36-grade high-strength marine steel and production method thereof

Abstract

The invention provides 36-grade high-strength marine steel and a production method thereof, and the 36-grade high-strength marine steel comprises the following components in percentage by mass: 0.06 wt% < = C < = 0.14 wt%, 0.10 wt% < = Si < = 0.30 wt%, 1.20 wt% < = Mn < = 1.50 wt%, 0.020 wt% < = P, 0.008 wt% < = S, 0.018 wt% < = Als < = 0.050 wt%, 0.0065 < = N < = 0.010 wt%, 0.0080 < = Ti < = 0.020 wt%, 0.020 wt% < = Nb < = 0.040 wt%, 0.025 wt% < = V < = 0.040 wt%, and the balance of steel. And the balance of iron and other inevitable impurities. By accurately controlling the content of alloy elements, the strength of the 36-grade high-strength marine steel is enhanced, and the service life of the product is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled steel plates, and in particular to a 36-grade high-strength shipbuilding steel and a production method thereof. Background Art

[0002] Grade 36 marine steel products are usually used in common structural parts such as hull decks and hull shells. They undergo complex process flows such as laser cutting, assembly welding, and fire calibration, so they need to have high stable mechanical properties and low internal stress quality requirements.

[0003] In order to meet the process requirements of high-temperature fire calibration and laser cutting processing, the 36-grade high-strength shipbuilding steel product materials are often produced using the TMCP+normalizing heat treatment process in common technology to meet the quality requirements of high performance stability, good welding performance and low internal stress. However, the normalizing heat treatment temperature is high and the production cost is high, resulting in high prices for coil-rolled Kaiping shipbuilding steel plate products.

[0004] Based on this, it is necessary to provide a grade 36 high-strength shipbuilding steel and a production method thereof to alleviate or solve the above problems. Summary of the invention

[0005] The invention aims to solve the technical problem that the normalizing heat treatment process is required for grade 36 ship steel in the above-mentioned common technology, which leads to the extension of the production line and the production cycle and causes the cost to rise. The invention provides a grade 36 high-strength ship steel, which comprises, by mass fraction: 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities.

[0006] Furthermore, the ratings of A, B, C and D inclusions in the grade 36 high-strength marine steel do not exceed 1.5.

[0007] Furthermore, the microstructure of the grade 36 high-strength shipbuilding steel includes ferrite, bainite, and pearlite, and the grain size rating of the grade 36 high-strength shipbuilding steel is above grade ten.

[0008] The present invention provides a method for producing grade 36 high-strength shipbuilding steel, comprising the steps of:

[0009] The steel is tapped from a converter and refined by LF to obtain a refined molten steel; the composition of the molten steel comprises, by mass fraction, 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities;

[0010] The refined molten steel is continuously cast to obtain a slab;

[0011] The slab is rolled and then coiled to obtain the grade 36 high-strength shipbuilding steel, and the coiling temperature exceeds 780°C.

[0012] Furthermore, in the step of tapping the steel from the converter and refining the steel by LF to obtain the refined molten steel, when the oxygen content in the molten steel is ≤20ppm, a lanthanide rare earth alloy is added to the molten steel, and the amount of the lanthanide rare earth alloy added is 0.30-0.40kg / T.

[0013] Furthermore, the rolling includes initial rolling and finishing rolling, the finishing rolling temperature is not lower than 900°C, the reduction rate during the finishing rolling process is not less than 50%, and the finishing rolling speed is 6-8m / s.

[0014] Furthermore, in the step of continuously casting the refined molten steel to obtain a slab, the continuous casting adopts a three-stage dynamic light reduction with a reduction of 3.5-4.5 mm, the pulling speed during the continuous casting is controlled to be 1.2-1.5 m / min, and the secondary cooling water volume is 0.70-0.85 L / Kg.

[0015] 8. The production method according to claim 4 is characterized in that, in the step of coiling the slab after rolling to obtain the grade 36 high-strength shipbuilding steel, the slab is heated before the rolling, the heating temperature is 1180-1220°C, and the heating time is 180-350 minutes.

