WO2018117724A1 - Tôle d'acier laminée à chaud de résistance élevée et tôle d'acier laminée à froid d'excellente productivité continue, tôle d'acier galvanisée par immersion à chaud de résistance élevée présentant une excellente qualité de surface et une excellente adhérence de plaquage, et son procédé de fabrication - Google Patents

Tôle d'acier laminée à chaud de résistance élevée et tôle d'acier laminée à froid d'excellente productivité continue, tôle d'acier galvanisée par immersion à chaud de résistance élevée présentant une excellente qualité de surface et une excellente adhérence de plaquage, et son procédé de fabrication Download PDF

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WO2018117724A1
WO2018117724A1 PCT/KR2017/015313 KR2017015313W WO2018117724A1 WO 2018117724 A1 WO2018117724 A1 WO 2018117724A1 KR 2017015313 W KR2017015313 W KR 2017015313W WO 2018117724 A1 WO2018117724 A1 WO 2018117724A1
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Prior art keywords
steel sheet
rolled steel
less
high strength
hot
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PCT/KR2017/015313
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English (en)
Korean (ko)
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김명수
강기철
박일정
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주식회사 포스코
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Priority to JP2019533551A priority Critical patent/JP6893990B2/ja
Priority to CN201780080336.5A priority patent/CN110100031B/zh
Publication of WO2018117724A1 publication Critical patent/WO2018117724A1/fr

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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C21D8/0221—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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips

Definitions

  • the present invention relates to a high strength hot rolled steel sheet and a cold rolled steel sheet having excellent continuous productivity, and a high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion and a method of manufacturing the same.
  • Mn, Si, Al, Cr, Ti, etc. are added to steel in order to secure both strength and ductility of automotive steel sheets at the same time.
  • a steel sheet having ductility can be produced.
  • the steel sheet used in the automobile for extending the life of the vehicle needs to improve the corrosion resistance, for which hot-dip galvanized steel sheet is used.
  • high strength steel sheets for automobiles having a strength of 950 MPa or more components such as Si, Mn, and Al are added to steel to secure a target strength and elongation.
  • high strength steel sheets containing Mn, Si and / or Al which are easily oxidized in steel, react with trace amounts of oxygen or water vapor in the annealing furnace to form Mn, Si, Al alone or composite oxides on the surface of the steel sheet, and melt It hinders the wettability of zinc, so that uncoated, which is not attached to zinc locally or entirely on the surface of the plated steel, occurs, which greatly reduces the surface quality of the plated steel sheet.
  • Mn, Si, and Al are mainly composed of Fe, Si, Mn, Al, etc.
  • the oxide present in the grain boundary of the steel sheet surface is destroyed by rolling, so that the grain is weakened and it is easy to fall off, and then in the annealing and plating process
  • the structure of the hot rolled steel sheet includes bainite or martensite structure, which causes an increase in the strength of the hot rolled steel sheet, which makes it difficult to cold roll.
  • the dents (Dent) generated in the steel sheet is a problem because it is a concave defect of the stamped form is clearly revealed in the coating process after processing to automotive parts.
  • a high strength steel sheet having a high tensile strength of 950 MPa or more which is used for automobile body structural members, can be stably produced continuously without occurrence of dent defects, but is manufactured to produce hot-dip galvanized steel sheet having excellent surface quality and plating adhesion.
  • the invention was proposed.
  • Patent Literature 1 controls air and fuel at an air-fuel ratio of 0.80 to 0.95 during annealing to oxidize the steel sheet in a direct flame furnace of an oxidizing atmosphere, so that Si, Mn, or Al alone to a certain depth inside the steel sheet.
  • the present invention provides a technique of forming iron oxide including a composite oxide, reducing annealing in a reducing atmosphere, and then reducing the iron oxide and performing hot dip galvanizing.
  • components having a high affinity for oxygen such as Si, Mn, and Al are internally oxidized at a predetermined depth from the surface of the steel sheet, and diffusion into the surface is suppressed.
  • the single or composite oxide is reduced, the wettability with zinc in the plating bath is improved, thereby reducing the unplating.
  • iron when heated under a high oxygen partial pressure where iron can be oxidized, iron is oxidized to a certain depth of the surface layer to form an iron oxide layer. Elements that are easier to oxidize than iron can no longer diffuse to the surface because they oxidize under the iron oxide layer and are present as oxides.
  • the iron oxide is easily reduced to iron in an atmosphere containing a certain amount of hydrogen and is present as a reduced iron layer in the surface layer, so that the wettability with zinc improves and the plating property is improved.
  • the plating property is improved by the post-oxidation reduction method of the high strength steel sheet, it is not possible to prevent liquefied brittle cracks during spot welding in the assembling process after forming the structural member using the steel sheet.
  • Patent Document 2 maintains the dew point in the annealing furnace to maintain a high dew point in the annealing furnace to oxidize components such as Mn, Si, Al, etc.
