JP2001172751A - Fe-BASE HEAT-RESISTING ALLOY FOR ENGINE VALVE, WITH EXCELLENT COLD WORKABILITY AND HIGH TEMPERATURE STRENGTH - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat resisting alloy improved in cold forgeability, without greatly changing the elementary range for securing high temperature strength and structure stability, from the alloy of publication number 07-109539 which is a cold-forgeable heat resisting alloy having a possibility of improving strength by direct aging treatment after cold forging and comparatively reduced in cost. SOLUTION: The Fe-base heat resisting alloy for engine valve, having excellent cold workability and high temperature strength, has a composition consisting of, by weight, <=0.08% C, <=1.0% Si, <=1.0% Mn, >25-<30%, in total, of Ni and <=3.0% (including 0%) Co, 10-18% Cr, 1.2-2.5% Al, 1.5-3.0% Ti, 1.5-6.0%, in total, of one or more elements selected from the group IVa and Va elements, and the balance essentially Fe with impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant alloy for an exhaust engine valve having good cold workability, excellent high-temperature strength, and produced by inexpensive cold forging.

[0002]

2. Description of the Related Art Today, heat-resistant steels and super-heat-resistant alloys are used in many applications. One of the typical applications is an exhaust engine valve.

Conventionally, as a material for an exhaust valve of a gasoline engine or a diesel engine, SU which is a high Mn gamma steel has been used.
H35 (Fe-8.5Mn-21Cr-4Ni-0.5C-0.4N) has been widely used. NCF751 (Ni-15.5Cr-1Nb-2.3Ti-1.2Al-7Fe) has come to be used for engines that are partially used at high temperatures and for engines that have high loads.

However, since NCF751 is very expensive including about 70% of Ni, it has recently been required to save resources and to reduce the cost of NCF751.
Alloys with high-temperature strength and structural stability close to F751 have been developed. Furthermore, recently, particularly for parts used in automobiles, suppression of characteristic deterioration after long-term use and structural stability of materials used have been required.

[0005] As a proposal satisfying the requirements, for example, Japanese Patent Application Laid-Open No. 7-109539 discloses that in weight percent C: 0.10% or less, Si: 1.0% or less, Mn: 3.0% or less, Ni: 30% or less. 49%, Cr: 1
0 to 18%, Al: 1.6 to 3.0%, contains 1.5 to 6.0% in total of one or more elements selected from the genus a and the genus Va, and contains Al, Ti, Zr, By defining the relational expressions of Hf, V, Nb, and Ta and the relational expressions of Cr, Mo, and W in atomic%, we proposed an alloy that suppressed the deterioration of characteristics after long-time heating and improved the structural stability.

[0006]

There are various methods for forming an exhaust engine valve, such as a hot upset method, a hot extrusion method and a cold forging method. The extrusion method is mainly used.

However, in the hot forming method which is currently performed, there are problems such as dimensional accuracy and many man-hours, and therefore, man-hour reduction for the purpose of quality improvement and cost reduction is required.
In order to solve these requirements, it has been proposed to form the engine valve by cold forging. According to this method, since a large number of engine valves can be manufactured in a unit time, cost reduction is expected due to reduction of man-hours.

In addition, when the material is used in a hardened state by performing an age hardening treatment after cold forging, the hardness during use is lower than that in the conventional hot forming. It is expected to increase significantly compared to.

However, when used as an engine valve, there is a risk that the structure will become unstable and the strength will decrease when exposed to a high temperature for a long time. Therefore, it is necessary to select a target alloy and adjust the composition of the alloy. Requires careful choice and care.

For example, when conventionally used SUH35 is used as the cold forged engine valve material, it is difficult to reduce the hardness after the solution treatment because the C content is high, and the Mn content is low. Due to its high cost, it was difficult to produce it by cold forging to cause work hardening.

The alloy disclosed in Japanese Patent Application Laid-Open No. 7-109539 has sufficient characteristics for high-temperature strength, which is a performance required for an engine valve. However, there is a problem that it is difficult to forge the steel.

An object of the present invention is to provide a heat-resistant alloy which can be cold forged and whose strength is expected to be improved by a direct aging treatment after the cold forging.
An object of the present invention is to provide a heat-resistant alloy having improved cold forgeability without greatly changing the element range for ensuring the high-temperature strength and the structural stability of the alloy disclosed in No. 7-109539.

[0013]

Means for Solving the Problems The present inventors have disclosed in Japanese Patent Laid-Open No.
Based on the alloy of No. 109539, optimization of each alloy element to improve cold forgeability was performed.

According to the study of the present inventors, the high-temperature strength can be directly applied to the alloy invention disclosed in Japanese Patent Application Laid-Open No. 7-109539, and a γ phase serving as a matrix and a γ ′ serving as a precipitation strengthening phase can be used. It has been found that this can be achieved by optimizing the composition of both phases of the phase and optimizing the quantitative ratio of both phases.

On the other hand, the cold forgeability is determined by a state in which the elements constituting the γ 'phase serving as the precipitation strengthening phase are completely dissolved in the γ phase serving as the matrix, that is, a high Ni content based on Fe. And various elements in the γ phase containing high Cr content
It is necessary to judge pass / fail based on deformation resistance at the time of cold working in a phase state in which a solid solution is formed by replacing Fe atoms.

Although the high-temperature strength and the cold forgeability are contradictory performances, the present inventors have taken the above findings into consideration in Japanese Patent Application Laid-Open No.
For the disclosed alloy described in No. 9539, Ni, Co, Mo, C,
By optimally controlling various alloying elements such as Al, Ti, and Nb, the present inventors have found an alloy having both good strength and good cold workability and maintaining a balance between the two properties, and reached the present invention.

That is, according to the present invention, C: not more than 0.08% by weight,
i: 1.0% or less, Mn: 1.0% or less, Ni and 3.0 or less (including 0%) Co in total exceeding 25% and less than 30%, Cr: 10 to 18%,
Al: 1.2 to 2.5%, Ti: 1.5 to 3.0, containing 1.5 to 6.0% in total of one or two or more elements selected from the IVa group and the Va group, with the balance being substantially Fe, excluding impurities Fe-based heat-resistant alloy for engine valves having excellent cold workability and high-temperature strength.

Preferably, C: 0.05 or less and Si: 0.5% by weight
Hereinafter, Mn: 0.5 or less, Ni and 3.0 or less (including 0%) Co in total 26.5 to 28.5, Cr: 12 to 16, Al: 1.2 to 2.5, Ti: 1.5
~ 3.0, Nb: 0.2 ~ 2.0, the remainder is Fe-based heat-resistant alloy for engine valves with good cold workability and high-temperature strength consisting essentially of Fe excluding impurities.
% Or less and one or two kinds of W: 3% or less, more preferably 0.015% or less by weight of B 2.

The above alloy preferably satisfies the following relational expression in terms of the content of Al and the content of other elements in atomic%.

0.50 ≦ [Al] / ([Al] + [Ti] + [Zr] + [Hf] + [V] + [N
b] + [Ta]) ≦ 0.60 Alternatively, in the above alloy, it is desirable that the content of Cr and the content of other elements in atomic% satisfy the following relational expression.

0.14 ≦ ([Cr] + [Mo] + [W]) / ([Ni] + [Co] + [Fe] +
[Cr] + [Mo] + [W]) ≦ 0.20 In the present invention, more preferably, Y and 0.01% by weight or less are used.
Contains one or two REMs of 0.01% or less.

The above-mentioned Fe-based heat-resistant alloy of the present invention has a content of 60% to 80%.
% 800 ° C after cold working, 800 ° C-2 after heating for 400 hours
The number of breaks in the rotational bending fatigue test at 45 MPa was 1.0
× 10 ⁶Or more times, and also required for 70% cold working.
Is less than or equal to 1800 MPa.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention minimizes the amount of solid solution elements such as Ni added to the minimum required for high-temperature strength, optimizes the amounts of each element, and achieves both strength and cold workability. An object of the present invention is to provide an Fe-base heat-resistant alloy for an engine valve, which is favorable and has particularly improved cold workability while maintaining a balance between the two properties.

