CN112481467A - Heat treatment method for improving strength of ferritic stainless steel - Google Patents
Heat treatment method for improving strength of ferritic stainless steel Download PDFInfo
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- CN112481467A CN112481467A CN202011287383.7A CN202011287383A CN112481467A CN 112481467 A CN112481467 A CN 112481467A CN 202011287383 A CN202011287383 A CN 202011287383A CN 112481467 A CN112481467 A CN 112481467A
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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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
- C21D6/00—Heat treatment of ferrous alloys
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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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- 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
- C21D2211/008—Martensite
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Abstract
The invention relates to ferritic stainless steel, in particular to a method for improving the strength of the ferritic stainless steel, and specifically relates to a heat treatment method for improving the strength of the ferritic stainless steel. The invention provides a novel heat treatment method for improving the strength of ferritic stainless steel, aiming at solving the problem of improving the strength of the ferritic stainless steel under the condition of keeping certain plasticity by a heat treatment method. The characteristics of high strength and good ferrite plasticity of a martensite structure are utilized to ensure the strength and the plasticity of the steel plate, and in addition, the retained austenite can generate martensite transformation in the subsequent deformation process to further improve the strength of the steel plate, and finally, the strength of the ferritic stainless steel is obviously improved.
Description
Technical Field
The invention relates to ferritic stainless steel, in particular to a method for improving the strength of the ferritic stainless steel, and specifically relates to a heat treatment method for improving the strength of the ferritic stainless steel.
Background
The ferritic stainless steel has good corrosion resistance and excellent forming performance, is widely applied to industries such as household appliances, buildings and the like, and is also very important in mechanical property as an important metal structure material in an application process. The mechanical property of the ferritic stainless steel (wherein the carbon content of the ferritic stainless steel is more than or equal to 0.01 and less than or equal to 0.30) is characterized by good plasticity and low strength (yield strength and tensile strength). The currently adopted heat treatment process is only a single recrystallization annealing treatment (for example, in the prior embodiment, the step of the recrystallization annealing process is to keep the temperature of a ferritic stainless steel cold-rolled plate with the thickness of 0.9 mm and the carbon content of 0.02 at 840 ℃ for 120min, and then cool the ferritic stainless steel to room temperature at the cooling rate of 10 ℃/min) to improve the strength of the ferritic stainless steel, the microstructure after the heat treatment is shown in figure 1, and it is obvious that the microstructure after the heat treatment only consists of a ferritic structure, and meanwhile, the strength and the plasticity of the ferritic stainless steel after the heat treatment are shown in table 1, and the mechanical properties of the ferritic stainless steel far do not exert the component advantages of the stainless steel, so that the application range of the ferritic stainless steel is very. In addition, although the prior art also has a heat treatment method capable of improving the strength of the ferritic stainless steel to a certain extent, the method obviously reduces the plasticity of the ferritic stainless steel while improving the strength, so that the application range of the ferritic stainless steel is very limited.
Table 1.
| Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | hardness/HV 0.1 |
| 295 | 530 | 28 | 198 |
Disclosure of Invention
The invention provides a novel heat treatment method for improving the strength of ferritic stainless steel, aiming at solving the problem of improving the strength of the ferritic stainless steel while keeping certain plasticity of the ferritic stainless steel by a heat treatment method.
The invention is realized by adopting the following technical scheme:
a heat treatment method for improving the strength of ferritic stainless steel, wherein the carbon content of the ferritic stainless steel is more than or equal to 0.01 and less than or equal to 0.30, and the method is realized by the following steps in sequence:
1) annealing the stainless steel plate: wherein the stainless steel plate is a ferritic stainless steel cold-rolled plate with the thickness less than or equal to 5.0mm (before heat treatment, the ferritic stainless steel is prepared into the ferritic stainless steel cold-rolled plate in advance, and how to prepare the ferritic stainless steel is well known by the personnel in the field), the heating temperature is 750-;
2) isothermal quenching of the stainless steel plate: the heating temperature is 950-;
3) and (3) dividing the quenched stainless steel plate: the heating temperature is 300-;
4) cooling the stainless steel plate after the distribution treatment to room temperature: the cooling speed is 10-50 ℃/min.
