KR20210005235A - Corrosion-resistant steel for docks of coal-only ships or coal-coal combined ships, and docks - Google Patents

Abstract

The corrosion-resistant steel for docks of this coal-only ship or coal-coal combined ship has a chemical composition in mass%, C: 0.01 to 0.20%, Mn: 0.10 to 2.00%, Sn: 0.05 to 0.50%, Cr: 0 to 5.00%, Al : 0 to 3.000%, Ni: 0 to 5.00%, Sb: 0 to 0.50%, Cu: 0 to 0.50%, Mo: 0 to 1.00%, W: 0 to 1.00%, Ti: 0 to 0.100%, Zr: 0 to 0.200%, Ca: 0 to 0.0500%, Mg: 0 to 0.0500%, REM: 0 to 0.0500%, Nb: 0 to 0.100%, V: 0 to 0.100%, B: 0 to 0.0100%, Si: 1.00 % Or less, P: 0.050% or less, S: 0.0300% or less, N: 0.0080% or less, O: 0.0100% or less, the balance is Fe and impurities, in the chemical composition, 0.10≦[Cr]≦5.00, 0.100< At least one of [Al]≦3.000 and 0.30≦[Ni]≦5.00 is satisfied.

Description

Corrosion-resistant steel for docks of coal-only ships or coal-coal combined ships, and docks

The present invention relates to a corrosion-resistant steel and a dock for a dock of a coal-only ship or a combined mine ship. This application claims priority based on Japanese Patent Application No. 2018-204699, Japanese Patent Application No. 2018-204700, and Japanese Patent Application No. 2018-204701, filed in Japan on October 31, 2018, I use the content here.

In recent years, corrosion in the dock of a coal-only ship carrying coal or a combined mine ship carrying iron ore and coal (hereinafter, sometimes referred to as a cargo hold) has been a problem. Conventionally, coating has been applied to the cargo hold where coal is loaded, but the coating is often peeled off due to mechanical damage caused by coal or scratches and abrasions caused by heavy machinery during unloading. It is exposed to a corrosive environment, and a sufficient anticorrosive effect is not obtained.

In order to maintain the anticorrosive effect due to the formation of the coating film, periodic repainting and repair are required, but a large cost is required to perform repainting or repair. Therefore, there is a demand for a steel sheet having excellent corrosion resistance (no-coating corrosion resistance) even in the portion where the coating has been peeled off. In response to such a demand, for example, in Patent Documents 1 to 3, corrosion-resistant steel having improved corrosion resistance by adding a small amount of an alloying element is proposed.

The techniques described in these patent documents are corrosion-resistant steels that contain alloying elements (oxygen-resistant elements) that suppress corrosion by acids such as Sb and Cu, and improve corrosion resistance in a low-pH environment.

Japanese Patent Application Publication No. 2012-177190 Japanese Patent Publication No. 2013-227610 Japanese Patent Publication No. 2016-027198

Conventionally, in a dock, sulfur contained in coal melts in the condensation water generated on the side wall of the dock, and sulfuric acid is produced by an increase in temperature, and it is thought that corrosion will proceed as the environment becomes low. However, the present inventors, in the interface between the analysis of the steel corrosion in the dock, the corrosion product and base iron chloride ions (Cl ^-) showed a sulfate ion (SO ₄ ^2-) and the like, was not observed. Thus, the major factor in the corrosion dock is not a sulfate ion (SO ₄ ^2-), chloride ion (Cl ^-) is considered.

Conventionally, since it was considered that corrosion of steel materials proceeds by sulfuric acid in the dock, an acid-resistant element is added to the steel materials used in the dock, and the addition of alloying elements such as Cr, which promotes corrosion by acid, could be avoided. However, the review by the present inventors, within the dock chloride ions (Cl ^-), and the corrosion factor was found out that the corrosion proceeds by the wet and dry repeatedly. Therefore, for the component design of the corrosion-resistant steel for a dock of a coal-only ship or a combined mine ship, a concept different from the conventional one is required.

In other words, according to the research of the present inventors, it was found that it is necessary to design the components of corrosion-resistant steel for docks in consideration of the corrosion form that chloride ions affect, not the corrosion form affected by sulfate ions.

