EP2097547A1 - High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the same - Google Patents
High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the sameInfo
- Publication number
- EP2097547A1 EP2097547A1 EP07851792A EP07851792A EP2097547A1 EP 2097547 A1 EP2097547 A1 EP 2097547A1 EP 07851792 A EP07851792 A EP 07851792A EP 07851792 A EP07851792 A EP 07851792A EP 2097547 A1 EP2097547 A1 EP 2097547A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- steel sheet
- steel
- added
- high strength
- surface quality
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 106
- 239000010959 steel Substances 0.000 title claims abstract description 106
- 238000000034 method Methods 0.000 title claims description 21
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 14
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 14
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 12
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 11
- 229910052787 antimony Inorganic materials 0.000 claims abstract description 9
- 229910052796 boron Inorganic materials 0.000 claims abstract description 9
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 9
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 8
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 7
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 7
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 6
- 238000000137 annealing Methods 0.000 claims description 18
- 238000005098 hot rolling Methods 0.000 claims description 10
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052719 titanium Inorganic materials 0.000 claims description 10
- 229910052684 Cerium Inorganic materials 0.000 claims description 9
- 229910052746 lanthanum Inorganic materials 0.000 claims description 9
- 238000005097 cold rolling Methods 0.000 claims description 7
- 238000003303 reheating Methods 0.000 claims description 5
- 229910052791 calcium Inorganic materials 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- 238000005554 pickling Methods 0.000 claims description 2
- 229910000885 Dual-phase steel Inorganic materials 0.000 abstract 1
- 239000011248 coating agent Substances 0.000 description 27
- 238000000576 coating method Methods 0.000 description 27
- 230000000694 effects Effects 0.000 description 23
- 239000011572 manganese Substances 0.000 description 17
- 230000007547 defect Effects 0.000 description 12
- 239000010410 layer Substances 0.000 description 9
- 239000010955 niobium Substances 0.000 description 9
- 239000010936 titanium Substances 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 8
- 229910052751 metal Inorganic materials 0.000 description 7
- 239000002184 metal Substances 0.000 description 7
- 239000011575 calcium Substances 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000005204 segregation Methods 0.000 description 5
- 239000011247 coating layer Substances 0.000 description 4
- 239000010960 cold rolled steel Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 230000002401 inhibitory effect Effects 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 239000011701 zinc Substances 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000009977 dual effect Effects 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000000593 degrading effect Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 229910052711 selenium Inorganic materials 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- 229910052727 yttrium Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000005279 austempering Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000001976 improved effect Effects 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 235000019362 perlite Nutrition 0.000 description 1
- 239000010451 perlite Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- VSZWPYCFIRKVQL-UHFFFAOYSA-N selanylidenegallium;selenium Chemical compound [Se].[Se]=[Ga].[Se]=[Ga] VSZWPYCFIRKVQL-UHFFFAOYSA-N 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Classifications
-
- 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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface treatment
-
- 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
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- 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
- C22C38/60—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
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/04—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings of inorganic non-metallic material
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
-
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
-
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0436—Cold rolling
Definitions
- the present invention relates to a high strength dual phase (DP) steel having excellent mechanical properties and surface quality, which is mainly used for inner and outer planes and structural parts of a vehicle, and more particularly, to a high strength Zn-coated steel sheet which can be more easily manufactured with superior mechanical properties and surface quality than a conventional high strength DP steel, and a method for manufacturing the same.
- DP dual phase
- material-reinforcing elements such as Si, Mn, Ti, Nb, and Al are added to manufacture the steel sheet.
- material-reinforcing elements such as Si, Mn, Ti, Nb, and Al are added to manufacture the steel sheet.
- most of these elements have higher affinity for oxygen than Fe, and thus cause surface concentration of oxide during cold-rolled annealing.
- This surface concentration of oxide may lead to poorer coating quality such as non- coating. Also, the surface concentration, if coarse, are adsorbed onto a hearth roll of a continuous annealing furnace, thereby triggering defects such as dent defects on a surface of the coated steel sheet.
- Japanese Patent Laid-open Application Nos. 2002-146477, 2001-64750, 2002-294397, and 2002-155317, and Korean Patent No. 2005-0128666 disclose a method of enhancing coating performance by adding specific elements such as Cr,Sb, and Sn.
- Japanese Patent Laid-open Application No. 2001-288550 teaches a method of inhibiting surface concentration from being formed during cold-rolled annealing by pre-oxidizing a hot-rolled coil before cold rolling.
- effects of the specific elements added are not evident and metallurgical behavior of the added elements has not been clearly examined. Thus, the methods are considered insufficient and hamper workability.
- the present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a high strength Zn- coated steel sheet having superior mechanical properties and surface quality whose alloy elements and hot-rolling coiling temperature are adequately regulated to ensure the steel sheet to be manufactured more easily than a conventional high-strength dual phase (DP) steel.
- DP dual phase
- the invention provides a high strength Zn- coated steel sheet having excellent mechanical properties and surface quality including, by weight: 0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, ⁇ 0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel sheet satisfying a relation of
- the invention provides a method for manufacturing a high strength Zn-coated steel sheet having excellent mechanical properties and surface quality, the method including: reheating a steel slab to 1100 to 125O 0 C, the steel slab comprising, by weight: 0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, ⁇ 0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel slab satisfying a relation of 5 ⁇ (7Mn+4Si+2Al+18B)/(4C+3P+20Sb) ⁇ 18; hot rolling the steel slab; coiling the steel slab at a coiling temperature satisfying a relation of
- CT (700-(30Mn+18Si+54P+15Cr+7Mo)+150B)+20°C; pickling and cold-rolling the steel slab; and annealing the steel slab at a temperature of 700 0 C to 86O 0 C.
- a high-strength DP steel having excellent surface properties and mechanical properties can be manufactured.
- FIG. 1 is a picture illustrating the shape of oxides of an Inventive Steel and a
- FIG. 2 is a graph illustrating the size distribution of oxides formed on a surface of an Inventive Steel. Best Mode for Carrying Out the Invention
- the inventors have conducted a research on a method for manufacturing a high- strength dual phase (DP) steel which can be more easily manufactured with superior mechanical properties and surface quality than a conventional high-strength DP phase.
- DP high- strength dual phase
- alloy elements and hot-rolling coiling temperature of a steel can be adequately regulated to suppress increase in diameter of oxide grains on a surface of a steel sheet, thereby ensuring excellent surface quality and improving mechanical properties.
- Carbon (C) is preferably in a range of 0.01 to 0.2%.
