JP2011179022A - Steel material superior in corrosion resistance after having been painted - Google Patents

Abstract

[PROBLEMS] To provide a relatively inexpensive component composition suitable for civil engineering and building structures such as bridges, and even if a defective portion occurs in a coating film, the defective portion does not corrode and the appearance of the surface is not impaired. Provide excellent steel materials.
SOLUTION: In mass%, C: more than 0.02%, 0.15% or less, Si: more than 0.1%, 0.7% or less, Mn: 0.2% or more, 1.5% or less, P: 0.001% or more, 0.03% or less, S: 0.0001% or more, 0.02% or less, Al: 0.01% or more, 0.1% or less, Cr: 0.3% or more, 1.0% or less, further including one or more of W, Sb, Sn in total of 0.01% or more and 0.2% or less, if necessary, Cu: 0.1% or more, 0.5% or less, Ni: 0.1% or more, 0.5% or less of one or more steel materials, the balance being Fe and inevitable impurities.
[Selection] Figure 1

Description

  The present invention relates to a steel material excellent in coating corrosion resistance, even if a defective portion occurs in a coated steel material, even if the defective portion is corroded and the surface appearance is not impaired, particularly for civil engineering structures such as bridges. And a relatively inexpensive component composition.

  Recently, in order to prevent corrosion of a structure, not only the initial cost but also a design that reduces the life cycle cost in consideration of the initial cost and the maintenance cost during the service period has been adopted.

  In the case of civil engineering structures for long-term use, painting is often applied to prevent corrosion, and since the coating blocks the external environment and the steel surface, it is normal even in high-salt environments where the corrosion of steel is severe. If it is in the range of the atmospheric environment, it has high anticorrosion performance.

  However, since the resin constituting the coating deteriorates due to ultraviolet rays and the like, and the anticorrosion performance decreases, repainting is required every certain period, and maintenance costs are generated. For this reason, in order to reduce the life cycle cost, it is necessary to extend the life of the coating.

  As a method for prolonging the life of the coating film itself, a method using a highly durable fluororesin paint is used (for example, see Non-Patent Document 1). In addition, even if rust is generated from a part of the coating film, a certain corrosion area is allowed, so it is not necessary to repaint immediately, and by delaying the progress of corrosion, the period until repainting is extended. can do.

  As a method of delaying the progress of corrosion, it has been proposed to apply a weathering steel material to the base steel or to use a steel material having a component similar to the weathering steel (for example, Patent Document 1, Patent Document 2, and Non-Patent Document). Reference 2).

JP 2003-171732 A JP 2007-46148 A

Steel road bridge painting and anticorrosion manual: Japan Road Association, December 2005 Rust prevention management, Japan Rust Prevention Technology Association Vol. 52, Evaluation of corrosion resistance of painted weathering steel Takeshi Matsumoto

  However, the method using a coating film excellent in durability described in Non-Patent Document 1 cannot prevent corrosion that proceeds from the part when the coating material is expensive and the coating film is once damaged.

  Moreover, since the steel plate excellent in corrosion resistance described in Patent Literature 1, Patent Literature 2 and Non-Patent Literature 2 contains a large amount of expensive alloy elements as a steel composition, the cost of the steel material is remarkably increased.

  Therefore, an object of the present invention is to provide a steel material for coating having a low component life and a low life cycle cost that is excellent in coating corrosion resistance.

The object of the present invention can be achieved by the following means.
1. In mass%, C: more than 0.02%, 0.15% or less, Si: more than 0.1%, 0.7% or less, Mn: 0.2% or more, 1.5% or less, P: 0.00. 001% or more, 0.03% or less, S: 0.0001% or more, 0.02% or less, Al: 0.01% or more, 0.1% or less, Cr: 0.3% or more, 1.0% Hereinafter, a steel material having excellent coating corrosion resistance, further including one or more of W, Sb, and Sn in a total amount of 0.01% or more and 0.2% or less, with the balance being Fe and inevitable impurities.
2. 2. The coating according to 1, further comprising one or more of Cu: 0.1% or more and 0.5% or less, Ni: 0.1% or more, and 0.5% or less in mass% Steel material with excellent corrosion resistance.

  According to the present invention, it is possible to obtain a steel material excellent in coating corrosion resistance, in which a defective portion generated in a coating film is prevented from corroding, with a relatively inexpensive component composition, which is extremely useful industrially.

The typical life cycle cost (LCC) figure which shows the effect of this invention. The figure explaining a corrosion acceleration test piece.

In the present invention, the component composition is defined. Hereinafter, the reason for component limitation will be described in detail. In the description,% is mass%.
C
C is added in excess of 0.02% in order to ensure a predetermined strength, but if it exceeds 0.15%, weldability and toughness deteriorate, so it exceeds 0.02% and is 0.15% or less. To do.

Si
Si is added in excess of 0.1% as a deoxidizer and strength improving element during steelmaking. However, if excessively added in excess of 0.7%, the toughness is significantly reduced. 0.7% or less.

