CN113025797B - High-strength medium manganese steel plate for low-temperature environment and preparation method thereof - Google Patents
High-strength medium manganese steel plate for low-temperature environment and preparation method thereof Download PDFInfo
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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
- C21D1/26—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
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
- C21D6/04—Hardening by cooling below 0 degrees Celsius
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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
- C21D2211/008—Martensite
Abstract
The invention relates to a high-strength medium manganese steel plate used in a low-temperature environment and a preparation method thereof, belonging to the technical field of steel preparation. According to the invention, cold treatment and low-temperature tempering are combined, so that the problems of structure embrittlement, hydrogen embrittlement and the like caused by transformation of risk Y of unstable performance into alpha phase due to low-temperature induced structure change of medium manganese steel in a low-temperature service environment are eliminated in advance. The preparation method can obviously enhance the low-temperature toughness and the stability of the high-strength medium manganese steel plate in a low-temperature environment, thereby obviously reducing the failure risk of the medium manganese steel plate in the low-temperature environment and improving the service stability and the safety of the medium manganese steel plate.
Description
Technical Field
The invention belongs to the technical field of steel preparation, and particularly relates to a high-strength medium manganese steel plate used in a low-temperature environment and a preparation method thereof.
Background
As a research hotspot of a new generation of advanced high-strength steel, the medium manganese steel has already realized good application in many fields. The medium manganese steel has excellent high plasticity and good low-temperature toughness. Due to the excellent low-temperature toughness of the medium manganese steel, the medium manganese steel has good application prospect and economic benefit in the related application field of low-temperature environment.
Chinese patent CN 104805378B discloses a high-strength and high-toughness ultra-low carbon medium manganese steel medium plate and a preparation method thereof, and emphasizes that the steel plate mainly comprising tempered martensite and reverse transformation austenite tissues is obtained after quenching to room temperature after hot rolling, then heat preservation is carried out for 50-100 min in a two-phase region (635-695 ℃) and cooling to room temperature, and the steel plate is mainly used for ocean platforms with lower service temperature.
Chinese patent CN109923233A discloses "medium manganese steel product for low temperature application and manufacturing method thereof", wherein the medium manganese steel structure is mainly martensite and reverse transformation austenite structure.
Both the above two patents are tissues mainly comprising martensite and reverse transformation austenite obtained by a medium manganese steel component system through a reverse transformation process of two-phase region heat preservation, and both the two patents are in service in a low-temperature environment. The medium manganese steel plate with the structure mainly comprising martensite and austenite is obtained after the medium manganese steel plate is heated and cooled to room temperature through the two-phase region, and the steel plates directly enter a low-temperature environment for use, so that certain risk is easily brought. Under the condition that the medium manganese steel structure possibly contains more reverse transformation austenite (5-30 vol.%), the serving low-temperature environment of the steel for ocean engineering can break through the martensite start transformation temperature (Ms point) of the reverse transformation austenite, and further part of the reverse transformation austenite is transformed into hard and brittle high-carbon martensite, namely the martensite of the type has poor deformability and high hardness, and cracks are easily formed under impact load; in addition, austenite acts as a hydrogen trap, and transformation of austenite causes a large amount of hydrogen to overflow due to reduction of the hydrogen trap, and once the transformation is accumulated at certain sensitive positions in the steel plate, the transformation easily causes hydrogen embrittlement of the steel plate, thereby causing hydrogen induced cracking and delaying the risk of fracture.
Disclosure of Invention
In view of the above problems, the present invention has been made to provide a high strength medium manganese steel sheet for low temperature environments and a method of manufacturing the same, which overcomes or at least partially solves the above problems.
