TWI663272B - Precipitation hardened high ni heat-resistant alloy - Google Patents

Abstract

The invention relates to a precipitation-hardening high-Ni heat-resistant alloy, which has the following component composition in mass%: Cr: 14 to 25%; Mo: 15% or less; Co: 15% or less; Cu: 5% Or below; Al: 4% or below; Ti: 4% or below; Nb: 6% or below; its restrictions are Al + Ti + Nb 1.0% or above; and inevitably including at least C and N Impurities, the rest being Ni, where the content of C is 0.01% or less, and the content of N fixed as a carbonitride is such that the Michelin point measured from the contents extracted by the evaluation method according to ASTM-E45 It is 100 or less.

Description

   Precipitation hardened high Ni heat resistant alloy   

The present invention relates to a precipitation-hardening high-Ni heat-resistant alloy having a high-temperature mechanical strength that is improved by dispersing and precipitating at least one intermetallic compound particle of Al, Ti, and Nb in a Ni matrix, and more particularly, to a highly Ni-resistant heat-resistant alloy having excellent Precipitation hardened high Ni heat-resistant alloy with high mechanical strength and machinability.

It is known that a precipitation-hardened high Ni heat-resistant alloy including a Ni matrix in which an intermetallic compound is well precipitated is an alloy material for heat-resistant parts requiring high-temperature mechanical strength such as engines for automobiles and turbine turntables for thermal power generation. The composition of the high Ni heat-resistant alloy includes precipitate-forming elements such as Al, Ti, and Nb, which form an intermetallic compound with Ni, but these elements have a strong binding force to C and easily form carbides. Therefore, in a high Ni heat-resistant alloy containing C, an excellent high-temperature mechanical strength is obtained by an intermetallic compound, but on the other hand, deterioration of cutting workability (machineability) due to precipitated carbides becomes a problem.

In order to improve the machinability of high-Ni heat-resistant alloys, a vacuum melting furnace, a remelting furnace, or the like is used to strictly control and adjust the composition of alloy components including carbon and precipitation forming elements. In addition, a controlled aging heat treatment is proposed, which can control the precipitation state of the precipitate.

For example, Patent Document 1 discloses a precipitation-hardened Ni-based heat-resistant alloy for hot working molds containing Al, Ti, and Nb, which is a high-Ni heat-resistant alloy containing Cr in an amount of about 14 to 25% by mass, where C The content is controlled to 0.03% by mass or less to suppress carbide precipitation, thereby improving machine processability. This patent document describes the poor machinability of alloys having high-Ni heat-resistant alloys which, in addition to the γ phase, have component compositions called "γ 'phase" and "γ" phase that precipitate intermetallic compounds. This patent document describes that poor machinability is generally believed to be due to the hardness of fine particles including an intermetallic compound as a hardening phase, but the influence caused by the original carbides precipitated during the solidification of the cast alloy is large, and Controlling the amount of C is also described to suppress precipitation of the original carbides.

Similar to Patent Document 1, Patent Document 2 discloses a machine for improving a high-Ni heat-resistant alloy containing about 14 to 25% by mass of Cr by dissolving precipitated fine primary carbides in a matrix by using a soaking heat treatment. Processability method. This patent document describes a soaking heat treatment system, for example, a heat treatment in which an alloy is maintained at a relatively high temperature region (such as 1,100 to 1,300 ° C) compared to the melting point of the alloy for a long period of 10 to 40 hours, and by this treatment, The Michelin point, which is the cleanliness index of the alloy, can be reduced to 100 or below.

Patent Document 1: JP-A-2009-167499

Patent Document 2: JP-A-2009-167500

As previously mentioned, the alloy is exposed to a relatively high temperature region compared to the melting point of the alloy during the soaking heat treatment for a long period of time. As a result, depending on the alloy, its mechanical strength may be deteriorated. In addition, depending on the carbide in the alloy, the carbide cannot be sufficiently dissolved in the matrix even by soaking heat treatment, and there is a case where the machinability cannot be improved.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-temperature strength that is improved by dispersing and precipitating at least one intermetallic compound particle of Al, Ti, and Nb in a Ni matrix without soaking. Precipitation hardened high Ni heat-resistant alloy with high machinability by heat treatment.

