RU2790721C1 - Pipe with high strain capacity of strength class k65 and method for its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention is related specifically to electric-welded longitudinal pipes of strength class K65 with an outer diameter of 508-1422 mm for the construction of gas pipelines designed for operating pressures up to 11.8 MPa inclusive, including those operated at the intersection of active tectonic faults, increased seismicity and permafrost soils, as well as in areas with weakly bearing, heaving and subsidence soils. The pipe is made of a steel sheet by moulding into a tubular billet when their longitudinal axes of symmetry are aligned, followed by welding of a technological seam in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges of the tubular billet from the inner and outer surfaces and expansion. The steel sheet contains in % by weight: carbon 0.04-0.07, silicon 0.10-0.35, manganese 1.45-1.90, chromium not more than 0.10, nickel 0.15-0.30, copper not more than 0.15, the total content of titanium, vanadium and niobium is 0.05-0.15, molybdenum 0.15-0.25, nitrogen not more than 0.007, aluminium 0.02-0.06, sulphur not more than 0.003, phosphorus not more than 0.013, iron and impurities - the balance. In the longitudinal direction, the pipe has a yield strength at full strain of 0.5% equal to 525-665 MPa, a tensile strength of 620-760 MPa, a ratio of yield strength at full strain of 0.5% to a tensile strength of not more than 0.91, relative elongation of at least 19%. In the transverse direction, the pipe has a yield strength at full strain of 0.5% equal to 555-665 MPa, a tensile strength of 650-760 MPa, a ratio of yield strength at full strain of 0.5% to a tensile strength of not more than 0.90, relative elongation of at least 18 %, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C not lower than 250 J/cm², the proportion of the viscous component in the fracture when tested by a falling load at a test temperature of minus 40°C not less than 85% and critical opening at the crack tip at a test temperature of minus 20°C not less than 0.20 mm. The welded joint has a tensile strength of 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the centre of the weld and along the fusion line of at least 70 J/cm² at a test temperature of minus 40°C, and critical opening at the crack tip on transverse specimens with a notch along the fusion line of at least 0.15 mm at a test temperature of minus 20°C.

EFFECT: achievement of increased strain capacity, determined by the requirements for the shape of the stretching curve in the area of plastic deformation.

5 cl, 5 tbl

Description

The invention relates to the field of metallurgy, in particular to the production of electrically welded longitudinal pipes (with high deformation capacity) of strength class K65 with an outer diameter of 508 to 1422 mm for gas pipelines designed for operating pressures up to 11.8 MPa inclusive, including those operated at intersections active tectonic faults, increased seismicity and permafrost soils, as well as in areas with weakly bearing, heaving and subsidence soils.

Known technical solution "Steel sheets for ultra-high-strength main pipes and ultra-high-strength main pipes with excellent low-temperature impact strength, and methods for their manufacture" (RF patent No. 2331698, C22C 38/04, 38/58, C21D 8/02, 8/10, 20.08.2008).

The main pipe is obtained from a steel sheet made of steel with the following content, wt. %: carbon 0.03-0.07; silicon not more than 0.6; manganese 1.5-2.5; phosphorus not more than 0.015; sulfur not more than 0.003; nickel 0.1-1.5; molybdenum 0.15-0.60; niobium 0.01-0.10; titanium 0.005-0.030; aluminum - no more than 0.06; one or more elements from the group: boron, nitrogen, vanadium, copper, chromium, calcium, REM and magnesium in the required quantities; iron - the rest and inevitable impurities. The characteristics of the sheet are: tensile strength in the transverse direction 880-1080 MPa; impact strength on samples with a V-shaped notch at a test temperature of minus 20 ° C is not lower than 200 J; the ratio of the yield strength at a total deformation of 0.2% to the ultimate strength is not more than 80% in the direction of rolling. The microstructure of the steel sheet is mainly composed of degenerate upper bainite. The sheet is made from a slab heated to a temperature of 1000-1250°C, rough rolling was carried out in the recrystallization temperature region, finishing rolling was carried out at a temperature of 900°C or lower with a total reduction of at least 75%, and then cooling from the austenite region at a rate of 1-10 °C/s until a temperature of 500°C or lower is obtained at the center of the sheet thickness. The microstructure of the sheet consists of degenerate upper bainite in an amount of more than 70%.

