FH47 marine steel plate resistant to bauschinger effect and manufacturing method thereof

Abstract

The present application relates to the technical field of marine steel plate resistant to Bauschinger effect, in particular to a kind of marine steel plate resistant to Bauschinger effect FH47 and manufacturing method thereof.Ni~Cu~Sn~Nb~V multi-component microalloying composition system is used, combined with casting machine heavy pressing, multi-directional forging, multi-stage gradient heating and two-stage controlled rolling and controlled cooling process, high-performance marine steel plate with excellent resistance to Bauschinger effect is developed.The yield strength attenuation rate of the steel plate is less than or equal to 15% under the condition of 2% residual strain, the resistance to Bauschinger effect is excellent, the uniform elongation is greater than or equal to 10%, and the comprehensive mechanical properties are significantly improved.The yield strength of the steel plate after controlled cooling treatment is greater than or equal to 460MPa, the tensile strength is 540~720MPa, the elongation is greater than or equal to 26%, and the core transverse charpy impact energy at-60 DEG C is greater than or equal to 150J.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of a Bauschinger effect resistant marine steel plate, in particular to a Bauschinger effect resistant FH47 marine steel plate and a manufacturing method thereof. BACKGROUND

[0002] Since the 21st century, with the development of Arctic resources and the growth of shipping demand, the development of polar marine and Arctic routes has continued to heat up, which has put forward higher requirements for ships and marine equipment. Under this background, the research and development of marine steel materials for extreme environments has become a focus of the industry, and related technologies are developing towards high frost resistance, corrosion resistance and Bauschinger effect resistance.

[0003] Current research and development of marine steel mainly focuses on three technical directions: first, micro-alloying technology, which improves the Bauschinger effect resistance and marine environment corrosion resistance of the material by adding trace alloying elements; second, innovative rolling process, which improves the low-temperature toughness and fatigue resistance of the steel by adjusting the organization; and third, optimization of heat treatment process, which improves the comprehensive performance by combining quenching and tempering processes. In addition, emerging technologies such as ultrasonic surface modification also provide new ways for performance improvement.

[0004] Although existing marine steels can meet most of the requirements, special steels with lower ductile-brittle transition temperature, better Bauschinger effect resistance and corrosion resistance are still the focus of research and development in various countries. The development of such high-strength steels faces challenges such as strict production processes, high equipment requirements and difficult development.

[0005] The Chinese patent application with publication number CN202311553244.8, "Production method of super-thick low-carbon equivalent high-strength low-temperature steel Q500F", proposes a low-C, low-Mn, low-alloy quenched and tempered super-thick steel plate. It uses a low-carbon equivalent chemical composition super-thick steel ingot to produce a 255mm super-thick steel plate, and combines quenching and tempering processes. It belongs to a low-cost quenched and tempered steel alloy composition system. Due to the low alloy cost, the core low-temperature toughness cannot be guaranteed. The 255mm steel plate rolling process is simple, and the deformation cannot penetrate to the core of the steel plate. It is also difficult to achieve excellent Bauschinger effect resistance while meeting the requirements of low-temperature toughness at -60℃. The Chinese patent application with publication number CN202010386014.7, "Composite blank rolling large thickness 500MPa grade high Z-direction layered performance low-temperature container steel plate and manufacturing method thereof", proposes a composite blank production of large thickness super high strength steel plate. High C and low Ni, Nb, V and other alloying elements are added to the composition. The purpose of using large thickness composite blank rolling steel plate is to use lower cost to ensure that the super-thick steel plate has excellent mechanical properties in a -40℃ environment, but this alloy system and production process is difficult to produce super-thick steel plates suitable for -60℃ polar environment and with excellent Bauschinger effect resistance. SUMMARY

[0006] In order to overcome the prior art, the present application provides a FH47 marine steel plate resistant to Bauschinger effect and a manufacturing method thereof, the steel plate with a maximum thickness of 120 mm is suitable for extremely cold marine environment at-60 DEG C and has excellent Bauschinger effect resistance.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A FH47 marine steel plate resistant to Bauschinger effect is composed of the following chemical components with weight percentage:

