WO2010010916A1 - Ferritic stainless steel for use in producing urea water tank - Google Patents
Ferritic stainless steel for use in producing urea water tank Download PDFInfo
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- WO2010010916A1 WO2010010916A1 PCT/JP2009/063169 JP2009063169W WO2010010916A1 WO 2010010916 A1 WO2010010916 A1 WO 2010010916A1 JP 2009063169 W JP2009063169 W JP 2009063169W WO 2010010916 A1 WO2010010916 A1 WO 2010010916A1
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- 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
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- 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
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Definitions
- the present invention is mainly an apparatus for reducing NO x of the urea water with the exhaust gas in an internal combustion engine consisting mainly of diesel engines, equipment used specifically in automobiles urea SCR (Selective Catalytic Reduction) system, specifically Relates to a ferritic stainless steel used in a urea water tank used for storing, manufacturing or transporting urea water.
- an internal combustion engine consisting mainly of diesel engines, equipment used specifically in automobiles urea SCR (Selective Catalytic Reduction) system, specifically Relates to a ferritic stainless steel used in a urea water tank used for storing, manufacturing or transporting urea water.
- the urea SCR system is one of NO x reduction systems and uses urea water as a reducing agent for NO x .
- urea water Compared to the case of using liquid ammonia or aqueous ammonia as a reducing agent, urea water has the advantage of being safe and relatively easy to handle.
- application to NO x reduction system has been studied.
- urea water injected into exhaust gas is decomposed by heat and moisture to generate ammonia, and ammonia and NO x are selectively reduced on the catalyst and decomposed into harmless nitrogen.
- the urea water used at this time is an aqueous urea solution having a high concentration of 25 to 45%.
- an aqueous urea solution having a lowest freezing point of about 32.5% is generally used.
- “diesel engine NO x reducing additive-AUS32—part 1: properties” The automobile standard JASO E502 is also defined in the same rule).
- the concentration of the impurity element is also strictly defined.
- Fe ⁇ 0.5, Cr: ⁇ 0.2, Ni: ⁇ 0.2, Cu: ⁇ 0. 2 (both units are mg / kg).
- the material used for the urea water tank is very Excellent corrosion resistance is required. Further, it is often used outdoors as represented by automobiles and used for a long period of 10 years or more. Therefore, there is a possibility that urea water in the tank leaks due to erosion by rainwater, sea salt particles, or the like. Leakage of the urea water, it is necessary to avoid the fact that there is a risk of losing the function of the NO x reduction system. Therefore, the material used for the urea water tank needs to have excellent corrosion resistance against salt damage from the outer surface side.
- Patent Document 1 discloses a high-grade urea water supply device and a high-grade urea water supply method using the device, and includes a high-grade urea water supply port with an air vent mechanism and a discharge hose with a gun nozzle.
- a supply device is shown which comprises an IBC (Intermediate Bulk Bulk Container) tank made of high density polyethylene having an electric pump and having an actual capacity of 1200 to 1500 L.
- IBC Intermediate Bulk Bulk Container
- a reinforced plastic is preferable as the electric pump
- a stainless alloy SUS304
- Hastelloy Hastelloy
- Inconel alloy is preferable for the pump shaft.
- SUS304 is an austenitic stainless steel and is not described directly with respect to ferritic stainless steel.
- Patent Document 2 discloses a duplex stainless steel for a urea production plant, a welding material, a urea production plant and its equipment, Cr: 26% to less than 28%, Ni: 6 to 10%, Mo: 0 Duplex stainless steels are shown that contain .2 to 1.7% and W: greater than 2% and less than 3%.
- Urea is synthesized using ammonia and carbon dioxide as raw materials under high temperature and high pressure, but due to the presence of synthetic reaction intermediate products such as ammonium carbamate, it has severe corrosivity, so it can withstand thinning due to corrosion and leak internal materials. A material that does not allow it to be used is required.
- the high-concentration urea water environment used near room temperature such as the urea SCR system is milder than the high-temperature and high-pressure corrosive environment in the urea synthesis plant because of its low temperature and the absence of synthesis reaction intermediate products.
- corrosion resistance against salt damage caused by rainwater or sea salt particles is required.
- Patent Document 3 discloses a ferritic stainless steel having excellent brazing properties. It is disclosed that this ferritic stainless steel has a complicated shape such as a urea water tank used in an automobile urea SCR system, and is suitable for a member manufactured by brazing joint.
- the present invention is mainly an apparatus for reducing NO x in exhaust gas by using urea water in an internal combustion engine consisting mainly of diesel engines, equipment used specifically in automobiles urea SCR system, specifically, urea water
- the purpose of the present invention is to provide a ferritic stainless steel which is suitable for a urea water tank used when storing, manufacturing or transporting, and has a small elution of constituent elements in high-concentration urea water and excellent salt corrosion resistance. To do.
- the present inventors have reduced elution of constituent elements from steel into a 25-45% high concentration urea aqueous solution on the inner surface side, and on the outer surface side.
- the present inventors have dissolved a passive film formed on the steel surface in 25-45% high-concentration urea water used in urea water tanks. It was found that a uniform passive film can be formed that can suppress the elution from the steel that is the base of the passive film through the passive film (Japanese Patent Application No. 2008-62598). On the other hand, even in the corrosion resistance against salt damage, forming a uniform passive film that can suppress elution increases the resistance to chloride ions contained in sea salt particles, etc., and suppresses the occurrence of corrosion. is important. Since the outdoor environment is a repeated wet and dry environment, chloride ions concentrate through the drying and wetting process.
- the lower limit of the Cr amount is 15%.
- the urea water tank that is the subject of the present invention is often joined and assembled by welding or brazing.
- An oxide film may be formed on the surface of the steel constituting the welded (or brazed) welded part (or brazed part). Even in the state where the oxide film is formed, it is necessary to suppress elution from the steel in the high-concentration urea water on the inner surface side and to withstand salt damage from the outer surface side. Since ferritic stainless steel diffuses Cr faster than austenitic stainless steel, Cr deficiency directly under the oxide film is suppressed. In order to suppress elution of steel with an oxide film into a high-concentration urea aqueous solution, it is important to have a large amount of Cr immediately below the oxide film. Therefore, ferritic stainless steel is more difficult than austenitic stainless steel. It is possible to suppress elution from the welded portion (or brazed portion) with a smaller amount of Cr.