- C increases strength of the steel sheet, and is very important in attaining a composite structure consisting of ferrite and martensite. C added at less than 0.01% does not ensure desired strength of the present invention. Meanwhile, C added at more than 0.2% is highly likely to degrade tensile strength and weldability. Thus, C may be added in an amount of 0.01 to 0.2%.
- Silicon (Si) is preferably in a range of 0.01 to 1.5%.
- [26] Si is beneficial for ensuring strength while not impairing ductility of the steel sheet.
- Si facilitates ferrite formation, and martensite formation by increasing C concentration of non-transformed austenite.
- Si added at less than 0.01% does not bring about the above effects.
- Si added at more than 1.5% is highly likely to deteriorate surface properties and weldability.
- Si may be added in an amount of 0.01 to 1.5%.
- Manganese (Mn) is preferably in a range of 0.2 to 4.0%.
- Mn is greatly effective for strengthening solid solution and facilitates formation of a composite structure consisting of ferrite and martensite. Mn added at less than 0.2% does not yield effects enough to realize high strength. Meanwhile, Mn added at more than 4.0% is highly likely to deteriorate weldability and hot-rolling properties. Thus, Mn may be added in an amount of 0.2 to 4.0%.
- Phosphor (P) is preferably in a range of 0.001 to 0.1 % .
- P is a major solid solution-strengthening element added to increase strength, together with Mn. P added at less than 0.001% does not bring about desired effects. Meanwhile, P added at more than 0.1% impairs weldability and leads to great diff erence in properties of the steel due to central segregation occurring during continuous casting. Thus, P may be added in an amount of 0.001 to 0.1%.
- Sulfer (S) is preferably added in an amount up to 0.03%.
- Aluminum (Al) is preferably in a range of 0.01 to 1.5%.
- Al is added to deoxidize a steel typically but increase ductility according to the present invention. Also, Al inhibits carbide from being formed during austempering and increases strength. Al added at less than 0.01% does not yield sufficient effects. On the other hand, Al added at more than 1.5% accelerates internal oxidation during annealing of the cold-rolled steel to prevent alloying of GA-plated layer, thereby requiring a high alloying temperature. Thus, Al may be added in an amount of 0.01% to 1.5%.
- Nitrogen (N) is preferably in a range of 0.001 to 0.03%.
- N is an effective element for stabilizing austenite. N added at less than 0.001% does not yield such an effect. Meanwhile, N, when added at more than 0.03%, binds with Al to produce a coarse AlN, thereby undermining mechanical properties. Thus, the N amount may not exceed 0.03%.
- Boron (B) is preferably in a range of 0.0002 to 0.005%.
- B is a grain boundary- strengthening element which enhances fatigue properties of a spot welding portion and prevents brittleness of P grain boundary. Also, in manufacturing the steel with high Al and Si contents, B improves hot ductility. In addition, B delays austenite from being transformed into perlite in a cooling process during annealing. B added at more than 0.005% causes an excessive amount of B to be concentrated on a surface of the steel, thus degrading coating adhesion. Therefore, to achieve desired effects, B should be added in an amount of at least 0.0002% but the B amount exceeding 0.005% drastically undermines workability and deteriorates surface properties of the coated steel sheet. Thus, B may be added in an amount of 0.0002 to 0.005%.
- Chrome (Cr) is preferably in a range of 0.01 to 2.0%.
- Cr is added to enhance hardenability and ensure high strength.
- the Cr amount less than 0.01% does not assure such effects.
- the Cr amount exceeding 2.0% yields no further effect and is highly likely to degrade ductility.
- Cr may be added in an amount of 0.01 to 2.0%.
- Molybdenum (Mo) is preferably in a range of 0.005 to 0.5%.
- Mo amount less than 0.005% does not ensure desired effects. Meanwhile, the Mo amount exceeding 0.5% does not lead to much improved effect and is economically disadvantageous. Thus, Mo may be added in an amount of 0.005 to 0.5%.
- Antimony (Sb) is preferably in a range of 0.005 to 0.1 % .
- Sb itself does not form an oxidation layer at a high temperature but is concentrated on a surface of the steel and a crystal grain boundary thereof to prevent the elements from spreading onto the surface. This as a result suppresses formation of an oxide. Also, Sb is remarkably effective in inhibiting selective oxidation from being developed along a grain boundary of the steel sheet. Sb is added to inhibit penetration of various oxides formed along the grain boundary of the steel sheet surface in a hot-rolling process due to a considerable amount of Si, Mn, and Al. When a grain boundary oxide of the hot-rolled steel sheet has a depth exceeding ID, the oxide remains inside the metal even after prickling, thereby causing various scale defects in a following cold- rolling process.
- Sb added to effectively inhibit the selective grain boundary oxidation of the hot-rolled steel sheet is also noticeably effective in suppressing scale defects.
- Sb is added to suppress formation of the oxide in an annealing due to a great amount of Si, Mn, and Al to thereby improve coating properties.
- Sb when added in conjunction with Mn and B effectively inhibits coarsening of a surface oxide layer.
- elements such as Sn, Se, and Y could be added to achieve similar effects but Sn is less capable of inhibiting the grain boundary oxidation of the hot- rolled steel sheet.
- Se and Y are more likely to be concentrated on the surface of the steel than other elements and also may coarsen the oxide since the oxide is formed under SiO and Al O formed on the surface of the steel.
- Sb should be added in an amount of at least 0.005% but, when added beyond a specific limit, does not ensure any further effects. Therefore, the Sb amount may not exceed 0.1%.
- an alloy of the steel sheet having the element content range as described above may satisfy a relation of 5 ⁇ (7Mn+4Si+2Al+18B)/(4C+3P+20Sb) ⁇ 18.
- Mn, Si, Al, and B characteristically form concentration on the surface of the steel in annealing. A greater amount of concentration of these elements degrades coating properties. Meanwhile, C, P, and Sb are prone to segregation at the crystal grain boundary. With segregation of these elements such as C, P, and Sb, the concentrated elements are blocked off the diffusion of Mn, Si, Al and B on the grain boundary, thus contributing to surface quality.
- the above relation indicates an empirical numerical value capable of preventing deterioration of the steel characteristics and ensuring superior surface quality depending on surface concentration behavior and segregation behavior of the elements. For example, in a case where a value calculated by the relation is smaller than 5, the steel is degraded in mechanical properties. On the other hand, in a case where a value calculated by the relation is greater than 18, the steel cannot attain desired surface quality.
