CN111690876A - High-strength wire rod for bolt and production method thereof - Google Patents

High-strength wire rod for bolt and production method thereof Download PDF

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CN111690876A
CN111690876A CN202010604060.XA CN202010604060A CN111690876A CN 111690876 A CN111690876 A CN 111690876A CN 202010604060 A CN202010604060 A CN 202010604060A CN 111690876 A CN111690876 A CN 111690876A
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wire rod
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尹德福
汪开忠
张晓瑞
丁雷
于同仁
龚梦强
牟祖茂
姜婷
郝震宇
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Maanshan Iron and Steel Co Ltd
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Maanshan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
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Abstract

The invention discloses a wire rod for a high-strength bolt and a production method thereof, and belongs to the technical field of steel for fasteners. The high-strength wire rod for the bolt comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, less than or equal to 0.10 percent of Si, 0.50 to 0.80 percent of Mn, 1.20 to 1.50 percent of Cr1.50 percent, 1.50 to 1.80 percent of Mo1, 0.02 to 0.10 percent of V, 0.02 to 0.08 percent of Nb0.02, 0.05 to 0.2 percent of Tis, 0.20 to 0.30 percent of Nis, 0.20 to 0.60 percent of Cu0.015 to 0.040 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0. By adopting the technical scheme of the invention, the problems that the corrosion prevention effect is not ideal when the existing high-strength bolt is subjected to corrosion prevention by adopting a coating mode and the problem of delayed fracture caused by hydrogen in the use process of the bolt is increased can be effectively solved, the corrosion resistance and the delayed fracture resistance of the wire rod for the bolt are obviously improved, and the use requirement of the high-strength bolt can be met.

Description

High-strength wire rod for bolt and production method thereof
Technical Field
The invention belongs to the technical field of steel for fasteners, and particularly relates to a wire rod for a high-strength bolt and a production method thereof.
Background
The fastener is a basic industry of equipment manufacturing industry in China and is widely applied to various fields of national economy. In recent years, along with the industries of automobiles, wind power, machinery, buildings and the like in ChinaThe rapid development of the technology has brought requirements on design stress and light weight of materials used for manufacturing parts such as various fasteners (such as bolts, nuts and the like), and the most effective measure is to improve the strength of the fasteners. The light weight of the automobile body is to improve the fuel efficiency of the automobile and reduce CO2One of the effective methods for emissions is that fasteners are used in a higher tensile load environment than ever due to the demand for smaller and lighter engine and chassis parts, and therefore, it is necessary to solve the technical problems of reduced fatigue strength due to surface defects or non-metallic inclusions in steel, and delayed fracture associated with increased atmospheric corrosion and hydrogen sensitivity.
As one of the most common fasteners, the bolts can be made of wire rod or round steel. The wire rod is a finished product which is coiled into a disc shape after hot rolling and delivered, and comprises a round shape, a square shape, a rectangular shape, a hexagonal shape and the like, and the wire rod is usually a round wire rod because most of the wire rod is round, and the diameter of the wire rod is relatively small; round steel is a solid long steel material with a circular cross section and a relatively large diameter.
The ultrahigh strength fastener is used as a fastener of a connecting part and other cold heading forming parts, the requirements of high design stress and light weight are provided, in this respect, the requirements of the automobile manufacturing industry are the strongest, and the original automobile fastener, especially an engine bolt, cannot meet the requirement of high stress of an automobile engine easily. However, since the environment for operating the automobile is complicated, the bolt may be corroded when used in various atmospheric environments, and in order to prolong the service life of the bolt, the high-strength bolt used for connecting the automobile is subjected to corrosion prevention in a coating manner, such as electroplating or hot galvanizing. However, the corrosion prevention time limit of the methods such as surface spraying is generally 5-10 years, the service life of the bolt can be reduced due to aging and differentiation of the coating, and the corrosion prevention effect is not ideal; meanwhile, the H element introduced in the processes of electroplating and hot galvanizing of the ultrahigh-strength bolt can also increase the problem of hydrogen-induced delayed fracture in the using process of the bolt, so that the ultrahigh-strength fastener for the automobile must have excellent corrosion resistance and also needs to have excellent delayed fracture resistance so as to meet the requirements of light weight and high safety of the automobile.
Through search, the patent of the steel for the bolt has related disclosures. For example, the chinese patent application No. 01129512.0 discloses a delayed fracture-resistant high-strength bolt steel having a strength of 1400 to 1600MPa, which comprises the following specific components: 0.35-0.5% of C, 0.01-0.09% of Si, less than or equal to 0.30% of Mn, less than or equal to 0.010% of P, less than or equal to 0.008% of S, 0.5-1.5% of Cr0.7-1.5% of Mo0.20-0.50% of V, 0.01-0.08% of Nb0.002-0.04% of RE, 0.005-0.05% of Al, 0.006-0.015% of N, 0.01-0.15% of any one or the sum of two of Ti and Zr, and the balance of Fe and inevitable impurities. The maximum tensile strength of the bolt is only 1580MPa, the performance requirements of high-strength bolts in certain special application occasions are difficult to meet, RE and the like are added to the chemical components of the bolt, and the production cost is obviously increased.
