CN115874116B - 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 110
- 239000010959 steel Substances 0.000 title claims abstract description 110
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 59
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 30
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 24
- 239000000956 alloy Substances 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims abstract description 24
- 239000011572 manganese Substances 0.000 claims abstract description 18
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 13
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 8
- 238000010438 heat treatment Methods 0.000 claims description 33
- 230000009466 transformation Effects 0.000 claims description 32
- 229910001562 pearlite Inorganic materials 0.000 claims description 25
- 238000001816 cooling Methods 0.000 claims description 17
- 239000002994 raw material Substances 0.000 claims description 15
- 229910052710 silicon Inorganic materials 0.000 claims description 15
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 14
- 238000010791 quenching Methods 0.000 claims description 14
- 230000000171 quenching effect Effects 0.000 claims description 14
- 229910052782 aluminium Inorganic materials 0.000 claims description 12
- 238000004321 preservation Methods 0.000 claims description 12
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 10
- 239000000463 material Substances 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 9
- 238000000265 homogenisation Methods 0.000 claims description 9
- 238000005098 hot rolling Methods 0.000 claims description 9
- 239000010703 silicon Substances 0.000 claims description 9
- 238000005096 rolling process Methods 0.000 claims description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 7
- 230000009467 reduction Effects 0.000 claims description 7
- 239000000377 silicon dioxide Substances 0.000 claims description 7
- 238000009826 distribution Methods 0.000 claims description 6
- CSDREXVUYHZDNP-UHFFFAOYSA-N alumanylidynesilicon Chemical compound [Al].[Si] CSDREXVUYHZDNP-UHFFFAOYSA-N 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 238000005242 forging Methods 0.000 claims 1
- 238000001556 precipitation Methods 0.000 abstract description 18
- 230000008569 process Effects 0.000 abstract description 13
- 230000000717 retained effect Effects 0.000 abstract description 10
- 238000003466 welding Methods 0.000 abstract description 4
- 230000009286 beneficial effect Effects 0.000 abstract description 2
- 229910052742 iron Inorganic materials 0.000 abstract description 2
- 150000003839 salts Chemical class 0.000 description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 8
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 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
- 239000011159 matrix material Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000001010 compromised effect Effects 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
- 238000011534 incubation Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 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
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 239000002893 slag Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
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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
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Abstract
The invention discloses a silicon-aluminum-free superfine bainitic steel and a preparation method thereof. The silicon-aluminum-free ultra-fine bainitic steel comprises a microstructure formed by stacking nanoscale lean-manganese bainitic ferrite strips and rich-manganese retained austenite sheets, wherein the alloy comprises the following components: 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 above alloy components, the preparation method comprises the process of pearlite-rapid austenitization-bainite. The invention breaks through the traditional thought that Si and/or Al elements are required to be added in the ultra-fine bainitic steel to inhibit carbide precipitation, creatively obtains the ultra-fine bainitic steel in a silicon-free and aluminum-free alloy system, has excellent welding performance and galvanization capability, 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 bainitic steel materials.
Background
The requirements of automobile light weight and safety promote the development of 3 rd generation advanced high-strength steel represented by ultra-fine bainitic steel. The ultra-fine bainitic steels were developed by Bhadeshia and Caballero et al, which succeeded in preparing a structure having nanoscale bainitic ferrite laths and residual austenite sheets stacked on each other by adopting a composition design of high carbon (C not less than 0.8 wt.%) and high silicon (Si not less than 1.5 wt.%) to perform bainitic transformation of the steels at a lower temperature and inhibiting precipitation of carbides by adding silicon elements. The ultra-fine bainitic steel has excellent mechanical properties, the strength is up to 2000MPa, and the toughness exceeds 30MPa.m 1/2 。
In the production of ultra-fine bainitic steels, si element is required to be added to the components of ultra-fine bainitic steels in order to prevent precipitation of carbides during formation of bainite, which makes it difficult to obtain retained austenite, as disclosed in patent documents CN 105695858A, CN 103451549a and CN 106521350 a. The addition of Si element promotes the diffusion of carbon element from bainitic ferrite to austenite, thereby obtaining austenite which is sufficiently stable to remain at room temperature. However, si element and oxygen element easily generate silicate with low melting point, on one hand, the fluidity of slag and molten metal can be increased, splash phenomenon is caused, and welding quality is affected; on the other hand, the wettability of the steel surface can be compromised, the thickness of the iron-zinc compound layer is increased, the quality of the galvanized layer is reduced, and the application of the ultra-fine bainitic steel in the field of automobiles is severely restricted.