The present inventors have found that in a precipitation-hardened high-Ni heat-resistant alloy having a specific component composition and having a high-temperature strength that is improved by dispersing and precipitating at least one intermetallic compound particle of Al, Ti, and Nb in a Ni matrix, Nitride greatly affects machinability compared to carbide. There is a limit in reducing the amount of carbon as an impurity. Nevertheless, it has developed a method for manufacturing alloys that can reduce nitrides and / or carbonitrides (hereinafter referred to as "carbonitrides") and has obtained a novel precipitation hardened high Ni heat resistance with excellent machinability. alloy.

The precipitation-hardening high-Ni heat-resistant alloy according to the present invention has a composition composition including the following in terms of mass: Cr: 14 to 25%; Mo: 15% or less; Co: 15% or less; Cu: 5% or less; Al: 4% or less; Ti: 4% or less; Nb: 6% or less; its limitation is that Al + Ti + Nb is 1.0% or more; and unavoidable impurities including at least C and N, the rest Is Ni, where the content of C is 0.01% or less, and the content of N fixed as a carbonitride is such that the Michelin point measured from the contents extracted by the evaluation method according to ASTM-E45 is 100 or the following.

According to the present invention, it is not intended to dissolve the formed carbonitride in the matrix, but to suppress the formation of fine carbonitride itself. It is not necessary to pass a soaking heat treatment at a high temperature, which may cause concerns such as deterioration of mechanical strength due to melting of grain boundaries, coarsening of grains, and the like, and achieves high machineability.

In the present invention described above, the component composition may further include Fe in an amount of 15 to 30% by mass%. According to the present invention, a part of Ni can be replaced with inexpensive Fe. As a result, the alloy is excellent in cost efficiency, and a high Ni heat-resistant alloy having high machinability is obtained.

In the present invention described above, in the component composition, the Michelin point may be a first-order ratio to (C + 4.5N) expressed by the amounts of C and N. In addition, the amount of N may be 0.0050% or less by mass%. According to the present invention, high machinability can be efficiently obtained by reducing the amount of N.

In the present invention described above, the component composition may further include P in an amount of 0.005 to 0.010% by mass%. According to the present invention, the mechanical strength at high temperature can be improved, especially the latent resistance.

10‧‧‧ Waste

10a‧‧‧Removed surface

10b‧‧‧ compound coating

11‧‧‧ raw alloy

12‧‧‧ injection facility

14‧‧‧jet stream

16‧‧‧ injection side

17‧‧‧ melting chamber

18‧‧‧Mould

20‧‧‧ Ingot

M‧‧‧ Melt

FIG. 1 is a table showing an example of the component composition of the high Ni heat resistant alloy according to the present invention.

FIG. 2 is a flowchart showing the steps of a method for manufacturing a high Ni heat-resistant alloy according to the present invention.

Figure 3 is a perspective view showing the bead blasting.

4A to 4C are schematic views showing an example of a melting process.

FIG. 5 is a table showing measurement results of C and N content and cleanliness of a high Ni heat-resistant alloy (Example 1).

FIG. 6 is a table showing measurement results of the C and N content and cleanliness of a high Ni heat-resistant alloy (Example 2 and Comparative Example 1).

7A to 7C are photographs showing cross sections of Alloy 1 having different total contents of C and N.

FIG. 8 is a graph showing the relationship between the total content of C and N and the cleanliness in the high Ni heat-resistant alloy according to the present invention.

Figure 9 is a graph showing the relationship between the P content and the creep properties.

10A and 10B are photographs of a tool tip after a turning test.

FIG. 11 is a table showing the component composition of alloys to which the manufacturing process of the present invention can be applied.

A high Ni heat-resistant alloy as an example of the present invention will be described below with reference to FIGS. 1 to 11.

The high-Ni heat-resistant system according to the present invention is a precipitation-hardening heat-resistant alloy, which includes a γ phase as a matrix of Ni, and in which fine intermetallic compounds called a γ 'phase or a γ ”phase are dispersed and precipitated, and specifically a type Precipitation hardened high Ni heat resistant alloy containing precipitate forming elements such as Al, Ti and Nb.

