JP2833437B2 - Wear resistant multi-layer steel pipe for boiler and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the bombardment of coal or COM (mixture of pulverized coal and heavy oil), fluid bed boilers, etc., in which the outer surface layer of the tube is crushed by unburned coal fine powder or coal-burning ash. TECHNICAL FIELD The present invention relates to a wear-resistant multi-layer steel pipe for a boiler comprising a hard layer having excellent wear resistance against water and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the diversification of energy sources, there has been a tendency to use coal again as an energy source instead of oil. In particular, coal-fired fluidized-bed boilers and pressurized fluidized-bed boilers have high power generation efficiency, can suppress the generation of nitrogen oxides, and can also use raw materials such as coal and coal ash that contain sulfur and have a high ash content. So it is getting more attention.

[0003] However, in these power generation methods, hard particles such as unburned coal fine powder and coal-burning ash are scattered in the boiler, causing high-temperature solids generated by high-speed collision with boiler members such as heater tubes and evaporator tubes. Particle erosion is becoming increasingly recognized as a serious form of damage to boiler components. In particular, recently, since it is desired that the power generation capacity and power generation efficiency per unit are comparable to those of oil-fired power generation, a boiler member that is less likely to undergo erosion damage even under increasingly severe conditions is required.

[0004] Hard materials such as stellite and other Co-based alloys can be overlaid and sprayed on the surface layer of steel tubes for boilers and heat exchangers to improve erosion resistance. The bending process is not possible because of poor performance.
An inconvenience that on-site thermal spraying is required occurs. Further, the Co-based alloy has a disadvantage that the production cost is increased because it is an expensive material.

Japanese Patent Application Laid-Open No. 60-196502 discloses a coal-fired boiler characterized by comprising a steel pipe for a boiler / heat exchanger and an outer layer steel having excellent high-temperature particle erosion resistance laminated on the outer surface thereof. Double-walled steel pipes have been proposed. However, this outer layer steel is an extremely common steel based on high Si and high Cr, cannot be said to have sufficient erosion resistance, and is insufficient as a coal-fired boiler member.

[0006] Japanese Patent Application Laid-Open No. 61-110714 discloses a steel pipe for a boiler / heat exchanger and an outer steel pipe of a precipitation hardening alloy laminated on the outer surface thereof. A heat transfer tube characterized by hardening the outer layer steel pipe by performing aging treatment after adding the above process has been proposed. However, in this method, although the hardness is increased by the aging treatment, the hardness is up to about Hv350, and a heat transfer tube having sufficient performance for high-temperature particle erosion resistance in a severe environment cannot be obtained.

[0007] Japanese Patent Application Laid-Open No. Hei 4-247851 discloses that C: 0.40 to
0.70%, Si: 0.10 to 3.00%, Mn: 12 to 30%, Cr: 4 to 8
% And a high Mn austenitic steel for wear resistance with a work hardening index of 0.40 to 0.50. However, a high Mn steel having a work hardening index of only 0.40 to 0.50, such as this steel, has a problem in erosion resistance, is not suitable as a material for steel pipes for boilers, and has insufficient hardness.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a wear-resistant multi-layer steel pipe for a boiler having the following characteristics and a method for producing the same.

[0009] Even in a coal-fired fluidized-bed boiler, abrasion due to the collision of high-temperature and high-hardness particles can be achieved.
To have sufficient wear resistance of the outer layer pipe surface and strength as boiler steel pipe.

[0010] The heat treatment of the steel tube for the boiler / heat exchanger as the inner tube also significantly increases the hardness of the outer tube.

[0011] A curved pipe member of a multi-layer steel pipe for a boiler can be manufactured.

[0012] The steel of the outer pipe is easily work hardened by cold working such as shot peening.

The outer pipe having a high hardness layer and the steel pipe for the boiler / heat exchanger of the inner pipe are completely adhered to each other, so that heat conduction is not hindered, and no hot spot due to local adhesion failure is generated.

[0014]

The gist of the present invention is as follows.
(1) The wear-resistant multi-layer steel pipe for a boiler according to (2) and the production method thereof according to (3) to (5).

