JP5339892B2 - Nickel-based alloy and manufacturing method thereof - Google Patents

Description

  The present invention relates to a cast slab of Ni-base alloy, and in particular, by reducing the macrosegregation at the center of the steel ingot by equiaxing the slab, improving the magnetic properties in the permalloy alloy, the Monel alloy Then, it is related with the technique which improves various characteristics of Ni base alloy, such as improving corrosion resistance.

  Ni-based alloys are austenitic and have a problem that significant segregation remains in the center of the steel ingot. This segregation is formed as a result of the solid phase growing in a dendrite shape with the heat dissipation direction as an axis during cooling of the ingot or the like, and as a result, columnar coarse crystals are formed along the axis. When there is such center segregation, various characteristics are deteriorated in the central portion of the plate thickness. For example, if it is a soft magnetic material, it will have a bad influence on the magnetic characteristics of the central part, and if it is a highly corrosion resistant alloy, the corrosion resistance of the cross section will be reduced. In order to prevent the deterioration of these characteristics, it is preferable that a large number of primary crystal nuclei are randomly formed in the ingot to form equiaxed crystals that grow minutely and uniformly regardless of the direction of heat dissipation.

By the way, in ferritic stainless steel, a technique for equiaxed crystallization using TiN as a nucleating agent for primary crystals is disclosed (for example, see Patent Documents 1 to 4). Also, there is a technique for spraying at least one of MgAl ₂ O ₄ , CaS, CeS, TiN, Ce ₂ O ₃ , TiC and SiC into a molten alloy for equiaxed crystallization of a continuous cast slab of ordinary steel. It is disclosed (for example, see Patent Document 5).
JP-A-11-350078 JP 2000-144342 A Japanese Patent Laid-Open No. 2001-20046 JP 2002-30395 A JP 2001-225153 A

  However, there is no optimal equiaxed crystal-forming material as described above for Ni-based alloys, and the problem of segregation in Ni-based alloys has not been solved. Therefore, an object of the present invention is to provide a Ni-based alloy that can suppress macro component segregation as much as possible by controlling the cast structure with a small amount of inclusions, and a method for producing the same.

This invention is made | formed in view of the said situation, Ni: 30 mass% of this invention, Ni: 30-85 mass%, Ti: 0.01-1.4 mass%, Al: 0.02-0.4 mass% O: 1 to 50 ppm, and a total of 1 to 40 mass% of Fe and Cu, the balance being a Ni-based alloy having a component composition consisting of inevitable impurities, wherein the following formulas (1) to (3) are expressed: It is characterized by satisfaction.
Al ≧ 0.38Ti−0.132 (1)
Al ≦ 0.1439Ti + 0.1986 (2)
Al ≧ −0.2051Ti + 0.1020 (3)
(In the formula, Ti-Al indicates the content of each component in mass%)

Furthermore, in the Ni-based alloy, it is a preferable aspect that Mo is further contained in an amount of 4.21 mass% or less , and 1 to 40 mass% in total of Fe, Cu, and Mo is contained.

  Moreover, the manufacturing method of the Ni-based alloy of the present invention is a method for manufacturing the above-mentioned Ni-based alloy, and melts raw materials in an Ar atmosphere to obtain a molten alloy. A Ti—Al-based oxide is produced by adding 1.5 mass% Ti and 0.02 to 0.5 mass% Al, cast into a mold, and cooled to form a steel ingot.

  According to the Ni-based alloy of the present invention and the method for producing the same, the formation of the columnar crystals formed by the above-described segregation is limited to a part of the peripheral portion of the ingot, and the columnar crystals are suppressed in the other central portions, thereby forming equiaxed crystals. Can be preferentially formed. Further, according to the present invention, the ratio of equiaxed crystals in the cross section of the steel ingot cast into the mold can be set to 30% or more in terms of area ratio.

  It is known that the characteristics of Ni-based alloys mass-produced at a level of several tons or more are greatly influenced by non-metallic inclusions and component segregation. In particular, when it grows as a columnar crystal from the mold during casting, macro component segregation occurs in the center of the steel ingot, which may adversely affect the required characteristics. Therefore, in order to suppress the segregation of components, it is effective to reduce the growth of columnar crystals as much as possible during solidification and to grow with equiaxed crystals. For equiaxed crystallization, when the molten alloy solidifies, non-metallic inclusions that become solid phase nucleation sites are dispersed, or the molten alloy itself forms nucleation sites and is equiaxed. It is desired to grow as a crystal.

