CN115011772B - 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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- CN115011772B CN115011772B CN202210414071.0A CN202210414071A CN115011772B CN 115011772 B CN115011772 B CN 115011772B CN 202210414071 A CN202210414071 A CN 202210414071A CN 115011772 B CN115011772 B CN 115011772B
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- 229910000859 α-Fe Inorganic materials 0.000 title claims abstract description 138
- 229910001039 duplex stainless steel Inorganic materials 0.000 title claims abstract description 130
- 238000000034 method Methods 0.000 title claims abstract description 61
- 238000007670 refining Methods 0.000 title claims abstract description 26
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 76
- 238000005097 cold rolling Methods 0.000 claims abstract description 48
- 238000005098 hot rolling Methods 0.000 claims abstract description 35
- 238000001816 cooling Methods 0.000 claims abstract description 33
- 238000005242 forging Methods 0.000 claims abstract description 14
- 238000010438 heat treatment Methods 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims description 8
- 238000005096 rolling process Methods 0.000 abstract description 8
- 238000002360 preparation method Methods 0.000 abstract description 4
- 239000000243 solution Substances 0.000 description 16
- 230000008569 process Effects 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 12
- 230000001276 controlling effect Effects 0.000 description 12
- 229910000831 Steel Inorganic materials 0.000 description 8
- 239000010959 steel Substances 0.000 description 8
- 238000004321 preservation Methods 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 230000006698 induction Effects 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 238000001953 recrystallisation Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000004146 energy storage Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007547 defect 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
- 238000001556 precipitation Methods 0.000 description 2
- 238000004886 process control Methods 0.000 description 2
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 230000007774 longterm Effects 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
- 230000001105 regulatory effect Effects 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000000126 substance Substances 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
Classifications
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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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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
-
- 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 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 severe preparation process and large rolling deformation of the existing duplex stainless steel. The method comprises the following steps: step one, forging and/or hot rolling a duplex stainless steel cast ingot, and controlling the final forging or hot rolling temperature to be T 50 +T; then air cooling to room temperature to obtain a billet; t (T) 50 A heating temperature representing 50% by volume of ferrite in the duplex stainless steel; t=70 to 110 ℃; secondly, cold rolling the billet, wherein the deformation of the cold rolling is 8% -50%; step three, the cold rolled billet is subjected to T 50 And (3) 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 refine austenite and ferrite grains in the duplex stainless steel at the same time, 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 duplex stainless steel.
Background
The duplex stainless steel comprising 50% of ferrite and austenite is widely applied to the fields of petroleum, chemical industry, ships and other severe service environments due to the excellent plasticity of the austenitic stainless steel and the higher strength and intergranular corrosion resistance of the ferritic stainless steel. The microstructure morphology of duplex stainless steel determines the quality of performance. In the field of processing and manufacturing duplex stainless steel, in order to improve the mechanical properties of the duplex stainless steel, especially improve strength and toughness simultaneously, an idea of refining the grain size is provided.
In the prior art, a method for refining the austenite grain size in duplex stainless steel is adopted, and the prior art mostly needs cold rolling with higher deformation and short-time critical annealing in combination 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%, industrial application is not possible, and the large cold rolling deformation is not suitable for preparing products with large section thickness. Moreover, due to the difference of the recrystallization capability and the grain growth speed of ferrite grains and austenite grains in the duplex stainless steel, the synchronous refinement of ferrite grains 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 refinement of the size of ferrite grains 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, which are used for solving the problems that ferrite and austenite cannot be refined simultaneously in the existing duplex stainless steel preparation process, and the existing duplex stainless steel fine grain preparation process is harsh, the rolling deformation is large, and short-time critical annealing is required to be matched.
The aim 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 a die-cast or continuously cast duplex stainless steel cast ingot, and controlling the final forging or hot rolling temperature to be T 50 +T; then air cooling to room temperature to obtain a billet; t (T) 50 Representing the heating temperature at which the volume percent of ferrite is 50% and the volume percent of austenite is 50% in the duplex stainless steel; t=70 to 110 ℃;
secondly, cold rolling the billet, wherein the deformation of the cold rolling is 8% -50%;
step three, the cold rolled billet is subjected to T 50 And (3) 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 1000-1150 ℃.
