CN115717220B - 590 MPa-grade polar region ship body structural steel with low-temperature toughness and preparation method thereof - Google Patents
590 MPa-grade polar region ship body structural steel with low-temperature toughness and preparation method thereof Download PDFInfo
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- 229910000746 Structural steel Inorganic materials 0.000 title claims abstract description 29
- 238000002360 preparation method Methods 0.000 title abstract description 11
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 97
- 239000010959 steel Substances 0.000 claims abstract description 97
- 239000012535 impurity Substances 0.000 claims abstract description 8
- 238000005096 rolling process Methods 0.000 claims description 57
- 238000000034 method Methods 0.000 claims description 38
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 24
- 239000000463 material Substances 0.000 claims description 23
- 238000003466 welding Methods 0.000 claims description 23
- 238000009749 continuous casting Methods 0.000 claims description 22
- 230000008569 process Effects 0.000 claims description 22
- 238000005496 tempering Methods 0.000 claims description 20
- 229910000734 martensite Inorganic materials 0.000 claims description 19
- 238000001816 cooling Methods 0.000 claims description 16
- 238000007670 refining Methods 0.000 claims description 15
- 239000002893 slag Substances 0.000 claims description 15
- 238000010438 heat treatment Methods 0.000 claims description 11
- 229910052742 iron Inorganic materials 0.000 claims description 11
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- 239000011575 calcium Substances 0.000 claims description 8
- 238000010791 quenching Methods 0.000 claims description 8
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- 238000003723 Smelting Methods 0.000 claims description 6
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- 238000010079 rubber tapping Methods 0.000 claims description 5
- 239000000126 substance Substances 0.000 claims description 5
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 4
- 229910052786 argon Inorganic materials 0.000 claims description 4
- 229910001563 bainite Inorganic materials 0.000 claims description 4
- 238000007664 blowing Methods 0.000 claims description 4
- 229910052791 calcium Inorganic materials 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 230000003068 static effect Effects 0.000 claims description 4
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- 230000023556 desulfurization Effects 0.000 claims description 3
- 229910001566 austenite Inorganic materials 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 7
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 5
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- 238000001556 precipitation Methods 0.000 description 4
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- 238000010276 construction Methods 0.000 description 3
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- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention relates to 590 MPa-level polar region ship body structural steel with low-temperature toughness and a preparation method thereof, belonging to the technical field of polar region ship special steel. 590 MPa-level polar region ship body structural steel with low-temperature toughness comprises the following components in percentage by mass: c:0.03 to 0.06 percent, si:0.10 to 0.25 percent, mn:0.5 to 2.0 percent, cu:1.0 to 1.5 percent, ni:2.5 to 4.5 percent; cr:0.4 to 0.6 percent, ti: 0.008-0.015%; mo:0.25 to 0.35 percent; nb:0.015 to 0.03 percent; als is more than or equal to 0.015%; n is less than or equal to 0.004%; p is less than or equal to 0.005%; s is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurity elements. The steel provided by the invention has the characteristics of high strength, excellent low-temperature toughness, low preheating temperature and the like, and meets the use condition of the polar environment temperature.
Description
Technical Field
The invention relates to the technical field of special steel for polar vessels, in particular to 590 MPa-level polar hull structural steel with low-temperature toughness and a preparation method thereof.
Background
With the gradual exhaustion of conventional oil and gas energy sources, the rich energy reserves in arctic regions are paid more attention to, and the requirements and development of large-scale high-technology extremely-low-transportation ice-breaking ships are promoted. However, extreme severe conditions put severe technical demands on the low-temperature steel for polar vessels, and the low-temperature steel for polar vessels having excellent low-temperature toughness, low-preheating welding, and high strength grade is an important development trend in the field of polar vessels.
