EP0016846A1 - Process for producing high-strength cold-rolled steel plate for press working - Google Patents
Process for producing high-strength cold-rolled steel plate for press working Download PDFInfo
- Publication number
- EP0016846A1 EP0016846A1 EP79901046A EP79901046A EP0016846A1 EP 0016846 A1 EP0016846 A1 EP 0016846A1 EP 79901046 A EP79901046 A EP 79901046A EP 79901046 A EP79901046 A EP 79901046A EP 0016846 A1 EP0016846 A1 EP 0016846A1
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- EP
- European Patent Office
- Prior art keywords
- rolled steel
- steel sheet
- rolling
- cold rolled
- cold
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims abstract description 14
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 36
- 239000010959 steel Substances 0.000 claims abstract description 36
- 238000000137 annealing Methods 0.000 claims abstract description 11
- 238000005097 cold rolling Methods 0.000 claims abstract description 7
- 238000005098 hot rolling Methods 0.000 claims abstract description 7
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 238000005096 rolling process Methods 0.000 claims description 15
- 239000000203 mixture Substances 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims 4
- 229910052742 iron Inorganic materials 0.000 claims 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 12
- 239000011572 manganese Substances 0.000 description 11
- 229910052748 manganese Inorganic materials 0.000 description 8
- 229910052799 carbon Inorganic materials 0.000 description 7
- 229910052757 nitrogen Inorganic materials 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000014759 maintenance of location Effects 0.000 description 6
- 229910000734 martensite Inorganic materials 0.000 description 6
- 238000001953 recrystallisation Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000002791 soaking Methods 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 1
- 238000007373 indentation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000005482 strain hardening Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- 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
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
Definitions
- This invention relates to a method of producing a high strength cold rolled steel sheet having excellent press formability, comparable to the conventional cold rolled steel sheet for drawing.
- the conventional cold rolled steel sheet for deep drawing has a tensile strength of 28 - 33 Kg/mm 2 and has been used as outer panels of automobile bodies after being press formed.
- a tensile strength of 28 - 33 Kg/mm 2
- more and more automobile bodies are using thinner outer panels.
- car manufactures demand cold rolled steel sheets whose formability is comparable to the conventional one'and having a tensile strength higher than the latter.
- the conventional high tensile steel has a high yielding point and experiences considerable spring back and as a result, it is difficult to provide a press formed article with a desired configuration.
- the steel permits only too small elongation, it can easily develop cracks during press forming.
- the dual phase steel of recent development has low yielding point, but since its tensile strength is 50 - 70 K g/mm 2 , it undergoes too rapid work hardening and provides high yielding point after slight press forming, making it difficult to produce a desired configuration free from the effect of spring back.
- the primary purpose of this invention is to provide a method of producing a cold rolled steel sheet having the above defined characteristics.
- a cold rolled steel sheet which has press formability and form retention comparable to the conventional cold rolled steel sheet and yet has high strength and dent resistance higher than the conventional one, thus making great contribution to making of lighter cars.
- dense resistance means the property of a cold rolled steel sheet that does not retain a depression (permanent deformation) resulting from an external force applied to a press formed article made of that sheet.
- This invention resides in a method of producing a high strength cold rolled steel sheet for press formation which is characterized by hot rolling a steel consisting of 0.005 - 0.080% of C, less than 0.30% of Si, 1.6 - 3.5% of Mn, 0.02 - 0.08% of Sol. Al, 0.005 - 0.020% of N, the balance of Fe and incidental impurities, cold rolling the same with a reduction of at least 30%, and annealing the cold rolled steel by heating it at 660 - 750°C for a period longer than 30 minutes.
- a hot rolled steel is desirably coiled at a temperature lower than 600°C.
- Temper rolling is not necessarily performed, but if it is performed for a special purpose, a desired elongation ratio is 0.5% at maximum.
- the caharacteristic feature of this invention consists in optimizing the Sol. Al content, N content, and optionally the coiling temperature after hot rolling in the production of a low yield ratio steel sheet from high-Mn steel for the purposes of limiting the number of recrystallizing nuclei to form large grains in the process of annealing after cold rolling as well as promoting the growth through recrystallization of grains having an orientation [111] parallel to the plate surface, thereby providing a cold rolled steel sheet having a yield ratio less than 0.60 and an r-value higher than 1.2.
- Fig. 1 is a photograph (x 500) showing a microstructure of a cold rolled steel sheet produced in accordance with this invention.
