Low-yield-ratio Q355B structural steel and production process thereof

Abstract

The invention discloses low-yield-ratio Q355B structural steel and a production process thereof, and relates to the technical field of steel production, and the low-yield-ratio Q355B structural steel comprises the following chemical components in percentage by mass: 0.10%-0.20% of C, 0.10%-0.35% of Si, 0.60%-1.60% of Mn, less than or equal to 0.030% of P, less than or equal to 0.025% of S, 0.005%-0.020% of Nb, 0.010%-0.030% of Ti, 0.020%-0.050% of Al and the balance of Fe and inevitable impurities.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, in particular to a low-yield ratio Q355B structural steel and a production process thereof. Background Art

[0002] Competition in the steel industry is becoming increasingly fierce, and downstream customers are constantly putting forward new requirements for steel plate performance. Ordinary structural steel is widely used in various industries of national production. As the country's requirements for safe production continue to strengthen, new requirements are put forward for the safety of steel structure design. On the premise of meeting the standard performance requirements, new requirements are put forward for the yield strength ratio of ordinary structural steel, requiring the yield strength ratio to be ≤0.85. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the disadvantages of the prior art and provide a low yield ratio Q355B structural steel and a production process thereof.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows: A low yield ratio Q355B structural steel, whose chemical composition and mass percentage are: C: 0.10%-0.20%, Si: 0.10%-0.35%, Mn: 0.60%-1.60%, P≤0.030%, S≤0.025%, Nb: 0.005%-0.020%, Ti: 0.010%-0.030%, Al: 0.020%-0.050%, and the balance is Fe and unavoidable impurities.

[0005] As a preferred embodiment of the low yield ratio Q355B structural steel described in the present invention, its chemical composition and mass percentage are: C: 0.10%-0.18%, Si: 0.10%-0.30%, Mn: 0.50%-1.50%, P≤0.020%, S≤0.010%, Nb: 0.005%-0.020%, Ti: 0.010%-0.030%, Al: 0.020%-0.050%, and the balance is Fe and unavoidable impurities.

[0006] The present invention also provides a production process of low yield ratio Q355B structural steel, comprising the following steps: S1, using converter smelting, LF+RH to refine and purify molten steel; S2, the molten steel is sent to the continuous casting for casting; S3. After the billet is cast, it is subjected to a cold surface inspection. After the surface inspection is qualified, it is heated; S4, rolling by TMCP rolling process; S5. After rolling, the steel plate is water-cooled. When the red-return temperature is 650-740℃, the cooling rate is reduced by using intermittent water; S6. After water cooling, the steel is straightened by a straightening machine and then sent to a cooling bed for air cooling; S7, the steel plate is finished after being cooled to below 300℃ on the cooling bed; S8. After the length is determined, the products are marked, inspected for flaws and put into storage.

[0007] As a preferred solution of the production process of the low yield ratio Q355B structural steel of the present invention, wherein: the casting superheat in the step S2 is controlled to be 20-30°C.

[0008] As a preferred solution of the production process of the low yield ratio Q355B structural steel described in the present invention, wherein: the heating temperature in step S3 is 1130±20°C.

[0009] As a preferred solution of the production process of the low yield ratio Q355B structural steel described in the present invention, wherein: in the step S4, the rough rolling temperature is 1050±50°C, the second rolling temperature is 860-1020°C, and the final rolling temperature is 780-860°C.

[0010] As a preferred solution of the production process of low yield ratio Q355B structural steel of the present invention, the water flow rate of a single header in step S5 is 80-120m 3 / h.

[0011] As a preferred solution of the production process of the low yield ratio Q355B structural steel of the present invention, wherein: the straightening temperature in step S6 is 500-700°C.

[0012] The beneficial effects of the present invention are: (1) The present invention effectively reduces the yield strength ratio of ordinary structural steel, meets the design requirement of product performance ≤ 0.85, increases production efficiency, and improves the safety and stability of structural parts.

[0013] (2) The present invention sets a high red-return temperature (650-740°C), which effectively reduces the cooling rate, reduces the hardening structure transformation, and effectively reduces the de-scaling. At the same time, hot straightening is carried out at high temperature, which improves the flatness of the steel plate and greatly reduces the crushing of the oxide scale on the surface of the steel plate, thereby increasing the surface aesthetics and corrosion resistance of the steel plate.

[0014] (3) The present invention adopts interval water, which effectively reduces the cooling rate near the surface of the steel plate, reduces the thickness of the near-surface rapid cooling layer, reduces the yield strength ratio of the steel plate, and reduces the surface cracking when the steel plate is bent. DETAILED DESCRIPTION

[0015] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation methods.

[0016] Example 1: This example provides a low yield ratio Q355B structural steel, whose chemical composition and mass percentage are as follows: C: 0.16%, Si: 0.25%, Mn: 1.26%, P: 0.022%, S: 0.012%, Nb: 0.012%, Ti: 0.016%, Al: 0.032%, and the remainder is Fe and unavoidable impurities.

