WO2022091709A1 - Hot-rolled steel sheet and method for producing same - Google Patents

Hot-rolled steel sheet and method for producing same Download PDF

Info

Publication number
WO2022091709A1
WO2022091709A1 PCT/JP2021/036705 JP2021036705W WO2022091709A1 WO 2022091709 A1 WO2022091709 A1 WO 2022091709A1 JP 2021036705 W JP2021036705 W JP 2021036705W WO 2022091709 A1 WO2022091709 A1 WO 2022091709A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
steel sheet
hot
rolled steel
mpa
Prior art date
Application number
PCT/JP2021/036705
Other languages
French (fr)
Japanese (ja)
Inventor
貴之 遠藤
英之 木村
Original Assignee
Ｊｆｅスチール株式会社
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 Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to JP2022512727A priority Critical patent/JP7298777B2/en
Publication of WO2022091709A1 publication Critical patent/WO2022091709A1/en

Links

Classifications

    • 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
    • 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
    • C22C38/06—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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

  • the present invention relates to a hot-rolled steel sheet suitable for a cylinder having a small anisotropy during cold squeezing and a small change in strength before and after heat treatment, and a method for manufacturing the same.
  • Patent Document 1 it is necessary to add an alloy element having a high unit price such as Nb to the hot-rolled steel sheet, so that the component design is economically unsuitable for industrial production.
  • additive elements such as Nb have poor anisotropy during cold squeezing.
  • the present invention has been made in view of the above circumstances, and is inexpensive, has a small anisotropy during cold squeezing, and has a small change in strength before and after heat treatment.
  • the purpose is to provide a method.
  • hot-rolled steel sheets for cylinders have a problem that the strength changes greatly before and after heat treatment, and the crystal grain size becomes coarse at the stage of the austenite phase, so that the strength cannot be maintained.
  • the unit price of the alloy is high, the production cost is high, and the anisotropy is deteriorated.
  • the gist of the present invention is as follows.
  • C 0.160 to 0.20%
  • Si 0.01 to 0.10%
  • Mn 0.70 to 0.90%
  • P 0.030%
  • S 0.030% or less
  • Al sol.
  • Al 0.001 to 0.10%
  • N 0.010% or less
  • the balance consists of Fe and unavoidable impurities.
  • Ceq represented by the following equation (1) is 0.30 or more and 0.32 or less.
  • the plate thickness is 6 mm or less,
  • the tensile strength is 410 MPa or more and 500 MPa or less
  • the normalizing temperature was maintained at a temperature of 890 ° C. or higher and 940 ° C.
  • r 0 , r 45 and r 90 are r values (Rankford values) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction of the steel sheet, respectively.
  • the component composition is Ti: 0.010 to 0.30%, Ni: 0.010 to 0.10%, Cu: 0.010 to 0.10%, Cr: 0 in mass%. .010 to 0.050%, V: 0.01 to 0.05%, Mo: 0.01 to 0.10%, Ca: 0.0001 to 0.0200%, Mg: 0.0001 to 0.0200
  • the hot-rolled steel sheet according to [1] which comprises one type or two or more types selected from%.
  • [3] The method for manufacturing a hot-rolled steel sheet according to [1] or [2].
  • the finish rolling output side temperature is set to 800 ° C. or higher and 900 ° C. or lower after rough rolling, and the final finish rolling.
  • the strength change before and after the heat treatment is small, it is possible to obtain a hot-rolled steel sheet which can guarantee the strength after the heat treatment and has a small anisotropy during cold squeezing.
  • C 0.160 to 0.20%
  • C is an element useful as a solid solution strengthening element to increase the strength of the steel sheet and secure the strength within this range. In order to obtain such an effect, C is set to 0.160% or more. On the other hand, if the content exceeds 0.20%, the weldability at the time of coupling is lowered. Therefore, the amount of C is set to 0.20% or less. It is preferably 0.18% or less.
  • Si acts as a deoxidizing agent and dissolves in the steel to increase the strength of the steel sheet.
  • Si is set to 0.01% or more. If the content exceeds 0.10%, it adheres to the surface layer of the base material as scale and deteriorates the surface roughness. Therefore, the Si content is set to 0.10% or less.
  • the range is preferably 0.01 to 0.05%. More preferably, it is 0.03% or less.
  • Mn 0.70 to 0.90%
  • Mn is an element that has the effect of dissolving and increasing the strength of the steel sheet, is inexpensive, and is contained as one of the purposes of minimizing the content of other expensive alloying elements.
  • the content of 0.70% or more is required to maintain the strength after the heat treatment. It is preferably 0.80% or more.
  • a content of more than 0.90% reduces the toughness of the steel sheet. Therefore, the amount of Mn is set to 0.90% or less. Therefore, it is preferably in the range of 0.80 to 0.90%.
  • P 0.030% or less
  • the content is preferably 0.001% or more.
  • it is an element that reduces toughness, especially the toughness of welds. If the content exceeds 0.030%, the above-mentioned adverse effects become remarkable, so the amount of P is set to 0.030% or less. It is preferably 0.010% or less.
  • S 0.030% or less S exists as sulfide-based inclusions such as MnS in the steel, deteriorates the toughness of the base metal and the welded portion, and is unevenly distributed in a large amount in the central segregated portion of the slab and cast. It makes it easy for defects in pieces to occur. Such a tendency becomes remarkable when the content exceeds 0.030%. Therefore, the amount of S is set to 0.030% or less. It is preferably 0.010% or less. On the other hand, the smaller the amount of S, the more preferable, so the lower limit is not limited and may be 0%.
  • sol. Al 0.001 to 0.10% sol.
  • Al is an element that is effective as a deoxidizing material and has an effect of forming a nitride to reduce the austenite particle size. From the viewpoint of obtaining this effect, sol.
  • the amount of Al is 0.001% or more. On the other hand, if the amount of Al is excessive, the toughness deteriorates. Therefore, sol.
  • the amount of Al is 0.10% or less, preferably 0.05% or less.
  • N 0.010% or less
  • N is an element that reduces ductility and toughness. Therefore, the amount of N is set to 0.010% or less. On the other hand, the smaller the amount of N is, the more preferable it is. Therefore, the lower limit is not limited and may be 0%. However, since N is usually contained in steel as an impurity inevitably, the amount of N may be industrially more than 0%. The amount of N is preferably 0.0050% or less in relation to the amount of effective Ti described later.
  • the above are the basic chemical components of the present invention, and the balance consists of Fe and unavoidable impurities.
  • Ti 0.010 to 0.30%, Ni: 0.010 to 0.10%, Cu: 0.010 to 0.10%, Cr: 0.010 to 0. Select from 050%, V: 0.01 to 0.05%, Mo: 0.01 to 0.10%, Ca: 0.0001 to 0.0200%, Mg: 0.0001 to 0.0200%.
  • One or more of these can be contained as a selective element.
  • Ti 0.010 to 0.30%
  • Ti is an element having a strong affinity for N, and has the effect of precipitating as TiN during solidification, reducing the solid solution N in steel, and reducing the deterioration of toughness due to strain aging of N after cold working. Further, the surplus Ti that has not been precipitated as TiN forms TiC, exerts a pinning effect as a precipitate, and suppresses coarsening of crystal grains.
  • the Ti amount is preferably 0.010% or more. It is more preferably 0.020% or more. Further, the effective Ti amount: (Ti / 48-N / 14) ⁇ 48 preferably contains 0.003% or more.
  • the Ti content is preferably 0.30% or less. More preferably, it is 0.10% or less.
  • the effective Ti amount is preferably 0.20% or less.
  • Ni 0.010 to 0.10% Ni suppresses phase transformation at high temperatures and increases the strength of the steel sheet.
  • Ni when Ni is contained, it is preferably 0.010% or more. However, if the Ni content is too high, the weldability of the steel sheet deteriorates. Therefore, the Ni content is preferably 0.10% or less. More preferably, it is 0.050% or less.
  • Cu 0.010 to 0.10% Cu is deposited in the steel as fine particles to increase the strength of the steel sheet.
  • Cu is contained for this purpose, it is preferably 0.010% or more.
  • the Cu content is preferably 0.10% or less.
  • Cr 0.010 to 0.050% Cr suppresses phase transformation at high temperatures and increases the strength of the steel sheet.
  • Cr When Cr is contained for this purpose, it is preferably 0.010% or more. However, if the Cr content is too high, the workability of the steel sheet is lowered and the productivity is lowered. Therefore, when Cr is contained, the Cr content is preferably 0.050% or less.
  • V 0.01-0.05% Similar to Ti, V enhances the strength of the steel sheet by precipitation strengthening, fine grain strengthening and dislocation strengthening. When V is contained for this purpose, it is preferably 0.01% or more. However, if the V content is too high, the carbonitride is excessively deposited and the formability of the steel sheet is deteriorated. Therefore, when V is contained, the V content is preferably 0.05% or less.
  • Mo 0.01-0.10% Similar to Ti and V, Mo enhances the strength of the steel sheet by precipitation strengthening, fine grain strengthening and dislocation strengthening. In order to obtain the above effect, the Mo content is preferably 0.01% or more. On the other hand, if the amount of Mo is excessive, the weldability is lowered. Therefore, when Mo is contained, the Mo content is 0.10% or less. It is preferably 0.05% or less.
  • Ca 0.0001-0.0200%
  • Ca is an element that improves weldability by forming an acid sulfide having high stability at high temperatures.
  • the Ca content is preferably 0.0001% or more.
  • the Ca content is preferably 0.0200% or less.
  • Mg 0.0001-0.0200%
  • Mg is an element that improves weldability by forming an acid sulfide having high stability at high temperatures.
  • the Mg content is preferably 0.0001% or more.
  • the Mg content is preferably 0.0200% or less.
  • Ceq is less than 0.30, the tensile strength after heat treatment cannot be maintained. On the other hand, if Ceq exceeds 0.32, the tensile strength after the heat treatment exceeds the target value, so the value is set to 0.32 or less.
  • Plate thickness 6 mm or less
  • the plate thickness of the hot-rolled steel sheet of the present invention shall be 6 mm or less from the viewpoint of squeezing workability after rolling.
  • Tensile strength is 410 MPa or more and 500 MPa or less
  • the tensile strength is 410 MPa or more and 500 MPa or less. This tensile strength is the tensile strength before heat treatment (before normalizing). If the tensile strength is less than 410 MPa, a flammable gas having a predetermined pressure cannot be sealed as a steel plate for a cylinder. It is preferably 450 MPa or more. If the tensile strength exceeds 500 MPa, the workability deteriorates during squeezing.
  • the tensile strength after heat treatment which was maintained at a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes and allowed to cool in the atmosphere to reach room temperature, was 410 MPa or higher and 500 MPa or lower, and the tensile strength before and after the heat treatment. The difference is 50 MPa or less.
  • Hot-rolled steel sheets used for cylinders are squeezed after blanking, welded, and heat-treated (normalized). Normally, normalizing (heat treatment) is performed with a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower and a soaking time of 30 minutes, and a material with little change in strength before and after this normalizing (heat treatment) is required. There is.
  • the tensile strength after heat treatment that is, after being held at a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes, allowed to cool in the atmosphere, and brought to room temperature, has a tensile strength of 410 MPa or higher and 500 MPa or lower.
  • a normalizing temperature 890 ° C. or higher and 940 ° C. or lower for 30 minutes
  • the material has little change in strength before and after the heat treatment.
  • the temperature and soaking time of the normalizing and for example, a heat treatment furnace may be used.
  • the tensile strength of the steel sheet (test piece) which has been allowed to cool in the atmosphere and has reached room temperature (for example, 25 ° C.) may be measured.
  • ⁇ r is ⁇ 0.20 or more and 0.20 or less
  • ⁇ r which is an index of anisotropy
  • ⁇ r is expressed by the following equation (2).
  • ⁇ r (r 0 + r 90 ) / 2-r 45 ...
  • r 0 , r 45 and r 90 are r values (Rankford values) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction of the steel sheet, respectively.
  • the structure of the hot-rolled steel sheet of the present invention may be a two-phase structure of a ferrite phase and a pearlite phase.
  • Steel having the above-mentioned composition is melted by a conventional method by a melting means such as a converter or an electric furnace, and is made into a slab by a conventional method such as a continuous casting method or an ingot lumping method. After that, the slab is heated, rough-rolled, finished-rolled, cooled by a cooling facility, and then wound into a coil.
  • a melting means such as a converter or an electric furnace
  • a conventional method such as a continuous casting method or an ingot lumping method.
  • the slab is heated, rough-rolled, finished-rolled, cooled by a cooling facility, and then wound into a coil.
  • the melting method and casting method are not limited to the above-mentioned methods.
  • Heating temperature of the slab 1100 ° C or higher and 1300 ° C or lower
  • the heating temperature is set in the range of 1100 ° C. or higher and 1300 ° C. or lower.
  • the temperature is preferably in the range of 1180 ° C. or higher and 1250 ° C. or lower.
  • Finish rolling Outside temperature 800 ° C or higher and 900 ° C or lower
  • the finished rolling output side temperature is 800 ° C. or higher and 900 ° C. or lower. If the temperature exceeds 900 ° C., the scale on the surface of the steel sheet becomes too thick, and there is a concern that the scale may peel off. On the other hand, if the temperature is less than 800 ° C., the scale is broken or becomes too thin during rolling, so that it does not act as a protective film as a black skin.
  • the temperature is preferably 850 ° C. or higher.
  • the temperature at the exit side of the finish rolling is the surface temperature of the steel sheet.
  • the rolling reduction of the final pass of the finish rolling is preferably 20% or more from the viewpoint of increasing the rolling reduction in the subsequent stage of the finish rolling.
  • Winding temperature 550 ° C or higher and 650 ° C or lower
  • the strength before heat treatment tends to be high, and the strength before heat treatment cannot be guaranteed.
  • the winding temperature exceeds 650 ° C.
  • the strength before the heat treatment also tends to be low, and the strength cannot be guaranteed.
  • CT * is expressed by the following equation (3) and is the result of extrapolation from the relationship between Ceq and the winding temperature.
  • CT * 5000 x Ceq-950 ... (3)
  • the formula (3) is established by Ceq: 0.30 to 0.32.
  • runout cooling may be performed and winding may be performed.
  • the tensile properties and ⁇ r before and after the heat treatment were evaluated according to the following test method.
  • JIS No. 5 tensile test piece (JIS Z 2201) was collected from the center position of the width of the hot-rolled steel sheet in a direction perpendicular to the rolling direction. Further, the hot-rolled steel sheet was heat-treated in a furnace heated to 930 ° C. for 30 minutes, taken out, and then allowed to cool to room temperature in the atmosphere, and the sample was used as the heat-treated hot-rolled steel sheet.
  • a JIS No. 5 tensile test piece (JIS Z 2201) was collected from a position 1/4 of the width direction of the hot-rolled steel sheet after the heat treatment in a direction parallel to the rolling direction. Using these test pieces, a tensile test was performed in accordance with JIS Z 2241 regulations with a strain rate of 10 -3 / s.
  • JIS No. 5 tensile test piece JIS Z 2201 was collected from each direction of 0 °, 45 °, and 90 ° with respect to the rolling direction from the center position of the width of the hot-rolled steel sheet, and this test piece was used. It was used and carried out in accordance with the regulations of JIS Z2241.

