490 Mpa grade flaw detection guaranteeing steel plate and production method thereof

Abstract

The invention discloses a 490 MPa grade flaw detection guaranteeing steel plate which comprises the following chemical components in percentage by weight: 0.17 to 0.19 percent of C, 0.20 to 0.30 percent of Si, 0.95 to 1.05 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.008 to 0.015 percent of Als, 0.008 to 0.012 percent of Nb and the balance of Fe and inevitable residual elements. The production method comprises the steps of converter steelmaking, LF refining, slab continuous casting, casting blank hot charging, casting blank heating, rolling, controlled cooling and online shearing. On the premise of ensuring flaw detection and mechanical properties of the steel plate, the traditional VD or RH vacuum treatment is omitted, the process is shortened, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical manufacturing, and specifically relates to a 490MPa grade flaw detection steel plate and a production method thereof. Background Art

[0002] Medium and thick plates are widely used in various important facilities or key parts of construction, usually in high-rise building structures, bridges, boiler pressure vessels and ships, etc., and strict requirements are placed on their flaw detection performance. Ensuring the internal quality of the steel plate and flaw detection are of great significance to the safe production of medium and thick plates.

[0003] Steel production enterprises usually use vacuum treatment during the steelmaking process to ensure the internal quality of steel plates, so as to meet the requirements of flaw detection. Vacuum treatment includes RH, VD, etc. From the process point of view, it adds a step, which makes the production cycle longer; from the cost point of view, it increases energy consumption, which is not conducive to energy saving and environmental protection. Summary of the invention

[0004] The present invention aims to provide a 490MPa grade flaw detection steel plate and a production method thereof, which eliminates the need for traditional VD or RH vacuum treatment, shortens the process and reduces production costs while ensuring the flaw detection and mechanical properties of the steel plate.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A 490MPa grade flaw detection steel plate, whose chemical composition is as follows by weight percentage: C: 0.17-0.19%, Si: 0.20-0.30%, Mn: 0.95-1.05%, P≤0.020%, S≤0.010%, Als: 0.008-0.015%, Nb: 0.008-0.012%, and the rest are Fe and unavoidable residual elements.

[0006] Furthermore, the 490MPa grade flaw detection steel plate of the present invention has a thickness of 20 to 35 mm.

[0007] Furthermore, the metallographic structure of the steel plate of the present invention is blocky ferrite + pearlite; the banded structure is ≤ level 2, the internal flaw detection meets level I in GB / T 2970-2004, and the pass rate is 100%; the mechanical properties of the steel plate meet the tensile strength of 490 to 530 MPa, the yield strength of 365 to 405 MPa, and the elongation of 22% to 27%.

[0008] Furthermore, the production method of the 490MPa grade flaw detection steel plate of the present invention includes: converter steelmaking, LF refining, slab continuous casting, hot charging of ingots, heating of ingots, rolling, controlled cooling and online shearing.

[0009] Furthermore, in the converter steelmaking of the present invention, the iron consumption is controlled at 950Kg / t to 980Kg / t.

[0010] Furthermore, the LF refining of the present invention ensures that Mn / s ≥ 120 in the outgoing smelting composition by adjusting the amount of low-carbon ferromanganese added and slag desulfurization.

[0011] Furthermore, in the slab continuous casting of the present invention, the superheat is controlled at 30-35° C., and the process casting speed is stably controlled at 0.85-0.9 m / min.

[0012] Furthermore, the heating temperature of the ingot according to the present invention is 1200-1250° C., and the holding time in the soaking section is ≥60 min.

[0013] Furthermore, the rolling described in the present invention adopts single-stand rolling, the waiting thickness is 2.5 to 3 times the thickness of the finished plate, the secondary rolling temperature is 880 to 900°C, and the final rolling temperature is 790 to 810°C.

[0014] Furthermore, in the controlled cooling of the present invention, the water cooling of the steel plate after rolling adopts a slow roller speed and small water volume cooling mode, the cooling roller speed is 0.4-0.5m / s, and the final cooling temperature is 650-670°C.

[0015] The inventive principle of the technical solution of the present invention is: Through reasonable chemical composition design, trace niobium alloying is used to replace part of the manganese alloy, reducing the impact of manganese segregation on the internal quality of the steel plate. By limiting the controlled rolling and controlled cooling process, the uniformity of the steel plate structure and segregation is further achieved, ensuring the high internal quality of the steel plate while achieving the matching of the 490MPa strength grade. After the composition and rolling cooling process are reasonably matched, the Mn / S in the refining process is limited to achieve the sequential precipitation of the segregated elements in the solidification process of the ingot, and the uniformity of the internal solidification structure of the ingot is achieved by limiting the matching of the superheat and the pulling speed range. The high internal quality ingot and steel plate have uniform structure, replacing the traditional VD or RH process, ensuring the high internal quality of the steel plate, and the flaw detection level can reach the national standard I level.

