US20110318217A1 - Cold-rolled steel sheet with excellent bending workability, method for manufacturing the same, and member using the same - Google Patents
Cold-rolled steel sheet with excellent bending workability, method for manufacturing the same, and member using the same Download PDFInfo
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- US20110318217A1 US20110318217A1 US13/254,050 US201013254050A US2011318217A1 US 20110318217 A1 US20110318217 A1 US 20110318217A1 US 201013254050 A US201013254050 A US 201013254050A US 2011318217 A1 US2011318217 A1 US 2011318217A1
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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
- 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
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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 by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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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 by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
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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 by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0436—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/003—Cementite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- 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
- C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
Definitions
- the present invention relates to cold-rolled steel sheets, used in fields such as electric appliances, building materials, and automobiles, for machining and particularly relates to a cold-rolled steel sheet with excellent bending workability, a method for manufacturing the same, and a member using the same.
- Cold-rolled steel sheets called SPCC specified in JIS G 3141, for general machining are used for members, such as electric appliance housings, construction scaffold planks, cabinet side plates, and cabinet top plates, not subjected to extremely severe drawing or stretching among members for use in electric appliances, building materials, automobiles, or the like.
- steel sheets used for members are preferably thin-gauged; however, thin gauging causes problems with a reduction in member strength.
- Such problems with a reduction in member strength are solved by the use of a high-strength steel sheet, disclosed in NPL 1, having a tensile strength TS of 390 MPa or more.
- Such high-strength steel sheets contain an expensive element such as Mn and therefore have high manufacturing costs. Thin gauging does not lead to a reduction in manufacturing cost in many cases.
- cold-rolled steel sheets used for electric appliances, building materials, automobiles, and the like are manufactured by recrystallization annealing after cold rolling.
- inexpensive high-strength steel sheets known are cold-rolled steel sheets which are not annealed after cold rolling and which are called full hard material.
- the full hard material has a rolling texture, does not contain a large amount of any expensive alloy element, and has high strength due to work hardening by cold working. Therefore, the full hard material is suitable for thin-gauging steel sheets at low cost.
- thin gauging causes a reduction in rigidity and therefore a steel sheet sometimes needs to be bent in the rolling direction and rolling transverse direction thereof.
- the bending workability thereof is preferably improved.
- members used in electric appliances have screw pilot holes formed by burring and are screwed in some cases.
- the full hard material preferably has good burring workability for screw pilot holes and high screw-breaking torque.
- PTL 6 discloses a technique in which the ductility of an extremely thin steel sheet with a thickness of 0.25 mm during flanging subsequent to DI processing is improved in such a manner that the crystal grain diameter thereof is adjusted to an ultra fine level, 8 ⁇ m or less, by the control of the content of each of C, Mn, and Al and the addition of Nb.
- PTL 7 proposes a method for manufacturing a full hard material suitable for applications such as such as electric appliances, building materials, and automobiles, that is, a method for manufacturing a steel sheet having a component composition of more than 0.0040% to 0.08% C, less than 0.030% P, less than 0.010% Ti, and less than 0.010% Nb, the remainder being Fe and unavoidable impurities, in such a manner that the temperature of coiling after hot rolling is adjusted to 650° C.
- the average grain diameter is adjusted to less than 30 ⁇ m before cold rolling, and an annealing step is not performed after cold rolling at 70% or more or in such a manner that hot rolling is performed at a finishing temperature lower than the Ar 3 transformation point and an annealing step is not performed after cold rolling at 70% or more.
- the present invention provides an inexpensive cold-rolled steel sheet which has excellent bending workability and which can be worked by severe 90-degree bending at a punch tip curvature of 2R or less even though being thin-gauged, the cold-rolled steel sheet being excellent in burring workability for screw pilot holes or being capable of advantageously achieving high screw-breaking torque; a method for manufacturing the same; and a member using the same.
- the sheet thickness direction ultimate ductility of the cold-rolled steel sheet is preferably adjusted to 1.3 or more in such a manner that the component composition, particularly the content of C, is appropriately adjusted and the morphology of precipitates in a hot-rolled steel sheet is adjusted before cold rolling.