The present invention is more suitable for a corrosive environment in which chloride ions in the dock (in the cargo hold) influence the corrosion-resistant steel component design based on the prior art containing oxygen-resistant elements such as Sb or Cu, and also suppresses corrosion. The task is to provide corrosion-resistant steel for docks of coal-only ships or mine-coal combined ships.

The inventors of the present invention have found, by research, that β-FeOOH is contained in the rust layer formed on the surface of the steel plate in the dock. Accordingly, the inventors have found that within the dock, as sulfate ion (SO ₄ ^2-) which was conventionally considered, chloride ions (Cl ^-) is the cause of corrosion, a neutral chloride environment, and high-concentration chloride environment the pH is reduced ( I thought that a low-pH, high-concentration chloride environment) became a repetitive corrosive environment. Specifically, the corrosive environment of the interface between the steel material and the coal in a state in which coal is loaded in the dock (referred to as a loading state) is a neutral chloride environment, while in a state in which coal is unloaded from the dock (referred to as an empty state). The corrosive environment on the surface of the steel material is considered to be a low-pH, high-concentration chloride environment.

During transport or transport, the coals come into contact with each other, producing fine powder of coal. In this environment, it is assumed that it is not a large lump of coal that particularly affects corrosion, but this fine powder. The fine powder covers the steel at the bottom of the cargo hold and keeps moisture.

Therefore, in the dropping state, between the surface of the coal and the steel due to the chloride ions contained in the coal stored in the port, sea salt such as sodium chloride, calcium chloride and magnesium chloride derived from seawater, and moisture such as rain or cooling water. It is assumed that a neutral chloride environment is always present in which a neutral solution containing chloride ions is present.

On the other hand, in the unloading state, the mixture of the fine powder of coal and the chloride remaining in the dock is absorbed, thereby forming a thin water film in which chloride ions are concentrated on the surface of the steel material, and the pH decreases as the corrosion progresses. It is estimated that this low-pH high-concentration chloride environment is established.

Therefore, it is considered that the corrosive environment in the dock of the coal-only ship or the combined use of coal mines is different from a simple seawater environment or a case in which only iron ore that is hard and hardly generates fine powder is dropped.

The present inventors investigated the alloying element that suppresses the corrosion of steel materials based on the assumption that the inside of the dock where coal is loaded, the neutral chloride environment and the low-pH high-concentration chloride environment as described above become a repeated corrosion environment. In addition, the present inventors, Cr or Al that inhibits corrosion in a neutral chloride environment, or Ni that inhibits corrosion of steel in any environment of a neutral chloride environment, a low pH, high concentration chloride environment, and corrosion in a low pH high concentration chloride environment. It was found that by simultaneously containing Sn to be suppressed, corrosion can be remarkably suppressed.

The present invention has been made based on these findings, and the summary is as follows.

(1) The corrosion-resistant steel for a dock of a coal-only ship or a combined coal-coal ship according to an aspect of the present invention has a chemical composition in mass%, C: 0.01 to 0.20%, Mn: 0.10 to 2.00%, Sn: 0.05 to 0.50%, Cr: 0 to 5.00%, Al: 0 to 3.000%, Ni: 0 to 5.00%, Sb: 0 to 0.50%, Cu: 0 to 0.50%, Mo: 0 to 1.00%, W: 0 to 1.00%, Ti : 0 to 0.100%, Zr: 0 to 0.200%, Ca: 0 to 0.0500%, Mg: 0 to 0.0500%, REM: 0 to 0.0500%, Nb: 0 to 0.100%, V: 0 to 0.100%, B: 0 to 0.0100%, Si: 1.00% or less, P: 0.050% or less, S: 0.0300% or less, N: 0.0080% or less, O: 0.0100% or less, the balance is Fe and impurities, in the above chemical composition, the following formula At least one of 1 to 3 is satisfied.

0.10≤[Cr]≤5.00: Equation 1

0.100<[Al]≤3.000: Equation 2

0.30≤[Ni]≤5.00: Equation 3

In the above formulas 1 to 3, [X] represents the content by mass% of the element X.

