JPS6033182B2 - How to select austenitic steel with excellent erosion resistance at high temperatures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to austenitic steel used as structural members of coal-fired power 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 to use coal instead of oil again, as can be seen in the increase in the number of operations and research on coal-fired power boilers, coal liquefaction gasifiers, etc., for example.

On the other hand, these coal-fired boilers, coal liquefaction, and gasification equipment are all manufactured with the same material composition as conventional oil-fired boilers, so there are no considerations in terms of materials when using coal. For this reason, for example, JIS-SUS 304, 31 is required for manufacturing parts such as superheaters and reheaters, which are 50,000 or more for coal-fired boilers.
Feed, 321 days, and 347 days are used, and austenitic steel, mainly 18-8 series, is 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 oil; 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 there is still no research on these materials. At present, no measures have been taken to protect against this problem, and 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 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 : 1.0 or less, Mn: 2% or less, Ni: 7 to 35
%, Cr: 16 to 28%, and optionally one or two of Tj and Nb: 1% or less, with the remainder consisting of Fe and inevitable impurities. (hereinafter referred to as austenitic steel A)
, and (B-C: 0.5% or less, N: 0.2% or less, Si: 0.8% or less, Mn: 10-22%, Cr: 4
~15%, Mo: 4% or less, Ni: 5% or less,
The remainder consists of Fe and unavoidable impurities (more than % by weight)
, below all percentages indicate weight) (hereinafter referred to as austenitic steel B), and at the operating temperature T, the empirical formula: 16000/T
(However, T is the operating temperature expressed in absolute temperature.) Proof strength or yield stress (unit: k9f/
By selecting an austenitic steel with a certain amount of solid particles, it was found that the resulting austenitic steel exhibits excellent erosion resistance, especially in a high-temperature erosion environment containing the above-mentioned solid particles.

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.

1 Composition ta of austenitic steel A} C
, C is an important element for stabilizing austenite and improving the strength of steel, and the higher the content, the more effective it is, but when it is included in excess of 0.5%, the workability deteriorates significantly. Therefore, the upper limit is set at 0.5%.

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

'c} SiSi is an essential element because it has a deoxidizing effect, but since its content exceeding 1.0% is meaningless from the viewpoint of deoxidizing, the upper limit is set at 1.0%. Ta.

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

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

{f) Cr Cr has the effect of improving oxidation resistance at high temperatures,
If the content is less than 16%, the desired effect cannot be obtained, while if the content exceeds 28%, the processability deteriorates, so the content was set at 16 to 28%. .

(g) Ti and Nb Ti and Nb combine with C and N in the steel to form precipitates, thereby strengthening the steel and improving erosion resistance. It is included as necessary when strength and erosion resistance are required, but even if it is added in excess of 1%, there is no further improvement effect, and rather the cleanliness of the steel deteriorates, such as weldability. Therefore, the upper limit content was set at 1%.

0 Composition of austenitic steel B {a- C, N, Si The reasons for limiting these elements are the same as those for austenitic steel A described above.

{b} Mn Austenitic steel B is Nj in austenitic steel A
However, if the Mn content is less than 10%, austenite cannot be stably secured, whereas if the Mn content is up to 22%, the austenitic steel cannot be stabilized. is sufficient, so its content is reduced to 1
It was set at 0 to 22%.

{c) Cr Cr 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 does not appear, its content is set at 4 to 15%.

{d} Mo Mo is an extremely effective element for increasing high-temperature strength, but even if it is contained in an amount exceeding 4%, the effect of improving high-temperature strength is small relative to the content, and it should also be considered that it is an expensive element. The upper limit was set at 4%.

{e} Ni Ni has the effect of improving oxidation resistance, but if the content exceeds 5%, the substitution effect by Mn will be reduced, so the upper limit was set at 5%.

Regarding austenitic steels A and B having the above-mentioned compositions, we investigated the relationship between the characteristics of these austenitic steels and the various factors that constitute the high-temperature erosion environment from various aspects, and found that these austenitic steels We discovered that there is a special correlation between the yield strength or yield stress of steel and the atmospheric temperature in a high-temperature erosion environment, that is, the operating temperature.As a result of further investigation into this relationship, we found that the austenitic steel A And the proof stress or yield stress of B (k9f/square) ≧ type failure.

(where T is the service temperature expressed as an absolute temperature), it has been empirically shown that the austenitic steels A and B exhibit excellent erosion resistance especially in the above-mentioned high-temperature erosion environment containing solid particles. It was concluded. Next, the method of the present invention will be specifically explained using examples. Examples Austenitic steels 1 to 6 of the present invention and Comparative steels 1 to 3 having the compositions and yield strength shown in Table 1 were produced by ordinary melting and forging methods, and test pieces were taken from these various steels. , using these test pieces, the temperature:
500, 650, 75000 (therefore, respectively,
Toyosora o = 2o-6, 7-3, 15.6),
JIS No. 7 artificial manure with an average grain size of 100 to 150 m as solid particles, sand as a carrier gas, and Ar as a carrier gas.
Using gas, the specimen was heated at 20oC at a flow rate of 65m/sec.
A high-temperature erosion test was conducted under the conditions of spraying at an impact angle of 1 hour for 1 hour, and the maximum erosion depth of each test piece was measured.

The measurement results are also shown in Table 1. Table 1 (Note) oy: Proof strength (b9f/fence) D: Maximum erosion depth (〃m) From the results shown in Table 1, the steel of the present invention has extremely good resistance at each test temperature compared to the comparative steel. It can be seen that it exhibits erosion properties.

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 FIG. 1, it is clear that the steel of the present invention and the comparative steel are clearly separated by the line 0 of the clay type. As mentioned above, according to this invention,
When selecting austenitic steel to be used as a component in a high-temperature erosion environment, especially in an atmosphere containing solid particles such as fine coal powder or coal combustion ash, based on both its composition and the operating temperature, this The resulting austenitic steel member exhibits excellent high-temperature erosion resistance and other industrially useful effects.

[Brief explanation of drawings]

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

Claims (1)

[Claims] 1. When using austenitic steel in an environment where erosion may occur at high temperatures, the austenitic steel contains (a) C: 0.5% or less, N: 0.2%
Below, Si: 1.0% or less, Mn: 2% or less, Ni: 7
~35%, Cr: 16~28%, Fe and inevitable impurities: remainder, (b) C: 0.5% or less, N: 0.2% or less, Si:
1.0% or less, Mn: 2% or less, Ni: 7-35%, C
r: 16-28%, one or more of Ti and Nb: 1% or less, Fe and unavoidable impurities: the remainder, (c) C: 0.5% or less, N: 0.2% or less, Si:
0.8% or less, Mn: 10-22%, Cr: 4-15%
, Mo: 4% or less, Ni: 5% or less, Fe and unavoidable impurities: the remainder, and has the following composition (hereinafter referred to as weight %), and at the operating temperature T, the empirical formula: 1600/T (however, T Erosion resistance at high temperatures is characterized by selecting an austenitic steel with a proof stress or yield stress (unit: kgf/mm^2) greater than the value determined by the operating temperature (expressed in absolute temperature). How to select austenitic steel with excellent properties.