64results about How to "Excellent stretch flangeability" patented technology

Disclosed is a high-strength steel plate having superior ductility and stretch flangeability and a tensile strength (TS) of 980 MPa or higher, and having 0.17-0.73% C, 3.0% or less Si, 0.5-3.0 or less Mn, 0.1% or less P, 0.07% S, 3.0% or less Al, 0.010% or less N, and 0.7% or more Si + Al, an area ratio of martensite of 10-90% with respect to the entire steel plate composition, a residual austenite amount of 5-50%, and an area ratio of bainitic ferrite in the upper bainite of 5% or less with respect to the entire steel plate composition. Twenty-five percent or more of the aforementioned martensite is tempered martensite, and the total of the area ratio of the aforementioned martensite with respect to the entire steel plate composition, the aforementioned residual austenite amount and the area ratio of the aforementioned bainitic ferrite in the upper bainite with respect to the entire steel plate composition is 65% or more. The area ratio of polygonal ferrite with respect to the entire steel plate composition is 10% or less (including 0%), and the average amount of C in the aforementioned residual austenite is 0.70% or more.

The invention provides a high-strength hot-dip zinc plated steel sheet which exhibits high TS-El balance, excellent stretch frangeability, excellent workability due to low YR, and excellent impact characteristics, and a process for manufacturing the same. A high-strength hot-dip zinc plated steel sheet excellent in workability and impact characteristics, having a composition which contains by mass C: 0.05 to 0.3%, Si: 0.01 to 2.5%, Mn: 0.5 to 3.5%, P: 0.003 to 0.100%, S: 0.02% or below, Al: 0.010 to 1.5%, and N: 0.007% or below and further contains at least one element selected from among Ti, Nb and V in a total amount of 0.01 to 0.2% with the balance being Fe and unavoidable impurities and a microstructure which comprises, in terms of area fraction, 20 to 87% of ferrite, 3 to 10% (in total) of martensite and retained austenite, and 10 to 60% of tempered martensite and in which the average grain diameter of the second phase consisting of the martensite, retained austenite, and tempered martensite is 3[mu]m or below.

The invention relates to an ultrahigh strength hot-rolled complex phase steel plate and a production method thereof. The ultrahigh strength hot-rolled complex phase steel plate comprises the followingchemical components of, by weight percentage, 0.05-0.15% of C, 0.1-0.8% of Si, 1.2-2.3% of Mn, no more than 0.012% of P, no more than 0.005% of S, 0.20-0.70% of Cr, 0.10-0.50% of Mo, 0.02-0.06% of Nb, 0.05-0.13% of Ti, 0.015-0.060% of Als and the balance Fe and inevitable impurities. The ultrahigh strength hot-rolled complex phase steel plate has the advantages that by controlling rolling and cooling, the effects of fine-grain strengthening, phase transformation strengthening and precipitation strengthening are comprehensively utilized, and the purposes that the high-strength performance of materials is maintained, the microhardness difference between two phases is reduced through precipitation strengthening, and the performance of chambering is improved are achieved.

The present invention provides a high-strength steel sheet having a tensile strength (TS) of at least 780 MPa, excellent ductility and stretch flangeability, and excellent material-quality stability, achieved by: having a specific component composition; the steel structure having, in terms of area ratio, a total of ferrite and bainitic ferrite of 25-80%, and 3-20% martensite, and having, in terms of volume fraction, at least 10% retained austenite; the average crystalline particle diameter of the retained austenite being not more than 2[mu]m; the average Mn volume (mass%) in the retained austenite being at least 1.2 times the Mn volume (mass%) in the steel; and the area ratio of retained austenite that has an average C volume (mass%) of at least 2.1 times the C volume (mass%) of the steel being at least 60% of the area ratio of the total retained austenite.

