JP6337514B2 - Precipitation hardening type Fe-Ni alloy and manufacturing method thereof - Google Patents

Description

The present invention relates to precipitation hardening Fe-Ni alloy and a manufacturing method thereof, and more particularly, high strength, and relates to a high precipitation hardening Fe-Ni alloy and a manufacturing method thereof in corrosion resistance.

  Precipitation-hardening stainless steel is steel that is precipitation hardened by adding elements such as Cu, Al, Ti, Nb, and Mo, and has both high corrosion resistance and high strength. In particular, austenitic precipitation hardening stainless steel represented by A286 alloy (SUH660) is an alloy that is excellent in both corrosion resistance and strength among Fe-based alloys. However, both corrosion resistance and strength are insufficient for use as a member that requires high strength in the marine environment.

On the other hand, in the Fe—Ni alloy, an alloy to which Ti, Al, and Nb are added has been proposed.
For example, in Patent Document 1 (Example 1), by weight, C: 0.027%, Mn: 0.08%, Si: 0.10%, P: 0.001%, S: 0.005 %, Cr: 15.81%, Ni: 39.89, Nb: 2.83%, Ti: 1.61%, Al: 0.3%, B: 0.0041%, the balance being Fe and impurities A nickel-iron base alloy is disclosed.

Patent Document 2 (No. 1) includes, by weight, C: 0.017%, Si: 0.15%, Mn: 0.14%, P: 0.010%, S: 0.003%, Ni: 40.32%, Cr: 16.20%, Mo: 1.02%, Al: 0.25%, Ti: 0.95%, Nb: 2.71%, the balance from Fe and impurities A Ni-based alloy is disclosed.
This document describes that, by using such a composition, the HAZ crack can be suppressed while having high strength from room temperature to extremely low temperature.

Further, in Patent Document 3 (alloy # 7), by weight, Ni: 44.2%, Cr: 19.5%, Mo: 3.4%, Cu: 2.0%, C: 0.006 %, Al: 0.3%, Nb: 3.8%, Ti: 1.6% and the balance Fe are disclosed.
This document describes that high strength can be obtained by precipitating a predetermined amount of γ ′ phase and γ ″ phase by annealing and aging treatment.

  In Patent Document 1, Mo and Cu are not added, and the corrosion resistance is insufficient. Patent Document 2 has insufficient strength due to the balance of Ni, Nb, Ti, and Al. In Patent Document 3, Ni and Nb are high, and raw material costs and manufacturing costs are high.

JP 47-042414 A Japanese Patent Laid-Open No. 03-097823 Special table 2009-515053

An object of the present invention is to provide is to provide a high corrosion resistance and precipitation hardening Fe-Ni alloy and a manufacturing method thereof combine high hardness.

In order to solve the above problems, the precipitation hardening type Fe—Ni alloy according to the present invention is summarized as having the following configuration.
(1) The precipitation hardening type Fe—Ni alloy
0.04 ≦ C ≦ 0.08 mass%,
0.02 ≦ Si ≦ 1.0 mass%,
Mn ≦ 1.0 mass%,
36.0 ≦ Ni ≦ 41.0 mass%,
14.0 ≦ Cr <20.0 mass%,
0.01 ≦ Mo ≦ 3.0 mass%,
0.1 ≦ Al ≦ 1.0 mass%,
1.0 ≦ Ti ≦ 2.5 mass%, and
2.0 ≦ Nb ≦ 3.5 mass%
And the balance consists of Fe and inevitable impurities.
(2) The precipitation hardening type Fe—Ni alloy satisfies the following formulas (1) and (2).
Ni ≧ 6 × Nb + 17 (1)
Nb / (Ti + Al) ≧ 0.8 (2)

The precipitation hardening type Fe—Ni alloy preferably satisfies the following formula (3).
Cr + 3Mo + 5Cu ≧ 19 (3)
The method for producing a precipitation effect type Fe—Ni alloy according to the present invention includes:
A melting and casting step of melting and casting the raw materials blended so as to be the composition of the precipitation effect type Fe-Ni based alloy according to the present invention;
A hot working step for hot working the ingot obtained in the melt casting step;
A solution heat treatment step of heating the material obtained in the hot working step at a predetermined temperature;
With
The area ratio of the carbide after the solution heat treatment is 0.4% or more.
This is the gist.

