JP2004027312A - Hot rolled steel sheet excellent in tight scale property and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet excellent in tight scale properties which has no defects in galvanizing and occurrence of Si scale, and has satisfactory scale adhesion over the whole length and whole width, and to provide a method for producing the same. <P>SOLUTION: The hot rolled steel sheet comprises, by mass, 0.02 to 0.20% C, 0.1 to 2.0% Mn, ≤0.3% Si, ≤0.03% P and ≤0.03% S, and further comprises one or more kinds of metals selected from 0.03 to 0.3% Ni, 0.04 to 0.5% Cu and 0.03 to 0.3% Cr, and the balance Fe with inevitable impurities. As the surface roughness of scale on the surface of the steel sheet and theinterface of the steel sheet, the counter of a rugged height of ≥0.5 μm per inch of a length is ≥300. <P>COPYRIGHT: (C)2004,JPO

Description

【００２２】
【発明の効果】
本発明によって、スケールの剥離し難い熱間圧延鋼材を供給することができる。
また、鋼材保管中の結露、水濡れによる錆びに対しても有効であり、色調も均一な鋼材としての用途拡大も期待でき、産業上有用な著しい効果を奏する。
【図面の簡単な説明】
【図１】酸洗後の表面粗度ＰＰＩと剥離評点の関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hot steel sheet for painting or the like that is used as a black scale coil that requires a tight scale of a surface scale.
[0002]
[Prior art]
Heretofore, there has been a demand for a material having excellent scale adhesion, that is, tight scale property, and a material to which Si and Cr are added has been mainly used. As a conventional tight-scale steel sheet, for example, Japanese Patent Application Laid-Open No. 2-185915 discloses a method of manufacturing a hot-rolled steel sheet having tight scale properties.
However, the conventional steel sheet is poor in hot-dip Zn plating due to the addition of Si and has poor surface properties due to the generation of Si scale, and a steel material free from these problems has been demanded.
[0003]
[Problems to be solved by the invention]
In recent years, the demand for tight scale has been further increased, and there is a demand for a hot-rolled steel sheet which has no defective hot-dip Zn plating and does not generate Si scale, and has good scale adhesion over the entire length and width.
In particular, problems have been pointed out, such as scale peeling of the coil edge portion of a thin material, poor appearance due to a floating scale of a full thickness coil, deterioration of corrosion resistance at the time of coating, poor cutting at the time of laser cutting, and deterioration of the working environment.
[0004]
In the black scale coil, it is very difficult to improve the peeling because the influence of the components, hot rolling, the cooling pattern of the steel sheet after hot rolling, and the temperature history such as air cooling after winding affect the scale.
Therefore, the specifications cannot be satisfied with the components and the production method disclosed in JP-A-2-185915.
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and to provide a steel material having a full-length and full-width tight scale property for both thin and thick materials and having uniform color tone and a method for producing the same.
[0005]
[Means for Solving the Problems]
Means of the present invention for achieving the above object are as described below in the claims.
(1) As mass%,
C: 0.02 to 0.20%,
Mn: 0.1 to 2.0%,
Si: 0.3% or less,
P: 0.03% or less,
S: contains 0.03% or less,
further,
Ni: 0.03 to 0.3%,
Cu: 0.04 to 0.5%;
Cr: contains one or more of 0.03 to 0.3%,
A hot-rolled steel sheet consisting of a balance of Fe and unavoidable impurities, and having a surface roughness of 0.5 μm or more per inch of surface roughness between the steel sheet surface scale and the steel plate interface of 300 or more. A hot-rolled steel sheet with excellent tight-scale properties.
[0006]
(2) As mass%,
Ti: 0.01-0.1%,
Nb: 0.01 to 0.07%,
V: 0.01 to 0.07%,
B: The hot-rolled steel sheet excellent in tight scale property according to (1), containing one or more of 0.0005 to 0.0050%.
(3) After heating the slab of the component described in (1) or (2) at 1100 ° C. or higher, finish hot rolling in a temperature range of 800 ° C. to 950 ° C., and wind up at 400 ° C. to 650 ° C. A method for producing a hot-rolled steel sheet having excellent tight-scale properties.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to solve the above-mentioned problems, the present inventors have conducted studies and investigations on the production of steel sheets of various steel types, and have reached the present invention. Hereinafter, embodiments of the present invention will be described in detail.
