WO2023027528A1 - 우수한 용접성, 강도 및 성형성을 갖는 냉연 강판 및 그 제조방법 - Google Patents
우수한 용접성, 강도 및 성형성을 갖는 냉연 강판 및 그 제조방법 Download PDFInfo
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 50
- 238000000034 method Methods 0.000 title claims abstract description 30
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- 229910000831 Steel Inorganic materials 0.000 claims description 96
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- 238000007747 plating Methods 0.000 claims description 8
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- 229910052748 manganese Inorganic materials 0.000 claims description 5
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- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
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- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
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- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 229910000794 TRIP steel Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
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- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- 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
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
-
- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/002—Bainite
Definitions
- the present invention relates to a cold-rolled steel sheet having excellent weldability, strength and formability and a manufacturing method thereof.
- Patent Document 1 Patent Publication No. 2017-7015003
- One aspect of the present invention is to provide a cold-rolled steel sheet having excellent weldability, strength and formability and a manufacturing method thereof.
- C 0.10 ⁇ 0.16%, Si: 0.3 ⁇ 0.8%, Al: 0.01 ⁇ 0.5%, Mn: 2.0 ⁇ 3.0%, Cr: 0.001 ⁇ 0.5%, Mo: 0.001 ⁇ 0.5%, B: 0.0001 ⁇ 0.001%, Nb: 0.001 ⁇ 0.05%, Ti: 0.001 ⁇ 0.05%, P: 0.04% or less (excluding 0%), S: 0.01% or less (excluding 0%), N : 0.01% or less (excluding 0%), including the balance Fe and other unavoidable unspoken statements,
- microstructure in % area, ferrite: less than or equal to 10% (excluding 0%), retained austenite: more than 1% and less than or equal to 5%, martensite: greater than or equal to 25% and less than 50% and bainite: greater than or equal to 35% and less than 70% including,
- An average size of martensite (MA) present in the bainite is 0.35 to 0.55 ⁇ m, providing a cold-rolled steel sheet.
- the alloy component of the cold-rolled steel sheet in order to have high local formability, can be controlled so that the value defined by the following relational expression 1 satisfies 70 or more.
- the alloy component of the cold-rolled steel sheet in order to have high local formability, can be controlled so that the value defined by the following relational expression 2 satisfies 270 or more and 330 or less there is.
- the value defined by the following relational expression 3 satisfies 1.8 or less, the C, Si and Al contents of the cold-rolled steel sheet. You can control your relationship.
- C 0.10 to 0.16%, Si: 0.3 to 0.8%, Al: 0.01 to 0.5%, Mn: 2.0 to 3.0%, Cr: 0.001 to 0.5%, Mo: 0.001 to 0.5%, B: 0.0001 to 0.001%, Nb: 0.001 to 0.05%, Ti: 0.001 to 0.05%, P: 0.04% or less (excluding 0%), S: 0.01% or less (excluding 0%), N: 0.01% or less (0% is heating a steel slab containing the balance Fe and other unavoidable fissures;
- V1/V2 ⁇ t > 0.5
- V1 represents the average cooling rate during primary cooling
- V2 represents the average cooling rate during secondary cooling
- t represents the thickness of the cold-rolled steel sheet.
- the alloy component of the steel slab may be controlled such that the value defined by the following relational expression 1 satisfies 70 or more.
- the alloy component of the steel slab in order to have high local formability, can be controlled so that the value defined by the following relational expression 2 satisfies 270 or more and 330 or less there is.
- the content of C, Si and Al of the steel slab is such that the value defined by the following relational expression 3 satisfies 1.8 or less. You can control your relationship.
- one embodiment of the present invention may further include plating the reheated steel sheet in a galvanizing bath at 450 to 470° C. after the reheating step, if necessary.
- the alloying heat treatment step of the plated steel sheet at a temperature in the range of 470 ⁇ 550 °C; may further include.
- Example 1 is a photograph of a cross section in the thickness direction observed at 5,000 magnification with a scanning electron microscope (SEM) in order to observe ball martensite (MA) present in bainite in a cold-rolled steel sheet obtained from Example 1 of the present application. is shown.
- SEM scanning electron microscope
- HER Hole Expansion Ratio
- HER Hole expandability
- the inventors of the present invention as a result of intensive studies to provide a cold-rolled steel sheet capable of suppressing the LME problem while securing high strength of 980 MPa or more in tensile strength and at the same time ensuring excellent formability and hole expandability, alloy composition And it was found that this can be solved by precisely controlling the manufacturing conditions, and the present invention has been completed.
- the content of the alloy composition mentioned below means weight%.
- Carbon (C) is an element that secures the strength of steel through solid solution hardening and precipitation hardening. If the C content is less than 0.10%, it is difficult to secure a tensile strength (TS) of 980 MPa. On the other hand, if the C content exceeds 0.16%, arc weldability and laser weldability deteriorate, and the risk of LME cracking increases. Therefore, the content of C preferably has a range of 0.10% or more and 0.16% or less. On the other hand, the lower limit of the C content is more preferably 0.137%. In addition, the upper limit of the C content is more preferably 0.151%.
- Silicon (Si) is a key element of TRIP (Transformation Induced Plasticity) steel that acts to increase the retained austenite fraction and elongation by inhibiting the precipitation of cementite. If the Si content is less than 0.3%, almost no retained austenite remains and the elongation is too low. On the other hand, when the content of Si exceeds 0.8%, it is impossible to prevent the deterioration of physical properties of the welded part due to the formation of LME cracks, and the surface properties and plating properties of the steel material deteriorate. Therefore, the Si content is preferably in the range of 0.3 to 0.8%. On the other hand, the lower limit of the Si content is more preferably 0.49%. In addition, the upper limit of the Si content is more preferably 0.70%.
