Low-yield-ratio 620-mpa-grade steel plate for bridge, and preparation method therefor

Abstract

Disclosed in the present invention is a low-yield-ratio 620-MPa-grade steel plate for a bridge. The steel plate comprises the following components in percentages by mass: 0.020-0.100% of C, 0.10-0.70% of Si, 1.21-1.81% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.10-0.80% of Ni, less than or equal to 0.80% of Cr, 0.08-0.60% of Mo, less than or equal to 0.70% of Cu, 0.01-0.10% of Nb, less than or equal to 0.020% of Ti, 0.01-0.06% of Al, and 0.0001-0.0010% of B, with the balance being Fe and inevitable impurities. Further disclosed is a preparation method for the steel plate. In the present invention, the steel plate is prepared by means of a method of cost design + TMCP + low-temperature short-time tempering, and the structure of the steel plate is ferrite and bainite. The structure of ferrite and bainite guarantees that the strength and toughness of the steel plate match; in addition, the preparation process flow is simple with no complicated post-rolling heat treatment process, and the preparation cost of the material is reduced.

Description

Low yield ratio bridge 620 MPa grade steel plate and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the field of steel, in particular to a low yield ratio bridge 620 MPa grade steel plate and a preparation method thereof. BACKGROUND

[0002] Bridge is the key node of road traffic engineering and the difficulty in road construction. With the gradual extension of road traffic engineering construction to underdeveloped areas, it puts forward requirements such as large span, large load and light weight for bridges, and the existing low-grade strength steel cannot meet the development goal of bridge construction. In view of the above requirements, in addition to optimizing the bridge structure design, improving the strength of bridge steel is also an effective way. At present, the steel used in most bridges is not more than 500 MPa grade. On the one hand, with the increase of bridge steel strength, the toughness of steel plate will inevitably decrease, accompanied by the decrease of welding performance and the increase of yield ratio, which limits the application of high-strength bridge steel. On the other hand, the alloy composition design and manufacturing process control of high-strength bridge steel are complex, which leads to the increase of preparation cost and also limits its application.

[0003] The 620 MPa grade bridge steel has the advantages of high strength level, good plasticity and toughness, and excellent weldability, which can effectively meet the demand of existing bridge construction for high-strength bridge steel.

[0004] The patent with publication number CN 112813344B discloses a yield strength 620 MPa grade high-strength high-toughness easy-to-weld structural steel plate and a preparation method thereof. It adopts 0.6% to 0.8% C and focuses on the TMCP+QT process, but the yield ratio of the steel plate is more than 0.95.

[0005] The patent with publication number CN 114480961B discloses a 620 MPa grade high-strength steel with a cold crack sensitivity coefficient ≤0.19 and a production method thereof. The invention starts from the purpose of reducing the cold crack sensitivity coefficient of the steel plate and ensuring its strength, adopts the measures of not adding Mo, Ni, Cu and V elements in the composition, and adopts TMCP+T in the process. However, the yield ratio of the steel plate is high, generally more than 0.90, and the tempering time in the furnace needs to be more than 100h, which restricts the production efficiency of the factory and increases the cost.

[0006] The patent with the application number 202310329877.4 discloses a 620MPa grade high-strength steel with a weld heat-affected zone impact energy of-60 DEG C greater than 150J and a preparation method thereof. The patent eliminates or weakens the banded structure caused by segregation by reducing the content of easy segregation elements and by performing offline normalizing treatment before quenching, and obtains a tempered sorbite structure by Q+T process, so as to improve the impact toughness of the base material and the HAZ. However, the patent does not involve the strength and plasticity indicators, and the preparation process is complex, which increases the preparation cost.

[0007] The 620MPa grade steel involved in the prior art all meet the strength and toughness requirements of Q620q of GB / T 714, but the yield strength ratio is relatively high, which is difficult to meet the requirement of low yield strength ratio of bridge steel for bridge manufacturing and application end. Meanwhile, the preparation process is relatively long and the cost is relatively high, which limits its large-scale application.

