08cr2almoe-21 steel and a preparation method thereof

Abstract

This invention relates to the field of alloy preparation technology, specifically to a 08Cr2AlMoE-21 steel and its preparation method. This invention discloses a 08Cr2AlMoE-21 steel and its preparation method. This invention employs EBT electric arc furnace smelting-LF refining-VD vacuum refining-continuous casting processes, combined with strict control of elements such as carbon, silicon, manganese, phosphorus, sulfur, chromium, aluminum, molybdenum, oxygen, hydrogen, and nitrogen, to develop a low-alloy heat-resistant steel grade 08Cr2AlMoE-21 specifically designed to resist hydrogen sulfide stress corrosion. The 08Cr2AlMoE-21 prepared by this invention possesses both excellent mechanical and processing properties, and the finished pipe exhibits strong corrosion resistance, meeting application requirements.

Description

Technical Field

[0001] This invention relates to the field of alloy preparation technology, specifically to a 08Cr2AlMoE-21 steel and its preparation method. Background Technology

[0002] In the wet hydrogen sulfide environment of petrochemical / refining processes, 12Cr2Mo tube bundles have a lifespan of only 4-6 months, frequently leading to leaks. While 12Cr2AlMoV exhibits good corrosion resistance, it suffers from poor weldability, high hardness (HB as high as 40-50), and difficulty in cold bending into tubes, making it unsuitable for manufacturing. 08Cr2AlMo, a low-carbon, low-sulfur, high-alumina alloy structural steel, possesses excellent comprehensive properties, including high hardness, uniform texture, resistance to hydrogen sulfide stress corrosion without cracking, and long fatigue life. It is a high-end steel grade for pipes, widely used in petrochemicals, boiler pressure vessels, and heat exchangers.

[0003] However, 08Cr2AlMo has extremely strict requirements for the precision of chemical composition, purity of molten steel, gas content, and surface quality of the billet, especially the aluminum content, which must be controlled between 0.30% and 0.70%, posing challenges to the smelting and continuous casting processes. Aluminum is a strong deoxidizing element and also an important alloying element for refining grains and improving corrosion resistance. High-aluminum steel is prone to problems such as increased Al2O3 inclusions, nozzle turbulence, and surface cracks in the billet during smelting. Therefore, developing a special low-alloy heat-resistant steel grade 08Cr2AlMoE-21 resistant to hydrogen sulfide stress corrosion and systematically studying the control of smelting and continuous casting processes are of great significance for improving its product quality and production stability. Summary of the Invention

[0004] The purpose of this invention is to provide a 08Cr2AlMoE-21 steel and its preparation method to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a 08Cr2AlMoE-21 steel, wherein the chemical composition of the 08Cr2AlMoE-21 steel, by weight percentage, consists of the following components: C: 0.05~0.10%; Si: 0.15~0.40%; Mn: 0.20~0.50%; P≤0.015%; S≤0.007%; Cr: 2.25~2.50%; Mo: 0.60~0.70%; Al: 0.30~0%. 50%; Ca: 0.0008~0.0020%; Cu≤0.20%; Ni≤0.20%; Nb≤0.20%; V≤0.05%; As≤0.015%; Sn≤0.015%; Sb≤0.010%; Pb≤0.010%; Bi≤0.010%; As+Sn+Sb+Pb+Bi≤0.035%; H≤0.0002%; O≤0.0020%; N≤0.0070%; Balance is Fe and unavoidable impurities.

[0006] A method for preparing 08Cr2AlMoE-21 steel includes: EAF electric arc furnace smelting - LF refining - VD vacuum refining - continuous casting; the specific steps are as follows:

[0007] S1, EBT electric arc furnace smelting

[0008] EAF electric arc furnace smelting: Steel should be tapped with C ≤ 0.06 wt.%, P ≤ 0.010 wt.%, and the temperature should reach 1610~1650℃, with a tapping rate of 125t. After tapping, 800kg / furnace of lime, 300kg / furnace of aluminum blocks, and 300kg / furnace of ferrosilicon are added, followed by the addition of alloying elements Mn and Cr. The Mn content in the molten steel should be 0.28~0.35 wt.%, and the Cr content 2.00~2.35 wt.%. Slag discharge after tapping is strictly prohibited.

