A method of rolling a low carbon alloy steel

Abstract

The application belongs to the technical field of material processing, and provides a rolling method of low-carbon alloy steel, which comprises the following steps: sequentially performing heating treatment, rough rolling and finish rolling on a low-carbon alloy steel billet, and finally obtaining a low-carbon alloy steel wire rod; the heating treatment comprises a heating section and a soaking section which are sequentially performed, and the temperature of the soaking section is 1090-1120 DEG C; the rough rolling temperature is 950-990 DEG C, and the single-pass deformation of the rough rolling is 28%-44%. The rolling process provided by the application promotes the recrystallization and crack healing of the billet, reduces the risk of grain boundary, effectively reduces the surface defect proportion of the finished wire rod, improves the finished product rate, and can prepare large-size (Φ>=16 mm) wire rods.

Description

Technical Field

[0001] This invention belongs to the field of materials processing technology, and specifically relates to a rolling method for low-carbon alloy steel. Background Technology

[0002] In the metal products industry, low-carbon alloy steel materials, such as ML20Cr and 51B20, are widely used in the manufacture of fasteners (such as bolts and nuts) and tools (such as wrenches). The carbon content of these low-carbon alloy steels is controlled within a low range, ensuring good workability for cold heading and extrusion. Furthermore, by adding alloying elements such as chromium, manganese, and molybdenum to varying degrees, the hardenability of the steel can be significantly improved, and temper brittleness can be suppressed, thereby specifically enhancing the mechanical properties of the material.

[0003] However, due to their low carbon content and high alloying element content, these steel grades present significant surface quality risks during the preparation of hot-rolled wire rod base materials. Alloying elements tend to segregate at grain boundaries or form complex carbides with carbon at rolling temperatures, reducing grain boundary strength. Improper rolling processes can cause red-hot steel to experience significant tensile stress or deformation in the brittle temperature range, easily inducing crack propagation at grain boundaries. Alloying elements can form a denser oxide scale, which is easily pressed into the matrix by the rolls, creating stress concentration points. The high hardenability of the steel generates significant microstructure transformation stress during cooling, making it highly susceptible to surface cracking.

[0004] Therefore, the rolling of low-carbon alloy steel generally faces a contradiction between excellent service performance and deterioration of rolling processability, resulting in a high proportion of defects such as cracks in finished wire rods. This not only directly reduces the yield of the product, but these minor defects are also more likely to expand further during subsequent processing, posing significant quality and safety hazards. Therefore, it is necessary to develop a rolling method for low-carbon alloy steel that effectively improves surface defects. Summary of the Invention

[0005] The purpose of this invention is to provide a rolling method for low-carbon alloy steel, which improves the surface defects of low-carbon alloy steel rolling, reduces the surface defect rate, and increases the yield by optimizing the rolling process.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a rolling method for low-carbon alloy steel, the rolling method comprising the following steps:

[0008] Low-carbon alloy steel billets are subjected to heat treatment, rough rolling and finish rolling in sequence to finally obtain low-carbon alloy steel wire rods.

[0009] The heating process includes a heating section and a homogenization section performed sequentially, wherein the homogenization temperature of the homogenization section is 1090-1120℃.

[0010] The initial rolling temperature of the roughing mill is 950-990℃, and the deformation per pass of the roughing mill is 28%-44%.

[0011] The rolling process provided by this invention effectively improves the surface defects of the resulting low-carbon alloy steel wire rods through optimization of rolling process parameters. By controlling the heating temperature, the healing of micro-defects in the billet is promoted; by controlling the initial rolling temperature, local bowing and interface migration within the billet are promoted, reducing spacing and enhancing internal diffusion healing; by controlling the deformation amount, the interatomic spacing is promoted to a large attractive range, thereby increasing diffusion and exchange to form metallic bonds. Furthermore, controlling the deformation amount can reduce the number of rolling passes for large-diameter wire rods. Through the synergistic matching of these three process parameters, recrystallization and crack healing in the billet are promoted, grain boundary risk is reduced, the proportion of surface defects in the finished wire rods is effectively reduced, the yield is improved, and large-diameter (Φ≥16mm) wire rods can be produced.

[0012] In this invention, the heat equalization temperature of the heat equalization section is 1090-1120℃, for example, it can be 1090℃, 1095℃, 1100℃, 1105℃, 1110℃, 1115℃ or 1120℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] In this invention, the initial rolling temperature of the roughing roll is 950-990℃, for example, it can be 950℃, 960℃, 970℃, 980℃ or 990℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] In this invention, the deformation amount of a single pass in the roughing rolling is 28%-44%, for example, it can be 28%, 30%, 32%, 35%, 38%, 40%, 42% or 44%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] In this invention, the deformation amount refers to the reduction rate of the rolled piece.