More specifically, as shown in FIG. 1, the high-Ni heat-resistant alloy is a type that includes at least one of Al, Ti, and Nb, which are Ni as a main component and co-precipitates an intermetallic compound with Ni, and further includes A predetermined amount of an alloy of Fe, Cr, Mo, Cu, Co, and the like. The term "high-Ni heat-resistant alloy" used herein means not only an alloy containing 50% by mass or more of Ni (see Example 1 in Fig. 1) but also means containing about 30% by mass or more and less than 50% by mass Ni alloy (see Example 2 in Table 1).

As shown by alloys 1 to 4 in FIG. 1, the high-Ni heat-resistant alloys of Examples 1 and 2 have the following component composition in mass%: Cr: 14 to 25%; Mo: 15% or less; Co: 15% or less; Cu: 5% or less; Al: 4% or less; Ti: 4% or less; and Nb: 6% or less; the restriction is that Al + Ti + Nb is 1.0% or more; the rest Is Ni.

These alloys further include unavoidable impurities containing at least C and N, wherein the amount of C as an unavoidable impurity is 0.01% by mass or less, and the amount of N fixed as a carbonitride is such that The Michelin point is 100 or less. As a result, at least one intermetallic compound particle of Al, Ti, and Nb is dispersed and precipitated in the Ni matrix, thereby improving the high-temperature mechanical strength. In this case, the alloy may further include Fe in an amount of 15 to 30% by mass, as shown by alloys 1 and 4 in FIG. 1.

The reason for limiting the composition range of each additional element in the high Ni heat-resistant alloy will be briefly explained below.

Al and Ti form a γ 'phase, which is an intermetallic compound with Ni, and is well dispersed and precipitated in the matrix phase γ, thereby improving high-temperature strength. In addition, Nb also forms a γ "phase, which is an intermetallic compound with Ni, and is well dispersed and precipitated in the matrix phase γ, thereby improving high-temperature strength. On the other hand, Al, Ti, and Nb have carbide and nitride High productivity. In particular, the ultra-fine carbonitrides formed after smelting do not greatly affect high temperature strength, but they quickly wear out tool blades during cutting, resulting in deterioration of machinability. Considering these factors, Al and Ti The amount is 4% by mass or less, the amount of Nb is 6% by mass or less, and in addition, the amount of Al + Ti + Nb is limited to 1.0% by mass or more.

Cr will improve the oxidation resistance, corrosion resistance and high temperature strength. On the other hand, an excessively high content of Cr relatively decreases the Ni content in the alloy, thereby deteriorating the high-temperature strength. Considering these factors, the amount of Cr added is in the range of 14 to 25% by mass.

Mo is dissolved in the matrix to harden the matrix. Considering this factor, the addition amount of Mo is 15% by mass or less, and preferably in the range of 0.1 to 10% by mass.

Cu improves corrosion resistance to chloride ions. However, its excessively high content will affect high temperature strength. Considering these factors, when Cu is added, the amount of Cu added is 5% by mass or less.

Co is dissolved in the matrix to harden the matrix. In addition, Co increases the precipitation amount of the intermetallic compound between Ni and (Al, Ti, and Nb), and therefore increases the high temperature strength of the alloy. Considering these factors, when Co is added, the amount of Co added is 15% by mass or less.

Fe replaces Ni in the γ 'phase. Therefore, the amount of Ni is reduced, and the cost of the alloy can be reduced. On the other hand, when Fe is contained excessively, the desired high-temperature strength cannot be achieved with a reduced amount of Ni. Considering these factors, when Fe is added, the amount of Fe added is 15 to 30% by mass.

An example of a manufacturing process of a high Ni heat-resistant alloy will be described with reference to FIGS. 2, 3, and 4A to 4C.

The smelting process S100 performs smelting of various high-Ni heat-resistant alloys having the component composition shown in FIG. 1, while controlling the upper limit of the content of unavoidable impurities (C and N in the present invention). The melting process S100 is generally carried out by combining waste materials (waste materials) whose composition composition is close to the composition composition shown in FIG. 1 and alloys used for composition adjustment. The term "waste" as used herein means, for example, waste materials for products that have reached the end of their lifespan allocated in the waste market, and waste materials with controlled composition that are produced in companies when alloy materials or products have been remanufactured . Of these waste materials, the latter's waste materials are referred to as "returned materials", and the returned materials are better in controlling components that include unavoidable impurities.

