A rolling method and a reinforcing bar for improving surface quality and rust resistance of hot-rolled ribbed steel bars

Abstract

The application discloses a rolling method for improving surface quality and rust resistance of hot-rolled ribbed steel bars and the steel bars, and the rolling method comprises the following steps: steel billet heating: the temperature of the soaking section of a heating furnace is controlled to be 1080-1120 DEG C, and the holding time t of the steel billet at the temperature of the soaking section satisfies t>=K*D / 2, wherein the unit of t is minute, D is the thickness of the steel billet and the unit is millimeter, and K is a coefficient and the value range is 0.9-1.3 min / mm; rolling: the heated steel billet is rolled, and the finish rolling temperature is controlled to be 960-1000 DEG C; and upper cooling bed cooling: the cooling intensity of the rolling post-cooling device is controlled, and the upper cooling bed temperature of the rolled steel bar is controlled to be 710-750 DEG C. The application forms a dense iron oxide scale layer while inhibiting surface blistering defects through the coordinated control of the heating system and the upper cooling bed temperature.

Description

Technical Field

[0001] This invention relates to the field of metal material rolling technology, and in particular to a rolling method and a steel bar for improving the surface quality and rust resistance of hot-rolled ribbed steel bars. Background Technology

[0002] During the post-rolling cooling process, if the temperature of the cooling bed on hot-rolled ribbed steel bars is too high, the dissolved gases (such as hydrogen) inside will rapidly precipitate to the surface. Alternatively, due to insufficient strength of the surface metal at high temperatures, the gas expands to form surface bubbles, which rupture after rolling, forming pit-like defects. This not only affects the product's appearance but may also become stress concentration points or corrosion initiation points. The iron oxide scale formed on the surface of the steel bars at high temperatures is its first line of defense against rust in the natural environment. Dense, continuous iron oxide scale can effectively delay the electrochemical corrosion of the matrix. The quality of the iron oxide scale is highly dependent on its formation temperature and time. Traditionally, to suppress blistering, a process of lowering the cooling bed temperature (e.g., below 680℃) is often adopted. However, this leads to insufficient iron oxide scale growth and a loose, porous structure, which severely weakens the initial rust resistance of the steel bars.

[0003] Existing processes cannot simultaneously address both surface blistering suppression and the requirement for dense iron oxide scale. While adding trace alloying elements can improve corrosion resistance, this increases costs; optimizing cooling water distribution to reduce thermal stress also falls short in controlling the root cause of blistering. Therefore, there is an urgent need for a rolling method that can synergistically improve the overall surface quality of reinforcing bars through pure process innovation, without altering the composition or significantly increasing costs. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of this invention is to provide a rolling method and a steel bar that improves the surface quality and rust resistance of hot-rolled ribbed steel bars.

[0005] The technical solution adopted by this invention to solve its technical problem is: a rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars, comprising the following steps:

[0006] (1) Steel billet heating: The temperature of the soaking zone of the heating furnace is controlled at 1080℃~1120℃, and the holding time t of the steel billet at the soaking zone temperature is controlled to satisfy: t≥K×D / 2, where t is in minutes, D is the thickness of the steel billet in millimeters, and K is a coefficient with a value range of 0.9~1.3 min / mm;

[0007] (2) Rolling: The heated steel billet is rolled, and the final rolling temperature is controlled at 960℃~1000℃;

[0008] (3) Cooling on the upper cooling bed: control the cooling intensity of the cooling device after rolling, and control the temperature of the upper cooling bed of the rolled steel bars to 710℃~750℃.

[0009] As a further improvement of the present invention, it also includes: in step (1), the heating temperature of the steel billet in the heating section of the heating furnace is 1060℃~1140℃.

[0010] As a further improvement of the present invention: in step (1), the value range of coefficient K is 1.0 to 1.2 min / mm.

[0011] As a further improvement of the present invention: in step (2), the final rolling temperature is 970℃~990℃.

[0012] As a further improvement of the present invention: in step (3), the temperature of the upper cooling bed is 720℃~740℃.