To solve the above problems, some of the prior art has improved the alloy composition by using aluminum (Al) element instead of some of Si element, such as patent documents CN 103898299B,CN 101693981B and CN
112981277a, etc. However, the addition of Al element can reduce the fluidity of molten steel, increase the smelting difficulty, cause the problems of nozzle plug in the casting process, and the like, harm the surface quality of castings, and simultaneously can cause the reduction of the hardenability of products, thereby bringing new problems to the products.
Therefore, how to obtain ultra-fine bainitic 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 ultra-fine bainitic steel without silicon elements and aluminum elements and the preparation method thereof, which breaks through the technical thought that Si and/or Al elements are added in the existing bainitic steel to inhibit carbide precipitation, and can obtain the ultra-fine bainitic steel with good welding performance and galvanization capability.
The invention firstly discloses the following technical scheme:
a silicon-aluminum-free ultra-fine bainitic steel comprising a structure formed by stacking nano-scale lean bainitic ferrite laths and rich retained austenite laths on each other, and comprising 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.
In the above scheme, the lean manganese refers to a state that the manganese element content is lower than the overall average manganese element content of the steel, and the rich manganese refers to a state that the manganese element content is higher than the overall average manganese element content of the steel.
According to some preferred embodiments of the invention, the non-silicon ultra-fine bainitic steel further comprises one or more of the following components: cr:0 to 1.5wt.%, ni:0 to 3wt.%, V:0 to 0.5wt.%, mo:0 to 0.5wt.%, nb:0 to 0.5wt.%.
The invention further provides a preparation method of the silicon-aluminum-free ultra-fine bainitic steel, which comprises the following steps:
(1) Heating the smelted raw material alloy to an austenite single-phase region and preserving heat, then cooling to a pearlite transformation temperature region and preserving heat, and performing pearlite treatment;
(2) Rapidly heating the steel subjected to pearlite treatment to an austenite single-phase region at a speed of more than or equal to 5 ℃/s, and preserving heat to perform 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 non-silicon-aluminum superfine bainitic steel based on heterogeneous manganese distribution;
wherein the raw material alloy is a steel material containing the alloy components without heat treatment; the austenite single-phase region is a temperature region with a temperature within a range of 10-200 ℃ above the austenite complete transformation temperature.
The phase change process of the preparation method comprises the following steps: pearlite: heating steel to an austenite single-phase region and preserving heat, and then cooling to a pearlite transformation temperature region and preserving heat to obtain a pearlite structure; rapid austenitization: rapidly heating the steel subjected to pearlite to an austenite single-phase region and preserving heat for a short time; bainitization: and cooling the steel subjected to rapid austenitizing treatment to a bainite transformation temperature range, preserving heat, performing bainite transformation, and finally cooling to room temperature.
In the preparation method, enrichment of Mn element from ferrite sheets to cementite sheets is achieved through pearlite treatment, sheet pearlite with heterogeneous Mn distribution is obtained, further, the inventor surprisingly found that Mn distribution in the prior pearlite can be retained through rapid heating to an austenite single-phase region, high-temperature austenite with heterogeneous Mn distribution is obtained, when the austenite is cooled to a bainite transformation temperature region, bainite transformation occurs preferentially in the Mn-poor austenite sheet region, the driving force of the austenite to the bainite transformation is insufficient due to strong stability of the Mn-rich austenite region, almost no bainite transformation occurs, meanwhile, the strong interaction exists between Mn and C element, the C element tends to diffuse to the Mn-rich austenite in the bainite transformation stage, so that precipitation of carbide is restrained, the austenite is more stable, and can be stabilized to room temperature to form sheet residual austenite, so that the precipitation of carbide is successfully restrained under the condition of not adding Si and/or Al element, and the microstructure of mutual overlapping of nano-scale bainite laths and residual austenite sheets is obtained.
