A rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete

Abstract

The invention belongs to the technical field of corrosion-resistant steel bar preparation, and particularly relates to a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa-grade reinforced concrete. The rolling process provided by the present invention comprises the following steps: continuously casting smelted molten steel to obtain a continuous casting billet, wherein the components of the continuous casting billet are, by weight percentage, C: 0.08-0.09%, Cr: 1.00-1.02%, Cu: 0.20-0.22%, Mo: 0.20-0.22%, Si: 0.24-0.28%, Mn: 0.4-0.42%, V: 0.03-0.035%, N: 0.04-0.045%, P: ≤0.02%, S: ≤0.01%, and the remainder is iron and inevitable impurities; heating the continuous casting billet, sequentially performing rough rolling and finish rolling on the heated continuous casting billet, and cooling after finish rolling to obtain chloride ion corrosion-resistant steel bars; and performing rough rolling passes 5-7 times, with a first pass reduction rate of 10-15%, a last pass reduction rate of 10-15%, and an intermediate pass reduction rate of 25-30%. The rolling process provided by the present invention achieves high strength and excellent chloride ion corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion-resistant steel bar preparation, and particularly relates to a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa-grade reinforced concrete. Background Art

[0002] As an important reinforcement material, concrete steel bars are widely used in construction, industry and other fields. With the development of society and the advancement of technology, people will gradually explore deeper into the ocean to better utilize marine resources. The unique high-salt and high-humidity environment in the marine environment poses higher challenges to concrete steel bars, which require steel bars to have excellent corrosion resistance, especially resistance to chloride ion corrosion.

[0003] Currently, there are two main methods for improving the corrosion resistance of steel bars: one is to coat the steel bars with a corrosion-resistant layer, and the other is to add alloying elements to the steel bars to fundamentally improve their corrosion resistance. Currently, corrosion-resistant steel bars mainly include stainless steel bars, galvanized steel bars, and alloy corrosion-resistant steel bars. Among these, alloy corrosion-resistant steel bars generally incorporate elements such as Ni, Cr, and Mo to improve their corrosion resistance. However, while the addition of alloying elements can improve the corrosion resistance of steel bars, it may also impair their mechanical properties. Therefore, balancing the mechanical and corrosion resistance of steel bars has become a major challenge. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the drawback of existing alloy corrosion-resistant steel bars, which cannot effectively balance the mechanical properties and corrosion resistance of the steel bars. Furthermore, a rolling process for chloride-ion corrosion-resistant steel bars for 500 MPa reinforced concrete is provided. By optimizing the selection of alloying elements, controlling their dosage, and combining them with a rolling process, the present invention achieves the production of 500 MPa-grade steel bars with excellent corrosion resistance.

[0005] In order to solve the above problems, the present invention provides the following solutions:

[0006] A rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete comprises the following steps:

[0007] 1) continuously casting the smelted molten steel to obtain a continuous casting billet, wherein the components of the continuous casting billet are, by weight percentage, C: 0.08-0.09%, Cr: 1.00-1.02%, Cu: 0.20-0.22%, Mo: 0.20-0.22%, Si: 0.24-0.28%, Mn: 0.4-0.42%, V: 0.03-0.035%, N: 0.04-0.045%, P: ≤ 0.02%, S: ≤ 0.01%, and the remainder is iron and unavoidable impurities, wherein N = 0.05Mo + V;

[0008] 2) heating the continuous casting billet, performing rough rolling and finish rolling on the heated continuous casting billet in sequence, and cooling the billet after finish rolling to obtain chloride ion corrosion resistant steel bars;

[0009] During the rough rolling process, the rough rolling passes are 5-7 times, the first pass reduction rate is 10-15%, the last pass reduction rate is 10-15%, and the intermediate pass reduction rate is 25-30%.

[0010] It can be understood that N=0.05Mo+V, which means that the N content is equal to 0.05 times the Mo content plus the V content.

[0011] Preferably, the heating temperature for heating the continuous casting slab is 1140-1165°C.

[0012] Preferably, the starting temperature of the rough rolling is 1130-1140°C, and the finishing temperature is 1040-1050°C.

