CN111826507A - Ultrahigh-yield-ratio steel and production process thereof - Google Patents
Ultrahigh-yield-ratio steel and production process 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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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
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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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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- 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
- C21D2211/002—Bainite
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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 provides a steel with ultrahigh yield ratio and a production process thereof.A dislocation source is provided by pre-strain treatment after strip steel is rapidly cooled, and dislocation pinning strengthening treatment is adopted after the pre-strain treatment; wherein the cross pinning strengthened steel belongs to low alloying steel, and the carbon content is 0.02-0.77%; the production process comprises the following steps: the process path is as follows: cold-rolled strip steel → continuous annealing → rapid cooling → pre-strain treatment → dislocation pinning strengthening treatment, the ultrahigh yield ratio steel of the scheme has enough plasticity and good welding performance. The method can be used for manufacturing parts which need good shape stability, high deformation resistance and high hole expansion requirements, such as parts of automobile battery guard plates, bumpers, seat guide rails, reinforcements, measuring tools and the like. It can also be used to manufacture spring steels requiring a high elastic limit.
Description
Technical Field
The invention relates to the fields of steel materials and metallurgy, in particular to steel with ultrahigh yield ratio and a production process thereof.
Background
The manufacture of some automotive parts has given high resistance to deformation to the materials used, requiring adequate shape stability and high yield strength, such as battery packs, seat rails, bumper beams, reinforcements, etc. The high-strength steel on the market at present comprises series products such as DP, CP, MP, TRIP, Q & P and the like, which have high enough tensile strength, but the materials have complex production process, or high cost, or have low yield strength, so that the production and use requirements cannot be well met.
Disclosure of Invention
The invention aims to provide an ultrahigh yield ratio steel with sufficiently high yield strength and a production process thereof.
In order to achieve the purpose, the technical scheme provided by the invention is as follows: a steel with ultrahigh yield ratio and a production process thereof are disclosed, wherein a dislocation source is provided through pre-strain treatment after strip steel is rapidly cooled, and dislocation pinning strengthening treatment is adopted after the pre-strain treatment; wherein the cross pinning strengthened steel belongs to low alloying steel, and the carbon content is 0.02-0.77%; the production process comprises the following steps:
the process path is as follows: cold-rolled steel strip → continuous annealing → rapid cooling → pre-strain treatment → dislocation pinning strengthening treatment, wherein,
1) the annealing temperature is the temperature and time for ensuring partial or complete austenitizing of the strip steel, the annealing temperature is 730-900 ℃, and the heat preservation time is more than or equal to 30 seconds;
2) the rapid cooling ensures that the martensite phase transformation exists, and the cooling rate is more than or equal to 15 ℃/s;
3) providing enough dislocation sources through pre-strain treatment, wherein the total deformation of the dislocation sources is 0.02-10%;
4) the temperature of sufficient dislocation pinning strengthening treatment is 100-550 ℃;
5) and sufficient dislocation pinning strengthening treatment time is more than or equal to 1 minute.
Preferably, the pre-strain treatment is rolling, straightening, bending, and the pre-strain treatment is an in-line continuous treatment.
Preferably, the yield strength of the steel strip after the dislocation pinning treatment is improved by at least 35MPa compared with that of the steel strip after rapid cooling.
Preferably, the composite material with the metal coating or the nonmetal coating is prepared by hot dipping, electroplating and coating processes before or after the pre-strain treatment and the dislocation pinning strengthening treatment.
Preferably, an aging treatment process is added after the rapid cooling.
Preferably, a flattening and straightening process is added after the dislocation pinning strengthening treatment.
Preferably, the microstructure is a ferrite-based material containing martensite, tempered martensite and retained austenite in a total volume fraction of at least 10%.
Preferably, the dislocation pinning strengthening process is a continuous process or an off-line cap process.
Preferably, the mechanical properties satisfy a ratio of yield strength to tensile strength of 0.65 or more.
The yield strength of the ultrahigh yield ratio steel is higher than that of DP steel, CP steel and the like which have the same components and are subjected to the quenching process, and the ultrahigh yield ratio steel has enough plasticity and good welding performance. The method can be used for manufacturing parts needing good shape stability and high deformation resistance, such as structural parts of bumpers, seat guide rails, reinforcements and the like of automobiles. The ultrahigh yield ratio steel belongs to cold-rolled strip steel, and mainly utilizes pinning effect formed by interstitial atoms to dislocation to improve yield strength. The heat treatment process is characterized in that after the strip steel is rapidly cooled, pre-strain treatment is carried out to provide enough dislocation sources, and then dislocation pinning strengthening treatment is carried out to improve the yield strength.
