110 results about "Yield ratio" patented technology

A method to achieve a yield ratio of 0.60 or more in a component from non-heat-treated steel having bainitic microstructure. The component includes a predetermined chemical composition, in mass %, in amounts such that a value of F1 obtained by Formula (1) is 0.65% or more, with the balance as Fe and inevitable impurity. Bainitic microstructure area fraction is 85% or more and Retained austenite area fraction is 5% or less. Crystal grains of the bainitic microstructure have an average diameter of 10 μm or more and 25 μm or less, an average aspect ratio of 0.5 or more, and an average ratio of crystal grain boundary length to crystal grain circumference of 60 or less.F⁢1=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14(1)

The invention discloses a production method of thick-wall pipeline steel X65MS for polar regions, which adopts ultra-low carbon and high Ni + casting blank secondary cogging extreme cooling + steel plate online ultrafast cooling, breaks the component design of the conventional pipeline steel standard, solves the problem of poor drop hammer low-temperature toughness of thick-wall acid-resistant pipeline steel at-55 DEG C, and has the transverse and longitudinal yield strength of 460-560MPa, the tensile strength of 590-650MPa, the yield ratio of less than or equal to 0.80, the tensile strength of 590-650MPa and the tensile strength of less than or equal to 0.80. The uniform elongation is 10%-12%, the impact value at-55 DEG C is 400-500 J, and the drop weight at-55 DEG C is 90%-95%; when the product is soaked in an NACE solution for 96 hours in an HIC test, CLR, CTR and CSR are all 0; sSC test: four-point bending constant load nominal yield is 90%, and the sample is soaked for 720 hours, and the surface of the sample has no crack; the CTOD value of the crack tip opening displacement of the CTOD test material at-55 DEG C is greater than or equal to 0.6 mm.

The present application relates to a low-yield ratio 420MPa low-alloy high-strength steel and a preparation method, belonging to the technical field of steel manufacturing. In terms of mass fraction, the chemical composition of the low-alloy high-strength steel includes: C: 0.07% to 0.12%, Si: 0.10% to 0.40%, Mn: 1.60% to 1.80%, P: ≤0.015%, S: ≤0.010%, Alt: 0.020% to 0.060%, Nb: 0.03% to 0.05%, Ti: 0.01% to 0.03%, N≤0.005%, and matrix element Fe. The composition design gives full play to the solid solution strengthening of C and Mn and the fine grain strengthening and precipitation strengthening of Nb and Ti microalloys. At the same time, the continuous full annealing process does not require slow cooling treatment, which improves production efficiency and obtains low-cost, low-yield ratio 420MPa low-alloy high-strength (yield ratio ≤0.8) steel with both strength and excellent plasticity. This type of steel can withstand greater plastic deformation while meeting higher strength requirements without plastic instability, achieving the needs of lightweight automotive industry and excellent stamping integral forming of structural parts, and has broad application prospects.

The invention discloses a high-toughness low-yield-ratio steel plate for a bridge and a preparation method of the high-toughness low-yield-ratio steel plate, and relates to the technical field of low-alloy high-strength structural steel, and the steel plate for the bridge comprises the following chemical components in percentage by weight: 0.05% < = C < = 0.09%, 0.20% < = Si < = 0.30%, 1.50% < = Mn < = 1.70%, 0.50% < = Cr < = 0.60%, 0.35% < = Cu < = 0.50%, 0.4% < = Ni < = 0.6%, 0.2% < = Mo < = 0.3%, 0.03% < = Nb < = 0.05%, 0.01% < = Ti < = 0.02%, 0 < = B < = 30 ppm, and the balance of Fe and inevitable impurities. The production method comprises the steps of billet heating and heat preservation; controlled rolling and controlled cooling; the yield strength of the produced steel plate is larger than or equal to 870 MPa, the tensile strength is larger than or equal to 780 MPa, the yield ratio is smaller than or equal to 0.86, the ductility is larger than or equal to 15%, and the impact energy at the temperature of minus 40 DEG C is larger than or equal to 150 J. On the basis that the alloy cost is remarkably reduced, the performance combination of high strength, high toughness and low yield ratio is obtained at the full thickness through process regulation and control, and the steel plate is suitable for the scene of outdoor bridge steel.