The pipe manufacturing method includes forming a steel sheet into a tubular billet using a UO process, welding longitudinal edges with submerged arc welding, and expanding. The characteristics of the pipe are: tensile strength in the tangential direction 900-1100 MPa; impact strength on samples with a V-shaped notch at a test temperature of minus 20 ° C is not lower than 200 J.

The disadvantage of this invention is that a large-diameter high-pressure trunk pipe made from a sheet has a structure of predominantly degenerate upper bainite, which does not provide a high deformability of the steel, expressed in a special form of a tensile diagram without a yield plateau. In addition, the lack of the ability to directly control the temperature - one of the parameters of the formula - in the center of the sheet thickness to determine the moment when accelerated cooling stops makes it much more difficult to comply with the technological regimes in production and their reproducibility, which can sporadically lead to non-conforming products and economic losses of the enterprise.

The closest technical solution, adopted as a prototype for two objects, is described in the patent of the Russian Federation No. 2656189, C21D 8/02, 8/10, C22C 38/0, 05/31/2018 the way it is made."

The main pipe is obtained from a steel sheet with a yield strength of over 480 MPa, containing, wt. %: carbon 0.04-0.08, silicon 0.10-0.30, manganese 1.60-1.85, chromium no more than 0.30, nickel 0.20-0.40, molybdenum 0.10- 0.25, copper not more than 0.30, aluminum not more than 0.05, niobium 0.03-0.06, titanium 0.010-0.020, vanadium not more than 0.01, sulfur not more than 0.003, phosphorus not more than 0.013, the rest – iron and inevitable impurities. SUBSTANCE: pipe manufacturing method includes forming a steel sheet into a billet, multi-arc submerged arc welding of the longitudinal edges of the billet from the inner and outer surfaces, and expansion, wherein welding is carried out according to modes that ensure the formation of a microstructure in the heat-affected zone, consisting of at least 60% of finely dispersed needle and lath bainite.

The main disadvantage of the prototype is that the claimed method of producing a sheet and a pipe with a similar degree of alloying and the cost of steel provides a lower strength class K60, which significantly affects the choice of a thicker wall in the strength calculations of pipelines, leads to an increase in the metal consumption of the entire structure, and, as consequently, an increase in capital costs for the project.

The technical result of the present invention is to provide increased deformation capacity, determined by the requirements for the shape of the tensile curve in the area of plastic deformation, of large-diameter pipes of strength class K65, made of steel sheet, for use in laying pipelines for operating pressures up to 11.8 MPa in areas where active tectonic faults, increased seismicity and permafrost soils, as well as in areas with weakly bearing, heaving and subsidence soils.

The technical result is achieved by the fact that the large-diameter pipe of strength class K65 is made of steel sheet by molding into a tubular billet when their longitudinal axes of symmetry are aligned, followed by welding of the technological seam in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges of the pipe billet both from the inner, and from the outer surface, and expansion, according to the invention, the steel sheet contains carbon 0.04-0.07%, silicon 0.10-0.35%, manganese 1.45-1.90%, chromium not more than 0.10 %, nickel 0.15-0.30%, copper not more than 0.15%, total content of titanium, vanadium and niobium 0.05-0.15%, molybdenum 0.15-0.25%, nitrogen not more than 0.007 %, aluminum 0.02-0.06%, sulfur not more than 0.003%, phosphorus not more than 0.013% iron and impurities - the rest, while the characteristics of the pipe in the longitudinal direction are: yield strength at full deformation 0.5% 525-665 MPa, tensile strength 620-760 MPa, yield strength ratio at full strain 0.5% to temporal resistance not more than 0.91, relative elongation not less than 19%; pipe characteristics in the transverse direction are: yield strength at full strain 0.5% 555-665 MPa, tensile strength 650-760 MPa, ratio of yield strength at full strain 0.5% to tensile strength no more than 0.90, relative elongation no more less than 18%, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C is not lower than 250 J/cm ² , the proportion of the viscous component in the PPG fracture at a test temperature of minus 40°C is not less than 85%, critical opening at the top cracks at a test temperature of minus 20°C are not less than 0.20 mm in the absence of a yield point in the tensile diagram in the longitudinal and transverse directions, and the characteristics of the welded joint are: tensile strength 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the center of the weld and along the fusion line is at least 70 J/ ^cm2 at a test temperature of minus 40°C, the critical opening at the crack tip on transverse samples The gap along the fusion line is at least 0.15 mm at a test temperature of minus 20°C.