- the present inventors have conducted extensive research to secure the amount of Cr immediately below the oxide film, and in the state where the oxide film is formed, the provisions relating to the elution of the constituent elements in the high-concentration urea water (Fe : ⁇ 0.5, Cr: ⁇ 0.2, Ni: ⁇ 0.2, Cu: ⁇ 0.2 (both units are mg / kg)), the following formula (I): It was found that the effective Cr amount represented by the formula (II) or (III) needs to be 10% or more (provided that the element symbol in the formulas (I) to (III) is the content of the element) (% By mass) The numerical value before the element symbol is a constant.) Moreover, it discovered that it was necessary to make the amount of effective Cr 15% or more with respect to salt damage more severe than high concentration urea water.
- the above formulas (I) to (III) are alloy element indices that take into account the effect of Si, Mn, Ti, and Nb contained in steel on the effect of improving the corrosion resistance of Cr, and are effective in contributing to the improvement of corrosion resistance of steel This is for calculating the effective Cr amount as a numerical value serving as an index of the Cr amount.
- the effects of Si, Mn, Ti, and Nb listed in the above formulas (I) to (III) are not fully understood, the effects of each element are inferred as follows.
- Si is a useful element that forms an oxide directly under Cr oxide and suppresses oxidation of Cr.
- Mn promotes the formation of a spinel oxide containing Cr and Mn and reduces the effective Cr amount.
- Ti has a great effect of significantly promoting the growth of Cr oxide and reducing the amount of effective Cr. Since Nb has the effect of reducing the Cr oxide growth promoting effect of Ti, it suppresses the decrease in the effective Cr amount due to Ti.
- the wetting and spreading characteristics of the braze are in a region satisfying Ti-3N ⁇ 0.03, Al ⁇ 0.5%, 10 (Ti-3N) + Al ⁇ 0.5. It turned out to be good.
- a thick oxide film of Ti and Al with a thickness of several tens to several hundreds nm was found. It was formed like this. It was considered that such film formation hinders the spread of the wetting of the wax.
- the urea water tank targeted by the present invention also requires strength, and it is desirable that the decrease in strength after brazing is small.
- brazing at a high temperature of 1000 to 1100 ° C. such as Ni brazing or Cu brazing, it was considered important to suppress a decrease in strength due to crystal grain coarsening.
- Pinning with precipitates is useful for suppressing coarsening of crystal grains
- the present inventors utilize carbonitrides of Ti and Nb as precipitates, and the content of C (mass%) + N It was found that by setting the amount (mass%) to 0.015% or more, the precipitation amount and stability of carbonitride useful for suppressing the coarsening of crystal grains are secured (Japanese Patent Application No. 2007-339732). .
- the present invention provides a ferritic stainless steel for a urea water tank that improves the salt corrosion resistance in addition to the two prior applications, has a small elution into high-concentration urea water, and is excellent in corrosion resistance against salt damage.
- the gist of the invention is as follows, as described in the claims.
- any one or two of Nb and Ti are contained in 8 (C + N) to 1% (where C and N indicate the contents (mass%) of C and N, respectively. (The previous numerical value is a constant)), and the balance contains iron and inevitable impurities, and the following formula (I), the following formula (II), or the following formula (III) (where (I) to The element symbol in the formula (III) indicates the content (mass%) of the element, and the numerical value before the element symbol is a constant.) Featuring ferritic stainless steel for urea water tanks.
- the ferritic stainless steel for urea water tank according to (1) characterized in that (3) Further, by mass%, it contains one or more selected from Ca: 0.002% or less, Mg: 0.002% or less, and B: 0.005% or less.
- urea water is used in exhaust gas.
- N An element useful for pitting corrosion resistance, but its content needs to be kept low in order to reduce intergranular corrosion resistance and workability. Therefore, it was made 0.05% or less. However, excessively lowering the scouring cost, it is desirable to make it 0.002% or more.
- Si An element that is useful as a deoxidizing element and effective in corrosion resistance, but its content is set to 0.02 to 1.5% in order to reduce workability.
- Mn Useful as a deoxidizing element, but if contained excessively, corrosion resistance deteriorates, so 0.02 to 2% or less.
- the most important element in the present invention at least 15% or more is required to exhibit extremely low elution into a high-concentration urea aqueous solution and to exhibit excellent corrosion resistance against salt damage. As the content is increased, the elution characteristics are stabilized, but the processability and manufacturability are lowered. For this reason, the upper limit was made 23% or less. Desirably, it is 16% or more, more desirably 18% or more.
- Nb, Ti The urea water tank targeted in the present invention is often joined and assembled by welding or brazing. Nb and Ti are useful elements, and have the effect of fixing C and N and improving the intergranular corrosion resistance of the welded part (or brazed part). However, since excessive addition adversely affects workability and manufacturability, either one or two of Nb and Ti are contained in the range of 8 (C + N) to 1% (provided that C, N Represents the content (% by mass) of C and N. The numerical values before the element symbols are constants. Desirably, it is 8 (C + N) to 0.6%.
- the content of Ti is limited so that Ti-3N ⁇ 0.03 is satisfied in order to ensure good brazing properties (however, the formula The element symbol in the figure indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.)
- the value of Ti-3N is desirably 0.02% or less. However, if the Ti content is too low, the workability deteriorates, so it is desirable to adjust the Ti content so that the value of Ti-3N satisfies ⁇ 0.08% or more. When workability is not particularly required, Ti need not be added.
- Effective Cr amount in the present invention, the effective Cr amount represented by the following formula (I), (II) or (III) is 15% or more (provided that in the formulas (I) to (III))
- the element symbol indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.)
- Nb Effective Cr amount Cr + 4Si-2Mn
- Ti Effective Cr amount Cr + 4Si-2Mn-10Ti
- Nb and Ti Effective Cr amount Cr + 4Si-2Mn- (10Ti-3Nb) (III)
- the effective Cr amount calculated by the above formulas (I) to (III) is the Cr immediately below the oxide film in the state where the oxide film is formed on the surface of the steel as in the case where the steel is welded or brazed.
- the elution into the high-concentration urea water is extremely small.
