WO2023048448A1 - 표면 품질이 우수하고 재질 편차가 적은 고강도 냉연강판 및 이의 제조 방법 - Google Patents
표면 품질이 우수하고 재질 편차가 적은 고강도 냉연강판 및 이의 제조 방법 Download PDFInfo
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 71
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 31
- 230000007547 defect Effects 0.000 claims abstract description 56
- 229910000831 Steel Inorganic materials 0.000 claims description 115
- 239000010959 steel Substances 0.000 claims description 115
- 238000001816 cooling Methods 0.000 claims description 35
- 229910000734 martensite Inorganic materials 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 23
- 238000004804 winding Methods 0.000 claims description 21
- 229910001563 bainite Inorganic materials 0.000 claims description 20
- 238000000137 annealing Methods 0.000 claims description 19
- 238000005097 cold rolling Methods 0.000 claims description 18
- 229910000859 α-Fe Inorganic materials 0.000 claims description 15
- 229910052748 manganese Inorganic materials 0.000 claims description 14
- 238000005098 hot rolling Methods 0.000 claims description 12
- 229910052710 silicon Inorganic materials 0.000 claims description 12
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 239000000498 cooling water Substances 0.000 claims description 9
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 7
- 229910052796 boron Inorganic materials 0.000 claims description 6
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 238000003303 reheating Methods 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 5
- 238000002347 injection Methods 0.000 claims description 3
- 239000007924 injection Substances 0.000 claims description 3
- 239000000463 material Substances 0.000 description 36
- 230000000694 effects Effects 0.000 description 34
- 239000011572 manganese Substances 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 15
- 239000011651 chromium Substances 0.000 description 14
- 238000007747 plating Methods 0.000 description 14
- 239000000203 mixture Substances 0.000 description 8
- 238000005728 strengthening Methods 0.000 description 8
- 230000006866 deterioration Effects 0.000 description 7
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- 230000009466 transformation Effects 0.000 description 6
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
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- 241000219307 Atriplex rosea Species 0.000 description 1
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- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 229910001335 Galvanized steel Inorganic materials 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
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
- B21C47/02—Winding-up or coiling
-
- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—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
- C22C38/04—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
Definitions
- the present invention relates to a high-strength cold-rolled steel sheet used for structural members having a large amount of molding, such as pillars, seat rails, and members of automobile bodies, and a method for manufacturing the same, and more particularly, automotive parts having excellent surface quality and low material variation. It relates to a high-strength cold-rolled steel sheet that can be suitably used for and a manufacturing method thereof.
- High-strength steels used in conventional automobile bodies include DP (Dual Phase) steel composed of a soft ferrite matrix and hard martensite two-phase, TRIP (Transformation Induced Plasticity) steel using transformation-induced plasticity of retained austenite, or ferrite and hard steel.
- DP Dual Phase
- TRIP Transformation Induced Plasticity
- CP Complexed Phase steel composed of a complex structure of bainite or martensite.
- the surface defect due to the dent in the furnace refers to a surface defect of the steel sheet formed by contact between the steel sheet and the roll during sheet passing, in which metal-based oxides on the surface of the steel sheet are adsorbed and accumulated on the annealing furnace rolls.
- Patent Document 1 discloses a process of cold rolling a hot-rolled steel sheet containing a low-temperature transformation phase of 60% or more by volume at a cold reduction ratio of more than 60% and less than 80%, and ferrite and austenite steel sheets after cold rolling.
- a high-strength cold-rolled steel sheet and its manufacturing method are presented through a continuous annealing process in the second phase.
- the cold-rolled steel sheet obtained from Patent Document 1 has a low strength of 370 to 590 MPa, so it is difficult to apply to an automobile shock-resistant member and has a problem that it is limited only to the use of inner and outer panels.
- Patent Document 2 discloses a method of manufacturing a cold-rolled steel sheet having high strength and high ductility at the same time by utilizing a tempered martensite phase and having excellent sheet shape after continuous annealing.
- the technology of Patent Document 2 has a problem of poor weldability due to a high carbon content of 0.2% or more in the steel, and a problem of surface defects due to dents in the furnace due to a large amount of Si.
- Patent Document 1 Korean Patent Publication No. 2004-0066935
- Patent Document 2 Japanese Unexamined Patent Publication No. 2010-090432
- the present invention is intended to provide a high-strength cold-rolled steel sheet with excellent surface quality and low material variation and a manufacturing method thereof.
