WO2000061829A1 - Atmospheric corrosion resistant steel product - Google Patents

Abstract

A steel product characterized as having a chemical composition which falls within a specific range and satisfies a specific formula which is set forth depending on the use environment for the product. The product is a steel product having excellent atmospheric corrosion resistance which is reduced in the occurrence of flow rust and forms a stable rust having good protecting ability even in an environment wherein much salt is contained in the air, such as a coastal area. Another steel product characterized as having the above chemical composition and also having a specific total amount of A type inclusions and B type inclusions as determined according to JIS G 0555. This steel product, including the portion affected by the heat of welding, has excellent atmospheric corrosion resistance and excellent vibration proof.

Description

 Description Weatherproof steel Technical field

 The present invention relates to a weather-resistant steel material, which can reduce flow rust generation advantageously in an environment having a relatively small amount of salt, such as a mountain area, a rural area, and an industrial area. The present invention relates to steel materials with excellent seismic resistance and shore weather resistance applicable to steel structures such as bridges used in many environments. The term "shore weather resistance" as used in the present invention refers to weather resistance when used in the air in coastal areas. Background art

 1) Environment with relatively low salt content

Weathering steel, which has alloys such as P, Cu, Cr, and Ni added to the steel to improve corrosion resistance in the air, is widely used for structures such as bridges. Weather resistant steel forms rust, which is a stable rust that is hard to penetrate oxygen and water, which cause corrosion, in a few years, and suppresses subsequent corrosion. For this reason, weather-resistant steel does not need to be coated with a weather-proof paint, and is a so-called bare-use highly corrosion-resistant material.

 However, weather-resistant steel requires a long time of several years before stable rust is formed.During that time, flow rust is generated, which impairs the landscape and causes environmental pollution. There was.

To deal with such a problem, for example, JP-A-6-136557 discloses a steel coated with an aqueous solution of chromium sulfate or an aqueous solution of copper sulfate, dried with water, and further coated with an organic resin. Surface treatment methods for materials have been proposed. Further, Japanese Patent Application Laid-Open No. 8-13158 proposes a surface treatment method for a steel material in which an aqueous solution containing aluminum ions is applied, and after drying with water, an organic resin film is further formed.

 However, in the techniques described in JP-A-6-136557 and JP-A-8-13158, although stable rust is grown in a short time, the process is complicated and the surface treatment agent used is expensive. However, the development of weather-resistant steel that does not require surface treatment has been demanded.

 Accordingly, an object of the present invention is to provide a flow-rust-reduced weather-resistant steel material capable of reducing the occurrence of flow rust during the formation of a stable rust in bare weather-resistant steel in order to meet such a demand. I do.

2) A salty environment such as a coastal area

 Since steel structures such as bridges have a long service life, they are generally provided with corrosion protection such as painting. As a result, the coating deteriorates due to choking by ultraviolet rays or rust swelling caused by corrosion under the coating, and the anticorrosion effect gradually decreases. For this reason, repainting has been forced at regular intervals. However, the recent shortage of paint and rising labor costs have made repainting difficult. Under these circumstances, weather resistant steels that do not require the application of heat-resistant paints and can be used naked are increasingly being applied to steel structures.

Weathering steel is a steel material to which P, Cu, Ni, and Cr are added. Under atmospheric conditions, a stable rust that forms a protective film on the steel surface will be formed in several years. Since the stable rust inhibits the further progress of corrosion, corrosion of steel materials is extremely small. Therefore, most are used without painting. However, in a salty environment such as a coastal zone, even weatherproof steel does not form stable rust even after several years, and the corrosion of the steel becomes severe.

 In recent years, the Ministry of Construction has issued a guideline on the application of weathering steel (“Joint Research Report on Application of Weathering Steel to Bridges (XX), 1993.3”, Ministry of Construction Public Works Research Institute, Steel Club,

(Published by The Japan Bridge Construction Association), and in areas where the amount of incoming salt is 0.05 mg / dm ² / day or more, that is, in coastal areas, conventional weathering steel CTIS G 3114: Weathering heat for welded structures Hot-rolled steel) cannot be used without painting.

 Accordingly, in a salty environment such as a coastal zone, a measure is taken by coating ordinary steel with phthalic acid resin, chlorinated rubber, tar epoxy resin, or the like. However, many bridges constructed in the coastal zone near the river mouth are long bridges, and because of the coastal zone, they are extremely corrosive, making repainting work extremely difficult.

 On the other hand, for example, as described above, JP-A-6-136557 has a problem.

 In addition, Japanese Patent No. 2572447, Japanese Patent Application Laid-Open No. 5-51668, and Japanese Patent Application Laid-Open No. 8-134587 disclose that a large amount of alloying elements such as P, Cu, Ni, and Mo are added to steel materials to improve shore weather resistance. A method has been proposed.

However, even if it is a bridge, the corrosive environment of steel is not always the same depending on the place where it is used. For example, considering a four-main girder bridge, the outside of the girder is exposed to rainfall, dew condensation, and sunshine, but the inside of the girder is exposed only to dew condensation, and there is no rainfall. In general, in a clean environment with almost no incoming salt, etc., it is said that the amount of corrosion is smaller inside the girder than inside the girder. On the other hand, in environments with high incoming salt, it is said that corrosion is greater inside the girder than outside the girder. This reversal occurs at a certain amount of incoming salt, but the amount has not been determined. The outer girder, main girder, web, etc. are exposed to two environments (with and without rain) simultaneously (on the back of the plate, on the front), and are used for steel structures such as bridges. The steel used must maintain high weather resistance in both environments.

 However, in the conventional technology, evaluation was performed only in one environment (with or without rain), and it was desired to develop a steel material having excellent coastal weather resistance in two environments at the same time. .

