JP2022035110A - High-strength and high-toughness iron-based alloy, and method for manufacturing the same - Google Patents

Abstract

To provide a high-strength and high-toughness iron-based alloy suitable for various structural components/members, particularly members for aerospace-related equipment which has a specific strength equivalent to maraging steel, in which toughness higher than that of maraging steel is obtained at -100°C, a material cost can be also reduced, and which has a high degree of freedom of a shape, and a method for manufacturing the alloy.SOLUTION: A high-strength and high-toughness iron-based alloy that contains C:0.12 to 0.3%, Si:0.15 to 0.7%, Mn:0.4 to 1.2%, P:0.015% or less, S:0.015% or less, Ni:2 to 4%, Cr:0.1 to 0.5%, and Mo:0.3 to 0.5% by mass%, in which the remainder consists of Fe and inevitable impurity, and which has a solidified structure with a dendrite secondary arm spacing of 5 μm or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a high-strength, high-toughness iron-based alloy suitable for various structural parts / members, particularly members for aerospace-related equipment, and having excellent specific strength and toughness, and a method for producing the same.

In recent years, structural members constituting various devices are often required to be lightweight in order to prevent an increase in the total weight. This is a very important requirement, especially for aerospace-related materials. Since steel materials have a higher specific gravity than aluminum alloys and titanium alloys, the range of application is limited, but maraging steel, whose specific strength is comparable to that of aluminum alloys and titanium alloys, is applied as an aerospace-related member. (For example, Non-Patent Document 1).

Aerospace-related materials used in areas close to the outside air may be exposed to low temperatures during operation. For example, an aircraft flying at an altitude of 10,000 m is said to be exposed to an environment of -50 ° C, and an artificial satellite orbiting the earth is exposed to an environment of -100 ° C. Structural members used in such a low temperature environment are not subject to low temperature embrittlement. It is indispensable to prevent serious accidents. Austenitic stainless steel (specific strength 130) and nickel steel (specific strength 100) are examples of steel materials that do not embrittle at low temperatures or are less embrittled, but their specific strength is about 1/2 that of aluminum alloys and titanium alloys. Is.

Further, although Patent Document 1 and Patent Document 2 disclose a cast alloy having high strength and high toughness, the specific strength is about 1/2 that of an aluminum alloy or a titanium alloy, and it is difficult to reduce the weight of the cast product. Therefore, the application has not progressed.

Japanese Patent Application Laid-Open No. 2008-007820 Japanese Unexamined Patent Publication No. 2014-181394

Daido Steel Co., Ltd. Press Release, [Search on June 3, 2nd year of Reiwa], Internet <URL: https://www.daido.co.jp/about/release/2017/0427_pw.html>

INDUSTRIAL APPLICABILITY The present invention has various structures having a specific strength equivalent to that of maraging steel, higher toughness than maraging steel at −100 ° C., low material cost, and high degree of freedom in shape. An object of the present invention is to provide a high-strength and high-toughness iron-based alloy suitable for parts / members, particularly members for aerospace-related equipment, and a method for manufacturing the same.

The present inventors have a high degree of freedom in shape, have a specific strength equivalent to that of maraging steel, can obtain higher toughness at −100 ° C., and can keep the material cost lower than that of maraging steel. Various studies were conducted for the purpose of obtaining an iron-based alloy.

As a result, for example, by laminating and molding a powder having a specific composition, which has a small content of expensive alloying elements as compared with the maraging height disclosed in Patent Document 1 and Patent Document 2, the structure is remarkably made finer. We have found that high specific strength and high toughness that could not be achieved in the past can be obtained.

The present invention has been completed based on these findings, and provides the following (1) to (7).

(1) By mass%,
C: 0.12-0.3%,
Si: 0.15 to 0.7%,
Mn: 0.4-1.2%,
P: 0.015% or less,
S: 0.015% or less,
Ni: 2-4%,
Cr: 0.1-0.5%,
Mo: 0.3-0.5%
Contains,
A high-strength, high-toughness iron-based alloy characterized by having a solidified structure in which the balance is composed of Fe and unavoidable impurities and the dendrite secondary arm spacing is 5 μm or less.

(2) By mass%, V: 0.05 to 0.15% is further contained, and the content of C and V is C × 0.3 ≦ V ≦ C × 0.6 by mass%.
The high-strength, high-toughness iron-based alloy according to (1) above, which is characterized by satisfying the above.

(3) By mass%, Ca: 0.01 to 0.05% is further contained, and the content of Ca and S is S × 2 ≦ Ca ≦ S × 4.5 by mass%.
The high-strength, high-toughness iron-based alloy according to (1) or (2) above, which is characterized by satisfying the above.

