Wear resistant pipe and method of chemical-heat treatment

 

(57) Abstract:

The invention relates to metallurgy, namely the production of pipes made of low carbon stages. The inventive wear-resistant pipe has an internal wear-resistant layer structure ledebur, external corrosion-resistant layer of ferrite and a layer of low carbon steel, located in the heart of the pipe wall between the layer with a monotonically increasing in the layer of ferrite to the value in the layer of low carbon steel and a layer with a monotonically increasing in the direction from the core hardness and carbon content in the range from values of hardness and carbon content in the layer of low carbon steel to their size in the layer structure ledebur, moreover, the thickness of the outer layer of the ferrite and the thickness of the inner layer with the structure of ledebur with hardness not less than 50 HRC is 0.01 to 0.1 of the pipe wall thickness. This pipe inner surface is heated by high frequency currents in carbon environment through the outer annular inductor and rotate around its longitudinal axis, and the tube is heated to achieve on the external surface temperature of not less than 100C below the melting temperature became the inner surface is performed in the liquid carbon environment, the average temperature of the medium inside the pipe support at this level, in which the inner surface of the pipe is formed continuous PropertyName layer, and a shutter speed are in a period of time sufficient for the formation on the inner surface of the pipe layer with ledeburitic structure with a thickness of 0.01 to 0.1 wall thickness. The speed of rotation of the pipe is chosen in the range where n is the rotational speed, Rev/min; D-outside diameter of pipe, mm, 2 S. and 1 C. p. F.-ly, 2 Il. 5 table.

The invention relates to the production of tubes, in particular tubes of low-carbon steels, and can be used in many technical applications that require a combination of wear resistance of the pipe and its ability to withstand the mechanical and thermodynamic deformation.

Tube of low-carbon steels are used in almost all branches of engineering, as they can be easily machined and relatively cheap. A significant disadvantage of low wear resistance and resistance to corrosion are eliminated by applying protective coatings, paint, plastic, enamel, ceramic, metal. The protective coating by known methods significantly increases the frequency of the desired wear resistance, enameled and ceramic are very expensive and can not withstand mechanical deformation, coating of plastic material critical to high temperatures, and processes for their production and deposition of toxic. The most widely used pipe with metal protective coatings, and above all galvanized.

A General lack of pipes with the described protective coatings low resistance to mechanical and thermal deformations, since the bending of the pipes, when the shock during transportation or tilting, when thermodynamic deformation protective coating is destroyed.

Known pipe with zinc coating, which is applied viscous corrosion-resistant coating (Pakaluk J. H. Proskurin E. C. Pipe with a metal anticorrosive coatings. M. metallurgy, 1985, S. 36). The PVC skin deposited on the outer surface of the galvanized pipes by welding. Such a tube may be subjected to bending without breaking cover, except in the case of damage to the pipe (e.g., scratches) does not occur, the distribution of corrosion under the coating surface.

The cost of manufacture of this pipe is very high (5-10 times more expensive than the cost of harvesting), lack CLASS="ptx2">

Closest to the proposed technical solution is wear-resistant tube made of low carbon steel with internal wear-resistant layer with ledeburite structure.

The lack of such pipe has low corrosion resistance, since the outer surface of the pipe has no protective coating. In addition, due to the different thickness of the inner layer along the perimeter of the pipe has a low resistance to thermodynamic deformation.

The purpose of the invention improve the stability of the pipe to thermodynamic deformation and increasing coresistance.

The aim is achieved in that a wear-resistant tube containing internal wear-resistant layer structure ledebur and a layer of low carbon steel, further comprises an external corrosion-resistant layer of ferrite, a layer of low carbon steel is located in the heart of the pipe wall between the layer with a monotonically increasing in the direction of the core carbon content of the value in the layer of ferrite to the value in the layer of low carbon steel and a layer with a monotonically increasing in the direction from the core hardness and carbon content in the range from values of hardness and carbon content in the layer of discoparade the morning of the layer structure of ledebur with hardness not less than 50 RC be 0.01-0.1 thickness of the pipe wall.

We offer wear resistant pipe is made by chemical-thermal processing of seamless or welded pipes made of carbon steels.

The known method of chemical-heat treatment (ed.St. USSR N 298698, CL 23 With 9/00, 21 D 7/14, 1971), in which a steel workpiece is heated in a carbon environment, the high-frequency currents to melting of the surface layer during the time required for the formation of the hardened layer having ledeburite structure, and then cooling stage pass around rollers for surface hardening and improved geometry. This method cannot be used in the manufacture of wear-resistant pipe, as it allows to obtain internal wear-resistant layer.