- the steel sheet containing the elements described above may further include at least one of 0.01 to 1.0% Co, 0.001 to 0.1% Zr, 0.001 to 0.1% Ti, 0.001 to 0.1% Nb, 0.0005 to 0.040% La, 0.0005 to 0.040% Ce and 0.0005 to 0.030% Ca.
- Cobalt Co is preferably in a range of 0.01 to 1.0% .
- Co is added to boost strength of the steel. Co inhibits formation of the oxide in high-temperature annealing, thereby improving wettability against a molten zinc steel sheet during molten coating. To achieve these effects, Co should be added in an amount of at least 0.01%. Meanwhile, Co added beyond a specific limit significantly reduces elongation of the steel. Thus, the Co amount may not exceed 1.0%.
- Zirconium (Zr) is preferably in a range of 0.001 to 0.1 %
- Zr is solved in a columnar grain boundary to increase a melting temperature of a Al- concentrated and low-melting point compound, thereby blocking formation of a liquid film at a temperature of 1300 0 C or less and strengthening the columnar grain boundary.
- Zr added at less than 0.001% does not ensure such effects.
- Zr added at more than 0.1% does not yield any further effects. Therefore, Zr may be added in an amount of 0.001 to 0.1%.
- Titanium (Ti) and Niobium (Nb) are preferably in a range of 0.001 to 0.1%, respectively.
- Ti and Nb are effective in increasing strength of the steel sheet and attaining fine grain size. Ti and Nb added at less than 0.001% do not ensure such effects. Meanwhile, Ti and Nb added at more than 0.1% may raise manufacturing costs and deteriorate ferrite ductility due to excessive precipitate. Therefore, Ti and Nb may be added in an amount of 0.001 to 0.1%, respectively.
- Lanthanum (La) and cerium (Ce) are preferably in a range of 0.0005 to 0.04%, respectively.
- La and Ce decrease the size and amount of columnar grains which cause em- brittlement to the grain boundary and increase the amount of equiaxed grains with superior high-temperature ductility, thereby enhancing hot-rolling workability of a cast structure. Also La and Ce are segregated at the grain boundary to form a compound with P and S which degrade rupture strength of the grain boundary, thereby ensuring P and S to have less negative effects. However, La and Ce added at less than 0.0005% do not bring about any effects. On the other hand, La and Ce added at more than 0.04% yield no further effects. Therefore, La and Ce may be added in an amount of 0.0005 to 0.04%, respectively. [79]
- Ca is preferably in a range of 0.0005 to 0.03%.
- Calcium Ca forms a compound together with a non-metallic inclusion such as MnO, and MnS in a molten steel to spherodize the non-metallic inclusion. This accordingly increases rupture strength of the columnar grains, allows the steel sheet to be less prone to the flange crack and increases bore expandability. However, the Ca amount exceeding 0.03% yields no further effect. Thus Ca may be added in an amount of 0.0005 to 0.030%.
- the steel sheet contains the balance of Fe and unavoidable impurities.
- an oxide layer on the surface of the steel sheet has a thickness of ID or less.
- the oxide layer formed on a metal surface in an annealing process after cold-rolling serves as an impediment between a metal matrix and a coating layer in the case of coating, thereby degrading coating adhesion.
- the oxide layer grown to a thickness exceeding ID causes dent defects and coating defects due to detachment of the oxide. Therefore, the oxide layer, when formed with a uniform but not great thickness in the annealing, advantageously ensures better quality in the coating layer.
- Sb added in an amount of 0.005 to 0.1% is not oxidized but concentrated on a metal surface layer to inhibit oxidization reaction. This ensures the oxide layer to be formed with a uniform thickness of ID or less.
- the steel slab At a reheating temperature of less than 1100 0 C, the steel slab is not uniform in structure and has Ti and Nb re-solved insufficiently therein. Meanwhile, at a reheating temperature of more than 125O 0 C, an oxidized scale is formed and a great amount of oxides such as SiO , MnO, and Al O are generated at a boundary with the metal and inside the metal, thereby impairing surface quality. Therefore, the reheating temperature may range from 1100 to 125O 0 C.
- the steel slab is hot finish rolled at a temperature ranging from an Ar transformation point to 95O 0 C.
- the steel slab hot finish rolled at a temperature of an Ar transformation point is very likely to become more highly resistant to hot deformation and may have manufacturing problems.
- the steel slab hot finish rolled at more than 950 0 C experiences too thick an oxidized scale and is very likely to be coarsened. Therefore, the hot finish rolled temperature may range from an Ar transform to 950 0 C.
- CT (700-(30Mn+18Si+54P+15Cr+7Mo)+150B)+20°C.
- elements such as Mn, Si, P, Cr, and Mo are added as an alloy element associated with formation of martensite out of microstructures.
- these elements are more likely to experience segregation at a higher coiling temperature.
- the added Mn, Si, P, Cr, and Mo achieve less effect, thereby not assuring desired strength and workability.
- a hot-rolled sheet manufactured by the above process is prickled, and cold-rolled to a desired thickness, and then recrystalized and annealed at a temperature of 700 to 860 0 C to remove microstructural defects.
- annealing temperature less than 700 0 C annealed oxides are formed minutely so that the added Sb does not yield noticeable effects.
- oxides are grown excessively so that the surface concentration can not be sufficiently inhibited.
- a steel slab containing elements as noted in Table 1 below was heated at 1200 0 C to be produced. Then the steel slab was hot rolled and coiled at a temperature(+20°C) satisfying relation 2 and cold-rolled to manufacture a cold-rolled steel sheet. Subsequently, the cold rolled steel strip was annealed and heat treated in an N -10%H O atmosphere at a temperature of 780 to 830 0 C and at a heating rate of 3°C/sec per 90 seconds. Thereafter, the steel strip was coated in a Zn bath having a temperature of 460 0 C and an Al range of 0.12 to 0.19%, and the coated steel was alloyed and heat- treated at a temperature of 540 to 560 0 C for 24 seconds.
- the steel sheet was observed to identify surface quality.
- the category of coating appearance includes non-coating, O for having no other coating defects and a defect name for any defect that occurs.
- the coating sheet was cut into a size of 20mmx50mm and subjected to a 60° bending test. Then, the coating sheet was straightened out to tape a bent portion. Here, a coating layer detached had a width measured as below.
- Inventive Steels 1 to 11 satisfying the element content range and manufacturing method of the present invention can be manufactured as a high strength DP steel superior in coating surface properties and strength elongation balance (TSxEl).
- Comparative steels 12 to 16 not satisfying the element content range and manufacturing method of the present invention were found inferior in terms of coating surface properties and strength elongation balance.
