Induction Heatable Stainless Steel Sheet Having Excellent Corrosion Resistance And Method Of Manufacturing The Same

Abstract

A stainless steel sheet for cookware and a method of manufacturing the same and, particularly, an induction heatable stainless steel sheet having excellent corrosion resistance and a method of manufacturing the same are provided. The induction heatable stainless steel sheet having excellent corrosion resistance includes, by wt %, C: 0.1% or less (excepting 0%), Si: 0.2% to 3.0%, Mn: 1.0% to 4.0%, Cr: 19.0% to 23.0%, Ni: 0.3% to 2.5%, N: 0.18% to 0.3%, Cu: 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities, and has relative permeability of 20.mu..sub.r to 80.mu..sub.r. In addition, a microstructure includes, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a stainless steel sheet for cookware and a method of manufacturing the same and, more particularly, to a stainless steel sheet having excellent induction heating properties and corrosion resistance and a method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance using a twin roll strip casting process.

BACKGROUND ART

[0002] In general, austenitic stainless steel having good workability and corrosion resistance includes iron (Fe) as a base metal as well as chrome (Cr) and nickel (Ni) as main alloying ingredients. Other alloying elements such as molybdenum (Mo) and copper (Cu) are commonly added thereto, and thus, various grades of steel have been developed for various uses. Austenitic stainless steel has excellent corrosion resistance and workability, but is non-magnetic.

[0003] Austenitic stainless steel having excellent corrosion resistance and workability includes Ni, Mo, and the like, which are relatively costly raw materials. As an alternative thereto, SUS 400-series stainless steel, a ferritic stainless steel, has been developed. 400-series stainless steels have the disadvantage that formability and corrosion resistance thereof are lower than those of SUS 300-series stainless steels, austenitic stainless steels, but have ferromagnetism.

[0004] Duplex stainless steel, in which an austenite phase and a ferrite phase are mixed, has all of the advantages of austenitic and ferritic stainless steels, and various types of duplex stainless steel have been developed to date, having magnetic properties between the properties of austenitic and ferritic stainless steels.

[0005] The magnetism described above is properties effective for induction heating, however, ferritic stainless steels are vulnerable to corrosion. Therefore, an induction heatable material having excellent corrosion resistance is required for use in the manufacturing of cookware.

[0006] The stainless steel described above has been widely used as a material for various types of cookware. As the leisure culture has developed, in consideration of safety in resorts and other types of accommodation, cooking with induction heaters has become commonplace.

[0007] Therefore, the ability to be induction heated, as described above, has become a main requirement in the properties of cookware. According to the content of ferrite in steel, magnetism may be present. According to a degree of magnetism, induction heating may be possible, and appropriate magnetism is required.

[0008] An example of a type of cookware using stainless steel may be a three ply pot, and the like.

[0009] In the case of a pot having a three layer structure formed using three kinds of material, an interior portion is formed of SUS 304 stainless steel, an outer cover portion is formed of SUS 430 stainless steel, and a middle portion is formed of aluminum (Al), bonded together. A reason that cookware is formed using three kinds of material as described above is to secure corrosion resistance and induction heating properties.

[0010] As described above, when cookware of a three ply pot is manufactured, a bonding process is added and a process using three kinds of material is complex, whereby processing costs are high.

[0011] Therefore, a material for cookware having excellent corrosion resistance, able to be heated, in detail, able to be induction heated, has been required.

DISCLOSURE

Technical Problem

[0012] An aspect of the present disclosure may provide an induction heatable stainless steel sheet having excellent corrosion resistance.

[0013] Another aspect of the present disclosure may provide a method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance using a twin roll strip casting process.

Technical Solution

[0014] According to an aspect of the present disclosure, an induction heatable stainless steel sheet having excellent corrosion resistance may include, by wt %, carbon (C): 0.1% or less (excepting 0%), silicon (Si): 0.2% to 3.0%, manganese (Mn): 1.0% to 4.0%, chromium (Cr): 19.0% to 23.0%, nickel (Ni): 0.3% to 2.5%, nitrogen (N): 0.18% to 0.3%, copper (Cu): 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities. A microstructure may include, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof. Relative permeability of the stainless steel sheet may be 20.mu..sub.r to 80.mu..sub.r.

