JP2023140295A - Antimicrobial corrosion low alloy steel - Google Patents

Abstract

To provide an antimicrobial corrosion low alloy steel.SOLUTION: An antimicrobial corrosion low alloy steel has a component composition composed of, in terms of mass%, 0.01-0.50% of C, 0.01-1.00% of Si, 0.10-3.00% of Mn, 0.030% or less of P, 0.0100% or less of S, 0.0100 or less of N, 0.001-0.30% of Al, 0.003-0.20% of Ag, 4.00% or less of Cr, and the rest, namely, Fe and inevitable impurities.SELECTED DRAWING: None

Description

The present invention relates to antimicrobial corrosion low alloy steel materials suitable for structural members such as automobile parts, power generation equipment parts, chemical plant parts, architectural parts, machine parts, ship parts, and oil field incidental equipment parts. .

Previously, pathogenic bacteria such as Escherichia coli and Salmonella, and corrosive bacteria such as sulfate-reducing bacteria and sulfur-oxidizing bacteria have been used in our social lives from a sanitary and industrial perspective. Bacteria whose proliferation should be avoided are known. Particularly in recent years, with significant advances in the fields of analysis and biology, the negative impact of bacteria on social life has become widely recognized. One of these is the phenomenon of microbial corrosion. Microbial corrosion is a highly localized corrosion phenomenon, and there is a risk that microbial corrosion that occurs in a structure may become a through hole, leading to a serious accident. Common countermeasures against microbial corrosion include reducing the number of microorganisms present in the environment using disinfectants and physically removing microorganisms attached to materials (cleaning with brushes, etc.). However, there are limits to the reduction of microbial corrosion by these means, and there is growing interest in approaches that increase the resistance of materials to microbial corrosion. In line with this trend, attempts have been made in the field of steel materials to impart resistance to microbial corrosion.

For example, in Patent Document 1, a layer containing zinc is provided between a steel material and an epoxy resin coating, and the layer containing zinc is a layer consisting only of zinc, or a layer containing 85% by mass or more of zinc, and other configurations. A method for preventing corrosion and paint peeling of steel materials has been reported, which is characterized by a layer made of an alloy containing any one of nickel, aluminum, magnesium, and iron as an element.

Furthermore, in Patent Document 2, an outer layer consisting of a Cr(III)-Fe(III)-based hydroxide and an inner layer of a film mainly composed of a Cr(III)-based oxide and/or hydroxide are formed on the surface. A stainless steel with excellent microbial corrosion resistance characterized by having a two-layer coating has been reported.

Further, in Patent Document 3, in mass %, Cu: 0.010% or more and less than 2.000%, Ni: 0.010% or more and 2.000% or less, Mo: 0.010% or more and 1.000% or less, Antibacterial properties and microbial corrosion resistance are enhanced by containing one or more selected from W: 0.010% to 1.000% and Sn: 0.010% to 0.500%. Steel materials have been proposed.

On the other hand, new knowledge has recently been obtained regarding the mechanism of sulfate-reducing bacteria (SRB), which is known to be the main cause of microbial corrosion, and its mechanism of promoting corrosion of steel materials.

For example, Non-Patent Document 1 reports that corrosion acceleration by SRB is based on the direct extraction of electrons from steel materials by SRB. That is, in the metabolic activity of SRB, SRB present on the surface of the steel material directly oxidizes Fe, thereby promoting dissolution of the steel material. S ^2- ions produced as a result of this metabolic activity combine with Fe ²⁺ ions produced as a result of steel material corrosion, and a hardly soluble FeS film is formed on the steel surface. This is because this FeS coating acts as a corrosion-resistant coating, and is generally considered to contribute to reducing corrosion of steel materials. However, in the microbial corrosion phenomenon caused by SRB, since FeS has relatively high conductivity, sulfate-reducing bacteria attached to the FeS surface can withdraw electrons from the base material (steel material) even through FeS. direct oxidation) is possible. In other words, since the FeS surface becomes a route for iron oxidation reaction by SRB, local corrosion by SRB is promoted as FeS is formed.

