WO2019093689A1 - Tôle d'acier laminée à froid à résistance élevée et faible ténacité ayant d'excellentes propriétés de rupture et son procédé de production - Google Patents

Tôle d'acier laminée à froid à résistance élevée et faible ténacité ayant d'excellentes propriétés de rupture et son procédé de production Download PDF

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WO2019093689A1
WO2019093689A1 PCT/KR2018/012596 KR2018012596W WO2019093689A1 WO 2019093689 A1 WO2019093689 A1 WO 2019093689A1 KR 2018012596 W KR2018012596 W KR 2018012596W WO 2019093689 A1 WO2019093689 A1 WO 2019093689A1
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steel sheet
cold
rolled steel
strength
mpa
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Korean (ko)
Inventor
장제욱
현영진
김용우
모경우
성민관
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Posco Holdings Inc
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Posco Co Ltd
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Priority to CN201880072180.0A priority Critical patent/CN111315901B/zh
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    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to the production of a high strength, low-phosphorus cold-rolled steel sheet which is mainly used as a construction flat tie and which is used as various long-term finishing materials.
  • the hot rolled steel sheet is subjected to cold rolling at a final reduction ratio of 20 to 70%
  • a cold-rolled steel sheet having a final thickness of 1.5 mm to 3.0 mm and a tensile strength of 950 MPa or more and a charge-absorbed energy of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ) .
  • a flat tie is a long bill of lading, sometimes called a nominal wall tie.
  • the flat tie is a tensile member that keeps the form at regular intervals for the purpose of construction and finally supports the side pressure after the concrete is laid.
  • the manufacturing process produces the product by slitting and pressing the cold rolled steel according to the final thickness. Since the required characteristics are to support the lateral pressure, it is necessary to have a tensile strength of 950 MPa or more based on the cold rolled raw material.
  • the flat tie protruding outside the formwork after construction on different wall thicknesses (spacing between the moldings) of the construction site should be easy to remove with a hammer.
  • the flat tie protrusion should be hit once with a hammer to cut the buried portion and the protrusion, and the fracture section should be cut in a one-piece form.
  • the raw material should have low impact toughness. Because of this unique property required for flat tie, it is required not only high strength and high toughness required for general steel but also high strength and low toughness.
  • flat tie In order to realize the unique low-temperature characteristics of flat tie, various methods exist, but due to too low impact toughness, there should be no problem in hot-rolled steel sheet production and production process should be possible without breaking until final press working.
  • flat tie is a consumable product and it is a product to be landfilled after final construction, so it should be possible to design / produce low cost.
  • the characteristics of the flat tie requiring such durability are not the high strength and high toughness required by general steels, and therefore there is no related art for realizing low durability.
  • Patent Document 1 Korean Patent Application No. 10-1998-0059176 (filed on December 28, 1998)
  • the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a high strength, low temperature cold rolled steel sheet for flattening by controlling steel composition components and hot rolling and cold rolling processes and a manufacturing method thereof.
  • the present invention for achieving the above object is a ferritic stainless steel comprising, by weight, 0.30 to 0.70% of C, 0.2 to 1.0% of Mn, 0.005 to 0.5% of Si, 0.005 to 0.02% of P, (Fe) and other unavoidable impurities, wherein the steel microstructure is composed of 50 to 95% of pearlite and the remaining ferrite, and the average grain size of the ferrite structure is in the range of 0.01 to 0.1%, Cr: 0.005 to 0.1%
  • the pearlite colony has an average size of 10 to 50 ⁇ , a thickness of 1.5 to 3.0 mmt and a charpy absorbed energy of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ) Resistant cold-rolled steel sheet.
  • the cold-rolled steel sheet may have a yield strength of 700 to 950 MPa, a tensile strength of 950 to 1200 MPa, and an elongation of 2 to 12%.
  • the steel microstructure is composed of 50 to 95% of pearlite and residual ferrite, and the average grain size of the ferrite structure is 10 to 50 ⁇ And producing a cold-rolled steel sheet having a pearlite colony average size of 10 to 50 ⁇ m and a thickness of 1.5 to 3.0 mmt.
  • the cold-rolled steel sheet may have a yield strength of 700 to 950 MPa, a tensile strength of 950 to 1200 MPa, an elongation of 2 to 12%, and a charpy absorbed energy of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ) have.
