Production method of non-quenched and tempered cold heading steel wire rod

Abstract

The invention discloses a production method of a non-quenched and tempered cold heading steel wire rod, which comprises the following chemical components in percentage by mass: 0.18 to 0.26 percent of C, 0.10 to 0.30 percent of Si, 1.20 to 1.60 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, 0.05 to 0.10 percent of Nb, 0.15 to 0.25 percent of V and the balance of Fe and inevitable impurities, and the total mass fraction is 100 percent. The invention further discloses a production method of the non-quenched and tempered cold heading steel wire rod MFT9. According to the invention, the MFT9 non-quenched and tempered cold heading steel wire rod with excellent comprehensive mechanical properties is successfully developed by controlling the processes of electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating of a casting blank heating furnace, controlled rolling and controlled cooling and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and rolling, and in particular relates to a production method of non-quenched and tempered cold heading steel wire rod. Background Art

[0002] With the development of the machinery manufacturing industry, the market demand for high-performance fasteners and mechanical parts continues to increase, especially in the automotive, aviation, construction and other industries. This provides a broad market prospect for the development of non-quenched and tempered cold heading steel wire rods. Non-quenched and tempered cold heading steel wire rods are suitable for the manufacture of various high-strength fasteners, such as bolts, nuts, screws, etc., which can meet the automotive industry's demand for lightweight and high-strength materials and improve the safety and reliability of vehicles. In various mechanical equipment and engineering machinery, a large number of high-strength and durable fasteners and connectors are required. Non-quenched and tempered cold heading steel wire rods can meet these needs and improve the performance and service life of the equipment. In energy fields such as wind power and nuclear power, non-quenched and tempered cold heading steel wire rods can be used to manufacture various high-strength fasteners and connectors to meet the use requirements in extreme environments. Non-quenched and tempered cold heading steel wire rods have high strength and toughness, and do not require additional heat treatment processes (such as quenching and tempering), which simplifies the production process and reduces production costs. By adjusting the alloy composition and manufacturing process, its performance can be optimized to meet different application requirements. The development of non-quenched and tempered cold heading steel wire rod has high feasibility and broad application prospects. Steel mills can improve product performance and competitiveness through technology research and development and process optimization, meet the needs of various industries for high-performance fasteners and mechanical parts, seize market opportunities and promote enterprise development. Summary of the invention

[0003] The purpose of the present invention is to provide a production method for non-quenched and tempered cold heading steel wire rod, which utilizes the principle of composite alloying of a small amount of Nb and V, combined with a suitable rolling process, to significantly improve the mechanical properties of the wire rod while reducing production costs, thereby producing non-quenched and tempered cold heading steel wire rod, thereby significantly improving the overall life and safety of downstream finished products.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention discloses a production method of non-quenched and tempered cold heading steel wire rod, comprising electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating in a casting furnace, and controlled rolling and controlled cooling; wherein:

[0006] Electric arc furnace is used for smelting. Aluminum particles, electrolytic manganese, pre-melted refined slag and lime are added in sequence before steel tapping. It is forbidden to add ferrosilicon and silicon-manganese containing silicon materials to control the Si content. At the same time, in order to ensure low P and low S content, the amount of lime and slag flow of the previous furnace of steel is increased; slag is blocked when steel is tapped;

[0007] In the LF furnace, the molten steel is deeply stripped and alloyed, and high basicity slag (R≥3.0) is made to strengthen the removal of sulfur and inclusions. The refining process adopts stirring throughout the whole process;

[0008] The bottom blowing pressure of molten steel in RH vacuum degassing should not be too high to avoid molten steel tumbling and contact with air to absorb nitrogen, and to prevent re-oxidation. Ensure that the weak stirring time before leaving the station is long enough to facilitate the floating of alumina inclusions.

[0009] During casting, protective sleeve + argon seal, molten steel covering agent + argon blowing protection and large-capacity tundish are used between the ladle and the tundish to ensure that the inclusions in the steel can fully float up; submerged nozzle, aluminum-killed steel special slag and tundish electromagnetic stirring are used between the tundish and the crystallizer to ensure the quality of the ingot;

[0010] When heating the ingot, the preheating section temperature is 700-800℃, the soaking section temperature is 950-1150℃, and the soaking section temperature is strictly controlled to be less than 1150℃, and the soaking time is more than 30min to ensure that Nb and V elements are fully dissolved and quickly pass through the decarburization sensitive temperature range of 850-900℃ for this steel grade;

[0011] Adopt low temperature rolling process and control the cooling rate after rolling; the starting rolling temperature is 950-1050℃, the final rolling temperature is 780-880℃, the cooling is slow after rolling, and the heat preservation cover is fully closed;

[0012] The mass percentage of its chemical composition includes: C 0.18%-0.26%, Si 0.10%-0.30%, Mn1.20%-1.60%, P≤0.015%, S≤0.015%, Nb 0.05-0.10%, V 0.15-0.25%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0013] Furthermore, the mechanical properties of the produced non-quenched and tempered cold heading steel wire rod meet the following requirements: Rm≥700MPa, A≥20.0%, Z≥60%, and the austenite grain size of the steel is ≥10 grades.

[0014] Furthermore, the produced non-quenched and tempered cold heading steel wire rod has no cracks, scars, folds or inclusions on the surface.