[0016] Furthermore, in the step of coiling the slab after rolling to obtain the grade 36 high-strength shipbuilding steel, the coiled steel coil is subjected to a flattening treatment, and the rough straightening entrance pressure is reduced to -5mm to -10mm during the flattening treatment;

[0017] In the flattening process, when the thickness of the grade 36 high-strength shipbuilding steel is required to be no more than 12 mm, the straightness is ≤2 mm / m; when the thickness of the grade 36 high-strength shipbuilding steel is required to be greater than 12 mm, the straightness is ≤3 mm / m or ≤5 mm / 2m.

[0018] Furthermore, the steel plate after the peening treatment is subjected to tempering heat treatment to obtain the 36-grade high-strength shipbuilding steel, the tempering temperature in the tempering heat treatment is 610±10°C, and the tempering heat treatment time is 1.4min / mm+12min.

[0019] Compared with the prior art, the present invention has at least the following advantages: the present invention controls the chemical composition of the 36-grade high-strength shipbuilding steel as follows:

[0020] Calculated by mass fraction, its composition includes: 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities.

[0021] Specifically, the present invention controls the carbon content of the 36-grade high-strength shipbuilding steel to 0.06wt% to 0.12wt%, which helps to improve the toughness and welding performance of the 36-grade high-strength shipbuilding steel.

[0022] The present invention controls the manganese content of the 36-grade high-strength shipbuilding steel to be 1.20wt%-1.50wt%, thereby enhancing the strength and toughness of the 36-grade high-strength shipbuilding steel in the present invention.

[0023] The present invention controls the phosphorus (P) and sulfur (S) contents of 36-grade high-strength shipbuilding steel to ≤0.020wt% and ≤0.008wt%, respectively, thereby improving the cleanliness, toughness and welding performance of the steel and reducing cracks and defects that may occur during welding.

[0024] The present invention also accurately controls the contents of alloying elements such as aluminum (Als), nitrogen (N), titanium (Ti), niobium (Nb) and vanadium (V), respectively, adopts Nb and V micro-alloying to refine grain strengthening, and adopts vanadium-nitrogen micro-alloying strengthening effect, which also reduces the difficulty of smelting process of controlling N content in molten steel; controls the addition of C and Mn elements to reduce the segregation defects of C and Mn elements; utilizes rare earth treatment smelting to control inclusions and improve the cleanliness of molten steel, further optimizes the mechanical properties and corrosion resistance of steel, and extends the service life of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0026] Figure 1 This is a physical picture of the 36-grade high-strength shipbuilding steel produced in Example 1 of the present invention.

[0027] Figure 2 This is a physical picture of the 36-grade high-strength shipbuilding steel produced in Comparative Example 1 of the present invention.

[0028] Figure 3 This is the metallographic structure diagram of the 36-grade high-strength shipbuilding steel prepared in Example 1 of the present invention.

[0029] Figure 4 This is the metallographic structure diagram of the 36-grade high-strength shipbuilding steel prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any method, device and material of the prior art similar or equivalent to the method, device and material in the embodiments of the present invention can also be used to implement the present invention.

[0033] In order to solve the technical problems faced by the above-mentioned conventional technologies, the present invention provides a grade 36 high-strength shipbuilding steel, characterized in that, calculated by mass fraction, its composition includes: 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities.

[0034] Specifically, the present invention controls the carbon content of the 36-grade high-strength shipbuilding steel to 0.06wt% to 0.12wt%, which helps to improve the toughness and welding performance of the 36-grade high-strength shipbuilding steel.

[0035] The present invention controls the phosphorus (P) and sulfur (S) contents of 36-grade high-strength shipbuilding steel to ≤0.020wt% and ≤0.008wt%, respectively, thereby improving the cleanliness, toughness and welding performance of the steel and reducing cracks and defects that may occur during welding.

[0036] The present invention also accurately controls the contents of alloying elements such as aluminum (Als), nitrogen (N), titanium (Ti), niobium (Nb) and vanadium (V), respectively, adopts Nb and V micro-alloying to refine grain strengthening, and adopts vanadium-nitrogen micro-alloying strengthening effect, which also reduces the difficulty of smelting process of controlling N content in molten steel; controls the addition of C and Mn elements to reduce the segregation defects of C and Mn elements; utilizes rare earth treatment smelting to control inclusions and improve the cleanliness of molten steel, further optimizes the mechanical properties and corrosion resistance of steel, and extends the service life of the structure.

