JPH02179302A - Steel sheet having good image clarity and press formability and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a steel sheet having good rust preventability and antislipping ability by forming finely rugged base surface of a specific average roughness and distributed recessed parts on at least one surface and specifying relations between an average area/recessed part, depth, center-to-center distance of adjacent recessed parts. CONSTITUTION:Random fine ruggedness whose centerline roughness Ra is in the range of 0.2-0.5mum and uniformly distributed recessed parts 2 are formed on a base surface 1 of at least one surface of the steel sheet. Relations shown by the inequalities I, II and III are met when an average area of the parts 2, average depth, and average center-to-center distance of adjacent parts 2 are denoted by S, (h), and P, respectively. Hence, requirements for improving overall characteristic of a steel sheet are met to comply with wide and various use.

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention has excellent moldability and beauty after painting, especially sharpness, and is suitable for use in automobile body exterior panels, home appliance exterior panels, etc. Related to steel plates and methods of manufacturing the same.

(Prior Art) Generally, thin steel sheets manufactured by hot rolling or cold rolling are used for the above-mentioned purposes. In particular, the cold-rolled steel sheets mainly used for these purposes are manufactured through the processes of cold rolling, degreasing, cleaning, annealing, and temper rolling, and are also coated with anti-rust coatings such as hot-dip galvanizing and electrogalvanizing as necessary. Processed. Users of cold-rolled steel sheets, such as automobile manufacturers and home appliance manufacturers, usually press-form cold-rolled steel sheets into a predetermined shape, assemble them into products, and then finish them with paint.

The main properties required of the above-mentioned steel sheets are press formability and beauty after painting. First, regarding press formability, it is desirable that the surface of the plate has a so-called dull finish.A dull surface with fine irregularities on the surface has good lubricant retention properties and prevents seizure with the mold during processing. The dull finish of cold-rolled steel sheets, which has a small amount of roughness, is usually achieved by dulling the surface of a temper rolling roll by means of sheet plastic blasting, electrical discharge machining, etc., and then transferring this to the surface of the steel sheet.

Regarding beauty after painting, recently there has been a demand for sharpness. This means that the image reflected on the surface of the steel board after painting will be clear and clear without distortion or blur. These properties are influenced by the condition of the base material, ie, the surface of the steel sheet, before painting. Generally, the smoother the steel plate surface, the better the image clarity. That is, in order to improve image clarity, it is desirable that the surface of the steel plate has a bright finish.

As can be seen from the above explanation, it is generally difficult to achieve both press formability and image clarity of a steel sheet with a single surface condition.

In recent years, a processing method using a laser beam has been proposed as a method for dulling the surface of a work roll used in temper rolling (Japanese Patent Publication No. 11922/1983).

When a roll is dull-finished by the sirotplast method or the electrical discharge machining method, an irregular roughness profile is formed on the roll surface. Therefore, the surface of a steel plate rolled with such rolls becomes a dull surface with irregular roughness, which is desirable for press forming, but it impairs image clarity.However, laser processing produces uneven patterns on the roll surface. The surface of the steel plate rolled by the rolls also consists of a flat base and regularly distributed concavities, and the surface of the steel plate rolled by the rolls is made up of a flat base and regularly distributed concavities. It is possible to maintain processability and image clarity at the same time. Publications such as JP-A-62-168602 and JP-A-62-230402 disclose that when dull finishing work rolls for skin pass rolling are obtained by laser processing, the pattern of surface irregularities is appropriately adjusted to improve press formability. It is disclosed that a steel plate with excellent image clarity after painting can be manufactured.

However, in the so-called Laser Dal method that has been proposed so far, no consideration has been given to the substrate surface of the steel sheet. The flat base surface of the roll surface is directly transferred and becomes a flat surface, and normally when looking at the center line average roughness (Ra), Ra < 0.2 (μ-). Therefore, laser processing It is necessary to improve press formability only by recessing the surface of the steel sheet by transferring the projections formed on the roll surface.
There was a limit to the improvement of press formability.