  • the thickness of the wound hot rolled steel sheet may be 2.5 to 4.5 mmt.
  • the present invention having the above-described constitution can effectively provide high-carbon steel having high strength and low-strength for construction flat and other long-lasting applications by optimizing the range of steel components and the manufacturing process conditions.
  • Example 1 is a microstructure photograph of Inventive Example 1 in an embodiment of the present invention.
  • the cold-rolled high-strength steel sheet according to the present invention is characterized in that it comprises 0.30 to 0.70% of C, 0.2 to 1.0% of Mn, 0.005 to 0.5% of Si, 0.005 to 0.02% of P, 0.01% (Fe) and other unavoidable impurities, wherein the steel microstructure is composed of 50 to 95% of pearlite and the remaining ferrite, and the mean grain size of the ferrite structure is in the range of 0.1 to 0.1%, Cr: 0.005 to 0.1%
  • the pearlite colony has an average size of 10 to 50 ⁇ , a thickness of 1.5 to 3.0 mm and a charpy absorbed energy of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ) .
  • the present invention is characterized by providing very low toughness in order to secure excellent fracture characteristics of the flat tie.
  • the pearlite fraction is 50 to 95%
  • the average grain size of the ferrite structure is 10 - 50 ⁇ m
  • pearlite colony average size of 10 ⁇ 50 ⁇ m very low coarse ferrite grain size and pearlite colony size were ensured and low toughness was achieved.
  • the cold-rolled steel sheet of the present invention has a thickness of 1.5 to 3.0 mm, a yield strength of 700 to 950 MPa, a tensile strength of 950 to 1200 MPa, an elongation of 2 to 12%, and a charpy absorbed energy, Is in the range of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ).
  • Carbon is an element that affects strength and toughness.
  • the carbon content is less than 0.30 wt%, it is difficult to secure the target strength.
  • the carbon content exceeds 0.7% by weight, there is a problem that moldability is deteriorated due to excessive strength increase and cementite formation.
  • the carbon content is preferably limited to 0.30 to 0.70% by weight.
  • Manganese is added as a solid solution strengthening element to increase the strength and to prevent the slag fusing brittleness by FeS formation. For this effect, it should be added in an amount of 0.2 wt% or more, and when it is contained in an amount exceeding 1.0 wt%, center segregation and micro segregation become serious and the final carbide becomes coarse. In the case of steel for flat tread where low cost design is important, the excessive Mn addition increases the cost, and the manganese content is limited to 0.2-1.0 wt%.
  • Silicon has an effect of improving strength by solid solution strengthening.
  • the amount is less than 0.005% by weight, the effect of improving the strength is insufficient, and when added in a large amount, the surface quality is adversely affected by an increase in the number of the scale-scale defects. Therefore, the content of silicon is preferably limited to 0.005 to 0.5% by weight.
  • Phosphorus is a strong element of employment enhancement. 0.005 wt% or more of phosphorus should be added in order to secure strength, while if it exceeds 0.02 wt%, there is a problem that the workability is impaired by P segregation, so the lower and upper limits are limited to 0.005 wt% and 0.02 wt%, respectively.
  • Sulfur is an element that tends to form non-metallic inclusions and is an impurity that increases the amount of precipitate. Therefore, it is necessary to control the sulfur content to a low level.
  • the upper limit is limited to 0.01% by weight, and the lower the content of sulfur, the better the moldability.
  • Aluminum is mainly added to deoxidize and to trap nitrogen with AlN.
  • the aluminum content is less than 0.01% by weight, the purpose of addition can not be achieved, the addition amount is not less than 0.1% by weight, and the content is limited to 0.01 to 0.1% by weight because excessive strength increase and slab defect may occur during performance.
  • Chromium should be added in an amount of 0.005% by weight or more for the purpose of solubility strengthening effect. On the other hand, if it is added in an amount exceeding 0.1% by weight, center segregation and unnecessary inclusions can be formed, and the cost also increases, so that the upper limit is preferably limited to 0.1% by weight.
  • the cold-rolled steel sheet of the present invention is composed of the above composition, and the other component not mentioned is iron (Fe). It is not possible to exclude other impurities which may inevitably be incorporated in ordinary manufacturing processes, but this is a matter known to a general engineer and is not specifically mentioned in this specification.