3) Earthquake resistance

On the other hand, from the viewpoint of safety, this type of structural steel material used for bridges, etc., includes a steel material in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction) in one-fifth of the Charpy impact test. It was required that the absorbed energy be 47 J or more. However, in the case of a large earthquake such as the Great Hanshin-Awaji Earthquake, depending on the structure and location of the structure, it was found that high stress may act in the plate thickness direction (Z direction) of the members used. Since the Great East Japan Earthquake, structural steel materials have been required to have improved toughness in the thickness direction (Z direction), including the heat affected zone, in order to further increase the seismic resistance of the steel materials. From the viewpoints of 1) to 3), the present invention provides a stable rust with good protection in an area with a relatively high salt content such as an area with a relatively low salt content and in a salty environment such as a coastal zone, irrespective of the presence of rain. An object of the present invention is to provide a steel material that can be formed, has excellent weather resistance, and has improved toughness in the Z direction including the heat-affected zone in weldability and has excellent earthquake resistance. Disclosure of the invention

 1) Flow rust reducing weathering steel

 The present inventors have diligently studied measures to reduce the flow rust of weathering steel, and as a result,

By adding B and adjusting the B content and the content of one or more of P, Cu, Ni, Cr, and Mo based on a certain correlation, the amount of flow rust can be dramatically reduced. It has been found that a weather-resistant steel material can be obtained.

The present invention has been made based on this finding, and has as its gist the weight _{^{0/0, C: 0.001 ~0.050}} %, Si: 0.60% or less, Mn: 0.50~3.00%, S: 0.01% or less, A1: 0.10% or less, B: 0.0003-0.0050%. : 0.005 to 0.15%, Cu: 0.1 to 2.0%, Ni: 0.1 to 6.0%, Cr: 0.005 to 1.0%, o: 0.005 to 1.0% And the following (1)

(20P + 3Cu + 3Ni + 6Cr + Mo) / (1-0.2 (10000 B) ⁰ · ⁴ ) ≥18 …… (1) [where, P, Cu, Ni, Cr, Mo, B: content of each element (% By weight)]

The present invention is directed to a weathering resistant steel material with reduced flow rust, characterized in that the steel material has a composition of Fe and inevitable impurities.

 In the present invention, one or more selected from Nb: 0.005 to 0.20%, Ti: 0.005 to 0.20%, and V: 0.005 to 0.20% by weight in addition to the composition. May be contained.

 Further, in the present invention, one or two selected from Ca: 0.02% or less and REM: 0.02% or less by weight% may be further contained in addition to the above composition.

2) Coastal weathering steel The present inventors have conducted intensive studies in order to improve coastal weather resistance, and as a result, have found that Cr deteriorates weather resistance in an environment containing a large amount of salt. In addition, the present inventors adjust the B content and the content of one or more of P, Cu, Ni, and Mo in relation to the amount of incoming salt, so that in a salty environment such as a coastal zone. However, they found that a steel material with excellent weather resistance could be obtained.

3) Compatibility with earthquake resistance

 Furthermore, the present inventors have found that the toughness in the Z direction is greatly affected by the total amount of inclusions of the A-type and B-type inclusions, even in the case of inclusions, and was derived based on JIS G 0555. It was found that the toughness in the Z direction was significantly improved by setting the total (dA + dB) value of the amounts of the A-type inclusions and the B-type inclusions to not more than 0.030%.

 First, regarding the relationship between the toughness in the Z direction and the amount of inclusions, the results of experiments performed by the present inventors will be described.

 Steel with various shapes and amounts of inclusions was melted and hot-rolled to form a 60-thick steel plate. From these steel plates, specimens for microscopic observation and Z-direction Charpy impact test specimens (JIS No. 4 test specimens) were sampled, and the form and amount of inclusions and the toughness (absorbed energy) in the Z direction were measured.

 Figure 1 shows the sum (dA + dB) of the amounts of A-based inclusions and B-based inclusions derived based on the provisions of JIS G 0555, and the Charpy absorbed energy in the Z direction at 15 (VE-5) Shows the relationship. The Charpy impact test used ten test pieces for each steel sheet. In the figure, the average value and the minimum value of 10 lines are plotted respectively.

From Fig. 1, if the (dA + dB) value is less than 0.030%, the absorbed energy at 15 ^ C including the lowest value is 47J or more, indicating high toughness in the Z direction. On the other hand, (d When the (A + dB) value exceeds 0.030%, a low value appears at the lowest value, and the average value also falls below 47J.

Fig. 2 shows the relationship between the C-based inclusion amount dC value derived based on the provisions of JIS G 0555 and the Charpy absorbed energy (vE-s) in the Z direction at -5. Fig. 2 shows the relationship between the dC value and vE- ₅ for steel plates with high (dA + dB) values in the range of 0.021% to 0.028%, which showed high Z-direction toughness in Fig. 1.

 From Fig. 2, it was not recognized that the C-based inclusion amount dC value had any particular effect on the toughness in the Z direction.

 Therefore, the present inventors have found that it is important to adjust the total (dA + dB) value of the A-based inclusions and the B-based inclusions in order to improve the toughness in the thickness direction. Got a look. In particular, it was found that setting the (dA + dB) value to 0.030% or less significantly improved the toughness in the thickness direction.

 Figures 1 and 2 show findings from coastal weathering steels, but similar results were obtained for flow rust reducing weathering steels (Figures 3 and 4).

 The present invention has been completed based on the above findings. BRIEF DESCRIPTION OF THE FIGURES

Figure 1

 4 is a graph showing the relationship between the toughness in the Z direction and the sum of the amounts of A-based inclusions and B-based inclusions in a coastal weathering steel.

dC = 0 ~ 0.020%

〇: Average, ·: Lowest

Figure 2 This is a graph showing the relationship between the toughness in the Z direction and the amount of C-based inclusions in coastal weathering steel.

dA + dB = 0.020〜0.028%

〇: Average value, K: Lowest value

Fig. 3

 3 is a graph showing the relationship between the toughness in the Z direction and the sum of the amounts of A-based inclusions and B-based inclusions in environmentally weatherable steel having relatively low salt content.

dC≤0.02%

 〇: Average value, 鲁: Lowest value

Fig. 4

 4 is a graph showing the relationship between the toughness in the Z direction and the amount of C-based inclusions in environmentally weatherable steel having relatively low salt content.

dA + dB = 0.020〜0.028%

〇: Average value, Hata: Lowest value

Fig. 5

 6 is a graph showing the relationship between the amount of flow rust and the A value (the value on the left side of equation (1)) in environmentally weatherable steel with relatively low salt content.