(4) C + Si / 24 + Mn / 6 + Ni / 40 + Mo / 4 + Cr / 5 + V / 14
The high-strength, high-toughness iron-based alloy according to any one of (1) to (3) above, wherein the value of carbon equivalent represented by (1) is 0.6% or less in mass%.

(5) The description according to any one of (1) to (4) above, which simultaneously satisfies the specific strength ≧ 200 kN ・ m / kg and the shock absorption energy ≧ 60J (2 mmV notch Charpy impact test piece) at −100 ° C. High-strength and high-toughness iron-based alloy.

(6) A high-strength, high-toughness iron-based alloy characterized in that an alloy material having the composition according to any one of (1) to (4) above is melted and solidified by a laser or an electron beam to form a laminate. Manufacturing method.

(7) The method for producing a high-strength, high-toughness iron-based alloy according to (6) above, wherein the alloy material is a powder.

According to the present invention, it has a specific strength equivalent to that of maraging steel, has higher toughness than maraging steel at −100 ° C., can suppress material cost low, and has a high degree of freedom in shape. Provided are high-strength, high-toughness iron-based alloys suitable for various structural parts / members, particularly members for aerospace-related equipment, and methods for manufacturing the same.

It is a conceptual diagram which shows the atomizing apparatus used in the Example of this invention. It is a figure which shows the relationship between DAS and cooling rate. This is an example of a microstructure photograph of the material of the present invention.

Hereinafter, the reasons for limiting the present invention will be described separately for the chemical composition and the production conditions.
In the following description, unless otherwise specified, the% representation of the components is mass%.

[Chemical composition]
C: 0.12 to 0.3%
C is an element effective for improving strength and hardenability. However, if the content is less than 0.12%, a specific strength of 200 kN ・ m / kg or more cannot be obtained, and if it exceeds 0.3%, ductility and toughness deteriorate, and cracks occur during manufacturing. It will be easier. Therefore, the C content is set in the range of 0.12 to 0.3%.

Si: 0.15 to 0.7%
Si is an element added for the purpose of deoxidation. However, if the content is less than 0.15%, deoxidation is insufficient and pores are generated, and if it exceeds 0.7%, ductility and toughness are lowered. Therefore, the Si content is set to 0.15 to 0.7%.

Mn: 0.4-1.2%
Mn is an element effective for improving strength and hardenability, and also has a deoxidizing effect. However, if the content is less than 0.4%, the effect is small, and if it exceeds 1.2%, the ductility and toughness are lowered and the weldability is deteriorated. Therefore, the Mn content is set in the range of 0.4 to 1.2%.

Ni: 2-4%
Ni is the most important element in the present invention, which seeks to obtain high strength, high ductility and high low temperature toughness at the same time. Ni is an element that is effective for strength and hardenability, but unlike other elements that have similar effects, it has a small adverse effect on ductility, toughness and weldability. In addition, Ni is an element with a large austenite stabilizing effect, and by moving the ferrite transformation region to the long-term side and expanding the bainite transformation region, ferrite precipitation is suppressed even in thick parts where the cooling rate is slow, and high strength is achieved. Is obtained. However, when Ni is less than 2%, a specific strength of 200 kN ・ m / kg or more cannot be obtained, and when it exceeds 4%, heat embrittlement becomes noticeable. Therefore, the Ni content is set in the range of 2 to 4%.

Cr: 0.1-0.5%
Cr is an element effective for improving the specific strength. However, if it is less than 0.1%, the effect is small, and if it exceeds 0.5%, the effect cannot be obtained and the carbon equivalent increases, which lowers the weldability. Therefore, the Cr content is set in the range of 0.1 to 0.5%.

Mo: 0.3-0.5%
Mo is added to improve hardenability and suppress tempering embrittlement. However, if it is less than 0.3%, the effect is small, and if it exceeds 0.5%, the effect cannot be obtained and the carbon equivalent increases, which lowers the weldability. Therefore, the Mo content is set in the range of 0.3 to 0.5%.

P: 0.015% or less S: 0.015% or less P and S are elements that have a great influence on toughness. If each is contained in excess of 0.015%, the toughness of the base metal is significantly reduced. Therefore, the content of P and S is set to 0.015% or less.