- C 0.05 to 0.3%
- Si 0.01 to 2.0%
- Mn 1.5 to 3.0%
- Al 0.01 to 0.1%
- P 0.001 to 0.015%
- S 0.001 to 0.01%
- N 0.001 to 0.001% 0.01%
- microstructure As a microstructure, by area%, ferrite: 50% or more, balance: including bainite and martensite,
- a high-strength cold-rolled steel sheet having an average number of surface defects satisfying at least one condition of a depth of 100 ⁇ m or more and a short side length of 1 mm or more is less than 10/m 2 .
- Another aspect of the present invention is,
- C 0.05 to 0.3%
- Si 0.01 to 2.0%
- Mn 1.5 to 3.0%
- Al 0.01 to 0.1%
- P 0.001 to 0.015%
- S 0.001 to 0.01%
- N 0.001 to 0.001% Reheating a steel slab containing 0.01%, the balance Fe and other unavoidable impurities, and satisfying a value defined by the following relational expression 1 of 0.6 or more and less than 0.9 to 1100 to 1350 ° C;
- the winding step is controlled so that the surface temperature (Te) of both ends in the width direction meets 601 to 700 ° C and the surface temperature (Tc) of the central portion meets 450 to 600 ° C, based on the entire width of the steel sheet.
- Te surface temperature
- Tc surface temperature
- Example 1 shows pictures taken with a general low-magnification camera of surface defects of each cold-rolled steel sheet obtained from Inventive Example 1 and Comparative Example 1 of the present invention.
- Figure 2 shows a photograph taken with a high-magnification scanning cell microscope (SEM) of the surface defect defined in the present invention.
- the inventors of the present invention conducted intensive studies to provide a cold-rolled steel sheet that satisfies all of the above-described characteristics while solving the problems of the prior art. As a result, the composition and manufacturing conditions of the steel sheet were optimized, and the microstructure and surface defects were controlled By doing so, it was found that the above object can be achieved and the present invention has been completed.
- the product of tensile strength and elongation satisfies 12,000 MPa% or more even though it has a high strength of 780 MPa or more, so that a structure such as a filler that requires a stable strength-elongation balance and shock absorption among parts constituting an automobile body
- a high-strength cold-rolled steel sheet that can be suitably applied to member parts can be effectively provided.
- C 0.05 to 0.3%
- Si 0.01 to 2.0%
- Mn 1.5 to 3.0%
- Al 0.01 to 0.1%
- P 0.001 to 0.015%
- S 0.001 to 0.01%
- N 0.001 to 0.01%
- the balance including Fe and other unavoidable impurities.
- the carbon (C) is a very important component in securing a martensitic structure effective in strengthening steel.
- the martensite phase and bainite phase fractions increase, resulting in an increase in tensile strength. Therefore, in order to secure high strength, the lower limit of the C content is controlled to 0.05%.
- the fraction of the martensite phase and bainite phase which are hard phases, increases by expanding the austenite region during the two-phase annealing, and the fraction of the ferrite phase, which is a soft phase, decreases, resulting in poor formability and poor weldability. It happens. Therefore, the upper limit of the C content is controlled to 0.3%.
- the lower limit of the C content may be 0.06%, or the upper limit of the C content may be 0.12%.
- the silicon (Si) is an element advantageous for deoxidizing molten steel, having a solid solution strengthening effect, and delaying the formation of coarse carbides to improve formability.
- Si content is less than 0.01%, it is difficult to improve formability due to the small effect described above.
- Si content exceeds 2.0%, red scale due to Si is severely formed on the surface of the steel sheet during hot rolling. Accordingly, surface defects are generated, or non-plating occurs due to concentration on the surface during the annealing process.
- the plating adhesion is inferior due to the formation of surface oxide, and the surface quality is very poor. Therefore, in the present invention, the Si content is controlled to 0.01 to 2.0%.
- the lower limit of the Si content may be 0.4%, or the upper limit of the Si content may be 1.2%.
- the aluminum (Al) is a component mainly added for deoxidation. If the Al content is less than 0.01%, the addition effect is insufficient. On the other hand, when the Al content exceeds 0.1%, AlN is formed in combination with nitrogen, so that corner cracks are likely to occur in the slab during cast casting, and defects due to inclusion formation are likely to occur. Therefore, in the present invention, the Al content is controlled to 0.01 to 0.1%. On the other hand, in terms of further improving the above effects, more preferably, the lower limit of the Al content may be 0.015%, or the upper limit of the Al content may be 0.06%.
