RU2500820C1 - Production method of rolled metal from low-alloy steel for manufacture of structural members of oil and gas lines - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: continuous cast steel billets of certain chemical composition are produced; their austenisation is performed at the temperature of 1180-1210°C; then, roughing-down is performed at the temperature of 940-1180°C with reduction of cross-sectional areas per pass of not less than 12%, air cooling of deformed billet to the temperature of 720-780°C is performed, finish rolling is performed at the temperature interval of 750-790°C with total reduction of cross-sectional area of 50-60% and accelerated cooling of a finished rolled metal is performed at temperature interval of 730-770°C to 580-620°C with cooling rate of 15-20°C/sec.

EFFECT: development of a 60-90 mm thick rolled metal production technology with guaranteed yield point of not less than 275 MPa and increased impact strength.

2 tbl, 1 ex

Description

The invention relates to metallurgy, and more particularly to the production of structural steels of normal strength, improved weldability for use in construction, engineering and other industries.

A known method of production of sheet metal, including obtaining a billet of steel of the following composition, wt.%:

Carbon 0.05-0.15 Manganese 1.2-2.0 Silicon 0.2-0.6 Niobium 0.01-0.1 Titanium 0.005-0.03 Aluminum 0.01-0.1 Chromium 0.03-0.5 Nickel 0.03-0.5 Copper 0.03-0.5 Nitrogen 0.005-0.02 Iron Rest

The billets are subjected to austenization, the deformation is carried out with reversible partial reductions at a total degree of deformation of 50-80%, after the end of the deformation process, the rolling at 760-900 ° C is cooled at a speed of 10-60 degrees / s to 300-20 ° C, and then produced heating to 590-740 ° C with a shutter speed of 0.2-3.0 min / mm and finally cooled in air to ambient temperature. [one]

The disadvantages of this method are that sheet steel has low viscous properties at low temperatures. This makes it impossible to use sheets for the manufacture of valves of oil and gas pipelines. In addition, the need for heat treatment of sheets after rolling complicates and increases the cost of production.

A known method for the production of steel sheets, including smelting and continuous casting into slabs of low alloy steel containing by wt.%:

Carbon 0.05-0.15 Manganese 1.2-2.0 Silicon 0.2-0.6 Niobium 0.01-0.1 Titanium 0.005-0.03 Aluminum 0.03-0.5 Nickel 0.03-0.5 Copper 0.03-0.5 Nitrogen 0.005-0.02 Iron Rest

The cast billets are heated to a temperature of 1250 ° C and rolled with a total compression of at least 75%. Laminated sheets are subjected to quenching from the austenitic region and high-temperature tempering [2]. The disadvantages of this method are that sheet steel has low plastic and viscous properties at low temperatures, poor weldability. This makes it impossible to use sheets for the manufacture of valves of oil and gas pipelines. In addition, the need for thermal improvement (hardening and tempering) of the sheets after rolling complicates and increases the cost of production.

There is also known a method of manufacturing plate low alloy steel, including casting a billet of the following chemical composition, wt.%:

Carbon 0.02-0.3 Manganese 0.5-2.5 Aluminum 0.005-0.1 Silicon 0.05-1.0 Niobium 0.003-0.01 Iron Rest

The billets are heated to a temperature of 950-1050 ° C and rolled at a temperature above the point Ar ₃ with a total compression of 50-70%. Laminated sheets are cooled in air [3].

With this method of production, the sheets have insufficient strength and ductility with a ratio of ^σ t / ^σ in exceeding 0.94. Such sheets do not satisfy the requirements for weldability and are not suitable for the manufacture of valves for oil and gas pipelines.