When a predetermined amount of Nb, Al, and Ti is added to the precipitation hardening type Fe—Ni alloy, a γ ′ phase (Ni ₃ (Al, Ti, Nb)) and γ containing Nb as a constituent element are formed by solution heat treatment and aging treatment. “Phase (Ni ₃ Nb) precipitates.
At this time, if the Nb content is optimized so as to satisfy the formula (2), the precipitation amount of the γ ″ phase increases. Therefore, higher strength can be obtained as compared with the conventional alloy.

On the other hand, as the amount of Nb added increases, the Laves phase (Fe ₂ Nb) tends to remain after the solution heat treatment. When a large amount of Laves phase remains, the amount of Nb in the matrix necessary for precipitation hardening decreases. As a result, even if aging treatment is performed, the required hardness cannot be obtained.
On the other hand, if the Ni content is optimized so as to satisfy the expression (1), the Laves phase remaining after the solution heat treatment can be suppressed.

  Furthermore, when a predetermined amount of Cr and Mo, or in addition to these, Cu is added to the precipitation hardening type Fe—Ni alloy, high corrosion resistance can be obtained while maintaining high strength. In particular, when the contents of Cr, Mo and Cu are optimized so as to satisfy the expression (3), high corrosion resistance can be obtained.

It is an optical microscope photograph of the material after the solution heat treatment obtained in Example 5 and Comparative Example 4.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Precipitation hardening type Fe-Ni alloy]
[1.1. Main constituent elements]
The precipitation hardening type Fe—Ni alloy according to the present invention contains the following elements, with the balance being Fe and inevitable impurities. The kind of additive element, its component range, and the reason for limitation are as follows.

(1) 0.01 ≦ C ≦ 0.08 mass%:
C is an element effective for forming a carbide together with Nb and Ti and increasing the strength. Further, the formation of carbides suppresses the coarsening of crystal grains during the solution heat treatment. In order to acquire such an effect, C content needs to be 0.01 mass% or more. The C content is more preferably 0.04 mass% or more.
On the other hand, when the C content is excessive, the toughness of the duct is lowered. Further, when a large amount of carbide is generated, the corrosion resistance is remarkably lowered. In order to suppress a decrease in toughness and corrosion resistance, the C content needs to be 0.08 mass% or less.

(2) 0.02 ≦ Si ≦ 1.0 mass%:
Si is effective as a deoxidizing element during melting. In order to acquire such an effect, Si content needs to be 0.02 mass% or more.
On the other hand, when the Si content is excessive, toughness is reduced. Therefore, the Si content needs to be 1.0 mass% or less.

(3) Mn ≦ 1.0 mass%:
Mn is effective as a deoxidizing element at the time of melting similarly to Si. However, if added in a large amount, the oxidation resistance at high temperatures is lowered. Excess Mn also reduces corrosion resistance. Therefore, the Mn content needs to be 1.0 mass% or less.

(4) 36.0 ≦ Ni ≦ 41.0 mass%:
Ni is essential as an austenite generating element. Further, the alloy is age-hardened by precipitating γ ′ phase (Ni ₃ (Al, Ti, Nb)) and γ ″ phase (Ni ₃ Nb) together with Ti, Al, and Nb by aging treatment. In order to obtain the Ni content, the Ni content needs to be 36.0 mass% or more, and the Ni content is more preferably 37.0 mass% or more.
On the other hand, when the Ni content is excessive, the raw material cost increases. Therefore, the Ni content needs to be 41.0 mass% or less. The Ni content is more preferably 40 mass% or less, and still more preferably 39.0 mass%.

(5) 14.0 ≦ Cr <20.0 mass%:
Cr is an essential component for improving the corrosion resistance of the precipitation hardening type Fe—Ni alloy. In order to acquire such an effect, Cr content needs to be 14.0 mass% or more.
However, Cr is a ferrite forming element, and when the Cr content is excessive, the structural stability is lowered. Excessive Cr also decreases hot workability. Therefore, the Cr content needs to be less than 20.0 mass%. The Cr content is more preferably 18 mass% or less, and further preferably 17.0 mass% or less.