- the phosphorus (P) is an alloying element having a very large solid solution strengthening effect, and is characterized in that a large strengthening effect can be obtained even with a small content.
- P phosphorus
- brittleness occurs due to grain boundary segregation, and fine cracks easily occur during molding, greatly deteriorating ductility and impact resistance.
- the upper limit of the P content is controlled to 0.015%.
- the manufacturing cost is excessively required to meet this, which is not only economically disadvantageous, but also the strength obtained is insufficient, so the lower limit of the P content is controlled to 0.001% or more.
- the P content it is preferable to control the P content to 0.001 to 0.015%.
- the lower limit of the P content may be 0.003%, or the upper limit of the P content may be 0.012%.
- S Sulfur
- the S content is an impurity present in steel, and when the S content exceeds 0.01%, it combines with Mn to form non-metallic inclusions. Accordingly, it is easy to generate fine cracks during cutting and processing of steel, and the elongation flange property and impact resistance are improved. There is a problem that is greatly aggravating.
- the S content in order to manufacture the S content to be less than 0.001%, there is a problem in that productivity is reduced due to the long time required during steelmaking operation. Therefore, in the present invention, it is preferable to control the S content to 0.001 to 0.01%.
- the lower limit of the S content may be 0.002%, or the upper limit of the S content may be 0.007%.
- N Nitrogen
- the solid solution strengthening effect of N is superior to that of carbon, but as the amount of N in steel increases, there is a problem in that toughness decreases significantly.
- the lower limit of the N content may be 0.002%, and the upper limit of the N content may be 0.006%.
- the cold-rolled steel sheet by weight%, Cr: 1.0% or less (including 0%), Mo: 0.2% or less (including 0%) and B : 0.005% or less (including 0%) may further include one or more selected from among.
- Cr 1.0% or less
- Mo 0.2% or less
- B 0.005% or less
- Chromium (Cr) is a component added to improve the hardenability of steel and secure high strength, and is an element that plays a very important role in the formation of martensite. It is advantageous. Therefore, the Cr may be selectively added for the above effect. However, when the Cr content exceeds 1.0%, the aforementioned effect is saturated, and there is a problem in that cold rolling property deteriorates due to an excessive increase in hot rolling strength. In addition, since the martensite fraction greatly increases after annealing, there is a problem of reducing the elongation, so the upper limit of the Cr content is controlled to 1.0% or less. On the other hand, in terms of further improving the above-mentioned effect, more preferably, the lower limit of the Cr content may be 0.01%, or the upper limit of the Cr content may be 0.8%.
- Molybdenum (Mo) is an element that suppresses pearlite formation and increases hardenability. Therefore, in order to secure the above effect, Mo may be selectively added in the present invention. However, when the Mo content exceeds 0.2%, the strength improvement effect is not greatly increased, but the ductility is deteriorated, which may be economically disadvantageous. Therefore, the Mo content is preferably controlled to 0.2% or less. On the other hand, in terms of further improving the above-mentioned effect, more preferably, the lower limit of the Mo content may be 0.01%, or the upper limit of the Mo content may be 0.1%.
- B Boron
- the B when present in a solid solution state in steel, has an effect of improving brittleness of steel in a low temperature range by stabilizing grain boundaries, and greatly increases hardenability of steel. Therefore, the B may be selectively added for the above effect.
- the upper limit of B exceeds 0.005%, recrystallization is delayed during annealing, and oxide is formed on the surface, resulting in poor plating properties. Therefore, it is preferable to control the content of B to 0.005% or less.
- the lower limit of the B content may be 0.0003%, or the upper limit of the B content may be 0.0025%.
- the remaining component of the present invention is iron (Fe).
- Fe iron
- unintended impurities may inevitably be mixed due to raw materials or surrounding environmental variables in a normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the ordinary steel manufacturing process, not all of them are specifically mentioned in this specification.
- the high-strength cold-rolled steel sheet may have a value defined by the following relational expression 1 of 0.6 or more and less than 0.9, thereby minimizing the material deviation of the cold-rolled steel sheet and suppressing the occurrence of surface defects to achieve the desired result. material can be obtained.
- the relational expression 1 is an expression representing the hardenability of the steel material according to the composition of the present invention, and the coefficient in front of each element quantitatively represents the scale that the corresponding element contributes to the hardenability.
