DE1229305B - Use of a nickel-chromium-cobalt alloy melted in a vacuum for the production of parts to be connected by welding - Google Patents

Description

Use of a nickel-chromium-cobalt alloy melted in a vacuum for the production of parts to be joined by welding, hot-formable, heat-resistant and creep-resistant nickel-chromium-cobalt alloys with 4 to 30% chromium, 0.5 to 8% titanium, 0.3 to 81 / o aluminum, 0 to 55% cobalt, 0.001 to 0.01% boron, 0.01 to 0.2% zirconium, 0 to 40.1 / 9 iron, 0 to 0.5 0 / 0 carbon, 0 to 20% molybdenum, 0 to 5% tungsten, 0.1% manganese, 0 to 2% silicon and 0 to 1% niobium and / or tantalum, the remainder nickel are known from Australian patent 166814 . Similar alloys with 10 to 25% chromium, 1.8 to 4.0% titanium, 0.5 to 40% aluminum, 0 to 25% cobalt, 0 to 10% iron, 0.03 to 0.15% % Carbon, up to 1% silicon, up to 2% copper, up to 10% molybdenum, up to 10% tungsten, up to 51 / o niobium, tantalum and vanadium individually or side by side, up to 0.3% zirconium and up to 0.05% Boron and the remainder nickel are described in British Patent 715140.

The aforementioned nickel-chromium-cobalt alloys form a precipitation phase of the Nis (Ti, Al) type, which separates out of the solid solution during heat treatment and in particular the creep rupture strength of the alloys is improved. The tenacity of the known alloys, however, decreases with increasing temperature, with results in a minimum in the temperature range from 700 to 850 ° C. Let the alloys weld up to a sheet thickness of about 3.5 mm with moderate requirements, however, the toughness of the weld greatly decreases in the aforementioned temperature range so that their elongation at high temperatures is below the minimum permissible 5 to 7% drops.

To compensate for the loss of toughness, attempts have already been made the welded workpieces after welding a heat treatment at high temperatures to subjugate. When welding sheet metal made from alloys of the above composition However, particularly great difficulties arise for nozzles of aircraft turbines, for example because the welded parts are subjected to high heat treatment temperatures Tend to break or warp. Often, however, built-in parts also have to go through Welding can be mended, with no possibility of the repaired Subsequent to the welding of parts to a special heat treatment.

Furthermore, welding has become difficult to install and use Temperature conditions, such as those that are consumed during welding, for example Electrode placed under argon has proven completely impracticable. This is likely also for the austenitic corrosion- and refractory alloys with 30 to 35 "/ o nickel, 12 to 15% chromium, 5.5 up to 7.5% tungsten, 2.5 to 5% molybdenum, 1.5 to 3% titanium, up to 0.50% aluminum, 0.1 to 0.50% zirconium, up to 0.10% carbon, a maximum content of manganese, silicon, Sulfur and phosphorus totaling 0.2%, the remainder iron, apply, although in the interpretative document Nothing is said about the weldability of these alloys. Finally is it according to "Metal Industry", Vol. 92 (1958), pp. 53 to 66, also known as heat-resistant To melt alloys of the type in question in a vacuum.

The object of the invention was now to provide a Alloy of highest strength, especially high creep rupture strength at high Temperatures, as they occur, for example, in gas turbines, to create the is weldable and does not lose its toughness when welding, so that a heat treatment following welding for recovery their toughness is not required. The solution to this problem starts with the finding found that although nickel-chromium-cobalt alloys usually melted in air and then deoxidized by magnesium and / or calcium, the residual contents of these Deoxidizers in the order of, for example, 0.08 to 0.012% that Making weld metal crack and embrittlement of the welded alloy lead: In order to avoid the aforementioned disadvantages, the total content of calcium is and magnesium according to the invention below 0.0051 / o, preferably below 0.004% or even 0.003%. In detail, the invention uses a melted in a vacuum Nickel-chromium-cobalt alloy with 18 to 221 / o chromium, 10 to 20% cobalt, 3 to 5.5119 Molybdenum, 0.04 to 0.1% carbon, 2 to 2.75% titanium ,. 0.75 to 1.30% aluminum, up to 0.005% calcium and / or magnesium, 0.002 to 0.1% zirconium, 0.001 to 0.0041 / o Boron, up to 0.5% silicon, up to 1% manganese, up to 5% iron, remainder nickel suggested, in which the contents of titanium and aluminum are coordinated so that their Sum 2.75 to 3.50% and the ratio of titanium to aluminum 1; 75: .1 to 2.80: 1 is. The superiority of the alloys according to the invention compared to the known from the German interpretation, results from their better creep strength in the temperature range from 700 to 850 ° C, as numerous tests have shown. The usability of the known alloy, however, depends on the temperature range limited to about 730 ° C.