- Fig. 2 is a photograph (x 500) showing a microstructure of a cold rolled steel sheet produced in accordance with the prior art.
- Fig. 3 is diagrammatical view explaining the test of form retention, in which a steel sheet is bent in a U-shaped form.
- Fig. 4 is a perspective view showing the measuring of residual indentation in dent resistance test.
- Figs. 1 and 2 are photomicrographs (x 500) showing, respectively, microstructures of our cold rolled steel sheet of Steel No. 1 and the conventional, high strength and low yield ratio cold rolled steel sheet of Steel No. 10 in Table 1.
- the grain size of steel sheet produced in accordance with this invention as shown in Fig. 1 is larger than that in Fig. 2. This is because, as mentioned hereinbefore, the formation of recrystallization nuclei has been restricted by optimizing the proportions of Sol.Al and nitrogen as well as coiling temperature after hot rolling.
- the lower yield point and the higher r-value which are obtained in accordance with this invention are due to the microstructure shown in Fig. 1.
- Carbon is effective for forming a dispersed phase of martensite in the cold rolled steel sheet to give a low yield ratio in the presence of manganese in an amount of more than 1.6%. A carbon content of less than 0.005% is not enough to give a thoroughly low yield ratio. On the other hand, more than 0.080% carbon raises tensile strength excessively and impairs spot weldability. The carbon content is restricted to from 0.005% to 0.080%.
- Silicon may be used as a deoxidizer and is effective for making the formation of martensite easier. However, a large amount of Si increases yield point and tensile strength, impairing formability and surface flatness of the cold rolled steel sheet. Thus, the Si content is restricted to less than 0.30%. Si is not required if the addition of Al achieves thorough deoxidation.
- Manganese is effective for forming-a dispersed phase of martensite in the presence of carbon. A manganese content of less than 1.6% is not enough to give a low yield ratio. A manganese content of more than 3.5% is not desirable, since such a large amount of manganese increases tensile strength excessively.
- Sol.Al is effective for lowering yield ratio, optimizing crystal grain and improving recrystallization texture i.e. increasing an r-value in the presence of nitrogen in an amount of more than 0.005%.
- the Sol.Al content of 0.02 - 0.08% is desirable for obtaining desired mechanical properties.
- Nitrogen is necessary to optimize crystal grain and to improve recrystallization texture in the presence of a suitable amount of Sol.Al. For this purpose, a nitrogen content of 0.005 - 0.020% is necessary. A nitrogen content of less than 0.005% is not effective for this purpose.
- the balance of the steel composition is Fe with incidental impurities, of which P and S are allowed to present in an amount of less than 0.05%, respectively.
- a preferred composition of the steel to which this invention is applied is:
- Coiling temperature after hot rolling determins the structure and arrangement of AlN and has an influence on the r-value of the resulting steel sheet containing Sol.Al, N and Mn in amounts specified in the above.
- the coiling temperature may be above 600°C.
- Annealing after cold rolling is necessary to obtain a cold rolled steel sheet which is softened due to removal of stress introduced dring cold rolling and which has a dual phase of ferrite pulse martensite, giving a tensile strength of 35 - 45 Kg/mm 2 , a yield ratio of 0.4 - 0.6 and an r-value of more than 1.2.
- the desirable annealing temperature is within the range of 660 - 750°C.
- the soaking time during annealing is also important. A soaking time of more than 30 minutes is necessary to effect concentration of C and Mn in the steel, and to form martensite during the period of cooling in annealing. A soaking time of less than 30 minutes is sometimes insufficient to form martensite.
- temper rolling with a reduction of more than about 1% is applied to a cold rolled steel sheet so as to avoid the formation of stretcher strains and to improve flatness of the steel sheet.
- temper rolling is not necessarily required. This is because the steel sheet produced in accordance with this invention does not show an elongation at yield point in the annealed state. Thus, it is not necessary to effect temper rolling in order to avoid the formation of stretcher strains.
- skin pass rolling may be applied to the cold rolled steel sheet in order to improve the surface flatness.
- the press formability of each steel sample was determined by the conventional Erichsen test and hole widening test.
- a 700 mm ⁇ dent resistance test piece in the form of a disc (2) was cut from each steel sample and subjected to shallow drawing to form a 400 mm ⁇ dome (3) having a maximum depth of 45 mm as illustrated in Fig. 4.
