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WO1998023785A1 - Plaque d'acier a haute resistance mecanique dotee d'une forte resistance a la deformation dynamique et procede de fabrication correspondant - Google Patents

Plaque d'acier a haute resistance mecanique dotee d'une forte resistance a la deformation dynamique et procede de fabrication correspondant Download PDF

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Publication number
WO1998023785A1
WO1998023785A1 PCT/JP1997/004359 JP9704359W WO9823785A1 WO 1998023785 A1 WO1998023785 A1 WO 1998023785A1 JP 9704359 W JP9704359 W JP 9704359W WO 9823785 A1 WO9823785 A1 WO 9823785A1
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Prior art keywords
less
deformation
strain
temperature
steel sheet
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PCT/JP1997/004359
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English (en)
Japanese (ja)
Inventor
Osamu Kawano
Yuzo Takahashi
Junichi Wakita
Hidesato Mabuchi
Manabu Takahashi
Akihiro Uenishi
Riki Okamoto
Yukihisa Kuriyama
Yasuharu Sakuma
Original Assignee
Nippon Steel Corporation
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First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=27521028&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO1998023785(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Priority claimed from JP33138096A external-priority patent/JPH10158735A/ja
Priority claimed from JP22300597A external-priority patent/JPH1161326A/ja
Priority claimed from JP25883497A external-priority patent/JP3530353B2/ja
Priority claimed from JP25888797A external-priority patent/JP3530355B2/ja
Application filed by Nippon Steel Corporation filed Critical Nippon Steel Corporation
Priority to EP97913471.5A priority Critical patent/EP0952235B2/fr
Priority to US09/308,986 priority patent/US6319338B1/en
Priority to AU50679/98A priority patent/AU711873B2/en
Priority to CA002273334A priority patent/CA2273334C/fr
Publication of WO1998023785A1 publication Critical patent/WO1998023785A1/fr

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Classifications

    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • 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
    • 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
    • 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
    • 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
    • C21D8/0273—Final recrystallisation annealing

Definitions

  • the present invention relates to a high-strength hot-rolled steel sheet having a high dynamic deformation resistance, which is used for automobile members and the like and can contribute to ensuring occupant safety by efficiently absorbing impact energy at the time of a collision.
  • the present invention relates to a high-strength cold-rolled steel sheet and a method for producing the same.
  • the present inventors reported in C AMP—ISIJ Vol. 9 (1996) pp. 11 12 to 11 15 that the high-speed deformation characteristics and impact energy absorption capacity of a high-strength thin steel plate were reported. and, in which, 1 0 3 (1 / s) about dynamic strength at high strain rate region of, 1 0 (1 / s) low The fact that the strength increases significantly compared to the static strength at the strain rate, and that the strain rate dependence of the deformation resistance changes due to the strengthening mechanism of the material.
  • TRIP Transformation Induced Plasticity
  • DP Light Z martensite two-phase
  • Japanese Patent Application Laid-Open No. 7-183732 discloses a high-strength steel sheet excellent in impact resistance including residual austenite and a method for manufacturing the same. It discloses that the solution can be solved only by the accompanying increase in yield stress, but it is clear how to control the properties of residual austenite other than the amount of residual austenite in order to improve the shock absorption capacity. It has not been.
  • the present invention provides a high-strength steel sheet exhibiting high impact energy absorbing capability, which is a steel material formed into a part that absorbs impact energy at the time of collision, such as a front side member, and used. The purpose is to do that.
  • a high impact energy absorption capacity according to the present invention is shown.
  • the microstructure of the finally obtained steel sheet contains finalite and / or veneite, and one of these microstructures is used as the main phase, and the residual austenite of 3 to 50% by volume fraction is used.
  • a composite structure of a third phase comprising bets, or one after giving 0% and 1 0% or less pre-deformation in equivalent strain, 5 X 1 0 2 ⁇ 5 X 1 0 3 of (1 / s)
  • the average value of the deformation stress ⁇ dyn (MPa) in the equivalent strain range of 3 to 10% when deformed in the strain rate range is 5 xl 0 " 4 to 5 X 1 before applying the pre-deformation — 3 (1 / s) satisfying the formula CT dyn ⁇ 0.766 x TS + 250 expressed by the maximum stress TS (MPa) in the static tensile test measured in the strain rate range of It is a high-strength steel sheet with high dynamic deformation resistance that satisfies a work hardening index
  • a high-strength steel sheet having a high dynamic deformation resistance in which the value of the work hardening index at the yield strength X strain of 1 to 5% satisfies 40 or more in the above (1).
  • the microstructure of the finally obtained steel sheet contains ferrite, Z or bainite, and any of these is the main phase, and the volume fraction is 3 to 50%.
  • residual austenite Ri composite structure der the third phase containing Bok, and after giving 0% and 1 0% or less pre-deformation in equivalent strain, 5 X 1 0 2 ⁇ 5 X 1 0 3 (1 /
  • the difference is 30% or more of the residual austenite volume fraction before giving the pre-deformation, the work hardening index of strain 1 to 5% is 0.080 or more, and the average crystal of the residual austenite
  • the particle size is 5 zm or less, and the ratio between the average crystal particle size of the residual austenite and the average crystal particle size of ferrite or bainite as the main phase is 0.6 or less.