The embodiment of the invention provides a preparation method of a high-strength medium manganese steel plate used in a low-temperature environment, which comprises the following steps:
obtaining a medium manganese steel plate;
heating the medium manganese steel plate to 580-620 ℃, preserving the heat for 10-80 min, and carrying out a two-phase region A c1 -A c3 Annealing treatment;
cooling the annealed medium manganese steel plate to-30 to-120 ℃, and preserving heat for 8 to 16 hours for cold treatment;
and (3) heating the cold-treated medium manganese steel plate to 150-300 ℃ for tempering, wherein the tempering time is 5-10 min/mm multiplied by the thickness mm of the medium manganese steel plate. And after tempering treatment, flaw detection procedures can be added according to actual technical conditions to eliminate the risk of hydrogen induced cracking in the medium manganese steel plate.
Optionally, the temperature of the medium manganese steel plate is increased to 580-620 ℃, the temperature is kept for 10-80 min, and a two-phase region A is carried out c1 -A c3 An annealing process comprising:
heating from room temperature to 580-620 ℃ at the speed of 2-5 ℃/min, preserving heat for 10-80 min, and cooling to room temperature after heat preservation.
Optionally, the annealing-treated medium manganese steel plate is cooled to-30 to-120 ℃ and kept warm for 8 to 16 hours, and the cold treatment comprises:
cooling from room temperature to-30 to-120 ℃ at the speed of 2-5 ℃/min, preserving heat for 8-16 h, and heating to room temperature after preserving heat.
Optionally, in the cold treatment, the temperature is reduced to-70 to-120 ℃.
Optionally, in the cold treatment, the cooling rate is 2 ℃/min.
In the cold treatment, the practical principle of the lowest heat preservation temperature is as follows: generally, the temperature of the medium manganese steel needs to be lower than the actual service environment temperature; preferably, the lowest heat preservation temperature of the cold treatment is 40-60 ℃ lower than the temperature of the service environment.
Optionally, the annealing-treated medium manganese steel plate is cooled to-30 to-120 ℃ and kept for 8 to 16 hours, and the cold treatment comprises the following steps:
performing cold treatment in a step cooling mode, wherein the temperature is firstly reduced to minus 30 to minus 50 ℃ from the room temperature at the speed of 2 to 5 ℃/min and is kept for 8 to 12min, the temperature is secondly reduced to minus 70 to minus 90 ℃ at the same speed after the first temperature reduction and is kept for 8 to 12min, the temperature is thirdly reduced to minus 100 to minus 120 ℃ at the same speed and is kept for 10 to 14h after the second temperature reduction, and the temperature is thirdly increased to the room temperature at the speed of 2 to 5 ℃/min after the third temperature reduction.
Optionally, in the low-temperature tempering, the temperature is raised from room temperature to 150-300 ℃ at the speed of 2-5 ℃/min, and the tempering time is 5-10 min/mm multiplied by the thickness of the medium manganese steel plate. After low-temperature tempering treatment, flaw detection procedures can be added according to actual technical conditions to eliminate the risk of hydrogen induced cracking in the medium manganese steel plate.
Optionally, the medium manganese steel plate comprises the following chemical components in percentage by mass: c:0.02 to 0.10%, si:0.15 to 0.30%, mn:4.0 to 8.0%, ti:0.008 to 0.025 percent, and the balance of Fe and inevitable impurities.
Based on the same inventive concept, the embodiment of the invention also provides a high-strength medium manganese steel plate used in a low-temperature environment, which is characterized in that the medium manganese steel plate comprises the following chemical components in percentage by mass: c:0.02 to 0.10%, si:0.15 to 0.30%, mn:4.0 to 8.0%, ti: 0.008-0.025%, and the balance of Fe and inevitable impurities.
