A nail-making steel SWRH42A and its manufacturing process

Abstract

This invention provides a nail-making steel SWRH42A and its production process. The chemical composition of the steel, by weight percentage, is: C 0.40%–0.45%, Si 0.18%–0.28%, Mn 0.35%–0.45%, P≤0.018%, S≤0.015%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, with the remainder being iron and unavoidable impurities. This invention employs a production process of "120t converter + LF refining + small billet continuous casting + heating furnace heating + controlled rolling and controlled cooling rolling" to manufacture SWRH42A wire rod for nail making, ensuring both the mechanical properties and drawing performance of the SWRH42A wire rod, as well as its qualified cold upsetting.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a nail-making steel SWRH42A and its production process. Background Technology

[0002] Steel nails are steel wire products used to fasten objects. They are widely used in various fields such as industry, agriculture, construction, and civil use, mainly for fixing objects with relatively small axial separation forces and radial shear forces. They are characterized by simple processing, convenient use, and rapid fastening. As the nail manufacturing industry develops towards adopting new processes and technologies, full mechanization and automation, advanced technology, low energy consumption, high efficiency, and economic scale, the requirements for the physical quality of hot-rolled wire rods used in nail manufacturing are further increasing.

[0003] SWRH42A wire rod for nail making should have its ends completely removed. Its surface quality requirements are smoothness, free from defects such as folds, burrs, knots, delamination, and visible cracks or inclusions. Localized indentations, bumps, scratches, and pitting are permissible, but their depth or height (measured from the actual dimensions) should not exceed 0.10 mm.

[0004] The internal quality requirements for SWRH42A wire rod used for nail making are stable tensile strength, high reduction of area, ability to meet the performance requirements of high-speed drawing, low wire breakage rate, and low cold heading cracking rate. To meet the above quality requirements, a nail-making steel SWRH42A and its production process have been developed. Summary of the Invention

[0005] The purpose of this invention is to provide a nail-making steel SWRH42A and its production process. The production process adopts "120t converter + LF refining + 150mm×150mm small square billet continuous casting + heating furnace heating + controlled rolling and controlled cooling rolling" to manufacture SWRH42A wire rod for nail making, which not only ensures the mechanical properties and drawing performance of SWRH42A wire rod, but also ensures that its cold upsetting is qualified.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A nail-making steel, SWRH42A, is characterized in that its chemical composition by weight percentage is: C 0.40%–0.45%, Si 0.18%–0.28%, Mn 0.35%–0.45%, P≤0.018%, S≤0.015%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, with the remainder being iron and unavoidable impurities.

[0008] The tensile strength of SWRH42A steel wire rod for nail making is 671-746 MPa, the elongation after fracture is 22.5%-27.5%, and the reduction of area is 55%-57%; the non-metallic inclusions A+C≤1.5; B+D≤1.5.

[0009] The microstructure of the steel is ferrite + pearlite, and the thickness of the decarburized layer is 0.04 to 0.07 mm.

[0010] The rationale for the design of the components in this invention is as follows:

[0011] C: Carbon increases the strength and hardness of steel, but as the carbon content increases, the steel's plasticity and toughness decrease. The C content should be controlled between 0.40% and 0.45%.

[0012] Silicon (Si): Silicon can increase the strength and hardness of steel, but reduce its plasticity and toughness. In the steelmaking process, silicon plays a deoxidizing role. The Si content should be controlled between 0.18% and 0.28%.

[0013] Mn: Manganese can increase the strength of steel, combine with sulfur to form manganese sulfide to eliminate the "hot brittleness" of steel, and improve the hardenability and wear resistance of steel. The Mn content should be controlled between 0.35% and 0.45%.

[0014] P and S: Phosphorus and sulfur are harmful elements in steel. Phosphorus dissolves in ferrite, and although it can improve the strength and hardness of steel, its greatest harm is severe segregation, which increases temper brittleness and significantly reduces the plasticity and toughness of steel, making it prone to brittle fracture during cold working, the so-called "cold brittleness" phenomenon. Sulfur reduces the plasticity of steel, increases its brittleness, and deteriorates the quality of steel. P ≤ 0.018%, S ≤ 0.015%.

[0015] A production process for SWRH42A nail-making steel, in order to ensure billet quality, utilizes effective measures such as steel superheating, casting speed, electromagnetic stirring in the continuous casting crystallizer, and electromagnetic stirring at the end of solidification to improve the surface quality of the billet and reduce internal cracks and central defects. The specific steps include the following:

[0016] 1) Converter smelting: Scrap steel accounts for 10%–15%, molten iron accounts for 85%–90%; oxygen is blown from top and bottom, tapping temperature is 1580–1600℃, and the final carbon content at tapping is 0.20%–0.30%. Double-slag smelting is used in the converter, with a target P ≤ 0.015% for each tapping; slag feeding is strictly prohibited. Auxiliary material addition per ton of steel: 30–35 kg of active lime, 5.5–8.5 kg of dolomite, 18–24 kg of ore, and 25–34 kg of limestone. Alloying in the ladle: Lime, pre-deoxidizer, and ferroalloys are added when the steel is 1 / 4–1 / 3 tapped for deoxidation and alloying, with argon blowing time ≥ 5 min; target alloy addition per ton of steel: 3.2–4.2 kg of silicon manganese and 1.4–2.2 kg of ferrosilicon.

