Marine engineering steel with corrosion resistance to high humidity and high temperature atmosphere and method for manufacturing same

Abstract

The present disclosure relates to a steel for ocean engineering containing the following chemical elements by mass percentage: C: 0.01 - 0.05%, Si: 0.05 - 0.60%, Mn: 0.50 - 1.30%, Cr: 0.6 - 1.20%, Ni: 2.0 - 3.0%, Al: 0.01 - 0.06%, Ti: 0.005 - 0.012%, and Mg: 0.0005 - 0.0015%; 0 < Ca ≤ 0.0045%, 0 < Cu ≤ 0.5%, and 0 < Mo ≤ 0.40%, with the balance being Fe and inevitable impurities. The present disclosure further discloses a manufacturing method of the steel for ocean engineering, comprising the following steps: (1) a smelting and continuous casting step; (2) a heating step; (3) a controlled rolling step where the original austenite grain size after rolling is 20 - 25 μm; (4) an air cooling step; and (5) a quenching and tempering step where the austenite grain size after quenching is 20 - 25 μm. The steel for ocean engineering according to the present disclosure can be applied to ships and ocean engineering structures, and is particularly suitable for high-humidity and high-temperature sea areas.

Description

[Technical field]

[0001] The present disclosure relates to steels and methods of manufacture thereof, in particular to marine engineering steels and methods of manufacture thereof. [Background technology]

[0002] As we all know, the South China Sea contains a great deal of energy and resources, and currently, a great deal of human and material resources are being invested in developing and utilizing these resources.

[0003] The environment of the South China Sea is special. Its high humidity and high temperature environment, accompanied by strong radiation and high chlorine, are prone to cause serious corrosion of steel, leading to saponification and aging of the coating film and causing serious corrosion. - is easily adsorbed on metal surfaces, leading to the occurrence of anodic dissolution and pitting corrosion, which may even cause cracking, and may lead to stress corrosion cracking under the combined action of hydrogen. These problems reduce the mechanical properties and service life of steels for offshore platforms. In addition, because offshore platforms have long service cycles and are far from the coast, regular repair and maintenance are very difficult, so steels for offshore platforms are required to have fairly high corrosion resistance.

[0004] In recent years, as China has gradually exercised its sovereignty over the South China Sea and begun to develop and utilize resources in the South China Sea, it has become urgent to develop corrosion-resistant steel suitable for the high humidity and high temperature marine environment in order to overcome the harsh environment of the South China Sea and meet the construction demand for marine engineering facilities.

[0005] Currently, many steel companies around the world are developing weathering steels that are resistant to atmospheric corrosion and seawater corrosion-resistant steels that are resistant to seawater corrosion, but the applications of these steels are not ideal and they cannot be applied well to high humidity and high temperature marine environments.

[0006] In the production and development process of existing marine engineering steels, the marine atmospheric corrosion resistance of steel plates was not fully considered, and the strength and impact properties of steel were the main considerations. In high humidity and high temperature areas such as the South China Sea, the marine atmospheric corrosion resistance of existing marine engineering steels is not good enough, so the service life of steel plates is not long.

[0007] For example, China Patent Publication No. 106756476(A), entitled "High-Strength Weathering Steel for Highly Humid and Hot Marine Atmospheric Environment and Manufacturing Method Therefor," published on May 31, 2017, discloses a high-strength weathering steel for high humid and hot marine atmospheric environments, which achieves the goal of improving corrosion resistance by increasing the Ni content, adding a very small amount of Cr element, compounding the addition of Mo, Sn, Sb, RE and other trace alloy elements, and refining the grain structure by Nb trace element. The crux of this patent is the use of Sn and Sb to improve the corrosion resistance of the steel plate. However, Sn and Sb are impurity elements that are strictly controlled in structural steels, which obviously have a negative effect on the comprehensive mechanical properties of the steel and adversely affect the safety of marine engineering platforms.

[0008] In another example, China Patent Publication No. 105132832(A), published on December 9, 2015, entitled "Steel Plate Having corrosion resistance to highly humid and hot marine atmosphere, and Manufacturing Method Therefor" discloses a steel plate having corrosion resistance to highly humid and hot marine atmosphere, and a manufacturing method therefor, the steel plate being added with 0.5-0.6% Si, 0.5-0.7% Mn, 0.5-0.6% Cu, 0.5-0.6% Ni, 0.3-0.5% Mo, and a high content of Cr (3.00-3.50%), and a combined addition of Sn (0.20-0.30%) and Sb (0.06-0.10%). This patent has the advantages of significantly improving the corrosion resistance of weathering steel in the severe atmospheric corrosion environment of high humidity and high temperature in the South China Sea, and being relatively low in manufacturing cost, which is economical and practical.

