US20140056751A1 - Cast austenitic stainless steel - Google Patents

Cast austenitic stainless steel Download PDF

Info

Publication number
US20140056751A1
US20140056751A1 US14/007,578 US201214007578A US2014056751A1 US 20140056751 A1 US20140056751 A1 US 20140056751A1 US 201214007578 A US201214007578 A US 201214007578A US 2014056751 A1 US2014056751 A1 US 2014056751A1
Authority
US
United States
Prior art keywords
percent
mass
austenitic stainless
cast steel
stainless cast
Prior art date
Legal status (The legal status 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 status listed.)
Abandoned
Application number
US14/007,578
Inventor
Nobuyuki Sakamoto
Makoto Hineno
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kubota Corp
Original Assignee
Kubota Corp
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 Kubota Corp filed Critical Kubota Corp
Assigned to KUBOTA CORPORATION reassignment KUBOTA CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HINENO, MAKOTO, SAKAMOTO, NOBUYUKI
Publication of US20140056751A1 publication Critical patent/US20140056751A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/20Measures not previously mentioned for influencing the grain structure or texture; Selection of compositions therefor
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D30/00Cooling castings, not restricted to casting processes covered by a single main group
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00Heat treatment of ferrous alloys
    • C21D6/004Heat treatment of ferrous alloys containing Cr and Ni
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00Heat treatment of ferrous alloys
    • C21D6/02Hardening by precipitation
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/001Ferrous alloys, e.g. steel alloys containing N
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/004Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/001Austenite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite

Definitions

  • the present invention relates to an austenitic stainless cast steel.
  • An austenitic stainless cast steel exhibits excellent properties especially in corrosion resistance, strength, weldability and the like, and has been widely used for piping, valves and the like in chemical plants and power plants.
  • the austenitic stainless cast steel is formed of, for example from metallurgical viewpoint, two phases including approximately 10-20% of an alpha phase and approximately 90-80% of a gamma phase (austenitic phase).
  • CF8C As for steel castings of the austenitic stainless steel, CF8C has been known.
  • a CF8C austenitic stainless steel casting includes: up to 0.08 percent by mass of C (carbon); up to 2.0 percent by mass of Si (silicon); up to 1.5 percent by mass of Mn (manganese); 18.0-21.0 percent by mass of Cr (chromium); 9.0-12.0 percent by mass of Ni (nickel); and up to 1.0 percent by mass of Nb (niobium).
  • CF8C includes approximately 12.0% of a ferrite phase.
  • the ferrite phase can be, for example, measured as ferrite content in the austenitic stainless steel with a known ferrite scope, or calculated using a Schaeffler diagram based on component elements, and is indicated with volume fraction (percent (%)).
  • the ferrite phase is considered effective for preventing weld cracking and reducing stress corrosion cracking.
  • a ferrite phase content is large, for example, exposure of CF8C to high temperature for a long period of time may transform the ferrite phase into a sigma phase ( ⁇ phase), which is a compound of iron and chromium. This may lead to embrittlement of the steel casting.
  • Patent Document 1 discloses CF8C-Plus, which is an alloy modified from CF8C, and describes that CF8C-Plus does not contain ferrite phase. Patent Document 1 also describes that CF8C-Plus includes: 0.05-0.15 percent by mass of C; 0.2-1.0 percent by mass of Si; 0.5-10.0 percent by mass of Mn; 18.0-25.0 percent by mass of Cr; 10.0-15.0 percent by mass of Ni; 0.1-1.5 percent by mass of Nb; and 0.05-0.5 percent by mass of N.
  • Patent Document 1 an absence of the ferrite phase from CF8C-Plus is considered important for retaining the properties imparted at casting of materials during a life of the component part produced from the materials.
  • Patent Document 1 Japanese translation of a PCT application Kohyo No. 2009-545675
  • the austenitic stainless cast steel of the present invention is excellent in, for example, aging ductility, tensile strength and oxidation resistance, as will be described in Examples. Especially, the aging ductility in Examples of the present invention was approximately 2.4 times as high as that in Comparative Examples. Likewise, oxidation resistance in Examples of the present invention was approximately 9.5 times as high as that in Comparative Examples.
  • the reason that the austenitic stainless cast steel exhibits such excellent properties seems to be that the volume fraction of the ferrite phase is 0.1-5.0%, and the contents of the components C, Si, Mn, Cr, Ni, Nb and N seem to play important roles. Hereinbelow, each component will be described in detail.
  • the volume fraction of the ferrite phase By setting the volume fraction of the ferrite phase to 0.1-5.0%, even when the cast steel is exposed to high temperature for a long period of time, a precipitation amount of the sigma phase can be suppressed low. Since the precipitation amount of the sigma phase is low, the austenitic stainless cast steel is unlikely to be embrittled, and exhibits excellent aging ductility.
  • an additive amount of C in the present invention is set to 0.01-0.10 percent by mass.
  • Si serves as deoxidizing agent for molten metal, and is effective for improving fluidity, oxidation resistance, and weldability.
  • an excessive addition will make the austenitic structure unstable, leading to deterioration of castability, hinder workability and weldability, and promotion of weld cracking. Therefore, an additive amount of Si in the present invention is set to 0.6-1.0 percent by mass.
  • Mn is effective as deoxidizing agent for molten metal, and enhances fluidity during the casting to thereby improve productivity. In addition, it is also effective for reducing weld cracking. Since an excessive addition will deteriorate oxidation resistance, an additive amount of Mn in the present invention is set to 2.0-2.8 percent by mass. When Mn is in this range, the austenitic stainless cast steel exhibiting excellent oxidation resistance can be obtained, as will be described in Examples.
  • N improves high-temperature strength and thermal fatigue resistance, and is a strong austenite forming element which stabilizes an austenitic matrix.
  • N is an element effective for grain refining. With this grain refining, ductility of the material which is important as structure can be secured, and in addition, a drawback of poor machinability, which is specific in the austenitic stainless cast steel, can be improved.
  • N renders excellent perforation machinability to a member to be perforated for connecting parts.
  • the amount of Cr is set to 18.0 percent by mass or more.
  • the upper limit of the Cr amount is set to 24.0 percent by mass.
  • Ni facilitates the formation of the stable austenitic matrix, stabilizes the austenitic phase, and enhances high-temperature strength and oxidation resistance of the steel. Taking excellent castability, corrosion resistance and weldability into consideration, an additive amount of Ni in the present invention is set to 8.0-15.0 percent by mass.
  • Nb binds with C to form fine carbide, and improves high-temperature strength.
  • the formation of Cr carbide is suppressed, and thus oxidation resistance can be improved.
  • the content of 0.2% or more is required.
  • an additive amount of Nb in the present invention is set to 0.2-0.7 percent by mass.
  • the austenitic stainless cast steel of the present invention can be produced by performing cooling from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more.
  • the produced austenitic stainless cast steel is used as, for example, materials for piping, valves and the like in chemical plants and power plants.
  • FIG. 1 is a graph showing results of oxidation resistance (mm/year) examined with respect to the austenitic stainless cast steel.
  • the austenitic stainless cast steel of the present invention is formed in such a manner that the volume fraction of the ferrite phase becomes 0.1-5.0%, preferably 0.5-3.0%.
  • the austenitic stainless cast steel of the present invention includes C, Si, Mn, Cr, Ni, Nb, N and the like as components thereof.
  • Si 0.6-1.0 percent by mass, preferably 0.7-0.9 percent by mass;
  • Mn 2.0-2.8 percent by mass, preferably 2.2-2.4 percent by mass
  • N 0.1-0.4 percent by mass, preferably 0.15-0.25 percent by mass
  • Ni 8.0-15.0 percent by mass, preferably 10.5-12.5 percent by mass
  • Nb 0.2-0.7 percent by mass, preferably 0.2-0.4 percent by mass.
  • compositions (percent by mass) of the austenitic stainless cast steel of the present invention, and of CF8C and CF8C-Plus for comparison, are shown in Table 1.
  • the austenitic stainless cast steel of the present invention by setting the volume fraction of the ferrite phase to 0.1-5.0%, even when the cast steel is exposed to high temperature for a long period of time, the precipitation amount of the sigma phase can be suppressed low. Therefore, the austenitic stainless cast steel of the present invention is unlikely to be embrittled, and exhibits excellent aging ductility.
  • the austenitic stainless cast steel of the present invention has a higher Mn content and a lower C content than those of CF8C. With this configuration, the strength and oxidation resistance at high temperature can be improved.
  • the austenitic stainless cast steel of the present invention may further include W, B, Al, Mo, Co, Ti, Zr, Cu, rare-earth element (La, Ce, Y, Pd, Nd and the like) or the like, and the balance is Fe and inevitable impurities.
  • the austenitic stainless cast steel of the present invention can be produced by melting the above-described metal components in a melting furnace and performing cooling from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more.
  • the produced austenitic stainless cast steel is used, for example, for piping, valves and the like in chemical plants and power plants.
  • Example of the present invention will be described.
  • the main components (percent by mass) of the austenitic stainless cast steel of the present invention (Examples 1-1-1-6) and CF8C (Comparative Examples 1-1-1-5) are shown in Tables 2 and 3, respectively.
  • Examples exhibited 113-134 Mpa, while Comparative Examples exhibited 93-127 Mpa.
  • Example exhibited excellent result in aging ductility, tensile strength and oxidation resistance.
  • an average value of the aging ductility in Examples was 24.8%, while an average value in Comparative Examples was 10.4%, and thus the value in Example was approximately 2.4 times as high as that in Comparative Example.
  • an average value of oxidation resistance in Examples was 0.290 mm/year, while an average value in Comparative Examples was 2.770 mm/year, and thus the value in Example was improved approximately 9.5 times as much as that in Comparative Example.
  • Example 1 the volume fraction of the ferrite phase of the austenitic stainless cast steel of the present invention was 0.2% (Examples 1-1-1-6).
  • Examples 1-1-1-6 the volume fraction of the ferrite phase is 1-3%
  • aging ductility, tensile strength, 0.2% proof stress and oxidation resistance were examined (Examples 2-1-2-4) under the same condition for Example 1.
  • the components of Examples 2-1-2-4 are shown in Table 5, and the results are shown in Table 6.
  • Example 3-1 0.5062
  • Example 3-2 0.4521 Comparative Example 3-1 1.2782 Comparative Example 3-2 2.6405 Comparative Example 3-3 1.7060 Comparative Example 3-4 3.6345 Comparative Example 3-5 3.4943
  • oxidation resistance can be reduced to 1 mm/year or less.
  • the present invention is applicable to the production of the austenitic stainless cast steel.

