JP2661711B2 - Cold rolled steel sheet excellent in mold resistance and galling resistance and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cold-rolled steel sheet having excellent anti-galling properties as a cold-rolled steel sheet for automobiles, and a method for producing the same.

<Conventional Technology> In recent years, the proportion of ultra-low carbon steel CAL materials in the production of cold-rolled steel sheets has been increasing. When these ultra-low carbon steel CAL materials are used as steel sheets for automobiles, various properties such as press workability and phosphatability required in the automobile manufacturing process are based on conventional box-annealed materials (hereinafter referred to as BA materials). ) Is expected to be at or above the level.

However, when the press formability of these ultra-low carbon steel CAL materials was examined, it was found that the CAL materials were inferior to the BA materials depending on the pressing conditions, although the materials such as tensile properties were excellent.

In particular, it has been raised as a problem that the occurrence of mold seizure is greater than that of the BA material. The inventors examined the cause of this in a laboratory experiment and found that during press working, the sliding resistance between the CAL material and the mold was larger than the sliding resistance between the BA material and the mold. Was found to be due to

When the sliding resistance increases in this way, severe die galling occurs at severe sliding points such as the beat portion of the press die, and as a result, the steel sheet becomes difficult to flow, and the steel sheet is broken due to the insufficient flow. May be more likely to occur.

<Problems to be Solved by the Invention> To improve the press workability by improving the slidability of the steel sheet surface, for example, as disclosed in JP-B-61-26600, a predetermined There is an invention in which a molecular film is formed on the surface of a steel sheet.

However, steel sheets for automobiles are subjected to phosphating as a pretreatment after coating after pressing.However, the phosphatability of cold-rolled steel sheets that have been conventionally lubricated is significantly inferior to that of untreated cold-rolled steel sheets. Had been raised.

Further, in the case of the formation of the organic film, there is a possibility that the organic film is deteriorated by aging and becomes a harmful substance.

It is also conceivable to improve the press workability by plating the steel plate in a sense that direct contact between the steel plate and the mold is avoided.
However, in the case of plating, there is a problem that uneven plating is likely to occur unless the steel sheet surface is strictly controlled, and
There is a disadvantage that the cost is high because the electrolysis must be performed literally.

An object of the present invention is to provide a cold-rolled steel sheet having excellent mold resistance and significantly improved press workability, and a method for producing the same, without impairing the phosphatability of the extremely low carbon steel CAL material. I have.

<Means for Solving the Problems> To achieve the above object, according to the present invention, C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1wt%, N ≦ 0.0050wt%, Ti: 0.01 ～ 0.07wt%, the balance being Fe and unavoidable impurities, on both sides of the steel plate, alkali metal of P and / or B oxide Provided is a cold-rolled steel sheet having excellent anti-galling properties, characterized in that a salt film is formed in an amount of 1 to 1000 mg / m ² (per side).

Further, according to the present invention, C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01 to 0.07 wt%, Nb: 0.001 to 0.010 wt%, the balance consisting of Fe and unavoidable impurities, both sides of which are coated with alkali metal salt films of P and / or B oxides (per side) Provided is a cold-rolled steel sheet having excellent mold resistance, characterized by being formed at 1 to 1000 mg / m ² .

Further, according to the present invention, C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01-0.07wt%, B: 0.0001-0.0030wt%, with the balance consisting of Fe and unavoidable impurities, on both surfaces of which alkali metal salt coatings of P and / or B oxides (per side) Provided is a cold-rolled steel sheet having excellent mold resistance, characterized by being formed at 1 to 1000 mg / m ² .

Further, according to the present invention, C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01 to 0.07 wt%, Nb: 0.001 to 0.010 wt%, B: 0.0001 to 0.0030 wt%, the balance being Fe and unavoidable impurities on both sides of the steel plate, the alkali of P and / or B oxide Provided is a cold-rolled steel sheet having excellent anti-galling properties, characterized in that a metal salt film is formed in an amount of 1 to 1000 mg / m ² (per side).

Further, according to the present invention, in producing each of the steel sheets, an alkali metal salt of an oxide of P and / or B is added to the steel sheet.
The present invention provides a method for producing a cold-rolled steel sheet having excellent galling resistance, comprising coating an aqueous solution containing at least g / g and having a pH of 6.0 or less and then drying.

 Hereinafter, the present invention will be described in more detail.

The present invention has been made based on the following findings.

Generally, ultra-low carbon steel is softer than low carbon steel, and continuous annealed material has a shorter heating time at high temperature than box-annealed material. is there. Therefore, the continuous annealed material of ultra-low carbon steel is clean with little component concentration on the steel sheet surface, and is soft in material.

