JP5782753B2 - Manufacturing method of high Cr high Ni alloy tube and high Cr high Ni alloy - Google Patents

Description

  The present invention relates to a method for producing a high Cr high Ni alloy tube having good toughness used as a high temperature structural material (heat resistant material). The present invention also relates to a high Cr high Ni 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.
“High Cr high Ni alloy”: An alloy containing Ni as a main component, the content of which is higher than that of stainless steel, less than that of the Ni-based alloy, and higher than that of Ni. Conceptually, it is an alloy located between stainless steel and a Ni-based alloy. Tubes, plates, other shaped or irregular shaped members, or processed products thereof, and the alloys within the component ranges are all high Cr high Ni alloys. The “high Cr high Ni alloy pipe” is a pipe made of high Cr high Ni alloy.

  “Cr precipitation amount”: In the manufacturing process of the high Cr high Ni alloy tube of the present invention, the amount of Cr that precipitates at the grain boundaries when heat treatment is performed after hot working or after cold working in addition to hot working. The ratio of the amount of Cr in the precipitate (mainly carbide) or the amount of Cr in the precipitate (mainly carbide) of Cr precipitated in the high Cr high Ni alloy of the present invention to the amount of the high Cr high Ni alloy ( Percentage display). This “Cr precipitation amount” is obtained by quantitative analysis of the extraction residue obtained by electrolyzing the high Cr high Ni alloy tube after the heat treatment.

  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.

  A high Cr high Ni alloy has been conventionally used as a heat resistant material having a high durability temperature in a thermal power plant, a high temperature part of a gas turbine, a steam generator of a nuclear power plant, and the like.

  However, in a tube made of a high Cr high Ni alloy, toughness (an impact value at 20 ° C. in the Charpy impact test, hereinafter referred to as “20 ° C. Charpy”), which is one of the important characteristics required for heat-resistant materials during the manufacturing process. “Impact value” or simply “20 ° C. impact value”) may be low.

  The high Cr high Ni alloy tube is subjected to, for example, uniform heat treatment, slabbing (forging), hot rolling or extrusion to the alloy ingot obtained by melting with an electric furnace, It is manufactured through various processes such as cold working by drawing or rolling, solution heat treatment, and pickling for removing scale.

  Specific examples include 22.8% Cr and 44.6% Ni, and specified C, Si, Mn, Ti, Nb, Al, B and W (the balance being Fe and impurities). After the solution heat treatment, the toughness (20 ° C. Charpy impact value) of the Cr high Ni alloy tube may decrease. 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 included 29.8% Cr and 50.1% Ni, and identified C, Si, Mn, Ti, Nb, Zr, Al, B and W (the balance being Fe and impurities). A Cr high Ni alloy tube was also confirmed by a solution heat-treated material.

  There is no literature or the like that takes up the suppression of toughness as a problem and presents a solution. However, research and development for reducing corrosion damage in the vicinity of grain boundaries and improving resistance to intergranular stress corrosion cracking has been performed conventionally.

  For example, Patent Document 1 discloses intergranular corrosion damage when a Ni-based alloy containing Ni: 58% or more and Cr: 28-31% is used in a steam generator heat transfer tube of a power plant of a pressurized water reactor. A method for producing a Ni-based alloy that greatly improves the properties is disclosed. This method combines 5-20% cold working and heat treatment at 1070-1200 ° C. for 1-60 minutes to cause recrystallization in the Ni-based alloy, corresponding grain boundaries with high corrosion resistance (on both sides) This is a method of increasing the resistance to intergranular corrosion damage by increasing the generation rate of crystal grain boundaries in which the crystal lattice is the same when the crystal axis is tilted several degrees symmetrically.

  Patent Document 2 discloses stress corrosion cracking resistance when a Ni-based alloy containing Cr: more than 35% and 40% or less and Ni: 50-57% is used in a heat exchanger tube of a pressurized water nuclear power plant. An excellent heat treatment method for Ni-based alloys is disclosed. In this method, in the final annealing (corresponding to the solution treatment) at the time of manufacturing the Ni-based alloy, the temperature range of 900 to 500 ° C. is held for 1 to 60 minutes, and the cooling rate is set to 900 to 500 ° C. This is a method of cooling at ~ 100 ° C / sec.

  However, in any of the methods described in Patent Documents 1 and 2, the content of Cr and Ni is different from the content in the high Cr high Ni alloy targeted in the present invention. Furthermore, the methods described in these documents are means for reducing the corrosion damage in the vicinity of the grain boundary or improving the intergranular stress corrosion cracking resistance, and nothing is described about the suppression of the toughness deterioration.

