CN114686765A - 420 MPa-grade high-toughness extra-thick plate and manufacturing method thereof - Google Patents
420 MPa-grade high-toughness extra-thick plate and manufacturing method thereof Download PDFInfo
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 16
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 134
- 239000010959 steel Substances 0.000 claims abstract description 134
- 238000001816 cooling Methods 0.000 claims abstract description 84
- 238000005096 rolling process Methods 0.000 claims abstract description 56
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 45
- 238000000034 method Methods 0.000 claims abstract description 33
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 18
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 18
- 238000010583 slow cooling Methods 0.000 claims abstract description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 10
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 8
- 239000000956 alloy Substances 0.000 claims abstract description 8
- 239000000126 substance Substances 0.000 claims abstract description 7
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 6
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 4
- 238000001953 recrystallisation Methods 0.000 claims description 19
- 238000010438 heat treatment Methods 0.000 claims description 12
- 238000004321 preservation Methods 0.000 claims description 8
- 238000002791 soaking Methods 0.000 claims description 6
- 229910001566 austenite Inorganic materials 0.000 abstract description 14
- 229910052799 carbon Inorganic materials 0.000 abstract description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 7
- 230000000694 effects Effects 0.000 abstract description 5
- 230000008569 process Effects 0.000 description 25
- 239000010955 niobium Substances 0.000 description 21
- 230000009466 transformation Effects 0.000 description 15
- 239000010936 titanium Substances 0.000 description 10
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 9
- 239000013078 crystal Substances 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 7
- 238000010791 quenching Methods 0.000 description 7
- 230000000171 quenching effect Effects 0.000 description 7
- 239000011572 manganese Substances 0.000 description 6
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 238000010899 nucleation Methods 0.000 description 5
- 230000006911 nucleation Effects 0.000 description 5
- 238000005728 strengthening Methods 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 4
- 229910001562 pearlite Inorganic materials 0.000 description 4
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000011056 performance test Methods 0.000 description 3
- 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 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- 229910000742 Microalloyed steel Inorganic materials 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000004512 die casting Methods 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 238000010606 normalization Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 238000009827 uniform distribution Methods 0.000 description 2
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000002068 genetic effect Effects 0.000 description 1
- 238000005087 graphitization Methods 0.000 description 1
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- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- 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
- C21D11/00—Process control or regulation for heat treatments
- C21D11/005—Process control or regulation for heat treatments for cooling
-
- 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
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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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
- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- 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
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
The invention relates to a 420MPa grade high-toughness extra-thick plate and a manufacturing method thereof, wherein the steel plate comprises the following chemical components: 0.03% -0.05%, Si: 0.25-0.45%, Mn: 1.40% -1.60%, Nb: 0.01 to 0.02 percent of Ti: 0.01 to 0.02 percent of the total weight of the alloy, less than 0.020 percent of P, less than 0.005 percent of S and the balance of Fe and inevitable impurities. According to the method, the carbon content is reduced, and technological means such as two-stage controlled rolling, stacking slow cooling, ultrafast cooling after rolling, off-line normalizing weak water cooling and the like are adopted, so that the finally obtained room temperature structure is a lath bainite and acicular ferrite complex phase structure, and the effect of segmenting the original austenite grain refined structure is achieved; the toughness is improved by introducing acicular ferrite; the finished steel plate has the characteristics of large thickness, high toughness, uniform structure and performance in the thickness direction, low alloy cost and the like.
Description
Technical Field
The invention relates to the technical field of steel plate production, in particular to a 420 MPa-grade high-toughness extra-thick plate and a manufacturing method thereof.
Background
The steel plate can obtain higher comprehensive mechanical property and better machining property after being normalized, and is an important heat treatment means for improving the uniformity and toughness of the steel plate structure. The normalizing steel plate is widely applied to the fields of pressure containers, high-rise buildings, bridges, engineering machinery and the like, particularly to wind power and container projects, and the normalizing steel plate is forcibly required to be used in the project design.
