US20230023569A1 - Steel sheet having excellent wear resistance and composite corrosion resistance, and method of manufacturing same - Google Patents

Steel sheet having excellent wear resistance and composite corrosion resistance, and method of manufacturing same Download PDF

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US20230023569A1
US20230023569A1 US17/787,009 US202017787009A US2023023569A1 US 20230023569 A1 US20230023569 A1 US 20230023569A1 US 202017787009 A US202017787009 A US 202017787009A US 2023023569 A1 US2023023569 A1 US 2023023569A1
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steel sheet
corrosion
resistant steel
acid solution
sulfuric acid
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Byoung Ho LEE
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Posco Holdings Inc
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Posco Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/001—Heat treatment of ferrous alloys containing Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0257—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to a steel sheet having excellent wear resistance and composite corrosion resistance and a method of manufacturing the same. More particularly, the present invention relates to a steel sheet having corrosion resistance to a phenomenon in which a steel sheet corrodes, due to sulfate acid/hydrochloric acid composite condensate water and sulfuric acid condensate water produced by SO x , Cl, and the like present in exhaust gas after fossil fuel combustion when an exhaust gas temperature is lowered, high strength, and excellent wear resistance, and a method of manufacturing the same.
  • Fossil fuel includes various impurity elements such as S and Cl. Since combustion is performed using the fossil fuel, there is always a problem in that piping which is a passage through which combustion gas passes and equipment are deteriorated by corrosion. The corrosion phenomenon is referred to as condensate water corrosion, and representative uses where piping and equipment are exposed to the corrosion environment are exhaust gas piping and environmental facilities of thermal power plants, automobile exhaust system, and the like.
  • the kinds of condensate corrosion includes sulfuric acid condensate water corrosion in which S included in exhaust gas burns to form SO x , and in particular, SO 3 meets moisture in the exhaust gas to form sulfuric acid, corrosion by hydrochloric acid condensate water in which chlorine included in exhaust gas or industrial water produces hydrochloric acid by various reactions, sulfuric acid/hydrochloric acid composite condensate water corrosion occurring when the sulfuric acid and the hydrochloric acid are mixed in combination, and the like.
  • a starting temperature of the acid condensation is related to the temperature of the exhaust gas itself, contents of SO x and Cl in the exhaust gas, and a water vapor content.
  • GGH Gas Gas Heater
  • EP electrostatic precipitator
  • the present invention has been made in an effort to provide a steel sheet having excellent wear resistance and composite corrosion resistance, and a method of manufacturing the same.
  • a steel sheet having corrosion resistance to a phenomenon in which a steel sheet corrodes, due to sulfate acid/hydrochloric acid composite condensate water and sulfuric acid condensate water produced by SO x , Cl, and the like present in exhaust gas after fossil fuel combustion when an exhaust gas temperature is lowered, high strength, and excellent wear resistance, and a method of manufacturing the same are provided.
  • An exemplary embodiment of the present invention provides a corrosion-resistant steel sheet having excellent wear resistance and composite corrosion resistance including, by weight: 0.04 to 0.10% of carbon (C), 0.10% or less (excluding 0%) of silicon (Si), 0.20 to 0.35% of copper (Cu), 0.1 to 0.2% of nickel (Ni), 0.05 to 0.15% of antimony (Sb), 0.07 to 0.22% of tin (Sn), 0.05 to 0.15% of titanium (Ti), 0.01% or less (excluding 0%) of sulfur (S), 0.005% or less (excluding 0%) of nitrogen (N), and 0.05 to 0.15% of molybdenum (Mo), with a balance of iron (Fe) and inevitable impurities, the corrosion-resistant steel sheet satisfying the following Formulae 1 and 2:
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention includes a TiC precipitate, and the TiC precipitate and an aggregate formed of the TiC precipitate may be included at 10 16 or more per 1 cm 3 .
  • the TiC precipitate may have a particle diameter of 1 to 10 nm.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention may satisfy the following Formula 3:
  • a concentrated layer may be formed on the surface of the steel sheet.