Japanese Patent Application Publication No. 2010-222606 Japanese Patent Application Publication No. 7-26395 JP 2017-190522 Publication

X. Deng et al, Angew. Chem. 132, (2020), p6051

Although the method for preventing corrosion of steel described in Patent Document 1 is considered to have sufficient antibacterial properties, it requires painting and forming an alloy film. This is a very expensive process, and will result in excessive performance except in severe applications where particularly high corrosion resistance is required. In other words, it is not practical to use it for parts to which low-alloy steel is originally applied due to cost considerations. Furthermore, once the surface is damaged by impact, cuts, etc., the durability of the damaged area cannot be expected, making it difficult to obtain long-term effects.

In addition, although the technology described in Patent Document 2 is considered to be effective as a measure to improve the microbial corrosion resistance of stainless steel materials, it is difficult to apply it to parts for which inexpensive low-alloy steel materials are expected to be applied due to cost reasons. is difficult. Further, as in Patent Document 1, resistance to microbial corrosion cannot be ensured in areas where the surface is once scratched and the coating structure effective in microbial corrosion resistance is lost.

Furthermore, regarding the steel material described in Patent Document 3, microbial corrosion resistance is evaluated based on local corrosion in an actual seawater environment containing sulfate-reducing bacteria, which are corrosive bacteria. In real environments, microbial corrosion becomes apparent in places where corrosive bacteria become locally active and the bacteria concentration is high, but we do not assume an environment that reflects the actual state of microbial corrosion. In other words, the technique described in Patent Document 3 is simply the result of evaluating local corrosion in a seawater corrosive environment, and is uncertain as a microbial corrosion reduction technique.

As described above, in the field of low-alloy steel materials, from the viewpoint of ensuring long-term microbial corrosion resistance at low cost, no suitable technology has been established, and technology that improves the microbial corrosion resistance of the material itself is desired. However, it has not been technically established.

It is an object of the present invention to solve the problems of the prior art and to provide an antimicrobial corrosion low alloy steel material that is practical for manufacturing.

The inventors have made extensive studies to solve the above problems. First, from the perspective of reducing sulfate-reducing bacteria (SRB), which is a typical causative agent of microbial corrosion, on the material surface, we found that improving the antibacterial properties of steel against SRB is effective in reducing microbial corrosion. It was found that, in particular, the addition of Ag significantly improves its properties. Furthermore, as a result of further investigation based on the corrosion mechanism caused by SRB described in Non-Patent Document 1, it was found that the inclusion of Ni changes the properties of the corrosion product FeS, further improving its resistance to microbial corrosion. did.
The present invention was completed after further studies based on the above-mentioned novel findings, and the gist and structure of the present invention is as follows.

1. In mass%,
C: 0.01-0.50%,
Si: 0.01-1.00%,
Mn: 0.10-3.00%,
P: 0.030% or less,
S: 0.0100% or less,
N: 0.0100% or less,
Al: 0.001-0.30%,
An antimicrobial corrosion low alloy steel material having a composition containing 0.003 to 0.20% Ag and 4.00% or less Cr, with the remainder consisting of Fe and inevitable impurities.

2. The component composition further includes, in mass%,
The antimicrobial corrosion low alloy steel material as described in 1 above, which contains Ni: 0.010 to 3.00%.

3. The antimicrobial corrosion low alloy steel material according to item 1 or 2 above, wherein the component composition further contains, in mass %, one or more selected from the following groups A to D.
[Group A]
Sb: 0.01 to 0.20%,
Sn: 0.01-0.20%,
Cu: 0.01 to 1.00%,
Mo: 0.01-1.00% and W: 0.01-1.00%
One or more types selected from [Group B]
Ca: 0.0001-0.0100%,
Mg: 0.0001-0.0200% and REM: 0.001-0.200%
One or more types selected from [Group C]
Ti: 0.005-0.100%,
Zr: 0.005-0.100%,
Nb: 0.005-0.100% and V: 0.005-0.100%
One or more types selected from [Group D]
B: 0.0001-0.0300%

According to the present invention, when used for structural members such as automobile parts, power generation equipment parts, chemical plant parts, architectural parts, machine parts, ship parts, and oil field incidental equipment parts, compared to conventional ones, It is possible to obtain inexpensive low-alloy steel materials with antimicrobial corrosion resistance, which is extremely useful industrially.