Furthermore, from the user side of steel plates, the handling properties of steel plates are good, specifically, the fact that there is no slipping when the steel plates are sucked and transported one by one, or the rust preventive oil is well retained so that no generation occurs until use. It is also required that there is no rust. Regarding the overall improvement of the properties of these steel sheets, sufficient measures have not been taken with conventional laser dull steel sheets.

(Problems to be Solved by the Invention) As mentioned above, recently, especially for automobile body exterior panels,
Both high press formability and high image clarity after painting are required, and in addition, improvements in various properties such as handling and rust prevention are required, and these requirements are becoming more stringent year by year.

This invention further improves the image clarity and press formability after painting steel plates using the conventional Laser Dal method, and also improves handling properties and rust prevention, which have not been considered in the past. To provide superior steel sheets, and furthermore,
It is an object of the present invention to provide a method for manufacturing such a steel plate.

(Means for solving problems) The gist of the first invention of the present application is the following steel plate.

"At least one side has a center line average roughness Ra of 0.2 to 0.
．． It is a surface consisting of a base surface with random minute irregularities in the range of 8 μ- and recesses uniformly distributed on the base surface, and the average area of each recess is S and the average depth is h. , when the average distance between the centers of adjacent recesses is P, 0.001≦S≦0.04 (■-2) 0.001
≦h≦0.02 (mm) J¥/4≦P≦41
"A steel plate with excellent post-painting sharpness and press formability that satisfies (wn)" FIG. ) is the plan view, (b) is (b) A-
This is the A section. As will be explained in detail later, this surface condition is obtained by rolling with a roll that has been subjected to uneven processing, and the unevenness of the roll is reversed and copied. The center line average roughness of substrate 1 (
It is a dull surface with random minute irregularities with Ra) of 0.2 to 0.8.

Concave portions (in this figure, the concave portions are ring-shaped, but there are no particular restrictions on the shape) are uniformly and regularly distributed on this base material. 3 is a plateau-shaped portion surrounded by a ring-shaped recess, the surface of which is not affected by the roll surface and remains the same as the surface of the steel sheet before rolling.

Here, the symbols SSh and P shown in FIG. 1 are defined as follows.

Average area of each recess 2 on the Sag plate surface (mm”
) ... Area of the shaded part in Fig. 1 (a) h; Average depth of the recesses 2 on the surface of the steel plate (+m) P: ll Average center open circuit Ws of adjacent recesses 2 on the surface of the plate (■) In the example shown in FIG. 1, the concave portion is ring-shaped, and there is a plateau-like flat portion 3 in the concave portion. This is because the unevenness created by melting and solidifying with the laser beam during laser processing of the roll often becomes crater-shaped, and the unevenness that is transferred to the surface of the steel sheet also becomes crater-shaped. . In such a case, the above P is the distance between the centers of the craters.

In the steel plate of the present invention, the substrate 1 has Ra: 0.2 to 0.8.
In addition to being a surface with random irregularities of μm, S
The mutual relationship of Sh, , P is 0.001≦S≦0.04 (-12)0.001
≦h≦0.02 (mm)5,,y 4≦p
≦45 (1111).

The reasons for determining these conditions will be explained below.

One of the major features of the steel sheet of the present invention is that the surface base is a surface having a random uneven shape, and the center line average roughness Ra is limited to the following range.

0.2≦Ra≦0.8 (μm) As mentioned earlier, in conventional so-called laser dull steel sheets, the steel plate is bright-finished in advance and then rolled with a laser-processed roll, so the base surface of the gi is on the surface of the roll. The flat base surface is directly transferred to form a flat surface, and the center line average roughness is usually less than 0.2 μ-.

