High-strength low-alloy steel for pressure vessel and manufacturing process thereof

Abstract

The application relates to the technical field of container steel, and discloses a high-strength low-alloy container steel and a preparation process thereof.The high-strength low-alloy container steel is composed of the following components in percentage by weight: C 0.14%-0.16%, Si 0.25%-0.40%, Mn 1.25%-1.38%, Cu 0.10%-0.15%, Ni 0.08%-0.13%, Cr 0.10%-0.13%, Mo 0.04%-0.07%, Nb 0.02%-0.04%, V 0.02%-0.05%, Ti 0.01%-0.03%, Al 0.04%-0.08%, P<=0.025%, S<=0.008%, and 25<=Mn / (Nb+Ti)<=27.6, and the balance is iron and inevitable impurities.The above technical scheme solves the problem of poor mechanical properties of the low-alloy container steel in the related art.

Description

Technical Field

[0001] This invention relates to the field of container steel technology, specifically to a high-strength low-alloy container steel and its preparation process. Background Technology

[0002] Low-alloy high-strength steel is widely used in engineering structures such as pressure vessels, storage tanks, and pipelines due to its excellent weldability and economy. With the increasing demands of modern industry for lightweight, safe, and long-lasting equipment, higher requirements are being placed on the strength and microstructure uniformity of steel used in containers.

[0003] Currently, low-alloy steels for containers still face some challenges in practical applications. For example, unreasonable element ratios lead to relatively poor strength and insufficient impact toughness, limiting their application in fields with higher safety requirements. Furthermore, in steel plates of different specifications, poor microstructure uniformity and coarse grains result in significant fluctuations in mechanical properties, making it difficult to meet stability and reliability requirements.

[0004] To address this, a low-alloy steel for containers is proposed, which possesses excellent mechanical properties and can meet the stringent material performance requirements of modern container manufacturing. Summary of the Invention

[0005] This invention proposes a high-strength low-alloy steel for containers and its preparation process, which solves the problem of poor mechanical properties of low-alloy steel for containers in related technologies.

[0006] The technical solution of the present invention is as follows: This invention proposes a high-strength, low-alloy steel for containers, composed of the following components by weight percentage: The composition is as follows: C 0.14%~0.16%, Si 0.25%~0.40%, Mn 1.25%~1.38%, Cu 0.10%~0.15%, Ni 0.08%~0.13%, Cr 0.10%~0.13%, Mo 0.04%~0.07%, Nb 0.02%~0.04%, V 0.02%~0.05%, Ti 0.01%~0.03%, Al 0.04%~0.08%, P≤0.025%, S≤0.008%, and 25≤Mn / (Nb+Ti)≤27.6, with the balance being iron and its unavoidable impurities.

[0007] As a further technical solution, the weights of Mn, Nb and Ti satisfy the following relationship: 26≤Mn / (Nb+Ti)≤27.2.

[0008] In this invention, by optimizing the content ratio of Mn, Nb, and Ti, the mechanical properties of low-alloy container steel can be further improved when the ratio of Mn / (Nb+Ti) to Ti is 25≤Mn / (Nb+Ti)≤27.6.

[0009] As a further technical solution, the weight ratio of Nb to Ti is 1~4:1.

[0010] This invention proposes a preparation process for high-strength low-alloy steel for containers, comprising the following steps: S1. Weigh the materials according to the stated weight percentage, mix and smelt them to obtain molten iron; S2. After pretreatment, the molten iron is smelted in a converter, refined by LF, vacuum degassed by RH, and continuously cast to obtain a slab. S3. After heating and rolling the slab, a controlled cooling treatment is performed to obtain a steel plate; S4. After heat treatment of the steel plate, high-strength low-alloy steel for containers is obtained.

[0011] As a further technical solution, during the pretreatment of molten iron, a desulfurizing agent is added to the molten iron and then desulfurization is carried out by injection, so that the weight percentage of S after molten iron pretreatment is ≤0.008%.

