CN113814269A - Rolling process for refining M-A component in low-carbon bainite steel - Google Patents
Rolling process for refining M-A component in low-carbon bainite steel Download PDFInfo
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- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
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- 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
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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
- C21D11/00—Process control or regulation for heat treatments
- C21D11/005—Process control or regulation for heat treatments for cooling
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- 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
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- 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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- 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
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
- B21B2001/386—Plates
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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
- C21D2211/002—Bainite
Abstract
The invention discloses a rolling process for refining an M-A component in low-carbon bainite steel, which belongs to the technical field of steel manufacturing and comprises three steps of heating, rolling and cooling. The beneficial technical effects of the invention are as follows: (1) the average size of the M-A component in the low-carbon bainite steel is not more than 1.5 mu M; (2) the thickness of the steel plate with the thickness of more than 50mm of low-carbon bainite steel is-40 ℃ at typical positions (1/4 and 1/2)KV 2The average value of the impact work is not lower than 200J, and the difference value between single values is not more than 20J; (3) the yield strength of a thick steel plate with the thickness of more than 50mm of the low-carbon bainite steel at typical positions (1/4 and 1/2) is 521-595 MPa, the tensile strength is 652-710 MPa, the yield ratio is 0.79-0.85, and the elongation is 19-23%; (4) the preparation scheme of the low-carbon bainite steel is easy to implement, the production process is easy to control, low-cost stable batch industrial production can be realized, and the construction requirements of main bearing structures such as bridges, buildings, marine engineering, pipelines, wind power towers and the like on high-strength steel with thick specifications can be met.
Description
Technical Field
The invention belongs to the technical field of steel manufacturing, and particularly relates to a rolling process for refining an M-A component in low-carbon bainite steel.
Background
In recent years, low-carbon bainite steel is widely applied to the fields of bridges, buildings, marine engineering, pipelines, wind power towers and the like due to excellent toughness and weldability. In the actual production process, the low-carbon bainite steel is subjected to phase change in the continuous cooling process to form a granular bainite room-temperature structure with all or a certain content. When the rolling or cooling penetration force is insufficient, particularly for a steel sheet with a thickness of 50mm or more, the martensite-austenite constituent (M-A constituent) in the near-core granular bainite structure is coarse in size and is distributed in the form of blocks or chains at the prior austenite grain boundary. When the steel plate bears impact load, the local stress concentration degree around the thick M-A component is large, crack nucleation tends to be initiated at the interface of the M-A component and the base body, straight-through crystal propagation is generated, the impact toughness is seriously deteriorated, and further the problems of low impact energy or fluctuation and the like of the steel plate are caused. However, the M-A component is rich in carbon elements and has an internal high-density dislocation substructure, and the M-A component exists in steel as a hard phase, so that the strength and the strain hardening capacity of the material can be remarkably improved.
Therefore, how to regulate and control to obtain the M-A component with proper refinement further improves the low-temperature toughness and the performance stability of the thick-specification steel plate, realizes good matching of the toughness and the toughness, and becomes a key technical problem in the field of low-carbon bainite steel manufacturing.
In order to solve the above problems, numerous scholars have conducted the following beneficial investigations in the regulation of the M-A component of such steels.
The invention patent with the granted publication number of CN109837367B discloses a heat treatment process for refining an M-A component in a granular bainite structure of low-carbon low-alloy steel, wherein a tempering treatment is added before austenitizing heat treatment in a two-phase region to control and obtain Mn-rich or Cr-rich carbide which is uniformly and dispersedly distributed, so that more nucleation sites are provided for film-shaped or acicular ferrite, and the purposes of refining the M-A component and improving the core impact toughness of a thick-specification steel plate are further achieved. However, this method requires a steel having a high Mn content of 2.5% or more or Cr content of 3% or less to form sufficient carbides, but the high Mn and Cr elements increase the M-A stability and are not easily decomposed during tempering, so that the M-A content can be reduced only to some extent and the size can be reduced, and therefore the impact toughness-improving effect is not significant, and the fluctuation between the impact strength values is large as in example 3 (86/124/145J). In addition, a plurality of heat treatment processes are added, so that the production efficiency is reduced, the energy consumption is improved, and the cost is increased.