According to some preferred embodiments of the invention, in 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 invention, in step (1), the pearlite transformation temperature range is 450-650 ℃ and the incubation time is 0.5-48 h.
According to some preferred embodiments of the invention, in 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 invention, in step (3), the bainite transformation temperature range is 150 to 450 ℃ and the holding time is 0.5 to 24 hours.
According to some preferred embodiments of the invention, the method of preparing further comprises: before step (1), homogenizing the raw alloy.
According to some preferred embodiments of the invention, the method of preparing further comprises: prior to step (1), the raw alloy is rolled and/or forged.
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 to perform homogenization treatment, and then performing hot rolling at 900-1100 ℃ with a rolling reduction 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 heat for 10-20 min to obtain fully austenitized steel;
(3) The fully austenitized steel is kept at 550-650 ℃ for 5-10 h, pearlite is carried out, and then water quenching is carried out to room temperature, so that the pearlitic steel is obtained;
(4) The steel after pearlite treatment is quickly heated to 750-850 ℃ at the heating rate of 5-80 ℃/s and is preserved for 10-100 s, and the steel after quick austenitization is obtained;
(5) And (3) preserving the temperature of the steel after the rapid austenitization for 1-10 hours at 200-500 ℃, carrying out bainitization treatment, and then quenching the steel to room temperature through water to obtain the silicon-aluminum-free ultrafine bainitic steel.
The invention has the following beneficial effects:
the invention breaks through the traditional thought that Si and/or Al are required to be added in the bainitic steel to inhibit carbide precipitation, creatively inhibits carbide precipitation through the strong interaction of the C element and the Mn element in a silicon-free and aluminum-free alloy system, successfully prepares the superfine bainitic structure of the mutual overlapping of the nanoscale bainitic ferrite lath and the residual austenite sheet, avoids the influence of the Si and Al elements on smelting, welding and hardenability of the superfine bainitic steel, particularly optimizes the galvanization capability of the superfine bainitic steel, and forcefully promotes the application of the superfine bainitic steel in the field of automobiles.
Drawings
FIG. 1 is a schematic diagram of a heat treatment process and a phase change process according to the present invention.
FIG. 2 is a Scanning Electron Microscope (SEM) image of the microstructure after the ultra-fine bainitizing treatment of example 1.
FIG. 3 is a Transmission Electron Microscope (TEM) image of the microstructure after the ultra-fine bainitizing treatment of example 1.
FIG. 4 is a SEM image of a microstructure obtained by conventional bainitizing treatment (after the same homogenization, hot rolling treatment, and heat preservation at 800 ℃ C. For 10min, then direct quenching to 400 ℃ C. For 12 h) of a steel material having the same composition as in example 1.
FIG. 5 is an XRD pattern of the sample after the conventional/ultra fine bainitization treatment of example 1.
FIG. 6 is a drawing of a sample after conventional/ultra fine bainitization treatment of example 1.
FIG. 7 is an SEM image of the microstructure after ultra-fine bainitization treatment of example 2.
Fig. 8 is a SEM image of the microstructure obtained by conventional bainitizing treatment (after the same homogenization treatment, hot rolling treatment, and further heat preservation at 800 ℃ for 10min, and then direct quenching to 300 ℃ for 6 h) of a steel ingot of example 2 with 1.5Si added thereto.
Fig. 9 is an XRD pattern of the sample after the conventional/ultra-fine bainitization treatment of example 2.
FIG. 10 is an SEM image of the microstructure after the ultra-fine bainitizing treatment of example 3.
Detailed Description
The present invention will be described in detail with reference to the following examples and drawings, but it should be understood that the examples and drawings are only for illustrative purposes and are not intended to limit the scope of the present invention in any way. All reasonable variations and combinations that are included within the scope of the inventive concept fall within the scope of the present invention.
