A production method for improving the structure homogenization of high carbon steel wire rod

Abstract

This invention relates to the field of metal wire technology, specifically to a production method for improving the uniformity of the microstructure of high-carbon steel wire rod. The wire rod is composed of the following chemical composition by weight percentage: C: 0.85%~0.95%, Si: 0.70%~1.00%, Mn: 0.4%~0.6%, P≤0.02%, S≤0.02%, Cr: 0.20%~0.40%, V: 0.02%~0.06%, Co: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities. The wire rod specifications are Φ5.0mm~Φ16.0mm. This invention suppresses carbon inclusions by adding alloying elements, and through wire heating, rolling, and controlled cooling processes, the high-carbon steel wire rod achieves good control of carbon inclusions while ensuring microstructure performance indicators, with a carbon inclusion level below grade 2 and a 100% pass rate.

Description

Technical Field

[0001] This invention relates to the field of metal wire technology, specifically to a production method for improving the uniformity of the microstructure of high-carbon steel wire rod. Background Technology

[0002] During the post-rolling cooling process of high-carbon steel, when the temperature range is Acm-Ar1, the solubility of carbon in austenite decreases. Excessively high carbon concentrations precipitate as cementite along the austenite grain boundaries, forming a network structure. The higher the final hot working temperature and the slower the subsequent cooling, the more severe the network cementite formation. Controlling carbon segregation in the center of high-carbon steel is particularly difficult; improper control can easily lead to the formation of network cementite in the core of the wire rod after hot rolling. During phase transformation, the network cementite precipitates along the original austenite grain boundaries, weakening them. This reduces the steel's mechanical properties, weakens intermetallic bonding, decreases impact toughness, increases brittleness, and easily causes intergranular cracking. It also affects processing performance. For hypereutectoid high-carbon steel, the high carbon content results in high strength and hardness but poor toughness; the presence of network cementite further exacerbates the brittleness, limiting processing and service performance. Furthermore, for alloy tool steels and bearing steels, it reduces wear resistance and affects service life.

[0003] In the carbon network rating, the main considerations are the bifurcation angle, size, and degree of network formation. If the network cementite has formed a network or occupies a large area, it will seriously affect the performance, causing pen tip breakage during material drawing, and will also cause pen tip tensile fracture during tensile testing of the produced steel strands, resulting in a decrease in the performance of the steel strands and posing a safety hazard in product use. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a production method for improving the uniformity of the microstructure of high carbon steel wire rod, so that while ensuring the microstructure performance indicators, the carbon content of the wire rod is controlled at a good level, with the carbon content grade below 2 and the carbon content qualification rate of 100%.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A high-carbon steel wire rod is composed of the following chemical composition in weight percentages: C: 0.85%~0.95%, Si: 0.70%~1.00%, Mn: 0.4%~0.6%, P≤0.02%, S≤0.02%, Cr: 0.20%~0.40%, V: 0.02%~0.06%, Co: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities.

[0006] The effect of selecting the above alloying elements and their contents: 1. Carbon (C) is the most important component element in steel, significantly affecting the strength and plasticity of wire rod. Increasing its content can improve strength, but drastically decreases plasticity. If the C content exceeds 0.85%, the formation of proeutectoid cementite at grain boundaries will reduce drawability, especially given segregation in the steel. Therefore, the C content can be reduced by adding alloying elements that suppress network carbon, thus compensating for the strength loss. The interlamellar spacing is a factor controlling the strength and plasticity of pearlitic steel. When the C content of pearlitic steel changes, both strength and plasticity are also affected by the proportion of the hard phase, namely cementite. Increasing the C content will improve the strength and work hardening coefficient of the steel wire. Therefore, this invention precisely controls the C content to be between 0.85% and 0.95%.

[0007] 2. Si plays a role in solid solution strengthening, refining lamellar layers, and improving hardenability. Simultaneously, it can reduce the softening of pearlitic steel wire during hot-dip galvanizing. The presence of Si at the ferrite / cementite interface reduces the solubility of carbon in ferrite, preventing the decomposition of lamellar cementite and thus preventing its cracking and spheroidization during high-temperature annealing. Therefore, Si prevents age-induced softening during hot-dip galvanizing. Therefore, this invention precisely controls the Si content to be 0.70%~1.00%.

[0008] 3. Mn can improve hardenability, refine the interlamellar spacing, and increase the strength of high-carbon steel. However, it easily produces low-temperature microstructure in the segregation zone, reducing drawability. Therefore, the Mn content should not exceed 0.60%. Thus, this invention precisely controls the Mn content to 0.4%~0.6%.

