A high-strength Q690E steel plate with large thickness and good low-temperature toughness and a preparation method thereof

Abstract

The application discloses a high-strength Q690E steel plate with large thickness and good low-temperature toughness and a preparation method thereof. The steel plate is composed of the following components: C: 0.13-0.18%, Mn: 1.00-1.35%, Si: 0.20-0.50%, Cr: 0.7-1.1%, Mo: 0.35-0.60%, Ti: 0.008-0.020%, Als: 0.025-0.050%, B: 0.0012-0.0025%, Nb: 0.015-0.035%, Ni: 0.30-0.50%, and the balance is iron. The preparation method comprises the following steps in sequence: molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling and heat treatment. The steel plate prepared by the scheme has a 1 / 4 position-40 DEG C impact energy of greater than or equal to 150 J and a 1 / 2 position-40 DEG C impact energy of greater than or equal to 59 J.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a thick, high-strength Q690E steel plate with good low-temperature toughness and its preparation method, which is applicable to the preparation of steel plates with a thickness of 120mm or more, especially steel plates with a thickness of 130-140mm. Background Technology

[0002] With the booming development of large-scale projects in China, Q690 high-strength steel has been widely used in engineering machinery, mining, and mining trucks. Because steel used in engineering machinery operates in harsh environments, especially at low temperatures, it is required to possess not only the general mechanical properties but also good low-temperature toughness, i.e., an impact energy of not less than 34J at -40℃. For extra-thick specifications, especially Q690 steel plates >120mm, due to their large thickness, high strength, and limited compression ratio, even after quenching and tempering heat treatment, poor low-temperature impact toughness is easily observed.

[0003] Patent CN 118979204 A discloses a method for preparing a thick, low-temperature toughness, high-strength Q690E steel plate and its preparation. This patent uses continuously cast billets to produce Q690E plates with a maximum thickness of 120mm. However, the addition of 0.9-1.1% Ni will inevitably increase the cost, and it does not describe the performance of steel plates with thicknesses greater than 120mm, such as 130 / 140mm.

[0004] Patent CN 114107805 B discloses a thick quenched and tempered Q690E / F high-strength steel and its manufacturing method. This patent uses continuous casting billets to produce Q690E / F with a maximum thickness of 120mm and good performance. However, the maximum thickness produced is 120mm, and it does not describe the production of steel plates with greater thickness.

[0005] Patent CN 104264064 A discloses an extra-thick Q690 high-strength structural steel plate and its manufacturing method. This method can produce 160-180mm Q690 grade high-strength steel. However, this invention can only guarantee that the impact energy at 0℃ meets the standard requirements, and cannot guarantee that the impact performance is qualified at lower impact temperatures. In addition, the addition of 0.8-1.0% Ni will inevitably increase the cost.

[0006] In summary, very few patents currently involve the development of steel plates with a strength level of 690MPa, a thickness greater than 120mm, and good low-temperature impact toughness. However, in the field of engineering machinery, given the increasing demand for large-scale equipment, ensuring the safe operation of thick, high-strength steel plates in low-temperature environments is crucial. Therefore, it is essential to develop a thick, high-strength Q690E steel plate with good low-temperature toughness. Summary of the Invention

[0007] The purpose of this invention is to provide a thick, high-strength Q690E steel plate with good low-temperature toughness and its preparation method, so as to solve the problems of the prior art.

[0008] To solve the above technical problems, the technical solution of the present invention is as follows: A thick, high-strength Q690E steel plate with good low-temperature toughness, characterized in that it comprises the following components in the following mass percentages: C: 0.13-0.18%, Mn: 1.00-1.35%, Si: 0.20-0.50%, Cr: 0.7-1.1%, Mo: 0.35-0.60%, Ti: 0.008-0.020%, Als: 0.025-0.050%, B: 0.0012-0.0025%, Nb: 0.015-0.035%, Ni: 0.30-0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities.

