JPS5834129A - Heat-resistant metallic material - Google Patents

Abstract

PURPOSE:To improve high-temp. characteristics, more particularly tensile strength and fatigue strength by heat-treating an alloy contained with prescribed ratios of Fe, C, Si, Mn, Ni, Cr, etc. under prescribed conditions. CONSTITUTION:A titled metallic material wherein the alloy contg. 0.01-0.2% C, <=2% Si, <=2% Mn, 25-50% Ni, 13-23% Cr, 1.5-3.5% Ti, 0.1-1.5% Al, >=2 Ti/Al, and the balance Fe or further contg. >=1 kind selected among <=3% Mo, <=3%, W, <=5% (Nb+Ta), <=1% V, <=3% Hf, <=0.5% Zr, <=0.05% B in addition to the above is preliminarily heat-treated at 700-975 deg.C, and is subjected the same to hot working at <=975 deg.C and further to solutionizing and aging treatments at <=975 deg.C. Such metallic material has excellent high temp. characteristics, more particularly tensile strength and fatigue strength.

Description

[Detailed description of the invention] Concerning heat-resistant metal materials with excellent workability.

For example, disks for planting gas turbine blades,
Nickel-based alloys are used as materials for manufacturing jet engine parts that require heat resistance. but,
These high alloy materials are extremely expensive, increasing the cost of the product.

Therefore, there was a strong desire to obtain a material that was less expensive, that is, had a lower alloy, but had the same performance.

One of the present inventors previously researched materials for exhaust valves of internal combustion engines, and found that an alloy with the following composition was obtained: C: 0.
0 1-0.2 0% Si:2. 0% or less Mn: 2
．． Q% or less Ni: 25-50% Cr:
13-23% Ti: 1.5-3.5% At: 0.
1-1.5% The remainder is substantially Fe Nickel-based alloy (e.g. Inconel 7'51
) and have already disclosed it (Japanese Patent Application Laid-Open No. 1982-0148).

Further research progressed, and this time, an alloy with the above composition was made with Ti.
/At ratio of 2.0 or more is subjected to heat treatment and processing under specific conditions to make the structure finer.
The present invention was achieved by discovering that high-temperature properties can be improved.

The heat-resistant metal material of the present invention has C: 0.01 to 0.20%,
Si: 2.0% or less, Mn: 2.0% or less, Ni: 25
~50%, Cr: 13 ~ 23%, Ti: 1.5
~3.5%, At: 0.1~1.5%, provided that the Ti/At ratio is 2.0 or more, and the remainder is substantially F.
The alloy consisting of E is preheat-treated at a temperature of 700 to 975°C, then hot worked at a temperature of 975°C or lower, and further subjected to solid solution treatment and aging treatment at a temperature of 975°C or lower.

In addition to the above basic composition, the heat-resistant metal material of the present invention has M
O: 3.0% or less, w: 3. Q% or less, (Nb+Ta
): 5.0% or less, V: 1.0% or less, Hf: 3
．． 0% or less, zr: 0.5% or less 1 and B: 0, 05%
It can contain one or more selected from the following, thereby exhibiting even better high temperature properties.

The reason why a high Ti/At ratio was selected in the heat-resistant metal material of the present invention is to precipitate a large amount of η phase (N l 3 7 r ). Precipitation hardening type N
In the case of i-based alloys, attempts have already been made to improve thermal fatigue properties by forming fine intermetallic compounds (Japanese Patent Application Laid-Open No. 46-6003). However, the target is I
nconel 718, Incoloy 901, Wa
Limited to high alloys such as spaloy, generally
In Fe-based alloys containing 50% or less Ni, precipitation of the η phase was considered harmful.

The present invention breaks the conventional wisdom and selects the above Ti/At ratio in an attempt to actively utilize the η phase,
Success was achieved by combining this with the heat treatment and processing conditions described above.

The above alloy composition will be explained as follows.

C: 0.01-0.20% C is necessary to combine with Cr and Ti to form carbide and increase high-temperature strength.

