Welded structure for sluice gates and method for manufacturing the same

Abstract

To provide a welded structure for a floodgate that uses different kinds of steel for reduced production costs, and also achieves excellent resistance to corrosion and prevention of warpage.SOLUTION: A welded structure for a floodgate has a skin plate, and a reinforcement material welded to the skin plate. The skin plate is stainless steel with a pitting corrosion index PREN of 36.5 or more. The reinforcement material is stainless steel with a pitting corrosion index PREN of 20.3 or more and less than 36.5. The difference between the linear expansion coefficient of the skin plate and the linear expansion coefficient of the reinforcement material is 2.5×10-6 / °C or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a welded structure for a sluice gate and a method for manufacturing the same.

Background Art

[0002] In the vicinity of the river mouth, in order to adjust the amount of water flowing in the river, a sluice gate may be provided as described in Non-Patent Document 1. Such sluice gates may have different required characteristics between the upstream part and the downstream part. For example, the upstream side of the sluice gate is an environment that comes into contact with fresh water flowing from the upstream of the river, but the downstream side is an environment where seawater containing a large amount of chloride ions is mixed with fresh water, and corrosion progresses more easily compared to the upstream side.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Stainless steel with relatively good corrosion resistance is often used for sluice gates. However, as described above, when the corrosion environment is different between the upstream side and the downstream side, it is preferable to separate the materials used for the upstream side and the downstream side. Specifically, it is preferable to use stainless steel with slightly inferior corrosion resistance but low manufacturing cost for the upstream side, and stainless steel with excellent corrosion resistance but high manufacturing cost for the downstream side.

[0005] However, traditionally, a single type of stainless steel has been used for sluice gates. This is because using different types of stainless steel on the upstream and downstream sides would require welding the different types together, which would cause warping due to welding heat. While warping can sometimes be corrected by altering the shape, this increases manufacturing costs. Furthermore, since sluice gates are generally very large structures, they are often assembled on-site, making shape correction difficult in many cases.

[0006] Therefore, when using different types of stainless steel to achieve superior corrosion resistance while keeping manufacturing costs down, there is a problem of warping occurring. In other words, in welded structures for sluice gates, it is difficult to achieve both good corrosion resistance and suppression of warping while keeping manufacturing costs down.

[0007] The present invention aims to solve the above problems and provide a welded structure for sluice gates that achieves both good corrosion resistance and suppression of warping while reducing manufacturing costs by using different types of steel. [Means for solving the problem]

[0008] This invention was made to solve the above-mentioned problems, and its gist is the following welded structure and method for manufacturing the same.

[0009] (1) Welded structures, It comprises a skin plate and a reinforcing material welded to the skin plate, The aforementioned skin plate is made of stainless steel with a pitting index PREN of 36.5 or higher. The reinforcing member is made of stainless steel with a pitting index PREN of 20.3 or more and less than 36.5. The difference between the coefficient of thermal expansion of the skin plate and the coefficient of thermal expansion of the reinforcing material is 2.5 × 10 -6 Welded structures for sluice gates that are below / ℃.

[0010] (2) The chemical composition of the stainless steel skin plate is, in mass%, C: 0.001 to 0.10%, Si: 0.05 to 1.50%, Mn: 0.10 to 2.00%, P: 0.05% or less, S: 0.004% or less, O: 0.02% or less, Cr: 23.0 to 27.0%, Ni: 5.0 to 8.5%, Mo: 2.0 to 5.5%, N: 0.05 to 0.35%, Cu: 0 to 2.0%, W: 0 to 1.0%, Co: 0 to 3.0%, V: 0 to 1.0%, Nb: 0 to 0.10%, Ta: 0 to 0.20%, Ca: 0 to 0.0050%, Al: 0 to 0.10%, Ti: 0 to 0.03%, Zr: 0 to 0.05%, Hf: 0 to 0.10%, B: 0 to 0.0050%, Mg: 0 to 0.0050%, REM: 0 to 0.10%, Sn: 0 to 0.10%, Balance: Fe and impurities, The welded structure for a water gate described in the above (1).

[0011] (3) The chemical composition of the stainless steel as the reinforcing material is in mass%, C: 0.001 to 0.10%, Si: 0.05 to 1.50%, [[ID=]62] Mn: 1.00 to 4.00%, P: 0.05% or less, S: 0.004% or less, O: 0 to 0.02%, Cr: 19.0 to 25.0%, Ni: 1.0 to 7.0%, N: 0.05 to 0.25%, Mo: 0 to 4.0%, Cu: 0 to 2.0%, W: 0 to 1.0%, Co: 0 to 3.0%, V: 0 to 1.0%, Nb: 0 to 0.10%, Ta: 0 to 0.20%, Ca: 0 to 0.0050%, Al: 0 to 0.10%, Ti: 0 to 0.03%, Zr: 0 to 0.05%, Hf: 0 to 0.10%, B: 0 to 0.0050%, Mg: 0 to 0.0050%, REM: 0 to 0.10%, Sn: 0 to 0.10%, The balance: Fe and impurities, The welded structure for a water gate according to (1) above.

[0012] (4) The chemical composition of the stainless steel which is the skin plate is in mass %, Cu: 0.01 to 2.0%, W: 0.01 to 1.0%, Co: 0.01 to 3.0%, V: 0.01 to 1.0%, Nb: 0.005 to 0.10%, Ta: 0.005 to 0.20%, Ca: 0.0010 to 0.0050%, Al: 0.003 to 0.10%, Ti: 0.001 to 0.03%, Zr: 0.001 to 0.05%, Hf: 0.001 to 0.10%, B: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, REM: 0.005 to 0.10%, and Sn: 0.001 to 0.10%, The welded structure for a water gate according to (2) above, containing one or more selected from the above.

