JP2020015925A - Cr-BASED TWO-PHASE ALLOY MANUFACTURED ARTICLE AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

To provide a Cr-based two-phase alloy having mechanical property similar to prior arts, higher corrosion resistance than the prior arts, and low cost, and a manufacturing method therefor.SOLUTION: The Cr-based two-phase manufactured article is a manufactured article using a Cr-based two-phase alloy in which two phases of a ferrite phase and an austenite phase exist, a chemical composition of the Cr-based two-phase alloy consists of a main component, an accessory component, impurities,, and voluntary accessory component, the main component consists of 34 to 70 mass% of Cr, 17 to 42 mass% of Ni, and 10 to 33 mass% of Fe, mass percentage content of the Cr is the largest, the accessory component consists of 0.1 to 2 mass% of Mn, 0.1 to 1 mass% of Si, 0.005 to 0.05 mass% of Al, 0.06 to 0.2 mass% of N, the impurities contains over 0 mass% and 0.04 mass% or less of P, over 0 mass% and 0.01 mass% or less of S, over 0 mass% and 0.03 mass% or less of C, and over 0 mass% and 0.05 mass% or less of O.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for high corrosion resistance and high strength alloys, and more particularly to a product using a chromium-based two-phase alloy in which two phases of a ferrite phase and an austenite phase are mixed and a method for producing the same.

  In the past, it was common to use a combination of carbon steel and a corrosion inhibitor (inhibitor) as a material for oil well equipment used for drilling of crude oil and natural gas. In recent years, due to changes in the drilling environment due to the progress of deepening in oil well drilling, higher corrosion resistance and mechanical properties (for example, hardness) have been required for oil well equipment materials than before, and they have excellent corrosion resistance. Steel (alloy steel) has come to be used. For example, since addition of chromium (Cr) significantly improves the corrosion resistance of iron (Fe), martensitic stainless steel containing 13% by mass of Cr (for example, SUS420) has been widely used in oil wells containing metal corrosion components. Was.

  However, in an environment containing chlorides and acid gases (for example, carbon dioxide and hydrogen sulfide), SUS420 has a weak point of easily causing stress corrosion cracking (SCC). Therefore, when drilling an oil well in such a severely corrosive environment, an expensive nickel (Ni) -based alloy (for example, an alloy containing 40% by mass or more of Ni) is often used in the past, and the material cost (therefore, the drilling cost) ) Increased significantly.

  On the other hand, there is a Cr-based alloy as a corrosion-resistant and heat-resistant alloy that is less expensive than a Ni-based alloy, and various Cr-based alloys have been proposed. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 04-301048) has a chemical composition comprising 65 to 80% of Cr, 10 to 15% of Co, balance Fe and impurities, and optionally containing 0.1 to 1.5% of N. Patent Document 2 (Japanese Patent Application Laid-Open No. 04-301049) discloses a heat-resistant alloy having a chemical composition consisting of Cr: 70 to 95%, N: 0.1 to 1.5%, balance Fe and impurities. It has been disclosed. According to Patent Literatures 1 and 2, it has excellent resistance to compression deformation in a high-temperature atmosphere furnace, oxidation resistance, etc., improves durability as a member to be heated to be heated, reduces maintenance, and improves furnace operation efficiency. It is said to greatly contribute to improvement.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 08-291355) discloses that, by mass%, Cr: more than 95%, N: 0.1 to 2.0%, and the balance of one or more of Fe, Ni and Co and unavoidable impurities That is, a Cr-based heat-resistant alloy further containing one or more of Ti, Al, Zr, Nb, B, and V as required and containing 0.3% or more in total is disclosed. According to Patent Literature 3, it is possible to provide a Cr-based heat-resistant alloy excellent in high-temperature strength used for a member requiring strength, ductility, and corrosion resistance at an ultra-high temperature (for example, a member for supporting a steel material to be heated in a heating furnace). ing.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 07-258801) discloses that Cr: 15 to 50%, Ni: 6.1 to 50%, O + P + S: 200 ppm or less, the balance being Fe and unavoidable impurities, and a crystal grain size number: 8 As described above, an Fe-Cr-Ni alloy excellent in corrosion resistance of a processed portion, wherein C + N is 400 to 1200 ppm as desired, is disclosed. According to Patent Literature 4, it is said that it is possible to provide an Fe—Cr—Ni alloy that has improved corrosion resistance without lowering workability and does not decrease in corrosion resistance even when processed.

JP 04-301048 A JP-A-04-31049 JP-A-08-291355 JP-A-07-258801

  High Cr-based alloys (alloys having a high Cr content) as described in Patent Documents 1 to 3 are intended for use in a high-temperature environment of 1300 ° C. or higher, and are excellent even in such a high-temperature environment. It is said to have corrosion resistance and mechanical properties. However, such a high Cr-based alloy shows brittleness (insufficient toughness) in the temperature range of an oil well environment (room temperature to about 350 ° C.), and is therefore considered unsuitable as an oil well equipment material.

  Further, the Fe-Cr-Ni alloy described in Patent Document 4 is intended for austenitic stainless steel, but austenitic stainless steel is subject to stress corrosion due to hydrogen embrittlement under a high temperature and high pressure environment containing chloride. It is known that cracking (SCC) is likely to occur, and it is considered that it is not suitable as a material for oil well equipment, like a high Cr-based alloy.

  As described above, due to the progress of deepening in oil well drilling, there is a strong demand for a metal material having corrosion resistance and mechanical properties higher than or equal to conventional ones and at a lower cost than a Ni-based alloy. As for the mechanical properties of oil well equipment materials, it is very important to secure wear resistance from the viewpoint of durability in addition to hardness and mechanical strength.

  Therefore, an object of the present invention is a metal material that can be suitably used even in a temperature range and a high corrosive environment such as an oil well, and has mechanical properties equivalent to those of the related art, higher corrosion resistance than before, and low cost. An object of the present invention is to provide a product using a Cr-based two-phase alloy and a method for producing the product.

(I) One embodiment of the present invention is a product using a Cr-based two-phase alloy in which two phases of a ferrite phase and an austenite phase are mixed,
The chemical composition of the Cr-based two-phase alloy is composed of a main component, a subcomponent, an impurity and an optional subcomponent,
The main components are:
34% by mass or more and 70% by mass or less of Cr;
17% by mass or more and 42% by mass or less of Ni,
10 mass% or more and 33 mass% or less of Fe, the mass content of the Cr is the largest,
The sub-component,
0.1% by mass or more and 2% by mass or less of Mn (manganese);
0.1% by mass or more and 1% by mass or less of Si (silicon),
0.005% by mass or more and 0.05% by mass or less of Al (aluminum);
0.06% by mass or more and 0.2% by mass or less of N (nitrogen),
The impurities are:
P (phosphorus) of more than 0% by mass and 0.04% by mass or less,
S (sulfur) of more than 0% by mass and 0.01% by mass or less,
C (carbon) of more than 0% by mass and 0.03% by mass or less,
An object of the present invention is to provide a Cr-based two-phase alloy product containing O (oxygen) of more than 0% by mass and 0.05% by mass or less.
In the present invention, the optional subcomponent means a component that may or may not be added.