In the ship sailing in extremely low environment, the ship is in service in the severe cold sea area throughout the year, the average working environment temperature is minus 20 ℃, the lowest air temperature can reach minus 70 ℃, and the ship is subjected to strong wind and wave and sea ice dynamic load, and the extremely low ecological environment is fragile, so that the construction of the polar ship is not separated from the construction of the key materials such as low-temperature steel which are suitable for extremely severe service environments, and the high-strength and excellent base metal and the high-performance steel with low-temperature toughness in the welding heat affected zone are the basic guarantee of the safe sailing of the polar ship.
At present, most countries and related international organizations generally lack research and data of polar marine materials except a few polar countries pay attention to and accumulate practical application experience of a small amount of polar marine materials, and marine steel meeting polar service environment requirements in China is still blank. The existing E-series steel plate can not completely meet the use condition of the polar environment temperature. There are three technical requirements for steel for polar vessels: (1) has high strength; (2) has high toughness, especially low temperature toughness; (3) good weldability; (4) the anti-collision device has certain anti-collision performance. Development of extremely high strength, high toughness, easy to weld steels is a direction of search in this field.
Disclosure of Invention
In view of the analysis, the invention aims to provide 590 MPa-grade polar ship body structural steel with low-temperature toughness and a preparation method thereof, which are used for solving the problem that the existing steel type cannot meet the use condition of the polar service environment.
The aim of the invention is mainly realized by the following technical scheme:
the invention provides 590 MPa-level polar ship body structural steel with low-temperature toughness, which comprises the following chemical components in percentage by mass: c:0.03 to 0.06 percent, si:0.10 to 0.25 percent, mn:0.5 to 2.0 percent, cu:1.0 to 1.5 percent, ni:2.5 to 4.5 percent; cr:0.4 to 0.6 percent, ti: 0.008-0.015%; mo:0.25 to 0.35 percent; nb:0.015 to 0.03 percent; als is more than or equal to 0.015%; n is less than or equal to 0.004%; p is less than or equal to 0.005%; s is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurity elements.
Further, the microstructure of the steel is lath martensite and a small amount of granular bainite, and the effective grain size of the lath martensite is less than or equal to 2 mu m.
Further, the content of lath martensite is more than or equal to 80 percent.
The invention also provides a preparation method of 590 MPa-grade polar region ship body structural steel with low-temperature toughness, which is used for preparing the 590 MPa-grade polar region ship body structural steel and comprises the steps of molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling control and cooling control and off-line tempering, wherein the molten iron pretreatment comprises KR desulfurization, the S content is less than or equal to 0.007%, and the slag thickness meets the slag skimming level 1.
Further, in the LF refining process, the added slag-forming material and deoxidizer must be dried, and the standby time of the feed bin is less than or equal to 24 hours; the holding time of the white slag is more than or equal to 10min;
in the RH refining process, calcium treatment is carried out before tapping, and the static argon blowing time after wire feeding is more than or equal to 10min, so that the Ca content in molten steel is ensured to be 0.001-0.0015%.
Further, the continuous casting process adopts whole-process protection casting, the heating temperature of a continuous casting billet is less than or equal to 1150 ℃, the target superheat degree of the ladle molten steel is less than or equal to 25 ℃, and the ladle molten steel enters a pit for treatment after continuous casting.
Further, the rolling and cooling control adopts two-stage rolling, the first-stage rolling is rough rolling, the final rolling temperature is more than or equal to 950 ℃, the single-pass deformation is 10-15%, and the accumulated deformation of the first-stage rolling is less than or equal to 50%.
Further, in the two-stage rolling, the second stage rolling is finish rolling, the rolling temperature is less than or equal to 850 ℃, the finish rolling temperature is less than 800 ℃, the finish rolling deformation is more than or equal to 15%, and the accumulated deformation of the second stage rolling is more than or equal to 60%.
Further, the off-line tempering is one-time quenching and one-time tempering, the one-time quenching is carried out at the heating temperature of 840-880 ℃, and the heat preservation time is 1-2 hours.
Further, the primary tempering process is to heat at 600-650 deg.c for 1-2 hr and air cooled to room temperature.