Abstract

The purpose of the present invention is to provide: a hot-rolled steel sheet which is obtained at low cost and has low anisotropy during cold drawing, while having a small strength change before and after a heat treatment; and a method for producing this hot-rolled steel sheet.　A hot-rolled steel sheet according to the present invention has a component composition that contains, in mass%, from 0.160% to 0.20% of C, from 0.01% to 0.10% of Si, from 0.70% to 0.90% of Mn, 0.030% or less of P, 0.030% or less of S, from 0.001% to 0.10% of sol. Al and 0.010% or less of N, with the balance being made up of Fe and unavoidable impurities. This hot-rolled steel sheet has a Ceq of from 0.30 to 0.32, a sheet thickness of 6 mm or less, a tensile strength of from 410 MPa to 500 MPa, a tensile strength after a heat treatment, wherein the hot-rolled steel sheet is held at a normalizing temperature of from 890°C to 940°C for 30 minutes, of from 410 MPa to 500 MPa, a tensile strength difference before and after the heat treatment of 50MPa or less, and ∆r of from -0.20 to 0.20, said ∆r being the index of anisotropy of the r value.

Description

熱延鋼板およびその製造方法Hot-rolled steel sheet and its manufacturing method
　本発明は、冷間でのしぼり加工の際の異方性が小さく、熱処理前後での強度変化が少ないシリンダー用として好適な熱延鋼板およびその製造方法に関するものである。 The present invention relates to a hot-rolled steel sheet suitable for a cylinder having a small anisotropy during cold squeezing and a small change in strength before and after heat treatment, and a method for manufacturing the same.
　インド、アフリカといった都市ガス等のインフラが整理されていない地域におけるエネルギーの供給は、薪を中心としたものから、ガスシリンダーのような圧力容器に可燃性のガスを封入するものが大半である。エネルギー需要の増加に伴いシリンダーの需要も拡大しつつある。シリンダー用に用いられる原板は、黒皮の熱延鋼板である。これをブランク加工後、しぼり加工を行い、溶接をして熱処理（焼準）を行う。このため、冷間でのしぼり加工の際の異方性が小さく、かつ熱処理前後の強度変化が少なく、さらに熱処理後の強度確保が要求される。 Most of the energy supply in areas such as India and Africa where infrastructure such as city gas is not organized is mainly firewood, or a pressure vessel such as a gas cylinder is filled with flammable gas. Demand for cylinders is also expanding as energy demand increases. The original plate used for the cylinder is a black-skinned hot-rolled steel plate. After blanking this, squeezing is performed, welding is performed, and heat treatment (normalizing) is performed. Therefore, it is required that the anisotropy during cold squeezing is small, the strength change before and after the heat treatment is small, and the strength after the heat treatment is secured.
　このようなシリンダー用の鋼板としては、特許文献１のように、化学成分として質量％で、Ｃ：０．０４０～０．１５０％、Ｓｉ：０～０．５００％、Ｍｎ：０．１０～１．５０％を含み、固溶Ｎｂ：０．００５～０．０３０％である熱延鋼板が知られている。この熱延鋼板を熱処理した場合、ＮｂがＮｂＣとして析出し、ピン止め効果を発揮し、熱処理後の鋼板の軟質化を防止することが、知られている。 As a steel sheet for such a cylinder, as in Patent Document 1, in terms of mass% as a chemical component, C: 0.040 to 0.150%, Si: 0 to 0.500%, Mn: 0.10 to Hot-rolled steel sheets containing 1.50% and having a solid melt Nb: 0.005 to 0.030% are known. It is known that when this hot-rolled steel sheet is heat-treated, Nb is precipitated as NbC, exerts a pinning effect, and prevents the steel sheet from being softened after the heat treatment.
ＷＯ２０１６－１７１２１２号公報WO2016-17212 Gazette
　特許文献１に記載した技術では、熱延鋼板に、Ｎｂのような単価の高い合金元素を添加する必要があることから、工業生産としては、経済的に不向きな成分設計であった。同時にＮｂのような添加元素は、冷間でのしぼり加工時に異方性が悪くなることが知られている。 In the technique described in Patent Document 1, it is necessary to add an alloy element having a high unit price such as Nb to the hot-rolled steel sheet, so that the component design is economically unsuitable for industrial production. At the same time, it is known that additive elements such as Nb have poor anisotropy during cold squeezing.
　一方、シリンダーの加工メーカーでは、加工性の観点から、原板の鋼板には低い強度を、かつ熱処理後は所定の強度を保証してほしいとの要望がある。このため、熱処理前後での強度変化が少なく、かつ安価な鋼板の供給が求められていた。 On the other hand, cylinder processing manufacturers are requesting that the steel plate of the original plate be guaranteed low strength and the specified strength after heat treatment from the viewpoint of workability. Therefore, there has been a demand for the supply of inexpensive steel sheets with little change in strength before and after heat treatment.
　また、加工時の歩留を向上させるため、絞り加工後の耳をトリムしないで使用する例もある。このため、冷間でのしぼり加工時に異方性の少ない鋼板が求められている。 In addition, in order to improve the yield during processing, there are cases where the ears are used without trimming after drawing. Therefore, there is a demand for a steel sheet having less anisotropy during cold squeezing.
　本発明は、上記のような事情に鑑みてなされたものであり、安価であり、冷間でのしぼり加工時の異方性が小さく、熱処理前後での強度変化の少ない熱延鋼板およびその製造方法を提供することを目的とする。 The present invention has been made in view of the above circumstances, and is inexpensive, has a small anisotropy during cold squeezing, and has a small change in strength before and after heat treatment. The purpose is to provide a method.
　一般に、シリンダー用の熱延鋼板では、熱処理前後での強度変化が大きく、オーステナイト相の段階で結晶粒径が粗大化してしまい、強度が保持できないという課題があった。同時に、炭化物を形成するＮｂを添加した上記の成分系においては、合金単価が高く製造コストが高くなり、かつ異方性が悪くなることが、知られている。 In general, hot-rolled steel sheets for cylinders have a problem that the strength changes greatly before and after heat treatment, and the crystal grain size becomes coarse at the stage of the austenite phase, so that the strength cannot be maintained. At the same time, it is known that in the above-mentioned component system to which Nb forming a carbide is added, the unit price of the alloy is high, the production cost is high, and the anisotropy is deteriorated.
　本発明者らは、シリンダー用の熱延鋼板について鋭意検討を重ねた結果、熱処理後の強度をＣｅｑによって予測可能であり、また、異方性を小さくするために仕上圧延時の圧下率を制御できるという知見を得た。 As a result of diligent studies on hot-rolled steel sheets for cylinders, the present inventors can predict the strength after heat treatment by Ceq, and control the reduction rate during finish rolling in order to reduce anisotropy. I got the finding that it can be done.
　本発明の要旨は次のとおりである。
［１］成分組成として、質量％で、Ｃ：０．１６０～０．２０％、Ｓｉ：０．０１～０．１０％、Ｍｎ：０．７０～０．９０％、Ｐ：０．０３０％以下、Ｓ：０．０３０％以下、ｓｏｌ．Ａｌ：０．００１～０．１０％、Ｎ：０．０１０％以下を含み、残部がＦｅ及び不可避的不純物からなり、
下記（１）式で表されるＣｅｑが０．３０以上０．３２以下であり、
板厚６ｍｍ以下であり、
引張強さが４１０ＭＰａ以上５００ＭＰａ以下であり、
かつ、焼準温度８９０℃以上９４０℃以下の温度で３０分保持し、大気中で放冷し、常温となった熱処理後の引張強さが４１０ＭＰａ以上５００ＭＰａ以下であって、熱処理前後での引張強さの差が、５０ＭＰａ以下であり、
下記（２）式で表されるΔｒが－０．２０以上０．２０以下である熱延鋼板。
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４・・・（１）
上記式（１）において、元素記号は各元素の含有量（質量％）を意味する。ただし、含有しない元素は０％とする。
Δｒ＝（ｒ０＋ｒ９０）／２－ｒ４５・・・（２）
ｒ０、ｒ４５およびｒ９０は、それぞれ、鋼板の圧延方向に対して、０°、４５°及び９０°方向のｒ値（ランクフォード値）である。
［２］前記成分組成は、さらに、質量％で、Ｔｉ：０．０１０～０．３０％、Ｎｉ：０．０１０～０．１０％、Ｃｕ：０．０１０～０．１０％、Ｃｒ：０．０１０～０．０５０％、Ｖ：０．０１～０．０５％、Ｍｏ：０．０１～０．１０％、Ｃａ：０．０００１～０．０２００％、Ｍｇ：０．０００１～０．０２００％から選択される１種または２種以上を含む［１］に記載の熱延鋼板。
［３］［１］または［２］に記載の熱延鋼板の製造方法であって、
前記成分組成を有するスラブを１１００℃以上１３００℃以下に加熱し、次いで、熱間圧延を施すに際し、粗圧延後、仕上圧延出側温度を８００℃以上９００℃以下とし、かつ、仕上圧延の最終パスを含む連続する３パスでの合計の圧下率を５０％以上８０％以下として仕上圧延を行った後、ランナウト冷却し、その後５５０℃以上６５０℃以下の巻取温度で巻き取る熱延鋼板の製造方法。 The gist of the present invention is as follows.
