JP5633489B2 - Ni-base alloy and method for producing Ni-base alloy - Google Patents

Description

  The present invention relates to a Ni-based alloy having good toughness used as a high-temperature structural material (heat-resistant material). The present invention also relates to a method for producing a Ni-based alloy having good toughness.

Unless otherwise stated, the definitions of terms in this specification are as follows.
“%”: Represents a mass percentage (mass%) of each component included in the object.

  “Cr precipitation amount”: In the manufacturing process of the Ni-based alloy of the present invention, Cr that is precipitated mainly at the grain boundaries after the hot working or after the cold working in addition to the hot working is performed. The ratio (mass%: mass percentage display) of the amount of Cr in the precipitate (mainly carbide) to the Ni-based alloy. This “Cr precipitation amount” is obtained by electrolyzing the Ni-based alloy after heat treatment to obtain an extraction residue, and quantitatively analyzing the extraction residue.

  Heat-resistant materials used in thermal power generation boilers, steam turbines and gas turbines, various chemical reactors, nuclear power plants, etc. have high high-temperature strength (tensile strength and creep strength), and high-temperature oxidation and corrosion resistance. It is required that the ductility and toughness are also good. As heat-resistant materials, Cr—Mo low alloy steel, ferritic and martensitic stainless steels with a Cr content of 9% or more, 18Cr-8Ni, Mo, Nb depending on the temperature (operating temperature) of the actual usage environment. An austenitic stainless steel to which an alloying element such as Ti is added or Cr or Ni is further increased, a high Cr high Ni alloy mainly containing Ni and having an increased Cr content, a Ni-based alloy containing almost no Fe, etc. It is used.

  Ni-based alloys have been conventionally used as heat-resistant materials with high durability temperatures in thermal power plants, high-temperature parts of gas turbines, steam generators of nuclear power plants, and the like.

  Among Ni-based alloys, Ni—Cr—Co alloys have toughness (an impact value at 20 ° C. in a Charpy impact test, hereinafter referred to as “20 ° C.”), which is one of important characteristics required for heat-resistant materials in the course of production. In some cases, the “Charpy impact value” or simply “20 ° C. impact value”) was lowered.

In the case of an alloy tube, the Ni-based alloy can be manufactured, for example, through the following steps.
(1) Ni-based alloy ingot obtained by melting in an electric furnace is subjected to soaking, slabbing (forging), hot rolling or extruding, and Ni-based alloy element tube (Ni-based alloy material) age,
(2) If necessary, subject the alloy base pipe (alloy material) to cold working by drawing or rolling,
(3) Further, the alloy base pipe (alloy material) is subjected to solution heat treatment and pickling for scale removal to obtain a Ni-based alloy pipe (product).

Various proposals have heretofore been made with respect to Ni—Cr—Co alloys that are Ni-based alloys. In Patent Documents 1 to 7, in a Ni—Cr—Co alloy, Mo and / or W is included to achieve solid solution strengthening, and Al and Ti are further included to form a γ ′ phase that is an intermetallic compound. Discloses a Ni—Cr—Co alloy that can be used under severe temperature environment by utilizing precipitation strengthening of Ni ₃ (Al, Ti).

  However, an alloy tube made of a Ni-based alloy having the composition disclosed in Patent Documents 1 to 7 (specific examples include 22.2% Cr, 11.9% Co, and 9.1 Mo). %, And C, Si, Mn, Ti, Nb, Al, and B are specified, and the balance is Ni and Ni-based alloy pipes that are impurities, the toughness (20 ° C Charpy impact value) decreases after solution heat treatment. There is a case. The decrease in toughness is due to the precipitation of Cr carbides at the grain boundaries during the solution heat treatment, as will be described in detail later. Similar toughness reductions include 20.0% Cr, 19.8% Co and 5.9% Mo, C, Si, Mn, Ti, Al and B are identified, the balance being Ni and impurities. It was also confirmed with a material obtained by solution heat treatment of an alloy pipe made of a Ni-based alloy.

Japanese Patent Laid-Open No. 51-84727 Japanese Unexamined Patent Publication No. 7-150277 JP-A-9-157779 JP 2002-518599 A JP 2010-150593 A International Publication WO2010 / 038826 International Publication WO2011 / 071054

  As described above, the Ni-based alloy used as the heat-resistant material sometimes has low toughness (20 ° C. Charpy impact value) during the manufacturing process. It has been confirmed that even Ni-base alloy pipes having the compositions disclosed in Patent Documents 1 to 7 may have reduced toughness after solution heat treatment.