- sheet thickness direction ultimate ductility refers to the natural logarithm Ln(t 0 /t 1 ) of the ratio of the thickness t 0 of an untested steel sheet to the thickness t 1 of the fracture surface of the tested steel sheet as determined by a tensile test.
- the average crystal grain diameter of a hot-rolled steel sheet is preferably controlled to 25 ⁇ m or less before cold rolling.
- the present invention has been made on the basis of the above findings and provides a cold-rolled steel sheet which is excellent in bending workability and which, according to exemplary embodiments, has a component composition of 0.025% or less C, 0.1% or less Si, 0.05% to 0.5% Mn, 0.03% or less P, 0.02% or less S, and 0.01% to 0.1% sol. Al on a mass basis, the remainder being Fe and unavoidable impurities; a microstructure that is a ferrite rolling texture; a tensile strength TS of 390 MPa or more, a thickness of 0.4 mm or more; and a sheet thickness direction ultimate ductility of 1.3 or more.
- the present invention also provides a cold-rolled steel sheet which is excellent in bending workability and which, according to exemplary embodiments, has a component composition of 0.025% or less C, 0.1% or less Si, 0.05% to 0.5% Mn, 0.03% or less P, 0.02% or less S, and 0.01% to 0.1% sol. Al on a mass basis, the remainder being Fe and unavoidable impurities; a tensile strength TS of 390 MPa or more, a yield ratio of 80% or more; a thickness of 0.4 mm or more; and a sheet thickness direction ultimate ductility of 1.3 or more.
- the present invention provides a cold-rolled steel sheet, prepared by cold rolling a hot-rolled steel sheet, having excellent bending workability.
- the cold-rolled steel sheet has, according to exemplary embodiments, a component composition of 0.025% or less C, 0.1% or less Si, 0.05% to 0.5% Mn, 0.03% or less P, 0.02% or less S, and 0.01% to 0.1% sol. Al on a mass basis, the remainder being Fe and unavoidable impurities; a tensile strength TS of 390 MPa or more; a yield ratio of 80% or more, a thickness of 0.4 mm or more; and a sheet thickness direction ultimate ductility of 1.3 or more.
- the number of cementite precipitates in the hot-rolled steel sheet is preferably less than 5.0 ⁇ 10 3 per mm 2 .
- the hot-rolled steel sheet preferably has an average crystal grain diameter of 25 ⁇ m or less.
- the content of C in the component composition is preferably 0.0040% or less on a mass basis.
- the component composition preferably further contains one or two of 0.002% to 0.05% Ti and 0.002% to 0.05% Nb or preferably further contains 0.0001% to 0.005% B.
- the tensile strength TS is preferably 490 MPa or more.
- the cold-rolled steel sheet is preferably used to form a member having a bent portion.
- the cold-rolled steel sheet with excellent bending workability according to the present invention can be manufactured in such a manner that a steel having the above component composition is hot-rolled at a finishing temperature not lower than the Ar 3 transformation point thereof, is coiled at a coiling temperature of 500° C. to 650° C., is pickled, and is then cold-rolled at a rolling reduction of 85% or less such that a cold-rolled steel sheet has a tensile strength TS of 390 MPa or more and a thickness of 0.4 mm or more.
- recovery annealing is preferably performed after cold rolling.
- the following steel sheet can be provided: a high-strength steel sheet which has a tensile strength TS of 390 MPa or more and which is capable of being worked by severe 90-degree bending at a punch tip curvature of 2R or less.
- the use of the steel sheet allows a member to be thin-gauged.
- the use of a cold-rolled steel sheet as cold-rolled or recovery annealed enables cost reduction without using any expensive strengthening element.
- the present invention can be applied to members having screw pilot hole-bored portions by adjusting the tensile strength TS of the cold-rolled steel sheet.
- a feature of the present invention is that high strength, that is, a tensile strength of 390 MPa or more, and excellent bending workability enabling severe 90-degree bending at a punch tip curvature of 2R or less can both be achieved in such a manner that the component composition and the state of precipitates present in a hot-rolled steel sheet are adjusted, the strength is increased by adjusting the rolling reduction during cold rolling, and a cold-rolled steel sheet, as cold-rolled or recovery annealed, having a sheet thickness direction ultimate ductility of 1.3 or more is obtained.
