JPS61238942A - Heat resisting alloy - Google Patents

Abstract

PURPOSE:To obtain an Fe-Ni-base heat resisting alloy excelling in corrosion resistance at high temp. and having high strength as well as high toughness by incorporating specific percentage of C, Si, Mn, Ni, Cr, Ti, Al, B, Ca and REM to Fe. CONSTITUTION:The alloy consisting of, by weight, 0.01-0.2% C, <=2% Si, <=2% Mn, 25-50% Ni, 13-23% Cr, 1.5-3.5% Ti, 0.1-0.7% Al, 0.001-0.05% B, 0.001-0.01% Ca, 0.001-0.1% REM, and the balance Fe with inevitable impurities is prepared. It is desirable that this alloy undergoes homogenization at a temp. as high as >=about 1,050 deg.C, working at <=about 1,000 deg.C to be given residual strain and then age-hardening treatment at about 650-850 deg.C.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The invention relates to a Fe-Ni-based heat-resistant alloy that has excellent high-temperature corrosion resistance, high toughness, and high strength. Exhaust valve, heat resistant spring.

High-strength Fe- suitable for materials for heat-resistant parts such as heat-resistant bolts
This relates to a Ni-based heat-resistant alloy.

(Prior Art) In recent years, interest in diesel engines with excellent fuel economy has gradually increased, and as a result, the usage conditions for exhaust valves for diesel engines have become increasingly severe. For this reason, requirements for exhaust valve materials have become even more stringent, and high-grade materials such as Ni-based heat-resistant alloys are used in some diesel engines without hardening overlay on the valve face. However, since this Ni-based heat-resistant alloy is expensive, there is a strong demand for cost reduction, and there is also the development of Ni-saving Fe-Ni-based heat-resistant alloys.

(Problems to be Solved by the Invention) The strengthening mechanism of this Fe-Ni-based heat-resistant alloy is similar to that of the Ni-based heat-resistant alloy, due to the γ' phase [N i 3 (AJl, Ti
)], but especially in the case of Fe-Ni-based heat-resistant alloys, the η phase [Ni3T
i] grain boundary precipitation is likely to occur, a decrease in strength and ductility is unavoidable, and in reality, from the perspective of structural stability, the amount of reinforcing elements such as AM and Ti added is relatively narrowly limited. is the reality.

Incidentally, the addition of B is effective in suppressing the grain boundary precipitation of the η phase described above, but in this case, a considerable amount of B is required to be added, and this B increases the local melting temperature of the grain boundaries. Therefore, there is a problem that hot workability is impaired by adding a large amount of B. Therefore, the amount of B added is limited to an extent that does not impair hot workability.

On the other hand, it has been found that increasing the amount of AM is also effective in suppressing grain boundary precipitation of the η phase, but the strengthening effect due to the precipitation of the γ' phase in Fe-Ni-based heat-resistant alloys is due to the precipitation of the γ' phase. This is caused by strain energy based on the difference in the crystal lattice constant of the matrix, so in order to obtain a large strength, it is necessary to increase the lattice constant of the γ' phase as much as possible. i/A l
Since it is effective to increase the ratio of , for this reason, an increase in AM does not contribute much to strengthening the Fe-Ni-based heat-resistant alloy, and therefore the amount of An added is restricted to a low value.

Therefore, in the Fe-Ni-based heat-resistant alloy, the present inventors
B. Adding an appropriate amount of AM can suppress the precipitation of the η phase, making it possible to improve strength even when the amount of AM added is limited to a low level, and further improving high-temperature corrosion resistance. As a result of intensive research aimed at obtaining a Fe-Ni-based heat-resistant alloy, this invention was completed.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a high-strength, high-toughness, high-corrosion-resistant Fe-
Ni-based heat-resistant alloy has C: 0.01 to 0.2% in weight%
, Si: 2% or less, M n: 2% or less, Ni: 25
~50%, Cr: 13-23%, Ti: 1.5-3.
5%, Al~0, 1~0.7%, B:O,OO
l ~0.05%, Ca: 0.001~0.01%,
REM (one or more rare earth elements): 0.0
01-0.1%, and if necessary, N: 0.003
~0.05%, also as necessary, Zr: 0.005
~0.05%, V:0.05-1%.

