JPH04131344A - Oxide dispersion strengthened type ni-base alloy and its production - Google Patents

Abstract

PURPOSE:To obtain an Ni-base alloy excellent in heat resistance, thermal shock resistance, creep strength, and fracture life by hat-working a powder of an oxide dispersion strengthened type Ni-base alloy prepared by a mechanical alloying method and then growing crystalline grains by means of heating at the specific temp. CONSTITUTION:The crystalline grains of refractory metal oxide, such as Y2O3, and pure metal, such as Ni and Cr, are put into a high kinetic energy type ball mill, pulverized, and mixed by means of mechanical alloying, by which a uniform metal mixture of pulverized powder having a composition consisting of, by weight, 18-40% Cr, <5% Fe, <5% Al, <5% Ti, and the balance Ni is prepared. This powder mixture is subjected to hot working, such as hot extrusion, and to heating up to >=1300 deg.C to undergo crystalline grain growth, thereby a secondary recrystallization structure in which the mean value of the aspect ratios of crystals is regulated to >=10 can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oxide dispersion strengthened Ni-based alloy and a method for producing the same.

(Prior Art) Oxide dispersion strengthened Ni-based alloys, which are strengthened by dispersing fine particles of high-melting-point oxides such as yttria Y-Os, in Ni-based alloys have been known (Japanese Patent Publication No. 1983-1999). 386
Publication No. 65).

This is intended to improve heat resistance and strength by dispersing fine particles of a high melting point oxide in a Ni-based base material.

(Problems to be Solved by the Invention) The present invention aims to improve such a Ni-based oxide dispersion type alloy by focusing on the characteristics of crystal grains and improving the creep strength and rupture life by a predetermined manufacturing method. The purpose of the present invention is to provide an oxide dispersion-strengthened alloy.

(Means for Solving the Problems) The oxide fractionally strengthened Ni-based alloy of the present invention has a composition of % by weight.
So, Cr: 18-40%, Fe: 5% or less, Al: 5%
Hereinafter, it is an alloy consisting of Ti: 5% or less and the remainder substantially Ni, and is characterized by growing crystal grains so that the average value of the aspect ratio of the crystal grains is 10 or more.

The method for producing an oxide dispersion strengthened Ni-based alloy of the present invention has a composition in weight% of Cr: 18 to 40%, Fe: 5% or less,
Aj2: 5% or less, Ti: 5% or less, remainder substantially Ni
An alloy consisting of 13
It is characterized in that it is heated at 00'C or more to grow crystal grains, and the average value of the aspect ratio of the crystal grains is 10 or more.

The reason why the oxide dispersion strengthened Ni-based alloy was used here is that it has excellent heat resistance, high temperature creep strength, and the like. Hot processing can be performed using hot extrusion, hot rolling, casting, hot isostatic pressing (HIP), etc., but is not limited to these processing methods. Heating at a temperature of 1300°C or higher after hot working causes the crystal grains of the hot worked alloy to preferentially grow abnormally (secondary recrystallization) in the working direction, resulting in a secondary recrystallized structure with a high aspect ratio. This is to obtain.

The reason for selecting the composition of the superalloy of the present invention as described above is as follows.
It is as follows.

Cr: 18-40% If the Cr content is less than this lower limit, desired heat resistance cannot be obtained. On the other hand, if the upper limit is exceeded, it becomes difficult to maintain the austenitic structure.The preferable Cr content is 18 to 40%, particularly 25 to 35%, as described above.

Fe: 5% or less The iron content is preferably 1% or less, but up to 5% allows alloys with higher Fe content to be used in thermal shock resistant materials, high temperature oxidation resistant materials, high temperature structural materials, e.g. skids. Can be used as rail material.

Aβ: 5% or less, Ti: 5% or less In ordinary high-temperature oxidation-resistant structural materials, such as skid rails, the content of these components may be 1% or less, but if you want to further increase the oxidation resistance, e.g. In a skid rail used in a heating furnace having an atmosphere with a relatively large amount of 02 (up to several %), favorable results can be obtained by adding these elements 19 and Ti in an amount up to 5%. Adding more than this will result in an increase in harmful large inclusions.

(Function) According to the manufacturing method of the present invention, an oxide dispersion strengthened Ni-based alloy powder manufactured by a mechanical alloying method is processed by hot working, and crystal grains are abnormally grown in the working direction. Since a secondary recrystallized structure with an average aspect ratio of 10 or more is obtained, the fracture life and creep strength can be significantly increased.

(Example) The present invention will be explained in detail below.

