CN114134293B - Preparation method of 9Ni steel for low-segregation LNG ship - Google Patents
Preparation method of 9Ni steel for low-segregation LNG ship Download PDFInfo
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- CN114134293B CN114134293B CN202111112727.5A CN202111112727A CN114134293B CN 114134293 B CN114134293 B CN 114134293B CN 202111112727 A CN202111112727 A CN 202111112727A CN 114134293 B CN114134293 B CN 114134293B
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 98
- 239000010959 steel Substances 0.000 title claims abstract description 98
- 238000005204 segregation Methods 0.000 title claims abstract description 27
- 238000002360 preparation method Methods 0.000 title claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims abstract description 26
- 238000000034 method Methods 0.000 claims abstract description 26
- 238000005096 rolling process Methods 0.000 claims abstract description 24
- 230000008569 process Effects 0.000 claims abstract description 18
- 238000010791 quenching Methods 0.000 claims abstract description 17
- 230000000171 quenching effect Effects 0.000 claims abstract description 17
- 238000005496 tempering Methods 0.000 claims abstract description 16
- 238000001816 cooling Methods 0.000 claims abstract description 11
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 10
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical group OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 claims abstract description 9
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 9
- 239000000126 substance Substances 0.000 claims abstract description 9
- 230000009466 transformation Effects 0.000 claims abstract description 8
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 5
- 238000005266 casting Methods 0.000 claims abstract description 4
- RMLPZKRPSQVRAB-UHFFFAOYSA-N tris(3-methylphenyl) phosphate Chemical compound CC1=CC=CC(OP(=O)(OC=2C=C(C)C=CC=2)OC=2C=C(C)C=CC=2)=C1 RMLPZKRPSQVRAB-UHFFFAOYSA-N 0.000 claims abstract description 3
- 238000004321 preservation Methods 0.000 claims description 5
- 239000000203 mixture Substances 0.000 abstract description 5
- 229910000734 martensite Inorganic materials 0.000 abstract description 3
- 239000002279 physical standard Substances 0.000 abstract description 2
- 239000003949 liquefied natural gas Substances 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 11
- 238000004519 manufacturing process Methods 0.000 description 10
- 229910052799 carbon Inorganic materials 0.000 description 6
- 238000003466 welding Methods 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 238000003723 Smelting Methods 0.000 description 4
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005452 bending Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 210000001787 dendrite Anatomy 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
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- 238000007711 solidification Methods 0.000 description 2
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- 239000002436 steel type Substances 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
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- 238000007906 compression Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
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- 238000005520 cutting process Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000009851 ferrous metallurgy Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Abstract
The invention relates to a preparation method of 9Ni steel for a low-segregation LNG ship, which comprises the following steps: and (3) after the steel plate is rolled down, normalizing at a high temperature, wherein the normalizing heating temperature is 150 ℃ or higher than the ferrite austenite balance transformation Ac3 point, normalizing and cooling to obtain a bainite structure, and then quenching and tempering to obtain a tempered sorbite structure as the final steel plate structure. The chemical composition of 9Ni steel adopts the standard composition of 9Ni steel specified by the society of chemical and physical standards (GmbH) and GB/T37602. The rolling is to control rolling or TMCP rolling and cooling control process of casting blank meeting chemical composition. Carbide in the steel plate is fully dissolved as much as possible through high-temperature normalizing, the austenitic structure of the steel plate is homogenized, the center segregation of the 9Ni steel is improved, coarse austenitic grains are promoted to form, the C curve is shifted to the right, the possibility of generating bainite and martensite is improved, and the occurrence probability of ferrite as a diffusible phase transformation product is reduced.
Description
Technical Field
The invention belongs to the field of ferrous metallurgy, and particularly relates to a preparation method of a 9Ni steel plate for a low-segregation LNG ship.
Background
LNG is liquified natural gas, namely liquid natural gas for short, is a clean and efficient energy source, is liquefied at a low temperature of about 162 ℃ below zero, reduces the volume after the liquefaction to 1/600 of the original volume, greatly saves storage and transportation space, and also has the advantages ofHeat of the body Value ofLarge size, high performance, etc. With the increasing demand for LNG, 9Ni steel has been generally adopted as steel for its storage tanks. In the smelting process, the solidification front of the steel consists of solid solution and precipitated phase, the crystal form is dendrite, the crystal form has certain directivity, dendrite segregation or grain boundary segregation is inevitably generated in the crystallization process, and the solidification end at the liquid core can form casting blank center segregation. The segregation of the steel sheet cannot be completely eliminated even though the steel sheet is reheated and rolled. In the subsequent heat treatment, the ferrite austenite balance transformation point Ac of the 9Ni steel is used 1 /Ac 3 In order to obtain the high strength of 9Ni steel and the ultra-low temperature toughness index requirement of minus 196 ℃, the quenching temperature and the sub-temperature quenching temperature in the conventional heat treatment method are lower than those of common low-carbon steel, and the segregation improvement of 9Ni steel is not obvious.