Therefore, what contributes to the press formability of the steel sheet is essentially only the concave portions to which the convex portions of the rolls have been transferred, and there is a limit to the improvement in formability. By providing a predetermined roughness, we succeeded in providing excellent press formability while maintaining image clarity after painting. As will be described in detail in later Examples, this Ra needs to be 0.2 μm or more in order to obtain good press formability. In addition, in order to improve the image clarity after painting,
Ra must not exceed 0.8 μm.

By arranging concave portions (craters) shaped like a dolphin in the above-mentioned base surface in a dovetail-like manner, it is possible to improve the desired sharpness and press formability as well as rust prevention and, for example, blanking. A steel plate with excellent slip resistance on the line can be obtained. The shape and distribution of the crater at this time should be S≦0.04 (mm) h≦0.02 (ms) P≧ fg/4 <-1) in order to obtain good image clarity. is necessary. In addition, in order to obtain the best press formability, rust prevention, and slip resistance on the blanking line, S≧0.001 (mm”) h≧0.001 (s+a+) P≦4J'T ( mm).

The reason why the above conditions are necessary will be explained below.

If the value of S is less than 0.001 m5'', there will be too few oil pools or metal powder trap sites during press working, resulting in poor press formability.

In addition, rust prevention and slip resistance are also reduced. On the other hand, S is 0.0
If it exceeds 4 mm, image clarity will deteriorate.

When the value of h is less than 0.001 mm, all of press formability, rust prevention, and slip resistance deteriorate.

On the other hand, when h exceeds 0.02 m5+, image clarity deteriorates.

The value of P is affected by the value of S. If the value of P exceeds 43, any one of press formability, rust prevention, and slip resistance will deteriorate. Furthermore, if P is less than E74, image clarity will deteriorate.

The above-mentioned surface condition does not necessarily have to be the same on both sides of the steel plate. In many cases, only the surface that is exposed when assembled into a product is required to have good image clarity, and press workability It may be sufficient if the roughness of the surface facing the die is appropriate. Therefore, one side of the steel plate is the conventional dull side,
Alternatively, a bright surface may be provided, and only one surface may have the surface condition specified in the present invention.

In addition, currently, the exterior material of automobiles is mainly cold-rolled steel sheets.
Depending on the application, hot-rolled steel sheets may be used as exterior plates, and in that case, the required properties are the same. Therefore, the present invention can also be applied to hot rolled steel sheets.

Although cold-rolled steel sheets and hot-rolled steel sheets are often plated, the present invention can also be applied to steel sheets with a plating film.In the case of normal zinc plating, the thickness of the plating film is 2.5 It is as thin as ~9.0μ, and has the above-mentioned Ra, s, and h of the base surface.

P has no essential effect.0 The "steel plate" of the present invention includes cold rolled steel plates, hot rolled steel plates, and plated tI4 plates thereof.

Next, a second invention, which is a method of manufacturing a steel plate according to the invention, will be explained.

The gist of the second invention of the present application is the following method.

r A method for producing a steel plate according to claim 1 by performing temper rolling using a work roll that has been subjected to uneven processing by a high energy density beam, the surface of the work roll having a centerline average roughness. Ra' is 0.3 to 2.0
It consists of a base surface with random irregularities of μ- and micro-craters uniformly distributed on the base surface, and the micro-craters are ring-shaped or crescent-shaped bulges on the front side of the recess and the outer edge of the recess. The average center-to-center distance P' between adjacent recessed parts, the average area S' per raised part, and the average height h
o is 0.001≦S°≦0.03 (mm″) o, oo
t≦h'≦0.06 (mm)5
/4≦P'≦45 (-■), and use the work roll on one or both sides of the steel plate to be temper-rolled, and temper-roll the elongation rate at 0.3% or more. As described above, the method of the present invention involves skin-pass rolling a steel plate using rolls that have been subjected to uneven processing under special conditions. There are characteristics. That is, the centerline average roughness R is formed on the surface of the work roll for skin pass rolling by the siggit blasting method or the electric discharge dulling method.
Random irregularities with a in the range of 0.3 to 2.0 .mu.- are formed, and then minute or lattice-shaped recesses are uniformly formed.

