Low-cost low-carbon steel for cold upsetting and smelting method thereof

Abstract

The application discloses a low-cost low-carbon cold upsetting steel and a smelting method thereof, and relates to the field of metallurgical methods.The smelting method comprises converter primary smelting, argon station refining and continuous casting.The converter primary smelting controls the end-point carbon to be less than or equal to 0.04%, the molten steel P to be less than or equal to 0.020%, and the end-point temperature to be less than or equal to 1660 DEG C.The argon station refining controls the argon blowing flow to be 80 NL / min-400 NL / min, and the total argon blowing time to be greater than or equal to 10 min.The low-carbon cold upsetting steel comprises the following components in percentage by mass: C: 0.04-0.06%, Si: 0.07-0.15%, Mn: 0.25-0.30%, P: less than or equal to 0.025%, S: less than or equal to 0.030%, Al: less than or equal to 0.008%, and the balance of Fe and inevitable impurities.Under the premise that the cold upsetting steel meets the quality, the refining process is reduced, and the smelting cost and energy consumption index are lowered.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical method technology, specifically relating to a low-cost, low-carbon cold heading steel and its smelting method. Background Technology

[0002] Cold heading steel is steel subjected to one or more impact loadings at room temperature and is widely used in the production of standard parts such as screws, pins, and nuts. The cold heading process saves raw materials and reduces costs. Furthermore, it improves the tensile strength and performance of the workpiece through work hardening. Cold heading steel must possess good cold upsetting properties, high plasticity, toughness, and weldability, as well as good cold heading performance. For the smelting and forming of cold heading steel billets, it is necessary to ensure the billet composition, gas content, and billet quality to guarantee the cold forging performance of the cold heading steel.

[0003] Currently, the main methods for smelting low-carbon cold heading steel are primary steel refining followed by refining or double refining processes, specifically: primary refining in a converter - LF refining - continuous casting, or primary refining in a converter - LF refining - VD vacuum furnace - continuous casting, in order to meet the requirements of steel composition and purity and ensure the cold forging performance of cold heading steel.

[0004] The smelting process of the aforementioned cold heading steel is complex and energy-intensive. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a low-cost, low-carbon cold heading steel and its smelting method, which reduces the refining process and lowers the smelting cost and energy consumption index while meeting the quality requirements.

[0006] The technical solution of this invention is:

[0007] Firstly, a low-cost, low-carbon cold heading steel smelting method is provided, including converter primary smelting, argon station refining, and continuous casting;

[0008] In the primary refining process in the converter, the final carbon content should be controlled to be ≤0.04%, the phosphorus content in the molten steel to be ≤0.020%, and the final temperature to be ≤1660℃.

[0009] Argon station refining, argon blowing flow rate controlled between 80NL / min and 400NL / min, total argon blowing time ≥10min.

[0010] In some implementations of the first aspect, the primary smelting in the converter employs a low-lance decarburization technique, which is a rapid decarburization technique, with the oxygen lance height being 1.1m-1.4m higher than the molten steel surface.

[0011] The above technical solutions employ low-lance carbon extraction technology to precisely control the composition and temperature inside the converter. Furthermore, by improving the argon station refining conditions in the above smelting method, the refining process can be reduced while still obtaining low-carbon, high-purity steel billets.

[0012] In some implementations of the first aspect, the primary smelting in the converter employs a double-slag-blocking operation, with a slag discharge rate ≤0.8 kg / t steel.

[0013] In some implementations of the first aspect, the argon station refining process involves argon blowing throughout the ladle. When the converter taps 1 / 4 of the steel, 0.7–1.1 kg / t of aluminum granules, 0.5–1.0 kg / t of slag wash, and 0–1.0 kg / t of quicklime are sequentially added to the ladle.

[0014] In some implementations of the first aspect, the molten steel temperature at the end of the argon station refining process is 1580℃-1610℃.

[0015] By adopting the above technical solution, the steel ladle argon station refining process is used to replace LF refining. After the steel is tapped from the converter, deoxidation and composition are adjusted in one step, which reduces the refining process and lowers the smelting cost and energy consumption.

