JP6805583B2 - Manufacturing method of precipitation type heat resistant Ni-based alloy - Google Patents

Description

The present invention relates to a method for producing a precipitation type heat resistant Ni-based alloy.

Conventionally, a precipitation type heat-resistant Ni-based alloy used in a high temperature environment is required to exhibit excellent strength characteristics at a high temperature. Since this requirement can be satisfied when the grain size of the crystal grains constituting the alloy is large, the precipitation type heat-resistant Ni-based alloy is usually annealed at a high temperature for a long time.
Regarding the annealing method for Ni-based heat-resistant alloys, conventionally, for example, the methods described in Patent Documents 1 and 2 have been proposed.

Japanese Unexamined Patent Publication No. 2000-64005 Japanese Patent No. 5652730

Here, even if the precipitation-type heat-resistant Ni-based alloy is subjected to continuous brightness annealing at a high temperature for a long time instead of batch annealing, the crystal grain size becomes large. However, in order to carry out high-temperature and long-term treatment by continuous annealing, it is usually necessary to carry out the treatment at a low speed, so that the cooling speed is inevitably slowed down, and as a result, precipitates are likely to be generated. When precipitates are formed, they become hard and difficult to process.
For example, a final product may be obtained by annealing, processing, and then aging treatment to generate precipitates to increase hardness, but such treatment becomes extremely difficult.

An object of the present invention is to solve the above problems.
That is, an object of the present invention is that even if heat treatment is performed at a high temperature for a long time so that the crystal grain size can be greatly grown by the continuous annealing method, the generation of precipitates is suppressed after annealing and the processing is easy. It is an object of the present invention to provide a method for producing a precipitation type heat-resistant Ni-based alloy, which can obtain a precipitation-type heat-resistant Ni-based alloy.

The present inventor has made diligent studies to solve the above problems and completed the present invention.
The present invention is the following (1) to (3).
(1) The first step of holding the Ni-based alloy at a temperature of 1000 to 1200 ° C. for 5 to 60 minutes and then cooling it to room temperature at a cooling rate of 0.3 to 10 ° C./sec.
Then, after holding at a temperature of 1000 to 1200 ° C. for 0.5 to 10 minutes, the second step of cooling to room temperature at a cooling rate of 3 to 40 ° C./sec, and
The precipitation rate of the second step is faster than the cooling rate of the first step, and the holding time of the second step is shorter than the holding time of the first step. Mold Heat resistant Ni-based alloy manufacturing method.
(2) The method for producing a precipitation-type heat-resistant Ni-based alloy according to (1) above, which is carried out in a continuous annealing furnace.
(3) The method for producing a precipitation-type heat-resistant Ni-based alloy according to (1) or (2) above, wherein the Ni-based alloy is steel strip.

According to the present invention, even if heat treatment is performed at a high temperature for a long time so that the crystal grain size can be greatly grown by the continuous annealing method, the generation of precipitates is suppressed after annealing and the precipitation type is easy to process. It is possible to provide a method for producing a precipitation type heat-resistant Ni-based alloy, which can obtain a heat-resistant Ni-based alloy.

The production method of the present invention will be described.
The production method of the present invention includes a first step and a second step. Moreover, the first step and the second step are continuous.

<First step>
The first step will be described. In the first step, a Ni-based alloy is first prepared.
The Ni-based alloy is an alloy based on Ni and containing Cr, Ti, Al, Nb and the like.
The Ni-based alloy is preferably a material used to obtain a conventionally known precipitation-type heat-resistant Ni-based alloy in which the hardness is increased by combining Cr, Ti, Al, Nb and the like with Ni.

Examples of the Ni-based alloy include C: 0.02 to 0.10% by mass, Si: 0.15% by mass or less, Mn: 0.10% by mass or less, P: 0.015% by mass or less, S: 0. .015% by mass or less, Cr: 18.0 to 21.0% by mass, Fe: 2.0% by mass or less, Mo: 3.5 to 5.0% by mass, Cu: 0.10% by mass or less, Al: 1.20 to 1.60% by mass, Ti: 2.75 to 3.25% by mass, B: 0.003 to 0.010% by mass, Co: 12.0 to 15.0% by mass, Zr: 0. Examples include those having a composition of 02 to 0.08% by mass, Pb: 0.0005% by mass or less, Bi: 0.00003% by mass or less, Se: 0.0003% by mass or less, and Ni: the balance.

Examples of Ni-based alloys other than the above include C: 0.08% by mass or less, Si: 0.50% by mass or less, Mn: 1.00% by mass or less, P: 0.030% by mass or less, S. : 0.015% by mass or less, Ni: 70.00% by mass or more, Cr: 14.0 to 17.0% by mass, Fe: 5.00 to 9.00% by mass, Cu: 0.50% by mass or less, Examples thereof include those having a composition of Al: 0.40 to 1.00% by mass, Ti: 2.25 to 2.75% by mass, and Nb + Ta: 0.70 to 1.20% by mass.