BEST MODE FOR CARRYING OUT THE INVENTION

 First, the reasons for limiting the components of the steel material of the present invention will be described.

1) C: 0.001 to 0.050%

C is an element that increases the strength of steel.To obtain the desired strength, 0.001% Although the above content is required, if the content exceeds 0.050%, the toughness deteriorates. Therefore, in the present invention, the content is limited to 0.001 to 0.050%.

 The content is preferably 0.005 to 0.030%. Further, the content is preferably 0.005 to 0.025%.

 2) Si: 0.60% or less

 Si acts as a deoxidizing agent and further increases the strength of steel. However, if contained in a large amount, it deteriorates toughness and weldability, so it was limited to 0.60% or less. In addition, it is preferably 0.15 to 0.50%.

 3) Mn: 0.50 ~ 3.00%

 Mn is an element that greatly contributes to the increase in strength and toughness of steel.In order to secure desired strength, Mn needs to be contained at 0.50% or more in the present invention. Therefore, the weldability was adversely affected, so the range was limited to 0.50 to 3.00%. In addition, it is preferably 0.50 to 1.80%.

 4) S: 0.01% or less

 S is limited to 0.01% or less because it deteriorates the weather resistance and further deteriorates the weldability and toughness.

 In particular, it is preferable to limit the content to 0.005% or less in order to increase the amount of the A-based inclusions, and particularly to decrease the toughness in the thickness direction and to deteriorate the weather resistance.From the viewpoint of toughness, the content is preferably set to 0.003% or less. .

 5) A1: 0.10% or less

 A1 acts as a deoxidizing agent, but if it exceeds 0.10%, it adversely affects weldability, so the upper limit was set to 0.10%.

A1 is added as a deoxidizing agent, but if it exceeds 0.10%, aluminum Due to the formation of nascluster, B-based inclusions increase, leading to a decrease in toughness in the thickness direction. Therefore, A1 is preferably limited to 0.10% or less, and from the viewpoint of toughness, is preferably set to 0.05% or less.

 6) B: 0.0003 to 0.0050%

 B is an element that improves hardenability and further improves weather resistance, and is an important element in the present invention. Such an effect is recognized at a content of 0.0003% or more, but an effect commensurate with the content cannot be expected if the content exceeds 0.0050%. Therefore, B is limited to the range of 0.0003 to 0.0050%. Preferably, it is in the range of 0.0003 to 0.0030%.

 The details of the mechanism by which B improves the weather resistance are not clear, but are generally considered as follows.

 Generally, in order to reduce flow rust, it is necessary to generate rust from ground iron at an early stage and to further refine the rust. The purpose of densification is to improve the anti-corrosion effect of the rust layer and to improve the adhesion of the rust layer to the base steel. It is considered that the rust particles adhere to the ground iron due to the anchor effect. Therefore, the denser the rust particles, the greater the anchor effect. By the way, the rust particles formed by the anodic dissolution of iron due to rainfall and dew condensation water are coarsened by water and become denser as the pH rises. This suggests that B raises the pH of the submerged rust layer and promotes the densification of rust particles.

 7) P: 0.005 to 0.15%

P is an element that promotes anode dissolution in the initial stage of corrosion of ground iron and densifies rust particles.In the present invention, P is preferably contained positively, but if the P content is less than 0.005%, These effects are not observed. Over 0.15% In this case, the effect of improving the weather resistance is saturated, and the weldability further deteriorates. For this reason, P is preferably limited to the range of 0.005 to 0.15%. Incidentally, the content is preferably 0.010 to 0.120%.

 8) Cu: 0.1 to 2.0%

 Cu also has the same effect as P. In other words, it is an element that promotes anode dissolution in the early stage of corrosion of ground iron and densifies rust particles. However, if the Cu content is less than 0.1%, the effect is small. On the other hand, if the Cu content exceeds 2.0%, the hot workability is impaired and the effect of improving weather resistance is saturated, which is economically disadvantageous. Therefore, the Cu content is preferably in the range of 0.1 to 2.0%. Preferably, it is in the range of 0.1 to 1.5%.

 9) Ni: 0.1 to 6.0%

 Ni densifies rust particles and improves weather resistance, but less than 0.1% has little effect. On the other hand, if the content exceeds 6.0%, the effect is saturated and no effect commensurate with the content is recognized, which is economically disadvantageous. For this reason, Ni is preferably in the range of 0.1 to 6.0%. The range is preferably 0.1 to 3.5% from the viewpoint of weather resistance.

 10) Cr: 0.005 to 1.0%

 Cr is an element that improves the weather resistance in a low salt environment. The effect is small when the content is less than 0.005%. On the other hand, if the content exceeds 1.0%, the effect of improving the weather resistance saturates and becomes economically disadvantageous. Therefore, the Cr content is preferably in the range of 0.005 to 1.0%.

 As described in the disclosure of the invention, Cr is not actively added in an environment containing a large amount of salt because Cr deteriorates the weather resistance.

 11) Mo: 0.005 to 1.0%

Mo improves weather resistance and further increases strength, but contains less than 0.005% Then the effect is small. On the other hand, if the content exceeds 1.0%, the effect is saturated and no effect commensurate with the content is recognized, which is economically disadvantageous. Therefore, Mo is preferably in the range of 0.005 to 1.0%. In addition, a range of 0.005 to 0.5% is preferable from the viewpoint of toughness.

12) Limited composition formula (1)

 ① Environment with relatively low salt content

 In the present invention, the above-described effects are exhibited by selecting one or more of the five elements of P, Cu, Ni, Cr, and Mo, and including them in the above ranges. However, these five elements have the following formula (1) in relation to B

(20P + 3Cu + 3Ni + 6Cr + Mo) / (1-0 · 2 (10000B) ⁰ · ⁴ ) ≥18 …… (1) [Here, Ρ, Cu, Ni, Cr, Mo, B: content of each element Amount (% by weight)]

It is necessary to adjust the content so as to satisfy the following. As a result, the amount of generated flow rust can be significantly reduced.