According to the present invention, the following improvements and modifications can be added to the Cr-based two-phase alloy product (I) according to the present invention.
(I) The optional auxiliary components are Mo (molybdenum) of 0.5% to 4% by mass, Cu (copper) of 0.1% to 5% by mass, and Sn (tin) of 0.02% to 0.3% by mass. ) At least one of
When the Cr-based two-phase alloy contains the optional subcomponent, the total atomic content of the Mo, Cu, and Sn is 5% by mass or less.
(Ii) The occupancy of the ferrite phase is 10% or more and 90% or less.
(Iii) The product is a cast formed body having a cast structure.
(Iv) The product is a hot worked compact having a hot worked structure.
(V) The hot worked compact is a rod or a linear body.
(Vi) The hot worked structure is a forged structure.
(Vii) The hot worked compact is a shaft or a bearing of a rotating machine.
(Viii) The product is a rapidly solidified compact having a rapidly solidified structure.
(Ix) The rapidly solidified compact is a powder.
(X) The formed body is a composite in which a coating layer of a Cr-based two-phase alloy having the rapidly solidified structure is formed on a base material.
(Xi) The product is a welded joint in which alloy members are welded to each other via a welded portion, and the welded portion is made of the Cr-based two-phase alloy.

(II) Another aspect of the present invention is a method for producing the above-described Cr-based two-phase alloy product,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
A casting step of casting the molten metal to form a cast molded body,
A solution heat treatment step of performing a solution treatment in a temperature range of 1050 ° C. or more and 1250 ° C. or less for the cast molded body,
In the raw material mixing and melting step, a Cr-based two-phase alloy product is manufactured using a nitride of a metal component other than Cr as the raw material for adjusting the content of the N component in the Cr-based two-phase alloy. It provides a method.

(III) Still another embodiment of the present invention is a method for producing the above-described Cr-based two-phase alloy product,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
A casting step of casting the molten metal to form a cast molded body,
A hot working forming step of performing hot working on the cast formed body in a temperature range of 900 ° C. or more and 1300 ° C. or less to form a hot worked formed body,
Having a solution heat treatment step of performing a solution treatment in a temperature range of 1050 ° C. or more and 1250 ° C. or less for the hot-worked molded body,
In the raw material mixing and melting step, a Cr-based two-phase alloy product is manufactured using a nitride of a metal component other than Cr as the raw material for adjusting the content of the N component in the Cr-based two-phase alloy. It provides a method.

According to the present invention, the following improvements and modifications can be added to the method (III) for producing a Cr-based two-phase alloy product according to the present invention.
(Xii) The hot working in the hot working forming step is hot forging.

(IV) Still another embodiment of the present invention is a method for producing the above Cr-based two-phase alloy product,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
Atomizing step of forming an alloy powder from the molten metal,
In the raw material mixing and melting step, a Cr-based two-phase alloy product is manufactured using a nitride of a metal component other than Cr as the raw material for adjusting the content of the N component in the Cr-based two-phase alloy. It provides a method.

According to the present invention, the following improvements and modifications can be added to the above-described methods (II) to (IV) for producing a Cr-based two-phase alloy product according to the present invention.
(Xiii) After the solution heat treatment step, the method further includes an aging heat treatment step of subjecting the solution-processed molded body to an aging treatment in a temperature range of 800 ° C or more and 1000 ° C or less.
(Xiv) The nitride of the metal component other than Cr is iron nitride.
(Xv) The raw material mixing / melting step includes mixing and melting the raw materials to form a molten metal and then solidifying the raw material to form a raw alloy mass, and remelting and cleaning the raw alloy mass. It consists of a re-melting step of preparing molten metal,
The casting step is a step of casting the purified molten metal to form the cast molding.

  According to the present invention, as a metal material that can be suitably used even in a temperature range and a high corrosive environment such as an oil well, it has the same mechanical properties as before and higher corrosion resistance than before and has a low cost of Cr. A product using the base two-phase alloy and a method for producing the product can be provided.

1 is an optical microscope photograph showing an example of a metal structure on the surface of a cast molded product as an example of a Cr-based two-phase alloy product according to the present invention. It is another example of the Cr-based two-phase alloy product according to the present invention, and is an optical microscope photograph showing an example of a metal structure on the surface of a hot forged product. It is another example of the Cr-based two-phase alloy product according to the present invention, and is an optical microscope photograph showing an example of a metal structure on the surface of a rapidly solidified compact. It is an example of the method of manufacturing a Cr-based two-phase alloy product according to the present invention, and is a process diagram illustrating a method of manufacturing a cast formed body. FIG. 4 is another example of the method for producing a Cr-based two-phase alloy product according to the present invention, and is a process diagram illustrating a method for producing a hot-worked compact. It is another example of the method for producing a Cr-based two-phase alloy product according to the present invention, and is a process diagram showing a method for producing a rapidly solidified compact. 13 is an optical micrograph of a metal structure of Conventional Example 4. FIG. 3 is a schematic cross-sectional view showing an example of a composite in which a coating layer for overlay welding is formed on a base material.

  The present inventors have found that a product using a Cr-Ni-Fe-based alloy containing Cr, Ni and Fe as main components, especially a Cr-Ni-Fe-based alloy containing 34% by mass or more of Cr, The present inventors have conducted intensive studies on the relationship between the structure, mechanical properties, and corrosion resistance, and completed the present invention.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to the embodiments described here, and can be appropriately combined or improved without departing from the technical idea of the present invention.

(Chemical composition of the Cr-based two-phase alloy of the present invention)
As described above, the two-phase alloy according to the present invention is a Cr-Ni-Fe-based alloy containing Cr, Ni and Fe as main components, and contains at least Mn, Si, Al and N as subcomponents and contains impurities. Including. Optionally, it may further comprise one or more of Mo, Cu and Sn. Hereinafter, the composition (each component) of the Cr-based two-phase alloy according to the present invention will be described.

Cr: 34 mass% or more and 70 mass% or less
The Cr component is one of the main components of the present Cr-based two-phase alloy, and is a component that forms a high-strength ferrite phase and also forms a solid solution with the austenite phase to contribute to improvement of corrosion resistance. The content of the Cr component is preferably from 34% by mass to 70% by mass, more preferably from 34% by mass to 65% by mass, and still more preferably from 40% by mass to 60% by mass. If the Cr content is less than 34% by mass, the mechanical strength of the Cr-based two-phase alloy decreases. On the other hand, if the Cr content exceeds 70% by mass, the ductility and toughness of the Cr-based two-phase alloy decrease. Further, from the viewpoint of corrosion resistance and material cost, it is preferable that the Cr component has the maximum content among the three main components (Cr, Ni, Fe).

Ni: 17 mass% or more and 42 mass% or less
The Ni component is one of the main components of the present Cr-based two-phase alloy, and stabilizes the austenite phase and contributes to maintaining the two-phase state of the alloy (for example, even if the solution treatment is performed, the two-phase state of the alloy is maintained). It is a component that imparts ductility and toughness to the Cr-based two-phase alloy. The content of the Ni component is preferably from 17% by mass to 42% by mass, and more preferably from 20% by mass to 41% by mass. If the Ni content is less than 17% by mass, the ductility and toughness of the Cr-based two-phase alloy decrease. On the other hand, when the Ni content exceeds 42% by mass, the mechanical strength of the Cr-based two-phase alloy decreases.

Fe: 10 mass% or more and 33 mass% or less
The Fe component is also one of the main components of the present Cr-based two-phase alloy, and is a basic component for ensuring mechanical strength. The content of the Fe component is preferably from 10% by mass to 33% by mass, and more preferably from 12% by mass to 32% by mass. When the Fe content is less than 10% by mass, the ductility and toughness of the Cr-based two-phase alloy decrease. On the other hand, when the Fe content exceeds 33% by mass, the σ phase of the intermetallic compound is easily generated in a temperature range around 800 ° C., and the ductility and toughness of the Cr-based two-phase alloy are significantly reduced (so-called σ phase). Embrittlement). In other words, by controlling the Fe content in the range of 10 to 33% by mass, the formation of the σ phase is suppressed while the mechanical strength of the Cr-based two-phase alloy is ensured, and the decrease in ductility and toughness is suppressed. be able to.

