JP2002327240A - Dark-violet hot-rolled steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a mill scale to be a uniform color tone throughout its length, of which the composition and thickness vary according to temperature and oxidizing atmosphere in the forming stage of a steel sheet. SOLUTION: The uniform dark-violet hot-rolled steel sheet is characterized by having a scale thickness of 10 μm or less, after being hot rolled in a hot rolling process, then cooled, and wound up, and having a color tone of 15<=L*<=40, -2<=a*<=2, and -5<=b*<=-3 in color specification by L*a*b*, for the scale on the surface. The steel material includes, by mass%, 0.01-0.2 C, 0.3 or less Si, 0.05-2 Mn, 0.1 or less P, 0.02 or less S, 0.1 or less Al, 0.01 or less N, and the balance Fe. The manufacturing method comprises winding up the steel material after roughing rolling it, then finish rolling it continuously by sequentially joining the end of the strip with the top of the following strip, after rewinding the coil, then water cooling it to 300-650 deg.C at 30 deg.C/s or more rapidly, and winding it up after 2-15 seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate having a dark purple surface tone required for a building material, a steel material for furniture, etc., which is used as a hot-rolled black scale material.

[0002]

2. Description of the Related Art The final product of a hot-rolled steel sheet includes a black scale material having a scale on the surface used as it is wound after hot rolling, and a surface scale removed by rewinding and pickling. Pickling materials with metallic luster. While can be shipped as it is, the scale is dissolved or exfoliated while passing through a heated hydrochloric acid or sulfuric acid bath after unwinding. Such pickling materials increase the number of steps, so that the price of steel materials also increases. Therefore, inexpensive black scale materials are often used for applications that can be used as a scale.

[0003] Although the scale material has scale remaining on the surface, the composition and thickness of the scale slightly change depending on the temperature and the oxidizing atmosphere in the process of forming the steel sheet. I have. In conventional steel,
It is difficult to make this a uniform color tone over the entire length. Regarding the color tone of the steel material, the user prefers black color because of the image expressing the strength of iron and the fact that it is hardly rusted, and gray and red steel materials often remain unsold at stores.

[0004] Conventional knowledge on the color tone of scales is, for example, as described in JP-A-6-73504, depending on the ratio of the scale composition, when the amount of Fe ₂ O ₃ is large, the color becomes red and the F
It merely showed that a large amount of e ₃ O ₄ turned black, and nothing was disclosed about the subtle color tone of the scale surface.

[0005]

With respect to such a subtle color tone of the scale surface, the following problems had to be solved in order to bring black skin material which is required and preferred by the end user to the market. (1) The scale color of the black scale material is black. (2) The entire coil has a uniform color.

[0006] However, it is difficult to solve the above-mentioned problem, and at present it has not been able to meet the demands of users. Further, even though black is preferred as the scale color, the appearance of the color varies depending on the light, so that the user's request was not accurately transmitted to the manufacturing side. In addition, it was technically difficult to make the entire coil uniform, and no knowledge of the method was found.

[0007]

The present invention has been made to achieve the above object, and the means are as follows.

(1) In the hot rolling step, after hot rolling is completed, the scale thickness after cooling and winding is 10 μm or less, and the scale color of the surface layer is L * a * b *.
15 ≦ L * ≦ 40, −2 ≦ a * ≦ 2, −5 ≦ b * ≦ −3
It is a dark purple hot rolled steel sheet characterized by the following.

(2) As mass%, C: 0.01 to
0.2%, Si: 0.3% or less, Mn: 0.05-2.
0%, P: 0.1% or less, S: 0.02% or less, Al:
0.1% or less, N: 0.01% or less, with the balance being F
e) and the unavoidable impurities.

(3) As mass%, B: 0.01% or less, Ni: 1.0% or less, Cr: 1.0% or less, Cu:
1.0% or less, Mo: 1.0% or less, Ti: 0.1% or less, Nb: 0.1% or less, Zr: 0.1% or less, V:
The dark purple hot rolled steel sheet according to the above (2), wherein one or more kinds of the steel sheets are contained in an amount of 0.1% or less.

