DE1943264C - Use of a cobalt chromium nickel alloy with high creep strength and high creep elongation and constriction at high temperatures - Google Patents

Description

The invention relates to the use of a cobalt-chromium-nickel alloy for objects that have a high creep rupture strength and high time rupture elongation and necking at high temperatures have to.

Such alloys are used in particular for components of gas turbines and engines, such as blades. Flame tubes and afterburners, as well as in engine construction for combustion chambers, bolts and others Engine parts used. All of these components are subject to high stress at high temperatures to withstand.

An alloy of this type is known under the designation X 40 CoCrNi 4520 (·> Material Handbook Steel and iron «. 1965, sheet 0 93-2). It has roughly the following composition:

0.32 to 0.42% carbon
maximum 1.0% silicon
19.0 to 21.0% chromium
19.0 to 21.0 ¹ Vo nickel

3.5 to 4.5% molybdenum

3.5 to 4.5% tungsten

3.5 to 4.5% niobium -} tantalum
maximum of 5.0% iron
Remainder cobalt.

This alloy has relatively good mechanical properties up to temperatures of 900C.

From the British patent 821 745 cobalt-based alloys are known that at high Temperatures can be used. These alloys are for high demands, especially on the creep rupture strength with simultaneous high Zeilbruch elongation and constriction, not suitable. The requirements for alloys of the specified Type are getting higher and higher. It is therefore necessary to develop alloys that still have better properties at high temperatures. This task is solved by using a cobalt-chromium-nickel alloy, consisting of

ίο up to 1.50% manganese, up to 0.045% phosphorus, up to 0.030% Sulfur, 19.0 to 21.0% chromium, 19.0 to 21% nickel, 3.5 to 4.5% tungsten, 3.5 to 4.5% molybdenum, 3.5 to 4.5% niobium and / or tantalum, up to 5.0% iron, 0.0030 to 0.010% boron, the remainder cobalt, due to a carbon content of up to 0.26 'n in combination with a silicon content of up to 0.30 "ι · and a heat treatment, consisting from a solution heat treatment between 1150 and 12 (K) C, water quenching, at least 16 hours

ao digemAusiasern at 700 to 850 C and then Cooling in air a coherent plate-shaped Has network from Lavesphase, for objects that have a high at high temperatures Must have creep rupture strength and high elongation and constriction.

Although an alloy of the specified composition is not yet known. does not become a substance / coveted for this alloy.

The alloy according to the invention differs essentially from known alloys through specifically changed and coordinated contents of carbon and silicon. These only slightly As changes appear, we expect significant improvements, especially the break time at high temperatures. The elongation at break and the constriction at break show sufficiently good values.

This decrease in mechanical properties at high temperatures is due to the precipitation of a Laves phase traced back, which in the present case as a coherent, plate-shaped network is formed while avoiding coagulation of the phase on the grain boundaries.

There was a prejudice against cobalt materials.

which, due to their composition, tend to form a Laves phase, as highly heat-resistant To use materials with good time stability, since, according to previous experience, the formation of Laves phase was always associated with an embrittlement of the material (Journal of Metals, November 1968, pp. 36 to 53; "Trans, of the ASM", 1963, p. 287 to 303). Numerous attempts have been made to reduce the excretion of Laves phase. One known possibility is to keep the silicon content as low as possible.

However, the inventors have surprisingly found that the level of the carbon content is particular Is important; it determines whether and in what amount at a corresponding temperature Laves phase we formed, d. The silicon content is less noticeable and influences the rate of formation and the form of excretion of the Laves phase. the Invention is based, among other things, on the knowledge that the contents of carbon and silicon must be specifically coordinated in order to achieve high creep strength at high temperatures to come with high ductility.

i 943 264

The invention is explained in more detail with reference to the figures.

There are the known alloy X 40 CoCrNi 4520 (alloy A) and the alloy according to the invention (Alloy B) can be compared with each other. Their compositions are:

Legie
tion C. Si Mn 0.004
0.010 S. Cr Ni Co W. Mon Nb Pe 0.003 A.
H 0.41
0.15 0.30
0.05 0.66
0.68 0.0Ü9
0.010 19.6
19.2 20.8
21.0 rest
rest 4.25
4.1 4.12
4.18 3.95
3.98 0.70
0.6

Both alloys were solution annealed at a temperature of 1175 ° C., quenched in water, then aged at 760 ^° C. for 16 hours and then cooled in air. The alloys treated in this way had structures according to FIGS. 1 and 2. This clearly shows the difference in the percentage of precipitation obtained after annealing at 730 ° C. for 100 hours. While the known alloy (lig. 1) has reinforced carbide precipitations, the alloy used according to the invention in FIG. 2. a dense network of Lavesphase. X-ray fine structure and electron diffraction recordings showed for this Laves phase almost the same lines as are given in the literature for Ke ₂ Mo. The Laves phase therefore has a hexagonal structure and is precipitated in the form of a plate at the temperature mentioned.

The importance of the special type of Laves phase, as it is eliminated in the invention, is clearly the F i g. 3 and 4. F i g. 3 shows the initial structure of the invention Alloy with a dense Laves phase network. On a creep test (Fig. 4) that has pre-aged for 300 hours After testing at 730 ° C, it can be seen that the Laves phase plates are in the matrix crystallites followed the individual glides. This means the Laves phase, as it is in the case of the invention Alloy is precipitated is extremely ductile in heat.

The residual properties (0.2 limit and tensile strength) at room temperature show no noticeable differences. In contrast, the Bruchdehnund ^ ₅ and the reduction of area 7 in the alloy according to the invention (Alloy B) are higher than in the known alloy (alloy A).

This can also be seen in a comparison of the mechanical properties of the two compared Alloys.

Strength properties at 20 C ( 18.5 V Ό 18.0 Time stand fracture
deh BriKh-
one-
Schnu- 'Ό 42.6 52.9 40 42.1 strengths tion tion 46.1 76.2 η B at 730 C σ 0.2 mm ² Testing load: Le kp 111.7 27 kg mm gie
tion 58.8 105.1 Fracture-
time 56.6 Sid. A. 202 B. 1645

The essential advantages of the alloy used in accordance with the invention lie in its use high temperatures. As can be seen from the table above, this alloy has an exceptional quality high rupture time corresponding to a high creep rupture strength with still good elongation at break and Fracture constriction.

The high degree of cross-linking of the Laves phase is necessary

the high break times. As has been shown, that precipitated with the alloy of the present invention Laves phase very ductile in the heat and follows the sliding processes.

Therefore there is no impairment of the time elongation and constriction instead.

1 sheet of drawings

Claims (1)

Claim: Use of a cobalt-chromium-nickel alloy, consisting of up to 1.50% manganese, up to 0.045% phosphorus, up to 0.030% sulfur, 19.0 to 21.0% chromium, 19.0 to 21% nickel, 3.5 up to 4.5% tungsten, 3.5 to 4.5% molybdenum. 3.5 to 4.5% niobium and / or tantalum, up to 5.0% iron, 0.0030 to 0.010 "u boron, the remainder cobalt, which is due to a carbon content of up to 0.26" o in combination with a silicon content of up to 0.30 ^J ti and a heat treatment, consisting of a solution heat treatment between 1150 and 1200 ° C, a water quenching, an aging at least 1 hour at 700 to H5u'C and aii5:! flowing cooling in air has a coherent plate-shaped network of Laves phase , for objects that have to have a high level of temporal strength and high elongation and constriction at high temperatures.