WO2018025942A1 - Acier inoxydable austénitique - Google Patents

Acier inoxydable austénitique Download PDF

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WO2018025942A1
WO2018025942A1 PCT/JP2017/028146 JP2017028146W WO2018025942A1 WO 2018025942 A1 WO2018025942 A1 WO 2018025942A1 JP 2017028146 W JP2017028146 W JP 2017028146W WO 2018025942 A1 WO2018025942 A1 WO 2018025942A1
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stainless steel
austenitic stainless
sulfuric acid
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PCT/JP2017/028146
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English (en)
Japanese (ja)
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伸之佑 栗原
雅之 相良
孝裕 小薄
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新日鐵住金株式会社
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Priority to KR1020197005733A priority Critical patent/KR20190034286A/ko
Priority to CA3032772A priority patent/CA3032772A1/fr
Priority to JP2018531964A priority patent/JP6724991B2/ja
Priority to CN201780048557.4A priority patent/CN109563589B/zh
Priority to EP17837044.1A priority patent/EP3495526A4/fr
Priority to US16/322,228 priority patent/US20190177808A1/en
Publication of WO2018025942A1 publication Critical patent/WO2018025942A1/fr

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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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    • C21D6/00—Heat treatment of ferrous alloys

Definitions

  • the present invention relates to an austenitic stainless steel, and particularly to an austenitic stainless steel excellent in acid resistance.
  • So-called “fossil fuels” such as petroleum and coal used as boiler fuel for thermal power generation or industrial use contain sulfur (S). For this reason, when fossil fuel burns, sulfur oxides (SO x ) are generated in the exhaust gas. When the temperature of the exhaust gas decreases, SO x reacts with moisture in the gas to become sulfuric acid, and condensation occurs on the surface of the low-temperature member that is below the dew point temperature, thereby causing sulfuric acid dew point corrosion.
  • the exhaust gas temperature is maintained at a high temperature of 150 ° C. or higher so that sulfuric acid does not dew on the surface of the member.
  • low alloy steel When the exhaust gas temperature is not maintained at 150 ° C. or higher, sulfuric acid having a high concentration of about 80% is condensed on the surface of the member in the temperature range of about 140 ° C. In such an environment, so-called “low alloy steel” has been used as steel for various members. This is because the low alloy steel has higher corrosion resistance than the general-purpose stainless steel against the high temperature and high concentration sulfuric acid as described above.
  • Non-Patent Document 1 the amount of sulfuric acid that condenses in the region where the temperature is lowered by 20 to 60 ° C. below the dew point of sulfuric acid is the largest, so that corrosion due to sulfuric acid increases. For this reason, when the exhaust gas temperature is not maintained at 150 ° C. or higher, it is generally an area where the most corrosion resistance is required at a temperature in the vicinity of 100 ° C., where the concentration of sulfuric acid is about 70%. However, in this region, not only general-purpose stainless steel but also low alloy steel cannot be used due to the large amount of corrosion.
  • Patent Document 1 discloses a sulfuric acid dew-point corrosion stainless steel excellent in hot workability. Is disclosed.
  • Patent Document 2 discloses an austenitic stainless steel having excellent resistance to sulfuric acid corrosion and excellent workability.
  • the stainless steel described in Patent Document 1 is intended to stabilize the austenite structure and ensure corrosion resistance by containing 0.05% by weight or more of N (nitrogen).
  • N nitrogen
  • the sulfuric acid corrosion resistance of the austenitic stainless steel to which Cu, Cr, and Mo are added in combination decreases.
  • the N content is 0.05% by weight or more, if the Cu content is increased in order to increase the resistance to sulfuric acid corrosion, the hot workability in the temperature range below 1000 ° C. is significantly reduced. There is a problem of becoming.
  • the austenitic stainless steel described in Patent Document 2 has excellent sulfuric acid corrosion resistance and workability. However, there is still room for improvement regarding the resistance to sulfuric acid corrosion.
  • An object of the present invention is to solve the above problems and to provide an austenitic stainless steel having excellent acid resistance in an environment where high concentration sulfuric acid is condensed.
  • an environment in which high-concentration sulfuric acid condenses means an environment in which sulfuric acid having a concentration of 40 to 70% is condensed at a temperature of 50 to 100 ° C.
  • the present invention has been made to solve the above-mentioned problems, and the gist thereof is the following austenitic stainless steel.
  • An austenitic stainless steel comprising a base material and a film formed on at least a part of the surface of the base material,
  • the chemical composition of the base material is mass%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.040% or less, S: 0.010% or less, O: 0.020% or less, N: less than 0.050%, Ni: 12.0-27.0%, Cr: 15.0% or more and less than 20.0%, Cu: more than 3.5% and 8.0% or less, Mo: more than 2.0% and 5.0% or less, Co: 0.05% or less, Sn: 0.05% or less, V: 0 to 0.5% Nb: 0 to 1.0%, Ti: 0 to 0.5%, W: 0 to 5.0% Zr: 0 to 1.0%, Al: 0 to 0.5%, Ca: 0 to 0.01%, B: 0 to 0.01% REM: 0 to 0.01%, Balance: Fe and impurities,
  • the chemical composition of the base material is mass%, V: 0.01 to 0.5% Nb: 0.02 to 1.0%, Ti: 0.01 to 0.5%, W: 0.1-5.0% Zr: 0.02 to 1.0%, Al: 0.01 to 0.5%, Ca: 0.0005 to 0.01%, B: 0.0005 to 0.01%, and REM: 0.0005 to 0.01%, Containing one or more selected from The austenitic stainless steel according to (1) above.
  • an austenitic stainless steel having excellent acid resistance can be obtained in an environment where high concentration sulfuric acid is condensed.
  • the composition of the film formed on the base material surface that comes into contact with a high concentration of sulfuric acid is important.
  • the acid resistance can be greatly improved.
  • an oxide film mainly composed of Fe is formed on the surface, and then an acid treatment is performed to preferentially dissolve the Fe component. It has been found that Ni, Cu and Mo can be concentrated.
  • An austenitic stainless steel according to the present invention includes a base material and a film formed on at least a part of the surface of the base material. Each of the base material and the coating will be described in detail below.
  • C 0.05% or less C is an element having an effect of increasing strength. However, it combines with Cr to form Cr carbide at the grain boundary, thereby reducing the intergranular corrosion resistance. Therefore, the C content is 0.05% or less. In addition, when it is necessary to raise intensity
  • Si 1.0% or less Si is an element having a deoxidizing action. However, if its content exceeds 1.0%, it reduces the hot workability, and coupled with the increase in Cu content, it becomes extremely difficult to process the product on an industrial scale. Therefore, the Si content is 1.0% or less.