- TRIP Transformation Induced Plasticity
- Aluminum (Al) is not only an element included for deoxidation of steel, but also an element effective in stabilizing retained austenite by inhibiting the precipitation of cementite. If the Al content is less than 0.01%, the deoxidation of the steel material is not sufficiently performed, and the cleanliness of the steel material is impaired. On the other hand, when the Al content exceeds 0.5%, the castability of the steel material is impaired. Therefore, the Al content is preferably in the range of 0.01 to 0.5%. On the other hand, the lower limit of the Al content is more preferably 0.027%. In addition, the upper limit of the Al content is more preferably 0.085%.
- Manganese (Mn) is an element added to secure strength.
- Mn Manganese
- the content of Mn is less than 2.0%, it becomes difficult to secure strength.
- the content exceeds 3.0% the bainite transformation rate slows down and too much fresh martensite is formed, making it difficult to obtain high hole expandability.
- a band structure is formed due to segregation of Mn, which impairs material uniformity and formability of the material. Therefore, the Mn content is preferably in the range of 2.0 to 3.0%.
- the lower limit of the Mn content is more preferably 2.2%, and even more preferably 2.3%.
- the upper limit of the Mn content is more preferably 2.8%, and even more preferably 2.7%.
- Chromium (Cr) is an element added to secure strength and hardenability.
- Mn is added alone, a very large amount of Mn must be added beyond the Mn content range of the present invention, but this problem can be solved by adding 0.001% or more of Cr.
- the Cr content is preferably in the range of 0.001 to 0.5%.
- the lower limit of the Cr content is more preferably 0.002%, and the upper limit of the Cr content is more preferably 0.38%.
- Molybdenum (Mo) is an element added to secure strength and hardenability.
- Mo Molybdenum
- the Mo content is preferably in the range of 0.001 to 0.5%.
- the lower limit of the Mo content is more preferably 0.07%.
- the upper limit of the Mo content is more preferably 0.3%, and most preferably 0.21%.
- Boron (B) is an element added to secure hardenability.
- Mn is added alone, a very large amount of Mn must be added beyond the Mn content range of the present invention, but this problem can be solved by adding 0.0001% or more of B.
- the content of B is preferably in the range of 0.0001 to 0.001%.
- the lower limit of the B content is more preferably 0.00010%, and the upper limit of the B content is more preferably 0.0005%.
- Niobium is an element added to secure the strength of the steel sheet and refine the structure.
- the Nb content is preferably in the range of 0.001 to 0.05%.
- the lower limit of the Nb content is more preferably 0.015%.
- the upper limit of the Nb content is more preferably 0.031%.
- Titanium (Ti) is an element added to secure the strength of the steel sheet and refine the structure. In the case of adding less than 0.001% of the Ti, it is difficult to obtain the effect of improving strength and refining the structure. On the other hand, when the Ti content exceeds 0.05%, castability is impaired due to excessive formation of TiN, and recrystallization is delayed due to local crystal grain fixation, thereby damaging the uniformity of the structure. Therefore, the Ti content is preferably in the range of 0.001 to 0.05%. Meanwhile, the lower limit of the Ti content is more preferably 0.015%, or the upper limit of the Ti content is more preferably 0.03%.
- Phosphorus (P) exists as an impurity in steel, and it is advantageous to control its content as low as possible. Therefore, the lower limit of the P content excludes 0% (ie, more than 0%) in view of the case where P is inevitably included. However, P is sometimes deliberately added to increase the strength of steel. However, since the toughness of the steel deteriorates when the P is excessively added, in the present invention, it is preferable to limit the upper limit to 0.04% in order to prevent this. Meanwhile, the lower limit of the P content is more preferably 0.002%, or the upper limit of the P content is more preferably 0.0173%.
- the lower limit of the S content excludes 0% (ie, more than 0%) in consideration of the case where S is inevitably included.
- the upper limit it is preferable to limit the upper limit to 0.01%.
- the lower limit of the S content is more preferably 0.0009%, or the upper limit of the S content is more preferably 0.0021%.
- nitrogen (N) is included in the steel as an impurity, and it is advantageous to control its content as low as possible. Therefore, the lower limit of the N content excludes 0% (ie, more than 0%) in consideration of the case where N is inevitably included.
- the upper limit of the N content is preferably limited to 0.01%.
- the lower limit of the N content is more preferably 0.0005%.
- the upper limit of the N content is more preferably 0.007%, more preferably 0.006%, and most preferably 0.0052%.
- the rest may include Fe and unavoidable impurities. Inevitable impurities can be unintentionally mixed in the normal steel manufacturing process, and cannot be completely excluded, and those skilled in the ordinary steel manufacturing field can easily understand the meaning. Further, the present invention does not entirely exclude the addition of other compositions than the aforementioned steel composition.
- the cold-rolled steel sheet is optionally selected from the group consisting of Cu: 0.1% or less (excluding 0%) and Ni: 0.1% or less (excluding 0%).
- One or more selected species may be further included.
- the copper (Cu) and nickel (Ni) are elements that increase the strength of steel.
- the above elements are elements that increase the strength and hardenability of steel, but if added in an excessive amount, they may exceed the target strength grade, and since they are expensive elements, the upper limit is set to 0.1% or less, respectively, from an economic point of view. It is desirable to limit
- Cu and Ni act as a solid solution strengthening element, when adding one or more of Cu and Ni, if less than 0.03% is added, the solid solution strengthening effect may be insignificant, so it is preferable to add 0.03% or more of each. .
- the cold-rolled steel sheet may optionally further include V: 0.05% or less (excluding 0%).
