RU2580773C2 - Tube rolling method with thermomechanical treatment - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: tube rolling method with thermomechanical treatment includes heating of tubular billet up to temperature of 1150-1300°C, piercing and further deforming with total radial deformation degree of at least 70%, at that radial deformation degree at each stage of deformation upon piercing shall not exceed 35%. Before the last stage of deformation the rough-edged tube with temperature of 700-880°C is subject to accelerated induction heating up to temperature of 850-1000°C, thereafter, not later than in 5 s, final deformation is carried out at sizing mill or tube-reducing machine and then cooled in the air.

EFFECT: improved application properties of the tube due to excluded structure with different grain-size, increased viscosity and plasticity of steel, improved strength properties of steel.

2 cl, 1 tbl

Description

The invention relates to pipe rolling production and is aimed at improving the technology of hardening of oil assortment pipes from microalloyed steels with carbide and nitride forming elements directly in the process of hot deformation.

A known method of thermomechanical processing of oil pipes from carbon and microalloyed Nb, V, Mo, Cr steels, including pre-deformation, exposure to air, heating, final deformation and controlled cooling, the heating combined with the final deformation due to the heat generated during the final deformation (RF patent No. 2387718, M. class. C21D 8/00, publ. 04/27/2010). The disadvantage of this method is the need for strict exposure to the parameters of the degree and speed of deformation, as well as the temperature regime. In practice, this is difficult to achieve, since with a change in the rental rate during setup, equipment starts, various delays in the deformation process, both the deformation rate and temperature change significantly.

A known method of rolling pipes with thermomechanical treatment, which consists in heating, piercing the workpiece, cooling with water from the outer surface with a pressure of at least 15 atm, deformation in a continuous mill with a degree of deformation of at least 50% and cooling during deformation to a temperature of 800-900 ° C the outer surface of the rolls and flows of cooling water and from the inner surface of the mandrel pre-cooled to 150-250 ° C, induction heating and final deformation in the reduction mill (RF patent No. 2291903, M. CL C21D 8/10, publ. 20.01.2007) . The disadvantage of this method is its limited applicability only for pipe rolling units with a continuous mill, as well as the use of accelerated controlled water cooling, which leads to additional curvature of the products. The method does not take into account the heating temperature for the final deformation, which is fundamental for the formation of the metal structure of pipes made in the state after hot deformation (without subsequent heat treatment). The method does not limit the maximum degree of deformation in a continuous mill, at high degrees of which a sharp increase in anomalously large grains occurs in microvolumes maximally saturated with dislocations. As a result, some large grains are present in the fine-grained structure, which significantly degrades the consumer properties of the pipes made.

The technical problem to which the invention is directed is to eliminate the heterogeneity of the metal structure, increase the viscosity and ductility of steel, increase the strength properties of steel, reduce the defect in the geometric dimensions of the pipes, which ensures an increase in the efficiency of thermomechanical processing, expansion of its scope, as well as improvement of consumer pipe properties.

This result is achieved by the fact that the tube billet is heated to a temperature of 1150-1300 ° C, then it is flashed and then deformed with a total radial degree of deformation of at least 70%, while the radial degree of deformation at each stage of deformation (depending on the equipment used - radial deformation on each mill) after flashing should not exceed 35%. Before the last stage of deformation, the roughing pipe with a temperature of 700-880 ° C is subjected to accelerated induction heating to a temperature of 850-1000 ° C, after which no later than 5 s are the final deformation in a calibration or reduction mill and cooling in air.

The lower limit of the temperature range of metal heating for firmware provides the best ductility of the metal, and the upper one ensures the absence of metal overheating. Temperatures are selected experimentally for medium-carbon microalloyed Nb, V, Mo, Cr steels.

The total radial degree of deformation of not less than 70% ensures the production of a fine-grained structure, and it also provides the precipitation of carbides, nitrides, and carbonitrides of Nb, V, Mo, Cr in finely dispersed form.

The radial deformation (or deformation in thickness) of the wall is calculated by the formula:

ε _s = (S ₀ -S ₁ ) / S ₀ * 100,

where S ₁ - wall thickness after deformation, mm;

S ₀ - wall thickness before deformation, mm.

The radial degree of deformation at each stage of deformation after flashing no more than 35% avoids a significant accumulation of dislocation in individual microvolumes and, consequently, the growth of abnormally large grains. The resulting structure is finely dispersed over the entire cross section of the manufactured pipes.

Cooling the pipe during deformation to a temperature of 700-880 ° C ensures the release of the maximum amount of carbides, nitrides and carbonitrides Nb, V, Mo, Cr. Lowering the indicated temperature (less than 700 ° C) is impractical due to the difficulty of the deformation process and the formation of defects during tube rental. An increase in this temperature (over 880 ° C) leads to incomplete precipitation (reduction of the amount of precipitation) of carbides, nitrides, and carbonitrides, which reduces the effect of hardening.

Conducting accelerated induction heating avoids significant structural changes during heating, and the final deformation immediately after accelerated heating will allow even greater refinement of the structural components while maintaining the dispersion of carbide, nitride and carbonitride precipitates.

A time of not more than 5 s, after which the final deformation is performed after accelerated cooling, prevents grain growth and the dissolution of fine particles.

The lack of use (in comparison with the prototype) of accelerated controlled water cooling eliminates additional pipe bending.

The proposed and known solutions are tested in an industrial environment. Tube blanks with a diameter of 156 mm were smelted in a 150-ton arc steelmaking furnace from 38G2SF steel with a carbon content of 0.38%, manganese 1.30%, vanadium 0.09%. Hot-deformed pipes with dimensions of 73 × 5.5 mm, 89 × 6.5 mm (with final deformation in a reduction mill) were made from a tube billet under the conditions of Sinarsky Pipe Plant OJSC; 146 × 7.0 mm (with final deformation in the calibration mill).

The results of the study of the properties of the pipes are shown in table 1.

The proposed processing method allows to obtain pipes from microalloyed Nb, V, Mo, Cr steels with a favorable set of viscoplastic properties, and also contributes to obtaining a fine-grained uniform structure for pipes of the entire assortment and reduces rejects in geometric dimensions.

Claims (2)

1. A method of rolling pipes with thermomechanical treatment, including heating the tube stock, pre-deformation, heating, final deformation, cooling, characterized in that the tube preform is heated to a temperature of 1150-1300 ° C, the preliminary deformation is carried out with a total degree of radial deformation of not less than 70%, the degree of radial deformation at each stage of deformation after flashing is no more than 35%, heating under the final deformation is carried out to a temperature of 850-1000 ° C after accelerated induction heating, while the final deformation is carried out in a calibration or reduction mill no more than 5 seconds after accelerated induction heating, and cooling is carried out in air. 2. The method according to p. 1, characterized in that the accelerated induction heating is carried out at a temperature of 700-880 ° C.