  This invention is made | formed in view of such a condition, and provides the manufacturing method of Ni base alloy provided with favorable toughness, and Ni base alloy, without a toughness (20 degreeC Charpy impact value) falling. For the purpose.

The gist of the present invention is as follows.
(1) By mass%, C: 0.03 to 0.09%, Si: 0.05 to 0.4%, Mn: 0.01 to 1.0%, P: 0.015% or less, S: 0.005% or less, Cr: 19-25%, Mo + 0.5W: 5.5-10%, Co: 9-21%, Ti: 0.2-2.5%, Al: 0.3-1. 5% and B: 0.001 to 0.005%, the balance being Ni-based alloy consisting of Ni and impurities, obtained by quantitative analysis of the extraction residue obtained by electrolyzing the Ni-based alloy A Ni-based alloy having a Cr precipitation amount of 0.3% by mass or less.

(2) Ni as described in (1) above, which contains one or more elements belonging to any of the following first group to third group in mass% instead of a part of Ni Base alloy.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Second group: Ca: 0.005% or less, Mg: 0 0.005% or less and Nd: 0.05% or less Third group: Fe: 5.0% or less

(3) By mass%, C: 0.03-0.09%, Si: 0.05-0.4%, Mn: 0.01-1.0%, P: 0.015% or less, S: 0.005% or less, Cr: 19-25%, Mo + 0.5W: 5.5-10%, Co: 9-21%, Ti: 0.2-2.5%, Al: 0.3-1. 5% and B: 0.001 to 0.005% in content, and the balance is a Ni-based alloy manufacturing method consisting of Ni and impurities, and cold processing is performed after hot processing or in addition to hot processing in the heat treatment of the Ni-base alloy material after, after the soaking treatment for heating the Ni-base alloy material above 1150 ° C., followed cooling, controlled cooling or by helium gas under conditions satisfying the following formula (1) Quantitative analysis of the extraction residue obtained by starting quenching with water cooling and electrolyzing the Ni-based alloy after the heat treatment A method of producing a Ni based alloy, characterized in that the Cr deposition amount required for 0.3% by weight or less.
ΔT × Δt / 2.5 ≦ 75 (1)
However, ΔT: difference between the soaking temperature and the rapid cooling start temperature after soaking (° C)
Δt: Time from soaking to the start of rapid cooling (min)

(4) Ni as described in (3) above, which contains one or more elements belonging to any of the following first group to third group in mass% instead of a part of Ni A manufacturing method of a base alloy.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Second group: Ca: 0.005% or less, Mg: 0 0.005% or less and Nd: 0.05% or less Third group: Fe: 5.0% or less

  In the present invention, the “Cr precipitation amount” is as defined above.

The Ni-based alloy of the present invention has the following remarkable effects.
(1) The Ni-based alloy of the present invention is a Ni-based alloy having good toughness without lowering toughness (20 ° C. Charpy impact value) because the Cr precipitation amount is 0.3 mass% or less. is there.
(2) For this reason, the Ni-based alloy of the present invention has good toughness even if it is a tube, a plate or any other shape member or a processed product thereof.

  According to the method for producing a Ni-based alloy of the present invention, since the toughness does not decrease due to grain boundary precipitation of Cr carbide during the solution heat treatment, a Ni-based alloy having good toughness can be produced.

FIG. 1A shows the relationship between the Cr precipitation amount and the 20 ° C. impact value, FIG. 1A shows the relationship in the test piece A, and FIG. It is a figure which shows the relationship between (DELTA) Tx (DELTA) t / 2.5 and Cr precipitation amount, FIG.2 (a) shows the relationship in the test piece A, FIG.2 (b) shows the relationship in the test piece B, respectively. It is a figure which shows typically the time-dependent temperature change of the alloy element pipe | tube in heat processing.

In order to obtain a Ni-based alloy having good toughness while suppressing a decrease in toughness (20 ° C. Charpy impact value), the present inventors conducted first and second investigations on the material having lowered toughness. The material whose toughness has decreased is a Ni base whose impact value at 20 ° C. in the Charpy impact test has fallen from the generally considered good range (150 J / cm ² or more) to about 100 J / cm ² by solution heat treatment. An alloy small-diameter tube (outer diameter 50.8 mm) was used. In the investigation, the material surface and the structure in the vicinity were observed.

