KR20100083847A - Austenitic heat-resistant nickel-base alloy - Google Patents

Abstract

Austenitic heat-resistant nickel-base alloy comprising (in % by mass) 0.03-0.1% of C, 28-32% of Cr, 0.01-< 0.5% of Mn, 0.01-< 0.3% of Si, 0.01-< 1.0% of Mo, 2.5-3.2% of Ti, 0.01-< 0.5% of Nb, 0.01-< 0.5% of Cu, 0.05-< 2.0% of Fe, 0.7-1.0% of Al, 0.001-< 0.03% of Mg, 0.01-< 1.0% of Co, 0.01-0.10% of Hf, 0.01-0.10% of Zr, 0.002-0.02% of B, 0.001-0.01% of N, max. 0.01% of S, max. 0.005% of Pb, max. 0.0005% of Bi, max. 0.01% of Ag, balance Ni and minor components due to the production method, where the sum of Ti + Al is from 3.3 to 4.3%, the sum of C + (10 8B) is from 0.05 to 0.2%, the sum of Hf + Zr is from 0.05 to 0.15% and the Ti/Al ratio is > 3.

Description

Austenitic heat-resistant nickel-base alloy

The present invention relates to an austenitic heat resistant nickel alloy.

In the Proceedings of the Diesel Engine Combustion Chamber Materials for Heavy Fuel Operation (1990), the Institute of Marine Engineers is a summary of the intensive research and development that has been undertaken over the past several years in the field of valve materials. Provide a summary. According to this, firstly, Alloy 80 A having 0.08% C, 19.5% Cr, 75% Ni, 1.4% Al, and 2.4% Ti in mass% is in the field.

In some cases, Alloy 81 with 0.5% C, 30% Cr, 66% Ni, 0.9% Al, and 1.8% Ti in mass% was also used. Sometimes these alloys are used as the base material for valves, where the valve seat section is also coated with a wear resistant material as disclosed, for example, in EP-B 0521821. This document provides chemical compositions for the base material of the following mass%: 0.04-0.10% C, <1.0% Si, <0.2% Cu, <1.0% Fe, <1.9% Mn, 18-21% Cr, 1.8-2.7% Ti, 1.0-1.8% Al, <2.0% Co, <0.3% Mo, B, Zr, and the balance is nickel. In addition, modifications of these alloys are also provided, especially in the case of 29-31% Cr.

At current service temperatures below 750 ° C, Alloy 80 A was noticed for longer service life and better wear resistance in LCF tests, while Alloy 81 was for example marine diesel due to its better corrosion resistance. Tested under the same conditions found in the engine. Each of these alloys has particular advantages, but none of them satisfy all the requirements for mechanical and corrosion properties. Remedies using additional coatings entail additional undesired production and material costs. Powder metallurgical production is also undesirable in terms of cost. Such costs should be avoided to the greatest extent possible.

US-A 6,139, 660 and US-A 6,039,919 are all concerned with this; These documents describe alloys having the following mass% composition for intake valves and exhaust valves in diesel engines: ≤ 0.1% C, ≤ 1.0% Si, ≤ 0.1% Mn, ≥ 25-≤ 32.2% Cr, ≤ 3% Ti,> 1-<2% Al, the rest is Ni. However, this alloy also does not provide adequate high temperature corrosion resistance. It is also true that future more powerful engines, such as diesel marine engines, will operate at temperatures up to about 850 ° C, which also valves high demands, especially when the service life must be maintained and no further maintenance work is desired. Requires on the material.

The austenitic heat resistant nickel based alloy disclosed in DE-C 101 23 566 has the following mass% composition: 0.03-0.1% C, up to 0.005% S, up to 0.05% N, 25-35% Cr, up to 0.2% Mn, 0.1% Si max., 0.2% Mo max., 2-3% Ti, 0.02-1.1% Nb, max 0.1% Cu, max 1% Fe, max 0.08% P, 0.9-1.3% Al, max 0.01% Mg, 0.02- The sum of 0.1% Zr, up to 0.2% Co, Al + Ti + Nb is at least 3.5%, the remainder is Ni and process related impurities. The alloy is characterized by the addition of 0.001-0.005% B, 0.01-0.04% Hf, and 0.01-0.04% Y in mass%.