The technical result is achieved by the fact that in a method for producing a pipe of strength class K65, including austenitization of a continuously cast billet, rough rolling with regulated reduction per pass, chilling of a roll, finishing rolling, cooling in still air, followed by accelerated cooling in a controlled cooling installation, straightening, forming of steel sheet into a tubular blank when the longitudinal axes of symmetry are aligned, followed by welding of a technological seam in an atmosphere of shielding gases and multi-arc submerged arc welding of the longitudinal edges of the tubular blank both from the inner and outer surfaces, and expansion, according to the invention, a continuously cast billet is obtained from steel with the following the ratio of elements: carbon 0.04-0.07%, silicon 0.10-0.35%, manganese 1.45-1.90%, chromium not more than 0.10%, nickel 0.15-0.30% , copper not more than 0.15%, the total content of titanium, vanadium and niobium 0.05-0.15%, molybdenum 0.15-0.25%, nitrogen not more than 0.007%, aluminum 0.02- 0.06%, sulfur not more than 0.003%, phosphorus not more than 0.013% iron and impurities - the rest, while the austenization of the continuously cast billet is carried out to a temperature of 1190-1240 ° C, rough rolling begins at a temperature not lower than 980 ° C and is carried out at the thickness of the rolled product, which is at least 4 thicknesses of the finished sheet, finishing rolling begins and ends in the temperature range of 760-820°C, after which the sheet is cooled in still air to a temperature of the start of accelerated cooling of 710-750°C, and then subjected to accelerated cooling in the installation for controlled cooling at a cooling rate of 10-35°C/s to a temperature not exceeding 200°C, then the sheet is straightened in a roller sheet straightening machine with provision in the longitudinal direction: yield strength at full deformation 0.5% 510-640 MPa, temporary resistance 610-740 MPa, the ratio of the yield strength at full deformation of 0.5% to the ultimate strength of not more than 0.91, relative elongation of not less than 20%, relative uniform elongation at least 7.5%; in the transverse direction: yield strength at full strain 0.5% 530-670 MPa, tensile strength 640÷750 MPa, ratio of yield strength at full strain 0.5% to tensile strength not more than 0.90, relative elongation not less than 19, 5%, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C is not lower than 270 J/cm ² , the share of the viscous component in the PPG fracture at a test temperature of minus 40°C is not less than 90%, critical opening at the crack tip at a test temperature of minus 20°C not lower than 0.25 mm in the absence of a yield point on the tensile diagram in the longitudinal and transverse directions, after forming the steel sheet into a tubular billet, when their longitudinal axes of symmetry are aligned, the process seam is welded in a shielding gas atmosphere and multi-arc welding is carried out under the flux layer of the longitudinal edges both from the inner and outer surfaces, and expansion, while the welded joint has the following characteristics: Resistivity 650-760 MPa, impact strength on transverse samples with a V-shaped notch along the center of the weld and along the fusion line is at least 70 J/cm ² at a test temperature of minus 40°C, critical opening at the crack tip on transverse samples with a notch along the fusion line is at least 0.15 mm at a test temperature of minus 20°C.

The technical result is also achieved by the fact that rough rolling is carried out with partial relative reductions of at least 10%.

The technical result is also achieved by the fact that in the longitudinal and transverse directions the following conditions are met: σ _p0.6 / σ _p0.4 ≥ 1.070, σ _p1.0 / σ _p0.6 ≥ 1.050, σ _p2.0 / σ _p1.0 ≥ 1.020 (where σ _p0.6 , σ _p0.4 , σ _p1.0 , σ _p2.0 - stress value with a tolerance for the total deformation of 0.6%, 0.4%, 1.0%, 2.0%, respectively , MPa).

The essence of the invention is as follows. According to the proposed method, a continuously cast billet is made of steel with a given chemical composition. The content of chemical elements in the specified ratios provides the necessary mechanical properties of the sheets in the implementation of the proposed technological regimes.

To obtain the required strength, the carbon content must be at least 0.04%, while its addition in an amount of more than 0.07% leads to a deterioration in the plastic properties of the steel.

The addition of silicon is necessary for the deoxidation of steel during smelting. To ensure the required level of deoxidation, its content should be at least 0.10%, but not more than 0.35% to limit the amount of silicate inclusions that worsen impact strength and crack resistance.