- corrosion damage resistance on the outer surface is required, and in order to achieve compatibility with the corrosion resistance in high-concentration urea water, it is necessary to be 15% or more. Desirably, it is 16% or more, more desirably 18% or more.
- Mo 3% or less can be contained as necessary to improve corrosion resistance. It is 0.3% or more that a stable effect can be obtained. Excessive addition degrades the workability and leads to an increase in cost because it is expensive. Therefore, it is desirable to contain 0.3 to 3%.
- Ni 3% or less can be contained as required to improve corrosion resistance. It is 0.2% or more that a stable effect is obtained. Excessive addition degrades the workability and leads to an increase in cost because it is expensive. Therefore, it is desirable to contain 0.2 to 3%.
- Cu 3% or less can be contained as necessary to improve corrosion resistance. It is 0.2% or more that a stable effect is obtained. Excessive addition degrades the workability and leads to an increase in cost because it is expensive. Therefore, it is desirable to contain 0.2 to 3%.
- V 3% or less can be contained if necessary for improving the corrosion resistance. It is 0.2% or more that a stable effect is obtained. Excessive addition degrades the workability and leads to an increase in cost because it is expensive. Therefore, it is desirable to contain 0.2 to 3%.
- W 5% or less can be contained as necessary to improve corrosion resistance. It is 0.5% or more that a stable effect is obtained. Excessive addition degrades the workability and leads to an increase in cost because it is expensive. Therefore, it is desirable to contain 0.5 to 5%.
- Ca An element having a deoxidizing effect and the like and useful for scouring, and is contained in an amount of 0.002% or less as necessary. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
- Mg An element having a deoxidizing effect and the like and useful for scouring, and also useful for improving the workability and toughness by refining the structure. For this reason, it is made to contain 0.002% or less as needed. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
- B An element useful for improving the secondary workability, and is contained in an amount of 0.005% or less as necessary. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
- C + N When brazing joint is used for assembling the urea water tank, C + N is 0.015% or more, and preferably 0.02 from the viewpoint of suppressing the strength reduction accompanying the coarsening of crystal grains during brazing. % Or more. Since excessive addition of C and N decreases intergranular corrosion resistance and workability, it is desirable that the upper limit value of C + N is 0.04% or less.
- Al An element that has a deoxidizing effect and the like, is an element useful for scouring, has an effect of improving moldability, and can be contained as necessary.
- it is necessary to ensure good brazing performance, and it is desirable to limit it to 0.5% or less.
- it is desirable to satisfy 10 (Ti-3N) + Al ⁇ 0.5 in order to ensure good brazeability (however, The element symbol in the formula indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.
- P which is an inevitable impurity
- S it is desirable to set it as 0.01% or less from a corrosion-resistant viewpoint.
- the method for producing stainless steel of the present invention may be a general process for producing ferritic stainless steel. Generally, it is made into molten steel in a converter or electric furnace, refined in an AOD furnace or VOD furnace, and made into a steel piece by a continuous casting method or an ingot-making method, followed by hot rolling-annealing of hot-rolled sheet-pickling-cooling Manufactured through a process of hot rolling, finish annealing and pickling. If necessary, annealing of the hot-rolled sheet may be omitted, or cold rolling, finish annealing, and pickling may be repeated.
- the brazing area after heating was measured. Regarding the brazing property, when the brazing area after heating was 2 times or more with respect to the brazing area before heating, it was judged good (good), and when it was less than 2 times, bad (bad).
- the specific liquid amount was 3.6 ml ⁇ cm ⁇ 2 in accordance with the metal corrosion test in JIS K2234 “Antifreeze”, and a special grade reagent was used for urea used for preparing the urea aqueous solution. After completion of the corrosion test, the sample was weighed to obtain the corrosion rate, and solution analysis was performed by ICPS. Analytical elements were Fe, Cr, Ni, and Cu.
- the wetting spreadability of the wax was evaluated in the same manner as the “wax wetting spreadability” described above. Thereafter, the cross-sectional microstructure of the test piece was observed. The number of crystal grains existing in the plate thickness direction is measured over a range of 20 mm in length parallel to the rolling direction, and one having two or more crystal grains in the plate thickness direction is good. Those that did not were considered bad.
- the steels of Experimental Examples 1 to 11 had a maximum corrosion depth of less than 1 mm in the combined cycle test, and had good salt corrosion resistance. Further, the corrosion rate in the urea aqueous solution immersion test is less than 0.001 g ⁇ m ⁇ 2 ⁇ h ⁇ 1 , and the amounts of Fe, Cr, Cu and Ni in the solution after the test satisfy the provisions of JIS K2247-1. The internal corrosion resistance was also good. Among these, the value of C + N is 0.015 or more, and Experimental Examples 1, 3, 4, 6, 7, 8, 9, 10, 11 satisfying the formulas (IV) and (V) of the present invention.
- both the Cr amount and the effective Cr amount are less than 10%, and the corrosion rate in the urea aqueous solution immersion test is as small as 0.005 g ⁇ m ⁇ 2 ⁇ h ⁇ 1 or less, but in the solution after the test.
- the amount of Fe and Cr did not satisfy the requirements of JIS K2247-1.
- the characteristics are good, the maximum erosion depth in the combined cycle test is 1 mm or more, and the salt corrosion resistance is poor.
- Ferritic stainless steels of the present invention mainly by using urea water in an internal combustion engine consisting mainly of a diesel engine apparatus for reducing NO x in an exhaust gas, with particular reference to automotive urea SCR systems, stores urea water, produced Or it is a material suitable for the tank used when transporting.
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Abstract
Description
本願は、2008年7月23日に、日本に出願された特願2008-190065号に基づき優先権を主張し、その内容をここに援用する。 The present invention is mainly an apparatus for reducing NO x of the urea water with the exhaust gas in an internal combustion engine consisting mainly of diesel engines, equipment used specifically in automobiles urea SCR (Selective Catalytic Reduction) system, specifically Relates to a ferritic stainless steel used in a urea water tank used for storing, manufacturing or transporting urea water.
This application claims priority on July 23, 2008 based on Japanese Patent Application No. 2008-190065 filed in Japan, the contents of which are incorporated herein by reference.