Figure 2 is an enlarged schematic diagram of the surface layer of this roll.
(a) is a plan view, and (b) is a BB sectional view of (a).

Although this figure shows a circular crater that is most commonly obtained during laser processing, the crater shape is not limited to this, and may be semicircular or crescent shaped, for example.

In Fig. 2, 1° of the base surface of the roll is a randomly minute uneven surface with a center line average roughness (Ra') of 0.3 to 2.0 μm. The processing of this base surface is by shot blasting. It can be carried out by a method known per se, such as a method or an electric discharge machining method.Here, the center line average roughness Ra of the base surface
' is set in the range of 0.3 to 2.0 μ- because when this surface is transferred to the surface of the steel plate during temper rolling, it acts as the base surface of the steel plate and the above Ra 0.3 to 0.8 This is to ensure that the ! The reduction ratio of 11 quality rolling is usually 0.8~
However, in this case, the unevenness of the rolling roll is not completely transferred to the plate surface, but the transfer rate (Ra
/Ra') is approximately 40-60%. Therefore, by setting the Ra' of the roll base surface to 0.3 to 2.0 μm, the Ra of the steel sheet base surface can be set in the range of 0.2 to 0.8 μm.

Uniformly distributed irregularities (craters) are formed on the base surface obtained in the above manner by processing using a high energy density beam such as a laser beam or an electron beam. This process involves rotating the roll and feeding it in the axial direction while intermittently irradiating the roll surface with beam pulses.The energy of the beam locally melts the roll surface, creating regular microcraters. It forms. In FIG. 2, 3° is a depression defined by melting, and 2' is a convex portion formed by the raised metal in the depression. Here, the concavity and the protrusion on its periphery are collectively referred to as a single crater. This kind of crater is formed because the metal that is instantaneously melted by the beam irradiation is applied to the periphery by the energy of the beam. This is because it is removed and solidified by cooling.

Therefore, the shape of the crater can be changed depending on the energy intensity of the beam, the irradiation angle, the way assist gas is applied, etc. Furthermore, the interval between craters (P') can be arbitrarily adjusted by changing the pitch at which the beams are interrupted.

As can be seen from Figure 2, between the craters formed by the high energy density beam, there is a rough surface created by the random unevenness machining using the shot blasting method or electrical discharge machining method. (the bare surface) remains as it is. Here, the distance between adjacent craters (P゛) can be determined, for example, by controlling the frequency of the beam pulse in relation to the roll rotation speed in the roll rotation direction, and by controlling the beam pulse frequency in relation to the roll rotation speed. The roll is 1
Adjustment is made by controlling the pitch at which the laser irradiation position is moved in the roll axis direction each time the roll rotates. Here, S': Average area of each raised crater on the roll surface (mm") h': Average height of 2° protrusions on the roll surface (-) P': Adjacent area on the roll surface The average central open circuit of the crater l1lI (
- Zeng), then 0.001≦S1≦0.03 (-Kari 0.001
≦h°≦0.06 (ms) / 4 ≦P”≦
45 <-1) The surface of the roll is made uneven. These conditions are based on the Rao of the base surface mentioned above.
This is to make the steel plate surface have the above-mentioned s, h, and the desired relationship between S and P when temper rolling is performed using these rolls, as in the above conditions.

A W4 plate is temper-rolled using a work roll whose base surface has been processed and textured as described above.
For example, by subjecting an annealed cold-rolled steel plate to rolling at a light reduction rate, the unevenness of the roll is transferred to the surface of the steel plate, thereby forming a desired pattern of unevenness on the surface of the steel plate.

The above-mentioned FIG. 1 shows the surface layer of the steel sheet when it is rolled with the rolls shown in FIG. 2.