Compared with the prior art, the invention has at least one of the following beneficial effects:
1. the structure of the steel plate prepared by the preparation method is characterized by lath martensite and a small amount of granular bainite, wherein the lath martensite content is more than or equal to 80 percent, the production process of the steel plate prepared by the preparation method is simple, and the produced polar-region ship structure steel can be used for ship construction in a polar region.
2. The welding preheating temperature of the steel plate prepared by the preparation method is not higher than-10 ℃, so that the welding efficiency in ship manufacturing and the welding repair efficiency in a polar environment are remarkably improved.
3. According to the invention, by controlling element types and element contents, particularly element proportions of Ni, cr, mo, cu, and combining rolling, cooling and off-line tempering processes, the steel plate has excellent mechanical properties, yield strength of more than or equal to 590MPa, tensile strength of more than or equal to 690MPa, elongation of more than or equal to 19.5%, ductile-brittle transition temperature of the steel plate of not higher than-90 ℃, good weldability of the steel plate, impact energy of a welding joint heat affected zone of more than or equal to 47J at-60 ℃, CTOD performance of a welding heat affected zone of more than or equal to 0.15mm at-40 ℃, and meets the use conditions of a polar service environment.
In the invention, the technical schemes can be mutually combined to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, like reference numerals being used to refer to like parts throughout the several views.
FIG. 1 is a metallographic structure of a quarter position of a rolled steel sheet according to example 1 of the present invention;
FIG. 2 shows the series of impact energy of the surface layer position of the rolled steel plate provided in example 1 of the present invention;
FIG. 3 shows the series of impact energy at a quarter position of a rolled steel sheet according to example 1 of the present invention.
Detailed Description
The invention provides 590 MPa-level polar ship body structural steel with low-temperature toughness and a preparation method thereof, and the marine steel has the characteristics of high strength, excellent low-temperature toughness, low preheating temperature and the like, and is used for solving the problem that the existing steel plate cannot meet the use condition of polar environment temperature.
The invention provides 590 MPa-level polar region ship body structural steel with low-temperature toughness, which comprises the following chemical components in percentage by mass: c:0.03 to 0.06 percent, si:0.10 to 0.25 percent, mn:0.5 to 2.0 percent, cu:1.0 to 1.5 percent, ni:2.5 to 4.5 percent; cr:0.4 to 0.6 percent, ti: 0.008-0.015%; mo:0.25 to 0.35 percent; nb:0.015 to 0.03 percent; als is more than or equal to 0.015%; n is less than or equal to 0.004%; p is less than or equal to 0.005%; s is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurity elements.
At present, the ship steel meeting the regional service environment requirements in China is still blank. The existing E-series steel plate can not completely meet the use condition of the polar environment temperature. The 590 MPa-level polar region ship body structural steel has the characteristics of high strength, excellent low-temperature toughness, low preheating temperature and the like, and can solve the problem that the existing steel plate cannot meet the use condition of polar region environment temperature.
Preferably, the 590 MPa-grade polar region ship body structural steel with low-temperature toughness comprises the following chemical components in percentage by mass: c:0.04 to 0.06 percent, si:0.10 to 0.20 percent, mn:0.9 to 1.5 percent, cu:1.3 to 1.5 percent of Ni:2.5 to 4.0 percent; cr:0.4 to 0.55 percent, ti:0.01 to 0.015 percent; mo:0.25 to 0.35 percent; nb:0.02 to 0.03 percent; als is more than or equal to 0.015%; n is less than or equal to 0.004%; p is less than or equal to 0.005%; s is less than or equal to 0.0044%, and the balance is Fe and unavoidable impurity elements.
The reason why the casting blank composition of 590 MPa-grade steel for a polar hull of the present invention and a method for producing the same are limited will be described, and the mass percentage in the composition will be expressed only in% below.