[0009] 4. P and S elements have no benefit to the mechanical properties of steel plates, especially elongation. P should be controlled to ≤0.02% and S to ≤0.02%.

[0010] 5. Cr can improve hardenability and refine the interlamellar spacing of pearlite, effectively increasing the strength and work hardening rate of steel wire. Adding Cr refines the interlamellar spacing, improving plasticity, while simultaneously reducing the deformability of cementite. Therefore, this invention precisely controls the Cr content to 0.20%~0.40%.

[0011] 6. V (Volume) refines grain size, improving the strength and toughness of steel. However, excessive V can form large inclusions in the steel. When added synergistically with Si (Si), the addition of V and Si can suppress the formation of continuous cementite at grain boundaries in high-carbon steel with a carbon content of 0.8% or higher. Adding V can break up the grain boundary network cementite, while Si can inhibit the growth of cementite during phase transformation. Therefore, this invention precisely controls the V content to 0.02%~0.06%.

[0012] 7. Co can lower the diffusion activation energy of carbon in iron, thus accelerating the diffusion rate of carbon in austenite. During cooling, it promotes more uniform and finer precipitation of cementite, refining cementite particles and thereby improving the microstructure and properties of high-carbon steel. Therefore, this invention precisely controls the Co content to 0.1%~0.3%.

[0013] A production method for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes a wire heating, rolling, and controlled cooling process. The specific steps of this production method are as follows: 1) Heating: Heating temperature: 1050~1150℃.

[0014] 2) Rolling: The temperature at which the wire enters the finishing mill is 820~880℃, the temperature at which it enters the double module is 820~880℃, and the temperature at which it spins out is 820~880℃.

[0015] 3) Wire rod cooling: After spinning, the wire rings are continuously cooled by an EDC water bath device. The temperature of the wire entering the EDC device is controlled to be 800~860℃, the water bath temperature is 90~100℃, and the wire outlet water temperature is 520~620℃.

[0016] The diameter of the wire rod is Φ5.5mm~Φ16.0mm, and the inlet velocity of the intermediate EDC is adjusted according to the wire rod diameter. When the diameter is Φ5.0~10.0mm, the EDC inlet velocity is 0.60~0.80m / s; when the diameter is Φ11.0~16.0mm, the EDC inlet velocity is 0.30~0.59m / s.

[0017] The wire rod produced using the above method has the following properties: wire rod carbon grade below level 2, carbon qualification rate of 100%, tensile strength of 1350MPa or above, and surface shrinkage rate of 25% or above.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention precisely adds specific alloying elements Cr and V to inhibit the precipitation of proeutectoid cementite at grain boundaries, thereby effectively blocking the formation of network carbides. The alloy design takes into account both strength and plasticity, avoiding excessive addition that would lead to increased costs or decreased processing performance.

[0019] 2. This invention employs short-term heat preservation at a high temperature of 1050~1100℃ to control austenite grain growth, reduce the risk of subsequent carbide segregation, and implements "low-temperature precision rolling" (final rolling temperature ≤900℃). Combined with large deformation rolling, it breaks up the initial carbides and refines the grains.

[0020] 3. The present invention adopts a "rapid cooling + slow cooling" composite mode: immediately after rolling, it is rapidly cooled to 520~620℃ at a rate of ≥15℃ / s to suppress the precipitation of network carbides; then it is slowly cooled to below 500℃ to avoid martensite transformation.

[0021] This invention overcomes the limitations of traditional methods that rely on post-annealing to eliminate carbon residue. Through process reengineering, it achieves 100% first-pass carbon residue qualification, reducing energy consumption per ton of steel by 12%, thus combining quality and economic advantages. The wire rod diameter is Φ5.5mm~Φ16.0mm, the carbon residue level is below grade 2, the carbon residue qualification rate is 100%, the tensile strength is above 1350MPa, and the reduction of area is above 25%. This ensures that high-carbon steel wire rod maintains good carbon residue control while ensuring its microstructure and performance indicators. Attached Figure Description

[0022] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention. Detailed Implementation

[0023] This invention discloses a production method for improving the uniformity of the microstructure of high-carbon steel wire rod. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0024] Example 1: A high-carbon steel wire rod with a specification of Φ5.0mm. Its chemical composition and mass percentage are as follows: C: 0.85%, Si: 0.70%, Mn: 0.40%, P: 0.020%, S: 0.020%, Cr: 0.20%, V: 0.02%, Co: 0.1%, with the balance being Fe and unavoidable impurities.