- V 0.05% or less (excluding 0%)
- Vanadium (V) can increase the strength of steel even with the addition of a small amount, but it does not have a great effect on elongation improvement, so it is preferable to control the content to 0.05% or less.
- the content of V is more preferably 0.04% or less, and even more preferably 0.03% or less.
- microstructure of the cold-rolled steel sheet according to one embodiment of the present invention in area%, is ferrite: 10% or less (excluding 0%), retained austenite: more than 1% and 5% or less, martensite: 25% or more 50% Less than and bainite: It is preferable to include more than 35% and less than 70%.
- the purpose of the cold-rolled steel sheet is to secure excellent formability even at a tensile strength (TS) of 980 MPa or more, in particular, in order to obtain high local formability, constituting the steel sheet
- TS tensile strength
- the components are controlled so that the value defined by the following relational expression 1 satisfies 70 or more, an austenite single phase is obtained and the ferrite fraction is reduced to 10 area% or less. It was confirmed that it can be kept low. If the ferrite fraction exceeds 10 area%, there is a concern that the yield strength is lowered and the hole expandability is deteriorated.
- the lower limit of the ferrite fraction may be 2 area%, and the upper limit of the ferrite fraction may be 7 area%.
- the soft ferrite phase can be avoided, but it may be difficult to secure the ductility of the steel if the bainite phase, which is soft next to ferrite, is not sufficiently introduced. More preferably, in terms of further improving the above effects, the lower limit of the value defined by the relational expression 1 may be 75.7, or the upper limit of the value defined by the relational expression 1 may be 90.
- the value defined by the following relational expression 2 satisfies 270 or more and 330 or less. can be controlled to
- the cold-rolled steel sheet according to the present invention is mainly composed of martensite and bainite, and when the hardness difference between these main phases is large, local formability deteriorates. Since bainite usually has lower strength than martensitic structure, it is necessary to improve the strength of bainite structure in order to reduce the hardness variation.
- the present inventors conducted an intensive study to improve the properties by reducing the hardness deviation between martensite and bainite, and as a result, by controlling the average size of martensite (MA) existing inside bainite to an appropriate range, It was found that the difference in hardness between the two main phases could be drastically reduced.
- MA martensite
- the average size of martensite (MA) present in the bainite may be in the range of 0.35 to 0.55 ⁇ m.
- the average size of martensite (MA) existing inside the bainite is less than 0.35 ⁇ m, as the strength of bainite decreases, the hardness difference with the martensite phase increases, making it difficult to secure high hole expandability. .
- the average size of the ball martensite (MA) present in the bainite exceeds 0.55 ⁇ m, the action of the hard ball martensite increases, causing brittleness and lowering the hole expandability.
- the lower limit of the average size of the martensite (MA) present in the bainite may be 0.4 ⁇ m, or the The upper limit of the average size of the martensite (MA) present in the bainite may be 0.5 ⁇ m.
- the average size of the island martensite (MA) present inside the aforementioned bainite is, based on the cross section of the steel sheet cut in the thickness direction, the island martensite completely contained inside the entire bainite. It represents the measured value of the average size of the site (MA).
- the average size of the island martensite (MA) means the average value of the maximum lengths penetrating the inside of the island martensite (MA).
- the value defined by the relational expression 2 can be controlled to satisfy 270 or more and 330 or less. Therefore, even under normal annealing conditions, bainite having an MA phase (Martensite-Austenite aggregate) as the second phase is formed in an area% of 35% or more and less than 70%, and hole expandability can be further improved. The reason why the strength of the bainite phase is secured close to that of martensite is determined to be because the relatively hard second phase MA phase is contained therein through carbon distribution.
- the value defined by the relational expression 2 exceeds 330, it is difficult to secure a sufficient bainite fraction of 35 area% or more, resulting in excessively high strength and poor elongation and HER value.
- the value defined by the relational expression 2 is less than 270, the ductility is sufficient, but the steel sheet is too soft and it may be difficult to obtain a tensile strength of 980 MPa or more.
- the lower limit of the value defined by the relational expression 2 may be 286, or the upper limit of the value defined by the relational expression 2 may be 311.
- retained austenite is a structure that increases the elongation of steel through the TRIP effect, and the higher the fraction, the higher the elongation. It is preferable that the fraction exceed 1 area%. However, in order to obtain austenite exceeding 5 area%, a large amount of C and Si must be added, and in this case, the spot welding LME resistance deteriorates. Therefore, in the present invention, the retained austenite fraction can be controlled to 5 area % or less. At this time, more preferably from the viewpoint of further improving the above-mentioned effect, the lower limit of the retained austenite fraction may be 2 area%, or the upper limit of the retained austenite fraction may be 4 area%.
- the fraction of martensite may be 25 area% or more and less than 50 area%. If the fraction of martensite is less than 25 area%, the total tensile strength of the steel may be insufficient, and if the fraction of martensite is more than 50 area%, the strength is excessively high, resulting in a problem of low hole expandability. can At this time, more preferably from the viewpoint of further improving the above-mentioned effect, the lower limit of the martensite fraction may be 29 area%, or the upper limit of the martensite fraction may be 49 area%.
- the fraction of bainite may be 35 area% or more and less than 70 area%. If the fraction of bainite is less than 35 area%, the fraction of martensite or ferrite is relatively high, and hole expandability may be lowered. Lack of strength can cause problems. At this time, more preferably from the viewpoint of further improving the above-mentioned effect, the lower limit of the bainite fraction may be 45 area%, or the upper limit of the bainite fraction may be 63%.
- the cold-rolled steel sheet may further include other phases in addition to the above-described microstructure.
- the other phase may include island martensite (MA) and the like, and for example, island martensite (MA) and the like existing inside bainite may exist.