Ni + Fe: 35 mass% or more and 65 mass% or less
The total content of the Ni component and the Fe component is preferably from 35% by mass to 65% by mass, more preferably from 36% by mass to 64% by mass, and still more preferably from 37% by mass to 63% by mass. If the total content is less than 35% by mass, the ductility and toughness of the Cr-based two-phase alloy become insufficient. On the other hand, if the total content exceeds 65% by mass, the mechanical strength is greatly reduced.

Mn: 0.1 mass% or more and 2 mass% or less
The Mn component plays a role of desulfurization and deoxidation in the present Cr-based two-phase alloy, and is a subcomponent that contributes to improvement in mechanical strength and toughness and improvement in carbon dioxide gas corrosion resistance. The content of the Mn component is preferably from 0.1% by mass to 2% by mass, and more preferably from 0.3% by mass to 1.8% by mass. If the Mn content is less than 0.1% by mass, the effect of the Mn component cannot be sufficiently obtained. On the other hand, when the Mn content exceeds 2% by mass, coarse particles of sulfide (for example, MnS) are formed, which causes deterioration of corrosion resistance and mechanical strength.

Si: 0.1 mass% or more and 1 mass% or less
The Si component plays a role of deoxidation in the present Cr-based two-phase alloy and is a subcomponent that contributes to improvement in mechanical strength and toughness. The content of the Si component is preferably from 0.1% by mass to 1% by mass, more preferably from 0.3% by mass to 0.8% by mass. If the Si content is less than 0.1% by mass, the effect of the Si component cannot be sufficiently obtained. On the other hand, when the Si content exceeds 1% by mass, coarse particles of an oxide (for example, SiO ₂ ) are formed, which causes a reduction in toughness.

Al: 0.005 mass% or more and 0.05 mass% or less
The Al component is a subcomponent that contributes to the improvement of the deoxidizing action when combined with the Mn and Si components. The content of the Al component is preferably 0.005% by mass or more and 0.05% by mass or less, and more preferably 0.01% by mass or more and 0.03% by mass or less. When the Al content is less than 0.005% by mass, the effect of the Al component cannot be sufficiently obtained. On the other hand, if the Al content exceeds 0.05% by mass, coarse particles of oxides and nitrides (eg, Al ₂ O ₃ and AlN) are formed, which causes a reduction in toughness.

N: 0.06% by mass or more and 0.2% by mass or less
The N component is a subcomponent that contributes to maintaining the two-phase state of the alloy by stabilizing the austenite phase by dissolving in the present Cr-based two-phase alloy and also improving corrosion resistance.

  It has been known that the N component has such an effect. However, in the production method of the prior art (for example, a method of dissolving nitrogen gas in an alloy melting atmosphere in a molten metal), in the process of dissolving nitrogen gas, it combines with a metal component of a Cr-based two-phase alloy to form a nitride (for example, , CrN) easily formed and precipitated, and the disadvantages of lowering the ductility and toughness of the Cr-based two-phase alloy were greater. Therefore, conventionally, it has been general to treat the N component as a kind of impurity, and it has been considered preferable to control the N content in the alloy to 0.02% by mass or less.

  Against such a technical background, the present inventors have intensively studied a method for maximizing the effect of the N component. As a result, by using a nitride of a metal component other than Cr (for example, iron nitride) as the main source of the N component of the Cr-based two-phase alloy, the formation and precipitation of chromium nitride in the alloy can be suppressed. It has been found that the effect of the N component can be increased by increasing the N content. In other words, the greatest feature of the present invention resides in that the N component which has been conventionally treated as a kind of impurity is positively added in a larger amount than the conventional technology.

  The content of the N component is preferably from 0.06% by mass to 0.2% by mass, and more preferably from 0.08% by mass to 0.19% by mass. If the N content is less than 0.06% by mass, the effect of the N component cannot be sufficiently obtained. When the N content exceeds 0.2% by mass, undesired chromium nitride (eg, CrN) is excessively generated and precipitated in the Cr-based two-phase alloy, and the ductility and toughness of the Cr-based two-phase alloy are remarkable. To decline.

Impurities The impurities in the present Cr-based two-phase alloy include P, S, C and O. Hereinafter, these impurities will be described.

P: More than 0% by mass and 0.04% by mass or less
The P component is an impurity component that tends to segregate at the crystal grain boundaries of the present Cr-based two-phase alloy and reduces the toughness of the alloy and the corrosion resistance of the grain boundaries. By controlling the content of the P component to 0.04% by mass or less, these negative effects can be suppressed. The P content is more preferably 0.03% by mass or less.

S: More than 0% by mass and 0.01% by mass or less
The S component is easily combined with the constituents of the present Cr-based two-phase alloy to form a sulfide having a relatively low melting point (eg, Fe sulfide, Mn sulfide), and reduces the toughness and pitting resistance of the alloy. It is an impurity component. By controlling the content of the S component to 0.01% by mass or less, these negative effects can be suppressed. The S content is more preferably 0.003% by mass or less.

C: More than 0% by mass and 0.03% by mass or less
The C component has the effect of hardening the alloy by forming a solid solution, but combines with the constituents of the present Cr-based two-phase alloy to form carbides (for example, Cr carbides) and easily precipitate at grain boundaries, and It is also an impurity component that lowers corrosion resistance and toughness. By controlling the content of the C component to 0.03% by mass or less, these negative effects can be suppressed. The C content is more preferably 0.02% by mass or less.

O: More than 0 mass% and 0.05 mass% or less
The O component is an impurity component that easily forms and precipitates a metal oxide (for example, Fe oxide) by combining with the constituent components of the present Cr-based two-phase alloy, and lowers the toughness of the alloy. By controlling the content of the O component to 0.05% by mass or less, the negative effect can be suppressed. The O content is more preferably 0.04% by mass or less, and still more preferably 0.03% by mass or less.

Optional sub-components The present Cr-based two-phase alloy contains, as optional sub-components, 0.5% to 4% by mass of Mo, 0.1% to 5% by mass of Cu, and 0.02% to 0.3% by mass of Sn. One or more of them may be further included. When the present alloy contains these optional subcomponents, the total atomic content of Mo, Cu and Sn is preferably 5% by mass or less. Hereinafter, these optional subcomponents will be described. As described above, the optional subcomponent means a component that may or may not be added.

Mo: 0.5 mass% or more and 4 mass% or less
The Mo component is an optional subcomponent that contributes to the improvement of corrosion resistance in the present Cr-based two-phase alloy. Specifically, it contributes to stabilization of the passivation film and can be expected to improve pitting corrosion resistance. When the Mo component is added, the content is preferably 0.5% by mass or more and 4% by mass or less, more preferably 1% by mass or more and 3% by mass or less. If the Mo content is less than 0.5% by mass, the effect of the Mo component cannot be sufficiently obtained. If the Mo content exceeds 4% by mass, the generation of an embrittlement phase (for example, a σ phase) is promoted, and the ductility and toughness of the alloy are reduced.

Cu: 0.1 mass% or more and 5 mass% or less
The Cu component is an optional subcomponent that contributes to the improvement of corrosion resistance and the stabilization of the austenite phase in the present Cr-based two-phase alloy. When adding a Cu component, its content is preferably from 0.1% by mass to 5% by mass, more preferably from 0.3% by mass to 3% by mass. If the Cu content is less than 0.1% by mass, the effect of the Cu component cannot be sufficiently obtained. Further, when the Cu content exceeds 5% by mass, Cu precipitates are easily generated in the ferrite phase, and the ductility and toughness of the alloy are reduced.