The conventional normalizing adopts an air cooling mode, the phase transition temperature is high due to the slow cooling speed, although a refined pearlite structure can be obtained, the impact energy and the elongation are improved, while the toughness is improved, ferrite grains can grow greatly, and the strength of a steel plate is reduced; after the niobium microalloyed steel is normalized, the precipitation strengthening effect is reduced due to the growth of niobium carbonitride, so that the strength of the steel plate is greatly reduced after the normalization, and particularly, a rolling-control and cooling-control steel plate can generate unqualified products due to excessive strength loss.
In order to prevent the strength of the steel plate from being greatly reduced after normalizing, Normalizing Controlled Cooling (NCC) is developed in each domestic steel mill in sequence: after the steel plate is normalized, a water cooling means is adopted, the phase transformation temperature of the steel plate is reduced by controlling the cooling speed and the final cooling temperature, the growth of microalloy carbonitride is inhibited, and meanwhile, the atom diffusion capacity is reduced by reducing the phase transformation temperature, so that a refined pearlite structure with small pearlite lamellar spacing is obtained, the stress and hardness of the steel plate are increased, the strength is improved, and the elongation and the impact toughness are greatly improved. Although the strength index is obviously improved compared with the normalized air cooling, the strength index has a larger gap compared with the strength index of the TMCP steel plate. Although the heat treatment link of the TMCP delivery steel plate is omitted, more alloy is added for ensuring the low-temperature toughness, the performance fluctuation is easily caused by the uneven structure, the production difficulty is higher, and the purposes of energy saving and cost reduction cannot be really achieved.
Chinese patent with publication number CN101343685B discloses a heat treatment method for a high-strength steel plate for buildings with yield strength of 420MPa, wherein a steel plate with thickness of 45mm is obtained after controlled rolling and cooling of a continuous casting billet, the steel plate is heated to the normalizing temperature of 890-950 ℃, the temperature is kept for 10-30 minutes, the temperature is reduced at the speed of 2-6 ℃/s after the temperature is kept, and the final cooling temperature is 600-750 ℃; straightening; air cooling in a cooling bed to obtain a high-performance steel plate for the building; but the corresponding mechanical property can be met only when the Nb content reaches more than 0.03 percent, and the aim is to enlarge the temperature of a non-recrystallization zone through high Nb and improve the finish rolling temperature. The method is beneficial to controlling the shape of the steel plate, but after the finish rolling temperature is increased, the ultra-fast cooling effect can be weakened, the core of the steel plate is not beneficial to rapidly passing through an austenite region to reach a phase transformation region, and therefore the precipitation of Nb in the core of the steel plate in the phase transformation process is not beneficial, and the strength of the core of the steel plate is lower.
Chinese patent with publication No. CN104962814B discloses a normalized high strength and toughness 150mm extra-thick plate and a production method thereof, which adopts a controlled cooling mode of stacking and slow cooling after rolling, because deformation energy is greatly released in the slow cooling process, the dislocation density is reduced, nucleation mass points of ferrite are reduced, and the temperature of a phase transformation point is higher due to lower cooling speed, ferrite crystal grains grow up, the strength allowance of a rolled steel plate is reduced, and the comprehensive mechanical property of the steel plate is not favorably improved.
Chinese patent with publication No. CN102115806B discloses a "heat treatment process for improving low-temperature toughness of extra-thick plates", which adopts sub-temperature normalizing, and adopts air cooling in a cooling mode, wherein the microstructure of the plate generally contains about 20% of undissolved ferrite, so that the microstructure after normalizing is uneven, stress concentration is caused, and the impact toughness is mainly fluctuated; meanwhile, for thick steel plates, the air cooling speed is slow, and the ferrite nucleation rate is low when austenite is converted into ferrite, so that part of ferrite grains are coarse, and the strength of the steel plate fluctuates.
Chinese patent No. CN102061373B discloses a "heat treatment process for improving mechanical properties of high-strength extra-thick plates", wherein a water cooling process is added in the normalizing process of extra-thick plates, and water cooling is used instead of air cooling for normalizing, but a quenching water tank is used for controlled cooling, so that it is difficult to accurately measure the target outlet water temperature of steel plates in water, the actual operation difficulty is high, and it is difficult to equip large quenching tanks for most medium-thick plate production lines due to the limitation of site space.
