A 400MPa grade hot-rolled ribbed steel bar and its preparation method

Abstract

This invention relates to the field of steel bar production technology, specifically to a 400MPa grade hot-rolled ribbed steel bar and its preparation method, comprising the following steps: Step 1: Converter steelmaking, controlling the final carbon content to 0.07%-0.09%, and sequentially adding a composite deoxidizer, silicon-manganese alloy, and ferrotitanium to the ladle; Step 2: Continuous casting, using a crystallizer immersion nozzle protection casting process; employing a secondary cooling process; the superheat of the tundish is 10-15℃; Step 3: Heating, with the heating temperature controlled at 1000-1040℃; Step 4: Rolling, with an initial rolling temperature of 1000-1040℃ and a controlled rolling temperature of 900-950℃; Step 5: Cooling, with a controlled cooling temperature of 860-890℃; Step 6: Producing the finished product. This invention improves the titanium recovery rate, reduces smelting costs, and improves the mechanical properties of hot-rolled ribbed steel bars.

Description

Technical Field

[0001] This invention relates to the field of steel bar production technology, specifically to a 400MPa grade hot-rolled ribbed steel bar and its preparation method. Background Technology

[0002] Hot-rolled ribbed steel bars, commonly known as threaded steel, are a type of steel commonly used in construction engineering. They possess excellent mechanical properties and good weldability, making them widely used in the construction industry. In recent years, with the continuous development of the construction industry and the increasing emphasis on earthquake safety, earthquake-resistant steel bars, as a new type of building material, have gradually been promoted in buildings in earthquake-prone areas. Earthquake-resistant steel bars refer to ribbed steel bars with high strength, high toughness, increased strain capacity, and the ability to withstand dynamic loads.

[0003] Hot-rolled ribbed steel bars have long been a focus of attention in earthquake-resistant steel reinforcement due to their high tensile strength, good ductility, and toughness. Current technologies typically employ microalloying processes to improve the mechanical properties of hot-rolled ribbed steel bars, introducing microalloying elements such as vanadium and niobium into the steel. Vanadium microalloying, niobium microalloying, vanadium-nitrogen microalloying, or niobium-vanadium microalloying are used to improve the overall performance of hot-rolled ribbed steel bars. However, vanadium microalloying and vanadium-nitrogen microalloying require high vanadium content, leading to higher alloy costs. Niobium microalloyed hot-rolled ribbed steel bars are prone to yielding defects, reducing their performance. Furthermore, niobium microalloyed steel continuously cast billets often exhibit surface cracks, making it difficult to meet earthquake resistance requirements. Titanium, as a strong carbonitride-forming element, can significantly improve the strength and plasticity of steel, enhancing its overall performance. Given the abundance of titanium alloy resources, introducing titanium into steel can significantly reduce alloy costs. However, titanium has a strong affinity for elements such as nitrogen, sulfur, carbon, and oxygen in steel, which leads to problems such as low and unstable recovery rates and high smelting costs during microalloying. These issues limit the application of titanium in earthquake-resistant hot-rolled ribbed steel bars. Summary of the Invention

[0004] To address the technical problems of low and unstable titanium recovery rate and high smelting cost in hot-rolled ribbed steel bars, this invention provides a 400MPa grade hot-rolled ribbed steel bar and its preparation method. The process flow is "converter steelmaking → direct casting after tapping → heating → hot charging → rolling → cooling → finished product production", which improves the titanium recovery rate, reduces smelting cost, and improves the mechanical properties of hot-rolled ribbed steel bars.

[0005] In a first aspect, the present invention provides a method for preparing 400MPa grade hot-rolled ribbed steel bars, comprising the following steps:

[0006] Step 1: Converter steelmaking, control the final carbon content at 0.07%-0.09%. After tapping 1 / 3 of the steel, blow argon gas into the ladle at a flow rate of 200-500 L / min for at least 3 minutes. During the bottom blowing process, add composite deoxidizer, silicon manganese alloy and ferrotitanium to the ladle in sequence.

[0007] Step 2: Continuous casting, using immersion nozzle protection for the crystallizer; a secondary cooling process is adopted, with water cooling as the secondary cooling method, and a specific water volume of 1.02 L / kg. The water volume distribution ratio in Section I is 47%, and the water volume distribution ratio in Section II is 9%; the superheat of the tundish is 10-15℃.

