Online quenching and tempering heat treatment process for EH690 medium-thickness steel plate

Abstract

The invention relates to an on-line quenching and tempering heat treatment process for an EH690 medium-thickness steel plate. The on-line quenching and tempering heat treatment process comprises the following steps: firstly, feeding a rolled piece subjected to finish rolling into a temperature compensation furnace for heating; then the rolled piece subjected to the temperature compensation operation is subjected to heat preservation; then quenching is conducted, and a multi-section type cooling mode is adopted for quenching; and finally, feeding back into the temperature compensation furnace for tempering, naturally air-cooling, and discharging. The finish rolling temperature of a rolled piece is fully utilized to greatly reduce the heating time of quenching, and the heating time is reduced to 0.5-1 h from about 8 h in a traditional process; the steel plate circulation link is reduced, and the energy consumption is saved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical industry, and in particular to an online quenching and tempering heat treatment process for EH690 medium and thick steel plates. Background Art

[0002] E690 extra-thick rack steel plate for ultra-high strength marine engineering is used for the manufacture of self-elevating marine platform pile legs and cranes in extreme service environments. It is a core key material in the field of large-scale marine engineering equipment manufacturing. The steel plate is required to have large thickness, ultra-high strength, excellent low-temperature toughness, as well as good wear resistance, weldability and cutting performance. The manufacturing difficulty is extremely high. From steel ingots to steel plates that meet the target size and customer performance requirements, the traditional manufacturing process requires steel ingot heating, descaling, rolling, cooling, heat treatment, and then normalizing heating, followed by offline quenching, offline tempering, sampling inspection, and cutting and flattening, until the spray engraving inspection is qualified before storage and shipment.

[0003] Among the above processes, quenching and tempering of rolled pieces are two key processes. In the existing technology, it is usually necessary to spend huge amounts of money to build additional quenching and tempering equipment for rolled piece production, which invisibly increases production costs and greatly weakens the competitiveness of enterprises. In addition, in actual production, after the final rolling of the rolled pieces, even if the rolling temperature is 850°C, the rolled pieces still need to be cooled to room temperature and then heated to 910°C before quenching, and then enter the tempering process. The above operations are clearly contrary to the widely respected green and low-carbon development concept. Summary of the invention

[0004] The purpose of the present invention is to provide an online quenching and tempering heat treatment process for EH690 medium and thick steel plates, which greatly shortens the quenching time of rolled pieces and fully utilizes the self-heat of rolled pieces after final rolling to save energy consumption.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides an online quenching and tempering heat treatment process for EH690 medium and thick steel plates, comprising the following steps: ⅠSupplementary heating: the rolled piece after final rolling is sent into the supplementary heating furnace for heating; II. Insulation: Insulating the rolled piece that has undergone the temperature supplementation operation in step I; III. Online quenching: quenching the rolled piece after the heat preservation operation in step II, wherein the quenching adopts a multi-stage cooling method; IV. Tempering: sending the rolled piece that has been quenched in step III back into the supplementary temperature furnace for tempering; V. Air cooling and rolling off the production line: the rolled piece which has been tempered in step IV is naturally air cooled and then rolled off the production line; Wherein, the final rolling temperature in step I is 840-860°C, the heating temperature is 910-930°C, and the heating rate is 30-180°C / h; and the insulation time in step II is 0.5-1h.

[0006] Furthermore, the multi-stage cooling method in step III includes: section A, section B, section C and section D; wherein, section A adopts a rapid cooling method; and section B, section C and section D jointly adopt a swing slow cooling method.

[0007] Furthermore, the quenching temperature of the A section is 500-530°C, the water pressure is ≥0.8Mpa, and the flow rate is 8800-9200 m3 / h.

[0008] Furthermore, the speed at which the rolled piece passes through the section A is 0.5 m / s.

[0009] Furthermore, the swing slow cooling temperature of the B section, the C section and the D section is 230-290°C, the water pressure is ≤0.2Mpa, and the flow rate is 2800-3200m3 / h for each section.

[0010] Furthermore, the speed at which the rolled piece passes through the B section, the C section and the D section is 0.1 m / s.

[0011] Furthermore, in step IV, the tempering temperature is 620-630° C., and the tempering time is 7-9 hours.

[0012] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: The present invention changes the traditional offline quenching and tempering Q+T process into an online DQ+T process, fully utilizes the final rolling temperature of the steel plate rolled piece, reduces the energy consumption of the quenching process, and greatly saves energy and the circulation link of the steel plate through a short process. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings: Figure 1 The present invention is a process flow chart of an online quenching and tempering heat treatment process for EH690 medium and thick steel plates. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] The present invention provides an online quenching and tempering heat treatment process for EH690 medium and thick steel plate, comprising the following steps: ⅠSupplementary heating: the rolled piece after final rolling is sent into the supplementary heating furnace for heating; Ⅱ Insulation: Insulate the rolled piece after the heating operation; III. Online quenching: quenching the rolled piece after the heat preservation operation, wherein the quenching adopts a multi-stage cooling method; IV. Tempering: The rolled piece after quenching operation is sent back into the above-mentioned supplementary temperature furnace for tempering; Ⅴ Air cooling off the line: The rolled products that have undergone tempering operation are naturally air-cooled before being taken off the line.