Optionally, the metallographic structure of the medium manganese steel plate comprises, by volume: 74-90% of martensite and 10-26% of retained austenite, wherein, compared with the content of the martensite and the austenite in the structure after the temperature of the conventional two-phase region is preserved and then cooled to room temperature, the proportion of the martensite in the structure can be increased by 3-6% and the proportion of the austenite can be decreased by 3-6% after the treatment of the technology.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the preparation method of the high-strength medium manganese steel plate for the low-temperature environment, provided by the embodiment of the invention, comprises the following steps: obtaining a medium manganese steel plate; heating the medium manganese steel plate to 580-620 ℃, preserving the heat for 10-80 min, and carrying out a two-phase region A c1 -A c3 Annealing treatment; cooling the annealed medium manganese steel plate to-30 to-120 ℃, and preserving heat for 8 to 16 hours for cold treatment; and (3) heating the cold-treated medium manganese steel plate to 150-300 ℃ for tempering, wherein the tempering time is 5-10 min/mm multiplied by the thickness mm of the medium manganese steel plate. By adopting a production process of two-phase zone annealing, cold treatment and tempering treatment, part of relatively unstable austenite in the medium manganese steel is converted into martensite through the cold treatment in the treatment method, the hydrogen content in the steel is increased due to the austenite transformation serving as a hydrogen trap in the process, and the hydrogen is spilled or diffused from the steel into the nearby stable residual austenite (hydrogen trap) through the combination of the cold treatment and the low-temperature tempering, so that the problems of unstable performance of the medium manganese steel in service under a low-temperature environment due to low-temperature induced structure change, and structure embrittlement and hydrogen embrittlement caused by gamma-to-alpha phase transformation are solved in advance. The preparation method can obviously enhance the low-temperature toughness and the stability of the high-strength medium manganese steel plate in a low-temperature environment, thereby obviously reducing the failure risk of the medium manganese steel plate in the low-temperature environment and improving the service stability and the safety of the medium manganese steel plate.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a flowchart illustrating a method for manufacturing a high-strength medium manganese steel sheet for a low-temperature environment according to an embodiment of the present invention;
FIG. 2 is a process diagram illustrating a method for manufacturing a high-strength medium manganese steel sheet for use in a low-temperature environment according to an embodiment of the present invention;
FIG. 3 is an SEM photograph of a manganese steel sheet in comparative example 1 of the present invention;
FIG. 4 is an SEM photograph of a medium manganese copper plate in example 1 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are illustrative of the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
according to an exemplary embodiment of the present invention, there is provided a method for manufacturing a high-strength medium manganese steel sheet for use in a low temperature environment, as shown in fig. 1, the method including:
s1, obtaining a medium manganese steel plate;
s2, heating the medium manganese steel plate to 580-620 ℃, preserving the heat for 10-80 min, and carrying out a two-phase region A c1 -A c3 Annealing treatment;
s3, cooling the annealed medium manganese steel plate to-30 to-120 ℃, preserving heat for 8 to 16 hours, and performing cold treatment;
and S4, heating the cold-treated medium manganese steel plate to 150-300 ℃ for tempering, wherein the tempering time is 5-10 min/mm multiplied by the thickness mm of the medium manganese steel plate.
In this embodiment, after the medium manganese steel sheet is annealed in the two-phase region, the cold treatment and the low-temperature tempering treatment are sequentially performed, so that a part of reverse transformation austenite in the medium manganese steel sheet is transformed by the cold treatment process, and then the low-temperature tempering treatment is performed. The effect is as follows: on the one hand, the transformation of a portion of the relatively unstable reverse transformed austenite in the medium manganese steel sheet into martensite by cold treatment eliminates the risk of the reverse transformed austenite undergoing transformation in service in a low temperature environment, which, for example, remains in the final steel sheet product structure, is liable to cause the transformation of the portion of austenite into hard and brittle martensite in the low temperature service environment, thereby posing an uncontrolled risk. The newly transformed martensite is generally a hard and brittle high-carbon martensite, and by adding tempering treatment after cold treatment, the martensite obtained by quenching and the supersaturated martensite newly formed in the cold treatment process have a recovery effect, so that the risk of the brittleness tendency of the martensite in a low-temperature environment is reduced. On the other hand, through the tempering treatment after the cold treatment, the diffusibility of the discharged hydrogen in the steel due to reduction of austenite hydrogen traps can be improved, the hydrogen released due to austenite transformation after the cold treatment can be dispersed or diffused from the steel to the nearby stable residual austenite (hydrogen traps), and the risk of hydrogen embrittlement caused by austenite transformation of the medium manganese steel in the service process in a low-temperature environment can be eliminated by combining a flaw detection means.