[0009] C: 0.065%~0.095%, Si: 0.25%~0.45%, Mn: 1.5%~2.0%, P≤0.02%, S≤0.01%, Als: 0.015%~0.045%, Ni: 0.7%~1.0%, Cu: 0.22%~0.5%, Sn: 0.02%~0.1%, Nb: 0.01%~0.02%, V: 0.01%~0.03%, Ti: 0.005%~0.015%, N: 0.002%~0.004%, and the rest is Fe and inevitable impurities.

[0010] The role of selecting the above alloy element types and contents is:

[0011] 1. C is a basic strengthening element in steel, and the increase of C element in the present application can refine the grain by forming carbide, thereby improving the yield point and tensile strength of the steel plate. Too low C content will reduce the grain refinement effect, and too high C content will produce a large amount of hardened structure, significantly reducing the plasticity, toughness, welding performance and Bauschinger effect resistance of the steel plate, so the C content in the steel should be accurately controlled. Therefore, the C content is accurately controlled to be 0.065%~0.095% in the present application.

[0012] 2. Si can improve the strength of the steel plate, and Si can be used as a deoxidizer and a reducing agent in the steelmaking process. When the Si content is greater than 0.45%, hard phase will appear in the structure, affecting the Bauschinger effect resistance, and too much Si should not be added. Therefore, the Si content is accurately controlled to be 0.25%~0.45% in the present application.

[0013] 3. Mn element can be largely dissolved in Fe matrix to improve the strength of the steel plate. Mn combines with S to form MnS, avoiding the formation of FeS at the grain boundary to cause hot cracking. The present application adopts a heavy pressing method to prepare continuous casting billets, and the billet core Mn segregation and columnar crystal are broken by forging method. This method can avoid the composition segregation caused by high Mn content in the billet core, so that the core of the thick plate has high low-temperature toughness and Bauschinger effect resistance. Therefore, the Mn content is accurately controlled to be 1.5%~2.0% in the present application.

[0014] 4. P and S elements have no benefit to the mechanical properties of steel plates, especially elongation. P should be controlled to ≤0.02% and S to ≤0.01%.

[0015] 5. Al is the main deoxidizing element in steel. Simultaneously, Al reacts with metal ions in steel to mitigate corrosion fatigue and improve the fatigue performance of the steel plate. When the Al content is too low, the deoxidation effect is poor; thicker ultra-high-strength steel plates require a more appropriate increase in the Al content. Conversely, excessive Al content leads to the formation of large inclusions, resulting in reduced toughness and resistance to the Bauschinger effect. Therefore, this invention precisely controls the Al content between 0.015% and 0.045%.

[0016] 6. The role of Ni is to improve the toughness and hot workability of steel plates. A large addition can achieve a lower ductile-brittle transition temperature and improve the uniform elongation during tensile testing. Simultaneously, Ni can work synergistically with elements such as Cu and Sn to reduce the reactive forces caused by dislocation concentration during plastic deformation of the steel plate while ensuring strength, thereby reducing the Bauschinger effect. Ni also has a certain degree of corrosion resistance. Therefore, this invention precisely controls the Ni content to 0.7%~1.0%.

[0017] 7. Cu in steel can improve the wear resistance and resistance to the Bauschinger effect of steel plates. A certain amount of Cu exists in the matrix as a nanoscale phase, working together with Ni and Sn to replace dislocation strengthening through precipitation strengthening and grain refinement, reducing the back stress caused by dislocation pile-up during plastic deformation and improving the Bauschinger effect resistance of the steel plate. However, excessive Cu can lead to high-temperature thermal cracking of the steel plate. Therefore, this invention precisely controls the Cu content to 0.22%~0.5%.

