JPS583948A - Selecting method for ferrite steel with superior erosion resistance at high temperature - Google Patents

Abstract

PURPOSE:To select a ferrite steel with a specified value or above of yield strength and superior erosion resistance at high temp. by specifying the contents of C, Si, Mn, Cr, and Mo in a ferrite steel. CONSTITUTION:The composition of a ferrite steel used in a hot erosive environment is composed of, by weight, <=0.6% C, 0.1-2% Si, <=1% Mn, 0.5-14% Cr, 0.3-2.5% Mo and the balance Fe with inevitable impurities. To the composition may be added <=1.5% in total of one or more among V, W, Ti and Nb. In the composition range, the steel is selected so taht the yield strength or yield stress exceeds a value obtd. by an empirical formula 16,000/T (T is service temp. represented by absolute temp.). Thus, a ferrite steel with superior erosion resistance at high temp. for structural members of a coal-fired boiler, a coal liquefier, etc. is obtd.

Description

[Detailed Description of the Invention] This invention relates to ferritic steel used as a structural member of coal-fired boilers, coal liquefaction equipment, gasification equipment, etc.
The present invention relates to a method for selecting ferritic steel that exhibits excellent erosion properties, particularly when used in environments exposed to high temperature erosion.

2- 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 caboilers and coal liquefaction and gasification equipment.

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

In this way, the existing coal-fired Capoira 9 coal liquefaction.

In terms of materials, gasifiers and other equipment are simply designed in the same way as those that use petroleum, but high-temperature erosion that contains solid particles such as fine coal powder and coal combustion ash occurs uniquely when using coal. It is not known for sure what kind of high-temperature erosion resistance the constituent part I exhibits when exposed to the environment, and no research or measures have been taken regarding these materials. At present, only a few measures have been taken from a design perspective, such as the use of protectors.

Therefore, from the above-mentioned viewpoint, the present inventors focused on ferritic steel members that are used in high-temperature erosion environments containing 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, it was found that ferritic steel used in the above environment has an O content of 0.6% or less, Si': 0.1 to 2%, Mn content of 1% or less,
Contains Cr: 0.5 to 14%, Mo: 0.3 to 25%, and optionally ■.

One or more of W, Ti, and Nb: total amount 1.5
% or less, with the remainder consisting of Fe and unavoidable impurities (the above is by weight, the below is by weight), and has an empirical formula: C (where T is the operating temperature expressed in absolute temperature) Ferritic steel, which has a yield strength or yield stress at the relevant temperature that is greater than the value determined by We obtained the knowledge to show that

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) O C is an important element for ensuring the strength of steel, and has the effect of enhancing the quenching effect and increasing the yield stress (yield strength) and tensile strength of steel. If the content exceeds 6%, not only is cracking likely to occur during heat treatment, but also cold working becomes difficult, so the upper limit was set at a factor of 0.6.

(b) 5i Sl is an indispensable element for the purpose of deoxidizing in steel smelting, but if its content is less than 1% O, the desired deoxidizing effect cannot be obtained, On the other hand, if the content exceeds 2 parts, cold working may become difficult, so the content was set at 0.1 to 2 parts.

Furthermore, since Si has the effect of increasing the strength of steel, it is desirable to contain it in an amount of 0.5% or more especially when high strength is required.

(c) Mn Mn 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 be obtained. , the upper limit of its content was set at 1%.

(a) cr Or is an important element in ensuring high-temperature oxidation resistance and high-temperature strength, and has the effect of enhancing the quenching effect and further improving strength, but if its content is less than 0.5% In this case, the amount to achieve the desired effect was determined to be 0.5 to 14%.

(e) M.

6-Mo has the effect of improving high-temperature strength, but if the content is less than 83%, the desired high-temperature strength cannot be secured, while if it is contained in excess of 2.5%, the Since no improvement effect was observed, the content was determined to be 0.3 to 2.5% in consideration of economic efficiency.

(f) fV, W, Ti, and l1tb These components, like Or and 140, have the uniform effect of precipitating fine carbides and increasing the high-temperature strength of brass, so they can achieve even higher strength. It is included as needed when required, but even if it is contained in a total amount exceeding 1.5 parts, no further improvement effect will be obtained. Ta.

B. Proof 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, and found that the yield strength of the ferritic steel ( We found that there is a special correlation between the yield stress (yield stress) and the operating temperature in a high-temperature erosion environment, and after further investigation into this relationship, we were able to satisfy the following criteria (where T is the operating temperature expressed in absolute hot water temperature). In this case, it has been empirically concluded that the ferritic steel exhibits excellent erosion resistance under the above-mentioned high-temperature erosion environment.

Next, the method of the present invention will be explained using examples and comparing with comparative examples.

Example Ferritic steel 1 of the present invention having the composition and rigidity shown in Table 1 by ordinary melting method and forging method, respectively.
- 8 and conventional steels 1 to 3 were prepared, test pieces were taken from these various steels, and test specimens were obtained from these steels.
A high-temperature erosion test was carried out under the condition that No. 7 artificial silica sand was sprayed onto the specimen at a flow rate of 120 m/sec for 1 hour at an impact angle of 20° using Ar gas as a carrier gas, and each specimen The maximum erosion depth was measured.

8- The measurement results are also shown in Table 1.

As is clear from the results shown in Table 1, 28 K9
/++J) Conventional steels 1 to 3 that have a lower yield strength than
Compared to the ferritic steels of the present invention which have yield strength of 28 Kr/- or more] to 8, the conventional steel 3 has significantly inferior l111 erosion resistance even though it is a high-grade steel. There is.

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.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazu Husband

Claims (2)

[Claims] (1) When using ferritic steel in an environment where erosion may occur at high temperatures, the ferritic steel should have C: o, 6% or less, S+4. : 0.1
~2%, Mn: ], % or less, cr:
0.5~], 4%, Mo: 03~25%, and the remainder is Fe and unavoidable impurities (weight%), and the empirical formula: 16000/T (however, T is A method for selecting a ferritic steel with excellent erosion resistance at high temperatures, characterized by selecting a ferritic steel with a square dimension or yield stress greater than the value determined by the operating temperature (expressed in absolute temperature). . (2) Environment that may cause erosion at high temperatures 1-Failure under the environment! - When using steel, as the ferritic steel, C: 0.6% or less + S ], : 0
．． 1-2LII), Mn: 1% or less, Cr: 0.5
]4%, Mo: 0.3 to 2.5%, and further contains one or more of V, W, Ti, and Nb: -5% or less in total, and the remainder is It has a composition (hereinafter referred to as weight ratio) consisting of Fe and unavoidable impurities, and has the empirical formula:
], 6000/T, (where T is the service temperature expressed in absolute temperature) How to select an excellent ferritic steel.