- LME Liquid Metal Embrittlement
- spot welding of steel materials is performed below the minimum current value at which explosion occurs, and the minimum current value at which explosion occurs can be regarded as a condition for providing the highest heat input when performing spot welding in practice. there is. If the LME resistance is high, LME may not occur even at a welding current value equal to or higher than the minimum current value for scattering.
- the AE value has a unit of kA.
- the alloy has excellent LME resistance, that is, the AE value is 0 or more Component conditions were derived, and as a result, it was recognized that the content relationship of C, Si and Al needs to be controlled so that the value defined by the following relational expression 3 satisfies 1.8 or less.
- the aforementioned cold-rolled steel sheet has a tensile strength (TS) of 980 MPa or more (preferably, 980 to 1150 MPa, more preferably 980 to 1075 MPa), and 740 to 950 MPa (more preferably, 790 to 920 MPa) yield strength (YS), 45% or more (more preferably, 50 to 65%) hole expandability (HER), 12% or more (more preferably, 12 to 20%) elongation ( El), excellent strength, ductility and hole expandability can be secured at the same time.
- TS tensile strength
- HER hole expandability
- El elongation
- a hot-dip galvanized layer is formed on at least one surface of the cold-rolled steel sheet of the present invention.
- the configuration of the hot-dip galvanized layer is not particularly limited, and any hot-dip galvanized layer commonly applied in the art can be preferably applied to the present invention.
- the hot-dip galvanized layer may be an alloyed hot-dip galvanized layer alloyed with some alloy components of the steel sheet.
- the heating temperature is preferably 1150 to 1250 ° C. If the slab heating temperature is less than 1150 ° C, hot rolling, which is the next step, may not be performed, whereas if it exceeds 1250 ° C, a lot of energy is unnecessarily required to increase the slab temperature. Therefore, the slab heating temperature is preferably in the range of 1150 ⁇ 1250 °C.
- the lower limit of the slab heating temperature is more preferably 1170 ° C, and even more preferably 1180 ° C.
- the upper limit of the slab heating temperature is more preferably 1230 ° C, and even more preferably 1220 ° C.
- the heated slab is finished hot-rolled at 830 to 980° C. to obtain a hot-rolled steel sheet.
- the finish hot rolling temperature (hereinafter, also referred to as 'FDT') is less than 830 ° C.
- the rolling load is large and shape defects increase, resulting in poor productivity.
- the finish hot rolling temperature exceeds 980 ° C.
- the finish hot rolling temperature preferably has a range of 830 ⁇ 980 °C.
- the lower limit of the finish hot rolling temperature is more preferably 880°C.
- the upper limit of the finish hot rolling temperature is more preferably 950°C, and still more preferably 930°C.
- the hot-rolled steel sheet is wound at 450 to 700°C.
- the coiling temperature (hereinafter, also referred to as 'CT') exceeds 700° C.
- coarse internal oxidation of hot rolling is caused, and surface properties are deteriorated.
- the coiling temperature is less than 450° C., it corresponds to the transition boiling range, resulting in poor coiling temperature controllability and poor steel sheet shape.
- the lower limit of the coiling temperature is more preferably 480°C, and even more preferably 500°C.
- the upper limit of the coiling temperature is more preferably 670°C, and even more preferably 640°C.
- the average cooling rate is preferably in the range of 10 to 100 °C/s.
- the coiled hot-rolled steel sheet is cold-rolled.
- the cold rolling reduction may be 30 to 60%. If the cold reduction ratio is less than 30%, it may be difficult to secure a target thickness accuracy and it may be difficult to correct the shape of the steel sheet. On the other hand, when the cold rolling reduction ratio exceeds 60%, the possibility of cracks occurring at the edge of the steel sheet increases, and the cold rolling load may be excessively increased. Therefore, the cold reduction ratio is preferably in the range of 30 to 60%.
- the cold-rolled steel sheet is continuously annealed in the range of 790 ° C to 830 ° C.
- the continuous annealing step is to form austenite close to 100% by heating the steel sheet to the austenite single phase region and then use it for phase transformation. If the continuous annealing temperature (hereinafter, also referred to as 'SS') is less than 790 ° C., sufficient recrystallization and austenite transformation are not achieved, so that the target martensite and bainite fractions cannot be secured after annealing.
- the continuous annealing temperature exceeds 830 ° C., productivity is lowered, coarse austenite is formed, the material may be deteriorated, and surface quality such as peeling of the plating material is deteriorated.
- the continuous annealing may be carried out in a continuous alloying hot-dip galvanizing furnace.
- the atmosphere in the continuous annealing furnace with a gas composed of nitrogen: 95% or more and the balance hydrogen in terms of volume%. If the fraction of nitrogen is less than 95%, if the proportion of hydrogen is not increased accordingly, an oxidizing atmosphere is formed in the furnace and oxides are formed on the surface of the steel sheet, resulting in poor surface quality, and when the proportion of hydrogen increases, explosion prevention and Difficulties in the same process are aggravated.
- the continuously annealed steel sheet is subjected to less than 10 °C/s (more preferably, 1 °C/s or more and less than 10 °C/s) to a primary cooling end temperature of 450 to 600 °C (hereinafter also referred to as 'SCS').
- the first cooling is performed at an average cooling rate of
- the end temperature of the first cooling may be defined as a time point at which the second cooling (quick cooling) starts when a quench facility not applied in the first cooling is additionally applied.
- the bainite structure of the present invention must be actively formed from the first cooling step to obtain the target elongation.
- the primary cooling end temperature is less than 450 ° C
- the bainite fraction is excessively high, and it is difficult to cool to below 450 ° C at a cooling rate of less than 10 ° C / s on the actual length of the equipment.