Provided is a steel sheet that may be used for automobile parts and the like, and to a steel sheet having an excellent balance of strength and ductility, an excellent balance of strength and hole expansion ratio, and an excellent yield ratio evaluation index, and a method for manufacturing the same. The steel sheet includes: by wt %, C: 0.1 to 0.25%, Si: 0.01 to 1.5%, Mn: 1.0 to 4.0%, Al: 0.01 to 1.5%, P: 0.15% or less, S: 0.03% or less, N: 0.03% or less, B: 0.0005 to 0.005%, a balance of Fe, and unavoidable impurities; and as microstructures, bainite, tempered martensite, fresh martensite, retained austenite and unavoidable structures.

The present invention belongs to the field of ferrous metallurgy, and relates to an EH40 crack arrest steel plate for a container ship and a manufacturing method therefor. The steel plate comprises the following chemical components in percentages by mass: C: 0.03-0.06%, Si: 0.15-0.30%, Mn: 1.10-1.30%, P≤0.0080%, S≤0.0030%, Nb: 0.010-0.020%, V: 0.035-0.055%, Ti: 0.008-0.020%, Ni: 0.45-0.65%, Cu: 0.10-0.30%, Ca: 0.0005-0.0020%, H≤0.00015%, Ceq≤0.42%, and the balance of Fe and inevitable impurity elements. The steel plate has a yield strength of 409-440 MPa, a tensile strength ranging from 595 MPa to 625 MPa, a yield ratio of 0.84-0.88, and a longitudinal impact toughness value at -60ºC of greater than or equal to 250 J; and during instrumented impact testing, the energy E3 for crack arrest / unstable propagation and the absorbed energy E4 after crack arrest / unstable propagation account for more than or equal to 20% of the total impact absorption energy, and therefore the steel plate has good crack arrest performance.

The invention relates to the technical field of maritime work steel, in particular to anti-fatigue 550 Mpa-grade low-temperature toughness maritime work steel and a manufacturing method thereof. The high-strength steel is composed of the following chemical components in percentage by weight: 0.06%-0.08% of C, 0.25%-0.45% of Si, 1.5%-2.0% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.04%-0.06% of Als, 0.95%-2.05% of Ni, 0.001%-0.15% of Mo, 0.22%-0.28% of Cu, 0.001%-0.15% of Co, 0.03%-0.05% of Nb, 0.008%-0.02% of Ti, 0.002%-0.004% of N and the balance of Fe and inevitable impurities. The yield strength of the steel plate is larger than or equal to 550 Mpa, the tensile strength ranges from 640 Mpa to 820 Mpa, the ductility is larger than or equal to 19%, the Charpy impact energy at the temperature of-60 DEG C is larger than or equal to 120 J, and the yield ratio is smaller than or equal to 0.84.

The invention discloses a steel plate for EH550 ocean engineering and a manufacturing method thereof. The steel comprises the following chemical components in percentage by mass: 0.06%-0.12% of C, 0.10%-0.50% of Si, 1.20%-1.80% of Mn, 0.20%-0.50% of Cr or 0.20%-0.50% of Mo, less than or equal to 0.03% of Nb, 0.02%-0.04% of V, 0.01%-0.03% of Ti, 0.015%-0.045% of Al, less than or equal to 0.015% of P, less than or equal to 0.006% of S and the balance of Fe and inevitable impurities. The thickness of the steel plate is 6-50 mm, the yield strength is not lower than 550 MPa, the uniform elongation is not lower than 10%, the yield ratio is not higher than 0.80, and the impact energy at the temperature of-40 DEG C is not lower than 200 J. And through high-temperature controlled rolling and controlled cooling, a bainite structure with the dislocation density evenly distributed is obtained, and the problems that the steel plate for ocean engineering produced through a traditional quenching and tempering technology is insufficient in even elongation and too high in yield ratio are solved.