A known method for the production of sheet metal of the following chemical composition, wt.%:

Carbon 0.008-0.10 Manganese 0.008-1.53 Silicon 0.008-0.63 Sulfur 0.001-0.008 Phosphorus 0.001-0.27 Chromium 0.001-0.25 Copper 0.001-0.27 Aluminum 0.02-0.06 Titanium 0.001-0.021 Iron Rest

The method for producing 10 mm thick rolled products from low alloy steel involves heating slabs for rolling above Ac ₃ + (90-70) ° C, which corresponded to 950 and 930 ° C, and then subjected to rough rolling to an intermediate thickness with a total compression of 80% and partial 20% and 25% per pass and ended at a temperature of 890 ° C, then the rolling was cured to a temperature of 830 ° C and 850 ° C, with which the finish rolling was carried out with a total compression of 78% and partial reductions from 7% to 24% to a temperature 770 ° C and 790 ° C, after which the sheets were subjected to accelerated cooling rate of 60 ° C / min to a temperature of 300 ° C and 200 ° C, followed by cooling in air to a temperature of 100 ° C with a single-row arrangement of the rack. [4] is a prototype.

The main disadvantage of this method of production is a wide range of chemical elements, insufficient stability of the performance characteristics of sheet metal in thicknesses of 60-90 mm, primarily unstable characteristics, when testing impact samples at temperatures below -60 ° C, which does not allow the use of this product for valves used for transportation of hydrocarbons in the Far North and the Arctic Seas.

The technical results of this invention is the development of a method for the production of rolled products with a thickness of 60-90 mm with a guaranteed yield strength of at least 275 MPa and high impact strength at a test temperature of -60 ° C.

The technical result is achieved by the fact that in the method of production of rolled steel from low alloy steel for the manufacture of structural elements of oil and gas pipelines, including the production of slabs, their austenization, deformation in a given temperature range and cooling to a regulated temperature, in contrast to the closest analogue, slabs of the following chemical composition wt.% Are obtained :

Carbon 0.09-0.11 Manganese 1.45-1.60 Silicon 0.40-0.50 Sulfur 0.001-0.005 Phosphorus 0.005-0.015 Chromium 0.20-0.30 Copper 0.15-0.25 Nickel 0.001-0.30 Aluminum 0.02-0.05 Titanium 0.015-0.03 Iron Rest

austenization is performed at a temperature of 1180-1210 ° C, preliminary deformation is carried out at a temperature of 940-1180 ° C with relative compressions in one pass of at least 12%, then the deformed workpiece is cooled to a temperature of 720-780 ° C in air, the final deformation is carried out to temperature in the range of 750-790 ° C with a total compression of 50-60%, accelerated cooling of the finished product is carried out from a temperature range of 730-770 ° C to a temperature range of 580-620 ° C with a cooling rate of 15-20 ° C / sec.

Increasing the impact strength at low temperatures is achieved by ensuring the best metallurgical quality of the workpiece by reducing harmful impurities, gases and non-metallic inclusions, a narrow range of chemical elements, as well as grinding grain during rolling of the workpiece and forming a structure with a given morphology.

Modification of molten steel with calcium reduces the overall level of metal contamination with non-metallic inclusions, allows for a low mass fraction of sulfur and prevents the formation of inclusions of unfavorable morphology (acute-angled, film), leading to a decrease in cold resistance of rolled products. Oxide and sulfide inclusions during the modification of steel with calcium are small inclusions of a globular shape that do not affect the level of cold resistance [5-8].

Regulation of the content of impurity elements, especially sulfur and phosphorus, provides high steel resistance to brittle and layered fractures in the direction of sheet thickness and welded joints. With an increase in sulfur content, the number of sulfide inclusions causing layered fracture increases, the work of crack propagation and toughness decrease [9]. Sulfur increases the tendency of the metal to form cracks during welding due to the formation of dispersed film precipitates of sulfides in the weld zone. The harmful effect of phosphorus is based on its influence on the expansion of the liquidus-solidus region, leading to the development of primary segregation processes. As well as a significant narrowing of the G-region, which facilitates the development of segregation in the solid state [10].