(6) 0.01 ≦ Mo ≦ 3.0 mass%:
Mo improves the corrosion resistance (particularly pitting corrosion resistance) by dissolving in the matrix. In order to acquire such an effect, Mo content needs to be 0.01 mass% or more.
On the other hand, if the Mo content is excessive, the Laves phase (Fe ₂ (Mo, Nb)) precipitates during the aging treatment, and the precipitation amount of the γ ′ phase and the γ ″ phase decreases. As a result, the strength of the alloy decreases. Therefore, the Mo content needs to be 3.0 mass% or less.

(7) 0.1 ≦ Al ≦ 1.0 mass%:
Al age-hardens the alloy by precipitating a γ ′ phase (Ni ₃ (Al, Ti, Nb)) together with Ni, Ti, and Nb. In order to acquire such an effect, Al content needs to be 0.1 mass% or more.
On the other hand, when the Al content is excessive, hot workability is reduced. Therefore, the Al content needs to be 1.0 mass% or less.

(8) 1.0 ≦ Ti ≦ 2.5 mass%:
Ti age-hardens the alloy by precipitating a γ ′ phase (Ni ₃ (Al, Ti, Nb)) together with Ni, Al, and Nb. In order to acquire such an effect, Ti content needs to be 1.0 mass% or more. The Ti content is preferably 1.5 mass% or more, more preferably 1.8 mass% or more.
On the other hand, when the Ti content is excessive, hot workability is reduced. Therefore, the Ti content needs to be 2.5 mass% or less.

(9) 2.0 ≦ Nb ≦ 3.5 mass%:
Nb precipitates a γ ′ phase (Ni ₃ (Al, Ti, Nb)) and a γ ″ phase (Ni ₃ Nb) together with Ni to age-harden the alloy. In order to obtain such an effect, Nb Content needs to be 2.0 mass% or more.
On the other hand, when the Nb content is excessive, a coarse Laves phase remains after the solution heat treatment, and the amount of precipitation of the γ ′ phase and the γ ″ phase decreases. As a result, the required strength and hardness cannot be obtained. The Nb content needs to be 3.5 mass% or less, and the Nb content is more preferably 3.0 mass% or less.

[1.2. Sub-constituent elements]
The precipitation hardening type Fe—Ni alloy according to the present invention may further contain the following one or more sub-constituent elements in addition to the main constituent elements described above. The kind of additive element, its component range, and the reason for limitation are as follows.

(10) 0.0005 ≦ B ≦ 0.01 mass%:
B has the effect of improving hot workability by adding a small amount. Further, the presence of B at the grain boundary can suppress the precipitation of the η phase at the grain boundary. In order to obtain such an effect, the B content is preferably 0.0005 mass% or more.
On the other hand, when the B content is excessive, hot workability is reduced. Therefore, the B content is preferably 0.01 mass% or less.

(11) 0.05 ≦ Cu ≦ 1.0 mass%:
Cu has the effect of improving the corrosion resistance in a non-oxidizing corrosive environment. In order to obtain such an effect, the Cu content is preferably 0.05 mass% or more.
On the other hand, when Cu content becomes excessive, hot workability will fall. Therefore, the Cu content is preferably 1.0 mass% or less.

(12) 0.05 ≦ V ≦ 1.0 mass%:
V, like Nb and Ti, forms carbides and increases strength. In addition, by reducing the proportion of Nb in the carbide, the amount of precipitation of the γ ′ phase and the γ ″ phase, which affects the strength, is increased. 05 mass% or more is preferable.
On the other hand, when V content becomes excessive, toughness and workability will fall. Therefore, the V content is preferably 1.0 mass% or less.

