TECHNICAL FIELD

The present invention relates to a technique for an alloy having high corrosion resistance and high strength, more specifically a product produced using a chromium(Cr)-iron(Fe)-nickel(Ni)-based alloy.

BACKGROUND ART

Among various members used in internal combustion engines, those members which come into contact with fuels having various qualities or deteriorated lubricant oils or combustion gases (e.g., a member for fuel injection devices, a timing chain member, a member for exhaust gas recirculation devices) are required to have high corrosion resistance enough to withstand severe corrosive environments and high-temperature environments and high mechanical properties. As a material that can meet these requirements, a martensitic stainless steel, which has excellent corrosion resistance and mechanical properties, has been used widely at present.

For example, PTL 1 (JP 6-58218 A) discloses a highly corrosion-resistant fuel injection device provided with a nozzle body which has a fuel injection hole and a valve which can slide in a guide hole formed in the nozzle body, wherein the fuel injection hole can be opened/closed in response to the movement of the valve in the direction of the axis of the nozzle body, the device being characterized in that at least one of the valve and at least an injection hole sheet part in the nozzle body on which the valve is to be seated is a cold-forging martensitic stainless steel containing, in % by weight, 0.1 to 0.5% of C, 12 to 18% of Cr, 0.5 to 1.5% of Mo, 0.03 to 1.0% of Si, 0.03 to 0.75% of Mn, with the remainder made up by Fe and unavoidable impurities.

PTL 2 (JP 2015-40307 A) discloses a high-hardness martensitic stainless steel having excellent corrosion resistance to an organic acid, the martensitic stainless steel being characterized by containing, in % by mass, 0.60 to 0.75% of C, 0.05 to 0.30% of Si, 0.01 to 0.30% of Mn, 10.00 to 12.00% of Cr, 0.10 to 2.00% of Cu, with the remainder made up by Fe and unavoidable impurities.

CITATION LIST

Patent Literatures

PTL 1: JP 6-58218 A

PTL 2: JP 2015-40307 A

SUMMARY OF INVENTION

Technical Problem

According to PTL 1, the sheet part and the valve are never eroded or damaged by a highly corrosive fuel such as a gasoline-alcohol mixed fuel, and therefore it is possible to provide a fuel injection device having high durability and reliability. According to PTL 2, it is possible to provide a high-hardness martensitic stainless steel which can exhibit excellent resistance to formic acid and acetic acid even in deteriorated gasoline environments when used in an automotive fuel injection pump member or the like that is used under high-pressure environments or the like.

In recent years, internal combustion engines having higher efficiency than before have been developed through the progression of fuel control techniques. However, the research/development for achieving further higher efficiency has been growing intense. For the members to be used in the internal engines, higher corrosion resistance and higher mechanical properties than before have also been demanded with the progress of the above-mentioned research/development.

In a martensitic stainless steel, the increase in the content of component carbon is effective for the improvement of the mechanical properties of the martensitic stainless steel. In this case, however, the corrosion resistance of the martensitic stainless steel is deteriorated disadvantageously. On the other hand, as a metallic material having both of excellent corrosion resistance and excellent mechanical properties, a nickel-based alloy is known. However, a nickel-based alloy has a disadvantage that the cost for materials thereof is very expensive.

In the research/development of metal members, to meet requirements for various demanded properties is an essential factor. Accordingly, the provision of such metal members at low costs is one of top priority issues from the viewpoint of the realization of practical and commercial use of the members.

Thus, the object of the present invention is to provide an alloy product which has both of high corrosion resistance enough to withstand severe corrosive/high-temperature environments and mechanical properties equivalent to or better than those of a martensitic stainless steel, and which can be produced at lower cost than a nickel-based alloy.

Solution to Problem

One aspect of the present invention provides a Cr—Fe—Ni-based alloy product which is a product produced using a Cr—Fe—Ni-based alloy containing Cr as a largest-content component,

wherein the product has such a microstructure that a dual-phase structure having a ferrite phase and an austenite phase coexisting therein serves as a matrix phase and an L12-type Ni-based intermetallic compound phase is dispersed and precipitated in the austenite phase.

In the Cr—Fe—Ni-based alloy product of the present invention, the following modifications and changes can be added.

(i) The Ni-based intermetallic compound phase comprises an Ni3Al phase and/or an Ni3(Al,Ti) phase.

(ii) The chemical composition of the Cr—Fe—Ni-based alloy contains

44 to 75% by mass inclusive of Cr,

10 to 33% by mass inclusive of Fe,

10 to 40% by mass inclusive of Ni,

0.05 to 2% by mass inclusive of Mn (manganese),

0.05 to 1% by mass inclusive of Si (silicon),

0.5 to 5% by mass inclusive of Al (aluminum),

more than 0% by mass and 0.1% by mass or less of C (carbon),

more than 0% by mass and 2% by mass or less of N (nitrogen),

more than 0% by mass and 0.2% by mass or less of O (oxygen),

more than 0% by mass and 0.04% by mass or less of P (phosphorus), and

more than 0% by mass and 0.01% by mass or less of S (sulfur); and

the occupancy of the ferrite phase in the microstructure in the product is 60% by area or more.

(iii) The Cr—Fe—Ni-based alloy further contains at least one of Ti (titanium) in an amount of more than 0% by mass and 4% by mass or less and Cu (copper) in an amount of more than 0% by mass and 2% by mass or less as an optional auxiliary component. The term “optional auxiliary component” as used herein refers to a component which may be contained or may not be contained.

(iv) The product is a cast molded body having a cast structure.

(v) The product is a recrystallized molded body having a recrystallized structure.

(vi) The product is a rapidly solidified body having a rapidly solidified structure.

(vii) The rapidly solidified body is a composite body in which a coating layer composed of a Cr—Fe—Ni-based alloy and having the rapidly solidified structure is formed on a base.

(viii) The product is a powder metallurgically molded body having a sintered structure.

(ix) The room-temperature Vickers hardness is 650 Hv or more, the high-temperature Vickers hardness at 800° C. is 320 Hv or more, and the tensile strength at 700° C. is 650 MPa or more when a high-temperature tensile test is carried out in accordance with JIS G 0567.

(x) The product is a powder having a rapidly solidified structure.

(xi) The average mass loss rate is less than 0.1 g/(m2·h) when a sulfuric acid corrosion test is carried out in accordance with JIS (Japanese Industrial Standards) G 0591.

Advantageous Effects of Invention

According to the present invention, a Cr—Fe—Ni-based alloy product can be produced, which has both of high corrosion resistance enough to withstand severe corrosive/high-temperature environments and mechanical properties equivalent to or better than those of a martensitic stainless steel, and which can be produced at lower cost than a Ni-based alloy.