[0008] The protective flux for the crystallizer comprises the following components: SiO2 34.3wt%, CaO 25.66wt%, Al2O3 5.20wt%, R2O 7.5wt%, F - 5.00wt%, C 全 14.80 wt%; hemispherical point temperature: 1165℃; viscosity at 1300℃: 0.55 Pa·s; crystallizer stroke: 8 mm; crystallizer frequency: 60*55V. 拉速 ;

[0009] Step 3: Heating. The heating temperature is controlled at 1000-1040℃. After heating, the continuously cast billet is directly conveyed to the hot rolling furnace through the hot conveyor roller.

[0010] Step 4: Rolling. The initial rolling temperature is 1000-1040℃, and the controlled rolling temperature is 900-950℃. Setting the initial rolling temperature to 1000-1040℃ can reduce the wear of the rolls, extend the service life of the rolls, and improve the negative deviation rate of the steel.

[0011] Step 5: Cooling, with the cooling temperature controlled at 860-890℃;

[0012] Step 6: Produce the finished product, hot-rolled ribbed steel bars.

[0013] Furthermore, by mass fraction, hot-rolled ribbed steel bars comprise the following components: C 0.20%-0.25%, Si 0.60%-0.80%, Mn 1.40%-1.60%, S≤0.035%, P≤0.035%, Ti 0.007%-0.025%, with the remainder being Fe and unavoidable impurity elements.

[0014] Furthermore, in step one, the composite deoxidizer is an aluminum-calcium-carbon composite deoxidizer, and the addition amount of the composite deoxidizer is 0.3-0.6 kg / t of steelmaking raw materials, preferably 0.5 kg / t of steelmaking raw materials. Adding the composite deoxidizer to the ladle can achieve deoxidation during the steel tapping process, stabilize the recovery rate of titanium elements, and reduce inclusions in the molten steel. In the silicon-manganese alloy, the mass percentage of silicon element is 14%-20%, and the mass percentage of manganese element is 64%-72%. The addition amount of silicon-manganese alloy is 26-30 kg / t of steelmaking raw materials, preferably 28 kg / t of steelmaking raw materials. The addition amount of silicon-manganese alloy can be adjusted according to the internal control chemical composition standard of the billet.

[0015] Furthermore, in step one, ferrotitanium is added to the argon blowing port, and the titanium content of the ferrotitanium is 65%-75%. The amount of ferrotitanium added can be adjusted according to the steel grade. Adding ferrotitanium to the argon blowing port can prevent titanium from oxidizing during the steel tapping process.

[0016] Furthermore, in step one, during the tapping process, a desulfurizing agent is added to the tapped steel, with lime being the preferred desulfurizing agent.

[0017] Furthermore, in step two, R2O is an oxide of sodium and / or potassium, and C is all carbon.

[0018] Furthermore, in step two, the thickness of the protective slag layer is 30mm-50mm.

[0019] Furthermore, in step three, the hot delivery temperature is 640-660℃, preferably 650℃.

[0020] Furthermore, in step five, cooling includes controlled rolling cooling and post-rolling cooling.

[0021] Secondly, the present invention also provides a hot-rolled ribbed steel bar prepared by the preparation method described above. The hot-rolled ribbed steel bar has a grain size of 9-10, a strength-to-yield ratio >1.30, a yield strength of 430-480 MPa, and a cross-sectional metallographic structure including ferrite and pearlite.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention provides a 400MPa grade hot-rolled ribbed steel bar and its preparation method. The process flow is "converter steelmaking → continuous casting → heating → rolling → cooling → finished product production". The process flow is omitted, the LF refining process is avoided, the use of high-alumina deoxidation and the full-process protective casting of continuous casting are avoided. The process flow is shortened while improving the titanium recovery rate, the smelting cost is reduced and the preparation efficiency of hot-rolled ribbed steel bars is improved. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a partial photograph of the steel billet obtained by continuous casting in Embodiment 1 of the present invention.

[0026] Figure 2 This is a metallographic diagram of the hot-rolled ribbed steel bar in Embodiment 1 of the present invention.