The hot-rolled steel sheet is generally rolled after initial scale (primary scale) formed on the surface when the slab is heated in a heating furnace, after descaling, rough rolling and finish rolling, and water cooling.
A scale (secondary scale) of the hot-rolled steel sheet is generated between the finish rolling, water cooling, winding, and coil cooling.
[0008]
At this time, as a result of intensive studies, the inventors have found that the purpose can be achieved by effectively utilizing Ni, Cu and Cr for tight scale formation.
In other words, it was found that when Ni and Cr were included as components, the interface between the base iron and the scale was disturbed by irregularities to increase the adhesion area, and further, the scale penetrated into the base iron to improve the tight scale property by the “anchor effect”. .
In addition, when Cu is contained, Cu in the liquid phase is generated at the interface between the scale and the steel plate on the steel sheet side when the primary scale is formed, and the scale in contact with this liquid phase has good wettability and high adhesion, and the scale of the secondary scale is formed. As a base, it was found that the secondary scale also had an effect of adhering to the base steel.
[0009]
However, on the other hand, when Cu has a low melting point and excessively melts into the grain boundaries in the steel sheet structure during heating of the slab before hot rolling, it becomes grain boundary cracks during hot rolling, and the obtained hot-rolled steel sheet is converted to Cu. It can also have a negative effect as a game. For this reason, conventionally, in the production of Cu-added steel, slabs in a heating furnace before rolling were extracted and rolled at a relatively low temperature so as not to dissolve Cu. At the same time, there is a problem that spatter on the Cu spatters and becomes unstable in terms of quality.
Therefore, the relationship between the surface roughness, which is the unevenness state of the steel material surface, and the scale peeling score was investigated. FIG. 1 shows the results. The steel sheet used in the investigation is based on the following components: C = 0.7%, Mn = 1.45%, Si = 0.01%, P = 0.015%, S = 0.01%, with the components as mass%. Further, the slab in which each component is changed in the range of Ni = 0.01 to 0.25%, Cu = 0.01 to 0.37%, and Cr = 0.01 to 0.28% is heated to 1150 ° C. Then, after rough rolling, finish rolling is completed at 900 ° C., and the film is wound at 550 ° C.
[0010]
The vertical axis in FIG. 1 is a 90 ° bending test of a steel plate after hot rolling (radius R (mm) = 1.5 × a punch having a thickness of 1.5 mm), and a tape is applied to a bent outer surface of a steel plate piece bent to 90 °. And then peeled off, the scale peeling area ratio (%) was determined, and this was rated in 9 categories), and the result of the peeling score was shown as an evaluation of tight scale properties. Here, the smaller the peeling score is, the smaller the amount of scale transferred to the tape is, the better the tight scale property is, and particularly, when the rating is 3 or less, the level is significantly higher than the quality acceptance level of the user, and the rating is 4 to 6, Although there is a case where some scale peeling is observed, it is a pass level slightly exceeding the user's quality passing level, and a score of 7 to 9, indicating that the scale peeling is remarkably rejected. In addition, the horizontal axis in FIG. 1 is that the steel sheet obtained under the same conditions is pickled, the surface scale is completely peeled off, and then, using a surface roughness meter, the surface of the steel sheet is 0.5 μm or more per inch in length. 3 shows the result of measuring the number of times of the uneven height as the surface roughness PPI (peak per inch).
[0011]
As shown in FIG. 1, the larger the surface roughness PPI and the larger the unevenness, the smaller the peeling score. In particular, when the surface roughness PPI is 300 times or more, a score of 66 or less, which is a steel quality acceptance standard for users, is achieved. It became clear. Furthermore, as a condition that the surface roughness PPI satisfies 300 times or more, at least one or more of Ni, Cu, and Cr components is Ni ≧ 0.03% and Cu ≧ 0.04 as mass%. %, Cr ≧ 0.03%. In addition, it was confirmed that the surface roughness PPI did not occur even when the Cu roughness was 300 or more times by properly adding Ni to the conventional problem of Cu barge.
Moreover, it turned out that 3-12 micrometers is preferable as a scale thickness of a surface. If the scale thickness is thinner than this, the corrosion resistance is liable to be inferior, while if it is thicker, the scale is easily cracked and peeled when processing the steel sheet.