[0015] According to another aspect of the present disclosure, a method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance and having relative permeability of 20.mu..sub.r to 80.mu..sub.r, in which a microstructure may include, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof, may include: preparing molten steel including, by wt %, carbon (C): 0.1% or less (excepting 0%), silicon (Si): 0.2% to 3.0%, manganese (Mn): 1.0% to 4.0%, chromium (Cr): 19.0% to 23.0%, nickel (Ni): 0.3% to 2.5%, nitrogen (N): 0.18% to 0.3%, copper (Cu): 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities; and manufacturing a thin plate by supplying the molten steel to a space between twin rolls of a twin roll strip caster including the twin rolls rotating in opposite directions.

Advantageous Effects

[0016] According to an exemplary embodiment in the present disclosure, a single material is applied to smoothly perform induction heating, whereby induction heating properties may be easily applied to cookware. In the case of a conventional triple bottom material, an interior portion is formed of SUS 304 stainless steel, an outer cover portion is formed of SUS 430 stainless steel, and a middle portion formed of Al or the like, bonded together, and a process of manufacturing the same is very complex. However, a stainless steel sheet, solving a problem described above, may be provided.

[0017] According to an exemplary embodiment in the present disclosure, a twin roll strip casting process is used to stably manufacture an induction heatable stainless steel sheet having excellent corrosion resistance.

DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a schematic diagram illustrating an example of a twin roll strip casting process preferably used to manufacture a stainless steel sheet according to an exemplary embodiment in the present disclosure.

[0019] FIGS. 2A and 2B are photographs of microstructures of an example of representative austenitic stainless steel and a conventional example of representative ferritic stainless steel. FIG. 2A illustrates austenitic stainless steel (Austenite: FCC), and FIG. 2B illustrates ferritic stainless steel (Ferrite: BCC).

[0020] FIG. 3 is a microstructure picture of Inventive example 1 in accordance with an exemplary embodiment in the present disclosure.

[0021] FIG. 4 is a graph illustrating relationship of relative permeability and pitting potential for each type of steel.

[0022] FIG. 5 is a graph illustrating induction heating properties of a conventional three ply pot (Conventional example) and a single ply pot according to Inventive example 1.

[0023] FIG. 6 is a graph illustrating relationship of the content of ferrite and relative permeability.

BEST MODE FOR INVENTION

[0024] Hereinafter, the present disclosure will be described in detail.

[0025] According to an exemplary embodiment in the present disclosure, ferrite microstructures and austenite microstructures are properly mixed to provide an induction heatable stainless steel material having good corrosion resistance.

[0026] When the content of ferrite in a stainless steel material is controlled to be 30% to 70%, the stainless steel material may have appropriate magnetism to be used as a material for induction heatable cookware.

[0027] Furthermore, high nitrogen duplex stainless steel is appropriate for improving corrosion resistance, and is manufactured using a twin roll strip casting process to prevent bubbles or the like, caused by nitrogen gas in solidification in an exemplary embodiment in the present disclosure.

[0028] According to an exemplary embodiment in the present disclosure, an induction heatable stainless steel sheet having excellent corrosion resistance may preferably include, by wt %, carbon (C): 0.1% or less (excepting 0%), silicon (Si): 0.2% to 3.0%, manganese (Mn): 1.0% to 4.0%, chromium (Cr): 19.0% to 23.0%, nickel (Ni): 0.3% to 2.5%, nitrogen (N): 0.18% to 0.3%, Cu: 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities.

[0029] Hereinafter, components contained in a stainless steel sheet according to an exemplary embodiment in the present disclosure and the contents thereof will be described.

