CN115216683B - Method for regulating and controlling ferrite morphology in casting blank tissue and prepared microalloyed steel - Google Patents
Method for regulating and controlling ferrite morphology in casting blank tissue and prepared microalloyed steel Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0006—Adding metallic additives
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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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
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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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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- C—CHEMISTRY; METALLURGY
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/12—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
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Abstract
The invention discloses a method for regulating and controlling ferrite morphology in a casting blank tissue and micro-alloy steel prepared by the method, and belongs to the field of ferrous materials and metallurgical manufacturing. The production method comprises the procedures of molten iron pretreatment, converter smelting, external refining and continuous casting. Specifically, boron alloy is added in an LF refining process, rare earth Ce alloy is added in an RH refining process, the B content and the rare earth Ce content in steel are reasonably controlled, and the temperature of a casting blank is controlled through cooling water in a continuous casting process. According to the invention, through the cooling control synergistic effect of boron, rare earth and continuous casting process, the addition amount of alloy elements is reduced, ferrite is regulated and controlled to be separated out in the form of intra-crystal ferrite, the content of the intra-crystal ferrite is improved, and the reduction of area of a casting blank is detected to be more than 70% by a Gleeble1500 thermal simulation machine, so that the surface quality of the casting blank can be effectively improved.
Description
Technical Field
The invention belongs to the field of steel materials and metallurgical manufacturing, and particularly relates to a method for regulating and controlling ferrite morphology in a casting blank tissue and micro-alloy steel prepared by the method, which are suitable for improving the surface quality of a casting blank in the continuous casting process of the micro-alloy steel.
Background
With the development of industry and society, the performance requirements on steel materials are increasingly improved. At present, a trace amount of alloying elements such as Nb, V, ti and the like are added into steel, the microalloy elements can be combined with C, N in the steel to generate carbonitride, the carbonitride can prevent austenite grains from growing up, and the tiny dispersed carbonitride can play a second-phase strengthening role, so that steel with high strength, high toughness and excellent welding performance is obtained, and therefore, the microalloy elements are widely applied to various fields such as engineering machinery, railway vehicles, bridge construction, pressure vessels and the like.
However, in the continuous casting process, the fine carbonitrides in the microalloyed steel can pin grain boundaries, solid-solution Nb atoms have strong dragging effect on the grain boundaries and dislocation, the occurrence of dynamic recrystallization is restrained, a large amount of reticular along-grain ferrite is easily generated, and the strength of the grain boundaries is reduced. When the microalloy steel casting blank passes through the straightening section in continuous casting, microcracks are formed along the ferrite of the lower strength under the action of straightening stress, and the microcracks are expanded into macrocracks along the grain boundary, so that the surface cracks of the casting blank, in particular to the transverse cracks of the corners, are finally formed. The prior art can not eliminate the generation of transverse cracks at the corners of the casting blank, and can only reduce the influence by continuous casting chamfer and rolling trimming, thereby reducing the yield of steel. Therefore, in order to fundamentally solve the surface quality problem of microalloyed steel in the continuous casting process, it is necessary to improve ferrite morphology in the cast slab structure to suppress formation of ferrite along the crystal, and a new method for regulating ferrite morphology in the cast slab structure is developed.
Disclosure of Invention
In order to solve the problems, the invention provides a method for regulating and controlling the form of ferrite in a casting blank tissue and a prepared microalloy steel, wherein the method comprises the steps of molten iron pretreatment, converter smelting, external refining and continuous casting, the steel is controlled in the refining process, the boron and the rare earth with proper contents are added, and the temperature of the casting blank is controlled in the continuous casting process through cooling water. Through the synergistic effect of boron and rare earth, certain content of solid solution boron and solid solution rare earth exist in the steel, rare earth inclusion and boride are generated at the same time, the segregation of S, P at a grain boundary is reduced, the occurrence of dynamic recrystallization is facilitated, and the ferrite is promoted to be precipitated in an intragranular ferrite form; meanwhile, the cooling control is matched with the continuous casting process, so that the content of ferrite in the crystal in the structure is further improved, the surface quality of a final casting blank is improved, and the yield of steel is obviously improved.
