WO2021125730A2 - 내마모성과 복합내식성이 우수한 강판 및 그 제조방법 - Google Patents

내마모성과 복합내식성이 우수한 강판 및 그 제조방법 Download PDF

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WO2021125730A2
WO2021125730A2 PCT/KR2020/018285 KR2020018285W WO2021125730A2 WO 2021125730 A2 WO2021125730 A2 WO 2021125730A2 KR 2020018285 W KR2020018285 W KR 2020018285W WO 2021125730 A2 WO2021125730 A2 WO 2021125730A2
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steel sheet
corrosion
hot
sulfuric acid
equation
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PCT/KR2020/018285
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French (fr)
Korean (ko)
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WO2021125730A3 (ko
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이병호
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주식회사 포스코
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Priority to CN202080097242.0A priority Critical patent/CN115135791A/zh
Priority to JP2022538245A priority patent/JP2023507804A/ja
Priority to US17/787,009 priority patent/US20230023569A1/en
Publication of WO2021125730A2 publication Critical patent/WO2021125730A2/ko
Publication of WO2021125730A3 publication Critical patent/WO2021125730A3/ko

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    • 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
    • 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
    • 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
    • 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
    • C22C38/08—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 for manufacturing the same. More specifically, SO x , Cl, etc. present in the exhaust gas after combustion of fossil fuels have high strength and abrasion resistance as well as corrosion resistance against the corrosion of steel sheets due to sulfuric acid/hydrochloric acid complex condensate and sulfuric acid condensate generated as the flue gas temperature decreases.
  • the present invention relates to an excellent steel sheet and a method for manufacturing the same.
  • Fossil fuels contain various impurity elements such as S and Cl. Since these fossil fuels are used for combustion, there is always a problem in that pipes and equipment, which are passages through which combustion gases pass, deteriorate due to corrosion. This corrosion phenomenon is called condensate corrosion, and typical uses where piping and equipment are exposed to these corrosive environments are exhaust gas piping and environmental equipment of thermal power plants, and automobile exhaust systems. As the types of condensation corrosion, SO x is formed as S contained in the flue gas is burned. In particular, sulfuric acid condensate corrosion where SO 3 meets moisture in the flue gas to form sulfuric acid, and chlorine contained in the flue gas or industrial water is diverse.
  • Hydrochloric acid is generated through the reaction, corrosion by the generated hydrochloric acid condensate, and sulfuric acid/hydrochloric acid composite condensate corrosion occurring in a state in which sulfuric acid and hydrochloric acid are mixed.
  • the starting temperature of the acid condensation is related to the temperature of the flue-gas itself , the content of SO x , Cl and the water vapor content in the flue-gas.
  • GGH Gas Heater
  • EP electrostatic precipitator
  • An object of the present invention is to provide a steel sheet having excellent wear resistance and composite corrosion resistance and a method for manufacturing the same. More specifically, SO x , Cl, etc. present in the exhaust gas after combustion of fossil fuels have high strength and abrasion resistance as well as corrosion resistance against the corrosion of steel sheets due to sulfuric acid/hydrochloric acid complex condensate and sulfuric acid condensate generated as the flue gas temperature decreases. An object of the present invention is to provide an excellent steel sheet and a method for manufacturing the same.
  • Corrosion-resistant steel sheet excellent in wear resistance and composite corrosion resistance by weight, carbon (C): 0.04 to 0.10%, silicon (Si): 0.10% or less (excluding 0%), copper ( Cu): 0.20 to 0.35%, nickel (Ni): 0.1 to 0.2%, antimony (Sb): 0.05 to 0.15%, tin (Sn): 0.07 to 0.22%, titanium (Ti): 0.05 to 0.15%, sulfur ( S): 0.01% or less (excluding 0%), nitrogen (N): 0.005% or less (excluding 0%), molybdenum (Mo): 0.05 to 0.15%, and the remainder including iron (Fe) and unavoidable impurities and the following Equations 1 and 2 are satisfied.
  • Equations 1 and 2 [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention includes TiC precipitates, and the aggregates made of TiC precipitates and TiC precipitates may be included in an amount of 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 embodiment of the present invention may satisfy Equation 3 below.
  • Equation 3 [Mo], [Sn], [Sb], and [Cu] represent the contents (weight %) of Mo, Sn, Sb, and Cu in the steel sheet, respectively.
