JPS60238442A - Heat and corrosion resistant alloy - Google Patents

Abstract

PURPOSE:To obtain a heat and corrosion resistant alloy having improved resistance to corrosion and stress corrosion cracking at high temp. at a low cost by reducing the amount of Co in a conventional heat and corrosion resistant Cr- Ni-Co-Fe alloy and increasing the amount of Cr. CONSTITUTION:This heat and corrosion resistant alloy consists of <=0.1% C, <=1% Si, <=1% Mn, 40-48% Ni, 20-30% Cr, 6-16% Co, 2-4% Mo, >2-4% Ti, <=0.5% Al, <=0.05% Zr, <=0.01% B and the balance Fe. The alloy has improved resistance to corrosion and stress corrosion cracking at high temp. as compared with a conventional alloy. It has satisfactory strength at high temp., the forgeability and machinability are comparable to those of the conventional alloy, and the cost is reduced because of the reduced Co content.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a heat-resistant and corrosion-resistant alloy that has high corrosion resistance at high temperatures and high strength, and is mainly applied to high-temperature bolt materials and dynamic materials of gas turbines and steam turbines. Cr −
The present invention relates to a Ni-Co-Fe-based heat-resistant and corrosion-resistant alloy.

[Background technology]

In gas turbines and steam turbines, precipitation hardening type C! shown in Table 1 is used for bolt materials and blade materials used at temperatures of approximately 500°C or higher. r-Ni-Co-Fe alloys may be used.

Table 1 Composition of 0r-Ni-Co-Fe alloys However, these alloys contain approximately 20% of Cr, resulting in high costs. Stress corrosion cracking properties in high-temperature water with 1 ions and dissolved oxygen are insufficient.

[Object of the present invention]

Therefore, the present invention has a higher carbon content than the conventional alloy shown in Table j above.
o By reducing the amount, the cost can be reduced. Or By increasing the amount, the corrosion resistance and stress corrosion cracking characteristics at high temperatures are improved, and the strength at high temperatures is also sufficient, and the forgeability and machinability are also the same as before. Or -Ni is comparable to the alloy of
An object of the present invention is to provide a -Co-Fe-based heat-resistant and corrosion-resistant alloy.

[Configuration of the present invention]

The present invention, as a means to achieve the above object, sets the amount of Co to about % in the conventional alloy mentioned above, and also
The point is to set the amount of r to 20 to 30%. That is, the present invention provides CO 1% or less, 811% or less, Mn 1% or less, Ni 40-4B, Or 20-50%, CO 6
~16q6, M.

2-4%, Ti more than 2°0% and less than 4%, AtO, 5
This is a heat-resistant and corrosion-resistant alloy containing ZrO, 0.5% or less, BQ, 0.1% or less, and the remainder Fe and non-wallable impurities.

The range limitation of each element of the alloy in the present invention and the reason therefor will be explained in detail below.

C is necessary for improving high temperature strength, but in the present invention, CD,
It should contain 1% or less, but if it is too small, the effect of improving high temperature strength will be small, and if it exceeds 0.1%,
Chromium carbide CM230s type (M is O
Indicates r, MO, etc. )] is precipitated in excess, which impedes corrosion resistance and stress corrosion cracking resistance, and also reduces ductility, so in the present invention, (!0.1% or less,
Preferably it contains 0.01 to (L1%).

Sl and Mn have a deoxidizing effect and are effective in cleaning this type of alloy. However, in the present invention, the vacuum melting method may be adopted, and the elements are not necessarily necessary, and if the amount is too large, the high temperature strength (creep rupture strength) and ductility (creep rupture elongation) will decrease, and the Machinability also decreases. Therefore, in the present invention, −81 and M
The content of both elements n is 1 or less.

N1 is the precipitation hardening phase of the alloy N15 (At, TI) [
It is called the γ′ phase. ] is necessary to precipitate
Furthermore, if the Cr content is 20% or more, σ)11], an intermetallic compound that inhibits strength and ductility, is likely to occur, but 40% or more is required to suppress the precipitation of this σ phase. . Further, Ni improves corrosion resistance and stress corrosion cracking resistance in coexistence with Or. However, Ni 4
Even if a large amount of N1 is contained, the effect is not significantly improved, and in consideration of economic efficiency, the N1 content is set to 40 to 48% in the present invention.

Coexisting with N1, Cr improves corrosion resistance and stress corrosion cracking as the amount increases, but when the amount exceeds 20%, the effect becomes significant. However, when it exceeds 30, hot workability (forgeability) deteriorates, and during long-term use at high temperatures, the σ phase, which is an intermetallic compound, tends to precipitate, resulting in a decrease in creep rupture strength and ductility. do. Therefore, in the present invention,
The Or content is 20 to 30%.

Co stabilizes the austenite phase of the matrix, and in the solid solution treatment of the alloy, the precipitated phase γ' phase (Ni, 3
(At, Ti)] is easily dissolved in solid solution, and during aging treatment, this γ' phase is uniformly precipitated to improve creep rupture strength1.Also, CO is Cr.