[0037] Exemplarily, the carbon content in grade 36 high-strength shipbuilding steel can be 0.07wt% to 0.14wt%; in some specific embodiments, the carbon content in grade 36 high-strength shipbuilding steel can be 0.07wt% to 0.08wt%; in some more specific embodiments, the carbon content in grade 36 high-strength shipbuilding steel can be 0.13wt% to 0.14wt%.

[0038] For example, the silicon content in grade 36 high-strength shipbuilding steel may be 0.1wt% to 0.2wt%; the silicon content in grade 36 high-strength shipbuilding steel may be 0.2wt% to 0.3wt%.

[0039] For example, the manganese content in grade 36 high-strength shipbuilding steel may be 1.2wt% to 1.3wt%; the manganese content in grade 36 high-strength shipbuilding steel may be 1.25wt% to 1.35wt%; the manganese content in grade 36 high-strength shipbuilding steel may be 1.3wt% to 1.4wt%.

[0040] Exemplarily, the phosphorus content in grade 36 high-strength shipbuilding steel may be 0.012wt% to 0.014wt%; the phosphorus content in grade 36 high-strength shipbuilding steel may be 0.012wt% to 0.013wt%; the phosphorus content in grade 36 high-strength shipbuilding steel may be 0.013wt% to 0.014wt%.

[0041] For example, the sulfur content in grade 36 high-strength shipbuilding steel may be 0.002 wt% to 0.003 wt%.

[0042] Exemplarily, the acid-soluble aluminum content in grade 36 high-strength shipbuilding steel may be 0.02wt% to 0.03wt%; the acid-soluble aluminum content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.04wt%; the acid-soluble aluminum content in grade 36 high-strength shipbuilding steel may be 0.02wt% to 0.04wt%.

[0043] For example, the nitrogen content in grade 36 high-strength shipbuilding steel may be 0.007wt% to 0.008wt%; the nitrogen content in grade 36 high-strength shipbuilding steel may be 0.005wt% to 0.008wt%.

[0044] For example, the titanium content in grade 36 high-strength shipbuilding steel may be 0.013wt% to 0.015wt%; the titanium content in grade 36 high-strength shipbuilding steel may be 0.008wt% to 0.015wt%.

[0045] For example, the niobium content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.04wt%; the niobium content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.036wt%; the niobium content in grade 36 high-strength shipbuilding steel may be 0.032wt% to 0.036wt%.

[0046] For example, the vanadium content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.032wt%; the vanadium content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.035wt%; the vanadium content in grade 36 high-strength shipbuilding steel may be 0.03wt% to 0.04wt%.

[0047] The rating of A, B, C, and D inclusions in grade 36 high-strength shipbuilding steel does not exceed 1.5. In metallographic testing, A, B, C, and D inclusions are classified according to their morphology and composition. A inclusions (sulfide inclusions): B inclusions (alumina inclusions): C inclusions (silicate inclusions): D inclusions (spherical oxide inclusions).

[0048] The microstructure of grade 36 high-strength shipbuilding steel includes ferrite, bainite and pearlite. The grain size rating of grade 36 high-strength shipbuilding steel is above grade 10, and the pearlite and bainite structures are evenly dispersed, ensuring strength and excellent low-temperature toughness.

[0049] The present invention also provides a method for producing grade 36 high-strength shipbuilding steel, comprising the steps of:

[0050] S1. The steel is tapped from a converter and refined by LF to obtain a refined molten steel; the composition of the molten steel comprises, by mass fraction, 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities.

[0051] In some embodiments, in the step of obtaining refined molten steel through LF refining, when the molten steel alloy is adjusted in place, the molten steel is well deoxidized, and the oxygen content is not more than 20ppm, a lanthanide rare earth alloy is added to the molten steel, and the amount of the lanthanide rare earth alloy added is 0.30-0.40kg / T.

