Steel plate for ocean engineering and preparation method thereof

Abstract

The invention provides a steel plate for ocean engineering and a preparation method thereof, and belongs to the technical field of steel and iron materials. The steel plate comprises the following components in percentage by mass: 0.08%-0.15% of C, 0.18%-0.42% of Si, 1.40%-1.60% of Mn, 2.00%-3.10% of Ni, 0.045%-0.06% of Nb, 0.03%-0.08% of Al, 0.01%-0.02% of Ti, 0.02%-0.065% of V, 0.10%-0.25% of Cu, less than or equal to 0.013% of P, less than or equal to 0.0021% of S, less than or equal to 0.59% of Ceq, less than or equal to 0.29% of Pcm and the balance of Fe and inevitable impurities. Wherein Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5, and Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B. By adding the high-content Ni element and Nb element, the steel plate has high strength, weldability and low-temperature fracture toughness.

Description

Technical Field

[0001] The present disclosure relates to the technical field of steel materials, and in particular to a steel plate for marine engineering and a preparation method thereof. Background Art

[0002] Marine engineering steel plays the most important role in ensuring the safety of marine equipment in service. At present, marine engineering steel is mainly used in offshore engineering, mainly with a yield strength of less than 355MPa. However, as marine equipment develops towards extreme service environments such as deep sea and extremely cold environment, steel plates for offshore platforms must have high strength, high toughness, good weldability and strict requirements for thick specifications, and special attention is paid to the fracture toughness performance of the material.

[0003] Chinese patent CN201310124065.2 "Ultra-low temperature steel capable of large heat input welding and manufacturing method thereof", Chinese patent CN201310244712.3 "Ultra-high toughness and excellent weldability HT550 steel plate and manufacturing method thereof", Chinese patent CN201410300713.X "A 550MPa grade steel plate capable of large heat input welding and manufacturing method thereof" and Chinese patent CN201310244706.8 "Low-cost high-strength and toughness steel plate capable of large heat input welding and manufacturing method thereof" solve the problem of unstable low-temperature impact toughness of steel plate base material and welding heat affected zone, and the steel plate can withstand large welding heat input and is successfully used in major engineering construction at home and abroad; however, the above patents do not involve the problem of low-temperature CTOD of base material steel plate and welding heat affected zone.

[0004] Therefore, how to prepare thick, high-strength, excellent low-temperature toughness and fracture toughness steel plates for marine engineering is an important research direction at present. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a steel plate for marine engineering and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present disclosure is as follows: on the one hand, a steel plate for marine engineering is provided, wherein the composition of the steel plate includes, by mass percentage, C: 0.08%-0.15%, Si: 0.18%-0.42%, Mn: 1.40%-1.60%, Ni: 2.00%-3.10%, Nb: 0.045%-0.06%, Al: 0.03%-0.08%, Ti: 0.01%-0.02%, V: 0.02%-0.065%, Cu: 0.10%-0.25%, P≤0.013%, S≤0.0021%, Ceq≤0.59%, Pcm≤0.29%, and the balance is Fe and unavoidable impurities;

[0007] Where, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5,

[0008] Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0009] In some embodiments, the thickness of the steel plate is 180-250 mm.

[0010] In some embodiments, the steel plate has a yield strength of 420 MPa or more, an average core impact energy of 300 J or more at -40°C, an elongation of 24.5% or more, and a CTOD value of a heat affected zone after welding at -10°C of 0.4 mm or more.

[0011] In some embodiments, the metallographic structure of the steel plate is a mixture of ferrite and pearlite.

[0012] On the other hand, a method for preparing the marine engineering steel plate is provided, comprising the following steps: subjecting a first steel billet to a heating treatment, a rolling treatment, a water cooling treatment, and a quenching and tempering heat treatment in sequence to obtain the marine engineering steel plate;

[0013] The rolling process comprises the following steps: performing first rolling and second rolling on the second steel billet obtained by the heat treatment to obtain a third steel billet; the first rolling temperature is 1100-1150°C, the last two rolling reductions are ≥16%, and the cumulative compression ratio is not less than 2.6; the second rolling temperature is 800-820°C, the final rolling temperature is ≥790°C, and the single rolling reduction is 1-5%;

[0014] The steps of water cooling treatment are: laminar cooling of the third steel billet, the water inlet temperature of the third steel billet is 760-790°C, and the red-returning temperature is 300-400°C.

[0015] In some embodiments, the first steel billet has a thickness of 600-950 mm and a width of ≥1870 mm.

[0016] In some embodiments, the first steel billet is prepared through molten steel smelting, LF refining, vacuum treatment, and continuous casting processes.

[0017] In some embodiments, the heat treatment temperature is 1100-1200° C., and the heating coefficient is 12-15 min / cm.