[0013] (5) The chemical composition of the stainless steel that is the reinforcing material is, in mass%, Mo: 0.01~4.0%, Cu: 0.01~2.0%, W: 0.01~1.0%, Co: 0.01~3.0%, V: 0.01~1.0%, Nb: 0.005~0.10%, Ta: 0.005~0.20%, Ca: 0.0010~0.0050%, Al: 0.003~0.10%, Ti: 0.001~0.03%, Zr: 0.001~0.05%, Hf: 0.001~0.10%, B: 0.0001~0.0050%, Mg: 0.0001~0.0050%, REM: 0.005~0.10%, and Sn: 0.001~0.10%, A welded structure for a sluice gate as described in (3) above, comprising one or more selected from the above.

[0014] (6) A method for manufacturing welded structures for sluice gates, The process involves hot-rolling the steel that will be used as the material for the skin plate, followed by heat treatment at a heat treatment temperature T1 in the temperature range of 1000 to 1150°C, and hot-working the steel that will be used as the material for the reinforcing material, followed by heat treatment at a heat treatment temperature T2 in the temperature range of 950 to 1100°C. The process includes welding the skin plate and the reinforcing material with a heat input of 40 kJ / cm or less. A method for manufacturing a welded structure for a sluice gate according to (1) to (5) above, wherein the difference between the heat treatment temperature T1 and the heat treatment temperature T2 is 150°C or less. [Effects of the Invention]

[0015] According to the present invention, by using different types of steel, it is possible to obtain a welded structure for sluice gates that achieves both good corrosion resistance and suppression of warping while keeping manufacturing costs down. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a schematic diagram showing the test specimens manufactured in the example. [Modes for carrying out the invention]

[0017] The inventors of this invention investigated the occurrence of warping in welded structures for sluice gates and obtained the following findings (a) to (c).

[0018] (a) In order to reduce the cost of welded structures for sluice gates, it is preferable to use different types of stainless steel on the upstream and downstream sides, and in particular, it is desirable to use stainless steel with high corrosion resistance on the downstream side. This is because, although corrosion resistance is not so required for the stainless steel on the upstream side, which is only in contact with fresh water, the downstream side, where seawater and fresh water mix, has a higher concentration of chloride ions and becomes a more severe corrosive environment.

[0019] (b) For this reason, it is effective to use stainless steel with a pitting index PREN of 20.3 or higher and less than 36.5 on the upstream side, and stainless steel with a pitting index PREN of 36.5 or higher on the downstream side.

[0020] (c) Furthermore, warping caused by welding heat is due to the difference in thermal expansion between different stainless steels. Therefore, it is preferable to reduce the difference in the coefficient of linear expansion between the upstream and downstream stainless steels to suppress warping caused by thermal expansion. Specifically, the difference in the coefficient of linear expansion between the upstream and downstream stainless steels should be 2.5 × 10 -6 The temperature must be below / °C. Here, the coefficient of linear expansion of stainless steel is affected by the heat treatment temperature during manufacturing. In particular, for stainless steel used in sluice gates, it is important to control the heat treatment temperature after hot working or hot rolling. It is preferable to perform annealing at a temperature that maintains the corrosion resistance of the stainless steel on both the upstream and downstream sides, and so that the difference in heat treatment temperatures between the two stainless steels is 150°C or less.

[0021] This invention is based on the above findings. The requirements of each embodiment of this invention will be described in detail below.

[0022] 1. Composition of welded structures The welded structure of this embodiment comprises a skin plate and a reinforcing member welded to the skin plate. The welded structure of this embodiment includes the skin plate and the reinforcing member, and, if welding material is used, the weld metal portion formed by the melting and solidification of the welding material by welding heat. Furthermore, the welded structure of this embodiment may also include, for example, other components necessary for sluice gate applications, such as guide roller fixing members, watertight members, and handling tabs, in addition to the skin plate and the reinforcing member welded to the skin plate.

[0023] 2. Skin plate 2-1. Pitting index PREN and chemical composition of skin plates The skin plate is made of stainless steel containing elements such as Cr (chromium), Mo (molybdenum), and N (nitrogen), and having a pitting index PREN of 36.5 or higher. Here, the pitting index PREN is one of the indicators of the corrosion resistance of stainless steel, and the higher the PREN value, the better the corrosion resistance. The pitting index PREN is calculated using the following formula (a). PREN = Cr + 3.3Mo + 16N ... (a) However, each element symbol in the above formula represents the content (mass %) of each element contained in the steel, and zero is used if the element is not present.

[0024] If the PREN (Pitting Index) of a skin plate is less than 36.5, it becomes difficult to fully exhibit and maintain corrosion resistance in relatively corrosive environments where seawater and freshwater mix. For this reason, the PREN of a skin plate should be 36.5 or higher, preferably 36.6 or higher, and more preferably 36.7 or higher. There is no particular upper limit to the PREN of a skin plate, but it is generally considered to be 49.0 or lower.

[0025] The reasons for limiting the chemical composition of the stainless steel skin plate by each element are as follows. In the following explanation, "%" for content refers to "mass%".

[0026] C: 0.001~0.10% Carbon (C) degrades corrosion resistance and increases the coefficient of thermal expansion. Therefore, a lower C content is preferable, preferably 0.10% or less. A C content of 0.080% or less is more preferable, and 0.070% or less is even more preferable. However, excessively reducing the C content increases refining costs. Therefore, a C content of 0.001% or more is preferable.

[0027] Si: 0.05~1.50% Si is an element that has a deoxidizing effect during refining. For this reason, the Si content is preferably 0.05% or more. A Si content of 0.06% or more is preferable, and a Si content of 0.07% or more is more preferable. However, if the Si content is excessive, cracking will occur during manufacturing. For this reason, the Si content is preferably 1.50% or less. A Si content of 1.45% or less is more preferable, and a Si content of 1.40% or less is even more preferable.