According to a first aspect of the invention, there is provided a method of controlling ferrite morphology in a cast slab structure, the method comprising molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting, adding boron alloy during LF refining, adding rare earth Ce alloy during RH refining, and controlling the temperature of the cast slab by cooling water during continuous casting.
Further, adding 25-35 t of scrap steel in the converter smelting process, wherein the sulfur content in the scrap steel is less than or equal to 0.025%, and controlling the ratio of molten iron to be fed into the converter to be 80-90%; deoxidizing and alloying, and controlling the content of tapping oxygen to be less than or equal to 0.050 percent.
Preferably, 32t of scrap steel is added in the converter smelting process, the sulfur content in the scrap steel is 0.015%, and the proportion of molten iron entering the converter is controlled at 85%.
Here, the sulfur content in the scrap steel and the oxygen content of converter tapping are controlled at lower levels, so that the burden of deoxidation and desulfurization in the refining process can be reduced, and the guarantee is provided for improving the yield and solid solution quantity of the subsequent B and Ce.
Further, adding boron alloy in the LF refining process, sequentially adding aluminum alloy deoxidization and titanium alloy nitrogen fixation before adding boron alloy, wherein the molten steel temperature is more than 1580 ℃, so that the total amount of B in molten steel after LF refining is 0.0010-0.0020%.
Preferably, the temperature of the molten steel is 1610 ℃, and the total amount of B in the molten steel is 0.0016% after LF refining is finished.
Further, the boron alloy includes, but is not limited to, ferroboron with a mass percent of 16.4% boron; the aluminum alloy comprises, but is not limited to, aluminum iron with the mass percentage of aluminum being 38.9%; the titanium alloy includes, but is not limited to, titanium iron with a titanium mass percentage of 25.6%.
Further, rare earth Ce alloy is added in the RH refining process, the vacuum degree is 0.20kPa, the vacuum treatment time is more than 15min, the oxygen content in molten steel is controlled to be less than or equal to 0.0020 percent, and the nitrogen content is controlled to be less than or equal to 0.0030 percent, so that the total amount of rare earth Ce in molten steel after the RH refining is 0.025-0.050 percent.
Preferably, the vacuum treatment time is 20min, the oxygen content in the molten steel is controlled to be 0.0015%, the nitrogen content is controlled to be 0.0025%, and the total amount of rare earth Ce in the molten steel after RH refining is finished is controlled to be 0.030%.
Further, the rare earth Ce alloy includes, but is not limited to, cerium-iron, wherein the mass percentage of Ce in the cerium-iron is 20.0%, and the total mass percentage of the rest impurity elements such as carbon, sulfur, oxygen, phosphorus and the like is less than 0.02%.
Further, the surface temperature of the casting blank in the secondary cooling area is controlled to be 630-920 ℃ in the continuous casting process, and the surface temperature of the casting blank in the straightening area is controlled to be higher than 1050 ℃.
Preferably, the surface temperature of the casting blank in the secondary cooling area is controlled to be 700 ℃ in the continuous casting process, and the surface temperature of the casting blank in the straightening area is controlled to be 1100 ℃.
Here, the temperature of the cast slab is controlled in the formation region of the intra-crystalline ferrite in the secondary cooling region of the casting machine, the content of the intra-crystalline ferrite in the structure before the cast slab enters the straightening region is increased, and the intra-crystalline ferrite having good toughness can alleviate stress concentration caused by the straightening stress.
Further, the continuous casting process employs a gas-water atomized secondary cooling nozzle. The nozzle mixes the compressed air and the water, so that the water drop penetrating capacity is strong, and the cooling efficiency is high; meanwhile, the coverage area of the nozzle is wide, the casting blank is cooled uniformly, the surface temperature is controlled accurately, and the fluctuation range is 40-100 ℃.
