420 mpa-class high-toughness high-strength steel for ship plate having crack propagation resistance in ultra-low temperature environment and manufacturing method therefor

Abstract

The present invention relates to the technical field of steel production, and disclosed are a 420 MPa-class high-toughness high-strength steel for ship plate having crack propagation resistance in an ultra-low temperature environment and a manufacturing method therefor. The steel comprises the following chemical components in percentage by mass: C: 0.03-0.07%, Si: 0.10-0.30%, Mn: 1.25-1.40%, P≤0.012%, S≤0.003%, Nb: 0.025-0.040%, Ni: 0.20-0.35%, Alt: 0.020-0.050%, Mo≤0.05%, N≤60 ppm, H≤2 ppm, impurity elements: Ca≤0.0050%, B≤0.005%, and the balance being Fe and inevitable impurities. In the present invention, by means of a low-C composition design, and low-temperature heating, TMCP controlled rolling, and controlled cooling processes, a uniform microstructure across an entire full-thickness section of a steel plate, ultra-fine grains, good low-temperature toughness, and strong low-temperature crack propagation resistance are achieved, satisfying the requirements of large ships in special low-temperature sea areas for the steel.

Description

A high-toughness, high-strength ship plate steel with 420MPa grade and resistance to crack propagation in ultra-low temperature environments, and its manufacturing method. Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a high-toughness, high-strength ship plate steel with 420MPa grade and resistance to crack propagation in ultra-low temperature environments, and its manufacturing method. Background Technology

[0002] With the continuous development of polar resources and shipping routes, the development of high-strength ships for ultra-low temperature environments in polar regions has become particularly urgent. Currently, the low-temperature toughness of 420MPa grade high-strength ship steel produced by major steel companies for ultra-low temperature environments is mainly at -60℃, without requirements for crack propagation resistance. This cannot meet the needs of ship steel for low-temperature toughness and crack propagation resistance in special environments. Therefore, the development of a 420MPa grade high-strength ship plate with crack propagation resistance for ultra-low temperature environments is of great significance.

[0003] A search was conducted on relevant patents. Patent 1 (201910365883.9) discloses a low-temperature, high-toughness cerium composite-treated FH40 ship plate steel and its preparation method. The steel plate of this invention has a yield strength ≥435MPa, tensile strength ≥530MPa, elongation ≥22.4%, and impact energy ≥244J at -60℃; however, it cannot meet the requirements for low-temperature impact at -80℃ and CTOD at -60℃, and its thickness is only 16-26mm, which cannot meet the requirements for large thickness specifications. Patent 2 (201310730193.1) discloses a high-strength FH40 marine engineering steel plate and its production method. The steel plate of this invention has a yield strength of 420-440MPa, tensile strength of 530-580MPa, and elongation of only 22-24%; its V-shaped impact energy at -60℃ is only 180-240J; it cannot meet the requirements for low-temperature impact at -80℃ and CTOD at -60℃. Patent 3 202110392459.0 discloses a thick FH40 shipbuilding steel plate with good aging impact toughness and its manufacturing method. The steel plate has a yield strength ≥400MPa, tensile strength ≥550MPa, Z-direction properties ≥70%, and aging impact energy ≥160J at -60℃. However, it cannot meet the requirements for low-temperature impact at -80℃ and CTOD value at -60℃, and therefore cannot meet the needs of steel for ships in ultra-low temperature environments. Patent 4201710086846.5 discloses a steel plate for polar ships and its manufacturing method. The steel plate has an impact energy ≥200J in a low-temperature environment of -60℃ to -80℃, a CTOD fracture toughness value ≥0.25mm at -60℃, a yield strength ≥315MPa, and a tensile strength ≥510MPa. However, the yield strength of this patent cannot meet the requirement of 420MPa high-strength ship plates, and the CTOD value at -60℃ is low, which cannot meet the requirements for crack propagation resistance in special environments. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a high-toughness and high-strength ship plate steel with resistance to crack propagation in ultra-low temperature environment of 420MPa and its manufacturing method.