[0013] As a further improvement of the present invention: in step (1), the steel billet is a continuous casting billet, and the thickness D of the steel billet is 150mm to 200mm.

[0014] As a further improvement of the present invention: in step (2), the method of controlling the final rolling temperature includes: adjusting the opening of the cooling water valve between the finishing mill stands, and / or adjusting the opening of the cooling water valve after final rolling.

[0015] As a further improvement of the present invention: in step (3), the method of controlling the temperature of the upper cooling bed of the rolled steel bar includes: adjusting the number of opening pipes of the laminar flow cooling device or the cooling water pressure according to the surface temperature signal collected by the infrared temperature measuring device, so that the temperature of the upper cooling bed of the steel bar falls within the set range.

[0016] The present invention also provides a reinforcing bar prepared using the rolling method described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention achieves simultaneous reduction of surface blistering defects and improvement of surface oxide scale density by coordinating a heating regime with a soaking temperature of 1080℃~1120℃ and a soaking time t≥K×D / 2 and a cooling regime with an upper cooling bed temperature of 710℃~750℃. This allows the solid solution gas in the billet to diffuse and escape in advance during the heating stage, and form a dense iron oxide scale layer in the temperature range of 710℃~750℃ after rolling. Without changing the chemical composition of the steel, this invention achieves simultaneous reduction of surface blistering defects and improvement of surface oxide scale density. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In order to solve the technical problems in the prior art, the present invention will now be further described in conjunction with the accompanying drawings and embodiments:

[0022] like Figure 1 As shown, this invention discloses a rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars, comprising the following steps:

[0023] (1) Steel billet heating: The temperature of the soaking zone of the heating furnace is controlled at 1080℃~1120℃, and the holding time t of the steel billet at the soaking zone temperature is controlled to satisfy: t≥K×D / 2, where t is in minutes, D is the thickness of the steel billet in millimeters, and K is a coefficient with a value range of 0.9~1.3 min / mm;

[0024] (2) Rolling: The heated steel billet is rolled, and the final rolling temperature is controlled at 960℃~1000℃;

[0025] (3) Cooling on the upper cooling bed: control the cooling intensity of the cooling device after rolling, and control the temperature of the upper cooling bed of the rolled steel bars to 710℃~750℃.

[0026] To address the technological contradiction in existing hot-rolled ribbed steel bars where "lowering the upper cooling bed temperature reduces blistering but compromises rust resistance, while ensuring rust resistance requires higher temperatures that exacerbate blistering," the rolling method of this invention achieves simultaneous reduction of surface blistering defects and improvement of surface oxide scale density without altering the chemical composition of the steel, through synergistic optimization of the heating process and the initial cooling temperature. This significantly enhances the surface quality and atmospheric corrosion resistance of the steel bars.

[0027] Specifically, a heating strategy of "controlled temperature and homogenization, promoting diffusion" is adopted. The temperature of the steel billet in the homogenization zone of the heating furnace is controlled at 1080℃~1120℃, and the total homogenization time t (min) of the steel billet at this temperature is guaranteed to satisfy: t≥K×D / 2. Through relatively mild heating temperature and sufficient holding time, the internal structure of the steel billet is homogenized, and the dissolved hydrogen and other gases in the steel have sufficient time to slowly and uniformly diffuse out of the billet, thereby reducing the content of internal gases that cause blistering from the source.

[0028] In some embodiments, the heating temperature of the billet in the heating section of the heating furnace in step (1) is 1060℃~1140℃.

[0029] In some implementations, in step (1), the coefficient K ranges from 1.0 to 1.2 min / mm.

[0030] In some implementations, the final rolling temperature in step (2) is 970°C to 990°C.

[0031] The steel billet, after optimized heating, is subjected to conventional rolling deformation. However, by adjusting the cooling intensity between the finishing mill stands and the water cooling intensity after final rolling, the final rolling temperature of the steel bar is controlled at 970℃~990℃. This ensures that the rolling is completed within the austenitic single-phase region, resulting in uniform deformation and providing a suitable initial temperature for subsequent surface oxidation reactions.

