Surface corrosion-resistant invar alloy precision strip for liquefied natural gas ship liquid cargo warehouse and manufacturing method of surface corrosion-resistant invar alloy precision strip

Abstract

The invention discloses a surface corrosion-resistant invar alloy precision strip for a liquid cargo cabin of a liquefied natural gas carrier and a manufacturing method. The surface corrosion-resistant invar alloy precision strip comprises the following components: 35.6%-37.1% of Ni, 0.35%-0.80% of Si, 0.05%-0.10% of Ce, 0.015%-0.030% of C, less than or equal to 0.35% of Mn, 0-0.0008% of O, less than or equal to 0.01% of N, less than or equal to 0.003% of S, less than or equal to 0.005% of P, less than or equal to 0.20% of Cr, less than or equal to 0.20% of Cu, less than or equal to 0.05% of Al, less than or equal to 0.003% of Ti and the balance of iron and inevitable impurity elements. According to the formula, through EAF, AOD, LF, continuous casting or die casting, hot continuous rolling or solid solution pickling after forging, cold rolling in multiple rolling processes, annealing and protective film prefabrication treatment, the temperature range of the prepared material is about 1.5-1.8 * 10 <-6 > / DEG C from-163 DEG C to 20 DEG C, the yield strength Rp0.2 value is larger than or equal to 300 MPa, the tensile strength Rm value is larger than or equal to 480 MPa, the ductility A50 is larger than or equal to 35%, surface corrosion does not occur within the machining period or storage and transportation time of 15 days under the conventional condition, and the service life of the material is prolonged. And particularly, the risk of surface rusting in the processing, storage and transportation processes is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a surface-corrosion-resistant Invar alloy precision strip for liquefied natural gas (LNG) ship cargo holds and its manufacturing method. Background Technology

[0002] Driven by the growth in natural gas trade under the trend of carbon neutrality and the surge in demand for energy alternatives in Europe, the global demand for membrane-type cargo tanks for large LNG carriers has experienced explosive growth. Membrane-type technology accounts for over 70% of this demand (with the MARK III type being the mainstream), and its core advantages lie in its high cargo tank volume efficiency and a 25% reduction in insulation thickness compared to traditional models. In membrane-type cargo tanks for large LNG carriers (such as the MARK III or NO96 systems), Invar alloy (grade 4J336 in Chinese national standard GB / T 37797-2019) is mainly used for the secondary barrier, with its core requirement being an extremely low coefficient of thermal expansion (approximately 1.6 × 10⁻⁶ in the temperature range of -163℃ to 20℃). -6 The temperature is measured in °C to ensure that no destructive thermal stress is generated between the material and the main insulation material (such as plywood and glass wool) during drastic temperature fluctuations during LNG loading, unloading, and navigation (-163 °C). The composition is primarily based on approximately 36% nickel and the balance iron, with extremely strict control over impurities such as carbon, sulfur, and phosphorus to ensure excellent low-temperature stability, weldability, toughness, and long-term service reliability. Standard thicknesses range from 0.5 mm to 1.0 mm. 0.7 mm is the most commonly used and standard thickness.

[0003] The main technical challenges in manufacturing marine Invar alloys lie in their unique low thermal expansion characteristics and the processing challenges brought about by their high nickel content. (1) Strict composition and metallurgical control: Precise control of nickel content (~36%) and extremely low content of impurities such as carbon, sulfur, and phosphorus is the key to ensuring an ultra-low coefficient of thermal expansion (CTE). (2) Difficult hot working: Invar alloys have a narrow hot working temperature range (approximately 900-1200℃), high high-temperature strength, and relatively poor plasticity. (3) Prone to oxidation defects: Invar alloys are prone to selective oxidation at high temperatures. During the heating process, a honeycomb oxide layer composed of iron and nickel oxides and the base metal will form on the surface of the billet. It is difficult to completely remove during hot rolling descaling, resulting in dense oxides pressing into the surface of the hot-rolled strip, affecting cold rolling production. (4) Finished materials cannot be coated with oil for rust prevention during storage and transportation, and are extremely prone to surface corrosion. In particular, most shipyards are located along the coast, and the surface of finished products is extremely prone to corrosion, leading to material scrap. In response to the above problems, a large number of optimizations have been carried out on the composition and process of marine Invar alloys.

