CN101802236A - High-strength steel sheet for can manufacturing and process for manufaturing the sheet - Google Patents

Abstract

The present invention provides a high-strength steel sheet for can making that can pass the regulations of ASTM and has excellent workability in both strength and ductility. The high-strength steel sheet for can making with a product thickness t of 0.1 to 0.5 mm is characterized by: It has the following steel composition: C: 0.04 to 0.13% by mass %, Si: more than 0.01% to 0.03%, Mn: 0.1 to 0.6%, P: 0.02% or less, S: 0.03% or less, Al: 0.01 ～0.2%, N: 0.001～0.02%, the balance is composed of Fe and unavoidable impurities; and the steel structure is a composite structure of ferrite and martensite with ferrite as the main body, and the martensite fraction It is defined as 5% or more and less than 30%, the martensite grain size d (μm) and the product plate thickness t (mm) satisfy the following formula <A>, and the 30T hardness is 60 or more. 1.0<(1-EXP(-t×3.0))×4/d Formula <A>.

Description

High-strength thin steel plate for can making and manufacturing method thereof

technical field

The present invention relates to a high-strength thin steel sheet for can making used as a raw material for food cans and beverage cans and a method for producing the same. Here, the high-strength thin steel sheet refers to a thin steel sheet with a tensile strength of 590 MPa or more.

Background technique

As steel sheets for can making, cold-rolled thin steel sheets having a product sheet thickness t of 0.1 to 0.5 mm are generally used. As a steel plate for can making, the higher the strength, the thinner the plate thickness t of the product, and therefore, as high a strength as possible is required.

Therefore, in the past, high-strength thin steel sheets for cans were generally produced by the secondary cold rolling method. This method, for example, as described in Japanese Patent Publication No. 38-8563 and Japanese Patent Application Publication No. 8-5039, is to anneal the steel plate after the first cold rolling, and then carry out the second cold rolling to adjust the hardness. method to a specified value. In addition, a method of cold-rolling a soft hot-rolled sheet containing coarse crystal grains, etc. have also been proposed.

However, the high-strength thin steel sheets for can-making produced by these conventional techniques have a defect that the workability is very low, and forming defects tend to occur in the can-making process. In particular, when the final step is cold rolling, the above-mentioned tendency is more pronounced because the finished product is formed of a cold-rolled structure with low ductility. In addition, a method of performing stress relief annealing after cold rolling has been proposed, but the ductility is also low because the steel sheet is not recrystallized.

Therefore, these high-strength thin steel sheets for can making can be used when bending is the main part and ductility is not very required, but they cannot be used when high ductility is required. In addition, in recent years, due to rapid thinning of can materials, the ductility of steel sheets tends to decrease, and there is a problem that it cannot cope with changes in the design of food and beverage cans. In this way, strength and ductility are required for steel sheets for can making.

Furthermore, steel sheets for automobiles are also required for strength and ductility. In this technical field, as described in JP-A-2004-285366, it has been proposed to form a ferrite phase with excellent ductility and a hard precipitated phase. The 2-phase (DP) organization is a solution that takes into account both ductility and strength. However, unlike steel sheets for automobiles, for steel sheets for food cans and beverage cans, ASTM strictly limits the alloy composition from the viewpoint of harmlessness to the human body, so the manufacturing method of steel sheets for automobiles cannot be applied to high-grade steel sheets for cans. Strength thin steel plate. For example, in the invention of Japanese Unexamined Patent Application Publication No. 2004-285366, crystal grains are refined by containing 1.5 to 3.5% of Mn, but the upper limit of Mn is specified as 0.6% in ASTM, so the range of Mn mentioned above is not standard. of.

In addition, if the product sheet thickness t is reduced to 0.1 to 0.5 mm, the elongation improvement shown in the steel sheet for automobiles cannot be obtained. This is considered to be because, in an extremely thin material, stress concentration at the interface between martensite and ferrite tends to occur due to the thin plate thickness. Furthermore, if the alloy composition is reduced in order to pass ASTM, the grain size of martensite increases. For these reasons, it is impossible to apply the DP technology of steel sheets for automobiles to high-strength thin steel sheets for can making, and it is impossible to achieve both strength and ductility.

Contents of the invention

Therefore, an object of the present invention is to solve the above-mentioned conventional problems and provide a high-strength steel sheet for can making that can pass the ASTM regulations and has both strength and ductility and excellent workability. In addition, the prescribed upper limit value of the alloy composition of the steel plate for cans of ASTM is as follows.