The invention patent with the publication number of CN108998726A discloses a thick 420 MPa-grade low-yield-ratio low-temperature bridge steel plate, which is rolled by a conventional TMCP process and then is tempered, so that the impact energy of a 100mm thick Q420qE steel plate at the position of 1/4 ℃ below zero to 40 ℃ reaches more than 250J, the yield ratio is less than or equal to 0.84, and the obdurability is well matched. However, the production process has higher finish rolling temperature and larger size of the M-A component, and the M-A component is decomposed by adding one tempering process, so that the low-temperature toughness is improved. However, the size of the M-A component in the core of the steel plate and the low-temperature toughness are not reported. Although the coarse M-A components can be decomposed by tempering heat treatment to achieve the aim of improving the low-temperature toughness of the sheet thickness 1/4, the problem of the uniformity of the thick sheet thickness property cannot be thoroughly solved because the low-temperature toughness of the core is difficult to improve due to insufficient core rolling and cooling permeability.
The invention patents with the grant publication numbers of CN1323187C, CN103451537B and CN103451561B control the addition amount of lower elements such as C, Si, Mn or Cr by regulating and controlling alloy components to reduce the brittle phase of the M-A component, which is beneficial to improving the impact toughness of the parent metal, but often leads the tensile strength to be insufficient, the yield ratio to be higher and the strength not to meet the service requirement.
Therefore, in the existing research, most of the M-A components are regulated and controlled by adopting alloy components or a heat treatment process, and the regulation and control research on the M-A components through a rolling process is not deep enough, so that a thick steel plate still has a plurality of defects in the aspects of regulating and controlling the toughness, the performance stability and the thickness uniformity, and the development of related preparation process technology is urgently needed.
Disclosure of Invention
The invention aims to provide a rolling process for refining an M-A component in low-carbon bainite steel, so that obdurability matching of thick (more than 50 mm) steel plates is realized, and impact property stability and thickness property uniformity are improved.
In order to solve the technical problems, the invention adopts the technical scheme that: a rolling process for refining M-A components in low-carbon bainite steel comprises the following steps:
(1) a heating stage: casting low-carbon bainite steel blank at T1Heating to 1100-1200 ℃ within minutes and then keeping the temperature T2 Min 280. ltoreq. T.ltoreq.352, where T = T1+T2，T1=（0.80~1.10）H，T2H, H is the thickness of a casting blank, and the unit is mm;
(2) and (3) rolling stage: comprises a rough rolling stage and a finish rolling stage,
the initial rolling temperature of the rough rolling stage is 1020-1080 ℃, the final rolling temperature is 980-1060 ℃, the intermediate blank is formed in 3-5 rolling passes, and the total rolling reduction rate is not lower than 55%;
the initial rolling temperature in the finish rolling stage is 730-840 ℃, the final rolling temperature is 710-780 ℃, low-carbon bainite steel plates are formed in 4-6 rolling passes, the single-pass reduction rate is more than or equal to 8%, and the final three-pass reduction rate is more than or equal to 40%;
(3) and (3) a cooling stage: and (3) cooling the low-carbon bainite steel plate by laminar flow water after rolling, wherein the start cooling temperature is 710-750 ℃, the re-reddening temperature is 350-450 ℃, and the cooling speed is 15-25 ℃/s.
The technical scheme of the invention achieves the aim by the following principle and mode.
The rolling process comprises three stages of billet heating, rolling and cooling.