  The Ni-based alloy tube used in the first investigation has a chemical composition of mass%, C: 0.07%, Si: 0.10%, Mn: 0.10%, P: 0.010%, S: Contains 0.0004%, Cr: 22.2%, Co: 11.9%, Mo + 0.5W: 9.1%, Ti: 0.41%, Al: 1.01% and B: 0.0023% The balance was Ni and impurities, that is, a Ni—Cr—Co alloy tube. As a result of the first investigation, it was found from the structure observation by optical microscope observation that a relatively coarse precipitate was deposited at the crystal grain boundary. It was estimated that this coarse precipitate contributed to the decrease in toughness.

  Further, when the material surface of the Ni-based alloy tube used in the first investigation was observed, the material surface was roughened by pickling (hereinafter referred to as “acid rough”).

  The Ni alloy tube used in the second investigation has a chemical composition of mass%, C: 0.07%, Si: 0.12%, Mn: 0.11%, P: 0.009%, S: Contains 0.0005%, Cr: 20.0%, Co: 19.8%, Mo + 0.5W: 5.9%, Ti: 2.29%, Al: 0.48% and B: 0.0026% The balance was Ni and impurities, that is, a Ni—Cr—Co alloy tube. As a result of the second investigation, it was found from the observation of the structure with an optical microscope that relatively coarse precipitates were deposited at the grain boundaries. It was estimated that this coarse precipitate contributed to the decrease in toughness.

  Further, when the material surface of the Ni-based alloy pipe used in the second investigation was observed, acid roughening was observed.

Therefore, the material was electrolyzed with a 10% acetylacetone-1% tetramethylammonium chloride-methanol solution to extract the precipitate as a residue, and the extraction residue was quantitatively analyzed. As a result of the analysis, the Cr precipitation amount (that is, the percentage of the Cr amount in the precipitate with respect to the material mass) is 0.42% for the material used in the first investigation and 0.39 for the material used in the second investigation. % Became clear. From the analysis results, the carbides precipitated at the grain boundaries were estimated to be Cr carbides such as M ₂₃ C ₆ .

By summing up the above results, we can conclude as follows.
(A) In the Ni-based alloy pipe used for the investigation, Cr carbide precipitates at the grain boundary during the solution heat treatment, and the toughness decreases.
(B) It is presumed that a region having a low Cr concentration (hereinafter referred to as “Cr-deficient region”) is formed around the carbide (near the grain boundary). In a material having a Cr concentration of 25% or less in the material, formation of a Cr-deficient region promotes corrosion by an acid near the grain boundary during pickling, and may cause acid roughening or cracking along the grain boundary. .

  Therefore, in order to ensure the toughness of the Ni-based alloy, it is considered important to suppress the precipitation of carbides at the grain boundaries after the solution heat treatment.

  Therefore, in order to suppress the precipitation of carbides at the grain boundaries after the solution heat treatment, what kind of heat treatment is necessary was examined.

  A test piece A was collected from the same alloy material as the Ni-based alloy tube used in the first investigation, and a test piece B was obtained from the same alloy material as the Ni-based alloy tube used in the second investigation. The dimensions of the collected test pieces A and B were 11 mm thick × 11 mm wide × 55 mm long. These test pieces were subjected to heat treatment. In the heat treatment, the central portion 10 mm of the test piece was subjected to high-frequency induction heating, soaking, and then rapidly cooled. The soaking temperature of the soaking was 1180 ° C., the rapid cooling was controlled cooling with helium gas, and the temperature gradient from the end of soaking to the start of quenching was set to have a linear relationship with time. Table 1 shows the heat treatment conditions applied to the test piece A, and Table 2 shows the heat treatment conditions applied to the test piece B, respectively.

  An impact test piece (V-notch Charpy test piece defined in JIS Z 2202) was taken from the heat-treated test piece and subjected to an impact test at 20 ° C., and an extraction residue was taken to investigate the Cr precipitation amount. The result of the test piece A is shown in Table 1, and the result of the test piece B is also shown in Table 2.

The meanings of the symbols in the “20 ° C. impact value” column of Tables 1 and 2 are as follows.
○: Good. The 20 ° C. impact value is 150 J / cm ² or more.
X: Defect. The 20 ° C. impact value is less than 150 J / cm ² .