Hereinafter, a low alloy steel material according to an embodiment of the present invention will be described. First, we will discuss the reasons for limiting the composition of steel materials. In this specification, "%" representing the content of each component element means "% by mass" unless otherwise specified.

C: 0.01-0.50%
C is an element necessary to ensure the strength of steel, and is contained in an amount of 0.01% or more, preferably 0.02% or more. On the other hand, if the C content exceeds 0.50%, workability and weldability will be significantly deteriorated, so the C content is limited to 0.50% or less. Preferably it is 0.40% or less, more preferably 0.30% or less.

Si: 0.01~1.00%
Si is added for deoxidation. In order to obtain a sufficient deoxidizing effect, the Si content is set to 0.01% or more, preferably 0.03% or more. If the Si content exceeds 1.00%, toughness and weldability will deteriorate, so the Si content should be 1.00% or less. It is preferably 0.80% or less, more preferably 0.70% or less.

Mn: 0.10-3.00%
Mn is added to improve strength and toughness. If the Mn content is less than 0.10%, the effect is not sufficient, so the Mn content is 0.10% or more, preferably 0.20% or more. On the other hand, if the Mn content exceeds 3.00%, weldability deteriorates, so the Mn content is set to 3.00% or less, preferably 2.50% or less. More preferably, it is 2.00% or less.

P: 0.030% or less When P content increases, toughness and weldability deteriorate, so the P content was suppressed to 0.030% or less. Preferably it is 0.025% or less. Since it is difficult to reduce the P content to less than 0.002% in industrial scale production, a content of 0.002% or more is permissible.

S: 0.0100% or less S is a harmful element that deteriorates the toughness and weldability of steel, so it is desirable to reduce it as much as possible. In particular, when the S content exceeds 0.0100%, the base metal toughness and weld zone toughness deteriorate significantly. Therefore, the S content is set to 0.0100% or less. Preferably it is 0.0080% or less, more preferably 0.0070% or less. Since it is difficult to reduce the S content to less than 0.0002% in industrial scale production, a content of 0.0002% or more is permissible.

N: 0.0100% or less When N is contained in a large amount, it forms coarse nitrides and reduces the toughness and weldability of the steel. For this reason, the N content was limited to 0.0100% or less. Preferably it is 0.0070% or less. Since it is difficult to reduce the N content to less than 0.0005% in industrial scale production, a content of 0.0005% or more is permissible.

Al: 0.001-0.30%
Al is an element added as a deoxidizing agent, and the Al content is 0.001% or more. However, when the Al content exceeds 0.30%, the toughness of the steel decreases. Therefore, the Al content is 0.30% or less, preferably 0.20% or less.

Ag: 0.003-0.20%
Ag is an essential element in order to obtain antimicrobial corrosion properties in the low alloy steel material of this embodiment. In a humid environment, a very small amount of Ag ⁺ ions are released from the surface of the steel material. This free Ag ⁺ ion is taken up by microorganisms on the surface of the steel material and strongly binds to amino acids and proteins having -SH groups present in the microorganism's enzyme system, inhibiting metabolic activity. As a result, it becomes difficult for corrosive microorganisms such as SRB to metabolize on the surface of the steel material, and microbial corrosion is suppressed. This effect can be obtained by containing 0.003% or more, so the Ag content should be 0.003% or more, preferably 0.005% or more, and more preferably 0.008% or more. . However, since Ag is an expensive metal, excessive inclusion is not preferable in terms of cost. Therefore, the Ag content is 0.20% or less, preferably 0.15% or less, and more preferably 0.10% or less.