[0018] 8. Sn is an important element in the steel plate of this invention. It can work together with Ni and Cu to dissolve in the matrix, improving the hardness and strength while reducing the work hardening of the steel plate. This gives the steel plate both high yield strength and uniform plastic deformation. The reverse stress caused by dislocation pile-up is reduced, improving the steel plate's resistance to the Bauschinger effect. However, excessive Sn content can lead to temper brittleness and reduce low-temperature toughness. Therefore, this invention precisely controls the Sn content to be between 0.02% and 0.1%.

[0019] 9. Nitrogen (Nb) can effectively refine the grain size of steel, thereby improving the balance between strength and toughness. The addition of Nb can effectively improve rolling efficiency and reduce the rolling compression ratio of steel plates. Simultaneously, Nb can prevent intergranular corrosion in steel plates, extending the service life of steel plates for extremely cold marine environments. However, excessive carbide particles generated by Nb can also increase the Bauschinger effect in steel plates. Therefore, this invention precisely controls the Nb content to 0.01%~0.02%.

[0020] 10. V can improve the strength, low-temperature toughness, and resistance to the Bauschinger effect of steel plates by refining grain size. However, excessive V addition has no significant effect on improving the low-temperature toughness of steel plates. On the contrary, excessive precipitation of carbonitrides can cause dislocation pile-up during plastic deformation, resulting in a severe Bauschinger effect. Therefore, this invention precisely controls the V content to 0.01%~0.03%.

[0021] 11. Ti can form Ti(C,N) particles in the matrix, which can refine and strengthen the grains. At the same time, adding an appropriate amount of Ti to steel can improve the strength and low-temperature toughness of the steel plate. Therefore, this invention precisely controls the Ti content to 0.005%~0.015%.

[0022] 12. Nitrogen (N) in steel can improve the strength and hardness of steel plates, reduce their susceptibility to cracking, and extend their service life under plastic deformation conditions. Therefore, this invention precisely controls the N content to be between 0.002% and 0.004%.

[0023] The aforementioned FH47 marine steel plate with resistance to the Bauschinger effect has a maximum thickness of 120mm, a yield strength ≥460MPa, a tensile strength of 540~720MPa, an elongation ≥26%, a Charpy impact energy of -60℃ in the core of the steel plate ≥150J, a yield strength reduction of ≤15% at 2% residual strain, excellent resistance to the Bauschinger effect, and a uniform elongation ≥10%.

[0024] The microstructure at 1 / 4 of the steel plate thickness consists of 45%~55% acicular ferrite and 30%~40% granular bainite, with an effective grain size of 2~10μm.

[0025] The aforementioned manufacturing method for FH47 marine engineering steel plate resistant to the Bauschinger effect employs a high-cleanliness and alloying smelting + continuous casting under heavy pressure + forging + multi-stage heating + double rolling + controlled cooling process. The specific steps of this manufacturing method are as follows:

[0026] 1. Steel refining:

[0027] The molten steel is refined through a converter, LF furnace, RH or VD furnace to further reduce the content of P, S and non-metallic inclusions.

[0028] 2. Continuous casting:

[0029] Under heavy pressure from two sets of compression rollers in the solidification liquid phase zone of the billet core, each compression roller compresses ≥8mm, with a total compression ≥16mm. The purpose of this heavy pressure on the casting machine is to squeeze the segregated liquid phase in the billet core into the subsequently solidified molten pool, thereby promoting the densification and refinement of the as-cast microstructure in the billet core, eliminating segregation in the core of extra-thick plate billets, and preparing the microstructure for subsequent forging and rolling.

[0030] 3. Forging:

[0031] The blank forging cogging adopts compression in two directions of width and thickness, and the total compression ratio is 40% to 50%, the edge and corner cracks are removed by oxygen blowing, and each of the upper and lower surfaces is ground by 1 to 5 mm. During the forging process, the blank is plastically deformed under the action of the water pressure machine, which helps to break the brittle shell of the primary crystal and columnar crystal, makes the structure more dense, and the two-direction forging deformation can eliminate the anisotropy of the rolled steel plate to a certain extent, which is beneficial to eliminating the Bauschinger effect caused by the subsequent plastic deformation of the steel plate.