The primary object of the present invention is to provide a material having high temperature corrosion resistance up to 850 ° C. and having mechanical properties comparable to Alloy 80 A.

This object is achieved using an austenitic heat resistant nickel based alloy having the following mass%:

0.03-0.1% C

28-32% Cr

0.01-≤ 0.5% Mn

0.01-≤ 0.3% Si

0.01-≤ 1.0% Mo

2.5-3.2% Ti

0.01-≤ 0.5% Nb

0.01-≤ 0.5% Cu

0.05-≤ 2.0% Fe

0.7-1.0% Al

0.001-≤ 0.03% Mg

0.01-≤ 1.0% Co

0.01-0.10% Hf

0.01-0.10% Zr

0.002-0.02% B

0.001-0.01% N

0.01% S max

0.005% Pb Max

0.0005% Bi Max

0.01% Ag max

The rest are Ni and process related impurities,

The sum of Ti + Al is 3.3 to 4.3%,

The sum of C + (10 x B) is from 0.05 to 0.2%,

The sum of Hf + Zr is 0.05 to 0.15%,

And Ti / Al> 3.

Advantageous refinements of the nickel-based alloys of the invention that are high temperature corrosion resistance up to 850 ° C. can be found in the dependent claims.

The alloys of the present invention are also generally particularly suitable for producing valves for large diesel engines, ie for producing valves for large diesel engines, for example, which are introduced into stationary systems for obtaining electricity.

Such high temperature corrosion resistant materials achieve mechanical properties comparable to Alloy 80 A. In this regard, the materials of the present invention are generally suitable for valve material applications and can be introduced in next generation diesel marine engines, especially in the temperature range up to 850 ° C.

Table 1 provides by way of example the chemical compositions of two examples E1 and E2 of the present invention. Typical comparisons of two commercial alloys Alloy 80 A and Alloy 81 are provided for comparison.

Alloys E1 and E2 were analyzed from a series of laboratory molten metals, which were melted in 10 kg blocks in a vacuum induction oven, followed by hot roll and solution for 2 hours at 1180 ° C. in air. After annealing (solution anneal), it was quenched with water (quenched). The alloys were cured with two additional annealing:

After 6 h at 850 ° C. under air cooling

4 hours at 700 ° C. under air cooling.

Since the alloys differ in the content of the elements under discussion, their mechanical properties and their behavior in corrosive medium have been evaluated to arrive at the analysis of the present invention.

Chemical Composition of Alloys E1 and E2 of the Invention Compared to Alloy 80A and Alloy 81 element Alloy 80A Alloy 81 E1 E2 Ni Remainder Remainder Remainder Remainder Cr 19.5 28.4 29.1 31 Fe 0.13 0.09 0.1 1.7 Ti 2.25 2.1 2.8 3.1 Al 1.45 1.13 0.85 0.75 C 0.041 0.07 0.03 Mn 0.09 0.01 0.01 0.2 Si 0.20 0.04 0.02 0.1 Nb 0.001 <0.01 0.04 0.01 Mo 0.008 0.01 0.01 0.02 Cu 0.004 0.01 0.01 0.01 Mg 0.002 <0.001 0.001 0.005 S 0.004 0.003 0.002 P 0.002 0.002 0.002 N 0.002 0.006 0.0015 Hf 0.04 0.06 Co 0.039 0.01 0.01 0.3 B 0.003 0.003 Zr 0.02 0.02 0.04 Ti + Al 3.7 3.23 3.75 3.85 C + (10 x B) 0.1 0.06 Hf + Zr 0.06 0.10 Ti / Al 1.55 1.86 3.29 4.13

(mass %)

Since one object of the present invention was to achieve heat resistance comparable to Alloy 80 A at service temperature, tensile strength and yield point were measured at 600 ° C and 800 ° C. Table 2 shows comparable to Alloy 80 A and stronger at 600 ° C. The alloys are comparable at 800 ° C.

Tensile strength and yield point of E1 and E2 compared to Alloy 80 A at 600 ° C and 800 ° C alloy 600 ℃ 800 ℃ R _m / MPa R _{p0 .2} / MPa R _m / MPa R _{p0 .2} / MPa E1 1053 738 636 552 E2 1062 690 617 573 Alloy 80 A 851 646 594 546

In order to investigate the corrosion behavior, the first experiment was carried out in a synthetic oil ash with the following composition in the laboratory:

40% V ₂ O ₃ + 10% NaVO ₃ + 20% Na ₂ SO ₄ + 15% CaSO ₄ + 15% NiSO ₄ .

The atmosphere was air with 0.5% SO ₂ content. Samples were aged at both 750 ° C. and 850 ° C. for 20 hours, 100 hours, and 400 hours in each case. For 400 hours aging, the ash was refreshed after 100 hours, 200 hours, and 300 hours to maintain corrosiveness. The depth of internal corrosion could be reliably measured by laboratory tests.

Corrosion investigations of marine diesel valves themselves can be considered more reliable, since these investigations can be better assessed and also take into account the errosive effect. Samples from each laboratory molten metal and also from Alloy 81 and Alloy 80 for comparison were used in marine diesel valves. These marine diesel valves were operated for 3000 hours in the main engine of ocean sailing vessels. This sample was then taken from the valve and examined for corrosion using metallography. This investigation made it possible to distinguish between material loss, layer thickness and internal corrosion in detail.

The investigation found the following relationship between the corrosion behavior and the content of the individual alloying elements.

Cr: Cr content should be as high as possible from a corrosion standpoint. However, a suitable upper metallurgical limit is 32%. The difference between the alloy strain with about 30% Cr and the alloy strain with 20% Cr clearly shows this. In the best case, the corrosion of the former alloy is only half that of the latter alloy. In extreme close-up, samples tested in a valve with a Cr content of 30% appear as a wavy specimen surface in the abraded micrograph section, which is only an indication of normal corrosion wear. It has a cobblestone appearance. In contrast, Cr-poor samples already show severe symmetrical spalling.

Ti: Al ratios in excess of Ti, Al: 3 show better corrosion resistance results than lower Ti: Al ratios. This is due to the formation of a Ti-rich margin between the outer oxide layer and the interior sulfidation region with high Ti content. Aluminum and titanium have a positive effect on heat resistance by forming a γ 'phase. The sum of the elements Al + Ti should advantageously be 3.5 to 4.3%. If the total content of these elements is too high, it becomes more difficult to hot-form the material.

Si: Silicon has not been shown to have a positive effect on the corrosion properties and should be at most 0.5%, with less than 0.1% being better.

Nb: Niobium-alloyed sample has in principle the thinnest corrosion layer, but this does not have any effect on the material loss itself. Since the thick corrosion layer has a protective effect against corrosion progression, the Nb content should be limited to a maximum of 0.5%. Moreover, Nb affects the material strength due to its high solubility on γ '. Ti and Al content need not match lower Nb content of less than 0.5%.

Since the addition of boron in a content of B, C: 0.002-0.01% improves the corrosion resistance, preferably the interior sulfidation following the grain boundary is reduced and thus all corrosion is reduced. Carbon preferably forms Cr carbide on the grain boundaries. Boron forms borides, which contribute to grain boundary stabilization and long-term strength. In particular, the formed Cr carbide causes Cr deficiency near the grain boundary, which leads to an accelerated rate of corrosion when the C content is too high. In addition, carbides and borides should not cover the grain boundaries too tightly because they drastically reduce the ductility of the material as hard deposits. As a compromise, it was found that the sum of C + (10 x B) should not exceed 0.1%. The sum above is advantageously about 0.08%.

Hf: Hafnium is often added to improve the resistance to high temperature oxidation and also has a positively positive effect on the sample's resistance in vanadium ash and SO ₂ atmospheres. Moreover, Hf also changes grain boundary properties, forming carbides or carbosulfides. Too high Hf content should be avoided because otherwise hot forming is no longer possible. The preferred concentration range is therefore 0.02 to 0.08%, preferably 0.05%. The effect of Hf on grain boundaries is comparable to that of Zr, which is why Hf + Zr is less than 0.10%.

Zr: Zirconium forms carbosulfide, which positively affects long-term strength and also contributes to high temperature corrosion resistance by combining with sulfur. It has been demonstrated that Zr content of 0.01 to 0.05% has a positive effect. A Zr content of 0.02% region should be pursued.

Co: Co is an element that mainly increases resistance to sulfur-containing media. However, it is also too expensive, so Co is not added to the alloy. Nevertheless, due to the components in the materials used, the Co content can reach up to 2% without increasing the cost.

Fe: Elemental iron appears as an accompanying element in particular. Clearly reducing the iron content to less than 1% increases the cost because higher quality raw materials must be selected. If the Fe content is limited to 3%, it is not necessary to predict that the corrosion resistance will obviously deteriorate or the cost will be too high. Nevertheless, a Fe content of less than 1% should be pursued.

The conditions mentioned for Mn: Fe also apply to Mn, and it is possible to reduce the Mn content by less than 1% without great difficulty.

Although the effects of the various elements on corrosion behavior and heat resistance often conflict with each other, in alloys E1 and E2, finding compositions that simultaneously meet the requirements mentioned for high temperature corrosion behavior and heat resistance at temperatures ranging from 600 ° C. to 850 ° C. It was possible. Good corrosion resistance may be due to the addition of reactive elements such as hafnium and zirconium without exceeding the selected optimum range (0.05-0.10%). Higher content reinforces the corrosion applied to the material. Limiting the carbon content below 0.1% and magnesium below 1% also contributes to corrosion resistance. The heat resistance has proved to be particularly advantageous when aluminum and titanium are added and their total content is in the range of 3.5 to 4.3% as mentioned. This heat resistance makes it unnecessary to coat the valve seat portion, thus reducing the manufacturing cost.

The alloy can be made using a conventional melting operation, which is advantageously suitable for melting in vacuo and subsequently remelting in an electroslag process. For example, there is formability for manufacturing rods for further processing to make valves such as marine diesel valves.

The alloys of the present invention are also generally particularly suitable for producing valves for large diesel engines, ie for producing valves for large diesel engines which are introduced, for example, into stationary systems for obtaining electricity.

Claims (14)

Austenitic heat-resistant nickel-based alloy having the following mass%:
0.03-0.1% C
28-32% Cr
0.01-≤ 0.5% Mn
0.01-≤ 0.3% Si
0.01-≤ 1.0% Mo
2.5-3.2% Ti
0.01-≤ 0.5% Nb
0.01-≤ 0.5% Cu
0.05-≤ 2.0% Fe
0.7-1.0% Al
0.001-≤ 0.03% Mg
0.01-≤ 1.0% Co
0.01-0.10% Hf
0.01-0.10% Zr
0.002-0.02% B
0.01-0.01% N
0.01% S max
0.005% Pb Max
0.0005% Bi max
0.01% Ag max
The rest are Ni and process related impurities,
The sum of Ti + Al is 3.3 to 4.3%,
The sum of C + (10 x B) is from 0.05 to 0.2%,
The sum of Hf + Zr is 0.05 to 0.15%,
And Ti / Al> 3. The method of claim 1,
Alloy containing 28-31% Cr by mass. The method according to claim 1 or 2,
Alloy containing 29-31% Cr by mass. The method according to any one of claims 1 to 3,
Alloy containing 2.8-3.2 Ti by mass. The method according to any one of claims 1 to 4,
Alloy containing 2.8-3.0% Ti by mass%. The method according to any one of claims 1 to 5,
An alloy comprising 0.002-0.01%, in particular 0.002-0.005%, of boron by mass as an additive. The method according to any one of claims 1 to 6,
Alloys with a sum of C + (10 x B) from 0.05 to 0.1%, in particular from 0.05 to 0.08%. The method according to any one of claims 1 to 7,
Alloys with a Zr content of from 0.01 to 0.05%. The method according to any one of claims 1 to 8,
Alloys having an Hf content of 0.01 to 0.08%. The method according to any one of claims 1 to 9,
Alloys with the following relationship:
Zr / Hf = 0.1-0.5% The method according to any one of claims 1 to 10,
Ti / Al is an alloy, characterized in that 3.3 to 4.2. Use of the alloy according to any one of claims 1 to 11 as valve material, in particular for valves which can be used in diesel engines. Use of the valve material of the alloy according to any one of claims 1 to 11 as a valve material for valves that can be used in diesel engines in ships with a temperature range of 850 ° C. or less. A valve, in particular a valve for a large diesel engine, comprising at least partly an alloy according to claim 1.