the surface of the stainless steel plate.

[0014] A heat exchanger according to one embodiment of the present invention includes a plurality of heat transfer plates and a plurality of heat transfer passages existing between the plurality of heat transfer plates, and the heat transfer plates may be manufactured from stainless steel plates according to the above.

[0015] A method for manufacturing a stainless steel sheet for brazing joints according to one embodiment of the present invention may include the steps of: manufacturing a hot-rolled steel sheet by hot-rolling a steel material containing, in weight %, C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities, at 1,100°C to 1,300°C; the steps of annealing, pickling, and heating the hot-rolled steel sheet at 1,000°C to 1,100°C; manufacturing a cold-rolled steel sheet by cold-rolling and annealing the heated hot-rolled steel sheet; and forming a surface depletion layer by controlling the fractions of Fe, Cr, Mn, Si, and Cu on the surface of the cold-rolled steel sheet. there is.

[0016] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the thickness of the hot-rolled steel sheet may be 3.0 mm to 5.0 mm.

[0017] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the thickness of the cold-rolled steel sheet may be 0.3 mm to 1.0 mm.

[0018] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the thickness of the surface depletion layer may be 1.0 μm to 10.0 μm.

[0019] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the surface deficiency layer may be formed on both sides of the cold-rolled steel sheet.

[0020] In a method for manufacturing a stainless steel plate for brazing according to one embodiment of the present invention, the surface depletion layer obtained by adjusting the fractions of Fe, Cr, Mn, Si, and Cu may have a composition of 50% or more Cu content, less than 50% of the following formula (1), and unavoidable impurities.

[0021] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0022] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0023] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the surface depletion layer, which has undergone the step of controlling the fractions of Fe, Cr, Mn, Si, and Cu, has a composition of 50% or more Cu content, less than 50% of the following formula (1), and unavoidable impurities, and the surface of the surface depletion layer may have an area fraction of metallic Cu of 50% or more.

[0024] According to the stainless steel plate for brazing joints and the method for manufacturing the same according to the present invention, brazing joints can be performed without using a metal bonding agent.

[0025] A heat exchanger made of stainless steel plates for brazing according to the present invention exhibits excellent bondability and corrosion resistance, and the problem of residual Cu can be improved. In addition, it is possible to reduce manufacturing costs and simplify the manufacturing process.

[0026] Figure 1 is a scanning electron microscope (SEM) image of the surface of Example 5.

[0027] Figure 2 is a scanning electron microscope (SEM) image of the surface of Example 6.

[0028] Figure 3 is a scanning electron microscope (SEM) image of the surface of Comparative Example 2.

[0029] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0030] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0031] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense.

[0032] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0033] Unless otherwise specifically stated in this specification, the % indicating the content of each element is based on weight.

[0034] A stainless steel sheet for brazing according to one embodiment of the present invention comprises, in weight %, a base material including C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities, and a surface depletion layer located on top of the base material, wherein the surface depletion layer may have a composition of 50% or more of Cu content, less than 50% of the following formula (1), and unavoidable impurities.

[0035] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0036] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0037] base material

[0038] Hereinafter, the reason for limiting the numerical value of the alloy component content of the stainless steel base material according to one embodiment of the present invention will be explained. In order to achieve the objective of the present invention, which is to obtain a stainless steel plate that can omit the metal bonding agent during brazing, there is no need to specifically limit the alloy composition. However, a preferred alloy composition according to one embodiment is as follows.

[0039] C (carbon) may be greater than 0.00% and less than or equal to 0.10%.

[0040] C is an element effective for austenite stabilization, δ-ferrite suppression, and strength increase through solid solution strengthening. However, when the C content is excessive, it readily combines with carbide-forming elements (Cr, Ti, Nb, etc.) to reduce the corrosion resistance, ductility, and toughness of the base material. Considering this, it is desirable to keep the C content greater than 0.00% and less than or equal to 0.10%.

[0041] Si (silicon) may be greater than 0.00% and less than or equal to 1.50%.

[0042] Si helps improve the strength and corrosion resistance of steel through solid solution strengthening. Considering this, Si can be added in an amount of 0.10% or more. However, if added excessively as a ferrite-stabilizing element, it forms intermetallic compounds such as the sigma phase, which reduces the ductility and toughness of the base material. Considering this, it is desirable to keep the Si content greater than 0.00% and less than or equal to 1.50%.

[0043] Mn (manganese) may be greater than 0.00% and less than or equal to 5.00%.

