WO2005056856A1 - 自動車構造部材用鋼材およびその製造方法 - Google Patents
自動車構造部材用鋼材およびその製造方法 Download PDFInfo
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- WO2005056856A1 WO2005056856A1 PCT/JP2004/018776 JP2004018776W WO2005056856A1 WO 2005056856 A1 WO2005056856 A1 WO 2005056856A1 JP 2004018776 W JP2004018776 W JP 2004018776W WO 2005056856 A1 WO2005056856 A1 WO 2005056856A1
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- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21D8/0226—Hot rolling
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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- 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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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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
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Definitions
- the present invention relates to a steel material suitable for an automobile structural member and a method for manufacturing the same.
- the present invention relates to the improvement of formability, fatigue strength after quenching, low-temperature toughness, and delayed blasting properties of steel materials used as materials for forming and quenching suspension arms and axle beams.
- the steel material according to the present invention includes a steel strip and a steel pipe.
- Patent Literature 1 discloses a technique related to a method for manufacturing a hot-rolled steel material for a body-catching ERW steel pipe manufactured by induction hardening. According to the technology described in Patent Document 1, a body-reinforced ERW steel pipe requiring high strength, such as a door impact bar or a core material for a bumper, which is excellent in shock absorption characteristics by induction hardening can be obtained. However, with this technology, there is a problem in that it is not possible to obtain the formability, fatigue strength after quenching, and low-temperature properties required for the suspension and chassis components.
- Patent Document 2 discloses a technique for induction hardening steel sheets having excellent hardenability and a quenched part having toughness and excellent shock absorption properties, an induction hardening strengthening member, and a method of manufacturing the same. According to the technology described in Patent Document 2, it is possible to obtain a pod-strengthening member such as a center biller / bumper reinforce which is excellent in shock absorbing ability at the time of collision by induction hardening. However, this technique has a problem in that it is not possible to obtain the fatigue properties and low-temperature toughness after quenching required for the suspension and chassis members.
- Patent Document 3 discloses a technique relating to a high toughness heat-treated electric resistance welded steel pipe that can be imparted with high strength and toughness by performing heat treatment. According to the technique described in Patent Document 3, for example, by quenching after induction heating, a steel pipe door reinforcing material having high strength and excellent low-temperature toughness can be obtained. However, this technique has a problem in that it is not possible to obtain the fatigue properties required for suspension and chassis members, delayed fracture resistance, and corrosion fatigue strength.
- Patent Document 4 discloses a technique relating to a low-alloy steel sheet having good heat treatment properties by high-density energy beam irradiation, fatigue properties after heat treatment, and good calorie properties. According to the technology described in Patent Document 4, local fatigue characteristics can be improved. However, with this technology, the suspension The required fatigue properties cannot be ensured for the entire components and chassis, and the required delayed rupture resistance and corrosion fatigue strength cannot be obtained with these members.
- Patent Document 5 discloses a technique relating to an electric resistance welded pipe for a hollow stabilizer having excellent workability. According to the technology described in Patent Document 5, a hollow stabilizer excellent in workability, having a uniform metallographic structure in an electric portion and a base material portion, is obtained by subjecting an electric resistance welded steel pipe to high-frequency heating and then diameter-reduction rolling. ERW welded steel pipe can be obtained.
- this technique has a problem in that it is not possible to obtain the fatigue properties required for the suspension and chassis members, the delayed rupture resistance, and the corrosion fatigue strength.
- Patent Literature 6, Patent Literature 7, and Patent Literature 8 disclose techniques relating to high tensile strength steel pipes having excellent resistance to hydrogen cracking. According to these techniques, a high tensile strength steel pipe having excellent hydrogen cracking resistance can be obtained by increasing the tensile strength at the steel strip stage and then forming the pipe.
- these technologies have a problem in that the formability and fatigue characteristics required for the suspension and chassis members cannot be obtained.
- Patent Document 1 Japanese Patent Publication No. 7-74382
- Patent Document 2 JP-A-2000-248338
- Patent Document 3 Patent No. 2605171
- Patent document 4 JP-A-2000-248331
- Patent Document 5 International Publication W0 02/070767 A1 Pan fret
- Patent Document 6 Patent No. 3111861
- Patent Document 7 Patent No. 3374659
- Patent Document 8 JP-A-2003-138316 Disclosure of the Invention
- the present invention advantageously solves the above-described problems of the prior art, and has excellent formability, excellent fatigue strength after quenching, excellent low-temperature toughness, and excellent resistance required for suspensions and chassis members.