[0016] Preferably, the total heating time is 90-120 minutes, for example, 90 minutes, 95 minutes, 100 minutes, 105 minutes, 110 minutes, 115 minutes or 120 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the time of the heat soaking section accounts for 30-40 minutes of the total heating treatment time, for example, 30 minutes, 33 minutes, 35 minutes, 38 minutes, or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, when the mass percentage of C in the low-carbon alloy steel is ≥0.18%, the temperature of the soaking zone is 1100-1120℃, for example, it can be 1100℃, 1102℃, 1105℃, 1108℃, 1110℃, 1112℃, 1115℃, 1118℃ or 1120℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0019] Preferably, when the mass percentage of C in the low-carbon alloy steel is <0.18%, the temperature of the soaking zone is 1090-1100℃, for example, it can be 1090℃, 1092℃, 1095℃, 1098℃ or 1100℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, when the mass percentage of C in the low-carbon alloy steel is ≥0.18%, the initial rolling temperature of the rough rolling is 970-990℃, for example, it can be 970℃, 972℃, 975℃, 978℃, 980℃, 982℃, 985℃, 988℃ or 990℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0021] Preferably, when the mass percentage of C in the low-carbon alloy steel is ≥0.18% and the diameter of the low-carbon alloy steel wire is <22mm, the initial rolling temperature of the rough rolling is 970-980℃, for example, it can be 970℃, 972℃, 975℃, 978℃ or 980℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, when the mass percentage of C in the low-carbon alloy steel is ≥0.18% and the diameter of the low-carbon alloy steel wire is ≥22mm, the initial rolling temperature of the rough rolling is 975-990℃, for example, 975℃, 978℃, 980℃, 982℃, 985℃, 988℃ or 990℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] Preferably, when the mass percentage of C in the low-carbon alloy steel is <0.18%, the initial rolling temperature of the rough rolling is 950-970℃, for example, 950℃, 955℃, 960℃, 965℃ or 970℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, when the mass percentage of C in the low-carbon alloy steel is <0.18% and the diameter of the low-carbon alloy steel wire is <22mm, the initial rolling temperature of the rough rolling is 950-960℃, for example, 950℃, 952℃, 955℃, 958℃ or 960℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] Preferably, when the mass percentage of C in the low-carbon alloy steel is <0.18% and the diameter of the low-carbon alloy steel wire is ≥22mm, the initial rolling temperature of the rough rolling is 960-970℃, for example, 960℃, 962℃, 965℃, 968℃ or 970℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] Preferably, the temperature difference between two adjacent passes of the roughing mill is 0-5℃, for example, it can be 0℃, 1℃, 2℃, 3℃, 4℃ or 5℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the final rolling temperature of the roughing roll is ≥940℃, for example, it can be 940℃, 942℃, 945℃, 947℃, 950℃, 955℃ or 960℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] Preferably, in the rough rolling process, the billet passes through two adjacent passes in a time range of 4-20 seconds, for example, 4 seconds, 5 seconds, 8 seconds, 10 seconds, 12 seconds, 15 seconds, 18 seconds, or 20 seconds, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] In this invention, by coordinating the control of deformation amount, rolling temperature and rolling time in different passes, static recrystallization during the rolling process is promoted, ensuring a high proportion of static recrystallization in the billet, thereby reducing the risk of cracking in the finished product and improving surface quality.

[0030] Preferably, in the rough rolling, the recrystallization ratio of the billet between each pass is ≥80%, for example, it can be 80%, 82%, 85%, 88%, 90%, 92%, 95% or 98%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, and 85%-95% is more preferred.

[0031] Preferably, the shape factor δ of the precision rolling is controlled to be 1.0-2.0, for example, it can be 1.0, 1.2, 1.5, 1.8 or 2.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] In this invention, the finishing rolling is performed using a reducing sizing mill. The formula for calculating the shape factor δ is as follows:

[0033] δ=L / h.

[0034] Where L is the contact arc length between the roll and the workpiece during finishing rolling, and h is the average thickness of the workpiece.

[0035] Preferably, the finishing rolling process involves at least two passes.

[0036] In this invention, by controlling the shape coefficient, the deformation penetration of the diameter reduction process is regulated, so that the rolling deformation of the diameter reduction mill can fully penetrate to the center of the red steel, promote the full flow of the deformed metal, and thus promote the healing of residual micro-defects on the surface.