  • a thickening layer may be formed on the surface of the steel sheet.
  • a thickening layer may be formed on the surface of the steel sheet.
  • the thickening layer may include Mo, Cu, Sb, and Sn.
  • the concentration of the thickening layer may be 10% by weight or more.
  • the concentration means the sum (weight %) of the content of the concentration elements Mo, Cu, Sb, and Sn holding the boundary point at which Fe and O are equal in weight %.
  • the thickening layer thickness may be 10 nm or more.
  • the recrystallization fraction after the annealing heat treatment of the steel sheet may be 80% or more.
  • the corrosion loss ratio is 0.8 mg/cm 2 /hr. may be below.
  • the corrosion loss ratio is 37 mg/cm 2 /hr. may be below.
  • Corrosion reduction ratio when the steel sheet is immersed in 50 wt% sulfuric acid solution at 70°C for 6 hours and when the steel sheet is immersed in a solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 60°C for 6 hours The product of the corrosion reduction ratio may be 20 or less.
  • the tensile strength of the hot-rolled steel sheet may be 580 MPa or more, and the surface hardness may be 85 or more based on HRB.
  • the tensile strength of the cold rolled steel sheet may be 540 MPa or more, and the surface hardness may be 80 or more based on HRB.
  • the method of manufacturing a corrosion-resistant steel sheet according to an embodiment of the present invention by weight, carbon (C): 0.04 to 0.10%, silicon (Si): 0.10% or less (excluding 0%), copper (Cu): 0.20 to 0.35%, nickel (Ni): 0.1 to 0.2%, antimony (Sb): 0.05 to 0.15%, tin (Sn): 0.07 to 0.22%, titanium (Ti): 0.05 to 0.15%, sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.005% or less (excluding 0%), molybdenum (Mo): 0.05 to 0.15%, the balance including iron (Fe) and unavoidable impurities, Preparing a steel slab satisfying Equation 1 and Equation 2; heating the slab at 1,200° C. or higher; and hot-rolling the heated slab to a finish rolling temperature of 850 to 1000° C. to prepare a hot-rolled steel sheet; includes
  • Equations 1 and 2 [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.
  • a hot-rolled steel sheet Thereafter, winding the hot-rolled steel sheet at 450 to 750 °C; manufacturing a cold rolled steel sheet by cold rolling the wound hot rolled steel sheet at a reduction ratio of 54 to 70%; and annealing and heat-treating the cold-rolled steel sheet at 750 to 880°C.
  • the ash time may be 150 minutes or more.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention can be effectively used as a raw material for piping through which exhaust gas passes after combustion of fossil fuels, hot-rolled products for fossil fuel combustion facilities, and cold-rolled products.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention can be applied to the GGH facility. In this case, it can satisfy both wear resistance and complex corrosion resistance requirements despite the large environmental change.
  • Example 1 is a graph showing the element concentration of the surface portion of the steel sheet by measuring the element distribution from the surface to the inside through GDS measurement after immersing the steel sheet of Inventive Example 2 in a 50 wt% sulfuric acid solution for 24 hours.
  • Figure 2 (a) shows the microstructure in the case of winding Inventive Example 4 at the hot-rolling temperature of Condition 1, (b) shows the microstructure when the component system of Inventive Example 4 is wound at the low winding temperature of Condition 4. .
  • first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.
  • the term “combination of these” included in the expression of the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush form, and the components It means to include one or more selected from the group consisting of.
  • % means weight %, and 1 ppm is 0.0001 weight %.
  • the meaning of further including the additional element means that the remaining iron (Fe) is included by replacing the additional amount of the additional element.
  • the inventors of the present invention when adding an element capable of forming precipitates, such as Ti, to a normal medium to low carbon steel sheet, if appropriate manufacturing conditions are used in the manufacturing process, the intermediate material of the hot rolled material and the final material of the cold rolled material It was confirmed that hardness and strength can be significantly increased.
  • Corrosion-resistant steel sheet by weight, carbon (C): 0.04 to 0.10%, silicon (Si): 0.10% or less (excluding 0%), copper (Cu): 0.20 to 0.35 %, nickel (Ni): 0.1 to 0.2%, antimony (Sb): 0.05 to 0.15%, tin (Sn): 0.07 to 0.22%, titanium (Ti): 0.05 to 0.15%, sulfur (S): 0.01% or less (excluding 0%), nitrogen (N): 0.005% or less (excluding 0%), molybdenum (Mo): 0.05 to 0.15% remainder iron (Fe) and unavoidable impurities, and the following formula 1 and formula 2 is satisfied.