In the first step, 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 control of the cold rolling followsWherein epsilon is the cold rolling deformation.
Further, in the second step, the deformation amount of the cold rolling is 8% -29%.
In the third step, the solution treatment time is 20-60 min.
Further, in the third step, the obtained duplex stainless steel has a structure of ferrite and austenite, wherein the volume percentage of ferrite is 45% -55%.
Further, 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.
Further, in the third step, ultrafine austenite grains are dispersed in the ferrite strip in the structure of the obtained duplex stainless steel.
Further, the duplex stainless steel comprises the following components in percentage by mass: c:0.01 to 0.07 percent, si:0.1 to 0.8 percent of Mn:0.3 to 5.0 percent, cr:20% -33%, ni:1% -8%, mo:0.05 to 6 percent of N:0.1 to 0.51 percent, cu:0.01% -0.7%, W:0 to 2.0 percent and the balance of Fe.
The invention also provides the duplex stainless steel, which is prepared by adopting the method.
Compared with the prior art, the invention has at least one of the following beneficial effects:
1. the method of the invention is firstly realized by controlling the higher final heat distortion temperature T 50 +T to obtain ferrite volume percentA duplex stainless steel base structure in an amount greater than 50%; then cold rolling the duplex stainless steel with a 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 the austenite phase and ferrite are subjected to plastic deformation, dislocation defects are accumulated in the two phases, and deformation energy is stored; finally, carrying out solution treatment on the cold-rolled duplex stainless steel at a temperature lower than the final heat deformation temperature, wherein deformed austenite and deformed ferrite are recovered and recrystallized in the heat preservation process of the solution treatment, but the transformation from ferrite to austenite is carried out in the solution treatment process because the solution temperature is lower than the final heat deformation temperature; the ferrite is subjected to cold rolling, deformation energy storage provides driving force for recrystallization and austenite transformation, and recrystallized ferrite grain boundaries and dislocation in the ferrite provide more polymorphonuclear positions for austenite transformation, so that precipitation of austenite in the ferrite is promoted; on the one hand, the newly generated austenite in ferrite is used as a second phase, on the other 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 austenite and the ferrite grains in the duplex stainless steel is realized simultaneously.
2. The structure of the duplex stainless steel obtained by the method is ferrite and austenite, wherein the volume percentage of ferrite is about 50%, sigma phase is not contained, and fine equiaxed grains are uniformly distributed in ferrite and austenite strips in the structure of the duplex stainless steel. In particular, a large number of ultrafine austenite grains are dispersed in the ferrite strip, with the grain size being less than 1 μm, for example 0.1 to 0.8 μm. The ultra-fine austenite grains divide the ferrite strip into ferrite grains of not more than 3 μm. The obtained duplex stainless steel has excellent comprehensive performance.
3. The method is simple, the cold rolling deformation is small, the final cooling speed is small, the process control is simple, the method can be suitable for preparing products with larger section thickness, the comprehensive performance is excellent, and the method is 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 objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the written description.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, like reference numerals being used to refer to like parts throughout the several views.
FIG. 1 is a microstructure of the steel of example 1 of the present invention after the 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 of the steel of comparative example 2 of the present invention.
Detailed Description
The following detailed description of preferred embodiments of the invention is made in connection with the accompanying examples which form a part hereof, and which together with the description of the embodiments of the invention serve to explain the principles of the invention, and are not intended to limit the scope of the invention.
