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CN-121992286-A - Continuous casting blank for sulfur-resistant pipe and preparation method thereof

CN121992286ACN 121992286 ACN121992286 ACN 121992286ACN-121992286-A

Abstract

The invention relates to a continuous casting blank for a sulfur-resistant pipe and a preparation method thereof, belonging to the technical field of continuous casting blank preparation. The invention provides a preparation method of a continuous casting blank for a sulfur-resistant pipe, which aims to solve the problems of obvious strip-shaped structure, concave surface cracks, poor internal density and low control rate of aluminum element charging in the furnace of the conventional continuous casting blank for the sulfur-resistant pipe. According to the invention, through the cooperative regulation and control of the whole flow of a converter, refining and vacuum, the special refining slag is matched, so that the accurate control of the molten steel components is realized, the component segregation and the impurity aggregation are stopped, the banding structure of the formed billet is less than or equal to 2.0 levels, and the performance requirement of the sulfur-resistant pipe is met. The problem of surface dishing of peritectic steel is solved by combining closed-loop regulation and control of a continuous casting process, the surface quality and the yield of a casting blank are greatly improved, the internal quality qualification rate of the casting blank reaches 100%, the tissue guarantee is provided for sulfur pipe corrosion resistance, and the severe working condition of a high-acidity oil-gas field is adapted.

Inventors

  • LIU JIAQI
  • Wang haida
  • LIAN XINGGUO
  • CHEN LIE

Assignees

  • 建龙北满特殊钢有限责任公司

Dates

Publication Date
20260508
Application Date
20260325

Claims (9)

  1. 1. The preparation method of the continuous casting blank for the sulfur-resistant pipe is characterized by comprising the following steps of: step one, primary smelting in a converter: Molten steel and clean scrap steel are selected As raw materials, as is controlled to be less than or equal to 0.015%, S is controlled to be less than or equal to 0.040%, P is controlled to be less than or equal to 0.130%, the scrap steel is free of harmful element exceeding standard materials, an oxygen top-bottom combined blown converter is adopted for smelting, the tapping C content is 0.04-0.06%, the tapping temperature is not lower than 1600 ℃, the P content is less than or equal to 0.008%, aluminum ingots, alloys, lime and refining slag are added step by step in the tapping process, the in-place Al content of the molten steel is ensured to be stable at 0.040-0.050 wt%, and slag is strictly forbidden; Step two, refining treatment: Heating molten steel to 1580 ℃, carrying out two-stage electrifying refining after temperature measurement and sampling, wherein the total refining time is not less than 60min, the white slag holding time is not less than 30min, feeding calcium wires in the later refining stage, and then carrying out vacuum treatment; step three, vacuum treatment: Controlling the deep vacuum degree to be less than or equal to 67Pa, keeping the vacuum time to be not less than 15min, and keeping the soft blowing time to be not less than 15min after the vacuum breaking; Step four, continuous casting molding: According to the superheat degree matching pulling speed of the molten steel in the tundish, the superheat degree is stabilized at 25+/-3 ℃, the pulling speed is 1.2m/min, the water quantity of a crystallizer is 110m 3 /h, the electromagnetic stirring of the crystallizer is matched with 250A/3Hz, and the electromagnetic stirring of the solidification tail end is 50A/8Hz, so that the continuous casting blank for the sulfur-resisting pipe is prepared.
  2. 2. The method for preparing the continuous casting billet for the sulfur-resistant pipe, according to claim 1, wherein in the first step, the internal control index of molten iron is less than or equal to 0.030%, as is less than or equal to 0.014% and Cr is less than or equal to 0.20%.
  3. 3. The method for producing a continuous casting slab for sulfur-resistant pipe according to claim 1 or 2, characterized in that in step one, the tapping temperature of the transfer furnace is not lower than 1610 ℃, the tapping amount is 100 tons, 160kg of aluminum ingot is added when tapping to 20 tons, 2.6kg/t of ferrosilicon, 11.5kg/t of low carbon ferromanganese are added when tapping to 30 tons, 600kg of lime and 400kg of deoxidized and desulfurized refining slag are added when tapping to 50 tons.
  4. 4. The method for preparing the continuous casting blank for the sulfur-resistant pipe, according to claim 3, wherein 300-400 kg of lime, 0-100 kg of fluorite, 40-60 kg of aluminum particles, 20-30 kg of ferrosilicon powder and 10-20 kg of silicon carbide are added in the second step through electrifying.
  5. 5. The method for preparing the continuous casting blank for the sulfur-resistant pipe, according to claim 4, is characterized in that in the second step, 100-200 kg of lime, 0-50 kg of fluorite, 10-20 kg of aluminum particles, 30-40 kg of silicon carbide or ferrosilicon powder are added in a secondary power-on mode, and the length of a feeding calcium line is 40-80 m.
  6. 6. The method for preparing the continuous casting billet for the sulfur-resistant pipe, as claimed in claim 5, wherein in the fourth step, a six-machine six-strand continuous casting machine is adopted to custom manufacture the round billet with the diameter of 210 mm.
  7. 7. The method for preparing the continuous casting billet for the sulfur-resistant pipe, which is disclosed in claim 6, is characterized in that in the fourth step, double argon sealing protection pouring is adopted, and the full ladle liquid level of the tundish is kept during ladle replacement.
  8. 8. The method for preparing a continuous casting billet for a sulfur-resistant pipe according to claim 7, wherein the heat of the copper tube of the crystallizer in the fourth step is strictly less than or equal to 100.
  9. 9. A continuous casting blank for a sulfur-resistant pipe prepared by the preparation method according to any one of claims 1 to 8, which is characterized by comprising ：C 0.10~0.13%、Si 0.20~0.35%、Mn 0.95~1.10%、P≤0.015%、S≤0.003%、Alt 0.015~0.040%、Cr≤0.30%、N≤0.0120%、O≤0.0010%、Ni≤0.30%、Cu≤0.20%、Mo≤0.10%、As≤0.0150%、Sn≤0.0150%、Pb≤0.0030%、Bi≤0.0030%、Sb≤0.0100%、Ti≤0.04%、V≤0.05%、Ca≤0.006%、B≤0.0005%, weight percent of Fe and unavoidable impurities as the rest, wherein Alt/N is not lower than 2:1, V+Nb is not more than 0.06%, V+Nb+Ti is not more than 0.15%.

