WO2023096453A1 - Tôle d'acier laminée à froid ultra-haute résistance ayant un excellent allongement et son procédé de fabrication - Google Patents

Tôle d'acier laminée à froid ultra-haute résistance ayant un excellent allongement et son procédé de fabrication Download PDF

Info

Publication number
WO2023096453A1
WO2023096453A1 PCT/KR2022/019037 KR2022019037W WO2023096453A1 WO 2023096453 A1 WO2023096453 A1 WO 2023096453A1 KR 2022019037 W KR2022019037 W KR 2022019037W WO 2023096453 A1 WO2023096453 A1 WO 2023096453A1
Authority
WO
WIPO (PCT)
Prior art keywords
steel sheet
cold
rolled steel
less
content
Prior art date
Application number
PCT/KR2022/019037
Other languages
English (en)
Korean (ko)
Inventor
김은영
구민서
Original Assignee
주식회사 포스코
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by 주식회사 포스코 filed Critical 주식회사 포스코
Publication of WO2023096453A1 publication Critical patent/WO2023096453A1/fr

Links

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
    • 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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

Definitions

  • the present invention relates to an ultra-high-strength cold-rolled steel sheet having excellent elongation and a method for manufacturing the same, and more particularly, to a cold-rolled steel sheet having a tensile strength of 1.5 GPa and having an excellent elongation rate, which can be suitably used for cold stamping, and a cold-rolled steel sheet thereof It's about manufacturing methods.
  • dual steel (pre-steel) and transformation induced plasticity steel Transformation Induced Plasticity Steep; TRIP
  • transformation induced plasticity steel Transformation Induced Plasticity Steep; TRIP
  • HER elongation and hole expansion ratio
  • ultra-high strength steel composed of bainite, particularly martensite, which is a low-temperature transformation phase, has been manufactured, and it is mainly formed by roll forming even though its bendability is low. It is used as a possible part.
  • Patent Document 1 Korean Publication No. 2017-7022118
  • Patent Document 2 Japanese Unexamined Publication No. 2016-28760
  • an ultra-high-strength cold-rolled steel sheet having excellent elongation and a manufacturing method thereof.
  • a cold-rolled steel sheet that can be suitably used for cold stamping and a manufacturing method thereof, having a total elongation of 10% or more while having an ultra-high strength of 1.5 GPa or more.
  • C 0.15 to 0.3%
  • Si 0.1 to 1.5%
  • Mn 2.5 to 5.0%
  • P 0.1% or less (excluding 0%)
  • S 0.03% or less (excluding 0%)
  • Al 0.01 ⁇ 0.1%
  • N 0.01% or less (excluding 0%)
  • B 0.005% or less (excluding 0%)
  • Microstructure by area%, including retained austenite: 0.5-20% and martensite: 80-99.5%,
  • Another aspect of the present invention is,
  • C 0.15 to 0.3%
  • Si 0.1 to 1.5%
  • Mn 2.5 to 5.0%
  • P 0.1% or less (excluding 0%)
  • S 0.03% or less (excluding 0%)
  • Al 0.01 reheating to 1100-1300° C.
  • a steel slab having a composition comprising ⁇ 0.1%, N: 0.01% or less (excluding 0%), B: 0.005% or less (excluding 0%), the balance being Fe and other unavoidable impurities;
  • the secondary annealed cold-rolled steel sheet averaged over 30 °C / s It provides a method for manufacturing a cold-rolled steel sheet comprising a; secondary cooling step of cooling at a cooling rate.
  • an ultra-high strength cold-rolled steel sheet having excellent elongation and a manufacturing method thereof.
  • a cold-rolled steel sheet that has a total elongation of 10% or more while having an ultra-high strength of 1.5 GPa or more, and can be suitably used for cold stamping and a manufacturing method thereof.
  • the main structure is the same from the martensite main structure obtained in the annealing region and the Mn content gradient of the retained austenite, rather than controlling the microstructure having a uniform chemical composition by utilizing the C and Mn contents of the entire steel sheet.
  • a non-uniform gradient in chemical composition occurs, microstructure yielding with a relatively low Mn content occurs during processing, and local stress and deformation occur within the boundary as hard martensitic transformation progresses, resulting in a microstructure with a low Mn content.
  • the elongation rate can provide an additional strength increase effect, thereby providing a 1.5 GPa class ultra-high strength steel sheet.