[0037] Preferably, the shape factor of the first pass of the finishing rolling is 1.65-2.0, for example, it can be 1.65, 1.658, 1.692, 1.698, 1.7, 1.705, 1.732, 1.75, 1.756, 1.8, 1.85, 1.9, 1.95 or 2.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the shape factor of the final pass of the finishing rolling is 1.3-1.7, for example, it can be 1.3, 1.35, 1.392, 1.4, 1.446, 1.45, 1.488, 1.497, 1.5, 1.511, 1.523, 1.55, 1.6, 1.65, 1.686 or 1.7, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, when the finishing rolling is performed in at least three passes, the shape factor of the intermediate passes is between the shape factors of the first and last passes.

[0040] Preferably, the rolling method further includes: intermediate rolling and pre-finishing rolling performed sequentially between the roughing and finishing rolling.

[0041] Preferably, in the intermediate rolling and / or pre-finishing rolling, the recrystallization ratio between each pass is 75-80%, for example, it can be 75%, 76%, 77%, 78%, 79% or 80%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, in the intermediate rolling and / or pre-finishing rolling, the throughput time between two adjacent passes is 0.5-3s, for example, it can be 0.5s, 0.8s, 1s, 1.5s, 2s, 2.5s or 3s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the rolling method further includes: sequentially coiling and cooling after finishing rolling.

[0044] Preferably, the lead rate of the winding is 0.8-1.5, for example, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the outer amplitude of the winding is set to 5.5-9.5, for example, it can be 5.5, 6, 7, 8, 9 or 9.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the inner amplitude of the winding is set to 4.5-7.8, for example, it can be 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 7.8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the cooling rate is 0.15-0.3℃ / s, for example, it can be 0.15℃ / s, 0.18℃ / s, 0.2℃ / s, 0.22℃ / s, 0.25℃ / s, 0.28℃ / s or 0.3℃ / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the inlet temperature of the cooling system is ≥820℃, for example, it can be 820℃, 822℃, 825℃, 828℃, 830℃, 835℃, 840℃ or 850℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the cooling time is ≥40 minutes, for example, it can be 40 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 50 minutes, 55 minutes, 60 minutes or 70 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] In this invention, by controlling the winding parameters, the density of coil collection is increased, and the cooling rate is controlled to achieve slow cooling, thereby extending the high-temperature residence time of the coil. Combined with the deformation penetration and flow of the finishing mill, the diffusion, recrystallization, and healing of the micro-defects after the repair are promoted, further reducing the micro-defects on the surface of the finished product and improving and consolidating the surface quality of the finished coil.

[0051] Preferably, the chemical composition of the low-carbon alloy steel, in mass percentage, includes: C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, and Cr 0.7%-1.2%.

[0052] The mass percentage of C in the low-carbon alloy steel is 0.13%-0.25%, for example, it can be 0.13%, 0.15%, 0.18%, 0.2%, 0.22% or 0.25%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] The mass percentage of Si in the low-carbon alloy steel is 0.1%-0.35%, for example, it can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or 0.35%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] The mass percentage of Mn in the low-carbon alloy steel is 0.5%-0.9%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8% or 0.9%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] The Cr content in the low-carbon alloy steel is 0.7%-1.2% by mass, for example, it can be 0.7%, 0.8%, 0.9%, 1.0%, 1.1% or 1.2%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] Preferably, the chemical composition of the low-carbon alloy steel, by mass percentage, further includes: Mo 0.15%-0.25%, for example, 0.15%, 0.18%, 0.20%, 0.22% or 0.25%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0057] The chemical composition of the low-carbon alloy steel, in mass percentage, includes: C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, Cr 0.7%-1.2%, and Mo 0.15%-0.25%.

[0058] Preferably, the chemical composition of the low-carbon alloy steel, by mass percentage, further includes: B 0.0015%-0.0025%, for example, it can be 0.0015%, 0.0018%, 0.0020%, 0.0022%, 0.0024% or 0.0025%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] The chemical composition of the low-carbon alloy steel, in mass percentage, includes: C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, Cr 0.7%-1.2%, and B 0.0015%-0.0025%.

[0060] Preferably, the diameter of the low-carbon alloy steel wire is 16-38mm, for example, it can be 16mm, 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 34mm or 38mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] The rolling process provided by this invention promotes recrystallization and crack healing of steel billets, reduces grain boundary risk, effectively reduces the surface defect ratio of finished wire rods, improves yield, and can produce large-size (Φ≥16mm) wire rods by optimizing rolling process parameters and synergistic matching of the three. Attached Figure Description

[0063] Figure 1 This is a cross-sectional metallographic image of the low-carbon alloy steel wire provided in Example 1;

[0064] Figure 2 This is a cross-sectional metallographic image of the low-carbon alloy steel wire provided in Example 2;

[0065] Figure 3 This is a cross-sectional metallographic image of the low-carbon alloy steel wire provided in Example 3;

[0066] Figure 4 This is a cross-sectional metallographic image of the low-carbon alloy steel wire provided in Example 4. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0068] Example 1

[0069] This embodiment provides a rolling method for low-carbon alloy steel.