Manganese increases the degree of ferrite saturation with dissolved elements involved in the precipitation hardening mechanism. For its rational use, the manganese content must be at least 1.45%. With a manganese content of more than 1.90%, the impact strength of steel decreases.

In the proposed method, the chromium content is limited to a residual concentration of 0.1%. Chromium increases the hardenability of steel and, upon accelerated cooling of the roll, leads to the formation of brittle structural components that reduce the ability of the material to resist the development of cracks.

To increase the stability of austenite, nickel and copper are added to steel. To obtain the desired effect, the nickel content should not be less than 0.15%. It is not economically feasible to add more than 0.30% nickel. To save nickel in the proposed method, the steel may contain copper up to half of its maximum concentration of not more than 0.15%. The presence of copper in steel increases strength, but reduces ductility and toughness, weakening grain boundaries during slow cooling with an enriched phase.

To use the additional mechanism of dispersion strengthening, the steel must be with the addition of titanium, vanadium and niobium in an amount not less than 0.05% and not more than 0.15% in total. When the total content of these elements is less than 0.05%, the required strengthening effect is not achieved, more than 0.15%, the effect of excessive hardening occurs.

Molybdenum additives give the steel a fine-grained structure, increase strength with equal ductility. Molybdenum in an amount of less than 0.15% does not have a significant effect on the properties, and its content of more than 0.25% already significantly increases the cost of steel, which is not economically feasible.

Nitrogen is needed to precipitate finely dispersed nitrides to inhibit the growth of austenite grains. When the nitrogen content is above 0.007%, its concentration in the solid solution increases, which worsens the impact strength and crack resistance of steel at low temperatures.

Aluminum deoxidizes and modifies steel, binds nitrogen into nitrides. To reduce the oxygen content in molten steel, it is necessary to add at least 0.02% aluminum. When its content is more than 0.06%, the viscoplastic properties of steel decrease.

Sulfur and phosphorus are harmful impurities, therefore, the indicated low values of sulfur content not more than 0.003% and phosphorus not more than 0.013% are necessary to obtain high values of impact strength at low temperatures.

With a sulfur content of more than 0.003%, sulfide inclusions are formed in the steel, which significantly reduce the impact strength and crack resistance.

Phosphorus is one of the elements that have the highest tendency to segregation and the formation of segregation along the grain boundaries, and, as a result, negatively affecting the impact strength of steel and crack resistance, therefore, the upper limit of the phosphorus content is set to no more than 0.013%.

Chemical elements within the stated limits also provide the required mechanical properties of the welded joint and satisfactory weldability of the steel. When steel is exposed to a thermal welding cycle, they inhibit the growth of austenite grains and contribute to the formation of a fine-grained microstructure in the heat-affected zone, which consists mainly of acicular and lath bainite.

The optimal technological parameters of the method were determined empirically.

Pipes (with high deformation capacity) of strength class K65 for high-pressure main pipelines are made of steel sheets. To do this, slabs are heated to a temperature of 1190-1240 ^o C before rolling. Exceeding the upper limit of the interval stimulates abnormal growth of austenite grains, leading to a decrease in strength and toughness properties. When the lower limit of the heating temperature range is not reached, carbonitrides are poorly soluble in austenite, which has a negative effect on the course of recrystallization processes, and also reduces the strength and toughness properties. The rough rolling stage is carried out above the austenite recrystallization temperature, but not below 980°C, which ensures active grain refinement due to its re-growth. To ensure satisfactory results of the drop load test, taking into account the increased thickness of rolled products, it is necessary to provide an intermediate cooling thickness of at least four thicknesses of the finished sheet. Obtaining, for example, five-fold intermediate rolling in thickness reduces the total degree of deformation in the rough rolling stage, preventing the required refinement of austenite grains.

The temperature interval for the beginning and end of deformation at the finishing stage of rolling is chosen based on the need to prepare austenite for subsequent transformation by creating deformed austenite grains containing deformation bands and having a high dislocation density. The rational temperature range for finishing rolling is 760-820°C.

Accelerated cooling has a positive effect on the strength and viscoplastic properties of the finished rolled product. The selected conditions for single-stage accelerated cooling: the temperature range of the start of cooling 710-750°C and the cooling rate of 10-35°C/s to a temperature not higher than 200°C provide the target ferrite-bainitic structure. In this case, a higher temperature at the end of accelerated cooling leads to the appearance in the structure of a proportion of an undesirable structural component of perlite. Next, the sheets are straightened in a roller sheet straightening machine.