The known method of chemical-heat treatment, in which a steel workpiece with a cylindrical internal surface rotate around the longitudinal axis of the cylindrical surface with the speed of 3000-3500 rpm and the inner surface is heated by high frequency currents in carbon environment to the temperature of melting. This method also cannot be used in the manufacture of wear-resistant pipe, as it allows to obtain internal SNOL of the invention enable the manufacture of wear-resistant pipes with high resistance to corrosion and resistance to mechanical and thermal deformations.

In addition, the proposed method has a lower energy costs.

The aim is achieved by a method of chemical-heat treatment of pipes, comprising heating the inner surface high-frequency currents in carbon environment through the outer ring of the inductor and the rotation of the pipe around its longitudinal axis, the tube is heated to achieve on the external pipe surface temperature is not less than 100aboutC below the melting temperature of steel fabricated pipe and on the inside within +50-(-70)aboutWith the melting temperature of ledebur, heating of the inner surface is carried out in liquid carbon environment, with the average temperature of the medium inside the pipe support at this level, in which the inner surface of the pipe is formed continuous propenolatomethyl layer, and a shutter speed are in a period of time sufficient for the formation on the inner surface of the pipe layer with ledeburitic structure with a thickness of 0.01-0.1 of the thickness of the pipe wall.

The speed of rotation of the pipe is chosen equal to n (0.5 to 12)X103x1/, where n is the rotational speed, Rev/min; D-outside diameter of pipe, mm

In Fig. 1 shows the design of the wear resistant pipe; P> Wear resistant pipe includes an outer layer 1 of the ferrite layer 2 of low carbon steel, the inner layer 3 of ledebur, layer 4 with a monotonically increasing in the direction towards the core content of the carbon from the carbon content in the layer 1 to the carbon content in the layer 2, layer 5 with a monotonically increasing in the direction from the core hardness and carbon content from the values of hardness and carbon content in the layer 2 to the value of hardness and carbon content in the layer 3. The thickness of the layer 1 and layer 3 depends on the thickness of pipe walls and environments and is 0,01-0,1 wall thickness of the pipe. The external layer of ferrite increases the resistance to corrosion resistant tube 5-8 times. Layer 5 plays a role in damping the mechanical deformations of the type curve and thermodynamic deformations. Wear resistant pipe with an inner layer of ledebur and outer layer of ferrite has a stretch factor to 1.3 without destroying the inner layer.

Pipe described structure is manufactured by chemical-heat treatment of steel seamless or welded blanks.

In Fig.2 the following notation: 1 tube blank; 2, the inductor; 3 current generator high the rotation drive tube, including engine; 10 and 11 of the reducer; 12 rotating hollow grips; 13 the supply of liquid uglevodorodno environment, including clutch 14; 15 cooler, pump 16; 17 accumulating tank; 18 fan of the exhaust gas; valve 19.

Tube blank 1 is inserted into the grippers 12 of the actuator 9 tube rotation, the workpiece is put on the circular inductor 2 connected to a generator 3 of the high frequency current. The generator 3 is mounted on the support plate 8 drive 4 horizontal movement of the inductor 2. Through the workpiece 1, through the hollow gripper 12, the sleeve 14 from the storage tank 17 is fed uglerodvodorodsoderzhaschih liquid. Simultaneously with the insertion of the inductor 2 is activated, the actuator 4 of rotation of the workpiece 1. The workpiece 1 is rotated at a given speed, heated by the inductor 2, which is moved along the workpiece 1 with the speed to heat the workpiece 1 to a predetermined value. Uglerodvodorodsoderzhaschih liquid flows out of the workpiece 1 in the cooler 15, whence it is pumped by pump 16 in a storage tank 17. The temperature of the liquid inside the tube is maintained constant by regulating the speed of the expiring chilled liquid from the storage tank 17 through valve 19.

The essence of the processes which are stated external and internal surface of the workpiece tube. In contact with the inner surface uglerodvodorodsoderzhaschih fluid is a thermal decomposition of its components with the formation of the active atoms of carbon and hydrogen.

