JP7340627B2 - Manufacturing method of 7Ni steel plate for LNG storage tank - Google Patents

Description

The present invention belongs to the technical field of steel smelting, and particularly relates to a 7Ni steel plate for LNG storage tanks and a manufacturing method.

With economic development, environmental and resource issues are becoming the top priority for the development of countries, and as a clean, non-polluting, high-calorific energy source, LNG will gradually occupy a larger proportion of energy use, and natural Expanding the scope of gas utilization has become an important means for my country to optimize its energy structure and protect the ecological environment. Currently, the steel plate widely used for LNG storage and transportation tools at home and abroad is 9Ni steel.As a Ni-poor country, China has reduced the Ni content based on ensuring performance in order to save costs. Reducing it is one of the important methods. Related research on nickel-saving 7Ni steel has just begun, and there are currently several patents on 7Ni steel sheets, including ``Nickel-saving 7Ni steel for ultra-low temperature environments and its heat treatment'' in Patent Document 1 (China Patent Application No. 201711306269.2). discloses a heat treatment process for nickel-saving 7Ni steel for ultra-low temperature environments, the composition of 7Ni steel is Ni: 7.00% to 7.60%, C: 0.02% to 0.06%, Si : 0.03% to 0.80%, Mn: 0.10% to 0.90%, Cr: 0.30% to 0.60%, the remainder being Fe and inevitable impurities, and was not subjected to QLT heat treatment. The 7Ni steel had a good plasticity combination and excellent low-temperature toughness, and its performance reached the level of 9Ni steel. The Ni mass fraction of the steel according to "High nickel steel for ultra-low temperature pressure vessels and its manufacturing method" of Patent Document 2 (China Patent Application No. 201310285597.4) is 7.00% to 7.50%, and the Ni mass fraction is 7.00% to 7.50%. The 7Ni steel plate obtained by the quenching + tempering process is used in the production of LNG storage tanks instead of 9Ni steel. The Mn mass fraction of the steel according to Patent Document 3 (China Patent Application No. 201310494688.9) "Low Ni, high Mn, economical low temperature steel that can be used at -196°C and its manufacturing method" is 1.00% to 1. .50%, the Ni mass fraction is 7.00% to 8.00%, and the Ni steel obtained by the two-time quenching + tempering process has excellent toughness at -196°C. Patent Document 4 (China Patent Application No. 201410369201.9) "Low-cost ultra-low temperature nickel steel and its manufacturing method" states that Ni steel obtained by normal rolling + quenching + tempering process has excellent toughness at -196°C. has. In addition, a method of simplifying the heat treatment process by rapidly cooling the steel plate to below the martensitic transition temperature immediately after rolling by the UFC+TMCP process instead of the offline quenching process improves the low-temperature toughness of the 7Ni steel plate.

China Patent Application Publication No. 107937824 China Patent Application Publication No. 104278210 China Patent Application Publication No. 103498100 China Patent Application Publication No. 104131225

Considering the above technical problems, the present invention provides a 7Ni steel plate and manufacturing method for LNG storage tanks that overcomes the shortcomings of the prior art, and under the premise of ensuring the performance of LNG storage and transportation steel, To reduce the Ni content as much as possible and provide an economical and viable preparation method.

In order to solve the above technical problem, the 7Ni steel plate for LNG storage tank provided by the present invention has a chemical composition and mass percentage of C: 0.02% to 0.06%, Si: 0.20 %~0.35%, Ni: 4.0%~8.0%, Mn: 0.3%~0.7%, P≦0.005%, S≦0.005%, Al: 0.03 % to 0.05%, Nb: 0.02% to 0.05%, Cr: 0.2% to 0.4%, and the remainder is Fe and inevitable impurities.

The present invention innovates the regular rolling + two-phase quenching + tempering manufacturing method by designing a Nb-Cr microalloy Ni-saving alloy, which eliminates the quenching process after rolling, which not only saves energy, but also Provide a good plate shape for the quenching process to run smoothly, and finally obtain LNG storage tank steel with excellent mechanical properties.

Further technical solutions of the present invention are:
Furthermore, the thickness is between 8 and 30 mm.

