420MPa-grade marine steel plate capable of resisting ice collision in frigid zone and manufacturing method of 420MPa-grade marine steel plate

Abstract

The invention relates to a 420MPa-grade marine steel plate resistant to ice collision in a frigid zone and a manufacturing method of the 420MPa-grade marine steel plate. The steel plate comprises the following chemical components: 0.05%-0.08% of C, 0.2%-0.35% of Si, 1.35%-1.55% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.015%-0.045% of Als, 0.2%-0.48% of Ni, 0.1%-0.25% of Mo, 0.22%-0.35% of Cu, 0.01%-0.1% of Co, 0.02%-0.06% of Nb, 0.008%-0.015% of Ti, 0.003%-0.005% of N and the balance of Fe and impurities. The steel plate of which the mechanical property and the service safety both meet the service conditions of ocean engineering equipment is obtained by matching unique component design with a corresponding production process.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore steel production, and in particular to a cold zone ice-resistant 420MPa offshore steel plate and a manufacturing method thereof. Background Art

[0002] Since the beginning of the 21st century, the shipbuilding and marine engineering sectors have experienced rapid development. The accelerated development of shipping routes in cold oceans and the Arctic Circle has placed higher demands on related technologies and equipment. Simultaneously, with the deepening of research into offshore steel materials for use in extreme environmental conditions, new offshore steels are emerging to meet increasingly stringent requirements. The Arctic region, rich in resources such as oil and natural gas, holds enormous development potential. Arctic shipping demands not only technical performance in cryogenics, corrosion, and fatigue resistance, but also environmental protection, such as ship emissions and the prevention of marine pollution, which also require relevant technologies and equipment. To adapt to these changes and challenges, research into new offshore steel materials is currently focused on microalloying, controlled rolling, controlled cooling, and heat treatment processes, aiming to improve the materials' frost resistance, corrosion resistance, and other application properties.

[0003] Microalloying technology is currently a hot topic in the research and development of marine steel materials. By adding appropriate trace alloying elements, the fatigue resistance and service life of steel plates can be significantly improved. Controlled rolling, controlled cooling and heat treatment process optimization are also an important research direction. The use of controlled rolling technology can effectively control the structure and phase transformation of steel, and improve the toughness and fatigue resistance of steel. The fatigue resistance of steel plates is of great significance to marine engineering equipment, and can significantly improve its reliability, safety and economic benefits. By adding appropriate trace alloying elements and combining with advanced heat treatment processes, the fatigue resistance of steel plates can be effectively improved. In response to the new requirements for the fatigue resistance of marine steel plates, fatigue crack growth tests, fatigue life tests and low-cycle fatigue strength tests can be used for verification.

[0004] When selecting steel materials and processing techniques, factors such as performance, cost, and feasibility must be comprehensively considered. While new marine steel materials are constantly emerging, they are generally expensive, requiring a rational selection based on specific needs and economic viability for specific applications. Furthermore, in addition to micro-alloying and heat treatment processes, emerging technologies such as ultrasonic surface treatment can also be used to enhance material fatigue resistance.

[0005] Existing marine engineering steels can already meet most market demands, but special steels with lower ductile-brittle transition temperatures and excellent overall performance remain a research and development target for countries around the world. The development of high-strength steel plates with high service safety is difficult, requires rigorous production processes, and places high demands on equipment. For example, the Chinese patent application published under application number CN116162869A, titled "A Fatigue-Resistant Steel Plate for Marine Environments and Its Production Method," produces a ferrite + bainite fatigue-resistant steel plate with a low-C and low-Mn composition design and the addition of elements such as Ni, Mo, Cr, V, Sn, and Re. While this helps improve the steel plate's corrosion fatigue resistance, few elements can effectively enhance its strength and toughness. Furthermore, it utilizes only conventional controlled rolling processes, making it impossible to produce fatigue-resistant, low-temperature tough marine steel with a maximum thickness of 120 mm and a grade of 420 MPa. The Chinese invention patent with authorization announcement number CN111676425B discloses "a bridge steel with excellent toughness and strong fatigue resistance at extremely low temperatures and its manufacturing method." It adopts an alloy composition design with high Si, high Mn, and high Cr to produce steel plates with a thickness of 10-60mm. The finished steel plates have high strength and hardness, but there are many hard phases in the steel plates, and the ability to resist fatigue crack initiation and expansion is insufficient. It is also impossible to produce fatigue-resistant low-temperature toughness steel plates with a maximum thickness of 120mm. Summary of the Invention

