DE1533202C3 - Use of a cobalt chrome tungsten alloy as a material for ductile precision welding rods - Google Patents

Description

The invention relates to the use of a cobalt-chromium-tungsten alloy as a material for duk-tile precision welding rods for the production of Weld seams that have to be resistant to high temperatures.

For certain purposes, especially for welding seams of jet engine turbine blades from one high temperature resistant alloy of 56% nickel, 14% cobalt, 19% chromium, 4.3% molybdenum, 3% Titanium, 1.3% aluminum, 1% iron, 0.7% manganese and 0.4% silicon, which are subject to constant hammering takes place at the welds of the interlocking turbine blades are high temperature resistant ductile alloys required. To machine such weld seams and, if necessary, automatically To be able to produce, the welding rods used must have a small diameter and machined very evenly and flawlessly, which is practically only possible by grinding in a centerless Grinding machine can be done. For this, however, the welding rods must be sufficiently ductile, since they are brittle Break welding rods during such grinding.

The invention is now based on the object of using a cobalt-chromium-tungsten alloy as the material for ductile precision welding rods for the production of weld seams that are resistant to high temperatures need to use.

A cobalt alloy with 18.75 to 23.25% tungsten and 26 to 30% chromium is known from US Pat. No. 2,801165, which, however, is practically nickel-free. This alloy shows a short-term stability of about 28.10 kp / mm ^{2 at 982 ° C.} This creep behavior is not yet sufficient for particularly high requirements. In addition, this alloy cannot be processed into precision welding rods by centerless grinding because it is too brittle.

"" Are also from the USA. Patents 2,030,342, particularly claim 4, and 2,030,343, particularly claims 3 and 6, welding rods made of cobalt-chromium-tungsten alloys known, which, however, are nickel-free and in some cases, according to the last-mentioned patent, are also boron-free and have a carbon content of at least 1% and a vanadium content of at least 1.5%. These well-known Welding rods are intended for the production of hard and abrasion-resistant build-up welds and for the purpose of the invention because of insufficient long-term stability at high temperature and insufficient Ductility not suitable.

The welding rod known from claim 7 of said US Pat. No. 2,030,342 from 1 to 4% Carbon, 10 to 35% chromium, 0.5 to 15% vanadium, 10 to 30% tungsten and / or molybdenum, 0.1 to 2.5% boron, 0.1 to 1% manganese, 0.1 to 1% silicon, the remainder iron, nickel, cobalt, but nickel and iron each not exceeding 5%, is also intended for hard, wear-resistant build-up welds. Over suitability for the purpose of the invention is not known.

The above-mentioned object is now achieved according to the invention by using a cobalt-chromium-tungsten alloy, consisting of 26 to 30% chromium, 18 to 21% tungsten, 4 to 6% nickel, 0.7 to 1% carbon, 0.005 to 0.1% boron, 0 to 1% silicon, 0 to 1% manganese, 0 to 3% iron, 0.75 to 1.25% vanadium, the remainder cobalt, in which the cobalt-chromium ratio is always at least 1.4: 1, as a material for ductile precision welding rods for the production of weld seams that have to be resistant to high temperatures.

An alloy is preferably used for the stated purpose, which consists of 28% chromium, 19.5%

30, tungsten, 5% nickel, 0.85% carbon, 0.05% boron, 0.2% silicon, 0.1% manganese, 0.4% iron, 0.9% vanadium and 45% cobalt.

If a maximum amount of chromium is used in the alloy, the minimum amount must be Cobalt should be 42% in order to maintain the mentioned minimum cobalt-chromium ratio. If the The minimum amount of chromium is used, the minimum amount of cobalt must be 36.4%. In practice, the minimum cobalt range of the alloy is between 36.4 and 42%, the depending on the amounts of the other components contained in the alloy, mainly the tungsten ■ and amounts of nickel, can be increased beyond this range.

It was found that the maximum values of the short-term stability remain at high temperature when increasing the nickel content of the Alloy's tungsten content is reduced.

The alloy to be used according to the invention not only shows a considerable increase in the short-term stability at 982 ° C., namely to at least 33.60 kp / mm ² compared to 28.10, compared with the alloy known from the US Pat. No. 2,801,165 kp / mm ² in the known alloys, but also a significant increase in ductility, so that they can be machined in a centerless grinding machine without any risk of breakage and weld seams made from them withstand even strong hammering impacts at high temperatures.

