DE10123566C1 - Nickel-based austenitic alloy used as a valve material for diesel engines of ships contains alloying additions of carbon, chromium, aluminum and zirconium - Google Patents

Abstract

Austenitic alloy comprises (in weight %): 0.03-0.1 carbon, maximum 0.005 sulfur, maximum 0.05 nitrogen, 25-35 chromium, maximum 0.2 manganese, maximum 0.1 silicon, maximum 0.2 molybdenum, 2-3 titanium, 0.02-1.1 niobium, maximum 0.1 copper, maximum 1 iron, maximum 0.008 phosphorus, 0.9-1.3 aluminum, maximum 0.01 magnesium, 0.02-0.1 zirconium, maximum 0.2 cobalt, at least 3.5 aluminum + titanium + niobium, and a balance of nickel. Preferred Features: The alloy comprises (in weight %): 0.03-0.08 carbon, maximum 0.005 sulfur, maximum 0.01 nitrogen, 28-31 chromium, maximum 0.1 manganese, maximum 0.1 silicon, maximum 0.1 molybdenum, 2-3 titanium, 0.02-1.1 niobium, maximum 0.1 copper, maximum 0.5 iron, maximum 0.006 phosphorus, 0.9-1.3 aluminum, maximum 0.01 magnesium, 0.02-0.1 zirconium, maximum 0.2 cobalt, at least 3.5 aluminum + titanium + niobium, and a balance of nickel. The alloy additionally contains (in weight %) 0.001-0.005 boron, 0.01-0.04 hafnium and 0.01-0.04 yttrium.

Description

The invention relates to an austenitic heat-resistant nickel-based alloy.

The Institute of Marine Engineers with the Proceedings "Diesel Engine Combustion Chamber Materials for Heavy Fuel Operation "1990 a summary of what has been done for about ten years intensive research and development work in the field of Valve materials.

Alloy 80A with (in Mass%) 0.08% C, 19.5% Cr, 75% Ni, 1.4% Al and 2.4% Ti.

Alloy 81 was also isolated with (in mass%) 0.05% C, 30% Cr, 66% Ni, 0.9% Al and 1.8% Ti used.

Occasionally, these alloys are used as valve base materials, the valve seat part being additionally coated with an abrasion-resistant material, as described, for example, in EP 0521821 B1. This publication specifies the chemical composition (in mass%) for the base material as follows:
0.04-0.10% C
≦ 1.0% Si
≦ 0.2% Cu
≦ 1.0% Fe
≦ 1.9% Mn
18.0-21.0% Cr
1.8-2.7% Ti
1.0-1.8% Al
≦ 2% Co
≦ 0.3% Mo, B, Zr,
Rest of nickel.

Furthermore, a variant of this alloy is also with 29-31% Cr cited.

At the current operating temperatures of below 750 ° C stands out Alloy 80A due to a longer service life in LCF tests and a better one Abrasion resistance, while Alloy 81 because of its better Hot corrosion resistance under the conditions, such as in Marine diesel engine can be found, has been checked. Any of these alloys So has its special advantages, but none meets all requirements the mechanical and corrosive properties. The remedy with a additional coating brings more undesirable manufacturing and Material costs with it. From a cost point of view, that is also unfavorable powder metallurgical production route. Such costs should be as possible be avoided.

This relates to US Pat. No. 6,139,660 A, which describes an alloy of the following composition (in% by mass) for intake and exhaust valves of diesel engines:
≦ 0.1% C
≦ 1.0% Si
≦ 01% Mn
≧ 25- ≦ 32.2% Cr
≦ 3% Ti
≧ 1- ≦ 2% Al
Rest Ni.

But this alloy also does not bring sufficient Resistance to hot corrosion.

In addition, more powerful engines such as Marine diesel engines, work at temperatures up to about 850 ° C, which also the valve material places higher demands, especially as the service life should be preserved and no additional maintenance work is desired are.

The invention has for its object one up to temperatures of 850 ° C hot corrosion resistant material with mechanical properties, which are not inferior to those of Alloy 80A.