[0044] Mn is an austenite-stabilizing element that inhibits the formation of deformation-induced martensite and can replace expensive Ni. Therefore, it can be added to improve stability in hydrogen environments while lowering the cost of steel. However, it can combine with sulfur (S) inevitably contained during the steel manufacturing process to form MnS, which can cause corrosion of the base material. Considering this, it is desirable to keep the Mn content greater than 0.00% and less than or equal to 5.00%.

[0045] The content of Cr (chromium) can be 11.00% to 25.00%.

[0046] Cr improves corrosion resistance and plays an effective role in enhancing hardness and wear resistance by forming chromium carbides. To ensure corrosion resistance, Cr may be added at a level of 11.00% or more. However, excessive addition leads to an excessive retention of δ-ferrite, which reduces hot workability. Additionally, since the austenite becomes unstable and requires a large amount of Ni to maintain phase stability, manufacturing costs may increase. Considering this, the upper limit of the Cr content may be restricted to 25.00%.

[0047] The content of Ni (nickel) can be 5.00% to 14.00%.

[0048] Ni is a strong austenite-stabilizing element along with Mn and N, and is an alloying element necessary to maintain the austenite structure in a hydrogen environment. Therefore, it is desirable to add at least 5.00%. However, since it is an expensive element, adding large amounts may increase manufacturing costs. Considering this, it is desirable to limit the upper limit of the Ni content to 14.00%.

[0049] The content of N (nitrogen) may be greater than 0.00% and less than or equal to 0.40%.

[0050] N is an austenite-stabilizing element and is also effective for increasing strength through solid solution strengthening and nitride precipitation. Furthermore, the strength-increasing effect only appears when it is included in an amount exceeding a certain threshold. However, excessive addition reduces hot workability. Considering this, it is desirable to limit the N content to more than 0.00% and less than or equal to 0.40%.

[0051] The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be incorporated during the ordinary manufacturing process, they cannot be excluded. As these impurities are known to any person skilled in the ordinary manufacturing process, all details thereof are not specifically mentioned in this specification.

[0052] Surface depletion layer

[0053] The upper part of the above base material includes a surface depletion layer. The composition of the surface depletion layer may include a Cu content of 50% or more, less than 50% of the following formula (1), and unavoidable impurities.

[0054] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0055] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0056] Fe, Cr, Mn, and Si are elements that are essential in stainless steel. The surface depletion layer according to the present invention has a total content of Fe, Cr, Mn, and Si elements of less than 50%. Therefore, in stainless steel sheets produced through a general stainless steel production process, a surface depletion layer satisfying the value of Equation (1) of less than 50% by weight cannot be formed.

[0057] In addition, the surface depletion layer contains a Cu content of 50% or more. Accordingly, the metallic Cu concentrated on the surface can be used as a metal bonding agent during brazing. Therefore, according to the present invention, the thin Cu sheet used as a metal bonding agent during brazing can be omitted.

[0058] The Cu present on the aforementioned surface must exist in a metallic state, not as an oxide. This is because if it exists as the oxide state of CuO, it cannot melt during brazing and thus cannot function as a metal bonding agent.

[0059] It is desirable that the surface of the surface deficiency layer of the stainless steel sheet for brazing has an area fraction of 50% or more of metallic Cu to increase bonding performance during brazing.

[0060] The thickness of the surface depletion layer of the stainless steel sheet for brazing may be 1.0 μm to 10.0 μm. The thickness is the depth measured in the vertical direction from the surface of the stainless steel sheet. By having a surface depletion layer with a thickness range of 1.0 μm to 10.0 μm, the problem of residual Cu after brazing can be improved, thereby achieving excellent heat exchange efficiency. In addition, excellent bonding properties can be achieved. If the thickness of the surface depletion layer is less than 1.0 μm, bonding properties may be reduced. On the other hand, if the thickness of the surface depletion layer exceeds 10.0 μm, residual Cu after brazing may block the heat transfer path of the heat exchanger, thereby reducing heat exchange efficiency. More preferably, the thickness of the surface depletion layer may be 5.0 μm to 7.0 μm.

[0061] A surface defect layer of the stainless steel sheet for brazing joints can be formed on both sides of the base material.

[0062] The surface depletion layer of the stainless steel plate for brazing may be formed entirely on the surface of the stainless steel plate. Figure 1 is a scanning electron microscope (SEM) image of the surface of Example 5. Referring to Figure 1, the uniform presence of metallic Cu as on the surface of Example 5 can improve the bonding performance between stainless steel plates during brazing.