[0030] Carbon (C): 0.1% or Less (Excepting 0%)

[0031] C, an austenite phase forming element, is an element effective for increasing strength of a material by solid solution strengthening. However, when C is added excessively, C is easily combined with an element for forming carbides, such as Cr, effective for providing corrosion resistance at a ferrite-austenite phase boundary to lower the content of Cr around a grain boundary, thereby reducing corrosion resistance. In this case, in order to significantly increase corrosion resistance, it is preferable to add C within a range of 0.1% or less.

[0032] Silicon (Si): 0.2% to 3.0%

[0033] Si is partially added for a deoxidation effect. Si, a ferrite phase forming element, is an element concentrated in ferrite in an annealing heat treatment. Thus, in order to secure a proper ferrite phase fraction, 0.2% or more of Si is required to be added. However, when Si is added in excess of 3.0%, hardness of a ferrite phase is sharply increased, to reduce elongation. Thus, an austenite phase affecting securing of elongation may be difficult to secure. Moreover, when Si is added excessively, slag fluidity is decreased in a steelmaking process, Si is combined with oxygen to form an inclusion, and corrosion resistance is decreased. Thus, it is preferable to limit the content of Si to 0.2% to 3.0%.

[0034] Nitrogen (N): 0.18% to 0.3%

[0035] N is an element greatly contributing to the stabilization of an austenite phase along with Ni in stainless steel, and an element concentrated in an austenite phase in an annealing heat treatment. Thus, the content of N is increased to incidentally improve corrosion resistance and improve strength. However, solid solubility of N may be changed according to the content of added Mn, and thus, controlling the content thereof may be required. When the content of N exceeds 0.3% in a range of Mn, according to an exemplary embodiment in the present disclosure, a blow hole, a pin hole or the like may be generated during casting due to excess of nitrogen solid solubility, thereby causing a surface defect of a product.

[0036] In order to secure corrosion resistance and material properties at a level of 304 stainless steel, N and Mn, which are different austenite stabilizing elements, are added in an amount equal to a reduced amount of Ni, an austenite stabilizing element, to adjust a ferrite phase fraction. Only when at least 0.15% or more of N is added, may an appropriate phase fraction be secured. In addition, in order to allow a value of Md30 to be managed to be 80 or less, the content of N is required to be 0.18% or more. It is preferable to limit the content of N to 0.18% to 0.30%.

[0037] Manganese (Mn): 1.0% to 4.0%

[0038] Mn is a deoxidizer and an element for increasing nitrogen solid solubility, and Mn, an austenite forming element, is replaced with relatively expensive Ni to be added. When the content of Mn is added in excess of 4%, nitrogen solid solubility may be improved. However, Mn may be combined with sulfur (S) in steel to form MnS and to reduce corrosion resistance, and thus, there may be limitations in securing corrosion resistance at a level equal to that of 304 stainless steel.

[0039] When the content of Mn is less than 1.0%, a proper austenite phase fraction is limited to being secured even by adjusting Ni, Cu, N or the like, an austenite forming element. In addition, as solid solubility of added N is low, a sufficient solid solution amount of nitrogen may not be obtained at atmospheric pressure. Thus, it is preferable to limit the content of Mn to 1.0% to 4.0%.

[0040] Chromium (Cr): 19.0% to 23.0%

[0041] Cr, a ferrite stabilizing element along with Si, mainly serves to secure a ferrite phase of stainless steel, and is an essential element for securing corrosion resistance. When the content of Cr is increased, corrosion resistance is increased. However, in order to maintain a phase fraction, the content of relatively expensive Ni or other austenite forming elements is required to be increased. Thus, in order to secure a level of corrosion resistance equal to or greater than that of 304 stainless steel while maintaining a phase fraction of stainless steel, it is preferable to limit the content of Cr to 19.0% to 23.0%.

[0042] Nickel (Ni): 0.3% to 2.5%

[0043] Ni, an austenite stabilizing element along with Mn, Cu, and N, mainly serves to secure an austenite phase of stainless steel. For cost reductions, instead of significantly reducing the content of relatively expensive Ni, amounts of added Mn and N, different austenite phase forming elements, are commonly increased to maintain sufficient phase fraction balance due to a reduction in Ni.

