JPS6350448A - Dispersion reinforced alloy - Google Patents

Abstract

A dispersion strengthened powder metallurgical iron-base alloy combines good stress rupture strength and high resistance to oxidation attack at temperatures as high as 1300 DEG C and contains special amounts of chromium, aluminum, a refractory metal dispersoid and preferably titanium in addition to iron. Advantageously, the alloy is prepared by mechanical alloying.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to dispersion strengthened (DS) alloys, and more particularly to dispersion strengthened (DS) alloys that exhibit exceptional oxidation resistance at temperatures as high as 1300°C (approximately 2400'F) and thereby provide advances in the field of dispersion strengthened (DS) alloys. Oxide dispersion strengthening (ODS) is useful in the manufacture of aircraft gas turbine engine components and when industrial applications are required.
) Regarding iron-based alloys.

BACKGROUND OF THE INVENTION U.S. Pat. No. 3,992,161 describes ODS iron-chromium alloys as having very good oxidation resistance combined with high strength at high temperatures. The results described therein reflect certain improvements over iron-chromium alloys produced by more conventional melt/ingot processing methods. More specifically, ODS alloys are produced using the now well-known mechanical alloying process, which was developed approximately 20 years ago and was published in U.S. Patent No. 3,591.
No. 62, US Pat. No. 3,837,930, and the like.

Despite the advantages of the alloys described in US Pat. No. 3,992,161, such materials have been found to be unsuitable in aerospace and industrial environments. By way of illustration, the ODS material (commercially containing approximately 20% chromium and 4.5% aluminum) described in U.S. Pat. , prone to premature calcification attack (formation of low melting point phases/compounds due to corrosive deposits from the environment and/or chemical reactions with the environment itself) and/or to accelerated attack upon exposure to high temperatures over short time intervals ( Corruption is catastrophic). In this context, accelerated oxidation can be considered as a rapid change in mass of the alloy due to oxidation. If all the oxide is collected and weighed, the mass change is virtually always dramatically positive. Upon undergoing the destruction caused by such attacks, the alloy surface converts to a fragile iron oxide and iron-chromium spinel structure.

For example, burner cans in aircraft gas turbine engines of advanced design are now operating at increasingly higher operating temperatures, i.e., above about 1250°C (2308°C), e.g.
2372 guns). Similarly, industrial applications involving close contact with corrosive materials such as dust, fly ash, and molten glass require more oxidation- and/or corrosion-resistant materials.

Apart from the foregoing, what is required for such applications is high strength at operating temperatures, including stress-rupture and tensile properties, as well as flat rolled products such as sheets, strips, etc. The material is sufficiently processable that it can be formed into tubing, rings, canisters, and other shapes.

Without processability, the utility of ODS materials is significantly reduced.

Apart from U.S. Pat. No. 3,992,161, the study of Kornilov, S.C. Case and R. Pan Horn, "Aluminium in Steel", John Wiley & Sons (1953) You can also refer to Kornilov cast Fe-Cr-A'1 alloy and wrought F
The effect of up to 10% aluminum and up to 65% chromium on burnout in both e-Cr-A1 alloys was studied. Aluminum is beneficial for scaling resistance, but apparently at 1100-1400°C
There is little benefit conferred by chromium in amounts greater than 5%. Kolnikov's research did not include the processability of ODS products or the production of sheets.

R. Allen and R. Barkins (May 1973, in contract for Naval e-Air Systems φ Command) ODS iron-chromium with 16-25% chromium in 5.7-6.0% aluminum content. Aluminum-yttrium alloy vs. conventional wrought and cast 25%C
r/4%A1 and 15%Cr/4%A1 alloys were investigated.

Although such alloys could be extruded, it was pointed out that they offered nothing in terms of processability and production of important sheet product forms, for example.

SUMMARY OF THE INVENTION An ODS iron-based composition having special correlated percentages of chromium and aluminum and refractory dispersoids comprises:
To provide the alloy with a significant degree of oxidation/corrosion resistance such that it can be used in the heated sections of gas turbine engines, such as burner cans, and in industrial applications where corrosives such as molten glass, dust, fly ash, etc. are encountered. has now been discovered.

