A flash heat treatment method for high-strength steel plates

Abstract

This invention discloses a flash heat treatment method for high-strength steel plates, belonging to the field of metallic materials. The chemical composition of the high-strength steel and the mass percentage (wt.%) of its alloying elements are: C: 0.10–0.20, Mn: 1.75–1.85, Si: 1.10–1.35, Al: 0.30–0.45, Ti: 0.10–0.30, S≤0.008, P≤0.015, with the balance being Fe and other unavoidable impurities. The preparation method involves vacuum furnace smelting, forging, rolling in the single-phase region, then directly online water cooling to room temperature, and finally heating to 800–900℃ at a heating rate of 8–15℃ / s, holding at that temperature for 1–10s, and water cooling to room temperature. This flash heat treatment technology not only eliminates the secondary heating and quenching process but also shortens the heat treatment time. It can replace the traditional QT (quenching and tempering) process, achieving green and efficient production of high-strength steel and possessing significant practical value.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and specifically relates to a flash heat treatment method for high-strength steel plates. Background Technology

[0002] Driven by the "dual carbon" context, shortening the steel production process is a crucial direction for reducing carbon emissions. Traditional high-strength steel heat treatment typically involves QT (quenching and tempering), while the later-developed DQT (online quenching and tempering) process has shortened the process flow to some extent, contributing to carbon emission reduction. However, in both of these traditional heat treatment processes, the tempering process often requires the steel plate to be held at a high temperature in the furnace for an extended period. Therefore, shortening the tempering time while ensuring mechanical properties is a key strategy for improving production efficiency and reducing energy consumption.

[0003] Invention patent CN 102115812 A proposes a rapid tempering heat treatment method for Q690D steel. This invention solves the problem of excessively long tempering time caused by inaccurate furnace tempering time by accurately calculating the furnace tempering time. Similarly, patent CN 109161670 A proposes a low-temperature rapid tempering heat treatment method for Q550D steel using the TMCP process. This invention improves tempering efficiency by reducing the furnace holding coefficient through gradient heating in the furnace. Patent CN 10614882A proposes a method for online production of high-strength Q890 medium-thick plates. This patent uses an online quenching + tempering process to shorten the process and reduce costs. Although many inventions have contributed to improving the production efficiency of the QT process, none of them have significantly reduced the furnace tempering time for QT steel.

[0004] Therefore, this invention mainly addresses the problem that the existing QT process for high-strength steel requires a long time to maintain during heat treatment, especially during tempering and holding, and the air cooling process after tempering also takes a lot of time. It proposes a flash heat treatment technology for high-strength steel to replace the traditional long tempering process. Summary of the Invention

[0005] This invention addresses the problem of excessively long tempering cycles and low production efficiency in traditional QT processes by proposing a highly efficient heat treatment process based on flash heat treatment technology. This process can significantly improve the tempering efficiency of high-strength steel plates, achieving energy conservation, emission reduction, and efficient production.

[0006] A flash heat treatment method for high-strength steel plates, wherein the high-strength steel has the following composition by mass percentage (wt.%): C: 0.10-0.20, Mn: 1.75-1.85, Si: 1.10-1.35, Al: 0.30-0.45, Ti: 0.10-0.30, S≤0.008, P≤0.015, with the balance being Fe and other unavoidable impurities; the high-strength steel uses lath martensite obtained by online quenching as its initial structure and undergoes flash heat treatment, resulting in a microstructure similar to that obtained by tempering under QT process, and mechanical properties including tensile strength, yield strength, and elongation after fracture are all at the same level.

[0007] Furthermore, the high-strength steel is rolled in the single-phase region and then directly water-cooled to room temperature online. The sample is then heated to 800-900℃ at a heating rate of 8-15℃ / s, held for 1-10s, and then rapidly water-cooled to room temperature to obtain high-strength steel with performance comparable to that of traditional QT heat treatment process.

[0008] The flash heat treatment method for high-strength steel plates described above involves the following specific steps:

[0009] (1) Smelting and forging: Smelting in a vacuum induction furnace, with precise control of alloy composition and strict control of P, S and other elements during the process, and then forging into a 50mm×50mm square billet with a final forging temperature greater than 1000℃.

[0010] (2) Heating: KSL-1200X resistance furnace is used for heating. The heating temperature is 1150-1200℃ and the holding time is 90-120min. After taking it out of the furnace, remove the iron oxide scale.

[0011] (3) Rolling: The heated billet is rolled at an initial rolling temperature of 1050-1100℃ and after multiple rolling passes, the final rolling temperature is 950-980℃.

[0012] (4) Cooling: The rolled steel plate obtained in step (3) is subjected to rapid water cooling treatment;

[0013] (5) Heat treatment: The online quenched sample obtained in step (4) is subjected to rapid heat treatment. The sample is placed in a resistance heating furnace and heated to 800-900℃ at a heating rate of 8-15℃ / s. It is held for 1-10s and then rapidly water-cooled to room temperature to obtain high-strength steel with performance comparable to QT process.