FIG. 1 illustrates the results shown in Tables 1 and 2, and shows the relationship between the Cr precipitation amount and the 20 ° C. impact value. FIG. 1 (a) shows the relationship in the test piece A, and FIG. ) Shows the relationship in the test piece B, respectively. According to FIGS. 1A and 1B, there is a clear correlation between the Cr precipitation amount and the 20 ° C. impact value. If the 20 ° C. impact value is 150 J / cm ² or more, it can be said that the toughness of the Ni-base alloy heat resistant material is good.

1 (a) and 1 (b), it can be seen that the amount of Cr deposited when the 20 ° C. Charpy impact value is 150 J / cm ² or more is 0.3 mass% or less. Therefore, by setting the carbide precipitation at the grain boundaries after the solution heat treatment to 0.3 mass% or less in terms of the Cr precipitation amount, it is possible to obtain a Ni-based alloy having good toughness with suppressed toughness reduction.

  FIG. 2 illustrates the results shown in Table 1 and Table 2 in the same manner as FIG. 1 and shows the relationship between ΔT × Δt / 2.5 and the amount of Cr deposited. FIG. FIG. 2B shows the relationship in the test piece A, and FIG. According to FIGS. 2A and 2B, there is a clear correlation between ΔT × Δt / 2.5 and the amount of Cr deposited.

  2 (a) and 2 (b), in order to reduce the Cr precipitation amount to 0.3% by mass or less, the cooling condition after the solution heat treatment is controlled, and ΔT × Δt / 2.5 is set to 75 ° C. · It can be seen that it may be less than min.

  The present invention has been made based on the above findings.

  Hereinafter, the reason why the chemical composition of the Ni-based alloy, the heat treatment conditions after cold working, and the Cr precipitation amount in the electrolytic extraction residue of the alloy are determined as described above in the present invention will be described in detail.

1. Chemical composition of Ni-based alloy C: 0.03 to 0.09%
C is a component necessary for forming carbides and ensuring high-temperature tensile strength and high-temperature creep strength necessary as a Ni-based alloy, and it is necessary to contain 0.03% or more. However, if the content exceeds 0.09%, Cr carbide increases, which may adversely affect the toughness of the Ni-based alloy, so the upper limit was made 0.09%. A desirable C content is 0.05 to 0.085%.

Si: 0.05-0.4%
Si is an element necessary as a deoxidizer at the time of melting, and it is necessary to contain at least 0.05%. However, if the content is excessive, the workability of the alloy decreases, so the upper limit was made 0.4%. A desirable Si content is 0.08 to 0.3%.

Mn: 0.01 to 1.0%
Mn combines with the impurity S contained in the alloy to form MnS to improve hot workability, but this effect is not sufficient if its content is less than 0.01%. On the other hand, if the content is excessive, the alloy becomes hard and the workability and weldability are impaired, so the upper limit was made 1.0%. A desirable Mn content is 0.05 to 0.8%.

P: 0.015% or less P is inevitably mixed as an impurity. Since excess P impairs weldability and workability, the upper limit is made 0.015%. A desirable upper limit is 0.012%.

S: 0.005% or less S, like P, is inevitably mixed as an impurity. Since excessive S impairs weldability and workability, the upper limit is made 0.005%. A desirable upper limit is 0.0015%.

Cr: 19-25%
Cr is an important alloying element for ensuring high-temperature oxidation resistance and corrosion resistance. In order to ensure sufficient corrosion resistance at high temperatures, it is necessary to contain 19% or more. On the other hand, if the Cr content exceeds 25%, the austenite structure becomes unstable and the creep strength is lowered, so the upper limit was made 25%.

Mo + 0.5W: 5.5-10%
Mo and W are elements that improve the creep strength by the solid solution strengthening action. The effect of Mo and W is similar, and the effect can be arranged by the value calculated by Mo + 0.5W from the content. If the content is Mo + 0.5W and less than 5.5%, this effect cannot be obtained. On the other hand, if the content is excessive, the alloy is remarkably hardened and the workability and weldability are deteriorated, so the upper limit was made 10% with Mo + 0.5W. A desirable content is 5.5 to 9.5% at Mo + 0.5W. Mo and W may contain both, or may contain only one of Mo or W, and the value calculated by Mo + 0.5W should just be in said range.