An ultra soft high carbon hot-rolled steel sheet having excellent workability. The steel sheet is a high carbon hot-rolled steel sheet containing 0.2 to 0.7% C, and has a structure in which mean grain size of ferrite is 20 [mu]m or larger, the volume percentage of ferrite grains having 10 [mu]m or smaller size is 20% or less, mean diameter of carbide is in a range from 0.10 [mu]m to smaller than 2.0 [mu]m, the percentage, of carbide grains having 5 or more of aspect ratio is 15% or less, and the contact ratio of carbide is 20% or less. The steel sheet is manufactured by the steps of: rough-rolling the steel; finish-rolling the rough-rolled steel sheet at a temperature of 1100 DEG C or below at inlet of finish rolling, a reduction in thickness of 12% or more at the final pass, and a finishing temperature of (Ar3 - 10) DEG C or above; primary-cooling the finish-rolled steel sheet to a cooling-stop temperature of 600 DEG C or below within 1.8 seconds after the finish rolling at a cooling rate of higher than 120 DEG C/sec; secondary-cooling the primary-cooled steel sheet to hold the steel sheet at a temperature of 600 DEG C or below; coiling the secondary-cooled steel sheet at a temperature of 580 DEG C or below; pickling the coiled steel sheet; and spheroidizing-annealing the pickled steel sheet by the box annealing method at a temperature in a range from 680 DEG C to Ac1 transformation point.

The invention provides a process for manufacturing a high -strength steel sheet which has a strength of 490MPa or above and excellent stretch flange formability with a hole enlargement ratio of 80% or above after 10% working and which is reduced in the local property variation in a coil. A process for manufacturing a high-strength hot-rolled steel sheet, characterized by heating a billet which contains by mass C: 0.05 to 0.15%, Si: 0.1 to 1.5%, Mn: 0.5 to 2.0%, P: 0.06% or below, S: 0.005% or below, and Al: 0.10% or below with the balance consisting of Fe and unavoidable impurities to 1150 to 1300 DEG C, subjecting the resulting billet to hot rolling with a finishing temperature of 800 to 1000 DEG C, cooling the obtained sheet at an average cooling rate of 30 DEG C/s or above to a cooling stop temperature of 525 to 625 DEG C, stopping the cooling of the sheet for 3 to 10seconds, cooling the resulting sheet by such a cooling method as to cause nucleate boiling, and then coiling the sheet at 400 to 550 DEG C.

Disclosed is a steel sheet including 0.10 to 0.20 mass % of C, 0.8 to 2.5 mass % of Si, 1.5 to 2.5 mass % of Mn, and 0.01 to 0.10 mass % of Al, wherein P is limited to less than 0.1 mass %, and S is limited to less than 0.002 mass % and more than 0.1 mass %, and the structure includes bainitic ferrite and residual austenite such that area percentage of the bainitic ferrite in relation to the entire structure is at least 70%, area percentage of the residual austenite is 2 to 20%, and total area percentage of polygonal ferrite and quasi-polygonal ferrite is up to 15%, and proportion of the residual austenite having an average particle size of up to 5 μm in the residual austenite is at least 60%. The steel sheet is a TRIP steel sheet which has bainitic ferrite as its matrix, and it has a tensile strength (TS) of at least 980 MPa as well as an excellent stretch flangeability.

The invention discloses a single-ferrite-precipitated steel plate with high strength and a high pore-expansion property and a preparation method for the same. Steel comprises 0.05%-0.12% of C, 0.1%-0.7% of Si, 0.8%-2.2% of Mn, 0.05%-0.10% of Ti, less than 0.035% of P, less than 0.035% of S, 0.015%-0.060% of Als, 0.0015%-0.0050% of Ca, less than 0.0050% of Mg and less than 0.005% of N, at least oneof ingredients including 0.15%-0.3% of Cr and 0.05%-0.3% of Mo, at least one of ingredients including 0.02%-0.06% of Nb and 0.05%-0.25% of V as well as the balance being Fe and inevitable impurities.The linear speed of Si-Ca feeding is more than or equal to 3.5m/s, and a superheat degree of the molten steel is less than or equal to 30 DEG C; and the heating temperature of a casting blank is 1150-1250 DEG C, the multi-pass rolling total reduction rate is more than or equal to 80%, the final rolling temperature of hot rolling is 850-950 DEG C, the after-rolling cooling rate is 15-45 DEG C/s, and the rolling temperature is 550-650 DEG C. The finished steel plate has the good pore-expansion property.

