Method for rolling ultra-wide and ultra-thick low-alloy structural steel with thickness larger than 3500 mm

Abstract

The invention discloses a method for rolling ultra-wide and ultra-thick low-alloy structural steel of more than 3500 mm. The method comprises the following steps: (1) redesigning blank components for producing an ultra-thick plate; (2) blank design adopts a 460mm continuous casting blank or a 600mm directional solidification blank; (3) the heating temperature of the blank is adjusted to be 1180-1220 DEG C, and the heating time is 1.5-2.5 min / mm; (4) in the ultra-wide and ultra-thick plate rolling process, due to the fact that the width of a finished product order is too large, large-pressure rolling cannot be conducted, passes are increased, and meanwhile controlled rolling must be adopted to guarantee the impact toughness of the steel plate; and (5) adopting an NAC heat treatment process after rolling the steel plate to further ensure the strength and performance uniformity of the steel plate and eliminate the internal stress of the steel plate. The production method has the advantages that the production method of the ultra-wide and ultra-thick low-alloy structural steel is developed, so that the mechanical property and the impact toughness of the ultra-wide and ultra-thick low-alloy structural steel meet the standard requirements, the surface and the plate shape meet the use requirements of customers, and long-term stable supply can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for rolling ultra-wide and ultra-thick low-alloy structural steel with a thickness of more than 3500 mm. Background Art

[0002] With the large-scale water conservancy, tunnel, and mechanical engineering projects in the domestic and export markets in recent years, the market demand for ultra-wide and extra-thick plates has gradually increased. At the same time, the ultra-thick continuous casting billet and ultra-thick directional solidification technology have made continuous breakthroughs, and the quality and tonnage of the output billet have gradually increased, paving the way for the formation technology of ultra-wide and extra-thick steel plates. Ultra-wide and extra-thick plates of low-alloy structural steel are gradually being demanded by the market for their good mechanical properties and cost advantages.

[0003] At present, it is still very technically difficult to produce ultra-wide and extra-thick plates of low-alloy structural steel with a thickness of 150mm or more and ≥3500mm. Most of them are supplied by ingot forging and welding assembly. At the same time, ultra-wide and extra-thick plates have always been a difficult point in the production of continuous casting billets, and the mechanical properties requirements are difficult to meet. Summary of the invention

[0004] The purpose of the present invention is to solve the problem of great difficulty in producing existing ultra-wide and extra-thick plates and poor mechanical properties, and to provide a method for rolling ultra-wide and extra-thick low-alloy structural steels of more than 3500mm, to ensure that the strength, impact and other mechanical properties of the steel plates meet the standard requirements of low-alloy structural steels, while the surface and plate shape meet the customer's use requirements, thereby achieving the technical capability of long-term and stable supply.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for rolling ultra-wide and ultra-thick low-alloy structural steel with a thickness of more than 3500 mm, comprising: (1) Redesign the composition of the billet for producing extra-thick plates: Control the CEV and PCM values ​​through low C and low Mn composition design to ensure the performance of steel plate processing and welding machine use; (2) Billet selection: The billet design uses 460mm continuous casting billet or 600mm directional solidification billet; (3) Setting of billet heating parameters: Adjust the billet heating temperature to 1180~1220℃ and the heating time to 1.5~2.5min / mm to make the billet sufficiently uniform during the rolling process and ensure the uniformity of steel plate heating; (4) Controlled rolling: In the rolling process of ultra-wide and extra-thick plates, since the width of the finished product order is too large to be rolled with a large reduction, the number of passes is increased, and controlled rolling must be used to ensure the impact toughness of the steel plate; (5) Selection of heat treatment process: After the steel plate is rolled, the NAC heat treatment process is used to further ensure the strength and performance uniformity of the steel plate, eliminate the internal stress of the steel plate, and ensure the shape and surface quality of the steel plate.

[0006] Furthermore, in the step (1), the composition of the blank includes, by mass percentage, the following: C: 0.12-0.15, Mn: 1.25-1.35, P≤0.012, S≤0.003, Ni: 0.2-0.3, Nb: 0.03-0.04, V: 0.02-0.05, and Ti: 0.005-0.02.

[0007] Furthermore, in the step (1), the composition of the blank includes, by mass percentage, the following: C: 0.12-0.14, Mn: 1.25-1.35, P≤0.012, S≤0.003, Ni: 0.2-0.3, Nb: 0.03-0.04, V: 0.04-0.05, and Ti: 0.005-0.02.

[0008] Furthermore, in the step (2), the low magnification of the blank is class B 1.0.

[0009] Furthermore, in the step (4), a total of 19 passes are used to complete the rolling, and the intermediate billet is kept at a temperature for 205 seconds.

[0010] Furthermore, in the step (5), the heat treatment process is 890±20°C, and the holding time is 2.2*H, where H is the thickness of the steel plate after rolling.