Drawings
FIG. 1 is a microstructure of the present invention.
FIG. 2 is a stress-strain-tensile curve of the present invention.
Fig. 3 is a stress-strain tensile curve with an upper yield strength according to the present invention.
FIG. 4 is a chemical composition comparison table of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings, in which preferred embodiments of the invention are: referring to fig. 1 to 4, the ultrahigh yield ratio steel of the present embodiment has sufficient plasticity and good welding performance, and simultaneously has high plastic deformation resistance, and can be used for manufacturing parts or safety structural members which maintain stable shapes under the action of high stress and are not easy to generate plastic deformation. Compared with DP, CP and other steels with the same components and quenching process, the plasticity of the invention is slightly reduced, but the yield strength is higher, and even the tensile strength is increased. Therefore, the production method provided by the invention has low cost, and the produced product has stable and reliable performance.
1949 Cootrell and Bilby propose the Coriolis gas mass theory, explaining the pinning effect of interstitial atoms in BCC and FCC grains on dislocations. The ultrahigh yield ratio steel mainly utilizes the phenomenon of pinning of dislocation by interstitial atoms such as C, N and the like so as to improve the upper yield strength of the steel. The continuous heat treatment process of the invention is mainly characterized in that: the strip steel needs to be subjected to pre-strain treatment after being rapidly cooled, so that enough deformation is provided; and heating and insulating the strip steel after pre-straining to form dislocation pinning strengthening.
The heat treatment process can be that after the strip steel is rapidly cooled, the deformation of more than or equal to 0.02% -10% or higher deformation amount is carried out, and then the dislocation pinning strengthening treatment of more than or equal to 1 minute at 100-550 ℃ is carried out. The preferred dislocation pinning strengthening treatment process can be carried out on the strip steel for 1-20 minutes at 300-450 ℃. Or treating at 200-300 deg.c for 2-25 min. Or treating at 150-250 ℃ for 3-30 minutes. The longer the treatment time, the lower the treatment temperature can be.
After the dislocation pinning process, the strip may have an upper yield point, as shown in fig. 4, which may result in an upper yield point strength greater than or equal to the tensile strength under a certain process treatment. However, at a certain dislocation pinning strengthening treatment temperature, the amount of increase in strength and the amount of pre-strain treatment are approximately linear, and there is also a certain relationship between the tensile strength and the dislocation pinning strengthening treatment. There is also a relationship between the quenching temperature before the pre-strain treatment, the aging temperature and the strength improvement. Therefore, the dislocation pinning strengthening temperature can be researched by determining the heat treatment process, the ultrahigh yield ratio steel with a proper strength range can be designed by matching with the pre-strain amount, and the phenomenon that the upper yield point is more than or equal to the tensile strength can be designed or avoided according to the requirement.
The tensile strength is a critical value of uniform plastic deformation and local concentrated plastic deformation transition after the material is subjected to yield deformation, and is not just the maximum stress value under the static stretching condition. For a material that yields continuously, it is the maximum stress value under static tensile conditions. For materials with upper and lower yield points, the maximum stress value after yield deformation of the material under static tensile conditions occurs.
Fitting equations for estimating yield strength and tensile strength are provided below, and are used for assisting in designing ultrahigh-yield-ratio steel with proper strength, and the definition domain and coefficient of the equations need to be determined according to actual material characteristics.
(1) When the conditions such as processing temperature and time are fixed, the calculation method of the yield strength variation and the deformation amount can be approximated as follows:
wherein:
QUOTE
-yield strength variation, MPa;
QUOTE
-a first order item coefficient;
QUOTE
-amount of pre-strain deformation,%;
QUOTE
-a constant.
(2) Under other conditions, the calculation method of the yield strength variation and the dislocation pinning strengthening treatment temperature can be approximated as follows:
wherein:
QUOTE
-yield strength variation, MPa;
QUOTE
-a quadratic term coefficient;
QUOTE
-dislocation pinning strengthening treatment temperature, deg.c;
QUOTE
-a first order item intensity coefficient;
QUOTE
-a constant.