[1] As a component composition, in mass%, C: 0.160 to 0.20%, Si: 0.01 to 0.10%, Mn: 0.70 to 0.90%, P: 0.030%. Hereinafter, S: 0.030% or less, sol. Al: 0.001 to 0.10%, N: 0.010% or less, the balance consists of Fe and unavoidable impurities.
Ceq represented by the following equation (1) is 0.30 or more and 0.32 or less.
The plate thickness is 6 mm or less,
The tensile strength is 410 MPa or more and 500 MPa or less,
In addition, the normalizing temperature was maintained at a temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes, and the product was allowed to cool in the atmosphere. The difference in strength is 50 MPa or less,
A hot-rolled steel sheet in which Δr represented by the following equation (2) is −0.20 or more and 0.20 or less.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ... (1)
In the above formula (1), the element symbol means the content (mass%) of each element. However, the element not contained is 0%.
Δr = (r 0 + r 90 ) / 2-r 45 ... (2)
r 0 , r 45 and r 90 are r values (Rankford values) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction of the steel sheet, respectively.
[2] Further, the component composition is Ti: 0.010 to 0.30%, Ni: 0.010 to 0.10%, Cu: 0.010 to 0.10%, Cr: 0 in mass%. .010 to 0.050%, V: 0.01 to 0.05%, Mo: 0.01 to 0.10%, Ca: 0.0001 to 0.0200%, Mg: 0.0001 to 0.0200 The hot-rolled steel sheet according to [1], which comprises one type or two or more types selected from%.
[3] The method for manufacturing a hot-rolled steel sheet according to [1] or [2].
When a slab having the above component composition is heated to 1100 ° C. or higher and 1300 ° C. or lower, and then hot-rolled, the finish rolling output side temperature is set to 800 ° C. or higher and 900 ° C. or lower after rough rolling, and the final finish rolling. A hot-rolled steel sheet that is runout-cooled after finishing rolling with the total rolling reduction in three consecutive passes including the pass set to 50% or more and 80% or less, and then wound at a winding temperature of 550 ° C or higher and 650 ° C or lower. Production method.
　本発明によれば、熱処理前後での強度変化が少ないため、熱処理後の強度を保証でき、かつ冷間でのしぼり加工時の異方性が小さい熱延鋼板が得られる。 According to the present invention, since the strength change before and after the heat treatment is small, it is possible to obtain a hot-rolled steel sheet which can guarantee the strength after the heat treatment and has a small anisotropy during cold squeezing.
　以下、本発明の熱延鋼板について説明する。 Hereinafter, the hot-rolled steel sheet of the present invention will be described.
　まず、本発明における成分の限定理由について説明する。なお、各元素の％表示は、特に記載がない限り質量％を意味する。 First, the reason for limiting the components in the present invention will be described. The% indication of each element means mass% unless otherwise specified.
　Ｃ：０．１６０～０．２０％
　Ｃは、この範囲内において固溶強化元素として働き鋼板の強度を増加させ、強度を確保するのに有用な元素である。このような効果を得るために、Ｃは０．１６０％以上とする。一方、０．２０％を超える含有は、カップリングの際の溶接性を低下させる。このため、Ｃ量は０．２０％以下とする。好ましくは０．１８％以下である。 C: 0.160 to 0.20%
C is an element useful as a solid solution strengthening element to increase the strength of the steel sheet and secure the strength within this range. In order to obtain such an effect, C is set to 0.160% or more. On the other hand, if the content exceeds 0.20%, the weldability at the time of coupling is lowered. Therefore, the amount of C is set to 0.20% or less. It is preferably 0.18% or less.
　Ｓｉ：０．０１～０．１０％
　Ｓｉは、脱酸剤として作用するとともに、鋼中に固溶し鋼板の強度を増加させる。このような効果を得るために、Ｓｉは０．０１％以上とする。０．１０％を超える含有は、母材の表層にスケールとして付着し表面粗度を悪化させるため、Ｓｉの含有は０．１０％以下とする。なお、鋼板に所望の強度を持たせるために、好ましくは０．０１～０．０５％の範囲とする。より好ましくは０．０３％以下とする。 Si: 0.01-0.10%
Si acts as a deoxidizing agent and dissolves in the steel to increase the strength of the steel sheet. In order to obtain such an effect, Si is set to 0.01% or more. If the content exceeds 0.10%, it adheres to the surface layer of the base material as scale and deteriorates the surface roughness. Therefore, the Si content is set to 0.10% or less. In order to give the steel sheet the desired strength, the range is preferably 0.01 to 0.05%. More preferably, it is 0.03% or less.
　Ｍｎ：０．７０～０．９０％
　Ｍｎは、固溶して鋼板の強度を増加させる作用を有する元素で安価であり、高価な他の合金元素の含有を最小限に抑えることを目的の一つとして含有する。本発明では、熱処理後の強度を維持するために、０．７０％以上の含有を必要とする。好ましくは０．８０％以上とする。一方、０．９０％を超える含有は、鋼板の靱性を低下させる。このため、Ｍｎ量は０．９０％以下とする。従って、好ましくは０．８０～０．９０％の範囲である。 Mn: 0.70 to 0.90%
Mn is an element that has the effect of dissolving and increasing the strength of the steel sheet, is inexpensive, and is contained as one of the purposes of minimizing the content of other expensive alloying elements. In the present invention, the content of 0.70% or more is required to maintain the strength after the heat treatment. It is preferably 0.80% or more. On the other hand, a content of more than 0.90% reduces the toughness of the steel sheet. Therefore, the amount of Mn is set to 0.90% or less. Therefore, it is preferably in the range of 0.80 to 0.90%.
　Ｐ：０．０３０％以下
Ｐは、鋼の強度を増加させる作用を有する元素である。この目的では０．００１％以上の含有が好ましい。しかし、靱性、とくに溶接部の靱性を低下させる元素である。０．０３０％を超えて含有すると、上記した悪影響が顕著となるため、Ｐ量は０．０３０％以下とする。好ましくは０．０１０％以下である。 P: 0.030% or less P is an element having an action of increasing the strength of steel. For this purpose, the content is preferably 0.001% or more. However, it is an element that reduces toughness, especially the toughness of welds. If the content exceeds 0.030%, the above-mentioned adverse effects become remarkable, so the amount of P is set to 0.030% or less. It is preferably 0.010% or less.
　Ｓ：０．０３０％以下
Ｓは、鋼中ではＭｎＳ等の硫化物系介在物として存在し、母材および溶接部の靱性を劣化させるとともに、鋳片中央偏析部などに多量に偏在して鋳片等における欠陥を発生しやすくする。このような傾向は０．０３０％を超える含有で顕著となる。このため、Ｓ量は０．０３０％以下とする。好ましくは０．０１０％以下である。一方でS量は少ないほど好ましいため、下限は限定されず０％であってよい。 S: 0.030% or less S exists as sulfide-based inclusions such as MnS in the steel, deteriorates the toughness of the base metal and the welded portion, and is unevenly distributed in a large amount in the central segregated portion of the slab and cast. It makes it easy for defects in pieces to occur. Such a tendency becomes remarkable when the content exceeds 0.030%. Therefore, the amount of S is set to 0.030% or less. It is preferably 0.010% or less. On the other hand, the smaller the amount of S, the more preferable, so the lower limit is not limited and may be 0%.
　ｓｏｌ．Ａｌ：０．００１～０．１０％
　ｓｏｌ．Ａｌは、脱酸材として有効であるとともに、窒化物を形成してオーステナイト粒径を小さくする効果を有する元素である。この効果を得る観点からｓｏｌ．Ａｌ量は０．００１％以上とする。一方でＡｌ量が過多の場合、靭性が劣化する。よってｓｏｌ．Ａｌ量は、０．１０％以下とし、好ましくは、０．０５％以下とする。 sol. Al: 0.001 to 0.10%
sol. Al is an element that is effective as a deoxidizing material and has an effect of forming a nitride to reduce the austenite particle size. From the viewpoint of obtaining this effect, sol. The amount of Al is 0.001% or more. On the other hand, if the amount of Al is excessive, the toughness deteriorates. Therefore, sol. The amount of Al is 0.10% or less, preferably 0.05% or less.
