A method for producing hot-formed carbon steel

Abstract

This invention relates to a method for producing hot-formed carbon steel. The chemical composition of the carbon steel, by mass percentage, is: C: 0.19%–0.25%; Si: 0.15%–0.35%; Mn: 1.10%–1.30%; P≤0.020%; S≤0.005%; Cr: 0.10%–0.30%; Ti: 0.020%–0.035%; Nb: 0.010%–0.0 25%; B: 0.015%~0.030%; Als: 0.025%~0.055%; N≤0.006%; H≤0.0002%; O≤0.0015%; The process flow is as follows: electric arc furnace smelting of scrap carbon steel and alloys, AOD+LF refining, VOD refining and degassing + LF X-ray, continuous casting of flat steel billets with protective casting, slow cooling of billets, heating in a heating furnace, rolling, slow cooling of steel coils, and warehousing of products. This invention uses a short process of electric arc furnace smelting, and reduces carbon emissions by controlling raw materials, processes, and using green electricity. The carbon emissions per ton of steel are less than 0.78t.CO2 / t.CS, which greatly reduces the carbon emissions per ton of steel.

Description

Technical Field

[0001] This invention relates to carbon steel production, and particularly to a method for producing hot-formed carbon steel. Background Technology

[0002] With the development of the automotive industry, countries around the world are imposing increasingly stringent requirements on vehicle safety, energy efficiency, and low carbon emissions. Using ultra-high strength hot-formed carbon steel to manufacture automotive parts can reduce vehicle weight while achieving energy conservation and emission reduction. Current hot-formed carbon steel production processes mainly involve the traditional blast furnace long-process smelting: blast furnace hot metal → converter smelting → RH furnace vacuum refining → continuous casting → rolling. Using this traditional blast furnace long-process process to produce hot-formed carbon steel for wheel hubs results in high carbon emissions per ton of steel, which is inconsistent with the current development concept of energy conservation, carbon reduction, and emission reduction. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for producing hot-formed carbon steel, thereby solving the problem of high carbon emissions in long-process carbon steel production.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A method for producing hot-formed carbon steel, the process flow of which includes: electric furnace smelting of scrap carbon steel and alloys, AOD+LF refining, VOD refining and degassing + LF X-ray, continuous casting of flat steel billets with protective casting, slow cooling of the billets, heating in a heating furnace, rolling, slow cooling of the steel coils, and product warehousing; specifically including:

[0006] 1) The chemical composition of carbon steel, by mass percentage, is as follows: C: 0.19%–0.25%; Si: 0.15%–0.35%; Mn: 1.10%–1.30%; P≤0.020%; S≤0.005%; Cr: 0.10%–0.30%; Ti: 0.020%–0.035%; Nb: 0.010%–0.025%; B: 0.015%–0.030%; Als: 0.025%–0.055%; N≤0.006%; H≤0.0002%; O≤0.0015%;

[0007] 2) Smelting of scrap carbon steel and alloys in electric furnaces: The electric furnace is cleaned, and scrap carbon steel and alloys with low phosphorus content are used as raw materials for smelting.

[0008] 3) AOD+LF refining: AOD is used for final control of steel tapping, with a tapping temperature of 1740±20℃ and a carbon content of ≤0.0100%; LF is used for deep desulfurization by adding lime and fluorite slag, with an alkalinity >2.0 and an argon flow rate >1500L / min to vigorously stir the molten steel, reducing the sulfur content in the molten steel to below 0.005%; and alloys are added for fine-tuning of the composition according to the target composition; aluminum ingots are added for deep deoxidation of the molten steel, with a target Als ≥0.02%;

[0009] 4) VOD refining and degassing: First, evacuate for 15-30 minutes. When the vacuum reaches below 10 Mbar, maintain the vacuum for 30-45 minutes to carry out deep degassing, controlling the nitrogen content N≤0.004%, hydrogen content H≤0.0002%, and oxygen content O≤0.0008%.

[0010] 5) After degassing and LF refining and fine-tuning of composition, inject Ti line to ensure Ti content; then inject Ca line to allow Ca to combine with Al oxide inclusions and float to the surface; and perform weak argon blowing for 15-30 minutes with slight stirring.

[0011] 6) Continuous casting;

[0012] 7) Heating in a heating furnace;

[0013] 8) Rolling: Hot rolling start temperature 1100±20℃, final rolling temperature range 880±20℃, coiling temperature 680±20℃, and slow cooling of the coil for 24 to 48 hours after coiling.