  • the average particle size of the main phase is 10 m or less, preferably 6 m or less, the volume fraction of martensite is 3 to 30%, and the average crystal grain size of the martensite is 10 m. In the following, it is preferable that the particle size is not more than 5 ⁇ m and the volume fraction of the light is not less than 40%. Ratio 8 5% or less, a high-strength steel sheet having a high dynamic deformation resistance tensile strength X total elongation values 2 0, 0 0 0 or more that it is to satisfy either.
  • the high-strength steel sheet of the present invention has a C content of not less than 0.03% and not more than 0.3% by weight, and a total of at least one of Si and A1 or not less than 0.5%. 3.0% or less, if necessary, include one or more of Mn, Ni, Cr, Cu, and Mo in a total of 0.5% or more and 3.5% or less, with the remainder Fe A high-strength steel plate mainly composed of Nb, Ti, V, P, B, C a, and REM, if necessary.
  • Ti, V one or more of them are 0.3% or less in total, 0.3% or less for P, 0.01% or less for B, and Contains 0.005% or more and 0.01% or less, and REM: 0.05% or more and 0.05% or less, with the balance having high dynamic deformation resistance mainly composed of Fe. High strength steel plate.
  • the high-strength hot-rolled steel sheet having high dynamic deformation resistance As a production method, the continuous production slab having the component composition of the above (4) is directly sent to a hot rolling process as it is, or is cooled once, heated again, and then hot rolled. 3 — 50 ° C to Ar 3 + 120 ° C Finish hot rolling at a finishing temperature of 5 ° C. After cooling in the cooling process following hot rolling, the average cooling rate is 5 ° CZ seconds or more.
  • the microstructure of the hot-rolled steel sheet which is characterized in that it is wound at a temperature of 0 ° C or less, contains ferrite and / or veneite, with either one as the main phase and a volume fraction of 3 1-5 0% of the composite structure of the third phase containing residual austenite, and after giving equivalent to 0% and 1 0% or less pre-deformation at strain, 5 X 1 0 2 - 5 X 1 0 Three
  • the average value of the deformation stress ⁇ dyn (MPa) in the equivalent strain range of 3 to 10% when deformed at the strain rate range of (1 / s) is 5 XI 0 — 4 to 5 ⁇ before the pre-deformation is given.
  • the high-strength cold-rolled steel having a high dynamic deformation resistance according to the present invention.
  • a continuous production slab having the component composition of the above (4) is directly sent to a hot rolling process as it is, or is cooled once, then heated again, and then hot rolled.
  • More specific cooling conditions after annealing are as follows: 0.2 IX (A c 3 -A c,) + After annealing for 10 seconds to 3 minutes at a temperature of A c, ° C or more and A c 3 + 50 ° C or less, At the primary cooling rate of 10 ° CZ seconds, the secondary cooling start temperature Tq in the range of 550 ° C to 720 ° C is cooled to Tq, and then the secondary cooling rate of 1 (! ⁇ 200 ° CZ seconds) The temperature determined by the steel material composition and the annealing temperature T0: After cooling to the secondary cooling end temperature Te of not less than Tem-100 ° C and not more than Tem, it is not less than 50 ° C of Te-50 ° C.
  • the microstructure of the finally obtained cold-rolled steel sheet which is kept at a temperature Toa of 0 ° C or less for 15 seconds to 20 minutes and cooled to room temperature, is characterized by ferrite and Z or bainite, which is the main phase, and has a composite structure with the third phase containing 3 to 50% by volume residual austenite, and the equivalent strain exceeds 0% 1 after giving 0% following pre-deformation, the average of 5 X 1 0 2 ⁇ 5 X 1 0 3 deformation stress in the equivalent strain range of 3 to 1 0% when deformed in a strain rate range of (1 / s)
  • the value ⁇ dyn (MPa) gives the predeformation
  • CT dyn ⁇ 0 expressed by the maximum stress TS (MP a) in a static tensile test measured in the strain rate range from the previous 5 xl 0 "to 5 X 1 (J — 3 (1 / s).
  • Figure 1 is an indication of the impact energy absorbing ability at the time of collision in the present invention, 5 X 1 0 2 ⁇ 5 X 1 0 3 (1 / s) 3 ⁇ 1 0% when deformed in a strain rate range of FIG. 7 is a diagram showing the relationship between the average value of the deformation stress ff dyn — TS and TS in the equivalent strain range of FIG.
  • Fig. 2 is a graph showing the relationship between the work hardening index at 1-5% strain and the dynamic energy absorption (J) of a steel sheet.
  • Figure 3 is a graph showing the relationship between the yield strength of steel sheets and the work hardening index at 1% to 5% strain and the dynamic energy absorption (J).
  • Fig. 4a is a schematic view of the parts (hat model) used in the impact crush test for measuring the dynamic energy absorption in Fig. 3.
  • Fig. 4b is a cross-sectional view of the test piece used in Fig. 4a.
  • Figure 4c is a schematic diagram of the impact crush test method.
  • FIG. 5 is a diagram showing the relationship between ⁇ T and metallographic parameter A in the hot rolling step in the present invention.
  • FIG. 6 is a diagram showing the relationship between the winding temperature and the metallurgical parameter A in the hot rolling step in the present invention.
  • FIG. 7 is a schematic diagram showing an annealing cycle in a continuous annealing step according to the present invention.