[0018] In some embodiments, the tempering heat treatment includes quenching and tempering; the quenching temperature is 890-900°C, and the holding time is 1.5-2 mm / min; the tempering temperature is 600-620°C, and the holding time is 2.5-3.5 mm / min.

[0019] In some embodiments, the cooling rate of the laminar cooling is 5-10° C. / s.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention improves the core hardenability of the steel plate and refines the microstructure of the steel plate by adding high contents of Ni and Nb elements, so that the steel plate has higher strength, weldability and low-temperature fracture toughness; in addition, the steel plate of the present invention does not have additional Cr and Mo elements, which reduces the types of alloy elements, reduces the difficulty of controlling the composition of the steel plate, and improves the machinability of the steel plate.

[0022] 2. In the preparation process of steel plates for marine engineering, the present invention allows the rolling force to penetrate into the core of the steel billet through rolling treatment and water cooling treatment, and eliminates the internal stress generated during the rolling of the steel plate through tempering heat treatment, while changing the internal structure of the steel plate, refining the grains, improving the uniformity of the structure of the core of the steel plate, and the strength, weldability and low-temperature fracture toughness of the steel plate.

[0023] 3. The yield strength of the marine engineering steel plate disclosed in the present invention is above 420 MPa, the average core impact energy at -40°C is above 300 J, the elongation is above 24.5%, and the CTOD value of the heat affected zone after welding at -10°C is above 0.4 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The metallographic structure diagram of the steel plate obtained in Example 1 at 1 / 2 thickness;

[0025] Figure 2 Metallographic structure diagram of the steel plate obtained in Example 2 at 1 / 2 thickness;

[0026] Figure 3 Metallographic structure diagram of the steel plate obtained in Example 3 at 1 / 2 thickness;

[0027] Figure 4 Metallographic structure diagram of the steel plate at 1 / 2 thickness obtained in Comparative Example 1;

[0028] Figure 5 Metallographic structure diagram of the steel plate at 1 / 2 thickness obtained in Comparative Example 2;

[0029] Figure 6 Metallographic structure diagram of the steel plate obtained in Comparative Example 3 at 1 / 2 thickness. DETAILED DESCRIPTION

[0030] In order to facilitate understanding of the present disclosure, the present disclosure will be described more fully below. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present disclosure more thorough and comprehensive.

[0031] As used herein:

[0032] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0033] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0034] When amount, concentration or other value or parameter is represented by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1-5", described range should be interpreted as including range "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0035] In these examples, parts and percentages are by mass unless otherwise indicated.

[0036] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0037] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0038] On the one hand, the present disclosure provides a steel plate for marine engineering, wherein the composition of the steel plate includes, by mass percentage, C: 0.08%-0.15%, Si: 0.18%-0.42%, Mn: 1.40%-1.60%, Ni: 2.00%-3.10%, Nb: 0.045%-0.06%, Al: 0.03%-0.08%, Ti: 0.01%-0.02%, V: 0.02%-0.065%, Cu: 0.10%-0.25%, P≤0.013%, S≤0.0021%, Ceq≤0.59%, Pcm≤0.29%, and the balance is Fe and unavoidable impurities;

[0039] Where, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5,

[0040] Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0041] The present invention improves the core hardenability of the steel plate and refines the microstructure of the steel plate by adding high contents of Ni and Nb elements, so that the steel plate has higher strength, weldability and low-temperature fracture toughness; in addition, the steel plate of the present invention does not have additional Cr and Mo elements, which reduces the types of alloy elements, reduces the difficulty of controlling the composition of the steel plate, and improves the machinability of the steel plate.

[0042] Specifically, the mechanism of action of each alloy component in the steel plate disclosed in the present invention is as follows:

[0043] C: The content determines the equilibrium structure of the iron-carbon alloy, which in turn affects the mechanical properties of the material. The mass fraction of carbon in steel, as well as the form and distribution of carbon, affect the plasticity of steel at room temperature. During the thermal deformation of the steel plate, the C element will cause band segregation, thereby reducing the isotropy of the steel and deteriorating the room temperature plasticity; as the carbon content increases, carbides will aggregate in large quantities in the aggregate, producing coarse precipitates, which will affect the mechanical properties of the material, so the present invention controls the C content range to be 0.08%-0.15%.

[0044] Si: It is a commonly used deoxidizer, used to remove oxygen from molten steel. It exists in the form of SiO2 and can also play a role in solid solution strengthening. However, when the Si content is high, the toughness and plasticity of the steel will be reduced. Adding an appropriate amount of Si to steel can also inhibit the growth of carbides, thereby improving the toughness of the steel. However, the higher the Si content, the better. Too much Si content will affect the surface properties of the material and the toughness of the steel. Therefore, the present invention controls the Si content range to be 0.18%-0.42%.