[0006] The present invention provides a cold zone ice-resistant 420MPa grade marine steel plate and its manufacturing method. Through a unique composition design and corresponding production process, a steel plate with mechanical properties and service safety that meet the service conditions of marine engineering equipment is obtained. The maximum thickness of the finished steel plate is 120mm, and the Charpy impact energy at -60℃ is ≥120J; the fatigue crack growth performance of the base material and the welding heat-affected zone is: when Lg(ΔK)=3.5MPa·m 0.5 When, Lg(da / dN)≤-2.4mm / cycle.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A cold-zone ice-impact resistant 420MPa-grade marine steel plate, the chemical composition of the steel plate comprising, by weight percentage, C: 0.05%-0.08%, Si: 0.2%-0.35%, Mn: 1.35%-1.55%, P≤0.02%, S≤0.01%, Als: 0.015%-0.045%, Ni: 0.2%-0.48%, Mo: 0.1%-0.25%, Cu: 0.22%-0.35%, Co: 0.01%-0.1%, Nb: 0.02%-0.06%, Ti: 0.008%-0.015%, N: 0.003%-0.005%, and the remainder being Fe and unavoidable impurities.

[0009] The yield strength of the finished steel plate is ≥420MPa, the tensile strength is 520~680MPa, the transverse elongation is ≥26%; the average Charpy impact energy at -60℃ is ≥120J; the fatigue crack growth performance of the base material and the welding heat affected zone is: when Lg(ΔK)=3.5MPa·m 0.5 When, Lg(da / dN)≤-2.4mm / cycle.

[0010] The maximum thickness of the finished steel plate is 120mm.

[0011] The metallographic structure at 1 / 2 of the thickness of the finished steel plate is acicular ferrite + bainite + polygonal ferrite, and the volume ratio of acicular ferrite is 60% to 80%, the volume ratio of bainite is 15% to 30%, and the rest is polygonal ferrite.

[0012] A method for manufacturing a cold zone ice-resistant 420MPa grade marine steel plate comprises the following steps:

[0013] 1) Smelting and continuous casting: After smelting in a converter, the molten steel undergoes LF refining, RH refining or VD refining to reduce the content of P, S and non-metallic inclusions; continuous casting is protected throughout the entire casting process;

[0014] 2) Heating: The billet is placed in a heating furnace at 500-650°C for a holding time of ≥60 min; then the temperature is raised to 1120-1200°C at a heating rate of 3-6°C / min, the soaking temperature is 1150-1180°C, and the total time in the furnace is 6-9 h;

[0015] 3) Two-stage rolling: the first-stage rolling temperature is 1100-1150℃, the single-pass reduction of at least the first three passes is ≥30mm, and the total rolling reduction rate of the first stage is ≥60%; the second-stage rolling temperature is 800-900℃, the single-pass reduction of the second stage is 6-10mm, and the final rolling temperature is ≥800℃;

[0016] 4) Controlled cooling: the steel plate water inlet temperature is 680-750℃, the red-hot temperature is 250-450℃, the upper and lower nozzle water volume ratio is 1-1.4, and the roller speed is 0.3-1.5m / s;

[0017] 5) Tempering: The tempering temperature of the steel plate is 325-450°C, and the tempering time is 2-4 min / mm.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) By adopting a composition design with the addition of elements such as C, Mn, Ni, Co, Mo, and Cu, and combining it with appropriate production processes, we can produce cold-zone ice-resistant 420MPa-grade marine steel plates with a maximum thickness of 120mm.

