JPS6029459A - Steel product with resistance to erosion by particle at high temperature - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a steel product with an oxide film on the surface, particularly a steel product with a Cr2O3 film on the surface, which exhibits excellent resistance to high-temperature particle erosion as seen in coal-fired boilers. Regarding.

High-temperature energy devices, such as fuel-fired boilers, fluidized bed reactors, coal gasification and liquefaction equipment, are attracting attention as coal utilization technologies reflecting the recent energy situation. For example, in fuel-burning boilers, petroleum has traditionally been the main resource, but today, as a result of the recognition of the need to use alternative energy, the use of coal is increasing.

However, even in such high-temperature energy devices, the device design is based on the design concept when using oil, and the problems when using coal have not yet been fully resolved. For example, coal-fired boilers are manufactured using the same material composition as conventional oil-fired boilers. However, unlike oil-fired boilers, in coal-fired boilers, the solid ash inside the boiler becomes clinker and falls, or it floats in the combustion gas stream as fly ash. Boiler tubes suffer significant erosion damage at high temperatures.

Although such problems are well recognized by those skilled in the art,
The erosion behavior caused by high-temperature particles is still unclear.
There are almost no material countermeasures, and only design countermeasures based on experience, such as reducing flow velocity and installing protectors, have been taken. However, even if these design measures are taken, even if the flow velocity is restricted, a drift section where the flow velocity is faster than expected will be created, and even if a protector is used, the protector itself will be damaged quickly, making it impractical in practice. There have been reports of cases where it was not helpful.

In addition, from the viewpoint of materials, Jls3 is the boiler tube.
o4si, same < 1 such as 321, 347, 316 steel
An 8-8 austenitic stainless steel mesh or an alloy such as Incoloy 800°310 is used. Furthermore, various high-temperature austenitic stainless steels are used as general high-temperature components, but none of these are designed with high-temperature particle erosion resistance in mind, and are only used based on experience with oil-fired boilers. It's just that.

By the way, various materials and methods have been developed and proposed for wear resistance such as rubbing wear or corrosion resistance. There's no way. Note that rubbing wear usually occurs when objects make reciprocating or rotating contact, while erosion occurs when a solid collides with an object at high speed, causing thinning, and both mechanisms are Essentially different.

Therefore, there is no commonality or relationship between rubbing wear resistance and high-temperature particle erosion resistance, and there is no knowledge regarding high-temperature particle erosion resistance in the prior art.

As already mentioned, there are currently almost no material measures to prevent erosion damage caused by high-temperature particles. However, if there were material measures, it would be possible to create design leeway in the production of coal-fired boilers such as those mentioned above. It has great effects such as making it possible to make a good judgment on the material of the protector, and furthermore,
If such material measures are taken, it will be possible to increase the average flow velocity of the gas flow within the boiler, and benefits such as miniaturization of the equipment and improvement of thermal efficiency can be expected.

It is therefore an object of the present invention to provide a metal article that exhibits excellent resistance to erosion by hot particles such as those found in coal-fired boilers.

In addition, erosion damage in the aforementioned general high-temperature energy equipment often occurs in areas where the flow velocity of the fluid is locally high, such as in uneven flow areas, and local countermeasures are often required. The aim is also to provide metal products exhibiting localized resistance to erosion by high-temperature particles from such a point of view.

The present inventors have now completed the present invention by discovering that high-temperature particle erosion resistance can be significantly improved by forming a specific oxide film on the surface of the M product prior to use.

Thus, the gist of the present invention is a high-temperature particle erosion resistant steel product having a substantially Cr2O3 coating on its surface with a thickness of 1 μm or more.

In addition, here, in the film of substantially Cr2O3, substantially α-
Refers to the crystal structure of Cr203, FB%Aβ,
Mn etc. may also be included.

As described above, according to the present invention, the oxide film that is effective in improving the high temperature particle erosion resistance is a Cr2 of 1 μM or more.
Formation of an O3 film is necessary. If the thickness is less than 1 μm, the film will not be effective against high-temperature particle erosion under high-temperature conditions near actual high-temperature equipment.

Note that this limitation regarding the film thickness applies when very fine particles with an average particle size of about 20 μm, such as boiler coal combustion ash, collide at a flow rate of about loom/sec or less, and when irregularly shaped large-diameter particles (50 μm or more) ) is 50m/s
This provides conditions for preventing erosion of high-temperature particles when they collide at a flow velocity of less than ec.

To form such an oxide film, heat treatment is performed in air or in a weakly oxidizing atmosphere prior to use.

For example, an oxide film of 1 μm or more can be changed by heating at 1000° C. for about 5 hours or more. By performing the thermal oxidation treatment at a higher temperature and for a longer period of time, the thickness of the oxide film formed on the surface can be further increased. however,
If the heating temperature is less than 900°C, it takes too much time to obtain a 1 μm thick film, which is not economical.

The above heating conditions, that is, pretreatment conditions, are conditions that are not observed under normal usage conditions such as boiler tubes, and the oxide film that is formed is The thickness is at most 0.1 μm.

