EP0572666B1 - Cold-rolled steel sheet and galvanized cold-rolled steel sheet which are excellent in formability and baking hardenability, and production thereof - Google Patents
Cold-rolled steel sheet and galvanized cold-rolled steel sheet which are excellent in formability and baking hardenability, and production thereof Download PDFInfo
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- EP0572666B1 EP0572666B1 EP92905304A EP92905304A EP0572666B1 EP 0572666 B1 EP0572666 B1 EP 0572666B1 EP 92905304 A EP92905304 A EP 92905304A EP 92905304 A EP92905304 A EP 92905304A EP 0572666 B1 EP0572666 B1 EP 0572666B1
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- steel sheet
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- rolled steel
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- 239000010960 cold rolled steel Substances 0.000 title claims description 42
- 238000004519 manufacturing process Methods 0.000 title description 24
- 229910000831 Steel Inorganic materials 0.000 claims description 180
- 239000010959 steel Substances 0.000 claims description 180
- 238000000034 method Methods 0.000 claims description 52
- 238000000137 annealing Methods 0.000 claims description 50
- 229910052799 carbon Inorganic materials 0.000 claims description 42
- 238000005098 hot rolling Methods 0.000 claims description 40
- 239000006104 solid solution Substances 0.000 claims description 39
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 28
- 238000001816 cooling Methods 0.000 claims description 28
- 238000007747 plating Methods 0.000 claims description 28
- 230000008569 process Effects 0.000 claims description 24
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Images
Classifications
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- 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
-
- 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
-
- 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
- C21D8/0447—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 heat treatment
- C21D8/0473—Final recrystallisation annealing
Definitions
- the present invention relates to a cold-rolled steel sheet and a galvanized cold-rolled steel sheet that have high moldability, workability and painting-baking hardenability and are suitable for use as panels etc. for automobiles, and a process for producing the same.
- a representative measure of the moldability is an r value (Lankford value), elongation value or an n value, and the necessary level of these values has increased more and more.
- the dent resistance is the strength of the product, that is, the strength after molding, assembling, mounting and painting-baking.
- the painting-baking is usually a heat treatment at 170°C for about 20 min, and the material should have a good painting-baking hardenability (usually called "BH property") which is a hardening property in this heat treatment.
- BH property painting-baking hardenability
- strain aging In the painting-baking, use is made of strain aging by C and N contained in a solid solution form in the steel and sufficiently diffusible usually even at a low temperature of about 170°C.
- the strain is the sum of a strain caused in temper rolling which is the final step in the production of a steel sheet, and a strain caused in molding at an automobile manufacturing plant.
- Ultra low carbon steel is usually used for these applications.
- C and N in a solid solution form are used as a solute element involved in the impartment of the BH property to the steel.
- the BH property is a kind of aging property and gives rise to a deterioration in the moldability at room temperature, so that an excessively high moldability leads to a problem.
- C and N are different from each other in the temperature dependence of aging, that is, activation energy of aging, and the activation energy of C is larger than that of N.
- the effect of C on aging has a feature that aging at room temperature is slow and becomes fast with increasing the temperature. For this reason, it is a common practice to use C in a solid solution form for imparting the BH property.
- the technique for imparting the BH property to extra low carbon steel is roughly classified into two methods.
- steel used is not literally an IF steel, and a carbide forming element is added in a stoichiometrically equivalent amount or less relative to the carbon content.
- This technique is described in Japanese Unexamined Patent Publication (Kokai) Nos. 59-31827, 59-38337, 63-128149 and 2-197549.
- Nb is added in a stoichiometrically equivalent amount or less relative to the carbon content.
- Japanese Unexamined Patent Publication (Kokai) No. 2-194126 describes a technique where Ti is added in such an amount that C is not completely immobilized as TiC.
- EP-A-0 295 697 discloses a cold rolled steel sheet having improved strength are toughness in weld portion, characterized in that said steel comprises not more than 0.004 wt% of not more than 0.1 wt% of Si, not more than 0.5 wt% of Mn, not more than 0.025 wt% of P. not more than 0.025 wt% of S. not more tnan 0.0040 wt% of N. 0.01-0.04 wt% of Ti. 0.003-0.010 wt% of Nb. 0.0001-0.0010 wt% of B. 0.01-0.10 wt% of Al and the remainder being substantially Fe, and fine precipitates of Ti having a grain size of not more than 0.05 ⁇ m are uniformly dispersed into said steel in an amount at not less than 30 ppm as Ti conversion amount.
- EP-A-0 484 960 a document under Art. 54(3) EPC discloses a cold-rolled steel strip having excellent combined press formability, consisting by weight, of not more than 0.0025% C, not more than 0.05% Si. not more than 0.30% Mn, not less than 0.007% but not more than 0.30% P, not more than 0.020% S.
- said steel strip having tensile strength in 45° direction (expressed as T.S 45 ) of 28.5 to 31.0 kgf/mm 2 and r value in 45° direction (expressed as r 45 ) of not less than 1.90.
- EP-A-0 203 809 discloses a method of manufacturing a cold-rolled steel sheet having a good deep drawability wherein a not rolled steel sheet having a composition of C ⁇ 0.0035%, Si ⁇ 1.0%. Mn ⁇ 1.0%, Al: 0.005-0.10%, P ⁇ 0.15%, N ⁇ 0.0035%.
- An object of the present invention is to realize a process for producing a cold-rolled steel sheet and a galvanized cold-rolled steel sheet having a combination of moldability capable of withstanding a high degree of working with face strain resistance and dent resistance and further free from embrittlement during fabricating.
- the BH property is evaluated by applying a preliminary strain of 2 % in a tensile test, removing the strain, heat-treating the steel sheet at 170°C for 20 min, again pulling the steel sheet, and subtracting the strength value at yield point from the flow stress value at 2 % preliminary strain. That is, this value is an increment allowance of yield point in a strain aging test under conditions of 2 % preliminary strain, 170°C and 20 min.
- the plated steel sheet has plating properties including a powdering property.
- the powdering resistance is a measure of unpeelability of the plating layer during molding.