[0020] 2) A unique alloy composition system is used in conjunction with the production process to ensure that the mechanical properties and service safety of the finished steel plate meet the service conditions of marine engineering equipment, namely, yield strength ≥420MPa, tensile strength 520~680MPa, transverse elongation ≥26%, -60℃ Charpy impact energy ≥120J; fatigue crack growth performance of the base material and welding heat affected zone: when Lg(ΔK)=3.5MPa·m 0.5 When, Lg(da / dN)≤-2.4mm / cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a metallographic photograph of the finished steel plate of the present invention at 1 / 2 of the thickness. DETAILED DESCRIPTION

[0022] The present invention targets the performance requirements of ultra-high-strength marine steel in extremely cold marine environments. By utilizing a composition design combining C, Mn, Ni, Co, Mo, Cu and other microalloying elements, and coordinating it with a production process suitable for ice-resistant 420MPa-grade marine steel plates in cold zones, a large number of systematic experimental studies have been conducted on various aspects, including alloy element screening and proportioning, steel cleanliness control, two-stage rolling, precise cooling control, tempering process optimization and parameter selection. Ultimately, an alloy element proportion and production process that can meet the objectives of the present invention have been determined.

[0023] The cold zone ice-resistant 420MPa-grade marine steel plate described in the present invention comprises, by weight percentage, C: 0.05%-0.08%, Si: 0.2%-0.35%, Mn: 1.35%-1.55%, P≤0.02%, S≤0.01%, Als: 0.015%-0.045%, Ni: 0.2%-0.48%, Mo: 0.1%-0.25%, Cu: 0.22%-0.35%, Co: 0.01%-0.1%, Nb: 0.02%-0.06%, Ti: 0.008%-0.015%, N: 0.003%-0.005%, and the remainder is Fe and unavoidable impurities.

[0024] The composition design reasons of the low-cold zone ice-resistant 420MPa grade marine steel plate described in the present invention are as follows:

[0025] 1) Carbon, a fundamental strengthening element in steel, plays a key role in ensuring strength and hardness in the marine steel plates described herein. Too low a carbon content leads to reduced carbon solid solution content and carbide content, reduced grain refinement, and insufficient steel plate strength. Too high a carbon content produces a large amount of hardened structure, reducing impact toughness. Therefore, the carbon content in the steel must be precisely controlled. The present invention controls the carbon content to 0.05% to 0.08%.

[0026] 2) Si can increase the strength of the steel plate and refine the grain size, thereby improving the fatigue resistance of the steel plate. At the same time, Si can reduce the O content as a deoxidizer. When the Si content is less than 0.2%, the deoxidation effect is not obvious. When the Si content is greater than 0.35%, it will cause the structure to coarsen and reduce the toughness. Therefore, the present invention controls the Si content to 0.2% to 0.35%.

[0027] 3) Mn, with a similar atomic radius to Fe, can be dissolved in large quantities in the Fe matrix, improving the strength and wear resistance of the steel plate. Mn also enhances the heat transfer capacity of extra-thick steel plates. When the Mn content is below 1.35%, the core heat transfer rate is low. When the Mn content exceeds 1.55%, Mn segregation results in poor low-temperature toughness in the thick plate core. Therefore, the present invention controls the Mn content to 1.35% to 1.55%.

[0028] 4) P and S elements have no benefit on the mechanical properties of the steel plate, especially the elongation. The present invention controls P≤0.02% and S≤0.01%.

[0029] 5) Al is the main deoxidizing element in steel. When the Al content is too low, the deoxidation effect is poor. Microalloying elements such as Ti are oxidized and cannot play a role in grain refinement. In particular, for thicker high-strength steel plates, the Als content in the steel needs to be appropriately increased. Conversely, if the Al content is too high, large inclusions will form. Therefore, the Als content in the present invention is controlled to 0.015% to 0.045%.

[0030] 6) Ni improves the toughness of the steel plate. Adding a large amount of Ni can lower the ductile-brittle transition temperature and improve the low-temperature toughness of the steel plate. Adding a certain amount of Ni to the steel can also refine the ferrite grains, prevent intergranular corrosion, and thus improve fatigue resistance. The addition of Ni can also reduce the hot cracking tendency of Cu in the steel. The present invention controls the Ni content to 0.2% to 0.48%.

[0031] 7) Mo forms fine carbides in steel, effectively increasing the strength of the steel plate. Adding a certain amount of Mo to the steel can also improve the cooling control of extra-thick steel plates. Mo also provides a certain degree of corrosion resistance in conjunction with Ni. Furthermore, Mo improves the tempering stability of the steel plate, enhancing its low-temperature toughness and fatigue resistance after tempering. The present invention controls the Mo content to 0.1% to 0.25%.