Two-phase region A c1 -A c3 In the annealing treatment, the reasons for heating to 580-620 ℃ and keeping the temperature for 10-80 min are as follows: in order to fully ensure the formation of reverse transformed austenite in the structure and the stability and uniformity of the whole structure, the adverse effects of the over-high temperature and the under-low temperature are respectively: the overhigh temperature can cause the formation of excessive reverse transformed austenite, thereby causing the carbon content in the reverse transformed austenite to be lower, and the content and the stability of the reverse transformed austenite stored after the reverse transformed austenite is cooled to the room temperature are difficult to ensure; the low temperature results in less reverse transformation austenite generated in the two-phase region, which is difficult to ensureEnough reverse transformed austenite is continuously provided to ensure the toughness of the medium manganese steel, and the adverse effects of overlong heat preservation time and overlong heat preservation time are that the excessive heat preservation time can cause segregation caused by carbon diffusion and alloy diffusion in the heat preservation process of a two-phase region, so that the toughness is further influenced; the too short heat preservation time can cause the non-uniform mixed structure of reverse transformation austenite and martensite, and the expected structure with good gamma phase and alpha phase uniform distribution can not be achieved, thus finally affecting the performance of the medium manganese steel;
the reason for cooling to-30-120 ℃ and keeping the temperature for 8-16 h in the cold treatment is that: in order to transform the residual austenite in the structure, part of relatively unstable reverse transformation austenite in the medium manganese steel plate is transformed into martensite through cold treatment, so that the adverse effects caused by transformation of the residual austenite in a low-temperature service environment are avoided, wherein the adverse effects caused by overhigh temperature and overlow temperature are respectively as follows: the excessively high temperature can cause insufficient transformation of austenite, the excessively low temperature can cause excessive transformation of retained austenite to cause great change of performance, and further influence the use of products, and the adverse effects of excessively long and short heat preservation time are that after the purposes of effective homogenization and retained austenite transformation are achieved, respectively, the excessively long heat preservation time can cause cost increase and excessive transformation in a low-temperature environment, and the excessively short heat preservation time can cause insufficient transformation of retained austenite;
in the tempering treatment, the reason that the temperature is raised to 150-300 ℃ and the time is 5-10 min/mm multiplied by the thickness mm of the medium manganese steel plate is as follows: in order to ensure sufficient penetration of the medium manganese steel sheet, with additional homogenization of the structure and time for hydrogen discharge, the adverse effects of the excessively high and low temperatures are: the too low temperature can cause insufficient homogenization of the structure in the tempering process, the too high temperature can cause excessive precipitation of carbide in the structure to influence the final performance, the too long tempering treatment time and the too short adverse effect are respectively that the too long tempering treatment time can cause excessive precipitation, and the too short tempering treatment time can cause insufficient diffusion process of hydrogen to cause hydrogen embrittlement;
in this embodiment, the medium manganese steel sheet may be a hot rolled medium manganese steel sheet.
The high-strength medium manganese steel sheet for a low temperature environment and the method for manufacturing the same according to the present application will be described in detail with reference to examples, comparative examples, and related experiments.
Example 1
In the example, the chemical components of the medium manganese steel plate are as follows by mass fraction: c:0.02 to 0.1%, si:0.1 to 0.5%, mn:4 to 8%, cu:0.2 to 0.6%, ni:0.1 to 0.5%, cr:0.2 to 0.5%, mo:0.1 to 0.4%, ti: 0.005-0.01%, and the balance of Fe and inevitable impurities;
a group of steel plates with the thickness of 40mm of the chemical components are subjected to two-phase zone heating, the heating temperature is 580-620 ℃, and the heat preservation time is 80min. And after annealing and cooling to room temperature, placing the steel plate in a refrigerator within 0.5h, setting the cooling rate to be 2 ℃/min, cooling to-100 ℃, preserving heat for 12h, heating to room temperature at 2 ℃/min, and then tempering at 200 ℃ for 400min to obtain the medium manganese steel plate.