The microstructure morphology of duplex stainless steel determines the quality of performance. The inventors have found in long-term intensive studies that duplex stainless steel is prone to precipitate sigma phase when kept at 950 ℃ or below, sigma phase is a deleterious brittle phase, the occurrence of this phase in microstructure causes a decrease in mechanical properties, and in addition, 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 amount and is matched with short-time critical annealing, and complicated pretreatment work is needed. 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%, industrial application is not possible, and the large cold rolling deformation is not suitable for preparing products with large section thickness. Therefore, the inventor has conducted intensive studies to provide a method for preparing duplex stainless steel, which has simple process, does not require severe multi-working procedures such as cold rolling-short time annealing treatment and ultra-high cooling speed with large deformation, and can refine ferrite and austenite phases in duplex stainless steel at the same time, i.e. the invention provides a method for refining ferrite grain size in 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 a die-cast or continuously cast 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 (T) 50 Representing the heating temperature at which the volume percent of ferrite is 50% and the volume percent of austenite is 50% in the duplex stainless steel; t=70 to 110 ℃;
secondly, cold rolling the billet, wherein the deformation of the cold rolling is 8% -50%;
step three, the cold rolled billet is subjected to T 50 And (3) carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel.
The principle of the method is as follows: in duplex stainless steel, the austenite phase content increases with a decrease in heating temperature, while the ferrite content increases with an increase in heating temperature; the invention utilizes the thermodynamic characteristics that the ratio of austenite to ferrite in the duplex stainless steel changes along with the heating temperature, and utilizes the obstruction of the newly generated austenite phase and the migration of the pinning ferrite grain boundary to achieve the effect of refining the ferrite grain size. Based on the above principle, first, by controlling a higher final heat distortion temperature (T 50 +T, where T 50 The heating temperature is 50 percent of ferrite volume percent, T=70-110 ℃ to obtain a duplex stainless steel basic structure with ferrite volume percent more than 50 percent; secondly, cold rolling the duplex stainless steel with a basic structure containing more than 50% of ferrite by volume, wherein the cold rolling deformation is 8-50%, preferably 8-29, enabling the austenite phase and ferrite to generate plastic deformation, and accumulating dislocation defects and deformation energy storage in the two phases; finally, carrying out solution treatment on the cold-rolled duplex stainless steel at a temperature lower than the final heat deformation temperature, wherein deformed austenite and deformed ferrite are recovered and recrystallized in the heat preservation process of the solution treatment, but the transformation from ferrite to austenite is carried out in the solution treatment process because the solution temperature is lower than the final heat deformation temperature; the ferrite is subjected to cold rolling, deformation energy storage provides driving force for recrystallization and austenite transformation, and recrystallized ferrite grain boundaries and dislocation in the ferrite provide more polymorphonuclear positions for austenite transformation, so that precipitation of austenite in the ferrite is promoted. On the one hand, the newly generated austenite in ferrite is used as a second phase, on the other 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 ferrite grains in the duplex stainless steel is realized.
Specifically, in the first step, T 50 1000-1150 ℃.
Specifically, in the first step, a higher final heat distortion temperature T is used 50 +T, ensuring that the volume percentage of ferrite in the structure of the billet obtained by air cooling to room temperature is 60% -70%, such as 63%, 65%, 68%; this is to ensure that at least 10% of the newly formed austenite phase is formed during the solution treatment after cold deformation, thereby serving as a break of ferrite grains and a barrier to migration of ferrite grain boundaries, and realizing effective refinement of ferrite grains in duplex stainless steel. When the ferrite amount is too small, the volume percentage of ferrite in the finally obtained duplex stainless steel is not ensured to be about 50%, and the comprehensive performance of the duplex stainless steel cannot be ensured.
Specifically, in the second step, the larger cold rolling deformation is considered to be unsuitable for preparing the product with larger section thickness. The inventors have conducted intensive studies to control the deformation amount control of cold rolling to followWherein epsilon is cold rolling changeShape quantity.
Specifically, in the second step, the deformation amount of the cold rolling is controlled to be 8% -29%.
In the second step, the deformation amount of the cold rolling is controlled to be 8% -29% by controlling the temperature of T=70-110 ℃, and the effect of refining the austenite grains and the ferrite grains can be ensured by combining the process treatment of the third step. At the moment, the cold rolling deformation is small, the process is simple, and the method is suitable for preparing products with larger section thickness.