For another example, chinese patent application No. 200810049411.4 discloses a method for making a 16.9-grade bolt resistant to delayed fracture, the chemical composition range of the steel ingot should be controlled to be C0.15-0.19%, Mn not more than 0.10%, Si not more than 0.10%, S not more than 0.005%, P not more than 0.008%, S + P not more than 0.010%, cr 1.80-2.00%, ni 9.50-10.50%, co 13.50-14.50%, mo 0.90-0.10%, Ti not more than 0.015%, O not more than 0.0020%, N not more than 0.0015%. The steel for the bolt not only adopts the more complex production processes of vacuum induction melting, vacuum consumable melting, forging forming, composite heat treatment and the like, but also has higher content of noble elements such as Ni, Co and the like, so that the production cost is higher, and the steel is not suitable for industrial production.
Disclosure of Invention
1. Problems to be solved
The invention aims to overcome the defects that the corrosion prevention effect is not ideal when the existing high-strength bolt is subjected to corrosion prevention by adopting a coating mode, and the problem of delayed fracture caused by hydrogen in the using process of the bolt is increased, and provides a wire rod for a high-strength bolt with excellent atmospheric corrosion resistance and delayed fracture resistance and a production method thereof. By adopting the technical scheme of the invention, the problems can be effectively solved, the corrosion resistance and delayed fracture resistance of the wire rod for the bolt are obviously improved, and the use requirement of the high-strength bolt can be met.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention relates to a high-strength wire rod for bolts, which comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, less than or equal to 0.10 percent of Si, 0.50 to 0.80 percent of Mn, 1.20 to 1.50 percent of Cr1.50 percent, 1.50 to 1.80 percent of Mo1, 0.02 to 0.10 percent of V, 0.02 to 0.08 percent of Nb0.02, 0.05 to 0.2 percent of Tis, 0.20 to 0.30 percent of Nis, 0.20 to 0.60 percent of Cu0.015 to 0.040 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0.
Further, the weight percentage of each chemical component of the wire rod satisfies 0.7[ C ] or more and 0.2[ Mo ] or less +0.20[ V ] or more and 0.10[ Nb ] or more and 0.03[ Ti ] or less and 0.25[ Ni ] or more and 0.8[ C ] or less.
The invention relates to a production method of a wire rod for a high-strength bolt, which comprises the chemical components and specifically comprises the following steps: electric furnace smelting → LF + RH vacuum refining → Phi 380mm big round billet continuous casting → heating → cogging and cogging → six-stand continuous rolling → 150mm square billet rolling → flaw detection, coping → high-speed wire heating furnace heating → controlled rolling and controlled cooling → reducing and sizing mill → wire laying head → stelmor cooling line → finished wire rod → packaging and warehousing.
Furthermore, the target temperature of the molten steel of the tundish is stably controlled to be 10-30 ℃ above the liquidus temperature during the continuous casting of the large round billet.
Furthermore, the temperature of a soaking section during steel heating is 1210-1250 ℃, and the heat preservation time is 370-390 min.
Furthermore, the heating temperature of the high-speed wire heating furnace is 980-1070 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is not more than 110 min.
Furthermore, the process parameters of rolling control and cooling control are as follows: the initial rolling temperature is 880-950 ℃, and the final rolling temperature is 780-840 ℃; the spinning temperature of the spinning machine is 760-820 ℃.
Furthermore, the wire rod is required to be subjected to performance test, and the heat treatment process for testing the mechanical property of the wire rod comprises quenching heating treatment and high-temperature tempering treatment, wherein the heating temperature is 900-960 ℃ during quenching heating, and the tempering temperature is 590-610 ℃ during high-temperature tempering.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the high-strength wire rod for the bolt, the chemical components and the content of the wire rod are optimally designed, micro-alloying elements such as Nb, V, Ti and Mo are added while the content of C is increased, and the comprehensive coordination effect of the elements is utilized, so that the atmospheric corrosion resistance of the obtained wire rod can be effectively improved, the hydrogen embrittlement resistance of the wire rod can be improved, the delayed fracture resistance of the wire rod is improved, the strength grade of the obtained wire rod is improved, the use requirement of a high-strength fastener is met, and the problem caused by the fact that the existing bolt is subjected to coating corrosion prevention is solved.
(2) According to the high-strength wire rod for the bolt, the content ranges of Nb, V, Ti, Mo and Ni are further limited, and the compounding coordination effect of all elements is utilized, so that the delayed fracture resistance of the wire rod can be further improved, and the high-strength use requirement of the wire rod is met; the added Mo and V also obviously improve the tempering softening resistance, and realize the ultrahigh strength at high temperature; the added Mo and Ni can also improve the atmospheric corrosion resistance of the wire rod.
