WO2004113581A1 - Produit en acier a excellentes caracteristiques de resistance a l'extension de fissure de fatigue et procede de fabrication dudit produit - Google Patents

Produit en acier a excellentes caracteristiques de resistance a l'extension de fissure de fatigue et procede de fabrication dudit produit Download PDF

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WO2004113581A1
WO2004113581A1 PCT/JP2004/008905 JP2004008905W WO2004113581A1 WO 2004113581 A1 WO2004113581 A1 WO 2004113581A1 JP 2004008905 W JP2004008905 W JP 2004008905W WO 2004113581 A1 WO2004113581 A1 WO 2004113581A1
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cooling
steel
fatigue crack
steel material
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PCT/JP2004/008905
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English (en)
Japanese (ja)
Inventor
Kazuki Fujiwara
Noboru Konda
Shuji Okaguchi
Kazushige Arimochi
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Sumitomo Metal Industries, Ltd.
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Application filed by Sumitomo Metal Industries, Ltd. filed Critical Sumitomo Metal Industries, Ltd.
Priority to JP2005507281A priority Critical patent/JP4706477B2/ja
Priority to CN200480017070.2A priority patent/CN1809648B/zh
Publication of WO2004113581A1 publication Critical patent/WO2004113581A1/fr

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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
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • 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

Definitions

  • the present invention relates to a hull, a civil engineering structure, a construction machine, a penstock, an offshore structure,
  • the present invention relates to a steel material such as a thick steel plate used as a structural material, particularly a steel material having excellent fatigue crack propagation characteristics of 490 MPa class and a manufacturing method thereof.
  • JP-A-7-90478 discloses a steel sheet having good fatigue crack propagation resistance and a method for producing the same.
  • This steel sheet has a structure in which a striped hard second phase extending in the rolling direction is scattered in a soft matrix at an area ratio of 5 to 50%.
  • the soft phase is present as a parent phase
  • the hard second phase is striped, extending in the rolling direction of the steel sheet, and suppressing crack growth.
  • the effect of suppressing the growth of fatigue cracks is only in the thickness direction, and the effect of suppressing the growth in other directions is small.
  • Japanese Patent Application Laid-Open No. Hei 6-271985 discloses that the structure is mainly composed of one or more of ferrite, pearlite, and bainite, and further, the average existence interval is 20 im or less and the average aspect ratio is 5 or more.
  • a steel sheet with excellent fatigue crack propagation resistance in which shaped island-like martensite is present at a volume ratio of 0.5 to 5% is shown.
  • the presence of island-like martensite with a high average aspect ratio in high-strength steel results in deterioration of toughness.
  • 7-242992 is characterized in that the structure is composed of a hard part base material and a soft part dispersed in the base part, and the hardness difference between the two parts is 150 or more in terms of the hardness of the powder.
  • a steel sheet having an effect of suppressing fatigue crack growth is disclosed.
  • the present invention has been made to solve these problems, and has as its object to be used as a structural material such as a hull, a civil engineering structure, a construction machine, a penstock, an offshore structure, and a line pipe. It is an object of the present invention to provide a steel material which is excellent in fatigue crack growth suppression characteristics and a method for producing the same.
  • the present inventors have conducted various studies on the relationship between the crystal structure of steel and fatigue crack propagation resistance, and have obtained the following findings.
  • the dislocation density in the structure of the hard phase affects the fatigue crack growth rate.
  • the hard phase is mainly used. Even in a steel having a microstructure, a high strength steel material having high fatigue crack propagation resistance and excellent fatigue resistance can be obtained. Even in steels having such a structure mainly composed of a hard phase, the excellent fatigue crack propagation resistance is due to the fact that the hardness of the hard phase having a high dislocation density decreases during the process of repeated deformation of the steel, thereby reducing the fatigue. It was considered that the reduction of the opening load at the crack tip contributed.
  • Such a structure having a high dislocation density can be obtained as a structure transformed at a low temperature. Furthermore, the structure transformed at a low temperature and having a high dislocation density contains a large amount of lattice strain, so that the width of the peak in the diffraction intensity distribution when an X-ray diffraction test is performed becomes wide. Therefore, sufficient fatigue crack growth resistance is at least a certain value of the half width of the diffraction intensity obtained in the X-ray diffraction test (the distribution width at half the peak intensity, the unit is “degree”). If you can get.