尿素SCRシステムでは、排出ガス中に噴射された尿素水が、熱及び水分により分解してアンモニアを生成し、アンモニアとNOxが触媒上で選択還元されて無害な窒素に分解される。このとき使用される尿素水は25~45%の高濃度の尿素水溶液である。自動車尿素SCRシステムにおいては、一般に凝固点の最も低い約32.5%の尿素水溶液が使用されており、JIS K2247-1によって、「ディーゼル機関NOx還元添加材-AUS32-第一部:性状」(自動車規格JASO E502も同様の規定)に規定されている。規格中には、不純物元素の濃度も厳しく規定されており、ステンレス鋼に関連する元素では、Fe:<0.5、Cr:<0.2、Ni:<0.2、Cu:<0.2(いずれも単位はmg/kg)と規定されている。 Among these, the urea SCR system is one of NO x reduction systems and uses urea water as a reducing agent for NO x . Compared to the case of using liquid ammonia or aqueous ammonia as a reducing agent, urea water has the advantage of being safe and relatively easy to handle. application to NO x reduction system has been studied.
In the urea SCR system, urea water injected into exhaust gas is decomposed by heat and moisture to generate ammonia, and ammonia and NO x are selectively reduced on the catalyst and decomposed into harmless nitrogen. The urea water used at this time is an aqueous urea solution having a high concentration of 25 to 45%. In an automobile urea SCR system, an aqueous urea solution having a lowest freezing point of about 32.5% is generally used. According to JIS K2247-1, “diesel engine NO x reducing additive-AUS32—part 1: properties” ( The automobile standard JASO E502 is also defined in the same rule). In the standard, the concentration of the impurity element is also strictly defined. For elements related to stainless steel, Fe: <0.5, Cr: <0.2, Ni: <0.2, Cu: <0. 2 (both units are mg / kg).
また、自動車に代表されるように屋外で使用され、かつ10年あるいはそれ以上の長期間使用される場合が多い。そのため、雨水や海塩粒子等によって侵食を受け、タンク内部の尿素水が漏出する恐れがある。尿素水の漏出は、NOx低減システムの機能を失う恐れがあることから避ける必要がある。そのため、尿素水タンクに使用される材料には、外面側からの塩害に対して優れた耐食性が必要である。 Since the elution from the materials used in the equipment for storing, manufacturing or transporting urea water does not allow the impurity concentration in the urea water to exceed the above regulations, the material used for the urea water tank is very Excellent corrosion resistance is required.
Further, it is often used outdoors as represented by automobiles and used for a long period of 10 years or more. Therefore, there is a possibility that urea water in the tank leaks due to erosion by rainwater, sea salt particles, or the like. Leakage of the urea water, it is necessary to avoid the fact that there is a risk of losing the function of the NO x reduction system. Therefore, the material used for the urea water tank needs to have excellent corrosion resistance against salt damage from the outer surface side.
鋼の表面にCrを含む不動態皮膜を形成することにより、鋼の耐食性が向上することはよく知られている。しかし、例えば自動車尿素SCRシステムにおいて使用される尿素水タンクでは、大気中に曝された使用前の通常の状態から高濃度尿素水溶液に曝された瞬間に、尿素水タンクに使用される鋼の不動態皮膜自身が溶出したり、不動態皮膜の下地となっている鋼が溶出したりする恐れがあった。 As a result of intensive studies to solve the above-mentioned problems, the present inventors have reduced elution of constituent elements from steel into a 25-45% high concentration urea aqueous solution on the inner surface side, and on the outer surface side. In order to develop excellent corrosion resistance against salt damage, it was important to form a passive film containing Cr on the surface of the steel, and it was necessary to make steel with an appropriate amount of Cr added. .
It is well known that the corrosion resistance of steel is improved by forming a passive film containing Cr on the surface of the steel. However, in a urea water tank used in, for example, an automobile urea SCR system, the steel used in the urea water tank is not instantly exposed to a high-concentration urea aqueous solution from the normal state before being exposed to the atmosphere. There was a risk that the dynamic film itself may be eluted, or the steel that is the base of the passive film may be eluted.
一方、塩害に対する耐食性においても、溶出を抑制できるような一様な不動態皮膜を形成することは、海塩粒子等に含まれる塩化物イオンに対する抵抗性を高め、腐食の発生を抑制する上で重要である。屋外環境は、乾湿繰り返し環境であるため、乾燥と湿潤の過程を経て塩化物イオンは濃縮していく。そのため高濃度の塩化物イオン環境となり、前記高濃度尿素水環境よりも腐食性が厳しくなるため、一様で安定な不動態皮膜の形成には、より多くのCr量が必要となる。本発明では、そのCr量の下限が15%であることを見出した。 By incorporating 10% or more of Cr into ferritic stainless steel, the present inventors have dissolved a passive film formed on the steel surface in 25-45% high-concentration urea water used in urea water tanks. It was found that a uniform passive film can be formed that can suppress the elution from the steel that is the base of the passive film through the passive film (Japanese Patent Application No. 2008-62598).
On the other hand, even in the corrosion resistance against salt damage, forming a uniform passive film that can suppress elution increases the resistance to chloride ions contained in sea salt particles, etc., and suppresses the occurrence of corrosion. is important. Since the outdoor environment is a repeated wet and dry environment, chloride ions concentrate through the drying and wetting process. Therefore, it becomes a high-concentration chloride ion environment and becomes more corrosive than the high-concentration urea aqueous environment. Therefore, a larger amount of Cr is required to form a uniform and stable passive film. In the present invention, it has been found that the lower limit of the Cr amount is 15%.
有効Cr量=Cr+4Si-2Mn ・・ (I)
Tiのみを含有する場合
有効Cr量=Cr+4Si-2Mn-10Ti ・・ (II)
NbおよびTiを含有する場合
有効Cr量=Cr+4Si-2Mn-(10Ti-3Nb) ・・ (III) When containing only Nb Effective Cr amount = Cr + 4Si-2Mn (I)
When containing only Ti Effective Cr amount = Cr + 4Si-2Mn-10Ti (II)
When containing Nb and Ti Effective Cr amount = Cr + 4Si-2Mn- (10Ti-3Nb) (III)
上記(I)~(III)式に挙げたSi、Mn、Ti、Nbの効果について、十分理解されているわけではないが、各元素の効果について次のように推察している。 The above formulas (I) to (III) are alloy element indices that take into account the effect of Si, Mn, Ti, and Nb contained in steel on the effect of improving the corrosion resistance of Cr, and are effective in contributing to the improvement of corrosion resistance of steel This is for calculating the effective Cr amount as a numerical value serving as an index of the Cr amount.