  The present inventors have intensively studied a method for making a solidified structure fine and equiaxed, not columnar crystals, and adding Ti and Al to add non-metallic inclusions of Ti and Al. And succeeded in obtaining fine equiaxed crystals. Although the clear equiaxed crystal formation mechanism has many unclear points, it is presumed that the Ti—Al-based oxide has a role of assisting nucleation of the austenite phase.

Usually, when a molten alloy of Ni-base alloy is cooled, the temperature of the molten alloy once falls below the melting point and goes through a supercooled state, and then the temperature rises to reach the freezing point. In this process, the solid alloy containing a lot of columnar crystals is obtained. Form a phase. Here, when a predetermined amount of Ti and Al specified in the present invention is added to the Ni-based alloy, Ti and Al react with oxygen in the molten alloy and / or oxygen contained in the Ar atmosphere to react with TiO ₂ -Al. _{A 2} O ₃ composite oxide layer is formed on the bath surface. When this molten alloy is cooled, a solid phase containing more equiaxed crystals is formed than when Ti and Al are not added. As this mechanism, a complex oxide layer formed on the bath surface of the molten alloy is used as a starting point, and a large number of Ni-based alloy nuclei are generated, and the generated nuclei settle in the molten alloy to form fine equiaxed crystals. Many are considered to be generated.

That is, the present invention is a Ni-based alloy having a component composition comprising Ti: 0.01 to 1.4 mass%, Al: 0.02 to 0.4 mass%, the balance being Ni and inevitable impurities, A Ni-based alloy characterized by satisfying the formulas (1) to (3).
Al ≧ 0.38Ti−0.132 (1)
Al ≦ 0.1439Ti + 0.1986 (2)
Al ≧ −0.2051Ti + 0.1020 (3)
(In the formula, Ti-Al indicates the content of each component in mass%)

  The Ni-based alloy of the present invention contains 30 to 85 mass% of Ni, and further contains one or more selected from Fe, Mo and Cu in a total of 1 to 40 mass%. Has the best effect.

  Furthermore, a manufacturing method is also proposed. That is, the raw material is melted in an Ar atmosphere to obtain a molten alloy, and 0.03 to 1.5 mass% Ti and 0.02 to 0.5 mass% Al are added to the molten alloy to form a Ti-Al system. This is a method for producing a Ni-base alloy, characterized in that an oxide is produced, cast into a mold, and cooled to form a steel ingot. According to this manufacturing method, the equiaxed crystal ratio in the cross section of the steel ingot cast into the mold can be 30% or more in terms of area ratio, and macro segregation can be suppressed.

Hereinafter, the constituent elements of the present invention will be described in detail.
(Ti: 0.01-1.4 mass%)
When Ti is lower than 0.01 mass%, solidified nuclei are formed in the Ni-based alloy, and the amount of Ti-based oxides generated among the Ti-Al-based oxides necessary for the formation of equiaxed crystals is insufficient. The tendency to crystal growth becomes stronger. In some cases, the equiaxed crystal ratio will be lower than 30%. On the other hand, when Ti exceeds 1.4 mass%, the Ti-based oxide in the Ti-Al-based oxide becomes excessive. As a result, the solidified structure grows as columnar crystals. In some cases, the equiaxed crystal ratio will be lower than 30%. Therefore, it was set to 0.01 to 1.4 mass%. Preferably, it is 0.02-0.6 mass%, More preferably, it is 0.1-0.5 mass%.

(Al: 0.02-0.4 mass%)
If Al is lower than 0.02 mass%, the amount of Al-based oxide generated in the Ti-Al-based oxide necessary for forming equiaxed crystals by forming solid nuclei in the Ni-based alloy is insufficient, and the solidified structure is columnar. The tendency to crystal growth becomes stronger. In some cases, the equiaxed crystal ratio will be lower than 30%. On the other hand, when Al exceeds 0.4 mass%, the Al-based oxide of the Ti-Al-based oxide becomes excessive. As a result, the solidified structure grows as columnar crystals. In some cases, the equiaxed crystal ratio will be lower than 30%. Therefore, it was set to 0.02 to 0.4 mass%. Preferably, it is 0.04 to 0.35 mass%, and more preferably 0.07 to 0.32 mass%.