(13) 0.001 ≦ (Zr, Ta, W, Hf, Mg, REM) ≦ 0.50 mass%:
Zr, Ta, W, Hf, Mg, and REM are all effective in reducing carbides and crystal grains. In order to obtain such an effect, the total content of these elements is preferably 0.001 mass% or more.
On the other hand, when the content of these elements becomes excessive, the toughness decreases. Therefore, the total content of these elements is preferably 0.50 mass% or less.
Any one of these elements may be added, or two or more of these elements may be used in combination.

(14) 0.0005 ≦ Ca ≦ 0.01 mass%:
Ca improves machinability. In order to obtain such an effect, the Ca content is preferably 0.0005 mass% or more.
On the other hand, when Ca content becomes excessive, hot workability will fall. Therefore, the Ca content is preferably 0.01 mass% or less.

[1.3. Ingredient balance]
The precipitation hardening stainless steel according to the present invention needs to satisfy the following formulas (1) and (2) in addition to the component elements being in the above-mentioned range.
In order to obtain high corrosion resistance, the precipitation hardening stainless steel preferably further satisfies the following formula (3).
Ni ≧ 6 × Nb + 17 (1)
Nb / (Ti + Al) ≧ 0.8 (2)
Cr + 3Mo + 5Cu ≧ 19 (3)

[1.3.1. (1) Formula]
Equation (1) is related to the amount of Laves phase after solution heat treatment. When the amount of Ni and the amount of Nb are optimized so as to satisfy the formula (1), the Laves phase (Fe ₂ Nb) can be completely dissolved after the solution heat treatment. As a result, the amount of precipitation of the γ ′ phase and the γ ″ phase during the aging treatment is increased, thereby improving the strength of the alloy.
The formula (1) is more preferably Ni ≧ 6 × Nb + 18.0, and more preferably Ni ≧ 6 × Nb + 20.0.

[1.3.2. (2) Formula]
Equation (2) is related to the amount of γ ″ phase during aging treatment. Optimizing the amounts of Nb, Ti and Al to satisfy Equation (2) increases the amount of precipitation of γ ″ phase. This further improves the strength of the alloy.

[1.3.3. (3) Formula]
Equation (3) is related to the corrosion resistance of the precipitation hardening type Fe—Ni alloy. All of Cr, Mo, and Cu have an effect of improving the corrosion resistance of the precipitation hardening type Fe—Ni alloy. In particular, when the contents of these elements are optimized so as to satisfy the expression (3), high corrosion resistance is exhibited while maintaining high strength.

[1.4. 0.2% yield strength]
As described above, when each component is optimized and an appropriate solution heat treatment is performed, the Laves phase is almost completely dissolved in the matrix. When an appropriate aging treatment is applied to such a material, a large amount of γ ′ phase and γ ″ phase are precipitated. As a result, the 0.2% proof stress at room temperature is 850 MPa or more. Is further optimized, the 0.2% yield strength at room temperature is 900 MPa or more, or 950 MPa or more.

[1.5. Carbide area ratio]
The precipitation hardening type Fe—Ni alloy according to the present invention preferably has a carbide area ratio of 0.4% or more after solution heat treatment. When a predetermined amount of carbide is dispersed in the matrix at the time of the solid solution heat treatment, the coarsening of the crystal grains can be suppressed.
Here, the “area ratio of carbide” refers to the ratio of the area of carbide to the total area of the cross-sectional microstructure (0.034 mm ² × 30 field of view).

[2. Method for producing precipitation hardening type Fe—Ni alloy]
The manufacturing method of the precipitation hardening type Fe-Ni alloy which concerns on this invention is equipped with the melt casting process, the hot working process, the solution heat treatment process, and the aging treatment process.

[2.1. Melting and casting process]
The melt casting step is a step of melting and casting a raw material blended with predetermined components. The melting method and the casting method are not particularly limited, and various methods can be used depending on the purpose.

[2.2. Hot working process]
The hot working process is a process of hot working the ingot obtained in the melt casting process. Hot working is performed to destroy the cast structure and casting defects. The hot working conditions are not particularly limited, and optimum conditions can be selected according to the purpose.

