Low-cost smelting method for normalizing and rolling H-shaped steel for ocean engineering

Abstract

The invention discloses a low-cost smelting method for normalizing and rolling H-shaped steel for ocean engineering. The smelting process comprises the steps of blast furnace molten iron, molten iron pretreatment, converter smelting, LF refining and special-shaped blank continuous casting. The steel comprises the following chemical components in percentage by mass: 0.08%-0.14% of C, 0.25%-0.35% of S i, 1.30%-1.50% of Mn, less than or equal to 0.02% of P, less than or equal to 0.010% of S, 0.05%-0.09% of V, 0.015%-0.035% of Nb and the balance of Fe and impurities, and the total mass fraction is 100%. The prepared H-shaped steel not only has very high yield strength and tensile strength, but also has very good impact toughness.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel smelting, and particularly relates to a smelting method for low-cost normalized rolling H-beams for offshore engineering. Background Art

[0002] In recent years, the use of low-alloy steels in the market has become increasingly widespread, and the quality requirements for low-alloy steels have also become higher and higher. It can be predicted that with the development of new technologies and the high standards of product quality required by users, the replacement of low-grade steel grades by high-grade steel grades has become a development trend. At present, low-alloy steel series are widely used in the market, especially in the wind power and construction industries, and the usage frequency of Q345C / D / E steel is gradually increasing.

[0003] For low-alloy steels used in some alpine and other regions, due to the particularity of their geographical environment and the inconvenience of product manufacturing and installation, there are special requirements for processing raw materials. The steel used in this region should have a more uniform organizational structure, stable physical and chemical properties after long-term low-temperature service, and good anti-fatigue characteristics. In this regard, ordinary low-alloy steel plates no longer meet the quality requirements of customers. Therefore, it is necessary to propose new composition design ideas, develop short-process production process routes based on microstructure control, and achieve the reduction of high-quality steel product manufacturing and the reduction of production costs. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a smelting method for low-cost normalized rolling H-beams for offshore engineering, with excellent performance.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A smelting method for low-cost normalized rolling H-beams for offshore engineering of the present invention, the smelting process is: blast furnace hot metal → hot metal pretreatment → converter smelting → LF refining → special-shaped billet continuous casting; characterized in that:

[0007] During the hot metal pretreatment process, pretreated desulfurized hot metal is used: [S] in the converter < 0.030%; the hot metal temperature is greater than or equal to 1250 °C;

[0008] During the converter smelting process, combined blowing converter smelting is carried out, and the final slag basicity is controlled at 3.0; the end point C ≥ 0.03%, the end point temperature is greater than or equal to 1610 °C, and final deoxidation is carried out with Al deoxidation; alloying copper and nickel are added with scrap steel; quicklime is added during the tapping process;

[0009] During the LF refining process, for the operation of refining white slag, argon blowing is carried out according to the refining regulations throughout the process; desulfurization, composition fine-tuning and temperature increase operations are carried out according to the composition and temperature of the converter molten steel; 60 - 70 kg / heat of vanadium-nitrogen alloy is added in the later stage of refining. If the vanadium content is insufficient, ferrovanadium is used to supplement it, and the composition is fine-tuned; 150 m of silicon-calcium wire is fed at the end of refining to ensure that the soft blowing time is greater than or equal to 15 min, and the molten steel shall not be exposed during soft blowing.

[0010] Protecting casting is adopted throughout the process; the liquidus temperature TL = 1513 °C; the superheat is ≤ 35 °C; a weak cooling system is adopted; a constant casting speed operation of 0.7 - 1.0 m / s is adopted; after the continuous casting billet is cut, it is immediately taken offline for stacking and slow cooling. The lower layer is covered and the upper layer is covered. The slow cooling time is greater than or equal to 48 hours.

[0011] Furthermore, 65 kg / heat of vanadium-nitrogen alloy is added in the later stage of refining.

[0012] Furthermore, the cross-sectional dimensions of the continuous casting billet are 555×440×105 mm.

