JPH10121141A - Method for producing hot-rolled steel sheet with excellent jump resistance, scale and enamel adhesion - Google Patents

Abstract

(57) [Problem] To provide a method for producing a hot-rolled steel sheet which is excellent in scale adhesion during molding, enamel adhesion after enameling, and pinch resistance. When a hot-rolled steel sheet is produced by directly enamelling the steel sheet surface without descaling, the weight ratio of C: 0.005% or less, Mn: 1.0% or less, S:
0.05% or less, Al: 0.10% or less, N: 0.00
2 to 0.020%, Ti: 4 × C (%) + 1.5 × S
(%) + 3.4 × N (%) to 0.20%, Cu: 0.0
In addition to 1 to 0.10%, if necessary, contains trace components,
After heating the continuous casting slab consisting of iron and unavoidable impurities and rough rolling, the inlet temperature of the hot-rolling finish rolling is adjusted to Ar.
₃ Transformation point or less, outlet temperature 600 ° C or more and 570 ° C
After winding as described above to form FeO to a thickness of 2 to 20 μm on the steel sheet surface, 50% or more of the entire scale is made of Fe ₃ O.
_The above problem is solved by transforming to ₄ .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet which can omit a descaling step after hot rolling and has excellent enamel adhesion and toughness after enamel firing.

[0002]

2. Description of the Related Art Generally, in the production process of enamel products, after processing, pretreatments such as degreasing, pickling, Ni treatment, and neutralization are performed, and after drying, glaze and firing are performed. However,
Such a method is costly because it involves a number of steps. Further, the use of acids further causes pollution problems such as environmental degradation and waste liquid treatment. Therefore, there have been problems such as the necessity of many facilities and costs for these measures.

[0003] As a material for the enamel, a cold-rolled steel sheet having good dimensional accuracy and workability is mainly used, and a hot-rolled steel sheet is used for a material requiring strength and rigidity. As is well known, hot-rolled steel sheets are covered with a thick scale, so they are generally pickled and shot-blasted, descaled and shipped to users, but recently the cost of steel materials has been reduced. There is a tendency to replace cold-rolled products with thin-rolled hot-rolled products for the purpose of, and a steel sheet that can be enameled without descaling has been desired. In other words, if a cold-rolled steel sheet is replaced with a hot-rolled steel sheet, the sheet thickness becomes thinner and the same weight, so that the thinner the sheet thickness, the larger the surface area of the steel sheet becomes. This is because the properties are significantly reduced.

On the other hand, it has been considered that pretreatment such as pickling and Ni treatment described above is indispensable in order to enhance the adhesion of the enamel, but at present, the adhesion promotion of Ni and Co during enamel top dressing is performed. Since a steel sheet containing a relatively large amount of an agent has been used, a steel sheet capable of performing enamel work without descaling and enamel pretreatment is disclosed in Japanese Patent Application Laid-Open Nos. 61-296902 and 61-296902. 62-1
No. 818 has been disclosed.

[0005] However, these steel sheets have a very low exit temperature (FDT) of hot rolling finish rolling, and the oxide film is too thin to obtain Fe ₃ O ₄ having excellent scale adhesion.
Conversely, FeO having poor adhesion is generated. for that reason,
There is no problem in the case of mild processing, but there is a problem that the scale is easily peeled off when tight bending or sheet metal processing is performed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to reduce the scale adhesion and the scale during molding without engraving and descaling before enamelling. An object of the present invention is to provide a method capable of producing a hot-rolled steel sheet having excellent enamel adhesion after enamel processing and further having excellent anti-sticking property at low cost and with high productivity.

[0007]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of intensive studies on the method of manufacturing a hot-rolled steel sheet with excellent scale adhesion during forming processing and enamel adhesion after enamel processing, and with excellent anti-sticking properties, the Ar ₃ transformation point as in the past Rather than performing hot rolling for finish rolling as described above, hot rolling is performed at a low temperature equal to or lower than the Ar ₃ transformation point to give processing strain and actively precipitate fine precipitates such as carbides and sulfides. The present invention has been found to produce a target hot-rolled steel sheet by generating a scale having a predetermined thickness at the same time as imparting the jumping property and generating a scale having strong adhesion by transforming the steel sheet. It is a thing.