  • C and Mn in martensite are additionally distributed to the remaining austenite, thereby finally securing more stable austenite than before, minimizing martensitic transformation in the uniform elongation section during plastic deformation, and high strength / high resistance It is possible to provide a method for manufacturing a cold-rolled steel sheet having a compound ratio and excellent workability.
  • FIG. 1 is a schematic diagram schematically showing a manufacturing process of a cold-rolled steel sheet according to an aspect of the present invention.
  • Figure 2 is a photograph of the final microstructure after secondary annealing-secondary cooling for Example 8 of Table 2 measured at high magnification by electron backscattering diffraction (EBSD)
  • Figure 2 (a) is a crystallographic orientation map (Inverse Pole Figure, IPF)
  • Figure 2(b) shows the phase distribution map for inventive steel
  • Figure 2(c) is a phase distribution map that enlarges a specific area where retained austenite is distributed in the final microstructure indicates
  • the cold-rolled steel sheet contains, by weight, C: 0.15-0.3%, Si: 0.1-1.5%, Mn: 2.5-5.0%, P: 0.1% or less (excluding 0%), S: 0.03 % or less (excluding 0%), Al: 0.01 to 0.1%, N: 0.01% or less (excluding 0%), B: 0.005% or less (excluding 0%), the balance including Fe and other unavoidable impurities.
  • Carbon (C) is an essential element for securing the strength and hardenability of martensitic steel, and it is preferable to add 0.15% or more in order to have a tensile strength of 1.5 GPa or more.
  • the upper limit is 0.3%. It is preferable to control below.
  • the degree of generation of carbides increases when martensite is formed as the carbon content increases, more preferably, the upper limit of the C content can be controlled to 0.27%.
  • Si is added as a deoxidizer in the steelmaking process, and is an element that suppresses the formation of carbides together with a solid solution strengthening element.
  • the addition of Si serves to uniformly disperse the structure during annealing heat treatment, increases the stability of austenite during cooling, and makes it possible to secure retained austenite at room temperature. Therefore, in order to secure the above effect, it is preferable to add 0.15% or more of Si.
  • the Si content exceeds 1.5%, excessive Si-based oxides are generated on the surface of the steel sheet during hot rolling, which may cause surface defects during cold rolling.
  • the Si content is controlled to 1.5% or less because the resistivity of the final cold-rolled steel sheet increases and spot weldability deteriorates.
  • the upper limit of the Si content may be 1.25%.
  • Manganese (Mn) is an austenite stable element, which is added to secure martensite hardenability, and is easy to suppress ferrite generation during annealing heat treatment after cold rolling.
  • Mn content is less than 2.5%, it is possible to secure martensitic hardenability, but it is difficult to generate a gradient of Mn concentration in the cold-rolled steel sheet, making it difficult to secure a non-uniform microstructure according to the Mn concentration difference sought in the present invention.
  • the Mn content exceeds 5.0%, excessive strength and Mn bands may occur in the base iron in the thickness direction from the steelmaking and casting stages, and thus the crash resistance deteriorates, so the upper limit of the Mn content is set to 5.0% or less. It is desirable to control However, more preferably, the lower limit of the Mn content may be controlled to 3.0% and the upper limit of the Mn content may be controlled to 4.12% in order to achieve the object of the present invention.
  • Phosphorus (P) is an impurity element in steel, and when it exceeds 0.1%, weldability deteriorates due to P segregation, and the upper limit of the P content is controlled to 0.1% because the potential to cause brittleness of the steel is high.
  • the lower limit of the P content may exclude 0% (ie, greater than 0%) in consideration of the case where it is inevitably included.
  • the lower limit of the P content may be controlled to 0.005.
  • the upper limit of the P content may be controlled to 0.03%, most preferably 0.02%.
  • S Sulfur
  • the upper limit of the S content is controlled to 0.03% or less.
  • the lower limit of the S content may exclude 0% (ie, greater than 0%) in consideration of the case where it is inevitably included.
  • the lower limit of the S content may be controlled to 0.002%, and the upper limit of the S content may be controlled to 0.005%.
  • Al is controlled to 0.01% or more.
  • the upper limit of the Al content is limited to 0.1%.
