WO2023087350A1 - 高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法 - Google Patents

高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法 Download PDF

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WO2023087350A1
WO2023087350A1 PCT/CN2021/132953 CN2021132953W WO2023087350A1 WO 2023087350 A1 WO2023087350 A1 WO 2023087350A1 CN 2021132953 W CN2021132953 W CN 2021132953W WO 2023087350 A1 WO2023087350 A1 WO 2023087350A1
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steel
resistant
corrosion
temperature
rolling
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PCT/CN2021/132953
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French (fr)
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严玲
王�华
王长顺
张鹏
王晓航
李广龙
王东旭
齐祥羽
李博雍
韩鹏
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鞍钢股份有限公司
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Priority to US18/013,134 priority Critical patent/US20240018616A1/en
Priority to KR1020227044900A priority patent/KR20230074416A/ko
Priority to EP21945363.6A priority patent/EP4227432A4/en
Publication of WO2023087350A1 publication Critical patent/WO2023087350A1/zh

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    • C21D2211/009—Pearlite

Definitions

  • the invention relates to the technical field of low-alloy ship steel, in particular to a low-temperature-resistant and corrosion-resistant cargo oil tank steel welded with high heat input and a manufacturing method thereof.
  • the International Maritime Organization mandated that cargo oil tanks be protected by coatings or constructed of corrosion-resistant steel to ensure that the structural steel of cargo oil tanks can resist the corrosion of high chloride ions, alternating temperatures, and acidic gas phase media, and prevent Crude oil leakage from oil tankers due to corrosion causes marine environmental pollution and endangers the safety of oil tankers.
  • the coating protection can only last for 5-7 years. During the 25-year life cycle of the oil tanker, it needs to be repaired and re-sprayed 3-4 times, which not only increases the maintenance hours, but also the operating environment is harsh; The outage of the oil tanker due to dock repair will greatly increase the operating cost of the oil tanker.
  • JP 4935578 Corrosion-resistant steel for ships
  • JP 5130828 Manufacturing method of high-strength corrosion-resistant steel for ships
  • quality grade is E grade, -40 °C
  • welding heat input is only 60kJ/cm, and it does not provide the evaluation effect of the corrosion performance of the upper deck and inner bottom plate based on the IMO standard.
  • it also has one or more weight percentages: Sb: 0.02-0.15%, W: 0.03-0.10%, Mo: 0.05-0.15%, RE: 0.05-0.10%.
  • the unavoidable impurities include N, H and O, and the weight percentage of N is 0.0020-0.0060%, the weight percentage of H is ⁇ 0.00015%, and the weight percentage of O is ⁇ 0.0020%.
  • Ti/N is 2.43-3.56.
  • the thickness of the steel plate made of corrosion-resistant steel for cargo oil tanks suitable for high heat input welding is 8-50mm, and the volume fraction of pearlite in the microstructure of the corrosion-resistant steel whose yield strength is required to be ⁇ 355MPa (36Kg) is ⁇ 30 %, yield strength requirements ⁇ 370MPa (40Kg) and ⁇ 420MPa corrosion-resistant steel bainite volume fraction ⁇ 35%.
  • the content is 0.04% and above, but when the content exceeds a certain amount, it will increase the sensitivity of welding cracks and lead to the deterioration of welding performance.
  • the increase of C content will also increase the pearlite phase content of the lamellar cementite in the steel.
  • the pearlite becomes the cathode, which can promote corrosion, and the HAZ (heat-affected zone) near the refusion line of the steel plate after welding ) position is easy to produce MA, which significantly reduces the low-temperature toughness of the material, so the upper limit is 0.13%.
  • Si It is the main deoxidizing component in the steelmaking process, and it must contain more than 0.10% in order to obtain sufficient deoxidizing effect. However, if the upper limit is exceeded, the toughness of the base metal and the welded part will be reduced. Si in solid solution can increase the strength and increase the ductile-brittle transition temperature, so the Si content is 0.10-0.40%.
  • Mn It is a necessary element to ensure the strength and toughness of steel. Mn combines with S to form MnS, which avoids hot cracks caused by the formation of FeS at grain boundaries, and Mn is also a good deoxidizer. As a low-cost strengthening and toughening element, manganese content is too low to ensure the strength of the material, but when the Mn content is higher than 1.30%, it will increase the segregation of the billet and deteriorate the low-temperature toughness of the coarse-grained heat-affected zone (CGHAZ). Therefore, the Mn content should be controlled at 0.60-1.30%.
  • P It is an inevitable impurity element in steel, which will deteriorate the toughness and weldability of steel. Studies have shown that when the P content is higher than 0.012%, its corrosiveness in the acidic gas phase medium condition of the upper deck is significantly reduced, so the upper limit is 0.012%.
  • the upper limit of the S content is determined to be 0.006%.
  • the added content is generally more than 0.01%, but when the content is too high, hot cracks in the slab are likely to occur, and a large number of Al 2 O 3 inclusions are formed. This hard phase inclusion will significantly Reduce the toughness of steel, so the upper limit of Al content is 0.05%.
  • Sn It is a corrosion-resistant component that must be added in the present invention. It exists in the steel in the form of solid solution and can significantly increase the electrochemical corrosion self-potential of the steel, thereby inhibiting the corrosion of the steel in an acidic corrosion environment. However, when the content is less than 0.03%, the purpose of effectively improving the corrosion resistance cannot be achieved, and when it exceeds 0.15%, it will be enriched in the austenite grain boundary during continuous casting and rolling, which will reduce the high-temperature plasticity, so Sn The content ranges from 0.03 to 0.15%.
  • Ni Adding an appropriate amount of Ni element is conducive to the formation of a dense rust layer on the steel surface, which can inhibit the corrosion reaction of steel, especially under the condition of coexistence with Cu, Cr, etc., the effect is better, because nickel can increase the strength and reduce the critical Cooling speed delays pearlite transformation, which is beneficial to microstructure control and grain refinement, and improves low-temperature toughness; but under the condition of Ni containing S, the formation of nickel sulfide will cause red hot brittleness of steel, so the nickel content should not be too high. High, therefore, the Ni content of the present invention is controlled at 0.15-0.40%.
  • Cu can significantly improve the corrosion resistance of the steel plate, especially the seawater corrosion resistance, and has a significant effect on ensuring the corrosion resistance of the steel plate described in the present invention.
  • too high Cu content is unfavorable to the toughness and easily causes embrittlement of the steel plate.
  • the Cu content of the present invention is controlled at 0.15-0.50%.
  • Cu/Ni composite addition its main mechanism of action in steel is manifested in the following two aspects: on the one hand, the addition of Cu and Ni promotes the formation of ⁇ -FeOOH in steel, and in the alternating dry and wet environment, Ni can promote the formation of spinel
  • the formation of stone oxides increases the density of the rust layer; Cu can become the core of oxide crystallization in the rust layer, thereby promoting the formation of ⁇ -FeOOH, because ⁇ -FeOOH is a relatively stable phase in the rust layer, Once it is formed, it is difficult to transform into other phases, so there will be no cracks and defects caused by volume changes due to phase transitions.
  • the dissolution of Cu can form Cu 2+ , and form an insoluble protective film with some anions, such as Cu 2 S effectively protects the matrix, and these insoluble protective films of Cu Soluble salt can repair and protect cracks and holes, thereby improving the compactness of the continuous rust layer.