Abstract

An austenitic stainless cast steel having a volume fraction of a ferrite phase of 0.1-5.0%.

Description

    TECHNICAL FIELD
  • The present invention relates to an austenitic stainless cast steel.
  • BACKGROUND ART
  • An austenitic stainless cast steel exhibits excellent properties especially in corrosion resistance, strength, weldability and the like, and has been widely used for piping, valves and the like in chemical plants and power plants. The austenitic stainless cast steel is formed of, for example from metallurgical viewpoint, two phases including approximately 10-20% of an alpha phase and approximately 90-80% of a gamma phase (austenitic phase).
  • As for steel castings of the austenitic stainless steel, CF8C has been known. For example, a CF8C austenitic stainless steel casting includes: up to 0.08 percent by mass of C (carbon); up to 2.0 percent by mass of Si (silicon); up to 1.5 percent by mass of Mn (manganese); 18.0-21.0 percent by mass of Cr (chromium); 9.0-12.0 percent by mass of Ni (nickel); and up to 1.0 percent by mass of Nb (niobium).
  • CF8C includes approximately 12.0% of a ferrite phase. The ferrite phase can be, for example, measured as ferrite content in the austenitic stainless steel with a known ferrite scope, or calculated using a Schaeffler diagram based on component elements, and is indicated with volume fraction (percent (%)).
  • The ferrite phase is considered effective for preventing weld cracking and reducing stress corrosion cracking. However, if a ferrite phase content is large, for example, exposure of CF8C to high temperature for a long period of time may transform the ferrite phase into a sigma phase (σ phase), which is a compound of iron and chromium. This may lead to embrittlement of the steel casting.
  • Patent Document 1 discloses CF8C-Plus, which is an alloy modified from CF8C, and describes that CF8C-Plus does not contain ferrite phase. Patent Document 1 also describes that CF8C-Plus includes: 0.05-0.15 percent by mass of C; 0.2-1.0 percent by mass of Si; 0.5-10.0 percent by mass of Mn; 18.0-25.0 percent by mass of Cr; 10.0-15.0 percent by mass of Ni; 0.1-1.5 percent by mass of Nb; and 0.05-0.5 percent by mass of N.
  • In Patent Document 1, an absence of the ferrite phase from CF8C-Plus is considered important for retaining the properties imparted at casting of materials during a life of the component part produced from the materials.
  • When CF8C is exposed to high temperature for a long period of time under usage environment, the sigma phase is precipitated to cause aging embrittlement, and thus aging ductility may become poor. Also in the case of CF8C-Plus described in Patent Document 1, further improvement has been demanded in oxidation resistance.
  • Therefore, it has been desired to provide an austenitic stainless cast steel exhibiting excellent aging ductility and oxidation resistance.
  • CITATION LIST Patent Literature
  • Patent Document 1: Japanese translation of a PCT application Kohyo No. 2009-545675
  • SUMMARY OF INVENTION
  • In order to provide such an austenitic stainless cast steel, the inventions of the following items (1)-(6) are provided.
    • (1) An austenitic stainless cast steel having a volume fraction of a ferrite phase of 0.1-5.0%.
    • (2) The austenitic stainless cast steel according to item (1), including: 0.01-0.10 percent by mass of C; 0.6-1.0 percent by mass of Si; 2.0-2.8 percent by mass of Mn; and 0.1-0.4 percent by mass of N.
    • (3) The austenitic stainless cast steel according to item (1) or (2), including: 18.0-24.0 percent by mass of Cr; 8.0-15.0 percent by mass of Ni; and 0.2-0.7 percent by mass of Nb.
    • (4) An austenitic stainless cast steel, wherein a volume fraction of the ferrite phase is 0.1-5.0%, and the cast steel includes: 0.01-0.10 percent by mass of C; 0.6-1.0 percent by mass of Si; 2.0-2.8 percent by mass of Mn; 0.1-0.4 percent by mass of N; 18.0-24.0 percent by mass of Cr; 8.0-15.0 percent by mass of Ni; 0.2-0.7 percent by mass of Nb; and the balance is Fe and inevitable impurities. (5) The austenitic stainless cast steel according to any one of items (1)-(4), obtained by performing cooling from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more. (6) A valve formed of austenitic stainless cast steel according to any one of items (1)-(5).
  • The austenitic stainless cast steel of the present invention is excellent in, for example, aging ductility, tensile strength and oxidation resistance, as will be described in Examples. Especially, the aging ductility in Examples of the present invention was approximately 2.4 times as high as that in Comparative Examples. Likewise, oxidation resistance in Examples of the present invention was approximately 9.5 times as high as that in Comparative Examples.
  • The reason that the austenitic stainless cast steel exhibits such excellent properties seems to be that the volume fraction of the ferrite phase is 0.1-5.0%, and the contents of the components C, Si, Mn, Cr, Ni, Nb and N seem to play important roles. Hereinbelow, each component will be described in detail.