Sn: 0.02% by mass or more and 0.3% by mass or less
The Sn component plays a role of strengthening the passive film in the present Cr-based two-phase alloy and is an optional subcomponent that contributes to the improvement of corrosion resistance and wear resistance. Specifically, improvement in resistance to chloride ions and acidic corrosive environments can be expected. The content of the Sn component is preferably from 0.02% by mass to 0.3% by mass, more preferably from 0.05% by mass to 0.3% by mass. If the Sn content is less than 0.02% by mass, the effect of the Sn component cannot be sufficiently obtained. On the other hand, when the Sn content exceeds 0.3% by mass, grain boundary segregation of the Sn component occurs, which causes a reduction in ductility and toughness of the alloy.

(Metal structure of Cr-based two-phase alloy product of the present invention)
First, the metal structure (fine structure) of the Cr-based two-phase alloy product according to the present invention will be described.

  The alloy of the present invention is a Cr-Ni-Fe alloy containing Cr, Ni and Fe as main components. The metal structure of an alloy containing Fe as a main component generally includes a ferrite structure having a body-centered cubic lattice crystal structure (also referred to as a ferrite phase and an α-phase) and an austenitic structure having a face-centered cubic lattice crystal structure (austenite phase). , Γ phase) and a martensite structure having a distorted body-centered cubic crystal structure (also referred to as a martensite phase or α 'phase).

  Generally, the ferrite phase has excellent corrosion resistance (eg, SCC resistance) and high mechanical strength (eg, 0.2% proof stress), but has relatively low ductility and toughness compared to the austenitic phase. ing. The austenite phase has relatively high ductility and toughness as compared with the ferrite phase, but has a relatively low mechanical strength. It also shows high corrosion resistance in a normal environment, but it is said that the SCC resistance rapidly decreases when the corrosive environment becomes severe. The martensite phase is said to have high mechanical strength (eg, hardness) but relatively low corrosion resistance.

  On the other hand, the two-phase alloy according to the present invention is an alloy in which two phases of an austenite phase and a ferrite phase are mixed as a metal structure (fine structure). The two-phase alloy has the characteristics of combining the advantages of an austenitic phase (excellent ductility and toughness) and the advantages of a ferrite phase (high mechanical strength, excellent corrosion resistance including SCC resistance). In addition, the two-phase alloy of the present invention has an advantage that the material cost can be reduced as compared with a Ni-based alloy containing Ni as a maximum component because Cr is a main component that is less expensive than Ni.

  In the two-phase alloy of the present invention, the occupancy of the ferrite phase (hereinafter sometimes simply referred to as “ferrite ratio”) is 10% or more and 90% or less, and the balance (ie, 90% or less and 10% or more) is austenite. Preferably it is a phase. The phase occupancy in the present invention is defined as the content (unit:%) of the phase when a backscattered electron diffraction image (EBSP) analysis is performed on the polished surface of the alloy bulk sample.

  If the ferrite ratio exceeds 90%, the ductility of the two-phase alloy is excessively reduced, and it is difficult to secure the expected durability. On the other hand, when the ferrite ratio is less than 10%, it is difficult to secure expected mechanical strength (for example, 0.2% proof stress, tensile strength). The ferrite ratio is more preferably 20% or more and 70% or less, further preferably 25% or more and 60% or less.

  The metal structure of the Cr-based two-phase alloy product of the present invention is not particularly limited, and may be a cast structure, a hot worked structure, or a rapidly solidified structure. Is also good. From the viewpoint of mechanical properties and corrosion resistance, it is more advantageous to have a metal structure with a small crystal grain size (for example, a hot-worked structure, a rapidly solidified structure). Specifically, the average crystal grain size is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

  The average crystal grain size in the present invention was binarized after reading an optical microscopic observation image or an electron microscopic observation image of the polished surface of the alloy bulk sample with image analysis software (NIH Image, public domain software). It is defined as the average value calculated from the minor axis and major axis of the crystal grains. Further, the metal structure may be a metal structure subjected to a solution heat treatment after molding, or a metal structure subjected to an aging heat treatment after the solution heat treatment.

  FIG. 1 is an example of a Cr-based two-phase alloy product according to the present invention, and is an optical microscope photograph showing an example of a metal structure on the surface of a cast product. As shown in FIG. 1, it was confirmed that the Cr-based two-phase alloy product according to the present invention had a metal structure in which a dark ferrite phase P1 and a light austenitic phase P2 were dispersed and mixed with each other. Was. Since the sample in FIG. 1 is a cast molded product, the ferrite phase P1, which is a primary crystal (although it is difficult to understand in FIG. 1), is a structure in which a dendritic crystal peculiar to casting solidification is crystallized (a so-called cast structure). It was confirmed that. Further, it was confirmed that the average crystal grain size was 40 μm or less.

  FIG. 2 is an optical microscope photograph showing another example of the Cr-based two-phase alloy product according to the present invention and showing an example of a metal structure on the surface of a hot forged product. As in FIG. 1, it was confirmed that the ferrite phase P1 in the dark color and the austenitic phase P2 in the light color had a metal structure dispersed and mixed with each other. Since the sample in FIG. 2 is a hot forged product, the structure in which the cast structure is broken and equiaxed recrystallized grains having a smaller particle size than the cast structure are observed (a so-called hot worked structure). Was confirmed. Further, it was confirmed that the average crystal grain size was 20 μm or less. In the hot forged compact, a structure having a forging line (metal flow line) along the shape of the compact on the cross section (so-called forged structure) is observed. It is difficult.

  FIG. 3 is another example of the Cr-based two-phase alloy product according to the present invention, and is an optical microscope photograph showing an example of a metal structure on the surface of a rapidly solidified compact. FIG. 3 shows the surface of a weld metal on which overlay welding was performed using the Cr-based two-phase alloy of the present invention. As in FIGS. 1 and 2, it was confirmed that the ferrite phase P1 in a dark color and the austenitic phase P2 in a light color had a metal structure dispersed and mixed with each other. Since the sample in FIG. 3 is a rapidly solidified compact, the average crystal grain size is small, and a structure like dendritic buds (a structure that starts to form dendrites, a so-called rapidly solidified structure) is confirmed. You. Further, it was confirmed that the average crystal grain size was 30 μm or less. In addition, it was separately confirmed that the Cr-based two-phase alloy powder produced by the atomizing method also had the same metal structure as in FIG.

(Production method of Cr-based two-phase alloy product of the present invention)
Next, a method for producing the above-described Cr-based two-phase alloy product will be described. FIG. 4 is an example of a method for manufacturing a Cr-based two-phase alloy product according to the present invention, and is a process diagram illustrating a method for manufacturing a cast molded product.

  As shown in FIG. 4, first, a raw material of a Cr-based two-phase alloy is mixed and melted to have a desired composition (main component + subcomponent + optional subcomponent if necessary) to form a molten metal 10. A raw material mixing and dissolving step (Step 1: S1) is performed. At this time, a nitride (for example, iron nitride) of a metal component other than Cr is used as a main source of the N component of the Cr-based two-phase alloy. Nitrogen gas may be present in the alloy melting atmosphere. As a result, the N content in the alloy can be increased as compared with the related art while suppressing generation and precipitation of undesired chromium nitride.