Furthermore, as the scale composition, _Fe 3 _{O 4} is preferably in the range 85 to 100%. That is, when Fe ₂ O _{3 as} another scale composition is increased, the ductility of the scale is inferior and the scale is easily peeled.
[0012]
Next, the reasons for limiting the additional elements of the present invention including Ni, Cu and Cr will be described in detail below. In addition, the unit of the following components is described as%, but all means mass%.
<C>
C is used as an element for increasing the strength. In addition to solid solution strengthening, carbides can be formed with Ti and Nb and used as precipitation strengthening. However, excessive use lowers workability. Since the workability decreases as the steel material strength increases, the C content is preferably as low as possible. The reason why the lower limit is set to 0.02% is that if it is lower than this, burrs at the time of slitting or shearing become a problem. The reason why the content is set to 0.20% or less is to prevent cracking due to processing.
[0013]
<Mn>
Mn is an element necessary for increasing the strength of a steel material. If the amount is less than 0.1%, there is a problem in the processed structure because the strength and the AR3 point are increased. Further, if it is added in excess of 2.0%, it becomes difficult to maintain workability, so the content is set in the range of 0.1 to 2.0%.
<Si>
Si is an element that becomes firelite (2FeO.SiO ₂ ) on the surface of the steel sheet, leaves fine Fe ₂ O ₃ on the outermost surface, and easily generates red scale. When red scale is formed on the surface of the steel plate, it becomes mottled and is shunned by users. Further, since plating failure occurs during hot-dip Zn plating, the upper limit of the Si content is 0.3%.
[0014]
<P>
P causes embrittlement of the steel material, and deteriorates workability and weldability. It is better not to add as much as possible, and the upper limit was made 0.03%.
<S>
S forms sulfide MnS with Mn. These sulfides are easily deformed, are elongated by rolling, and exist in the steel material. MnS deteriorates the workability of a steel material. It is better to reduce as much as possible, but the upper limit was made 0.03% according to the processing level.
[0015]
<Ni>
Ni, as described above, causes the interface between the base iron and the scale to be uneven, so that the adhesion area increases, and the scale bites into the base iron to improve the adhesion of the scale due to the anchor effect. In order to effectively utilize this effect, it is necessary to add 0.03% or more as described above. On the other hand, Ni is an expensive metal, and its effect is saturated when it exceeds about 0.3%, so the upper limit is set to 0.3%.
[0016]
<Cu>
As described above, liquid Cu is generated at the interface between the scale and the iron base when the primary scale is generated as described above. The scale in contact with this liquid phase has good wettability and high adhesion, and serves as a base for forming a secondary scale, and the secondary scale is also adhered to the base iron. In order to effectively utilize this effect, it is necessary to add 0.04% or more as described above. On the other hand, if it is added too much, a problem of Cu diffusion occurs, and it is necessary to increase the amount of expensive Ni as a countermeasure. Since a sufficient effect can be obtained with about 0.5%, the upper limit is set to 0.5%.
<Cr>
Like Ni, Cr is also an element effective for forming tight scale due to the unevenness of the interface between the base iron and the scale, which increases the adhesion area, and the scale penetrates the base iron to form an anchor effect. In order to effectively utilize this effect, 0.03% or more is necessary as described above. However, the effect does not change even if it exceeds 0.3%, so it was set to 0.03 to 0.3%.
Furthermore, in order to manufacture a high-strength steel sheet, it is effective to utilize precipitation strength. The four elements that can utilize the following precipitation effects compensate for the lack of strength, and can achieve their purpose by using one or more of them.
[0017]
<Ti>
Ti forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is exhibited by adding 0.01% or more, and the effect is not changed by adding 0.1% or more.
<Nb>
Nb also forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is exhibited by adding 0.01% or more, and the effect is not changed by adding 0.07% or more.
[0018]
<V>
V also forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is exhibited by adding 0.01% or more, and the effect is not changed by adding 0.07% or more.
<B>
B is an element that forms carbides and nitrides, is also effective in improving hardenability, and is effective in improving strength. The effect is exhibited when 0.0005% or more is added, and the effect is not changed even when 0.0050% or more is added.
Next, the reasons for limiting the manufacturing conditions will be described.
The reason why the heating temperature was set to 1100 ° C. or higher was set from the viewpoint of securing the finish rolling temperature.