[2.3. Solution heat treatment process]
The solution heat treatment step is a step of heating the hot-processed material at a predetermined temperature.
The solution heat treatment is mainly performed to dissolve the precipitates dispersed in the steel. When the heat treatment temperature is too low, the solid solution of the precipitate becomes insufficient. The heat treatment temperature is preferably 900 ° C. or higher.
On the other hand, if the heat treatment temperature is too high, the crystal grains become coarse. The heat treatment temperature is preferably 1200 ° C. or lower.
The heat treatment time may be a time during which the precipitate is dissolved. The optimum heat treatment time varies depending on the heat treatment temperature, but is usually about 30 minutes to 2 hours. After the heat treatment, the material is rapidly cooled.

[2.4. Aging treatment process]
The aging treatment step is a step of aging treatment of the material after the solution heat treatment at a predetermined temperature.
In both cases where the aging treatment temperature is too high and too low, the target precipitate does not precipitate, and age hardening cannot be achieved. The aging treatment temperature is preferably 600 ° C. or higher and 750 ° C. or lower.
The aging treatment temperature may be a time for depositing a sufficient amount of precipitates. The optimum aging treatment time varies depending on the aging treatment temperature, but is usually about 8 to 24 hours.

[3. Action]
When a predetermined amount of Nb is added to the precipitation hardening type Fe—Ni alloy, a γ ′ phase (Ni ₃ (Al, Ti, Nb)) and a γ ″ phase (Ni) containing Nb as a constituent element are obtained by a solution heat treatment and an aging treatment. ₃ Nb) is precipitated.
At this time, if the Nb content is optimized so as to satisfy the formula (2), the precipitation amount of the γ ″ phase increases. Therefore, higher strength can be obtained as compared with the conventional alloy.

On the other hand, as the amount of Nb added increases, the Laves phase (Fe ₂ Nb) tends to remain after the solution heat treatment. When a large amount of Laves phase remains, the amount of Nb in the matrix necessary for precipitation hardening decreases. As a result, even if aging treatment is performed, the required hardness cannot be obtained.
On the other hand, if the Ni content is optimized so as to satisfy the expression (1), the Laves phase remaining after the solution heat treatment can be suppressed.

  Furthermore, when a predetermined amount of Cr and Mo, or in addition to these, Cu is added to the precipitation hardening type Fe—Ni alloy, high corrosion resistance can be obtained while maintaining high strength. In particular, when the contents of Cr, Mo and Cu are optimized so as to satisfy the expression (3), high corrosion resistance can be obtained.

(Examples 1-37, Comparative Examples 1-4, Reference Example 5)
[1. Preparation of sample]
Steels having various components shown in Tables 1 and 2 were melted and then cooled to produce ingots. The ingot was tempered by solution treatment and aging treatment after hot working.
The solution heat treatment temperature was set to 900 to 1200 ° C. The aging treatment temperature was 600 to 750 ° C.

[2. Test method]
[2.1. Tensile test]
A JIS No. 4 test piece was cut out from the material after aging treatment. Tensile tests were performed at room temperature to evaluate tensile strength and 0.2% yield strength.
[2.2. Corrosion resistance test]
Corrosion resistance was evaluated by the degree of corrosion when immersed in 10%, 80 ° C. hydrochloric acid for 6 hours. The case the degree of corrosion is less than or equal to 100g / m ² / h "◎", the case in the following cases: 100g / m ² / h ultra-~200g / m ² / h "○", of 200g / m ² / h more than " × ”.
[2.3. Carbide area ratio]
For the quantification of the carbide, the area ratio was measured in 30 fields of 400 times microstructure photograph (1 field of view: 0.034 mm ² ) using image analysis software.