  • the lower limit of the Al content may be 0.02% and the upper limit of the Al content may be 0.06% in order to secure the desired effect of the present invention.
  • Nitrogen (N) is an impurity element in steel, and if its content exceeds 0.01%, the risk of cracking during playing due to AlN formation greatly increases, so the upper limit of the N content is limited to 0.01%.
  • the lower limit of the N content may exclude 0% (ie, greater than 0%) in consideration of the case where it is unavoidably included.
  • the lower limit of the N content may be controlled to 0.007%, and the upper limit of the N content may be controlled to 0.03%.
  • Boron (B) is an element that is advantageous for inhibiting ferrite phase transformation during annealing heat treatment, and can improve the hardenability of martensite through grain boundary reinforcement and solid solution strengthening.
  • the upper limit of the B content is 0.005%. limited to less than %.
  • the lower limit of the B content may exclude 0% (ie, more than 0%) in consideration of the case where it is inevitably included.
  • the lower limit of the B content may be controlled to 0.001%, and the upper limit of the B content may be controlled to 0.003%.
  • 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 cold-rolled steel sheet may optionally further include one or more selected from Cr: 0.1% or less and Mo: 0.1% or less.
  • Cr 0.1% or less
  • Mo 0.1% or less
  • Chromium is an element that increases the hardenability of martensite and suppresses ferrite transformation, thereby finally enabling martensite having appropriate strength to be produced. Therefore, when the Mn content is designed within a certain range, since the hardenability effect according to the Cr content is lowered, martensitic strength can be secured without adding it, so that a small amount of Cr can be added. On the other hand, if the Cr content exceeds 0.1%, there is a risk of causing cracks due to local deformation and stress generation at the boundary between the carbide and the steel structure during part molding due to the formation of coarse Cr-based carbides, so the upper limit of the Cr content is 0.1%.
  • the lower limit of the Cr content may be 0%.
  • the lower limit of the Cr content may be controlled to 0.005%, and the upper limit of the Cr content may be controlled to 0.05%.
  • Molybdenum is an element effective in increasing martensitic hardenability and suppressing ferrite generation in the cooling section during annealing heat treatment in the same way as Cr.
  • Mo Molybdenum
  • the upper limit of the Mo content is limited to 0.1% or less.
  • the lower limit of the Mo content may be 0% and the upper limit of the Mo content may be 0.05%. there is.
  • the microstructure of the cold-rolled steel sheet includes, in area fraction, retained austenite: 0.5 to 20% and martensite: 80 to 99.5%.
  • the retained austenite is less than 0.5% or the martensite exceeds 99.5%, the Mn content distribution does not occur properly, and a cold-rolled steel sheet having a martensite matrix is manufactured, resulting in insufficient elongation. can occur
  • the retained austenite is more than 20% or the martensite is less than 80%, carbon stability in the retained austenite is poor, resulting in martensite transformation due to strain-induced transformation during processing, resulting in formability. This can lead to exacerbation of the problem.
  • the lower limit of the area fraction of retained austenite may be 1.2%, or the upper limit of the area fraction of retained austenite may be 10%.
  • the lower limit of the area fraction of martensite may be 90%, or the upper limit of the area fraction of martensite may be 98.5%.
  • the cold-rolled steel sheet may satisfy the following relational expression 1-1.
  • the lower limit of the value of may be 9, or The upper limit of the value of may be 19.
  • the measurement method of is not particularly limited.
  • the EPMA surface analysis is performed quantitatively for the Mn content at an area magnification of 30 ⁇ m to 30 ⁇ m. Subsequently, it can be measured by analyzing a region having a martensitic structure having a locally high Mn content and a region having a martensitic structure having a locally low Mn content, respectively.
  • the cold-rolled steel sheet may satisfy the following relational expression 1-2.
