CN110079723B - High-strength high-plasticity 304 stainless steel and preparation method thereof - Google Patents
High-strength high-plasticity 304 stainless steel and preparation method thereof Download PDFInfo
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Abstract
The invention provides high-strength high-plasticity 304 stainless steel and a preparation method thereof, belonging to the technical field of metal materials, wherein the preparation method comprises the following steps: (1) ball-milling and mixing the first micron 304 stainless steel powder and the La solid-dissolved nano 304 stainless steel powder to obtain a mixture; (2) pressing the mixture to obtain a green body; (3) rolling the blank to obtain a rolled blank; (4) and annealing the rolled blank to obtain the high-strength high-plasticity 304 stainless steel. The preparation method has the advantages of simple process, few and easily controlled parameters, low energy consumption, energy conservation and environmental protection, meets the current national requirements for industrial production, and simultaneously has good performances of high strength and high plasticity.
Description
Technical Field
The invention relates to the technical field of metal materials, in particular to high-strength high-plasticity 304 stainless steel and a preparation method thereof.
Background
The 304 stainless steel is a universal stainless steel, is widely used for manufacturing equipment and parts which require good comprehensive performance (corrosion resistance and formability), and is widely used for developing hands and feet in the industries of aerospace, chemical energy, automobile industry, ship manufacturing, food medical treatment and the like. In recent years, with the development of times, higher requirements are put on 304 stainless steel materials by the industries, and the research on high-strength high-plastic steel becomes a hot spot.
At present, many reports and researches on improving the strong plasticity of 304 stainless steel at home and abroad are carried out, and the structural design and the heat treatment process are mainly focused. Chinese patent CN106319370A discloses a good plasticity medium chromium ferrite stainless steel, which is added with 18-22% of chromium element to ensure corrosion resistance and economy, and obtains tensile strength of more than 510MPa, yield strength of more than 350MPa and elongation of more than 35% through hot rolling, cold rolling and annealing.
Chinese patent CN102994905A discloses a preparation method of nickel-containing micro-nano structure ultra-high plasticity stainless steel, which is characterized in that 0.05-0.15% of Nb element is added on the basis of 316 austenitic stainless steel, and then processes such as vacuum induction furnace smelting, casting blank forging, hot rolling, solution treatment, cold deformation, annealing treatment and the like are carried out, and finally, a micro-nano scale ultra-fine austenitic structure with the tensile strength of 1100-1200 MPa, the yield strength of 750-800 MPa and the elongation of 35-45% is obtained.
Chinese patent CN107502721A discloses a high toughness stainless steel with tensile strength 930MPa, yield strength 725MPa and uniform elongation 34.5%, which is similar to the super high plasticity steel of patent CN102994905A in structure. In the former CN107502721A, the process of shot blasting surface nanocrystallization and annealing treatment is adopted to convert the nanocrystalline structure into a dual-scale structure, i.e. ultrafine grain and micron-sized coarse grain. The strength of the stainless steel is improved by using the ultra-fine grains, and the plasticity of the stainless steel is maintained by the combined action of the micron-sized coarse grain part on the surface layer and the central original coarse grain part which is not thinned in the shot blasting process. Compared with CN102994905A, the former has simple process, less variable parameters and easy operation. The materials in patent CN102994905A and patent CN107502721A are ultra-high plasticity stainless steels in terms of elongation, but high strength stainless steels in the sense of not being complete in terms of yield strength.
The Chinese patent CN108531817A also adopts a vacuum induction furnace for smelting, casting blank forging, hot rolling and solution treatment, then cold rolling and annealing are carried out for two times, the ultrahigh strength plasticity of the stainless steel is comprehensively realized through fine grain strengthening, back stress strengthening, deformation induced twinning effect and deformation induced martensite effect, the tensile strength can reach 1350-1440 MPa, the yield strength can reach 1150-1320 MPa, and the elongation can reach 39-47%. Compared with patent CN102994905A, the process flow of the two is complex and substantially consistent, but there is a small difference in strength, which indicates that the heat treatment process parameters have a great influence on the material properties.