  Unfortunately, the mechanism of the above-mentioned effects (increases the N content in the alloy compared to the conventional one while suppressing the generation and precipitation of undesired chromium nitride) has not been elucidated at this stage. In other words, the raw material mixing and melting method of the present invention (the method of using a nitride of a metal component other than Cr as the main source of the N component of the Cr-based two-phase alloy) is the same as the method of melting N Because the chemical potential of the component is sufficiently high, the difference between the chemical potential of the N component in the alloy melting atmosphere and the chemical potential of the N component is small, so that the dissolution of nitrogen gas into the molten alloy (and the undesirable chemical reaction) is suppressed. Possibilities are possible.

  There is no particular limitation on the method of mixing and melting the raw materials, and conventional methods in the production of high corrosion resistant and high strength alloys can be used. For example, high frequency melting can be suitably used as a melting method. It is preferable to refine the molten metal 10 by using a carbon deoxidation method or the like.

  In order to further reduce the content of the impurity components (P, S, C and O) in the alloy (to increase the cleanliness of the alloy), the raw material mixing and melting step S1 mixes the raw materials of the Cr-based two-phase alloy. A raw material alloy lump forming step (Step 1a: S1a) of melting and forming a molten metal 10 and then solidifying to form a raw material alloy lump 11, and re-melting the raw material alloy lump 11 to prepare a purified molten metal 12. More preferably, it comprises a re-dissolution step (step 1b: S1b). There is no particular limitation on the remelting method as long as the cleanliness of the alloy can be increased. For example, vacuum arc remelting (VAR) or electroslag remelting (ESR) can be preferably used.

  Next, a casting step (Step 2: S2) of casting the molten metal 10 using a predetermined mold to form a cast molded body 20 is performed. When the remelting step S1b is performed as described above, the casting step S2 is a step of casting the purified molten metal 12 to form the cast molded body 20. In a cast molded product in which a cast product has a substantially final shape, it is preferable to secure a cooling rate capable of suppressing coarsening of crystal grains during solidification (coarse cast solidified structure) from the viewpoint of mechanical properties and corrosion resistance of the final product.

  After the casting step S2, if necessary, a solution heat treatment step (step 3: S3) for performing a solution treatment on the cast molded body 20 may be performed. The temperature of the solution heat treatment is preferably in the range of 1050 to 1300 ° C, more preferably in the range of 1100 to 1250 ° C. By performing the solution treatment, the chemical composition can be homogenized in each of the austenite phase and the ferrite phase. Further, by performing the solution treatment, the phase ratio of the two phases can be adjusted (the ferrite ratio can be adjusted).

  In addition, an aging heat treatment step (Step 4: S4) may be performed after the solution heat treatment step S3. The temperature of the aging heat treatment is preferably in the range of 800 to 1000C, more preferably around 900C. The heat treatment time may be appropriately adjusted within the range of 0.5 to 6 hours. By performing the aging heat treatment, the phase ratio of two phases can be adjusted (ferrite ratio adjustment).

  For example, if the ferrite phase is excessive than the expected ferrite rate from the composition, by performing this aging heat treatment, a part of the ferrite phase is transformed into an austenite phase to adjust the ductility and toughness of the product. be able to. Conversely, when the ferrite phase is too small (the austenite phase is excessive) than expected from the composition, the part of the austenite phase is transformed into a ferrite phase to adjust the mechanical strength of the product. Can be.

  FIG. 5 is another example of the method for producing a Cr-based two-phase alloy product according to the present invention, and is a process diagram showing a method for producing a hot-worked compact. FIG. 5 shows a process for producing a rod-shaped material or a linear material made of the Cr-based two-phase alloy of the present invention.

  As shown in FIG. 5, the method for manufacturing a hot-formed body includes a hot-forming step between the casting step S2 and the solution heat treatment step S3 in the method for manufacturing a cast body in FIG. S5), and the other steps are the same. Therefore, only the hot working and forming step S5 will be described.

  In the method for manufacturing a hot-formed body, a hot-work forming step S5 of subjecting the cast body 20 obtained in the casting step S2 to hot working to form a substantially final shape is performed. There is no particular limitation on the type and method of hot working, and conventional types and methods (eg, hot extrusion, hot drawing, hot rolling, hot forging) can be used, but the temperature of hot working is 900 A range of 11300 ° C. is preferred.

  By performing hot working within the temperature range (the temperature does not deviate during the hot working), the cast solidified structure of the cast formed body 20 is broken, and the grain size is smaller than the crystal grains of the cast structure. It is possible to obtain a hot-worked compact 30 (a hot-stretched compact 31, a hot-forged compact 32) of a Cr-based two-phase alloy having a structure in which axial recrystallized grains are observed (a hot-worked structure). it can. In the hot forged molded body 32, a structure having a forging line along the shape of the molded body is further observed in the cross section.

  FIG. 6 is another example of the method for producing a Cr-based two-phase alloy product according to the present invention, and is a process diagram showing a method for producing a rapidly solidified compact. FIG. 6 shows a process for producing a powder comprising the Cr-based two-phase alloy of the present invention.

  As shown in FIG. 6, in the method for producing a rapidly solidified and compacted body (powder in this case), the raw material mixing and dissolving step S1 is the same as the production method in FIG. 4, and instead of the casting step S2, an atomizing step (step 6: S6) is different. Therefore, the atomizing step S6 will be described.

  By performing the atomizing step S6, a rapidly solidified alloy powder 40 of a Cr-based two-phase alloy can be obtained from the molten metal 10 or the purified molten metal 11. There is no particular limitation on the atomizing method, and a conventional atomizing method can be used. For example, a gas atomizing method capable of obtaining highly clean, homogeneous composition and spherical particles can be preferably used.

  After the atomizing step S6, a classification step S7 may be performed on the rapidly solidified alloy powder 40 to adjust the particle diameter to a desired particle size, if necessary. Although there is no particular limitation on the particle size to be classified, it is preferable to classify the rapidly solidified alloy powder 40 so as to have an average particle size of, for example, 10 μm or more and 200 μm or less from the viewpoint of handling properties. The obtained rapidly solidified alloy powder 40 can be suitably used, for example, as a welding material, a powder metallurgy material, or a material for additive manufacturing. Further, in the present invention, the welded joint and the build-up welded material manufactured using the rapidly solidified alloy powder 40 and the hot stretched molded body 31 as a welding material also have a rapidly solidified structure at the welded portion. Is regarded as a kind of rapidly solidified compact of the Cr-based two-phase alloy according to the above.

  The product manufactured as described above is made of a two-phase alloy containing Cr as the largest component, which is inexpensive compared to Ni, so it has Ni-based alloys with high corrosion resistance and mechanical properties equivalent to or higher than those of conventional products. The cost can be reduced as compared with a product made of an alloy. As a result, the two-phase alloy product according to the present invention can be used for oil well equipment members (for example, members (shafts, bearings, etc.) of rotary machines (compressors, pumps, etc.)) and seawater environmental devices used in severe corrosive environments. It can be suitably used as a member (eg, a seawater desalination plant equipment member, an umbilical cable) or a chemical plant equipment member (eg, a liquefied natural gas vaporizer member).

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Note that the present invention is not limited to these examples.

[Experiment 1]
(Production of alloy products of Examples 1 to 9 and alloy products of Conventional Examples 1 to 7)
An alloy product of a hot-worked product using alloys A1-1 to A1-8 (alloys of the present invention) and alloys R1 to R7 (conventional alloys which do not fall within the scope of the present invention) having the chemical compositions shown in Table 1. (Examples 1 to 9 and Conventional Examples 1 to 7) were produced. The content (unit: mass%) of each component is converted so that the sum of the chemical compositions shown in Table 1 becomes 100 mass%. The alloy R7 is a commercially available duplex stainless steel called super duplex stainless steel.

