DE1195053B - Use of a nickel-chromium alloy for casting - Google Patents

Description

Use of a nickel-chromium alloy for die casting. The invention refers to nickel-chromium alloys. It is based on the task of being easily pourable To create alloys which, after solution annealing and aging, are exposed to high hot and scale resistance must be.

It is known that chromium-nickel melts have a relatively high viscosity on, which affects the castability of such melts so largely that if need be, they can still be used for ingot casting. When molding however, is the viscosity of the melt and the resulting castability of primary importance. The casting technique requires that the material has a high Flexibility and the characteristic "playful" flow shows.

It is known that heat-resistant fittings of complicated shape, for. B. turbine blades, although it can be made by casting that there are however, result in considerable difficulties. Because of the high operational stress and especially when hardening after casting, the fittings must have a stress-free, have a homogeneous structure. With the heat-resistant ones that have become known so far, by casting to be processed and then hardened nickel-chromium alloys is a Such a structure cannot be achieved and the result is unsatisfactory yield.

Based on the knowledge that alloying with niobium improves castability the nickel-chromium alloys are significantly improved, even with low-carbon ones Nickel-chromium alloys high heat resistance can be achieved as a solution to the problem underlying the invention, the use of an aluminum and titanium containing at most as impurities 10 to 35 "/, Chromium, 2 to 12 "/, niobium including small amounts of tantalum, less than 0.1 "/, Carbon, at most 0.5" /, silicon and at most 0.5 "/, manganese, where the remainder is nickel. Nickel-chromium alloys of this type can be used with the best Use the result for those objects to be produced by casting that are after solution heat treatment and aging must be of high heat and scale resistance.

The alloys according to the invention can also contain the following elements individually or in groups: up to 40 "/, cobalt, up to 5" /, iron, 4 to 16 "/, molybdenum, 3 to 12" /, tungsten, up to 0.10 /, Zirconium, with tungsten contents up to 1 "/, zirconium, up to 10 /, beryllium, 0.1 boron and the remainder at least 25" /, nickel. The objects produced from the alloys mentioned by casting are aged after solution heat treatment at a maximum of 750 ° C. It is true that niobium-containing heat-resistant nickel-chromium alloys are already known which are also said to be suitable for use in the as-cast state. Compared to the alloys according to the invention, they differ essentially in their carbon content, which is preferably 0.30 to 0.600 /, or 0.48 to 0.520 / , while in the alloys according to the invention it is less than 0.1 "/ , and preferably only 0.030 / . It was by no means obvious to forego the high carbon content of the known alloys, since the formation of carbides in the precipitation hardening of heat-resistant alloys is known to play a decisive role High-temperature strength niobium carbides, which are particularly effective because of their low carbon content, are not able to form them, surprisingly they are nevertheless precipitation-hardenable and to a high degree heat-resistant.

Finally, nickel-chromium alloys are known, in addition to niobium also contain tungsten and molybdenum, but these alloys have either one compared to the alloy according to the invention increased iron content or again higher Carbon levels.

In the commercially available niobium there is usually also some tantalum. For example, niobium is available in the form of an alloy that 40 % Nickel and 60% niobium, but often 10% of the nominal niobium content Is tantalum. The alloy according to the invention therefore also contains small amounts Tantalum.

The alloys to be used according to the invention contain niobides, form the hardening phases. You can make niobium compounds with nickel, cobalt, iron or chromium such as NisNb, Co2Nb, Fe2Nb or Cr2Nb. Whether these phases are such Whether or not they have compositions, they are rich in niobium and divide while increasing the strength properties of the alloys, preferably after a heat treatment. Because of the affinity of niobium for carbon, it must be used the carbon content of the alloy must be kept low, since it contributes to the formation of the Hardening phase can only serve unbound niobium. An increase in the carbon content also leads to a reduction in the ductility of the alloys at room temperature. Their carbon content should therefore preferably not be more than 0.03%.

In practice it is difficult to determine the carbon content of the alloys to be kept accordingly low. But now it has been found that if one was present small amount of zirconium in the tungsten-containing alloys is a detrimental effect on the malleability at room temperature is prevented and the alloys nonetheless can be hardened by niobides. As a result 'contain the tungsten-containing Alloys preferably zirconium, which in these cases can be present up to 10/0 can.

The preferred alloys contain 15 to 25% chromium, 4 to 10% Niobium, not more than 0.03% carbon, not more than 0.4% silicon, not more than 0.3% Manganese, 3 to 8% tungsten, at most 12% molybdenum, 0.003 to 0.0150 /, boron, 0.03 to 0.07% zircon, 0 to 15% cobalt and 0 to 5% iron. Exceeds the iron content 51) 1, the strength and ductility of the alloys will be at room temperature decreased.

For alloys with a low iron content, the total content should be Molybdenum and tungsten are at least 8%.

In order to achieve optimal properties, the alloys according to the Invention to heat treat by solution treatment and aging.

Example 1 Contains one of the alloys to be used according to the invention 0.01% carbon, 24% chromium, 8.2% molybdenum, 7.5% niobium, 0.3% silicon, 0.30 /, Manganese, the rest nickel.