　Ｎ：０．０１０％以下
　Ｎは、延性および靭性を低下させる元素である。このため、Ｎ量は、０．０１０％以下とする。一方でＮ量は少ないほど好ましいため、下限は限定されず０％であってよい。ただし通常、Ｎは不純物として鋼中に不可避的に含有されるため、Ｎ量は工業的には０％超であってよい。後述の有効Ｔｉ量との関係から、Ｎ量は０．００５０％以下が好ましい。 N: 0.010% or less N is an element that reduces ductility and toughness. Therefore, the amount of N is set to 0.010% or less. On the other hand, the smaller the amount of N is, the more preferable it is. Therefore, the lower limit is not limited and may be 0%. However, since N is usually contained in steel as an impurity inevitably, the amount of N may be industrially more than 0%. The amount of N is preferably 0.0050% or less in relation to the amount of effective Ti described later.
　以上が本発明の基本化学成分であり、残部はＦｅ及び不可避的不純物からなる。 The above are the basic chemical components of the present invention, and the balance consists of Fe and unavoidable impurities.
　本発明では、必要に応じて、Ｔｉ：０．０１０～０．３０％、Ｎｉ：０．０１０～０．１０％、Ｃｕ：０．０１０～０．１０％、Ｃｒ：０．０１０～０．０５０％、Ｖ：０．０１～０．０５％、Ｍｏ：０．０１～０．１０％、Ｃａ：０．０００１～０．０２００％、Ｍｇ：０．０００１～０．０２００％の中から選ばれる１種または２種以上を選択元素として含有することができる。 In the present invention, Ti: 0.010 to 0.30%, Ni: 0.010 to 0.10%, Cu: 0.010 to 0.10%, Cr: 0.010 to 0. Select from 050%, V: 0.01 to 0.05%, Mo: 0.01 to 0.10%, Ca: 0.0001 to 0.0200%, Mg: 0.0001 to 0.0200%. One or more of these can be contained as a selective element.
　Ｔｉ：０．０１０～０．３０％
　Ｔｉは、Ｎとの親和力が強い元素であり、凝固時にＴｉＮとして析出し、鋼中の固溶Ｎを減少させ、冷間加工後のＮの歪時効による靭性劣化を低減する作用を有する。また、ＴｉＮとして析出していない余剰分のＴｉは、ＴｉＣを形成し、析出物としてピン留め効果を発揮し、結晶粒の粗大化を抑止する。このような効果を得るため、Ｔｉ量は０．０１０％以上とすることが好ましい。０．０２０％以上とすることがさらに好ましい。さらに、有効Ｔｉ量：（Ｔｉ／４８－Ｎ／１４）×４８において０．００３％以上含有することが好ましい。一方、Ｔｉ量が０．３０％を超えて含有すると、ＴｉＮ粒子が粗大化し、上記した効果が期待できなくなる。このため、Ｔｉを含有する場合、Ｔｉの含有量は０．３０％以下とすることが好ましい。より好ましくは０．１０％以下とする。有効Ｔｉ量では、０．２０％以下とすることが好ましい。 Ti: 0.010 to 0.30%
Ti is an element having a strong affinity for N, and has the effect of precipitating as TiN during solidification, reducing the solid solution N in steel, and reducing the deterioration of toughness due to strain aging of N after cold working. Further, the surplus Ti that has not been precipitated as TiN forms TiC, exerts a pinning effect as a precipitate, and suppresses coarsening of crystal grains. In order to obtain such an effect, the Ti amount is preferably 0.010% or more. It is more preferably 0.020% or more. Further, the effective Ti amount: (Ti / 48-N / 14) × 48 preferably contains 0.003% or more. On the other hand, if the Ti content exceeds 0.30%, the TiN particles become coarse and the above-mentioned effect cannot be expected. Therefore, when Ti is contained, the Ti content is preferably 0.30% or less. More preferably, it is 0.10% or less. The effective Ti amount is preferably 0.20% or less.
　Ｎｉ：０．０１０～０．１０％
　Ｎｉは、高温での相変態を抑止し、鋼板の強度を高める。この目的ではＮｉを含有する場合は、０．０１０％以上であることが好ましい。しかしながら、Ｎｉの含有量が多すぎると、鋼板の溶接性が低下する。したがって、Ｎｉの含有量は０．１０％以下であることが好ましい。より好ましくは、０．０５０％以下である。 Ni: 0.010 to 0.10%
Ni suppresses phase transformation at high temperatures and increases the strength of the steel sheet. For this purpose, when Ni is contained, it is preferably 0.010% or more. However, if the Ni content is too high, the weldability of the steel sheet deteriorates. Therefore, the Ni content is preferably 0.10% or less. More preferably, it is 0.050% or less.
　Ｃｕ：０．０１０～０．１０％
　Ｃｕは、微細な粒子として鋼中に析出し、鋼板の強度を高める。この目的でＣｕを含有する場合は、０．０１０％以上であることが好ましい。しかしながら、Ｃｕの含有量が多すぎると、鋼板の溶接性が低下する。したがって、Ｃｕを含有する場合、Ｃｕの含有量は０．１０％以下であることが好ましい。 Cu: 0.010 to 0.10%
Cu is deposited in the steel as fine particles to increase the strength of the steel sheet. When Cu is contained for this purpose, it is preferably 0.010% or more. However, if the Cu content is too high, the weldability of the steel sheet deteriorates. Therefore, when Cu is contained, the Cu content is preferably 0.10% or less.
　Ｃｒ：０．０１０～０．０５０％
　Ｃｒは、高温での相変態を抑止し、鋼板の強度を高める。この目的でＣｒを含有する場合は、０．０１０％以上であることが好ましい。しかしながら、Ｃｒ含有量が多すぎると、鋼板の加工性が低下して、生産性が低下する。したがって、Ｃｒを含有する場合、Ｃｒの含有量は０．０５０％以下であることが好ましい。 Cr: 0.010 to 0.050%
Cr suppresses phase transformation at high temperatures and increases the strength of the steel sheet. When Cr is contained for this purpose, it is preferably 0.010% or more. However, if the Cr content is too high, the workability of the steel sheet is lowered and the productivity is lowered. Therefore, when Cr is contained, the Cr content is preferably 0.050% or less.
　Ｖ：０．０１～０．０５％
　ＶはＴｉと同様に、鋼板を析出強化、細粒強化及び転位強化して、鋼板の強度を高める。この目的でＶを含有する場合は、０．０１％以上であることが好ましい。しかしながら、Ｖの含有量が多すぎると、炭窒化物が過剰に析出して鋼板の成形性が低下する。したがって、Ｖを含有する場合、Ｖの含有量は０．０５％以下であることが好ましい。 V: 0.01-0.05%
Similar to Ti, V enhances the strength of the steel sheet by precipitation strengthening, fine grain strengthening and dislocation strengthening. When V is contained for this purpose, it is preferably 0.01% or more. However, if the V content is too high, the carbonitride is excessively deposited and the formability of the steel sheet is deteriorated. Therefore, when V is contained, the V content is preferably 0.05% or less.
　Ｍｏ：０．０１～０．１０％
　Ｍｏは、Ｔｉ、Ｖと同様に、鋼板を析出強化、細粒強化及び転位強化して、鋼板の強度を高める。前記効果を得るために、Ｍｏ含有量を０．０１％以上とすることが好ましい。一方、Ｍｏ量が過多になると溶接性が低下する。そのため、Ｍｏを含有する場合、Ｍｏの含有量は０．１０％以下とする。好ましくは、０．０５％以下とする。 Mo: 0.01-0.10%
Similar to Ti and V, Mo enhances the strength of the steel sheet by precipitation strengthening, fine grain strengthening and dislocation strengthening. In order to obtain the above effect, the Mo content is preferably 0.01% or more. On the other hand, if the amount of Mo is excessive, the weldability is lowered. Therefore, when Mo is contained, the Mo content is 0.10% or less. It is preferably 0.05% or less.
　Ｃａ：０．０００１～０．０２００％
　Ｃａは、高温での安定性が高い酸硫化物を形成することで溶接性を向上させる元素である。前記効果を得るために、Ｃａ含有量を０．０００１％以上とすることが好ましい。一方、Ｃａ含有量が０．０２００％を超えると、清浄度が低下して鋼板の靭性が損なわれる。そのため、Ｃａを含有する場合、Ｃａの含有量は０．０２００％以下とすることが好ましい。 Ca: 0.0001-0.0200%
Ca is an element that improves weldability by forming an acid sulfide having high stability at high temperatures. In order to obtain the above effect, the Ca content is preferably 0.0001% or more. On the other hand, if the Ca content exceeds 0.0200%, the cleanliness is lowered and the toughness of the steel sheet is impaired. Therefore, when Ca is contained, the Ca content is preferably 0.0200% or less.
　Ｍｇ：０．０００１～０．０２００％
　Ｍｇは、高温での安定性が高い酸硫化物を形成することで溶接性を向上させる元素である。前記効果を得るためには、Ｍｇ含有量を０．０００１％以上とすることが好ましい。一方、Ｍｇ含有量が０．０２００％を超えると、Ｍｇの添加効果が飽和して含有量に見合う効果が期待できず、経済的に不利となる。そのため、Ｍｇを含有する場合、Ｍｇ含有量は０．０２００％以下とすることが好ましい。 Mg: 0.0001-0.0200%
Mg is an element that improves weldability by forming an acid sulfide having high stability at high temperatures. In order to obtain the above effect, the Mg content is preferably 0.0001% or more. On the other hand, if the Mg content exceeds 0.0200%, the effect of adding Mg is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. Therefore, when Mg is contained, the Mg content is preferably 0.0200% or less.