  • the cold-rolled steel sheet of the present invention is composed of 50 to 95% of pearlite and residual ferrite.
  • the average grain size of the ferrite structure is 10 to 50 ⁇ and the average size of the pearlite colony is 10 to 50 ⁇ .
  • the ferrite grain size and the pearlite colony size are ensured, It is possible to effectively provide a cold-rolled steel sheet.
  • the steel microstructure of the cold-rolled steel sheet proposed in the present invention is a mixed structure of pearlite and ferrite.
  • the pearlite has higher strength than ferrite but lacks toughness, so crack formation and propagation are much easier than ferrite when an external impact is applied. Accordingly, in the present invention, 50 to 95% of pearlite in the microstructure of the final cold-rolled steel sheet must be secured to ensure low impact toughness of 1 to 5J.
  • the pearlite colony has an average size of 5 to 40 ⁇ ⁇ , and the average grain size of the ferrite structure is 10 to 50 ⁇ ⁇ .
  • the steel sheet of the present invention having the above-described steel microstructure has a yield strength of 700 to 950 MPa, a tensile strength of 950 to 1200 MPa, an elongation of 2 to 12% and a charpy absorbed energy of 1.0 to 5.0 J (0.05 to 0.35 J / cm 2 ) can be satisfied.
  • the method for manufacturing cold-rolled steel sheets of high strength and low-strength comprises the steps of: preparing a steel slab having a composition as described above; A reheating step of heating the steel slab to a temperature of 1100 to 1300 ° C; Subjecting the reheated slab to rough rolling at 1000 to 1100 ⁇ ⁇ , followed by finish hot rolling at a temperature range of 850 to 950 ⁇ ⁇ ; Cooling the hot-rolled steel sheet at a rate of 10 to 200 ° C / s and then winding it at a temperature of 550 to 750 ° C; Wherein the steel microstructure is composed of 50 to 95% of pearlite and residual ferrite, and the average grain size of the ferrite structure is 10 to 50 ⁇ And a cold-rolled steel sheet having a pearlite colony average size of 10 to 50 ⁇ m and a thickness of 1.5 to 3.0 mmt.
  • the steel slab having the above-described alloy composition is reheated, and at this time, the reheating temperature is preferably set at a normal level between 1100 ° C and 1300 ° C.
  • the reheating temperature of the slab is set at 1100-1300 ° C .
  • the reheated slab is hot-rolled as described above. That is, the steel sheet is subjected to ordinary rough rolling at a temperature between 1000 and 1100 ° C, followed by hot rolling.
  • the hot rolling is preferably performed at a temperature between 850 and 950 ⁇ , and more preferably between 900 ⁇ and 950 ⁇ .
  • austenite grains can be grown to coalesce the final ferrite grain and pearlite colony size.
  • the hot rolling finish should be performed at the Ar3 transformation point or higher, to prevent 2-phase rolling, and when 2-phase rolling is performed, a carbide-free super-crystalline ferrite is generated.
  • finishing temperature of 850 °C or less is subject to a large rolling load, which makes it difficult to carry out subsequent processes. Finishing temperatures of 950 °C or more may cause scale defects on the surface, so that the hot rolling finishing temperature is limited to 850 ⁇ 950 °C.
  • the hot-rolled steel sheet is cooled as described above.
  • the cooling rate is limited to the range of 10 ° C / s to 200 ° C / s.
  • the pearlite transformation and the colony size and the ferrite grain size can be maximized by cooling at the above-mentioned cooling rate and keeping it slightly on the run-out table (ROT).
  • ROT run-out table
  • a cooling rate of less than 10 DEG C / s it is difficult to obtain a pearlite fraction of 50% or more because of insufficient time to maintain the ROT phase, and a cooling rate exceeding 200 DEG C / s is difficult to uniformly cool due to non- The coil shape can be very bad. Therefore, it is preferable to limit the cooling rate to 10 to 200 DEG C / s.
  • the cooled hot-rolled steel sheet is wound at a temperature of 550 to 750 ° C., more preferably at a temperature of about 700 ° C. or more.
  • the reason for limiting the coiling temperature to 550 to 750 ⁇ ⁇ is that the temperature interval is the interval in which the size of the pearlite colony can be maximized. Concretely, if the coiling temperature is less than 550 ⁇ ⁇ , uniform pearlite can not be obtained because bainite or martensite structure, which is a low-temperature transformed structure, comes out. On the other hand, if the coiling temperature exceeds 750 ⁇ ⁇ , surface defects such as scales to be.
