TWI333507B - High-carbon hot-rolled steel sheet and process for producing the same - Google Patents

Description

1333507 IX. Description of the Invention: The present invention relates to a high carbon hot-rolled steel sheet, in particular, a high-carbon hot-rolled steel sheet excellent in bending properties after processing and a method for producing the same. [Prior Art] High-carbon steel sheets used for tools or automobile parts (gears, bumpers) and the like are required to be processed into various complicated shapes, so that they are required to have excellent workability. On the other hand, in recent years, the demand for lowering the manufacturing cost of parts has become more and more intense, and the omission of the processing steps or the change of the processing method has been carried out. For example, as described in Non-Patent Document 1, as a processing technique for a part of an automobile drive system using a high-carbon steel sheet, a reversing processing technique capable of achieving thickening and forming, and a large step shortening has been developed, and has been partially practical. Chemical. Along with this, it is required to process a plurality of types of stretching, twisting, expanding, and squeezing/synthesis, and processing can be performed without any problem. In particular, when the bending process is performed after the stretching process, the bending portion is often broken or the like, and therefore the bending property after the excellent drawing process is expected. In order to date, the technology has been reviewed in order to improve the processability of high carbon steel sheets. For example, Patent Document 1 proposes a method for producing a high-carbon steel belt which is soft and has a disordered structure: an excellent process of the eighth-two process, which is a predetermined chemical: steel is hot-rolled, after derusting, at 95% by volume In the above, the heating rate or the soaking time k specified by the chemical component is followed by cooling at a cooling rate of iOOt: /hr or less. In addition, the literary literature 2 Φ technology, find a method for manufacturing high-carbon steel sheet with good workability 96194870 6 1333507 method, which will be rolled at the finishing temperature of (Ac) metamorphosis point +3(TC) The steel plate 'cools to 20 to 500 at a cooling rate of (:/sec.) (:, after 1 to 10 seconds, reheats at a temperature of 500 to (Αα metamorphic point +3 (TC)) And coiling, if necessary, soaking for 650 ° (Aci metamorphosis + 30 ° C) for more than 1 hour. Further, Patent Document 3 proposes a method for producing a high carbon hot rolled steel sheet excellent in elongation flangeability, which is Steel containing 〇. 2~〇7 . % by mass of the steel is milled at a finishing temperature (Αϊ*3 transformation point _2(rc) or more. _ After hot rolling, the cooling rate exceeds 12{rc/sec and cooling stops. The temperature is cooled at 65 〇c or less, and then coiled at a coiling temperature of 600 Å or less, and annealed at an annealing temperature of 640 ° C or higher and at an Ac! transformation point or less. Non-Patent Document 1: journal 〇f th JSTp, 44 2〇 (10) * P.409-413 ' 'Japanese Patent Laid-Open No. Hei 9-157758A Japanese Patent Laid-Open No. Hei 5-9588 003-13145 Patent Document 1 Patent Document 2 Patent Document 3 > [Summary of the Invention] ...: The characteristics of a high-carbon hot-rolled steel sheet which has been carried out in a single processing mode such as Xin: Although it is excellent, in the case of a combination of a plurality of processing patterns in the case of stretching processing:

