CN115874116A - Silicon-aluminum-free superfine bainitic steel and preparation method thereof - Google Patents
Silicon-aluminum-free superfine bainitic steel and preparation method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 111
- 239000010959 steel Substances 0.000 title claims abstract description 111
- 238000002360 preparation method Methods 0.000 title abstract description 16
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 85
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 56
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 24
- 239000011572 manganese Substances 0.000 claims abstract description 22
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 21
- 239000000956 alloy Substances 0.000 claims abstract description 21
- 238000000034 method Methods 0.000 claims abstract description 21
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 14
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 13
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 11
- 229910052742 iron Inorganic materials 0.000 claims abstract description 3
- 230000009466 transformation Effects 0.000 claims description 38
- 238000010438 heat treatment Methods 0.000 claims description 31
- 229910052782 aluminium Inorganic materials 0.000 claims description 17
- 238000004321 preservation Methods 0.000 claims description 15
- 239000002994 raw material Substances 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 14
- 238000010791 quenching Methods 0.000 claims description 14
- 230000000171 quenching effect Effects 0.000 claims description 14
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 13
- 238000000265 homogenisation Methods 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- 238000005098 hot rolling Methods 0.000 claims description 9
- 238000005096 rolling process Methods 0.000 claims description 8
- 230000009467 reduction Effects 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 238000009826 distribution Methods 0.000 claims description 5
- 238000005242 forging Methods 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 238000001556 precipitation Methods 0.000 abstract description 17
- 230000008569 process Effects 0.000 abstract description 13
- CSDREXVUYHZDNP-UHFFFAOYSA-N alumanylidynesilicon Chemical compound [Al].[Si] CSDREXVUYHZDNP-UHFFFAOYSA-N 0.000 abstract description 5
- 238000003466 welding Methods 0.000 abstract description 4
- 230000015572 biosynthetic process Effects 0.000 abstract description 3
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 230000000717 retained effect Effects 0.000 description 11
- 150000003839 salts Chemical class 0.000 description 9
- 229910052710 silicon Inorganic materials 0.000 description 9
- 239000000203 mixture Substances 0.000 description 6
- 150000001247 metal acetylides Chemical class 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- 229910052725 zinc Inorganic materials 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 241000446313 Lamella Species 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000007747 plating Methods 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- KFZAUHNPPZCSCR-UHFFFAOYSA-N iron zinc Chemical compound [Fe].[Zn] KFZAUHNPPZCSCR-UHFFFAOYSA-N 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses silicon-free aluminum-silicon superfine bainite steel and a preparation method thereof. The silicon-free aluminum-silicon superfine bainitic steel comprises a microstructure formed by mutually stacking nanoscale manganese-poor bainitic ferrite laths and manganese-rich residual austenite sheet layers, and the alloy components of the silicon-free aluminum-silicon superfine bainitic steel comprise: c:0.1 to 1.0wt.%, mn:2.0 to 8.0wt.% and Fe, and does not contain Al element and Si element. On the basis of the alloy components, the preparation method comprises the processes of pearlite formation, rapid austenitization and bainite formation. The invention breaks through the traditional thought that Si and/or Al elements are required to be added into the superfine bainite steel to inhibit carbide precipitation, obtains the superfine bainite steel in a silicon-free and aluminum-free alloy system innovatively, has excellent welding performance and galvanization capacity, and is beneficial to large-scale application and popularization in the field of automobiles.
Description
Technical Field
The invention relates to the technical field of steel materials, in particular to the technical field of bainite steel materials.
Background
The requirements of light weight and safety of automobiles promote the development of 3 rd generation advanced high-strength steel represented by ultra-fine bainite steel. The ultra-fine bainite steel is developed by Bhadeshia, cabilllero and the like, and the ultra-fine bainite steel adopts the component design of high carbon (C is more than or equal to 0.8 wt.%) and high silicon (Si is more than or equal to 1.5 wt.%), so that the steel is subjected to bainite transformation at a lower temperature, and the precipitation of carbides is inhibited by adding silicon elements, and the structure with nanoscale bainite ferrite laths and residual austenite sheets stacked mutually is successfully prepared. The superfine bainite steel has excellent mechanical performance, strength up to 2000MPa and toughness over 30MPa 1/2 。
In the production of ultra-fine bainite steel, in order to prevent carbide precipitation during bainite formation and thereby make it difficult to obtain residual austenite, it is necessary to add Si element to the composition of ultra-fine bainite steel, as shown in the technical solutions disclosed in patent documents CN105695858A, CN103451549A, and CN 106521350A. The addition of Si can promote the diffusion of carbon from bainitic ferrite to austenite, resulting in sufficiently stable austenite that can be retained at room temperature. However, the Si element and the oxygen element are easy to generate low-melting-point silicate, so that on one hand, the fluidity of slag and molten metal is increased, the splashing phenomenon is caused, and the welding quality is influenced; on the other hand, the wettability of the steel surface is damaged, the thickness of the iron-zinc compound layer is increased, the quality of a zinc coating is reduced, and the application of the superfine bainite steel in the field of automobiles is severely restricted.
