CN115011772A - Method for refining ferrite grain size in duplex stainless steel and duplex stainless steel - Google Patents
Method for refining ferrite grain size in duplex stainless steel and duplex stainless steel Download PDFInfo
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- 229910000859 α-Fe Inorganic materials 0.000 title claims abstract description 135
- 229910001039 duplex stainless steel Inorganic materials 0.000 title claims abstract description 125
- 238000000034 method Methods 0.000 title claims abstract description 62
- 238000007670 refining Methods 0.000 title claims abstract description 29
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 76
- 238000005097 cold rolling Methods 0.000 claims abstract description 48
- 238000001816 cooling Methods 0.000 claims abstract description 32
- 238000005098 hot rolling Methods 0.000 claims abstract description 30
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 19
- 239000010959 steel Substances 0.000 claims abstract description 19
- 238000005242 forging Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 14
- 239000010960 cold rolled steel Substances 0.000 claims abstract description 3
- 239000000203 mixture Substances 0.000 claims description 8
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 229910052721 tungsten Inorganic materials 0.000 claims description 4
- 238000009827 uniform distribution Methods 0.000 claims 1
- 238000005096 rolling process Methods 0.000 abstract description 9
- 238000002360 preparation method Methods 0.000 abstract description 5
- 239000000243 solution Substances 0.000 description 16
- 230000000052 comparative effect Effects 0.000 description 12
- 230000001276 controlling effect Effects 0.000 description 10
- 230000009466 transformation Effects 0.000 description 7
- 230000006698 induction Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 238000001953 recrystallisation Methods 0.000 description 5
- 238000004146 energy storage Methods 0.000 description 4
- 238000004321 preservation Methods 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 238000012369 In process control Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004512 die casting Methods 0.000 description 1
- 238000010965 in-process control Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/04—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- 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
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Abstract
The invention relates to a method for refining ferrite grain size in duplex stainless steel and the duplex stainless steel, belongs to the technical field of duplex stainless steel, and is used for solving the problems of rigorous preparation process and large rolling deformation of the existing duplex stainless steel fine grains. The method comprises the following steps: step one, forging and/or hot rolling the duplex stainless steel ingot, and controlling the final forging or hot rolling temperature to be T 50 + T; then air-cooling to room temperature to obtain a steel billet; t is 50 A heating temperature representing 50% by volume of ferrite in the duplex stainless steel; t is 70-110 ℃; step two, feeding the steel billet into a steel billet feeding deviceCold rolling is carried out, and the deformation of the cold rolling is 8 to 50 percent; step three, placing the cold-rolled steel billet in T 50 And carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel. The method can simultaneously refine austenite grains and ferrite grains in the duplex stainless steel, and the obtained duplex stainless steel has excellent comprehensive performance.
Description
Technical Field
The invention relates to the technical field of duplex stainless steel, in particular to a method for refining ferrite grain size in duplex stainless steel and the duplex stainless steel.
Background
The duplex stainless steel which consists of the ferrite phase and the austenite phase with the content of 50 percent respectively has the excellent plasticity of the austenite stainless steel and the higher strength and the intergranular corrosion resistance of the ferrite stainless steel, and is widely applied to the fields of harsh service environments such as petroleum, chemical engineering, ships and the like. The microstructure morphology of the duplex stainless steel determines the performance. In the field of duplex stainless steel processing and manufacturing, in order to improve the mechanical properties of duplex stainless steel, particularly simultaneously improve the strength and the toughness, the idea of refining the grain size is provided.