It is thought that the reason why the low-carbon steel continuous annealed material has lower mold resistance than the low-carbon steel box annealed material is due to the clean steel sheet surface and soft material as described above. Can be In other words, in the case of low-carbon steel box-annealed material, there is a concentrated layer between the press die and the base iron due to selective oxidation during annealing,
Since the base iron and the press die do not have direct metal contact, they have excellent seizure resistance during sliding and consequently have good mold galling resistance. Then
Since the base iron and the press die are in direct metal contact, seizure is likely to occur and the die resistance is poor. Further, when pressed at the same pressure, soft ultra-low carbon steel has a large contact area with a mold and is likely to cause seizure.

Therefore, in order to make use of the excellent material of the ultra-low carbon continuous annealing material and to improve the formability, it is necessary to improve the seizure resistance of the steel sheet, that is, the mold galling resistance, by coating the surface with some kind of coating. is there.

However, the coating can be completely or not completely treated by pretreatment (washing, degreasing, surface conditioning, etc.) of the phosphate treatment after pressing. It must be dissolved and removed to the extent that it does not inhibit production.

If this is insufficient, the adhesion of the phosphate film will be reduced, and the corrosion resistance after painting will be degraded.

The present inventors, by applying to the continuous annealing material of the ultra-low carbon steel, significantly improve the mold galling resistance of the continuous annealing material of the ultra-low carbon steel, and completely dissolve in the pretreatment of the phosphate treatment Or
Or, if not completely, dissolve to the extent that it does not interfere with normal zinc phosphate crystal formation during phosphating,
After extensive experimentation to find a substance that maintains the same good phosphatability as low carbon steel box annealing, the alkali metal salts of oxides of phosphorus and / or boron are extremely effective Was found.

First, the limited range of each component in the present invention will be described.

C, N; When these interstitial solid solution elements are contained in excess, ductility,
Deterioration of drawability is caused. If the content of C exceeds 0.0040 wt% and the content of N exceeds 0.0050 wt%, ductility and drawability deteriorate. Therefore, C is 0.0040 wt% or less, and N is
0.0050 wt% or less.

Si, Mn, P; These substitutional solid-solution elements have less adverse effects on ductility and drawability than C and N, and can be contained according to the intended strength level. In the case of the present invention,
The upper limit of the material is 0.04 wt% for Si, 0.35 wt% for Mn, and 0.1 wt% for P.

S: From the viewpoint of descaling and chemical conversion treatment, the larger the S content is, the better. However, if the S content exceeds 0.02 wt%, the corrosiveness of the steel sheet deteriorates. Further, since the addition of a large amount of S causes deterioration of the material, the upper limit of the amount of S is set to 0.02 wt%.

Al; effective for deoxidation in steel, but if it exceeds 0.1 wt%, the inclusion deteriorates the surface properties and chemical conversion properties.
The upper limit is 0.1 wt%.

Ti; not only effectively contributes to fixation of solid solution components such as C, N, S, etc., but also has a great effect in improving the material by forming precipitates with C, N, S, etc.

In particular, when each of C, N, and S is the upper limit of the limited range, the addition amount desirably satisfies the following expression (1) in order to completely fix it. From this formula, Ti
Is set to 0.07 wt%. However, if the content is 0.01
If it is less than wt%, the effect of the addition is poor. Therefore,
The amount of Ti added is set to 0.01 to 0.07 wt%.

Next, the additive element N according to claims 2 to 4 of the present invention.
The reasons for limiting b and B will be described.

Nb; Nb has an effect of improving in-plane anisotropy after securing a high El and a high r value by adding composite with Ti. However,
If the content is less than 0.001 wt%, the effect of the addition is poor. On the other hand, if the addition exceeds 0.010 wt%, the effect of improving anisotropy is saturated, and conversely, El is reduced. Therefore, the amount of Nb is
0.001 to 0.010 wt%.

B; It is useful for improving secondary processing embrittlement resistance by adding a small amount. However, since the addition of a large amount causes deterioration of the material, the B content is set to 0.0001 to 0.0030 wt%.

In the present invention, the adhesion amount of the alkali metal salt of the oxide of P and / or B applied to the continuously annealed ultra-low carbon steel sheet is set to 1 to 1000 mg / m ² because the adhesion amount shown in FIG. and as is clear from the relationship of the sliding resistance and pulling up load, the film is because it is less than 1 mg / m ² is insufficient slidability improvement of cold-rolled steel sheet, also coating thickness is 1000 mg / m ² If the thickness is larger, the film cannot be removed in the pretreatment (washing, degreasing, surface adjustment, etc.) of the phosphate treatment after pressing, and the phosphate treatment property may be deteriorated. Also,
Increasing the coating amount is not desirable from the viewpoint of cost.

