CN109023112B - High-strength atmospheric corrosion resistant cold forging steel and preparation method thereof - Google Patents
High-strength atmospheric corrosion resistant cold forging steel and preparation method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention relates to the technical field of cold forging steel, and particularly discloses high-strength atmospheric corrosion resistant cold forging steel and a preparation method thereof. The high-strength atmospheric corrosion resistant cold forging steel comprises the following components in percentage by weight: 0.28-0.40% of C, 0.15-0.30% of Si, 0.60-0.90% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.60-1.00% of Cr, 0.20-0.50% of Ni, 0.20-0.45% of Cu, 0.005-0.050% of Ti, and one or more of Mo, 0.15-0.35% of V, 0.09-0.12% of Nb and 0.005-0.015% of any element; the balance being Fe and unavoidable impurities. The cold heading steel prepared by the invention has higher strength and hardness, simultaneously has good hardenability, meets the requirement of hardenability of large-size bolts, also has certain delayed fracture resistance, and has the characteristics of low production cost, good corrosion resistance, high tensile strength, good surface quality, excellent performance and the like.
Description
Technical Field
The invention relates to the technical field of cold forging steel, in particular to high-strength atmospheric corrosion resistant cold forging steel and a preparation method thereof.
Background
The connecting bolt applied to facilities such as railway, highway steel structure bridges and the like is a high-strength bolt, and because the bolt is in a field environment for a long time, the surface of the bolt and surrounding media (water vapor, salt and the like) are easy to generate chemical and electrochemical actions, so that the bolt is rusted. Particularly, the steel bridge generally spans across rivers, the temperature and humidity are high all the year round, the environment is severe, and bolts are prone to rusting and corrosion after being placed in the environment for a long time, and finally break or crack is caused, so that a potential accident source is formed.
At present, the main measures for solving the corrosion problem are generally to enlarge the corrosion allowance or to coat with an anti-rust paint. The former causes material waste and increases production cost; the latter requires regular maintenance paint repainting, which is costly and sometimes affects the normal use of the railway or bridge. Another common protection measure is to use a metal coating for protection, mainly hot dip coating or spray coating of a zinc or aluminum metal layer, and utilize the cathodic protection performance of metal to prolong the service life of the steel structure, but the application of the metal coating also has the problems of high cost, environmental pollution, difficulty in application of large-sized components, poor bolt tightening ratio and the like. Therefore, the corrosion-resistant steel is developed, so that the performance of the material meets the mechanical performance requirement of the bolt steel and the corrosion resistance requirement of the material, the service life of the material is prolonged, the maintenance cost of the material in the subsequent use process is reduced, and the corrosion-resistant steel has very important significance.
Disclosure of Invention
The invention provides high-strength atmospheric corrosion resistant cold forging steel and a preparation method thereof, aiming at the problem that the strength and the corrosion resistance of the existing bolt are required to be further improved.
In order to solve the technical problem, the embodiment of the invention provides the following technical scheme:
the high-strength atmospheric corrosion resistant cold forging steel comprises the following components in percentage by weight: 0.28-0.40% of C, 0.15-0.30% of Si, 0.60-0.90% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.60-1.00% of Cr, 0.20-0.50% of Ni, 0.20-0.45% of Cu, 0.005-0.050% of Ti, and one or more of Mo, 0.15-0.35% of V, 0.09-0.12% of Nb and 0.005-0.015% of any element; the balance being Fe and unavoidable impurities.
In the prior art, C, Cr and Mn elements are added in the component design of the invention, so that the strength of the material is improved; the content of the impurity element P, S is reduced, Ti element is added to generate dispersed fine carbon-nitrogen compound to refine austenite grains, the toughness of the steel can be improved while the strength of the steel is improved, the formed carbon-nitrogen compound can also be used as a hydrogen trap to inhibit the diffusion of hydrogen and enable the hydrogen to be uniformly distributed, the grain boundary segregation is reduced, and the low-temperature brittleness and the delayed fracture resistance of the material are improved; adding alloy elements such as Cu, Ni and Cr to form a passive film on the surface of the alloy, reducing the invasion of hydrogen, preventing the generation of hydrogen induced cracks, and simultaneously effectively improving the atmospheric corrosion resistance; adding Si element, and improving the weather resistance of the steel by matching with Cu and Cr; cr, Mn and Si are completely dissolved in austenite, so that the hardenability of the steel is improved; any one or more elements of Mo, Nb and V with strong tempering and softening resistance are also added, the tempering temperature and the grain boundary strength are improved, and carbides can be refined. The components are matched with each other in a specific proportion, so that the material can meet the mechanical performance requirement of bolt use and has higher atmospheric corrosion resistance.