[0052] S2. The refined molten steel is continuously cast to obtain slabs.

[0053] In some embodiments, the thickness of the slab may be 230 mm.

[0054] The center segregation and center porosity of the slab shall not exceed C1.5.

[0055] In some embodiments, continuous casting can adopt three-stage dynamic soft reduction, with a reduction of 3.5-4.5 mm, and the pulling speed during the continuous casting process is controlled to be 1.2-1.5 m / min, and the secondary cooling water volume is 0.70-0.85 L / Kg. The hot-rolled raw material slab not only has a small inclusion content, but also has stable slab quality, especially slight internal segregation defects, and the center segregation and center porosity of the slab do not exceed C1.5 level.

[0056] S3. The slab is rolled and then coiled to obtain the grade 36 high-strength shipbuilding steel, and the coiling temperature exceeds 780°C.

[0057] In some embodiments, the slab may be subjected to a heating treatment before the rolling treatment, the heating treatment temperature being 1180-1220° C., and the heating treatment time being 180-350 min.

[0058] In some embodiments, rolling includes initial rolling and finishing rolling, the finishing rolling temperature is not less than 900° C., the reduction ratio during the finishing rolling process is not less than 50%, and the finishing rolling speed is not less than 6 m / s.

[0059] In some embodiments, the temperature of the finish rolling may be no higher than 950°C.

[0060] For example, the temperature of the finish rolling may be 900-950°C.

[0061] The coiling temperature is not less than 780℃.

[0062] In some embodiments, the coiling temperature may be no higher than 850°C.

[0063] An exemplary coiling temperature may be 780-850°C.

[0064] In some embodiments, the finishing rolling, layer cooling and coiling processes are controlled without water cooling, and a heat preservation cover is used from the initial rolling to the finishing rolling process, and the process control time is 30 to 60 seconds.

[0065] The coiled steel coils can be stacked to ensure uniform cooling of the entire steel coil. The rolled steel coils can be transported out of the hot rolling warehouse after being stacked for 24 hours after hot rolling to avoid repeated heating of the steel coils.

[0066] For example, the steel coil may be unrolled until the overall temperature of the coiled steel coil is lower than 60° C.

[0067] During the Kaiping process, the rough straightening entrance pressure can be reduced to -5mm~-10mm.

[0068] In the flattening process, when the thickness of the grade 36 high-strength shipbuilding steel is required to be no more than 12 mm, the straightness is ≤2 mm / m; when the thickness of the grade 36 high-strength shipbuilding steel is required to be greater than 12 mm, the straightness is ≤3 mm / m or ≤5 mm / 2m.

[0069] In some embodiments, the steel plate after the peening treatment is subjected to tempering heat treatment to obtain the 36-grade high-strength shipbuilding steel, the tempering temperature in the tempering heat treatment is 610±10°C, and the tempering heat treatment time is 1.4min / mm+12min.

[0070] Grade 36 Grade 36 high-strength marine steel plates have relatively low material grades and are mainly used for main hull structures such as shipbuilding plywood components. Especially with the popularization of automation such as laser cutting and automatic welding in shipyard processing and the improvement of construction appearance requirements, steel plate materials not only need to have high toughness, but also need to be resistant to high-temperature fire calibration during use and have high flatness after laser cutting, and have high quality requirements for mechanical properties stability, residual internal stress, etc. In order to meet the process requirements of high-temperature fire calibration and laser cutting processing, the 36-grade high-strength marine steel product materials are produced using the TMCP+ normalizing heat treatment process to meet the quality of high mechanical properties stability and low internal stress.

[0071] The functions of normalizing heat treatment process are as follows: first, the strength and toughness of steel parts can be accurately controlled to achieve the best balance state, meeting the dual requirements of strength and toughness of marine steel; second, the structure of steel parts after normalizing treatment is more uniform, which is beneficial to improve the corrosion resistance of steel and extend the service life of the hull structure; finally, the hardness of steel parts after normalizing treatment is moderate, which is beneficial to heat conduction and weld formation during welding, ensuring welding quality.

