A heat treatment method for recovering the properties of a high-toughness container steel sheet after hot forming

Abstract

This invention discloses a heat treatment method for restoring the properties of high-toughness container steel plates after hot forming, comprising a first quenching, a second quenching, and a tempering heat treatment process; wherein, during the first and second quenching, the heating rate is controlled within the range of 350℃ / h-450℃ / h; the first quenching is held at a temperature of 900℃-910℃ for 20-30 minutes; the second quenching is held at a temperature of 840℃-850℃ for 50-60 minutes; and the tempering is held at a temperature of 600℃-640℃ for 60-80 minutes. The steel plate treated by this method exhibits excellent toughness, with an impact absorption energy of ≥200J at -70℃ at the surface, 1 / 4, and 1 / 2 sections. The microstructure of the steel plate is uniform and fine granular bainite with a grain size of 9.5-11.5.

Description

Technical Field

[0001] This invention relates to a heat treatment method for steel plates, and more particularly to a heat treatment method for restoring the properties of high-toughness container steel plates after hot forming. Background Technology

[0002] In industrial production systems, steel cryogenic pressure vessels are crucial equipment, significantly impacting safe production and processing; therefore, ensuring their performance is paramount. However, cryogenic pressure vessels often require hot forming, especially as steel plate thickness increases, making hot forming indispensable. To reduce hot forming pressure, the steel plate must be heated to high temperatures and then air-cooled to room temperature, resulting in coarsening of the steel structure and a significant reduction in its properties, particularly its low-temperature toughness. Therefore, researching how to restore material properties after hot forming is a key step in fully realizing the material's potential. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a heat treatment method for restoring the properties of high-toughness container steel plates after hot forming.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A heat treatment method for restoring the properties of high-toughness container steel plates after hot forming includes a first quenching, a second quenching, and a tempering heat treatment process; wherein, during the first and second quenching, the heating rate is controlled within the range of 350℃ / h-450℃ / h.

[0006] The first quenching described in this invention involves a holding temperature of 900℃-910℃ and a holding time of 20min-30min. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0007] The second quenching described in this invention involves holding the steel plate at a temperature of 840℃-850℃ for 50-60 minutes, followed by water cooling to room temperature after the steel plate is removed from the furnace.

[0008] The tempering described in this invention involves a holding temperature of 600℃-640℃ and a holding time of 60min-80min. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0009] The high-toughness container steel plate of the present invention has an Ac3 temperature of 850℃-860℃ and a steel plate thickness of 80mm-150mm.

[0010] The high-toughness container steel plate of the present invention is hot-formed at a temperature of 930℃-960℃ and cooled by air cooling after hot forming.

[0011] The steel plate treated by the method described in this invention has a uniform and fine granular bainite microstructure with a grain size of 9.5-11.5. The steel plate has excellent toughness, and the impact absorption energy at -70℃ at the surface, 1 / 4 and 1 / 2 of the plate is ≥200J.

[0012] The high-toughness container steel plate of this invention is based on the standard GB3531-2014; the performance testing method for steel plates for low-temperature pressure vessels after heat treatment is based on the standards GB / T229 and GB / T228.1.

[0013] The beneficial effects of adopting the above technical solution are as follows:

[0014] This invention increases the nucleation rate and refines the grains by employing rapid heating and cooling. Simultaneously, it controls the heating rate to ensure uniform heating along the thickness direction of thick steel plates.

[0015] The two-cycle quenching process uses a stepped temperature: first, high-temperature short-time heating is used as a pretreatment step to ensure sufficient homogenization of austenite and lay a good microstructure foundation for subsequent processes; then, low-temperature long-time heating is used, with the temperature in the two-phase region. The resulting initial austenite grains are relatively small, and the undissolved microstructure also plays a cutting role, hindering the growth of austenite grains, thereby effectively refining the grain size and improving toughness.

[0016] 3. By combining a reasonable tempering process, the internal stress of the steel plate after water cooling is eliminated, the hardness is reduced and the toughness is improved. The impact absorption energy of the steel plate surface, 1 / 4 and 1 / 2 at -70℃ is ≥200J, which fully meets the market demand for this type of low temperature pressure vessel steel plate. Attached Figure Description

[0017] Figure 1 The metallographic structure of the steel plate after heat treatment in Example 1 of the present invention is shown in 200X.