Rough rolling is carried out with partial relative reductions of at least 10%. With an increase in the degree of deformation, the activation energy of recrystallization decreases and the rate of formation of new crystalline grains increases. Empirically, a minimum sufficient degree of deformation of at least 10% has been established, which positively affects the recrystallization and mechanical properties of the finished rolled product. To obtain the required thickness of the intermediate roll, it is allowed to carry out the last passes through the roll gap with a lower degree of deformation.

The production process for producing pipes includes forming a steel sheet into a tubular billet when their longitudinal axes of symmetry are aligned, followed by welding of a technological seam in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges of the tubular blanks both from the inner and outer surfaces, and expansion.

The produced pipes have the following characteristics in the longitudinal direction: yield strength at full deformation 0.5% 525-665 MPa, tensile strength 620-760 MPa, ratio of yield strength at full deformation 0.5% to tensile strength no more than 0.91, relative elongation of at least 19%; in the transverse direction: yield strength at full strain 0.5% 555-665 MPa, tensile strength 650-760 MPa, ratio of yield strength at full strain 0.5% to tensile strength no more than 0.90, relative elongation no less than 18% , impact strength on samples with a V-shaped notch at a test temperature of minus 40°C is not lower than 250 J/cm ² , the proportion of the viscous component in the PPG fracture at a test temperature of minus 40°C is not less than 85%, critical crack opening at a temperature of test minus 20°C not less than 0.20 mm in the absence of a yield point on the tensile diagram in the longitudinal and transverse directions, which implies the fulfillment of the conditions

σ _p0.6 / σ _p0.4 ≥ 1.070, σ _p1.0 / σ _p0.6 ≥ 1.050, σ _p2.0 / σ _p1.0 ≥ 1.020,

and the characteristics of the welded joint are: tensile strength 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the center of the weld and along the fusion line is at least 70 J/cm ² at a test temperature of minus 40°C, critical opening at the top cracks on transverse specimens with a notch along the fusion line is at least 0.15 mm at a test temperature of minus 20°C.

The production of large-diameter pipes with increased deformation capacity by the proposed method ensures that the values of strength properties are higher than the standard level of requirements for pipes K65 (STO Gazprom 2-4.1-713-2013, ISO 3183, API Spec 5L), which allows the design organization to reduce the thickness walls and reduce the metal consumption of projects.

The application of the method is illustrated by an example of its implementation in the production of sheet metal and pipes in PAO Severstal.

Under the conditions of converter production at the Cherepovets Metallurgical Plant of PJSC Severstal, five experimental melts were smelted, three of which had the same chemical composition as declared (Nos. 1, 2 and 3), two did not (Nos. 4 and 5). The chemical composition of the smelted metal is shown in Table 1. Experimental melts were cast into slabs 313 mm thick, which were rolled on a mill 5000 into sheets 33.4 mm thick. Options for implementing the proposed method and test results are shown in tables 2 and 3, 4, respectively.

The test results showed that the proposed method for the production of rolled products (option No. 1-5) from steel of the selected chemical composition (No. 1, 2 and 3) provides a satisfactory level of mechanical properties.

From steel sheets according to option 1-1 and 5-5, large-diameter pipes 1220 × 33.4 mm in size were manufactured using the JCO-forming method in the conditions of the pipe welding shop of Izhora Pipe Plant JSC. axes of symmetry, carried out welding of a technological seam in an atmosphere of shielding gases and multi-arc welding under a flux layer of longitudinal edges both from the inner and outer surfaces, and expansion.

Table 5 shows the mechanical properties of the base metal (BM) and welded joint (SS) of pipes made of steel with chemical composition 1 and 5 according to technology 1 and 5, respectively (options 1-1, 5-5).

From table 5 it can be seen that pipes made from steel sheet from steel with a variant of the chemical composition No. 1 according to the proposed method No. 1 have a set of mechanical properties that provide increased deformability.

Pipes made of steel with a variant of the chemical composition No. 5 according to the proposed method No. 5 do not have such a set of mechanical properties.