The technical scheme of low-temperature heating, heating time prolonging and heat preservation time shortening is adopted in the heating stage, the heating temperature of the blank is controlled to be 1100-1200 ℃, and the heating time is controlled to be T according to different thicknesses of the blank1H (0.80-1.10) and keeping the temperature for T2= 0.14-0.22H, where T = T1+T2And need to ensureT is more than or equal to 280 and less than or equal to 352, so that sufficient austenitizing can be ensured, and the phenomenon that austenite grains grow to be large and coarsened due to overhigh heating temperature or overlong heat preservation time can be avoided, and if the T value is smaller, the austenitizing degree is lower, grains are easy to mix, and the performance is seriously deteriorated; if the T value is larger, austenite grains are easy to grow and coarsen, and further the final room-temperature tissue M-A component is coarsened.
The rolling process with low temperature and high pressure is adopted in the rolling stage, the initial rolling temperature in the rough rolling stage is 1020-1080 ℃, the final rolling temperature is 980-1060 ℃, the rolling pass is 3-5 passes, the single pass reduction rate is more than or equal to 12%, the total reduction rate is not less than 55%, the lower rolling temperature interval is matched with the larger pass reduction amount, the austenite is ensured to be fully recrystallized, and the growth of crystal grains caused by the higher temperature in the rolling process of the austenite can be avoided. The thickness h of the intermediate blank is controlled to be (1.8-2.2) t, and t is the final target thickness of the steel plate. And in the intermediate billet temperature waiting stage (the temperature waiting stage between the rough rolling and the finish rolling) the water spraying device erected at the stand beside the rolling mill sprays water to accelerate the cooling of the intermediate billet, so that the temperature is reduced and the retention time in the stage is shortened. The water spraying quantity L of the water spraying device is controlled to be more than or equal to 1100 and less than or equal to 1400m3And L = (8-12) h, wherein the larger the final rolling target plate thickness t is, the larger the intermediate billet thickness h is, and the larger the water spraying amount is needed, so that the intermediate billet can be cooled quickly at a sufficient cooling speed. The intermediate billet is cooled by passing water at the side of the intermediate billet when the intermediate billet is at the temperature, and the water quantity is controlled to be 1100-1400 m3The cooling speed of the intermediate blank can be greatly improved, the high-temperature retention time is reduced, the large driving force of austenite grain growth is reduced, the austenite grains are refined, and further the M-A component is refined. The starting temperature of finish rolling is controlled to be 730-840 ℃, the finishing temperature is controlled to be 710-780 ℃, the rolling passes are controlled to be 4-6 times, the single pass reduction rate is larger than or equal to 8%, the last three pass reduction rate is larger than or equal to 40%, the original austenite is fully deformed by controlling the lower rolling temperature and the smaller reduction rate in the finish rolling stage, sufficient substructures and dislocations are generated in the austenite, more nucleation sites are provided for the ferrite phase transformation in the next step while micro-alloy elements are induced to be separated out, austenite grains are refined, and therefore M-A components are refined, and meanwhile, the lower finish rolling temperature is also beneficial to the penetration of rolling force to the thick plate core and the thinning of the M-A components in the core.
In the cooling stage, the technical scheme of low-temperature start cooling, high cooling speed and low-temperature red return is adopted, so that the cooling permeability can be improved, the core of the thick plate is fully cooled, the grain size of the core is refined, and the M-A component is further refined; the temperature drop of the upper surface of a common thick plate is faster than that of the surface, and in order to improve the uniformity of the thick-direction performance of the thick plate, the ratio of the water amount of the lower surface to the water amount of the upper surface is controlled to be 1.2-1.5, so that the uniformity of the thick-direction performance can be greatly improved. Besides, lambda is controlled to be more than or equal to 0.125 and less than or equal to 0.8, the difference between the finish rolling temperature and the start cooling temperature is properly controlled according to the difference of the plate thickness, so that sufficient relaxation time is provided before cooling is started, a proper amount of massive ferrite soft phase structures are separated out, the soft phase ratio in the structures is improved, the strain hardening amount is further improved, the yield ratio is reduced, and the problems that the yield ratio is high due to high grain refinement degree, the lambda is too small, the relaxation time is short, a sufficient amount of massive ferrite structures cannot be separated out, the lambda is too large, the relaxation time is too long, the grains grow up, and the structures are coarsened can be avoided. And finally, naturally cooling the steel plate after cooling to obtain a finished steel plate.