- FIG. 1 shows the shape of oxides of Inventive Steel 11 and Comparative Steel 16, respectively depending on addition or non-addition of Sb.
- FIG. IA denotes Comparative Steel 16 and
- FIG. IB denotes Inventive Steel 11.
- Inventive Steel 11 shows an oxide whose grains are noticeably smaller. That is, the oxide growth is inhibited due to addition of Sb.
- FIG. 2 shows the size distribution of oxides formed on a surface of
- the oxides formed on a metal surface in an annealing process have sizes stably distributed around ID or less. That is, the minute oxides uniformly distributed serve to form a more uniform coating layer.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
There is provided a high strength Zn-coated steel sheet having excellent mechanical properties and surface quality, which is mainly used for inner and outer panels and structural parts of a vehicle. The steel sheet having excellent mechanical properties and surface quality includes, by weight: 0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, ≤0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel sheet satisfying a relation of 5≤(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)≤18 and having an oxide layer with a thickness of 1μm or less on a surface thereof. According to the present invention, a high-strength dual phase steel having excellent mechanical properties and surface quality can be manufactured.
Description
Description
HIGH STRENGTH ZN-COATED STEEL SHEET HAVING
EXCELLENT MECHANICAL PROPERITES AND SURFACE
QUALITY AND THE METHOD FOR MANUFACTURING THE
SAME Technical Field
[1] The present invention relates to a high strength dual phase (DP) steel having excellent mechanical properties and surface quality, which is mainly used for inner and outer planes and structural parts of a vehicle, and more particularly, to a high strength Zn-coated steel sheet which can be more easily manufactured with superior mechanical properties and surface quality than a conventional high strength DP steel, and a method for manufacturing the same.
[2]
Background Art
[3] Recently, a steel sheet for vehicles needs to possess higher formability since forming products thereof tend to be complicated and integrated. In the meantime, as generally known, the steel sheet for vehicles should be superior in work embrittlement and fatigue characteristics of welding parts to enhance usability of the vehicles. Moreover, the steel sheet for vehicles should have an aesthetically satisfying coating surface.
[4] In general, to enhance formability and strength of the steel sheet, material-reinforcing elements such as Si, Mn, Ti, Nb, and Al are added to manufacture the steel sheet. However, most of these elements have higher affinity for oxygen than Fe, and thus cause surface concentration of oxide during cold-rolled annealing.
[5] This surface concentration of oxide may lead to poorer coating quality such as non- coating. Also, the surface concentration, if coarse, are adsorbed onto a hearth roll of a continuous annealing furnace, thereby triggering defects such as dent defects on a surface of the coated steel sheet.
[6] To improve coating defects as described above, a known technology of manufacturing a thin steel sheet for deep processing has been developed by Japanese blast furnace companies. In a brief description, Japanese Patent Laid-open Application Nos. 2002-146477, 2001-64750, 2002-294397, and 2002-155317, and Korean Patent No. 2005-0128666 disclose a method of enhancing coating performance by adding specific elements such as Cr,Sb, and Sn. Also, Japanese Patent Laid-open Application No. 2001-288550 teaches a method of inhibiting surface concentration from being formed
during cold-rolled annealing by pre-oxidizing a hot-rolled coil before cold rolling. However, in these methods, effects of the specific elements added are not evident and metallurgical behavior of the added elements has not been clearly examined. Thus, the methods are considered insufficient and hamper workability.
[7] In addition, some of the conventional technologies cannot be realized in the current general hot-rolling and cold-rolling-continuous annealing facility, not ensuring any commercially viable production. Disclosure of Invention Technical Problem
[8] The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a high strength Zn- coated steel sheet having superior mechanical properties and surface quality whose alloy elements and hot-rolling coiling temperature are adequately regulated to ensure the steel sheet to be manufactured more easily than a conventional high-strength dual phase (DP) steel.
[9]
Technical Solution
[10] According to an aspect of the invention, the invention provides a high strength Zn- coated steel sheet having excellent mechanical properties and surface quality including, by weight: 0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, <0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel sheet satisfying a relation of
5<(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)<18 and having an oxide layer with a thickness of ID or less on a surface thereof.
[11] According to another aspect of the invention, the invention provides a method for manufacturing a high strength Zn-coated steel sheet having excellent mechanical properties and surface quality, the method including: reheating a steel slab to 1100 to 125O0C, the steel slab comprising, by weight: 0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, <0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel slab satisfying a relation of 5<(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)<18; hot rolling the steel slab; coiling the steel slab at a coiling temperature satisfying a relation of
CT=(700-(30Mn+18Si+54P+15Cr+7Mo)+150B)+20°C; pickling and cold-rolling the steel slab; and annealing the steel slab at a temperature of 7000C to 86O0C.
Advantageous Effects
[13] According to the present invention, a high-strength DP steel having excellent surface properties and mechanical properties can be manufactured.
[14]
Brief Description of the Drawings
[15] FIG. 1 is a picture illustrating the shape of oxides of an Inventive Steel and a
Comparative Steel, respectively depending on addition or non-addition of Sb; and
[16] FIG. 2 is a graph illustrating the size distribution of oxides formed on a surface of an Inventive Steel. Best Mode for Carrying Out the Invention
[17] Exemplary embodiments of the present invention will now be described in detail.
[18] The inventors have conducted a research on a method for manufacturing a high- strength dual phase (DP) steel which can be more easily manufactured with superior mechanical properties and surface quality than a conventional high-strength DP phase. In the course of the research, the inventors have discovered that alloy elements and hot-rolling coiling temperature of a steel can be adequately regulated to suppress increase in diameter of oxide grains on a surface of a steel sheet, thereby ensuring excellent surface quality and improving mechanical properties.
[19]
[20] Hereinafter, an element content range of a steel according to the present invention will be described.
[21]
[22] Carbon (C) is preferably in a range of 0.01 to 0.2%.
[23] C increases strength of the steel sheet, and is very important in attaining a composite structure consisting of ferrite and martensite. C added at less than 0.01% does not ensure desired strength of the present invention. Meanwhile, C added at more than 0.2% is highly likely to degrade tensile strength and weldability. Thus, C may be added in an amount of 0.01 to 0.2%.
[24]
[25] Silicon (Si) is preferably in a range of 0.01 to 1.5%.
[26] Si is beneficial for ensuring strength while not impairing ductility of the steel sheet.
Also, Si facilitates ferrite formation, and martensite formation by increasing C concentration of non-transformed austenite. Si added at less than 0.01% does not bring about the above effects. On the other hand, Si added at more than 1.5% is highly likely to deteriorate surface properties and weldability. Thus, Si may be added in an amount of 0.01 to 1.5%.