The action and the proportion of each element are as follows:
c is the most important constituent element in steel and is also the main element for determining the metallographic structure and the performance of the solidified carbon steel. When the carbon content in the steel is increased, the hardness and the strength are both improved, the plasticity and the toughness are reduced, and Cr carbide is easily formed and precipitated at a grain boundary when the C content is too high, so that a local Cr-poor region of the grain boundary appears, and the atmospheric corrosion resistance of the steel grade is reduced; meanwhile, the precipitation of the carbide is easy to attract hydrogen atoms to gather around the carbide, so that the periphery, particularly the sharp corner of the carbide is easy to become a crack source of hydrogen induced cracking, and the corrosion resistance of the steel is reduced. In order to ensure the strength of the steel, the carbon content must be 0.28% or more, but since an excessive carbon content deteriorates the toughness of the steel and causes a decrease in the corrosion resistance of the steel, the C content is designed to be 0.28 to 0.40%.
Si is important deoxidizer and reducer in steel-making process, it can be dissolved in ferrite and austenite to raise strength and hardness of steel, and when the Si-containing steel is heated in oxidizing atmosphere, a layer of SiO is formed on the surface2Si can also improve the resistivity of the steel, enhance the corrosion resistance of the steel under natural conditions, improve the weather resistance of the steel by matching with other elements of Cu, Cr and P, and the higher Si content is favorable for refining α -FeOOH so as to reduce the overall corrosion rate of the steel, but the too high Si content can improve the strength and the corrosion resistance of the steel, but can reduce the ductility and the toughness of the steel, and the solid solution strengthening and the atmospheric corrosion resistance of the Si are comprehensively considered, and the design target of the Si content is 0.15-0.30%.
Mn can greatly improve the strength and toughness of steel grades, is an effective deoxidizer and has the function of removing S, but excessive Mn can also reduce the toughness of the steel grades, and in addition, the precipitation of MnS can greatly reduce the corrosion resistance of the steel, so the content of Mn is designed to be 0.60-0.90%. In the invention, Cr, Mn and TiC act together to make the steel generate stronger strength, hardness and toughness.
P, S is a chemical element which easily causes cold and hot embrittlement and deteriorates the plasticity and delayed fracture resistance of steel, and therefore, the content of P is controlled to 0.02% or less and the content of S is controlled to 0.020% or less, the lower the content, the better.
Cr forms a multi-element alloy oxide of iron and chromium in the rust layer, and is enriched at microcracks and grain boundaries in the rust layer to block a channel from an external medium to a matrix, so that the grains of the rust layer are prevented from further growing, the rust layer is more compact, and the matrix metal is prevented from being further corroded; the Cr elements exceeding the solubility are repelled into the matrix, so that the enrichment of the Cr elements is generated in the matrix at the interface, the electrochemical potential of the matrix can be improved by improving the content of the Cr elements in the matrix near the interface, and the atmospheric corrosion resistance of the matrix can be improved, therefore, the content of the Cr elements is designed to be 0.60-1.00%. Particularly, when Cr is used in combination with Cu, the passivation ability of steel can be remarkably improved.
The Ni can improve the strength, toughness and hardenability of the steel, and can also greatly improve the low-temperature impact and corrosion resistance of the steel, and the Ni can be matched with a Cu element to change the surface of the steel from a copper-enriched layer to a copper-nickel-enriched layer with the melting point of over 1200 ℃, so that the defect of copper brittleness is reduced; however, the Ni element is particularly sensitive to white spots, and particularly, the H element inevitably penetrates into the steel during wet corrosion, so that the Ni content is designed to be 0.20 to 0.50%.
Cu is beneficial to forming a passive film and a corrosion product film on the surface of the steel grade, so that the atmospheric corrosion resistance of the steel is improved, but the mechanical property and the hot working property of the steel grade are reduced due to the excessively high content of Cu, so that the content of Cu is designed to be 0.20-0.50%.