(3) Under other conditions, the calculation method of the tensile strength variation and the dislocation pinning strengthening treatment temperature can be approximated as follows:
wherein:
QUOTE
-tensile strength variation, MPa;
QUOTE
-cubic degree coefficients;
QUOTE
-dislocation pinning strengthening treatment temperature, deg.c;
QUOTE
-a quadratic term intensity coefficient;
QUOTE
-a first order item coefficient;
QUOTE
-a constant.
The ultrahigh yield ratio steel belongs to low-alloying steel, and the chemical components can meet the following requirements: c% is 0.02% -0.25%; si is 0.08 to 2.2 percent; mn is 0.8 to 3.0 percent; p is less than or equal to 0.08 percent; s is less than or equal to 0.03 percent; cr + Mo is less than or equal to 1.4 percent, and Nb + Ti is less than or equal to 0.5 percent; b is less than or equal to 0.005 percent; v is less than or equal to 0.25 percent; cu is less than or equal to 0.20 percent; more than or equal to 0.01 percent of Al, and the balance of Fe and inevitable impurity elements. The strip steel adopts a component scheme with lower carbon equivalent so as to obtain good welding performance, and the general carbon equivalent is less than or equal to 0.8 percent by adopting the following formula for calculation.
Chemical components more favorable for welding: c% is 0.02% -0.10%; si% is 0.1% -0.4%; mn is 1.0 to 2.8 percent; p is less than or equal to 0.05 percent; s is less than or equal to 0.025 percent; b is less than or equal to 0.005 percent; cr is less than or equal to 0.5 percent; mo is less than or equal to 0.5 percent; v is less than or equal to 0.5 percent; ni is less than or equal to 0.5 percent; nb is less than or equal to 0.15 percent; ti is less than or equal to 0.15 percent; al is more than or equal to 0.01 percent, wherein Cr + Mo is less than or equal to 1.4 percent, and Nb + Ti is less than or equal to 0.20 percent. The balance of Fe and inevitable impurity elements. And the carbon equivalent is less than or equal to 0.65 percent. The above alloy composition can be further reduced to reduce the carbon equivalent for improving the weldability.
The annealing temperature of the strip is selected to be in the partial or full austenitizing temperature region. During rapid cooling, the austenite will have martensite, bainite, retained austenite and other phase transformation, and the microstructure of the steel with ultrahigh yield ratio is ferrite as matrix, and the volume fractions of martensite, tempered martensite and retained austenite are at least 10%. Therefore, the microstructure of the ultrahigh yield ratio steel is a dual-phase or multi-phase structure containing martensite, bainite, retained austenite, and the like, with ferrite as a matrix.
The pre-strain treatment aims to provide enough dislocation sources for dislocation pinning strengthening treatment, generally can adopt deformation modes such as rolling, bending, pulling and straightening, and the like, is on-line continuous treatment, namely, different steel coils are kept to be subjected to head and tail butt welding after being uncoiled during production, and continuous production is realized.
The invention utilizes the influences of the Coriolis effect, martensite tempering, the participation of austenite decomposition, the precipitation of second phase particles and the like to improve the yield limit or the upper yield strength, thereby improving the yield ratio or the elastic limit. The Coriolis gas mass effect and the effect of second phase particles on dislocation pinning are mainly applied, one purpose of the dislocation pinning treatment is to enable C, N and other gap atoms to be gathered in the dislocation direction after obtaining energy during the dislocation pinning treatment to form Coriolis gas mass, and therefore pinning is formed on the dislocation. In fact, during rapid cooling, free dislocations are present around the martensite, which also provide strengthening of the dislocation pinning. The ultrahigh yield ratio steel utilizes the pinning strengthening effect of C, N and other interstitial atoms on dislocations, and C, N and other interstitial atoms hinder the movement of dislocations during the deformation of the ultrahigh yield ratio steel, so that the yield strength of steel is improved. Thus increasing the amount of pre-strain increases the dislocation density, causing the effect of pinning by interstitial atoms to be more pronounced. In particular, the pre-strain treatment increases the dislocation density, causing an increase in the number of pinned dislocations, resulting in an increase in the Coriolis gas mass density and an increase in the yield strength. And the upper yield strength is caused to appear, and when the comprehensive effect of each strengthening reaches a certain degree, such as Coriolis gas masses, second-phase particle pinning, strain hardening and the like, the ultrahigh yield effect that the upper yield strength is close to or more than or equal to the tensile strength can appear.