[0004] The prior art has been disclosed as follows: CN120041743A discloses a low-cost method for preparing Invar alloy strip. A special production process route was designed to meet the high purity requirements of the Invar alloy material used in metal photomasks: EAF → AOD → LF → ingot casting electrode billet → VAR → billet preparation → hot continuous rolling → cold rolling. The mass percentages of the Invar alloy composition are as follows: C≤0.05%, Si≤0.30%, 0.2%≤Mn≤0.6%, P≤0.02%, S≤0.002%, 35.0%≤Ni≤37.0%, with the remainder being Fe and unavoidable impurities. This process route ensures that the inclusions in the strip meet user requirements and can replace imported materials.

[0005] CN119456694A provides a method for producing Invar alloy 4J36 hot-rolled coils. By adjusting the heating process, the surface oxidation generated during the heating process is reduced. Through rolling with a furnace coil mill, dynamic recrystallization is fully carried out, and the surface quality of the produced Invar alloy 4J36 hot-rolled coils meets product requirements.

[0006] CN118326279A discloses a method for additive manufacturing a low-temperature near-zero expansion Invar alloy and its preparation, specifically relating to the field of additive manufacturing technology for metallic materials. The raw materials contain the following chemical composition by weight percentage: copper: 0.35%~0.42%, cobalt: 4.2%~4.7%, manganese: 0.15%~0.25%, titanium: 0.5%~1.2%, nickel: 30.5%~32.0%, carbon: ≤0.01%, silicon: ≤0.1%, with the balance being iron and unavoidable impurities.

[0007] CN118531297A discloses a high-strength, low-expansion coefficient Invar alloy wire and its preparation method. The wire, by mass percentage, comprises: C: 0.22-0.24%; Si: ≤0.1%; Mn: ≤0.2%; P: ≤0.02%; S: ≤0.02%; V: 0.65-0.75%; Mo: 2.0-2.1%; Ni: 38.0-39.0%; with the balance being Fe. The preparation method includes: smelting, electroslag remelting, hot forging, hot rolling, a single cold drawing, annealing heat treatment, and a second cold drawing.

[0008] CN117144263A discloses a technology related to Invar alloys, specifically relating to high-strength, low-thermal-expansion Invar alloy wire for high-capacity conductors and its preparation method. A high-strength, low-thermal-expansion Invar alloy wire for high-capacity conductors is composed of the following raw material components by weight percentage: C 0.1~0.25%, Si≤0.6%, Mn≤0.6%, V 0.8~1.1%, Cu 0.2~0.4%, Ni 34~38%, Al 0.1~0.15%, Nb 0.02~0.03%, rare earth elements 0.01-0.02%, and the balance iron; wherein the rare earth elements are selected from one or more of Sc, Sm, or Nd.

[0009] CN117821842A discloses an ultra-high strength, low-expansion Invar alloy wire and its manufacturing method. The alloy wire has the following composition by weight percentage: C 0.075–0.32%; Si 0.01–0.70%; Mn 0.20–0.60%; P ≤0.02%; S ≤0.02%; Ni 38.0–43.0%; Mo 1.0–3.0%; V 0.1–1.0%; Al 0.3–1.3%; the balance includes Fe and other unavoidable impurities, with the total amount of impurity elements less than 0.05%. This high-strength Invar alloy overcomes the contradiction between excellent mechanical properties and expansion properties in alloys.

[0010] Japanese Invention Patent JP9604892A discloses a high-strength Invar alloy whose composition by mass percentage satisfies <=0.05% C, <=0.03% N, 0.01 to 2.0% Si, 0.01 to 3.0% Mn, 25 to 45% Ni, 0.01 to 1.0% Cr, 1.0 to 5.0% Ti and <=0.01% S, or containing 0.1 to 3.0% of one or more elements selected from Al, V, Zr, Nb, Ta, Hf, and Be, with the remainder being Fe and unavoidable impurities.