[0032] In some implementations, the temperature of the upper cooling bed in step (3) is 720°C to 740°C.

[0033] The surface temperature of the rolled steel bars when they enter the cooling bed is controlled at 720℃~740℃. This temperature is within the ideal temperature window for the rapid formation of Fe3O4 (magnetite) and the formation of a dense layer. At this temperature, the surface of the steel bars can form a layer of iron oxide scale of suitable thickness, continuous structure, and denseness during the subsequent slow cooling process, significantly improving the rust resistance of the base.

[0034] Meanwhile, the upper temperature limit is significantly lower than the excessively high temperature (>780℃) traditionally used to preserve iron oxide scale, avoiding increased gas evolution pressure due to overheating and softening of the surface metal. More importantly, it works in conjunction with the optimized heating regime in step 1: since the internal gas content has been reduced in advance, the driving force and destructive force of gas evolution are greatly weakened when the steel bars are placed on the cooling bed in this "medium temperature range," thereby effectively suppressing the formation of bubbles.

[0035] In some embodiments, in step (1), the billet is a continuously cast billet, and the billet thickness D is 150mm to 200mm.

[0036] In some implementations, the method of controlling the final rolling temperature in step (2) includes: adjusting the opening of the cooling water valve between the finishing mill stands, and / or adjusting the opening of the cooling water valve after final rolling.

[0037] In some implementations, step (3) involves controlling the temperature of the upper cooling bed of the rolled steel bars by adjusting the number of manifolds opened or the cooling water pressure of the laminar flow cooling device based on the surface temperature signal collected by the infrared temperature measuring device, so that the temperature of the upper cooling bed of the steel bars falls within the set range.

[0038] Implementation Case 1:

[0039] This embodiment discloses a rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars. By systematically optimizing heating and cooling process parameters, the method synergistically improves the surface blistering defects and atmospheric corrosion resistance of the steel bars. The rolling method includes billet heating, rolling, cooling on a cooling bed, cooling on a cold bed, and subsequent processing steps, specifically including the following steps:

[0040] Step 1: Optimize the heating regime

[0041] A heating strategy of "temperature control and homogenization, promoting diffusion" is adopted. The temperature of the steel billet in the homogenization zone of the heating furnace is controlled at 1080℃~1120℃, and the total homogenization time t (min) of the steel billet at this temperature is guaranteed to satisfy: t≥K×D / 2, where D is the thickness of the steel billet (unit: mm), and K is a coefficient with a value range of 0.9~1.3 min / mm.

[0042] The core purpose of this step is to homogenize the internal structure of the steel billet through relatively mild heating temperature and sufficient holding time, and to allow sufficient time for dissolved gases such as hydrogen in the steel to slowly and evenly diffuse out of the billet, thereby reducing the content of internal gases that cause bubbling from the source.

[0043] Step 2: Control the rolling and final rolling temperatures

[0044] The optimized heated steel billets are subjected to conventional rolling deformation, but the final rolling temperature of the reinforcing bars is precisely controlled between 960 and 1000°C by adjusting the inter-stand cooling of the finishing mill and the intensity of water cooling after final rolling. This temperature range ensures that rolling is completed within the austenitic single-phase region, resulting in uniform deformation and providing a suitable initial temperature for subsequent surface oxidation reactions.

[0045] Step 3: Coordinated control of upper cooling bed temperature

[0046] The surface temperature of the rolled steel bars when they enter the cooling bed (i.e., the upper cooling bed temperature) is precisely controlled between 710℃ and 750℃. This temperature range is the key point for achieving synergistic optimization in this invention.

[0047] (1) Contribution to rust resistance: This temperature is within the ideal temperature window for the rapid formation and dense layer of Fe3O4 (magnetite). At this temperature, when the steel bar is placed on a cooling bed, a layer of iron oxide scale of suitable thickness, continuous structure and dense structure can be formed on the surface of the steel bar during the subsequent slow cooling process, which significantly improves the rust resistance of the foundation.