Ti can generate strong precipitation strengthening effect, so that the strength of the steel is improved, austenite recrystallization can be prevented, a grain refining effect is generated, the yield strength of the steel is improved, TiN or TiC hydrogen traps can be formed by Ti, and the delayed fracture resistance of the steel is improved; however, when the Ti content is too high, the inclusion of carbide and nitride increases, and the strength is deteriorated, and the Ti content is 0.005-0.050%.
Mo can obviously improve hardenability in steel, improve the tempering stability of the steel, improve the low-temperature impact resistance of the steel, and simultaneously improve the hydrogen ion corrosion resistance of the steel, and is particularly suitable for steel materials resistant to humid atmosphere corrosion, but the excessive Mo content can cause the increase of overheat sensitivity, Mo is a noble alloy, the excessive Mo content can increase the production cost, and the Mo content in the designed steel is 0.15-0.35%.
The V is dissolved in austenite, so that the hardenability of steel can be obviously improved, and carbide or carbonitride of the V is precipitated in ferrite, so that the purposes of fine-grain strengthening and precipitation strengthening can be achieved, and the content of the V is 0.09-0.12%.
Nb can improve the strength of the steel, and simultaneously, the Nb content is improved, so that the corrosion resistance of the steel in an acid environment is improved. Nb generates Nb oxide on the surface to form a protective film, thereby improving the local corrosion resistance of the steel. By adding Mo, the solid solubility of Nb (C, N) in austenite is improved, the precipitation temperature of Nb (C, N) is reduced, more Nb (C, N) is precipitated in low-temperature ferrite, and the precipitation strengthening effect of Nb (C, N) is improved. The Nb content is 0.005-0.015%.
Preferably, the weight percentage of C is 0.32-0.38%.
The preferable content of C can improve the strength of the material without influencing the plasticity and toughness of the material.
Preferably, the weight percentage of P is less than or equal to 0.008 percent.
Preferably, the weight percentage of S is less than or equal to 0.008 percent.
P, S tend to cause cold and hot shortness, and the preferred P, S level may reduce the hazard to a negligible level.
Preferably, the weight percentage of the Ni is 0.30-0.40%.
The preferred Ni content improves the corrosion resistance of the material.
Preferably, the weight percentage of Mo is 0.20-0.35%.
The preferred Mo content can improve the strength and atmospheric corrosion resistance of the material.
The invention also provides a preparation method of the high-strength atmospheric corrosion resistant cold forging steel, which comprises the following steps:
(1) smelting in a converter: adding molten iron of a blast furnace into a combined blown converter for smelting after desulfurization treatment, and adding aluminum blocks, carburant, alloy and top slag for deoxidation and alloying in the tapping process;
(2) refining in an LF furnace: after the LF enters the station, adding 2.0-3.0 kg/t of lime, 1-1.75 kg/t of calcium carbide and 0.5-0.75 kg/t of aluminum particles for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 67-266 Pa, the vacuum circulation treatment time is 15-25 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process, and casting the ladle into a bloom, wherein the ladle temperature is 1518-1528 ℃ and the casting speed is 0.73m/S in the continuous casting process;
(5) rolling and cooling control: after cogging the bloom, heating the bloom in a heating furnace to 1090-1150 ℃ for 80-120 min, and rolling the bloom in a high-speed rolling mill; and (3) carrying out finish rolling at the temperature of 880-940 ℃ and spinning at the temperature of 850-910 ℃ in the rolling process, and then carrying out a coil collecting process to obtain the high-strength atmospheric corrosion resistant cold forging steel.
According to the preparation method of the high-strength atmospheric corrosion resistant cold forging steel, provided by the invention, the aluminum ingot, the carburant and the alloy are added in a specific sequence in the converter tapping process, so that the alloy can be fully melted, and the alloy yield is improved; the heating temperature of the steel billet is adjusted to ensure that the alloy elements are fully austenitized and excessive growth of crystal grains is avoided; the austenite grains are fully recrystallized and refined by controlling the rolling temperature, so that the toughness of the material is improved; by reducing the cooling speed, the transformation time from austenite to ferrite is prolonged, the nucleation and growth of the ferrite are promoted, and the content proportion of the ferrite is improved; and the good surface quality and the core structure are ensured by reasonably controlling the rolling parameters.
