JPH0931539A - Production of metallic strip with improved deep drawability - Google Patents

Abstract

A ductile steel band is made from an alloy containing the following proportions of elements indicated in thousandths of percent by weight: 0-20, pref. 2-20 of C, 0-500, pref. 100-500 Si, 0-1000 Mn, 0-100, pref. 50-100 P, 0-50 S, 0-100 Al, 0-10, pref. 2-8 N and one or more of 0-150 Ti, 0-150, pref. 10-50 Nb and 0-5, pref. 0-2 B, the remainder being Fe. The alloy is first hot-rolled, then cold-rolled to reduce its thickness by over 20%, annealed at up to 920 degrees C, cold rolled again, also reducing the thickness by over 20% while impressing a degree of rugosity on the surface, and finally annealed at above recrystallisation temp. A thin steel band made the process is also claimed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to thin metal strips with improved deep drawing properties, and in particular to expansion during deep drawing.
The present invention relates to a method for producing a metal thin strip excellent in deformability and thinning deformability, and a thin metal strip obtained by this method.

[0002]

BACKGROUND OF THE INVENTION Deep drawing steel must have many properties that enable it to be formed. For example, in the case of a steel sheet for containers, thinning deformability is required, and in the case of the automobile industry and the like, expansion deformability is required. To facilitate the deformation must low as possible yield stress R _e of the steel for a given tensile strength R _m, work hardening coefficient n must be as high as possible. That is, the work hardening coefficient defines the expansive deformability of a material, and the higher this coefficient, the better the material deforms. The elongation of the metal strip during rolling in cold working creates a crystal structure after annealing, which causes anisotropy in mechanical properties. Therefore, the anisotropy coefficient in the weakest direction [Chemical formula 1]:

[0003]

Embedded image And the average anisotropy coefficient [Chemical formula 2]:

[0004]

Embedded image Must also be high. Yield stress R of this anisotropy coefficient
_The effects on _e , tensile strength R _m and elongation at break A% are relatively small, but this cannot be said when processing a metal thin plate to which stress is applied during forming.

The ratio [Chemical formula 1] used in the measurement of anisotropy is the ratio of the logarithmic strain of the width to the logarithmic strain of the thickness of the test piece in the tensile test (where ψ is the tensile direction of the test example). Represents the angle between the rolling direction of the sheet metal). The average anisotropy coefficient of steel [Chemical formula 2] is also called the Lankford coefficient and is calculated by the following [Equation 1]:

[0006]

[Equation 1]

(Here, r ₀ , r ₉₀ , and r ₄₅ are anisotropy coefficient values r in the longitudinal direction, the lateral direction, and the 45 ° oblique direction with respect to the rolling direction of the metal blank). The average anisotropy coefficient [Chemical formula 2] represents the ability of the metal plate to be thinned. In order to ensure optimum deep drawing conditions, that is, sufficient metal flow in all directions, it is necessary to make the Rankford coefficient [Formula 2] as large as possible.

It is important that the anisotropy coefficient r _{min in} the direction of the lowest anisotropy coefficient [Chemical formula 1] is as high as possible. This ensures that the metal does not become too thin in all stressed directions. These two coefficients r _min
The fact that [Chemical formula 2] is high means that the metal can be sufficiently deformed by thinning.

It is also important to increase the elongation at break A%. This means that the material has a high ductility. Finally, Young's modulus should be as high as possible. The higher this characteristic, the higher the deep drawability of the steel.

It is known to use standard steels for this type of application, for example steels with the following chemical composition (1000% by weight): carbon <5 eg = 3 silicon <200 eg = 9 manganese <. 500 eg = 140 phosphorus <30 eg = 8 sulfur <50 eg = 5 aluminum <100 eg = 35 nitrogen <10 eg = 3 titanium <150 eg = 56 balance iron and impurities due to manufacturing hot rolled this steel Then, cold rolling is performed at a reduction rate of 75 to 85%, for example 80%, followed by continuous annealing at 800 ° C., and a light skin-pass operation at a reduction rate of 1% is performed. This type of steel has excellent deep drawing properties.

Further, a special steel for further increasing the deep drawing characteristics, in particular, the Rankford coefficient [Chemical formula 2], for example, Rankford obtained by smelting steel having the following chemical composition (1000 times the weight%) Steels with a coefficient of 3 are also known: carbon <2 silicon <41 manganese <120 phosphorus <11 sulfur <11 aluminum <45 nitrogen <2 balance iron and manufacturing impurities.

This steel was hot rolled, cold rolled at a reduction rate of 50%, then annealed at 750 ° C. for 20 seconds, cold rolled again at a reduction rate of 77% and then at 870 ° C. for a second time of 20 seconds. Anneal. The steel sheet thus obtained has a high Rank Ford coefficient [Chemical formula 2], but naturally does not have other properties necessary for excellent deep drawing, and it is necessary to lower the carbon content in order to increase the Rank ford coefficient. In addition, since it requires annealing at a high temperature, the manufacturing cost becomes extremely high.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide an economical method for producing a thin metal strip which is excellent in deep drawing property in terms of expansion deformability and thinning deformability and has improved elongation at break. To provide.