JP 2002-309355 A Japanese Patent Laid-Open No. 239739

An object of the present invention is to produce a high Cr high Ni alloy pipe having good toughness without causing a decrease in toughness (impact value at 20 ° C. in Charpy impact test) in producing a high Cr high Ni alloy pipe as a heat resistant material. It is to provide a manufacturing method.
Another object of the present invention is to provide a high Cr high Ni alloy with good toughness.

(1) By mass%: C: 0.05 to 0.09%, Si: 0.1 to 0.3% , Mn: 0.05 to 1.3%, P: 0.015% or less, S: 0 0.005% or less, Ni: 44 to 52%, Cr: 27 to 32%, Ti: 0.05 to 1.0%, sol. Al: 0.005-0.2%, B: 0.001-0.008% and W: 4-10%, and Nb: 0.005-0.25% and Zr: 0.001-0.05 %, And the balance is made of Fe and impurities, and the heat treatment using a continuous heat treatment furnace or a batch furnace after hot working, The high Cr high Ni alloy tube is subjected to soaking treatment in which the high Cr high Ni alloy tube is heated to 1180 ° C. or higher, and then cooled under a condition that satisfies the following formula (i) in the water cooling process following the cooling process. Manufacturing method of alloy pipe.
ΔT × Δt / 2 ≦ 100 (i)
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)

  According to the method for producing a high Cr high Ni alloy pipe of the present invention, high toughness with good toughness that does not cause a decrease in toughness (20 ° C. Charpy impact value) due to grain boundary precipitation of Cr carbide during solution heat treatment occurs. Cr high Ni alloy tubes can be manufactured. Moreover, the high Cr high Ni alloy of this invention is equipped with favorable toughness even if it is a pipe, a plate, a member of any shape, or a processed product thereof.

It is a figure which shows the relationship between Cr precipitation amount and a 20 degreeC impact value, (a) shows the result of the high Cr high Ni alloy pipe used for the 1st investigation, (b) shows the high used for the 2nd investigation. The result of a Cr high Ni alloy pipe is shown. It is a figure which shows the relationship between (DELTA) Tx (DELTA) t / 2 and Cr precipitation amount, (a) shows the result of the high Cr high Ni alloy pipe | tube used for the 1st investigation, (b) was used for the 2nd investigation. The result of the high Cr high Ni alloy pipe is shown. It is a figure which shows typically the time-dependent temperature change of the alloy element pipe | tube in heat processing.

In order to establish a manufacturing method of a high Cr high Ni alloy tube having good toughness while suppressing a decrease in toughness (20 ° C. Charpy impact value), the present inventors have conducted 20 in a Charpy impact test by solution heat treatment. impact value ℃ is, for generally being a good range (150 J / cm ² or more) smaller diameter tubes of high Cr and high Ni alloy decreases to about 110J / cm ² off the (outer diameter 50.8 mm), the material surface And the organization in the vicinity was investigated.

  The chemical composition of the high Cr high Ni alloy tube used in the first investigation is as follows: C: 0.08%, Si: 0.30%, Mn: 0.92%, P: 0.010%, S: 0.00. 0005%, Cr: 22.8%, Ni: 44.6%, W: 6.87%, Ti: 0.10%, Nb: 0.18%, sol. Al: 0.027 and B: 0.0047% are contained, and the balance is Fe and impurities. As a result of the first investigation, surface roughness of the material due to pickling (hereinafter referred to as “acid roughness”) was observed. Further, observation with an optical microscope revealed that cracks occurred at the grain boundaries near the material surface, and relatively coarse precipitates were deposited at the grain boundaries.

  The chemical composition of the high Cr high Ni alloy tube used in the second investigation is as follows: C: 0.07%, Si: 0.11%, Mn: 0.15%, P: 0.010%, S: 0.00. 0005%, Cr: 29.8%, Ni: 50.1%, W: 4.95%, Ti: 0.77%, Nb: 0.02%, Zr: 0.026%, sol. Al: 0.100% and B: 0.0023% are contained, and the balance is Fe and impurities. 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. On the other hand, acid roughening due to pickling after heat treatment was not 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 0.40% for the material used in the first investigation and 0.46% 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 high Cr high Ni alloy pipe used for the investigation, Cr carbide precipitates at the grain boundaries 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. . When the Cr content of the base material is as high as 29.8%, no acid roughening is observed.