The Chinese patent application with the publication number of CN105154631A discloses a method for accelerating cooling of a quenching machine for improving the strength of a normalized steel plate with the thickness of more than or equal to 50mm, wherein the normalized steel plate enters the quenching machine along with a roller way of the quenching machine after being discharged from the quenching furnace to start water cooling, but the method mainly relates to equipment parameters of the quenching machine, including the opening degree of a low-pressure section, the proportion of the upper opening degree and the lower opening degree, the speed of the roller way, the water quantity control angle and the like, so as to ensure accurate hit of the temperature after the controlled cooling of the normalized steel plate, and the influence of the normalized temperature, the heat preservation time, the cooling speed and the like on the performance of the steel plate is not researched from the process angle.
Different from the technical scheme, the method greatly reduces the carbon content and controls the lower limit of the content of the microalloy elements on the basis of the Q420 steel in the GB/T1591-2018 standard, and simultaneously combines the processes of two-stage controlled rolling, ultra-fast cooling after rolling, stacking slow cooling and offline normalizing weak water cooling to realize the manufacturing of the 420MPa grade high-toughness extra-thick plate. Through two-stage controlled rolling and ultrafast cooling after rolling, a large amount of acicular ferrite tissues which are nucleated on original austenite grain boundaries or in-grain subgrain boundaries and are not precipitated are obtained, and when the tissues enter a stacking and slow cooling stage after the ultrafast cooling, the quantity of acicular ferrite is gradually increased, so that the uniform distribution of the acicular ferrite can be realized; through off-line sub-temperature normalizing, a steel plate is partially austenitized and rolled acicular ferrite is reserved, after the normalizing, the steel plate firstly enters a medium temperature transformation area at a low cooling speed, crystal boundary and crystal interior nucleation is further carried out, newly generated acicular ferrite is obtained, when the acicular ferrite reaches a certain quantity, the cooling speed is increased, lath bainite transformation occurs in the medium temperature transformation area, and finally a complex phase structure consisting of the acicular ferrite and the lath bainite is obtained. Through the measures, the problems of insufficient toughness and insufficient strength of the conventional normalizing process in the production of the Q420-grade low-alloy structural steel by the conventional TMCP process are effectively solved.
Disclosure of Invention
The invention provides a 420 MPa-grade high-toughness extra-thick plate and a manufacturing method thereof, on the premise of not increasing the content of alloy elements, the finally obtained room temperature tissue is a lath bainite and acicular ferrite complex phase tissue by reducing the carbon content and adopting the technological means of two-stage controlled rolling, stacking slow cooling, ultra-fast cooling after rolling, off-line normalizing weak water cooling and the like, thereby playing the role of dividing the original austenite grain refined tissue; the toughness is improved by introducing acicular ferrite; the finished steel plate has the characteristics of large thickness, high toughness, uniform structure and performance in the thickness direction, low alloy cost and the like.
In order to achieve the purpose, the invention adopts the following technical scheme:
a420 MPa grade high tenacity extra-thick plate, the steel plate chemical composition is according to the weight percent C: 0.03-0.05%, Si: 0.25-0.45%, Mn: 1.40% -1.60%, Nb: 0.01 to 0.02 percent of Ti: 0.01 to 0.02 percent of the total weight of the alloy, less than 0.020 percent of P, less than 0.005 percent of S and the balance of Fe and inevitable impurities; the steel plate has a room temperature structure which is a complex phase structure composed of acicular ferrite and lath bainite, wherein the volume ratio of the acicular ferrite is 30-50%, and the volume ratio of the lath bainite is 50-70%.
The mechanical properties of the finished steel plate are as follows:
yield strength: 450-480 MPa at the position of 1/2 mm, 460-490 MPa at the position of 1/4 mm and 510-540 MPa at the position close to the surface of the steel plate;
tensile strength: 580-610 MPa at the position of 1/2 mm steel plate thickness, 600-630 MPa at the position of 1/4 mm steel plate thickness, and 640-670 MPa at the position close to the surface of the steel plate;
-40 ℃ work of impact: 120-155J at the steel plate thickness 1/2, 190-210J at the steel plate thickness 1/4 and 204-260J at the near surface of the steel plate.
The thickness of the finished steel plate is not less than 65 mm and not more than 100 mm.