Aluminum is introduced into steel as a deoxidizer, as well as for the purpose of grinding grain. When the aluminum content in steel exceeds 0.05%, the steel purity decreases with respect to non-metallic inclusions of the aluminum oxide system, which adversely affects the mechanical properties of the base metal and welded joints.

The most effective mechanism for improving the cold resistance is the grinding of real grain. The refinement of the structure is achieved by the use of complex alloying with titanium, chromium, and copper, which, forming fine particles, inhibit the growth of austenite grains during heating and have an inhibitory effect on collective recrystallization during the high-temperature rolling stage.

Titanium is a strong carbide-forming element, contributing to the grinding of grain at a selected concentration due to the formation of dispersed compounds with nitrogen. Dispersed nitrides modify the cast structure, providing a fine austenitic grain that is not subject to significant growth at selected heating temperatures for rolling.

Alloying with titanium, chromium and copper within the claimed limits contributes to the effective creation during the rolling process and accelerated cooling of ultrafine-grained ferrite-pearlite or ferrite-bainitic structure, with fine particles of titanium carbonitrides stabilizing the created structure during operational influences.

At a low alloying level of the basic composition of steel with chromium (up to 0.6%), it does not lead to a noticeable deterioration in the brittle fracture resistance characteristics; in all other cases, a monotonic increase in t ₅₀ with an increase in chromium content is observed [11].

The main distinguishing features of the production method are:

- a narrow range of chemical elements;

- restriction of grain growth due to fine precipitates of titanium carbonitrides when heated for rolling in the temperature range of 1180-1210 ° C, allowing to provide the most complete dissolution of finely dispersed particles of chromium and copper to further improve the cold-resistance characteristics of steel;

- increasing the temperature range of the first (draft) rolling stage to 940-1180 ° C and single compression of more than 12% for grinding austenitic grain due to the processes of recrystallization and deformation;

- ensuring the temperature of the end of rolling sheets with a thickness of 60-90 mm in the temperature range 750-790 ° C with a total compression of 50-60% for the formation of a finely divided structure;

- regulation of the temperature range of accelerated cooling at a temperature of 580-620 ° C allowing the formation of a uniform ferrite-pearlite or ferrite-bainitic structure over the entire thickness of the rolled product;

Tests of sheet metal manufactured by this technology showed that the proposed modes for steel of the selected chemical composition provide stable resistance to brittle fracture at temperatures up to -70 ° C on impact specimens with a “sharp” notch in rolled 60-90 mm thick.

Example:

Steel was smelted in a 370-ton oxygen converter with a magnesium desulfurization process in a casting ladle. Initial alloying, preliminary deoxidation, and metal treatment with argon in a steel pouring ladle were carried out at the outlet. The final alloying, microalloying, metal processing with calcium and evacuation were carried out on a two-position installation “Ladle furnace”. Casting was carried out at a continuous casting machine with metal protection with argon from secondary oxidation on workpieces 300 mm thick. The chemical composition of steel is given in table 1.

According to the specified method, the preform was subjected to austenization at a temperature of 1180-1210 ° C for 5-7 hours. Rolling on sheets with a thickness of 60-90 mm was carried out on a reversible plate mill with a maximum force of 11 thousand tons. Rolling was carried out in two stages: roughing and finishing. In the draft stage, the deformation was carried out with strictly regulated reductions, at least 12% in one pass, in the temperature range 940-1180 ° C. The reel was cooled in air to a temperature of 720-780 ° C. Deformation in the finishing stage was carried out in the temperature range 750-790 ° C with a total compression of 50-60%. After deformation, the sheets were cooled in an accelerated cooling unit to a temperature range of 580-620 ° C with a cooling rate of 15-20 ° C / s

The mechanical properties (Table 2) of sheet metal were determined on transverse samples. Static tensile tests were carried out on type III specimens according to GOST 1497, and impact bending on specimens with a V-shaped notch (type 11, GOST 9454).