  • additional strength is realized in the region where the Mn content is relatively low, making it possible to manufacture a 1.5 GPa class cold-rolled steel sheet, thereby reducing the difference in hardness within the structure and providing excellent elongation compared to conventional martensitic steel. it is possible to secure
  • the The lower limit of the value of may be 829 MPa, or the above The upper limit of the value of may be 1844 MPa.
  • the above and Is defined by the following relational expression 1-3 for each region can be obtained based on Therefore, the above can be obtained as the content of each component obtained through EPMA analysis in a region having a martensitic structure with a high Mn content locally. Also, the above can be obtained by the content of each component obtained through EPMA analysis in a region having a martensitic structure with a low Mn content locally.
  • a hard/soft phase is obtained according to the Mn concentration, and additional reinforcement is induced in the hard phase from the resulting strain distribution. Should be.
  • austenite stability in the hard Mn phase due to the Mn concentration gradient retained austenite can be secured at room temperature to provide ultra-high strength steel having excellent elongation.
  • the cold-rolled steel sheet according to the present invention has a tensile strength of 1500 MPa or more (or 1500 MPa or more and 1700 MPa or less, or 1554 MPa or more and 1660 MPa or less), and a total elongation of 10% or more (or 10% or more and 12% or less, or 10.2% or more and 11.2% or more). below) can be satisfied, and by satisfying this, it can be suitably used for cold stamping as an ultra-high-strength cold-rolled steel sheet having excellent elongation.
  • the yield strength of the cold-rolled steel sheet is 940MPa or more (or, 940MPa or more and 1200MPa or less, 1000MPa or more, or 1000MPa or more and 1200MPa or less) can be Further, according to one aspect of the present invention, the uniform elongation of the cold-rolled steel sheet may be 5.0% or more, or may be 5.0% or more and 7.0% or less.
  • 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 method for manufacturing a cold-rolled steel sheet according to an aspect of the present invention includes reheating a steel slab having the above composition at 1,100 to 1,300 °C.
  • the composition of the steel slab is the same as the composition of the above-mentioned cold-rolled steel sheet, and the description of the above-described cold-rolled steel sheet can be equally applied to the reason for adding each component and the reason for limiting the content in the slab.
  • the present invention it is preferable to go through a process of reheating and homogenizing the steel slab prior to performing hot rolling, and at this time, it is preferable to perform the temperature at 1,100 ⁇ 1,300 °C during reheating. If the reheating temperature is less than 1100° C., a problem in that the load rapidly increases during subsequent hot rolling may occur. In addition, when the reheating temperature exceeds 1,300° C., the amount of surface scale increases, which may lead to material loss.
  • a hot-rolled steel sheet by hot-rolling the above-described reheated slab at 800 to 1,000 ° C. If the temperature of the hot rolling is less than 800 ° C., it is not preferable because there is a possibility that the rolling load may increase due to the introduction of non-recrystallized ferrite. On the other hand, if the temperature of the hot rolling exceeds 1,000 ° C., it is not preferable because the possibility of increasing surface defects and wear of the rolling roll due to scale increases.
  • the hot-rolled steel sheet manufactured according to the above-described hot rolling it is preferable to wind the hot-rolled steel sheet manufactured according to the above-described hot rolling at 400 to 700 ° C.
  • the coiling temperature exceeds 700° C.
  • an excessive oxide film is formed on the surface of the steel sheet to cause defects, so it is preferable to limit this.
  • the coiling temperature is lower than 400 ° C, the strength of the hot-rolled steel sheet is excessively high, so that the rolling load in the cold-rolling process is increased, and productivity is deteriorated because there are many control variables during the cold-rolling process to control it. .
  • cold rolling is performed at a reduction ratio of 20 to 75% to manufacture a cold-rolled steel sheet. If the reduction ratio is less than 20% during the cold rolling, it is difficult to secure the target thickness, and the remaining hot-rolled crystal grains affect the generation of austenite and final physical properties during annealing heat treatment. Therefore, the reduction ratio during cold rolling is preferably performed in the range of 20 to 75%.