  • the concentrated layer may include Mo, Cu, Sb, and Sn.
  • the concentrated layer may have a concentrated amount of 10 wt % or more.
  • the concentrated amount refers to the sum of the contents (wt %) of concentrating elements Mo, Cu, Sb, and Sn, at a boundary point at which Fe and O have the same wt %.
  • the concentrated layer may have a thickness of 10 nm or more.
  • a recrystallization fraction after subjecting the steel sheet to an annealing heat treatment may be 80% or more.
  • a corrosion weight loss ratio may be 8.0 mg/cm 2 /hr or less.
  • a corrosion weight loss ratio may be 37 mg/cm 2 /hr or less.
  • the product of the corrosion weight loss ratio when the steel sheet is immersed in 50 wt % of the sulfuric acid solution at 70° C. for 6 hours and the corrosion weight loss ratio when the steel sheet is immersed in the mixed solution of 28.5 wt % of the sulfuric acid solution and 0.5 wt % of the hydrochloric acid solution at 60° C. for 6 hours may be 20 or less.
  • the hot rolled steel sheet may have a tensile strength of 580 MPa or more and a surface hardness of 85 or more based on HRB.
  • the cold rolled steel sheet may have a tensile strength of 540 MPa or more and a surface hardness of 80 or more based on HRB.
  • Another embodiment of the present invention provides a method of manufacturing a corrosion-resistant steel sheet including: preparing a steel slab which includes, by weight: 0.04 to 0.10% of carbon (C), 0.10% or less (excluding 0%) of silicon (Si), 0.20 to 0.35% of copper (Cu), 0.1 to 0.2% of nickel (Ni), 0.05 to 0.15% of antimony (Sb), 0.07 to 0.22% of tin (Sn), 0.05 to 0.15% of titanium (Ti), 0.01% or less (excluding 0%) of sulfur (S), 0.005% or less (excluding 0%) of nitrogen (N), and 0.05 to 0.15% of molybdenum (Mo), with a balance of iron (Fe) and inevitable impurities, and satisfies the following Formulae 1 and 2; heating the slab at 1,200° C. or higher; and hot rolling the heated slab at a finish rolling temperature of 850 to 1000° C. to manufacture a hot rolled steel sheet:
  • winding the hot rolled steel sheet at 450 to 750° C.; cold rolling the wound hot rolled steel sheet at a reduction rate of 54 to 70% to manufacture a cold rolled steel sheet; and subjecting the cold rolled steel sheet to an annealing heat treatment at 750 to 880° C. may be further included.
  • a residence time may be 150 minutes or more.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention may be useful for piping through which exhaust gas passes after combustion of fossil fuel, hot rolled products for fossil fuel combustion equipment, and raw materials of cold rolled products.
  • FIG. 1 is a graph showing an element concentration degree of a surface portion of a steel sheet, by measuring an element distribution from the surface to the inside by GDS measurement, after the steel sheet of Inventive Example 2 was immersed in 50 wt % of a sulfuric acid solution for 24 hours.
  • FIG. 2 shows (a) a microstructure when Inventive Example 4 was wound at a hot rolling winding temperature of Condition 1, and (b) a microstructure when the component system of Inventive Example 4 was wound at a low winding temperature of Condition 4.
  • first, second, and third are used for describing various parts, components, areas, layers, and/or sections, but are not limited thereto. These terms are used only for distinguishing one part, component, area, layer, or section from other parts, components, areas, layers, or sections. Therefore, a first part, component, area, layer, or section described below may be mentioned as a second part, component, area, layer, or section without departing from the scope of the present invention.
  • the term “combination thereof” included in a Markush-type expression refers to a mixture or a combination of one or more selected from the group consisting of constituent elements described in a Markush-type expression, and refers to inclusion of one or more selected from the group consisting of the constituent elements.
  • the part when it is mentioned that a part is present “on” the other part, the part may be present directly on the other part, or another part may be involved between them. In contrast, when it is mentioned that a part is present “directly on” the other part, there is no part interposed between them.
