JP3688643B2 - Method for producing rolled steel having a scale with good adhesion - Google Patents

Description

【００３８】
【表２】

【００３９】
表２から明らかなように、本発明例であるサンプル番号：５、６、９、１１、１３は、矯正後の外観も良好であり、剥離率も低く、良好な密着性を有するスケールが得られた。
【００４０】
これに対して、本発明範囲内のＣｒを含む符号（１）〜（４）の鋼であっても、サンプル番号：１、２、１０、１２は、最終デスケーリング温度が本発明範囲を超えるので、表面のスケール厚が厚く、部分的に膨れ状のスケール欠陥が見られ、矯正後のスケール剥離率も高い値を示していた。
【００４１】
サンプル番号３、４、８は、６００〜４００℃間の冷却速度が本発明範囲よりも大きいので、矯正前の外観は比較的良好であったが、矯正後はスケール剥離率が高くなった。
【００４２】
サンプル番号：７は、圧延終了温度が本発明範囲より低いので、表面が赤スケールで覆われており、矯正後のスケールは著しく剥がれ外観も不良であった。
【００４３】
Ｃｒ含有量が本発明範囲外の符号（５）、（６）の鋼を用いたサンプル番号：１４〜１８は、矯正によりスケールは剥離しており、外観も不良であった。
【００４４】
【発明の効果】
以上、説明したように、この発明によれば、製造効率を低下させることなく、圧延時および矯正工程でのスケール剥離がなくなり、しかも、外観および塗装性等に優れた圧延形鋼を製造することができるといった有用な効果がもたらされる。
【図面の簡単な説明】
【図１】 実施例１で圧延した山形鋼を示す断面図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a rolled shape steel having a scale with good adhesion, and particularly to a method for producing a rolled shape steel having a scale with good adhesion without deteriorating production efficiency.
[0002]
[Prior art]
When coating is performed in a mill scale state without applying shots to a thick steel plate, unevenness of the scale may damage the appearance after coating, which may be a problem. Moreover, when performing laser cutting, it is calculated | required that the steel material surface is covered with the black scale with sufficient adhesiveness. Thus, regarding the surface scale properties of rolled steel, there is a strong demand for having a dense scale with good adhesion. For that purpose, it becomes a problem how to suppress the generation of a scale having a bulge-like defect with poor adhesion and how to form a scale that does not peel even during correction after hot rolling.
[0003]
As a method for improving the adhesion of the scale, in the field of hot-rolled wire, iron and steel, 65 (1979) S390 was distorted by lowering the heating temperature and reducing the thickness of the scale. A method for improving the adhesion of the scale is disclosed. Hereinafter, this method is referred to as Prior Art 1.
[0004]
As a method for reducing the thickness of the scale and controlling the composition of the scale, Japanese Patent Application Laid-Open No. 64-83615 discloses a hot-rolled steel sheet that is rolled up at 570 to 650 ° C. after rolling and up to 570 to 500 ° C. at 10 ° C. / A method of cooling below hr is disclosed. Hereinafter, this method is referred to as Prior Art 2.
[0005]
In JP-A-6-277706, as a method for producing a tight-scale hot-rolled thick steel sheet, a descaling facility having a certain capacity is arranged in a rolling mill, and cooling water having a cooling capacity exceeding a specified level is injected. A method is disclosed. Hereinafter, this method is referred to as Prior Art 3.
[0006]
Japanese Patent Laid-Open No. 9-87799 discloses a method of controlling the reduction rate and temperature after heating, that is, accelerated cooling is started at a cooling rate of 5 ° C./second or more within 30 seconds after rolling, Discloses a method in which accelerated cooling is stopped in a temperature range of 500 to 750 ° C. and then air cooling is performed. Hereinafter, this method is referred to as Prior Art 4.
[0007]
Japanese Laid-Open Patent Publication No. 1-159348 discloses a method of gradually cooling H-shaped steel at 700 to 850 ° C. after rolling. Hereinafter, this method is referred to as Prior Art 5.
[0008]
[Problems to be solved by the invention]
As means for obtaining steel having good scale adhesion, it can be found from the prior arts 1 and 2 that the scale thickness is reduced and the scale composition is controlled. However, in actual production, when cooling from 570 to 500 ° C. at 10 ° C./hr or less with a thick steel plate, a reduction in production efficiency is inevitable.
[0009]
Further, improving the descaling equipment and improving the cooling capacity as in the above-described prior art 3 requires a large-scale equipment and has the disadvantage of increasing the equipment cost.
[0010]
In the prior art 4, the reduction ratio and temperature must be controlled in a complicated manner, and the present inventors stopped the accelerated cooling at 500 to 750 ° C., and then set a scale with good adhesion at a cooling rate of about air cooling. The knowledge that it cannot be generated is obtained.
[0011]
Prior art 5 proposes a method of slow cooling after completion of rolling, but does not disclose a detailed slow cooling range.
[0012]
Accordingly, an object of the present invention is to provide a method for producing a rolled steel having a scale having good appearance and good adhesion by optimizing rolling conditions, final descaling conditions, and cooling conditions.
[0013]
[Means for Solving the Problems]
The present inventors diligently studied a method for manufacturing a rolled steel having a scale having good adhesion. As a result, after heating the steel of a specific component within a temperature range of 1050 to 1350 ° C., hot rolling is performed, final descaling is performed at 960 ° C. or less, and rolling is finished at a temperature range of 700 to 960 ° C., In the subsequent cooling process, by rolling the temperature range from 600 to 400 ° C. at an average cooling rate in the range from 0.05 to 0.5 ° C./second, it is possible to produce a rolled steel having a scale with good adhesion. I found out.
