Heat treatment method of 09MnNiDR steel plate with low compression ratio and high toughness

Abstract

The invention discloses a heat treatment method of a 09MnNiDR steel plate with a low compression ratio and high toughness. The heat treatment method comprises the working procedures of normalizing, subcritical quenching and tempering. In the subcritical quenching step, the temperature of the steel plate is increased to Ac3-(30-40) DEG C, and heat preservation is carried out for 3.0-3.5 min / mm; the steel plate directly enters a quenching machine after being discharged out of the furnace, and is rapidly cooled to the room temperature by adopting a large water amount of 5000-5500 m < 3 > / h and a low roller speed of 2-3 m / min; the thickness of the steel plate ranges from 85 mm to 100 mm, and the compression ratio ranges from 3: 1 to 3.5: 1. The transverse impact energy of the core part of the steel plate obtained by the method at-70 DEG C reaches more than 200J, the tensile strength is 430-480MPa, and the steel plate completely meets the manufacturing requirements of equipment such as low-temperature ethylene spherical tanks and low-temperature reactors at low environment temperature.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, specifically relating to a heat treatment method for 09MnNiDR steel plates with low compression ratio and high toughness. Background Technology

[0002] With the rapid development of the national petrochemical industry, the importance of chemical product storage and transportation has become increasingly prominent. 09MnNiDR steel plate, as a commonly used low-temperature pressure vessel steel plate, is widely used in the manufacture of equipment for the storage and transportation of products such as ethylene, propylene, liquid ammonia, and liquefied petroleum gas. Furthermore, its thickness is increasing, and the requirements for low-temperature toughness are becoming more stringent. In particular, the low-temperature impact resistance of the core has become an important indicator for evaluating the performance of the steel plate.

[0003] As the thickness of the steel plate increases, its low-temperature toughness decreases significantly, especially in the core area, which is a weak point during smelting, rolling, and heat treatment. In terms of metallurgical quality, inclusions, gases, and other harmful elements tend to accumulate in the core; during rolling, the rolling force struggles to penetrate the core, making it difficult to weld micro-defects and refine the grains; during heat treatment, heat is transferred to the core last, and the cooling rate in the core is the lowest. These factors result in poor metallurgical quality, the largest grains, the worst low-temperature toughness, and extreme instability in the core.

[0004] Therefore, finding a suitable heat treatment process for 09MnNiDR steel plates to ensure good impact resistance at -70℃ in the core, especially under harsh conditions of low compression ratio and large thickness, is a very difficult but practically significant task that can meet users' needs for high-performance cryogenic spherical tanks and storage tanks. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a heat treatment method for 09MnNiDR steel plate with low compression ratio and high toughness, wherein the transverse impact energy of the core of the steel plate at -70℃ reaches more than 200J and the steel plate has moderate strength.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A heat treatment method for 09MnNiDR steel plate with low compression ratio and high toughness includes normalizing + sub-temperature quenching + tempering processes.

[0007] Furthermore, the compression ratio of the steel plate described in this invention is 3:1 to 3.5:1. The national standards for pressure vessels GB / T 150-2011 and GB / T 713.3-2023 specify a compression ratio of ≥3:1, meaning that this invention uses a relatively small limiting compression ratio and achieves excellent low-temperature toughness in the core through a specially optimized heat treatment process.

[0008] Furthermore, the steel plate of the present invention has a thickness of 85-100 mm; it is made from a 300 mm thick continuously cast billet.

[0009] Furthermore, the nickel content of the steel plate described in this invention is 0.45% to 0.55%, with the remainder being Fe, other elements specified in the standard, and unavoidable impurities. Nickel and iron can be infinitely dissolved, expanding the austenite region, lowering the austenite transformation temperature, affecting the diffusion rate of carbon and alloying elements, preventing the transformation of austenite to pearlite, thus improving the hardenability of steel and refining the grain size. Nickel can increase the lattice slip plane during plastic deformation, providing a buffering effect when the steel is subjected to external impact, improving the toughness and plasticity of the material. Therefore, nickel is an element that can simultaneously improve strength and toughness. However, nickel is a precious metal with a high price, so its content should not be too high; this invention controls its content to around 0.50%. The steel plate of this invention has a low content of precious alloys, resulting in lower cost. Measurements show that the Ac3 temperature of the high-toughness 09MnNiDR steel plate described in this invention is 860℃.

[0010] Furthermore, the normalizing process described in this invention is carried out in a normalizing furnace, where the steel plate is heated to Ac3+ (30-40°C), held at that temperature for 2.5-3.0 min / mm, and then air-cooled after exiting the furnace.

[0011] Furthermore, the sub-temperature quenching described in this invention is carried out in a quenching furnace, where the steel plate is heated to Ac3-(30~40)℃ and held for 3.0~3.5min / mm; after exiting the furnace, it is directly fed into a quenching machine using a 5000~5500m... 3 A large water volume of 2-3 m / min and a low roller speed of 2-3 m / min are used to quickly cool the water to room temperature.

