Low-carbon low-silicon low-nitrogen aluminum-containing hot-rolled wire rod for cold heading and preparation method thereof

Abstract

The invention discloses a low-carbon low-silicon low-nitrogen aluminum-containing hot-rolled wire rod for cold heading and a preparation method of the low-carbon low-silicon low-nitrogen aluminum-containing hot-rolled wire rod. The hot-rolled wire rod comprises the following chemical components in percentage by mass: 0.05-0.10% of C, less than or equal to 0.10% of Si, 0.30-0.5% of Mn, less than or equal to 0.030% of P, less than or equal to 0.030% of S, less than or equal to 0.20% of Ni, less than or equal to 0.20% of Cr, less than or equal to 0.20% of Cu, 10.0-0.050% of Al, 0.020-0.040% of Ti, less than or equal to 15 ppm of O, less than or equal to 35 ppm of N and the balance of Fe and inevitable impurities. The hot-rolled wire rod has excellent comprehensive mechanical properties and large deformation and can meet the machining requirements of special-shaped parts with large deformation, the yield strength of the hot-rolled wire rod is 205-230 MPa, the tensile strength of the hot-rolled wire rod is 330-360 MPa, the ductility of the hot-rolled wire rod is 35-38%, and the cracking ratio of the hot-rolled wire rod under the deformation of 1 / 5 cold upsetting is smaller than or equal to 0.05%.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled wire rods for cold heading, and specifically relates to a low-carbon, low-silicon, low-nitrogen, aluminum-containing hot-rolled wire rod for cold heading and a preparation method thereof. Background Art

[0002] Cold heading steel is a special steel used to manufacture various fasteners by cold heading and cold extrusion. Its processing technology has many advantages: small material loss, no or little finishing, high productivity, and the processed products have a tight internal structure, high strength, elastic limit and toughness, and its development prospects are particularly broad.

[0003] Cold heading steel has high requirements for wire rod raw materials, requiring hot rolled wire rods to have good strength, plasticity, toughness, low P and S content, high cleanliness, good surface quality, etc.

[0004] At present, the downstream processing enterprises of low-carbon and low-silicon cold heading steel in China mainly use it to produce various special-shaped parts, and have extremely high requirements for the cold heading performance of the materials. Sometimes the height ratio of the sample after cold heading is less than 1 / 5 of the height ratio of the sample before cold heading. However, when the deformation amount of domestically produced materials is large, the cracking ratio gradually increases. It is difficult to ensure the processing quality of special-shaped parts with large deformation amount by using the cold heading steel wire rod produced by the existing process. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading and a preparation method thereof. The hot-rolled wire rod for cold heading has excellent comprehensive mechanical properties and a large deformation amount, and can meet the processing requirements of special-shaped parts with a large deformation amount.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, the chemical composition and mass percentage of the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading are: C 0.05-0.10%, Si≤0.10%, Mn 0.30-0.5%, P≤0.030%, S≤0.030%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, A1 0.025-0.050%, Ti0.020-0.040%, O≤15ppm, N≤35ppm, and the balance is Fe and unavoidable impurities.

[0008] The metallographic structure of the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading is ferrite+pearlite.

[0009] The low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading has a yield strength of 205-230 MPa, a tensile strength of 330-360 MPa, an elongation of 35-38%, and a cracking ratio of ≤0.05% at a deformation amount of 1 / 5 of cold heading.

[0010] The present invention also provides a method for preparing the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, which comprises the following steps: converter smelting—LF refining—continuous casting—heating in a heating furnace—rolling—controlled cooling.

[0011] Furthermore, in the converter smelting step, low carbon ferromanganese and aluminum blocks with a C content of ≤4% are used for molten steel deoxidation and alloying. After the molten steel enters the argon blowing station, the aluminum wire is fed to reach the target value.

