JP2918422B2 - Manufacturing method of corrosion resistant tough cast iron pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cast iron pipe having excellent toughness and corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, cast iron tubes of various materials have been manufactured by centrifugal casting, and if necessary, ferrite annealing is performed after casting in order to improve toughness. This heat treatment transforms the cementite in the base of the as-cast cast iron pipe into ferrite, and is usually 900 to 1%.
It is carried out by maintaining the temperature at a high temperature of about 000 ° C. for several tens minutes.

[0003] In order to impart not only toughness but also good corrosion resistance to cast iron tubes, in recent years, corrosion resistant metals such as stainless steel and brass have been sprayed on the surface of cast iron tubes after ferritizing annealing, and corrosion resistant metal spraying has been performed on the tube surfaces. A layer is formed.

[0004]

However, since the thermal sprayed layer is porous, it is inferior in corrosion resistance, and because it is only mechanically attached to the tube surface, it is easily peeled off, and the sprayed layer is locally formed from the peeled portion. There is a problem that corrosion progresses. The present invention has been made in view of such a problem, and an object of the present invention is to provide a method for manufacturing a cast iron tube having both excellent toughness and corrosion resistance.

[0005]

The method for producing a corrosion-resistant tough cast iron pipe according to the present invention is a method for producing a cast iron pipe in which a cast pipe body is subjected to ferritizing annealing. to cast iron pipe after the lower sprayed layer and the melting point of Al or Al alloy forming the upper sprayed layer made of a high corrosion-resistant metal M than the annealing temperature, the whole the template iron pipe
To the lower sprayed layer by ferrite annealing
For the iron on the iron tube surface and the corrosion resistant metal M constituting the upper sprayed layer
Diffusion solid solution, the former is Fe-Al alloy layer, the latter is MA
An M-Al alloy layer is formed by forming an Fe-Al alloy layer.
Directly metallurgically bonded to the alloy layer and firmly bonded to the pipe body
I tried to make it.

[0006]

Since the surface of the cast iron pipe body in an as-cast state is treated by shot blasting or sand blasting, a lower sprayed layer made of Al or the like is directly formed on the background of the pipe body without passing through an oxide film or the like. Furthermore, when ferrite-forming annealing is performed on the pipe body on which the upper sprayed layer made of a corrosion-resistant metal having a melting point higher than the annealing temperature is formed, cementite in the matrix is transformed into ferrite, and the toughness is improved. Al and the like in the lower sprayed layer are melted, and Al atoms are cast iron on the tube surface and the porous corrosion-resistant metal M constituting the upper sprayed layer.
To form a solid solution by diffusion into Fe-Al alloy layer and dense M-Al
M-Al alloy layer with excellent corrosion resistance
Direct metallurgical bonding with the e-Al alloy layer ;
Can be firmly connected. In particular, the present invention
Cost since diffusion treatment is carried out at the same time as annealing treatment
Significantly reduced, and production efficiency improved greatly.

[0007] Although the diffusion of Al can be expected in the plating layer instead of the thermal spray layer, large-scale equipment is required as compared with thermal spraying, and the running cost increases. In this regard, thermal spraying can be easily performed with simple equipment, and a coating having a uniform thickness can be easily formed.

[0008]

FIG. 1 shows the process of forming a coating of a corrosion-resistant alloy layer according to the present invention. First, as shown in FIG. And the upper thermal spray layer 3 made of the corrosion-resistant metal M are laminated in the same order. The thickness of the lower sprayed layer 2 is about 50 to 150 μm, and the thickness of the upper sprayed layer 3 is 50 to 2 μm.
It may be about 00 μm. The surface of the tube body 1 is activated by removing the oxide film and the like on the surface by shot blasting or sand blasting, etc., and before the annealing, there is a lot of cementite in the matrix.

The tube main body 1 covered with the lower and upper thermal spray layers 2 and 3 is subjected to ferritizing annealing as shown in FIG. Since the annealing is performed at a high temperature of about 900 to 1000 ° C., Al and the like in the lower sprayed layer 2 are melted, and diffusion of Al atoms occurs at a solid-liquid interface between the melted layer 4 and the pipe body 1 and the upper sprayed layer 3. As shown in FIG. 2C, an Fe-Al alloy layer 5 is formed on the tube body 1 side, and an M-Al alloy layer (corrosion-resistant alloy layer) 6 is formed on the tube body 1 via the Fe-Al alloy layer 5. 1
To form a strong bond.