　Ｃｅｑが０．３０以上０．３２以下
　本発明において、熱処理後の強度確保の点から、Ｃｅｑは０．３０以上０．３２以下とする。Ｃｅｑは下記（１）式で表される。
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４・・・（１）
上記式（１）において、元素記号は各元素の含有量（質量％）を意味する。ただし、含有しない元素は０％とする。 Ceq is 0.30 or more and 0.32 or less In the present invention, Ceq is 0.30 or more and 0.32 or less from the viewpoint of ensuring strength after heat treatment. Ceq is expressed by the following equation (1).
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ... (1)
In the above formula (1), the element symbol means the content (mass%) of each element. However, the element not contained is 0%.
　Ｃｅｑが０．３０未満では、熱処理後の引張強さを維持することができない。一方、Ｃｅｑが０．３２を超えると、熱処理後の引張強さが目標値を超過してしまうため０．３２以下とした。 If Ceq is less than 0.30, the tensile strength after heat treatment cannot be maintained. On the other hand, if Ceq exceeds 0.32, the tensile strength after the heat treatment exceeds the target value, so the value is set to 0.32 or less.
　板厚：６ｍｍ以下
　本発明の熱延鋼板の板厚は、圧延後のしぼり加工性の点から、６ｍｍ以下とする。 Plate thickness: 6 mm or less The plate thickness of the hot-rolled steel sheet of the present invention shall be 6 mm or less from the viewpoint of squeezing workability after rolling.
　引張強さが４１０ＭＰａ以上５００ＭＰａ以下
　本発明において、引張強さは４１０ＭＰａ以上５００ＭＰａ以下とする。なお、この引張強度は熱処理前（焼準前）の引張強さである。引張強さが４１０ＭＰａ未満では、シリンダー用鋼板として所定の圧力の可燃性のガスを封入することができない。好ましくは４５０ＭＰａ以上とする。引張強さが５００ＭＰａ超えでは、しぼり加工時に加工性が悪化する。 Tensile strength is 410 MPa or more and 500 MPa or less In the present invention, the tensile strength is 410 MPa or more and 500 MPa or less. This tensile strength is the tensile strength before heat treatment (before normalizing). If the tensile strength is less than 410 MPa, a flammable gas having a predetermined pressure cannot be sealed as a steel plate for a cylinder. It is preferably 450 MPa or more. If the tensile strength exceeds 500 MPa, the workability deteriorates during squeezing.
　焼準温度８９０℃以上９４０℃以下の温度で３０分保持し、大気中で放冷し、常温となった熱処理後の引張強さが４１０ＭＰａ以上５００ＭＰａ以下であって、熱処理前後での引張強さの差が、５０ＭＰａ以下
　シリンダー用に用いられる熱延鋼板は、ブランク加工後、しぼり加工を行い、溶接をして熱処理（焼準）を行う。通常、焼準温度は８９０℃以上９４０℃以下、３０分の均熱時間にて焼準（熱処理）が行われており、この焼準（熱処理）前後での強度変化が少ない材料が求められている。本発明において、熱処理後、すなわち、焼準温度８９０℃以上９４０℃以下の温度で３０分保持し、大気中で放冷し、常温となった後の引張強さが４１０ＭＰａ以上５００ＭＰａ以下とする。熱処理後の引張強さを４１０ＭＰａ以上５００ＭＰａ以下とし、さらに、熱処理前後での引張強さの差が５０ＭＰａ以下とすることにより、熱処理前後での強度変化が少ない材料となる。なお、焼準については温度および均熱時間については特段制限がなく、例えば熱処理炉を用いて行えばよい。また、３０分の均熱後は、例えば大気中で放冷し、常温（例えば２５℃）となった鋼板（試験片）について、引張強さを測定すればよい。 The tensile strength after heat treatment, which was maintained at a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes and allowed to cool in the atmosphere to reach room temperature, was 410 MPa or higher and 500 MPa or lower, and the tensile strength before and after the heat treatment. The difference is 50 MPa or less. Hot-rolled steel sheets used for cylinders are squeezed after blanking, welded, and heat-treated (normalized). Normally, normalizing (heat treatment) is performed with a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower and a soaking time of 30 minutes, and a material with little change in strength before and after this normalizing (heat treatment) is required. There is. In the present invention, the tensile strength after heat treatment, that is, after being held at a normalizing temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes, allowed to cool in the atmosphere, and brought to room temperature, has a tensile strength of 410 MPa or higher and 500 MPa or lower. By setting the tensile strength after the heat treatment to 410 MPa or more and 500 MPa or less, and further setting the difference in the tensile strength before and after the heat treatment to 50 MPa or less, the material has little change in strength before and after the heat treatment. There are no particular restrictions on the temperature and soaking time of the normalizing, and for example, a heat treatment furnace may be used. Further, after 30 minutes of soaking, the tensile strength of the steel sheet (test piece) which has been allowed to cool in the atmosphere and has reached room temperature (for example, 25 ° C.) may be measured.
　Δｒが－０．２０以上０．２０以下
　本発明では、異方性の指標であるΔｒを－０．２０以上０．２０以下とする。なお、Δｒは下記（２）式で表される。
Δｒ＝（ｒ０＋ｒ９０）／２－ｒ４５・・・（２）
ｒ０、ｒ４５およびｒ９０は、それぞれ、鋼板の圧延方向に対して、０°、４５°及び９０°方向のｒ値（ランクフォード値）である。 Δr is −0.20 or more and 0.20 or less In the present invention, Δr, which is an index of anisotropy, is −0.20 or more and 0.20 or less. In addition, Δr is expressed by the following equation (2).
Δr = (r 0 + r 90 ) / 2-r 45 ... (2)
r 0 , r 45 and r 90 are r values (Rankford values) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction of the steel sheet, respectively.
　Δｒが－０．２０未満および０．２０超えでは、しぼり加工後に端面が耳伸びを起こし、組立時の溶接性が悪化する。 When Δr is less than -0.20 and more than 0.20, the end face is stretched after squeezing, and the weldability at the time of assembly deteriorates.
　なお、本発明の熱延鋼板の組織としては、フェライト相とパーライト相の２相組織であればよい。 The structure of the hot-rolled steel sheet of the present invention may be a two-phase structure of a ferrite phase and a pearlite phase.
　つぎに、本発明の製造方法について説明する。 Next, the manufacturing method of the present invention will be described.
　上述した成分組成を有する鋼を、転炉、電気炉等の溶製手段で常法により溶製し、連続鋳造法または造塊分塊法等で常法によりスラブとする。その後、スラブを加熱し、粗圧延を行い、仕上圧延後に冷却設備で冷却したのち、コイル状に巻取を行う。なお、溶製方法、鋳造方法については上述した方法に限定されるものではない。 Steel having the above-mentioned composition is melted by a conventional method by a melting means such as a converter or an electric furnace, and is made into a slab by a conventional method such as a continuous casting method or an ingot lumping method. After that, the slab is heated, rough-rolled, finished-rolled, cooled by a cooling facility, and then wound into a coil. The melting method and casting method are not limited to the above-mentioned methods.
　スラブの加熱温度：１１００℃以上１３００℃以下
　加熱温度が１１００℃未満では、炭化物が完全に溶解せず、固溶Ｃが不足するため、強度が低下しやすい。一方、加熱温度が１３００℃を超えると、組織が粗大化して鋼板の靱性が低下する。このため、スラブの加熱温度は１１００℃以上１３００℃以下の範囲とする。なお、好ましくは１１８０℃以上１２５０℃以下の範囲である。 Heating temperature of the slab: 1100 ° C or higher and 1300 ° C or lower When the heating temperature is lower than 1100 ° C, the carbides are not completely dissolved and the solid solution C is insufficient, so that the strength tends to decrease. On the other hand, when the heating temperature exceeds 1300 ° C., the structure becomes coarse and the toughness of the steel sheet decreases. Therefore, the heating temperature of the slab is set in the range of 1100 ° C. or higher and 1300 ° C. or lower. The temperature is preferably in the range of 1180 ° C. or higher and 1250 ° C. or lower.
　仕上圧延出側温度：８００℃以上９００℃以下