  FIG. 1 is a graph showing the relationship between Ti concentration and Al concentration in a Ni-based alloy and the solidification form formed. In the figure, in the region surrounded by points A to D, Ti oxide and Al oxide coexist as described above to form a complex oxide layer on the bath surface of the molten alloy, which is a trigger for nucleation. Thus, equiaxed crystals are mainly formed in the Ni-based alloy. Above the straight line AD connecting points A and D, that is, in a region where the Al concentration is too higher than the range of the present invention, the amount of Al oxide is excessive as compared with Ti oxide, and solidification nuclei are formed in the Ni-based alloy. The action is weakened and the formation of columnar crystals becomes dominant.

  In the right side of the straight line CD, that is, in a region where the Ti concentration is too higher than the range of the present invention, the amount of Ti oxide is excessive as compared with the Al oxide, and the action of forming solidified nuclei in the Ni-based alloy is weakened. The formation of becomes dominant. Below the straight line BC, the amount of both Al oxide and Ti oxide produced is insufficient, and the action of forming solidification nuclei in the Ni-based alloy is weakened, and the formation of columnar crystals becomes dominant.

(Oxygen: 1-50 ppm)
When oxygen is less than 1 ppm, Ti-Al composite oxides that are solidification nuclei are reduced, so that the tendency to grow columnar crystals becomes stronger. In some cases, the equiaxed crystal ratio will be lower than 30%. On the other hand, when oxygen becomes higher than 50 ppm, the generated oxide is not a Ti—Al-based oxide, and the solidified structure has a tendency to grow columnar crystals. In some cases, the equiaxed crystal ratio will be lower than 30%. Preferably, it is 4-48 ppm, More preferably, it is 7-45 ppm.

  The present invention also proposes a manufacturing method. The basic process is to melt and mix alloy raw materials such as electrolytic iron, pure Ni, molybdenum and copper, add Ti and Al, and cast into a mold. At this time, a more preferable aspect will be described. First, a high frequency induction furnace is suitable for the melting furnace. In addition, an electric resistance furnace, an arc electric furnace, a plasma melting furnace, and the like are also suitable. It is more preferable that the melting furnace has a chamber whose atmosphere can be adjusted. For example, a vacuum induction furnace can be said to be a more suitable embodiment. The crucible for holding the molten alloy is preferably a relatively chemically stable material, and is preferably alumina in order to help produce a Ti—Al composite oxide that is the starting point for the formation of equiaxed crystals. Quartz is not suitable because it tends to react with Ti.

  The atmosphere is preferably dissolved in an Ar atmosphere to prevent significant oxidation of the raw material. More preferably, when the Ar gas is introduced after evacuating before melting, the oxygen and nitrogen concentrations can be further reduced to suitable concentrations. Further, although the temperature depends on the melting point of the alloy, about 1500 to 1600 ° C. is suitable. Since oxygen contained in Ar is consumed to form a Ti—Al based composite oxide on the surface of the molten alloy, the oxygen concentration in Ar is preferably 0.1 to 100 ppm.

  Thus, after melt | dissolving a main raw material, 0.03-1.5 mass% of Ti and 0.02-0.5 mass% of Al are added. At this time, oxygen in the molten alloy is dissolved by several tens to several hundred ppm, but reacts with Ti and Al to form a Ti—Al composite oxide. In order to form the Ti—Al composite oxide on the bath surface of the molten alloy, it is preferable to hold for at least 1 minute.

  In addition, in the above-mentioned Ti content item, 0.01 to 1.4 mass% was specified, and in the Al content item, 0.02 to 0.4 mass%. The reason for adding 0.5 mass% Ti and 0.02 to 0.5 mass% Al is that a part of Ti-Al composite oxide is added in anticipation that some Ti-Al composite oxide will be levitated and removed, and finally contained This is because the amounts are set to Ti: 0.01 to 1.4 mass% and Al: 0.02 to 0.4 mass%.

