WO1996025530A1 - Acier ferritique thermoresistant a haute durete non sujet a la fragilisation due au depot des composes intermetalliques - Google Patents

Acier ferritique thermoresistant a haute durete non sujet a la fragilisation due au depot des composes intermetalliques Download PDF

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Publication number
WO1996025530A1
WO1996025530A1 PCT/JP1996/000319 JP9600319W WO9625530A1 WO 1996025530 A1 WO1996025530 A1 WO 1996025530A1 JP 9600319 W JP9600319 W JP 9600319W WO 9625530 A1 WO9625530 A1 WO 9625530A1
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WIPO (PCT)
Prior art keywords
steel
strength
intermetallic compound
creep rupture
rupture strength
Prior art date
Application number
PCT/JP1996/000319
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English (en)
Japanese (ja)
Inventor
Yasushi Hasegawa
Masahiro Ohgami
Hisashi Naoi
Original Assignee
Nippon Steel Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel Corporation filed Critical Nippon Steel Corporation
Priority to EP96902438A priority Critical patent/EP0758025B1/fr
Priority to DE69608744T priority patent/DE69608744T2/de
Priority to US08/722,057 priority patent/US5772956A/en
Publication of WO1996025530A1 publication Critical patent/WO1996025530A1/fr

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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
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt

Definitions

  • the present invention relates to a heat-resistant steel-based steel, and more particularly, to an excellent creep rupture strength for use in a high-temperature and high-pressure environment and an excellent intermetallic compound precipitation embrittlement resistance. This is related to heat-resistant steels. Background art
  • the refractory materials used in thermal power plants are exposed to different environments depending on where they are used. In areas with high ambient temperatures, called so-called superheater tubes and reheater tubes, austenitic materials with particularly excellent corrosion resistance and strength at high temperatures, or 9 to 12 when considering steam oxidation resistance and thermal conductivity Martensite-based materials containing% Cr are often used.
  • JP-A-5-263196 JP-A-5-311342, JP-A-5-311343, and JP-A-5-311344.
  • the high-temperature strength of the heat-resistant steel is controlled by solid solution strengthening and precipitation strengthening.
  • Recent technologies have succeeded in increasing the high-temperature creep strength by blending the two in a well-balanced manner.
  • W and Mo are used for solid solution strengthening
  • Nb and V and their carbides or nitrides are used for precipitation strengthening. It has been confirmed that it is effective for improving the break rupture strength.
  • the only practical problem with these additive elements that are effective in improving the strength is that any of them is a ferrite stabilizing element, so the Cr equivalent value of the material is increased, and as a result, the structure becomes Instead of a single phase, it will have a two-phase structure of delta-plated tempered martensite.
  • the two-phase structure has characteristics different from those of the martensite single-phase structure, and is often avoided when uniform material properties are required.
  • a problem may occur in a material having insufficient corrosion resistance.
  • a single-phase structure in the material of a heat-resistant steel that achieves high strength by obtaining a tempered martensite structure.
  • the usual method is to add a certain amount of a stabilizing element and to design the components to obtain a martensitic single-phase structure during cooling after solution heat treatment.
  • Austenitic stabilizing elements used for the above purposes include Ni, Mn, Co, Cu, C, N, etc., where high-temperature creep strength is important.
  • Ni and Mn are excluded from the selection candidate elements based on the reason for inducing a decrease in the creep strength, and Cu is excluded in order to ensure weldability.
  • N and N greatly change the mechanical properties of a material, its design is often determined in consideration of the balance between the strength and toughness of the material. In many cases, it cannot be used for addition. Therefore, Co, which is expensive but does not significantly affect other mechanical properties, is finally selected and is being used in recent heat-resistant steels.
  • the present inventors have paid attention to the new ferritic heat-resistant steel technology mainly composed of W, Mo, and Co. Depending on the chemical composition and heat treatment conditions, ferrite-based heat-resistant steel In general, Cr 4 was not observed. Mo 2 . Co 2. W,. An intermetallic compound having a composition of C 2 —Fe (presumed to be a subspecies of ASTM force number 23-196) was found to precipitate. Therefore, this intermetallic compound precipitates in a Cr steel to which Co, W, and Mo are added in a practical use environment, and its morphology is film-like, and 50 m along the grain boundary. It has been found that it can grow rapidly to oversize.
  • the creep rupture strength is about 30% as the estimated rupture strength outside the straight line for 100,000 hours, and the ductile brittle fracture fiber temperature rises about 40 ° C in the toughness test after aging. This was also found as a result of the study.
  • the present invention has the above-mentioned disadvantages of the conventional steel, namely, approximately Cr. 3 ⁇ 4 ⁇ 0 2 . (; 0 2. ⁇ ⁇ . Prevents precipitation of intermetallic compounds having a composition of C 2 _Fe, contains 8 to 13% of Cr, has sufficient corrosion resistance, and contains Mo and W. It is an object of the present invention to provide a new frit-based heat-resistant steel having a Co-containing martensite single-phase structure having high creep rupture strength. According to
  • Nb 0.002 to 0.500% N 0.002 to 0.200%
  • One or two of the above may be used alone or in combination.
  • the present invention provides a high-strength, high-temperature, heat-resistant steel excellent in intermetallic compound precipitation embrittlement resistance, characterized in that the balance is limited to Fe and inevitable impurities.
  • Figure 1 is a perspective view showing the steel sheet specimen, the rolling direction, and the sampling direction of the creep rupture strength evaluation specimen;
  • Figure 2 is a graph showing the effect of adding Ti, Zr and Ca, Ba, in steel
  • Fig. 3 is a graph showing the effect of adding Ti, Zr and La, Ce, Y in steel
