Rolling process of chloride ion corrosion resistant steel bar for 500 MPa grade reinforced concrete

Abstract

The invention belongs to the technical field of corrosion-resistant steel bar preparation, and particularly relates to a rolling process of a chloride ion corrosion-resistant steel bar for 500 MPa-grade reinforced concrete. The rolling technology provided by the invention comprises the following steps that molten steel obtained after smelting is subjected to continuous casting, a continuous casting billet is obtained, and the continuous casting billet comprises the following components in percentage by weight: 0.08%-0.09% of C, 1.00%-1.02% of Cr, 0.20%-0.22% of Cu, 0.20%-0.22% of Mo, 0.24%-0.28% of Si, 0.4%-0.42% of Mn, 0.03%-0.035% of V, 0.04%-0.045% of N, smaller than or equal to 0.02% of P, smaller than or equal to 0.01% of S and the balance of iron and inevitable impurities; the continuous casting billet is heated, rough rolling and finish rolling are sequentially conducted on the heated continuous casting billet, cooling is conducted after finish rolling, and the chloride ion corrosion resistant steel bar is obtained; the rough rolling pass is 5-7 times, the reduction rate of the first pass is 10-15%, the reduction rate of the last pass is 10-15%, and the reduction rate of the middle pass is 25-30%. By means of the rolling technology, high strength is achieved, and meanwhile excellent chloride ion corrosion resistance is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion-resistant steel bar preparation, and specifically relates to a rolling process of 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 are gradually exploring 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] There are currently two main methods to improve the corrosion resistance of steel bars. One is to coat the steel bar surface with a corrosion-resistant layer, and the other is to add alloy elements to the steel bar to fundamentally improve the corrosion resistance of the steel bar. Currently, corrosion-resistant steel bars mainly include stainless steel bars, galvanized steel bars, and alloy corrosion-resistant steel bars. Among them, alloy corrosion-resistant steel bars generally add elements such as Ni, Cr, and Mo to the steel bars to improve the corrosion resistance of the steel bars. However, although the addition of alloy elements can improve the corrosion resistance of the steel bars, it may also cause damage to the mechanical properties of the steel bars. Therefore, how to balance the mechanical properties and corrosion resistance of the 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 defect that the existing alloy corrosion-resistant steel bars cannot effectively take into account both the mechanical properties and corrosion resistance of the steel bars, and further provide a rolling process for chloride ion corrosion-resistant steel bars for 500 MPa reinforced concrete. The present invention achieves the production of 500 MPa steel bars with excellent corrosion resistance by optimizing the selection of alloy elements, controlling the dosage and coordinating the rolling process.

[0005] In order to solve the above problems, the scheme of the present invention is as follows:

[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 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 rest are 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 the finish rolling to obtain a chloride ion corrosion resistant steel bar;

[0009] During the rough rolling process, the rough rolling passes are 5-7 times, the first pass has a reduction rate of 10-15%, the last pass has a reduction rate of 10-15%, and the intermediate passes have a reduction rate of 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 billet 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 rolling 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 for 5 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%, and a fifth pass reduction rate of 10-15%.

[0015] Preferably, the rough rolling process is performed 6 times, 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%, and a sixth pass reduction rate of 10-15%.

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

[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, such as molten iron 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 elements can effectively improve the corrosion resistance of the steel bars. However, the addition of the element Mo will affect the mechanical properties of the steel bars to a certain extent. For this reason, specific contents of V and N are added in the present invention. During the rolling process, by controlling the number of passes in the rough rolling process and the pressing rate of each pass, VN and (MoV)C and (MoV)N are precipitated through uniform deformation induction during the transformation of the steel bars 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. The steel bars have excellent chloride ion corrosion resistance while achieving 500 MPa high strength.

[0022] In terms of element design, the present invention controls the contents of Mo, N and V to meet N=0.05Mo+V, introduces a high content of Mo and increases the content of N, 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 rolling passes to be 5-7 times during the rough rolling process, and controls the reduction rates of the first and last passes to be lower than the reduction rate of the intermediate passes. On this basis, the intermediate passes are kept at a relatively high reduction rate. Through specific rough rolling steps, particles such as Mo, N, and V can be uniformly precipitated, and the chloride ion corrosion resistance and mechanical properties of the steel bars can be improved simultaneously with the specific element content. Meanwhile, the process is simple and the cost is low. DETAILED DESCRIPTION

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

[0025] The experimental steps or conditions not specified in the following embodiments of the present invention can be implemented according to the conventional experimental steps and conditions used in the existing literature in the field. The reagents or instruments used without specifying the manufacturer are all conventional reagents or instruments that can be purchased commercially.