[0028] Mn: 0.10~2.00% Mn has the effect of increasing strength. For this reason, the Mn content is preferably 0.10% or more. A more preferable Mn content is 0.20% or more, and even more preferable is 0.30% or more. However, if the Mn content is excessive, the corrosion resistance deteriorates. Also, the coefficient of linear expansion increases excessively. For this reason, the Mn content is preferably 2.00% or less. A more preferable Mn content is 1.90% or less, and even more preferable is 1.80% or less.

[0029] P:0.05% or less P is an element present as an impurity in steel, and it reduces manufacturability and weldability. Therefore, it is preferable that the P content be 0.05% or less. While it is preferable to reduce P as much as possible, excessive reduction increases refining costs. Therefore, it is preferable that the P content be 0.001% or more.

[0030] S: 0.004% or less S is an element present as an impurity in steel that reduces its corrosion resistance. Therefore, it is preferable that the S content be 0.004% or less. While it is preferable to reduce S as much as possible, excessive reduction increases refining costs. Therefore, it is preferable that the S content be 0.0001% or more.

[0031] O: 0.02% or less O is an element present as an impurity in steel, and it acts as an initiation point for pitting corrosion, reducing corrosion resistance. For this reason, it is preferable to keep the O content below 0.02%. While it is preferable to reduce O as much as possible, excessive reduction increases refining costs. For this reason, it is preferable to keep the O content above 0.001%.

[0032] Cr: 23.0~27.0% Cr is an element that improves oxidation resistance and corrosion resistance. For this reason, the Cr content is preferably 23.0% or more. A Cr content of 23.2% or more is more preferable, and 23.5% or more is even more preferable. However, if the Cr content is excessive, the alloy cost increases and the corrosion resistance decreases. For this reason, the Cr content is preferably 27.0% or less. A Cr content of 26.7% or less is more preferable, and 26.5% or less is even more preferable.

[0033] Ni: 5.0~8.5% Ni improves corrosion resistance. For this reason, the Ni content is preferably 5.0% or more, and more preferably 5.2% or more. However, since Ni is an expensive element, excessive inclusion increases manufacturing costs. In addition, the coefficient of thermal expansion increases excessively. For this reason, the Ni content is preferably 8.5% or less, and more preferably 8.3% or less.

[0034] Mo: 2.0~5.5% Mo has the effect of improving corrosion resistance. For this reason, the Mo content is preferably 2.0% or more, and more preferably 2.2% or more. However, if the Mo content is excessive, the hot workability decreases. Also, the manufacturing cost increases. For this reason, the Mo content is preferably 5.5% or less, and more preferably 5.3% or less.

[0035] N: 0.05~0.35% N is an element that improves corrosion resistance and stabilizes austenite. For this reason, the N content is preferably 0.05% or more, and more preferably 0.07% or more. However, if the N content is excessive, excess nitrides will be formed, which will actually reduce corrosion resistance. For this reason, the N content is preferably 0.35% or less, and more preferably 0.33% or less.

[0036] In addition to the elements listed above, one or more elements selected from Cu, W, Co, V, Nb, Ta, Ca, Al, Ti, Zr, Hf, B, Mg, REM, and Sn may be included within the ranges shown below. The reasons for limiting each element are explained below.

[0037] Cu: 0~2.0% Cu may be included as needed because it has the effect of improving corrosion resistance. However, excessive Cu content leads to increased costs and decreased hot workability. It also excessively increases the coefficient of thermal expansion. Therefore, the Cu content is preferably 2.0% or less, and preferably 1.9% or less. On the other hand, in order to obtain the above effects, the Cu content is preferably 0.01% or more.

[0038] W: 0~1.0% Like copper, water (W) has the effect of improving corrosion resistance. It also has the effect of lowering the coefficient of thermal expansion, so it may be included as needed. However, excessive amounts of water lead to increased costs and decreased hot workability. For this reason, it is preferable to keep the water content at 1.0% or less, and preferably at 0.7% or less. On the other hand, in order to obtain the above effects, it is preferable to keep the water content at 0.01% or more.

[0039] Co: 0~3.0% Co is an element that improves the toughness and corrosion resistance of steel. For this reason, it may be included as needed. However, Co is an expensive element, and excessive inclusion increases manufacturing costs. It also excessively increases the coefficient of thermal expansion. For this reason, the Co content is preferably 3.0% or less, and more preferably 2.8% or less. On the other hand, to obtain the above effects, the Co content is preferably 0.01% or more.

[0040] V: 0~1.0% V has the effect of improving the corrosion resistance of the welded joint. It also has the effect of lowering the coefficient of thermal expansion. For this reason, it may be included as needed. However, if V is included in excess, a large amount of V nitride will precipitate, reducing toughness. For this reason, the V content is preferably 1.0% or less, and more preferably 0.8% or less. On the other hand, in order to obtain the above effects, the V content is preferably 0.01% or more.

[0041] Nb: 0~0.10% Nb combines with C and N, improving the corrosion resistance and strength of the welded joint. It also has the effect of reducing the coefficient of thermal expansion. For this reason, it may be included as needed. However, excessive Nb content leads to a decrease in corrosion resistance and an increase in alloy costs. For this reason, it is preferable to have an Nb content of 0.10% or less, and more preferably 0.090% or less. On the other hand, in order to obtain the above effects, it is preferable to have an Nb content of 0.005% or more.

[0042] Ta: 0~0.20% Like Nb, Ta has the effect of improving the corrosion resistance and strength of welded joints. For this reason, it may be included as needed. However, if Ta is included in excess, a large amount of Ta nitride will precipitate, reducing toughness. For this reason, the Ta content is preferably 0.20% or less, and more preferably 0.18% or less. On the other hand, in order to obtain the above effect, the Ta content is preferably 0.005% or more.

[0043] Ca: 0~0.0050% Ca has the effect of improving hot workability. For this reason, it may be included as needed. However, if Ca is included in excess, the manufacturability will decrease. For this reason, the Ca content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the Ca content is preferably 0.0010% or more.