[0014]

[Means for Solving the Problems] The present invention is characterized by the following steps 1) to 6), which are excellent in elongation deformability and thinning deformability during deep drawing and have improved deep drawing characteristics with excellent elongation at break. A method for producing thin metal strips: 1) Carbon content of 20 or less, silicon content of 500 or less, manganese content of 1,000 or less, and 100 at a content of 1,000 times wt%.
Contains less than phosphorus, less than 50 sulfur, less than 100 aluminum, less than 10 nitrogen and no titanium, niobium and boron, or less than 150 titanium, less than 150 niobium
The ratio is 150 or less, boron is included in the ratio of 5 or less, and the balance is smelting iron and steel that is an impurity caused by manufacturing, 2) hot rolling, 3) cold rolling with a reduction rate of 20% or more, 4 ) Annealing at steel recovery temperature ~ 920 ℃, 5) Second cold rolling with reduction rate of 20% or more to give metal strip a predetermined roughness (rugosite), 6) Steel recrystallization temperature or more Second annealing is performed.

Other characteristics of the present invention are as follows: 1) The steel to be smelted in the first stage has a carbon content of 2 to 20 and a silicon content of 100 to 500 at a content of 1000 times by weight. , 0-1000 Manganese, 50-100 Phosphorus, 0-50 Sulfur, 9-100 Aluminum, 2-8 Nitrogen, 0-150 Titanium,
1 selected from 10 to 50 niobium and 0 to 2 boron
It contains one or more elements, the balance being iron and manufacturing-related impurities. 2) The first annealing is performed at the steel recovery temperature to the steel recrystallization temperature. 3) Increase the reduction ratio in the first cold rolling and decrease the reduction ratio in the second cold rolling. 4) Lower the reduction ratio in the first cold rolling and increase the reduction ratio in the second cold rolling. 5) Reduce the reduction ratio in the first cold rolling to 35-50%, and
Reduce the reduction rate in the cold rolling for the sixth time to 65-75%. 6) Reduce the reduction ratio in the first cold rolling to 65-75%, and
Reduce the reduction ratio in the cold rolling for the third time to 35 to 50%. 7) 0.9 ~ for thin metal strip in the second cold rolling
It gives the average roughness R _a of 1.7 microns. Another subject of the invention is the thin metal strip obtained by the above method, which has excellent deep drawing properties.

[0016]

The subject of the invention is a thin metal strip with improved deep drawing properties, i.e. a low yield stress, a Rankford coefficient of 2 or more, preferably 2.4 or more in all directions of the sheet metal, and a strain hardening degree. (Strain hardening), high ductility, Young's modulus is above 23.000kg / mm ² .

In order to obtain such thin metal strips, first a steel having the following chemical composition (1000% by weight) is smelted in a converter or the like in a known manner: carbon <20 silicon <500 manganese. <1000 Phosphorus <100 Sulfur <50 Aluminum <100 Nitrogen <10 The following elements are zero or less than the following chemical composition: Titanium <150 Niobium <150 Boron <5 The balance is iron and impurities due to manufacturing

The steel preferably has the following chemical composition (1000% by weight): 2 <carbon <20 100 <silicon <500 0 <manganese <1000 50 <phosphorus <1000 <sulfur <500 <aluminum < 100 2 <Nitrogen <8 The following elements are zero or within the following range: 0 <Titanium <150 10 <Niobium <500 0 <Boron <2 The balance is iron and impurities due to manufacturing

It will be understood that if the steel has a maximum carbon content of 20, it can be smelted by argon blasting and is less expensive than vacuum refining. The smelted steel is then cast into a slab and hot rolled.
After that, the hot-rolled strip is cold-rolled at a reduction rate of 20% or more, and then the cold-rolled strip is subjected to a steel recovery temperature of ~ 92.
Anneal at 0 ° C., preferably between the recovery temperature of the steel and the recrystallization temperature of the steel. The anneal may be either a basic anneal or a continuous anneal. Further, a second cold rolling was performed at a reduction rate of 20% or more to give the metal strip a predetermined roughness. Finally, a second annealing is performed above the recrystallization temperature of the steel.

The Applicant has found that when the first annealing is performed at 40 to 60 ° C. which is higher than the recovery temperature of steel to the recrystallization temperature of steel, preferably the recovery temperature of steel, the Rankford coefficient value of the metal sheet [ It has been found that Chemical formula 2] can be increased to 2 or more, preferably 2.4 or more. Young's modulus 23.000
In order to achieve kg / mm ² or higher and Rankford coefficient of 2 or higher, preferably 2.4 or higher, the reduction ratio in the second cold rolling is increased and the reduction ratio in the first cold rolling is lowered. Or conversely, it is necessary to reduce the reduction ratio in the first cold rolling and increase the reduction ratio in the second cold rolling.