Example 1
The silicon-free ultrafine bainitic steel is prepared by adopting the raw materials containing the following elements:
| element name | C | Mn | Fe |
| Elemental content, wt.% | 0.39 | 3.69 | Allowance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1200 ℃, preserving heat for 48 hours for homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total reduction rate is 80%, and cooling to room temperature after rolling to obtain a hot rolled steel plate;
(2) Heating the hot rolled steel plate to 800 ℃ by a box-type resistance furnace, preserving heat for 10min (the austenite complete transformation temperature is 720 ℃), fully austenitizing, transferring to a salt bath furnace at 570 ℃ for preserving heat for 6h, carrying out pearlite, and quenching to room temperature by water;
(3) Transferring the steel product obtained after the treatment 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 (3) rapidly transferring the steel obtained after the treatment in the step (3) into a salt bath furnace at 400 ℃ for heat preservation for 1h, performing bainite transformation, and finally quenching to room temperature by water to obtain the ultrafine bainitic steel without silicon and aluminum.
The heat treatment process and the corresponding phase change process in the steps (2) - (4) are shown in figure 1.
The final microstructure of the ultrafine bainitic steel without silica alumina obtained in this example is shown in fig. 2, and comprises an ultrafine lamellar structure formed by stacking nano-scale gray retained austenite lamellar and black lath-shaped bainitic ferrite lamellar.
Further, the product was subjected to transmission electron microscope and matched energy spectrometer characterization, and the result is shown in fig. 3. As can be seen from fig. 3, the microstructure of the ultra-fine bainitic steel has rich Mn retained austenite sheets and lean Mn bainitic ferrite sheets, and carbide precipitation is effectively prevented.
In contrast, the microstructure of the same-component steel obtained by using the same alloy components under the conventional bainite process (after the same homogenization and hot rolling process treatment and further heat preservation at 800 ℃ for 10min, and then direct quenching to 400 ℃ for 12 h) is shown in fig. 4, and mainly consists of gray flaky residual austenite, black ferrite matrix, gray massive residual austenite and nascent martensite structures, and flocculent carbide precipitation is obviously visible, and compared with the microstructure of the product of the embodiment shown in fig. 2, the microstructure of the product obtained by the conventional bainite process is obviously coarser, the residual austenite content thereof is obviously lower, and the product of the embodiment has a more obvious lamellar structure and higher residual austenite content.
XRD characterization was performed on the product obtained by the conventional bainite process and the product of this example, which is compared with that of fig. 5, and it can be seen that the product obtained by the conventional bainite process has a residual austenite content of 17% and only 61% of that 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 technology and the product of the embodiment, and compared with the product shown in figure 6, it can be seen that after the ultra-fine bainitization treatment of the embodiment, the tensile strength of the product is 1160MPa, and the total elongation is 14.5%; and the total elongation of the sample after the conventional bainite treatment is only 6.2% under the similar tensile strength under the influence of carbide precipitation and residual austenite reduction.
Therefore, the invention breaks through the traditional thought that the addition of Si and Al in the bainitic steel inhibits carbide precipitation, and compared with the conventional bainitic treatment without Si and Al, the process also effectively inhibits carbide precipitation, obtains an ultrafine bainitic structure, retains more residual austenite, and obtains mechanical properties obviously superior to those of products of the conventional bainitic treatment.