Specifically, in the third step, the solution treatment time is 20-60 min.
Specifically, in the third step, the cooling mode may be air cooling, mist cooling, water cooling, or the like. In view of the severe process conditions of the rapid cooling method, air cooling is preferred here.
Specifically, in the third step, the structure of the obtained duplex stainless steel is ferrite+austenite, wherein the volume percentage of ferrite is about 50%, for example 45% -55%, and the duplex stainless steel does not contain sigma phase.
Specifically, in the third step, fine equiaxed grains are uniformly distributed in the ferrite and austenite strips in the microstructure of the obtained duplex stainless steel. In particular, a large number of ultrafine austenite grains are dispersed in the ferrite strip, with the grain size being less than 1 μm, for example 0.1 to 0.8 μm. The ultra-fine austenite grains divide the ferrite strip into ferrite grains of not more than 3 μm. The tissue is characterized in that fine crystals can be kept stable in long-time heat preservation, and can not be combined and grown along with the extension of the heat preservation time. For example, ferrite has a grain size of 0.7 to 2.4. Mu.m, and austenite has a grain size of 0.2 to 3.5. Mu.m.
Specifically, the duplex stainless steel of the invention comprises the following components in percentage by mass: c:0.01 to 0.07 percent, si:0.1 to 0.8 percent of Mn:0.3 to 5.0 percent, cr:20% -33%, ni:1% -8%, mo:0.05 to 6 percent of N:0.1 to 0.51 percent, cu:0.01% -0.7%, W:0 to 2.0 percent and the balance of 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 to 0.5 percent, mn:0.7 to 1.2 percent, cr:22 to 32.3 percent of Ni:5.5 to 7.1 percent, mo:3.2 to 3.8 percent, N:0.17 to 0.51 percent, cu:0.01% -0.2%, W:0.1 to 2.0 percent and the balance of Fe.
Through the process, the duplex stainless steel prepared by the invention has the advantages that austenite grains and ferrite grains in the duplex stainless steel are thinned at the same time, sigma phase is not contained, and the obtained duplex stainless steel has excellent comprehensive performance. For example, the yield strength is more than 560MPa (for example 566-601 MPa), the tensile strength is more than 900MPa (for example 912-1003 MPa), and the elongation after break is more than 40% (for example more than 46%). The duplex stainless steel prepared by the components and the method of the invention 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 of refining the ferrite grain size in duplex stainless steel, the composition of which is shown in table 1# 1 below,
table 1 composition of duplex stainless steel (mass percent)
| Numbering device | 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 cast ingot with the component No. 1 in table 1 by adopting a vacuum induction furnace, forging the cast ingot into a plate blank after heating at 1200 ℃ and hot-rolling, controlling the final rolling temperature of the hot rolling to 1100 ℃, carrying out multi-pass hot rolling to 4.3mm, and carrying out air cooling to room temperature after hot rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage content 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%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1000 ℃ for 20min, and cooling the cold-rolled plate to room temperature to obtain the duplex stainless steel.
The microstructure of the duplex stainless steel of this example, which was subjected to hot rolling in step 1 and then to solid solution at 1000℃for 1 hour, was shown in FIG. 1, and the average grain size of austenite was 25. Mu.m, and the average grain size of ferrite was 27. Mu.m. 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 strips, and in particular, a large number of ultrafine austenite grains are dispersed in the ferrite strips, and the grain size is smaller than 0.3 μm; the ultra-fine austenite grains divide the ferrite strip into ferrite grains of not more than 3 μm. Since a fine austenite phase is newly formed in the large-grain ferrite after the prior hot rolling, the average size of the recrystallized and refined ferrite grains is 2.35 μm and the size of the finest ferrite grains is 0.7 μm during annealing; the austenite average grain size was 2.75 μm, and the finest austenite grain size was 0.2 μm. The process method of the invention refines the austenite grains and ferrite grains in the duplex stainless steel at the same time.