- An object of the present invention is to provide a steel material having delayed rupture properties and excellent corrosion fatigue strength, and a technique for producing the same.
- excellent formability refers to a case where the elongation E1 in a tensile test using a JIS No. 12 test piece shows 20% or more.
- excellent fatigue strength after quenching This refers to the case where the maximum stress amplitude ⁇ ⁇ ⁇ ⁇ without fatigue rupture in the plane bending fatigue characteristics (stress ratio: 1.0) is 450 MPa or more.
- excellent low-temperature toughness refers to the Charpy impact test.
- the present inventors have studied the chemical composition, micro-hardening prior to quenching, in order to obtain a steel material that has excellent contradictory properties such as formability, fatigue strength after quenching, low-temperature toughness, delayed bi-peeling resistance, and corrosion fatigue strength.
- a systematic experimental study was conducted with various changes in the structure, quenching method and its conditions.
- the chemical composition, steel strip manufacturing conditions, material steel pipe manufacturing conditions, and pre-quenching structure within certain limited ranges, the formability and post-quenching required for suspensions and chassis parts It has been found that a steel material can be obtained that simultaneously satisfies all of the fatigue strength, low temperature 3 ⁇ 4) properties, delayed blasting resistance, and corrosion fatigue strength.
- the present invention has been completed based on the above findings, with further studies. That is, the gist of the present invention is as follows.
- a steel material for automotive structural members having excellent formability, fatigue strength after quenching, low-temperature toughness, and delayed fracture resistance characterized by having: (2) In (1), in addition to the above composition, further, in mass%, Cu: 0.001 to 0.175%, Ni:
- V 0.001 ⁇ 0.029% 1 kind or automotive structural member for a steel material characterized that you containing two or more species selected from among.
- a method for producing a hot-rolled steel strip for a structural member of an automobile comprising:
- Figure 1 is a graph showing the effect of carbon equivalent on the rupture time in a 4-point bending test in 0.1N hydrochloric acid after quenching, the fracture surface transition temperature in a Charpy impact test, and the fatigue limit in a plane bending fatigue test.
- FIG. 2 is an explanatory diagram schematically showing a stress loading method in a four-point bending test.
- FIG. 3 is a graph showing the effect of the total hardening multiple X of each element on the fatigue limit CTf of the plane bending fatigue test.
- FIG. 4 is a graph showing the effect of the average ferrite circle equivalent diameter d f of the structure before quenching on the fatigue limit d f after quenching.
- C is an element necessary for securing the fatigue properties after quenching.However, if it is less than 0.18%, it becomes difficult to secure the desired fatigue strength, while if it exceeds 0.29%, the resistance is increased. Delayed blasting properties deteriorate. Therefore, C was limited to the range of 0.118 to 0.29%. The content is preferably 0.18 to 0.24%.
- Si is an element that promotes ferrite transformation in the hot rolling process.
- the content of Si is required to be not less than 0.06%. If t Si is less than 0.06%, the ferrite volume fraction becomes insufficient, and the formability deteriorates. On the other hand, when the content exceeds 0.45%, the ERW property is deteriorated and the low-temperature toughness after quenching is also reduced. Therefore, Si was limited to the range of 0.06 to 0.45%. Preferably, the content is 0.15 to 0.35%.
- Mn is an element that suppresses ferrite transformation in the quenching process.
- Mn is 0.91% or more in the present invention. Is required. If the Mn content is less than 0.91%, a ferrite structure appears particularly in the surface layer during quenching, and desired fatigue characteristics cannot be obtained. On the other hand, if the content exceeds 1.85%, the martensite transformation temperature (Ms point) of the steel decreases, and the martensite self-tempering (fine Precipitation of fine carbides) is suppressed, the quenching strain of the quenched member increases, and the delayed blasting resistance property deteriorates. Therefore, Mn was limited to the range of 0.90 to 1.85%. Preferably, it is more than 1.0% and 1.6% or less.