[0027] Figure 3 This is a metallographic diagram of the hot-rolled ribbed steel bar in Embodiment 2 of the present invention.

[0028] Figure 4 This is a metallographic diagram of the hot-rolled ribbed steel bar in Comparative Example 1 of this invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0030] Example 1

[0031] A type of HRB400E grade hot-rolled ribbed steel bar, comprising the following components by mass fraction: C 0.20%-0.25%, Si 0.60%-0.80%, Mn 1.40%-1.60%, S≤0.035%, P≤0.035%, Ti 0.007%-0.025%, with the remainder being Fe and unavoidable impurity elements. The preparation method includes the following steps:

[0032] Step 1: Converter steelmaking. The final carbon content is controlled at 0.08%. After 1 / 3 of the steel is tapped, argon is blown into the ladle at a flow rate of 500 L / min for 3 minutes. During this process, an aluminum-calcium-carbon composite deoxidizer, silicon-manganese alloy, and ferrotitanium are added sequentially to the ladle for deoxidation and alloying. The ferrotitanium is added to the argon inlet. The aluminum-calcium-carbon composite deoxidizer is added at a rate of 0.5 kg / t of steelmaking raw material and is purchased from Xinyu Fuhai Company, model XY-1. The silicon-manganese alloy is added at a rate of 28 kg / t of steelmaking raw material and is Mn64 purchased from Hainan Lulian Industrial Co., Ltd. The ferrotitanium is added at a rate of 0.4 kg / t and is 70Ti purchased from Jinan Guoxing Materials Technology Co., Ltd. During the tapping process, a lime-based desulfurizing agent is added to the molten steel. This utilizes the mixing and flushing of the molten steel during tapping to advance slag formation, shorten refining time, and reduce the scouring of the ladle wall by slag during refining. This reduces inclusions formed by refractory material detached from the ladle wall. The lime added is 2.5 kg / t, and the lime is self-produced. The oxygen supply intensity of the lance in the later stage of converter steelmaking is 4.0 m³ / t·min, with a decarburization rate of 0.4% / min. The lance is lifted 20 seconds before the end of the process, while ensuring a 20-second lance pressing time to guarantee uniform composition and temperature. The ladle uses all-magnesia-carbon bricks, which reduces Class B inclusions caused by refractory detachment due to refractory erosion and reduces nozzle blockage caused by the combined action of titanium and aluminum oxides. The titanium recovery rate of the deoxidized and alloyed molten steel is 40%.

[0033] Step 2: Continuous casting, using immersion nozzle protection for the crystallizer; a secondary cooling process is adopted, with water cooling as the secondary cooling method, and a specific water volume of 1.02 L / kg. The water volume distribution ratio in Section I is 47%, and the water volume distribution ratio in Section II is 9%; the superheat of the tundish is 10-15℃.

[0034] The protective flux for the crystallizer comprises the following components: SiO2 34.3wt%, CaO 25.66wt%, Al2O3 5.20wt%, R2O 7.5wt%, F - 5.00wt%, C 全 14.80 wt%; hemispherical point temperature: 1165℃; viscosity at 1300℃: 0.55 Pa·s; crystallizer stroke: 8 mm; crystallizer frequency: 60*55V. 拉速 Wherein, R₂O is an oxide of sodium and / or potassium, and C 全 It is entirely carbon-based. The thickness of the protective slag layer is 30mm-50mm.

[0035] A partial photograph of the steel billet obtained by continuous casting is shown below. Figure 1As shown, the continuously cast steel billets do not have obvious corner cracking problems, the crack control level of the middle crack is 2.0, the crack control level of the corner crack is 1.0, and there are basically no shrinkage cavities.

[0036] Step 3: Heating. The heating temperature is controlled at 1030-1040℃. After heating, the continuously cast billet is directly conveyed to the hot rolling furnace through the hot conveying roller conveyor. The hot conveying temperature is 650℃.

[0037] Step 4: Rolling. The initial rolling temperature is 1030-1040℃, the controlled rolling temperature is 940-950℃, and the K1 rolling amount is 1200 tons.