[0011] In the technical solution of the present invention, by optimizing the composition design, improving the continuous casting process and the rolling process, the technical conditions and supply capacity of ultra-thick low-alloy structural steel plates with a thickness of more than 150mm and a width of ≥3500mm are developed, filling the gap in the production capacity of ultra-wide and ultra-thick low-alloy structural steel plates with guaranteed performance, ensuring that the strength, impact and other mechanical properties of the steel plates meet the standard requirements of low-alloy structural steels, while the surface and plate shape meet the customer's use requirements, meeting the market demand of this type of order market and improving the market competitiveness of ultra-thick plate demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is an actual sampling diagram of a 460 mm continuous casting billet in an embodiment of the present invention; Figure 2 This is a photo of the surface of a steel plate produced by the method of the present invention in an example. DETAILED DESCRIPTION Example

[0013] To make the present invention more clear, a method for rolling ultra-wide and ultra-thick low-alloy structural steel of more than 3500 mm is further described below in conjunction with the accompanying drawings. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0014] Take the steel grade Q355NDZ35, 250*3700mm specification order as an example, it uses 460mm, specification continuous casting billet, the billet low multiple is about Class B 1.0, such as Figure 1 shown.

[0015] (1) The composition design of the blank is as follows: Table 1 adds a new design scheme:

[0016] (2) The rolling furnace temperature is 1200±20℃; the actual steel tapping temperature is 1198℃.

[0017] (3) Controlled rolling is adopted as shown in Table 2 below. 19 passes are required to complete the rolling, and the intermediate billet is kept at temperature for 205s:

[0018] (4) The steel plate is rolled under low temperature control and then heat treated. The steel plate is sampled and analyzed. The performance distribution of the four corners of the steel plate is shown in Table 3:

[0019] (5) The mechanical properties of the steel plate in the rolled state are tested and meet the standard requirements. The -20℃ impact performance meets the standard requirements but the performance margin is small. The impact toughness is improved by adding normalizing heat treatment. The heat treatment process is 890±20℃ and the insulation time is 2.2*H (thickness). The steel plate is sampled again for analysis. The performance distribution of the four corners of the steel plate is as shown in Table 4:

[0020] (6) After heat treatment, the mechanical properties of the steel plate still meet the standard requirements, and the low-temperature impact toughness margin is sufficient. The relative quality rating of the macrostructure of the steel plate after rolling is 0.5 level for center segregation and 1.0 level for center porosity. Figure 2 According to the performance survey, the 250mm*3700mm specification Q355NDZ35 has the technical capability for stable production.

[0021] After the method of the present invention is used to roll ultra-wide and extra-thick low-alloy structural steel of more than 3500mm, the gap in the production capacity of ultra-wide and extra-thick low-alloy structural steel plates with guaranteed performance is filled. It is expected that the annual order volume of such extra-thick plates can be increased by 2000-5000 tons, the gross profit per ton of steel is about 500-800 yuan / ton, the direct sales volume is increased by about 8 million to 30 million yuan, the profit is about 1 million to 4 million yuan, and the market prospect is good.

[0022] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for rolling ultra-wide and ultra-thick low-alloy structural steel with a thickness of more than 3500 mm, characterized in that: (1) Redesign the billet composition for producing extra-thick plates: Control the CEV and PCM values ​​through low C and low Mn composition design; (2) Billet selection: The billet design uses 460mm continuous casting billet or 600mm directional solidification billet; (3) Setting of billet heating parameters: Adjust the billet heating temperature to 1180~1220℃ and the heating time to 1.5~2.5min / mm to ensure that the billet is sufficiently uniform during the rolling process; (4) Controlled rolling: In the rolling process of ultra-wide and extra-thick plates, since the width of the finished product order is too large to be rolled with a large reduction, the number of passes is increased, and controlled rolling must be used to ensure the impact toughness of the steel plate; (5) Selection of heat treatment process: NAC heat treatment process is adopted after the steel plate is rolled to further ensure the uniformity of the strength and performance of the steel plate and eliminate the internal stress of the steel plate.

2. The method for rolling ultra-wide and ultra-thick low-alloy structural steel with a thickness of more than 3500 mm according to claim 1, characterized in that: In the step (1), the blank composition includes, by mass percentage, C: 0.12-0.15, Mn: 1.25-1.35, P≤0.012, S≤0.003, Ni: 0.2-0.3, Nb: 0.03-0.04, V: 0.02-0.05, and Ti: 0.005-0.

02.

3. The method for rolling ultra-wide and ultra-thick low-alloy structural steel with a width of more than 3500 mm according to claim 1, characterized in that: In the step (1), the blank composition includes, by mass percentage: C: 0.12-0.14, Mn: 1.25-1.35, P≤0.012, S≤0.003, Ni: 0.2-0.3, Nb: 0.03-0.04, V: 0.04-0.05, Ti: 0.005-0.

02.

4. The method for rolling ultra-wide and ultra-thick low-alloy structural steel of more than 3500 mm according to any one of claims 1 to 3, characterized in that: In the step (2), the blank is low-powered and is of class B grade 1.

0.

5. The method for rolling ultra-wide and ultra-thick low-alloy structural steel with a width of more than 3500 mm according to any one of claims 1 to 3, characterized in that: In the step (4), a total of 19 passes are used to complete the rolling, and the intermediate billet is kept at temperature for 205 seconds.

6. The method for rolling ultra-wide and ultra-thick low-alloy structural steel with a thickness of more than 3500 mm according to any one of claims 1 to 3, characterized in that: In the step (5), the heat treatment process is 890±20°C, and the holding time is 2.2*H, where H is the thickness of the steel plate after rolling.

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