Another object of the present invention is to provide a method for manufacturing a 7Ni steel plate for LNG storage tanks, which method includes:
Preparation of casting billet: preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace and casting it into an ingot, then forging the ingot into a square casting billet and air cooling in a leeward place;
Regular rolling: The cast billet is kept warm at 1150 to 1250 °C for 2 to 3 hours, and the cast billet is rolled in two stages.The rolling start temperature of rough rolling is 1000 to 1100 °C, and the total compression ratio is 40% to 60%. The rolling start temperature of finish rolling is 850 to 900°C, the total compression ratio is 40% to 70%, the rolling end temperature is 750 to 850°C, and an air cooling step;
Two-phase quenching + tempering: The rolled steel plate is quenched at 600-700℃ to below 300℃, tempered at 500-580℃, the tempering speed is 5-20℃/s, 0.5-2 hours. The method includes steps of keeping warm and cooling with air.

In the above method for manufacturing a 7Ni steel plate for an LNG storage tank, the chemical composition and mass percentage of the steel plate are C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045%, S: 0.0030%, Al: 0.038%, Cr: 0.28%, Nb: 0.043%, the remainder being Fe and inevitable impurities,
Preparation of casting billet: The step of preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace, and casting it into an ingot, then forging the ingot into a square casting billet with a thickness of 80 mm and air cooling in a leeward place. and,
Regular rolling: The cast billet is placed in a heating furnace, heated to 1156°C, kept warm for 2.6 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 63%, and the rolling end temperature is 790° C. and air cooling to form a 12 mm thick hot rolled steel plate;
Two-phase quenching + tempering: The rolled steel plate is quenched at 660°C to 300°C or less, tempered at 560°C, the tempering speed is 10°C/s, and includes the steps of keeping warm for 1 hour and then air cooling. .

The manufacturing method of the above 7Ni steel plate for LNG storage tank, the chemical composition and mass percentage of the steel plate are C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P : 0.0043%, S: 0.0031%, Al: 0.035%, Cr: 0.25%, Nb: 0.040%, the remainder is Fe and inevitable impurities,
Preparation of casting billet: The step of preparing smelting raw materials with chemical composition, smelting them in a vacuum smelting furnace, and casting them into ingots, then forging the ingots into square casting billets with a thickness of 80 mm, and air-cooling them in a leeward place. and,
Regular rolling: The cast billet is placed in a heating furnace, heated to 1239°C, kept warm for 2.1 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 45%, and the rolling end temperature is 790° C. and air cooling to form a hot rolled steel sheet having a thickness of 18 mm;
Two-phase quenching + tempering: A rolled steel plate is quenched at 660°C to 300°C or less, tempered at 560°C, the tempering rate is 10°C/s, and includes the steps of keeping warm for 1 hour and cooling in air.

The present invention has the following beneficial effects.
(1) The nickel of the present invention is a non-carbide-forming element that can expand the γ phase region, and is an austenite-forming and stabilizing element, improving low-temperature toughness without reducing strength. Because nickel plays an important role in shifting the CCT curve to the right, reducing the critical quenching rate, and improving hardenability, nickel also improves low-temperature toughness and lowers the toughness-brittle transition temperature. Ni is the main alloying element of the present invention.
(2) In the present invention, carbon is a solution-strengthening element and a strong austenite-stabilizing element, which positively affects the strength of steel sheets, but has a negative effect on toughness, plasticity, and weldability. In order to produce low-temperature steel sheets with good impact resistance and welding performance, it is necessary to control the carbon content within a low range.
(3) In the present invention, manganese mainly plays the role of solution strengthening, compensating for the decrease in strength caused by the decrease in carbon content, and at the same time, similar to nickel, manganese lowers the phase transition temperature of steel, and Mn In the present invention, Mn is one of the main alloying elements because an appropriate increase in /C and Mn/S leads to improved toughness.
(4) In the present invention, silicon is a solution strengthening element and a deoxidizing element, which can improve the strength of steel and reduce the content of oxygen, which is a harmful element during the steel drawing process, and silicon is a solution strengthening element and a deoxidizing element. It exists in steel in a certain proportion with manganese to suppress segregation, and can suppress the segregation of phosphorus at grain boundaries, but silicon reduces the low-temperature toughness of the weld heat affected zone of steel. The silicon content is controlled at 0.15-0.3%.
(5) In the present invention, the addition of chromium increases the hardenability and strength of the steel plate, and adding a small amount of Nb within a certain Nb/Si range not only has no effect on strength and plasticity, but also enables welding of a wide range of plates. S and P are harmful elements in steel, which tend to cause segregation, reduce the low-temperature toughness of steel, and reduce thermal crack sensitivity during welding. It is necessary to strictly control the content of
(6) As the cross-sectional structure of the present invention, martensite and rotated austenite are distributed in the ferrite matrix, and the mechanical performance indicators include yield strength of 590 to 700 MPa, tensile strength of 690 to 790 MPa, and elongation rate. is 24% or more, and the lateral impact energy at -196°C is 100J or more.