  • the Si content is preferably 0.6% or less. Since Si does not necessarily need to be contained, a lower limit is not particularly provided. However, in order to obtain the above effect, the Si content is preferably 0.05% or more.
  • the Al content is extremely low for the purpose of improving hot workability, it is preferable that 0.1% or more of Si is contained to sufficiently perform the deoxidation action.
  • Mn 2.0% or less Mn has the effect of fixing S to improve hot workability and stabilize the austenite phase. However, even if Mn is contained in an amount exceeding 2.0%, the effect is saturated and the cost is increased. Therefore, the Mn content is set to 2.0% or less.
  • the Mn content is preferably 1.5% or less. Since it is not always necessary to contain Mn, a lower limit is not particularly provided. However, in order to obtain the above effect, the Mn content is preferably 0.1% or more.
  • P 0.040% or less
  • the content is preferably as low as possible.
  • the corrosion resistance is significantly deteriorated in an environment in which a high concentration of sulfuric acid is condensed. Therefore, the P content is 0.040% or less.
  • S 0.010% or less S is contained as an impurity in steel and deteriorates hot workability. Therefore, the content is preferably as low as possible. In particular, when the S content exceeds 0.010%, the hot workability is significantly deteriorated. Therefore, the S content is set to 0.010% or less.
  • O 0.020% or less O is contained in the steel as an impurity and reduces hot workability and ductility. Therefore, the content is preferably as low as possible. In particular, when the O content exceeds 0.020%, the hot workability and ductility are significantly reduced, so the O content is set to 0.020% or less.
  • N Less than 0.050% N has heretofore been actively added for the purpose of stabilizing the austenite structure or increasing the resistance to local corrosion such as pitting corrosion or crevice corrosion.
  • N content is 0.050% or more
  • Cu exceeds 3.5%
  • Mo exceeds 2.0%
  • the corrosion resistance of the austenitic stainless steel containing less than% Cr is lowered.
  • the hot workability is reduced when the N content is 0.050% or more. .
  • the N content is set to less than 0.050%.
  • the N content is preferably as low as possible and is preferably 0.045% or less.
  • Ni 12.0-27.0%
  • Ni has the effect of stabilizing the austenite phase and also has the effect of enhancing the corrosion resistance in an environment where high concentration of sulfuric acid is condensed.
  • it is necessary to contain Ni in an amount of 12.0% or more.
  • the effect is saturated even if it contains exceeding 27.0%.
  • Ni is an expensive element, the cost is extremely high and the economy is lacking. Therefore, the Ni content is 12.0 to 27.0%.
  • Cr 15.0% or more and less than 20.0% Cr is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
  • N is regulated to the above-described content
  • a high concentration Good corrosion resistance can be ensured in an environment where sulfuric acid condenses.
  • Cr is excessively contained, even in the case of austenitic stainless steel in which the N content is reduced and Cu and Mo are added in combination, the corrosion resistance in the environment described above deteriorates, and the workability is further improved. Also occurs.
  • the Cr content when the Cr content is 20.0% or more, the corrosion resistance of the austenitic stainless steel in the environment is significantly deteriorated.
  • the Cr content by making the Cr content less than 20.0%, the hot workability of the austenitic stainless steel combined with Cu and Mo can be improved, and product processing on an industrial scale can be facilitated. It becomes possible. Therefore, the Cr content is 15.0% or more and less than 20.0%.
  • Cu More than 3.5% and not more than 8.0% Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
  • Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
  • Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
  • Mo more than 2.0% to 5.0% or less Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
  • Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
  • Mo is contained together with the above-mentioned amounts of Cr and Cu, good corrosion resistance is imparted to austenitic stainless steel having the above-mentioned content in an environment where high-concentration sulfuric acid is condensed. can do.
  • Mo when Mo is excessively contained, the hot workability is lowered.
  • the Mo content exceeds 5.0%, the hot workability is significantly deteriorated even if N is contained as described above. Therefore, the Mo content is more than 2.0% and not more than 5.0%.
  • Co 0.05% or less
  • Co is an element contained in steel as an impurity. Co is an effective element for increasing the toughness of steel, but it is an expensive element and therefore does not need to be actively added. Therefore, the Co content is 0.05% or less.
  • Sn 0.05% or less Since Sn is contained as an impurity in steel and deteriorates hot workability, its content is preferably as low as possible. In particular, when the Sn content exceeds 0.05%, the hot workability is significantly deteriorated. Therefore, the Sn content is 0.05% or less.
  • V 0.5% or less
  • V has an effect of fixing C and enhancing corrosion resistance, particularly intergranular corrosion resistance, and may be contained as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the V content is 0.5% or less. In order to acquire said effect, it is preferable that V content shall be 0.01% or more.
  • Nb 0 to 1.0%
  • Nb has the effect of fixing C and improving the corrosion resistance, particularly intergranular corrosion resistance, so it may be contained if necessary.
  • its content exceeds 1.0%, even when N is made the above-mentioned content, a nitride is formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Nb content is 1.0% or less.
  • the Nb content is preferably 0.02% or more.
  • Ti 0 to 0.5% Ti, like Nb, has the effect of fixing C and improving corrosion resistance, particularly intergranular corrosion resistance. Therefore, Ti may be included as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Ti content is 0.5% or less. In order to acquire said effect, it is preferable that Ti content shall be 0.01% or more.
  • W 0-5.0% W has an effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and may be contained as necessary. However, if the content exceeds 5.0%, the above effect is saturated and the cost is increased. Therefore, the W content is 5.0% or less. In order to acquire said effect, it is preferable that W content shall be 0.1% or more.
  • Zr 0 to 1.0%
  • Zr has the effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and thus may be contained as necessary. However, if the content exceeds 1.0%, the above effect is saturated and the cost is increased. Therefore, the Zr content is 1.0% or less. In order to acquire said effect, it is preferable that Zr content shall be 0.02% or more.
  • Al 0 to 0.5% Since Al has a deoxidizing action, Al may be contained when the Si content is extremely low. However, when the content exceeds 0.5%, hot workability is deteriorated even in the austenitic stainless steel in which N is the above content. Therefore, the Al content is 0.5% or less.