[0015] Furthermore, the chemical composition includes by weight percentage: C 0.19%, Si 0.26%, Mn 1.28%, P0.012%, S 0.0058%, Nb 0.06%, V 0.17%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0016] Furthermore, the mass percentage of its chemical composition includes: C 0.23%, Si 0.28%, Mn 1.32%, P0.014%, S 0.0075%, Nb 0.08%, V 0.23%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0017] Furthermore, the chemical composition includes by weight percentage: C 0.20%, Si 0.27%, Mn 1.30%, P0.013%, S 0.0055%, Nb 0.07%, V 0.21%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] (1) The steel of the present invention has the advantage of high strength; (2) The present invention reduces the preparation cost by optimizing the preparation process, and improves the cleanliness of the material by degassing and removing inclusions, thereby significantly improving the strength and toughness of the steel and the life of the material. The preparation method is simple in process, low in energy consumption, and is suitable for the preparation technology of the existing industrial equipment level.

[0020] The mechanical properties meet the following requirements: Rm ≥ 700MPa, A ≥ 20.0%, Z ≥ 60%, the austenite grain size of the steel ≥ grade 10, and there are no cracks, scars, folds or inclusions on the surface of the steel. DETAILED DESCRIPTION

[0021] Table 1 shows the chemical compositions of three embodiments of the present invention, and Tables 2 and 3 further illustrate the present invention.

[0022] Table 1 Chemical composition of each example of non-quenched and tempered cold heading steel wire rod MFT9 (mass percentage / %)

[0023] Example C Si Mn P S Nb V Example 1 0.19 0.26 1.28 0.012 0.0058 0.06 0.17 Example 2 0.23 0.28 1.32 0.014 0.0075 0.08 0.23 Example 3 0.20 0.27 1.30 0.013 0.0055 0.07 0.21

[0024] Table 2 Process parameters of each example

[0025]

[0026] Table 3 Mechanical properties of non-quenched and tempered cold heading steel wire rod MFT9

[0027]

[0028] Table 4 Non-metallic inclusions and austenite grain size of each example of non-quenched and tempered cold heading steel wire rod MFT9

[0029]

[0030]

[0031] It can be seen from Tables 1-4 that the non-quenched and tempered cold heading steel wire rod MFT9 of the present invention has excellent mechanical properties.

[0032] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing non-quenched and tempered cold heading steel wire rod, characterized in that: Including electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating in billet heating furnace, controlled rolling and controlled cooling; among which: Electric arc furnace is used for smelting. Aluminum particles, electrolytic manganese, pre-melted refined slag and lime are added in sequence before steel tapping. It is forbidden to add ferrosilicon and silicon-manganese containing silicon materials to control the Si content. At the same time, in order to ensure low P and low S content, the amount of lime and slag flow of the previous furnace of steel is increased; slag is blocked when steel is tapped; In the LF furnace, the molten steel is deeply stripped and alloyed, and high-basicity slag is made to strengthen the removal of sulfur and inclusions. The refining process adopts stirring throughout the whole process. The bottom blowing pressure of molten steel in RH vacuum degassing should not be too high to avoid molten steel tumbling and contact with air to absorb nitrogen, and to prevent re-oxidation. Ensure that the weak stirring time before leaving the station is long enough to facilitate the floating of alumina inclusions. During casting, protective sleeve + argon seal, molten steel covering agent + argon blowing protection and large-capacity tundish are used between the ladle and the tundish to ensure that the inclusions in the steel can fully float up; submerged nozzle, aluminum-killed steel special slag and tundish electromagnetic stirring are used between the tundish and the crystallizer to ensure the quality of the ingot; When heating the ingot, the preheating section temperature is 700-800℃, the soaking section temperature is 950-1150℃, and the soaking section temperature is strictly controlled to be less than 1150℃, and the soaking time is more than 30min to ensure that Nb and V elements are fully dissolved and quickly pass through the decarburization sensitive temperature range of 850-900℃ for this steel grade; Adopt low temperature rolling process and control the cooling rate after rolling; the starting rolling temperature is 950-1050℃, the final rolling temperature is 780-880℃, the cooling is slow after rolling, and the heat preservation cover is fully closed; The mass percentage of its chemical composition includes: C 0.18%-0.26%, Si 0.10%-0.30%, Mn1.20%-1.60%, P≤0.015%, S≤0.015%, Nb 0.05-0.10%, V 0.15-0.25%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

2. The method for producing non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The mechanical properties of the produced non-quenched and tempered cold heading steel wire rod meet the following requirements: Rm≥700MPa, A≥20.0%, Z≥60%, and the austenite grain size of the steel is ≥10 grade.

3. The method for producing non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The non-quenched and tempered cold heading steel wire rod produced has no cracks, scars, folds or inclusions on the surface.

4. The method for producing non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.19%, Si 0.26%, Mn 1.28%, P 0.012%, S0.0058%, Nb 0.06%, V0.17%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

5. The method for producing non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The mass percentage of its chemical composition includes: C 0.23%, Si 0.28%, Mn 1.32%, P 0.014%, S0.0075%, Nb 0.08%, V0.23%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

6. The method for producing non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The mass percentage of its chemical composition includes: C 0.20%, Si 0.27%, Mn 1.30%, P 0.013%, S0.0055%, Nb 0.07%, V0.21%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

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