[0016] The beneficial effects of the technical solution of the present invention are: Under the premise of ensuring the flaw detection and mechanical properties of the steel plate, the present invention eliminates the traditional VD or RH vacuum treatment, shortens the process and reduces the production cost; and by controlling the Mn / S in the LF process and the matching of the superheat and the drawing speed in the continuous casting process, the quality of the low-multiple grades of the ingot is improved, and by controlling the heating temperature and time of the ingot and the rolling temperature and the cooling rate, the core segregation and uniform structure of the steel plate are achieved, the slow cooling process of the steel plate off the line is eliminated, the production process is short, and the energy cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the metallographic structure diagram of the steel plate at the 1 / 4 thickness position in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the embodiments. Example 1

[0019] A 490MPa grade flaw detection steel plate, whose chemical composition by weight percentage is as follows: C: 0.17%, Si: 0.20%, Mn: 1.05%, P: 0.017%, S: 0.008%, Als: 0.008%, Nb: 0.012%, and the rest are Fe and unavoidable residual elements; its production method includes: converter steelmaking, LF refining, slab continuous casting, hot charging of ingot, heating of ingot, rolling, controlled cooling and online shearing, as follows: (1) Converter steelmaking: iron consumption is controlled at 950 kg / t; (2) Refining: Mn / s=131 in the outgoing smelting composition; (3) Slab continuous casting: superheat is controlled at 30°C and the process casting speed is controlled at 0.85m / min; (4) Billet heating: The billet is sent into the furnace for heating at a temperature of 1200°C and a holding time of 60 minutes in the soaking section; (5) Rolling: Single-stand rolling is adopted, the waiting thickness is 2.5 times the thickness of the finished plate, the secondary rolling temperature is 880°C, and the final rolling temperature is 790°C; (6) Controlled cooling: After rolling, the steel plate is water-cooled in a slow roller speed and small water volume cooling mode, with a cooling roller speed of 0.4 m / s and a final cooling temperature of 650 °C; The metallographic structure of the steel plate in this embodiment is as follows Figure 1 As shown, it can be seen that the metallographic structure is blocky ferrite + pearlite; the metallographic structures of the steel plates in other embodiments are the same as those in embodiment 1 and are not shown in sequence again.

[0020] The banded structure of the steel plate in this embodiment is ≤ Grade 2, the internal flaw detection of the steel plate meets Grade I in GB / T 2970-2004, and the mechanical properties are detailed in Table 1. Example 2

[0021] A 490MPa grade flaw detection steel plate, whose chemical composition by weight percentage is as follows: C: 0.19%, Si: 0.30%, Mn: 0.95%, P: 0.011%, S: 0.005%, Als: 0.015%, Nb: 0.008%, and the rest are Fe and unavoidable residual elements; its production method includes: converter steelmaking, LF refining, slab continuous casting, hot charging of ingot, heating of ingot, rolling, controlled cooling and online shearing, as follows: (1) Converter steelmaking: iron consumption is controlled at 980 kg / t; (2) Refining: ensure that the outgoing smelting composition has Mn / s = 190; (3) Slab continuous casting: superheat is controlled at 35°C and the process casting speed is controlled at 0.9 m / min; (4) Billet heating: The billet is sent into the furnace for heating at a temperature of 1250°C and a holding time of 80 minutes in the soaking section; (5) Rolling: Single-stand rolling is adopted, the waiting thickness is 3 times the thickness of the finished plate, the secondary rolling temperature is 900°C, and the final rolling temperature is 810°C; (6) Controlled cooling: After rolling, the steel plate is water-cooled in a slow roller speed and small water volume cooling mode, with a cooling roller speed of 0.5 m / s and a final cooling temperature of 670 °C; The metallographic structure of the steel plate in this embodiment is massive ferrite + pearlite; the banded structure is ≤ level 2, the internal flaw detection of the steel plate meets level I in GB / T 2970-2004, and the mechanical properties are detailed in Table 1. Example 3