However, since a large amount impairs toughness and ductility, the above range should be selected.

Si: 2.0% or less Although added as a deoxidizing agent, it is better to have less from the viewpoint of toughness and ductility, so it was limited to 20% or less.

Mn: 2.0% or less Like Si, Mn is used as a deoxidizing agent, but if the amount is too large, it will reduce the oxidation resistance of the material at high temperatures, so it should be kept within the above limit.

Ni: 25-50% Stabilization of austenite structure and γ' mentioned later
It is necessary to form the (Ni3(AtTi)) phase.

The lower limit of 25% was set to avoid the formation of brittle phases such as 6-phase during use at high temperatures, but on the other hand, adding more than necessary will not improve high-temperature performance, and Since it goes against the purpose of providing materials for
Marketed to %.

Cr: 13-23% Added to ensure corrosion resistance and oxidation resistance.

If it is too much, it will lead to the formation of dust phase and reduce toughness and ductility.
Keep it within the above range.

Ti: 1.5-35% As mentioned above, the γ' phase (Ni3(A4T) is effective for precipitating the η phase (Ni3Ti) and improving high temperature strength.
It is necessary to form i)), and the content is appropriately within the above range.

At: O81~1.5% Like Ti, it is necessary for the formation of the γ' phase.

The above limit was set because the presence of an excessive amount reduces precipitation of the η phase and is also unfavorable for hot workability.

Ti/At: 2.0 or more As mentioned above, it is necessary for the precipitation of the η phase. Ti
Regarding components other than At and At, various alloys with typical compositions within the scope of the present invention are heat-treated at 900° x 24 hours, and the η phase accounts for the precipitates of intermetallic compounds. When examining how the ratio changes to 5 depending on the T i /A 1 ratio, the results shown in FIG. 1 were obtained. From this graph it can be seen that the Ti/At ratio should be greater than 2.0, preferably 3-4 or more.

The main effects of the above-mentioned elements that can be added as desired are as follows.

Mo:3. Q% or less, w: 3. Q% and below are solid-dissolved in the particles and strengthened.

(Nb+Ta): 5.0% or less, V: 1.0% or less, Z
r: 0.5% or less, Hf: 3.0% or less These elements form carbides and strengthen grain boundaries. In addition, (Nb+
Ta) and Hf, like Moj and W, also have the function of solid solution strengthening. It also forms intermetallic compounds that contribute to precipitation and strengthening.

B: 0.05% or less Segregates at grain boundaries and strengthens them.

If the above metal elements are present in excessive amounts, they may impair oxidation resistance or have a negative effect on high-temperature strength.

A large amount of B reduces hot workability. Therefore, both should be added within the above limits.

Next, regarding the heat treatment and processing conditions, the preliminary heat treatment performed on the alloy having the above composition at a temperature of 700 to 975°C is, of course, for precipitating the η phase. For alloys with representative compositions within the scope of the present invention, η
The result of drawing the precipitation curve of the phase (Ni3Ti) is as shown in FIG. 2, and from this graph it can be seen that the treatment should be within the above temperature range, preferably 800 to 950°C.

By hot working at a temperature of 975° C. or lower, the η phase precipitated by the preliminary heat treatment is destroyed and dispersed uniformly and finely in the structure.

By solid solution treatment and aging treatment at temperatures below 975° C., a fine structure (grain size, finer than Nn8) with no coarse grains can be obtained. it is,
The above-mentioned uniform and finely dispersed η phase has the effect of inhibiting the movement of grain boundaries.

The following examples demonstrate that the heat-resistant metal material of the present invention obtained as described above has excellent high-temperature properties, especially tensile strength and fatigue strength.

EXAMPLE An alloy having the chemical composition shown in Table 1 (the balance being Fe) was melted in a high frequency vacuum induction furnace and cast into a 509 ingot.

A billet with a diameter of 90 Iu was obtained by subjecting it to soaking treatment and forging in a temperature range of 1150 to 950°C. This billet was cut to a length of 90 m to produce a forged material.