[0017] 2) Static argon blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1530~1580℃, posttreatment temperature 1525~1555℃, after static argon blowing, feed pure calcium cored wire 1~1.2kg / t, feeding speed 2.8~3.2m / s.

[0018] 3) LF furnace refining: White slag operation is required. While ensuring slag fluidity, the slag basicity and oxygen potential must be controlled. The molten steel must be continuously monitored, and alloying adjustments made to ensure the steel composition meets standard requirements. LF refining time is 60–80 min, and the full analysis temperature is 1495–1565℃. Auxiliary material addition per ton of steel: 5.3–6.5 kg of active lime, 0.33–0.67 kg of fluorite, 0.40–0.60 kg of calcium carbide slag, and 0.50–1.0 kg of carbonized rice husks. Additionally, 0.8–1.2 kg of medium-carbon ferromanganese and 0.85–1.45 kg of low-calcium ferrosilicon are added per ton of steel. The molten steel must be continuously monitored, and alloying adjustments made to ensure the steel composition meets standard requirements. Soft blowing time is ≥15 min.

[0019] 4) Continuous casting: The electromagnetic stirring current in the crystallizer is 260-300A, frequency 4-6Hz, rotating in both directions; the electromagnetic stirring current at the end is 230-270A, frequency 6-10Hz, rotating continuously. The platform temperature is 1506-1575℃, the tundish temperature is 1515-1540℃, the superheat is maintained at 25-35℃, and the casting speed is 2.2-2.4m / min; the entire process is protected during casting, and the mold flux uses medium carbon steel mold flux for square billets; billet cutting is done using a combination of automatic and manual methods.

[0020] 5) Heating process: Walking beam furnace heating, preheating section 860~900℃, heating section 1100~1140℃, soaking section 1130~1170℃, heating time ≤2.5h;

[0021] 6) Rolling process: Roughing temperature 1000~1040℃; Finishing inlet temperature 880~920℃; Wire drawing temperature 880~920℃; Air-cooled roller speed: Head roller speed 0.70~0.90m / s; Insulation cover fully open; Fan: 1 # -3 # Frequency modulation 30-40Hz; 4 # -5 # FM 25-35Hz; 6 # Fans are 100% operational; 7 # -11 # All off.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This method adopts a production mode of "converter + LF refining furnace + continuous casting + controlled rolling and controlled cooling process" to provide high physical quality requirements such as stable tensile strength, high reduction of area, performance requirements for high-speed drawing, low wire breakage rate, and low cold heading cracking rate of SWRH42A wire rod for nail making.

[0024] This invention effectively improves the quality of SWRH42A wire rod for nail making. Through composition design, controlled rolling and cooling processes, and positive tolerance rolling to control dimensional accuracy, it ensures the stability of tensile strength, high reduction of area, and cold heading performance of the wire rod. Continuous casting employs electromagnetic stirring in the crystallizer and at the end of the casting process to improve the surface quality of the billet and reduce center segregation and center defects. The Stellmore controlled rolling and cooling process, combined with strong fan cooling, yields a metallographic structure composed of ferrite and pearlite, ensuring the strength and toughness of the wire rod. Attached Figure Description

[0025] Figure 1 This is a metallographic diagram of the product from Example 1.

[0026] Figure 2 This is a diagram showing the thickness of the decarburized layer in Example 1. Detailed Implementation

[0027] The specific implementation of the present invention will be further described below with reference to the embodiments.

[0028] The chemical composition of the embodiments of the present invention is shown in Table 1; the manufacturing process parameters of the embodiments of the present invention are shown in Table 2; the amount of smelting auxiliary materials added in the embodiments of the present invention is shown in Table 3; the low magnification defects of the cast billet in the embodiments of the present invention are shown in Table 4; the mechanical properties of the products in the embodiments of the present invention are shown in Table 5; the microstructure and non-metallic inclusions in the embodiments of the present invention are shown in Table 6.

[0029] Table 1 Chemical composition of the examples

[0030]

[0031]

[0032] Table 2 Manufacturing process parameters for the first embodiment

[0033]

[0034] Table 2 Manufacturing process parameters for Example (II)

[0035]

[0036]

[0037] Table 3. Amount of smelting auxiliary materials added in the examples.