[0014] The product of this invention is smelted in a vacuum furnace, with strict control over the content of harmful elements such as P and S. It is then forged in the laboratory into a billet awaiting rolling. Specifically, the rolling process employs a simulated on-site TMCP + online quenching method. The billet is placed in a heating furnace and heated to 1150–1200℃, held for 1.5 hours, and then the surface iron oxide scale is removed. It is then rolled on a laboratory rolling mill at a bite temperature of 1000–1050℃. After 7 passes, a steel plate with a thickness of 5mm is formed, with a final rolling temperature >950℃. The plate is then directly water-quenched to room temperature. The water-quenched sample is then heated to 800–900℃ at a heating rate of 8–15℃ / s. Specifically, the quenched sample is placed in a heating furnace and held at a stable furnace temperature for 1–10 seconds. Finally, it is directly water-cooled to room temperature, thus obtaining the high-strength steel plate prepared by the flash heat treatment technology described in this invention.

[0015] Compared with existing inventions, the main advantages of this invention are as follows:

[0016] (1) In terms of production process, the present invention adopts online quenching production method to greatly shorten the entire production process and omit secondary quenching, which not only improves production efficiency but also saves energy consumption.

[0017] (2) The core of this invention is the use of flash heat treatment technology, which heats the material to 800℃~900℃ at a heating rate of 8~15℃ / s, holds it at that temperature for 1-10s, and then cools it to room temperature with water. The time from heating to holding and finally cooling is greatly shortened. This flash heat treatment technology has a good effect on improving production efficiency by replacing the QT process. Attached Figure Description

[0018] Figure 1 SEM images of high-strength steel produced under the traditional QT process;

[0019] Figure 2 SEM image of high-strength steel prepared in Example 1 using flash heat treatment technology (heating to 900°C);

[0020] Figure 3 This is a SEM image of the high-strength steel prepared in Example 2 using flash heat treatment technology (heating to 890°C);

[0021] Figure 4 This is a SEM image of the high-strength steel prepared in Example 3 using flash heat treatment technology (heating to 850°C);

[0022] Table 1 compares the mechanical properties of the samples prepared by the traditional QT process with those prepared in Examples 1, 2 and 3. Detailed Implementation

[0023] The technical solution of the present invention will be further illustrated by the following embodiments, but the invention is not limited to the following embodiments.

[0024] This embodiment describes the composition design and production process of high-strength steel plate obtained by the flash heat treatment technology. The finished plate has a thickness of 5mm and its chemical composition and alloy element mass percentage (wt.%) are as follows: C: 0.10~0.20, Mn: 1.75~1.85, Si: 1.10~1.35, Al: 0.35~0.45, Ti: 0.10~0.30, S≤0.008, P≤0.015, with the balance being Fe and other unavoidable impurities.

[0025] Example 1

[0026] This embodiment describes a high-strength steel plate obtained using the flash heat treatment technology. The finished plate thickness is 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. After holding, the billet is removed, the iron oxide scale is removed, and it undergoes seven rolling passes to form a 5mm thick steel plate. The bite temperature during rolling is 1050℃, and the final rolling temperature is 980℃. During the post-rolling cooling process, the cooling rate is controlled to be ≥40℃ / s to cool to room temperature. Then, the sample is heated to 900℃ at a heating rate of 10℃ / s, stabilized at 900℃, held for 3 seconds, and directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that obtained using the traditional QT process. Its microstructure is similar to that of a typical tempered steel. See details... Figure 2 The mechanical properties are compared with those of the traditional QT process, as shown in Table 1.

[0027] Example 2

[0028] This embodiment describes a high-strength steel plate obtained using the flash heat treatment technology. The finished plate thickness is 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. After holding, the billet is removed, the iron oxide scale is removed, and it undergoes seven rolling passes to form a 5mm thick steel plate. The bite temperature during rolling is 1053℃, and the final rolling temperature is 965℃. The cooling rate after rolling is controlled to be ≥40℃ / s to cool to room temperature. Then, the sample is heated to 890℃ at a heating rate of 10℃ / s, stabilized at 890℃, held for 5 seconds, and directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that obtained using the traditional QT process. Its microstructure is similar to that of a typical tempered steel. See details... Figure 3 The mechanical properties are compared with those of the traditional QT process, as shown in Table 1.

[0029] Example 3

[0030] This embodiment describes a high-strength steel plate obtained using the flash heat treatment technology. The finished plate thickness is 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. After holding, the billet is removed, the iron oxide scale is removed, and it undergoes seven rolling passes to form a 5mm thick steel plate. The bite temperature during rolling is 1048℃, and the final rolling temperature is 973℃. The cooling rate after rolling is controlled to be ≥40℃ / s to room temperature. The sample is then heated to 850℃ at a heating rate of 10℃ / s, stabilized at 850℃, held for 8 seconds, and then directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that obtained using the traditional QT process. Its microstructure is similar to that of a typical tempered steel. See details... Figure 3 The mechanical properties are compared with those of the traditional QT process, as shown in Table 1.