In addition, FIG. 1 shows that the ultra-low carbon steel sheet was immersed in an aqueous solution of alkali phosphate having a different concentration, the amount of adhesion to the steel sheet was changed, and the maximum pulling force was measured by the sliding property inspection method described below for each, The relationship with the adhesion amount was determined.

Next, a method for producing a cold-rolled steel sheet having excellent galling resistance according to the present invention will be described.

The concentration of the alkali metal salts of the oxides of P and / or B used in the present invention is required to be 10 g / or more in order to secure the lower limit of the amount of adhesion on the steel sheet. is there.

As the alkali metal salt of the oxide, NaH ₂ PO ₄ , K ₂ HP
O ₄ , Na ₃ PO ₄ , Na ₂ HPO ₄ , Na ₂ B ₄ O ₇ , K ₂ B ₄ O _7, etc. are possible, and it is desirable that they further contain a Ti colloid. If the pH of the solution is higher than 6.0, hydroxides and the like of these salts are formed and precipitated, which is not preferable. Therefore, the pH of the aqueous solution to be applied is desirably 6.0 or less.

Examples of the method of coating the aqueous solution on the ultra-low carbon steel sheet include a method of immersing the steel sheet in a bath, a method of applying with a roll coater, and a method of applying the aqueous solution by spraying. There is no limitation on the drying method.

<Example> Hereinafter, the present invention will be specifically described based on examples.

A steel slab having the chemical composition shown in Table 1 was produced by a converter-continuous casting method, then heated to 1250 ° C., soaked, then rough-rolled and finish-rolled to obtain a 3.2 mm-thick hot-rolled steel sheet. Then, after pickling, the resultant was cold-rolled into a cold-rolled steel sheet having a thickness of 0.7 mm, subjected to continuous annealing (soaking temperature: 750 to 850 ° C.), and then subjected to skin-pass rolling (rolling rate: 0.7%).

Table 2 shows the results of cutting out JIS No. 5 test pieces for tensile tests from the obtained cold rolled sheets and examining mechanical properties.

As is clear from Table 2, each of the cold-rolled steel sheets obtained according to the present invention exhibited excellent materials as compared with the comparative steel.

Next, Examples and Comparative Examples in which these invention steels are coated with an alkali metal salt will be described.

The evaluation of the examples and the comparative examples was performed by the following methods for examining slidability and phosphating properties, respectively.

(1) Method of investigating slidability The slidability was evaluated using the slidability measuring device shown in Fig. 2a.
The maximum pull-out load when pulling out the test piece 5 held by the chuck 4 was measured by the tensile tester 1. Cylinder 3
The pressing load of punch 2 was 100 kg. Test piece 5
For the two types, those having no oil coating and those having rust-preventive oil applied, those having a size of 20 mm × 300 mm × 0.7 mm were prepared.

The speed at which the test piece 5 was pulled out was 500 mm / min, and the sliding distance was 50 mm.

In addition, the test piece 5 is sandwiched between the punches 2 having the shape shown in FIG. 2b, D of 15 mm and h of 1 mm, and a vertical load N is applied to the test piece 5 with the punch 2 and the maximum load (kg) when the test piece 5 is pulled upward. Was measured.

(2) Phosphate Treatment Investigation Method A steel sheet coated with an alkali metal salt of an oxide of P and / or B was subjected to phosphatization as described below after degreasing, washing and surface conditioning.

Treatment solution: Palbond L3020 treatment solution manufactured by Nippon Parkerizing Co., Ltd. Treatment method: FULL DIP method Treatment condition: Immersion at 42 ° C for 120 seconds Evaluation method: P ratio, phosphate film weight (g / m ² ) and water resistance 2
Evaluation by Secondary Adhesion Investigation Method Here, the P ratio is Phosphophyllite (Zn ₂ Fe (PO ₄ ) ₂
· 4H ₂ O) of the (100) plane and _{Hopeite (Zn 3 (PO 4)} 2 · 4H 2 O)
X-ray diffraction intensity ratio of the (020) plane, and the higher the value, the better the film.

In addition, the evaluation by the water resistance secondary adhesion inspection method is as follows.

Each process was performed on the obtained test piece of each steel plate in the following order assuming a process of manufacturing an automobile body.