  • % means wt %, and 1 ppm is 0.0001 wt %.
  • an additional element in an exemplary embodiment of the present invention is including an additional element in place of iron (Fe) as a balance at the added amount of the additional element.
  • the inventors of the present invention confirmed that when an element to form precipitates such as Ti is added to a common medium-low carbon steel sheet, in the case of using appropriate manufacturing conditions in the manufacturing process, the hardness and the strength of a hot rolled material which is an intermediate material and a cold rolled material which is a final material may be greatly increased.
  • the inventors of the present invention confirmed that when the steel sheet is subjected to a sulfuric acid or a sulfuric acid/hydrochloric acid composite corrosive environment, precipitates are formed by a corrosive product produced depending on the kind and the contents of the element contained in the steel sheet, and a composite relation, but additional corrosion is inhibited.
  • a corrosion-resistant steel sheet includes, by weight: 0.04 to 0.10% of carbon (C), 0.10% or less (excluding 0%) of silicon (Si), 0.20 to 0.35% of copper (Cu), 0.1 to 0.2% of nickel (Ni), 0.05 to 0.15% of antimony (Sb), 0.07 to 0.22% of tin (Sn), 0.05 to 0.15% of titanium (Ti), 0.01% or less (excluding 0%) of sulfur (S), 0.005% or less (excluding 0%) of nitrogen (N), and 0.05 to 0.15% of molybdenum (Mo), with a balance of iron (Fe) and inevitable impurities, and satisfies the following Formulae 1 and 2:
  • the corrosion-resistant steel sheet may further satisfy the following Formula 3:
  • a carbon content in a low-carbon steel sheet may be 0.04 to 0.10 wt %.
  • a carbon content in a steel is too high, deterioration of corrosion resistance, in particular, deterioration of sulfuric acid/hydrochloric acid composite corrosion resistance may occur by excessive TiC formation and carbide formation.
  • the carbon content is too low, it may be impossible to secure the strength to be desired in the present invention. More specifically, it may be 0.042 to 0.10 wt %.
  • a silicon content in the low-carbon steel sheet may be 0.10 wt % or less.
  • the Si content in a steel is too high, a large amount of red scale may be caused by a composite phase shape of SiO 2 and Fe oxides on the surface. Therefore, the Si content may be in the range above for overcoming the surface defects. More specifically, it may be 0.05 wt % or less. More specifically, it may be 0.045 wt % or less. More specifically, it may be 0.01 to 0.045 wt %.
  • Cu is a representative element which is, in the case of corrosion in an acid immersion environment, concentrated between the surface of a steel material and a corrosion product to prevent further corrosion. In order to show the effect, an appropriate amount of Cu may be added. However, when added too much, cracks may be caused in the manufacture due to the low melting point of Cu.
  • Nickel(Ni) 0.1% to 0.2 wt %
  • Ni is added for the purpose of raising the melting point with the addition to limit occurrence of cracks.
  • a Ni content is too low, it does not sufficiently serve to raise the melting point of Cu, and on the contrary, when the Ni content is too high, surface defects due to Ni may occur. More specifically, the Ni content may be 0.11 to 0.19 wt %.
  • Ni and Cu may be added in the above range, in order to appropriately increase a melting point and not to cause surface defects due to Ni.
  • the value of Formula 1 is too high, surface defects due to Ni may occur, and when the value of Formula 1 is too low, an effect of raising a melting point by Ni may be insignificant.
  • [Ni] and [Cu] represent contents (wt %) of Ni and Cu in the steel sheet, respectively.
  • Sb is added for forming a stable concentrated layer on the surface, like Cu.
  • a sufficient concentrated layer may not be formed.
  • surface cracks may be caused.
  • Sn is added for forming a stable concentrated layer on the surface like Cu and Sb.
  • Sn is first dissolved in an acid immersion environment such as sulfuric acid to serve to greatly improve steel type corrosion resistance. More specifically, though it is not clear, it is considered that Sn improves steel type corrosion resistance by the following mechanism.
  • Sn and Cu are dissolved, and Sn is dissolved before Cu.