  • the present invention is to manufacture a highly-stretched cold-rolled steel sheet having mechanical properties of 10% or more in elongation while securing a tensile strength of 1.5 GPa.
  • primary annealing - primary cooling - secondary A two-stage annealing process including an annealing-secondary cooling process is performed. It is explained in detail below.
  • the cold-rolled steel sheet obtained from the aforementioned cold rolling is heated to a range of 600 to 700° C. (or 620 to 700° C.) and maintained for 2 to 24 hours.
  • the temperature increase rate of 30 °C / s or more is longer than the cementite is decomposed
  • the holding time is controlled to 2 hours or more so that Mn decomposition can occur at an annealing temperature with an inverse temperature (T I A ) range of 600 ° C to 700 ° C.
  • the temperature increase rate during the primary annealing is less than 30° C./s, a problem of insignificant C and Mn inhomogeneity may occur during the primary annealing.
  • the temperature increase rate during the primary annealing exceeds 50° C./s, the accuracy of the primary annealing target temperature may be lowered, resulting in material problems of the final steel type due to temperature deviations in the annealing station.
  • cooling proceeds at an average cooling rate of 30°C/s or more in the first cooling step described later. This is to generate a difference in the Mn concentration of the nitrite and to obtain ferrite with a low Mn concentration and martensite with a high Mn content during cooling. In order to maximize the Mn concentration more preferably in the primary annealing, it is carried out in a holding time range of up to 24 hours.
  • the primary annealing step has a maximum temperature in the temperature range of 600 ⁇ 700 °C based on the surface temperature of the steel sheet. It is heated to be, and the time to maintain in the temperature range of 600 ⁇ 700 °C from the time of reaching the maximum temperature may be 2 to 24 hours.
  • the holding time during the primary annealing is less than 2 hours, the distribution effect of C and Mn in the ideal range temperature range is insignificant, so that the C and Mn concentrations in the ferrite martensite may be uniform during cooling.
  • the holding time during the primary annealing exceeds 24 hours, material deterioration may occur due to coarsening of grains, and a problem in that heterogeneity of C and Mn concentrations in ferrite and austenite may be weakened during annealing may occur.
  • the primary cooling to cool at the cooling rate is performed. More specifically, the first cooling step may be cooled at an average cooling rate in the range of 30 ⁇ 50 °C / s to 25 °C or less.
  • the average cooling rate in the primary cooling step is less than 30° C./s, redistribution of C and Mn may occur during cooling after primary annealing, which may cause problems in securing chemical heterogeneity.
  • the temperature range in the primary cooling step exceeds 25 ° C, due to the extreme distribution of Mn and C during primary annealing, the formation of martensite and the end point temperature between each grain are different, resulting in untransformed austenite fraction even in the low temperature range. This may cause problems with the introduction of phase 2.
  • the primary cooled cold-rolled steel sheet is heated at 30 ° C / s or more (more preferably 30 to 50%). Secondary annealing is performed by heating to a temperature higher than the austenite single phase region at an average temperature increase rate of °C/s range).
  • controlling the average temperature increase rate to 30 ° C / s or more is to maintain the Mn distribution obtained from the first annealing, and the average temperature increase rate in the second annealing step is 30 ° C / s If it is less than s, there may be a problem that the Mn concentration difference becomes uniform due to Mn redistribution.
  • the temperature above the austenite single phase region may be 820 ° C. or higher (more preferably, 850 ° C. or higher and 900 ° C. or lower), and the reason for controlling the temperature range is Mn distributed austenite. This is to produce martensite of 80% or more, which is the final microstructure.
  • the average temperature increase rate in the primary annealing step and the secondary annealing step may be controlled to satisfy the following relational expression 2.