[0012] In the LF refining step, white slag is produced, Ca wire is fed for calcification treatment, soft blowing is performed for 15-20 minutes, and continuous casting is performed after adding covering agent; the refining station temperature is 1530-1550℃, the outlet temperature is 1600-1610℃, and the refining cycle is 35-40min.

[0013] During the continuous casting step, protective pouring is carried out to control the molten steel seal in the tundish so that it is not exposed and the tundish cover plate and the tundish are completely sealed.

[0014] In the rolling steps, the new rolling groove is used in the initial rolling mill, pre-finishing rolling mill, finishing rolling mill and sizing reduction.

[0015] In the rolling step, the starting rolling temperature is 1030-1040°C, the finishing rolling inlet temperature is 900-920°C, the sizing inlet temperature is 860-880°C, and the spinning temperature is 830-870°C.

[0016] In the controlled cooling step, the air cooling roller of the Stelmore air cooling line reaches a speed of 0.12-0.27m / min, and the rolls are air-cooled after leaving the hood.

[0017] The low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading provided by the present invention has a chemical composition in which C can improve strength but deteriorate the plasticity and toughness of steel, so the present application controls the C content to be 0.05-0.10%; Si can improve strength and hardness but deteriorate the plasticity and toughness of steel, and at the same time, Si can increase the cold deformation hardening rate of ferrite, making cold processing of steel difficult, so it has a very adverse effect on cold heading performance, so the present application controls the Si content to be below 0.10%; P, S and non-metallic inclusions will deteriorate the plasticity, toughness, Fatigue strength and corrosion resistance are greatly reduced, especially non-metallic inclusions will destroy the matrix continuity of steel, under the action of static load and dynamic load, often become the starting point of cold heading steel cracks, therefore, cold heading steel requires that P and S in steel be as low as possible and non-metallic inclusions be reduced; N is the most important element causing strain aging, interstitial solutes (C, N) in the solid solution state interact with dislocations, pinning dislocations to prevent deformation, resulting in increased yield strength, a sharp drop in plasticity, and increased brittleness, therefore, this application requires strict control of N content ≤35ppm.

[0018] The aluminum content in low-carbon, low-silicon, low-nitrogen aluminum-containing steel for cold heading is relatively high, and the submerged nozzle is very prone to flocculence during the continuous casting production process. Therefore, in the production method of low-carbon, low-silicon, aluminum-containing, low-nitrogen hot-rolled wire rod for cold heading provided by the present invention, the molten steel must be treated with calcium in the LF refining step, but aluminum and calcium are both elements that are easily oxidized and are relatively difficult to control. During the smelting process, on the one hand, argon protection is used to prevent aluminum and calcium from contacting with oxygen, thereby reducing the possibility of oxidation; on the other hand, the temperature needs to be strictly controlled during the smelting process, with the refining station temperature at 1530-1550°C and the outlet temperature at 1600-1610°C. At the same time, the refining cycle is controlled to 35-40min to avoid rapid oxidation of aluminum and calcium due to high temperature for too long. At the same time, low-carbon, low-silicon aluminum-containing steel has very strict requirements on the content of sulfur, silicon, carbon and non-metallic inclusions. The converter passes through the starting point of inclusion formation and adopts a step-by-step deoxidation method to reduce the oxygen content at the end of the converter, thereby reducing the S content. At the same time, low-carbon and low-silicon alloy auxiliary materials are used, and full diffusion deoxidation is adopted after refining. Aluminum particles, carbon powder and other materials are added during the process to strengthen slag surface deoxidation. The soft blowing time is guaranteed to be 15-20 minutes, so that the inclusions in the molten steel have enough time to float. Continuous casting adopts argon protection in the whole process to stabilize and improve the quality of low-carbon, low-silicon aluminum-containing steel.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The low-carbon, low-silicon, aluminum-containing, and low-nitrogen hot-rolled wire rod for cold heading provided by the present invention has low production cost, and the produced hot-rolled wire rod for cold heading has a large deformation amount, and can meet the processing requirements of special-shaped parts with a large deformation amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1is the metallographic structure diagram of the hot-rolled wire rod in Example 1;

[0022] Figure 2 is the metallographic structure diagram of the hot-rolled wire rod in Example 2;

[0023] Figure 3 is the metallographic structure diagram of the hot-rolled wire rod in Example 3;

[0024] Figure 4 This is the metallographic structure diagram of the hot-rolled wire rod in Comparative Example 1. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the embodiments.