[0019]
In the case of adding Ti, Nb, V, and B, in order to utilize the precipitation effect, carbides and nitrides are dissolved in the slab stage to generate fine precipitates at the time of steel sheet production, thereby reducing the precipitation effect. The temperature is set to 1200 ° C. or more in accordance with the amount of addition in order to make full use.
The finish rolling temperature was 800 ° C. in order to secure _three or more Ar points. In order to make the precipitates finer, 850 ° C. or higher is necessary. However, if the temperature exceeds 950 ° C., there is a problem that crystal grains become coarse and scale flaws are easily generated. It was 950 ° C.
The winding temperature affects the size of the precipitate and the degree of the precipitation effect varies. When wound up at a high temperature, precipitates grow and become too large to reduce the strength effect. On the other hand, if it is too low, the formation of precipitates becomes insufficient, so that an increase in strength cannot be expected. For this reason, the appropriate temperature regulation range in which an increase in strength can be expected is set to 400 to 650 ° C.
[0020]
【Example】
Table 1 shows Examples 1 to 8 and Comparative Examples 1 to 5, which are examples of the present invention.
In Examples 1 to 3, the strength level of the steel sheet is TS = 320 MPa class, Examples 4 to 5 are TS 400 MPa class, Examples 6 to 7 are TS = 590 MPa class, and Example 8 is TS = 690 MPa class.
A slab having the components shown in Table 1 was heated to 1100 ° C. or higher in a heating furnace, and subjected to rough rolling to produce a rolling temperature of Ar ₃ or higher and a winding temperature of 450 to 630 ° C.
[0021]
Here, the tight scale property was evaluated by a nine-point evaluation of the peeling score by tape transfer after a 90-degree bending test (R = 1.5 × plate thickness) as described above. In Table 1, the peeling score is shown for the surface roughness PPI. In the legend, ◎ is a rating of 1 to 3, which is a level significantly exceeding the quality acceptance level of the user, ○ is a rating of 4 to 6, and slightly scaled. Although peeling may be observed, a pass level slightly exceeding the user's quality passing level, and x is a score of 7 to 9, indicates that scale peeling is remarkably poor.
Examples 1 to 8 which are examples of the present invention all have a scale thickness of 3 to 12 μm, a scale composition of Fe ₃ O ₄ in the range of 85 to 98%, and a tight scale property of peeling scores 1 to 3. ◎ The product passed the quality acceptance criteria of the level or peeling score of 4 to 6, and further no Cu burrs occurred.
On the other hand, in each of Comparative Examples 1 to 5, Cu, Ni, and Cr were all lower than the range of the present invention, the scale thickness was sometimes less than 3 μm or 12 μm or more, and the scale composition was 85% Fe ₃ O _4. In some cases, the tight scale property was at an X level of a peeling score of 7 to 8, and Cu off was also generated.
[Table 1]

[0022]
【The invention's effect】
According to the present invention, it is possible to supply a hot-rolled steel material in which the scale is not easily peeled.
In addition, it is effective against dew condensation during storage of steel materials and rust due to water wetting, and can be expected to expand the use as a steel material having a uniform color tone, and has a remarkable industrially useful effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the surface roughness PPI after pickling and the peeling score.

Claims (3)

As mass%,
C: 0.02 to 0.20%,
Mn: 0.1 to 2.0%,
Si: 0.3% or less,
P: 0.03% or less,
S: contains 0.03% or less,
further,
Ni: 0.03 to 0.3%,
Cu: 0.04 to 0.5%;
Cr: contains one or more of 0.03 to 0.3%,
A hot-rolled steel sheet consisting of a balance of Fe and unavoidable impurities, wherein the number of irregularities of 0.5 μm or more per inch in length is 300 or more per inch in surface roughness between the steel sheet surface scale and the steel sheet interface. Hot-rolled steel sheet with excellent tight-scale properties. As mass%,
Ti: 0.01-0.1%,
Nb: 0.01 to 0.07%,
V: 0.01 to 0.07%,
B: The hot-rolled steel sheet having excellent tight-scale properties according to claim 1, comprising one or more of 0.0005 to 0.0050%. After heating the slab of the component according to claim 1 or 2 at a temperature of 1100 ° C. or more, hot rolling is completed in a temperature range of 800 ° C. to 950 ° C., and the slab is wound up at a temperature of 400 ° C. to 650 ° C. Of hot-rolled steel sheet with excellent tight-scale properties.

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