(4) As mass%, C: 0.01 to
0.2%, Si: 0.3% or less, Mn: 0.05-2.
0%, P: 0.1% or less, S: 0.02% or less, Al:
0.1% or less, N: 0.01% or less, with the balance being F
e, a steel material consisting of unavoidable impurities is heated, wound up after the completion of rough rolling, then unwound, and the rear end of the steel material is joined to the front end of the succeeding material to finish rolling successively. And then water-cooling at a cooling rate of 30 ° C./s or more to 300 to 650 ° C., and winding after 2 to 15 seconds, to produce a dark purple hot rolled steel sheet.

(5) As mass%, B: 0.01% or less, Ni: 1.0% or less, Cr: 1.0% or less, Cu:
1.0% or less, Mo: 1.0% or less, Ti: 0.1% or less, Nb: 0.1% or less, Zr: 0.1% or less, V:
The method for producing a dark purple hot-rolled steel sheet according to the above (4), wherein one or more of 0.1% or less are contained.

Hereinafter, the reasons for limiting the steel sheet and the manufacturing method of the present invention will be described in detail.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION To solve the above-mentioned problems, the present inventors have conducted many market surveys and studied various steel plate manufacturing methods, and have reached the present invention. Hereinafter, the present invention will be described in detail.

[0015] In order to standardize the recognition between the user and the manufacturing side regarding the color tone in the scale of many steel plates, it is necessary to digitize the color. There are various methods for displaying colors, but JISZ
The L * a * b * color specification shown in 8729 was found to be effective. This method uses lightness as shown in FIGS. 1 and 2 showing the hue and saturation of L * a * b * in FIG. 1 and the hue and saturation of L * a * b * in a three-dimensional image. (L *:
0 is black, and the larger the value, the higher the brightness and the whiter. )
And chromaticity (a *: red to green, b *: yellow to blue / respectively,
−: Green / blue, +: red / yellow, at this time, saturation = ｛(a
*) Expressed as 2+ (b *) 2｝ 1/2. ). For example, when the color tone of a general black-scale steel material is digitized, the lightness of the black-scale material is about 10 to 50, and the saturation is within 10, indicating that the color tone is slightly different.

As a result of market research, the black steel plate preferred in the market is dark purple, and 15 ≦ L * ≦ 40, −2 ≦ a * ≦
2. It was found that the range satisfies -3 ≦ b * ≦ −5. It was also found that this dark purple steel sheet was satisfied only when the scale thickness was 10 μm or less. For this reason, the lightness, chromaticity, and scale thickness of the present invention are 15 ≦ L * ≦
40, −2 ≦ a * ≦ 2, −5 ≦ b * ≦ −3, and scale thickness ≦ 10 μm.

Next, the reasons for limiting the steel components will be described.

C: 0.01% to 0.2% Dark purple steel sheets are preferred for use in building materials and furniture parts. C has a strong effect on the workability and strength of the steel sheet,
When the C content is less than 0.01%, the strength of the above-mentioned application material is insufficient, and burrs are easily generated at the time of processing into a product. On the other hand, if it exceeds 0.2%, the workability is reduced, and it becomes difficult to process the product, so C was set to 0.01% to 0.2%.

Si: 0.3% or less Si is made of firelite (2FeO.SiO.
₂ ) is an element that easily causes red scale by leaving fine Fe ₂ O ₃ on the outermost surface. When red scale is formed on the surface of the steel plate, it becomes mottled and is shunned by users. In addition, since the surface is concentrated with SiO, it is not possible to make the target dark purple, so that the Si content is 0.3%.
% As the upper limit.

Mn: 0.05 to 2.0% Mn fixes S in steel to form MnS and has an effect of improving the workability of the steel sheet. If it is less than 0.05%, the workability is degraded due to S remaining unfixed S. Also,
Mn is a strengthening element for steel materials, and if it exceeds 2.0%, workability is deteriorated along with improvement in strength. Therefore, the Mn content is set to 0.05% to 2.0%.