(3) According to the high-strength wire rod for the bolt, the Cu, the Ni and the Mo are added into the chemical components, the content of the Cu, the Ni and the Mo is optimally designed, and the content of the Mo can meet the empirical formula, so that the corrosion resistance of the wire rod is further improved, the atmospheric corrosion resistance index I of the chemical components is more than or equal to 7.0, and the atmospheric corrosion resistance of the wire rod is ensured; and the generation and absorption of hydrogen in a corrosive environment are inhibited, and higher notch toughness is obtained.
(4) According to the production method of the wire rod for the high-strength bolt, disclosed by the invention, the chemical components, the content and specific process parameters in the production process are optimally designed, the comprehensive action of each element is utilized, and the process parameters are strictly controlled in the production process, so that the mechanical property of the wire rod for the high-strength bolt is further ensured, the corrosion resistance and the delayed fracture resistance of the wire rod are also ensured, the requirements of light weight and high safety of an automobile are met, and the energy can be saved and the cost is reduced by adopting the production method of the wire rod for the ultrahigh-strength bolt.
Drawings
FIG. 1 is a chemical composition and cold heading property diagram (wt%) of examples 1 to 5 of the present invention and comparative examples 1 to 2.
FIG. 2 is a graph showing mechanical properties, delayed fracture resistance and corrosion resistance of examples 1 to 5 of the present invention and comparative examples 1 to 2.
FIG. 3 is a notched tensile delayed fracture specimen of the present invention.
FIG. 4 is a graph of chemical composition and cold heading performance (wt%) of 5 sets of tests and 2 sets of comparative tests in example 9 of the present invention.
FIG. 5 is a graph showing mechanical properties, delayed fracture resistance and corrosion resistance of 5 sets of tests and 2 sets of comparative tests in example 9 of the present invention.
Detailed Description
The invention provides a wire rod for a high-strength bolt, which aims to solve the problems that the corrosion prevention effect of the existing high-strength bolt for an automobile is not ideal when the existing high-strength bolt is subjected to corrosion prevention by adopting an electroplating or hot galvanizing coating mode, and hydrogen caused delayed fracture in the using process of the bolt is increased by an H element introduced in the electroplating and hot galvanizing processes of the ultrahigh-strength bolt, and the wire rod for the high-strength bolt comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, less than or equal to 0.10 percent of Si, 0.50 to 0.80 percent of Mn, 1.20 to 1.50 percent of Cr1.50 percent, 1.50 to 1.80 percent of Mo1, 0.02 to 0.10 percent of V, 0.02 to 0.08 percent of Nb0.02, 0.05 to 0.20 percent of Tis, 0.20 to 0.30 percent of Nis, 0.20 to 0.60 percent of Cu0.015 to 0.040 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0. And the weight percentage of the chemical components of the wire rod also satisfies:
①、0.7[C]≤0.2[Mo]+0.20[V]+0.10[Nb]+0.03[Ti]+0.25[Ni]≤0.8[C]。
the wire rod for the high-strength bolt is different from round steel for the high-strength bolt in chemical components, performance and production process, and because a cold heading process is required when the wire rod is adopted for manufacturing the bolt, the content of Si in the wire rod is not too high, and the wire rod is not beneficial to cold deformation if the content of Si is higher. In order to ensure high strength performance, the chemical components and contents of the wire rod for the high-strength bolt are optimally designed, the content range of each added element is limited, the C content is slightly increased on the basis of SCM435, meanwhile, micro-alloying elements such as Nb, V, Ti, Mo and the like are added, and the comprehensive coordination action of each element is utilized, so that the atmospheric corrosion resistance of the obtained wire rod can be effectively improved, the hydrogen embrittlement resistance of the wire rod can be improved, the delayed fracture resistance of the wire rod is improved, the strength grade of the obtained wire rod is improved, the use requirement of a high-strength fastener is met, and the problem caused by the fact that the existing bolt is subjected to coating corrosion prevention is avoided.
Meanwhile, the content ranges of the added Nb, V, Ti, Mo and Ni are further limited by adopting a formula I, and Mo, Nb, Ti, V and composite carbon-nitrogen alloy compounds with the size of below 45nm are dispersed and precipitated during high-temperature tempering by utilizing the compounding and coordination action of all elements (namely, the formula I is met to ensure that fine carbide is precipitated), so that the hydrogen embrittlement resistance is favorably improved, and the delayed fracture resistance is further improved; on the other hand, the carbides precipitated in a dispersion mode, particularly Mo and V, can obviously improve tempering softening resistance, so that the carbides are fine, uniform and spheroidized, the ultrahigh strength at high temperature is realized through precipitation hardening and strengthening of a prior austenite grain boundary, and the wire rod has creep property, the added Mo element can reduce the amount of hydrogen invading the surface of steel, inhibit the generation of corrosion pits and improve the atmospheric corrosion resistance of the wire rod.