In order to solve the above problems, some of the prior arts improve the alloy composition, such as using aluminum (Al) element instead of part of Si element, as shown in the technical solutions disclosed in patent documents CN103898299B, CN101693981B and CN112981277A, etc. However, the addition of Al element can reduce the fluidity of molten steel, increase the smelting difficulty, cause the problems of nozzle blockage in the casting process and the like, damage the surface quality of a casting, and simultaneously cause the reduction of the hardenability of a product, thereby bringing new problems to the product.
Therefore, how to obtain the ultra-fine bainite steel without adding silicon and aluminum elements is a problem to be solved urgently in the prior art.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the superfine bainite steel without silicon element and aluminum element and the preparation method thereof, the preparation method breaks through the technical idea that Si and/or Al element must be added in the existing bainite steel preparation to inhibit carbide precipitation, and the superfine bainite steel with good welding performance and zinc plating capability can be obtained.
The invention firstly discloses the following technical scheme:
a silicon-free aluminum-containing ultra-fine bainitic steel comprising a structure of nanoscale manganese-depleted bainitic ferrite laths and manganese-rich residual austenite sheet layers stacked on top of each other and comprising the following alloy compositions: c:0.1 to 1.0wt.%, mn:2.0 to 8.0wt.% and Fe, and which does not contain Al element and Si element.
In the above scheme, the manganese-poor state refers to a state in which the manganese content is lower than the overall average manganese content of the steel, and the manganese-rich state refers to a state in which the manganese content is higher than the overall average manganese content of the steel.
According to some preferred embodiments of the invention, the silicon-free aluminium ultra bainite steel further comprises one or more of the following components: cr:0 to 1.5wt.%, ni: 0-3 wt.%, V: 0-0.5 wt.%, mo:0 to 0.5wt.%, nb:0 to 0.5wt.%.
The invention further provides a preparation method of the silicon-aluminum-free superfine bainite steel, which comprises the following steps:
(1) Heating the smelted raw material alloy to an austenite single-phase region, preserving heat, then cooling to a pearlite transformation temperature region, preserving heat, and carrying out pearlite treatment;
(2) Rapidly heating the steel subjected to pearlite transformation treatment to an austenite single-phase region at a speed of more than or equal to 5 ℃/s, preserving heat, and performing rapid austenitizing treatment;
(3) Cooling the steel subjected to austenitizing treatment from an austenite single-phase region to a bainite transformation temperature region, preserving heat, performing bainite transformation, and finally cooling to room temperature to obtain the silicon-aluminum-free superfine bainite steel based on heterogeneous manganese distribution;
wherein the raw material alloy is a steel material which contains the alloy components and is not subjected to heat treatment; the austenite single-phase region is a temperature range with the temperature being 10-200 ℃ higher than the austenite complete transformation temperature.
The phase change process of the preparation method comprises the following steps: pearlite ization: heating the steel to an austenite single-phase region, preserving heat, then cooling to a pearlite transformation temperature region, and preserving heat to obtain a pearlite structure; rapid austenitizing: rapidly heating the pearlized steel to an austenite single-phase region and carrying out short-time heat preservation; bainitizing: and cooling the steel subjected to the rapid austenitizing treatment to a bainite transformation temperature range, preserving heat, carrying out bainite transformation, and finally cooling to room temperature.
