Abstract: A high-strength low-carbon bainitic fire-resistant steel and a preparation method thereof, belong to the technical field of low-carbon air-cooled bainitic fire-resistant steels. The problems of low yield strength, complicated production process and poor high-temperature mechanical properties of the fire-resistant steel in the prior art are solved herewith. The high-strength low-carbon bainitic fire-resistant steel disclosed herein have chemical components by mass percent of: 0.07%-0.1% of C, 0.7%-0.9% of Si, 1.0%-1.5% of Mn, 0.7%-0.8% of Cr, 1.0%-1.3% of Ni, 0.3%-0.35% of Cu, 0.6%-0.8% of Mo, 0.025%-0.035% of Nb, 0.09%-0.15% of V, 0.01%-0.015% of Ti, <0.2% of Nb+V+Ti, <0.02% of Alt, <0.003% of S, <0.008% of P, and the balance is Fe and inevitable impurities. Improvements are realized in the yield strength and high-temperature mechanical properties of the fire-resistant steel.

Abstract: The invention relates to a steel for a tool holder. The steel comprises the following main components (in wt. %): C 0.07-0.13 Si 0.10-0.45 Mn 1.5-3.1 Cr 2.4-3.6 Ni 0.5-2.0 Mo 0.1-0.7 Al 0.001-0.06 S?0.003 The steel has a bainitic microstructure comprising up to 20 volume % retained austenite and up to 20 volume % martensite.

Abstract: Provided are a steel sheet which has a tensile strength of 900 MPa or higher and excellent weldability, and a method for producing the steel sheet. The steel sheet has a specific composition and a microstructure containing, in terms of area fraction, ferrite of 30% or less (including 0%), tempered martensite of 70% or more (including 100%), and the balance other than ferrite and the tempered martensite of 10% or less (including 0%) in total, the tempered martensite having an average grain size thereof is 5 ?m or lower, the tempered martensite having iron-based carbides, which have average particle sizes of 100 nm or less, precipitated on grain boundaries, and the tempered martensite containing, in terms of atomic concentration, 5 atom % or more in total of Si and Mn on the grain boundaries of the tempered martensite. The steel sheet has a tensile strength of 900 MPa or higher.

Abstract: A high-strength air-hardenable multiphase steel having minimal tensile strengths in a non air hardened state of 750 MPa and excellent processing properties, said steel comprising the following elements in % by weight: C?0.075 to ?0.115; Si?0.200 to ?0.300; Mn?1.700 to ?2.300; Cr?0.280 to ?0.4800; Al?0.020 to ?0.060; N?0.0020 to ?0.0120; S?0.0050; Nb?0.005 to ?0.050; Ti?0.005 to ?0.050; B?0.0005 to ?0.0060; Ca?0.0005 to ?0.0060; Cu?0.050; Ni?0.050; remainder iron, including usual steel accompanying smelting related impurities, wherein for a widest possible process window during continuous annealing of hot rolled or cold rolled strips made from the steel a sum content of M+Si+Cr in the steel is a function of a thickness of the steel strips according to the following relationship: for strip thicknesses of up to 1.00 mm the sum content of M+Si+Cr is ?2.350 and ?2.500%, for strip thicknesses of over 1.00 to 2.00 mm the sum of Mn+Si+Cr is ?2.500 and ?2.950%, and for strip thicknesses of over 2.

Abstract: A steel strip continuous annealing device has a vertical annealing furnace 10 in which a heating zone 14, a soaking zone 16, and a cooling zone 18 are arranged in this order, and anneals a steel strip P passing through the zones 14, 16, and 18 in the order while being conveyed in the vertical direction in the vertical annealing furnace 10. The heating zone 14, the soaking zone 16, and the cooling zone 18 communicate through an atmosphere separation portion 36. One of a gas delivery port 38 and a gas discharge port 40 is positioned in an upper part and the other one of the gas delivery port 38 and the gas discharge port 40 is positioned in a lower part in each of the heating zone 14, the soaking zone 16, and the cooling zone 18.

Abstract: A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.

