RU2387502C2 - Fabrication method of cold-rolled pipes of large and mean diametres from difficult-to-form grades of steel and alloys with increased wall accuracy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves shaping of plate workpiece on roll mills to tube workpiece in order to roll commercial or conversion tubes of large diametre, welding of longitudinal edges by consumable electrode under flux layer, removal of weld reinforcement from external and internal surface of conversion tube, heat treatment of conversion longitudinal welded tube workpiece and rolling on a conical holder in gauges with variable radius; at that, conversion tube workpiece is rolled to commercial cold-rolled tube in one or several rolls with total drawing of not less than 1.2. Cold-rolled tubes are made in several passes; at that, absolute wall crimping during the first pass is taken equal to 1-2 mm, and weld reinforcement is removed by local dressing not throughout the length of the tube, but from external and internal surface from the front tube end as to the rolling at the length of 100-150 mm from the edge with smooth transition at the length of 10-15 mm.

EFFECT: invention decreases labour intensity of preparation of electric welded workpiece for the rolling by 5-6 times.

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Description

The invention relates to pipe rolling production, and in particular to a method for the production of cold-rolled large and medium diameter pipes from hardly deformable steel grades and alloys from welded straight-line seam pipe billets, and can be used in the production of cold-rolled large and medium diameter pipes from hard-to-deform steel grades and high-precision alloys along the wall at the mills HPT 250 and HPT 450.

In pipe rolling production, there is a known method for the production of large and medium-diameter cold-rolled pipes from hot-rolled pig billets with a diameter of 273-325 mm according to GOST 9940, which includes casting ingots by electroslag remelting from stainless steel grades 08-12X18H10T and 08-12X18H12T of 420-520 × 1750 mm in size , machining ingots into ingot blanks (turning) of 400-500 × 1750 mm in size, drilling a central hole with a diameter of 100 ± 5.0 mm, heating ingot ingots to plasticity temperature, piercing ingots - blanks in the braid mill oh rolling in the sleeves, rolling the sleeves on a pilgrim mill in commodity or conversion pipes according to GOST 9940 with lining carbon rings (RF patent No. 2175899, No. 32, 2001 and USSR author's certificate No. 732043, 1980).

This method of production of commodity and conversion pipes according to GOST 9940 from ESR ingots has the following disadvantages: due to increased loads for one piercing, in oblique rolling mills it is possible to flash ingots with a diameter of not more than 500 mm, from which pipes with a diameter of up to 325 mm can be rolled on pilgrim mills and only from stainless steel grades 08-12X18H10T and 08-12X18H12T, and pipes from hard to deform steel grades and alloys like 06XH28MDT, KhN30MDB, KhN65MVU and 20Kh25N25TYu-Sh cannot be produced using this technology.

Conveyor pipes made by this technology have an increased longitudinal difference, since the rolling process on pilgrim mills is carried out on mandrels with a taper of 5-8 mm over a length of about 3000 mm; a large number of defects in the form of captures, for the removal of which it is necessary to subject the conversion pipes to mechanical processing on the outer and inner surfaces (turning and boring) with metal removal of 6-8 mm per side.

In pipe production, in order to reduce the loads on oblique rolling mills in the production of hot-rolled commodity and conversion pipes of large and medium diameters from corrosion-resistant hard-to-form steel grades and alloys on TPU with pilgrim mills, the method of double flashing of ingots - billets, including the first flashing of ESR ingots with a diameter of 540-600 mm in a piercing mill with an extractor hood μ = 1.2-1.4, and the second and subsequent, if necessary, firmware rolls with a rise or landing in diameter of not more than 5.0% and a hood μ = 1.4 -1.75 (RF patent No. 2247612, No. 7, 2005 and RF patent No. 2207199, No. 18, 2003).

The use of these methods allows the production of commodity and conversion pipes of large and medium diameters from hard-to-deform grades of steel and alloys on tube-rolling plants with pilgrim mills, to reduce the likelihood of jamming (puffs) of mandrels in pipes when rolling on pilgrim mills, and to reduce the expenditure coefficient of metal. Moreover, the use of this method does not exclude the need for mechanical processing of conversion pipes on the outer and inner surfaces. This method also has drawbacks associated with double heating (ESR ingots and first insertion sleeves), double firmware (ESD ingots and rolling up sleeves on mandrels of a larger diameter), which lead to a decrease in the performance of pilgrim mills, as well as to increased lateral and longitudinal differences conversion and commodity pipes.