- the hardenability of the steel is high, it is advantageous to secure hard low-temperature transformation phases such as bainite and martensite phases, contributing to strength improvement, and when the hardenability is low, ferrite transformation is promoted, which is disadvantageous in securing strength.
- the value defined by the relational expression 1 in order to secure high strength of 780 MPa or more of tensile strength (TS), which is the target in the present invention, the value defined by the relational expression 1 must satisfy 0.6 or more.
- the value defined by the relational expression 1 when the value defined by the relational expression 1 is 0.9 or more, the strength is excessively high, resulting in deterioration of elongation.
- the value defined by the relational expression 1 is 0.9 or more, the phase transformation of ferrite is greatly delayed in the step of cooling the hot-rolled steel sheet to 450 to 700 ° C. at an average cooling rate of 10 to 70 ° C. / s immediately after hot rolling.
- the value defined by the relational expression 1 it is preferable to control the value defined by the relational expression 1 to satisfy 0.6 or more and less than 0.9.
- the lower limit of the value defined by the relational expression 1 may be 0.62, or the upper limit of the value defined by the relational expression 1 may be 0.84.
- the high-strength cold-rolled steel sheet includes ferrite: 50% or more, balance: bainite and martensite, in area%.
- ferrite 50% or more
- balance: bainite and martensite in area%.
- the microstructures if ferrite is less than 50%, there is a problem of poor formability due to insufficient elongation. Also, the remainder may be 50% or less as bainite and martensite. If the sum of the bainite and martensite exceeds 50%, there is a problem in that the strength is too high and the elongation is insufficient.
- the microstructure of the high-strength cold-rolled steel sheet is, in area %, ferrite: 50 to 85% and bainite and martensite Total: May contain 15-50%.
- the microstructure of the high-strength cold-rolled steel sheet may include, more preferably, ferrite: 66 to 75% in area %.
- the microstructure of the high-strength cold-rolled steel sheet may include bainite: 3-7%, and/or martensite: 19- may contain 31%.
- bainite 3-7%
- martensite 19- may contain 31%.
- the bainite is less than 3%
- a problem may occur that the target strength is not met, and if it exceeds 7%, the strength is high but the elongation is low.
- the martensite is less than 19%, a problem may occur that the target strength is not reached, and if it exceeds 31%, the strength is high but the elongation is low.
- the average number of surface defects that satisfy at least one condition of a depth of 100 ⁇ m or more and a short side length of 1 mm or more is less than 10 / m 2 (0 / m 2 included).
- the condition of 'depth is 100 ⁇ m or more' or 'short side length is 1 mm or more' is only a sufficient criterion for measuring the average number of surface defects. do.
- the upper limit values of the aforementioned depth and short side length are not particularly limited.
- a surface defect means a defect having a groove shape, and specifically, a defect in the form of a depression in the thickness direction, and refers to a defect that can be confirmed when the surface of the steel sheet is observed with the naked eye.
- the depth of the surface defect is the 'maximum depth' in the thickness direction of the groove-shaped defect, based on the cross section in the thickness direction of the cold-rolled steel sheet (ie, on a cross-sectional basis, meaning a direction perpendicular to the rolling direction).
- the short side length of the surface defect may mean the shortest length passing through the point where the maximum depth is obtained based on the surface of the cold-rolled steel sheet.
- the inventors of the present invention have been intensively researched to provide a cold-rolled steel sheet capable of solving the problems of the prior art and minimizing surface defects and material variations while securing desired levels of strength and formability.
- the above effect can be secured by controlling the average number of surface defects satisfying at least one of the aforementioned depth of 100 ⁇ m or more and short side length of 1 mm or more to less than 10/m 2 . That is, in the present invention, if the average number of surface defects is 10/m 2 or more, surface dents may occur. On the other hand, in terms of further improving the above-described effect, preferably, the average number of the above-described surface defects may be 8/m 2 or less.
- the present inventors are conducting additional research to provide a cold-rolled steel sheet capable of securing desired levels of strength and formability at the same time without affecting material variation, even if surface defects exist on the surface of the steel sheet. repeated.
- surface defect characteristics of a level that does not affect material variation or the like were additionally discovered.
- the maximum depth of the surface defect may satisfy 500 ⁇ m or less. In this case, the maximum depth of the surface defect may mean the maximum value of the depth of each surface defect existing on the surface of the steel sheet.