[0013] Preferably, the start temperature of the finishing rolling is 960-980°C, and the final rolling temperature is 820-860°C.

[0014] Preferably, the rough rolling process is performed 5 times, with a first pass reduction of 10-15%, a second pass reduction of 25-30%, a third pass reduction of 25-30%, a fourth pass reduction of 25-30%, and a fifth pass reduction of 10-15%.

[0015] Preferably, the rough rolling process is performed 6 times, with a first pass reduction of 10-15%, a second pass reduction of 25-30%, a third pass reduction of 25-30%, a fourth pass reduction of 25-30%, a fifth pass reduction of 25-30%, and a sixth pass reduction of 10-15%.

[0016] Preferably, the rough rolling process is carried out for 7 passes, with a first pass reduction rate of 10-15%, a second pass reduction rate of 25-30%, a third pass reduction rate of 25-30%, a fourth pass reduction rate of 25-30%, a fifth pass reduction rate of 25-30%, a sixth pass reduction rate of 25-30%, and a seventh pass reduction rate of 10-15%.

[0017] Preferably, the first pass reduction ratio and the last pass reduction ratio in the rough rolling process are the same.

[0018] Preferably, after the finish rolling, the temperature is lowered to 640-660°C and then cooled to room temperature. More preferably, after the finish rolling, the temperature is mist-cooled to 640-660°C and then air-cooled to room temperature.

[0019] Preferably, the molten steel smelting process in the present invention is a conventional process in the art, for example, molten iron is obtained after pre-desulfurization, converter smelting, and LF refining.

[0020] The technical solution of the present invention has the following advantages:

[0021] The present invention provides a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete. Elements such as C, Cr, Cu, Mo, Si, Mn, V, and N are introduced into the steel bars. The addition of Cr, Cu, and Mo can effectively improve the corrosion resistance of the steel bars. However, the addition of Mo will affect the mechanical properties of the steel bars to a certain extent. To this end, the present invention adds specific amounts of V and N. During the rolling process, by controlling the number of passes and the reduction rate of each pass in the rough rolling process, VN and (MoV)C and (MoV)N are precipitated through uniform deformation in the process of the steel bars transforming from austenite to ferrite. The precipitated fine particles further hinder the growth of ferrite grains, thereby effectively improving the strength and toughness of the steel bars. This achieves 500 MPa high strength while also having excellent chloride ion corrosion resistance.

[0022] In terms of element design, the present invention controls the contents of Mo, N, and V to meet the requirement of N=0.05Mo+V. While introducing a high content of Mo, the content of N is increased, so that more VN, (MoV)C, and (MoV)N are formed in the steel bar during deformation-induced precipitation. The uniform precipitation of VN, (MoV)C, and (MoV)N further affects the size of ferrite grains, thereby playing a role of fine grain strengthening, improving the chloride ion corrosion resistance of the steel bar and effectively improving the mechanical properties of the steel bar.

[0023] The present invention controls the number of rolling passes to 5-7 during the rough rolling process, and controls the reduction rates of the first and last passes to be lower than the reduction rates of the intermediate passes. On this basis, a higher reduction rate is maintained in the intermediate passes. Through specific rough rolling steps, uniform precipitation of particles such as Mo, N, and V can be ensured, and the chloride ion corrosion resistance and mechanical properties of the steel bars can be improved simultaneously with the combination of specific element contents. At the same time, the process is simple and the cost is low. DETAILED DESCRIPTION

[0024] The following examples are provided for further understanding of the present invention and are not intended to limit the best mode of implementation and do not limit the scope of protection of the present invention.

[0025] Any experimental steps or conditions not specified in the following embodiments of the present invention may be carried out according to conventional experimental steps and conditions used in existing literature in the field. Reagents or instruments used without specifying the manufacturer are all commercially available conventional reagents or instruments.