In the heat treatment method, the heating temperature and the heat preservation time in the step 1) enable the ferritic stainless steel cold-rolled plate to form fine recrystallized grains or crystal nuclei, and sufficient nucleation particles are provided for austenite phase transformation in the step 2), so that a fine austenite structure can be formed; the heating temperature and the holding time of the quenching in the step 2) form a certain content of austenite with small size (the austenite content after formation is 20-45%), at the moment, the microstructure consists of about 55-80% of ferrite structure and about 20-45% of austenite structure with small size, wherein, the function of forming the austenite structure with small size improves the stability of the austenite structure and ensures that the retained austenite structure does not generate martensite structure transformation in the cooling process in the step 3) and the step 4), in addition, the fine austenite structure generates incomplete martensite phase transformation and part of the austenite structure remains as the retained austenite structure in the following processes of the holding temperature and the holding time of the quenching medium, at the moment, the microstructure consists of 55-80% of ferrite structure, 4-10% of retained austenite structure, 16% -35% of martensite structure; the purpose of the temperature and the heat preservation time for the distribution treatment of the quenched stainless steel plate in the step 3) is to diffuse carbon elements in a martensite structure into a residual austenite structure, increase the carbon content in the residual austenite structure and improve the stability of the residual austenite structure, if the process is not carried out, the residual austenite structure is converted into a ferrite structure or a martensite structure, and the strength of the ferrite stainless steel is not enough or the plasticity is obviously weakened, in addition, the time for placing the stainless steel plate into a heating furnace from a quenching medium is not more than 50s, and if the stainless steel plate stays at room temperature for too long time, the residual austenite structure is also unstable; in the step 4), the plate after the distribution treatment is cooled to room temperature, the retained austenite structure is retained in the cooling process, but the cooling speed must be 10-50 ℃/min, if the cooling speed is too high, the retained austenite structure still undergoes martensite structure transformation, so that the strength of the ferritic stainless steel is improved, but the plasticity is obviously weakened. After the heat treatment, the microstructure of the ferritic stainless steel consists of 55-80% of ferrite structure, 4-10% of residual austenite structure and 16-35% of martensite structure.
The beneficial effects produced by the invention are as follows: the heat treatment method for improving the strength of the ferritic stainless steel can convert a ferrite structure in the ferritic stainless steel into a ferrite + martensite + austenite complex phase structure, fully utilizes the characteristics of high strength and good plasticity of a martensite structure, ensures the plasticity of the ferritic stainless steel by reserving a residual austenite structure and most of the ferrite structure, improves the strength of a stainless steel ferrite by a martensite structure after phase transformation, simultaneously, in the subsequent deformation (subsequent deformation: such as a tensile test or a process of processing a workpiece) process of the ferritic stainless steel after heat treatment, the residual austenite structure generates martensite transformation, thereby further improving the strength and the plasticity of the ferritic stainless steel (the subsequent deformation process belongs to deformation and improves the plasticity, the residual austenite structure generates martensite transformation and belongs to phase transformation, increasing its strength). By the heat treatment method, the strength of the ferritic stainless steel is improved under the condition that certain plasticity of the ferritic stainless steel is maintained, and the application range of the ferritic stainless steel is expanded.
Drawings
FIG. 1 is an exemplary view of a microstructure of a ferritic stainless steel using a conventional heat treatment method;
FIG. 2 is a schematic process diagram of the heat treatment method of the present invention;
FIG. 3 is an exemplary view of the microstructure of a ferritic stainless steel after heat treatment in example 1;
fig. 4 is a drawing curve of a ferritic stainless steel after three examples of the present invention and a conventional heat treatment method.
In the figure: wherein: alpha represents a ferrite structure; alpha is alpha’Represents a martensite structure; gamma represents an austenite structure; msRepresents the martensite start temperature point; mfRepresenting the martensite finish temperature point.
Detailed Description
A heat treatment method for improving the strength of ferritic stainless steel, wherein the carbon content of the ferritic stainless steel is more than or equal to 0.01 and less than or equal to 0.30 (for example, the carbon content is 0.01, 0.05, 0.08, 0.1, 0.16, 0.2, 0.23, 0.27 and 0.3), and the method is realized by the following steps in sequence:
1) annealing the stainless steel plate: wherein the stainless steel plate is a ferritic stainless steel cold-rolled plate (before heat treatment, the ferritic stainless steel is prepared into the ferritic stainless steel cold-rolled plate in advance, and how to prepare the ferritic stainless steel is well known to those skilled in the art) with the thickness of less than or equal to 5.0mm (for example, the thickness of 0.1mm, 0.5mm, 1.0mm, 1.6mm, 2mm, 2.4mm, 2.5mm, 3mm, 3.7mm, 4mm, 4.5mm, 4.9mm and 5.0 mm), the heating temperature is 750 ℃ and 850 ℃ (for example, the heating temperature is 750 ℃, 780 ℃, 800 ℃, 820 ℃ and 850 ℃), the heat preservation time is 1-30min (for example, the heat preservation time is 1min, 6min, 10min, 15min, 18min, 20min, 27min and 30 min), the temperature is preserved, and then the ferritic stainless steel plate is cooled to the room temperature, and the cooling rate is 5-20 ℃/min (for example, the cooling rate is 5 ℃/min, 8 ℃/min, 10 ℃/min, 15 ℃/min, 20 ℃/min);
2) isothermal quenching of the stainless steel plate: heating at 950 + 1050 deg.C (such as 950 deg.C, 1000 deg.C, 1009 deg.C, 1010 deg.C, 1015 deg.C, 1020 deg.C, 1030 deg.C, 1040 deg.C, 1042 deg.C, 1050 deg.C), holding for 2-30min (such as 2min, 5min, 8min, 10min, 16 min, 20min, 24 min, 30 min), rapidly placing into quenching medium at 140-180 deg.C (such as 140 deg.C, 145 deg.C, 150 deg.C, 160 deg.C, 166 deg.C, 170 deg.C, 178 deg.C, 180 deg.C), and retaining in the quenching medium for 10-60min (such as 10min, 15min, 20min, 30min, 36 min, 42 min, 45 min, 50min, 55 min, 60 min);
3) and (3) dividing the quenched stainless steel plate: heating at 300-;
4) cooling the stainless steel plate after the distribution treatment to room temperature: the cooling rate is 10-50 deg.C/min (such as 10 deg.C/min, 15 deg.C/min, 20 deg.C/min, 24 deg.C/min, 30 deg.C/min, 38 deg.C/min, 40 deg.C/min, 45 deg.C/min, and 50 deg.C/min).