C: carbon is an element that ensures the strength of the steel sheet and significantly affects the weldability of the material. In order to meet the requirement that the ductile-brittle transition temperature of the steel plate is lower than the low-temperature toughness of 84 ℃ below zero, the C content is required to be lower than 0.06%; when the C content is less than or equal to 0.03%, the low-temperature toughness of the steel plate cannot be improved. Therefore, the C content is controlled to be 0.03-0.06%.
Mn: mn is dissolved in steel to raise the strength of steel, and Mn content should be controlled to over 0.6% to ensure the strength of steel. When the Mn content exceeds 1.2%, on one hand, center segregation is generated, so that a hardening structure is generated in the cooling process of the steel plate, and the low-temperature toughness of the base metal is reduced. Therefore, the Mn content is controlled to be 0.5 to 2.0%.
Si: si is generally used as a deoxidizer in steel making, and when the Si content is less than 0.1%, the molten steel is easily oxidized. Si is also a solid solution strengthening element, but a large amount of Si is generally detrimental to welding properties, and Si content should be controlled to less than 0.2% in order to secure toughness of a weld heat affected zone. Therefore, the Si content is controlled to be 0.1 to 0.25%.
N: the N with a certain content can form TiN with Ti, so that the toughness of the steel plate and a welding heat affected zone is improved, and carbon nitride is formed with Ti, nb and the like, so that the strength is improved; however, too high an N content will affect the low temperature toughness of the material. Therefore, the N content is controlled to be less than or equal to 0.004%.
Ti: ti and N are combined to form TiN, on one hand, the growth process of austenite grains of the continuous casting blank in the heating process is inhibited, and the size of the austenite grains is pinned in the welding thermal cycle process, so that the toughness of the steel plate and a welding heat affected zone is improved. The Ti content is less than 0.01 percent, and the above functions are not easy to be exerted; excessive Ti causes the reduction of TiN precipitation time, the increase of temperature and the reduction of pinning effect on austenite grains. Therefore, the Ti content is controlled to be 0.008% -0.015%.
Als: als is an important deoxidizing element in the steelmaking process, and when the Als content is less than 0.015%, the oxygen content is difficult to control to be below 0.004%; when the Als content is high, coarse Al oxide inclusions are formed and aggregated into clusters, and clogging of the steel-making nozzle occurs or the toughness is lowered as a crack source. Therefore, the Als content should be controlled to be not less than 0.015%.
Nb: niobium element generally acts by solute drag and precipitation of particles (Nb (C, N)) which act on the one hand to pin the original austenite grain boundaries during deformation of the material and on the other hand to enhance the strength of the material by precipitation strengthening. The Nb content is controlled to be 0.015-0.03%.
Cr: cr can improve the hardenability of the material and can improve the strength of the material in the form of carbide, and if the Cr content is less than 0.5%, it is difficult to exert its effect, but if the Cr content exceeds 0.7%, it will lower the low temperature toughness of the base material and the weld heat affected zone, and increase the manufacturing cost of the material, so that Cr is controlled to 0.4 to 0.6%.
Cu: cu and Ni elements are generally added in a complex manner. The strength of the high-strength steel plate can be improved by utilizing Cu aging precipitation particles, the strength reduction caused by ultra-low carbon is compensated, but excessive Cu element can improve carbon equivalent (Ceq) and cold crack sensitivity index (Pcm), so that the preheating temperature is increased during material welding. Therefore, the Cu content is controlled to be 1.0 to 1.5%.
Ni: ni can improve the low temperature toughness of the material. In order to meet the low-temperature toughness requirement of the polar region on the polar region ship steel, a certain content of Ni element needs to be added to improve the low-temperature toughness of the steel plate and a welding joint heat affected zone, but the content of Ni is too high to improve Ceq and Pcm, so that the preheating temperature of the steel plate is too high, and therefore, the content of Ni cannot be higher than 3.5%. Therefore, the Ni content is controlled to be 2.5 to 4.5%.