Abstract: A large continuous annealing device that anneals a steel strip by multiple passes in a vertical annealing furnace and is capable of quickly switching the atmosphere in the furnace is provided. A steel strip continuous annealing device 100 has a vertical annealing furnace 10 in which a heating zone 14, a soaking zone 16, and a cooling zone 18 are arranged in this order, and anneals a steel strip P passing through the zones 14, 16, and 18 in the order while being conveyed in the vertical direction in the vertical annealing furnace 10. Adjacent zones communicate through a communicating portion 30 or 32 connecting upper parts or lower parts of the zones. A gas delivery port 38 is provided in each zone, in the position opposite in the vertical direction to the position of the communicating portion with the immediately preceding zone in the steel strip P passing order.

Abstract: A high-strength steel sheet has good ductility and stretch-flangeability and has a tensile strength (TS) of 980 MPa or more. The steel sheet contains 0.17%-0.73% C, 3.0% or less Si, 0.5%-3.0% Mn, 0.1% or less P, 0.07% or less S, 3.0% or less Al, and 0.010% or less N, in which Si+Al is 0.7% or more.

Abstract: A method for forming and treating a steel article of a high strength and ductile alloy. The method includes the steps of providing a starting steel composition for the steel article, preheating the composition, heating the starting material to a peak temperature range in less than forty seconds, holding the heated steel composition at the peak temperature range for between two and sixty seconds, quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of 200 to 3000° C./sec (360 and 5400° F./sec), removing residual quench media from the surface of the quenched steel composition, tempering the quenched steel composition at a temperature of 100 to 704° C. (212 to 1300° F.); and air cooling the tempered steel composition to less than 100° C. (212° F.) to form a steel having desired mechanical properties.

Abstract: Provided is a method that enables manufacture, with good productivity, of a high-strength cold-rolled steel with improved elongation (EL), stretch-flangeability (?), bendability (R), and balance of these properties (TS×EL×?/1000), outstanding composite workability as evaluated by Erichsen test, and a tensile strength of at least 980 MPa. A steel material satisfying a prescribed constituent composition is held and soaked for at least fifty seconds at a temperature at or above the Ac3 point, after which the steel material is cooled at an average cooling rate of at least 15° C./sec to a discretionary temperature (T) that satisfies expression (1) below, held for 5-180 seconds in a temperature range that satisfies expression (1) below, then heated to a temperature region that satisfies expression (2) below, held for at least 50 seconds in this temperature region, and then cooled. 300° C.?T1 (° C.)<400° C. ??(1) 400° C.?T2 (° C.)<540° C.

Abstract: A hot-dip galvanizing layer or an alloyed hot dip galvanizing layer is formed on the surface of a base steel sheet in which in volume fraction, 40 to 90% of a ferrite phase and 5% or less of a retained austenite phase are contained, and a ratio of non-recrystallized ferrite to the entire ferrite phase is 50% or less in volume fraction, and further a grain diameter ratio being a value of, of crystal grains in the ferrite phase, an average grain diameter in the rolling direction divided by an average grain diameter in the sheet width direction is 0.75 to 1.33, a length ratio being a value of, of hard structures dispersed in island shapes, an average length in the rolling direction divided by an average length in the sheet width direction is 0.75 to 1.33, and an average aspect ratio of inclusions is 5.0 or less.

Abstract: A high-strength cold-rolled steel sheet has a specific chemical composition and has a steel microstructure meeting conditions: a total content of bainitic ferrite (BF) and tempered martensite (TM) is 65% (in area percent, hereinafter the same for steel microstructure) or more; a fresh martensite (M) content is 3% to 18%; a retained austenite content is 5% or more; and a polygonal ferrite (F) content is 5% or less. The steel sheet has a specific average KAM<1.00° of 0.50° or more and has a tensile strength of 980 MPa or more. The high-strength cold-rolled steel sheet excels in formability and shape fixability.

Abstract: The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 780 MPa.

Abstract: A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.