[0016] In some implementations of the first aspect, the continuous casting process includes a ladle, a tundish, and a crystallizer; the ladle to the tundish and the tundish to the crystallizer are both protected by long nozzle argon seals, and the tundish is argon-swept; the tundish uses a carbon-free tundish covering agent, and the crystallizer uses a low-carbon special protective slag.

[0017] In some implementations of the first aspect, the high liquid level pouring in the tundish is such that the liquid level is ≥600mm higher than the molten steel outlet of the tundish.

[0018] In some implementations of the first aspect, the continuous casting process is performed with constant casting speed of 2.0 to 2.5 m / min.

[0019] By implementing the above technical solutions, the continuous casting process can be better prevented from oxidizing due to contact with oxygen, thereby protecting the casting process and improving the purity of the molten steel.

[0020] In some implementations of the first aspect, after continuous casting, an inspection process is also included, including online infrared detection and offline pickling detection.

[0021] Through the above technical solutions, online infrared detection and offline pickling detection can provide real-time and comprehensive feedback on process compliance, and conduct full-coverage inspection of the billet condition for each flow within a casting cycle, ensuring the representativeness of the detection.

[0022] Secondly, a low-cost, low-carbon cold heading steel is provided, obtained according to any of the above-described smelting methods for low-cost, low-carbon cold heading steel, comprising the following components by mass percentage: C: 0.04–0.06%, Si: 0.07–0.15%, Mn: 0.25–0.30%, P ≤ 0.025%, S ≤ 0.030%, Al ≤ 0.008%, with the balance being Fe and unavoidable impurities.

[0023] Through the above technical solution, the composition of the steel billet is limited, ensuring that the low-carbon cold heading steel has better plasticity and toughness. Furthermore, the above smelting method allows for precise control of the billet's composition within this narrow range.

[0024] In summary, this application includes at least the following beneficial technical effects:

[0025] 1. This invention, through reasonable process design, adopts LF removal treatment in production and achieves precise control of components.

[0026] 2. This invention optimizes the final composition and temperature of converter blowing, and uses double slag tapping to ensure that the finished product composition meets the high plasticity requirements of cold heading steel. 3. This invention employs argon station refining, and achieves deoxidation and alloying effects through reasonable control of argon flow rate. 4. This invention uses continuous casting with full protective pouring to prevent secondary oxidation, constant casting speed, resulting in high billet purity and excellent internal quality. 5. This invention, with precise control of narrow composition and simplified process flow, fully meets the requirements for cold heading steel, producing billets with good low-magnification quality, achieving low cost and low energy consumption. Attached Figure Description

[0027] Figure 1 This is a low-magnification image of the cast billet obtained in Example 1;

[0028] Figure 2 This is a low-magnification image of the cast billet obtained in Example 2;

[0029] Figure 3 This is a low-magnification image of the cast billet obtained in Example 3;

[0030] Figure 4 Low-magnification image of the cast billet obtained in Example 4

[0031] Figure 5 This is a low-magnification image of the cast billet obtained in Example 5;

[0032] Figure 6 This is a low-magnification image of the cast billet obtained in Example 6;

[0033] Figure 7 This is a low-magnification image of the cast billet obtained in Example 7;

[0034] Figure 8 This is a low-magnification image of the cast billet obtained in Example 8;

[0035] Figure 9 This is a low-magnification image of the cast billet obtained in Example 9. Detailed Implementation

[0036] This application will be further described in detail below.

[0037] A low-cost, low-carbon cold heading steel has the following chemical composition and mass percentage: C: 0.04–0.06%, Si: 0.07–0.15%, Mn: 0.25–0.30%, P≤0.025%, S≤0.030%, Al≤0.008%, with the balance being Fe and unavoidable impurities. This low-carbon cold heading steel is used for high-end pin sleeves.

[0038] A low-cost, low-carbon cold heading steel smelting method includes converter primary smelting, argon station refining, continuous casting, and billet inspection processes.