  • Sn is dissociated in the solution. The dissociated Sn lowers corrosion potential of the solution, thereby partially delaying a corrosion phenomenon of the steel sheet.
  • a corrosion potential refers to a potential to a combination electrode (reference electrode) of metal undergoing corrosion.
  • a corrosion delay layer may be formed in a process in which dissolved Sn is fused again on the surface of the steel sheet, and it is considered that the corrosion delay layer may delay corrosion of the steel sheet.
  • Sn is included too little, a sufficient concentrated layer may not be formed.
  • Sn is added too much, serious surface cracks may be caused in the production process. More specifically, the Sn content may be 0.073 to 0.22 wt %.
  • Mo is added for forming a stable concentrated layer on the surface, like Sn, Sb, Cu, and the like.
  • Mo shows particularly excellent corrosion resistance under an environment where a sulfuric acid and a hydrochloric acid are condensed in combination as well as a sulfuric acid condensation environment.
  • Mo does not sufficiently serves to prevent continuous release of the concentrated layer by the intervention of Cl.
  • Mo is an element which significantly increases hardenability, when added too much, a martensite or bainite phase may be formed in the steel, which causes reduced corrosion resistance.
  • a recrystallization temperature is excessively increased to cause rapid reduction of ductility after cold rolling. More specifically, it may be 0.07 to 0.15 wt %.
  • Mo, Cu, Sb, and Sn are elements which form a concentrated layer on the surface of the steel sheet under a sulfuric acid/hydrochloric acid composite condensation atmosphere or a sulfuric acid condensation atmosphere, and the relationship of Formula 3 as well as appropriate contents of each element may be satisfied. When the value of Formula 3 is too low, a sufficient concentrated layer may not be formed.
  • [Mo], [Sn], [Sb], and [Cu] represent contents (wt %) of Mo, Sn, Sb, and Cu in the steel sheet, respectively. More specifically, Formula 3 may be 16 to 27. More specifically, Formula 3 may be 16.3 to 21.86.
  • Ti acts as an element which forms precipitates and is added for increasing the strength and the wear resistance of the steel sheet. That is, Ti is bonded to C to form a TiC precipitate. TiC is a fine precipitate, may improve the hardness and the wear resistance of a steel sheet due to precipitation strengthening, and also, may increase strength. In this regard, the details of TiC will be described later.
  • a Ti content is too low, precipitates are not sufficiently formed to show no strength increase effect.
  • Ti content is too high, TiC is excessively formed to cause cracks in rolling, and Ti and Al-based composite oxides are formed in a steelmaking step to block a tundish nozzle to cause manufacturing defects and surface defects. Therefore, more specifically, Ti may be included at 0.05 to 0.145 wt %. More specifically, Ti may be included at 0.052 to 0.145 wt %.
  • the present invention is characterized by increasing wear resistance by precipitation hardening by TiC precipitate formation, but since TiS is formed before TiC is formed, the more S content interferes with the formation of TiC. Therefore, the maximum component range may be the range described above. More specifically, it may be 0.0097 wt % or less. More specifically, it may be 0.001 to 0.0097 wt %.
  • N may cause a reverse effect of limiting a Ti content effective for forming a Ti carbide.
  • the present invention is characterized by increasing wear resistance by precipitation hardening by TiC precipitate formation, but since TiN is formed before TiC is formed, the more N content interferes with the formation of TiC.
  • the range of the maximum component may be in the above range. More specifically, it may be 0.004 wt % or less. More specifically, it may be 0.001 to 0.004 wt %.
  • the effective Ti(Ti*) content may be calculated by Formula 2. Even in the case in which the component ranges of S and N are satisfied, when the range of Formula 2 is not satisfied, sufficient TiC may not be formed to cause drop in strength.
  • [Ti], [S], and [N] represent contents (wt %) of Ti, S, and N in the steel sheet, respectively. More specifically, the range of Formula 2 may be 0.04 to 0.12.
  • steel sheet may further include manganese (Mn) and aluminum (Al).
