A method for producing a microalloyed hot-rolled round steel for mooring chains

Abstract

The application discloses a production method of a micro-alloyed hot-rolled round steel for a chain, which utilizes a rare earth and a small amount of Cr, Mo, V and Cu composite alloying mode, and combines with optimized production process parameters to obtain a micro-alloyed hot-rolled round steel for a chain with excellent longitudinal mechanical properties, and meets the requirements of Rm>=1100MPa, Rp0.2>=990MPa, A>=16%, Z>=60%, impact energy KV2 at-20 DEG C >=118J and hydrogen embrittlement performance Z1 / Z2>=0.95.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for producing hot-rolled round steel for microalloyed mooring chains. Background Technology

[0002] With the continuous development of deep-sea oil and marine energy, the demand for deep-sea mooring chains is increasing. Mooring chains withstand complex loads from ocean currents, surges, and strong winds in the deep-sea environment, thus requiring their constituent materials to possess exceptional high strength and tensile properties. Hot-rolled round steel, as a key component of mooring chains, must be able to withstand extremely high tensile forces to ensure the safety and reliability of the entire mooring chain system. The high salinity and corrosiveness of seawater in the deep-sea environment pose challenges to the long-term exposure of mooring chain materials. Hot-rolled round steel products need to possess good corrosion resistance to extend their service life in the marine environment. The temperature fluctuations in the deep-sea environment are significant, and mooring chains need to maintain good toughness at extreme low temperatures to cope with potential impacts and deformations. Through in-depth research and development in these key technologies, the applicant aims to promote the innovation and development of hot-rolled round steel products for mooring chains to meet the urgent need for high-performance materials in the deep-sea energy sector. Summary of the Invention

[0003] The purpose of this invention is to provide a method for producing hot-rolled round steel for mooring chains with microalloying. This method utilizes the principle of composite alloying with trace amounts of rare earth elements and small amounts of Cr, Mo, V, and Cu to significantly improve the hardenability, corrosion resistance, fatigue resistance, and low-temperature toughness of the steel for mooring chains while reducing production costs. This significantly improves the overall lifespan and safety of the steel for mooring chains, thereby producing low-cost, high-performance steel for mooring chains.

[0004] One aspect of this invention provides a method for producing hot-rolled round steel for microalloyed mooring chains, comprising the following process steps: smelting in a combined blowing converter, refining in an LF furnace, vacuum degassing in a VD furnace, continuous casting, heating in a billet heating furnace, and rolling of the round steel; wherein:

[0005] In the aforementioned combined blowing converter smelting process, the final slag basicity is controlled at 3.0, the final control target is C≥0.05%, the temperature is controlled at 1650-1660℃, and SiMn, MnFe and CrFe are used for deoxidation and alloying. The final deoxidation is carried out with Al.

[0006] In the LF refining process, white slag refining is employed, and Ar blowing is carried out throughout the refining process. Desulfurization, composition fine-tuning, and temperature increase operations are performed according to the composition and temperature of the converter steel. The soft blowing time is 10-14 minutes. In the LF refining process, the chemical composition of the molten steel is controlled as follows by mass percentage: C 0.19%~0.24%, Si 0.15%~0.20%, Mn 1.10%~1.20%, P≤0.010%, S≤0.010%, Cr 0.82%~0.90%, Mo 0.10%~0.30%, V 0.60%~0.80%, Cu 0.10%~0.20%, Alt 0.010%~0.030%, Re 0.020%~0.035%, with the remainder being Fe and unavoidable trace impurities.

[0007] In the VD vacuum degassing process, the vacuum degree is controlled at 0.08-0.10 kPa, the deep vacuum time is 18-20 min, after the vacuum is broken, the silicon-calcium wire is fed in, the soft blowing time is 10-14 min, and the molten steel must not be exposed during the soft blowing process.

[0008] In the continuous casting process, constant casting speed control and electromagnetic stirring are adopted. The superheat of molten steel ΔT is 25-26℃. After obtaining the billet, it is placed in a slow cooling pit for slow cooling.

[0009] In the billet heating furnace heating process, the heating temperature is controlled at 1000-1200℃, and the total heating time is not less than 3.5h to prevent overheating, burning and decarburization. The temperature is raised slowly to ensure uniform heating temperature of the billet and reduce temperature difference.

[0010] In the round steel rolling process, the initial rolling temperature is controlled at 1100-1200℃ and the final rolling temperature is controlled at 920-960℃. Attention should be paid to the condition of the rolls, turning machine, guide plate, roller table and cover plate, and they should be kept smooth and free of sharp edges to avoid defects such as scratches and dents on the surface of the rolled workpiece.

[0011] In some embodiments, in the LF refining process, the chemical composition of the molten steel is controlled as follows by mass percentage: C 0.19%–0.24%, Si 0.15%–0.19%, Mn 1.11%–1.16%, P ≤0.010%, S ≤0.010%, Cr 0.82%–0.89%, Mo 0.11%–0.24%, V 0.60%–0.72%, Cu 0.12%–0.18%, Alt 0.014%–0.027%, Re 0.021%–0.032%, with the remainder being Fe and unavoidable trace impurities.