According to a second aspect of the present invention, there is provided a microalloyed steel smelted according to the method for controlling ferrite morphology in a cast slab structure according to any one of the above aspects, wherein the microalloyed steel comprises the following chemical components in percentage by mass: 0.10 to 0.14 percent, si:0.20 to 0.35 percent, mn:1.4 to 1.7 percent, nb:0.04 to 0.07 percent, V: 0.06-0.08%, al:0.010 to 0.040 percent, ti:0.010 to 0.030 percent, N:0.0015 to 0.0030 percent, O is less than or equal to 0.0020 percent, S is less than or equal to 0.0060 percent, the balance is iron and unavoidable impurity elements, meanwhile, the content of B is 0.0010 to 0.0015 percent, and the content of rare earth Ce is 0.020 to 0.050 percent.
Further, the Ce in the steel casting blank is mainly spherical or ellipsoidal 2 O 2 S rare earth inclusions in an amount of 300/mm 2 Above, and more than 85% of rare earth inclusions are smaller than 2 μm in size.
Preferably, the quantity of the rare earth inclusions is 350 pieces/mm 2 And more than 85% of rare earth inclusions have a size smaller than 1 mu m.
Here, the linear expansion coefficient of the rare earth inclusions which are distributed finely and uniformly is close to that of the steel matrix, and stress concentration is not easy to occur when the steel matrix is stressed; at the same time rare earth inclusion Ce 2 O 2 S may provide a nucleation core for the formation of intra-granular ferrite, thereby promoting the formation of intra-granular ferrite.
Further, the steel cast blank has no existence along the ferrite in the structure near the stretching fracture at 650-1050 ℃, the ferrite is precipitated as the ferrite in the crystal, and the ferrite in the crystal accounts for more than 40%.
Preferably, the intra-crystalline ferrite accounts for 45%.
Further, the steel casting is detected without surface crack defects, and the reduction of area of the casting blank in the range of 650-1050 ℃ is measured to be more than 70%.
The invention has the beneficial effects that:
aiming at microalloy steel, the invention carries out boron and rare earth composite treatment in the external refining process, reasonably controls the boron content and the rare earth content in molten steel, controls the temperature of a casting blank through cooling water in the continuous casting process, and effectively regulates and controls the form of ferrite in a casting blank tissue. The core of the method of the invention is: the characteristic that boron and rare earth which are in solid solution in steel are easy to be biased to a grain boundary is utilized, so that the energy of the grain boundary is reduced, and meanwhile, the dragging effect of solid solution Nb atoms on the grain boundary and dislocation is reduced, thereby having the effects of purifying the grain boundary and promoting dynamic recrystallization and being capable of inhibiting the formation of ferrite along the grain; rare earth Ce can modify coarse inclusions in steel into Ce with fine dispersion distribution 2 O 2 S rare earth inclusion, the linear expansion coefficient of the rare earth inclusion is similar to that of a steel matrix, stress concentration is not easy to occur, and the rare earth inclusion is coordinated with the matrix during deformation; rare earth inclusions and Fe 23 (C,B) 6 Boride can be used as a nucleation core of intragranular ferrite, so that the generation amount of intragranular ferrite is increased; and controlling the temperature of the casting blank to be in a formation interval of the intra-crystal ferrite by using cooling water, further improving the content of the intra-crystal ferrite in a structure, and finally regulating and controlling the ferrite in the casting blank to be precipitated in the form of the intra-crystal ferrite with good toughness, wherein the intra-crystal ferrite accounts for more than 40%. The casting blank smelted according to the invention has no surface crack defect in the offline detection, and the reduction of area of the casting blank in the range of 650-1050 ℃ is obviously higher than 70%.
Drawings
FIG. 1 shows a typical inclusion Ce in a cast slab according to one embodiment of the present invention 2 O 2 S。
FIG. 2 shows typical inclusion Al in a comparative casting billet according to the present invention 2 O 3 -MnS。
Figure 3 shows a microstructure near a tensile fracture at 750 ℃ according to one embodiment of the invention.
Fig. 4 shows a microstructure near a tensile break at 750 ℃ according to a comparative example of the present invention.
Figure 5 shows a microstructure near a stretch break at 650 c according to one embodiment of the invention.
The specific embodiment is as follows:
the present invention will be described in further detail below by way of examples in order to make the objects, technical solutions and advantages of the present invention more apparent.