[27]
[28] Manganese (Mn) is preferably in a range of 0.2 to 4.0%.
[29] Mn is greatly effective for strengthening solid solution and facilitates formation of a composite structure consisting of ferrite and martensite. Mn added at less than 0.2% does not yield effects enough to realize high strength. Meanwhile, Mn added at more than 4.0% is highly likely to deteriorate weldability and hot-rolling properties. Thus, Mn may be added in an amount of 0.2 to 4.0%.
[30]
[31 ] Phosphor (P) is preferably in a range of 0.001 to 0.1 % .
[32] P is a major solid solution-strengthening element added to increase strength, together with Mn. P added at less than 0.001% does not bring about desired effects. Meanwhile, P added at more than 0.1% impairs weldability and leads to great diff erence in properties of the steel due to central segregation occurring during continuous casting. Thus, P may be added in an amount of 0.001 to 0.1%.
[33]
[34] Sulfer (S) is preferably added in an amount up to 0.03%.
[35] S is inevitably added in manufacturing the steel and thus the S amount may not exceed 0.03%.
[36]
[37] Aluminum (Al) is preferably in a range of 0.01 to 1.5%.
[38] Al is added to deoxidize a steel typically but increase ductility according to the present invention. Also, Al inhibits carbide from being formed during austempering and increases strength. Al added at less than 0.01% does not yield sufficient effects. On the other hand, Al added at more than 1.5% accelerates internal oxidation during annealing of the cold-rolled steel to prevent alloying of GA-plated layer, thereby requiring a high alloying temperature. Thus, Al may be added in an amount of 0.01% to 1.5%.
[39]
[40] Nitrogen (N) is preferably in a range of 0.001 to 0.03%.
[41] N is an effective element for stabilizing austenite. N added at less than 0.001% does not yield such an effect. Meanwhile, N, when added at more than 0.03%, binds with Al to produce a coarse AlN, thereby undermining mechanical properties. Thus, the N amount may not exceed 0.03%.
[42]
[43] Boron (B) is preferably in a range of 0.0002 to 0.005%.
[44] B is a grain boundary- strengthening element which enhances fatigue properties of a spot welding portion and prevents brittleness of P grain boundary. Also, in manufacturing the steel with high Al and Si contents, B improves hot ductility. In addition, B delays austenite from being transformed into perlite in a cooling process during
annealing. B added at more than 0.005% causes an excessive amount of B to be concentrated on a surface of the steel, thus degrading coating adhesion. Therefore, to achieve desired effects, B should be added in an amount of at least 0.0002% but the B amount exceeding 0.005% drastically undermines workability and deteriorates surface properties of the coated steel sheet. Thus, B may be added in an amount of 0.0002 to 0.005%.
[45]
[46] Chrome (Cr) is preferably in a range of 0.01 to 2.0%.
[47] Cr is added to enhance hardenability and ensure high strength. The Cr amount less than 0.01% does not assure such effects. On the other hand, the Cr amount exceeding 2.0% yields no further effect and is highly likely to degrade ductility. Thus, Cr may be added in an amount of 0.01 to 2.0%.
[48]
[49] Molybdenum (Mo) is preferably in a range of 0.005 to 0.5%.
[50] Mo is added to improve work embrittlement and coating properties. However, the
Mo amount less than 0.005% does not ensure desired effects. Meanwhile, the Mo amount exceeding 0.5% does not lead to much improved effect and is economically disadvantageous. Thus, Mo may be added in an amount of 0.005 to 0.5%.
[51]
[52] Antimony (Sb) is preferably in a range of 0.005 to 0.1 % .
[53] Sb itself does not form an oxidation layer at a high temperature but is concentrated on a surface of the steel and a crystal grain boundary thereof to prevent the elements from spreading onto the surface. This as a result suppresses formation of an oxide. Also, Sb is remarkably effective in inhibiting selective oxidation from being developed along a grain boundary of the steel sheet. Sb is added to inhibit penetration of various oxides formed along the grain boundary of the steel sheet surface in a hot-rolling process due to a considerable amount of Si, Mn, and Al. When a grain boundary oxide of the hot-rolled steel sheet has a depth exceeding ID, the oxide remains inside the metal even after prickling, thereby causing various scale defects in a following cold- rolling process. Therefore, it is important to regulate the depth of the grain boundary oxide of the hot-rolled steel sheet to ID or less. Sb added to effectively inhibit the selective grain boundary oxidation of the hot-rolled steel sheet is also noticeably effective in suppressing scale defects. Sb is added to suppress formation of the oxide in an annealing due to a great amount of Si, Mn, and Al to thereby improve coating properties. Particularly, Sb when added in conjunction with Mn and B effectively inhibits coarsening of a surface oxide layer.
[54]
[55] In a case where an annealed oxide is grown coarsely, the oxide is deposited
repeatedly on the roll, thereby causing dents on the surface of the cold-rolling steel and coating steel. Here, Sb added to inhibit the surface oxide is remarkably effective in suppressing such dent defects. Sb added in an appropriate amount enhances strength and ductility of the steel sheet, thereby improving mechanical properties thereof.
[56]
[57] In addition to Sb, elements such as Sn, Se, and Y could be added to achieve similar effects but Sn is less capable of inhibiting the grain boundary oxidation of the hot- rolled steel sheet. Moreover, Se and Y are more likely to be concentrated on the surface of the steel than other elements and also may coarsen the oxide since the oxide is formed under SiO and Al O formed on the surface of the steel.
2 2 3
[58]
[59] Therefore, Sb added is superbly effective in inhibiting surface concentration of
MnO, SiO , and Al O in annealing the cold-rolled steel sheet and serves to improve mechanical properties. Sb should be added in an amount of at least 0.005% but, when added beyond a specific limit, does not ensure any further effects. Therefore, the Sb amount may not exceed 0.1%.
[60]
[61] In designing an alloy of the steel sheet having the element content range as described above may satisfy a relation of 5<(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)<18.
[62] Mn, Si, Al, and B characteristically form concentration on the surface of the steel in annealing. A greater amount of concentration of these elements degrades coating properties. Meanwhile, C, P, and Sb are prone to segregation at the crystal grain boundary. With segregation of these elements such as C, P, and Sb, the concentrated elements are blocked off the diffusion of Mn, Si, Al and B on the grain boundary, thus contributing to surface quality.