Mo: mo can improve the hardenability of the material, promote low-temperature tissue transformation, improve the strength of the material, and promote the formation of acicular ferrite tissue under the condition of no recrystallization rolling; if the Mo content is less than 0.4%, the effect of Mo is lower; if the Mo content exceeds 0.6%, not only the manufacturing cost is increased, but also the weldability of the steel sheet, particularly the low-temperature toughness under high heat input welding, is impaired. Therefore, the Mo content is controlled to be 0.25-0.35%.
P: phosphorus is an impurity element in steel, and may impair toughness of steel plates and weld heat affected zones. Therefore, the P content is controlled to be 0.005% or less.
S: sulfur is an impurity element in steel, and forms sulfide inclusions, which become a crack source. Therefore, the S content is controlled to be 0.005% or less.
The invention also provides a preparation method of the 590 MPa-level polar ship body structural steel with low-temperature toughness, which comprises the following steps:
step 1: and (3) molten iron pretreatment: impurity elements in steel are reduced through molten iron pretreatment, S content is guaranteed to be less than or equal to 0.007% after KR desulfurization, and slag thickness meets the 1-stage slag skimming.
Step 2: smelting in a converter: when slag stopping and tapping are carried out, the thickness of a slag layer is required to be less than or equal to 100mm, and the added alloy material, lime, sinter, dolomite and other auxiliary materials must be dried, and the ladle alloying deoxidization sequence is from strong to weak.
Step 3: LF refining: in the LF furnace working procedure, the added slag-forming material and deoxidizer must be dried, and the standby time of the bin is less than or equal to 24 hours, so that the slag has good fluidity; the white slag is kept for more than or equal to 10min, and Ti and Fe are added after the deoxidation is complete.
Step 4: RH refining: in the RH furnace working procedure, calcium treatment is carried out before tapping, and the static argon blowing time after wire feeding is more than or equal to 10min, so that the Ca content in molten steel is ensured to be 0.001-0.0015%;
step 5: continuous casting: the continuous casting process adopts whole-course protection casting, electromagnetic stirring and light pressing are carried out, the superheat degree of a tundish is less than or equal to 25 ℃, and after continuous casting, the continuous casting blank is obtained after entering a slow cooling pit for treatment;
step 6: rolling and cooling control: heating the continuous casting billet, and performing controlled rolling and controlled cooling on the continuous casting billet;
step 7: offline tempering: and performing off-line tempering on the continuous casting billet subjected to controlled rolling and controlled cooling to obtain the polar region ship body structural steel.
Specifically, in the step 5, the thickness ratio of the continuous casting blank to the polar region ship body structural steel is controlled to be more than 8, and in the step 5, the heating temperature of the continuous casting blank is less than or equal to 1150 ℃, so that austenite grains are ensured not to grow.
Specifically, in step 6, the controlled rolling adopts a two-stage rolling method: the method is divided into a first stage rolling and a second stage rolling, and the refining effect of the controlled rolling and cooling technology on the grain size of the material is fully exerted. The first stage rolling is rough rolling, rapid deformation is carried out in an austenite recrystallization temperature range, the final rolling temperature is more than or equal to 950 ℃, the single-pass deformation is 10-15%, and the accumulated deformation of the first stage rolling is less than or equal to 50%. The second stage rolling is finish rolling, the initial rolling temperature is less than or equal to 850 ℃, the final rolling temperature is less than 800 ℃, the final rolling deformation is more than or equal to 15%, and the accumulated deformation of the second stage rolling is more than or equal to 60%. And then air-cooling to room temperature.
Specifically, in step 7, the offline tempering is a primary quenching and primary tempering process: the off-line quenching process of the polar region ship body structural steel is 840-880 ℃, and the heat preservation time is 1-2 h; tempering and heating treatment temperature is 600-650 ℃, heat preservation time is 1-2 h, and air cooling is carried out after heat preservation.