[0009] This invention also discloses a method for preparing a thick, high-strength Q690E steel plate with good low-temperature toughness, characterized by comprising the following steps: hot metal pretreatment—converter smelting—LF refining—RH refining—continuous casting—rolling—heat treatment; wherein: Hot metal pretreatment includes: desulfurization of hot metal using the KR method or injection method, followed by slag removal. After hot metal pretreatment, the mass fraction of sulfur in the hot metal is ≤0.010%. Converter smelting includes: using a top-and-bottom blown converter for decarburization, desiliconization, and desulfurization of molten iron, and slag blocking before tapping steel; LF refining includes: white slag operation, maintaining submerged arc operation during heating, and reducing atmosphere; RH refining includes: vacuum holding time ≥15min, and argon gas blowing throughout the production of this steel grade; Continuous casting includes: implementing full-process protective casting, incorporating electromagnetic stirring and light pressure, and maintaining a superheat of 20±5℃ in the tundish during continuous casting; maintaining a constant casting speed and controlling liquid level fluctuations within ±3mm. The rolling process includes: billet heating temperature of 1240±20℃, heating time of 1.0~1.3min / mm, and three heating plus homogenization time of 0.4-0.7min / mm; two-stage controlled rolling is adopted, with the first stage starting rolling temperature ≥1000℃, the target final rolling temperature of 840±20℃, and water cooling to 750±20℃ after rolling; the single-pass reduction rate of the last three passes of roughing rolling reaches more than 15%; The heat treatment includes: quenching at a temperature of 870–910℃ for 2.8–3.5 min / mm; tempering at a temperature of 600–650℃ for 2.8–3.5 min / mm; and slow cooling to room temperature.

[0010] Furthermore: the impact energy at -40℃ at 1 / 4 of the thickness of the prepared steel plate is ≥150J, and the impact energy at -40℃ at 1 / 2 of the thickness is ≥59J; the yield strength is ≥690MPa, the tensile strength is 710~900MPa, and the elongation after fracture is ≥16%.

[0011] The beneficial effects of this invention are: (1) The present invention adopts a medium carbon composition design and adds trace amounts of alloying elements Cr, Ni and Mo. The carbon equivalent (CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15)≤0.66%, the production cycle is short and the cost is low.

[0012] (2) The present invention uses a reasonable rolling process to produce high-strength steel with a thickness of 140mm and uses the optimal quenching and tempering heat treatment process to make the performance meet the standard requirements of engineering machinery for material design. The yield strength is ≥650MPa, the tensile strength is 710~900MPa, the elongation after fracture is ≥16%, the impact energy at -40℃ at 1 / 4 of the thickness is ≥150J, and the impact energy at -40℃ at 1 / 2 of the thickness is ≥59J.

[0013] (3) Due to the high strength requirements, the present invention adopts a large reduction mode for controlled rolling, uses a 475mm thick billet, controls the heat treatment temperature at 1240℃, and appropriately extends the furnace time to ensure uniform steel temperature of the billet.

[0014] (4) The maximum thickness of the product of the present invention is 140mm. In order to avoid core segregation during the rolling process, which would affect mechanical properties and low-temperature impact toughness, the single-pass reduction rate of the last three passes of rough rolling reaches more than 15% to ensure that there is no obvious difference between the surface and core structure. Attached Figure Description

[0015] Figure 1 Metallographic structure (500x) at 1 / 4 position of the thickness of the 140mm thick steel plate of this invention. Figure 2 The metallographic structure (500x) at 1 / 2 position of the thickness of the 140mm thick steel plate of this invention. Detailed Implementation

[0016] This invention provides a thick, high-strength Q690E steel plate with good low-temperature toughness. Its chemical composition and mass percentage are as follows: C: 0.13-0.18%, Mn: 1.00-1.35%, Si: 0.20-0.50%, Cr: 0.7-1.1%, Mo: 0.35-0.60%, Ti: 0.008-0.020%, Als: 0.025-0.050%, B: 0.0012-0.0025%, Nb: 0.015-0.035%, Ni: 0.30-0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities.