  • the present invention has been completed on the basis of these findings, and the gist of the present invention is to provide a steel material excellent in fatigue crack growth resistance described in the following (1) to (8), and (9) to (13) The manufacturing method described in the above.
  • the structure is mainly composed of ferrite and bainite, the area ratio of pearlite is 10% or less, and the half width of the X-ray diffraction intensity from the (1 10) plane is 0.13 ° or more.
  • a steel material with excellent fatigue crack propagation resistance characterized by the following features.
  • the structure is mainly composed of ferrite and bainite, the area ratio of pearlite is 10% or less, and the steel component (% by mass) satisfies the following formulas (1) and (2) A steel material with excellent fatigue crack growth resistance characteristics.
  • the structure is mainly composed of ferrite and bainite, the area ratio of pearlite is 10% or less, the half width of the X-ray diffraction intensity from the (110) plane is 0.13 degrees or more, and the steel composition (% By mass) that satisfies the following formulas (1) and (2).
  • the chemical composition of steel is further selected from the group consisting of: Nb: 0.005% or more, 0.08% or less, Ti: 0.005% or more, 0.03% or less, V: 0.005% or more, 0.080% or less in mass%.
  • the chemical composition of the steel is further selected from the group consisting of: mass%, Cu: less than 0.7%, Ni: 3.0% or less, Cr: less than 1.0%, Mo: 0.80% or less, W: 0.05 to 0.50%
  • the chemical composition of the steel is, in mass%, Ca: 0.007% or less, Mg: 0.007% or less, Ce: 0.007% or less, Y: 0.5% or less, Nd: 0.5% or less, REM: 0.05% or less
  • a structural slab having the chemical composition according to any of (4) to (8) above is subjected to A heating step of heating to 1250 ° C., a hot rolling step of performing hot rolling on the heated slab, and a cooling step of cooling the hot-rolled steel material. Performs accelerated cooling at an average cooling rate of 5 to 25 ° C / s between 650 ° C and 400 ° C, stops the accelerated cooling at a temperature of 400 ° C or less, and then sets the reheating temperature A method for producing a steel material excellent in fatigue crack propagation resistance, wherein cooling is terminated so that the width is 70 or less.
  • accelerated cooling at an average cooling rate of 5 to 25 / s between 650 ° C and 400 ° C is performed, the cooling is stopped at a temperature of 400 ° C or less, and then the reheating temperature range
  • a method for producing a steel material excellent in fatigue crack growth resistance comprising performing the reheating and cooling steps according to (10) at least twice.
  • a steel material excellent in fatigue crack growth resistance characterized by being further heated to a temperature of less than Ac, point and tempered.
  • the performance of the steel material excellent in fatigue crack growth resistance according to the present invention is not particularly limited, but a desirable performance is a fatigue crack growth rate of 3 ⁇ 10 mm / cycle or less.
  • the absorbed energy in impact tests is vE- 2 . It has characteristics of 100J or more.
  • FIG. 1 is a schematic diagram for explaining a method of measuring the half width of X-ray diffraction
  • FIGS. 1 (a) and 1 (b) are graphs each showing the diffraction intensity on the (110) plane.
  • Fig. 2 (a) is a schematic diagram showing the outline of the Suppo-Pulsa fatigue test apparatus, and Fig. 2 (b) is a fatigue test piece. It is a schematic diagram which shows the shape of. BEST MODE FOR CARRYING OUT THE INVENTION
  • the structure of the steel according to the present invention is mainly composed of ferrite and bainite in order to easily obtain high strength.
  • the bainite includes structures such as upper bainite, lower bainite, ashkiyura-ferrite, and dynayura-bainite.
  • the term “mainly” means that the total composition ratio of the ferrite and bainite structures in the steel structure is 90% or more in terms of area ratio.
  • the remaining tissue is not particularly limited, and may be a normally observed tissue such as a pearlite or pseudo-pearlite structure.