Zinc phosphate treatment (using Nippon Parkerizing's Palbond L3020 treatment solution) Cathodic electrodeposition coating (using Nippon Paint's Powertop U-100 paint, 250 V, film thickness 20 µm) Intermediate coating (Kansai Paint's Amirac chipping sealer) N3 used, film thickness 35-40 μm) Top coat (Neoamirac B002 manufactured by Kansai Paint Co., Ltd.)
(Use, film thickness: 35 to 40 μm) The coated steel sheet obtained by the above procedure was immersed in pure water at 40 ° C. for 10 days, cross-cut off with a cellophane tape, and evaluated by a coating film remaining rate (%).

(Example 1) Steel A of the present invention steel in Table 1 was degreased, immersed in a bath shown below for 10 seconds, and then dried with hot air at 80 ° C. Attached
The amount of Na ₂ HPO ₄ was 2 mg / m ² .

Bath composition: Ha ₂ HPO ₄ 15 g / pH 2.0 (Example 2) After degreasing steel B of the present invention in Table 1, the following aqueous solution was applied by a roll coater, and then dried with hot air at 100 ° C. Was. The amount of K ₂ B ₄ O ₇ attached was 350 mg / m ² .

Aqueous solution composition: K ₂ B ₄ O ₇ 200 g / ph4.6 (Example 3) After degreasing C steel of the present invention steel in Table 1, the following aqueous solution was added to 20
After spray coating for 2 seconds, it was dried with hot air at 65 ° C.
The amount of Na ₂ B ₄ O ₇ attached was 85 mg / m ² .

Aqueous solution composition: Na ₂ O ₄ O ₇ 150 g / ph3.7 (Example 4) E steel of the present invention steel in Table 1 was degreased, immersed in the bath shown below for 5 seconds, and then heated to 120 ° C hot air. And dried. The sum of the attached NaH ₂ PO ₄ and K ₂ HPO ₄ was 970 mg / m ² .

Bath composition: NaH ₂ PO ₄ 120 g / K ₂ HPO ₄ 170 g / ph5.4 (Example 5) After degreasing F steel of the steel of the present invention in Table 1, the following aqueous solution was applied by a roll coater, and then 150 ° C. And dried with hot air. The amount of Na ₃ po ₄ attached was 14 mg / m ² .

Aqueous solution composition: 52 g of Na ₃ PO ₄ / pH 2.4 (Example 6) After degreasing the steel H of the steel of the present invention in Table 1, the aqueous solution shown
After spray coating for seconds, it was dried with hot air at 85 ° C.
The sum of the attached Na ₂ B ₄ O ₇ and K ₂ B ₄ O ₇ was 50 mg / m ² .

Aqueous solution composition: Na ₂ B ₄ O ₇ 10 g / K ₂ B ₄ O ₇ 22 g / pH 3.0 (Example 7) The steel I of the present invention in Table 1 was degreased and immersed in a bath shown below for 15 seconds. After that, it was dried with hot air at 75 ° C. Attached
The sum of Na ₂ HPO ₄ and Na ₃ PO ₄ was 570 mg / m ² .

Bath composition: Na ₂ HPO ₄ 150 g /, Na ₃ PO ₄ 160 g / pH 4.7 (Example 8) After degreasing the steel J of the present invention in Table 1, the following aqueous solution was applied with a roll coater, It dried with the hot air of ° C. The amount of K ₂ B ₄ O ₇ attached was 120 mg / m ² .

Aqueous solution composition: K ₂ B ₄ O ₇ 100 g / pH 4 (Example 9) After degreasing the steel L of the present invention in Table 1, the aqueous solution shown
After spray coating for seconds, it was dried with 120 ° C. hot air. The amount of Na ₂ B ₄ O ₇ attached was 35 mg / m ² .

Aqueous solution composition: Na ₂ B ₄ O ₇ 190 g / pH3.5 (Example 10) M steel of the present invention steel in Table 1 was degreased, immersed in a bath shown below for 20 seconds, and then heated to 100 ° C hot air. And dried. The amount of K ₂ HPO ₄ attached was 600 mg / m ² .

Bath composition: K ₂ HPO ₄ 130 g / pH 3.3 (Example 11) After degreasing the N steel of the present invention steel in Table 1, the following aqueous solution was applied by a roll coater, and then dried with hot air at 100 ° C. Was. The amount of Na ₂ HPO ₄ attached was 20 mg / m ² .

Aqueous solution composition: Na ₂ HPO ₄ 45 g / pH 2.6 (Comparative Example 1) After degreasing the steel B of the present invention in Table 1, the steel was immersed in the bath shown below for 30 seconds, and then dried with hot air at 80 ° C. I let it. K ₂ attached
The sum of HPO ₄ and Na ₂ HPO ₄ was 0.5 mg / m ² .

