JPH02282461A - Treatment of self-fluxing alloy for cr-mo steel tube for boiler - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cracks and peeling in a self-fluxing alloy layer and to improve wear resistance by thermally spraying a self-fluxing alloy on the external surface of a Cr-Mo steel tube as a generating tube in the layer in a fluidized bed boiler and then applying fusing and cooling to the above thermally sprayed layer while controlling the temp. in an electric furnace. CONSTITUTION:A self-fluxing alloy is thermally sprayed to 0.3-1.2mm thickness on the external surface of a generating tube made of Cr-Mo steel for use in a fluidized bed boiler. This generating tube is put into an electric furnace and heated up to 600-800 deg.C by means of an acetylene burner to fuse the thermally sprayed self-fluxing alloy layer, and successively, the tube is cooled slowly, while held in the electric furnace, down to <=200 deg.C at 50-100 deg.C/hr cooling rate and then taken out from the electric furnace. By this method, the generating tube having superior wear resistance in the self-fluxing alloy layer on the external surface of the generating tube, reduced in wear due to fluidized medium, etc., in the boiler, free from the occurrence of cracks and peeling, and capable of withstanding long use can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a Cr
-Regarding a method of treating a self-fusing alloy to a Mo tube.

[Conventional technology]

In a fluidized bed boiler, an appropriate amount of fluidized medium (for example, limestone, etc.) is filled in the combustion chamber, air is flowed upward from the lower nozzle, and the fluidized medium, such as limestone powder, is floated to form a fluidized state. Fuel such as pulverized coal is put into the combustion chamber and combustion is carried out while it is brought into contact with a fluidized medium.

The intrabed evaporation tube in contact with this mixed phase of pulverized coal and fluidized medium is exposed to high temperatures and is subjected to severe abrasion due to constant collisions with the hard fluidized medium.

To protect the intralayer evaporation tube from such severe wear,
Conventionally, thermal spraying of MiCr alloys and ceramics and treatment of self-fluxing alloys have been carried out.

[Problem to be solved by the invention]

However, Nior alloy thermal spraying does not provide sufficient wear resistance, and ceramic thermal spraying has the drawback that it peels off due to the difference in thermal elongation with the Cr-Mo steel pipe material when the boiler starts and stops. There is. Furthermore, conventionally, in the treatment of self-fusing alloys, the fusing treatment after thermal spraying of self-fusing alloys is performed by heating directly with an acetylene burner in the atmosphere, so the cooling rate of the fusing tube is significantly faster, and the self-fusing alloy treatment layer The drawback is that cracks often occur in the pipes, which can be the starting point for corrosion and damage to the pipe during practical use. Furthermore, because the tube cooling rate after fusing is insufficiently adjusted, the tube material undergoes structural changes and becomes extremely hardened and brittle.

[Means to solve the problem]

While conducting research to solve the drawbacks of conventional self-fusing alloy treatment for Cr-Mo steel pipes, the present inventors sprayed a self-fluxing alloy onto Cr-Mo steel pipes and then controlled the temperature in an electric furnace. However, it has been found that satisfactory results can be obtained by performing fusing and cooling.

The present invention has been completed based on the above findings, and consists of applying a self-fusing alloy to the outer surface of a Cr-Mo steel tube for boilers.
After thermal spraying to a thickness of ~1.21 mm, the self-fusing alloy is fused with an acetylene burner in an air furnace maintained at 600 to 800 °C, and even after fusing is completed, it is maintained in an electric furnace to a thickness of 50 to 100 mm. This is a method for treating a self-fluxable alloy on a Cr-Mo steel pipe for a boiler, which is characterized in that the steel tube is cooled to 200° C. or lower at a rate of °C/Hr and then taken out from a 9C furnace.

In the present invention, JISusy-y is used as a self-fusing alloy.
l-1, m5F-N1-2. MsF-N1-4 (all made of Ni-0r-131-B, Cri different)
.

MSFOol (Co-Ni-Cr-8i-B) from J.
etc., any one can be used.

[Effect]

(1) The self-fusing alloy treatment layer is hard and has excellent erosion resistance, which not only prevents wear caused by collisions between fluid media and powdered coal, but also has thermal conductivity equivalent to that of the low alloy material that makes up the peripheral wall tube. Therefore, the thermal conductivity of the peripheral wall tube is not impaired.

(2) In fusing and subsequent heat treatment,
Since the cooling rate is reduced by 50 to 50 b, no cracks or peeling occur in the sprayed self-fluxing alloy layer, and structural changes in the tube material are also smoothed out, so the mechanical properties of the tube material are not impaired.