[0012] As a further technical solution, the desulfurizing agent includes one or two of magnesium powder and lime powder, preferably magnesium powder.

[0013] As a further technical solution, the heating temperature is 1180~1230℃ and the time is 1.5~2h; During the rolling process, rough rolling is performed first, followed by finish rolling, with a total reduction rate > 60%. During rough rolling, the initial rolling temperature is 980~1040℃; during finish rolling, the initial rolling temperature is 850~950℃, and the final rolling temperature is 780~820℃.

[0014] As a further technical solution, during the controlled cooling process, cooling is performed at an ultra-fast cooling rate of 50~75℃ / s, and the reddening temperature is controlled at 650~680℃.

[0015] As a further technical solution, the ultra-fast cooling rate is 55~60℃.

[0016] In this invention, during controlled cooling, the ultra-rapid cooling rate is 50~75℃ / s, for example, it can be 50℃ / s, 52℃ / s, 55℃ / s, 58℃ / s, 60℃ / s, 61℃ / s, 62℃ / s, 65℃ / s, 68℃ / s, 70℃ / s, or 75℃ / s, preferably 55~60℃. Cooling at an ultra-rapid cooling rate of 55~60℃ rapidly reduces the temperature of the rolled steel, allowing it to reach a suitable red-hot temperature. Ultra-rapid cooling can suppress the transformation of austenite into coarse ferrite and pearlite at high temperatures, facilitating the formation of fine ferrite grains, thereby increasing the grain boundary area, hindering crack propagation, and improving the impact toughness of low-alloy container steel to a certain extent.

[0017] As a further technical solution, the heat treatment is divided into a first heat treatment, a second heat treatment, and a third heat treatment; During the first stage of heat treatment, the temperature is increased to 730-780℃ at a heating rate of 5-25℃ / min, and the holding time is 40-45min; During the second stage of heat treatment, the temperature is increased from 730-780℃ to 980-1020℃ at a heating rate of 5-25℃ / min, and the holding time is 15-20min. During the third stage of heat treatment, the furnace is cooled from 980~1020℃ to room temperature.

[0018] In this invention, the steel plate undergoes segmented heat treatment. The first stage involves heating to 730-780°C at a rate of 5-25°C / min and holding for 40-45 minutes. During this process, the temperature gradually increases to 730-780°C, releasing some residual stress and providing a homogeneous compositional environment for subsequent microstructural transformation. The second stage involves heating from 730-780°C to 980-1020°C at a rate of 5-25°C / min and holding for 15-20 minutes. During this process, carbon, alloying elements, and other elements in the system have sufficient temperature and time to further diffuse and redistribute, optimizing the austenitic microstructure. Finally, the steel is cooled from 980-1020°C to room temperature in the furnace. This slow cooling further optimizes the internal microstructure and fully eliminates internal stress. Segmented heat treatment helps eliminate stress, forming a more uniform and stable microstructure, avoiding microstructural stress and defects caused by excessively rapid cooling, thereby further improving the impact toughness of the steel.

[0019] As a further technical solution, the heating rate of the first heat treatment stage is greater than the heating rate of the second heat treatment stage.

[0020] In this invention, by adjusting the heating rates of the first and second heat treatment stages, the inventors discovered that when the heating rate of the first heat treatment stage is greater than that of the second heat treatment stage, it is more conducive to improving impact toughness. The reason for this is speculated to be that the heating rate of the first heat treatment stage is relatively fast, which can quickly release some residual stress. The heating rate of the second heat treatment stage is relatively slow. The slower heating rate allows the steel to austenitize more fully and uniformly in a higher temperature range, which is more conducive to forming a uniform and stable microstructure, and further improving the impact toughness of low alloy container steel.