For example, Fig. 5 shows the results obtained from a one-year atmospheric exposure test in a rural area using weather-resistant steel sheets having various compositions, and the horizontal axis shows the value (A value) on the left side of equation (1). The vertical axis plots the amount of flow rust (Fe ²⁺ ) from the test piece. As is clear from this figure, setting the A value to 18 or more reduces the amount of flow rust. To be reduced.

 (2) Environments with high salt content such as coastal areas

 In the present invention, the B content and the content of one or more of P, Cu, Ni, and Mo are determined by the following formula (1) in relation to the amount of incoming salt.

(IIP +4. OCu + 3. LNi + 2.6Mo) Bruno ^{(1- 0.1 (10000B) 0 ·} 3 5) ≥ 1 + 13X

… (1)

(Where, P, Cu, Ni, Mo, B: content (% by weight) of each element, X: flying salt content (mg / dm ² / day))

Adjust to satisfy.

 By adjusting the content of B and the content of one or more of P, Cu, Ni, and Mo to satisfy equation (1), coastal areas with high incoming salt The weather resistance in the above is remarkably improved. In addition, by adjusting the B, P, Cu, Ni, and Mo contents according to the incoming salt content X, the steel material becomes compatible with the corrosive environment (flying salt content X), and contains unnecessary alloying elements. It is economically advantageous because it can be prevented.

 Left side of equation (1)

A = (II P + 4.OCu + 3.lNi + 2.6Mo) / (1 -0.KlOOOOB) ⁰ ■ ^{3 5} ) is the right side of equation (1)

 B = 1 + 13X

If it is smaller than that, that is, if A <B, it indicates that the effect of deterioration of corrosion resistance due to flying salt is greater than the effect of improving corrosion resistance due to alloying elements. In order to overcome the corrosion resistance deterioration effect of flying salt and improve weather resistance, it is necessary to adjust the contents of B, P, Cu, Ni and Mo so that A> B. In the present invention, when there is an element that is not added among the alloy elements in the formula (1), the content of the element is calculated as 0. X is the amount of incoming salt measured by the JIS Z2381 gauze method.

 13) Nb: 0.005 to 0.20%, Ti: 0.005 to 0.20%, V: 0.005 to 0.20%, one or more selected from

Nb, V, and Ti are elements that increase the strength of steel, and one or more of them can be added as necessary. Nb, V, and Ti all show an effect at a content of 0.005% or more, but the effect saturates when they are contained at more than 0.20% each. For this reason, Nb, V, and Ti are each desirably 0.005 to 0.20%.

 14) Ca: 0.02% or less, REM: 1 or 2 types selected from among 0.02% or less REM and Ca have an effect of improving weldability and can be added as necessary. Both REM and Ca are effective when added at 0.0005% or more, but the upper limit is set at 0.02%, because a large amount will degrade the cleanliness of the steel.

 15) Other balance Fe and inevitable impurities

 ① Environment with relatively low salt content

 In addition, the steel material of the present invention is composed of the balance of Fe and inevitable impurities, and N: 0.010% or less and O: 0.010% or less are inevitable as inevitable impurities.

 (2) Environments with high salt content such as coastal areas

 Similarly, as unavoidable impurities, Cr: 0.1% or less, N: 0.010% or less, and O: 0.010% or less are acceptable. Cr is an element that improves corrosion resistance and is added to currently marketed weathering steels. However, this is the case in an environment with a low salt content, especially in a region with a high amount of incoming salt such as a coastal zone, which is an element that decreases the weather resistance, and is not intentionally added in the present invention. However, as inevitable impurities, up to 0.1% is acceptable.

 16) (dA + dB) value: 0.030% or less

 In the present invention, in addition to the limitation of the chemical components described above, considering the seismic resistance, from the viewpoint of securing the toughness in the Z direction (absorbed energy in the Charby impact test) of -5 to 47 J or more, the specification of JIS G 0555 is adopted. The total (dA + dB) value of the amount of A-based inclusions and the amount of B-based inclusions derived on the basis of is set to 0.030% or less.

Here, the A-based inclusions are those viscously deformed by processing, and the B-based inclusions are those in which the granular inclusions are arranged discontinuously in a group in the processing direction. In addition, The c-type inclusions (inclusions that are irregularly dispersed without viscous deformation) are included in the classification.

 By setting the (dA + dB) value to 0.030% or less, the toughness in the Z direction is significantly improved. It is considered that the inclusions of the A system and the B system are sensitive sources of stress and affect the toughness in the Z direction. The decrease in the amount of inclusions (dA + dB) in the A and B systems can be reduced by reducing the number of stress concentration sources, especially by reducing the (dA + dB) value to less than 0.030%. Therefore, it is considered that the toughness in the Z direction is significantly improved. In addition, the reduction of the (dA + dB) value improves corrosion resistance. This is thought to be because the decrease in the amount of inclusions suppresses local corrosion occurring from the interface between the base and the inclusions.

17) Manufacturing method

 The method for producing the steel material of the present invention will be described.

 The steel material of the present invention is smelted by a commonly known smelting method such as a converter method or an electric furnace method, and is made into a steel material by a continuous forming method or an ingot-making method. In the smelting process, vacuum degassing and the like may be performed. Next, these steel materials are heated in a heating furnace or the like, or are directly rolled to a desired shape by hot rolling without heating. The steel material of the present invention includes a thick steel plate, a thin steel plate, a steel bar, a section steel, and the like. Example 1

Steels having the chemical compositions shown in Table 1 were melted in a converter, slabs were formed by a continuous production method, and these slabs were heated and then hot-rolled into steel plates having a thickness of 25 mm and a width of 2500 thighs. The tensile properties and impact properties of these steel sheets were investigated. In addition, as weldability, a heat cycle of 100 kJ m was applied to the weld heat affected zone and a reproducible heat cycle equivalent to 1 band was given. To determine the absorption energy _V E _ ₅ of ruby impact test. The results are shown in Table 2. Corrosion test pieces of 5 thighs x 50 marauders x 100 mm were collected from these steel plates. These test pieces were subjected to an air exposure test after shot blasting. In the air exposure test, a rural area with a flying salt content of 0.02 _mg / dm ² / day was selected, and each test piece was placed at a 30 ° angle from the ground to the south and exposed for one year. Simultaneously, the flow rust from the test piece was received in a plastic tank, and the flow rust (Fe + ² ) amount was measured. After the exposure test, the rust layer formed on the surface of the ground steel was removed, the weight loss of the test piece was measured, and the result was converted to the thickness loss. The results are shown in Table 2.