In the above preparation method, enrichment of Mn elements from ferrite sheet layers to cementite sheet layers is realized by pearlite treatment, lamellar pearlite with heterogeneous Mn distribution is obtained, and further, the inventors surprisingly found that Mn distribution in original pearlite can be retained by rapid heating to an austenite single-phase region, high-temperature austenite with heterogeneous Mn distribution is obtained, when the high-temperature austenite is cooled to a bainite transformation temperature region, bainite transformation preferentially occurs in a Mn-poor austenite sheet layer region, and due to strong stability of a Mn-rich austenite region, bainite transformation hardly occurs in the austenite to bainite due to insufficient driving force for transformation from austenite to bainite, and meanwhile, due to strong interaction between Mn and C elements, C elements in a bainite transformation stage tend to diffuse to Mn-rich austenite, so that precipitation of carbides is inhibited, the austenite is more stable, and lamellar retained austenite can be formed stably at room temperature, and precipitation of carbides is successfully inhibited under the condition that no Si and/or Al elements are added, and a microstructure of ferrite of nanoscale laths and retained austenite sheet layers is obtained.
According to some preferred embodiments of the present invention, in the step (1), the temperature of the austenite single-phase region is 700 to 900 ℃, and the holding time is 10 to 120min.
According to some preferred embodiments of the present invention, in step (1), the pearlite transformation temperature is in the range of 450 to 650 ℃, and the holding time is in the range of 0.5 to 48 hours.
According to some preferred embodiments of the present invention, in the step (2), the temperature of the austenite single-phase region is 700 to 900 ℃, and the holding time is 0 to 10min.
According to some preferred embodiments of the present invention, in step (3), the bainite transformation temperature is 150-450 ℃ and the holding time is 0.5-24 h.
According to some preferred embodiments of the invention, the preparation method further comprises: before the step (1), carrying out homogenization treatment on the raw material alloy.
According to some preferred embodiments of the invention, the preparation method further comprises: rolling and/or forging the raw alloy prior to step (1).
According to some preferred embodiments of the invention, the preparation method specifically comprises:
(1) Heating the smelted raw material alloy to 1100-1300 ℃, preserving heat for 20-50 h for homogenization treatment, then performing hot rolling at 900-1100 ℃ with the reduction rate of 70-90%, and performing air cooling to room temperature after rolling to obtain a hot rolled steel plate;
(2) Heating the hot-rolled steel plate to 700-900 ℃ and preserving the heat for 10-20 min to obtain fully austenitized steel;
(3) Preserving the heat of the fully austenitized steel for 5-10 h at 550-650 ℃, performing pearlite transformation, and then quenching the steel to room temperature by water to obtain pearlite transformed steel;
(4) Rapidly heating the steel subjected to pearlite transformation treatment to 750-850 ℃ at a heating rate of 5-80 ℃/s, and preserving the temperature for 10-100 s to obtain the steel subjected to rapid austenitizing;
(5) And (3) preserving the heat of the steel subjected to rapid austenitizing for 1-10 h at 200-500 ℃, performing bainitization treatment, and then quenching the steel to room temperature through water to obtain the silicon-free aluminum superfine bainite steel.
The invention has the following beneficial effects:
the method breaks through the traditional thought that Si and/or Al are required to be added into the bainite steel to inhibit carbide precipitation, innovatively inhibits carbide precipitation through the strong interaction of C element and Mn element in a silicon-free and aluminum-free alloy system, successfully prepares the ultrafine bainite structure with overlapped nanoscale bainite ferrite laths and residual austenite sheet layers, avoids the influence of Si and Al elements on the smelting, welding and hardenability of the ultrafine bainite steel, particularly optimizes the zinc plating capacity of the ultrafine bainite steel, and powerfully promotes the application of the ultrafine bainite steel in the field of automobiles.
Drawings
FIG. 1 is a schematic diagram of the heat treatment process and phase transition process of the present invention.
FIG. 2 is a Scanning Electron Microscope (SEM) image of the microstructure after the ultra-fine bainitization treatment in example 1.
FIG. 3 is a Transmission Electron Microscope (TEM) image of the microstructure after the ultra-fine bainitization treatment in example 1.
FIG. 4 is an SEM image of the microstructure of the steel material of the same composition of example 1, which is obtained by the conventional bainiting treatment (after the same homogenization and hot rolling treatment, the heat preservation at 800 ℃ for 10min, and then the direct quenching to 400 ℃ for 12 h).
FIG. 5 is an XRD pattern of the sample after conventional/ultra-fine bainitization treatment of example 1.
FIG. 6 is a tensile curve of the sample after the conventional/ultra-fine bainitization treatment of example 1.
FIG. 7 is an SEM photograph of a microstructure after an ultra-fine bainitization treatment in example 2.
FIG. 8 is an SEM image of a microstructure obtained by subjecting the steel ingot of example 2, which has the same other components and is additionally added with 1.5Si, to conventional bainitization treatment (after the same homogenization and hot rolling treatment, heat preservation at 800 ℃ for 10min, direct quenching to 300 ℃ and heat preservation for 6 h).
FIG. 9 is an XRD pattern of the sample after conventional/ultra-fine bainitization treatment of example 2.
FIG. 10 is an SEM photograph of the microstructure after the ultra-fine bainitization treatment in example 3.
Detailed Description
The present invention is described in detail below with reference to the following embodiments and the attached drawings, but it should be understood that the embodiments and the attached drawings are only used for the illustrative description of the present invention and do not limit the protection scope of the present invention in any way. All reasonable variations and combinations that fall within the spirit of the invention are intended to be within the scope of the invention.
Example 1
The silicon-free aluminum-silicon superfine bainite steel is prepared by adopting the following raw materials:
| element name | C | Mn | Fe |
| Content of elements, wt. -%) | 0.39 | 3.69 | Balance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1200 ℃, preserving heat for 48 hours, carrying out homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total reduction rate is 80%, and air-cooling to room temperature after rolling to obtain a hot-rolled steel plate;
(2) Heating the hot-rolled steel plate to 800 ℃ by using a box-type resistance furnace, preserving heat for 10min (the austenite complete transformation temperature is 720 ℃), fully austenitizing, then transferring to a salt bath furnace at 570 ℃ for preserving heat for 6h, carrying out pearlite transformation, and then quenching to room temperature by water;
(3) Transferring the steel processed in the step (2) into a salt bath furnace at 750 ℃, and rapidly heating to 750 ℃ at a heating rate of 80 ℃/s and preserving heat for 90s;
(4) And (4) quickly transferring the steel obtained after the treatment in the step (3) to a salt bath furnace at 400 ℃ for heat preservation for 1h, carrying out bainite transformation, and finally carrying out water quenching to room temperature to obtain the silicon-free aluminum superfine bainite steel.
The heat treatment process and the corresponding phase transformation process of the steps (2) to (4) are shown in the attached figure 1.
The final microstructure of the silumin-free ultra-fine bainite steel obtained in this example is shown in fig. 2, and comprises an ultra-fine lamellar structure formed by stacking nanoscale gray retained austenite lamellae and black ferrite lamellae.
Further, the product was characterized by a transmission electron microscope and a matching spectrometer, and the results are shown in fig. 3. As can be seen from the attached figure 3, the residual austenite lamella in the microstructure of the ultra-fine bainite steel is rich in Mn, the bainite ferrite lamella is poor in Mn, and the carbide precipitation is effectively prevented.
For comparison, the microstructure of the steel with the same composition obtained by using the same alloy composition in the conventional bainite process (after the same homogenization and hot rolling process treatment, the temperature preservation at 800 ℃ for 10min and the direct quenching to 400 ℃ for the temperature preservation for 12 h) is shown in fig. 4, the microstructure mainly comprises gray flaky residual austenite, black ferrite matrix, gray massive residual austenite and new martensite structure, and flocculent carbides are obviously separated out, compared with the microstructure of the product in the embodiment shown in fig. 2, the microstructure of the product obtained by the conventional bainite process is obviously coarser, and the residual austenite content is obviously lower, and the product in the embodiment has a more obvious lamellar structure and higher residual austenite content.
The XRD characterization of the product obtained by the conventional bainite process compared with the product of this example is shown in fig. 5, and it can be seen that the residual austenite content of the product obtained by the conventional bainite process is 17% and only 61% of the residual austenite content of the product obtained by this example due to the large amount of carbide precipitation.
The mechanical property test is carried out on the product obtained by the conventional bainite process and the product obtained by the embodiment, and the comparison is shown in figure 6, so that the tensile strength of the product is 1160MPa and the total elongation is 14.5 percent after the superfine bainite treatment of the embodiment; the samples subjected to the conventional bainitization treatment have a total elongation of only 6.2% at similar tensile strengths, under the influence of carbide precipitation and reduction of residual austenite.
Therefore, the method breaks through the traditional thought of adding Si and Al into bainite steel to inhibit carbide precipitation, and compared with the conventional bainite treatment without Si and Al, the method effectively inhibits the precipitation of carbide, obtains an ultrafine bainite structure, retains more residual austenite and obtains the mechanical property of a product which is obviously superior to that of the conventional bainite treatment.
Example 2
The silicon-aluminum-free superfine bainite steel is prepared by adopting the following raw materials:
| element name | C | Mn | Fe |
| Content of elements, wt. -%) | 0.35 | 3.83 | Balance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1250 ℃, preserving heat for 24 hours, carrying out homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total reduction rate is 80%, and air-cooling to room temperature after rolling to obtain a hot-rolled steel plate;
(2) Heating the hot-rolled steel plate to 800 ℃ by using a box-type resistance furnace, preserving heat for 15min (the austenite complete transformation temperature is 722 ℃), sufficiently austenitizing, transferring to a salt bath furnace at 570 ℃ for preserving heat for 6h, performing pearlite transformation, and then quenching to room temperature by water;
(3) Transferring the steel material treated in the step (2) into a salt bath furnace at the temperature of 770 ℃, and rapidly heating to 770 ℃ at the heating rate of 80 ℃/s and preserving heat for 10s;
(4) And (4) quickly transferring the steel obtained after the treatment in the step (3) to a salt bath furnace at 300 ℃ for heat preservation for 6h, carrying out bainite transformation, and finally carrying out water quenching to room temperature to obtain the silicon-free aluminum superfine bainite steel.
The final microstructure of the silumin-free bainite steel obtained in this example is shown in fig. 7, and includes an ultrafine lamellar structure formed by stacking nanoscale gray retained austenite lamellae and black ferrite lamellae, and the microstructure also includes a small amount of block retained austenite due to the slow transformation of bainite.
For comparison, 1.5wt.% of Si element was added to the raw material, and a comparative steel material was obtained by a conventional bainite process (after the same homogenization and hot rolling process, heat preservation at 800 ℃ for 10min, and direct quenching to 300 ℃ for 6 h), and its microstructure was as shown in fig. 8, and it was seen that the steel material consisted mainly of gray flaky retained austenite, black ferrite matrix, and part of gray massive retained austenite. Compared with the comparative steel, the microstructure of the product of the embodiment is more refined, and the product has a more obvious lamellar structure.
XRD characterization of the comparative steel and the product of this example, comparing them as shown in fig. 9, shows that Mn and C in the product of this example have strong interaction, effectively suppressing carbide precipitation, and having residual austenite contents (27% and 31%, respectively) similar to those of the sample to which Si element of 1.5wt.% was added.
Therefore, the method breaks through the traditional thought of adding Si and Al into the bainite steel to inhibit carbide precipitation, effectively inhibits the precipitation of residual austenite of the carbide under the condition of not containing Si and Al, and successfully prepares the ultra-fine bainite structure.
Example 3
The silicon-aluminum-free superfine bainite steel is prepared by adopting the following raw materials:
| element name | C | Mn | Mo | Fe |
| Content of elements, wt. -%) | 0.42 | 3.76 | 0.15 | Balance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1250 ℃, preserving heat for 24 hours to carry out homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total rolling reduction is 80%, and air-cooling to room temperature after rolling to obtain a hot-rolled steel plate;
(2) Heating the hot-rolled steel plate to 800 ℃ by using a box-type resistance furnace, preserving heat for 10min (the austenite complete transformation temperature is 716 ℃), sufficiently austenitizing, transferring to a 590 ℃ salt bath furnace, preserving heat for 6h, performing pearlite transformation, and quenching to room temperature by water;
(3) Transferring the steel material treated in the step (2) into a salt bath furnace at 790 ℃, and rapidly heating the steel material to 790 ℃ at a heating rate of 80 ℃/s for 10s;
(4) And (4) quickly transferring the steel obtained after the treatment in the step (3) to a salt bath furnace at 300 ℃ for heat preservation for 1h, carrying out bainite transformation, and finally carrying out water quenching to room temperature to obtain the silicon-free aluminum superfine bainite steel.