[0032] 8) Cu improves the wear resistance and fatigue resistance of steel. Cu, in combination with Ni, lowers the ductile-brittle transition temperature and improves low-temperature toughness. However, adding excessive amounts of Cu alone can reduce low-temperature toughness and cause hot brittleness. The present invention limits the Cu content to 0.22% to 0.35%.

[0033] 9) Co and Mn work together to significantly strengthen the steel plate through solid solution, improving its strength and fatigue resistance. However, excessive addition can reduce the steel's low-temperature toughness. Co also improves the steel's tempering stability; in this invention, the Co content is controlled to 0.01% to 0.1%.

[0034] 10) Nb is a key additive element in the steel of this invention. Nb forms fine compounds with carbon and nitrogen, improving the strength and hardness of the steel. During heating, undissolved Nb carbon and nitrogen compounds form particles at the austenite grain boundaries, hindering austenite grain growth. Nb also effectively delays the recrystallization of deformed austenite, preventing austenite grain growth, raising the austenite recrystallization temperature, refining grains, and improving fatigue resistance. During controlled cooling of the steel, large amounts of Nb (CN) precipitate, further promoting dislocation entanglement and grain refinement. The present invention controls the Nb content to 0.02% to 0.06%.

[0035] 11) Ti is added to form TiN with N, which prevents grain growth during heating, rolling, and welding, improving the toughness of the steel plate. A certain amount of Ti can enhance the steel's resistance to intergranular corrosion. In this invention, the Ti content is controlled to be 0.008% to 0.015%.

[0036] 12) Nitrogen combines with Nb and Ti to form fine, dispersed nitride precipitates, effectively promoting the nucleation and growth of intragranular ferrite and controlling the growth of prior austenite grains. Increasing the nitrogen content increases the amount of TiN in the steel. However, excessive dissolved nitrogen content reduces the steel's thermoplasticity, reduces the toughness of the steel plate, and predisposes the steel plate to numerous microcracks. Therefore, the present invention limits the nitrogen content to 0.003% to 0.005%.

[0037] The cold zone ice-resistant 420MPa grade marine steel plate described in the present invention adopts a production process of high-cleanliness alloying smelting + low-temperature heating + two-stage low-temperature controlled rolling + controlled cooling + low-temperature tempering. The specific process is as follows:

[0038] (1) High cleanliness alloy smelting and continuous casting;

[0039] After smelting in a converter, the molten steel is refined in an LF furnace, RH furnace, or VD furnace to further reduce the content of P, S, and non-metallic inclusions. The resulting molten steel meets the chemical composition requirements and is protected throughout the continuous casting process.

[0040] (2) Two-stage rolling and controlled cooling;

[0041] The continuous casting billet is loaded into the heating furnace at 500-650°C for a holding time of 60 minutes or more. The temperature is then raised to 1120-1200°C at a heating rate of 3-6°C / min. The soaking temperature is 1150-1180°C, and the total time in the furnace is 6-9 hours. The purpose of ensuring the total heating time is to ensure that the core of the thick billet reaches the target temperature. The purpose of controlling the soaking temperature is to avoid excessive soaking temperature, and the purpose of controlling the soaking time is to prevent abnormal growth of the billet structure, which will affect the fatigue resistance and low-temperature toughness of the steel plate core during rolling.

[0042] The first-stage rolling temperature is 1100-1150℃, and the reduction of each pass in at least the first three passes is ≥30mm. The total reduction rate of the first-stage rolling is ≥60%; the second-stage rolling temperature is 800-900℃, the reduction of each pass in the second stage is 6-10mm, and the final rolling temperature is ≥800℃.

[0043] The water entry temperature of the rolled steel plate is 680-750°C, the red-return temperature is 250-450°C, the water volume ratio of the upper and lower nozzles is 1-1.4, and the roller speed is 0.3-1.5m / s.

[0044] The purpose of adopting two-stage controlled rolling is to maximize the pass reduction ratio under the condition of relatively low hardness of the high-temperature steel plate, further break up the as-cast grains, increase deformation energy storage and grain nucleation sites, and improve the low-temperature toughness and resistance to fatigue crack initiation and propagation of the core of the extra-thick plate. The purpose of controlled cooling after rolling is to quickly reduce the steel plate to below the dynamic recrystallization temperature to prevent further grain growth within the steel plate.

[0045] (3) Tempering;

[0046] The tempering temperature is 325-450°C, and the tempering time is 2-4 min / mm.