  • Equations 1 and 2 [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.
  • the corrosion-resistant steel sheet may further satisfy the following formula (3).
  • Equation 3 [Mo], [Sn], [Sb], and [Cu] represent the contents (weight %) of Mo, Sn, Sb, and Cu in the steel sheet, respectively.
  • the carbon content of the low-carbon steel sheet may be 0.04 to 0.10 wt%. If the content of carbon in the steel is too large, corrosion resistance may be deteriorated due to excessive TiC formation and carbide formation, in particular, deterioration of sulfuric acid/hydrochloric acid composite corrosion resistance may occur. Conversely, if the carbon content is too small, it may be impossible to secure the strength desired in the present invention. More specifically, it may be 0.042 to 0.10 wt%.
  • the silicon content of the low-carbon steel sheet may be 0.10 wt% or less. If the silicon content in the steel is too large, a large amount of scale may be induced on the surface due to the complex phase shape of SiO 2 and Fe oxide. Accordingly, the Si content may be within the above range for resolving surface defects. More specifically, it may be 0.05 wt% or less. More specifically, it may be 0.045% by weight or less. More specifically, it may be 0.01 to 0.045 wt%.
  • Cu is a representative element that, when corroded in an acid immersion environment, is concentrated between the steel surface and corrosion products to prevent further corrosion. In order to exhibit the effect, an appropriate amount of Cu may be added. However, when too much is added, there is a possibility of causing cracks during manufacturing due to the low melting point of Cu.
  • Nickel (Ni) 0.1% to 0.2% by weight
  • Ni is added for the purpose of limiting the occurrence of cracks by raising the melting point by adding Ni.
  • the content of Ni is too small, it does not sufficiently serve to increase the melting point of Cu.
  • the content of Ni is too large, surface defects due to Ni may occur. More specifically, it may be 0.11 to 0.19 wt%.
  • Equation 1 For the same reason as adding Ni together with Cu, Ni and Cu may be added in the above ranges in order to properly increase the melting point and not cause surface defects due to Ni. If the value of Equation 1 is too high, surface defects may occur due to Ni, and if the value of Equation 1 is too low, the effect of increasing the melting point by Ni may be insignificant. In this case, in Equation 1, [Ni] and [Cu] represent Ni and Cu contents (weight %) in the steel sheet, respectively.
  • Sb like Cu
  • Sb is added to form a stable thickening layer on the surface.
  • a sufficient thickening layer may not be formed. Conversely, too much may cause surface cracks.
  • Sn like Cu and Sb, is added to form a stable thickening layer on the surface.
  • Sn was first dissolved in an acid immersion environment such as sulfuric acid, thereby greatly improving the corrosion resistance of steel grades. More specifically, although it is not clear, it is thought that Sn improves the corrosion resistance of steel grades by the following mechanism.
  • Sn dissolves out before Cu, Sn dissociates in solution. It is thought that the dissociated Sn lowers the corrosion potential of the solution, thereby partially delaying the corrosion phenomenon of the steel sheet.
  • the corrosion potential means a potential with respect to the combination electrode (Reference Electrode) of the metal corrosion is in progress.
  • a corrosion retardation layer may be formed in the process of re-fusion of Sn dissolved on the surface of the steel sheet, and it is believed that this corrosion retardation layer may delay corrosion of the steel sheet.
  • Sn is included too little, it may not be possible to form a sufficient thickening layer. If Sn is added too much, it can cause serious surface cracks in the production process. More specifically, it may be 0.073 to 0.22 wt%.
  • Mo is added to form a stable thickening layer on the surface, such as Sn, Sb, Cu, or the like.
  • Mo exhibits particularly excellent corrosion resistance in an environment where hydrochloric acid is condensed in combination with sulfuric acid as well as sulfuric acid. If the content of Mo is too small, sufficient corrosion resistance against complex acid corrosion cannot be secured, but it is judged that Mo does not play a sufficient role in preventing the continuous drop-off of the thickened layer due to the intervention of Cl.
  • Mo is an element that dramatically increases hardenability, if it is added too much, it may form martensite or bainite phases in steel, which leads to a decrease in corrosion resistance.