  Thereafter, it may be cast into a mold according to a conventional method, or hardened in a crucible as it is. In any hardening method, it is desirable to control the cooling rate in the range of 0.1 to 100 ° C./second. The reason is that if it is too fast, shrinkage-like defects are generated inside the steel ingot, and if it is too late, the tendency of the crystal grains to become coarse increases. More desirable is 0.3 to 50 ° C./second.

  According to this manufacturing method, the equiaxed crystal ratio in the cross section of the steel ingot cast into the mold can be 30% or more, preferably 40% or more in terms of the area ratio, and the forged product, hot-rolled product, cold-rolled product can be obtained. It is possible to suppress macro segregation in products such as products.

In particular, the Ni-based alloy in the present invention contains 30 to 85 mass% of Ni, contains Fe and Cu, further contains 4.21 mass% or less of Mo selectively, and includes Fe + Cu in total or Fe + Cu + Mo in total. A Ni-based alloy characterized by containing ˜40 mass% or less has the best effect.

  Specifically, PC (Permalloy C: Ni-4 mass% Mo-5 mass% Cu-13 mass% Fe) and NW4400 (Monel400: Ni-33 mass% Cu) are suitable alloys.

  Of course, not limited to this, NW2201 (99 mass% Ni), NCF690 (Ni-30.0 mass% Cr-9.5 mass% Fe), NW6022 (Hastelloy C-22: Ni-21.3 mass% Cr-13.5 mass%) Mo-4 mass% Fe-3 mass% W), NW0276 (Hastelloy C-276: Ni-15.5 mass% Cr-16 mass% Mo-5.5 mass% Fe-3.8 mass% W), NCF600 (INCONEL 600: Ni- 15.5 mass% Cr-7 mass% Fe), NCF800 (30-35 mass% Ni-21 mass% Cr-Fe), NCF800H (30-35 mass% Ni-21 mass% Cr-Fe), NW6002 (Ni-21.5 mass%) C -9 mass% Mo-18.5 mass% Fe-1.2 mass% Co), Fe-36% Ni, Fe-42% Ni, PB (Permalloy B), Fe-50.5% Ni, Fe-42% Ni- Ni-based alloys such as 6% Cr and Fe-47% Ni-6% Cr are also effective.

An example is shown and the effect of the present invention is explained more clearly.
300 g of each raw material made of Ni, Fe, Mo, and Cu of Invention Examples 1 to 15 and Comparative Examples 1 to 11 weighed so as to have an alloy system having a predetermined chemical composition shown in Table 1 was charged into a high frequency melting furnace did. The equipment used was a vacuum induction furnace, and the atmosphere was argon containing 0.5 ppm of oxygen. The dissolution temperature was 1600 ° C. After complete dissolution, the molten metal was kept for 10 minutes, and then Al or Ti, or a composite addition operation thereof was performed in some cases. This operation is shown by the amounts of Ti-Al added in Table 1. After completion of the addition, the melting furnace was turned off after holding for 3 minutes, and then cooled as it was in an alumina crucible to prepare an ingot. The cooling curve at this time is shown in the graph of FIG.

  A 15 mm portion was cut out from the bottom of the prepared ingot, and after mirror polishing, it was corroded with aqua regia and observed for macro structure. Moreover, among these, the picked-up image of the ingot of the invention example 10 and the comparative example 10 was shown to FIG. In the figure, a fan-shaped portion with a central angle of 90 degrees represents a quarter-divided portion of the ingot, and the other portions show the holding member. In addition, Table 1 shows the results of the equiaxed crystal ratio of each invention example and comparative example.

  In Table 1, the added element addition amount indicates the amount added in the manufacturing process, and the chemical composition item indicates the composition of the ingot after actual manufacture. Therefore, the former Ti addition amount is related to the range of claim 5 (0.03 to 1.5 mass%), and the latter chemical composition is the range of claim 1 (0.01 to 1.4 mass%). Related. The same applies to Al.

Each measurement method and evaluation method will be described below.
(Chemical composition)
Oxygen concentration was analyzed by an inert gas impulse melting infrared absorption method by wet chemical analysis. The balance is Ni. Although not shown here, Si and Mn may be included as alloy elements, and P, S, and N are included as a total of about 0.2 mass% or less as unavoidable impurities.