On the other hand, the improvement of yield strength is also related to precipitation strengthening of the second phase particles. The increase of the pre-strain amount can cause the decomposition of the retained austenite to form martensite, namely, the deformation induced transformation effect, and simultaneously cause the precipitation of carbides in ferrite and martensite to increase, thereby improving the yield strength. Within a certain range, the yield strength is improved by raising the temperature of the dislocation pinning treatment, fine precipitates are present in the medium martensite, and more precipitates are present with the increase of the tempering temperature, but simultaneously the precipitates become coarse, and carbides in the martensite are gradually spheroidized. The movement of dislocation nails can be hindered by the precipitation of the second phase, and the strengthening effect generated by the precipitated phase can ensure that the strip steel obtains greater strengthening effect under the condition that the second phase is small in size and large in quantity. However, as the temperature increases, martensite is decomposed, ferrite is recrystallized, dislocation density is decreased, and strength is lowered. For the non-deformable second phase particles, the dislocation can bypass the second phase to generate dislocation increment and dislocation loops, and the stress required by deformation is improved, namely the Olympic precipitation strengthening. When the second phase is deformable, dislocations will pass through the mass point to cause coherent strain, and certain strengthening effect occurs due to elastic interaction.
The occurrence of the upper yield point can be explained as being related to the solute existing in the metal, the Coriolis gas mass formed by dislocation of solute atoms has a pinning effect on dislocations, and the dislocations need to obtain higher energy when being pinned by breaking loose the gas mass, so that the yield point is increased, or the upper yield point is increased. When the dislocations break loose the atomic pinning, the energy required for the dislocations to move is reduced.
In addition, the hot-dip process can be added after cooling to realize the production of the steel with the ultrahigh yield ratio of the metal coating. In order to obtain more C, N equi-gap atoms in the dislocation pinning process, an overaging process can be added before the pre-strain treatment. After the dislocation pinning strengthening treatment, the processes of flattening, pulling and straightening and the like can be added to improve the plate shape and the surface quality.
Preferably, when the ultrahigh yield ratio steel has the upper yield strength, the upper yield strength is more than or equal to 500 MPa; when the yield strength is not high, the stress (namely the yield strength) corresponding to 0.2 percent deformation is more than or equal to 500 MPa. The tensile strength is more than or equal to 600 MPa.
Preferably, when the ultrahigh yield ratio steel has the upper yield strength, the upper yield strength is more than or equal to 650 MPa; when the yield strength is not high, the stress (namely the yield strength) corresponding to 0.2 percent deformation is more than or equal to 650 MPa. The tensile strength is more than or equal to 800 MPa.
Preferably, when the ultrahigh yield ratio steel has the upper yield strength, the upper yield strength is more than or equal to 850 MPa; when the yield strength is not high, the stress (namely the yield strength) corresponding to 0.2 percent deformation is more than or equal to 850 MPa. The tensile strength is more than or equal to 1000 MPa.
Preferably, when the ultrahigh yield ratio steel has the upper yield strength, the upper yield strength is more than or equal to 1000 MPa; when the yield strength is not higher, the stress (namely the yield strength) corresponding to 0.2 percent deformation is more than or equal to 1000 MPa. The tensile strength is more than or equal to 1200 MPa.
Increasing the temperature of the dislocation pinning strengthening treatment is beneficial to improving the hole expansion rate. After the dislocation pinning strengthening treatment, martensite is tempered to reduce the hardness, the interface strength of phases is enhanced, and particularly, the invention provides that the dislocation pinning strengthening treatment is adopted to improve the strength of ferrite. The comprehensive result is that the strength of each phase and interface tends to be consistent, the energy required by crack propagation is improved, the initiation and propagation of cracks in martensite, phase boundaries and ferrite are more uniform, and the hole expansion rate is improved. Therefore, the temperature of the dislocation pinning strengthening treatment is increased, which is also advantageous for increasing the hole expansion rate.
Generally, for materials with the tensile strength of more than or equal to 600MPa, the hole expansion rate is improved by at least 5 percent; for the material with the tensile strength more than or equal to 1000MPa, the hole expansion rate is improved by at least 10 percent. If under proper components and process conditions, for example, when the temperature of dislocation pinning strengthening treatment is more than or equal to 250 ℃, the hole expansion rate can be more than or equal to 40 percent; when the temperature of the dislocation pinning strengthening treatment is more than or equal to 350 ℃, the hole expansion rate can reach 50 percent. Even the effects of dislocation pinning strengthening treatment and tempering are integrated, the parameters such as the process and the like are further optimized, the tensile strength is more than or equal to 1000MPa, and the hole expansion rate can reach 90%.
