600MPa-grade low-cost corrosion-resistant steel bar and production method thereof

Abstract

The invention discloses a 600MPa-grade low-cost corrosion-resistant steel bar and a production method thereof. The steel bar comprises the following chemical components: 0.10 to 0.13 percent of C, 0.70 to 0.80 percent of Si, 1.30 to 1.50 percent of Mn, 0.120 to 0.150 percent of V, 1.00 to 1.50 percent of Cr, 0.50 to 0.80 percent of Ni, 0.5 to 0.8 percent of Cu, 0.018 to 0.022 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S and the balance of Fe and inevitable impurities. The production method comprises a converter or electric furnace smelting process, an LF furnace refining process, a continuous casting process, a heating process and a rolling process. The alloy components are optimized and adjusted, the micro-nitrogen alloy and the vanadium-nitrogen alloy are added for alloying, and the Cu element is added, so that the proportion of Cr and Ni elements is greatly reduced, and the production cost is greatly reduced on the basis that the corrosion resistance is not reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a 600MPa-grade low-cost corrosion-resistant steel bar and a manufacturing method thereof. Background Art

[0002] Hot-rolled steel bars are the most consumed type of steel material products in China, accounting for about 1 / 5 of China's steel production. With the continuous development of steel bar technology, the development and application of 400MPa Grade III steel bars in China have been fruitful, while the application of 500MPa Grade IV steel bars is still relatively small.

[0003] The corrosion of steel bars has always been the main cause of early deterioration of reinforced concrete structures. With the increasing requirements for building safety and economy, the key to ensuring structural safety is to ensure corrosion resistance while improving strength. The inherent porosity of reinforced concrete causes steel bars to rust, which will lead to concrete cracking, peeling of the protective layer, reduction of the building, and even loss of bearing capacity, resulting in catastrophic accidents.

[0004] The patent application with application number 202011060542.X discloses an ultra-high strength corrosion-resistant steel bar and a manufacturing method thereof. The chemical composition of the steel bar is: C: 0.04~0.07wt%, Si: 0.20~0.40wt%, Mn: 1.00~1.40wt%, Al: 0.020~0.050wt%, V: 0.02~0.05wt%, Ti: 0.02~0.05wt%, Cr: 4.00~6.00wt%, Ni: 1.00~3.00wt%, Mo: 0.2~0.5wt%, P≤0.015wt%, S≤0.005wt.%, and the rest are Fe and unavoidable impurities; the yield strength of the steel bar exceeds 600MPa, but due to the addition of more precious metals, the alloy cost is relatively high. Summary of the invention

[0005] The purpose of the present invention is to provide a 600MPa low-cost corrosion-resistant steel bar and a manufacturing method thereof, which reduces the production cost of the corrosion-resistant steel bar by controlling the components and proportions in the alloy, and achieves a yield strength of 600MPa by a controlled rolling and controlled cooling process.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows: A 600MPa-grade low-cost corrosion-resistant steel bar, whose chemical composition, in percentage by mass, is as follows: C: 0.10-0.13%, Si: 0.70-0.80%, Mn: 1.30-1.50%, V: 0.120-0.150%, Cr: 1.00-1.50%, Ni: 0.50-0.80%, Cu: 0.5-0.8%, N: 0.018%-0.022%, P: <0.015%, S: <0.015%, and the rest is Fe and unavoidable impurities.

[0007] The 600MPa-level low-cost corrosion-resistant steel bar of the present invention comprises 1.00-1.50% Cr, 0.60-0.80% Ni and 0.6-0.8% Cu in the chemical composition.

[0008] The microstructure types of the 600MPa-grade low-cost corrosion-resistant steel bar of the present invention are pearlite and ferrite, wherein the proportion of pearlite is 20% to 30%.

[0009] The 600MPa-grade low-cost corrosion-resistant material of the present invention has a yield strength of ≥620MPa, a tensile strength of ≥800MPa, an elongation after fracture of ≥16%, a total elongation at maximum force of ≥9.0%, and a relative corrosion rate of ≤48%.

[0010] The production method of the 600MPa grade corrosion-resistant steel bar of the present invention comprises converter or electric furnace smelting, LF furnace refining, continuous casting, heating and rolling processes.

[0011] Furthermore, the production method of 600MPa grade corrosion-resistant steel bars of the present invention, wherein the converter or electric furnace smelting process: alloying with silicon-manganese alloy, ferrosilicon, vanadium-nitrogen alloy, micro-nitrogen alloy, nickel plate, and copper plate; deoxidation with silicon-aluminum-barium deoxidizer, the amount of the deoxidizer added is 0.1-1.0kg / t; the endpoint composition is controlled to be C≤0.04%, S≤0.020%, P≤0.015%, and the endpoint temperature is 1650-1680°C.