[0021] The working principle and beneficial effects of this invention are as follows: In this invention, the high-strength low-alloy steel for containers comprises C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, and Al elements. By combining these components and adjusting their amounts, a low-alloy steel with a uniform and stable internal structure and excellent mechanical properties is prepared. Mn, Nb, and Ti are introduced into the low-alloy steel. Mn plays a role in solid solution strengthening, increasing the resistance to dislocation movement. Nb and Ti can form fine, dispersed carbonitride precipitates with C and N in the system. These fine precipitates pin dislocations, further hindering dislocation movement. By combining Mn, Nb, and Ti, and ensuring that the content ratio of Mn, Nb, and Ti is 25 ≤ Mn / (Nb+Ti) ≤ 27.6, Optimizing the microstructure of alloy container steel has a better effect and can effectively improve the mechanical properties of low alloy container steel. When Mn / (Nb+Ti)>27.6, the content of Mn is relatively higher than that of Nb+Ti, which easily leads to increased Mn segregation and a decrease in microstructure uniformity. When Mn / (Nb+Ti)<25, the content of Nb+Ti microalloying is relatively higher than that of Mn, and the dispersed precipitates are relatively coarse and precipitate too early, which is not conducive to the stable adjustment of the microstructure of container steel. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Mn 1.25%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, Nb 0.02%, V 0.02%, Ti 0.03%, Al 0.04%, P 0.025%, S 0.008%, with the balance being iron and its unavoidable impurities; A manufacturing process for high-strength low-alloy steel for containers includes the following steps: S1. Weigh the components according to their weight percentages, blend and smelt them to obtain molten iron; S2. After adding magnesium powder to the molten iron, desulfurization is carried out by injection to make the weight percentage of S in the molten iron 0.008% after pretreatment. Then, the molten iron is smelted in a converter, refined by LF, vacuum degassed by RH, and continuously cast to obtain a slab. S3. The slab is heated at 1180℃ for 2 hours, first roughed, then finished, and then cooled at an ultra-fast cooling rate of 50℃ / s to control the reddening temperature at 650℃, thus obtaining the steel plate. The roughing temperature is 980℃, the finishing temperature is 850℃, and the final rolling temperature is 780℃, with a total rolling reduction of 65%. S4. The steel plate is heated from 650℃ to 1020℃ at a heating rate of 25℃ / min, held at that temperature for 60min, and then cooled to room temperature in the furnace from 1020℃ to obtain high-strength low-alloy steel for containers.

[0024] Example 2 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.30%, Mn 1.38%, Cu 0.13%, Ni 0.11%, Cr 0.11%, Mo 0.05%, Nb 0.03%, V 0.04%, Ti 0.02%, Al 0.06%, P 0.02%, S 0.005%, with the balance being iron and its unavoidable impurities; A manufacturing process for high-strength low-alloy steel for containers includes the following steps: S1. Weigh the components according to their weight percentages, blend and smelt them to obtain molten iron; S2. After adding magnesium powder to the molten iron, desulfurization is carried out by injection to make the weight percentage of S in the molten iron 0.005% after pretreatment. Then, the molten iron is smelted in a converter, refined by LF, vacuum degassed by RH, and continuously cast to obtain a slab. S3. The slab is heated at 1200℃ for 2 hours, first roughed, then finished, and then cooled at an ultra-fast cooling rate of 50℃ / s to control the reddening temperature at 650℃, thus obtaining the steel plate. The roughing temperature is 1020℃, the finishing temperature is 900℃, the finishing temperature is 800℃, and the total rolling reduction is 65%. S4. The steel plate is heated from 650℃ to 1020℃ at a heating rate of 25℃ / min, held at that temperature for 60min, and then cooled to room temperature in the furnace from 1020℃ to obtain high-strength low-alloy steel for containers.