- r value, El value and n value are each an in-plane average value, and when values in directions at angles of 0°, 45° and 90° to the rolling direction are X0, X45 and X90, the in-plane average value is defined by the equation (X0 + 2X45 + X90) ⁇ 4.
- the r value is a measure of deep drawability and defined by [(logarithmic strain in width direction) ⁇ (logarithmic strain in sheet thickness)] for the direction of pull.
- El is an elongation at break.
- the n value is a work hardening index which represents an inflow property of the material and is a representative index for workability.
- the present invention is characterized by comprising constituent features of 1 ⁇ 0 ⁇ Nb (%) - 93/12C (%) ⁇ 0.25, 2 ⁇ Ti: 24/14N (%) to 72/14N (%), 3 ⁇ quenching within 2 sec after the completion of hot rolling, 4 ⁇ a coiling temperature of 650 to 770°C and 5 ⁇ an annealing temperature of 820°C or above.
- the steel sheet is quenched immediately after finish rolling in the step of hot rolling for the purpose of refining ferrite in the hot-rolled steel sheet. Further, the whole carbon in the hot-rolled steel sheet is immobilized as a precipitate NbC to eliminate C in a solid solution form.
- Nb is added in a stoichiometrically equivalent amount (93/12C) or more relative to C, and coiling is effected at a temperature of 650°C or above.
- the amount of addition of Nb is less than the stoichiometrically equivalent amount (93/12C) relative to C or the coiling temperature is below 650°C, C in a solid solution form remains.
- the presence of C in a solid solution form in a stage before annealing inhibits the development of an aggregate structure having an orientation useful for improving the r value during annealing, so that it becomes difficult to ensure a high r value.
- An aggregate structure having an orientation useful for improving the r value is developed during temperature rise in the step of annealing by refining ferrite in the hot-rolled steel sheet and rendering C in a solid solution form absent in the hot-rolled steel sheet. Thus, a high r value can be obtained.
- C in a solid solution form is provided by decomposing the precipitate NbC into Nb and C (NbC ⁇ Nb + C) immediately after annealing, that is, around an annealing temperature after recrystallization at which grain growth is substantially completed.
- the annealing temperature it is necessary for the annealing temperature to be 820°C or above. -Tiis added for the purpose of immobilizing the N which is detrimental to the BH property.
- the amount of addition of Ti in an excessive amount causes fine TiC to be formed in the stage of hot rolling, it becomes impossible to provide a good recrystallized aggregate structure.
- the amount of addition of Ti should be in the range of from 0.5 to 1.5 relative to the stoichiometrically equivalent amount of N (48/14 x Ti).
- the content of S should be 0.01 % or less, preferably less than 0.004 %.
- C and N are lowered to the extreme limit, doping addition of C in an amount of about 20 ppm is effected for the purpose of imparting BH property.
- C and N are immobilized by Nb and Ti, respectively. Immobilization of N is compensated for also by Al.
- ferrite is refined under particular hot rolling conditions, and a hot-rolled steel sheet, wherein impurities in a solid solution form have been sufficiently scavenged, that is, a hot-rolled sheet in a state satisfactory in a stage before cold rolling, is provided, and the steel sheet is then subjected to particular cold rolling and recrystallization annealing and, in the case of the production of a plated steel sheet, further subjected to a plating treatment.
- a (galvanized) cold-rolled steel sheet for an automobile comprising, in terms of % by mass, 0.0010 to 0.0040 % of C, 0.0030 % or less of N, 0.02 to 1.5 % of Mn, 0.08 % or less of P, 0.01 % or less of S, 0.005 to 0.07 % of acid soluble Al, 0.05 % or less of Nb satisfying a requirement of a ⁇ Nb (%) - 93/12C (%) ⁇ value of more than zero to 0.025 %, 24/14 ⁇ N (%) to 72/14 ⁇ N (%) of Ti and 0.5 % or less of Si with the balance consisting of Fe and unavoidable impurities and having an aggregate structure such that, in X-ray diffraction, the natural logarithm ratio (ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ )) of the diffraction intensity I ⁇ 222 ⁇ of a ⁇ 222 ⁇ plane to the diffraction intensity I
- a process for producing a (galvanized) cold-rolled steel sheet for an automobile comprising hot-rolling a steel composed of the above-described ingredients at a finish termination temperature of the Ar 3 transformation point or above, quenching the hot-rolled steel sheet within 2 sec after the completion of the hot-rolling at a rate of 30 to 300°C/sec to attain a temperature fall of 100°C or above, coiling the cooled steel sheet at a temperature of 650 to 770°C, subsequently cold-rolling the coiled steel sheet with a reduction ratio of 72 to 92 %, subjecting the cold-rolled steel sheet to annealing in a temperature range of from 820 to 880°C for 20 sec or more and cooling the annealed steel sheet from that temperature to room temperature at a cooling rate of 3°C/sec or more.
- Japanese Unexamined Patent Publication (Kokai) Nos. 61-276927 and 61-276930 disclose a technique where quenching is effected after the completion of finish rolling in the step of hot rolling. This technique is different from the present invention in the chemical ingredients of the steel, and gives no consideration to the BH property, so that the difference between this technique and the present invention is self-explanatory.
- the amounts of addition of Ti and Nb are Ti ⁇ 48/14N + 48/32S and Nb ⁇ 93/12C, respectively.
- Ti is added in a stoichiometrically equivalent amount or more relative to N and S to immobilize the whole N and S, and part of C is immobilized by the remaining Ti.
- Nb is added in a stoichiometrically equivalent amount or less relative to C, and the remaining C not immobilized by Ti is immobilized by Nb.
- N is immobilized by Ti or Al and the whole C is immobilized by Nb
- the present invention are different from each other in not only metallurgy but also percentage composition.
- Ti may be a stoichiometrically equivalent amount or less relative to N (Ti ⁇ 24/14N), and Nb is larger than a stoichiometrically equivalent amount relative to C (Nb > 93/12C), so that the amount of addition of at least Nb specified in the present invention is outside the scope of the invention described in the above-described patent applications.