  • TH1 represents the highest temperature of the steel sheet surface in the first annealing step
  • TH2 represents the highest temperature of the steel sheet surface in the second annealing step.
  • the secondary annealed cold-rolled steel sheet is averaged at 30 ° C / s or more (more preferably, in the range of 30 to 50 ° C / s). Secondary cooling to cool at the cooling rate is performed. At this time, if the average cooling rate in the secondary cooling step is less than 30° C./s, problems may arise in securing elongation due to redistribution of C and Mn during cooling.
  • the critical heating rate and heat treatment temperature, and the critical cooling rate and cooling in the cooling process Precise control of temperature is required. If it is out of this range, it may be difficult to secure the tensile strength and elongation within the desired range in the present invention.
  • the cold-rolled steel sheet thus prepared was heated at an average temperature increase rate of 30° C./s in various ideal temperature ranges, and then primary annealing was performed by varying the holding time. Subsequently, after performing primary cooling to 25 ° C at an average cooling rate of 30 ° C / s, secondary annealing was performed by heating at an average heating rate of 30 ° C / s in the austenite single-phase region of 870 ° C, and 30 ° C Secondary cooling was performed at an average cooling rate of /s to simulate continuous annealing heat treatment.
  • the fraction of retained austenite in the specimen including minute austenite was measured using a magnetic induction method (Metis), and the other fractions were calculated as martensite.
  • Methodis magnetic induction method
  • EPMA surface analysis was performed at 1,000 times or more and shown in Table 2 below, and the results of measuring mechanical properties are shown in Table 3 below.
  • the yield strength, tensile strength, and elongation were measured by processing perpendicular to the rolling direction according to the JIS standard and attaching a tensile tester and an extensometer. also, and was measured in the same way as the method and method described herein.
  • Example 1 A CAL 500 2 870 19 0 99.7 0 0.3
  • Example 2 A CAL 600 12 870 19 0 98 0 2 example 3
  • Example 4 A CAL 720 2 870 One 0 100 0 0
  • Example 5 B CAL 660 2 870 9 0 98.8 0 1.2
  • Example 6 B CAL 720 24 870 19 0 99.45 0 0.55 yes 7 B CAL 660 24 870 5.7 0 99.2 0 0.8 yes 8 C CAL 660 2 870 9 0 97 0 3 yes 9 D CAL 660 24 870 3 0 100 0 0
  • Example 10 D CAL 720 24
  • Example 1 1095 1643 9.1 1390 5.2
  • Example 2 943 1554 11.2 1844 6.7
  • Example 3 1021 1643 10.2 829 5.0 example 4 1020 1561 8.9 277 4.6
  • Example 5 1200 1660 10.5 922 6.2
  • Example 6 1050 1580 9.8 720 4.7 yes 7 1158 1645 10.1 645 5.3 yes 8 1011 1632 10.5 829 6.7 yes 9 1020 1520 8.9 450
  • Example 10 975 1508 7.8 225 3.8
  • Example 11 1011 1570 8.3 425 3.5
  • Example 12 987 1562 7.8 389 3.9
  • Example 13 950 1523 6 150 2.8
  • Example 14 980 1565 9.2 438 4.6 yes15 1080 1589 8.9 573 3.7
  • the relational expression 1-1 was satisfied, whereby the tensile strength was 1500 MPa or more, the yield strength was 1000 MPa or more, the total elongation was 10% or more, and In addition to satisfying the uniform elongation of 5.0% or more, uniformity was also secured by satisfying the relational expression 1-2.
  • FIG. 2 a photograph of the final microstructure after secondary annealing and secondary cooling for Example 8 measured at high magnification by electron backscattering diffraction (EBSD) is shown in FIG. 2 .
  • Figure 2 (a) shows the crystallographic orientation map (Inverse Pole Figure, IPF)
  • Figure 2 (b) shows the phase distribution map for the inventive steel
  • Figure 2 (c) shows the retained austenite in the final microstructure It shows a phase distribution map in which a specific area of distribution is enlarged.
  • Example 1 which meets the alloy composition of the present invention but does not meet the manufacturing conditions because the primary annealing temperature is too low, the cementite generated in the ferrite phase is not completely dissolved, and there is a problem remaining after secondary annealing. , which resulted in a total elongation of less than 10%.
  • the primary annealing temperature is 720 ° C.
  • the difference in Mn concentration was small, and due to this, it was difficult to secure the retained austenite fraction in the final microstructure, and the elongation was less than 10%.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