The 9Ni steel segregation is easy to cause a series of problems such as uneven performance in the thickness direction of the steel plate, unqualified cold bending of the steel plate, cutting deformation in the use process, welding joint cracking in the welding process, cold bending cracking of the welding joint and the like. For safety, the upper limit thickness of the existing 9Ni steel classification society is only 50mm thick, and the upper limit thickness of GB/T37602 newly revised in 2019 is only 60mm. In order to improve the comprehensive performance of the 9Ni steel, the 9Ni steel is easier to process and weld, the quality of the 9Ni steel is required to be improved, the thickness specification is enlarged, the application performance of the 9Ni steel is improved, and the 9Ni steel is easy to use by downstream enterprises.
The prior art rarely relates to 9Ni steel for low-segregation LNG ships and a preparation method thereof. The technical layer has only been to develop 9Ni steel meeting delivery conditions. At present, all large-scale production enterprises mainly prepare 9Ni steel in a QLT mode, namely a quenching, sub-temperature quenching and tempering heat treatment mode, and the 9Ni steel obtained in the mode has better toughness and higher safety coefficient. Also, as in chinese patent CN103602888, a hot rolled low compression ratio 9Ni thick steel sheet and a method for manufacturing the same are disclosed, in which 9Ni steel is obtained by hot rolling without heat treatment, and the structure is tempered martensite as a matrix and 4-15% reverse transformation tempered austenite. Chinese patent CN101215668 discloses a method for manufacturing a low-carbon 9Ni steel thick plate, which shortens the production process flow by simulating the continuous casting and rolling process, but is difficult to realize in industrial mass production, and the obtained 9Ni steel has low strength and cannot meet the actual supply requirement. Chinese patent CN101864537 discloses a method for manufacturing Cu-containing 9Ni steel, the thickness of which is 20mm. The laminar cooling after hot rolling is controlled below 200 ℃, and a large amount of residual stress cannot be released at the temperature, so that the method is not suitable for controlling the shape of a wide and thin steel plate. In addition, the yield strength of the steel plate is up to 710MPa, but the high toughness of 9Ni steel is sacrificed, the impact toughness value of the steel plate at minus 196 ℃ is only 120J, and in the current ordering technical protocol, the average value of the transverse impact toughness at minus 196 ℃ is more than or equal to 100J.
As described above, the prior art has not been able to develop a 9Ni steel sheet for LNG ships having a low segregation degree, high strength and high toughness at-196 ℃.
Disclosure of Invention
According to the standard components of 9Ni steel specified by the prior classification society specification and GB/T37602, the invention designs high-temperature normalizing (the normalizing temperature is higher than the ferrite austenite balance transformation Ac) on the premise of prior smelting and rolling 3 The 9Ni steel plate for the LNG ship with low segregation degree is obtained by the mode of point 150 ℃ or above) +quenching and tempering heat treatment.
The invention solves the problems by adopting the following technical scheme: preparation method of 9Ni steel for low-segregation LNG ship, steel plate is subjected to high-temperature normalizing after rolling down line, and normalizing heating temperature is higher than ferrite austenite balance transformation Ac 3 And normalizing and cooling at the temperature of more than 150 ℃ to obtain a bainite structure, quenching and tempering to obtain a tempered sorbite structure as a final steel plate structure.
The chemical components of the 9Ni steel are 9Ni steel standard components specified in the society of chemical and physical standards (GmbH) and GB/T37602.
The rolling of the 9Ni steel is to subject a casting blank conforming to chemical components to a controlled rolling or TMCP controlled rolling and cooling process.
In the method, the normalizing temperature is 880-980 ℃, and the heating and heat preserving time of the normalizing is 2.0-2.3 min/mm; quenching temperature is 790-820 ℃, and quenching heat preservation time is 2.0-2.3 min/mm; the tempering temperature is 580-620 ℃, and the tempering heat preservation time is 4.0-4.5 min/mm.