  • FIG. 8 is a view showing the relationship between the secondary cooling stop temperature (T e) and the subsequent holding temperature (T o a) in the continuous annealing step of the present invention.
  • Impact absorbing members such as front side members of automobiles in the event of a collision are manufactured by bending and pressing a steel plate. You. The impact of a car collision is applied after processing in this way, typically after paint baking. Therefore, it is necessary to have a steel sheet that exhibits high impact energy absorption capacity after being processed into parts and subjected to paint baking.
  • the present inventors have conducted long-term studies on high-strength steel sheets as shock-absorbing members that satisfy the above-mentioned requirements, and as a result, in such molded real parts, the steel sheets contain an appropriate amount of residual austenite. This proved to be suitable for high-strength steel sheets exhibiting excellent shock absorption characteristics.
  • the optimal microstructure includes a filament and / or bainite which is easily solid-solution-enhanced by various types of substitutional elements. It has been found that when it has a composite structure with a third phase containing 3 to 50% by volume of residual austenite that transforms into hard martensite, it exhibits high dynamic deformation resistance. It has been found that even in the case of a composite structure containing martensite in the third phase of the initial microstructure, a high-strength steel sheet with high dynamic deformation resistance can be obtained if certain conditions are satisfied. Was.
  • the present inventors have conducted experiments and studies based on the above findings, and as a result, the amount of pre-deformation corresponding to the forming process of a shock absorbing member such as a front side member is maximum at some parts. Although it may reach 20% or more, it was also found that most of the parts had an equivalent strain of more than 0% and 10% or less. Therefore, it was found that by grasping the effect of pre-deformation in this range, it is possible to estimate the behavior of the entire member after pre-deformation. Therefore, in the present invention, a deformation of more than 0% and not more than 10% is selected as a considerable strain as a pre-deformation amount given at the time of working the member.
  • Fig. 1 shows the deformation rate in the range of 5 X 10 2 to 5 X 10 3 (1 / s), which is an index of the impact energy absorption capacity at the time of collision in the present invention.
  • Impact absorbing members such as the front side member have a hat-shaped cross-sectional shape. Although deformation is progressing to a high strain of 40% or more, it is found that 70% or more of the total absorbed energy is absorbed in a strain range of 10% or less in a high-speed stress-strain diagram. Was. Therefore, the dynamic deformation resistance at the time of high-speed deformation of 10% or less was adopted as an index of the absorption capacity of the collision energy at high speed.
  • the mean stress of from 3 to 1 0% of the high-speed deformation shed dyn are the static tensile strength of the steel material prior to pre-deformation and baked come with processing is performed ⁇ 5 X 1 0 - 4 ⁇ 5 X 1 0 - 3
  • it increases with increasing TS (MPa) ⁇ in a static tensile test measured in the strain rate range of (1 / s). Therefore, increasing the static tensile strength of steel (which is synonymous with static material strength) directly contributes to the improvement of the impact energy absorption capacity of the member.
  • the strength of the steel material increases, the formability of the member deteriorates, and it becomes difficult to obtain a required member shape.
  • a steel material with the same tensile strength (TS) and high cr dyn is desirable. From this relationship, 0% after giving ultra-1 0% or less pre-deformation, 5 X 1 0 2 - 5 X 1 0 3 (1 / s) 3 ⁇ 1 0% when deformed in a strain rate range of Of deformation stress in equivalent strain range sigma dyn (MPa) is 5 x 1 0 one 4 ⁇ 5 x 1 0 before giving pre-deformation '- 3 (1 Z s) the maximum stress TS in static tensile test as measured at a strain rate range of ( MPa), the steel material that satisfies the formula ⁇ dyn _ TS ⁇ — 0.234 x TS + 250 has a higher shock absorbing energy absorption capacity as a real member than other steel materials.
  • the present inventors increased the work hardening at the time of pre-working represented by a work hardening index of 1 to 5% of strain, thereby increasing the initial deformation at the start of the collision. It was also found that it is necessary to increase the ff dyn by increasing the work hardening during collision deformation through the presence of martenside transformed during pre-deformation, in addition to increasing the resistance.
  • the work hardening index of the steel is higher than 0.080, preferably 0.10.
  • the above-mentioned collision safety can be enhanced by setting the work hardening index of not less than 8 and the yield strength X strain of 1 to 5% to a work hardening index of 40 or more, preferably 54 or more.
  • the dynamic energy absorption which is an index of the collision safety of automotive components
  • the work hardening index and yield strength X work hardening index of the steel sheet the dynamic energy absorption increases as these values increase.
  • the work hardening index of the steel sheet at the same yield strength level, and the yield strength of the steel sheet at different yield strengths It is considered appropriate to evaluate with the X work hardening index.
  • the dynamic energy absorption is shown in Figure 4a, 4b and 4c.
  • the work hardening index of the steel sheet with a strain of 1 to 5% and the yield strength X were obtained as follows. That is, a steel sheet is processed into a JIS-5 test piece (gauge length 5 O mm, parallel part width 25 mm), and a tensile test is performed at a strain rate of 0.001 ZS, yield strength and work hardening index ( 11 values of distortion 1-5%) were obtained.
  • an appropriate amount of residual austenite is present in the steel sheet, it is transformed into a very hard martensite by being distorted during deformation (during forming).
  • the appropriate amount of residual austenite mentioned above is preferably 3% to 50%.