Although the effects of Si, Mn, Ti, and Nb listed in the above formulas (I) to (III) are not fully understood, the effects of each element are inferred as follows.
Ti-3N≦0.03 ・・・ (IV)
10(Ti-3N)+Al≦0.5 ・・・ (V) Moreover, when brazing joining is used for the assembly of the urea water tank, brazing properties with Ni or Cu are required. As a result of intensive studies on the influence of alloying elements on brazeability, the present inventors, in ferritic stainless steel, the Ti content often added for the purpose of improving workability and intergranular corrosion, and Regarding the content of Al added for the purpose of deoxidation, it was found that there is an upper limit value that can ensure good brazing properties as shown in the following formulas (IV) and (V) (however, (IV ), (V) represents the element content (mass%), and the numerical value before the element symbol is a constant.
Ti-3N ≦ 0.03 (IV)
10 (Ti-3N) + Al ≦ 0.5 (V)
ろう付け雰囲気では、Fe、Crの酸化物が還元される条件を維持できたとしても、Fe、Crよりも酸化しやすいTi、Alは酸化物を形成して、ろうのぬれ広がりを阻害して、ろう付け性を劣化させる。こうした皮膜形成に寄与するのは、固溶しているTi、Alであり、ろう付け温度でも比較的安定な窒化物として存在している場合には、皮膜形成には寄与せず、ろうのぬれ広がりを阻害しない。こうした点から、Ti及びAlの含有量とろうのぬれ広がり性との関係を検討した。 In order to obtain good brazing properties, it is necessary that the molten brazing wets and spreads on the stainless steel surface, but the wettability is affected by the surface film formed on the stainless steel in the brazing atmosphere.
In the brazing atmosphere, even if the conditions under which the oxides of Fe and Cr can be reduced can be maintained, Ti and Al, which are easier to oxidize than Fe and Cr, form oxides and inhibit the wetting spread of the brazing. Degradation of brazing. It is Ti and Al that are in solid solution that contribute to such film formation. If they exist as relatively stable nitrides even at the brazing temperature, they do not contribute to film formation, and wetting of the braze. Does not hinder spread. From these points, the relationship between the content of Ti and Al and the wettability of the wax was examined.
Nbのみを含有する場合
有効Cr量=Cr+4Si-2Mn ・・ (I)
Tiのみを含有する場合
有効Cr量=Cr+4Si-2Mn-10Ti ・・ (II)
NbおよびTiを含有する場合
有効Cr量=Cr+4Si-2Mn-(10Ti-3Nb) ・・ (III) (1) By mass, C: 0.05% or less, N: 0.05% or less, Si: 0.02 to 1.5%, Mn: 0.02 to 2%, and Cr: 15 to 23% In addition, any one or two of Nb and Ti are contained in 8 (C + N) to 1% (where C and N indicate the contents (mass%) of C and N, respectively. (The previous numerical value is a constant)), and the balance contains iron and inevitable impurities, and the following formula (I), the following formula (II), or the following formula (III) (where (I) to The element symbol in the formula (III) indicates the content (mass%) of the element, and the numerical value before the element symbol is a constant.) Featuring ferritic stainless steel for urea water tanks.
When containing only Nb Effective Cr amount = Cr + 4Si-2Mn (I)
When containing only Ti Effective Cr amount = Cr + 4Si-2Mn-10Ti (II)
When containing Nb and Ti Effective Cr amount = Cr + 4Si-2Mn- (10Ti-3Nb) (III)
(3)さらに、質量%で、Ca:0.002%以下、Mg:0.002%以下、及びB:0.005%以下から選択される1種または2種以上を含むことを特徴とする(1)または(2)のいずれかに記載の尿素水タンク用フェライト系ステンレス鋼。
(4)C+N:0.015%以上であることを特徴とする(1)~(3)のいずれかに記載の尿素水タンク用フェライト系ステンレス鋼。
(5)さらに、質量%で、Al:0.5%以下を含有し、かつ(IV)式及び(V)式(但し、(IV)(V)式中における元素記号は、その元素の含有量(質量%)を示す。また、元素記号の前の数値は定数である。)を満足することを特徴とする(1)~(4)のいずれかに記載の尿素水タンク用フェライト系ステンレス鋼。
Ti-3N≦0.03 ・・・ (IV)
10(Ti-3N)+Al≦0.5 ・・・ (V) (2) Further, by mass%, one or more selected from Mo: 3% or less, Ni: 3% or less, Cu: 3% or less, V: 3% or less, and W: 5% or less The ferritic stainless steel for urea water tank according to (1), characterized in that
(3) Further, by mass%, it contains one or more selected from Ca: 0.002% or less, Mg: 0.002% or less, and B: 0.005% or less. The ferritic stainless steel for urea water tank according to either (1) or (2).
(4) The ferritic stainless steel for urea water tank according to any one of (1) to (3), wherein C + N: 0.015% or more.
(5) Further, by mass%, Al: 0.5% or less, and the formulas (IV) and (V) (provided that the element symbols in the formulas (IV) and (V) are the contents of the elements) The ferritic stainless steel for urea water tanks according to any one of (1) to (4), characterized in that the quantity (mass%) is indicated and the numerical value before the element symbol is a constant) steel.
Ti-3N ≦ 0.03 (IV)
10 (Ti-3N) + Al ≦ 0.5 (V)
尿素水タンクの組み立てにろう付け接合を用いる場合には、良好なろう付け性を確保するために、Ti-3N≦0.03を満足するように、Tiの含有量を制限する(但し、式中における元素記号は、その元素の含有量(質量%)を示す。また、元素記号の前の数値は定数である。)。Ti-3Nの値は、望ましくは0.02%以下である。しかしながら、Tiの含有量が低すぎると、加工性を劣化させるため、Ti-3Nの値が-0.08%以上を満足するようにTiの含有量を調整することが望ましい。加工性などが特に要求されない場合は、Tiを添加しなくてもよい。 Nb, Ti: The urea water tank targeted in the present invention is often joined and assembled by welding or brazing. Nb and Ti are useful elements, and have the effect of fixing C and N and improving the intergranular corrosion resistance of the welded part (or brazed part). However, since excessive addition adversely affects workability and manufacturability, either one or two of Nb and Ti are contained in the range of 8 (C + N) to 1% (provided that C, N Represents the content (% by mass) of C and N. The numerical values before the element symbols are constants. Desirably, it is 8 (C + N) to 0.6%.
