Production method of high-Ni ultrahigh-strength high-toughness steel plate

Abstract

The invention discloses a production method of a high-Ni ultrahigh-strength high-toughness steel plate. The steel comprises the following chemical components in percentage by mass: 0.03-0.05% of C, 0.10-0.35% of Si, 0.50-0.70% of Mn, less than or equal to 0.008% of P, less than or equal to 0.0053% of S, 8.6-9.0% of Ni and the balance of Fe and inevitable impurities. The steel plate is produced by adopting a continuous casting billet with the thickness of 180-220 mm, and the thickness of the steel plate is 10 In the casting process, 1-2 kg / min of iron powder is added into a crystallizer so as to control the lower superheat degree; a high-temperature short-time heating process is adopted for the blank, the heating temperature ranges from 1240 DEG C to 1260 DEG C, the heat preservation time ranges from 20 min to 40 min, and water cooling is conducted to the temperature below 350 DEG The heat treatment adopts a quenching, tempering and water cooling process, the quenching temperature is 780-820 DEG C, the tempering temperature is 580-620 DEG C, and water cooling is performed after tempering. According to the steel plate produced through the method, the tensile strength ranges from 760 MPa to 820 MPa, the yield strength ranges from 650 MPa to 690 MPa, and the impact absorption energy at the temperature of minus 196 DEG C is larger than or equal to 120 J.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy and relates to a production method of high-Ni super-high-strength and high-toughness steel plate. BACKGROUND

[0002] With the increasing demand for clean energy worldwide, the storage and transportation technology of liquefied natural gas (LNG) has become a key link in energy strategy. LNG needs to be stored at an extremely low temperature of about -196℃, which puts extremely stringent requirements on the low-temperature mechanical properties, especially the low-temperature toughness and strength, of the storage tank building materials.

[0003] When the Ni content in steel reaches 8.5% or more, it is generally referred to as 9Ni steel. 9Ni steel still has excellent low-temperature toughness, good welding performance and relatively reasonable cost at -196℃, and has become the preferred material for building large LNG storage tank inner tanks. Traditional 9Ni steel mainly obtains stable reversed austenite organization through heat treatment processes such as quenching + tempering (QT) or two-phase zone quenching (QLT), thereby ensuring its ultra-high low-temperature impact toughness.

[0004] However, with the development of LNG storage and transportation technology towards higher efficiency, greater safety and more challenging environments such as polar ships, offshore floating storage tanks and the like, higher requirements are put forward for the comprehensive performance of the steel for storage tanks. Although the existing conventional 9Ni steel has sufficient toughness reserve, its strength level is usually at the yield strength level of 680-730 MPa, which has shown limitations in certain specific application scenarios. For example, in the pursuit of lightweight design to improve transportation efficiency or increase effective payload, in resisting extreme external force impact or complex stress state, there is an urgent need for a steel plate that has ultra-high strength such as a tensile strength higher than 750 MPa level while maintaining the excellent low-temperature toughness of 9Ni steel.

[0005] At present, simply adjusting the existing heat treatment process to simultaneously greatly improve the strength and toughness of 9Ni steel faces great challenges. The increase in strength is often accompanied by a decrease in the number and stability of reversed austenite, thereby leading to the deterioration of low-temperature toughness; and excessive pursuit of toughness makes it difficult to achieve a breakthrough in strength grade. This inverted relationship between strength and toughness restricts the application of 9Ni steel in high-end and special LNG equipment.

[0006] Therefore, developing an innovative production process method that can break through the traditional performance bottleneck and produce high-Ni steel plates with ultra-high strength and high toughness has great engineering application value and urgent practical significance for promoting the technological progress of LNG storage and transportation equipment and realizing the coordinated improvement of lightweight and safety. SUMMARY

[0007] The present application aims to provide a high Ni super high strength high toughness steel plate production method, the steel plate produced by the method has a tensile strength of 760-820 MPa, a yield strength of 650-690 MPa, and an impact energy at -196 ℃ of ≥120 J.

[0008] The technical scheme adopted by the present application is: A high Ni super high strength high toughness steel plate production method, the chemical composition of the steel plate is as follows: C=0.03%-0.05%, Si=0.10%-0.35%, Mn=0.50%-0.70%, P≤0.008%, S≤0.005%, Ni=8.6%-9.0%, and the rest is Fe and inevitable impurities; a 180-220 mm thick continuous casting billet is used to produce a steel plate with a thickness of 10-30 mm; the steel plate has a tensile strength of 760-820 MPa, a yield strength of 650-690 MPa, and an impact energy at -196 ℃ of ≥120 J; the key process steps include: 1) Casting: during casting, 1-2 kg / min of iron powder is added to the crystallizer, and the superheat is controlled to be 5-15 ℃; 2) Billet heating and rolling: the billet is heated by a high-temperature short-time heating process, the heating temperature is 1240-1260 ℃, the holding time is 20-40 min, and the water cooling temperature after rolling is below 350 ℃; 3) Heat treatment: a quenching + tempering process is adopted, the quenching temperature is 780-820 ℃, the holding time is 40-60 min, the water quantity in the high-pressure section during quenching is 5000-9000 m 3 / h, the water quantity in the low-pressure section is 7000-12000 m 3 / h, the roller speed of the quenching machine is 8-16 m / min; during tempering, first, the temperature is held at 580-600 ℃ for 30-50 min, then the temperature is raised to 600-620 ℃ for 10-20 min, after tempering, only the low-pressure section is opened for water cooling, the water quantity is 4000-8000 m 3 / h, and the roller speed is 15-20 m / min.