The final microstructure of the non-silicon aluminum ultra-fine bainite steel obtained in this example is shown in fig. 10, and includes an ultra-fine lamellar structure formed by stacking nanoscale gray retained austenite lamellae and black ferrite lamellae, and the structure contains a part of blocky retained austenite due to the short heat preservation time of bainite. Therefore, the process can also inhibit the precipitation of carbides in complex alloy components (such as Mo element addition) and prepare the ultra-fine bainite structure. Therefore, the method has wide application prospect in steel materials and is very suitable for popularization and application of the ultra-fine bainite structure.
The above examples are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the above examples. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.
Claims (9)
1. A silicon-aluminum-free superfine bainitic steel is characterized in that: it comprises a structure formed by stacking nanoscale manganese-poor bainite ferrite laths and manganese-rich residual austenite sheet layers, and comprises the following alloy components: c:0.1 to 1.0wt.%, mn:2.0 to 8.0wt.% and Fe, and which does not contain Al element and Si element.
2. The silumin-free ultra-fine bainite steel as claimed in claim 1, further comprising one or more of the following: cr:0 to 1.5wt.%, ni: 0-3 wt.%, V: 0-0.5 wt.%, mo:0 to 0.5wt.%, nb:0 to 0.5wt.%.
3. The method for producing silicon-free aluminum ultra-fine bainite steel according to claim 1 or 2, characterized in that: it includes:
(1) Heating the smelted raw material alloy to an austenite single-phase region, preserving heat, then cooling to a pearlite transformation temperature region, preserving heat, and carrying out pearlite treatment;
(2) Rapidly heating the steel subjected to pearlite transformation treatment to an austenite single-phase region at a speed of more than or equal to 5 ℃/s, preserving heat, and performing rapid austenitizing treatment;
(3) Cooling the steel subjected to austenitizing treatment from an austenite single-phase region to a bainite transformation temperature region, preserving heat, performing bainite transformation, and finally cooling to room temperature to obtain the silicon-aluminum-free superfine bainite steel based on heterogeneous manganese distribution;
wherein the raw material alloy is a steel material which contains the alloy components and is not subjected to heat treatment; the austenite single-phase region is a temperature range with the temperature being 10-200 ℃ higher than the austenite complete transformation temperature.
4. The method of manufacturing silumin-free ultra-fine bainite steel according to claim 3, characterised in that: in the step (1), the temperature of the austenite single-phase region is 700-900 ℃, and the heat preservation time is 10-120 min.
5. The method of manufacturing silumin-free ultra-fine bainite steel according to claim 3, characterised in that: in the step (1), the pearlite transformation temperature range is 450-650 ℃, and the heat preservation time is 0.5-48 h.
6. The method for preparing silicon-free aluminum ultra-fine bainite steel according to claim 3, wherein: in the step (2), the temperature of the austenite single-phase region is 700-900 ℃, and the heat preservation time is 0-10 min.
7. The method of manufacturing silumin-free ultra-fine bainite steel according to claim 3, characterised in that: in the step (3), the bainite transformation temperature interval is 150-450 ℃, and the heat preservation time is 0.5-24 h.
8. The method for preparing silicon-free aluminum ultra-fine bainite steel according to claim 3, wherein: it still includes: before the step (1), carrying out homogenization treatment on the raw material alloy; and/or, prior to step (1), rolling and/or forging the feedstock alloy.
9. The method of manufacturing silumin-free ultra-fine bainite steel according to claim 3, characterised in that: the method specifically comprises the following steps:
(1) Heating the smelted raw material alloy to 1100-1300 ℃, preserving heat for 20-50 h for homogenization treatment, then performing hot rolling at 900-1100 ℃ with the reduction rate of 70-90%, and performing air cooling to room temperature after rolling to obtain a hot rolled steel plate;
(2) Heating the hot-rolled steel plate to 700-900 ℃ and preserving the temperature for 10-20 min to obtain fully austenitized steel;
(3) Preserving the heat of the fully austenitized steel for 5-10 h at 550-650 ℃, performing pearlite transformation, and then quenching the steel to room temperature by water to obtain pearlite transformed steel;
(4) Rapidly heating the steel subjected to pearlite transformation treatment to 750-850 ℃ at the heating rate of 5-80 ℃/s, and preserving the heat for 10-100 s to obtain the steel subjected to rapid austenitization;
(5) And (3) preserving the heat of the steel subjected to rapid austenitizing for 1-10 h at 200-500 ℃, performing bainitization treatment, and then quenching the steel to room temperature through water to obtain the silicon-free aluminum superfine bainite steel.
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