(1) On the outer surface of a steel tube for a boiler / heat exchanger, C: 0.1 to 1.2%, Si: 1.0% or less, Mn: 10 to 25% by weight.
%, Cr: 15% or less, Ni: 5% or less, Mo: 3% or less, V:
0.1-4.0%, Al: 1% or less and N: 0.3% or less,
The balance consists of Fe and unavoidable impurities, and P
Is a wear-resistant multi-layer steel pipe for a boiler, wherein high-manganese steel of 0.010% or less and S of 0.005% or less are laminated.

(2) In addition to the chemical components described in the above (1), W: 3% or less, Nb: 3% or less, Ti: 1.0% or less, Zr:
The wear-resistant multi-layer steel pipe for a boiler according to the above (1), wherein a high manganese steel containing one or more of 1.0% or less and Ta: 1.0% or less is multi-layered.

(3) A composite comprising a high manganese steel pipe manufactured from a molten high manganese steel having the chemical composition described in the above (1) or (2), and a steel pipe for a boiler / heat exchanger disposed inside the high manganese steel pipe. The billet is assembled, the composite billet is hot-extruded to produce a clad steel pipe, then the steel pipe for a boiler / heat exchanger is subjected to a normalizing treatment, followed by a tempering treatment, and further cold working to form an outer layer of high manganese. A method for producing a wear-resistant multi-layer steel pipe for a boiler, comprising forming a surface hardened layer on the steel pipe.

(4) The high manganese steel having the chemical composition described in (1) or (2) above is a powdered high manganese steel.
(3) The method for producing a wear-resistant multi-layer steel pipe for a boiler.

(5) In the production method according to the above (3) or (4), the composite billet is hot-extruded to produce a clad steel pipe, and then subjected to bending, and then to a boiler / heat exchanger steel pipe. A method for producing a wear-resistant double-walled steel pipe for a boiler, wherein a normalizing treatment is performed, a tempering treatment is performed, and a surface hardened layer is formed on an outer high manganese steel pipe by shot peening.

[0020]

[Action] As a coal-fired fluidized-bed boiler, a steel pipe that has both sufficient abrasion resistance on the outer surface and the strength of a boiler steel pipe against abrasion due to the collision of high-temperature and high-hardness particles, the operating conditions of the equipment Steel pipes applicable to boiler / heat exchanger steel pipes conforming to (for example, boiler / heat exchanger carbon steel pipe specified in JIS G 3461, alloy steel pipe for boiler / heat exchanger specified in JIS G 3462, Further, a clad steel pipe in which a high-temperature, high-hardness material is multi-layered and closely adhered to the outer layer of the inner layer pipe, which is a stainless steel pipe for boilers and heat exchangers specified in JIS G 3463, and the like is most suitable.

A high manganese steel is used as a high hardness material to be adhered to the outer layer of the tube. The hardness of this high manganese steel is increased by age hardening treatment, and the surface hardness is increased by performing cold working, and the attained value satisfies the object of the present invention and is a build-up material. It is cheaper than stellite or high speed steel or cemented carbide as a tool material.

The advantage of such a hardness improvement effect and cost over cemented carbide is based on either the high manganese steel produced by the smelting method produced by the smelting method or the high manganese steel produced by the powdered material produced by the atomizing method. The same applies to the case of

The reason why the alloying elements of the high manganese steel and the appropriate content thereof are determined as described above and the characteristics of this steel will be described in detail.

C: 0.1-1.2% If less than 0.1%, the desired hardness is not reached. Meanwhile, 1.2%
If it exceeds, embrittlement occurs. Therefore, the range of the C content is
0.1 to 1.2%.

Si: 1.0% or less Deoxidizer, but if it exceeds 1.0%, hot workability deteriorates. Therefore, the upper limit of the Si content is set to 1.0%.

Mn: 10 to 25% When the content is less than 10%, cracks are liable to occur during working, and when the content exceeds 25%, work hardening becomes difficult. Therefore, the range of the Mn content is set to 10 to 25%.

Cr: 15% or less Cr is contained to improve corrosion resistance and heat resistance. But 15
%, The ferrite structure tends to appear, the structure becomes unstable, and cold work hardening becomes difficult. Therefore, the upper limit of the Cr content is set to 15%.