[0025] Example 3 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.16%, Si 0.40%, Mn 1.38%, Cu 0.10%, Ni 0.13%, Cr 0.10%, Mo 0.07%, Nb 0.04%, V 0.05%, Ti 0.01%, Al 0.08%, P 0.02%, S 0.008%, with the balance being iron and its unavoidable impurities; A manufacturing process for high-strength low-alloy steel for containers includes the following steps: S1. Weigh the components according to their weight percentages, blend and smelt them to obtain molten iron; S2. After adding magnesium powder to the molten iron, desulfurization is carried out by injection to make the weight percentage of S in the molten iron 0.008% after pretreatment. Then, the molten iron is smelted in a converter, refined by LF, vacuum degassed by RH, and continuously cast to obtain a slab. S3. The slab is heated at 1230℃ for 1.5 hours, first roughed, then finished, and then cooled at an ultra-fast cooling rate of 50℃ / s to control the reddening temperature at 680℃, thus obtaining the steel plate. The roughing temperature is 1040℃, the finishing temperature is 950℃, the finishing temperature is 820℃, and the total rolling reduction is 65%. S4. The steel plate is heated from 680℃ to 1020℃ at a heating rate of 25℃ / min, held at that temperature for 60min, and then cooled to room temperature in the furnace from 1020℃ to obtain high-strength low-alloy steel for containers.

[0026] Example 4 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.30%, Mn 1.38%, Cu 0.13%, Ni 0.11%, Cr 0.11%, Mo 0.05%, Nb 0.025%, V 0.04%, Ti 0.025%, Al 0.06%, P 0.02%, S 0.005%, with the balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 2.

[0027] Example 5 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.30%, Mn 1.3%, Cu 0.13%, Ni 0.11%, Cr 0.11%, Mo 0.05%, Nb 0.025%, V 0.04%, Ti 0.025%, Al 0.06%, P 0.02%, S 0.005%, with the balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 2.

[0028] Example 6 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.30%, Mn 1.36%, Cu 0.13%, Ni 0.11%, Cr 0.11%, Mo 0.05%, Nb 0.025%, V 0.04%, Ti 0.025%, Al 0.06%, P 0.02%, S 0.005%, with the balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 2.

[0029] Example 7 The only difference between this embodiment and Embodiment 6 is that in the preparation process of the high-strength low-alloy container steel in this embodiment, the ultra-fast cooling rate is 75℃ / s.

[0030] Example 8 The only difference between this embodiment and Embodiment 6 is that in the preparation process of the high-strength low-alloy container steel in this embodiment, the ultra-fast cooling rate is 55℃ / s.

[0031] Example 9 The only difference between this embodiment and Embodiment 6 is that in the preparation process of the high-strength low-alloy container steel in this embodiment, the ultra-fast cooling rate is 60℃ / s.

[0032] Example 10 The only difference between this embodiment and Embodiment 9 is that step S4 in the preparation process of high-strength low-alloy steel for containers is different in this embodiment, specifically: The steel plate was heated from 650℃ to 730℃ at a heating rate of 25℃ / min, held at that temperature for 45 minutes, then heated from 730℃ to 1020℃ at a heating rate of 25℃ / min, held at that temperature for 15 minutes, and then cooled from 1020℃ to room temperature in the furnace to obtain high-strength low-alloy steel for containers.

[0033] Example 11 The only difference between this embodiment and Embodiment 9 is that step S4 in the preparation process of high-strength low-alloy steel for containers is different in this embodiment, specifically: The steel plate was heated from 650℃ to 730℃ at a heating rate of 5℃ / min, held at that temperature for 45 minutes, then heated from 730℃ to 1020℃ at a heating rate of 5℃ / min, held at that temperature for 15 minutes, and then cooled from 1020℃ to room temperature in the furnace to obtain high-strength low-alloy steel for containers.

[0034] Example 12 The only difference between this embodiment and Embodiment 9 is that step S4 in the preparation process of high-strength low-alloy steel for containers is different in this embodiment, specifically: The steel plate was heated from 650℃ to 780℃ at a heating rate of 5℃ / min, held at that temperature for 40 minutes, then heated from 780℃ to 980℃ at a heating rate of 5℃ / min, held at that temperature for 20 minutes, and then cooled from 980℃ to room temperature in the furnace to obtain high-strength low-alloy steel for containers.