The Chinese patent CN104017967A puts the austenitic stainless steel sample into a preheated ECAP die for heat preservation, and then carries out annealing after multiple times of extrusion, and then carries out air cooling to room temperature, thereby realizing the change from a single nanocrystalline structure to a double-scale structure and obtaining the best mechanical property with the yield strength of 1045MPa and the elongation of 26%.
In summary, the above patents are intended to achieve the purpose of high strength and high plasticity in a certain way, and the way of providing strength by fine grains and providing plasticity by coarse grains is the thought of most researchers. However, most methods with good comprehensive performance in the prior art have the disadvantages of complex process flow, more parameter variables, difficult control, high energy consumption and no compliance with the current theme of energy conservation and environmental protection.
Disclosure of Invention
The invention aims to provide high-strength high-plasticity 304 stainless steel and a preparation method thereof, the preparation method provided by the invention has the advantages of simple process, low cost, energy conservation and environmental protection, and the prepared 304 stainless steel has higher strength and plasticity.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of high-strength high-plasticity 304 stainless steel, which comprises the following steps:
(1) ball-milling and mixing the first micron 304 stainless steel powder and the La solid-dissolved nano 304 stainless steel powder to obtain a mixture;
(2) pressing the mixture to obtain a green body;
(3) rolling the blank to obtain a rolled blank;
(4) and annealing the rolled blank to obtain the high-strength high-plasticity 304 stainless steel.
Preferably, the particle size of the first micron 304 stainless steel powder in the step (1) is 5-13 μm;
the first micron 304 stainless steel powder comprises the following components in percentage by mass: 18.59-18.75% of Cr18.59%, 0.19-0.68% of Mn, 0.96-10.76% of Ni, 0.056-0.31% of O, 0.84-0.93% of Si and the balance of iron.
Preferably, the particle size of the La solid solution nano 304 stainless steel powder in the step (1) is 90-96 μm, and the grain size is 17-31 nm;
the La solid solution nano 304 stainless steel powder comprises the following components in percentage by mass: 16.69-18.50% of Cr, 0.36-0.42% of Cu, 0.49-1.54% of Mn, 1.48-2.48% of La, 0.056-0.112% of N, 10.45-13.93% of Ni10, 0.06-0.30% of O, 0.002-0.003% of P, 0.89-0.94% of Si and the balance of Fe.
Preferably, the La solid solution nano 304 stainless steel powder in the step (1) is prepared by mixing and ball-milling metal La and second micron 304 stainless steel powder.
Preferably, the mass ratio of the first micron 304 stainless steel powder to the La solid solution nano 304 stainless steel powder in the step (1) is (2.5-3): (7-7.5).
Preferably, the pressure of the pressing in the step (2) is 3-5 GPa, the temperature is 1000-1300 ℃, and the pressure maintaining and heat preserving time is 30-60 min.
Preferably, the rolling mode in the step (3) is jacket rolling.
Preferably, the rolling temperature in the step (3) is 900-1100 ℃, and the rolling deformation is 75-85%.
Preferably, the annealing treatment temperature is 1000-1200 ℃, and the time is 30-60 min.
The invention also provides the high-strength high-plasticity 304 stainless steel prepared by the preparation method in the technical scheme, wherein the high-strength high-plasticity 304 stainless steel is micro-nano composite crystal steel, and the grain size of nano crystal grains in the micro-nano composite crystal steel is 196-306 nm.