 The examples of the present invention (steel types Nos. 1 to 11) are excellent in both toughness and weldability. On the other hand, the toughness and weldability of the comparative example (steel type Nos. 12 to 21) and the conventional example (steel type No. 22) are as follows. , 17, 18), but has the same characteristics as those of the example of the present invention.

The flow rust amount of the present invention example (steel type Nos. 1 to 11) is as low as 29 to 67 / xg / cra ^2, and the A value is low without adding B. It is 420 / zg / cm ^{2 of the} conventional example (steel type No. 22). In addition, the thickness reduction of the present invention example is 8 to 23 // m, which is smaller than 38 m of the conventional example, and the steel material of the present invention has excellent weather resistance. You can see that it is.

On the other hand, the flow rust amount of the comparative examples (steel types Nos. 12 to 16, 20, and 21) out of the range of the present invention is 300 to 390 μg / cm ² , which is larger than that of the present invention examples. In other words, No. 12 has too low P content and A value, No. 13 has too high S content and A value too low, No. 14 has too low Cu content and A value, and No. 16 In both cases, the B content and A value are too low. In Nos. 20 and 21, the A value is too low, and the flow rust amount is large in both cases. In the comparative example (steel type No. 17) where the P content is too high and the comparative example (steel type No. 18) where the Cu content is too high, the weather resistance (flow rust amount, sheet thickness reduction amount) is not significant. Invention examples and Comparative Example (Steel type N

In the case of 0.19), although the weather resistance, toughness and weldability can be compared with those of the present invention, the strength is too high and the elongation is small. Example 2

 Steels with the chemical components shown in Table 3 (Tables 3-1 and 3-2) were melted in a converter and made into slabs by a continuous production method. After heating these slabs, they were hot rolled into 25mm thick x 2500mm wide steel sheets. In addition to some steel sheets, H-sections of 800 X 400 X 16 X 36 size were also manufactured by hot rolling.

 The tensile properties and impact properties of these steel sheets and H-section steels were investigated. In addition, the specimens were sampled at the center of the plate thickness (l / 2t part) in the L and Z directions for steel plates, and for the H-section steel, the center of the plate thickness of the 1/4 flange (l / 2t part). L direction and Z direction. The Charpy impact test specimen in the thickness direction (Z direction) was sampled so that the steel plate was pressed against the front and back surfaces of the steel plate to increase the thickness to 55 thighs, and the notch portion became l / 2t. The pressure welding was carried out under conditions that took care not to change the structure and properties of the l / 2t part.

Furthermore, for a test piece (Z direction) to which a repetitive heat cycle equivalent to 1 orchid was applied to a heat-affected zone of 100 kJ / cm welding heat input, the absorbed energy of vE- ₅ in a Charpy impact test at 15 mm was determined, and the weldability was determined. evaluated.

In addition, corrosion test specimens of 5mra X 50mm X 100mm were sampled from these steel sheets and H-section steels, shot blasted, and subjected to an atmospheric exposure test to evaluate weather resistance. In the atmospheric exposure test, a rural area with a flying salt content of 0.01 rag / dm ² / day was selected, and each test piece was placed at a 30 ° angle from the ground to the south and exposed for one year. At the same time from the specimen Was measured for the amount of flow rust (Fe ^{2 +} ). After the exposure test, the rust layer formed on the surface of the ground iron was removed, the weight loss of the test piece was measured, and the result was converted to the thickness loss.

 The test results are shown in Table 4 (Table 4-1 and Table 4-2).

The examples of the present invention (steel materials Nos. 1 to 17) have high toughness of vE- ₅ : 61 J or more including toughness in the Z direction. Further, the examples of the present invention are excellent in weather resistance evaluated by the amount of reduction in thickness and the amount of flow rust. The flow rust amount of the present invention example (steel material No. 1 to steel material No. 17) is as small as 25 to 68 μg / cm ^2, and is smaller than the flow rust amount of the conventional example (steel material No. 26) of 420 μg / cm ² . Thus, it can be seen that the steel material of the present invention has excellent weather resistance. On the other hand, the comparative examples (steel materials Nos. 18 to 26) out of the scope of the present invention have low one of the properties of toughness in the Z direction, HAZ toughness (weldability), and weather resistance. Not suitable. Example 3

 Steel with the chemical composition shown in Table 5 was melted in a converter and converted into a slab by a continuous production method. After heating these slabs, they were hot rolled into 25rara thick X2500ram wide steel plates or 800 X400 X 16 X 36 size H-sections.

 For these steel sheets and H-section steels, the amount of inclusions, tensile properties and impact properties were investigated in accordance with the provisions of JIS G 0555. The specimen was sampled at the center of the plate thickness (l / 2t portion) (L direction) for steel plates and at the 1 / 4B flange (l / 2t portion) (L direction) for H-beams. .

A Charpy impact test in the thickness direction (Z direction) was also performed. The Charpy impact test specimen in the thickness direction (Z direction) was sampled so that the steel plate was pressed against the front and back surfaces of the steel plate, the thickness was increased to 55 thighs, and the notch became 1 / 2t. In the case of pressure welding, The test was conducted under the condition that the structure and properties of l / 2t part did not change.

Also, heat input 100kJ N m HAZ lmm equivalent imparted with simulated heat cycle test specimens for (Z-direction), obtains the absorbed energy VE_ ₅ of Charpy impact test in an 5 ° C, were evaluated weldability.

 The survey of the amount of inclusions is derived based on the provisions of JIS G 0555 (dA + d

B).

 Also, corrosion test specimens of 5mra X 50 marauder X lOOram were collected from these steel sheets and H-section steels, shot blasted, and subjected to an atmospheric exposure test to evaluate the weather resistance.