[0009] S2, LF Refining

[0010] After entering the LF (Refining Processing Unit), slag is formed by energizing for 10 minutes. Once the molten steel temperature exceeds 1550℃, samples are taken for testing, and Al is added to 0.060 wt.%. Calcium carbide and lime are added, and the refining white slag time is controlled to ≥15 minutes. The total calcium carbide usage is 1.5 kg / t, and the lime usage is 0~200 kg / furnace. Mn and Cr are added to adjust the Cr / Mn content. Before refining and exiting the station, aluminum wire is fed, and the target Al range for the ladle is 0.500~0.520 wt.%. Si exiting the station is controlled according to the lower limit of the internal control.

[0011] S3, VD vacuum treatment

[0012] During the VD vacuum treatment process, the vacuum degree is <67Pa, the holding time is 15min, and after breaking the vacuum, aluminum wire is added to replenish Al to the target value of 0.440wt.%; the soft blowing time after breaking the vacuum is not less than 20min; no calcium is added during VD vacuum treatment.

[0013] S4, Continuous Casting

[0014] The billet cross-section of the continuous casting machine is 180mm wide and 180mm high; the billet casting speed during continuous casting is 1.70m / min, and the primary cooling water flow rate is 120m³ / min. 3 / h; specific water volume is 0.4L / Kg; continuous casting tundish baking and pouring zone temperature >1200℃, baking time >4h, protective pouring is used throughout the process; long nozzle argon flow rate is 150L / min.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0016] This invention provides a 08Cr2AlMoE-21 steel. To ensure the mechanical properties and service conditions of the steel in applications, this invention precisely controls the composition of each alloying element. Specifically: This invention strictly controls the carbon (C) content to 0.05–0.10 wt.%, thereby meeting the basic strength and hardness requirements and avoiding cold penetration cracking, weld hardening, and decreased resistance to SSCC due to excessive carbon content, while also addressing the insufficient strength caused by insufficient carbon content. The silicon (Si) content is controlled at 0.15–0.40%, which effectively achieves deoxidation, improves the fluidity of molten steel, and facilitates billet formation. Strict control of the upper limit avoids deterioration of low-temperature toughness and corrosion resistance. The manganese (Mn) content is 0.20–0.50%, which can moderately strengthen and toughen the steel and refine the microstructure. Excessive levels are strictly prohibited to avoid exacerbating segregation, increasing inclusions, and reducing resistance to HIC. Phosphorus content (P) ≤0.015% suppresses grain boundary segregation to maintain toughness and resistance to stress corrosion, preventing toughness deterioration, internal bending of tubes, and stress corrosion cracking. Sulfur content (S) ≤0.007% reduces sulfide inclusions and eliminates defects such as hydrogen-induced cracking, corrosion pitting, and tube perforation. Chromium (Cr) content controlled at 2.25–2.50% is crucial for ensuring resistance to wet H2S and uniform corrosion. Aluminum (Al) content controlled at 0.30–0.50% not only avoids defects such as insufficient deoxidation due to low aluminum content and casting nodules due to high aluminum content, but also promotes the formation of a dense oxide film, improving resistance to H2S corrosion. Molybdenum (Mo) content of 0.60–0.70% enhances tempering stability, resistance to hydrogen embrittlement and stress corrosion, and stable smelting can avoid batch-to-batch variations in tube bundles, extending service life.