[0044] However, as formation of plasticity-induced martensite generated in cold working is suppressed, 0.3% or more of Ni should be added to secure sufficient stability of an austenite phase. When Ni is added excessively, an austenite phase fraction is increased, and thus, there may be limitations in securing an appropriate austenite fraction. In detail, due to relatively expensive Ni, manufacturing costs of a product are increased, and thus, there may be limitations in securing competitiveness in comparison with 304 stainless steel. Thus, the content of Ni is preferable to be limited to being 0.3% to 2.5%.

[0045] Copper (Cu): 0.3% to 2.5%

[0046] It is preferable to significantly reduce the content of Cu in the interest of cost reductions. In addition, as the formation of plasticity-induced martensite, generated in cold working, is suppressed, 0.3% or more of Cu should be added to secure sufficient stability of an austenite phase.

[0047] When the content of Cu exceeds 2.5%, there may be limitations in processing a product due to hot brittleness, whereby it is preferable to limit the content of Cu to 0.3% to 2.5%.

[0048] A residual component of the stainless steel sheet according to an exemplary embodiment in the present disclosure other than components described above may include iron (Fe) and other unavoidable impurities. Other unavoidable impurities may include, for example, phosphorous (P), sulfur (S) or the like.

[0049] A stainless steel sheet according to an exemplary embodiment in the present disclosure may have a microstructure including, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof.

[0050] Ferrite is a structure having magnetism, and thus may have induction heating properties. When a fraction thereof is less than 30%, the content of ferrite having magnetism is low, whereby induction heating efficiency may be low. When a fraction thereof exceeds 70%, the content of ferrite having magnetism is high, whereby induction heating efficiency may be excessively high. In this case, for example, when food is cooked, food may be stuck to a bottom of a cooking vessel.

[0051] Thus, it is preferable to limit a fraction of ferrite of a microstructure of a steel sheet according to an exemplary embodiment in the present disclosure to 30% to 70%.

[0052] It is preferable to limit relative permeability of a stainless steel sheet according to an exemplary embodiment in the present disclosure to 20.mu..sub.r to 80.mu..sub.r. When the relative permeability thereof is less than 20.mu..sub.r, relative permeability is weak not to efficiently perform induction heating. When the relative permeability thereof exceeds 80.mu..sub.r, relative permeability is too excessive, whereby food may be stuck to a bottom of a cooking vessel or may be easily burnt.

[0053] It is preferable to Md30 [Here, Md30=551-462.times.(C %+N %)-9.2.times.Si %-8.1.times.Mn %-29.times.(Ni %+Cu %)-13.7.times.Cr %-18.5.times.Mo %-68.times.Al %] of a stainless steel sheet according to an exemplary embodiment in the present disclosure to 80 or less.

[0054] When Md30 is great, martensite may be easily generated in a case of deformation.

[0055] In order to improve pickling properties in a process of annealing and pickling a steel sheet, the steel sheet is bent before a pickling process. In this case, when bending severely occurs and a value of Md30 is great, an occurrence probability of strip breakage may be increased due to brittleness caused by martensite generation.

[0056] Thus, it is preferable to limit Md30 to 80 or less.

[0057] Elongation of a steel sheet according to an exemplary embodiment in the present disclosure may be 40% or more, and pitting potential thereof may be 280 mV or more.

[0058] A steel sheet according to an exemplary embodiment in the present disclosure may be used to manufacture cookware. When 500 cc of water at room temperature is heated by an induction heater, the water may be heated to boiling point within 10 minutes.

[0059] Hereinafter, a method of manufacturing a stainless steel sheet according to another exemplary embodiment in the present disclosure will be described.

[0060] In order to manufacture a stainless steel sheet according to another exemplary embodiment in the present disclosure, a molten steel including, by wt %, C: 0.1% or less (excepting 0%), Si: 0.2% to 3.0%, Mn: 1.0% to 4.0%, Cr: 19.0% to 23.0%, Ni: 0.3% to 2.5%, N: 0.18% to 0.3%, Cu: 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities, is prepared.