- Another feature thereof is that burring workability for screw pilot holes and screw-breaking torque are improved by appropriately adjusting the crystal grain diameter of the hot-rolled steel sheet and the tensile strength TS of the cold-rolled steel sheet.
- a cold-rolled steel sheet with excellent bending workability according to embodiments of the present invention is described below in detail.
- the unit “%” relating to the component composition refers to “% by mass” unless otherwise specified.
- the content of C is more than 0.025%, a large number of coarse cementite precipitates are formed during hot rolling and therefore 90-degree bending at a punch tip curvature of 2R or less is seriously deteriorated.
- the content of C is preferably 0.025% or less and more preferably 0.020% or less.
- the Content of C is preferably 0.0040% or less and more preferably 0.0030% or less. An extremely reduction in the Content of C leads to an increase in cost; hence, the Content of C is preferably 0.0010% or more.
- the Content of C is as low as less than 0.0010%, the crystal grain diameter of the hot-rolled steel sheet is large, a machined portion thereof is likely to be disfigured, and the burring workability thereof is likely to be low particularly in the case of performing burring for the purpose of forming screw pilot holes.
- the Content of C is preferably 0.0010% or more.
- the upper limit thereof is preferably 0.1% and more preferably 0.013% or less.
- Mn is an element that forms a sulfide to improve hot shortness; hence, the content thereof is 0.05% or more. On the other hand, when the content thereof is large, the effect thereof is likely to be saturated and costs are increased; hence, the upper limit thereof is 0.5%.
- the upper limit thereof is preferably 0.02% and more preferably 0.010% or less.
- the content of S is extremely low, the crystal grain diameter of the hot-rolled steel sheet is likely to be large and the burring workability thereof is sometimes low in the case of performing burring for the purpose of forming screw pilot holes; hence, the lower limit thereof is preferably about 0.003%.
- Al has a deoxidizing action and therefore the content of sol.
- Al is 0.01% or more. In view of low cost, the upper limit thereof is 0.1%.
- Ti and Nb have the effect of reducing the crystal grain diameter of the hot-rolled steel sheet to improve the appearance of a bent portion.
- the Content of C is 0.0040% or less, the crystal grain diameter of the hot-rolled steel sheet is likely to be large and burring workability for screw pilot holes is deteriorated in some cases.
- at least one thereof is preferably contained.
- 0.0001% to 0.005% B may be further contained.
- Ti has the effect of reducing the crystal grain diameter of the hot-rolled steel sheet and therefore 0.002% or more Ti is preferably added.
- the crystal grain diameter of the hot-rolled steel sheet is large, the bent portion is surface-roughened and is disfigured. This can be improved by the effect of Ti.
- burring workability is likely to be reduced and a problem is likely to occur particularly when the Content of C is 0.004% or less.
- the content thereof is more than 0.05%, the effect thereof is saturated and costs are increased; hence, the upper limit of the content of Ti is preferably 0.05% and more preferably 0.04% or less.
- Nb as well as Ti, has the effect of reducing the crystal grain diameter of the hot-rolled steel sheet, the effect of improving the appearance of the bent portion, and/or the effect of improving burring workability for screw pilot holes. Therefore, the content thereof is preferably 0.002% or more. On the other hand, when the content thereof is more than 0.05%, the effect thereof is saturated and costs are increased; hence, the upper limit of the content of Nb is preferably 0.05% and more preferably 0.04% or less.
- B has stronger affinity to N as compared with Al and therefore suppresses the formation of fine AlN precipitates which are unevenly formed after hot rolling to cause a difference in longitudinal strength of a coil and reduces a difference in thickness of the cold-rolled steel sheet.
- solute C and solute N in steel are fixed by the addition of Ti and/or Nb, B segregates at grain boundaries and increases the strength of the grain boundaries to improve cold shortness, which is remarkable particularly when the content of C is 0.004% or less.
- the content of B is preferably 0.0001% or more.
- the upper limit of the content of B is preferably 0.005% and more preferably 0.003%.