The invention provides a preparation method of high-strength high-plasticity 304 stainless steel, which comprises the following steps: (1) ball-milling and mixing the first micron 304 stainless steel powder and the La solid-dissolved nano 304 stainless steel powder to obtain a mixture; (2) pressing the mixture to obtain a green body; (3) rolling the blank to obtain a rolled blank; (4) and annealing the rolled blank to obtain the high-strength high-plasticity 304 stainless steel. According to the invention, the first micron 304 stainless steel powder and the La solid-solution nano 304 stainless steel powder are directly mixed to prepare the high-strength high-plasticity 304 stainless steel, the obtained stainless steel is the micro-nano composite crystal steel, the original powder is of a micro-nano structure, the process of converting the nano crystal structure into a double-scale structure by a complex heat treatment method is omitted, and the preparation process is simple; the first micron 304 stainless steel powder and the La solid solution nano 304 stainless steel powder have similar physical and chemical properties, good compatibility and good wettability, compact blanks are formed after pressing, then the strength and plasticity of the stainless steel are further improved through rolling and annealing, and the obtained 304 stainless steel has an obvious micro-nano composite structure and good strength and plasticity. The results of the examples show that the tensile strength of the 304 stainless steel prepared by the invention is 1257-1440 MPa, the yield strength is 1080-1230 MPa, and the elongation is 12-17%.
The high-strength high-plasticity 304 stainless steel is prepared in a micro-nano composite mode, the preparation process is simple, the operation is convenient, the cost is low, and the large-scale industrial production is convenient;
the invention has simple heat treatment process, low energy consumption, energy saving and environmental protection, and meets the current national requirements for industrial production.
Drawings
FIG. 1 is an optical micrograph of a green body obtained after pressing of example 1;
FIG. 2 is a statistical micrometer grain plot of the green bodies obtained after pressing in example 1;
FIG. 3 is a TEM image of the green body obtained after pressing of example 1;
FIG. 4 is a statistical plot of the nanocrystals of the green body obtained after pressing in example 1;
FIG. 5 is an SEM image of tensile fracture of high-strength and high-ductility 304 stainless steel prepared in example 1;
FIG. 6 is a TEM image of a high-strength and high-ductility 304 stainless steel prepared in example 1;
FIG. 7 is a statistical chart of the nano-grains of the high-strength and high-plasticity 304 stainless steel prepared in example 1;
FIG. 8 is a drawing curve of 304+ La nanocrystalline steel, 304 microcrystalline steel and high-strength and high-ductility 304 stainless steel prepared in examples 1 to 3;
fig. 9 is a graph comparing the strength and toughness of the 304 stainless steel of the present invention with that of the prior 304 stainless steel.
Detailed Description
The invention provides a preparation method of high-strength high-plasticity 304 stainless steel, which comprises the following steps:
(1) ball-milling and mixing the first micron 304 stainless steel powder and the La solid-dissolved nano 304 stainless steel powder to obtain a mixture;
(2) pressing the mixture to obtain a green body;
(3) rolling the blank to obtain a rolled blank;
(4) and annealing the rolled blank to obtain the high-strength high-plasticity 304 stainless steel.
The method comprises the steps of carrying out ball milling and mixing on first micron 304 stainless steel powder and La solid solution nanometer 304 stainless steel powder to obtain a mixture.
In the invention, the particle size of the first micron 304 stainless steel powder is preferably 5-13 μm, and more preferably 6-12 μm. The micron in the first micron 304 stainless steel powder refers to the grain size of micron, and because the grains are not easy to agglomerate at the micron level, one micron grain is a micron particle, the grain size of the first micron 304 stainless steel powder is not only the grain size of the grain, but also the grain size of the powder. The first micron 304 stainless steel powder disclosed by the invention preferably comprises the following components in percentage by mass: 18.59-18.75% of Cr, 0.19-0.68% of Mn, 0.96-10.76% of Ni, 0.056-0.31% of O, 0.84-0.93% of Si and the balance of iron, and further preferably comprises 18.59% of Cr, 0.19% of Mn, 10.76% of Ni, 0.31% of O, 0.84% of Si and the balance of iron. The present invention has no special requirement on the source of the first micron 304 stainless steel powder, and commercial products well known to those skilled in the art can be adopted.
