Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• the present invention provides an antimicrobial corrosion-resistant low-alloy steel material 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, and a method for producing the same. It is related to.
• 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.
• 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 a steel material 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.
• 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.
• 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, By containing one or more selected from W: 0.010% to 1.000% and Sn: 0.010% to 0.500%, antibacterial properties and microbial corrosion resistance properties are enhanced. Steel materials have been proposed.
• SRB sulfate-reducing bacteria
• 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.
• Patent Document 1 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.
• Patent Document 2 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 against antimicrobial corrosion is lost.
• microbial corrosion resistance is evaluated based on local corrosion in an actual seawater environment containing sulfate-reducing bacteria, which are corrosive bacteria.
• sulfate-reducing bacteria which are corrosive bacteria.
• 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.
• 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.
• the purpose of the present invention is to solve the problems of the prior art and provide a practical antimicrobial corrosion low alloy steel material and a method for manufacturing the same.
• SRB reducing sulfate reducing bacteria
• Cu significantly improves its properties.
• the activity of SRB is greatly influenced by the dislocation density on the steel surface, and by increasing the uniformity of the dislocation density on the steel surface, the active field of SRB will be delocalized and localized corrosion will be suppressed.
• An antimicrobial corrosion-resistant low alloy steel material having a ratio of the minimum value to the maximum value (minimum value/maximum value) of dislocation density on the surface of the steel material is 0.40 or more.
• the component composition is in mass%, The antimicrobial corrosion low alloy steel material according to 1 above, containing Cu: 0.10 to 1.00%.
• the antimicrobial corrosion low alloy steel material according to 1 or 2 above, wherein the component composition contains one or more groups selected from the following groups A to E in mass %.
• groups A to E in mass %.
• Group B Sb: 0.01-0.20%; Sn: 0.01-0.20%; One or more types selected from Mo: 0.01 to 1.00% and W: 0.01 to 1.00%
• Group C Ca: 0.0001-0.0100%; One or more types selected from Mg: 0.0001 to 0.0200% and REM: 0.001 to 0.200%
• Group D Ti: 0.005-0.100%; Zr: 0.005-0.100%; One or more types selected from Nb: 0.005 to 0.100% and V: 0.005 to 0.100%
• Group E B: 0.0001 to 0.0300%.
• the final pass reduction rate is controlled in the range of 5 to 20% in the temperature range of 1000 to 1100°C, antimicrobial corrosion. Method of manufacturing low alloy steel.
• 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.
• the C content exceeds 0.50%, workability and weldability will be significantly deteriorated, so the C content is limited to 0.50% or less.
• it is 0.40% or less, more preferably 0.30% or less.
• Si 0.01 ⁇ 1.00% Si is added for deoxidation.
• 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, preferably 0.80% or less, and more preferably 0.70%. It is as follows.
• 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 should be 3.00% or less, preferably 2.50% or less, and more preferably 2.00% or less. be.
• P 0.030% or less
• the P content increases, toughness and weldability deteriorate, so the P content was suppressed to 0.030% or less.
• it is 0.025% or less. Since it is difficult to reduce the 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.
• the S content is set to 0.0100% or less.
• it is 0.0080% or less, more preferably 0.0070% or less. Since it is difficult to make the content less than 0.0002% in industrial scale production, a content of 0.0002% or more is allowed.
• N 0.0100% or less
• the N content was limited to 0.0100% or less.
• Preferably it is 0.0070% or less. Since it is difficult to reduce the 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.
• the Al content is 0.30% or less, preferably 0.20% or less.
• Cu 0.10-2.50%
• Cu is an essential element in order to obtain antimicrobial corrosion properties in the low alloy steel material of this embodiment.
• a very small amount of Cu 2+ is liberated from the surface of the steel material as Cu 2+ ions.
• These free Cu 2+ ions are taken up by microorganisms on the surface of the steel material and strongly bind to -SH group-containing amino acids and proteins present in the microorganism's enzyme system, thereby inhibiting metabolic activity.
• the Cu content should be 0.10% or more, preferably 0.15% or more, more preferably 0.20% or more. be.
• the Cu content is 2.50% or less, preferably 1.50% or less, more preferably 1.00% or less, still more preferably 0.80% or less, and even more preferably 0.60% or less. % or less.
• Cr 4.00% or less
• Cr is an element that greatly affects the development of antimicrobial corrosion properties of Cu 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 Cu 2+ ions from the surface of the steel material. As a result, the antimicrobial mechanism due to the Cu content is not expressed, and antimicrobial corrosion effects cannot be obtained.
• This inhibitory effect on Cu 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.
• Cr when it 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.
• 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.
• an unavoidable impurity for example, O may be contained in an amount of 0.0060% or less.
• Ni 0.030-3.00% Ni is an effective element in supplementing the antimicrobial corrosion improvement effect of Cu in the low alloy steel material of this embodiment.
• 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.
• the metabolic activity of corrosive microorganisms on the steel surface is inhibited by Cu, and they are no longer able to contribute to corrosion.
• 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 are For microorganisms, uptake of Cu 2+ 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.
• Ni In order to obtain this effect, Ni must be contained in an amount of at least 0.030%. Preferably it is 0.050% or more, more preferably 0.080% or more. On the other hand, when Ni is contained excessively, weldability and steel material manufacturability deteriorate, which is disadvantageous from a cost standpoint. For this reason, the Ni content is set to 3.00% or less. Preferably it is 2.50% or less, more preferably 2.00% or less.