  • the volume fraction of residual austenite is less than 3%, the member after molding cannot exhibit excellent work hardening ability when subjected to collision deformation, and the deformation load remains at a low level and the deformation work Since the amount is small, the amount of dynamic energy absorption is low, so that it is not possible to achieve an improvement in collision safety, and it is not possible to obtain a high tensile strength X total elongation due to insufficient squeezing suppressing effect.
  • the volume fraction of residual stenite exceeds 50%, continuous deformation due to slight forming distortion occurs. Chain-like process-induced martensite transformation occurs, and it is not possible to expect an increase in tensile strength X total elongation.On the contrary, the hole expansion ratio deteriorates due to remarkable hardening during punching, and further molding of components Even if this is possible, the above-mentioned residual austenite amount is determined from the viewpoint that the member after molding cannot exhibit excellent work hardening ability when subjected to collision deformation.
  • the average crystal grain size of the residual austenite should be 5 m or less, preferably 3 ⁇ m or less. Is a desirable condition. Even if the volume fraction of the residual austenite satisfies 3% to 50%, if the average crystal grain size exceeds 5 m, the residual austenite cannot be finely dispersed in the steel. This is not preferable because the action of improving the properties of the residual austenite stops locally.
  • the ratio between the average grain size of the residual austenite and the average grain size of ferrite or bainite, which is the main phase is 0.6 or less, and It has been found that when it has a microstructure such that the average grain size of the particles is 10 m or less, preferably 6 zm or less, it exhibits excellent collision safety and formability. .
  • the present inventors have found that, for the same level of tensile strength (TS: MPa), the average stress: adyn in the range of 3% to 10% with the above-mentioned equivalent strain is processed into a member.
  • the amount of solute carbon in the residual austenite contained in the previous steel sheet: expressed in [C], (wt%) and the average Mn equivalent of the steel material (Mneq): Mneq Mn + ( N i + C r + C u + M o) Z 2.
  • the carbon concentration in the residual austenite can be determined experimentally by X-ray analysis or Messbauer spectroscopy.
  • the X-ray analysis using Mo K-rays makes it possible to obtain the (200 ) Plane, (2 1 1) plane and austenite Calculated by the method shown in Journal of The Iron and Steel Institute, 206 (1968), p60, using the integrated reflection intensity of the (2 0 0), (2 2 0), and (3 1 1) planes. it can. From the experimental results conducted by the present inventors, the amount of solute carbon in the residual austenite obtained in this way [C] and the M n eq obtained from the substitutional alloy element added to the steel material were used.
  • M 6 7 8 — 4 2 8 x [C] 1 3 3 x M n eq is 70 or more and 250 or less, and the residual austenite volume integral before pre-deformation is given Difference between the residual austenite volume fraction (V 5 ) after applying a 5% pre-deformation with equivalent strain and the equivalent strain: ⁇ (V.) _ (V 5) ⁇ before the pre-deformation It was also found that when the residual austenite volume fraction was 30% or more, a large ⁇ dyn was shown for the same static tensile strength (TS).
  • the residual austenite is adjacent to ferrite.
  • the volume is 40% or more, preferably 60% or more, and the average crystal grain size (corresponding to the average equivalent circle diameter) is 10 / zm or less. Preferably it is less than 6 zm.
  • the fluoride is the softest of the constituent structures, it is an important factor that determines the work hardening index and yield ratio of yield strength x strain of 1 to 5%. Therefore, it is preferable that the volume fraction is within the regulation value. Furthermore, since the carbon content of untransformed austenite is increased and finely dispersed by increasing the volume fraction of the ferrite and refining, the fineness of the martensite and the remaining structure generated from the untransformed austenite is reduced. It effectively acts to increase the volume fraction of residual austenite and to make it finer, and contributes to the improvement of crash resistance and formability.
  • the martensite has a volume fraction of 3% to 30% and an average crystal grain size (corresponding to an average circle equivalent diameter) of 10 zm or less, preferably 6 ⁇ m or less. I prefer that there be.
  • Martensite contributes to the reduction of the yield ratio and the improvement of the work hardening index by generating mobile dislocations mainly in the surrounding furnaceite.
  • the work hardening index ⁇ 54 and the yield ratio ⁇ 75% with more preferable characteristic levels of yield strength X strain 1-5% can be achieved.
  • the relationship between the volume fraction of the martensite and the average crystal grain size is that even if the volume fraction is small or the average crystal grain size is large, the effect is limited to local effects, Cannot be satisfied.
  • the martensite is adjacent to the ferrite.
  • the high-strength steel sheet used in the present invention is, by weight%, C: 0.03% or more and 0.3% or less, and one or both of Si and A1 in a total of 0.5% or more and 3.0% or more.
  • C 0.03% or more and 0.3% or less
  • Si and A1 in a total of 0.5% or more and 3.0% or more.
  • Mn, Ni, Cr, Cu, and Mo are included in a total of 0.5% or more and 3.5% or less, and the remainder is mainly composed of Fe.
  • C is the most important element in the present invention because it is the cheapest element that contributes to stabilization of austenite, which is necessary for stabilizing and retaining austenite at room temperature.
  • the average C content of steel not only affects the residual austenite volume fraction that can be secured at room temperature, but also stabilizes the residual austenite during processing by concentrating in the untransformed austenite during the thermomechanical heat treatment. Performance can be improved. However, if the addition amount is less than 0.03%, the residual austenite volume fraction of 3% or more cannot be finally secured, so the lower limit was made 0.03%.