- the present invention provides a high-strength cold-rolled steel sheet which can be thin-gauged and which preferably has a thickness of 0.4 mm or more and a tensile strength TS of 390 MPa or more.
- the thickness is advantageously 0.4 mm or more and more preferably 0.5 mm or more.
- the upper limit of the thickness thereof is preferably about 3.2 mm.
- the upper limit of the thickness thereof is about 1.6 mm.
- a tensile strength TS of 390 MPa or more is preferred as described above.
- high strength is achieved by work hardening during cold rolling. That is, high strength is achieved by cold rolling the hot-rolled steel sheet having the component composition specified in embodiments of the present invention.
- the sheet thickness direction ultimate ductility, Ln (the thickness of an untested sheet/the thickness of a fracture surface of the tested sheet), is preferably used in the present invention.
- Ln the thickness of an untested sheet/the thickness of a fracture surface of the tested sheet.
- the sheet thickness direction ultimate ductility is 1.3 or more, 90-degree bending at a punch tip curvature of 2R or less can be performed and most severe 90-degree bending at 0R (a punch tip curvature of 0 mm) can be performed.
- the sheet thickness direction ultimate ductility is 1.5 or more, contact bending can be performed.
- the sheet thickness direction ultimate ductility is preferably 1.3 or more and more preferably 1.5 or more.
- the sheet thickness direction ultimate ductility is determined as described below. That is, JIS #5 tensile specimens are taken along a rolling direction and a rolling transverse direction and are subjected to a tensile test specified in JIS Z 2241, fracture surfaces of the fractured specimens are measured for thickness, the sheet thickness direction ultimate ductility in the rolling direction and that in the rolling transverse direction are averaged, and the average is defined as the sheet thickness direction ultimate ductility.
- the number of cementite precipitates in the hot-rolled steel sheet is preferably controlled.
- Cementite has a significant effect on the bending workability of the cold-rolled steel sheet therefore the number of the cementite precipitates is preferably small.
- the number of the cementite precipitates is less than 5.0 ⁇ 10 3 per mm 2 , severe 90-degree bending at a punch tip curvature of 2R or less can be performed.
- the number thereof is preferably less than 2.3 ⁇ 10 3 per mm 2 .
- the content of C is 0.0040% or less, the number of the cementite precipitates is small and is less than 0.1 ⁇ 10 3 per mm 2 .
- the average ferrite crystal grain diameter of the hot-rolled steel sheet, which is a cold-rolling material is preferably 25 ⁇ m or less.
- punched holes are sometimes burred and are then threaded for the purpose of boring screw pilot holes.
- burring workability is reduced when the average ferrite crystal grain diameter is more than 25 ⁇ m. Therefore, the upper limit thereof is preferably 25 ⁇ m.
- the average ferrite crystal grain diameter is preferably 15 ⁇ m or less.
- An excessive reduction in grain diameter requires a special manufacturing process such as large strain inducing during hot rolling and therefore causes an increase in cost, which is not preferred.
- the average crystal grain diameter of the hot-rolled steel sheet is 8 ⁇ m or more, there is no problem with burring workability; hence, the average crystal grain diameter thereof is preferably 8 ⁇ m or more.
- the cold-rolled steel sheet preferably has a tensile strength TS of 490 MPa or more and a screw-breaking torque of 20 kgf ⁇ cm or more. That is, in the present invention, the average ferrite crystal grain diameter of the hot-rolled steel sheet, which is a cold rolling material, is preferably adjusted to 25 ⁇ m or less and the tensile strength TS thereof is preferably adjusted to 490 MPa or more, whereby the cold-rolled steel sheet is allowed to have excellent bending workability and excellent screw-breaking torque.
- the cold-rolled steel sheet according to the present invention can be manufactured in such a manner that the steel having the above component composition is hot-rolled at a finishing temperature not lower than the Ar 3 transformation point thereof, is coiled at a coiling temperature of 500° C. to lower than 650° C., is pickled, and is then cold-rolled at a rolling reduction of 85% or less such that a cold-rolled steel sheet has a tensile strength TS of 390 MPa or more and a thickness of 0.4 mm or more.