V: 0.05 to 0.15%, C × 0.3 ≦ V ≦ C × 0.6
V is an element effective for maintaining the specific strength during tempering heat treatment by forming carbides in combination with C and increasing the tempering softening resistance. In addition to facilitating the control of tempering heat treatment conditions, the machine of the weld heat affected zone Since it is possible to prevent deterioration of the target property, it may be added as needed. Below 0.05%, the effect is inadequate, and above 0.15%, ductility and toughness decrease. Therefore, when V is added, the V content is set in the range of 0.05 to 0.15%. Further, even if V satisfies the above range, a sufficient specific strength cannot be obtained if it is less than C × 0.3, and if it exceeds C × 0.6, the effect of improving the specific strength is saturated and the material cost increases. Therefore, when V is added, the range is C × 0.3 ≦ V ≦ C × 0.6.

Ca: 0.01-0.05%, S × 2 ≦ Ca ≦ S × 4.5
Ca combines with S to form a high melting point sulfide, prevents the formation of low melting point FeS and MnS at the grain boundaries, and has the effect of improving ductility. Therefore, Ca may be added as necessary. .. When S is contained in an amount of 0.015% or less, the effect is hardly obtained when the Ca content is less than 0.01%, and when it exceeds 0.05%, the effect becomes excessive with respect to the S content, and the material cost is simply increased. It only leads to an increase in. Therefore, when Ca is added, the Ca content is set in the range of 0.01 to 0.05%. Further, it is preferable to adjust the Ca content according to the S amount. When Ca <S × 2, the effect of Ca is small, and when Ca> S × 4.5, the effect is saturated and the material cost increases. Therefore, when Ca is added, the Ca content is in the range of S × 2 ≦ Ca ≦ S × 4.5.

C + Si / 24 + Mn / 6 + Ni / 40 + Mo / 4 + Cr / 5 + V / 14 ≦ 0.6%
The carbon equivalent represented by C + Si / 24 + Mn / 6 + Ni / 40 + Mo / 4 + Cr / 5 + V / 14 is a value for evaluating weldability. When the carbon equivalent exceeds 0.6%, the curability increases, so special thermal control is required to prevent the occurrence of low-temperature cracks and the decrease in ductility of the weld. Therefore, the carbon equivalent is preferably 0.6% or less. If necessary, it is also possible to adjust the carbon equivalent to the same as that of the cast steel product for welded structure (JIS G5102) within the composition range of the present invention.

The balance of the alloy component having the above composition is Fe and unavoidable impurities.

[Coagulation tissue]
In the high specific strength and high toughness alloy according to the present invention, the alloy having the above composition is 200 kN. A specific strength of m / kg or more and a shock absorption energy of -100 ° C. of 60 J or more can be obtained at the same time.

The reason is that by rapidly solidifying an alloy with an appropriate composition, in addition to the "high strength by miniaturizing the structure" explained in the relationship of hole petch, the toughness is improved by reducing the microsegregation of the microstructure and alloying elements. However, it is thought that it was realized.

[Manufacturing conditions]
An alloy material having the above composition is melted and solidified by a laser or an electron beam to form a laminated structure. As a result, the alloy material is melted and then rapidly cooled, so that the DAS interval can be made into a fine structure of 5 μm or less.

Specifically, an alloy powder is prepared as an alloy material having a composition within the above range, and is melted and solidified by a laser or an electron beam to form a laminated structure. By using a laser or an electron beam, the cooling rate during solidification of the alloy is set to 3000 ° C./sec. The above can be achieved, and an alloy having a fine solidification structure having a DAS interval of 5 μm or less can be obtained.

On the other hand, as is clear from FIG. 2 below, in the case of a copper alloy mold casting method capable of industrially casting a high melting point iron-based alloy such as the alloy of the present invention, the DAS can never be 5 μm or less. In addition, the die casting method for non-iron alloys has the highest cooling rate in the casting process, but even with this, the cooling rate is insufficient to reduce the DAS to 5 μm or less, which is the expected reason. It is impossible to obtain the characteristics.

Hereinafter, examples of the present invention will be described.
Specimens were prepared for alloys having the chemical components and compositions shown in Table 1. No. 1 in Table 1. Examples 1 to 15 are within the scope of the present invention, No. 16 to 27 are comparative examples outside the scope of the present invention. No. Specimens 1 to 26 were produced by laminated molding, and No. The 27 test pieces were produced by sand casting.