Example 2
This example provides a method of refining the ferrite grain size in duplex stainless steel, the composition of which is shown in table 1# 2 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 cast ingot by adopting a vacuum induction furnace, heating the cast ingot at 1200 ℃, hot-rolling, controlling the final rolling temperature of the hot rolling to 1150 ℃, hot-rolling for multiple times to 4mm, and air-cooling to room temperature after hot-rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage content of about 63%;
step 2: carrying out multi-pass cold rolling on the hot rolled plate until the thickness of the hot rolled plate reaches 2.88mm, wherein the total deformation of the cold rolled thickness is 28%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1055 ℃ for 20min, and cooling the cold-rolled plate to room temperature to obtain the duplex stainless steel.
After the treatment by the method of the embodiment, as shown in fig. 3, fine equiaxed grains are uniformly distributed in the ferrite and austenite strips, particularly, the ferrite strips are internally filled with ultra-fine grain equiaxed newly-generated austenite, and the grain size is smaller than 0.3 mu m; the newly grown ultrafine 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 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 of the invention refines the austenite grains and ferrite grains in the duplex stainless steel at the same time.
Example 3
This example provides a method of refining the ferrite grain size in duplex stainless steel, the composition of which is shown as 3# 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 cast ingot by adopting a vacuum induction furnace, forging the cast ingot into a plate blank after heating the cast ingot at 1200 ℃, carrying out hot rolling, controlling the final rolling temperature of the hot rolling to 1180 ℃, carrying out hot rolling for multiple times to 4.1mm, and carrying out air cooling to room temperature after hot rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage content 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%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1095 ℃ for 30min, and cooling the cold-rolled plate to room temperature to obtain the duplex stainless steel.
After the treatment by the method of this example, as shown in fig. 4, fine equiaxed grains are uniformly distributed in the ferrite and austenite strips, and particularly, the ferrite strips are filled with ultra-fine equiaxed neoaustenite, which divides the ferrite strips into finer ferrite grains. Wherein the average size of ferrite grains is 2.11 μm and the size of 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 of the invention refines the austenite grains and ferrite grains in the duplex stainless steel at the same time.
Example 4
This example provides a method of refining the ferrite grain size in duplex stainless steel, the composition of which is shown in table 1# 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 cast ingot by adopting a vacuum induction furnace, forging the cast ingot into a plate blank after heating the cast ingot at 1200 ℃, carrying out hot rolling, controlling the final rolling temperature of the hot rolling to 1100 ℃, carrying out hot rolling for multiple times to 20mm, and carrying out air cooling to room temperature after hot rolling to obtain a duplex stainless steel basic structure with the ferrite volume percentage content 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%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1000 ℃ for 25min, and cooling the cold-rolled 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 ferrite grain size is 2.55. Mu.m, and the finest ferrite grain size is 1.1. Mu.m; the austenite average grain size was 3.17 μm, and the finest austenite grain size was 0.5 μm. The process method of the invention refines the austenite grains and ferrite grains in the duplex stainless steel at the same time.
Comparative example 1
This comparative example provides a method for producing a duplex stainless steel having a composition shown in table 1# 1 above, comprising:
step 1: preparing duplex stainless steel by adopting a vacuum induction furnace, forging an ingot into a plate blank after heating the ingot at 1200 ℃ and hot-rolling, controlling the final rolling temperature of the hot rolling to 1100 ℃, hot-rolling to 4mm by multiple passes, and air-cooling to room temperature after hot-rolling;
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%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1050 ℃ for 20min, and cooling the cold-rolled 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, in which the austenite average grain size is 28. Mu.m, and the ferrite average grain size is 30. Mu.m. It can be seen that, in the duplex stainless steel subjected to cold rolling with 25% deformation in this comparative example, although finer grains can be obtained by heat preservation at 1050 ℃ in a short period of time, the fine grains rapidly grow up with the increase of the heat preservation time, and finally reach a grain size equivalent to that before cold rolling. In addition, the final deformation temperature and the solid solution temperature gradient after cold rolling are small, and the cold rolling reserve energy is insufficient to promote recrystallization and transformation from ferrite to austenite at the same time, so that new fine-grain austenite cannot be generated inside a ferrite strip, the ferrite grains recrystallized in the solid solution process after cold rolling are free from the limitation of a second phase, and therefore, along with the extension of the heat preservation time, the ferrite grains are continuously grown, and finally the grain size equivalent to that before cold rolling is reached.