[0026] Example 1

[0027] A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, the chemical composition and mass percentage of which are: C0.06%, Si 0.05%, Mn 0.35%, P 0.010%, S 0.003%, Cr 0.04%, A1 0.035%, Ti0.030%, in addition, the gas O content is 12ppm, the N content is 30ppm, and the balance is Fe and unavoidable impurities.

[0028] The preparation process of the aluminum-containing low-carbon, low-silicon, low-nitrogen hot-rolled wire rod for cold heading is as follows: converter smelting - LF refining - continuous casting - heating furnace heating - rolling - controlled cooling, specifically:

[0029] In the converter smelting step, low-carbon ferromanganese with a C content of ≤4% and aluminum blocks are used for deoxidation and alloying of molten steel. The final oxygen content of the converter is 725ppm. After the molten steel enters the argon blowing station, the aluminum wire is fed to achieve an Al content of 0.060% in the converter.

[0030] In the LF refining step, the refining arrival temperature is 1530℃, the outlet temperature is 1600℃, and the refining cycle is 40min; refining temperature measurement sampling, white slag making operation and Ca line feeding calcification treatment, soft blowing for 15min, composition measurement, and covering agent addition are performed before leaving the station and going on stage.

[0031] During the continuous casting step, argon gas is used to protect the pouring throughout the entire process, the molten steel in the tundish is controlled to be sealed without being exposed, and the tundish cover plate and the tundish are completely sealed to produce continuous casting billets.

[0032] The rolling process uses new rolling grooves for the initial rolling mill, pre-finishing rolling mill, finishing rolling mill and sizing reduction. The production team checks the cooling water pipe effect of the online rolling mill before production to ensure effective cooling. The starting rolling temperature is controlled at 1030℃, the finishing rolling inlet temperature is 900℃, the sizing inlet temperature is 860℃, and the wire laying temperature is 830℃; the air-cooled roller speed of the Stelmor air-cooled line is 0.14m / min, and the coil is air-cooled after leaving the hood to obtain low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rods for cold heading.

[0033] Example 2

[0034] A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, the chemical composition and mass percentage of which are: C0.07%, Si 0.08%, Mn 0.40%, P 0.013%, S 0.007%, Cr 0.05%, A1 0.045%, in addition, the gas O content is 15ppm, the N content is 47ppm, and the balance is Fe and unavoidable impurities.

[0035] The preparation process of the aluminum-containing low-carbon, low-silicon, low-nitrogen hot-rolled wire rod for cold heading is as follows: converter smelting - LF refining - continuous casting - heating furnace heating - rolling - controlled cooling, specifically:

[0036] In the converter smelting step, low-carbon ferromanganese with a C content of ≤4% and aluminum blocks are used for deoxidation and alloying of molten steel to meet the deoxidation requirements of molten steel. The final oxygen content of the converter is 775ppm. After the molten steel enters the argon blowing station, the Al content of the aluminum wire is 0.050%.

[0037] In the LF refining step, the refining arrival temperature is 1540℃, the outlet temperature is 1600℃, and the refining cycle is 35min; refining temperature measurement sampling, white slag making operation and Ca line feeding calcification treatment, soft blowing, composition measurement, and covering agent addition are performed before leaving the station and going on stage.

[0038] During the continuous casting step, argon gas is used to protect the pouring throughout the entire process, the molten steel in the tundish is controlled to be sealed without being exposed, and the tundish cover plate and the tundish are completely sealed to produce continuous casting billets.