2 is a photograph of the metallographic structure of Example 1. 3 is a photograph of the metallographic structure of Example 2.

(Example 1)
In the 7Ni steel plate for LNG storage tank and the manufacturing method provided by this example, the chemical composition and mass percentage of the steel plate are C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045%, S: 0.0030%, Al: 0.038%, Cr: 0.28%, Nb: 0.043%, and the remainder is Fe and inevitable impurities. be.

Preparation of casting billet: Prepare the smelting raw material with chemical composition, smelt it in a vacuum smelting furnace, and cast it into an ingot, then forge the ingot into a square casting billet with a thickness of 80 mm, and air-cool it in a leeward place.

Regular rolling: The cast billet is placed in a heating furnace, heated to 1156°C, kept warm for 2.6 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 63%, and the rolling end temperature is 790° C. and air-cooled to form a 12 mm thick hot rolled steel plate.

Two-phase quenching + tempering: A rolled steel plate is quenched at 660°C below 300°C, tempered at 560°C, the tempering rate is 10°C/s, kept warm for 1 hour, and then air cooled.

The low-temperature steel plate obtained in this example was detected according to national standards, and the detection results are shown in Table 1.

(Example 2)
In the 7Ni steel plate for LNG storage tank and the manufacturing method provided by this example, the chemical composition and mass percentage of the steel plate are C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P: 0.0043%, S: 0.0031%, Al: 0.035%, Cr: 0.25%, Nb: 0.040%, and the remainder is Fe and inevitable impurities. be.

Preparation of casting billet: Prepare the smelting raw material with chemical composition, smelt it in a vacuum smelting furnace, and cast it into an ingot, then forge the ingot into a square casting billet with a thickness of 80 mm, and air-cool it in a leeward place.

Regular rolling: The cast billet is placed in a heating furnace, heated to 1239°C, kept warm for 2.1 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 45%, and the rolling end temperature is 790° C. and air-cooled to form a hot rolled steel plate with a thickness of 18 mm.

Two-phase quenching + tempering: A rolled steel plate is quenched at 660°C below 300°C, tempered at 560°C, the tempering rate is 10°C/s, kept warm for 1 hour, and air cooled.

The low-temperature steel plate obtained in this example was detected according to national standards, and the detection results are shown in Table 2.

Compared with the prior art, the present invention designs a nickel-saving alloy and adopts the manufacturing method of normal rolling + two-phase quenching + tempering, so that the performance meets the 9Ni standard for low temperature pressure vessel steel in GB 3531-2014. fully reached, significantly reducing production costs.

In addition to the embodiments described above, the invention can also be implemented in other forms. All technical solutions formed by equivalent substitution, equivalent transformation, etc. should fall within the protection scope of the present invention.

(Additional note)
(Additional note 1)
Chemical composition and mass percentage are C: 0.02% to 0.06%, Si: 0.20% to 0.35%, Ni: 4.0% to 8.0%, Mn: 0.3% to 0.7%, P≦0.005%, S≦0.005%, Al: 0.03% to 0.05%, Nb: 0.02% to 0.05%, Cr: 0.2% to 0.4%, the remainder being Fe and unavoidable impurities.
A 7Ni steel plate for LNG storage tanks characterized by the following.