  • the amount added to the steel is Ni+Cu ⁇ 0.35%, and at the same time, Ni/Cu ⁇ 0.70, so as to suppress the adverse effect of Cu on low temperature toughness.
  • Sb It is similar to Sn in improving the corrosion resistance of steel. It has been proved that it can effectively improve the corrosion resistance in acidic corrosion environment. If it is added together with Sn, it can further improve the corrosion resistance of steel. It is an optional addition element in the present invention. If the Sb content exceeds 0.15%, the corrosion resistance effect is saturated and the thermoplasticity of the steel is lowered. Therefore, when added, the Sb content ranges from 0.02 to 0.15%.
  • W In the present invention, it is an optional additive element for improving corrosion resistance.
  • W can form WO 4 2- ions in an acidic corrosion environment to inhibit the erosion of anions such as Cl - ions, and can also form a dense layer of FeWO 4 to inhibit corrosion.
  • the W content exceeds 0.10%, the corrosion inhibitory effect reaches saturation, and it is not conducive to welding performance, so the upper limit is 0.10%.
  • Cr As the oxidation proceeds, a dense Cr 2 O 3 layer is formed on the steel surface, which can inhibit the anion intrusion in acidic corrosion environment, thereby reducing the enrichment of Cl - and other anions on the steel surface, and has a good effect on the steel plate in the inner bottom plate environment Anti-pitting effect.
  • the Cr content is too high, it will increase the sensitivity of welding cracks.
  • the preferred content range of Cr is 0.10-0.25%.
  • Mo The effect on improving the corrosion resistance of steel is similar to that of W and Cr. It can promote the formation of a dense rust layer on the surface and prevent the further development of corrosion. Considering the cost and the effect of corrosion resistance, the preferred content range of addition is 0.05-0.15%. .
  • RE It has the effect of steel purification, which can effectively purify the grain boundary, thereby improving the corrosion resistance of the grain boundary and reducing the overall corrosion rate; at the same time, it is a good desulfurization and deoxidizing agent, which can improve low-temperature toughness and easy weldability; RE is used as the metamorphic agent, which can improve the shape, size and distribution of inclusions, and further improve the comprehensive mechanical properties of the material, but when the content is too high, it will increase the difficulty of smelting and continuous casting, and increase the manufacturing cost of the product. Therefore, the RE content of the present invention is controlled at 0.05 ⁇ 0.10%.
  • Nb It can effectively refine the grain size of steel, and is an element added to improve the strength and toughness of steel.
  • the Nb content is less than 0.005%, it has little effect on the strength and toughness of the steel, and when it exceeds 0.020%, it is easy to produce MA brittle components during high heat input welding, which reduces the weldability and low temperature toughness of the steel. Therefore, the Nb content The range is 0.005 to 0.020%.
  • Ti It is a component added to improve the toughness of steel and welded parts. As a strong N-fixing element, it is easy to form TiN and improve the ability of the weld metal to resist N porosity. When it is less than 0.005%, the effect has little effect, and when it exceeds 0.021%. It is easy to form large particles of TiN and lose its effect. In order to obtain low-temperature toughness under high heat input, the steel plate needs to control the ratio of Ti:N in the steel between 2.43 and 3.56, so the added Ti content ranges from 0.005 to 0.021%.
  • Ca The combination of Ca and S to form CaS can coat alumina and other inclusions to realize the denaturation and spheroidization of inclusions, which is beneficial to improve corrosion resistance, toughness and fatigue resistance; at the same time, the fine and dispersed CaS formed in the early stage can reduce MnS To form a ratio, CaS reacts with H 2 O to dissociate alkaline OH - ions, which can reduce the acidification degree of corrosion pits and reduce pitting corrosion sensitivity.
  • the fine-sized CaO formed in the steel can also refine the grains and improve the toughness of the material.
  • N can form fine precipitates with Nb, Ti, and V, exert strengthening and fine-grain effects, and improve toughness, but too high content will deteriorate toughness, and its content is preferably controlled at 0.0020-0.0060%.
  • H and O are harmful impurity elements in the present invention; an increase in their content will lead to an increase in the tendency of hydrogen-induced cracking, an increase in inclusions, and a decrease in corrosion resistance and fatigue resistance. Therefore, the present invention controls H ⁇ 0.00015%, O ⁇ 0.0020 %.
  • the invention also discloses a method for manufacturing high heat input welded low-temperature-resistant and anti-corrosion steel for cargo oil tanks, including:
  • Refining Secondary refining of molten steel taken out from the converter
  • Continuous casting continuous casting of molten steel after secondary refining to obtain steel slabs
  • Heating heating the steel slab to 1100°C ⁇ 1150°C, the heating time of the steel slab is 3 ⁇ 5 hours;
  • the heated steel slab is rolled, and the intermediate billet is obtained by one-stage rolling, and then the intermediate billet is subjected to two-stage rolling.
  • the starting rolling temperature is 850°C ⁇ 900°C
  • the final rolling temperature of the two-stage rolling is 800°C ⁇ 860°C;
  • On-line cooling cooling the rolled steel plate to 500°C-600°C at a cooling rate of 5°C/s-20°C/s to obtain a steel plate.
  • the starting rolling temperature of the two-stage rolling is 850°C to 900°C
  • the finishing temperature of the two-stage rolling is 840°C to 860°C
  • the rolled steel plate Cool to 550°C to 600°C at a cooling rate of 5°C/s to 15°C/s.
  • the starting rolling temperature of the second-stage rolling is 850°C-890°C
  • the finishing temperature of the second-stage rolling is 800°C-840°C for the rolled steel plate
  • the rolled steel plate is cooled to 500°C-560°C, and the cooling rate is 7°C/s-20°C/s.
  • off-line cooling is also included: for finished steel plates with a thickness of less than 40 mm, the steel plates are sheared off-line and transported to the finished product stacking area; for finished steel plates with a thickness ⁇ 40 mm, stacking and slow cooling should be performed after straightening, and the slow cooling start temperature
  • the temperature is 250°C ⁇ 400°C, the stacking time is not less than 24 hours, and then it is cut off the assembly line and transported to the finished product stacking area.
  • high-drawn carbon is used for smelting production by one-shot blowing.
  • the final slag basicity of smelting is 3.2-4.1, and the time for putting steel is not less than 5 minutes;
  • aluminum particles, silicon carbide, and calcium carbide are used to adjust the slag, and the basicity of the final refined slag is ⁇ 2.4.
  • Ca treatment is performed after refining, and the feeding line for each furnace of molten steel is 200-300 meters.
  • the degree of superheat is ⁇ 25°C
  • the secondary cooling is weak cooling in the continuous casting process
  • the casting speed of the continuous casting slab is 0.8m/min ⁇ 1.2m/min
  • the thickness of the cast steel slab is 200mm ⁇ 360mm;
  • the ratio of the thickness of the intermediate slab to the thickness of the finished steel plate is not less than 2.5:1, and the cumulative reduction ratio of the first-stage rolling and the second-stage rolling is not less than 50%.
  • the steel plate formed by the steel provided by the present invention has a Charpy impact toughness ⁇ 198J at -60°C, an ECL corrosion rate (25-year extrapolated corrosion rate) ⁇ 2.0mm, and a fracture toughness that satisfies the characteristic value of CTOD at -10°C ⁇ c ⁇ c 0.8mm. And after welding at 240KJ/cm, the Charpy impact toughness (AKv) of the welded joint at -40°C is ⁇ 170J.
  • the invention is a corrosion-resistant steel designed mainly for the overall uniform corrosion of the upper deck of the storage and transportation tank of the polar region route oil tanker and the local pitting corrosion of the inner bottom plate.