- the first cooling end temperature exceeds 600° C.
- the amount of cooling up to the second cooling end temperature increases, resulting in poor shape of the steel sheet, and the bainite fraction may be lower than the target level.
- the primary cooling rate is less than 1 ° C / s, it is difficult to obtain high-strength steel due to the increased precipitation of the ferrite phase during cooling, and if it exceeds 10 ° C / s, the cooling amount in the secondary cooling increases, resulting in a final temperature deviation and material variation increases. More preferably, in terms of improving the above effects, the lower limit of the primary cooling rate may be 3 °C / s, and the upper limit of the primary cooling rate may be 8 °C / s.
- the primary cooled steel sheet is secondary cooled at an average cooling rate of 10 °C/s or more to a secondary cooling end temperature of 250 to 350 °C (hereinafter also referred to as 'RCS').
- the secondary cooling end temperature is set to be equal to or less than the Ms temperature of the steel sheet, so that martensitic transformation occurs during cooling, and the martensite finally becomes a tempered martensite phase through a reheating step, which is a post-process. Since the Ms temperature of the 980 MPa class high-elongation steel sheet is mostly 400 ° C or lower, the secondary cooling end temperature was controlled in the range of 250 to 350 ° C in the present invention.
- the secondary cooling end temperature is less than 250 ° C, the amount of initial martensite transformation is too large, resulting in high yield strength and poor formability.
- the secondary cooling end temperature exceeds 350 ° C., martensite is not generated during cooling, making it difficult to obtain high yield strength and hole expandability.
- the secondary cooling rate is less than 10° C./s, even when the target secondary cooling end temperature is reached, a high-temperature phase transformation occurs during cooling, making it impossible to obtain a target martensite fraction and high strength. More preferably, the lower limit of the secondary cooling rate may be 11 °C / s, and the upper limit of the secondary cooling rate may be 30 °C / s.
- a quenching facility not applied in the primary cooling may be additionally applied, and in the present invention, the type of the quenching facility is not particularly limited, but as a preferred example, a hydrogen quenching facility available. More specifically, the hydrogen quenching facility may use a gas composed of 5 to 80% hydrogen and the balance nitrogen by volume%. If the fraction of hydrogen exceeds 80%, there may be a disadvantage in that management such as explosion control of the facility becomes difficult, and if it is less than 5%, it is difficult to utilize the efficient heat transfer characteristics of hydrogen, which is a light element. There may be a disadvantage. .
- the secondary cooled steel sheet is reheated to 350 to 480°C.
- the end point temperature of the heating section is referred to as a reheating temperature (hereinafter, also referred to as 'RHS') for convenience. If the reheating temperature is less than 350° C., the strength is excessively high and the elongation rate is deteriorated. On the other hand, when the reheating temperature exceeds 480 ° C., the austenite phase remains without being transformed, and then becomes fresh martensite during final cooling, impairing hole expandability and elongation.
- the so-called nose temperature at which the transformation of bainite is most active is about 400 to 420 ° C.
- the lower limit of the reheating temperature is more preferably 411°C, or the upper limit of the reheating temperature is more preferably 440°C.
- the average temperature increase rate during the reheating may be 0.5 ⁇ 2.5 °C / s. If the average temperature increase rate is less than 0.5 ° C / s, the total process time may be excessively long, resulting in excessive heat treatment, and if it exceeds 2.5 ° C / s, it may be difficult to secure the desired physical properties in the present invention. .
- the present inventors conducted an intensive study and precisely controlled the conditions of the above-mentioned primary cooling and secondary cooling so as to satisfy the following relational expression 4, thereby sufficiently obtaining a bainite structure in the primary cooling and secondary cooling section. It was found that the hole expandability could be improved by reducing the difference in hardness between the phases.
- V1/V2 ⁇ t > 0.5
- V1 represents the average cooling rate during primary cooling
- V2 represents the average cooling rate during secondary cooling
- t represents the thickness of the cold-rolled steel sheet.
- hot-dip galvanizing, alloying hot-dip galvanizing, and temper rolling may be additionally performed on the reheated steel sheet.
- plating the reheated steel sheet in a galvanizing bath at 450 to 470° C.; may be further included.
- alloying heat treatment of the plated steel sheet at a temperature in the range of 470 ⁇ 550 °C; may further include.
- the alloying heat treatment is to obtain an appropriate alloying level, and the temperature is determined according to the surface state of the steel sheet. By controlling the surface state of the steel material, the alloying heat treatment temperature should not exceed 550 ° C. The loss of austenite can be prevented.
- the alloying heat treatment temperature is preferably higher than the hot-dip galvanizing temperature in order to accelerate alloying, the lower limit is controlled to 470°C.
- temper rolling at a reduction ratio of less than 1% may be further included after cooling the alloyed heat treatment steel sheet to room temperature in order to correct the shape of the steel sheet and adjust the yield strength.
- Table 3 shows the tensile properties, hole expandability, and spot welding LME evaluation results of the steel sheet prepared as described above.
- Tensile strength (TS), yield strength (YS), and elongation (EL) were measured through a tensile test in the direction perpendicular to rolling, and the gauge length was 50 mm and the width of the tensile specimen was 25 mm. used
- the hole expandability was measured according to the ISO 16330 standard, and the hole was sheared with a clearance of 12% using a 10mm diameter punch.
- the AE value means a value obtained by subtracting the minimum current value for scattering from the minimum current value for LME generation.
- the current was increased by 0.5 kA from a low current value, but a cooling time was given for a while between each current value to prevent excessive heat from entering the material.