(2) The corrosion-resistant steel for the dock of the coal-only ship or the coal-coal combined ship according to the above (1), in mass%, Sb: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Mo: 0.05 to 1.00%, and W: 0.05 to You may contain 1 type or 2 or more types selected from the group consisting of 1.00%.

(3) The corrosion-resistant steel for the dock of the coal-only ship or the coal-coal combined ship according to (1) or (2) above, in mass%, Ti: 0.005 to 0.100%, Zr: 0.005 to 0.200%, Ca: 0.0010 to 0.0500%, Mg: 0.0010 to 0.0500% and REM: 0.0010 to 0.0500% may contain one or more selected from the group consisting of.

(4) The corrosion-resistant steel for the dock of the coal-only ship or the coal-coal combined ship according to any one of the above (1) to (3) is, in mass%, Nb: 0.005 to 0.100%, V: 0.005 to 0.100%, and B: 0.0003 to 0.0100 You may contain 1 type or 2 or more types selected from the group consisting of %.

(5) The dock of a coal-only ship or a coal mine combined use ship according to another aspect of the present invention is made of the corrosion-resistant steel for a dock according to any one of the above (1) to (4).

Advantageous Effects of Invention According to the above aspect of the present invention, it is possible to provide a corrosion-resistant steel for a dock of a coal-only ship or a combined mine ship, and a dock having excellent corrosion resistance in a corrosive environment in a dock where coal is loaded. And, according to the dock manufactured using the corrosion-resistant steel for the dock of such a coal-only ship or a combined mine ship, it is possible to drastically reduce maintenance costs due to member changeover or repainting due to corrosion in the dock. Therefore, the industrial contribution of the present invention is very remarkable.

Hereinafter, the corrosion-resistant steel for the dock of the coal-only ship or the combined use of a coal mine according to an embodiment of the present invention (hereinafter, sometimes referred to as corrosion-resistant steel for a dock according to the present embodiment) will be described in detail.

First, the chemical composition of the corrosion resistant steel for docks according to the present embodiment will be described. "%" showing the content of each element in the chemical composition means mass%. In addition, in the numerical range in the chemical composition, the numerical range expressed using "to" means a range including the numerical values before and after "to" as a lower limit value and an upper limit value, unless otherwise specified. Therefore, for example, 0.01 to 0.20% means a range of 0.01% or more and 0.20% or less. On the other hand, about exceeding or less than, it means not including the value.

(C: 0.01 to 0.20%)

C (carbon) is an element that increases the strength of steel. In order to sufficiently obtain this effect, the C content is made 0.01% or more. Preferably, the C content is set to 0.03% or more.

On the other hand, when the C content becomes excessive, corrosion resistance decreases due to generation of cementite. Therefore, the C content is set to 0.20% or less. Preferably, the C content is 0.15% or less.

(Mn: 0.10 to 2.00%)

Mn (manganese) is an element that improves the strength and toughness of steel. In order to obtain this effect, the Mn content is made 0.10% or more. The Mn content is preferably made 0.20% or more, more preferably 0.50% or more.

On the other hand, Mn is an element that forms MnS, which is a starting point of corrosion. In order to avoid deterioration of the corrosion resistance of the steel material, the Mn content is set to 2.00% or less. Preferably, the Mn content is 1.50% or less, more preferably 1.20% or less.

(Sn: 0.05 to 0.50%)

Sn (tin) is an important element that reduces the anode dissolution rate of steel and suppresses the cathode reaction in a low-pH high-concentration chloride environment. In order to improve the corrosion resistance in the dock in an emptying state, the Sn content is made 0.05% or more. Preferably, the Sn content is set to 0.07% or more, more preferably 0.10% or more.

On the other hand, when Sn is contained excessively, manufacturability is impaired. Therefore, the Sn content is set to 0.50% or less. Preferably, the Sn content is made 0.35% or less.

(Cr: 0 to 5.00%)

Cr (chromium) is an important element that rapidly reduces the anode dissolution rate of steel in a neutral chloride environment. When Cr improves the corrosion resistance in the dock in the dropping state, the Cr content is made 0.10% or more. The Cr content is preferably 0.20% or more, more preferably 0.30% or more. In the case of improving the corrosion resistance in the dock in the dropping state with Al and/or Ni, the Cr content may be 0%, but since Cr has a greater effect of improving corrosion resistance than Al and Ni, it is preferable to contain Cr.