On the basis of the designed components, the microstructure of the cold heading steel prepared by the preparation method is composed of 40-70% of ferrite and 30-60% of pearlite, the tensile strength can reach 700-850 MPa, the yield strength is 550-650 MPa, 1/3 cold heading is qualified, the corrosion resistance I index is not less than 6.5, the reduction of area can reach 42-60%, and the hardenability J15 is not less than 42HRC, so that the cold heading steel has good cold processing performance and hardenability, and can meet the requirements of downstream users on producing large-size 10.9-grade high-strength fasteners.
Preferably, in the step (1), the top slag is lime and refined synthetic slag; the adding amount of the lime and the refined synthetic slag is 3-4 kg/t; the refining synthetic slag comprises the following components: CaO: 45-55% of Al2O3：30～40％，SiO2≤6％，MgO≤3％，CaF2≤5％，S≤0.15％，P≤0.08％，H2O≤0.2％。
The optimized refined synthetic slag has strong deoxidation and desulfurization effects, can reduce gas in steel, reduce impurities in steel and improve the purity of molten steel.
Preferably, in the step (1), the alloy is manganese-silicon alloy, high-carbon ferromanganese and high-carbon ferrochrome; the adding time of each component is as follows: and (3) adding an aluminum block when the total tapping amount is 1/8-3/20, and sequentially adding a carburant, a manganese-silicon alloy, high-carbon ferromanganese, high-carbon ferrochromium and top slag when the total tapping amount is 3/16-1/4.
Adding an aluminum block when the total steel tapping amount is 1/8-3/20, enabling an aluminum ingot to be in direct contact with molten steel, ensuring that the aluminum ingot is quickly melted and ensuring the pre-deoxidation effect, wherein impurities generated by deoxidation at the moment are large-particle Al2O3The upward floating discharge of the deoxidation product is facilitated; the recarburizing agent is added for deoxidation, then the alloy is added, the oxidation of the alloy is reduced, the alloy yield is improved, and finally the top slag is added, so that the top slag and the alloy are prevented from rolling together, the alloy is not fully melted, and the molten steel components are not uniform, therefore, the alloy yield can be improved by the specific adding sequence of the components.
Preferably, in the step (3), the RH circulation time is 25 to 40 minutes.
The RH circulation time is set to be 25-40 minutes, the vacuum circulation treatment time is set to be 15-25 minutes, the effects of removing and controlling inclusions in steel can be achieved, the number of inclusions in finished molten steel is reduced, and the purity of molten steel is improved.
Preferably, in the step (5), the bloom specification is 325 × 280mm2(ii) a Cogging the bloom into 160mm multiplied by 160mm2And (5) specification.
Preferably, in the step (5), the rolled wire rod is cooled after the coil collecting process, and the cooling rate before phase change is controlled to be 0.4-0.6 ℃/s.
The cooling speed is controlled to be 0.4-0.6 ℃/s, and abnormal tissue forms such as martensite can be avoided, so that the hardness is reduced, and the subsequent drawing process is facilitated.
The traditional 10.9-grade high-strength bolt is mostly produced by medium carbon steel and medium carbon alloy steel, however, the steel has high carbon content and poor process performance, the spheroidizing softening annealing treatment which consumes energy and wastes time is required before cold machining, and the hardenability of the medium carbon steel is slightly insufficient for large-size bolts. In the prior art, the hardenability of steel is generally considered to be reduced by adding Ti, but the hardenability and the processability of the cold forging steel are obviously improved by adding Ti and one or more of Mo, V and Nb elements and by the synergistic effect of Ti and Mo, Nb or V, so that the prepared cold forging steel is suitable for producing 10.9-grade high-strength bolts with the size of phi 20 or more, and the prepared cold forging steel has higher strength and atmospheric corrosion resistance and is suitable for producing 10.9-grade large-size high-strength atmospheric corrosion-resistant bolts by cooperating with other components and the optimization development of the preparation process.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to better illustrate the invention, the following examples are given by way of further illustration.
Example 1
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.40% of C, 0.25% of Si, 0.90% of Mn, 0.01% of P, 0.002% of S, 0.60% of Cr, 0.20% of Ni, 0.40% of Cu, 0.020% of Ti, 0.10% of V, and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding a carburant, a manganese-silicon alloy, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 9/40 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.1kg/t lime, 1.3kg/t calcium carbide and 0.56kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 90Pa, the vacuum circulation treatment time is 17 minutes, and the RH circulation time is 28 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature in the continuous casting process is 1520 ℃, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1120 ℃ for 80min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; and (3) carrying out finish rolling at the rolling temperature of 910 ℃ and the spinning temperature of 880 ℃ in the rolling process, cooling the rolled wire rod after a coil collecting process, and controlling the cooling rate to be 0.4 ℃/s before phase change to obtain the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 24 mm.