Coexistence with N1 also improves corrosion resistance. In the present invention,
The Co content is set to 6 to 16%, and the above effect becomes noticeable when the Co content is 6% or more, but if a large amount is added, the effect does not improve further, and it is not economically viable. Since this is disadvantageous, the upper limit is set at il-16%.

Mo2, as a solid solution strengthening element, improves high temperature strength, but the effect is insufficient in small amounts such as 2%. On the other hand, 4
Even if a large amount of MO is added, the effect will not become significant, and on the contrary, it will promote the precipitation of the σ phase, which is a harmful intermetallic compound. It is something to do.

T1 is the γ' phase (Ni3 (At), which is a precipitated phase that is absolutely necessary for improving high-temperature strength in this type of alloy.

T1)]. T1 amount is 2
If it is less than 4%, the high temperature strength will not be improved sufficiently, and if too much is added, hot workability will become difficult, so the content should be 4 or less. That is, in the present invention, the Ti content is reduced to 2
．． It shall be more than 0% and less than 4%.

At forms a γ' phase (Ni3(At, Ti):l, which prevents the tendency of coarsening during long-term use at high temperatures, that is, improves the stability of the γ' phase and improves high-temperature strength. Although it is effective, in the present invention, it contains 0.5% or less, preferably 6-1 o, i to 0.5%. Even if a large amount is added, the effect is not significant and hot workability is inhibited, so the upper limit is set at 0.5% or less.

Zr strengthens grain boundaries and improves high temperature strength (creep rupture strength) and ductility (creep rupture elongation), but in the present invention, the Zr content is set to 0.05% or less, preferably 0. The content should be between .005% and .005%.

This is because the above effects are not sufficient if it is less than 0.005%.
Also, even if too much is added, the effect will not be noticeable,
On the other hand, non-metallic inclusions such as zirconium nitride are formed and the ductility is reduced, so the upper limit is set at 0.05%.

Like Zr, B is also an effective element for strengthening grain boundaries and improving high temperature strength (creep rupture strength), but in the present invention, this B content is set to 0.01% or less, Preferably it is o, o o i to 0.01 h. The above effect becomes noticeable when o, oo is 1% or more, but if too much is added, hot workability is inhibited, and
Since it forms borides and reduces ductility, the upper limit should be set to 0.
．． 01ch.

The range limitations of each component element of the alloy in the present invention and the reasons therefor have been explained in detail above. However, the alloy in the present invention contains non-wallable impurities, that is, impurity elements that cannot be avoided in this type of alloy, such as P, S, Ag
, Pb, Ou, 8n.

It also contains a very small amount of Sb.

Hereinafter, the present invention will be explained in detail by giving examples of the present invention.

〔Example〕

The alloy composition shown in Table 2 was melted by vacuum high frequency melting to 20K.
g ingot is melted and hot-prepared to about 65 g ingot.
It was forged into a bar with dimensions of φmm x 1500tmm.

Next, these bars were subjected to the heat treatment shown in Table 6, tensile tests were carried out at room temperature and 570°C, and cuff tests were conducted at a temperature of 570°C.
kg7m-, creep rupture test, stress corrosion cracking property test (a tensile stress of 1 to 2 times the normal temperature proof stress of the material was applied in boiling 42% magnesium chloride water, and evaluated by the rupture time), high temperature corrosion test ( 90% Na25o4 +
20 at 800°C in a corrosive medium of 10% kJact
hr and evaluated based on the maximum corrosion depth. ) was carried out.

Table 3 Heat treatment of test materials The results are shown in Table 4.

As is clear from Table 4, the alloy composition of the present invention has a comparative material (
Compared to conventional alloys, the Cr content has been increased and the CO content has been reduced, but in all tests it was found to be an excellent alloy, especially in stress corrosion cracking property tests and high temperature corrosion tests. It became clear that

[Effects of the present invention]

As detailed above, the present invention is based on the conventional Or-Ni
-Co -Fe-based alloys with lower co content,
Since it has an increased amount of r, it has the effect of improving corrosion resistance and stress corrosion cracking characteristics at high temperatures.Moreover, it has sufficient strength at high temperatures, and has better forgeability and machinability than conventional products. The effect is comparable to that of the seed alloy.Furthermore, by reducing the cotft, remarkable effects such as cost reduction are produced.

Among the sub-agents: 1) Akira Sub-agent Ryo Hagi Hara -

Claims (1)

[Claims] co 1% or less, sl 1% or less, Mn 1% or less, N
i40~48%, Cr 20~30chi, 006~16%
, Mo 2-4%, T greater than 12.0% and less than 4%, At
A heat-resistant and corrosion-resistant alloy containing O, 5% or less, ZrO, 05% or less, B O, 01% or less, and the balance Fe and non-wallable impurities.