Bath composition: Ha ₂ HPO ₄ 4 g /, K ₂ HPO ₄ 4 g / pH 4.0 (Comparative Example 2) After degreasing F steel of the present invention steel in Table 1, 15
After spray coating for 2 seconds, it was dried with hot air at 140 ° C. The amount of K ₂ B ₄ O ₇ attached was 1150 mg / m ² .

Aqueous solution composition: K ₂ B ₄ O ₇ 350 g / pH 2.7 (Comparative Example 3) After degreasing the steel I of the present invention in Table 1, the following aqueous solution was applied with a roll coater, and then dried with hot air at 120 ° C. I let it. The amount of Na ₃ PO ₄ attached was 0.8 mg / m ² .

Aqueous solution composition: Na ₃ PO ₄ 10 g / pH 7 (Comparative Example 4)
After spray coating for 2 seconds, it was dried with hot air at 90 ° C.
The sum of the attached K ₂ B ₄ O ₇ and Na ₂ B ₄ O ₇ was 1200 mg / m ² .

Aqueous solution composition: K ₂ B ₄ O ₇ 150 g /, Na ₂ B ₄ O ₇ 150 g / pH 3.2 (Comparative Example 5) After degreasing the N steel of the steel of the present invention in Table 1, 61 wt% of polyurethane was applied to the steel sheet surface. An organic film composed of 12 wt% of polyacrylate, 16 wt% of polyethylene oxide and 11 wt% of glycine was formed.

Table 3 shows the mold galling property, that is, the sliding property and the phosphating property of the products of the above Examples and Comparative Examples.

From this table, it can be seen that in Examples 1 to 11 in which the alkali metal salt was applied according to the present invention, the slidability was significantly improved without impairing the phosphatability.

<Effects of the Invention> Since the present invention is configured as described above,
It is possible to obtain a cold-rolled steel sheet having excellent moldability and significantly improved press workability without impairing phosphatability.

In addition, a cold-rolled steel sheet having excellent mold resistance can be obtained at low cost by coating the steel sheet with an aqueous solution of an alkali metal salt of an oxide of P and / or B by the production method of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the amount of P salt attached and the slidability. 2a and 2b are explanatory views of a slidability measuring device and a punch used for the same. DESCRIPTION OF SYMBOLS 1... Tensile tester 2... Punch 3... Cylinder 4... Chuck 5.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kozo Kadoyama 1 Kawasaki-cho, Chiba-shi, Chiba Pref. 56-96081 (JP, A) JP-A-61-276951 (JP, A) JP-A-59-140333 (JP, A)

Claims (5)

(57) [Claims] 1. C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt% N ≦ 0.0050 wt%, Ti: 0.01 ~ 0.07 wt%, the balance being Fe and unavoidable impurities, on both surfaces of which alkali metal salt coatings of P and / or B oxides are formed (from one side) 1 to 1000 mg / m ^2. A cold-rolled steel sheet with excellent mold resistance. 2. C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01 0.07 wt%, Nb: 0.001 to 0.010 wt%, the balance being Fe and unavoidable impurities on both sides of the steel plate, an alkali metal salt coating of P and / or B oxide is 1 to 1000 mg (per one side) / m ² Cold rolled steel sheet with excellent mold resistance, characterized by being formed. 3. C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01 0.07 wt%, B: 0.0001 to 0.0030 wt%, the balance being Fe and unavoidable impurities, both sides of which are coated with alkali metal salt coatings of P and / or B oxides of 1 to 1000 mg on each side. / m ² Cold rolled steel sheet with excellent mold resistance, characterized by being formed. 4. C ≦ 0.0040 wt%, Si ≦ 0.04 wt%, Mn ≦ 0.35 wt%, P ≦ 0.1 wt%, S ≦ 0.02 wt%, Al ≦ 0.1 wt%, N ≦ 0.0050 wt%, Ti: 0.01 0.07 wt%, B: 0.0001 to 0.0030 wt%, the balance being Fe and unavoidable impurities, on both sides of the steel sheet, an alkali metal salt coating of P and / or B oxide is 1 to 1000 mg (per one side) / m ² Cold rolled steel sheet with excellent mold resistance, characterized by being formed. 5. An aqueous solution containing 10 g / or more of an alkali metal salt of an oxide of P and / or B and having a pH of 6.0 or less when producing the steel sheet according to claim 1. A method for producing a cold-rolled steel sheet having excellent mold resistance, which is characterized by drying after coating.