Thus, when a mixture of uglevodorodov of different composition can be assumed that on the inner surface of the workpiece is formed steam-shirt containing CH4, Co, CO2C, H2H2O, and on the metal surface reactions occur

CH Fe(C)+H2;

CO-Fe(C)+CO2;

CO+H Fe(C)+H2O;

CO2+H Fe(C)+H2O

As a result of these reactions there is an avalanche saturation of the surface layer of the inner side of the pipe carbon with the formation of ledeburite patterns. The hydrogen atoms pass through the wall thickness adsorbed on the external surface of the pipe and are held there by the magnetic field of the inductor. In the surface layers on the outer pipe wall carbon atoms combine with hydrogen with the formation of gaseous compounds of the type CH, CH2CH3that are released from the metal and removed by suction. Is annealing in a hydrogen environment, resulting in the surface layers of the outer wall of the pipe, the carbon content is reduced below 0 is authorized by the resistance to corrosion.

Monolithic external ferrite layer and the inner layer with ledeburite structure depends on the stability of steam-shirts at the inner surface of the pipe. When it breaks in the boiling liquid or low temperature cooling reduced the strength characteristics of the internal layer and external corrosion.

The quality of the pipe surface after chemical-thermal treatment depends on the speed of rotation of the workpiece. At low speed of rotation increases the waviness of the inner surface of the pipe due to uneven spreading of the molten metal. At high speeds deteriorate the characteristics of the outer surface due to the destruction of the hydrogen environment and because of the disruption from the surface of the molten metal.

Experimentally it was found that the geometrical dimensions are not intended for use when the speed of rotation lying within n (0,5-12)x 103x 1/, rpm, where D is the average diameter of pipe, mm

The proposed method were fabricated and tested several samples of wear-resistant pipes with an inner diameter of 27 mm and the wall thickness of 2.5 mm and an inner diameter of 76 mm and the wall thickness is 4 mm, Material procurement Article.3 for pipes which I was handling the pipe diameter 27 mm averaged 25 kW, for pipes with a diameter of 76 mm 55 kW.

The results are given in table.1-5.

From the above table.1-5 data we can draw the following conclusions: factors affecting the quality ledeburite layer are the temperature of the processing, the speed of rotation of the sample, the temperature of the electrolyte. For pipes with a diameter of 76 mm, the optimal temperature of the heating surface 1150aboutWith the speed of 1100 rpm, temperature of electrolyte 40aboutC. To obtain a corrosion-resistant ferritic layer on the outer surface of the pipe, the heating temperature of the inner layer must be +50-(-70)aboutWith the melting temperature of ledebur.

The cost of manufacturing the wear resistant pipe using the proposed chemical-thermal treatment below the cost of production of pipes for the prototype method, since the rate of saturation of the carbon inner layer of the proposed method on the order above and is not required pipe preparation processing (dressing from scale, rust).

Processed by the proposed method, the pipe has a high corrosion resistance, is not afraid to shock loads, resistant to mechanical deformation type bending deformation and thermodynamic what Loy low-carbon steel, characterized in that it further comprises an external corrosion-resistant layer made of ferrite, and a layer of low carbon steel is located in the heart of the pipe wall between the layer with a monotonically increasing in the direction of the core carbon content of the value in the layer of ferrite to the value in the layer of low carbon steel and a layer with a monotonically increasing in the direction from the core hardness and carbon content in the range from values of hardness and carbon content in the layer of low carbon steel to their size in the layer structure ledebur, moreover, the thickness of the outer layer of the ferrite and the thickness of the inner layer with the structure of ledebur with hardness not less than 50 HRC amount of 0.01-0.1 of the thickness of the pipe wall.

2. The method of chemical-heat treatment of wear-resistant pipe, comprising heating the inner surface high-frequency currents in carbon environment through the outer ring of the inductor and the rotation of the pipe around its longitudinal axis, characterized in that the pipe is heated to achieve on the external pipe surface temperature is not less than 100oC below the melting temperature of steel fabricated pipe and on the inside within +50. -70oed, the average temperature of the medium inside the pipe support at this level, in which the inner surface of the pipe is formed continuous PropertyName layer, and a shutter speed are in a period of time sufficient for the formation on the inner surface of the pipe layer with ledeburitic structure with a thickness of 0.01-0.1 of the thickness of the wall.

3. The method according to p. 2, characterized in that the rotation speed of the pipe is chosen within

< / BR>
where n is the rotation speed, rpm;

D outside diameter of pipe, mm

 

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1 tbl

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5 cl, 2 dwg

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