  • the half width is a value indicating the distribution width of the portion where the diffraction intensity is half of the peak intensity in the distribution of the X-ray diffraction intensity by the diffraction angle. It is formed at high temperature and the half value width becomes smaller as the dislocation density becomes smaller. The larger the half width, the higher the dislocation density and the better the resistance to fatigue crack growth.
  • the (110) plane was targeted.
  • the half width of the diffraction intensity on the (110) plane is 0.13 degrees or more in the present invention.
  • FIG. 1 is a schematic diagram illustrating a method of analyzing a half width in X-ray diffraction intensity data.
  • FIGS. 1 (a) and 1 (b) are graphs each showing the diffraction intensity on the (1 10) plane.
  • the half-value width is the angle of the width of the distribution at half the intensity value where the diffraction intensity is the highest at the diffraction intensity peak.
  • the value is 1/2 of the higher peak.
  • the half width it appears independently K shed i and kappa alpha 2 peaks at diffraction pattern, kappa alpha values of E, when appearing overlap values of kappa alpha E and kappa alpha 2 is the sum of Measure in width.
  • the measurement of the half-value width shall be performed on a plane parallel to the rolled surface at a position within 1 mm from the steel surface in the thickness direction.
  • Equation (1) shows the ratio of the bainite structure as the hard phase. If it is full, the ratio of ferrite + bainite in the bainite structure is not sufficient, and even if a steel sheet is manufactured under the manufacturing conditions of the present invention, an appropriate half-width cannot be obtained, and good fatigue strength progresses Resistance cannot be obtained.
  • Equations (2), (3) and (4) 0.01 or more and 0.10 or less
  • the content is 0.01% or more. However, if the content exceeds 0.10%, the toughness deteriorates. To avoid this, the C content should be 0.10% or less. More preferably, it is 0.03 to 0.07%.
  • Si An element that is effective in deoxidizing steel. In order to obtain the effect, 0.03% or more is contained. However, if the content exceeds 0.60%, the formation of the MA tissue is promoted.
  • the M-A structure is a type of island-like martensite formed in the bainite structure and is a M-A transformation product containing retained austenite. It is known that the M—A structure has very high hardness and easily deteriorates toughness. Therefore, the Si content should be 0.60% or less to avoid toughness degradation. More preferably, it is at least 0.3% and at most 0.5%.
  • Mn An element effective for improving hardenability, and 0.5% or more is contained in order to increase strength and improve fatigue crack propagation resistance. On the other hand, if it exceeds 2.0%, the toughness deteriorates, so the Mn content is set to 2.0% or less.
  • Mn may be set to 0.3% or more and 2.0% or less.
  • sol.Al is an element necessary for deoxidation together with Si, and contains more than 0.005% sol. A1 to obtain its effect.
  • the M—A ratio the existence ratio of the M—A structure
  • the A1 content should be 0.10% or less.
  • N Combines with Al and Ti to form precipitates, which contribute to refinement of austenite grains and have the effect of improving toughness. In order to obtain this effect, N should be contained at 0.0005% or more.
  • the N content exceeds 0.008%, the M—A ratio increases and the toughness deteriorates. In order to avoid this, the N content should be 0.008% or less.
  • B Although not an essential element, B has the effect of significantly increasing hardenability and is effective in increasing strength and improving fatigue crack growth resistance. Therefore, it may be contained in order to further obtain these effects. To achieve the above effects, it is effective to contain 0.0003% or more. However, if B is contained in excess of 0.0030%, the toughness deteriorates. Therefore, the upper limit is preferably set to 0.0030%. When B is contained, the lower limit of Mn can be set to 0.3%.
  • Nb Although not an essential element, it has an effect of improving toughness through a grain refining action. In addition, it increases the hardenability and is effective for improving strength and suppressing fatigue crack growth. Therefore, it may be contained in order to obtain these effects. In such a case, it is desirable that Nb be contained in an amount of 0.005% or more. On the other hand, if the content exceeds 0.08%, the toughness deteriorates, so the upper limit is made 0.08%. More preferably, it is 0.06% or less.