[0012] Furthermore, the production method of 600MPa grade corrosion-resistant steel bars of the present invention, wherein the LF furnace refining: adding micro-carbon ferrochromium alloy to the molten steel to alloy the molten steel, feeding calcium iron wire for calcium treatment at the end of refining, the ladle leaves the station, adding insulation agent to cover the entire steel liquid surface, and black slag on the surface; after the refining is completed, the soft argon blowing time is ensured to be ≥8min, and the refining lifting temperature is 1580-1620℃.

[0013] Furthermore, the production method of 600MPa grade corrosion-resistant steel bars of the present invention, wherein the casting process: adopts a stopper rod package for full-process protection casting, and the temperature of the molten steel in the tundish is controlled at 1520-1540°C; a long nozzle seal is used from the ladle to the tundish for protection, and an immersed nozzle seal is used from the tundish to the crystallizer for protection to ensure good sealing; the secondary cooling water volume is 0.9-1.2L / kg, and the liquid level in the tundish is controlled above 600mm during normal steel drawing, and shall not be lower than 300mm before the last furnace stops pouring; the continuous casting drawing speed is 1.8-2.2m / min.

[0014] Furthermore, in the production method of the 600MPa grade corrosion-resistant steel bar of the present invention, the heating step is as follows: the ingot is charged into a heating furnace for heating, the furnace outlet temperature is 1080-1100°C, and the heat preservation time is 1-2 hours.

[0015] Furthermore, in the production method of the 600MPa grade corrosion-resistant steel bar of the present invention, the rolling process comprises: the starting rolling temperature is 1060-1080°C, the final rolling temperature is 950-980°C, and the steel bar is air-cooled to room temperature after rolling.

[0016] The inventive principle and beneficial technical effects of the technical solution of the present invention are: (1) Adding microalloying element V to steel can combine with C and N to form carbonitrides, which can play a precipitation strengthening role at low temperatures; V in steel can control strain aging, reduce the brittle transition temperature of steel, and make strength and toughness better matched. Therefore, the present invention optimizes the content of C and N elements and adds V element, thereby effectively improving the tensile strength, toughness and yield strength of steel bars.

[0017] (2) The steel bar structure provided by the present invention is pearlite plus ferrite, and the finished product structure is uniform. After rolling, it only needs to be air-cooled to room temperature without other heat treatment processes, which can reduce processing costs.

[0018] (3) The present invention greatly reduces the proportion of Cr and Ni elements by adding Cu element, thereby greatly reducing the production cost without reducing the corrosion resistance. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below in conjunction with specific embodiments.

[0020] A 600MPa grade low-cost corrosion-resistant steel bar, whose chemical composition is calculated by mass percentage: C: 0.10-0.13%, Si: 0.70-0.80%, Mn: 1.30-1.50%, V: 0.120-0.150%, Cr: 1.00-1.50%, Ni: 0.50-0.80%, Cu: 0.5-0.8%, N: 0.018%-0.022%, P≤0.015%, S≤0.015%, and the rest is Fe and unavoidable impurities. The chemical composition and content of the steel bars in each embodiment are shown in Table 1.

[0021] Table 1 Chemical composition and content of steel bars in various examples (wt%)

[0022] In Table 1, the balance is Fe and inevitable impurities.

[0023] The production process of the steel bar is: molten iron → converter smelting → LF furnace refining → billet casting → 165×165 billet → heating in heating furnace → high-pressure water descaling → rough rolling, intermediate rolling, pre-finishing rolling unit rolling → finishing rolling unit rolling → cooling bed → packaging; the details are as follows: (1) Converter smelting: alloying with silicon-manganese alloy, ferrosilicon, vanadium-nitrogen alloy, micro-nitrogen alloy, nickel plate and copper plate; deoxidation with silicon-aluminum-barium deoxidizer, the amount of the deoxidizer added is 0.1-1.0 kg / t; the end point composition is controlled to be C≤0.04%, S≤0.020%, P≤0.015%, and the end point temperature is 1650-1680°C.

[0024] (2) LF furnace refining: Add micro-carbon ferrochromium alloy to the molten steel for alloying. At the end of refining, feed calcium iron wire for calcium treatment. The ladle leaves the station and adds insulation to cover the entire steel liquid surface, leaving black slag on the surface. After refining, ensure that the soft argon blowing time is ≥8 minutes and the refining lifting temperature is 1580~1620℃.

[0025] The control parameters of the converter smelting and LF furnace refining process in each embodiment are shown in Table 2.

[0026] Table 2 Parameters of converter smelting and LF furnace refining process in various embodiments

[0027] (3) Continuous casting: A stopper rod is used to protect the casting process throughout, and the temperature of the molten steel in the tundish is controlled at 1520-1540℃; a long nozzle seal is used to protect the ladle to the tundish, and an immersed nozzle seal is used to protect the tundish to the crystallizer to ensure good sealing; the secondary cooling water volume is 0.9-1.2L / kg, and the liquid level in the tundish is controlled above 600mm during normal steel drawing, and shall not be lower than 300mm before the last furnace is stopped; the continuous casting speed is 1.8-2.2m / min.