Cr: 4.00% or less Cr is an element that greatly affects the expression of antimicrobial corrosion properties of Ag in the low alloy steel material of this embodiment, and its content needs to be appropriately limited. Cr forms an oxide film on the surface of steel materials in a humid environment where microorganisms exist. When this oxide film is strongly formed, the resistance of the steel material to wet corrosion increases excessively, thereby inhibiting release of Ag ⁺ ions from the surface of the steel material. As a result, the antimicrobial mechanism due to the Ag content is not expressed, and antimicrobial corrosion effects cannot be obtained. This inhibitory effect on Ag becomes apparent when the Cr content exceeds 4.00%. Therefore, the Cr content is set to 4.00% or less. Including the viewpoint of alloy cost reduction, it is preferably 3.00% or less. Although there is no need to limit the lower limit, when Cr is intentionally included, it is preferably 0.05% or more based on the viewpoint of improving resistance to wet corrosion due to Cr. More preferably, it is 0.10% or more, and still more preferably 0.15% or more. However, when a small amount of Cr is contained, resistance to wet corrosion is improved halfway, which may pose a risk of pitting corrosion occurring during wet corrosion. Therefore, it is more preferably more than 0.50%.

The basic components of this embodiment have been explained above. The remainder other than the above components is Fe and unavoidable impurities, but the following elements may also be included as appropriate. As an unavoidable impurity, for example, O may be contained in an amount of 0.0060% or less.

Ni: 0.010-3.00%
Ni is an effective element in supplementing the antimicrobial corrosion improvement effect of Ag in the low alloy steel material of this embodiment. As mentioned above, one of the mechanisms of microbial corrosion is direct oxidation of the steel material via the corrosion product FeS on the surface of the steel material. Ag inhibits the metabolic activity of corrosive microorganisms on the steel surface, making them unable to contribute to corrosion. On the other hand, once the corrosion product FeS is formed on the surface, corrosive microorganisms that are active on the FeS surface that is not in direct contact with the steel surface. For microorganisms, uptake of Ag ⁺ ions becomes insufficient and it is difficult to completely inhibit metabolic activity. Such microbial corrosion due to the metabolic activity (direct oxidation of iron) of corrosive microorganisms far away from the steel surface (on FeS corrosion products) is not as much as the corrosion caused by corrosive microorganisms on the steel surface, but By suppressing this FeS-mediated microbial corrosion (direct oxidation of iron), further antimicrobial corrosion properties can be obtained. Due to the Ni content, NiS is generated in addition to FeS due to microbial corrosion. When this NiS coexists with FeS as a corrosion product, the uniformity of the corrosion product FeS film is lost, and the conductivity of the corrosion product film is reduced. As a result, the microbial corrosion reaction (direct oxidation of iron) mediated by corrosion products does not proceed sufficiently. In order to obtain this effect, it is necessary to contain at least 0.010% or more of Ni, so it is preferable that the Ni content is 0.010% or more. On the other hand, when Ni is contained excessively, weldability and steel material manufacturability deteriorate, which is disadvantageous from a cost standpoint. Therefore, when Ni is contained, the Ni content is set to 3.00% or less. Preferably it is 2.50% or less, more preferably 2.00% or less.

[Group A]
Sb: 0.01~0.20%, Sn: 0.01~0.20%, Cu: 0.01~1.00%, Mo: 0.01~1.00% and W: 0.01~ One or more selected from 1.00% of Sb, Sn, Cu, Mo, and W are elements that improve corrosion resistance in a wet environment where microbial corrosion occurs, especially in a seawater environment. Therefore, apart from microbial corrosion, one or more types can be included for the purpose of improving seawater corrosion resistance. However, if the amount added is too large, it will cause deterioration of the toughness of the welded part and increase cost, so when one or more of these elements is added, the content should be Sb: 0.01 to 0.0. 20%, Sn: 0.01 to 0.20%, Cu: 0.01 to 1.00%, Mo: 0.01 to 1.00%, and W: 0.01 to 1.00%. .

[Group B]
One or more types selected from Ca: 0.0001 to 0.0100%, Mg: 0.0001 to 0.0200%, and REM: 0.001 to 0.200% Ca, Mg, and REM are For the purpose of ensuring toughness, one or more types can be contained. However, if the amount added is too large, it will lead to deterioration of the toughness of the welded part and increase in cost. Therefore, when one or more of these elements is added, the content should be Ca: 0.0001 to 0.0. 0100%, Mg: 0.0001 to 0.0200%, and REM: 0.001 to 0.200%.