[0039] In the smelting process, the converter adopts low-lance carbon extraction technology. In this technology, the oxygen lance is 1.1m-1.4m higher than the molten steel surface. This allows for precise control of the converter's internal composition and temperature, ensuring that the final carbon content is ≤0.04%, the molten steel P content is ≤0.020%, the final temperature is ≤1660℃, and the oxygen content in the final steel is ≤670ppm. The steel is tapped using a double-slag-blocking operation, with a slag discharge rate of ≤0.8kg / t steel.

[0040] Argon station refining: Argon is blown into the ladle throughout the process. When 1 / 4 of the steel is tapped, aluminum granules of 0.7-1.1 kg / t steel, slag wash of 0.5-1.0 kg / t steel, and quicklime (i.e. CaO) of 0-1.0 kg / t steel are added sequentially into the ladle. The argon blowing flow rate is controlled at 80 NL / min-400 NL / min, the total argon blowing time is ≥10 min, and the steel temperature is 1580℃-1610℃.

[0041] Continuous casting includes the ladle, tundish, and crystallizer. Long nozzle argon seal protection is used between the ladle and the tundish and between the tundish and the crystallizer. Tundish argon sweeping, high liquid level pouring (liquid level ≥ 600 mm), constant casting speed (casting speed 2.0~2.5 m / min), carbon-free tundish covering agent, and low-carbon special protective slag are used to achieve the purpose of protecting the pouring and improving the purity of molten steel.

[0042] The inspection process described in this invention, including online infrared detection and offline pickling detection, provides real-time and comprehensive feedback on process compliance.

[0043] This invention relates to a low-cost, low-carbon cold heading steel product standard references GB / T700 and GB / T701.

[0044] The product performance testing method standard refers to GB / T222, and the low magnification testing standard for cast billets refers to YB / T2011 and YB / T153.

[0045] The chemical composition and weight percentage of the low-cost, low-carbon cold heading steel used in Examples 1-6 below are shown in Table 1.

[0046] Table 1: Weight percentage (wt%) of chemical composition in low-carbon cold heading steel for each embodiment

[0047]

[0048]

[0049] In Table 1, the balance of chemical composition is Fe and unavoidable impurities.

[0050] Example 1

[0051] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0052] Converter smelting: final composition [C] 0.04wt%, [P] 0.016wt%, oxygen content in the final steel of the converter 562ppm, final temperature 1660℃; tapping time 4.5min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 0.8kg / ton of steel, slag wash 1.0kg / ton of steel, and quicklime 0kg / ton of steel; double slag baffle operation, slag amount 0.3kg / ton of steel; argon blowing begins 3min before tapping.

[0053] Argon station refining: After blowing argon at a flow rate of 300 NL / min for 4 minutes, measure the temperature, take a steel sample, add heat preservation agent, and then keep the slag surface "not exposed" for clean blowing. After blowing argon at a flow rate of 100 NL / min for 8 minutes, the total blowing time is 12 minutes, and the molten steel temperature is 1600℃.

[0054] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 700mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.3m / min.

[0055] Inspection process: The sampled casting billet meets the testing standard requirements. The low-magnification test results for this embodiment are shown in Table 2, and the low-magnification images are shown below. Figure 1 .

[0056] Example 2

[0057] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0058] Converter smelting: final composition [C] 0.04wt%, [P] 0.018wt%, oxygen content in the final steel of the converter 607ppm, final temperature 1650℃; tapping time 4.2min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 1.0kg / ton of steel, slag wash 0.5kg / ton of steel, and quicklime 0.5kg / ton of steel; double slag baffle operation, slag amount 0.8kg / ton of steel; argon blowing begins 3min before tapping.

[0059] Argon station refining: After blowing argon at a flow rate of 400 NL / min for 5 minutes, measure the temperature, take a steel sample, add heat preservation agent, and then keep the slag surface "not exposed" for clean blowing. After blowing argon at a flow rate of 100 NL / min for 9 minutes, the total blowing time is 14 minutes, and the steel temperature is 1580℃.