Generally speaking, the present invention provides approximately 22.5-30% chromium.
and about 5-8% aluminum. If the flat-rolled product, e.g. sheet, is required for the intended application and a significant degree of processing is required, the aluminum content should not exceed 6.25%, and the aluminum content should be between about 5% and 6.25%. It should be. In this regard, the chromium should advantageously be between 23 and 27% and the aluminum between 5 and 6%. The alloy also contains up to 5% titanium, up to 2% each of zirconium, hafnium, tantalum and vanadium.
up to 6% each of molybdenum and tungsten, up to 0.5% each of silicon and niobium, up to 0.05% each of calcium, yttrium and rare earth metals, up to 0.2% boron (the remainder being iron in nature), and strength a small but effective amount selected from the group consisting of oxides, nitrides, carbides, borides and other refractory metals having a melting point of at least about 1510°C (2750°C), such as 0. It can contain 2% by volume of at least one finely ground dispersoid. In this connection, oxides may be present up to about 10% by volume, while carbides should not exceed about 2% by volume. Nitrides and borides do not exceed 5% by volume.

In the practice of this invention, chromium may be topologically close-packed (TC
P) should not exceed 30% to minimize phase formation. On cost, there is no significant benefit derived from % chromium above about 27%.

If less harsh operating parameters are intended, the % of chromium can range up to 20%, but
At risk, oxidation resistance will decrease in a given aluminum.

Aluminum is about 5% for oxidation and corrosion resistance
It should be ~8%, but as mentioned above, preferably it should not exceed 6% when looking for optimum values in terms of processing sheets, strips, etc. Elements such as nickel, cobalt, etc. are not necessary and do not confer any particular benefits.

Although percentages higher than 0.1% are acceptable, carbon
It does not exceed %. Our studies have not shown that silicon or boron are particularly beneficial.

When heat treating sheet product forms at high temperatures, boron is
It is considered to be a cause (or cause) of distortion. Boron should preferably not exceed 0.1%. Components such as titanium, zirconium, tantalum, niobium, hafnium, zirconium, vanadium, etc. do not exceed 1%. For example, a 1% amount of tantalum resulted in a loss of processability. Tantalum tends to stiffen the alloys of the present invention, sometimes raising the ductile-brittle transformation temperature too high. Titanium in the range 0.2 to 0.75%,
preferable.

Although other dispersoid-reinforced powder metallurgy methods can be used,
The alloys of the present invention are most preferably disclosed in U.S. Patent No. 3,992
, 161 by mechanical alloying.

EXAMPLES In order to give those skilled in the art a better understanding of the invention, the following information and data are presented.

A series of alloy compositions were prepared as follows. raw material powder,
Namely, elements (e.g. Fe, Cr, AS), master alloys (e.g. Fe-Cr-AI-Ti) and yttrium supported oxides (Y2O2) were used. The powders were then blended to yield the chemical compositions given in Table I. Using steel balls as the impact/grinding media, the powder blend was mechanically alloyed in a high energy ball mill under an argon atmosphere at a ball to powder ratio of about 20=1 for about 24 hours (
HA). The MA powder was sieved to remove coarse particles (larger than about 600 microns), placed in mild steel cans, sealed, and hot compacted by extrusion. The extrudate is removed from the can, then hot rolled and cold rolled to 1.25 mm (0.05
inch) thick sheet, and then the sheet was subjected to a final anneal. This final anneal was typically 1315° C. (2400° C.) for 1 hour to achieve recrystallization.

