28 results about "Ferrite grain size" patented technology

The invention provides a seamless steel pipe for a hollow anchor rod and a strength regulation and control method thereof. Alloy steel round steel is heated and then subjected to hot piercing to be manufactured into a hollow pipe blank; the hollow pipe blank is subjected to spheroidizing annealing treatment and then cooled, and a first treated steel pipe is obtained; wherein the ferrite grain size D1 of the first treated steel pipe is calculated according to a spheroidizing annealing grain size model; the first treated steel pipe is subjected to cold finish rolling forming and cleaned to obtain a second treated steel pipe; the ferrite effective grain size Ddef of the second treatment steel pipe is calculated according to the cold deformation grain refinement model; recrystallizing and annealing the second treated steel pipe to obtain the seamless steel pipe; the ferrite grain size D2 of the seamless steel pipe is calculated according to the recrystallization grain evolution model; the yield strength Rp0.2 of the seamless steel pipe is calculated according to a strength model; reverse design of the yield strength of the seamless steel pipe is achieved, and meanwhile it is guaranteed that the seamless steel pipe has good plasticity.

A ferrite structure edge extraction method based on a microstructural phase diagram of steel, comprising: performing edge detection on a metallographic image of a low-carbon steel cold rolled sheet; closing grain boundaries; removing redundant boundaries; detecting grain parts of unconnected parts and grain unclosed parts in a labeled image on the basis of a network topology structural diagram, performing grain boundary edge determination, and when the vertex of each unclosed part grain remains unchanged, continuously traversing different grain boundary arcs connected to the unclosed part grain so as to determine whether the unclosed part grain satisfies the characteristics of a completely closed grain, thereby achieving grain reconstruction; and then performing reconstruction detection to finally complete extraction and reconstruction of ferrite structure edges. Thus, ferrite grains of a microstructural phase diagram of steel are accurately reconstructed, two grains connected by a narrow area are effectively segmented, accurate ferrite grains of a low-carbon steel cold rolled sheet can be extracted, and ferrite grain size grading of the low-carbon steel cold rolled sheet is assisted on the basis of the extracted accurate ferrite grains of the low-carbon steel cold rolled sheet.

The invention provides a rolling method of cathode flat steel, which comprises the following steps: firstly, heating a casting blank to obtain a heated blank, then carrying out surface descaling on the heated blank, and carrying out multi-pass rough rolling to obtain an intermediate blank; the heating treatment comprises a preheating section and a soaking section; the heating treatment is specifically a heating treatment process for controlling the austenite grain size of the casting blank; the multi-pass rough rolling comprises multi-pass rough rolling of which the reduction rate is sequentially reduced; and carrying out multi-pass finish rolling on the intermediate billet obtained in the previous step, carrying out on-line cooling, and then carrying out stacking slow cooling to obtain the rolled and formed cathode flat steel. According to the method, directional improvement of the conductivity of the electrolytic aluminum cathode flat steel is achieved through rolling process optimization, heating under a rolling path of a low-temperature ferrite area and rolling pass reduction distribution design are focused, the ferrite grain size and the conductive texture of a material are cooperatively regulated, the normal conductivity of the cathode flat steel is improved, and the conductivity of the cathode flat steel is improved. And a core material support is provided for reducing ineffective current loss in the electrolytic aluminum industry.

A hot-rolled strip steel product having a chemical composition consisting of, in terms of weight percentages (wt. %): 0.025%-0.070% C, 0%-1.10% Si, 0.50%-2.0% Mn, <0.020% P, <0.050% S, <0.010% N, 0%-0.60% Cr, 0%-0.20% Ni, 0%-0.25% Cu, 0%-0.20% Mo, 0%-0.15% Al, 0%-0.050% Nb, 0.020%-0.20-% V, 0.020%-0.15% Ti, 0%-0.0010% B, remainder Fe and inevitable impurities, wherein the strip steel product has a microstructure comprising of, in terms of volume percentages (vol. %), ferrite ≥90%, wherein the ferrite structure comprises 10%-50% quasi-polygonal ferrite and a reminder of ferrite structure is polygonal ferrite and / or bainite: and wherein the steel strip product has an average ferrite grain size of <10 μm, an average hole expansion ratio of ≥50%, a yield strength (Rp0.2%) longitudinal to rolling direction of ≥660 MPa and a tensile strength of ≥760 MPa.