[0008] Therefore, it is necessary to develop a new type of 620MPa grade steel plate for bridges and a preparation method thereof, so as to reduce the yield strength ratio of the steel plate, simplify the preparation process and reduce the cost.

[0009] SUMMARY

[0010] The present application provides a low yield strength ratio 620MPa grade steel plate for bridges and a preparation method thereof, which is prepared by the method of cost design+TMCP+low temperature short time tempering. The microstructure of the steel plate is ferrite plus bainite, which ensures the matching of the strength and toughness of the steel plate on the one hand, and the preparation process is simple without complex post-rolling heat treatment process, thereby reducing the preparation cost of the material.

[0011] TECHNICAL SOLUTION The low yield strength ratio 620MPa grade steel plate for bridges provided by the present application comprises the following components in mass percentage: C: 0.020%-0.100%, Si: 0.10%-0.70%, Mn: 1.21%-1.81%, P: ≤0.020%, S: ≤0.010%, Ni: 0.10%-0.80%, Cr: ≤0.80%, Mo: 0.08%-0.60%, Cu: ≤0.70%, Nb: 0.01%-0.10%, Ti: ≤0.020%, Al: 0.01%-0.06%, B: 0.0001%-0.0010%, and the balance is Fe and inevitable impurities.

[0012] The steel plate has a carbon equivalent CEV of 0.62 (CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15) and a cold crack sensitivity coefficient Pcm of 0.25 (Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B).

[0013] The steel plate has a thickness of 50 mm.

[0014] The preparation method of the 620MPa-grade steel plate for low yield ratio bridges comprises the following steps: molten iron pretreatment, converter smelting, LF+RH refining, continuous casting, heating, phosphorus removal, rolling, plate cooling and tempering.

[0015] After the molten iron pretreatment, converter smelting and LF+RH refining, a slab with a thickness of 460 mm is obtained through continuous casting.

[0016] In the heating and phosphorus removal, the heating temperature is 1150-1220 DEG C, the heating speed is 4-7 DEG C / s, the soaking time is greater than or equal to 100 min, high-pressure water is used for descaling, the descaling pressure is greater than or equal to 18 MPa, and the descaling pass is 1-2.

[0017] The rolling is divided into two-stage controlled rolling: the first stage is recrystallization zone rolling, the rolling temperature is 1050-1150 DEG C, the rolling reduction is greater than or equal to 75%, the second stage is non-recrystallization zone rolling, the rolling temperature is 790-870 DEG C, the finish rolling temperature is 780-860 DEG C, and the rolling reduction is 60-70%.

[0018] The plate cooling is controlled cooling: after the rolling is completed, the rolled piece is air-cooled to below 770 DEG C, then water-cooled, the cooling speed is 5-10 DEG C, the roller speed is less than or equal to 0.8 m / s, and the controlled red temperature range is less than or equal to 450 DEG C.

[0019] In the tempering, the tempering temperature is less than or equal to 550 DEG C, the tempering soaking time is 20-40 min, and the plate is air-cooled after the tempering.

[0020] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: the steel plate is prepared by the method of cost design + TMCP + low-temperature short-time tempering, and the microstructure is ferrite plus bainite. On the one hand, the ferrite plus bainite microstructure ensures the matching of the strength and toughness of the steel plate; on the other hand, the preparation process is simple, and there is no complex post-rolling heat treatment process, thereby reducing the preparation cost of the material. The prepared steel plate has a thickness of ≤50 mm, a yield strength of >620 MPa, a tensile strength of >720 MPa (sufficient strength margin), a yield strength ratio of <0.85, an impact energy of >250 J at -20℃ and -40℃, and an impact energy of >150 J at -60℃ after short-time low-temperature tempering. The TMCP (+T) state is adopted for delivery, and the process is simple; meanwhile, the performance of the steel plate meets the demand of bridge application end for high strength-toughness matching and low yield strength ratio of bridge steel. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 is a microstructure diagram of the steel plate prepared in Example 1 of the present application;

[0022] Fig. 2 is a microstructure diagram of the steel plate prepared in Example 4 of the present application. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further described below in combination with the drawings and specific embodiments.