In the prior art, a method for refining the size of austenite grains in duplex stainless steel is adopted, and in the prior art, cold rolling with higher deformation is required, short-time critical annealing is matched, and complicated pretreatment work is required. When the cold rolling deformation is too large, for example, 70%, the elongation at break of the duplex stainless steel annealed for a short time is only 10.1%, and it is not industrially applicable, and the large cold rolling deformation is not suitable for the production of products having a large cross-sectional thickness. In addition, because of the recrystallization ability and the grain growth speed difference of ferrite and austenite grains in the duplex stainless steel, synchronous refinement of ferrite and austenite grains is difficult to realize; the growth speed of ferrite grains in the duplex stainless steel is faster than that of austenite grains, so that the refined ferrite grain size becomes a main bottleneck for regulating and controlling the performance of the duplex stainless steel.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a method for refining ferrite grain size in duplex stainless steel and duplex stainless steel, so as to solve the problems that ferrite and austenite cannot be refined simultaneously during the preparation of the existing duplex stainless steel, and the existing duplex stainless steel has harsh fine grain preparation process, large rolling deformation and needs to be matched with short-time critical annealing.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides a method for refining ferrite grain size in duplex stainless steel, which comprises the following steps:
step one, forging and/or hot rolling the die-cast or continuously-cast duplex stainless steel ingot, and controlling the final forging or hot rolling temperature to be T 50 + T; then air-cooling to room temperature to obtain a steel billet; t is 50 A heating temperature representing 50% by volume of ferrite and 50% by volume of austenite in the duplex stainless steel; t is 70-110 ℃;
step two, cold rolling the steel billet, wherein the cold rolling deformation is 8-50%;
step three, placing the cold-rolled steel billet in T 50 And carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel.
Further, T 50 Is 1000 to 1150 ℃.
Further, in the step one, the volume percentage of ferrite in the structure of the billet obtained by air cooling to room temperature is 60-70%.
Further, in the second step, the deformation amount control of the cold rolling is followed
Wherein epsilon is cold rolling deformation.
Furthermore, in the second step, the cold rolling deformation is 8-29%.
Further, in the third step, the time of the solution treatment is 20-60 min.
Further, in the third step, the structure of the obtained duplex stainless steel is ferrite and austenite, wherein the volume percentage content of the ferrite is 45-55%.
Further, in the third step, fine equiaxial grains are uniformly distributed in the ferrite and austenite strips in the structure of the obtained duplex stainless steel.
Further, in the third step, in the structure of the obtained duplex stainless steel, ultrafine austenite grains are dispersed in the ferrite band.
Further, the duplex stainless steel comprises the following components in percentage by mass: c: 0.01 to 0.07 percent of Si: 0.1-0.8%, Mn: 0.3% -5.0%, Cr: 20% -33%, Ni: 1% -8%, Mo: 0.05% -6%, N: 0.1-0.51%, Cu: 0.01% -0.7%, W: 0-2.0%, and the balance Fe.
The invention also provides the duplex stainless steel which is prepared by the method.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
1. the method of the invention firstly controls the higher final heat distortion temperature T 50 + T, obtaining a duplex stainless steel basic structure with the ferrite volume percentage of more than 50%; then cold rolling the duplex stainless steel with the basic structure with the ferrite volume percentage content of more than 50%, wherein the cold rolling deformation is 8-50%, preferably 8-29%, so that an austenite phase and ferrite are subjected to plastic deformation, and dislocation defects and deformation energy storage are accumulated in the two phases; finally, carrying out solution treatment on the cold-rolled duplex stainless steel at a temperature lower than the final thermal deformation temperature, wherein both deformed austenite and deformed ferrite are recovered and recrystallized in the heat preservation process of the solution treatment, but because the solution temperature is lower than the final thermal deformation temperature, the phase transformation from ferrite to austenite is generated in the solution treatment process; the ferrite is subjected to cold rolling, deformation energy storage provides a driving force for recrystallization and austenite phase transformation, and the recrystallized ferrite grain boundary and dislocation in the ferrite provide more nucleation positions for austenite phase transformation, so that the precipitation of austenite in the ferrite is promoted; the newly generated austenite in the ferrite is used as a second phase, on one hand, the ferrite is divided, so that ferrite grains are obviously refined, on the other hand, the newly generated austenite prevents the further growth of recrystallized ferrite grains, and finally, the two-phase non-phase is realized simultaneouslyThe grains of austenite and ferrite in the steel are refined.