[0045] Mn: It is also one of the deoxidizers, which can effectively improve the hot working performance and tear resistance of steel. Mn has the effect of delaying the transformation of austenite to ferrite in steel, which is beneficial to refining ferrite and improving strength and toughness. When the Mn content is low, the above effect is not significant, the strength and toughness of the steel plate are low, etc., and too high will cause segregation of the continuous casting billet and poor toughness. Therefore, the present invention takes into account the comprehensive addition of the alloy and the requirements of the classification society specifications, and controls the Mn content range to be 1.40%-1.80%.

[0046] Ni: It is a solid solution strengthener in steel and also a good hardenability additive. It can effectively improve the low temperature performance of steel, especially the low temperature fracture toughness. In addition, the compounding effect with the residual Cr and P in the steel will help improve the corrosion resistance of the steel. Therefore, the content of Ni in the present invention is controlled within the range of 2.00%-3.10%.

[0047] Nb: It can effectively prevent the recovery and recrystallization of deformed austenite during the rolling stage, has the effect of refining the grains, and can also play a role in precipitation strengthening. The solute drag effect of Nb and the pinning effect of Nb (C, N) on the austenite grain boundaries both inhibit the recrystallization of deformed austenite, expand the non-recrystallization range of austenite, and reduce the waiting time for the production of extra-thick plates. Precipitates are formed during cooling or tempering, thereby improving both the strength and toughness, and can also improve the corrosion resistance of the steel. The present invention controls the Nb content range to be 0.045%-0.06%.

[0048] Al: It is an important deoxidizing element in the steelmaking process. Adding a small amount of Al to steel can also effectively reduce the inclusion content in the steel and refine the grains. However, too much Al will promote surface cracks in the continuous casting billet, produce internal aluminum inclusions, and reduce the quality of the continuous casting billet. Therefore, the present invention controls the total Al content range to 0.03%-0.08%.

[0049] Ti: It also has the effect of grain refinement and precipitation strengthening. Studies have shown that TiN can effectively increase the austenite grain coarsening temperature and prevent the tendency of grain coarsening during thermal deformation. Ti has a strong affinity with O, C, N, and S. Ti combines with CN to form stable TiC, Ti (C, N) or TiN particles, which can withstand high temperatures above 1300°C without dissolving, and play a role in pinning austenite grain boundaries and maintaining austenite grain refinement. Ti and S can combine to form Ti4C2S2 or (MnTi)S, which reduces the content of MnS inclusions in steel, improves the heterogeneity of the structure, and thus improves the impact toughness of steel. Therefore, the present invention controls the Ti content range to be 0.01%-0.02%.

[0050] V: It has the highest solid solubility in steel. It mainly affects the structure and performance of steel by forming V (C, N). It precipitates in the ferrite at the austenite grain boundary. During the rolling process, it can inhibit the recrystallization of austenite and prevent the growth of grains, thereby refining the ferrite grains and improving the strength and toughness of steel. However, the amount of V added should not be too much. Therefore, the content of V in the present invention is controlled to be 0.02%-0.065%.

[0051] Cu: As an important additive element for improving the mechanical properties, corrosion resistance and cold working properties of steel plates, Cu exists in the form of solid solution and precipitation in steel, so the strengthening mechanism of Cu on steel is mainly solid solution strengthening and precipitation strengthening. The content of Cu in the present invention is controlled within the range of 0.10%-0.35%.

[0052] P and S are unfavorable elements in steel, which seriously affect the strength, toughness and corrosion resistance of steel, and their content needs to be controlled as low as possible. Therefore, the present invention controls the content of P to be below 0.013%, and the content of S to be below 0.0021%.

[0053] For example, in different embodiments, the mass percentage of C may be, but is not limited to, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%;

[0054] For example, in different embodiments, the mass percentage of Si may be, but is not limited to, 0.18%, 0.2%, 0.22%, 0.25%, 0.27%, 0.3%, 0.33%, 0.35%, 0.38%, 0.40%, 0.42%;

[0055] For example, in different embodiments, the mass percentage of Mn may be, but is not limited to, 1.4%, 1.42%, 1.44%, 1.46%, 1.48%, 1.5%, 1.52%, 1.54%, 1.56%, 1.58%, 1.6%;

[0056] For example, in different embodiments, the mass percentage of Ni may be, but is not limited to, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%;

[0057] For example, in different embodiments, the mass percentage of Nb may be, but is not limited to, 0.045%, 0.048%, 0.05%, 0.052%, 0.054%, 0.056%, 0.058%, 0.06%;

[0058] For example, in different embodiments, the mass percentage of Al may be, but is not limited to, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.06%, 0.065%, 0.07%, 0.075%, 0.08%;

[0059] For example, in different embodiments, the mass percentage of Ti may be, but is not limited to, 0.01%, 0.012%, 0.014%, 0.016%, 0.018%, 0.02%;

[0060] For example, in different embodiments, the mass percentage of V may be, but is not limited to, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065%;

[0061] For example, in different embodiments, the mass percentage of Cu may be, but is not limited to, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.23%, or 0.25%.