Carbon content is the most important element affecting the strength and low temperature performance of the material. accordingtotheinvention,thecarbonequivalent,thecoldcracksensitivityindexandtheM-Acontentaregreatlyreducedafterthecarboncontentisreducedtobelow0.06%,sothatthelow-temperatureperformanceofthesteelplateandaweldingheataffectedzoneisremarkablyimproved. However, after the carbon content is reduced, the strength of the steel plate cannot be ensured, and the strength loss of the material needs to be compensated by supplementing alloy elements and strengthening tissues, so that the strength is improved by adopting a NiCrMoCu component design and dispersing Cu particles separated out by aging of Cu elements in the tempering process in the aspect of component composition; the quenching and tempering process is adopted in the production process to obtain a fine lath martensite structure, and the strength of the tempered lath martensite is improved. The microstructure of the steel is lath martensite and a small amount of granular bainite, the content of the lath martensite is more than or equal to 80 percent, the effective grain size of the lath martensite is less than or equal to 2 mu m, and the lath martensite has excellent low-temperature toughness while ensuring the strength of the material after tempering.
The yield strength of the hull structural steel prepared by the method is more than or equal to 590Mpa (e.g. 621-633 Mpa), the tensile strength is more than or equal to 690Mpa (e.g. 690-710 Mpa), the elongation is more than or equal to 19.5% (e.g. 19.5-20.5%), the ductile-brittle transition temperature of the steel plate is not higher than-90 ℃ (e.g. -110-90 ℃), meanwhile, the weldability of the steel plate is good, the impact energy of a welding joint heat affected zone at-60 ℃ is more than or equal to 47J, the CTOD performance of the welding heat affected zone at-40 ℃ is more than or equal to 0.15mm (e.g. 0.17-0.22 mm), and the use conditions of the polar service environment are met.
The advantages of the invention in terms of precise control of the elemental chemistry, content and manufacturing process parameters will be demonstrated in the following specific examples and comparative examples.
Example 1
The present example discloses six (1 # -3# steels) 590MPa grade hull steels suitable for polar environments, and two (4 #, 5 #) steels were selected as comparative steels.
1# -3# all adopt the same process:
(1) And (3) molten iron pretreatment: the S of molten iron entering the furnace is less than or equal to 0.008 percent;
(2) Smelting in a converter: the thickness of the slag layer is less than or equal to 100mm;
(3) LF refining: the stand-by time of the bin is less than or equal to 24 hours, so that the slag is ensured to have good fluidity; the white slag is kept for more than or equal to 10min, and Ti and Fe are added after the deoxidation is complete.
(4) RH refining: and (3) carrying out calcium treatment before tapping, and carrying out static argon blowing for more than or equal to 10min after wire feeding, so as to ensure that the Ca content in the molten steel is 0.001-0.0015%.
(5) Continuous casting: the target superheat degree of the ladle molten steel is less than or equal to 25 ℃, and the ladle molten steel enters a slow cooling pit for treatment after continuous casting;
(6) Rolling and cooling control: the reheating temperature of the continuous casting blank is less than or equal to 1150 ℃; two-stage rolling, wherein the first stage (rough rolling) rolling is carried out rapid deformation in an austenite recrystallization temperature range, the single-pass deformation is 10-15%, the final rolling temperature is more than or equal to 950 ℃, and the accumulated deformation is less than or equal to 40%; the rolling start temperature of the second stage (finish rolling) is less than or equal to 850 ℃, the finishing temperature is less than 800 ℃, the finishing deformation is more than or equal to 15%, and the accumulated deformation is more than or equal to 60%;
(7) Offline tempering: the quenching process comprises the following steps: heating at 840-880 ℃ for 2h; tempering: heating at 600-650 deg.c for 2 hr; the thickness of the rolled plate is less than or equal to 35mm.