- the difference between the yield strength (YS) of both ends and the central portion may be 100 MPa or less.
- the 'both ends' refers to a 30% section (total: corresponding to 60%) from both ends based on the total width (referred to as 100%) in the width direction of the cold-rolled steel sheet, and the 'central part' refers to the cold-rolled steel sheet Based on the entire width in the width direction of the steel sheet, it may mean the remaining 40% section excluding the both ends.
- the cold-rolled steel sheet may have a tensile strength (TS) of 780 MPa or more, preferably 780 MPa or more and less than 1180 MPa, and more preferably 800 MPa or more and 1100 MPa or less. If the tensile strength of the cold-rolled steel sheet is less than 780 MPa, there may be a problem of not satisfying the target strength required for the applied part, and if it exceeds 1100 MPa, cracks may occur during molding of the part or the impact resistance of the part may be significantly reduced. .
- TS tensile strength
- the yield strength (YS) of the cold-rolled steel sheet may be 380 MPa or more, more preferably 390 MPa or more and 650 MPa or less. If the yield strength of the cold-rolled steel sheet is less than 380 MPa, a problem of deteriorating collision resistance of the part may occur, and if it exceeds 650 MPa, a problem of deterioration in formability may occur.
- the cold-rolled steel sheet has a product of tensile strength and elongation of 12,000 MPa% or more (more preferably, 12,000 MPa% or more and 16,500 MPa% or less, most preferably 12,000 MPa% or more and 16,200 MPa%). below).
- the cold-rolled steel sheet may further include a plating layer formed on a surface thereof.
- the plating layer may be formed by a plating process to be described later.
- the composition of the plating layer can be applied differently depending on the purpose, it is not particularly limited in the present specification, and a zinc-based plating layer and the like can be cited as an example.
- the manufacturing method of the cold-rolled steel sheet according to the present invention does not necessarily mean that it must be manufactured by the following manufacturing method.
- a steel slab meeting the above composition is reheated to 1100-1350°C.
- the composition of the steel slab is the same as that of the above-mentioned cold-rolled steel sheet, and at this time, the description of the cold-rolled steel sheet described above is equally applied to the reason for adding each component and the reason for limiting the content of each component in the steel slab.
- the reheating temperature of the steel slab is less than 1100 ° C., alloy elements segregated in the center of the slab remain, and the starting temperature of hot rolling is too low, causing a problem that the rolling load becomes severe.
- the reheating temperature of the steel slab exceeds 1350° C.
- a problem in that strength is lowered due to coarsening of austenite crystal grains occurs. Therefore, in the present invention, it is preferable to control the reheating temperature of the steel slab to 1100 to 1350 ° C.
- the reheated steel slab is hot rolled at 850 to 1150 ° C.
- the temperature of the hot rolling exceeds 1150° C.
- the temperature of the hot-rolled steel sheet increases, resulting in a coarse grain size and deterioration in surface quality of the hot-rolled steel sheet.
- the temperature of the hot rolling is less than 850 ° C., due to the development of elongated grains due to excessive recrystallization delay, the load during rolling increases and the temperature at both ends decreases significantly, resulting in an uneven microstructure during cooling, resulting in increased material deviation. And formability is also deteriorated.
- the hot-rolled steel sheet is cooled to 450 to 700°C at an average cooling rate of 10 to 70°C/s (more preferably, 20 to 50°C/s).
- an average cooling rate 10 to 70°C/s (more preferably, 20 to 50°C/s).
- hot-rolled oxides increase and are adsorbed to the rolls during annealing, resulting in accumulation of oxides on the rolls, and friction between the steel sheet and the rolls during sheet passing, causing surface defects such as dent defects on the surface of the steel sheet. do.
- the hot-rolled oxide remains on the steel sheet, plating quality and plating adhesion are deteriorated during plating of the steel sheet.
- the hot-rolled steel sheet with large material variation not only deteriorates in shape during cold rolling, but also causes material variation by position in the width direction even in the final annealed material, so the present inventors have conducted intensive research to solve the above-mentioned problem. As a result, a manufacturing method of differently controlling the temperature of both ends and the central part in the winding step has been sought.
- the surface temperature (Te) of both ends in the width direction based on the entire width of the steel sheet during the winding is controlled to satisfy 601 to 700 ° C, and the surface temperature (Tc) of the central portion to meet 450 to 600 ° C.
