Method for controlling smelting process of high-quality and high-grade pipeline steel

Abstract

The invention relates to a method for controlling the smelting process of high-quality and high-grade pipeline steel. The method comprises the working procedures of converter, LF refining, RH refining and continuous casting. In the LF refining process, molten steel is subjected to electric arc heating through an electrode, meanwhile, quicklime, aluminum blocks and the like are added for white slag making, molten steel desulfurization treatment is achieved, after refining is finished, the S content is smaller than or equal to 0.0015%, the temperature of the molten steel is 1630-1660 DEG C, 550-600 kg of silicon-calcium wires are driven into the molten steel for calcium treatment before the molten steel is discharged out of a station, the calcium content of the molten steel after calcium treatment is controlled to be 0.0010-0.0045%, clean blowing treatment is conducted after calcium treatment, the clean blowing time is 6-10 min, and the molten steel is cooled to the room temperature. Two points of the steel ladle are ventilated, and the steel slag liquid level slightly moves and the molten steel is not exposed. The yield strength of the high-quality and high-grade pipeline steel is larger than or equal to 485 MPa, the-20 DEG C low-temperature impact absorption value is larger than or equal to 200 J, and the inclusion rating is that class A and class C are smaller than or equal to 0.5 grade, class B is smaller than or equal to 1.5 grade, and class D is smaller than or equal to 0.5 grade.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for controlling the smelting process of high-quality and high-level pipeline steel. Background Art

[0002] Pipeline steel is mainly used in the construction of oil and natural gas pipelines. The particularity of the transportation medium indicates special requirements for pipeline steel products, especially key engineering projects such as the West-East Gas Pipeline and the China-Russia Natural Gas Pipeline. Their ultra-long transportation distances and large-diameter pipelines require pipeline steel to withstand long-term high-pressure tolerance, that is, the product must have high strength, good impact toughness and internal quality.

[0003] At present, the domestic pipeline steel production technology is relatively mature, and many steel companies have the stable production capacity of X80 and below grade pipeline steel coils. However, with the advancement of natural gas pipeline laying projects, pipeline laying routes tend to be complex, and pipelines in many locations need to withstand high altitude, severe cold, open-air laying and other service environments. Therefore, the pipeline design indicators for indicators such as low-temperature toughness are more stringent than the standard requirements. At the same time, the complexity of the transportation medium of some projects also puts forward special requirements for the internal quality of pipeline steel. Therefore, it is urgent to develop a high-quality and high-level pipeline steel smelting process control method to further improve the inclusion level and low-temperature toughness index of pipeline steel.

[0004] The patent with publication number CN107365890 discloses "A method for controlling inclusions in X80 pipeline steel", including: 1) molten iron pretreatment: when the sulfur content in the molten iron is ≤0.003wt%, it is transferred to the converter for smelting; 2) converter smelting: the carbon content in the molten steel is ≤0.06wt%, the oxygen content is 0.05~0.09wt%, and the steel is tapped when the molten steel temperature in the converter reaches 1650~1690℃; 3) LF electric furnace refining: when the sulfur content in the steel is ≤0.002wt%, silicon alloy is added, and when the molten steel temperature reaches 1630~1650℃, it is transferred to the vacuum refining process; 4) RH vacuum refining: Ca treatment is performed after vacuum treatment: the weight ratio of Ca / s in the molten steel is controlled to be 2~5, and it is transferred to the continuous casting process; 5) continuous casting: a covering agent is added for protective pouring. This invention mainly achieves the purpose of controlling inclusions in steel by adjusting the deoxidation process, but this method has low requirements for the C at the converter end point. Although the inclusion control level is improved, the increase in C content will deteriorate the low-temperature toughness to a certain extent.

[0005] The patent with publication number CN114058978 discloses "X80 pipeline steel with low temperature toughness", which is an X80 pipeline steel with low temperature toughness. The chemical composition of the X80 pipeline steel with low temperature toughness includes C, Mn, S, P, Si, Nb, Ti, Mo, Cu, Ni, Cr, limiting elements B, Ca, N, O, and the rest are iron and unavoidable impurities. It is obtained according to the following steps: the pipeline steel continuous casting billet is subjected to heating, rough rolling, finish rolling, rapid cooling and coiling to obtain the X80 pipeline steel with low temperature toughness. The invention improves the low temperature toughness of X80 pipeline steel by optimizing the chemical composition of pipeline steel, controlled rolling and controlled cooling processes, etc., and utilizing the fine grain strengthening effect. However, the addition of Ni and Mo elements will significantly increase the manufacturing cost of pipeline steel and reduce product benefits.