[0009] In another example, China Patent Publication No. 103741056(A), entitled "Corrosion-Resistant Steel Plate for Marine Environment in the South China Sea and Manufacturing Process Therefor," published on April 23, 2014, discloses a corrosion-resistant steel plate for the marine environment of the South China Sea, employing a low carbon composition and adding significant amounts of Si, Mn, Cu, Cr and Ni, as well as some Sn elements. The steel plate has a single-phase polygonal ferrite structure, an average grain size of 10.17 μm, a steel grade yield strength of 355 MPa, a tensile strength of 490-630 MPa, and a Charpy impact energy at -40°C of more than 34 J.

[0010] Considering the shortcomings of the existing technologies mentioned above, it is expected to obtain a new marine engineering steel that not only has excellent toughness, but also has excellent fracture and crack resistance properties and corrosion resistance to high humidity and high temperature marine atmosphere. Summary of the Invention [Problem to be solved by the invention]

[0011] One of the objectives of the present disclosure is to provide a steel for ocean engineering that not only has excellent toughness but also has excellent fracture and crack resistance properties and corrosion resistance against high humidity and high temperature marine atmospheres. The steel for ocean engineering of the present disclosure can be used for ships and ocean engineering structures, particularly for the marine atmosphere structural members of ocean engineering structures, can be used in various sea areas, is particularly suitable for high humidity and high temperature sea areas such as the South China Sea, and broad applications are expected.

Means for Solving the Problems

[0012] To achieve the above object, the present disclosure provides a steel for ocean engineering containing the following chemical elements by mass percentage: C: 0.01 to 0.05%, Si: 0.05 to 0.60%, Mn: 0.50 to 1.30%, Cr: 0.6 to 1.20%, Ni: 2.0 to 3.0%, Al: 0.01 to 0.06%, Ti: 0.005 to 0.012%, and Mg: 0.0005 to 0.0015%, 0 < Ca ≤ 0.0045%, 0 < Cu ≤ 0.5%, and 0 < Mo ≤ 0.40%, with the balance being Fe and unavoidable impurities.

[0013] In one embodiment, the mass percentages of the chemical elements in the steel for ocean engineering of the present disclosure are as follows: C: 0.015 to 0.04%, Si: 0.15 to 0.60%, Mn: 0.50 to 1.30%, Cr: 0.6 to 0.90%, Ni: 2.0 to 2.85%, Al: 0.01 to 0.06%, Ti: 0.005 to 0.012%, and Mg: 0.0005 to 0.0015%, 0 < Ca ≤ 0.0045%, 0 < Cu ≤ 0.5%, and 0 < Mo ≤ 0.40%, with the balance being Fe and unavoidable impurities.

[0014] The steel for ocean engineering of the present disclosure has ultra-low C and is designed using a microalloying of Mn, Nb, V, and Ti and a Cr-Ni-Mo-Cu alloying composition system. In the steel for ocean engineering of the present disclosure, the design principles of the chemical elements are specifically described as follows.

[0015] C: The marine engineering steel of the present disclosure adopts an ultra-low carbon design, and not only utilizes the interstitial strengthening effect of carbon to ensure the suitable strength of the steel plate of the present invention, but also effectively prevents excessive carbide precipitation, reduces the potential difference between the matrix and the carbide phase to obtain good corrosion resistance, and at the same time, the steel plate also has good low-temperature toughness and welding performance. Therefore, in the marine engineering steel of the present disclosure, the mass percentage of C is controlled to 0.01-0.05%.

[0016] Si: In the marine engineering steel of the present disclosure, the Si element is a common weak deoxidizing element in steelmaking and has a certain solid solution strengthening effect. - It should be noted that under certain conditions, the Si element forms a composite oxide of FeAlSiO in the rust layer of the steel, filling voids and cracks, thereby playing a role in protecting the steel. For this reason, in the marine engineering steel of the present disclosure, the mass percentage of Si is controlled to 0.05-0.60%.

[0017] Mn: In the marine engineering steel of the present disclosure, Mn is the most basic alloying element of low-alloy high-strength steels, and can improve the strength of the steel by solid solution strengthening and compensate for the strength reduction caused by the reduction in the C element content in the steel. However, it should be noted that the Mn element content in the steel should not be too high. If the Mn element content in the steel is too high, segregation is likely to occur in the center of the steel plate, and the low-temperature toughness of the steel is reduced. For this reason, in the marine engineering steel of the present disclosure, the mass percentage of Mn is controlled to 0.50 to 1.30%.