To test the operational reliability of pipes according to option 1-1, they were bench tested with hydraulic pressure. The tests were carried out with the application of an artificial defect on the base metal, the center of the weld, and the fusion line. The destruction occurred at a pressure exceeding the calculated pressure, and the cracks did not go beyond the applied artificial defect. Field pneumatic tests were also carried out. The crack stopped on both sides within the first test pipe at a distance of 4.4 m from the annular joint with the initiator pipe. Both tests showed high operational reliability of pipes with VDS.

Thus, the application of the described method for the production of rolled products and pipes with a given chemical composition ensures the achievement of the required level of quality characteristics of electric-welded longitudinal pipes (with high deformation capacity) of strength class K65 with an outer diameter of 508 to 1422 mm for gas pipelines designed for operating pressures up to 11, 8 MPa inclusive, including those operated at the intersection of active tectonic faults, increased seismicity and permafrost soils, as well as in areas with weakly bearing, heaving and subsidence soils:

- in the longitudinal direction: yield strength at full strain 0.5% 525-665 MPa, tensile strength 620-760 MPa, ratio of yield strength at full strain 0.5% to tensile strength no more than 0.91, relative elongation no less than 19 %;

- in the transverse direction: yield strength at full strain 0.5% 555-665 MPa, tensile strength 650-760 MPa, ratio of yield strength at full strain 0.5% to tensile strength no more than 0.90, relative elongation no less than 18 %, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C is not lower than 250 J/cm ² , the proportion of the viscous component in the PPG fracture at a test temperature of minus 40°C is not less than 85%, the critical opening at the crack tip at at a test temperature of minus 20°C, not less than 0.20 mm in the absence of a yield point on the tensile diagram in the longitudinal and transverse directions, which implies the fulfillment of the conditions

σ _p0.6 / σ _p0.4 ≥ 1.070, σ _p1.0 / σ _p0.6 ≥ 1.050, σ _p2.0 / σ _p1.0 ≥ 1.020;

- characteristics of the welded joint: tensile strength 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the center of the weld and along the fusion line is at least 70 J/cm ² at a test temperature of minus 40°C, critical opening at the crack tip on transverse specimens with a notch along the fusion line is at least 0.15 mm at a test temperature of minus 20°C.

Table 1

Mass fraction of chemical elements, %

Chemical
compound WITH Si Mn Cr Ni Cu Ti+V+Nb Mo N Al S P 1 0.041 0.11 1.45 0.04 0.15 0.05 0.05 0.15 0.005 0.02 0.002 0.011 2 0.055 0.24 1.54 0.07 0.23 0.08 0.08 0.19 0.005 0.04 0.002 0.011 3 0.065 0.31 1.90 0.10 0.30 0.14 0.15 0.25 0.006 0.05 0.003 0.012 4 0.038 0.15 1.39 0.17 0.11 0.06 0.01 0.05 0.007 0.01 0.003 0.012 5 0.071 0.35 1.95 0.20 0.34 0.29 0.18 0.29 0.007 0.07 0.003 0.013

table 2

Technological parameters of sheet production

Production option Chemical composition Austenitization temperature, °С Rough rolling start temperature, °C Roll multiplicity by thickness Partial relative reductions at the roughing stage, % Finish rolling start temperature, °C Finish rolling end temperature, °C Start temperature of accelerated cooling, °C Cooling rate, °С/s End temperature of accelerated cooling, °C 1 1 1191 982 4 10 762 777 712 12 195 2 2 1205 1011 5 12 790 800 734 20 105 3 3 1229 1039 6 eleven 817 820 748 31 52 4 4 1210 1007 5 10 788 792 745 18 98 5 5 1220 992 4 13 773 779 739 15 93 6 1 1150 940 3 9 748 752 689 8 218 7 2 1245 950 3 8 840 849 761 39 37

Table 3

The results of testing samples from sheet metal for static tension

Production option Chemical composition σ _p0.5 , MPa σ _in , MPa _δ5 , % σ _p0.5 / σ _in σ _st0.6 / σ _st0.4 σ _st1.0 / σ _st0.6 σ _p2.0 / σ _p1.0 1 1 545 640 23 0.85 1.09 1.07 1.03 2 2 570 650 20 0.88 1.08 1.07 1.02 3 3 600 695 21 0.86 1.08 1.05 1.03 4 4 530 630 22 0.84 1.08 1.04 1.02 5 5 560 645 19 0.87 1.07 1.06 1.01 6 1 520 635 24 0.82 1.06 1.05 1.03 7 2 690 760 20 0.91 1.05 1.04 1.02 Note:
σ _p0.5 - conditional yield strength with a tolerance for the total deformation of 0.5%;
σ _in - temporary resistance;
δ ₅ - relative elongation after rupture;
σ _p0.6 - stress value with a tolerance for the value of total deformation of 0.6%;
σ _p0.4 - stress value with a tolerance for the total deformation value of 0.4%;
σ _p1.0 is the stress value with a tolerance for the total deformation value of 1.0%;
σ _p2.0 is the stress value with a tolerance for the total deformation value of 2.0%.