[0014] Step 2) Produce low-alloy steel grades before electric furnace production.

[0015] Step 2) The phosphorus content in the scrap carbon steel and alloy is P≤0.025%.

[0016] Step 6) Continuous casting adopts protective pouring, the superheat is controlled within 35℃, and the pouring speed is 0.9~1.2m / min.

[0017] Step 7) Heating in the furnace: The slab exit temperature is 1210±20℃;

[0018] Compared with existing technologies, the beneficial effects of this invention are:

[0019] This invention utilizes a short-process electric furnace for smelting and optimizes the short-process production technology. It optimizes and improves the smelting and refining processes at each station, such as the AOD furnace, LF furnace, and VOD furnace. The produced steel billets are kept warm in a heating furnace and then hot-rolled into the furnace for production, reducing the energy consumption of the hot-rolling heating furnace. At the same time, the temperature of each station in the hot rolling process is precisely controlled, and the produced steel coils are slowly cooled to obtain steel coils with stable performance.

[0020] The production of hot-formed carbon steel begins with the production of low-alloy steel grades to reduce residual alloying elements such as Cr and Ni; VOD degassing treatment achieves low N, H, and O levels; hot billet holding during hot rolling reduces energy consumption; and precise temperature control during hot rolling ensures the final material's mechanical properties. The hot-rolled steel coils exhibit uniform internal and external grain structure with a grain number of 10.0#. Black-skinned steel coils with thicknesses of 3.0–6.0 mm and widths of 800–1600 mm can be produced.

[0021] Throughout the entire steelmaking and hot rolling production process, the company connects its own photovoltaic green electricity to reduce conventional electricity consumption and thus lower carbon emissions.

[0022] This invention reduces carbon emissions by controlling raw materials, processes, and using green electricity. The carbon emissions per ton of steel are less than 0.78 t.CO2 / t.CS, while the traditional long-process blast furnace process is about 2.4 t.CO2 / t.CS. This invention reduces carbon emissions per ton of steel by more than 50%, significantly reducing carbon emissions per ton of steel. Attached Figure Description

[0023] Figure 1 This is the microstructure of the hot-rolled steel coil of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0025] A hot-formed carbon steel production method, the process flow is as follows: electric furnace scrap carbon steel and alloy smelting → AOD+LF refining → VOD refining degassing + LF X-ray → flat steel billet continuous casting with protective casting → billet slow cooling → heating furnace heating → rolling → steel coil slow cooling → product warehousing.

[0026] 1) The chemical composition of carbon steel, by mass percentage, is as follows: C: 0.19%–0.25%; Si: 0.15%–0.35%; Mn: 1.10%–1.30%; P≤0.020%; S≤0.005%; Cr: 0.10%–0.30%; Ti: 0.020%–0.035%; Nb: 0.010%–0.025%; B: 0.015%–0.030%; Als: 0.025%–0.055%; N≤0.006%; H≤0.0002%; O≤0.0015%;

[0027] 2. The electric furnace produces low-alloy steel grades (such as carbon steel Q235 steel grade and low-alloy steel 4SUH1 steel grade) and then cleans the furnace to reduce the residue of trace elements. Then, it uses scrap carbon steel with a phosphorus content ≤0.025% and alloys to smelt the initial molten steel.

[0028] 3) AOD is used for final control of steel tapping, with tapping temperature of 1740±20℃ and carbon content of tapped steel ≤0.0100%; LF is used for deep desulfurization by adding lime and fluorite slag, with basicity >2.0, and argon gas flow rate >1500L / min for vigorous stirring of the molten steel to reduce the S content in the molten steel to below 0.005%; and alloys are added for fine-tuning of the composition according to the target composition; aluminum ingots are added for deep deoxidation of the molten steel, with a target Als ≥0.02%;

[0029] 4) VOD is used for deep degassing to reduce the content of [N], [O], and [H] in the steel. After degassing, LF refining is used to fine-tune the composition. Ti line is injected to ensure the Ti content. Then, Ca line is injected to allow Ca to combine with Al oxide inclusions and float to the surface. Weak argon blowing is performed for 15-30 minutes with slight stirring. The final control is to ensure that the nitrogen content N≤0.004%, the hydrogen content H≤0.0002%, and the oxygen content O≤0.0008%.