[0047] The yield strength of the finished steel plate is ≥420MPa, the tensile strength is 520~680MPa, the transverse elongation is ≥26%, and the average Charpy impact energy at -60℃ is ≥120J. Fatigue crack growth performance of the base material and the welding heat affected zone: When Lg(ΔK)=3.5MPa·m 0.5 When Lg(da / dN)≤-2.4mm / cycle. The maximum thickness of the finished steel plate is 120mm.

[0048] like Figure 1 As shown in the figure, the metallographic structure of the finished steel plate at 1 / 2 of the thickness is acicular ferrite + bainite + polygonal ferrite, and the volume ratio of acicular ferrite is 60% to 80%, the volume ratio of bainite is 15% to 30%, and the rest is polygonal ferrite. The finished product has good mechanical properties.

[0049] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the scope of protection of the present invention.

[0050] [Example]

[0051] The chemical composition of the steel in each example is shown in Table 1, the production process parameters are shown in Table 2-1 and Table 2-2, and the properties of the finished steel plate are shown in Table 3.

[0052] Table 1 Chemical composition of steel (weight percentage, %)

[0053]

[0054] Table 2-1 Production process parameters (I)

[0055]

[0056] Table 2-2 Production process parameters (II)

[0057]

[0058] Table 3 Mechanical properties of finished steel plates

[0059]

[0060] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A cold zone ice-resistant 420MPa grade marine steel plate, characterized by: The chemical composition of the steel plate, by weight percentage, includes C: 0.05%~0.08%, Si: 0.2%~0.35%, Mn: 1.35%~1.55%, P≤0.02%, S≤0.01%, Als: 0.015%~0.045%, Ni: 0.2%~0.48%, Mo: 0.1%~0.25%, Cu: 0.22%~0.35%, Co: 0.01%~0.1%, Nb: 0.02%~0.06%, Ti: 0.008%~0.015%, N: 0.003%~0.005%, and the rest is Fe and unavoidable impurities.

2. The cold zone ice impact resistant 420MPa grade marine steel plate according to claim 1, characterized in that: The yield strength of the finished steel plate is ≥420MPa, the tensile strength is 520~680MPa, the transverse elongation is ≥26%; the average Charpy impact energy at -60℃ is ≥120J; the fatigue crack growth performance of the base material and the welding heat affected zone is: when Lg(ΔK)=3.5MPa·m 0.5 When, Lg(da / dN)≤-2.4mm / cycle.

3. The cold zone ice-resistant 420MPa grade marine steel plate according to claim 1, characterized in that: The maximum thickness of the finished steel plate is 120mm.

4. The cold zone ice-resistant 420MPa grade marine steel plate according to claim 1, characterized in that: The metallographic structure at 1 / 2 of the thickness of the finished steel plate is acicular ferrite + bainite + polygonal ferrite, and the volume ratio of acicular ferrite is 60% to 80%, the volume ratio of bainite is 15% to 30%, and the rest is polygonal ferrite.

5. A method for manufacturing the cold zone ice-resistant 420 MPa grade marine steel plate according to any one of claims 1 to 4, characterized in that: The steps include: 1) Smelting and continuous casting: After smelting in a converter, the molten steel undergoes LF refining, RH refining or VD refining to reduce the content of P, S and non-metallic inclusions; continuous casting is protected throughout the entire casting process; 2) Heating: The billet is placed in a heating furnace at 500-650°C for a holding time of ≥60 min; then the temperature is raised to 1120-1200°C at a heating rate of 3-6°C / min, the soaking temperature is 1150-1180°C, and the total time in the furnace is 6-9 h; 3) Two-stage rolling: the first-stage rolling temperature is 1100-1150℃, the single-pass reduction of at least the first three passes is ≥30mm, and the total rolling reduction rate of the first stage is ≥60%; the second-stage rolling temperature is 800-900℃, the single-pass reduction of the second stage is 6-10mm, and the final rolling temperature is ≥800℃; 4) Controlled cooling: the steel plate water inlet temperature is 680-750℃, the red-hot temperature is 250-450℃, the upper and lower nozzle water volume ratio is 1-1.4, and the roller speed is 0.3-1.5m / s; 5) Tempering: The tempering temperature of the steel plate is 325-450°C, and the tempering time is 2-4 min / mm.

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