(Equiaxial crystal ratio)
After mirror polishing, the surface was corroded with aqua regia and macroscopic observation was performed, and the area ratio of equiaxed crystal parts was determined by image analysis. The average crystal grain size l is calculated from the number n of crystal grains within a specific range and the area S using the following formula (4), and those having an average grain size of 0.6 mm or less are defined as equiaxed crystals. Those exceeding 20 were regarded as columnar crystals.

Details of the results of the examples will be described.
In Invention Examples 1 to 15, in order to satisfy the scope of the present invention, the solidification structure is mainly composed of equiaxed crystals, and the equiaxed crystal ratio is controlled to 30% or more. As a result, the average particle size was also fine and all were 0.5 mm or less.

  On the other hand, in the comparative example, since any one of the conditions was removed, the solidified structure was mainly composed of columnar crystals. Specifically, in Comparative Examples 1, 6 and 7, since Ti was not added, no Ti—Al-based oxide was generated, and no equiaxed crystal was formed. In Comparative Examples 3 to 5 and 11, since Al was not added, Ti-Al oxide was not generated in addition to the Al component obtained from the crucible, and although equiaxed crystals were formed to some extent, the equiaxed crystal ratio was low. It was. Since Comparative Examples 2 and 10 have an excessive amount of Ti and Comparative Examples 8 and 9 have an excessive amount of Al, the generation amount of Ti—Al-based oxide is insufficient, and equiaxed crystals are formed to some extent. Was low.

  According to the present invention, it is possible to effectively equiaxially crystallize a Ni-based alloy ingot. As a result, it is possible to reduce macro segregation at the center of the steel ingot and improve various characteristics. In particular, permalloy alloys improve the magnetic properties and improve the performance of the magnetic head, magnetic shield material, transformer core, and the like. Monel alloys have improved corrosion resistance and can be effectively applied to chemical plants.

  When the alloy of the present invention is used as a welding rod for a Ni-based alloy plate or welded with a non-filler, the structure of the weld metal part is effectively equiaxed. For this reason, the corrosion resistance, particularly the stress corrosion cracking property, which tends to be a problem with an austenitic alloy, is improved depending on the environment.

  Permalloy alloys have improved magnetic properties and are suitable for magnetic heads, magnetic shield materials, transformer cores, and the like. Monel alloys have improved corrosion resistance and are suitable for chemical plants and the like.

It is a graph which shows the relationship between Ti and Al density | concentration of this invention, and the solidification form formed. It is a graph which shows the cooling curve of the molten alloy in this invention. It is an image which shows the solidification structure | tissue (Inventive crystal ratio 100%) of Invention Example 10. 10 is an image showing a solidified structure (equiaxial crystal ratio 20%) of Comparative Example 10.

Claims (5)

Ni: 30 to 85 mass%, Ti: 0.01 to 1.4 mass%, Al: 0.02 to 0.4 mass%, O: 1 to 50 ppm, and 1 to 40 mass% in total of Fe and Cu, A Ni-based alloy having a component composition consisting of unavoidable impurities in the balance, wherein the following formulas (1) to (3) are satisfied.
Al ≧ 0.38Ti−0.132 (1)
Al ≦ 0.1439Ti + 0.1986 (2)
Al ≧ −0.2051Ti + 0.1020 (3)
(In the formula, Ti-Al indicates the content of each component in mass%) The Ni-based alloy according to claim 1 , wherein the Ni-based alloy further contains Mo in an amount of 4.21 mass% or less, and contains 1 to 40 mass% in total of Fe, Cu, and Mo. The Ni-based alloy according to claim 1 or 2 , wherein the ratio of equiaxed crystals in the cross section of the Ni alloy is 30% or more in terms of area ratio. It is a manufacturing method of the Ni base alloy in any one of Claims 1-3 , Comprising: A raw material is melt | dissolved in Ar atmosphere, a molten alloy is obtained, 0.03-1.5 mass% of Ti and A method for producing a Ni-base alloy, characterized in that a Ti-Al-based oxide is produced by adding 0.02 to 0.5 mass% Al, cast into a mold, and cooled to form a steel ingot. 5. The method for producing a Ni-based alloy according to claim 4 , wherein the ratio of equiaxed crystals in the cross section of the steel ingot cast in the mold is 30% or more in terms of area ratio.

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