[0048] (2) Contribution to suppressing blistering: This upper temperature limit (750℃) is significantly lower than the excessively high temperature (>780℃) traditionally used to preserve iron oxide scale, thus avoiding increased gas evolution pressure due to overheating and softening of the surface metal. More importantly, it works in conjunction with the optimized heating regime in step 1: Since the internal gas content has been reduced in advance, when the steel bars are placed on the cooling bed in this "medium temperature range", the driving force and destructive force of gas evolution are greatly weakened, thereby effectively suppressing the generation of blistering.

[0049] (3) Subsequent cooling and treatment: The steel bars are cooled to room temperature on the cooling bed by natural air cooling or by weak wind-assisted cooling, and then routine straightening, length cutting, inspection and bundling are carried out.

[0050] This embodiment addresses the technological contradiction in existing hot-rolled ribbed steel bars where "lowering the upper cooling bed temperature reduces blistering but compromises rust resistance, while ensuring rust resistance requires higher temperatures, which exacerbates blistering." By synergistically optimizing the heating regime and cooling initiation temperature, this embodiment achieves simultaneous reduction of surface blistering defects and improvement of surface oxide scale density without altering the chemical composition of the steel, thereby significantly enhancing the surface quality and atmospheric corrosion resistance of the steel bars.

[0051] Implementation Case 2:

[0052] This embodiment optimizes the heating and cooling process parameters to produce HRB400E hot-rolled ribbed steel bars with a specification of Φ25mm. The steel billet is a continuously cast billet with a thickness D=155mm, and its chemical composition conforms to GB / T 1499.2-2018 standard. The specific steps are as follows:

[0053] Heating: The steel billet is fed into a walking beam furnace. The heating section temperature is set to 1100℃, and the soaking section temperature is also set to 1100℃. According to the formula t≥K×D / 2, taking K=1, the minimum soaking time tmin is calculated to be 77 minutes. The actual controlled soaking time is 85 minutes.

[0054] Rolling: The rolling process involves roughing, intermediate, and finishing mills. The final rolling temperature is controlled to 980℃ by adjusting the cooling water after the finishing mill.

[0055] Upper cooling bed: After rolling, the steel bars are regulated by a laminar flow cooling system and monitored by an infrared thermometer to ensure that the temperature of the steel bars on the upper cooling bed is 730℃±5℃.

[0056] Subsequent steps: The product is naturally cooled to room temperature on a cooling bed, then straightened, sheared, inspected, bundled, and stored.

[0057] Comparative Example 1 (Traditional Cryogenic Process):

[0058] For the same steel billet, a conventional heating regime is adopted (soaking zone 1180℃, holding for 65 minutes), the final rolling temperature is 980℃, and the upper cooling bed temperature is controlled at 680℃.

[0059] Comparative Example 2 (Traditional High-Temperature Process):

[0060] For the same steel billet, a conventional heating regime is adopted (soaking zone 1180℃, holding for 65 minutes), the final rolling temperature is 980℃, and the upper cooling bed temperature is controlled at 780℃.

[0061] Performance testing and effect comparison:

[0062] Surface blistering inspection: Ten 12-meter lengths of material were taken from each process and inspected after acid washing. The surface of this example is smooth with no visible blistering (defect rate 0%); Comparative Example 1 has scattered shallow pits (defect rate approximately 0.5%); Comparative Example 2 has obvious pitted blistering on the surface (defect rate approximately 3.5%).

[0063] Iron oxide scale observation: The iron oxide scale of the present invention is about 10-12 μm thick, has a dense structure, and is well bonded to the substrate; the iron oxide scale of Comparative Example 1 is thin (about 5-7 μm) and discontinuous; the iron oxide scale of Comparative Example 2 is thicker (about 15 μm) but loose and porous, with local cracks.