A scrap such as Fe-Nb or Fe-Cr, Ni and a raw material alloy are prepared (raw material preparation step: S101). In this case, this step prepares an alloy containing a low C and N content as a raw material alloy, and further includes a removing step (coating removing step: S101a) of removing the coating on the surface of the waste. As mentioned above, in order to manufacture various high-Ni heat-resistant alloys having the compositional composition shown in FIG. 1, the compositional composition of the composition is close to that of the compositional composition, which has carbides, nitrides, or carbonitrides on its surface. Coatings of compounds and oxide coatings. In particular, nitrides or carbonitrides are easily contained by precipitation-forming elements including Al, Ti, and Nb, and the amount of N is likely to increase with the overall alloy. When these coatings are removed from the surface of the waste, the impurities that become the source of carbon C and nitrogen N can be removed before melting in the melting furnace in the subsequent melting step S102, so the high Ni heat resistance that is finally produced can be reduced C and N content in the alloy.

An example of the coating removing step S101a includes "bead blasting" as shown in FIG. The bead blasting is a blast 14 containing hard fine particles is injected from the injection mechanism 12 such as a nozzle to the surface of the waste material 10, and the fine particles collide with the injection surface 16 on the surface to mechanically remove the compound coating on the surface. Layer 10b. The removed surface 10a is continuously formed by moving the injection mechanism 12 along the waste material 10. In recent years, high-Ni heat-resistant alloys have been used in components having complicated shapes, such as drilling rigs for drilling oil. Even in the waste material 10 having such a complicated shape, the workability in bead blasting is excellent, and it is not necessary to manufacture a jig to adapt to the shape. Alternative techniques for removing compound coatings from the surface of the waste can also be applied.

Subsequently, the waste material 10 having the removed surface and the raw material alloy controlled to a low C and a low N are heated to a predetermined temperature so as to be equal to the melting in a vacuum melting furnace (melting step: S102). The composition of the alloy is adjusted by, for example, supplying additional additive elements as needed (composition adjustment step: S103). Thereafter, a melt having a controlled component is cast in a mold having a predetermined shape, thereby casting ingots having various shapes (ingot manufacturing step: S104).

In detail, as shown in FIGS. 4A to 4C, the waste material 10 and the raw material alloy 11 from which the compound coating on the surface has been removed in the coating removal step S101 a are fed into the melting chamber 17 of the vacuum melting furnace together. (Fig. 4A), and heated to a predetermined temperature to cause it to melt (Fig. 4B). Thereafter, a melt M having a controlled composition is cast in a mold 18, and an ingot 20 having various shapes is cast (FIG. 4C).

As long as thermal damage is allowed, soaking heat treatment can be further performed appropriately to further suppress carbides and nitrides from remaining in the ingot. In the case where the amount of C is an extremely low amount of 0.01% by mass or less, the amount of carbide precipitated in the alloy block after melting is extremely small. Therefore, it is desirable to perform the soaking heat treatment step only when the amount of C exceeds 0.01% by mass.

The ingot is forged, cut, and the like, and is further processed appropriately after secondary melting. As a result, an end product is formed. In the high-Ni heat-resistant alloy produced by this manufacturing process, a coating removal step of removing the surface of the waste material in the melting stage of the raw material has been performed, thereby suppressing the precipitation of carbides and nitrides in the ingot. As a result, the machinability of the high Ni heat resistant alloy can be improved.

Regarding the manufacturing process of the high Ni heat resistant alloy, the following features can be mentioned.

The manufacturing process is a method for manufacturing a precipitation-hardened Ni-based heat-resistant alloy, and includes at least one smelting step. The smelting step includes: a preparation step of preparing a raw material containing a waste material including a Ni-based alloy; A melting step; and a composition adjusting step of adjusting an alloy component of the molten alloy in a furnace, wherein the preparing step includes a removing step of removing a surface of a waste material.

The scrap may be a Ni-based alloy including at least one of Al, Ti, and Nb, wherein the total of these components exceeds 1% by mass.