In addition, the corrosion resistance of the alloy is further improved by adding elements such as Cu, Ni and the like, optimally designing the content of the added elements such as Cu, Ni and the like, and enabling the added elements to meet an empirical formula (namely the formula I), and the added elements such as Ni, Cu and the like not only improve the corrosion resistance, but also inhibit the generation and absorption of hydrogen in a corrosion environment, and simultaneously obtain higher notch toughness. In order to ensure the corrosion resistance, the chemical components need to meet the requirement that the atmospheric corrosion resistance index is more than or equal to 7.0, and the corrosion resistance is ensured.
Among the chemical components of the wire rod for a bolt of the present invention, C is an element necessary for securing hardenability and strength, and as the content thereof increases, ductility and corrosion resistance thereof decrease. A relatively high C content is advantageous for the strength and the like of the steel, but is extremely disadvantageous for the cold heading property, plasticity and toughness of the steel, and also causes a reduction in yield ratio, an increase in decarburization sensitivity, and deterioration in fatigue resistance and workability of the steel. Si is a main deoxidizing element in steel and has a strong solid solution strengthening effect, but Si can obviously improve the deformation resistance of the steel, the high content of Si can cause cold heading cracking and is extremely unfavorable for cold heading and cold extrusion, Si can also promote grain boundary segregation of impurity elements, delayed fracture sensitivity of the steel is increased, plasticity and toughness of the steel are reduced, fatigue resistance of the steel is deteriorated, and therefore the Si content is not high.
Mn is also an element for improving hardenability and is useful for achieving high strength properties, but too high Mn content deteriorates the weather resistance of steel. The addition of the Ni element can improve the structure of a rust layer, improve the compactness and the cohesiveness to the surface of steel, improve the corrosion resistance of the steel, inhibit the adsorption of hydrogen and further be beneficial to improving the delayed fracture resistance. Cu is an element which, like the above-mentioned Ni element, can improve corrosion resistance and inhibit hydrogen intrusion, is effective for further improving delayed fracture resistance, and can form a rust layer having good protection; and the Cu element can also change the hygroscopicity of the rust layer, so that the critical humidity is improved, but the high-temperature plasticity of the steel is reduced due to the excessively high Cu content, and cracks are easily generated in the hot working process. The Cr element is the most commonly used alloy element in high-strength bolt steel, Cr can effectively improve the hardenability and the tempering resistance of the steel so as to obtain the required high strength, meanwhile, the composite addition of Cr and Cu can obviously improve the weather resistance of the steel, the effect is difficult to be achieved when the Cr content is small, but the toughness and the cold workability of the steel are deteriorated when the Cr content is large.
Mo element is also a more commonly adopted alloy element in high-strength bolt steel, so that the tempering resistance of the steel can be obviously improved, and carbide Mo formed by the Mo element2C has a trapping effect on hydrogen and can also improve the delayed fracture resistance of the steel; and the segregation of Mo element in the prior austenite grain boundary can also improve the grain boundary bonding strength of steelDegree; in addition, Mo also reduces the amount of hydrogen entering the steel surface, inhibits the formation of corrosion pits, and thus also improves the corrosion resistance of the wire rod. V can refine the crystal grains of the steel and improve the strength and delayed fracture resistance by carbides precipitated at the time of tempering; the V element can also improve the tempering resistance of the steel, vanadium carbonitride precipitated during tempering at higher temperature can generate secondary hardening to further improve the strength of the steel, and the vanadium carbonitride has stronger trap energy and can trap hydrogen to uniformly disperse the hydrogen in crystal, thereby inhibiting the diffusion of the hydrogen and the segregation of crystal boundary, and further improving the delayed fracture resistance of the steel. The Nb element can also finely refine grains, the grain refinement can not only improve the toughness of the steel, but also improve the low-temperature performance of the steel, simultaneously improve the tempering resistance and also improve the delayed fracture resistance of the high-strength steel, the hydrogen trap bonding energy of the carbide is lower than that of vanadium carbide and titanium carbide, and the trapping effect on hydrogen is slightly poor.
Besides the functions of grain refinement, precipitation strengthening and fixation N, S, the dispersed and precipitated TiC is one of hydrogen traps with the highest trap energy in steel, and can trap hydrogen to be uniformly dispersed in the grains, so that the diffusion of the hydrogen is inhibited, and the delayed fracture resistance of the steel is improved. The above effect cannot be obtained when the Ti content is low, but the ductility and toughness of the steel are deteriorated by coarse nitrides formed when the Ti content is high. S, P, the delayed fracture resistance is greatly reduced, the P element can form micro segregation when the molten steel is solidified, and then the P element is deviated at the grain boundary when the austenitizing temperature is heated, so that the brittleness of the steel is obviously increased, and the delayed fracture sensitivity of the steel is increased; the S element forms MnS inclusion to be segregated in the grain boundary, thereby increasing the delayed fracture sensitivity of the steel, and the grain boundary strengthening can be realized by reducing Mn which promotes the grain boundary segregation while reducing the impurity P, S as much as possible. H is the most harmful element in steel, has extremely low solubility in solid steel, is melted into molten steel at high temperature, cannot escape in time during cooling, accumulates in tissues to form high-pressure fine pores, and is easy to generate hydrogen embrittlement and delay fracture in the later use process particularly for ultrahigh-strength fasteners. O forms various oxide inclusions in the steel, which under the action of stressStress concentration is easy to generate, and microcrack is easy to generate, so that the mechanical properties, particularly toughness and fatigue resistance, of the steel are deteriorated, and therefore, proper measures are needed to reduce the content of the steel as far as possible in metallurgical production. N precipitation of Fe in steel4N, the diffusion rate is slow, resulting in the steel being time-efficient, and N also reduces the cold workability of the steel.