This task is solved by an austenitic heat-resistant nickel-based alloy, with (in mass%)
0.03-0.1% C
Max. 0.005% S
Max. 0.05% N
25-35% Cr
Max. 0.2 mn
Max. 0.1% Si
Max. 0.2% Mo
2-3% Ti
0.02-1.1% Nb
Max. 0.1% Cu
Max. 1% Fe
Max. 0.008% P
0.9-1.3% Al
Max. 0.01% Mg
0.02-0.1% Zr
Max. 0.2% Co,
where the sum of Al + Ti + Nb ≧ 3.5%,
Rest of Ni as well as manufacturing-related additives.

Advantageous further developments of the invention up to 850 ° C. hot corrosion-resistant nickel-based alloy are the associated See subclaims.

Such hot corrosion resistant materials reach mechanical Properties that are not inferior to those of Alloy 80A. To that extent Material according to the invention can be used generally as a valve material and in Especially for future generations of marine diesel engines in the Temperature range up to max. Can be used at 850 ° C.

The literature shows that particularly corrosive engine conditions can be simulated through an SO ₂ -containing atmosphere and an ash of the following composition (in mass%):
40% V2O3 + 10% NaVO3 + 20% Na2SO4 + 15% CaSO4 + 15% NiSO4.

The nickel-based alloy according to the invention has excellent properties with regard to hot corrosion resistance up to 850 ° C if the nickel-based Alloy about 30 mass% chromium and max. 0.1 mass% carbon has, but which differs from the previously used alloys by additives reactive elements, such as yttrium, hafnium and zircon, which distinguishes the Hot corrosion resistance under conditions such as those in Ensure that the ship's engine can be found. Your encore must be in one narrow range, otherwise the positive effect otherwise ins The opposite is reversed and leads to internal oxidation. Like the one below  examples show, has the narrowing of the sum of yttrium, Proven hafnium, zircon and 10 × boron to 0.03-0.1 mass%. To increase The hot stretch limit is used in addition to aluminum and titanium niobium. To meet the requirements, the sum of these elements ≧ 3.5 Mass%.

Table 1 shows an example of the chemical compositions of two examples E1 and E2 according to the invention. For a better comparison, two typical analyzes of the commercially available alloys Alloy 80A and Alloy 81 are listed. These were melted in 10 kg blocks in a vacuum induction furnace, hot-rolled and solution-annealed in air at 1180 ° C. for 2 hours with subsequent water quenching. Because the materials are used in the hardened state, a two-stage annealing was connected:
6 hours at 850 ° C with air cooling followed by
4 hours at 700 ° C with air cooling.

Since a target according to the invention with Alloy 80A comparable heat resistance at operating temperature, tensile strength and yield point were at 600 ° C and 800 ° C measured. Table 2 shows that at 600 ° C E1 Alloy 80A comparable and E2 is even firmer. The three alloys are at 800 ° C comparable.  

Table 1

Chemical compositions of the alloys according to the invention compared to Alloy 80A and Alloy 81

Table 2

Tensile strength and yield strength of E1 and E2 compared to Alloy 80A at 600 ° C and 800 ° C

Cured were used to test the high-temperature corrosion behavior Samples in an ash of composition (in% by mass) 40% V2O3 + 10% NaVO3 + 20% Na2SO4 + 15% CaSO4 + 15% NiSO4.  

The furnace chamber was flooded with 0.2% SO ₂ . These tests were carried out at 750 ° C and 850 ° C, and after 20 hours and after 100 hours the internal and external corrosion attack were determined under the light microscope. Alloy 81 was tested as a reference alloy. At 750 ° C, no inner corrosion attacks or outer shells that were thicker than 0.05 mm were found for Alloy 81 or E1 and E2, at 850 ° C all values are less than 0.08 mm, whereas Alloy 80A internal corrosion attack of about 0.15 mm was found. These tests prove that the corrosion behavior of alloys E1 and E2 according to the invention is comparable to that of Alloy 81.