[0025] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: heating temperature 1050℃; 2) Wire rolling temperature: 820℃ for entering the finishing mill, 820℃ for entering the double-module mill, and 820℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out, it continuously passes through an EDC water bath for controlled cooling. The wire rod enters the EDC device at 800°C, the water bath at 90°C, and the water temperature exits at 520°C. The steel EDC inlet velocity is 0.80 m / s. 4) Wire rod structure and properties: Wire rod carbon grade 0, carbon qualification rate 100%, wire rod tensile strength 1350MPa, and surface shrinkage rate 30%.

[0026] Example 2: A high-carbon steel wire rod with a specification of Φ8.0mm. Its chemical composition and mass percentage are as follows: C: 0.87%, Si: 0.8%, Mn: 0.45%, P: 0.015%, S: 0.015%, Cr: 0.25%, V: 0.03%, Co: 0.15%, with the balance being Fe and unavoidable impurities.

[0027] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: Heating temperature 1080℃; 2) Wire rolling temperature: 835℃ for entering the finishing mill, 840℃ for entering the double-module mill, and 830℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out the wire, it is continuously cooled by an EDC water bath device. When the wire rod enters the EDC device, the wire rod temperature is 810°C and the water bath temperature is 95°C. When the wire rod exits the water temperature, it is 540°C. The steel EDC inlet velocity is 0.7m / s. 4) Wire rod structure and properties: Wire rod carbon grade 0, carbon qualification rate 100%, wire rod tensile strength above 1360MPa, and surface shrinkage rate 28%.

[0028] Example 3: A high-carbon steel wire rod with a specification of Φ10.0mm. Its chemical composition and mass percentage are as follows: C: 0.88%, Si: 0.85%, Mn: 0.50%, P: 0.012%, S: 0.010%, Cr: 0.28%, V: 0.04%, Co: 0.2%, with the balance being Fe and unavoidable impurities.

[0029] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: Heating temperature 1100℃; 2) Wire rolling temperature: 840℃ for entering the finishing mill, 845℃ for entering the double-module mill, and 845℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out the wire, it is continuously cooled by an EDC water bath device. When the wire rod enters the EDC device, the wire rod temperature is 830°C and the water bath temperature is 95°C. When the wire rod exits the water temperature, it is 540°C. The steel EDC inlet velocity is 0.60m / s. 4) Wire rod structure and properties: Wire rod carbon grade 0, carbon qualification rate 100%, wire rod tensile strength above 1360MPa, and surface shrinkage rate 30%.

[0030] Example 4: A high-carbon steel wire rod with a specification of Φ14.0mm. Its chemical composition and mass percentage are as follows: C 0.90%, Si 0.90%, Mn 0.55%, P 0.010%, S 0.009%, Cr 0.30%, V 0.05%, Co 0.25%, with the balance being Fe and unavoidable impurities.

[0031] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: Heating temperature 1120℃; 2) Wire rolling temperature: 860℃ for entering the finishing mill, 855℃ for entering the double-module mill, and 855℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out the wire, it is continuously cooled by an EDC water bath device. When the wire rod enters the EDC device, the wire rod temperature is 840°C and the water bath temperature is 98°C. When the wire rod exits the water temperature, it is 570°C. The steel EDC inlet rate is 0.50. 4) Wire rod structure and properties: Wire rod carbon grade 1, carbon qualification rate 100%, wire rod tensile strength 1380MPa, and shrinkage rate 32%.

[0032] Example 5: A high-carbon steel wire rod with a specification of Φ14.0mm. Its chemical composition and mass percentage are as follows: C 0.92%, Si 0.95%, Mn 0.58%, P 0.009%, S 0.011%, Cr 0.35%, V 0.06%, Co 0.28%, with the balance being Fe and unavoidable impurities.

[0033] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: Heating temperature 1140℃; 2) Wire rolling temperature: 880℃ for entering the finishing mill, 865℃ for entering the double-module mill, and 865℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out the wire, it is continuously cooled by an EDC water bath device. When the wire rod enters the EDC device, the wire rod temperature is 850°C and the water bath temperature is 100°C. When the wire rod exits the water temperature, it is 590°C. The steel EDC inlet velocity is 0.40m / s. 4) Wire rod structure and properties: Wire rod carbon grade 2, carbon qualification rate 100%, wire rod tensile strength above 1420MPa, and surface shrinkage rate 34%.