[0035] Example 13 The only difference between this embodiment and Embodiment 12 is that step S4 in the preparation process of high-strength low-alloy steel for containers is different, specifically: The steel plate was heated from 650℃ to 780℃ at a heating rate of 5℃ / min, held for 40 min, then heated from 780℃ to 980℃ at a heating rate of 25℃ / min, held for 20 min, and then cooled from 980℃ to room temperature in the furnace to obtain high-strength low-alloy steel for containers.

[0036] Example 14 The only difference between this embodiment and Embodiment 12 is that step S4 in the preparation process of high-strength low-alloy steel for containers is different, specifically: The steel plate was heated from 650℃ to 780℃ at a heating rate of 25℃ / min, held at that temperature for 40 minutes, then heated from 780℃ to 980℃ at a heating rate of 5℃ / min, held at that temperature for 20 minutes, and then cooled from 980℃ to room temperature in the furnace to obtain high-strength low-alloy steel for containers.

[0037] Comparative Example 1 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Mn 1.25%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, V 0.02%, Ti 0.05%, Al 0.04%, P≤0.025%, S≤0.008%, balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 1.

[0038] Comparative Example 2 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Mn 1.25%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, Nb 0.05%, V 0.02%, Al 0.04%, P≤0.025%, S≤0.008%, balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 1.

[0039] Comparative Example 3 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Mn 1.3%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, V 0.02%, Al 0.04%, P≤0.025%, S≤0.008%, balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 1.

[0040] Comparative Example 4 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, Nb 0.52%, V 0.02%, Ti 0.78%, Al 0.04%, P≤0.025%, S≤0.008%, balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 1.

[0041] Comparative Example 5 A high-strength, low-alloy steel for containers is composed of the following components by weight percentage: C 0.14%, Si 0.25%, Cu 0.15%, Ni 0.08%, Cr 0.13%, Mo 0.04%, V 0.02%, Al 0.04%, P≤0.025%, S≤0.008%, balance being iron and its unavoidable impurities; Its preparation process is the same as that in Example 1.

[0042] Experimental Example 1 The low-alloy container steels prepared in Examples 1-6 and Comparative Examples 1-5 were tested for tensile strength according to the test methods in GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature," with a test speed of 0.002 s. -1 The test results are shown in Table 1.

[0043] Table 1 Performance test results of Examples 1-6 and Comparative Examples 1-5

[0044] Compared with Comparative Examples 1-5, the tensile strength of the low-alloy container steel prepared in Examples 1-6 is improved. This indicates that when Mn, Nb, and Ti are added to the low-alloy container steel and the content ratio of the three is adjusted to 25≤Mn / (Nb+Ti)≤27.6, the mechanical properties of the low-alloy container steel can be effectively improved by using the three in combination, and its tensile strength can be increased to above 554MPa.

[0045] Compared with Examples 1-4, the tensile strength of the low-alloy container steel prepared in Examples 5-6 was further improved, indicating that by optimizing the content ratio of Mn, Nb and Ti to make 26≤Mn / (Nb+Ti)≤27.2, the mechanical properties of the low-alloy container steel can be further improved, and its tensile strength can be increased to above 591MPa.

[0046] Experiment Example 2 The low-alloy container steels prepared in Examples 6-14 were subjected to longitudinal impact energy tests at 0°C according to the method in GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method". The sample size was 55 mm in length and 10 mm × 10 mm in cross-section. The test results are shown in Table 2.

[0047] Table 2 Performance test results of Examples 6-14

[0048] Compared with Examples 6-7, the low-alloy container steel prepared in Examples 8-9 showed an increase in longitudinal impact energy at 0°C, indicating that cooling at an ultra-fast cooling rate of 55-60°C and controlling the reddening temperature to 650-680°C after rolling is beneficial to improving the impact toughness of the low-alloy container steel.