[0070] In this embodiment, the chemical composition of the low-carbon alloy steel, by mass percentage, includes: C 0.18%, Si 0.15%, Mn 0.65%, and Cr 0.90%.

[0071] The rolling method includes the following steps:

[0072] The low-carbon alloy steel billet is subjected to heat treatment, rough rolling, intermediate rolling, pre-finish rolling, finish rolling, coiling, and cooling in sequence to obtain low-carbon alloy steel wire rod. Wherein:

[0073] Heating treatment: including a heating section and a heat soaking section, the total heating treatment time is controlled to be 100 minutes, the heat soaking temperature of the heat soaking section is 1120℃, and the heat soaking time is 35 minutes.

[0074] Rough rolling: A total of 6 passes are performed, with the temperature difference between adjacent passes controlled within 5℃. First pass: Initial rolling temperature is 970℃, deformation is 28.48%; the billet's passage time between the first and second passes is controlled at 18.5s, achieving a recrystallization rate of 85%. Second pass: Rolling temperature is 966℃, deformation is 31.18%; the billet's passage time between the second and third passes is controlled at 13.8s, achieving a recrystallization rate of 80%. Third pass: Rolling temperature is 961℃, deformation is 43.35%; the billet's passage time between the third and fourth passes is controlled at 8.5s, achieving a recrystallization rate of 94%. Fourth pass: Rolling temperature is 956℃, deformation is 36.86%; the billet's passage time between the fourth and fifth passes is controlled at 6.5s, achieving a recrystallization rate of 88%. Fifth pass: Rolling temperature is 952℃, deformation is 43.71%; the billet's throughput time between the fifth and sixth passes is controlled at 4.5s, and the recrystallization ratio of the billet reaches 90%. Sixth pass: Finishing rolling temperature is 947℃, deformation is 39.11%; the billet's throughput time between the sixth and seventh passes is controlled at 8.9s, and the recrystallization ratio of the billet reaches 92%.

[0075] Intermediate rolling and pre-finishing rolling: Intermediate rolling and pre-finishing rolling are completed sequentially between the seventh and sixteenth passes. The deformation amounts of each pass are 38.08%, 40.42%, 39.87%, 36.68%, 36.41%, 36.38%, 42.16%, 40.28%, and 33.25%, respectively. The throughput times between adjacent passes are 2.5s, 1.7s, 1.2s, 1.0s, 1.4s, 2.3s, 0.9s, 0.7s, and 0.7s, respectively. The short throughput time of the billet results in a recrystallization ratio of 75%-80%, which plays a role in deformation and dimensional determination.

[0076] Finishing rolling: Four passes of finishing rolling are performed. For bars and wires with a diameter of Φ16mm, the shape factor δ of the first finishing rolling pass is controlled at 2.000, and the shape factor δ of the last finishing rolling pass is controlled at 1.686.

[0077] Rewinding: A large coil winding machine is used for collection. For bar wire with a fixed diameter of Φ16mm, the winding lead rate is 0.9, the external amplitude is controlled at 5.5, and the internal amplitude is controlled at 4.5, thereby increasing the density of coil collection.

[0078] Cooling: The collected wire rods are placed in a sealed, insulated corridor for slow cooling. The entry temperature of the wire rods is controlled at 820℃, the residence time for slow cooling is 40 minutes, and the average cooling rate is controlled at 0.16℃ / s. After cooling, low-carbon alloy steel wire rods are obtained.

[0079] Example 2

[0080] This embodiment provides a rolling method for low-carbon alloy steel.

[0081] In this embodiment, the chemical composition of the low-carbon alloy steel, by mass percentage, includes: C 0.23%, Si 0.30%, Mn 0.90%, Cr 0.70%, and B 0.0021%.

[0082] The rolling method includes the following steps:

[0083] The low-carbon alloy steel billet is subjected to heat treatment, rough rolling, intermediate rolling, pre-finish rolling, finish rolling, coiling, and cooling in sequence to obtain low-carbon alloy steel wire rod. Wherein:

[0084] Heating treatment: including a heating section and a heat soaking section, the total heating treatment time is controlled at 120 minutes, the heat soaking temperature in the heat soaking section is 1100℃, and the heat soaking time is 40 minutes.