[0072] In common technology, normalizing is a heat treatment process in which steel parts are heated to an appropriate temperature (30 to 50°C above Ac3 for hypoeutectoid steel and above Accm for hypereutectoid steel), kept at this temperature for a certain period of time, and then cooled in air.

[0073] The present invention utilizes the rolling temperature to propose a high-temperature rolling method to increase the rolling and coiling temperatures in the rolling process, so as to achieve high stability of the material performance in the conventional heat treatment production process, and subsequently adopts a tempering heat treatment production process at about 600°C to further reduce the residual internal stress of the material. The inclusions of A, B, C, and D in the high-strength shipbuilding steel prepared by the present invention are controlled to be no more than 1.5, the microstructure of the material is mainly ferrite, bainite, and pearlite, the grains are uniform, the flatness of the steel plate is good, and the quality stability of mechanical properties and internal stress is high. Therefore, the steel plate material has high processing stability and aesthetics.

[0074] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0075] Example 1: The production order thickness specification is 6mm, the actual picture is as follows Figure 1 Shown

[0076] This embodiment provides a method for producing and manufacturing a low-cost, high-quality, grade 36 high-strength shipbuilding steel. The specific implementation process includes:

[0077] S1. Composition of molten steel in the middle package: C: 0.075wt%, Si: 0.183wt%, Mn: 1.256wt%, P: 0.0122wt%, S: 0.0022wt%, Als: 0.0276wt%, N: 0.0075wt%, Ti: 0.0150wt%, Nb: 0.032wt%, V: 0.030wt%, and the rest are iron and unavoidable elements.

[0078] S2. Rare earth addition amount is 0.30Kg / T, rare earth element content of molten steel is 0.0019%, oxygen content is 0.0015%, casting speed is 1.35m / min, dynamic soft pressure is 4.5mm for casting, specific water content is 0.77L / Kg. Center segregation of casting is C1.5.

[0079] S3. Rolling process: Finishing rolling temperature is 920°C, coiling temperature is 810°C, ingot thickness is 230mm, continuous casting ingot outlet temperature is 1215°C, and total heating time is 212 minutes.

[0080] S4. According to the hot rolling process, the rolled steel coil is shipped out for 24 hours to be cooled. When the steel coil is naturally cooled to below 60℃, it is processed for flattening and cutting. The production specification of the order thickness is 6mm, and the pressure reduction at the entrance of the rough straightening is reduced to -4mm. The straightness of the steel plate does not exceed 3mm / 2m.

[0081] S5. The rolled flat steel plate is subjected to tempering heat treatment, the tempering temperature is 600±5℃, and the tempering time is 20min.

[0082] Example 2: Production order thickness specification 5mm

[0083] This embodiment provides a method for producing and manufacturing a low-cost, high-quality, grade 36 high-strength shipbuilding steel. The specific implementation process includes:

[0084] S1. Composition of molten steel in the middle package: C: 0.135wt%, Si: 0.253wt%, Mn: 1.326wt%, P: 0.0132wt%, S: 0.003wt%, Als: 0.0326wt%, N: 0.0080wt%, Ti: 0.0130wt%, Nb: 0.0352wt%, V: 0.032wt%. The rest are iron and unavoidable elements.

[0085] S2. Rare earth addition amount is 0.35Kg / T, rare earth element content of molten steel is 0.0015%, oxygen content is 0.0020%, casting speed is 1.40m / min, dynamic soft pressure is 4.5mm for casting, specific water content is 0.73L / Kg. Center segregation of casting is not more than C1.5.

[0086] S3. Rolling process: Finishing rolling temperature is 900°C, coiling temperature is 800°C, ingot thickness is 230mm, continuous casting ingot outlet temperature is 1205°C, and total heating time is 226 minutes.

[0087] S4 is rolled according to the hot rolling process. The rolled steel coil is shipped out for cooling within 24 hours. After the steel coil is naturally cooled to below 60℃, it is processed for cutting and flattening. The production specification of the order thickness is 5mm, and the pressure reduction at the entrance of the rough straightening is reduced to -5mm. The straightness of the steel plate does not exceed 4mm / 2m.