Table 4

Results of dynamic tests for bending and crack resistance CTOD

Production option Chemical composition KCV ^-40 , J / cm ² ICE at IPG ^-40 , % δ _c , mm 1 1 350 100 0.58 2 2 328 100 0.46 3 3 312 95 0.42 4 4 270 85 0.25 5 5 250 85 0.23 6 1 260 90 0.25 7 2 245 80 0.19 Note:
KCV ^-40 - impact strength at a test temperature of minus 40 ^o C;
ICE at IPG ^-40 - the proportion of the viscous component in the fracture of IPG at a test temperature of minus 40 ^o C;
δ _c – crack tip opening.

Table 5

The results of mechanical tests of samples from the base metal (BM) and
welded joint (SS) pipes

Characteristic Option 1-1 Option 5-5 Samples from OM in the longitudinal / transverse direction Yield strength σ _p0.5 , MPa 535 / 550 555 / 570 Tensile strength σ _in , MPa 630 / 650 630 / 655 Relative elongation δ ₅ % 23 / 23 20 / 19 The ratio σ _p0.5 / σ _in 0.85 / 0.85 0.88 / 0.87 Ratio σ _p0.6 / σ _p0.4 1.09 / 1.09 1.05/ 1.05 Ratio σ _p1.0 / σ _p0.6 1.07 / 1.07 1.03 / 1.03 Ratio σ _p2.0 / σ _p1.0 1.03 / 1.03 1.00 / 1.01 Impact strength KCV ^-40 , J / cm ² - /350 - /250 The share of the viscous component at IPG ^-40 , % - /95 - /85 Crack tip opening δ _c , mm - / 0.56 - / 0.22 Samples from the SS in the transverse direction (notch along the fusion line) Tensile strength σ _in , MPa - / 690 - / 730 Impact strength KCV ^-40 , J / cm ² - / 110 - / 53 Crack tip opening δ _c , mm - / 0.46 - / 0.08

Claims (23)

