JPS61163238A - Heat and corrosion resistant alloy for turbine - Google Patents

Abstract

PURPOSE:To obtain an alloy for a turbine having superior heat and corrosion resistances by adding specified amounts of C, Si, Mn, P, S, Ni, Cr, Mo, Ti, Al, B and Cu to Fe. CONSTITUTION:The composition of an alloy for a turbine is composed of, by weight, <0.08% C, <1% Si, <1.5% Mn, <0.03% P, <0.015% S, 35-48% Ni, 18-28% Cr, 0.5-3.5% Mo, 1-3% Ti, 0.1-1% Al, 0.001-0.02% B, <0.25% Cu and the balance Fe with inevitable impurities. The composition may further contain one or more among <2% Co, <0.5% V, <1.5% Nb, <1% W and 0.001-0.1% Zr.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an alloy for turbines having excellent heat resistance and corrosion resistance.

Conventional technology 0r-N shown in Table 1 is a relatively inexpensive heat-resistant and corrosion-resistant alloy for forging used in various parts such as moving blades, stationary blades, bolts, disks, and rotors of gas turbines and steam turbines.
There is an i-Fθ group precipitation hardening alloy.

Interosseous IIIa61-1tiJ”i6 U3) The precipitation hardening alloy shown in Table 1 has a maximum Cr content of approximately 16%, and has excellent oxidation resistance, high temperature corrosion resistance (sulfide corrosion), and stress resistance. Corrosion cracking resistance is insufficient.

In recent years, in order to improve the performance and efficiency of gas turbines, the combustor outlet gas temperature has increased, and as a result, the metal temperature of various high-temperature components has also increased.
Increasingly, inferior fuel containing a large amount of sulfide is being used than ever before. For this purpose, an inexpensive heat-resistant alloy that has excellent oxidation resistance and high-temperature corrosion resistance has become necessary.

On the other hand, in recent years, steam turbines have also improved in performance and efficiency.
Steam temperatures also tend to rise, and metal temperatures also tend to rise accordingly.

566° C.), and the precipitation hardening type alloy shown in Item 1 above is increasingly being used. Materials for high-temperature parts of steam turbines are selected based on the maximum metal temperature, but the temperature distribution within the same member is uneven, and even within the same member, the temperature is relatively low between 40℃ and 400℃ There may be long-term exposure to environments containing substances. Under such an environment, it has become necessary for austenitic alloys such as Fe-based precipitation hardening alloys to have excellent stress corrosion cracking resistance.

This Fθ-based heat-resistant alloy has excellent oxidation resistance, high-temperature corrosion resistance,
Alternatively, in order to improve stress corrosion cracking resistance, it is effective to contain a large amount of Cr. However, when this type of alloy contains a large amount of Cr, intermetallic compounds such as σ phase precipitate when used at high temperatures for a long period of time, resulting in poor high-temperature strength such as creep strength and creep rupture strength, and impact properties. Sexuality decreases.

In order to prevent precipitation of the σ phase, which is the problem to be solved by the present invention, it is effective to increase the amount of Ni in a Fe-based precipitation hardening alloy. As a result of intensive research, the present inventors discovered the γ' phase (Nis(A4Ti>)) which provides high-temperature strength of this type of alloy.
precipitation hardening effect of Mo.

With the increase in Cr content and Cr amount, which is effective for sufficiently improving oxidation resistance, high-temperature corrosion resistance, and stress corrosion cracking resistance, without hindering solid solution strengthening effects such as w, iib, v, and z, precipitation The present invention was based on the discovery of an N1 content that is effective in preventing the precipitation of the harmful intermetallic compound σ phase, which tends to increase. In addition, in the present invention alloy, M, which is an expensive element, is
o.

W, V, Nb, Co, etc. should be kept as small as possible within a few pieces, and C
Properties are improved by adding relatively inexpensive elements such as r and NiZ.