  • Heat input welding line energy up to 240KJ/cm.
  • the mechanical performance evaluation and simulation of the mixed gas O 2 -CO 2 -SO 2 -H 2 S
  • the mechanical performance evaluation and simulation of the mixed gas O 2 -CO 2 -SO 2 -H 2 S
  • the present invention has the following advantages:
  • the present invention is based on the chemical composition system specified by the classification society, and adopts low C and low Mn elements, which can reduce corrosion sensitivity; adding appropriate amount of Ni, Cu, and Mo can improve the corrosion resistance while making up for the strength; Utilize Nb, Ti, V to form fine carbonitride precipitation, play a strengthening and fine-grained role, and ensure that the steel plate still has excellent low-temperature toughness at -60°C; by reducing the content of P, S, H, and O, strictly control the N content, The size, shape, and segregation of inclusions ensure corrosion resistance, improve low-temperature toughness and weldability; among them, the segregation of continuous casting slabs does not exceed 0.5 grades, and the sum of the four types of inclusions grades A, B, C, and D is ⁇ 2.0 grades, passing The cleanliness of the steel and the control of the weight, size and quantity of the inclusions ensure the strength, toughness, corrosion resistance and weldability of the invented steel.
  • the corrosion-resistant steel plate suitable for high heat input welding has a maximum thickness of 50mm, and can cover 355MPa (36kg) level, 390MPa (40kg) level and 420MPa level on the strength level of the steel plate through the control of composition and rolling process,
  • the low-temperature toughness can meet the F-level toughness index, especially at low temperature, it has excellent fracture toughness (CTOD), reaching more than 0.8mm; when the welding heat input reaches 240KJ/cm, it still has good strength and toughness, which meets the requirements of the polar region.
  • CTOD fracture toughness
  • the present invention provides an environmentally friendly, long-life high-performance steel for the construction of cargo oil tanks of oil tankers on polar routes, which can realize that the oil tanker does not need maintenance during the entire life cycle, and can save a lot of painting and maintenance operating costs.
  • the present invention can be widely promoted in fields such as low-alloy ship steel.
  • Fig. 1 is a microstructure diagram of a 355MPa-grade corrosion-resistant steel for cargo oil tanks suitable for high heat input welding in a specific embodiment of the steel of the present invention.
  • Fig. 2 is a microstructure diagram of a 420MPa-grade corrosion-resistant steel for cargo oil tanks suitable for high heat input welding in a specific embodiment of the steel of the present invention.
  • Fig. 3 is a corrosion microstructure diagram of the lower bottom plate in the specific embodiment of the present invention.
  • Fig. 4 is a three-dimensional analysis diagram of the corrosion autofocus of the middle and lower bottom plate according to the specific embodiment of the present invention.
  • Fig. 5 is a corrosion microstructure diagram of the upper deck in a specific embodiment of the present invention.
  • Fig. 6 is an autofocus three-dimensional topography analysis diagram of corrosion on the upper deck in a specific embodiment of the present invention.
  • the present invention discloses high heat input welded steel for low temperature and corrosion resistant cargo oil tanks, the weight percentage of its chemical composition is:
  • the unavoidable impurities include N, H and O, and the weight percentage of N is 0.0020%-0.0060%, the weight percentage of H is ⁇ 0.00015%, and the weight percentage of O is ⁇ 0.0020%.
  • the thickness of the steel plate made of corrosion-resistant steel for cargo oil tanks suitable for high-heat input welding is 8-50mm, and the volume fraction of pearlite in the microstructure of the corrosion-resistant steel with a yield strength requirement of ⁇ 355MPa (36Kg level) is ⁇ 30%. (see Figure 1), yield strength requirements ⁇ 390MPa (40Kg) and ⁇ 420MPa corrosion-resistant steel bainite volume fraction ⁇ 35% (see Figure 2).
  • the microstructure of polygonal ferrite+a small amount of pearlite See Figure 1
  • the volume fraction of pearlite is less than or equal to 30%.
  • the structure of acicular ferrite + a small amount of bainite is adopted (see Figure 2), and bainite Tensile volume fraction ⁇ 35%, and effectively control the grain size of steel plates of various steel grades and thicknesses. This is because the relatively single microstructure has a good effect on reducing the corrosion potential difference between different phases and achieving high corrosion resistance of the material.
  • This embodiment also discloses a method for manufacturing high heat input welded steel for low-temperature and corrosion-resistant cargo oil tanks, including:
  • the molten steel discharged from the converter is subjected to secondary refining to further reduce the content of harmful impurities such as O, S, and non-metallic inclusions.
  • harmful impurities such as O, S, and non-metallic inclusions.
  • aluminum particles, silicon carbide, and calcium carbide are used to adjust the slag, and the basicity of the final refined slag is ⁇ 2.4 ("double slag" refers to the final slag of smelting and the final slag of refining), and Ca treatment is carried out after refining.
  • Furnace molten steel feeding line is 200-300 meters.
  • Continuous casting The molten steel after secondary refining is continuously cast to obtain steel slabs; the superheat in the continuous casting process is ⁇ 25°C, and the secondary cooling is weak cooling in the continuous casting process, and the casting speed of the continuous casting slab is 0.8m/min ⁇ 1.2m /min, cast steel slab thickness 200mm ⁇ 360mm;
  • Heating heat the steel slab to 1100°C-1150°C, and the heating time of the steel slab is 3-5 hours; this heating temperature is used because the temperature lower than 1100°C is not enough to completely dissolve the alloy elements into the austenite, The finishing temperature required for hot rolling cannot be guaranteed. However, if the temperature is higher than 1150°C, the original austenite grains will be significantly coarsened, which will significantly reduce the low-temperature toughness of the steel plate.
  • the heated steel slab is rolled, and the intermediate billet is obtained by one-stage rolling, and then the intermediate billet is subjected to two-stage rolling.
  • the starting rolling temperature is 850°C ⁇ 900°C
  • the final rolling temperature of the two-stage rolling is 800°C ⁇ 860°C
  • the rolling temperature is selected to meet the mechanical properties requirements of corrosion-resistant steel, and the temperature of 950°C ⁇ 1100°C is austenite Recrystallization zone, 850°C ⁇ 900°C is austenite non-recrystallization zone
  • the ratio of the thickness of the intermediate billet to the thickness of the steel plate obtained after the second-stage rolling is not less than 2.5:1, the accumulation of the first-stage rolling and the second-stage rolling
  • the reduction rate is not less than 50%.
  • On-line cooling cooling the rolled steel plate to 500°C-600°C at a cooling rate of 5°C/s-20°C/s to obtain a steel plate.
  • the preferred two-stage rolling start rolling temperature is 850°C to 900°C
  • the final rolling temperature range is 840°C ⁇ 860°C
  • the cooling method is multi-stage laminar flow cooling
  • the cooling rate is controlled at 5°C ⁇ 15°C/s
  • the rolled steel plate is cooled to 550°C ⁇ 600°C.
  • the volume fraction of pearlite in the microstructure of the obtained steel plate is ⁇ 30%.
  • the preferred starting temperature of the two-stage rolling is 850°C ⁇ 890°C, and the final rolling temperature is 850°C ⁇ 890°C.
  • the rolling temperature is 800°C-840°C, and then the steel plate is cooled to 500°C-560°C at a cooling rate of 7°C/s-20°C/s.