[0018] Cr: In the marine engineering steel of the present disclosure, Cr element can improve the passivation performance of the steel, promote the formation of a dense oxide film on the steel surface, and is enriched in the inner rust layer, which is easy to refine α-iron oxyhydroxide. However, it should be noted that the Cr element content in the steel should not be too high. Cl - If too much Cr is added in the environment, the corrosion resistance of the steel will be seriously deteriorated in the later stage of corrosion. Therefore, taking into consideration the beneficial and adverse effects of the Cr element comprehensively, the mass percentage of the Cr element in the marine engineering steel of the present disclosure is controlled to 0.6-1.20%.

[0019] Ni: In the marine engineering steel of the present disclosure, Ni element can be infinitely dissolved with the iron base material, and can improve the low-temperature toughness of the steel, especially the impact toughness of the central part of the thick steel plate, and can improve the fracture resistance and crack resistance properties of the steel plate. In addition, an increase in the Ni element content in the steel also plays a major role in improving the corrosion resistance of the steel in the marine environment. Ni can delay the corrosion progression trend of the material over time, and suppress the adverse effect of corrosion and the tendency of pitting corrosion. However, it should be noted that the Ni element content in the steel should not be too high. If the Ni element content in the steel is too high, it is easy for a highly viscous iron oxide scale that is difficult to remove to be generated on the slab surface, which affects the surface quality and fatigue performance of the steel plate. For this reason, in the marine engineering steel of the present disclosure, the mass percentage of Ni is controlled to 2.0 to 3.0%.

[0020] Al: In the marine engineering steel of the present disclosure, Al belongs to the grain refining element. The Al element is added to the steel for deoxidation. After the deoxidation is completed, the O content in the material is reduced, and the aging property is improved. In addition, it should be noted that adding an appropriate amount of Al to the steel is also beneficial to refine the grains and improve the toughness of the steel. Therefore, in the marine engineering steel of the present disclosure, the mass percentage of the Al element is controlled to be 0.01-0.06%.

[0021] Ti: In the marine engineering steel of the present disclosure, Ti element is a strong N-fixing element, which can effectively suppress the N element content in the steel and prevent the adverse effect on the properties of the steel caused by excessively high N content. In addition, the TiN precipitate phase formed by Ti and N element can suppress the excessive growth of crystal grains in the slab and steel plate during heating. Therefore, in the marine engineering steel of the present disclosure, the mass percentage of the added Ti element is controlled to 0.005-0.012%.

[0022] Mg: In the steel for ocean engineering of the present disclosure, the Mg element can effectively improve the morphology of sulfides, refine inclusions, and enhance the corrosion resistance of the steel plate. The Mg element is an important element for realizing the beneficial modification technology of inclusions in the present disclosure. If the Mg element content in the steel is too low, the modification of inclusions cannot be realized. If the Mg element content in the steel is too high, MgO and MgS are likely to be formed, which may clog the tundish nozzle. Therefore, in the steel for ocean engineering described in the present invention, the mass percentage of the added Mg element is controlled to be 0.0005 - 0.0015%.

[0023] Ca: In the steel for ocean engineering of the present disclosure, by Ca treatment, the morphology of sulfides in the steel can be controlled, the anisotropy of the steel plate can be improved, and the low-temperature toughness can be enhanced. Also, the Ca element is an important element for realizing the beneficial modification technology of inclusions in the present disclosure, and its content needs to be consistent with the Mg content. Therefore, in the steel for ocean engineering of the present disclosure, the mass percentage of the added Ca element is controlled to be 0 < Ca ≦ 0.0045%.

[0024] Cu: In the steel for ocean engineering of the present disclosure, the Cu element can appropriately improve the hardenability of the steel and enhance the atmospheric corrosion resistance of the steel. However, the Cu element content in the steel should not be too high. If the Cu content in the steel is too high, the welding performance of the steel deteriorates. Therefore, in the steel for ocean engineering of the present disclosure, it is preferable to control the mass percentage of Cu to be 0 < Cu ≦ 0.5%.

[0025] Mo: In the steel for ocean engineering of the present disclosure, the Mo element can effectively improve the pitting corrosion resistance of the steel. However, if the Mo content is too high, the tendency of the steel plate to crack at low temperature increases. Therefore, in the steel for ocean engineering of the present disclosure, the mass percentage of the Mo element can be controlled to be 0 < Mo ≦ 0.40%.

[0026] In one embodiment, the steel for ocean engineering of the present disclosure further contains at least one of the following chemical elements: 0 < Nb ≦ 0.04%, 0 < V ≦ 0.05%, and 0 < B ≦ 0.0005%.