- the target quality is Al ⁇ 3 kgf/mm 2 and, in an application example in the working example, Al is 1.2 kgf/mm 2 or less.
- ingredients of the steel of the present invention will be described together with contents (all the contents being in % by mass) of these ingredients.
- C is an interstitial element in a solid solution form and detrimental to the impartment of workability to cold-rolled steel sheets, that is, the formation of an aggregate structure or the growth of sufficiently large grains, so that the content thereof should be minimized.
- the BH property depends upon the content of carbon in a solid solution form in a final product sheet, carbon should be present in a minimum amount necessary for ensuring the BH property.
- carbon in a solid solution it is preferred for carbon in a solid solution to be present at grain boundaries for the purpose of preventing zinc from penetrating into the grain boundary of the matrix. In this respect as well, carbon in a solid solution form should be ensured in the latter period of the recrystallization annealing.
- the lower limit and upper limit of the C content should be 0.0010 % and 0.0050 %, respectively.
- the upper limit is desirably 0.0040 %.
- N too is an interstitial element in a solid solution form and detrimental to the steel sheet contemplated in the present invention. Further, since N is diffusible at room temperature, it is also difficult to attain a combination of the BH property with the cold aging resistance, so that the use thereof for ensuring the BH property is disadvantageous. For this reason, the N content should be 0.0030 % or less.
- Si strengthens a steel through solid solution strengthening. It, however, is detrimental to the workability, and since an oxide of Si is stable and cannot be easily reduced, there occurs a failure of plating adhesion during galvanizing. Therefore, when Si is added for the purpose of increasing the strength, the amount of addition thereof is 0.5 % or less, and the lower limit is 0.1 %. In the case of a soft steel sheet, the amount of addition of Si may be less than 0.1 %, and the lower limit is at an unavoidably included level, for example, 0.004 %.
- Mn too strengthens a steel through solid solution strengthening. It is a favorable element particularly because it is less liable to deteriorate the ductility for its function of strengthening the steel. Further, it has been found that Mn serves to alleviate an adverse effect of Si and P on plating properties. The addition of Mn in an excessive amount reduces the ductility of the material and deteriorates the workability. For this reason, in the case of a high-strength steel sheet, Mn is added in an amount of 0.3 to 1.5 %.
- the upper limit of addition of Mn is less than 0.3 % from the viewpoint of preventing the deterioration of the workability, and the lower limit is 0.02 % from the viewpoint of preventing hot shortness.
- P too is a solid solution strengthening element which is useful for increasing the strength but deteriorates the workability and gives rise to brittle fracture and, in the case of a plated steel sheet, further deteriorates alloying of the steel sheet after plating.
- P should be minimized for a soft steel sheet, and the upper limit is less than 0.03 %, preferably 0.010 % or less.
- the lower limit is an unavoidably included level, for example, 0.001 %.
- the amount of addition is limited to 0.03 to 0.08 % from the above-described viewpoint.
- Mn plays a particularly important role in plated steel plates.
- a hot-dip galvanizing treatment although the surface layer of the steel sheet is usually subjected to reduction after heating in a non-oxidizing furnace, if the strengthening element is concentrated on the surface, the plating treatment cannot be successfully effected, which gives rise to various problems including that the adhesion of plating to the steel sheet is deteriorated, alloying does not proceed or a proper alloy layer cannot be provided to render the powdering resistance unsatisfactory.
- the function of additional elements varies from element to element and, even though they are added in the production of a high-strength steel, satisfactory plating properties can be imparted if the following requirement is met.
- the Mn/(Si + 10P) value should be 1.0 or more. This means that Mn serves to alleviate an adverse effect of Si or P on plating properties.
- Mn exhibits the above-described function is believed to reside in the difference in properties between formed oxides, it has not been fully elucidated yet. This effect cannot be attained when the above-described value is less than 1.0.
- S is an impurity and forms an inclusion to deteriorate the workability of the steel, so that the S content is preferably as low as possible. Further, if S combines with Ti to form TiS, Ti 4 C 2 S 2 is further formed, which often gives rise to scattering of the BH property. Therefore, it is also important for substantially no TiS to be contained in the steel. Also for this reason, the S content should be lowered. For the reasons set out above, the S content is limited to 0.01 % or less, preferably less than 0.004 %.
- Al is used for deoxidation. Further, it is used also as assistant to immobilization of N which is an interstitial impurity. For this reason, Al should be present in an amount of 0.005 % in terms of acid soluble Al. On the other hand, the addition of Al in an amount exceeding 0.07 % deteriorates the workability of the steel.
- Nb is a very important element for the present invention.
- Nb is added in an amount exceeding a stoichiometrically equivalent amount relative to the precipitated carbide NbC. That is, the addition of Nb in an amount exceeding 93/12xC is necessary.
- the addition of Nb in an excessive amount deteriorates the workability of the steel. For this reason, the upper limit is 0.05 %.
- This lower limit means that Nb is added in an amount exceeding a stoichiometrically equivalent amount relative to C.
- this constituent feature is important to the present invention for attaining a sufficiently scavenged state in the stage before cold rolling to impart a high workability to the steel sheet.
- the upper limit is an indicator for specifying the dissolution of NbC in a continuous annealing line or a hot-dip galvanizing line, and when the value exceeds the upper limit, no satisfactory BH property can be provided.
- Ti is added to immobilize N.
- the addition of Ti in an excessive amount causes fine TiC to be formed in the stage of hot rolling, so that a good recrystallized aggregate structure cannot be provided.
- Ti is added in an amount in the range of from 0.5 to 1.5 relative to the stoichiometrically equivalent amount (48/14xTi) of N.
- the N content becomes somewhat excessive.
- the residual N is immobilized as AlN by particular hot rolling according to the present invention, and there is no possibility that N in a solid solution form remains in a stage before cold rolling.
- carbon in a solid solution form is allowed to remain in the final product for the purpose of imparting the BH property and segregates also at grain boundaries, which has a favorable effect on fabrication embrittlement.
- B is added.
- the amount of addition of B is preferably 0.0008 % or less.