Examples of Ni-based alloys different from the above include C: 0.08% by mass or less, Si: 0.35% by mass or less, Mn: 0.35% by mass or less, P: 0.015% by mass or less, S: 0.015% by mass or less, Ni: 50.00 to 55.00% by mass, Cr: 17.0 to 21.0% by mass, Mo: 2.80 to 3.30% by mass, Cu: 0.30 Mass% or less, Al: 0.25 to 0.80 mass%, Ti: 0.65 to 1.15 mass%, Nb + Ta: 4.75 to 5.50 mass%, B: 0.006 mass% or less, Fe : Those having the composition of the balance can be mentioned.

Examples of Ni-based alloys different from the above include C: 0.04 to 0.08% by mass, Si: 0.40% by mass or less, Mn: 0.60% by mass or less, and P: 0.020% by mass. % Or less, S: 0.015% by mass or less, Cr: 19.0 to 21.0% by mass, Fe: 0.70% by mass or less, Mo: 5.6 to 6.1% by mass, Cu: 0.20 Mass% or less, Al: 0.30 to 0.60 mass%, Ti: 1.9 to 2.4 mass%, B: 0.005 mass% or less, Co: 19.0 to 21.0 mass%, Ni : Those having the composition of the balance can be mentioned.
Some of the above alloys are included in the JIS G 4902 standard, and the present invention can be applied to alloys of the JIS G 4902 standard other than those included.

The reasons for adding each component in the Ni-based alloy are as follows.

C has the effect of increasing the strength of the grain boundaries. When C is excessively contained, coarse carbides are formed, which reduces the strength and hot workability. The above-mentioned amount of C is used in consideration of such effects and the balance with other additive elements.

Cr is an element that improves oxidation resistance and corrosion resistance. When Cr is excessively contained, an embrittled phase such as a σ phase is formed, and the strength and hot workability are lowered. The amount of Cr added is set in consideration of such effects and the balance with other additive elements.

Co improves the stability of the composition and makes it possible to maintain its hot workability even when the alloy contains a large amount of Ti, which is a reinforcing element. As the amount of Co increases, the hot workability improves, but when it becomes excessive, harmful phases such as σ phase and η phase are formed, and the strength and hot workability decrease. The above-mentioned amount of Co is used in consideration of such effects and the balance with other additive elements.

Al is an essential element that forms a γ'(Ni ₃ Al) phase, which is a strengthening phase, and improves high-temperature strength. Excessive addition reduces hot workability and causes material defects such as cracks during processing. The above-mentioned amount of Al is used in consideration of such effects and the balance with other additive elements.

Like Al, Ti is also an essential element that forms a γ'phase and strengthens the γ'phase by solid solution to increase high-temperature strength. Excessive addition causes the γ'phase to become unstable at high temperatures, leading to coarsening at high temperatures, forming a harmful η (eta) phase, and impairing hot workability. The above-mentioned Ti addition amount is used in consideration of such effects and the balance with other additive elements.

Mo contributes to the solid solution strengthening of the matrix and has the effect of improving the high temperature strength. When Mo is excessive, an intermetallic compound phase is formed, which impairs high-temperature strength. The amount of Mo added is determined from the balance between such effects and other additive elements.

B is an element that improves grain boundary strength and improves creep strength and ductility. B has a large effect of lowering the melting point. Further, when a coarse boride is formed, the processability is hindered. The amount of B added is set from the viewpoint of such effects and the balance with other additive elements.

Like B, Zr has the effect of improving the grain boundary strength. When Zr is excessive, the melting point is lowered, and high temperature strength and hot workability are impaired. The amount of Zr added is determined from the balance between such effects and other additive elements.

The method for producing the Ni-based alloy is not particularly limited. For example, the raw material can be prepared, melted, and cast so as to contain a specific chemical component (composition) as described above. By applying the vacuum melting method, it is possible to suppress the oxidation of active elements such as Al and Ti and reduce inclusions. In order to obtain a higher quality Ni-based alloy, secondary and tertiary melting such as electroslag redissolving and vacuum arc redissolving may be performed. Further, after melting, preliminary processing such as hammer forging, press forging, rolling, and extrusion may be performed.

The shape and size of the Ni-based alloy are not particularly limited.
The Ni-based alloy is preferably strip steel. This is because it is suitable for continuous annealing.

In the first step, the Ni-based alloy as described above is held at a temperature of 1000 to 1200 ° C. for 5 to 60 minutes.

Here, the temperature at which the Ni-based alloy is heated is 1000 to 1200 ° C., preferably 1050 ° C. or higher. This is because at such a temperature, the size of the crystal grains tends to be larger.

The time for holding the Ni-based alloy at the above temperature is 5 to 60 minutes, preferably 10 minutes or more. This is because the size of the crystal grains tends to be larger at such a time.

In the first step, as described above, the Ni-based alloy is held at a temperature of 1000 to 1200 ° C. for 5 to 60 minutes, and then cooled to room temperature at a cooling rate of 0.3 to 10 ° C./sec.

<Second step>
After the Ni-based alloy is treated by the first step as described above, it is continuously treated in the second step.

In the second step, the Ni-based alloy after being subjected to the first step is held at a temperature of 1000 to 1200 ° C. for 0.5 to 10 minutes.

The heating temperature here is 1000 to 1200 ° C., preferably 1050 ° C. or higher. When heated at such a temperature, the precipitate generated due to the slow cooling rate in the first step can be solidified again.

The time for holding the Ni-based alloy after being subjected to the first step at the above temperature is 0.5 to 10 minutes, preferably 1 to 5 minutes, and preferably about 2 minutes. Is more preferable. Here, the holding time of the second step is shorter than the holding time of the first step.

In the second step, as described above, the Ni-based alloy is held at a temperature of 1000 to 1200 ° C. for 0.5 to 10 minutes, and then cooled to room temperature at a cooling rate of 3 to 40 ° C./sec.

Here, the cooling rate of the second step is made faster than the cooling rate of the first step. In this case, it is preferable because precipitation is less likely to occur.

The production method of the present invention is preferably carried out in a continuous annealing furnace.

As described above, in the production method of the present invention, two consecutive annealings are performed. The crystal grains are enlarged by the first continuous annealing at a low speed (low-speed sheeting). Since the cooling rate is slow here, the hardness increases due to precipitation hardening during cooling. Then, the precipitate is solidified again by the second continuous annealing at a high speed (high-speed passing plate), and the cooling rate is increased to prevent precipitation hardening, thereby reducing the hardness.

The raw materials were mixed so as to have the composition shown in Table 1 below, and melted in a vacuum melting furnace. Then, it was redissolved using an electroslag remelting furnace, and the obtained steel pieces were hot-rolled and cold-rolled to obtain a test piece having a plate thickness of 0.2 mm. This test piece corresponds to a Ni-based alloy in the production method of the present invention.

<Example>
First, the obtained test pieces were subjected to the following continuous annealing.
In this continuous annealing, the test piece is held at a temperature of 1130 ° C. for 10 minutes, cooled to room temperature at a cooling rate of 2 ° C./sec, and then held again at a temperature of 1130 ° C. for 2 minutes, and then 9 ° C./. It is a process of cooling to room temperature at a cooling rate of seconds.
The product obtained by subjecting the test piece to such continuous annealing is referred to as "Sample 1" below.

<Comparison example>
Next, the other test piece obtained was subjected to the following continuous annealing.
This continuous annealing is a process in which the test piece is held at a temperature of 1130 ° C. for 10 minutes and then cooled to room temperature at a cooling rate of 2 ° C./sec.
The product obtained by subjecting the test piece to such continuous annealing is referred to as "Sample 2" below.

The hardness, tensile strength, and elongation of the obtained Samples 1 and 2 were measured.
Each measurement method is described below.

<Hardness>
Hardness (Hv) was measured according to JIS Z 2244 (Vickers hardness test method). The measurement results are shown in Table 2.

<Tensile strength, elongation rate>
JIS Z 2 2 41 subjected to a tensile test according to (metal tensile test method), tensile strength of the (N / mm ²⁾ and elongation (%) were measured. The measurement results are shown in Table 2.

Comparing the sample 1 which is within the scope of the present invention and corresponds to the example and the sample 2 which is outside the scope of the present invention and corresponds to the comparative example, the sample 1 has a lower hardness than the sample 2 and is tensile. The strength is also low. The reason for this is considered to be that in the case of the example in which the annealing is performed twice, the precipitate dissolves during the second annealing and the material is softened. Such a softened material is preferable in that it can be easily processed. On the other hand, in the case of sample 2, since the heat treatment temperature is high and the plate passing speed is slow, precipitates are deposited during cooling. Therefore, the material is hard and difficult to process thereafter.

Claims (2)

The first step of holding the Ni-based alloy at a temperature of 1000 to 1200 ° C. for 5 to 60 minutes and then cooling it to room temperature at a cooling rate of 0.3 to 10 ° C./sec.
Then, after holding at a temperature of 1000 to 1200 ° C. for 0.5 to 10 minutes, the second step of cooling to room temperature at a cooling rate of 3 to 40 ° C./sec, and
Has a cooling rate of the second step is faster than the cooling rate of the first step, and the retention time of the second step is being shorter than the retention time of the first step, continuous A method for producing a precipitation type heat-resistant Ni-based alloy , which is carried out in an annealing furnace . The method for producing a precipitation-type heat-resistant Ni-based alloy according to claim 1, wherein the Ni-based alloy is a strip-shaped plate material.