[0005] To solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A high-toughness, high-strength ship plate steel with 420MPa grade and resistance to crack propagation in ultra-low temperature environments has the following chemical composition and mass percentage: C: 0.03-0.07%, Si: 0.10-0.30%, Mn: 1.25-1.40%, P≤0.012%, S≤0.003%, Nb: 0.025-0.040%, Ni: 0.20-0.35%, Alt: 0.020-0.050%, Mo≤0.05%, N≤60ppm, H≤2ppm, and impurity elements: Ca≤0.0050%, B≤0.005%, with the remainder being Fe and unavoidable impurities.

[0007] The present invention also provides a method for manufacturing high-toughness and high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance, which includes the following steps in sequence: low temperature heating, TMCP controlled rolling, and controlled cooling.

[0008] As a preferred embodiment of the manufacturing method of the high toughness and high strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance described in this invention, wherein: in the low temperature heating process, the billet heating temperature is 1130℃~1180℃.

[0009] As a preferred embodiment of the manufacturing method of the high-toughness and high-strength ship plate steel with anti-crack propagation in ultra-low temperature environment of 420MPa grade according to the present invention, in the TMCP controlled rolling process, the cumulative reduction rate of the last three passes of rough rolling of steel plate is ≥30%, the thickness of the steel plate in the second stage of drying is ≥2h, where h is the thickness of the finished steel plate, the initial rolling temperature is 780℃~830℃, the single-pass reduction rate of the first three passes of finishing rolling is ≥10%, and the water immersion temperature is 760℃~810℃.

[0010] As a preferred embodiment of the manufacturing method of the high toughness and high strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance described in this invention, wherein: in the controlled rolling process, the steel plate red-hot temperature is 450~620℃, and the cooling rate is 5~8℃ / s.

[0011] As a preferred embodiment of the manufacturing method of the high-toughness and high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance described in this invention, the steel plate obtained has a yield strength ≥420MPa, a tensile strength of 520-680MPa, an elongation ≥25%, an impact strength of ≥200J at -80℃, a yield strength ratio ≤0.85, and a CTOD value of ≥0.60mm at -60℃.

[0012] As a preferred embodiment of the manufacturing method of the high-toughness and high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance described in this invention, the thickness of the steel plate obtained is 20-70mm.

[0013] The beneficial effects of this invention are:

[0014] This invention achieves uniform microstructure, ultra-fine grains, good low-temperature toughness, and strong resistance to low-temperature crack propagation across the entire thickness of the steel plate through low-carbon composition design, low-temperature heating, TMCP controlled rolling, and controlled cooling processes. This meets the requirements for steel used in large ships operating in special low-temperature marine environments. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 is a schematic diagram of the near-surface metallographic structure of the 420MPa grade high-strength marine steel resistant to crack propagation in ultra-low temperature environment prepared in Example 3.

[0017] Figure 2 is a schematic diagram of the metallographic structure at 1 / 4 of the thickness of the high-strength marine steel with 420MPa-grade ultra-low temperature environment crack propagation resistance obtained in Example 3.

[0018] Figure 3 is a schematic diagram of the metallographic structure at 1 / 2 thickness of the high-strength marine steel with 420MPa-grade ultra-low temperature environment crack propagation resistance obtained in Example 3. Detailed Implementation

[0019] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0020] Example 1: This example provides a high-strength marine steel with a thickness of 20mm and resistance to crack propagation in ultra-low temperature environments of 420MPa grade. Its chemical composition and mass percentage are shown in Table 1.

[0021] This embodiment also provides a method for manufacturing high-strength marine steel with resistance to crack propagation in ultra-low temperature environments of 420MPa. During smelting, LF and RH refining technologies are used to ensure that the gaseous H content of the steel plate is 1.2ppm and the N content is 50ppm.