Example 2
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.30% of C, 0.15% of Si, 0.60% of Mn, 0.025% of P, 0.010% of S, 0.90% of Cr, 0.50% of Ni, 0.20% of Cu, 0.040% of Ti, 0.35% of Mo, 0.005% of Nb, and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 1/8 of the total tapping amount, and sequentially adding ferrosilicon, a carburant, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 3/16 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.5kg/t lime, 1.5kg/t calcium carbide and 0.7kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 150Pa, the vacuum circulation treatment time is 20 minutes, and the RH circulation time is 35 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature in the continuous casting process is 1528 ℃, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1150 ℃ for 90min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; and (3) carrying out finish rolling at 940 ℃ and spinning at 850 ℃ in the rolling process, cooling the rolled wire rod after a coil collecting process, and controlling the cooling rate to be 0.5 ℃/s before phase change to obtain the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 28 mm.
Example 3
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.28% of C, 0.30% of Si, 0.70% of Mn, 0.008% of P, 0.020% of S, 0.80% of Cr, 0.30% of Ni0.30% of Cu, 0.050% of Ti, 0.15% of Mo, 0.12% of V, and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding ferrosilicon, a carburant, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 1/4 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 3.0kg/t lime, 1.75kg/t calcium carbide and 0.75kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing and carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 266Pa, the vacuum circulation treatment time is 25 minutes, and the RH circulation time is 40 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature is 1518 ℃ in the continuous casting process, and the casting speed is 0.73 m/S;
(5) controlled rollingAnd (3) cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1090 ℃ for 100min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; and in the rolling process, the finish rolling temperature is 880 ℃, the spinning temperature is 850 ℃, the rolled wire rod is cooled after the coil collecting process, and the cooling rate before phase change is controlled to be 0.6 ℃/s, so that the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 30mm is obtained.
Example 4
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.35% of C, 0.19% of Si, 0.80% of Mn, 0.002% of P, 0.006% of S, 0.75% of Cr, 0.40% of Ni0.40% of Cu, 0.005% of Ti, 0.20% of Mo, and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding ferrosilicon, a carburant, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 9/40 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.6kg/t lime, 1.3kg/t calcium carbide and 0.65kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 186Pa, the vacuum circulation treatment time is 23 minutes, and the RH circulation time is 37 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature in the continuous casting process is 1520 ℃, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1140 ℃ for 110min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; temperature of finish rolling in rolling processAnd the temperature is 910 ℃, the spinning temperature is 860 ℃, the rolled wire rod is cooled after the coil collecting process, and the cooling rate before phase change is controlled to be 0.4 ℃/s, so that the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 32mm is obtained.
Example 5
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.30% of C, 0.20% of Si, 0.80% of Mn, 0.004% of P, 0.005% of S, 0.80% of Cr, 0.40% of Ni, 0.45% of Cu, 0.010% of Ti, 0.35% of Mo, 0.09% of V, 0.015% of Nb and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding ferrosilicon, a carburant, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 9/40 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.8kg/t lime, 1.7kg/t calcium carbide and 0.56kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 230Pa, the vacuum circulation treatment time is 23 minutes, and the RH circulation time is 38 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature in the continuous casting process is 1521 ℃, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1130 ℃ for 120min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; the finish rolling temperature in the rolling process is 900 ℃, the spinning temperature is 890 ℃, the rolled wire rod is cooled after the collecting and coiling process, the cooling rate before phase change is controlled to be 0.5 ℃/s, and the high-strength atmospheric corrosion resistance with the specification of phi 28mm is obtainedAnd (3) cold heading steel hot rolling wire rods.
Example 6
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.40% of C, 0.25% of Si, 0.90% of Mn, 0.01% of P, 0.002% of S, 1.00% of Cr, 0.20% of Ni, 0.40% of Cu, 0.030% of Ti, 0.01% of Nb, and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding ferrosilicon, a carburant, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 9/40 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.0kg/t lime, 1kg/t calcium carbide and 0.5kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 250Pa, the vacuum circulation treatment time is 22 minutes, and the RH circulation time is 37 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature in the continuous casting process is 1522 ℃, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1130 ℃ for 95min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; and in the rolling process, the finish rolling temperature is 920 ℃, the spinning temperature is 900 ℃, the rolled wire rod is cooled after the coil collecting process, and the cooling rate before phase change is controlled to be 0.4 ℃/s, so that the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 38mm is obtained.