C: 0.13%, Mn: 0.60%, P: 0.020%, S: 0.03%, Si: 0.020%, Cu: 0.60%, Ni: 0.15%, Cr: 0.10%, Mo: 0.05%, Al: 0.20%, Other: 0.02%. However, Si: 0.03% is allowed in the case of Al-killed steel.

The first invention of the present invention made to solve the above-mentioned problems is a high-strength thin steel plate for can making with a product plate thickness t of 0.1 to 0.5 mm, characterized in that:

The high-strength thin steel sheet for can-making has a steel composition as follows: C: 0.04 to 0.13%, Si: more than 0.01% to 0.03%, Mn: 0.1 to 0.6%, P: 0.02% or less, S: 0.03% or less, Al: 0.01-0.2%, N: 0.001-0.02%, the balance is composed of Fe and unavoidable impurities;

The steel structure is a composite structure of ferrite and martensite with ferrite as the main body;

The martensite fraction shall be above 5% and below 30%;

Martensite particle size d (μm) and product plate thickness t (mm) satisfy the following formula <A>;

30T hardness is above 60.

1.0＜(1-EXP(-t×3.0))×4/d Formula (A)

Furthermore, the second invention of the present invention is a high-strength thin steel sheet for can making with a product sheet thickness t of 0.1 to 0.5 mm, characterized in that:

The high-strength thin steel sheet for can-making has a steel composition as follows: C: 0.04 to 0.13%, Si: more than 0.01% to 0.03%, Mn: 0.1 to 0.6%, P: 0.02% or less, S: 0.03% or less, Al: 0.01-0.2%, N: 0.001-0.02%, the balance is composed of Fe and unavoidable impurities;

The steel structure is a composite structure of ferrite and martensite with ferrite as the main body;

The martensite fraction is specified as more than 5% and less than 30%;

Martensite particle size d (unit μm), product plate thickness t (mm) and martensite hardness (Hv) satisfy the following formula <B>, and the 30T hardness is 60 or more.

1.0＜{(1-EXP(-t×3.0))×2400/Hv}/d Formula<B>

In addition, the third invention of the present invention is that in the steel composition of the first or second invention, Mo: 0.05% or less, Ni: 0.15% or less, Cr: 0.10% or less, V: 0.02% or less are further contained in mass % , B: 0.02% or less, Nb: 0.02% or less, Ti: 0.02% or less one or two or more can improve hardenability.

Furthermore, a fourth invention of the present invention is the method for producing a high-strength steel sheet for can making according to any one of the first to third inventions, characterized in that hot finish rolling is performed at a finishing temperature Ar _{of 3} or higher, and then After coiling at a temperature of 750°C or less, cold rolling is performed at a cold rolling ratio of 80 _% or more. The temperature zone up to 400°C is cooled to below 300°C at a cooling rate of above 100°C/sec.

Furthermore, in the fifth invention of the present invention, in the fourth invention, it is preferable that the finishing temperature of the hot finish rolling is not less than Ar ₃ and not more than 920°C, and the average cooling from 850°C to 600°C in the subsequent cooling step is preferably The speed is 20°C/sec or more, and the coiling temperature is set to be 550°C or less.

According to the first to second inventions of the present invention, by controlling the martensite grain size d in accordance with the thickness t of the product, it is possible to obtain a high-strength steel sheet for can making that satisfies ASTM regulations and has both strength and ductility . Furthermore, in the second invention, the martensite grain size d is controlled in consideration of the product plate thickness t and the martensite hardness Hv, thereby achieving both strength and ductility at a higher level.

In addition, according to the third aspect of the present invention, hardenability can be improved by adding alloy elements that promote martensite precipitation, and strength can be improved by adding alloy elements that can supplement insufficient strength. In addition, the can can be recycled and reused, but the alloy composition of the third invention does not contain elements (elements that are difficult to remove) that become obstacles in the recycling process.

In addition, according to the fourth and fifth inventions of the present invention, it is possible to efficiently produce steel sheets with martensite particle diameters controlled as described in the first to third inventions of the present invention without repeating cold rolling twice. d's high-strength thin steel plate for canning.

Description of drawings

Fig. 1 is a graph showing whether elongation is good or bad according to plate thickness and martensite grain size.