In addition, the addition amount of key alloy components C, Mn, Si, Ni, Cr, Mo, Cu and N of the low-carbon bainite steel blank is controlled to meet the requirement that gamma is not less than 3.89 and not more than 6.86, wherein gamma = C + Mn/6+ Si/5+ Ni/15+ Cr/2+ Mo/4+ Cu/13+ N/0.001. C. Mn, Ni, Cu and N elements have the function of stabilizing austenite in steel, can obviously improve the stability of retained austenite, and further increase the size and the content of the M-A component. Cr and Mo are medium-strength carbide forming elements, which can inhibit the diffusion of carbon elements in austenite, remarkably improve the stability of retained austenite, convert more undercooled austenite into M-A components and further increase the size and content of the M-A components. Although Si is a non-carbide forming element, in the medium-temperature and low-temperature phase transition region, the Si element can enhance the binding force of iron atoms, improve the diffusion activation energy of carbon atoms, reduce the corresponding diffusion coefficient of carbon in austenite, effectively improve the content of residual austenite and the mechanical stability and the thermal stability of the residual austenite in steel, convert more undercooled austenite into M-A components, and further increase the size and the content of M-A. The elements are added into the steel by regulating and controlling the scientific and reasonable proportion of the elements, so that gamma is more than or equal to 3.89 and less than or equal to 6.86, and if the gamma value is too large, the size of an M-A component in the steel is increased, and the content is increased; if the gamma value is too small, a higher heating temperature is needed to make the steel completely austenitized, austenite grains are easy to grow and coarsen, and further the size of the M-A component in the steel grows and coarsens.
The beneficial technical effects of the invention are as follows: (1) the average size of the M-A component in the low-carbon bainite steel is not more than 1.5 mu M; (2) the thickness of the steel plate with the thickness of more than 50mm of low-carbon bainite steel is-40 ℃ at typical positions (1/4 and 1/2)KV 2The average value of the impact work is not lower than 200J, and the difference value between single values is not more than 20J; (3) the yield strength of a thick steel plate with the thickness of more than 50mm of the low-carbon bainite steel at typical positions (1/4 and 1/2) is 521-595 MPa, the tensile strength is 652-710 MPa, the yield ratio is 0.79-0.85, and the elongation is 19-23%; (4) the preparation scheme of the low-carbon bainite steel is easy to implement, the production process is easy to control, low-cost stable batch industrial production can be realized, and the construction requirements of main bearing structures such as bridges, buildings, marine engineering, pipelines, wind power towers and the like on high-strength steel with thick specifications can be met.
The present invention will be described in detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a view of an M-A component at a typical position in the thickness direction in example 2 of the present invention;
FIG. 2 is an observation of the M-A component at a typical position in the thickness direction of comparative example 2.
Detailed Description
The invention provides a rolling process for refining an M-A component in a low-carbon bainite steel structure, which comprises the following steps.
(1) A heating stage: casting blank is arranged at T1Heating to 1100-1200 ℃ within minutes, and keeping the temperature T2 Min, and 280 ≤ T ≤ 352, wherein T = T1+T2，T1=（0.80~1.10）H，T2H, where H is the thickness of a casting blank (mm).
(2) And the rolling stage comprises a rough rolling stage and a finish rolling stage.
The initial rolling temperature of the rough rolling stage is 1020-1080 ℃, the final rolling temperature is 980-1060 ℃, the intermediate blank is formed in 3-5 rolling passes, the single-pass reduction rate is more than or equal to 12%, and the total reduction rate is not less than 55%.