  • Figure 4 shows the results of the creep rupture strength evaluation of the steel of the present invention and an example of the estimated creep rupture strength outside the straight line at 650 ° C for 100,000 hours based on the results. This is a graph shown in comparison with the data band of the break rupture strength;
  • Figure 5 is a graph showing the relationship between W content in steel and creep rupture strength;
  • Figure 6 is a graph showing the relationship between the Co content in steel and creep rupture strength.
  • C is necessary for maintaining strength, but if it is less than 0.01%, it is not enough to secure strength, and if it exceeds 0.30%, the heat affected zone is hardened significantly, causing low temperature cracking during welding. Therefore, the range was set to 0.01 to 0.30%. C is contained in trace amounts even in harmful intermetallic compounds, but there is no correlation between the amount of added C and the precipitation conditions of intermetallic compounds.
  • Si is important for ensuring oxidation resistance and is a necessary element as a deoxidizing agent.However, if it is less than 0.01%, it is insufficient, and if it exceeds 0.80%, the creep strength is reduced, so 0.02 to 0.80 % Range.
  • Mn is a component necessary not only for deoxidation but also for maintaining strength. To obtain a sufficient effect, it is necessary to add 0.20% or more, and if it exceeds 1.50%, the creep strength may decrease. Therefore, the range was set to 0.20 to 1.50%.
  • Cr is an element essential to the oxidation resistance, Cr 2 combines with C at the same time
  • the lower limit was set to 8.00%, and the upper limit was set to 13.00% in order to stably obtain a martensite single phase structure.
  • W is an element that significantly increases creep strength by solid solution strengthening, and significantly enhances long-term creep strength especially at high temperatures of 500 ° C or higher. .
  • a large amount of Laves phase intermetallic compound precipitates mainly at the grain boundaries and significantly lowers the base metal toughness and the creep strength, so the upper limit was set to 5.00%. If the content is less than 0.10%, the effect of solid solution strengthening is insufficient, so the lower limit was set to 0.10%.
  • Co is an effective element for lowering the Cr equivalent value without significantly changing the mechanical properties and the thermodynamic properties such as the transformation point of the material, such as the strength and toughness.
  • No effect as the austenite stability element is less than 0.05%, if added over 6.00%, the intermetallic compound of Co entity (schematic C ⁇ 4 . ⁇ 2 (:. ⁇ 2 . ⁇ ⁇ . (Different in structure and properties from the intermetallic compound having the composition of 2 —Fe) precipitates in large quantities, and the creep rupture strength of the base material is reduced. Therefore, the addition range is determined to be 0.05 to 6.00%. did.
  • Mo is also an element that enhances high-temperature strength by solid solution strengthening. ⁇ Less than 0.01%, the effect is insufficient.If it is more than 3.00%, a large amount of Mo 2 C-type carbide precipitates, or Fe 2 Mo-type The upper limit was set to 3.00% because the toughness of the base metal may be significantly reduced when it is added simultaneously with W due to the precipitation of intermetallic compounds.
  • V is an element that remarkably enhances the high-temperature creep rupture strength of steel, whether it precipitates as a precipitate or forms a solid solution in the matrix like W.
  • the content is less than 0.002%, precipitation strengthening by V precipitates is insufficient, and if it exceeds 0.800%, clusters of V-based carbide or carbonitride are formed, resulting in a decrease in toughness.
  • the range was 0.002 to 0.800%.
  • Nb enhances high-temperature strength by precipitation as MX-type carbide or carbonitride, and also contributes to solid solution strengthening. If less than 0.002%, the effect of addition was not recognized, and if added more than 0.500%, coarse precipitation occurred and the toughness was reduced, so the addition range was limited to 0.002 to 0.500%.
  • N forms solid solution in the matrix or precipitates as nitride or carbonitride.
  • VN, NbN, or their respective carbonitrides they contribute to both solid solution strengthening and precipitation strengthening. Addition of less than 0.002% hardly contributes to strengthening, and the upper limit of addition is set to 0.200% in consideration of the upper limit value that can be added to molten steel depending on the amount of Cr added up to 13%.
  • Ca, Ba, Mg, Y, Ce, and La Ca: 0.0005-0.0050%, Ba: 0.0003-0.0020%, Mg: 0.0005-0.0050%, La: 0.001-0.020% , Ce: 0.001 to 0.020%, and Y: 0.001 to 0.020%, are just one of the fundamental technologies of the present invention.
  • W 1. Prevents about 90% of grain boundary film-like precipitation of intermetallic compounds having the composition of C 2 —Fe.
  • Ca, Ba, and Mg hardly form a solid solution in steel, and exist mainly as sulfides near the grain boundaries or as inclusions in the form of oxides inside the grain boundaries. Each is strong 0 2 . (: 0 2 ..
  • La, Ce, and Y exist in the form of sulfides and oxides, or dissolve in steel, and suppress the formation of intermetallic compounds by the same mechanism as Ca, Ba, and Mg.