Therefore, in order to ensure the toughness of the alloy of the present invention, 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 material having a thickness of 11 mm, a width of 11 mm, and a length of 55 mm is collected from the same material as that of the high Cr high Ni alloy tube used in the first and second investigations, and the central portion of the test piece is 10 mm. High-frequency induction heating was performed, and heat treatment was performed under the conditions shown in Tables 1 and 2. The soaking temperature was 1230 ° C. For rapid cooling, controlled cooling with helium gas was performed, and the temperature gradient until the start of rapid cooling was set to have a linear relationship with time.

  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 results of the high Cr high Ni alloy pipe used in the first investigation are shown in Table 1, and the results of the high Cr high Ni alloy pipe used in the second investigation are shown in Table 2.

Tables 1 and 2 also show the 20 ° C. impact test results and the investigation results of the Cr precipitation amount.
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 is a diagram illustrating the relationship between the Cr precipitation amount and the 20 ° C. impact value. FIG. 1A shows the result of the high Cr high Ni alloy pipe used in the first investigation, and FIG. 1B shows the result of the high Cr high Ni alloy pipe used in the second investigation. According to the figure, 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 high Cr high Ni alloy heat resistant material is good.

1 (a) and 1 (b), it can be seen that the Cr deposition amount is 0.3% or less when the 20 ° C. Charpy impact value is 150 J / cm ² or more. Therefore, by setting the carbide precipitation to the grain boundary after the solution heat treatment to be 0.3% or less in terms of the Cr precipitation amount, it is possible to suppress the decrease in toughness and maintain good toughness.

  FIG. 2 illustrates the results shown in Table 1 and Table 2 and shows the relationship between ΔT × Δt / 2 and the amount of deposited Cr. FIG. 2A shows the result of the high Cr high Ni alloy pipe used in the first investigation, and FIG. 2B shows the result of the high Cr high Ni alloy pipe used in the second investigation. A clear correlation is observed between ΔT × Δt / 2 and the amount of deposited Cr.

    2 (a) and 2 (b), in order to make the Cr precipitation amount 0.3% or less, the cooling condition after the solution heat treatment should be controlled so that ΔT × Δt / 2 should be 100 or less. I understand that.

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

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

1. Chemical composition of high Cr high Ni alloy C: 0.05-0.09%
C is a component necessary for forming carbide and ensuring high-temperature tensile strength and high-temperature creep strength necessary as a high Cr high Ni alloy, and it is necessary to contain 0.05% or more. However, if its content exceeds 0.09%, Cr carbide increases, which may adversely affect the toughness of the high Cr high Ni alloy, so the upper limit was made 0.09%. A desirable C content is 0.055 to 0.085%.

Si: 0.1 to 0.3%
Si is an element necessary as a deoxidizer at the time of melting, and it is necessary to contain at least 0.05%. However, the workability of the alloy decrease if the content is excessive. The Si content is 0.1 to 0.3%.

Mn: 0.05 to 1.3%
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 0.05%. 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 1.3%. A desirable Mn content is 0.7 to 1.1%, and more desirably 0.9 to 1.1%.

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%.

Ni: 44-52%
Ni is a main component of the high Cr high Ni alloy of the present invention, and is an element that stabilizes the austenite structure. It is an important alloying element from the viewpoint of ensuring high temperature corrosion resistance. Since the amount of Ni is determined from the balance with the amount of Cr, it is difficult to determine the upper and lower limits in general, but even when the lower limit of Cr is 22%, 44% or more is necessary. On the other hand, when the upper limit of Cr is 32%, an excessive Ni content causes an increase in cost, so the upper limit was set to 52%.

Cr: 27 ~32%
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 22% or more. The higher the Cr content, the higher the high temperature corrosion resistance. Further, when Cr is contained in an amount of 27% or more, fine precipitates mainly composed of Cr are deposited during use at a high temperature and contribute to the high temperature strength. Therefore, when it is desired to increase the high temperature strength, 27% or more of Cr is contained. On the other hand, if the content exceeds 32%, the Ni content must be increased in order to stabilize the austenite structure, leading to an increase in cost, so the upper limit was made 32%.

Ti: 0.05-1.0%
Ti has an effect of improving high temperature strength due to precipitation of carbides during use in a high temperature range. The alloy of the present invention contains 0.05% or more for the purpose of securing high temperature strength. On the other hand, if its content is excessive, it causes non-uniform creep deformation and ductility reduction, so the upper limit was made 1.0%.