Example 2
The silicon-free ultrafine bainitic steel is prepared by adopting the raw materials containing the following elements:
| element name | C | Mn | Fe |
| Elemental content, wt.% | 0.35 | 3.83 | Allowance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1250 ℃, preserving heat for 24 hours for homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total reduction rate is 80%, and cooling to room temperature after rolling to obtain a hot rolled steel plate;
(2) Heating the hot rolled steel plate to 800 ℃ by a box-type resistance furnace, preserving heat for 15min (the austenite complete transformation temperature is 722 ℃), fully austenitizing, transferring to a salt bath furnace at 570 ℃ for preserving heat for 6h, carrying out pearlite, and quenching to room temperature by water;
(3) Transferring the steel product obtained after the treatment in the step (2) into a salt bath furnace at 770 ℃, and rapidly heating to 770 ℃ at a heating rate of 80 ℃/s for 10s;
(4) And (3) rapidly transferring the steel obtained after the treatment in the step (3) into a salt bath furnace at 300 ℃ for heat preservation for 6 hours, performing bainite transformation, and finally quenching to room temperature by water to obtain the ultrafine bainitic steel without silicon and aluminum.
The final microstructure of the ultrafine bainitic steel without silica-alumina obtained in this example is shown in fig. 7, and includes an ultrafine lamellar structure formed by stacking nano-scale gray retained austenite lamellar and black lath-shaped bainitic ferrite lamellar, and the microstructure also contains a small amount of blocky retained austenite due to slower transformation of bainite.
For comparison, 1.5wt.% of Si element was added to the raw material, and a comparative steel material was obtained under a conventional bainite process (after the same homogenization, hot rolling process treatment, and further heat preservation at 800 ℃ for 10min, and then direct quenching to 300 ℃ for 6 h), and the microstructure thereof was shown in fig. 8, and it can be seen that the steel material consisted mainly of gray flaky residual austenite, black ferrite matrix, and part of gray bulk residual austenite. Compared with the comparative steel, the microstructure of the product of the embodiment is finer, and has more obvious lamellar structure.
XRD characterization of the comparative steel material was performed with respect to the product of the present example, which is compared with that shown in fig. 9, and it can be seen that the Mn element and the C element in the product of the present example have strong interactions, effectively suppressing precipitation of carbide, so that it has residual austenite contents (27% and 31%, respectively) similar to those of the sample to which 1.5wt.% Si element was added.
Therefore, the invention breaks through the traditional thought that the addition of Si and Al in the bainitic steel inhibits carbide precipitation, effectively inhibits the precipitation of residual austenite of the carbide under the condition of no Si and Al, and successfully prepares the ultra-fine bainitic structure.
Example 3
The silicon-free ultrafine bainitic steel is prepared by adopting the raw materials containing the following elements:
| element name | C | Mn | Mo | Fe |
| Elemental content, wt.% | 0.42 | 3.76 | 0.15 | Allowance of |
The preparation process comprises the following steps:
(1) Heating the smelted raw material steel ingot to 1250 ℃, preserving heat for 24 hours for homogenization treatment, then carrying out hot rolling at 1000 ℃, wherein the total reduction rate is 80%, and cooling to room temperature after rolling to obtain a hot rolled steel plate;
(2) Heating the hot rolled steel plate to 800 ℃ by a box-type resistance furnace, preserving heat for 10min (the austenite complete transformation temperature is 716 ℃), fully austenitizing, transferring to a salt bath furnace at 590 ℃ for preserving heat for 6h, carrying out pearlite, and quenching to room temperature by water;
(3) Transferring the steel product obtained after the treatment in the step (2) into a salt bath furnace at 790 ℃, and rapidly heating to 790 ℃ at a heating rate of 80 ℃ per second for 10s;
(4) And (3) rapidly transferring the steel obtained after the treatment in the step (3) into a salt bath furnace at 300 ℃ for heat preservation for 1h, performing bainite transformation, and finally quenching to room temperature by water to obtain the ultrafine bainitic steel without silicon and aluminum.
The final microstructure of the ultrafine bainitic steel without silica-alumina obtained in this example is shown in fig. 10, and includes an ultrafine lamellar structure formed by stacking nano-scale gray retained austenite lamellar and black lath-shaped bainitic ferrite lamellar, and meanwhile, the microstructure contains partial blocky retained austenite due to shorter bainite heat preservation time. From this, it is apparent that the process of the present invention can also suppress precipitation of carbide in complex alloy components (e.g., mo element addition) to prepare an ultra-fine bainitic structure. Therefore, the method has wide application prospect in steel materials, and is very suitable for popularization and application of the ultra-fine bainitic structures.