A manufacturing method of a 420MPa grade high-toughness extra-thick plate comprises the following steps:
1) heating a steel billet; soaking temperature is 1160-1200 ℃, and total in-furnace time is 4-6 hours;
2) two-stage controlled rolling is adopted; the initial rolling temperature of the recrystallization zone is 1100-1200 ℃, the initial rolling temperature of the non-recrystallization zone is 880-920 ℃, and the final rolling temperature is 780-820 ℃;
3) ultra-fast cooling after rolling; the cooling speed is 40-50 ℃/s, the final cooling temperature is 450-650 ℃, and stacking and slow cooling are carried out after ultra-fast cooling;
4) performing off-line normalizing and cold and heat control treatment on the hot rolled steel plate; normalizing at 825-845 ℃ and keeping the net heat preservation time for 10-20 min;
5) and immediately cooling by adopting a weak water cooling mode after heat preservation, wherein the final cooling temperature is 560-600 ℃, and the cooling speed is 8-12 ℃/s.
The steel billet is a continuous casting steel billet or a die casting cogging steel billet, and the thickness of the steel billet is divided by the thickness of a steel plate finish rolling thickness is more than or equal to 3.5.
After the recrystallization zone is rolled, the thickness of the intermediate blank is 2-2.5 times of that of the finished steel plate.
Compared with the prior art, the invention has the beneficial effects that:
1) the niobium microalloyed steel can cause the precipitation strengthening effect to be reduced because the niobium carbonitride grows up in the air cooling process after rolling and normalizing, and compared with the traditional normalizing process, the process route of controlled rolling, ultrafast cooling, stacking slow cooling, normalizing and weak water cooling is adopted, so that the strength of the steel plate can be effectively improved, and the low-temperature toughness of the steel plate is improved;
2) by adding 2 processes of ultra-fast cooling after rolling and weak water cooling after normalizing, the abnormal segregation zone of granular bainite can be completely eliminated, the starting temperature of gamma → alpha phase transition can be reduced, the growth of austenite grains before transformation is greatly inhibited, and the ferrite grains at the core of the steel plate are refined; after rolling, a large amount of acicular ferrite tissues which are nucleated on original austenite grain boundaries or intra-grain subgrain boundaries and are not precipitated are obtained in an ultra-fast cooling stage; after ultra-fast cooling, entering a stacking slow cooling stage, gradually increasing the quantity of acicular ferrite, and uniformly distributing the acicular ferrite in the slow cooling process; in the off-line sub-temperature normalizing stage, the steel plate is partially austenitized and rolling acicular ferrite is reserved; after normalizing, newly generated acicular ferrite is obtained at a low cooling speed, when the acicular ferrite reaches a certain quantity, the cooling speed is increased, lath bainite transformation occurs in a medium-temperature transformation region, and finally the room-temperature structure of the steel plate is a complex-phase structure consisting of the acicular ferrite and the lath bainite;
3) the mechanical properties of the final steel plate are yield strength: 450-480 MPa at the position of 1/2 mm, 460-490 MPa at the position of 1/4 mm and 510-540 MPa at the position close to the surface of the steel plate; tensile strength: 580-610 MPa at the position of 1/2 mm steel plate thickness, 600-630 MPa at the position of 1/4 mm steel plate thickness, and 640-670 MPa at the position close to the surface of the steel plate; -40 ℃ work of impact: 120-155J at the position of the steel plate with the thickness 1/2, 190-210J at the position of the steel plate with the thickness 1/4 and 220-260J at the position close to the surface of the steel plate.
Drawings
FIG. 1 is a metallographic structure photograph of a normalized extra-thick plate in example 1 of the present invention.
Detailed Description
The invention relates to a 420MPa grade high-toughness extra-thick plate, which comprises the following chemical components in percentage by weight: 0.03% -0.05%, Si: 0.25-0.45%, Mn: 1.40% -1.60%, Nb: 0.01 to 0.02 percent of Ti: 0.01 to 0.02 percent of Fe, less than 0.020 percent of P, less than 0.005 percent of S and the balance of Fe and inevitable impurities; the steel plate has a room temperature structure which is a complex phase structure composed of acicular ferrite and lath bainite, wherein the volume ratio of the acicular ferrite is 30-50%, and the volume ratio of the lath bainite is 50-70%.