  • By setting the volume fraction of the ferrite phase to 0.1-5.0%, even when the cast steel is exposed to high temperature for a long period of time, a precipitation amount of the sigma phase can be suppressed low. Since the precipitation amount of the sigma phase is low, the austenitic stainless cast steel is unlikely to be embrittled, and exhibits excellent aging ductility.
  • C has an effect of lowering a melting point and improving fluidity, i.e. castability of molten metal. In addition, it is preferable that the amount of C is low from the viewpoint of corrosion resistance, and if a large amount is added, the corrosion resistance of the base metal is reduced. In view of these, in order to improve high-temperature ductility, an additive amount of C in the present invention is set to 0.01-0.10 percent by mass.
  • Si serves as deoxidizing agent for molten metal, and is effective for improving fluidity, oxidation resistance, and weldability. However, an excessive addition will make the austenitic structure unstable, leading to deterioration of castability, hinder workability and weldability, and promotion of weld cracking. Therefore, an additive amount of Si in the present invention is set to 0.6-1.0 percent by mass.
  • Mn is effective as deoxidizing agent for molten metal, and enhances fluidity during the casting to thereby improve productivity. In addition, it is also effective for reducing weld cracking. Since an excessive addition will deteriorate oxidation resistance, an additive amount of Mn in the present invention is set to 2.0-2.8 percent by mass. When Mn is in this range, the austenitic stainless cast steel exhibiting excellent oxidation resistance can be obtained, as will be described in Examples.
  • N improves high-temperature strength and thermal fatigue resistance, and is a strong austenite forming element which stabilizes an austenitic matrix. In addition, N is an element effective for grain refining. With this grain refining, ductility of the material which is important as structure can be secured, and in addition, a drawback of poor machinability, which is specific in the austenitic stainless cast steel, can be improved. Especially, N renders excellent perforation machinability to a member to be perforated for connecting parts. When N is added in a large amount, embrittlement is promoted, while an effective Cr amount is reduced and thus oxidation resistance is deteriorated. Therefore, an additive amount of N in the present invention is set to 0.1-0.4 percent by mass.
  • Cr improves oxidation resistance and stabilizes the ferrite structure. In order to reliably attain this effect, the amount of Cr is set to 18.0 percent by mass or more. On the other hand, an excessive addition will lower the aging ductility of the steel due to excessive precipitation of Cr carbide when the case steel is used at high temperature, and thus the upper limit of the Cr amount is set to 24.0 percent by mass.
  • Ni facilitates the formation of the stable austenitic matrix, stabilizes the austenitic phase, and enhances high-temperature strength and oxidation resistance of the steel. Taking excellent castability, corrosion resistance and weldability into consideration, an additive amount of Ni in the present invention is set to 8.0-15.0 percent by mass.
  • Nb binds with C to form fine carbide, and improves high-temperature strength. In addition, the formation of Cr carbide is suppressed, and thus oxidation resistance can be improved. In order to effectively exert these effects, the content of 0.2% or more is required. However, when Nb is added in an excessive amount, heat cracking susceptibility is notably enhanced, and inner quality will be deteriorated. Therefore, an additive amount of Nb in the present invention is set to 0.2-0.7 percent by mass.
  • In addition, the austenitic stainless cast steel of the present invention can be produced by performing cooling from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more. By producing the austenitic stainless cast steel of the present invention under the above-described conditions, even when the cast steel is left as-cast, excellent strength property can be obtained, and thus solution heat treatment can be omitted.
  • The produced austenitic stainless cast steel is used as, for example, materials for piping, valves and the like in chemical plants and power plants.
  • BRIEF DESCRIPTION OF DRAWINGS
  • FIG. 1 is a graph showing results of oxidation resistance (mm/year) examined with respect to the austenitic stainless cast steel.
  • DESCRIPTION OF EMBODIMENTS
  • Hereinbelow, embodiments of the present invention will be described with reference to the drawings.
  • The austenitic stainless cast steel of the present invention is formed in such a manner that the volume fraction of the ferrite phase becomes 0.1-5.0%, preferably 0.5-3.0%. The austenitic stainless cast steel of the present invention includes C, Si, Mn, Cr, Ni, Nb, N and the like as components thereof.
  • The contents are as follows:
  • C: 0.01-0.10 percent by mass, preferably 0.02-0.04 percent by mass;
  • Si: 0.6-1.0 percent by mass, preferably 0.7-0.9 percent by mass;
  • Mn: 2.0-2.8 percent by mass, preferably 2.2-2.4 percent by mass;