[0061] The molten steel prepared as described above, is supplied to a space between twin rolls of a twin roll strip caster, rotating in opposite directions, to manufacture a thin plate.

[0062] The twin roll strip caster is not particularly limited and may be, for example, a twin roll strip caster such as that illustrated in FIG. 1 or the like.

[0063] With reference to FIG. 1 illustrating an example of a twin roll strip manufacturing process preferably applied to manufacture a stainless steel sheet according to an exemplary embodiment in the present disclosure, an example of a method of manufacturing a stainless steel sheet according to an exemplary embodiment in the present disclosure will be described in detail.

[0064] As illustrated in FIG. 1, the molten steel prepared as described above is accommodated in a ladle 1, and flows into a tundish 2 through a nozzle. The molten steel flowing into the tundish 2 is supplied through a molten steel injection nozzle 3 between edge dams 6 installed in both ends of casting rolls 5, in other words, between the casting rolls 5, to be solidified. In this case, in order to prevent molten metal between casting rolls from being oxidized, a meniscus shield 7 protects a molten metal surface and an appropriate gas is injected inside the meniscus shield 7 to appropriately adjust an atmosphere.

[0065] While a thin plate exits a roll nip in which both rolls meet each other, the thin plate is manufactured to be drawn out. After the thin plate is rolled in a rolling mill 8, the thin plate passes through a cooling device 9 to be cooled. The thin plate is wound in a winding device 10 thereafter. In FIG. 1, an unexplained number 4 denotes a sump.

[0066] In the method of manufacturing the stainless steel sheet, an induction heatable stainless steel sheet, having relative permeability of 20.mu..sub.r to 80.mu..sub.r, in which a microstructure including, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof, may be manufactured.

[0067] Hereinafter, an exemplary embodiment in the present disclosure will be described in more detail byway of an example.

Example 1

[0068] 90 tons of molten steel having a composition as described in Table 1 was prepared to be cast using a twin roll strip caster illustrated in FIG. 1, thereby manufacturing a thin steel sheet. In this case, a casting width was 1,300 mm, and a casting thickness was 4.0 mm.

[0069] As described above, immediately after the thin steel sheet was cast, the thin steel sheet was hot-rolled at a high temperature to continuously manufacture a hot-rolled plate having a thickness of about 2.5 mm. The hot-rolled plate was cold rolled at a reduction rate of 50% to 70% and was annealed at a temperature of 1150.degree. C.

[0070] FIGS. 2A and 2B are pictures, in which microstructures of representative examples of conventional austenitic stainless steel (SUS 304 stainless steel) and ferritic stainless steel (SUS 430 stainless steel) are illustrated by way of example.

[0071] FIG. 3 is a picture in which a microstructure of Inventive example 1 in Table 2 is visible, and FIG. 4 illustrates investigated relative permeability and pitting potential with respect to Inventive example 1, along with SUS 304, SUS 430, and SUS 201 stainless steel.

[0072] A pot was manufactured using the stainless steel of Inventive example 1 in Table 2. In this case, when 500 cc of water at room temperature was heated by an induction heater, heating properties were investigated and results thereof are illustrated in FIG. 5.

[0073] FIG. 5 also illustrates heating properties with respect to a conventional three ply pot (Conventional example).

[0074] The conventional three ply pot was manufactured, as an interior portion was formed of SUS 304 stainless steel, an outer cover portion was formed of SUS 430 stainless steel, and a middle portion was formed of aluminum (Al), bonded together.