  • Ti Although not an essential element, it is effective for improving strength and suppressing fatigue crack growth. Therefore, Ti may be included to obtain these effects. In order to obtain the above effects, it is desirable to contain 0.005% or more. On the other hand, if it exceeds 0.03%, the toughness deteriorates, so the upper limit is preferably set to 0.03%.
  • V Although not an essential element, it is effective for improving strength, so it may be included to obtain these effects. When it is contained, it is desirable to contain it in an amount of 0.005% or more in order to obtain the above effects. On the other hand, if it exceeds 0.080%, the toughness deteriorates, so the upper limit is preferably set to 0.080%.
  • Cu Although not an essential element, it has the effect of increasing the strength of steel, so it may be included for that purpose. In order to obtain the effect, it is desirable to contain 0.3% or more. However, if the content exceeds 0.7%, the toughness of the steel deteriorates. Therefore, even when the content is contained, the upper limit is set to less than 0.7%. Desirably less than 0.5%.
  • Ni Although not an essential element, it has the effect of increasing the strength of steel and is also effective in suppressing the growth of fatigue cracks. Therefore, it may be contained in order to obtain these effects. In order to obtain the effect, it is desirable to contain 0.2% or more. However, if the content exceeds 3.0%, there is no effect of increasing strength and suppressing fatigue crack growth in proportion to the increase in cost. Even if it is contained, its upper limit is 3.0%.
  • Cr Although not an essential element, it has the effect of increasing the strength of steel and is also effective in suppressing the growth of fatigue cracks. Therefore, it may be contained in order to obtain these effects. In that case, it is desirable to contain 0.3% or more. However, if it is contained excessively, the toughness deteriorates. Therefore, even when it is contained, it is desirable to make the content less than 1.0%.
  • Mo Although not an essential element, it has the effect of increasing the strength of steel and is also effective in suppressing the growth of fatigue cracks. Therefore, it may be contained in order to obtain these effects. In that case, it is desirable to contain 0.3% or more. However, if it is contained excessively, the toughness deteriorates. Therefore, even when it is contained, it is desirable that the content be 0.80% or less.
  • W is an effective element for increasing the base metal strength and improving the corrosion resistance. To obtain this effect, add 0.05% or more. However, when it exceeds 0.50%, toughness is deteriorated.
  • Ca contributes to improvement of toughness through microstructural refinement. However, if the content exceeds 0.007%, the amount of Ca inclusions becomes excessive and the toughness deteriorates. Therefore, the Ca content should be 0.007% or less.
  • the desirable range of the addition amount is 0.0015% or more and 0.0030% or less.
  • Mg contributes to improvement of toughness through microstructural refinement. However, if the content exceeds 0.007%, the amount of Mg inclusions becomes excessive and the toughness is deteriorated. Therefore, the Mg content should be 0.007% or less. A desirable range of the addition amount is 0.0005% or more and 0.0030% or less.
  • Ce contributes to improvement of toughness through microstructural refinement. However, if the content exceeds 0.007%, the amount of Ce inclusions becomes excessive and the toughness is deteriorated. Therefore, the amount of Ce is set to 0.007% or less. A desirable range of the addition amount is 0.0005% or more and 0.0030% or less.
  • Y contributes to improvement in toughness through microstructural refinement. However, if the content exceeds 0.5%, the amount of Y inclusions becomes excessive and the toughness is deteriorated. Therefore, the Y content should be 0.5% or less.
  • a desirable range of the addition amount is 0.01% or more and 0.05% or less.
  • Nd contributes to improvement in toughness through microstructural refinement. However, if the content exceeds 0.5%, the amount of Nd inclusions becomes excessive and the toughness is deteriorated. Therefore, the Nd content should be 0.5% or less. A desirable range of the addition amount is 0.01% or more and 0.05% or less.
  • REM contributes to improved toughness through microstructural refinement. However, if the content exceeds 0.05%, the amount of Nd inclusions becomes excessive and the toughness is deteriorated. Therefore, the amount of REM should be less than 0.05%. A desirable range of the addition amount is 0.005% or more and 0.03% or less.