Abstract: The invention relates to a method for producing a component from transformable steel by hot forming, in which a plate first is cut out of a strip or sheet as the pre-material, and is then heated to forming temperature and pre-formed, having an at least partially martensitic transformation structure after forming. Instead of a press mould hardening, the at least partially martensitic transformation structure is created in the pre-material, or in the plate to be formed, by austenitisation and quenching already before forming, and then the thus-conditioned plate is reheated after forming, while maintaining the at least partially martensitic transformation structure, to a temperature below the Ac1 transformation temperature, and formed at this temperature.

Abstract: In a process for producing a cold- or hot-rolled steel strip from an ultrahigh-strength multiphase steel having a particular composition the required multiphase microstructure is generated during continuous heat treatment. The cold- or hot-rolled steel strip is heated in the continuous heat treatment furnace to a temperature in the range from 700 to 950° C. and the heat-treated steel strip is subsequently cooled from the heat treatment temperature at a cooling rate of from 15 to 100° C./s to a first intermediate temperature of from 300 to 500° C. followed by cooling at a cooling rate of from 15 to 100° C./s to a second intermediate temperature of from 200 to 250° C.; the steel strip is subsequently cooled at a cooling rate of from 2 to 30° C./s in air to room temperature or the cooling at a cooling rate of from 15 to 100° C./s is maintained from the first intermediate temperature to room temperature.

Abstract: A high-strength multi-phase steel having tensile strengths of no less than 580 MPa, preferably with a dual-phase structure for a cold-rolled or hot-rolled steel strip having improved forming properties, in particular for lightweight vehicle construction is disclosed, containing the following elements (contents in % by mass): C 0.075 to ?0.105; Si 0.200 to ?0.300; Mn 1.000 to ?2.000; Cr 0.280 to ?0.480; Al 0.10 to ?0.060; P ?0.020; Nb ?0.005 to ?0.025; N ?0.0100; S ?0.0050; the remainder iron, including conventional steel-accompanying elements not mentioned above.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: A method for controlling the atmosphere in a protective gas chamber for the continuous treatment of metal strips. A metal strip is guided into and out of the protective gas chamber via locks. At least one lock has at least two sealing elements for the metal strip which runs through it, with the result that a sealed chamber is formed between the two sealing elements. The gas pressure (P2, PD) is measured in the protective gas chamber and in the sealed chamber of the lock and the pressure (PD) in the sealed chamber is regulated, to be precise in such a way that, during operation, the differential pressure between the protective gas chamber and the sealed chamber is kept as far as possible to an optimum value.

Abstract: Steel with high strength and good formability is produced with compositions and methods for forming austenitic and martensitic microstructure in the steel. Carbon, manganese, molybdenum, nickel copper and chromium may promote the formation of room temperature stable (or meta-stable) austenite by mechanisms such as lowering transformation temperatures for non-martensitic constituents, and/or increasing the hardenability of steel. Thermal cycles utilizing a rapid cooling below a martensite start temperature followed by reheating may promote formation of room temperature stable austenite by permitting diffusion of carbon into austenite from martensite.

Abstract: Steel with high strength and good formability is produced with compositions and methods for forming austenitic and martensitic microstructure in the steel. Carbon, manganese, molybdenum, nickel copper and chromium may promote the formation of room temperature stable (or meta-stable) austenite by mechanisms such as lowering transformation temperatures for non-martensitic constituents, and/or increasing the hardenability of steel. Thermal cycles utilizing a rapid cooling below a martensite start temperature followed by reheating may promote formation of room temperature stable austenite by permitting diffusion of carbon into austenite from martensite.

Abstract: A method for annealing a strip of steel having a variable thickness in its length direction with at least thicker and thinner sections, wherein the strip has been cold rolled to form the thicker and thinner sections, one thicker and one thinner section having a length of at most a few meter. The annealing is performed by continuous annealing.

Abstract: There is provided a heat treatment method in which high-quality tempering treatment can be performed in a short period of time. In this method, when an object to be treated is tempered after being quenched, the object to be treated is rapidly cooled to a 90% martensite transformation finishing temperature without being cooled to the ordinary temperature after quench heating, and then is subjected to 100% martensite transformation by using a 100° C. liquid, and thereafter, tempering treatment is performed after the whole of the object to be treated is soaked by using the 100° C. liquid.