(3) In the present invention, the temperature of the electric furnace during fusing is set at 600 to 800°C, but the temperature required for fusing a self-fusing alloy at 600°C or lower (1ooo to 1
It takes time to heat up to 100℃, and the temperature drops to 600℃ relatively quickly after fusing, so
Cracks often occur in the coating layer.

Furthermore, if the IT electric furnace temperature is 800° C. or higher, it is likely to be overheated during fusing, which will adversely affect the coating layer and the tube material.

(4) Furthermore, in the present invention, the thickness of the self-fusing alloy layer is 0.
．． The thickness was set at 3 to 1.2 m, but if it is less than α31111, it is insufficient to exhibit wear resistance in actual cans, and if it is thermally sprayed thicker than 1 or 2 m, cracks etc. often occur in the coating layer.

〔Example〕

As an embodiment of the present invention, a J-engineering 5STBA24 steel pipe (50 x 4000 x 6ff) is used as a Cr-Mo steel pipe.
He J Engineering 8 M81F-Ni-4 self-fluxing alloy (Nt-Cr
-81-B series) processing results are shown.

That is, as shown in Table 1, after masking, blasting, and thermal spraying are performed in the usual manner, fusing is performed in an electric furnace maintained at 700°C, and then the temperature is lowered at a rate of 50°C/hour to 200°C or less. It was taken out from the furnace when it reached its final stage. A temperature control chart during the fusing and slow cooling treatments after thermal spraying is shown in FIG. In the self-fusing alloy treated layer according to the present invention, no cracks or the like were detected at all when inspected by penetrant testing. Furthermore, we cut and investigated a part of it.
No pores or foreign matter were observed at the boundary between the self-fusing alloy layer and the pipe material. In addition, there were no structural abnormalities in the pipe material, and the hardness was 1.
No particular tendency to harden was observed at 50 to 180 mHv. In contrast, conventional methods often have a hardness of 200 to 4
00 mHv (embrittlement).

Table 1 Processing procedure for self-fusing alloys on Cr-Mom tubes for boilers Steel pipe inspection Masking grid Plast Masking removal Self-fusing alloy thermal spraying: Acetylene thermal spraying Film thickness a3-1.2 Installation of pipe (6) in the air furnace: Temperature 70 (Ic(7)) Fusing: Acetylene burner 1000-1100℃ (
8) Allow to cool to 700℃ in electric furnace (9) Slow cooling 5
0 to b αIf Taken out from the air furnace: 200°C or less Author b
There was no increase in hardness, and it was confirmed that there were no structural abnormalities. In addition, the numerical values in Table 2 (1, 2, 3 and 1', 2
', 3', 4') and numerical values (α1, α2) indicate the measurement positions and measurement intervals of the coach ink layer and the base material shown in FIG.

Table 2 Test piece hardness measurement results after thermal spray fusing of self-fusing alloy (JXB MSP-Ni-4). Figure 3 shows the wear resistance improvement effect of the present invention, and the results of no treatment and conventional method (self-fusing alloy). The following shows the results of comparing the abrasion resistance of a method in which the sprayed surface is heated and melted using an acetylene burner after thermal spraying.

The test method uses alumina particles at a blasting pressure of 5 kg/cM.
'', with a plast angle of 30'. It is clear from FIG. 3 that the method of the present invention exhibits excellent wear resistance.

〔Effect of the invention〕

According to the present invention, a self-fluxing alloy sprayed layer with excellent wear resistance can be formed on the outer surface K of a cr-Mo W4 tube, which is an evaporation tube in a fluidized bed, without cracking or peeling. Because the fusing and subsequent cooling rates are well adjusted,
Tissue changes and mechanical properties of the tube base material can be prevented.

[Brief explanation of drawings]

Figure tIc1 is a diagram illustrating the temperature control conditions of an example of the present invention, and Figure 2 is an explanatory diagram of hardness measurement points of the test piece of the self-fluxing alloy coating layer and base material obtained in the example of the present invention. , FIG. 3 is a chart proving the improvement in wear resistance of the evaporator tube obtained by the present invention.

Claims (1)

[Claims] 0.3% of self-fusing alloy is applied to the outer surface of Cr-Mo steel pipe for boiler.
After thermal spraying to a thickness of ~1.2 mm, the self-fusing alloy is fusing with an acetylene burner in an electric furnace kept at 600 to 800 °C, and even after fusing is completed, it is heated to 50 to 100 °C while being kept in the electric furnace. A method for treating a self-fusing alloy on a Cr-Mo steel pipe for a boiler, the method comprising cooling the steel pipe to 200°C or less at a temperature of 200°C or less at a temperature of 200°C or less and then taking it out from an electric furnace.