  • Mn serves to improve strength by solid solution strengthening in a steel, but when the content is too excessive, coarse MnS is formed to rather deteriorate strength. Therefore, it is preferred that the Mn content in the present invention is limited to 0.5 to 1.5 wt %.
  • Al is an element which is inevitably added in the manufacture of an aluminum-killed steel, and it is preferred to add Al in an appropriate content for a deoxidation effect.
  • the Al content is more than 0.02 wt %, surface defects of the steel sheet are more likely to be caused, and weldability may be reduced. Therefore, in the present invention, it is preferred to limit the Al content to 0.02 to 0.05 wt %.
  • the present invention includes Fe and inevitable impurities. Since the inevitable impurities are well known in the art, detailed description thereof will be omitted. In an exemplary embodiment of the present invention, addition of effective components other than the above components is not excluded, and when an additional component is further included, it is included by replacing the balance of Fe.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention is characterized by having excellent wear resistance, and includes a TiC precipitate in this regard.
  • the TiC precipitate is a fine precipitate and may improve the hardness and the wear resistance of a steel sheet due to precipitation hardening, and also, may increase strength.
  • the TiC precipitate and the aggregate formed of the TiC precipitate may be included at 10 16 or more per 1 cm 3 .
  • the strength and the wear resistance to be desired may not be secured. More specifically, they may be included at 10 16 to 10 18 per 1 cm 3 .
  • the TiC precipitate may have a spherical shape.
  • the TiC precipitate may have a particle diameter of 1 to 10 nm.
  • the precipitates interfere with movement of potential inside a steel material and form a potential band to increase strength, and when the particle diameter of the precipitates is too small, potential may easily move so that there is no effect of strength increase, but when the particle diameter of the precipitates is too large, potential cuts and passes through the precipitates to facilitate movement, and thus, the effect of strength increase is also deteriorated.
  • the particle diameter of the TiC precipitate may be 2 to 8 nm.
  • a particle diameter refers to a diameter of a sphere, when the sphere having the same volume as the particle is assumed.
  • the TiC precipitate may be uniformly distributed in the steel sheet.
  • Cu, Sb, Sn, and the like form a concentrated layer under a sulfuric acid/hydrochloric acid composite condensate atmosphere or a sulfuric acid condensation atmosphere, which suppresses additional corrosion.
  • the concentrated layer may be produced on the surface of the steel sheet.
  • the concentrated layer may be produced on the surface of the steel sheet. More specifically, when the steel sheet is immersed therein for 4 to 8 hours, the concentrated layer may be produced.
  • the concentrated layer refers to a layer in which Mo, Cu, Sb, and Sn start to be concentrated, and on the other hand, it is generally similar to the point at which oxidation starts.
  • the concentrated layer in the present invention refers to a layer in which the total amount of Mo, Cu, Sb, and Sn is more than 4 times the total amount of Mo, Cu, Sb, and Sn of the steel sheet.
  • the concentrated layer may be an amorphous concentrated layer.
  • the concentrated layer is produced with the formation of a corrosive layer when immersed in an acid.
  • the corrosive layer refers to a layer in which Fe is oxidized by O.
  • Fe is oxidized before Mo, Cu, and Sb, and when immersed in an acid, Fe is dissociated into a Fe ion and escapes into an acid solution, but Mo, Cu, and Sb are stable in a solid state and remain on the surface. Therefore, though the acid reaction continues and a Fe content reduction continuously occurs on the surface of the steel sheet, Mo, Cu, and Sb remain on the surface to form a high concentration layer. This is produced on the surface in the form of a concentrated layer after a certain reaction time, and the concentrated layer prevents a direct contact between an acid and interior iron to suppress further corrosion.
  • the concentrated layer may include Mo, Cu, Sb, and Sn, and the concentrated amount of the concentrated layer may be 10 wt % or more as a total amount of Mo, Cu, Sb, and Sn.
  • the concentrated amount refers to the sum of the contents (wt %) of concentrating element Mo, Cu, Sb, and Sn, at a boundary point at which Fe and O have the same wt %.