  • the present invention provides a technique for improving plating property by reducing oxides that are externally oxidized. Internal oxidation of the oxidizing component by this method reduces the external oxidation and improves the plating property, but like the internal oxide in the hot rolling process, the internal oxide formed at the grain boundary of the steel sheet during the annealing is attached to various rolls in the annealing furnace. There is a problem that a dent defect occurs.
  • the present invention suppresses the generation of internal oxides in the steel plate surface layer after hot rolling and winding high-strength steel containing a large amount of Mn, Si, and / or Al in the steel, thereby suppressing the occurrence of steel sheet dent during subsequent annealing, thereby continuously producing
  • the purpose of the present invention is to provide a high-strength hot-dip galvanized steel sheet having excellent surface quality and adhesion by suppressing the formation of Mn, Si, Al, etc. alone or composite oxide on the surface of the steel sheet during annealing.
  • Patent Document 1 Korean Unexamined Patent Publication No. 10-2010-0030627
  • Patent Document 2 Korean Unexamined Patent Publication No. 10-2009-0006881
  • One of the various objects of the present invention is to provide a high strength hot rolled steel sheet and a cold rolled steel sheet having excellent continuous productivity, a high strength hot dip galvanized steel sheet having excellent surface quality and plating adhesion, and a method of manufacturing the same.
  • C 0.14 to 0.3%
  • Si 1 to 2.0%
  • Mn 2.6 to 5%
  • sol.Al 0.001 to 2%
  • An internal oxide containing an element is present, and the maximum depth of the internal oxide is 0.3 ⁇ m or less (excluding 0 ⁇ m) to provide a high strength hot dip galvanized steel sheet.
  • Another aspect of the invention is, in weight percent, C: 0.14-0.3%, Si: 1-2.0%, Mn: 2.6-5%, sol.Al: 0.001-2%, Ti: (48/14) * [N]-0.1%, P: 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), Sb, Bi, Sn, or Zn Or more: reheating the slab containing a total of 0.08 to 0.2%, balance Fe and unavoidable impurities, and then hot rolling to obtain a hot rolled steel sheet under a condition of a finish hot rolling temperature Ar3 ° C. or higher, and the hot rolled steel sheet at a temperature of 600 to 800 ° C. Winding at, provides a method for producing a high strength hot rolled steel sheet comprising the step of cooling the wound hot rolled steel sheet to a temperature of 550 °C or less at an average cooling rate of 2 °C / min or more.
  • Another aspect of the invention is, in weight percent, C: 0.14-0.3%, Si: 1-2.0%, Mn: 2.6-5%, sol.Al: 0.001-2%, Ti: (48/14) * [N]-0.1%, P: 0.04% or less (excluding 0%), S: 0.015% or less (excluding 0%), N: 0.02% or less (excluding 0%), Sb, Bi, Sn, or Zn Or more: reheating the slab containing a total of 0.08 to 0.2%, balance Fe and unavoidable impurities, and then hot rolling to obtain a hot rolled steel sheet under a condition of a finish hot rolling temperature Ar3 ° C. or higher, and the hot rolled steel sheet at a temperature of 600 to 800 ° C.
  • Winding in the step cooling the wound hot rolled steel sheet to an average cooling rate of 2 ° C./min or more to a temperature of 550 ° C. or less, cold rolling the cooled hot rolled steel sheet to obtain a cold rolled steel sheet, and dew point the cold rolled steel sheet.
  • the recrystallized annealing cold rolled steel sheet After heating to a temperature of 820 ⁇ 870 °C under a temperature of -60 ⁇ -30 °C, and holding for 5 ⁇ 120 seconds to recrystallize annealing, the recrystallized annealing cold rolled steel sheet at a rate of 20 °C / sec or more 250 ⁇ 350 Up to a temperature of °C After cooling, holding for 50 to 150 seconds, and heating the cooled and held cold rolled steel sheet to a temperature of 460 ⁇ 500 °C at a rate of 30 °C / sec or more, and then plated by plating in a zinc plating bath within 7 seconds It provides a method of manufacturing a high strength hot dip galvanized steel sheet comprising a step.
  • the high strength hot rolled steel sheet according to the present invention has an advantage of excellent continuous productivity.
  • the high strength hot-dip galvanized steel sheet according to the present invention has an advantage of excellent surface quality and plating adhesion.
  • Figure 1 shows the results of analyzing the cold rolled steel sheet according to Inventive Example 9 by 3D-AP.
  • Figure 2 (a) is an SEM image of the cross section of the cold rolled steel sheet according to Comparative Example 31,
  • Figure 2 (b) is an SEM image of the cross section of the invention example 33.
  • alloy component and the preferred content range of the high strength hot rolled steel sheet of the present invention will be described in detail. It is noted that the content of each component described below is based on weight unless otherwise specified.