  • the lower limit of the Al content is not particularly defined and may be in the range of impurities. However, in order to keep the Si content extremely low, it is preferable that the Si content is positively added to contain 0.02% or more to sufficiently perform the deoxidation action. Even when 0.05% or more of Si is contained, the Al content is preferably set to 0.01% or more in order to sufficiently exhibit the deoxidation effect.
  • Ca 0 to 0.01% Since Ca has an effect of combining with S and suppressing a decrease in hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the Ca content is 0.01% or less. In order to obtain the above effect, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.
  • B 0 to 0.01% Since B has an effect of improving hot workability, B may be contained as necessary. However, excessive addition of B promotes the precipitation of Cr—B compounds at the grain boundaries, leading to deterioration of corrosion resistance. In particular, when the B content exceeds 0.01%, the corrosion resistance is remarkably deteriorated. Therefore, the B content is 0.01% or less. In order to obtain the above effect, the B content is preferably 0.0005% or more, and more preferably 0.001% or more.
  • REM 0 to 0.01% Since REM (rare earth element) has an effect of improving hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the REM content is 0.01% or less. In order to acquire said effect, it is preferable that REM content shall be 0.0005% or more.
  • REM refers to a total of 17 elements of Sc, Y, and lanthanoid
  • the content of REM refers to the total content of these elements.
  • the balance is Fe and impurities.
  • impurities are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when steel is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
  • membrane is formed in at least one part of the surface which a base material has. And it becomes possible to improve acid resistance significantly by raising the total content of Cr, Ni, Cu and Mo relative to Fe in the film.
  • the maximum Cr depth at which the Cr concentration is maximum exists in the film, and the chemical composition at the maximum Cr depth needs to satisfy the following formula (i).
  • the maximum Cr depth there is no restriction
  • each element symbol in the above formula represents the content (at%) of each element on the steel surface.
  • the coating according to the present invention generally has a structure including a surface layer layer in which Cr is relatively concentrated and a base material layer in which Ni or the like is relatively concentrated. That is, a minimum Cr depth at which the Cr concentration is minimum exists on the base material side from the above maximum Cr depth.
  • the chemical composition at the maximum Cr depth preferably satisfies the following formula (ii), and the chemical composition at the minimum Cr depth preferably satisfies the following formula (iii).
  • each element symbol in the above formula represents the content (at%) of each element.
  • the thickness of the film is not particularly limited, but is preferably in the range of 2 to 10 nm, for example. If the thickness of the film is less than 2 nm, the sulfuric acid corrosion resistance may not be sufficiently obtained. On the other hand, if the thickness of the film exceeds 10 nm, the film composition may be uneven and the film may be easily peeled off.
  • the chemical composition of the film is measured by depth analysis using X-ray photoelectric spectroscopy (XPS). From the depth analysis described above, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C, and N. Then, by specifying the maximum Cr depth and the minimum Cr depth, the concentration of each element at the depth is obtained, and the above formulas (i) to (iii) are calculated from these values.
  • XPS X-ray photoelectric spectroscopy
  • the thickness of the film is determined from the O (oxygen) concentration profile. Specifically, the position at which the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the film and the base material, and the length from the film surface to the above boundary is defined as the thickness of the film. . It is desirable to measure the composition and thickness of the film at a plurality of locations and adopt the average value.
  • ⁇ Heat treatment process> The steel material is first subjected to heat treatment for 60 to 600 seconds in a temperature range of 1060 to 1140 ° C. Thereby, an oxide film mainly composed of Fe is formed on the surface of the steel material. If the heat treatment temperature is less than 1060 ° C., the formation of the Fe oxide film becomes insufficient. On the other hand, when the heat treatment temperature exceeds 1140 ° C., the crystal grains of the base material become coarse and Fe diffusion is reduced, so that the Fe oxide film becomes non-uniform and the film is more easily peeled off. As a result, in any of the above cases, the concentration of Cr, Ni, Cu and Mo is less likely to occur.
  • the steel material is subjected to acid treatment following the heat treatment.
  • the acid treatment step it is possible to concentrate Cr, Ni, Cu and Mo on the steel surface by preferentially dissolving the Fe component.
  • it is preferably immersed in hydrofluoric acid at 30 to 50 ° C., 5 to 8% by volume HNO 3 , and 5 to 8% by volume HF for 1 to 5 hours.
  • the chemical composition and thickness of the coating formed on the surface of each steel pipe were measured by depth analysis using XPS. Specifically, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C and N, and after specifying the maximum Cr depth and the minimum Cr depth, each element at the depth is determined. The concentration of was determined. Then, the above formulas (i) to (iii) were calculated from these values. In this example, test no. In the examples other than 18, the maximum Cr depth exists in the outermost layer of the coating, and in all the examples, the minimum Cr depth exists on the base material side from the maximum Cr depth.
  • the thickness of the film was determined from the O (oxygen) concentration profile. Specifically, the position where the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the coating and the base material, and the length from the coating surface to the above-described boundary is defined as the thickness of the coating. .
  • a corrosion test was carried out in a sulfuric acid environment.
  • the corrosion test was performed by immersing each steel pipe in a solution having a temperature of 100 ° C. and a sulfuric acid concentration of 70%. And the corrosion weight loss after being immersed for 8 hours was measured, and the corrosion rate per unit area was computed.
  • the corrosion rate is 1.00 g / (m 2 ⁇ h) or less, it is determined that the sulfuric acid corrosion resistance is excellent.
  • the test No. 1 which satisfied the provisions of the present invention and concentrated Cr, Ni, Cu and Mo in the film.
  • the corrosion rate was 1.00 g / (m 2 ⁇ h) or less, which was excellent in sulfuric acid corrosion resistance.
  • the austenitic stainless steel which has the outstanding acid resistance in the environment where a high concentration sulfuric acid condenses is obtained. Therefore, the austenitic stainless steel according to the present invention is used in heat exchangers, flues and chimneys used in thermal power generation or industrial boilers, exhaust gas desulfurization equipment members used in various industries, or sulfuric acid environments. It can be applied to various members such as structural members used in equipment.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