[0063] A heat exchanger according to one embodiment of the present invention comprises a plurality of heat transfer plates and a plurality of heat transfer passages existing between the plurality of heat transfer plates, and the heat transfer plates may be made of stainless steel plates according to any one of claims 1 to 5.

[0064] Generally, the heat transfer plates of a plate heat exchanger are formed by alternately laminating stainless steel plates and thin copper plates, and then joining them by melting the copper bonding agent using heat treatment equipment in a vacuum atmosphere. However, in the case of a plate heat exchanger according to one embodiment of the present invention, stainless steel plates for brazing are processed into an appropriate shape, laminated, and heat-treated so that the parts of the stainless steel plates in contact with each other are heated and melted to form a brazed structure. Consequently, the thin copper plates can be omitted, resulting in the simplification of the manufacturing method and cost reduction. Furthermore, the problem of residual copper blocking the heat transfer paths inside the plate heat exchanger can be improved.

[0065] A method for manufacturing a stainless steel sheet for brazing joints according to one embodiment of the present invention comprises the steps of: manufacturing a hot-rolled steel sheet by hot-rolling a steel material at 1,100°C to 1,300°C, wherein the steel material comprises, in weight %, C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities; the steps of annealing, pickling, and heating the hot-rolled steel sheet at 1,000°C to 1,100°C; and manufacturing a cold-rolled steel sheet by cold-rolling and annealing the heated hot-rolled steel sheet. and may include the step of forming a surface depletion layer by controlling the fractions of Fe, Cr, Mn, Si, and Cu on the surface of the cold-rolled steel sheet.

[0066] The reason for limiting the value of the alloy composition of the steel is the same as the reason for limiting the value of the alloy composition of the base material above. The form of the steel may be any form including slabs, billets, blooms, ingots, etc.

[0067] When the above steel is hot-rolled at a temperature below 1,100°C, sufficient recrystallization does not occur, resulting in a problem of microstructure non-uniformity. When the above steel is hot-rolled at a temperature exceeding 1,300°C, there is a problem of reduced strength and ductility due to grain coarsening. In addition, significant decarburization occurs, which can worsen drawing workability.

[0068] The step of forming a surface depletion layer by controlling the fractions of Fe, Cr, Mn, Si, and Cu on the surface of cold-rolled steel sheets can be carried out by various methods. For example, high-temperature heat treatment, physical vapor deposition (PVD) through physical methods, chemical vapor deposition (CVD) through chemical methods, electroplating through electrochemical methods, and methods using acid solutions may be used.

[0069] In the method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the hot-rolled steel sheet that has undergone the hot rolling step may have a thickness of 3.0 mm to 5.0 mm.

[0070] In the method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the cold-rolled steel sheet that has undergone the cold rolling and annealing steps may have a thickness of 0.3 mm to 1.0 mm.

[0071] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the surface depletion layer, which has undergone the step of controlling the fractions of Fe, Cr, Mn, Si, and Cu on the surface, may have a thickness of 1.0 μm to 10.0 μm. More preferably, the thickness of the surface depletion layer may be 5.0 μm to 7.0 μm.

[0072] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the surface deficiency layer may be formed on both sides of the cold-rolled steel sheet.

[0073] In a method for manufacturing a stainless steel plate for brazing according to one embodiment of the present invention, the surface depletion layer obtained by adjusting the fractions of Fe, Cr, Mn, Si, and Cu may have a composition of 50% or more Cu content, less than 50% of the following formula (1), and unavoidable impurities.

[0074] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0075] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0076] In a method for manufacturing a stainless steel sheet for brazing according to one embodiment of the present invention, the surface depletion layer, which has undergone the step of controlling the fractions of Fe, Cr, Mn, Si, and Cu, has a composition of 50% or more Cu content, less than 50% of the following formula (1), and unavoidable impurities, and the surface of the surface depletion layer may have an area fraction of metallic Cu of 50% or more.

[0077] Hereinafter, the structure and operation of the present invention will be explained in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and should not be interpreted in any way as limiting the present invention.

[0078] Examples

[0079] A steel grade having the alloy composition shown in Table 1 below was manufactured into a steel material, and the manufactured steel material was hot-rolled at 1,200°C to produce a hot-rolled steel sheet with a thickness of approximately 4.5 mm, followed by annealing and pickling treatments. Afterward, the hot-rolled steel sheet was heated to 1,050°C, and then cold-rolled and annealed at 1,000°C were repeated to produce a cold-rolled steel sheet with a thickness of approximately 0.4 mm.