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 30 to 95%, and bainite: 5 to 70%. When a region that is surrounded by a grain boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14° to all crystal grains is 20 to 100% by area ratio. An average aspect ratio of ellipses equivalent to the crystal grains is 5 or less. An average distribution density of the total of Ti-based carbides and Nb-based carbides each having a grain size of 20 nm or more on ferrite grain boundaries is 10 carbides/μm or less.

A hot-rolled steel sheet includes a predetermined chemical composition, and a structure which includes, by area ratio, a ferrite in a range of 5% to 60% and a bainite in a range of 30% to 95%, in which in the structure, in a case where a boundary having an orientation difference of equal to or greater than 15° is defined as a grain boundary, and an area which is surrounded by the grain boundary and has an equivalent circle diameter of equal to or greater than 0.3 μm is defined as a grain, the ratio of the grains having an intragranular orientation difference in a range of 5° to 14° is, by area ratio, in a range of 20% to 100%.

Provided are: a high-strength steel sheet having excellent stretchability and stretch flangeability, and a low yield ratio; and a method for manufacturing the high-strength steel sheet. A low-yield-ratio high-strength cold-rolled steel sheet having a chemical composition containing, by mass, 0.05 to 0.10% of C, 0.6 to 1.3% of Si, 1.4 to 2.2% of Mn, 0.08% or less of P, 0.010% or less of S, 0.01 to 0.08% of Al, and 0.010% or less of N, with the remainder made up by Fe and unavoidable impurities. The low-yield-ratio high-strength cold-rolled steel sheet has a microstructure in which the average crystal grain size of ferrite is equal to or smaller than 15 μm, the volume fraction of ferrite is equal to or greater than 70%, the volume fraction of bainite is equal to or greater than 3%, the volume fraction of residual austenite is 4 to 7%, the average crystal grain size of martensite is equal to or smaller than 5 μm, and the volume fraction of martensite is 1 to 6%. The average C concentration (mass%) in the residual austenite is 0.30 to 0.70%. The steel sheet characteristics are such that the yield ratio is equal to or less than 64% and the tensile strength is equal to or greater than 590 MPa.

The purpose of the present invention is to provide: a high strength steel sheet that has high strength such that tensile strength is at least 780 MPa, and excellent blanking quality combined with stretch-flangeability; and a manufacturing method therefor. Provided is a high strength steel sheet wherein: the steel sheet contains, in mass%, C: 0.05-0.30%, Si: 0.6-2.0%, Mn 1.3-3.0%, P: not more than 0.10%, S: not more than 0.030%, Al: not more than 2.0%, N: not more than 0.010%, and one or more of Ti, Nb and V: 0.01-1.0% each, the balance being obtained from iron and unavoidable impurities; the steel sheet comprises at least 50% area ratio of ferrite structure; the amount of Fe deposited is at least 0.04 mass%; the steel sheet contains a deposit in which the particle diameter is less than 20 nm; and C* defined by expression (1) and C*p defined by expression (2) satisfy the conditions in expressions (3)-(5). C*=([Ti]/48+[Nb]/93+[V]/51+[Mo]/96+[Ta]/181+[W]/184) * 12... (1) C*p=([Ti]p/48+[Nb]p/93+[V]p/51+[Mo]p/96+[Ta]p/181+[W]p/184)*12... (2) C* >= 0.035... (3) -0.015 <=[C]-C* <= 0.03... (4) C*p/C* >=0.3... (5)

Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability at a range in which the tensile strength is at least 980 MPa and the 0.2% yield strength is at least 700 MPa. In this high-strength cold-rolled steel sheet, the chemical composition is adjusted as appropriate, and the area ratio of the belowmentioned metal structure at a position of 1/4 sheet thickness in the steel sheet satisfies the following: at least 30 area% of tempered martensite; 15-70 area%, inclusive, of bainite; at least 90 total area% of tempered martensite and bainite; 0-5 area%, inclusive, of ferrite; and 0-4 area%, inclusive, of retained austenite. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of at least 980 MPa and a 0.2% yield strength of at least 700 MPa.