  • the wound hot-rolled coil is pickled.
  • the pickling temperature is naturally cooled to a range of from room temperature to 200 ° C, then pickled to remove the surface scale scale. At this time, if the pickling temperature of the hot-rolled steel sheet exceeds 200 ° C, there is a problem that the surface layer portion of the hot-rolled steel sheet is over-pickled and the surface roughness of the surface layer is deteriorated, so the pickling temperature is limited to room temperature to 200 ° C.
  • the pickled hot-rolled steel sheet is cold-rolled at a reduction ratio of 50 to 70%. Since the tensile strength of the cold-rolled steel sheet is proportional to the rolling reduction rate, the tensile strength of the final cold-rolled steel sheet is required to be at least 950 MPa. Therefore, for a tensile strength of 950 MPa or more, a cold reduction rate of 50% or more is required. However, since excessive rolling reduction increases the load of equipment, it is impossible to produce. Therefore, the rolling reduction upper limit is set to 70% considering rolling load and production efficiency. In cold rolled steel, impact toughness has the maximum value at a specific reduction rate and low toughness at a low pressure rate.
  • the impact toughness decreases again when the impact toughness is maximum at around 40% of the cold reduction rate and at the low pressure ratio of 30% or the high pressure ratio of 70%. This is a common feature of cold-rolled materials as a factor associated with the formation of shear-lip.
  • a reduction rate of 50% or more is advantageous.
  • a high pressure ratio of 50 to 70% is used in the aspect of strength and durability.
  • the cold-rolled steel sheet produced through cold rolling as described above has a steel microstructure composed of 50 to 95% of pearlite and residual ferrite.
  • the average grain size of the ferrite structure is in the range of 10 to 50 ⁇ and the average size of the pearlite colony is in the range of 10 to 50 ⁇ .
  • very coarse ferrite crystal grains and pearlite colony size can be ensured and low toughness can be maintained.
  • the cold-rolled steel sheet of the present invention having the above-described steel microstructure has a yield strength of 700 to 950 MPa, a tensile strength of 950 to 1200 MPa, an elongation of 2 to 12% and a charpy absorbed energy of 1.0 to 1.0 MPa.
  • 5.0 J (0.05 to 0.35 J / cm 2 ) can be satisfied.
  • the steel slabs satisfying the alloy components listed in Table 1 were reheated at 1200 ° C for 2 hours and then hot rolled under the conditions shown in Table 2 at which time the thicknesses of the hot rolled materials were also shown in Table 2 below.
  • the average grain size ( ⁇ ), the pearlite fraction (%) and the pearlite colony size ( ⁇ ) of the ferrite average grain size were measured by observing the microstructure of the cold-rolled steel sheet specimen.
  • the yield strength (YS), tensile strength (TS) and elongation (El) of the cold-rolled steel sheet were measured and the results are also shown in Table 3 below.
  • the tensile strength is a tensile test value obtained by taking JIS No. 5 standard in the rolling direction of the rolled plate, and the impact toughness is measured in terms of V-notch Charpy impact test at a room temperature in terms of a thickness of 1.9 mm Lt; / RTI >
  • the steel type 1 is a steel type in which the content of C is less than the content range of the present invention.
  • Comparative Example 1-2 having the composition of the steel grade 1 the conditions of FDT, CT, cold rolling reduction and the like satisfy the range of the present invention, but the carbon content is out of the allowable range of the present invention and the tensile strength of the final material is 893 MPa and 910 MPa, respectively.
  • the impact toughness of Comparative Example 1-2 did not satisfy the allowable range of 1.0 ⁇ 5.0J of 22J and 19J, respectively. This is because the carbon content is so low that sufficient strength can not be secured, It is analyzed that it is difficult.
  • the steel grade 2 is a steel grade in which the content of Mn is less than the content range of the present invention.
  • Comparative Example 3-4 having a composition of steel grade 2 satisfies the range of the present invention while the conditions of FDT, CT and cold rolling reduction satisfy the range of the present invention.
  • the Mn content exceeds the allowable range of the present invention, the tensile strength of the final material is 920 MPa, not good at 931 MPa. This is because Mn content is low and it is impossible to secure sufficient strength.