　熱間圧延に際し、粗圧延後、仕上圧延を行う。本発明では、仕上圧延出側温度は、８００℃以上９００℃以下とする。９００℃を超えると鋼板表面のスケールが厚くなりすぎてしまい、スケール剥離することが懸念される。一方で、温度が８００℃未満では、圧延中にスケールが破壊されたり、薄くなりすぎてしまうため黒皮としての保護性被膜として作用しなくなる。好ましくは８５０℃以上とする。なお、仕上圧延出側温度は鋼板の表面温度とする。 Finish rolling Outside temperature: 800 ° C or higher and 900 ° C or lower In hot rolling, rough rolling and then finish rolling are performed. In the present invention, the finished rolling output side temperature is 800 ° C. or higher and 900 ° C. or lower. If the temperature exceeds 900 ° C., the scale on the surface of the steel sheet becomes too thick, and there is a concern that the scale may peel off. On the other hand, if the temperature is less than 800 ° C., the scale is broken or becomes too thin during rolling, so that it does not act as a protective film as a black skin. The temperature is preferably 850 ° C. or higher. The temperature at the exit side of the finish rolling is the surface temperature of the steel sheet.
　仕上圧延の最終パスを含む連続する３パスでの合計の圧下率を５０％以上８０％以下として仕上圧延を行う
　仕上圧延の最終パスを含んだ連続する３パス、すなわち、仕上圧延の後段での圧下率を上げることにより、結晶粒度を上げ、加工時の異方性が小さい鋼板を製造することが可能になる。仕上圧延の最終パスを含んだ連続する３パスでの合計の圧下率が５０％を下回ると結晶粒が粗大化し、異方性の指標であるΔｒ値が－０．２０以上０．２０以下の範囲外となり、加工時に耳切代が大きくなる。なお、好ましくは６０％以上である。また、通板性の観点から８０％以下とする。また、温度低下に伴い圧延荷重が大きくなることから７０％以下が好ましい。 Perform finish rolling with the total rolling reduction in 3 consecutive passes including the final pass of finish rolling 50% or more and 80% or less. In 3 consecutive passes including the final pass of finish rolling, that is, in the latter stage of finish rolling. By increasing the rolling ratio, it becomes possible to increase the crystal grain size and manufacture a steel sheet having a small anisotropy during processing. When the total rolling reduction in three consecutive passes including the final pass of finish rolling is less than 50%, the crystal grains become coarse and the Δr value, which is an index of anisotropy, is -0.20 or more and 0.20 or less. It is out of the range, and the ear cutting allowance becomes large during processing. It is preferably 60% or more. Further, it is set to 80% or less from the viewpoint of plate-passability. Further, 70% or less is preferable because the rolling load increases as the temperature decreases.
　さらに本発明では、仕上圧延の後段での圧下率を上げるという点から、仕上圧延の最終パスの圧下率が２０％以上であることが好ましい。 Further, in the present invention, the rolling reduction of the final pass of the finish rolling is preferably 20% or more from the viewpoint of increasing the rolling reduction in the subsequent stage of the finish rolling.
　巻取温度：５５０℃以上６５０℃以下
　巻取温度が５５０℃未満では、熱処理前の強度が高くなる傾向にあり、熱処理前の強度を保証できない。一方で、巻取温度が６５０℃超えでは、同様に熱処理前の強度が低くなる傾向にあり強度を保障できない。また、成分実績のＣｅｑに応じて巻取温度を設定することで、強度を適正値に制御することがより好ましい。具体的には、Ｃｅｑから推奨される巻取温度（ＣＴ＊とする）と実際の巻取温度との差を３０℃以内に管理することが好ましい。なお、ＣＴ＊は以下の式（３）で表され、Ｃｅｑと巻取温度の関係から外挿した結果である。
ＣＴ＊＝５０００×Ｃｅｑ－９５０・・・（３）
ただし、式（３）はＣｅｑ：０．３０～０．３２で成立するものとする。 Winding temperature: 550 ° C or higher and 650 ° C or lower When the winding temperature is lower than 550 ° C, the strength before heat treatment tends to be high, and the strength before heat treatment cannot be guaranteed. On the other hand, when the winding temperature exceeds 650 ° C., the strength before the heat treatment also tends to be low, and the strength cannot be guaranteed. Further, it is more preferable to control the strength to an appropriate value by setting the winding temperature according to the Ceq of the actual component. Specifically, it is preferable to control the difference between the winding temperature recommended by Ceq (referred to as CT *) and the actual winding temperature within 30 ° C. Note that CT * is expressed by the following equation (3) and is the result of extrapolation from the relationship between Ceq and the winding temperature.
CT * = 5000 x Ceq-950 ... (3)
However, it is assumed that the formula (3) is established by Ceq: 0.30 to 0.32.
　なお、仕上圧延後はランナウト冷却を行い、巻き取ればよい。 After finishing rolling, runout cooling may be performed and winding may be performed.
　以下、本発明の実施例について説明する。 Hereinafter, examples of the present invention will be described.
　表１に示す成分組成の鋼を転炉により溶製し、連続鋳造法でスラブとした後、１２３０℃でスラブを加熱し、表２に示す条件にて仕上げ圧延を７パスとする熱間圧延を行った。なお、板厚は、２．６ｍｍとした。 Steel with the composition shown in Table 1 is melted by a converter to make a slab by a continuous casting method, then the slab is heated at 1230 ° C., and hot rolling with 7 passes of finish rolling under the conditions shown in Table 2. Was done. The plate thickness was 2.6 mm.
　得られた熱延鋼板を用いて、以下の試験方法に従い、熱処理前後での引張特性、Δｒの評価を行った。 Using the obtained hot-rolled steel sheet, the tensile properties and Δr before and after the heat treatment were evaluated according to the following test method.
　熱処理前の熱延鋼板について、熱延鋼板の幅中央位置より、圧延方向に対して直角方向にＪＩＳ５号引張試験片（ＪＩＳ　Ｚ　２２０１）を採取した。また、熱延鋼板を９３０℃に均熱した炉で３０分熱処理を行い、取り出し後、大気中で室温まで放冷したサンプルを、熱処理後の熱延鋼板とした。熱処理後の熱延鋼板の幅方向１／４の位置より、圧延方向に対して平行方向にＪＩＳ５号引張試験片（ＪＩＳ　Ｚ　２２０１）を採取した。これらの試験片を用いて、歪速度が１０－３／ｓとするＪＩＳ　Ｚ　２２４１の規定に準拠した引張試験を行った。 With respect to the hot-rolled steel sheet before the heat treatment, a JIS No. 5 tensile test piece (JIS Z 2201) was collected from the center position of the width of the hot-rolled steel sheet in a direction perpendicular to the rolling direction. Further, the hot-rolled steel sheet was heat-treated in a furnace heated to 930 ° C. for 30 minutes, taken out, and then allowed to cool to room temperature in the atmosphere, and the sample was used as the heat-treated hot-rolled steel sheet. A JIS No. 5 tensile test piece (JIS Z 2201) was collected from a position 1/4 of the width direction of the hot-rolled steel sheet after the heat treatment in a direction parallel to the rolling direction. Using these test pieces, a tensile test was performed in accordance with JIS Z 2241 regulations with a strain rate of 10 -3 / s.
　Δｒの評価は、熱延鋼板の幅中央位置より、圧延方向に対して０°、４５°、９０°のそれぞれの方向からＪＩＳ５号引張試験片（ＪＩＳ　Ｚ　２２０１）を採取し、この試験片を用いて、ＪＩＳ　Ｚ２２４１の規定に準拠して実施した。 For the evaluation of Δr, JIS No. 5 tensile test piece (JIS Z 2201) was collected from each direction of 0 °, 45 °, and 90 ° with respect to the rolling direction from the center position of the width of the hot-rolled steel sheet, and this test piece was used. It was used and carried out in accordance with the regulations of JIS Z2241.
　各試験結果を表２に記載する。 The results of each test are shown in Table 2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
 　表２の結果から、本発明例はいずれも熱処理前後の引張強さの差が小さく、かつ異方性が小さい。なお、参考例としてＮｂを含有させた鋼種Ｑについては、異方性が大きくなった。
Figure JPOXMLDOC01-appb-T000002
 From the results in Table 2, in each of the examples of the present invention, the difference in tensile strength before and after the heat treatment is small, and the anisotropy is small. As a reference example, the anisotropy of the steel grade Q containing Nb became large.

