JP5622165B2 - Powder alloy for overlay thermal spraying with excellent wear resistance and high temperature corrosion resistance - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a powder alloy for overlay spraying, and more particularly, thermal spraying having excellent characteristics against wear and high temperature corrosion which are problematic in heavy oil or coal-fired boiler tubes, marine valves, gasoline refining equipment, and the like. It relates to a powder alloy.

  Marine diesel engines mainly use heavy oil as fuel, and output is obtained by explosive combustion of heavy oil. The exhaust valve is closed during the combustion stroke, the flaming surface is exposed to high-temperature combustion gas, and the valve seat surface is in contact with the valve seat. Next, at the exhaust stroke, the exhaust valve opens and exhaust gas is discharged from the gap between the seat surface and the valve seat. Therefore, the place exposed to the highest temperature by the exhaust valve reaches a temperature of 650 to 700 ° C. at the maximum temperature near the center of the flaming surface, and therefore it is necessary to be a material having excellent heat resistance. On the other hand, although the valve seat surface is not so hot, it is required to be a material having high hardness and excellent wear resistance in order to repeat contact with the valve seat in a corrosive environment.

  Fuel heavy oil contains a large amount of V (vanadium), S (sulfa), and the like. Since S causes S attack due to sulfide generated on the valve surface, and V also causes high temperature corrosion called V attack, the exhaust valve is required to corrode even when exposed to a high temperature environment including V and S. Corrosion resistance at high temperatures such as V attack resistance and S attack resistance that do not progress is required.

  Furthermore, heavy oil generates a large amount of hard dust when burned, so that exhaust valve wear becomes severe. It is also important that the material for the exhaust valve is a material having high hardness and excellent wear resistance.

  Conventionally, heat exhaust steel such as SUH35 (Fe-9Mn-21Cr-4Ni-0.5C-0.4N) is used for exhaust valves of marine diesel engines, and Ni is used for high output engines where the temperature of combustion gas is increased. Nimonic 80A (registered trademark) containing 20Cr, which is a basic superalloy, has been used.

  However, in recent years, marine diesel engines have become increasingly hot due to higher output and higher efficiency, and even Nimonic 80A (registered trademark) has wear resistance, S attack resistance, and V attack resistance. Sex is not enough.

  Therefore, as a method for solving the above-described problems, for example, as in Patent Document 1, C: 0.1% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr, : Exhaust valve characterized by consisting of more than 25 to 32%, Ti: more than 2.0 to 3.0%, Al: 1.0 to 2.0%, Co: 12 to 20%, and the balance substantially Ni There is an alloy disclosure, and there is one that improves wear resistance, S attack resistance, and V attack resistance by improving the performance of the exhaust valve alloy itself.

  On the other hand, as in Patent Document 2, a stellite alloy is built up on the valve seat surface, Cr, Al, Ti, and Ni are essential components on the flaming surface, Cr: 10 to 30 wt%, Al + Ti: 2.5 6.0% by weight, Co + Mo + W + Nb + Fe: 30% by weight or less, and wear resistance and S-attack resistance to the most severe environments such as building up an age-hardening Ni-based alloy containing Ni as a balance component, There is a disclosure of an exhaust valve by building up a material excellent in V-attack resistance.

JP 2000-328163 A Japanese Patent Laid-Open No. 11-50821

  However, the technique for improving the performance of the valve material itself as in Patent Document 1 requires the addition of a large amount of expensive elements, which increases raw material costs, and such alloys are generally very inferior in productivity. Since the manufacturing cost also increases, there is a problem that the unit price is very high for a ship valve having a very large size.

  On the other hand, as disclosed in Patent Document 2, an inexpensive austenitic heat-resistant steel is used for the exhaust valve body, and a material excellent in wear resistance, S-attack resistance, and V-attack resistance in a part exposed to the most severe environment. In the method of overlaying, it is only necessary to overlay an alloy having excellent characteristics required for a necessary portion, so that the valve unit price can be greatly reduced.