And h = (1.8-2.2) t of the intermediate blank, wherein t is the final target thickness (mm) of the steel plate. Spraying water by a water spraying device beside the intermediate billet time when the intermediate billet is heated, so as to accelerate the cooling of the intermediate billet, wherein the water spraying amount L is not less than (8-12) h, and the L is not less than 1100 and not more than 1400m3/h。
The initial rolling temperature of the finish rolling stage is 730-840 ℃, the final rolling temperature is 710-780 ℃, the low-carbon bainite steel plate is formed in 4-6 rolling passes, the single-pass reduction rate is more than or equal to 8%, and the final three-pass reduction rate is more than or equal to 40%.
(3) And (3) a cooling stage: after finish rolling, the low-carbon bainite steel plate is cooled by laminar flow water, the start cooling temperature is 710-750 ℃, the re-reddening temperature is 350-450 ℃, the cooling speed is 15-25 ℃/s, the water quantity ratio of the lower surface to the upper surface is 1.2-1.5, and lambda is more than or equal to 0.125 and less than or equal to 0.8, wherein lambda is = (T = (T) (/))Jing Fin (seminal emission)-TOpen cold）/ t。TJing Fin (seminal emission)Is the finish rolling temperature of the finish rolling stage, TOpen coldT is the final target thickness of the steel sheet in mm, which is the start-cooling temperature in the cooling stage.
The low-carbon bainite steel blank comprises the following chemical components in percentage by weight: 0.04-0.09% of C, less than or equal to 0.55% of Si, 0.90-1.70% of Mn, 0.20-0.70% of Cr, 0.25-0.65% of Ni, 0.25-0.55% of Cu, less than or equal to 0.30% of Mo, 0.010-0.050% of Nb, 0.015-0.035% of V, 0.010-0.030% of Ti, 0.0035-0.0070% of N, less than or equal to 0.020% of P, less than or equal to 0.005% of S, and the balance of Fe and inevitable impurities, wherein gamma is more than or equal to 3.89 and less than or equal to 6.86, and gamma = C + Mn/6+ Si/5+ Ni/15+ Cr/2+ Mo/4+ Cu/13+ N/0.001.
The present invention will be further described with reference to examples and comparative examples.
The invention provides a rolling process for refining an M-A island in thick low-carbon bainite steel, which mainly comprises unavoidable impurities of Fe, C, Si, Mn, Cr, Ni, Cu, Nb, V, Ti and N, wherein the mass percentage of the elements meets the requirement that gamma is more than or equal to 3.89 and less than or equal to 6.86, wherein gamma = C + Mn/6+ Si/5+ Ni/15+ Cr/2+ Mo/4+ Cu/13+ N/0.001. The chemical compositions of the steel of the examples and the comparative examples are shown in Table 1, and the rolling process is shown in Table 2.
TABLE 1
TABLE 2
Note: (1) 280 ≦ T ≦ 352, where T = T1+T2，T1=（0.80~1.10）H，T2H, H is the thickness (mm) of a casting blank; (2) 1100 is less than or equal to 1400, wherein L = (8-12) h, h = (1.8-2.2) t, and t is the final target thickness (mm) of the steel plate; (3) 0.125 ≦ λ ≦ 0.8, where λ = (T)Jing Fin (seminal emission)-TOpen cold）/ t。
Examples 1-4 are 50mm and 80mm thick Q500qENH weathering bridge steels produced by the process of the present invention, comparative examples 1 and 2 are molten steels from the same heats as in the examples, cast different billets, of the same composition as in examples 1 and 2, but prepared by a different conventional rolling process from the present invention.
The compositions of comparative examples 3 and 4 are not within the scope of the present invention and are designed differently from the compositions of the present invention, but are prepared by the rolling process of the present invention.
The mechanical property of the steel plate prepared by the method is detected by sampling, and the results are shown in Table 3, the yield strength, the tensile strength, the yield ratio and the elongation at three typical positions in the thickness direction in examples 1-4 all meet the requirements of steel with the yield strength of 500MPa, and the allowance is large; the impact energy at minus 40 ℃ is more than 200J, the difference value between single values in a single group of impact energy numerical values is less than 20J, the stability is good, and the impact toughness uniformity in the thickness direction is excellent. In comparative examples 1 to 4, the impact toughness was poor, the difference in impact energy was large at different positions in the plate thickness direction, and the fluctuation in impact energy value was large among 3 parallel samples at the same position, and the difference between the individual values reached 270J at the maximum.