[0032] 4. Rolling:

[0033] The blank is loaded into the heating furnace at a furnace temperature of 600 to 700 DEG C, and the purpose is to keep the thickness direction temperature of the blank consistent in the low temperature stage, and to prepare for the uniform structure in the high temperature stage. Subsequently, the heating rate of the steel plate is controlled at 5 to 8 DEG C / min, so as to avoid uneven heating of the blank caused by too fast heating. The heating temperature is 1050 to 1100 DEG C, the soaking temperature is 1070 to 1120 DEG C, and the soaking time is 60 to 90 min. If the soaking time is too long, a large number of carbonitride particles will be formed in the blank, which will reduce the reverse stress caused by dislocation pile-up when the steel plate is plastically deformed, and improve the Bauschinger effect resistance of the steel plate. Therefore, the soaking time during heating should be avoided to be too long.

[0034] The first rolling cogging temperature is 950 to 1050 DEG C, and the single pass reduction is greater than or equal to 30 mm. The thickness of the first rolled steel plate is 1.5 to 2 times the thickness of the finished product. The purpose of the first rolling is to increase the single pass rolling reduction as much as possible in the stage with low deformation resistance, and to improve the as-cast structure of the slab. The large deformation is rapidly penetrated into the core of the blank, and the core structure and the Bauschinger effect resistance are improved.

[0035] The second blank heating temperature is 800 to 900 DEG C, and the total heating time is 3 to 5 h. The second rolling cogging temperature is 700 to 800 DEG C, and the final rolling temperature is less than or equal to 700 DEG C. Low temperature rolling can effectively improve the internal deformation energy storage of the steel plate, increase the grain boundary area, refine the grains, replace the precipitation strengthening, and improve the strength and low temperature toughness of the steel plate, while improving the Bauschinger effect resistance.

[0036] 5. Controlled cooling:

[0037] The water inlet temperature is 600 to 650 DEG C, and the red temperature is 330 to 430 DEG C. The purpose of the controlled cooling process is to avoid the formation of a large number of carbonitride particles, reduce the reverse stress caused by dislocation pile-up, and improve the Bauschinger effect resistance of the steel plate.

[0038] Compared with the prior art, the beneficial effects of the present application are:

[0039] 1. The present application improves the toughness and hot workability of the steel plate by adding Ni, obtains a lower ductile-to-brittle transition temperature by adding a large amount, improves the uniform elongation during tensile process, and the Cu element in a certain content exists in the matrix in the form of nano-scale phase, which, together with Ni and Sn elements, replaces dislocation strengthening by precipitation strengthening and fine-grain strengthening, reduces the back stress caused by dislocation pile-up during plastic deformation of the steel plate, and the Sn element, together with Ni and Cu elements, is dissolved in the matrix to improve the strength and hardness, while reducing the work hardening degree of the steel plate, so that the steel plate has high yield strength and can uniformly deform plastically, and the resistance to Bauschinger effect performance of the steel plate is improved. The addition of Nb effectively refines the grain size of the steel, and the balance between strength and toughness of the steel is improved by the way of grain refinement. The addition of Nb element effectively improves the rolling efficiency and reduces the rolling compression ratio of the steel plate. At the same time, Nb element can organize the occurrence of intergranular corrosion of the steel plate, and improve the service life of the steel plate in extremely cold marine environment.

[0040] 2. The present application implements heavy pressing on the two compression rollers in the solidification liquid phase zone of the core of the casting blank, each compression roller compresses ≥8mm, and the total compression amount is ≥16mm. The purpose of heavy pressing of the casting machine is to extrude the liquid phase of the segregation in the core of the blank to the subsequent solidification pool, promote the as-cast structure of the core of the blank to be dense and refined, eliminate the segregation in the core of the thick plate blank, and make good organizational preparation for subsequent forging and rolling.