Ni: 5% or less The wear-resistant double-walled steel pipe for a boiler of the present invention is a high Mn steel having a high C content in the outer layer. There is. Ni has the effect of improving ductility, and even if ductility is reduced by long-term use at high temperature, Ni can still maintain high ductility as compared with those containing no Ni. Ni also has the effect of improving corrosion resistance. However, when the content exceeds 5%, these effects are saturated, and the economy is deteriorated. Therefore, the upper limit of the Ni content is set to 5%.

Mo: 3% or less Like Cr, it is contained for improving corrosion resistance and heat resistance. However, if it exceeds 3%, the effect is saturated.
The upper limit of the Mo content was set to 3% in consideration of economy.

V: 0.1 to 4.0% If less than 0.1%, age hardening does not occur during tempering treatment of the steel pipe for the boiler / heat exchanger as the inner layer pipe. But 4.0
%, The effect saturates. The upper limit of the V content is set to 4.0% in consideration of economy.

Al: 1% or less Effective for improving corrosion resistance and heat resistance. However, if it exceeds 1%, the melting point of steel decreases and hot workability deteriorates. Further, a ferrite structure is likely to appear. For this reason, Al
The upper limit of the content was 1%.

N: not more than 0.3% If more than 0.3%, embrittlement occurs. Also, blow holes are generated during welding.

For this reason, the upper limit of the N content is set to 0.3%.

In order to further improve the wear resistance and heat resistance of the high manganese steel, one or more of the following W, Nb, Ti, Zr and Ta are selected and contained as necessary. .

W: 3% or less W is a carbide-forming element and is contained in order to improve wear resistance and heat resistance. However, if it exceeds 3%, the effect is saturated. The upper limit of the W content is set to 3% in consideration of economy.

Nb: 3% or less Nb is an element forming carbides and nitrides, and is contained to improve wear resistance and heat resistance. However, if it exceeds 3%, the effect is saturated. The upper limit of the Nb content is set to 3% in consideration of economy.

Ti: 1.0% or less Ti is an element forming carbides and nitrides, and is contained in order to improve wear resistance and heat resistance. However, if it exceeds 1.0%, the effect becomes saturated. Considering economy, the upper limit of the Ti content is set to 1.0%.

Zr: 1.0% or less Zr is an element for forming carbide and nitride, and is contained in order to improve wear resistance and heat resistance. However, if it exceeds 1.0%, the effect becomes saturated. The upper limit of the Zr content is set to 1.0% in consideration of economy.

Ta: 1.0% or less Ta is an element for forming carbides and nitrides, and is contained in order to improve wear resistance and heat resistance. However, if it exceeds 1.0%, the effect becomes saturated. In consideration of economy, the upper limit of the Ta content is set to 1.0%.

P and S: P and S are impurities, but if the content exceeds 0.01% and 0.005%, respectively, a low melting point compound is precipitated, hot brittleness becomes remarkable, and extrusion becomes difficult. S should be less than 0.01% and S should be less than 0.005%. In particular, S in high manganese steel tends to form low melting point compound MnS, so it is necessary to suppress S to such a low value.

The above-mentioned high manganese steel is subjected to normalizing treatment of a steel tube for a boiler / heat exchanger as an inner layer tube (JIS G346).
1, stipulated in JIS G3462 and JIS G3463) During the tempering process, age hardening treatment will be applied, and therefore, the hardness will greatly increase due to age hardening where carbides and nitrides precipitate. .

The hardened layer of high manganese steel due to age hardening during the above tempering treatment covers the entire high manganese steel even in the depth direction and has a room temperature hardness of 300 at Hv.
It is desirable to make it above. After such age hardening, cracking does not occur even if cold rolling is performed at a rolling reduction of about 20%.

In this high manganese steel, a high hardness layer is easily formed by further cold working the surface. Therefore, cold drawing or shot peening in the conventional process of manufacturing a steel tube for a boiler / heat exchanger. If cold-worked,
A desired wear-resistant multi-layer steel pipe can be manufactured.

Furthermore, a curved pipe can be hot or cold bent from a clad steel pipe having the above-mentioned high manganese steel steel pipe as an outer layer pipe manufactured by hot extrusion. This is because, before the age hardening, cracking does not occur even if cold rolling is performed at a rolling reduction of about 40%.