TABLE 3
The M-A components of examples 1-4 and comparative examples 1-4 were colored and etched with a Lepera reagent (4% picric acid alcohol solution mixed with 1% sodium bisulfite aqueous solution in equal proportion), and then quantified and counted with Image-Pro-Plus software, and the results are shown in Table 4, and the results of colored and etched corrosion in examples 2 and comparative examples 2 are shown in FIGS. 1-2.
TABLE 4
The maximum M-A component size of examples 1 to 4 is 1.46 μ M, not more than 1.5 μ M, area ratio is 15.32%, not more than 20% and the M-A component size is similar at the upper 1/4 and lower 1/4 positions, while the M-A component size is thicker at the typical position of comparative examples 1 to 4, the minimum is 1/4 position from the lower thickness of comparative example 4, 1.58 μ M, more than 1.5 μ M, and area ratio is 21.21%, more than 20%; and the size difference of the M-A component at the upper 1/4 and lower 1/4 positions in the thickness direction of the comparative test steel plate is larger, which is mainly caused by improper control of the ratio of upper water to lower water, and the presented organization relation is corresponding to the performance relation.
Compared with comparative examples 1 to 4, in the examples 1 to 4, a thermomechanical rolling process of low-temperature heating, properly prolonged heat preservation time, low-temperature rolling, low-temperature cold starting, high cooling speed and low-temperature reddening is adopted, T is controlled to be more than or equal to 280 and less than or equal to 352, L is more than or equal to 1100 and less than or equal to 1400, and lambda is more than or equal to 0.125 and less than or equal to 0.8, the water content ratio of the upper surface to the lower surface is controlled to be 1.2-1.5 in the cooling stage, and meanwhile, the addition amount of key alloy elements in the test steel is controlled to meet gamma of more than or equal to 3.89 and less than or equal to 6.86, so that a finer M-A component structure is obtained, and further excellent low-temperature toughness and performance uniformity are obtained.
The results show that the steel plate of each example of the invention has smaller M-A component size, each typical position along the plate thickness is not more than 1.5 μ M, the low-temperature toughness is better, and the performance uniformity in the thickness direction is better, while the comparative example has larger M-A component size, large impact performance fluctuation and poor thickness performance uniformity.
In conclusion, the rolling process for refining the M-A component in the low-carbon bainite steel, which is disclosed by the invention, is a 50-80mm thick steel plate produced industrially, has the advantages of excellent low-temperature toughness at a typical position in the thickness direction, high performance stability and good thickness-direction performance uniformity, realizes excellent matching of the toughness of the thick-specification low-carbon bainite steel, is easy to implement a scheme, is easy to control a production process, can be used for stable batch industrial production, and can be widely applied to construction of main bearing structures such as bridges, buildings, marine engineering, pipelines, wind power towers and the like.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention and not to limit it; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art will understand that: modifications to the specific embodiments of the invention or equivalent substitutions for parts of the technical features may be made; without departing from the spirit of the present invention, it is intended to cover all aspects of the invention as defined by the appended claims.