Abstract: A high-strength cold-rolled steel sheet providing a product with a good surface condition after press forming, having excellent bake hardenability and anti room temperature aging property, and having a dual phase structure with a tensile strength of at least 340 MPa is provided. A high-strength cold-rolled steel sheet has a structure comprising a main phase which is a ferrite and a secondary phase which is a low temperature transformation product including a martensite and has a hardness distribution of the ferrite phase in an arbitrary cross section having a length of 10 mm in the widthwise 10 direction of the sheet which satisfies the relationship prescribed by (HV(max)?HV(ave))<0.5×(Hv(ave). HV(max) is the maximum Vickers hardness of ferrite grains in a region at a distance of from (?)t to (¼)t in the thickness direction from the surface when the thickness of the high-strength cold-rolled steel sheet is t, and Hv(ave) is the average Vickers hardness of ferrite grains in this region.

Abstract: A high strength steel, including about 0.05 to about 0.25% of C, less than about 0.5% of Si, about 0.5 to about 3.0% of Mn, not more than about 0.06% of P, not more than about 0.01% of S, about 0.50 to about 3.0% of Sol. Al, not more than about 0.02% of N, about 0.1 to about 0.8% of Mo, about 0.02 to about 0.40% of Ti, and the balance of iron and unavoidable impurities, wherein the steel has a structure formed of at least three phases including a bainite phase, and a retained austenite phase in addition to a ferrite phase having a composite carbide containing Ti and Mo dispersed and precipitated therein, wherein the total volume of the ferrite phase and the bainite phase is not smaller than 80%, the volume of the bainite phase is about 5% to about 60%, and the volume of the retained austenite phase is about 3 to about 20%.

Abstract: A method for the manufacturing of high strength cold rolled steel sheets includes continuously annealing a cold rolled steel sheet that has a composition containing C: 0.05-0.3% mass, Si: 0.6-3.0% mass, Mn: 1.0-3.0% mass, P: ?0.1% mass, S: ?0.02% mass, Al: 0.01-1% mass, N: ?0.01% mass, and Fe and inevitable impurities: balance, in a manner such that the cold rolled steel sheet is heated in a furnace using an oxidizing burner to a steel sheet temperature of ?700° C., then soak-annealed in a reducing atmosphere furnace at 750-900° C., then cooled so the average cooling rate between 500° C. and 100° C. is ?50° C./s. High-Si cold rolled steel sheets with high strength and good phosphatability while containing Si?0.6% are obtained without controlling conditions so as to increase the dew point in the reducing atmosphere in the soaking furnace or to increase the vapor hydrogen partial pressure ratio.

Abstract: A hot forming die that includes a first die and a second die. The first die has a first die structure that is formed of a tool steel. The first die structure has a first die surface and a plurality of first cooling apertures. The first die surface has a complex shape. The first cooling apertures are spaced apart from the die surface by a first predetermined distance. The second die has a second die surface. The first and second die surfaces cooperate to form a die cavity. Related methods for forming a hot forming die and for hot forming a workpiece are also provided.

Abstract: The invention relates to a high strength multi-phase steel for a cold- or hot-rolled steel strip having excellent forming properties, in particular for light vehicle construction, comprising the elements (contents in mass %): C 0.060 to=0.115; Al 0.020 to=0.060; Si 0.100 to=0.500; Mn 1.300 to=2.500; P=0.025; S=0.0100; Cr 0.280 to=0.480; Mo<0.150; Ti=0.005 to=0.050; Nb=0.005 to=0.050; B=0.0005 to=0.0060; N=0.0100; the remainder being iron including the usual elements present in steel and which are not mentioned above.

Abstract: The invention relates to a method and equipment for controlling flatness of a stainless steel strip in connection with cooling after annealing in a finishing line.