[0044] Al: 0-0.10% Al has a deoxidizing effect on steel. For this reason, it may be included as needed. However, excessive Al content reduces the cleanliness and toughness of the steel. Therefore, the Al content is preferably 0.10% or less, and more preferably 0.08% or less. On the other hand, to obtain the above effect, the Al content is preferably 0.003% or more.

[0045] Ti: 0~0.03% Ti has the effect of refining the crystal grains and improving strength by forming nitrides. It also has the effect of lowering the coefficient of thermal expansion, so it may be included as needed. However, if Ti is included in excess, coarse nitrides will form and the toughness will decrease. For this reason, the Ti content is preferably 0.03% or less, and more preferably 0.02% or less. On the other hand, in order to obtain the above effects, the Ti content is preferably 0.001% or more.

[0046] Zr: 0~0.05% Zr, like Ti, has the effect of refining the crystal grain and improving strength by forming nitrides. It also has the effect of lowering the coefficient of thermal expansion. For this reason, it may be included as needed. However, if Zr is included in excess, coarse nitrides will form, reducing toughness. For this reason, the Zr content is preferably 0.05% or less, and more preferably 0.04% or less. On the other hand, in order to obtain the above effects, the Zr content is preferably 0.001% or more.

[0047] Hf: 0~0.10% Like Ti and Zr, Hf has the effect of refining the crystal grains and improving strength. For this reason, it may be included as needed. However, if Hf is included in excess, coarse nitrides will form, reducing toughness. For this reason, the Hf content is preferably 0.10% or less, and more preferably 0.09% or less. On the other hand, in order to obtain the above effect, the Hf content is preferably 0.001% or more.

[0048] B: 0~0.0050% B has the effect of improving hot workability. For this reason, it may be included as needed. However, if B is included in excess, coarse nitrides will form, reducing toughness. For this reason, the B content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the B content is preferably 0.0001% or more.

[0049] Mg: 0~0.0050% Like B, Mg has the effect of improving hot workability. For this reason, it may be included as needed. However, if Mg is included in excess, the manufacturability will decrease. For this reason, the Mg content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the Mg content is preferably 0.0001% or more.

[0050] REM: 0~0.10% REM, like B and Mg, has the effect of improving hot workability. For this reason, it may be included as needed. However, excessive REM content reduces manufacturability. For this reason, the REM content is preferably 0.10% or less, and more preferably 0.08% or less. On the other hand, in order to obtain the above effect, the REM content is preferably 0.005% or more.

[0051] Here, REM refers to the 17 elements totaling Sc, Y, and lanthanides, and the REM content mentioned above means the total content of these elements. Industrially, REM is often added in the form of mischmetal.

[0052] Sn: 0~0.10% Sn has the effect of improving the corrosion resistance of stainless steel to acids. For this reason, it may be included as needed. However, if too much Sn is included, the hot workability will decrease. For this reason, the Sn content is preferably 0.10% or less, and more preferably 0.080% or less. On the other hand, in order to obtain the above effect, the Sn content is preferably 0.001% or more.

[0053] In the chemical composition of the stainless steel skin plate, the remainder consists of Fe and impurities. Here, "impurities" refers to components that are mixed in during the industrial production of stainless steel for the skin plate due to various factors in the raw materials such as ore and scrap, and in the manufacturing process, and which are acceptable as long as they do not adversely affect the present invention.

[0054] 2-2. Skin plate shape Skin plates are typically plate-shaped. While there are no specific thickness limitations, they are typically stainless steel plates with a thickness of 6.0 to 25.0 mm. This is because a thickness of less than 6.0 mm makes it difficult to obtain sufficient strength when used in sluice gates, while a thickness exceeding 25.0 mm increases costs and reduces the ease of welding.

[0055] 3. Reinforcement 3-1. Pitting index PREN and chemical composition of reinforcing materials The reinforcing material is stainless steel containing elements such as chromium (Cr) and nitrogen (N), with a pitting index (PREN) of 20.3 or higher and less than 36.5.

[0056] If the pitting index PREN of the reinforcing material is less than 20.3, it becomes difficult to fully exhibit and maintain corrosion resistance in an environment that is only in contact with freshwater. For this reason, the pitting index PREN of the reinforcing material should be 20.3 or higher, preferably 20.4 or higher, and more preferably 20.5 or higher. On the other hand, if the pitting index PREN of the reinforcing material is 36.5 or higher, the corrosion resistance performance becomes excessive, and manufacturing costs increase. For this reason, the pitting index PREN of the reinforcing material should be less than 36.5, preferably 36.4 or lower, and more preferably 36.3 or lower.

[0057] The reasons for the limitations on each element in the chemical composition of the reinforcing stainless steel are as follows. In the following explanation, "%" for content refers to "mass%".

[0058] C: 0.001~0.10% Carbon (C) degrades corrosion resistance and increases the coefficient of thermal expansion. Therefore, a lower C content is preferable, preferably 0.10% or less. A C content of 0.085% or less is more preferable, and 0.070% or less is even more preferable. However, excessively reducing the C content increases refining costs. Therefore, a C content of 0.001% or more is preferable.

[0059] Si: 0.05~1.50% Si is an element that has a deoxidizing effect during refining. For this reason, the Si content is preferably 0.05% or more. Preferably, the Si content is 0.06% or more, and more preferably 0.07% or more. However, if the Si content is excessive, cracking will occur during manufacturing. Also, the coefficient of thermal expansion will increase excessively. For this reason, the Si content is preferably 1.50% or less. More preferably, the Si content is 1.45% or less, and even more preferably 1.40% or less.