The removing step may be a step of removing a compound coating containing nitride and / or carbonitride on the surface of the waste.

The removing step may be a step of bead spraying on the surface of the waste.

The manufacturing method may further include a soaking heat treatment step of the compound particles formed by melting after the melting step.

The precipitation-hardened Ni-based heat-resistant alloy may have a component composition in which the amount of N is greater than the amount of C in terms of mass equivalents of the formed carbides and / nitrides.

A specific example of manufacturing a high-Ni heat-resistant alloy by the above-mentioned manufacturing process of a high-Ni heat-resistant alloy is clearly explained below.

A high Ni heat resistant alloy is used as the raw material. The target composition of the final alloy is that of alloys 1 to 5 in FIG. 1. Alloy 5 is an alloy similar to alloy 4 containing Ni in an amount of about 44% by mass, but is an alloy that does not contain Cr, so it is used as a comparative example.

The returned material as a raw material and the raw material alloy controlled to a low C and a low N are fed to a vacuum induction melting furnace, and heated and melted. The alloy for adjusting the chemical composition range of alloys 1 to 5 is fed to a melting furnace to adjust the composition, and the resulting melt is cast in a mold to prepare an ingot. The ingot was thermally calcined at a temperature of about 1,100 ° C to form a round rod, and then subjected to a heat treatment at a temperature of 1,050 ° C for 30 minutes to manufacture a small embryo.

The test piece was cut from the small embryo, and the contents of carbon C and nitrogen N were measured. In addition, the "cleanliness" based on the Michelin point was measured as an index of its machinability. The obtained results are shown in Figs. 5 and 6, and for alloy 1, cross-sectional photographs of the alloy used to measure the Michelin point are shown in Figs. 7A to 7C. As shown in Figures 5 and 6, the surface of each returned material collected as a raw material was sprayed with beads before melting in test numbers 1, 2, 4, 7, 8, 10, 11, 13 and 14. A coating removal step is performed. In the bead blasting, steel particles having an average particle diameter of 0.8 mm and a hardness of HRC 40 to 50 were sprayed onto the surface of the returned material.

The term "cleanliness" as used herein is defined by the "Michelin point", which indicates the degree of non-metallic inclusions (such as carbides and nitrides) contained in the metallographic structure. The term "Michelin point" as used herein is used to evaluate the index of inclusions by the "Michelin Method" according to ASTM-E45. Use a magnification of 400 times to observe a cross-sectional structure with an area to be detected of 60.5 square millimeters, and measure the size of non-metallic inclusions dispersed in the structure with an aspect ratio of 2 or less and a width of 5 microns or more . In the measured inclusions, multiply the number of inclusions having a size (length) of 5 μm or more and less than 10 μm by a factor of 1, and include inclusions having a size of 10 μm or more and less than 20 μm. Multiply the number by a factor of 5 and multiply the number of inclusions with a size of 20 microns or more by a factor of 10. The sum of these values is defined as the Michelin point value. Therefore, when the Michelin point value is small, the number of inclusions in the observation field is small, and the cleanliness is evaluated as high. On the other hand, when the Michelin point value is large, the number of inclusions in the observation field is large, and the cleanliness is evaluated as low.

    [Example 1]    

As shown in FIG. 5, regarding an alloy containing 50% by mass or more of Ni, in the three specimens of Alloy 1, the content of carbon C is 0.0030 to 0.0250% by mass, and the content of nitrogen N is 0.0030 to 0.0087% by mass. %, And the cleanliness in this case is 40 to 300. Similarly, in the three test pieces of Alloy 2, the content of carbon C is 0.0020 to 0.0310% by mass, the content of nitrogen N is 0.0029 to 0.0112% by mass, and the cleanliness is 20 to 400. In addition, in the three specimens of Alloy 3, the content of carbon C was 0.0040 to 0.0600 mass%, the content of nitrogen N was 0.0050 mass%, and the cleanliness was 20 to 150.

    [Example 2]    

As shown in FIG. 6, regarding an alloy containing about 30% by mass or more of Ni and less than 50% by mass of Ni, the content of carbon C is 0.0050 to 0.0300% by mass and the content of nitrogen N in three test pieces of Alloy 4 It is 0.0030 to 0.0070% by mass, and the cleanliness in this case is 10 to 130.