  • the concentrated layer is not sufficiently formed to increase a corrosion weight loss ratio. More specifically, it may be 11 to 27 wt %.
  • the concentrated layer may have a thickness of 10 nm or more. More specifically, the concentrated layer may be formed at a thickness of 10 to 500 nm.
  • the concentrated layer When the concentrated layer is too thin, it is difficult for the concentrated layer to serve to prevent corrosion as described above. When the concentrated layer is formed to be too thick, cracks occur inside the concentrated layer, so that an acid may penetrate along the cracks to cause corrosion. More specifically, the concentrated layer may be formed at a thickness of 12 to 100 nm.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention may be a hot rolled steel sheet or a cold rolled steel sheet.
  • the steel sheet may have a thickness of 2.5 to 5.5 mm. More specifically, the thickness may be 3.5 to 5.5 mm.
  • the steel sheet may have a thickness of 1.0 to 2.5 mm. More specifically, the thickness may be 1.0 to 2.0 mm.
  • a recrystallization fraction after subjecting the steel sheet to an annealing heat treatment may be 80% or more. More specifically, the recrystallization fraction may be 100%.
  • the recrystallization fraction refers to an area of grains which is recrystallized based on the total steel sheet area.
  • a corrosion weight loss ratio may be 0.8 mg/cm 2 /hr or less.
  • the corrosion weight loss ratio may be 37 mg/cm 2 /hr or less.
  • the product of the corrosion weight loss ratio when the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention is immersed in 50 wt % of the sulfuric acid solution at 70° C. for 6 hours and the corrosion weight loss ratio when the steel sheet is immersed in the mixed solution of 28.5 wt % of the sulfuric acid solution and 0.5 wt % of the hydrochloric acid solution at 60° C. for 6 hours may be 20 or less.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention is a hot rolled steel sheet
  • the hot rolled steel sheet may have a tensile strength of 580 MPa or more and a surface hardness of 85 or more based on HRB.
  • the corrosion-resistant steel sheet according to an exemplary embodiment of the present invention is a cold rolled steel sheet
  • the cold rolled steel sheet may have a tensile strength of 540 MPa or more and a surface hardness of 80 or more based on HRB.
  • a method of manufacturing a corrosion-resistant steel sheet includes: preparing a steel slab which includes, by weight: 0.04 to 0.10% of carbon (C), 0.10% or less (excluding 0%) of silicon (Si), 0.20 to 0.35% of copper (Cu), 0.1 to 0.2% of nickel (Ni), 0.05 to 0.15% of antimony (Sb), 0.07 to 0.22% of tin (Sn), 0.05 to 0.15% of titanium (Ti), 0.01% or less (excluding 0%) of sulfur (S), 0.005% or less (excluding 0%) of nitrogen (N), and 0.05 to 0.15% of molybdenum (Mo), with a balance of iron (Fe) and inevitable impurities, and satisfies the following Formulae 1 and 2; heating the slab at 1,200° C. or higher; and hot rolling the heated slab at a finish rolling temperature of 850 to 1000° C. to manufacture a hot rolled steel sheet:
  • winding the hot rolled steel sheet at 450 to 750° C.; cold rolling the wound hot rolled steel sheet at a reduction rate of 54 to 70% to manufacture a cold rolled steel sheet; and subjecting the cold rolled steel sheet to an annealing heat treatment at 750 to 880° C. may be further included.
  • a slab satisfying the composition described above is heated. Since the reason for limiting the addition ratio of each composition in the slab is the same as the reason for limiting the composition of the steel sheet described above, repeated description will be omitted. Since the composition of the slab is substantially not changed in the manufacturing process such as hot rolling, winding, pickling, cold rolling, and annealing, as described later, the composition of the slab and the composition of the finally manufactured corrosion-resistant steel sheet is substantially the same.
  • the slab By heating the slab, a subsequent hot rolling process is performed well, and the slab may be homogenized. More specifically, the heating may refer to reheating.