  • the volume fraction of bainite in the microstructure of the obtained steel plate is ⁇ 35%.
  • Off-line cooling for finished steel plates with a thickness of less than 40mm, they are cut off the line and transported to the finished product stacking area; for finished steel plates with a thickness of ⁇ 40mm, they should be stacked and slowly cooled after straightening, and the slow cooling starts at 250-400 °C, the stacking time is not less than 24 hours, and then it is cut off the assembly line and transported to the finished product stacking area.
  • the thickness of the corrosion-resistant steel plate made by the above method is 8mm-50mm, which has excellent comprehensive mechanical properties and is suitable for welding with high heat input. It has excellent corrosion resistance after being tested by the corrosion evaluation method stipulated by IMO, and can be used without coating protection. use.
  • the heating-rolling-controlling process parameter of embodiment 1 ⁇ 10 is as shown in table 2:
  • Examples 1-3 are steel products whose yield strength is required to be 355 MPa and above; Examples 4-6 are steel products whose yield strength is required to be 390 MPa. Examples 6-10 are steel products whose yield strength is required to be 420 MPa.
  • the difference between the final rolling temperature and the initial water cooling temperature is because the temperature will naturally decrease during transportation.
  • the yield strength of the 355MPa steel provided by the present invention is between 367 ⁇ 402MPa, the tensile strength is between 512 ⁇ 526MPa, and the elongation after fracture is above 25.5%; Between 244J and 329J; the fracture toughness meets the CTOD -10°C ⁇ 0.82mm, which is higher than the standard of ⁇ 0.40mm in ship regulations.
  • the yield strength of the 390MPa steel provided by the invention is between 395-435MPa, the tensile strength is between 518-572MPa, and the elongation after fracture is above 24.5%; at -60°C, the impact toughness is between 254J-332J ;Fracture toughness meets CTOD -10°C ⁇ 0.90mm, which is higher than the standard of ship regulations ⁇ 0.40mm.
  • the yield strength of the 420MPa steel provided by the invention is between 435-475MPa, the tensile strength is between 565-602MPa, and the elongation after fracture is above 22.5%; the impact toughness is between 198J-232J at -60°C; Fracture toughness meets CTOD -10°C ⁇ 0.80mm, which is much higher than the standard of ⁇ 0.40mm in ship regulations.
  • the corrosion-resistant steels of various steel grades have good stability of mechanical properties and a margin of strength and toughness indicators. It can fully meet the material design requirements of high-strength, easy-to-weld and corrosion-resistant steel for oil tankers.
  • Embodiments 1 to 10 are based on the IMO289 (87) standard corrosion-resistant steel corrosion rate measurement for the upper deck as shown in Table 5:
  • Embodiments 1 to 10 are based on the IMO 289 (87) standard corrosion-resistant steel corrosion rate measurement for the inner bottom plate as shown in Table 6:
  • the high heat input welded low-temperature corrosion-resistant steel for cargo oil tanks provided by the present invention meets the requirements of ship regulations, and its performance far exceeds the requirements of ship regulations. It has excellent low-temperature toughness, and still has good strength and toughness when the welding heat input reaches 240KJ/cm, so it meets the application technical requirements for materials required for the construction of cargo oil tanks for oil tankers on polar routes.