Co: 9-21%
Co, like Ni, is an austenite-forming element and contributes to the improvement of creep strength by increasing the stability of the austenite phase. In order to reliably obtain the effect of Co in a heat resistant alloy having excellent high temperature strength and corrosion resistance, it is necessary to contain 9% or more. The Co content is preferably more than 9.5%, and more preferably 10% or more. On the other hand, if the Co content exceeds 21%, the hot workability deteriorates and the price of the Ni-based alloy becomes extremely high and becomes impractical, so the upper limit was made 21%. The Co content is preferably 20.5% or less.

Ti: 0.2 to 2.5%
Al: 0.3 to 1.5%
Ti and Al contribute to the creep strength by creating intermetallic compounds such as Ni and Ni ₃ (Al, Ti) during use in a high temperature range. In order to acquire the effect, it is necessary to contain Ti 0.2% or more and Al 0.3% or more. On the other hand, if the content is excessive, it causes non-uniform creep deformation and ductility reduction, so the upper limit was made 2.5% for Ti and 1.5% for Al.

B: 0.001 to 0.005%
B is an element having a creep inhibiting action, but if its content is less than 0.001%, this effect cannot be obtained. On the other hand, if the content is excessive, weldability is impaired, so the upper limit was made 0.005%. A desirable B content is 0.001 to 0.003%.

  “Ni” in the balance of the Ni-based alloy of the present invention is an element that stabilizes the austenite structure, and is also an important element for ensuring corrosion resistance in the Ni-based heat-resistant alloy of the present invention. In the present invention, the Ni content does not need to be specified, and the impurity content is excluded from the remainder. However, the Ni content in the balance is desirably over 50%.

  Further, the “impurities” in the balance of the Ni-based alloy of the present invention refers to those mixed due to various factors in the manufacturing process, including raw materials such as ore or scrap, when the alloy is manufactured industrially. . The Ni-based alloy of the present invention having such a chemical composition is a Ni—Cr—Co alloy.

The Ni-based alloy of the present invention preferably contains one or more elements belonging to any of the following first group to third group, instead of a part of Ni.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less and Zr: 0.2% or less Second group: Ca: 0.005% or less, Mg: 0 0.005% or less and Nd: 0.05% or less Third group: Fe: 5.0% or less

Hereinafter, the above optional elements will be described.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Nb, V, Ta and Zr as elements of the first group are Since both have the effect of improving the strength at high temperatures, the above elements may be contained in order to obtain this effect. Hereinafter, the elements of the first group will be described in detail.

Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Nb, V, Ta, and Zr as elements of the first group are matrices. Since it precipitates as a solid solution or carbide in the austenite structure and contributes to the improvement of strength at high temperatures, the above-described elements may be contained in order to obtain such an effect. However, if these elements are contained excessively, the amount of carbides precipitated increases. In particular, if the content of any element exceeds 0.2%, a large amount of carbides precipitate and the toughness decreases. . Therefore, the contents of Nb, V, Ta, and Zr in the case of inclusion are all 0.2% or less. The desirable upper limit of the content is 0.1% for any element. On the other hand, in order to reliably obtain the effects of Nb, V, Ta, and Zr, the lower limit of the content is preferably 0.003% for any element, and more preferably 0.005%. .

Second group: Ca: 0.005% or less, Mg: 0.005% or less, and Nd: 0.05% or less The Ca, Mg, and Nd elements of the second group all improve hot workability. Since it has an effect | action, in order to acquire this effect, you may contain said element. Hereinafter, the elements of the second group will be described in detail.

Ca: 0.005% or less and Mg: 0.005% or less Since Ca and Mg have an effect of improving hot workability, the above-described elements may be contained in order to obtain this effect. However, when these elements are contained excessively, the cleanliness of the alloy is reduced by combining with O. In particular, when the content of any element exceeds 0.005%, the cleanliness of the alloy is significantly reduced. On the other hand, hot workability is reduced. Therefore, when Ca is contained, the contents of Ca and Mg are both 0.005% or less. In addition, the upper limit with preferable content is 0.004% about any element. On the other hand, in order to reliably obtain the effects of Ca and Mg, the lower limit of the content is preferably 0.0005% for any element, and more preferably 0.001%.