[3. result]
Table 3 shows the results. Table 3 shows the following.
(1) Comparative Example 1 (equivalent to A286 alloy) has low tensile strength and 0.2% proof stress. This is because Nb is not added and the γ ″ phase does not precipitate. Comparative Example 1 has low corrosion resistance. This is because the amount of Ni is small.
(2) Comparative Example 2 has a slightly low 0.2% yield strength. This is because a sufficient amount of γ ″ phase cannot be obtained because the Ni content is low. In addition, Comparative Example 2 has low corrosion resistance. This is because the Ni content is low.
(3) Comparative Example 3 has a slightly low 0.2% yield strength. This is because a sufficient amount of γ ″ phase cannot be obtained because Nb / (Ti + Al) −0.8 is low.
(4) Comparative Example 4 has a slightly low 0.2% yield strength. This is because Ni- (6 × Nb + 17) is low, and a coarse Laves phase remains after the solution heat treatment. As a result, the amount of Nb in the matrix decreases, and the amount of precipitation of the γ ′ phase and the γ ″ phase during the aging treatment decreases.
(5) Reference Example 5 has a slightly low 0.2% yield strength. This is because the crystal grains are coarsened because the carbide area ratio is small, that is, there are few carbides that suppress the grain coarsening during the solution heat treatment.

(6) In Examples 1 to 37, the 0.2% proof stress exceeded 850 MPa, and good corrosion resistance was exhibited.
(7) Among the examples, materials satisfying the formula (3) have particularly high corrosion resistance.

  In FIG. 1, the optical microscope photograph of the material after the solution heat treatment obtained in Example 5 and Comparative Example 4 is shown. From FIG. 1, it can be seen that Comparative Example 4 shows a Laves phase in addition to carbide, whereas Example 5 shows no Laves phase.

  The embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the present invention.

  The precipitation hardening type Fe—Ni alloy according to the present invention can be used for excavation members, automobile engine parts, thermal power plant members, and the like.

Claims (9)

Precipitation hardening type Fe-Ni alloy provided with the following composition.
(1) The precipitation hardening type Fe—Ni alloy
0.04 ≦ C ≦ 0.08 mass%,
0.02 ≦ Si ≦ 1.0 mass%,
Mn ≦ 1.0 mass%,
36.0 ≦ Ni ≦ 41.0 mass%,
14.0 ≦ Cr <20.0 mass%,
0.01 ≦ Mo ≦ 3.0 mass%,
0.1 ≦ Al ≦ 1.0 mass%,
1.0 ≦ Ti ≦ 2.5 mass%, and
2.0 ≦ Nb ≦ 3.5 mass%
And the balance consists of Fe and inevitable impurities.
(2) The precipitation hardening type Fe—Ni alloy satisfies the following formulas (1) and (2).
Ni ≧ 6 × Nb + 17 (1)
Nb / (Ti + Al) ≧ 0.8 (2) 0.0005 ≦ B ≦ 0.01 mass%
The precipitation hardening type Fe-Ni alloy of Claim 1 which further contains these. 0.05 ≦ Cu ≦ 1.0 mass%
The precipitation hardening type Fe-Ni alloy according to claim 1 or 2, further comprising : 0.05 ≦ V ≦ 1.0 mass%
The precipitation hardening type Fe-Ni alloy according to any one of claims 1 to 3 , further comprising : 0.001 ≦ (Zr, Ta, W, Hf, Mg, REM) ≦ 0.50 mass%
The precipitation hardening type Fe-Ni alloy according to any one of claims 1 to 4 , further comprising :
However, the central part of the above formula represents the total amount of elements in parentheses. 0.0005 ≦ Ca ≦ 0.01 mass%
The precipitation hardening type Fe-Ni alloy according to any one of claims 1 to 5 , further comprising : The precipitation hardening type Fe-Ni alloy according to any one of claims 1 to 6 , further satisfying the following expression (3).
Cr + 3Mo + 5Cu ≧ 19 (3)   A melting and casting step of melting and casting the raw material blended so as to have the composition according to any one of claims 1 to 7;
  A hot working step for hot working the ingot obtained in the melt casting step;
  A solution heat treatment step of heating the material obtained in the hot working step at a predetermined temperature;
With
  The area ratio of the carbide after the solution heat treatment is 0.4% or more.
A method for producing a precipitation hardening type Fe—Ni alloy.   An aging treatment step of aging treatment of the material obtained in the solution heat treatment step at a predetermined temperature;
  The method for producing a precipitation hardening type Fe-Ni alloy according to claim 8, wherein the 0.2% yield strength at normal temperature is 900 MPa or more.

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