- P degrades to the former austenite grain boundaries during quenching and heating, or segregates at the cementite-Fe matrix interface during the precipitation of cementite in the martensite tempering process. This is an element that causes deterioration. If the content exceeds 0.019%, this adverse effect becomes significant. For this reason, P was limited to 0.019% or less. Preferably, the content is 0.014% or less.
- the upper limit of S is set to 0.0029%. Incidentally, it is preferably 0.0020% or less.
- A1 is a deoxidizing element at the time of steel making and an element that suppresses the growth of austenite grains in the hot rolling process.
- sol. Al in order to obtain a desired structure and grain size in combination with the hot rolling conditions, At least 0.015%. If the content of sol. Al is less than 0.015%, the above effect is small. On the other hand, if the content exceeds 0.075%, the effect is saturated, and the amount of oxide inclusions increases, thereby deteriorating the manufacturability and fatigue properties. Therefore, sol. Al was limited to 0.015 to 0.075%.
- N combines with Ti and precipitates as TiN, but the amount of variation is the amount of variation in the amount of residual solid solution Ti, which is the amount of variation in strength and properties. Therefore, its component range must be strictly specified. If the content exceeds 0.0049%, the precipitation of excessive TiN lowers the low-temperature toughness. Therefore, the upper limit of N is 0.0049%.
- O mainly remains in the steel as inclusions and reduces formability and fatigue strength. If the content exceeds 0.0049%, this adverse effect becomes significant. Therefore, O is made the upper limit 0.004 9%.
- the content is preferably 0.0020% or less.
- Cu 0.001 to 0.175%
- Ni 0.001 to 0.145%
- V 0.001 to 0.029%
- Two or more and Z or Ca: 0.0001 to 0.0029% can be contained.
- Cu, Ni, and V are elements that improve delayed fracture resistance and low-temperature S property, and one or more of them can be selected as necessary.
- Cu concentrates as a metal element in the surface layer, especially the MnS anode part, as corrosion progresses, and suppresses the progress of corrosion, and also has the effect of suppressing the intrusion of hydrogen into steel and improving the delayed rupture resistance. It is an element and can be contained as needed. These effects are exhibited when the content is 0.001% or more, but when the content exceeds 0.175%, there is an increased concern that surface flaws due to molten Cu during hot rolling may occur. Therefore, Cu is preferably set to 0.001 to 0.175%.
- Ni is an element that has the effect of improving the strength-toughness balance and concentrating in the surface layer to improve delayed crushing resistance, and can be contained as necessary. These effects are manifested when the content is 0.001% or more, but when the content exceeds 0.145%, the austenite-ferrite transformation is suppressed during hot rolling, the desired structure cannot be obtained, and the formability before quenching is reduced. descend. Therefore, Ni is preferably set to 0.001 to 0.145%.
- V is an element that has the function of complementing the effect of Nb, and can be contained as necessary. This effect is manifested at a content of 0.001% or more, but a content of more than 0.029% reduces the formability before quenching. Therefore, V is preferably set to 0.001 to 0.029%.
- Ca is an element that precipitates as granular CaS in steel and improves the formability, low-temperature toughness, fatigue properties, delayed rupture resistance, and corrosion fatigue properties by reducing the amount of expanded MnS inclusions. , Can be included as needed. This effect is manifested at a content of 0.0001% or more, but if it exceeds 0.0029%, adverse effects on these properties due to CaO-based inclusions become apparent. Therefore, Ca is preferably 0.0001 to 0.0029%. B: 0.0001 to 0.0029%
- B is an element necessary for securing hardenability without deteriorating the delayed fracture resistance, and such an effect is exhibited when the content is 0.0001% or more.
- the content exceeds 0.0029%, the delayed crushing resistance is reduced. Therefore, B was limited to 0.0001 to 0.0029%. Preferably, it is 0.0008 to 0.0018%.
- Nb is an element that can refine the structure in the hot rolling process and achieve a desired structure and particle size by synergistic effect with A1N. Furthermore, it suppresses the growth of austenite grains during molding and heating, and after quenching. Improve the low temperature toughness of. These effects are exhibited even with a very small content of 0.001% or more, but a content of more than 0.019% lowers the formability before quenching. Therefore, Nb was limited to the range of 0.001-0.019%.