The creep test with 14.2 kg / mm2 and at a temperature of 815 ° C resulted in a service life of 150 to 200 hours in the cast state. In the case of a heat treatment in the temperature range from 1050 to 1125'C, e.g. B at 1100 ° C for 8 hours and aging at a temperature between 700 and 900 ° C, e.g. B. at 850 ° C for 16 hours, the life of this alloy to break under the same test conditions is 300 to 500 hours.

This alloy also has good properties at room temperature, especially with regard to the proportional limit, tensile strength and elongation, as the table below shows: Proportional load Condition nality limit (yield point at different tensile strength elongation permanent strains) kg / mm $ 0, l ° / 0 I 0.2% I or 5 ° / 0 kg / mma ° / 0 Cast ......................... 25.8 47.2 51.0 56.0 69.3 5.6 Heat treated as described ..... 47; 0 63.0 73.7 - 76.9 1.12 Example 2 Further alloys can be found in the following list: Alloy composition in ° / 0 tion Cr IW I. Mo I Nb ICI Si I Mn IBI Zr I Co I Fe A ..... 18 5.9 6.1 5.9 0.03 0.4 0.3 - - - - B ..... 18 5.9 6.1 5.9 0.03 0.4 0.3 - - - 1.8 C .... 18 5.9 6.1 5.9 0.03 0.4 0.3 - - - 4.5 D .... 15.4 5.8 10.5 5.8 0.03 0.4 0.3 - - - - E ..... 2 1 , 5 5.9 6.1 6.0 0.03 0.4 0.3 - - - - F ..... 21.5 5.9 6.1 6.0 0.03 0.4 0.3 0.01 - - - 18 5.9 6.1 6.0 0.03 0.4 0.3 - - 4.7 - H .... 18 6.0 6.0 6.5 0.03 0.4 0.3 0.01 0.05 4.7 - In all cases, with the exception of the impurities, the remainder consists of nickel.

The properties of these alloys after the same heat treatment as in Example 1 and a creep test carried out under the same load at 870 ° C result from the following summary: Minimum lifetime elongation up to Alloy secondary creep to break to break rank speed ° / o per hour hours o / ' A ..... 0.03 62 5 B ..... 0.037 50 5.5 C ... - 45 2.6 D .... 0.02 73 4.2 E ..... 0.04 72 1 0.6 F ..... 0.009 372 10.3 G .... 0.0 1 8 26 1.8 H .... 0017 208 15 The favorable influence of boron is evident from these values. The importance of the carbon content is evident from the fact that an alloy identical to alloy E, but with 0.2% carbon instead of 0.03% carbon, was brittle at room temperature and had zero elongation with a tensile strength of 52.3 kg / mm2 had.

The properties of the alloys at room temperature are greatly improved, if the aging temperature does not exceed 750 ° C.

Example 3 This example shows that the addition of zirconium in alloys containing tungsten counteracts the influence of a higher carbon content. Three alloys with the following composition were made, the remainder being nickel in each case: Alloy Cr W Mo 1 Nb C Si Mn Zr B Co i I ........... 21.5 5.9 6.1 6.0 0.1 0.4 0.3 1.0 - - J. .-.-. . . . . . . . . 2l, 5 5.9 6.1 6.0 0.1 0.4 0.3 1.0 - - - K .......... 21.5 5.9 6.1 - 6.0 0.03 0.4 0.3 - - - After the heat treatment described in Example 1, the following values were determined for tensile strength and elongation at room temperature: Alloy tensile strength, kg / mm2 elongation tion I ...... 76.2 6.75 J ....... 65.2 3.37 K ...... 64.6 6.7 From the foregoing it can be seen that titanium and aluminum are not part of the alloys of the present invention, even though each of these elements may be present in such small amounts that it forms an impurity. It is believed that a primary reason for the good castability of the alloys in air is the exclusion of titanium and aluminum. Even in amounts of 0.1% titanium affects the behavior of the alloys during casting due to the formation of undesirable oxides, which become trapped in the casting and cause localized weak spots. On the other hand, niobium causes a noticeable increase in the fluidity of the alloys and prevents the formation of oxide layers on the melt.

Claims (3)

Claims: 1. The use of an aluminum and titanium at most as an alloy based on nickel-chromium containing impurities with the following composition: 10 to 350 /, chromium, 2 to 120 /, niobium, including small amounts of tantalum, less as 0.1% carbon, not more than 0.5% silicon, not more than 0.5% manganese remainder Nickel for objects to be produced by casting (cast parts) that are after solution heat treatment and aging must be of high heat and scale resistance. 2. The use of the alloy according to claim 1, which, however, also contains the following elements, individually or in groups: up to 400% cobalt, up to 5% iron, 4 to 16% molybdenum, 3 to 12% tungsten , up to 0.1% zirconium, with tungsten contents up to 10 /, zirconium up to 10 /, beryllium, up to 0.10 /, boron, the remainder at least 25% nickel for the purpose according to claim 1. 3. Use of the alloys according to Claims 1 and 2 for objects to be produced by casting which are aged at a maximum of 750 ° C after solution heat treatment. Considered publications: German Patent Nos. 729 423, 735 991; French Patent Specification No. 1,043,378. British Patent No. 508,319; U.S. Patent Nos. 2,373,490, 2,397,034, 432,617; Nickel Reports, Vol. 16 (1958), pp. 180, 223, 224.