  • the balance of the chemical composition in the present invention is Fe and unavoidable impurities.
  • P and S are exemplified as one of the impurities, and P and S are preferably 0.015% or less and 0.005% or less, respectively. Limited to below.
  • Means for producing a steel material excellent in fatigue crack propagation resistance according to the present invention is not particularly limited, and as long as desired characteristics can be obtained, a known hot rolling facility or a known hot rolling facility And a known heat treatment facility. However, the method described below is suitable for the production conditions.
  • the structural slab having the chemical composition according to the present invention is heated to 1000 ° C. to 1250 ° C. and then subjected to hot rolling. Then, when cooling it, in the cooling step of the obtained hot-rolled steel material, the average cooling rate between 650 ° C and 400 ° C is 5 ° C / s or more, preferably more than 5 ° C / s, 25 ° C. Perform accelerated cooling at a rate of not more than C / s, stop the accelerated cooling at a temperature of 400 ° C or less, and then terminate the cooling so that the recuperation temperature width becomes 70 ° C or less.
  • the recuperation temperature range means the difference between the ultimate temperature when cooling is stopped and the temperature when the surface temperature rises and stabilizes due to the heat inside the steel sheet after cooling is stopped. Specifically, it is the difference between the temperature measured immediately after leaving the water cooling device and the temperature measured 20 to 50 seconds later depending on the plate thickness.
  • the heating temperature of the slab is less than 1000 ° C, the ferrite rate increases and the crack growth rate increases. If the temperature exceeds 1250 ° C, the structure becomes coarse and the toughness deteriorates.
  • accelerated cooling is performed. If the average cooling rate between 650 ° C and 400 ° C during the cooling process is less than 5 ° C / s, the ferrite rate is reduced.
  • the crack growth rate increases as well. Preferably, it is 25 ° C / s or less.
  • the accelerated cooling stop temperature exceeds 400 ° C, the ferrite ratio increases and the growth rate increases. Preferably it is above 350 ° C.
  • recuperation temperature range between the stop of accelerated cooling and the end of cooling exceeds 70, the dislocation density decreases and the propagation speed increases.
  • Such accelerated cooling may be performed by allowing the steel sheet to cool once after hot rolling and then reheating.
  • the stop temperature of the accelerated cooling is set to 400 ° C or less.
  • the reacceleration is performed by re-heating to an Ac point of + 50 ° C or more. I do.
  • reheating to a temperature higher than the Ac, point + 50 ° C is not performed when the temperature is lower than the Ac, point + 50 ° C.
  • the reheating temperature was set to Ac, point + 50 ° C. Desirable heating temperature is 3 points or more of Ac.
  • the cooling conditions are as described above. This condition is the same for online accelerated cooling and offline accelerated cooling.
  • the tempering temperature is exceeds A C l point occurs Osutenaito transformation, causing reduction and strength of the repeated softening, a decrease in toughness. Therefore, the tempering temperature was set to below Ac, point.
  • the tempering temperature is preferably 550 ° C or lower.
  • the step of reheating to the temperature of ACl point + 50 ° C or more and cooling may be performed twice or more as necessary.
  • the steps of reheating and cooling to Ac point + 50 ° C or more twice or more, the structure after cooling becomes finer, and the strength and toughness are improved.
  • the present invention relates to a steel material.
  • the steel material includes not only a plate material but also many other materials such as a pipe material, a rod material, a shape material, and a wire material.
  • a steel having the chemical composition shown in Table 1 was vacuum-melted in a laboratory to form a slab with a thickness of 100 to 160 mm, hot-rolled under various conditions, and cooled under various conditions to a thickness of 12 to 40 dragon thick steel plates were used.
  • Table 2 shows the hot rolling conditions and cooling conditions.
  • the structure, X-ray diffraction half width, tensile strength, toughness and fatigue crack growth rate of the obtained steel sheet were investigated by the following methods.
  • the steel structure was measured by polishing the cross section of a sample taken from a part corresponding to 1/4 of the plate thickness, etching the surface with 2% Nital etching solution, and observing 10 visual fields per sample by optical microscopy.
  • the structure of the steel sheet was determined by averaging 10 measured values.