- Ti combines with N and precipitates preferentially as TiN, leaving solid solution B effectively, contributing to the hardenability. Further reduction of solid solution N contributes to ensuring formability before quenching. Although these effects are expressed from content of not less than 001% 0.5, containing more than 0, 02 9%, formability before quenching, reduces the low temperature toughness. Therefore, Ti was limited to the range of 0.001 to 0.029%.
- Cr is contained in the present invention in order to complement the action of Mn and B as a hardenability improving element.
- the degree of decrease in the Ms point due to the addition of Cr is smaller than that of Mn, so that quenching distortion can be suppressed.
- Cr hardly co-segregates with P at the austenite grain boundaries during quenching heating, so that the addition of Cr has little adverse effect on delayed fracture resistance. These effects are exhibited at a content of 0.001% or more, but a content of more than 0.195% reduces the formability before quenching. Therefore, Cr was set to 0.001 to 0.195%.
- Mo captures the effects of Mn and B as hardenability improving elements and also reduces the C potential in steel, thus suppressing surface decarburization during quenching heating and significantly improving fatigue strength after quenching. These effects are expressed at a content of not less than 001% 0.5, but containing more than 0.1 95% reduces the formability before quenching. Therefore, Mo was set to 0.001 to 0.195%.
- the above components are contained within the above range, and the following formula (1)
- the carbon equivalent Ceq was set between 0.5 and 0.58. Preferably, it is 0.44 or more and 0.54 or less. (1) In the calculation of the formula, the elements that are not contained shall be calculated as zero. ⁇
- Figure 1 shows the relationship between the carbon equivalent Ceq, the four-point bending rupture time in 0.1N hydrochloric acid after quenching, the fracture surface transition temperature vTrs in the Charpy impact test, and the plane bending fatigue strength ⁇ f.
- Ceq is 0.4 or more and less than 0.58
- the steel material is excellent in delayed rupture resistance after quenching, low-temperature toughness, and fatigue strength.
- the four-point bending test was performed by cutting out a test piece having a width of 5 mm and a length of 80 thighs from the formed and quenched member.
- the test piece was immersed in 0.1N hydrochloric acid, and the following formula
- the applied stress ⁇ calculated in the above was set to 1180 MPa, and the test was conducted up to a maximum of 200 h to determine the rupture time, and the delayed rupture resistance was evaluated.
- Figure 2 shows the stress loading method for the four-point bending test.
- a 1/4 size (2.5 mm thick) 2 mm V notch impact test specimen was sampled from the formed and quenched member, and a Charpy impact test was conducted to determine the fracture surface transition temperature vTrs and to obtain low temperature toughness. was evaluated.
- a specimen with a width of 30 corruption and a length of 90 mm was cut out from the formed and quenched member, and a plane bending fatigue test was performed to evaluate the fatigue characteristics.
- the test was performed at a repetition rate of 25 Hz and a maximum repetition rate of 10 7 cycles with a swing of a stress ratio of -1.0, and the maximum stress amplitude ⁇ f without fatigue rupture was defined as the fatigue limit. I asked.
- the quenchability factor by Grossmann is a material parameter that needs to be controlled in order to obtain the desired formability, hardness after quenching and fatigue strength of the original sheet.
- Hardenability fold by Grossmann, in the present invention for example, Leslie Author: Steels Science, Maruzen, used with reference to the value of each element listed in Table 3 P 4 02- 4 0 5. . That is, a numerical value was determined for each element according to the content, and the total% for each element was determined and used.
- the quenchability multiple of C adopts the value of ASTM particle size No. 7, and for B with no quenchability multiple, the solid solution of N is more than N equivalent considering the adhesion by TiN. In the case where is contained, it was set to 0.2 regardless of the content.
- the hardness after quenching decreases, and it is not possible to obtain excellent post-quenching fatigue strength with a maximum stress amplitude ⁇ f of 450 MPa or more that does not cause fatigue failure in a plane bending fatigue test.
- the deviation is 1.7 or more
- the ferrite volume ratio of the steel material is less than 30%, the formability of the original sheet is reduced, the locally reduced thickness becomes a stress concentration part, and the ⁇ f after quenching is 450 MPa or more. It is not possible to obtain such excellent fatigue strength. Therefore, the total of the hardenability multiples by Grossmann in consideration of B was limited to X: 1.2 or more and less than 1.7.