The increase in short-term stability by at least 20% is surprising with regard to the relatively low nickel content of the alloy and probably proportionate to the applied high chromium content in connection with the small amount of nickel.

It has been found that the nickel range from 4 to 6% of the materials to be used according to the invention

3 4

alloy for the ductility or non-brittleness of which the dark phase present is considerably smaller than

is extremely critical. in fig. 1 and 2. These according to the invention to be

This is explained with reference to the micrographs. turning alloy was completely free of

These each show brittleness at a magnification of 270 times, showed high ductility, and none

F i g. 1 shows an alloy which the 5 according to the invention exhibited of the welding rods of this composition

preferred alloy composition, when running through the centerless grinding

however, if it contains 10% nickel and 40% cobalt, it will show any signs of breakage.

F i g. 2 an alloy according to the invention. 4 it can be seen that a gray phase

according to the preferred alloy together of a similar total area as the dark phase in

settlement, but with 7% nickel content and 43% colo Fig. 2 is present, in which, however, a fine precipitate

balt content, is formed, which causes an increase in hardness,

3 shows an alloy according to the invention, which in turn causes the alloy as a whole

According to the preferred alloy together a lower impact strength than the alloy of

setting and fi g. 3 owns. Such an alloy is ductile,

4 shows an alloy according to the invention, however, because of this increased hardness and the brittleness of the alloy, which is preferred according to this, for the production of welds, but with 3% nickel content and 47% rods and castings, hardly suitable,
balt content. The differences between the alloys of the

From Fig. 1 the presence of an oversized Fig. 1, 2, 3 and 4 have been further clarified by

Amount of continuous black or dark 20 testing of the alloys with a Knoop impression-

Phase can be seen which is an acicular carbide hardness tester using a 200 g load.

and although it gives the alloy abrasion resistance, the differences in the Knoop values result from

however, it is extremely disadvantageous in that it is shown in the following table:

makes the alloy brittle. _. _T,, -

This brittleness gives the alloy both 25 alloy Knoop value

. This brittleness, which makes the alloy 25

for the production of build-up welds as ί, ί § · } _

also makes castings from it unusable, £, ] S- ~

shows £ i in the following quite drastic way. From ί, ί § · · ·; η <\ λ

Welding rods made of the alloy were made by. -t ¹ 1 g 4 .. -

A centerless grinding machine passed through to 30 ^: These Knoop values are another indication of how to grind them and to make the suitability or adaptability of the alloy useful for welding purposes. Because of the brittleness of the welding rods contested use for welding rods and small ones, almost all rods broke while passing through castings. As can be seen from the table, this was the centerless grinder. Knoop value of the alloy with 10% nickel

From Fig. 2 it can be seen that the proportion of 35 is low. With 7% nickel, the Knoop value for the black or dark phase of the alloy was an optimum. With 3% nickel, the knoop rose a little less, but still considerably and continuously, up to an undesirable level.
borrowed, so that this alloy was also brittle. The entirety of the above tests and results

and the great majority of welding rods this nisse show that optimum results from the standpoint Composition made by the centerless grinding 40 a combination of ductility and abrasion resistance machine was led, in its passage through the rather narrow and critical inventive fallout, obtained in the appropriate range of 4 to 6% nickel

From Fig. 3 it can be seen that the surface will be one.

1 sheet of drawings

Claims (2)

Patent claims: 1. Use of a cobalt-chromium-tungsten alloy consisting of 26 to 30% chromium, 18 to 21% tungsten, 4 to 6% nickel, 0.7 to I ⁰ Zo carbon, 0.005 to 0.1% boron, 0 up to 1% silicon, 0 to 1% manganese, 0 to 3% iron, 0.75 to 1.25% vanadium, the remainder cobalt, in which the cobalt-chromium ratio is always at least 1.4: 1, as a material for ductile Precision welding rods for producing weld seams that have to be resistant to high temperatures. 2. Use of a cobalt-chromium-tungsten alloy of the composition specified in claim 1, consisting of 28% chromium, 19.5% tungsten, 5% nickel, 0.85% carbon, 0.05% boron, 0.2% silicon, 0.1% manganese, 0.4% iron, 0.9% vanadium and 45% cobalt, for the purpose stated in claim 1.