    [Comparative Example 1]    

Further, regarding the alloy containing about 30% by mass or more and less than 50% by mass of Ni but not containing Cr, in the four specimens of Alloy 5, the content of carbon C is 0.0020 to 0.0080% by mass, and The content is 0.0010 to 0.0024% by mass, and the cleanliness is 50 to 500.

As shown in Figs. 5 and 6, it has been clear that by removing the compound coating formed on the surface of the waste material during the melting step, the high Ni heat-resistant alloy according to the embodiment can achieve C: 0.01 mass% or less and N: 0.0050 mass%. Or below, and also with regard to N fixed as a carbonitride, the Michelin point measured from the contents extracted by the evaluation method according to ASTM-E45 can be suppressed to 100 or below. In addition, in the data shown in Figures 5 and 6, it has been found that when comparing the content of C and N with the cleanliness based on the Michelin point value, the total value X (X is summed up at a ratio of C: N = 1: 4.5 = C + 4.5N) is almost proportional to cleanliness.

Specifically, as shown in FIG. 8, when the (C + 4.5N) value represented by the content of carbon C and nitrogen N of the high Ni heat-resistant alloy is the horizontal axis and the cleanliness based on the Michelin point is the vertical axis, One graph should understand that all alloys 1 to 5 have a total content of (C + 4.5N) which is almost proportional to the Michelin point. This makes it possible to predict the Michelin point value of the high Ni heat resistant alloy by controlling the total content of carbon C and nitrogen N (C + 4.5N) contained in the high Ni heat resistant alloy to be manufactured. However, in the alloy 5, the change of the Michelin point value to the (C + 4.5N) value is large, and in the prediction of the Michelin point value, the accuracy is lower than that of the alloys 1 to 4.

The high cleanliness of the high Ni heat resistant alloy (ie, a small Michelin point value) means that the amount of inclusions in the structure is small. Therefore, a high Ni heat resistant alloy with high cleanliness exhibits high machinability. Therefore, when the compound coating such as carbide or nitride is removed in the smelting step, and additionally, the composition range is as described above and the X value is suppressed, it is possible to obtain a high level having both improved high-temperature strength and machinability. Ni heat resistant alloy.

For example, when the X value is determined such that in Alloys 1 to 4, the cleanliness (Michelin point value) shown in FIG. 8 is 100 or less, excellent machining is achieved in the produced high Ni heat resistant alloy Sex.

    [Example 3]    

FIG. 9 shows the results of a creep test using a test piece having various P contents of 0.003% by mass, 0.005% by mass, 0.010% by mass, and 0.017% by mass in Alloy 1. FIG. In the creep test, the temperature was 649 ° C, and the load in terms of stress was 689 MPa.

As shown in FIG. 9, the breaking time and elongation, which are creep properties, tend to improve as the P content increases. In addition, in the test piece in which the P content was changed in Alloy 4, the creep properties were similarly improved by including a small amount of P. Specifically, in the above-mentioned high-Ni heat-resistant alloy, from the viewpoint of high-temperature creep properties, it is preferable to include P in an amount that does not degrade hot workability and manufacturability, and its content is 0.005 to 0.010 mass%. Within range.

    Turning test    

10A and 10B show photographs of a tool tip when a turning test is performed in a small embryo of Alloy 2 using a carbide tool. The picture shows the tip of the carbide tool 11 minutes after the start of the turning test. The turning test conditions were machine processing rate: 50 m / min, feed rate: 0.4 mm / rev and cutting depth: 2.0 mm.

As shown in FIG. 10A, in a small embryo manufactured by a conventional manufacturing method of directly forging an ingot without bead blasting of a waste material contained in a raw material, as shown by a white arrow in a photograph, a tool The tips are greatly worn.

On the other hand, as shown in FIG. 10B, in the small embryo prepared by the above-mentioned manufacturing process of removing the compound coating of the waste, as shown by the white arrow in the photograph, it can be confirmed that the wear of the carbide tool is greatly reduce. In other words, a result is obtained that the high Ni heat-resistant alloy produced by the manufacturing process in the example is excellent in the machinability of the same carbide tool.