[63]
[64] However, too much elements segregated at the grain boundary deteriorate properties such as elongation. On the other hand, too much elements prone to surface concentration undermine surface properties, thus required to be adequately regulated in the amount. The above relation indicates an empirical numerical value capable of preventing deterioration of the steel characteristics and ensuring superior surface quality depending on surface concentration behavior and segregation behavior of the elements. For example, in a case where a value calculated by the relation is smaller than 5, the steel is degraded in mechanical properties. On the other hand, in a case where a value calculated by the relation is greater than 18, the steel cannot attain desired surface quality.
[65]
[66] According to the present invention, the steel sheet containing the elements
described above may further include at least one of 0.01 to 1.0% Co, 0.001 to 0.1% Zr, 0.001 to 0.1% Ti, 0.001 to 0.1% Nb, 0.0005 to 0.040% La, 0.0005 to 0.040% Ce and 0.0005 to 0.030% Ca.
[67]
[68] Cobalt Co is preferably in a range of 0.01 to 1.0% .
[69] Co is added to boost strength of the steel. Co inhibits formation of the oxide in high-temperature annealing, thereby improving wettability against a molten zinc steel sheet during molten coating. To achieve these effects, Co should be added in an amount of at least 0.01%. Meanwhile, Co added beyond a specific limit significantly reduces elongation of the steel. Thus, the Co amount may not exceed 1.0%.
[70]
[71 ] Zirconium (Zr) is preferably in a range of 0.001 to 0.1 %
[72] Zr is solved in a columnar grain boundary to increase a melting temperature of a Al- concentrated and low-melting point compound, thereby blocking formation of a liquid film at a temperature of 13000C or less and strengthening the columnar grain boundary. Zr added at less than 0.001% does not ensure such effects. On the other hand, Zr added at more than 0.1% does not yield any further effects. Therefore, Zr may be added in an amount of 0.001 to 0.1%.
[73]
[74] Titanium (Ti) and Niobium (Nb) are preferably in a range of 0.001 to 0.1%, respectively.
[75] Ti and Nb are effective in increasing strength of the steel sheet and attaining fine grain size. Ti and Nb added at less than 0.001% do not ensure such effects. Meanwhile, Ti and Nb added at more than 0.1% may raise manufacturing costs and deteriorate ferrite ductility due to excessive precipitate. Therefore, Ti and Nb may be added in an amount of 0.001 to 0.1%, respectively.
[76]
[77] Lanthanum (La) and cerium (Ce) are preferably in a range of 0.0005 to 0.04%, respectively.
[78] La and Ce decrease the size and amount of columnar grains which cause em- brittlement to the grain boundary and increase the amount of equiaxed grains with superior high-temperature ductility, thereby enhancing hot-rolling workability of a cast structure. Also La and Ce are segregated at the grain boundary to form a compound with P and S which degrade rupture strength of the grain boundary, thereby ensuring P and S to have less negative effects. However, La and Ce added at less than 0.0005% do not bring about any effects. On the other hand, La and Ce added at more than 0.04% yield no further effects. Therefore, La and Ce may be added in an amount of 0.0005 to 0.04%, respectively.
[79]
[80] Ca is preferably in a range of 0.0005 to 0.03%.
[81] Calcium Ca forms a compound together with a non-metallic inclusion such as MnO, and MnS in a molten steel to spherodize the non-metallic inclusion. This accordingly increases rupture strength of the columnar grains, allows the steel sheet to be less prone to the flange crack and increases bore expandability. However, the Ca amount exceeding 0.03% yields no further effect. Thus Ca may be added in an amount of 0.0005 to 0.030%.
[82]
[83] According to the present invention, the steel sheet contains the balance of Fe and unavoidable impurities.
[84]
[85] According to the present invention, an oxide layer on the surface of the steel sheet has a thickness of ID or less.
[86] The oxide layer formed on a metal surface in an annealing process after cold-rolling serves as an impediment between a metal matrix and a coating layer in the case of coating, thereby degrading coating adhesion. The oxide layer grown to a thickness exceeding ID causes dent defects and coating defects due to detachment of the oxide. Therefore, the oxide layer, when formed with a uniform but not great thickness in the annealing, advantageously ensures better quality in the coating layer. According to the present invention, Sb added in an amount of 0.005 to 0.1% is not oxidized but concentrated on a metal surface layer to inhibit oxidization reaction. This ensures the oxide layer to be formed with a uniform thickness of ID or less.
[87]
[88] Hereinafter, a method for manufacturing a steel sheet containing the element content range as above will be described in detail.
[89] First, a steel slab having a composition as described above is reheated at 1100 to
125O0C. At a reheating temperature of less than 11000C, the steel slab is not uniform in structure and has Ti and Nb re-solved insufficiently therein. Meanwhile, at a reheating temperature of more than 125O0C, an oxidized scale is formed and a great amount of oxides such as SiO , MnO, and Al O are generated at a boundary with the metal and inside the metal, thereby impairing surface quality. Therefore, the reheating temperature may range from 1100 to 125O0C.
[90]
[91] Thereafter, the steel slab is hot finish rolled at a temperature ranging from an Ar transformation point to 95O0C. The steel slab hot finish rolled at a temperature of an Ar transformation point is very likely to become more highly resistant to hot deformation and may have manufacturing problems. On the other hand, the steel slab hot finish
rolled at more than 9500C experiences too thick an oxidized scale and is very likely to be coarsened. Therefore, the hot finish rolled temperature may range from an Ar transform to 9500C.
[92]
[93] The hot finish rolling is followed by hot-rolling coiling. Here, a coiling temperature
(CT) should satisfy a relation of
CT=(700-(30Mn+18Si+54P+15Cr+7Mo)+150B)+20°C. According to the present invention, elements such as Mn, Si, P, Cr, and Mo are added as an alloy element associated with formation of martensite out of microstructures. However, these elements are more likely to experience segregation at a higher coiling temperature. In this case, the added Mn, Si, P, Cr, and Mo achieve less effect, thereby not assuring desired strength and workability.
[94]
[95] The above relation has been devised empirically as a means to attain desired strength and workability depending on the coiling temperature and the amount of the alloy elements. The coiling process described above ensures high-quality steel to be obtained.