  • the half-width of the X-ray diffraction was measured by taking a test piece of 25 square angles and electropolishing the surface parallel to the rolled surface 1 mm inside from the surface in the thickness direction.
  • X-ray measurement was performed using RU-200 manufactured by Rigaku Denki Co., Ltd. The output was 30 kV and 100 mA using a cobalt source. Of the 25 test specimens with horn angles, a range of 20 mm in diameter was assumed.
  • Tensile test specimens were taken from the center of the thickness of the specimens in parallel with the IS14A tensile test specimen in the direction of extension and subjected to a tensile test.
  • the toughness was determined by measuring the Charpy impact test specimen of No. 4 specified in ⁇ IS-Z2202 from the center of the sheet thickness in parallel with the direction of extension, and conducting a Charpy impact test to determine the impact absorption energy (vE-2 0, the unit was J).
  • Fig. 2 (a) Fatigue crack growth rate was measured by a fatigue test method using the sapo pulsar apparatus shown in Fig. 2 (a) and the CT specimen 1 shown in Fig. 2 (b).
  • reference numeral 1 is a CT test piece
  • 2 is a test solution tank
  • 3 is a solution circulation pump
  • 4 is a load cell
  • 5 is a hydraulic cylinder
  • 6 is a hydraulic source
  • 7 is a support valve.
  • 8 is a waveform generator
  • 9 is a load controller
  • 10a and 10b are load bars.
  • the CT specimen 1 (60 x 62.5 band, thickness 12.5 mm) shown in Fig. 2 (b) has a 2.5 mm cut 10, and a load rod 10 a And 10b.
  • This apparatus cuts the test piece 1 in the test solution tank 2 from the hydraulic cylinder 5 via the load rods 10a and 10b, and repeatedly applies stress to the tip.
  • the test piece was sampled from the center of the plate thickness in the thickness direction such that the longitudinal direction of the cut was parallel to the rolling vertical direction.
  • the fatigue test conditions were as follows.
  • the test atmosphere is air.
  • da / dN C (AK), where ⁇ : kN / mm,
  • Table 3 shows the results of the above investigation, measurement and fatigue test.
  • reference symbols B in the column of main structure mean bainite
  • M means martensite
  • F means ferrite
  • P means pearlite.
  • the steel sheets of Test Nos. 1 to 17 in which the structure and the half-value width satisfy the conditions specified by the present invention have a fatigue crack growth rate as low as 4 X 10 bandages / cycle or less, which is extremely excellent. Fatigue crack growth resistance.
  • the steel sheets of Test Nos. 18 to 35 had a strength of 490MPa class or more (TS ⁇ 620MPa, YS ⁇ 500MPa) and the absorbed energy was less than 100J.
  • the fatigue crack growth rate exceeded 4 ⁇ 10 mm / cycle, and the desired fatigue crack growth resistance Sex was not obtained.
  • the steel material according to the present invention has good fatigue crack propagation resistance and mainly has a hard structure, it is easy to increase the strength of the steel.
  • excellent toughness can be provided by adjusting the chemical composition. Therefore, it is suitable for steel plates of any thickness used as structural materials such as hulls, civil engineering structures, construction machinery, penstocks, marine structures, and line pipes. Further, the steel material of the present invention can be easily manufactured by cooling control after hot rolling, and therefore has great industrial value.

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Abstract

L'invention concerne un produit en acier présentant une structure principalement constituée d'une phase dure ainsi que d'excellentes caractéristiques de résistance à l'extension de fissure de fatigue. Selon la présente invention, ce produit présente une structure principalement constituée de ferrite/bainite ; son diagramme de force de diffraction des rayons X par rapport au plan (110) affiche une largeur de pic à mi-hauteur supérieure ou égale à 0,13° et ce produit est composé de 0,01 à 0,10 % de C, 0,03 à 0,6 % de Si, 0,5 à 2,0 % de Mn, 0,005 à 0,10 % d'Al sol., 0,0005 à 0,008 % de N et 4,0 à 6,0 % de Ft (3Mn + Cu + 1,5Cr + 1,8 Ni + 1,5Mo) ou d'au maximum 0,0030 % de B, 3,5 à 5,5 % de Ft et contient éventuellement un ou plusieurs éléments parmi Cu, Ni, Cr et Mo. Cette invention concerne également un procédé de fabrication du produit en acier susmentionné comprenant le laminage à chaud et consistant ensuite à soumettre le produit laminé à chaud à un traitement de trempe.