After this bending, the steel pipes for boilers and heat exchangers are age-hardened by tempering after normalizing.
Further, by performing shot peening of an air type, a wheel type, or the like, a curved pipe portion having a high hardness on the outer surface can also be manufactured.

The outermost surface hardness layer of the high manganese steel pipe formed by the cold working described above has a depth of 0.1 mm or more and a normal temperature hardness of 45 Hv.
It is desirable to set it to 0 or more. The effect of increasing the hardness at this time extends to a depth of about 0.5 mm.

Usually, the thickness of the outer high manganese steel pipe is 2 to
A thickness of about 4 mm is sufficient. For example, when the thickness is 4 mm, the overall hardness is Hv 300 by aging treatment during tempering, and the outermost surface hardness is Hv 500 by shot peening, the depth of the outer high manganese steel pipe is The hardness distribution in the thickness (thickness) direction is Hv 450 or more from the outermost surface to about 0.1 mm.
At a depth of 1 mm to about 0.5 mm, it gradually decreases to about Hv450 to Hv300, and at a depth of about 0.5 mm to 4 mm, Hv300 is maintained.

A multi-layered steel pipe having a high manganese steel pipe having such characteristics as an outer layer, if the high hardness layer falls off for some reason during actual use in a boiler or the like, uncombusted on the newly emerging surface. The hardness increases again due to the work hardening effect due to the impact of hard particles such as coal fine powder and coal combustion ash, so that as long as the high manganese steel outer tube remains, it will be essentially durable against abrasion .

The features and advantages of the above high manganese steel cannot be obtained with stellite or tool steel. That is, since stellite does not soften even by heat treatment, when producing a boiler steel tube of an intimate two-layer tube, cracks occur at a rolling reduction of 5% or less in cold rolling, and cold working for dimensional correction is substantially performed. Impossible. In the case of tool steel, the heat treatment of the boiler steel pipe causes a decrease in hardness.

Next, a method of forming a composite billet to be subjected to hot extrusion in the production method of the present invention will be described with reference to FIGS.
This will be described with reference to FIG.

FIG. 1 is a longitudinal sectional view of a composite billet showing an example in the case of using high manganese steel powder. Inner layer steel pipe 1
A high-manganese steel powder 3 having a particle size of 500 μm or less is filled between the thin carbon steel cylinder 2 and the outer thin-walled low carbon steel cylinder 2 and sealed with a carbon steel disk member 4, preferably at a pressure of about 400 MPa to reduce cold hydrostatic pressure. In addition, the layer of the powder 3 is compression-molded to obtain a composite billet in which the powder 3 is densified. In this case, it is necessary to form a clad steel pipe by heating and hot extruding in the presence of the low carbon steel cylinder 2, and then to remove a portion corresponding to the clad steel pipe by cutting or the like.

The reason for applying the cold isostatic pressing method when using powdered high manganese steel is as follows. First, in the upsetting state at the time of hot extrusion, since the high manganese steel powder has a higher hardness than the boiler steel pipe which is the inner layer pipe, the powder layer is cut into the steel pipe surface,
The oxide film on the surface of the steel pipe is destroyed. Since the interface is extended with the extrusion, the oxide film is divided. Under such circumstances, diffusion of elements occurs at the interface between the powder layer and the steel pipe, and a strong bond is achieved. Further, since the powder 3 is densified by compression molding using cold hydrostatic pressure, the temperature distribution is stabilized when the composite billet is heated.

FIG. 2 is a longitudinal sectional view of a composite billet showing an example of a case in which a steel pipe manufactured from ingot-hardened high manganese steel is formed by a cold press-fitting method. A high-manganese steel pipe 5 of the same length, which is manufactured from a molten material by a usual method, is cold-pressed and closely adhered to the outer surface of the inner steel pipe 1, and both ends (upper and lower in the figure) are desirably bonded with a carbon steel disk member 4. Seal to form a composite billet.

The relationship between the outer diameter of the inner steel pipe and the inner diameter of the outer steel pipe at the time of cold press fitting is equal or the inner diameter is larger than the outer diameter.
It is desirable to reduce the thickness by 0.00 to 1.00 mm so that close contact at the time of press-fitting is sufficiently performed.