[0013] Furthermore, the mass percentage content of its chemical composition includes: C 0.08% - 0.14%, Si 0.25% - 0.35%, Mn 1.30% - 1.50%, P ≤ 0.02%, S ≤ 0.010%, V 0.05% - 0.09%, Nb 0.015% - 0.035%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0014] Furthermore, the mass percentage content of its chemical composition includes: C 0.12%, Si 0.27%, Mn 1.35%, P 0.0109%, S 0.007%, V 0.05%, Nb 0.017%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0015] Furthermore, the mass percentage content of its chemical composition includes: C 0.08%, Si 0.29%, Mn 1.40%, P 0.0114%, S 0.006%, V 0.065%, Nb 0.023%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0016] Furthermore, the mass percentage content of its chemical composition includes: C 0.09%, Si 0.33%, Mn 1.42%, P 0.0111%, S 0.008%, V 0.054%, Nb 0.023%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0017] Furthermore, the mass percentage of its chemical components includes: C 0.10%, Si 0.27%, Mn 1.49%, P 0.009%, S 0.006%, V 0.078%, Nb 0.034%, and the rest are Fe and impurities, with the total mass fraction being 100%.

[0018] The main functions of each element are as follows:

[0019] C: The C element is the most effective element in improving the strength of steel. The increase in C content can improve the tensile strength and yield strength of the steel, but the elongation and impact toughness will decrease to some extent. To ensure that the normalized rolled H-beam for low-temperature resistance obtains good comprehensive performance, the C element content of the steel in this invention is designed to be 0.08 - 0.14%.

[0020] Mn: Mn is an important element for strengthening and toughening, and its cost is low. With the increase in manganese content, the strength of the steel is significantly improved, and the processing performance of the steel is improved, while the ductile-brittle transition temperature hardly changes. However, if the manganese content is too high, it will inhibit the transformation of ferrite, affect the yield strength of the steel, and is not conducive to the control of the yield ratio. The Mn element content of the steel in this invention is designed to be 1.30 - 1.50%.

[0021] Si: Si can improve the strength of steel. By increasing the Si element, the strength of the steel can be improved to a certain extent. However, with the further increase in the mass percentage of Si, it is easy to form martensite structure in the steel. Therefore, for the normalized H-beam for offshore engineering and its production method described in this invention, the mass percentage of Si is controlled within 0.25 - 0.35%.

[0022] V: V can play a role in precipitation strengthening, grain refinement strengthening, and grain boundary strengthening in steel, and can reduce the ductile-brittle transition temperature. The carbonitrides of V can effectively refine the ferrite grains. In low-temperature steel, a small amount of V can refine the grains and increase the toughness. The V element content of the steel in this invention is designed to be 0.05% - 0.09%.

[0023] P: P has strong solid solution strengthening and cold work hardening effects in steel. P acts on ferrite. Although it can improve the strength and hardness of the steel, the biggest harm is that it has serious segregation, increases temper brittleness, and significantly reduces the plasticity and toughness of the steel, resulting in the phenomenon that the steel is prone to brittle fracture during cold processing, that is, the so-called "cold brittleness" phenomenon. Therefore, the P element content of the steel in this invention is designed to be ≤0.020%.

[0024] S: S is an element of hot brittleness and easy machinability. It is known that the cutting performance improves with the increase in the mass percentage of sulfur, but the hot workability deteriorates with the increase in sulfur content. Therefore, in the preparation method of the normalized rolled low-alloy structural steel described in this invention, the mass percentage of S is limited to S ≤ 0.015%.

[0025] Nb: Adding trace alloying element Nb to steel has a strong effect of preventing the growth of austenite grains and is easy to obtain a fine-grained structure. Niobium will produce significant grain refinement and moderate precipitation strengthening during controlled rolling. The content of Nb element in the steel of the present invention is designed to be 0.015% - 0.035%.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0027] The H-shaped steel prepared by the present invention not only has high yield and tensile strength, but also has good impact toughness. Specific embodiments

[0028] Table 1 shows the chemical compositions of the steel grades in each embodiment. Tables 2, 3, and 4 further illustrate the present invention in combination with each embodiment.