[0062] In some embodiments, the thickness of the steel plate is 180-250 mm, for example, but not limited to 180 mm, 200 mm, 220 mm, 240 mm, 250 mm.

[0063] In some embodiments, the steel plate has a yield strength of 420 MPa or more, an average core impact energy of 300 J or more at -40°C, an elongation of 24.5% or more, and a CTOD value of a heat affected zone after welding at -10°C of 0.4 mm or more.

[0064] Specifically, the yield strength of the steel plate is 420-510 MPa, the average core impact energy at -40°C is 300-320 J, the elongation is 24.5-32%, and the CTOD value of the heat affected zone after welding at -10°C is 0.4-0.9 mm.

[0065] In some embodiments, the metallographic structure of the steel plate is a mixture of ferrite and pearlite.

[0066] On the other hand, a method for preparing the marine engineering steel plate is provided, comprising the following steps:

[0067] The first steel billet is subjected to heating treatment, rolling treatment, water cooling treatment, and tempering heat treatment in sequence to obtain the marine engineering steel plate.

[0068] The rolling process comprises the following steps: performing first rolling and second rolling on the second steel billet obtained by the heat treatment to obtain a third steel billet; the first rolling temperature is 1100-1150°C, the last two rolling reductions are ≥16%, and the cumulative compression ratio is not less than 2.6; the second rolling temperature is 800-820°C, the final rolling temperature is ≥790°C, and the single rolling reduction is 1-5%;

[0069] The steps of water cooling treatment are: laminar cooling of the third steel billet, the water inlet temperature of the third steel billet is 760-790°C, and the red-returning temperature is 300-400°C.

[0070] Specifically, the starting rolling temperature of the first rolling may be, but is not limited to, 1100°C, 1120°C, 1130°C, 1140°C, or 1150°C.

[0071] Specifically, the first rolling passes are 5-8 passes, the reduction ratio of the last two passes is 16-20%, and the cumulative compression ratio is 2.6-2.9.

[0072] Specifically, the thickness of the steel billet obtained by the first rolling is ≥230 mm, such as 230-330 mm.

[0073] Specifically, the first rolling adopts large reduction rolling, and the rolling does not perform steel transfer rolling, maintaining full longitudinal rolling to ensure that the reduction rate of each pass in the first rolling process is set as much as possible according to the maximum rolling capacity; the second rolling adopts small reduction rolling to reduce the warping and deformation of the steel plate.

[0074] The first rolling under the above parameters can reduce the austenite grain size, make the high temperature austenite repeatedly undergo dynamic recovery and dynamic recrystallization behavior, and make the austenite grains fully refined by virtue of the inhibitory effect of microalloying elements Nb, Ti and their carbonitrides on recrystallization.

[0075] The second rolling under the above parameters can fully deform the austenite grains and increase the nucleation position and driving force of ferrite. Under the effect of lower finishing temperature and pass reduction rate, the effective grain size of the organization can be reduced, which is conducive to obtaining fine pearlite and ferrite organizations, thereby significantly improving the strength, weldability and low-temperature fracture toughness of the steel plate.

[0076] The use of laminar cooling for water cooling and control of the parameters of the water cooling treatment can promote the pearlite phase transformation and obtain a uniform and fine pearlite structure. The lamellar pearlite structure can further enhance the low-temperature fracture toughness of the steel plate.

[0077] In the water cooling treatment disclosed herein, the cooling rate of the laminar cooling is 5-10°C / s, for example, it can be but not limited to 5°C / s, 6°C / s, 7°C / s, 8°C / s, 9°C / s, 10°C / s.

[0078] Within the above cooling rate range, the phase transformation structure and size can be further controlled.

[0079] In some embodiments, in order to ensure the rolling reduction ratio of the steel billet, the thickness of the first steel billet is 600-950 mm and the width is ≥1870 mm.

[0080] In some embodiments, the first steel billet is prepared through molten steel smelting, LF refining, vacuum treatment, and continuous casting processes.

[0081] Specifically, the preparation steps of the first steel billet are as follows:

[0082] The molten iron is sequentially subjected to desulfurization, converter smelting, LF refining, RH vacuum treatment, calcium treatment, and continuous casting to obtain the first steel billet, wherein the molten iron desulfurization is ≤0.0021%, the converter smelting adopts the double slag method to control P≤0.013%, the LF refining adopts white slag operation for desulfurization and deoxidation, the vacuum degree of the RH vacuum treatment is ≤3.0mbar, the vacuum holding time is ≥15min, the calcium treatment is carried out after the vacuum is ended, and then the static stirring time is ≥12min, the continuous casting controls the superheat of the tundish to be 10-15℃, and the continuous casting implements full-process protective casting.