- Figure 3 shows the relationship between the total hardening multiple X of each element and the fatigue limit in the plane bending fatigue test.
- the balance other than the above components is substantially Fe.
- the steel material of the present invention has a structure in which the average ferrite circle equivalent particle size df is less than 1.1 / ⁇ and the ferrite volume fraction V f is 30% or more and less than 98%.
- the microstructure of the material before quenching is an important material parameter for ensuring excellent formability and high fatigue strength after quenching. If the average ferrite circle equivalent particle diameter df is less than 1.1 x m, the desired formability cannot be ensured, the locally reduced thickness portion becomes a stress concentration portion, and the fatigue strength after quenching is greatly reduced. On the other hand, when df is 12 / zm or more, the hardenability of the material surface is reduced, and the fatigue strength is significantly reduced. For this reason, the average ferrite circle equivalent grain size df of the steel material is limited to 1.1 / zm or more and less than 12 ⁇ .
- Figure 4 shows the relationship between the average ferrite circle equivalent grain size df of the material (steel) structure before quenching and the fatigue limit in the plane bending fatigue test after quenching.
- the average ferrite circle equivalent grain size df of the material (steel material) before quenching is ⁇ . ⁇ or more, a high fatigue strength with ⁇ f of 450MPa or more is obtained.
- df is in the range of 2.0 to 7.9 im, high fatigue strength of 500MPa or more It can be seen that it can be obtained.
- the ferrite herein includes polygonal ferrite, acidic ferrite, Widmanstatten ferrite, and vanitic ferrite.
- the average ferrite circle equivalent particle size df referred to in the present invention is obtained by measuring the area of each ferrite grain by imaging a structure and performing image processing, converting each ferrite grain into a circle equivalent diameter, and obtaining the equivalent ferrite circle equivalent.
- the average particle size was used. Since a material having quenchability, such as the steel material handled in the present invention, contains irregular ferrite grains, the average ferrite grain size was determined not by the cutting method but by the circle equivalent diameter by surface image processing.
- the second phase other than ferrite is preferably carpide, pearlite, bainite, martensite, or a mixture thereof.
- the average circle equivalent particle diameter ds of the second phase is preferably ⁇ . ⁇ or more and less than 12 / zm, like ferrite.
- the ferrite volume fraction Vf of the raw material (steel material) before quenching is less than 30%, the desired formability cannot be ensured, the locally reduced thickness becomes a stress concentration portion, and the fatigue properties after quenching are greatly reduced. On the other hand, it is difficult to secure a volume fraction of 98% or more in the above-mentioned component range.
- the ferrite volume fraction is obtained by observing and imaging two or more fields of view at 1000 times with a scanning electron microscope (SEM) after nital etching the cross section, stratifying the grain boundaries and the second phase, and The ferrite volume fraction is obtained by the treatment.
- the molten steel having the above-mentioned composition by a normal smelting method such as a converter, and to form a steel slab such as a slab by a normal smelting method such as a continuous smelting method.
- a normal smelting method such as a converter
- a steel slab such as a slab by a normal smelting method such as a continuous smelting method.
- the steel slab having the above-mentioned yarn is heated and hot-rolled to form a hot-rolled steel strip.
- elements that form hardly soluble carbonitrides are essential elements.
- the slab heating temperature is lower than 1160 ° C, the local re-dissolution of carbonitrides is insufficient.
- the grain size of the hot-rolled partly exceeds 12 ⁇ , and the workability before quenching decreases.
- the slab heating temperature exceeds 1320, the surface quality of the product steel pipe / steel strip will deteriorate.
- the slab heating temperature is preferably from 1160 to I320 ° C.
- the temperature is more preferably 1180 to 1280 ° C.
- Finish rolling finish temperature 750 ⁇ 980 ° C
- the finish rolling end temperature of hot rolling is an important manufacturing parameter that determines the ferrite grain size after hot rolling. If the finish rolling end temperature is lower than 750 ° C, it will be in the ferrite region rolling, and the rolling distortion will remain even after winding and the formability before quenching will decrease. On the other hand, when the temperature exceeds 9S0 ° C, the ferrite grain size becomes coarse and the formability before quenching is reduced. Therefore, the finish rolling finish temperature is preferably 750 to 980 ° C. The temperature is more preferably 820 to 940 ° C.