[0060] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 750mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.5m / min.

[0061] Inspection process: The sampled casting billet meets the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 2 .

[0062] Example 3

[0063] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0064] Converter smelting: final composition [C] 0.03wt%, [P] 0.019wt%, oxygen content in the final steel of the converter 665ppm, final temperature 1660℃; tapping time 4.3min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 1.0kg / ton of steel, slag wash 0.7kg / ton of steel, and quicklime 0.4kg / ton of steel; double slag baffle operation, slag amount 0.4kg / ton of steel; argon blowing begins 3min before tapping.

[0065] Argon station refining: After blowing argon at a flow rate of 300 NL / min for 3 minutes, measure the temperature, take a steel sample, add heat preservation agent, and then keep the slag surface "not exposed" for clean blowing. After blowing argon at a flow rate of 80 NL / min for 7 minutes, the total blowing time is 10 minutes, and the molten steel temperature is 1610℃.

[0066] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 600mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.0m / min.

[0067] Inspection process: The sampled casting billet meets the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 3 .

[0068] Example 4

[0069] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0070] Converter smelting: final composition [C] 0.04wt%, [P] 0.016wt%, oxygen content in the final steel of the converter 570ppm, final temperature 1645℃; tapping time 4.0min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 0.7kg / ton of steel, slag wash 0.5kg / ton of steel, and quicklime 0.5kg / ton of steel; double slag baffle operation, slag amount 0.5kg / ton of steel; argon blowing begins 3min before tapping.

[0071] Argon station refining: After blowing argon at a flow rate of 290 NL / min for 4 minutes, measure the temperature, take a steel sample, add heat preservation agent, and then keep the slag surface "not exposed" for clean blowing. After blowing argon at a flow rate of 90 NL / min for 11 minutes, the total blowing time is 15 minutes, and the molten steel temperature is 1590℃.

[0072] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 750mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.3m / min.

[0073] Inspection process: The sampled casting billet meets the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 4 .

[0074] Example 5

[0075] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0076] Converter smelting: final composition [C] 0.03wt%, [P] 0.015wt%, oxygen content in the final steel of the converter 550ppm, final temperature 1655℃; tapping time 4.0min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 0.8kg / ton steel, slag wash 0.9kg / ton steel, and quicklime 0kg / ton steel; double slag blocking operation, no slag added; argon blowing begins 3min before tapping.

[0077] Argon station refining: After blowing argon at a flow rate of 280 NL / min for 4 minutes, measure the temperature, take a steel sample, add insulation agent, and then keep the slag surface "not exposed" for clean blowing. After blowing argon at a flow rate of 80 NL / min for 10 minutes, the total blowing time is 14 minutes and the molten steel temperature is 1600℃.

[0078] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 750mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.5m / min.

[0079] Inspection process: The sampled casting billet meets the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 5 .

[0080] Example 6

[0081] The specific process of this low-cost, low-carbon cold heading steel and its smelting method is described below.

[0082] Converter smelting: final composition [C] 0.04wt%, [P] 0.020wt%, oxygen content in the final steel of the converter 670ppm, final temperature 1660℃; tapping time 4.5min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 1.0kg / ton of steel, slag wash 0.5kg / ton of steel, and quicklime 1.0kg / ton of steel; double slag blocking operation, no slag added; argon blowing begins 3min before tapping.

[0083] Argon station refining: After blowing argon at a flow rate of 400 NL / min for 4 minutes, the temperature is measured and a steel sample is taken. Insulating agent is added, and then the slag surface is kept "not exposed" for clean blowing. After blowing argon at a flow rate of 80 NL / min for 7 minutes, the total blowing time is 11 minutes and the molten steel temperature is 1610℃.

[0084] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 650mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.1m / min.

[0085] Inspection process: The sampled castings obtained through the above embodiments meet the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 6 .

[0086] Examples 7-9

[0087] The low-carbon cold heading steel used in Examples 7-9 has the same composition and the same converter smelting steps, only the conditions for argon station refining and billet continuous casting are different.