Nb+Ta (including cases where either one is 0) ~ 0.0
5-3%, Mo: 0, 05-3%, W: 0.
05 to 3%, the balance being Fe and unavoidable impurities, and more preferably, as a normal heat treatment, after solid solution treatment at a temperature of 1050 ° C. or higher, 650 ° C. Age hardening treatment is performed at 850°C, and more preferably, as processing heat treatment, 105
After homogenization at a high temperature of 0°C or higher, processing is performed at a temperature of 10006°C or lower to give residual strain, and age hardening treatment is performed at 650 to 850°C, thereby forming the γ' phase [Ni3(A
In order to promote the intragranular ratio of JI, Ti) and suppress the precipitation of the harmful η phase [Ni3Ti], we can obtain a heat-resistant alloy that has high strength without impairing toughness and has outstanding high-temperature corrosion resistance. It is characterized by what it did.

Next, the high-strength, high-toughness, high-corrosion-resistant Fe-Ni according to the present invention
The reason for limiting the component range (wt%) of the base heat-resistant alloy will be explained.

C: 0.01 NO, 2% C is an element that combines with Cr and Ti to form carbides and is an effective element for increasing high-temperature strength. It is necessary to contain it. However, if added in a large amount, the toughness and ductility will be impaired and, for example, when applied to exhaust pulp, the performance will be lowered, so it is necessary to limit the amount to 0.92% or less.

Si: 2% or less St is mainly added as a deoxidizing agent during melting, but since adding too much will reduce toughness and ductility, it is limited to 2% or less.

Mn: 2% or less Mn, like Si, is added as a deoxidizing and desulfurizing agent during melting, but since adding too much will reduce oxidation resistance at high temperatures, it is limited to 2% or less.

Ni: 25-50% Ni is an element necessary for stabilizing the austenite structure and at the same time forming the γ' phase [Ni3 (A-cross, Ti)]. However, if it is less than 25%, brittle phases such as σ phase will be formed during use at high temperatures and the high-temperature properties will deteriorate. This is not expected and would only lead to an increase in costs, so we limited it to 50% or less.

Cr: 13-23% Cr is an effective element for ensuring the corrosion resistance and oxidation resistance required for heat-resistant alloys, and in order to obtain such effects, it is necessary to add 13% or more. However, if the content is too large, a σ phase will be formed and the toughness and ductility will decrease, so the content should be 23% or less.

Tf: 1, 5-3.5% Ti combines with Ni and An to form the γ' phase [N
i3 (see A, Ti)], and is added in an amount of 1.5% or more for this purpose. However, if added in a large amount, the high-temperature properties will deteriorate due to the precipitation of the η phase [N15Til, so it is necessary to limit the content to 3.5% or less.

Al: 0.1-0.7% A! Like Ti, Q is an element necessary for forming the γ' phase, and for this purpose it is added in an amount of 0.1% or more. However, if added in a large amount, the Ti/Al ratio decreases and the strength decreases, so it is necessary to limit the amount to 0.7% or less.

B: O, OO 1 to 0.05% B is an element that has the effect of suppressing precipitation of the η phase, and in order to obtain such an effect, it is necessary to add O, OO% or more. However, if the amount is too large, the local melting temperature of grain boundaries will be significantly lowered and hot workability will be impaired, so 0.05%
It is necessary to do the following.

Ca: 0.001' to 0.01% Ca improves hot workability by fixing S, increases toughness and ductility by controlling the distribution form of carbides, and is an effective element for AM. It is an element that contributes to improving strength even when the amount added is limited to a low level, and in order to obtain this effect, it should be added in an amount of 0.001% or more. However, if added in a large amount, processability deteriorates, so it is necessary to limit the amount to 0.01% or less.

REM (one or more rare earth elements): 0.0
01-0.1% REM is an element that significantly improves the adhesion of the oxide film, and is effective in improving high-temperature corrosion resistance.

Since the effect of REM addition is particularly noticeable when the operating temperature fluctuates significantly, REM is added in an amount of 0.001% or more in order to obtain such an effect. However, if the REM content exceeds 0.1%, hot workability is likely to be impaired, so it is set to a range of 0.001 to 0.1%.

Zr: 0.005-0.05%, V: 0.05-1%
, Nb+Ta ('l-0 including the case where either one is 0)
, 05-3%, Mo: 0.05-3%.

W: One or more of 0.05 to 3% Zr, V, Nb, Ta, Mo, and W are effective elements for forming carbides and increasing high-temperature strength and toughness,
Among them, Zr is an effective element for strengthening grain boundaries, and in order to obtain this effect, Zr, V, Nb, T
a, Mo, Wc7) One or more types can be added as necessary. However, if the amount is too large, the toughness and workability will deteriorate, so it is necessary to limit the amount to the range shown in E.

N: 0.003 to 0.05% N is an effective element for suppressing the growth of crystal grains and refining the structure, so it can be added in an amount of 0.003% or more as necessary. . However, if it is too large, stringers with agglomerated nitrides will be formed and the ductility will be reduced.
It is necessary to keep it below 0.5%.

The Fe-Ni-based heat-resistant alloy according to the present invention, which has high strength, high toughness, and excellent high-temperature corrosion resistance, has the above-mentioned composition, and as a normal heat treatment, it is heated at 1050°C or higher. It is more desirable to perform solution treatment at a temperature of 1,000 to 850'C, and then age harden at a temperature of 650 to 850'C. It has become clear from various experiments that it is better to apply processing strain at a temperature of 650 to 850 degrees Celsius and age harden at a temperature of 650 to 850 degrees Celsius. This is a Fe-Ni heat-resistant alloy that suppresses phase precipitation, provides high strength without impairing toughness, and at the same time significantly improves high-temperature corrosion resistance. (Example 1) Shown in Table 1 An alloy of chemical components was melted in a 50 kg high-frequency induction furnace and formed into a 30 kg ingot.Then, after homogenization treatment under the conditions of 1150 ° C. x 16 hours,
It was forged into a 40mm square billet.

First, in order to investigate the hot workability of each test steel, a test piece with a diameter of 5 mm and a length of 20 mm cut from each billet was heated to 900 to 1150°C, and an upset test was performed using a mechanical press. The critical reduction rate at which cracks occur on the surface was determined.

Table 2 shows the upset test results at a typical processing temperature of 1100°C.

Next, a part of the billet is subjected to processing heat treatment,
The remaining samples were subjected to normal heat treatment (solution aging) and their mechanical properties were measured. The conditions for the processing heat treatment performed at this time are as follows.

That is, after first soaking the billet at 1000°C,
Press quickly to 50% processing rate with an air hammer,
It was immediately quenched and then aged at 750° C. for 16 hours. On the other hand, normal heat treatment is 1000'0
After solid solution treatment under the conditions of X1hr, it was rapidly cooled and then
Aging treatment was performed under the conditions of 0'0 x 16 hr. The results are also shown in Table 2.

As shown in Table 2, the critical reduction rate at which cracks occur is only 47% for comparative alloy A, but it is as high as 60-72% for alloys B-F of the present invention, demonstrating the effectiveness of Ca addition. gender is obvious.

In addition, the mechanical properties of the invention alloys B-F and the comparative alloy A
It was found that the strength and toughness of the alloys were higher than those of the alloys that were heat-treated, and that the alloys that had been heat-treated had even higher strength and sufficiently high ductility than the alloys that had been heat-treated.

(Example 2) An alloy having the chemical components shown in Table 3 was melted in an electric furnace,
A billet with a diameter of 180 mm was manufactured by forging and elongating a 1 ton ingot, and a large marine exhaust valve was manufactured from this billet. The forging of the exhaust valve that was carried out at this time was divided into forging of the shaft part and molding of the umbrella part. First, for the forging of the shaft part, the heating was set to 1000 degrees Celsius, and the diameter was 70 mm over 3 heats.
m, and the processing rate of the third heat was 30%,
The final temperature was approximately 900°C. Next, in the forging of the umbrella part, the heating temperature was set to 1000°C, and the molding was performed to form a diameter of about 300 mm in one heat.

The finishing temperature at this time is approximately 850° at the face of the valve.
The temperature at the center of the C9 umbrella tip was approximately 900°C.

Furthermore, the maximum machining rate was 60% on the face portion.

Next, this valve was subjected to age hardening treatment at 750°C in diameter for 16 hours, that is, one that was subjected to processing heat treatment.
750'0X after 1000℃xihr water cooling solid solution treatment
The tensile strength of the shaft portion and the hardness of the cap portion were investigated for those subjected to 16 hours of aging treatment, that is, those subjected to normal heat treatment. The results are shown in Table 4.

As is clear from the results shown in Table 4, both valves subjected to mechanical heat treatment and conventional heat treatment have better results than conventional valves, and in particular, the valves subjected to mechanical heat treatment have better results than those subjected to conventional heat treatment. It was confirmed that the tensile strength of the shaft, yield strength, and hardness of the cap were superior to those of the valves tested, and that the ductility of the shaft was superior to practical values.