When sealed with the carbon steel disk member 4, both the steel pipes 1 and 5 undergo thermal expansion during heating before hot extrusion, but the effect of this is to prevent the interface from being oxidized by the formation of a gap at the interface. effective. The cold press method is used because the outer surface of the inner steel tube and the inner surface of the outer steel tube are brought into close contact with each other to cause diffusion of elements at the interface during heating before hot extrusion, and the clad steel tube with good interface adhesion after working. In order to manufacture.

FIG. 3 is a longitudinal sectional view of a composite billet showing an example of the case where the steel pipe manufactured from the ingot-melted high manganese steel is used to form the steel pipe by an insertion method. A high-manganese steel pipe 5 of the same length, which is manufactured from a molten material by a normal method, is inserted into the outer surface of the inner steel pipe 1, and both ends (up and down in the figure) are sealed with a carbon steel disk member 4.

In the case of the insertion method, the relationship between the outer diameter of the inner steel pipe 1 and the inner diameter of the outer high manganese steel pipe 5 is such that the inner diameter is 0.1 to 2.0 mm larger than the outer diameter. If the gap between the two steel pipes is too large, there may be places where the interface between the clad steel pipes after hot extrusion becomes insufficiently adhered. In this case, it is merely insertion, and since air is present in the gap between the two steel pipes, the deaeration pipe 6 is attached to one place serving as a clad surface as shown in the figure to perform vacuum deaeration. Thereafter, the deaeration pipe 6 is sealed by welding to form a composite billet.

By using these three methods, an oxide film which is easily formed on the clad surface when the composite billet is heated is suppressed. In addition, in the method shown in FIG. 1, you may use together the deaeration pipe 6 shown in FIG.

In the above-mentioned composite billet, the element obtained by the cold isostatic pressing and the cold press-in method is heated from the time of heating, and the element obtained by the insertion method is obtained by the hot extrusion at the interface between the powder and the steel pipe or at the interface between the steel pipes. Diffusion occurs to form a good joint, and a clad steel pipe having excellent interfacial adhesion can be obtained.

[0060]

【Example】

[Invention Example 1] A high manganese steel powder having a chemical composition of type 1 to type 7, type 9 to type 13 and type 16 to type 19 shown in Table 1 was produced by N ₂ gas atomizing method,
Using the method shown in FIG. 1, a high-grain steel pipe with a particle size of 500 μm or less is placed between the inner steel pipe 1 (outer diameter 130 mm, inner diameter 31 mm, length 780 mm) of JIS STBA22 and the outer thin low-carbon steel cylinder 2. Filled with manganese steel powder 3 and sealed with carbon steel disk member 4, 40
Cold isostatic pressing at a pressure of 0 MPa, outer diameter 174 mm, inner diameter 31
A composite billet having a length of 800 mm and a length of 800 mm was prepared. After heating this billet to 1200 ° C., it was subjected to hot extrusion at an extrusion ratio of 12 to produce a clad steel pipe having an outer diameter of 57 mm, an inner diameter of 28 mm and a length of 7 m.

These clad steel pipes were subjected to a normalizing treatment at 980 ° C. × 10 minutes, and further a tempering treatment at 680 ° C. × 40 minutes (a high manganese steel pipe portion corresponds to an age hardening treatment). A portion corresponding to the carbon steel cylinder 2 was removed by cutting.

The outer layer of the clad steel pipe manufactured in this manner was sprayed with a wheel type shot peening (using a steel ball having an average of 0.8 mm, from a position 800 mm away at a speed of 70 m / sec until the coverage reached 300%. Attached)
The surface was work hardened to produce a product multi-layer steel pipe. Thereafter, samples were cut out from the respective surface layers, and the following evaluation tests were performed.

(1) Room temperature hardness test: Measured under the conditions of a load of 100 g and a test temperature of 20 ° C. using a Vickers hardness tester. The position is 0.1mm from the outermost layer.

(2) Warm erosion test: The test was carried out for 2 hours under the conditions shown in Table 2 using a blast type erosion test apparatus, and the thinning rate at that time was measured.