[0012] Furthermore, the tempering described in this invention is carried out in a tempering furnace, where the steel plate is heated to 610-630°C, held at that temperature for 3.0-4.0 min / mm, and then air-cooled to room temperature after being taken out of the furnace.

[0013] The metallographic structure of the steel plate described in this invention consists of ferrite, pearlite, and a small amount of bainite, with a grain size of 9.0-10.0.

[0014] The steel plate of the present invention has a transverse impact energy of ≥200J at -70℃, a tensile strength of 430~480MPa, a yield strength of 335~360MPa, and an elongation A≥30%.

[0015] This invention employs a billet forming method with a relatively small compression ratio (3:1 to 3.5:1). Between the conventional normalizing and tempering heat treatment, a sub-critical quenching at a temperature much lower than Ac3 is added, resulting in a steel plate with a higher proportion of soft ferrite, a certain amount of pearlite, and a small amount of bainite. The grains are fine and uniform, with a grain size of 9.0 to 10.0 grade. The resulting steel plate has excellent transverse impact energy at -70°C, especially the core, which reaches over 200J at -70°C. The steel plate has moderate strength, fully meeting the requirements for manufacturing equipment such as low-temperature ethylene spherical tanks and low-temperature reactors under low ambient temperatures.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Using a smaller compression ratio of 3:1 to 3.5:1, steel plates with a thickness of 85mm to 100mm are produced, providing a process route and case study for steel mills with smaller billet thickness to produce thicker steel plates.

[0017] (2) The metallographic structure of the steel plate is a mixture of ferrite, pearlite and a small amount of bainite. The grains are fine and uniform, with a grain size of 9.0 to 10.0 grade. The core has good low-temperature toughness and the transverse impact energy at -70℃ reaches ≥200J.

[0018] (3) The heat treatment process described in this invention is simple, the product prepared has stable performance, and can be mass-produced, thus meeting the domestic demand for petrochemical steel. Attached Figure Description

[0019] Figure 1 The metallographic structure at 100x magnification is shown at 1 / 4 of the thickness of the steel plate in Example 1.

[0020] Figure 2 The metallographic structure at 500x magnification is shown at 1 / 4 of the thickness of the steel plate in Example 1.

[0021] Figure 3 The metallographic structure at 100x magnification is shown at 1 / 2 the thickness of the steel plate in Example 1.

[0022] Figure 4 The metallographic structure at 500x magnification is shown at 1 / 2 the thickness of the steel plate in Example 1. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments. Example 1

[0024] In this embodiment, the mass percentage content of each element in the 09MnNiDR steel plate is as follows: Ni: 0.45%, C: 0.06%, Si: 0.26%, Mn: 1.45%, Nb: 0.025%, P: 0.010%, S: 0.003%, with the remainder being Fe and unavoidable impurities. The steel is produced from a 300mm thick continuously cast billet with a compression ratio of 3.5:1, resulting in a finished steel plate thickness of 85mm. The heat treatment process includes normalizing + sub-critical quenching + tempering, as detailed below: (1) Normalizing: Heat in a normalizing furnace. When the temperature reaches 890℃, hold for 2.5 min / mm and then air cool after exiting the furnace.

[0025] (2) Sub-temperature quenching: The steel plate is heated in a quenching furnace and held at 820℃ for 3.0 min / mm. After the steel plate is taken out of the furnace, it is directly put into the quenching machine, using a 5000m quenching machine. 3 A large water flow rate of / h and a low roller speed of 2min are used to quickly cool the steel plate to room temperature.

[0026] (3) Tempering: Heat in a tempering furnace. When the temperature reaches 610℃, hold for 3.0 min / mm. After taking it out of the furnace, air cool to room temperature.

[0027] In this embodiment, the metallographic structures at 1 / 4 and 1 / 2 of the steel plate thickness, magnified at 100x and 500x magnification respectively, are shown below. Figures 1-4 .Depend on Figures 1-4 It can be seen that its metallographic structure is a mixture of ferrite, pearlite and a small amount of bainite, with a grain size of 9.5 grade, and the grains are fine and uniform; its specific impact properties and tensile properties are detailed in Table 1. Example 2

[0028] In this embodiment, the mass percentage content of each element in the 09MnNiDR steel plate is as follows: Ni: 0.50%, C: 0.07%, Si: 0.15%, Mn: 1.43%, Nb: 0.035%, P: 0.009%, S: 0.002%, with the remainder being Fe and unavoidable impurities. The steel is produced from a 300mm thick continuously cast billet with a compression ratio of 3.3:1, resulting in a finished steel plate thickness of 90mm. The heat treatment process includes normalizing + sub-critical quenching + tempering, as detailed below: (1) Normalizing: Heat in a normalizing furnace. When the temperature reaches 895℃, hold for 3.0 min / mm and then air cool after exiting the furnace.