Nd: 0.05% or less Since Nd has an action of improving hot workability, Nd may be contained in order to obtain this effect. However, if it is contained excessively, it will combine with O and the cleanliness of the alloy will be reduced. In particular, if the Nd content exceeds 0.05%, the cleanliness of the alloy will be significantly reduced and the hot workability will be reduced. Come on. Therefore, the Nd content in the case of inclusion is 0.05% or less. A desirable upper limit of the Nd content is 0.04%. On the other hand, in order to surely obtain the above-described effect of Nd, the lower limit of the Nd content is desirably 0.003%, and more desirably 0.005%.

Third group: Fe: 5.0% or less Fe, which is an element of the third group, has an effect of improving the hot workability of the Ni-based alloy, and may be contained as necessary. In an actual manufacturing process, about 0.5 to 1% Fe may be contained as an impurity due to contamination from a furnace wall such as an electric furnace. When Fe is contained, if the Fe content exceeds 5.0%, the thermal expansion coefficient of the alloy increases and the oxidation resistance also deteriorates. Therefore, the upper limit of the content when Fe is contained is 5.0%. On the other hand, in order to obtain the effect of Fe, the lower limit of the Fe content is desirably 1.2%.

2. Cr Precipitation Amount As described above, in Ni-based alloys, Cr carbide may precipitate at grain boundaries during the cooling process during solution heat treatment, and the toughness may be reduced. The Ni-based alloy of the present invention has the above-described chemical composition, and the Cr precipitation amount obtained by quantitative analysis of the extraction residue obtained by electrolyzing the Ni-based alloy is 0.3% by mass or less. As shown in FIGS. 1 (a) and 1 (b), when the Cr precipitation amount is 0.3 mass% or less, the 20 ° C. Charpy impact value is 150 J / cm ² or more. The alloy has good toughness.

  The electrolysis of Ni-based alloy and the quantitative analysis of the extraction residue (Cr quantitative) may be performed according to a conventional method. For example, electrolysis of a Ni-based alloy can be performed by electrolysis at room temperature using a 10% acetylacetone-1% tetramethylammonium chloride-methanol solution. The amount of Cr in the extraction residue can be determined by ICP spectroscopy (inductively coupled high-frequency plasma spectroscopy) or the like.

3. Heat treatment conditions after hot working or cold working In the production of the Ni-based alloy of the present invention, an alloy having the above chemical composition is melted. Next, the obtained alloy ingot is soaked, processed in the order of ingot (forging) and hot working (rolling or extrusion, etc.), and then cold-worked as necessary to perform heat treatment. A Ni-based alloy material is obtained. Examples of cold working include drawing or rolling in the case of tubes, and rolling in the case of plates and bars. Thereafter, the Ni-based alloy material is subjected to a heat treatment (that is, a solution heat treatment for rapid cooling after soaking). If necessary, the heat-treated Ni-based alloy material is subjected to pickling or mechanical treatment (internal / external cutting with a tool, shot blasting, etc.) to obtain a Ni-based alloy.

  In the Ni-based alloy manufacturing method of the present invention, the Ni-based alloy material is heated to 1150 ° C. or higher in the heat treatment performed on the Ni-based alloy material after hot working or after cold working in addition to hot working. Perform soaking. This is to sufficiently dissolve the precipitate in the Ni-based alloy material. When the soaking temperature is less than 1150 ° C., stable solid carbides and oxides containing Ti, Al, B, and Cr are present in the alloy material after treatment, and the alloy material is not homogenized. In addition, although the upper limit of heating temperature is not specifically limited, If it heats to the temperature exceeding 1270 degreeC, a grain boundary melting will arise, Therefore It is good for the upper limit of heating temperature to be 1270 degreeC.

  The heating time is not specified. What is necessary is just to determine suitably so that the objective of heat equalization may be achieved in consideration of the conventional work management standard.

In the Ni-based alloy manufacturing method of the present invention, in the heat treatment, after the soaking, cooling is performed under a condition satisfying the following expression (1). This is to suppress the precipitation of carbides on the grain boundaries after the solution heat treatment. In the following definitions of ΔT and Δt in the equation (1), “soaking temperature” is the temperature at which the soaking is actually performed. The “rapid cooling start temperature” is a temperature at which water cooling is started (see FIG. 3 described below).
ΔT × Δt / 2.5 ≦ 75 (1)
However, ΔT: difference between the soaking temperature and the rapid cooling start temperature after soaking (° C)
Δt: Time from soaking to the start of rapid cooling (min)

FIG. 3 is a diagram schematically showing a change in temperature of the alloy base pipe over time during the heat treatment. This figure shows the temperature of the alloy base tube when solution heat treatment is performed. The solution heat treatment is performed in the continuous soaking furnace at a feed rate of 1000 mm / min. It was carried out by cooling after soaking to 1150 ° C. or higher while passing.