[0017] Furthermore, this invention strictly controls the oxygen (O), hydrogen (H), and nitrogen (N) content in the steel, controlling the total oxygen content to ≤0.0020% to avoid fatigue cracks and corrosion initiation points caused by oxide inclusions; controlling the hydrogen content to ≤0.0002% to avoid hydrogen-induced cracking of steel pipes; and controlling N to ≤0.0070% to avoid the formation of AlN inclusions, which can cause grain boundary embrittlement and reduced cold working plasticity. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The preparation method of 08Cr2AlMoE-21 steel described in Examples 1-3 of this invention includes: EBT electric arc furnace smelting - LF refining - VD vacuum refining - continuous casting; the specific steps are as follows:

[0020] S1, EBT electric arc furnace smelting

[0021] EAF electric arc furnace smelting: Steel should be tapped with C ≤ 0.06 wt.%, P ≤ 0.010 wt.%, and the temperature should reach 1610~1650℃, with a tapping rate of 125t. After tapping, 800kg / furnace of lime, 300kg / furnace of aluminum blocks, and 300kg / furnace of ferrosilicon are added, followed by the addition of alloying elements Mn and Cr. The Mn content in the molten steel should be 0.28~0.35 wt.%, and the Cr content 2.00~2.35 wt.%. Slag discharge after tapping is strictly prohibited.

[0022] S2, LF Refining

[0023] After entering the LF (Refining Processing Unit), slag is formed by energizing for 10 minutes. Once the molten steel temperature exceeds 1550℃, samples are taken for testing, and Al is added to 0.060 wt.%. Calcium carbide and lime are added, and the refining white slag time is controlled to ≥15 minutes. The total calcium carbide usage is 1.5 kg / t, and the lime usage is 0~200 kg / furnace. Mn and Cr are added to adjust the Cr / Mn content. Before refining and exiting the station, aluminum wire is fed, and the target Al range for the ladle is 0.500~0.520 wt.%. Si exiting the station is controlled according to the lower limit of the internal control.

[0024] S3, VD vacuum treatment

[0025] During the VD vacuum treatment process, the vacuum degree is <67Pa, the holding time is 15min, and after breaking the vacuum, aluminum wire is added to replenish Al to the target value of 0.440wt.%; the soft blowing time after breaking the vacuum is not less than 20min; no calcium is added during VD vacuum treatment.

[0026] S4, Continuous Casting

[0027] The billet cross-section of the continuous casting machine is 180mm wide and 180mm high; the billet casting speed during continuous casting is 1.70m / min, and the primary cooling water flow rate is 120m³ / min. 3 / h; specific water volume is 0.4L / Kg; continuous casting tundish baking and pouring zone temperature >1200℃, baking time >4h, protective pouring is used throughout the process; long nozzle argon flow rate is 150L / min.

[0028] Example 1: A 08Cr2AlMoE-21 steel is provided, wherein the chemical composition of the 08Cr2AlMoE-21 steel, by weight percentage, consists of the following components: C: 0.058%; Si: 0.18%; Mn: 0.25%; P≤0.015%; S≤0.007%; Cr: 2.27%; Mo: 0.64%; Al: 0.32%; Ca: 0.0009%; Cu≤0.20%; Ni≤0.20%; Nb≤0.20%; V≤0.05%; As≤0.015%; Sn≤0.015%; Sb≤0.010%; Pb≤0.010%; Bi≤0.010%; As+Sn+Sb+Pb+Bi≤0.035%; H≤0.0002%; O≤0.0020%; N≤0.0070%; the balance being Fe and unavoidable impurities.

[0029] Example 2: A 08Cr2AlMoE-21 steel is provided, wherein the chemical composition of the 08Cr2AlMoE-21 steel, by weight percentage, consists of the following components: C: 0.07%; Si: 0.31%; Mn: 0.32%; P≤0.015%; S≤0.007%; Cr: 2.32%; Mo: 0.64%; Al: 0.39%; Ca: 0.0015%; Cu≤0.20%; Ni≤0.20%; Nb≤0.20%; V≤0.05%; As≤0.015%; Sn≤0.015%; Sb≤0.010%; Pb≤0.010%; Bi≤0.010%; As+Sn+Sb+Pb+Bi≤0.035%; H≤0.0002%; O≤0.0020%; N≤0.0070%; the balance being Fe and unavoidable impurities.