That is, according to the present invention, when producing a hot-rolled steel sheet in which the surface of the steel sheet is directly enameled without descaling, the weight ratio of C: 0.005% or less,
Mn: 1.0% or less, S: 0.05% or less, Al:
0.10% or less, N: 0.002 to 0.020%, T
i: 4 × C (%) + 1.5 × S (%) + 3.4 × N
(%) To 0.20%, Cu: 0.01 to 0.10%, and if necessary, one out of Nb, B and rare earth elements.
0.0001 to 0.10% in total of two or more species,
And / or heating a continuously cast slab containing one or more of Sb, Se, Bi, Te, and As in total of 0.001 to 0.10%, with the balance being iron and unavoidable impurities. After the rough rolling, the inlet temperature of the hot rolling finish rolling is set to the Ar ₃ transformation point or lower, and the outlet temperature is set to 600 ° C. or higher.
Wind up at 70 ° C or more and apply FeO to the steel plate surface at 2 to 20 μm
After forming to a thickness of 50% or more of the entire scale,
resistance Tsumatobi resistance, characterized in that to transform the e ₃ O _4,
An object of the present invention is to provide a method for producing a hot-rolled steel sheet having excellent scale and enamel adhesion.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a hot-rolled steel sheet having excellent stickiness, scale and enamel adhesion according to the present invention will be described in more detail.

The reasons for limiting the steel composition and the production process of the present invention will be described. C: The weight ratio is limited to 0.005% or less. The reason why C is set to 0.005% or less is that if it exceeds 0.005%, fine TiC increases and workability deteriorates. If the amount is extremely small, the anti-sticking property is reduced. Therefore, the lower limit is preferably 0.001%. Preferably, the content is 0.001 to 0.003%.

Mn: Limited to 1.0% or less. Mn is an element effective for fixing S which causes red hot embrittlement, and sulfide is effective for improving the anti-sticking property. Therefore, in the present invention, the content of at least 0.05% is preferable, but the content of more than 1.0% unnecessarily increases the steel cost, so the upper limit is made 1.0%. Preferably, it is 0.05 to 0.50%.

S: Limited to 0.05% or less. S forms sulfides and is effective for improving the anti-sticking property. Therefore, in the present invention, the content is preferably at least 0.001%, but if the content exceeds 0.05%, the workability is deteriorated, so the upper limit is made 0.05%. Preferably 0.00
5 to 0.03% is good.

Al: Limited to 0.10% or less. Al is used as a deoxidizing agent in steelmaking, and should contain at least 0.01% to facilitate deoxidation. However, the content of more than 0.10% unnecessarily increases the steel cost, so the upper limit is made 1.0%. Preferably 0.
01-0.05% is good.

N: Limited to 0.002 to 0.020%. N forms TiN and is effective for improving the anti-sticking property. Therefore, in the present invention, at least 0.0
A content of 02% is necessary, but a content of more than 0.020% deteriorates workability, so the upper limit is made 0.02%. Preferably, it is 0.002 to 0.010%.

Ti: 4 × C (%) + 1.5 × S (%) +
It is limited to 3.4 × N (%) to 0.20%. Ti is T
This is effective in forming precipitates such as iC, TiS, and TiN, and improving the toughness. In addition, solid solution (C,
4 × C (%) +
It is necessary to contain 1.5 × S (%) + 3.4 × N (%) or more. However, if the content exceeds 0.20%, the adhesion of the enamel is deteriorated, so the upper limit is made 0.20%.
Preferably 4 × C (%) + 1.5 × S (%) + 3.4 ×
N (%) to 0.15% is good.

Cu: limited to 0.01 to 0.10%.
Cu is an effective element for improving the adhesion. Therefore, the content of at least 0.01% is necessary. However, the content of more than 0.10% deteriorates the composition of the scale of the surface, so the upper limit is made 0.1%. Preferably 0.
01 to 0.10% is good.

Nb, B, REM (rare earth element): One or more of them are limited to 0.0001 to 0.10% in total. Nb, B, and REM, which are added as necessary, form carbides, nitrides, and sulfides, respectively, and further improve the jump-resistant property, and are particularly effective elements when Ti is relatively small. In order to exert the effect, one or more kinds need to be 0.0001% or more in total. However, the content of 0.10% unnecessarily increases steel cost, so the upper limit is set to 0.10%.

Sb, Se, Bi, Te, As: One type or two or more types is limited to 0.001 to 0.10% in total.
Sb, Se, Bi, Te and As, which are added as necessary, are effective elements for further improving the adhesion of the enamel, and in order to bring out the effect, one or two or more of them are added in a total amount of 0.001. % Or more is required. However,
Since the content of 0.10% unnecessarily increases the steel cost, the upper limit is set to 0.10%.

Entry temperature and exit temperature of hot rolling finish rolling are limited to Ar ₃ transformation point or lower and 600 ° C. or higher, respectively. The reason why the inlet temperature is lower than the Ar ₃ transformation point and the outlet temperature is 600 ° C. or higher is that if the inlet temperature is higher than the Ar ₃ transformation point, precipitates such as fine carbides and sulfides that are effective for toe skipping resistance are formed. This is because precipitation becomes difficult, and the outlet temperature is set to 600
If the temperature is lower than ° C, a scale having a predetermined thickness cannot be obtained.