On the other hand, when Cr is contained excessively, the weldability falls. Therefore, the Cr content is made 5.00% or less. Preferably, the Cr content is set to 3.00% or less, more preferably 2.50% or less, still more preferably 2.00% or less or 0.80% or less, 0.60% or less, or 0.50% or less.

Cr is known to lower the corrosion resistance in a low-pH, high-concentration chloride environment, but by containing it with a predetermined amount of Sn at the same time, such adverse effects are eliminated.

(Al: 0 to 3.000%)

Al (aluminum) is an important element that reduces the anode dissolution rate of steel in a neutral chloride environment. When Al improves the corrosion resistance in the dock in the dropping state, the content of Al is made more than 0.100%. However, when Cr and/or Ni improves the corrosion resistance in the dock in the dropping state, the Al content may be 0.100% or less or 0%.

On the other hand, if Al is contained excessively, weldability is deteriorated. Therefore, the Al content is set to 3.000% or less. The Al content is preferably 2.500% or less, more preferably 2.000% or less.

In addition, Al is also an element effective for deoxidation of steel. Deoxidation can be performed with elements other than Al, and the Al content may be 0%. However, in order to obtain a deoxidation effect by Al, the Al content is preferably 0.001% or more, and the Al content is further 0.005% or more. It is preferable, and it is more preferable to make Al content into 0.010% or more.

(Ni: 0 to 5.00%)

Ni is an element which improves the corrosion resistance in the dock in a dropping state and a flying state. When Ni improves the corrosion resistance in the dock in the dropping state, the Ni content is made 0.01% or more. More preferably, the Ni content is made 0.05% or more. Ni is also effective in suppressing surface scratches generated when hot rolling of steel containing Cu. When the corrosion resistance in the dock is improved by Cr and/or Al, the Ni content may be 0%.

On the other hand, the upper limit of the Ni content is 5.00% or less from the viewpoint of cost. The Ni content is preferably less than 0.30%, more preferably 0.20% or less.

On the other hand, in the corrosive environment inside the dock, in order to further increase the corrosion resistance of the steel material, particularly in an empty state, in addition to the above-described components, one or two or more of Sb, Cu, Mo, and W may be contained.

In addition, in addition to the above-described components, one or two or more of Ti, Zr, Ca, Mg, and REM may be contained for the purpose of suppressing the formation of MnS which lowers the corrosion resistance and controlling the form.

Further, in order to increase the strength of the steel material, in addition to the above-described components, one or two or more of Nb, V, and B may be contained.

Since all of these elements do not necessarily need to be contained, the lower limit of the content is 0%.

(Sb: 0 to 0.50%)

Sb (antimony), like Sn, is an element that improves corrosion resistance in an empty state. When obtaining this effect, it is preferable to make Sb content into 0.01% or more. More preferably, the Sb content is made 0.05% or more.

On the other hand, when Sb is contained excessively, manufacturability is impaired. Therefore, even when making it contain, the Sb content is made 0.50% or less. Preferably, the Sb content is made 0.35% or less.

(Cu: 0 to 0.50%)

Cu (copper), like Sn and Sb, is an element that improves corrosion resistance in an empty state. When obtaining this effect, it is preferable to make the Cu content into 0.01% or more. More preferably, the Cu content is 0.05% or more. Further, when Cu and Sn are coexisted, the corrosion resistance in the dock is remarkably improved, so it is preferable to coexist.

On the other hand, when Cu is contained excessively, manufacturability is impaired. Therefore, even when making it contain, the Cu content is made 0.50% or less. Preferably, the Cu content is made 0.35% or less.

(Mo: 0 to 1.00%)

Mo (molybdenum) is an element that forms oxygenate ions MoO ₄ ^2- , acts as an inhibitor in an acidic solution, and suppresses the dissolution of the anode of steel. In order to improve the corrosion resistance in an emptying state, it is preferable to make the Mo content 0.05% or more. More preferably, the Mo content is made 0.10% or more. On the other hand, even if the Mo content exceeds 1.00%, the effect is saturated. Therefore, even when making it contain, Mo content is made into 1.00% or less. Preferably, the Mo content is 0.50% or less.