[0083] In some embodiments, the temperature of the heating treatment is 1100-1200° C., and the heating coefficient is 12-15 min / cm. The heating treatment under the above parameters can prevent the steel billet from being overheated and the original austenite grains from being coarsened during the heating process.

[0084] In some embodiments, the tempering heat treatment includes quenching and tempering; the quenching temperature is 890-900°C, and the holding time is 1.5-2 mm / min; the tempering temperature is 600-620°C, and the holding time is 2.5-3.5 mm / min.

[0085] In the present disclosure, through quenching treatment, the steel plate can have a good hardening effect along the entire thickness section, and a microstructure mixed with ferrite and pearlite is obtained; through tempering treatment, it is beneficial to eliminate the residual stress of the steel plate, make the performance of the steel plate more uniform, and improve the strength, weldability and low-temperature fracture toughness.

[0086] Specifically, the cooling method after quenching treatment is laminar cooling, and the cooling rate is 5-10°C / s; the cooling method after tempering treatment is air cooling.

[0087] In order to further illustrate the present invention, the marine engineering steel plate and the preparation method thereof provided by the present invention are described in detail below in combination with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0088] Example 1

[0089] The chemical composition of a steel plate for marine engineering in this embodiment is calculated by weight percentage: C: 0.08%, Si: 0.35%, Mn: 1.60%, Ni: 3.01%, Nb: 0.045%, Al: 0.05%, Ti: 0.02%, V: 0.021%, Cu: 0.15%, P: 0.013%, S: 0.0010%, and the remainder is Fe and unavoidable impurities.

[0090] The present embodiment provides a method for preparing a steel plate for marine engineering, comprising the following steps:

[0091] Preparation of the first steel billet: the molten iron is sequentially subjected to desulfurization, converter smelting, LF refining, RH vacuum treatment, calcium treatment, and continuous casting to obtain a first steel billet with a thickness of 600 mm and a width of 2350 mm, wherein the sulfur content of the molten iron after desulfurization is 0.0010%, the converter smelting adopts a double slag method to control P=0.013%, the LF refining adopts white slag operation for desulfurization and deoxidation, the vacuum degree of the RH vacuum treatment is 3.0 mbar, the vacuum holding time is 15 minutes, the calcium treatment is carried out after the vacuum is completed, and static stirring is carried out for 15 minutes after the calcium treatment is completed, the continuous casting controls the superheat of the tundish to be 10°C, and the continuous casting implements full-process protective casting;

[0092] Heating treatment: heating the first steel billet in a soaking furnace to obtain a second steel billet; the heating treatment time is 800 min and the heating treatment temperature is 1160° C.;

[0093] Rolling treatment: the second steel billet is subjected to the first rolling to obtain the third steel billet, and the third steel billet is subjected to the second rolling to obtain the fourth steel billet, wherein the first rolling adopts large reduction rolling, and no steel transfer rolling is performed during rolling, and full longitudinal rolling is maintained to ensure that the reduction rate of each pass is set as much as possible according to the maximum rolling capacity, the start rolling temperature of the first rolling is 1120°C, the final rolling temperature is 1070°C, the number of passes is 8, the reduction rates of the last two passes are 16 and 17% respectively, the cumulative compression ratio is 2.6, and the thickness of the third steel billet is 230mm; the start rolling temperature of the second rolling is 818°C, the final rolling temperature is 801°C, and a total of 8 rolling passes are performed, and the reduction rates of the passes are 5%, 5%, 5%, 4%, 4%, 3%, 3%, and 3% respectively; the thickness of the fourth steel billet is 180mm;

[0094] Water cooling treatment: the fourth steel billet is cooled by laminar cooling, the cooling rate is 5.3℃ / s, the water inlet temperature of the fourth steel billet is 770℃, and the red-returning temperature is 320℃;

[0095] Quenching and tempering heat treatment: the steel billet obtained by water cooling treatment is sequentially subjected to quenching treatment and tempering treatment, wherein the quenching temperature is 890°C, the holding time is 1.5 mm / min, and after the holding is completed, it is cooled to room temperature by laminar cooling, and the cooling rate is 7°C / s; the tempering temperature is 600°C, the holding time is 2.5 mm / min, and after the holding is completed, it is cooled to room temperature by air cooling to obtain a marine engineering steel plate with a thickness of 180 mm.