The process principle of heat treatment after rolling is as follows: through a high-temperature normalizing process, the temperature is higher than that of ferrite austenite balance transformation Ac 3 The temperature is above 150 ℃, and the heating and heat preserving time is 2.0-2.3 min/mm. The carbide in the steel plate is fully dissolved as far as possible, the austenitic structure of the steel plate is homogenized, the center segregation of the 9Ni steel is favorably improved, alloy elements such as C, mn, P, S, ni and the like can be fully homogenized again in the austenite growing process, coarse austenite grains are promoted to form, the C curve is shifted to the right, the possibility of generating bainite and martensite is also improved, the occurrence probability of ferrite serving as a diffusible phase change product is reduced, and the bainitic structure is obtained after normalizing and cooling. The subsequent quenching and tempering are performed to ensure that the material meets the high-strength and high-toughness requirements of the 9Ni steel plate. The transverse yield strength of the 9Ni steel plate is 725-745 MPa, the tensile strength is 746-770 MPa, and the elongation is more than or equal to 22%. The transverse impact toughness value at the temperature of 196 ℃ below zero is more than or equal to 221J, and the structure is uniform along the thickness direction of the steel plate.
The 9Ni steel plate for the low-segregation LNG ship has the following advantages:
the 9Ni steel plate component design of the invention can still be according to the 9Ni steel standard component system specified by Jiunational classification society and GB/T37602, other alloy elements are not required to be additionally added, the existing smelting and rolling technology of 9Ni steel is continuously used, the tempering process (quenching and tempering) is consistent with the corresponding process of the heat treatment of the existing 9Ni steel, and the risk of steel plate smelting, rolling and trial production is reduced.
The 9Ni steel component system still does not increase the carbon equivalent according to the standard component system specified by the society specifications and GB/T37602, and does not need the subsequent welding, including the matching of welding materials, the design adjustment of the welding process and the whole ship by a user.
The 9Ni steel has the advantages that the phase transition point is lower than that of the conventional low-carbon steel by about 100 ℃, so that the production arrangement is difficult, the normalizing temperature of the 9Ni steel is increased, the temperature interval is larger, the operation is easy, the normalizing can be carried out together with other steel types, the heat treatment temperature rise and drop frequency is reduced, the batch production of multiple batches, multiple specifications and multiple steel types can be met, and the productivity of a heat treatment furnace is improved.
The 9Ni steel plate for the low-segregation LNG ship, which is obtained by the invention, has higher impact toughness, the transverse impact toughness value at minus 196 ℃ is more than or equal to 221J, the steel plate low-power is obviously superior to the 9Ni steel plate low-power produced by other methods, and the steel plate strength is high.
Drawings
FIG. 1 is a steel sheet microstructure of comparative example 1;
FIG. 2 is a typical microstructure of the present invention-the microstructure of the steel sheet of example 1;
FIG. 3 is a structural morphology of the steel sheet of comparative example 1, and it can be seen that the bright-dark alternation phenomenon is caused by segregation;
FIG. 4 is a further magnification of the morphology of the metallographic structure of comparative example 1 of FIG. 3, showing that tempered sorbite grains in different regions are different in size;
FIG. 5 shows a typical structure of the present invention, i.e. the structure of the steel plate in example 1, wherein the structure is uniform tempered sorbite, and the phenomenon of light and shade alternation does not exist;
fig. 6 shows a typical structure of the present invention-the morphology of the metallographic structure of the steel sheet of example 1 at a further magnification, which is a uniform and fine tempered sorbite structure.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
5 billets with the thickness of 150mm and the composition meeting the requirements of classification society specifications and GB/T37602 9Ni steel are selected for conventionally producing 9Ni steel, the chemical compositions of the 9Ni steel plates for the low-segregation LNG ship corresponding to each example and comparative example are shown in a table 1, the data in the table are the mass percent content of each element, and the balance is Fe and unavoidable impurity elements. Ac was determined by thermal simulation of Gleeble 3800 3 The point is approximately 725 ℃.
TABLE 1
The finished steel plate with the thickness of 18-50mm is rolled, the rolling process temperature is controlled according to the process for producing the 9Ni steel plate with the thickness of less than or equal to 50mm, the rough rolling temperature is 1050-1150 ℃, the finish rolling starting temperature is less than or equal to 880 ℃, the pass is controlled according to the production rhythm, the application of dephosphorization water among passes is paid attention to, and the surface quality in the steel plate rolling process is ensured. The rolled steel plate is cooled by ACC or laminar flow, the cooling redback temperature is 600-660 ℃, and the rolled steel plate can be directly cooled by air without cooling.