  • C is an essential element for securing martensite strength, and in order to obtain such an effect in the present invention, it is preferably included 0.14% or more. However, if the content is excessive, the ductility, bending workability and weldability is reduced, the press formability and roll workability is deteriorated, the upper limit is preferably limited to 0.3%.
  • Si improves the yield strength of the steel and at the same time stabilizes ferrite and residual austenite at room temperature.
  • TRIP Tranformation Induced Plasticity
  • it inhibits cementite precipitation from austenite during cooling and inhibits the growth of carbides. Thereby stabilizing residual austenite. Therefore, it is an essential element for producing a steel sheet excellent in ductility with a tensile strength of 950 MPa or more as in the present invention.
  • it is preferably included 1% or more, more preferably 1.1% or more.
  • the upper limit of the Si content is preferably limited to 2.0%.
  • Mn is well known as a hardenability increasing element that inhibits ferrite formation and stabilizes austenite.
  • Mn is preferably contained at 2.6% or more.
  • the upper limit is preferably limited to 5%.
  • sol.Al is an element added for deoxidation in the steelmaking process.
  • sol.Al also helps to form carbonitrides and reduces the annealing cost by expanding the ferrite region and lowering the Ac1 transformation point.
  • the upper limit is preferably limited to 2%.
  • Ti is a nitride forming element, lowers the content of solid solution N in steel, and serves to suppress AlN formation, which is a cause of hot rolling cracks. In order to obtain such an effect in the present invention, it is necessary to add chemically equivalent (48/14) * [N] or more. However, if the content is excessive, the carbon concentration and strength of martensite may be reduced by additional carbide precipitation in addition to the removal of solid solution N, so the upper limit is preferably limited to 0.1%.
  • P is an inevitable impurity contained in steel.
  • the content thereof is excessive, weldability is lowered, brittleness of steel is more likely to occur, and dent defects are more likely to occur.
  • the upper limit of the P content is preferably limited to 0.04%.
  • S is an inevitable impurity contained in steel.
  • the upper limit of the S content is preferably limited to 0.015%.
  • N is an inevitable impurity contained in steel, and if the content is excessive, the risk of cracking during playing due to AlN formation is greatly increased.
  • the upper limit of the N content is preferably limited to 0.02%.
  • At least one of Sb, Bi, Sn, and Zn 0.08 to 0.2% in total
  • Sb, Sn, Bi, Zn components are first concentrated in the steel plate surface and surface layer to prevent the diffusion of oxidizing components such as Si, Mn, Al in the steel plate surface.
  • oxidizing components such as Si, Mn, Al
  • zinc serves to facilitate adhesion in the galvanizing bath.
  • One or two or more of the Sb, Sn, Bi, and Zn components suppress the formation of oxides of Si, Mn, and Al on the surface of the annealing steel sheet even when the addition amount is less than 0.08%, thereby facilitating adhesion of zinc in the galvanizing bath, thereby facilitating the plating quality. And it is possible to manufacture a high strength hot-dip galvanized steel sheet excellent in adhesion. However, since the internal oxidation of the hot rolled steel sheet is not sufficiently suppressed, this causes the surface iron crystals attached to various rolls in the annealing furnace, which causes dent defects in the steel sheet, which become more severe as steel sheet production increases. Therefore, even if the first 1 to 2 coils are manufactured with high-strength hot-dip galvanized steel sheet having excellent plating quality and adhesion, the product cannot be produced due to the occurrence of dent defects.
  • At least one or more of Sb, Sn, Bi, and Zn components to be added to steel to suppress internal oxidation must be at least 0.08% or more, and the internal oxidation depth of the hot-rolled steel sheet defined in the present invention is 1 ⁇ m or less, and then pickling.
  • the minimum addition amount to secure the plating quality by inhibiting the formation of annealing oxide on the surface of the steel sheet is limited to 0.08%. It is preferable to.
  • an alloying inhibiting layer containing 0.001 to 0.05% by weight of the total content of one or more of Sb, Bi and Sn, as described later, one or more of the elements of Sb, Sn, Bi It may include the sum of the content of more than 0.08%.
  • an effective component other than the composition may further include one or more selected from the group consisting of Cr, Mo, Nb, B.
  • the Cr is an effective hardening element to increase the strength of steel, but there is no major problem in securing physical properties even without adding Cr. On the other hand, when the Cr content is excessive, the manufacturing cost increases rapidly, which is not preferable. In consideration of this, the upper limit of the Cr content is preferably limited to 1.0%.
  • Mo is an effective ingredient for improving the strength of the steel without deteriorating the molten zinc wettability, but even without adding it, there is no major problem in securing the physical properties.
  • the Mo content is excessive, it is not preferable that the manufacturing cost increases rapidly.
  • the upper limit of the Mo content is preferably limited to 0.2%.
  • Nb segregates in the form of carbides in the austenite grain boundary, thereby suppressing grain coarsening of austenite during annealing heat treatment, thereby improving the strength of the steel, but there is no major problem in securing the physical properties even if Nb is not added.