In the invention, the particle size of the La solid solution nano 304 stainless steel powder is preferably 90-96 μm, and more preferably 91-95 μm; the crystal grain size of the La solid solution nano 304 stainless steel powder is preferably 17-31 nm, and more preferably 25 nm. The La solid solution nano 304 stainless steel powder comprises the following components in percentage by mass: 16.69-18.50% of Cr16.36-0.42% of Cu0.36-0.42%, 0.49-1.54% of Mn, 1.48-2.48% of La, 0.056-0.112% of N, 10.45-13.93% of Ni0.06-0.30% of O, 0.002-0.003% of P, 0.89-0.94% of Si and the balance of Fe. In the invention, the La solid solution nano 304 stainless steel powder is preferably prepared by mixing and ball milling metal La and second micron 304 stainless steel powder. In the invention, the dosage and the components of the metal La and the second micron 304 stainless steel powder correspond to the composition of the La solid solution nanometer 304 stainless steel powder. In the invention, the grain diameter of the second micron 304 stainless steel powder is preferably-100 meshes, and the grain diameter of the metal La is preferably-100 meshes. In the invention, the rotation speed of the ball milling is preferably 300-400 rpm, more preferably 350rpm, and the ball milling time is preferably 60-90 h, more preferably 70-80 h; the ball milling atmosphere is preferably argon atmosphere; the ball to feed ratio is preferably 5:2. In the ball milling process, micron 304 stainless steel powder is ground into nano-scale grain particles, and meanwhile, metal La enters the 304 stainless steel powder to be subjected to solid solution to generate La-solid-solution nano 304 stainless steel powder.
According to the invention, La is dissolved in the nano 304 stainless steel powder in a solid manner, so that the growth of the nano crystal 304 at a high temperature stage can be effectively inhibited, and the finally obtained stainless steel is ensured to be of a micro-nano composite structure.
After the first micron 304 stainless steel powder and the La solid solution nano 304 stainless steel powder are obtained, the first micron 304 stainless steel powder and the La solid solution nano 304 stainless steel powder are subjected to ball milling and mixing to obtain a mixture.
In the invention, the mass ratio of the first micron 304 stainless steel powder to the La solid solution nano 304 stainless steel powder is preferably (2.5-3): (7-7.5).
In the invention, the rotation speed of the ball mill is preferably 300-400 rpm, and more preferably 300-350 rpm; the ball milling time is preferably 15-45 min, and more preferably 30 min; the ball milling atmosphere is preferably a vacuum atmosphere; the ball-to-feed ratio is preferably 5: 2; the ball milling equipment is preferably a Miqi planetary ball mill (model: QM-QX 4L). The invention only realizes the uniform mixing of the raw materials without changing the particle size of the raw materials in the ball milling process by controlling the ball milling parameters.
After the mixture is obtained, the mixture is pressed to obtain a green body.
In the invention, the pressing pressure is preferably 3-5 GPa, the temperature is preferably 1000-1300 ℃, and the pressure maintaining and heat preserving time is preferably 30-60 min. The invention preferably puts the mixture into a boron nitride mould and presses the mixture by a cubic hydraulic press. The boron nitride mould disclosed by the invention can well transfer heat and pressure, does not react with a mixture, and can obtain a very compact blank by matching with pressing conditions. After pressing, the invention preferably further comprises the step of carrying out water cooling on the pressed blank for 5-15 min to obtain the blank.
After a blank is obtained, the blank is rolled to obtain a rolled blank.
In the invention, the rolling temperature is preferably 900-1100 ℃, and more preferably 900-1050 ℃. In the invention, the rolling is preferably multi-pass rolling, the reduction of each pass of rolling is preferably 1-2 mm, and the total rolling deformation is preferably 75-85%, and more preferably 75-80%. Before each pass of rolling, the blank is preferably heated to the rolling temperature, and the temperature is kept for 5-15 min. In the present invention, the rolling mode is preferably jacket rolling, and the material of the jacket is preferably 45 # steel. The present invention does not require special embodiments of the jacket rolling, which is well known to those skilled in the art. The invention adopts the sheath rolling, which is beneficial to the heat preservation of the billet body on one hand and is beneficial to preventing the billet body from cracking in the rolling process on the other hand. In the invention, the thickness of the rolled blank is preferably 1-3 mm. After the last rolling pass, the invention preferably further comprises cooling the rolled blank. In the present invention, the cooling is preferably air-cooled to room temperature. In the rolling process, the nano crystal grains in the material slightly grow up, and the size of the micron crystal grains is basically unchanged.