Provided is an angular steel pipe having a low yield ratio and excellent low-temperature toughness and ductility. This angular steel pipe has a prescribed steel component composition, and the steel structure in the center of the plate thickness of the flat plate section has ferrite as the main phase, the area ratio of a second phase comprising one or more elements selected from pearlite, pseudo-pearlite, and upper bainite is 5-30%, and the average crystal grain size is 10.0-30.0 [mu] m. The number of pearlites and pseudo pearlites having an equivalent circle diameter of 2-20 [mu] m inclusive is 500 / mm2 or more, the yield strength of the flat plate section is 295 MPa or more, the tensile strength of the flat plate section is 400 MPa or more, the yield ratio of the flat plate section is 0.85 or less, the uniform elongation of the flat plate section is 8.0% or more, the elongation at break of the flat plate section is 27.0% or more, and the Charpy absorption energy of the corner section at-10 DEG C is 80 J or more. And the ductile-brittle transition temperature of the corner section is-10 DEG C or less.

The invention relates to high heat input welding resistant steel for a deep sea jacket and a preparation method thereof, and belongs to the technical field of iron-based alloys. The steel plate comprises, by mass, 0.08%-0.10% of C, 0.15%-0.25% of Si, 1.55%-1.70% of Mn, smaller than or equal to 0.0070% of P, smaller than or equal to 0.0030% of S, 0.008%-0.020% of Ti, 0.0020%-0.0040% of N, 0.20%-0.30% of Cu, 0.45%-0.60% of Ni, 0.010%-0.025% of V, 0.0010%-0.0020% of B and the balance Fe and inevitable impurity elements, the yield ratio of the steel plate is 0.84%-0.88, the yield strength is 430 MPa to 480 MPa, the tensile strength is 520 MPa to 580 MPa, and the ballistic work at the temperature of 40 DEG C below zero and 50 DEG C below zero is larger than or equal to 200 J. On the basis that the steel grade component range of the European standard En10025-4 S420ML is met, the carbon content is further reduced, Mn, Ni, Cu-, V and B elements beneficial to the toughness of the steel plate are added, in the TMCP rolling process, the pass reduction is increased, the total pass number is controlled, and the yield of the steel plate is increased. And the steel plate for high heat input welding, which has a mixed structure mainly consisting of acicular ferrite and a small amount of blocky ferrite, is obtained.

The invention provides a TMCP delivery 550MPa-grade steel plate for engineering machinery and a preparation method thereof, and the steel plate comprises the following components in percentage by mass: the balance of Fe and inevitable impurities. The 550MPa-grade ultra-thin specification steel plate is stable in mechanical property, good in internal quality, good in strength, toughness and plasticity and low in yield ratio, flaw detection meets the national standard requirement, especially the carbon equivalent is low, the welding performance is excellent, and the 550MPa-grade ultra-thin specification steel plate has high industrial application and popularization value.

The present invention relates to a steel sheet that can be used for automobile parts, etc., and relates to a steel sheet that is excellent in balance between strength and ductility, balance between strength and hole expandability, and yield ratio evaluation index, and a method for producing the same.

The application provides a low yield ratio and 370MPa-grade marine atmosphere corrosion resistant heavy steel plate without coating and a manufacturing method thereof. The steel plate is composed of the following components in percentage by weight: C: 0.04% to 0.06%, Si: 0.10% to 0.30%, Mn: 0.30% to 0.50%, P: less than or equal to 0.012%, S: less than or equal to 0.005%, Ni: 2.7% to 3.5%, Cu: 0.35% to 0.85%, Mo: 0.05% to 0.15%, Nb: 0.005% to 0.015%, Ti: 0.006% to 0.030%, Al: 0.015% to 0.040%, B: 0.0008 to 0.0016%, and the balance of iron and inevitable impurities. The components satisfy 22 <= 15[Mo]+6[Ni]+5[Cu] <= 26, the Pcm value (%) is less than or equal to 0.19%, the production method of the steel plate comprises smelting, slab continuous casting, slab heating, controlled rolling, controlled cooling and heat treatment. The yield strength of the steel plate is greater than or equal to 370MPa, the tensile strength is greater than or equal to 510MPa, the elongation after fracture is greater than or equal to 20%, the yield ratio is less than or equal to 0.77, the KV2 impact energy at-40 DEG C is greater than or equal to 200J, the corrosion rate of the steel plate in a marine atmosphere environment in a one-year period is 0.024mm / a to 0.030mm / a, and the thickness of the steel plate is 100mm to 130mm.