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Abstract

本发明提供一种高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法，其化学成分重量百分比为：C：0.04～0.13％、Si：0.10～0.40％、Mn：0.60～1.30％、P：0.005～0.012％、S≤0.006％、Al：0.01～0.05％、Sn：0.03～0.15％、Nb：0.005～0.020％、Ti：0.005～0.025％、Ni：0.15％～0.40％、Cu：0.15～0.50％、Cr：0.10～0.25％、Ca：0.007％～0.024％，余量为Fe及不可避免的杂质。本发明主要针对极区航线油船的储运罐上甲板和内底板设计的耐腐蚀钢，该钢具有优异的低温韧性，且可进行大热输入量焊接。

Description

高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法 技术领域
本发明涉及低合金船舶用钢技术领域，具体而言是一种高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法。
背景技术
随着经济和社会的发展，对原油需求和消耗持续增大，也推动了原油运输的极速增长。同时，气候变暖使得北极航线的运输成为可能，通过北极东北航道的油船数量显著增加。在原油储运过程中，作为主要储运容器的货油舱(COT)内底板会覆盖着一层含有油泥、高浓度Cl -卤水及H 2S的沉积油膜，使油舱内底板发生严重的局部点状腐蚀，腐蚀坑最深可达10mm，这种腐蚀成为了原油船运营中的极大安全隐患。航行北极航道的油船，需要承受低温环境，其货油舱结构用钢需要具备良好的可焊性、低温韧性和耐腐蚀性等优异的综合力学性能。
2012年，国际海事组织(IMO)强制要求采用货油舱涂层防护或采用耐腐蚀钢建造的方式，以保证货油舱结构钢抵御高氯离子和温度交变、酸性气相介质的腐蚀，防止油船因腐蚀而产生的原油泄露造成海洋环境污染、危及油船安全等问题。然而，涂层防护仅能维持5-7年，在油船25年的全寿命周期内，需要进行3-4次的修复和重新喷涂，不仅提高了维护的工时，而且作业环境恶劣；而因回坞修复导致油船停运，则大大增加了油船的运营成本。与此同时，随着油船建造的大型化、高效化发展趋势，船企在油船建造过程中，其工作量的80％来自于焊接工序，因此，对货油舱体用耐蚀钢实现高热输入焊接的意愿更为强烈，目前适用于油船的耐蚀钢仅能满足50KJ/cm及以下常规低热输入量的焊接要求，对于适用高热输入焊接的耐蚀钢尚未见报道。为提高造船效率，大型船厂普遍引进了多丝埋弧焊、FCB、气电立焊等高热输入焊接设备，以实现油船建造的高效化。因此，对于适合高热输入焊接的油船用耐蚀钢提出迫切需求。
目前，国内外对货油舱用耐腐蚀钢有一些研究，经检索发现了部分专利和文献，但其所记载的内容与本发明技术方案所述成分、生产方法、易 焊接性、耐腐蚀性、低温韧性等方面存在明显不足。
相关专利1：CN103290337A《一种原油油船货油舱上甲板用耐腐蚀钢》提供了一种仅用于货油舱上甲板的普通强度和高强度耐蚀钢，ECL为1.95mm，低温韧性仅满足-20℃，没有给出焊接性评价指标，更未提及是否具备高热输入焊接特性。
相关专利2：CN103305761A《一种原油油船货油舱内底板用耐腐蚀钢》提供了一种仅用于货油舱上甲板的普通强度和高强度耐蚀钢，其低温韧性仅满足-20℃，同样的，没有给出焊接性评价指标，更未提及是否具备高热输入焊接特性。
相关专利3：CN103469101A《一种高Nb原油船货轮舱底板用耐蚀钢》提供了一种含有高Nb成分体系的32Kg强度级别货油舱内底板用钢，质量等级仅为A级(常温)，无法满足0℃及更低温度条件下的应用。
相关专利4：JP 4935578《船舶用耐蚀钢材》和相关专利5：JP 5130828《高强度船舶用耐蚀钢材的制造方法》，提供了一种具有良好低温韧性(质量等级为E级，-40℃)的耐蚀钢，但其焊接热输入量仅为60kJ/cm，并且未提供基于IMO标准下的上甲板和内底板腐蚀性能评价效果。
相关专利6：CN102974661A《一种原油货油仓耐蚀钢板的矫直工艺》，涉及一种钢板厚度为30-50mm货油仓用钢板的矫直工艺，未提及材料的成分、制造工艺等关键技术。
综上所述，现有技术对具备耐腐蚀、耐低温高韧性、适宜高热输入焊接的等综合性能的油船货油舱用钢的产品开发尚存在不足，无法满足船厂高效建造需要和适宜极区航行耐低温且耐高硫高酸油气腐蚀原油船货油舱对材料综合性能的需求。
发明内容
根据上述技术问题，而提供一种高热输入焊接的耐低温抗腐蚀货油舱用钢及其制造方法。
本发明采用的技术手段如下：
高热输入焊接的耐低温抗腐蚀货油舱用钢，其化学成分重量百分比为：
C：0.04～0.13％、Si：0.10～0.40％、Mn：0.60～1.30％、P：0.005～0.012％、S≤0.006％、Al：0.01～0.05％、Sn：0.03～0.15％、Nb：0.005～0.020％、Ti：0.005～0.025％、Ni：0.15～0.40％、Cu：0.15～0.50％、Cr：0.10～0.25％、Ca：0.007～0.024％，余量为Fe及不可避免的杂质。
优选地，还具有重量百分比为：Sb：0.02～0.15％、W：0.03～0.10％、Mo：0.05～0.15％、RE：0.05～0.10％中的一种或多种。
优选地，不可避免杂质中包括N、H、O，且N的重量百分比为0.0020～0.0060％，H的重量百分比≤0.00015％，O的重量百分比≤0.0020％。
优选地，Ti/N为2.43～3.56。
优选地，Ni+Cu≥0.35％，且Ni/Cu≥0.70；Ca/S为1.8～4。
优选地，适宜高热输入焊接的货油舱用耐腐蚀钢所制成的钢板厚度为8～50mm，屈服强度要求≧355MPa(36Kg)的耐蚀钢的显微组织中珠光体的体积分数≤30％，屈服强度要求≧370MPa(40Kg)和≧420MPa的耐蚀钢的贝氏体体积分数≤35％。
以下详细阐述本发明的酸性原油储运罐用耐腐蚀钢中各合金成分作用机理，其中百分符号％代表重量百分比：
C：是保证钢强度的必要元素，含量在0.04％及以上，但当含量超过一定量时，将提高焊接裂纹敏感性，导致焊接性能的恶化。此外C含量的增加还会增加钢中的含片层渗碳体的珠光体相含量，在酸性环境下珠光体成为阴极，能促进腐蚀，而且焊接后钢板再熔合线附近的HAZ(热影响区)位置易产生MA，显著降低材料的低温韧性，因此上限为0.13％。
Si：是炼钢过程中主要的脱氧成分，为了得到充分的脱氧效果必须含0.10％以上。但若超过上限则会降低母材及焊接部位的韧性，以固溶形式存在的Si提高强度的同时也能提高韧脆转变温度，因此Si含量为0.10～0.40％。
Mn：是保证钢的强度和韧性的必要元素，Mn与S结合形成MnS，避免晶界处形成FeS而导致的热裂纹，同时Mn也是良好的脱氧剂。锰作为低成本的强韧化元素，其含量过低，无法保证材料的强度，但当Mn含量高于1.30％时，会加重铸坯偏析并恶化粗晶热影响区(CGHAZ)的低温韧性，因此Mn含量应该控制在0.60～1.30％。
P：是钢中不可避免的杂质元素，会恶化钢的韧性和焊接性能。研究表明，当P含量高于0.012％时，其在上甲板酸性气相介质条件下的腐蚀性显著下降，因此上限为0.012％。
S：在钢中易形成MnS夹杂，而MnS夹杂位置是点状腐蚀的起源，从而降低钢的耐腐蚀性，因此要采取措施使钢中S含量尽可能降低。因此本发明中，确定S含量上限为0.006％。