In the air exposure test, a coastal area with a flying salt content of 0.8 mg / dm ² / day measured by the JIS Z2381 gauze method was selected, and the ground iron surface of each test piece was placed horizontally upward with no rainfall. And exposed for one year. After the air exposure test, the rust layer formed by the exposure was removed, and the thickness reduction was measured from the weight loss before and after the test. Table 6 shows the test results.

The sheet thickness reduction of the example of the present invention is 6 to 32; zm, which is remarkably smaller than the sheet thickness reduction (143 μπι) of the comparative example (commercially weatherable steel, steel material No. 19). Shows weather resistance. Direction toughness Ζ of the present invention example, weldability of the present invention example VE_ ₅ indicates a more excellent earthquake resistance 59J are all excellent, including the vE of weld heat affected zone is 169J or more, the weld It shows earthquake resistance. Further, the example of the present invention has a low yield ratio YR of 76% or less, and is excellent in earthquake resistance.

 On the other hand, the comparative examples outside the scope of the present invention all have a large amount of reduction in sheet thickness, and have reduced shore weather resistance, or have deteriorated toughness in the Z direction.

The sheet thickness reductions of the steel materials No. 11, No. 13, No. 14, No. 15, and No. 17 of the comparative example are much larger than the sheet thickness reductions of the present invention example, and the weather resistance is deteriorated. . The thickness reduction of steel material No. 12 is the same as that of the present invention, but the inclusion (dA + dB) value is as high as 0.074%, and the toughness in the Z direction is as low as 10E of vE- ₅ : 10J. Is declining. In addition, the steel sheet No. 16 with a high P content has the same reduction in sheet thickness as the example of the present invention and has excellent shore weather resistance, but the toughness in the Z direction is as low as vE- ₅ : 33J and the seismic resistance is low. decreased, the toughness of the HA Z portion in Luo, vE_ _5: 31J as low weldability is degraded.

 Further, in steel material No. 18 in which Ni is out of the range of the present invention, although the thickness reduction is small, the strength TS: 926 MPa is too high. Example 4

 Steels with the chemical components shown in Table 7 were melted in a converter, converted into slabs by continuous forming, heated, and then hot-rolled to form a 25 mm thick x 2500 mm wide steel plate or 800 400 x 16 x 36 The size was H-shaped steel.

 For these steel sheets and H-section steels, the amount of inclusions, tensile properties and impact properties were investigated in accordance with the provisions of JIS G 0555. The specimens were sampled at the center of the plate thickness (l / 2t section) (C direction) for steel plates, and at the 1 / 4B flange (1 / 2t section) (L direction) for H-section steels. did.

 A Charpy impact test in the thickness direction (Z direction) was also performed. The Charpy impact test specimen in the thickness direction (Z direction) was sampled so that the steel plate was pressed against the front and back surfaces of the steel plate to increase the thickness to 55 thighs, and the notch became 1 / 2t. The pressure welding was carried out under conditions that took care not to change the structure and properties of the l / 2t part.

Also, heat input 100kJ N m HAZ lmm equivalent imparted with simulated heat cycle test specimens for (Z-direction), obtains the absorbed energy VE_ ₅ of Sharubi one impact test in an 5 ° C, were evaluated weldability . In addition, in the survey of the amount of inclusions, (dA + dB) was derived based on the provisions of JIS G 0555.

 In addition, corrosion test specimens of 5 mm x 50 ram x 100 mm were sampled from these steel sheets and H-section steels, shot blasted, subjected to an atmospheric exposure test, and weather resistance was evaluated.

In the air exposure test, a seashore area with a flying salt content of 0.45 mg / dm ² / day was selected by the JIS Z2381 gauze method, and the ground iron surface of each test piece was placed horizontally and upward under conditions without rain. And exposed for one year. After the air exposure test, the rust layer formed by the exposure was removed, and the thickness loss was measured from the weight loss before and after the test.

 Table 8 shows the test results.

The sheet thickness reduction of the present invention example is 14 to 40 / xm, which is significantly smaller than the sheet thickness reduction a05 / xm) of the comparative example (commercial weathering steel, steel material N 0.2-16), which is excellent. Shows coastal weather resistance. In addition, the toughness in the Z direction of the present invention example is excellent in earthquake resistance with vE of 70 J or more. Moreover, weldability of the present invention example are all the VE_ ₅ of the welding heat affected zone is shown and more than 292 J, the excellent earthquake resistance. In addition, in the present invention example, the yield ratio YR is also

Low, less than 80%, and excellent in earthquake resistance.

 On the other hand, the comparative examples outside the scope of the present invention all have a large amount of reduction in sheet thickness, and have reduced shore weather resistance, or have deteriorated toughness in the Z direction.

 In Comparative Examples of steel materials No. 2-11, o. 2-13, No. 2-14, and No. 2-15, the A value was out of the range of the present invention due to insufficient adjustment of the alloy content. Since the corrosion resistance deteriorated due to the amount of salt, the amount of reduction in sheet thickness was larger than that of the present invention, and the weather resistance was deteriorated.

In the steel No. 2-12 of the comparative example, the thickness reduction was almost the same as that of the steel of the present invention, but the amount of inclusions was large (dA + dB), and the value was higher than 0.030%. Toughness decreases There is a problem with earthquake resistance.

 As described above, the steel material of the present invention is a steel material having excellent weather resistance (shore weather resistance) for coastal areas having a large amount of flying salt, and excellent in toughness in the Z direction including a welded portion, and excellent in earthquake resistance. It can be seen that it is suitable as a steel material for steel structures.

Industrial applicability

 According to the present invention, it is possible to provide a weather-resistant steel material having excellent earthquake resistance and reduced flow rust. When these steel materials are used for structures such as bridges, painting, surface treatment, etc. can be omitted, and the economic effect of reducing maintenance costs can be expected.

In addition, in a salty environment such as a coastal zone, stable rust with good protection can be formed, and it is possible to produce steel with excellent coastal weather resistance and excellent seismic resistance including weldable heat-affected zone at low cost. Can be manufactured. The steel material of the present invention can omit painting, surface treatment, and the like even in an environment with a high salt content such as a coastal zone, can be expected to have an economic effect of reducing maintenance costs, and has a remarkable industrial effect.