The mechanical properties of the finished steel plate are as follows:
yield strength: 450-480 MPa at the position of 1/2 mm, 460-490 MPa at the position of 1/4 mm and 510-540 MPa at the position close to the surface of the steel plate;
tensile strength: 580-610 MPa at the position of 1/2 mm steel plate thickness, 600-630 MPa at the position of 1/4 mm steel plate thickness, and 640-670 MPa at the position close to the surface of the steel plate;
-40 ℃ work of impact: 120-155J at the steel plate thickness 1/2, 190-210J at the steel plate thickness 1/4 and 204-260J at the near surface of the steel plate.
The thickness of the finished steel plate is not less than 65 mm and not more than 100 mm.
A manufacturing method of a 420MPa grade high-toughness extra-thick plate comprises the following steps:
1) heating a steel billet; soaking temperature is 1160-1200 ℃, and total in-furnace time is 4-6 hours;
2) two-stage controlled rolling is adopted; the initial rolling temperature of the recrystallization zone is 1100-1200 ℃, the initial rolling temperature of the non-recrystallization zone is 880-920 ℃, and the final rolling temperature is 780-820 ℃;
3) ultra-fast cooling after rolling; the cooling speed is 40-50 ℃/s, the final cooling temperature is 450-650 ℃, and stacking and slow cooling are carried out after ultra-fast cooling;
4) performing off-line normalizing and cold and heat control treatment on the hot rolled steel plate; normalizing at 825-845 ℃ and keeping the net heat preservation time for 10-20 min;
5) and immediately cooling by adopting a weak water cooling mode after heat preservation, wherein the final cooling temperature is 560-600 ℃, and the cooling speed is 8-12 ℃/s.
The steel billet is a continuous casting steel billet or a die casting cogging steel billet, and the thickness of the steel billet is divided by the thickness of a steel plate finish rolling thickness is more than or equal to 3.5.
After the recrystallization zone is rolled, the thickness of the intermediate blank is 2-2.5 times of that of the finished steel plate.
The design principle of the chemical components of the 420 MPa-grade high-toughness extra-thick plate is as follows:
1. the carbon mainly plays a role in forming a large amount of (Nb, Ti) (C, N) in the controlled cooling process after normalizing to play a role in precipitation strengthening; the other part of carbon is used for solid solution strengthening, so that the loss of strength performance is effectively reduced; the invention aims to control the content of C to be 0.03-0.05% so as to ensure that excessive martensite is not formed due to incomplete bainite transformation, and the content of C is enough to react with Nb to generate (Nb, Ti) (C, N); due to the lower control of the carbon content, the volume fraction of martensite is reduced, and the toughness of the steel can be improved without causing strength loss.
2. The silicon has the function of reducing the graphitization tendency of carbon, plays a certain role of improving the strength through solid solution strengthening, but the content of the silicon is not suitable to be too high, otherwise, the segregation of impurity elements in crystal boundaries is aggravated, and the toughness after normalizing is reduced. Therefore, the content of Si is controlled to be 0.25-0.45 percent in the invention.
3. Manganese can improve the pearlite strength of the normalized steel and the solubility of niobium in steel, but the high manganese content can promote the growth of crystal grains, so the Mn content is controlled to be 1.40-1.60. Is based on
4. Niobium mainly has the functions of precipitation and precipitation in the ferrite phase change process and improving the strength through grain refinement; however, the higher niobium content affects the recrystallization temperature, inhibits austenite recrystallization, enables the non-recrystallization finishing rolling temperature to be higher, and easily causes phase transformation precipitation to form polygonal ferrite during controlled cooling, so the niobium content is limited to 0.01-0.02 percent in the invention.
5. Titanium mainly cooperates with niobium to form (Nb, Ti) (C, N), dislocation movement is hindered at the normalizing temperature, but excessive titanium can cause (Nb, Ti) (C, N) polymerization coarsening, and the effect of inhibiting austenite grain growth is not achieved at the normalizing temperature, so that the Ti content is controlled to be 0.01-0.02%.
