JPS6033179B2 - How to select ferrite steel with excellent erosion resistance at high temperatures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ferritic steel used as a structural member of coal-fired boilers, coal-fired power plants, gasifiers, etc.
The present invention relates to a method for selecting ferritic steel that exhibits excellent erosion resistance, particularly when used in an environment exposed to high temperature erosion.

Due to changes in the energy situation in recent years, there is a tendency for coal to be used again in place of oil, as can be seen, for example, in the increase in the number of operating coal-fired boilers, coal liquefaction, and gasification equipment.

On the other hand, these coal-fired boilers and coal liquefaction gasifiers
It is manufactured using the same material composition as conventional oil-fired boilers, and therefore no consideration is given to the use of coal in terms of materials. Regarding villages, in many cases, high-temperature ferritic steel is used when the environmental temperature is 550 qo or less, and carbon steel is used when the environmental temperature is 400 qo or less.

In this way, existing coal-fired boilers, coal liquefaction equipment, gasification equipment, etc. are designed based on the materials used when using petroleum, but they are not completely free from the coal powder and coal particles that are uniquely produced when using coal. It is not known with certainty what kind of high-temperature erosion resistance the constituent members exhibit when exposed to a high-temperature erosion environment containing solid particles such as coal combustion ash, and even more so, there is no clear understanding of the material aspects of these components. Currently, no research or countermeasures have been taken, and only a few countermeasures such as the use of protectors have been taken from a design perspective.

Therefore, from the above-mentioned viewpoint, the present inventors focused on ferritic steel members that are used in high-temperature erosion environments that contain coal powder and coal combustion ash, and found that they have excellent resistance to such high-temperature erosion environments. As a result of research on ferritic steel that exhibits erosion properties, we found that ferritic steel used in the above environment has C: 0.6% or less, Si: 0.1-2%, Mu: 1% or less, Cr. :0.
5 to 14%, Mo: 0.3 to 2.5%, and if necessary, one or more of V, W, Tj and Nb: 1.5% or less in total, The remainder is Fe and unavoidable impurities (wt%)
), and the empirical formula: 1 at the operating temperature.
6000 T (where T is the service temperature expressed in absolute temperature) or more, the proof stress or yield stress (
It has been found that ferritic steel with a weight (unit: kgf/min) exhibits excellent erosion resistance particularly in high-temperature erosion environments containing fixed particles such as the above-mentioned fine coal powder and coal combustion ash.

This invention has been made based on the above knowledge, and the reason why the composition and proof stress (yield stress) of the ferritic steel are limited as described above will be explained below.

A Composition [a) C C is an important element to ensure the strength of steel, and has the effect of increasing the quenching effect and increasing the yield stress (yield strength) and tensile strength of the steel, but 0.6 If the content exceeds 0.6%, it not only tends to cause cracks during heat treatment but also makes cold working difficult, so the upper limit was set at 0.6%.

'b} Si Si is an indispensable element for deoxidizing purposes in copper smelting, but if its content is less than 0.1%, the desired deoxidizing effect cannot be obtained; Since cold working may become difficult if the content exceeds 0.1% to 2%, the content is set at 0.1% to 2%.

Furthermore, since Si has the effect of increasing the strength of copper, it is desirable to contain it in an amount of 0.5% or more especially when high strength is required. {c- Mu Mu has a deoxidizing effect like Si, and also has the effect of improving hot workability, but even if it is contained in an amount exceeding 1%, no further improvement effect will appear. The upper limit of its content was set at 1%.

'd) Cr Cr is an important element in ensuring oxidation resistance and high-temperature strength, and has the effect of enhancing the hardening effect and further improving strength, but if its content is less than 0.5, The desired effect as described above cannot be obtained, and if the content exceeds 14%, there is a possibility that 475°C brittleness will occur, so the content was set at 0.5 to 14%.