- the 'width direction of the steel sheet' means a direction perpendicular to the transport direction of the steel sheet based on the surface of the steel sheet.
- the Te is less than 601 ° C, there is a problem that material deviation due to overcooling of both ends is intensified, and if the Te exceeds 700 ° C, there is a problem that material deviation and surface defects are intensified due to deterioration of the central part.
- the Tc is less than 450 ° C, the temperature difference between the central part and both ends becomes severe, resulting in a problem of material deviation, and if the Tc exceeds 600 ° C, the temperature of the central part is too high, resulting in material deviation and surface defects.
- the cooling water injected at both ends may be blocked before reaching the steel sheet, or the amount of cooling water injected may be controlled differently , or both methods may be combined.
- the amount of cooling water injected onto both ends in the width direction is higher than the injection amount of the cooling water injected into the central portion excluding the both ends.
- the amount of cooling water can be controlled to be larger.
- the winding step is the surface temperature of the both ends and the surface temperature of the central part
- the difference (Te-Tc) can be 150 ° C or less.
- the value of Te-Tc exceeds 150 ° C.
- the lower limit may not be separately limited, and may be preferably 0°C.
- the lower limit of the Te-Tc value may be 50°C
- the upper limit of the Te-Tc value may be 90°C.
- the above-described winding step may optionally be moved into a heat-retaining cover and maintained at a temperature of 400 to 500° C. for 6 hours or more.
- the winding step by maintaining in the heat-retaining cover for a long time, when the steel sheet is maintained at a temperature in the range of 601 to 700 ° C and 450 to 600 ° C, respectively, both ends and the center in the width direction of the steel plate for a long time, both ends and the center of the coil lengthwise.
- a large amount of uniformly formed bainite structure is excellent in shape quality, and it is possible to manufacture a cold-rolled steel sheet having a uniform thickness with a small rolling load during cold rolling.
- the surface temperature of the steel sheet can be adjusted to 400 to 500°C.
- the surface temperature of the steel sheet is less than 400 ° C, the above-mentioned effect cannot be secured, and if it exceeds 500 ° C, coarse carbides are formed locally and hot-rolled oxides increase, thereby increasing the formability and surface of the steel. Quality may deteriorate.
- the holding time in the heat insulating cover is less than 6 hours, material deviation may occur, and the upper limit of the holding time in the heat insulating cover is not particularly limited, but may be 8 hours or less as an example.
- the rolled steel sheet can be stored in the heat-retaining cover within 90 minutes immediately after winding, and if the time before being accommodated in the heat-retaining cover exceeds 90 minutes, due to excessive air cooling
- the range of 450 to 600 ° C. may not be satisfied due to supercooling occurring in the central portion in the width direction.
- air cooling or water cooling may be additionally performed to room temperature after the step of maintaining the heat insulating cover.
- the coiled steel sheet is subjected to cold rolling at a cold rolling reduction of 40 to 70%. If the cold reduction ratio is less than 40%, it is difficult to secure the target thickness and it is difficult to correct the shape of the steel sheet. On the other hand, if it exceeds 70%, cracks at the edge of the steel sheet are likely to occur and the cold rolling load is There is a problem to come. Therefore, in the present invention, it is preferable to limit the cold rolling reduction to 40 to 70%.
- the cold-rolled steel sheet is continuously annealed at 740 to 900 ° C. If the annealing temperature is less than 740 ° C, non-recrystallization may occur, resulting in insufficient strength and elongation, and if the annealing temperature exceeds 900 ° C, surface oxide may occur. On the other hand, in terms of further improving the above-mentioned effect, more preferably the annealing temperature may be 750 ⁇ 850 °C.
- the continuous annealing step optionally primary cooling to 650 ⁇ 700 °C at a cooling rate of 1 ⁇ 10 °C / sec; After the primary cooling step, secondary cooling at a cooling rate of 11 to 20 °C/sec from Ms-100 °C to Ms+100 °C; may be further included.
- an overaging step may be further included while selectively maintaining a constant temperature. the primary cooling step; Strength and elongation can be further improved by satisfying the conditions of the secondary cooling step and overaging step.
- the Ms means the starting temperature at which martensite is generated when the steel sheet is cooled after annealing, and from the following relational expression 2 can be saved
- a step of plating preferably, hot-dip galvanizing
- the cold-rolled steel sheet may be further included, and a coated steel sheet may be obtained by performing the plating.