[0085] Rough rolling: A total of 6 passes are performed, with the temperature difference between adjacent passes controlled within 5℃. First pass: Initial rolling temperature is 980℃, deformation is 28%; the billet's throughput time between the first and second passes is controlled at 18s, achieving a recrystallization rate of 86%. Second pass: Rolling temperature is 975℃, deformation is 30%; the billet's throughput time between the second and third passes is controlled at 14.5s, achieving a recrystallization rate of 82%. Third pass: Rolling temperature is 971℃, deformation is 43%; the billet's throughput time between the third and fourth passes is controlled at 9s, achieving a recrystallization rate of 95%. Fourth pass: Rolling temperature is 966℃, deformation is 36.5%; the billet's throughput time between the fourth and fifth passes is controlled at 6s, achieving a recrystallization rate of 89%. Fifth pass: Rolling temperature is 962℃, deformation is 43%; the billet's throughput time between the fifth and sixth passes is controlled at 4s, and the recrystallization ratio of the billet reaches 91%. Sixth pass: Finishing rolling temperature is 957℃, deformation is 38.5%; the billet's throughput time between the sixth and seventh passes is controlled at 8s, and the recrystallization ratio of the billet reaches 93%.

[0086] Intermediate rolling and pre-finishing rolling: Intermediate rolling and pre-finishing rolling are completed sequentially between the seventh and sixteenth passes. The throughput time between two adjacent passes is between 0.5 and 2.5 seconds. The billet throughput time is short, and the recrystallization ratio is 75%-80%, which plays a role in deformation and dimensional determination.

[0087] Finishing rolling: Four passes of finishing rolling are performed. For bar and wire rod with a diameter of Φ22mm, the shape factor δ of the first finishing rolling pass is controlled at 1.698, and the shape factor δ of the last finishing rolling pass is controlled at 1.497.

[0088] Rewinding: A large coil winding machine is used for collection. For bar wire with a fixed diameter of Φ22mm, the winding lead rate is 1.3, the external amplitude is controlled at 9.5, and the internal amplitude is controlled at 5.7, thereby increasing the density of coil collection.

[0089] Cooling: The collected wire rods are placed in a sealed, insulated corridor for slow cooling. The entry temperature of the wire rods is controlled at 825℃, the residence time for slow cooling is 45 minutes, and the average cooling rate is controlled at 0.18℃ / s. After cooling, low-carbon alloy steel wire rods are obtained.

[0090] Example 3

[0091] This embodiment provides a rolling method for low-carbon alloy steel.

[0092] In this embodiment, the chemical composition of the low-carbon alloy steel, by mass percentage, includes: C 0.13%, Si 0.20%, Mn 0.75%, Cr 1.0%, and Mo 0.25%.

[0093] The rolling method includes the following steps:

[0094] The low-carbon alloy steel billet is subjected to heat treatment, rough rolling, intermediate rolling, pre-finish rolling, finish rolling, coiling, and cooling in sequence to obtain low-carbon alloy steel wire rod. Wherein:

[0095] Heating treatment: including a heating section and a heat soaking section, the total heating treatment time is controlled at 90 minutes, the heat soaking temperature in the heat soaking section is 1090℃, and the heat soaking time is 30 minutes.

[0096] Rough rolling: A total of 5 passes are performed, with the temperature difference between adjacent passes controlled within 5℃. First pass: Initial rolling temperature is 960℃, deformation is 29%; the billet's throughput time between the first and second passes is controlled at 19s, achieving a recrystallization rate of 84%. Second pass: Rolling temperature is 955℃, deformation is 33%; the billet's throughput time between the second and third passes is controlled at 15s, achieving a recrystallization rate of 80%. Third pass: Rolling temperature is 951℃, deformation is 44%; the billet's throughput time between the third and fourth passes is controlled at 9.5s, achieving a recrystallization rate of 93%. Fourth pass: Rolling temperature is 947℃, deformation is 38%; the billet's throughput time between the fourth and fifth passes is controlled at 7s, achieving a recrystallization rate of 89%. Fifth pass: The final rolling temperature is 942℃, and the deformation is 41%; the billet's passage time between the fifth and sixth passes is controlled at 9.5s, and the recrystallization ratio of the billet reaches 91%.

[0097] Intermediate rolling and pre-finishing rolling: Intermediate rolling and pre-finishing rolling are completed sequentially between the sixth and fifteenth passes. The throughput time between two adjacent passes is between 0.5 and 2.5 seconds. The billet throughput time is short, and the recrystallization ratio is between 75% and 80%, which plays a role in deformation and dimensional determination.

[0098] Finishing rolling: Four passes of finishing rolling are performed. For bars and wires with a diameter of Φ20mm, the shape factor δ of the first finishing rolling pass is controlled at 1.756, and the shape factor δ of the last finishing rolling pass is controlled at 1.511.