The invention relates to a low-yield-ratio high-strength steel plate and a manufacturing method thereof, and belongs to the field of metallurgy. The metallographic structure of the steel plate is bainite, ferrite and nanoscale TiC precipitates, the proportion of the ferrite is 10%-20%, and the grain size is larger than or equal to 7 grades. The yield strength Rp0.2 is greater than or equal to 700MPa, the tensile strength Rm is greater than or equal to 850MPa, the yield ratio is less than or equal to 0.86, the cold bending property d is equal to 2a, and no crack is generated during 90-degree cold bending. The steel plate has high strength, high toughness and excellent cold bending performance, and can be widely applied to manufacturing of large-scale engineering machinery equipment or steel structures with strict requirements on formability and weldability, such as high-rise buildings, bridges, ocean platforms and the like.

The present invention discloses an annealing-free cold heading steel for workpieces with large deformation, a preparation method and an application thereof, and relates to the technical field of steel production. The area reduction rate of the cold heading wire in the cold working deformation process is ≥70%; the pearlite content in the metallographic structure of the cold heading wire is ≤5wt%, the hardness is 48-55HRB, and the strength-to-yield ratio is 0.60-0.75. By controlling the low pearlite content, low hardness and low yield-to-strength ratio of the cold heading wire, the smooth production of workpieces with large deformation (area reduction rate ≥70%) in the cold heading process is achieved, and no annealing treatment is required in the project, no additional energy consumption is generated, and the production cost is reduced.

The purpose of the present invention is to provide a technology relating to: a steel sheet which still has high collision resistance characteristics after being subjected to cold pressing and being formed into a component; and a method for producing the steel sheet.　Disclosed is a steel sheet which has a specific component composition and a specific steel structure, and has a yield ratio of 0.80 or less, wherein: in a tensile test according to JIS Z2241, the retained austenite that disappears during the period from the start of the tensile test to the processing of imparting 1% strain in terms of nominal strain is 0.8% or more in terms of the area ratio with respect to the entire steel structure; and when the processing of imparting 1% strain and a heat treatment at a temperature of 100°C are performed, the amount of increase in YS obtained by subtracting YS before (the processing and the heat treatment) from YS after (the processing and the heat treatment) is 200 MPa or more, and El after (the processing and the heat treatment) is not less than 0.9 × (El before (the processing and the heat treatment)). YS and El represent the yield stress and total elongation of the steel sheet, respectively.

The present invention provides: a steel sheet and a member, both having a tensile strength TS of 1180 MPa or more, a yield ratio YR of 65% or more, and excellent ductility, fatigue resistance of a shear end surface part, and delayed fracture resistance in corrosive environments; and methods for manufacturing the steel sheet and the member.　This steel sheet has a specific component composition, where, at a 1 / 4 thickness position of the steel sheet, the tempered martensite content is 83% or more in terms of area fraction, the residual austenite content is less than 3% in terms of volume fraction, and the total ferrite and bainitic ferrite content is 5% to 15% in terms of area fraction. When the average value of the occupancy of packets having the greatest occupancy in prior austenite grains at the center of the steel sheet thickness is defined as P(C) and the average value of the occupancy of packets having the greatest occupancy in prior austenite grains at a depth of 100 μm from the surface of the steel sheet is defined as P(S), the steel sheet has a microstructure satisfying P(C) ≤ 70% and {P(S) – P(C)} ≤ 20%.

The invention relates to steel and a preparation method and application thereof. The steel comprises the following chemical components in percentage by mass: 0.045% to 0.065% of C, 0.28% to 0.40% of Si, 0.60% to 0.80% of Mn, 0.072% to 0.090% of P, 0.001% to 0.010% of S, 0.25% to 0.28% of Cu, 0.32% to 0.42% of Cr, 0.015% to 0.030% of Ti, less than or equal to 0.007% of N, 0.015% to 0.050% of Als and the balance of Fe and inevitable impurities. The steel is nickel-free, low in production cost, low in yield ratio, excellent in mechanical property, good in stamping performance, good in weather resistance and high in yield, and is suitable for the weather-resistant steel for the low-yield-ratio container for stamping.