[0080] Classification CsiMnCrNiN Example 10.080.900.8015.508.200.05 Example 20.020.802.4017.905.600.23 Example 30.030.601.0016.3010.500.25 Example 40.020.701.2016.1011.200.06 Example 50.030.601.2018.108.100.04 Example 60.020.601.4018.208.100.04 Example 70.030.801.1019.2011.400.05 Example 80.020.800.8023.8012.600.12 Example 90.020.704.8022.0013.100.32 Comparative Example 10.070.801.0016.208.100.06 Comparative Example 2<0.010.300.5026.000.100.01 Comparative Example 30.020.801.3018.108.000.06 Comparative Example 40.020.701.8018.309.600.12

[0081] The fraction of metallic elements such as Fe, Cr, Mn, Si, and Cu on the surface of the manufactured cold-rolled steel sheets was controlled through various methods.

[0082] There are various methods to control the fraction of metallic elements on the surface of stainless steel, including high-temperature heat treatment, physical vapor deposition (PVD) through physical methods, chemical vapor deposition (CVD) through chemical methods, electroplating through electrochemical methods, and methods using acid solutions.

[0083] In the present invention, electrochemical electroplating, an immersion method using an acid solution, and heat treatment were performed to control the metal element fraction on the surface of stainless steel.

[0084] However, the method utilized above is merely an example to aid in understanding the present invention and does not limit the technical concept of the present invention.

[0085] Table 2 shows the surface formula (1) value of the stainless steel cold-rolled sheet, Cu content, surface metal Cu area fraction, and whether the stainless steel is joined when heat treated at 1,100℃.

[0086] The values ​​of the following equation (1) and Cu content in Table 2 were measured by performing depth-direction analysis of each element in the surface depletion layer, i.e., the thickness region between the surface of the stainless steel plate and 1.0 μm using X-ray Photoelectron Spectroscopy (XPS).

[0087] Equation (1): [Fe]+[Cr]+[Mn]+[Si]

[0088] In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.

[0089] The area fraction of metallic Cu was measured by processing Scanning Electron Microscope (SEM) images using image analysis equipment.

[0090] Whether the stainless steel plates were bonded was determined by stacking two stainless steel plates from the examples and comparative examples and exposing them to a hydrogen reducing atmosphere at a temperature of 1,100°C for 30 minutes. Here, the reducing atmosphere can be various atmospheres such as hydrogen, nitrogen, and argon.

[0091] Classification Formula (1) Value (weight%) Cu Content (weight%) Metal Cu Area Fraction (%) Whether bonded between stainless steel Example 1 178 1790 Example 2 366 0560 Example 3 435 3490 Example 4 108 9880 Example 5 <199 1000 Example 6 257 2690 Example 7 138 6830 Example 8 59 4990 Example 989 1980 Comparative Example 1 257 0 <1X Comparative Example 2 88 43X Comparative Example 3 70 2318X Comparative Example 4 58 36 32X

[0092] Hereinafter, embodiments and comparative examples will be described in detail with reference to the drawings.

[0093] Referring to Table 2, it can be confirmed that Examples 1 to 9 form a surface depletion layer by satisfying the condition that the Cu content is 50% or more in the thickness region between the surface of the stainless steel plate and 1.0 μm, and the sum of the Fe, Cr, Mn, and Si contents is less than 50 wt%. Accordingly, as a result of exposure to a hydrogen reducing atmosphere at a temperature of 1,100°C for 30 minutes, bonding between the stainless steels was achieved.

[0094] Figure 1 is a scanning electron microscope (SEM) image of the surface of Example 5. Referring to Figure 1, it can be seen that metallic Cu is uniformly present on the surface of Example 5. This enables bonding between stainless steels.

[0095] Figure 2 is a scanning electron microscope (SEM) image of the surface of Example 6. Referring to Figure 2, it can be seen that metallic Cu is not uniformly present on the surface of Example 6. However, bonding between stainless steels is possible through heat treatment at a high temperature (1,100°C).