[0099] Rewinding: A large coil winding machine is used for collection. For bar wire with a fixed diameter of Φ20mm, the winding lead rate is 0.8, the external amplitude is controlled at 6.9, and the internal amplitude is controlled at 4.6, thereby increasing the density of coil collection.

[0100] Cooling: The collected wire rods are placed in a sealed, insulated corridor for slow cooling. The entry temperature of the wire rods is controlled at 820℃, the residence time for slow cooling is 40 minutes, and the average cooling rate is controlled at 0.17℃ / s. After cooling, low-carbon alloy steel wire rods are obtained.

[0101] Example 4

[0102] This embodiment provides a rolling method for low-carbon alloy steel.

[0103] In this embodiment, the chemical composition of the low-carbon alloy steel, by mass percentage, includes: C 0.17%, Si 0.25%, Mn 0.60%, Cr 1.20%, and Mo 0.15%.

[0104] The rolling method includes the following steps:

[0105] The low-carbon alloy steel billet is subjected to heat treatment, rough rolling, intermediate rolling, pre-finish rolling, finish rolling, coiling, and cooling in sequence to obtain low-carbon alloy steel wire rod. Wherein:

[0106] Heating treatment: including a heating section and a heat soaking section, the total heating treatment time is controlled at 110 minutes, the heat soaking temperature in the heat soaking section is 1100℃, and the heat soaking time is 35 minutes.

[0107] Rough rolling: A total of 6 passes are performed, with the temperature difference between adjacent passes controlled within 5℃. First pass: Initial rolling temperature is 970℃, deformation is 28.48%; the billet's throughput time between the first and second passes is controlled at 19s, achieving a recrystallization rate of 85%. Second pass: Rolling temperature is 966℃, deformation is 31%; the billet's throughput time between the second and third passes is controlled at 13.8s, achieving a recrystallization rate of 80%. Third pass: Rolling temperature is 961℃, deformation is 44%; the billet's throughput time between the third and fourth passes is controlled at 8.5s, achieving a recrystallization rate of 95%. Fourth pass: Rolling temperature is 957℃, deformation is 36.86%; the billet's throughput time between the fourth and fifth passes is controlled at 6.5s, achieving a recrystallization rate of 88%. Fifth pass: Rolling temperature is 952℃, deformation is 43.71%; the billet's throughput time between the fifth and sixth passes is controlled at 4.5s, and the recrystallization ratio of the billet reaches 90%. Sixth pass: Finishing rolling temperature is 947℃, deformation is 39.11%; the billet's throughput time between the sixth and seventh passes is controlled at 8.9s, and the recrystallization ratio of the billet reaches 92%.

[0108] Intermediate rolling and pre-finishing rolling: Intermediate rolling and pre-finishing rolling are completed sequentially between the seventh and sixteenth passes. The throughput time between two adjacent passes is between 0.5 and 2.5 seconds. The billet throughput time is short, and the recrystallization ratio is 75%-80%, which plays a role in deformation and dimensional determination.

[0109] Finishing rolling: Two stands of reducing mills are set up for four passes of finishing rolling. For bars and wires with a sizing diameter of Φ28mm, the shape factor δ of the first finishing rolling pass is controlled at 1.658, and the shape factor δ of the last finishing rolling pass is controlled at 1.392.

[0110] Rewinding: A large coil winding machine is used for collection. For bar wire with a fixed diameter of Φ28mm, the winding lead rate is 1.2, the external amplitude is controlled at 8.9mm, and the internal amplitude is controlled at 7.8mm, thereby increasing the density of coil collection.

[0111] Cooling: The collected wire rods are placed in a sealed, insulated corridor for slow cooling. The entry temperature of the wire rods is controlled at 820℃, the residence time for slow cooling is 40 minutes, and the average cooling rate is controlled at 0.15℃ / s. After cooling, low-carbon alloy steel wire rods are obtained.

[0112] Comparative Example 1

[0113] This comparative example provides a rolling method for low-carbon alloy steel.

[0114] The chemical composition of the low-carbon alloy steel is the same as that in Example 1.

[0115] In the rolling method described, compared with Example 1, the homogenization temperature of the homogenization section is set to 1050℃, and the rest are the same as in Example 1.

[0116] Comparative Example 2

[0117] This comparative example provides a rolling method for low-carbon alloy steel.

[0118] The chemical composition of the low-carbon alloy steel is the same as that in Example 1.

[0119] In the rolling method described, compared with Example 1, the initial rolling temperature of the roughing roll is set to 940°C, but the temperature difference between adjacent passes in the roughing roll remains consistent with that in Example 1, and the rest is the same as in Example 1.