Preferably, the tensile strength is not less than 600MPa and the hole expansion ratio is not less than 50%.
Preferably, the steel sheet has a tensile strength of 600MPa or more and a hole expansion ratio of 60% or more.
Preferably, the tensile strength is not less than 800MPa and the hole expansibility is not less than 45%.
Preferably, the steel sheet has a tensile strength of not less than 800MPa and a hole expansion ratio of not less than 55%.
Preferably, the tensile strength is not less than 1000MPa and the hole expansion ratio is not less than 40%.
Preferably, the steel sheet has a tensile strength of 1000MPa or more and a hole expansion ratio of 50% or more.
Preferably, the tensile strength is generally 1200MPa or more and the hole expansion ratio is 35% or more.
Preferably, the steel sheet has a tensile strength of 1200MPa or more and a hole expansion ratio of 45% or more.
In order to explain the characteristics of the present invention, the control group added with the same chemical composition is explained from the following four aspects of chemical composition, process path, metallographic structure and mechanical properties.
The chemical components are shown in the table in the attached figure 4, and note that: other elements that improve hardenability are not listed.
The process route of the invention 1 is as follows: cold-rolled steel strip → annealing → rapid cooling → galvanizing → pre-modification → dislocation strengthening → leveling. Wherein:
1) annealing temperature 760 ℃ for 2 minutes;
2) the rapid cooling rate is 45 ℃/s;
3) the pre-deformation amount is 0.5 percent;
4) dislocation strengthening treatment time is 5 minutes, and the treatment temperature is 200 ℃;
5) and the leveling elongation is 0.5%.
Secondly, the process route of the invention 2 is as follows: cold-rolled steel strip → annealing → rapid cooling → galvanizing → pre-modification → dislocation strengthening → leveling. Wherein:
1) annealing temperature 760 ℃ for 2 minutes;
2) the rapid cooling rate is 45 ℃/s;
3) the pre-deformation amount is 1.0 percent;
4) dislocation strengthening treatment time is 5 minutes, and the treatment temperature is 300 ℃;
5) and the leveling elongation is 0.5%.
Thirdly, the process route of the comparison group is as follows: cold-rolled steel strip → annealing → rapid cooling → galvanization → flattening. Wherein:
1) annealing temperature 760 ℃ for 2 minutes;
2) the rapid cooling rate is 45 ℃/s;
3) and the leveling elongation is 0.5%.
Microstructure of
Through the above treatment, the present invention and the control group had similar microstructures. The metallographic microscopic structure of the invention is shown in the figure, and comprises a microstructure structure of ferrite, martensite, tempered martensite, a small amount of bainite and the like, wherein the volume ratio of the sum of the martensite, the tempered martensite and the residual austenite is more than or equal to 25 percent.
Mechanical properties: the yield strength is the lower yield strength, or stress corresponding to 0.2% without a yield plateau.
As shown in FIG. 2, the present invention 1 had a yield strength of 985MPa, a tensile strength of 1020MPa and an elongation of 10%. Compared with the control group, although the elongation of the invention is reduced by 3%, the yield strength of the strip steel is increased by 349MPa, and the yield ratio reaches 0.97. The yield ratio of the invention 2 reached more than 1.04, and the ultra-high yield effect that the upper yield strength became the highest stress point on the tensile curve appeared.
The yield strength of the ultrahigh yield ratio steel is higher than that of DP steel, CP steel and the like which have the same components and are subjected to the quenching process, and the ultrahigh yield ratio steel has enough plasticity and good welding performance. The method can be used for manufacturing parts needing good shape stability and high deformation resistance, such as structural parts of bumpers, seat guide rails, reinforcements and the like of automobiles. The present invention can provide a steel material having an ideal ultra-high yield effect if the structural member is required to obtain high shape stability regardless of adverse effects caused by stress concentration. If a protective plate made of ultrahigh yield effect steel is added to the battery, the protective plate is ensured to be elastically deformed or only subjected to limited plastic deformation when being impacted, and internal circuits are protected from being extruded to short circuits. And steel with ultrahigh yield effect can be adopted as the measuring tools of some precise instrument structural parts and metal materials. It can also be used to manufacture spring steels requiring a high elastic limit.