[0009] The present application has the following beneficial effects: during casting, low superheat is adopted, which can effectively reduce the composition segregation of the casting billet; the billet is heated by a high-temperature short-time heating process, which can reduce the composition segregation and avoid the generation of iron oxide scale, thereby ensuring the surface quality of the steel plate; the water cooling temperature after rolling is below 350 ℃, which can refine the grains; the heat treatment adopts a quenching + tempering process, the quenching temperature is higher than the AC3 temperature and the holding time is long, and a large amount of water is used for cooling, thereby producing a martensite structure; during tempering, the temperature is held below the AC1 temperature for a long time, thereby generating a certain amount of reversed austenite to ensure the low-temperature performance of the steel plate; then the temperature is raised to slightly above the AC1 temperature for a short time, and then water cooling, which can retain a small amount of martensite structure with high strength, thereby improving the strength of the steel plate. DETAILED DESCRIPTION

[0010] The application will be further described in connection with specific examples. Example 1

[0011] The production method of the high-Ni super-high-strength and high-toughness steel plate has a thickness of 30 mm, uses a 220 mm thick continuous casting billet for rolling, and the steel plate has a component mass percentage of C=0.05%, Si=0.35%, Mn=0.70%, P=0.008%, S=0.005%, Ni=9.0%, and the rest is Fe and inevitable impurities, and the key process steps include: 1) Casting: During the casting process, 1 kg / min of iron powder is added to the crystallizer, and the superheat is controlled to be 5 ℃.

[0012] 2) Billet heating and rolling: The billet uses a high-temperature short-time heating process, the heating temperature is 1240 ℃, the holding time is 40 min, and the water cooling after rolling is to 350 ℃.

[0013] 3) Heat treatment: The heat treatment uses a quenching + tempering process: the quenching temperature is 820 ℃, the holding time is 60 min, the water quantity in the high-pressure section during the quenching process is 9000 m 3 / h, the water quantity in the low-pressure section is 12000 m 3 / h, the roller speed of the quenching machine is 8 m / min; during the tempering, first, the temperature is held at 600 ℃ for 50 min, then the temperature is raised to 620 ℃, the holding time is 20 min, after the tempering, the water cooling is only opened in the low-pressure section, the water quantity is 8000 m 3 / h, and the roller speed is 15 m / min. Example 2

[0014] The production method of the high-Ni super-high-strength and high-toughness steel plate has a thickness of 10 mm, uses a 180 mm thick continuous casting billet for rolling, and the steel plate has a component mass percentage of C=0.03%, Si=0.1%, Mn=0.50%, P=0.008%, S=0.003%, Ni=8.6%, and the rest is Fe and inevitable impurities, and the key process steps include: 1) Casting: During the casting process, 2 kg / min of iron powder is added to the crystallizer, and the superheat is controlled to be 15 ℃.

[0015] 2) Billet heating and rolling: The billet uses a high-temperature short-time heating process, the heating temperature is 1260 ℃, the holding time is 20 min, and the water cooling after rolling is to 330 ℃.

[0016] 3) Heat treatment: The heat treatment uses a quenching + tempering process: the quenching temperature is 780 ℃, the holding time is 40 min, the water quantity in the high-pressure section during the quenching process is 5000 m 3 / h, the water quantity in the low-pressure section is 7000 m 3 / h, quenching roller speed 16 m / min; tempering first at 580°C for 30 min, then heated to 600°C, holding time 10 min, after tempering water cooling only low pressure section, water volume 4000 m 3 / h, roller speed 20 m / min. Example 3

[0017] The production method of high Ni super high strength high toughness steel plate, the thickness of the steel plate is 15 mm, the 180 mm thick continuous casting billet is rolled, the steel plate has the component mass percentage of C=0.04%, Si=0.20%, Mn=0.55%, P=0.007%, S=0.004%, Ni=8.7%, the rest is Fe and inevitable impurities, the key process steps include: 1) Casting: during the casting process, the iron powder is added to the crystallizer at 1.3 kg / min, and the superheat is controlled at 13°C.

[0018] 2) Billet heating and rolling: the billet adopts high temperature short time heating process, the heating temperature is 1245°C, the holding time is 32 min, and the water cooling is performed to 310°C after rolling.