[0120] That is, in this comparative example, the rolling temperatures of the six passes in the roughing mill are 940℃, 936℃, 931℃, 926℃, 922℃, and 917℃, respectively.

[0121] Comparative Example 3

[0122] This comparative example provides a rolling method for low-carbon alloy steel.

[0123] The chemical composition of the low-carbon alloy steel is the same as that in Example 1.

[0124] In the rolling method described, compared with Example 1, the deformation amounts of each pass in the roughing rolling are set to 22.61%, 21.54%, 38.27%, 34.58%, 35.54% and 34.88%, respectively, while the rest are the same as in Example 1.

[0125] Comparative Example 4

[0126] This comparative example provides a rolling method for low-carbon alloy steel.

[0127] The chemical composition of the low-carbon alloy steel is the same as that in Example 2.

[0128] In the rolling method described, compared with Example 2, the homogenization temperature of the homogenization section is set to 1050℃, and the rest is the same as in Example 2.

[0129] Comparative Example 5

[0130] This comparative example provides a rolling method for low-carbon alloy steel.

[0131] The chemical composition of the low-carbon alloy steel is the same as that in Example 2.

[0132] In the rolling method described, compared with Example 2, the initial rolling temperature of the roughing mill is set to 945°C, but the temperature difference between adjacent passes in the roughing mill remains consistent with that in Example 2, and the rest is the same as in Example 2.

[0133] That is, in this comparative example, the rolling temperatures of the six passes in the roughing mill are 945℃, 940℃, 936℃, 931℃, 927℃, and 922℃, respectively.

[0134] Comparative Example 6

[0135] This comparative example provides a rolling method for low-carbon alloy steel.

[0136] The chemical composition of the low-carbon alloy steel is the same as that in Example 2.

[0137] In the rolling method described, compared with Example 2, the deformation amounts of each pass in the rough rolling are set to 25.42%, 29.83%, 42.58%, 35.88%, 35.91% and 37.86%, respectively, while the rest are the same as in Example 2.

[0138] Comparative Example 7

[0139] This comparative example provides a rolling method for low-carbon alloy steel.

[0140] The chemical composition of the low-carbon alloy steel is the same as that in Example 3.

[0141] In the rolling method described, compared with Example 3, the homogenization temperature of the homogenization section is set to 1045℃, and the rest are the same as in Example 3.

[0142] Comparative Example 8

[0143] This comparative example provides a rolling method for low-carbon alloy steel.

[0144] The chemical composition of the low-carbon alloy steel is the same as that in Example 3.

[0145] In the rolling method described, compared with Example 3, the initial rolling temperature of the roughing roll is set to 940°C, but the temperature difference between adjacent passes in the roughing roll remains consistent with that in Example 3, and the rest is the same as in Example 1.

[0146] That is, in this comparative example, the rolling temperatures of the five passes in the roughing mill are 940℃, 935℃, 931℃, 927℃, and 922℃, respectively.

[0147] Comparative Example 9

[0148] This comparative example provides a rolling method for low-carbon alloy steel.

[0149] The chemical composition of the low-carbon alloy steel is the same as that in Example 3.

[0150] In the rolling method described, compared with Example 3, the deformation amounts of each pass in the rough rolling are set to 24.65%, 27.15%, 43.43%, 36.78% and 41.22%, respectively, while the rest are the same as in Example 3.

[0151] Comparative Example 10

[0152] This comparative example provides a rolling method for low-carbon alloy steel.

[0153] The chemical composition of the low-carbon alloy steel is the same as that in Example 4.

[0154] In the rolling method described, compared with Example 4, the homogenization temperature of the homogenization section is set to 1050℃, and the rest is the same as in Example 4.

[0155] Comparative Example 11

[0156] This comparative example provides a rolling method for low-carbon alloy steel.

[0157] The chemical composition of the low-carbon alloy steel is the same as that in Example 4.

[0158] In the rolling method described, compared with Example 4, the initial rolling temperature of the roughing mill is set to 945°C, but the temperature difference between adjacent passes in the roughing mill remains consistent with that in Example 4, and the rest is the same as in Example 4.

[0159] That is, in this comparative example, the rolling temperatures of the six passes in the roughing mill are 945℃, 941℃, 936℃, 932℃, 927℃, and 922℃, respectively.

[0160] Comparative Example 12

[0161] This comparative example provides a rolling method for low-carbon alloy steel.

[0162] The chemical composition of the low-carbon alloy steel is the same as that in Example 4.

[0163] In the rolling method described, compared with Example 4, the deformation amounts of each pass in the rough rolling are set to 25.32%, 27.16%, 39.76%, 36.55%, 43.16% and 38.92%, respectively, while the rest are the same as in Example 4.