1. Pipe of strength class K65, made of steel sheet by molding into a tubular billet when their longitudinal axes of symmetry are aligned, followed by welding of a technological seam in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges of the tubular billet from the inner and outer surfaces and expansion, which differs the fact that the steel sheet contains, wt.%: carbon 0.04-0.07 silicon 0.10-0.35 manganese 1.45-1.90 chromium no more than 0.10 nickel 0.15-0.30 copper no more than 0.15 total titanium content, vanadium and niobium 0.05-0.15 molybdenum 0.15-0.25 nitrogen no more than 0.007 aluminum 0.02-0.06 sulfur no more than 0.003 phosphorus no more than 0.013 iron and impurities rest, at the same time, in the longitudinal direction, the pipe has a yield strength at full deformation of 0.5% 525-665 MPa, a tensile strength of 620-760 MPa, a ratio of the yield strength at full deformation of 0.5% to the tensile strength of not more than 0.91, relative elongation is not less than 19%, and in the transverse direction the pipe has a yield strength at full deformation of 0.5% 555-665 MPa, a tensile strength of 650-760 MPa, a ratio of yield strength at full deformation of 0.5% to a tensile strength of not more than 0.90, relative elongation of not less than 18%, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C is not lower than 250 J/cm ² , the fraction of the viscous component in the fracture during the drop load test (PLG) at a test temperature of minus 40°C not less than 85% and the critical opening at the crack tip at a test temperature of minus 20°C is not less than 0.20 mm, while the welded joint has a tensile strength of 650-760 MPa, impact strength on transverse specimens with a V-shaped notch ohm in the center of the weld and along the fusion line, which is not less than 70 J/cm ² at a test temperature of minus 40°C, and a critical opening at the crack tip on transverse specimens with a notch along the fusion line, which is not less than 0.15 mm at a test temperature minus 20°C. 2. The pipe according to claim 1, characterized in that the following conditions are met in the longitudinal and transverse directions: σ _p0.6 / σ _p0.4 ≥1.070, σ _st1.0 / σ _st0.6 ≥1.050, σ _p2.0 /σ _p1.0 ≥1.020, where σ _p0.6 is the stress value with a tolerance for the total deformation of 0.6%, MPa; σ _p0.4 - stress value with a tolerance for the value of total deformation of 0.4%, MPa; σ _p1.0 - stress value with a tolerance for the value of total deformation of 1.0%, MPa; σ _p2.0 is the stress value with a tolerance for the total deformation of 2.0%, MPa. 3. A method for the production of a pipe of strength class K65, including the production of continuously cast steel billets, their austenitization, rough rolling with regulated reduction per pass, chilling of the roll, finishing rolling, cooling in still air, followed by accelerated cooling in a controlled cooling installation, straightening, forming a steel sheet into a tubular billet when the longitudinal axes of symmetry are aligned, followed by welding of a technological seam in an atmosphere of shielding gases and multi-arc submerged arc welding of the longitudinal edges of the tubular billet from the inner and outer surfaces and expansion, characterized in that continuously cast billets are obtained from steel with the following ratio of elements, wt.%: carbon 0.04-0.07 silicon 0.10-0.35 manganese 1.45-1.90 chromium no more than 0.10 nickel 0.15-0.30 copper no more than 0.15 total titanium content, vanadium and niobium 0.05-0.15 molybdenum 0.15-0.25 nitrogen no more than 0.007 aluminum 0.02-0.06 sulfur no more than 0.003 phosphorus no more than 0.013 iron and impurities rest, at the same time, austenitization of the continuously cast billet is carried out to a temperature of 1190-1240°C, rough rolling is started at a temperature of at least 980°C and is carried out for a rolled thickness of at least four thicknesses of the finished sheet, finishing rolling is started and completed in the temperature range of 760 -820°C, after which the sheet is cooled in still air to the start temperature of accelerated cooling of 710-750°C, and then subjected to accelerated cooling in a controlled cooling unit with a cooling rate of 10-35°C/s to a temperature not exceeding 200°C , then the sheet is straightened in a roller straightening machine with the provision in the longitudinal direction of the yield strength at full deformation of 0.5% 510-640 MPa, tensile strength of 610-740 MPa, the ratio of the yield strength at full deformation of 0.5% to the tensile strength of not more than 0.91, a relative elongation of at least 20%, a relative uniform elongation of at least 7.5%, and in the transverse direction - the yield strength at full deformation 0.5% 530-670 MPa, tensile strength 640÷750 MPa, ratio of yield strength at full deformation 0.5% to tensile strength not more than 0.90, relative elongation not less than 19.5%, impact strength on specimens with V-shaped notch at a test temperature of minus 40°C is not lower than 270 J/cm ² , the share of the viscous component in the fracture of the PPG at a test temperature of minus 40°C is not less than 90%, the critical opening at the crack tip at a test temperature of minus 20°C is not below 0.25 mm, after forming the steel sheet into a tubular billet, when their longitudinal axes of symmetry are aligned, the process seam is welded in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges from the inner and outer surfaces and expansion, while the welded joint has a temporary resistance 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the center of the weld and along the fusion line, not less than 70 J/ ^cm2 at a test temperature of minus 40°C , critical opening at the crack tip on transverse specimens with a notch along the fusion line, which is not less than 0.15 mm at a test temperature of minus 20°C. 4. The method according to p. 3, characterized in that rough rolling is carried out with partial relative reductions of at least 10%. 5. The method according to claim 3, characterized in that the following conditions are met in the longitudinal and transverse directions: σ _p0.6 / σ _p0.4 ≥1.070, σ _st1.0 / σ _st0.6 ≥1.050, σ _p2.0 /σ _p1.0 ≥1.020, where σ _p0.6 is the stress value with a tolerance for the total deformation of 0.6%, MPa; σ _p0.4 - stress value with a tolerance for the value of total deformation of 0.4%, MPa; σ _p1.0 - stress value with a tolerance for the value of total deformation of 1.0%, MPa; σ _p2.0 is the stress value with a tolerance for the total deformation of 2.0%, MPa.