[0038] Step 5: Cooling, which includes controlled rolling cooling and post-rolling cooling. The controlled cooling temperature is 870-880℃. Post-rolling cooling adopts a continuous cooling mode to overcome the problem of large fluctuations in the bending and yield strength aging properties of steel caused by uneven heating. After water-cooled controlled cooling, the forward and reverse blowing pipes in the water tank are configured in a 4+2 configuration to blow away the water covering the surface of the steel bars, fundamentally eliminating the problem of uneven steel bar temperature caused by water and affecting the bending of the steel bars.

[0039] Step Six: Produce the finished product, hot-rolled ribbed steel bars. The grain size of the hot-rolled ribbed steel bars is grade 10, the strength-to-yield ratio is 1.32-1.35, and the yield strength is 440-470 MPa. Figure 2 As shown, the cross-sectional metallographic structure of hot-rolled ribbed steel bars includes ferrite and pearlite.

[0040] Example 2

[0041] A type of HRB400E grade hot-rolled ribbed steel bar, comprising the following components by mass fraction: C 0.22%-0.24%, Si 0.60%-0.75%, Mn 1.42%-1.52%, S≤0.035%, P≤0.035%, Ti 0.008%-0.015%, with the remainder being Fe and unavoidable impurity elements. The preparation method includes the following steps:

[0042] Step 1: Converter steelmaking. The final carbon content is controlled at 0.07%. After 1 / 3 of the steel is tapped, argon is blown into the ladle at a flow rate of 0.00 L / min for 3 minutes. During this process, an aluminum-calcium-carbon composite deoxidizer, silicon-manganese alloy, and ferrotitanium are added sequentially to the ladle for deoxidation and alloying. The ferrotitanium is added to the argon inlet. The aluminum-calcium-carbon composite deoxidizer is added at a rate of 0.5 kg / t of steelmaking raw material, purchased from Xinyu Fuhai Company, model XY-1. The silicon-manganese alloy is added at a rate of 28 kg / t of steelmaking raw material, purchased from Chayouqianqi Yuxing Carbon Co., Ltd. (Mn64). The ferrotitanium is added at a rate of 0.4 kg / t, purchased from Jinzhou Guotai Industrial Co., Ltd. (70Ti). During the tapping process, a lime-based desulfurizing agent is added to the molten steel. This utilizes the mixing and flushing of the molten steel during tapping to advance slag formation, shorten refining time, and reduce the scouring of the ladle wall by slag during refining. This reduces inclusions formed by refractory material detached from the ladle wall. The lime addition is 2.5 kg / t, and the lime is self-produced. The oxygen supply intensity of the lance in the later stages of converter steelmaking is 4.0 m³ / t·min, with a decarburization rate of 0.4% / min. The lance is lifted 20 seconds before the end of the process, while ensuring a 25-second lance pressing time to guarantee uniform composition and temperature. The ladle uses all-magnesia-carbon bricks, which reduces Class B inclusions caused by refractory detachment due to refractory erosion and reduces nozzle blockage caused by the combined action of titanium and aluminum oxides. The titanium recovery rate of the deoxidized and alloyed molten steel is 39%.

[0043] Step 2: Continuous casting, using immersion nozzle protection for the crystallizer; a secondary cooling process is adopted, with water cooling as the secondary cooling method, a specific water volume of 1.02 L / kg, a water distribution ratio of 46% in section I and 10% in section II; the superheat of the tundish is 10-15℃.

[0044] The protective flux for the crystallizer comprises the following components: SiO2 34.3wt%, CaO 25.66wt%, Al2O3 5.20wt%, R2O 7.5wt%, F - 5.00wt%, C 全 14.80 wt%; hemispherical point temperature: 1165℃; viscosity at 1300℃: 0.55 Pa·s; crystallizer stroke: 8 mm; crystallizer frequency: 60*55V. 拉速 Wherein, R₂O is an oxide of sodium and / or potassium, and C 全 It is entirely carbon-based. The thickness of the protective slag layer is 30mm-50mm.

[0045] The continuously cast steel billets do not have obvious corner cracking problems. The crack control level of the middle crack is 2.0, the crack control level of the corner crack is 1.0, and there are basically no shrinkage cavities.

[0046] Step 3: Heating. The heating temperature is controlled at 1020-1030℃. After heating, the continuously cast billet is directly conveyed to the hot rolling furnace through the hot conveying roller conveyor. The hot conveying temperature is about 650℃.