[0049] Compared with Examples 6-9, the longitudinal impact energy at 0°C of the low-alloy container steel prepared in Examples 10-14 was further improved, indicating that the heat treatment process involved segmented heat treatment. In the first stage, the temperature was increased to 730-780°C at a heating rate of 5-25°C / min and held for 40-45 min. In the second stage, the temperature was increased from 730-780°C to 980-1020°C at a heating rate of 5-25°C / min and held for 15-20 min. In the third stage, the temperature was cooled to room temperature in the furnace from 980-1020°C. Through the combined treatment of the first, second, and third stages, the impact toughness of the low-alloy container steel can be further improved, increasing its longitudinal impact energy at 0°C to over 68 J.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, low-alloy steel for containers, characterized in that, It consists of the following components by weight percentage: The composition is as follows: C 0.14%~0.16%, Si 0.25%~0.40%, Mn 1.25%~1.38%, Cu 0.10%~0.15%, Ni 0.08%~0.13%, Cr 0.10%~0.13%, Mo 0.04%~0.07%, Nb 0.02%~0.04%, V 0.02%~0.05%, Ti 0.01%~0.03%, Al 0.04%~0.08%, P≤0.025%, S≤0.008%, and 25≤Mn / (Nb+Ti)≤27.6, with the balance being iron and its unavoidable impurities.

2. The high-strength low-alloy steel for containers according to claim 1, characterized in that, The weights of Mn, Nb, and Ti satisfy the following relationship: 26 ≤ Mn / (Nb+Ti) ≤ 27.

2.

3. The high-strength low-alloy steel for containers according to claim 1, characterized in that, The weight ratio of Nb to Ti is 1 to 4:

1.

4. A process for preparing high-strength low-alloy steel for containers, used to prepare the high-strength low-alloy steel for containers as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Weigh the materials according to the stated weight percentage, mix and smelt them to obtain molten iron; S2. After pretreatment, the molten iron is smelted in a converter, refined by LF, vacuum degassed by RH, and continuously cast to obtain a slab. S3. After heating and rolling the slab, a controlled cooling treatment is performed to obtain a steel plate; S4. After heat treatment of the steel plate, high-strength low-alloy steel for containers is obtained.

5. The preparation process of high-strength low-alloy steel for containers according to claim 4, characterized in that, During the molten iron pretreatment, a desulfurizing agent is added to the molten iron and then desulfurization is carried out by injection, so that the weight percentage of S after molten iron pretreatment is ≤0.008%.

6. The preparation process of high-strength low-alloy steel for containers according to claim 4, characterized in that, During the heating process, the temperature is 1180~1230℃ and the time is 1.5~2h; During the rolling process, rough rolling is performed first, followed by finish rolling, with a total reduction rate > 60%. During rough rolling, the initial rolling temperature is 980~1040℃; during finish rolling, the initial rolling temperature is 850~950℃, and the final rolling temperature is 780~820℃.

7. The preparation process of high-strength low-alloy steel for containers according to claim 4, characterized in that, During the controlled cooling process, cooling is performed at an ultra-fast cooling rate of 50~75℃ / s, and the reddening temperature is controlled at 650~680℃.

8. The preparation process of high-strength low-alloy steel for containers according to claim 7, characterized in that, The ultra-fast cooling rate is 55~60℃.

9. The preparation process of high-strength low-alloy steel for containers according to claim 1, characterized in that, The heat treatment is divided into a first heat treatment stage, a second heat treatment stage, and a third heat treatment stage. During the first stage of heat treatment, the temperature is increased to 730-780℃ at a heating rate of 5-25℃ / min, and the holding time is 40-45min; During the second stage of heat treatment, the temperature is increased from 730-780℃ to 980-1020℃ at a heating rate of 5-25℃ / min, and the holding time is 15-20min. During the third stage of heat treatment, the furnace is cooled from 980~1020℃ to room temperature.

10. The preparation process of high-strength low-alloy steel for containers according to claim 9, characterized in that, The heating rate of the first heat treatment stage is greater than the heating rate of the second heat treatment stage.

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