[0017] This embodiment also provides a production process of low yield ratio Q355B structural steel, which specifically includes the following steps: S1, using converter smelting, LF+RH to refine and purify molten steel; S2, the molten steel is sent to the continuous casting for casting, and the casting superheat is controlled at 24°C; S3. After the billet is cast, it is subjected to a cold surface inspection. After the surface inspection is qualified, it is heated at a temperature of 1115°C. S4, the rough rolling temperature is 1082℃, the TMCP rolling process is adopted, the second rolling temperature is 1000℃, and the final rolling temperature is 852℃; S5, ultra-fast cooling header flow rate 100m3 / h, using 1-8 groups of headers, of which 1 and 3 groups of headers do not boil water, and the return temperature is 688℃; S6. After water cooling, straightening is carried out using a straightening machine at a straightening temperature of 635°C, and then sent to a cooling bed for air cooling; S7, the steel plate is cooled to below 300℃ on the cooling bed and then finished (head and tail cutting, edge cutting, sampling, and sizing); S8. After the length is determined, the products are marked, inspected for flaws and put into storage.

[0018] The product obtained in Example 1 was sampled and tested for mechanical properties. The results are shown in Table 1:

[0019] Table 1 Example 2: This example provides a low yield ratio Q355B structural steel, whose chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.31%, Mn: 1.32%, P: 0.018%, S: 0.011%, Nb: 0.015%, Ti: 0.016%, Al: 0.032%, and the remainder is Fe and unavoidable impurities.

[0020] This embodiment also provides a production process of low yield ratio Q355B structural steel, which specifically includes the following steps: S1, using converter smelting, LF+RH to refine and purify molten steel; S2, the molten steel is sent to the continuous casting for casting, and the casting superheat is controlled at 25°C; S3. After the billet is cast, it is subjected to a cold surface inspection. After the surface inspection is qualified, it is heated at a temperature of 1128°C. S4, the rough rolling temperature is 1088℃, the TMCP rolling process is adopted, the second rolling temperature is 900℃, and the final rolling temperature is 832℃; S5, ultra-fast cooling header flow rate 100m3 / h, using 1-14 groups of headers, of which 1, 3, and 5 groups of headers do not boil water, and the return temperature is 662℃; S6. After water cooling, use a straightening machine for straightening at a temperature of 641°C. Then send to a cooling bed for air cooling; S7, the steel plate is cooled to below 300℃ on the cooling bed and then finished (head and tail cutting, edge cutting, sampling, and sizing); S8. After the length is determined, the products are marked, inspected for flaws and put into storage.

[0021] The product obtained in Example 2 was sampled and tested for mechanical properties. The results are shown in Table 2:

[0022] Table 2 Therefore, the technical solution of the present application effectively reduces the yield strength ratio of ordinary structural steel, meets the design requirement of product performance ≤0.85, increases production efficiency, and improves the safety and stability of structural parts.

[0023] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A low yield ratio Q355B structural steel, characterized by: Its chemical composition and its mass percentage are: C: 0.10%~0.20%, Si: 0.10%~0.35%, Mn: 0.60%~1.60%, P≤0.030%, S≤0.025%, Nb: 0.005%~0.020%, Ti: 0.010%~0.030%, Al: 0.020%~0.050%, and the balance is Fe and unavoidable impurities.

2. The low yield ratio Q355B structural steel according to claim 1, characterized in that: Its chemical composition and its mass percentage are: C: 0.10%~0.18%, Si: 0.10%~0.30%, Mn: 0.50%~1.50%, P≤0.020%, S≤0.010%, Nb: 0.005%~0.020%, Ti: 0.010%~0.030%, Al: 0.020%~0.050%, and the balance is Fe and unavoidable impurities.

3. A production process of low yield ratio Q355B structural steel according to claim 1 or 2, characterized in that: The following steps are involved: S1, using converter smelting, LF+RH to refine and purify molten steel; S2, the molten steel is sent to the continuous casting for casting; S3. After the billet is cast, it is subjected to a cold surface inspection. After the surface inspection is qualified, it is heated; S4, rolling by TMCP rolling process; S5. After rolling, the steel plate is water-cooled. When the red-return temperature is 650-740℃, the cooling rate is reduced by using intermittent water; S6. After water cooling, the steel is straightened by a straightening machine and then sent to a cooling bed for air cooling; S7, the steel plate is finished after being cooled to below 300℃ on the cooling bed; S8. After the length is determined, the products are marked, inspected for flaws and put into storage.

4. The production process of low yield ratio Q355B structural steel according to claim 3, characterized in that: In step S2, the casting superheat is controlled to be 20-30°C.

5. The production process of low yield ratio Q355B structural steel according to claim 3, characterized in that: The heating temperature in step S3 is 1130±20°C.

6. The production process of low yield ratio Q355B structural steel according to claim 3, characterized in that: In step S4, the rough rolling temperature is 1050±50°C, the second rolling temperature is 860-1020°C, and the final rolling temperature is 780-860°C.

7. The production process of low yield ratio Q355B structural steel according to claim 3, characterized in that: The water flow rate of a single header in step S5 is 80-120m 3 / h.

8. The production process of low yield ratio Q355B structural steel according to claim 3, characterized in that: The straightening temperature in step S6 is 500-700°C.

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