[0047] Step 4: Rolling. The initial rolling temperature is 1020-1030℃, the controlled rolling temperature is 930-950℃, and the K1 rolling amount is 1200 tons.

[0048] Step 5: Cooling, which includes controlled rolling cooling and post-rolling cooling. The controlled cooling temperature is 870-880℃. Post-rolling cooling adopts a continuous cooling mode to overcome the problem of large fluctuations in the bending and yield strength aging properties of steel caused by uneven heating. After water-cooled controlled cooling, the forward and reverse blowing pipes in the water tank are configured in a 4+2 configuration to blow away the water covering the surface of the steel bars, fundamentally eliminating the problem of uneven steel bar temperature caused by water and affecting the bending of the steel bars.

[0049] Step Six: Produce the finished product, hot-rolled ribbed steel bars. The grain size of the hot-rolled ribbed steel bars is grade 9.5, the strength-to-yield ratio is 1.31-1.34, and the yield strength is 440-460 MPa. Figure 3 As shown, the cross-sectional metallographic structure of hot-rolled ribbed steel bars includes ferrite and pearlite.

[0050] Comparative Example 1

[0051] A type of HRB400E grade hot-rolled ribbed steel bar, by mass fraction, comprises the following components: C 0.23%-0.24%, Si 0.65%-0.75%, Mn 1.45%-1.55%, S≤0.035%, P≤0.035%, with the remainder being Fe and unavoidable impurity elements. The preparation method includes the following steps:

[0052] Step 1: Converter steelmaking. The final carbon content is controlled at 0.09%. After tapping 1 / 3 of the steel, argon is blown into the ladle at a flow rate of 400 L / min for 3 minutes. During this process, an aluminum-calcium-carbon composite deoxidizer and a silicon-manganese alloy are added sequentially to the ladle for deoxidation and alloying. The aluminum-calcium-carbon composite deoxidizer is added at a rate of 0.5 kg / t of steelmaking raw material, and is the XY-1 type purchased from Xinyu Fuhai Company. The silicon-manganese alloy is added at a rate of 28 kg / t of steelmaking raw material, and is Mn64 purchased from Ulanqab Xiongwei Guangda New Materials Co., Ltd. No lime-based desulfurizer is added during tapping. The oxygen supply intensity of the lance in the later stage of converter steelmaking is 4.0 m³ / t·min, and the decarburization rate is calculated at 0.4% / min. The lance is lifted 20 seconds before the end point, while ensuring a 20-second lance pressing time to guarantee uniform composition and temperature. The ladle uses a full magnesia-carbon brick ladle, which can reduce Class B inclusions caused by refractory peeling due to refractory erosion.

[0053] Step 2: Continuous casting, using immersion nozzle protection for the crystallizer; a secondary cooling process is adopted, with water cooling as the secondary cooling method, and a specific water volume of 1.07 L / kg. The water volume distribution ratio in Section I is 49%, and the water volume distribution ratio in Section II is 9%; the superheat of the tundish is 10-15℃.

[0054] The protective flux of the crystallizer comprises the following components: SiO2 35.2wt%, CaO 28.16wt%, Al2O3 5.5wt%, R2O 6.7wt%, F - 4wt%, C 全 14.68 wt%; hemispherical point temperature: 1165℃; viscosity at 1300℃: 0.65 Pa·s; crystallizer stroke: 7 mm; crystallizer frequency: 100*40V. 拉速 ;

[0055] The continuously cast steel billets do not have obvious corner cracking problems, the crack control level of the middle crack is 2.0, the crack control level of the corner crack does not exceed 1.0, and there are basically no shrinkage cavities.

[0056] Step 3: Heating. The heating temperature is controlled at 940-960℃. After heating, the continuously cast billet is directly conveyed to the hot rolling furnace through the hot conveying roller conveyor. The hot conveying temperature is about 650℃.

[0057] Step 4: Rolling. The initial rolling temperature is 940-960℃, the controlled rolling temperature is 940-950℃, and the K1 rolling amount is 600 tons.