According to the technical scheme, proper amounts of B and Ce are added in the external refining process, and the temperature of the casting blank is controlled through cooling water in the continuous casting process, so that the form of ferrite in a casting blank structure is effectively regulated and controlled. The method sequentially comprises molten iron pretreatment, converter smelting, external refining and continuous casting. According to the invention, the synergistic effect of boron and rare earth is exerted by controlling the boron content of the casting blank to be 0.0010-0.0015% and the rare earth content to be 0.020-0.050%, so that certain content of solid solution boron and solid solution rare earth exist in the steel, meanwhile, rare earth inclusion and boride are generated, the segregation of S, P at the grain boundary is reduced, the occurrence of dynamic recrystallization is facilitated, and the ferrite is promoted to be precipitated in the form of intragranular ferrite; meanwhile, the cooling control is matched with the continuous casting process, so that the content of ferrite in the crystal in the structure is improved, the surface quality problem of a casting blank in the continuous casting process is solved, and the yield of the steel is greatly improved. The reason is that the boron and the rare earth are dissolved in the steel to suppress the formation along the ferrite, the rare earth inclusion and boride increase the amount of the ferrite produced in the crystal, and the casting temperature is controlled in the formation zone of the ferrite in the crystal to promote the formation of the ferrite in the crystal.
Examples
The production method of the microalloy steel comprises the procedures of molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting, and the specific process steps are as follows:
(1) The molten iron is pretreated to carry out deep desulfurization.
(2) Molten iron and scrap steel are filled into a 210t converter for smelting in the converter smelting process, wherein the addition amount of the scrap steel is 25-35 t, the sulfur content in the scrap steel is less than or equal to 0.025%, and the ratio of molten iron to molten iron in the converter is controlled to be 80% -90%. Adding silicomanganese and ferromanganese for deoxidization and alloying, and controlling the content of tapping oxygen to be less than or equal to 0.050 percent.
(3) Adding boron alloy in the LF refining process, sequentially adding aluminum alloy and titanium alloy before adding boron alloy, wherein the temperature of molten steel is more than 1580 ℃, and the total amount of B in molten steel after LF refining is 0.0010-0.0020%.
(4) Rare earth Ce alloy is added in the RH refining process, the temperature of the molten steel reaching the station is 1590-1600 ℃, the vacuum degree is 0.20kPa, the vacuum treatment time is more than 15min, the oxygen content in the molten steel is controlled to be less than or equal to 0.0020 percent, the nitrogen content is controlled to be less than or equal to 0.0030 percent, and the total amount of rare earth Ce in the molten steel after the RH refining is finished is 0.025-0.050 percent.
(5) In the continuous casting process, a secondary cooling nozzle for gas-water atomization is adopted to adjust the temperature of a casting blank, the surface temperature of the casting blank in a secondary cooling area is controlled to be 630-920 ℃, and the surface temperature of the casting blank in a straightening area is controlled to be higher than 1050 ℃, so that a continuous casting slab with the thickness of 250mm is prepared.
The chemical components of the microalloy steel prepared by smelting are as follows by mass percent: 0.10 to 0.14 percent, si:0.20 to 0.35 percent, mn:1.4 to 1.7 percent, nb:0.04 to 0.07 percent, V: 0.06-0.08%, al:0.010 to 0.040 percent, ti:0.010 to 0.030 percent, N:0.0015 to 0.0030 percent, O is less than or equal to 0.0020 percent, S is less than or equal to 0.0060 percent, the balance is iron and unavoidable impurity elements, meanwhile, the content of B is 0.0010 to 0.0015 percent, and the content of rare earth Ce is 0.020 to 0.050 percent.
The chemical compositions and mass percentages of the three specific examples and the comparative examples are shown in Table 1.
Table 1 chemical composition (wt%) of examples and comparative examples
Exemplary inclusions in a cast slab according to an embodiment of the present invention are shown in fig. 1, and exemplary inclusions in a cast slab according to a comparative example of the present invention are shown in fig. 2. The inclusions in the microalloy steel are formed by coarse Al with edges and corners by adopting the method of the invention 2 O 3 Modification of MnS composite inclusions into small-sized ellipsoids-shaped Ce 2 O 2 S rare earth inclusion.