The results of mechanical properties depending on the chemical composition and technological parameters are presented in table 1 and 2.

The test results show that the proposed production method for steel of the selected chemical composition provides a more stable level of “cold resistance" at low temperatures that meet the requirements of "Hot-rolled sheet metal from low-alloy steel grade 09G2S" (TS 14-101-627-2007 with changes 1, 2) than the known method.

Table 1 Chemical composition Mode of production Rental options FROM Si Mn S P Ni Cr Cu Ti Al Fe no more or within rest Prototype 0.008-0.10 0.008-0.63 0.008-1.53 0.001-0.008 0.008-0.010 0.001-0.27 0.001-0.25 0.001-0.27 0.01-0.021 0.02-0.06 The claimed one 0.10 0.43 1,53 0.003 0.008 0,03 0.23 0.20 0,021 0,032 2 0.10 0.43 1,53 0.003 0.008 0,03 0.23 0.20 0,021 0,032 3 0.11 0.42 1.51 0.003 0.01 0.04 0.23 0.18 0.019 0,031 four 0.10 0.50 1.47 0.002 0.009 0.05 0.28 0.21 0.024 0,043 5 0.11 0.45 1,53 0.004 0.010 0.06 0.21 0.21 0,020 0,031

Literary sources

1. RF patent No. 2062795 IPC C21D 9/46, C21D 8/02 1996

2. Japanese application No. 61-163210, IPC C21D 8/00, 1986

3. Japanese application No. 61-223125, IPC C21D 8/02, C22C 38/54, 1986

4. Patent No. 2311465, IPC. C21D 8/02, 2005.

5. Berezhnitsky L.T., Gromyak R.S., Trush I.I. // FKHMM. 1975. No. 5, p.40.

6. Brodetsky I.L., Kharchevnikov V.P., Trotsan A.I. et al. On the effect of calcium on grain boundary embrittlement of structural steel with carbonitride hardening. MITOM. 1995, No. 5. p.24-26.

7. Kovalenko B.C., Kuchkin V.I., Pilchuk V.E., Zayats E.L. On the effect of calcium on the structure and properties of steel. Metals, 1983, No. 6. p. 92-96.

8. Volchok I.P., Fedkov V.A., Lutov M.V. Non-metallic inclusions and steel failure at low temperatures. FKHMM, 1977, No. 2, pp. 10-12.

9. Odessa P.D., Smirnov L.A., Kulik D.V. Micro-alloyed steels for northern and unique metal structures. M .: Intermet Engineering, 2006, 176 p.

10. Goodremont E. Special steel. 2nd ed. M., Metallurgy, 1966, v. 1-2.

11. Shabalov IP, Morozov Yu.D., Efron LI, “Steel for pipes and building structures with enhanced operational properties”. - M.: ZAO Metallurgizdat, 2003. p. 20.

Claims (1)

A method of manufacturing rolled steel from low alloy steel for the manufacture of structural elements of oil and gas pipelines, including the preparation of billets, their austenization, rough and finish hot rolling in a given temperature range and accelerated cooling to a regulated temperature, characterized in that billets of the following chemical composition are obtained, wt.%:
carbon 0.09-0.11 manganese 1.45-1.60 silicon 0.40-0.50 sulfur 0.001-0.005 phosphorus 0.005-0.015 chromium 0.20-0.30 copper 0.15-0.25 nickel 0.001-0.30 aluminum 0.02-0.05 titanium 0.015-0.03 iron rest,
austenization is carried out at a temperature of 1180-1210 ° C, rough rolling is carried out at a temperature of 940-1180 ° C with relative compressions in one pass of at least 12%, then the deformed workpiece is cooled to a temperature of 720-780 ° C in air, finishing rolling is carried out in a temperature range of 750-790 ° C with a total compression of 50-60%, and accelerated cooling of the finished product is carried out from a temperature range of 730-770 ° C to a temperature range of 580-620 ° C with a cooling rate of 15-20 ° C / s.