  • the residual austenite volume fraction that can be secured increases as the average C content of the steel increases, and it becomes possible to secure the stability of the residual austenite while securing the residual austenite volume fraction.
  • the amount of C added to the steel material is excessive, the strength of the steel material is unnecessarily increased, not only impairing the formability of press working and the like, but also increasing the static strength.
  • the upper limit of the amount of c was set to 0.3% in order to restrict the use of steel as a part due to the fact that the increase in stress would be hindered and the weldability would be degraded. .
  • Both S i, A 1 are stabilizing elements of the fly, and have the function of improving the workability of steel by increasing the ferrite volume fraction.
  • both Si and A1 suppress the generation of cementite and allow C to be effectively enriched in austenite
  • the volume fraction at an appropriate volume fraction at room temperature can be obtained.
  • the additional element having such a function of suppressing the generation of cementite include P, Cu, Cr, and Mo in addition to Si and A1, and such an element is appropriately added. This is expected to have the same effect.
  • the upper limit was set to 3.5% to reduce the workability and toughness of the steel material and further increase the cost of the steel material.
  • Nb, Ti, and V which are added as necessary, are the forces that can increase the strength of steel by forming carbides, nitrides, or carbonitrides. If it exceeds 3%, a large amount of carbides, nitrides, or carbonitrides precipitates in the ferrite or bainite grains, which are the parent phase, or at the grain boundaries, As a source of movable dislocations during high-speed deformation, high dynamic deformation resistance cannot be obtained. Further, the formation of carbides inhibits the enrichment of C in residual austenite, which is the most important for the present invention, and wastes C, so the upper limit was set to 0.3%.
  • B or P is added as needed.
  • B grain boundary strengthening
  • the addition amount exceeds 0.01%, the effect is saturated and the steel sheet strength is increased more than necessary, reducing the deformation resistance during high-speed deformation.
  • the upper limit was set to 0.01%.
  • P is effective in increasing the strength of steel and securing residual austenite.
  • the content of S contained as an unavoidable impurity is set to 0.01% or less from the viewpoint of the formability (particularly the hole expansion ratio) due to the sulfide inclusions and the prevention of deterioration of the spot weldability. Is desirable.
  • Ca is added in an amount of 0.0005% or more in order to improve the formability (particularly the hole expansion ratio) by controlling the form (spheroidization) of the sulfide inclusions, but the effect is saturated.
  • the upper limit was set to 0.01% from the viewpoint of the opposite effect (deterioration of hole expansion ratio) due to the increase in the inclusions. Since REM also has the same effect as Ca, the addition amount is set to 0.005% to 0.05%.
  • the method for producing the high-strength hot-rolled steel sheet and the cold-rolled steel sheet having high dynamic deformation resistance includes, as a production method, directly sending a continuous production slab having the above-described component composition to a hot rolling step as it is produced Or, after cooling once and heating again, hot rolling is performed.
  • a hot rolling in addition to normal continuous forming, thin-wall continuous forming and hot rolling continuous (Endless rolling) is also possible, but considering the decrease in the volume fraction of the fly and the coarsening of the average crystal grain size of the microstructure of the thin steel sheet, the billet on the hot-rolling side of the finish is considered.
  • the thickness (initial billet thickness) is preferably 25 mm or more.
  • the finishing temperature in the above-mentioned hot rolling is determined by the chemical composition of the steel material, and is a temperature between Ar 3 — 50 ° C and Ar 3 + 120 ° C. It is preferable to do it in a range.
  • Ar 3 _50 ° C effluent is generated, deteriorating the dynamic deformation resistance CT dyn, work hardening ability by 1 to 5%, and formability.
  • Ar 3 + 120 ° C the steel sheet microstructure becomes coarse, etc., which degrades the dynamic deformation resistance CT dyn, the work hardening ability of 1 to 5%, and is also preferable from the viewpoint of scale flaws. Absent .
  • the steel sheet hot-rolled as described above enters a winding step, but is cooled on a runtable before that.
  • the average cooling rate at this time is 5 ° CZ sec or more.
  • the cooling rate is determined from the viewpoint of securing the austenite space factor.
  • This cooling method may be performed at a fixed cooling rate, or may be a combination of a plurality of types of cooling rates including a low cooling rate area in the middle.
  • the hot-rolled steel sheet enters a winding step, and is preferably wound at a winding temperature of 500 ° C or less. If the winding temperature exceeds 500 ° C, the residual austenite space factor will decrease. If you want to obtain a martensite, set the winding temperature to 350 ° C or less.
  • the above-mentioned winding conditions are the conditions when the rolled steel sheet is used as it is after the winding, and when the cold-rolled steel sheet is further cold-rolled and annealed for use. Does not require the above-mentioned limiting conditions, and may be wound under normal manufacturing conditions. In particular, in the present invention, it has been found that there is a correlation between the finishing temperature in the hot rolling process, the finishing temperature, and the winding temperature.
  • the finishing temperature of hot rolling is A r 3 - In 5 0 ° C ⁇ A r 3 + 1 2 0 ° temperature range and C, main cod Jiparame over data one: A Chikaraku, (1) and (2) Hot rolling is performed to satisfy the formula.
  • the meta-parameter: A can be represented as follows.