The ultrahigh yield ratio steel belongs to cold-rolled strip steel, and utilizes the pinning effect formed by interstitial atoms to dislocation to improve the yield strength. The heat treatment process is characterized in that after the strip steel is rapidly cooled, pre-strain treatment is carried out to provide enough dislocation sources, and then dislocation pinning strengthening treatment is carried out to improve the yield strength.
Claims (10)
1. The steel with ultrahigh yield ratio and the production process thereof are characterized in that: after the strip steel is rapidly cooled, a dislocation source is provided through pre-strain treatment, and dislocation pinning strengthening treatment is adopted after the pre-strain treatment so as to improve the mechanical properties such as yield strength, hole expansion rate and the like; wherein, the steel with ultrahigh yield ratio belongs to low-alloying steel, and the carbon content is 0.02 to 0.77 percent; the ratio of the yield strength to the tensile strength is more than or equal to 0.85;
the production process comprises the following steps:
the process path is as follows: cold-rolled steel strip → continuous annealing → rapid cooling → pre-strain treatment → dislocation pinning strengthening treatment, wherein:
1) the annealing temperature is the temperature and time for ensuring partial or complete austenitizing of the strip steel, the annealing temperature is 730-900 ℃, and the heat preservation time is more than or equal to 30 seconds;
2) the rapid cooling ensures that the martensite phase transformation exists, and the cooling rate is more than or equal to 15 ℃/s;
3) providing enough dislocation sources through pre-strain treatment, wherein the total deformation of the dislocation sources is 0.02-10%;
4) providing enough dislocation pinning strengthening treatment temperature, wherein the temperature is 100-550 ℃;
5) and providing enough time for strengthening the dislocation pinning for more than or equal to 1 minute.
2. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the pre-strain treatment is rolling, straightening and bending, and the pre-strain treatment is on-line continuous treatment; the yield strength of the band steel after the dislocation pinning treatment is at least improved by 35MPa compared with that of the band steel after the band steel is rapidly cooled.
3. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: before or after the pre-strain treatment and the dislocation pinning strengthening treatment, the composite material with the metal coating or the nonmetal coating is prepared by adopting hot dipping, electroplating and coating processes.
4. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: adding an aging treatment process after the rapid cooling; and after the dislocation pinning strengthening treatment, a flattening and straightening process is added.
5. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the microstructure is a material with ferrite as a matrix, and the sum of the volume fractions of martensite, tempered martensite and retained austenite is at least 10%.
6. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the dislocation pinning strengthening treatment is continuous treatment or off-line cover type treatment; the hole expansion rate of the band steel after the dislocation pinning treatment is at least improved by 5 percent compared with that of the band steel after the rapid cooling.
7. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the mechanical properties satisfy: when the temperature of the dislocation pinning strengthening treatment is increased, the hole expanding rate is favorably increased, and when the tensile strength is more than or equal to 1000MPa and the temperature of the dislocation pinning strengthening treatment is more than or equal to 250 ℃, the hole expanding rate is more than or equal to 40 percent; when the temperature of the dislocation pinning strengthening treatment is more than or equal to 350 ℃, the hole expansion rate is more than or equal to 50 percent.
8. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the yield ratio is as follows: 1) if an upper yield strength is present: yield ratio = upper yield strength ÷ tensile strength; 2) if no upper yield strength is present: yield ratio = strength at 2% deformation ÷ tensile strength.
9. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: the chemical composition, the prestrain amount, the dislocation pinning strengthening treatment temperature and other processes can be adjusted as required, the ultrahigh yield ratio steel with a proper yield strength range is designed, and the phenomenon that the upper yield point is greater than or equal to the tensile strength is designed or avoided.
10. The steel with ultra-high yield ratio and the production process thereof as claimed in claim 1, wherein: when the method is used for producing spring steel, the raw materials are cold-rolled strip steel, bars, wires, plates and profiles.
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| CN114799059A (en) * | 2022-06-06 | 2022-07-29 | 江苏吉鑫风能科技股份有限公司 | High-temperature-resistant combined sand box module and preparation process thereof |
| CN115110001A (en) * | 2022-06-27 | 2022-09-27 | 洪泽永振精密管业有限公司 | High-strength fine steel pipe and preparation method thereof |
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| CN115110001A (en) * | 2022-06-27 | 2022-09-27 | 洪泽永振精密管业有限公司 | High-strength fine steel pipe and preparation method thereof |
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