[0022] A 490MPa grade flaw detection steel plate, whose chemical composition by weight percentage is as follows: C: 0.18%, Si: 0.22%, Mn: 1.00%, P: 0.016%, S: 0.007%, Als: 0.012%, Nb: 0.010%, and the rest are Fe and unavoidable residual elements; its production method includes: converter steelmaking, LF refining, slab continuous casting, hot charging of ingot, heating of ingot, rolling, controlled cooling and online shearing, as follows: (1) Converter steelmaking: iron consumption is controlled at 970 kg / t; (2) Refining: Ensure that the outgoing smelting composition has Mn / s = 143; (3) Slab continuous casting: superheat is controlled at 32°C and the process casting speed is controlled at 0.87m / min; (4) Billet heating: The billet is sent into the furnace for heating at a temperature of 1230°C and a holding time of 75 minutes in the soaking section; (5) Rolling: Single-stand rolling is adopted, the waiting thickness is 2.5 times the thickness of the finished plate, the secondary rolling temperature is 890°C, and the final rolling temperature is 800°C; (6) Controlled cooling: After rolling, the steel plate is water-cooled in a slow roller speed and small water volume cooling mode, with a cooling roller speed of 0.42 m / s and a final cooling temperature of 660 °C; The metallographic structure of the steel plate in this embodiment is massive ferrite + pearlite; the banded structure is ≤ level 2, the internal flaw detection of the steel plate meets level I in GB / T 2970-2004, and the mechanical properties are detailed in Table 1. Example 4

[0023] A 490MPa grade flaw detection steel plate, whose chemical composition by weight percentage is as follows: C: 0.17%, Si: 0.25%, Mn: 1.03%, P: 0.013%, S: 0.008%, Als: 0.010%, Nb: 0.009%, and the rest are Fe and unavoidable residual elements; its production method includes: converter steelmaking, LF refining, slab continuous casting, hot charging of ingot, heating of ingot, rolling, controlled cooling and online shearing, as follows: (1) Converter steelmaking: iron consumption is controlled at 960 kg / t; (2) Refining: ensure that the outgoing smelting composition has Mn / s = 129; (3) Slab continuous casting: superheat is controlled at 34°C and the process casting speed is controlled at 0.88m / min; (4) Billet heating: The billet is sent into the furnace for heating at a temperature of 1220°C and a holding time of 70 minutes in the soaking section; (5) Rolling: Single-stand rolling is adopted, the waiting thickness is 3 times the thickness of the finished plate, the secondary rolling temperature is 880°C, and the final rolling temperature is 810°C; (6) Controlled cooling: After rolling, the steel plate is water-cooled in a slow roller speed and small water volume cooling mode, with a cooling roller speed of 0.45 m / s and a final cooling temperature of 670 °C; The metallographic structure of the steel plate in this embodiment is massive ferrite + pearlite; the banded structure is ≤ level 2, the internal flaw detection of the steel plate meets level I in GB / T 2970-2004, and the mechanical properties are detailed in Table 1.

[0024] Table 1 Mechanical properties of steel plates in various examples .

Claims

1. A 490MPa grade flaw detection steel plate, characterized in that: Its chemical composition by weight percentage is as follows: C: 0.17-0.19%, Si: 0.20-0.30%, Mn: 0.95-1.05%, P≤0.020%, S≤0.010%, Als: 0.008-0.015%, Nb: 0.008-0.012%, and the rest are Fe and unavoidable residual elements.

2. A 490MPa grade flaw detection steel plate according to claim 1, characterized in that: The thickness of the steel plate is 20 to 35 mm.

3. The 490MPa grade flaw detection steel plate according to claim 1, characterized in that: The metallographic structure of the steel plate is blocky ferrite + pearlite; the banded structure is ≤ level 2, and the internal flaw detection meets level I in GB / T 2970-2004; the mechanical properties of the steel plate meet the tensile strength of 490 to 530 MPa, the yield strength of 365 to 405 MPa, and the elongation of 22% to 27%.

4. The method for producing the 490MPa grade flaw detection steel plate according to any one of claims 1 to 3, characterized in that: It includes converter steelmaking, LF refining, slab continuous casting, hot charging of ingot, ingot heating, rolling, controlled cooling and online shearing.

5. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: In the converter steelmaking, the iron consumption is controlled at 950Kg / t to 980Kg / t.

6. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: The LF refining ensures that the outgoing smelting composition has Mn / s ≥ 120.

7. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: In the slab continuous casting, the superheat is controlled at 30-35° C., and the process casting speed is controlled at 0.85-0.9 m / min.

8. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: The heating temperature of the ingot is 1200-1250° C., and the holding time in the soaking section is ≥60 min.

9. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: The rolling adopts single-stand rolling, the waiting thickness is 2.5 to 3 times the thickness of the finished plate, the secondary rolling temperature is 880 to 900°C, and the final rolling temperature is 790 to 810°C.

10. The method for producing a 490MPa grade flaw detection steel plate according to claim 4, characterized in that: The controlled cooling adopts a slow roller speed and small water volume cooling mode for water cooling of the steel plate after rolling, the cooling roller speed is 0.4-0.5 m / s, and the final cooling temperature is 650-670°C.

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