  • a slab heating temperature may be 1,200° C. or higher. The reason why the heating temperature of the slab is in the above range is for sufficient Ti re-solid solution. When Ti is sufficiently re-solid solubilized, the TiC precipitate is precipitated later.
  • a residence time in the slab heating may be 150 minutes or more. When the residence time is too short, re-solid solution of Ti may not sufficiently occur.
  • a finish rolling temperature of the hot rolling may be 850 to 1000° C.
  • the hot rolled plate may have a thickness of 2.5 to 5.5 mm.
  • a step of winding the hot rolled steel sheet may be included.
  • the step of winding the hot rolled steel sheet may be performed at 450 to 750° C.
  • the winding temperature is too low, final cold rolling may be difficult due to an increase of the initial strength of the hot rolled material, and on the contrary, when the winding temperature is too high, buckling may occur and strength may be lowered due to the phase transformation in a winding section.
  • a step of pickling the wound hot rolled steel sheet may be included.
  • a step of cold rolling the wound hot rolled steel sheet at a reduction rate of 54 to 70% to manufacture a cold rolled steel sheet may be included.
  • the reduction rate is too low, it may be difficult to secure complete recrystallization in the cold rolling, which causes a decrease in elongation of materials, and cracks in later customer processing.
  • rolling may not be performed by a motor load in the rolling process.
  • a step of subjecting the cold rolled steel sheet to an annealing heat treatment at 750 to 880° C. may be included.
  • the annealing heat treatment temperature is too low, it may be difficult to secure complete recrystallization, which causes a decrease in elongation of materials, and cracks in later customer processing.
  • the annealing heat treatment temperature is too high, it is difficult to secure the strength of the steel sheet.
  • the slab was heated at 1250° C. for 200 minutes, and then hot rolled to a thickness of 3.5 mm, thereby manufacturing a hot rolled plate.
  • a finish rolling temperature (FDT) was 920° C., and winding was performed at 650° C.
  • an immersion test was performed by the method described in the standard of ASTM G31.
  • the immersion test was performed by a method of preparing 50 wt % of an aqueous sulfuric acid solution and performing immersion at 70° C. for 6 hours. After the immersion, the steel sheet was washed by the specimen surface washing method of ASTM G1, and a weight loss was measured to measure weight losses per unit time and per unit surface.
  • a mixed aqueous solution of 28.5 wt % of a sulfuric acid solution and 0.5 wt % of a hydrochloric acid solution was prepared, and a test of immersion at 60° C. for 6 hours was performed. After the immersion, as described above, a weight loss after washing was measured by a specimen surface washing method of ASTM G1, and weight losses per unit time and per unit surface were measured.
  • the hot rolled plates of each of the inventive examples and the comparative examples were immersed in a mixed aqueous solution of 28.5 wt % of a sulfuric acid solution and 0.55 wt % of a hydrochloric acid solution at 60° C. for 24 hours, and then the specimen was measured for an element distribution from the surface to the inside by GDS measurement.
  • the thickness of the concentrated layer measured therefrom and the concentrated amount of the surface concentrating elements were measured and are shown in the following Table 2.
  • the concentrated layer refers to a layer in which Mo, Cu, Sb, and Sn starts to be concentrated, and on the other hand, is generally similar to the point at which oxidation starts.
  • the thickness of the concentrated layer was measured as the thickness of the layer in which the total amount of Mo, Cu, Sb, and Sn was more than 4 times the total amount of Mo, Cu, Sb, and Sn in the steel sheet.
  • the highest concentrated amount was calculated as the sum of the contents (wt %) of concentrating elements Cu, Sb, and Sn, at a point at which the contents (wt %) of Fe and O were the same.
  • the concentrated layer formed of Mo, Sb, Sn, and Cu was present at about 10 wt % on the surfaces of the steel material and the corrosion product. It was found that the thickness of the concentrated layer and the concentrated amount determine the corrosion resistance in immersion.