[0024] Example 1:

[0025] The low-yield-strength-ratio bridge steel plate of 620 MPa grade in the present embodiment is configured with chemical components in percentage by mass, and the content of each element is C: 0.046, Si: 0.39, Mn: 1.49, P: 0.016, S: 0.002, Ni: 0.43, Cr: 0.21, Mo: 0.42, Cu: 0.41, Nb: 0.076, Ti: 0.019, Al: 0.055, B: 0.0005, and the balance is Fe and inevitable impurities.

[0026] During preparation, after converter smelting, a 460 mm thick slab is continuously cast. Then the slab is heated to 1180℃ at a rate of 5℃ / s in a heating furnace, and the soaking section is kept at 115 min. Then the slab is discharged, descaled and subjected to first-stage rolling, and the opening rolling temperature is 1060℃. The slab is rolled to a thickness of 100 mm, and then is kept warm in air, and the rolling reduction rate is 78%. The slab is kept warm to 860℃, and then is subjected to second-stage rolling, and finally is rolled to a 40 mm thick plate, and the rolling reduction rate is 60%, and the finish rolling temperature is 820℃. The plate is cooled to 730℃ in air, and then is subjected to water cooling, and the cooling rate is 8℃ / s, the roll speed is 0.4 m / s, the re-red temperature is 420℃, and then the plate is air-cooled on a cooling bed.

[0027] Example 2:

[0028] The 620 MPa grade steel plate for low yield ratio bridge of the embodiment is configured with chemical components in percentage by mass, and the content of each element is C: 0.085, Si: 0.18, Mn: 1.24, P: 0.011, S: 0.004, Ni: 0.16, Cr: 0.49, Mo: 0.58, Cu: 0.64, Nb: 0.020, Ti: 0.010, Al: 0.020, B: 0.0009, and the balance is Fe and inevitable impurities.

[0029] In preparation, after converter smelting, a 460 mm thick slab is continuously cast. Then the slab is heated to 1210 ℃ at 4 ℃ / s in a heating furnace, and the soaking section is kept for 110 min. Then the slab is discharged, descaled and subjected to first stage rolling, and the rolling temperature is 1120 ℃. The slab is rolled to a thickness of 110 mm, and then is kept warm in air, and the rolling reduction is 76%. The slab is kept warm to 790 ℃, and then is subjected to second stage rolling, and finally is rolled to a 50 mm thick plate, and the rolling reduction is 55%, and the finish rolling temperature is 780 ℃. The plate is cooled to 770 ℃ in air, and then is water cooled, and the cooling rate is 10 ℃ / s, the roll speed is 0.7 m / s, the re-red temperature is 450 ℃, and then the plate is air cooled on a cooling bed.

[0030] Example 3

[0031] The 620 MPa grade steel plate for low yield ratio bridge of the embodiment is configured with chemical components in percentage by mass, and the content of each element is C: 0.026, Si: 0.62, Mn: 1.76, P: 0.007, S: 0.007, Ni: 0.73, Cr: 0.71, Mo: 0.11, Cu: 0.14, Nb: 0.048, Ti: 0.005, Al: 0.039, B: 0.0002, and the balance is Fe and inevitable impurities.

[0032] In preparation, after converter smelting, a 460 mm thick slab is continuously cast. Then the slab is heated to 1150 ℃ at 7 ℃ / s in a heating furnace, and the soaking section is kept for 120 min. Then the slab is discharged, descaled and subjected to first stage rolling, and the rolling temperature is 1150 ℃. The slab is rolled to a thickness of 90 mm, and then is kept warm in air, and the rolling reduction is 80%. The slab is kept warm to 830 ℃, and then is subjected to second stage rolling, and finally is rolled to a 30 mm thick plate, and the rolling reduction is 67%, and the finish rolling temperature is 850 ℃. The plate is cooled to 710 ℃ in air, and then is water cooled, and the cooling rate is 6 ℃ / s, the roll speed is 0.3 m / s, the re-red temperature is 400 ℃, and then the plate is air cooled on a cooling bed.