[0096] Example 2

[0097] The chemical composition of a steel plate for marine engineering in this embodiment is calculated by weight percentage: C: 0.14%, Si: 0.41%, Mn: 1.55%, Ni: 2.06%, Nb: 0.055%, Al: 0.07%, Ti: 0.018%, V: 0.055%, Cu: 0.13%, P: 0.013%, S: 0.0021%, and the balance is Fe and unavoidable impurities;

[0098] The present embodiment provides a method for preparing a steel plate for marine engineering, comprising the following steps:

[0099] Preparation of the first steel billet: the molten iron is sequentially subjected to desulfurization, converter smelting, LF refining, RH vacuum treatment, calcium treatment, and continuous casting to obtain a first steel billet with a thickness of 950 mm and a width of 1870 mm, wherein the sulfur content of the molten iron after desulfurization is 0.0021%, the converter smelting adopts the double slag method to control P=0.013%, the LF refining adopts white slag operation for desulfurization and deoxidation, the vacuum degree of the RH vacuum treatment is 3.0 mbar, the vacuum holding time is 15 minutes, the calcium treatment is carried out after the vacuum is completed, and the static stirring is carried out for 15 minutes after the calcium treatment is completed, the continuous casting controls the superheat of the tundish to be 10°C, and the continuous casting implements full-process protection casting;

[0100] Heating treatment: heating the first steel billet in a soaking furnace to obtain a second steel billet; the heating treatment time is 1200 minutes and the heating treatment temperature is 1200°C;

[0101] Rolling treatment: the second steel billet is subjected to the first rolling to obtain the third steel billet, and the third steel billet is subjected to the second rolling to obtain the fourth steel billet, wherein the first rolling adopts large reduction rolling, and no steel transfer rolling is performed during rolling, and full longitudinal rolling is maintained to ensure that the reduction rate of each pass is set as much as possible according to the maximum rolling capacity, the first rolling start temperature is 1150°C, the final rolling temperature is 1060°C, the number of passes is 8, the reduction rates of the last two passes are 20 and 18% respectively, the cumulative compression ratio is 2.88, and the thickness of the third steel billet is 330mm; the second rolling start temperature is 820°C, the final rolling temperature is 790°C, and a total of 8 rolling passes are performed, and the pass reduction rates are 5%, 5%, 5%, 4%, 4%, 2%, 2%, and 1% respectively; the thickness of the fourth steel billet is 250mm;

[0102] Water cooling treatment: the fourth steel billet is cooled by laminar cooling, the cooling rate is 9.7°C / s%, the water inlet temperature of the fourth steel billet is 780°C, and the red-returning temperature is 370°C;

[0103] Quenching and tempering heat treatment: the steel billet obtained by water cooling treatment is sequentially subjected to quenching treatment and tempering treatment, wherein the quenching temperature is 890°C, the holding time is 2.7 mm / min, and after the holding is completed, it is cooled to room temperature by laminar cooling, and the cooling rate is 10°C / s; the tempering temperature is 620°C, the holding time is 3 mm / min, and after the holding is completed, it is cooled to room temperature by air cooling to obtain a marine engineering steel plate with a thickness of 250 mm.

[0104] Example 3

[0105] The chemical composition of a steel plate for marine engineering in this embodiment is calculated by weight percentage as follows: C: 0.11%, Si: 0.18%, Mn: 1.60%, Ni: 2.45%, Nb: 0.045%, Al: 0.03%, Ti: 0.01%, V: 0.065%, Cu: 0.25%, P: 0.013%, S: 0.0021%, and the remainder is Fe and unavoidable impurities.

[0106] The present embodiment provides a method for preparing a steel plate for marine engineering, comprising the following steps:

[0107] Preparation of the first steel billet: the molten iron is sequentially subjected to desulfurization, converter smelting, LF refining, RH vacuum treatment, calcium treatment, and continuous casting to obtain a first steel billet with a thickness of 760 mm and a width of 1870 mm, wherein the sulfur content of the molten iron after desulfurization is 0.0021%, the converter smelting adopts the double slag method to control P=0.013%, the LF refining adopts white slag operation for desulfurization and deoxidation, the vacuum degree of the RH vacuum treatment is 3.0 mbar, the vacuum holding time is 15 minutes, the calcium treatment is carried out after the vacuum is completed, and static stirring is carried out for 15 minutes after the calcium treatment is completed, the continuous casting controls the superheat of the tundish to be 10°C, and the continuous casting implements full-process protection casting;

[0108] Heating treatment: heating the first steel billet in a soaking furnace to obtain a second steel billet; the heating treatment time is 1200 minutes and the heating treatment temperature is 1200°C;