Al：作为脱氧和细化晶粒元素，一般添加含量在0.01％以上，但超过含量过高时容易产生铸坯热裂纹，且形成大量的Al 2O 3夹杂，这种硬质相夹杂会显著降低钢的韧性，因此Al含量上限为0.05％。
Sn：是本发明必须添加的提高耐腐蚀性成分，以固溶形式存在于钢中，能显著提高钢的电化学腐蚀自电位，从而抑制钢在酸性腐蚀环境下的腐蚀。但含量低于0.03％时达不到有效提高耐腐蚀性目的，而超过0.15％时，会在连铸和轧制等热加工过程富集在奥氏体晶界而使高温塑性降低，因此Sn含量范围为0.03～0.15％。
Ni：添加适量的Ni元素，有利于在钢表面形成致密的锈层，能抑制钢发生腐蚀反应，特别是在与Cu、Cr等共存的条件下效果更佳，由于镍可以提高强度，降低临界冷却速度，延迟珠光体转变，有利于微观组织控制和晶粒细化，改善低温韧性；但Ni在含S气氛条件下，硫化镍的形成会引起钢的赤热脆性，因此，镍含量不宜过高，因此，本发明Ni含量控制在0.15～0.40％。
Cu：能够明显提升钢板耐腐蚀尤其是耐海水腐蚀能力，对保证本发明所述钢板的耐腐蚀性能作用明显。但Cu含量过高对韧性不利，易引起钢板脆化，本发明Cu含量控制在0.15～0.50％。
Cu/Ni复合添加：其在钢中的主要作用机制表现在以下两个方面：一方面Cu、Ni的添加促进了钢中α-FeOOH的形成，在干湿交替环境下，Ni可以促进尖晶石类氧化物的形成，提高锈层的致密度；Cu可以成为锈层中氧化物结晶的核心，从而促进α-FeOOH的形成，由于α-FeOOH在锈层中是一种相对稳定的相，它一旦形成就很难转化为其他物相，因此不会产生由于物相转变导致体积变化所引起的裂纹和缺陷。另一方面，在腐蚀介质中满足一定电 位的条件下，Cu的溶解可形成Cu 2+，并与某些阴离子形成难溶性的保护膜，如Cu 2S有效地保护了基体，Cu的这些难溶性的盐对裂纹和孔洞有修复和保护作用，从而提高连续锈层的致密性。据此确定钢中添加量为Ni+Cu≥0.35％，同时，Ni/Cu≥0.70，以抑制Cu对低温韧性的不利影响。
Sb：对提高钢的耐腐蚀性能作用与Sn相似，被证明能有效提高酸性腐蚀环境下的耐腐蚀性能，若与Sn一起添加可进一步提高钢的耐腐蚀性能，是本发明可选添加元素。Sb含量超过0.15％则耐腐蚀效果饱和且钢的热塑性降低。因此添加时Sb含量范围为0.02～0.15％。
W：在本发明中是可选的提高耐腐蚀性的添加元素。W可在酸性腐蚀环境中形成WO 4 2-离子而抑制Cl -离子等阴离子的侵蚀，还可形成FeWO 4的致密层而抑制腐蚀。W含量超过0.10％后抑制腐蚀效果达到饱和，且不利于焊接性能，因此上限为0.10％。
Cr：随着氧化进行在钢表面形成致密的Cr 2O 3层，可抑制酸性腐蚀环境下的阴离子侵入，从而减少Cl -等阴离子在钢表面的富集，对于内底板环境的钢板具有良好的抗点腐蚀效果。但Cr含量过高，则会增加焊接裂纹敏感性。从焊接性和耐腐蚀效果综合考虑，添加Cr的优选含量范围为0.10～0.25％。
Mo：对提高钢的耐腐蚀性作用与W、Cr相似，能促进表面致密锈层形成，阻止腐蚀的进一步发展，从成本和发挥耐腐蚀效果方面考虑，添加的优选含量范围为0.05～0.15％。
RE：具有钢质净化作用，可有效净化晶界，从而提高晶界的耐腐蚀能力，降低全面腐蚀速率；同时是良好的脱硫、脱氧剂，可提高低温韧性和易焊接性；采用RE作为变质剂，可改善夹杂物的形态、尺寸和分布，进一步提升材料的综合力学性能，但含量过高时，会增加冶炼连铸难度、且提高了产品的制造成本，因此本发明RE含量控制在0.05～0.10％之间。
Nb：可以有效细化钢的晶粒尺寸，是作为提高钢的强度和韧性而添加的元素。当Nb含量小于0.005％时对钢的强度和韧性作用很小，而超过0.020％时，在高热输入焊接时，极易产生MA脆性组元，使钢的焊接性能和低温韧性降低，因此Nb含量范围为0.005～0.020％。
Ti：是作为提高钢和焊接部位韧性而添加的成分，作为强烈的固N元素，易形成TiN而提高焊缝金属的抗N气孔的能力，小于0.005％时效果作用甚微，超过0.021％时易形成大颗粒TiN而失去效果。钢板为获得高热输入下的低温韧性，需要控制钢中Ti：N的比例在2.43～3.56之间，因此添加Ti含量范围为0.005～0.021％。
Ca：Ca与S结合形成CaS可包覆氧化铝等夹杂，实现夹杂物变性和球化，有利于提高耐腐蚀性、韧性和抗疲劳性；同时，先期形成的细小弥散的CaS，可降低MnS形成比例，CaS与H 2O作用，离解出碱性的OH -离子，可降低腐蚀坑的酸化程度，较小点腐蚀敏感性。而钢中形成的尺寸细小的CaO还可起到细化晶粒、提高材料韧性的作用。在本发明中，优选Ca：0.007～0.024％、Ca/S在1.8～4之间。
N可以与Nb、Ti、V形成细小析出物，发挥强化和细晶作用，提高强韧性，但含量过高使韧性恶化，其含量控制在0.0020～0.0060％为宜。
H、O在本发明中为有害杂质元素；其含量增加会导致氢致开裂倾向增大，夹杂物增加，耐腐蚀性和抗疲劳性能下降，因此，本发明控制H≤0.00015％、O≤0.0020％。
本发明还公开了一种高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，包括：
冶炼：采用深脱硫铁水，深脱硫铁水中的硫的重量百分比≤0.002％，铁水至转炉后，进行冶炼，并在转炉内调整并添加上述化学成分，使转炉内的化学成分满足一种高热输入焊接的耐低温抗腐蚀货油舱用钢所述的重量百分比；
精炼：从转炉搬出的钢水进行二次精炼；
连铸：二次精炼后的钢水进行连铸，得到钢板坯；
加热：将钢板坯加热到1100℃～1150℃，钢板坯的加热时间为3～5小时；
轧制：将加热后的钢板坯进行轧制，进行一段轧制得到中间坯，之后中间坯进行二段轧制，其中一段轧制的开轧温度为950℃～1100℃，二段轧制的开轧温度为850℃～900℃，二段轧制的终轧温度为800℃～860℃；
在线冷却：将轧制后的钢板冷却至500℃～600℃，冷却速率为5℃/s～20℃/s，得到钢板。
其中，所述二段轧制的开轧温度为850℃～900℃，所述二段轧制的终轧温度为840℃～860℃；在所述在线冷却过程中，对轧制后的钢板冷却至550℃～600℃，冷却速率为5℃/s～15℃/s。或在所述轧制过程中，所述二段轧制的开轧温度为850℃～890℃，所述二段轧制的终轧温度轧制后的钢板为800℃～840℃；在所述在线冷却过程中，对轧制后的钢板冷却至500℃～560℃，冷却速率为7℃/s～20℃/s。
优选地，还包括线下冷却：对于成品钢板厚度＜40mm的钢板进行剪切下线运至成品堆放区；对于成品钢板厚度≥40mm钢板，矫直后应进行堆垛缓冷，缓冷开始温度为250℃～400℃，堆垛时间不小于24小时，之后进行剪切下线运至成品堆放区。
优选地，在冶炼过程中，采用高拉碳一次点吹方式进行冶炼生产。
优选地，在冶炼过程中，冶炼的终渣碱度为3.2～4.1，放钢的时间不小于5min；
优选地，在精炼过程中，采用铝粒、碳化硅、碳化钙调渣，精炼的终渣碱度≥2.4，精炼结束后进行Ca处理，每炉钢水喂线为200～300米。
优选地，在连铸过程中，过热度≤25℃，且连铸过程中二冷采用弱冷，连铸坯拉速0.8m/min～1.2m/min，浇铸钢板坯厚度200mm～360mm；
优选地，在轧制过程中，中间坯厚度与成品钢板厚度比不小于2.5：1，一段轧制和二段轧制的累积压下率不低于50％。
本发明提供的钢形成的钢板，在-60℃情况下夏比冲击韧性≧198J，ECL腐蚀速率(25年外推腐蚀速率)≤2.0mm，断裂韧性满足-10℃下CTOD的特征值δc≧0.8mm。且在240KJ/cm焊接后，焊接接头在-40℃情况下夏比冲击韧性(AKv)≧170J。
本发明主要针对极区航线油船的储运罐上甲板全面均匀性腐蚀和内底板局部点蚀腐蚀而设计的耐腐蚀钢，该材料同时具有优异的低温韧性(满足-60℃)，可进行大热输入量焊接(线能量达到240KJ/cm)。采用本发明制备出的母材及高热输入焊接接头，经过力学性能评价和模拟实际油船货油舱顶 部混合气体(O 2-CO 2-SO 2-H 2S)干湿交替腐蚀环境和底部高酸性溶液(pH＝0.85的10％NaCl溶液)腐蚀环境下的腐蚀性能评价。结果表明，其综合力学性能和耐腐蚀性能均满足IACS和IMO规范评价指标要求。