The purpose of a month is to provide a hot-rolled steel sheet after drawing and a method of manufacturing the same. U: The inventors conducted in-depth studies on the properties of high-carbon hot-rolled copper sheets, and found that proper control of steel::: special 96194870 7 1333507 = milk = cooling conditions, coiling temperature and annealing temperature are important factors... It is found that the particle size of the ferrite-grained iron obtained by the measurement method described later is controlled to be less than or equal to the core, and the area ratio of the ferrite-grained iron having an aspect ratio of 4 〇 or more is controlled to 15% or less. According to the above findings, the present invention provides a method for producing a high-carbon hot-rolled steel sheet, which is characterized in that it has the following steps: C: 0.2 to 〇.7 %, Si: 2% or less, Mn: 2% or less, p: 〇〇3% or less, s: 0.03% or less, S〇1.A1: 〇〇1% or less, ν: 〇〇ι% or less Steel, which is subjected to hot rolling to obtain a hot-rolled steel sheet at a finishing temperature of (Ara metamorphic point _2 〇t) or higher; ± 〇 热 hot steel sheet is more than 6 〇 t / sec and less than 12 ( The cooling rate of rc/sec is cooled to 65 (the temperature below rc); the above-mentioned cooled hot L-steel plate is taken at a coiling temperature of _t or less And the step of annealing the hot-rolled steel sheet after the coiling is performed at an annealing temperature of 640 Å or more and below the ACl transformation point. In the method of the present invention, in the step of cooling, it is preferred to heat-roll the steel sheet The temperature is cooled to 600 ° C or lower at a cooling rate of 80 ° C / sec or more and less than 12 (TC / sec; and, in the above winding step, the winding is performed at a temperature of 55 〇 ° C or less The present invention also provides a high-carbon hot-rolled steel sheet, which is characterized in that the hot-rolled spheroidizing annealed material is characterized by having a mass percentage of C: 0.2 to 0.7%, Si: 2% or less, such as 2% or less.汴: 〇.03% or less, 5: 〇〇3% or less, 3〇1 八1: 0. 01% or less, N · 0.01% or less; fat iron particle size is 5· 〇vm 96149870 8 1333507 The following 'and the aspect ratio is 4. The area ratio of the ferrite iron above 〇, the ferrite iron particle size is approximated by the image analysis by the image analysis: the average of the particle diameters obtained by the pounds, The aspect ratio is obtained by approximating the ferrite 2 iron particle as an ellipse by image analysis (the long axis of the rounding) / (the shortest plate SI average value. In terms of body, the parallel two-plate thickness section is ground in the rolling direction of the steel plate, and the 1/4 position of the plate thickness is taken by the scanning electron microscope with the sodium nitrate liquid "coffee, nitrate and material surname after the rhyme" 1 500 times f weaving observation, using M heart Cyberneties company horse intrrimaSe Pr〇P1US ν-·4·〇^ΤΜ), ^^; in each fat grain: = is the aspect ratio of ΤΓ. In addition, find The relative value is the area ratio of the L field, and the average value of the 50 fields of view is taken as the vertical 4: the area ratio of the ferrite grains of 4. The area ratio of the ferrite particles above ΓU is preferably 10% - step contains; t from the invention, in addition to the composition of the above steel, can also enter w, two medium = content range Β々, Νι , "At least one selected from R dry; B: 〇.005 mass% or less; Cr: 3.5 mass or less; M.:"·below; = 〇. 1 mass 詈. /, ν π υ·丄贝里% The following; Ti: Quality: = lower; ^.. (10) or less; ", -." 曲 = 5 can be manufactured even after the processing such as drawing processing, high-carbon hot-rolled steel sheet. [Embodiment] 96149870 9 1333507 Hereinafter, a high carbon hot dry steel sheet of the present invention and its production will be described in detail. In addition, the single-portion 仃孑 Γ % of the component content means the meaning of "% by mass" unless otherwise specified. [Composition of steel] C amount: C is an important element that forms carbides and imparts hardness after bonfire. If the amount of C is less than .2%, the sufficient strength of the parts for mechanical construction cannot be obtained after quenching. On the other hand, if the amount exceeds G.7%, even if the grain size of the ferrite iron particles with a particle size of 5 Å or less and an aspect ratio of 4 〇 or more is 15% or less, sufficient stretching processing cannot be obtained. The bending characteristics of the latter. Further, the hardness after hot rolling is remarkably improved, and the steel sheet becomes brittle, so that it is difficult to handle, and the strength of the parts for mechanical construction after quenching is also saturated. Therefore, the amount of C is defined as 〇.2 to 〇·7%. In addition, in the case where the hardness after quenching is more important, the amount of C is preferably more than 5% 5%, and in the case of more emphasis on the workability, the amount of C is preferably less than 5%. In S1, the Si is a graph that the carbide is graphitized to impede the hardenability, and therefore the amount is preferably 2% or less, preferably 〇. Μ η stomach amount: If an excessive amount of Mn is contained, the ductility tends to be lowered. Therefore, the amount is preferably 2% or less, preferably 1% or less. When the P content is excessively contained, the ductility of the elongation flange property or the like is lowered, and the rupture is likely to occur. Therefore, the content is preferably 3% or less, preferably 0.02% or less. 007%以下。 When the amount of S is in the range of 〇〇3% or less, preferably 0.001% or less, as in the case of P, the ductility of the stretch flangeability or the like is lowered and the rupture is likely to occur. 96149870 10 1333507

Sol.": s〇lAl is the most important element in the present invention. That is, if the amount of 'S〇l A1 exceeds 〇.°%, the nitrogen is used in a relatively low-cost non-oxidizing environment. When the mysterious steel sheet is annealed in a nitrogen atmosphere, A1N is formed on the surface layer of the steel sheet, and the surface layer of the steel sheet is hardened to significantly reduce the tensile processing characteristics. Therefore, the amount of s〇iai is defined as U · (J1 / 6 or less).