[0109] Rolling treatment: the second steel billet is subjected to the first rolling to obtain the third steel billet, and the third steel billet is subjected to the second rolling to obtain the fourth steel billet, wherein the first rolling adopts large reduction rolling, and no steel transfer rolling is performed during rolling, and full longitudinal rolling is maintained to ensure that the reduction rate of each pass is set as much as possible according to the maximum rolling capacity, the start rolling temperature of the first rolling is 1150°C, the final rolling temperature is 1060°C, the number of passes is 5 times, the reduction rates of the last two passes are 20 and 18% respectively, the cumulative compression ratio is 2.7, and the thickness of the third steel billet is 280mm; the start rolling temperature of the second rolling is 820°C, the final rolling temperature is 790°C, and a total of 8 rolling passes are performed, and the reduction rates of the passes are 5%, 5%, 5%, 4%, 4%, 2%, 2%, and 1% respectively; the thickness of the fourth steel billet is 200mm;

[0110] Water cooling treatment: the fourth steel billet is cooled by laminar cooling, the cooling rate is 6.8℃ / s, the water inlet temperature of the fourth steel billet is 780℃, and the red-returning temperature is 370℃;

[0111] Quenching and tempering heat treatment: the steel billet obtained by water cooling treatment is sequentially subjected to quenching treatment and tempering treatment, wherein the quenching temperature is 890°C, the holding time is 2.7 mm / min, and after the holding is completed, it is cooled to room temperature by laminar cooling, and the cooling rate is 10°C / s; the tempering temperature is 620°C, the holding time is 3 mm / min, and after the holding is completed, it is cooled to room temperature by air cooling to obtain a marine engineering steel plate with a thickness of 200 mm.

[0112] Comparative Example 1

[0113] The chemical composition of a steel plate for marine engineering in this comparative example is as follows by weight percentage: C: 0.08%, Si: 0.35%, Mn: 1.60%, Ni: 1.50%, Nb: 0.045%, Al: 0.05%, Ti: 0.02%, V: 0.021%, Cu: 0.15%, P: 0.013%, S: 0.0010%, and the remainder is Fe and unavoidable impurities.

[0114] The preparation method of a marine engineering steel plate in this comparative example is the same as that in Example 1.

[0115] Comparative Example 2

[0116] The chemical composition of a steel plate for marine engineering in this comparative example is as follows by weight percentage: C: 0.08%, Si: 0.35%, Mn: 1.60%, Ni: 3.01%, Nb: 0.032%, Al: 0.05%, Ti: 0.02%, V: 0.021%, Cu: 0.15%, P: 0.013%, S: 0.0010%, and the remainder is Fe and unavoidable impurities.

[0117] The preparation method of a marine engineering steel plate in this comparative example is the same as that in Example 1.

[0118] Comparative Example 3

[0119] The chemical composition of a steel plate for marine engineering in this comparative example is as follows by weight percentage: C: 0.08%, Si: 0.35%, Mn: 1.60%, Ni: 3.01%, Nb: 0.045%, Al: 0.05%, Ti: 0.02%, V: 0.021%, Cu: 0.15%, P: 0.013%, S: 0.0010%, and the balance is Fe and unavoidable impurities.

[0120] The only difference between the preparation method of a marine engineering steel plate in this comparative example and Example 1 is that the red-returning temperature in the water cooling treatment is different. The red-returning temperature in the water cooling treatment in this comparative example is 450°C.

[0121] Performance Testing

[0122] The performance test of the marine engineering steel plates obtained in each embodiment and comparative example is carried out as follows:

[0123] (1) Mechanical properties: The tensile properties of the steel plate were tested at room temperature according to GB / T228.1-2021 standard;

[0124] (2) Impact performance: The impact performance test was carried out on the welded joint cooled to room temperature after welding according to GB / T 2650-2008, and the low-temperature impact energy of -40°C at 1 / 2 thickness of the heat affected zone of the welded joint was obtained;

[0125] (3) Low-temperature fracture toughness: Referring to the standard ISO 15653:2018, the steel plates were welded by gas shielded welding with a welding line energy of 7 kJ / cm. The three-point bending test was used to detect the CTOD characteristic value of the crack tip opening displacement of the full thickness of the welded joint at -10°C. The notch position was located in the coarse-grained area of ​​the welding heat affected zone (GCHAZ).

[0126] The test results are shown in Table 1.

[0127] Table 1

[0128]

[0129]

[0130] It can be seen from the experimental data in Table 1 that the mechanical properties of the implementation cases of the marine engineering steel plate disclosed in the present invention all meet the claims, while changing the content of main elements and the preparation process will significantly reduce the mechanical properties of the material.

[0131] In Comparative Example 1, adding less Ni will reduce the strength and low-temperature toughness and deteriorate the welding performance; in Comparative Example 2, adding less Nb will cause the strength and toughness to decrease. In Comparative Example 3, the higher red-return temperature causes a significant decrease in both strength and toughness.

[0132] Take samples of 15×15 cm from the head of the steel plate, make metallographic samples along the rolling direction, and after mechanical grinding and polishing, nitric acid alcohol corrosion, put them under a metallographic microscope for organization observation. The metallographic structure at 1 / 2 thickness of the steel plate is measured. The results are as follows: Figure 1-6 shown.