- a steel slab satisfying the composition of Table 1 below was reheated at 1200 ° C, hot rolled at 900 ° C, cooled to 450 to 700 ° C at a cooling rate of 20 to 50 ° C / s, and then wound.
- the surface temperature (Te) of the steel sheet at both ends of the 30% section from both ends and the surface temperature (Tc) of the remaining 40% of the central portion of the steel sheet are as follows, based on the total width of the steel sheet in the width direction
- the amount of cooling water injected into the central portion excluding the both ends was controlled to be greater than the amount of cooling water injected onto both end portions in the width direction of the steel sheet.
- the rolled hot-rolled steel sheet was moved into the heat-retaining cover and controlled to satisfy the average temperature and holding time before and after charging into the cover as conditions for the heat-retaining cover described in Table 2 below. Subsequently, the hot-rolled steel sheet is cold-rolled at a cold rolling reduction of 50%, continuously annealed at 800°C, followed by primary cooling at an average cooling rate of 8°C/s to 670°C, and then average cooling rate up to Ms+100°C. A cold-rolled steel sheet was obtained by secondary cooling at 12°C/s.
- the average number of surface defects is obtained by visually observing the surface of the manufactured steel sheet and measuring the average number of surface defects that satisfy at least one condition of a depth of 100 ⁇ m or more and a short side length of 1 mm or more.
- the maximum depth of the surface defect was measured in the same manner as described herein.
- the yield strength was measured in the same manner as described above, and the material deviation in the width direction was measured and shown in Tables 4 and 5 below. was
- Comparative Examples 1 to 16 that do not satisfy at least one of the composition and manufacturing conditions of the present invention, material variation is poor, surface defects occur, and / or it is difficult to secure desired physical properties in the present invention.
- Comparative Steel 1 did not satisfy Relational Expression 1 because the amount of Si added exceeded 2.0%. Therefore, in the case of Comparative Examples 13 and 14 using Comparative Steel 1, even if the material deviation is good by satisfying the manufacturing conditions presented in the present invention, a dent problem occurs due to the accumulation of Si oxide in the annealing furnace, resulting in product surface defects. There was a problem that the average number exceeded the target value.
- Comparative Steel 2 did not satisfy Relational Equation 1 because the amount of added alloy was small. Therefore, in the case of Comparative Examples 15 and 16 using Comparative Steel 2, even though surface defects and material variation were good by satisfying the manufacturing conditions presented in the present invention, the tensile strength was less than 780 MPa and did not satisfy the target material.
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Abstract
Description
Claims (13)
- 중량%로, C: 0.05∼0.3%, Si: 0.01∼2.0%, Mn: 1.5∼3.0%, Al: 0.01∼0.1%, P: 0.001∼0.015%, S: 0.001∼0.01%, N: 0.001∼0.01%, 잔부 Fe 및 기타 불가피한 불순물을 포함하고,하기 관계식 1로 정의되는 값은 0.6 이상 0.9 미만을 충족하고,미세 조직으로서, 면적%로, 페라이트: 50% 이상, 잔부: 베이나이트 및 마르텐사이트를 포함하고,깊이가 100㎛ 이상 및 단변 길이가 1㎜ 이상 중 하나 이상의 조건을 충족하는 표면 결함의 평균 개수는 10개/m2 미만인, 고강도 냉연강판.[관계식 1]C + (1.3×Si+Mn)/6 + (Cr+1.2×Mo)/5 + 100×B(상기 관계식 1에 있어서, 상기 C, Si, Mn, Cr, Mo 및 B는 각 원소에 대한 중량% 평균 함량을 나타낸다. 또한, 상기 각 원소가 미첨가되는 경우에는 0을 대입한다.)
- 청구항 1에 있어서,상기 미세 조직은, 면적%로, 페라이트: 50~85% 및 베이나이트와 마르텐사이트의 합계: 15~50%를 포함하는, 고강도 냉연강판.
- 청구항 1에 있어서,상기 미세 조직은, 면적%로, 페라이트: 66~75%를 포함하는, 고강도 냉연강판.
- 청구항 3에 있어서,상기 미세 조직은, 면적%로, 베이나이트: 3~7%를 포함하는, 고강도 냉연강판.
- 청구항 3에 있어서,상기 미세 조직은, 면적%로, 마르텐사이트: 19~31%를 포함하는, 고강도 냉연강판.