  • ⁇ * (V / V R X h.) x ( ⁇ ⁇ ⁇ ⁇ ) ⁇ 1 ⁇ ⁇ 1 / (1-r
  • Thickness on the last pass entrance side h Thickness on the last pass exit side r: (h I-h 2 ) / h IR: Lorenole diameter
  • a r 3 90 1-32 C% + 33 S i%-92 M n. q Thereafter, the average cooling rate in the run table is set to 5 ° CZ seconds or more, and furthermore, the relationship between the above-mentioned metal parameter: A and the winding temperature (CT) satisfies the expression (3). It is preferable to wind up under conditions. 9 ⁇ 1 og A ⁇ 1 8 (1)
  • the lower limit of ⁇ is relaxed by a decrease of 10 gA.
  • the winding temperature does not satisfy the relationship of the equation (3), the amount of the residual a becomes adversely affected, and even when the residual 7 is obtained, the residual a becomes excessively stable, and is being deformed.
  • the transformation of the residual metal proceeds, the transformation does not sufficiently occur in the low strain region, and the dynamic deformation resistance and dyn, and the work hardening ability of 1 to 5% are deteriorated.
  • the limit of the winding temperature is relaxed by increasing 1 ogA.
  • C T ⁇ 350 ° C may be set. However, it is preferable to set C T ⁇ 250 ° C from the viewpoint of suppressing excessive martensite formation.
  • the cold-rolled steel sheet according to the present invention is obtained by subjecting the steel sheet that has undergone the steps of hot rolling and winding to cold rolling at a rolling reduction of 40% or more, and then annealing the cold-rolled steel sheet. Attached to For this annealing, continuous annealing with an annealing cycle as shown in Fig. 7 is optimal. When the final product is annealed, 0.1 IX (A c-A c, + A c!
  • annealing temperature To is determined by the chemical composition of the steel material. IX (Ac-Ac,) + Ac ⁇ ° expressed by the temperatures A c and A c 3 (for example, “Steel materials science”: WC Leslie, Maruzen.
  • the temperature is less than C, the amount of austenite obtained at the annealing temperature is small, so that it is not possible to stably leave residual austenite in the final steel sheet. 0.
  • the annealing temperature is A c + 50 ° C under can not any improve the properties of the steel sheet exceeds, moreover to the upper limit of the annealing temperature in order to cause the co-be sampled rose A c 3 + 5 0 ° C .
  • Annealing time at this temperature the steel sheet A minimum of 10 seconds or more is required to make the temperature uniform and secure the amount of austenite. However, if the time exceeds 3 minutes, the effect becomes saturated and causes an increase in cost.
  • the primary cooling is necessary in order to promote transformation from austenite to filler and to enrich C in untransformed austenite to stabilize austenite. If the cooling rate is less than 1 ° CZ seconds, the lower limit is 1 ° CZ seconds from the viewpoint that a long production line is required and productivity is deteriorated. On the other hand, if the cooling rate exceeds 10 ° CZ seconds, ferrite transformation does not occur sufficiently, making it difficult to secure the residual austenite in the final steel sheet.Therefore, the upper limit was set to 10 ° C / second. .
  • the primary cooling power is reduced to less than 550 ° C, pearlite is generated during cooling, and C, which is an austenite stabilizing element, is wasted, and eventually a sufficient amount of residual austenite is produced. No longer available. Also, the cooling is 7 If the transformation is carried out only up to over 20 ° C, the progress of fly transformation becomes insufficient.
  • the subsequent rapid cooling of secondary cooling requires a cooling rate of at least 10 ° CZ seconds or more so that pearlite transformation and precipitation of iron carbide do not occur during cooling. If the temperature exceeds ° C / sec, it will be difficult in terms of equipment capacity.
  • the cooling stop temperature of the secondary cooling is lower than 150 ° C, almost all of the austenite remaining before cooling is transformed into martensite and finally retained austenite can be secured. Disappears.
  • the cooling stop temperature exceeds 450 ° C., the finally obtained dynamic deformation resistance ⁇ dyn decreases.
  • the secondary cooling stop temperature is lower than the temperature maintained for the payite transformation process, heating is performed to the maintained temperature. If the heating rate at this time is in the range of 5 ° CZ seconds to 50 ° C / second, the final properties of the steel sheet will not be degraded.
  • the secondary cooling stop temperature is higher than the payinite processing temperature, even if the cooling is forcibly performed at a cooling rate of 5 VZ seconds to 200 ° C./second to the payinite processing temperature, Even if the steel sheet is transported directly to the heating zone where the target temperature is set in advance, the final properties of the steel sheet will not be degraded. On the other hand, a sufficient amount of residual austenite cannot be secured when the steel sheet is kept below 150 ° C or when it is kept above 500 ° C. The range was 150 ° C to 500 ° C.
  • the holding temperature at 150 ° C to 500 ° C is less than 15 seconds, the progress of bainite transformation is not enough, so that it is not possible to finally obtain the required amount of residual austenite. If it exceeds 20 minutes, precipitation of iron carbide and pearlite transformation occur after bainite transformation, which is indispensable for the formation of residual austenite.
  • the holding time was set in the range of 15 seconds to 20 minutes.
  • the holding at 150 ° C. to 500 ° C. to promote the bainite transformation may be carried out at an isothermal temperature or by giving a conscious temperature change within this temperature range.
  • the preferred cooling conditions after annealing in the present invention are 0.1 X (A c-A c) + A c, ° C or more.