Cette invention concerne un acier inoxydable austénitique qui comprend un matériau de base et un film de revêtement qui est formé sur au moins une partie de la surface du matériau de base, et dans lequel : la composition chimique du matériau de base contient, en % en masse, 0,05 % ou moins de C, 1,0 % ou moins de Si, 2,0 % ou moins de Mn, 0,040 % ou moins de P, 0,010 % ou moins de S, 0,020 % ou moins d'O, moins de 0,050 % de N, 12,0 à 27,0 % de Ni, 15,0 % ou plus mais moins de 20,0 % de Cr, plus de 3,5 % mais 8,0 % ou moins de Cu, plus de 2,0 % mais 5,0 % ou moins de Mo, 0,05 % ou moins de Co, 0,05 % ou moins de Sn, 0 à 0,5 % de V, 0 à 1,0 % de Nb, de 0 à 0,5 % de Ti, de 0 à 5,0 % de W, 0 à 1,0 % de Zr, 0 à 0,5 % d'Al, 0 à 0,01 % de Ca, 0 à 0,01 % de B et 0 à 0,01 % de terres rares, le reste étant du Fe et des impuretés. La composition chimique du film de revêtement à la profondeur maximale du Cr satisfait, en % at., (Cr + Ni + Cu + Mo)/Fe ≥ 1,0.
PCT/JP2017/028146 2016-08-03 2017-08-02 Acier inoxydable austénitique WO2018025942A1 (fr)