[0088] The specific processes for low-carbon cold heading steel and its smelting methods are described below:

[0089] Converter smelting: final composition [C] 0.05wt%, [P] 0.018wt%, oxygen content in the final steel of the converter 600ppm, final temperature 1650℃; tapping time 4.3min; aluminum granules, ferrosilicon manganese, ferrosilicon, and quicklime are added sequentially when 1 / 4 of the steel is tapped for deoxidation and alloying, of which aluminum granules 0.8kg / ton steel, slag wash 0.6kg / ton steel, and quicklime 0.7kg / ton steel; double slag blocking operation, no slag added; argon blowing begins 3min before tapping;

[0090] Argon station refining in Example 7: After blowing argon at a flow rate of 500 NL / min for 2 minutes, the temperature was measured and a steel sample was taken. Insulating agent was added, and then the slag surface was kept "not exposed" for clean blowing. After blowing argon at a flow rate of 200 NL / min for 3 minutes, the total blowing time was 5 minutes and the steel temperature was 1605℃.

[0091] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 700mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.0m / min.

[0092] Argon station refining in Example 8: After blowing argon at a flow rate of 400 NL / min for 4 minutes, the temperature was measured and a steel sample was taken. Insulating agent was added, and then the slag surface was kept "not exposed" for clean blowing. After blowing argon at a flow rate of 100 NL / min for 7 minutes, the total blowing time was 11 minutes and the steel temperature was 1600℃.

[0093] Billet continuous casting: full-process protective casting, the long nozzle of the ladle is protected by argon, and the tundish cover is tightly sealed; 2 minutes before the ladle starts casting, the air in the tundish is driven out by argon; the molten steel surface in the tundish is covered with a carbon-free covering agent, and carbonized rice husk is added on top; the temperature measuring hole and stopper rod hole are sealed with fiber blankets before casting starts; after casting starts, the molten steel level in the tundish is 700mm, the crystallizer uses low-carbon special protective slag, and the casting speed is 2.0m / min.

[0094] Argon station refining in Example 9: After blowing argon at a flow rate of 500 NL / min for 2 minutes, the temperature was measured and a steel sample was taken. Insulating agent was added, and then the slag surface was kept "not exposed" for clean blowing. After blowing argon at a flow rate of 200 NL / min for 3 minutes, the total blowing time was 5 minutes and the steel temperature was 1605℃.

[0095] Billet continuous casting: The casting from ladle to tundish and from tundish to crystallizer is protected by a long nozzle. The long nozzle is not protected by argon seal. The molten steel surface in the tundish is treated with carbonized rice husk heat preservation agent. After casting begins, the molten steel surface in the tundish is 600 mm, and the casting speed is 2.5 m / min.

[0096] Inspection process: The sampled castings obtained through the above embodiments meet the testing standard requirements. The low-magnification test results of this embodiment are shown in Table 2, and the low-magnification images (selected) are shown below. Figure 7 , Figure 8 , Figure 9 .

[0097] Performance testing

[0098] Table 2: Low-magnification inspection results of cast billets in each embodiment

[0099]

[0100]

[0101] The billets obtained in Examples 1-6 were all subjected to the following processing steps to obtain cold heading steel. The cold heading steel was tested, and the test results are shown in Table 3.

[0102] The processing steps for the cast billet include:

[0103] (1) Heating: The billet is heated and sent to the walking beam furnace. It is heated to 950-1050℃ through the preheating section, heating section and soaking section and then taken out of the furnace for rolling.

[0104] (2) Rolling: The heated billet is rolled into the required finished product specifications and dimensions by roughing, intermediate rolling and finishing mills in sequence. The rolling process can be temperature controlled according to performance requirements.

[0105] (3) Obtain the finished product and collect it.