The above examples are only 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 concept of the invention belong to the protection scope of the invention. It should be noted that modifications and adaptations to the present invention may occur to one skilled in the art without departing from the principles of the present invention and are intended to be within the scope of the present invention.
Claims (9)
1. A non-silicon-aluminum ultra-fine bainitic steel is characterized in that: it comprises a structure formed by stacking nano-scale lean bainitic ferrite laths and rich residual austenite sheets, and comprises the following alloy components: c: 0.1-1.0 wt%, mn:2.0 to 8.0. 8.0wt percent and the balance of Fe, and does not contain Al element and Si element; the preparation method comprises the following steps:
(1) Heating the smelted raw material alloy to an austenite single-phase region and preserving heat, then cooling to a pearlite transformation temperature region and preserving heat, and performing pearlite treatment;
(2) Rapidly heating the steel subjected to pearlite treatment to an austenite single-phase region at a speed of more than or equal to 5 ℃/s, and preserving heat to perform 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 ultrafine bainitic steel based on heterogeneous manganese distribution;
wherein the raw material alloy is a steel material containing the alloy components without heat treatment; the austenite single-phase region is a temperature region with the temperature within the range of 10-200 ℃ above the austenite complete transformation temperature.
2. The ultrafine bainitic steel free of silicon and aluminum according to claim 1, further comprising one or more of the following components: cr: 0-1.5 wt%, ni: 0-3 wt%, V: 0-0.5 wt%, mo: 0-0.5 wt%, nb: 0-0.5 wt%.
3. The method for preparing the ultrafine bainitic steel without silica-alumina according to claim 1 or 2, which is characterized in that: it comprises the following steps:
(1) Heating the smelted raw material alloy to an austenite single-phase region and preserving heat, then cooling to a pearlite transformation temperature region and preserving heat, and performing pearlite treatment;
(2) Rapidly heating the steel subjected to pearlite treatment to an austenite single-phase region at a speed of more than or equal to 5 ℃/s, and preserving heat to perform 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 ultrafine bainitic steel based on heterogeneous manganese distribution;
wherein the raw material alloy is a steel material containing the alloy components without heat treatment; the austenite single-phase region is a temperature region with the temperature within the range of 10-200 ℃ above the austenite complete transformation temperature.
4. The method for preparing the ultrafine bainitic steel without silica alumina according to claim 3, wherein: 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 for preparing the ultrafine bainitic steel without silica alumina according to claim 3, wherein: 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 the ultrafine bainitic steel without silica alumina 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 for preparing the ultrafine bainitic steel without silica alumina according to claim 3, wherein: in the step (3), the bainite transformation temperature range is 150-450 ℃, and the heat preservation time is 0.5-24 h.
8. The method for preparing the ultrafine bainitic steel without silica alumina according to claim 3, wherein: it also includes: homogenizing the raw alloy prior to step (1); and/or, prior to step (1), rolling and/or forging the feedstock alloy.
9. The method for preparing the ultrafine bainitic steel without silica alumina according to claim 3, wherein: the method specifically comprises the following steps:
(1) Heating the smelted raw material alloy to 1100-1300 ℃, preserving heat for 20-50 h to perform homogenization treatment, and then performing hot rolling at 900-1100 ℃ with a rolling reduction 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 heat for 10-20 min to obtain fully austenitized steel;
(3) The fully austenitized steel is kept at 550-650 ℃ for 5-10 hours, pearlite is carried out, and then water quenching is carried out to room temperature, so that the pearlitic steel is obtained;
(4) Rapidly heating the steel subjected to pearlite treatment to 750-850 ℃ at a heating rate of 5-80 ℃/s, and preserving heat for 10-100 s to obtain rapidly austenitized steel;
(5) And (3) preserving the temperature of the steel subjected to rapid austenitization for 1-10 hours at 200-500 ℃, performing bainitization treatment, and then quenching the steel to room temperature through water to obtain the silicon-aluminum-free ultrafine bainitic steel.
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