[0027] In the above technical solution of the present disclosure, all of the Cu, Mo, Nb, V, and B elements can further improve the performance of the steel for ocean engineering of the present disclosure.

[0028] Nb: In the steel for ocean engineering of the present disclosure, Nb is a strong carbide and nitride forming element with a strong grain refinement effect. By adding an appropriate amount of Nb to the steel to obtain a uniform crystal grain size, it is possible to effectively prevent the excessive growth of some crystal grains during heating, the formation of mixed crystal structures, and the deterioration of toughness and corrosion resistance. Therefore, in the steel for ocean engineering of the present disclosure, the mass percentage of the Nb element can be controlled to be 0 < Nb ≤ 0.04%.

[0029] V: In the steel for ocean engineering of the present disclosure, the V element can contribute to the strengthening of the steel by forming fine precipitation particles of VN or V(CN) together with C and N. Furthermore, the V element is also beneficial in improving the stability of hardness after quenching and tempering. However, it should be noted that the content of the V element in the steel should not be too high. If the content of the V element in the steel is too high, the cost will increase significantly. Therefore, in the steel for ocean engineering of the present disclosure, the mass percentage of the V element can be controlled to be 0 < V ≤ 0.05%.

[0030] B: In the steel for ocean engineering of the present disclosure, the B element can improve the hardenability of the steel and affect the low-temperature cracking characteristics of the steel. Therefore, in the steel for ocean engineering of the present disclosure, the mass percentage of the B element can be controlled to be 0 < B ≤ 0.0005%.

[0031] It should be noted that the addition of the above-mentioned Cu, Mo, Nb, V, and B elements increases the cost of the material. Therefore, considering comprehensively the performance and cost control, in the technical solution of the present disclosure, it is preferable to add at least one of the above elements.

[0032] In one embodiment, in the steel for ocean engineering of the present disclosure, among the inevitable impurities, P ≤ 0.015% and / or S ≤ 0.0040%.

[0033] In the above technical solutions, P and S are both impurity elements in steel. Therefore, in order to obtain better performance and better quality of steel, the impurity element content in steel should be reduced as much as possible as long as technical conditions permit. If the P and S element content in steel is too high, defects such as segregation and inclusion are likely to occur, and the welding performance, impact toughness and HIC resistance of the steel plate will be deteriorated.

[0034] Therefore, in the steel for marine platforms of the present disclosure, it is preferable to control P≦0.015% and S≦0.0040%. It is more preferable to use beneficial modification techniques for inclusions to make their shape spherical, refine their size, and achieve uniform distribution, thereby reducing the impact of inclusions on toughness and corrosion.

[0035] In one embodiment, the mass percentages of the chemical elements in the marine engineering steel of the present disclosure are: 1.8≦α≦2.0 (in the formula, α=1.2Cr+5Ni-Cr 2 -Ni 2 -4.61); 4.2≦β≦7.9 (in the formula,

[0036]

number

[0037]

number

[0038] For each chemical element, the value preceding the percent sign of the mass percentage of the chemical element is substituted into the above formula.

[0039] In the above technical solution, while controlling the mass percentage of individual elements in the marine engineering steel of the present disclosure, it is also preferred to control the mass percentage of chemical elements in the steel to satisfy at least one of 1.8≦α≦2.0, 4.2≦β≦7.9, and 35≦γ≦65, to ensure a balance between the alloying element contents, so that the steel has good corrosion resistance to high humidity and high temperature, as well as balanced improved strength and toughness.

[0040] In one embodiment, the microstructure of the marine engineering steel of the present disclosure is tempered bainite with a phase ratio of 95% or more.

[0041] In the above technical solution, the microstructure of the marine engineering steel of the present disclosure is a tempered bainite structure, and the phase ratio of tempered bainite is more than 95%, so that the steel has more balanced and improved strength and toughness.

[0042] In one embodiment, the marine engineering steel of the present disclosure has a yield strength of 355 MPa or more, a tensile strength of 500-650 MPa, an elongation of 22% or more, an impact energy of 100 J or more at -60°C, a crack tip opening displacement (CTOD) of 0.8 mm or more at -60°C, a non-ductile transition temperature (NDTT) of -65°C or less, and a fatigue strength of 0.85 g / (m 2 *The corrosion rate is as follows:

[0043] Correspondingly, another object of the present disclosure is to provide a method for producing marine engineering steel, which is simple to implement, and which not only has excellent toughness, but also has excellent fracture and crack resistance properties and corrosion resistance to high humidity and high temperature marine atmosphere.