TABLE-US-00001 TABLE 1 Classi- Steel composition (by wt %) fication C Si Mn Cr Ni Cu N Md30 Compar- 0.041 0.34 0.45 16.25 0.34 0.26 0.041 266.3 ative example 1 Compar- 0.031 0.56 2.89 19.84 0.86 0.61 0.227 88.8 ative example 2 Compar- 0.032 0.51 2.85 19.3 0.849 0.63 0.178 118.9 ative example 3 Inventive 0.0318 0.626 3.001 19.89 1.01 0.778 0.2267 77.2 example 1 Inventive 0.0337 0.598 2.92 20.38 0.96 0.62 0.2412 69.8 example 2 Inventive 0.0419 0.582 3.108 20.74 0.86 0.614 0.2373 64.6 example 3 Inventive 0.0347 0.56 2.995 20.02 1.03 0.759 0.2455 66.0 example 4 [In Table 1, Md30 = 551 - 462 .times. (C % + N %) - 9.2 .times. Si % - 8.1 .times. Mn % - 29 .times. (Ni % + Cu %) - 13.7 .times. Cr % - 18.5 .times. Mo % - 68 .times. Al %]

TABLE-US-00002 TABLE 2 Microstructure Pitting *Whether (Volume %) Elongation potential Relative of strip Classification ferrite austenite (%) (mV) permeability breakage Comparative 100 0 28.9 145 120 X example 1 Comparative 59 41 41.2 288 60 .largecircle. example 2 Comparative 62 38 34.4 265 63 .largecircle. example 3 Inventive 49 51 43.6 293 52 X example 1 Inventive 46 54 42.5 302 48 X example 2 Inventive 44 56 40.8 305 37 X example 3 Inventive 45 55 41.5 303 46 X example 4 *.largecircle.: strip breakage occurred, X: no strip breakage occurred

[0075] As shown in Tables 1 and 2, in the case of Inventive example 1 to 4 in accordance with an exemplary embodiment in the present disclosure, a material has excellent corrosion resistance and induction heating properties. In the case of Comparative examples (1 and 3) out of a range of an exemplary embodiment in the present disclosure, corrosion resistance thereof was low. In the case of Comparative examples (2 and 3), strip breakage occurred when a heat treatment process was performed. A cause of strip breakage occurrence was Md30 greater than 80. In this case, as martensite was easily generated in deformation, strip breakage occurred when a heat treatment process was performed.

[0076] Comparative example 1 was a complete ferrite structure. In this case, when a heat treatment process was performed, a martensite structure due to deformation did not occur. Thus, Comparative example 1 was determined not to be affected by a value of Md30.

[0077] As shown in FIG. 2A, a microstructure of austenitic stainless steel was formed of austenite, and ferrite was finely present therein. As shown in FIG. 2B, a microstructure of ferritic stainless steel was formed of ferrite. Austenite was a nonmagnetic body, and ferrite was a ferromagnetic body and has strong magnetism.

[0078] As shown in FIG. 3, Inventive example 1 in accordance with an exemplary embodiment in the present disclosure had structural properties in which an austenite structure and a ferrite structure were stacked to be complex composed, thereby having properties of austenite and ferrite at the same time. In detail, magnetism thereof was between those of austenitic stainless steel (SUS 300-series stainless steel) and ferritic stainless steel (SUS 400-series stainless steel), and had magnetism, to allow for induction heatable properties.

[0079] As shown in FIG. 4, an SUS 400-series material had a high degree of magnetism, but had significantly low pitting potential properties, a corrosion resistance index. An SUS 200-series material had very little magnetism, but a value of pitting potential was significantly low to have poor corrosion resistance. An SUS 300-series material had good corrosion resistance, but had no magnetism, thereby having properties without induction heating properties. In general, pitting potential of an SUS 304 steel grade is 280 mV or more, which may be a measure of good corrosion resistance.

[0080] Inventive example 1 in accordance with an exemplary embodiment in the present disclosure had corrosion resistance similar to that of an SUS 300-series material, had a median value of relative permeability indicating magnetism, and had proper induction heating properties. In other words, Inventive example 1 had good corrosion resistance and was induction heatable.

[0081] As shown in FIG. 5, a conventional pot (Conventional example), formed to have a conventional three layer structure, had heating properties similar to those of a pot having a single layer structure formed using a material of Inventive example 1.