(W: 0 to 1.00%)

W (tungsten), like Mo, is an element that forms oxygenate ions WO ^4- and acts as an inhibitor in an acidic solution to suppress the dissolution of the anode of steel. In order to improve the corrosion resistance in an empty state, it is preferable to make the W content into 0.05% or more. More preferably, the W content is made 0.10% or more.

On the other hand, even if the W content exceeds 1.00%, the effect is saturated. Therefore, even when making it contain, W content is made into 1.00% or less. Preferably, the W content is made 0.50% or less.

(Ti: 0 to 0.100%)

Ti (titanium) is an element that combines with S to form sulfides or carbosulfides, and is an element having an effect of suppressing the formation of MnS, which becomes a starting point of corrosion and deteriorates corrosion resistance. When obtaining this effect, it is preferable to make the Ti content 0.005% or more. More preferably, the Ti content is set to 0.010% or more.

On the other hand, when Ti is contained excessively, toughness may deteriorate. Therefore, even when making it contain, the Ti content is made 0.100% or less. Preferably, the Ti content is set to 0.050% or less.

(Zr: 0 to 0.200%)

Zr (zirconium) is an element that combines with S to form a sulfide, and is an element having an effect of suppressing the formation of MnS, which becomes a starting point of corrosion and deteriorates corrosion resistance. When obtaining this effect, it is preferable to make the Zr content 0.005% or more. More preferably, the Zr content is set to 0.010% or more.

On the other hand, when Zr is contained excessively, toughness may deteriorate. Therefore, even when making it contain, the Zr content is made into 0.200% or less. The Zr content is preferably 0.100% or less, more preferably 0.050% or less.

(Ca: 0 to 0.0500%)

(Mg: 0 to 0.0500%)

(REM: 0 to 0.0500%)

Ca, Mg, and REM are elements that combine with S to form sulfides or carbosulfides, and are elements having an effect of suppressing the formation of MnS, which becomes a starting point of corrosion and deteriorates corrosion resistance. Therefore, in the corrosion-resistant steel for a dock according to the present embodiment, one type or two or more types selected from these may be contained. In the case of suppressing the generation of MnS which becomes a starting point of corrosion and deteriorates corrosion resistance, the content of any element among Ca, Mg, and REM is preferably 0.0010% or more. In addition, these sulfides dissolve in water during a corrosion reaction and become alkali, and have an effect of suppressing a decrease in pH at the steel material interface. Therefore, more preferably, the content of any element is made 0.0030% or more, and still more preferably 0.0050% or more.

On the other hand, even if Ca, Mg, and REM are contained in excess, the effect is saturated. Therefore, even when making it contain, the Ca, Mg, and REM contents are made into 0.0500% or less, respectively. It is preferably 0.0300% or less, more preferably 0.0100% or less.

REM is a generic term for rare earth metal elements, namely Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. REM content means the total content of these elements.

(Nb: 0 to 0.100%)

(V: 0 to 0.100%)

Nb and V are elements that form carbide or nitride and increase the strength of steel. When obtaining this effect, it is preferable to contain at least any element 0.005% or more. More preferably, the content of any element among Nb and V is set to 0.010% or more.

On the other hand, when Nb and V are contained excessively, the toughness of the steel material decreases. Therefore, even when making it contain, the content of Nb and V is made 0.100% or less, respectively. Preferably, it is set to 0.050% or less.

(B: 0 to 0.0100%)

B is an element which improves the hardness of steel and improves the strength. When obtaining this effect, it is preferable to make the B content 0.0003% or more. More preferably, the B content is 0.0005% or more, and still more preferably 0.0010% or more.

On the other hand, if B is contained excessively, mechanical properties of the steel may be impaired. Therefore, even when making it contain, the B content is set to 0.0100% or less. Preferably, the B content is 0.0050% or less, more preferably 0.0030% or less.

(Si: 1.00% or less)

Si (silicon) is an element that increases the strength of steel while being useful as a deoxidizing agent. Deoxidation can also be performed with elements other than Si, and the Si content may be 0%, but when the effect of deoxidation is obtained, the Si content is preferably 0.01% or more. More preferably, the Si content is made 0.02% or more, and still more preferably 0.05% or more.