  • the Nb content is excessive, the manufacturing cost increases rapidly, which is not preferable.
  • the upper limit of the Nb content is preferably limited to 0.1%.
  • B is an effective component for securing the strength of the steel, but there is no major problem in terms of securing physical properties even without adding B. However, when the B content is excessive, it may be concentrated on the annealing surface and greatly degrade the plating property.
  • the upper limit of the content is preferably limited to 0.005%.
  • an internal oxide containing at least one element of Si, Mn, Al, Fe characterized in that the maximum depth of the internal oxide is 1 ⁇ m or less (including 0 ⁇ m).
  • the maximum depth of the internal oxide exceeds a certain range, a dent defect is caused in the annealing process after cold rolling, thereby lowering the continuous productivity.
  • the maximum depth of the internal oxide includes 0 ⁇ m, which means that the internal oxide does not exist at all.
  • the maximum depth of the internal oxide may be 0.8 ⁇ m or less (including 0 ⁇ m).
  • the microstructure of the hot rolled steel sheet is not particularly limited.
  • the microstructure of the hot rolled steel sheet may include at least one of ferrite, pearlite, and bainite at an appropriate ratio.
  • the strength of the hot rolled steel sheet is excessively increased, which may cause cracks in the steel sheet during the cold rolling process.
  • the upper limit of the area fraction of bainite is preferably controlled to 50%, and more preferably, the upper limit may be set to 40%.
  • the high strength cold rolled steel sheet according to another aspect of the present invention has the aforementioned component system, and an internal oxide containing at least one element of Si, Mn, Al, and Fe is present in the surface layer portion of the cold rolled steel sheet, and the maximum depth of the internal oxide is It is characterized by being 0.3 ⁇ m or less (excluding 0 ⁇ m). If the maximum depth of the internal oxide of the cold rolled steel sheet exceeds 0.3 ⁇ m, a dent defect is caused during the annealing process, and thus continuous productivity may be lowered. According to one example of the present invention, the maximum depth of the internal oxide may be 0.2 ⁇ m or less (excluding 0 ⁇ m).
  • Another aspect of the present invention is a high strength hot-dip galvanized steel sheet, comprising a cold-rolled steel sheet having the above-described component system and a hot-dip galvanized layer formed on the surface of the cold-rolled steel sheet, wherein the surface layer portion of the cold-rolled steel sheet has one of Si, Mn, Al, and Fe.
  • Internal oxides containing more than one element are present, and the maximum depth of the internal oxides is 0.3 ⁇ m or less (excluding 0 ⁇ m). If the maximum depth of the internal oxide of the cold rolled steel sheet exceeds 0.3 ⁇ m, a dent defect is caused during the annealing process, and thus continuous productivity may be lowered.
  • the maximum depth of the internal oxide may be 0.2 ⁇ m or less (excluding 0 ⁇ m).
  • the sum of the contents of at least one of Sb, Bi, Sn, Zn in the thickness direction 0.001 ⁇ m from the surface of the cold rolled steel sheet Sb, Bi, Sn in the thickness direction 0.02 ⁇ m from the surface of the cold rolled steel sheet , Zn may be 3 to 15 times the sum of one or more contents of Zn.
  • the concentration of Sb, Bi, Sn and Zn components in the surface layer of cold rolled steel sheet has the effect of suppressing the surface diffusion of Mn, Si and / or Al during the high temperature annealing process, so the higher the concentration of these components, the higher the surface of Mn, Si, Al.
  • the effect of suppressing diffusion is great, and in order to secure plating quality and adhesion, at least 0.001 ⁇ m in the thickness direction of the base iron from the interface of the plating layer and the base iron is 0.02 ⁇ m in the thickness direction of the base iron from the base iron interface. It needs to be concentrated at least three times as much.
  • the upper limit is limited to 15 times because the adhesion decreases by preventing the formation of the alloying inhibitory layer composed of Fe-Al-Zn in the plating bath.
  • the content at the 0.001 ⁇ m point and the content of the 0.02 ⁇ m point in the thickness direction of the base iron may be determined as an average of five measurements each.
  • the microstructure of the cold rolled steel sheet is not particularly limited.
  • the microstructure of the cold rolled steel sheet may include at least one of ferrite, pearlite, bainite, martensite, and retained austenite in an appropriate ratio.
  • the area fraction of the double retained austenite is preferably controlled to 5 to 50%.
  • the high-strength hot-dip galvanized steel sheet of the present invention may further include an alloying suppression layer formed at the interface between the cold-rolled steel sheet and the hot-dip galvanized layer, in this case, the alloying inhibitory layer is one of Sb, Bi and Sn
  • the alloying inhibitory layer is one of Sb, Bi and Sn
  • the alloying inhibitory layer is one of Sb, Bi and Sn
  • the alloying inhibitory layer is one of Sb, Bi and Sn
  • the alloying inhibitory layer is one of Sb, Bi and Sn
  • the alloying suppression layer may be coarse, and plating adhesion may be reduced, thereby controlling the sum of the content to 0.05 wt% or less.