The lower thermal spray layer 2 can be made of not only pure Al but also various Al alloys such as 1000 series to 7000 series. Further, as the corrosion resistant metal forming the upper sprayed layer 3, any material such as stainless steel or brass can be used as long as its melting point is higher than the annealing temperature. The thermal sprayed layer is usually formed on the outer surface of the pipe, but if the inner diameter of the pipe is large, it can be applied to the inner surface of the pipe.

Next, specific embodiments will be described. Inner diameter φ10
The outer peripheral surface of the as-cast ductile cast iron pipe main body of 0 mm x wall thickness 7.5 mm x length 4 m was subjected to shot blasting to remove an oxide layer, and then Al was sprayed at 90 g / m ² (average sprayed layer thickness 75 µm). ), And stainless steel (SUS30)
4) was sprayed at 45 g / m ² .

[0012] and annealed while rolling the rollover furnace the cast iron pipe in accordance with the heat cycle shown in FIG. 2. In FIG.
A section at 80 ° C. for 20 minutes is a ferritizing annealing section.
After annealing, a sample was taken from the cast iron tube, and the cross-sectional structure on the outer peripheral surface side was observed under a microscope. As a result, a dense corrosion-resistant alloy layer of about 120 μm was formed. 75 × 15 from the cast iron tube
A 0 mm corrosion test piece was sampled, and a sample in which only the outer surface of the tube was exposed and other portions were embedded in a synthetic resin was manufactured, and a salt water corrosion test was performed using the sample. In this test, the above data were stored in a test room where a 3% concentration saline solution was constantly sprayed.
It is carried out by holding for days and measuring the corrosion loss. As a result, the corrosion weight loss is 0.001 to 0.002 g
It was confirmed that the corrosion-resistant alloy layer was hardly corroded.

[0013]

The production method of the present invention is applied to a pipe body after casting.
In a method of manufacturing a cast iron pipe subjected to ferrite annealing,
Blasting the pipe body after fabrication, Al or Al alloy
The lower thermal spray layer made of and the melting point is higher than the annealing temperature
For the cast iron pipe after forming the upper sprayed layer made of corrosion resistant metal M
On the other hand, the entire cast iron pipe was subjected to
The sprayed layer is melted to form Fe on the surface of the cast iron tube and the upper sprayed layer.
Diffusion and solid solution in the corrosion-resistant metal M to be formed.
Forming an M-Al alloy layer on the gold layer and the latter;
The alloy layer is directly metallurgically bonded to the Fe-Al alloy layer
Because it is firmly bonded to the body, it has excellent toughness and
And corrosion resistance, especially when the M-Al alloy layer
Because it is directly metallurgically bonded to the gold layer, it is firmly attached to the pipe body.
There is no fear of peeling due to bonding. Further, the present invention provides a ferrite
Diffusion treatment is performed at the same time as annealing treatment, so cost is greatly increased
It has greatly reduced the production efficiency. Moreover, the present invention
The method of manufacturing, without newly providing a special equipment, can be implemented only by using a simple spraying equipment, it is excellent in productivity.

[Brief description of the drawings]

FIG. 1 is a partially sectional explanatory view of a cast iron pipe showing a process of forming a coating of a corrosion-resistant alloy layer according to the present invention.

FIG. 2 is a heat treatment diagram of a cast iron tube in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tube main body 2 Lower sprayed layer 3 Upper sprayed layer 4 Fused layer 5 Fe-Al alloy layer 6 M (corrosion resistant metal) -Al alloy layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C23C 10 / 28,4 / 08,4 / 16 C21D 5 / 00,9 / 08

Claims (1)

(57) [Claims] 1. A method for manufacturing a cast iron pipe subjected to ferrite annealing the tube body after casting, subjected to blasting tubes body after casting, the lower sprayed layer and the melting point of Al or an Al alloy than the annealing temperature Cast iron tube after forming an upper sprayed layer made of a high corrosion resistant metal M
On the other hand, ferrite annealing was performed on the entire cast iron
Melt the sprayed layer and remove Fe on the surface of the cast iron tube and the upper sprayed layer.
Diffusion and solid solution in the constituent corrosion resistant metal M, and the former is Fe-Al
Forming an M-Al alloy layer on the alloy layer,
l alloy layer is directly metallurgically bonded to the Fe-Al alloy layer
A method for producing a corrosion-resistant tough cast iron pipe, characterized in that it is firmly bonded to a pipe body .