On the other hand, when the Si content exceeds 1.00%, the toughness of the base metal and the welded joint is impaired. Therefore, the Si content is set to 1.00% or less. Preferably, the Si content is set to 0.50% or less, more preferably 0.30% or less.

(P: 0.050% or less)

P (phosphorus) is an element that is generally contained as an impurity, and is an element that deteriorates the mechanical properties and weldability of steel materials. Therefore, the P content is set to 0.050% or less. Preferably it is 0.025% or less. The P content may be 0%, but from the viewpoint of manufacturing cost, 0.0001% or more of P may be contained. Further, P is an element that improves the corrosion resistance of steel in a chloride environment, and for the purpose of obtaining this effect, the P content may be 0.001% or more.

(S: 0.0300% or less)

S (sulfur) is an impurity, and is an element forming MnS that promotes corrosion. Therefore, the S content is limited to 0.0300% or less. The S content is preferably 0.0050% or less, and more preferably 0.0030% or less. Although the S content may be 0%, from the viewpoint of manufacturing cost, the S content may be 0.0001% or more.

(N: 0.0080% or less)

N (nitrogen) is an impurity, and is an element that forms coarse nitrides that lower the toughness of steel materials. In order to suppress the formation of coarse nitride, the N content is set to 0.0080% or less. Preferably, the N content is 0.0060% or less. The lower limit of the N content may be 0%, but from the viewpoint of manufacturing cost, it may be 0.0010% or more.

(O: 0.0100% or less)

O (oxygen) is an impurity, and is an element that forms a coarse oxide that lowers the toughness of a steel material. In order to suppress the formation of coarse oxides, the O content is set to 0.0100% or less. The O content is preferably 0.0060% or less, more preferably 0.0040% or less. The lower limit of the O content may be 0%, but from the viewpoint of manufacturing cost, it may be 0.0001% or more.

Components other than the above components of the corrosion-resistant steel for a dock according to the present embodiment are basically Fe and impurities. Here, impurities are components that are incorporated by various factors in the manufacturing process, including raw materials such as ore or scrap, when industrially manufacturing a steel sheet, and do not adversely affect the properties of the corrosion-resistant steel for docks according to the present embodiment. Means what is allowed in the range.

(0.10≤[Cr]≤5.00: Equation 1, 0.100<[Al]≤3.000: Equation 2, 0.30≤[Ni]≤5.00: Satisfies at least one of Equation 3)

As described above, in order to improve the corrosion resistance in a neutral chloride environment in the dock where coal is loaded, it is necessary to contain at least one of 0.10% or more of Cr, 0.100% of Al, and 0.30% or more of Ni. . That is, in the corrosion-resistant steel for a dock according to the present embodiment, after making the content of each element as described above, it is necessary to satisfy at least one of the following equations 1 to 3.

0.10≤[Cr]≤5.00: Equation 1,

0.100<[Al]≤3.000: Equation 2,

0.30≤[Ni]≤5.00: Equation 3

In the above formulas 1 to 3, [X] represents the content by mass% of the element X.

Cr content may be in the range of the following formula 1'.

0.10≤[Cr]≤3.00: Equation 1'

In the present embodiment, the shape of the corrosion-resistant steel for a dock is not particularly limited, and may be a steel plate, a steel strip, a shape steel, a steel pipe, a bar, a steel wire or the like. The thickness of steel materials, such as a steel plate, a steel strip, a shape steel, and a steel pipe, is not particularly limited, but is usually 3 to 50 mm. A preferable lower limit is 6 mm, and a more preferable lower limit is 10 mm. In addition, a preferable upper limit of the thickness is 40 mm, and a more preferable upper limit is 30 mm.

In addition, in the corrosion-resistant steel for a dock according to the present embodiment, the metal structure is not limited. The metal structure may be appropriately selected, such as ferrite/pearlite, bainite, or martensite, depending on mechanical properties such as required strength.

Next, a description will be given of a dock for a coal-only ship or a combined mine ship (the dock according to the present embodiment) according to an embodiment of the present invention.