[0026] Example 1

[0027] This embodiment provides a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete, comprising the following steps:

[0028] 1) continuously casting the smelted molten steel to obtain a continuous casting billet, wherein the components of the continuous casting billet are, by weight percentage, C: 0.08%, Cr: 1.02%, Cu: 0.20%, Mo: 0.20%, Si: 0.28%, Mn: 0.42%, V: 0.03%, N: 0.04%, P: 0.02%, S: 0.01%, and the remainder is iron and unavoidable impurities;

[0029] 2) The continuous casting slab is heated to 1150° C. and subjected to rough rolling and finish rolling in sequence. The rough rolling start temperature is 1130° C., the finish rolling temperature is 1050° C., and the rolling passes are 5 times. The first pass has a reduction rate of 10%, the second pass has a reduction rate of 25%, the third pass has a reduction rate of 25%, the fourth pass has a reduction rate of 25%, and the fifth pass has a reduction rate of 10%. The finish rolling start temperature is 980° C. and the finish rolling temperature is 860° C. After finish rolling, the slab is mist-cooled to 650° C. and finally air-cooled to room temperature to obtain 500 MPa grade chloride ion corrosion-resistant steel bars for reinforced concrete (specification φ14 mm).

[0030] Example 2

[0031] This embodiment provides a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete, comprising the following steps:

[0032] 1) continuously casting the smelted molten steel to obtain a continuous casting billet, wherein the components of the continuous casting billet are, by weight percentage, C: 0.09%, Cr: 1.01%, Cu: 0.22%, Mo: 0.2%, Si: 0.24%, Mn: 0.40%, V: 0.032%, N: 0.042%, P: 0.015%, S: 0.009%, and the remainder is iron and unavoidable impurities;

[0033] 2) The continuous casting slab is heated to 1160° C. and subjected to rough rolling and finish rolling in sequence. The rough rolling start temperature is 1135° C., the finish rolling temperature is 1050° C., and the rolling passes are 5 times. The first pass has a reduction rate of 15%, the second pass has a reduction rate of 30%, the third pass has a reduction rate of 30%, the fourth pass has a reduction rate of 30%, and the fifth pass has a reduction rate of 15%. The finish rolling start temperature is 980° C. and the finish rolling temperature is 860° C. After finish rolling, the slab is mist-cooled to 650° C. and finally air-cooled to room temperature to obtain a chloride ion corrosion-resistant steel bar (specification φ14 mm) for 500 MPa reinforced concrete.

[0034] Example 3

[0035] This embodiment provides a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete, which differs from Example 2 in that in step 2): the continuous casting billet is heated to a temperature of 1165° C., and the heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, the rough rolling start temperature is 1135° C., the finish rolling temperature is 1045° C., and there are 6 rolling passes, with a first pass reduction of 12%, a second pass reduction of 30%, a third pass reduction of 30%, a fourth pass reduction of 30%, a fifth pass reduction of 30%, and a sixth pass reduction of 12%; the finish rolling start temperature is 980° C., and the finish rolling temperature is 850° C.; after finish rolling, the steel bars are mist-cooled to 640° C. and finally air-cooled to room temperature to obtain chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete (specification φ14 mm).

[0036] Example 4

[0037] This embodiment provides a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete, which differs from Example 2 in that in step 2): the continuous casting billet is heated to a temperature of 1155° C., and the heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, the rough rolling start temperature is 1140° C., the finish rolling temperature is 1040° C., and there are 7 rolling passes, with a first pass reduction of 15%, a second pass reduction of 30%, a third pass reduction of 30%, a fourth pass reduction of 30%, a fifth pass reduction of 30%, a sixth pass reduction of 30%, and a seventh pass reduction of 15%; the finish rolling start temperature is 960° C., and the finish rolling temperature is 820° C.; after finish rolling, the steel bar is mist-cooled to 660° C. and finally air-cooled to room temperature to obtain chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete (specification φ14 mm).

[0038] Comparative Example 1

[0039] This comparative example provides a rolling process for chloride ion corrosion-resistant steel bars for reinforced concrete, which differs from Example 1 in that the nitrogen content in the continuous casting billet in step 1) is 0.02%.