  • the recrystallization temperature is excessively increased in the annealing process after cold rolling, resulting in a sharp decrease in ductility after cold rolling. More specifically, it may be 0.07 to 0.15 wt%.
  • the Mo, Cu, Sb, and Sn are elements that form a concentrated layer on the surface of the steel sheet in a sulfuric acid/hydrochloric acid complex condensing atmosphere or a sulfuric acid condensing atmosphere, and may satisfy the relationship of Equation 3 as well as an appropriate content of each element. If the value of Equation 3 is too small, there is a disadvantage that a sufficient thickening layer cannot be formed.
  • Equation 3 [Mo], [Sn], [Sb], and [Cu] represent the contents (weight %) of Mo, Sn, Sb, and Cu in the steel sheet, respectively. More specifically, Equation 3 may be 16 to 27. More specifically, it may be 16.3 to 21.86.
  • Ti acts as an element for forming precipitates and is added to increase the strength and wear resistance of the steel sheet. That is, Ti combines with C to form TiC precipitates. TiC as a fine precipitate may improve the hardness and wear resistance of the steel sheet due to precipitation strengthening, and may also increase strength. In this regard, specific details of TiC will be described later.
  • Ti may include 0.05 to 0.145 wt%. More specifically, it may contain 0.052 to 0.145 wt%.
  • S may have an adverse effect of limiting the effective content of Ti in forming Ti carbides.
  • the reason is that, in the present invention, although the wear resistance is improved by precipitation hardening according to the formation of TiC precipitates, since TiS is formed first before TiC formation, a large amount of S interferes with the formation of TiC. Therefore, the range of the largest component can be made into said range. More specifically, it may be 0.0097 wt% or less. More specifically, it may be 0.001 to 0.0097 wt%.
  • N may have an adverse effect of limiting the effective content of Ti in forming Ti carbide.
  • the wear resistance is improved by precipitation hardening according to the formation of TiC precipitates, but since TiN is first formed before TiC formation, a large amount of N interferes with the formation of TiC.
  • Ti when Ti is formed as a precipitate, it is formed in the order of TiN, TiS, and TiC. Therefore, the range of the largest component can be made into said range. More specifically, it may be 0.004 wt% or less. More specifically, it may be 0.001 to 0.004 wt%.
  • the effective content of Ti(Ti * ) can be calculated by Equation 2. Even if the component ranges of S and N are satisfied, if the range of Equation 2 is not satisfied, sufficient TiC may not be formed, resulting in a decrease in strength. At this time, in Equation 2, [Ti], [S], and [N] represent the contents (weight %) of Ti, S, and N in the steel sheet, respectively. More specifically, the range of Equation 2 may be 0.04 to 0.12.
  • steel sheet may further include manganese (Mn) and aluminum (Al).
  • Mn plays a role in improving strength through solid solution strengthening in steel, but if the content is too large, coarse MnS is formed, which reduces strength. Therefore, the content of Mn in the present invention is preferably limited to 0.5 to 1.5% by weight.
  • Al is an element that is unavoidably added during the production of aluminum-killed steel, and is preferably added in an appropriate amount for the deoxidation effect.
  • the Al content exceeds 0.02% by weight, there is a problem that not only increases the possibility of causing surface defects of the steel sheet, but also deteriorates weldability. Therefore, in the present invention, it is preferable to limit the Al content to 0.02 to 0.05 wt%.
  • the present invention contains Fe and unavoidable impurities. Since unavoidable impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of effective components other than the above components is not excluded, and when additional components are further included, the remaining Fe is included.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention has a feature of excellent wear resistance, and in relation to it includes TiC precipitates.
  • TiC precipitates are fine precipitates and can improve the hardness and wear resistance of the steel sheet due to precipitation hardening, and also increase strength.
  • TiC precipitates and aggregates made of TiC precipitates may be included in an amount of 10 16 or more per 1 cm 3 . If the content of the precipitates is too small, there is a disadvantage in that the desired strength and wear resistance cannot be secured. More specifically, it may be 10 16 to 10 18 pieces per 1 cm 3 .
  • the TiC precipitate may be spherical.
  • the TiC precipitate may have a particle diameter of 1 to 10 nm.