N amount: When N is excessively contained, the ductility is lowered. Therefore, the amount is preferably 0.01% or less, preferably 0.005% or less. Here, if the above elements are reduced to a predetermined amount or less (for example, less than 0.001%), the cost will increase, so it is preferable to contain 〇. The remainder is Fe and unavoidable impurities, but for example to further enhance the shore fire! For the purpose of 'raw or & anneal softening resistance, at least one element such as B, Cr, Ni, Mo, Cu, Ti, Nb, W, V, Zr, etc. is added within the range of general addition, and the present invention is not damaged. The effect of the invention. Specifically, the elements may be: 〇. 〇〇 5% or less; Cr: & 5% or less; Ni: 3. 5% or less;

Mo: 0. 7% or less; Cu: 〇·1% or less; Ti: 0.1% or less; Nb: 0. U or less; W, V, Zr: total 〇. Further, for the above purpose, B: 0.0005% or more; Cr: 0.05% or more; Ni: 0.05% or more; Mo: 〇. 〇 5% or more; Cu: 0.01% or more; Ti: 〇. 〇1〇% or more; he: 0.01% or more 1, 乂, 21': a total of 0.01% or more. Further, even if elements such as Sn and Pb are mixed as impurities during the production process, the effects of the present invention are not impaired. [Manufacturing conditions] 96149870 1333507 Finishing temperature of hot rolling: If the finishing rolling temperature is not full (Ar3 transformation point -20 °C), it is partially rolled in the ferrite iron area, due to the ferrite iron after annealing Since the particle diameter exceeds 5 · 0 in m, the bending property after the drawing process is deteriorated. Therefore, the finish rolling temperature of hot rolling is set to be (An change point - 20 ° C) or more. Further, the Αη metamorphic point can be calculated by the following formula (1), but the actually measured temperature can also be used.

Ar3 metamorphic point = 910-203x [C] 1/2 + 44. 7x [Si] - 30x [Mn] . (1) Here, '[Μ] indicates the content (%) of the element Μ. In addition, a correction term may be introduced corresponding to the element, for example, in the case of containing Cr, Mo, and Ni, or -llx[Cr], +31.5x [Mo], -15.2 may be added to the right side of the formula (1). The correction of x[Ni]. Cooling conditions after hot rolling: In the present invention, the amount of S〇 1 · a 1 is low, which is not easy