Claims (3)

  1. 　成分組成として、質量％で、Ｃ：０．１６０～０．２０％、Ｓｉ：０．０１～０．１０％、Ｍｎ：０．７０～０．９０％、Ｐ：０．０３０％以下、Ｓ：０．０３０％以下、ｓｏｌ．Ａｌ：０．００１～０．１０％、Ｎ：０．０１０％以下を含み、残部がＦｅ及び不可避的不純物からなり、
    下記（１）式で表されるＣｅｑが０．３０以上０．３２以下であり、
    板厚６ｍｍ以下であり、
    引張強さが４１０ＭＰａ以上５００ＭＰａ以下であり、
    かつ、焼準温度８９０℃以上９４０℃以下の温度で３０分保持し、大気中で放冷し、常温となった熱処理後の引張強さが４１０ＭＰａ以上５００ＭＰａ以下であって、熱処理前後での引張強さの差が、５０ＭＰａ以下であり、
    下記（２）式で表されるΔｒが－０．２０以上０．２０以下である熱延鋼板。
    Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４・・・（１）
    上記式（１）において、元素記号は各元素の含有量（質量％）を意味する。ただし、含有しない元素は０％とする。
    Δｒ＝（ｒ０＋ｒ９０）／２－ｒ４５・・・（２）
    ｒ０、ｒ４５およびｒ９０は、それぞれ、鋼板の圧延方向に対して、０°、４５°及び９０°方向のｒ値（ランクフォード値）である。     As a component composition, in mass%, C: 0.160 to 0.20%, Si: 0.01 to 0.10%, Mn: 0.70 to 0.90%, P: 0.030% or less, S : 0.030% or less, sol. Al: 0.001 to 0.10%, N: 0.010% or less, the balance consists of Fe and unavoidable impurities.
    Ceq represented by the following equation (1) is 0.30 or more and 0.32 or less.
    The plate thickness is 6 mm or less,
    The tensile strength is 410 MPa or more and 500 MPa or less,
    In addition, the normalizing temperature was maintained at a temperature of 890 ° C. or higher and 940 ° C. or lower for 30 minutes, and the product was allowed to cool in the atmosphere. The difference in strength is 50 MPa or less,
    A hot-rolled steel sheet in which Δr represented by the following equation (2) is −0.20 or more and 0.20 or less.
    Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ... (1)
    In the above formula (1), the element symbol means the content (mass%) of each element. However, the element not contained is 0%.
    Δr = (r 0 + r 90 ) / 2-r 45 ... (2)
    r 0 , r 45 and r 90 are r values (Rankford values) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction of the steel sheet, respectively.
  2. 　前記成分組成は、さらに、質量％で、Ｔｉ：０．０１０～０．３０％、Ｎｉ：０．０１０～０．１０％、Ｃｕ：０．０１０～０．１０％、Ｃｒ：０．０１０～０．０５０％、Ｖ：０．０１～０．０５％、Ｍｏ：０．０１～０．１０％、Ｃａ：０．０００１～０．０２００％、Ｍｇ：０．０００１～０．０２００％から選択される１種または２種以上を含む請求項１に記載の熱延鋼板。 Further, the component composition is Ti: 0.010 to 0.30%, Ni: 0.010 to 0.10%, Cu: 0.010 to 0.10%, Cr: 0.010 to 0.010 to% by mass. Select from 0.050%, V: 0.01 to 0.05%, Mo: 0.01 to 0.10%, Ca: 0.0001 to 0.0200%, Mg: 0.0001 to 0.0200% The hot-rolled steel sheet according to claim 1, which comprises one kind or two or more kinds thereof.
  3. 　請求項１または２に記載の熱延鋼板の製造方法であって、
    前記成分組成を有するスラブを１１００℃以上１３００℃以下に加熱し、次いで、熱間圧延を施すに際し、粗圧延後、仕上圧延出側温度を８００℃以上９００℃以下とし、かつ、仕上圧延の最終パスを含む連続する３パスでの合計の圧下率を５０％以上８０％以下として仕上圧延を行った後、ランナウト冷却し、その後５５０℃以上６５０℃以下の巻取温度で巻き取る熱延鋼板の製造方法。     The method for manufacturing a hot-rolled steel sheet according to claim 1 or 2.
    When a slab having the above component composition is heated to 1100 ° C. or higher and 1300 ° C. or lower, and then hot-rolled, the finish rolling output side temperature is set to 800 ° C. or higher and 900 ° C. or lower after rough rolling, and the final finish rolling. A hot-rolled steel sheet that is runout-cooled after finishing rolling with the total rolling reduction in three consecutive passes including the pass set to 50% or more and 80% or less, and then wound at a winding temperature of 550 ° C or higher and 650 ° C or lower. Production method.
PCT/JP2021/036705 2020-10-30 2021-10-04 Hot-rolled steel sheet and method for producing same WO2022091709A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2022512727A JP7298777B2 (en) 2020-10-30 2021-10-04 Hot-rolled steel sheet and manufacturing method thereof