The invention belongs to the technical field of steel smelting, and relates to steel for a low-temperature U-shaped bolt and a smelting method of the steel. The steel comprises the following chemical components in percentage by weight: 0.33%-0.38% of C, 0.20%-0.30% of Si, 0.60%-0.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.95%-1.10% of Cr, 0.18%-0.22% of Mo, 0.020%-0.050% of Al, less than or equal to 0.0010% of O and the balance of Fe and inevitable residual elements. The tensile strength of produced steel is larger than or equal to 980 MPa, the yield ratio Rel / Rm is larger than or equal to 0.9, the percentage elongation after fracture A is larger than or equal to 12%, the percentage reduction of area Z is larger than or equal to 45%, the impact absorbing energy AKV at the temperature of-20 DEG C is larger than or equal to 80 J, and the austenite grain size reaches the grade 7 or above.

The application discloses a rare earth low-alloy high-strength corrosion-resistant low-temperature-resistant low-yield ratio hot-rolled H-shaped steel for large-span steel structures, which comprises the following components: C 0.09%-0.13%, Si 0.40%-0.50%, Mn 1.20%-1.30%, P 0.01%-0.03%, S≤0.010%, V 0.04%-0.05%, Cr 0.25%-0.30%, Ni 0.13%-0.15%, Cu 0.25%-0.30%, Ce 0.0010%-0.0030%, N 0.0050%-0.0070% and O≤0.0025%. A manufacturing method thereof is also disclosed. The H-shaped steel manufactured by the application satisfies the following conditions: lower yield strength ReL≥380MPa, tensile strength Rm≥520MPa, yield ratio≤0.75, impact toughness at-60 DEG C≥80J and elongation after fracture≥30%.

This invention discloses a heat treatment method for improving the yield strength ratio of steel used in continuous extrusion dies. Specifically, the steel is subjected to the following sequential heat treatments: high-temperature normalizing, low-temperature normalizing, spheroidizing annealing, high-temperature quenching, high-temperature tempering, and low-temperature tempering. The high-temperature normalizing temperature is 1070℃~1100℃; the low-temperature normalizing temperature is 710℃~730℃; the spheroidizing annealing temperature is 840℃~870℃; the high-temperature quenching temperature is 1070℃~1100℃; the high-temperature tempering temperature is 620℃~640℃; and the low-temperature tempering temperature is 530℃~550℃. The yield strength ratio of the die steel after heat treatment using this method is ≥0.91, and the hardness is 48~52 HRC.

The high-strength steel plate comprises the following components in percentage by weight: 0.03-0.06% of C, 0.10-0.25% of Si, 0.3-0.8% of Mn, less than or equal to 0.005% of S, less than or equal to 0.006% of P, 8.5-10.0% of Ni, 0.5-2.0% of Cu and the balance of Fe and other inevitable impurities, and the components also need to simultaneously meet the following conditions: 30C + 4Mn + 1.5 Cu + Ni is more than or equal to 12.5% and less than or equal to 16%. The steel plate has high strength, excellent low-temperature toughness and low yield ratio at the same time, and has higher deformation allowance in a low-temperature environment of not lower than-196 DEG C, so that the steel plate has very high service safety; the yield strength of the steel plate is larger than or equal to 690 MPa, the tensile strength is 770-940 MPa, the ductility is larger than or equal to 18%, the impact energy at the temperature of-196 DEG C is larger than or equal to 100 J, the yield ratio is smaller than or equal to 0.90, and the steel plate is suitable for manufacturing liquefied natural gas (LNG) containers, ships, storage tanks and various low-temperature structures.