  • FIG. 1 is a graph showing an element concentration degree of a surface portion of a steel sheet, by measuring an element distribution from the surface to the inside by GDS measurement, after the steel sheet of Inventive Example 2 was immersed in a mixed aqueous solution of 28.5 wt % of a sulfuric acid solution and 0.55 wt % of a hydrochloric acid solution for 24 hours.
  • a boundary point at which Fe and O met corresponds to the red dotted line of FIG. 1
  • the concentrated amount which is the total amount of Mo, Cu, Sb, and Sn in the layer was 13.03 wt %.
  • the strength, the hardness, and the crack occurrence thereof were confirmed before acid immersion.
  • the hot rolled materials of the inventive examples and the comparative examples were processed into a tensile specimen conforming to the standards of JIS13B, a tensile test was performed at length in a rolling direction, and the results of measuring HRB surface hardness based on Rockwell hardness are shown in the following Table 2.
  • Comparative Example 1 having a low C content, due to the reduced content of the TiC precipitate by the low C content, the tensile strength of the hot rolled material was lower than 580 MPa, and the surface hardness was low, and thus, strength and abrasiveness were not able to be secured.
  • the C content was excessively high as in Comparative Example 2, a phenomenon in which composite corrosion resistance was reduced due to the increased TiC precipitate was observed.
  • the content of Si was greatly lowered, and the reason therefor is that it was confirmed that as the Si content was higher as in Comparative Example 3, red scale excessively occurred on the surface of the hot rolled material, leading to cracks.
  • Comparative Example 4 having a low Cu content, in particular, the corrosion resistance to a sulfuric acid alone was reduced, and in Comparative Example 5 having an excessively high Cu content, cracks in cast iron due to the liquefaction of Cu in the continuous casting process was confirmed.
  • Mo is an element which may form a hard phase such as bainite and martensite, while forming a MoC carbide with C.
  • the hard phase may increase the strength of the hot rolled material as in Inventive Examples 2 and 12 and Comparative Example 2, but when the Mo content is high as in Comparative Example 18, it is known that the hard phase formed at a high fraction deteriorates resistance the corrosion resistance to a sulfuric acid alone.
  • Condition 2 in which a hot finish rolling temperature (FDT) was high, edge cracks occurred in the hot rolling production process, and this was the same in Condition 4 having a low winding temperature (CT).
  • FDT hot finish rolling temperature
  • FIG. 2 compares (a) a photograph of a microstructure after Inventive Example 4 was hot rolled under Condition 1, and (b) a photograph of a microstructure after Inventive Example 4 was hot rolled under Condition 4.
  • a material which had a low CT and a relatively high cooling rate to winding had a high tensile strength of a hot rolled material, and thus, was not able to be rolled to a desired thickness when cold rolling.
  • corrosion resistance was poor.
  • Condition 3 having a high hot finish rolling temperature (FDT) of 1050° C.
  • FDT hot finish rolling temperature
  • CT winding temperature
  • the steel type of the present invention has high contents of C and Ti and is characterized by a high recrystallization temperature after cold rolling, and under Condition 6 having a cold reduction rate of 53%, the recrystallization fraction of the final cold rolled material was about 70%, which did not form complete recrystallization, and in Condition 8 having an annealing temperature was 740° C. which was low also, the recrystallization fraction was 65%, which did not form complete recrystallization.
  • the material which did not undergo complete recrystallization may cause cracks in the customer processing due to a lowered elongation, and thus, in the present invention, when it is used as a cold rolling material, the reduction rate was limited to 54% or more and the annealing temperature was limited to 750° C. or higher.
  • Condition 4 and Condition 7 in which the strength of the hot rolled material was high or the cold reduction rate was high, rolling was not performed by a motor loading in the rolling process, and thus, the final product was not able to be obtained.
  • the present invention is not limited to the implementations and/or the exemplary embodiments, but may be produced in various forms different from each other.
  • a person with ordinary skill in the art to which the present invention pertains will understand that the present invention may be carried out in other specific forms without changing the technical idea or the essential feature of the present invention. Therefore, the implementations and/or the exemplary embodiments described above should be understood to be illustrative in all respects, and not to be restrictive.

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