- Slow cooling after finish rolling refers to cooling at a cooling rate of 20 ° C / s or less.
- Winding temperature 560 ⁇ 740 ° C
- the winding temperature after hot rolling is an important manufacturing parameter that determines the ferrite volume fraction after hot rolling.
- ⁇ Ri temperature is less than 5 6 0 ° C, it can not be obtained the desired ferrite volume fraction, formability before quenching is decreased.
- the winding temperature is higher within the specified range, the formability before quenching is improved, but when the temperature exceeds 740 ° C, the amount of C in the surface layer is significantly reduced, and the fatigue properties after quenching are reduced. Therefore, the winding temperature is preferably 560 to 740 ° C.
- the temperature is more preferably 600 to 700 ° C.
- the average ferrite circle equivalent grain size l.l ⁇ 12 / zm, ferrite volume integral Hot-rolled steel strip with the desired microstructure which is most suitable for the formability before quenching and the fatigue strength after quenching, such as 30-98%, formability, fatigue strength after quenching, low-temperature toughness and delay resistance It is possible to obtain a hot-rolled steel strip for an automobile structural member having excellent fracture characteristics.
- the formability, the fatigue strength after quenching, the low-temperature toughness, and the delayed fracture resistance are obtained by forming an electroformed tube under appropriate conditions using the hot-rolled steel strip manufactured by the above-described manufacturing method. It is possible to obtain a steel pipe for an automobile structural member having excellent resistance.
- a hot-rolled steel strip manufactured under the above conditions is used as a material.
- the material may be hot rolled, but is preferably used after being subjected to an acid washing treatment to remove black scale on the surface. It is preferable that the material that has been subjected to the hot rolling or the pickling treatment is formed into a steel pipe by subjecting an electric pipe having a ⁇ drawing ratio of 8% or less to an electric steel pipe.
- the width reduction ratio is an important manufacturing parameter for securing desired formability before quenching. If the ⁇ ⁇ drawing ratio exceeds 8%, the formability of the tube is greatly reduced, and the required formability before quenching cannot be obtained. Therefore, it is preferable that the width reduction ratio be 8% or less (including 0%).
- the width reduction ratio is a value defined by the following equation.
- Width drawing ratio (%) [(width of steel strip) — ⁇ ⁇ (product outer diameter—product thickness) (product outer diameter) — (product thickness) ⁇ ] ⁇ 100
- the material is not limited to a hot-rolled steel strip.
- the belt There is no problem using the belt.
- the 26 types of steel slabs (1) to (6) shown in Table 1 were reheated to the slab heating temperature shown in Table 3 and then hot-rolled under the conditions shown in Table 3 to obtain a sheet thickness of 2.6 thigh hot rolled steel. It was a band.
- the obtained hot-rolled steel strip was subjected to pickling treatment and slitting, then roll-formed, and subjected to ERW welding to form a welded steel pipe having an outer diameter of 101.6 brittle.
- Table 3 shows the width reduction ratio during pipe making.
- Table 2 shows the values of the hardenability multiples of each element of each steel and their sum.
- a specimen for microstructure observation was sampled, polished and corroded, observed with a SEM ( ⁇ 1000), imaged, and image-processed to obtain a ferrite volume fraction and an average ferrite.
- Circle equivalent particle size The second phase circle equivalent particle size was measured.
- the method of obtaining the circle equivalent particle size was to determine the area of each grain, set the diameter of the circle corresponding to the area as the circle equivalent particle size, and use the average value of each grain.
- the steel pipe thus obtained was formed into an axle beam with a closed cross-section, and then subjected to a quenching process of heating to about 920 ° C and cooling with water in a continuous furnace with controlled atmosphere. After quenching, a section hardness test, a plane bending fatigue test, a Charpy impact test, a four-point bending test, and a plane bending fatigue test after a corrosion test were performed.
- the test method was as follows.
- a test piece was cut out from the formed and quenched member, the Vickers hardness (load: lOkgf) was measured over the entire thickness direction, and the average value was defined as the cross-sectional hardness of the member after quenching.