[0006] It can be seen from the above literature that the current high-level pipeline steel mainly provides methods such as relaxing the C content control and adding Ni, Mo precious alloys to achieve the purpose of increasing the level of inclusions in the steel or improving the low-temperature toughness. This either has certain side effects or will significantly increase the manufacturing cost. No one has proposed how to improve the level of inclusions in the steel by optimizing the smelting method without sacrificing product quality or manufacturing cost. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-quality and high-level pipeline steel smelting process control method, which can provide good quality ingots for subsequent rolling, so that the final product has good inclusion rating and low-temperature toughness.

[0008] In order to solve the above technical problems, the technical scheme adopted by the present invention is: a high-quality and high-level pipeline steel smelting process control method, the method comprises converter, LF refining, RH refining, and continuous casting processes; in the LF refining process, the molten steel is arc heated by electrodes, and quicklime, aluminum blocks and other white slag are added at the same time to achieve molten steel desulfurization treatment. After the refining, the S content is ≤0.0015%, the molten steel temperature is 1630-1660°C, and 550-600kg / furnace (converter volume 260t) of silicon calcium wire is driven into the furnace before leaving the station for calcium treatment. After the calcium treatment, the calcium content of the molten steel is controlled at 0.0010-0.0045%, and the clean blowing treatment is carried out after the calcium treatment. The clean blowing time is 6-10min, and the ladle is required to be breathable at two points, and the slag liquid level moves slightly without exposing the molten steel.

[0009] The converter process of the present invention adopts a top and bottom double-blowing alkaline converter and a one-key steelmaking mode, with a molten steel blowing stop C≤0.04%, a blowing stop P≤0.010%, and a blowing stop temperature of 1560-1610°C.

[0010] The RH process of the present invention uses a vacuum chamber to degas and remove inclusions from the molten steel. The vacuum degree of the vacuum chamber is reduced to ≤1mbar and maintained. Argon gas is introduced into an immersion tube with an argon gas flow rate of 2000-4000m 3 / min, to make the molten steel circulate, and the vacuum treatment time is 15 to 30 minutes.

[0011] The continuous casting process of the present invention adopts conventional slab continuous casting production technology. After the molten steel in the ladle is hoisted to the continuous casting turntable, it flows into the tundish through the long water inlet and then flows into the continuous casting machine crystallizer through the SEN. The continuous casting machine adopts a constant pulling speed casting of 0.9 to 1.2 m / min. The fan-shaped segment is subjected to 8 mm light pressure reduction control at the solidification end, and the resulting cast billet is cold inspected off the line.

[0012] The high-quality and high-grade pipeline steel of the present invention has a thickness of 12 to 20 mm.

[0013] The high-quality and high-level pipeline steel prepared by the method of the present invention has a yield strength of ≥485MPa and a low-temperature impact absorption value of -20°C of ≥200J.

[0014] The inclusion rating of the high-quality and high-level pipeline steel prepared by the method of the present invention is: Class A, Class C ≤ Grade 0.5, Class B ≤ Grade 1.5, Class D ≤ Grade 0.5.

[0015] The present invention significantly improves the purity of molten steel by adjusting the smelting process without increasing the manufacturing cost, thereby achieving the purpose of improving the level of inclusions and low-temperature toughness in the steel. The main method is: adjusting the time of calcium treatment in the refining process, migrating the calcium treatment after RH refining of conventional pipeline steel to calcium treatment after LF refining, calcium elements and alumina generated in the LF refining process form low-melting point complex oxides, completing the transformation from pointed clusters to spherical, using the subsequent RH vacuum refining and clean blowing process to collide, grow, fully float, and achieve the smelting of high-cleanliness molten steel.

[0016] The beneficial effect of adopting the above technical solution is that the method of the present invention obtains a high-quality and high-grade pipeline steel with a yield strength of ≥485MPa, a low-temperature impact absorption value of -20°C ≥200J, and inclusion ratings: Class A, Class C ≤0.5, Class B ≤1.5, and Class D ≤0.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a micrograph of inclusion rating of high-quality, high-grade pipeline steel of Example 1. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Example 1

[0019] The thickness of the high-grade pipeline steel based on the high-quality high-grade pipeline steel smelting process control method in this embodiment is 12 mm. The production method includes converter, LF refining, RH, and continuous casting processes. The specific process steps are as follows: (1) Converter process: The C content of molten steel at the end of blowing is 0.04%, the P content at the end of blowing is 0.010%, and the blowing temperature is 1560℃.

[0020] (2) LF refining process: After refining, the S content is 0.0015%, the molten steel temperature is 1630℃, 550kg of silicon-calcium wire is injected, the calcium content of the molten steel is 0.0010%, the net blowing time is 6min, the ladle is ventilated at two points, the slag liquid surface moves slightly and the molten steel is not exposed.