  • High strength hot-dip galvanized steel sheet of the present invention has the advantages of excellent strength and ductility, according to one embodiment, the high-strength hot-dip galvanized steel sheet of the present invention is a tensile strength of 950Mpa or more, the product of tensile strength and elongation is 16000Mpa ⁇ % or more Can be.
  • the high strength hot rolled steel sheet, the high strength cold rolled steel sheet, and the high strength hot dip galvanized steel sheet of the present invention described above may be manufactured by various methods, and the manufacturing method thereof is not particularly limited. However, as a preferred example, it may be prepared by the following method.
  • reheating temperature is 1100-1300 degreeC. If the reheating temperature is less than 1100 ° C., the hot rolling load may increase rapidly. On the other hand, if the reheating temperature is higher than 1300 ° C., the reheating cost may increase and the amount of surface scale may be excessively increased.
  • hot rolling is carried out under the condition of the finish hot rolling temperature Ar3 ° C or higher to obtain a hot rolled steel sheet. If the finish rolling temperature is less than Ar3 °C, two-phase or ferritic rolling of ferrite and austenite is carried out to create a hybrid structure and because of the possibility of malfunction due to fluctuation of the hot rolling load, limit to the temperature of Ar3 °C or more.
  • the hot rolled steel sheet is wound at a temperature of 600 to 800 ° C. If the coiling temperature is less than 600 °C the strength of the hot rolled steel sheet is too high may cause the fracture of the rolling roll during cold rolling process, and also the material variation in the width direction of the steel sheet is prone to bend bending easily occurs after cold rolling. On the other hand, if the coiling temperature exceeds 800 °C, the maximum depth of the internal oxide in the hot-rolled steel sheet exceeds 1 ⁇ m, the oxidation depth inside the surface layer of the cold-rolled steel sheet exceeds 0.3 ⁇ m during the subsequent annealing process, resulting in a dent The defect can be severe.
  • the wound hot rolled steel sheet is cooled to an average cooling rate of 2 ° C / min or more to a temperature of 550 ° C or lower.
  • natural cooling that is, air cooling is performed in air at room temperature.
  • the cooling rate is slow, so that it takes a long time until the internal oxidation ends up to 550 ° C. or lower, so that the internal oxidation occurs even after winding. Further progress will be made. Therefore, it is necessary to perform forced cooling until at least the surface temperature of the wound hot rolled steel sheet reaches a temperature of 550 ° C. or lower, and in the case of the present invention, it is necessary to cool at an average cooling rate of 2 ° C./min or more.
  • the present invention is not particularly limited to the upper limit, but if the cooling rate is too fast, the strength of the hot rolled steel sheet may increase to increase the cold rolling load. Therefore, since cold rolling may become difficult, when considering this, the upper limit may be limited to 10 degrees C / min.
  • the cooled hot-rolled steel sheet may be washed after pickling, in this case, pickling may be performed for 15 to 20% by volume of hydrochloric acid aqueous solution having a temperature of 60 to 80 °C for 30 to 60 seconds.
  • the pickling process removes the oxidation scale present on the hot rolled steel sheet and also dissolves a portion of the surface layer portion of the hot rolled steel sheet, thereby partially dissolving internal oxides that may be present in the surface layer portion of 1 ⁇ m or less. Therefore, the higher the acid concentration, the higher the temperature, and the longer the time, the greater the amount of dissolution of the surface layer of the iron, which may reduce the internal oxidation depth after pickling.
  • the pickling time requires at least 30 seconds to remove the surface oxidation scale, and if it is too long, productivity is limited to 60 seconds.
  • the cold rolled hot rolled steel sheet is cold rolled to obtain a cold rolled steel sheet.
  • the cold reduction rate may be 30 to 60%. If the cold rolling reduction is less than 30%, hot rolling may be difficult because the thickness of the hot rolled sheet needs to be made too thin. On the other hand, if the cold rolling rate exceeds 60%, the load on the cold rolling roll may increase significantly, resulting in breakage of the rolling roll. Can be.
  • a lead gold layer made of at least one element among Fe, Ni, Co, and Sn may be formed on the surface of the cold rolled steel sheet.
  • the amount of the lead gold layer deposited may be 0.01-2 g / m 2 per side. Can be controlled. As described above, when the lead is applied, it is very effective in controlling the dew point in the target range in the subsequent recrystallization annealing process.
  • the cold rolled steel sheet is heated to a temperature of 820 ⁇ 870 °C under a dew point temperature of -60 ⁇ -30 °C, then maintained for 5 to 120 seconds and recrystallized annealing.
  • the annealing temperature is heated to the austenite single phase in order to obtain the target material.