  However, since there is no alloy that satisfies the wear resistance of the valve seat surface, the S-attack resistance and the V-attack resistance of the flaming surface required for the exhaust valve at the same time, there is no conventional cladding alloy as in Patent Document 2. In addition, the valve seat surface that requires wear resistance is built up of a high hardness and high wear resistance stellite alloy, and the contact surface that requires S attack resistance and V attack resistance is corrosion resistant at high temperatures. Therefore, it was necessary to build up a completely different alloy, such as building up an age-hardening type Ni-based invention alloy that is superior to the above.

  As described above, when two kinds of completely different alloys are built up on one exhaust valve, heat treatment such as age hardening after building up is selected so that one of the alloy properties has a peak. There is a problem that the characteristics of the other alloy deteriorate, and eventually, the conditions are balanced in consideration of the required characteristics required for the valve seat surface and the contact surface and the characteristics of the two overlaying alloys. Therefore, the best characteristics of each alloy cannot be used, resulting in a decrease in the performance of the exhaust valve itself. Furthermore, there are problems such as a long heat treatment time, and it is very difficult to select heat treatment conditions from the viewpoint of cost.

  The present invention has been made in view of the above circumstances, and its purpose is to have both excellent hardness and high temperature corrosion resistance by combining both high hardness and excellent high temperature corrosion resistance. In addition, the present invention relates to a thermal spraying powder alloy capable of aging treatment in a short time.

  In order to solve the above-described problems, the present inventors diligently studied on the Ni—Cr—Al-based component composition. As a result, by addition of Fe, cellular precipitation of a lamellar structure comprising an α-Cr phase, which is a solid solution phase of Cr, and a γ / γ 'phase in which a γ' (gamma prime) phase is finely precipitated inside the γ phase. As a result of accelerating, the aging treatment time can be shortened, and the knowledge that the wear resistance and the hot corrosion resistance are hardly impaired is obtained.

  This invention is made | formed based on this knowledge, The powder alloy for thermal spraying which concerns on this invention is the mass%, Cr: 32% -50%, Al: 0.5% -10%, Fe: 0 Including the content of 1% to 20%, the balance being Ni and inevitable impurities.

  The powder alloy for thermal spraying according to the present invention is further in mass% as necessary, Si: 0.5% to 5%, B: 0.001% to 0.01%, C: 0.01% to 0 1%, Cu: 0.1% to 5%, Ti, Nb, Ta, or one or more of V: Ti: 0.1% or less, Nb: 0.1% or less, Ta: 0.1 % Or less, V: 0.1% or less, and Ti + Nb + Ta + V: 0.1% or less.

  Since the powder alloy for thermal spraying according to the present invention contains, in mass%, Cr: 32% to 50%, Al: 0.5% to 10%, Fe: 0.1% to 20%, wear. And excellent properties against high temperature corrosion. Therefore, it is particularly suitable as a build-up material for exhaust valves.

  Hereinafter, an embodiment of the present invention will be described in detail. The powder alloy for thermal spraying according to the present invention contains the following constituent elements, and the balance consists of Ni and inevitable impurities. The types, content ratios, reasons for limitation, and the like of the constituent elements included are as follows.

Cr: 32% by mass to 50% by mass
Cr is a main forming element of the α-Cr phase and is an important element contributing to high strength and high hardness by complex precipitation with γ ′. It also contributes to the improvement of high temperature corrosion resistance. If it is less than 32% by mass, sufficient hardness cannot be obtained. Preferably it is good in it being 35 mass% or more. On the other hand, excessive addition makes the hot corrosiveness worse. Therefore, the Cr addition amount is limited to 50% by mass or less. Preferably it is 45 mass% or less.