[0014]
The present invention has been made on the basis of the above-described knowledge, and is characterized by the following.
[0015]
The invention according to claim 1 is: C: 0.05-0.20%, Si: 0.6% or less, Mn: 0.3-1.6%, Al: 0.06% or less, Cr: 0.00. 1 to 1.0%, P: 0.02% or less, S: 0.029% or less, N: 0.02% or less (above, mass%), the balance being Fe and inevitable impurities After the steel slab is heated, hot rolling is performed, final descaling is performed at a temperature of 960 ° C. or less, rolling is finished within a temperature range of 843 to 960 ° C., and in the subsequent cooling process, 600 to 400 ° C. It is characterized in that the cooling is performed at an average cooling rate in the range of 0.05 to 0.5 ° C./second in the temperature range up to.
[0016]
According to a second aspect of the present invention, the steel slab further comprises Cu: 0.5% or less, Ni: 1.0% or less, Mo: 1.0% or less, Nb: 0.1% or less, V: 0 It is characterized in that it contains at least one of 2% or less and Ti: 0.02% or less (above, mass%).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the component composition and production conditions defined in the present invention will be described in detail.
[0018]
First, the component composition will be described.
[0019]
C: 0.05-0.20 mass%
C needs to be 0.05 mass% or more in order to secure the strength, but if added over 0.20 mass%, the toughness or weldability is lowered. Therefore, the C content is in the range of 0.05 to 0.20 mass%.
[0020]
Si: 0.6 mass% or less Si is an element that also contributes to deoxidation and securing of strength of steel, but if the Si content exceeds 0.6 mass%, it has an undesirable effect from the viewpoint of HAZ toughness and weldability. Therefore, the Si content is set to 0.6 mass% or less.
[0021]
Mn: 0.3 to 1.6 mass%
Mn is also necessary for deoxidation, improvement of strength toughness, and suppression of FeS formation. If it is less than 0.3 mass%, the cleanliness of the steel is lowered and the workability is impaired. On the other hand, if it exceeds 1.6 mass%, impact properties and toughness are lowered. Therefore, the Mn content is in the range of 0.3 to 1.6 mass%.
[0022]
Al: 0.06 mass% or less Al is a cheap and strong deoxidizing material. However, if contained in a large amount, the cleanliness of the steel is impaired and the toughness of the welded portion is deteriorated, so the upper limit is made 0.06 mass%.
[0023]
Cr: 0.1-1.0 mass%
Cr is concentrated on the scale side of the interface between the ground iron and the scale, and has the effect of suppressing the growth of the scale and making the scale dense. In order to obtain this effect, addition of 0.1 mass% or more is necessary, and addition of a large amount deteriorates the toughness of the weld heat affected zone, so the upper limit is made 1.0 mass%.
[0024]
Moreover, 1 type, or 2 or more types of the following alloy components can be added as needed.
[0025]
Cu: 0.5 mass% or less Cu has an effect of improving strength and corrosion resistance. Addition of a large amount causes hot cracking of the slab, so the upper limit is made 0.5 mass%.
[0026]
Ni: 1.0 mass% or less Ni has an effect of improving both strength and toughness. Addition of a large amount significantly impairs the economy, so the upper limit is made 1.0 mass% or less.
[0027]
Mo: 1.0 mass% or less Mo has an effect of increasing hardenability and an effect of increasing resistance to temper softening. Addition in large amounts degrades the weld heat affected zone, so the upper limit is made 1.0 mass%.
[0028]
Nb: 1.0 mass% or less, V: 0.2 mass% or less, Ti: 0.02 mass% or less Nb, V, and Ti precipitate as carbonitrides in the steel to increase the strength. By making the microstructure fine, it has the effect of improving both strength, base metal toughness, and toughness of the weld heat affected zone. Addition of a large amount of each element greatly deteriorates the toughness of the weld heat affected zone. Therefore, the upper limit is set to Nb is 1.0 mass% or less, V is 0.2 mass% or less, and Ti is 0.02 mass% or less.
[0029]
Next, the reasons for limiting the manufacturing conditions will be described.
[0030]
The method according to the present invention comprises a heating process of steel having the above composition, a hot rolling process, and a subsequent cooling process.
[0031]
Heating process: 1050-1300 ° C
The heating temperature of the steel before rolling is not particularly limited, but is preferably in the range of 1050 to 1300 ° C. When the heating temperature is less than 1050 ° C., not only a sufficient shape cannot be obtained due to an increase in hot deformation resistance, and not only rolling cracks are generated, but also when using a slab, homogenization is possible. It is not performed sufficiently and adversely affects the subsequent characteristics. Moreover, when heating temperature exceeds 1300 degreeC, a crystal grain coarsens and the toughness of a product may be impaired especially. Therefore, the heating temperature is desirably in the temperature range of 1050 to 1300 ° C.
