JPH04329852A - Alloy for waste incineration furnace boiler and multiple layered steel tube - Google Patents

Abstract

PURPOSE:To offer a multiple layered steel tube constituted of an alloy for a waste incineration furnace boiler having high corrosion resistance and wear resistance and usable in the range up to 500 deg.C steam temp. in every combustion system waste incineration furnace, and a multiple layered steel tube constituted of the above alloy, at low cost. CONSTITUTION:This is an alloy contg., by weight, 0.02 to 0.1% C, 1 to 5% Si, <=5% Mn, >10 to 20% Cr, 30 to 50% Ni, 0.5 to 3% Mo, 10 to 40% Co and 0.5 to 5% W, furthermore contg. both items or either of one or two kinds of 0.05 to 0.4% N, 0.2 to 0.5% Cu, one or two kinds of 0.05 to 2% Nb, 0.02 to 0.5% Ti and the balance Fe with inevitable impurities, and a multiple layered steel tube using the above alloy as an outer tube and using a well-known steel tube for boiler as an inner tube is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy for waste incinerator boilers and multilayer steel pipes that can be used at steam temperatures up to 500°C.

0002

2. Description of the Related Art In order to effectively utilize waste heat generated by combustion as an energy source, municipal waste incinerators are increasingly equipped with waste heat boilers to generate electricity. It is obvious that the thermal efficiency of a power generation boiler improves as the steam conditions become higher temperature and higher pressure. Due to the combustion of vinyl chloride, etc., which is contained in large amounts in
When the steam temperature exceeds 300°C, corrosion is significantly accelerated, and in order to avoid corrosion, the current situation is that steam conditions are forced to be kept below 300°C for low-efficiency operation. However, from the perspective of effective energy use, increasing the temperature and pressure of waste power generation is strongly desired.

In the environment of hydrogen chloride gas and molten hydrochloride, Cr
forms chlorides with high vapor pressure, so conventional corrosion-resistant alloys such as stainless steel cannot provide sufficient corrosion resistance.
In the current waste incineration boiler, the steam temperature is below 300℃, and the C
r-Mo based low alloy steel is used. In response, the present inventors have proposed, in Japanese Patent Application No. 2-107147, an alloy for boilers that has corrosion resistance in the corrosive environment up to a steam temperature of 500°C.

0004

[Problems to be Solved by the Invention] In recent years, fluidized bed waste incinerators, which have advantages such as superior combustion efficiency compared to conventional grate-type incinerators, have become popular. Abrasion resistance due to fluidized sand is also required for materials used for this purpose. An object of the present invention is to provide an alloy for a boiler, which can be used up to a steam temperature of 500° C. in any combustion type garbage incinerator, and is inexpensive, and a multilayer steel pipe made of the alloy.

[0005]

[Means for Solving the Problems] As a result of research conducted to solve the above problems, the present invention has been developed by adding 10% or more Co and
．． It was discovered that adding 5% or more of W is very effective in improving wear resistance, and that adding 10% or more of Co also improves high-temperature corrosion resistance due to hydrogen chloride gas and molten hydrochloride. It has been completed, and its gist is that in weight percent, C: 0.02-0.1%,
Si: 1 to 5%, Mn: 5% or less, Cr more than 10 to 20%
, Ni: 30-50%, Mo: 0.5-3%, Co: 1
0-40%, W: 0.5-5%, or further (1) N: 0.05-0.4%, Cu: 0.2-0
．． 5% of one or two types (2) Nb: 0.05-2
%, Ti: 0.02 to 0.5% of one or both of them, the balance being Fe and unavoidable impurities, and an outer tube made of these alloys, known steel pipes for boilers. It is a multilayer steel pipe with an inner pipe.

[0006]

[Operation] The reasons for limiting the ingredients will be explained below. C is harmful to the corrosion resistance caused by hydrogen chloride and molten hydrochloride, so it is preferable to reduce it as much as possible, but it is necessary to ensure strength at high temperatures and is also effective in stabilizing the austenite phase, so it is important to reduce each characteristic. The upper limit was set at 0.1%, and the lower limit was set at 0.02% as a range that does not impair the properties.

[0007]Si is an extremely effective element for ensuring corrosion resistance in a hydrogen chloride or molten hydrochloride environment. However, if the content exceeds 5%, it will cause deterioration of workability and weldability, and 1%
If it is less than 5%, sufficient corrosion resistance effect cannot be obtained, so the upper limit is set at 5%.
, the lower limit was set to 1%. Mn is an element that contributes to the formation of an austenite phase, but excessive addition causes problems in melting and hot working, so the upper limit was set at 5%.