[0011] In summary, existing technologies have proposed a series of methods to address the mechanical properties and low expansion characteristics of Invar alloys, high-purity alloy preparation methods, and hot rolling process optimization. However, no effective solution has yet been proposed for the problem of Invar alloys being prone to rusting during product manufacturing, storage, and transportation due to their low content of corrosion-resistant elements such as Cr, Mo, and Al (increasing the content leads to an increase in the coefficient of thermal expansion and a decrease in processing performance). In particular, since Invar alloy finished products require extensive welding in shipyards, applying oil to the surface for corrosion protection is not permitted.

[0012] Therefore, there is an urgent need to develop a surface-resistant Invar alloy precision strip for LNG carrier cargo holds and a manufacturing method therefor. Through the combination of formula and process, a protective film (passivation film) of nanometer thickness can be generated on the material surface, similar to stainless steel, to prevent surface rusting. At the same time, it takes into account the comprehensive requirements of low expansion coefficient, excellent mechanical properties and processing performance, so as to better meet the demand for Invar alloy precision strip for LNG carrier cargo holds. Summary of the Invention

[0013] The purpose of this invention is to provide a surface-resistant Invar alloy precision strip for liquefied natural gas (LNG) cargo holds and its manufacturing method. This formulation promotes the formation of a dense CeO2+SiO2 protective film on the surface, imparting a certain degree of rust resistance to the material and ensuring that it does not rust during processing, storage, and transportation. Simultaneously, by using Ce and Si deoxidation instead of conventional Al deoxidation, the adverse effects of hard Al oxides on hot working properties can be avoided while reducing the O content. The material obtained through the above composition and process exhibits a low coefficient of thermal expansion, excellent mechanical properties, and certain rust resistance. The material's thermal expansion coefficient is approximately 1.5~1.8×10⁻⁶ within a temperature range of -163℃ to 20℃. -6 / ℃, yield strength Rp0.2 value ≥300MPa, tensile strength Rm value ≥480MPa, elongation A50 ≥35%, and no surface corrosion occurs within 15 days of processing or storage and transportation under normal conditions.

[0014] To achieve the above objectives, the following technical solutions are used: A surface-resistant Invar alloy precision strip for use in liquefied natural gas (LNG) carrier cargo tanks comprises the following components by weight percentage: Ni: 35.6% - 37.1%; Si: 0.35–0.80%; Ce: 0.05% - 0.10%; C: 0.015~0.030%; Mn: ≤0.35%; O: 0~0.0008%; N: ≤0.01%; S: ≤0.003%; P: ≤0.005%; Cr: ≤ 0.20%; Cu: ≤ 0.20%; Al: ≤ 0.05%; Ti: ≤0.003%; The remainder consists of iron and unavoidable impurity elements.

[0015] As a further improvement to this scheme, the following relationship must also be satisfied: Mn+Si≤0.95%.

[0016] As a further improvement to this solution, the following relationship must also be satisfied: (Si+5Ce): O≥1000; As a further improvement to this scheme, the following relationship must also be satisfied: Si: (Al+Ti)≥8.

[0017] A method for preparing the aforementioned rust-resistant Invar alloy precision strip for liquefied natural gas (LNG) ship cargo tanks includes the following preparation steps: EAF→AOD→LF→Continuous casting or ingot casting→Hot continuous rolling or forging followed by solution pickling→Multiple rolling passes of cold rolling→Annealing and pre-made protective film treatment.

[0018] As a further improvement to this solution, the specific process for annealing and pre-prepared protective film treatment is as follows: A protective film is generated during annealing at 650~750℃ in a reducing atmosphere with relative humidity >60% RH.

[0019] As a further improvement to this scheme, the alloy billet is heated in the temperature range of 1100 to 1150°C; Solution heat treatment at 850~900℃ produces a softened all-austenitic microstructure. If subsequent cold working is to be performed, intermediate annealing is permitted, with an annealing temperature of 750–850℃.