{el Mo Mo has the effect of improving high-temperature strength, but if its content is less than 0.3%, the desired high-temperature strength cannot be secured; on the other hand, even if it is contained in excess of 2.5%, Since no further improvement effect was observed, the content was determined to be 0.3 to 2.5%, taking economic considerations into account.

{f) W, W, Ti, and Nb These components, like Cr and Mo, have the uniform effect of precipitating fine carbides and increasing the high-temperature strength of steel, so even higher strength is required. Although it is included as necessary when the total amount exceeds 1.5%, no further improvement effect will be obtained, so the upper limit of its content was set at 1.5%.

B Yield Strength Regarding the ferritic steel having the above-mentioned composition, we investigated the relationship between the characteristics of this ferritic steel and the various factors that make up the high-temperature erosion environment from various aspects. We found that there is a special correlation between the ferritic steel's yield strength (yield resistance: k9f/
It has been empirically concluded that the ferritic steel exhibits excellent erosion resistance in the above-mentioned high-temperature erosion environment when the following condition is satisfied: (T is the operating temperature expressed in absolute temperature) It was.

Next, the method of the present invention will be explained using examples and comparing with comparative examples. Example
※※ Invention ferritic steels 1 to 8 and comparative steels 1 to 3, each having the composition and yield strength shown in Table 1, were prepared by ordinary melting and forging methods, and test pieces were taken from these various steels. , using these test pieces, temperature: 100, 300, 50000 (therefore, single temperature).

= 43, 28, 21) - JIS No. 7 artificial poppy having an average particle size of 100 to 150 m as solid particles,
A high-temperature erosion test was carried out under the condition that sand was blown onto the test piece for 1 hour at an impact angle of 20o at a flow rate of 120/sand using Ar gas as a carrier gas, and the maximum erosion depth in each test piece was determined. was measured. The results are also shown in Table 1. Table 1 (items) oy: Proof strength (vertical) D: Maximum erosion depth (''m) As is clear from the results shown in Table 1, the steel of the present invention was better in each test than the comparative steel. It can be seen that it exhibits extremely good erosion resistance at various temperatures.

Furthermore, it is clear that the steel of the present invention has a higher yield strength than the comparative steels, and the range of these yield strength values with respect to temperature as a parameter is shown in FIG. From Figure 1, Mingyo)
It can be seen that the steel of the present invention and the comparative steel can be clearly distinguished from each other by looking at the line marked 〇. As described above, according to the present invention, ferritic steel used as a structural member can be used in a high-temperature erosion environment, particularly in an atmosphere containing solid particles such as fine coal powder and coal combustion ash. By selecting from both sides, it is possible to obtain excellent high-temperature erosion resistance, which brings about industrially useful effects.

[Brief explanation of the drawing]

FIG. 1 is a graph comparing the yield strength of the invention steel and comparative steel at each test temperature.

Claims (1)

[Claims] 1. When using ferrite steel in an environment where erosion may occur at high temperatures, the ferrite steel may contain C: 0.6% or less, Si: 0.1-2%, Mu: 1
% or less, Cr: 0.5-14%, Mo: 0.3-2.5
%, with the remainder consisting of Fe and unavoidable impurities (
(wt%) and at the operating temperature T, the empirical formula:
16000/T (where T is the service temperature expressed as an absolute temperature) or a yield stress (unit: kgf/mm^2) is selected. How to select ferrite steel with excellent erosion resistance at high temperatures. 2 When using ferrite in an environment where erosion may occur at high temperatures, as the ferrite steel, C: 0.6% or less, Si: 0.1 to 2%, Mu: 1%.
Below, Cr: 0.5-14%, Mo: 0.3-2.5%
and further contains one or more of V, W, Ti and Nb in a total amount of 1.5% or less, with the remainder consisting of Fe and unavoidable impurities (wt%), and At the operating temperature T, the proof stress or yield stress (unit: kgf/mm^2) is greater than the value determined by the empirical formula: 16000/T (where T is the operating temperature expressed in absolute temperature). A method for selecting ferrite steel with excellent erosion resistance at high temperatures, which is characterized by selecting ferrite steel.