[0060] Mn: 1.00~4.00% Mn has the effect of increasing strength. For this reason, the Mn content is preferably 1.00% or more. A more preferable Mn content is 1.05% or more, and even more preferable is 1.10% or more. However, if the Mn content is excessive, the corrosion resistance deteriorates. Also, the coefficient of linear expansion increases excessively. For this reason, the Mn content is preferably 4.00% or less. A more preferable Mn content is 3.90% or less, and even more preferable is 3.80% or less.

[0061] P:0.05% or less P is an element present as an impurity in steel, and it reduces manufacturability and weldability. Therefore, it is preferable that the P content be 0.05% or less. While it is preferable to reduce P as much as possible, excessive reduction increases refining costs. Therefore, it is preferable that the P content be 0.001% or more.

[0062] S: 0.004% or less S is an element present as an impurity in steel, and it reduces corrosion resistance. Therefore, it is preferable that the S content be 0.004% or less. While it is preferable to reduce S as much as possible, excessive reduction increases refining costs. Therefore, it is preferable that the S content be 0.0001% or more.

[0063] O: 0.02% or less O is an element present as an impurity in steel, and it acts as an initiation point for pitting corrosion, reducing corrosion resistance. For this reason, it is preferable to keep the O content below 0.02%. While it is preferable to reduce O as much as possible, excessive reduction increases refining costs. For this reason, it is preferable to keep the O content above 0.001%.

[0064] Cr: 19.0~25.0% Cr is an element that improves oxidation resistance and corrosion resistance. For this reason, the Cr content is preferably 19.0% or more. A Cr content of 19.2% or more is more preferable, and 19.5% or more is even more preferable. However, if the Cr content is excessive, the alloy cost increases and the corrosion resistance actually decreases. In addition, the coefficient of thermal expansion increases excessively. For this reason, the Cr content is preferably 25.0% or less. A Cr content of 24.8% or less is more preferable, and 24.6% or less is even more preferable.

[0065] Ni: 1.0~7.0% Ni improves corrosion resistance and also reduces the coefficient of thermal expansion. For this reason, the Ni content is preferably 1.0% or more, and more preferably 1.2% or more. However, since Ni is an expensive element, excessive amounts increase manufacturing costs. For this reason, the Ni content is preferably 7.0% or less, and more preferably 6.8% or less.

[0066] N: 0.05~0.25% N is an element that improves corrosion resistance and stabilizes austenite. For this reason, the N content is preferably 0.05% or more, and more preferably 0.07% or more. However, if the N content is excessive, excess nitrides will be formed, which will actually reduce corrosion resistance. For this reason, the N content is preferably 0.25% or less, and more preferably 0.23% or less.

[0067] In addition to the elements listed above, one or more elements selected from Mo, Cu, W, Co, V, Nb, Ta, Ca, Al, Ti, Zr, Hf, B, Mg, REM, and Sn may be included within the ranges shown below. The reasons for limiting each element are explained below.

[0068] Mo: 0~4.0% Mo has the effect of improving corrosion resistance. For this reason, it may be included as needed. However, if Mo is included in excess, the hot workability decreases. In addition, the coefficient of linear expansion increases excessively, and the manufacturing cost also increases. For this reason, the Mo content is preferably 4.0% or less, and more preferably 3.80% or less. On the other hand, in order to obtain the above effect, the Mo content is preferably 0.01% or more.

[0069] Cu: 0~2.0% Cu may be included as needed because it has the effect of improving corrosion resistance. However, excessive Cu content leads to increased costs and decreased hot workability. It also excessively increases the coefficient of thermal expansion. Therefore, the Cu content is preferably 2.0% or less, and preferably 1.9% or less. On the other hand, in order to obtain the above effects, the Cu content is preferably 0.01% or more.

[0070] W: 0~1.0% Since W, like Cu, has the effect of improving corrosion resistance, it may be included as needed. However, excessive W content leads to increased costs and decreased hot workability. Therefore, it is preferable to keep the W content at 1.0% or less, and preferably at 0.7% or less. On the other hand, in order to obtain the above effects, it is preferable to keep the W content at 0.01% or more.

[0071] Co: 0~3.0% Co is an element that improves the toughness and corrosion resistance of steel. For this reason, it may be included as needed. However, Co is an expensive element, and excessive inclusion increases manufacturing costs. Therefore, the Co content is preferably 3.0% or less, and more preferably 2.8% or less. On the other hand, to obtain the above effects, the Co content is preferably 0.01% or more.

[0072] V: 0~1.0% V has the effect of improving the corrosion resistance of the welded joint. For this reason, it may be included as needed. However, if V is included in excess, a large amount of V nitride will precipitate, reducing toughness. Also, the coefficient of thermal expansion will increase excessively. For this reason, the V content is preferably 1.0% or less, and more preferably 0.8% or less. On the other hand, in order to obtain the above effect, the V content is preferably 0.01% or more.

[0073] Nb: 0~0.10% Nb combines with C and N, improving the corrosion resistance and strength of the welded joint. Therefore, it may be included as needed. However, excessive Nb content leads to a decrease in corrosion resistance and an increase in alloy costs. It also excessively increases the coefficient of thermal expansion. For this reason, the Nb content is preferably 0.10% or less, and more preferably 0.090% or less. On the other hand, to obtain the above effects, the Nb content is preferably 0.005% or more.

[0074] Ta: 0~0.20% Like Nb, Ta has the effect of improving the corrosion resistance and strength of welded joints. For this reason, it may be included as needed. However, if Ta is included in excess, a large amount of Ta nitride will precipitate, reducing toughness. Also, the coefficient of thermal expansion will increase excessively. For this reason, the Ta content is preferably 0.20% or less, and more preferably 0.18% or less. On the other hand, in order to obtain the above effects, the Ta content is preferably 0.005% or more.

[0075] Ca: 0~0.0050% Ca has the effect of improving hot workability. For this reason, it may be included as needed. However, if Ca is included in excess, the manufacturability will decrease. For this reason, the Ca content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the Ca content is preferably 0.0010% or more.