The grain growth inhibition caused by the pinning of AIN occurs, and the fine graining of the ferrite grains can be achieved. This phenomenon is presumed to be due to rapid cooling after hot rolling, and it is easy to accumulate the strain imparted to the Worthfield iron particles during rolling, and in the subsequent annealing, the accumulated strain becomes the nucleation base point of the ferrite iron particles. (site). If the cooling rate after hot rolling is less than 6 〇 t: / sec, the strain imparted to the Worthfield iron particles during rolling is less likely to accumulate, and thus the nucleation base point of the ferrite granules in the subsequent I fire is reduced. Fertilizer iron particles are easy to grow. As a result, the size of the ferrite iron was over 355. 〇", and the bending after the drawing process was degraded. On the other hand, the cooling rate is i 2 generations/second or more, and the grain size of the ferrite particles after annealing is 5 {)^, but the area ratio of the fertilizer filaments on the aspect ratio of 4 〇2 is more than 15%. As described above, the f-curve characteristics after the drawing process are deteriorated. This phenomenon is presumed to be that if the cooling rate of 96194870 12 1333507 is 120 ° C / sec or more, the strain imparted to the Worthfield iron grain during rolling is excessively present after rolling, so in the subsequent annealing, isometric The fat iron particles are difficult to grow. From the above, the cooling rate after hot rolling was set to be 601:/sec or more and less than 120 °C/sec. The upper limit of the cooling rate is preferably 115 ° C / sec. If the end temperature of the hot-rolled steel sheet cooled by such a cooling rate (that is, the cooling stop temperature) is higher than 650 ° C, the strain accumulated in the Worthite iron is liberated in the cooling up to the coiling of the hot-rolled steel sheet. . As a result, the particle size of the ferrite iron after the retreat was more than 5.0 m, and the bending property after the drawing process was deteriorated. Therefore, the cooling stop temperature is 650 ° C or lower, preferably 600 ° C or lower. In addition, due to the problem of temperature measurement accuracy, the cooling is stopped. • The temperature is preferably set to 50 (TC or more. Cooling after reaching the cooling stop temperature is not specified, it can be natural cooling, or the cooling power can be reduced. The forced cooling β is preferably forced cooling to the extent that reheating can be suppressed from the viewpoint of uniformity of the steel sheet, etc. φ Coiling temperature: The hot-rolled steel sheet after cooling is taken up, and at this time, if the coiling temperature exceeds 60 (TC), the strain accumulated in the Worthite iron during hot rolling is: put, so the grain size of the ferrite iron after annealing is more than 5. The bending property after stretching is deteriorated. The coiling temperature is set to be 600 C or less. In addition, in order to sufficiently obtain the above-mentioned quenching effect, the coiling temperature is preferably lower than the above-described cooling stop temperature. Further, since the shape of the hot-rolled steel sheet is deteriorated, the coiling temperature is preferably It is determined to be 2〇〇ΐ or more, and more preferably it is more than the offspring. If the aspect ratio of the iron particles with an aspect ratio of 4·〇 or more is (10) to 96194870 13 1333507, the bending property can be further improved, and the effect is further improved. Must be cooled Set to 8 (TC / sec or more and less than 12 〇 t / sec, set the cooling stop temperature to 6 〇〇 ° C or less ' and set the coiling temperature to 55 (TC or less.) Rust removal: heat after coiling The rolled steel sheet is usually subjected to rust removal after annealing the hot-rolled steel sheet thereafter. The rust-removing means is not particularly limited, and is preferably pickled by a general method. Annealing temperature of the hot-rolled steel sheet is washed by pickling After the rust removal, the hot-rolled steel sheet is spheroidized in order to perform spheroidization, and is annealed as a spheroidizing annealing. At this time, if the annealing temperature is less than 640. (:, the growth of the ferrite particles is insufficient. The area ratio of the ferrite grains having an aspect ratio of 4.0 or more is more than 15%, and the bending property is deteriorated after the stretching is turned on. On the other hand, if the annealing temperature exceeds the Aci metamorphic point, the Worthite ferrochemical system partially The bending property after stretching is generated during the cooling process. Therefore, the annealing temperature of the hot-rolled steel sheet is set to 64 (TC or more and Aci transformation point or less. In order to obtain a more excellent elongation flange) Preferably, the annealing temperature of the hot rolled steel sheet is determined to be 680 ° C or more. , Acn transformation point by the following formula (2) is calculated, but also the actual temperature measured.