Table 2

Chemical composition (wt%) c Si Un p s Al Cu Ni Cr B its lib A cardlia

o 0.016 0.31 1.03 0.005 0.0028 0.029 0.70 0.15 0.50 0.0019 16.1

 P 0.016 0.30 1.02 0.063 0.0025 0.031 0.35 0.25 0.46 0.0019 16.6

 Q 0.014 0.29 1.06 0.009 0.0030 0.031 0.01 0.0018 0.7

 R 0.025 0.28 1.35 0.064 0.0080 0.029 0.50 0.45 0.45 0.0020 20.3

 S 0.052 0.26 1.05 0.020 0.0025 0.032 0.63 0.26 0.50 0.0024 21.2

 T 0.026 0.36 1.39 0.220 0.0018 0.032 0.60 0.0025 29.1

 U 0.011 0.36 1.39 0.070 0.0028 0.023 0.70 0.10 0.51 0.0009 Mo: 0.20 13.6

 V 0.013 0.35 1.34 0.068 0.0030 0.024 6.37 0.52 0.0008 43.6

W 0.110 0.40 1.05 0.014 0.0050 0, 025 0.35 0.15 0.50 4.8

Steel type #i Inclusions 候 Weather resistance Tensile properties Toughness Weldability Remarks

No. No. dA + dB dC (dA + dB + dC) Flow rust Plate thickness Yield strength Tensile strength vE-5 vE-5

 (Fe2 +) 减 small amount YS TS L direction Z direction

(tX) (wtX) (wt¾) (/ zg / cm ² ) (μ ιη) (MPa) (MPa) (J)

 1 Sales board A 0.029 0.000 0.029 68 23 455 571 383 73 Zo Example of the present invention

2 H-section steel 0.027 0.000 0.027 66 22 432 566 292 66

3 Steel sheet B 0.026 0.000 0.026 62 21 450 564 394 91 Example of the present invention

4 Steel plate C 0.023 0.000 0.023 64 26 438 546 395 105 Example of the present invention

5 H-type copper 0.025 0.000 0.025 64 27 411 563 341 80 Example of the present invention

6 Steel plate D 0.025 0.043 0.068 65 11 441 554 381 92 Example of the present invention

7 Copper plate E 0.015 0.000 0.015 37 25 438 539 406 124 077 Example of the present invention

8 Steel plate F 0.028 0.000 0.028 56 22 440 552 389 83 261 Example of the present invention

9 Pan plate G 0.007 0.012 0.019 58 11 439 528 421 146 292 Example of the present invention

10 H shape promotion 0.009 0.016 0.025 60 13 408 528 399 138 Example of the present invention

11 Sales board H 0.023 0.000 0.023 48 16 483 574 408 88 300 Example of the present invention

12 Copper plate I 0.027 0.000 0.027 52 15 485 588 391 61 284 Example of the present invention

13 Steel plate J 0.010 0.012 0.022 39 11 534 645 356 68 273 Example of the present invention

14 Plate K 0. 019 0. 021 0. 040 57 5 477 573 409 90 278 Example of the present invention

15 Plate L 0.005 0.003 0.008 30 13 442 519 406 153 308 Example of the present invention

16 Steel plate M 0.005 0.007 0.012 32 9 474 568 359 200 270 Example of the present invention

17 Steel plate N 0.007 0.000 0.007 25 27 452 542 383 108 263 Example of the present invention

鐦 Material Type Steel Inclusion 邐 Weather resistance Pull 31 Property Toughness Weldability Remarks

No. No. dA + dB dC (dA + dB + dC) Flow rust Sheet thickness Yield strength Tensile strength vE-5 vE-5

 ,

(Fe reduction YS TS L direction Z direction HA Z wt% wt% wt% (/ xg / cm 2) (/ m) (MPa) (MPa) (J) (J) (J)

18 Sales board 0 0.028 0.000 0.028 81 26 449 520 400 86 306 Comparative example

19 Copper plate P 0.029 0.000 0.029 78 30 429 535 414 87 267 Comparative example

20 Steel plate 9 0.028 0.000 0.028 200 717 387 437 428 92 339 Comparative example

00 21 Steel plate R 0.048 0.000 0.048 63 23 454 570 379 18 238 Comparative example

22 Copper plate S 0.029 0.000 0.029 65 26 449 516 406 36 110 Comparative example

23 Steel plate T 0.023 0.000 0.023 42 31 400 608 269 21 33 Comparative example

24 Steel plate U 0.029 0.000 0.029 97 21 453 572 379 78 230 Comparative example

25 Steel plate V 0.031 0.000 0.031 27 5 710 932 105 20 111 Comparative example

26 Steel plate W 0.048 0.000 0.048 420 38 365 505 380 20 50 Conventional example

Table 6

 Steel material Inclusion amount (wt! Weather resistance Tensile property Toughness Weldability Remarks

No. Thickness Yield strength Tensile strength Yield ratio L direction Z direction HA Z

 Birch decrease 1> 县

 Heavy

 dA + dB dC dA + dB + dC YS TS YR vE-5 vE-5 vE-5 *

 (MPa) (MPa) (MPa) 0) (J) (J)

1 sale board 0.028 0.000 0.028 19 488 681 72 277 60 208

2 H promotion 0.020 0.000 0.020 10 498 673 74 309 91 250

3 steel plate 0.013 0.000 0.013 32 471 674 70 260 116 178

4 sale board 0.012 0.035 0.047 29 470 681 69 257 129 169

5 H shape promotion 0.025 0.000 0.025 14 493 673 73 293 71 259 shots

6 Steel plate 0.029 0.000 0.029 25 474 651 73 287 59 248

7 H promotion 0.006 0.014 0.020 32 466 646 72 296 135 257

UJ Example o 8 steel plate 0.027 0.000 0.027 6 491 663 74 291 65 285

 9 Steel plate 0.0012 0.000 0.012 13 488 645 76 313 126 313

10 H type 鉀 0.029 0.015 0.044 11 491 650 76 306 63 308

11 sale board 0.028 0.000 0.028 58 423 594 71 304 65 272

12 sale board 0.074 0.000 0.074 36 456 636 72 299 10 262

13 Steel plate 0.029 0.000 0.029 56 424 593 71 309 65 279

14 Pan plate 0.027 0.000 0.027 42 485 684 71 265 59 186

15 steel plate 0.027 0.000 0.027 92 382 528 72 393 88 348

16 Copper plate 0.028 0.000 0.028 6 485 763 64 158 33 31

17 steel plate 0.026 0.000 0.026 43 526 743 71 238 54 147

18 钢 plate 0.012 0.000 0.012 16 684 926 74 126 49 173

19 steel plate 0.048 0.000 0.048 143 365 505 72 380 20 50

*) Z direction

表 7

Table 7

 Steel chemical composition (wt%)