(Example of experiment) In addition to having excellent strength and toughness, a practical exhaust valve must also have corrosion resistance against high-temperature corrosion caused by It is something. In particular, even in cases where the operating temperature fluctuates significantly, such as in the case of exhaust valves, it is required that the oxide film has excellent adhesion. Therefore, a so-called vanadium attack test was conducted using a test piece cut out from the face of the exhaust valve manufactured in Example 2.

In this test, each test piece was immersed for 5 hours in a molten mixed salt of vanadium pentoxide and sodium sulfate held at 800°C, and then the weight loss due to corrosion was measured. The results are shown in FIG. As shown in Figure 1, exhaust valves made of the alloys listed in Table 3 that have been subjected to processing heat treatment have excellent high-temperature corrosion resistance that is comparable to those that have been normally heat treated. It was confirmed that it has almost the same performance as Nimonic 80A, which is an expensive Nt-based heat-resistant alloy used.

[Effects of the Invention] As explained above, the Fe-Ni-based heat-resistant alloy according to the present invention has C: 0.01 to 0.2%, Si
: 2% or less, Mn: 2% or less, Ni: 25-50
%, Cr: 13-23%, Ti: 1.5-3.5%, A
l2 0.1-0.7%, B:O,OOl ~0.05%
, Ca: 0.001-0.01%, REM (one or more rare earth elements): 0.001-0.1%, and if necessary, N: 0.003-0.05% , Similarly, as necessary, Zr: 0.005 to 0.05%, ■: 0
．． 05-1%, Nb+Ta (including the case where either one is O): 0. u5~3%, Mo: 0°05~3%, W:
One or more of 0.05 to 3%, balance Fe
It is made of Fe as a base, and the addition of Ni and Cr improves heat resistance and corrosion resistance, and the addition of Ti and A causes the formation of γ' phase, which is effective in improving high-temperature strength. , B, and AM are added to suppress the precipitation of the η phase, Ca is added to improve strength, REM is added to improve high-temperature corrosion resistance, and Zr is added as necessary.

V, Nb, Ta, Mo, and W are added to further improve the strength, and if necessary, N is also added to make the structure finer, and the product is used after being subjected to normal heat treatment or processing heat treatment. Therefore, the precipitation of the γ' phase, which is effective for improving high-temperature strength, is promoted within the grains, and the grain boundary precipitation of the η phase, which is harmful to strength and notch sensitivity, can be suppressed, resulting in high strength and It has high toughness and excellent high-temperature corrosion resistance, and is cheaper than Ni-based heat-resistant alloys.
This provides an e-Ni-based heat-resistant alloy, which has the great effect of being suitable as a material for heat-resistant parts such as exhaust valves of internal combustion engines, heat-resistant springs, #thermal ports, etc.

[Brief explanation of drawings]

FIG. 1 is a graph showing the experimental results of high-temperature corrosion resistance investigated in Examples of the present invention.

Claims (1)

[Claims] (1) In weight%, C: 0.01 to 0.2%, Si: 2%
Below, Mn: 2% or less, Ni: 25-50%, Cr: 1
3-23%, Ti: 1.5-3.5%, Al: 0.1-
0.7%, B: 0.001-0.05%, Ca: 0.001-0.01
%, REM: 0.001 to 0.1%, the balance consisting of Fe and inevitable impurities High strength Fe-N
I-base heat-resistant alloy. (2) In weight%, C: 0.01-0.2%, Si: 2%
Below, Mn: 2% or less, Ni: 25-50%, Cr: 1
3-23%, Ti: 1.5-3.5%, Al: 0.1-
0.7%, B: 0.001-0.05%, Ca: 0.001-0.01
%, REM: 0.001-0.1%, and Zr: 0.
005-0.05%, V: 0.05-1%, Nb+Ta
:0.05~3%, Mo:0.05~3%, W:0.0
High-strength Fe-
Ni-based heat-resistant alloy. (3) In weight%, C: 0.01-0.2%, Si: 2%
Below, Mn: 2% or less, Ni: 25-50%, Cr: 1
3-23%, Ti: 1.5-3.5%, Al: 0.1-
0.7%, B: 0.001-0.05%, Ca: 0.001-0.01
%, REM: 0.001-0.1%, N: 0.003-
0.05%, and Zr: 0.005-0.05%, V
:0.05~1%, Nb+Ta:0.05~3%, Mo
A high-strength Fe-Ni-based heat-resistant alloy comprising one or more of the following: 0.05 to 3%, W: 0.05 to 3%, and the balance being Fe and inevitable impurities.