When brazing joint is used for assembling the urea water tank, the content of Ti is limited so that Ti-3N ≦ 0.03 is satisfied in order to ensure good brazing properties (however, the formula The element symbol in the figure indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.) The value of Ti-3N is desirably 0.02% or less. However, if the Ti content is too low, the workability deteriorates, so it is desirable to adjust the Ti content so that the value of Ti-3N satisfies −0.08% or more. When workability is not particularly required, Ti need not be added.
Nbのみを含有する場合
有効Cr量=Cr+4Si-2Mn ・・ (I)
Tiのみを含有する場合
有効Cr量=Cr+4Si-2Mn-10Ti ・・ (II)
NbおよびTiを含有する場合
有効Cr量=Cr+4Si-2Mn-(10Ti-3Nb) ・・ (III) Effective Cr amount: In the present invention, the effective Cr amount represented by the following formula (I), (II) or (III) is 15% or more (provided that in the formulas (I) to (III)) The element symbol indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.)
When containing only Nb Effective Cr amount = Cr + 4Si-2Mn (I)
When containing only Ti Effective Cr amount = Cr + 4Si-2Mn-10Ti (II)
When containing Nb and Ti Effective Cr amount = Cr + 4Si-2Mn- (10Ti-3Nb) (III)
Mg:脱酸効果等を有し、精練上に有用な元素であり、また、組織を微細化し、加工性、靭性の向上にも有用である。このため、必要に応じて0.002%以下含有させる。含有させる場合には、安定した効果を得るために0.0002%以上含有させることが望ましい。
B:2次加工性を向上させるのに有用な元素であり、必要に応じて0.005%以下含有させる。含有させる場合には、安定した効果を得るために0.0002%以上含有させることが望ましい。 Ca: An element having a deoxidizing effect and the like and useful for scouring, and is contained in an amount of 0.002% or less as necessary. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
Mg: An element having a deoxidizing effect and the like and useful for scouring, and also useful for improving the workability and toughness by refining the structure. For this reason, it is made to contain 0.002% or less as needed. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
B: An element useful for improving the secondary workability, and is contained in an amount of 0.005% or less as necessary. When contained, it is desirable to contain 0.0002% or more in order to obtain a stable effect.
また、Alと同様にろう付け性に影響を与えるTiとの関係において、良好なろう付け性を確保するために、10(Ti-3N)+Al≦0.5を満足することが望ましい(但し、式中における元素記号は、その元素の含有量(質量%)を示す。また、元素記号の前の数値は定数である。)。 Al: An element that has a deoxidizing effect and the like, is an element useful for scouring, has an effect of improving moldability, and can be contained as necessary. However, when brazing joint is used for assembling the urea water tank, it is necessary to ensure good brazing performance, and it is desirable to limit it to 0.5% or less.
In addition, in relation to Ti, which affects the brazeability similarly to Al, it is desirable to satisfy 10 (Ti-3N) + Al ≦ 0.5 in order to ensure good brazeability (however, The element symbol in the formula indicates the content (% by mass) of the element, and the numerical value before the element symbol is a constant.
(ろうのぬれ広がり性)
冷延鋼板より、幅50mm、長さ70mmの試験片を切り出した後、エメリー紙にて片面を#400まで湿式研磨を施した。その後、研磨面上に0.1gのNiろうを置き、1100℃、5×10-3torr(約0.6666Pa)の真空雰囲気で10分加熱した。
常温まで冷却後、加熱後のろう面積を測定した。ろう付け性について、加熱前のろう面積に対して加熱後のろう面積が2倍以上あるときは良(good)、2倍未満のときは不良(bad)とした。 No. shown in Tables 1 and 2. 1-No. Using a cold-rolled steel sheet having a chemical composition of 14, the wettability of the wax was evaluated. In Table 2, the column of formula (IV) shows the value of Ti-3N, and the column of formula (V) shows the value of 10 (Ti-3N) + Al.
(Wet wet spread)
A test piece having a width of 50 mm and a length of 70 mm was cut out from the cold-rolled steel sheet, and then one side was wet-polished to # 400 with emery paper. Thereafter, 0.1 g of Ni solder was placed on the polished surface and heated in a vacuum atmosphere at 1100 ° C. and 5 × 10 −3 torr (about 0.6666 Pa) for 10 minutes.
After cooling to room temperature, the brazing area after heating was measured. Regarding the brazing property, when the brazing area after heating was 2 times or more with respect to the brazing area before heating, it was judged good (good), and when it was less than 2 times, bad (bad).
なお、表4中、*1の有効Cr量の欄は、Nbのみを含有する場合には、Cr+4Si-2Mnの値を示し、Tiのみを含有する場合には、Cr+4Si-2Mn-10Tiの値を示し、NbおよびTiを含有する場合には、Cr+4Si-2Mn-(10Ti-3Nb)の値を示す。
また、表4中、*2のIV式の欄は、Ti-3Nの値を示し、*3のV式の欄は、10(Ti-3N)+Alの値を示す。
表3,4中、下線部は、本発明の範囲外であることを示す。 Steel having a chemical composition shown in Tables 3 and 4 was melted, and a steel sheet having a thickness of 1 mm was manufactured through normal hot rolling, cold rolling, and annealing processes. Using this cold-rolled steel sheet, corrosion resistance was evaluated by a corrosion test, and brazeability was evaluated. As the corrosion test, an immersion test in an aqueous urea solution targeting the inner surface side and a combined cycle test targeting the outer surface side were performed. The results are shown in Table 5 and FIG.
In Table 4, the effective Cr amount column of * 1 indicates the value of Cr + 4Si-2Mn when containing only Nb, and the value of Cr + 4Si-2Mn-10Ti when containing only Ti. In the case of containing Nb and Ti, the value of Cr + 4Si-2Mn- (10Ti-3Nb) is shown.