[0039] The rolling process uses new rolling grooves for the initial rolling mill, pre-finishing rolling, finishing rolling mill and sizing reduction. The production team checks the cooling water pipe effect of the online rolling mill before production to ensure effective cooling. The starting rolling temperature is controlled at 1035℃, the finishing rolling inlet temperature is 910℃, the sizing inlet temperature is 870℃, and the wire laying temperature is 850℃; the air-cooled roller speed of the Stelmor air-cooled line is 0.20m / min, and the coil is air-cooled after leaving the hood to obtain low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading.

[0040] Example 3

[0041] A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, the chemical composition and mass percentage of which are: C0.08%, Si 0.08%, Mn 0.38%, P 0.010%, S 0.006%, Cr 0.03%, A1 0.033%, Ti0.020%, in addition, the gas O content is 15ppm, the N content is 51ppm, and the balance is Fe and unavoidable impurities.

[0042] The preparation process of the aluminum-containing low-carbon, low-silicon, low-nitrogen hot-rolled wire rod for cold heading is as follows: converter smelting - LF refining - continuous casting - heating furnace heating - rolling - controlled cooling, specifically:

[0043] In the converter smelting step, low carbon ferromanganese with C content ≤ 4% and aluminum blocks are used for molten steel deoxidation and alloying to meet the molten steel deoxidation requirements. The oxygen content at the converter end is 850ppm. After the molten steel enters the argon blowing station, the Al content of the aluminum wire is 0.050%.

[0044] In the LF refining step, the refining arrival temperature is 1550℃, the outlet temperature is 1610℃, and the refining cycle is 35min; refining temperature measurement sampling, white slag making operation and Ca line feeding calcification treatment, soft blowing, composition measurement, and covering agent addition are performed before leaving the station and going on stage.

[0045] During the continuous casting step, argon gas is used to protect the pouring throughout the entire process, the molten steel in the tundish is controlled to be sealed without being exposed, and the tundish cover plate and the tundish are completely sealed to produce continuous casting billets.

[0046] The rolling process uses new rolling grooves for the initial rolling mill, pre-finishing rolling, finishing rolling mill and sizing reduction. The production team checks the cooling water pipe effect of the online rolling mill before production to ensure effective cooling. The starting rolling temperature is controlled at 1040℃, the finishing rolling inlet temperature is 930℃, the sizing inlet temperature is 890℃, and the wire laying temperature is 870℃; the air-cooled roller speed of the Stelmor air-cooled line is 0.25m / min, and the coil is air-cooled after leaving the hood to obtain low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading.

[0047] Comparative Example 1

[0048] A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, the chemical composition and mass percentage of which are: C0.07%, Si 0.09%, Mn 0.39%, P 0.014%, S 0.010%, Cr 0.05%, A1 0.029%, Ti0.005%, in addition, the gas O content is 35ppm, the N content is 65ppm, and the balance is Fe and unavoidable impurities.

[0049] The preparation process of the aluminum-containing low-carbon, low-silicon, low-nitrogen hot-rolled wire rod for cold heading is as follows: converter smelting - LF refining - continuous casting - heating furnace heating - rolling - controlled cooling, specifically:

[0050] In the converter smelting step, low-carbon ferromanganese with a C content of 5-7% and aluminum blocks are used for deoxidation and alloying of molten steel to meet the deoxidation requirements of molten steel. The final oxygen content of the converter is 900-1000ppm. After the molten steel enters the argon blowing station, the aluminum wire is fed to achieve an Al content of 0.045-0.06%.

[0051] In the LF refining step, the refining arrival temperature is 1500℃, the outlet temperature is 1590℃, and the refining cycle is 40min; refining temperature measurement sampling, white slag making operation and Ca line feeding calcification treatment, soft blowing, composition measurement, and covering agent addition are performed before leaving the station and going on stage.