(Additional note 2)
The thickness is 8-30mm.
7Ni steel plate for LNG storage tank according to appendix 1, characterized in that:

(Additional note 3)
Preparation of casting billet: preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace and casting it into an ingot, then forging the ingot into a square casting billet and air cooling in a leeward place;
Regular rolling: The cast billet is kept warm at 1150 to 1250 °C for 2 to 3 hours, and the cast billet is rolled in two stages.The rolling start temperature of rough rolling is 1000 to 1100 °C, and the total compression ratio is 40% to 60%. The rolling start temperature of finish rolling is 850 to 900°C, the total compression ratio is 40% to 70%, the rolling end temperature is 750 to 850°C, and an air cooling step;
Two-phase quenching + tempering: The rolled steel plate is quenched at 600-700℃ to below 300℃, tempered at 500-580℃, the tempering speed is 5-20℃/s, 0.5-2 hours. Insulating and air cooling steps;
A method for manufacturing a 7Ni steel plate for an LNG storage tank, characterized in that:

(Additional note 4)
The chemical composition and mass percentage of the steel plate are C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045%, S: 0.0030%. , Al: 0.038%, Cr: 0.28%, Nb: 0.043%, the remainder being Fe and inevitable impurities,
Preparation of casting billet: The step of preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace, and casting it into an ingot, then forging the ingot into a square casting billet with a thickness of 80 mm and air cooling in a leeward place. and,
Regular rolling: The cast billet is placed in a heating furnace, heated to 1156°C, kept warm for 2.6 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 63%, and the rolling end temperature is 790° C. and air cooling to form a 12 mm thick hot rolled steel plate;
Two-phase quenching + tempering: The rolled steel plate is quenched at 660°C to 300°C or less, tempered at 560°C, the tempering speed is 10°C/s, and includes the steps of keeping warm for 1 hour and then air cooling. ,
The method for manufacturing a 7Ni steel plate for an LNG storage tank according to appendix 3, characterized in that:

(Appendix 5)
The chemical composition and mass percentage of the steel plate are C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P: 0.0043%, S: 0.0031%. , Al: 0.035%, Cr: 0.25%, Nb: 0.040%, the remainder being Fe and inevitable impurities,
Preparation of casting billet: The step of preparing smelting raw materials with chemical composition, smelting them in a vacuum smelting furnace, and casting them into ingots, then forging the ingots into square casting billets with a thickness of 80 mm, and air-cooling them in a leeward place. and,
Regular rolling: The cast billet is placed in a heating furnace, heated to 1239°C, kept warm for 2.1 hours, taken out and rolled, the cast billet is rolled in two stages, and the rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 45%, and the rolling end temperature is 790° C. and air cooling to form a hot rolled steel sheet having a thickness of 18 mm;
Two-phase quenching + tempering: The rolled steel plate is quenched at 660 °C to 300 °C or less, tempered at 560 °C, the tempering rate is 10 °C / s, and includes the steps of keeping warm for 1 hour and cooling in air.
The method for manufacturing a 7Ni steel plate for an LNG storage tank according to appendix 3, characterized in that:

Claims (4)