Means for Solving the Problems The present invention has the following features in terms of weight: C: 108% or less, 81: 1% or less, Mn: 1.5% or less, P: (103 cm or less, S:
0.015 cm or less, Ni: 35-48%, Cr = 1
8~28eIIj%Mo: 0.5~! L5qb1T1
: 1~3%, Mut: CL1~1%, B: 0.0
The present invention relates to a heat-resistant and corrosion-resistant alloy for a turbine, characterized in that it contains O2%, Cu: 0.25% or less, and the remainder consists of Fθ and unavoidable impurities.

Furthermore, the present invention allows the above composition to contain rare earth elements: 0.1% or less, Oa: 0.1qb or less, Mg: 0.1% or less, or Fi, co: 2% or less, v: o ,
S chi or less, N'b: 1.5 or less, W: 1% or less, Z
A heat-resistant and corrosion-resistant alloy for turbines containing one or more of r: 0.001 to α1%, and the latter composition further includes 701% or less of rare earth elements, Oa: 11% or less, Mg: 0
．． The present invention also proposes a heat-resistant and corrosion-resistant alloy for turbines containing 1% or less of one or more kinds.

That is, the characteristics of the alloy of the present invention are that the conventional Fθ shown in Table IK
Based on the chemical composition of the precipitation hardening type alloy, Mo, W,
Cr and N1 without increasing the amount of expensive alloying elements such as V, Mb, and Co'lx.
The addition of relatively inexpensive alloying elements improves the above-mentioned properties (oxidation resistance, high temperature corrosion resistance, stress corrosion cracking resistance), and also improves forgeability and machinability without impairing high temperature strength and toughness. The machinability is also the same as before! It is a precipitation hardening alloy that is comparable to the θ-based precipitation hardening alloy.

The alloy of the present invention has 0. Si, M0. P.S.

Ni, Cr, Mo, Ti, At, B,
0ut - the basic component, and the rest is Fθ, and the others are Sn.

It may also contain inevitable impurities such as As, Sb, and Ag. In addition to the above basic ingredients, rare earth elements:
α1% or less, Oa: 0.1% or less, Mg: [I include upper and lower ratios, or in addition to the above basic components, Oo: 2% or less, ■: α5 or less, Nb: 1.5 or less, W : 1%
, Zr:l11001~[one of N1chi or 1i2
In addition to this latter component, Y:0
．． 1% or less, Oa: 0.1% or less, Mg: α1 or less.

Various elements related to the alloy of the present invention will be explained below.

o: Necessary for improving cFi high temperature strength, but 0. O
If it exceeds 8%, chromium carbide (MhsCg
(M is Cr, Mo, W, etc.) precipitates excessively and impairs high temperature corrosion resistance and stress corrosion cracking resistance, and also reduces ductility and toughness, so it is set to aOa or less. However, 101
If it is less than %, the effect is small, so it is preferable that α01
~0.08chi.

Ni: Ni is the precipitation hardening phase Ni3 (A4 T
i) Necessary for total precipitation (referred to as γ' phase), and if Cr content is 18% or more, σ phase, which is composed of intermetallic compounds that inhibit high-temperature strength and toughness, is likely to occur. However, in order to suppress the precipitation of this σ phase, t is required to be 35 or more. In addition, N1 improves high temperature corrosion resistance and stress corrosion cracking resistance in coexistence with Cr.

However, even if the N1 content exceeds 48%, no significant improvement in the effect was observed.
Let's say 48chi.

Cr: The more Cr coexists with N1, the more Cr increases.

It improves high-temperature corrosion resistance and stress corrosion cracking resistance, and the effect becomes noticeable from 18% or higher. However, if it exceeds 28%, hot workability (forgeability) deteriorates, and the σ phase formed by intermetallic compounds tends to precipitate during long-term use at ^ temperature9, high temperature strength, and toughness. and ductility decreases. Therefore, Cr children should be between 18 and 28 years old.