  • start secondary cooling in the range of 550 to 720 ° C at a primary cooling rate of 1 to 10 ° CZ seconds Cooling down to temperature T q, then at a secondary cooling rate of 10 to 200 ° C / sec., Determined by steel composition and annealing temperature T0: Tem—100 ° C or more, Tem
  • T e Tem
  • T 1 is a temperature calculated by the concentration of solid solution elements other than C
  • T 2 is T c determined by A c, A c 3 determined by the composition of the steel sheet, and the annealing temperature T o. Is the temperature calculated from the C concentration in the residual austenite at the same time.
  • a c, 7 2 3-0.7 x M n%-1 6.9 x N i% + 2 9.1 x S i% + 1 6.9 x C r%, and
  • T 2 4 7 4 x (Ac 3 — A c,) x C / (T o-A c,),
  • ⁇ 2 4 7 4 x (A c-A c,) x C / (3 x (A c 3 -A c,) x C + C (M n + S i / 4 + N i / 7 + C r + C u + l. 5 Mo) / 2-0.85)] x (T o — A c,).
  • the microstructure of the steel sheet contains ferrite and / or veneite, and either of them is the main phase and the volume is This is a composite structure with the third phase containing 3 to 50% residual austenite in fraction, and after giving a pre-deformation of more than 0% and less than 10% with equivalent strain, 5 X 10 2 to 5 X 1 0 3 (l Z s ) 5 x 1 0 before the average value sigma dyn of the deformation stress in the equivalent strain range of 3 to 1 0% when deformed at a strain observed speed range (MPa) gives pre-deformation of The expression ⁇ dy ⁇ ⁇ 0.766 XTS expressed by the maximum stress TS (MPa) in a static tensile test measured in the strain rate range of ⁇ 5 X 10 — 3 (1 / s) Accordingly, it is possible to obtain a high-strength steel sheet having a high dynamic deformation resistance satisfying +250 and a work hard
  • the steel values satisfying the composition conditions and the production conditions according to the present invention have an M value of 70 or more determined by the solid solution [C] in the residual austenite and the average M neq of the steel material.
  • the initial residual contains 3% to 50% by volume of stenite and (initial residual austenite volume fraction – 5% residual austenite volume fraction after pre-deformation) / initial residual austenite It has a moderate stability of volume fraction ⁇ 0.3, and all have dyn ⁇ 0.766 XTS + 250, a work hardening index of 1 to 5% ⁇ 0.080, It is evident that the steel exhibits excellent collision safety with a work hardening index of 1 to 5% and a yield strength of ⁇ 40, and also has both formability and spot weldability.
  • B bainite
  • P perlite
  • Example 2>'Hot rolling was completed on 25 types of steel materials shown in Table 5 with an Ar of 3 or more, rolled up after cooling, pickled, and cold rolled. After that, the temperatures of Ac1 and Ac3 were determined from the components of each steel, and heating, cooling, and holding were performed under the annealing conditions shown in Table 6, and then cooled to room temperature. As shown in Tables 7 and 8, each steel sheet that satisfies the manufacturing conditions and component conditions according to the present invention has an M value of 70 or more determined by the solid solution [C] in the residual austenite and the average Mneq of the steel material. Under 50 or less, dyn ⁇ 0.076 x TS + 250, and a work hardening index value of 1 to 5% strain is 40 or more. It is.
  • the mouth tissue was evaluated by the following method. ⁇ The identification of the bright, bainite, martensite and residual structures, observation of their locations, and measurement of the average crystal grain size (average equivalent circle diameter) and space factor are carried out using the Nital reagent and JP 59 — Corrosion of the cross-section in the rolling direction of the steel sheet by the reagent disclosed in 219473.
  • the average equivalent circle diameter of the retained austenite was determined from the photomicrograph at a magnification of 1000 times, where the cross section in the rolling direction was corroded by the reagent disclosed in Japanese Patent Application No. 3-351209. The location was also observed using the same photograph.
  • the residual austenite volume fraction (Va: unit is%) was calculated by X-ray analysis using Mo-K rays according to the following equation.
  • V r (2/3) (100 / (0.7 X a (211) / r (220) +
  • the residual 7 C concentration (C a: unit is%) is calculated from the reflection angle of the (200), (220), and (311) planes of austenite by X-ray diffraction using Cu— ⁇ -line.
  • the unit is calculated as follows: 7 ⁇
  • the characteristic evaluation was performed by the following method.
  • Stretch flangeability is achieved by expanding a 20nra punched hole from a non-burr surface with a 30 ° conical punch, and drilling the hole diameter (d) and initial hole diameter (d., D) when the crack penetrates the plate thickness. 20 omission) and the hole expansion ratio (d / d.).
  • Spot weldability is a so-called peeling fracture when a spot welding test piece joined with an electrode having a tip diameter 5 times the square root of the thickness of the steel sheet with a current 0.9 times the chilling current is broken with a steel beam.
  • a spot welding test piece joined with an electrode having a tip diameter 5 times the square root of the thickness of the steel sheet with a current 0.9 times the chilling current is broken with a steel beam.
  • the present invention makes it possible to provide high-strength hot-rolled steel sheets and cold-rolled steel sheets for automobiles, which have both unprecedented excellent collision safety and formability, at low cost and stably. As a result, the applications and conditions for using high-strength steel sheets will be greatly expanded.