Al: 0.5 mass% to 10 mass%
Al is an important element that forms the γ 'phase. It also contributes to improvement of high temperature corrosion resistance and oxidation resistance. If it is less than 0.5% by mass, sufficient hardness cannot be obtained. Preferably, it is 3.4 mass% or more. On the other hand, excessive addition makes the built-up layer brittle due to the formation of an excessive γ ′ phase, and conversely deteriorates the characteristics, so it is limited to 10% by mass or less. Preferably it is 5.0 mass% or less.

Fe: 0.1% by mass to 20% by mass
Fe is an element to be added that has the effect of accelerating cellular precipitation of a lamellar structure composed of an α-Cr phase, which is a solid solution phase of Cr, and a γ / γ 'phase in which a γ' phase is finely precipitated inside the γ phase. . In order to obtain the effect, addition of 0.1% by mass or more is necessary. Preferably it is 2 mass% or more. On the other hand, excessive addition is limited to 20% by mass or less in order to deteriorate the hot corrosion resistance. Preferably it is 10 mass% or less.

Si: 0.5% by mass to 5% by mass
Si is an element having the same effect as Al and forming a γ ′ phase. It also contributes to improvement of high temperature corrosion resistance and oxidation resistance. If the amount is less than 0.5% by mass, the effect does not appear remarkably.
Therefore, addition of 0.5% by mass or more is necessary. Preferably, it is 1.0% by mass or more. On the other hand, excessive addition makes the built-up layer brittle due to the formation of an excessive γ ′ phase, and conversely deteriorates the characteristics. Therefore, the addition amount is limited to 5% by mass or less. Preferably it is 3.5 mass% or less.

B: 0.001 mass% to 0.01 mass%
B is an element which has the effect of segregating at the grain boundaries and strengthening the grain boundaries. Also,
It also has the effect of reducing the viscosity of the molten metal during spraying to increase the wettability with the base material and improving the adhesion between the base and the coating and between the coatings. In order to obtain the effect, addition of 0.001% by mass or more is necessary. Preferably, it is good in it being 0.002 mass% or more. On the other hand, since excessive addition makes the grain boundaries brittle, the amount of B added is limited to 0.01% by mass or less. Preferably, it is 0.005 mass% or less.

C: 0.01% by mass to 0.1% by mass
C forms carbides and contributes to improvement in hardness. In order to obtain the effect, addition of 0.01% by mass or more is necessary. On the other hand, if it exceeds the upper limit, the high temperature corrosion resistance deteriorates. Therefore, the addition amount of C is limited to 0.1% by mass or less.

Ti: 0.1 mass% or less, Nb: 0.1 mass% or less, Ta: 0.1 mass% or less, V: 0.1 mass% or less, and Ti + Nb + Ta + V: 0.1 mass% or less Ti, Nb , Ta and V are carbide forming elements, and may be added to contribute to improvement in hardness by forming a carbide by combining with C. However, excessive addition causes excessive carbide to deteriorate the hot corrosion resistance, so Ti: 0.1% by mass or less, Nb: 0.1% by mass or less, Ta: 0.1% by mass or less, V : 0.1% by mass or less and Ti + Nb + Ta + V: 0.1% by mass or less.

Cu: 0.1% by mass to 5% by mass
Although Cu is less effective than Fe, Cu is an element that has the effect of accelerating the precipitation of the cellular structure of γ-αCr. In order to obtain the effect, addition of 0.1% by mass or more is necessary. Preferably it is 1.0 mass% or more. On the other hand, the excessive addition is limited to 5% by mass or less because the build-up layer becomes brittle due to excessive solid solution in the γ phase of the parent phase.

Examples of the present invention and comparative examples will be described below.
(Composition of thermal spraying powder)
First. About Examples 1-29 and Comparative Examples 1-9, the powder for thermal spraying which has each component element (mass%) shown in Tables 1 and 2 was created by the gas atomization method.

(Creation of specimen)
The powder was placed on a pre-prepared SNCRW (0.3C-1.2Si-1.0Mn-8.6Ni-18.6Cr-0.5Mo-1.7W-Bal.Fe) 100 mm x 100 mm plate. Then, a thickness of 20 mm was built up by plasma spraying, and a test sample was taken from the top of the built-up portion, that is, from a portion having the same composition as the powder component, and subjected to various tests.