- the hot-rolled steel sheet is likely to have a large average crystal grain diameter and a dual-phase microstructure; hence, the finishing temperature is not lower than the Ar 3 transformation point.
- a strain of 10% to less than 25% is preferably induced therein during final rolling in finish rolling. This is because a strain of less than 10% causes the generation frequency of transformation nuclei to be reduced and causes grains in the hot-rolled steel sheet to be coarse and a strain of 25% or more causes the crown control of the hot-rolled steel sheet to be difficult and is likely to cause a reduction in quality after cold rolling.
- the Ar 3 transformation point can be determined from a thermal expansion curve that is obtained in such a manner that an 8-mm p machining Formaster test piece with a height of 12 mm is prepared, is heated to 1200° C., is cooled to 1000° C. at a rate of 10° C./s, is compressed at 1000° C. with a strain of 30%, and is then cooled to 200° C. at a rate of 5° C./s.
- the coiling temperature is preferably 650° C. or lower and more preferably 600° C. or lower.
- the coiling temperature is 500° C. or higher.
- the hot-rolled steel sheet is pickled under ordinary conditions.
- the rolling reduction which is the reduction achieved by cold rolling
- the rolling reduction is more than 85%, the bending workability in the rolling transverse direction is significantly reduced and therefore 90-degree bending at a punch tip curvature of 2R or less is difficult.
- the rolling reduction is preferably 85% or less and more preferably 75% or less.
- the rolling reduction may be appropriately determined such that a desired tensile strength TS of 390 MPa or more is achieved.
- the rolling reduction in order to achieve a tensile strength TS of 390 MPa or more, the rolling reduction is preferably 9% or more.
- the rolling reduction is preferably 30% or more.
- the cold-rolled steel sheet can be improved in bending workability by recovery annealing after cold rolling.
- recovery annealing refers to annealing under conditions capable of maintaining TS 390 MPa and YR ⁇ 80%.
- a ferrite rolling texture is substantially maintained in the form of a microstructure. That is, in such recovery annealing, the strain energy accumulated in a steel sheet by cold rolling is partly released by the thermal energy applied thereto during annealing, a ferrite rolling texture is mostly maintained in the form of a microstructure, and the area fraction of polygonal ferrite grains that are recrystallized grains is about 10% or less.
- annealing at 500° C. for 50 s to 150 s is preferred in the case of the addition of none of Ti and Nb or annealing at 600° C. for 50 s to 150 s is preferred in the case of the addition of Ti and/or Nb.
- the cold-rolled steel sheet according to the present invention may be plated with zinc, nickel, or the like for automobile or for home appliance use.
- plating when plating is performed by a hot dipping process, immersion in a plating bath or heat treatment subsequent to plating can serve as recovery annealing. Even if the cold-rolled steel sheet is coated with a chemical conversion coating or is processed into a laminated steel sheet, advantageous effects of the present invention are not impaired.
- the bending workability was evaluated on the basis that a specimen with no cracks caused by the 90-degree V-bending test or the contact bending test was rated as A, one with no cracks caused by the 90-degree V-bending test was rated as B, and one with cracks caused by the 90-degree V-bending test was rated as C.
- the bent portion was checked for surface roughness.
- 100 mm ⁇ 100 mm specimens for a hole expanding test were cut out from the cold-rolled steel sheets. After a 10-mm ⁇ hole was punched at the center of each specimen, a 60-degree conical punch was pushed up through the hole in the direction opposite to burrs.
- the yield ratio YR 0.2% proof stress was regarded as the yield strength (YS).
- Fracture surfaces of the fractured specimens were measured for thickness, the sheet thickness direction ultimate ductility in the rolling direction and that in the rolling transverse direction were averaged, and the average was defined as the sheet thickness direction ultimate ductility.
- Results are shown in Table 1.
- the number of cementite precipitates in every hot-rolled steel sheet is less than 5.0 ⁇ 10 3 per mm 2
- the sheet thickness direction ultimate ductility of each cold-rolled steel sheet is 1.3 or more
- no cracks are present in the cold-rolled steel sheet although the cold-rolled steel sheet was worked by most severe 90-degree bending at a punch tip curvature of 0R, which is less than 2R, for both L-bending and C-bending, which shows excellent bending workability.