FIG. 3 is a cross-sectional view schematically showing the state of contact between the roll and the steel plate during rolling. Although the unevenness of the roll (upper side) bites into the surface of the steel plate (lower side), the unevenness is not necessarily completely transferred to the steel plate, and the transfer rate is approximately 40 to 60% as described above. Moreover, since the center part of the 3° recess of the roll does not touch the steel plate surface, the plateau-like flat part 3, which is slightly raised due to the metal removed from the recessed part 2 on the steel plate side, remains the same surface as the original steel plate surface. The part to which the base surface 1 of the roll made of the apparatus is pressed becomes the base surface 1 on the steel plate surface, and a base surface having a smaller Ra than the base surface of the roll is formed. Therefore, the surface of the steel plate after temper rolling has plateau-like peaks 3 on the base material, as shown in Fig. 1.
Craters consisting of a ring-shaped recess 2 formed to surround all or part of the periphery of the crater are distributed in a manner similar to the above.

Here, the relationship h'>h usually holds between the depth h of the recess in the steel plate and the height h' of the convex part of the roll. The reason for this is that as a result of the superimposition of elastic deformation in addition to plastic deformation on the steel plate side, dents are formed in the steel plate as shown in FIG. That is, the shape of the steel sheet after rolling returns to its pre-rolling state by the contribution of elastic deformation, so the depth of the recess becomes shallower than the height of the roll convex portion. In addition, when rolled with rolls, the metal removed from the recesses on the steel plate side enters the recesses of the rolls and rises slightly above the flat part of the steel plate, forming a plateau-like flat part 3, but in this case ,
The area of the plateau-like flat part decreases depending on the degree of bulge, and conversely, the area S of the concave part of the steel plate increases.For reasons greater than 0, the area S° of the convex part in the roll is usually smaller.
The area S of ti becomes large.

When performing temper rolling using the above rolls, the temper rolling elongation rate λ must be 0.3% or more,
In other words, the temper rolling elongation rate λ has a large influence on the transfer rate of the roughness profile of the steel sheet surface to the roughness profile of the roll surface (for the base surface, Ra/Ra'), but if λ is too large, If it is smaller than 111, the rolling operation itself becomes unstable and it becomes difficult to apply dullness to the surface of the steel sheet.6According to the experiments conducted by the present inventors, the iJl quality rolling is 0.3%.
If this is the case, the uneven profile of the roll will be efficiently transferred to the surface of the steel plate, and a desirable surface condition will be obtained.

In addition, when producing a steel plate with only one side having the surface condition defined by the present invention, only the work roll on that side may be a roll manufactured under the above conditions.

After temper rolling, if necessary, zinc or other plating is applied by a conventional method.

(Example) After annealing a cold-rolled steel sheet equivalent to JIS 5PCC, it was subjected to temper rolling with an elongation rate λ = 0.8% using a temper rolling roll that had been subjected to uneven processing under various conditions, and one surface was Steel plates with various roughness profiles were produced. Regarding these steel plates, the image clarity after painting, press formability, rust prevention,
and slip properties were evaluated.

■Test and evaluation method: i. Press workability: 50X by mold galling tester
Commercially available anti-corrosion oil was applied to the die side of a 200 mm test piece and pressed, evaluated by the ratio (%) of area without mold galling, 80
% or more was considered to have good press workability.

ii. Rust prevention: The edges and back of a To
It was left in an environment of 95% relative humidity at °C (humidity test) and evaluated by the rust area ratio (%) after 200 hours.

A content of less than 1% was considered to have good rust prevention properties.

i. Slip property: Apply commercially available rust preventive oil to a 300 x 300+ am test piece, suction it with a 70@mφ suction vat at a set vacuum of 140+ mHg, pull the test piece laterally, and measure the force when it starts to slide. (kg), and if it is 4 kg or more, it is judged to be good because it will prevent steel plate users from slipping accidents on the blanking line.

iv. Sharpness: For a 70 x 150mm test piece,
Cationic electrodeposition primer soil coating + top coating for automobile exterior panels 3
Apply a coat (80μ thick) and PGD (Por
table [11g1ta! -Gloss mete
Measured using a portable gloss meter), a PGDo of 7 or higher is considered good image clarity.