较现有技术相比，本发明具有以下优点：
(1)本发明基于船级社规范的化学成分体系下，采用低C、低Mn元素，可降低腐蚀敏感性；加入适量Ni、Cu、Mo，在弥补强度的同时，提高了耐腐蚀性能；利用Nb、Ti、V形成细小碳氮化物析出，发挥强化和细晶作用，保证钢板的在-60℃仍具有优异的低温韧性；通过降低P、S、H、O含量，严控N含量、夹杂物尺寸和形态、偏析等保证耐腐蚀性能，提高低温韧性和焊接性；其中，连铸坯偏析不超过0.5级，A、B、C、D四类夹杂物级别之和≤2.0级，通过对钢质的洁净度和夹杂物重量、尺寸和数量的控制，保了发明钢的强韧性、耐蚀性和焊接性。
(2)采用本发明成分设计和制造方法获得了多边形铁素体+珠光体和多边形铁素体+贝氏体的微观组织，同时，组织的单一性对于降低电位差、实现高耐腐蚀性起到良好效果。
(3)本发明所述适宜高热输入焊接的耐腐蚀钢板最大厚度达到50mm，通过成分与轧制工艺调控，在钢板强度等级上可覆盖355MPa(36kg)级别、390MPa(40kg)级别和420MPa级别，低温韧性均可满足F级韧性指标，特别是低温下具有优异的断裂韧性(CTOD)，达到0.8mm以上；在焊接热输入量达到240KJ/cm时，仍具有良好的强韧性，满足了极区航线油船货油舱建造所需材料的应用技术要求。
(4)本发明为建造极区航线油船货油舱提供了一种环保、长寿命的高性能用钢，可实现油船在全寿命周期内无需维护，可节约大量的涂装和维护运营成本。
基于上述理由本发明可在低合金船舶用钢等领域广泛推广。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图做以简单地介绍，显而易见地，下 面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明钢具体实施方式中一种适宜高热输入焊接的货油舱用耐腐蚀钢355MPa级别的显微组织图。
图2为本发明钢具体实施方式中一种适宜高热输入焊接的货油舱用耐腐蚀钢420MPa级别的显微组织图。
图3为本发明具体实施方式中下底板腐蚀显微组织图。
图4为本发明具体实施方式中下底板腐蚀自动对焦三维形貌分析图。
图5为本发明具体实施方式中上甲板腐蚀显微组织图。
图6为本发明具体实施方式中上甲板腐蚀自动对焦三维形貌分析图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为对本发明及其应用或使用的任何限制。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
需要注意的是，这里所使用的术语仅是为了描述具体实施方式，而非意图限制根据本发明的示例性实施方式。如在这里所使用的，除非上下文另外明确指出，否则单数形式也意图包括复数形式，此外，还应当理解的是，当在本说明书中使用术语“包含”和/或“包括”时，其指明存在特征、步骤、操作、器件、组件和/或它们的组合。
除非另外具体说明，否则在这些实施例中阐述的部件和步骤的相对布置、数字表达式和数值不限制本发明的范围。同时，应当清楚，为了便于描述，附图中所示出的各个部分的尺寸并不是按照实际的比例关系绘制的。对于相关领域普通技术人员己知的技术、方法和设备可能不作详细讨论，但在适当情况下，所述技术、方法和设备应当被视为授权说明书的一部分。在这 里示出和讨论的所有示例中，任向具体值应被解释为仅仅是示例性的，而不是作为限制。因此，示例性实施例的其它示例可以具有不同的值。应注意到：相似的标号和字母在下面的附图中表示类似项，因此，一旦某一项在一个附图中被定义，则在随后的附图中不需要对其进行进一步讨论。
如图1～6所示，本发明公开了高热输入焊接的耐低温抗腐蚀货油舱用钢，其化学成分重量百分比为：
C：0.04～0.13％、Si：0.10～0.40％、Mn：0.60～1.30％、P：0.005～0.012％、S≤0.006％、Al：0.01～0.05％、Sn：0.03～0.15％、Nb：0.005～0.020％、Ti：0.005～0.025％、Ni：0.15％～0.40％、Cu：0.15～0.50％、Cr：0.10～0.25％、Ca：0.007％～0.024％，余量为Fe及不可避免的杂质。
还具有重量百分比为：Sb：0.02～0.15％、W：0.03～0.10％、Mo：0.05～0.15％、RE：0.05～0.10％中的一种或多种。
不可避免杂质中包括N、H、O，且N的重量百分比为0.0020％～0.0060％，H的重量百分比≤0.00015％，O的重量百分比≤0.0020％。
其中，Ni+Cu≥0.35％，且Ni/Cu≥0.70；Ti/N为2.43～3.56；Ca/S为1.8～4。
适宜高热输入焊接的货油舱用耐腐蚀钢所制成的钢板厚度为8～50mm，屈服强度要求≧355MPa级别(36Kg级别)的耐蚀钢的显微组织中珠光体的体积分数≤30％(见图1)，屈服强度要求≧390MPa(40Kg)和≧420MPa耐蚀钢的贝氏体体积分数≤35％(见图2)。
采用本发明成分设计和制造方法，针对不同强度等级的耐蚀钢实施了组织构成及相比例的调控，针对355KPa(36Kg)级别高强钢，获得了多边形铁素体+少量珠光体的微观组织(见图1)，珠光体的体积分数≤30％，针对390MPa(40Kg)级别和420MPa级别的超高强度钢，采用以针状铁素体+少量贝氏体的组织(见图2)，贝氏体体积分数≤35％，同时对各钢级、各厚度的钢板进行晶粒尺寸的有效控制。这是由于，显微组织的相对单一对于降低不同相之间的腐蚀电位差、实现材料的高耐腐蚀性起到良好效果。
实施例1～10的各元素成分及其重量百分比如表1所示：
表1
Figure PCTCN2021132953-appb-000001
本实施方式还公开了一种高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，包括：
冶炼：采用深脱硫铁水，深脱硫铁水中的硫的重量百分比≤0.002％，铁水至转炉后，并在转炉内调整各元素含量满足上述内容中各化学成分及其重 量百分比，采用“双渣”脱磷与炉后钢水“扒渣”相结合的工艺冶炼，采用高拉碳一次点吹方式进行冶炼生产；冶炼的终渣碱度为3.2～4.1，通过有效的挡渣操作，杜绝大量下渣，放钢的时间不小于5min；
精炼：从转炉搬出的钢水进行二次精炼，进一步降低O、S、非金属夹杂等有害杂质含量。精炼过程中采用铝粒、碳化硅、碳化钙调渣，精炼的终渣碱度≥2.4(“双渣”指的就是冶炼的终渣和精炼的终渣)，精炼结束后进行Ca处理，每炉钢水喂线为200米～300米。
连铸：二次精炼后的钢水进行连铸，得到钢板坯；连铸过程中过热度≤25℃，且连铸过程中二冷采用弱冷，连铸坯拉速0.8m/min～1.2m/min，浇铸钢板坯厚度200mm～360mm；
加热：将钢板坯加热到1100℃～1150℃，钢板坯的加热时间为3～5小时；采用此加热温度是由于，低于1100℃的温度不足以让合金元素完全溶解到奥氏体中，无法保证热轧所需的终轧温度。而高于1150℃，使得原始奥氏体晶粒粗化显著，会显著降低钢板的低温韧性。
轧制：将加热后的钢板坯进行轧制，进行一段轧制得到中间坯，之后中间坯进行二段轧制，其中一段轧制的开轧温度为950℃～1100℃，二段轧制的开轧温度为850℃～900℃，二段轧制的终轧温度为800℃～860℃；轧制的温度选择是为了满足耐腐蚀钢的力学性能要求，950℃～1100℃为奥氏体再结晶区，850℃～900℃为奥氏体未再结晶区，中间坯厚度与二段轧制完成后得到的钢板的厚度比不小于2.5：1，一段轧制和二段轧制的累积压下率不低于50％。
在线冷却：将轧制后的钢板冷却至500℃～600℃，冷却速率为5℃/s～20℃/s，得到钢板。
根据钢板的力学性能需求，可选择不同的未再结晶区轧制温度和冷却速率。对于屈服强度要求≧355MPa级别(36kg级别)的高强度钢，且满足冲击温度-60℃的要求，则优选二段轧制的开轧温度为850℃～900℃，终轧温度范围为840℃～860℃，冷却方式为多阶段层流冷却，冷却速率控制在5℃～15℃/s，将轧制后的钢板冷却至550℃～600℃。得到的钢板的显微组织中珠光体的体积分数≤30％。