[0018] Figure 2 The metallographic structure of the steel plate after heat treatment in Example 2 of the present invention is shown in the image (200X).

[0019] Figure 3 This is a metallographic image (200X) of the steel plate after heat treatment in Example 3 of the present invention.

[0020] Figure 4 The metallographic structure of the steel plate after heat treatment in Example 4 of the present invention is shown in 200X.

[0021] Figure 5 The metallographic structure of the steel plate of Comparative Example 5 after heat treatment (200X). Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] A heat treatment method for restoring the properties of high-toughness container steel plates after hot forming includes a first quenching, a second quenching, and a tempering heat treatment process; wherein, during the first and second quenching, the heating rate is controlled within the range of 350℃ / h-450℃ / h.

[0024] The first quenching is performed at a holding temperature of 900℃-910℃ for 20-30 minutes, after which the steel plate is water-cooled to room temperature. The second quenching is performed at a holding temperature of 840℃-850℃ for 50-60 minutes, after which the steel plate is water-cooled to room temperature. The tempering is performed at a holding temperature of 600℃-640℃ for 60-80 minutes, after which the steel plate is air-cooled to room temperature.

[0025] The high-toughness container steel plate Ac3 has a temperature of 850℃-860℃ and a thickness of 80mm-150mm. The hot forming temperature of the steel plate is 930℃-960℃, and it is cooled by air cooling after hot forming.

[0026] Examples 1-5

[0027] The steel plate thickness, Ac3 temperature, and hot forming process in Examples 1-5 are shown in Table 1; the heat treatment process for restoring properties is shown in Table 2; the properties and grain size of the steel plate after heat treatment are shown in Table 3; the microstructure of the steel plate after heat treatment is uniform and fine granular bainite, as detailed in Table 3. Figures 1-5 .

[0028] Table 1. Steel plate thickness, Ac3 temperature, and hot forming process for Examples 1-5

[0029]

[0030] Table 2 Heat treatment processes for restoring steel plate properties in Examples 1-5

[0031]

[0032] Table 3 Properties and grain size of steel plates after heat treatment in Examples 1-5

[0033]

[0034] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A heat treatment method for recovering the properties of a high-toughness container steel sheet after hot forming, characterized in that, The process includes a first quenching, a second quenching, and a tempering heat treatment; wherein, during the first and second quenching, the heating rate is controlled within the range of 350℃ / h-450℃ / h. The first quenching is performed at a holding temperature of 900℃-910℃ for 20-30 minutes. After the steel plate is taken out of the furnace, it is water-cooled to room temperature. The second quenching is performed at a holding temperature of 840℃-850℃ for 50-60 minutes. After the steel plate is taken out of the furnace, it is water-cooled to room temperature. The tempering process involves holding at a temperature of 600℃-640℃ for 60-80 minutes, followed by air cooling of the steel plate to room temperature after it is removed from the furnace. The thickness of the high-toughness container steel plate is 80mm-150mm.

2. The heat treatment method for recovering the properties of a high-toughness container steel sheet after thermoforming according to claim 1, characterized by, The Ac3 temperature of the high-toughness container steel plate is 850℃-860℃.

3. The heat treatment method for recovering the properties of a high-toughness container steel sheet after hot forming according to claim 1, characterized by, The hot forming temperature of the high-toughness container steel plate is 930℃-960℃, and it is cooled by air cooling after hot forming.

4. The heat treatment method for recovering the properties of a high-toughness container steel sheet after thermoforming according to claim 1, characterized by, The steel plate treated by the method has a uniform and fine granular bainite microstructure with a grain size of 9.5-11.

5.

5. The heat treatment method for recovering the properties of a high-toughness container steel sheet after thermoforming according to claim 1, characterized by, The steel plate treated by the method has excellent toughness, and the impact absorption energy at -70℃ at the surface, 1 / 4 and 1 / 2 is ≥200J.

Images