The rolling advantages of the invention mainly include two: 1) the metal plasticity is high during hot rolling, the deformation resistance is small, and the energy consumption of metal deformation is greatly reduced; 2) the tissue structure of the material is refined, the microcracks are healed, the defects of the microstructure are reduced and eliminated, and the mechanical property of the material is improved.
After the rolled blank is obtained, annealing treatment is carried out on the rolled blank to obtain the high-strength high-plasticity 304 stainless steel.
In the invention, the annealing temperature is preferably 1000-1200 ℃, and more preferably 1050-1200 ℃; the time is preferably 30 to 60min, and more preferably 35 to 55 min. In the present invention, the atmosphere of the annealing treatment is preferably an argon atmosphere, and the cooling method of the annealing treatment is preferably furnace cooling to room temperature. During annealing, the micron grain size is substantially unchanged with a slight growth of the nano-grains. The annealing treatment of the invention can promote chemical components to be homogenized, and simultaneously can eliminate stress generated by rolling deformation and improve the plasticity of 304 stainless steel.
The invention also provides the high-strength high-plasticity 304 stainless steel prepared by the preparation method in the technical scheme, and the high-strength high-plasticity 304 stainless steel is micro-nano composite crystal steel. In the invention, the grain size of the nano crystal grain in the micro-nano composite crystal steel is 196-306 nm, preferably 210-280 nm. The size of the micron crystal grain in the micro-nano composite crystal steel is determined by the preparation method of the micro-nano composite crystal steel. The components of the high-strength high-plasticity 304 stainless steel correspond to the components of the raw materials in the preparation method; the tensile strength of the high-strength and high-plasticity 304 stainless steel is preferably 1257-1440 MPa, the yield strength is preferably 1080-1230 MPa, and the elongation is preferably 12-17%.
The high-strength and high-plasticity 304 stainless steel provided by the invention and the preparation method thereof are explained in detail below with reference to examples, but the invention is not to be construed as being limited by the scope of the invention.
In the following examples, the preparation steps of the La solid solution nano 304 stainless steel powder used are as follows:
the grain diameter of the metal La is-100 meshes, the grain diameter of the second micron 304 stainless steel powder is-100 meshes, and the preparation method comprises the following specific steps:
in a pure argon atmosphere glove box, according to the atomic mass percentage, metal La powder and second micron 304 stainless steel powder are loaded into a Miqi planetary ball mill (model: QM-QX4L) according to the ball-to-material ratio of 5:2, the rotating speed is 350rmp, and the ball milling time is 70 h.
In the following examples, nano 304 stainless steel powder with nano (304+ La) as solid solution of La is referred to as La; the first micron 304 stainless steel powder is denoted by micron 304.
Example 1
The composition of the micron (304) is as follows by mass percent: 18.59% of Cr, 0.29% of Mn, 0.99% of Ni, 0.066% of O, 0.84% of Si and the balance of iron; the grain size (i.e., particle size) was 12 μm.
The nano (304+ La) comprises the following components in percentage by mass: 16.69% of Cr, 0.38% of Cu0.67% of Mn0.67%, 1.50% of La1.50%, 0.056% of N, 10.45% of Ni, 0.10% of O, 0.002% of P, 0.91% of Si and the balance of iron; the particle size of the particles is 92 μm, and the grain size is 25 nm.
The nano (304+ La) and the micron (304) are put into a ball milling tank according to the mass ratio of 7.25:2.75, the ball-material ratio is 5:2, the rotating speed is 300rpm, and the mixture is uniformly mixed for 15 min. And (3) maintaining the pressure and the temperature for 30min by using a cubic hydraulic press under the conditions of high temperature and high pressure of 4GPa and 1200 ℃, and cooling for 5min to obtain a blank. Rolling the green body by using a sheath, wherein the rolling temperature is 1000 ℃; the rolling process adopts multi-pass deformation rolling, the rolling reduction is 2mm each time, the alloy is kept in a 1000 ℃ high-temperature muffle furnace for 5min before rolling each time, the final rolling thickness is 2mm, and the deformation is 80%. And after the last rolling is finished, cooling the alloy sample to room temperature in air. And then, filling Ar into the rolled alloy sample in a vacuum tube furnace, preserving the temperature at 1200 ℃ for 30min, annealing, and cooling to room temperature along with the furnace after the heat preservation is finished to obtain the high-strength high-plasticity 304 stainless steel.