The production of each alloy product was performed according to the production method shown in FIG. First, as a raw material mixing and melting step, the raw materials of each alloy were mixed, and the raw materials were melted (melting temperature of 1500 ° C. or more, in an Ar atmosphere or in an Ar-5 vol% N ₂ atmosphere) using a high-frequency melting furnace. At this time, in the alloy products of Examples 1-9 (alloy A1-1～A1-8), was used iron nitride (Fe ₃ N) as the primary source of N component alloy. On the other hand, in the alloy products of Conventional Examples 1 to 7 (alloys R1 to R7), no metal nitride was used as a raw material.

  After the raw material mixing and melting step, as a casting step, a molten metal was cast using a predetermined mold to produce a cast formed body (here, an ingot for hot working) of each alloy.

  Next, as a hot working forming step, each of the above-mentioned ingots for hot working was formed into a predetermined shape by hot forging. The hot forging conditions were a forging temperature of 1050 to 1250 ° C., a strain rate of 8 mm / s or less, a reduction of 10 mm or less per forging, and a forging frequency of 6 or more.

  In addition, the range of the forging temperature was determined as follows. A test specimen for a tensile test was separately cut out from each ingot, and a high-temperature tensile test (test temperature: 800 to 1350 ° C., tensile speed: 10 mm / s) was performed on the test specimen using a grease tester. As a result of the high-temperature tensile test, the temperature range in which the drawing was 60% or more was defined as the forging temperature range.

  Next, as a solution heat treatment step, a solution heat treatment (holding at 1100 to 1250 ° C. for 1 hour, followed by water cooling) was performed on each of the alloy samples subjected to hot forging. Through the above steps, alloy products for testing and evaluation (Examples 1 to 9 and Conventional Examples 1 to 7) were produced. The alloy types and solution heat treatment conditions for each alloy product are described in Table 2 below.

(Test / evaluation for alloy products of Examples 1 to 9 and alloy products of Conventional Examples 1 to 7)
(1) Evaluation of microstructure After a test piece for observing the structure was collected from each alloy product, the surface of the test piece was mirror-polished and subjected to electric field etching in an oxalic acid aqueous solution. The polished surface was observed with an optical microscope. FIG. 2 shown above is an optical micrograph of the metal structure of Example 3. FIG. 7 is an optical micrograph of the metal structure of Conventional Example 4.

  The Cr-based two-phase alloy products of Example 3 (FIG. 2) and Conventional Example 4 (FIG. 7) both have a metal structure in which a dark ferrite phase P1 and a light austenitic phase P2 are dispersed and mixed with each other. It turns out that there is. In addition, the structure in which the cast solidification structure (for example, dendrites peculiar to the cast solidification) is destroyed due to hot working, and equiaxed recrystallized grains having a smaller particle size than the cast structure are observed. (A so-called hot worked structure). In addition, a forging line was observed in the cross section, and it was separately confirmed that the forging structure was obtained.

  On the other hand, there was a difference in the crystal grain size between Example 3 (FIG. 2) and Conventional Example 4 (FIG. 7). Example 3 containing a large amount of N component has a clearly smaller crystal grain size than Conventional Example 4 in which the content of N component is suppressed. The mechanism by which the crystal grain size is reduced by including a large amount of the N component has not been elucidated at this stage, but it is possible that the N component may pin the grain boundary migration during recrystallization by hot working. Can be Further, the effect of improving mechanical properties and corrosion resistance is expected from the refinement of crystal grains (details will be described later).

  Next, as another method of evaluating the microstructure, the ferrite ratio was measured. Backscattered electron diffraction (EBSP) analysis was performed on the polished surface of the above-mentioned specimen for structure observation, and the occupancy of the ferrite phase (ferrite ratio, unit:%) was measured. For the measurement, a device obtained by adding a crystal orientation measuring device manufactured by TSL Solutions to a scanning electron microscope (S-4300SE) manufactured by Hitachi High-Technologies Corporation was used. The results are also shown in Table 2.

(2) Evaluation of mechanical properties As one of the mechanical property evaluations, a Vickers hardness test (load 1 kg, load application time 15 s) was performed on the above-mentioned specimen for structure observation using a Vickers hardness meter. . Vickers hardness was determined as an average of five measurements. The results are also shown in Table 2.

  Next, abrasion resistance was evaluated as another one of the mechanical property evaluations. A wear test specimen (diameter 10 mm, length 20 mm) was sampled from each prepared alloy product, and subjected to a friction wear test using a Pin-on-Disk type friction wear tester. went.

  The friction and wear test method is as follows. Attach water-resistant abrasive paper with a grain size of 240 to the disk, rotate the disk at 200 rpm, and press the test piece that becomes a pin at room temperature and atmospheric environment with a load of 4 kgf against the water-resistant abrasive paper, the outermost periphery of the water-resistant abrasive paper (The outermost diameter was 156 mm) and moved toward the center (total travel distance of the pins = about 6 m). The results of the friction and wear test were obtained by measuring the amount of change in the length of the pin as the amount of wear, and calculating the average of two measurements.

  As a reference sample for evaluation of wear resistance, a commercially available cobalt-based alloy (Stellite (registered trademark), which is considered to have excellent wear resistance, chemical composition 59.8Co-29.0Cr- 4.1W- 2.9Fe- 1.7Ni- 1.3Si- 0.026P-0.0023S-1.2C-0.090-0.022N:% by mass). As a result of the friction and wear test, the amount of wear of the reference sample was 0.087 mm. With this as 100%, the ratio of the wear amount of each alloy product was calculated. The smaller the ratio of the wear amount, the higher the wear resistance. Table 2 also shows the results of the wear resistance evaluation.

(3) Corrosion resistance evaluation As one type of corrosion resistance evaluation, a sulfuric acid resistance test was performed. Samples (13 mm wide, 40 mm long, 3 mm thick) for the sulfuric acid resistance test were collected from each prepared alloy product, and the corrosion rate in sulfuric acid was determined according to JIS G0591 (2000). evaluated. Specifically, a test in which the test piece was immersed in boiling 5% sulfuric acid for 6 hours was performed. The mass of each test piece before and after the test was measured, the average mass reduction rate m (unit: g / (m ² · h)) due to corrosion was measured, and the average value of the two measurements was obtained.

  As a result of the measurement of the average mass reduction rate, “m <0.1” was evaluated as A rank, “0.1 ≦ m <0.3” was evaluated as B rank, “0.3 ≦ m <0.5” was evaluated as C rank, 0.5 ≦ m ”was evaluated as D rank. A rank was judged as pass, and B rank or less was judged as reject. Table 2 also shows the results of the corrosion resistance evaluation.

  As shown in Tables 1 and 2, in Conventional Examples 1 to 7, the chemical composition of the alloy was out of the range specified in the present invention, and there were difficulties in either mechanical properties (Vickers hardness, wear resistance) or corrosion resistance. was there.

  More specifically, Conventional Example 1 (both the contents of Ni and N are less than the stipulations of the present invention) is an alloy having a single ferrite phase (100% ferrite ratio), and has high Vickers hardness and good wear resistance. However, there was a problem in corrosion resistance. Conventional Example 2 (Ni content is higher than specified in the present invention and N content is lower than specified in the present invention) is an alloy of austenite single phase (ferrite ratio 0%), Vickers hardness, wear resistance And all of the corrosion resistance had drawbacks. In Conventional Example 7 made of a commercially available duplex stainless steel (the contents of the three main components and N deviate from the provisions of the present invention), the ferrite ratio was within the range of the present invention, but the corrosion resistance was insufficient. . Further, Conventional Examples 3 to 6 (the N content is smaller than the stipulation of the present invention) had a problem in corrosion resistance.