Example 7
The embodiment of the invention provides high-strength atmospheric corrosion resistant cold forging steel which comprises the following chemical components:
0.35% of C, 0.2% of Si, 0.80% of Mn, 0.015% of P, 0.008% of S, 0.85% of Cr, 0.30% of Ni, 0.30% of Cu, 0.015% of Ti, 0.10% of V, 0.01% of Nb and the balance of Fe and inevitable impurities.
The preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: the method comprises the following steps of adding molten iron of a blast furnace into a combined blowing converter for smelting after desulfurization treatment, adding aluminum blocks into the molten iron when the molten iron is tapped to 3/20 of the total tapping amount, and sequentially adding a carburant, a manganese-silicon alloy, high-carbon ferromanganese, high-carbon ferrochrome, lime and refined synthetic slag when the molten iron is tapped to 9/40 of the total tapping amount;
(2) refining in an LF furnace: after LF enters the station, 2.0kg/t lime, 1kg/t calcium carbide and 0.5kg/t aluminum particles are added for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 67Pa, the vacuum circulation treatment time is 15 minutes, and the RH circulation time is 25 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process to cast into a bloom with the specification of 325 x 280mm2The tundish temperature is 1518 ℃ in the continuous casting process, and the casting speed is 0.73 m/S;
(5) rolling and cooling control: cogging the bloom into 160mm multiplied by 160mm2After specification, heating in a heating furnace to 1120 ℃ for 105min, removing phosphorus from the discharged steel billet by high-pressure water, and rolling in a high-speed rolling mill; and in the rolling process, the finish rolling temperature is 910 ℃, the spinning temperature is 910 ℃, the rolled wire rod is cooled after the coil collecting process, and the cooling rate before phase change is controlled to be 0.4 ℃/s, so that the high-strength atmospheric corrosion resistant cold heading steel hot rolled wire rod with the specification of phi 20mm is obtained.
Comparative example 1
The embodiment of the invention provides cold heading steel which comprises the following chemical components:
0.35% of C, 0.2% of Si, 0.80% of Mn, 0.015% of P, 0.008% of S, 0.85% of Cr, 0.30% of Ni, 0.30% of Cu, 0.10% of V, 0.01% of Nb and the balance of Fe and inevitable impurities.
The preparation steps and the process parameters of the cold heading steel are the same as those of the embodiment 7, and the specification of the finished wire rod is phi 20mm, which is not described again here.
The high strength atmospheric corrosion resistant cold heading steels of examples 1 to 7 and comparative example 1 were subjected to the performance test, and the results are shown in table 1.
Table 1 results of performance test of cold heading steels prepared in examples 1 to 7 and comparative example 1
Comparative example 1 compared with example 7, comparative example 1 did not add Ti element, the kind and content of other elements were the same as those of example 7, and it can be seen from the above table that the core hardness of the wire rod prepared in comparative example 1 after removing Ti element was reduced to 85HRB and the hardenability of the wire rod was insufficient, the hardenability at J15mm after quenching was < 42HRC and the impact properties also became unacceptable, the tensile strength also decreased, and the properties of the hardened and tempered bolt could not satisfy the strength requirement of the 10.9 grade bolt. The synergistic effect of Mo, Nb or V and Ti elements is demonstrated, the properties of the cold forging steel are obviously improved, and the method is suitable for preparing 10.9-grade high-strength large-size bolts.
The large-size bolt prepared from the cold heading steel prepared in the embodiments 1 to 7 has atmospheric corrosion resistance 2 to 8 times that of common carbon steel, tensile strength of more than 1040MPa, delayed fracture resistance higher than that of the existing 20MnTiB steel, low-temperature impact performance Akv (-20 ℃) of more than or equal to 27J, meets the stress requirement of high strength in use, and can achieve the purpose of preventing atmospheric corrosion and prolong the service life of the bolt when used in an atmospheric environment.