Abstract: The present invention relates to a method for acting on the temperature of a travelling strip (4) by blowing gas or a water/gas mixture, whereby a plurality of jets of gas or a water/gas mixture, extending toward the surface of the strip and arranged in such a way that the impacts (24, 34) of the jets of gas or water/gas mixture on each surface of the strip are distributed at the nodes of a two-dimensional network, are sprayed onto each face of the strip. The impacts (24) of the jets on one face (A) are not opposite the impacts (34) of the jets on the other face (B), and the jets of gas or water/gas mixture come from tubular nozzles (23, 33) which are supplied by at least one distribution chamber (21, 31) and extend at a distance from the distribution chamber in such a way as to leave a free space for the flow of the returning gas or water/gas mixture parallel to the longitudinal direction of the strip and perpendicular to the longitudinal direction of the strip.

Abstract: A steel sheet contains, on a mass percent basis, 0.03%-0.12% C, 0.5% or less Si, 0.8%-1.8% Mn, 0.030% or less P, 0.01% or less S, 0.005%-0.1% Al, 0.01% or less N, 0.035%-0.100% Ti, and the balance being Fe and incidental impurities and has microstructures with a fraction of polygonal ferrite of 80% or more, the polygonal ferrite having an average grain size of 5 to 10 ?m. The amount of Ti present in a precipitate having a size of less than 20 nm is 70% or more of the value of Ti* calculated using expression (1): Ti*=[Ti]?48×[N]/14??(1) where [Ti] and [N] represent a Ti content (percent by mass) and a N content percent by mass), respectively, of the steel sheet.

Abstract: A manufacturing apparatus comprises a final stand, with standing side members, and a cooling apparatus. The cooling apparatus comprises rows of upper surface cooling nozzles, rows of lower surface cooling nozzles, and an upper surface guide on the upper surface side of the steel sheet. An end portion of the cooling apparatus on a side of the final stand is arranged between the standing side members of the housing. When defining a width of a uniformly cooled region, an average gap distance (Wsw) between the end portion of the width of the uniformly cooled region and the standing side member of the housing; a gravity acceleration rate, an average water volume density of the width of the uniformly cooled region, and a value determined by Wsw and an average distance h between the upper surface guide and the upper surface of the steel sheet, a specific relation is satisfied.

Abstract: A high carbon steel sheet having superior strength and ductility and a method for manufacturing the same comprising: 0.2 to 1.0 wt % carbon (C), 0 to 3.0 wt % silicon (Si), 0 to 3.0 wt % manganese (Mn), 0 to 3.0 wt % chromium (Cr), 0 to 3.0 wt % nickel (Ni), 0 to 0.5 wt % molybdenum (Mo), 0 to 3.0 wt % aluminum (Al), 0 to 0.01 wt % boron (B), 0 to 0.5 wt % titanium (Ti), and the remainder substantially being iron (Fe) and inevitable impurities. The contents of carbon, manganese, chromium, and nickel satisfy the following Equation 1, and the contents of silicon and aluminum satisfy the following Equation 2: (3.0?2.5×C)wt %?(Mn+Cr+Ni/2)?8.5 wt %—(Equation 1) Si+Al>1.0 wt % (Equation 2).

Abstract: A method for manufacturing a high strength steel sheet includes heating a steel sheet containing at least 0.10 mass % of carbon to either a temperature in an austenite single phase region or a temperature in an (austenite+ferrite) two-phase region; cooling the steel sheet to a cooling stop temperature as a target temperature set within a cooling temperature region ranging from Ms to (Ms?150° C.) to allow a portion of non-transformed austenite to proceed to martensitic transformation; retaining a coldest part in a sheet widthwise direction of the steel sheet at a temperature in a temperature range from the cooling stop temperature as the target temperature to (the cooling stop temperature+15° C.) for 15 seconds to 100 seconds; and heating the sheet to a temperature to temper said martensite, wherein “Ms” represents martensitic transformation start temperature and said cooling temperature region is exclusive of Ms and inclusive of (Ms?150° C.).