[0028] The continuous casting process parameters of each embodiment are shown in Table 3.

[0029] Table 3 Continuous casting process parameters of each embodiment

[0030] (4) Heating: The ingot is placed in a heating furnace and heated. The furnace temperature is 1080-1100°C and the insulation time is 1-2 hours.

[0031] (5) Rolling: dephosphorization pressure ≥ 15 MPa, rough rolling start temperature 1060 ~ 1080 ° C, finishing rolling final temperature 950 ~ 980 ° C, after rolling, air cooling to room temperature.

[0032] The heating and rolling process parameters of each embodiment are shown in Table 2.

[0033] Table 4 Heating and rolling process parameters of various embodiments

[0034] The hot-rolled mechanical properties and relative corrosion resistance rates of the corrosion-resistant steel bars produced in each embodiment are shown in Table 5.

[0035] Table 5 Performance of 600MPa grade corrosion resistant steel bars in various examples

[0036] In summary, the mechanical properties of the product of the present invention reach the requirements of 600MPa grade corrosion-resistant steel bars through VN microalloying. By adding Cu elements to replace or partially replace Cr and Ni elements, the production cost of steel bars is reduced while ensuring the corrosion resistance requirements of the product. The product structure is pearlite + ferrite, and the structure is uniform, the internal participating stress is low, and no stress relief heat treatment is required, and the production cost of steel bars is low.

[0037] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A 600MPa grade low-cost corrosion-resistant steel bar, characterized in that: The chemical composition of the steel bar is calculated by mass percentage as follows: C: 0.10-0.13%, Si: 0.70-0.80%, Mn: 1.30-1.50%, V: 0.120-0.150%, Cr: 1.00-1.50%, Ni: 0.50-0.80%, Cu: 0.5-0.8%, N: 0.018%-0.022%, P: <0.015%, S: <0.015%, the rest is Fe and unavoidable impurities.

2. A 600MPa grade low-cost corrosion-resistant steel bar according to claim 1, characterized in that: The metallographic structure of the steel bar is ferrite and pearlite, wherein the proportion of pearlite is 20% to 30%.

3. The 600MPa low-cost corrosion-resistant steel bar according to claim 1, characterized in that: The mechanical properties of the steel bar are: yield strength ≥620MPa, tensile strength ≥800MPa, elongation after fracture ≥16%, total elongation at maximum force ≥9.0%, and relative corrosion rate ≤48%.

4. A method for producing a 600MPa grade low-cost corrosion-resistant steel bar according to any one of claims 1 to 3, characterized in that: It includes converter or electric furnace smelting, LF furnace refining, continuous casting, heating and rolling processes.

5. The method for producing a 600MPa grade low-cost corrosion-resistant steel bar according to claim 4, characterized in that: The converter or electric furnace smelting process: alloying with silicon-manganese alloy, ferrosilicon, vanadium-nitrogen alloy, micro-nitrogen alloy, nickel plate and copper plate; deoxidation with silicon-aluminum-barium deoxidizer, the amount of the deoxidizer added is 0.1-1.0kg / t; the end point composition is controlled to be C≤0.04%, S≤0.020%, P≤0.015%, and the end point temperature is 1650-1680°C.

6. The method for producing a 600MPa grade low-cost corrosion-resistant steel bar according to claim 4, characterized in that: The LF furnace refining comprises the following steps: adding a micro-carbon ferrochrome alloy to the molten steel to alloy the molten steel; feeding a calcium iron wire to perform calcium treatment at the end of the refining; the ladle leaves the station; adding a heat preservation agent to cover the entire steel liquid surface, and removing black slag on the surface; after the refining is completed, ensuring that the soft argon blowing time is ≥8 minutes, and the refining lifting temperature is 1580-1620°C.

7. The method for producing a 600MPa grade low-cost corrosion-resistant steel bar according to claim 4, characterized in that: The continuous casting process: a stopper rod is used to protect the casting throughout the whole process, and the temperature of the molten steel in the tundish is controlled at 1520-1540°C; a long nozzle seal is used to protect the ladle to the tundish, and an immersed nozzle seal is used to protect the tundish to the crystallizer to ensure good sealing; the secondary cooling water volume is 0.9-1.2L / kg, and the liquid level in the tundish is controlled above 600mm during normal steel drawing, and shall not be lower than 300mm before the last furnace stops pouring; the continuous casting drawing speed is 1.8-2.2m / min.

8. The method for producing a 600MPa low-cost corrosion-resistant steel bar according to claim 4, characterized in that: The heating process is as follows: the ingot is placed in a heating furnace for heating, the furnace temperature is 1080-1100° C., and the heat preservation time is 1-2 hours.

9. The method for producing a 600MPa grade low-cost corrosion-resistant steel bar according to claim 4, characterized in that: The rolling process comprises: a starting rolling temperature of 1060-1080° C., a final rolling temperature of 950-980° C., and air cooling to room temperature after rolling.

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