Method of manufacture of cast iron tubes

FIELD: metallurgy; deformation thermal treatment of iron-carbon alloys; manufacture of hot-deformed seamless tubes.

SUBSTANCE: proposed method includes preliminary heat treatment of high-strength cast-iron billet at temperature Ac3+200°C continued for 10 h and followed by heating the billet at deformation temperature, deformation of billet and heat treatment of tube.

EFFECT: improved quality of tubes; extended field of application of this method.

4 cl, 2 ex

 

The invention relates to metallurgy, and more specifically to the technology of deformation and heat treatment of alloys, and can be used in the production of hot-deformed seamless cast-iron pipes.

The known method of obtaining products of cast iron, comprising heating the billet and extrusion through a die, and heating the workpiece to carry 800-1000°and pressing exercise with a loading rate of 10-100 m/s and the degree of compression of 0.2-0.9 passage (SU 988398, 15.01.83, bull.№2).

The disadvantage of this method in the production of pipes is the low quality of the pipes due to the presence of cracks on their surface.

Closest to the claimed is a method of manufacturing cast iron pipes, including preliminary heat treatment of the workpiece from high-strength cast iron, consisting of heating to a temperature of 830-950°S, shutter speed within 1-5 hours, heating the billet to a temperature of deformation, deformation of the workpiece and the heat treatment tube (EN 2166389 C2, IPC 7 21 23/08, 10.05.2001 year).

The disadvantage of this method is the low quality of the pipes, the presence of surface defects such as cracks.

The technical result improved quality of manufactured pipes and enhancing the technical capacity of the method of manufacturing a pipe.

This technical result is achieved in that in the method of manufacturing cast iron pipes, including pre-heat treated billet of ductile iron, heating the billet to a temperature of deformation, the deformation of the billet and heat treated pipe, a preliminary heat treatment of the workpiece is carried out at a temperature of ≥(AC3+10)°, but <(AC3+30)°or at temperatures >(AC3+150)°, but ≤(AC3+300)°aged for <1 hour, but ≥0.5 hours or within ≤48 hours, but >5 hours. Heat treatment of the pipe is carried out at a temperature of 700-1100°and incubated for 2-48 hours.

Possible options hot deformation in the form of a helical rolling, extrusion and others.

The invention consists in the following. For the manufacture of pipes take billet of ductile cast iron, in particular with nodular or compacted graphite iron.

Billet after their manufacture have a heterogeneous structure, caused by uneven cooling during crystallization. Typically, the cross-section of the workpiece closer to the outside, where there was an increased cooling rate, the structure has a large number of ledebur and carbides. In addition, after crystallization, the workpiece has a high volume stress state. Use this piece to deformation will result formed the Yu in the pipe cracks and even rupture of the walls.

To improve the quality of the pipe workpiece is subjected to a preliminary heat treatment to dissolve carbides, elimination patterns of ledebur, alignment of the mechanical properties of the workpiece cross section and reduce the level of residual casting stresses. The preliminary heat treatment of the workpiece is carried out at a temperature of ≥(AC3+10)°, but <(AC3+30)°or at temperatures >(AC3+150)°, but ≤(AC3+300)°aged for <1 hour, but ≥0.5 hours or within ≤48 hours, but >5 hours. Failure to comply with these modes of preliminary thermal processing fabricated pipe obtained with micro - and Microterminal that dramatically reduces the quality of the finished product.

Using this preliminary heat treatment of the workpiece expands technical capabilities of the method, since it becomes possible to use for hot deformation of a billet of ductile cast iron is not only a spherical form of graphite and compacted, and in the presence of both forms of graphite in the matrix. In addition, this preliminary heat treatment allows the deformation of the workpiece not only by extrusion, but also produced by cross-helical rolling and other methods.

Additional improvement of the quality of the pipes is achieved PR is carrying out heat treatment of pipe by heating at a temperature of 700-1100° From within 2-48 hours. In the heat treatment is observed shortening of elongated graphite inclusions, which are extended in the process of deformation of the workpiece. When carrying out the heat treatment decreases the anisotropy of mechanical properties in both longitudinal and transverse section of the pipe.

Examples of implementation of the method.

Example 1. Casting method receive a sleeve of ductile cast iron with compacted graphite CGI-40 length 300 mm and an external diameter of 160 mm cast iron Chemical composition by weight: 3.2% of carbon; 2,3% of silicon; 0.5% manganese, 0.02% magnesium, 0.1% of REM; 0.4% of Cu, and the rest iron. On the edges of the workpiece structure - ledebur. For iron this part of the value of the critical temperature AU3=800°C. Cast sleeve is subjected to a preliminary heat treatment in a furnace at a temperature of 825°With a higher value than AU3on 25°C. the holding Time at the heat treatment 0.75 hours (45 minutes). The heating rate is 20°C/min, Then the workpiece is cooled together with the furnace to a temperature of 700°, then in the air. For rolling the workpiece is heated to a temperature of 915°and using the method of cross-helical rolling get a pipe outer diameter of 85 mm with wall thickness 5 mm ventilation during hot rolling of the billet in the pipe is λ=11,28. The finished pipe is cooled in the air. After por the rollers pipe is heated at a rate of 20° C/min and subjected to a final heat treatment at 750°C for 12 hours, then cool with the oven to 300°, then in the air.

Example 2. Casting method receive a sleeve of the same size and composition as in example 1. Cast sleeve is subjected to a preliminary heat treatment: heat rate of 20°C/min up to 1000°that is (°C3+200)°C and maintained for 10 hours. Then the workpiece is cooled together with the furnace to a temperature of 700°From then on the air. For rolling the workpiece is heated to a temperature of 915°and using the method of cross-helical rolling get a pipe outer diameter of 85 mm with wall thickness 5 mm of the Finished pipe is cooled in the air. Ventilation during hot rolling of the billet in the pipe is λ=11,28. After rolling the pipe is heated at a rate of 20°C/min and subjected to a final heat treatment at 800°C for 10 hours, then cool with the oven to 300°, then in the air.

In implementing this method, the surface of the pipe has no macro-or micro-cracks, which is regulated by a preliminary heat treatment of the workpiece. Significantly expand the technical capabilities of the method: it is possible to obtain ductile iron pipes with various forms of graphite and races is Iraida number of ways, used in the deformation of the workpiece.

1. A method of manufacturing cast iron pipes, including pre-heat treated billet of ductile iron, heating the billet to a temperature of deformation, the deformation of the billet and heat treated pipe, characterized in that the preliminary heat treatment of the workpiece is carried out at a temperature of ≥(AC3+10)°, but <(AC3+30)°or at temperatures >(AC3+150)°, but ≤(AC3+300)°exposure time during <1 h, but ≥0.5 h or for ≤48 h, but >5 hours

2. The method according to claim 1, characterized in that the deformation of conduct produced by cross-helical rolling.

3. The method according to claim 1, characterized in that the deformation is performed by extrusion.

4. The method according to any one of claims 1 to 3, characterized in that the heat treatment of the pipe is carried out at a temperature of 700÷1100°C and maintained for 2÷48 hours



 

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2 cl, 2 tbl

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1 tbl

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1 tbl

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11 cl, 2 tbl, 1 ex

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1 ex

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1 ex

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