The invention relates to a production method of a wire rod for a high-strength bolt, which comprises the chemical components and specifically comprises the following steps: electric furnace smelting → LF + RH vacuum refining → Phi 380mm big round billet continuous casting → heating → cogging and cogging → six-stand continuous rolling → 150mm square billet rolling → flaw detection, coping → high-speed wire heating furnace heating → controlled rolling and controlled cooling → reducing and sizing mill → wire laying head → stelmor cooling line → finished wire rod → packaging and warehousing.
When smelting in an electric furnace, the tapping is deoxidized and alloyed, and the slag is strictly controlled during the tapping process. During LF furnace refining, elements such as C, Si, Cr, Mn, Mo, V, Nb, Ti, Ni, Cu and the like are adjusted to target values. The pure degassing time is not less than 20 minutes during the vacuum degassing of the RH furnace, and the H is not more than 0.00015 percent after the vacuum treatment. When large round billets are continuously cast, the target temperature of molten steel in the tundish is stably controlled to be 10-30 ℃ above the liquidus temperature, and round billets with phi of 380mm are continuously cast.
Wire rod rolling route: round billet with phi 380mm → heating → rolling 150mm × 150mm square billet → flaw detection, coping → high-speed wire heating furnace heating → high-speed wire controlled rolling controlled cooling rolling → stelmor cooling line controlled cooling → finished product of wire rod with phi 16 mm. Wherein the temperature of a soaking section during steel heating is 1210-1250 ℃, and is preferably 1230 ℃; the heat preservation time is 370-390 min, preferably 380min (if a phi 450mm round billet is adopted for rolling, the heat preservation time can be 420 min). The heating temperature of the high-speed wire heating furnace is 980-1070 ℃ during heating, and is preferably 1020-1060 ℃; the time of the billet in the furnace is not more than 110min, preferably 90-105 min. When the wire is rolled in a controlled rolling and controlled cooling mode, the initial rolling temperature of the wire is 880-950 ℃, and the optimal rolling temperature is 900-920 ℃; the finishing temperature is 780-840 ℃, and preferably 800-820 ℃. The spinning temperature of the spinning machine is 760-820 ℃, and preferably 780-800 ℃.
The wire rod steel is also required to be subjected to performance inspection, the heat treatment process for inspecting the mechanical performance of the wire rod comprises quenching heating treatment and high-temperature tempering treatment, and in the heat treatment process, in order to fully dissolve alloy elements such as Nb, V, Mo and the like into austenite, the quenching heating temperature cannot be too low; however, because the austenite grains are easily excessively grown due to an excessively high temperature and decarburization is easily caused, which results in poor toughness and delayed fracture resistance of the fastener, the heating temperature is set to 900 to 960 ℃, preferably 910 to 930 ℃ during quenching heating. The precipitation strengthening characteristic of carbide formed by Nb, V, Mo and other alloy elements can be shown at the temperature of more than 500 ℃, but the carbide grows excessively at the high temperature, which is not beneficial to precipitation strengthening; meanwhile, the high-temperature tempering heat treatment can finely disperse carbides in prior austenite grains and improve the delayed fracture characteristic of the fastener, so the tempering temperature is preferably 590-610 ℃ during high-temperature tempering.
The invention optimizes the chemical components, contents and specific process parameters in the production process, utilizes the comprehensive effect of each element, strictly controls the process parameters in the production process, and particularly controls the process parameters in the processes of RH furnace vacuum degassing time, steel heating temperature and heat preservation time, high-speed wire heating furnace heating, controlled rolling and controlled cooling and the like, and controls the quenching and high-temperature tempering temperature in the heat treatment in the inspection process, thereby further ensuring the mechanical property of the wire rod for the high-strength bolt, ensuring the corrosion resistance and delayed fracture resistance of the wire rod, and meeting the requirements of light weight and high safety of automobiles. The high-strength wire rod for the bolt with excellent corrosion resistance and delayed fracture resistance, which is produced by the invention, has the tensile strength R after heat treatmentmMore than or equal to 1600MPa and the yield ratio RP0.2/RmMore than or equal to 0.9 percent, the elongation A after fracture is more than or equal to 10 percent, the reduction of area Z is more than or equal to 50 percent, the structure is tempered sorbite and fine carbide which is evenly dispersed, the content of the tempered sorbite is more than or equal to 94 percent, and the normal temperature impact absorption power KV2The cold heading is not less than 50J, 1/3 is completely qualified, the fatigue life is not less than 1000 ten thousand times under the condition of 720MPa cyclic stress, the evaluation is carried out by adopting a slow strain rate tensile test (SSRT) at room temperature, and the delayed fracture strength ratio R is equal to Rch/Rch0> 0.55 (hydrogen filling trial)The notched tensile strength of the sample is RchThe notched tensile strength of the non-hydrogenated sample is Rch0) The notch sensitivity was evaluated by using a notch intensity ratio, NSR ═ σc/RmGreater than 1 (tensile strength of smooth specimen R)mNotched tensile Strength of σc) And the atmospheric corrosion resistance index I of the wire rod is more than or equal to 7.0.