Two special examples were tested. In the first test, the reduction ratio in the first cold rolling was reduced (however,
20% or more), preferably about 35 to 50%, and a large reduction ratio in the second cold rolling, preferably about 65 to 75%. In the second test, the reduction ratio in the first cold rolling was increased, preferably about 65 to 75%, and the reduction ratio in the second cold rolling was 20% or more, preferably about 35 to Lowered to 50%. In order to obtain a desired deep-drawing property, it is also preferable to impart a desired roughness to the thin metal sheet with a rolling roll in the second cold rolling. It gave average roughness R _a of 0.9 to 1.7 microns as an example. For good deep drawing, the average roughness R _a is preferably set to 1.2 to 1.7 microns. However, in order to improve the brilliance of the thin metal plate while maintaining excellent deep drawing characteristics, it is desirable to set the average roughness _Ra to 0.9 to 1.4 microns.

This operation can ensure a high Rankford coefficient of 2 or more, preferably 2.4 or more, and a low yield stress by eliminating the tempering operation. That is, the refining operation has the effect of increasing the yield stress of the metal and lowering the work hardening coefficient [Chemical formula 3]. Furthermore, by not performing this tempering operation, the manufacturing process of the metal strip can be reduced by one step, and thus the cost can be reduced.

[0023]

Embedded image

[0024]

EXAMPLES Several tests were carried out with several types of steel. Steel with the following chemical composition (1000 times weight%) was used (the balance is iron):

Steels A and B are the steels of the present invention, and steel C is a steel of known composition. Steel A had a recovery temperature of 450 ° C and a recrystallization temperature of 1st annealing as basic annealing.
It was 680 ° C. Steel B has a recovery temperature of 450 ° C and a recrystallization temperature of 6 when the first annealing is performed by continuous annealing.
It was 30 ° C. The above three kinds of steels were subjected to different rolling treatments and annealing treatments to obtain thin metal strips having a thickness of 1 mm or less. A series of test pieces were taken from each thin metal plate and various tests were performed to determine the characteristic parameters of each steel. The various processes and characteristics are summarized in [Table 1].

[0026]

[Table 1]

As can be seen from this table, the steel of the present invention has significantly improved ductility and deep drawing characteristics as compared with the known steel C, and can control the roughness in the second cold rolling. The advantage is that the yield stress R _e is considerably lower than if the roughness is not controlled.

Claims (9)

[Claims] 1. A content rate expressed as 1,000 times the weight% 2
Contains 0 or less carbon, 500 or less silicon, 1,000 or less manganese, 100 or less phosphorus, 50 or less sulfur, 100 or less aluminum, and 10 or less nitrogen, and titanium, niobium and boron are Not included or 150 for titanium
In the following, niobium is included in a ratio of 150 or less and boron is included in a ratio of 5 or less,
The balance is smelting iron and steel that is an impurity caused by manufacturing, 2) hot rolling, 3) cold rolling at a reduction rate of 20% or more, and 4) annealing at a steel recovery temperature of ~ 920 ° C. 5) The second cold rolling at a reduction rate of 20% or more to give a certain roughness to the metal strip, and 6) the second annealing, which is performed at the second reannealing temperature of steel or more, during deep drawing. A method for producing a thin metal strip, which is excellent in elongation deformability and thinning deformability and has an improved deep drawing property that is excellent in elongation at break. 2. The steel smelted in the first stage contains 10% by weight.
2 to 20 carbon, 100 to 500 silicon, 0 to 1000 manganese, 50 to 100 phosphorus, 0 to 50 sulfur, 9 to 100 aluminum, 2 to 8 nitrogen, in a content of 00 times. 0 to 150
2. The method according to claim 1, comprising one or more elements selected from among titanium, 10 to 50 niobium, and 0 to 2 boron, with the balance being iron and manufacturing-related impurities. 3. The method according to claim 1, wherein the first annealing is performed at a steel recovery temperature to a steel recrystallization temperature. 4. The reduction ratio of the first cold rolling is increased,
The method according to claim 1 or 2, wherein the reduction ratio in the second cold rolling is lowered. 5. The method according to claim 1, wherein the reduction ratio in the first cold rolling is lowered and the reduction ratio in the second cold rolling is increased. 6. The reduction ratio in the first cold rolling is 35 to 50.
%, And the reduction rate in the second cold rolling is set to 65 to 75%. 7. The reduction ratio in the first cold rolling is 65 to 75.
%, And the reduction rate in the second cold rolling is set to 35 to 50%. The method of claim 1, 8. The sheet metal strips in the second cold rolling provides a mean roughness R _a of 0.9 to 1.7 microns. 9. A thin metal strip obtained by the method according to any one of claims 1 to 8, which is excellent in expansion deformability and thinning deformability in deep drawing and has improved deep drawing characteristics.