[0041] 3. The present application adopts width and thickness compression in the forging and blooming of the casting blank, the total compression ratio is 40%~50%, the edge and corner cracks are removed by blowing oxygen, and the upper and lower surfaces are each polished by 1~5mm. During the forging process, the blank occurs plastic deformation under the action of the hydraulic press, which helps to break the brittle shell of the primary crystal and columnar crystal, makes the structure more dense, and the two-direction forging deformation can eliminate the anisotropy of the rolled steel plate to a certain extent, which is beneficial to eliminate the Bauschinger effect brought by the subsequent plastic deformation of the steel plate.

[0042] 4. The present application controls the soaking time to be 60~90min. Avoiding a large number of carbonitride particles formed in the blank, these large particles will cause dislocation pile-up and reduce the back stress during the subsequent plastic deformation of the steel plate, and improve the resistance to Bauschinger effect of the steel plate.

[0043] 5. The first rolling of the present application aims to increase the single pass rolling reduction rate as much as possible in the stage of low deformation resistance, and improve the as-cast structure of the slab. The large deformation amount is rapidly penetrated into the core of the blank, and the core structure and the resistance to Bauschinger effect performance are improved. The second rolling adopts low temperature rolling, which effectively improves the internal deformation energy storage of the steel plate, increases the grain boundary area of the small and flat grains, refines the grains, replaces the precipitation strengthening, improves the strength and low temperature toughness of the steel plate, and improves the resistance to Bauschinger effect performance.

[0044] 6、The application controls the water inlet temperature to be 600-650 DEG C, and the red temperature to be 330-430 DEG C, avoids forming a large number of carbon-nitrogenized particles, reduces the reverse stress caused by dislocation accumulation, and improves the steel plate resistance to Bauschinger effect.

[0045] In summary, the application innovatively adopts a Ni-Cu-Sn-Nb-V multi-component micro-alloying component system, combines a caster heavy pressing, multi-directional forging, multi-stage gradient heating and two-stage controlled rolling and controlled cooling process, and develops a high-performance offshore steel plate with excellent resistance to Bauschinger effect. The yield strength attenuation rate of the steel plate under 2% residual strain is less than or equal to 15%, the resistance to Bauschinger effect is excellent, the uniform elongation is greater than or equal to 10%, and the comprehensive mechanical properties are significantly improved.

[0046] The innovative alloy component system of the application can ensure that the yield strength of the steel plate after controlled cooling treatment is greater than or equal to 460 MPa, the tensile strength is 540-720 MPa, the elongation is greater than or equal to 26%, and the core transverse Charpy impact energy at-60 DEG C is greater than or equal to 150 J. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a metallographic structure diagram of embodiment 1 of the application. DETAILED DESCRIPTION

[0048] The application discloses an FH47 offshore steel plate with resistance to Bauschinger effect and a manufacturing method thereof. Those skilled in the art can refer to the content herein, and appropriately improve process parameters to realize. It is particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are regarded as being included in the application. The method and application of the application have been described through preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the method and application described herein without departing from the content, spirit and scope of the application, to realize and apply the technical field of the application.

[0049] The steel chemical components of the embodiment of the application are shown in Table 1, the continuous casting and forging process of the embodiment of the application is shown in Table 2, the rolling and controlled cooling process of the embodiment of the application is shown in Table 3, and the mechanical properties of the steel plate of the embodiment of the application are shown in Table 4.

[0050] Table 1 Steel chemical components (wt%) of the embodiment of the application

[0051]

[0052] Table 2 Continuous casting and forging process of the embodiment of the application

[0053]

[0054] Table 3 Rolling and controlled cooling process of the embodiment of the application

[0055]

[0056] Table 4 Mechanical properties of steel plates in embodiments of the present invention

[0057]

[0058] like Figure 1 As shown, the metallographic structure of Example 1 has a structure of 45%~55% acicular ferrite + 30%~40% granular bainite at 1 / 4 of the steel plate thickness, with an effective grain size of 2~10μm and good mechanical properties.