The manufacturing process design principle of the 420MPa grade high-toughness extra-thick plate is as follows:
1. the thickness of a steel billet; when the total compression ratio is less than 3.5, the low-temperature toughness of the steel plate is difficult to improve by simply increasing the total compression ratio and the single-pass reduction in the rough rolling or finish rolling stage; and when the total compression ratio is more than 3.5, the low-temperature toughness can be greatly improved by distributing the deformation to the rough rolling stage or the finish rolling stage. Therefore, the invention limits the thickness of the steel billet to the thickness of the steel plate finish rolling to be more than or equal to 3.5.
2. The soaking temperature of the steel billet; when the soaking temperature of the billet exceeds 1200 ℃, Nb (C, N) particles can quickly dissolve back, and the crystal grains in a coarse crystal area grow up quickly; in order to ensure that the rolled structure steel plate has higher strength margin and the original crystal grains are refined, the invention adopts lower casting blank heating temperature, controls the soaking temperature of the steel blank to be 1160-1200 ℃ and heats for 4-6 h.
3. Controlling rolling in two stages; the traditional process adopts austenite recrystallization zone controlled rolling, because the finishing rolling temperature is higher, austenite grains are coarse, and because of the genetic effect, ferrite grains are also coarse; the invention adopts a two-stage controlled rolling process, austenite tissues deform and recrystallize in a recrystallization zone to refine grains, and austenite is flattened and elongated along the rolling direction when a non-recrystallization zone deforms, so that a deformation zone is generated in the grains, the nucleation point position of ferrite is increased, and the refinement of ferrite grains is promoted;
and controlling the thickness of the recrystallization zone after rolling to reduce the deformation in the finish rolling stage so as to reduce the influence of low-temperature deformation on the uneven structure in the thickness direction.
Considering that the yield strength is increased along with the increase of the initial rolling temperature, the decrease of the final cooling temperature and the increase of the cooling speed, the elongation is increased along with the decrease of the initial rolling temperature, the decrease of the final cooling temperature and the increase of the cooling speed, the granular bainite and the acicular ferrite are obviously increased along with the decrease of the final cooling temperature, and the M/A islands are more dispersed; finally, the initial rolling temperature of a recrystallization zone is 1100-1200 ℃, the initial rolling temperature of a non-recrystallization zone is 880-920 ℃, and the final rolling temperature is 780-820 ℃; .
4. After rolling, adopting an ultrafast cooling and stacking slow cooling process; the ultra-fast cooling speed is 40-50 ℃/s, and the final cooling temperature is 450-650 ℃. The ultra-fast cooling obtains a large amount of acicular ferrite tissues which are nucleated on original austenite grain boundaries or in-grain subgrain boundaries and are not precipitated, and when the ultra-fast cooling enters a stacking slow cooling stage, the amount of acicular ferrite is gradually increased, so that the uniform distribution of the acicular ferrite can be realized in the slow cooling process;
5. offline sub-temperature normalizing at 825-845 ℃, and keeping the net heat preservation time for 10-20 min; during the period, the steel plate is partially austenitized and rolled acicular ferrite is reserved, nucleation is carried out on the grain boundary and the grain interior at a low cooling speed of 8-12 ℃/s after normalization, newly generated acicular ferrite is obtained, when the cooling speed is increased after the acicular ferrite reaches a certain quantity, lath bainite transformation is carried out in a medium temperature transformation region, and finally a complex phase structure consisting of the acicular ferrite and the lath bainite is obtained.
The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation processes are given, but the scope of the invention is not limited to the following examples.
[ examples ] A
The chemical composition of the steel blanks of the examples is shown in table 1. The process parameters for heating the steel slabs of the examples in the heating furnace are shown in Table 2. The controlled rolling and cooling process parameters of the billets of the examples are shown in Table 3. The steel plate normalizing and cooling control process parameters of each example are shown in a table 4. The results of the performance test (steel thickness 1/4) of the finished steel sheets of each example are shown in Table 5. The results of the performance tests (steel thickness 1/2) of the finished steel sheets of each example are shown in Table 6; the results of the performance test (near surface of steel sheet) of the finished steel sheets of each example are shown in Table 7.
The metallographic structure of the normalized extra-thick plate with the thickness of 420MPa and the thickness of 100mm produced in example 1 is shown in FIG. 1 and is complete acicular ferrite and lath bainite.