• Sb 0.01 to 0.20%, Sn: 0.01 to 0.20%, Mo: 0.01 to 1.00% and W: 0.01 to 1.00%
• Sb, Sn, 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%, Mo: 0.01 to 1.00%, and W: 0.01 to 1.00%.
• 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%.
• Ti 0.005 to 0.100%
• Zr 0.005 to 0.100%
• Nb 0.005 to 0.100%
• V 0.005 to 0.100%
• Ti, Zr, Nb and V can be contained in order to ensure the desired strength.
• 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 amount added was within the range.
• each content is in the range of 0.005 to 0.050%.
• 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.
• the ratio of the minimum value to the maximum value of the dislocation density on the surface of the steel material is 0.40 or more.
• Cu is an element necessary to ensure the antimicrobial corrosion property of the steel material. be.
• Cu turns into a liquid phase on the surface of the high-temperature steel material during the manufacturing process of the steel material, making scale adhesion on the surface of the steel material non-uniform. Therefore, uneven cooling occurs on the surface of the steel material, causing a large difference between the maximum and minimum values of dislocation density in the surface layer of the steel material.
• the dislocation density on the steel surface greatly affects the metabolism of sulfate-reducing bacteria on the steel surface.
• the dislocation field on the steel surface has high microscopic unevenness and high activity, so sulfate-reducing bacteria easily adsorb to it.
• growth after adsorption shows a disadvantageous tendency in dislocation fields.
• the ratio of the minimum value of the dislocation density on the surface of the steel material to the maximum value of the dislocation density on the surface of the steel material is set to 0.40 or more. More preferably, it is 0.45 or more. More preferably, it is 0.50 or more. Note that the upper limit is not particularly limited and may be 1.00.
• the surface of the steel material is polished to remove scale, and measurements are taken at three points on the polished surface. Each measurement point should be spaced at intervals of 10 mm or more, avoiding the same location.
• the measurement method is not particularly limited, but in general, a method using X-ray diffraction (XRD) and transmission electron microscopy (TEM) is suitably applied.
• XRD X-ray diffraction
• TEM transmission electron microscopy
• the following method is applied in which X-ray diffraction is used and the dislocation density is converted using the strain obtained from the half width ⁇ of the X-ray diffraction measurement.
• ⁇ means a peak angle calculated by the ⁇ -2 ⁇ method of X-ray diffraction
• ⁇ means the wavelength of X-rays used in X-ray diffraction
• b is the Burgers vector of Fe( ⁇ ).
• 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.
• a known furnace such as a converter or an electric furnace
• a steel material such as a slab or billet
• a known method such as a continuous casting method or an ingot forming method.
• vacuum degassing refining or the like may be performed upon melting.
• a known steel refining method may be used to adjust the composition of the molten steel.
• the heating temperature is preferably 1030°C or higher, more preferably 1050°C or higher.
• 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. be. Note that if the temperature of the steel material is originally in the range of 1030 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.
• the final pass reduction rate in the temperature range of 1000 to 1100°C in the range of 5 to 20% during hot rolling of steel materials is extremely important. That is, as described above, in a steel material containing Cu, Cu turns into a liquid phase on the surface of the steel material during the heating process, and an embrittled surface is formed. During hot rolling in this state, the brittle surface may peel off unevenly together with the surface scale, resulting in uneven surface texture. As a result, an uneven surface may be formed in the cooling state during the hot rolling process.
• the final pass reduction should be controlled within the range of 5 to 20% at a temperature of 1000°C or more and 1100°C or less, and at the final stage of the hot rolling process. , it is important to uniformly peel off the brittle surface together with the scale. If the final pass rolling reduction ratio is less than 5%, the brittle structure on the surface will not be completely peeled off and a portion will remain. In addition, when the final pass reduction rate exceeds 20%, excessive load is applied to the surface, which causes not only the embrittled structure but also some of the insufficiently embrittled structure to peel off along with the surface scale, resulting in uneven
• the surface texture is as follows.
• the pass rolling reduction ratio is expressed as a percentage of the plate thickness before rolling divided by the amount of reduction in plate thickness due to rolling.
• 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.
• the dislocation density ⁇ on the hot-rolled sheet surface was measured by the method of converting from the strain obtained from the half width ⁇ of the X-ray diffraction measurement described above, and the dislocation density on the hot-rolled sheet surface was calculated.
• the ratio (minimum value/maximum value) of the minimum value of the dislocation density on the surface of the hot rolled sheet to the maximum value was calculated. This ratio is also listed in Tables 2-1 and 2-2.
• a piece measuring 25 mm x 25 mm x 3 mm (t means thickness) was cut out from the above hot-rolled sheet, and the entire surface was polished to a 600-grip 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.
• 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 procedure for a test piece immersion test using the above-mentioned high concentration SRB culture solution is shown below.
• the Teflon tube (registered trademark) and nylon for suspending the test piece were sterilized with high temperature steam in an autoclave in advance. 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 fixed 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.
• 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 ⁇ m) 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 antimicrobial corrosion properties were 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 2-1 and 2-2. ⁇ : Less than 10 ⁇ m ⁇ : 10 ⁇ m or more and less than 30 ⁇ m ⁇ : 30 ⁇ m or more
• the unit of volume "L" herein represents 10 ⁇ 3 m 3 .

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