Example 2
In the example, the chemical components of the medium manganese steel plate are as follows by mass fraction: c:0.02 to 0.1%, si:0.1 to 0.5%, mn:4 to 8%, cu:0.2 to 0.6%, ni:0.1 to 0.5%, cr:0.2 to 0.5%, mo:0.1 to 0.4%, ti: 0.005-0.01%, and the balance of Fe and inevitable impurities;
the medium manganese steel plate with the thickness of 40mm of the chemical composition is heated in a two-phase region at 580-620 ℃ for 80min. And after annealing and cooling to room temperature, placing the steel plate in a refrigerator within 0.5h, setting the cooling rate to be 2 ℃/min, cooling to-50 ℃, then preserving heat for 10min, continuously cooling to-80 ℃ at the same cooling rate, preserving heat for 10min, finally cooling to-100 ℃, preserving heat for 12h, then heating to room temperature at 2 ℃/min, and then tempering at 200 ℃ for 400min to obtain the medium manganese steel plate.
Example 3
In the example, the chemical components of the medium manganese steel plate are as follows by mass fraction: c:0.02 to 0.1%, si:0.1 to 0.5%, mn:4 to 8%, cu:0.2 to 0.6%, ni:0.1 to 0.5%, cr:0.2 to 0.5%, mo:0.1 to 0.4%, ti: 0.005-0.01%, and the balance of Fe and inevitable impurities;
a group of steel plates with the thickness of 40mm of the chemical components are subjected to two-phase zone heating, the heating temperature is 580-620 ℃, and the heat preservation time is 80min. And after annealing and cooling to room temperature, placing the copper plate in a refrigeration box within 0.5h, setting the cooling rate to be 2 ℃/min, cooling to-100 ℃, preserving heat for 12h, directly placing the copper plate in the refrigeration box into a tempering furnace, and tempering at the temperature of 180 ℃ for 400min to obtain the medium manganese steel plate.
Example 4
In this example, the medium manganese copper plate comprises the following chemical components in mass fraction: c:0.02 to 0.1%, si:0.1 to 0.5%, mn:4 to 8%, cu:0.2 to 0.6%, ni:0.1 to 0.5%, cr:0.2 to 0.5%, mo:0.1 to 0.4%, ti: 0.005-0.01%, and the balance of Fe and inevitable impurities;
a group of steel plates with the thickness of 40mm of the chemical components are subjected to two-phase zone heating, the heating temperature is 580-620 ℃, and the heat preservation time is 80min. Annealing and cooling to room temperature, placing the steel plate in a low-temperature storage at-30 to-80 ℃ within 0.5h, keeping the temperature for 12h, taking out of the storage, and tempering at 250 ℃ for 400min to obtain the medium manganese steel plate.
Comparative example 1
In the example, the chemical components of the medium manganese steel plate are as follows by mass fraction: c:0.02 to 0.09%, si:0.1 to 0.5%, mn:4 to 8%, cu:0.2 to 0.6%, ni:0.1 to 0.5%, cr:0.2 to 0.5%, mo:0.1 to 0.4%, ti: 0.005-0.01%, and the balance of Fe and inevitable impurities;
the molten steel with the chemical components is sequentially smelted and cast to obtain a slab with the thickness of 400 mm. And heating, rolling, straightening and cooling the plate blank in sequence to obtain a steel plate with the thickness of 40 mm. And (3) heating one group of steel plates in a two-phase region at 580-620 ℃ for 80min, annealing and cooling, then keeping the temperature at 300 ℃ for 120min, and then cooling to room temperature to obtain the medium manganese steel plate.
Related experiments:
the middle manganese steel plates prepared in examples 1 to 4 and comparative example 1 were respectively placed in a low temperature environment of-60 ℃ for 12 hours, and then tensile and impact property tests were performed, and the test results are shown in table 1.
TABLE 1 comparison of mechanical properties of comparative examples and examples
As can be seen from Table 1, the strength and toughness of the steel plates of the examples are improved as a whole after the steel plates are treated by the technology, and particularly, the low-temperature impact performance is obviously improved.