The dock according to the present embodiment is manufactured by using the corrosion-resistant steel for a dock according to the present embodiment described above as a material, processing them as necessary, and combining them by welding or the like. The chemical composition of the corrosion-resistant steel for a dock according to the present embodiment does not change during the process of the steel plate becoming a dock. Therefore, about the range of the chemical composition and the reason for limitation of the dock according to the present embodiment, it is substantially the same as the corrosion-resistant steel for the dock according to the present embodiment described above.

That is, it can be said that the dock according to the present embodiment is provided with the corrosion resistant steel for the dock according to the present embodiment.

Next, the corrosion-resistant steel for a dock according to the present embodiment and a method for manufacturing the dock according to the present embodiment will be described. The corrosion-resistant steel for a dock according to the present embodiment includes a steel plate, a shape steel, a steel pipe, etc. manufactured by performing hot rolling and performing cold rolling as necessary.

The corrosion-resistant steel for a dock according to the present embodiment is manufactured by melting steel by a conventional method, adjusting the components to the above-described range, hot rolling the steel piece obtained by casting, and performing cold rolling as necessary. After hot rolling, water cooling may be performed as it is, or air cooling may be performed and then reheated to perform quenching or tempering. After hot rolling, you may wind up in a coil shape. After hot rolling, cold rolling may be performed and further heat treatment may be performed.

In the present embodiment, in the case of manufacturing a steel pipe, a steel plate may be formed into a tubular shape and welded, and a UO steel pipe, an electric resistance welded steel pipe, a single welded steel pipe, a spiral steel pipe, or the like can be used.

A seamless steel pipe manufactured by subjecting a steel piece to hot extrusion or perforation rolling is also included in the corrosion-resistant steel for a dock of the present embodiment.

The dock according to the present embodiment may be manufactured from the corrosion-resistant steel for a dock according to the present embodiment thus obtained as a material by a known method.

Example

Hereinafter, examples are shown for the corrosion-resistant steel for a dock of a coal-only ship or a combined mine ship of the present invention. However, the embodiments described below are to be described in accordance with specific examples, and do not limit the content of the claims relating to the present invention.

A test piece having a length of 100 mm, a width of 60 mm, and a thickness of 5 mm was produced (collected) from a steel piece of chemical composition (the remainder is Fe and impurities) shown in Tables 1 and 2 described later. The surface of the test piece was subjected to a blast treatment so that the roughness was not less than Sa 2.5 (ISO 8501-1). Using these test pieces, a corrosion test was carried out simulating the environment inside the dock where coal is dropped.

The corrosion test was carried out in a test tank in which the temperature was maintained at 40°C and the relative humidity was maintained at 98%. In the state where the powdery coal containing artificial seawater was loaded on the test piece, it was held in the test tank for one week to reproduce the dropping condition, and then, the coal adhering to the surface of the test piece was lightly removed with a scraper, and 1 The process of holding for a week and reproducing an emptying state was set as one cycle. After performing this cycle for 6 cycles, rust on the surface of the test piece was removed with a scraper, and rust was removed with an ammonium citrate solution.

Thereafter, the weight of the test piece was measured, and the corrosion loss was calculated by subtracting from the weight of the test piece before the test, and the corrosion rate [mm/y] was calculated from the corrosion loss of 6 cycles (12 weeks). y means the year.

Steel No. 101 shown in Tables 1 and 2 described later does not contain Sn, and is a conventional steel in which the content of Cr, Al, and Ni does not satisfy any of the formulas 1 to 3. The corrosion rate of steel No. 101 is equivalent to the corrosion rate of the steel material exposed in the actual ship, and it is found that the environment in the ship can be simulated by the above corrosion test. Therefore, the corrosion resistance of each steel was evaluated by the corrosion rate ratio (%), which is the ratio of the corrosion rate of each steel to the corrosion rate of steel No. 101 in Tables 1 and 2.

The chemical composition and the results of the above tests are shown in Tables 1 and 2.

As shown in Tables 1 and 2, steel Nos. 1 to 11, 21 to 36, and 41 to 51 had a corrosion rate suppressed to 70.0% or less compared to steel No. 101, and the corrosion resistance was good.

On the other hand, steel No. 102 containing Cr and having a small Al content and not containing Ni and Sn, and steel No. 103 having insufficient Sn content had insufficient effect of improving corrosion resistance.