  • N: 0.1-0.4 percent by mass, preferably 0.15-0.25 percent by mass;
  • Cr: 18.0-24.0 percent by mass, preferably 19.5-21.5 percent by mass;
  • Ni: 8.0-15.0 percent by mass, preferably 10.5-12.5 percent by mass; and
  • Nb: 0.2-0.7 percent by mass, preferably 0.2-0.4 percent by mass.
  • The compositions (percent by mass) of the austenitic stainless cast steel of the present invention, and of CF8C and CF8C-Plus for comparison, are shown in Table 1.
  • TABLE 1
    Austenitic
    stainless cast
    steel of the CF8C-
    present invention CF8C Plus
    Ferrite (volume 0.1-5.0 12.0
    fraction (%))
    C (percent by mass) 0.01-0.10  Up to 0.08 0.05-0.15
    Si (percent by mass) 0.6-1.0 Up to 2.0 0.2-1.0
    Mn (percent by mass) 2.0-2.8 Up to 1.5  0.5-10.0
    Cr (percent by mass) 18.0-24.0 18.0-21.0 18.0-25.0
    Ni (percent by mass)  8.0-15.0  9.0-12.0 10.0-15.0
    Nb (percent by mass) 0.2-0.7 Up to 1.0 0.1-1.5
    N (percent by mass) 0.1-0.4 0.05-0.5 
  • In the austenitic stainless cast steel of the present invention, by setting the volume fraction of the ferrite phase to 0.1-5.0%, even when the cast steel is exposed to high temperature for a long period of time, the precipitation amount of the sigma phase can be suppressed low. Therefore, the austenitic stainless cast steel of the present invention is unlikely to be embrittled, and exhibits excellent aging ductility.
  • In addition, the austenitic stainless cast steel of the present invention has a higher Mn content and a lower C content than those of CF8C. With this configuration, the strength and oxidation resistance at high temperature can be improved.
  • In addition to the components described above, the austenitic stainless cast steel of the present invention may further include W, B, Al, Mo, Co, Ti, Zr, Cu, rare-earth element (La, Ce, Y, Pd, Nd and the like) or the like, and the balance is Fe and inevitable impurities.
  • The austenitic stainless cast steel of the present invention can be produced by melting the above-described metal components in a melting furnace and performing cooling from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more. By producing the austenitic stainless cast steel of the present invention under the above-described conditions, even when the cast steel is left as-cast, excellent strength property can be obtained, and thus solution heat treatment can be omitted.
  • The produced austenitic stainless cast steel is used, for example, for piping, valves and the like in chemical plants and power plants.
  • Example 1
  • Example of the present invention will be described. The main components (percent by mass) of the austenitic stainless cast steel of the present invention (Examples 1-1-1-6) and CF8C (Comparative Examples 1-1-1-5) are shown in Tables 2 and 3, respectively.
  • TABLE 2
    Example
    1-1 1-2 1-3 1-4 1-5 1-6
    Ferrite (volume 0.2 0.2 0.2 0.2 0.2 0.2
    fraction (%))
    C 0.04 0.03 0.04 0.03 0.08 0.06
    (percent by mass)
    Si 0.76 0.86 0.76 0.86 0.89 0.86
    (percent by mass)
    Mn 2.07 2.15 2.07 2.15 2.07 2.12
    (percent by mass)
    Cr 20.55 19.90 20.55 19.90 22.35 22.10
    (percent by mass)
    Ni 11.38 11.12 11.38 11.12 10.50 10.34
    (percent by mass)
    Nb 0.27 0.26 0.27 0.26 0.29 0.32
    (percent by mass)
    N 0.21 0.20 0.21 0.20 0.19 0.21
    (percent by mass)
  • TABLE 3
    Comparative Example
    1-1 1-2 1-3 1-4 1-5
    Ferrite (volume fraction (%)) 12.0 9.0 0 0 0
    C (percent by mass) 0.03 0.03 0.017 0.08 0.06
    Si (percent by mass) 0.47 0.63 0.37 0.48 0.57
    Mn (percent by mass) 1.04 4.48 1.83 1.02 2.02
    Cr (percent by mass) 19.98 19.93 19.93 19.35 19.60
    Ni (percent by mass) 9.92 9.45 11.63 11.49 11.55
    Nb (percent by mass) 0.59 0.42 0.43 0.69 0.71
    N (percent by mass) 0.03 0.10 0.24 0.25 0.24
  • In these Examples and Comparative Examples, aging ductility (700° C.-620 hours), tensile strength (900° C.), 0.2% proof stress (900° C.) and oxidation resistance (1,000° C.) were examined, and further a high-temperature low-cycle fatigue test (alternate triangular waves, strain rate of 0.1%/sec, 700° C., total strain of 0.5%) was performed.
  • It should be noted that both in Examples and Comparative Examples, casting was performed using normal static casting method. In Examples 1 and 2, the cast steel was left as-cast, while in the other Examples and Comparative Examples, the cast steel was subjected to SHT (solution heat treatment). Aging ductility, tensile strength, 0.2% proof stress, and oxidation resistance were examined and the results are shown in Table 4.
  • TABLE 4
    Aging 0.2% High-temper-
    duc- Tensile proof Oxidation ature low-
    tility strength stress resistance cycle fatigue
    (%) (Mpa) (Mpa) (mm/year) test (times)
    Example 1-1 24.4 120 90 0.300
    Example 1-2 28.8 125 87 0.370 6200
    Example 1-3 24.0 113 91 0.066 3400
    Example 1-4 29.2 134 89 0.122 2420
    Example 1-5 20.4 131 91 0.489
    Example 1-6 22.1 129 88 0.394
    Comparative 17.2 93 70 1.278 2388
    Example 1-1
    Comparative 6.8 101 75 3.494
    Example 1-2
    Comparative 8.6 127 84 1.854
    Example 1-3
    Comparative 11.2 98 73 4.101