The closest technical solution is a method for producing cold-rolled pipes of large and medium diameters from hard-deformed steel grades and alloys with increased accuracy along the wall from a conversion pipe billet, including forming a sheet preparation on rollers into a pipe conversion billet for rolling commodity or conversion pipes of larger diameter, welding under a flux layer, removing the reinforcement of the weld from the outer and inner surfaces of the conversion pipes, heat treatment of the conversion straight-line seam ki and rolling on a conical mandrel in calibers with a variable radius (TU 14-158-135 "Cold-deformed corrosion-resistant pipes for technological pipelines" and N. G. Danovsky, B. S. Litvak, A. V. Safyanov and others. Development technologies and production of pilot batches of cold-rolled pipes from hard-to-deform steel grades and alloys from welded steel billets. Forging and stamping: prospects and development, pp. 729-731, Ekaterinburg, 2005).

The use of this method for the production of cold-rolled large and medium-diameter pipes from hard-to-deform grades of steel and alloys with increased accuracy on the wall, although it eliminates the process of producing a converted billet on pipe rolling plants with pilgrim mills, significantly reduces the consumption of expensive metal, and therefore the cost of the pipes, but it has disadvantages associated with increased complexity in preparing the workpiece for rolling, caused by the need to remove the reinforcement of the weld.

The objective of the proposed method is to reduce the complexity of preparing the pipe billet for rolling in the manufacture of cold-deformed pipes from corrosion-resistant steel grades from electrowelded billets.

The technical result is achieved by the fact that in the known method for the production of cold-rolled pipes of large and medium diameters from hard-deformed steel grades and alloys with increased accuracy on the wall, including forming a sheet billet on rollers into a tube billet for rolling commodity or conversion pipes of larger diameter, welding longitudinal edges consumable electrode under the flux layer, austenization of a straight-line welded pipe billet, removal of weld reinforcement from the outer and inner surfaces she and rolling on a conical mandrel in calibers with a variable radius, rolling a conversion billet into a cold-rolled commodity pipe in several steps with a total exhaust of at least 1.2, cold-rolled pipes are made in several passes, while the absolute wall compression during the first pass is taken equal 1-2 mm, and the reinforcement of the weld is removed by local cleaning from the outer and inner surfaces from the rental end of the pipe at a length of 100-150 mm from the end with a smooth transition at a length of 10-15 mm.

The essence of the method lies in the fact that cold-rolled pipes are made in several passes, while the absolute compression along the wall at the first pass is taken to be 1-2 mm, and the reinforcement of the weld is removed by local cleaning from the outer and inner surfaces from the front of the rolled pipe end along the length 100-150 mm from the end with a smooth transition on a length of 10-15 mm.

A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that cold-rolled pipes are made in several passes, while the absolute wall compression during the first pass is taken to be 1-2 mm, and the reinforcement of the weld is removed by local stripping from the outside and the inner surface from the front of the rolled pipe end at a length of 100-150 mm from the end with a smooth transition at a length of 10-15 mm. These differences allow us to conclude that the criterion of "inventive step".

Comparison of the proposed method not only with the prototype, but also with other technical solutions in the art did not allow them to identify signs that distinguish the claimed method from the prototype, which corresponds to the patentability "inventive step".

The method has been tested and implemented at ChTPZ OJSC in the manufacture of cold-deformed pipes of size 325 × 8 mm from a corrosion-resistant alloy grade 06KHN28MDT and steel 12Kh18N10T from an electric-welded billet.

The table shows that the use of the proposed method for the production of cold-rolled pipes of large and medium diameters from hard-deformed grades of steel and alloys with increased accuracy on the wall reduces the laboriousness of preparing an electric-welded billet for hire by 5.7 times while maintaining the expenditure coefficient of the metal at the same level and satisfying the requirements normative documentation on the accuracy of geometric parameters and mechanical properties.

Thus, the use of the proposed method for the production of cold-rolled pipes of large and medium diameters from hard-deformed steel grades and alloys with increased accuracy on the wall reduces the laboriousness of preparing an electric-welded billet for hire by 5.7 times while maintaining the expenditure coefficient of the metal at the same level and meeting the requirements of regulatory documentation according to the accuracy of geometric parameters and mechanical properties.

Claims (1)

A method for the production of cold-rolled large and medium diameter pipes from hard-deformed grades of steel and alloys with increased accuracy on the wall, including forming a sheet billet on rollers into a tube billet for rolling commodity or conversion pipes of a larger diameter, welding longitudinal edges with a consumable electrode under a flux layer, austenization of the conversion longitudinal welded tubular billet, removal of reinforcement of the weld from the outer and inner surfaces and rolling on a conical mandrel in gauges with changes radius, rolling the conversion pipe billet into a cold rolled commodity pipe in several steps with a total exhaust of at least 1.2, characterized in that the cold-rolled pipes are made in several passes, while the absolute wall compression during the first pass is taken to be 1-2 mm, and the reinforcement of the weld is removed by local cleaning from the outer and inner surfaces from the front rental end of the pipe at a length of 100-150 mm from the end with a smooth transition at a length of 10-15 mm.