To determine the calcium and magnesium levels in the alloys according to the To keep invention as low as possible, raw materials and in particular need the remelted scrap must be carefully selected. On the other hand, however, there are traces of calcium and / or magnesium required to be in the cast ingots and the weld metal to avoid the formation of oxide films and thus damaged weld seams. In general it is unavoidable that traces, for example 0.0005 to 0.001% calcium and / or magnesium are introduced into the alloys with the raw materials, so that a special addition of these elements is usually not necessary. If necessary, however, calcium and magnesium can be used in the form of calcium-silicon or Nickel-magnesium can be added to the melt.

The - carbon content should with regard to an optimal creep rupture strength be as low as possible. On the other hand, a certain carbon content is required, to ensure sufficient toughness of the welded joints. It resulted that both conditions by a carbon content of 0; 05 to 0; 08 1 / o is sufficient.

Cobalt serves to solidify the basic mass of the alloy and to increase their creep rupture strength at high temperatures. For optimum toughness the cobalt content should not exceed 15%. With a cobalt content of over 20% begins to decrease: The elements that most favor the strength are titanium and aluminum. Your influence grows with increasing proportions of these elements, but they also increase the toughness of the alloy at high temperatures decreased. The reduction in toughness has a stronger effect in the welding zone out than in the alloy itself.

The total content of the elements titanium and aluminum must therefore be measured in this way be that it lies within the narrow limits of 2.75 to 3.51 / o and preferably 3.1% does not exceed. The ratio of titanium: aluminum must be in the range of 1.75 to 2.8. By increasing the ratio of titanium to aluminum For a given total titanium and aluminum content, the toughness of the alloy is determined elevated. If the ratio of titanium to aluminum is too small, then that's enough Toughness does not end or it arises - a brittle phase.

Boron and zircon both promote creep rupture strength and toughness of the alloys at high temperatures. The legal range of bears is: however extremely tight, as this is of great importance for: the weld bars of the alloy is. If the boron content exceeds 0.004%, the alloy tends to be welded to become cracked, - 1n - especially with thick cross-sections. d. H. for cross-sections about 5mm. To ensure that the maximum level. Boron 0.004o / δ-not. the lining of the melting furnace must not contain boron. The boron will then preferably introduced by an alloy that contains little bear, e.g. B. an alloy with 4% boron and. 96% nickel, which ensures optimal yield of the Bors. Guarantees: If the alloy. contains more than 0.1: 0 / ö zirconium is a Welding the alloy. without creating weld cracks even with cross-sections excluded below about 5 mm.

Molybdenum makes a particularly valuable contribution to the properties of the alloy. It was found that, in the absence of molybdenum, the alloy cracked when thick cross-sections were welded in the clamped state, even if it contained calcium, magnesium, boron and zirconium within the limits given above. For example, a molybdenum-free alloy which contained 0.002% calcium, 0.002% magnesium, 0.004% boron and 0.6% zirconium had and. with the other elements within the limits according to the invention, there was considerable cracking when butt welding two clamped, 16 mm thick plates using the Sigma method. On the other hand, in alloys free of molybdenum, boron and zirconium, much larger proportions of calcium and magnesium, e.g. E.g. 0.02%; without cracking of the weld seams, but the strength of these alloys is lower than in the presence of boron and zirconium. Apart from the fact that good weldability of the alloy is achieved in the presence of boron and zirconium; Molybdenum increases the creep rupture strength of the alloy in a way that would otherwise only be achieved by increasing the total content of titanium and aluminum to such an extent that there is a marked decrease in toughness at higher temperatures. In order to achieve these advantages, the alloy should contain at least 30% molybdenum. However, since the corrosion resistance of the alloy is impaired with increasing molybdenum content, the molybdenum content should not exceed 5.5110; step, the optimum molybdenum content being 4 to 4.5%. The molybdenum can be completely or partially replaced by the same atomic percent of tungsten. In practice, the alloy contains silicon, manganese and iron only as impurities. These elements should therefore only be added carefully to the alloy. To achieve good welding conditions, the silicon content of the alloy should be less than 0.3%.

