Testing a technology for the production of pump-compressor tubes of steel 08Kh2G2Fa made on the basis of metallized pellets

Abstract

High-strength pump-compressor tubes of strength groups E, L, M, and R under GOST 633 (Oy = 552-930 N/mm 2) are used for extreme service conditions, such as in deep (deeper than 2000 m) wells, to fracture the seam and maintain formation pressure. The technology used to make pump-compressor tubes of steels of type D (steel 45) and 37G2S includes hot rolling followed by cooling in air. As a result, a pearlitic or ferritic-pearlitic structure is formed during cooling, and the guaranteed strength is just 490-530 N/mm 2 (the lowest strength group -D, or group K under GOST 633). To obtain higher strength values, the steel must be made with a stronger structure, such as a martensitic structure, i.e., it is necessary to ensure the complete hardenability of the metal. The latter can be achieved by resorting to quenching in liquids, but the specialized equipment that would be needed is not presently available at factories in Russia and the nations of the CIS (Commonwealth of Independent States). Thus, it is impossible to use the technology which has been adopted in world practice: hot rolling with a specified degree of deformation in a narrow temperature range, followed by controlled cooling and straightening.In light of this, it would be best to make high-strength pipes by using low-carbon martensitic steels with stable austenite [1, 2]. That would ensure the production of pipes with a strength of up to (yy = 930 N/mm 2 (group R -the highest strength group under GOST 633) after hot roiling and quenching in air from the finishing temperature.Thus, quenching is eliminated as a separation operation in the proposed production cycle. The new technology does not require an investment in complicated equipment for quenching and tempering with a controlled feed of coolant -which is necessary to ensure that the cooling of the metal is uniform and that quenching takes place without deformation.It is known that the reliability of pipes in service depends on the strength and fracture toughness. However, increasing the strength of a steel also usually decreases its fracture toughness. One effective method of increasing fracture toughness is using clean charge materials to make the steel [3, 4].Thus, the experimental production of high-strength pipes lbr service under extreme conditions from steel made at OI~MK (Oskol Electrometallurgical Combine) with low contents of sulfur, phosphorus, nonferrous metal impurities, and nonmetallic inclusions by using a "fresh" charge was an important practical test.Features of the technology used to make semifinished tubes of steel 08Kh2G2FA at the OEMK. The electric steelmaking shop at the OI~MK made trial heats of steel 08Kh2G2FA, which is intended for high-strength pipes. The stringent requirements established for pipes of the given type have necessitated the following regimes for steelmaking, out-of-fumace treatment, and continuous casting.The steels were made in a 150-ton electric-arc furnace. To achieve low concentrations of sulfur, phosphorus, and nonferrous-metal impurities, we used a charge con...