- a loop tester (1) was forced against the center of the domed test piece under a load of 20 kg, and the residual deflection 6 after removal of the load was measured.
- a greater residual deflection ⁇ is not desired since it provides an outer panel of an automobile body that easily forms a dent if it is pressed with a finger or hit by a bouncing pebble.
Abstract
A process for producing a high-strength cold-rolled steel plate for press working having a tensile strength of 35-45 kg/mm2 and a yield ratio of 0.4-0.6, which comprises hot-rolling steel comprising 0.005-0.080% of C, not more than 0.30% of Si, 1.6-3.5% of Mn, 0.02-0.08% of sol. Al, 0.005-0.020% of N, and balance of Fe and unavoidable impurities, and, after cold- rolling, annealing at 660-750°C for not shorter than 30 minutes.
Description
- This invention relates to a method of producing a high strength cold rolled steel sheet having excellent press formability, comparable to the conventional cold rolled steel sheet for drawing.
- The conventional cold rolled steel sheet for deep drawing has a tensile strength of 28 - 33 Kg/mm2 and has been used as outer panels of automobile bodies after being press formed. However, with the recent trend in the auto industry to reduce the weight of automobiles in an attempt to improve mileage economy, more and more automobile bodies are using thinner outer panels. Thus, car manufactures demand cold rolled steel sheets whose formability is comparable to the conventional one'and having a tensile strength higher than the latter.
- The outer panels of automobile bodies assume various configurations depending on car models and their mounting locations, but since most of them undergo only a slight degree of press formation, form retention after pressing is a very important factor.
- The conventional high tensile steel has a high yielding point and experiences considerable spring back and as a result, it is difficult to provide a press formed article with a desired configuration. In addition, since the steel permits only too small elongation, it can easily develop cracks during press forming. The dual phase steel of recent development has low yielding point, but since its tensile strength is 50 - 70 Kg/mm2, it undergoes too rapid work hardening and provides high yielding point after slight press forming, making it difficult to produce a desired configuration free from the effect of spring back.
- Disclosure of the Invention:
- The. inventors of this invention have found, after carrying out intensive-study to solve these problems, that a cold rolled steel sheet having a tensile strength of 35 - 45 Kg/mm2, a yield ratio (yield strength/tensile strength)-of 0.4 - 0.6, an r-value of more than 1.2 is most suitable for providing the desired steel sheet for use as outer panels of an automobile body.
- The primary purpose of this invention is to provide a method of producing a cold rolled steel sheet having the above defined characteristics.
- In general, the higher the strength of steel, the less the press formability and form retention. However, according to this invention, a cold rolled steel sheet can be provided which has press formability and form retention comparable to the conventional cold rolled steel sheet and yet has high strength and dent resistance higher than the conventional one, thus making great contribution to making of lighter cars. The term "dent resistance" means the property of a cold rolled steel sheet that does not retain a depression (permanent deformation) resulting from an external force applied to a press formed article made of that sheet.
- This invention resides in a method of producing a high strength cold rolled steel sheet for press formation which is characterized by hot rolling a steel consisting of 0.005 - 0.080% of C, less than 0.30% of Si, 1.6 - 3.5% of Mn, 0.02 - 0.08% of Sol. Al, 0.005 - 0.020% of N, the balance of Fe and incidental impurities, cold rolling the same with a reduction of at least 30%, and annealing the cold rolled steel by heating it at 660 - 750°C for a period longer than 30 minutes.
- In carrying out the method of this invention a hot rolled steel is desirably coiled at a temperature lower than 600°C. Temper rolling is not necessarily performed, but if it is performed for a special purpose, a desired elongation ratio is 0.5% at maximum.
- The caharacteristic feature of this invention consists in optimizing the Sol. Al content, N content, and optionally the coiling temperature after hot rolling in the production of a low yield ratio steel sheet from high-Mn steel for the purposes of limiting the number of recrystallizing nuclei to form large grains in the process of annealing after cold rolling as well as promoting the growth through recrystallization of grains having an orientation [111] parallel to the plate surface, thereby providing a cold rolled steel sheet having a yield ratio less than 0.60 and an r-value higher than 1.2.
- Fig. 1 is a photograph (x 500) showing a microstructure of a cold rolled steel sheet produced in accordance with this invention. Fig. 2 is a photograph (x 500) showing a microstructure of a cold rolled steel sheet produced in accordance with the prior art. Fig. 3 is diagrammatical view explaining the test of form retention, in which a steel sheet is bent in a U-shaped form. Fig. 4 is a perspective view showing the measuring of residual indentation in dent resistance test.