TABLE 1 chemical composition (wt%) of steel billet in each example
| Examples | C | Si | Mn | P | S | Nb | Ti |
| 1 | 0.04 | 0.36 | 1.59 | 0.016 | 0.002 | 0.017 | 0.016 |
| 2 | 0.05 | 0.33 | 1.52 | 0.015 | 0.003 | 0.014 | 0.014 |
| 3 | 0.04 | 0.29 | 1.48 | 0.016 | 0.003 | 0.012 | 0.011 |
| 4 | 0.03 | 0.35 | 1.44 | 0.015 | 0.002 | 0.010 | 0.009 |
| 5 | 0.04 | 0.34 | 1.49 | 0.016 | 0.003 | 0.015 | 0.013 |
| 6 | 0.04 | 0.032 | 1.50 | 0.016 | 0.002 | 0.016 | 0.011 |
TABLE 2 Steel billet heating Process parameters of the examples
TABLE 3 controlled rolling and cooling process parameters of steel billet in each example
TABLE 4 normalizing and cooling-controlling technological parameters of steel plates of various examples
TABLE 5 test results of the properties of the finished steel plates (thickness of steel plate 1/4)
TABLE 6 test results of the properties of the finished steel plates (thickness 1/2 of steel plate)
TABLE 7 test results of the properties of the finished steel plates (near surface of steel plate) of the examples
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (6)
1. A420 MPa grade high tenacity extra-thick plate is characterized in that the steel plate comprises the following chemical components in percentage by weight: 0.03% -0.05%, Si: 0.25-0.45%, Mn: 1.40% -1.60%, Nb: 0.01 to 0.02 percent of Ti: 0.01 to 0.02 percent of the total weight of the alloy, less than 0.020 percent of P, less than 0.005 percent of S and the balance of Fe and inevitable impurities; the steel plate has a room temperature structure which is a complex phase structure composed of acicular ferrite and lath bainite, wherein the volume ratio of the acicular ferrite is 30-50%, and the volume ratio of the lath bainite is 50-70%.
2. The 420MPa grade high-toughness extra-thick steel plate according to claim 1, wherein mechanical properties of a finished steel plate are as follows:
yield strength: 450-480 MPa at the position of 1/2 mm, 460-490 MPa at the position of 1/4 mm and 510-540 MPa at the position close to the surface of the steel plate;
tensile strength: 580-610 MPa at the position of 1/2 mm steel plate thickness, 600-630 MPa at the position of 1/4 mm steel plate thickness, and 640-670 MPa at the position close to the surface of the steel plate;
-40 ℃ work of impact: 120-155J at the steel plate thickness 1/2, 190-210J at the steel plate thickness 1/4 and 204-260J at the near surface of the steel plate.
3. The 420MPa grade high toughness extra-thick plate according to claim 1, characterized in that the thickness of the finished steel plate is 65 mm or more and 100mm or less.
4. The manufacturing method of the 420MPa grade high toughness extra-thick plate according to claim 1, characterized by comprising the following steps:
1) heating a steel billet; soaking temperature is 1160-1200 ℃, and total in-furnace time is 4-6 hours;
2) two-stage controlled rolling is adopted; the initial rolling temperature of the recrystallization zone is 1100-1200 ℃, the initial rolling temperature of the non-recrystallization zone is 880-920 ℃, and the final rolling temperature is 780-820 ℃;
3) ultra-fast cooling after rolling; the cooling speed is 40-50 ℃/s, the final cooling temperature is 450-650 ℃, and stacking and slow cooling are carried out after ultra-fast cooling;
4) performing off-line normalizing and cold and heat control treatment on the hot rolled steel plate; normalizing at 825-845 ℃ and keeping the net heat preservation time for 10-20 min;
5) and immediately cooling by adopting a weak water cooling mode after heat preservation, wherein the final cooling temperature is 560-600 ℃, and the cooling speed is 8-12 ℃/s.
5. The method as claimed in claim 4, wherein the thickness of the billet is not less than 3.5/the final thickness of the steel plate.
6. The method for manufacturing the 420MPa grade high toughness extra-thick plate according to claim 4, wherein after the recrystallization zone rolling, the thickness of the intermediate blank to be heated is 2-2.5 times of the thickness of the finished steel plate.
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