[0076] Al: 0-0.10% Al has a deoxidizing effect on steel. For this reason, it may be included as needed. However, excessive Al content reduces the cleanliness and toughness of the steel. It also excessively increases the coefficient of thermal expansion. For this reason, the Al content is preferably 0.10% or less, and more preferably 0.08% or less. On the other hand, to obtain the above effects, the Al content is preferably 0.003% or more.

[0077] Ti: 0~0.03% Ti has the effect of refining the crystal grains and improving strength by forming nitrides. For this reason, it may be included as needed. However, if Ti is included in excess, coarse nitrides will form, reducing toughness. For this reason, the Ti content is preferably 0.03% or less, and more preferably 0.02% or less. On the other hand, in order to obtain the above effect, the Ti content is preferably 0.001% or more.

[0078] Zr: 0~0.05% Zr, like Ti, has the effect of refining the crystal grains and improving strength by forming nitrides. For this reason, it may be included as needed. However, if Zr is included in excess, coarse nitrides will form, reducing toughness. For this reason, the Zr content is preferably 0.05% or less, and more preferably 0.04% or less. On the other hand, in order to obtain the above effect, the Zr content is preferably 0.001% or more.

[0079] Hf: 0~0.10% Like Ti and Zr, Hf has the effect of refining the crystal grains and improving strength. For this reason, it may be included as needed. However, if Hf is included in excess, coarse nitrides will form, reducing toughness. For this reason, the Hf content is preferably 0.10% or less, and more preferably 0.09% or less. On the other hand, in order to obtain the above effect, the Hf content is preferably 0.001% or more.

[0080] B: 0~0.0050% B has the effect of improving hot workability. For this reason, it may be included as needed. However, if B is included in excess, manufacturability will decrease. Also, the coefficient of linear expansion will increase excessively. For this reason, the B content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the B content is preferably 0.0001% or more.

[0081] Mg: 0~0.0050% Like B, Mg has the effect of improving hot workability. For this reason, it may be included as needed. However, if Mg is included in excess, the manufacturability will decrease. For this reason, the Mg content is preferably 0.0050% or less, and more preferably 0.0040% or less. On the other hand, in order to obtain the above effect, the Mg content is preferably 0.0001% or more.

[0082] REM: 0~0.10% REM, like B and Mg, has the effect of improving hot workability. For this reason, it may be included as needed. However, excessive REM content reduces manufacturability. For this reason, the REM content is preferably 0.10% or less, and more preferably 0.08% or less. On the other hand, in order to obtain the above effect, the REM content is preferably 0.005% or more.

[0083] Here, REM refers to the 17 elements totaling Sc, Y, and lanthanides, and the REM content mentioned above means the total content of these elements. Industrially, REM is often added in the form of mischmetal.

[0084] Sn: 0~0.10% Sn has the effect of improving the corrosion resistance of stainless steel to acids. For this reason, it may be included as needed. However, if too much Sn is included, the hot workability will decrease. For this reason, the Sn content is preferably 0.10% or less, and more preferably 0.08% or less. On the other hand, in order to obtain the above effect, the Sn content is preferably 0.001% or more.

[0085] In the chemical composition of the reinforcing stainless steel, the remainder consists of Fe and impurities. Here, "impurities" refers to components that are mixed in during the industrial production of the reinforcing stainless steel due to various factors in the raw materials such as ore and scrap, and in the manufacturing process, and which are acceptable as long as they do not adversely affect the present invention.

[0086] 3-2. Shape of the reinforcing material The shape of the reinforcing material is not particularly limited, but some examples include C-shaped channels, L-shaped angles, H-beams, steel pipes, square steel pipes, other angle steel, and plate materials.

[0087] 4. Difference in coefficient of linear expansion In the welded structure of this embodiment, the difference between the coefficient of thermal expansion of the skin plate and the coefficient of thermal expansion of the reinforcing material (hereinafter simply referred to as "difference in coefficient of thermal expansion") is 2.5 × 10⁻⁶ -6 The temperature should be less than or equal to / ℃. The difference in the coefficient of linear expansion is 2.5 × 10⁻⁶. -6 This is because warping occurs in either the skin plate or the reinforcing material when the temperature exceeds / ℃. Therefore, the difference in the coefficient of linear expansion is 2.5 × 10 -6 Set to below / ℃, 2.4 × 10 -6 It is more preferable to keep the temperature below / ℃.

[0088] The difference in linear thermal expansion coefficients can be measured using the following procedure: Take test pieces of 4mm x 4mm x 20mm from the stainless steel skin plate and the stainless steel reinforcing material, and use a push-rod thermal expander to determine the average linear thermal expansion coefficients from room temperature to 100°C. Subtract the smaller of the two average linear thermal expansion coefficients to calculate the difference in linear thermal expansion coefficients.

[0089] 5. Manufacturing method A preferred manufacturing method for the welded structure according to this embodiment will be described. The welded structure of this embodiment can achieve the effects described above regardless of the manufacturing method, as long as it has the above-described configuration, but it can be stably manufactured by, for example, the following manufacturing method.

[0090] 5-1. Skin Plate Manufacturing Stainless steel satisfying the chemical composition of the skin plate described above is melted and hot-rolled to produce hot-rolled steel sheets. While there are no particular limitations on the conditions for hot rolling, the heating temperature is usually in the range of 1000 to 1300°C. Similarly, there are no particular limitations on other conditions for hot rolling; the conditions for hot rolling should follow conventional methods.

[0091] Next, it is preferable to perform a heat treatment on the obtained hot-rolled steel sheet at a heat treatment temperature T1 in the temperature range of 1000 to 1150°C to maintain uniform heat. If the heat treatment temperature T1 is less than 1000°C, the carbonitrides formed during manufacturing will not dissolve, and the corrosion resistance will decrease. For this reason, it is preferable that the heat treatment temperature T1 be 1000°C or higher, and more preferably 1010°C or higher. On the other hand, if the heat treatment temperature T1 exceeds 1150°C, the manufacturing cost will increase. For this reason, it is preferable that the heat treatment temperature T1 be 1150°C or lower, and more preferably 1140°C or lower. The heat treatment time during the above heat treatment is not particularly limited, but is usually 1 to 30 minutes.