[0020] The present invention provides a method for preparing surface-corrosion-resistant Invar alloy precision strip for liquefied natural gas (LNG) ship cargo tanks, which has the following beneficial effects: 1. The chemical composition and the role of the main chemical elements in this invention Chemical composition (mass percentage): Ni: 35.6% - 37.1%, Si: 0.35~0.80%, Ce: 0.05% - 0.10%, C: 0.015~0.030%, Mn: ≤0.35%, O: 0~0.0008%, N: ≤0.01%, S: ≤0.003%, P: ≤0.005%, Cr: ≤0.20%, Cu: ≤0.20%, Al: ≤0.05%, Ti: ≤0.003%, with the remainder being iron and unavoidable impurity elements. All the above elements must simultaneously satisfy the following relationships: Mn+Si≤0.95%, (Si+5Ce):O≥1000, and Si:(Al+Ti)≥8.

[0021] Nickel is an austenite-forming element. Its addition ensures a stable austenite microstructure, resulting in excellent processing, forming, and welding properties. In particular, ensuring a nickel content of around 36% is crucial for achieving ultra-low expansion characteristics, and the nickel content must be strictly controlled between 35.6% and 37.1%.

[0022] Silicon is a deoxidizer. Adding a certain amount of silicon during the smelting process and ensuring a sufficient silicon content in the alloy can guarantee a low oxygen content in the material. Unlike conventional composition design, this invention adds and ensures a certain silicon content, while utilizing the silicon pre-oxidation to form a silica protective film, which can impart good rust resistance to the material. However, the Mn and Si contents need to be controlled; excessively high contents lead to a significant increase in the coefficient of thermal expansion, decreased machinability, and a higher likelihood of hot-rolling cracks. Through extensive experimentation, this invention controls the silicon content to 0.35–0.80%, while Mn+Si ≤ 0.95% to avoid deterioration of hot working performance and the low coefficient of thermal expansion.

[0023] Cerium is a rare earth element with excellent deoxidizing properties, which can further reduce the oxygen content based on silicon deoxidation. Simultaneously, this invention adds a certain amount of cerium, utilizing its interaction with silicon during oxidation to form a protective oxide film, further enhancing the material's rust resistance. However, excessive cerium addition leads to increased costs and coarse oxidation. Therefore, this invention controls the cerium content to 0.05% - 0.10%, and (Si+5Ce):O ≥ 1000.

[0024] Carbon promotes the formation and stabilization of the austenite phase, and also improves the yield strength of alloys. However, when the carbon content exceeds a certain threshold, it will promote the precipitation of carbides, which is detrimental to its processing and corrosion resistance. This invention controls the carbon content to be 0.015–0.030%.

[0025] Manganese is both a deoxidizing element and an austenite stabilizing element. Excessive manganese content leads to a significant increase in the coefficient of thermal expansion and is detrimental to corrosion resistance. In particular, the sulfides of Mn affect corrosion resistance. The manganese content of this invention is designed to be 0.10-0.40%.

[0026] Oxygen, nitrogen, sulfur, and phosphorus are impurity elements introduced into the alloy from raw materials or during the smelting process. They adversely affect hot working properties, coefficient of thermal expansion, and weldability. However, complete removal is technically difficult and costly. In particular, controlling the oxygen content to a low level requires the addition of deoxidizers such as silicon, aluminum, or rare earth elements. When a large amount of aluminum deoxidizer is added, it leads to a high content of hard inclusions, which deteriorates hot rolling performance. This invention is designed with O: 0-0.0008%, N: ≤0.01%, S: ≤0.003%, P: ≤0.005%, controlling their contents at a low level and (Si+5Ce):O ≥1000 to ensure high purity of the material.

[0027] Excessive levels of chromium and copper significantly affect the coefficient of thermal expansion. This invention is designed with Cr: ≤ 0.20% and Cu: ≤ 0.20% to ensure that the alloy has a low coefficient of thermal expansion.