[Invention Example 2] A high-manganese steel powder having a chemical composition of type 8 shown in Table 1 was produced by the N ₂ gas atomizing method, and was equivalent to a low-carbon steel cylinder having the same dimensions and the same size as in Invention Example 1. A clad steel pipe with a portion removed by cutting was manufactured. This clad steel tube was heated at 980 ° C for 10 minutes,
After bending the pipe with a bending radius of 2D (twice the diameter D of the steel pipe) in a hot state, normalize it at 980 ° C. for 5 minutes, and further 68
Tempering treatment was performed at 0 ° C. for 30 minutes (the high manganese steel pipe portion corresponds to age hardening treatment).

The outer layer of the clad steel pipe thus produced was subjected to surface processing by air shot peening (using a steel ball of 177 to 590 μm and spraying from a position 200 mm away at a pressure of 5 kg / cm ² ). After hardening, a product multi-layer steel pipe was manufactured. Thereafter, a sample was cut out from the surface layer portion of the curved tube portion, and the same evaluation test as that of Example 1 of the present invention was performed.

[Invention Example 3] A steel pipe for an outer layer (outer diameter 172 mm,
An inner diameter steel pipe 1 (outer diameter 140 mm) of STBA22 of JIS standard is manufactured using the method shown in FIG.
, Inside diameter 31mm, length 680mm)
After cold-pressing with a press, both ends are sealed with a carbon steel disk member 4, and the outer diameter is 172mm, the inner diameter is 31mm, and the length is 700mm.
Was prepared. After heating this billet to 1200 ° C, it was subjected to hot extrusion processing at an extrusion ratio of 20 and an outer diameter of 48 mm ×
A clad steel pipe having an inner diameter of 28 mm and a length of 12 m was manufactured.

The clad steel pipe was cold bent at a bending radius of 2D.
, A normalizing treatment was performed at 1000 ° C. for 10 minutes, and a tempering treatment was performed at 660 ° C. for 60 minutes (the high manganese steel pipe portion corresponds to age hardening treatment).

The outer layer of the clad steel pipe thus produced was subjected to surface work hardening treatment by the same air-type shot peening as in Example 2 of the present invention to produce a product multilayer steel pipe.
Thereafter, a sample was cut out from the surface layer portion of the curved tube portion, and the same evaluation test as that of Example 1 of the present invention was performed.

[Invention Example 4] A steel pipe for an outer layer (outer diameter: 172 mm,
An inner diameter steel pipe 1 (outer diameter 140mm, outer diameter 140mm, JIS standard STBA22) was manufactured using the method shown in FIG.
A high manganese steel pipe 5 is inserted outside the inner diameter of 31 mm and the length is 680 mm), and both ends are sealed with a carbon steel disk member 4 and a deaeration pipe 6 is attached. With welding, outer diameter 172mm, inner diameter 31
A composite billet having a length of 700 mm and a length of 700 mm was prepared. After heating this billet to 1200 ° C., it was subjected to hot extrusion at an extrusion ratio of 12 to produce a clad steel pipe having an outer diameter of 57 mm × inner diameter of 28 mm × length of 8 m.

The clad steel pipe was subjected to a normalizing treatment at 960 ° C. for 20 minutes, and further a tempering treatment at 700 ° C. for 30 minutes (a high manganese steel pipe portion corresponds to an age hardening treatment).

The outer layer of the clad steel pipe manufactured as described above was subjected to surface work hardening treatment by the same air-type shot peening as in Example 2 of the present invention to produce a product multi-layer steel pipe.
Thereafter, a sample was cut out from the surface layer portion and the same evaluation test as that of Example 1 of the present invention was performed. Comparative Example A normal hollow billet shown in FIG. 4 was manufactured from ingots of steel (STBA22 of JIS standard) having a chemical composition of type 20 shown in Table 1.

FIG. 4 is a longitudinal sectional view of a billet used for manufacturing a conventional alloy steel pipe for a boiler / heat exchanger. In the drawing, reference numeral 7 denotes an outer diameter of 174 m manufactured from the above STBA22 steel.
It is a hollow billet with m, inner diameter of 31 mm and length of 700 mm.

After heating this billet to 1200 ° C., it was subjected to hot extrusion processing at an extrusion ratio of 20 to obtain an outer diameter of 48 mm × inner diameter of 28 mm × length.
A 12m single-layer steel pipe was manufactured.