P: 0.1% or less P is a strengthening element. However, P tends to segregate at crystal grain boundaries, and if it exceeds 0.1%, workability is deteriorated and weld cracks are liable to occur. The upper limit was set to 0.1%.

S: 0.02% or less S causes workability deterioration, and further causes embrittlement of the heat-affected zone when performing bar joining by continuous hot rolling. 0.
If it exceeds 02%, the embrittlement of the bar joint becomes remarkable and the heat-affected zone of the bar is broken, so the content was regulated to 0.02% or less.

Al: 0.1% or less Al is added as a deoxidizing element if necessary.
If the content exceeds 1%, the ductility is deteriorated, so the upper limit is set to 0.1%.

N: 0.01% or less N is preferably as small as possible with respect to workability. If the content exceeds 0.01%, an adverse effect appears, so the upper limit is made 0.01%.

Cr: 1.0% or less Cr is added for strength adjustment. It is also effective in preventing the generated scale from peeling off. Cr content is 1.0
%, There is no further increase in reinforcement, so the upper limit is set to 1.0%.

Cu: 1.0% or less Cu improves the solid solution strength and is effective in improving fatigue characteristics. Also, it has a role of improving corrosion resistance. However, 1.
When a large amount of addition exceeds 0%, the concentration is locally concentrated at the scale / base iron interface and a dark purple color cannot be obtained. Therefore, the upper limit is set to 1.0%.

Ni: 1.0% or less Ni is effective in improving corrosion resistance and strength.
If the ratio exceeds 1, workability deteriorates, so the upper limit was made 1.0%.

Mo: 1.0% or less Mo is used for improving heat resistance and strength. If the content exceeds 1.0%, the workability deteriorates.
%.

Ti, Nb, Zr, V: 0.1% or less Each of Ti, Nb, Zr, V is a carbonitride-forming element, and is formed by strengthening or fine-graining by precipitates, and decreasing solid solution C / N. It is used to improve deep drawability. However, in any case, when the content exceeds 0.1%, this effect is saturated. Therefore, each upper limit is set to 0.1%.

B: 0.01% or less B also forms a carbonitride and has a large effect on strength. Has the function of increasing hardenability. It also has the property of lowering the transformation point. In any case, the effect is manifested in a very small amount. However, 0.01
%, The effect is saturated and the workability deteriorates. Therefore, the upper limit is set to 0.01%.

Next, a method of manufacturing the dark purple hot rolled steel sheet in the hot rolling step of the present invention will be described.

The present inventors have conducted investigations on the above-described production method for making the hot-rolled steel sheet dark violet by changing various production conditions. As a result, it was found that the production of the target hot-rolled steel sheet was possible by restricting to the following method.
The details are described below.

In the hot rolling step, each time the steel sheet is elongated by rolling, a new surface that is not oxidized is formed on the surface of the steel sheet. Normally, deske treatment is performed before rolling, and the scale, which is an oxide on the surface, is forcibly peeled off by water pressure. Therefore, immediately after rolling, all the front and back surfaces of the steel sheet become new surfaces. However, the steel sheet temperature was 7
Since the temperature is as high as 00 ° C. or more, it is immediately oxidized in the atmosphere or in a steam atmosphere, and a new scale is generated. The scale color of the steel sheet surface is affected by the temperature and atmosphere at the time of oxidation, and is further influenced by the scale growth / transformation environment (temperature, atmosphere, time, etc.).

In the present invention, in order to produce a dark purple steel sheet, a step of winding and rewinding after rough rolling is required. This is because by winding the thick scale generated from heating to rough rolling into a coil shape, many scales are peeled off at the time of winding, and up to scales that were difficult to peel off as a plate due to the strain applied at this time. This is because it can be peeled off by deske as it is. Further, it is effective to temporarily reduce the surface area by winding a steel sheet having a large surface area after being extended, and to equalize the overall temperature. Thus, a uniform scale color can be obtained when the entire coil has a uniform temperature.