2. The structure of the duplex stainless steel obtained by the method of the invention is ferrite and austenite, wherein the volume percentage content of the ferrite is about 50%, the structure does not contain sigma phase, and fine equiaxial grains are uniformly distributed in the ferrite and the austenite strips in the structure of the duplex stainless steel. In particular, a plurality of ultrafine austenite grains having a grain size of less than 1 μm, for example, 0.1 to 0.8 μm, are dispersed in the ferrite band. The ultrafine austenite grains divide the ferrite band into ferrite grains of not more than 3 μm. The obtained duplex stainless steel has excellent comprehensive performance.
3. The method disclosed by the invention is simple, small in cold rolling deformation, small in final cooling speed, simple in process control, capable of being suitable for preparing products with large section thickness, excellent in comprehensive performance and suitable for industrial production.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description.
Drawings
The drawings, in which like reference numerals refer to like parts throughout, are for the purpose of illustrating particular embodiments only and are not to be considered limiting of the invention.
FIG. 1 is a microstructure of a steel of example 1 of the present invention after direct solution treatment without cold rolling;
FIG. 2 is a final microstructure of the steel of example 1 of the present invention;
FIG. 3 is a final microstructure of the steel of example 2 of the present invention;
FIG. 4 is a final microstructure of the steel of example 3 of the present invention;
FIG. 5 is a final microstructure of the steel of example 4 of the present invention;
FIG. 6 is a final microstructure of the steel of comparative example 1 of the present invention;
fig. 7 is a final microstructure diagram of the steel of comparative example 2 of the present invention.
Detailed Description
The following detailed description of preferred embodiments of the invention, taken in conjunction with the accompanying examples, which form a part of this application, illustrate the principles of the invention and, together with the embodiments of the invention, serve to explain the principles of the invention and not to limit the scope of the invention.
The microstructure morphology of the duplex stainless steel determines the performance. The inventors have found, in extensive studies for a long time, that duplex stainless steels tend to precipitate a sigma phase when kept at 950 ℃ or below, which is a harmful brittle phase that appears in the microstructure causing a decrease in mechanical properties, and that the sigma phase reduces the corrosion resistance of the material.
The existing preparation method of the duplex stainless steel mostly needs cold rolling with higher deformation and short-time critical annealing, and also needs complex pretreatment work. When the cold rolling deformation is too large, for example, 70%, the elongation at break of the duplex stainless steel annealed for a short time is only 10.1%, and industrial application is impossible, and the large cold rolling deformation is not suitable for the production of products having a large section thickness. Therefore, through intensive research, the inventor provides a preparation method of the duplex stainless steel, the method has simple process, does not need harsh multiple procedures of cold rolling with large deformation, short-time annealing treatment, ultrahigh cooling speed and the like, and can simultaneously refine ferrite and austenite phases in the duplex stainless steel, namely the invention provides a method for refining ferrite grain size in the duplex stainless steel.
The invention provides a method for refining ferrite grain size in duplex stainless steel, which comprises the following steps:
step one, forging and/or hot rolling the die casting or continuous casting duplex stainless steel ingot, and controlling the final forging or hot rolling temperature to be (T) 50 + T); forging or hot rolling, and then air cooling to room temperature to obtain a billet; t is a unit of 50 A heating temperature representing 50% by volume of ferrite and 50% by volume of austenite in the duplex stainless steel; t is 70-110 ℃;
step two, cold rolling the steel billet, wherein the cold rolling deformation is 8-50%;
step three,Cold rolling the steel billet at T 50 And carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel.