  • Y, Ce, and La in a solid solution state have a higher effect of suppressing the formation of intermetallic compounds than in a precipitation state.
  • the effect is the highest in the above component range, the effect is insufficient when the amount is less than the lower limit, and when the amount is excessive, the hot workability decreases with Ca, Ba, and Mg, and Y, Ce, La defines the above-mentioned component range because a large number of coarse oxides are generated and the toughness is reduced.
  • Ti and Zr have a strong carbide-producing ability to capture C, a trace constituent element in the intermetallic compound, and as a result, have the function of spheroidizing the intermetallic compound.
  • This technique is also the basis of the present invention. Less than 0.002% The effect is insufficient, and if added over 0.500%, coarse carbides, carbonitrides, or nitrides precipitate and reduce toughness, so the addition range was limited to 0.002 to 0.500%.
  • steels in the chemical composition range of the present invention are melted with V1M (vacuum induction heating furnace) and EF (electric furnace), and A0D (Ar oxygen blow decarburizer), V0D (Vacuum exhaust oxygen blow decarburizer), LF (Molten steel ladle refiner) and use it continuously or with a normal steel ingot
  • V1M vacuum induction heating furnace
  • EF electric furnace
  • A0D Ar oxygen blow decarburizer
  • V0D Vauum exhaust oxygen blow decarburizer
  • LF Molten steel ladle refiner
  • creep rupture strength evaluation specimens (2) were sampled in the direction shown in Fig. 1 for the hot rolled material in parallel with the rolling direction (3) of the steel sheet (2), and from the forged ingots, Similarly, creep rupture test pieces were collected from the longitudinal direction of the test pieces. Intermetallic compound precipitation behavior of test materials In order to investigate this, a block test piece was cut out from the creep-ruptured test piece, the substrate was electrolyzed with an organic acid, and the precipitate was separated and extracted by suction filtration. The extracted residue is quantitatively analyzed using a calibration curve by atomic absorption spectroscopy or gas chromatography, or
  • X-ray diffraction qualitative analysis confirmed the presence of each precipitate.
  • thin film samples or replica samples were prepared as necessary, and the structure of the precipitates was analyzed and the morphology was observed.
  • the creep rupture strength was evaluated by estimating the creep rupture strength of 100,000 hours outside the straight line based on the creep rupture strength measurement data for 10,000 hours at 650 ° C. Assuming the boiler operating conditions at 650 ° C and 350 bar, the OOMPa was set to the standard value, taking into account the stress applied to parts such as steam piping and heat exchangers. That is, if the creep rupture strength estimated at 650 ° C. and 100,000 hours by linear extrapolation exceeds l OOMPa, there is almost no precipitation of intermetallic compounds, and the creep rupture which is the object of the present invention is intended. It was considered that the strength was achieved.
  • FIG. 4 is a diagram plotting the concentration of each additive element when one of them is added.
  • the number in the plot circle indicates the creep rupture strength (MPa).
  • Element symbols below or beside the circle indicate the selected additive element type.
  • one kind of Ti or Zr and one kind of Ca, Mg, Ba When the amount of addition is within the range, that is, when Ti and Zr are 0.002 to 0.500%, Ca and Mg are 0.0005 to 0.0050%, and Ba is 0.0003 to 0.0020%, the creep rupture strength exceeds lOOMPa, and the Microscopic analysis and quantification and qualitative analysis of electrolytic extraction residues indicated that the specimens with a creep rupture strength of 10 OMPa or more were roughly rated C. It was confirmed that no intermetallic compound having a composition of MO CO W-Fe (presumed to be a subspecies of ASTM force No. 23-196) was not precipitated.
  • the steel to which Ti, Zr, Ca, Mg, and Ba are added has approximately Cr 4 . Mo 2 . Co 2. W,.
  • An intermetallic compound having a composition of C 2 —Fe was detected, and its presence was confirmed.
  • Figure 3 shows the results of performing exactly the same experiment, replacing the Ca, Mg, and Ba groups in Figure 2 with Y, Ce, and La.
  • the behavior of ⁇ , Ce, La was exactly the same as Ca, Mg, Ba.
  • Y, Ce, and La are 0.001 to 0.020% and Ti and Zr are 0.002 to 0.500%, out of a straight line at 650 ° C for 100,000 hours.
  • the estimated creep rupture strength is lOOMPa or more, and 4 . Mo 2 . Co 20 W,.
  • An intermetallic compound having a composition of C 2 —Fe was not detected.
  • steels containing Ti, Zr, Ca, Mg, and Ba that are out of the component range of the present invention
  • the method for melting the steel of the present invention is not limited at all, and the process to be used may be determined in consideration of the chemical composition and cost of the steel, such as a converter, an induction heating furnace, an arc melting furnace, and an electric furnace. .