Alloy CSi Mn AI
Cr'A O,0180,100
,134,3618,040B O,0200,
140,144J8 20.07 0CO,
0230,0g 0.10 4.27
19.50 0D O,0190,0
90,134,4123,500End
nd nd 4.3
24.0F nd nd
red 4.5 25.0
(G nd nd n
d 4.5 30.0 (HO
,0210,160,168,5824,73 [I
O, 0300, 025, 5020, 93 + [feather n
d = UI not determined Ba1-Remaining iron ☆-Public
Name (wt%) i, 27 0.011 0.006 0.0
52 0.21 Bat, 0.27
1.3B 0.007 0.001 0
．． 040 0.18 Bat, 0.
3B1.36 0.00B 0.004
0.02B 0.20 Thigh 1. 0
．． 5☆1.34 0.007 0.007
0.038 0.19 Bat,
0J4nd nd nd O
,0230,28Ba1. 0.5☆1.5
nd nd 0.051
+1.42 Ba1. 0.5☆1.5
nd nd O,0290,
42Bal, 0.5☆), 42 0.0
10 0.005 0.075 0.21
Ba1. 0.42], 47 −
- 0.100 0J2 Ba
1. 0.66 standard size specimens were cut from the manufactured sheets and then ground to approximately 600 grit for use in facilitated participation testing. A cyclic oxidation test was used. This allows samples to be heated at 1200°C, 1250°C and 13
It consisted of cycling for 24 hours in air + 5% H2O at a temperature of 00°C, then cooling to room temperature and weighing. Results are reported in Tables ■ and ■.

Table■ A 3216★ 1152 168B 4
704 1838★★ 348C4800n, d,
n, d.

D 4224 1992 168E 3
384 1656 528F 3384
1320 148G 4498 1656
480H82083216600 I 4656 3624 576★Average of 2 results; ★★Average of 5 results; n.

d, - Not measured. Report the time from start to completion of accelerated oxidation in Table 1 below.

Table ■ Compositional variation, promoted acid weight % Cr/ at 1300°C
Alloy AI from start to finish
Time★B, C20/4.3 Less than 2 days D 23.5/4.4 5 days H24, 7/6.5 10 days H24, 7/6.5 21 days★ Completed at 1200°C Test piece Attack over 100% of the surface area of (alloy A vs alloy B and C).

The results were quite poor at the test temperature of 1300°C.

However, increasing the chromium content to 23.5% (
Alloy D) did not show any significant improvement, especially under the test conditions of 1300°C.

Alloys B and C are described in U.S. Patent No. 3.992. 161 (i.e., 20% Cr/4.5% AI
) represents. At 1300° C., accelerated oxidation took two days from initiation to completion. See table ■. Increasing the chromium content to 24% slows the accelerated oxidation rate by half;
% to 6.5% again significantly slowed down the attack speed (Alloy H in Table ■). This pattern of behavior has practical importance, since a significant reduction in attack speed extends service life, allows repair operations, and avoids the consequences of catastrophic failure.

Figures 1 to 3 show that, apart from different amounts of chromium, 0.0
2%C, 4.5%A1.0.3%Ti10.5%Y 2
0 B, U.S. Patent No. 3,992 containing incidental impurities
．． 16'1 provides a more graphical illustration of what occurs by increasing the amount of chromium in a typical commercial alloy (essentially balance iron) as described in US Pat. 1200℃, 1250℃
At each test temperature of 1300° C. and 1300° C., the crushing rate (mass change) was greater for higher percentages of chromium. According to the invention, the aluminum content should also be increased, preferably proportionally, in order to reduce the crushing speed and ensure better integrity of the alloy composition. This is the fourth
As reflected by FIGS. In these figures, C
At 25% rfit, the crushing speed is
, 992,161.
% aluminum is significantly slowed down.

Yet another practical advantage of the alloys of the present invention is that they appear to provide improved high temperature oxidation and corrosion resistance in thin gauge compared to prior art materials. Sheet thicknesses, such as 1.25 mm (0.05 inch), are typical for the 20Cr/4.5A1 alloy described in US Pat. No. 3,992,161 as commercially manufactured. Such gauge sections are prone to early accelerated oxidation attack due to the relative lack of bulk concentrations of aluminum and chromium atoms effective for surface (oxide) protection. In other words, such encroachment attacks may result in pitting (eg, pitting that would penetrate the sheet). The alloys of the present invention provide higher concentrations of stored aluminum and/or chromium atoms.