[0017] This application also provides a method for preparing a thick, high-strength Q690E steel plate with good low-temperature toughness, the method comprising the following steps: Hot metal pretreatment: Hot metal pretreatment and desulfurization are carried out using the KR method or injection method, followed by slag removal; the mass fraction of sulfur in the hot metal after pretreatment is ≤0.010%; Converter smelting: Top and bottom blowing converters are used for decarburization, desiliconization, and desulfurization of molten iron, and slag blocking is used for steel tapping; LF refining: white slag operation, during heating, maintain submerged arc operation and ensure a slightly positive pressure state and reducing atmosphere inside the furnace; RH refining: vacuum holding time ≥15min, argon gas is blown throughout the production of this steel grade; Continuous casting: Implement full-process protective casting, with the machine initiating electromagnetic stirring and light pressure, and the superheating temperature of the tundish in the continuous casting furnace is 20±5℃; maintain constant casting speed, and control the liquid level fluctuation within ±3mm; Slab heating: The heating temperature is 1240±20℃, and the heating time is 1~1.3min / mm (the thickness of the slab). The heating adopts a three-stage heating and homogenization process, in which the third stage + homogenization stage time is 0.4-0.7min / mm. Rolling: Two-stage controlled rolling is adopted. The first stage rolling temperature is ≥1000℃, and the single-pass reduction rate of the last three passes of roughing reaches more than 15%. The target final rolling temperature is 840±20℃, and the rolling temperature is water-cooled to 750±20℃. Heat treatment: Quenching temperature is 870~910℃, furnace time is 2.8~3.5min / mm, tempering temperature is 600~650℃, furnace time is 2.8~3.5min / mm, and slow cooling to room temperature.

[0018] The above technical solution will be described below through specific embodiments.

[0019] Example 1: The target steel plate obtained in this example has a thickness of 140 mm. The chemical composition and mass percentage of the steel plate are as follows: C: 0.157%, Si: 0.311%, Mn: 1.12%, P: 0.011%, S: 0.0026%, Als: 0.049%, Cr: 0.83%, B: 0.0018%, Mo: 0.41%, Ni: 0.35%, Nb: 0.026%, Ti: 0.013%.

[0020] In preparing the target steel plate, after alloying and deoxidation in the converter steelmaking process, the billet is refined by LF+RH, continuously cast, heated to 1240℃, with an initial rolling temperature of 1046℃, a final rolling temperature of 844℃, a quenching temperature controlled at 900℃, a furnace time of 420min, a tempering temperature controlled at 620℃, a furnace time of 420min, and then slowly cooled to room temperature.

[0021] Example 2: The target steel plate obtained in this example has a thickness of 130 mm. The chemical composition and mass percentage of the steel plate are as follows: C: 0.148%, Si: 0.385%, Mn: 1.11%, P: 0.012%, S: 0.0024%, Als: 0.038%, Cr: 0.86%, B: 0.0015%, Mo: 0.43%, Ni: 0.37%, Nb: 0.028%, Ti: 0.013%.

[0022] In the preparation of the above-mentioned target steel plate, after alloying and deoxidation in converter steelmaking, it is refined by LF+RH, continuously cast, heated to 1240℃, first rolling temperature 1051℃, final rolling temperature 851℃, quenching temperature controlled at 890℃, furnace time 382min, tempering temperature controlled at 610℃, furnace time 393min, and slowly cooled to room temperature.

[0023] Table 1 Actual properties of steel plates corresponding to Examples 1 and 2

[0024] As can be seen from Table 1, the high-strength Q690E steel plates with good low-temperature toughness and large thickness prepared in Examples 1-2 meet the strength requirements. The longitudinal impact toughness at -40℃ is stable and excellent. The impact energy at 1 / 4 of the thickness at -40℃ is above 150J, and the impact energy at 1 / 2 of the thickness at -40℃ is above 60J, which shows good strength and toughness.

