JPS583953A - Selecting method for austenite steel with superior erosion resistance at high temperature - Google Patents

Abstract

PURPOSE:To select an austenite steel with superior yield strength and superior erosion resistance at high temp. by specifying the contents of C, N, Si, Mn, Ni, Cr, etc. in an austenite steel. CONSTITUTION:The composition of an austenite steel used in a hot erosive environment is composed of, by weight, <=0.5% C, <=0.2% N, <=1.0% Si, <=2% Mn, 7-35% Ni, 16-28% Cr and the balance Fe with inevitable impurities. To the composition may be added <=1% Ti and Nb. The composition may be composed of <=0.5% C, <=0.2% N, <=0.8% Si, 10-22% Mn, 4-15% Cr, <=4% Mo, <=5% Ni and the balance Fe. In the composition range, the steel is selected so as to provide yield strength or yield stress obtd. by an empirical formula 16,000/T (T is service temp. represented by absolute temp.). Thus, an anstenite stainless steel with superior erosion resistance at high temp. for structural members of a coal- fired boiler, etc. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to austenitic steel used as structural members of coal-fired boilers, coal liquefaction, gasification equipment, etc., especially when used in environments where erosion may occur at high temperatures. This invention relates to a method for selecting austenitic steel that exhibits excellent erosion resistance.

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

On the other hand, these coal-fired boilers, coal liquefaction, and gasification equipment are all manufactured using the same material composition as conventional oil-fired boilers, and therefore, consideration is not taken in terms of materials when using coal. For this reason, for example, JIS-8US 304H, 31 is required for manufacturing parts such as superheaters and reheaters that are heated to 500°C or higher in coal-fired boilers.
6H, 321H.

and 347H are used, and austenitic steels mainly 18-8 series are used in coal liquefaction and gasification equipment.

In this way, existing coal-fired boilers, coal liquefaction, and gasification equipment are designed based on the materials used when using petroleum; It is not known for sure what kind of high-temperature erosion resistance the constituent parts exhibit when exposed to a high-temperature erosion environment containing solid particles such as coal combustion ash and coal combustion ash. Currently, no research or measures have been taken, and only a few measures have been taken from a design perspective, such as using protectors.

Therefore, from the above-mentioned viewpoint, the present inventors focused on austenitic steel members that are used in high-temperature erosion environments that contain solid particles such as fine coal powder and coal combustion ash. As a result of conducting research to select austenitic steel that exhibits excellent erosion resistance in the environment, we found that the austenitic steel used in the above environment is (A) C: 0.5 inch or less, N: 0.2 Below, Si:
1.0 or less, Mn: 2% or less, Nj: 'i'
~35%, Cr: 16 to 28%, and optionally one or two of T1 and Nb:
an austenitic steel (hereinafter referred to as austenitic steel A) containing less than or equal to 1% and having a composition in which the remainder consists of Fe and unavoidable impurities, and ([3] O: 0.5% or less, N: 0.2% or less, Si
: 0.8 cm or less, Mn: 10-22%, Or:
4-15'%, M.

: 4% or less, Ni: 5% or less, and the remainder consists of Fe and unavoidable impurities (hereinafter referred to as austenitic steel B). At the same time, empirical formula: 16000/T 5
- If an austenitic steel is selected with a proof strength or yield stress greater than the value determined by They found that it exhibits excellent erosion resistance in high-temperature erosion environments.

This invention has been made based on the above findings, and the reason why the composition and proof stress (or yield stress) of the austenitic steels A and B are limited as described above will be explained below.

■Composition of austenitic steel A (a) O C is an important element for stabilizing austenite and improving the strength of steel, and the higher its content, the more effective it is, but if it exceeds 0.5% If it is included, the workability deteriorates significantly, so the upper limit was set at 0.5%.

(b) Like C, N also has the effect of stabilizing austenite and increasing the strength of steel, but if the content exceeds 0.2%, the workability similarly decreases. , its upper limit was set at 0.2.

(c) Si Sj is an essential element because it has a deoxidizing effect, but]
Since a content exceeding 0% is meaningless from the viewpoint of deoxidation, the upper limit was set as ], 0%.

(d) Mn In addition to its deoxidizing effect, Mn has the effect of stabilizing austenite, but even if it is contained in an amount exceeding the 2nd coefficient, no further improvement effect will appear, so the upper limit value has been set to 2%. It was determined that

(e) If the Nj content is less than 7 parts, it is not possible to stably secure austenite, while if the content exceeds 35 parts, it is meaningless for austenitization. It was set at 35%.

(f) 0r Or has the effect of improving oxidation resistance at high temperatures,
If the content is less than -6%, the desired effect cannot be obtained, while if it is more than 28%, the processability will deteriorate, so the content should be adjusted to]6 to 28%.
It was determined that

(g) Ti and Nb T1 and Nb combine with C and 1\■ in the steel to form precipitates, thereby strengthening the steel and improving erosion resistance. It is included as necessary when higher strength and erosion resistance are required, but even if it is added in excess of 1φ, it will not have any further improvement effect, but rather will improve the cleanliness and weldability of the steel. Therefore, the upper limit of the content]-
It was determined that there were many.