- the minimum current value at which the weld nugget explodes is measured, and at the same time, the minimum current value at which the LME occurs is measured from the surface and cross-section observation of the welded joint, and the results are listed in Table 3 below. did The occurrence of the LME was determined to be pass if cracks due to the LME were not observed with the naked eye when the surface of the welded part was observed at 10 times and the cross section was observed at 100 times.
- Table 4 shows the results of measuring the microstructure of the prepared cold-rolled steel sheet and the calculation results of relational expressions 1 to 3 used in the present invention.
- microstructure was measured by a point counting method from a scanning electron microscope (SEM) picture, and the fraction of retained austenite was measured by XRD.
- V1* Average cooling rate during primary cooling [°C/s]
- V2* average cooling rate during secondary cooling [°C/s]
- Vh* Average heating rate during reheating [°C/s]
- L MA * average size of island martensite (MA) present inside the bainite [ ⁇ m]
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Abstract
Description
구분 | 합금 | 조성 | (중량%) | |||||||||
강종 | C | Si | Al | Mn | Cr | Mo | B | Nb | Ti | P | S | N |
A | 0.137 | 0.49 | 0.085 | 2.55 | 0.04 | 0.21 | 0.0002 | 0.031 | 0.019 | 0.0067 | 0.0015 | 0.0034 |
B | 0.141 | 0.55 | 0.038 | 2.57 | 0.002 | 0.207 | 0.0001 | 0.019 | 0.018 | 0.0173 | 0.0015 | 0.0052 |
C | 0.151 | 0.6 | 0.034 | 2.61 | 0.38 | 0.11 | 0.0003 | 0.019 | 0.021 | 0.0072 | 0.0021 | 0.0042 |
D | 0.149 | 0.57 | 0.027 | 2.54 | 0.22 | 0.09 | 0.0002 | 0.021 | 0.022 | 0.0084 | 0.0009 | 0.0048 |
E | 0.105 | 0.75 | 0.09 | 2.45 | 0.32 | 0.15 | 0.0002 | 0.045 | 0.021 | 0.0095 | 0.0014 | 0.0042 |
F | 0.12 | 0.42 | 0.315 | 2.42 | 0.402 | 0.195 | 0.0002 | 0.03 | 0.021 | 0.012 | 0.0012 | 0.0045 |
G | 0.102 | 0.15 | 0.1 | 2.44 | 0.2 | 0.05 | 0.0001 | 0.001 | 0.002 | 0.0142 | 0.0019 | 0.0044 |
H | 0.133 | 0.53 | 0.035 | 2.56 | 0.42 | 0.15 | 0.0003 | 0.012 | 0.015 | 0.0093 | 0.0032 | 0.0067 |
I | 0.166 | 0.43 | 0.025 | 2.71 | 0.14 | 0.05 | 0.0001 | 0.022 | 0.025 | 0.0088 | 0.0007 | 0.0072 |
J | 0.142 | 0.67 | 0.055 | 2.92 | 0.45 | 0.33 | 0.0002 | 0.005 | 0.005 | 0.0065 | 0.0023 | 0.0051 |
K | 0.125 | 1.23 | 0.15 | 2.57 | 0.33 | 0.21 | 0.0001 | 0.022 | 0.019 | 0.0077 | 0.0018 | 0.0038 |
L | 0.175 | 1.35 | 0.09 | 2.75 | 0.21 | 0.05 | 0.0001 | 0.032 | 0.018 | 0.0076 | 0.0018 | 0.0044 |
M | 0.192 | 0.77 | 0.45 | 2.62 | 0.44 | 0.12 | 0.0002 | 0.002 | 0.0005 | 0.0124 | 0.0022 | 0.0057 |
구분 | 강종 | 열연두께 [㎜] |
냉연 두께 (t) [㎜] |
압하율 [%] |
FDT [℃] |
CT [℃] |
SS [℃] |
SCS [℃] |
V1* | RCS [℃] |
V2* | Vh* | RHS [℃] |
GI Pot [℃] |
GA [℃] |
발명예 1 | A | 2.3 | 1.2 | 48 | 905 | 605 | 830 | 549 | 5.0 | 323 | 11.8 | 1.1 | 425 | 458 | 517 |
발명예 2 | B | 2.2 | 1.1 | 50 | 911 | 582 | 823 | 571 | 7.2 | 312 | 14.7 | 1.3 | 440 | 461 | - |
발명예 3 | C | 2.1 | 1 | 52 | 924 | 616 | 819 | 490 | 6.2 | 299 | 11.9 | 1.2 | 411 | 463 | 521 |
발명예 4 | D | 2.6 | 1.4 | 46 | 895 | 591 | 823 | 523 | 4.7 | 315 | 12.8 | 1.3 | 432 | 460 | 519 |
비교예 1 | E | 2.4 | 1.2 | 50 | 899 | 621 | 810 | 561 | 6.2 | 335 | 14.3 | 1.1 | 425 | 456 | 520 |