[0021] (3) RH process: the vacuum degree of the vacuum chamber is reduced to 1 mbar, and the argon flow rate is 2000 m 3 / min, vacuum treatment time 30min.

[0022] (4) Continuous casting process: pouring at a constant pulling speed of 0.9 m / min, and a light pressure reduction control of 8 mm at the end of solidification of the fan-shaped segment. The resulting ingot is cold inspected off the line.

[0023] The pipeline steel with a thickness of 12 mm produced in this embodiment has the following mechanical properties test and plate shape test results: yield strength 515 MPa, -20°C low temperature impact absorption value 260 J, inclusion rating: Class A, Class C 0, Class B 1.5, Class D 0.5. Figure 1 This is a micrograph of inclusion rating of high-quality and high-grade pipeline steel in Example 1 (the figures of other examples are similar and therefore omitted). Example 2

[0024] The thickness of the high-grade pipeline steel based on the high-quality high-grade pipeline steel smelting process control method in this embodiment is 20 mm. The production method includes converter, LF refining, RH, and continuous casting processes. The specific process steps are as follows: (1) Converter process: The C content of molten steel at the end of blowing is 0.02%, the P content at the end of blowing is 0.006%, and the blowing temperature is 1610℃.

[0025] (2) LF refining process: After refining, the S content is 0.0005%, the molten steel temperature is 1660℃, 600kg of silicon-calcium wire is injected, the calcium content of the molten steel is 0.0045%, the net blowing time is 10min, the ladle is ventilated at two points, the slag liquid surface moves slightly and the molten steel is not exposed.

[0026] (3) RH process: the vacuum degree of the vacuum chamber is reduced to 0 mbar, and the argon flow rate is 4000 m 3 / min, vacuum treatment time 15min.

[0027] (4) Continuous casting process: pouring at a constant pulling speed of 1.2 m / min, and a light pressure reduction control of 8 mm at the end of the solidification of the fan-shaped segment. The resulting ingot is cold inspected off the line.

[0028] The pipeline steel with a thickness of 20 mm produced in this embodiment has the following mechanical properties test and plate shape test results: yield strength 620 MPa, -20°C low temperature impact absorption value 450 J, inclusion rating: Class A, Class C 0, Class B 0.5, Class D 0.5. Example 3

[0029] The thickness of the high-grade pipeline steel based on the high-quality high-grade pipeline steel smelting process control method in this embodiment is 14 mm. The production method includes converter, LF refining, RH, and continuous casting processes. The specific process steps are as follows: (1) Converter process: The C content of molten steel at the end of blowing is 0.03%, the P content at the end of blowing is 0.006%, and the blowing temperature is 1570℃.

[0030] (2) LF refining process: After refining, the S content is 0.0010%, the molten steel temperature is 1640℃, 560kg of silicon-calcium wire is injected, the calcium content of the molten steel is 0.0020%, the net blowing time is 8min, the ladle is ventilated at two points, the slag liquid surface moves slightly and the molten steel is not exposed.

[0031] (3) RH process: the vacuum degree of the vacuum chamber is reduced to 0.1 mbar, and the argon flow rate is 2400 m 3 / min, vacuum treatment time 18min.

[0032] (4) Continuous casting process: pouring at a constant pulling speed of 0.95 m / min, and a light pressure reduction control of 8 mm at the end of solidification of the fan-shaped segment. The resulting ingot is cold inspected off the line.

[0033] The pipeline steel with a thickness of 14 mm produced in this embodiment has the following mechanical properties test and plate shape test results: yield strength 525 MPa, -20°C low temperature impact absorption value 420 J, inclusion rating: Class A, Class C 0, Class B 0.5, Class D 0.5. Example 4

[0034] The thickness of the high-grade pipeline steel based on the high-quality high-grade pipeline steel smelting process control method in this embodiment is 18 mm. The production method includes converter, LF refining, RH, and continuous casting processes. The specific process steps are as follows: (1) Converter process: The C content of molten steel at the end of blowing is 0.02%, the P content at the end of blowing is 0.009%, and the blowing temperature is 1600℃.

[0035] (2) LF refining process: After refining, the S content is 0.0012%, the molten steel temperature is 1650℃, 570kg of silicon-calcium wire is injected, the calcium content of the molten steel is 0.0040%, the net blowing time is 8min, the ladle is ventilated at two points, the slag liquid surface moves slightly and the molten steel is not exposed.

[0036] (3) RH process: the vacuum degree of the vacuum chamber is reduced to 0.2 mbar, and the argon flow rate is 3200 m 3 / min, vacuum treatment time 20min.

[0037] (4) Continuous casting process: pouring at a constant pulling speed of 1.1 m / min, and a light pressure reduction control of 8 mm at the end of the solidification of the fan-shaped segment. The resulting ingot is cold inspected off the line.