The invention discloses a rolling method of low-yield-ratio Q420qE bridge steel, and belongs to the technical field of steel. The steel comprises the following chemical components in percentage by weight: 0.08 to 0.11 percent of C, 0.15 to 0.30 percent of Si, 1.3 to 1.6 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.03 to 0.05 percent of Nb, 0.03 to 0.05 percent of V, 0.010 to 0.020 percent of Ti, 0.017 to 0.027 percent of Als and the balance of Fe and inevitable impurities. Through the process of controlled rolling, relaxation and controlled cooling, the yield ratio of the steel plate is reduced, the yield ratio is stably controlled to be 0.85 or below, and the yield ratio qualification rate of Q420qE is remarkably improved.

The invention belongs to the technical field of rolling, and relates to a rolling process for preparing ER50-6E welding wire steel with the tensile strength not larger than 1360 MPa and application of the ER50-6E welding wire steel. Billet steel is continuously fed, the in-furnace time is controlled to be not shorter than 110 minutes, the heating temperature is 1100-1150 DEG C, and the soaking temperature is 1170-1220 DEG C; the initial rolling temperature is 1070 DEG C to 1120 DEG C; the finish rolling temperature is not lower than 960 DEG C; and the water amount of finish rolling cooling water is reduced so that the finish rolling outlet temperature can be increased to be not lower than 1050 DEG C, the spinning temperature can be 920-950 DEG C, a heat preservation cover is completely closed, the roller way speed is low, and the cover outlet temperature is controlled to be 650 DEG C or below. The tensile strength of a hot-rolled wire rod does not exceed 500 MPa, the yield strength does not exceed 310 MPa, the yield ratio does not exceed 0.63, the hot-rolled wire rod is suitable for drawing a 0.8 mm welding wire from a phi 6.5 mm wire rod, the tensile strength of the welding wire is not larger than 1360 MPa, and the hot-rolled wire rod has good wire feeding performance.

The invention relates to a low-yield-ratio 785MPa-grade ultra-high-strength thin plate and a preparation method thereof, belongs to the technical field of ultra-high-strength steel, and solves the problem of high yield ratio of existing ultra-high-strength steel. The invention discloses a low-yield-ratio 785MPa-grade ultra-high-strength thin plate. The low-yield-ratio 785MPa-grade ultra-high-strength thin plate comprises the following chemical components in percentage by mass: 0.08-0.12% of C, 0.10-0.20% of Si, 0.5-1.0% of Mn, 5.5-6.5% of Ni and the balance of Fe. 0.5 to 1.0 percent of Cr, and 0.5 to 1.0 percent of Mo; 0.06% to 0.10% of V; ti: 0.008% to 0.015%; p < = 0.005%; ni * Mn is greater than or equal to 3.0 * 10 <-4 > and less than or equal to 6.5 * 10 <-4 >. The yield ratio of the steel is not higher than 0.90, and the steel has the comprehensive characteristics of high strength, excellent low-temperature toughness and the like.

The invention relates to a low-cost A630-420H hot-rolled steel bar and a production method thereof. The low-cost A630-420H hot-rolled steel bar comprises the following components in percentage by mass: 0.45-0.52% of C, 0.10-0.40% of Si, 0.50-0.80% of Mn, less than or equal to 0.045% of P, less than or equal to 0.045% of S, 0.015-0.020% of N and the balance of Fe and inevitable impurities. The production method comprises the steps of continuous casting, casting blank heating, rolling and cooling. According to the invention, steel-making and steel-rolling process parameters are strictly controlled, so that an A630-420H hot-rolled steel bar product with strength, plasticity and other technical indexes meeting NCh 204: 2020 standard requirements and low cost is obtained, the yield strength is 440-520 MPa, the tensile strength is 650-730 MPa, the yield-strength ratio is 1.40-1.55, and the percentage elongation after fracture is 13.5-17.5%.

The invention relates to the technical field of dual-phase steel, in particular to 800MPa-grade hot-rolled dual-phase steel with excellent reaming performance and a production method thereof, and the 800MPa-grade hot-rolled dual-phase steel comprises the following chemical components in percentage by mass: 0.045%-0.055% of C, 0.50%-1.00% of Si, 1.50%-2.50% of Mn, less than or equal to 0.015% of P, less than or equal to 0.008% of S, 0.03%-0.05% of Alt, 0.25%-0.55% of Cr, 0.01%-0.03% of Ti and the balance of Fe and inevitable impurities. The martensite with high-proportion toughness is prepared, and the hole expansion rate reaches up to 55%-75%. And the addition amount of alloy elements is small, and the alloy cost is greatly reduced. The yield strength of the dual-phase steel ranges from 550 MPa to 580 MPa, the tensile strength ranges from 820 MPa to 870 MPa, the percentage elongation after fracture ranges from 16% to 22%, and the yield ratio ranges from 0.64 to 0.74.