[Group C]
One type selected from Ti: 0.005 to 0.100%, Zr: 0.005 to 0.100%, Nb: 0.005 to 0.100% and V: 0.005 to 0.100% One or more of Ti, Zr, Nb and V can be contained in order to ensure the desired strength. However, if the content of any of these elements is too large, the toughness and weldability will deteriorate, so when one or more of these elements is included, the content should be 0.005 to 0.100%, respectively. The range of addition amount was set as follows. Preferably, each content is in the range of 0.005 to 0.050%.

[Group D]
B: 0.0001-0.0300%
B is an element that improves the hardenability of steel materials. Further, B can be contained for the purpose of ensuring the strength of the steel material. The strength improving effect is poor if the B content is less than 0.0001%, so when B is included, it is set to 0.0001% or more. However, if B is contained excessively, the toughness will be significantly deteriorated, so the content of B is set to 0.0300% or less.

Incidentally, the inclusion of components other than those mentioned above is not prohibited as long as the effects of the present invention are not impaired.

Next, manufacturing conditions for the low alloy steel material according to this embodiment will be explained.
Molten steel having the above-mentioned composition is melted in a known furnace such as a converter or an electric furnace, and is made into a steel material such as a slab or billet by a known method such as a continuous casting method or an ingot forming method. Incidentally, upon melting, vacuum degassing refining or the like may be performed. A known steel refining method may be used to adjust the composition of the molten steel.

Next, when hot rolling the above steel material into a desired size and shape, it is preferable to heat it to a temperature of 1000°C to 1350°C. If the heating temperature is less than 1000°C, the deformation resistance will be large and hot rolling will be difficult, so the heating temperature is preferably 1000°C or higher, more preferably 1030°C or higher. On the other hand, heating above 1350°C may cause surface marks, increase scale loss and fuel consumption, so the heating temperature is preferably 1350°C or lower, more preferably 1300°C or lower. It is. Note that if the temperature of the steel material is originally in the range of 1000 to 1350°C, it may be directly subjected to hot rolling without being heated. In addition, after hot rolling, reheating treatment, pickling, and cold rolling may be performed to obtain a cold rolled sheet having a predetermined thickness.

In hot rolling, it is preferable that the finish rolling end temperature be 600° C. or higher. If the finish rolling end temperature is less than 600° C., the rolling load increases due to an increase in deformation resistance, making it difficult to carry out rolling. Cooling after completion of hot finish rolling is preferably performed by air cooling or accelerated cooling at a cooling rate of 150° C./s or less, but this does not apply when heat treatment is performed in a subsequent step.
Other manufacturing conditions may follow general manufacturing methods for low alloy steel materials.

Next, examples of the present invention will be described. Note that the present invention is not limited only to the following examples.
Molten steel having the chemical composition shown in Tables 1-1 and 1-2 was melted by a commonly known method and continuously cast into a slab (steel material). Next, the slab was heated to 1200° C. and then hot-rolled into a hot-rolled plate having a thickness of 20 mm. In the column of component composition in Tables 1-1 and 1-2, "-" indicates that nothing is added.

A piece measuring 25 mm x 25 mm x 3 mm (t means thickness) was cut out from the above-mentioned hot-rolled plate, and the entire surface was polished to a No. 600 polishing surface to form a test piece. The antimicrobial corrosion properties were evaluated by a test piece immersion test in a sulfate-reducing bacteria culture solution. The evaluation procedure and method are shown below.