Further, steel No. 104, which lacked all of the Cr content, Al content, Ni content, and Sn content, had more corrosion loss than steel No. 101. This is considered to be because a sufficient effect of improving corrosion resistance was not obtained, and Cr contained in a trace amount in an acidic environment had a rather adverse effect.

Even if Sn was sufficiently contained, steel No. 105, which had insufficient Cr content, Al content, and Ni content, had a small corrosion inhibiting effect in a neutral chloride environment, and sufficient corrosion resistance improvement was not observed.

Even if it contains more than 0.100% of Al, steel No. 202 which does not contain Sn has insufficient effect of improving corrosion resistance. Even if Al or Cr was sufficiently contained, the corrosion inhibiting effect in the low-pH high-concentration chloride environment of No.204 and steel No.205, which were insufficient in Sn content, was small, and sufficient corrosion resistance improvement effect was not observed.

Steel No.402 containing 0.30% or more of Ni and not containing Sn, or steel No.403 having insufficient Sn content even if it contained Ni and Sn had insufficient effect of improving corrosion resistance.

In addition, even if Sn is sufficiently contained, steel No.404 whose Cr content, Al content, and Ni content all do not satisfy Equation 1 to Equation 3 has a small effect of inhibiting corrosion in a neutral chloride environment, and sufficient corrosion resistance improvement is achieved. I didn't see it.

Steel No.405, in which both Cr content, Al content, and Ni content do not satisfy Equation 1 to Equation 3, and also lack Sn content, has a small corrosion inhibiting effect in both an acidic environment and an acidic chloride environment, and corrosion resistance is not improved. .

Advantageous Effects of Invention According to the present invention, since it is possible to significantly reduce maintenance costs due to member switching or repainting due to corrosion in a dock, the industrial contribution is very large.

Claims (5)

The chemical composition is mass%,
C: 0.01 to 0.20%,
Mn: 0.10 to 2.00%,
Sn: 0.05 to 0.50%,
Cr: 0 to 5.00%,
Al: 0 to 3.000%,
Ni: 0 to 5.00%,
Sb: 0 to 0.50%,
Cu: 0 to 0.50%,
Mo: 0 to 1.00%,
W: 0 to 1.00%,
Ti: 0 to 0.100%,
Zr: 0 to 0.200%,
Ca: 0 to 0.0500%,
Mg: 0 to 0.0500%,
REM: 0 to 0.0500%,
Nb: 0 to 0.100%,
V: 0 to 0.100%,
B: 0 to 0.0100%,
Si: 1.00% or less,
P: 0.050% or less,
S: 0.0300% or less,
N: 0.0080% or less,
O: 0.0100% or less,
The balance is Fe and impurities,
In the above chemical composition, satisfying at least one of the following formulas 1 to 3,
Corrosion-resistant steel for docks of coal-only ships or mines.
0.10≤[Cr]≤5.00: Equation 1
0.100<[Al]≤3.000: Equation 2
0.30≤[Ni]≤5.00: Equation 3
In the above formulas 1 to 3, [X] represents the content by mass% of the element X. The method according to claim 1, by mass%,
Sb: 0.01 to 0.50%,
Cu: 0.01 to 0.50%,
Mo: 0.05 to 1.00% and,
W: 0.05 to 1.00%
Corrosion-resistant steel for the dock of a coal-only ship or a combined mine ship, containing one or two or more selected from the group consisting of. The method according to claim 1 or 2, by mass%,
Ti: 0.005 to 0.100%,
Zr: 0.005 to 0.200%,
Ca: 0.0010 to 0.0500%,
Mg: 0.0010 to 0.0500% and
REM: 0.0010 to 0.0500%
Corrosion-resistant steel for the dock of a coal-only ship or a combined mine ship, containing one or two or more selected from the group consisting of. The method according to any one of claims 1 to 3, by mass%,
Nb: 0.005 to 0.100%,
V: 0.005 to 0.100% and
B: 0.0003 to 0.0100%
Corrosion-resistant steel for the dock of a coal-only ship or a combined mine ship, containing one or two or more selected from the group consisting of. A dock of a coal-only ship or a combined coal-coal ship made of the corrosion-resistant steel for a dock according to any one of claims 1 to 4