[0019] 3) Heat treatment: the heat treatment adopts quenching + tempering process: the quenching temperature is 790°C, the holding time is 52 min, the water volume of the high pressure section during the quenching process is 7000 m 3 / h, the water volume of the low pressure section is 11000 m 3 / h, quenching roller speed 14 m / min; tempering first at 597°C for 40 min, then heated to 605°C, holding time 13 min, after tempering water cooling only low pressure section, water volume 6000 m 3 / h, roller speed 18 m / min. Example 4

[0020] The production method of high Ni super high strength high toughness steel plate, the thickness of the steel plate is 13 mm, the 220 mm thick continuous casting billet is rolled, the steel plate has the component mass percentage of C=0.05%, Si=0.21%, Mn=0.51%, P=0.006%, S=0.002%, Ni=8.9%, the rest is Fe and inevitable impurities, the key process steps include: 1) Casting: during the casting process, the iron powder is added to the crystallizer at 1.5 kg / min, and the superheat is controlled at 14°C.

[0021] 2) Billet heating and rolling: the billet adopts high temperature short time heating process, the heating temperature is 1251°C, the holding time is 38 min, and the water cooling is performed to 210°C after rolling.

[0022] 3) Heat treatment: the heat treatment adopts quenching + tempering process: the quenching temperature is 800°C, the holding time is 43 min, the water volume of the high pressure section during the quenching process is 8000 m 3 / h, water quantity in low pressure section 10000 m 3 / h, roller speed of quenching machine 9 m / min; during tempering, first holding at 584℃ for 35 min, then heating to 609℃, holding for 17 min, after tempering, water cooling only in low pressure section, water quantity 7000 m 3 / h, roller speed 16 m / min. Example 5

[0023] A method for producing a high-Ni super-high-strength and high-toughness steel plate, the steel plate having a thickness of 24 mm and being rolled from a 220 mm thick continuous casting billet, the steel plate having a composition by mass percentage of C=0.05%, Si=0.28%, Mn=0.61%, P=0.004%, S=0.003%, Ni=8.6%, and the balance being Fe and unavoidable impurities, the key process steps comprising: 1) Casting: During casting, 1.8 kg / min of iron powder is added to the crystallizer, and the superheat is controlled to be 10℃.

[0024] 2) Billet heating and rolling: The billet is heated using a high-temperature short-time heating process, the heating temperature is 1247℃, and the holding time is 31 min, and after rolling, the water cooling temperature is 209℃.

[0025] 3) Heat treatment: The heat treatment adopts a quenching + tempering process: the quenching temperature is 799℃, the holding time is 54 min, and during quenching, the water quantity in high pressure section is 6000 m 3 / h, water quantity in low pressure section 9000 m 3 / h, roller speed of quenching machine 11 m / min; during tempering, first holding at 594℃ for 41 min, then heating to 617℃, holding for 14 min, after tempering, water cooling only in low pressure section, water quantity 6000 m 3 / h, roller speed 17 m / min.

[0026] The detection results of the surface quality and mechanical properties of the steel plate of the example are shown in Table 1.

[0027] Table 1: Detection results of surface quality and mechanical properties of steel plate of example .

[0028] The steel plate produced in the above example is executed according to the standard EN10028-4-2014. After hot forming and quenching and tempering treatment, the yield strength is 650-690 MPa, the tensile strength is 750-820 MPa, and the average impact energy at -196℃ is ≥120 J.

Claims

1. A method for producing a high-Ni ultrahigh-strength high-toughness steel sheet, characterized by comprising: The steel has a chemical composition by mass percent of C=0.03-0.05%, Si=0.10-0.35%, Mn=0.50-0.70%, P≤0.008%, S≤0.005%, Ni=8.6-9.0%, and the balance of Fe and unavoidable impurities; a 180-220 mm thick continuous casting billet is used to produce a 10-30 mm thick steel plate; the steel plate has a tensile strength of 760-820 MPa, a yield strength of 650-690 MPa, and an impact energy at -196 ℃ of ≥120 J; Key process steps include: ​ 1) Casting: during casting, 1-2 kg / min of iron powder is added to the crystallizer, and the superheat is controlled to be 5-15 ℃; 2) Billet heating and rolling: the billet is heated using a high-temperature short-time heating process, the heating temperature is 1240-1260 ℃, the holding time is 20-40 min, and the billet is water cooled to below 350 ℃ after rolling; 3) Heat treatment: Quenching and tempering process is adopted. The quenching temperature is 780-820℃, the holding time is 40-60min, and the water flow rate in the high-pressure section during quenching is 5000-9000m³. 3 / h, low-pressure section water volume 7000~12000m³ 3 The quenching machine roller speed is 8–16 m / min; during tempering, it is first held at 580–600℃ for 30–50 min, then heated to 600–620℃ and held for 10–20 min. After tempering, water cooling is only applied to the low-pressure section, with a water flow rate of 4000–8000 m³ / h. 3 / h, roller speed 15~20m / min.