PCT/JP2004/008905 2003-06-19 2004-06-18 Produit en acier a excellentes caracteristiques de resistance a l'extension de fissure de fatigue et procede de fabrication dudit produit WO2004113581A1 (fr)

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JP2005507281A JP4706477B2 (ja) 2003-06-19 2004-06-18 耐疲労亀裂進展特性に優れた鋼材とその製造方法
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CN100463995C (zh) * 2005-12-12 2009-02-25 鞍钢股份有限公司 钨系低碳贝氏体钢及其生产方法
WO2011040621A1 (fr) * 2009-09-30 2011-04-07 Ｊｆｅスチール株式会社 Acier pour des structures possédant une excellente résistance aux intempéries et structure en acier
JP2011157573A (ja) * 2010-01-29 2011-08-18 Nippon Steel Corp 靱性に優れた高強度極厚ｈ形鋼およびその製造方法
JP2011157582A (ja) * 2010-01-29 2011-08-18 Nippon Steel Corp 靱性に優れた高強度極厚ｈ形鋼およびその製造方法
JP2013155422A (ja) * 2012-01-31 2013-08-15 Nippon Steel & Sumitomo Metal Corp 溶接継手
JP2019504200A (ja) * 2015-12-23 2019-02-14 ポスコＰｏｓｃｏ 応力腐食割れ抵抗性及び低温靭性に優れた低降伏比高強度鋼材及びその製造方法

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KR100905368B1 (ko) * 2006-05-23 2009-07-01 가부시키가이샤 고베 세이코쇼 내피로균열 진전성이 우수한 강판
KR101467031B1 (ko) * 2012-06-28 2014-12-01 현대제철 주식회사 강판 및 그 제조 방법
JP6211946B2 (ja) * 2013-09-20 2017-10-11 株式会社神戸製鋼所 疲労特性に優れた厚鋼板およびその製造方法
CN109797343A (zh) * 2019-01-22 2019-05-24 山东钢铁股份有限公司 一种适用于极寒地区的低合金高强度热轧钢带及其制备方法
CN110106444B (zh) * 2019-05-30 2020-08-25 首钢集团有限公司 一种驱动桥壳700MPa级热轧板卷及其制备方法

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JPH08199286A (ja) * 1995-01-20 1996-08-06 Nippon Steel Corp 板厚方向の疲労き裂伝播速度が低い厚鋼板およびその製造方法
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Publication number Priority date Publication date Assignee Title
CN100463995C (zh) * 2005-12-12 2009-02-25 鞍钢股份有限公司 钨系低碳贝氏体钢及其生产方法
WO2011040621A1 (fr) * 2009-09-30 2011-04-07 Ｊｆｅスチール株式会社 Acier pour des structures possédant une excellente résistance aux intempéries et structure en acier
EP2484790A4 (fr) * 2009-09-30 2016-11-30 Jfe Steel Corp Acier pour des structures possédant une excellente résistance aux intempéries et structure en acier
JP2011157573A (ja) * 2010-01-29 2011-08-18 Nippon Steel Corp 靱性に優れた高強度極厚ｈ形鋼およびその製造方法
JP2011157582A (ja) * 2010-01-29 2011-08-18 Nippon Steel Corp 靱性に優れた高強度極厚ｈ形鋼およびその製造方法
JP2013155422A (ja) * 2012-01-31 2013-08-15 Nippon Steel & Sumitomo Metal Corp 溶接継手
JP2019504200A (ja) * 2015-12-23 2019-02-14 ポスコＰｏｓｃｏ 応力腐食割れ抵抗性及び低温靭性に優れた低降伏比高強度鋼材及びその製造方法

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JP4706477B2 (ja) 2011-06-22
CN1809648B (zh) 2010-07-21

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