The alloy should be as free of trace elements as possible, which affect their toughness at high temperature. To remove such Elements and in order to achieve alloys of the highest possible degree of purity must they are melted under vacuum and preferably also cast. To when welding to achieve welded joints of high strength and flexibility of the alloys, the alloys should remain exposed to the vacuum for some time after the Melting process is complete, preferably at least 10 to 30 minutes a temperature of at least 1500 ° C and under a vacuum of no more than 0.5 mm Hg.

With a view to optimal technological properties, the alloys must heat-treated by solution annealing at 1050 to 1150 ° C with subsequent air cooling will. The annealing time depends on the cross-section of the parts. For cross-sections up to to 5 mm the annealing time should be 2 to 30 minutes and for thicker cross-sections 2 to 8 hours. This treatment is followed by an aging period of 2 to 16 hours at 650 to 850 ° C. If the alloys are to be welded, then they must they are subjected to a solution heat treatment prior to welding. A curing is not required before welding. After welding generally needs no further heat treatment is to be carried out. If, however, maximum strength is required, then it is advisable to follow the welding with hardening, which consists in an annealing at 650 to 900 ° C for 2 to 16 hours and preferably takes place in the upper part of the temperature range.

In the number table 1 below, four alloys are identified, of which alloy No. 1 has a composition according to the invention, while alloys No. 2, 3 and 4 do not correspond to the invention. Number board 1 Alloy no. 1 I 2 I 3 I 4 in ° / o C ....... 0.04 0.07 0.1 0.08 Cr ...... 19.1 18.6 18.8 18.7 Co ...... 13.9 11.1 11.2 10.7 Mo ..... 5.0 5.02 5.03 4.62 Ti ...... 2.13 2.0 2.14 2.05 Al ...... 1.13 0.77 1.08 0.95 Si ...... <0.3 0.24 0.19 0.13 Mn ..... <0.05 <0.03 0.03 <0; 02 B ....... 0.003 <0.001 <0.001 <0.001 Zr ...... 0.06 0.02 0.02 <0.02 Fe ...... traces 0.28 0.25 0.17 Approx ...... <0.002 <0.002 0.002 <0.002 Mg ..... <0.002. <0.002 0.002 <0.002 Ni ...... remainder remainder remainder remainder The four alloys were made from virgin raw materials with no added scrap. Alloy No. 1 was melted at at least 1500 ° C. under vacuum, held in the molten state at a pressure of 0.001 mm Hg for 40 minutes, and then cast under vacuum. Alloys No. 2, 3 and 4 were melted down in air. After melting, the alloys were placed in a vacuum furnace, held there in the molten state at 1520 to 1580 ° C. for 30 minutes under a pressure of 0.3 mm Hg and then cast in air.