[0032]
Rolling final descaling: 960 ° C. or less, finish rolling temperature: 843 960 ° C.
Hot rolling is performed, final descaling is performed at 960 ° C. or less, and rolling is finished at a temperature range of 843 to 960 ° C. When the final descaling temperature is higher than 960 ° C., bulging scale defects are liable to occur, and the adhesion of the scale is significantly impaired. Rolling at 960 ° C. or lower suppresses the swollen scale and suppresses the growth of the scale more than necessary. Moreover, if it is less than 843 degreeC , since a deformation | transformation resistance becomes large, not only shaping | molding of material will become difficult, but there exists a tendency for a scale to be crushed and to become what is called a red scale. Therefore, the final descaling temperature is limited to 960 ° C. or lower, and the rolling finishing temperature is limited to a temperature range of 843 to 960 ° C.
[0033]
Cooling step: Average cooling rate at 600 to 400 ° C. 0.05 ° C./sec to 0.5 ° C./sec. After rolling, the average cooling to 600 to 400 ° C. is 0.05 ° C./sec to 0.5 ° C./sec. Slowly cool at speed. By cooling under this cooling condition, transformation (wustite → magnetite) sufficient to ensure adhesion can be produced without harming productivity. In addition, there is no restriction | limiting in particular about cooling to slow cooling after completion | finish of rolling, and cooling to normal temperature after completion | finish of slow cooling. That is, after rolling is complete, it may be cooled to water or slowly. A specific method for setting the average cooling rate at 600 to 400 ° C. to 0.05 ° C./second to 0.5 ° C./second is to install a heat insulating cover on the cooling floor.
[0034]
According to the present invention described above, it is possible to produce a rolled steel having a scale with good adhesion that does not peel during correction and has good appearance and paintability.
[0035]
【Example】
Next, the present invention will be further described with reference to examples.
[0036]
( Example 1 )
The chemical components shown in Table 1 were rolled into angle irons as shown in FIG. 1, and after rolling, correction was performed with a leveler at room temperature, and the corrected appearance and scale peeling rate were measured. The results are shown in Table 2 .
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
As apparent from Table 2 , Sample Nos. 5, 6, 9, 11, and 13 which are examples of the present invention have a good appearance after correction, a low peel rate, and a scale having good adhesion. It was.
[0040]
On the other hand, even in the steels of the signs (1) to (4) containing Cr within the scope of the present invention, the final descaling temperatures of the sample numbers: 1, 2, 10, and 12 exceed the scope of the present invention. Therefore, the scale thickness on the surface was thick, partially swelled scale defects were observed, and the scale peeling rate after correction showed a high value.
[0041]
In Sample Nos. 3, 4, and 8, the cooling rate between 600 and 400 ° C. was larger than the range of the present invention, so the appearance before correction was relatively good, but the scale peeling rate increased after correction.
[0042]
Sample No. 7 had a rolling end temperature lower than the range of the present invention, so the surface was covered with a red scale, and the scale after correction peeled off significantly and the appearance was poor.
[0043]
In Sample Nos. 14 to 18 using the steels with the Cr content outside the scope of the present invention and the codes (5) and (6) , the scale was peeled off by correction and the appearance was poor.
[0044]
【The invention's effect】
As described above, according to the present invention, without reducing production efficiency, there is no scale peeling at the time of rolling and in a straightening process, and a rolled section steel having excellent appearance and paintability is produced. This is a useful effect.
[Brief description of the drawings]
1 is a cross-sectional view showing an angle steel rolled in Example 1. FIG.

Claims (2)

C: 0.05-0.20%,
Si: 0.6% or less,
Mn: 0.3 to 1.6%
Al: 0.06% or less,
Cr: 0.1 to 1.0%
Containing
P: 0.02% or less,
S: 0.029% or less,
N: 0.02% or less (above, mass%)
And the steel slab with the balance being Fe and inevitable impurities is heated and then hot rolled, the final descaling is performed at a temperature of 960 ° C. or less, and the rolling is finished within a temperature range of 843 to 960 ° C. In the subsequent cooling process, a scale with good adhesion is characterized in that cooling is performed at an average cooling rate in the range of 0.05 to 0.5 ° C./second in the temperature range of 600 to 400 ° C. The manufacturing method of the rolled shape steel which has. The billet further comprises:
Cu: 0.5% or less,
Ni: 1.0% or less,
Mo: 1.0% or less,
Nb: 0.1% or less,
V: 0.2% or less,
Ti: 0.02% or less (above, mass%)
The method for producing a rolled steel having a scale with good adhesion according to claim 1, comprising at least one of the following.

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