    Example 1-4
    Comparative 8.2 104 77 3.124
    Example 1-5
  • As a result, regarding aging ductility, Examples exhibited 20.4% or more, while Comparative Examples exhibited 17.2% or less.
  • Regarding tensile strength, Examples exhibited 113-134 Mpa, while Comparative Examples exhibited 93-127 Mpa.
  • Regarding 0.2% proof stress, Examples exhibited 87-91 Mpa, while Comparative Examples exhibited 70-84 Mpa.
  • Regarding oxidation resistance, Examples exhibited 0.489 mm/year or less, while Comparative Examples exhibited 1.278 mm/year or more.
  • To sum up, though Examples and Comparative Examples were not notably distinguishable in the 0.2% proof stress, it was found that Example exhibited excellent result in aging ductility, tensile strength and oxidation resistance. Especially, an average value of the aging ductility in Examples was 24.8%, while an average value in Comparative Examples was 10.4%, and thus the value in Example was approximately 2.4 times as high as that in Comparative Example. Likewise, an average value of oxidation resistance in Examples was 0.290 mm/year, while an average value in Comparative Examples was 2.770 mm/year, and thus the value in Example was improved approximately 9.5 times as much as that in Comparative Example.
  • The above-described results shows the case where the volume fraction of the ferrite phase of the austenitic stainless cast steel of the present invention was 0.2%, and it is considered that similar results will be obtained when a lower limit of the volume fraction of the ferrite phase is set to 0.1%.
  • Example 2
  • In Example 1, the volume fraction of the ferrite phase of the austenitic stainless cast steel of the present invention was 0.2% (Examples 1-1-1-6). In addition, also for a case in which the volume fraction of the ferrite phase is 1-3%, aging ductility, tensile strength, 0.2% proof stress and oxidation resistance were examined (Examples 2-1-2-4) under the same condition for Example 1. The components of Examples 2-1-2-4 are shown in Table 5, and the results are shown in Table 6.
  • TABLE 5
    Example
    2-1 2-2 2-3 2-4
    Ferrite (volume fraction (%)) 2 1 3 1
    C (percent by mass) 0.014 0.013 0.020 0.013
    Si (percent by mass) 0.67 0.72 0.62 0.72
    Mn (percent by mass) 2.26 2.37 2.00 2.22
    Cr (percent by mass) 21.10 21.10 21.70 22.22
    Ni (percent by mass) 11.29 11.38 12.09 11.54
    Nb (percent by mass) 0.29 0.29 0.27 0.27
    N (percent by mass) 0.22 0.23 0.16 0.23
  • TABLE 6
    Aging Tensile 0.2% proof Oxidation
    ductility strength stress resistance
    (%) (Mpa) (Mpa) (mm/year)
    Example 2-1 27.0 128 89 0.006
    Example 2-2 24.0 123 88 0.058
    Example 2-3 27.0 95 63 0.558
    Example 2-4 20.4 137 88 0.015
  • As a result, an average value of aging ductility in Examples 2-1-2-4 was 24.6%, and an average value of oxidation resistance was 0.159 mm/year. Like in Example 1, these values are recognized as being excellent over the values in Comparative Example. It is considered that similar results will be obtained when an upper limit of the volume fraction of the ferrite phase of the austenitic stainless cast steel of the present invention is set to 5%.
  • Example 3
  • With respect to the austenitic stainless cast steel whose Mn content was approximately 1.0-4.5 percent by mass, oxidation resistance (mm/year) was examined. As the austenitic stainless cast steel of the present invention, those with the Mn content of 2.26 percent by mass (Example 3-1) and 2.33 percent by mass (Example 3-2) were used. As the austenitic stainless cast steel of Comparative Example, those with the Mn content of 1.04 percent by mass (Comparative Example 3-1), 1.17 percent by mass (Comparative Example 3-2), 1.81 percent by mass (Comparative Example 3-3), 4.37 percent by mass (Comparative Example 3-4), and 4.48 percent by mass (Comparative Example 3-5) were used. The components for these Examples and Comparative Examples are shown in Table 7. The results are shown in Table 8 and FIG. 1.
  • TABLE 7
    Example Comparative Example
    3-1 3-2 3-1 3-2 3-3 3-4 3-5
    Ferrite (volume 2 3 12 8 0.2 10 9
    fraction (%))
    C (percent by mass) 0.03 0.03 0.03 0.03 0.017 0.03 0.03
    Si (percent by mass) 0.65 0.64 0.47 0.61 0.36 0.62 0.63
    Mn (percent by mass) 2.26 2.33 1.04 1.17 1.81 4.37 4.48
    Cr (percent by mass) 20.45 20.47 19.98 20.09 19.87 19.87 19.93
    Ni (percent by mass) 11.35 11.33 9.92 9.92 12.49 9.35 9.45
    Nb (percent by mass) 0.65 0.62 0.59 0.62 0.29 0.66 0.42
    N (percent by mass) 0.14 0.12 0.03 0.12 0.20 0.10 0.10
  • TABLE 8
    Oxidation resistance
    (mm/year)
    Example 3-1 0.5062
    Example 3-2 0.4521
    Comparative Example 3-1 1.2782
    Comparative Example 3-2 2.6405
    Comparative Example 3-3 1.7060
    Comparative Example 3-4 3.6345
    Comparative Example 3-5 3.4943
  • As can be seen in FIG. 1, in the austenitic stainless cast steel of the present invention where the Mn content is 2.0-2.8 percent by mass, oxidation resistance can be reduced to 1 mm/year or less.
  • Industrial Applicability
  • The present invention is applicable to the production of the austenitic stainless cast steel.