Fig. 2 is a graph showing whether the elongation is good or not according to the ultra-fine Vickers hardness of martensite and the grain size of martensite.

Detailed ways

The high-strength thin steel sheet for can making according to the present invention has a steel composition containing, by mass %, C: 0.04 to 0.13%, Si: more than 0.01% to 0.03%, Mn: 0.1 to 0.6%, and P: 0.02% or less , S: 0.03% or less, A1: 0.01 to 0.2%, N: 0.001 to 0.02%, and the balance is composed of Fe and unavoidable impurities. Therefore, the reason for limiting the numerical values of each component will be described first.

C: 0.04 to 0.13%

Regarding C, in order to secure the strength required for steel sheets for cans, it is specified to be 0.04% or more. However, if it exceeds 0.13%, ASTM cannot be passed, so C is limited to the range of 0.04 to 0.13%. It is more preferable to limit according to the target steel sheet strength level, but if the amount of C increases, the strength of the obtained martensite tends to increase, so in order to achieve a high balance between elongation and strength, the amount of C is preferably 0.04% or more. And less than 0.07%.

Si: more than 0.01% and less than 0.03%

Si is an element that increases deformation resistance during hot rolling and cold rolling, and needs to be contained in an amount exceeding 0.01% in order to secure strength, and more preferably 0.015% or more. Its upper limit is specified at 0.03% specified by ASTM.

Mn: 0.1-0.6%

Mn is an element useful for preventing hot cracks caused by S, suppressing an increase in strength of a hot-rolled steel sheet, increasing the strength of a cold-rolled steel sheet, and refining crystal grains, and it needs to be contained at least 0.1%. By containing 0.1% or more of Mn, martensitic transformation easily occurs in a relatively short period of time even during heat retention at the coiling temperature or slow cooling from the coiling temperature. Its upper limit is specified at 0.60% as specified by ASTM. It is more preferable to specify according to the intended strength level, but since Mn is a solid-solution strengthening element, it tends to increase the strength by increasing the amount of addition, so in order to balance elongation and strength, it is preferably 0.1% or more and less than 0.1%. 0.5%.

P: less than 0.02%

P is an element that lowers the ductility of a steel sheet, and P tends to segregate strongly in steel, causing embrittlement due to segregation. Therefore, it is preferable to reduce P as much as possible, and the upper limit thereof is made 0.02% in the present invention. This upper limit is consistent with the value specified by ASTM.

S: 0.03% or less

S exists as inclusions in steel, which lowers the ductility of the steel sheet and further deteriorates the corrosion resistance. Therefore, it is preferable to reduce its content as much as possible, and the upper limit is set at 0.03% in the present invention. This upper limit is consistent with the value specified by ASTM.

A1: 0.01 to 0.2%

Al is a useful element that functions as a deoxidizer, improves the cleanliness of steel, and has a function of making the structure finer. In order to obtain such an effect, it is preferable to contain 0.01% or more. In addition, the upper limit thereof is specified as 0.2% specified by ASTM.

N: 0.001～0.02%

N is an element that has the effect of increasing the strength (yield strength and tensile strength) of the steel sheet through solid solution strengthening and strain age hardening, and in order to obtain such effects, it needs to be contained in an amount of 0.001% or more. Moreover, if it contains more than 0.02%, it will cause cracks in a slab and an increase in the internal defect of a steel plate, so it is unpreferable.

In the present invention, in the above-mentioned basic steel composition, Mo: 0.05% or less, Ni: 0.15% or less, Cr: 0.10% or less, V: 0.02% or less, B: 0.02% or less may be further contained in mass %. 1 or more than 2 types. These elements are components for improving the hardenability of the steel sheet and are effective for increasing the strength, but the upper limit thereof is limited by ASTM as described above. Addition of these components is not essential, but it is preferable to add them appropriately when the intended strength is high. Excessive addition suppresses ferrite and leads to a decrease in ductility, so it is appropriate to consider the above range from this point of view.

In addition, in the present invention, one or two of Nb: 0.02% or less and Ti: 0.02% or less may be further contained in the above-mentioned basic steel composition in mass %. These are all precipitation strengthening elements, and are effective for improving strength. The upper limits of these components are also limited according to ASTM as described above. The components for improving the above-mentioned annealing properties and the precipitation strengthening components may be used alone or in combination.