The chemical composition and mass percentage of the steel plate are C: 0.02% to 0.06%, Si: 0.20% to 0.35%, Mn: 0.3% to 0.7%, Ni: 4.0 % to 8.0%, P≦0.005%, S≦0.005%, Al: 0.03% to 0.05%, Cr: 0.2% to 0.4%, Nb: 0.02 % to 0.05%, the remainder being Fe and unavoidable impurities,
Preparation of casting billet: preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace and casting it into an ingot, and then forging the ingot into a square casting billet and air-cooling it in a leeward location;
Rolling : The cast billet is kept warm at 1150 to 1250 °C for 2 to 3 hours, and the cast billet is rolled in two stages, the rolling start temperature of rough rolling is 1000 to 1100 °C, and the total compression ratio is 40% to 60. %, the rolling start temperature of finish rolling is 850-900°C, the total compression ratio is 40%-70%, the rolling end temperature is 750-850°C, and the thickness is 8-30mm by air cooling. forming a hot rolled steel sheet ;
Two-phase quenching + tempering: The rolled steel plate is quenched at 600 to 700 °C to below 300 °C, tempered at 500 to 580 °C, and the tempering temperature increase rate is 5 to 20 °C/s, 0.5 Insulating for ~2 hours and cooling in air,
A method for manufacturing a 7Ni steel plate for an LNG storage tank, characterized in that: The chemical composition and mass percentage of the steel plate are C: 0.05%, Si: 0.25%, Mn: 0.60%, Ni: 7.2%, P: 0.0045%, S: 0.0030%. , Al: 0.038%, Cr: 0.28%, Nb: 0.043%, the remainder being Fe and inevitable impurities,
Preparation of casting billet: Prepare the smelting raw material according to the chemical composition, smelt it in a vacuum smelting furnace, cast it into an ingot, then forge the ingot into a square casting billet with a thickness of 80 mm, and air-cool it in a leeward place. the step of
Rolling : The cast billet is placed in a heating furnace, heated to 1156°C, kept warm for 2.6 hours, taken out and rolled, the cast billet is rolled in two stages, and rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 63%, and the rolling end the temperature is 790° C. and air cooling to form a hot rolled steel sheet with a thickness of 12 mm;
Two-phase quenching + tempering: The rolled steel plate is quenched at 660°C to 300°C or less, tempered at 560°C, the temperature increase rate of tempering is 10°C/s, and the step is to keep it warm for 1 hour and then air cool it. ,including,
The method for manufacturing a 7Ni steel plate for an LNG storage tank according to claim 1 . The chemical composition and mass percentage of the steel plate are C: 0.06%, Si: 0.23%, Mn: 0.55%, Ni: 7.3%, P: 0.0043%, S: 0.0031%. , Al: 0.035%, Cr: 0.25%, Nb: 0.040%, the remainder being Fe and inevitable impurities,
Preparation of casting billet: Prepare the smelting raw material with the above chemical composition, smelt it in a vacuum smelting furnace, and cast it into an ingot . Then, the ingot is forged into a square casting billet with a thickness of 80 mm, and air-cooled in a leeward place. the step of
Rolling : The cast billet is placed in a heating furnace, heated to 1239°C, kept warm for 2.1 hours, taken out and rolled, the cast billet is rolled in two stages, and rough rolling is rolled in an austenite complete recrystallization zone. The rolling start temperature is 1100°C, the compression amount is 60%, the finish rolling is performed in an austenite non-recrystallization zone, the rolling start temperature is 900°C, the compression amount is 45%, and the rolling end is the temperature is 790° C. and air cooling to form a hot rolled steel sheet with a thickness of 18 mm;
Two-phase quenching + tempering: The rolled steel plate is quenched at 660 °C to 300 °C or less, tempered at 560 °C, the temperature increase rate of tempering is 10 °C/s, kept warm for 1 hour, and air-cooled; including,
The method for manufacturing a 7Ni steel plate for an LNG storage tank according to claim 1 . The chemical composition and mass percentage of the steel plate are C: 0.02% to 0.06%, Si: 0.20% to 0.35%, Mn: 0.3% to 0.7%, Ni: 4.0 % to 8.0%, P≦0.005%, S≦0.005%, Al: 0.03% to 0.05%, Cr: 0.2% to 0.4%, Nb: 0.02 % to 0.05%, the remainder being Fe and unavoidable impurities,
Preparation of casting billet: preparing the smelting raw material according to the chemical composition, smelting it in a vacuum smelting furnace and casting it into an ingot, and then forging the ingot into a square casting billet and air-cooling it in a leeward location;
Rolling: The cast billet is kept warm at 1150 to 1250 °C for 2 to 3 hours, and the cast billet is rolled in two stages, the rolling start temperature of rough rolling is 1000 to 1100 °C, and the total compression ratio is 40% to 60%. The rolling start temperature of finish rolling is 850 to 900°C, the total compression ratio is 40% to 70%, the rolling end temperature is 750 to 850°C, and an air cooling step,
Two-phase quenching + tempering: The rolled steel plate is quenched at 600 to 700 °C to below 300 °C, tempered at 500 to 580 °C, and the tempering temperature increase rate is 5 to 20 °C/s, 0.5 Insulating for ~2 hours and cooling in air,
A method for manufacturing a 7Ni steel plate for an LNG storage tank, characterized in that:

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