[0022] Furthermore, the manufacturing method of high-strength marine steel with 420MPa grade ultra-low temperature environment crack propagation resistance provided in this embodiment includes low temperature heating, TMCP controlled rolling, and controlled cooling processes. The specific process steps are as follows:

[0023] (1) Low temperature heating process: 260mm cross section billet is used, the billet is heated at 1180℃ for 300min to ensure alloy solid solution, while avoiding the length of billet grains and ensuring that the overall grains of the billet are relatively uniform.

[0024] (2) TMCP controlled rolling process: The cumulative reduction of the last three passes of rough rolling is 35%; the thickness of the steel billet in the second stage of drying is 60mm, the initial rolling temperature is 830℃, the reduction rate of the first three passes is 12%, 12%, and 10%, and the water immersion temperature is 810℃. By achieving a large reduction rate in the last three passes of rough rolling, the deformation of the billet penetrates to the core. By increasing the drying thickness and precisely controlling the initial rolling temperature and single-pass reduction rate of finishing rolling, more distortion zones are formed, providing more nucleation points for microstructure transformation.

[0025] (3) Controlled cooling process: The red-hot temperature of the steel plate is limited to 620℃, and the cooling rate is 3℃ / s. By using an appropriate cooling rate, the formation of martensitic hard structures on the surface is avoided, and precise control of the microstructure and properties of the steel plate throughout its thickness is achieved.

[0026] The mechanical properties of the 20mm thick, 420MPa grade high-strength marine steel plate with resistance to crack propagation in ultra-low temperature environments obtained in this implementation are shown in Table 2.

[0027] Example 2: This example provides a high-strength marine steel with a thickness of 40mm and resistance to crack propagation in ultra-low temperature environments of 420MPa grade. Its chemical composition and mass percentage are shown in Table 1.

[0028] This embodiment also provides a method for manufacturing high-strength marine steel with resistance to crack propagation in ultra-low temperature environments of 420MPa grade. During smelting, LF and RH refining technologies are used to ensure that the gaseous H content of the steel plate is 1.0ppm and the N content is 40ppm.

[0029] Furthermore, the manufacturing method for high-strength marine steel plates with 420MPa-grade ultra-low temperature environment crack propagation resistance provided in this embodiment includes low-temperature heating, TMCP controlled rolling, and controlled cooling processes. The specific process steps are as follows:

[0030] (1) Low temperature heating process: 370mm cross section billet is used, the billet is heated at 1150℃ for 400min to ensure alloy solid solution, while avoiding the length of billet grains and ensuring that the overall grains of the billet are relatively uniform.

[0031] (2) Rolling process: TMCP controlled rolling process: The cumulative reduction of the last three passes of rough rolling is 32%; the thickness of the steel plate in the second stage of drying is 90mm, the initial rolling temperature is 810℃, the reduction rate of the first three passes is 13%, 12%, and 11%, and the water immersion temperature is 800℃. By achieving a large reduction rate in the last three passes of rough rolling, the deformation of the billet penetrates to the core. By increasing the drying thickness and precisely controlling the initial rolling temperature and single-pass reduction rate of finishing rolling, more distortion zones are formed, providing more nucleation points for microstructure transformation.

[0032] (3) Controlled cooling process: The red-hot temperature of the steel plate is limited to 580℃, and the cooling rate is 4℃ / s. By using an appropriate cooling rate, the formation of martensitic hard structures on the surface is avoided, and precise control of the microstructure and properties of the steel plate throughout its thickness is achieved.

[0033] The mechanical properties of the 40mm thick, 420MPa grade high-strength marine steel plate with resistance to crack propagation in ultra-low temperature environments obtained in this implementation are shown in Table 2.

[0034] Example 3: This example provides a high-strength marine steel with a thickness of 70 mm and resistance to crack propagation in ultra-low temperature environments of 420 MPa. Its chemical composition and mass percentage are shown in Table 1.

[0035] This embodiment also provides a method for manufacturing high-strength marine steel with resistance to crack propagation in ultra-low temperature environments of 420MPa grade. During smelting, LF and RH refining technologies are used to ensure that the gaseous H content of the steel plate is 0.8ppm and the N content is 38ppm.