  • the precipitates interfere with the movement of dislocations inside the steel and increase the strength by forming bands of dislocations. If the particle size of the precipitates is too small, the dislocations can easily move, so there is a disadvantage that there is no strength-increasing effect. If it is too large, dislocations cut and pass through the precipitates to facilitate movement, so there is a disadvantage that the effect of increasing the strength is also reduced. More specifically, it may be 2 to 8 nm.
  • the particle diameter means a diameter of the sphere, assuming a sphere having the same volume as the particle.
  • TiC precipitates may be uniformly distributed in the steel sheet.
  • Cu, Sb, and Sn form a thickening layer in a sulfuric acid/hydrochloric acid complex condensing atmosphere or a sulfuric acid condensing atmosphere, which suppresses additional corrosion. More specifically, when the steel sheet is immersed in a mixture of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 40 to 80° C., a thickening layer may be formed on the surface of the steel sheet. In addition, when the steel sheet is immersed in a 50 wt% sulfuric acid solution at 50 to 90°C, a thickening layer may be formed on the surface of the steel sheet. More specifically, when immersed for 4 to 8 hours, a thickening layer may be formed.
  • the thickening layer means a layer in which Mo, Cu, Sb, and Sn start to be concentrated, and in other respects, it is similar to the point where oxidation generally starts.
  • the thickened layer in the present invention means a layer in which the total amount of Mo, Cu, Sb, and Sn in the layer exceeds four times the total amount of Mo, Cu, Sb, and Sn of the steel sheet.
  • the thickening layer may be an amorphous thickening layer.
  • the thickening layer is generated along with the formation of a corrosion layer when immersed in acid.
  • the corrosion layer means a layer in which Fe is oxidized by O.
  • Fe is oxidized before Mo, Cu, and Sb, and when immersed in acid, Fe is dissociated into Fe ions and escapes into an acid solution, but Mo, Cu, and Sb are stable in a solid state and remain on the surface. do. Therefore, even if the reduction of the Fe content on the surface of the steel sheet continues to occur due to the continued acid reaction, Mo, Cu, and Sb remain on the surface to form a layer with high concentration. It is formed on the surface in the form of a thickening layer after a certain reaction time has passed, and the thickening layer prevents direct contact between the acid and the internal iron to suppress further corrosion.
  • the concentrating layer may include Mo, Cu, Sb, and Sn, and the concentration of the concentrating layer may be 10 wt % or more of Mo, Cu, Sb, and Sn.
  • the concentration means the sum (weight %) of the content of the concentration elements Mo, Cu, Sb, and Sn holding the boundary point at which Fe and O are equal in weight %. If the amount of thickening is too small, the thickening layer may not be sufficiently formed, so that the corrosion reduction ratio increases. More specifically, it may be 11 to 17% by weight.
  • the thickening layer thickness may be 10 nm or more. More specifically, the thickening layer may be formed to a thickness of 10 to 500 nm. When the thickness of the thickening layer is too thin, it is difficult to prevent the above-mentioned corrosion. If the thickened layer is formed too thickly, cracks may occur inside the thickened layer, and acid may penetrate along the crack to cause corrosion. More specifically, the thickening layer may be formed to a thickness of 12 to 100 nm.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention may be a hot-rolled steel sheet or a cold-rolled steel sheet.
  • the thickness of the steel sheet may be 2.5 to 5.5 mm. More specifically, it may be 3.5 to 5.5 mm.
  • the thickness of the steel sheet may be 1.0 to 2.5 mm. More specifically, it may be 1.0 to 2.0 mm.
  • the recrystallization fraction after the annealing heat treatment of the steel sheet may be 80% or more. More specifically, it may be 100%. If the recrystallization fraction is too low, the strength is increased, but the ductility is sharply decreased, so there is a disadvantage of forming defects during customer processing. In this case, the recrystallized fraction means the area of the recrystallized grain (grain) based on the total area of the steel sheet.
  • Corrosion loss ratio when the corrosion-resistant steel sheet according to an embodiment of the present invention is immersed in a mixed solution of 28.5 wt% sulfuric acid solution and 0.5 wt% hydrochloric acid solution at 60 °C for 6 hours is 0.8 mg/cm 2 /hr. may be below.
  • the corrosion loss ratio is 37 mg/cm 2 /hr. may be below.
  • the product of the corrosion loss ratio when immersed at °C for 6 hours may be 20 or less.