Next, after normalizing at 1000 ° C. × 10 minutes, and further tempering at 660 ° C. × 60 minutes, the tube was bent at a bending radius of 2D in the cold. The outer layer of the steel pipe was subjected to the surface work hardening treatment by the same air-type shot peening as in Example 2 of the present invention, and a sample was cut out from the surface layer portion of the curved pipe portion, and the same evaluation test as in Example 1 of the present invention was performed.

The test results are shown in Table 1.

[0077]

[Table 1 (1)]

[0078]

[Table 1 (2)]

[0079]

[Table 2]

As is evident from Table 1, the multilayer steel pipe manufactured under the conditions specified in the present invention has excellent erosion resistance.

[0081]

The multilayered steel pipe of the present invention is excellent in erosion resistance, ductility, heat transfer efficiency and workability required for a steel pipe for a coal-fired power generation boiler. It can be implemented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a composite billet in the case of using a powder material of high Mn steel.

FIG. 2 is a vertical cross-sectional view illustrating a composite billet assembled by a cold press-sealing method in the case of a high-melting material Mn steel pipe.

FIG. 3 is a longitudinal sectional view illustrating a composite billet assembled by an insertion-sealing-degassing method in the case of a high-Mn steel pipe made of ingot material.

FIG. 4 is a longitudinal sectional view illustrating a billet used in a method for manufacturing a general alloy steel pipe for a boiler / heat exchanger.

[Explanation of symbols]

1: Inner steel pipe 2: Low carbon steel cylinder 3:
Powdered high manganese steel, 4: Carbon steel disk member, 5: High melting manganese steel pipe, 6: Degassing pipe, 7: Normal hollow billet

Claims (5)

(57) [Claims] (1) The weight% is added to the outer surface of a steel pipe for a boiler / heat exchanger.
And C: 0.1 to 1.2%, Si: 1.0% or less, Mn: 10 to 25%, C
r: 15% or less, Ni: 5% or less, Mo: 3% or less, V: 0.1 ~
4.0%, Al: 1% or less and N: 0.3% or less, with the balance being Fe and unavoidable impurities.
A wear-resistant multi-layer steel pipe for a boiler, wherein high-manganese steel of 010% or less and S of 0.005% or less are laminated. 2. The weight percentage of the outer surface of the steel pipe for boiler / heat exchanger is
And C: 0.1 to 1.2%, Si: 1.0% or less, Mn: 10 to 25%, C
r: 15% or less, Ni: 5% or less, Mo: 3% or less, V: 0.1 ~
4.0%, Al: 1% or less, N: 0.3% or less, W: 3% or less, Nb: 3% or less, Ti: 1.0% or less, Zr: 1.0
% And Ta: 1.0% or less, the balance being Fe and unavoidable impurities. P in the impurities is 0.010% or less and S is 0.005% or less. A multi-layer, abrasion-resistant steel pipe for a boiler, characterized by having a multi-layer structure. 3. A composite billet comprising a high manganese steel pipe manufactured from a molten high manganese steel having the chemical composition according to claim 1 and a steel pipe for a boiler / heat exchanger disposed inside the high manganese steel pipe. Assembling, hot extruding this composite billet to produce clad steel pipes, then normalizing the steel pipes for boilers and heat exchangers, then performing tempering, and then cold working to form the outer layer of high manganese steel pipes A method for producing a wear-resistant multilayer steel pipe for a boiler, comprising forming a surface hardened layer. 4. A composite billet comprising a high manganese steel pipe manufactured from the powdered high manganese steel having the chemical composition according to claim 1 and a steel pipe for a boiler / heat exchanger disposed inside the high manganese steel pipe. Assembling, hot extruding this composite billet to produce clad steel pipes, then normalizing the steel pipes for boilers and heat exchangers, then performing tempering, and then cold working to form the outer layer of high manganese steel pipes A method for producing a wear-resistant multilayer steel pipe for a boiler, comprising forming a surface hardened layer. 5. The method according to claim 3 or 4, wherein the composite billet is hot-extruded to produce a clad steel pipe, and then subjected to bending, followed by sintering of the steel pipe for a boiler / heat exchanger. A method for producing a wear-resistant multi-layer steel pipe for a boiler, comprising: performing a tempering treatment after performing a heat treatment; and forming a hardened surface layer on an outer high manganese steel pipe by shot peening.