No. In the case of the test specimens of 1 to 26 laminated molding, first, No. 1 in Table 1 is used. Alloys having chemical compositions of 1 to 26 are melted in a high-frequency induction furnace, the molten metal at 1700 ° C. is dropped using the atomizing device shown in FIG. 1, and an inert gas (argon gas in this example) is sprayed from a nozzle. By doing so, it was divided into droplets and rapidly solidified to obtain a spherical powder as a raw material. Next, the spherical powder was sieved to obtain a modeling powder having a particle size of 10 to 45 μm. Then, using a laser-type laminated molding device, the molding powder was laminated and modeled under the conditions of an output of 300 W, a laser moving speed of 1000 mm / sec, a laser scanning pitch of 0.1 mm, and a powder laminated thickness of 0.04 mm. A test piece conforming to 1b) was prepared.

No. In the case of the test piece of sand casting of No. 27, No. The alloy of 27 was melted in a high-frequency induction furnace and cast into a sand mold conforming to FIG. 1b) of JIS G0307 to prepare a test piece.

FIG. 2 estimates the cooling rate of a sample from the DAS measured by observing the microstructure of the sample of the present invention by observing the structure of the sample with an optical microscope and the extrapolation line of the relationship between the DAS and the cooling rate described in Document 1 below. The cooling rates of various molds obtained from the information of 2 to 4 are also shown.
R = (DAS / 709) ^{1 / -0.386} ... (1)
R: Cooling rate (° C / min.), DAS: Dendrite secondary arm spacing (μm)
Reference 1: "Cast Steel Production Technology" P378, Raw Material Center
Reference 2: "Casting", Vol. 63 (1991) No. 11, P915
Reference 3: "Casting Engineering", Vol. 68 (1996) No. 12, P1076
Reference 4: "Shaping Material", Vol.54 (2013) No.1, P13

The test piece by laminated molding is separated from the base plate for molding by electric discharge wire cutting, and the test piece by sand casting is held at 880 ° C. for 1 hour and then cooled with water at 600 ° C. for 2 hours after removing the mold sand. It was tempered.

From these test pieces, JIS-Z2241 and 14A test pieces were prepared for tensile test, and JIS-Z2242 and 2 mm V notch test pieces were prepared for Charpy impact test. The tensile test was carried out at 20 ° C. and the Charpy impact test was carried out at −100 ° C. Table 2 shows the test results.

As shown in Table 2, No. In each of the examples of the present invention 1 to 15, the DAS was 5 μm or less, and the specific strength was 200 kN ・ m / kg or more and the impact absorption energy was -100 ° C. of 60 J or more. FIG. 3 shows an example of a microstructure photograph of the material of the present invention.

On the other hand, No. Among the comparative examples 16 to 27, No. Since 16 to 26 were manufactured by laminated molding, the DAS value was 5 μm or less, but since the composition was out of the range of the present invention, either the specific strength or the impact absorption energy was low. In addition, No. In No. 27, the composition range was within the range of the present invention, but the DAS value was extremely large, and both the specific strength and the impact absorption energy were low values.

Claims (7)

By mass%,
C: 0.12-0.3%,
Si: 0.15 to 0.7%,
Mn: 0.4-1.2%,
P: 0.015% or less,
S: 0.015% or less,
Ni: 2-4%,
Cr: 0.1-0.5%,
Mo: 0.3-0.5%
Contains,
A high-strength, high-toughness iron-based alloy characterized by having a solidified structure in which the balance is composed of Fe and unavoidable impurities and the dendrite secondary arm spacing is 5 μm or less. By mass%, V: 0.05 to 0.15% is further contained, and the content of C and V is C × 0.3 ≦ V ≦ C × 0.6 by mass%.
The high-strength, high-toughness iron-based alloy according to claim 1, which is characterized by satisfying the above. By mass%, Ca: 0.01 to 0.05% is further contained, and the content of Ca and S is S × 2 ≦ Ca ≦ S × 4.5 by mass%.
The high-strength, high-toughness iron-based alloy according to claim 1 or 2, wherein the above is satisfied. C + Si / 24 + Mn / 6 + Ni / 40 + Mo / 4 + Cr / 5 + V / 14
The high-strength, high-toughness iron-based alloy according to any one of claims 1 to 3, wherein the value of carbon equivalent represented by 1 is 0.6% or less in mass%. The high strength according to any one of claims 1 to 4, wherein the specific strength ≧ 200 kN · m / kg and the shock absorption energy ≧ 60J (2 mmV notch Charpy impact test piece) are simultaneously satisfied. Tough iron-based alloy. Manufacture of a high-strength, high-toughness iron-based alloy, which comprises melting and solidifying an alloy material having the composition according to any one of claims 1 to 4 by a laser or an electron beam to form a laminate. Method. The method for producing a high-strength, high-toughness iron-based alloy according to claim 6, wherein the low thermal expansion alloy material is a powder.

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