It should be noted that the principle of the above method is: in the duplex stainless steel, the austenite phase content increases with a decrease in the heating temperature, while the ferrite phase content increases with an increase in the heating temperature; the invention utilizes the thermodynamic characteristic that the ratio of two phases of austenite and ferrite in the duplex stainless steel changes along with the heating temperature, and utilizes the newly generated austenite phase to block and pin the ferrite grain boundary migration, thereby achieving the effect of refining the ferrite grain size. Based on the above principle, firstly, by controlling the final heat distortion temperature (T) to be higher 50 + T, wherein, T 50 Heating at a temperature of 50% ferrite by volume, wherein T is 70-110 ℃), and obtaining a duplex stainless steel basic structure with the ferrite by volume more than 50%; secondly, cold rolling the duplex stainless steel with the basic structure with the ferrite volume percentage content of more than 50%, wherein the cold rolling deformation is 8-50%, preferably 8-29%, so that an austenite phase and ferrite are subjected to plastic deformation, and dislocation defects and deformation energy storage are accumulated inside the two phases; finally, carrying out solution treatment on the cold-rolled duplex stainless steel at a temperature lower than the final thermal deformation temperature, wherein both deformed austenite and deformed ferrite are recovered and recrystallized in the heat preservation process of the solution treatment, but because the solution temperature is lower than the final thermal deformation temperature, the phase transformation from ferrite to austenite is generated in the solution treatment process; the ferrite is subjected to cold rolling, the deformation energy storage provides driving force for recrystallization and austenite phase transformation, and the recrystallized ferrite grain boundary and dislocation in the ferrite provide more nucleation positions for austenite phase transformation, so that the precipitation of austenite in the ferrite is promoted. The newly generated austenite in the ferrite is used as a second phase, on one hand, the ferrite is divided, so that ferrite grains are obviously refined, on the other hand, the newly generated austenite prevents the recrystallized ferrite grains from further growing, and finally, the refinement of the ferrite grains in the duplex stainless steel is realized.
Specifically, in the step one, T 50 Is 1000 to 1150 ℃.
In particular, the method comprises the following steps of,in the first step, the higher final heat distortion temperature T is adopted 50 + T, ensuring that the volume percentage content of ferrite in the structure of the billet obtained by air cooling to room temperature is 60-70 percent, such as 63 percent, 65 percent and 68 percent; this is to ensure that at least 10% of a new austenite phase is generated during the solution treatment after cold deformation, thereby performing the fracture of ferrite grains and the obstruction to the migration of ferrite grain boundaries, and realizing the effective refinement of ferrite grains in the duplex stainless steel. If the amount of ferrite is too small, the volume percentage of ferrite in the finally obtained duplex stainless steel cannot be ensured to be about 50%, and the comprehensive performance of the duplex stainless steel cannot be ensured.
Specifically, in the second step, it is considered that a large cold rolling deformation amount is not suitable for the production of a product having a large cross-sectional thickness. The inventors have conducted extensive studies and have confirmed that the amount of deformation in cold rolling is controlled
Wherein epsilon is the cold rolling deformation.
Specifically, in the second step, the deformation amount of the cold rolling is controlled to be 8-29%.
In the second step, the T is controlled to be 70-110 ℃, the cold rolling deformation is 8-29%, and the process treatment in the third step can ensure the achievement of the function of refining austenite grains and ferrite grains. At the moment, the cold rolling deformation is small, the process is simple, and the method is suitable for preparing products with large section thickness.
Specifically, in the third step, the time of the solution treatment is 20-60 min.
Specifically, in the third step, the cooling mode may be air cooling, mist cooling, or water cooling. In view of the severe process conditions of the rapid cooling method, air cooling is preferred here.
Specifically, in the third step, the obtained duplex stainless steel has a structure of ferrite + austenite, wherein the ferrite content is about 50% by volume, for example, 45% to 55%, and the sigma phase is not included.