[0096] In the case of Comparative Example 1, the Cu content was 50% or more in the thickness region between the surface of the stainless steel plate and 1.0 μm, and the sum of the contents of Fe, Cr, Mn, and Si was less than 50 wt%. However, the area fraction of metallic Cu on the surface was less than 50%. Through this, it can be seen that although Cu enrichment was achieved on the surface of Comparative Example 1, Cu existed in an oxide state rather than a metallic state. Since Cu existing as an oxide state (CuO) cannot be melted during brazing, the surface Cu cannot function as a metal bonding agent during brazing. Therefore, in the case of Comparative Example 1, bonding between the stainless steels was not achieved even after heat treatment at 1,100°C.

[0097] In the case of Comparative Examples 2 to 4, the Cu content is less than 50% in the thickness region between 1.0 μm from the surface of the stainless steel plate, and the sum of the Fe, Cr, Mn, and Si contents is 50 wt% or more. Therefore, even when heat-treated at high temperatures, no bonding between the stainless steels was achieved.

[0098] Figure 3 is a scanning electron microscope (SEM) image of the surface of Comparative Example 2. Referring to Figure 3 and Table 2, metallic Cu is not uniformly present on the surface of Comparative Example 2, and the area fraction of metallic Cu is only 3%. Therefore, even with heat treatment at high temperatures, bonding between stainless steels was not achieved.

[0099] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and concept of the claims set forth below.

Claims

1. A base material comprising, in weight %, C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities, and It includes a surface deficiency layer located on the upper part of the above base material, and The above surface depletion layer is a stainless steel plate for brazing joints comprising a Cu content of 50% or more, less than 50% of the following formula (1), and unavoidable impurities. Equation (1): [Fe]+[Cr]+[Mn]+[Si] (In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.) 2. In Claim 1, The surface of the above-mentioned surface deficiency layer is a stainless steel sheet for brazing joints having an area fraction of metallic Cu of 50% or more.

3. In Claim 1, The above surface depletion layer is a stainless steel plate for brazing joints having a thickness of 1.0 μm to 10.0 μm.

4. In Claim 1, The above surface deficiency layer is a stainless steel plate for brazing joints formed on both sides of the base material.

5. In Claim 1, The above surface deficiency layer is formed entirely on the surface of the stainless steel plate for brazing joints.

6. Multiple heat transfer plates; A heat exchanger comprising a plurality of heat transfer channels existing between the plurality of heat transfer plates; wherein the heat transfer plates are made of stainless steel plates according to any one of claims 1 to 5.

7. A step of manufacturing a hot-rolled steel sheet by hot-rolling a steel material containing, in weight %, C: greater than 0.00% and less than or equal to 0.10%, Si: greater than 0.00% and less than or equal to 1.50%, Mn: greater than 0.00% and less than or equal to 5.00%, Cr: 11.00% to 25.00%, Ni: 5.00% to 14.00%, N: greater than 0.00% and less than or equal to 0.40%, and the remainder being Fe and impurities, at 1,100℃ to 1,300℃; Steps of annealing, pickling, and heating the above hot-rolled steel sheet at 1,000℃ to 1,100℃; A method for manufacturing a stainless steel sheet for brazing, comprising: a step of manufacturing a cold-rolled steel sheet by cold-rolling and annealing the heated hot-rolled steel sheet; and a step of forming a surface depletion layer by controlling the fractions of Fe, Cr, Mn, Si, and Cu on the surface of the cold-rolled steel sheet.

8. In Claim 7, The above hot-rolled steel sheet is a method for manufacturing a stainless steel sheet for brazing joints having a thickness of 3.0 mm to 5.0 mm.

9. In Claim 7, The above cold-rolled steel sheet is a method for manufacturing a stainless steel sheet for brazing joints having a thickness of 0.3 mm to 1.0 mm.

10. In Claim 7, A method for manufacturing a stainless steel sheet for brazing, wherein the surface depletion layer has a thickness of 1.0 μm to 10.0 μm.

11. In Claim 7, A method for manufacturing a stainless steel sheet for brazing, wherein the above surface defect layer is formed on both sides of the above cold-rolled steel sheet.

12. In Claim 7, A method for manufacturing a stainless steel sheet for brazing, wherein the surface depletion layer, which has undergone the step of controlling the fractions of Fe, Cr, Mn, Si, and Cu, has a composition of 50% or more Cu content, less than 50% of the following formula (1), and unavoidable impurities. Equation (1): [Fe]+[Cr]+[Mn]+[Si] (In Equation (1), [Fe], [Cr], [Mn] and [Si] represent the content (weight%) of each element.) 13. In Claim 12, A method for manufacturing a stainless steel sheet for brazing, wherein the surface of the above-mentioned surface deficiency layer has an area fraction of metal Cu of 50% or more.

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