[0028] Aluminum and calcium are deoxidation products and also the main elements interacting between steel slag and alloy liquid during the smelting process. When the aluminum and calcium content is high, hard inclusions are easily formed, which deteriorates the hot working performance. This invention makes full use of this and therefore controls Al: ≤ 0.05%, Ti: ≤ 0.003% and Si: (Al+Ti) ≥ 8.

[0029] Specifically, this invention prioritizes rare earth elements and silicon for deoxidation. Therefore, it is designed with (Si+5Ce):O ≥ 1000 and Si:(Al+Ti) ≥ 8, achieving a low oxygen content while avoiding the adverse effects of deoxidation by aluminum, calcium, manganese, etc., on hot working and welding performance. Simultaneously, the rare earth elements cerium and silicon are the main elements forming the protective film in the composition of this invention, imparting rust resistance to the material. This is a unique design feature of this invention.

[0030] Manufacturing method and key processes of the present invention The manufacturing process of this invention is as follows: EAF → AOD → LF → continuous casting or ingot casting → hot continuous rolling or forging followed by solution pickling → multi-pass cold rolling → annealing and pre-prepared protective film treatment. The alloy billet is heated within a temperature range of 1100–1150°C to achieve a uniform austenitic microstructure, ensuring reduced high-temperature strength and higher high-temperature plasticity in the billet or continuously cast billet. Hot rolling is completed at a temperature above 900°C, as the higher final rolling temperature partially eliminates work hardening. Solution heat treatment at 850–900°C results in a softened, fully austenitic microstructure. If subsequent cold working is performed, intermediate annealing is permitted at a temperature of 750–850°C.

[0031] Specifically, the annealing and pre-forming protective film treatment of the formulation of this invention are performed after the final cold rolling. Annealing is carried out at 650-750°C in a reducing atmosphere at >60% RH (relative humidity), promoting the recovery and recrystallization of the cold-rolled structure while fully utilizing the silicon and rare earth element cerium in the formulation to generate a dense CeO2+SiO2 protective film with a thickness of 3-8 nm, imparting a certain degree of rust resistance to the material. Unlike the usual method of generating an oxide film by chromic acid or phosphoric acid oxidation after annealing, this invention combines the addition of silicon and rare earth element cerium with the oxide film formation process, pre-forming the protective film during annealing. The material's temperature range is approximately 1.5-1.8 × 10⁻⁶ °C from -163°C to 20°C. -6 / ℃, yield strength Rp0.2 value ≥300MPa, tensile strength Rm value ≥480MPa, elongation A50 ≥35%, and no surface corrosion occurs within 15 days of processing or storage and transportation under normal conditions. Attached Figure Description

[0032] Figure 1 Annealing microstructure diagram of Example 3 of the Invar alloy precision strip for surface corrosion resistant in liquefied natural gas ship cargo tanks of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to embodiments: A surface-resistant Invar alloy precision strip for liquefied natural gas (LNG) ship cargo tanks and its manufacturing method belong to the field of materials technology. It has the following chemical composition (mass percentage %): Ni: 35.6% - 37.1%, Si: 0.35~0.80%, Ce: 0.05% - 0.10%, C: 0.015~0.030%, Mn: ≤0.35%, O: 0~0.0008%, N: ≤0.01%, S: ≤0.003%, P: ≤0.005%, Cr: ≤0.20%, Cu: ≤0.20%, Al: ≤0.05%, Ti: ≤0.003%, with the remainder being iron and unavoidable impurities. Furthermore, the above elements must simultaneously satisfy the following relationships: Mn+Si≤0.95%, (Si+5Ce):O≥1000, and Si:(Al+Ti)≥8.