In Table 4, the column of the IV formula of * 2 shows the value of Ti-3N, and the column of the V formula of * 3 shows the value of 10 (Ti-3N) + Al.
In Tables 3 and 4, the underlined portion indicates that it is outside the scope of the present invention.
冷延鋼板より、幅20mm、長さ40mmの試験片を切り出した後、エメリー紙にて#600まで湿式研磨を施した。その後、溶接熱影響部の表面状態を模擬するために、大気中にて700℃で1秒保持する熱処理を実施した。
続いて、熱処理を施した実験例1~14の試験片を、60℃、30%の尿素水溶液中に144時間浸漬する腐食試験を行った。比液量は、JIS K2234「不凍液」中の金属腐食性試験に準じて3.6ml・cm-2とし、尿素水溶液の調製に用いた尿素には特級試薬を用いた。腐食試験終了後、秤量して腐食速度を求めると共に、ICPSによる溶液分析を行った。分析元素はFe、Cr、Ni、Cuとした。 (Immersion test in urea aqueous solution)
A test piece having a width of 20 mm and a length of 40 mm was cut out from the cold-rolled steel sheet and then wet-polished to # 600 with emery paper. Thereafter, in order to simulate the surface state of the weld heat affected zone, a heat treatment was performed in the atmosphere at 700 ° C. for 1 second.
Subsequently, a corrosion test was performed in which the heat-treated test pieces of Experimental Examples 1 to 14 were immersed in a 30% urea aqueous solution at 60 ° C. for 144 hours. The specific liquid amount was 3.6 ml · cm −2 in accordance with the metal corrosion test in JIS K2234 “Antifreeze”, and a special grade reagent was used for urea used for preparing the urea aqueous solution. After completion of the corrosion test, the sample was weighed to obtain the corrosion rate, and solution analysis was performed by ICPS. Analytical elements were Fe, Cr, Ni, and Cu.
冷延鋼板より、幅70mm、長さ150mmの試験片を切り出した後、エメリー紙にて#320まで湿式研磨を施した。その後、溶接熱影響部の表面状態を模擬するために、大気中にて700℃で1秒保持する熱処理を実施した。
続いて、熱処理を施した実験例1~14の試験片の端面と裏面をシールテープにより被覆し、図3に示す条件にて乾湿繰り返し試験を行った。180サイクル完了後、腐食生成物を除去して、腐食部の侵食深さを顕微鏡焦点深度法により測定した。なお、ここに定めた条件以外については、JASO M609-91に規定される条件に準じた。 (Composite cycle test)
A test piece having a width of 70 mm and a length of 150 mm was cut out from the cold-rolled steel sheet and then wet-polished to # 320 with emery paper. Thereafter, in order to simulate the surface state of the weld heat affected zone, a heat treatment was performed in the atmosphere at 700 ° C. for 1 second.
Subsequently, the end face and the back face of the test pieces of Experimental Examples 1 to 14 subjected to heat treatment were covered with a sealing tape, and a dry and wet test was performed under the conditions shown in FIG. After 180 cycles were completed, the corrosion products were removed, and the erosion depth of the corroded portion was measured by a microscope depth of focus method. The conditions other than those specified here were in accordance with the conditions specified in JASO M609-91.
上述した「ろうのぬれ広がり性」と同様にしてろうのぬれ広がり性を評価した。その後、試験片の断面ミクロ組織を観察した。圧延方向に平行に長さ20mmの範囲にわたって、板厚方向に存在する結晶粒の数を測定し、板厚方向に2個以上の結晶粒が存在するものを良(good)、1個しか存在しないものを不良(bad)とした。 (Brassability)
The wetting spreadability of the wax was evaluated in the same manner as the “wax wetting spreadability” described above. Thereafter, the cross-sectional microstructure of the test piece was observed. The number of crystal grains existing in the plate thickness direction is measured over a range of 20 mm in length parallel to the rolling direction, and one having two or more crystal grains in the plate thickness direction is good. Those that did not were considered bad.
このうち、C+Nの値が0.015以上であり、本発明の(IV)式ならびに(V)式を満足している実験例1、3、4、6、7、8、9、10、11の鋼は、ろう付け時のろうのぬれ広がり性が良好であると共に、結晶粒の粗大化が抑制されている。また、C+Nの値が0.015以上であるが、本発明の(IV)式ならびに(V)式を満足していない実験例5の鋼は、結晶粒の粗大化が抑制されているが、ろうのぬれ広がり性が不良(bad)となった。
また、C+Nの値が0.015未満で、本発明の(IV)式ならびに(V)式を満足していない実験例2の鋼は、結晶粒の粗大化が顕著であるとともに、ろうのぬれ広がり性が不良(bad)となった。 As shown in Table 5 and FIG. 2, the steels of Experimental Examples 1 to 11 had a maximum corrosion depth of less than 1 mm in the combined cycle test, and had good salt corrosion resistance. Further, the corrosion rate in the urea aqueous solution immersion test is less than 0.001 g · m −2 · h −1 , and the amounts of Fe, Cr, Cu and Ni in the solution after the test satisfy the provisions of JIS K2247-1. The internal corrosion resistance was also good.
Among these, the value of C + N is 0.015 or more, and Experimental Examples 1, 3, 4, 6, 7, 8, 9, 10, 11 satisfying the formulas (IV) and (V) of the present invention. In this steel, the wetting spreadability of the brazing at the time of brazing is good and the coarsening of crystal grains is suppressed. Moreover, although the value of C + N is 0.015 or more, in the steel of Experimental Example 5 that does not satisfy the formula (IV) and the formula (V) of the present invention, coarsening of crystal grains is suppressed. The wettability of the wax became bad (bad).
Further, in the steel of Experimental Example 2 in which the value of C + N is less than 0.015 and does not satisfy the formulas (IV) and (V) of the present invention, the coarsening of the crystal grains is remarkable, and the wetting of the wax The spreadability was bad (bad).
Cr量、有効Cr量が共に本発明範囲から外れる実験例13の鋼、及び有効Cr量が本発明範囲から外れる実験例14の鋼は、JIS K2247-1の規定を満足して尿素水溶液に対する溶出特性は良好であるものの、複合サイクル試験における最大侵食深さが1mm以上であり塩害耐食性に劣る。 In the steel of Experimental Example 12, both the Cr amount and the effective Cr amount are less than 10%, and the corrosion rate in the urea aqueous solution immersion test is as small as 0.005 g · m −2 · h −1 or less, but in the solution after the test. The amount of Fe and Cr did not satisfy the requirements of JIS K2247-1.