- Cr is added in an amount of 1.2 % or less.
- Cr is a favorable element because it improves the work hardening property and minimizes the deterioration of the n value for its function of increasing the strength of the steel. If Cr is added in an amount exceeding 1.2 %, since plating properties deteriorate due to the formation of a passive film of Cr on the surface layer, when Cr is added, the upper limit of amount of addition thereof is 1.2 %.
- a steel comprising the above-described chemical ingredients according to the present invention is refined in a converter, decarbonized by a vacuum degassing process and subjected to ingot making/blooming or continuous casting to form a slab.
- the slab is heated to a temperature in the range of from an Ar 3 transformation point to 1,250°C and hot-rolled.
- the finish rolling temperature is the Ar 3 transformation point or above, preferably in the range of from 960°C to Ar 3 transformation point.
- the total reduction ratio in the hot rolling is preferably in the range of from 80 to 99 %.
- a slab having a thickness of 240 mm is rolled in the above-described temperature range into a hot rolled sheet (a steel strip) having a thickness of 3.5 to 6 mm.
- Conditions for cooling after hot rolling are important. Grain boundaries of the hot-rolled sheet are positions where nuclei having a crystal orientation favorable for the r value occur during annealing for recrystallization, and the nucleation becomes increasingly active with increasing fineness of the structure, so that a better r value can be provided. For this reason, quenching should be effected within 2 sec after the completion of rolling. When the time between the completion of the hot rolling and the initiation of cooling exceeds 2 sec, the hot-rolled structure becomes so coarse that a good r value cannot be provided. It is preferred for the cooling to be initiated within 0.8 sec after the completion of hot rolling.
- the rapid cooling rate may be about 30°C/sec or more, which is a cooling rate attained by spray according to conventional means, preferably 50°C/sec or more, to attain a temperature fall of about 100°C or more.
- the upper limit of the cooling rate is 300°C/sec from the viewpoint of the capacity of facilities.
- the coiling temperature should be in the range of from 650 to 770°C. This causes impurities in a solid solution form, such as C, remaining in the stage of hot rolling to be sufficiently scavenged. Specifically, with respect to C as an example, the reaction Nb + C ⁇ NbC is allowed to proceed. When the temperature is below 650°C, the diffusion is insufficient, and no scavenging effect can be attained. On the other hand, when the temperature exceeds 770°C, grains grow, so that the effect attained by the particular hot rolling is lost.
- the hot-rolled sheet is then cold-rolled.
- the reduction ratio in the cold rolling in order to provide a high r value, it is necessary for the reduction ratio in the cold rolling to be a relatively high 72 to 92 %.
- the reduction ratio is preferably 77 % or more. A reduction ratio exceeding 92 % is unfeasible from the viewpoint of the limitation of current facilities.
- the steel sheet is held in a temperature range of from 820 to 880°C for 20 to 600 sec to effect recrystallization annealing.
- Such annealing is effected for the purpose of providing an aggregate structure of recrystallized grains having a uniform ⁇ 111 ⁇ orientation and a sufficiently large size and, at the same time, dissolving part of the NbC into Nb and C to ensure carbon in a solid solution form for imparting the BH property, which is very important to the present invention.
- the annealing temperature for this purpose should be 820°C at the lowest.
- the annealing at a high temperature provides very high r value and elongation, and an n value which is not excessively high.
- grains becomes excessively large, which leads to a rough surface defect in the press molding.
- the holding time at a high temperature is important for ensuring the workability and BH property, and, in a continuous annealing line, the holding time should be 20 to 600 sec.
- the rate of cooling after annealing should be 3°C/sec or more.
- NbC precipitates again during cooling, so that no satisfactory BH property can be provided.
- the upper limit of the cooling rate is about 300°C/sec from the viewpoint of the capacity of facilities.
- a slab having a chemical composition comprising 0.0010 % of C, 0.13 % of Mn, 0.004 % of P, 0.003 % of S, 0.025 % of acid soluble Al, 0.0003 % of B, 0.007 % of Ti, 0.009 % of Nb and 0.0016 % of N with the balance consisting of Fe and unavoidable impurities was hot-rolled into a steel sheet having a finish thickness of 6.5 mm which was then coiled at about 700°C and cold-rolled into a steel sheet having a finish thickness of 1.6 mm. The cold-rolled sheet was subjected to recrystallization annealing at a temperature of about 850°C to provide a soft cold-rolled steel sheet.
- the average r value improves with increasing ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ ).
- the ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ ) value was so high that the average r value was also high.
- the ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ ) value it is necessary for the ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ ) value to be 2.8 or more.
- I ⁇ 222 ⁇ and I ⁇ 200 ⁇ mean X-ray reflection intensity ratios for random samples of ⁇ 222 ⁇ plane and ⁇ 200 ⁇ plane determined by the inverse method.
- a slab having a chemical composition comprising 0.0013 % of C, 0.15 % of Si, 1.00 % of Mn, 0.051 % of P, 0.0010 % of S, 0.03 % of acid soluble Al, 0.004 % of Ti, 0.028 % of Nb and 0.0018 % of N with the balance consisting of Fe and unavoidable impurities was heated to a temperature of 1100 to 1150°C, hot-rolled at a finish temperature of 900 to 935°C, coiled at a temperature of 705 to 725°C, cold-rolled with a reduction ratio of 78 % and subjected to recrystallization annealing under conditions of an annealing temperature of 850°C and a holding time of 40 sec to provide a high-strength cold-rolled steel sheet.
- quenching was effected within 2 sec (0.3 to 0.5 sec) after the completion of hot rolling, while in another example, quenching was effected after more than 2 sec (3 to 5 sec) elapsed after the completion of hot rolling.
- the relationship between the average r value and the logarithm ratio (ln(I ⁇ 222 ⁇ /I ⁇ 200 ⁇ )) of the X-ray diffraction intensities with respect to the above-described two examples is shown in Fig. 2.
- ⁇ represents data for the former, and ⁇ represents data for the latter.