The examples and comparative examples of the present invention were tested for hot stretching by a Gleeble1500 thermal simulator. The specific process is as follows: 1) Sampling at 1/4 thickness of a casting blank, and processing into a high-temperature hot tensile sample with phi 10mm multiplied by 120mm and threads at two ends; 2) The high-temperature thermal tensile test was performed under the protection of argon, the sample was heated to 1250℃at a heating rate of 10℃per second, kept for 3 minutes to eliminate the temperature gradient and to make the components uniform, then cooled to the tensile temperature (650℃to 1050℃at an interval of 50 ℃) at a cooling rate of 3℃per second, kept for 30 seconds, and then heated at 1X 10 -3 Breaking the sample at the deformation rate of/s, and immediately spraying water to the fracture to cool to room temperature after breaking; 3) The reduction of area of each sample was calculated and the microstructure near the fracture was analyzed.
It is considered that the reduction of area is less than 60%, and the crack sensitivity of the cast slab is remarkably improved, and crack defects are likely to occur. The reduction of area at different stretching temperatures for the examples and comparative examples of the present invention are shown in Table 2.
Table 2 examples and comparative examples were shown to have a reduction of area (%)
As can be seen from the data in Table 2, the reduction of area of the examples is higher than that of the comparative examples at each stretching temperature. Specifically, examples 1 to 3 all have a reduction of area of more than 70% in the range of 650 to 1050 ℃; in comparative example 1, the reduction of area is lower than 60% in the temperature range of 700-850 ℃, the reduction of area is only 37.43% in the temperature range of 750 ℃, the casting blank is easy to form transverse cracks at the corner after passing through the straightening area of the continuous casting machine, and the surface quality is poor.
The microstructure near a 750 ℃ tensile break according to one embodiment of the invention is shown in FIG. 3 and the microstructure near a 750 ℃ tensile break according to one comparative example of the invention is shown in FIG. 4. As is clear from the figure, when the stretching temperature is 750 ℃, the structure in the vicinity of the fracture of the example is martensitic, and ferrite starts to precipitate along the austenite grain boundary in the comparative example structure, and cracks are easily formed along the ferrite grains, which is an important cause of the rapid reduction of area at 700 to 850 ℃ in the comparative example. The formation of ferrite along the crystal in the example structure is suppressed as compared with the comparative example.
The microstructure near a 650 ℃ tensile fracture according to one embodiment of the present invention is shown in fig. 5. As is clear from fig. 5, when the stretching temperature is 650 ℃, a large amount of ferrite exists in the structure in the vicinity of the fracture in the example, the ferrite precipitates as intra-crystalline ferrite, no along-crystalline ferrite exists, and the ratio of intra-crystalline ferrite in the structure exceeds 40%. Since the intra-crystalline ferrite has good ductility and toughness, a large amount of ferrite exists as intra-crystalline ferrite in the embodiment, so that the generation of cracks can be effectively avoided in the continuous casting process.
In summary, for microalloy steel, proper amounts of B and Ce are added in the refining process, the content of B in a casting blank is controlled to be 0.0010-0.0015% and the content of Ce is controlled to be 0.020-0.050%, the temperature of the casting blank is controlled through cooling water in the continuous casting process, and the synergistic effect of cooling control of boron, rare earth and the continuous casting process is fully exerted. Boron and rare earth which are in solid solution in steel are easy to be biased at a grain boundary, so that the energy of the grain boundary is reduced, and meanwhile, the dragging effect of solid solution Nb atoms on the grain boundary and dislocation is reduced, thereby playing roles in purifying the grain boundary and promoting dynamic recrystallization, and being capable of inhibiting the formation of ferrite along the grain; rare earth Ce can lead coarse Al with edges and corners in steel 2 O 3 Modification of MnS composite inclusions into Ce with fine dispersion distribution 2 O 2 S rare earth inclusion, the linear expansion coefficient of the rare earth inclusion is similar to that of a steel matrix, stress concentration is not easy to occur when the rare earth inclusion is stressed, and the rare earth inclusion is coordinated with the matrix when the rare earth inclusion is deformed; rare earth inclusions and Fe 23 (C,B) 6 Boride can be used as a nucleation core of intragranular ferrite, so that the generation amount of intragranular ferrite is increased; control of casting blank temperature using cooling waterThe degree is in the formation interval of the intra-crystalline ferrite, the content of the intra-crystalline ferrite in the structure is further improved, the ferrite in the casting blank is finally regulated and controlled to be precipitated in the form of the intra-crystalline ferrite with good plastic toughness, and the intra-crystalline ferrite accounts for more than 40 percent. The thickness specification of the casting blank smelted according to the invention is 250mm, no surface crack defect is found in the offline detection, and the area shrinkage of the casting blank is higher than 70% in the range of 650-1050 ℃.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, and the scope of the claims of the present invention should be covered.
Claims (6)
1. A method for regulating and controlling the morphology of ferrite in a casting blank tissue is characterized by sequentially comprising molten iron pretreatment, converter smelting, LF refining, RH refining and continuous casting, wherein boron alloy and rare earth Ce alloy are added in the LF refining and RH refining processes, the temperature of the casting blank is controlled in the continuous casting process,
wherein, adding boron alloy in the LF refining process, adding aluminum alloy and titanium alloy in sequence before adding boron alloy, the temperature of molten steel is more than 1580 ℃, and the total amount of B in molten steel is 0.0010-0.0020% after LF refining;
wherein, rare earth Ce alloy is added in the RH refining process, the vacuum degree is 0.20kPa, the vacuum treatment time is more than 15min, the oxygen content in molten steel is controlled to be less than or equal to 0.0020 percent, the nitrogen content is controlled to be less than or equal to 0.0030 percent, and the total amount of rare earth Ce in molten steel after the RH refining is finished is 0.025 to 0.050 percent;
wherein the surface temperature of the casting blank in the secondary cooling area is controlled to be 630-920 ℃ in the continuous casting process, the surface temperature of the casting blank in the straightening area is controlled to be higher than 1050 ℃,
wherein, the casting blank does not exist along the ferrite in the tissue near the stretching fracture at 650-1050 ℃, the ferrite is precipitated as the ferrite in the crystal, and the ferrite in the crystal accounts for more than 40 percent.
2. The method according to claim 1, wherein 25-35 t of scrap steel is added in the converter smelting process, the sulfur content in the scrap steel is less than or equal to 0.025%, and the ratio of molten iron to be charged is controlled to be 80% -90%; adding silicomanganese and ferromanganese for deoxidization and alloying, and controlling the content of tapping oxygen to be less than or equal to 0.050 percent.
3. The method according to claim 1, wherein the continuous casting process uses a gas-water atomized secondary cooling nozzle, and the fluctuation range of the surface temperature of the casting blank is 40-100 ℃.
4. A microalloyed steel, characterized in that the microalloyed steel is smelted by the method for regulating and controlling ferrite morphology in a casting blank structure according to any one of claims 1 to 3, and the microalloyed steel comprises the following chemical components in percentage by mass: 0.10 to 0.14 percent, si:0.20 to 0.35 percent, mn:1.4 to 1.7 percent, nb:0.04 to 0.07 percent, V: 0.06-0.08%, al:0.010 to 0.040 percent, ti:0.010 to 0.030 percent, N:0.0015 to 0.0030 percent, O is less than or equal to 0.0020 percent, S is less than or equal to 0.0060 percent, the balance is iron and unavoidable impurity elements, meanwhile, the content of B is 0.0010 to 0.0015 percent, and the content of rare earth Ce is 0.025 to 0.050 percent.
5. The microalloyed steel of claim 4, wherein said cast strand comprises Ce in the form of a sphere or an ellipsoid 2 O 2 S rare earth inclusions in an amount of 300/mm 2 Above, and more than 85% of rare earth inclusions are smaller than 2 μm in size.
6. The microalloyed steel of claim 4, wherein said strand is inspected for the absence of surface crack defects, and wherein the reduction of area of the strand is measured to be >70% in the range of 650-1050 ℃.
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