[0025] Therefore, the technical solution of this application adopts a medium-carbon composition design, adding trace amounts of alloying elements Cr, Ni, and Mo, with a carbon equivalent ≤0.66%, resulting in a short production cycle and low cost. Simultaneously, using a reasonable process, Q690E steel plates with good low-temperature toughness at the 1 / 2 thickness position and a maximum thickness of 140mm can be produced. Using the optimal quenching and tempering heat treatment process, the steel plate performance meets the standard requirements for material design in engineering machinery. Figure 1 It can be seen that the 1 / 4 position of the 140mm thick steel plate contains tempered sorbite with a small amount of bainite. This microstructure exhibits good overall mechanical properties. Figure 2 It can be seen that the 140mm steel plate has a bainitic + tempered sorbite microstructure at the 1 / 2 thickness position, which is slightly coarser than the microstructure at the 1 / 4 thickness position, but still meets the low-temperature toughness requirements. The yield strength is ≥690MPa, the tensile strength is 710~900MPa, the elongation after fracture is ≥16%, the impact energy at -40℃ at the 1 / 4 thickness position is above 150J, and the impact energy at -40℃ at the 1 / 2 thickness position is above 60J.

Claims

1. A thick, high-strength Q690E steel plate with good low-temperature toughness, characterized in that: The composition comprises the following components by mass percentage: C: 0.13-0.18%, Mn: 1.00-1.35%, Si: 0.20-0.50%, Cr: 0.7-1.1%, Mo: 0.35-0.60%, Ti: 0.008-0.020%, Als: 0.025-0.050%, B: 0.0012-0.0025%, Nb: 0.015-0.035%, Ni: 0.30-0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities.

2. The method for preparing a thick, high-strength Q690E steel plate with good low-temperature toughness according to claim 1, characterized in that: include: Hot metal pretreatment—converter smelting—LF refining—RH refining—continuous casting—rolling—heat treatment steps; wherein: Hot metal pretreatment includes: desulfurization of hot metal using the KR method or injection method, followed by slag removal. After hot metal pretreatment, the mass fraction of sulfur in the hot metal is ≤0.010%. Converter smelting includes: using a top-and-bottom blown converter for decarburization, desiliconization, and desulfurization of molten iron, and slag blocking before tapping steel; LF refining includes: white slag operation, maintaining submerged arc operation during heating, and reducing atmosphere; RH refining includes: vacuum holding time ≥15min, and argon gas blowing throughout the production of this steel grade; Continuous casting includes: implementing full-process protective casting, incorporating electromagnetic stirring and light pressure, and maintaining a superheat of 20±5℃ in the tundish during continuous casting; maintaining a constant casting speed and controlling liquid level fluctuations within ±3mm. The rolling process includes: billet heating temperature of 1240±20℃, heating time of 1.0~1.3min / mm, and three heating plus homogenization time of 0.4-0.7min / mm; two-stage controlled rolling is adopted, with the first stage starting rolling temperature ≥1000℃, the target final rolling temperature of 840±20℃, and water cooling to 750±20℃ after rolling; the single-pass reduction rate of the last three passes of roughing rolling reaches more than 15%; The heat treatment includes: quenching at a temperature of 870–910℃ for 2.8–3.5 min / mm; tempering at a temperature of 600–650℃ for 2.8–3.5 min / mm; and slow cooling to room temperature.

3. The method for preparing a thick, high-strength Q690E steel plate with good low-temperature toughness according to claim 2, characterized in that: The prepared steel plate has an impact energy of ≥150J at -40℃ at 1 / 4 of its thickness and ≥59J at 1 / 2 of its thickness; yield strength ≥690MPa, tensile strength ≥710~900MPa, and elongation after fracture ≥16%.

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