[0088] S5. The coiled flat steel plate is subjected to tempering heat treatment, the tempering temperature is 610±5℃, and the tempering time is 20min.

[0089] Comparative Example 1: The production order thickness specification is 8mm, the actual picture is as follows Figure 2 Shown

[0090] This comparative example provides a conventional high-quality DH36 grade shipbuilding steel production method, and the specific implementation process includes:

[0091] S1. Composition of molten steel in the middle package: C: 0.132wt%, Si: 0.353wt%, Mn: 1.35wt%, P: 0.0122wt%, S: 0.0042wt%, Als: 0.0266wt%, N: 0.0052wt%, Nb: 0.036wt%, and the rest are iron and unavoidable elements.

[0092] S2. After KR desulfurization, the hot metal is added to the top and bottom double-blown converter for smelting, LF refining + calcium treated steel refining, casting speed 1.40m / min, dynamic light pressure reduction 4.5mm for the ingot, specific water content 0.73L / Kg. The center segregation of the ingot is C2.0, and the middle crack is 0.5.

[0093] S3. The thickness of the casting is 230 mm, the temperature of the continuous casting is 1205 ° C, and the total heating time is 236 minutes. The rolling process is the finishing temperature of 860 ° C, the coiling temperature of 610 ° C, and the laminar cooling water ratio is 1:1.1.

[0094] S4. Rolling is controlled according to the hot rolling process. The rolled steel coil is placed in the hot coil warehouse for more than 48 hours. The steel coil is naturally cooled to below 60℃ for flattening and cutting. The pressure at the entrance of rough straightening is reduced to -5mm, and the straightness of the steel plate is 3mm / 2m.

[0095] S4. The coiled flat steel plate adopts normalizing heat treatment process, the normalizing temperature is 850℃, and the normalizing time is 16min.

[0096] Comparative Example 2: Production order thickness specification 6mm

[0097] This comparative example provides a conventional high-quality DH36 grade shipbuilding steel production method, and the specific implementation process includes:

[0098] S1. Composition of molten steel in the middle package: C: 0.142wt%, Si: 0.323wt%, Mn: 1.38wt%, P: 0.0142wt%, S: 0.0022wt%, Als: 0.0246wt%, N: 0.0060wt%, Nb: 0.037wt%, and the rest are iron and unavoidable elements.

[0099] S2. After KR desulfurization, hot metal is added to the top and bottom double-blown converter for smelting, LF refining + calcium treated steel refining, casting speed 1.40m / min, dynamic soft pressure reduction 4.5mm for the ingot, specific water content 0.73L / Kg. The center segregation of the ingot is C2.5, and the middle crack is 1.0.

[0100] S3. The thickness of the casting is 230mm, the temperature of the continuous casting is 1225℃, and the total heating time is 256 minutes. The rolling process is the finishing temperature of 870℃, the coiling temperature of 610℃, and the laminar cooling water ratio is 1:1.1.

[0101] S3. Rolling is controlled according to the hot rolling process. The rolled steel coil is placed in the hot coil warehouse for more than 48 hours. The steel coil is naturally cooled to below 60℃ for flattening and cutting. The pressure at the entrance of rough straightening is reduced to -5mm, and the straightness of the steel plate is 5mm / 2m.

[0102] S4. The coiled flat steel plate adopts normalizing heat treatment process, the normalizing temperature is 870℃, and the normalizing time is 12min.

[0103] Analysis example 1

[0104] 1. Comparison of mechanical properties:

[0105] By adopting rare earth treatment technology and V, Nb microalloying composition design, inclusion control is better than the conventional Nb microalloying, and the low carbon composition is conducive to the control of low-magnification center segregation of slabs.

[0106]

[0107] 2. Example inclusions and low magnification of ingots

[0108]

[0109] 3. Comparison of metallographic structures

[0110] The metallographic structure is mainly ferrite + pearlite + bainite. The structure of the material produced by the online non-water cooling high temperature rolling + high temperature tempering process ( Figure 3 ) and the offline conventional normalizing heat treatment process production material group prepared in comparative example 1, the short process production material of online normalizing ( Figure 4 ) are basically the same. Due to the high temperature coiling, the temperature of the material steel coiling process drops slowly, and the banded structure brought by ferrite and pearlite in the 36-grade high-strength shipbuilding steel prepared by the present invention is better than the high temperature normalizing heat treatment material in Comparative Examples 1-2.