Claims (6)

1. An austenitic stainless cast steel having a volume fraction of a ferrite phase of 0.1-5.0%.
2. The austenitic stainless cast steel according to claim 1, comprising: 0.01-0.10 percent by mass of C; 0.6-1.0 percent by mass of Si; 2.0-2.8 percent by mass of Mn; and 0.1-0.4 percent by mass of N.
3. The austenitic stainless cast steel according to claim 1 or 2, comprising: 18.0-24.0 percent by mass of Cr; 8.0-15.0 percent by mass of Ni; and 0.2-0.7 percent by mass of Nb.
4. An austenitic stainless cast steel, comprising:
a volume fraction of a ferrite phase is 0.1-5.0%, and 0.1-0.10 percent by mass of C; 0.6-1.0 percent by mass of Si; 2.0-2.8 percent by mass of Mn; 0.1-0.4 percent by mass of N; 18.0-24.0 percent by mass of Cr; 8.0-15.0 percent by mass of Ni; 0.2-0.7 percent by mass of Nb; and the balance is Fe and inevitable impurities.
5. The austenitic stainless cast steel according to claim 1, obtained by cooling a melted metal component from a temperature range of 1,150-1,350° C. to a temperature range of 600-800° C. at a cooling rate of 30° C./min or more.
6. A valve formed of comprising the austenitic stainless cast steel of claim 1.
US14/007,578 2011-03-31 2012-02-24 Cast austenitic stainless steel Abandoned US20140056751A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2011079965 2011-03-31
JP2011-079965 2011-03-31
PCT/JP2012/054523 WO2012132679A1 (en) 2011-03-31 2012-02-24 Cast austenitic stainless steel

Publications (1)

Publication Number Publication Date
US20140056751A1 true US20140056751A1 (en) 2014-02-27

Family

ID=46930439

Family Applications (1)

Application Number Title Priority Date Filing Date
US14/007,578 Abandoned US20140056751A1 (en) 2011-03-31 2012-02-24 Cast austenitic stainless steel

Country Status (7)

Country Link
US (1) US20140056751A1 (en)
EP (1) EP2692887B1 (en)
JP (1) JP5863770B2 (en)
KR (1) KR20140044318A (en)
CN (1) CN103429778B (en)
CA (1) CA2830586A1 (en)
WO (1) WO2012132679A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113699453A (en) * 2021-08-30 2021-11-26 上海海塔机械制造有限公司 Heat-resistant high-nitrogen steel and production method thereof
US11542569B2 (en) 2016-12-23 2023-01-03 Posco Co., Ltd. Austenitic stainless steel having excellent processability and surface characteristics, and manufacturing method therefor
US11686395B2 (en) 2020-06-17 2023-06-27 Kubota Corporation Gas valve and flow rate control method for propane gas

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3301199B1 (en) 2016-03-28 2021-01-20 LG Electronics Inc. -1- Bent pipe made of stainless steel
WO2018117683A1 (en) * 2016-12-23 2018-06-28 주식회사 포스코 Austenitic stainless steel having excellent processability and surface characteristics, and manufacturing method therefor
CN109454220A (en) * 2018-11-24 2019-03-12 共享铸钢有限公司 A kind of production method of austenitic stainless steel material steel-casting
CN110093561B (en) * 2019-05-13 2021-06-18 襄阳市立强机械有限公司 As-cast nonmagnetic austenitic stainless steel and preparation method thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0297647A (en) * 1988-09-30 1990-04-10 Aichi Steel Works Ltd Steel for valve stem having excellent torsional strength and its manufacture
US5203932A (en) * 1990-03-14 1993-04-20 Hitachi, Ltd. Fe-base austenitic steel having single crystalline austenitic phase, method for producing of same and usage of same
JP2004141940A (en) * 2002-10-25 2004-05-20 Nippon Steel Corp Method of manufacturing austenitic stainless steel and thin strip cast slab
EP1637785A1 (en) * 2004-09-15 2006-03-22 Sumitomo Metal Industries, Ltd. Steel tube excellent in exfoliation resistance of scale on inner surface
US20060193743A1 (en) * 2003-06-10 2006-08-31 Hiroyuki Semba Austenitic stainless steel for hydrogen gas and method for its manufacture

