JPH0598397A - Ferrous heat resistant alloy excellent in high temperature corrosion resistance - Google Patents

Abstract

PURPOSE:To provide an ferrous heat resistant allay excellent in high temp. corrosion resistance at low cost. CONSTITUTION:This alloy is an ferrous heat resistant allay having a compsn. contg., by weight, 25.0 to 35.0% Ni, 19.0 to 25.0% Cr, 2.5 to 3.5% Al, 0.15 to 0.60% Ti <=1.5% Mn, <=1.0% Si, <=0.75% Cu, <=0.10% C and <=0.05% S, furthermore contg. 0.005 to O.050% Y and the balance Fe with inevitable impurities and excellent in high temp. corrosion resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Fe-based heat-resistant alloys for producing reformer parts for fuel cells, various industrial furnace parts, such as heat treatment furnace trays and muffles, which are required to have high-temperature corrosion resistance. It is a thing.

[0002]

2. Description of the Related Art Conventionally, in order to manufacture a reformer part for a fuel cell and an in-furnace part for a heat treatment furnace, Cr: 21.0% by weight (hereinafter,% relating to the component composition indicates weight%). 25.0%, Fe: 7.0 to 20.0%, Mn: 1.5% or less, Al: 1.0 to 1.7% or less, C: 0.10% or less, Cu: 1.0% Hereinafter, Ni: Si: 0.5% or less, S: 0.015% or less, and the balance Ni consisting of Ni and unavoidable impurities
A base heat resistant alloy is used.

This Ni-base heat-resistant alloy has excellent high-temperature corrosion resistance and is widely used, but it is expensive because it contains a large amount of Ni in an amount of 58% or more.
In recent years, in place of the Ni-based heat-resistant alloy, Ni: 30.0 to 35.0%, Cr: 19.0 to 23.0%, Al: 0.15 to 0.60%, Ti: 0.15 to 0.60%, Si: 1.0% or less, Cu: 0.75% or less, C: 0.05 to 0.10% or less, S: 0.015% or less, and the balance is Fe and unavoidable. Inexpensive Fe-based heat-resistant alloys made of impurities have come to be used.

[0004]

However, the above-mentioned conventional F
Since the e-base heat-resistant alloy has insufficient properties as a high-temperature corrosion resistance material, it cannot be used as a material at a location requiring reliability especially for high-temperature corrosion resistance.

The above conventional Ni-base heat-resistant alloy and conventional F
Looking at the high temperature corrosion state of the e-base heat-resistant alloy, as shown in FIG. 1, a grain boundary corrosion layer 2 is generated under the black scale layer 1 on the surface, and the growth of the grain boundary corrosion layer 2 causes corrosion inside. And the intergranular corrosion layer 2 of the conventional Fe-based heat-resistant alloy
The growth rate of the intergranular corrosion layer 2 of the conventional Ni-based heat-resistant alloy is
It has also been found that the conventional Fe-based heat-resistant alloy is inferior in high-temperature corrosion resistance to the conventional Ni-based heat-resistant alloy because of its higher growth rate.

[0006]

Therefore, the present inventors have
As a result of conducting research to produce an inexpensive Fe-based heat-resistant alloy that is excellent in high-temperature corrosion resistance and suppresses the growth of the intergranular corrosion layer, the Al content of the conventional Fe-based heat-resistant alloy is 2.5 to
The growth of the intergranular corrosion layer 2 can be extremely reduced by increasing the amount to 3.5%, and further adding 0.005-0.05% yttrium (hereinafter referred to as Y), which is extremely excellent. We have obtained the knowledge that high temperature corrosion resistance can be imparted.

The present invention has been made on the basis of such knowledge, and Ni: 25.0 to 35.0%, Cr: 19.0 to 25.0%, Al: 2.5 to 3.5%. , Ti: 0.15 to 0.60%, Mn: 1.5% or less, Si: 1.0% or less, Cu: 0.75% or less, C: 0.10% or less, S: 0.005% The Fe-based heat-resistant alloy is characterized by containing the following, and further containing Y: 0.005 to 0.050% and the balance of Fe and inevitable impurities.

Next, the reason why the composition of the Fe-based heat-resistant alloy of the present invention is limited as described above will be explained.

(A) Ni Ni is an element that forms a solid solution in the Fe matrix to stabilize the austenite matrix and improve the high temperature corrosion resistance. However, if its content is less than 25.0%, the desired effect is obtained. On the other hand, even if the content exceeds 35.0%, only by raising the alloy price, there is little further improvement effect on high temperature corrosion resistance.

Therefore, the Ni content is 25.0 to 3
It was set to 5.0%.

(B) Cr Cr is an element which improves the high temperature corrosion resistance and further improves the high temperature strength by the intermetallic compound such as chromium carbide. If the content thereof is less than 19.0%, the high temperature oxidation resistance is high. The effect is reduced, which is not preferable. On the other hand, when the content exceeds 25.0%, the hot workability is deteriorated, which is not preferable.

Therefore, the Cr content is 19.0-2.
It was set to 5.0%.

(C) Al Al is an element that is added together with Y to improve the high temperature corrosion resistance, but if the content is less than 2.5%, the desired effect cannot be obtained, while on the other hand, 3.5% is added. If it is contained in excess, the hot workability is deteriorated, which is not preferable.

Therefore, the Al content is 2.5 to 3.
It was set to 5%.

(D) Ti Ti is an element that improves the high temperature strength, but if its content is less than 0.15%, it is not preferable because it is less effective, while if it exceeds 0.60%, it is hot. It is not preferable because the workability deteriorates.

Therefore, the Ti content is 0.15 to 0.
It was set at 60%.

(E) Mn Mn is a component usually added as a desulfurizing agent,
If its content exceeds 1.5%, the corrosion resistance is deteriorated, which is not preferable.

Therefore, the Mn content is set to 1.5% or less.

(F) Si Si is an effective component as a deoxidizing agent, but if its content exceeds 1.0%, hot workability and weldability deteriorate, which is not preferable.

Therefore, the Si content is set to 1.0% or less.

(G) Cu Cu is an element which is extremely effective in corrosion resistance when added in a trace amount, but it is not preferable because it contains more than 0.75% because it lowers the high temperature corrosion resistance.

Therefore, the Cu content is set to 0.75% or less.

(H) When C exceeds 0.10%, Ni ₆ C and Cr ₆ are contained.
Carbides such as C remarkably increase, and the ductility and toughness of the alloy are impaired, which is not preferable.

Therefore, the C content is set to 0.10% or less.

(I) S S is an element that is inevitably mixed in, and if a large amount is present in the alloy, it deteriorates the hot workability due to grain boundary segregation and also deteriorates the corrosion resistance. It was set to 005% or less.

(J) Y Y is an element which is contained together with Al: 2.5 to 3.5% to prevent the progress of intergranular corrosion, but its content is 0.00
If it is less than 5%, the desired effect cannot be obtained, while 0.00
If the content exceeds 5%, hot workability and weldability deteriorate, which is not preferable.

Therefore, the Y content is 0.005 to
It was set to 0.05%.

[0028]

EXAMPLES Next, the present invention will be specifically described based on Examples.

Invention F of the component composition shown in Tables 1 to 4
e-base heat-resistant alloy (hereinafter referred to as the present invention alloy) 1 to 30, comparative Fe-base heat-resistant alloy (hereinafter referred to as the comparative alloy) 1 to 9, conventional Ni-based heat-resistant alloy 1 (hereinafter referred to as conventional alloy 1) and conventional Fe-based heat-resistant Alloy 2 (hereinafter referred to as conventional alloy 2) was melted and cast to prepare an ingot, which was ingot-forged and then rolled to prepare a rolled plate having a thickness of 2 mm.
This rolled plate was cut into a length of 20 mm and a width of 30 mm to prepare a test piece.

A step of placing the above test piece in an electric furnace, keeping it in the air at a temperature of 1150 ° C. for 30 minutes, and then cooling it in air was defined as one step, and this step was repeated 20 times to perform a high temperature corrosion resistance test. ..

The test piece subjected to such a high temperature corrosion resistance test was embedded in an epoxy resin, fixed, cut at the center, and the cut surface was polished and observed with a metallurgical microscope. The thickness of the scale layer 1 shown in FIG. And the total thickness of the intergranular corrosion layer 2 were measured as the amount of corrosion (mm), and the values of the measured amounts of corrosion are shown in Tables 1 to 4.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4] From the results shown in Tables 1 to 4, the alloys of the present invention 1 to 30
It can be seen that is excellent in high temperature corrosion resistance because the corrosion amount is extremely smaller than that of the conventional alloys 1 and 2. Further, Comparative Alloy 1 whose composition was out of the conditions of the present invention
It can be seen that the corrosion amount is increased and the high temperature corrosion resistance is also deteriorated even when the composition is out of the conditions of the present invention (indicated by a mark *).

In order to more clearly show whether the alloy of the present invention is superior to the conventional alloy in corrosion resistance at high temperature, the alloy of the present invention 3 in Table 1, the conventional alloy 1 and the conventional alloy 2 in Table 4 are shown. The cross-section metallographic micrograph (X400) of the test piece after the high temperature corrosion resistance test was taken, and the photographs are shown in FIG.
Posted in FIG.

As is clear from the metallographic micrographs of the cross sections of the test pieces in FIGS. 2 to 4, the conventional alloy 1 (conventional Ni-base heat-resistant alloy) showed a grain boundary corrosion layer, and the conventional alloy 2 (conventional Fe).
It can be seen that a larger intergranular corrosion layer is found in the (base heat-resistant alloy), whereas the intergranular corrosion layer is hardly seen in the alloy of the present invention, which shows extremely high temperature corrosion resistance.

[0038]

Industrial Applicability Since it is possible to provide an Fe-based heat-resistant alloy that is inexpensive and has excellent corrosion resistance at extremely high temperatures, it is possible to reduce the cost of high-temperature industrial furnace parts such as fuel cell reformer parts and heat treatment furnaces. It has excellent effects.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a corrosion state of a conventional Ni-based heat-resistant alloy or Fe-based heat-resistant alloy after a high-temperature corrosion resistance test.

FIG. 2 is a metallographic micrograph of a cross section of the Fe-based heat-resistant alloy of the present invention after a high-temperature corrosion resistance test.

FIG. 3 is a metallographic micrograph of a cross section of a conventional Ni-base heat-resistant alloy after a high-temperature corrosion resistance test.

FIG. 4 is a metallographic micrograph of a cross section of a conventional Fe-based heat-resistant alloy after a high-temperature corrosion test.

[Explanation of symbols]

 1 Scale layer 2 Intergranular corrosion layer

Claims (1)

[Claims] 1. By weight%, Ni: 25.0 to 35.0%, Cr: 19.0 to 25.0% Al: 2.5 to 3.5%, Ti: 0.15 to 0.60 %, Mn: 1.5% or less, Si: 1.0% or less, Cu: 0.75% or less, C: 0.10% or less, S: 0.005% or less, and Y: An Fe-based heat-resistant alloy excellent in high-temperature corrosion resistance, characterized in that it contains 0.005 to 0.050% and the balance is Fe and inevitable impurities.