[0040] Comparative Example 2

[0041] This comparative example provides a rolling process for chloride ion corrosion-resistant steel bars for reinforced concrete. The difference between the comparative example and Example 1 is that in the rough rolling step in step 2), the starting rolling temperature is 1130°C, the finishing rolling temperature is 1050°C, the rolling passes are 5, the first pass has a reduction rate of 25%, the second pass has a reduction rate of 25%, the third pass has a reduction rate of 25%, the fourth pass has a reduction rate of 25%, and the fifth pass has a reduction rate of 25%.

[0042] Comparative Example 3

[0043] This comparative example provides a rolling process for chloride ion corrosion-resistant steel bars for reinforced concrete, which differs from Example 1 in that in the rough rolling step in step 2), the starting rolling temperature of the rough rolling is 1130°C, the finishing rolling temperature is 1050°C, the rolling passes are 5, the first pass has a reduction rate of 25%, the second pass has a reduction rate of 25%, the third pass has a reduction rate of 25%, the fourth pass has a reduction rate of 25%, and the fifth pass has a reduction rate of 10%.

[0044] Test Example 1

[0045] The chloride ion corrosion resistance of the chloride ion corrosion-resistant steel bars prepared by the methods of the above examples and comparative examples was tested (immersed in a 2% NaCl solution for 72 hours). The test results are shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] Test Example 2

[0050] The mechanical properties of the chloride ion corrosion resistant steel bars prepared by the methods of the above examples and comparative examples were tested, and the test results are shown in Table 2.

[0051] Table 2

[0052]

[0053] Obviously, for those skilled in the art, other variations can be made based on the above embodiments, and the obvious variations thus brought about are still within the scope of protection of the present invention.

Claims

1. A rolling process for chloride ion corrosion resistant steel bars for 500 MPa reinforced concrete, characterized in that: The steps include: 1) continuously casting the smelted molten steel to obtain a continuous casting billet, wherein the composition of the continuous casting billet is, by weight percentage, C: 0.08-0.09%, Cr: 1.00-1.02%, Cu: 0.20-0.22%, Mo: 0.20-0.22%, Si: 0.24-0.28%, Mn: 0.4-0.42%, V: 0.03-0.035%, N: 0.04-0.045%, P: ≤ 0.02%, S: ≤ 0.01%, and the remainder is iron and unavoidable impurities, wherein N = 0.05Mo + V; 2) The continuous casting billet is heated, and the heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, and then cooled after finish rolling to obtain chloride ion corrosion resistant steel bars; During the rough rolling process, the first pass reduction rate is the same as the last pass reduction rate; During the rough rolling process, the rough rolling passes are 5 times, with the first pass having a reduction rate of 10-15%, the second pass having a reduction rate of 25-30%, the third pass having a reduction rate of 25-30%, the fourth pass having a reduction rate of 25-30%, and the fifth pass having a reduction rate of 10-15%; Alternatively, in the rough rolling process, the rough rolling is performed for 6 passes, with a first pass reduction rate of 12%, a second pass reduction rate of 30%, a third pass reduction rate of 30%, a fourth pass reduction rate of 30%, a fifth pass reduction rate of 30%, and a sixth pass reduction rate of 12%; Alternatively, in the rough rolling process, the rough rolling passes are performed 7 times, with a first pass reduction rate of 15%, a second pass reduction rate of 30%, a third pass reduction rate of 30%, a fourth pass reduction rate of 30%, a fifth pass reduction rate of 30%, a sixth pass reduction rate of 30%, and a seventh pass reduction rate of 15%.

2. The rolling process according to claim 1, characterized in that The continuous casting slab is heated at a temperature of 1140-1165°C.

3. The rolling process according to claim 1, characterized in that The starting temperature of rough rolling is 1130-1140℃, and the finishing temperature is 1040-1050℃.

4. The rolling process according to claim 1, characterized in that The starting temperature of finishing rolling is 960-980℃, and the final rolling temperature is 820-860℃.

5. The rolling process according to claim 1 or 2, characterized in that: After finishing rolling, the temperature is lowered to 640-660°C and then cooled to room temperature.

6. The rolling process according to claim 5, characterized in that After finishing rolling, the steel is mist-cooled to 640-660°C and then air-cooled to room temperature.

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