First, a high concentration SRB culture solution was prepared. Microbial strains include Desulfovibrio vulgaris subsp. Vulgaris NBRC 104121 (=ATCC 29579) was used. ATCC Medium 1249 Modified Baar's (MB) Medium For Sulfate Reducers was used as the culture medium. D. subcultured in MB medium. vulgaris NBRC104121 was added to a screw cap test tube containing 5 mL of MB medium, and cultured at 37° C. for 4 days. Approximately 2.5 mL of the culture solution was then added to a sterile centrifuge tube containing fresh MB medium (1 L) in an anaerobic glove box. The sterilized centrifuge tube was set in a Gas Pack 100 anaerobic system to create an anaerobic condition and cultured at 21° C. for 3 days. After culturing, 0.1 mL of the 10-fold serial dilution was applied to the counting medium under anaerobic conditions, and cultured at 37°C for 4 days. After culturing, counts were performed at dilution stages where approximately 30 to 300 black colonies were observed (n = 3), and it was determined that the SRB concentration was 2.4 to 2.9 x 10 ⁷ (number of bacteria/mL). confirmed.

Next, the procedure of a test piece immersion test using the above-mentioned high concentration SRB culture solution is shown below. First, the Teflon (registered trademark) tube and nylon tube for suspending the test piece were previously subjected to high-temperature steam sterilization using an autoclave. After further immersion in 70% ethanol, it was wiped with a sterilized cloth and air-dried (under UV irradiation). The test piece was sprayed with approximately 70% ethanol and wiped off with a sterilized cloth. The specimen was secured with nylon thread and suspended in a Teflon tube. Thereafter, the test piece was set in a beaker and immersed in 2 L of culture solution. The culture solution in which the test piece was immersed was cultured in an anaerobic state at 21° C. for 28 days. At the 14th day, 3/4 (1.5 L) of the immersion culture solution was replaced with fresh culture solution. After being immersed for 28 days, the test material was taken out, and the corrosion products adhering to the surface were washed away with a sponge or the like, and then completely removed in an acid containing an inhibitor. Then, it was washed with pure water, then in ethanol, and air-dried. After that, the depth of pitting on the surface of the test piece was measured using a three-dimensional laser microscope (laser wavelength 658 nm, measurement pitch 0.5 μm) in two areas of 25 mm x 25 mm on the surface of the test piece, and the maximum pitting depth was It was evaluated as follows.

The microbial corrosion resistance was evaluated based on the maximum pitting depth value based on the following criteria. In addition, if it is ○ or ◎, it is determined that it has sufficient antimicrobial corrosion properties. The obtained results are also listed in Tables 1-1 and 1-2.
◎: Less than 10 μm ○: 10 μm or more and less than 30 μm ×: 30 μm or more

As shown in Tables 1-1 and 1-2, all of the invention examples have sufficient antimicrobial corrosion properties. On the other hand, all of the comparative examples have insufficient antimicrobial corrosion properties and are unsuitable as low alloy steel materials with antimicrobial corrosion properties.

The unit of volume "L" herein represents 10 ⁻³ m ³ .

Claims (3)

In mass%,
C: 0.01-0.50%,
Si: 0.01-1.00%,
Mn: 0.10-3.00%,
P: 0.030% or less,
S: 0.0100% or less,
N: 0.0100% or less,
Al: 0.001-0.30%,
An antimicrobial corrosion low alloy steel material having a composition containing 0.003 to 0.20% Ag and 4.00% or less Cr, with the remainder consisting of Fe and inevitable impurities. The component composition further includes, in mass%,
The antimicrobial corrosion low alloy steel material according to claim 1, characterized in that it contains Ni: 0.010 to 3.00%. The antimicrobial corrosion low alloy steel material according to claim 1 or 2, wherein the component composition further contains, in mass %, one or more selected from the following groups A to D.
[Group A]
Sb: 0.01 to 0.20%,
Sn: 0.01-0.20%,
Cu: 0.01 to 1.00%,
Mo: 0.01-1.00% and W: 0.01-1.00%
One or more types selected from [Group B]
Ca: 0.0001-0.0100%,
Mg: 0.0001-0.0200% and REM: 0.001-0.200%
One or more types selected from [Group C]
Ti: 0.005-0.100%,
Zr: 0.005-0.100%,
Nb: 0.005-0.100% and V: 0.005-0.100%
One or more types selected from [Group D]
B: 0.0001-0.0300%