[0036] Furthermore, the manufacturing method for high-strength marine steel plates with 420MPa-grade ultra-low temperature environment crack propagation resistance provided in this embodiment includes heating, TMCP controlled rolling, and controlled cooling processes. The specific process steps are as follows:

[0037] (1) Heating process: 370mm cross section billet is used, the billet heating temperature is 1130℃, and the heating time is 420min.

[0038] (2) Rolling process: TMCP controlled rolling process: the cumulative reduction of the last three passes of rough rolling of steel plate is 35%; the thickness of the steel in the second stage of drying is 150mm, the initial rolling temperature is 770℃, the reduction rate of the first three passes is 12%, 12%, and 10%, and the water temperature is 760℃.

[0039] (3) Controlled cooling process: The reddening temperature of the steel plate is limited to 450℃, and the cooling rate is 6℃ / s.

[0040] The mechanical properties of the 70mm thick, 420MPa grade high-strength marine steel plate with resistance to crack propagation in ultra-low temperature environments obtained in this implementation are shown in Table 2.

[0041] Table 1 Chemical composition of steel plates in Examples 1-3 (wt%)

[0042] Table 2. Mechanical property data of steel plates from Examples 1-3

[0043] It should be noted that the tensile test specimens for 20mm and 40mm thick steel plates are full-thickness rectangular tensile test specimens.

[0044] Therefore, the technical solution of this application achieves uniform microstructure, ultra-fine grains, good low-temperature toughness, and strong resistance to low-temperature crack propagation across the entire thickness of the steel plate through low-carbon composition design, low-temperature heating, TMCP controlled rolling, and controlled cooling processes, thus meeting the requirements for steel used in large ships in special low-temperature marine environments.

[0045] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A high-toughness, high-strength ship plate steel with 420MPa grade and resistance to crack propagation in ultra-low temperature environments, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.03~0.07%, Si: 0.10~0.30%, Mn: 1.25~1.40%, P≤0.012%, S≤0.003%, Nb: 0.025~0.040%, Ni: 0.20~0.35%, Alt: 0.020~0.050%, Mo≤0.05%, N≤60ppm, H≤2ppm, impurity elements: Ca≤0.0050%, B≤0.005%, the remainder being Fe and unavoidable impurities.

2. A method for manufacturing high-toughness, high-strength ship plate steel with resistance to crack propagation in ultra-low temperature environments as described in claim 1, characterized in that: The process includes the following steps in sequence: low-temperature heating, TMCP controlled rolling, and controlled cooling.

3. The method for manufacturing high-toughness, high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance according to claim 2, characterized in that: In the low-temperature heating process, the billet heating temperature is 1130℃~1180℃.

4. The method for manufacturing high-toughness, high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance according to claim 2, characterized in that: In the TMCP controlled rolling process, the cumulative reduction rate of the last three passes of rough rolling of steel plate is ≥30%, the thickness of the steel plate in the second stage of drying is ≥2h, where h is the thickness of the finished steel plate, the temperature of the initial rolling is 780℃~830℃, the single-pass reduction rate of the first three passes of finishing rolling is ≥10%, and the water temperature is 760℃~810℃.

5. The method for manufacturing high-toughness, high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance according to claim 2, characterized in that: In the controlled rolling process, the steel plate's red-hot temperature is 450–620°C, and the cooling rate is 5–8°C / s.

6. The method for manufacturing high-toughness, high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance according to claim 2, characterized in that: The resulting steel plate has a yield strength ≥420 MPa, a tensile strength of 520-680 MPa, an elongation ≥25%, an impact strength of ≥200 J at -80℃, a yield strength ratio ≤0.85, and a CTOD value of ≥0.60 mm at -60℃.

7. The method for manufacturing high-toughness, high-strength ship plate steel with 420MPa grade ultra-low temperature environment crack propagation resistance according to claim 2, characterized in that: The thickness of the steel plate produced is 20-70 mm.

Images