With respect to workability, Figure 6 illustrates the general scale of chromium and aluminum in terms of their combined effect on bendability (a criterion used to evaluate workability). In this regard, approximately 0.05 inches (1 t) thick and 1 t wide.
/2 inch (approximately 12.7 mm) and a length of approximately 2 to 4 inches (approximately 51 to 102 m11) with a thickness of approximately 0.
．． Bent onto a 1 inch (2t) bar. Tests were conducted in both longitudinal and transverse directions. The dark shaded area indicates that some cracking is evident from the test. As can be seen, U.S. Patent No. 3. 992. The 20Cr/4.5AI standard alloy described in No. 161 is quite workable. However, cracks occurred in 30Cr/4.5Alffi. Some cracks are mostly 19% chromium.
and in the transverse direction for the 5.2% aluminum alloy. 6.6% aluminum and approximately 25% chromium
The alloy containing . The bending angle was less than 50° versus the desired 105°.

For processability purposes, as mentioned above, the aluminum content is
Advantageously it should not exceed 6%, more preferably 5%.
．． No more than 75%.

Apart from flat rolled products, the alloys contemplated herein can be used in hot worked and/or machined bars and other mill product-like forms, such as forgings and tubing. For example, it may be cost effective to machine parts from rods for flame guides or glass extrusion dies.

Although the invention has been described with preferred embodiments, it is to be understood that modifications and variations can be made without departing from the spirit and scope of the invention, as would be readily apparent to those skilled in the art. Such modifications and variations are considered to be within the power and scope of the invention.

[Brief explanation of the drawing]

FIGS. 1 to 5 are graphs showing changes in crushing speed, and FIG. 6 is a graph showing workability (bendability) in the correlation between chromium and aluminum. Applicant’s agent: Sato-yuFIG! 15 581ee 1513
26elFIG 2 FIG 5 FIG phrase FIG 5

Claims (1)

[Claims] 1. Flat-rolled products such as sheets and strips characterized by good workability and oxidation resistance at high temperatures of about 1300°C [The products contain about 23-30% chromium and about 5-5% aluminum. 6.25%, a small but effective strength-enhancing amount of at least one refractory metal dispersoid selected from the group consisting of oxides, carbides, nitrides, and borides (the remainder being essentially Powder metallurgy iron-chromium-aluminum dispersion strengthened alloy products in the form of 2. The alloy product according to claim 1, containing 0.2 to 0.75% titanium. 3. The alloy product according to claim 2, wherein the aluminum content does not exceed 6%. 4. The refractory metal dispersoid contains one or more of oxides in an amount of up to 10% by volume, carbides in an amount of up to 2% by volume, nitrides in an amount of up to 5% by volume, and borides in an amount of up to 5% by volume. The alloy product according to claim 1. 5. The alloy product according to claim 2, wherein chromium is 23 to 27%. 6. As a new product, flat-rolled products such as sheets and strips characterized by good workability and oxidation resistance at high temperatures of about 1300°C [The product contains about 23-30% chromium and about 5-6% aluminum. 25%,
Formed from an alloy consisting of a small but effective amount of at least one refractory metal dispersoid to increase strength selected from the group consisting of oxides, carbides, nitrides, and borides (the remainder being essentially ferrous) A metal component in the hot section of an aircraft gas turbine engine formed from a powder metallurgical iron-chromium-aluminum dispersion strengthened alloy in the form of 7. The component according to claim 6 in the form of a burner can. 8. The alloy product according to claim 1, wherein the powder is produced by mechanical alloying. 9. Characterized by high oxidation resistance at high temperatures of around 1300℃, and contains 20-30% chromium and 5% aluminum.
% to 8%, small but effective amounts of refractory metal dispersoids to increase strength selected from the group consisting of oxides, carbides, nitrides, and borides, up to 5% titanium, zirconium, hafnium, tantalum and up to 2% each of vanadium, up to 6% each of molybdenum and tungsten, up to 0.5% silicon, up to 0.5% niobium, and 0 each of calcium, yttrium and rare earth metals.
．． up to 0.05%, boron up to 0.2% (the remainder is essentially iron)
A powder metallurgy iron-chromium-aluminum dispersion strengthened alloy characterized by comprising: 10. The alloy of claim 9 containing at least 22.5% chromium. 11. The alloy according to claim 9, containing 0.25 to 0.75% titanium. 12. The powder is produced by mechanical alloying,
An alloy according to claim 9.