[0044] In one embodiment, the marine engineering steel prepared by the manufacturing method of the present disclosure has a yield strength of 355 MPa or more, a tensile strength of 500-650 MPa, an elongation of 22% or more, an impact energy of 100 J or more at -60°C, a CTOD of 0.8 mm or more at -60°C, an NDTT of -65°C or more, and a hardness of 0.85 g / (m 2 The marine steel produced by the method of the present disclosure can be used in ships and marine structures, and has a wide range of potential applications.

[0045] In order to achieve the above object, the present disclosure provides a method for producing a steel for marine engineering, comprising the steps of: (1) Smelting and casting processes; (2) a heating step; (3) a controlled rolling process in which the original austenite grain size after rolling is 20-25 μm; (4) Air cooling process; (5) A quenching and tempering process in which the austenite grain size after quenching is 20-25 μm; The present invention provides a method of manufacturing the same.

[0046] In one embodiment, in the manufacturing method of the present disclosure, in step (1), hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions, and continuous casting are sequentially carried out, and in the beneficial treatment stage of inclusions, MgO+Al is obtained as a core coated with CaS and MnS. 2 O 3 The size of the composite inclusions is 0.2 to 2.5 μm, and the number of composite inclusions within the above size range accounts for 95% or more of the total number of inclusions.

[0047] In one embodiment, in the manufacturing method of the present disclosure, in step (1), in the converter smelting stage, slag cutoff tapping is performed to control the thickness of the slag layer to less than 30 mm; in the LF refining stage, the sum of the mass percentages of FeO and MnO in the slag is controlled to less than 1%, and (CaO+MgO+MnO) / (SiO 2 +P 2O 5 )>9 (where each substance is substituted with its mass percentage) is satisfied; at the stage of beneficial treatment of the inclusions, Mg treatment or combined treatment of Mg and Ca is carried out; if combined treatment of Mg and Ca is carried out, Ca and Mg must be fed simultaneously at a wire feed speed of 150-250 m / min.

[0048] In the above technical solution, in step (1) of the manufacturing method of the present disclosure, slag cut tapping is carried out in the converter smelting stage, and the thickness of the slag layer is controlled to be less than 30 mm, thereby reducing the oxidation of the slag in the ladle, preventing the increase in oxygen activity and rephosphorization of molten steel, and contributing to the subsequent generation of white slag and inclusion modification treatment.

[0049] In the above technical solution, (CaO+MgO+MnO) / (SiO 2 +P 2 O 5 ) to be greater than 9 to ensure good dephosphorization and desulfurization ability of the slag. In the process of producing white slag from the ladle, the sum of the mass percentages of FeO and MnO in the slag is controlled to be less than 1% to ensure the reduction of the slag, sufficient desulfurization, reduction of the inclusion content in the molten steel, and improvement of the toughness and corrosion resistance of the steel.

[0050] In one embodiment, in the manufacturing method of the present disclosure, in step (2), the slab heating temperature in °C

[0051]

number

[0052] In the above technical solution, in step (2) of the manufacturing method of the present disclosure, the purpose of controlling the slab heating temperature to the above value is to ensure sufficient solid solution of micro-alloyed carbonitrides, promote the homogenization of alloying elements, mitigate macro- and micro-segregation in the steel, reduce the formation of corrosion primary cells caused by potential differences between different phases and components, and improve the corrosion resistance of the steel sheet.

[0053] In one embodiment, in the manufacturing method of the present disclosure, in step (3), the initial rolling temperature T sr =0.92T h -0.96T h The final rolling temperature is controlled to be

[0054]

number

[0055] In the above technical solution, the initial rolling temperature T sr =0.92T h -0.96T h The purpose of controlling so that the steel sheet is rolled at a relatively high temperature in the recrystallization zone is mainly to ensure that the steel sheet is sufficiently recrystallized to form uniform and equiaxed austenite grains.

[0056] In the above technical solution, the final rolling temperature is

[0057]

number

[0058] In one embodiment, in the production method of the present disclosure, in step (3), the rolling reduction in a single pass is 8 to 12%, and the cumulative rolling reduction is 60% or more.

[0059] In the above technical solution of the present disclosure, the purpose of controlling the reduction in a single pass to 8-12% is mainly to ensure that the steel sheet has sufficient recrystallization driving force in each pass, and at the same time, the number of rolling passes is sufficient to achieve grain homogenization of the steel sheet so that the original austenite grain size after rolling is maintained at 20-25 μm. Furthermore, in step (3) of the present disclosure, the purpose of controlling the cumulative reduction to 60% or more is mainly to achieve sufficient recrystallization and sufficient homogenization in the core of the steel sheet to ensure the toughness and fracture- and crack-resistant properties of the core.