비교예 2 | F | 2.1 | 1.2 | 43 | 933 | 572 | 825 | 532 | 5.9 | 304 | 13.4 | 2.1 | 454 | 455 | 518 |
비교예 3 | G | 2.6 | 1.3 | 50 | 875 | 602 | 833 | 632 | 4.3 | 305 | 19.2 | 2.3 | 457 | 462 | - |
비교예 4 | H | 2.1 | 1 | 52 | 872 | 661 | 841 | 552 | 5.2 | 392 | 10.1 | 0.9 | 453 | 466 | 505 |
비교예 5 | I | 2.4 | 1.2 | 50 | 887 | 535 | 825 | 425 | 7.7 | 335 | 4.7 | 0.9 | 423 | 453 | - |
비교예 6 | J | 2.1 | 1.3 | 38 | 933 | 552 | 823 | 532 | 5.1 | 325 | 12.6 | 1.1 | 435 | 462 | 521 |
비교예 7 | K | 2.6 | 1.4 | 46 | 912 | 656 | 833 | 552 | 5.7 | 312 | 15.3 | 1.4 | 433 | 463 | - |
비교예 8 | L | 2.1 | 1.2 | 43 | 905 | 618 | 835 | 565 | 6.8 | 304 | 14.2 | 1.0 | 392 | 461 | 532 |
비교예 9 | M | 2.6 | 1.3 | 50 | 930 | 605 | 845 | 593 | 5.2 | 322 | 16.5 | 1.3 | 425 | 444 | 512 |
구분 | 강종 | 미세조직 분율 [면적%] | LMA* [㎛] |
관계식 | |||||
F | B | M | 잔류γ | [1] | [2] | [3] | |||
발명예 1 | A | 5 | 63 | 29 | 3 | 0.44 | 75.7 | 286 | 1.22 |
발명예 2 | B | 7 | 45 | 44 | 4 | 0.40 | 81.6 | 286 | 1.27 |
발명예 3 | C | 2 | 46 | 49 | 3 | 0.45 | 89.5 | 311 | 1.37 |
발명예 4 | D | 3 | 52 | 43 | 2 | 0.50 | 87.4 | 291 | 1.33 |
비교예 1 | E | 18 | 36 | 43 | 3 | 0.58 | 60.3 | 283 | 1.32 |
비교예 2 | F | 28 | 40 | 30 | 2 | 0.57 | 44.3 | 294 | 1.18 |
비교예 3 | G | 37 | 28 | 32 | 3 | 0.63 | 78.5 | 265 | 0.71 |
비교예 4 | H | 3 | 40 | 53 | 4 | 0.72 | 86.0 | 308 | 1.21 |
비교예 5 | I | 3 | 74 | 20 | 3 | 0.46 | 100.3 | 303 | 1.27 |
비교예 6 | J | 4 | 15 | 77 | 4 | 0.33 | 89.9 | 359 | 1.41 |
비교예 7 | K | 25 | 25 | 45 | 5 | 0.62 | 46.9 | 305 | 1.93 |
비교예 8 | L | 5 | 22 | 65 | 8 | 0.29 | 69.2 | 313 | 2.27 |
비교예 9 | M | 35 | 13 | 45 | 7 | 0.56 | 43.3 | 328 | 1.96 |
F: Ferrite, B: Bainite, M: Martensite, γ: Austenite |
구분 | 강종 | 기계적 특성 | LME 특성 | |||||
YS [MPa] |
TS [Mpa] |
EL [%] |
HER [%] |
AE | Expulsion 발생전류 [kA] |
LME 발생전류 [kA] |
||
발명예 1 | A | 798 | 1042 | 15 | 51 | 1.5 | 10.5 | 12 |
발명예 2 | B | 895 | 1071 | 13 | 65 | 1.0 | 11 | 12 |
발명예 3 | C | 912 | 1060 | 13 | 63 | 1.0 | 10.5 | 11.5 |
발명예 4 | D | 848 | 1035 | 14 | 59 | 1.0 | 10.5 | 11.5 |
비교예 1 | E | 723 | 1012 | 15 | 38 | 1.0 | 10 | 11 |
비교예 2 | F | 648 | 990 | 16 | 35 | 1.5 | 10 | 11.5 |
비교예 3 | G | 668 | 848 | 17 | 27 | 1.0 | 10 | 11 |
비교예 4 | H | 705 | 1108 | 13 | 37 | 0.5 | 10.5 | 11 |
비교예 5 | I | 673 | 967 | 15 | 47 | 1.0 | 10.5 | 11.5 |
비교예 6 | J | 1053 | 1172 | 11 | 46 | 0.5 | 11 | 11.5 |
비교예 7 | K | 797 | 1045 | 13 | 44 | -0.5 | 11 | 10.5 |
비교예 8 | L | 989 | 1112 | 14 | 42 | -1.0 | 11.5 | 10.5 |
비교예 9 | M | 852 | 1251 | 13 | 39 | -0.5 | 10.5 | 10 |
Claims (16)
- 중량%로, C: 0.10~0.16%, Si: 0.3~0.8%, Al: 0.01~0.5%, Mn: 2.0~3.0%, Cr: 0.001~0.5%, Mo: 0.001~0.5%, B: 0.0001~0.001%, Nb: 0.001~0.05%, Ti: 0.001~0.05%, P: 0.04% 이하 (0%는 제외), S: 0.01% 이하 (0%는 제외), N: 0.01% 이하 (0%는 제외), 잔부 Fe 및 기타 불가피한 불술문을 포함하고,미세조직으로서, 면적%로, 페라이트: 10% 이하 (0%는 제외), 잔류 오스테나이트: 1% 초과 5% 이하, 마르텐사이트: 25% 이상 50% 미만 및 베이나이트: 35% 이상 70% 미만을 포함하고,상기 베이나이트 내부에 존재하는 도상 마르텐사이트(MA)의 평균 크기는 0.35~0.55㎛인, 냉연 강판.
- 청구항 1에 있어서,하기 관계식 1로 정의되는 값이 70 이상을 충족하는, 냉연 강판.[관계식 1]234×[C] - 29×[Si] - 128×[Al] + 29×[Mn] + 10×[Cr] - 17×[Mo] -37×[Nb] - 49×[Ti] + 100×[B](상기 관계식 1에 있어서, 상기 [C], [Si], [Al], [Mn], [Cr], [Mo], [Nb], [Ti] 및 [B]은, 괄호 안의 각 원소에 대한 중량% 함량을 나타낸다.)
