JP3265867B2 - Welded structural steel with excellent weather resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welded structural steel excellent in high corrosion resistance and suitable for a welded structural material in a corrosive environment involving salt water, such as a bridge or a steel tower constructed in a coastal area.

[0002]

2. Description of the Related Art Steel structures such as bridges have a service period of several tens of years, and therefore require strict anti-corrosive measures such as strict coating. Painting is a very effective anticorrosion measure, but requires significant repairs due to its significant degradation in air-exposed environments. However, in recent years, there has been a problem that repairs become difficult due to a rise in labor costs and a decrease in the number of painters. To avoid this problem, weather resistant steel is increasingly used for steel structures such as bridges.

[0003] Weather-resistant steel is made of copper,
The corrosion-resistant and stable rust, which is enriched with effective elements such as phosphorus and chromium, covers the surface, so that the progress of corrosion is significantly slowed down. Because of its remarkable weather resistance, bridges made of weather resistant steel are known to withstand decades of service, often without paint. But,
It is known that rust of weather-resistant steel is difficult to stabilize and it is difficult to obtain practical corrosion resistance in an environment where salt content is relatively high, such as in coastal areas or in ballast tanks of ships. In order to produce a steel material that can withstand practical use in such an environment, a method of adding a large amount of an effective element such as copper, phosphorus, chromium, or tungsten is disclosed in, for example, Japanese Patent Publication No. 51-28048 and Japanese Patent Publication No. 57-109.
No. 41, JP-A-3-158436, and JP-A-4-6245.

[0004] In recent years, the results of exposure corrosion tests of weatherable steel at various locations in Japan have been published by the Ministry of Construction. Based on the test results, the Ministry of Construction has concluded that the area in which weather-resistant steel can be used without painting has a salt content of 0.05 m
It provides a guideline for limiting the area to dd and below. That is, even with the above technique, the amount of incoming salt is 0.05 md.
In regions d and above, conventionally produced weatherable steel cannot be used without painting. Also, steel structures such as bridges are constructed by welding, but steels containing a large amount of elements such as copper, phosphorus and chromium have extremely poor weldability. It is necessary to prevent the occurrence of cracks. That is, the conventionally manufactured weather-resistant steel is poor in practicality when used for a welded steel structure constructed in an area having a flying salt content of 0.05 mdd or more.

[0005]

The object of the present invention is to provide a.
It is an object of the present invention to provide a structural steel for welding having high weather resistance in an environment where a salt of not less than 05 mdd and less than 10 mdd flies and having practical weldability.

[0006]

Means for Solving the Problems The present inventors have intensively studied the composition of steel materials to achieve the above object. As a result, by adding Mo together with an appropriate amount of Ni, the weather resistance of the steel material can be significantly improved, and M
It has been found that by limiting the amount of o, welding crack susceptibility can be maintained in a practical range. It has been found that this makes it possible to produce a steel material having both high weather resistance and weldability.

[0007] That is, the first aspect of the present invention relates to the following:
0.15% or less, Si: 0.7% or less, Mn: 0.10
2.00%, P: 0.03-0.15%, S: 0.0
20% or less, Al: 0.010 to 0.10%, Cr:
0.10% or less, Ni: 0.20 to 4.0%, Cu:
It is a coastal weathering steel excellent in weldability , characterized by containing 0.1% or less and Mo: 0.10 to 4.0%, with the balance being Fe and unavoidable impurities.

[0008] The second invention is that C: 0.15% by weight.
Hereinafter, Si: 0.7% or less, Mn: 0.10 to 2.00
%, P: 0.03 to 0.15%, S: 0.020% or less, Al: 0.010 to 0.10%, Cr: 0.10%
In the following, Ni: 0.20 to 4.0%, Cu: 0.1% or less, Mo: 0.10 to 4.0%, the balance being Fe and unavoidable impurities, and further Ni and Mo , N
A coastal weathering steel excellent in weldability , which satisfies the relationship of i + 3Mo ≧ 1.2% and has a carbon equivalent Ceq shown below of 0.5% or less. Ceq = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14

[0009]

The reasons for adding the additional components and the reasons for limiting the range of addition will be described below. C: C is added to secure a predetermined strength.
If it exceeds 15%, the weldability and toughness deteriorate, so the upper limit was made 0.15%. Si: Si is added as a deoxidizing agent and a strength-improving element at the time of steel making, but if added excessively, the toughness is remarkably reduced. Mn: Mn is added in an amount of 0.10% or more in order to secure a predetermined strength. However, if it exceeds 2.00%, the weldability deteriorates. P: P is an important element in the present invention, and has an effect of improving the strength of steel and an effect of improving corrosion resistance. The addition of less than 0.03% has no effect on the improvement of corrosion resistance, and the addition of more than 0.15% deteriorates the weldability.
And S: 0.020% because S is an element harmful to corrosion resistance
It was as follows. Al: Al is added in an amount of 0.010% or more as a deoxidizing agent at the time of steel making. However, if it is added excessively, inclusions serving as corrosion starting points are easily generated.