  • one or two or more Sb, Bi, Sn, and Zn are added to improve the hot rolling internal oxidation and plating property, and these additions cause a decrease in elongation. Therefore, in the present invention, in order to increase the elongation, it is important to maximize the residual austenite after annealing and cooling, and then temper some of the austenite through reheating to secure the elongation. Therefore, it is necessary to heat it to at least 820 degreeC which is austenite single phase.
  • the annealing temperature is preferably limited to 820 ⁇ 870 °C.
  • the annealing time requires at least 5 seconds to obtain a uniform recrystallized structure, and if it is too long, productivity is reduced, so it is limited to 120 seconds.
  • the dew point temperature is lower than -60 ° C, the diffusion rate of Si and Al in the steel is faster than the diffusion rate of Mn, so that Si and Al of the composite oxides containing Si, Mn, and Al formed on the surface of the steel sheet as main components Since the content is significantly increased compared to Mn, and the Si or Al content of the surface complex oxide is higher than that of Mn, the plating property is inferior, which is insufficient to ensure the wettability of zinc even in the composition and manufacturing conditions of the present invention, and the dew point is -30 ° C. In case of exceeding, during the annealing process, some of the Si, Mn and Al components are oxidized in the grain boundary and the inside of the sheet steel of the steel sheet and present as internal oxides.
  • the recrystallization annealing may be carried out under 3 to 70 volume% H 2 -N 2 gas atmosphere conditions. If the hydrogen content is less than 3% by volume, the reduction of the iron oxide present on the surface of the steel sheet may be insufficient, and as the hydrogen content is increased, it is advantageous in terms of the reduction effect, but the economical efficiency is lowered and the productivity decreases, so the upper limit is 70% by volume. It is limited to.
  • the recrystallized annealed cold rolled steel sheet is cooled to a temperature of 250 ⁇ 350 °C at a rate of 20 °C / sec or more, and then maintained for 50 to 150 seconds.
  • the cooling process after recrystallization annealing is also a very important process for securing the strength and ductility of the material.
  • the cooling rate is better, the average cooling rate of at least 20 °C / sec or more It is necessary to cool to 250 ⁇ 350 °C. If the average cooling rate is less than 20 °C / sec, the ferrite transformation during cooling increases the target strength and ductility cannot be secured.
  • the cooling end temperature is required at least 250 ° C to maximize the residual austenite, and when the cooling temperature is less than 250 ° C some martensite phase is formed to increase the strength, but there is a problem that the elongation is greatly reduced. If the cooling temperature exceeds 350 °C, the amount of austenite transformation to bainite increases, which is disadvantageous to secure the target strength and ductility.
  • the cooled steel plate needs a maintenance process for 50 to 150 seconds. Maintain austenite stabilization and transformation of some austenite to bainite while maintaining at a cooling temperature for at least 50 seconds. However, if the holding time exceeds 150 seconds, the bainite transformation amount may increase, thereby reducing the ductility of the final product.
  • the cooled and held cold rolled steel sheet is heated to a temperature of 460 to 500 ° C. at a rate of 30 ° C./sec or more, and then plated by plating in a zinc plating bath within 7 seconds.
  • the steel plate maintained at the cooling temperature requires an elevated temperature to be immersed in the plating bath, which is the next process.
  • this temperature raising process some of the retained austenite is tempered, so that the tensile strength is slightly decreased, but the elongation that is decreased by the addition of Sb, Bi, Sn, Zn and the like can be ensured.
  • the heating rate is less than 30 °C per second, it takes a long time to heat, so the tempering is excessively proceeded and the tensile strength drop occurs, so it should be at least 30 °C / sec.
  • after heating to 460 ⁇ 500 °C it needs to be immersed in the plating bath within 7 seconds.
  • the tempering increases, causing a drop in strength.
  • the zinc plating bath may comprise 0.12 to 0.3% by weight of Al. If the alloyed hot-dip galvanized steel sheet is manufactured, it is better to manage the Al content of 0.12 to 0.15%, and when manufacturing the hot-dip galvanized steel sheet, it is better to manage it to 0.15% to 0.3%.
  • the temperature of the zinc plating bath may be 450 ⁇ 500 °C. It is not preferable because the viscosity of zinc increases below 450 ° C., so that the driveability of the roll in the zinc plating bath is lowered, and when the temperature exceeds 500 ° C., evaporation of zinc increases.
  • the alloying heat treatment may optionally be performed for 1 second or more at a temperature of 480 to 600 ° C.
  • the alloyed hot-dip galvanized layer may contain 7 to 13% by weight of Fe.
  • the steel slabs having the compositions of Tables 1 and 2 below were reheated at a temperature of 1200 ° C. for 1 hour, finish-rolled at 900 ° C. higher than Ar 3 of all steel slabs, and then cooled to the winding temperatures of Table 3, followed by 550 After forced cooling to an average cooling rate of 3 °C / min to a temperature of °C, Furnace cooling was carried out.