The present invention relates to a large-thickness submarine pipeline steel plate and a production method therefor. Steel plate components are designed by means of optimization of low-carbon low-alloy components, and the production method uses a matching special controlled rolling process of five-stage heating, low-temperature high-reduction rolling in a recrystallization region, instant cooling of intermediate slabs and high-temperature high-reduction rolling in a non-recrystallization region, and a matching multi-stage controlled cooling process of high-temperature region air cooling for redistribution, ferrite region cooling, temperature maintaining, bainite region cooling and air cooling self-tempering cooling. The steel plate product of the present invention has a relatively high proportion of acicular ferrite, and a relatively fine average ferrite grain size of 3-6μm, thus endowing the steel plate with good combination of strength and toughness. The steel plate has high strength, wherein the yield strength is ≥500MPa, the tensile strength is ≥630MPa, and the impact energy KV2 at -60℃ is ≥250J.

This invention relates to a high-power, low-loss Li-based microwave ferrite for LTCC and its preparation method, belonging to the field of electronic ceramics technology. The ferrite, based on its respective standard components, contains the following content: Li₂CO₃ 11.80–12.24 mol%, ZnO 19.87–20.41 mol%, TiO₂ 10.78–11.08 mol%, Mn₃O₄ 0.39–2.65 mol%, Co₃O₄ 0.04–0.58 mol%, Fe₂O₃ 54.70–56.18 mol%, and Bi₂O₃ 0.09 mol%. This invention introduces high-valence Mn ions into the Li-based microwave ferrite, altering the ferrite grain size distribution, particularly increasing the proportion of fine grains, thus improving the spin linewidth. Based on grain refinement, the introduction of an appropriate amount of Co ions with rapid relaxation characteristics further enhances the ferrite's spin linewidth.

This invention provides a method for producing 270MPa grade hot-dip galvanized deep-drawing steel strip. The method controls the chemical composition, the hot rolling process (including soaking temperature, final rolling temperature, and coiling temperature), and the hot-dip galvanizing process (including annealing temperature, galvanizing temperature, finishing, and tension leveling). This results in hot-dip galvanized steel strip with excellent mechanical properties (Rp0.2 = 185–255 MPa, Rm ≥ 270 MPa, A50mm ≥ 42%, n90 ≥ 0.17). It effectively overcomes the problems of mixed crystals and performance deterioration in the pickling-hot-dip galvanizing technology during annealing due to lack of deformation recovery, recrystallization, and grain growth. The product's microstructure is 100% ferrite with a ferrite grain size of 8.0–10.5. Furthermore, the pickling-direct hot-dip galvanizing process used in this invention omits the conventional cold rolling step, reducing process costs.

The invention discloses a preparation method of novel high-yield cold-rolled DP980 steel, and belongs to the field of advanced steel and iron materials. According to the method, Nb and Ti elements are added, solid solution strengthening, precipitation strengthening and fine grain strengthening are carried out in DP980 steel, then a DP980 steel plate with the uneven thickness is rolled through unique rolling process design, then heat treatment is carried out, a heterostructure appears, the yield strength is improved, and the yield strength is improved. The method comprises the following specific steps: S1, adding 0.02-0.05% of Nb and 0.01-0.03% of Ti on the basis of components of traditional DP980 during smelting of a steel ingot; s2, rolling the steel billet by adopting a concave-convex roller during rolling; and S3, the rolled steel plate is subjected to a critical annealing process of heat preservation at 790-810 DEG C for 2-5 minutes. By means of the method, the DP980 steel can obtain a heterostructure with an uneven structure, and the grain size of ferrite in a high-deformation area is smaller. The yield strength of the DP980 steel prepared through the technology ranges from 720 MPa to 800 MPa, and the yield strength of the DP980 steel is improved by about 15% compared with that of existing DP980 steel.

The invention discloses a method and a device for improving corrosion resistance of duplex stainless steel, the method adopts a galvanometer laser-induced arc hybrid welding method to weld the duplex stainless steel, the laser is a plurality of beams of pulse laser, a galvanometer controls the plurality of beams of pulse laser to be synchronous with a TIG (Tungsten Inert Gas) arc with different scanning parameters, and the corrosion resistance of the duplex stainless steel is improved by enhancing disturbance of a molten pool. And thus, defects are generated in the ferrite, and heterogeneous sites are provided for austenite nucleation. In the welding cooling process, austenite preferentially nucleates and grows at the defect position, so that generation of intragranular austenite is promoted, Widmannstan austenite structures are reduced, primary ferrite dendritic crystals can be broken through strong molten pool convection, a large number of dendritic crystal fragments are generated, and the ferrite grain size is effectively refined. According to the structure evolution, a corrosive medium can make contact with an austenite phase with the excellent corrosion resistance more easily, the potential corrosion expansion path is shortened, and therefore the corrosion resistance of the duplex stainless steel welded joint is improved.

The invention discloses a hot rolling production method of low-cost pure hydrogen delivery pipeline steel L360MH, which adopts a low-carbon equivalent design to remarkably improve weldability and hydrogen embrittlement resistance. Ti / Nb composite microalloying refined grains are added, so that a high-density nanoscale carbonitride precipitated phase is formed and effectively serves as a'hydrogen trap ', and hydrogen diffusion is inhibited; meanwhile, the content of P (smaller than or equal to 0.013%) and the content of S (smaller than or equal to 0.0015%) are strictly controlled, impurity segregation is reduced, and hydrogen induced cracking (HIC) sensitivity is reduced; through a controlled rolling and controlled cooling (TMCP) process, fine and uniform ferrite and a small amount of pearlite structures (the grain size of the ferrite is greater than or equal to 9 grades) are obtained; a high-proportion small-angle grain boundary and a uniform precipitated phase hinder crack propagation, so that the steel is endowed with excellent low-temperature toughness (the impact energy at-10 DEG C is more than or equal to 200J) and high hydrogen embrittlement resistance; and the structure uniformity also guarantees the strength stability (the yield strength is greater than or equal to 390MPa), and the mechanical requirements of pure hydrogen transportation are met.

The invention belongs to the technical field of metallurgy, and particularly relates to 420MPa-grade galvanized low-alloy high-strength steel and a production method thereof, and the 420MPa-grade galvanized low-alloy high-strength steel comprises the following components in percentage by mass: 0.06%-0.08% of C, 0.05%-0.08% of Si, 0.95%-1.15% of Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, 0.015%-0.060% of Al, less than or equal to 0.0060% of O, less than or equal to 0.0060% of N, 0.01%-0.03% of V, 0.01%-0.03% of Ti and the balance of Fe and inevitable impurities. The method has the advantages that through V-Ti composite microalloying, hot rolling and cold rolling process control, synergy of fine grain strengthening and precipitation strengthening is achieved, the ferrite grain size is 2-5 microns, the (Ti, V) C precipitation phase size is 20-30 nm, the yield strength of the steel plate is larger than or equal to 420 MPa, and the elongation is kept above 20%.

The invention discloses a production method of a high-toughness high-resistivity low-alloy steel medium plate. Steel comprises the following chemical components in percentage by weight: 0.06%-0.10% of C, 0.90%-1.30% of Si, 1.45%-1.7% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.020%-0.060% of Alt, 0.008%-0.020% of Ti, 1.3%-1.5% of Mn / Si, more than or equal to 3.42% of Ti / N and the balance of Fe and inevitable impurities. Through high-temperature finish rolling, the finish rolling temperature is 50 DEG C or above higher than the Ar3 temperature point, and complete recrystallization is ensured; after rolling, double-stage controlled cooling is adopted, the pearlite transformation temperature is skipped to 650-700 DEG C through fast cooling, and ferrite is promoted to grow sufficiently through slow cooling; the microstructure of the finally obtained steel plate is 85%-92% of ferrite and 8%-15% of pearlite, the grain size of the ferrite is 10-12 grades, high toughness and high resistivity are well matched, the alloy production cost is low, and the process is simple.

The present application relates to the technical field of high-strength deep-drawing cold-rolled steel sheet preparation, and particularly relates to a cold-rolled 780-grade DH steel with refined grains and uniform structure and a production method thereof.The chemical composition of the steel is as follows in terms of percentage by weight: C: 0.08%-0.12%, Si: 0.4%-0.6%, Mn: 1.6%-2.0%, Nb: 0.02%-0.04%, P: ≤0.012%, S: ≤0.005%, Ti: 0.01%-0.02%, Als: 0.025%-0.050%, N: ≤0.0035%, and the balance being Fe and inevitable impurities.The ferrite grain size of the steel is 5-8 mu m, and the grain size standard deviation is ≤1.2 mu m, thereby solving the problem of uneven structure.The finished steel has a tensile strength of ≥780 MPa, an elongation after fracture of ≥22%, and a earing rate of ≤1.5%, thereby meeting the requirement of complex deep-drawing.

The present invention relates to the technical field of cold-heading steel wire rod production, specifically to an annealing-free carbon cold-heading steel wire rod and its production method. The chemical composition of the wire rod, by weight, is as follows: C: 0.34% to 0.36%, Si ≤ 0.05%, Mn: 0.70% to 0.90%, P ≤ 0.010%, S ≤ 0.010%, Al: 0.02% to 0.04%, Ti: 0.015% to 0.040%, N ≤ 0.0050%, with the remainder being Fe and unavoidable impurities. The production method specifically comprises the following steps: 1) heating the steel billet; 2) rolling and spinning; 3) controlling the wire rod dimensions; and 4) cooling the wire rod using the EDC process, followed by slow cooling with a hood. The wire rod structure is composed of ferrite and pearlite. The ferrite content is not less than 50% by area, the ferrite grain size is 10-25μm, the cross-sectional shrinkage rate is not less than 55%, the hardness is not higher than 85HRB, and the extreme difference in hardness in the circumferential direction is not greater than 20HV, which reduces the production cost of the wire rod.

This invention discloses a material and processing method suitable for cold-stamped flexible wheels, belonging to the field of metal materials and forming technology. The material of this invention has a tensile strength of 500-550 MPa, a yield strength of 320-380 MPa, an elongation after fracture of 35-38%, an r-value of 2.0-2.3, a {111}-faceted ferrite content of ≥70%, and a ferrite grain size of ≥9 grade. Based on traditional high-quality medium-carbon alloy steel, this invention reduces the C element content and increases the AlN content. Combined with strict continuous casting control processes and online spheroidizing annealing after hot rolling, cold rolling with large cumulative deformation, and recrystallization annealing at lower temperatures, it fully refines the ferrite grains and spheroidizes the cementite. It controls the ferrite to be mainly distributed with a {111}-faceted texture, maximizing the plasticity of the steel plate while improving the r-value and deep-drawing performance, thus enabling the material of this invention to meet the basic requirements for cold-stamping of flexible wheels.

The invention discloses a method for improving plasticity of additive manufacturing duplex stainless steel, and belongs to the technical field of metal additive manufacturing. According to the method, in LPBF, by controlling technological parameters and the depth-to-width ratio of a molten pool, a rotating cubic texture and an alpha-fiber texture beneficial for improving the strength and plasticity are obtained, meanwhile, the grain size of ferrite is regulated and controlled, a high-density printing-state sample is prepared, then short-time heat treatment is conducted on the high-density printing-state sample, and by regulating and controlling the heat treatment time and controlling the austenite nucleation and growth process, the high-density printing-state sample is obtained. And a double-peak heterostructure of ferrite and austenite grains is formed in the material, and then the material is cooled, so that the duplex stainless steel with improved plasticity is obtained. According to a sample prepared through the method, the high strength is kept, meanwhile, the elongation rate can be increased by 40%, the strength and plasticity matching of the sample is remarkably superior to the ASTM 240 standard requirement, and the inversion rule limitation of high strength-low plasticity or low strength-high plasticity of traditional duplex stainless steel is effectively broken through.

This invention belongs to the field of metallurgical technology, and particularly relates to a 420MPa grade galvanized low-alloy high-strength steel and its production method. The steel composition by mass percentage is as follows: C: 0.06%~0.08%, Si: 0.05%~0.08%, Mn: 0.95%~1.15%, P≤0.025%, S≤0.010%, Al: 0.015%~0.060%, O≤0.0060%, N≤0.0060%, V: 0.01%~0.03%, Ti: 0.01%~0.03%, with the balance being Fe and unavoidable impurities. The advantages are: through V-Ti composite microalloying and controlled hot and cold rolling processes, synergistic effects of fine grain strengthening and precipitation strengthening are achieved. The ferrite grain size is 2~5μm, the (Ti,V)C precipitate size is 20~30nm, the steel plate yield strength is ≥420MPa, and the elongation is maintained above 20%.

The application discloses an anti-collision pressure container steel for storing and transporting ethane, which is characterized by the following components and wt%: C: 0.10-0.20%, Si: 0.20-0.40%, Mn: 1.58-1.80%, Al: 0.025-0.045%, P: ≤0.015%, S: ≤0.005%, V: 0.030-0.065%, and Nb: 0.025-0.045%. The application comprises the following steps: after smelting and casting into a blank, the cast blank is heated; rough rolling; finish rolling; cooling; normalizing; and stress relief. The static yield strength Rel of the steel is 420-480 MPa, the dynamic yield strength Re is 510-747 MPa, the tensile strength is 585-645 MPa, the yield strength ratio is ≤0.85, the static elongation after fracture A is 28-42%, the dynamic elongation after fracture A d The steel plate has the following properties: the static yield strength Rel is 420-480 MPa, the dynamic yield strength Re is 510-747 MPa, and the tensile strength is 585-645 MPa; the yield strength ratio is ≤0.85, the static elongation after fracture A is 27-40%, the dynamic elongation after fracture A is 27-40%, the product of strength and plasticity is 16800-26042 MPa%, the drop weight tear test (DWTT) energy is 15-19 kJ, the absorbed energy of the steel plate is 3.5-3.75 KJ when the collision speed is 5-50 m / s and the collision displacement is 1.5 m, and the ferrite grain size is ≤0.012 μm.

The invention discloses a material suitable for cold stamping forming of a flexible gear and a machining method, and belongs to the technical field of metal materials and forming. The tensile strength of the material is 500-550 MPa, the yield strength is 320-380 MPa, the percentage elongation after fracture is 35-38%, the r value is 2.0-2.3, the proportion of {111} surface texture ferrite is larger than or equal to 70%, and the grain size of the ferrite is larger than or equal to the level 9. On the basis of traditional high-quality medium-carbon alloy steel, the content of C is reduced, the content of AlN is increased, a strict continuous casting control process and online spheroidizing annealing, large-accumulated deformation cold rolling and low-temperature recrystallization annealing after hot rolling are combined, and on the basis of fully refining ferrite grains and spheroidizing cementite, the high-quality medium-carbon alloy steel is obtained. The orientation distribution of ferrite mainly in a {111} surface texture is controlled, the plasticity of the steel plate is improved to the highest level, meanwhile, the r value and the deep drawability are improved, and the material meets the basic requirement for cold stamping forming of the flexible gear.

The invention belongs to the technical field of metal materials, and particularly relates to a zinc-aluminum-magnesium alloy coated steel plate for ultra-deep drawing and a preparation method thereof. The plating layer of the alloy plating layer steel plate comprises the following components in percentage by weight: 1-3% of aluminum, 1-2% of magnesium, 1.0-1.5% of aluminum / magnesium and the balance of zinc and inevitable impurities. The steel base of the alloy coating steel plate is ultra-low carbon steel, the structure of the alloy coating steel plate is ferrite, the grain size is 10-30 microns, and the inclusion size needs to be smaller than or equal to 15 microns. The reflective rate of the surface of the coating is reduced through Al / Mg content control and large finishing elongation control, and the requirements of television backboards, automobile panels and other very complex parts with the size smaller than 85 inches are met.

A collision-resistant pressure vessel steel for storing and transporting carbonyl chloride, comprising the following components (wt%): C: 0.10–0.20%, Si: 0.25–0.50%, Mn: 1.65–1.90%, Al: 0.025–0.045%, P≤0.015%, S≤0.005%, V: 0.070–0.10%, Nb: 0.028–0.052%. The process involves: smelting, casting into a billet, heating the billet, rough rolling, finish rolling, cooling, normalizing, and stress relief. The static yield strength Rel of this invention is 500–570 MPa, and the dynamic yield strength Re is 520–787 MPa; the tensile strength is 650–730 MPa; the yield ratio is ≤0.85; and the static elongation after fracture A is 29–42% and the dynamic elongation after fracture A... d The strength-ductility product is 21054-28434 MPa·%; the drop hammer tear (DWTT) energy is 15.7-20 kJ; when the impact velocity is 5-50 m / s and the impact displacement is 1.5 m, the steel plate absorbs 3.85-4.15 kJ of energy, and the ferrite grain size does not exceed 0.008 μm.

The invention relates to a hot continuous rolling finishing mill group outlet strip steel performance forecasting method, and belongs to the technical field of hot rolling methods. According to the technical scheme, the method comprises the steps that main equipment and technological parameters of a hot rolling unit are collected, steel type and specification characteristic parameters of a product to be expanded are given, a finish rolling outlet temperature regression model and a two-dimensional temperature field equation are established through parameters influencing the finish rolling temperature of strip steel on the basis of a multiple linear regression model, and the finish rolling outlet temperature of the strip steel is calculated; the ferrite grain size and the ferrite volume fraction are obtained by combining a heat conduction control equation and a microstructure evolution relation, and the yield strength and tensile strength mechanical properties of the steel are calculated through chemical components and microstructures. The method has the beneficial effects that the two-dimensional temperature field model about the width and the thickness of the strip steel is established by utilizing the characteristic that the heat transfer characteristic in the strip steel finish rolling process influences the temperature, the performance distribution condition in the strip steel is researched, and a technical support is provided for achieving online prediction-real-time regulation and control-accurate delivery of the performance of the strip steel.

A low-strength thick steel sheet having excellent elongation properties and corrosion resistance, wherein a prescribed composition group is provided, in the metal structure, 70% or more of ferrite is contained in terms of area ratio with respect to the entire metal structure, the balance contains one or more selected from the group consisting of pearlite, bainite, and martensite, the ferrite grain size is 3 μm or more and 40 μm or less, when a tensile test is performed using a test piece of NK-U1 No. of 200 mm gauge according to the Ship Classification Rule K of the Nippon Kaiji Kyokai (2019 edition), the tensile strength is 400 MPa or more and 520 MPa or less, the elongation at break is 16% or more, and the uniform elongation is 13.5% or more.

This invention relates to the field of cold heading steel wire rod production technology, specifically to a non-annealed boron-containing cold heading steel wire rod and its production method. The chemical composition of the wire rod, by weight percentage, is as follows: C: 0.31%–0.33%, Si ≤ 0.05%, Mn: 0.70%–0.90%, P ≤ 0.010%, S ≤ 0.010%, Al: 0.02%–0.06%, B: 0.0010%–0.0025%, Cr: 0.20%–0.30%, Ti: 0.015%–0.040%, N ≤ 0.0050%, with the balance being Fe and unavoidable impurities. The wire rod structure consists of ferrite and pearlite. The ferrite content is not less than 55% by area, the ferrite grain size is 10-25μm, the reduction of area is not less than 60%, the hardness is not higher than 85HRB, and the hardness difference in the circumferential direction is not greater than 20HV, which reduces the production cost of wire rod.

The present application relates to the technical field of steel material preparation, in particular to a kind of ultra-fine grain high hole expansion rate hot rolled pickling 420MPa grade low alloy high strength steel and its preparation method.Chemical composition contains C, Si, Mn, Nb, Ti, Cu, Ni and other elements, and meet Ti / N=3.0~5.0, (Nb+Ti) / C=0.40~0.70.The method includes hot metal pretreatment, converter smelting, LF+RH refining, continuous casting, slab heating (1140~1160℃), hot rolling, controlled cooling, coiling (580~620℃), flattening and pickling.The steel plate microstructure is ultra-fine grain ferrite and a small amount of pearlite, ferrite grain size 3.0~4.5μm, yield strength 443~512MPa, tensile strength 508~578MPa, elongation 25.5%~35.0%, hole expansion rate 81%~115%, with high strength and excellent flanging formability.

The invention discloses a thin-gauge high-formability micro-carbon steel plate and a two-phase region hot rolling preparation process thereof, and belongs to the technical field of metal materials. The process comprises the following steps of continuous casting billet heating, austenite area rough rolling, two-phase area hot rolling, cooling, coiling, cold rolling and annealing. The structure of the hot-rolled plate obtained through the technology is ferrite and a small amount of pearlite, and the grain size of the ferrite is 4.5-5.0 grade; the yield strength Rp0.2 ranges from 180 MPa to 208 MPa, the tensile strength Rm ranges from 305 MPa to 320 MPa, the elongation is larger than or equal to 42%, and the average plastic strain ratio ranges from 0.96 to 1.20. The yield strength Rp0.2 of the cold-rolled sheet ranges from 220 MPa to 250 MPa, the tensile strength Rm ranges from 315 MPa to 330 MPa, the elongation is larger than or equal to 42%, the work hardening index n is larger than or equal to 0.25, the average plastic strain ratio ranges from 1.30 to 1.60, and the lug parameter delta r is smaller than or equal to 0.15.

The application provides a 09CrCuSb round steel with high strength and sulfuric acid dew point corrosion resistance, and the chemical components of the 09CrCuSb round steel are as follows in terms of mass percentage: C: 0.05%-0.10%, Si: 0.20%-0.36%, Mn: 0.45%-0.62%, P: ≤0.012%, S: ≤0.012%, Cr: 0.90%-1.20%, Cu: 0.40%-0.55%, Ni: 0.17%-0.26%, Sn: 0.12%-0.20%, Sb: 0.15%-0.20%, W: 0.15%-0.20%, Mo: 0.35%-0.45%, and the balance is Fe and inevitable impurities; wherein the mass ratio of Cu and Ni is 2-2.5, the average ferrite grain size of the 09CrCuSb round steel is 9-14 mu m, and the volume fraction of proeutectoid ferrite is ≤0.70%. The 09CrCuSb round steel prepared by adjusting the element ratio, optimizing the process flow and controlling the cooling rate after rolling has the properties of high strength and sulfuric acid dew point corrosion resistance.

This invention relates to the field of high-strength cold-rolled steel sheet preparation technology, and particularly to a cold-rolled 780 grade DH steel with refined grains and uniform microstructure, and its production method. The chemical composition of the steel, by weight percentage, is: C: 0.08%–0.12%, Si: 0.4%–0.6%, Mn: 1.6%–2.0%, Nb: 0.02%–0.04%, P≤0.012%, S≤0.005%, Ti: 0.01%–0.02%, Als: 0.025%–0.050%, N≤0.0035%, with the balance being Fe and unavoidable impurities. The ferrite grain size in the steel of this invention is 5–8 μm, with a grain size standard deviation ≤1.2 μm, solving the problem of uneven microstructure. The finished steel has a tensile strength ≥780 MPa, elongation after fracture ≥22%, and earing rate ≤1.5%, meeting the requirements of complex deep drawing.