- the cold-rolled steel sheet according to the present invention comprises a recrystallized aggregate structure capable of providing a high average r value, so that, in the present invention, it is possible to improve the ⁇ 111 ⁇ orientation and the size of the crystal grains.
- a cold-rolled steel sheet is produced, at least one surface of the steel sheet is subjected to galvanizing.
- plating may be effected at a coverage of 15 g/m 2 or more through an electrogalvanizing line.
- the steel sheet may be passed through a hot-dip galvanizing line to effect recrystallization annealing, cooling and plating.
- the line usually comprises a non-oxidizing heating zone, a reduction zone, a cooling zone, a zinc pot, an alloying furnace and a cooling zone, since it does not have a holding zone, it is necessary that annealing be effected at a temperature (830 to 890°C) somewhat higher than the above-described continuous annealing condition (820 to 880°C) and the steel sheet be travelled in such a manner that 40 sec or longer elapse during which time the temperature of the steel sheet is 800°C or above.
- the steel sheet After annealing, the steel sheet is cooled at a rate of 3°C/sec or more and dipped in a zinc pot having a temperature in the range of from 440 to 460°C so that at least one surface of the steel sheet is subjected to hot-dip galvanizing at a coverage of 15 g/m 2 or more.
- the steel sheet is pulled up from the zinc pot, and the plating layer is subjected to an alloying treatment at a temperature of 550 to 600°C.
- the temperature of the melted zinc in the zinc pot is determined by the state of melting of zinc, and the alloying temperature is a temperature for providing a proper alloy layer structure. When the alloying temperature is below 550°C, alloying does not satisfactorily proceed.
- the steel sheet was cooled and then subjected to temper rolling.
- the reduction ratio in the temper rolling should be as low as 0.5 % or less.
- Steels having chemical compositions specified in Table 1 were produced by a melt process and subjected to continuous casting to provide slabs.
- steels A to F and steels P and Q fall within the scope of the present invention, and the other steels are comparative steels.
- steels G and H the C content is outside the scope of the present invention.
- steels I to L the content of any of Mn, Nb, N and B is higher than that specified in the present invention.
- the Nb content is less than 93/12C which is excessively small relative to the C content of the steel.
- steel O the Ti content is excessively high relative to the N content of the steel.
- the finish termination temperature was Ar 3 or above. Thereafter, the materials were quenched under conditions specified in Table 2 to about 800°C to attain a temperature fall of 100 to 150°C. The finish thickness was 4 mm. Then, the steel sheets were pickled and cold-rolled into sheets having a thickness of 0.8 mm. Then, the cold-rolled steel sheets were continuously annealed and subjected to temper rolling with a reduction ratio of 0.5 %. Hot rolling and annealing conditions and mechanical properties are given in Table 2. The mechanical test was effected using a No. 5 specimen specified in JISZ2201 by a method specified in JISZ2241. In Table 2, ⁇ (AA) is the sum of the work hardening and the hardening by BH.
- YP-E1 is an elongation at yield point after artificial aging at 100°C for one hr. This value is preferably 0.2 % or less from the viewpoint of necessary delayed aging.
- the transition temperature in a fabrication embrittlement test was given as a measure of the fabrication resistance. The lower the transition temperature, the better the fabrication resistance.
- Nos. 1, 2, 5, 7, 12, 13, 14, 24 and 25 listed in Table 2 are sheets produced according to the present invention. They have an excellent r value, El value and n value and have satisfactory strength at yield point (YP), BH property and fabrication quality resistance (transition temperature) values as contemplated in the present invention.
- the other Nos. are steel sheets wherein production conditions are outside the scope of the present invention. In these steel sheets, at least one of the above-described properties is unsatisfactory.
- No. 3 since the time between the completion of finish annealing in the hot rolling and the initiation of quenching is excessively long, the structure of the hot-rolled sheet becomes coarsened, so that the r value and n value of the product are poor.
- No. 3 since the time between the completion of finish annealing in the hot rolling and the initiation of quenching is excessively long, the structure of the hot-rolled sheet becomes coarsened, so that the r value and n value of the product are poor.
- the Nb content is so high that not only the BH property but also the fabrication resistance (transition temperature) is poor.
- the B content is so high that the r value is poor.
- the Nb content is excessively low, C in a solid solution form remains in the stage before annealing, so that not only the workability (n value, r value and El value) but also the aging property are poor.
- the Ti content is excessively high, a number of fine TiC grains precipitates in the hot-steel sheet and the YP value is high and the n value is poor.
- steels having chemical compositions specified in Table 3 were subjected to refining in a converter and produced by a melt process. In all the steels, the carbon content was rendered extra low by RH vacuum degassing. Among these steels, steels A to E fall within the scope of the present invention, and the other steels are different from the steels of the present invention with respect to an item(s) enclosed in a thick frame.
- steel N is an excess carbon type steel having Nb/C ⁇ 1 (atomic weight) and, so to speak, a steel provided by a process commonly used in the art. These steels were continuously cast into slabs and then hot-rolled. The hot-rolled steel sheets were pickled, cold-rolled and then passed through a continuous annealing line to provide products.
- Hot rolling and annealing conditions are given in Table 4.
- the heating temperature in the hot rolling was 1110 to 1150°C, and the temperature fall in quenching after hot rolling was 100 to 120°C.
- the thickness of the hot-rolled steel sheets was 4.0 mm, and these hot-rolled steel sheets were cold-rolled with a reduction ratio of 80 %, into cold-rolled coils having a thickness of 0.8 mm. Finally, the cold-rolled coils were subjected to temper rolling with a reduction ratio of 0.3 to 0.4 %.
- the mechanical test values and chemical conversion treatment property for these steel sheets are also given in Table 4.
- the mechanical test was effected using a No. 5 specimen specified in JISZ2201 by a method specified in JISZ2241 to determine the strength YP at yield point, tensile strength TS and elongation El at break. The n value was calculated from (10 %-20 %) strain.
- the painting-baking property was expressed in terms of the BH property and the sum (a(AA)) of the 2 % work hardening and the hardening by BH as described above.