Cr is an effective element for improving general high-temperature oxidation and high-temperature corrosion properties, and it is desirable to include it in a larger amount.However, in an environment of hydrogen chloride or molten hydrochloride, the amount added may be reduced due to the volatilization of Cr chloride. If it is more than 20%, the amount of corrosion will actually increase. Further, in order to ensure resistance to hydrochloric acid dew point corrosion caused by dew condensation when the boiler is stopped and resistance to steam oxidation on the inner surface of the boiler steel pipes, it is necessary to add more than 10%. For this reason, the upper limit was set to 20% and the lower limit was set to over 10%.

Ni is particularly preferred for improving corrosion resistance in hydrogen chloride and molten hydrochloride environments, and is also a necessary component for forming an austenite phase. In order to obtain this effect at a steam temperature of 500°C, it is necessary to add at least 30% or more. On the other hand, as the amount of Ni increases, the price of the alloy also increases, but if it exceeds 50%, the improvement in properties commensurate with the price cannot be obtained. Therefore, the upper limit was set to 50% and the lower limit was set to 30%.

[0010] Although Mo has no effect on corrosion resistance at high temperatures,
This is a necessary component to prevent hydrochloric acid dew point corrosion caused by dew condensation when the boiler is stopped, and for that purpose, 0.
It is necessary to add 5% or more. However, in order to stabilize the austenite phase, the upper limit was set at 3%. Co is the most important element in the present invention, and as shown in Figures 1 and 2, it has excellent wear resistance in a fluidized bed environment, corrosion resistance in a hydrogen chloride and molten hydrochloride environment, and hot erosion resistance in a combined environment. It is particularly effective in improving corrosion characteristics. To obtain this effect at a steam temperature of 500°C, it is necessary to add at least 10%. On the other hand, when it exceeds 40%, the effect is saturated. For this reason,
The upper limit was set to 40% and the lower limit was set to 10%.

[0011] W is effective in improving wear resistance properties, and in order to obtain this effect, it is necessary to add 0.5% or more. Also,
If added in excess of 5%, intermetallic compounds will precipitate, resulting in deterioration of workability and corrosion resistance. Therefore, the upper limit was set to 5% and the lower limit was set to 0.5%. In the present invention, the following components may also be added. N is an element effective in improving high-temperature strength and forming an austenite phase, and is added as necessary depending on the amount of Cr and Si. To obtain this effect, it must be added in an amount of 0.05% or more. is necessary. However, 0.
Addition of more than 4% will generate bubbles in the alloy and
Since the formation of nitrides becomes significant and causes deterioration of toughness, the upper limit was set at 0.4% and the lower limit was set at 0.05%.

[0012] Nb and Ti are added when high-temperature strength is particularly required, and in order to obtain this effect, Nb needs to be at least 0.05% and Ti needs to be at least 0.02%. . However, if Nb and Ti exceed 2% and 0.5%, respectively, the amount of carbides and nitrides produced will be excessive, which will conversely cause a decrease in strength. Therefore, the amount of Nb added is 0.
．． The amount of Ti added was 0.02 to 0.5%.

[0013] Cu is an element effective in forming an austenite phase. It also has the effect of improving acid resistance, especially when corrosion resistance at low temperatures such as hydrochloric acid dew point corrosion is required.
Add 2-0.5%. The reason why the lower limit was set at 0.2% is because sufficient effects cannot be obtained with less than this, and also,
The reason why the upper limit is set to 0.5% is that if added in excess of 0.5%, hot workability will be significantly impaired.

The present invention is an alloy developed and invented as a superheater tube for a waste incinerator boiler that can be used under steam conditions up to 500°C. Of course, the alloy of the present invention can be used alone as a pipe, but since it was created with emphasis on corrosion and wear resistance on the outer surface of the pipe, in order to efficiently utilize its effects, it was necessary to use it as a multilayer steel pipe. It is also possible to use it as an outer tube material. In this case, the inner tube must have high temperature strength and steam oxidation resistance, and a known boiler steel tube having the required properties is appropriately selected and used.

Next, an example of the method for manufacturing the multilayer steel pipe of the present invention will be described. On the surface of the stainless steel billet for the specified inner tube manufactured by the normal stainless steel melting and casting process,
The powder of the alloy for outer tubes of the present invention is prepared by high-temperature isostatic pressing (HI).
P method). After soaking this double-tube billet, it is formed into a predetermined size by hot extrusion. When the outer tube material is a plate or tube, instead of the process of compressing powder using the HIP method described above, a plate having the components of the outer tube material is wrapped around the surface of the stainless steel billet for the inner tube, or Alternatively, after the step of fitting the tube, the outer tube material and the inner tube material billet are joined by welding, and the thus produced double tube billet is used to manufacture a multilayer steel tube by the method described above.