Specifically, in the third step, fine equiaxed grains are uniformly distributed in the ferrite and austenite strips in the structure of the obtained duplex stainless steel. In particular, a plurality of ultrafine austenite grains having a grain size of less than 1 μm, for example, 0.1 to 0.8 μm, are dispersed within the ferrite band. The ultrafine austenite grains divide the ferrite band into ferrite grains of not more than 3 μm. The tissue is characterized in that the stable existence of fine grains can be kept during long-time heat preservation, and the combination and the growth cannot occur along with the prolonging of the heat preservation time. For example, the grain size of ferrite is 0.7 to 2.4 μm, and the grain size of austenite is 0.2 to 3.5 μm.
Specifically, the duplex stainless steel of the present invention may comprise the following components by mass: c: 0.01 to 0.07%, Si: 0.1-0.8%, Mn: 0.3% -5.0%, Cr: 20% -33%, Ni: 1% -8%, Mo: 0.05% -6%, N: 0.1-0.51%, Cu: 0.01% -0.7%, W: 0-2.0%, and the balance Fe.
In order to further improve the performance of the duplex stainless steel, the duplex stainless steel comprises the following components in percentage by mass: c: 0.02% -0.03%, Si: 0.3% -0.5%, Mn: 0.7-1.2%, Cr: 22% -32.3%, Ni: 5.5% -7.1%, Mo: 3.2% -3.8%, N: 0.17-0.51%, Cu: 0.01% -0.2%, W: 0.1-2.0 percent and the balance of Fe.
Through the process, the duplex stainless steel prepared by the invention simultaneously refines austenite grains and ferrite grains in the duplex stainless steel, does not contain sigma phase, and has excellent comprehensive performance. For example, the yield strength is more than 560MPa (e.g., 566 to 601MPa), the tensile strength is more than 900MPa (e.g., 912 to 1003MPa), and the elongation after fracture is 40% or more (e.g., 46% or more). The duplex stainless steel prepared by the components and the method has the advantages of simple method, small cold rolling deformation, small final cooling speed, simple process control, suitability for preparing products with larger section thickness, excellent comprehensive performance and suitability for industrial production.
Example 1
This example provides a method for refining the ferrite grain size in a duplex stainless steel having the composition shown in # 1 in table 1 below,
TABLE 1 composition of duplex stainless steel (mass%)
| Numbering | C | Si | Mn | Cr | Ni | Mo | Cu | W | N | Fe |
| 1# | 0.025 | 0.5 | 1.2 | 22.5 | 5.5 | 3.2 | 0.1 | - | 0.17 | Allowance of |
| 2# | 0.02 | 0.4 | 0.7 | 25.2 | 6.8 | 3.8 | 0.2 | - | 0.27 | Allowance of |
| 3# | 0.03 | 0.38 | 1.4 | 32.3 | 7.1 | 3.5 | 0.01 | 0.1 | 0.51 | Allowance of |
The method for refining the ferrite grain size in the duplex stainless steel comprises the following steps:
step 1: preparing a duplex stainless steel ingot with a component No. 1 in a table 1 by using a vacuum induction furnace, heating the ingot at 1200 ℃, forging the ingot into a plate blank, hot rolling the plate blank, controlling the final rolling temperature of the hot rolling to be 1100 ℃, carrying out multi-pass hot rolling to 4.3mm, and air cooling the hot rolled ingot to room temperature to obtain a duplex stainless steel base structure with the ferrite volume percentage of about 60%;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 3.05mm, wherein the total deformation of the cold rolled thickness is 29%;
and step 3: and (3) keeping the temperature of the cold-rolled plate at 1000 ℃ for 20min, and air-cooling the plate to room temperature to obtain the duplex stainless steel.