The performance of the wire rod for the bolt produced by adopting the components and the process flow is tested, and the specific test process and test result are as follows:
tensile, impact and notched tensile delayed fracture performance test: quenching the steel, wherein the temperature of the steel is 900-960 ℃ during quenching and heating, preferably 910-930 ℃, and then carrying out heat preservation for 30min and then carrying out oil cooling; and then tempering treatment is carried out, the tempering temperature is 590-610 ℃, heat preservation is carried out for 120min, and the standard tensile sample with phi 10mm and the notch tensile delayed fracture sample with phi 5mm are processed through an air cooling heat treatment process, as shown in figure 3. The mechanical properties after quenching and tempering heat treatment are shown in fig. 2.
And (3) fatigue test: the rotating bending fatigue test was carried out according to the standard GB/T4337-2015 rotating bending method for fatigue test of metal materials. Processing the rough-processed and heat-treated steel into a rotary bending fatigue sample, performing 20 fundamental tests on a PQ1-6 fatigue testing machine, controlling by axial strain, wherein the strain cyclic ratio R is-1, the frequency is 83Hz, the room temperature is 20 ℃, the loading waveform of the fatigue test is a sine wave, and the test finishing criterion is 107Secondary or sample failure.
Atmospheric corrosion resistance test: in order to verify the atmospheric corrosion performance of the steel, 288h weekly immersion corrosion test and 72h salt spray corrosion test are carried out according to the methods of GB/T19746-2018 'Metal and alloy corrosive salt solution weekly immersion test' and GB/T10125-2012 'Artificial atmosphere corrosion test salt spray test'. The test results are shown in FIG. 2.
The invention is further described with reference to specific examples.
Example 1
The production process of the high-strength wire rod for the bolt adopts the production process of the invention, and the process parameters are as follows: pure degassing time is 20 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1210 ℃, and the heat preservation time is 370 min; the heating temperature of the high-speed wire heating furnace is 980 ℃ during heating, and the time of the square billet in the furnace is 90 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 880 ℃, and the final rolling temperature is 780 ℃; the spinning temperature of the spinning machine is 760 ℃. The heating temperature of the heat treatment process for testing the mechanical properties of the wire rod is 900 ℃ during quenching and heating, and the tempering temperature of the heat treatment process for testing the mechanical properties of the wire rod is 590 ℃ during high-temperature tempering.
The chemical compositions and contents used in this example are shown in fig. 1, and the test results of tensile, impact and notched tensile delayed fracture property test, fatigue test and atmospheric corrosion resistance test are shown in fig. 1 and fig. 2.
Example 2
The high-strength wire rod for the bolt adopts the production process, and the process parameters are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 20 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1070 ℃ when the high-speed wire heating furnace is used for heating, and the furnace time of the square billet is 105 min; the initial rolling temperature of the wire during controlled rolling and controlled cooling rolling is 950 ℃, and the final rolling temperature is 840 ℃; the spinning temperature of the spinning machine is 820 ℃. The heating temperature of the wire rod is 960 ℃ during quenching and heating and the tempering temperature of the wire rod is 610 ℃ during high-temperature tempering in the heat treatment process for testing the mechanical property of the wire rod
The chemical compositions and contents used in this example are shown in fig. 1, and the test results of tensile, impact and notched tensile delayed fracture property test, fatigue test and atmospheric corrosion resistance test are shown in fig. 1 and fig. 2.
Example 3
The high-strength wire rod for the bolt adopts the production process, and the process parameters are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section during the steel heating is 1250 ℃, and the heat preservation time is 390 min; the heating temperature of the high-speed wire heating furnace is 1020 ℃ when the high-speed wire heating furnace is used for heating, and the furnace time of the square billet is 110 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 900 ℃, and the final rolling temperature is 800 ℃; the spinning temperature of the spinning machine is 780 ℃. The heating temperature of the wire rod is 910 ℃ during quenching and heating and the tempering temperature of the wire rod is 600 ℃ during high-temperature tempering in the heat treatment process for testing the mechanical property of the wire rod.