[0034] The precision strip prepared using the above-mentioned Invar alloy formulation for large LNG ship cargo holds with surface corrosion resistance is described below. EAF→AOD→LF→Continuous casting or ingot casting→Hot continuous rolling or forging followed by solution pickling→Multi-pass cold rolling→Annealing and pre-coated protective film treatment. The alloy billet is heated within the temperature range of 1100–1150℃ to achieve a uniform austenitic microstructure, ensuring reduced high-temperature strength and high-temperature plasticity in the billet or continuously cast billet. Hot rolling is completed above 900℃, as the higher final rolling temperature partially eliminates work hardening. Solution heat treatment at 850–900℃ results in a softened, fully austenitic microstructure. If subsequent cold working is performed, intermediate annealing is permitted at a temperature of 750–850℃.

[0035] The annealing and pre-prepared protective film treatment of the formulation of the present invention are carried out after the final cold rolling. The annealing treatment is carried out at 650~750℃ in a reducing atmosphere and >60% RH (relative humidity) environment. While promoting the recovery and recrystallization of the cold-rolled structure, the silicon element and rare earth element cerium in the formulation are fully utilized to generate a dense CeO2+SiO2 protective film with a thickness of 3~8nm, which gives the material a certain degree of rust resistance.

[0036] Example Examples 1-10 describe the preparation of surface-resistant Invar alloy precision strips for liquefied natural gas (LNG) cargo holds according to the above-described formulas and processes. Specific formulas, processes, and test results for Examples 1-10 are shown in Tables 1 and 2. Examples 1-10 of the present invention are shown in Tables 1 and 2. As can be seen from the tables, when processed using the above-mentioned composition and process parameters, the material has a fully austenitic structure, and its finished product has a coefficient of thermal expansion of approximately 1.5~1.8×10⁻⁶ in the temperature range of -163℃ to 20℃. -6 At a temperature of / ℃, the yield strength Rp0.2 value is ≥300MPa, the tensile strength Rm value is ≥480MPa, and the elongation A50 is ≥35%. Under normal conditions, no surface corrosion occurs within 15 days of processing or storage. Strict control is exercised over the composition, especially for inclusions such as S and O, ensuring high material purity and preventing hot working cracking. Deoxidation is achieved using Si and rare earth element Ce, replacing Al deoxidation, thus reducing the adverse effects of hard inclusions such as alumina on hot working performance. In particular, alloying with Si and Ce simultaneously achieves the dual effects of deoxidation treatment and pretreatment to form a protective film, giving the material excellent rust resistance. Extensive experiments revealed that, under the aforementioned alloy formulation, a special integrated annealing and pre-formed protective film treatment process, performed after final cold rolling, at 650-750℃ in a reducing atmosphere with >60% RH (relative humidity), promotes the recovery and recrystallization of the cold-rolled structure. Simultaneously, it fully utilizes the silicon and rare earth element cerium in the formulation to generate a dense CeO2+SiO2 protective film with a thickness of 3-8 nm, imparting the material with the characteristic of not developing surface corrosion within 15 days of processing or storage. In Comparative Example 1, the Si content is 0.15%, which is within the range of conventional Invar alloys. Even with pre-formed protective film treatment, the low Si content prevents the rapid formation of a dense protective film, making the material prone to rust. Furthermore, Comparative Example 1 contains 38.50% Ni, resulting in a thermal expansion coefficient of 2.1 × 10⁻⁶. -6 / ℃, Comparative Example 1 shows that a certain amount of Si must be added and the Ni content must be controlled within an appropriate range. Comparative Example 2 did not add the rare earth element cerium and used an Al deoxidation process, resulting in an Al content of 0.120% in the alloy. The material cracked during hot working, and because (Si+5Ce):O≤1000, the material did not achieve sufficient rust resistance. Comparative Example 3 also used Al deoxidation and cracked during hot working; unlike Comparative Example 2, Comparative Example 3 added a higher Si content, resulting in better rust resistance, but the 1.20% Si increased the material's coefficient of thermal expansion to 1.9×10⁻⁶. -6 / ℃, therefore, an appropriate Si content needs to be designed to balance deoxidation, rust resistance, and coefficient of thermal expansion. Comparative Example 4 attempted to improve the rust resistance of the material using Cr, and found that when the Cr content was slightly increased to 0.45%, the coefficient of thermal expansion of the material increased to 2.3 × 10⁻⁶. -6 / ℃, in fact, the Cr content in conventional stainless steel materials must reach more than 12% to impart high corrosion resistance and rust resistance to the material. Comparative Example 5 found that when the O content in the alloy reached 0.02%, cracking occurred during the material processing, and the O content must be controlled at a low level. The alloy formulation of Comparative Example 6 is within the scope of this invention, but during the annealing and pre-prepared protective film treatment, the relative humidity was only 20% RH, which failed to effectively form a dense CeO2+SiO2 protective film.