The material was processed under the following conditions.

[Process X]

Preliminary heat treatment at 900°C for 24 hours (η phase precipitation) → 1/2U upsetting forging at heating temperature of 950°C → 930°C for 5 hours (recrystallization), water cooling → 750°C for 20 hours (γ-prime phase precipitation) Aging treatment, air cooling.

For comparison, an alloy having a composition according to the present invention was processed under the following conventional conditions that were not according to the present invention [Process Y] No preliminary heat treatment → 1/2 U at a heating temperature of 1,150°C Upsetting forging → 1,000℃ x 1 hour, water cooling → 750℃ x 2
Tests were also conducted in the case where the alloy was air-cooled for 0 hours and in the case where the process X was applied to an alloy having a composition not in accordance with the present invention.

(1) Microstructure.

The microstructures of specimen B having an alloy composition according to the present invention subjected to process X and process Y were examined.

The results are shown in Figure 3 (present invention) and Figure 4 (comparative example).
Shown below. (The magnification is 500 times) According to the present invention,
An extremely fine structure can be obtained compared to the comparative example using the conventional technology.

(2) Tensile properties A high-temperature tensile test at 600°C was conducted on the material of the present invention and the material of the comparative example. The results are shown in Table 2. As shown in the table, the 0.2% yield strength and tensile strength of the material of the present invention are much higher than those of the comparative example material.
Comparable to expensive nickel-based alloys.

Furthermore, the high-temperature ductility shown by elongation and reduction of area is also at the same level as the comparative example, despite the improvement in strength.

(3) Fatigue properties A high temperature fatigue test was conducted at the same temperature of <600°C. The results are listed in Table 2. Here again, the effects of the present invention can be clearly seen.

[Brief explanation of drawings]

Figure 1 shows the η phase (N + 3T
FIG. 2 is a graph showing how the ratio occupied by r ) changes depending on the Ti/At ratio in the alloy. FIG. 2 is an η phase precipitation curve of an alloy having a typical composition of the present invention, and is a graph showing the degree of η phase precipitation in relation to heat treatment temperature and holding time. 3 and 4 are micrographs showing the microstructure of an alloy having a composition according to the present invention, in which FIG. 3 is a heat treatment according to the present invention (processing), and FIG. 4 is a heat treatment according to the prior art. - Each processed item is hailed. (Both magnifications are 500x) Patent applicant: Daido Steel Co., Ltd. Agent: Patent attorney: Suga Sofusai 1 Figure 0 2 4 6 8 10Ti/
Al Figure 3 Figure 4 Figure-154-・

Claims (2)

[Claims] (1) C: 0.01-0.20%, Si: 2.0
% or less, Mn: 2.0% or less, Ni: 25-50%, C
r: 13-23%, Ti: 1.5-3.5%, At: 0
．． Contains 1 to 1.5%, provided that T i /Az:
2.0 or more, and the remainder is substantially Fe, is preheat-treated at a temperature of 700 to 975°C, and then
A patent characterized by hot working at a temperature of 5°C or lower, and further solid solution treatment and aging treatment at a temperature of 975°C or lower. (2) C: 0. 0 1 to 0.20%, Si:
2.0% or less, Mn: 2, Q% or less, Ni: 25
~50%, Cr: 13-23%, Ti: 1.5-3.
5%, At: 0.1-1, Contains 5%, provided that T
i/At: 2. 0 or more, and furthermore, Mo
: 3.0% or less, w: 3. Q% or less, (Nb+Ta
): 5.0% or less, V': 1.0% or less, Hf: 3
．． 0% or less, Zr: 0.5% or less and B: 0.05%
An alloy containing one or more selected from the following, with the remainder substantially consisting of Fe, is preheat-treated at a temperature of 700 to 975°C, then hot worked at a temperature of 975°C or less, and then further heated to 975°C. A heat-resistant metal material with excellent high-temperature properties, characterized by having been subjected to solid solution treatment and aging treatment at the following temperatures.