  On the other hand, Examples 1 to 9 according to the present invention are all two-phase alloys having a ferrite ratio in the range of 10% to 90%, and have the same mechanical properties (Vickers hardness) as those of Conventional Examples 3 to 6. , Abrasion resistance), while exhibiting better corrosion resistance than Conventional Examples 3 to 6. In addition, the ferrite ratio tended to increase with an increase in the Cr content, and it was confirmed that the Vickers hardness tended to increase with an increase in the ferrite ratio.

  Note that comparing Example 1 and Conventional Example 3 having similar chemical compositions other than the N content and comparing Example 5 and Conventional Example 5 similarly, Examples 1 and 5 having a high N content It can be seen that the ferrite rate is lower than that of Conventional Examples 3 and 5 where the content is low. This is considered to indicate that the N component contributes to stabilization of the austenite phase.

[Experiment 2]
(Production of Alloy Products of Examples 10 to 18 and Alloy Products of Conventional Examples 8 to 9)
Using the alloys A2-1 to A2-8 (alloys of the present invention) and the alloys R8 to R9 (conventional alloys which do not fall within the scope of the present invention) having the chemical compositions shown in Table 3, the alloy products of cast moldings (implemented) Examples 10 to 18 and Conventional Examples 8 to 9 were produced. The content (unit: mass%) of each component is converted so that the sum of the chemical compositions shown in Table 3 becomes 100 mass%.

The production of each alloy product was performed according to the production method shown in FIG. First, as a raw material alloy mass forming step, the raw materials of each alloy are mixed, and the raw materials are melted using a high-frequency melting furnace (melting temperature of 1500 ° C. or more, in an Ar atmosphere or in an Ar-5 vol% N ₂ atmosphere), and the molten metal is formed. Was once solidified to produce a raw alloy mass of each alloy. At this time, in the alloy product of Example 10 to 18 (alloy A2-1～A2-8), it was used iron nitride (Fe ₃ N) as the primary source of N component alloy. On the other hand, in the alloy products of Conventional Examples 8 to 9 (alloys R8 to R9), no metal nitride was used as a raw material.

  Next, as a remelting step, a raw alloy mass was remelted by an electroslag remelting method (ESR method) to prepare a purified molten metal.

  Next, as a casting step, a purified molten metal was cast using a water-cooled copper mold to produce a cast formed body (diameter 40 mm, length 100 mm) of each alloy.

  Next, as a solution heat treatment step, a solution heat treatment (holding at 1100 to 1250 ° C. for 1 hour, followed by water cooling) was performed on some of the castings. Through the above steps, alloy products for testing and evaluation (Examples 10 to 18 and Conventional Examples 8 to 9) were produced. The alloy species and solution heat treatment conditions for each alloy product are described in Table 4 below.

(Test / evaluation for alloy products of Examples 10 to 18 and alloy products of Conventional Examples 8 to 9)
Microstructure evaluation, mechanical property evaluation, and corrosion resistance evaluation were performed on each of the obtained alloy products in the same manner as in Experiment 1 described above. The results of the mechanical property evaluation and the corrosion resistance evaluation are also shown in Table 4.

  FIG. 1 shown above is an optical micrograph of the metal structure of Example 12. As described above, it can be seen that the Cr-based two-phase alloy product of Example 12 also has a metal structure in which the dark ferrite phase P1 and the light austenitic phase P2 are dispersed and mixed with each other. In addition, since it was a cast molded product, it was confirmed that the ferrite phase P1, which is the primary crystal (although it is difficult to understand in FIG. 1), crystallized as dendrites unique to casting solidification. In addition, although there was a difference in the ferrite rate, it was separately confirmed that the other castings had the same casting structure as that in FIG.

  As shown in Tables 3 and 4, in Conventional Examples 8 and 9, the N content of the alloy chemical composition was out of the range of the present invention, and there was a problem in corrosion resistance.

  In contrast, Examples 10 to 18 according to the present invention are all two-phase alloys having a ferrite ratio in the range of 10% to 90%, and have the same mechanical properties (Vickers hardness) as those of Conventional Examples 8 to 9. , Abrasion resistance), while exhibiting better corrosion resistance than Conventional Examples 8 to 9. In addition, the ferrite ratio tended to increase with an increase in the Cr content, and it was confirmed that the Vickers hardness tended to increase with an increase in the ferrite ratio.

[Experiment 3]
(Production of alloy products of Examples 19 to 30 and alloy products of Conventional Examples 10 to 13)
Using alloys A3-1 to A3-12 (alloys of the present invention) and alloys R10 to R13 (conventional alloys which do not fall within the scope of the present invention) having the chemical compositions shown in Table 5, an alloy product of a cast molded product (implemented) Examples 19 to 30 and Conventional Examples 10 to 13) were produced. The content (unit: mass%) of each component is converted so that the sum of the chemical compositions shown in Table 5 becomes 100 mass%.

The production of each alloy product was performed according to the production method shown in FIG. First, as a raw material alloy mass forming step, the raw materials of each alloy are mixed, and the raw materials are melted using a high-frequency melting furnace (melting temperature of 1500 ° C. or more, in an Ar atmosphere or in an Ar-5 vol% N ₂ atmosphere), and the molten metal is formed. Was once solidified to produce a raw alloy mass of each alloy. At this time, in the alloy product of Example 19 to 30 (alloy A3-1～A3-12), it was used iron nitride (Fe ₃ N) as the primary source of N component alloy. On the other hand, in the alloy products of Conventional Examples 10 to 13 (alloys R10 to R13), no metal nitride was used as a raw material.

  Next, as a remelting step, a raw alloy mass was remelted by an electroslag remelting method (ESR method) to prepare a purified molten metal.

  Next, as an atomizing step, a rapidly solidified compact (here, powder) of each alloy was prepared from the purified molten metal by a gas atomizing method. Thereafter, a classification process was performed on the rapidly solidified compact to obtain an alloy powder having a particle size in the range of 50 to 200 μm.

  Next, overlay welding was performed using the classified alloy powder to produce an alloy product comprising a composite having an alloy coating layer formed on a base material. FIG. 8 is a schematic cross-sectional view showing an example of a composite in which a coating layer for overlay welding is formed on a base material. As shown in FIG. 8, the composite 50 is formed by coating the alloy coating layers 52 to 54 on a commercially available SUS304 steel base material 51 so as to have a total thickness of about 5 mm by powder plasma overlay welding. It is formed. The welding conditions were an arc current of 120 A, a voltage of 25 V, and a welding speed of 9 cm / min. The alloy types used for each alloy product are described in Table 6 below.

(Tests / Evaluations for the Alloy Products of Examples 19 to 30 and the Alloy Products of Conventional Examples 10 to 13)
Microstructure evaluation, mechanical property evaluation, and corrosion resistance evaluation were performed on each of the obtained alloy products in the same manner as in Experiment 1 described above. The results of the mechanical property evaluation and the corrosion resistance evaluation are also shown in Table 6.

  FIG. 3 shown above is an optical micrograph of the metal structure of Example 21. As described above, it can be seen that the Cr-based two-phase alloy product of Example 21 also has a metal structure in which the dark ferrite phase P1 and the light austenitic phase P2 are dispersed and mixed with each other. In addition, since it was a rapidly solidified compact, it was confirmed that the crystal grain size was small and a dendrite bud-like structure (a structure that began to become a dendrite) was observed. In addition, although there was a difference in the ferrite rate, it was separately confirmed that other rapidly solidified compacts also had the same rapidly solidified structure as that of FIG.