[0064] Corrosion resistance test: Neutral salt spray test (NSS) was conducted according to GB / T 10125. The time it took for 5% of the sample surface to develop red rust was recorded. Results: The average time for the present invention was 128 hours; the average time for Comparative Example 1 was 72 hours; and the average time for Comparative Example 2 was 95 hours. The present invention exhibits significantly superior rust resistance.

[0065] Mechanical properties: The steel bars produced in all embodiments and comparative examples fully meet the requirements of HRB400E standard in terms of yield strength, tensile strength, elongation after fracture, and total elongation at maximum force, indicating that the process optimization has not compromised their core mechanical properties.

[0066] The performance test results of this embodiment, Comparative Example 1, and Comparative Example 2 are compared in the table below:

[0067]

[0068] Conclusion: This embodiment successfully solves the industry problem of balancing surface blistering and rust resistance of hot-rolled ribbed steel bars through the synergistic process of "1080-1120℃ homogenization + 710-750℃ upper cooling bed", producing high-quality products with excellent surface quality and durability.

[0069] The main functions of this invention are:

[0070] 1. By combining "source gas reduction (optimized heating)" with "process temperature control (precise cooling bed)," the traditional process breaks the reciprocal influence of temperature parameters on surface blistering and rust resistance. Within the same process window, this reduces the incidence of surface blistering defects to an industry-leading level while simultaneously increasing the initial atmospheric corrosion resistance of the reinforcing steel by over 30%.

[0071] 2. Significant economic benefits. No major equipment modifications are required to existing production lines, nor is it necessary to adjust the chemical composition of the steel or add expensive alloying elements. It increases production costs almost nothing and is easy to promote and apply quickly on existing production lines.

[0072] 3. Product quality is comprehensively improved and stabilized. The produced steel bars have a smooth surface with few defects and uniform and dense iron oxide scale, which not only enhances the appearance and market competitiveness of the products, but also extends the rust prevention period of the steel bars during storage, transportation and the initial exposure stage of the project due to their superior rust resistance. The process parameters are highly controllable, and the product quality is highly stable.

[0073] In summary, after reading this invention document, those skilled in the art can make various other corresponding modifications to the technical solutions and concepts based on this invention without creative mental effort, and all of these modifications fall within the scope of protection of this invention.

Claims

1. A rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars, characterized in that, Includes the following steps: (1) Steel billet heating: The temperature of the soaking zone of the heating furnace is controlled at 1080℃~1120℃, and the holding time t of the steel billet at the soaking zone temperature is controlled to satisfy: t≥K×D / 2, where t is in minutes, D is the thickness of the steel billet in millimeters, and K is a coefficient with a value range of 0.9~1.3 min / mm; (2) Rolling: The heated steel billet is rolled, and the final rolling temperature is controlled at 960℃~1000℃; (3) Cooling on the upper cooling bed: control the cooling intensity of the cooling device after rolling, and control the temperature of the upper cooling bed of the rolled steel bars to 710℃~750℃.

2. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, It also includes: in step (1), the heating temperature of the steel billet in the heating section of the heating furnace is 1060℃~1140℃.

3. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (1), the value of coefficient K ranges from 1.0 to 1.2 min / mm.

4. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (2), the final rolling temperature is 970℃~990℃.

5. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (3), the temperature of the upper cooling bed is 720℃~740℃.

6. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (1), the steel billet is a continuously cast billet, and the thickness D of the steel billet is 150mm to 200mm.

7. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (2), the methods for controlling the final rolling temperature include: adjusting the opening of the cooling water valve between the finishing mill stands, and / or adjusting the opening of the cooling water valve after final rolling.

8. The rolling method for improving the surface quality and rust resistance of hot-rolled ribbed steel bars according to claim 1, characterized in that, In step (3), the method of controlling the temperature of the upper cooling bed of the rolled steel bar includes: adjusting the number of opening pipes of the laminar flow cooling device or the cooling water pressure according to the surface temperature signal collected by the infrared temperature measuring device, so that the temperature of the upper cooling bed of the steel bar falls within the set range.

9. A type of reinforcing steel bar, characterized in that, It is prepared using the rolling method described in any one of claims 1 to 8.

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