[0031] Table 21 Comparison of mechanical properties between products prepared by flash heat treatment technology and products prepared by QT process

[0032]

[0033] (T600: tempered at 600℃; Q900, Q890 and Q850 are flash heat treated at 900℃, 890℃ and 850℃ respectively).

Claims

1. A method of flash heat treatment of a high-strength steel sheet, characterized by, The high-strength steel has the following composition by mass percentage (wt.%): C: 0.10~0.20, Mn: 1.75~1.85, Si: 1.10~1.35, Al: 0.30~0.45, Ti: 0.10~0.30, S≤0.008, P≤0.015, with the balance being Fe and other unavoidable impurities. This high-strength steel uses lath martensite obtained through online quenching as its initial structure, and undergoes flash heat treatment. Its microstructure is similar to that of tempered structures obtained under the QT process. Its mechanical properties, including tensile strength, yield strength, and elongation after fracture, are all at the same level. The high-strength steel is rolled in the single-phase region and then directly water-cooled to room temperature online. The sample is then heated to 800-900℃ at a heating rate of 8-15℃ / s, held for 1-10s, and then rapidly water-cooled to room temperature to obtain high-strength steel with performance comparable to that of traditional QT heat treatment process. The specific steps are as follows: (1) Smelting and forging: Smelting in a vacuum induction furnace, with precise control of alloy composition and strict control of P, S and other elements during the process, and then forging into a 50mm×50mm square billet with a final forging temperature greater than 1000℃. (2) Heating: KSL-1200X resistance furnace is used for heating. The heating temperature is 1150-1200℃ and the holding time is 90-120min. After taking it out of the furnace, remove the iron oxide scale. (3) Rolling: The heated billet is rolled at a bite temperature of 1000~1050℃. After 7 passes of rolling, it is rolled into a steel plate with a thickness of 5mm. The final rolling temperature is 950~980℃. (4) Cooling: The rolled steel plate obtained in step (3) is subjected to rapid water cooling treatment; (5) Heat treatment: The online quenched sample obtained in step (4) is subjected to rapid heat treatment. The sample is placed in a resistance heating furnace and heated to 800-900℃ at a heating rate of 8-15℃ / s. It is held for 1-10s and then rapidly cooled to room temperature to obtain high-strength steel with performance comparable to that of QT process.

2. The flash heat treatment method for high-strength steel plates according to claim 1, characterized in that, The high-strength steel plate obtained by the flash heat treatment method has a finished plate thickness of 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. Then, the steel billet is taken out after holding and the iron oxide scale is removed. After 7 passes of rolling, it is rolled into a 5mm steel plate. The bite temperature during rolling is 1050℃ and the final rolling temperature is 980℃. During the post-rolling cooling process, the cooling rate is controlled to be ≥40℃ / s to cool to room temperature. Then, the sample is heated to 900℃ at a heating rate of 10℃ / s, stabilized at 900℃ and held for 3 seconds, and then directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that under the traditional QT process. Its microstructure is similar to that of a typical tempered steel. The mechanical properties are: tensile strength of 999MPa, yield strength of 948MPa, and elongation of 20.9%.

3. The flash heat treatment method for high-strength steel plates according to claim 1, characterized in that, The high-strength steel plate obtained by the flash heat treatment method has a finished plate thickness of 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. Then, the steel billet is taken out after holding and the iron oxide scale is removed. After 7 passes of rolling, it is rolled into a 5mm steel plate. The bite temperature during rolling is 1053℃ and the final rolling temperature is 965℃. During the post-rolling cooling process, the cooling rate is controlled to be ≥40℃ / s to cool to room temperature. Then, the sample is heated to 890℃ at a heating rate of 10℃ / s, stabilized at 890℃ and held for 5 seconds, and then directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that under the traditional QT process. Its microstructure is similar to that of a typical tempered microstructure. The mechanical properties are: tensile strength of 1001MPa, yield strength of 953MPa, and elongation of 20.1%.

4. The flash heat treatment method for high-strength steel plates according to claim 1, characterized in that, The high-strength steel plate obtained by the flash heat treatment method has a finished plate thickness of 5mm. The specific production process is as follows: the forging billet is placed in a heating furnace at a set temperature of 1150℃ and held for 90 minutes. Then, the steel billet is taken out after holding and the iron oxide scale is removed. After 7 passes of rolling, it is rolled into a 5mm steel plate. The bite temperature during rolling is 1048℃ and the final rolling temperature is 973℃. During the post-rolling cooling process, the cooling rate is controlled to be ≥40℃ / s to cool to room temperature. Then, the sample is heated to 850℃ at a heating rate of 10℃ / s, stabilized at 850℃ and held for 8 seconds, and then directly water-cooled to room temperature. This yields a high-strength steel with performance comparable to that under the traditional QT process. Its microstructure is similar to that of a typical tempered microstructure. The mechanical properties are: tensile strength of 1012MPa, yield strength of 960MPa, and elongation of 19.8%.

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