[0016] Specifically, in step I, the final rolling temperature of the rolled piece is 840~860℃. After the final rolling is completed, the rolled piece is sent to a supplementary heating furnace for supplementary heating, and the heating temperature is set at 910~930℃. Therefore, the rolled piece is supplemented with temperature after the final rolling is completed. Compared with the prior art in which the rolled piece needs to be transferred to room temperature and then heated to the target temperature before the next quenching process can be carried out, the final rolling temperature of the rolled piece is fully utilized, which greatly reduces energy consumption and correspondingly shortens the process time.

[0017] In the embodiment of the present invention, the supplementary temperature furnace is arranged at about 35m from the outlet of the finishing mill, and the heating rate of the supplementary temperature furnace is controlled at 30-180°C / h. When the thickness of the EH690 medium and thick steel plate is larger, the corresponding heating rate is slower.

[0018] In step II, when the temperature of the rolled piece is heated to the aforementioned 910-930°C, the heat preservation operation is performed, and the heat preservation time is controlled to be 0.5-1h. Of course, the specific heat preservation time can also be adaptively adjusted according to the actual surface temperature of the rolled piece.

[0019] In step III, a multi-stage cooling method is used for quenching, specifically, including four stages, namely, section A, section B, section C and section D. The aforementioned section A adopts a rapid cooling method, while sections B, C and D are combined and cooled by swing slow cooling. In the embodiment of the present invention, after the rolled piece is cooled in section A, the surface temperature is cooled to 500~530℃, and high-pressure cooling is adopted in section A, the water pressure is controlled at ≥0.8Mpa, and the flow rate is set at 8800~9200 m3 / h. In addition, the speed of the rolled piece passing through section A is set at 0.5m / s.

[0020] Afterwards, the rolled piece enters the subsequent slow cooling section, where it swings back and forth in the slow cooling sections B, C, and D, aiming to cool the rolled piece to 230-290°C, with the water pressure controlled at ≤0.2Mpa and the flow rate at each section at 2800-3200m3 / h. The speed of the rolled piece passing through the slow cooling section is set at 0.1m / s, thus completing the four-stage cooling quenching.

[0021] In step IV, the quenched rolled piece is sent back to the supplementary temperature furnace for tempering. The specific tempering temperature is controlled at 620~630℃ and the tempering time is controlled at 7~9h. Of course, for EH690 medium and thick steel plates of different thicknesses, the specific tempering time needs to be adjusted and determined according to the tempering furnace working conditions and tempering process.

[0022] After the rolled piece has been tempered, it is naturally air-cooled to room temperature and then taken off the production line, thus completing the online quenching and tempering heat treatment of the EH690 medium and thick steel plate.

[0023] The yield strength of the EH690 medium and thick steel plate obtained by the above heat treatment process is not less than 700Mpa, the yield strength ratio is not greater than 0.92, the tensile strength is not less than 790Mpa, and the elongation is not less than 16%. At the same time, there is no supercooling structure on the surface of the EH690 medium and thick steel plate obtained. All properties of the steel plate after rolling meet the standard requirements.

[0024] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An online quenching and tempering heat treatment process for EH690 medium and thick steel plates, characterized in that: The steps include: ⅠSupplementary heating: the rolled piece after final rolling is sent into the supplementary heating furnace for heating; II. Insulation: Insulating the rolled piece that has undergone the temperature supplementation operation in step I; III. Online quenching: quenching the rolled piece after the heat preservation operation in step II, wherein the quenching adopts a multi-stage cooling method; IV. Tempering: sending the rolled piece that has been quenched in step III back into the supplementary temperature furnace for tempering; V. Air cooling and rolling off the production line: the rolled piece which has been tempered in step IV is naturally air cooled and then rolled off the production line; Wherein, the final rolling temperature in step I is 840-860°C, the heating temperature is 910-930°C, and the heating rate is 30-180°C / h; and the insulation time in step II is 0.5-1h.

2. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 1 is characterized in that: The multi-stage cooling method in step III includes: section A, section B, section C and section D; wherein, section A adopts a rapid cooling method; and section B, section C and section D jointly adopt a swing slow cooling method.

3. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 2 is characterized in that: The quenching temperature of section A is 500-530°C, the water pressure is ≥0.8Mpa, and the flow rate is 8800-9200 m3 / h.

4. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 2 is characterized in that: The speed at which the rolled piece passes through the section A is 0.5 m / s.

5. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 2 is characterized in that: The swing slow cooling temperature of the B section, the C section and the D section is 230-290°C, the water pressure is ≤0.2Mpa, and the flow rate is 2800-3200m3 / h for each section.

6. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 2 is characterized in that: The speed at which the rolled piece passes through the B section, the C section and the D section is 0.1 m / s.

7. The online quenching and tempering heat treatment process for EH690 medium and thick steel plate according to claim 1 is characterized in that: In step IV, the tempering temperature is 620-630° C., and the tempering time is 7-9 hours.

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