Adopting a QLT heat treatment process to produce a 9Ni steel plate on a heat treatment production line as comparative example 1, wherein the quenching temperature is 790-820 ℃, and the heating and heat preserving time is 2.0-2.3 min/mm; the subtemperature quenching temperature is 650-690 ℃, and the heating and heat preserving time is 2.0-2.3 min/mm; tempering temperature is 580-620 ℃, and heating and heat preserving time is 4.0-4.5 min/mm.
The low segregation degree LNG marine 9Ni steel plate of the embodiment 1-4 is produced by adopting a high-temperature normalizing, quenching and tempering process on a heat treatment production line, the normalizing temperature is 880-980 ℃, and the heating and heat preservation time is 2.0-2.3 min/mm; quenching temperature is 790-820 ℃, and heating and heat preserving time is 2.0-2.3 min/mm; tempering temperature is 580-620 ℃, and heating and heat preserving time is 4.0-4.5 min/mm.
The specific heat treatment processes of comparative example 1 and examples 1 to 4 are shown in Table 2.
TABLE 2
As shown in fig. 1 and 2, the microstructure of the typical steel sheet of comparative example 1 and example was inferior to that of comparative example 1, and the segregation was a phenomenon that the segregation was significantly uneven, indicating that the segregation was severe. While the bright-dark alternation phenomenon is hardly observed in fig. 2, the segregation degree is light.
The metallographic structure of the steel sheet of comparative example 1 is shown in FIGS. 3 and 4. It can be seen from fig. 3 that the steel sheet has a bright-dark alternation phenomenon caused by segregation of the steel sheet. Fig. 4 is a further magnification of the metallographic structure morphology of fig. 3, and it can be seen from fig. 4 that the tempered sorbite grains are larger in size in the white and bright areas than in the dark areas. This is because the tempered sorbite sheet has a small ferrite carbon content, and shows a white and bright color under a metallographic microscope, and the lower the carbon concentration is, the more favorable the ferrite grain nucleation growth is, and the larger the grain size is. And in the area with high carbon concentration, gray and dark colors are displayed under a metallographic microscope, and the grain size is small.
As shown in fig. 5, the typical structure of example 1 hardly sees the phenomenon of the alternating brightness in fig. 3. Fig. 6 shows the microstructure morphology of the steel sheet of example 1 at further magnification, the microstructure being uniform tempered sorbite and the grains being fine.
The properties of comparative example 1 and examples 1-4 are shown in Table 3. From the view point of the tensile property of the steel plate, the yield strength and the transverse tensile property of the steel plate are 725-745 MPa, the tensile strength is 746-770 MPa, and the elongation is moderate. The transverse impact toughness values of examples 1-4 are greater than or equal to 221J, which is significantly higher than that of comparative example 1. It is considered that the heat treatment mode corresponding to the example has better toughness than the structure finally obtained by quenching-sub-temperature quenching-tempering.
TABLE 3 Table 3
While the preferred embodiments of the present invention have been described in detail, it is to be clearly understood that the same may be varied in many ways by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (2)
1. A preparation method of 9Ni steel for a low-segregation LNG ship is characterized by comprising the following steps: after the steel plate is rolled down, the steel plate is normalized at high temperature, and the normalizing heating temperature is higher than the ferrite austenite balance transformation Ac 3 Normalizing and cooling to obtain bainite structure at a temperature above 150deg.C, and subjecting toQuenching and tempering, wherein the final steel plate structure is a tempered sorbite structure; the chemical components of the steel adopt 9Ni steel standard components specified by the specifications of the classification society and GB/T37602;
the heating and heat preserving time of normalizing is 2.0-2.3 min/mm; quenching temperature is 790-820 ℃, and quenching heat preservation time is 2.0-2.3 min/mm; tempering temperature is 580-620 ℃, and tempering heat preservation time is 4.0-4.5 min/mm;
the rolling is to subject a casting blank conforming to chemical components to a controlled rolling or TMCP controlled rolling and cooling process, and the rough rolling temperature is as follows: 1050-1150 ℃, the initial rolling temperature of finish rolling is less than or equal to 880 ℃, and after rolling, the cold return temperature is cooled by ACC or laminar flow: 600-660 deg.c or direct air cooling after rolling.
2. The method according to claim 1, characterized in that: steel sheet transverse yield strength: 725-745 MPa, tensile strength: 746-770 MPa, elongation is more than or equal to 22%, and transverse impact toughness value at minus 196 ℃ is more than or equal to 221J.
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2021
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