  • the production process is equipped with a hopper to which Ti, Zr, Ca, Mg, Ba, Y, Ce, and La can be added, and the oxygen concentration in the molten steel does not slag as an oxide of these added elements. It must be capable of controlling it sufficiently low. Therefore, it is useful to apply an LF or vacuum degassing device equipped with an Ar bubble blowing device, an arc heating device, or a plasma heating device, which enhances the effects of the present invention.
  • Other manufacturing processes specifically rolling, heat treatment, pipe making, welding, cutting, inspection, etc., which are considered necessary or useful for manufacturing steel or steel products according to the present invention, shall be applied. It does not hinder the effects of the present invention.
  • the steel of the present invention can also be provided in the form of a thick plate and a thin plate, and can be used in the form of various heat-resistant materials by using a plate subjected to a necessary heat treatment. Which has no effect on the effects of the present invention. Absent.
  • powder metallurgy methods such as HIP (hot isostatic pressing and sintering), C1P (cold isostatic pressing) and sintering can be applied. Therefore, it is possible to obtain products of various shapes by applying the necessary heat treatment after the molding process.
  • the above steps can be applied by repeating each step a plurality of times within a range necessary for sufficiently exhibiting material properties, and do not affect the effects of the present invention at all.
  • Example 1 The above steps may be appropriately selected and applied to the steel manufacturing process of the present invention.
  • Example 2 The above steps may be appropriately selected and applied to the steel manufacturing process of the present invention.
  • 300 tons, 120 tons, 60 tons, 1 ton, 300 kg, 100 kg, and 50 kg of the steel of the present invention were respectively blasted using a normal blast furnace iron-converter blowing method, VIM, EF or a laboratory vacuum melting equipment.
  • VIM normal blast furnace iron-converter blowing method
  • EF EF or a laboratory vacuum melting equipment
  • the ingot was made from 50 kg to 50 ton.
  • the obtained flakes, billets and ingots can be hot rolled or hot forged into plates of 50 thickness and 12 plates, or round billets.
  • a tube with an outer diameter of 74 mm and a wall thickness of 10 mm was manufactured by hot extrusion, and a pipe with an outer diameter of 380 mm and a wall thickness of 50 IMI was manufactured by seamless rolling. Furthermore, the thin plate was formed and subjected to ERW welding to form an ERW steel pipe with an outer diameter of 280 mm and a wall thickness of 12 mm.
  • All plates and tubes were subjected to solution heat treatment at a maximum heating temperature of 950 to 1350 ° C for 1 hour, then air-cooled, and then tempered at 750 to 800 hours for 1 hour.
  • the creep characteristics of the base metal were determined as shown in Fig. 1 by cutting out a 6 mm-diameter creep test specimen ⁇ and measuring the creep rupture strength at 650 ° C for up to 10,000 hours. The obtained data was extrapolated to a straight line to obtain a creep rupture strength of 100,000 hours.
  • Figure 4 shows the measurement results of the base metal's break rupture strength up to 10,000 hours, together with an extrapolated straight line of the estimated break strength at 100,000 hours. It can be seen that the high-temperature creep rupture strength of the steel of the present invention is higher than that of the conventional 9-12% Cr steel.
  • Figure 5 shows the W content and creep rupture estimated at 650 ° C for 100,000 hours. It is a figure which shows the relationship of intensity. When the W content is between 0.10 and 5.00%, the creep rupture strength exceeds 100MPa.
  • Figure 6 shows the relationship between the Co content and the estimated creep rupture strength at 650 ° C for 100,000 hours. If the Co content is 0.05% or more, the creep rupture strength becomes 100MPa or more.If the addition exceeds 6.0%, an intermetallic compound mainly composed of Co is precipitated and cleaved. Breaking strength decreases O
  • the 98th and 99th steels have no added Ti and Zr, and are outlined. 2 . .. (; 0 2 "/ 1 (2 - intermetallic compound having a 6 a composition Chikaraku, in click Li-loop test 650 ° C, precipitated in the grain boundaries in the full I Lum shape, 650 .C,
  • 109 steel had no added C and thus had low creep rupture strength.No. 110 steel had too much W and a large amount of Fe 2 W type Laves phase was precipitated, resulting in creep rupture strength. No. 111 steel lacked Co, a large amount of delta fluoride remained, and the creep rupture strength decreased.Steel No. 112 was excessive in Co and was mainly composed of Co. This is an example in which a compound (Fe 2 Co) is precipitated and the creep rupture strength is reduced.
  • CRS 650 ° C, chestnut up to 10,000 f ⁇ f3 ⁇ 4 ⁇ ], Naotsuru ⁇ Estimated 650 ° C, 100,000 estimated chestnut
  • Presence or absence of intermetallic compound X-ray diffraction of intermetallic ⁇ with composition Cr.nMo, nCo 20 W, nC 2 —Fe, by mm
  • the present invention has excellent high-temperature creep strength, contains Co, and has a high C temperature of 600 ° C. or more. Mo Co ⁇ W ,. (I) To provide a martensitic heat-resistant steel which does not generate an intermetallic compound having a composition of Fe.