[0164] Performance testing

[0165] The low-carbon alloy steel wires manufactured in the examples and comparative examples were subjected to surface defect detection and microstructure and properties testing. The results are shown in Table 1.

[0166] The metallographic testing method for surface defect detection is as follows: the wire rod sample is cut, inlaid, ground, polished and etched. After etching, the surface defects are examined under a microscope and the number is counted.

[0167] The detection ratio is calculated as the ratio of the defect area to the observed cross section.

[0168] Table 1

[0169]

[0170] As can be seen from the test results in Table 1, referring to the embodiments, the rolling process of the present invention effectively reduces surface defects in steel and improves the yield by optimizing and synergistically controlling process parameters. The metallographic images of the wire rod samples from Examples 1-4 are shown below. Figure 1-4 As shown, the depth of defects on the surface of the wire rod sample is effectively reduced overall. In contrast, in the comparative example, when the temperature or deformation in the rolling process exceeds the range of this invention, the number of surface defects in the steel increases significantly, and the defect depth also increases. This is because when the rolling process parameters are not set reasonably, the micro-defects in the billet cannot be healed, leading to an increase in defects.

[0171] In summary, the rolling process provided by this invention, through the optimization of rolling process parameters and the synergistic matching of the three, promotes the recrystallization and crack healing of steel billets, reduces grain boundary risk, effectively reduces the surface defect ratio of finished wire rods, improves yield, and can produce large-size (Φ≥16mm) wire rods.

[0172] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A rolling method of a low-carbon alloy steel, characterized by, The rolling method comprises the following steps: The low-carbon alloy steel billet is sequentially subjected to heating treatment, rough rolling and finish rolling, and finally a low-carbon alloy steel wire rod is obtained; The chemical composition of the low-carbon alloy steel comprises, in mass percentage, C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, and Cr 0.7%-1.2%; The heating treatment comprises a heating section and a soaking section which are sequentially performed; when the mass percentage of C in the low-carbon alloy steel is ≥0.18%, the temperature of the soaking section is 1100-1120℃; when the mass percentage of C in the low-carbon alloy steel is <0.18%, the temperature of the soaking section is 1090-1100℃; When the mass percentage of C in the low-carbon alloy steel is ≥0.18% and the diameter of the low-carbon alloy steel wire rod is <22mm, the opening rolling temperature of the rough rolling is 970-980℃; when the mass percentage of C in the low-carbon alloy steel is ≥0.18% and the diameter of the low-carbon alloy steel wire rod is ≥22mm, the opening rolling temperature of the rough rolling is 975-990℃; when the mass percentage of C in the low-carbon alloy steel is <0.18% and the diameter of the low-carbon alloy steel wire rod is <22mm, the opening rolling temperature of the rough rolling is 950-960℃; when the mass percentage of C in the low-carbon alloy steel is <0.18% and the diameter of the low-carbon alloy steel wire rod is ≥22mm, the opening rolling temperature of the rough rolling is 960-970℃; The single-pass deformation of the rough rolling is 28%-44%.

2. The rolling method of low carbon alloy steel according to claim 1, characterized in that, The total time of the heating treatment is 90-120 minutes; and the time of the soaking section is 30-40 minutes.

3. The rolling method of the low-carbon alloy steel according to claim 1, characterized in that, The temperature difference between two adjacent passes of the rough rolling is 0-5℃; And / or, the finish rolling temperature of the rough rolling is ≥940℃; And / or, in the rough rolling, the recrystallization ratio of the billet between each pass is ≥80%.

4. The rolling method of the low carbon alloy steel according to claim 1, characterized in that, The shape factor δ of the finish rolling is controlled to be 1.0-2.

0.

5. The rolling method of the low-carbon alloy steel according to claim 4, characterized in that, The shape factor of the first pass of the finish rolling is 1.65-2.0; And / or, the shape factor of the last pass of the finish rolling is 1.3-1.

7.

6. The rolling method of the low carbon alloy steel according to claim 1, characterized in that, The rolling method further comprises: The rough rolling and the finish rolling are sequentially followed by intermediate rolling and pre-finish rolling; and the finish rolling is sequentially followed by winding and cooling.

7. The rolling method of the low-carbon alloy steel according to claim 1, characterized in that, The chemical composition of the low-carbon alloy steel comprises, in mass percentage, C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, Cr 0.7%-1.2%, and Mo 0.15%-0.25%. Or, the chemical composition of the low-carbon alloy steel comprises, in mass percentage, C 0.13%-0.25%, Si 0.1%-0.35%, Mn 0.5%-0.9%, Cr 0.7%-1.2%, and B 0.0015%-0.0025%.

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