[0106] Table 3: Performance test results of steel for cold heading

[0107] Example Rm Z 1 / 3 Higher Grade Cold Top Forging 1 280 85 No cracks 2 290 88 No cracks 3 310 86 No cracks 4 295 93 No cracks 5 290 90 No cracks 6 305 89 No cracks 7 280 80 microcracks 8 285 85 No cracks 9 270 70 Cracks

[0108] According to Examples 1-6, the billets obtained by the smelting method of this application have the characteristics of low carbon, low oxygen, and high purity, and the cold heading steel has good plasticity, toughness, and upsetting performance; at the same time, the smelting method of this application has simpler process steps.

[0109] According to Examples 7 and 8, the argon station refining conditions are different. Compared with Example 7, Example 8 has a reduced argon flow rate, a longer argon blowing time, and a larger total argon blowing volume. The resulting billet has a more uniform and precise composition and temperature, fewer subcutaneous bubbles and non-metallic inclusions, and better overall billet quality. Therefore, the overall performance of the billet and the cold-heading steel is improved, and the argon station refining conditions of Example 8 are superior. That is, within the argon station refining conditions defined in this application, increasing the argon blowing time and appropriately controlling the argon blowing flow rate will make the billet composition more uniform and precise, reduce gas content and inclusions, and improve the performance of cold-heading steel.

[0110] According to Examples 7 and 9, the conditions for continuous casting of billets are different. Compared with Example 7, Example 9 did not use long nozzle argon sealing, tundish argon purging, and tundish molten steel surface treatment with carbon-free covering agent. The resulting billet has increased internal porosity, internal cracks, subcutaneous bubbles, and non-metallic inclusions, resulting in a deterioration in the overall quality of the billet. Therefore, the performance of both the billet and the cold heading steel deteriorates. The billet continuous casting conditions of Example 7 are better. That is, within the scope of billet continuous casting conditions defined in this application, using long nozzle argon sealing, tundish argon purging, and tundish molten steel surface treatment with carbon-free covering agent will reduce the gas content and inclusions in the billet, thereby improving the performance of the cold heading steel.

[0111] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A method for smelting a low-cost low-carbon steel for cold upsetting, characterized in that: The converter initial smelting, argon station refining and continuous casting are included. The converter initial smelting controls the end-point carbon to be less than or equal to 0.04%, the molten steel P to be less than or equal to 0.020%, and the end-point temperature to be less than or equal to 1660 DEG C. The converter initial smelting adopts a low-lance carbon extraction technology, and the height of the oxygen lance is 1.1m-1.4m higher than the liquid surface of the molten steel. The converter initial smelting adopts a double-slag-stopping operation, and the amount of the slag is less than or equal to 0.8kg / t of the steel. The argon station refining controls the argon blowing flow to be 80NL / min-400NL / min, and the total argon blowing time is greater than or equal to 10min. The argon station refining blows argon to the ladle all the time, and when the molten steel is 1 / 4 of the converter tapping, 0.7-1.1kg / t of the steel of aluminum particles, 0.5-1.0kg / t of the steel of slag washing material and 0-1.0kg / t of the steel of lime are sequentially added into the ladle. The continuous casting includes a large ladle, a middle ladle and a crystallizer, and the long nozzle argon sealing protection is adopted between the large ladle and the middle ladle and between the middle ladle and the crystallizer, and the middle ladle is argon-swept. The middle ladle is high-liquid-surface pouring, and the liquid surface height is greater than or equal to 600mm higher than the outlet of the middle ladle. The continuous casting is constant-pulling-speed pouring, and the pulling speed is 2.0-2.5m / min.

2. A method of smelting a low-cost low-carbon steel for cold upsetting according to claim 1, characterized in that: The low-cost low-carbon cold-upsetting steel includes the following components in percentage by mass: C: 0.04-0.06%, Si: 0.07-0.15%, Mn: 0.25-0.30%, P: less than or equal to 0.025%, S: less than or equal to 0.030%, Al: less than or equal to 0.008%, and the balance is Fe and inevitable impurities.

3. A method of smelting a low cost low carbon cold heading steel according to claim 1, characterized in that: The molten steel temperature at the end of the argon station refining is 1580 DEG C-1610 DEG C. After the continuous casting, the inspection process is further included, and the on-line infrared detection and off-line pickling detection are performed.

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