[0060] Further, in the manufacturing method of the present disclosure, in the step (5), the quenching temperature

[0061]

number

[0062]

number

[0063] In the above technical solution of the present disclosure, the purpose of setting the above quenching temperature is, firstly, to ensure that the steel sheet is completely austenitized, and secondly, by austenitizing at a relatively high temperature, sufficient solid solution of carbonitrides can be achieved, the uniform distribution of alloys in the steel can be promoted, and the microscopic electrochemical corrosion caused by segregation can be mitigated. In addition, the quenching temperature is not too high, and some of the austenite grains do not grow rapidly to cause mixed crystals. After that, water quenching can be performed, the purpose of which is to ensure that the austenite grain size after quenching is maintained at 20-25 μm by using a high cooling rate to form a single martensite structure.

[0064] In the above technical solution of the present disclosure, in step (5) of the present disclosure, the purpose of setting the above tempering temperature is, firstly, to ensure that the steel plate has good mechanical properties and fracture and crack resistance properties; secondly, to remove the quenching stress in the steel plate through tempering, thereby preventing corrosion caused by different forces at each position inside the steel plate; and finally, to reduce the microscopic corrosion primary cell caused by multiple phases by making the steel plate obtain a tempered bainite structure after tempering.

[0065] In the present disclosure, it should be noted that if the tempering temperature is too high, ferrite structure will be formed in the steel, and the strength and impact properties of the steel plate will be reduced; if the tempering temperature is too low, the strength of the steel plate will be too high and the impact toughness will be relatively low.

[0066] Compared with the prior art, the marine engineering steel and its manufacturing method of the present disclosure have the following advantages and beneficial effects: By controlling conditions such as composition design, structure adjustment, and manufacturing process, the steel plate of the present disclosure simultaneously achieves suitable strength properties, excellent impact toughness, good fracture and crack resistance properties, and excellent corrosion resistance in high-humidity and high-temperature marine atmospheres.

[0067] Compared with the prior art, the manufacturing method of the present disclosure uses unique composition design technology, pure steel smelting technology, inclusion beneficial control technology, steel homogenization technology, grain size control and microstructure adjustment technology to produce a steel grade that meets the 355 MPa level strength requirement, good low-temperature impact toughness, good fracture and crack resistance properties, and excellent corrosion resistance to high humidity and high temperature atmosphere. The steel plate manufactured by the method of the present disclosure is significantly different from existing steel plates in terms of structure, composition and process design.

[0068] The marine engineering steel disclosed herein has a yield strength of 355 MPa or more, a tensile strength of 500-650 MPa, an elongation of 22% or more, an impact energy of 100 J or more at -60°C, a CTOD of 0.8 mm or more at -60°C, an NDTT of -65°C or less, and a hardness of 0.85 g / (m 2 *The following corrosion rates can be achieved:

[0069] The marine engineering steel of the present disclosure can be used for key components of ships and marine engineering structures, meeting China's current development demand for steel for ships and marine engineering equipment, and is expected to have a wide range of applications. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] The specific implementation manner of the present invention will be further explained and described below by taking specific embodiments, however, the explanations and descriptions do not limit the technical solutions of the present disclosure.

[0071] Examples 1 to 6 and Comparative Example 1 Both the marine engineering steels of Examples 1 to 6 and the comparative steel of Comparative Example 1 are prepared by the following steps.

[0072] (1) Smelting and casting are performed according to the chemical compositions shown in Tables 1-1 and 1-2 below. Hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions, and continuous casting are performed in sequence, and MgO+Al is used as a core coated with CaS and MnS at the stage of beneficial treatment of inclusions. 2 O 3The size of the complex inclusions is 0.2 to 2.5 μm, and the number of complex inclusions within the above size range accounts for 95% or more of the total number of inclusions.

[0073] In the converter smelting stage, slag cut tapping is carried out to control the thickness of the slag layer to less than 30 mm; in the LF refining stage, the sum of the mass percentages of FeO and MnO in the slag is controlled to less than 1%, and the ratio of (CaO+MgO+MnO) / (SiO 2 +P 2 O 5 ) is controlled to be greater than 9 (wherein each substance is substituted by its mass percentage), and in the stage of beneficial treatment of the inclusions, Mg treatment or combined treatment of Mg and Ca is carried out, but when combined treatment of Mg and Ca is carried out, Ca and Mg need to be fed simultaneously at a wire feed speed of 150 to 250 m / min.