A steel sheet has a specific chemical composition and has a structure represented by, by area ratio, ferrite: 0 to 30%, and bainite: 70 to 100%. When a region that is surrounded by a grain boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more is defined as a crystal grain, the proportion of crystal grains each having an intragranular misorientation of 5 to 14° to all crystal grains is 20 to 100% by area ratio. A grain boundary number density of solid-solution C or a grain boundary number density of the total of solid-solution C and solid-solution B is 1 piece/nm² or more and 4.5 pieces/nm² or less. An average grain size of cementite precipitated at grain boundaries is 2 μm or less.

Provided are a coated steel sheet and so forth, the coated steel sheet having a tensile strength of 590 MPa or more and good stretch-flangeability. The coated steel sheet includes a specific component composition, in which the area fraction of a ferrite phase is 80% or more and 98% or less, the area fraction of a martensite phase of 2% or more and 15% or less, ferrite grains have an average thickness of 3.0 μm or less in the sheet-thickness direction, the martensite phase has an average grain size of 2.0 μm or less, and a Nb-containing carbide precipitated in the ferrite grains has an average grain size of 8 nm or less, and in which the steel sheet has a tensile strength of 590 MPa or more.

Provided are: a high-strength cold-rolled steel sheet having excellent ductility, stretch-flangeability and bendability; and a method for manufacturing the high-strength cold-rolled steel sheet. A high-strength cold-rolled steel sheet having the following chemical composition, in mass%: 0.12 to 0.22% of C; 0.8 to 1.8% of Si; 1.8 to 2.8% of Mn; 0.020% or less of P; 0.0040% or less of S; 0.005 to 0.08% of Al; 0.008% or less of N; 0.001 to 0.040% of Ti; 0.0001 to 0.0020% of B; and 0.0001 to 0.0020% of Ca; with the remainder made up by Fe and unavoidable impurities. The high-strength cold-rolled steel sheet has such a structure that the total area ratio of a ferrite phase and a bainite phase is 50 to 70%, the average crystal particle diameter of the ferrite phase and the bainite phase is 1 to 3 μm, the area ratio of a tempered martensite phase is 25 to 45%, the average crystal particle diameter of the tempered martensite phase is 1 to 3 μm, and the area ratio of a retained austenite phase is 2 to 10%.

Provided is a high tensile strength steel having a tensile strength of 780 MPa grade or higher which is used for structural members of automobiles, and more specifically relates to high tensile strength steel having excellent bendability and stretch-flangeability while still satisfying characteristics of DP steels of low yield ratio and high ductility, and to a manufacturing method thereof.

Provided are a high-strength steel plate having superior ductility and stretch flangeability and a method for manufacturing the same. This high-strength steel plate is formed from a prescribed component composition and has C/Mn of 0.08-0.20 with the balance being iron and inevitable impurities. The structure has, in surface area to total structure, a total of 40-70% of ferrite and bainitic ferrite, and 5-35% of martensite, with the remainder austenite being 5-30%, and furthermore, and the proportion of martensite (including the remainder austenite) adjacent to bainitic ferrite being 60% or greater of the total martensite (including the remainder austenite). The proportion of hardness differential for microhardness measured at a measurement interval of 0.5 [mu]m being 4.0 GPa or less is 70%or greater, and the proportion of structure out of the total structure having a microhardness of 8.0 GPa or less is 85% or greater.

The purpose of the present invention is to provide: a steel sheet having a high-strength of 1180 MPa or more, excellent component dimension accuracy, stretch-flange characteristics, bendability, and toughness; and a method for manufacturing the same. This high-strength steel sheet has a predetermined compositional makeup and a tensile strength is 1180 MPa or more, and has a steel structure, wherein: the area percentage of martensite having a carbon concentration of more than 0.7x[%C] but less than 1.5x[%C] is 55% or more; the area percentage of tempered martensite having a carbon concentration of not more than 0.7x[%C] is 5-40%; the ratio of the carbon concentration of retained austenite with respect to the volume percentage of the retained austenite is 0.05-0.40; the respective average crystal particle sizes of the martensite and the tempered martensite are not more than 5.3 [mu]m. Note that [%C] represents the contained amount (mass%) of componental element C in steel.