- 청구항 1에 있어서,하기 관계식 2로 정의되는 값이 270 이상 330 이하를 충족하는, 냉연 강판.[관계식 2]270×[C] + 90×[Mn] + 70×[Cr] + 80×[Mo](상기 관계식 2에 있어서, 상기 [C], [Mn], [Cr] 및 [Mo]은, 괄호 안의 각 원소에 대한 중량% 함량을 나타낸다.)
- 청구항 1에 있어서,하기 관계식 3으로 정의되는 값이 1.8 이하를 충족하는, 냉연 강판.[관계식 3]5×[C] + [Si] + 0.5×[Al](상기 관계식 3에 있어서, [C], [Si] 및 [Al]은, 괄호 안의 각 원소에 대한 중량% 함량을 나타낸다.)
- 청구항 1에 있어서,상기 미세조직은, 면적%로, 페라이트를 2~7% 포함하는, 냉연 강판.
- 청구항 1에 있어서,상기 미세조직은, 면적%로, 잔류 오스테나이트를 2~4% 포함하는, 냉연 강판.
- 청구항 1에 있어서,상기 미세조직은, 면적%로, 베이나이트를 45~63% 포함하는, 냉연 강판.
- 청구항 1에 있어서,상기 미세조직은, 면적%로, 마르텐사이트를 29~49% 포함하는, 냉연 강판.
- 청구항 1에 있어서,인장강도는 980~1150MPa이고, 항복강도는 740~950MPa인, 냉연 강판.
- 청구항 1에 있어서,구멍 확장성(HER)은 45% 이상인, 냉연 강판.
- 중량%로, C: 0.10~0.16%, Si: 0.3~0.8%, Al: 0.01~0.5%, Mn: 2.0~3.0%, Cr: 0.001~0.5%, Mo: 0.001~0.5%, B: 0.0001~0.001%, Nb: 0.001~0.05%, Ti: 0.001~0.05%, P: 0.04% 이하(0%는 제외), S: 0.01% 이하(0%는 제외), N: 0.01% 이하(0%는 제외), 잔부 Fe 및 기타 불가피한 불술문을 포함하는 강 슬라브를 가열하는 단계;상기 가열된 슬라브를 830~980℃에서 마무리 열간압연하여 열연강판을 얻는 단계;상기 열연강판을 450~700℃에서 권취하는 단계;상기 권취된 열연강판을 냉간압연하는 단계;상기 냉간압연된 강판을 790~830℃의 온도에서 연속소둔하는 단계;상기 연속소둔된 강판을 450~600℃의 1차 냉각종료온도까지 10℃/s미만의 평균 냉각속도로 1차 냉각하는 단계;상기 1차 냉각된 강판을 250~350℃의 2차 냉각종료온도까지 10℃/s 이상의 평균 냉각속도로 2차 냉각하는 단계; 및상기 2차 냉각된 강판을 350~480℃ 범위로 재가열하는 단계;를 포함하고,하기 관계식 4를 충족하는, 냉연 강판의 제조방법.[관계식 4]V1/V2×t > 0.5(상기 관계식 4에 있어서, V1은 1차 냉각 시의 평균 냉각 속도를 나타내고, V2는 2차 냉각 시의 평균 냉각 속도를 나타내고, t는 냉연 강판의 두께를 나타낸다.)
- 청구항 11에 있어서,상기 냉간압연 시, 냉간 압하율은 30~60% 범위인, 냉연 강판의 제조방법.
- 청구항 11에 있어서,상기 재가열된 강판을 450~470℃의 아연 도금욕에서 도금하는 단계;를 더 포함하는, 냉연 강판의 제조방법.
- 청구항 13에 있어서,상기 도금된 강판을 470~550℃ 범위의 온도에서 합금화 열처리하는 단계;를 더 포함하는, 냉연 강판의 제조방법.
- 청구항 14에 있어서,상기 합금화 열처리된 강판을 상온까지 냉각한 후, 1% 미만의 압하율로 조질 압연하는 단계를 더 포함하는, 냉연 강판의 제조방법.
- 청구항 11에 있어서,상기 재가열 시의 평균 승온 속도는 0.5~2.5℃/s인, 냉연 강판의 제조방법.
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KR20120074798A (ko) * | 2010-12-28 | 2012-07-06 | 주식회사 포스코 | 인장강도 1.5GPa급의 초고강도 강판의 제조방법 및 이에 의해 제조된 강판 |
KR20160001485A (ko) * | 2014-06-27 | 2016-01-06 | 현대제철 주식회사 | 냉연강판 및 그 제조 방법 |
JP2019099922A (ja) * | 2017-11-29 | 2019-06-24 | Jfeスチール株式会社 | 高強度亜鉛めっき鋼板 |
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 |
CN111748746A (zh) * | 2019-03-29 | 2020-10-09 | 宝山钢铁股份有限公司 | 一种780MPa级TRIP型冷轧热镀锌双相钢及其制造方法 |
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KR20120074798A (ko) * | 2010-12-28 | 2012-07-06 | 주식회사 포스코 | 인장강도 1.5GPa급의 초고강도 강판의 제조방법 및 이에 의해 제조된 강판 |
KR20160001485A (ko) * | 2014-06-27 | 2016-01-06 | 현대제철 주식회사 | 냉연강판 및 그 제조 방법 |
JP2019099922A (ja) * | 2017-11-29 | 2019-06-24 | Jfeスチール株式会社 | 高強度亜鉛めっき鋼板 |
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 |
CN111748746A (zh) * | 2019-03-29 | 2020-10-09 | 宝山钢铁股份有限公司 | 一种780MPa级TRIP型冷轧热镀锌双相钢及其制造方法 |
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