The steel of Experimental Example 13 in which both the Cr content and the effective Cr content are out of the scope of the present invention, and the steel of Experimental Example 14 in which the effective Cr content is out of the scope of the present invention satisfy the provisions of JIS K2247-1 and are dissolved in the aqueous urea Although the characteristics are good, the maximum erosion depth in the combined cycle test is 1 mm or more, and the salt corrosion resistance is poor.
Claims (5)
- 質量%で、
C:0.05%以下、
N:0.05%以下、
Si:0.02~1.5%、
Mn:0.02~2%、及び
Cr:15~23%を含有し、
さらにNb及びTiのいずれか1種または2種を8(C+N)~1%(但し、C、NはそれぞれC、Nの含有量(質量%)を示す。また、元素記号の前の数値は定数である。)の範囲で含有し、
残部として鉄及び不可避的不純物を含み、
下記(I)式、下記(II)式、又は下記(III)式(但し、(I)~(III)式中における元素記号は、その元素の含有量(質量%)を示す。また、元素記号の前の数値は定数である。)で示される有効Cr量が15%以上であることを特徴とする尿素水タンク用フェライト系ステンレス鋼。
Nbのみを含有する場合
有効Cr量=Cr+4Si-2Mn ・・ (I)
Tiのみを含有する場合
有効Cr量=Cr+4Si-2Mn-10Ti ・・ (II)
NbおよびTiを含有する場合
有効Cr量=Cr+4Si-2Mn-(10Ti-3Nb) ・・ (III) % By mass
C: 0.05% or less,
N: 0.05% or less,
Si: 0.02 to 1.5%,
Mn: 0.02 to 2%, and Cr: 15 to 23%,
Further, any one or two of Nb and Ti is 8 (C + N) to 1% (where C and N indicate the contents (mass%) of C and N, respectively. In a range of a constant)
Containing iron and inevitable impurities as the balance,
The following formula (I), the following formula (II), or the following formula (III) (wherein the element symbols in the formulas (I) to (III) indicate the content (% by mass) of the element. (The numerical value before the symbol is a constant.) Ferritic stainless steel for urea water tanks characterized in that the effective Cr content indicated by 15) is 15% or more.
When containing only Nb Effective Cr amount = Cr + 4Si-2Mn (I)
When containing only Ti Effective Cr amount = Cr + 4Si-2Mn-10Ti (II)
When containing Nb and Ti Effective Cr amount = Cr + 4Si-2Mn- (10Ti-3Nb) (III) - さらに、質量%で、Mo:3%以下、Ni:3%以下、Cu:3%以下、V:3%以下、及びW:5%以下から選択される1種または2種以上を含むことを特徴とする請求項1に記載の尿素水タンク用フェライト系ステンレス鋼。 Furthermore, it contains 1 or 2 or more types selected from Mo: 3% or less, Ni: 3% or less, Cu: 3% or less, V: 3% or less, and W: 5% or less in mass%. The ferritic stainless steel for urea water tank according to claim 1.
- さらに、質量%で、Ca:0.002%以下、Mg:0.002%以下、及びB:0.005%以下から選択される1種または2種以上を含むことを特徴とする請求項1に記載の尿素水タンク用フェライト系ステンレス鋼。 Furthermore, by mass%, it contains 1 type, or 2 or more types selected from Ca: 0.002% or less, Mg: 0.002% or less, and B: 0.005% or less. Ferrite stainless steel for urea water tanks as described in 1.
- C+N:0.015%以上であることを特徴とする請求項1に記載の尿素水タンク用フェライト系ステンレス鋼。 C + N: 0.015% or more Ferrite stainless steel for urea water tank according to claim 1.
- さらに、質量%で、Al:0.5%以下を含有し、かつ(IV)式及び(V)式(但し、(IV)(V)式中における元素記号は、その元素の含有量(質量%)を示す。また、元素記号の前の数値は定数である。)を満足することを特徴とする請求項1に記載の尿素水タンク用フェライト系ステンレス鋼。
Ti-3N≦0.03 ・・・ (IV)
10(Ti-3N)+Al≦0.5 ・・・ (V) Furthermore, it contains Al: 0.5% or less by mass%, and the formulas (IV) and (V) (provided that the element symbol in the formulas (IV) and (V) is the content (mass of the element). 2. The ferritic stainless steel for urea water tanks according to claim 1, wherein the numerical value before the element symbol is a constant.
Ti-3N ≦ 0.03 (IV)
10 (Ti-3N) + Al ≦ 0.5 (V)
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
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EP20090800430 EP2316979A4 (en) | 2008-07-23 | 2009-07-23 | Ferritic stainless steel for use in producing urea water tank |
US12/737,425 US20110110812A1 (en) | 2008-07-23 | 2009-07-23 | Ferrite stainless steel for use in producing urea water tank |
CN200980128401.2A CN102099500B (en) | 2008-07-23 | 2009-07-23 | Ferritic stainless steel for use in producing urea water tank |
JP2010521733A JP5588868B2 (en) | 2008-07-23 | 2009-07-23 | Ferritic stainless steel for urea water tank |
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JP2008-190065 | 2008-07-23 | ||
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PCT/JP2009/063169 WO2010010916A1 (en) | 2008-07-23 | 2009-07-23 | Ferritic stainless steel for use in producing urea water tank |
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US (1) | US20110110812A1 (en) |
EP (1) | EP2316979A4 (en) |
JP (1) | JP5588868B2 (en) |
KR (1) | KR20110018455A (en) |
CN (1) | CN102099500B (en) |
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Also Published As
Publication number | Publication date |
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EP2316979A4 (en) | 2014-01-22 |
KR20110018455A (en) | 2011-02-23 |
CN102099500B (en) | 2013-01-23 |
EP2316979A1 (en) | 2011-05-04 |
JPWO2010010916A1 (en) | 2012-01-05 |
JP5588868B2 (en) | 2014-09-10 |
CN102099500A (en) | 2011-06-15 |
US20110110812A1 (en) | 2011-05-12 |
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