The microstructure of the duplex stainless steel of this example, which was hot rolled in step 1 and then solutionized at 1000 ℃ for 1 hour, was as shown in FIG. 1, and the austenite average grain size was 25 μm and the ferrite average grain size was 27 μm. After the treatment by the method of this example, the microstructure is shown in fig. 2, fine equiaxed grains are uniformly distributed in the ferrite and austenite bands, and particularly, a large number of ultrafine austenite grains are dispersed in the ferrite band, and the grain size is less than 0.3 μm; the ultrafine austenite grains divide the ferrite band into ferrite grains of not more than 3 μm. Because a fine austenite phase is newly generated in the large-grain ferrite after the original hot rolling, the average grain size of the ferrite grains refined by recrystallization during annealing is 2.35 μm, and the grain size of the finest ferrite is 0.7 μm; the austenite average grain size was 2.75 μm and the finest austenite grain size was 0.2 μm. The process method simultaneously refines austenite grains and ferrite grains in the duplex stainless steel.
Example 2
This example provides a method for refining the ferrite grain size in a duplex stainless steel, the composition of which is shown as # 2 in table 1 above,
the method for refining the ferrite grain size in the duplex stainless steel comprises the following steps:
step 1: preparing a duplex stainless steel ingot by using a vacuum induction furnace, heating the ingot at 1200 ℃, then carrying out hot rolling, controlling the final rolling temperature of the hot rolling to 1150 ℃, carrying out multi-pass hot rolling to 4mm, and carrying out air cooling to room temperature after the hot rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage of about 63%;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 2.88mm, wherein the total deformation of the cold rolled thickness is 28%;
and step 3: and (3) keeping the temperature of the cold-rolled plate at 1055 ℃ for 20min, and air-cooling the plate to room temperature to obtain the duplex stainless steel.
After the treatment by the method of this embodiment, the microstructure is as shown in fig. 3, fine equiaxed grains are uniformly distributed inside the ferrite and austenite strips, and particularly, the ferrite strips are filled with ultra-fine equiaxed new austenite, and the grain size is less than 0.3 μm; the new ultra-fine grained austenite divides the ferrite strip into finer ferrite grains. Wherein the average size of ferrite grains is 2.15 μm, and the size of the finest ferrite grains is 0.9 μm; the austenite average grain size was 2.53 μm and the finest austenite grain size was 0.1. mu.m. The process method simultaneously refines austenite grains and ferrite grains in the duplex stainless steel.
Example 3
This example provides a method of refining the ferrite grain size in a duplex stainless steel having the composition shown in table 1 above as # 3,
the method for refining the ferrite grain size in the duplex stainless steel comprises the following steps:
step 1: preparing a duplex stainless steel ingot by using a vacuum induction furnace, heating the ingot at 1200 ℃, forging the ingot into a plate blank, hot rolling the plate blank, controlling the final rolling temperature of the hot rolling to 1180 ℃, carrying out multi-pass hot rolling to 4.1mm, and air cooling the hot rolled plate to room temperature to obtain a duplex stainless steel basic structure with the ferrite volume percentage of about 65%;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 3.07mm, wherein the total deformation of the cold rolled thickness is 25%;
and step 3: and (3) keeping the temperature of the cold-rolled plate at 1095 ℃ for 30min, and air-cooling the plate to room temperature to obtain the duplex stainless steel.
After the treatment by the method of this example, the microstructure is shown in fig. 4, fine equiaxed grains are uniformly distributed in the ferrite and austenite bands, and particularly, the ferrite bands are filled with ultra-fine equiaxed fresh austenite, and the fresh ultra-fine austenite divides the ferrite bands into finer ferrite grains. Wherein the average size of ferrite grains is 2.11 μm, and the size of the finest ferrite grains is 0.8 μm; the austenite average grain size was 3.24 μm and the finest austenite grain size was 0.3 μm. The process method simultaneously refines austenite grains and ferrite grains in the duplex stainless steel.