[0074] (2) Heating: Slab heating temperature in degrees Celsius

[0075]

number

[0076] (3) Controlled rolling: Maintain the original austenite grain size after rolling at 20-25 μm and keep the initial rolling temperature T sr =0.92T h -0.96T h The final rolling temperature is controlled to be

[0077]

number

[0078] (4) Air Cooling

[0079] (5) Quenching + tempering: Quenching temperature

[0080]

number

[0081]

number

[0082] It should be noted that in Examples 1-6 of the present disclosure, six different chemical compositions are designed and combined with suitable manufacturing processes to produce steel plates with different thickness specifications. The chemical composition designs and related processes of the marine engineering steels in Examples 1-6 all meet the design specification requirements of the present disclosure.

[0083] Tables 1-1 and 1-2 show the mass percentages of the chemical elements of the marine engineering steels of Examples 1 to 6 and the comparative steel of Comparative Example 1.

[0084] [Table 1-1]

[0085] [Table 1-2]

[0086] Table 2 shows the specific process parameters for producing the marine engineering steels of Examples 1 to 6 and the comparative steel of Comparative Example 1.

[0087] [Table 2]

[0088] The marine engineering steels obtained in Examples 1 to 6 and the comparative steel obtained in Comparative Example 1 are sampled, and the finished plates of the Examples and Comparative Example are subjected to tensile tests, Charpy V-notch impact tests, CTOD tests (an index for examining the fracture toughness of steel plates), NDTT performance inspection tests (an important index for measuring the crack resistance properties of steel plates), and corrosion tests under high humidity and high temperature conditions. The test results of the Examples and Comparative Example are shown in Table 3.

[0089] The test method is described below.

[0090] Tensile test: According to GB / T228.1, full thickness plate tensile test specimens are used for steel plates with a thickness of less than 50mm, and bar tensile test specimens are used for steel plates with a thickness of more than 50mm, and then the room temperature tensile properties of the steel plates are measured.

[0091] Charpy V-notch impact test: In accordance with GB / T229, a Charpy V-notch impact test piece is used to measure the impact properties of the material at a position of thickness t / 4 at -60°C.

[0092] CTOD Test: Measure the fracture toughness of a material at -60°C using a full thickness CTOD specimen in accordance with BS7448-1.

[0093] NDTT performance inspection test: According to GB / T6803-2008, P3 test piece is used to measure the non-ductile transition temperature of the material.

[0094] Corrosion test under high humidity and high temperature conditions: In the test process, the temperature was controlled to 35°C, the pH was 6.5-7.2, and the average deposition of salt spray was controlled to 1.5mL / (80cm 2 The temperature is controlled at 40°C (24°F) and the relative humidity is controlled at 95% to 100%.

[0095] Table 3 shows the test results of the marine engineering steels of Examples 1 to 6 and the comparative steel of Comparative Example 1.

[0096] [Table 3]

[0097] As can be seen from Table 3, the overall performance of the marine steels of Examples 1 to 6 is significantly better than that of the comparative steel of Comparative Example 1. In a high humidity and high temperature atmospheric environment, the corrosion rates of the marine steels of Examples 1 to 6 are significantly lower than that of the steel of Comparative Example 1. As can be seen, the marine steels of Examples 1 to 6 have better corrosion resistance to high humidity and high temperature than the comparative steel of Comparative Example 1.

[0098] As shown in Table 3, the marine engineering steels of Examples 1 to 6 have superior toughness, fracture and crack resistance properties, and corrosion resistance to high humidity and high temperature compared to the comparative steel of Comparative Example 1. All of the marine engineering steels of Examples 1 to 6 have a yield strength of 423 MPa or more, a tensile strength of 532 to 595 MPa, an impact energy of 270 J or more at -60°C, an elongation of 22% or more, a CTOD of 0.8 mm or more at -60°C, an NDTT of -65°C or less, and a tensile strength of 0.83 g / (m 2 *The corrosion rate is below 1000 rpm.

[0099] In summary, it can be seen that, through the rational chemical composition design combined with the optimized process, the marine engineering steel of the present disclosure simultaneously achieves suitable strength properties, excellent impact toughness, good fracture and crack resistance properties, and excellent corrosion resistance to high humidity and high temperature marine atmosphere. The marine engineering steel of the present disclosure can be effectively used in the manufacture of key components of ships and marine engineering structures, offshore wind power platforms, island constructions, etc. The steel meets the current development demand for steel for ships and marine engineering equipment in China, and is expected to have a wide range of applications.

[0100] In addition, the combinations of various technical features in the present disclosure are not limited to the combinations described in the claims or embodiments. All technical features in the present disclosure can be freely combined or incorporated in any manner as long as they are not mutually inconsistent.