FIG. 11 is a table showing alloys A to N as examples of high-Ni heat-resistant alloys to which the above manufacturing process can be applied, and chemical compositions considered to be respective final targets. In the same turning test as above, it was confirmed that good machinability can be obtained even in these alloys. In an alloy containing Ni in an amount of about 30% by mass or more, the same machinability improvement effect as in the manufacturing process is obtained. Therefore, the high-Ni heat-resistant alloy intended here includes alloys containing Ni in an amount of about 30% by mass or more.

In the above-mentioned conventional manufacturing method, although the processing time of the degassing treatment of the vacuum induction melting furnace is extended, it is difficult to achieve an N content of 100 ppm or less in the obtained ingot. On the other hand, the N content in the ingot obtained through the above manufacturing process is 60 ppm or less, and a similar N content is maintained in the small embryo. It is also understood that when the chemical composition and heat treatment conditions of the high Ni heat-resistant alloy are appropriately selected, the N content can be reduced to 50 ppm or less, and preferably 40 ppm or less, which can further reduce the wear of carbide tools, and can improve machining Sex.

Conventional machinability can be improved by reducing the amount of C. On the other hand, as shown in the turning test described above, it was confirmed that the amount of N greatly affected the machinability. It has been further confirmed that when the amounts of carbides and nitrides that affect the machinability are obtained by microscopic observation, there is a significant reduction in carbides and carbides when a predetermined amount of N is reduced instead of when the same amount of C is reduced. Trend in the amount of nitrides. This trend is the same in all of the above precipitation-hardened high-Ni heat-resistant alloys. In other words, in a high-Ni heat-resistant alloy having a component composition of N greater than C in terms of the mass equivalent of the carbides and / or nitrides formed, the machinability can be effectively improved by applying the above manufacturing process .

The representative embodiments of the present invention have been described above. However, the present invention is not always limited to these embodiments, and those skilled in the art can find various alternative and modified embodiments without departing from the gist of the present invention.

This application is based on Japanese Patent Application Nos. 2016-207947 filed on October 24, 2016, Japanese Patent Application Nos. 2016-242221 filed on December 14, 2016, and August 30, 2017 Japanese Patent Application No. 2017-166063 filed, the contents of which are incorporated herein by reference.

Claims (8)

A precipitation-hardening high-Ni heat-resistant alloy having the following component composition in terms of mass%: Cr: 14 to 25%; Mo: 15% or less; Co: 15% or less; Cu: 5% or less; Al : 4% or less; Ti: 4% or less; Nb: 6% or less; the limitation is that Al + Ti + Nb is 1.0% or more; and unavoidable impurities including at least C and N, the rest are Ni, where the content of C is 0.01% or less, the amount of N is 0.0050% or less by mass%, and the content of N fixed as a carbonitride is such that it is extracted by an evaluation method according to ASTM-E45 The Michelin point of the contents was 100 or less. The precipitation-hardening high-Ni heat-resistant alloy as claimed in claim 1, wherein the component composition further includes Fe in an amount of 15 to 30% by mass%. The precipitation-hardening high-Ni heat-resistant alloy as claimed in claim 1, wherein, in the component composition, the Michelin point is in a first-order proportion to (C + 4.5N) expressed by the amount of C and N. The precipitation-hardening high-Ni heat-resistant alloy as claimed in claim 2, wherein, in the component composition, the Michelin point is in a first-order proportion with (C + 4.5N) expressed by the amount of C and N. The precipitation-hardening high-Ni heat-resistant alloy according to claim 1, wherein the component composition further includes P in an amount of 0.005 to 0.010% by mass%. The precipitation-hardening high-Ni heat-resistant alloy according to claim 2, wherein the component composition further includes P in an amount of 0.005 to 0.010% by mass%. The precipitation-hardening high-Ni heat-resistant alloy according to claim 3, wherein the component composition further includes P in an amount of 0.005 to 0.010% by mass%. The precipitation-hardening high-Ni heat-resistant alloy according to claim 4, wherein the component composition further includes P in an amount of 0.005 to 0.010% by mass%.