Detailed description of the drawings:
fig. 3 is an SEM photograph of the manganese steel sheet in comparative example 1 of the present invention, and the arrows in fig. 3 indicate retained austenite in bulk, and the presence of retained austenite in the manganese steel sheet has an adverse effect that a small amount of retained austenite in bulk in the structure undergoes martensitic transformation to form hard and brittle high-carbon martensite in a low-temperature environment of-60 ℃. In the process of bearing impact, the newly formed high-carbon martensite in the low-temperature environment and the nearby austenite have larger hardness difference, so that microcracks firstly sprout from the high-carbon martensite or an alpha/gamma interface, and the low-temperature toughness of the steel is further deteriorated;
fig. 4 is an SEM photograph of the medium manganese steel sheet according to example 1 of the present invention, and the arrows in fig. 4 represent decomposed retained austenite, and the positive effect of decomposing the retained austenite is that the retained austenite having low stability can be transformed into martensite in advance by the process described in this patent, and the newly formed martensite is toughened by low temperature tempering, so that the possibility of crack initiation and propagation near the martensite is reduced, and the toughness of the steel is further optimized.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (5)
1. A method for manufacturing a high-strength medium manganese steel sheet for use in a low-temperature environment, the method comprising:
obtaining a medium manganese steel plate;
heating the medium manganese steel plate to 580-620 ℃, preserving the heat for 10-80 min, and carrying out a two-phase region A c1 -A c3 Annealing treatment;
cooling the annealed medium manganese steel plate to-30 to-120 ℃, and preserving heat for 8 to 16 hours for cold treatment;
heating the cold-treated medium manganese steel plate to 150-300 ℃ for tempering, wherein the tempering time is 5-10 min/mm multiplied by the thickness mm of the medium manganese steel plate;
heating the medium manganese steel plate to 580-620 ℃, preserving heat for 10-80 min, and carrying out two-phase region A c1 -A c3 Annealing treatment, comprising:
heating from room temperature to 580-620 ℃ at the speed of 2-5 ℃/min, preserving heat for 10-80 min, and cooling to room temperature after heat preservation;
the annealing treatment of the medium manganese steel plate is carried out by cooling to-30-120 ℃ and keeping the temperature for 8-16 h, and the cold treatment comprises the following steps: performing cold treatment in a step cooling mode, wherein the temperature is firstly reduced to minus 30 to minus 50 ℃ from the room temperature at the speed of 2 to 5 ℃/min and is kept for 8 to 12min, the temperature is secondly reduced to minus 70 to minus 90 ℃ at the same speed after the first temperature reduction and is kept for 8 to 12min, the temperature is thirdly reduced to minus 100 to minus 120 ℃ at the same speed and is kept for 10 to 14h after the second temperature reduction, and the temperature is thirdly increased to the room temperature at the speed of 2 to 5 ℃/min after the third temperature reduction.
2. The method of claim 1, wherein the cooling rate is 2 ℃/min in the cold treatment.
3. The method of claim 1, wherein the tempering is performed at a rate of 2-5 ℃/min from room temperature to 150-300 ℃, and the tempering time is 5-10 min/mm x the thickness of the middle manganese steel plate.
4. The method for manufacturing a high-strength medium manganese steel sheet for use in a low-temperature environment according to claim 1, wherein the medium manganese steel sheet comprises the following chemical components in mass fraction: c:0.02 to 0.10%, si:0.15 to 0.30%, mn:4.0 to 8.0%, ti:0.008 to 0.025 percent, and the balance of Fe and inevitable impurities.
5. A high-strength medium manganese steel sheet for low-temperature environments manufactured by the method of any one of claims 1 to 4, comprising the following chemical components in mass fraction: c:0.02 to 0.10%, si:0.15 to 0.30%, mn:4.0 to 8.0%, ti:0.008 to 0.025 percent, and the balance of Fe and inevitable impurities;
the metallographic structure of the medium manganese steel plate comprises the following components in percentage by volume: 74 to 90 percent of martensite and 10 to 26 percent of retained austenite.
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