Abstract

L'invention porte sur un acier martensitique thermorésistant au Co présentant une très bonne tenue au fluage à haute température et ne produisant pas de composés intermétalliques de Cr40Mo20Co20W10C2-Fe à des températures atteignant 600 °C, le dépôt de ces composés étant supprimé. On obtient une très bonne tenue au fluage à haute température par adjonction à un acier thermorésistant au Cr (8 %), Co, Mo et W, de faibles quantités de Mg, Ba, Ca, Y, Ce, La, etc. ainsi que de petites quantités de Ti et de Zr.
PCT/JP1996/000319 1995-02-14 1996-02-14 Acier ferritique thermoresistant a haute durete non sujet a la fragilisation due au depot des composes intermetalliques WO1996025530A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP96902438A EP0758025B1 (fr) 1995-02-14 1996-02-14 Acier ferritique thermoresistant a haute durete non sujet a la fragilisation due au depot des composes intermetalliques
DE69608744T DE69608744T2 (de) 1995-02-14 1996-02-14 Hochfester, warmfeste, ferritischer stahl mit hervorragender beständigkeit gegen durch ausscheidung intermetallischer verbindungen verursachte versprödung.
US08/722,057 US5772956A (en) 1995-02-14 1996-02-14 High strength, ferritic heat-resistant steel having improved resistance to intermetallic compound precipitation-induced embrittlement

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2573895 1995-02-14
JP7/25738 1995-02-14

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WO1996025530A1 true WO1996025530A1 (fr) 1996-08-22

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9789219B2 (en) 2007-03-26 2017-10-17 Prolitec Inc. Glycol sensor for feedback loop control

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5361514A (en) * 1976-11-16 1978-06-02 Daido Steel Co Ltd Ferriteebased precipitation hardening type stainless steel
JPS60224754A (ja) * 1984-04-19 1985-11-09 Daido Steel Co Ltd 合金工具鋼
JPS6169948A (ja) * 1984-09-12 1986-04-10 Nippon Steel Corp 高強度フエライト系耐熱鋼
JPS6389644A (ja) * 1986-10-03 1988-04-20 Nippon Steel Corp 高強度フエライト系ボイラ鋼管用鋼
JPH02290950A (ja) * 1989-02-23 1990-11-30 Hitachi Metals Ltd 高温強度の優れたフェライト系耐熱鋼
JPH04268044A (ja) * 1991-02-22 1992-09-24 Nippon Steel Corp 溶接性の優れたラインパイプ用高Ｃｒ鋼
JPH04371552A (ja) * 1991-06-18 1992-12-24 Nippon Steel Corp 高強度フェライト系耐熱鋼

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5361514A (en) * 1976-11-16 1978-06-02 Daido Steel Co Ltd Ferriteebased precipitation hardening type stainless steel
JPS60224754A (ja) * 1984-04-19 1985-11-09 Daido Steel Co Ltd 合金工具鋼
JPS6169948A (ja) * 1984-09-12 1986-04-10 Nippon Steel Corp 高強度フエライト系耐熱鋼
JPS6389644A (ja) * 1986-10-03 1988-04-20 Nippon Steel Corp 高強度フエライト系ボイラ鋼管用鋼
JPH02290950A (ja) * 1989-02-23 1990-11-30 Hitachi Metals Ltd 高温強度の優れたフェライト系耐熱鋼
JPH04268044A (ja) * 1991-02-22 1992-09-24 Nippon Steel Corp 溶接性の優れたラインパイプ用高Ｃｒ鋼
JPH04371552A (ja) * 1991-06-18 1992-12-24 Nippon Steel Corp 高強度フェライト系耐熱鋼

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Title
See also references of EP0758025A4 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9789219B2 (en) 2007-03-26 2017-10-17 Prolitec Inc. Glycol sensor for feedback loop control

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