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Abstract

Cette invention se rapporte à une plaque d'acier à haute résistance mécanique que l'on utilise pour mouler des pièces qui absorbent l'énergie d'impact lors d'une collision, telles qu'un longeron avant, et qui présente une forte capacité d'absorption de l'énergie d'impact, ainsi qu'à un procédé de fabrication d'une telle plaque d'acier. Dans cette plaque d'acier à haute résistance mécanique dotée d'une capacité d'absorption de l'énergie d'impact, la microstructure d'une plaque d'acier finie comporte deux phases à base de ferrite et/ou de bainite, la phase principale comportant soit de la ferrite soit de la bainite, et la troisième phase contenant 3 à 50 % en volume d'austénite résiduelle. Une valeur moyenne σdyn (MPa) de contrainte de déformation, qui appartient à une gamme de déformation équivalente comprise entre 3 et 10 %, de la microstructure déformée dans une gamme de vitesse de déformation comprise entre 5x102 et 5x103 après une déformation préalable à un degré supérieur à 0 % et inférieur ou égal à 10 % en terme de déformation équivalente, satisfait la relation σdyn ≥ 0.766xTS+250 où TS (MPa) est la contrainte maximum mesurée au cours d'un essai de tension statique dans une gamme de vitesse de déformation comprise entre 5x10-4 et 5x10-3 (1/s) avant l'application de la déformation préalable. Ladite plaque d'acier possède une forte résistance à la déformation dynamique satisfaisant à un indice d'écrouissage, pour une déformation comprise entre 1 et 5 %, supérieur ou égal à 0,080.
PCT/JP1997/004359 1996-11-28 1997-11-28 Plaque d'acier a haute resistance mecanique dotee d'une forte resistance a la deformation dynamique et procede de fabrication correspondant WO1998023785A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
EP97913471.5A EP0952235B2 (fr) 1996-11-28 1997-11-28 Procede de fabrication d'aciers à haute resistance mècanique ayant une haute capacite d'absorption d'energie de chock
US09/308,986 US6319338B1 (en) 1996-11-28 1997-11-28 High-strength steel plate having high dynamic deformation resistance and method of manufacturing the same
AU50679/98A AU711873B2 (en) 1996-11-28 1997-11-28 High-strength steels having high impact energy absorption properties and a method for producing the same
CA002273334A CA2273334C (fr) 1996-11-28 1997-11-28 Aciers a haute resistance ayant des proprietes d'absorption de chocs de forte energie et une methode pour les produire

Applications Claiming Priority (10)

Application Number Priority Date Filing Date Title
JP33138096A JPH10158735A (ja) 1996-11-28 1996-11-28 耐衝突安全性及び成形性に優れた自動車用熱延高強度薄鋼板とその製造方法
JP8/331380 1996-11-28
JP9/28296 1997-01-29
JP2829697 1997-01-29
JP22300597A JPH1161326A (ja) 1997-08-06 1997-08-06 耐衝突安全性及び成形性に優れた自動車用高強度鋼板とその製造方法
JP9/223005 1997-08-06
JP9/258887 1997-09-24
JP25883497A JP3530353B2 (ja) 1997-09-24 1997-09-24 高い動的変形抵抗を有する衝突時衝撃吸収用高強度冷延鋼板とその製造方法
JP25888797A JP3530355B2 (ja) 1997-09-24 1997-09-24 高い動的変形抵抗を有する衝突時衝撃吸収用高強度熱延鋼板とその製造方法
JP9/258834 1997-09-24

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KR (1) KR100318213B1 (fr)
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TW (1) TW384313B (fr)
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MATERIA, Vol. 35, No. 3, 20 May 1996, (Sendai Municipal Government) The Japan Institute Metals, KAZUYA MIURA, SHUSAKU TAKAGI, TOSHIYUKI KATO, OSAMU MATSUDA, SHINJI TANIMURA, "Development of Impact-Absorbing High Tensile Strength Steel Plate for Automobiles (in Japanese)", pages 570-572. *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1001041A1 (fr) * 1998-11-10 2000-05-17 Kawasaki Steel Corporation Tôle d'acier laminé à chaud ayant une structure granulaire ultrafine et procédé de sa production
EP1052301A4 (fr) * 1998-11-30 2002-03-13 Nippon Steel Corp Acier ferritique presentant une excellente dependance dans la vitesse de deformation, et automobile utilisant ledit acier ferritique
US6432228B1 (en) 1998-11-30 2002-08-13 Nippon Steel Corporation Ferritic steel sheet excellent at strain rate sensitivity of the flow stress, and automobile utilizing it

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EP2314730B1 (fr) 2012-03-21
KR100318213B1 (ko) 2001-12-22
EP2314730A1 (fr) 2011-04-27
CN1241219A (zh) 2000-01-12
EP0952235B2 (fr) 2015-09-30
CN1078623C (zh) 2002-01-30
TW384313B (en) 2000-03-11
CA2273334C (fr) 2006-03-28
EP0952235A1 (fr) 1999-10-27
CA2273334A1 (fr) 1998-06-04
EP0952235A4 (fr) 2003-05-21
EP0952235B1 (fr) 2011-10-12
AU5067998A (en) 1998-06-22
AU711873B2 (en) 1999-10-21
KR20000057266A (ko) 2000-09-15

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