[0030] 5) Continuous casting adopts protective casting, the crystallizer uses electromagnetic stirring, the target superheat of the molten steel in the tundish is controlled within 35℃, and the pouring speed is 0.90~1.30m / min, with a target of 1.20m / min. To promote hydrogen diffusion, after the billet is produced, it is sent to a slow cooling pit at a high temperature for more than 20 hours for slow cooling, and the temperature of the billet entering the pit is ≥600℃.

[0031] 6) To ensure sufficient dissolution of carbides in the billet, the furnace outlet temperature is controlled within the range of 1210±20℃, the heating time is 200~240 minutes, the initial rolling temperature is 1100±20℃, and the finishing rolling temperature is controlled at 880±20℃, with the coiling temperature at 680±20℃. After production, the steel coils are sent to a slow cooling pit for slow cooling, or arranged to be stacked together and other hot-rolled coils of different steel grades are suspended around them for slow cooling. The slow cooling time is 24~48 hours to improve the problem of uneven performance between the inner and outer rings of the steel coil.

[0032] 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.

[0033] The hot-formed carbon steel for wheel hubs produced using this invention meets all standard requirements. The steel coil composition, inclusions, and mechanical properties are all good, resulting in excellent product quality that meets customer requirements. The results are shown in Tables 1, 2, and 3.

[0034] Table 1. Ingredients of the Examples

[0035]

[0036] Table 2. Inclusion Inspection Results of Examples

[0037] Table 3. Mechanical properties of the examples

[0038] serial number Category A Category B Category C Category D 4-0510 0 0.5 0.5 0 5-1835 0 0.5 0 0.5 5-4385 0 0 0.5 0.5

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0040]

Claims

1. A method of producing hot formed carbon steel, characterized in that, The carbon emission is less than 0.78 t.CO2 / t.CS, and the process flow is: electric furnace waste carbon steel and alloy smelting, AOD+LF refining, VOD refining degassing+LF radiation, flat billet continuous casting protective casting, casting billet slow cooling, heating furnace heating, rolling, steel coil slow cooling, product storage; specifically comprising: 1) The chemical composition of carbon steel is as follows in terms of mass percentage: C: 0.19%-0.25%; Si: 0.15%-0.35%; Mn: 1.10%-1.30%; P≤0.020%; S≤0.005%; Cr: 0.10%-0.30%; Ti: 0.020%-0.035%; Nb: 0.010%-0.025%; B: 0.015%-0.030%; Als: 0.025%-0.055%; N≤0.006%; H≤0.0002%; O≤0.0015%; 2) Electric furnace smelting: the electric furnace is washed to reduce the residual trace elements, and then the waste carbon steel and alloy with phosphorus content≤0.025% is used to smelt into initial molten steel; 3) AOD+LF refining: AOD controls the tapping endpoint, the tapping temperature is 1740±20℃, and the tapping carbon content is≤0.0100%; LF adds lime and fluorite to slag depth desulfurization, the basicity is>2.0, the argon blowing flow is>1500L / min, the molten steel is stirred to make the S content in the molten steel be less than 0.005%; and the alloy is added according to the target composition to adjust the composition; the aluminum ingot is used to carry out deep deoxidation of the molten steel, and the target Als is≥0.02%; 4) VOD refining degassing: first, the gas is extracted for 15-30 minutes, then the vacuum is extracted to less than 10mbar, and the deep degassing is maintained for 30-45 minutes, the nitrogen content N≤0.004%, the hydrogen content H≤0.0002%, and the oxygen content O≤0.0008% are controlled; 5) After the degassing, the LF refining is adjusted, the Ti line is shot to ensure the Ti composition, the Ca line is shot, and the weak argon blowing is carried out for 15-30 minutes for micro-stirring; 6) The continuous casting adopts protective casting, the crystallizer adopts electromagnetic stirring, the target overheat degree of the molten steel in the tundish is controlled within 35℃, the target 1.20m / min is poured, and in order to promote the diffusion of hydrogen, the casting billet is sent to the slow cooling pit in the high temperature state for slow cooling for more than 20h, and the pit temperature is≥600℃; 7) Heating furnace heating: the heating furnace controls the out-of-furnace temperature range to be 1210±20℃, and the heating time is 200-240 minutes; 8) Rolling: the hot rolling opening temperature is 1100±20℃, the finish rolling temperature range is 880±20℃, the coiling temperature is 680±20℃, and the steel coil is slow cooled for 24-48 hours after coiling.

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