Abstract: Method of reducing the formation of folds on metal strips (1) exposed to rapid heating in continuous heat-treatment lines, in which lines said strips are caused to pass through heating sections (2) comprising successive and separate heating means (5; 5a; 5b; 5c; 5d), wherein the average slope of the increase in temperature of the strip between the inlet and the outlet of a heating means decreases from one heating means to the following heating means.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: A cooling device and a cooling method for a hot strip allow uniform and stable cooling of the strip at a high cooling rate when supplying the coolant to the upper surface of the hot strip. The cooling device includes an upper header unit 21 for supplying a rod-like flow to the upper surface of the strip 10. The upper header unit 21 is formed of the first upper header group including plural first upper headers 21a arranged in a conveying direction and a second upper header group including plural second upper headers 21b arranged in the conveying direction. The cooling device is provided with an ON-OFF mechanism 30 to allow each of the upper headers 21a and 21b of the first and the second upper header groups to independently execute the ON-OFF control (start/end injection control) of an injection (feeding) of the rod-like flow.

Abstract: A galvannealed steel sheet includes: a steel sheet; a galvannealed layer; and a Mn—P based oxide film. A Zn—Fe alloy phase in the galvannealed layer is measured by X-ray diffractometry. The value of a diffraction intensity ?(2.59 ?) of ? phase divided by a diffraction intensity ?1(2.13 ?) of ?1 phase is less than or equal to 0.1. The value of a diffraction intensity ?(1.26 ?) of ? phase divided by a diffraction intensity ?1(2.13 ?) of ?1 phase is greater than or equal to 0.1 and less than or equal to 0.4. The Mn—P based oxide film is formed using 5 to 100 mg/m2 of Mn and 3 to 500 mg/m2 of P on a surface of the galvannealed layer.

Abstract: A cooling method of steel plate able to raise a cooling uniformity in a steel plate conveyance direction comprising, at a front stage part of a cooling apparatus, not spraying while a front end region of steel plate is passing, spraying by successively increasing the cooling water rate from 80 to 95 vol % (Qfront) of a standard water density when the front part region passes so that the amount of cooling water becomes the standard water density when a boundary part of the front part region and a center part region arrives, and continuing spraying by the standard water density while the center part region is passing, then, at a rear stage part of the cooling apparatus, spraying by making the amount of cooling water 80 to 95 vol % of the standard water density while the front end region of the steel plate is passing, successively increasing the amount of cooling water rate from 80 to 95 vol % of the standard water density when the front part region passes so that the amount of cooling water becomes the standard

Abstract: The present invention provides a high strength steel sheet with 780 MPa class tensile strength excellent in bending workability and fatigue strength. The high strength steel sheet is (1) a steel sheet whose steel composition contains: C: 0.05-0.20%; Si: 0.6-2.0%; Mn: 1.6-3.0%; P: 0.05% or below; S: 0.01% or below; Al: 0.1% or below; and N: 0.01% or below, the balance comprising iron and inevitable impurities, in which (2) a microstructure comprises a polygonal ferrite structure and a structure formed by low-temperature transformation, in which, when a sheet plane located at a depth of 0.1 mm from a surface of the steel sheet is in the observation under a scanning electron microscope with respect to twenty sights in total in different positions in the sheet-width direction, the maximum value of the areal proportion of the polygonal ferrite (Fmax) and the minimum value of the areal proportion of the ferrite (Fmin) in a 50 ?m×50 ?m area in each sight satisfy Fmax?80%, Fmin?10%, and Fmax?Fmin?40%.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.

Abstract: A hot forming die that includes a first die and a second die. The first die has a first die structure that is formed of a tool steel. The first die structure has a first die surface and a plurality of first cooling apertures. The first die surface has a complex shape. The first cooling apertures are spaced apart from the die surface by a first predetermined distance. The second die has a second die surface. The first and second die surfaces cooperate to form a die cavity. Related methods for forming a hot forming die and for hot forming a workpiece are also provided.

Abstract: A continuous annealing and pickling process of flat cold-rolled products, such as stainless steel strips, to obtain a high surface quality product at high production rates and with a low environmental impact. It comprises the following steps: heating, up to a temperature comprised in the range 650-1050° C., in an atmosphere with an oxygen content comprised in the range from 0.5 to 12%; heating for a time comprised from 10 to 200 sec up to a temperature comprised in the range from 650 to 1200° C. in presence of oxidizing agents and/or inert agents; cooling down to temperatures comprised in the range from 650° C. to ambient temperature in presence of oxidizing agents and/or inert agents; thermochemical or electrolytic descaling and finally possible pickling and/or passivation, by means of the use of pickling baths consisting of mineral acid solutions.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: The present disclosure relates to an iron alloy sheet comprising ?-Fe, and/or ?-Fe phases wherein the alloy has a melting point in the range of 800 to 1500° C., a critical cooling rate of less than 105 K/s and structural units in the range of about 150 nm to 1000 nm.