The chemical compositions and contents used in this example are shown in fig. 1, and the test results of tensile, impact and notched tensile delayed fracture property test, fatigue test and atmospheric corrosion resistance test are shown in fig. 1 and fig. 2.
Example 4
The high-strength wire rod for the bolt adopts the production process, and the process parameters are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1060 ℃ when the high-speed wire heating furnace is used for heating, and the furnace time of the square billet is 100 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 920 ℃, and the final rolling temperature is 820 ℃; the spinning temperature of the spinning machine is 800 ℃. In the heat treatment process for testing the mechanical property of the wire rod, the heating temperature is 930 ℃ during quenching and heating, and the tempering temperature is 600 ℃ during high-temperature tempering;
the chemical compositions and contents used in this example are shown in fig. 1, and the test results of tensile, impact and notched tensile delayed fracture property test, fatigue test and atmospheric corrosion resistance test are shown in fig. 1 and fig. 2.
Example 5
The high-strength wire rod for the bolt adopts the production process, and the process parameters are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1050 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is 100 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃; the spinning temperature of the spinning machine is 790 ℃. In the heat treatment process for testing the mechanical property of the wire rod, the heating temperature is 920 ℃ during quenching and heating, and the tempering temperature is 600 ℃ during high-temperature tempering;
the chemical compositions and contents used in this example are shown in fig. 1, and the test results of tensile, impact and notched tensile delayed fracture property test, fatigue test and atmospheric corrosion resistance test are shown in fig. 1 and fig. 2.
The invention also provides a comparative example 1 and a comparative example 2, the production process of the invention is adopted, the used chemical components and the content of the production process are different from those of the production processes of the examples 1-5, the specific figure is shown in figure 1, and the test results of the tensile, impact and notched tensile delayed fracture performance test, the fatigue test and the atmospheric corrosion resistance test are shown in figure 2. As can be seen from FIG. 2, examples 1 to 5 all had a strength of 1600MPa, an elongation of 10% or more, and a face shrinkage of 50% or more, and exhibited excellent delayed fracture resistance and ductility, and examples 1 to 5 all had excellent fatigue characteristics with a fatigue strength of 720MPa or more, and the corrosion rate in the immersion test of examples 1 to 5 was less than 0.9 g/(m) as compared with the comparative example2H) corrosion rate of less than 0.8 g/(m) in salt spray test2H), the corrosion resistance is better.
Example 6
The production process of the invention is adopted in the high-strength wire rod for the bolt, and the high-strength wire rod for the bolt comprises the following chemical components in percentage by weight: 0.55% of C, 0.10% of Si, 0.50% of Mn0, 1.50% of Cr1, 1.50% of Mo1, 0.10% of V, 0.08% of Nb0.08%, 0.20% of Ti0, 0.30% of Ni0, 0.20% of Cu0, 0.015% of Als0, 0.010% of P, 0.010% of S, 0.00015% of H, 0.0010% of O, 0.006% of N, and the balance of Fe and other inevitable impurities, and the weight percentage of the Fe and the other inevitable impurities meets the formula (.
The technological parameters in the production process are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1050 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is 100 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃; the spinning temperature of the spinning machine is 790 ℃. And then, carrying out performance test on the wire rod produced by the method, wherein the heating temperature is 920 ℃ during quenching and heating in the heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering.
Example 7
The production process of the invention is adopted in the high-strength wire rod for the bolt, and the high-strength wire rod for the bolt comprises the following chemical components in percentage by weight: 0.60% of C, 0.10% of Si, 0.80% of Mn0, 1.20% of Cr1, 1.80% of Mo1, 0.02% of V, 0.02% of Nb0.02%, 0.05% of Ti0.30% of Ni0.30% of Cu0.60%, 0.040% of Als0.010% of P, 0.010% of S, 0.00015% of H, 0.0010% of O, 0.006% of N, and the balance of Fe and other inevitable impurities, and the weight percentage of the Fe-Cr alloy satisfies the formula I.
The technological parameters in the production process are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1050 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is 100 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃; the spinning temperature of the spinning machine is 790 ℃. Then, carrying out performance test on the wire rod produced by the method, wherein the heating temperature is 920 ℃ during quenching and heating in the heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering;
example 8
The production process of the invention is adopted in the high-strength wire rod for the bolt, and the high-strength wire rod for the bolt comprises the following chemical components in percentage by weight: 0.60% of C, 0.10% of Si, 0.80% of Mn0, 1.20% of Cr1, 1.80% of Mo1, 0.10% of V, 0.02% of Nb0.02%, 0.05% of Ti0.20% of Ni0.20%, 0.60% of Cu0.040% of Als0.010%, 0.010% of S, 0.00015% of H, 0.0010% of O, 0.006% of N, and the balance of Fe and other inevitable impurities, and the weight percentage of the Fe-based alloy satisfies the formula I.