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KR1020197005733A KR20190034286A (ko) 2016-08-03 2017-08-02 오스테나이트계 스테인리스 강
CA3032772A CA3032772A1 (fr) 2016-08-03 2017-08-02 Acier inoxydable austenitique
JP2018531964A JP6724991B2 (ja) 2016-08-03 2017-08-02 オーステナイト系ステンレス鋼
CN201780048557.4A CN109563589B (zh) 2016-08-03 2017-08-02 奥氏体系不锈钢
EP17837044.1A EP3495526A4 (fr) 2016-08-03 2017-08-02 Acier inoxydable austénitique
US16/322,228 US20190177808A1 (en) 2016-08-03 2017-08-02 Austenitic Stainless Steel

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WO2023170935A1 (fr) * 2022-03-11 2023-09-14 日本製鉄株式会社 Matériau d'acier inoxydable austénitique

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WO2019168119A1 (fr) * 2018-02-28 2019-09-06 日本製鉄株式会社 Joint soudé en acier inoxydable austénitique

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EP3495526A1 (fr) 2019-06-12
CA3032772A1 (fr) 2018-02-08
JP6724991B2 (ja) 2020-07-15
CN109563589A (zh) 2019-04-02
US20190177808A1 (en) 2019-06-13
KR20190034286A (ko) 2019-04-01
CN109563589B (zh) 2020-11-06
JPWO2018025942A1 (ja) 2019-06-06

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