RU2386497C2 - Method for production of thick-walled pipes of larger diametre from austenite grade steel - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to production of thick-walled pipes of large diametre from austenite grade steel. Method for production of thick-walled pipes of large diametre from austenite grade steel includes heating of drilled bar, double broaching with intermediate heating and rolling of rough tube at Pilger mill, besides prior to the first broaching drilled bar produced by electroslag remelting (ESR) is pressed in slant rolling mill without mandrel with setting along diametre of 9-13% and wall thinning by 18-21% due to lift in drilling diametre, and then after heating the bar is broached twice with lift to initial diametre.

EFFECT: invention provides for production of pipes from ESR bars made of austenite grade steel with guaranteed mechanical properties.

Description

The invention relates to pipe production, and in particular to a method for rolling large diameter pipes, and can be used in the production of pipes in plants with pilgrim mills.

There is a method of manufacturing pipes from austenitic class cast steel, where pipes with a diameter to wall thickness ratio of ≤ 7.3 in the cold state are repeatedly deformed on a straightening machine, in which the rolls are installed in a horizontal plane without the formation of pipe deflection, and before each pass rolls are reduced to the value Δ≤0.005Df, where Df is the actual diameter of the pipes, mm, and the deformation-the number of passes through the correct machine is stopped after the appearance of a burr on the rear end of the pipe (patent No. 2303498, Bull. No. 21, 07.27.2007).

The disadvantage of this method is that it can be used only when the yield strength during tensile testing of longitudinal samples at a temperature of + 350 ° C is less by 1 ÷ 2 kgf / mm ^{2 of the} required norm. With a lower yield strength obtained during testing, this method does not allow to provide the required properties. When rolling thick-walled tubes from ESR ingots, the structure of the central part of the tube wall from which the test specimens are cut is not sufficiently broken, and repeated dressing can raise the yield strength by no more than 2 kgf / mm ² .

A known method of increasing the degree of possible plastic deformation is the compaction of the ingot and the increase in the fractional deformation (Pipe rolling and tube welding, Moscow, 1954, p. 33. TI 158 - Tr. TB1-96-2004, Production of seamless hot-deformed machined pipes from steel 38KHN3MFA )

The disadvantage of this method is that the preliminary compression of the ingot and double flashing (fractional deformation) do not change the overall deformation, i.e. the degree of deformation remains the same and does not affect the increase in ductility.

The objective of the proposed method for the production of thick-walled pipes of large diameter from steels of the austenitic class is to obtain the required yield strength at the test temperature of the samples + 350 ° C.

The technical result is achieved by the fact that, before the first flashing, a drilled ESR ingot is crimped on a cross-helical rolling mill without a mandrel with a diameter of 9-13% in diameter and wall thinning by 18-21% by raising the drilling diameter, and then after heating the ingot two times flashing with intermediate heating and rise to the original diameter.

Comparative analysis with the prototype shows that the inventive method for the production of thick-walled large-diameter pipes from austenitic steels is characterized by the fact that before the first flashing, a drilled ESR ingot is crimped on a cross-helical rolling mill without mandrel with a diameter of 9-13% and a wall thinning by 18-21% due to the increase in the diameter of the drilling, and then after heating the ingot is flashed twice with intermediate heating and rise to the original diameter. 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 solution from the prototype, which corresponds to the patentability condition "inventive step".

The proposed method for the production of pipes with enhanced properties is that a geometric deformation factor is used (I.M. Pavlov. Theory of rolling, Moscow, 1950, pp. 104-106, I.A. Fomichev, Oblique rolling, Kharkov, 1963, p. .81-84). When an ingot is rolled in a cross-helical rolling mill without a mandrel with a diameter of 9–13%, a twist of the workpiece is intensively twisted while the inner diameter is raised and the wall is thinned, i.e. the grains formed in ESR ingots are deformed (elongated) in the direction of twisting, and thus, with the same general deformation, the mechanical properties of the metal increase.

This method was tested at the Chelyabinsk tube rolling plant. The technological process for the production of pipes from steel grade 08X18H10T-Sh was carried out along the route: a workpiece of 585 × 100 in. × 1600 mm diameter → a posad in diameter without a mandrel for a size of 530 × 140 in. × 1970 mm → I firmware 550 × 265 in. × 2140 mm → II firmware 585 × 365 in. × 2300 mm → rolling on pilgerstan 442 × 52 × 5800 mm → machining 426 × 40 × 5100 mm.

The yield strength on the samples at + 350 ° C was 24-27 kgf / mm ² with a norm according to TU 14-3R-197-2001 19-34 kgf / mm ² .

When rolling along an existing route: 585 × 100 in. × 1600 mm blank → I-st firmware 550 × 265 in. × 2200 mm → II-firmware 585 × 365 in. × 2300 mm → rolling on pilgerstan 442 × 52 × 5800 mm → machining 426 × 40 × 5100 mm. The spread of the yield strength on the samples at + 350 ° C was 11-22 kgf / mm ² . Using the proposed method for the production of pipes from ESR ingots of austenitic class steels will make it possible to obtain pipes with guaranteed mechanical properties in accordance with the technical conditions.

Claims (1)

A method for the production of thick-walled large-diameter pipes from austenitic-grade steels, including heating an ESR drill ingot, double piercing with intermediate heating and rolling the sleeve on a pilgrim mill, while before piercing, an ESR ingot is drilled on a cross-helical rolling mill without a mandrel with a diameter diameter fit of 9-13% and thinning of the wall by 18-21% due to the increase in the diameter of the drilling, and double piercing with intermediate heating is carried out with the rise to the original diameter.