  As shown in Tables 5 and 6, in Conventional Examples 10 to 13, the N content of the alloy chemical composition was out of the range of the present invention, and there was a problem in corrosion resistance.

  In contrast, Examples 19 to 30 according to the present invention are all two-phase alloys having a ferrite ratio in the range of 10% to 90%, and have the same mechanical properties (Vickers hardness) as those of Conventional Examples 10 to 13. , Abrasion resistance), while exhibiting better corrosion resistance than Conventional Examples 10 to 13. In addition, the ferrite ratio tended to increase with an increase in the Cr content, and it was confirmed that the Vickers hardness tended to increase with an increase in the ferrite ratio.

  From the test and evaluation results as described above, it was confirmed that the examples according to the present invention exhibited better corrosion resistance than the conventional materials while having the same mechanical properties as the conventional materials. Furthermore, since the content of the Cr component is high, it can be said that the cost can be reduced as compared with the conventional Ni-based alloy material.

  The above-described embodiments and examples have been described to assist understanding of the present invention, and the present invention is not limited to only the specific configurations described. For example, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. That is, according to the present invention, a part of the configuration of the embodiment or the example of the present specification can be deleted, replaced with another configuration, or added with another configuration.

P1: ferrite phase, P2: austenite phase,
10 ... Molten, 11 ... Ingot of raw material alloy, 12 ... Molten metal, 20 ... Molded casting,
30: hot-worked compact, 31: hot stretched compact, 32: hot forged compact,
40: rapidly solidified alloy powder, 50: composite, 51: base material, 52 to 54: alloy coating layer.

Claims (19)

A product using a Cr-based two-phase alloy in which two phases of a ferrite phase and an austenite phase are mixed,
The chemical composition of the Cr-based two-phase alloy is composed of a main component, a subcomponent, an impurity and an optional subcomponent,
The main components are:
34% by mass or more and 70% by mass or less of Cr;
17% by mass or more and 42% by mass or less of Ni,
10% by mass or more and 33% by mass or less of Fe,
The mass content of the Cr is the largest,
The sub-component,
0.1% by mass or more and 2% by mass or less of Mn,
0.1% by mass or more and 1% by mass or less of Si;
0.005% by mass or more and 0.05% by mass or less of Al;
Consisting of 0.06% by mass or more and 0.2% by mass or less of N,
The impurities are:
P of more than 0% by mass and 0.04% by mass or less,
S of more than 0% by mass and 0.01% by mass or less;
C of more than 0% by mass and 0.03% by mass or less,
A Cr-based two-phase alloy product comprising more than 0% by mass and 0.05% by mass or less of O. The Cr-based two-phase alloy product according to claim 1,
The optional subcomponent is:
0.5% to 4% by mass of Mo,
0.1 mass% or more and 5 mass% or less of Cu, and
Consisting of at least one of Sn of 0.02% by mass or more and 0.3% by mass or less,
When the Cr-based two-phase alloy contains the optional subcomponent, a total atomic content of the Mo, Cu, and Sn is 5% by mass or less. In the Cr-based two-phase alloy product according to claim 1 or claim 2,
A Cr-based two-phase alloy product, wherein the occupancy of the ferrite phase is 10% or more and 90% or less. The Cr-based two-phase alloy product according to any one of claims 1 to 3,
The Cr-based two-phase alloy product, wherein the product is a cast compact having a casting structure. The Cr-based two-phase alloy product according to any one of claims 1 to 3,
The Cr-based two-phase alloy product, wherein the product is a hot-worked compact having a hot-work structure. The Cr-based two-phase alloy product according to claim 5,
The two-phase alloy product, wherein the hot-formed body is a rod-shaped body or a linear body. The Cr-based two-phase alloy product according to claim 5,
The Cr-based two-phase alloy product, wherein the hot worked structure is a forged structure. The Cr-based two-phase alloy product according to claim 7,
The Cr-based two-phase alloy product, wherein the hot-formed body is a shaft or a bearing of a rotary machine. The Cr-based two-phase alloy product according to any one of claims 1 to 3,
The Cr-based two-phase alloy product, wherein the product is a rapidly solidified compact having a rapidly solidified structure. The Cr-based two-phase alloy product according to claim 9,
The rapidly solidified compact is a powder, and is a Cr-based two-phase alloy product. The Cr-based two-phase alloy product according to claim 9,
The Cr-based two-phase alloy product, wherein the rapidly solidified compact is a composite in which a coating layer of a Cr-based two-phase alloy having the rapidly solidified structure is formed on a substrate. The Cr-based two-phase alloy product according to any one of claims 1 to 3,
The product is a welded joint in which the alloy members are welded through a welded portion,
The Cr-based two-phase alloy product, wherein the welded portion is made of the Cr-based two-phase alloy. A method for producing a Cr-based two-phase alloy product according to claim 4,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
A casting step of casting the molten metal to form a cast molded body,
A solution heat treatment step of performing a solution treatment in a temperature range of 1050 ° C. or more and 1250 ° C. or less for the cast molded body,
In the raw material mixture melting step, a Cr-based two-phase alloy product characterized by using a nitride of a metal component other than the Cr component as the raw material for adjusting the content of the N component of the Cr-based two-phase alloy Production method. A method for producing a Cr-based two-phase alloy product according to any one of claims 5 to 8,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
A casting step of casting the molten metal to form a cast molded body,
A hot working forming step of performing hot working on the cast formed body in a temperature range of 900 ° C. or more and 1300 ° C. or less to form a hot worked formed body,
Having a solution heat treatment step of performing a solution treatment in a temperature range of 1050 ° C. or more and 1250 ° C. or less for the hot-worked molded body,
In the raw material mixing and melting step, a Cr-based two-phase alloy product is manufactured using a nitride of a metal component other than Cr as the raw material for adjusting the content of the N component in the Cr-based two-phase alloy. Method. The method for producing a two-phase alloy product according to claim 14,
A method for producing a Cr-based two-phase alloy product, wherein the hot working in the hot working forming step is hot forging. A method for producing a Cr-based two-phase alloy product according to claim 9 or claim 10,
A raw material mixing and melting step of forming a molten metal by mixing and melting the raw materials of the Cr-based two-phase alloy,
Atomizing step of forming an alloy powder from the molten metal,
In the raw material mixing and melting step, a Cr-based two-phase alloy product is manufactured using a nitride of a metal component other than Cr as the raw material for adjusting the content of the N component in the Cr-based two-phase alloy. Method. The method for producing a Cr-based two-phase alloy product according to any one of claims 13 to 15,
After the solution heat treatment step, a Cr-based two-phase alloy product, further comprising an aging heat treatment step of performing an aging treatment in the temperature range of 800 ° C or more and 1000 ° C or less for the solution-treated molded body. Manufacturing method. The method for producing a Cr-based two-phase alloy product according to any one of claims 13 to 17,
The method for producing a Cr-based two-phase alloy product, wherein the nitride of a metal component other than Cr is iron nitride. The method for producing a Cr-based two-phase alloy product according to any one of claims 13 to 18,
The raw material mixing and melting step is a raw material alloy lump forming step of mixing and melting the raw materials to form a molten metal and then solidifying once to form a raw material alloy lump, and remelting the raw material alloy lump to produce a purified molten metal. It consists of a re-dissolution step to prepare,
The method for producing a Cr-based two-phase alloy product, wherein the casting step is a step of casting the purified molten metal to form the cast molded body.

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