Aci metamorphic point 754·83-32·25x[C]+23.32x[Si]-17.76x[Mn] (2) Here, [Μ] represents the content (% by mass) of the element μ. In addition, the correction term may be introduced corresponding to the element, for example, in the case of containing Cr or Mo, V, or +17. 3x [Cr], +4. 51x [Mo] may be added to the right side of the formula (2). , + 15. 62x[V] corrections. The annealing time of the hot rolled steel sheet is preferably about 8 to 80 hours. The obtained steel 96149870 14 has a spheroidal carbide in the plate, and the average aspect ratio is about 5. 〇 below (the value measured at about 1/4 of the plate thickness). In the case of melting the high carbon steel of the present invention, either a converter or an electric furnace may be used. Further, the thus-melted high carbon steel is formed into a steel slab by agglomeration-block rolling or continuous casting. Steel blanks are usually hot rolled after heating. Further, the steel* produced by continuous casting can be subjected to direct rolling (direct rolling) by directly or in order to suppress the temperature reduction. Further, in order to avoid hot metal rolling, in order to avoid deterioration of the surface state due to rust, it is preferable to set the steel billet heating temperature to 128 (TC or less. Hot rolling may also omit rough rolling. In addition, in order to ensure the finish rolling temperature, it is also possible to heat the material to be rolled by a heating means such as a thin rod-shaped heater during hot rolling, and to promote spheroidization or hardness reduction. The steel coil may be insulated by a cold cover or the like after the coiling. The thickness of the hot-rolled steel sheet is as long as the manufacturing conditions of the present invention can be maintained, and the heat is limited to 1 〇 to 1 〇〇 mm. Rolled steel plate is particularly suitable for operation. The annealing of hot-rolled steel sheets can be carried out by box annealing or continuous annealing. After annealing, quenching and rolling is carried out as needed. The quenched milk does not affect the hardenability. The condition is not particularly limited. The hot-rolled steel sheet produced by the method of the present invention described above is a hot-rolled steel sheet subjected to hot-rolling spheroidizing annealing, which has an average aspect ratio of about 5 · 0 as described above. Following and spheroidized The hot-rolled steel sheet of carbide. Moreover, the particle size of the ferrite of the hot-rolled steel sheet of this case is 5. 〇am or less. The grain size of the ferrite-grained iron affects the bending property after the drawing process, and if the particle size of the ferrite-grain exceeds 96149870 15 1333507 After 5. 〇em, a large amount of fine carbides will be precipitated in the ferrite grains. Pull: the fineness of the interface between the carbide and the parent phase (fertilizer iron) in the process =, in the bending plus X It will be broken and will be broken. By making the ferrite iron particles less than von 5 〇em, the fine carbides in the ferrite grains will be less, and the fine voids generated in the stretching process will be bent in the stretching process. It is difficult to connect 'so it can suppress the occurrence of cracking. ' In addition, in the hot-rolled steel sheet of this case, the area ratio of the ferrite-grained iron particles with an aspect ratio of 4.0 or more is 5% or less. The shape of the ferrite-grained iron particles and the fertilizer The particle size of the granular iron: the sample will affect the -qu (4) after the drawing process. If the aspect ratio of the iron particles of the fertilizer is 4.0 or more, the iron particle of the iron ore with an aspect ratio of 4 or more is less than 4.0. The grain boundary of the ferrite grain is prone to occur in the drawing process - fine cracking. If the aspect ratio is 4 When the area ratio of the ferrite grains is more than 15%, the fine fracture in the drawing process is used as a starting point, and cracking occurs in the bending process. The area of the ferrite particles having an aspect ratio of 4·〇 or more When the rate is 15% or less, it is possible to suppress the occurrence of cracking in the bending after the drawing process. Preferably, the area ratio of the iron particles having an aspect ratio of 4. or more is 10% or less. (Example 1) The continuously cast steel slabs of steels A to E & z having the chemical composition shown in Table 1 were heated to 1,250 ° C, and hot rolled under the conditions shown in Table 2, and after pickling, hot rolling was also carried out under the conditions of Table 2. The steel sheet is annealed to produce a steel sheet having a thickness of 5.0 mm. No. 1 to 2 〇. The annealing is performed in a nitriding environment (N2 environment). Here, the steel sheet N〇. 1 to 丨〇 is an example of the present invention. , Steel plate No. 11~20 is 96149870!333507 Comparative example. Further, the grain size of the ferrite iron, the aspect ratio of the ferrite particles, and the area ratio were measured by the following methods. Further, the bending characteristics after the drawing process were evaluated by the following methods. The grain size of the fertilized iron, the aspect ratio and the area ratio of the ferrite particles: Here, the ferrite-particles of the ferrite are analyzed by image analysis to approximate the average particle size of the ferrite particles as a circle, and The ratio is an average value of the ellipse (the long axis of the ellipse) / (the short axis of the circle) obtained by approximating the ferrite iron particles by image analysis. Specifically, the parallel plate thickness section is ground in the rolling direction of the steel sheet, and the position of 1/4 of the thickness of the sheet is treated with nitrification liquid (nital, nitric acid + ethanol) after the rice is used. The microscope was micro-addressed at a magnification of 15 times, and the image analysis software Soft Image Pro Plus ver 4 〇(TM) manufactured by MediaCybernetic0 was used to obtain the ferrite iron (four) and the filament aspect ratio by image analysis. Further, the area ratio of each of the fields of view is obtained by dividing the area ratio of the iron particle aspect ratio by the area ratio of U or more, and dividing the area ratio of the field of view by the total area of the field of view, and the average aspect ratio of the 5 () fields of view is 4. Area ratio of ferrite particles. Further, in the rolling direction of the steel sheet, the parallel plate = the position of the bitter acid alcohol solution, the bitter acid: ethanol) rot: the thickness of the plate is reduced by an electron microscope at a magnification of 3000 times. The aspect ratio of the carbide (the longest diameter / the wide 爰 ' will be given to the aspect ratio of each carbide to pre-fire. The average number of the average), the average aspect ratio is obtained, and it is confirmed that it is spheroidized and retracted. Bending characteristics: used by a right angle relative to the rolling direction 96149870 17