- the recovery of elongation at yield point after the sample was allowed to stand at 40°C for 30 days was expressed in terms of YP-E1.
- YP-E1 is an quantity corresponding to a stretcher strain defect, and this defect occurs unless the YP-E1 value is 0.2 % or less.
- the fabrication embrittlement resistance was expressed in terms of the ductility-embrittlement temperature. This value is the transition temperature at which cracking occurs when a cup prepared by molding with a draw ratio of 2.2 is subjected to 10 % flaring at varied temperatures.
- steel sheets (Nos. 1, 2, 6, 10, 14, 15 and 17) according to the present invention had a tensile strength of about 350 to about 400 N/mm 2 , and, despite being high-strength high-dent-resistant steel sheets having a BH value of 40 N/mm 2 or more and an ⁇ (AA) value of 60 N/mm 2 or more, have a sufficiently low YP value (i.e., a sufficient face strain resistance), and good elongation, r value and n value (i.e., a high moldability).
- the aging property they had substantially no recovery of YP-E1 in cold aging and exhibited either no cold aging or delayed aging, and, with respect to the fabrication embrittlement, the transition temperature was so low that no problem occurred. Further, the chemical conversion was also good.
- the natural logarithm ratio (ln((I ⁇ 222 ⁇ /I ⁇ 200 ⁇ )) of the diffraction intensities in the X-ray diffraction was 2.7 or more.
- steel sheet No. 21 had a relatively good workability, it was poor in the chemical conversion.
- steels having chemical compositions specified in Table 5 were subjected to refining in a converter and produced by a melt process. In all the steels, the carbon content was rendered extra low by RH vacuum degassing.
- steels A to F, Q and R fall within the scope of the present invention, and the other steels are outside the scope of the present invention with respect to the C content for steels G and H, Mn content for steel I, Nb content/or (Nb ⁇ 93/12C) content for steels J and K, N content for steel L, B content for steel M and Ti/N value for steel P.
- steels N and O are of an excess carbon type steel having Nb/C ⁇ 1 which is different from the steels according to the present invention.
- Hot rolling, cold rolling and hot-dip galvanizing conditions are given in Table 6.
- the heating temperature in the hot rolling was 1110 to 1160°C, and the temperature fall in quenching after hot rolling was 100 to 120°C.
- the thickness of the hot-rolled steel sheets was 4.0 mm, and these hot-rolled sheets were cold-rolled with a reduction -ratio of 80 % into cold-rolled coils having a thickness of 0.8 mm.
- the cold-rolled coils were subjected to temper rolling with a reduction ratio of 0.3 to 0.4 %.
- the mechanical test values and plating properties for these steel sheets are also given in Table 6.
- the mechanical test was effected using a No. 5 specimen specified in JISZ2201 by a method specified in JISZ2241 to determine the strength YP at yield point, tensile strength TS and elongation El at break. The n value was calculated from (10 %-20 %) strain.
- the painting-baking property was expressed in terms of the BH property and the sum (a(AA)) of the 2 % work hardening and the hardening by BH as described above.
- the recovery of elongation at yield point after the sample was allowed to stand at 40°C for 30 days was expressed in terms of YP-E1.
- YP-E1 is an quantity corresponding to a stretcher strain defect, and this defect occurs unless the YP-E1 value is 0.2 % or less.
- the fabrication embrittlement resistance was expressed in terms of the ductility-embrittlement temperature. This value is the transition temperature at which cracking occurs when a cup prepared by molding with a draw ratio of 2.2 is subjected to 10 % flaring at varied temperatures.
- the plating properties were evaluated in terms of the iron content and powdering property of the alloyed layer.
- the P value the better the powdering property.
- the P value is 40 % or less, the powdering property is very good.
- the P value and iron content are 30 to 50 % and 8 to 12 %, respectively.
- steel sheets (Nos. 1, 2, 5, 7, 12 to 14, 25 and 26) according to the present invention had a sufficiently low YP value (i.e., a sufficient face strain resistance), good elongation, r value and n value (i.e., a high moldability) and, with respect to the aging property, had substantially no recovery of YP-E1 in cold aging (either no cold aging or delayed aging), and a high painting-baking hardening (a high dent resistance), and, with respect to the fabrication embrittlement, the transition temperature was so low that no problem occurred. Further, also with respect to plating properties, both the iron content as a measure of the degree of alloying and the P value as a measure of the evaluation of powdering were very good.
- steels having chemical compositions specified in Table 7 were subjected to refining in a converter and produced by a melt process. In all the steels, the carbon content was rendered extra low by RH vacuum degassing. Among these steels, steels A to F fall within the scope of the present invention, and the other steels are different from the steels of the present invention with respect to an item(s) enclosed in a thick frame.
- steels N and O are an excess carbon type steel having Nb/C ⁇ 1 (atomic weight) and, so to speak, a steel provided by a process commonly used in the art. These steels were continuously cast into slabs and hot-rolled.
- the hot-rolled steel sheets were pickled, cold-rolled and then travelled through a hot-dip galvanizing line to provide products.
- Hot rolling, cold rolling and hot-dip galvanizing conditions are given in Table 8.
- the heating temperature in the hot rolling was 1110 to 1150°C, and the temperature fall in quenching after hot rolling was 100 to 120°C.
- the thickness of the hot-rolled steel sheets was 4.0 mm, and these hot-rolled sheets were cold-rolled with a reduction ratio of 80 % into cold-rolled coils having a thickness of 0.8 mm. Finally, the cold-rolled coils were subjected to temper rolling with a reduction ratio of 0.3 to 0.4 %.
- the mechanical test values and plating properties for these steel sheets are also given in Table 8.
- the mechanical test was effected using a No. 5 specimen specified in JISZ2201 by a method specified in JISZ2241 to determine the strength YP at yield point, tensile strength TS and elongation E1 at break. The n value was calculated from (10%-20%) strain.
- the painting-baking property was expressed in terms of the BH property and the sum ( ⁇ (AA)) of the 2 % work hardening and the hardening by BH as described above.
- the recovery of elongation at yield point after the sample was allowed to stand at 40°C for 30 days was expressed in terms of YP-E1.