- Steel Nos. 4 and 11 which have a large C content of 0.048% and 0.035%, respectively, and Steel No.
- every hot-rolled steel sheet has a crystal grain diameter of more than 25 ⁇ m, every bent portion has a rough surface, ⁇ is less than 50%, and the burring workability necessary to machine screw pilot holes is poor.
- every hot-rolled steel sheet has a crystal grain diameter of 25 ⁇ m or less, every bent portion has no rough surface, ⁇ is 50% or more, and the burring workability necessary to machine screw pilot holes is excellent.
- the screw-breaking torque was incapable of being measured.
- the tensile strength TS is 490 MPa or more and the screw-breaking torque is 20 kgf ⁇ cm or more, which shows excellent workability for screw pilot holes.
- Hot-rolled steel sheets were manufactured using Steel No. 7 shown in Table 1 under substantially the same conditions as those described in Example 1. After the front and back of each of the hot-rolled steel sheets were ground such that the hot-rolled steel sheets had various thicknesses, the hot-rolled steel sheets were cold-rolled at a rolling reduction ranging from 0% to 72%, whereby cold-rolled steel sheets with a thickness of 0.8 mm were obtained.
- the hot-rolled steel sheet with a rolling reduction of 0% and the cold-rolled steel sheets were measured for tensile strength TS, yield ratio YR, average sheet thickness direction ultimate ductility, hole expansion ratio ⁇ , and screw-breaking torque and evaluated for bending workability in substantially the same manners as those described in Example 1.
- Results are shown in Table 2.
- a TS of 390 MPa is achieved at a rolling reduction of 9% or more. In this case, the bending workability and the hole expansibility are good regardless of the rolling reduction.
- the rolling reduction is 30% or more, the tensile strength TS is as high as 490 MPa or more and a high screw-breaking torque of 20 kgf ⁇ cm or more is achieved.
- the material with a rolling reduction of 0% and the material with a rolling reduction of 72% had no problems with stretchability and screw pilot hole boring, had no cracks or rough surface after 90-degree bending or contact bending, and were machined into the housing bottoms and the housing lids without any problem.
- the housing bottoms were combined with the housing lids and were then screwed to the housing lids with M3 tapping screws with a torque of 20 kgf ⁇ cm, resulting in that the screw pilot holes in the material with a rolling reduction of 0% were broken but those in the material with a rolling reduction of 72% were not broken and the housing bottom was fixed to the housing lid.
- the obtained cold-rolled steel sheets were evaluated in substantially the same manners as those described in Example 1.
- specimens worked by 90-degree V-bending were cooled in liquid nitrogen and were then tested in such a manner that the specimens were bent and returned to a flat shape at temperatures not higher than ⁇ 10° C. in 20° C. intervals.
- the temperature at which each specimen was broken was determined to be the transition temperature thereof.
- the bendability can be improved by performing annealing (recovery annealing) at 450° C. for 100 s such that TS 390 MPa and YR ⁇ 80% can be maintained.
- the screw-breaking torque is significantly reduced by performing annealing at 700° C. for 100 s such that TS ⁇ 390 MPa and YR ⁇ 80% are maintained.
- the area fraction of polygonal ferrite grains in the microstructure of a steel sheet annealed at 450° C. for 100 s is 10% or less.