[0034] Example 6: A high-carbon steel wire rod with a specification of Φ16.0mm. Its chemical composition and mass percentage are as follows: C 0.95%, Si 1.00%, Mn 0.60%, P 0.013%, S 0.012%, Cr 0.38%, V 0.06%, Co 0.3%, with the balance being Fe and unavoidable impurities.

[0035] The production process for improving the uniformity of the microstructure of the aforementioned high-carbon steel wire rod mainly includes heating, rolling, and controlled cooling processes. The wire rod is continuously cooled via an EDC water bath after being coiled. The production process is as follows: 1) Wire heating process: heating temperature 1150℃; 2) Wire rolling temperature: 870℃ for entering the finishing mill, 880℃ for entering the double-module mill, and 880℃ for wire drawing. 3) Wire rod cooling: After the wire ring spins out the wire, it is continuously cooled by an EDC water bath device. When the wire rod enters the EDC device, the wire rod temperature is 860°C and the water bath temperature is 100°C. When the wire rod exits the water temperature, it is 620°C. The steel EDC inlet velocity is 0.30m / s. 4) Wire rod structure and properties: Wire rod carbon grade 1, carbon qualification rate 100%, wire rod tensile strength above 1450MPa, and surface shrinkage rate 32%.

[0036] A production method for controlling the carbon content of high-carbon steel wire rod (a production method for improving the uniformity of the microstructure of high-carbon steel wire rod) using the above-mentioned technical solution, with wire rod specifications ranging from Φ5.0mm to Φ16.0mm, mainly suppresses carbon content through the addition of alloying elements. By designing the wire rod heating, rolling, and controlled cooling processes, the invention achieves good control of the carbon content of high-carbon steel while ensuring its microstructure performance indicators, achieving a carbon content level below grade 2 and a 100% carbon content qualification rate. Specific production data are shown in the table below: Table 1 Comparison of the properties of copper-clad steel wire rods and steel wires produced by the process of this invention and conventional processes. Experimental data show that the process of this invention is significantly superior to conventional methods, achieving a perfect balance between the strength and plasticity, microstructure uniformity, and carbon content control of high-carbon steel wire rod. It is suitable for the production of high-end steel wire products and has broad industrial application prospects. Thus, the technical solution described in this specification has been fully elucidated, and its innovation and practicality provide a reliable solution for the quality control of high-carbon steel.

[0037] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A production method for improving the uniformity of the microstructure of high-carbon steel wire rod, characterized in that, Wire rod consists of the following chemical components in weight percentage: composition: C: 0.85%~0.95%, Si: 0.70%~1.00%, Mn: 0.4%~0.6%, P≤0.02%, S≤0.02%, Cr: 0.20%~0.40%, V: 0.02%~0.06%, Co: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities; The production method specifically includes the following steps: 1) Heating: Heat the steel billet to 1050~1150℃; 2) Rolling: The rolling temperature is controlled so that the temperature at which the material enters the finishing mill is 820~880℃, the temperature at which the material enters the double module is 820~880℃, and the temperature at which the material exits the wire is 820~880℃. 3) Wire rod cooling: After spinning, the wire rings are continuously cooled by an EDC water bath device. The temperature of the wire entering the EDC device is controlled to be 800~860℃, the water bath temperature is 90~100℃, and the wire outlet water temperature is 520~620℃.

2. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, The diameter of the wire rod is Φ5.5mm~Φ16.0mm, and the EDC inlet speed in step 3) is adjusted according to the wire rod diameter. When the diameter is Φ5.0~10.0mm, the EDC inlet velocity is 0.60~0.80m / s; When the diameter is Φ11.0~16.0mm, the EDC inlet velocity is 0.30~0.59m / s.

3. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, The wire rod has a carbon content of ≥0.85wt%, a tensile strength of ≥1350MPa, and a shrinkage rate of ≥25%.

4. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, The heating temperature in step 1) is 1080~1120℃.

5. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, In step 2), the spinning temperature is 830~860℃.

6. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, In step 3), the temperature of the wire rod entering the EDC device is 820~850℃.

7. The production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, In step 3), the EDC water bath temperature is 92~98℃.

8. A production method for improving the uniformity of the microstructure of high-carbon steel wire rod according to claim 1, characterized in that, In step 3), the outlet water temperature of the wire rod is 550~600℃.

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