Claims (9)
1. A rolling process for refining an M-A component in low-carbon bainite steel is characterized by comprising the following steps:
(1) a heating stage: casting low-carbon bainite steel blank at T1Heating to 1100-1200 ℃ within minutes and then keeping the temperature T2 Min 280. ltoreq. T.ltoreq.352, where T = T1+T2，T1=（0.80~1.10）H，T2H, H is the thickness of a casting blank, and the unit is mm;
(2) and (3) rolling stage: comprises a rough rolling stage and a finish rolling stage,
the initial rolling temperature of the rough rolling stage is 1020-1080 ℃, the final rolling temperature is 980-1060 ℃, the intermediate blank is formed in 3-5 rolling passes, and the total rolling reduction rate is not lower than 55%;
the initial rolling temperature in the finish rolling stage is 730-840 ℃, the final rolling temperature is 710-780 ℃, low-carbon bainite steel plates are formed in 4-6 rolling passes, the single-pass reduction rate is more than or equal to 8%, and the final three-pass reduction rate is more than or equal to 40%;
(3) and (3) a cooling stage: and (3) cooling the low-carbon bainite steel plate by laminar flow water after rolling, wherein the start cooling temperature is 710-750 ℃, the re-reddening temperature is 350-450 ℃, and the cooling speed is 15-25 ℃/s.
2. The rolling process for refining the M-A component in the low-carbon bainite steel as claimed in claim 1, wherein the single-pass reduction rate is greater than or equal to 12% in the rough rolling stage, and the thickness h = (1.8-2.2) t of the intermediate blank after the rough rolling stage is completed is the final target thickness of the steel plate, and the unit is mm.
3. The rolling process for refining M-A components in low-carbon bainite steel as claimed in claim 1, wherein after the rough rolling stage is completed and before the finish rolling stage is started, the intermediate billet is cooled to the rolling temperature of the finish rolling stage by spraying water to the intermediate billet through a water spraying device, wherein the water spraying amount of the water spraying device is L = (8-12) h, and 1100 ≤ L ≤ 1400M3/h。
4. The rolling process for refining M-A components in lower bainite steel as claimed in claim 1, wherein the ratio of water amounts in the lower surface to the upper surface of the lower bainite steel plate in the cooling stage is 1.2-1.5 and 0.125 ≦ λ ≦ 0.8, where λ = (T =)Jing Fin (seminal emission)-TOpen cold）/ t，TJing Fin (seminal emission)Is the finish rolling temperature of the finish rolling stage, TOpen coldT is the final target thickness of the steel sheet in mm, which is the start-cooling temperature in the cooling stage.
5. The rolling process for refining the M-A component in the lower bainite steel as claimed in claim 1, wherein the lower bainite steel comprises the following components in percentage by mass: 0.04-0.09% of C, less than or equal to 0.55% of Si, 0.90-1.70% of Mn, 0.20-0.70% of Cr, 0.25-0.65% of Ni, 0.25-0.55% of Cu, less than or equal to 0.30% of Mo, 0.010-0.050% of Nb, 0.015-0.035% of V, 0.010-0.030% of Ti, 0.0035-0.0070% of N, less than or equal to 0.020% of P, less than or equal to 0.005% of S, and the balance of Fe and inevitable impurities;
C. the contents of Mn, Si, Ni, Cr, Mo, Cu and N satisfy 3.89-gamma 6.86, wherein gamma = C + Mn/6+ Si/5+ Ni/15+ Cr/2+ Mo/4+ Cu/13+ N/0.001.
6. A rolling process for refining M-A elements in lower bainite steel as claimed in any one of claims 1 to 5 wherein the average size of M-A elements in the cooled steel sheet is not more than 1.5 μ M and the area ratio is not more than 20%.
7. A process for rolling M-A elements in a refined lower bainite steel as claimed in any one of claims 1 to 5 wherein the thickness of the rolled lower bainite steel sheet is 50mm or more.
8. A process for rolling a refined lower bainite steel as claimed in any one of claims 1 to 5 in which the thickness of the lower bainite steel plate is-40 ℃ from the typical positionKV 2The average value of the impact work is not lower than 200J, and the difference between the single values is not more than 20J.
9. The rolling process for refining the M-A component in the low-carbon bainite steel as claimed in any one of claims 1 to 5, wherein the yield strength of the low-carbon bainite steel plate in the thickness direction at a typical position is 521-595 MPa, the tensile strength is 652-710 MPa, the yield ratio is 0.79-0.85, and the elongation is 19-23%.
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