P: P is contained as an unavoidable impurity, but if its content exceeds 0.03%, the susceptibility to stress corrosion cracking increases, so the maximum value is α03. Note that the lower the %P amount, the more desirable.

S:8 is included as an unavoidable impurity, but it generally inhibits sI/'i hot workability, and if it exceeds 0.015 inch, it will not work in large forged products or forged products with complex shapes such as wings.
Since forging becomes difficult, the maximum content is 0.015%. Note that the lower the amount of B, the more desirable.

Si:Sl has a deoxidizing effect and is effective in cleaning the alloy of the present invention. However, for the alloy of the present invention, a vacuum melting method or an electro-slag melting method may be employed.

It is not necessarily a necessary element. Also, if too much of Sl is present, it will reduce high-temperature strength and ductility and inhibit hot workability (forgeability), so it should be kept at 1% or less. - Mn: Like Sl, Mn also has a deoxidizing effect. However, it is effective in cleaning the alloy of the present invention.

However, in the alloy of the present invention, a vacuum melting method or an electro-slag melting method may be employed, and it is not necessarily a necessary element.

Furthermore, when Mn increases in amount, it lowers high-temperature strength and toughness and impedes hot workability (forgeability), but it has almost no effect on stress corrosion cracking resistance, so it should be kept at 1.5% or less.

Mo: Mo improves high temperature strength as a solid solution strengthening element, but the effect is not significant at less than 15%. On the other hand, even when added in large amounts, no significant improvement in the high-temperature strength improvement effect was observed, and instead σ was a harmful intermetallic compound.
Since it promotes phase precipitation, the upper limit is set to 1ji5%.

Ti: Ti is a precipitated phase (γ' phase (
It is necessary to generate Ni, (A4 Tl) ). If the amount of Ti is less than 1 inch, the high temperature strength will not be improved sufficiently, and if too much is added, the hot workability (forgeability) will be significantly reduced, so the upper limit is set to 3% ft.

ht: ht forms a γ' phase ()11n(A4Ti)] and prevents the γ' phase from becoming coarse during long-term use at high temperatures. That is, it is effective in improving the stability of the γ' phase and improving the high-temperature long-term strength. The effect is c
It becomes noticeable at L1 or above, but even if a large amount is added, the effect will not be significantly improved and hot workability will be hindered, so the upper limit is set at 1%.

B:Btj: Strengthens grain boundaries, improves high temperature strength (especially long-term creep rupture strength) and ductility (creep rupture elongation)2
Improve. The effect is 0. Less than 1% OO is not sufficient; on the other hand, if too much is added, hot workability is inhibited and borides are formed entirely, reducing ductility. Therefore, the content of B is set to 0.001 to 0.02%.

(!u: Cu is contained as an unavoidable impurity in the alloy of the present invention, but if it exceeds 0.25%, hot workability will be completely inhibited, so it should be kept at a coefficient of 0.25 or less.

co: CO strengthens the base of the austenite phase in the alloy of the present invention and is effective as a solid solution strengthening element, and also promotes solid solution of the γ' phase in the solution treatment of the alloy of the present invention. It is effective in promoting the precipitation of the γ' phase in the aging treatment. These effects tend to be saturated at about 2% in the alloy of the present invention, and since Co is an expensive element, it is set to 2% or less in consideration of economic efficiency.

v: vH is effective as a solid solution strengthening element, but if too much is added, ductility, toughness, and hot workability are inhibited, so it is set to α5 or less.

Nb: Nt), it is effective in improving the toughness by making the crystal grains finer, and it also enters the γ' phase replacing T1 and Mut, increasing the amount of precipitation of the γ' phase, and further , which has a solid solution strengthening effect and is effective in improving high-temperature strength. However, if too large a quantity is added, niobium carbide (NbO) 'i' is formed, which is stable even at high temperatures, and remains undissolved even in solution treatment, which may actually impede high-temperature strength. Therefore, the score should be 1.5 or less.

W: W improves high temperature strength as a solid solution strengthening element. However, when W becomes too dense, it inhibits oxidation resistance,
In addition, since W is an element with a high specific gravity of WI/'i, it segregates in large ingots, impairing the uniformity of the material.Furthermore, since W is an expensive alloying element, economic efficiency must also be considered. 1% or less.

Zr:Zrt! By strengthening grain boundaries, high-temperature strength (especially
long-term creep rupture strength) and ductility (creep rupture elongation)
improve.

The effect is not sufficient when it is less than 0.00196, and even if a large amount is added, the effect is not significant.
On the contrary, non-metallic inclusions such as zircon compounds (for example, zircon nitride) are generated and the ductility is reduced.
OO1 to 0.1ch.

Rare earth elements such as Y, Mg, Oa: These alloying elements are
Furthermore, since it improves hot workability, it is added as necessary when hot working is performed under severe conditions, but even if added in excess of 0.1% li,
Since no remarkable improvement effect on hot workability was observed, and on the contrary, there were cases where hot workability was even inhibited, the content was adjusted to ft0. Section I and below.

Examples are shown below.

Example A molten metal having the chemical composition shown in Table 2 was melted using a vacuum high-frequency melting furnace, cast into an ingot with a diameter of about 100 m, and hot forged in a temperature range of 1150 to 1070°C. , and was forged into a bar with a thickness of about 35-1 and a width of about 601.

During this hot forging, for the purpose of examining hot workability, it was observed whether or not cracks occurred in the bar material during forging.

However, no problematic cracks were observed in any of the bars, and the hot workability was good.

These bars were subjected to the following heat treatment.

Solution treatment: temperature 1040°C, holding time 4 hours.

Cooling method: oil cooling Aging treatment: temperature 745°C, holding time 20 hours.

Cooling method: The air-cooled alloy of the present invention has age hardenability and is preferably used after being subjected to an aging treatment in order to provide high-temperature strength.

Next, a test piece with a diameter of 6-0 mm and a gage length of 50 m was taken from the heat-treated bar, and subjected to a room temperature tensile test and a creep rupture test (temperature 593°C, stress 4 q, o kg/
(3) and a temperature of 649°C and a stress of 4 L Okg/w2), and a cylindrical high temperature corrosion test piece with a diameter of 10cm and a length of 60wa, and a stress corrosion cracking test as shown in Figure 1. A piece was taken and subjected to a high temperature corrosion test and a creep rupture test under the test conditions shown below.

In addition, the surface finish roughness of the above-mentioned high-temperature corrosion test piece is JI[
Finish code r V' of 3B 0031; corresponds to 7VJ. Also, Fig. 1(B) is a state in which Fig. 1(A) is bent,
Figure 1 (0) is an engineering diagram of Figure 1 (E).
y 600 (trade name of Inco, USA 76%Ni)
-I S 5 % Cr -a ro %pe-n
s% Mn-α2% 81
- Figure 1 (A) shows the state in which it is fixed with bolt 1 and nut 2 made of (El 0 8 % C)
The dimensions of ~ (0) are as shown in the table below) (i.e., a test piece bent into a U shape with a bending radius of 6 cm, abbreviations 6F+, -U-B
ent).

(Unit knee) In addition, the gauge length refers to a reference length for elongation measurement in which the gauge length is determined in advance in order to measure the elongation at break of a tensile test piece or a creep rupture test piece. Elongation is expressed by the following formula.

1゜δ: Elongation at break t: Length between gauge points measured by connecting the center points of both fractured pieces of the test specimen so that they are on a straight line. are the formulas shown in Tables S to Table 4.