The continuous rolling is performed by joining the rear end portion of the preceding material and the front end portion of the succeeding material and sequentially performing the finish rolling. This is to take a uniform cooling pattern. In continuous rolling, 1
Except for the leading part of the main steel and the trailing part of the final steel, the part sandwiched between them is always rolled and wound at the same time, so moderate tension is maintained between rolling and winding. Therefore, a predetermined cooling pattern can be obtained. In addition, since the shape of the steel plate is improved, the gap between the coils after winding is uniform, and it is easy to maintain a uniform oxidized and cooled state throughout the coil. In the case of rolling and winding steel materials one by one, since the leading and trailing portions of rolling are not rolled or wound on one side, the steel sheet moves in a table shape in a non-tension state. Not only can not be taken uniformly,
Since the back surface of the steel plate moves while hitting the table roll, the shape is deteriorated, and temperature and oxidation variations in the coil are likely to occur. For this reason, it is difficult to generate a uniform scale.

Next, three factors became apparent for controlling the scale color. They are scale thickness, stable oxidation temperature and oxidation time.

The reason for cooling with water at 30 ° C./s or more after the end of rolling is to control the scale thickness.
If the thickness exceeds 0 μm, dark purple cannot be obtained.

In controlling the color tone of the scale, the most important factors are the temperature and the time of oxidation. FIG. 3 shows a range in which the dark purple steel sheet of the present invention can be obtained from the relationship between the cooling stop temperature and the oxidation time. In a normal hot rolling process, a hot rolled steel material is manufactured in an atmospheric state. At the end of hot rolling, a new surface is formed on the surface of the steel sheet. However, since the temperature of the steel sheet is still high at this time, if the steel sheet is left in the air immediately after the end of rolling, a thick scale will be generated, and color tone control will not be effective. Therefore, it is necessary to perform water cooling at 30 ° C./s or more after the completion of rolling. Thereafter, when cooling is stopped, the scale grows at the oxidation rate at the stopped temperature. As shown in FIG. 3, when the temperature is higher than 650 ° C.,
L *> 40, a *> 2, resulting in a light red gray. At 300 ° C. or lower, L *> 40 and b * <− 5.
It becomes pale blue gray, and cannot obtain dark purple. The reason for setting the water cooling stop temperature to 300 ° C. to 650 ° C. is to make the scale color dark purple, and it is necessary to maintain the stable oxidation temperature for dark purple at 300 ° C. to 650 ° C.

However, the oxidation time also affects the scale thickness and color tone. When the oxidation time exceeds 15 seconds, L *> 40, a *> 2, b *>-3, and the gray becomes stronger and the scale becomes larger. It is easy to peel off. If shorter than 2 seconds, L *
> 40, b * <− 5, and the surface color stops at a pale blue color. After the cooling is stopped, it is necessary to wind up in 2 to 15 seconds. Therefore, in order to obtain an appropriate dark purple color, it is necessary to set the time from stopping cooling to winding up to 2 to 15 seconds.

[0040]

EXAMPLE After steel types 1 to 13 having the components shown in Table 1 were tapped, as shown in Table 2, they were heated to 1000 to 1250 ° C. and hot-rolled at a finishing temperature of 800 to 900 ° C.
The scale state and the scale thickness and color of the final steel material were measured by changing the winding after rough rolling, the bar joining effect, the cooling speed / cooling stop temperature after rolling, and the oxidation time to change the scale state.

No. 2 shown in Table 2 Regarding 1 to 10, both the steel type and the production conditions were within the scope of the present invention, and a dark purple steel plate could be produced with a predetermined scale thickness and color tone.

No. No. 11 has a large Cu thickness in the steel material, so that the surface of the steel material is rough, the scale thickness is large, and the fine surface Fe
_The a * became high due to the remaining ₂ O ₃ , and the color tone became red. No. In the case of No. 12, the surface was more severely roughened due to the large amount of Si, and the presence of the red scale was remarkable, the scale thickness was large, and the color tone was a red steel material.