[0082] The conventional pot and the pot having a single layer structure formed using a material of Inventive example 1 allowed water to be boiled within 10 minutes. The pot having a three layer structure formed using three kinds of material was manufactured with an interior portion formed of SUS 304 stainless steel, an outer cover portion formed of SUS 430 stainless steel, and a middle portion formed of Al, bonded together. A bonding process was added and a process using three kinds of material was complex, whereby process costs were high. According to an exemplary embodiment in the present disclosure, a material may be conveniently applied, thereby solving a conventional problem described above.

Example 2

[0083] Except that the content of ferrite was varied, a steel sheet was manufactured under the same conditions as those of Inventive example 1 of Example 1, and changes in the content of ferrite and relative permeability were investigated. Results thereof were illustrated in FIG. 6. In addition, induction heating properties with respect to relative permeability were also investigated.

[0084] As shown in FIG. 6, when the content of ferrite was 30% to 70%, relative permeability of 20.mu..sub.r to 80.mu..sub.r could be obtained. As a result of investigation of induction heating properties with respect to relative permeability, when relative permeability was between 20.mu..sub.r and 80.mu..sub.r, induction heating properties were good. When relative permeability was less than 20.mu..sub.r, induction heating properties were weak, whereby induction heating was not efficient. When relative permeability exceeded 80.mu..sub.r, induction heating properties were excessive, thereby allowing food to be stuck to a bottom of a cooking vessel or to be easily burnt.

Claims

1. An induction heatable stainless steel sheet having excellent corrosion resistance comprising, by wt %, carbon (C): 0.1% or less (excepting 0%), silicon (Si): 0.2% to 3.0%, manganese (Mn): 1.0% to 4.0%, chromium (Cr): 19.0% to 23.0%, nickel (Ni): 0.3% to 2.5%, nitrogen (N): 0.18% to 0.3%, copper (Cu): 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities, and having relative permeability of 20.mu..sub.r to 80.mu..sub.r, wherein a microstructure includes, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof.

2. The induction heatable stainless steel sheet having excellent corrosion resistance of claim 1, wherein Md30, where Md30=551-462.times.(C %+N %)-9.2.times.Si %-8.1.times.Mn %-29.times.(Ni %+Cu %)-13.7.times.Cr %-18.5.times. Mo %-68.times.Al %, of the stainless steel sheet is 80 or less.

3. The induction heatable stainless steel sheet having excellent corrosion resistance of claim 1, wherein elongation of the stainless steel sheet is 40% or more.

4. The induction heatable stainless steel sheet having excellent corrosion resistance of claim 1, wherein pitting potential of the stainless steel sheet is 280 mV or more.

5. The induction heatable stainless steel sheet having excellent corrosion resistance of claim 1, wherein cookware formed of the stainless steel sheet heats water to boiling point within 10 minutes when 500 cc of water at room temperature is heated by an induction heater.

6. A method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance and having relative permeability of 20.mu..sub.r to 80.mu..sub.r wherein a microstructure includes, by volume %, ferrite: 30% to 70% and austenite as a remainder thereof, comprising: preparing molten steel comprising, by wt %, carbon (C): 0.1% or less (excepting 0%), silicon (Si): 0.2% to 3.0%, manganese (Mn): 1.0% to 4.0%, chromium (Cr): 19.0% to 23.0%, nickel (Ni): 0.3% to 2.5%, nitrogen (N): 0.18% to 0.3%, copper (Cu): 0.3% to 2.5%, iron (Fe) as a residual component thereof, and other unavoidable impurities; and manufacturing a thin plate by supplying the molten steel to a space between twin rolls of a twin roll strip caster including the twin rolls rotating in opposite directions.

7. The method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance of claim 6, wherein Md30, where Md30=551-462.times.(C %+N %)-9.2.times.Si %-8.1.times.Mn %-29.times.(Ni %+Cu %)-13.7.times.Cr %-18.5.times.Mo %-68.times.Al %, of the stainless steel sheet is 80 or less.

8. The method of manufacturing an induction heatable stainless steel sheet having excellent corrosion resistance of claim 6, wherein pitting potential of the stainless steel sheet is 280 mV or more.