[0058] Step 5: Cooling, which includes controlled rolling cooling and post-rolling cooling. The controlled cooling temperature is 870-880℃. Post-rolling cooling adopts a continuous cooling mode to overcome the problem of large fluctuations in the bending and yield strength aging properties of steel caused by uneven heating. After water-cooled controlled cooling, the forward and reverse blowing pipes in the water tank are configured in a 4+2 configuration to blow away the water covering the surface of the steel bars, fundamentally eliminating the problem of uneven steel bar temperature caused by water and affecting the bending of the steel bars.

[0059] Step Six: Produce the finished product, hot-rolled ribbed steel bars. The grain size of the hot-rolled ribbed steel bars is grade 9, the strength-to-yield ratio is 1.27-1.30, and the yield strength is 430-450 MPa. Figure 4 As shown, the cross-sectional metallographic structure of hot-rolled ribbed steel bars includes ferrite and pearlite.

[0060] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing 400MPa grade hot-rolled ribbed steel bars, characterized in that, Includes the following steps: Step 1: Converter steelmaking, control the final carbon content at 0.07%-0.09%. After tapping 1 / 3 of the steel, blow argon gas into the ladle at a flow rate of 200-500 L / min for at least 3 minutes. During the bottom blowing process, add composite deoxidizer, silicon manganese alloy and ferrotitanium to the ladle in sequence. Step 2: Continuous casting, using immersion nozzle protection for the crystallizer; a secondary cooling process is adopted, with water cooling as the secondary cooling method, and a specific water volume of 1.02 L / kg. The water volume distribution ratio in Section I is 47%, and the water volume distribution ratio in Section II is 9%; the superheat of the tundish is 10-15℃. The protective flux of the crystallizer comprises the following components: SiO2 34.3wt%, CaO 25.66wt%, Al2O3 5.20wt%, R2O 7.5wt%, F - 5.00wt%, C 全 14.80 wt%; hemispherical point temperature: 1165℃; viscosity at 1300℃: 0.55 Pa·s; crystallizer stroke: 8 mm; crystallizer frequency: 60*55V. 拉速 ; Step 3: Heating. The heating temperature is controlled at 1000-1040℃. After heating, the continuously cast billet is directly conveyed to the hot rolling furnace through the hot conveyor roller. Step 4: Rolling, with an initial rolling temperature of 1000-1040℃ and a controlled rolling temperature of 900-950℃; Step 5: Cooling, with the cooling temperature controlled at 860-890℃; Step Six: Produce the finished product, obtaining hot-rolled ribbed steel bars; In step one, the composite deoxidizer is an aluminum-calcium-carbon composite deoxidizer, and the amount of composite deoxidizer added is 0.3-0.6 kg / t of steelmaking raw materials; in the silicon-manganese alloy, the mass percentage of silicon element is 14%-20%, the mass percentage of manganese element is 64%-72%, and the amount of silicon-manganese alloy added is 26-30 kg / t of steelmaking raw materials. In step two, R₂O is an oxide of sodium and / or potassium, C 全 It is all carbon; Titanium iron is added to the argon blowing port; The hot-rolled ribbed steel bars, by mass fraction, comprise the following components: C 0.20%-0.25%, Si 0.60%-0.80%, Mn 1.40%-1.60%, S≤0.035%, P≤0.035%, Ti 0.007%-0.025%, with the remainder being Fe and unavoidable impurity elements.

2. The method for preparing a 400MPa grade hot-rolled ribbed steel bar as described in claim 1, characterized in that, In step one, during the tapping process, a desulfurizing agent is added to the molten steel.

3. The method for preparing 400MPa grade hot-rolled ribbed steel bars as described in claim 1, characterized in that, In step two, the thickness of the protective slag layer is 30mm-50mm.

4. The method for preparing 400MPa grade hot-rolled ribbed steel bars as described in claim 1, characterized in that, In step three, the hot delivery temperature is 640-660℃.

5. The method for preparing a 400MPa grade hot-rolled ribbed steel bar as described in claim 1, characterized in that, In step five, cooling includes controlled rolling cooling and post-rolling cooling.

6. A hot-rolled ribbed steel bar prepared by the preparation method according to any one of claims 1-5, characterized in that, The grain size of hot-rolled ribbed steel bars is grade 9-10, the strength-to-yield ratio is >1.30, the yield strength is 430-480MPa, and the cross-sectional metallographic structure includes ferrite and pearlite.

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