  • the cold-rolled hot rolled steel sheet was observed by scanning electron microscopy to observe the steel sheet internal oxide. At this time, the maximum depth of the internal oxide of the hot-rolled steel sheet was measured five times at 5000 times to take the maximum depth of these.
  • the cooled hot rolled steel sheet was pickled with 60 ° C. and 17% by volume of HCl solution for 40 seconds to dissolve iron oxide on the surface, and then cold-rolled at a rolling reduction of 45%. Then, the cross section of the steel sheet was observed by scanning electron microscopy to observe the cold rolled oxide. At this time, the maximum depth of the internal oxide of the cold rolled steel sheet was measured five times at 5000 times to take the maximum depth of these. In addition, it was observed whether the crack of the cold rolled steel sheet, the results are shown in Table 3 below.
  • the plating bath temperature 460 °C, Al content 0.13wt% (for GA) or 0.22wt% (GI) After plating under the conditions of ()), using an air knife was adjusted to 60g / m 2 single-side reference plating deposition amount and cooled to obtain a plated steel sheet. At this time, some of the specimens were not plated to observe the surface and the base iron surface thickening after annealing. Subsequently, some of the specimens were additionally subjected to alloying heat treatment for 25 seconds at 550 ° C. In Table 4, the specimens subjected to the alloying heat treatment were shown as GA, GI for the specimens that had not been alloyed.
  • the surface of the plated steel sheet is visually checked for the presence of unplated parts and degree for surface quality evaluation, and the automotive structural adhesive is applied to the surface of the steel sheet to evaluate plating adhesion, and then dried. After bending the road was confirmed whether the plating layer is buried in the adhesive, and after evaluating the surface quality and plating adhesion on the basis of the following criteria, the results are shown in Table 5 together.
  • the tensile test was carried out in JIS No. 5 to measure the tensile strength and elongation of the plated steel sheet, the results are shown in Table 5 together.
  • the maximum depth of the internal oxide of the plated steel sheet was measured five times at 5000 times, and the maximum depth was selected among them.
  • Examples 1 to 2, 4 to 6, 9, 14 to 15, 20, and 22 to 24, which are examples of the present invention, are limited in the present invention using steel grades having a component range defined in the present invention.
  • a hot rolled steel sheet, a cold rolled steel sheet, and a hot dip galvanized steel sheet were manufactured by one manufacturing method, and the maximum internal oxide depth of the hot rolled steel sheet was 1 ⁇ m or less, the internal oxide maximum depth of the cold rolled steel sheet was 0.3 ⁇ m or less, and after annealing, The maximum internal oxide depth was 0.3 ⁇ m or less.
  • the surface concentration of Sb, Bi, Sn, and Zn is 3 to 15, and one or two or more of the Sb, Bi, Sn components in the galvanized layer and the cold-rolled steel interface Fe-Al alloy suppression layer contain 0.001 to 0.05%.
  • Tensile strength of more than 950mpa, Tensile strength (Mpa) x Elongation (%) 16000, excellent surface quality and plating adhesion.
  • Comparative Examples 3 and 13 are cases in which the steel sheet winding temperature is wound at a temperature lower than 550 ° C. defined in the present invention in the hot rolling process, and the area fraction of bainite is 74% and 69%, respectively, and the strength of the hot rolled steel sheet is too high. Cracks occurred in the steel sheet during cold rolling.
  • Comparative Example 5-1 the cold rolled steel sheet of Specimen No. 5 in Table 3 was used, but the annealing temperature was higher than the range defined in the present invention during the hot dip plating process. After annealing, the surface concentration of Sb, Bi, Sn, and Zn was observed. The surface quality and plating adhesion after plating were inferior in excess of 15 times the range defined in the present invention.
  • the annealing temperature was higher than the range defined in the present invention, and the surface layer thickening degree of Sb, Bi, Sn, and Zn exceeded the range defined in the present invention, and partial plating peeling occurred.
  • the hot-rolled coiling temperature is higher than the range defined in the present invention, and the content of the internal oxidation inhibiting components Sb, Bi, Sn, and Zn is within the hot-rolled internal oxidation depth even if the content defined in the present invention is satisfied.
  • the cold rolled steel sheet and the annealing depth after annealing exceeded the range defined in the present invention.
  • Comparative Example 16 is a steel component, hot rolling conditions satisfy the range defined in the present invention, but the average cooling rate in the annealing process is lower than the range defined in the present invention, respectively, austenite is transformed into ferrite during the cooling process remaining The austenite content was reduced so that TSxEL was lower than the range defined in the present invention.
  • Comparative Example 17 is a steel component, the hot rolling conditions satisfy the range defined in the present invention, but when the holding time at the cooling temperature is outside the limited range of the present invention, austenite stabilization does not occur, the amount of tempering increases after reheating TSxEL Was low.
  • Comparative Example 20-1 the cold rolled steel sheet of Specimen No. 20 of Table 3 was used, but the reheating rate during the hot dip plating process was lower than the range defined in the present invention, and tempering occurred during reheating for a long time. Significantly decreased, TsxEl was less than the range defined in the present invention.