[0033] Example 4

[0034] The low yield ratio bridge steel plate of 620 MPa grade of the embodiment is configured with chemical components in percentage by mass, and the content of each element is C: 0.046, Si: 0.39, Mn: 1.49, P: 0.016, S: 0.002, Ni: 0.43, Cr: 0.21, Mo: 0.42, Cu: 0.41, Nb: 0.076, Ti: 0.019, Al: 0.055, B: 0.0005, and the balance is Fe and inevitable impurities.

[0035] In preparation, after converter smelting, a 460 mm thick slab is continuously cast. Then the slab is heated to 1180℃ at 5℃ / s in a heating furnace, and the soaking section is kept for 115 min. Then the slab is discharged, descaled and subjected to first stage rolling, and the opening rolling temperature is 1060℃. The slab is rolled to a thickness of 100 mm, and then is kept warm in air, and the rolling reduction is 78%. The slab is kept warm to 860℃, and then is subjected to second stage rolling, and finally is rolled to a 40 mm thick plate, and the rolling reduction is 60%, and the finish rolling temperature is 820℃. The plate is cooled to 730℃ in air, and then is water cooled, and the cooling rate is 8℃ / s, the roll speed is 0.4 m / s, the re-red temperature is 420℃, and then the plate is air cooled on a cooling bed.

[0036] Example 5

[0037] The low yield ratio bridge steel plate of 620 MPa grade of the embodiment is configured with chemical components in percentage by mass, and the content of each element is C: 0.085, Si: 0.18, Mn: 1.24, P: 0.011, S: 0.004, Ni: 0.16, Cr: 0.49, Mo: 0.58, Cu: 0.64, Nb: 0.020, Ti: 0.010, Al: 0.020, B: 0.0009, and the balance is Fe and inevitable impurities.

[0038] In preparation, after converter smelting, a 460 mm thick slab is continuously cast. Then the slab is heated to 1180℃ at 5℃ / s in a heating furnace, and the soaking section is kept for 115 min. Then the slab is discharged, descaled and subjected to first stage rolling, and the opening rolling temperature is 1060℃. The slab is rolled to a thickness of 100 mm, and then is kept warm in air, and the rolling reduction is 78%. The slab is kept warm to 860℃, and then is subjected to second stage rolling, and finally is rolled to a 40 mm thick plate, and the rolling reduction is 60%, and the finish rolling temperature is 820℃. The plate is cooled to 730℃ in air, and then is water cooled, and the cooling rate is 8℃ / s, the roll speed is 0.4 m / s, the re-red temperature is 420℃, and then the plate is air cooled on a cooling bed.

[0039] Example 6

[0040] The 620 MPa grade steel plate for low yield ratio bridge of the embodiment is configured according to mass percentage of chemical components, and the content of each element is C: 0.026, Si: 0.62, Mn: 1.76, P: 0.007, S: 0.007, Ni: 0.73, Cr: 0.71, Mo: 0.11, Cu: 0.14, Nb: 0.048, Ti: 0.005, Al: 0.039, B: 0.0002, and the balance is Fe and inevitable impurities.

[0041] In the preparation, after converter smelting, continuous casting is performed to obtain a 460 mm thick slab. Then the slab is heated to 1150 DEG C at a rate of 7 DEG C / s in a heating furnace, and the soaking section is kept for 120 min. Then the slab is discharged, descaled and subjected to first-stage rolling, and the opening rolling temperature is 1150 DEG C. The slab is rolled to a thickness of 90 mm, and then is kept warm in air, and the rolling reduction is 80%. The slab is kept warm to 830 DEG C, and then is subjected to second-stage rolling, and finally is rolled to a 30 mm thick plate, and the rolling reduction is 67%, and the finish rolling temperature is 850 DEG C. The plate is cooled to 710 DEG C in air, and then is subjected to water cooling, and the cooling rate is 6 DEG C / s, the roll speed is 0.3 m / s, the re-red temperature is 400 DEG C, and then the plate is air cooled on a cooling bed. After air cooling, the plate is tempered at 430 DEG C for 20 min, and then is air cooled.