[0016] It goes without saying that the method for manufacturing a multilayer steel pipe of the present invention is not limited to the above-described manufacturing method, and that any known method for manufacturing a composite (multilayer) steel pipe can be employed. The present invention can also be carried out by layering the alloy of the present invention into a steel pipe or a high-temperature material having a similar shape (for example, a diffuser nozzle for a fluidized bed boiler) using a thermal spraying method such as low-pressure plasma spraying. It is possible.

[0017]

[Example] No. of Table 1. 20 kg of each of the alloys having the compositions according to any one of Claims 1 to 4 shown in Claims 1 to 10 were melted using a vacuum induction heating furnace. This was made into a 10mm plate by forging, heated at 1150℃ for 60min, and then rapidly cooled.
A test piece of 5 x 25 x 4 mm was prepared. Conventional materials include JIS standard SUS304 and SUS3 with chemical components shown in Table 1.
10 was used. Corrosion tests include KCl, NaCl, FeC
40 mg/cm2 of synthetic ash mixed with l2 at a molar ratio of 3:3:4 was applied uniformly to one surface of the test piece, and 0.2% HCl was applied.
This was carried out by heating at 600° C. for 48 hours in a mixed gas flow of +20%H2O+5%O2+balN2. When the steam temperature is 500°C, 600°C is the temperature that can be considered as the outer surface of the tube. The corrosion test results were evaluated based on the corrosion weight loss after descaling. The wear test was carried out by holding the sample at 600° C. for 200 hours in a fluidized bed heating furnace. Alumina particles with a particle size of 0.1 to 0.3 mm were used as the fluidizing medium. Corrosion test results and wear test results are also shown in Table 1.
Shown below. While the amount of corrosion of the conventional material is 30 mg/cm2 or more, the amount of corrosion of the alloy of the present invention is 15 mg/cm2.
It shows much higher corrosion resistance than the following. Furthermore, the amount of wear of the alloy of the present invention is about an order of magnitude lower than that of conventional materials. As described above, it has been revealed that the alloy of the present invention exhibits extremely high corrosion resistance in a hydrogen chloride gas and molten hydrochloride environment, and also has extremely high wear resistance in a fluidized bed environment.

[0018]

[Table 1]

[0019]

[Effects of the Invention] According to the present invention, superheater tubes of garbage incinerator boilers of all combustion methods used at steam temperatures up to 500°C have excellent corrosion resistance due to hydrogen chloride gas and molten hydrochloride. This makes it possible to provide a material with excellent wear resistance in a fluidized bed environment, which greatly contributes to the development of industry.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of Co content on the amount of corrosion in a hydrogen chloride gas and molten hydrochloride environment.

FIG. 2 is a graph showing the effect of Co content on the amount of wear in a fluidized bed environment.

Claims (5)

[Claims] Claim 1: C: 0.02 to 0.1%, Si: 1 to 5%, Mn: 5% or less, Cr: more than 10 to 20%, Ni: 30 to 50%, Mo: 0.5-3%, Co: 10-40%, W: 0.5-5%, with the balance consisting of Fe and inevitable impurities. Claim 2: C: 0.02 to 0.1%, Si: 1 to 5%, Mn: 5% or less, Cr: more than 10 to 20%, Ni: 30 to 50%, Mo: 0.5-3%, Co: 10-40%, W: 0.5-5%, and further N: 0.05-0.4%, Cu: 0.2-0.5%. An alloy for waste incinerator boilers, characterized in that it contains one or two species, and the remainder consists of Fe and inevitable impurities. Claim 3: C: 0.02 to 0.1%, Si: 1 to 5%, Mn: 5% or less, Cr: more than 10 to 20%, Ni: 30 to 50%, Mo: In addition to 0.5-3%, Co: 10-40%, W: 0.5-5%, one of Nb: 0.05-2%, Ti: 0.02-0.5% or An alloy for a waste incinerator boiler, characterized in that it contains two types, and the remainder consists of Fe and unavoidable impurities. 4. C: 0.02 to 0.1%, Si: 1 to 5%, Mn: 5% or less, Cr: more than 10 to 20%, Ni: 30 to 50%, Mo: 0.5-3%, Co: 10-40%, W: 0.5-5%, and one of the following: N: 0.05-0.04%, Cu: 0.2-0.5% or 2 types and 1 type or 2 types of Nb: 0.05-2%, Ti: 0.02-0.5%, and the remainder consists of Fe and inevitable impurities. Alloy for boiler 5. A multilayer steel pipe for a waste incinerator boiler, characterized in that the inner pipe is a known steel pipe for boilers, and the outer pipe is made of the alloy according to any one of claims 1 to 4.