Example 4
This example provides a method of refining the ferrite grain size in a duplex stainless steel having the composition shown in table 1# above,
the method for refining the ferrite grain size in the duplex stainless steel comprises the following steps:
step 1: preparing a duplex stainless steel ingot by using a vacuum induction furnace, heating the ingot at 1200 ℃, forging the ingot into a plate blank, hot rolling, controlling the finish rolling temperature of the hot rolling to be 1100 ℃, carrying out multi-pass hot rolling to reach 20mm, and air-cooling to room temperature after the hot rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage of about 60%;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 14.2mm, wherein the total deformation of the cold rolled thickness is 29%;
and step 3: and (3) keeping the temperature of the cold-rolled plate at 1000 ℃ for 25min, and air-cooling the plate to room temperature to obtain the duplex stainless steel.
After the treatment by the method of this example, the microstructure is shown in FIG. 5, the average size of ferrite grains is 2.55 μm, and the size of the finest ferrite grains is 1.1 μm; the austenite average grain size was 3.17 μm and the finest austenite grain size was 0.5 μm. The process method simultaneously refines austenite grains and ferrite grains in the duplex stainless steel.
Comparative example 1
This comparative example provides a method of manufacturing a duplex stainless steel having the composition shown as # 1 in table 1 above, comprising:
step 1: preparing the duplex stainless steel by using a vacuum induction furnace, heating an ingot at 1200 ℃, forging the ingot into a plate blank, hot rolling the plate blank, controlling the final rolling temperature of the hot rolling to be 1100 ℃, carrying out multi-pass hot rolling to reach 4mm, and air cooling the hot rolled plate to room temperature;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 3mm, wherein the total deformation of the cold rolled thickness is 25%;
and step 3: and (3) keeping the temperature of the cold-rolled plate at 1050 ℃ for 20min, and air-cooling the plate to room temperature to obtain the duplex stainless steel.
The microstructure of the duplex stainless steel of this comparative example is shown in FIG. 6, and the austenite average grain size is 28 μm and the ferrite average grain size is 30 μm. It can be seen that in the case of the duplex stainless steel of this comparative example, which was cold rolled with a 25% strain at 1050 c, fine grains were obtained by holding for a short time, but the fine grains rapidly grew with the increase of the holding time, and finally, the grain size equivalent to that before the cold rolling was achieved. In addition, the final deformation temperature and the solid solution temperature gradient after cold rolling are small, the cold rolling reserve energy is not enough to simultaneously promote recrystallization and ferrite-austenite phase transformation, so that new fine-grained austenite cannot be generated in a ferrite strip, ferrite grains recrystallized in the solid solution process after cold rolling are not limited by a second phase, and the ferrite grains continuously grow along with the extension of the holding time, and finally reach the grain size equivalent to that before cold rolling.
Comparative example 2
This comparative example provides a method of manufacturing a duplex stainless steel having the composition shown as # 1 in table 1 above, comprising:
step 1: preparing the duplex stainless steel by using a vacuum induction furnace, heating an ingot at 1200 ℃, forging the ingot into a plate blank, hot rolling the plate blank, controlling the final rolling temperature of the hot rolling to 1150 ℃, carrying out multi-pass hot rolling to 4mm, and air cooling the hot rolled plate to room temperature;
step 2: carrying out multi-pass cold rolling on the hot rolled plate to 2.3mm, wherein the total deformation of the cold rolled thickness is 43%;
and 3, step 3: and (3) keeping the temperature of the cold-rolled plate at 1100 ℃ for 20min, and air-cooling the cold-rolled plate to room temperature to obtain the duplex stainless steel.
The microstructure of the comparative example duplex stainless steel is shown in FIG. 7, and the austenite average grain size is 32 μm and the ferrite average grain size is 41 μm. It can be seen that the duplex stainless steel after the cold rolling with the deformation of 43% in the comparative example can not realize the effect of grain refinement when the temperature is maintained at 1100 ℃.
The mechanical properties of the steels of examples 1-4 and comparative examples 1-2 are shown in Table 2. The performance of example 1 of the present invention is significantly higher than that of comparative examples 1-2; therefore, the duplex stainless steel has excellent mechanical properties.