The reasons for limiting each element specified in the present invention will be described below. First, C is combined with Ti, Nb, Ta, etc. to form MC carbides and has an effect of preventing the crystal grains from becoming coarse, so that a small amount of C must be added. However, excessive addition exceeding 0.08% increases the hardness, deteriorating the cold workability,
Furthermore, when heated for a long time, a decomposition reaction occurs from MC to M _{2 3} C _6, and the ductility of grain boundaries at room temperature is reduced.

Further, when the valve is actually cold forged, if there is a large amount of MC carbide, there is a risk that the valve may be cracked starting from the carbide during molding. Therefore, C is set to 0.08% or less. A more preferred C range is 0.05% or less.

Although Si and Mn are added as deoxidizing elements in the alloy of the present invention, excessive addition of both causes reduction in high-temperature strength. Mn was further reduced to 1.0% or less in order to increase deformation resistance and reduce cold workability. More preferred ranges are each 0.5% or less.

Ni stabilizes the γ phase of the matrix and increases the high-temperature strength. Further, it is an essential element as a constituent element of the γ 'phase.

In addition, Co forms a solid solution in the γ matrix to stabilize the γ phase, and in the hot working region, promotes the solid solution of the γ ′ phase to improve hot workability. Increases the precipitation amount of the γ 'phase and improves the high-temperature strength.

Both Ni and Co stabilize the γ phase,
Co is Ni in order to do the same in increasing the high temperature strength.
Can be added in the form of substitution, but since Co is an element more expensive than Ni, when Co is added, the content is preferably 3% or less.

Then, Ni and Co of 3.0 or less (including 0%)
Is less than 25% in total, the strength becomes insufficient because the amount of the γ 'phase contributing to strengthening is reduced. In addition, the matrix structure may be destabilized and the γ 'phase itself may become coarse, resulting in a decrease in high-temperature strength. On the other hand, Ni and 3.
If a total of 0% or less (including 0%) of Co is added at 30% or more, the deformation resistance increases and the cold workability deteriorates.

Therefore, Ni and Co of 3.0 or less (including 0%)
Is limited to a range of more than 25% and less than 30% in total. A more desirable range is 26.5-28.5%.

Cr is an indispensable element for improving the oxidation resistance of the alloy, and at least 10% is necessary, but 18%
Above the chromium-rich sigma (σ) phase, martensite
Precipitate the (α ') phase or ferrite (α) phase, degrade the structure stability after long-time heating, and increase the deformation resistance to reduce the cold workability by 10 to 18%. . A more desirable range is 12-16%.

Al is an element indispensable in the present invention for precipitating a stable γ 'phase and obtaining a required high-temperature strength, and is also an element for improving cold workability. Therefore, at least
1.2% is necessary, and if it exceeds 2.5%, the hot workability is reduced, so it is limited to 1.2 to 2.5%. A more preferred range is 1.5
~ 2.0%.

Since Ti forms a γ ′ phase together with Ni and Al and strengthens the γ ′ phase to improve high-temperature strength, 1.5% or more is required. At high temperatures, the γ 'phase is transformed into an eta (η: Ni ₃ Ti) phase, which lowers the high-temperature strength, so the content is limited to 1.5 to 3.0%.
A more preferred range is 1.8-2.5%.

In the alloys of the present invention, the elements belonging to the group IVa and Va form an γ 'phase by binding with Ni together with Al to form a γ' phase, thereby strengthening the γ 'phase and improving the high-temperature strength. It is necessary to add 1.5% or more in total. However, if these elements exceed 6.0% in total, the hot workability is deteriorated, and the γ 'phase becomes unstable after heating at a high temperature for a long time, so that the γ phase and the delta (δ: Ni ₃ Nb) phase are formed. It is limited to 1.5 to 6.0% because of metamorphosis and reduced tissue stability. A more preferred range is 3.0-5.0%.

In the group IVa element, the addition of Ti is preferred. Zr and Hf have a lower solid solubility in γ than Ti, and cannot be added in a larger amount than Ti. Of the elements of the Va group, Nb is most preferably added, and 0.2 to 2.0% is preferably added. A more preferred range is from 0.3 to 1.2%.

On the other hand, V has a weaker solid solution strengthening action than Nb and also lowers the oxidation resistance, so excessive addition is not preferred. Ta
Although γ ′ is solid-solution strengthened more than Nb, it is a rare resource and expensive, so addition of a large amount is not preferable.

Like Cr, Mo and W are solid-solution strengthened in a γ matrix, and have the effect of improving high-temperature fatigue strength and high-temperature creep rupture strength. Therefore, if necessary, one or two kinds can be added in a range of 3% or less. However, since the ratio of the addition of these elements including Cr to the matrix contributes to the precipitation of the σ phase, α 'phase and α phase after heating at a high temperature for a long time, it is desirable to satisfy the following relational expression. That is, the B value is expressed as B = ([Cr] + [Mo] + [W]) / ([Ni] + [Co] + [Fe] + [Cr]
+ [Mo] + [W]), and 0.14 ≦ B ≦ 0.20.

As described above, in order to achieve the characteristics of the valve manufactured by cold forging, which is a feature of the alloy of the present invention, that the characteristics do not deteriorate even after heating at a high temperature for a long time, as described above, Cr, Mo, W
Group IVa which forms a γ 'phase with Ni and Al,
The V a group also needs to be limited.

That is, A value = [Al] / ([Al] + [Ti] + [Z
r] + [Hf] + [V] + [Nb] + [Ta]) It is possible to improve the stability of the γ 'phase at high temperatures by increasing the value.
If the value is too high, the high-temperature strength for a long time is reduced. Therefore,
The A value is preferably 0.50 to 0.60. A more preferred range for the A value is from 0.52 to 0.58.

B (boron) has the effect of strengthening the grain boundary in the present invention, improves high-temperature strength and ductility, and can be added in an appropriate amount. However, if added in a large amount, the initial melting temperature is lowered and hot workability is lowered. Is preferably added at 0.015% or less.

Mg and Ca as deoxidizing and desulfurizing elements increase the cleanliness of the alloy, improve the high-temperature strength and ductility, and can be added in one or two kinds in an appropriate amount. However, excessive addition lowers the initial melting temperature and lowers the hot workability, so that each addition is preferably 0.02% or less.

In the present invention, Y and REM are effective in increasing the oxidation resistance at high temperatures, and one or two of them can be added to the alloy of the present invention. However, if the added amount exceeds 0.01%, the hot workability is reduced, so that the upper limit is preferably set to 0.01%.

In addition, the following elements other than the above may be included in the alloy of the present invention as long as they are in the following ranges. Cu ≦ 0.3%, Ag ≦ 0.2%, P ≦ 0.04%, S ≦ 0.02%, O ≦ 0.
02%, N ≦ 0.05%, more preferably Cu ≦ 0.1%, Ag ≦ 0.1%, P ≦ 0.02%, S ≦ 0.005%, O ≦ 0.
01%, N ≦ 0.01% When the Fe-base heat-resistant alloy of the present invention is used as an engine valve,
For the purpose of softening the alloy, it is subjected to a solution heat treatment at a temperature in the range of 900 to 1050 ° C. for 30 to 60 minutes, followed by cold working. At that time, a large cold strain is applied, and if excessive strain is applied, the precipitation of the η phase is promoted. Therefore, it is preferable to perform the cold working within a range of 60 to 80%. After the cold working, it is preferable to perform aging treatment at, for example, 720 to 780 ° C. for about 3 to 5 hours in order to impart hardness required for an engine valve.

When the Fe-base heat-resistant alloy of the present invention is used as an engine valve, it is exposed to an ambient temperature of 700 to 800 ° C. for a long time in an operating engine.

In the simulation evaluation, the sample subjected to the cold working of 60 to 80% is heated to a temperature range of 700 to 800 ° C. At this time, in this temperature range, excess η during use is used.
Phase precipitation is likely to occur, and the strength may decrease.80
Heat for 400 hours at a temperature around 0 ° C.

Therefore, the simulated evaluation was carried out as a criterion for determining the high-temperature strength under particularly severe conditions, in which a sample subjected to heating at 800 ° C. for 400 hours after cold working at 60% to 80% (in Table 3, "After prolonged heating (overage treatment)") was subjected to a 245MPa rotational bending fatigue test at 800 ° C assuming the operating temperature, and if the number of fractures at that time was 1.0 × 10 ⁶ or more It was determined that good high temperature fatigue strength characteristics could be obtained.

As a criterion for judging the cold workability, 70% of the sample after solution heat treatment was subjected to an upsetting compression test.
% The true stress value corresponding to processing was set to 1800 MPa or less.

[0049]

EXAMPLES Tables 1 and 2 show the chemical compositions of the alloys tested. The sample was made into an ingot of 10 kg by vacuum induction melting the alloys of the compositions shown in Tables 1 and 2, and then 33 mmφ by hot working.
Was prepared.

After holding this sample at 1030 ° C. for 30 minutes and subjecting it to an oil-cooled solution treatment, a normal temperature hardness measurement and a cold workability test were conducted. Hardness was measured with a Rockwell hardness tester. In the cold workability test, the work of measuring the length of a sample of φ6 × 9 mm by applying a compressive load with an Amsler tester and sequentially increasing the load is performed, and the compression work rate and stress Seeking a relationship. The true stress at the room temperature hardness and the cold compressibility of 70% of the test results are shown in the column of "cold upset compression test after solution heat treatment" in Table 3.

The hot-worked rod was subjected to the following two types of heat treatment. First, the first heat treatment
70% after oil-cooled solution treatment after holding at 1030 ° C x 30 minutes
Cold-drawn at a processing rate of, and further subjected to oil-cooled solid solution treatment after holding at 1030 ° C for 30 minutes, and air-cooled aging treatment after holding at 750 ° C for 4 hours and subjected to “conventional heat treatment (with solution treatment heat treatment)”.
Material ". This is a solution treatment performed after cold drawing to eliminate the effect of strain imparted by processing, and it was expected that a material close to the characteristics when a conventional hot forging process was performed would be obtained. Things.

Next, as a second heat treatment, as a step of simulating cold forging, after being kept at 1030 ° C. for 30 minutes, an oil-cooled solution treatment was performed, and then a cold drawing was performed at a working rate of 70%. Then, directly hold at 750 ° C for 4 hours and then perform air-cooling aging treatment.This sample was treated as `` no solution heat treatment (direct aging)
Material ". Each sample subjected to these two types of heat treatment was subjected to each test.

Tensile tests were performed at room temperature and 800 ° C. for each of the two types of heat treatment, and measured by the ASTM method at a parallel part diameter of 6.35 mm and an elongation of 4D. The tensile strength is shown in the column of "Tensile strength (MPa)" in Table 3.

The long-time heat treatment (overage treatment)
The conventional heat-treated material and the material without solution heat treatment were each aged and then air-cooled after 800 ° C for 400 hours. A rotary bending fatigue test was performed as a test simulating the performance evaluation of an actual valve. The rotating bending fatigue test is a test in which a sample is rotated while a constant bending moment is applied to the sample. The sample was prepared with a parallel part diameter of 8 mm.
High temperature strength was evaluated by the number of breaks when a stress of 245 MPa was applied at 00 rpm, R = -1, and a test temperature of 800 ° C. The impact value was measured on a U-notched sample at a test temperature of 20 ° C.
The measurement was repeated and the average was determined. Micro observation was performed on the D / 4 part of the longitudinal section. In addition, the area ratio of the precipitated phase after high-temperature and long-time heat treatment was measured using a scanning electron microscope (SEM) by observing three fields of view at a magnification of 2500 times, taking a picture of it, and performing image analysis. .

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

In Tables 1 and 2, Nos. 1 to 14 are invention alloys and Nos. 15 to
No. 18 is a comparative alloy, No. 15 is an alloy in which the amount of Ni is out of the range of the present invention, No. 16 is an alloy in which the Cr and B values are higher than those of the present invention, and No. 17 is A No. 18 is an alloy having a small Ti value and a high Ti content and deviating from the composition range of the present invention, compared with the alloy of the present invention in an alloy having a composition range disclosed in Japanese Patent Application Laid-Open No. Alloy. Table 2
The A value and B value of are the values shown below expressed in atomic%, respectively.

A value = [Al] / ([Al] + [Ti] + [Zr] + [Hf] + [V] + [Nb] + [Ta]) B value = ([Cr] + [Mo] + [W]) / ([Ni] + [Co] + [Fe] + [Cr] + [Mo] +
[W]) As shown in Table 3, the cold workability of the comparative alloy
The No. 16 alloy contains a large amount of Cr and the No. 17 alloy has a large amount of Ti, so that it has high deformation resistance (true stress at 70% processing) and poor cold workability. No. 18 alloy is disclosed in Japanese Patent Application Laid-Open No. 7-109539. However, since the alloy contains a large amount of Ni, it has higher deformation resistance and insufficient cold workability as compared with the alloy of the present invention.

From the above, when the solid solution element is added in a larger amount than the range of the alloy of the present invention, the deformation resistance of the alloy increases,
There is a risk that the cold workability is reduced.

However, on the other hand, when the amount of Ni is reduced (No. 15 alloy) for the purpose of improving the cold workability, the high-temperature strength of the matrix is reduced, so that the fatigue strength and the tensile strength are reduced.

From the above, both characteristics cannot be satisfied at the same time if the amounts of alloying elements, such as Ni, are too large or too small. Invention alloy (No. 1
Based on this point, Nos. 14 to 14) optimize the amounts of alloying elements including Ni and achieve both strength and cold workability. The alloys of the present invention all show good cold workability, tensile strength, fatigue strength and high toughness (impact value).

However, among the alloys of the invention, a γ 'phase is formed.
No. 9 and No. 14 alloys with higher A values do not have high strength of the γ 'phase itself, so that the alloy of the present invention cannot be expected to increase in strength very much. Even if the A value is smaller than the range of the present invention,
Even if it is large, the fatigue strength cannot be sufficiently satisfied.

For example, regarding the fatigue strength, the comparative alloy No. 17 alloy has a low A value and a high Ti content, so that a large amount of η phase which does not contribute to the strength is precipitated after a long-time heat treatment. No increase in fatigue strength can be expected as compared to the alloy of No.

Further, the comparative alloy No. 17 in which the A value and the Ti content are out of the range of the present invention and No. 16 in which the B value is out of the component range, the η phase and the σ phase are precipitated. The impact value as an index of toughness is greatly reduced.

Therefore, similarly to the optimization of the element amounts described above, there is a risk that the characteristics of the fatigue strength and the impact value are greatly reduced by the A value and the B value.
The values also need to be strictly controlled.

In the alloy of the present invention, the material without the solution heat treatment (direct aging treatment) is compared with the conventional heat treated material.
High tensile strength after aging treatment, fatigue strength after overaging treatment
(Fatigue life), the impact value tends to decrease slightly, but all alloys show good characteristics, the alloy of the present invention,
It can be seen that even if the solution heat treatment is omitted, it has sufficient characteristics.

As explained above, the alloy of the present invention has almost the same toughness and mechanical properties as the conventional alloy necessary for the performance of the engine valve, but has better cold workability than the conventional alloy. It can be seen that the alloy was made.

[0069]

The Fe-base heat-resistant alloy for an engine valve according to the present invention can significantly improve cold workability by reducing the hardness after solution treatment, and can be cold forged at high temperatures. This makes it possible to manufacture an engine valve material having excellent structural stability and high-temperature fatigue strength, thereby significantly reducing engine valve manufacturing costs.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Sato 2107-2 Yasugi-cho, Yasugi-shi, Shimane Hitachi Metals Research Institute, Ltd. (72) Inventor Takehiro Ohno 2107-2 Yasugi-cho, Yasugi-shi, Shimane Hitachi Metals, Ltd. Yasugi Plant (72) Inventor Katsuaki Sato 1-4-1, Chuo, Wako-shi, Saitama Pref.

Claims (10)

[Claims] C: 0.08 or less, Si: 1.0 or less, Mn:
1.0 or less, Ni and 3.0 or less (including 0%) Co exceeding 25 and less than 30 in total, Cr: 10-18, Al: 1.2-2.5, Ti: 1.5-3.0
Good cold workability characterized in that one or two or more elements selected from the group IVa and the group Va are contained in a total amount of 1.5 to 6.0, and the balance is substantially made of Fe excluding impurities. And Fe-base heat-resistant alloy for engine valves with high temperature strength. 2. C: 0.05 or less, Si: 0.5 or less, Mn:
0.5 or less, Ni and 3.0 or less (including 0%) Co in total 26.5
~ 28.5, Cr: 12 ~ 16, Al: 1.2 ~ 2.5, Ti: 1.5 ~ 3.0, N
2. The Fe-base heat-resistant alloy for engine valves having good cold workability and high-temperature strength according to claim 1, wherein b: 0.2 to 2.0, with the balance being substantially Fe except for impurities. 3. Good cold workability and high-temperature strength according to claim 1 or 2, comprising one or two of Mo: 3% or less and W: 3% or less by weight%. Fe-base heat-resistant alloy for engine valves. 4. The Fe-base heat-resistant engine valve having good cold workability and high temperature strength according to claim 1, wherein the Fe-containing heat-resistant material contains 0.015% or less by weight of B 2. alloy. 5. The Fe-base heat-resistant alloy for an engine valve having good cold workability and high-temperature strength according to claim 1, wherein the following relational expression is satisfied in atomic%. 0.50 ≦ [Al] / ([Al] + [Ti] + [Zr] + [Hf] + [V] + [Nb] + [Ta]) ≦ 0.
60 6. The Fe-base heat-resistant alloy for engine valves having good cold workability and high-temperature strength according to claim 1, wherein the following relational expression is satisfied in atomic%. 0.14 ≦ ([Cr] + [Mo] + [W]) / ([Ni] + [Co] + [Fe] + [Cr] + [Mo] +
[W]) ≦ 0.20 7. The method according to claim 1, wherein one or two of Mg and 0.02% of Ca are contained in a percentage by weight of 0.02% or less.
7. An Fe-based heat-resistant alloy for an engine valve having good cold workability and high-temperature strength according to any one of claims 1 to 6. 8. The good cold workability and good cold workability according to claim 1, comprising one or two kinds of Y in less than 0.01% and REM in less than 0.01% by weight. Fe-based heat-resistant alloy for engine valves with high-temperature strength. 9. 60% to 80% at 800 ° C. after cold working at 40 ° C.
The good cold according to any one of claims 1 to 8, wherein the number of fractures in a rotational bending fatigue test at 800 ° C-245MPa after heating for 0 hour is 1.0 × 10 ⁶ times or more. Fe-base heat-resistant alloy for engine valves with workability and high-temperature strength. 10. The method according to claim 1, wherein a true stress required for performing 70% cold working is 1800 MPa or less.
13. An Fe-base heat-resistant alloy for an engine valve having good cold workability and high-temperature strength according to any one of the above.