JPH0448051A - Heat resistant steel - Google Patents

Abstract

PURPOSE:To obtain a heat resistant steel excellent in high temp. properties, particularly in thermal fatigue properties by incorporating Ni, Cr or the like in a specified compsn. into a steel and regulating the Ti/Al ratio. CONSTITUTION:A heat resistant steel contg., by weight, 0.03 to 0.30% C, <=2.5% Si, <=2.5% Mn, 20 to 30% Ni, 10 to 25% Cr, 1.5 to 2.5% Ti, 0.05 to 0.20% Al, 0.5 to 3.0% Mo, 0.1 to 3.0% V and 0.001 to 0.01% B, satisfying 10 to 40 Ti/Al ratio and the balance substantial iron is prepd. If required, one or more kinds among <=3.0% W, <=4.0% Nb+Ta, <=2.0% Hf, 0.001 to 0.05% rare earth metals, 0.001 to 0.03% Mg and 0.001 to 0.03% Ca are furthermore added to the above compsn. In this way, the heat resistant steel high in thermal fatigue properties, particularly in 0.02% proof stress and having a long creep rupture life can be obtd. and is suitable for gas turbine parts, aircraft engine parts or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-resistant steel that is suitable for gas turbine parts, aircraft engine parts, etc. and has excellent high-temperature properties, particularly thermal fatigue properties.

[Conventional technology]

For example, disks for planting gas turbine blades,
Conventionally, parts of jet engines that require heat resistance are
Nickel-based alloys are mainly used. However, since these nickel-based alloys use extremely expensive high-alloy materials, there is a problem in that the manufacturing cost is high.

In order to solve this problem, various proposals have been made regarding low alloys with low nickel content.

In precipitation hardening type nickel-based alloys, fine intermetallic compounds are generated to improve thermal fatigue resistance, but in general, in Fe-based alloys with Ni 50% or less, η phase (Ni, Ti ) was thought to be harmful. In order to break this conventional wisdom, it has been proposed to increase the Ti/Al ratio to precipitate the η phase to improve high-temperature properties. For example, in Japanese Patent Publication No. 1-38848, N
For heat-resistant metal materials containing 25-50% of i, T
Ni/A1 ratios of up to 6.6 are exemplified, and JP-A-60-46353 discloses Ni
For heat-resistant metal materials containing 15-25% Ti/
Examples include those with an Al ratio of up to 6.6.

[Problem to be solved by the invention]

By the way, the heat-resistant metal materials with low nickel content that have been proposed in the past do not yet have high-temperature properties equivalent to those of nickel-based alloys. There is a strong desire to obtain Especially high 0.02% required for aircraft parts etc.
As for yield strength, a heat-resistant steel with satisfactory yield strength has not yet been obtained.

The present invention has been made in view of the above-mentioned conventional demands.

Therefore, an object of the present invention is to provide an inexpensive heat-resistant steel with excellent thermal fatigue properties.

[Means and effects for solving the problem] The present inventor has
As a result of further research on the active use of phases, we found that for heat-resistant steels with specific alloy compositions containing Ni of 20 to 30%, a specific range of Ti/Al ratios that is much higher than the Ti/Al ratio described in the above publication was found. By selecting the Ti/Al ratio of η
It has been discovered that when a large amount of the phase is precipitated, a product with significantly improved thermal fatigue properties can be obtained, and the present invention has been completed.

The first heat-resistant steel of the present invention has a C: 0.03 to 0 by weight.
．． 30%, S f: 2.5% or less, Mn: 2.5%
Below, Ni: 20-30%, Cr: 10-25%, Ti
: 1.5~2.5%, A1: 0.05~0.20
%, Mo: 0.5-3.0%, V: 0.1-
3.0%, B: 0.001 to 0%, and Ti/Al is 10 to 40, with the remainder substantially consisting of Fe.

Moreover, the second heat-resistant steel has a C: 0.03 to 0.03 by weight.
30%, Si: 2.5% or less, Mn: 2.5% or less, Ni: 20-30%, Cr: 10-25%, Ti:
1.5-2.5%, AI: 0.05-0.20%
, Mo: 0.5-3.0%, V: 0.1-31%, B: 0.001-0.01%, and T
i/Al is lO ~ 40, furthermore, W: 3.0% or less, Nb + Ta: 4.0% or less, Hf: 2.0% or less,
REM: 0.001-0.05%, Mg: 0.0
01-0.03%, and Ca: 0.001-0.0
It is characterized in that it contains one or more selected from 3%, with the remainder consisting essentially of Fe.

Hereinafter, the alloy composition of the heat-resistant steel of the present invention and reasons for limitation will be explained.

C: 0.03 to 0.30% C is an element necessary to combine with Cr and Ti to form carbide and increase high-temperature strength. However, if it exists in a large amount, it will impair the hot side properties and toughness and ductility, so it is necessary to select it within the above range.

Si: 2.5% or less It is added as a deoxidizing agent, but from the viewpoint of toughness and ductility, less is better, so it is limited to 2.5% or less.

Mn: 2.5% or less It is added as a deoxidizing agent like Si, but if the amount is too large, it will reduce the oxidation resistance at high temperatures, so 2.5%
Limited to the following.

Ni: 20-30% Ni stabilizes the austenite phase and stabilizes the γ' phase [N i 3
(AITs) ]. The lower limit of 20% was set to avoid the formation of brittle phases such as σ phase during use at high temperatures. On the other hand, even if more Ni is added than necessary, no improvement in high-temperature performance can be expected, and this goes against the 1-1 objective of providing a low-cost key material, so the upper limit is set at 50%.