In FIG. 3, the broken line A represents the exit position of the continuous soaking furnace. Although the alloy pipe that has passed through the continuous soaking furnace is cooled , the cooling process is described in detail. The “cooling” process immediately after the alloy pipe is discharged from the continuous soaking furnace (FIG. 3). Between the broken line A and broken line B) and the “ rapid cooling ” process (after broken line B in FIG. 3) following the cooling process. As shown in FIG. 3, the time placed cooling process after the alloy raw pipe has passed a continuous soaking furnace is Δt (min). Further, the difference between the soaking temperature and the rapid cooling start temperature after soaking (that is, the temperature at which “water cooling” starts) is ΔT (° C.).

  As described above, the relationship of the formula (1) is that heat treatment is performed under the conditions shown in Tables 1 and 2 (that is, by changing ΔT and Δt) using a test piece taken from a Ni-based alloy material. The relationship was derived as a result of investigating the 20 ° C. Charpy impact value and the Cr precipitation amount.

That is, as shown in FIGS. 2A and 2B, when ΔT × Δt / 2.5 is 75 ° C. · min or less, the Cr precipitation amount is 0.3 mass% or less. As shown in FIGS. 1A and 1B, when the Cr precipitation amount is 0.3 mass% or less, the 20 ° C. Charpy impact value becomes 150 J / cm ² or more. The Ni-based alloy having good toughness can be obtained by cooling under the conditions satisfying the above formula while suppressing the precipitation of Cr carbide on the crystal grain boundaries.

  The heat treatment defined by the method for producing a Ni-based alloy of the present invention does not necessarily have to be performed in the above-described continuous soaking furnace, and the above-mentioned definition also applies to water cooling after soaking using a batch-type heat treating furnace. Good toughness can be obtained by controlling the same ΔT and Δt.

  Since the Ni-based alloy production method of the present invention performs the above-described heat treatment, the Cr precipitation amount obtained by quantitative analysis of the extraction residue obtained by electrolyzing the Ni-based alloy after the heat treatment is 0.3% by mass. It is as follows. For this reason, the Ni-based alloy manufacturing method of the present invention can stably obtain a Ni-based alloy having good toughness without lowering toughness.

  The “Ni-base alloy after heat treatment” in the method for producing the Ni-base alloy of the present invention may be one after the above-mentioned heat treatment, and in the case of an alloy pipe, an alloy base pipe before pickling treatment. It may be an alloy tube as a product after pickling treatment.

  In order to verify the effects of the Ni-based alloy and the Ni-based alloy manufacturing method of the present invention, an Ni-based alloy tube having an outer diameter of 50.8 mm, an inner diameter of 33.2 mm, a wall thickness of 8.8 mm, and a length of 7000 mm A test was conducted to investigate the Cr precipitation amount and toughness of the manufactured alloy pipe.

[Test method]
Table 3 shows the chemical compositions of the test materials 1 to 4 used in this test.

  In this test, an alloy tube was manufactured by hot extrusion from a billet when manufacturing the alloy tube, and a part of the alloy tube was directly subjected to heat treatment as a Ni alloy material. Moreover, a part was subjected to heat treatment as a Ni alloy material by performing cold rolling in addition to hot extrusion to form an alloy pipe of the above dimensions.

  The heat treatment was performed using a continuous soaking furnace or a batch heat treatment furnace. The continuous soaking furnace had a heating zone of 15 m and a distance from the heating zone to the water cooling zone of 750 mm. In the heating zone, the soaking temperature was set to 1180 ° C. The batch heat treatment furnace was a gas-fired atmosphere furnace having a length of 9000 mm, and the soaking temperature was set to 1180 ° C.

  In the cooling process after soaking, ΔT was changed within a range of 70 to 252 ° C., and Δt was changed within a range of 0.25 to 1.80 minutes. Moreover, in the test using a continuous soaking furnace, the pipe feeding speed was changed within a range of 300 to 1500 mm / min. Table 4 shows the heat treatment conditions for each test.

  After the heat treatment, descaling was performed by pickling or machining. The pickling was performed by immersing the alloy pipe in hydrofluoric acid (hydrofluoric acid: 5%, nitric acid: 10%).