对于屈服强度要求≧390MPa(40kg级别)和≧420MPa级别的高强度钢， 且为满足强度和冲击温度-60℃的要求，则优选二段轧制的开轧温度为850℃～890℃，终轧温度为800℃～840℃，其后以7℃/s～20℃/s的冷却速率将钢板冷却至500℃～560℃。得到的钢板的显微组织中贝氏体的体积分数≤35％。
线下冷却：对于成品钢板厚度＜40mm的钢板进行剪切下线运至成品堆放区；对于成品钢板厚度≥40mm的钢板，矫直后应进行堆垛缓冷，缓冷开始温度为250～400℃，堆垛时间不小于24小时，之后进行剪切下线运至成品堆放区。
上述方法制成的耐腐蚀钢板厚度为8mm～50mm，具有优异的综合力学性能、适宜高热输入焊接，经IMO规定的腐蚀评价方法检测，具有优异的耐腐蚀性能，可以在无涂装防护情况下使用。
实施例1～10的加热-轧制-控冷工序参数如表2所示：
表2
Figure PCTCN2021132953-appb-000002
在表2中，实施例1～3为屈服强度要求为355MPa及以上的钢材；实施例4～6为屈服强度要求为390MPa级别的钢材。实施例6～10为屈服强度要求为420MPa级别的钢材。终轧温度和开始水冷温度不同是因为运输过程中温度会自然的降低。
实施例1～10的力学性能如表3所示：
表3
Figure PCTCN2021132953-appb-000003
通过表3可知，本发明提供的355MPa钢的屈服强度在367～402MPa之间、抗拉强度在512～526MPa之间、断后伸长率在25.5％以上；在-60℃情况下，冲击韧性在244J～329J之间；断裂韧性满足CTOD -10℃≧0.82mm，高于船规≥0.40mm的标准。
本发明提供的390MPa钢的屈服强度在395～435MPa之间、抗拉强度在518～572MPa之间、断后伸长率在24.5％以上；在-60℃情况下，冲击韧性在254J～332J之间；断裂韧性满足CTOD -10℃≧0.90mm，高于船规≥0.40mm的标准。
本发明提供的420MPa钢的屈服强度在435～475MPa之间、抗拉强度在565～602MPa之间、断后伸长率在22.5％以上；在-60℃情况下冲击韧性在198J～232J之间；断裂韧性满足CTOD -10℃≧0.80mm，远高于船规≥0.40mm的标准。
综上，各钢级的耐蚀钢具有良好的力学性能稳定性和强韧性指标富余量。可充分满足油船用高强韧、易焊接耐蚀钢的材料设计要求。
实施例1～10经240KJ/cm焊接后的接头的力学性能如表4所示：
表4
Figure PCTCN2021132953-appb-000004
Figure PCTCN2021132953-appb-000005
通过表4可知，本发明提供的钢在240KJ/cm焊接后，抗拉强度、伸长率和硬度参数仍然符合船规，且焊接接头在-40℃情况下冲击韧性≧170J，远高于船规。
实施例1～10基于IMO289(87)标准的上甲板用耐腐蚀钢腐蚀速率测定如表5所示：
表5
Figure PCTCN2021132953-appb-000006
从表5中可以明显看出本发明提供的钢的ECL腐蚀速率(25年外推腐蚀速率)≤2.0mm，符合标准。而且通过图5～6能够直观的看出实施例4中腐蚀台阶高度为12μm，远远满足标准。
实施例1～10基于IMO 289(87)标准的内底板用耐蚀钢腐蚀速率测定如 表6所示：
表6
Figure PCTCN2021132953-appb-000007
从表6中可以明显看出本发明提供的钢的年平均腐蚀速率≤0.72mm，符合IMO标准，同时腐蚀台阶高度也符合IMO标准。从图3～4能够直观的看出实施例7中腐蚀台阶高度为4μm，更加的优于IMO标准要求值。
综上所述，本发明提供的一种高热输入焊接的耐低温抗腐蚀货油舱用钢满足船规要求，而且性能远远超过船规要求，具有良好的耐腐蚀性、在-60℃仍具有优异的低温韧性、在焊接热输入量达到240KJ/cm时，仍具有良好的强韧性，因此满足了极区航线油船货油舱建造所需材料的应用技术要求。
最后应说明的是：以上各实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (10)

  1. 高热输入焊接的耐低温抗腐蚀货油舱用钢，其特征在于，其化学成分重量百分比为：
    C：0.04～0.13％、Si：0.10～0.40％、Mn：0.60～1.30％、P：0.005～0.012％、S≤0.006％、Al：0.01～0.05％、Sn：0.03～0.15％、Nb：0.005～0.020％、Ti：0.005～0.025％、Ni：0.15～0.40％、Cu：0.15～0.50％、Cr：0.10～0.25％、Ca：0.007～0.024％，余量为Fe及不可避免的杂质。
  2. 根据权利要求1所述的高热输入焊接的耐低温抗腐蚀货油舱用钢，其特征在于，还具有重量百分比为：Sb：0.02～0.15％、W：0.03～0.10％、Mo：0.05～0.15％、RE：0.05～0.10％中的一种或多种。
  3. 根据权利要求1所述的高热输入焊接的耐低温抗腐蚀货油舱用钢，其特征在于，不可避免杂质中包括N、H、O，且N的重量百分比为0.0020～0.0060％，H的重量百分比≤0.00015％，O的重量百分比≤0.0020％。
  4. 根据权利要求3所述的高热输入焊接的耐低温抗腐蚀货油舱用钢，其特征在于，Ti/N为2.43～3.56。
  5. 根据权利要求1所述的高热输入焊接的耐低温抗腐蚀货油舱用钢，其特征在于，Ni+Cu≥0.35％，且Ni/Cu≥0.70；Ca/S为1.8～4。
  6. 高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，其特征在于，包括：
    加热：将具有权利要求1～5任一权利要求所述成分的钢板坯加热到1100℃～1150℃，所述钢板坯的加热时间为3～5小时；
    轧制：将加热后的所述钢板坯进行轧制，进行一段轧制得到中间坯，之后所述中间坯进行二段轧制，其中一段轧制的开轧温度为950℃～1100℃，二段轧制的开轧温度为850℃～900℃，二段轧制的终轧温度为800℃～860℃；
    在线冷却：将轧制后的钢板冷却至500℃～600℃，冷却速率为5℃/s～20℃/s，得到钢板。
  7. 根据权利要求6所述的高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，其特征在于：在所述轧制过程中，所述二段轧制的终轧温度为840℃～860℃；在所述在线冷却过程中，对轧制后的钢板冷却至550℃～600℃， 冷却速率为5℃/s～15℃/s，冷却后的钢板的珠光体体积分数≤30％。
  8. 根据权利要求6所述的高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，其特征在于：在所述轧制过程中，所述二段轧制的开轧温度为850℃～890℃，所述二段轧制的终轧温度为800℃～840℃；在所述在线冷却过程中，对轧制后的钢板冷却至500℃～560℃，冷却速率为7℃/s～20℃/s，冷却后的钢板的贝氏体体积分数≤35％。
  9. 根据权利要求6所述的高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，其特征在于：
    还包括线下冷却：对成品钢板厚度≥40mm的钢板，矫直后进行堆垛缓冷，缓冷开始温度为250℃～400℃，堆垛时间不小于24小时，之后进行剪切下线运至成品堆放区。
  10. 根据权利要求6所述的高热输入焊接的耐低温抗腐蚀货油舱用钢的制造方法，其特征在于：
    在所述轧制过程中，所述中间坯厚度与成品钢板厚度比不小于2.5，一段轧制和二段轧制的累积压下率不低于50％。
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