[0038]

[0039] Table 4: Low-magnification defect inspection results of the cast billets in the examples:

[0040]

[0041]

[0042] Table 5 Mechanical properties of the products in the examples

[0043] Example Tensile strength / MPa Elongation after fracture / % Reduction of area / % 1 709 26.5 55 2 698 24.5 57 3 717 24 57 4 716 24 55 5 671 23.5 57 6 722 27.5 55 7 710 27.5 55 8 687 22.5 57 9 692 24.5 57 10 684 24 57

[0044] Table 6. Microstructure and Non-metallic Inclusions of Products from Examples

[0045]

Claims

1. A type of nail-making steel SWRH42A, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C 0.40%~0.45%, Si 0.18%~0.28%, Mn 0.35%~0.45%, P≤0.018%, S≤0.015%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, with the remainder being iron and unavoidable impurities; The manufacturing process of SWRH42A steel for nail making includes the following steps: 1) Converter smelting with oxygen top and bottom blowing, tapping temperature 1580~1600℃, tapping endpoint C 0.20%~0.30%, converter double slag smelting, target P≤0.015% in one-time furnace turning; 2) Static argon blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1530~1580℃, posttreatment temperature 1525~1555℃; 3) LF furnace refining: LF refining time 60-80 min, total analysis temperature 1495-1565℃; 4) Continuous casting: Platform temperature 1506~1575℃, tundish temperature 1515~1540℃, superheat maintained at 25~35℃, casting speed 2.2~2.4m / min; 5) Heating process: Walking beam furnace heating, preheating section 860~900℃, heating section 1100~1140℃, soaking section 1130~1170℃, heating time ≤2.5h; 6) Rolling process: Roughing temperature 1000~1040℃; Finishing inlet temperature 880~920℃; Wire drawing temperature 880~920℃; Air-cooled roller speed: Head roller 0.70~0.90m / s; Heat insulation cover open; Fan: 1 # -3 # Frequency modulation 30-40Hz; 4 # -5 # FM 25-35Hz; 6 # The fan is 100% on; 7 # -11 # All off; The tensile strength of SWRH42A steel wire rod for nail making is 671-746 MPa, elongation after fracture is 22.5%-27.5%, and reduction of area is 55%-57%; non-metallic inclusions A+C≤1.5; B+D≤1.5; The microstructure of the steel is ferrite + pearlite, and the thickness of the decarburized layer is 0.04 to 0.07 mm.

2. A manufacturing process for SWRH42A nail-making steel as described in claim 1, characterized in that, The methods and steps include the following: 1) Converter smelting with oxygen top and bottom blowing, tapping temperature 1580~1600℃, tapping endpoint C 0.20%~0.30%, converter double slag smelting, target P≤0.015% in one-time furnace turning; 2) Static argon blowing: Static argon blowing time ≥ 8 min, pretreatment temperature 1530~1580℃, posttreatment temperature 1525~1555℃; 3) LF furnace refining: LF refining time 60-80 min, total analysis temperature 1495-1565℃; 4) Continuous casting: Platform temperature 1506~1575℃, tundish temperature 1515~1540℃, superheat maintained at 25~35℃, casting speed 2.2~2.4m / min; 5) Heating process: Walking beam furnace heating, preheating section 860~900℃, heating section 1100~1140℃, soaking section 1130~1170℃, heating time ≤2.5h; 6) Rolling process: Roughing temperature 1000~1040℃; Finishing inlet temperature 880~920℃; Wire drawing temperature 880~920℃; Air-cooled roller speed: Head roller 0.70~0.90m / s; Heat insulation cover open; Fan: 1 # -3 # Frequency modulation 30-40Hz; 4 # -5 # FM 25-35Hz; 6 # The fan is 100% on; 7 # -11 # All off.

3. The production process of SWRH42A nail-making steel according to claim 2, characterized in that, In step 1) above, the scrap steel in the converter smelting accounts for 10-15%, and the molten iron accounts for 85-90%.

4. The production process of SWRH42A nail-making steel according to claim 2, characterized in that, The following auxiliary materials are added per ton of steel in the converter smelting of step 1) above: 30-35 kg of active lime, 5.5-8.5 kg of dolomite, 18-24 kg of ore from Australia, and 25-34 kg of limestone; when the steel is tapped to 1 / 4-1 / 3, deoxidation and alloying are carried out, and the argon blowing time is ≥5 min.

5. The production process of SWRH42A nail-making steel according to claim 2, characterized in that, In the LF furnace refining process of step 3) above, the amount of auxiliary materials added per ton of steel is as follows: 5.3-6.5 kg of active lime, 0.33-0.67 kg of fluorite, 0.40-0.60 kg of carbide slag, and 0.50-1.0 kg of carbonized rice husk; and the alloy is fine-tuned, with a soft blowing time of ≥15 min.

6. The production process of SWRH42A nail-making steel according to claim 2, characterized in that, In step 4) above, the electromagnetic stirring current of the crystallizer is 260-300A, the frequency is 4-6Hz, and it rotates in both directions; the electromagnetic stirring current at the end is 230-270A, the frequency is 6-10Hz, and it rotates continuously.

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