[0037] Based on extensive experiments, a corrosion-resistant Invar alloy precision strip for liquefied natural gas (LNG) ship cargo tanks and its manufacturing method were optimized. By adding a certain amount of Si and rare earth element Ce, the conventional Al deoxidation process for Invar alloys is replaced, ensuring extremely low oxygen content and good machinability. Simultaneously, based on the above formula, a nano-scale dense CeO2+SiO2 protective film is generated on the alloy surface through annealing and pre-formed protective film, imparting a certain degree of rust resistance to the material. At the same time, the alloy maintains a low coefficient of thermal expansion and excellent mechanical properties.

[0038] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent modifications made using the present invention are within the patent protection scope of the present invention.

Claims

1. A surface corrosion-resistant iron-chromium-aluminum alloy precision strip for liquefied natural gas carrier liquid cargo tanks, characterized by, comprising the following mass percentages: Ni: 35.6% - 37.1%; Si: 0.35 - 0.80%; Ce: 0.05% - 0.10%; C：0.015～0.030％； Mn: ≤ 0.35%; O：0～0.0008％； N：≤0.01%； S：≤0.003％； P：≤0.005％； Cr: ≤ 0.20%； Cu: ≤ 0.20%; Al: ≤ 0.05%； Ti: ≤ 0.003%; the remainder being iron and unavoidable impurity elements.

2. The surface corrosion-resistant cast iron alloy precision strip for liquefied natural gas carrier liquid cargo tank according to claim 1, characterized by, At the same time, the following relationship must be satisfied: Mn + Si ≤ 0.95%.

3. The surface corrosion resistant cast iron alloy precision strip for liquefied natural gas carrier cargo tanks according to claim 1, characterized by, At the same time, the following relationship must be satisfied: (Si + 5Ce): O ≥ 1000.

4. The LNG ship cargo tank surface corrosion-resistant iron-chromium-aluminum alloy precision strip according to claim 1, characterized in that, At the same time, the following relationship must be satisfied: Si: (Al + Ti) ≥ 8.

5. A precision strip of a surface corrosion-resistant cast iron alloy for a liquid cargo tank of a liquefied natural gas carrier as claimed in any one of claims 1 to 4, characterized by comprising the following production steps: EAF → AOD → LF → continuous casting or mold casting → hot continuous rolling or forging after solution treatment and pickling → multiple rolling processes of cold rolling → annealing and pre-coating film treatment.

6. The precision strip of a surface corrosion-resistant cast iron alloy for a liquid cargo tank of a liquefied natural gas carrier as claimed in claim 5, characterized in that the annealing and pre-coating film treatment is specifically: a protective film is generated at the same time as annealing at 650 to 750°C in a reducing atmosphere and in an environment with a relative humidity of > 60% RH.

7. The precision strip of a surface corrosion-resistant cast iron alloy for a liquid cargo tank of a liquefied natural gas carrier as claimed in claim 5, characterized in that, in the hot continuous rolling or forging process, the alloy blank is heated to a temperature in the range of 1100 to 1150°C; in the solution treatment process, the heat treatment is performed at 850 to 900°C, and the microstructure is a softened, fully austenitic microstructure; in the multiple rolling processes of intermediate annealing and finished product annealing, if subsequent cold working is performed, intermediate annealing is allowed, and the annealing temperature is 750 to 850°C. ​ ​ ​

Images