[0038] The pipeline steel with a thickness of 18 mm produced in this embodiment has the following mechanical properties test and plate shape test results: yield strength 560 MPa, -20°C low temperature impact absorption value 410 J, inclusion rating: Class A, Class C 0, Class B 1.0, Class D 0.5. Example 5

[0039] The thickness of the high-grade pipeline steel based on the high-quality high-grade pipeline steel smelting process control method in this embodiment is 16 mm. The production method includes converter, LF refining, RH, and continuous casting processes. The specific process steps are as follows: (1) Converter process: The C content of molten steel at the end of blowing is 0.03%, the P content at the end of blowing is 0.008%, and the blowing temperature is 1590℃.

[0040] (2) LF refining process: After refining, the S content is 0.0010%, the molten steel temperature is 1640℃, 580g of silicon-calcium wire is injected, the calcium content of the molten steel is 0.0035%, the net blowing time is 10min, the ladle is ventilated at two points, the slag liquid surface moves slightly and the molten steel is not exposed.

[0041] (3) RH process: the vacuum degree of the vacuum chamber is reduced to 0 mbar, and the argon flow rate is 3600 m 3 / min, vacuum treatment time 26min.

[0042] (4) Continuous casting process: pouring at a constant pulling speed of 1.2 m / min, and a light pressure reduction control of 8 mm at the end of the solidification of the fan-shaped segment. The resulting ingot is cold inspected off the line.

[0043] The pipeline steel with a thickness of 16 mm produced in this embodiment has the following mechanical properties test and plate shape test results: yield strength 550 MPa, -20°C low temperature impact absorption value 390 J, inclusion rating: Class A, Class C 0, Class B 0.5, Class D 0.5.

[0044] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A high-quality and high-grade pipeline steel smelting process control method, characterized in that: The method comprises the steps of converter, LF refining, RH refining and continuous casting; in the LF refining step, the molten steel is arc heated by an electrode, and quicklime, aluminum block and the like are added to form white slag to achieve desulfurization of the molten steel. After the refining, the S content is ≤0.0015%, the temperature of the molten steel is 1630-1660°C, 550-600kg / furnace of silicon-calcium wire is driven into the furnace for calcium treatment before leaving the station, and the calcium content of the molten steel is controlled at 0.0010-0.0045% after the calcium treatment. After the calcium treatment, a clean blowing treatment is performed, and the clean blowing time is 6-10 minutes. It is required that the ladle is breathable at two points, and the slag liquid surface moves slightly without exposing the molten steel.

2. A high-quality and high-grade pipeline steel smelting process control method according to claim 1, characterized in that: The converter process adopts a top and bottom double-blowing alkaline converter and a one-key steelmaking mode, with a molten steel blowing stop C≤0.04%, a blowing stop P≤0.010%, and a blowing stop temperature of 1560-1610°C.

3. A high-quality and high-grade pipeline steel smelting process control method according to claim 1, characterized in that: In the RH process, the molten steel is degassed and impurities are removed by using a vacuum chamber. The vacuum degree of the vacuum chamber is reduced to ≤1 mbar and maintained. Argon gas is introduced into an immersion tube with an argon gas flow rate of 2000-4000 m 3 / min, to make the molten steel circulate, and the vacuum treatment time is 15 to 30 minutes.

4. The method for controlling the smelting process of high-quality and high-grade pipeline steel according to claim 1, characterized in that: The continuous casting process adopts conventional slab continuous casting production technology. After the molten steel in the ladle is hoisted to the continuous casting turntable, it flows into the tundish through the long water inlet, and then flows into the continuous casting machine crystallizer through the SEN. The continuous casting machine adopts a constant pulling speed casting of 0.9 to 1.2 m / min, and a light pressure reduction control of 8 mm is performed at the end of the solidification of the fan-shaped segment. The resulting cast billet is cold inspected off the line.

5. A high-quality and high-grade pipeline steel smelting process control method according to any one of claims 1 to 4, characterized in that: The high-quality and high-grade pipeline steel has a thickness of 12 to 20 mm.

6. A high-quality and high-grade pipeline steel smelting process control method according to any one of claims 1 to 4, characterized in that: The high-quality and high-grade pipeline steel prepared by the method has a yield strength of ≥485MPa and a low-temperature impact absorption value of -20°C of ≥200J.

7. A high-quality and high-grade pipeline steel smelting process control method according to any one of claims 1 to 4, characterized in that: The inclusion ratings of the high-quality and high-grade pipeline steel prepared by the method are: Class A and Class C ≤ Class 0.5, Class B ≤ Class 1.5, and Class D ≤ Class 0.5.

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