- the Charpy impact test was performed by taking 2/4 V-notch impact test specimens of 1/4 size (thickness: 2.5 thighs) from the formed and quenched members to determine the fracture surface transition temperature vTrs and evaluate the low-temperature conversion. did.
- test piece with a width of 5 mm and a length of 80 watts was cut out from a molded and quenched member, and the test piece was immersed in 0.1 N hydrochloric acid.
- the applied stress ⁇ calculated in the above was set to 1180MPa, and a test was performed up to a maximum of 200 hours to determine the fracture time, and the delayed rupture resistance was evaluated.
- the elongation E1 of the raw tube is 20 ° /. (JIS No. 12 test piece), cross-sectional hardness after quenching HV (10) is 350 to 550, plane bending fatigue limit ⁇ f is 500 MPa or more, Charpy impact test fracture surface transition temperature vTrs is -40 ° C or less, Excellent formability, fatigue strength, low temperature IS with a 4-point bending rupture time in 0.1 N hydrochloric acid of 200 h or more, and a fatigue life reduction of more than 1/2 cycle of non-corrosive material by corrosion fatigue test It shows resistance, delayed rupture resistance and corrosion fatigue strength.
- Comparative Examples No. 5 to No. 26 in which any one of steel composition, carbon equivalent, Ceq, and total hardenability is out of the range of the present invention, have formability, fatigue strength, low-temperature toughness, and delayed fracture resistance. , Or the corrosion fatigue strength has decreased.
- hot rolled steel strips were manufactured under the hot rolling conditions shown in Table 5. After pickling was performed on these hot-rolled steel strips to remove black scale, ERW pipes were manufactured under the pipe-forming conditions shown in Table 5. Some hot-rolled steel strips were left hot-rolled (with black scale). Some hot-rolled steel strips were cold-rolled and annealed, and Zn and A1 surface treatments were made. In some cases, press-welding and roll-forming-welding methods were used instead of electric pipes. Some steel pipes were galvanized after pipe making. Furthermore, for some steel pipes, the obtained steel pipes were subjected to warm reduction and hot reduction.
- the members obtained after quenching were subjected to cross-sectional hardness, plane bending fatigue test, Charpy impact test, 4-point bending test in 0.1N hydrochloric acid, and plane bending fatigue test after salt spray test (JIS Z2371) for 20 days. went.
- the test method was the same as in Example 1. Table 6 shows the obtained results.
- the elongation E1 of the raw tube was 20% or more (JIS No. 12 test piece), the cross-sectional hardness after quenching HV (10) was 350 to 550, the plane bending fatigue limit ⁇ f was 500 MPa or more, and the Charpy Fracture transition temperature of impact test vTrs is -40 ° C or less, 4-point bending rupture time in 0.1N hydrochloric acid is 200h or more, Fatigue life by corrosion fatigue test is more than 1/2 cycle of non-corrosive material, It shows excellent formability, fatigue strength, low temperature toughness, delayed fracture resistance and corrosion fatigue strength.
- the elongation E1 of the original tube is as high as 20% or more, but the .of is reduced due to surface decarburization.
- the elongation E1 of the original pipe is as low as 15%, and ⁇ f is also low.
- No. 40 is an example in which pickling after hot rolling is omitted
- No. 41 is an example in which a suspension arm of ⁇ 60.5 x 2.6 t is formed and then quenched
- No. 42 is hot rolled and then cold rolled and annealed.
- No. 43 is an example where the steel strip was press-formed and welded into a closed cross section (arc, laser, plasma), and No. 44 was a steel strip rolled into a closed cross section.
- No. 45, No. 46 is an example of hot-rolled Zn-plated, A1 type-plated original sheet with ERW pipe, No. 47 is Zn-plated after electroforming pipe
- No. 48 and No. 49 are examples of hot rolling or hot rolling, and No. 50 and No. 50 were heated as they were.
- No. 51 is an example in which shot blasting was performed after quenching
- No. 52 was an example in which shot peening was performed after quenching.