La présente invention concerne une tôle d'acier laminée à froid à ultra-haute résistance et son procédé de fabrication et, plus spécifiquement, une tôle d'acier laminée à froid et son procédé de fabrication, la tôle d'acier laminée à froid ayant une résistance à la traction de 1,5 GPa et présentant un excellent taux d'allongement, et en tant que telle, pouvant être utilisée de manière appropriée pour l'estampage à froid.
PCT/KR2022/019037 2021-11-29 2022-11-29 Tôle d'acier laminée à froid ultra-haute résistance ayant un excellent allongement et son procédé de fabrication WO2023096453A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2021-0166731 2021-11-29
KR1020210166731A KR20230081744A (ko) 2021-11-29 2021-11-29 연신율이 우수한 초고강도 냉연강판 및 이의 제조방법

Publications (1)

Publication Number Publication Date
WO2023096453A1 true WO2023096453A1 (fr) 2023-06-01

Family

ID=86540167

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/KR2022/019037 WO2023096453A1 (fr) 2021-11-29 2022-11-29 Tôle d'acier laminée à froid ultra-haute résistance ayant un excellent allongement et son procédé de fabrication

Country Status (2)

Country Link
KR (1) KR20230081744A (fr)
WO (1) WO2023096453A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016147549A1 (fr) * 2015-03-18 2016-09-22 Ｊｆｅスチール株式会社 Tôle d'acier laminée à froid à haute résistance et son procédé de fabrication
KR20170113858A (ko) * 2016-03-28 2017-10-13 주식회사 포스코 항복강도와 연성이 우수한 고강도 냉연강판, 도금강판 및 이들의 제조방법
KR20180021161A (ko) * 2015-08-11 2018-02-28 제이에프이 스틸 가부시키가이샤 고강도 강판용 소재, 고강도 강판용 열연재, 고강도 강판용 열연 소둔재, 고강도 강판, 고강도 용융 도금 강판 및 고강도 전기 도금 강판과, 이들의 제조 방법
KR20210036966A (ko) * 2018-08-31 2021-04-05 제이에프이 스틸 가부시키가이샤 고강도 강판 및 그의 제조 방법
KR20210132856A (ko) * 2020-04-28 2021-11-05 현대제철 주식회사 고강도 및 고성형성을 가지는 강판 및 그 제조방법

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6130465B2 (ja) 2015-10-30 2017-05-17 株式会社トプコン 視力表示装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016147549A1 (fr) * 2015-03-18 2016-09-22 Ｊｆｅスチール株式会社 Tôle d'acier laminée à froid à haute résistance et son procédé de fabrication
KR20180021161A (ko) * 2015-08-11 2018-02-28 제이에프이 스틸 가부시키가이샤 고강도 강판용 소재, 고강도 강판용 열연재, 고강도 강판용 열연 소둔재, 고강도 강판, 고강도 용융 도금 강판 및 고강도 전기 도금 강판과, 이들의 제조 방법
KR20170113858A (ko) * 2016-03-28 2017-10-13 주식회사 포스코 항복강도와 연성이 우수한 고강도 냉연강판, 도금강판 및 이들의 제조방법
KR20210036966A (ko) * 2018-08-31 2021-04-05 제이에프이 스틸 가부시키가이샤 고강도 강판 및 그의 제조 방법
KR20210132856A (ko) * 2020-04-28 2021-11-05 현대제철 주식회사 고강도 및 고성형성을 가지는 강판 및 그 제조방법