[0029] (2) Sub-temperature quenching: The steel plate is heated in a quenching furnace and held at 825℃ for 3.5 min / mm. After the steel plate is taken out of the furnace, it is directly put into the quenching machine, using a 5500m quenching machine. 3 A large water flow rate of / h and a low roller speed of 3min are used to quickly cool the steel plate to room temperature.

[0030] (3) Tempering: Heat in a tempering furnace. When the temperature reaches 620℃, hold for 3.5 min / mm. After taking it out of the furnace, air cool to room temperature.

[0031] The metallographic structure of the steel plate in this embodiment is F+P+B. 少 The grain size is grade 9.0; the specific impact and tensile properties of the steel plate are detailed in Table 1. Example 3

[0032] In this embodiment, the mass percentage content of each element in the 09MnNiDR steel plate is as follows: Ni: 0.55%, C: 0.06%, Si: 0.35%, Mn: 1.55%, Nb: 0.028%, P: 0.011%, S: 0.004%, with the remainder being Fe and unavoidable impurities. The steel is produced from a 300mm thick continuously cast billet with a compression ratio of 3.2:1, resulting in a finished steel plate thickness of 95mm. The heat treatment process includes normalizing + sub-critical quenching + tempering; details are as follows: (1) Normalizing: Heat in a normalizing furnace. When the temperature reaches 900℃, hold for 2.8 min / mm and then air cool after exiting the furnace.

[0033] (2) Sub-temperature quenching: The steel plate is heated in a quenching furnace and held at 830℃ for 3.2 min / mm. After the steel plate is taken out of the furnace, it is directly put into the quenching machine, using a 5300m quenching machine. 3 A large water flow rate of / h and a low roller speed of 2.5min allow for rapid cooling of the steel plate to room temperature.

[0034] (3) Tempering: Heat in a tempering furnace. When the temperature reaches 630℃, hold for 3.4 min / mm. After taking it out of the furnace, air cool to room temperature.

[0035] The metallographic structure of the steel plate in this embodiment is F+P+B. 少 The grain size is grade 10.0; the specific impact and tensile properties of the steel plate are detailed in Table 1. Example 4

[0036] In this embodiment, the mass percentage content of each element in the 09MnNiDR steel plate is as follows: Ni: 0.54%, C: 0.07%, Si: 0.22%, Mn: 1.51%, Nb: 0.033%, P: 0.0085%, S: 0.002%, with the remainder being Fe and unavoidable impurities. The steel is produced from a 300mm thick continuously cast billet with a compression ratio of 3.0:1, resulting in a finished steel plate thickness of 100mm. The heat treatment process includes normalizing + sub-critical quenching + tempering, as detailed below: (1) Normalizing: Heat in a normalizing furnace. When the temperature reaches 895℃, hold for 3.0 min / mm and then air cool after exiting the furnace.

[0037] (2) Sub-temperature quenching: The steel plate is heated in a quenching furnace and held at 830℃ for 3.2 min / mm. After the steel plate is taken out of the furnace, it is directly put into the quenching machine, using a 5300m quenching machine. 3 A large water flow rate of / h and a low roller speed of 2.5min allow for rapid cooling of the steel plate to room temperature.

[0038] (3) Tempering: Heat in a tempering furnace. When the temperature reaches 630℃, hold for 3.4 min / mm. After taking it out of the furnace, air cool to room temperature.

[0039] The metallographic structure of the steel plate in this embodiment is F+P+B. 少 The grain size is grade 9.5; the specific impact and tensile properties of the steel plate are detailed in Table 1.

[0040] Table 1 Mechanical properties of steel plates from various embodiments .

Claims

1. A heat treatment method for a low compression ratio and high toughness 09MnNiDR steel plate, characterized in that: The heat treatment method includes normalizing+sub-temperature quenching+tempering steps.

2. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: Normalizing: heat the steel plate to Ac3+ (30-40)°C, keep the temperature for 2.5-3.0min / mm, and air-cool after leaving the furnace.

3. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The sub-temperature quenching: the steel plate is heated to Ac3- (30 ~ 40) ℃, and kept warm for 3.0 ~ 3.5min / mm; the steel plate is directly put into the quenching machine after it comes out of the furnace, and the temperature is 5000 ~ 5500m 3 / h of large water volume, 2 ~ 3m / min of low roller speed, quickly cooled to room temperature.

4. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The tempering is as follows: the steel plate is heated to a temperature of 610-630° C., kept at a temperature of 3.0-3.5 min / mm, and air-cooled to room temperature after being taken out of the furnace.

5. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The compression ratio of the steel plate is 3:1 to 3.5:

1.

6. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The thickness of the steel plate is 85-100 mm.

7. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The Ni content of the steel plate is 0.45% to 0.55%, and the remainder is Fe, other elements specified by the standard, and unavoidable impurities.

8. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The metallographic structure of the steel plate is F+P+B 少 , the grain size is 9.0-10.

0.

9. The heat treatment method of a low compression ratio and high toughness 09MnNiDR steel plate according to claim 1, characterized in that: The transverse impact energy of the core of the steel plate at -70°C is ≥200J, and the tensile strength is 430-480MPa.

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