[0052] During the continuous casting step, argon gas is used to protect the pouring throughout the entire process, the molten steel in the tundish is controlled to be sealed without being exposed, and the tundish cover plate and the tundish are completely sealed to produce continuous casting billets.

[0053] The rolling process uses new rolling grooves for the initial rolling mill, pre-finishing rolling, finishing rolling mill and sizing reduction. The production team checks the cooling water pipe effect of the online rolling mill before production to ensure effective cooling. The starting rolling temperature is controlled at 1030℃, the finishing rolling inlet temperature is 940℃, the sizing inlet temperature is 890℃, and the wire laying temperature is 850℃; the air-cooled roller speed of the Stelmor air-cooled line is 0.27m / min, and the coil is air-cooled after leaving the hood to obtain low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading.

[0054] The properties of the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rods for cold heading prepared in the above embodiments and comparative examples and the cracking ratio at a deformation amount of 1 / 5 of cold upsetting are shown in Table 1.

[0055] Table 1

[0056]

[0057]

[0058] It can be seen from the above that the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading obtained according to the scheme of the present invention has excellent comprehensive mechanical properties and a large deformation amount, and can meet the processing requirements of special-shaped parts with a large deformation amount.

[0059] The above-mentioned reference embodiments provide a detailed description of a low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading and a preparation method thereof, which is illustrative rather than restrictive, and several embodiments may be listed within the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading, characterized in that: The chemical composition and mass percentage of the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading are: C 0.05-0.10%, Si≤0.10%, Mn 0.30-0.5%, P≤0.030%, S≤0.030%, Ni≤0.20%, Cr≤0.20%, Cu≤0.20%, A1 0.025-0.050%, Ti 0.020-0.040%, O≤15ppm, N≤35ppm, and the balance is Fe and unavoidable impurities.

2. The low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading according to claim 1, characterized in that: The metallographic structure of the low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading is ferrite+pearlite.

3. The low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading according to claim 1, characterized in that: The low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading has a yield strength of 205-230 MPa, a tensile strength of 330-360 MPa, an elongation of 35-38%, and a cracking ratio of ≤0.05% at a deformation amount of 1 / 5 of cold heading.

4. The method for preparing a low-carbon, low-silicon, low-nitrogen aluminum-containing hot-rolled wire rod for cold heading according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: converter smelting—LF refining—continuous casting—heating in a heating furnace—rolling—controlled cooling.

5. The preparation method according to claim 4, characterized in that: In the converter smelting step, low-carbon ferromanganese and aluminum blocks with a C content of ≤4% are used for molten steel deoxidation and alloying. After the molten steel enters the argon blowing station, the aluminum wire is fed to reach the target value.

6. The preparation method according to claim 4, characterized in that: In the LF refining step, white slag is produced, Ca wire is fed for calcification treatment, soft blowing is performed for 15-20 minutes, and continuous casting is performed after adding covering agent; the refining station temperature is 1530-1550℃, the outlet temperature is 1600-1610℃, and the refining cycle is 35-40min.

7. The preparation method according to claim 4, characterized in that: During the continuous casting step, protective pouring is carried out to control the molten steel seal in the tundish so that it is not exposed and the tundish cover plate and the tundish are completely sealed.

8. The preparation method according to claim 4, characterized in that: In the rolling steps, the new rolling groove is used in the initial rolling mill, pre-finishing rolling mill, finishing rolling mill and sizing reduction.

9. The preparation method according to claim 4, characterized in that: In the rolling step, the starting rolling temperature is 1030-1040°C, the finishing rolling inlet temperature is 900-920°C, the sizing inlet temperature is 860-880°C, and the spinning temperature is 830-870°C.

10. The preparation method according to claim 4, characterized in that: In the controlled cooling step, the air cooling roller speed of the Stelmore air cooling line is 0.12-0.27m / min, and the rolls are air-cooled after leaving the hood.

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