- the area fraction of polygonal ferrite grains in the microstructure of a steel sheet annealed at 700° C. for 100 s is more than 10%.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Bending Of Plates, Rods, And Pipes (AREA)
Applications Claiming Priority (5)
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JP2009051760 | 2009-03-05 | ||
JP2009-051760 | 2009-03-05 | ||
JP2009-290244 | 2009-12-22 | ||
JP2009290244A JP5655300B2 (ja) | 2009-03-05 | 2009-12-22 | 曲げ加工性に優れた冷延鋼板、その製造方法およびそれを用いた部材 |
PCT/JP2010/053016 WO2010101074A1 (ja) | 2009-03-05 | 2010-02-19 | 曲げ加工性に優れた冷延鋼板、その製造方法およびそれを用いた部材 |
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US20110318217A1 true US20110318217A1 (en) | 2011-12-29 |
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US13/254,050 Abandoned US20110318217A1 (en) | 2009-03-05 | 2010-02-19 | Cold-rolled steel sheet with excellent bending workability, method for manufacturing the same, and member using the same |
Country Status (9)
Country | Link |
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US (1) | US20110318217A1 (es) |
EP (1) | EP2405026B1 (es) |
JP (1) | JP5655300B2 (es) |
KR (2) | KR101431316B1 (es) |
CN (1) | CN102341519B (es) |
ES (1) | ES2704707T3 (es) |
MY (1) | MY161077A (es) |
PL (1) | PL2405026T3 (es) |
WO (1) | WO2010101074A1 (es) |
Cited By (4)
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RU2483121C1 (ru) * | 2012-01-23 | 2013-05-27 | Федеральное государственное автономное образовательное учреждение высшего профессионального образования "Национальный исследовательский технологический университет "МИСиС" | Способ производства нагартованной малоуглеродистой листовой стали |
US20170306430A1 (en) * | 2014-10-09 | 2017-10-26 | Thyssenkrupp Steel Europe Ag | Cold-rolled and recrystallisation annealed flat steel product, and mehtod for the production thereof |
CN113477711A (zh) * | 2021-06-03 | 2021-10-08 | 重庆理工大学 | 一种具有超细晶组织的非基面织构镁合金板材制备方法 |
US20230220510A1 (en) * | 2020-06-30 | 2023-07-13 | Jfe Steel Corporation | Steel sheet, member, and method for producing them |
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JP5903884B2 (ja) * | 2011-12-27 | 2016-04-13 | Jfeスチール株式会社 | 耐腰折れ性に優れた高強度薄鋼板の製造方法 |
KR101455470B1 (ko) * | 2012-09-27 | 2014-10-27 | 현대제철 주식회사 | 냉연강판 제조 방법 |
CN109023113B (zh) * | 2018-09-28 | 2020-10-23 | 上大鑫仑材料科技(上海)有限公司 | 一种变强度热冲压模具材料及其制备方法与应用 |
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KR20210079460A (ko) * | 2019-12-19 | 2021-06-30 | 주식회사 포스코 | 경도와 가공성이 우수한 구조부용 냉연강판 및 그 제조방법 |
KR102438481B1 (ko) * | 2020-12-21 | 2022-09-01 | 주식회사 포스코 | 가공성이 우수한 냉연강판 및 그 제조방법 |
CN113083910B (zh) * | 2021-03-09 | 2022-06-28 | 邯郸钢铁集团有限责任公司 | 一种5机架冷轧机停车复产启动控制钢带跑偏撕裂的方法 |
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WO2008102006A1 (en) * | 2007-02-23 | 2008-08-28 | Corus Staal Bv | Packaging steel, method of producing said packaging steel and its use |
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JPS541244B1 (es) | 1968-11-15 | 1979-01-23 | ||
JPS62146744A (ja) | 1985-12-20 | 1987-06-30 | Suminoe Orimono Kk | 自動車用成型内装材 |
JP3023385B2 (ja) * | 1991-03-11 | 2000-03-21 | 川崎製鉄株式会社 | 缶用鋼板の製造法 |
JPH06248339A (ja) * | 1993-02-26 | 1994-09-06 | Nippon Steel Corp | 高剛性容器用鋼板の製造方法 |
JP3571753B2 (ja) | 1994-05-24 | 2004-09-29 | 新日本製鐵株式会社 | 絞り乃至絞りしごき加工缶用高剛性表面処理薄鋼板 |
JP3394598B2 (ja) * | 1994-05-31 | 2003-04-07 | 川崎製鉄株式会社 | 梱包用バンド及びその製造方法 |