The appearance of the green body obtained after the high-temperature and high-pressure pressing and before the rolling in example 1 is observed, wherein fig. 1 is an optical microscope photograph of the green body, fig. 2 is a micrometer crystal grain statistical diagram of the green body, fig. 3 is a TEM image of the green body, and fig. 4 is a nanometer crystal grain statistical diagram of the green body.
As can be seen from fig. 1 and 3, the micro-particles and the nano-particles in the green body are uniformly distributed, the contrast of the micro-particles and the nano-particles is obvious, and a part of the nano-particles are agglomerated together and have equiaxed crystal-like shape, the micro-particles are distributed around the nano-particles, and the size of the micro-particles is about 9 μm, which indicates that one micro-particle is a micro-grain. The range of the grain sizes of the nano-and micro-grains in the green body is more accurately given in fig. 2 and 4, with the average grain size of the nano-grains being 29nm and the average grain size of the micro-grains being 9 μm.
The tensile fracture of the high-strength and high-plasticity 304 stainless steel prepared in example 1 is observed by SEM, and the result is shown in FIG. 5. Fig. 5 shows that the micro-nano boundary of the high-strength and high-plasticity 304 stainless steel is obvious, which indicates that the stainless steel is micro-nano composite crystal steel, in addition, the nano region is brittle fracture, and the micro region has a typical dimple, which indicates that the fracture is typical ductile fracture.
TEM observation of the high-strength and high-ductility 304 stainless steel prepared in example 1 is performed, and the result is shown in FIG. 6. Fig. 6 shows that the high-strength high-plasticity 304 stainless steel contains a plurality of nano particles, and the micro particles are deformed, which indicates that the high-strength high-plasticity 304 stainless steel prepared by the invention is of a micro-nano composite structure.
Statistics are made on the nanocrystalline grains of the high-strength and high-plasticity 304 stainless steel prepared in example 1, and the results are shown in fig. 7. FIG. 7 shows that the average grain size of the nano-crystalline grains in the high-strength and high-ductility 304 stainless steel is 251 nm.
Example 2
The composition of the micron (304) is as follows by mass percent: 18.62% of Cr, 0.57% of Mn, 5.38% of Ni, 0.13% of O, 0.91% of Si and the balance of iron; the grain size was 7 μm.
The nano (304+ La) comprises the following components in percentage by mass: 17.49% of Cr, 0.40% of Cu, 1.34% of Mn, 2.05% of La2, 0.078% of N, 12.36% of Ni, 0.21% of O, 0.002% of P, 0.89% of Si and the balance of iron; the particle size was 95 μm and the grain size was 37 nm.
The nano (304+ La) and the micron (304) are put into a ball milling tank according to the mass ratio of 7.5:2.5, the ball material ratio is 5:2, the rotating speed is 350rpm, and the mixture is uniformly mixed for 30 min. And (3) maintaining the pressure and the temperature for 45min by using a cubic hydraulic press under the conditions of 3GPa and 1100 ℃ high temperature and high pressure, and cooling for 10min by water after the temperature is maintained, so as to prepare a blank. And rolling the prepared blank by using the sheath, wherein the rolling temperature is 950 ℃. The rolling process adopts multi-pass deformation rolling, the rolling reduction is 1.5mm each time, the alloy is kept in a 950 ℃ high-temperature muffle furnace for 10min before each time of rolling, the final rolling thickness is 2mm, and the deformation is 75%. And after the last rolling is finished, cooling the alloy sample to room temperature in air. And then, filling Ar into the rolled alloy sample in a vacuum tube furnace, then preserving the temperature for 45min at 1100 ℃, carrying out annealing treatment, and cooling the alloy sample to room temperature along with the furnace after the heat preservation is finished, thereby obtaining the high-strength high-plasticity 304 stainless steel.
Example 3
The composition of the micron (304) is as follows by mass percent: 18.75% of Cr, 0.68% of Mn, 0.96% of Ni, 0.26% of O, 0.90% of Si and the balance of iron; the grain size was 9 μm.
The nano (304+ La) comprises the following components in percentage by mass: 18.50% of Cr, 0.42% of Cu, 0.68% of Mn, 2.36% of La2, 0.083% of N, 13.93% of Ni, 0.08% of O, 0.003% of P, 0.89% of Si and the balance of iron; the particle size was 93 μm and the grain size was 30 nm.
And (3) putting the nano (304+ La) and the micron (304) into a ball milling tank according to the mass ratio of 7:3, wherein the ball material ratio is 5:2, the rotating speed is 400rpm, and uniformly mixing for 45 min. And (3) maintaining the pressure and the temperature for 60min by using a cubic hydraulic press under the conditions of high temperature and high pressure of 5GPa and 1300 ℃, and cooling for 15min by water after the temperature is finished to prepare a blank. And rolling the prepared blank by using the sheath, wherein the rolling temperature is 900 ℃. The rolling process adopts multi-pass deformation rolling, the rolling reduction is 1mm each time, the alloy is subjected to heat preservation in a high-temperature muffle furnace at 900 ℃ for 15min before each time of rolling, the final rolling thickness is 2mm, and the deformation is 85%. And after the last rolling is finished, cooling the alloy sample to room temperature in air. And then, filling Ar into the rolled alloy sample in a vacuum tube furnace, preserving the temperature for 60min at 1000 ℃, carrying out annealing treatment, and cooling the alloy sample to room temperature along with the furnace after the heat preservation is finished to obtain the high-strength high-plasticity 304 stainless steel.
For the high-strength and high-plasticity 304 stainless steel and 304+ La nanocrystalline steel (components) prepared in examples 1 to 3Cr 18.50%, cu 0.36%, Mn 0.57%, La 1.54%, N0.079%, Ni 12.8%, O0.08%, P0.002%, Si 0.89%, and balance iron) and 304 microcrystalline steel (components Cr 18.59%, Mn 0.29%, Ni 2.58%, O0.066%, Si 0.84%, and balance iron) were wire cut, and both 304+ La nanocrystalline steel and 304 microcrystalline steel were prepared by the method of example 1, and tensile specimens (national standard: GBT228-2002), using a universal materials testing machine with an instrument model Instron5948 (manufacturer: instron, usa) at room temperature at a tensile rate of 5 x 10-4s-1The test results are shown in FIG. 8.
FIG. 8 shows: compared with 304+ La nanocrystalline steel, the elongation of the high-strength high-plasticity 304 stainless steel is greatly improved on the premise of keeping relatively good yield strength; compared with 304 micron crystal steel, the high-strength high-plasticity 304 stainless steel has obviously improved yield strength and tensile strength on the premise of keeping relatively good plasticity.
To ensure the repeatability of the experiment, 6 samples were cut per alloy while the tensile test was performed, and the results of the experiment were counted as shown in table 1.
TABLE 1 tensile test results
| Example 1 | Example 2 | Example 3 | 304+ La nanocrystalline steel | 304 micron crystal steel | |
| Tensile strength/MPa | 1440 | 1320 | 1257 | 2800 | 900 |
| Yield strength/MPa | 1146 | 1230 | 1080 | 2500 | 485 |
| Elongation/percent | 17 | 12 | 16 | 0.2 | 55 |
Note: the data in table 1 are the average of the test results.