- 청구항 1에 있어서,중량%로, Cr: 1.0% 이하(0% 포함), Mo: 0.2% 이하 (0% 포함) 및 B: 0.005% 이하 (0% 포함) 중에서 선택된 1종 이상을 더 포함하는, 고강도 냉연강판.
- 청구항 1에 있어서,인장강도가 780MPa 이상이고, 항복강도가 380MPa 이상인, 고강도 냉연강판.
- 청구항 1에 있어서,인장강도와 연신율의 곱이 12,000 MPa% 이상인, 고강도 냉연강판.
- 청구항 1에 있어서,상기 냉연강판의 폭방향으로, 양단부와 중앙부의 항복강도의 차이가 100MPa 이하, 고강도 냉연강판.
- 중량%로, C: 0.05∼0.3%, Si: 0.01∼2.0%, Mn: 1.5∼3.0%, Al: 0.01∼0.1%, P: 0.001∼0.015%, S: 0.001∼0.01%, N: 0.001∼0.01%, 잔부 Fe 및 기타 불가피한 불순물을 포함하고, 하기 관계식 1로 정의되는 값이 0.6 이상 0.9 미만을 충족하는 강 슬라브를 1100~1350℃로 재가열하는 단계;상기 재가열된 강 슬라브를 850~1150℃에서 열간압연하는 단계;상기 열간압연된 강판을 450~700℃까지 평균 냉각속도 10~70℃/s로 냉각하는 단계;상기 냉각된 강판의 450~700℃에서 권취하는 단계;상기 권취된 강판을 40~70%의 압하율로 냉간압연하는 단계; 및상기 냉간압연된 강판을 740~900℃에서 연속 소둔하는 단계;를 포함하고,상기 권취하는 단계는 강판의 전체 폭을 기준으로, 폭방향으로 양단부의 표면 온도(Te)가 601~700℃를 충족하고, 중앙부의 표면 온도(Tc)가 450~600℃를 충족하도록 제어하는, 고강도 냉연강판의 제조방법.[관계식 1]C + (1.3×Si+Mn)/6 + (Cr+1.2×Mo)/5 + 100×B(상기 관계식 1에 있어서, 상기 C, Si, Mn, Cr, Mo 및 B는 각 원소에 대한 중량% 평균 함량을 나타낸다. 또한, 상기 각 원소가 미첨가되는 경우에는 0을 대입한다.)
- 청구항 10에 있어서,상기 권취하는 단계 이후, 상기 권취된 강판을 보열 커버 내로 이동시켜 400~500℃ 범위에서 6시간 이상 유지하는 단계;를 더 포함하는, 고강도 냉연강판의 제조방법.
- 청구항 10에 있어서,상기 권취하는 단계는 상기 양단부의 표면 온도와 중앙부의 표면 온도의 차(Te-Tc)가 150℃ 이하를 충족하도록 제어하는, 고강도 냉연강판의 제조방법.
- 청구항 10에 있어서,상기 냉각하는 단계는, 강판의 전체 폭을 기준으로, 폭방향으로 양단부 상에 주입되는 냉각수의 주수량보다, 상기 양단부를 제외한 중앙부 상에 주입되는 냉각수의 주수량이 더 크도록 제어하는, 고강도 냉연강판의 제조방법.
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WO2020203159A1 (ja) * | 2019-03-29 | 2020-10-08 | 日本製鉄株式会社 | 鋼板及びその製造方法 |
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KR20210080044A (ko) * | 2019-12-20 | 2021-06-30 | 주식회사 포스코 | 강도 및 단면 감소율 편차가 균일한 선재 및 그 제조방법 |
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2021
- 2021-09-24 KR KR1020210126115A patent/KR20230043352A/ko unknown
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2022
- 2022-09-20 WO PCT/KR2022/014012 patent/WO2023048448A1/ko active Application Filing
- 2022-09-20 CN CN202280063315.3A patent/CN118019871A/zh active Pending
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KR20040066935A (ko) | 2002-06-25 | 2004-07-27 | 제이에프이 스틸 가부시키가이샤 | 고강도 냉연강판 및 그 제조 방법 |
JP2010090432A (ja) | 2008-10-08 | 2010-04-22 | Jfe Steel Corp | 延性に優れる超高強度冷延鋼板およびその製造方法 |
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WO2020203159A1 (ja) * | 2019-03-29 | 2020-10-08 | 日本製鉄株式会社 | 鋼板及びその製造方法 |
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