The ingots cast from the alloys were processed into sheets with a thickness of 1.2 mm by forging and hot rolling, and the sheets were then subjected to a solution heat treatment. Alloy No. 1 was annealed at 1150 ° C. for 8 minutes and alloys No. 2, 3 and 4 were annealed at the same temperature for 5 minutes. The samples were examined for their creep strength at 750 ° C. under a load of 26.7 kg / mm2. Parts of the heat-treated sheets were butt-welded without additional weld material under an argon protective gas, cured for 4 hours at 750 ° C. and tested again under the same conditions. The load acted across the welded joint. The results of these tests can be seen from Table 2 below. Number board 2 Alloy Unwelded samples Welded samples tion service life expansion service life expansion to break to break No. in hours % in hours % 1,220 4.1 198 3.2 2,177 3.9 36 5.5 3 122 4.3 0.7 1.4 4 203 4.1 35 3.0 The results of tensile tests on unwelded and welded samples at 750 ° C. are entered in number table 3. Here, too, the load acted across the welded joint. Number board 3 Alloy Unwelded samples Welded samples Tensile Strength Yield Strength Elongation Tensile Strength Yield Strength Elongation No. kg / mm2 kg / mm2% kg / mm2 kg / mm2 0/0 1 72.3 53.5 11 75.5 51.9 9 2 72.3 56.6 9 61.2 45th, 5 5 3 70.6 56.6 10 66.0 55.0 4 4 58.1 39.3 17 67.6 51.9 5 The results from tables 2 and 3 show that the tensile strength of alloy no. 1 in the welded state is only slightly below that in the unwelded state and the alloy in the welded state has an elongation drop of only about 2%. In contrast, the other alloys have a noticeably shorter service life until breakage and also less elongation in the welded state. The alloys all contained less than 0.001% boron.

A comparison of the properties of alloys Nos. 2, 3 and 4 shows also the influence of the total titanium and aluminum content of the alloys. the Tensile strength and elongation of alloy No. 3 with a total content of titanium and aluminum of more than 3.1% deteriorates significantly in welding greater than those of alloys Nos. 2 and 4, the titanium and aluminum contents of less than 3.1%.

Alloys # 1 and # 2 were also subjected to continuous vibration subjected to heat at a load of 12.6 kg / mm2 and a temperature of a maximum of 780 ° C. Under these conditions, a welded and hardened joint held Sample from alloy no. 1 4000 load cycles, while a similar sample from alloy no. 2 broke after just 800 load changes.

The alloys according to the invention are primarily suitable for sheet metal. But you can also use another form of processing with a similar advantage Find use. They are particularly useful in the production of Welding composite parts on, e.g. B. for objects made of sheet metal, which have to be stiffened by welding forged parts.

Claims (6)

Claims: 1. Use of a nickel-chromium-cobalt alloy melted in a vacuum, consisting of 18 to 221 / o chromium, 10 to 20% cobalt, 3 to 5.5% molybdenum, 0.04 up to 0.1% carbon, 2 to 2.75% titanium, 0.75 to 1.30% aluminum, up to 0.005% Calcium and / or magnesium, 0.002 to 0.1% zirconium, 0.001 to 0.004% boron, to 0.5% silicon, up to 1% manganese, up to 5% iron, the remainder nickel, with the proviso that their The contents of titanium and aluminum are adjusted to one another in such a way that their Total 2.75 to 3.50% and the ratio of titanium to aluminum 1.75: 1 to 2.80: 1 is for the production of parts to be connected by welding, in particular of sheet metal that has a high creep strength in the temperature range from 700 to 850 ° C and must result in welded joints that are also not heat-treated Condition of consistently good toughness, e.g. B. for nozzles of aircraft turbines. 2. Use of the alloy according to claim 1, its content of titanium and aluminum however does not exceed the value of 3.10% for the purpose according to claim 1. 3. Use the alloy according to claims 1 and 2, the cobalt content of which is at most 15% and whose silicon content is at most 0.3%, for the purpose according to claim 1. 4. Use the alloy according to claims 1 to 3, the calcium and magnesium content thereof Does not exceed 0.003% for the purpose of claim 1. 5. Use of the alloy according to claims 1 to 4, in which the molybdenum is wholly or partially by the same Atomic percent tungsten is replaced for the purpose of claim 1. 6. Using the Alloy according to Claims 1 to 5, which are melted in a vacuum, in the molten state Condition at least 10 minutes under a pressure not exceeding 0.5 mm Hg and Maintained at a temperature of at least 1500 ° C, then cast into blocks and have been processed into sheets, for the purpose according to claim 1. In consideration Extracted publications: German Auslegeschrift No. 1061521; British patent specification No. 715140; Australian Patent No. 166,814; Metal Industry, Vol. 92 (1958), Pp. 63 to 66.