  • Steel 3 is a steel grade in which the content of C exceeds the component range of the present invention.
  • Comparative Example 5-6 having the composition of the steel grade 3 satisfied FDT, CT and cold rolling reduction conditions of the present invention, but the carbon content exceeded the allowable range of the present invention, and the yield strengths of the final materials were 980 MPa, and 976 MPa, respectively, which were not within the allowable range of 750 to 950 MPa of the present invention.
  • the tensile strengths of Comparative Examples 5-6 were 1240 MPa and 1283 MPa, respectively, which were outside the allowable range of 950 ⁇ 1200 MPa, because the carbon was excessively added and the strength was increased too much.
  • the steel grade 4 is a steel grade satisfying the composition range of the present invention.
  • Comparative Example 7-10 having the composition of the steel grade 4 is a case where the FDT, CT, and cold rolling reduction rates do not satisfy the conditions of the present invention and thus can not satisfy the final required material.
  • FDT exceeded the range of 850 to 950 ° C under the condition of the present invention at 830 ° C, and the ultimate material had an impact toughness of 21J, which was too high to achieve a low impact resistance.
  • the CT was out of the range of 550 to 750 ° C under the condition of the present invention at 520 ° C, and the final material had an impact toughness of 18J, which was excessively high.
  • the cold rolling reduction rate was 16%, which was outside the range of 50 to 70% under the conditions of the present invention, and the final material had a tensile strength of 915 MPa and could not satisfy the tensile strength allowable range of 950 to 1200 MPa.
  • the cold rolling reduction rate was 76%, which was outside the range of 50 to 70% of the present invention.
  • the final material had a yield strength of 1030 MPa and could not satisfy the yield strength allowable range of 700 to 950 MPa. 1278MPa, the acceptable range of 950 ⁇ 1200MPa was not satisfied.
  • Comparative Example 11-13 is a case where the steel composition is manufactured through the manufacturing process (hot rolling and cold rolling) conditions of the present invention using the above steel types 5-7 which are outside the scope of the present invention, And the strength / toughness target required by the present invention is not satisfied.
  • the value of impact toughness at room temperature (Charpy absorbed energy) required by the final product is in the range of 1 to 5 J, and if it exceeds 5 J, the fracture / cutting property is deteriorated. Therefore, in the present invention, the low-temperature toughness is referred to as being in the range of 1 to 5J at room temperature impact toughness, which is excellent in breaking / cutting characteristics, exceeding 5J.
  • the breaking property means that the hammer can be cut by a hammer blow once, and the cut surface is cut into one shape like cut with a knife, which is obtained when the impact toughness value is 1 to 5J. If the impact toughness value is higher than 5J, it is difficult to cut with one stroke, and the fracture is increased due to ductile fracture, so that it can not be cut cleanly.

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  • Heat Treatment Of Sheet Steel (AREA)

Abstract

La présente invention concerne un procédé de production d'une tôle d'acier laminée à froid à résistance élevée et faible ténacité ayant d'excellentes propriétés de rupture. Une tôle d'acier laminée à froid selon la présente invention contient, en % en poids, de 0,30 à 0,70 % de C, de 0,2 à 1,0 % de Mn, de 0,005 à 0,5 % de Si, de 0,005 à 0,02 % de P, 0,01 % au maximum de S, de 0,01 à 0,1 % d'Al et de 0,005 à 0,1 % de Cr, le complément étant constitué de fer et d'impuretés inévitables; la microstructure de l'acier est composée de 50 à 95 % de perlite, le complément étant de la ferrite, la taille moyenne des grains de la ferrite est comprise entre 10 et 50 µm, la taille moyenne des colonies de perlite est comprise entre 10 et 50 µm, l'épaisseur de la tôle d'acier est comprise entre 1,5 et 3,0 mm et une ténacité lors d'un choc à température ambiante (énergie absorbée Charpy) de 1,0 à 5,0 J (0,05 à 0,35 J/cm2) est obtenue.
PCT/KR2018/012596 2017-11-07 2018-10-24 Tôle d'acier laminée à froid à résistance élevée et faible ténacité ayant d'excellentes propriétés de rupture et son procédé de production Ceased WO2019093689A1 (fr)

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KR10-2017-0147450 2017-11-07

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