  A V-notch Charpy test piece defined by JIS Z 2202 was taken from the descaled alloy tube and subjected to a Charpy impact test at 20 ° C. Further, the alloy tube was electrolyzed using a 10% acetylacetone-1% tetramethylammonium chloride-methanol solution, and Cr contained in the extraction residue was quantified by ICP spectroscopic analysis to obtain a Cr precipitation amount. The investigation results of the 20 ° C. Charpy impact value and the Cr precipitation amount are also shown in Table 4.

[Evaluation criteria]
The meanings of the symbols in the “20 ° C. impact test” column of Table 4 are the same as in Tables 1 and 2, and are as follows.
○: Good. The 20 ° C. impact value is 150 J / cm ² or more.
X: Defect. The 20 ° C. impact value is less than 150 J / cm ² .

[Test results]
From the results of Table 4, when the condition of ΔT × Δt / 2.5 ≦ 75 defined by the method for producing the Ni-based alloy of the present invention is satisfied, the Cr precipitation amount is 0.3% by mass or less. Further, when the condition that the Cr precipitation amount defined by the Ni-based alloy of the present invention is 0.3% by mass or less is satisfied, the 20 ° C. Charpy impact values are all 150 J / cm ² or more, and the Ni-based alloy is good. It was confirmed to have toughness. In these cases, acid roughening due to pickling was not observed.

  The Ni-based alloy of the present invention has a Cr precipitation amount of 0.3 mass% or less and has good toughness. Therefore, in a thermal power generation boiler, a steam turbine and a gas turbine, various reactors for the chemical industry, and a nuclear power plant It is suitable as a heat resistant material to be used. The method for producing a Ni-based alloy of the present invention can provide a Ni-based alloy having a good toughness with a Cr precipitation amount of 0.3% by mass or less by defining heat treatment conditions.

Claims (4)

By mass%, C: 0.03 to 0.09%, Si: 0.05 to 0.4%, Mn: 0.01 to 1.0%, P: 0.015% or less, S: 0.005 % Or less, Cr: 19-25%, Mo + 0.5W: 5.5-10%, Co: 9-21%, Ti: 0.2-2.5%, Al: 0.3-1.5% and B: a Ni-based alloy containing 0.001 to 0.005%, the balance being Ni and impurities,
A Ni-based alloy characterized in that a Cr precipitation amount obtained by quantitative analysis of an extraction residue obtained by electrolyzing the Ni-based alloy is 0.3% by mass or less. 2. The Ni-based alloy according to claim 1, wherein the Ni-based alloy contains at least one element belonging to any of the following first group to third group in mass% instead of a part of Ni.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Second group: Ca: 0.005% or less, Mg: 0 0.005% or less and Nd: 0.05% or less Third group: Fe: 5.0% or less By mass%, C: 0.03 to 0.09%, Si: 0.05 to 0.4%, Mn: 0.01 to 1.0%, P: 0.015% or less, S: 0.005 % Or less, Cr: 19-25%, Mo + 0.5W: 5.5-10%, Co: 9-21%, Ti: 0.2-2.5%, Al: 0.3-1.5% and B: A method for producing a Ni-based alloy containing 0.001 to 0.005%, with the balance being Ni and impurities,
In the heat treatment of the Ni-based alloy material after hot working or after cold working in addition to hot working, the Ni-based alloy material is heated to 1150 ° C. or higher and then allowed to cool. , Start quenching by controlled cooling with helium gas or water cooling under the conditions satisfying the following formula (1) ,
A method for producing a Ni-based alloy, characterized in that a Cr precipitation amount obtained by quantitative analysis of an extraction residue obtained by electrolyzing the Ni-based alloy after the heat treatment is 0.3% by mass or less .
ΔT × Δt / 2.5 ≦ 75 (1)
However, ΔT: difference between the soaking temperature and the rapid cooling start temperature after soaking (° C)
Δt: Time from soaking to the start of rapid cooling (min) 4. The production of a Ni-based alloy according to claim 3, comprising at least one element belonging to any one of the following first group to third group in mass% instead of a part of Ni. 5. Method.
First group: Nb: 0.2% or less, V: 0.2% or less, Ta: 0.2% or less, and Zr: 0.2% or less Second group: Ca: 0.005% or less, Mg: 0 0.005% or less and Nd: 0.05% or less Third group: Fe: 5.0% or less

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