One or two types of Nb: 0.005 to 0.25% and Zr: 0.001 to 0.05% Nb and Zr have an effect of improving the creep strength due to precipitation of carbides. However, when the respective contents are less than 0.005% Nb and 0.001% Zr, these effects are not sufficiently exhibited. On the other hand, if the content is excessive, weldability is impaired, so the upper limits of each were Nb 0.25% and Zr 0.05%.

sol. Al: 0.005 to 0.2%
Al is an element having a deoxidizing action similar to Si, and 0.005% or more is necessary to obtain a sufficient deoxidizing effect. On the other hand, if the content is excessive, the stability of the structure deteriorates, so the upper limit was made 0.2%. Desirable sol. Al content is 0.008 to 0.13%.

B: 0.001 to 0.008%
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 0.008%. A desirable B content is 0.001 to 0.003%.

W: 4-10%
W is an element having a creep inhibiting action due to a solid solution strengthening action, but if its content is less than 4%, 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%. A desirable W content is 4.5 to 9%.

  The high Cr high Ni alloy of the present invention contains the above components, with the balance being Fe and impurities. Here, “impurities” in “Fe and impurities” refers to those mixed due to various factors in the manufacturing process, including raw materials such as ore or scrap, when the alloy is industrially manufactured.

2. Heat treatment conditions after hot working or cold working In the method for producing a high Cr high Ni alloy tube of the present invention, an alloy having the above chemical composition is melted. Next, the obtained alloy lump is soaked and processed in the order of lump (forging) and hot working (rolling or extruding), and then cold working is performed as necessary. In cold working, drawing or rolling is used. Thereafter, a heat treatment (that is, a solution heat treatment for rapid cooling after soaking) is performed. Thereafter, pickling or mechanical treatment (internal / external cutting with a tool, shot blasting, etc.) is performed as necessary to obtain a high Cr high Ni alloy tube.

  In the above heat treatment, the soaking process in which the high Cr high Ni alloy pipe is heated to 1180 ° C. or higher is performed to sufficiently dissolve the precipitate in the alloy base pipe. When the soaking temperature is lower than 1180 ° C., stable solid solution carbides and oxides containing Ti, B, and Cr are present in the alloy pipe after the treatment, and the alloy 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.

The reason for cooling under the condition satisfying the following formula (i) after the soaking is to suppress the precipitation of carbides at the crystal grain boundaries after the solution heat treatment. In the following definitions of ΔT and Δt in the equation (i), “soaking temperature” is the temperature at which the soaking process 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 ≦ 100 (i)
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 an alloy when a solution heat treatment is performed in which a base of a high Cr high Ni alloy pipe is soaked at 1180 ° C. or higher while passing through a soaking furnace at a feeding speed of 1000 mm / min and then rapidly cooled. The temperature of the raw tube is shown.

  In FIG. 3, the broken line A represents the outlet position of the soaking furnace. The alloy tube that has passed through the soaking furnace is rapidly cooled, but the rapid cooling process will be described in detail. The “cooling” process (the broken line A in FIG. 3) immediately after the alloy tube is discharged from the soaking furnace. And a broken line B) and a “water cooling” process (after the broken line B in FIG. 3) following the cooling process. As shown in FIG. 3, Δt (min) is the time during which the alloy tube is allowed to cool after passing through the soaking furnace. 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 above formula (i) is the heat treatment using the high Cr high Ni alloy test material under the conditions shown in Tables 1 and 2 (that is, by changing ΔT and Δt). 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 is 100 ° C. · min or less, the Cr precipitation amount is 0.3% or less. As shown in FIGS. 1A and 1B, when the Cr precipitation amount is 0.3% or less, the 20 ° C. Charpy impact value is 150 J / cm ² or more. By cooling under conditions satisfying the equation, it is possible to manufacture a high Cr high Ni alloy tube having good toughness by suppressing the precipitation of Cr carbide to the crystal grain boundary.

  The heat treatment applied to the present invention does not necessarily need to be carried out in the above-mentioned continuous furnace, and even when water cooling is performed after soaking using a batch-type heat treatment furnace, it is good if the same ΔT and Δt as defined above are controlled. Toughness is obtained.

3. Cr Precipitation Amount As described above, the Cr precipitation amount is a Cr precipitation amount determined by quantitative analysis of an extraction residue obtained by electrolyzing an alloy tube after heat treatment. In the manufacturing method of the high Cr high Ni alloy pipe of the present invention, it is further desirable to adopt an embodiment in which the Cr precipitation amount of the high Cr high Ni alloy pipe to be manufactured is 0.3% or less. High Cr high Ni alloy tube with stable and good toughness by controlling the Cr precipitation amount of high Cr high Ni alloy tube to be manufactured by adding the rule that Cr precipitation amount is 0.3% or less It is because it can manufacture.