As shown in FIGS. 2, 3 and 4, specific examples will be described below.
Example 1: keeping the temperature of a ferrite stainless steel cold-rolled plate with the carbon content of 0.01 and the thickness of 0.1mm at 760 ℃ for 5min, cooling to room temperature at the cooling rate of 10 ℃/min, heating to 1000 ℃, keeping the temperature for 10min, then quenching in a quenching medium (quenching medium is quenching oil), wherein the temperature of the quenching medium is 150 ℃, the quenching time is 50min, then placing in a 400 ℃ heat-preservation furnace, keeping the temperature for 30min, placing the quenching plate in the heating furnace from the quenching medium for 30s, and finally cooling to room temperature at the cooling rate of 50 ℃/min. The microstructure of the ferritic stainless steel after the heat treatment is shown in fig. 3, and it is apparent that the microstructure is composed of a ferrite structure, a martensite structure, and a retained austenite structure.
The ferritic stainless steel sheets subjected to the heat treatment were subjected to tensile properties and hardness tests, and the results are shown in table 2.
TABLE 2
| Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | hardness/HV 0.1 |
| 440 | 730 | 24 | 293 |
Example 2: keeping the temperature of a ferrite stainless steel cold-rolled plate with the carbon content of 0.1 and the thickness of 2mm at 840 ℃ for 10min, cooling to room temperature at the cooling rate of 20 ℃/min, heating to 980 ℃, keeping the temperature for 20min, then quenching in a quenching medium (the quenching medium is molten salt), the temperature of the quenching medium is 160 ℃, the quenching time is 30min, then placing the quenching medium into a 350 ℃ heat-preserving furnace, keeping the temperature for 60min, placing the quenching plate into the heating furnace from the quenching medium for 40s, and finally cooling to room temperature at the cooling rate of 40 ℃/min.
The steel sheets subjected to the heat treatment were sampled and subjected to tensile properties and hardness tests, and the results are shown in table 3.
TABLE 3
| Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | hardness/HV 0.1 |
| 470 | 725 | 20 | 294 |
Example 3: keeping the temperature of a ferrite stainless steel cold-rolled plate with the carbon content of 0.3 and the thickness of 5mm at 850 ℃ for 15min, cooling to room temperature at the cooling rate of 20 ℃/min, heating to 1050 ℃, keeping the temperature for 8min, then quenching in a quenching medium (the quenching medium is molten salt), the temperature of the quenching medium is 150 ℃, the quenching time is 30min, then placing the quenching medium into a 450 ℃ heat-preserving furnace, keeping the temperature for 20min, placing the quenching plate into a heating furnace from the quenching medium for 50s, and finally cooling to room temperature at the cooling rate of 30 ℃/min.
The steel sheets subjected to the heat treatment were sampled and subjected to tensile properties and hardness tests, and the results are shown in table 4.
TABLE 4
| Yield strength/MPa | Tensile strength/MPa | Elongation after break/% | hardness/HV 0.1 |
| 455 | 745 | 18 | 299 |
As can be seen by comparing the experimental data in the above embodiments of the present invention, such as tables 2, 3, and 4, with the experimental data in the prior embodiments, such as table 1, the ferritic stainless steel plate obtained by the heat treatment method of the present invention has good mechanical properties, particularly, the yield strength, tensile strength, and Vickers hardness are greatly improved, and the problem of low strength of the ferritic stainless steel is effectively solved while maintaining a certain plasticity.
Claims (2)
1. A heat treatment method for improving the strength of ferritic stainless steel, wherein the carbon content of the ferritic stainless steel is more than or equal to 0.01 and less than or equal to 0.30, and the method is characterized by comprising the following steps in sequence:
1) annealing the stainless steel plate: wherein the stainless steel plate is a ferrite stainless steel cold-rolled plate with the thickness less than or equal to 5.0mm, the heating temperature is 750-;
2) isothermal quenching of the stainless steel plate: the heating temperature is 950-;
3) and (3) dividing the quenched stainless steel plate: the heating temperature is 300-;
4) cooling the stainless steel plate after the distribution treatment to room temperature: the cooling speed is 10-50 ℃/min.
2. The heat treatment method for improving the strength of ferritic stainless steel according to claim 1, characterized in that in step 2), the quenching medium is quenching oil or molten salt.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114086087A (en) * | 2021-11-29 | 2022-02-25 | 中北大学 | Method for treating embrittled high-chromium ferritic stainless steel plate |
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