Winding temperature after rolling: limited to 570 ° C. or higher. The reason for setting the winding temperature after rolling to 570 ° C. or higher is that 570 ° C. is required to generate a predetermined thickness of FeO on the steel sheet surface.
It is because it is difficult if the amount is less than. Although the cooling rate after winding is not particularly limited, a cooling rate as low as possible is preferable in order to transform to a desired scale thickness and scale composition, and a temperature of 500 ° C. or more is preferably 0.1 to 10.0 ° C./min.
It is good to be in the range of.

Scale thickness: Limited to 2 to 20 μm.
The reason for setting the thickness of the scale to 2 to 20 μm is that if the thickness is less than 2 μm, the good adhesion of Fe ₃ O ₄ is reduced to 50% of the entire scale.
% Is difficult to transform
If it exceeds μm, the enamel adhesion will be deteriorated.

Transformation rate of Fe ₃ O ₄ : Limited to 50% or more. The reason why the transformation rate of Fe ₃ O ₄ is 50% or more of the entire scale is that if it is less than 50%, the adhesion rate between the scale and the enamel is very poor.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

The continuous cast slab shown in Table 1 was hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 1.6 mm. That is, the slab heating temperature (SRT) is heated at a temperature of 1000 to 1200 ° C., and then the entrance temperature (FET) of the hot rolling finish rolling is performed.
After performing hot rolling in a range of 出 10 to 20 ° C. from the outlet side temperature (FDT), the film was wound at a winding temperature (CT) of 550 to 700 ° C. and cooled to room temperature. Table 2 also shows the results of examining the resistance to toe skipping, scale, and enamel adhesion of these steel sheets.

The anti-sticking property was determined by glazing and drying a commercially available ground coat (M type, manufactured by Nippon Fellows Co., Ltd.) to a thickness of 100 μm, followed by baking for 10 minutes in an electric furnace having a dew point of + 40 ° C. and 850 ° C. . Furthermore, it was inserted into a constant temperature bath at 160 ° C. for 16 hours to promote the occurrence of skipping, and the occurrence state of skipping (no occurrence: 印, presence: X) was determined by visual observation. Thereafter, the adhesion of the enamel was investigated according to the method of ASTM C313.

On the other hand, the thickness and composition of the scale were measured by optical microscope observation and X-ray diffraction, and the scale adhesion was evaluated by image processing on the scale peeling rate after 180-degree bending back. As a result, it was found that the steel sheets produced by the method of the present invention were all hot-rolled steel sheets having excellent toe skipping resistance, scale and enamel adhesion.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As described in detail above, the steel sheet manufactured by the method of the present invention is a hot-rolled steel sheet having excellent toe-batch resistance, adhesion to scale and enamel, and is excellent without descaling. Since it has enamel adhesion, it is possible to omit the pretreatment step of the enamel, and it is also possible to omit the descaling step such as pickling and shot blasting at a steel maker. Therefore, in the present invention, the yield of steel materials is improved and the cost is reduced, and the time required to produce the final product of the enamel can be significantly reduced.In addition, since waste liquid treatment such as acid is not required, it can greatly contribute to pollution and environmental problems. This has the effect of having an extremely high industrial value.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C22C 38/16 C22C 38/16 C23D 5/00 C23D 5/00 F (72) Inventor Takashi Sakata Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba No. 1 Kawasaki Steel Engineering Co., Ltd. (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Co., Ltd.

Claims (1)

[Claims] When producing a hot-rolled steel sheet in which the surface of the steel sheet is directly enameled without descaling, C: 0.005% or less; Mn: 1.0% or less; : 0.05% or less, Al: 0.10% or less, N: 0.002 to 0.020%, Ti: 4 × C (%) + 1.5 × S (%) + 3.4 × N
(%) To 0.20%, Cu: 0.01 to 0.10%, and if necessary, one or more of Nb, B and rare earth elements in a total of 0.0001 to 0. .10
%, And / or one or more of Sb, Se, Bi, Te, and As in total of 0.001 to 0.10.
%, With the balance consisting of iron and unavoidable impurities, and after rough rolling, the hot-rolling finish rolling has an inlet temperature of not more than the Ar ₃ transformation point and an outlet temperature of not less than 600 ° C. Ｆｅ ° C or higher and apply FeO to the steel plate surface
A method for producing a hot-rolled steel sheet having excellent anti-sticking property and adhesion to scale and enamel, wherein 50% or more of the entire scale is transformed into Fe ₃ O ₄ after being formed to a thickness of 0 μm.