- YP-E1 is an quantity corresponding to a stretcher strain defect, and this defect occurs unless the YP-E1 value is 0.2 % or less.
- the fabrication embrittlement resistance was expressed in terms of the ductility-embrittlement temperature. This value is the transition temperature at which cracking occurs when a cup prepared by molding with a draw ratio of 2.2 is subjected to 10 % flaring at varied temperatures.
- the plating properties were evaluated in terms of the iron content, degree of alloying and powdering property of the alloyed layer.
- the iron content was determined by analysis, and the degree of alloying was evaluated with the naked eye.
- the P value the better the powdering property.
- the P value is 40 % or less, the powdering property is very good.
- the P value and iron content are 30 to 50 % and 8 to 12 %, respectively.
- steel sheets (Nos. 1, 2, 5, 7 and 12 to 14) according to the present invention had a tensile strength of about 350 to about 400 N/mm 2 , and, despite being a high-strength high-dent-resistant steel sheet having a BH value of 40 N/mm 2 or more and an ⁇ (AA) value of 60 N/mm 2 or more, had a sufficiently low YP value (i.e., a high face strain resistance), good elongation, r value and n value (i.e., a high moldability), and, with respect to the aging property, had substantially no recovery of YP-E1 in cold aging (cold non-aging or delayed aging), and a high painting-baking hardening (a high dent resistance), and, with respect to the fabrication embrittlement, the transition temperature was so low that no problem occurred. Further, also with respect to plating properties, both the iron content as a measure of the degree of alloying and the P value as a measure of the
- Automobiles are related to an environmental problem, and an attempt to reduce the body weight of automobiles has been made for the purpose of reducing fuel consumption.
- Panels for automobiles are not an exception to object materials for a reduction in the body weight of automobiles, and since they occupy a large proportion of the weight of an automobile, importance is attached to the reduction in the weight thereof. Further, since the panels attract much attention in connection with the quality of automobiles, the importance of design of panels has increased. This has led to an ever-increasing demand for panels having a complicated shape. Under these circumstances, the present invention is very important because it can provide a cold-rolled steel sheet having a combination of high workability and strength with a good dent resistance which can satisfy the above-described demand. Further, even when such a steel sheet is galvanized, the above-described demand can be satisfied, which renders the effect of the present invention very valuable now that importance has become attached to a high corrosion resistance.
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Description
Claims (12)
- A cold-rolled steel sheet, for an automobile, having excellent moldability and painting-baking hardenability, comprising, in terms of % by mass, 0.0010 to 0.0040 % of C, 0.0030 % or less of N, 0.5 % or less of Si, 0.02 to 1.5 % of Mn, 0.08 % or less of P, 0.01 % or less of S, 0.005 to 0.07 % of acid soluble Al, 0.05 % or less of Nb satisfying the requirement of a {Nb % - 93/12·C %} value of more than zero to 0.025 % and 24/14·N % to 72/14·N % of Ti, optionally 0.0001 to 0.002 % of B and from 0.02 to 1.2 % of Cr, with the balance consisting of Fe and unavoidable impurities and further having carbon in a solid solution form provided through dissolution of a precipitated carbide by recrystallization annealing and an aggregate structure such that, in X-ray diffraction, the natural logarithm ratio (log(I{222}/I{200})) of the diffraction intensity I {222} of a {222} plane to the diffraction intensity I {200} of a {200} plane is 2.7 or more.
- The steel sheet according to claim 1, which is a mild cold-rolled steel sheet, comprising, in terms of % by mass, less than 0.1 % Si, 0.02 to less than 0.3 % of Mn, less than 0.03 % of P, wherein the natural logarithm ratio (log(I{222}/I{200})) is 2.8 or more.
- The mild cold-rolled steel sheet, for an automobile, according to claim 2, which has at least one surface galvanized at a coverage of 15 g/m2 or more.
- The steel sheet according to claim 1, which is a high-strength cold-rolled steel sheet, comprising, in terms of % by mass, 0.1 to 0.5 % of Si, 0.3 to 1.5 % of Mn and 0.03 to 0.08 % of P.
- The high-strength cold-rolled steel sheet, for an automobile, according to claim 4, which has a value of Mn%/(Si+10P)% in terms of % by mass of 1.0 or more and at least one surface galvanized at a coverage of 15 g/m2 or more.
- A process for producing a cold-rolled steel sheet, for an automobile, having excellent moldability and painting-baking hardenability, comprising hot-rolling a steel composed of, in terms of % by mass, 0.0010 to 0.0040 % of C, 0.0030 % or less of N, 0.5 % or less of Si, 0.02 to 1.5 % of Mn, 0.08 % or less of P, 0.01 % or less of S, 0.005 to 0.07 % of acid soluble Al, 0.05 % or less of Nb satisfying a requirement of a {Nb % - 93/12·C %} value of more than zero to 0.025 % and 24/14·N % to 72/14·N % of Ti, optionally 0.0001 to 0.002 % of B and from 0.02 to 1.2 % of Cr, with the balance consisting of Fe and unavoidable impurities at a finish termination temperature of an Ar3 transformation point or above, quenching the hot-rolled steel sheet within 2 sec after the completion of the hot-rolling at a rate of 30°C/sec or more to attain a temperature fall of 100°C or above, coiling the cooled steel sheet at a temperature of 650 to 770°C, subsequently cold-rolling the coiled steel sheet with a reduction ratio of 72 to 92 %, subjecting the cold-rolled steel sheet to annealing in a temperature range of from 820 to 880°C for 20 sec or more and cooling the annealed steel sheet from that temperature to room temperature at a cooling rate of 3°C/sec or more.
- The process of claim 6 for producing a mild cold-rolled steel sheet, comprising hot-rolling a steel as mentioned in claim 6, comprising, in terms of % by mass, less than 0.1 % of Si, 0.02 to less than 0.3 % of Mn and less than 0.03 % of P, wherein the hot-rolled steel sheet after the completion of the hot-rolling is quenched at a rate of 30 to 300°C/sec or more.
