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.

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• 2021
  • 2021-10-04 WO PCT/JP2021/036705 patent/WO2022091709A1/ja active Application Filing
  • 2021-10-04 JP JP2022512727A patent/JP7298777B2/ja active Active

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