Steel as a base material on which such an oxide film is formed is a material whose surface is enriched with Cr through diffusion treatment or the like, or whose base material contains more than a certain amount of Cr, and which is Cr2 under the usage environment.
It is necessary to use one that has the ability to regenerate O3. This is because the above-mentioned film may generate cracks when subjected to erosion, and as a result, ineffective scales such as (Fe, Cr) 30a are formed in those areas, which deteriorates the erosion resistance. be. However, if there is a Cr2O3 regeneration ability, even if a crank or the like occurs, Cr2O3 is generated from the lower part, and resistant Cr2O3 is repaired and formed again. Due to the presence of the pre-oxidation film in this way, the ability to maintain Cr2O3 is further enhanced and erosion resistance is maintained.

Such Cr-enriched base materials are broadly classified into austenitic steel and ferritic steel.

In the case of ferritic steel, preferably 18 to 30% Cr
containing C in a surface layer with a thickness of at least 50 μm from the surface.
It has an enrichment of at least 18 to 80% r, but is not necessarily limited thereto. In the case of such suitable ferritic steels, 90%
A Cr2O3 film with a thickness of 1 μm or more can be easily formed on the steel surface by heating to 0° C. or higher for a predetermined period of time.

In the above preferred embodiment, the reason why Cr is limited to 18 to 30% is that Cr improves high temperature corrosion resistance and improves Cr2O3.
It is a necessary component to improve forming and holding ability, and it is 1 as a steel composition.
Add 8% or more. On the other hand, if it exceeds 30%, the toughness of the tMM product will deteriorate. When Cr is contained in steel as a steel composition, it may be contained at 18 to 30%, but if it is enriched only in the surface layer by surface treatment such as chromizing, it may be contained up to about 80% without affecting the quality of the steel. No deterioration will occur. Further, in order to obtain the regenerating ability of the Cr2O3 film during use, it is sufficient to set the Cr content in the surface portion 50 μm thick from the surface to 18 to 80%.

Next, in the case of austenitic steel, preferably 15 to
Contains 50% Cr, 15-70% Ni, and 18-80% Cr in at least a 50 μm thick surface layer from the surface.

Regarding Cr, the same can be said for ferritic steel, but regarding Ni, it is necessary to increase the amount of Ni in order to stabilize the austenite phase. Contained below. but,
When enriching the surface layer with Cr by surface treatment, Ni
The lower limit of the content may be set to 8%.

In any case, other common alloying elements may be added in appropriate amounts as necessary, and various specific steel compositions may be used within the scope of the purpose of the present invention. In particular, when the base material contains active elements such as Y (yttrium) and REM (rare earth elements) or dispersed fine oxides, the Cr2O3 formed in advance is strengthened and the erosion resistance is improved. This is preferable because it is large.

Next, the present invention will be further explained with reference to Examples, but these are shown as illustrations of the present invention and are not intended to limit the present invention in any way. In this specification, "%" means "% by weight" unless otherwise specified.

Erosion tests using high-temperature particles were carried out using specimens with steel compositions shown in Table 1, which were subjected to various preliminary treatments to form oxide films on their surfaces, under the conditions shown in Table 2 below. I did it. The test piece used was 3 mm thick x 20 mm wide x 30 mm long.

The above-mentioned high temperature particle erosion test was conducted using a blast type erosion test device. That is, solid particles (coal combustion ash with an average particle diameter of about 15 μm was used in this example) and gas were heated separately to 650°C under condition (1) and to 800°C under condition (2). The mixture was mixed at the inlet of a nozzle with an inner diameter of 4 mm, and after being accelerated in the nozzle, it was made to collide with a test piece also maintained at 650°C or 800°C. The gas flow velocity when colliding with the test piece was 20 m/s and 30 m/s.
550 over an hour in each case
g of solid particles were impinged on the test surface.

After the test, the thinned area formed at the center of each test piece was measured using a surface roughness meter to determine the maximum amount of thinned metal, and the resistance of each sample material to high-temperature particle erosion was evaluated. The results are the same (collectively shown in Table 3).

As is clear from the results shown in Table 3, when the thickness of the Cr2O3 film is as small as 0.7 μm or less as in the comparative example, or when such a Cr2O3 film is not formed, the erosion resistance is No major improvement was observed. However, when a substantially Cr2O3 film of a predetermined thickness according to the present invention is provided, a remarkable improvement in high temperature particle erosion resistance is observed.

Thus, according to the present invention, a steel product having excellent resistance to high-temperature particle erosion can be obtained, and the present invention greatly contributes to the practical application and spread of high-temperature energy devices, which have been attracting attention in recent years.

Table 1 (weight%) Table 2 Table 3 (?) 9 Pre-acid (ts&) Both were carried out in the air.

Claims (1)

[Claims] A high-temperature particle erosion resistant steel product with a Cr2O3 film with a thickness of 1 μm or more on the surface.