  A 10 mm × 10 mm × 2 mm thickness was cut out from the material obtained above and subjected to an aging treatment at 750 ° C. Then, it grind | polished and grind | polished and measured hardness using the micro Vickers hardness tester. Tables 3 and 4 show the peak hardness of the 750 ° C. aging treatment. In addition, the heat treatment time at which the peak hardness was obtained is also shown.

As a corrosion resistance test, an S attack test and a V attack test were performed under the following test conditions in accordance with ZIS Z 2292. After the test, the weight after removing the scale was measured, and the corrosion weight loss from before the treatment was measured. The measurement results are shown in Tables 3 and 4.
<Test conditions>
・ Test specimen dimensions: 15 mm x 10 mm x 4 mm
Application amount: 20 mg / cm ²
Test temperature: 800 ° C
Retention time: 20 hours Salt: 90% Na ₂ SO ₄ + 10% NaCl (S attack test)
85% V ₂ O ₅ + 15% Na ₂ SO ₄ (V attack test)

The peak hardness after aging at 750 ° C. was evaluated as ◎ when the HV was 500 or more, ◯ when 400 or more and less than 500, and × when 400 or less. Similarly, when the peak hardness after aging at 750 ° C. is obtained, the aging time is within 1 hour, ◎ over 1 hour to 2 hours, ◯ over 2 hours to 4 hours, △ evaluates those 4 hours than as ×, S attack, corrosion weight loss, 2.0 mg / cm ² less than what the ◎, 2.0 mg / cm ² or more 10.0 mg / cm ² less than that of ○ as × ones 10.0 mg / cm ² or more, V attack, corrosion weight loss, those of less than ^{18mg / cm 2 ◎, 18mg /} cm 2 or more 24 mg / cm ² less ○ things, 24 mg / cm ^Two or more were evaluated as x. The comparative powders 6 and 7 in the table could not be evaluated because cracks occurred after building up.

  As shown in Table 4, the comparative powders 1 and 2 to which Fe was not added have a long aging time, and are considered to be inferior in manufacturability. Since the comparative powders 3 and 4 having a low Cr addition amount do not have sufficient α-Cr phase, the driving force for precipitation is low, the hardness is low, and precipitation takes time. The comparative powder 5 in which the added amount of Cr is too large is deteriorated in high temperature corrosivity. It is considered that the comparative powders 6 and 7 in which the added amount of Si or Cu was too large were cracked due to brittleness of the build-up layer. It is considered that the comparative powders 8 and 9 in which the addition amount of C is too large resulted in inferior hot-corrosion resistance due to excessive generation of carbides. It is considered that the comparative powder 10 in which the amount of Fe added is too large is inferior in high-temperature corrosion resistance because the Ni content is relatively reduced.

  On the other hand, as is apparent from Table 3, the inventive powder is excellent in hardness, short in aging time, and excellent in high temperature corrosion resistance.

Claims (5)

% By mass
Cr: 32% to 50%,
Al: 0.5% to 10%
Fe: including 0.1% to 20%,
Wear resistance and high temperature corrosion resistance with excellent thermal spraying powder alloy that you the balance Ni and unavoidable impurities and feature. The powder alloy for thermal spraying according to claim 1, further comprising Si: 0.5% to 5% by mass. B: 0.001% to 0.01% by mass%,
The powder alloy for thermal spraying according to claim 1, further comprising: C: 0.01% to 0.1% by mass%
The powder alloy for thermal spraying according to any one of claims 1 to 3 , further comprising Ti + Nb + Ta + V: 0.1% or less of one or more of Ti, Nb, Ta, and V. Cu by mass: 0.1% to 5%,
The powder alloy for thermal spraying according to any one of claims 1 to 4, further comprising: