552 results about "Bainite" patented technology

The invention relates to a high-strength complex-phase hot-rolled wire rod for a 2360MPa-grade stranded wire and a manufacturing method of the high-strength complex-phase hot-rolled wire rod. After a Mo-V high-carbon component system is rolled and spun into a wire rod, the wire rod is subjected to on-line molten salt weak quenching toughening treatment, so that the wire rod is subjected to front-section molten salt treatment to be quickly cooled, enters a bainite and sorbite mixed phase region from an austenite state, and is subjected to high-temperature heat treatment to form a high-strength complex-phase hot-rolled wire rod; the method comprises the following steps: firstly, carrying out heat treatment on residual austenite to form a structure mainly comprising bainite and sorbite, then carrying out later-section molten salt treatment, increasing the temperature of molten salt, promoting decomposition and conversion of unconverted residual austenite into sorbite, carrying out isothermal tempering, and finally, carrying out roller way slow cooling to prepare a hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure consisting of tempered bainite and tempered sorbite, the method has the advantages that the structure toughness can be regulated and controlled on line, the tensile strength is 1574-1627 MPa, the percentage reduction of area is 28-33%, the mechanical property fluctuation is reduced, the material cost and the production efficiency are both considered, the ultra-high-strength stranded wire can be produced without off-line heat treatment, and the wire breaking risk is reduced.

According to the high-strength complex-phase hot-rolled wire rod for the 2300 MPa grade stranded wire and the manufacturing method of the high-strength complex-phase hot-rolled wire rod, after Mo-V high-carbon components are rolled and spun into the wire rod, online molten salt section quenching isothermal treatment is conducted, the wire rod is subjected to front-section molten salt treatment and cooled at the cooling speed larger than or equal to 39 DEG C / s, the wire rod enters a bainite phase region from an austenite state, and then the high-strength complex-phase hot-rolled wire rod is obtained; the method comprises the following steps: carrying out high-temperature treatment on austenite to promote part of austenite to be converted into bainite, then carrying out later-section molten salt treatment, increasing the molten salt temperature, promoting unconverted retained austenite to be decomposed and converted into sorbite, carrying out isothermal tempering, and finally carrying out roller way slow cooling to prepare the hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure consisting of tempered bainite, tempered sorbite and ferrite, by means of the method, complex-phase structure regulation and control and online toughening can be achieved, the material cost and the production efficiency are both considered, the tensile strength is 1552-1602 MPa, the percentage reduction of area is 32%-38%, and therefore off-line heat treatment is avoided, and ultrahigh-strength stranded wires are efficiently produced.

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 invention relates to a high-strength complex-phase hot-rolled wire rod for a 2330MPa-grade stranded wire and a manufacturing method of the high-strength complex-phase hot-rolled wire rod. After a Mo-containing high-carbon component is rolled and spun into a wire rod, the wire rod is subjected to online fused salt mixed quenching toughening treatment, so that the wire rod is subjected to front-section fused salt treatment and is rapidly cooled, and enters a bainite and sorbite mixed phase region from an austenite state; the method comprises the following steps: firstly, carrying out heat treatment on residual austenite to form a structure mainly comprising bainite and sorbite, then carrying out later-section molten salt treatment, increasing the temperature of molten salt, promoting decomposition and conversion of unconverted residual austenite into sorbite, carrying out isothermal tempering, and finally, carrying out roller way slow cooling to prepare a hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure consisting of tempered bainite and tempered sorbite, according to the hot-rolled steel wire rod, complex-phase structure regulation and control and online toughening can be achieved, the production efficiency is considered, the tensile strength of the hot-rolled steel wire rod can reach 1563-1613 MPa, the percentage reduction of area can reach 29%-34%, offline heat treatment is not needed when the ultrahigh-strength stranded wire is produced, and the wire breaking risk is reduced.

The invention discloses an anti-oxidation packaging material for hot rolling of thermoelectric materials and a preparation method of the anti-oxidation packaging material, and relates to the technical field of new materials. The packaging material is of a three-layer composite tubular structure and sequentially comprises, from inside to outside, an anti-oxidation barrier layer which is a composite material with an Fe-Al intermetallic compound as a matrix and Y2O3 particles dispersed and distributed; the transition layer is a Ni-Cr-Fe-Mn-C series solid solution alloy with Ni as a matrix; and the structure supporting layer is made of microalloyed low-carbon bainite steel. The layers are metallurgically bonded through hot isostatic pressing, and then the hollow composite pipe is manufactured through cold drawing. The packaging material has excellent high-temperature oxidation resistance, good plastic deformation capacity and structural strength, can effectively isolate oxygen, coordinate strain and maintain overall integrity in the high-temperature hot rolling process, is suitable for protection and densification of Bi2Te3-based, PbTe-based and SiGe-based thermoelectric materials and the like, and remarkably improves thermoelectric performance and production consistency of the thermoelectric materials.

One embodiment of the present invention provides a high-strength thin-wall API steel material having excellent deformation stability and a manufacturing method thereof, the thin-wall API steel material comprising, in weight %, C: 0.05-0.15 %, Si: 0.5 % or less (except 0 %), Mn: 0.5-2.5 %, Nb: 0.05 % or less (except 0 %), V: 0.004 % or less (except 0 %), Mo: 0.03-0.2 %, Cr: 0.1-0.3 %, P: 0.03 % or less (except 0 %), S: 0.015 % (except 0 %), Al: 0.05 % or less (except 0 %), N: 0.01 % or less (except 0 %), Fe and other inevitable impurities in a balance, and a microstructure comprising, in area %, 10-30 % of ferrite having an average grain size of 15-30 μm and a balance of bainite, the thin-wall API steel material comprising 3000 / μm 2 V-based precipitates below.

The invention relates to a preparation method of bainite steel with high toughness and strength at low temperature, and the strength and toughness of the bainite steel at low temperature are improved by designing process parameters and steel ingot components. The bainite steel with high toughness and strength at low temperature is finally obtained by designing the components of the steel ingot, avoiding the addition of elements such as nickel, molybdenum and vanadium, reducing the material cost and the processing difficulty and accurately controlling the cooling rate of heat treatment. The prepared bainite steel is composed of strip-shaped bainite and thin strip-shaped retained austenite, and the volume fraction of the retained austenite is 5-10%. The tensile strength is not lower than 1240 MPa, the normal-temperature impact is not lower than 120 J, and the impact toughness at-40 DEG C is not lower than 80 J.

Provided is a steel sheet for a CO2 transport line pipe that is suitably provided to a pipeline for transporting a liquid and / or supercritical state CO2. A steel sheet according to the present invention has: a component composition that contains, in mass%, 0.03-0.08% of C, 1.50-2.50% of Mn, 0.030% or less of P, 0.0100% or less of S, 0.0100% or less of N, 0.010-0.200% of Al, 0.10-1.00% of Si, and 0.0005-0.0050% of O, that further contains a prescribed amount of one or more selected from Cu, Ni, Cr, Mo, and W, that exhibits a [Si] / [O] value of 20-900, and in which the remaining portion comprises Fe and unavoidable impurities; a micro structure in which the area ratio of bainite is not less than 90% and the area ratio of island martensite is less than 3%; a strength where the tensile strength is not less than 625 MPa; and a toughness in which the Charpy impact absorption energy at -40°C is not less than 320 J.

The application discloses a low-carbon-equivalent 355MPa grade normalized rolled thick plate organization uniformity control method, wherein the temperature of the billet before charging is less than or equal to 400 DEG C, the temperature of the soaking furnace is 1130-1150 DEG C, the time of the soaking section is 45-55 minutes, the total furnace time is 170-185 minutes, the second opening temperature of the billet is 880-940 DEG C, the finishing rolling is 6-8 passes, the cumulative reduction is 60-70%, and the final rolling temperature is 860-900 DEG C; the steel plate cooling is realized by adopting a laminar flow cooling system, the full-automatic water pouring control cooling mode is adopted, the water inlet temperature is 720-740 DEG C, the red temperature is 640-660 DEG C, and the surface temperature of the steel plate after cooling is monitored. The head and tail and the full-thickness organization type of the normalized rolled steel plate are all 'ferrite + pearlite' organizations, the grain size level is all above 9.0, there is no obvious banded structure and no bainite structure, and the problem of the organization difference of the 355MPa grade thick plate product caused by the normalized rolling is solved.

Provided in the present invention are a hardness evaluation method and system for a heat affected zone of a multi-layer and multi-pass welded joint of hull steel. The method comprises: establishing a finite element model of a welded joint, and acquiring welding thermal cycles at nodes in a heat affected zone of the finite element model; performing solving to obtain critical temperatures for microstructural transformations of a study object, and performing solving to obtain volume fractions of transformation products during the thermal cycles, and a volume fraction of an austenite-ferrite-pearlite mixture after all the thermal cycles; acquiring hardness values of a martensite and a bainite in each thermal cycle, and a hardness value of the austenite-ferrite-pearlite mixture after all the thermal cycles; and on the basis of the acquired hardness values of the martensite and the bainite in each thermal cycle, and the the acquired hardness value of the austenite-ferrite-pearlite mixture after all the thermal cycles, acquiring a comprehensive hardness value of the heat affected zone. The present invention can accurately reproduce heat conduction and a microstructure transformation process in a heat affected zone during multi-layer and multi-pass welding of full steel, thereby assisting engineers in evaluating a welding temperature field and the structure distribution of the heat affected zone.

The invention discloses a method for preparing bainite steel through multi-element microalloying, and belongs to the technical field of advanced steel and iron materials. The method comprises the following steps that a forged steel ingot is subjected to first austenitizing and cooling treatment, and a martensite matrix is obtained; and then secondary phase precipitation treatment, secondary austenitizing treatment and cooling are sequentially carried out, and the bainite steel is prepared. According to the invention, an innovative heat treatment process path of martensite initial structure-medium-temperature second phase precipitation-short-time austenitizing-salt bath isothermal bainite transformation is constructed, and the synergistic effect of microalloy elements such as V, Nb, Ti and B is combined, so that the heat treatment process has the advantages that the heat treatment efficiency is greatly improved on the premise of not depending on precious alloy elements such as Cr and Ni; and the superfine bainite steel which is uniform in structure and excellent in comprehensive performance is successfully prepared.

The invention relates to a delayed fracture resistant non-quenched and tempered 14.9-grade high-strength cold heading steel wire rod and a preparation method thereof. The wire rod comprises the following chemical components: 0.33%-0.55% of C, less than or equal to 0.10% of Si, 1.5%-2.3% of Mn, 0.4%-0.6% of Cr, 0-0.04% of Nb, 0-0.1% of V, 0-0.1% of Ti, 0.004%-0.008% of B, more than or equal to 0.020% of Als, less than or equal to 0.040% of Alt, less than or equal to 0.015% of P, less than or equal to 0.010% of S, less than or equal to 1ppm of H and the balance of Fe and impurity elements. Fine control is adopted in the steelmaking process, the H content is strictly controlled to be lower than 1 ppm, a hydrogen trap is manufactured by adding microalloy elements such as Nb, V and Ti, and the delayed fracture resistance is improved; the air cooling speed of the rolled hot-rolled wire rod is precisely controlled, so that the structure of the hot-rolled wire rod is lath bainite, and high strength is realized by utilizing a medium-carbon bainite structure; the finished wire rod has high strength, high plasticity, excellent low-temperature impact toughness and good delayed fracture resistance.

The invention relates to a non-quenched and tempered 10.9-grade high-strength cold heading steel wire rod with low cost and high structure stability and a preparation method. The wire rod comprises the following chemical components in percentage by weight: 0.03-0.05% of C, less than or equal to 0.10% of Si, 1.2-1.7% of Mn, 0.4-0.6% of Cr, 0-0.04% of Nb, 0.004-0.008% of B, more than or equal to 0.020% of Als, less than or equal to 0.040% of Alt, less than or equal to 0.015% of P, less than or equal to 0.010% of S and the balance of Fe and inevitable impurity elements. The cooling speed of the hot-rolled wire rod on the after-rolling air cooling roller way is precisely controlled, the structure of the hot-rolled wire rod is full-granular bainite, and the wire rod finished product has high strength and high plasticity and also has excellent low-temperature impact toughness; and the production process is simple, the production cost is greatly reduced compared with a high-cost production process adopting salt bath treatment / isothermal treatment, and large-scale and low-cost stable production can be realized.

The invention relates to the technical field of metal material heat treatment, in particular to a metal lock body toughness strengthening heat treatment process, a metal lock body is low-carbon steel or medium-carbon steel, the carbon content is 0.12%-0.45%, and the metal lock body toughness strengthening heat treatment process comprises the steps that surface cleaning and stress pretreatment are sequentially conducted on the metal lock body; the treated metal lock body is placed in a heat treatment furnace, and segmented heating is conducted to the austenitizing temperature according to a preset heating curve; first-stage heat preservation is conducted in the austenitizing temperature interval, and then cooling is conducted to the bainite transformation temperature interval for second-stage heat preservation; after double-temperature-area heat preservation is completed, stepped cooling treatment is conducted on the metal lock body; and the cooled metal lock body is sequentially subjected to low-temperature tempering, shot blasting treatment and secondary tempering. Through surface cleaning, stress treatment, segmented heating, double-temperature-zone heat preservation, stepped cooling, low-temperature tempering, graded shot blasting and secondary tempering, lock body stress is fully released, structure defects are reduced, internal stress is slowly released, and toughness, strength and performance stability are improved.

The application discloses a kind of automobile structure steel with yield strength 1000MPa and above and its manufacturing method, its component weight percentage is as follows: C 0.15~0.23%;Si 0.12~0.5%;Mn 1.6~2.4%;B 0.001~0.004%;Al 0.01~0.04%;Cr;0.05~0.5%;Mo 0.15~0.5%;P≤0.015%;S≤0.005%;Rest contains Fe and other inevitable impurities, and need to satisfy the following relationship: the eigenvalue Bs of lower bainite formation rate=0.6~1.4, Bs=(Mo+B*100-Mn / 5) / C;Its microstructure lower bainite≥95%.The automobile structure steel of the application has yield strength≥1000MPa, tensile strength≥1180MPa, elongation≥7%, 180° bending performance d≤3.5T.The automobile structure steel obtained by the application not only has ultrahigh strength, but also has excellent forming performance, especially bending forming performance, and is especially suitable for manufacturing automobile chassis system parts.

The application discloses a low-temperature high-strength container steel with tensile strength greater than or equal to 600 MPa, which comprises C, Si, Mn, P, S, Ni, Mo, Alt, Cr, V, Fe and residual elements; the steel plate obtained through controlled rolling and controlled cooling and normalizing and fast cooling has a main structure of 60-75% of bainite, 25-35% of ferrite and a small amount of pearlite, the yield strength of the heat-treated delivery state steel plate is 533-620 MPa, the tensile strength is 640-700 MPa, the elongation is greater than or equal to 19%, and the impact energy at-20 DEG C is 200-310 J; after maximum die welding at 580-620 DEG C for 10-12 h, the yield strength is 530-600 MPa, the tensile strength is 630-680 MPa, the elongation is greater than or equal to 20%, and the impact energy at-20 DEG C is 170-250 J. The scheme has low alloy cost and short production process, the obtained steel plate has stable performance, and after maximum die welding, the tensile strength and impact energy of the steel plate still meet the use requirements of low-temperature container steel.

The steel sheet has a prescribed chemical composition, and in the metallographic structure at a position 1 / 4 of the sheet thickness from the surface, the steel sheet contains, in area%, 60.0% or more but less than 90.0% of bainite, more than 10.0% but 40.0% or less of martensite, and 10.0% or less in total of ferrite, pearlite and retained austenite, with the balance being Fe and unavoidable impurities. The value obtained by dividing the standard deviation of the aspect ratio of the old austenite crystal grains by the average value of the aspect ratio of the old austenite crystal grains is 0.50 or less, and the average grain diameter of the old austenite crystal grains is 30 [mu] m or less.

A steel sheet has a certain chemical composition and a steel microstructure containing, in area fraction, martensite: 40% or more and 78% or less, bainite: 20% or more and 58% or less, and retained austenite: 2% or more. Carbides in tempered martensite in the martensite have an average particle size of 0.40 μm or less, an average amount of C in the retained austenite is 0.5% by mass or more, a Si concentration in a region within 100 μm in a thickness direction from a surface of the steel sheet is 1.3% by mass or less, and a tensile strength is 1,470 MPa or more.

Provided are a high-strength hot-rolled steel sheet having high strength, high ductility, excellent strain dispersibility, high stretch flangeability, and bendability, a member, and methods for manufacturing the same.　The high-strength hot-rolled steel sheet has a prescribed component composition, and has a steel structure in which, in terms of area ratio, the total of bainite and tempered martensite is 80.0% or more, pearlite is 10.0% or less, retained austenite is 15.0% or less, the total of retained austenite and pearlite is 1.0% or more, the total of tempered martensite and bainite having a circle-equivalent diameter of 5.0 μm or more is 10.0% or less, and the proportion of line segments having a hard phase fraction of 20.0% or more among line segments having a length of 200 μm parallel to the rolling direction is 30.0% or less, the tensile strength TS (MPa) and the component composition (mass%) satisfy the expression 0 ≦ 730 + 2000 × (C + Si / 16 + Mn / 40 + Al / 18 + Cr / 40 + Ni / 40 + Mo / 20 + Ti / 3) – TS ≦ 250, where each element symbol in the formula represents the content (mass%) of each element, and the high-strength hot-rolled steel sheet has a tensile strength of 980 MPa or more.

The invention relates to the field of metal material processing, in particular to 610 MPa thin-gauge automobile steel and a preparation method thereof. The steel comprises chemical components in percentage by weight as follows: 0.04%-0.06% of C, 0.35%-0.45% of Si, 1.40%-1.50% of Mn, smaller than or equal to 0.050% of Als, 0.030%-0.050% of Nb, 0.25%-0.35% of Cr, smaller than or equal to 0.015% of P, smaller than or equal to 0.003% of S, smaller than or equal to 0.0050% of N and the balance of Fe and inevitable impurities. According to the invention, a ferrite and bainite structure is realized through combination of component design and process design, and high-strength, high-plasticity and high-surface-quality steel plate production is realized.

The invention relates to the technical field of metal material production, in particular to a 20CrMnTiH steel banded structure control method based on non-recrystallization zone rolling. The method comprises the following steps: heating a continuous casting steel billet in a soaking section at the temperature of 1,160-1,200 DEG C; after descaling, carrying out rolling at 1120-1180 DEG C, and carrying out rough rolling and intermediate rolling; the intermediate billet is subjected to water cooling before finish rolling, the outlet temperature of the intermediate billet is controlled to be 850-930 DEG C, and the intermediate billet enters an austenite non-recrystallization area; and then finish rolling is carried out, and the temperature on a cooling bed is controlled to be 900-950 DEG C. According to the method, through the synergistic effect of'segregation reduction at a high soaking temperature 'and'grain refinement through rolling in a non-recrystallization region', the technical contradiction between bainite inhibition and banded structure improvement is successfully solved. After the method is implemented, the average grade of the banded structure of the 20CrMnTiH steel can be reduced from 1.55 grade to 0.99 grade, and the maximum grade does not exceed 1.5 grade, so that the structure uniformity is obviously improved, the quenching deformation of subsequent heat treatment is reduced, and the requirements of high-end customers are met.

The application discloses a high-toughness bainite non-quenched and tempered steel and a manufacturing method thereof, and belongs to the technical field of steel production. The high-toughness bainite non-quenched and tempered steel comprises the following components in percentage by mass: C: 0.10-0.30%, Si: 0.2-0.6%, Mn: 1.8-2.8%, P: 0.003-0.03%, S: 0.04-0.07%, Cr: 0.3-0.8%, V: 0.06-0.15%, Zr: 0.001-0.01%, Te: 0.001-0.01%, N: 0.01-0.02%, O: 0.0005-0.005%, and the balance of Fe and inevitable impurity elements. By adding Zr and Te and cooperating with a specific preparation process, the application remarkably improves the inclusion morphology and distribution and refines the structure, thereby greatly improving the toughness while maintaining high strength.

The present invention provides a high-strength steel sheet having a tensile strength of 1180 MPa or higher, and excellent formability, impact resistance, and axial crushing properties. Therefore, the composition, in mass%, includes C: 0.15-0.30%, Si: 0.10-1.50%, Mn: 1.50-4.00%, P: 0.020% or less, S: 0.0020% or less, sol.Al: 0.100% or less, and N: 0.0150% or less. The total content of ferrite and bainite is 10% or less, tempered martensite is 80% or more, retained austenite is 10.0% or less, and fresh martensite is 10% or less. The C concentration in retained austenite is 0.50% by mass or less, and the Fe carbide content is 0.10-0.30% by mass.

A method for producing a steel sheet, the method containing the following successive steps:providing a cold-rolled steel sheet, the chemical composition of the steel containing in weight %: 0.15%≤C≤0.23%, 2.0%≤Mn≤2.8%, 1.0%≤Si≤2.1%, 0.02%≤Al≤1.0%, with 1.7%≤Si+Al≤2.1%, 0≤Nb≤0.035%, 0≤Mo≤0.3%, 0≤Cr≤0.4%, the remainder being Fe and unavoidable impurities,annealing the steel sheet at an annealing temperature TA so as to obtain a structure comprising at least 65% of austenite and up to 35% of intercritical ferrite,quenching the sheet at a cooling rate of at least 20° C. / s from a temperature of at least 600° C. down to a quenching temperature QT comprised between Ms−170° C. and Ms−80° C.,heating the sheet up to a partitioning temperature PT between 350° C. and 450° C. and maintaining the sheet at this temperature for a partitioning time Pt comprised between 80 s and 440 s,immediately cooling the sheet down to the room temperature,the steel sheet having a final microstructure consisting of, in surface fraction:between 40% and 70% of tempered martensite,between 7% and 15% of retained austenite,between 15% and 35% of ferrite,at most 5% of fresh martensite,at most 15% of bainite.

The invention relates to a method for producing a rolling element bearing component (1), wherein: the rolling element bearing component (1) is formed from a rolling element bearing steel of the type 100CrMnSi6-4 or 100Cr6; the rolling element bearing component (1) is heated to form an austenitic microstructure and subsequently quenched in a hot salt bath to a first temperature of between 170°C and 200°C, such that a pearlitic and / or ferritic microstructure is present at least in a core region (8) of the rolling element bearing component (1); thereafter, the rolling element bearing component (1) is heated to at least a second temperature in the temperature range from 220°C to 280°C and held for at least 7 hours, forming a predominantly bainitic microstructure at a surface (7) of the rolling element bearing component (1). The invention also relates to a rolling bearing component (1) and to a rolling bearing (2).

The invention relates to the field of material structure control and heat treatment, in particular to a method for improving the performance of low alloy steel through inclusions. According to the method, phase change driving force is regulated and controlled through accurate temperature control, foreign substance heterogeneous nucleation is promoted, and the effect that bainite nucleates with the foreign substance as a core and wraps the foreign substance to grow is achieved. According to the method, stress concentration caused by the inclusions can be remarkably reduced, sharp reduction of impact toughness of the low alloy caused by the inclusions is avoided, impact energy fluctuation caused by the inclusions is remarkably improved, meanwhile, the structure can be remarkably refined, and the mechanical property of the low alloy steel is further improved.

The application provides a corrosion agent and method for displaying G20CrNi4 granular bainite structure, the corrosion agent is prepared by 2%-4% nitric acid alcohol solution, hydrochloric acid and ferric chloride in the proportion of 100ml:0.3-0.7ml:0.4g-0.6g; the method for displaying granular bainite structure comprises sample preparation, corrosion agent preparation, granular bainite structure corrosion and metallographic microscope observation. The corrosion agent provided by the application is simple to prepare, the method for displaying granular bainite structure is stable and reliable, simple to operate, and can realize corrosion and clear display of granular bainite structure of carburizing bearing steel.

A welded joint in which the chemical composition of the base material has a specific chemical composition in which [alpha] is 4.0-16.0 represented by the following formula, the tensile strength is 590-930 MPa, the microstructure of a site that is 1 / 4 of the thickness from the surface contains lower bainite and martensite, the total area ratio of the lower bainite and martensite being 15.0% or more, and the thickness of the lower bainite and martensite being 1 / 4 of the thickness of the surface. The total area ratio of the upper bainite, the lower bainite, and the martensite is 90.0% or more, and the effective crystal grain size of the welding heat-affected portion is 100.0 [mu] m or less. Alpha = 0.50 * square root [C] * (1 + 0.64 [Si]) * (1 + 4.10 [Mn]) * (1 + 0.27 [Cu]) * (1 + 0.52 [Ni]) * (1 + 2.33 [Cr]) * (1 + 3.14 [Mo])

The invention relates to a high strength zinc coated steel sheet made of a steel having a composition comprising, by weight percent C: 0.20 - 0.35 %, Mn: 0.5 – 3.0 %, B: 0.0005 – 0.005%, Si 0.01- 1.20 %, Cr 0.01 - 1.5 % S ≤ 0.010 %, P ≤ 0.020 %, N ≤ 0.008 % and comprising optionally one or more of the following elements, in weight percentage: Al ≤ 1%, Mo ≤ 0.4 %, Ti ≤ 0.05 %, Nb ≤ 0.05 %, said steel sheet having a microstructure comprising, in area fraction, bainite and tempered martensite, the sum being comprised from 25% to 65%, the rest being fresh martensite and martensite-austenite islands.

The application discloses a preparation method of a bainite high-strength steel with a rapid phase change induced by deformation and precipitation, and belongs to the alloy field.The preparation method disclosed by the application comprises the following steps: S1, melting and casting;S2, hot rolling to refine grains;S3, warm rolling deformation to induce precipitation;S4, bainite phase change isothermal;S5, a small amount of martensite is introduced;S6, bainite phase change isothermal is performed again;the application utilizes the deformation to induce the precipitation of a submicron second phase, optimizes a heat treatment process, and obtains the bainite high-strength steel with no incubation period, and the phase change completion time is within 70 minutes, so that the isothermal transformation rate of the nano bainite is greatly improved, the preparation time is significantly shortened, and the production efficiency is improved.