Although the influence of the various elements on corrosion behavior and Heat resistance is often opposed to that of alloys E1 and E2 Compositions are found that meet the requirements the high temperature corrosion behavior and the heat resistance Meet temperatures in the range between 600 ° C and 850 ° C at the same time. The good corrosion resistance can be explained by the addition of the reactive Elements, especially hafnium and zircon, without doing an optimum of (Y + Hf + Zr) of max. Exceed 0.08 mass%. Higher levels intensify the corrosion attack directed into the material. The Limitations of the carbon content to 0.05 mass% and those of manganese to 0.2 mass% also contribute to corrosion resistance. For the Heat resistance has proven to be particularly favorable if aluminum, Titanium and niobium are added, their total content above 3.5 Mass% should be. This heat resistance makes a coating of the Seat section unnecessary, which can save manufacturing costs.

The mode of operation of the added elements is discussed below:

• - Carbon and boron form carbides and borides and thus contribute Stabilization of grain boundaries and long-term strength, but offer Attack points for corrosion, which is why the sum of C + 10 × B 0.08 Mass% should not exceed. For example, the internal corrosion attack shown in Table 3 Alloy composition G1 at 750 ° C to 0.17 mm after 100 Hours and after the same time at 850 ° C even to 0.45 mm.

Table 3

Chemical compositions (in mass%) of alloys with properties that do not meet the requirements

• - Zircon, on the other hand, forms carbosulfides, which have a positive effect on the Long-term strength impact and also by binding sulfur Hot corrosion resistance contribute and should therefore be between 0.02 and 0.1% by mass.  
• - Yttrium and hafnium are often added to improve the high-temperature oxidation resistance, but apparently, within certain limits, also have a positive effect on the resistance in vanadium ash and SO ₂ atmosphere. These elements should be used, but their sum plus zircon must not exceed 0.08% by mass. This is evidenced by the alloy G2 in Table 3, which shows up to 0.18 mm internal corrosion attack after 100 hours.
• - Aluminum and titanium act through the formation of γ'- and in combination with niobium from γ "phases positively on the heat resistance. The sum of these three elements should be over 3.5% by mass. With G2 this is for example not the case, which means that the yield point at 800 ° C only reached 458 MPa.

The alloy can be made using the usual methods of smelting are produced, advantageously a vacuum treatment is to be provided. The formability for the production of bars for Manufacturing as ship valves is given.

Claims (7)

1. Austenitic heat-resistant nickel-based alloy with (in mass%)
0.03-0.1% C
Max. 0.005% S
Max. 0.05% N
25-35% Cr
Max. 0.2% Mn
Max. 0.1% Si
Max. 0.2% Mo
2-3% Ti
0.02-1.1% Nb
Max. 0.1% Cu
Max. 1% Fe
Max. 0.008% P
0.9-1.3% Al
Max. 0.01% Mg
0.02-0.1 Zr
Max. 0.2% Co
where the sum of Al + Ti + Nb ≧ 3.5%,
Rest of Ni as well as manufacturing-related additives. 2. Alloy according to claim 1 with (in mass%)
0.03-0.08% C
Max. 0.005% S
Max. 0.01% N
28-31% Cr
Max. 0.1% Mn
Max. 0.1% Si
Max. 0.1% Mo
2-3% Ti,
0.02-1.1% Nb
Max. 0.1% Cu
Max. 0.5% Fe
Max. 0.006% P
0.9-1.3% Al
Max. 0.01% Mg
0.02-0.1% Zr
Max. 0.1% Co,
where the sum of Al + Ti + Nb ≧ 3.5%,
Rest of Ni as well as manufacturing-related additives 3. Alloy according to claim 1 or 2, characterized by additives (in mass%) of
0.001-0.005% B
0.01-0.04% Hf
0.01-0.04% Y 4. Alloy according to one of claims 1 to 3, wherein (in mass%) the sum of the elements Y + Hf + Zr ≦ 0.08%. 5. Alloy according to one of claims 1 to 4, characterized in that (in mass%) is the sum of the elements C + 10 × B 0.03-0.1%. 6. Alloy according to claim 5, characterized in that (in% by mass) the Sum of C + 10 × B is <0.08%. 7. Use of the one of claims 1 to 6 produced alloy as valve material, especially for valves of marine diesel engines.