Mn
Mn is added in an amount of 0.2% or more in order to ensure a predetermined strength, but if added over 1.5%, a bainite structure is likely to occur, and mechanical properties, particularly toughness, deteriorate. 2% or more and 1.5% or less.

P
In the stage where the rust layer in the initial stage of use is thin, P is easily dissolved out in water as phosphate ions and goes out of the rust layer. Phosphate ions that have come out of the rust layer tend to precipitate iron divalent ions as “rust”, and may cause the piers to become fouled. Therefore, P is limited to 0.03% or less, preferably 0.02% or less from the viewpoint of suppressing flow rust. In the present invention, P is an impurity and the smaller the better, the lower limit is 0.001% in terms of steelmaking cost.

S
If S is added over 0.02%, weldability and toughness deteriorate, so 0.02% or less. In the present invention, S is an impurity, and the smaller the better, but the lower limit is made 0.0001% in terms of steelmaking cost.

Al
Al is added in an amount of 0.01% or more as a deoxidizer during steelmaking, but if added over 0.1%, inclusions that become the starting point of corrosion tend to occur, so 0.01 to 0.1% The following.

Cr
Cr is the most effective element for improving the coating corrosion resistance in this patent, and details are unknown, but it is considered that the adhesion between the coating film and the steel material is improved. If it is less than 0.3%, the effect is small, and if it exceeds 1.0%, the weldability when used as a structure is inferior. Therefore, 0.3% or more and 1.0% or less are added.

One, two or more of W, Sb and Sn have the effect of suppressing the promotion of corrosion by chloride ions entering from the wound. Accordingly, when one or more of W, Sb, and Sn are added, the total content is 0.01% or more and 0.2% or less.

  As described above, excellent coating corrosion resistance can be obtained with the basic component composition of the present invention. However, when improving the coating corrosion resistance, at least one of Cu and Ni is added.

Cu
Cu has the effect of densifying rust and suppressing the progress of corrosion from scratches at 0.1% or more. However, if added over 0.5%, cracks are likely to occur during production. Therefore, when adding, it is 0.1 to 0.5%.

Ni
Ni has an effect of densifying rust and suppressing the progress of corrosion from scratches at 0.1% or more. However, since Ni is an expensive element, the upper limit is 0.5%. 1% or more and 0.5% or less.

  In the present invention, production conditions are not particularly defined. It can be manufactured by conventional methods to steel materials of various shapes such as thick plates, strips, and shaped steel.

  After heating the steel slabs of various component compositions to 1150 ° C., and making a steel plate (plate thickness 6 mm) by hot rolling at a finish rolling temperature of 900 ° C., applying C-5 coating (based on Non-Patent Document 1), The corrosion test piece shown in FIG. 2 was collected. Corrosion test piece 2 is a rectangle of 100 mm t x 50 mm x 6 mm, and a cross cut 1 is made on the C-5 painted surface to create a defective portion. 1200 cycles were performed using a test apparatus (manufactured by Suga Test Instruments Co., Ltd.). The coating corrosion resistance was evaluated as an amount of corrosion (unit: mm) by measuring an average value obtained by measuring 10 swelling widths from the crosscut (corrosion part 3 in the figure).

  JASO-M609-91 is a combined cycle test in which one cycle (8 hr) is composed of salt spray 2 hr-dry 4 hr-wet 2 hr, salt spray conditions are temperature 35 ± 1 ° C., sodium chloride concentration 5 ± 0.5%, The drying conditions were a temperature of 60 ± 1 ° C., a relative humidity of RH20-30%, a wet condition temperature of 50 ± 1 ° C., and a relative humidity of RH of 95% or more.

  Table 1 shows the amount of corrosion along with the chemical components of the test steel. Sample No. 1 to 11 are examples of the present invention. 12 to 25 are comparative examples. In all the examples of the present invention, the corrosion amount is 2.8 mm or less, and the conventional steel (ordinary steel) No. It was confirmed that the amount of corrosion was not more than 0.35 times that of 26. On the other hand, Comparative Example No. 12 to 25 were inferior in corrosion amount to 5.3 mm or more as compared with the examples of the present invention. FIG. 1 schematically shows a life cycle cost (LCC) calculated based on the results of the example. According to the present invention, the life cycle cost (LCC) is significantly reduced.

1 Cross cut 2 Corrosion test piece 3 Corrosion part

Claims (2)

  In mass%, C: more than 0.02%, 0.15% or less, Si: more than 0.1%, 0.7% or less, Mn: 0.2% or more, 1.5% or less, P: 0.00. 001% or more, 0.03% or less, S: 0.0001% or more, 0.02% or less, Al: 0.01% or more, 0.1% or less, Cr: 0.3% or more, 1.0% Hereinafter, a steel material having excellent coating corrosion resistance, further including one or more of W, Sb, and Sn in a total amount of 0.01% or more and 0.2% or less, with the balance being Fe and inevitable impurities.   2. The composition according to claim 1, further comprising one or more of Cu: 0.1% or more and 0.5% or less and Ni: 0.1% or more and 0.5% or less in mass%. Steel material with excellent coating corrosion resistance.

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