[0092] 5-2. Manufacturing of reinforcing materials Skin plates are manufactured under the conditions described above, and reinforcing materials are manufactured under the conditions described below. Stainless steel satisfying the chemical composition of the reinforcing material described above is melted and hot-worked. The method of hot working is not particularly limited, but conventional hot working methods such as hot rolling and hot forging may be used. The conditions during hot working are not particularly limited, but for example, in the case of hot rolling, the heating temperature of the steel is often in the range of 1000 to 1300°C. Other hot working conditions are also not particularly limited; conventional conditions may be used.

[0093] Next, it is preferable to perform a heat treatment on the hot-worked steel at a heat treatment temperature T2 in the temperature range of 950 to 1100°C to maintain uniform heat. If the heat treatment temperature T2 is below 950°C, the carbonitrides formed during manufacturing will not dissolve, and the corrosion resistance will decrease. For this reason, it is preferable that the heat treatment temperature T2 be 950°C or higher, and more preferably 960°C or higher. On the other hand, if the heat treatment temperature T2 exceeds 1100°C, the manufacturing cost will increase. For this reason, it is preferable that the heat treatment temperature T2 be 1100°C or lower, and more preferably 1090°C or lower. The heat treatment time during the above heat treatment is not particularly limited, but is usually 1 to 30 minutes.

[0094] Furthermore, the difference between the heat treatment temperature T1 and the heat treatment temperature T2 (hereinafter simply referred to as the "heat treatment temperature difference") is preferably 150°C or less. This is because if the heat treatment temperature difference exceeds 150°C, warping will occur in the skin plate and reinforcing material, and the deflection of the entire welded structure will increase. For this reason, the heat treatment temperature difference is preferably 150°C or less, and more preferably 90°C or less. When calculating the heat treatment temperature difference, simply subtract the smaller of the two values, heat treatment temperature T1 and heat treatment temperature T2, from the larger of the two.

[0095] 5-3. Welding The skin plate and reinforcing material obtained in the above process are welded together. The welding method is not particularly limited, but fillet welding is usually performed by arc welding. Here, the amount of heat input during welding affects the warping of the welded structure, and in particular, excessive heat input makes warping more likely to occur. For this reason, it is preferable to keep the heat input during welding to 40 kJ / cm or less. In addition, when performing multi-pass welding, it is preferable to keep the interpass temperature to 150°C or less. Other welding conditions should be adjusted to ensure that appropriate welding is performed.

[0096] The welding material used during welding is not particularly limited, but it is preferable that it is, for example, C: 0.001~0.12%, Si: 0.05~1.50%, Mn: 0.40~3.00%, P: 0.05% or less, S: 0.004% or less, Cr: 17.5~27.5%, Ni: 7.0~16.5%, Mo: 0~5.0%, N: 0~0.35%, Cu: 0~2.0%, W: 0~1.0%, with the remainder being Fe and impurities.

[0097] The welded structures of this embodiment will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0098] Stainless steel having the chemical composition shown in Table 1 was melted down to produce a 10 mm thick plate-shaped skin plate. Similarly, stainless steel having the chemical composition shown in Table 2 was melted down to produce a plate-shaped reinforcing material. The plate thickness was 10 mm, the same as the skin plate.

[0099] [Table 1]

[0100] [Table 2]

[0101] The skin plates were hot-rolled and then heat-treated under the conditions described in Table 3. Similarly, the reinforcing materials were hot-worked and then heat-treated under the conditions described in Table 4. The coefficient of linear expansion of the obtained skin plates and reinforcing materials was measured and their corrosion resistance was evaluated using the method described below.

[0102] (Measurement of linear thermal expansion coefficient) Test specimens measuring 4 mm x 4 mm x 20 mm were taken from the stainless steel skin plate and the stainless steel reinforcing material, and the average linear expansion coefficients were measured from room temperature to 100°C using a push-rod thermal expander.

[0103] (Evaluation of corrosion resistance) A pitting corrosion test was conducted to evaluate corrosion resistance. The pitting corrosion test followed the ferric chloride immersion corrosion test in accordance with ASTM G 48E. Specifically, corrosion test specimens measuring 50 mm × 25 mm × 2 mm were taken from each skin plate and reinforcing material. After wet polishing the entire surface of the specimens to 400 grit, the weight of the collected corrosion test specimens was measured. The test solution used was a mixture of 68.72 g of ferric chloride, 600 mL of pure water, and 16 mL of concentrated hydrochloric acid. This test solution was maintained at different temperatures in 5°C increments, and the corrosion test specimens were immersed for 24 hours. The lowest temperature at which pitting corrosion occurred was defined as the CPT (critical point for pitting corrosion). For skin plates, a CPT of 30°C or higher was considered good corrosion resistance, and for reinforcing materials, a CPT of 5°C or higher was considered good corrosion resistance. The results for skin plates and reinforcing materials are summarized in Tables 3 and 4.

[0104] [Table 3]

[0105] [Table 4] [Examples]

[0106] Furthermore, test specimens were cut from some of the skin plates and reinforcing materials obtained in Example 1, and fillet welds were performed using FCAW welding with a heat input of 40 kJ / cm to produce test specimens as shown in Figure 1. TS2209 series welding wire was used as the welding material. Other conditions included the use of CO2 as the shielding gas and maintaining the interpass temperature at 150°C or less. Subsequently, the height of the warpage of the welded test specimens was evaluated using the following method. The dimensions of the welded skin plate test specimens and reinforcing material test specimens were 500 mm in length, 100 mm in width, and 10 mm in thickness, respectively. The skin plate test specimens were pre-ground to a flatness of less than 0.1 mm using a surface grinder.