As can be seen from Table 1, the high-strength and high-plasticity 304 stainless steel has the tensile strength of 1257-1440 MPa, the yield strength of 1080-1230 MPa and the elongation of 12-17%; the tensile strength of the 304+ La nanocrystalline steel is 2800MPa, the yield strength is 2500MPa, and the elongation is 0.2%; the tensile strength of the 304 micron crystal steel is 900MPa, the yield strength is 485MPa, and the elongation is 55%; the elongation rate of the high-strength high-plasticity 304 stainless steel is greatly improved on the premise of keeping relatively good yield strength compared with 304+ La nanocrystalline steel; compared with 304 micron crystal steel, the high-strength high-plasticity 304 stainless steel has obviously improved yield strength and tensile strength on the premise of keeping relatively good plasticity.
Fig. 9 is a comparison graph of strength and plasticity of 304 stainless steel (shown by a 304 micro-nano composite icon) prepared by the invention and the existing 304 stainless steel, and fig. 9 shows that the performance research of 304 stainless steel in the prior art mainly includes two directions, one of which is high in strength and good in plasticity, but the process is complex, has many parameters, is not easy to control, is high in cost and energy consumption, and does not meet the current national requirements for energy-saving and environment-friendly industrial production; the second one is that the heat treatment process is simple, the energy consumption is low, energy-saving and environment-friendly, and the requirements of the current country for industrial production are met, but the requirements of the industry for the strong plasticity of the 304 stainless steel material cannot be met. The invention integrates the advantages of the two directions, has simple process, few parameters, easy control, low energy consumption, energy saving and environmental protection, meets the current national requirements for industrial production, and simultaneously has good performances of high strength and high plasticity.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (7)
1. A preparation method of high-strength high-plasticity 304 stainless steel is characterized by comprising the following steps:
(1) ball-milling and mixing the first micron 304 stainless steel powder and the La solid-dissolved nano 304 stainless steel powder to obtain a mixture;
(2) pressing the mixture to obtain a green body;
(3) rolling the blank to obtain a rolled blank;
(4) annealing the rolled blank to obtain high-strength high-plasticity 304 stainless steel;
the particle size of the first micron 304 stainless steel powder in the step (1) is 5-13 microns;
the first micron 304 stainless steel powder comprises the following components in percentage by mass: 18.59-18.75% of Cr, 0.19-0.68% of Mn0.96-10.76% of Ni, 0.056-0.31% of O, 0.84-0.93% of Si and the balance of iron;
the grain diameter of the La solid solution nano 304 stainless steel powder in the step (1) is 90-96 mu m, and the grain diameter of the crystal grain is 17-31 nm;
the La solid solution nano 304 stainless steel powder comprises the following components in percentage by mass: 16.69-18.50% of Cr, 0.36-0.42% of Cu, 0.49-1.54% of Mn, 1.48-2.48% of La, 0.056-0.112% of N, 10.45-13.93% of Ni10, 0.06-0.30% of O, 0.002-0.003% of P, 0.89-0.94% of Si and the balance of iron;
the mass ratio of the first micron 304 stainless steel powder to the La solid solution nano 304 stainless steel powder in the step (1) is (2.5-3): (7-7.5).
2. The preparation method according to claim 1, wherein the La solid solution nano 304 stainless steel powder in the step (1) is prepared by mixing and ball-milling metal La and second micron 304 stainless steel powder.
3. The preparation method according to claim 1, wherein the pressing pressure in the step (2) is 3-5 GPa, the temperature is 1000-1300 ℃, and the pressure and heat preservation time is 30-60 min.
4. The production method according to claim 1, wherein the rolling manner in the step (3) is a jacket rolling.
5. The production method according to claim 1 or 4, wherein the rolling temperature in the step (3) is 900 to 1100 ℃ and the rolling deformation is 75 to 85%.
6. The method according to claim 1, wherein the annealing is performed at 1000 to 1200 ℃ for 30 to 60 min.
7. The high-strength high-plasticity 304 stainless steel prepared by the preparation method according to any one of claims 1 to 6 is characterized in that the high-strength high-plasticity 304 stainless steel is micro-nano composite crystal steel, and the grain size of nano crystal grains in the micro-nano composite crystal steel is 196 to 306 nm.
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