 No. Type A value B value

 C Si Un P S Al Cu Ni B Other book **

2-1 kneading 0.022 0.31 1.37 0.073 0.0023 0.030 0.63 0.70 0.0018 7.6 6.9

2-2 H type 钢 0.017 0.30 1.40 0.075 0.0030 0.030 0.58 0.71 0.0015 Mo'.0.22 8.0 6.9

2-3 Steel plate 0.027 0.27 1.40 0.070 0.0025 0.031 0.60 0.70 0.0020 V: 0.032 7.5 6.9

2-4 Steel plate 0.020 0.30 1.40 0.071 0.0006 0.006 0.55 0.73 0.0021 b: 0.031, Ti: 0.016 7.4 6.9

 Restaurant: 0.0042

 2-5 H type 鉀 0.017 0.30 1.36 0.055 0.0015 0.029 0.62 1.14 0.0016 9.0 6.9i 2-6 Copper plate 0.020 0.30 1.33 0.051 0.0020 0.032 0.45 1.03 0.0020 7.8 6.9

 2-7 um 0.011 0.23 1.27 0.054 0.0005 0.001 0.43 1.10 0.0014 Ti: 0.020 7.7 6.9

2-8 Steel plate 0.020 0.25 1.00 0.050 0.0030 0.035 0.20 1.92 0.0011 9.5 6.9

2-9 Steel plate 0.022 0.31 0.98 0.036 0.0025 0.030 0.20 2.01 0.0007 9.3 6.9

2-10 Steel plate 0.026 0.28 1.02 0.016 0.0090 0.002 0.80 1.53 0.0014 Ti: 0.014 10.9 6.9

2-11 Sales board 0.015 0.25 1.48 0.015 0.0028 0.025 0.41 0.98 0.0020 6.8 6.9

2-12 Steel plate 0.021 0.30 1.35 0.048 0.0070 0.033 0.51 1.00 0.0018 7.8 6.9

2-13 Copper plate 0.015 0.15 1.42 0.055 0.0027 0.030 0.02 1.05 0.0020 5.5 6.9

2-14 Steel plate 0.018 0.33 1.38 0.051 0.0022 0.033 0.45 0.02 0.0015 3.3 6.9

2-15 Steel sheet 0.015 0.31 1.40 0.055 0.0025 0.025 0.42 1.08 0.0001 6.3 6.9

2-16 Steel plate 0.110 0.40 1.05 0.014 0.0050 0.025 0.35 0.15 Cr: 0.50 2.0 6.9

 *) z direction

Claims

The scope of the claims 1, by weight _{^{0/0, C: 0.001 ~0.050}} %, Si: 0.60% or less, Mn: 0.50~3.00%, S: 0.01% or less, A1: 0.10% or less, B: comprises .0003 to 0.0050%, P: 0.005 to 0.15%, Cu: 0.1 to 2.0%, Ni: 0.1 to 6.0%, Cr: 0.005 to 1.0%, Mo: 0.005 to 1.0% And a composition which satisfies the following formula α) and has a composition comprising the balance of Fe and unavoidable impurities.  Record (20P + 3Cu + 3Ni + 6Cr + Mo) / (1—0.2 (10000 B) ^{0 4} ) ≥18 …… (1) where, P, Cu, Ni, Cr, Mo, B: Content of each element (weight ^_0/0) 2.The weather resistance, which has the above composition, and the sum (dA + dB) value of the amount of A-based inclusions and the amount of B-based inclusions derived based on the provisions of JIS G 0555 is 0.030% or less. Steel. 3. In addition to the above composition, Nb: 0.005 to 0.20% by weight,  The weatherable steel material according to claim 1, comprising one or more selected from Ti: 0.005 to 0.20% and V: 0.005 to 0.20%. 4. The method according to claim 1, wherein the composition further comprises one or two selected from Ca: 0.02% or less and REM: 0.02% or less by weight% in addition to the composition. The weathering steel described. 5, by weight%  C: 0.001 to 0.030%, Si: 0.60% or less,  Mn: 0.50 to 3.00%, S: 0.005% or less,  Al: 0.10% or less, B: 0.0003 to 0.0050% In addition, P: 0.005 to 0.15%, Cu: 0.1 to 1.5%, Ni: 0.1 to 6.0%, Mo: 0.005 to 0. It contains one or more selected from 5%, satisfies the following formula (1), has a composition consisting of the balance of Fe and inevitable impurities, and complies with JIS G 0555. A weathering steel material characterized in that the total (dA + dB) value of the derived A-based inclusion amounts and B-based inclusion amounts is 0.030% or less. (IIP +4. OCu + 3. lNi + 2.6Mo) Z (1- 0.1 (10000Β) ⁰ · ³⁵ ) ≥1 + 13X… (1) Here, P, Cu, Ni, Mo , B: content of each element (wt ^_0/0) X: airborne salt amount ^{_{(m g / dm 2 / day}} ) 6. In addition to the above composition, Nb: 0.005% to 0.20% by weight%  6. The weatherable steel material according to claim 5, comprising one or more selected from Ti, 0.005 to 0.20%, and V: 0.005 to 0.20%. 7. The weatherable steel material according to claim 5, further comprising REM: 0.02% or less by weight in addition to the composition. The weather-resistant steel material _{c according to} claim 1, wherein the steel material is a thick steel plate. The weather-resistant steel material _{c according to} claim 1, wherein the steel material is an H-section steel.