[0029] Table 1 Chemical compositions of each example (mass percentage / %)

[0030] Example C Si Mn P S V Nb Example 1 0.12 0.27 1.35 0.0109 0.007 0.05 0.017 Example 2 0.08 0.29 1.40 0.0114 0.006 0.065 0.023 Example 3 0.09 0.33 1.42 0.0111 0.008 0.054 0.023 Example 4 0.10 0.27 1.49 0.009 0.006 0.078 0.034

[0031] Table 2 Casting speed and superheat control of each example

[0032] Example Superheat (°C) Drawing speed (m / min) Example 1 33 0.7 Example 2 34 0.8 Example 3 30 0.7 Example 4 31 0.9

[0033] Table 3 Surface temperature of the continuous casting billet entering the straightening machine in each example

[0034] Example End of flange plate (°C) R corner (°C) Web (°C) Example 1 873 959 913 Example 2 877 962 926 Example 3 881 966 917 Example 4 876 950 931

[0035] Table 4 Mechanical properties of the rolled H-shaped steel in each example (rolling process: the starting rolling temperature is 1150 °C, and the controlled finishing rolling temperature is 900 °C)

[0036]

[0037] It can be seen from the above examples that the H-shaped steel has high strength and stable impact toughness.

[0038] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A low-cost normalizing and rolling H-beam smelting method for marine engineering, the smelting process is: blast furnace molten iron → molten iron pretreatment → converter smelting → LF refining → special-shaped billet continuous casting; the characteristics are: In the process of hot metal pretreatment, the hot metal to be pretreated and desulfurized is used: [S] < 0.030% when entering the converter; the hot metal temperature is greater than or equal to 1250°C; During converter smelting, double-blowing converter smelting, control the final slag basicity to 3.0; end point C ≥ 0.03%, end point temperature greater than or equal to 1610 ° C, final deoxidation using Al deoxidation; alloy copper and nickel are added with scrap steel; lime is added during steel tapping; During the LF refining process, the white slag is refined and Ar blowing is performed according to the refining procedures. Desulfurization, composition fine-tuning and temperature-raising operations are performed according to the composition and temperature of the converter molten steel. In the later stage of refining, vanadium-nitrogen alloy is added at 60-70kg / furnace. If the vanadium content is insufficient, ferrovanadium is used to supplement it and the composition is fine-tuned. At the end of refining, 150m of silicon-calcium wire is fed to ensure that the soft blowing time is greater than or equal to 15min. The molten steel must not be exposed during the soft blowing. Protective pouring is adopted throughout the whole process; liquidus temperature TL=1513℃; superheat ≤35℃; weak cooling system is adopted; constant casting speed operation is adopted at 0.7-1.0m / s; after the continuous casting billet is cut, it is promptly stacked and slowly cooled, and the cover mold is laid on the bottom, and the slow cooling time is greater than or equal to 48 hours.

2. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 1 is characterized by: In the later stage of refining, 65kg / furnace of vanadium-nitrogen alloy is added.

3. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 1 is characterized by: The cross-sectional dimensions of the continuous casting billet are 555×440×105mm.

4. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 1 is characterized by: The mass percentage of its chemical composition includes: C 0.08%~0.14%, Si 0.25%~0.35%, Mn 1.30%~1.50%, P≤0.02%, S≤0.010%, V 0.05%~0.09%, Nb 0.015%~0.035%, and the rest are Fe and impurities, with a total mass fraction of 100%.

5. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 4 is characterized in that: The mass percentages of its chemical components include: C 0.12%, Si 0.27%, Mn 1.35%, P 0.0109%, S0.007%, V 0.05%, Nb 0.017%, and the rest are Fe and impurities, with a total mass fraction of 100%.

6. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 4 is characterized by: The mass percentage of its chemical composition includes: C 0.08%, Si 0.29%, Mn 1.40%, P 0.0114%, S0.006%, V 0.065%, Nb 0.023%, and the rest are Fe and impurities, with a total mass fraction of 100%.

7. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 4 is characterized by: The mass percentages of its chemical components include: C 0.09%, Si 0.33%, Mn 1.42%, P 0.0111%, S0.008%, V 0.054%, Nb 0.023%, and the rest are Fe and impurities, with a total mass fraction of 100%.

8. The low-cost normalizing and rolling H-beam smelting method for marine engineering according to claim 4 is characterized by: The mass percentages of its chemical components include: C 0.10%, Si 0.27%, Mn 1.49%, P 0.009%, S0.006%, V 0.078%, Nb 0.034%, and the rest are Fe and impurities, with a total mass fraction of 100%.

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