[0012] In some embodiments, the billet obtained in the continuous casting process is a rectangular billet with dimensions of 320mm × 415mm.

[0013] In some embodiments, the continuous casting process involves slow cooling in a slow cooling pit for 48 hours.

[0014] In some embodiments, the longitudinal mechanical properties of the hot-rolled round steel for the microalloyed mooring chain meet the following requirements: Rm≥1100MPa, Rp0.2≥990MPa, A≥16%, Z≥60%, -20℃ impact energy KV2≥118J, and hydrogen embrittlement resistance Z1 / Z2≥0.95.

[0015] In another aspect, the present invention provides a hot-rolled round bar for microalloyed mooring chains, which is obtained by the above-described production method.

[0016] The beneficial effects of this invention are: (1) This invention saves costs by using lower contents of Mn, Cr, and V. Under the premise of reducing the total content of alloying elements, it adds trace amounts of rare earth elements to make the material have high low-temperature toughness and corrosion resistance, as well as high hardenability; (2) The steel of this invention has the advantages of high strength and high toughness, good welding performance and low-temperature impact performance. The longitudinal mechanical properties meet the following requirements: Rm≥1100MPa, Rp0.2≥990MPa, A≥16%, Z≥60%, -20℃ impact energy KV2≥118J, and hydrogen embrittlement performance Z1 / Z 2≥0.95 (the area reduction rate without slow cooling treatment, the area reduction rate after holding at 250℃ for 2h), the austenitic grain size of the steel is greater than or equal to grade 8.0, after ultrasonic testing, its qualification level reaches grade A in GB / T4162-2012, after eddy current testing for surface quality inspection, the steel surface has no cracks, scars, folds or inclusions; (3) This invention optimizes the preparation process, uses a converter instead of an electric furnace to reduce the preparation cost, and performs degassing and removal of inclusions to improve the cleanliness of the material, thereby significantly improving the strength and toughness of the steel and the fatigue life of the material. The preparation method is simple, has low energy consumption, and is suitable for the current level of industrial equipment. Detailed Implementation

[0017] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0018] Example: Production of hot-rolled round steel for microalloyed mooring chains

[0019] The production method of hot-rolled round steel for microalloyed mooring chains in this embodiment includes the following processes: smelting in a combined blowing converter, LF refining, VD vacuum degassing, continuous casting, heating in a billet heating furnace, and rolling of round steel; wherein:

[0020] In the combined blowing converter smelting process, the final slag basicity is controlled at 3.0, the final control target is C≥0.05%, the temperature is controlled at 1650-1660℃, and SiMn, MnFe and CrFe are used for deoxidation and alloying. The final deoxidation is carried out with Al.

[0021] In the aforementioned LF refining process, white slag refining is employed, and Ar blowing is performed throughout the refining process. Desulfurization, composition fine-tuning, and temperature increase operations are conducted based on the converter steel composition and temperature, with a soft blowing time of 10-14 minutes. Furthermore, in the LF refining process, the chemical composition of the molten steel is controlled as follows (by mass percentage): C 0.19%–0.24%, Si 0.15%–0.20%, Mn 1.10%–1.20%, P ≤ 0.010%, S ≤ 0.010%, Cr 0.82%–0.90%, Mo 0.10%–0.30%, V 0.60%–0.80%, Cu 0.10%–0.20%, Alt 0.010%–0.030%, Re 0.020% to 0.035%, with the remainder being Fe and unavoidable trace impurities; the chemical composition and content of the refined steel from Examples 1-3 are shown in Table 1 below;

[0022] In the VD vacuum degassing process, the vacuum degree is controlled at 0.08-0.10 kPa, the deep vacuum time is 18-20 min, after the vacuum is broken, the silicon-calcium wire is fed in, the soft blowing time is 10-14 min, and the molten steel must not be exposed during the soft blowing process.

[0023] In the continuous casting process, constant casting speed control and electromagnetic stirring are adopted. The superheat of molten steel ΔT is 25-26℃, and a rectangular billet with a billet size of 320mm×415mm is obtained. The billet is then placed in a slow cooling pit for slow cooling for 48 hours.

[0024] In the billet heating furnace heating process, the heating temperature is controlled at 1000-1200℃, and the total heating time is not less than 3.5h to prevent overheating, burning and decarburization. The temperature is raised slowly to ensure uniform heating temperature of the billet and reduce temperature difference.

[0025] In the round steel rolling process, the initial rolling temperature is controlled at 1100-1200℃ and the final rolling temperature is controlled at 920-960℃. Attention should be paid to the condition of the rolls, turning machine, guide plate, roller table and cover plate, and they should be kept smooth and free of sharp edges to avoid defects such as scratches and dents on the surface of the rolled workpiece. The rolled product specification is φ123mm.