[0111] 4. Residual internal stress

[0112] Material Residual internal stress, MPa Laser cutting straightness, mm Example 1 23 3.0 Example 2 -18 2.0 Comparative Example 1 66 3.0 Comparative Example 2 80 5.0

[0113] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A grade 36 high-strength shipbuilding steel, characterized in that: Calculated by mass fraction, its composition includes: 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities.

2. The 36-grade high-strength shipbuilding steel according to claim 1, characterized in that: The ratings of A, B, C and D inclusions in the grade 36 high-strength shipbuilding steel do not exceed 1.

5.

3. The 36-grade high-strength shipbuilding steel according to claim 2, characterized in that: The microstructure of the grade 36 high-strength shipbuilding steel includes ferrite, bainite and pearlite, and the grain size rating of the grade 36 high-strength shipbuilding steel reaches more than grade 10.

4. A method for producing grade 36 high-strength shipbuilding steel, characterized in that: Includes steps: Steel is tapped from the converter and refined by LF to obtain refined molten steel; The composition of the molten steel includes, by mass fraction, 0.06wt%≤C≤0.14wt%, 0.10wt%≤Si≤0.30wt%, 1.20wt%≤Mn≤1.50wt%, P≤0.020wt%, S≤0.008wt%, 0.018wt%≤Als≤0.050wt%, 0.0065≤N≤0.010wt%, 0.0080≤Ti≤0.020wt%, 0.020wt%≤Nb≤0.040wt%, 0.025wt%≤V≤0.040wt%; the rest is iron and other inevitable impurities; The refined molten steel is continuously cast to obtain a slab; The slab is rolled and then coiled to obtain the grade 36 high-strength shipbuilding steel, and the coiling temperature exceeds 780°C.

5. The production method according to claim 4, characterized in that: In the step of tapping the steel from the converter and obtaining the refined molten steel through LF refining, when the oxygen content in the molten steel is ≤20ppm, a lanthanide rare earth alloy is added to the molten steel, and the amount of the lanthanide rare earth alloy added is 0.30-0.40kg / T.

6. The production method according to claim 4, characterized in that: The rolling includes initial rolling and finishing rolling. The finishing rolling temperature is not lower than 900° C., the reduction rate during the finishing rolling process is not less than 50%, and the finishing rolling speed is 6-8 m / s.

7. The production method according to claim 4, characterized in that: In the step of continuously casting the refined molten steel to obtain a slab, the continuous casting adopts a three-stage dynamic light reduction with a reduction of 3.5-4.5 mm. The pulling speed during the continuous casting process is controlled to be 1.2-1.5 m / min, and the secondary cooling water volume is 0.70-0.85 L / Kg.

8. The production method according to claim 4, characterized in that: In the step of coiling the slab after rolling to obtain the grade 36 high-strength shipbuilding steel, the slab is heated before rolling, the heating temperature is 1180-1220° C., and the heating time is 180-350 min.

9. The production method according to claim 4, characterized in that: In the step of coiling the slab after rolling to obtain the grade 36 high-strength shipbuilding steel, the coiled steel coil is subjected to a flattening treatment, and the pressure reduction amount at the rough straightening entrance is reduced to -5mm to -10mm during the flattening treatment; In the flattening process, when the thickness of the grade 36 high-strength shipbuilding steel is required to be no more than 12 mm, the straightness is ≤2 mm / m; when the thickness of the grade 36 high-strength shipbuilding steel is required to be greater than 12 mm, the straightness is ≤3 mm / m or ≤5 mm / 2m.

10. The production method according to claim 9, characterized in that: The steel plate after the peening treatment is subjected to tempering heat treatment to obtain the 36-grade high-strength shipbuilding steel. The tempering temperature in the tempering heat treatment is 610±10° C., and the tempering heat treatment time is 1.4 min / mm+12 min.

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