The mass percentages of the element components of the No. 1 steel to the No. 3 steel and the No. 5 steel meet the requirements of the invention, the mass percentage of the element component of the No. 4 steel does not meet the requirements of the invention, and the difference of the element compositions is shown in the table 1. The process parameters of the No. 5 steel do not meet the requirements of the invention, and the differences of the process parameters are shown in Table 2. The microstructure of steel # 1 is shown in FIG. 1.
Table 11 # -5# chemical composition (wt.%)
| Steel grade | C | Si | Mn | S | P | Nb | Ti | Ni | Cr | Mo | Cu |
| 1# | 0.05 | 0.15 | 0.9 | 0.0020 | 0.005 | 0.02 | 0.01 | 2.5 | 0.40 | 0.25 | 1.3 |
| 2# | 0.04 | 0.10 | 1.0 | 0.0035 | 0.004 | 0.03 | 0.015 | 3.0 | 0.50 | 0.30 | 1.5 |
| 3# | 0.06 | 0.20 | 1.5 | 0.0044 | 0.0035 | 0.025 | 0.010 | 4.0 | 0.55 | 0.35 | 1.4 |
| 4# | 0.05 | 0.15 | 1.0 | 0.0060 | 0.0050 | 0.030 | 0.020 | 1.0 | 0.30 | 0.30 | 1.0 |
| 5# | 0.05 | 0.14 | 1.0 | 0.0033 | 0.0045 | 0.025 | 0.01 | 3.3 | 0.45 | 0.25 | 1.4 |
Controlled rolling process for steel with the following table 21 # -5# -
The mechanical properties, martensite content and grain size of No. 1-3 meet the requirements of the invention, the results are shown in Table 3, the yield strength, martensite content and grain size of No. 4 steel do not meet the requirements of the invention, and the martensite content, grain size and yield strength of No. 5 steel do not meet the requirements of the invention, and the differences are shown in Table 3.
Table 3 shows the mechanical properties and grain size of 1# -5# steel
Table 4 shows that 1# -5# -560 MPa-level hull steel is subjected to weldability test under the line energy of 20kJ/cm, the groove is a K-type groove, and the welding preheating temperature and the welding joint performance are shown in Table 4. As can be seen from the table, the welding heat preheating temperature of the 1# -5# steel is not higher than-10 ℃, the welding fusion line of the 4# steel, the impact energy at the position of the fusion line plus 2mm and the CTOD performance of the heat affected zone at-40 ℃ do not meet the technical index requirements.
Table 4 1# -5# steel welded joint mechanical properties and grain size
As can be seen by comparison, the smelting method and the technological parameters of the No. 1-No. 5 steel are the same or similar, but the mass percentages of the element components of the No. 1-No. 3 steel and the No. 5 steel meet the requirements of the invention, the mass percentages of the element components of the No. 4 steel do not meet the requirements of the invention, the indexes such as impact energy at minus 60 ℃ and impact energy at minus 60 ℃ of the No. 4 steel are obviously reduced compared with the indexes such as the No. 1-No. 3 and the No. 5 steel, the yield strength, the martensite content and the grain size of the No. 4 steel do not meet the requirements of the invention, and the welding performance and the mechanical performance of the No. 4 steel are difficult to meet the polar ship body. The mass percentage of the element components of the No. 5 steel meets the requirements of the invention, but the technological parameters of the No. 5 steel do not meet the requirements of the invention, the yield strength, the martensite content and the grain size of the No. 5 steel do not meet the requirements of the invention, and the mechanical properties of the No. 5 steel are difficult to meet the requirements of the polar ship body.
According to comparison, the invention realizes excellent mechanical properties of the steel plate based on special steel element composition and rolling cooling process, the yield strength is more than or equal to 590MPa, the tensile strength is more than or equal to 690MPa, the elongation is more than or equal to 19.5%, the ductile-brittle transition temperature of the steel plate is not higher than-90 ℃, meanwhile, the weldability of the steel plate is good, the impact energy of a welded joint at-60 ℃ is more than or equal to 47J, and the CTOD of the welded joint at-40 ℃ is more than or equal to 0.15mm.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.