- Fatigue limit ⁇ f is 500MPa or more, Fracture transition temperature of Charpy impact test vTrs temperature 40 ° C or less, 4-point bending rupture time in 0.1N hydrochloric acid 200h or more, Fatigue life decrease by corrosion fatigue test It shows excellent formability, fatigue strength, low-temperature toughness, delayed rupture resistance and corrosion fatigue strength of less than 1/2 cycle of non-corrosive material.
- a steel material for an automobile structural member having the following can be easily and inexpensively manufactured.
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Abstract
Description
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Priority Applications (3)
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CA2548560A CA2548560C (en) | 2003-12-12 | 2004-12-09 | Steel for structural part of automobile and method for producing the same |
US10/582,717 US8747578B2 (en) | 2003-12-12 | 2004-12-09 | Steel for structural part of automobile and method for producing the same |
EP04807135A EP1693476B1 (en) | 2003-12-12 | 2004-12-09 | Steel product for structural member of automobile and method for production thereof |
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JP2003414336A JP4443910B2 (ja) | 2003-12-12 | 2003-12-12 | 自動車構造部材用鋼材およびその製造方法 |
JP2003-414336 | 2003-12-12 |
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WO2005056856A1 true WO2005056856A1 (ja) | 2005-06-23 |
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PCT/JP2004/018776 WO2005056856A1 (ja) | 2003-12-12 | 2004-12-09 | 自動車構造部材用鋼材およびその製造方法 |
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US (1) | US8747578B2 (ja) |
EP (1) | EP1693476B1 (ja) |
JP (1) | JP4443910B2 (ja) |
CN (1) | CN100436629C (ja) |
CA (1) | CA2548560C (ja) |
WO (1) | WO2005056856A1 (ja) |
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EP2050835A1 (en) * | 2006-08-11 | 2009-04-22 | Nippon Steel Corporation | Steel for automobile undercarriage component excelling in fatigue performance and process for manufacturing automobile undercarriage component using the steel |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2050835A1 (en) * | 2006-08-11 | 2009-04-22 | Nippon Steel Corporation | Steel for automobile undercarriage component excelling in fatigue performance and process for manufacturing automobile undercarriage component using the steel |
US20090277542A1 (en) * | 2006-08-11 | 2009-11-12 | Hideyuki Nakamura | Steel material for automobile chassis parts superior in fatigue characteristics and method of production of automobile chassis parts using the same |
CN102174684A (zh) * | 2006-08-11 | 2011-09-07 | 新日本制铁株式会社 | 疲劳特性优异的异型截面形状的汽车行走部件 |
EP2050835A4 (en) * | 2006-08-11 | 2011-10-12 | Nippon Steel Corp | STEEL FOR AUTOMOBILE ROLLER COMPONENT HAVING EXCELLENT FATIGUE PERFORMANCE AND METHOD FOR MANUFACTURING AUTOMOBILE RUNNING COMPONENT USING THE STEEL |
US20120093678A1 (en) * | 2006-08-11 | 2012-04-19 | Toyota Jidosha Kabushiki Kaisha | Steel material for automobile chassis parts superior in fatigue characteristics and method of production of automobile chassis parts using the same |
US8778261B2 (en) | 2006-08-11 | 2014-07-15 | Nippon Steel & Sumitomo Metal Corporation | Steel material for automobile chassis parts superior in fatigue characteristics and method of production of automobile chassis parts using the same |
US8828159B2 (en) | 2006-08-11 | 2014-09-09 | Nippon Steel & Sumitomo Metal Corporation | Steel material for automobile chassis parts superior in fatigue characteristics and method of production of automobile chassis parts using the same |
CN100434560C (zh) * | 2006-12-26 | 2008-11-19 | 宋立华 | 汽车空气悬架随动转向桥 |
Also Published As
Publication number | Publication date |
---|---|
CN100436629C (zh) | 2008-11-26 |
CA2548560C (en) | 2012-06-26 |
US8747578B2 (en) | 2014-06-10 |
EP1693476B1 (en) | 2012-08-15 |
EP1693476A1 (en) | 2006-08-23 |
US20070144632A1 (en) | 2007-06-28 |
JP4443910B2 (ja) | 2010-03-31 |
CA2548560A1 (en) | 2005-06-23 |
EP1693476A4 (en) | 2009-07-22 |
CN1890394A (zh) | 2007-01-03 |
JP2005171337A (ja) | 2005-06-30 |
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