JPH0892692A (ja) | 1994-09-22 | 1996-04-09 | Nippon Steel Corp | フランジ加工性に優れた容器用鋼板 |
JPH0892638A (ja) | 1994-09-29 | 1996-04-09 | Nippon Steel Corp | 容器用原板の製造方法 |
JPH08127815A (ja) | 1994-10-28 | 1996-05-21 | Nippon Steel Corp | 容器用原板の製造方法 |
JP4081823B2 (ja) * | 1996-03-08 | 2008-04-30 | Jfeスチール株式会社 | 焼鈍省略工程による缶用鋼板の製造方法 |
JP3448422B2 (ja) | 1996-04-10 | 2003-09-22 | 新日本製鐵株式会社 | 焼鈍省略型良加工性鋼板の製造方法 |
US20060145587A1 (en) * | 2003-08-18 | 2006-07-06 | Toyo Kohan Co. Ltd. | Material for shadow mask, process for producing the same, shadow mask from the shadow mask material and picture tube including the shadow mask |
JP2007211321A (ja) * | 2006-02-13 | 2007-08-23 | Nisshin Steel Co Ltd | Cpuソケット枠又はcpu固定カバー用鋼板の製造方法 |
JP5076544B2 (ja) * | 2007-02-21 | 2012-11-21 | Jfeスチール株式会社 | 缶用鋼板の製造方法 |
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- 2009-12-22 JP JP2009290244A patent/JP5655300B2/ja active Active
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2010
- 2010-02-19 MY MYPI2011003360A patent/MY161077A/en unknown
- 2010-02-19 KR KR1020117019568A patent/KR101431316B1/ko active IP Right Grant
- 2010-02-19 CN CN201080010706.6A patent/CN102341519B/zh not_active Expired - Fee Related
- 2010-02-19 KR KR1020137022206A patent/KR101612593B1/ko active IP Right Grant
- 2010-02-19 US US13/254,050 patent/US20110318217A1/en not_active Abandoned
- 2010-02-19 ES ES10748669T patent/ES2704707T3/es active Active
- 2010-02-19 WO PCT/JP2010/053016 patent/WO2010101074A1/ja active Application Filing
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Patent Citations (1)
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WO2008102006A1 (en) * | 2007-02-23 | 2008-08-28 | Corus Staal Bv | Packaging steel, method of producing said packaging steel and its use |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
RU2483121C1 (ru) * | 2012-01-23 | 2013-05-27 | Федеральное государственное автономное образовательное учреждение высшего профессионального образования "Национальный исследовательский технологический университет "МИСиС" | Способ производства нагартованной малоуглеродистой листовой стали |
US20170306430A1 (en) * | 2014-10-09 | 2017-10-26 | Thyssenkrupp Steel Europe Ag | Cold-rolled and recrystallisation annealed flat steel product, and mehtod for the production thereof |
US10683560B2 (en) * | 2014-10-09 | 2020-06-16 | Thyssenkrupp Steel Europe Ag | Cold-rolled and recrystallization annealed flat steel product, and method for the production thereof |
US20230220510A1 (en) * | 2020-06-30 | 2023-07-13 | Jfe Steel Corporation | Steel sheet, member, and method for producing them |
US11976341B2 (en) * | 2020-06-30 | 2024-05-07 | Jfe Steel Corporation | Steel sheet, member, and method for producing them |
CN113477711A (zh) * | 2021-06-03 | 2021-10-08 | 重庆理工大学 | 一种具有超细晶组织的非基面织构镁合金板材制备方法 |
Also Published As
Publication number | Publication date |
---|---|
EP2405026A4 (en) | 2014-04-23 |
JP2010229545A (ja) | 2010-10-14 |
KR101431316B1 (ko) | 2014-08-20 |
JP5655300B2 (ja) | 2015-01-21 |
KR101612593B1 (ko) | 2016-04-15 |
EP2405026B1 (en) | 2018-11-28 |
CN102341519A (zh) | 2012-02-01 |
EP2405026A1 (en) | 2012-01-11 |
KR20110105403A (ko) | 2011-09-26 |
MY161077A (en) | 2017-04-14 |
WO2010101074A1 (ja) | 2010-09-10 |
ES2704707T3 (es) | 2019-03-19 |
KR20130101588A (ko) | 2013-09-13 |
CN102341519B (zh) | 2015-02-18 |
PL2405026T3 (pl) | 2019-06-28 |
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