[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 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 rest are iron and unavoidable impurities;

[0029] 2) The continuous casting billet is heated to 1150°C, and the heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, the starting temperature of the rough rolling is 1130°C, the final rolling temperature is 1050°C, the rolling passes are 5 times, the reduction rate of the first pass is 10%, the reduction rate of the second pass is 25%, the reduction rate of the third pass is 25%, the reduction rate of the fourth pass is 25%, and the reduction rate of the fifth pass is 10%; the starting temperature of the finish rolling is 980°C, and the final rolling temperature is 860°C; after the finish rolling, the billet 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 φ14mm).

[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 rest are iron and unavoidable impurities;

[0033] 2) The continuous casting billet is heated to 1160°C, and the heated continuous casting billet is subjected to rough rolling and finish rolling in sequence, the starting temperature of the rough rolling is 1135°C, the final rolling temperature is 1050°C, the rolling passes are 5 times, the reduction rate of the first pass is 15%, the reduction rate of the second pass is 30%, the reduction rate of the third pass is 30%, the reduction rate of the fourth pass is 30%, and the reduction rate of the fifth pass is 15%; the starting temperature of the finish rolling is 980°C, and the final rolling temperature is 860°C; after the finish rolling, the billet 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 φ14mm).

[0034] Example 3

[0035] The present 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 final rolling temperature is 1045°C, the rolling passes are 6 times, the first pass has a reduction rate of 12%, 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%, the fifth pass has a reduction rate of 30%, and the sixth pass has a reduction rate of 12%; the finish rolling start temperature is 980°C, and the final 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 φ14mm).

[0036] Example 4

[0037] The present 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 final rolling temperature is 1040°C, the rolling passes are 7 times, the first pass reduction rate is 15%, the second pass reduction rate is 30%, the third pass reduction rate is 30%, the fourth pass reduction rate is 30%, the fifth pass reduction rate is 30%, the sixth pass reduction rate is 30%, and the seventh pass reduction rate is 15%; the finish rolling start temperature is 960°C, and the final rolling temperature is 820°C; after finish rolling, the steel bars are 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 φ14mm).

[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 N 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, 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 final rolling temperature is 1050°C, the rolling passes are 5 times, the first pass reduction rate is 25%, the second pass reduction rate is 25%, the third pass reduction rate is 25%, the fourth pass reduction rate is 25%, and the fifth pass reduction rate is 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 final rolling temperature is 1050°C, the rolling passes are 5 times, the first pass reduction rate is 25%, the second pass reduction rate is 25%, the third pass reduction rate is 25%, the fourth pass reduction rate is 25%, and the fifth pass reduction rate is 10%.

[0044] Test Example 1

[0045] The chloride ion corrosion resistance (immersion in 2% NaCl solution for 72 hours) of the chloride ion corrosion-resistant steel bars prepared by the methods of the above-mentioned embodiment and comparative example were tested respectively. 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 embodiments and comparative examples were tested respectively, and the test results are shown in Table 2.

[0051] Table 2

[0052]

[0053] Obviously, for ordinary technicians in the field, other modifications can be made based on the above embodiments, and the obvious modifications brought about by these modifications are still within the protection scope 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 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; 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; 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%.

2. The rolling process according to claim 1, characterized in that The heating temperature for heating the continuous casting slab is 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: During the rough rolling process, the rough rolling passes are 5 times, 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%, and a fifth pass reduction rate of 10-15%.

6. The rolling process according to claim 1 or 2, characterized in that: During the rough rolling process, the rough rolling passes are 6 times, 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%, and a sixth pass reduction rate of 10-15%.

7. The rolling process according to claim 1 or 2, characterized in that: During the rough rolling process, the rough rolling passes are 7 times, with a reduction rate of 10-15% in the first pass, 25-30% in the second pass, 25-30% in the third pass, 25-30% in the fourth pass, 25-30% in the fifth pass, 25-30% in the sixth pass, and 10-15% in the seventh pass.

8. The rolling process according to claim 1 or 2, characterized in that: During the rough rolling process, the first pass reduction rate is the same as the last pass reduction rate.

9. 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.

10. The rolling process according to claim 9, 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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