Family Cites Families (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5218418A (en) * 1975-08-02 1977-02-12 Jgc Corp Stainless cast steel for low temperature use
JPS5487627A (en) * 1977-12-23 1979-07-12 Kubota Ltd Stainless steel for extreme low temperature excellent in weld ability
JPS5547370A (en) * 1978-09-30 1980-04-03 Kubota Ltd Stainless cast steel for cryogenic temperature use
JPS60121098A (en) * 1983-12-05 1985-06-28 Kawasaki Steel Corp Prevention of hydrogen peeling crack in build-up welding of austenitic stainless steel
JPS6353244A (en) * 1986-08-25 1988-03-07 Aichi Steel Works Ltd Stainless steel excellent in strength and corrosion resistance and having small anisotropy and its production
JPS63169362A (en) * 1986-12-29 1988-07-13 Aichi Steel Works Ltd Nonmagnetic tool steel
JPH0297648A (en) * 1988-09-30 1990-04-10 Aichi Steel Works Ltd Austenitic stainless steel excellent in creep rupture strength and its production
JP2915691B2 (en) * 1992-05-08 1999-07-05 日本冶金工業株式会社 High ductility austenitic-ferrite dual phase heat resistant steel and method for producing the same
JPH0830248B2 (en) * 1993-05-27 1996-03-27 工業技術院長 Stainless cast steel for seawater pumps at nuclear power plants
JP3336820B2 (en) * 1995-07-25 2002-10-21 株式会社日立製作所 Seawater corrosion resistant austenitic cast stainless steel and seawater pump
US20060266439A1 (en) 2002-07-15 2006-11-30 Maziasz Philip J Heat and corrosion resistant cast austenitic stainless steel alloy with improved high temperature strength
RU2461641C2 (en) * 2007-12-20 2012-09-20 ЭйТиАй ПРОПЕРТИЗ, ИНК. Austenitic stainless steel with low content of nickel and including stabilising elements
CN101845605B (en) * 2009-03-24 2013-01-02 宝山钢铁股份有限公司 Austenitic stainless steel plate with excellent strength at medium and low temperature and manufacturing method thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0297647A (en) * 1988-09-30 1990-04-10 Aichi Steel Works Ltd Steel for valve stem having excellent torsional strength and its manufacture
US5203932A (en) * 1990-03-14 1993-04-20 Hitachi, Ltd. Fe-base austenitic steel having single crystalline austenitic phase, method for producing of same and usage of same
JP2004141940A (en) * 2002-10-25 2004-05-20 Nippon Steel Corp Method of manufacturing austenitic stainless steel and thin strip cast slab
US20060193743A1 (en) * 2003-06-10 2006-08-31 Hiroyuki Semba Austenitic stainless steel for hydrogen gas and method for its manufacture
EP1637785A1 (en) * 2004-09-15 2006-03-22 Sumitomo Metal Industries, Ltd. Steel tube excellent in exfoliation resistance of scale on inner surface

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11542569B2 (en) 2016-12-23 2023-01-03 Posco Co., Ltd. Austenitic stainless steel having excellent processability and surface characteristics, and manufacturing method therefor
US11686395B2 (en) 2020-06-17 2023-06-27 Kubota Corporation Gas valve and flow rate control method for propane gas
CN113699453A (en) * 2021-08-30 2021-11-26 上海海塔机械制造有限公司 Heat-resistant high-nitrogen steel and production method thereof

Also Published As

Publication number Publication date
EP2692887A4 (en) 2015-01-21
JP5863770B2 (en) 2016-02-17
WO2012132679A1 (en) 2012-10-04
KR20140044318A (en) 2014-04-14
CN103429778B (en) 2016-01-06
EP2692887B1 (en) 2017-07-19
CA2830586A1 (en) 2012-10-04
EP2692887A1 (en) 2014-02-05
CN103429778A (en) 2013-12-04
JPWO2012132679A1 (en) 2014-07-24

Similar Documents

Publication Publication Date Title
US20140056751A1 (en) Cast austenitic stainless steel
JP5794945B2 (en) Heat resistant austenitic stainless steel sheet
US8137613B2 (en) Austenitic stainless steel welded joint and austenitic stainless steel welding material
JP5709875B2 (en) Heat-resistant ferritic stainless steel sheet with excellent oxidation resistance
JP5838933B2 (en) Austenitic heat resistant steel
JP2012512960A (en) Ferritic-austenitic stainless steel
KR20090078813A (en) Duplex stainless steel alloy and use of this alloy
JP2012519780A (en) High corrosion resistance austenitic steel
JP5846076B2 (en) Austenitic heat-resistant alloy
JP2015062910A (en) Austenitic stainless steel welding material
US20210164067A1 (en) High-mn steel and method for manufacturing same
JP2018031028A (en) Fe-Ni-Cr-Mo ALLOY AND METHOD FOR PRODUCING THE SAME
JP5937861B2 (en) Heat-resistant ferritic stainless steel sheet with excellent weldability
JP2010159438A (en) High corrosion-resistant alloy excellent in grain-boundary corrosion resistance
JP6201731B2 (en) Austenitic heat-resistant casting alloy
JP6337514B2 (en) Precipitation hardening type Fe-Ni alloy and manufacturing method thereof
JP2014012877A (en) Austenitic heat resistant alloy
JP6045823B2 (en) Manufacturing method of reinforcing steel bars used for stud welding
JP6787246B2 (en) Alloy original plate for heat-resistant parts, alloy plate for heat-resistant parts, and gasket for exhaust system parts of engine
JP6322145B2 (en) Duplex steel with improved notched impact strength and machinability
CN103014552A (en) Novel corrosion-resisting special fastener
TW201816124A (en) Martensitic stainless steel and method for the manufacture
JP2017145437A (en) Ferritic stainless steel
JP2015098630A (en) Austenite stainless steel
JP2015108177A (en) Nickel-based alloy

Legal Events

Date Code Title Description
AS Assignment

Owner name: KUBOTA CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SAKAMOTO, NOBUYUKI;HINENO, MAKOTO;REEL/FRAME:031940/0850

Effective date: 20131105

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION