JPS60162760A - Production of high-strength heat resistant material - Google Patents

Abstract

PURPOSE:To obtain a high-strength heat-resistant material having high-temp. strength and high hardness by subjecting an Ni-base alloy incorporated therein with a specific amt. of C, Cr and Al, Ti, etc. to soaking to the solutionizing temp. of a gamma phase or above and to work hardening at the recrystallization temp. or below and further to age hardening. CONSTITUTION:An Ni-base alloy contg. 0.01-0.20wt% C, 13.0-23.0% Cr, 1.5- 3.5% Ti and 0.1-4.5% Al (where >=2.0% Ti+Al) is melted. The billet of such Ni-base alloy is soaked to the temp. above the solubilizing temp. of the gamma phase [Ni3(Ti; Al)]. The billet is then work-hardened by >=20% working at the recrystallization temp. or below and is age-hardened at 600-850 deg.C in this state. The inter-granular precipitation of the gamma phase is thereby accelerated and the eta phase at the grain boundary is suppressed. This material is applicable to a material for the exhaust valve of an internal-combustion engine and a material for heat-resistant parts of a turbine, etc.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a high-strength heat-resistant material suitable for producing a high-strength heat-resistant material suitable as, for example, an exhaust valve material for an internal combustion engine or a material for heat-resistant parts such as a turbine. This invention relates to a method for manufacturing materials.

(Prior art) For example, in the exhaust valve used in marine diesel engines, the face part in particular can withstand repeated thermal stress due to heating and cooling, and can also withstand double lotion corrosion caused by the adhesion of combustion residues. Normally, JIS 5UH is required for this type of application.
Martensitic heat-resistant steels such as No. 3 and austenitic heat-resistant steels such as 5UH32 are used, and welding of hardened alloys such as cobalt-based alloys has been applied to the valve face surface, which requires particularly high hardness.

Incidentally, in recent years, with the demand for higher engine efficiency and the trend toward lower quality fuel, the environment in which valves are used has become increasingly harsh, and higher performance valve materials are being sought.

Recently, Nimonic has been developed for such applications.
) Nickel-based heat-resistant alloys such as 80A have come into use, but this type of nickel-based heat-resistant alloys was originally developed for gas turbine blades, and creep strength is the most important factor due to the conditions of use. The heat treatment applied was also developed for this purpose.

However, the important properties for the above-mentioned exhaust valves are strength at high temperatures, particularly fatigue strength and hardness. Therefore, the standard heat treatment applied to gas turbine blades and the like described above is not necessarily appropriate for such uses.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to manufacture a high-strength heat-resistant material that has excellent strength at high temperatures, particularly fatigue strength, and at the same time has high hardness. The purpose of this study is to provide a method for producing high-strength, heat-resistant materials that can

(Structure of the Invention) A method for producing a high-strength heat-resistant material according to the present invention includes, in weight percent, C: 0.01 to 0.20%, Cr: 13.0 to 23.
0%, Ti: 1.5-3.5%, A text: 0.1-4
．． 5% and ("rt+A sentence): 2.0% or more is the basic component, B: 0.02% or less, Zr:
0.10% or less, Hf: 1 or 2 of 2.0% or less, Ca: 0.03% or less, Mg: 0.03% or less, REM: 0.03% or less Or two or more types, Mo: 5.0% or less, W: 5.0% or less, Nb+T
a: One or more of 5.0% or less, Co
When heat-treating a Ni-based alloy containing one or two of the following: 20% or less, Fe: 40% or less, the alloy is heated to a temperature below the solid solution temperature of the γ' phase [Ni3 (Ti, text A)]. After soaking at a temperature of 2, it is work hardened by 20% or less at a temperature below the recrystallization temperature.
It is characterized by being age hardened at 0°C.

The structure obtained by the processing heat treatment of the Ni-based alloy described above is a γ′ phase [N i 3 (T i *AM)]
and consists of a cellular structure of dislocations bottled by carbides. ' Such a substructure does not change much even when used at temperatures of 700°C or higher, so high strength is maintained, and excellent toughness and ductility can be obtained because dislocations move relatively easily within the cell structure.

On the other hand, in the case of conventional standard heat-treated materials, in order to increase the strength, γ' phase forming elements such as Ti, AJ, Nb, etc. are added, or Mo.

Measures are taken to increase solid solution strengthening elements such as W and Ta. However, in the tissue created in this way, γ′
Due to the dislocation structure caused by coherent strain due to homogeneous precipitation of phases, its toughness and ductility decrease significantly with increasing strength.

As described above, the processed and heat-treated material according to the present invention has considerably superior toughness and ductility compared to standard heat-treated materials of the same strength level, and high strength can be obtained without necessarily increasing the alloying element. Of course, it goes without saying that alloying elements may be added as necessary.

Next, the reasons for limiting the preferred range of components (wt%) of the Ni-based heat-resistant alloy to which the present invention is applied will be explained.

C: 0.0L-0.20% C forms a carbide with Ti, Cr, etc., and is an effective element for stabilizing the dislocation cell structure and grain boundaries by precipitation of this carbide. As a result, the structural stability is sufficiently maintained up to high temperatures, and in order to obtain this effect, the C content is preferably 0.01% or more.

If the C4 content is less than o, oi%, the crystal grains tend to become coarse, and it is difficult to obtain sufficient properties even through mechanical heat treatment.On the other hand, if the Ci content exceeds 0.20%, the amount of carbides increases excessively and inhibits workability. Therefore, it is not desirable.

Cr: 13.0-23.0% 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 must be added in an amount of 13.0% or more. It's good. However, if the amount is too high, σ phase will be formed and the toughness and ductility will decrease.
It is better to keep it below %.

Ti: 1.5-3.5% Ti is an element necessary to combine with Ni and AM to form a γ' phase [Ni3 (Ti, text A)] that is effective in improving high-temperature strength. For this purpose, it is preferable to add 1.5% or more. However, if a large amount is added, η phase [Ni
3Ti], the high temperature properties deteriorate due to the precipitation of 3.5
It is better to keep it below %.

A text = 0.1 to 4.5% A text is an element necessary for the formation of the γ' phase like Ti,
For this purpose, it is preferable to add 0.1% or more. but,
If added in a large amount, the Ti/A, l ratio decreases, resulting in a decrease in strength, so it is preferable to limit the amount to 4.5% or less.

Ti+A: 2.0% or more Ti and Al are added for the reasons mentioned above, but the strength of the alloy increases with the amount of (Ti+A). therefore,
For example, for applications such as exhaust valves (TI+AM
) If the amount is less than 260%, it is difficult to obtain sufficient hardness, so it is necessary to make it 2.0% or more. but,(
If the amount of Ti+A11) is too large, the workability in hot and warm conditions will deteriorate, so it is more desirable that the amount is 5.0% or less.

B: 0.02% or less B is an element that has the effect of suppressing the precipitation of the η phase. In order to obtain such an effect, it is more desirable to contain 0.02% or less.
It is good to add more than 0.001%□ if necessary, but adding too much will significantly lower the local melting temperature of the grain boundaries and impair hot workability, so it is better to limit it to 0.02% or less.

One of Zr: O, 10% or less, Hf: 2.0% or less
Zr and Hf are effective elements for forming carbides and increasing high temperature strength and toughness, and are also effective for strengthening grain boundaries and increasing strength and toughness, so they can be used as needed. It is good to add Zr to 0.1θ% or less, and Hf to 2.0% because too much will deteriorate toughness and workability.
It is better to keep it below %.

Ca: 0.03% or less, Mg: 0.03% or less.

REM: 0.03% or less of one or more of Ca, Mg, and REM improves hot workability by fixing S, and also improves toughness and ductility by controlling the distribution form of carbides. It is good to add one or more of these elements.However, if added in large amounts, workability deteriorates, so it is better to limit each to 0.03% or less.

Mo: 5.0% or less, W: 5.0% or less, Nb+Ta
(Including cases where either one is O): 5.0% or less of one or more of Mo, W, Nb, and Ta form carbides to improve high-temperature strength and toughness. It is an effective element, and in order to obtain such an effect, M o , W ,
Nb.

It is also good to add one or more of Ta.
However, if it is too much, the toughness and workability will deteriorate, so Mo
: 5.0% or less, W: 5.0% or less, Nb+Ta: 5.
It is preferable to set it to 0% or less.

Co: 20% or less, Fe: 40% or less Co can be added as a replacement element for Ni, and is an element that strengthens the base and at the same time contributes to increasing creep strength. Therefore, it can be added in an amount of 20% or less. Further, Fe can also be added as a substituent element for Ni, and since it becomes possible to reduce the cost of the alloy, it can also be added in a range of 40% or less.

Ni: Remaining Ni is an element necessary for stabilizing the austenite structure and at the same time forming the γ' phase [Ni3 (Ti, Al)], so it was left as the remainder.

The method for producing a high-strength heat-resistant material according to the present invention is to prepare a Ni-based heat-resistant alloy having the composition as exemplified above, at a temperature higher than the solid solution temperature of the γ' phase [Ni3 (Ti, A pattern)]. , for example, after soaking at a temperature of 1050~ttoo℃ or higher, the temperature is lower than the recrystallization temperature, for example, 980~
It is work hardened by adding 20% or more processing at a temperature of 102060 or less, and the work hardened state is 600 ~
The γ' phase [Ni3 (
Ti, A11)] is promoted in the grains, and at the same time, the precipitation of the η phase [Ni3Ti] at the grain boundaries is suppressed.

Next, the above processing heat treatment will be explained in more detail.

In order to obtain high hardness through processing heat treatment, it is necessary to first soak the material at a sufficiently high temperature, then apply processing strain to the material below the recrystallization temperature to harden it, and then perform age hardening treatment.

Figure 1 shows Nimonic 80A.
(See Table 1 for component composition) and Waspaloy (Wasp
This figure shows the effects of processing temperature and amount of processing on the aging hardness of alloys (see Table 3 for component composition). Among these, the recrystallization temperature of Nimonic 80A is 9
Although it is around 80℃, work hardening does not occur when the processing temperature is above the recrystallization temperature, and when the processing temperature is below the recrystallization temperature, the lower the processing temperature and the greater the amount of processing, the harder the material after 700℃ aging tends to increase. There is.

On the other hand, since the recrystallization temperature of Waspaloy is around 1020℃, there is almost no work hardening when processing at 1050℃, which is above the recrystallization temperature, but below the recrystallization temperature, the lower the processing temperature and the greater the amount of processing. The amount of work hardening increases, and the hardness after aging at 750°C increases.

From these results, in actual processing, depending on the composition of the Ni-based heat-resistant alloy, 105
After soaking to about 0-tioo”c, processing starts from this temperature, and in the case of Nimonic 80A, it is 980℃ or less,
In the case of Waspaloy, the processing is carried out at 1020° C. or below so as to leave at least 20% or more, more preferably 30% or more of the processing amount.

By the way, if the above-mentioned processing is performed at a temperature that is too low, for example, lower than 800°C, the mode of deformation becomes planar sliding, which tends to cause non-uniform strain deformation, and even after aging treatment, the non-uniformity of mechanical properties continues. However, when used in applications where repeated stress is applied, fatigue failure is likely to occur at an early stage.For this reason, when machining parts that require particularly high fatigue strength, it is better to finish processing at a relatively high temperature, e.g., 800°C or higher. desirable.

In order to harden the steel by precipitation of the γ' phase over the entire surface in the aging treatment after processing, the aging treatment at 600 to 850°C is necessary. That is, Tl in aging treatment at a temperature lower than 600°C.