  • the corrosion-resistant steel sheet according to an embodiment of the present invention is a hot-rolled steel sheet
  • the tensile strength of the hot-rolled steel sheet may be 580 MPa or more
  • the surface hardness may be 85 or more based on HRB.
  • the tensile strength of the cold-rolled steel sheet may be 540 MPa or more, and the surface hardness may be 80 or more based on HRB.
  • Equations 1 and 2 [Ni], [Cu], [Ti], [S], and [N] are the contents (wt%) of Ni, Cu, Ti, S, and N in the steel sheet, respectively. indicates.
  • manufacturing a hot-rolled steel sheet Thereafter, winding the hot-rolled steel sheet at 450 to 750 °C; manufacturing a cold rolled steel sheet by cold rolling the wound hot rolled steel sheet at a reduction ratio of 54 to 70%; and annealing and heat-treating the cold-rolled steel sheet at 750 to 880°C.
  • the slab that satisfies the above-described composition is heated.
  • 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, and thus repeated description will be omitted. Since the composition of the slab does not substantially change in the manufacturing process of hot rolling, winding, pickling, cold rolling, annealing, etc. to be described later, the composition of the slab and the composition of the finally manufactured corrosion-resistant steel sheet are substantially the same.
  • heating may refer to reheating.
  • the slab heating temperature may be 1,200 °C or more. The reason why the heating temperature of the slab is in the above range is for sufficient Ti re-dissolution. This is because TiC precipitates are later precipitated only when Ti is sufficiently re-dissolved.
  • the ash furnace time at the time of heating the slab may be 150 minutes or more. If the time for ash is too short, the re-recruitment of Ti may not occur sufficiently.
  • a hot-rolled steel sheet is manufactured by hot rolling the heated slab.
  • the finish rolling temperature of the hot rolling may be 850 to 1000 °C. If the finish rolling temperature is too low, sufficient rolling ability may not be exhibited. On the other hand, if the finish rolling temperature is too high, it may be difficult to secure the strength of the steel sheet. In this case, the thickness of the hot-rolled sheet may be 2.5 to 5.5 mm.
  • winding the hot-rolled steel sheet may include winding the hot-rolled steel sheet.
  • Winding the hot-rolled steel sheet may be made at 450 to 750 °C. If the coiling temperature is too low, the final cold rolling may be difficult due to an increase in the initial strength of the hot rolled material. On the other hand, if the coiling temperature is too high, there may be problems of buckling and strength drop due to phase transformation in the winding section.
  • the step of pickling the wound hot-rolled steel sheet may include.
  • cold rolling the wound hot-rolled steel sheet at a reduction ratio of 54 to 70% to manufacture a cold-rolled steel sheet may include. If the reduction ratio is too low, it may be difficult to secure complete recrystallization during cold rolling, which may cause a decrease in the elongation of the material and may cause cracks during customer processing in the future. On the other hand, if the reduction ratio is too high, there may be a problem in that rolling is not performed due to a motor load during the rolling process.
  • annealing the cold-rolled steel sheet at 750 to 880 °C may include. If the annealing heat treatment temperature is too low, it may be difficult to secure complete recrystallization, which may cause a decrease in the elongation of the material, and may cause cracks during customer processing in the future. On the other hand, if the annealing heat treatment temperature is too high, there is a problem in that 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 to prepare a hot-rolled sheet.
  • the finish rolling temperature (FDT) was 920 °C, and the 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 preparing a 50% by weight aqueous solution of sulfuric acid and immersing it at 70° C. for 6 hours. After immersion, the weight loss per unit time and per unit surface area was measured by measuring the weight loss after washing through the method of cleaning the surface of the specimen in ASTM G1.
  • the hot-rolled sheet of each invention example and comparative example was immersed in a mixed aqueous solution of 28.5 wt% sulfuric acid solution and 0.55 wt% hydrochloric acid solution at 60°C for 24 hours, and then the specimen was GDS.
  • the element distribution was measured from the surface to the inside through the measurement.
  • Table 2 the thickness of the concentrating layer measured therefrom and the concentrating amount of the surface concentrating elements were measured and shown.
  • the thickening layer means a layer in which Mo, Cu, Sb, and Sn start to be concentrated, and in other respects, it is similar to the point where oxidation generally starts.
  • the thickness of the thickening layer was empirically measured as the thickness of the layer in which the sum of MO, Cu, Sb, and Sn in the layer exceeds four times the sum of Mo, Cu, Sb, and Sn of the steel sheet.