[0059] This invention innovatively employs a Ni~Cu~Sn~Nb~V multi-component microalloying system, combined with heavy casting pressure, multi-directional forging, multi-stage gradient heating, and two-stage controlled rolling and cooling processes, to develop a high-performance marine engineering steel plate with excellent resistance to the Bauschinger effect. This steel plate exhibits a yield strength attenuation rate ≤15% under 2% residual strain conditions, excellent resistance to the Bauschinger effect, uniform elongation ≥10%, and significantly improved comprehensive mechanical properties.

[0060] The innovative alloy composition system of this invention can guarantee that the yield strength of the steel plate after controlled cooling treatment is ≥460MPa, the tensile strength is 540~720MPa, the elongation is ≥26%, and the transverse Charpy impact energy of the core at -60℃ is ≥150J.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A FH47 marine steel plate resistant to Bauschinger effect, characterized in that, consists of the following chemical components by weight percentage: C: 0.065%~0.095%, Si: 0.25%~0.45%, Mn: 1.5%~2.0%, P≤0.02%, S≤0.01%, Als: 0.015%~0.045%, Ni: 0.7%~1.0%, Cu: 0.22%~0.5%, Sn: 0.02%~0.1%, Nb: 0.01%~0.02%, V: 0.01%~0.03%, Ti: 0.005%~0.015%, N: 0.002%~0.004%, the rest being Fe and unavoidable impurities; The maximum thickness of the finished steel plate is 120mm, the yield strength is ≥460MPa, the tensile strength is 540~720MPa, the elongation is ≥26%, and the Charpy impact energy of the core of the steel plate at -60℃ is ≥150J; The yield strength reduction of the steel plate at 2% residual strain is ≤15%, and the uniform elongation is ≥10%; The microstructure at the thickness of 1 / 4 of the steel plate is 45%~55% acicular ferrite + 30%~40% granular bainite, and the effective grain size is 2~10μm.

2. The method of manufacturing the FH47 marine steel plate resistant to the Bauschinger effect according to claim 1, characterized by, The manufacturing method specifically comprises the following steps: 1) steel refining; 2) continuous casting: The two sets of compression rollers in the solidification liquid phase zone of the core of the casting blank are subjected to heavy compression, each compression roller is compressed by ≥8mm, and the total compression amount is ≥16mm; 3) forging: The width and thickness of the casting blank are compressed during the cogging, and the total compression ratio is 40%~50%; 4) rolling: The first rolling opening temperature is 950~1050℃, the single pass reduction is ≥30mm, and the thickness of the first rolled steel plate is 1.5~2 times the thickness of the finished product; The second blank heating temperature is 800~900℃, the total heating time is 3~5 hours, the second rolling opening temperature is 700~800℃, and the final rolling temperature is ≤700℃; 5) controlled cooling: The water entry temperature is 600~650℃, and the re-red temperature is 330~430℃.

3. The manufacturing method of the FH47 offshore steel plate resistant to Bauschinger effect according to claim 2, wherein, 1) the molten steel is refined by a converter, an LF furnace, an RH or a VD furnace.

4. The manufacturing method of the FH47 offshore steel plate resistant to Bauschinger effect according to claim 2, wherein, 3) the blank corner cracks are removed by oxygen blowing, and the upper and lower surfaces are each ground by 1~5mm.

5. The manufacturing method of the FH47 offshore steel plate resistant to Bauschinger effect according to claim 2, wherein, 4) the blank is loaded into the heating furnace when the furnace temperature is 600~700℃, and the blank is kept for 20~45min or more.

6. The manufacturing method of the FH47 offshore steel plate resistant to Bauschinger effect according to claim 5, wherein, then the steel plate is heated at a rate of 5~8℃ / min, the heating temperature is 1050~1100℃, the soaking temperature is 1070~1120℃, and the soaking time is 60~90min.

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