[0107] (Evaluation of curvature) For warping, the skin plate side of the welded specimen was placed on a flat base, and the gap between the surface of the skin plate specimen and the base was measured at three points: the center in the width direction, and the ends and the center in the longitudinal direction. The widest of these gaps was evaluated as the warping height. The results are shown in Table 5. Note that the size of the specimen can be arbitrary, as long as the length, width, and thickness of the skin plate specimen and the reinforcing material specimen are the same. If the length is changed, the size of the gap obtained from the specimen measurement should be converted to a size per 500 mm and evaluated. For example, if measured at a length of 1000 mm, the size of the gap obtained from the measurement should be divided by 2 to obtain the warping height.

[0108] Furthermore, in the measurement of warpage in the examples, both the skin plate and the reinforcing material are made of sheet material. This is because, when both the skin plate and the reinforcing material are made of sheet material, even if the shape or thickness of the reinforcing material changes, the warpage will be relatively small as long as the coefficient of thermal expansion remains within a predetermined range.

[0109] [Table 5]

[0110] Examples that satisfied the requirements of this embodiment exhibited good corrosion resistance and minimal warping. On the other hand, examples that did not satisfy the requirements of this embodiment exhibited poor corrosion resistance or warping. [Explanation of Symbols]

[0111] 1: Skin Plate 2: Reinforcement material

Claims

1. Welded structures, It comprises a skin plate and a reinforcing material welded to the skin plate, The aforementioned skin plate has a PREN of 36.5 or higher, calculated from the following formula (a). In mass percent, C: 0.001 to 0.10%, Si: 0.05-1.50%, Mn: 0.10-2.00%, P: 0.05% or less, S: 0.004% or less, O: 0.02% or less, Cr: 23.0-27.0%, Ni: 5.0 to 8.5%, Mo: 2.0 to 5.5%, N: 0.05-0.35%, Cu: 0-2.0%, W: 0-1.0%, Co: 0-3.0%, V: 0-1.0%, Nb: 0 to 0.10%, Ta: 0 to 0.20%, Ca: 0-0.0050%, Al: 0-0.10%, Ti: 0 to 0.03%, Zr: 0 to 0.05%, Hf: 0-0.10%, B: 0 to 0.0050%, Mg: 0 to 0.0050%, REM: 0-0.10%, Sn: 0 to 0.10%, The remainder is stainless steel with a chemical composition of Fe and impurities. The aforementioned reinforcing material has a PREN of 20.3 or more and less than 36.5, calculated from the following formula (a). In mass percent, C: 0.001 to 0.10%, Si: 0.05-1.50%, Mn: 1.00-4.00%, P: 0.05% or less, S: 0.004% or less, O: 0.02% or less, Cr: 19.0-25.0%, Ni: 1.0 to 7.0%, N: 0.05-0.25%, Mo: 0-4.0%, Cu: 0-2.0%, W: 0-1.0%, Co: 0-3.0%, V: 0-1.0%, Nb: 0 to 0.10%, Ta: 0 to 0.20%, Ca: 0-0.0050%, Al: 0-0.10%, Ti: 0 to 0.03%, Zr: 0 to 0.05%, Hf: 0-0.10%, B: 0 to 0.0050%, Mg: 0 to 0.0050%, REM: 0-0.10%, Sn: 0 to 0.10%, The remainder is stainless steel with a chemical composition of Fe and impurities. The difference between the coefficient of thermal expansion of the skin plate and the coefficient of thermal expansion of the reinforcing material is 2.5 × 10 －６ Welded structures for sluice gates that are below / ℃. PREN=Cr+3.3Mo+16N...(a) However, each element symbol in the above formula represents the content (mass %) of each element contained in the steel, and zero is used if the element is not present.

2. The chemical composition of the aforementioned stainless steel skin plate is, in mass%, Cu: 0.01-2.0%, W: 0.01-1.0%, Co: 0.01 to 3.0%, V: 0.01-1.0%, Nb: 0.005-0.10%, Ta: 0.005-0.20%, Ca: 0.0010-0.0050%, Al: 0.003-0.10%, Ti: 0.001 to 0.03%, Zr: 0.001 to 0.05%, Hf: 0.001-0.10%, B: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, REM: 0.005–0.10%, and Sn: 0.001 to 0.10%, A welded structure for a sluice gate according to claim 1, comprising one or more selected from the following.

3. The chemical composition of the aforementioned reinforcing material, stainless steel, is, in mass%, Mo: 0.01-4.0%, Cu: 0.01-2.0%, W: 0.01-1.0%, Co: 0.01 to 3.0%, V: 0.01-1.0%, Nb: 0.005-0.10%, Ta: 0.005-0.20%, Ca: 0.0010-0.0050%, Al: 0.003-0.10%, Ti: 0.001 to 0.03%, Zr: 0.001 to 0.05%, Hf: 0.001-0.10%, B: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, REM: 0.005–0.10%, and Sn: 0.001 to 0.10%, A welded structure for a sluice gate according to claim 1, comprising one or more selected from the following.

4. A method for manufacturing welded structures for sluice gates, After hot-rolling the steel that is the material for the skin plate, a heat treatment temperature T is applied in the temperature range of 1000 to 1150°C. １ In addition to heat treatment, the steel, which is the material for the reinforcing material, is hot-worked, and then subjected to a heat treatment temperature T in the temperature range of 950 to 1100°C. ２ The process involves heat treatment, The process includes welding the skin plate and the reinforcing material with a heat input of 40 kJ / cm or less. The heat treatment temperature T １ and the heat treatment temperature T ２ A method for manufacturing a welded structure for a sluice gate according to any one of claims 1 to 3, wherein the difference between the temperature and the temperature is 150°C or less.

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