The high-strength thin steel plate for can making according to the present invention has the above-mentioned steel composition, and the product plate thickness t is 0.1 to 0.5 mm. When the product plate thickness t is less than 0.1 mm, it is difficult to make cans with the current technology, and the plate thickness exceeding 0.5 mm exceeds the concept of a thin steel plate, so the product plate thickness t is specified as 0.1 to 0.5 mm. More preferably, the product plate thickness t is in the range of 0.1 to 0.3 mm.

The steel structure of the high-strength thin steel sheet for can making according to the present invention is a composite structure of ferrite and martensite mainly composed of ferrite. Since ferrite is an essential phase for improving the workability of steel sheets, it is defined as the main phase. On the other hand, in order to increase the strength of the steel sheet, martensite is an essential phase in the present invention, and by forming a two-phase structure of these ferrite and martensite, both ductility and strength can be achieved.

Furthermore, the martensite fraction (area ratio of martensite in the structure) is preferably 5% or more and less than 30%. This is because if the martensite is less than 5%, the strength will be insufficient, and if it exceeds 30%, the ferrite fraction will decrease relatively, and the workability will decrease.

In the high-strength thin steel sheet for can making of the present invention, the martensite grain size d (μm) is controlled in relation to the product plate thickness t (mm), and the following formula <A> is satisfied in the first invention.

1.0＜(1-EXP(-t×3.0))×4/d Formula<A>

Regarding Table 2 and Table 3 (continued from Table 2) of Example 1 described later, in Fig. 1, the abscissa represents the plate thickness, and the ordinate represents the martensite grain size, and those with an elongation of 5% or more are qualified, and are indicated by ○ , less than 5% is unqualified, represented by ×, the above formula <A> is obtained by approximating the boundary between qualified and unqualified by natural logarithm. That is, when the product thickness t is close to 0.1 mm, the upper limit of the martensite grain size d is close to 1 μm, and when the product thickness t is close to 0.3 mm, the upper limit of the martensite grain size d is close to 2.5 μm. The reason why the upper limit of the martensite grain size d is defined according to the product plate thickness t is that, if the hard martensite grain size d is larger than the product plate thickness t, the workability decreases.

In addition, in the second invention, it is set to satisfy the following formula <B obtained by substituting 4/d of the above formula <A> with 2400/Hv and dividing the whole formula by the martensite grain size d (μm). >.

1.0＜{(1-EXP(-t×3.0))×2400/Hv}/d Formula<B>

Regarding Table 4 and Table 5 (continued Table 4) of Example 2 described later, when the product plate thickness t (mm)=0.22mm in Fig. 2, the horizontal axis is the ultra-micro Vickers hardness of martensite, The axis is the martensite grain size, and the elongation rate of more than 5% is defined as qualified, and it is indicated by ○, and less than 5% is defined as unqualified, and it is indicated by ×. The above formula <B> is approximated by natural logarithm Pass and fail boundaries.

Here, Hv is a martensitic ultra-fine Vickers hardness, and is a hardness obtained by measuring, for example, HMV-1AD manufactured by Shimadzu Corporation, and setting a measurement load to 10 g or less according to the structure. If the ultrafine Vickers hardness Hv is greater than 300, the upper limit of the martensite grain size d is smaller than the value specified by the above formula.

The hardness of 30T is evaluated based on 30T of JISZ2245. If the hardness of 30T is lower than 60, the strength is insufficient when used in the body of the tank. Therefore, 60 or more is necessary, and the cooling rate of 100°C/s or more described later and the Cooling to below 300°C is achieved. The upper limit is not particularly limited, but the current upper limit of the hardness of 30T that can be achieved by rapid cooling is about 90, which is regarded as the upper limit. Furthermore, it is more preferably 65-85 from the balance of elongation and strength.

The method for producing the high-strength steel sheet for can making according to the present invention will be described below.

The high-strength thin steel sheet for can making of the present invention is basically manufactured through the processes of hot rolling, coiling, cold rolling, annealing, and rapid cooling. Small, by cold-rolling it at a high cold-rolling rate of 80% or more to reduce the grain size, by producing austenite transformation in the annealing process, and properly controlling the rapid cooling rate, so that the fine Martensite body produced.