Also Published As

Publication number Publication date
KR20230081744A (ko) 2023-06-08

Similar Documents

Publication Publication Date Title
WO2018110853A1 (fr) Acier à deux phases à haute résistance présentant d'excellentes propriétés d'ébavurage dans une plage de basse température, et son procédé de production
WO2009145563A2 (fr) Tôle d'acier à très haute résistance présentant d'excellentes propriétés de traitement à chaud pour le pressage à chaud, élément trempé, et procédé de production correspondant
WO2010074370A1 (fr) Tôle d'acier étirable à haute résistance, tôle d'acier laminée à chaud, tôle d'acier laminée à froid, tôle d'acier revêtue de zinc et procédé de fabrication d'une tôle d'acier allié revêtue de zinc
WO2017188654A1 (fr) Tôle d'acier à très haute résistance et à haute ductilité ayant un excellent rapport d'élasticité et son procédé de fabrication
WO2017222159A1 (fr) Tôle d'acier laminée à froid de haute résistance ayant une excellente aptitude au façonnage et procédé pour la fabriquer
WO2015099222A1 (fr) Tôle d'acier laminée à chaud qui présente une excellente propriété de soudage et une excellente propriété d'ébarbage, et son procédé de fabrication
WO2020111856A2 (fr) Tôle à haute résistance ayant une excellente ductilité et une excellente ténacité à basse température et son procédé de fabrication
WO2022124609A1 (fr) Tôle d'acier galvanisée par immersion à chaud à haute résistance présentant une ductilité élevée et une excellente formabilité, et son procédé de fabrication
WO2017051998A1 (fr) Tôle d'acier plaquée et procédé de fabrication associé
WO2021085800A1 (fr) Acier inoxydable austénitique ayant un rapport limite d'élasticité plus élevé et procédé pour sa fabrication
WO2021117989A1 (fr) Tôle d'acier laminée à froid à résistance ultra-élevée et son procédé de fabrication
WO2013154254A1 (fr) Tôle d'acier laminée à chaud à teneur élevée en carbone présentant une excellente uniformité et son procédé de fabrication
WO2021010599A2 (fr) Acier inoxydable austénitique ayant une résistance améliorée et procédé de fabrication associé
WO2019088552A1 (fr) Tôle d'acier laminée à froid à ultra-haute résistance présentant une excellente aptitude au laminage à froid et son procédé de fabrication
WO2019125018A1 (fr) Tôle d'acier laminée à froid à ultra-haute résistance et son procédé de fabrication
WO2023096453A1 (fr) Tôle d'acier laminée à froid ultra-haute résistance ayant un excellent allongement et son procédé de fabrication
WO2017111303A1 (fr) Tôle d'acier laminée à chaud de haute résistance présentant une excellente aptitude au cintrage et son procédé de production
WO2021261884A1 (fr) Acier inoxydable austénitique à haute résistance présentant une excellente productivité et un excellent effet de réduction des coûts et son procédé de production
WO2020130614A2 (fr) Tôle d'acier laminée à chaud et à haute résistance ayant un excellent rapport d'extension des trous et son procédé de fabrication
WO2023234502A1 (fr) Tôle d'acier laminée à froid à résistance ultra-élevée et son procédé de fabrication
WO2024143768A1 (fr) Tôle d'acier laminée à froid à ultra-haute résistance et son procédé de fabrication
WO2024080657A1 (fr) Tôles d'acier et leurs procédés de fabrication
WO2019039774A1 (fr) Acier inoxydable ferritique ayant une ténacité à l'impact à basse température améliorée et son procédé de production
WO2023048450A1 (fr) Tôle d'acier laminée à froid à haute résistance ayant une excellente qualité de surface et une faible variation de matériau, et son procédé de fabrication
WO2023068763A1 (fr) Tôle d'acier écologique ayant une résistance élevée et une formabilité élevée, et procédé de fabrication y afférant

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22899135

Country of ref document: EP

Kind code of ref document: A1