- Figs. 1 and 2 are photomicrographs (x 500) showing, respectively, microstructures of our cold rolled steel sheet of Steel No. 1 and the conventional, high strength and low yield ratio cold rolled steel sheet of Steel No. 10 in Table 1. The grain size of steel sheet produced in accordance with this invention as shown in Fig. 1 is larger than that in Fig. 2. This is because, as mentioned hereinbefore, the formation of recrystallization nuclei has been restricted by optimizing the proportions of Sol.Al and nitrogen as well as coiling temperature after hot rolling. The lower yield point and the higher r-value which are obtained in accordance with this invention are due to the microstructure shown in Fig. 1.
- The reasons for limiting the chemical composition of the steel to which this invention is applied will be described in detail hereinafter.
- Carbon (C): Carbon is effective for forming a dispersed phase of martensite in the cold rolled steel sheet to give a low yield ratio in the presence of manganese in an amount of more than 1.6%. A carbon content of less than 0.005% is not enough to give a thoroughly low yield ratio. On the other hand, more than 0.080% carbon raises tensile strength excessively and impairs spot weldability. The carbon content is restricted to from 0.005% to 0.080%.
- Silicon (Si): Silicon may be used as a deoxidizer and is effective for making the formation of martensite easier. However, a large amount of Si increases yield point and tensile strength, impairing formability and surface flatness of the cold rolled steel sheet. Thus, the Si content is restricted to less than 0.30%. Si is not required if the addition of Al achieves thorough deoxidation.
- Manganese (Mn): Manganese is effective for forming-a dispersed phase of martensite in the presence of carbon. A manganese content of less than 1.6% is not enough to give a low yield ratio. A manganese content of more than 3.5% is not desirable, since such a large amount of manganese increases tensile strength excessively.
- Acid soluble aluminium (Sol.Al): Sol.Al is effective for lowering yield ratio, optimizing crystal grain and improving recrystallization texture i.e. increasing an r-value in the presence of nitrogen in an amount of more than 0.005%. The Sol.Al content of 0.02 - 0.08% is desirable for obtaining desired mechanical properties.
- Nitrogen (N): Nitrogen is necessary to optimize crystal grain and to improve recrystallization texture in the presence of a suitable amount of Sol.Al. For this purpose, a nitrogen content of 0.005 - 0.020% is necessary. A nitrogen content of less than 0.005% is not effective for this purpose.
- The balance of the steel composition is Fe with incidental impurities, of which P and S are allowed to present in an amount of less than 0.05%, respectively.
- A preferred composition of the steel to which this invention is applied is:
- Coiling temperature after hot rolling determins the structure and arrangement of AlN and has an influence on the r-value of the resulting steel sheet containing Sol.Al, N and Mn in amounts specified in the above. In order to obtain a steel sheet having an r-value of around 1.2, the coiling temperature may be above 600°C. However, in order to obtain an r-value of more than 1.2 constantly, it is necessary to coil a hot rolled steel sheet at a temperature lower than 600°C. Annealing after cold rolling is necessary to obtain a cold rolled steel sheet which is softened due to removal of stress introduced dring cold rolling and which has a dual phase of ferrite pulse martensite, giving a tensile strength of 35 - 45 Kg/mm2, a yield ratio of 0.4 - 0.6 and an r-value of more than 1.2. For this purpose the desirable annealing temperature is within the range of 660 - 750°C.
- The soaking time during annealing is also important. A soaking time of more than 30 minutes is necessary to effect concentration of C and Mn in the steel, and to form martensite during the period of cooling in annealing. A soaking time of less than 30 minutes is sometimes insufficient to form martensite.
- Usually temper rolling with a reduction of more than about 1% is applied to a cold rolled steel sheet so as to avoid the formation of stretcher strains and to improve flatness of the steel sheet. However, according to this invention, such temper rolling is not necessarily required. This is because the steel sheet produced in accordance with this invention does not show an elongation at yield point in the annealed state. Thus, it is not necessary to effect temper rolling in order to avoid the formation of stretcher strains. However, even in this invention skin pass rolling may be applied to the cold rolled steel sheet in order to improve the surface flatness. However, since skin pass rolling (temper rolling) with a reduction of more than 0.5% results in increase in yield point with deterioration of formability, when temper rolling is applied, it is advisable to restrict the reduction on temper rolling to not more than 0.5%. Embodiments of the Invention:
- The working examples of this invention will be described hereinafter.