  • the enrichment elements Cu, Sb, Sn It was calculated as the sum of the contents (% by weight).
  • the thickened layer made of Mo, Sb, Sn, and Cu was present on the surface of steel and corrosion products at a level of about 10 wt%. It was found that the thickness and amount of the thickening layer determine the corrosion resistance during immersion.
  • Comparative Example 1 having a low C content
  • the tensile strength of the hot rolled material was lower than 580 MPa and the surface hardness was low due to a decrease in the TiC precipitate content due to the low C content, so strength and abrasion could not be secured.
  • the C content was excessively high as in Comparative Example 2, a phenomenon in which the composite corrosion resistance was decreased due to the increase of TiC precipitates was observed.
  • the content of Si was characteristically significantly lowered, because as in Comparative Example 3, the higher the Si content, the excessively the red scale occurred on the surface of the hot rolled material, and it was confirmed that this leads to cracks. to be.
  • Comparative Example 4 having a low Cu content resulted in a decrease in corrosion resistance of sulfuric acid alone, and in Comparative Example 5 having an excessively high Cu content, cracks in the cast slab due to Cu liquefaction during continuous casting were confirmed.
  • the most important elements for corrosion resistance are Mo, Cu, Sb, and Sn.
  • Comparative Example 8 with a low Sb content and Comparative Example 12 with a low Sn content the corrosion resistance of sulfuric acid alone was significantly reduced, and Comparative Example with a low Mo content In the case of 17, the corrosion resistance of sulfuric acid alone showed similar values, but it was found that the combined corrosion resistance of sulfuric acid/hydrochloric acid decreased.
  • Comparative Example 9 having an excessively high Sb content, Comparative Example 13 having an excessively high Sn content, and Comparative Example 18 having an excessively high Mo content it was confirmed that surface defects and cracks were induced in the hot rolled material.
  • Mo is an element capable of forming MoC carbides together with C and forming hard phases such as bainite and martensite at the same time.
  • the hard phase can increase the strength of the hot-rolled material, but as in Comparative Example 18, when the Mo content is high, the hard phase formed in a high fraction is known to reduce corrosion resistance and corrosion resistance of sulfuric acid alone.
  • Ti was actively added to form precipitates to ensure strength and surface hardness.
  • the Ti content is low as in Comparative Example 10, it can be seen that the tensile strength and surface hardness of the hot rolled material are rapidly decreased.
  • Comparative Example 11 having a high Ti content, particularly 0.15 wt% or more nozzle clogging may be caused in the continuous casting process, and severe nozzle clogging was confirmed in the actual test process of Comparative Example.
  • Table 3 below shows the characteristics of the hot-rolled material and the cold-rolled material after manufacturing under different manufacturing conditions with the component system of Invention Example 4 in order to examine the influence of the manufacturing conditions on the production possibility and strength.
  • FIG. 2 is a photograph comparing the microstructure after (a) hot rolling of Inventive Example 4 under condition 1 and (b) microstructure after hot rolling of Inventive Example 4 under condition 4. From this, in the case of a material with a low CT and a relatively fast cooling rate until coiling, the tensile strength of the hot rolled material was high, so that during cold rolling, it was not rolled to the desired thickness. In particular, when a large amount of fine bainite phase is formed as in condition 4, the corrosion resistance is poor.
  • condition 3 where the hot finish rolling temperature (FDT) was high at 1050°C, the target material could not be secured due to the low tensile strength of the hot rolled material and cold rolled material, and this is also the case in condition 5 when the coiling temperature (CT) was high.
  • FDT hot finish rolling temperature
  • the steel grade of the present invention has a high recrystallization temperature after cold rolling due to high C and Ti content.
  • condition 6 where the cold rolling reduction ratio was 53%, the recrystallization fraction of the final cold rolled material was 70%, so complete recrystallization was not achieved.
  • condition 8 where the annealing temperature was as low as 740 °C, the recrystallization fraction was 65% and complete recrystallization was not achieved.
  • the reduction ratio is 54% or more, and the annealing temperature is limited to 750 ° C or more. do.

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PCT/KR2020/018285 2019-12-20 2020-12-14 내마모성과 복합내식성이 우수한 강판 및 그 제조방법 WO2021125730A2 (ko)

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