  In determining the Cr precipitation amount, the alloy tube used for collecting the extraction residue may be the one after heat treatment, even if it is an alloy base tube before pickling treatment, as a product after pickling treatment. An alloy tube may be used.

  The electrolytic analysis of the alloy tube and the quantitative analysis of the extraction residue (Cr determination) may be performed according to a conventional method. For example, electrolysis of the alloy tube 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.

  As described above, the high Cr high Ni alloy of the present invention is an alloy having the same chemical composition as the high Cr high Ni alloy tube manufactured by the manufacturing method of the present invention, and the high Cr high Ni alloy is electrolyzed. It is a high Cr high Ni alloy characterized in that the Cr precipitation amount obtained by quantitative analysis of the obtained extraction residue is 0.3% or less.

  The reason why the high Cr high Ni alloy of the present invention has the above chemical composition is as described above.

The high Cr high Ni alloy of the present invention is shown in FIGS. 1 (a) and 1 (b) because the Cr precipitation amount obtained by quantitative analysis of the extraction residue obtained by electrolyzing the alloy is 0.3% or less. Thus, the 20 ° C. Charpy impact value is 150 J / cm ² or more, and it has good toughness.

  High Cr high Ni having the chemical composition of specimen 1 and specimen 2 shown in Table 3, outer diameter: 50.8 mm, inner diameter: 33.2 mm, wall thickness: 8.8 mm, and length of 7000 mm An alloy tube was manufactured, and the effect of the present invention was confirmed by examining the 20 ° C. Charpy impact value and the Cr precipitation amount.

  In manufacturing the alloy pipe, a steel pipe was manufactured by hot extrusion from a billet, and a part thereof was subjected to heat treatment as it was. Further, some of the alloy pipes having the above dimensions were formed by cold rolling.

  The heat treatment was performed using a continuous heat treatment furnace or a batch furnace. The continuous furnace has a heating zone: 15 m and a distance from the heating zone to the water cooling zone: 750 mm. In the heating zone, the soaking temperature was set to 1230 ° C. The batch furnace was a gas-fired atmosphere furnace with a length of 9000 mm, and the soaking was set to 1230 ° C.

  In the cooling process after soaking, ΔT was changed within a range of 50 to 230 ° C., and Δt was changed within a range of 0.25 to 1.8 minutes. Moreover, the pipe feeding speed was changed within a range of 300 to 1500 mm / min. Table 4 shows heat treatment conditions when the sample material 1 is used, and Table 5 shows heat treatment conditions when the sample material 2 is used.

  After the heat treatment, descaling was performed by pickling or machining. The pickling was performed by immersing the alloy tube 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 shown together in Tables 4 and 5.
The meanings of the symbols in the “20 ° C. impact test” column of Tables 4 and 5 are the same as those 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 .

From the results of Table 4 and Table 5, when the condition of ΔT × Δt / 2 ≦ 100 defined in the present invention is satisfied, the 20 ° C. Charpy impact value is 150 J / cm ² or more, and the high Cr high Ni alloy tube is It was confirmed that it had good toughness. In this case, acid roughening due to pickling was not observed.

  The present invention can be used for the production of a high Cr high Ni alloy having good toughness as a heat resistant material.

Claims (2)

C: 0.05 to 0.09% by mass, Si: 0.1 to 0.3%, Mn: 0.05 to 1.3%, P: 0.015% or less, S: 0.005% Hereinafter, Ni: 44 to 52%, Cr: 27 to 32%, Ti: 0.05 to 1.0%, sol. Al: 0.005-0.2%, B: 0.001-0.008% and W: 4-10%, and Nb: 0.005-0.25% and Zr: 0.001-0.05 %, And the balance is made of Fe and impurities, and a high Cr high Ni alloy tube manufacturing method comprising:
In the heat treatment using a continuous heat treatment furnace or a batch furnace after hot working, after performing soaking treatment in which the high Cr high Ni alloy tube is heated to 1180 ° C. or higher, the cooling process is followed by the following (i ) A method for producing a high Cr high Ni alloy tube, characterized by cooling under conditions satisfying the formula.
ΔT × Δt / 2 ≦ 100 (i)
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)   2. The method for producing a high Cr high Ni alloy tube according to claim 1, wherein the heat treatment is performed after cold working in addition to hot working.

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