No. As for No. 13, the S content was large and the bar was broken at the joint. No. In No. 14, since the coarse bar was not wound by the coil box, the scale generated from heating to rough rolling was not sufficiently removed, and the scale was thick and grey-red. Similarly, No. No. 15 did not perform bar joining, so the steel plate shape after finish rolling was poor,
For this reason, the color tone was poor and a uniform state could not be obtained.

No. In No. 16, the cooling rate was low after rolling, so that the scale thickness became thick and the color tone became light blue. No. 17 has a low cooling stop temperature,
Thereafter, there was no effect of oxidation, which is a color tone adjustment, and no dark purple color was obtained. In addition, No. In No. 18, the cooling stop temperature was too high, so that oxidation became remarkable, and gray and red became strong. In addition, No. In No. 19, the time from cooling stop to winding was short, and the progress of oxidation was insufficient. 2
In the case of No. 0, the time until winding was too long and the oxidation proceeded too much, and none could obtain a dark purple color.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

According to the present invention, the hot-rolled steel material can be supplied with the surface color being dark purple. In addition, since this steel material can be manufactured stably, it can be expected to expand its use as a uniform-tone steel material, and the economic effect on the industrial world is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing hue and saturation of L * a * b *.

FIG. 2 is a diagram showing the hue and saturation of L * a * b * in a three-dimensional image.

FIG. 3 is a diagram showing a relationship between a cooling stop temperature / oxidation time and a dark purple steel plate.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4K037 EA01 EA02 EA05 EA06 EA11 EA13 EA15 EA17 EA18 EA19 EA20 EA23 EA25 EA27 EA31 EA32 EA35 EB06 EB07 EB08 FA02 FC03 FC04 FD04 FD06 FD08 FE01 FE02

Claims (5)

[Claims] In the hot rolling step, after hot rolling is completed, the scale thickness after cooling and winding is 10 μm or less, and the scale color of the surface layer is L ≦ a * b *, and 15 ≦ L * ≦ 40, −2 ≦ a * ≦ 2, −5 ≦ b * ≦ −3, a dark purple hot rolled steel sheet. 2. C: 0.01 to 0.2 as mass%
%, Si: 0.3% or less, Mn: 0.05 to 2.0%,
P: 0.1% or less, S: 0.02% or less, Al: 0.1
The hot-rolled dark purple steel sheet according to claim 1, wherein the hot-rolled steel sheet has a content of not more than 0.01% and N: not more than 0.01%, and the balance consists of Fe and unavoidable impurities. 3. As mass%, B: 0.01% or less, N
i: 1.0% or less, Cr: 1.0% or less, Cu: 1.0
%, Mo: 1.0% or less, Ti: 0.1% or less, N
b: 0.1% or less, Zr: 0.1% or less, V: 0.1%
The dark purple hot rolled steel sheet according to claim 2, wherein the steel sheet contains one or more of the following. 4. C: 0.01 to 0.2 as mass%
%, Si: 0.3% or less, Mn: 0.05 to 2.0%,
P: 0.1% or less, S: 0.02% or less, Al: 0.1
% And N: 0.01% or less, and the balance is heated by heating a steel material composed of Fe and inevitable impurities, wound up after the completion of the rough rolling, then unwound, and the rear end of the steel material and the following material After rolling by hot rolling continuity in which the leading end portions are joined and finish rolling is sequentially performed, water-cooling is performed at a cooling rate of 30 ° C./s or more.
A method for producing a dark purple hot-rolled steel sheet, comprising winding at 0 to 650 ° C and 2 to 15 seconds later. 5. As mass%, B: 0.01% or less, N
i: 1.0% or less, Cr: 1.0% or less, Cu: 1.0
%, Mo: 1.0% or less, Ti: 0.1% or less, N
b: 0.1% or less, Zr: 0.1% or less, V: 0.1%
The method for producing a dark purple hot rolled steel sheet according to claim 4, wherein one or more of the following are contained.