The composition of the Ni-based oxide dispersion strengthened alloy is as shown in Table 1. The method for producing powder of this alloy is as follows. Using the mechanical alloying method, pure metals as alloying components and crystal particles of a high-melting point metal oxide such as ittria are placed in a high kinetic energy ball mill, finely pulverized, and mixed to form fine powders of each component. Build a homogeneous mixture.

This alloy powder mixture was molded by hot extrusion. At that time, the extrusion ratio was varied.

The obtained extruded body was maintained at 1315° C. or higher for about 1 hour. The purpose of this heat treatment is to abnormally grow (secondary recrystallization) the long crystal grains processed by extrusion molding and obtain a second recrystallized structure with a high aspect ratio.

The heat-treated extruded body was subjected to (1) a tensile creep test and (2) a compression creep test. The results are shown in Tables 2 and 3 and FIGS. 1 and 2.

(2) Tensile Creep Test A creep fracture test was conducted under the conditions of a temperature of 1623 K and a pressure of 49 MPa. As a result, as is clear from Table 2 and FIG. 1, it can be seen that the creep strength increases when the aspect ratio is 4 or more, and reaches the maximum rupture life when the aspect ratio is about 60, reaching saturation.

(2) Compression Creep Test A compression creep test was conducted on the fused body of crystal grains with an aspect ratio of 10 in Example 1 shown in Table 2 so that compressive stress was generated in a direction perpendicular to the extrusion direction. The test conditions were a temperature of 1623 K and a pressure of 49 MPa. The result is the third
It is shown in the table and in FIG.

As a result of the test, when compressive force was applied in the direction parallel to the long axis direction of the crystal grains, the rupture life was approximately 23 times longer than when the compressive force was applied in the direction perpendicular to the short axis direction of the crystal grains. The creep rate was approximately 1/18 times as high. From this, it was found that when a compressive force was applied in the long axis direction (growth direction) of the crystal grains 1, as shown in the schematic diagram in FIG. 3, the rupture life was long and the creep rate was slow.

A skid rail for use in a heating furnace for steel billets was manufactured using the manufacturing method described above. The structure of the skid rail is as shown in FIG. 4, for example. In the skid rail 5, a metal saddle 3 is welded and fixed to a water-cooled skid vibe 2, a skid rail main body 4 is attached to the saddle 3, and a fireproof heat insulating material 6 is coated around the skid pipe 2 and the saddle 3.

In the above examples, the compact formed by hot extrusion was held at high temperature, but in the present invention, after hot isostatic pressing (HIP) a predetermined alloy powder, rolling, casting, forging, etc. It may be heated and maintained at a temperature higher than ℃. Further, after performing vacuum hot pressing (VHP), it may be plastically deformed by rolling, forging, etc., and then heated at 1300° C. or higher to form a secondary recrystallized structure.

(Effects of the Invention) As explained above, according to the method for producing an oxide fractionally strengthened Ni-based alloy of the present invention, a Ni-based alloy having a predetermined composition is produced by a mechanical alloying method, and this alloy is heated. In order to produce a Ni-based alloy with a large secondary recrystallized structure with an average grain aspect ratio of 10 or more by heating after processing, the resulting oxide dispersion-strengthened Ni-based alloy has high heat resistance and thermal shock resistance. It has the effect of becoming a heat-resistant alloy with excellent properties, creep strength, and fracture life.

(Hereafter, margin.)

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing the relationship between aspect ratio and fracture life of oxide dispersion strengthened Ni-based alloys according to examples and comparative examples of the present invention, Fig. 2 is a characteristic diagram showing the creep rate, and Fig. 3 is a characteristic diagram of the present invention. Oxide dispersion strengthened N obtained by the production method of the invention
FIG. 4 is a schematic diagram showing a secondary recrystallized structure of an i-based alloy, and a cross-sectional view showing a skid rail according to an embodiment of the present invention. 1... Crystal grain, 5... Skid rail.

Claims (2)

[Claims] (1) An alloy whose composition is Cr: 18 to 40%, Fe: 5% or less, Al: 5% or less, Ti: 5% or less, and the balance is substantially Ni, and which grows crystal grains. An oxide dispersion strengthened Ni-based alloy characterized in that the average value of the aspect ratio of crystal grains is 10 or more. (2) An alloy having a composition in weight% of Cr: 18 to 40%, Fe: 5% or less, Al: 5% or less, Ti: 5% or less, and the balance is substantially Ni, and is processed by mechanical alloying method. The oxide dispersion strengthened Ni-based alloy produced in 13
1. A method for producing an oxide dispersion strengthened Ni-based alloy, which comprises heating at 00° C. or higher to grow crystal grains so that the average aspect ratio of the crystal grains is 10 or higher.