Comparative example 2
This comparative example provides a method for producing a duplex stainless steel having a composition shown in table 1# 1 above, comprising:
step 1: preparing duplex stainless steel by adopting a vacuum induction furnace, forging an ingot into a plate blank after heating the ingot to 1200 ℃, carrying out hot rolling, controlling the final rolling temperature of the hot rolling to 1150 ℃, carrying out hot rolling for multiple times to 4mm, and cooling to room temperature after hot rolling;
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%;
step 3: and (3) preserving the heat of the cold-rolled plate at 1100 ℃ for 20min, and cooling the cold-rolled plate to room temperature to obtain the duplex stainless steel.
As shown in FIG. 7, the microstructure of the duplex stainless steel of this comparative example was such that the austenite average grain size was 32. Mu.m, and the ferrite average grain size was 41. Mu.m. It can be seen that the duplex stainless steel subjected to cold rolling with a deformation of 43% in this comparative example cannot achieve 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 steel
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.
Claims (7)
1. A method of refining ferrite grain size in duplex stainless steel, the method comprising the steps of:
step one, forging and/or hot rolling a die-cast or continuously cast duplex stainless steel cast ingot, and controlling the final forging or hot rolling temperature to be T 50 +T; then air cooling to room temperature to obtain a billet; t (T) 50 Representing the heating temperature at which the volume percent of ferrite is 50% and the volume percent of austenite is 50% in the duplex stainless steel; t=70 to 110 ℃;
secondly, cold rolling the billet, wherein the deformation of the cold rolling is 8% -50%;
step three, the cold rolled billet is subjected to T 50 Carrying out solution treatment at the temperature, and cooling to room temperature after the solution treatment to obtain the duplex stainless steel;
in the first step, the volume percentage of ferrite in the structure of the billet obtained by air cooling to room temperature is 60-70%;
in the second step, the deformation control of the cold rolling followsWherein epsilon is the cold rolling deformation;
in the third step, the obtained duplex stainless steel has a structure of ferrite and austenite, wherein the volume percentage of ferrite is 45% -55%;
in the third step, fine equiaxed grains are uniformly distributed in ferrite and austenite strips in the obtained duplex stainless steel structure;
in the third step, superfine austenite grains are dispersed in the ferrite strip in the structure of the obtained duplex stainless steel;
in the structure of the duplex stainless steel, the grain size of ferrite is 0.7-2.4 mu m, and the grain size of austenite is 0.2-3.5 mu m;
the elongation after break of the duplex stainless steel is more than 40 percent.
2. The method of refining ferrite grain size in duplex stainless steel according to claim 1, wherein T is 50 1000-1150 ℃.
3. The method of 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 billet obtained by air cooling to room temperature is 60% -68%.
4. The method of refining ferrite grain size in duplex stainless steel according to claim 1, wherein in the second step, the deformation amount of cold rolling is 8% -29%.
5. The method of refining ferrite grain size in duplex stainless steel according to claim 1, wherein in the third step, the structure of the obtained duplex stainless steel is ferrite + austenite, wherein the ferrite is 45-50% by volume.
6. The method of refining ferrite grain size in duplex stainless steel according to any of claims 1-5, wherein the duplex stainless steel comprises the following compositions in mass percent: c:0.01 to 0.07 percent, si:0.1 to 0.8 percent of Mn:0.3 to 5.0 percent, cr:20% -33%, ni:1% -8%, mo:0.05 to 6 percent of N:0.1 to 0.51 percent, cu:0.01% -0.7%, W:0 to 2.0 percent and the balance of Fe.
7. A duplex stainless steel, characterized in that it is produced by the method according to any one of claims 1-6.
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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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