[0101] It should be noted that the above-mentioned embodiments are merely specific implementations of the present disclosure. Naturally, the present disclosure is not limited to the above-mentioned embodiments, and modifications or variations similar to the above-mentioned embodiments can be directly obtained or easily conceived by those skilled in the art from the contents of the present disclosure, and all should be included in the protection scope of the present disclosure.

Claims

1. The following chemical elements by mass percentage: C: 0.01-0.05%, Si: 0.05-0.60%, Mn: 0.50-1.30%, Cr: 0.6-1.20%, Ni: 2.0-2.85%, Al: 0.01-0.06%, Ti: 0.005-0.012%, Mg: 0.0005-0.0015%; 0<Ca≦0.0045%, 0<Cu≦0.5%, 0<Mo≦0.40%, P≦0.015%, and S≦0.0040%, with the balance being Fe and other unavoidable impurities. Marine engineering steel.

2. The mass percentages of the above chemical elements are as follows: C: 0.015-0.04%, Si: 0.15-0.60%, Mn: 0.50-1.30%, Cr: 0.6-0.90%, Ni: 2.0-2.85%, Al: 0.01-0.06%, Ti: 0.005-0.012%, Mg: 0.0005-0.0015%; 0<Ca≦0.0045%, 0<Cu≦0.5%, 0<Mo≦0.40%, P≦0.015%, and S≦0.0040%, with the balance being Fe and other unavoidable impurities.

2. Marine engineering steel according to claim 1.

3. said steel further comprising at least one of the following chemical elements: 0<Nb≦0.04%, 0<V≦0.05%, and 0<B≦0.0005%; 3. Marine engineering steel according to claim 1 or 2.

4. The mass percentages of the above chemical elements are expressed by the following relationship: 1.8≦α≦2.0 (in the formula, α=1.2Cr+5Ni-Cr ２ -Ni ２ -4.61); and 35≦γ≦65 (in the formula, [0010] ） and 3. Marine engineering steel according to claim 1 or 2.

5. The steel has a tempered bainite microstructure with a phase ratio of 95% or more.

3. Marine engineering steel according to claim 1 or 2.

6. The mass percentage of the above chemical elements is 4.2≦β≦7.9 (in the formula, [0025] ) further fulfills the above requirements, 4. Marine engineering steel according to claim 3.

7. The steel has a yield strength of 355 MPa or more, a tensile strength of 500-650 MPa, an elongation of 22% or more, an impact energy of 100 J or more at -60°C, a CTOD of 0.8 mm or more at -60°C, an NDTT of -65°C or less, and a compressibility of 0.85 g / (m ２ * The corrosion rate is as follows:

3. Marine engineering steel according to claim 1 or 2.

8. A method for producing a marine engineering steel according to claim 1, comprising the steps of: (1) Smelting and continuous casting processes; (2) a heating step; (3) a controlled rolling step in which the original austenite grain size after rolling is 20-25 μm; (4) an air cooling step; (5) a quenching and tempering process in which the austenite grain size after quenching is 20-25 μm; A manufacturing method comprising:

9. In step (1), hot metal pretreatment, converter smelting, LF refining, RH refining, beneficial treatment of inclusions and continuous casting are carried out in sequence, and in the beneficial treatment stage of the inclusions, composite inclusions having a size of 0.2-2.5 μm are formed, and the composite inclusions are formed into MgO+Al as a core coated with CaS and MnS. ２ O ３ wherein the number of said composite inclusions within said size range accounts for 95% or more of the total number of inclusions; The method according to claim 8.

10. In step (1), in the converter smelting stage, slag cut tapping is performed to control the thickness of the slag layer to less than 30 mm; in the LF refining stage, the sum of the mass percentages of FeO and MnO in the slag is controlled to less than 1%, and (CaO + MgO + MnO) / (SiO ２ +P ２ O ５ )>9 (wherein each substance represents its corresponding mass percentage); in the step of beneficially treating the inclusions, Mg treatment or combined Mg and Ca treatment is carried out; when combined Mg and Ca treatment is carried out, Ca and Mg are fed simultaneously at a wire feed speed of 150-250 m / min; The method of claim 9.

11. In step (2), the slab heating temperature T ｈ But in units of °C, [0030] Fulfilling The method of claim 9.

12. In step (3), the initial rolling temperature T ｓｒ But, T ｓｒ = 0.92T ｈ -0.96T ｈ and the final rolling temperature T ｆｒ but, [0045] Fulfilling The method of claim 11.

13. In step (3), the rolling reduction in a single pass is 8 to 12%, and the cumulative rolling reduction is 60% or more. The method of claim 11.

14. In step (5), the quenching temperature T ｑ but, [0050] and / or the tempering temperature T ｔ but, [006] Fulfilling The method of claim 11.

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