- The process of claim 6 for producing a high-strength cold-rolled steel sheet, comprising hot-rolling a steel as mentioned in claim 6, comprising in terms of % by mass, 0.1 to 0.5 % of Si, 0.3 to 1.5 % of Mn and 0.03 to 0.08 % of P.
- The process according to claim 7, wherein said cold-rolled steel sheet is transferred to a plating tank where at least one surface of said steel sheet is galvanized at a coverage of 15 g/m2 or more.
- A process for producing a galvanized high-strength cold-rolled steel sheet, for an automobile, according to claim 8, wherein said steel sheet has a composition further regulated to have a Mn%/(Si+10P)% in terms of % by mass of 1.0 or more and is transferred to a plating tank where at least one surface of said steel sheet is galvanized at a coverage of 15 g/m2 or more.
- The process of claim 7 for producing an alloyed and galvanized mild cold-rolled steel sheet, wherein the steel sheet after the cold-rolling step is passed through a hot-dip galvanizing line, subjecting the galvanized steel sheet to annealing in a temperature range of from 830 to 890°C, cooling the annealed steel sheet from said temperature range to 440 to 460°C at a cooling rate of 3°C/sec or more, subjecting said cooled steel sheet to hot-dip galvanizing at said temperature and subjecting said galvanized steel sheet to an alloying treatment in a temperature range of from 550 to 600°C.
- The process of claim 8 for producing an alloyed and galvanized high-strength cold-rolled steel sheet, wherein the steel sheet after the cold-rolling step is passed through a hot-dip galvanizing line, subjecting the galvanized steel sheet to annealing in a temperature range of from 830 to 890°C, cooling the annealed steel sheet from said temperature range to 440 to 460°C at a cooling rate of 3°C/sec or more, subjecting said cooled steel sheet to hot-dip galvanizing at said temperature and subjecting said galvanized steel sheet to an alloying treatment in a temperature range of from 550 to 600°C.
Applications Claiming Priority (7)
Application Number | Priority Date | Filing Date | Title |
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JP4566591 | 1991-02-20 | ||
JP45665/91 | 1991-02-20 | ||
JP15983191 | 1991-06-05 | ||
JP159831/91 | 1991-06-05 | ||
JP19603991 | 1991-07-11 | ||
JP196039/91 | 1991-07-11 | ||
PCT/JP1992/000181 WO1992014854A1 (en) | 1991-02-20 | 1992-02-20 | Cold-rolled steel sheet and galvanized cold-rolled steel sheet which are excellent in formability and baking hardenability, and production thereof |
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EP0572666A1 EP0572666A1 (en) | 1993-12-08 |
EP0572666A4 EP0572666A4 (en) | 1994-06-01 |
EP0572666B1 true EP0572666B1 (en) | 1998-05-06 |
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EP92905304A Revoked EP0572666B1 (en) | 1991-02-20 | 1992-02-20 | Cold-rolled steel sheet and galvanized cold-rolled steel sheet which are excellent in formability and baking hardenability, and production thereof |
Country Status (4)
Country | Link |
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EP (1) | EP0572666B1 (en) |
DE (1) | DE69225395T2 (en) |
ES (1) | ES2114932T3 (en) |
WO (1) | WO1992014854A1 (en) |
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EP3498877B1 (en) * | 2016-08-12 | 2024-06-19 | POSCO Co., Ltd | High strength steel sheet having excellent formability and manufacturing method thereof |
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CN107201477A (en) * | 2016-10-11 | 2017-09-26 | 宝钢集团新疆八钢铁有限公司 | A kind of cold-rolling production process of the zinc-plated door-plate steel of deep-draw |
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JPS59226149A (en) * | 1983-06-03 | 1984-12-19 | Nippon Steel Corp | Hot rolled steel sheet with superior formability and its manufacture |
JPS6126756A (en) * | 1984-07-17 | 1986-02-06 | Kawasaki Steel Corp | Dead soft steel sheet having high suitability to chemical conversion treatment |
JPS61276927A (en) * | 1985-05-31 | 1986-12-06 | Kawasaki Steel Corp | Production of cold rolled steel sheet having good deep drawability |
US4889566A (en) * | 1987-06-18 | 1989-12-26 | Kawasaki Steel Corporation | Method for producing cold rolled steel sheets having improved spot weldability |
JPH01123058A (en) * | 1987-11-06 | 1989-05-16 | Kawasaki Steel Corp | Alloying hot dip galvanized steel sheet for superdrawing excellent in resistance to secondary working brittleness and its production |
JPH02194126A (en) * | 1989-01-20 | 1990-07-31 | Sumitomo Metal Ind Ltd | Manufacture of steel sheet having baking hardenability |
ATE135414T1 (en) * | 1990-11-09 | 1996-03-15 | Nippon Steel Corp | COLD ROLLED STEEL STRIP WITH EXCELLENT FORMABILITY AND PROCESS FOR PRODUCTION |
-
1992
- 1992-02-20 EP EP92905304A patent/EP0572666B1/en not_active Revoked
- 1992-02-20 WO PCT/JP1992/000181 patent/WO1992014854A1/en not_active Application Discontinuation
- 1992-02-20 DE DE69225395T patent/DE69225395T2/en not_active Expired - Fee Related
- 1992-02-20 ES ES92905304T patent/ES2114932T3/en not_active Expired - Lifetime
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP3498877B1 (en) * | 2016-08-12 | 2024-06-19 | POSCO Co., Ltd | High strength steel sheet having excellent formability and manufacturing method thereof |
TWI652355B (en) | 2018-01-30 | 2019-03-01 | 中國鋼鐵股份有限公司 | Hot-dipped galvanized steel and method of forming the same |
Also Published As
Publication number | Publication date |
---|---|
ES2114932T3 (en) | 1998-06-16 |
DE69225395D1 (en) | 1998-06-10 |
EP0572666A1 (en) | 1993-12-08 |
DE69225395T2 (en) | 1998-09-10 |
WO1992014854A1 (en) | 1992-09-03 |
EP0572666A4 (en) | 1994-06-01 |
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