First, hot rolling is performed by setting the finishing temperature of hot finish rolling to Ar ₃ or higher. In order to refine the grain size of the cold-rolled steel sheet, it is effective to refine the crystal grains of the hot-rolled sheet. Therefore, it is preferable to lower the hot-rolling temperature as much as possible, and it is preferably set to 920° C. or lower. However, if the hot-rolling temperature is below Ar ₃ , coarse grains will be formed on the surface of the hot-rolled sheet due to rolling in the ferrite-austenite two-phase region, and martensite cannot be performed in the subsequent process. Therefore, it is preferable to set the hot finish rolling temperature to Ar ₃ or higher and 920° C. or lower.

The hot-rolled steel sheet is cooled and coiled, but the average cooling rate from 850°C to 600°C in the cooling step is preferably 20°C/sec or more. This is because the cooling rate from 850° C. to 600° C. is important in order to refine the crystal grain size of the hot-rolled steel sheet. If the average cooling rate in this temperature range is lower than 20° C./sec, the particle diameter will increase, and subsequent miniaturization cannot be performed. The coiling temperature is 750°C or lower, preferably 550°C or lower. If the coiling temperature is higher than this temperature, a lamellar structure of ferrite and pearlite is formed in the hot rolling stage, impairing the uniformity, and thus workability is lowered even if cold rolling or annealing is performed thereafter.

The steel sheet obtained from the coil is then cold-rolled to a desired thickness in the range of 0.1 to 0.5 mm. However, it is important in the present invention to set the cold-rolling ratio in the cold-rolling to a high value of 80% or more. If the cold rolling ratio is less than 80%, the ferrite grain size increases during annealing, and martensite cannot be refined to a predetermined fineness. In addition, in view of the performance of the cold rolling mill, it is difficult to regulate the cold rolling ratio to be 95% or more, so the cold rolling ratio is made within the range of 80 to 95%, preferably 83 to 93%.

The following annealing and rapid cooling are important steps for obtaining a composite structure of ferrite and martensite. In the annealing step, the cold-rolled steel sheet is kept at a temperature of Ar ₁ or more and 870° C. or less for 3 minutes or less. If the holding temperature is below Ar ₁ , austenite transformation does not occur in the annealing step, so martensite cannot be generated even if rapid cooling is performed. However, if the holding temperature is 870° C. or higher, recrystallization during annealing proceeds excessively, ferrite becomes coarse-grained, and martensite cannot be reduced to a predetermined size or less. Furthermore, the reason for setting the holding time to 3 minutes or less is to suppress the progress of recrystallization.

In the final rapid cooling step, fine martensite is precipitated in ferrite by controlling the cooling rate in the temperature range from 750°C to 400°C to 100°C/sec or more and cooling to 300°C or less. If the cooling rate is lower than this rate, martensite cannot be formed. In addition, the temperature range for cooling at a cooling rate of 100°C/s or more is specified as 750°C to 400°C in order to precipitate martensite most effectively. If the rapid cooling start temperature is lower than 750°C, the ferrite It is difficult to refine the martensite because of the progress of the growth of the martensite. In addition, if it is not rapidly cooled to at least 400°C, the strength is insufficient because martensite cannot be formed. As long as it is cooled to 300° C. or lower in this way, the high-strength steel sheet for can making of the present invention having a stable crystal structure and fine martensite grains dispersed in ferrite can be obtained. In addition, the cooling rate in the temperature range of 400 degrees C or less is arbitrary.

The high-strength steel sheet for can manufacturing thus produced has the martensite grain size d described in the first and second inventions, and can achieve both strength and ductility. Moreover, the alloy composition meets ASTM, so it can be safely used as a raw material for food cans and beverage cans. Examples of the present invention are shown below.

Example

(Example 1)

Melting the steel having the composition shown in Table 1, for the steel plates A1 to S1 manufactured under the manufacturing conditions shown in Table 2 and Table 3 (continued from Table 2), the state of martensite, formula <A> The calculation results on the left, 30T hardness, and elongation were evaluated.

Here, regarding the state of martensite, the martensite was identified by LePera (レペラ-) etching, and image analysis was carried out on at least 100 fields of view with a field of view of 0.2 μm × 0.2 μm with a 1000-magnification optical microscope to obtain Martensite fraction (the area ratio of martensite in the structure). In addition, regarding the martensite grain size, the circle-equivalent diameter was calculated by the same measurement and averaged.

About hardness, it evaluated based on 30T of JISZ2245. If the 30T hardness is less than 60, the strength is insufficient when used for the main body of a can as described above, so 60 or more is defined as acceptable. Regarding the elongation, a material test was performed in accordance with JIS No. 5 sheet of JIS Z2241, and as described above, those with an elongation of 5% or more were defined as acceptable, and those with an elongation of less than 5% were defined as unacceptable.