[0030] Example 3: A 08Cr2AlMoE-21 steel is provided, wherein the chemical composition of the 08Cr2AlMoE-21 steel, by weight percentage, consists of the following components: C: 0.094%; Si: 0.38%; Mn: 0.46%; P≤0.015%; S≤0.007%; Cr: 2.45%; Mo: 0.69%; Al: 0.48%; Ca: 0.0019%; Cu≤0.20%; Ni≤0.20%; Nb≤0.20%; V≤0.05%; As≤0.015%; Sn≤0.015%; Sb≤0.010%; Pb≤0.010%; Bi≤0.010%; As+Sn+Sb+Pb+Bi≤0.035%; H≤0.0002%; O≤0.0020%; N≤0.0070%; the balance being Fe and unavoidable impurities.

[0031] The 08Cr2AlMoE-21 steel prepared in Examples 1-3 of this invention is of excellent quality. The hardness of the finished tubes is stable at ≤75HRB, meeting the requirements for heat exchanger tube bending, expansion, and vibration resistance. It exhibits good machinability and mechanical strength, and does not crack, peel, or fold internally during skew rolling, cold drawing / cold rolling, and U-bending. The finished tubes also demonstrate strong corrosion resistance, meeting standards for resistance to wet H2S stress corrosion cracking (SSCC), HIC, and HCl dew point corrosion.

[0032] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 08Cr2AlMoE-21 steel, characterized in that: The process includes the following steps: EBT electric arc furnace smelting - LF refining - VD vacuum refining - continuous casting; the specific steps are as follows: S1, EBT electric arc furnace smelting: EAF electric arc furnace smelting, controlling the steel output C≤0.06wt.%, P≤0.010wt.%, and tapping the steel after the temperature reaches 1610~1650℃, with a steel output of 125t; after tapping, add 800kg / furnace of lime, 300kg / furnace of aluminum blocks, and 300kg / furnace of ferrosilicon, and then add alloying elements Mn and Cr in sequence, with the Mn content in the molten steel being 0.28~0.35wt.% and the Cr content being 2.00~2.35wt.%; slag discharge after tapping is strictly prohibited; S2 and LF refining: After entering the LF furnace, energize for 10 minutes to slag. After the molten steel temperature exceeds 1550℃, take a sample for testing and add Al to 0.060 wt.%; add calcium carbide and lime, and control the white slag refining time to ≥15 minutes; the total calcium carbide usage is 1.5 kg / t, and the lime usage is 0~200 kg / furnace; add Mn and Cr to adjust the Cr / Mn content; feed aluminum wire before refining and the target Al range for the ladle is 0.500~0.520 wt.%. S3, VD Vacuum Treatment: During VD vacuum treatment, the vacuum degree is <67Pa, the pressure holding time is 15min, and after breaking the vacuum, aluminum wire is added to replenish Al to the target value of 0.440wt.%; the soft blowing time after breaking the vacuum is not less than 20min; VD vacuum treatment does not add calcium. S4. Continuous Casting: The cross-sectional dimensions of the billet cast by the continuous casting machine are 180mm wide and 180mm high; the billet casting speed during continuous casting is 1.70m / min, and the primary cooling water flow rate is 120m³ / min. 3 / h; specific water volume is 0.4L / Kg; continuous casting tundish baking and pouring zone temperature >1200℃, baking time >4h, protective pouring is used throughout the process; long nozzle argon flow rate is 150L / min.

2. The 08Cr2AlMoE-21 steel prepared according to claim 1, characterized in that: The chemical composition of the 08Cr2AlMoE-21 steel, by weight percentage, consists of the following components: C: 0.05~0.10%; Si: 0.15~0.40%; Mn: 0.20~0.50%; P≤0.015%; S≤0.007%; Cr: 2.25~2.50%; Mo: 0.60~0.70%; Al: 0.30~0.50%; Ca: 0.0008~0.0020%. %; Cu≤0.20%; Ni≤0.20%; Nb≤0.20%; V≤0.05%; As≤0.015%; Sn≤0.015%; Sb≤0.010%; Pb≤0.010%; Bi≤0.010%; As+Sn+Sb+Pb+Bi≤0.035%; H≤0.0002%; O≤0.0020%; N≤0.0070%; Balance is Fe and unavoidable impurities.