The invention discloses a production method of a Q620qE steel plate with a low yield ratio. The steel comprises the following chemical components in percentage by weight: 0.07%-0.08% of C, 0.25%-0.3% of Si, 1.5%-1.55% of Mn, less than or equal to 0.012% of P, less than or equal to 0.002% of S, 0.035%-0.045% of Nb, 0.01%-0.02% of Ti, 0.25%-0.3% of Mo, 0.45%-0.55% of Cr and 0.2%-0.3% of Ni. The process comprises the steps of smelting, continuous casting, heating, controlled rolling and controlled cooling and tempering. A Q620qE steel plate with the thickness reaching 50 mm is produced through a continuous casting billet with the section of 260 mm, the structure of the steel is bainite and ferrite, the yield strength Rp0.2 is larger than or equal to 620 MPa, the tensile strength Rm is larger than or equal to 720 MPa, the ductility A is larger than or equal to 15%, the yield ratio is smaller than or equal to 0.85, and the Charpy impact energy at the temperature of-40 DEG C is larger than or equal to 120 J. A welding evaluation test shows that under the submerged-arc welding heat input of 35 kJ / cm, the impact energy at the temperature of-40 DEG C of a heat affected zone is larger than or equal to 120 J, and the impact energy at the center of a welding seam is larger than or equal to 100 J.

The invention discloses a novel high-strength steel bar process control method which comprises the following steps: (1) firstly, in order to ensure that the strength and the yield ratio reach the standard, presetting the weight percentage of C, Si, Mn, V, Nb and Ceq in initial components of steelmaking, and presetting the temperature of a heating furnace, the steel throwing temperature, the heating time and the continuous casting cooling speed; (2) test rolling is conducted, and when the yield strength does not reach the standard, adjustment is conducted according to whether the tensile strength has allowance or not till the yield strength is larger than 635 Mpa, and the yield-strength ratio is larger than 1.26; (3) whether Agt reaches the standard or not and the bending brittle failure condition are checked, and then adjustment is conducted according to a small-specification steel bar technology and a large-specification steel bar technology so that it can be guaranteed that the yield strength and the yield strength ratio reach the standard; and (4) on the basis of the adjustment, the small-specification reinforcing steel bar technology and the large-specification reinforcing steel bar technology are solidified respectively. The high-strength steel bar can be prepared, and meanwhile the problems that the yield strength is not up to the standard, the strength-to-yield ratio is not up to the standard, Agt is not up to the standard and bending is prone to brittle failure are solved.

The invention discloses 540 MPa-grade low-silicon hot-rolled high-strength dual-phase steel and a manufacturing method thereof. The 540 MPa-grade low-silicon hot-rolled high-strength dual-phase steel comprises, by weight, 0.04%-0.15% of C, smaller than or equal to 0.03% of Si, 1.0%-2.0% of Mn, 0.02%-0.22% of Al, 0.005%-0.025% of Nb, 0.005%-0.025% of Ti, 0.01%-0.10% of V, smaller than or equal to 0.015% of P, smaller than or equal to 0.02% of S and the balance Fe and inevitable impurities. The elements also need to meet the condition that C + Si / 24 + Mn / 6 is greater than or equal to 0.20% and less than or equal to 0.49%; 0.5 < = (Nb + V + Ti) / C < = 1.5. The requirements that the steel plate has high strength and plasticity, low yield ratio and high formability are met at the same time, the high surface requirement is met, the tensile strength of the obtained dual-phase steel is larger than or equal to 540 MPa, the ductility is larger than or equal to 22%, the yield ratio is smaller than or equal to 0.72, and the hole expansion rate is larger than or equal to 40%.