By optimizing the components and the process, the prepared cold forging steel has higher strength and hardness, simultaneously has good hardenability, meets the requirement of hardenability of large-size bolts, and also has certain delayed fracture resistance; the microstructure consists of uniform ferrite and pearlite, the tensile strength can reach 700-850 MPa, the yield strength is 550-650 MPa, the reduction of area can reach 42-60%, 1/3 cold heading is qualified, the corrosion resistance I index is not less than 6.5, the hardenability J15 is not less than 42HRC, the production cost is low, and the steel has the characteristics of good corrosion resistance, high tensile strength, good surface quality, excellent performance and the like.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. The high-strength atmospheric corrosion resistant cold forging steel is characterized by comprising the following components in percentage by weight: 0.28-0.40% of C, 0.15-0.30% of Si, 0.60-0.90% of Mn, less than or equal to 0.025% of P, less than or equal to 0.008% of S, 0.60-1.00% of Cr, 0.20-0.50% of Ni, 0.20-0.45% of Cu, 0.005-0.050% of Ti, and one or more of Mo, V, 0.09-0.12% of V and Nb, 0.005-0.015%; the balance of Fe and inevitable impurities;
the preparation method of the high-strength atmospheric corrosion resistant cold forging steel comprises the following steps:
(1) smelting in a converter: adding molten iron of a blast furnace into a combined blown converter for smelting after desulfurization treatment, and adding aluminum blocks, carburant, alloy and top slag for deoxidation and alloying in the tapping process;
(2) refining in an LF furnace: after the LF enters the station, adding 2.0-3.0 kg/t of lime, 1-1.75 kg/t of calcium carbide and 0.5-0.75 kg/t of aluminum particles for deoxidation and slagging;
(3) and (3) refining in an RH furnace: hoisting the molten steel to an RH furnace, pre-vacuumizing, carrying out oxygen blowing forced decarburization operation, vacuumizing after the oxygen blowing forced decarburization treatment is finished, wherein the vacuum degree is 67-266 Pa, the vacuum circulation treatment time is 15-25 minutes, and then carrying out calcium treatment and soft blowing;
(4) continuous casting: hoisting the ladle to a continuous casting process, and casting the ladle into a bloom, wherein the ladle temperature is 1518-1528 ℃ and the casting speed is 0.73m/s in the continuous casting process;
(5) rolling and cooling control: after cogging the bloom, heating the bloom in a heating furnace to 1090-1150 ℃ for 80-120 min, and rolling the bloom in a high-speed rolling mill; in the rolling process, the finish rolling temperature is 880-940 ℃, the spinning temperature is 850-910 ℃, and then the high-strength atmospheric corrosion resistant cold forging steel is obtained through the coiling process and cooling;
wherein in the step (1), the alloy is manganese-silicon alloy, high-carbon ferromanganese and high-carbon ferrochrome; the adding time of each component is as follows: and (3) adding an aluminum block when the total tapping amount is 1/8-3/20, and sequentially adding a carburant, a manganese-silicon alloy, high-carbon ferromanganese, high-carbon ferrochromium and top slag when the total tapping amount is 3/16-1/4.
2. The high-strength atmospheric corrosion resistant cold heading steel as claimed in claim 1, wherein the percentage by weight of C is 0.32-0.38%.
3. The high-strength atmospheric corrosion resistant cold heading steel as claimed in claim 1, wherein P is 0.008% or less in weight percentage.
4. The high-strength atmospheric corrosion resistant cold heading steel as claimed in claim 1, wherein the weight percentage of Ni is 0.30-0.40%; and/or
The weight percentage of Mo is 0.20-0.35%.
5. The high-strength atmospheric corrosion resistant cold forging steel as claimed in claim 1, wherein in the step (1), the top slag is lime and refined synthetic slag; the adding amount of the lime and the refined synthetic slag is 3-4 kg/t; the refining synthetic slag comprises the following components: CaO: 45-55% of Al2O3：30～40％，SiO2≤6％，MgO≤3％，CaF2≤5％，S≤0.15％，P≤0.08％，H2O≤0.2％。
6. The high-strength atmospheric corrosion resistant cold heading steel as claimed in claim 1, wherein in step (3), the RH circulation time is 25-40 minutes.
7. The high-strength atmospheric corrosion resistant cold forging steel as claimed in claim 1, wherein in step (5), the bloom specification is 325 x 280mm2(ii) a Cogging the bloom into 160mm multiplied by 160mm2Specification of。
8. The high-strength atmospheric corrosion resistant cold heading steel as claimed in claim 1, wherein in step (5), the cooling rate before phase transformation is controlled to be 0.4-0.6 ℃/s.
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