Description

Continuous casting blank for sulfur-resistant pipe and preparation method thereof Technical Field The invention belongs to the technical field of continuous casting billet preparation, and particularly relates to a continuous casting billet for a sulfur-resistant pipe and a preparation method thereof. Background The sulfur-resistant pipe is a special industrial pipeline adapting to the working condition of strong corrosive media such as hydrogen sulfide, and the like, is mainly applied to the fields of petroleum and natural gas exploitation, chemical production and the like, and is a key component of an acid oil-gas field development and medium conveying system. The core value of the method is to resist corrosion failure modes such as stress corrosion cracking induced by hydrogen sulfide, hydrogen induced cracking, sulfide stress corrosion cracking and the like, and ensure long-term safe and stable operation of a pipeline system under extremely severe working conditions. At present, the sulfur-resistant pipe is mostly prepared from low-carbon and ultralow-carbon low-alloy steel, corrosion resistance is optimized by adding alloy elements such as chromium, molybdenum and nickel, the content of impurities such as carbon, sulfur and phosphorus is strictly controlled, corrosion sensitivity is reduced, but a plurality of inherent short plates exist in the existing smelting, continuous casting and forming processes, the performance of the pipe is difficult to meet the strict requirements of high-acidity oil-gas fields, and the core technical problem is outstanding. Under the conventional production process, obvious banded structures are easy to appear in the tube blank, the tube blank is influenced by component segregation and uneven distribution of inclusions, ferrite and pearlite are distributed in a layered manner along the rolling direction, the uniformity of a matrix is destroyed, the difference of longitudinal and transverse mechanical properties of the tube is increased, channels for hydrogen atom aggregation and crack initiation and expansion are further formed, the sensitivity of hydrogen induced cracking and sulfide stress corrosion is increased, and the hereditary structure defects are difficult to thoroughly eliminate through subsequent heat treatment. Most of sulfur-resistant tube blanks are peritectic steel, peritectic reaction in the continuous casting process easily causes uneven solidification and shrinkage of a primary green shell and unbalanced heat transfer of a crystallizer, defects such as surface pits and longitudinal cracks of the continuous casting blank are directly caused, the defects are further expanded in subsequent rolling, surface flaws of finished tubes are formed, and stress concentration is generated at the same time, so that the defects become break-up openings for corrosion failure. Meanwhile, the conventional continuous casting process parameters are controlled widely, the defects of loose inside, shrinkage cavity, center segregation and the like of the continuous casting blank are difficult to manage and control, the tissue compactness is insufficient, the overall toughness of the pipe is reduced, and a path is provided for corrosive medium permeation. In addition, aluminum is used as an element easy to oxidize in the smelting process, aluminum oxide inclusion is extremely easy to combine with oxygen to form, the control rate of the effective aluminum element entering the furnace is low, the effects of refining grains and purifying grain boundaries of the aluminum element cannot be fully exerted, the continuity of a matrix can be damaged by hard inclusion, and the corrosion resistance and service life of the sulfur-resistant pipe are further influenced. Disclosure of Invention The invention provides a continuous casting blank for a sulfur-resistant pipe and a preparation method thereof, which are used for solving the problems of obvious strip-shaped structure, concave surface cracks, poor internal density and low control rate of aluminum element entering a furnace of the conventional continuous casting blank for the sulfur-resistant pipe. The technical scheme of the invention is as follows: A preparation method of a continuous casting blank for a sulfur-resistant pipe comprises the following steps: step one, primary smelting in a converter: Molten steel and clean scrap steel are selected As raw materials, as is controlled to be less than or equal to 0.015%, S is controlled to be less than or equal to 0.040%, P is controlled to be less than or equal to 0.130%, the scrap steel is free of harmful element exceeding standard materials, an oxygen top-bottom combined blown converter is adopted for smelting, the tapping C content is 0.04-0.06%, the tapping temperature is not lower than 1600 ℃, the P content is less than or equal to 0.008%, aluminum ingots, alloys, lime and refining slag are added step by step in the tapping process, the in-place Al content of the molten steel is ensu