Claims (8)
1. The 590 MPa-level polar ship body structural steel with low-temperature toughness is characterized by comprising the following chemical components in percentage by mass: c:0.04 to 0.05 percent, si:0.10 to 0.15 percent, mn:0.9 to 1.0 percent, cu:1.3 to 1.5 percent of Ni:2.5 to 3.0 percent; cr:0.4 to 0.5 percent, ti:0.01 to 0.015 percent; mo:0.25 to 0.30 percent; nb:0.02 to 0.03 percent; als is more than or equal to 0.015%; n is less than or equal to 0.004%; p is less than or equal to 0.005%; s is less than or equal to 0.005 percent, and the balance is Fe and unavoidable impurity elements;
the microstructure of the steel comprises lath martensite and a small amount of granular bainite, the effective grain size of the lath martensite is less than or equal to 2 mu m, and the content of the lath martensite is more than or equal to 80%;
the 590 MPa-level polar region ship body structural steel is prepared through the process steps of molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling and cooling control and off-line tempering;
the impact energy of a welding joint heat affected zone of 590 MPa-level polar ship body structural steel at minus 60 ℃ is more than or equal to 47J, and the CTOD performance of the welding heat affected zone at minus 40 ℃ is more than or equal to 0.15mm.
2. The method for preparing 590 MPa-grade polar hull structural steel with low-temperature toughness is used for preparing 590 MPa-grade polar hull structural steel according to claim 1 and is characterized by comprising the steps of molten iron pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling control and cooling control and off-line tempering, wherein the molten iron pretreatment comprises KR desulfurization, S content is less than or equal to 0.007%, and slag thickness meets the slag skimming level 1.
3. The method for preparing 590 MPa-level polar region hull structural steel according to claim 2, wherein in the LF refining process, the added slag-forming material and deoxidizer must be dried, and the stand-by time in the bunker is less than or equal to 24 hours; the holding time of the white slag is more than or equal to 10min;
in the RH refining process, calcium treatment is carried out before tapping, and the static argon blowing time after wire feeding is more than or equal to 10min, so that the Ca content in molten steel is ensured to be 0.001-0.0015%.
4. The method for preparing 590 MPa-level polar ship-body structural steel according to claim 3, wherein the continuous casting process adopts full-process protection casting, the heating temperature of a continuous casting billet is less than or equal to 1150 ℃, the target superheat degree of ladle molten steel is less than or equal to 25 ℃, and the ladle molten steel enters a pit for treatment after continuous casting.
5. The method for preparing 590 MPa-grade polar region hull structural steel according to claim 4, wherein the rolling and cooling control is performed in two stages, the first stage rolling is rough rolling, the final rolling temperature is not less than 950 ℃, the single-pass deformation is 10-15%, and the accumulated deformation of the first stage rolling is not more than 50%.
6. The method for preparing 590 MPa-level polar region hull structural steel according to claim 5, wherein in the two-stage rolling, the second-stage rolling is finish rolling, the rolling temperature is equal to or less than 850 ℃, the final rolling temperature is equal to or less than 800 ℃, the final rolling deformation is equal to or more than 15%, and the accumulated deformation of the second-stage rolling is equal to or more than 60%.
7. The method for preparing 590 MPa-level polar region hull structural steel according to claim 6, wherein the off-line tempering is one-time quenching and one-time tempering, the one-time quenching is carried out at a heating temperature of 840-880 ℃, and the heat preservation time is 1-2 h.
8. The method for preparing 590 MPa-level polar region hull structural steel according to claim 7, wherein the primary tempering process is heating at 600-650 ℃, preserving heat for 1-2 h, and air cooling to room temperature after preserving heat.
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| CN113322420A (en) * | 2020-02-28 | 2021-08-31 | 宝山钢铁股份有限公司 | Yield ratio controlled steel with excellent low-temperature impact toughness and manufacturing method thereof |
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