Because the diffusion rate of An is slow and the precipitation of the γ' phase does not occur actively, it is difficult to obtain sufficient hardness.
If aging treatment is performed at a temperature exceeding 0℃, the rearrangement of the dislocation cell structure formed by the previous processing will be promoted and the amount of work hardening will decrease, so it is difficult to obtain sufficient hardness through the final aging treatment. This is because it becomes difficult. 1 (Example 1) A medium-sized marine exhaust valve was manufactured using a billet with a diameter of 180 mm that was forged from an ingot with a diameter of 400+U melted in a vacuum arc furnace. The chemical components of the materials used are shown in Table 1.

The forging of the valve is divided into the forging of the shaft and the molding of the cap.First, in the forging of the shaft, the heating temperature was 1050°C and the diameter was 75mm. At this time, the finishing heat processing rate was 30%, and the final temperature was 900°C.

Next, in the forging of the umbrella part, the heating temperature was set to 1050°C, and the mold was put into a mold, and it was finished to a diameter of about 3001111 mm in one heat. At this time, the finishing temperature at the face of the valve is approximately 85.
The temperature at the center of the 0°C1 umbrella tip was approximately 900°C. In addition, the machining rate was at most 60% on the face portion, and a valve 1 having the shape shown in Fig. t$2 was manufactured.

Next, this valve 1 was heated for 1 t (76,700°C
1080℃X
After heating for 1 hour and solid solution treatment with water cooling, 700°C for 16 hours.
A tensile test was conducted on the shaft portion of each specimen subjected to standard heat treatment including aging treatment of r. The results are summarized in Table 2.

As shown in Table 2, it is clear that the processed and heat-treated materials have significantly higher yield strength and tensile strength up to high temperatures of 700° C. or higher, and maintain high toughness without much decrease in ductility.

FIG. 3 shows the hardness distribution of the face portion 1a of the valve 1 in the depth direction. In Fig. 3, the hardness of the finished surface of the processed and heat-treated material is at a high level comparable to that of the welded area of ordinary cobalt-based hardfacing alloys, and is approximately 20 mm hard from the finished surface.
(2) Even at the depth of the intestines, the amount of decrease in hardness is only about Hv30, and it is clear that the hardened layer extends deep.

In this way, valves produced by processing heat treatment have excellent corrosion resistance and high strength and hardness even without the addition of solid solution strengthening elements such as Mo, W, and Ta. It is extremely excellent in that it can sufficiently withstand repeated stress up to high temperatures in a severe corrosive environment without necessarily performing build-up hardening welding.

(Example 2) A medium-sized marine exhaust valve was manufactured using a billet with a diameter of 50 mm that was forged from an ingot with a diameter of 4001II11 melted in a vacuum arc furnace. The chemical components of the materials used are shown in Table 3.

The forging of the valve is divided into the forging of the shaft part and the molding of the cap part.First, in the forging of the shaft part, the heating temperature was 1120°C and the diameter was 25 mm. At this time, the finishing heat processing rate was 30%, and the final temperature was 950°C.

Next, in the forging of the umbrella part, the heating temperature was set to 1100°C, and the mold was put into a mold, and it was finished with a diameter of about 1201I11 with 1 heat. At this time, the finishing temperature at the valve face is approximately 90°C.
0'0, and the temperature at the center of the umbrella tip was approximately 940°C. Also,
The maximum machining rate was 60% on the face portion, and a valve 1 having the shape shown in FIG. 2 was manufactured.

Next, this valve 1 was directly aged at 760°C for 16 hours, and then heated at 1040°C for 1 hour.
After heating and water-cooling solid solution treatment.

Tensile tests were conducted on the shaft portions of the standard heat-treated specimens, which were subjected to aging treatments of 845° C. for 4 hrs and 760° C. for 16 hrs. The results are summarized in Table 4.

As shown in the t54 table, the processed and heat-treated material has significantly higher yield strength and tensile strength up to high temperatures of 700°C or higher, and it is clear that the ductility does not decrease much and high toughness is maintained. It is.

FIG. 4 shows the hardness 11j of the face portion 1a of the valve 1 in the depth direction. In Figure 4, the hardness of the finished surface of the processed and heat-treated material is at a high level comparable to that of the welded area of ordinary cobalt-based hardfacing alloys, and even at a depth of approximately 10 m+s from the finished surface, the hardness decreases only slightly. to Hv
It is only about 20, and it is clear that the hardened layer extends deep.

In this way, valves manufactured by processing heat treatment have excellent corrosion resistance and high strength and hardness, and can be used up to high temperatures in harsh corrosive environments without necessarily having to undergo overlay hardening welding. (Effects of the Invention) As explained above, the method for producing a high-strength heat-resistant material according to the present invention has a C: 0.01% by weight. ~0.20%
, Cr: 13.0-23.0%, Ti: 1.5-3.5
%, A standing: o, i ~ 4.5% and (Ti + AJlj)
: 2, 0% or more as basic components, B: 0.02% or less, Zr: 0.10% or less, Hf as necessary.
: 1 or 2 of 2.0% or less, Ca: 0.0
3% or less, Mg: 0. C1% or less, REM: 0.03%
One or more of the following.

Mo: 5.0% or less, W: 5.0% or less, Nb+Ta:
One or more of 5.0% or less, Co:
When heat-treating a Ni-based alloy containing one or two of the following: 20% or less, Fe: 40% or less, the alloy is converted into a γ' phase [Ni3 (Ti).

A)] is soaked at a temperature above the solid solution temperature, then work hardened by working at 20% or more below the recrystallization temperature, and then age hardened at 600 to 850°C. The processed and heat-treated material according to the invention has higher strength and hardness than standard heat-treated materials, and at the same time has significantly superior toughness and ductility.It is possible to obtain high strength and high toughness without necessarily adding various kinds of alloying elements in large amounts. In addition, the hardness of the finished surface is at a high level comparable to that of the welded parts of ordinary cobalt-based hardfacing alloys, and the hardened layer extends deep. When applied to the industry, it can produce a product that can sufficiently withstand repeated stress up to high temperatures in a severe corrosive environment without necessarily performing expensive overlay hardening welding.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the results of investigating the relationship between processing conditions and hardness after aging for Ni-based heat-resistant alloys, FIG. 2 is a partial explanatory diagram showing the shape of a valve manufactured in an example of the present invention, FIG. 3 and fJJA are graphs showing the hardness distribution in the depth direction of the valves investigated in Examples 1 and 2 of the present invention, respectively. Patent Applicant: Daido Steel Co., Ltd. Representative Patent Attorney Shio Ko Shio Old Figure 1 Sword Craftsman's Badge (%) Figure 3 Stainless Steel 14II Isu J: 114b

Claims (1)

[Claims] (1) In weight%, C: O, 01-0.20%, Cr
: 13.0-23.0%, Ti: 1.5-3.5%,
A sentence = 0.1 to 4.5% and (Ti + A sentence): 2.0
When heat-treating a Ni-based alloy having a basic content of 5 or more, the alloy is soaked at a temperature above the solid solution temperature of the γ' phase, and then work-hardened by working by 20% or more at a temperature below the recrystallization temperature. A method for producing a high-strength, heat-resistant material, which is then age-hardened at 600 to 850°C. (2) The method for producing a high-strength heat-resistant material according to claim (1), wherein the Ni-based alloy contains 0.02% or less of B. (3) Ni-based alloy contains Zr:O, 10% or less. Hf: A method for producing a high-strength heat-resistant material according to claim 1 or 2, which contains one or two of 2.0% or less. (4) Ni-based alloy contains Ca: 0.03% or less. Claim No. 1 containing one or more of Mg: 0.03% or less and REM: 0.03% or less
) to (3), the method for producing a high-strength heat-resistant material. (5) Ni-based alloy, Mo: 5.0% or less, W: 5.0
% or less, and Nb+Ta: 5.0% or less. (8) Ni-based alloy contains Co: 20% or less, Fe: 4
The method for producing a high-strength heat-resistant material according to any one of claims (1) to (5), which contains one or two of 0% or less.