Table 1 summarizes the values of Ra of the base surface of the steel plate surface, S, h, and P of the recesses, and the evaluation results of the above 1xiv.

As can be seen by comparing the evaluation results of the present invention examples and comparative examples in Table 1, when the Ra of the base surface is less than 0.2μ- and when the S is less than 0.00111M, the press formability and
Ratings are low in both rust prevention and slip resistance, while
If the Ra of the base surface exceeds the 0.8 μ threshold, and S is 0
．． If it exceeds 04e+n, both are N1! iL properties deteriorate. From this result, the Ra of the base surface is 0.2 to 0.8
It can be said that μrin and S must be in the range of 0.001 to 0.04a+kasu.

The same can be said about the average depth h of the 11 plate recesses.

That is, in examples where h is less than 0.001 mm, press formability,
Rust prevention and slip resistance were all poor; on the other hand, 0.02m
If it exceeds 5+, image clarity will deteriorate.

The average center-to-center path MP of the recess depends on S. In cases where P exceeds 45, press formability, rust prevention, and slip resistance are poor (
, less than 58, the image sharpness is poor.

(Hereinafter, blank spaces) (Effects of the invention) The steel sheet of the present invention not only surpasses conventional steel sheets in press formability and image clarity (but also has excellent rust prevention and slip resistance. This steel plate can be produced relatively easily by the manufacturing method of the present invention.The steel plate of the present invention can be used in a wide variety of applications in response to the increasingly strict requirements for improving the overall properties of steel plates. be.

[Brief explanation of the drawing]

FIG. 1 is a schematic view showing an example of the surface shape of the steel plate of the present invention, in which (a) is a plan view and (b) is a cross-sectional view taken along line AA in (a). FIG. 2 is a schematic diagram showing an example of the surface condition of a roll used in the steel sheet manufacturing method of the present invention, (a) is a plan view, (b)
is a BB sectional view of (A). FIG. 3 is a schematic cross-sectional view showing the state of contact between the roll surface and the steel sheet surface when the steel sheet shown in FIG. 1 is produced by rolling using the rolls shown in FIG. 2. FIG.

Claims (1)

[Claims] (1) At least one side has a center line average roughness Ra of 0.2.
It is a surface consisting of a base surface having random minute irregularities in the range of ~0.8 μm and recesses uniformly distributed on the base surface, where the average area of each recess is S, and the average depth is When h is the average center-to-center distance between adjacent recesses, P is 0.001≦S≦0.04 (mm^2) 0.001≦h≦0.02 (mm) √S/4≦P≦ A steel plate with excellent image clarity and press formability after painting, which satisfies 4√S (mm). (2) A method for manufacturing a steel plate according to claim 1 by performing skin pass rolling using a work roll that has been subjected to uneven processing by a high energy density beam, wherein the surface of the work roll is aligned with the center line. Average roughness Ra is 0.3 to 2.0
It consists of a base surface with random unevenness of μm and micro craters uniformly distributed on the base surface.The micro craters are a ring-shaped or crescent-shaped raised part on the front side of the concave part and the outer edge of the concave part. and the average center-to-center distance P' between adjacent recesses, the average area S' per raised part, and the average height h'
The following conditions are satisfied: 0.001≦S'≦0.03 (mm^2) 0.001≦h'≦0.06 (mm) √S/4≦P'≦4√S (mm) and the work roll is used on one or both sides of a steel plate to be temper-rolled, and the temper-rolling is carried out at a temper-rolling elongation of 0.3% or more. Method of manufacturing steel plates.