  • the annealing temperature was lower than the range defined in the present invention.
  • the annealing temperature was lowered in the ferrite and austenite abnormal zone, and then the residual austenite content was reduced through cooling, maintenance, and reheating, thereby lowering TSxEL.
  • Comparative Example 26 is a case in which the annealing temperature is higher than the range defined in the present invention after the annealing in the anomaly zone other than the austenite single-phase zone defined in the present invention, the residual austenite content is low TSxEL is limited in the present invention Lower than the range.
  • Comparative Example 29 is a case where the Si content of the steel component exceeds the range defined in the present invention, the abnormal reverse rolling is carried out in the hot rolling process, whereby a large amount of work hardened ferrite and cementite in which recrystallization does not occur in the hot rolled steel sheet As a result, the strength of the hot rolled steel sheet was greatly increased, which caused plate breakage during cold rolling.
  • Comparative Example 30 is a case in which the Mn content in the steel component exceeds the range defined in the present invention, even if the addition amount of the Sb, Bi, Sn, and Zn components satisfies the scope of the present invention, Si, Mn, Due to the large amount of annealing oxides, such as Al, unplated spots of less than 2 mm occurred in the steel sheet, and partial peeling occurred.
  • Figure 1 shows the results of the analysis of the cold rolled steel sheet according to Inventive Example 9 by 3D-AP.
  • the cross section of the steel sheet was observed with a scanning electron microscope to observe the hot rolled oxide.
  • the maximum depth of the internal oxide of the steel sheet was measured five times at 5000 times, and the maximum depth was selected.
  • the pickling of the hot rolled steel sheet was performed at 70 ° C. and 17 Vol% HCl solution for 30 to 50 seconds, followed by cold rolling immediately.
  • Cold rolled steel sheet was observed by scanning electron microscopy to observe the cross-sectional internal oxidation depth. In this case, the maximum depth of the internal oxide of the steel sheet was measured five times at 5000 times, and the maximum depth was selected.
  • the cold rolled steel sheet is subjected to annealing under the heating and cooling conditions of the following Table 8 after removing foreign substances on the surface through pretreatment, and then plated under the conditions of the plating bath temperature of 456 ° C and the Al content of 0.22wt% in the plating bath. It was used to adjust the coating weight of coating on one side of 60g / m 2 and cooled to prepare a plated steel sheet.
  • the same steel is continuously produced for 15 coils under the same conditions, and the number of dent generating start coils is measured. It is shown in Table 9 below.
  • Comparative Example 31 there is no component that can inhibit the hot rolling internal oxidation in steel, so it is internally oxidized to the depth of 12 ⁇ m from the base iron surface of the hot rolled steel sheet, and then to the depth of 5.2 ⁇ m from the high iron surface of the cold rolled steel sheet even after pickling and cold rolling. After internal oxidation, the internally oxidized grains of the surface layer were dropped during the annealing process, and the Dent defects were observed from the second coil after being attached to the roll in the annealing furnace.
  • Figure 2 (a) is an SEM image observed the cross section of the cold rolled steel sheet according to Comparative Example 31
  • Figure 2 (b) is an SEM image observed the cross section according to the invention example 33.

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Abstract

La présente invention concerne une tôle d'acier laminée à chaud de résistance élevée et similaire, la tôle d'acier laminée à chaud comprenant : en % massiques, de 0,14 à 0,3 % de C, de 1 à 2,0 % de Si, de 2,6 à 5 % de Mn, de 0,001 à 2 % d'Al sol., (48/14) * [N] - 0,1 % de Ti, 0,04 % ou moins (à l'exclusion de 0 %) de P, 0,015 % ou moins (à l'exclusion de 0 %) de S, 0,02 % ou moins (à l'exclusion de 0 %) de N, 0,08 à 0,2 % d'une somme d'un ou de plusieurs types parmi Sb, Bi, Sn et Zn, et le reste se composant de Fe et des impuretés inévitables, un oxyde interne contenant un ou plusieurs types d'éléments parmi Si, Mn, Al, et Fe étant présent dans la partie de couche de surface de la tôle d'acier laminée à chaud, une profondeur maximale de l'oxyde interne étant de 1 µm ou moins (y compris 0 µm).
PCT/KR2017/015313 2016-12-23 2017-12-22 Tôle d'acier laminée à chaud de résistance élevée et tôle d'acier laminée à froid d'excellente productivité continue, tôle d'acier galvanisée par immersion à chaud de résistance élevée présentant une excellente qualité de surface et une excellente adhérence de plaquage, et son procédé de fabrication WO2018117724A1 (fr)

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CN201780080336.5A CN110100031B (zh) 2016-12-23 2017-12-22 高强度热轧钢板和冷轧钢板、高强度热浸镀锌钢板及它们的制造方法

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