TABLE 2 mechanical Properties of Duplex stainless steels
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A method of refining ferrite grain size in duplex stainless steel, comprising the steps of:
step one, forging and/or hot rolling the die-cast or continuously-cast duplex stainless steel ingot, and controlling the final forging or hot rolling temperature to be T 50 + T; then air-cooling to room temperature to obtain a steel billet; t is 50 A heating temperature representing 50% by volume of ferrite and 50% by volume of austenite in the duplex stainless steel; t is 70-110 ℃;
step two, cold rolling the steel billet, wherein the cold rolling deformation is 8-50%;
step three, placing the cold-rolled steel billet in T 50 And carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel.
2. The method for refining ferrite grain size in duplex stainless steel according to claim 1, wherein the T is 50 Is 1000 to 1150 ℃.
3. The method for refining ferrite grain size in duplex stainless steel according to claim 1, wherein in the first step, the volume percentage of ferrite in the structure of the steel slab obtained by air-cooling to room temperature is 60% to 70%.
4. The method for refining ferrite grain size in duplex stainless steel according to claim 1, wherein in said second step, the deformation amount control of the cold rolling is followed
Wherein epsilon is cold rolling deformation.
5. The method for refining ferrite grain size in duplex stainless steel according to claim 1, wherein the cold rolling deformation amount in the second step is 8% to 29%.
6. The method for refining the ferrite grain size in duplex stainless steel according to claim 1, wherein the structure of duplex stainless steel obtained in the third step is ferrite + austenite, wherein the ferrite content is 45-55% by volume.
7. A method for refining the size of ferritic grains in duplex stainless steel according to claim 1, characterized in that in step three the microstructure of the obtained duplex stainless steel has a uniform distribution of fine equiaxed grains within the ferritic and austenitic strips.
8. The method for refining ferrite grain size in duplex stainless steel according to claim 7, wherein in the third step, the duplex stainless steel is obtained with ultra fine austenite grains dispersed inside ferrite bands.
9. A method for refining the ferrite grain size in a duplex stainless steel according to any of claims 1-8, characterized in that the composition of the duplex stainless steel is, in mass percent: c: 0.01 to 0.07 percent of Si: 0.1-0.8%, Mn: 0.3-5.0%, Cr: 20% -33%, Ni: 1% -8%, Mo: 0.05% -6%, N: 0.1-0.51%, Cu: 0.01% -0.7%, W: 0-2.0%, and the balance Fe.
10. Duplex stainless steel, characterized in that it is produced by a method according to any of claims 1-9.
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| CN103205653A (en) * | 2013-03-27 | 2013-07-17 | 宝钢不锈钢有限公司 | Duplex stainless steel with excellent thermoplasticity and corrosion resistance and manufacturing method thereof |
| CN107829043A (en) * | 2017-11-06 | 2018-03-23 | 东北大学 | A kind of near-net forming preparation method of super-duplex stainless steel strip |
| CN111944973A (en) * | 2019-05-17 | 2020-11-17 | 南京理工大学 | Preparation method of heterogeneous layered structure duplex stainless steel |
| CN112899444A (en) * | 2021-01-20 | 2021-06-04 | 东北大学 | Heat treatment process of high-strength high-toughness ferrite-austenite duplex stainless steel |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103205653A (en) * | 2013-03-27 | 2013-07-17 | 宝钢不锈钢有限公司 | Duplex stainless steel with excellent thermoplasticity and corrosion resistance and manufacturing method thereof |
| CN107829043A (en) * | 2017-11-06 | 2018-03-23 | 东北大学 | A kind of near-net forming preparation method of super-duplex stainless steel strip |
| CN111944973A (en) * | 2019-05-17 | 2020-11-17 | 南京理工大学 | Preparation method of heterogeneous layered structure duplex stainless steel |
| CN112899444A (en) * | 2021-01-20 | 2021-06-04 | 东北大学 | Heat treatment process of high-strength high-toughness ferrite-austenite duplex stainless steel |
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