- Steels having chemical composition as shown in Table 1 were prepared with a converter to produce slabs 230 mm thick by a continuous casting method. Sulfur and phosphorous in each steel were restricted to 0.006 - 0.020% P and 0.002 - 0.020% S. These slabs were heated at a temperature of 1150 - 1270°C and then hot rolled to provide steel sheets 2.8 mm thick. Finishing temperature was 800 - 870°C.' The hot rolled steel sheets were coiled at a temperature of 520 - 580°C. The thus obtained hot rolled steel sheets were, after pickling, subjected to cold rolling with a reduction of about 70% to provide cold rolled steel sheets 0.8 mm thick. Annealing was applied to the cold.steel sheets to finish the sheets. Some of the finished steel sheets were thereafter subjected to temper rolling. The conditions of annealing and temper rolling are summarized in Table 2.
- A JIS No. 5 test piece was cut from each of the thus produced steel samples and used for a tensile test wherein it was stretched in the rolling direction. The results are given in Table 3 below, from which it can be seen that the cold rolled steel sheets having a yield ratio less than 0.60, an r-value more than 1. and a tensile strength of 35 - 45 Kg/m2 could only.be produced by the method of this invention. It is also clear from the Table that excessive temper rolling resulted in an elevated yield point.
- The press formability of each steel sample was determined by the conventional Erichsen test and hole widening test. The form retention was determined using a test piece 90 mm wide and 400 mm long cut from each steel sample and subjected to a U-shaping as illustrated in Fig. 3 followed by measurement of the amount of spring back (AL=L-50). A 700 mmφ dent resistance test piece in the form of a disc (2) was cut from each steel sample and subjected to shallow drawing to form a 400 mmφ dome (3) having a maximum depth of 45 mm as illustrated in Fig. 4. A loop tester (1) was forced against the center of the domed test piece under a load of 20 kg, and the residual deflection 6 after removal of the load was measured. A greater residual deflection δ is not desired since it provides an outer panel of an automobile body that easily forms a dent if it is pressed with a finger or hit by a bouncing pebble.
- Thus, it is apparent from the foregoing that the cold rolled steel sheets produced in accordance with this invention are all satisfactory with respect to mechanical properties, formability, form retention and dent resistance.
Claims (5)
1. A method of producing high strength cold rolled steel sheet having improved press formability, the composition of which consists essentially of 0.005 - 0.080% of C, up to 0.30% of Si, 1.6 - 3.5% of Mn, 0.02 - 0.08% of Sol.Al, 0.005 - 0.020% of N and the balance iron and incidental impurities, which comprises, after hot rolling, cold rolling the steel sheet with a reduction of more than 30% and then annealing the cold rolled steel sheet at a temperature of 660 - 750°C for a period longer than 30 minutes.
2. The method of Claim 1, which further comprises coiling the hot rolled steel sheet after hot rolling at a temperature of lower than 600°C.