Cr: 10-25% Added to maintain corrosion resistance and oxidation resistance, but too much Cr causes the formation of σ phase and reduces toughness and ductility, so it is set in the range of 10-25%. do.

Ti: 1.5 to 2.5% Ti is an element necessary for precipitating the η phase (N 13 T r ) and forming the γ' phase that is effective in improving high temperature strength, A suitable range is 1.5-2
．． Set 5%.

A I: 0.05-0.20% Like Ti, it is an important element for generating the γ' phase, but adding an excessive amount reduces the precipitation of the η phase, while decreasing hot workability. Since it causes deterioration, the upper limit is set to 0.20%.

Mo: 0.5 to 3.0% Mo exhibits the effect of solid solution in particles and strengthening, but if the amount is too large, high temperature strength decreases and embrittlement due to precipitation of σ phase is caused. , set the upper limit to 3.0%.

V: 0.1 to 3.0% (2) exhibits the effect of solid solution in particles to strengthen them, as well as the effect of forming carbides to strengthen grain boundaries, similar to Mo, so 0.1 is an appropriate range. The content is set to 3.0%, preferably 0.5 to 1.0%.

B: 0.001 to 0.01 It segregates at grain boundaries and shows the effect of strengthening the grain boundaries, but adding a large amount impairs hot workability, so the upper limit should be set at 0.01%.
Set to .

Ti/Al: 10 to 40 As the Ti/Al ratio increases, the amount of η phase precipitated increases. And Ti/Al is in the range of 1O~40, especially 1
In the range of 2 to 36, the 0.02% yield strength is significantly increased, a material with a high elastic modulus is obtained, and the creep rupture life is also improved.

In the heat-resistant steel of the present invention, W, Nb+Ta, H
One or more elements selected from f, REM, Mg, and Ca may be contained. The composition range when these elements are contained will be explained below.

W: 3.0% or less W exhibits a strengthening effect through solid solution strengthening and grain boundary segregation of carbides, but the upper limit is set to 3.0% as a preferable range.

Nb+Ta: 4.0% or less, Hf: 2.0% or lessN
The elements b, Ta, and Hf form carbides to strengthen grain boundaries. Note that these elements include Mo and W.
Similarly, it shows solid solution strengthening effect.

It also forms intermetallic compounds and contributes to improving precipitation strength. However, addition of an excessive amount causes deterioration of oxidation resistance, so the upper limits are set to 4.0% for N))+Ta and 2.0% for Hf.

REM・0.001-0.05%, Mg: 0.0
01-0.03%, and Ca: 0.001-0.0
3% All of these elements have deoxidizing and desulfurizing effects, increasing the cleanliness of steel. Furthermore, Mg and Ca segregate at grain boundaries and have the effect of strengthening steel. However, if added in excess, hot workability and toughness and ductility will be impaired, so the upper limit is set at REM.
:0.05%, Mg:0.03%, Ca:0.03%.

〔Example〕

Hereinafter, the heat-resistant steel of the present invention will be explained with reference to Examples.

The alloy components shown in Table 1 (the remainder is Fe) are melted in a 50 kg high-frequency induction furnace to produce a steel ingot, and then forged to produce a steel ingot.
A plate-shaped test material with a size of 0 mm x 85+++* was obtained.

Note that the sample materials were collected in a direction perpendicular to the forging direction. These test materials were subjected to solution treatment at 900°C for 1 hour, cooled in air, then aged at 705°C for 16 hours, and then aged at 650°C for 16 hours before being subjected to testing.

0.02% yield strength and 650
℃、45℃、7kgr/nu+tO) Chickrea rupture life (time to rupture) was measured. The results for Rei are shown in Table 2 and Figure 1.

Table 2 with blank space below [Effects of the Invention] Since the heat-resistant steel of the present invention is composed of an alloy composition within the above-mentioned specific composition range, it has extremely high thermal fatigue resistance, especially 0.02% yield strength, and also has creep resistance. This results in a long lifespan. Moreover, it is cheap and lightweight, so
It is useful for parts that require high thermal fatigue resistance, such as gas turbine parts and aircraft engine parts.

From Table 2 and Figure 1, Ti/Al is 10-40 (7)
It can be seen that the heat-resistant steel of the present invention within the range has a significantly high 0.02% yield strength and a long creep-loveture life.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the 0.02 proof stress and creep rupture life of the heat-resistant steel of the present invention and the T i /A I ratio. Patent applicant: Daido Steel Co., Ltd.

Claims (2)

[Claims] (1) By weight, C: 0.03-0.30%, Si: 2.
5% or less, Mn: 2.5% or less, Ni: 20 to 30%,
Cr: 10-25%, Ti: 1.5-2.5%, Al:
0.05-0.20%, Mo: 0.5-3.0%, V:
0.1 to 3.0%, B: 0.001 to 0.01%, Ti/Al is 10 to 40, and the remainder is substantially Fe. (2) By weight, C: 0.03-0.30%, Si: 2.
5% or less, Mn: 2.5% or less, Ni: 20 to 30%,
Cr: 10-25%, Ti: 1.5-2.5%, Al:
0.05-0.20%, Mo: 0.5-3.0%, V:
0.1 to 3.0%, B: 0.001 to 0.01%, Ti/Al is 10 to 40, and W:
3.0% or less, Nb+Ta: 4.0% or less, Hf: 2.
0% or less, REM: 0.001-0.05%, Mg: 0
．． 001-0.03%, and Ca: 0.001-0.0
A heat-resistant steel containing one or more selected from 3% and the remainder substantially consisting of Fe.