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2020182036 2020-10-30
JP2020-182036 2020-10-30

Publications (1)

Publication Number Publication Date
WO2022091709A1 true WO2022091709A1 (en) 2022-05-05

Family

ID=81382448

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2021/036705 WO2022091709A1 (en) 2020-10-30 2021-10-04 Hot-rolled steel sheet and method for producing same

Country Status (2)

Country Link
JP (1) JP7298777B2 (en)
WO (1) WO2022091709A1 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS54143720A (en) * 1978-04-28 1979-11-09 Nippon Steel Corp Manufacture of nb-containing high tensile hot rolled steel plate with low plane plastic anisotropy
JP2001164335A (en) * 1999-12-06 2001-06-19 Nippon Steel Corp High workability and good weldability sulfuric acid dew point corrosion resistant steel sheet
JP2004099935A (en) * 2002-09-05 2004-04-02 Jfe Steel Kk Hot-rolled material of steel pipe for hydroform forming, and manufacturing method therefor
JP2007175767A (en) * 2005-12-26 2007-07-12 Mitsubishi-Hitachi Metals Machinery Inc Method for shear-joining continuously hot-rolled low-carbon steel material, and continuous hot-rolling apparatus

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS54143720A (en) * 1978-04-28 1979-11-09 Nippon Steel Corp Manufacture of nb-containing high tensile hot rolled steel plate with low plane plastic anisotropy
JP2001164335A (en) * 1999-12-06 2001-06-19 Nippon Steel Corp High workability and good weldability sulfuric acid dew point corrosion resistant steel sheet
JP2004099935A (en) * 2002-09-05 2004-04-02 Jfe Steel Kk Hot-rolled material of steel pipe for hydroform forming, and manufacturing method therefor
JP2007175767A (en) * 2005-12-26 2007-07-12 Mitsubishi-Hitachi Metals Machinery Inc Method for shear-joining continuously hot-rolled low-carbon steel material, and continuous hot-rolling apparatus

Also Published As

Publication number Publication date
JPWO2022091709A1 (en) 2022-05-05
JP7298777B2 (en) 2023-06-27

Similar Documents

Publication Publication Date Title
JP5846311B2 (en) Thick high-strength steel excellent in welding heat affected zone CTOD characteristics and method for producing the same
EP2272994B1 (en) High-tensile strength steel and manufacturing method thereof
JP5750546B2 (en) Low yield ratio high toughness steel sheet and manufacturing method thereof
JP4644076B2 (en) High strength thin steel sheet with excellent elongation and hole expansibility and manufacturing method thereof
WO2015088040A1 (en) Steel sheet and method for manufacturing same
JPWO2018199145A1 (en) High Mn steel and method of manufacturing the same
JP2006291348A (en) Low yield-ratio high-tensile steel having excellent weldability, and its production method
JP4644075B2 (en) High-strength steel sheet with excellent hole expansibility and manufacturing method thereof
JP2015004081A (en) High-yield-ratio high-strength hot-rolled steel sheet which is reduced in variation of strength in coil width direction and is excellent in toughness and production method thereof
JP4514150B2 (en) High strength steel plate and manufacturing method thereof
JP5087966B2 (en) Method for producing hot-rolled steel sheet with excellent surface quality and ductile crack propagation characteristics
JP2004124113A (en) Non-water-cooled thin low yield ratio high tensile steel, and production method therefor
JP4133175B2 (en) Non-water cooled thin low yield ratio high strength steel with excellent toughness and method for producing the same
JPH1112657A (en) Manufacture of ti added hot rolled high tensile steel plate having excellent formability
JP4433844B2 (en) Method for producing high strength steel with excellent fire resistance and toughness of heat affected zone
WO2022091709A1 (en) Hot-rolled steel sheet and method for producing same
JPH1030122A (en) Production of hot rolled steel strip with high strength and high toughness
KR102112172B1 (en) Cold-rolled steel sheet for flux cored wire and manufacturing the same
WO2016068094A1 (en) High-tensile steel sheet having excellent low-temperature toughness in weld heat-affected zone, and method for manufacturing same
JP2020525647A (en) Flux-cored wire cold-rolled steel sheet and method for producing the same
JP7207358B2 (en) Manufacturing method of low yield ratio high tensile steel plate
JP3823628B2 (en) Method for producing high-strength steel of 60 kg with excellent weldability and toughness after strain aging
JP2001089816A (en) Method of manufacturing high strength hot rolled steel plate
JP2003129133A (en) Method for manufacturing thick steel plate with high strength and high toughness
JP3383156B2 (en) Manufacturing method of steel sheet for high strength electric resistance welded steel pipe

Legal Events

Date Code Title Description
ENP Entry into the national phase

Ref document number: 2022512727

Country of ref document: JP

Kind code of ref document: A

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

Ref document number: 21885828

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 21885828

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 523440524

Country of ref document: SA