[96]
[97] A hot-rolled sheet manufactured by the above process is prickled, and cold-rolled to a desired thickness, and then recrystalized and annealed at a temperature of 700 to 8600C to remove microstructural defects. At an annealing temperature less than 7000C, annealed oxides are formed minutely so that the added Sb does not yield noticeable effects. Meanwhile, at an annealing temperature exceeding 8600C, oxides are grown excessively so that the surface concentration can not be sufficiently inhibited. Mode for the Invention
[98] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[99] [Example]
[100] A steel slab containing elements as noted in Table 1 below was heated at 12000C to be produced. Then the steel slab was hot rolled and coiled at a temperature(+20°C) satisfying relation 2 and cold-rolled to manufacture a cold-rolled steel sheet. Subsequently, the cold rolled steel strip was annealed and heat treated in an N -10%H O atmosphere at a temperature of 780 to 8300C and at a heating rate of 3°C/sec per 90 seconds. Thereafter, the steel strip was coated in a Zn bath having a temperature of 4600C and an Al range of 0.12 to 0.19%, and the coated steel was alloyed and heat- treated at a temperature of 540 to 5600C for 24 seconds. Then, the steel sheet was observed to identify surface quality.
[102] In Table 2 below, the category of coating appearance includes non-coating, O for having no other coating defects and a defect name for any defect that occurs. Also, to evaluate the category of coating adhesion, the coating sheet was cut into a size of 20mmx50mm and subjected to a 60° bending test. Then, the coating sheet was straightened out to tape a bent portion. Here, a coating layer detached had a width measured as below.
[103] © : when no coating was detached or a coating had a width less than lmm [104] O : when the coating detached had a width ranging from 1 to less than 3mm [105] Δ : when the coating detached had a width ranging from 3 to less than 5mm [106] x : when the coating detached had a width of 5mm or more [107] Table 1
[108] [109] [HO] Table 2
[111] [112] As seen in Table 2, Inventive Steels 1 to 11 satisfying the element content range and manufacturing method of the present invention can be manufactured as a high strength DP steel superior in coating surface properties and strength elongation balance (TSxEl).
[113] [114] However, Comparative steels 12 to 16 not satisfying the element content range and manufacturing method of the present invention were found inferior in terms of coating surface properties and strength elongation balance.
[115] [116] Moreover, FIG. 1 shows the shape of oxides of Inventive Steel 11 and Comparative Steel 16, respectively depending on addition or non-addition of Sb. FIG. IA denotes Comparative Steel 16 and FIG. IB denotes Inventive Steel 11. As shown in FIG. 1, Inventive Steel 11 shows an oxide whose grains are noticeably smaller. That is, the
oxide growth is inhibited due to addition of Sb.
[117] In addition, FIG. 2 shows the size distribution of oxides formed on a surface of
Inventive Steel 11. In Inventive Steels, the oxides formed on a metal surface in an annealing process have sizes stably distributed around ID or less. That is, the minute oxides uniformly distributed serve to form a more uniform coating layer.
[118]
[119]
[120]
[121]
Claims
[1] A high strength Zn-coated steel sheet having excellent mechanical properties and surface quality comprising, by weight:
0.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, <0.03% S, 0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel sheet satisfying a relation of
5<(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)<18 and having an oxide layer with a thickness of ID or less on a surface thereof.
[2] The high strength Zn-coated steel sheet of claim 1, wherein a critical oxide thickness of the steel sheet is ID or less in a hot-rolling process.
[3] The high strength Zn-coated steel sheet of claim 1, wherein the oxide layer is formed in an annealing process after cold-rolling.
[4] The high strength Zn-coated steel sheet of claim 1, further comprising, by weight, at least one of 0.01 to 1.0% Co, 0.001 to 0.1% Zr, 0.001 to 0.1% Ti, 0.001 to 0.1% Nb, 0.0005 to 0.040% La, 0.0005 to 0.040% Ce and 0.0005 to 0.030% Ca.
[5] A method for manufacturing a high strength Zn-coated steel sheet having excellent mechanical properties and surface quality, the method comprising: reheating a steel slab to 1100 to 125O0C, the steel slab comprising, by weight: 0
.01 to 0.2% C, 0.01 to 1.5% Si, 0.2 to 4.0% Mn, 0.001 to 0.1% P, <0.03% S,
0.01 to 1.5% Al, 0.001 to 0.03% N, 0.0002 to 0.005% B, 0.01 to 2.0% Cr, 0.005 to 0.5% Mo, 0.005 to 0.1% Sb, and the balance of Fe and unavoidable impurities, the steel slab satisfying a relation of
5<(7Mn+4Si+2Al+18B)/(4C+3P+20Sb)<18; hot rolling the steel slab; coiling the steel slab at a coiling temperature satisfying a relation of
CT=(700- (30Mn+ 18Si+54P+ 15Cr+7Mo)+ 150B)+20°C; pickling and cold-rolling the steel slab; and annealing the steel slab at a temperature of 7000C to 86O0C.
[6] The method of claim 5, wherein the steel slab further comprises, by weight, at least one of 0.01 to 1.0% Co, 0.001 to 0.1% Zr, 0.001 to 0.1% Ti, 0.001 to 0.1% Nb, 0.0005 to 0.040% La, 0.0005 to 0.040% Ce and 0.0005 to 0.030% Ca.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
KR1020060136999A KR20080061853A (en) | 2006-12-28 | 2006-12-28 | High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the same |
PCT/KR2007/006867 WO2008082146A1 (en) | 2006-12-28 | 2007-12-27 | High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the same |
Publications (1)
Publication Number | Publication Date |
---|---|
EP2097547A1 true EP2097547A1 (en) | 2009-09-09 |
Family
ID=39588758
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP07851792A Withdrawn EP2097547A1 (en) | 2006-12-28 | 2007-12-27 | High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the same |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP2097547A1 (en) |
JP (1) | JP5354600B2 (en) |
KR (1) | KR20080061853A (en) |
CN (1) | CN101495661A (en) |
WO (1) | WO2008082146A1 (en) |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR101153485B1 (en) * | 2008-12-24 | 2012-06-11 | 주식회사 포스코 | High-strength colled rolled steel sheet having excellent deep-drawability and yield ratio, hot-dip galvanized steel sheet using the same, alloyed hot-dip galvanized steel sheet using the same and method for manufacturing thereof |
JP4623233B2 (en) | 2009-02-02 | 2011-02-02 | Jfeスチール株式会社 | High-strength hot-dip galvanized steel sheet and manufacturing method thereof |