[0010] Cr: Cr has the effect of improving the corrosion resistance of steel in an environment with a low salt content, and therefore has been positively added to conventionally produced weathering steel.
However, examinations by the present researchers have revealed that Cr has an effect of promoting perforated corrosion in an environment with a high amount of salt. Cr is an element that significantly deteriorates weldability. Therefore, in the present invention, basically, C
It is better not to add r. However, 0.1 as an impurity
%, The effect of the present invention is not impaired, so the upper limit was made 0.10%. Ni: Ni is an important element in the present invention.
Has the effect of improving corrosion resistance in an environment with a high salt content. Addition of less than 0.20% of Ni has no effect, and addition of more than 4% is disadvantageous in terms of economy, so it was set to 0.20% to 4%. Cu: Cu is an element that improves corrosion resistance.
%, The effect saturates and is economically disadvantageous. Mo: Mo is an important element in the present invention,
Has the effect of improving corrosion resistance in an environment with a high salt content. Addition of less than 0.10% has no effect, and addition of more than 4% is disadvantageous in terms of economy, so it was set to 0.10% to 4%.

The effect of Ni and Mo on the corrosion resistance is not clear, but is considered as follows.
Mo is considered to have an effect of increasing the rusting property of rust and preventing corrosion factors such as moisture and salt from coming into contact with the steel surface. On the other hand, Mo has the property of making rust brittle, and defects such as cracks are likely to occur. Ni has the property of improving the property of rust that is easily cracked and making it difficult to generate defects such as cracks. Since a synergistic effect is exhibited by these two different properties, it is considered that by adding Mo together with an appropriate amount of Ni, the corrosion resistance is remarkably improved.

When Mo is added together with 0.20% or more of Ni, the effect of corrosion resistance appears. However, if Ni + 3Mo <1.2%, the effect is not sufficient, so that Mo is limited to Ni + 3Mo ≧ 1.2%.

Further, in order to make the weldability a practical level,
The upper limit of the carbon equivalent (Ceq) was set to 0.5%. That is, Ceq = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14 ≦ 0.5 This invention steel is melted in a converter or an electric furnace and then continuously cast or It is suitable to be manufactured by a method of forming a slab by the ingot-bulking method and then into a steel plate or a shaped steel by rolling, but it can also be manufactured by other methods. In addition, after rolling, it can be manufactured without specifying a processing method such as a method of cooling or accelerated cooling and a method of controlled rolling.

[0014]

EXAMPLE A steel ingot having the composition shown in Table 1 was prepared, a steel plate having a thickness of 3 mm was formed by hot rolling, allowed to cool to room temperature, and the obtained test material was subjected to a combined cycle corrosion test shown in FIG. did. FIG. 2 shows the relationship between the exposure period and the maximum drilling depth created from the results of an exposure test conducted on Miyakojima, Okinawa. Since the amount of incoming salt of Miyakojima in Okinawa is about 0.5 to 1 mdd, it is a standard exposure area in the applicable range of the steel of the present invention. FIG. 3 shows the results of the combined cycle test of the steel H of the present invention. The similarity between the graphs of FIGS. 2 and 3 indicates that the combined cycle test is appropriate as a test replacing the exposure test. That is, those having excellent weather resistance in the combined cycle test are considered to have excellent weather resistance even in an environment where a salt content of 0.05 to 10 mdd flies.

FIG. 4 shows the value of the maximum perforated depth of the test material together with the value of the carbon equivalent by the combined cycle corrosion test . The ratio較鋼N~W the maximum apertured depth is 0.
Corrosion resistance is inferior because of 5 mm or more. Comparative steel X has a relatively small maximum piercing depth and is excellent in corrosion resistance, but has no practical weldability because the carbon equivalent reaches 0.68%. On the other hand, it can be seen that Invention Steels A to M both have good corrosion resistance and good weldability.

[0016]

[Table 1]

[0017]

As is clear from the above examples, according to the present invention, the value of the maximum perforation depth is high, so that it has high weather resistance, and since the carbon equivalent is low, the weldability is maintained. You. Therefore, according to the present invention, 0.05 mdd or more and 1
It is possible to economically produce a structural steel for welding that has high weather resistance in an environment where a salt content of less than 0 mdd comes and has practical weldability.

[Brief description of the drawings]

FIG. 1 is a view showing test conditions of a combined cycle corrosion test.

FIG. 2 is a diagram showing the relationship between the exposure period and the maximum perforated depth created from the results of an exposure test conducted on Miyako Island in Okinawa.

FIG. 3 is a view showing a result of a combined cycle test of the steel H of the present invention.

FIG. 4 is a diagram showing the maximum depth of perforated corrosion of each test material caused by a combined cycle corrosion test.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhito Inohara 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Yoshiaki Shimizu 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan (56) References JP-A-57-2865 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 C22C 38/44 C22C 38/58

Claims (2)

(57) [Claims] C. 0.15% or less by weight, Si:
0.7% or less, Mn: 0.10-2.00%, P: 0.
03-0.15%, S: 0.020% or less, Al: 0.
010 to 0.10%, Cr: 0.10% or less, Ni:
0.20-4.0%, Cu: 0.1% or less, Mo: 0.
Containing from 10 to 4.0%, the balance being excellent in weldability, characterized in that it consists of Fe and unavoidable impurities coast weather
Sex steel. 2. In% by weight, C: 0.15% or less, Si:
0.7% or less, Mn: 0.10-2.00%, P: 0.
03-0.15%, S: 0.020% or less, Al: 0.
010 to 0.10%, Cr: 0.10% or less, Ni:
0.20-4.0%, Cu: 0.1% or less, Mo: 0.
10 to 4.0%, the balance being Fe and unavoidable impurities, and Ni and Mo satisfying the relationship of Ni + 3Mo ≧ 1.2%, and having a carbon equivalent (Ceq) of 0.5 % Or less, which is excellent in weldability. Ceq = C + Si / 24 + Mn / 6 + Cr / 5 + Ni / 40 + Mo / 4 + V / 14