The technological parameters in the production process are as follows: pure degassing time is 25 minutes when the RH furnace is subjected to vacuum degassing; the target temperature of the tundish molten steel is stably controlled to be 30 ℃ above the liquidus temperature during the continuous casting of the large round billet; the temperature of a soaking section when the steel is heated is 1230 ℃, and the heat preservation time is 380 min; the heating temperature of the high-speed wire heating furnace is 1050 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is 100 min; the initial rolling temperature of the wire rod during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃; the spinning temperature of the spinning machine is 790 ℃. And then, carrying out performance test on the wire rod produced by the method, wherein the heating temperature is 920 ℃ during quenching and heating in the heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering.
Example 9
The production process adopted by the embodiment of the invention is different from the production process of the embodiment in chemical components and content, and the high-strength wire rod for the bolt comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, less than or equal to 0.10 percent of Si, 0.50 to 0.80 percent of Mn, 1.20 to 1.50 percent of Cr1.50 percent, 1.50 to 1.80 percent of Mo1, 0.20 to 0.40 percent of V, 0.02 to 0.07 percent of Nb0.20 to 0.30 percent of Ni0.20 to 0.30 percent of Cu0.20 to 0.60 percent of Als0.015 to 0.040 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0.006 percent of N, and the balance of Fe and other inevitable impurities, wherein:
0.7[C]≤0.2[Mo]+0.20[V]+0.10[Nb]+0.03[Ti]+0.25[Ni]≤0.8[C]。
for the chemical components proposed in this example, 5 sets of tests and 2 sets of comparative tests were performed, and the chemical components and contents of the 2 sets of comparative tests and the 5 sets of tests are different, specifically, see fig. 4, and the test results are shown in fig. 4 and fig. 5. The corrosion and delayed fracture resistance and the remaining mechanical properties were also well improved relative to the comparative experiments according to the tests carried out with the chemical composition of this example.

Claims (8)

1. The wire rod for the high-strength bolt is characterized by comprising the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, less than or equal to 0.10 percent of Si, 0.50 to 0.80 percent of Mn, 1.20 to 1.50 percent of Cr1.50 percent, 1.50 to 1.80 percent of Mo1, 0.02 to 0.10 percent of V, 0.02 to 0.08 percent of Nb0.02, 0.05 to 0.2 percent of Tis, 0.20 to 0.30 percent of Nis, 0.20 to 0.60 percent of Cu0.015 to 0.040 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0.
2. The wire rod for a high-strength bolt according to claim 1, wherein: the weight percentage of each chemical component of the wire rod meets 0.7[ C ] or more and 0.2[ Mo ] or more +0.20[ V ] or more +0.10[ Nb ] or more and 0.03[ Ti ] or more +0.25[ Ni ] or more and 0.8[ C ] or less.
3. A method for producing a wire rod for high-strength bolts, wherein the wire rod comprises the chemical composition as set forth in claim 1 or 2, and the production method specifically comprises the steps of: electric furnace smelting → LF + RH vacuum refining → large round billet continuous casting → heating → blooming and cogging → six-stand continuous rolling → square billet rolling → flaw detection, coping → high-speed wire heating furnace heating → controlled rolling and controlled cooling → reducing and sizing mill → laying head → stelmor cooling line → finished wire rod → packaging and warehousing.
4. A method for producing a wire rod for a high-strength bolt according to claim 3, characterized in that: the target temperature of the tundish molten steel is stably controlled to be 10-30 ℃ above the liquidus temperature during large round billet continuous casting.
5. The method for producing a wire rod for a high-strength bolt according to claim 4, wherein: the temperature of a soaking section during steel heating is 1210-1250 ℃, and the heat preservation time is 370-390 min.
6. A method for producing a wire rod for high-strength bolts according to any one of claims 3 to 5, wherein: the heating temperature of the high-speed wire heating furnace is 980-1070 ℃ when the high-speed wire heating furnace is used for heating, and the time of the square billet in the furnace is not more than 110 min.
7. The method for producing the wire rod for the high-strength bolt according to any one of claims 3 to 5, wherein the process parameters of rolling and cooling control are as follows: the initial rolling temperature is 880-950 ℃, and the final rolling temperature is 780-840 ℃; the spinning temperature of the spinning machine is 760-820 ℃.
8. A method for producing a wire rod for a high-strength bolt according to claim 3, characterized in that: the wire rod is required to be subjected to performance inspection, and the heat treatment process for inspecting the mechanical property of the wire rod comprises quenching heating treatment and high-temperature tempering treatment, wherein the heating temperature is 900-960 ℃ during quenching heating, and the tempering temperature is 590-610 ℃ during high-temperature tempering.
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CN114107822A (en) * 2021-11-30 2022-03-01 马鞍山钢铁股份有限公司 15.9-grade high-strength bolt steel and production method and heat treatment method thereof
CN114892078A (en) * 2022-04-26 2022-08-12 湖南华菱湘潭钢铁有限公司 Production method of 10.9-grade tempering-free U-shaped bolt steel

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