[Corrosion environment conditions in high temperature corrosion test] Artificial method: 15
% Na1Ei04-85 % V20B artificial ash Artificial method 0 Misaki/-1 Application temperature: 850°C Time: 24 hours [Environmental conditions for stress corrosion cracking test] Temperature: 3
60 ℃ Atmosphere: Degassed pure water (solid solution oxygen: 5 ppb or less) Pressure
Crab 175 to 9/Country 1・0 Time: 4,00. Oh Table 4 Results of high-temperature corrosion tests and stress corrosion cracking tests for the alloys of the present invention and comparative alloys As is clear from the above results, the room temperature strength of the alloys of the present invention (
Tensile strength, yield strength) and high temperature strength (evaluated by rupture time in creep rupture test) are at least the same as those of comparative alloys. So, #i is not accepted. on the other hand,
In high temperature corrosion tests and stress corrosion cracking tests, relatively
In the case of low-volume alloys, compared to comparative alloys (R),
Are the B to Q alloys superior to the comparative alloy (R?
), the corrosion loss was about 100%, and no cracking was observed in the stress corrosion cracking test, indicating that the alloy of the present invention has even better high-temperature corrosion resistance and stress corrosion resistance. This was recognized.

Effects of the Invention As described above, the alloy of the present invention has room temperature strength and high temperature strength compared to those of conventional precipitation hardening Fθ-based heat-resistant alloys.
Although it is comparable or slightly superior, it has even better high-temperature corrosion resistance and stress corrosion cracking resistance9, and has suitable performance for various high-temperature parts of gas turbines and steam turbines.

[Brief explanation of the drawing]

FIG. 1 shows the shape of the test piece and the bending condition of the test piece used in the stress corrosion cracking test in the example. Sub-agents 1) Meiji agent Ryo Ashihara - Figure 1 (A)

Claims (4)

[Claims] (1) In weight%, C: 0.08% or less, Si: 1% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.
015% or less, Ni: 35-48%, Cr: 18-28
%, Mo: 0.5-3.5%, Ti: 1-3%, Al:
0.1-1%, B: 0.001-0.02%, Cu: 0
．． 1. A heat-resistant and corrosion-resistant alloy for a turbine, characterized in that the alloy contains 25% or less of Fe, with the remainder consisting of Fe and unavoidable impurities. (2) In weight%, C: 0.08% or less, Si: 1% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.
015% or less, Ni: 35-48%, Cr: 18-28
%, Mo: 0.5-3.5%, Ti: 1-3%, Al:
0.1-1%, B: 0.001-0.02%, Cu: 0
．． Contains 25% or less, furthermore, Co: 2% or less, V:
0.5% or less, Nb: 1.5% or less, W: 1% or less, Z
A heat-resistant and corrosion-resistant alloy for a turbine, characterized in that it contains one or more of r: 0.001 to 0.1%, with the remainder consisting of Fe and unavoidable impurities. (3) In weight%, C: 0.08% or less, Si: 1% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.
015% or less, Ni: 35-48%, Cr: 18-28
%, Mo: 0.5-3.5%, Ti: 1-3%, Al:
0.1-1%, B: 0.001-0.02%, Cu: 0
．． Contains 25% or less, and further contains rare earth elements: 0.1%
A heat-resistant and corrosion-resistant alloy for a turbine, characterized by containing one or more of the following: Ca: 0.1% or less, Mg: 0.1% or less, and the remainder consisting of Fe and unavoidable impurities. (4) In weight%, C: 0.08% or less, Si: 1% or less, Mn: 1.5% or less, P: 0.03% or less, S: 0.
015% or less, Ni: 35-48%, Cr: 18-28
%, Mo: 0.5-3.5%, Ti: 1-3%, Al:
0.1-1%, B: 0.001-0.02%, Cu: 0
．． Contains 25% or less, Co: 2.0% or less, V: 0.
5% or less Nb: 1.5% or less, W: 1% or less, Zr: 0
．． 001 to 0.1%, and further contains rare earth elements: 0.1% or less, Ca: 0.1% or less,
A heat-resistant and corrosion-resistant alloy for a turbine, characterized in that it contains one or more types of Mg: 0.1% or less, with the remainder consisting of Fe and unavoidable impurities.