3. The method of Claim 1 or 2, which comprises temper- rolling, after annealing, the annealed cold rolled steel sheet.
4. The method of Claim 3, in which the reduction on temper rolling is less than 0.5%.
5. The method of any of Claims 1 - 4, in which the composition of steel is 0.008 - 0.05% of C, 0 - 0.2% of Si, 1.8 - 2.5% of Mn, 0.02 - 0.08% of Sol.Al, 0.005 - 0.010% of N, less than 0.05% of P, less than 0.05% of S and the balance substantially iron.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10417278A JPS5531159A (en) | 1978-08-26 | 1978-08-26 | Manufacture of high strength cold rolled steel plate for press working |
| JP104172/78 | 1978-08-26 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| EP0016846A1 true EP0016846A1 (en) | 1980-10-15 |
| EP0016846A4 EP0016846A4 (en) | 1980-11-14 |
| EP0016846B1 EP0016846B1 (en) | 1983-08-17 |
Family
ID=14373606
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP79901046A Expired EP0016846B1 (en) | 1978-08-26 | 1979-08-25 | Process for producing high-strength cold-rolled steel plate for press working |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0016846B1 (en) |
| JP (1) | JPS5531159A (en) |
| DE (1) | DE2953072C1 (en) |
| GB (1) | GB2039951B (en) |
| IT (1) | IT1121469B (en) |
| WO (1) | WO1980000456A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9718883B2 (en) | 2003-09-10 | 2017-08-01 | Amgen Fremont Inc. | Antibodies to M-CSF |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56150135A (en) * | 1980-01-18 | 1981-11-20 | British Steel Corp | Binary steel |
| JPS579831A (en) * | 1980-05-21 | 1982-01-19 | British Steel Corp | Steel production |
| JPS62139848A (en) * | 1985-12-11 | 1987-06-23 | Kobe Steel Ltd | High strength and high ductility cold rolled steel sheet for automobile strengthening member |
| KR101147975B1 (en) * | 2010-04-27 | 2012-05-24 | 태성정밀공업 주식회사 | Rope for carrying something anchor for musical instrument |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4918713A (en) * | 1972-06-13 | 1974-02-19 | ||
| JPS51107218A (en) * | 1975-03-19 | 1976-09-22 | Nippon Kokan Kk | Buruuinguoshojinai kochoryokureienkohanno seizohoho |
| US4062700A (en) * | 1974-12-30 | 1977-12-13 | Nippon Steel Corporation | Method for producing a steel sheet with dual-phase structure composed of ferrite- and rapidly-cooled-transformed phases |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3709744A (en) * | 1970-02-27 | 1973-01-09 | United States Steel Corp | Method for producing low carbon steel with exceptionally high drawability |
| JPS4837565A (en) * | 1971-09-20 | 1973-06-02 | ||
| GB1376266A (en) * | 1971-12-27 | 1974-12-04 | Nippon Steel Corp | Cold-rolled steel sheet for pressforming |
| JPS5627583B2 (en) * | 1973-12-10 | 1981-06-25 | ||
| JPS5943531B2 (en) * | 1976-08-17 | 1984-10-23 | 新日本製鐵株式会社 | Manufacturing method for high-strength cold-rolled steel sheets with excellent workability |
| JPS5381544A (en) * | 1976-12-16 | 1978-07-19 | Shinto Paint Co Ltd | Continuous powder electrodeposition painting method |
| JPS5425948A (en) * | 1977-07-28 | 1979-02-27 | Kansai Paint Co Ltd | Supplying of cationic electrodeposit coating compound |
-
1978
- 1978-08-26 JP JP10417278A patent/JPS5531159A/en active Pending
-
1979
- 1979-08-24 IT IT68708/79A patent/IT1121469B/en active
- 1979-08-25 WO PCT/JP1979/000227 patent/WO1980000456A1/en unknown
- 1979-08-25 EP EP79901046A patent/EP0016846B1/en not_active Expired
- 1979-08-25 DE DE2953072A patent/DE2953072C1/en not_active Expired
- 1979-08-25 GB GB8013072A patent/GB2039951B/en not_active Expired
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4918713A (en) * | 1972-06-13 | 1974-02-19 | ||
| US4062700A (en) * | 1974-12-30 | 1977-12-13 | Nippon Steel Corporation | Method for producing a steel sheet with dual-phase structure composed of ferrite- and rapidly-cooled-transformed phases |
| JPS51107218A (en) * | 1975-03-19 | 1976-09-22 | Nippon Kokan Kk | Buruuinguoshojinai kochoryokureienkohanno seizohoho |
Non-Patent Citations (3)
| Title |
|---|
| JOURNAL OF METALS, Vol. 30, No 3, March 1978, New York US J. MORROW et al.: "Molybdenum in intercritically annealed dual-phase steel strip", pages 16-19. * |
| See also references of WO8000456A1 * |
| SHEET METAL INDUSTRIES, Vol. 55, No. 2, February 1978, Redhill GB M. GRUMBACH: "High strength cold rolled sheet for deep drawing", page 180-190. * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9718883B2 (en) | 2003-09-10 | 2017-08-01 | Amgen Fremont Inc. | Antibodies to M-CSF |
| US10280219B2 (en) | 2003-09-10 | 2019-05-07 | Amgen Fremont Inc. | Antibodies to M-CSF |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2039951A (en) | 1980-08-20 |
| GB2039951B (en) | 1982-10-06 |
| WO1980000456A1 (en) | 1980-03-20 |
| EP0016846A4 (en) | 1980-11-14 |
| JPS5531159A (en) | 1980-03-05 |
| IT7968708A0 (en) | 1979-08-24 |
| EP0016846B1 (en) | 1983-08-17 |
| DE2953072C1 (en) | 1985-03-21 |
| IT1121469B (en) | 1986-04-02 |
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