[0133] Figure 1 This is the metallographic structure diagram of the steel plate obtained in Example 1 at 1 / 2 thickness. Figure 2 This is the metallographic structure diagram of the steel plate obtained in Example 2 at 1 / 2 thickness. Figure 3 This is the metallographic structure diagram of the steel plate obtained in Example 3 at 1 / 2 thickness. Figure 4 This is the metallographic structure diagram of the steel plate obtained in Example 4 at 1 / 2 thickness. Figure 5 This is the metallographic structure diagram of the steel plate at 1 / 2 thickness obtained in Example 1. Figure 6 This is a metallographic structure diagram of the steel plate obtained in Example 2 at 1 / 2 thickness. It can be seen from the figure that the metallographic structure of the steel plate obtained in the embodiment of the present disclosure is a mixed structure of ferrite and pearlite, with fine grains. Figure 1-3 It can be seen that with the increase of thickness, the size of ferrite and pearlite increases. Figure 1 and Figure 4 It can be seen that the reduction of Ni content reduces the content of polygonal ferrite and increases the content of acicular ferrite, thus affecting the toughness and strength. Figure 1 and Figure 5 It can be seen that the reduction of Nb content increases the size of austenite mechanism, reduces precipitation strengthening and solid solution strengthening, and leads to a decrease in strength and low-temperature toughness. Figure 1 and Figure 6 It can be seen that the higher red-returning temperature mainly causes the grains to coarsen and the ferrite and pearlite grain sizes to increase, thereby causing the mechanical properties of the material to deteriorate.

[0134] Finally, it should be noted that the above embodiments are used to illustrate the technical solution of the present disclosure rather than to limit the protection scope of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present disclosure can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present disclosure.

Claims

1. A steel plate for marine engineering, characterized in that: The steel plate comprises, by mass percentage, C: 0.08%-0.15%, Si: 0.18%-0.42%, Mn: 1.40%-1.60%, Ni: 2.00%-3.10%, Nb: 0.045%-0.06%, Al: 0.03%-0.08%, Ti: 0.01%-0.02%, V: 0.02%-0.065%, Cu: 0.10%-0.25%, P≤0.013%, S≤0.0021%, Ceq≤0.59%, Pcm≤0.29%, and the balance is Fe and unavoidable impurities; Where, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

2. The marine engineering steel plate according to claim 1, characterized in that: The thickness of the steel plate is 180-250 mm.

3. The marine engineering steel plate according to claim 1, characterized in that: The steel plate has a yield strength of more than 420 MPa, an average core impact energy of more than 300 J at -40°C, an elongation of more than 24.5%, and a CTOD value of a heat-affected zone after welding at -10°C of more than 0.4 mm.

4. The marine engineering steel plate according to claim 1, characterized in that: The metallographic structure of the steel plate is a mixture of ferrite and pearlite.

5. The method for preparing a steel plate for marine engineering according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: subjecting the first steel billet to heating treatment, rolling treatment, water cooling treatment, and quenching and tempering heat treatment in sequence to obtain the marine engineering steel plate; The rolling process comprises the following steps: performing first rolling and second rolling on the second steel billet obtained by the heat treatment to obtain a third steel billet; the first rolling temperature is 1100-1150°C, the last two rolling reductions are ≥16%, and the cumulative compression ratio is not less than 2.6; the second rolling temperature is 800-820°C, the final rolling temperature is ≥790°C, and the single rolling reduction is 1-5%; The steps of water cooling treatment are: laminar cooling of the third steel billet, the water inlet temperature of the third steel billet is 760-790°C, and the red-returning temperature is 300-400°C.

6. The method for preparing a steel plate for marine engineering according to claim 5, characterized in that: The first steel billet has a thickness of 600-950 mm and a width of ≥1870 mm.

7. The method for preparing a steel plate for marine engineering according to claim 5, characterized in that: The first steel billet is prepared through molten steel smelting, LF refining, vacuum treatment and continuous casting processes.

8. The method for preparing a steel plate for marine engineering according to claim 5, characterized in that: The temperature of the heating treatment is 1100-1200° C., and the heating coefficient is 12-15 min / cm.

9. The method for preparing a steel plate for marine engineering according to claim 5, characterized in that: The quenching and tempering heat treatment includes quenching treatment and tempering treatment; the temperature of the quenching treatment is 890-900°C, and the holding time is 1.5-2mm / min; the temperature of the tempering treatment is 600-620°C, and the holding time is 2.5-3.5mm / min.

10. The method for preparing a steel plate for marine engineering according to claim 5, characterized in that: The cooling rate of the laminar cooling is 5-10°C / s.

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