[0026] Table 1: Chemical composition (mass percentage) of hot-rolled round steel for microalloyed mooring chains in Examples 1-3

[0027] Example C Si Mn P S Cu Cr Mo V Alt Re Example 1 0.19 0.15 1.16 0.008 0.007 0.18 0.82 0.11 0.60 0.021 0.021 Example 2 0.24 0.19 1.11 0.007 0.009 0.14 0.86 0.24 0.72 0.014 0.027 Example 3 0.20 0.17 1.14 0.009 0.005 0.12 0.89 0.18 0.65 0.027 0.032

[0028] Table 2 shows the longitudinal mechanical properties of the hot-rolled round steel for microalloyed mooring chains produced in Examples 1-3, wherein the heat treatment process is: quenching at 910℃ and tempering at 580℃.

[0029] Table 2: Longitudinal mechanical properties of hot-rolled round steel for microalloyed mooring chains in Examples 1-3

[0030]

[0031] Table 3 shows the non-metallic inclusions and austenite grain size properties of the hot-rolled round steel for microalloyed mooring chains produced in Examples 1-3. The austenite grain size of the steel is greater than or equal to grade 8.0. After ultrasonic testing, its qualification level reaches Grade A in GB / T4162-2012. After eddy current testing for surface quality inspection, the steel surface is free of cracks, scabs, folds or inclusions.

[0032] Table 3: Non-metallic inclusions and austenite grain size properties of hot-rolled round steel for microalloyed mooring chains in Examples 1-3

[0033]

[0034] 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 producing hot-rolled round steel for microalloyed mooring chains, characterized in that, The method includes the following process steps: smelting in a combined blowing converter, refining in an LF furnace, vacuum degassing in a VD furnace, continuous casting, heating in a billet heating furnace, and rolling of round bars; wherein: In the aforementioned combined blowing converter smelting process, the final slag basicity is controlled at 3.0, the final control target is C≥0.05%, the temperature is controlled at 1650-1660℃, and SiMn, MnFe and CrFe are used for deoxidation and alloying. The final deoxidation is carried out with Al. In the LF refining process, white slag refining is employed, and Ar blowing is carried out throughout the refining process. Desulfurization, composition fine-tuning, and temperature increase operations are performed according to the composition and temperature of the converter steel. The soft blowing time is 10-14 min. In the LF refining process, the chemical composition of the molten steel is controlled as follows by mass percentage: C 0.19%~0.24%, Si 0.15%~0.20%, Mn 1.10%~1.20%, P≤0.010%, S≤0.010%, Cr 0.82%~0.90%, Mo 0.10%~0.30%, V 0.60%~0.80%, Cu 0.10%~0.20%, Alt 0.010%~0.030%, Re 0.020%~0.035%, with the remainder being Fe and unavoidable trace impurities. In the VD vacuum degassing process, the vacuum degree is controlled at 0.08-0.10 kPa, the deep vacuum time is 18-20 min, after the vacuum is broken, the silicon-calcium wire is fed in, the soft blowing time is 10-14 min, and the molten steel must not be exposed during the soft blowing process. In the continuous casting process, constant casting speed control and electromagnetic stirring are adopted. The superheat of molten steel ΔT is 25-26℃. After obtaining the billet, it is placed in a slow cooling pit for slow cooling. In the billet heating furnace heating process, the heating temperature is controlled at 1000-1200℃, and the total heating time is not less than 3.5h to prevent overheating, burning and decarburization. The temperature is raised slowly to ensure uniform heating temperature of the billet and reduce temperature difference. In the round steel rolling process, the initial rolling temperature is controlled at 1100-1200℃ and the final rolling temperature is controlled at 920-960℃. Attention should be paid to the condition of the rolls, turning machine, guide plate, roller table and cover plate, and they should be kept smooth and free of sharp edges to avoid scratches and dents on the surface of the rolled workpiece. The longitudinal mechanical properties of the hot-rolled round steel for the microalloyed mooring chain meet the following requirements: Rm≥1100 MPa, Rp0.2≥990MPa, A≥16%, Z≥60%, -20℃ impact energy KV2≥118J, and hydrogen embrittlement resistance Z1 / Z2≥0.

95.

2. The production method according to claim 1, characterized in that, In the LF refining process, the chemical composition of the molten steel is controlled as follows by mass percentage: C 0.19%–0.24%, Si 0.15%–0.19%, Mn 1.11%–1.16%, P≤0.010%, S≤0.010%, Cr 0.82%–0.89%, Mo 0.11%–0.24%, V 0.60%–0.72%, Cu 0.12%–0.18%, Alt 0.014%–0.027%, Re 0.021%–0.032%, with the remainder being Fe and unavoidable trace impurities.

3. The production method according to claim 1, characterized in that, In the continuous casting process, the obtained billet is a rectangular billet with dimensions of 320mm × 415mm.

4. The production method according to claim 1, characterized in that, In the continuous casting process, the material is slowly cooled in a slow cooling pit for 48 hours.

5. A hot-rolled round bar for microalloyed mooring chains, obtained by the production method according to any one of claims 1-4.

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