(2) Composition of austenitic steel B (a) C, N, Sj The reasons for limiting these elements are the same as those for austenitic steel A described above.

(b) Mn austenitic steel B is N1 in austenitic steel A
However, if the Mn content is less than 10%, it is not possible to stably secure austenite, and on the other hand, if the content is up to 22%, austenite cannot be stabilized. It is enough, so the content is 10
-22%.

(c) 0rOr has the effect of improving oxidation resistance, especially at high temperatures, but if its content is less than 4%, the desired effect cannot be obtained; on the other hand, if it is contained in excess of 15%, Since the effect of further improving oxidation resistance was not apparent, the content was set at 4 to 15 inches.

(d) M.

Mo is an extremely effective element for increasing high-temperature strength, but even if it is contained in amounts exceeding 4%, the effect of improving high-temperature strength is small relative to the content, and considering that it is an expensive element, The upper limit is set at 4.

(e) NiN1 has the effect of improving oxidation resistance, but if it is contained in excess of 5 Ti, the substitution effect by Mn will be reduced, so the upper limit was set at 5 Ti.

■Proof strength Concerning austenitic steels A and B having the above-mentioned compositions, we investigated the relationship between the characteristics of austenitic steel 9- and various factors that constitute the high-temperature erosion environment from various aspects. As a result, they discovered that there is a special correlation between the diagonal strength and yield stress of these austenitic steels and the atmospheric temperature in the high-temperature erosion environment, that is, the operating temperature, and further investigated this relationship. As a result, when the proof stress or yield stress of the austenitic steel A6000 and B satisfies ≧-1'- (where T is the service temperature expressed by the feed temperature), the austenitic steel A and B have the above-mentioned solid particles in particular. It has been empirically concluded that the material exhibits excellent erosion resistance in a high-temperature erosion environment.

Next, the method of the present invention will be specifically explained using examples.

Examples Austenitic steels of the present invention] to 6 and conventional steels 1 to 3 having the compositions and yield strength shown in Table 1 were manufactured by ordinary melting and forging methods, respectively, and test pieces were taken from these various steels. , using these test pieces, temperature: 650℃ (160℃)
JI No. 87 artificial silica sand having an average particle size of 00 to 1.50 μm was used as the solid particles, and Ar gas was used as the gear gas.
A high-temperature erosion test was conducted under the conditions of spraying the test pieces at a flow rate of 20°/sec for 1 hour at an impact angle of 20°, and the maximum erosion depth of each test piece was measured. The measurement results are also shown in Table 1.

From the results shown in Table 1, the value of 16000-, i.e., the yield strength (-1,7,3 kg/, corresponding to ]7.3
All of the austenitic steels 1 to 6 of the present invention, which have a yield strength higher than B), have even better high-temperature erosion resistance than conventional steels 1 to 3, which have a yield strength of 7.3 kg/- or less. It is clear to show.

As described above, according to the present invention, an austenitic steel member used as a structural member in a high-temperature erosion environment, particularly in an atmosphere containing solid particles such as fine coal powder and coal combustion ash, is If selected based on both aspects, the resulting austenitic steel member will exhibit industrially useful effects such as excellent high-temperature erosion resistance.

Applicant: Sumitomo Metal Industries, Ltd. Agent Tomi 1) Kazuo 13-

Claims (3)

[Claims] (1) When using austenitic steel in an environment where erosion may occur at high temperatures, the austenitic steel should include C: 0.5% or less, N: 0.2% or less, and Si: 1.0% or less. , Mn: 2% or less. The composition contains Ni: 7 to 35%, Cr: 16 to 28%, and the remainder is Fe and inevitable impurities (more than 1% by weight).
), and the empirical formula: 16000/T, (however,
A method for selecting an austenitic steel with excellent erosion resistance at high temperatures, the method comprising selecting an austenitic steel having a proof stress or yield stress greater than a value determined by the operating temperature (T is the service temperature expressed as an absolute temperature). (2) When using austenitic steel in an environment where erosion may occur at high temperatures, the austenitic steel should contain O: 0.5% or less, N: 0.2% or less, and Si: 1.0% or less. , Mn: 2% or less. Contains Ni: 7 to 35%, Or: 16 to 28%, and one or two of T1 and Nb:
16000 or less, and has a composition (by weight) with the remainder consisting of Fe and unavoidable impurities, and has an empirical formula: 16000
/T, (where T is the service temperature expressed in absolute temperature) an austenitic steel with excellent erosion resistance at high temperatures, characterized by selecting an austenitic steel with proof stress or yield stress greater than the value determined by How to select steel. (3) When using austenitic steel in an environment where erosion may occur at high temperatures, the austenitic steel should contain O: 0.5% or less, N: 0.2% or less, and Si: 0.8% or less. , Mn: 10-22%,
Car: 4-15%, Mo: 4% or less, N
i: 5% or less, with the remainder consisting of Fe and unavoidable impurities (weight% or more), and empirical formula: 160
00/T, (where T is the service temperature expressed in absolute temperature) an austenitic steel with a proof stress or yield stress greater than the value determined by the method. Excellent erosion resistance at high temperatures. How to select austenitic steel.