The tensile test was carried out by the method in which the width of the parallel portion to be sampled was 3 () mln t J = Γ 241, and the second line was subjected to the compression bending test based on Jisz 2248. In the ringing test, the punching diameter is D4 lmm, and it is indicated that: if the crack does not occur, it is expressed as 〇, and if one crack occurs and the crack occurs, the rupture is not △, and the three cracks are expressed as χ. In addition, the condition is an invention example. " 〇 〇 表 表 表 表 本 本 本 本 本 本 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板 钢板The following 'excellent bending characteristics after drawing processing are excellent. Further, in the examples of the present invention, the average aspect ratio of the carbides was 5 G or less, and it was confirmed that the carbides were spheroidized by the spheroidizing annealing. In Fig. 1, in the case where the particle size of the ferrite is not more than m, the area ratio of the ferrite particles having an aspect ratio of 4.0 or more is related to the bending characteristic after the drawing process. It can be seen that, as in the case of the steel sheet of the present invention, the area ratio of the ferrite particles is less than 5. 〇# m, and the aspect ratio is 4. When it is 15% or less, excellent bending properties after stretching processing can be obtained. Ref. A 0. 26 0.22 0.83 0.010 0. 0025 0.007 0.0031 791 737 B 0.34 0.20 0.74 0.015 0. 0018 0. 005 0. 0033 778 735 C 0.35 0.02 0.15 0.009 0. 0030 0.006 0. 0036 786 741 D 0.49 0.19 0. 76 0.011 0. 0027 0.010 0. 0032 754 730 E 0.66 0.21 0. 75 0.014 0.0045 0.003 0. 0030 732 725 Z 0.36 0.21 0. 73 0.013 0. 0022 0.032 0. 0032 776 735 (Table 2)

Steel plate No. Steel hot rolling condition Annealing of hot rolled steel sheet Finishing rolling temperature (°C) Cooling rate (t/sec) Cooling stop temperature (.〇Reeling temperature (°C) 1 A 801 110 620 550 700〇Cx40hr Inventive Example 2 A 811 95 560 510 720〇Cx40hr Inventive Example 3 β 788 115 610 540 680 eCx40hr Inventive Example 4 B 808 85 570 520 710〇Cx40hr Inventive Example 5 C 801 75 610 590 670〇Cx40hr Inventive Example 6 C 806 105 580 490 720 ° Cx40 hr Example 7 of the invention D 774 90 620 580 710 〇 Cx40 hr Example 8 of the invention D 784 100 550 500 720 〇 Cx 40 hr Example 9 of the invention E 752 65 600 570 700 ° C x 40 hr Example 10 of the invention E 772 100 540 490 720 〇 Cx40hr Inventive Example 11 A 801 80 680 580 700 〇 Cx40 hr Comparative Example 12 A 751 100 610 570 700 〇 Cx 40 hr Comparative Example 13 B 798 110 620 560 600 〇 C x 40 hr Comparative Example 14 B 793 90 600 塁 690 〇 C x 40 hr Comparative Example 15 C 816 150 580 520 720 〇 Cx40hr Comparative Example 16 C 806 55 630 550 710 〇 Cx40hr Comparative Example 17 D 794 115 670 590 720 〇 Cx40 hr Comparative Example 18 D 719 95 610 580 680 〇 Cx40 hr Comparative Example 19 E 752 130 590 550 710〇Cx40hr Comparative Example 20 Z 805 100 580 530 720 〇 Cx40hr Comparative Example 96194870 19 1333507 (Table 3) Steel plate No. Fertilizer iron particle size (^m) Area ratio of the grain size of the iron particles with an aspect ratio of 4.0 or more (%) Remarks on bending characteristics after drawing

(Example 2) After the steel sheets shown in the following Table 1 and Table 1 were successively formed into steel slabs, they were heated to 1,230 C and subjected to hot rolling and annealing of hot-rolled steel sheets under the conditions shown in Table 4 to produce a sheet thickness. 4. 5mm steel plate No. 21~37. In addition, the annealing is performed under the nitriding % & (heart environment) for the obtained hot-dried steel sheet? In the same manner as in Example 1, the grain size of the ferrite iron, the aspect ratio of the ferrite particles and the area ratio were measured to evaluate the bending characteristics after the drawing process. Further, in the same manner as in Example 1, the spheroidized state of the carbide was confirmed. F steel (C: 0.31%; Si: 〇·18%, · Μ η: 0. 68% '· P : 〇· 〇 12% ; 96149870 20 1333507 s: 0.00m; S〇LM: 0.005%; N : 0 0040%; Ar3ftgit: 785 ° C; Ac! metamorphic point: 737 ° C); GI, (C: 0.23%; Si: 〇. 18 〇 / 〇; Mn: 〇 > 76 〇 / 〇; p: 〇<〇l6〇/〇; s : ; s〇l. A1 : 〇· _% ; N ·· 〇. 〇()m ; Cr : L 2% ;

Ar3 metamorphic point: 785 °C; ACl metamorphic point: 759t:); RM (C · 0. 32/i, Si. 1. 2%; Mn: 1. 5%; P: 〇. 025%; S: omSoLM :0·0_; N:〇.〇〇m; Ar3 metamorphic point: s〇4 °C; Ac! metamorphic point: 746 °C); i steel (c · o. 35 /., Si. 〇 · 2〇 %; Mn mp :QQ12% = S : 0·0038% ; Sol. A1 : 〇· 0〇5% ; N : 〇〇〇33% ; m〇 m

Cr·: 〇· Ar3 metamorphic point: 77 generations; Aci metamorphic point: navigation). In addition, F steel to I steel. ΑΓ3 虻 state point, ACl metamorphic point system is determined by the above formula (1) or formula (2), G steel containing Cr or M 、, steel system using the above correction And find it. The results are shown in Table 5. It can be seen that the conditions of the cold material are all in the steel plate No. 21 to 27, and the bending of the cold portion is within the scope of the present invention. Qut steepness is excellent. It can be seen that the steel sheet No. 23 7 can have an area ratio of the ferrite iron particles having an aspect ratio of 4.〇 or more and 10%: lower. In addition, the steel plate H33 which was observed with a constant cooling rate was found to have a cooling stop temperature and a coiling temperature of the steel sheets No. 3G to 33 in the range of the present invention, and the aspect ratio was 4 ·. Above the surface of the ferrite grain iron II = below. Further, in the examples of the present invention, the average aspect ratio of the carbides was 5 〇 to 96149870 21 1333507, and it was confirmed that the carbides were spheroidized by spheroidizing annealing. The E to I steel having a steel composition within the scope of the present invention (G steel and I steel containing an alloying element other than the basic component) exhibits excellent bending properties after drawing. (Table 4)

Steel plate No. Steel hot rolling condition Annealing of hot rolled steel sheet Finishing temperature (°C) Cooling rate (〇C/sec) Cooling stop temperature (°C) Coiling temperature (°C) 21 F 820 50 560 530 700〇 Cx30hr Comparative Example 22 F 820 70 560 530 700 〇 Cx30hr Inventive Example 23 F 820 85 560 530 70 (TCx30hr Inventive Example 24 F 820 95 560 530 700 〇 Cx30hr Inventive Example 25 F 820 105 560 530 700 〇 Cx30hr The present invention Example 26 F 820 115 560 530 70 (TCx30hr Inventive Example 27 F 820 140 560 530 700 〇 Cx30hr Comparative Example 28 F 820 105 530 700 〇 Cx30hr Comparative Example 29 F 820 105 630 Leg 700 〇 Cx30hr Comparative Example 30 F 820 105 630 560 700〇Cx30hr Inventive Example 31 F 820 105 630 530 700〇Cx30hr Inventive Example 32 F 820 105 580 560 700〇Cx30hr Inventive Example 33 F 820 105 580 530 700〇Cx30hr Inventive Example 34 E 790 105 560 530 715 °Cx60hr Inventive Example 35 G 800 105 560 530 72 (TCx50hr Inventive Example 36 Η 810 105 560 530 700 〇 Cx30hr Inventive Example 37 I 820 105 560 530 700 〇 Cx30hr Inventive Example 96149870 22 1333507 (Table 5) Steel Plate No . Fermented iron particle size (//m) Area ratio (%) of ferrite particles with a transverse ratio of 4.0 or more. Bending characteristics after drawing processing Remarks 21 5^4 13.2 △ Comparative Example 22 4.7 11.3 〇 Inventive Example 23 3.6 8.8 〇 Inventive Example 24 3.1 7.9 〇 Inventive Example 25 2.9 8.5 〇 Inventive Example 26 3.2 7.6 〇 Inventive Example 27 4.5 21.9 X Comparative Example 28 Μ 14.2 △ Comparative Example 29 5^8 14.6 Δ Comparative Example 30 4.3 12.1 〇 Inventive Example 31 4.0 13.3 〇 The present invention Example 32 4.5 10.7 〇 Inventive Example 33 3.9 8.4 〇 Inventive Example 34 3.8 9.5 〇 Inventive Example 35 3.7 8.7 〇 Inventive Example 36 4.8 9.6 〇 Inventive Example 37 3.5 8.8 〇 Inventive Example

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relationship between the area ratio of the ferrite grains and the bending characteristics after the drawing process in which the aspect ratio is 4.0 or more. 96149870 23

Claims (1)

1333507 X. Patent Application Range: 1. A method for producing a high carbon hot rolled steel sheet, which is characterized by having the following steps: containing C1.2 to 〇.7%, Si: 2% or less, Mn by mass% : 2% or less, P: 〇. 〇 3% or less, s: 〇〇 3% or less, s〇 "i: 嶋 below, N: 0.01% or less of the composition of steel, (A. Metamorphic point 2〇C The finishing rolling temperature of m is hot-rolled to form a hot step; the hot-rolled steel sheet is cooled to a temperature of 65 (rc or less) at a cooling rate of 6 〇t/sec or more and less than 12 〇乞/sec. a step of winding the cooled hot-rolled steel sheet at a coiling temperature of 600 t or less; and annealing the hot-rolled steel sheet after the coiling at an annealing temperature of 64 〇t or more and A. 2. The method of manufacturing a high-carbon hot-rolled steel sheet according to the scope of the patent application, wherein in the above cooling step, the hot-rolled steel sheet is 8 (rc/sec or more and less than 120 °C/ The cooling rate of the second is cooled to 6 〇 (the temperature is less than rc; and in the above winding step, it is 55 〇. Degree: two coils. 3. As in the patent application (4), the high carbon reduction _ manufacturing method 'where the 'steel composition is in addition to the above composition, further includes the range of B, Cr, Ni, Mo, Cu , , IVb, W, I z ^ at least one selected; ^ in shell 1% as β: 〇. 005% or less; Cr · 3 or less... 96149870 24 1333507 3. 5% or less; Μ〇: 〇· 7 % or less; Cu: 〇, the following; Ti: 〇j % or less, Nb · 0.1% or less; w, V, Zr: total 0_1% or less. 4. A high carbon hot-rolled steel sheet, hot rolled spherical The annealed material is characterized by containing C: 〇. 2 to 〇. 7%, Si: 2% or less, Μη. 2% or less, p: 〇〇3% or less, s: 〇〇 3% or less, s〇1 A1 · 〇. 01% or less, N: 〇. 01% or less; The grain size of the ferrite iron is 5. 0 // m or less, and the area ratio of the ferrite iron with an aspect ratio of 4.0 or more is 15% or less. Here, the ferrite iron particle size is analyzed by image analysis. The grain is approximated by the average of the particle diameters obtained by the circle, and the aspect ratio is obtained by image analysis using the ferrite iron particles as an ellipse to obtain an average value of the minor axis of the ellipse. 5. The high carbon hot-rolled steel sheet according to item 4 of the patent application, wherein the aspect ratio of the ferrite-grained iron particles having an aspect ratio of 4.0 or more is 1% or less. 6. If the high-carbon hot-rolled steel sheet of the fourth or fifth patent application scope is applied, the composition of Lugang, in addition to the above composition, further contains B, Cr, Ni, Mo, Cu, Ti from the following content range. , at least one selected from Nb, W, V, and Zr*; 3: 0.005% or less in mass%; (: 1': 3.5% or less; 1^: 3.5% or less; Mo: 0.7% or less; Cu: 0.1% or less; Ti: 0.1% or less; Nb: 0·1% or less; w, V, Zr: a total of 0.1% or less. 96149870 25