JP5659604B2 (en) * | 2010-07-30 | 2015-01-28 | Jfeスチール株式会社 | High strength steel plate and manufacturing method thereof |
KR101671595B1 (en) | 2011-09-28 | 2016-11-01 | 제이에프이 스틸 가부시키가이샤 | High strength steel sheet and method for manufacturing the same |
KR101353787B1 (en) * | 2011-12-26 | 2014-01-22 | 주식회사 포스코 | Ultra high strength colde rolled steel sheet having excellent weldability and bendability and method for manufacturing the same |
CN102876967B (en) * | 2012-08-06 | 2014-08-13 | 马钢(集团)控股有限公司 | Aluminum hot galvanizing dual-phase steel plate with tensile strength of 600 MPa and preparation method of aluminum hot galvanizing dual-phase steel plate |
JP2014198874A (en) * | 2013-03-29 | 2014-10-23 | 株式会社神戸製鋼所 | Steel material excellent in corrosion resistance and magnetic properties and method of producing the same |
KR102046544B1 (en) * | 2015-04-15 | 2019-11-19 | 닛폰세이테츠 가부시키가이샤 | Hot rolled steel sheet and manufacturing method |
KR101786318B1 (en) * | 2016-03-28 | 2017-10-18 | 주식회사 포스코 | Cold-rolled steel sheet and plated steel sheet having excellent yield strength and ductility and method for manufacturing thereof |
KR101899688B1 (en) * | 2016-12-23 | 2018-09-17 | 주식회사 포스코 | High strength hot-rolled steel sheet having excellent continuously producing property, high strength gavanized steel sheet having excellent surface property and plating adhesion and method for manufacturing thereof |
CN107058853A (en) * | 2017-03-17 | 2017-08-18 | 广西浩昌敏再生资源利用有限公司 | A kind of preparation method of galvanized alloy steel |
CN106987758A (en) * | 2017-03-17 | 2017-07-28 | 广西浩昌敏再生资源利用有限公司 | A kind of preparation method of plated film alloy steel products |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP3951282B2 (en) * | 2000-01-28 | 2007-08-01 | Jfeスチール株式会社 | Hot-dip galvanized steel sheet and manufacturing method thereof |
JP3809074B2 (en) * | 2001-03-30 | 2006-08-16 | 新日本製鐵株式会社 | High-strength hot-dip galvanized steel sheet with excellent plating adhesion and press formability and method for producing the same |
JP2002249847A (en) * | 2001-02-23 | 2002-09-06 | Kawasaki Steel Corp | Steel having pitting resistance |
JP4288085B2 (en) * | 2003-02-13 | 2009-07-01 | 新日本製鐵株式会社 | Hot-dip galvanized high-strength steel sheet excellent in hole expansibility and method for producing the same |
JP2006274288A (en) * | 2005-03-28 | 2006-10-12 | Jfe Steel Kk | High strength hot dip galvanized steel sheet having excellent surface appearance |
-
2006
- 2006-12-28 KR KR1020060136999A patent/KR20080061853A/en not_active Application Discontinuation
-
2007
- 2007-12-27 WO PCT/KR2007/006867 patent/WO2008082146A1/en active Application Filing
- 2007-12-27 EP EP07851792A patent/EP2097547A1/en not_active Withdrawn
- 2007-12-27 JP JP2009528186A patent/JP5354600B2/en active Active
- 2007-12-27 CN CN 200780020207 patent/CN101495661A/en active Pending
Non-Patent Citations (1)
Title |
---|
See references of WO2008082146A1 * |
Also Published As
Publication number | Publication date |
---|---|
WO2008082146A9 (en) | 2008-10-23 |
JP5354600B2 (en) | 2013-11-27 |
KR20080061853A (en) | 2008-07-03 |
WO2008082146A1 (en) | 2008-07-10 |
CN101495661A (en) | 2009-07-29 |
JP2010502845A (en) | 2010-01-28 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
KR101852277B1 (en) | Cold rolled steel sheet, method of manufacturing and vehicle | |
CN111433380B (en) | High-strength galvanized steel sheet and method for producing same | |
EP2097547A1 (en) | High strength zn-coated steel sheet having excellent mechanical properites and surface quality and the method for manufacturing the same | |
JP4730056B2 (en) | Manufacturing method of high-strength cold-rolled steel sheet with excellent stretch flange formability | |
JP7150022B2 (en) | High-strength steel sheet with excellent workability and its manufacturing method | |
KR102544884B1 (en) | High-strength hot-dip galvanized steel sheet and manufacturing method thereof | |
KR101585311B1 (en) | Method for manufacturing high strength galvanized steel sheet having excellent stability of mechanical properties, formability, and coating appearance | |
JP4542515B2 (en) | High strength cold-rolled steel sheet excellent in formability and weldability, high-strength hot-dip galvanized steel sheet, high-strength galvannealed steel sheet, manufacturing method of high-strength cold-rolled steel sheet, and manufacturing method of high-strength hot-dip galvanized steel sheet , Manufacturing method of high strength galvannealed steel sheet | |
TW201335386A (en) | Galvanized steel sheet and method for manufacturing the same | |
JP2011052317A (en) | Dual phase steel sheet and method for manufacturing the same | |
TWI433960B (en) | High strength galvanized steel sheet having excellent formability and spot weldability and method for manufacturing the same | |
JP4507851B2 (en) | High-strength cold-rolled steel sheet and manufacturing method thereof | |
EP2749665B1 (en) | High strength hot dip galvanized steel sheet having excellent deep- drawability, and method for producing same | |
JP5648237B2 (en) | Galvanized steel sheet with excellent surface quality and manufacturing method thereof | |
CN113348259A (en) | High-strength hot-dip galvanized steel sheet and method for producing same | |
JP2023027288A (en) | Galvannealed steel sheet | |
JP4414563B2 (en) | High-strength steel sheet excellent in formability and hole expansibility and method for producing the same | |
JP2004068051A (en) | High strength hot-dip galvanized steel sheet and its manufacturing method | |
JP4500197B2 (en) | Manufacturing method of high-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength galvannealed steel sheet with excellent formability and weldability | |
KR102374498B1 (en) | hot dip coated steel sheet | |
WO2023149002A1 (en) | Steel sheet | |
JPH06306533A (en) | High-strength galvannealed hot rolled steel sheet excellent in formability and weldability and production thereof | |
JP2007186789A (en) | High-strength steel sheet excellent in strength-ductility balance and deep drawability, and its manufacturing method | |
JP3872595B2 (en) | Cold rolled steel sheet with low in-plane anisotropy and excellent formability | |
KR102606996B1 (en) | High strength cold rolled steel sheet having excellent bending workability, galva-annealed steel sheet and method of manufacturing the same |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
17P | Request for examination filed |
Effective date: 20081128 |
|
AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC MT NL PL PT RO SE SI SK TR |
|
DAX | Request for extension of the european patent (deleted) | ||
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN |
|
18D | Application deemed to be withdrawn |
Effective date: 20100701 |