From Table 2 and Table 3 (continued from Table 2), it can be seen that the steel that satisfies the specified conditions in composition, hot rolling to cold rolling, and annealing, and satisfies the formula <A> has a small martensite grain size and can ensure elongation.

(Example 2)

Under the manufacturing conditions shown in Table 4 and Table 5 (continued from Table 4), the steel having the composition shown in Table 1 was made into steel plates A21 to Q22, and the martensitic state of the steel plate, the left side of formula <B> The calculation results, martensite ultra-fine Vickers hardness, 30T hardness, and elongation were evaluated.

In addition, various evaluation methods were carried out based on the same method and standard as in Example 1. Regarding the ultra-micro Vickers hardness of martensite, HMV-1AD manufactured by Shimadzu Corporation was used, and the measurement load was 0.1gf. Determination.

From Table 4 and Table 5 (continued from Table 4), it can be seen that the steel which satisfies the specified conditions in hot rolling to cold rolling and annealing and satisfies the formula <B> has a small martensite grain size and can ensure elongation.

According to the present invention, it is possible to provide a high-strength steel sheet for can making that can pass the ASTM regulations and has both strength and ductility and excellent formability.

Claims (5)

1. a system jar is used high-strength steel sheet, and it is that goods thickness of slab t is the system jar high-strength steel sheet of 0.1～0.5mm, it is characterized in that:

Described system jar has following steel with high-strength steel sheet and forms: contain C:0.04～0.13%, Si in quality %: greater than 0.01% and be below 0.03%, Mn:0.1～0.6%, below the P:0.02%, below the S:0.03%, Al:0.01～0.2%, N:0.001～0.02%, surplus is made of Fe and unavoidable impurities; And structure of steel is based on the ferrite of ferrite and martensitic complex tissue;

Be defined in martensite branch rate more than 5% and be lower than 30%;

Martensite particle diameter d and goods thickness of slab t satisfy following formula＜A 〉, wherein the unit of d is μ m, the unit of t is mm;

1.0＜(1-EXP (t * 3.0)) * 4/d formula (A)

30T hardness is more than 60.

2. a system jar is used high-strength steel sheet, and it is that goods thickness of slab t is the system jar high-strength steel sheet of 0.1～0.5mm, it is characterized in that:

Described system jar has following steel with high-strength steel sheet and forms: contain C:0.04～0.13%, Si in quality %: greater than 0.01% and be below 0.03%, Mn:0.1～0.6%, below the P:0.02%, below the S:0.03%, Al:0.01～0.2%, N:0.001～0.02%, surplus is made of Fe and unavoidable impurities; And structure of steel is based on the ferrite of ferrite and martensitic complex tissue;

Be defined as martensite branch rate more than 5% and be lower than 30%;

Martensite particle diameter d, goods thickness of slab t and martensite hardness Hv satisfy following formula＜B 〉, wherein the unit of d is μ m, the unit of t is mm;

1.0＜(1-EXP (t * 3.0)) * 2400/Hv}/d formula＜B 〉

30T hardness is more than 60.

3. according to each described system jar high-strength steel sheet in the claim 1～2, it is characterized in that, in steel is formed, in quality % further contain below the Mo:0.05%, below the Ni:0.15%, below the Cr:0.10%, below the V:0.02%, below the B:0.02%, Nb; Below 0.02%, Ti:0.02% in following more than a kind or 2 kinds.

4. make jar manufacture method with high-strength steel sheet for one kind, it is characterized in that, it is each described system jar manufacture method with high-strength steel sheet in the claim 1～3,

At precision work temperature Ar ₃More than carry out hot finishing, then after having carried out under the temperature below 750 ℃ batching, carry out with the cold rolling rate more than 80% cold rolling, in annealing operation, at Ar ₁More than and under the temperature below 870 ℃ the insulation below 3 minutes after, 750 ℃ to 400 ℃ humidity provinces are cooled to below 300 ℃ with the speed of cooling more than 100 ℃/second.

5. the system according to claim 4 jar manufacture method with high-strength steel sheet, it is characterized in that: the precision work temperature of hot finishing is Ar ₃More than and below 920 ℃, the average cooling rate from 850 ℃ to 600 ℃ in the refrigerating work procedure thereafter is more than 20 ℃/second, coiling temperature is below 550 ℃.

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