Abstract: High yield ratio high-strength thin steel sheet superior in weldability and ductility characterized by: being comprised of steel containing, by mass %, C: over 0.030 to less than 0.10%, Si: 0.30 to 0.80%, Mn: 1.7 to 3.2%, P: 0.001 to 0.02%, S: 0.0001 to 0.006%, Al: 0.060% or less, N: 0.0001 to 0.0070%, containing further Ti: 0.01 to 0.055%, Nb: 0.012 to 0.055%, Mo: 0.07 to 0.55%, B: 0.0005 to 0.0040%, and simultaneously satisfying 1.1 ?14×Ti(%)+20×Nb(%)+3×Mo(%)+300×B(%)?3.7, the balance comprised or iron and unavoidable impurities, and having a yield ratio of 0.64 to less than 0.92, a TS×E11/2 of 3320 or more, an YR×TS×EL1/2 of 2320 or more, and a maximum tensile strength (TS) of 780 MPa or more.

Abstract: A hot-rolled high strength steel sheet in which, without using expensive Mo, and by effectively using Ti, which is an expensive element, the amount of precipitation hardening of which is large, both ductility and stretch-flangeability are improved at a tensile strength of 780 MPa or higher, and desirable tensile fatigue properties are exhibited. The hot-rolled high strength steel sheet has a composition including, in percent by mass, C: 0.06% to 0.15%, Si: 1.2% or less, Mn: 0.5% to 1.6%, P: 0.04% or less, S: 0.005% or less, Al: 0.05% or less, and Ti: 0.03% to 0.20%, the balance being Fe and incidental impurities, wherein the steel sheet has a structure in which the volume fraction of ferrite is 50% to 90%, the balance is substantially bainite, the total volume fraction of ferrite and bainite is 95% or more, precipitates containing Ti are precipitated in the ferrite, and the precipitates have an average diameter of 20 nm or less; and 80% or more of the Ti content in the steel is precipitated.

Abstract: In a method of manufacturing a high tensile strength thick steel plate, a steel slab contains 0.03-0.055% of C, 3.0-3.5% of Mn, and 0.002-0.10% of Al, the amount of Mo is limited to 0.03% or less, the amount of Si is limited to 0.09% or less, the amount of V is limited to 0.01% or less, the amount of Ti is limited to 0.003% or less, the amount of B is limited to 0.0003% or less, and of which Pcm value representing a weld cracking parameter is fallen within the range of 0.20-0.24% and DI value representing a hardenability index is fallen within the range of 1.00-2.60, is heated to 950-1100° C. The steel slab is subjected to a rolling process with a cumulative draft of 70-90% when a temperature is in a range of 850° C. or more, and then, the steel slab is subjected to a rolling process at 780° C. or higher with a cumulative draft of 10-40% when a temperature is in a range of 780-830° C., and subsequently, accelerated cooling at a cooling rate of 8-80° C./sec is started from 700° C.

Abstract: A cold-rolled steel sheet of carbon steel or low-alloy steel comprising C: 0.01 to 0.25% by mass with a ferrite main phase is has an average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfying formulas (5,6) and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and D (?m) satisfying formula (3): 1.2?D?9.3??(5) D?5.0?2.0·Cr+5000/(5+350·C+40·Mn)2??(6) D·X?0.1??(3) and, at said ¼ inch depth, the area percentage of ferrite crystal grains the crystal grain diameter d (?m) of which satisfying formula (4) is at least 80%: D/3?d?3D??(4) wherein C, Cr and Mn represent mass % of the respective elements in the steel.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances, machine structures, and of constructing buildings, and a manufacturing method thereof is provided. The steel sheet is a hot-rolled steel sheet of a carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D(?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D(?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.