[0042] The mechanical property data of the steel plate manufactured according to the embodiment of the present application is shown in Table 1:

[0043] Table 1: Performance table of steel plates in Examples 1-6

[0044] As can be seen from the data in the table, Examples 1-3 of the present application all meet the mechanical property requirements of Q620qE in GB / T 714-2015, and the impact energy at -60 DEG C of Examples 4-6 reaches 150 J or more after short-time low-temperature tempering based on Examples 1-3.

[0045] The present application realizes the matching of tensile strength and impact toughness of Q620qE steel in GB / T 714-2015 only by controlled rolling and controlled cooling without post-rolling heat treatment, the strength and toughness surplus is sufficient, the preparation process is simple, the product manufacturing cost is greatly reduced, and the application in factory is suitable. The product of the present application can realize that the impact energy at -60 DEG C of the steel plate reaches 150 J or more without reducing the strength under the premise of not changing the composition, rolling and cooling process.

Claims

1. A 620 MPa grade steel plate for low yield ratio bridges, characterized by: The steel plate comprises the following components in percentage by mass: C: 0.020% to 0.100%, Si: 0.10% to 0.70%, Mn: 1.21% to 1.81%, P: ≤0.020%, S: ≤0.010%, Ni: 0.10% to 0.80%, Cr: ≤0.80%, Mo: 0.08% to 0.60%, Cu: ≤0.70%, Nb: 0.01% to 0.10%, Ti: ≤0.020%, Al: 0.01% to 0.06%, B: 0.0001% to 0.0010%, and the balance of Fe and inevitable impurities.

2. The 620 MPa grade steel plate for low yield ratio bridge according to claim 1, characterized by: The carbon equivalent CEV of the steel plate is ≤0.62 (CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15), and the cold crack sensitivity coefficient Pcm is ≤0.25 (Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B).

3. The 620 MPa grade steel plate for low yield ratio bridge according to claim 1, characterized by: The thickness of the steel plate is ≤50 mm.

4. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to any one of claims 1 to 3, characterized in that: The steel plate is prepared by the method of hot metal pretreatment, converter smelting, LF + RH refining, continuous casting, heating, dephosphorization, rolling, plate cooling and tempering.

5. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to claim 4, characterized in that: After the hot metal pretreatment, converter smelting and LF + RH refining, a slab with a thickness of 460 mm is obtained by continuous casting.

6. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to claim 4, characterized in that: In the heating and dephosphorization, the heating temperature is 1150°C to 1220°C, the heating speed is 4°C / s to 7°C / s, and the soaking time is ≥100 min; high-pressure water is used for descaling, the descaling pressure is ≥18 MPa, and the descaling pass is 1 to 2.

7. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to claim 4, characterized in that: The rolling is divided into two-stage controlled rolling: the first stage is recrystallization zone rolling, the rolling temperature is 1050°C to 1150°C, and the rolling reduction is ≥75%; the second stage is non-recrystallization zone rolling, the rolling temperature is 790°C to 870°C, the finish rolling temperature is 780°C to 860°C, and the rolling reduction is 60% to 70%.

8. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to claim 4, characterized in that: The plate cooling is controlled cooling: after the rolling is completed, the rolled piece is air-cooled to below 770°C, and then water-cooled, the cooling speed is 5°C to 10°C, the roller speed is ≤0.8 m / s during water-cooling, and the controlled red temperature range is ≤450°C.

9. The method of producing a 620 MPa grade steel plate for low yield ratio bridges according to claim 4, characterized in that: In the tempering, the tempering temperature is ≤550°C, the tempering soaking time is 20 min to 40 min, and the plate is air-cooled after tempering.

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