WO2022247855A1 - 一种螺栓用钢及其制备方法 - Google Patents

一种螺栓用钢及其制备方法 Download PDF

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WO2022247855A1
WO2022247855A1 PCT/CN2022/094924 CN2022094924W WO2022247855A1 WO 2022247855 A1 WO2022247855 A1 WO 2022247855A1 CN 2022094924 W CN2022094924 W CN 2022094924W WO 2022247855 A1 WO2022247855 A1 WO 2022247855A1
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Prior art keywords
steel
bolts
controlled
present
manufacturing
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PCT/CN2022/094924
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English (en)
French (fr)
Inventor
姚赞
余子权
金峰
赵四新
赵浩洋
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宝山钢铁股份有限公司
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Priority to US18/563,290 priority Critical patent/US20240209469A1/en
Priority to JP2023573007A priority patent/JP2024521172A/ja
Priority to KR1020237043103A priority patent/KR20240007677A/ko
Priority to EP22810579.7A priority patent/EP4328332A1/en
Priority to CA3220444A priority patent/CA3220444A1/en
Priority to AU2022283344A priority patent/AU2022283344A1/en
Publication of WO2022247855A1 publication Critical patent/WO2022247855A1/zh

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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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
    • C—CHEMISTRY; METALLURGY
    • 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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    • 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
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    • 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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/84—Controlled slow cooling
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
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    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • 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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    • 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
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    • 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
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C21D9/5732—Continuous furnaces for strip or wire with cooling of wires; of rods
    • 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
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C21D9/5735—Details
    • 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
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • 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
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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
    • C—CHEMISTRY; METALLURGY
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
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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
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    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/18—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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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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Definitions

  • the invention relates to a metal material and a preparation method thereof, in particular to a steel type and a preparation method thereof.
  • Fastener is a general term for a type of mechanical parts used when two or more parts (or components) are fastened and connected into a whole. It is the most widely used and most used in various sectors of the national economy. Mechanical basic parts, known as "industrial rice”. Bolt fastener connection has the advantages of simplicity and convenience, multiple disassembly and reassembly, high degree of standardization, and low cost. Various and considerable fasteners are used in various mechanical equipment, vehicles and ships, aircraft satellites, railway bridges, building structures, tools and instruments, instruments and meters, and daily necessities.
  • fasteners are mainly used in the automotive industry, the electronics industry and the construction and maintenance industry. Among them, fasteners are the most widely used in the automotive industry. Common materials for automotive fasteners include titanium alloys, steel, copper, aluminum, nylon, and other metals and non-metals. Steel for automotive fasteners can be divided according to product characteristics.
  • Non-heat treatment type mainly low-carbon steel series, the finished product grade of processing is 3.6-5.8
  • quenched and tempered type mainly medium carbon steel, low alloy steel, alloy steel series
  • Surface hardening type represented by ML18Mn, ML22Mn, and ML20Cr, the main processed products are self-tapping screws, self-tapping self-drilling screws and other products requiring surface carburizing
  • Non-quenched and tempered steel also known as It is an alloy non-quenched and tempered steel, and the non-quenched and tempered steel for fasteners is mainly cold work hardened non-quenched and tempered steel.
  • the letter "LF" is often preceded by the brand name.
  • high-strength fasteners can usually include: cylinder head bolts, connecting rod bolts, flywheel bolts, bearing cap bolts, pulley bolts, etc. These types are also required for automotive fasteners.
  • Highest product During the driving process of the car, with the high-speed operation of the engine, the fastening bolts of the engine are subjected to tensile cyclic stress, and fatigue fracture failure is prone to occur.
  • Engine fastening bolts are high-strength fasteners above grade 8.8.
  • the strength of bolts has been continuously improved.
  • Such high-strength bolts are prone to hydrogen embrittlement delayed fracture. Once the engine fastening bolts If there is a problem, it will affect the normal operation of the car engine and bring great harm. It can be seen that the uniformity of fastening bolts such as engine cylinder head bolts will greatly affect engine reliability and fuel efficiency.
  • the publication number is CN111621714A
  • the publication date is September 4, 2020
  • the Chinese patent document entitled "A round steel for bolts with excellent corrosion resistance and delayed fracture resistance and its production method” discloses a corrosion-resistant and resistant
  • the round steel for bolts with excellent delayed fracture performance has a carbon content of 0.55-0.60%, a large amount of Si element is added to 1.80-2.00%, and 0.20-0.35% of Cu element is also required.
  • the publication number is CN108754303A
  • the publication date is November 6, 2018
  • the Chinese patent document titled "A High-Strength Bolt Steel with Excellent Atmospheric Corrosion Resistance and Delayed Fracture Resistance” discloses an atmospheric corrosion-resistant and High-strength bolt steel with excellent delayed fracture resistance not only needs to add 0.30-1.20% Ni and 0.20-0.60% Cu, but also needs to add 0.005-0.030 Re rare earth elements, the alloy cost is very high, and the smelting control High difficulty.
  • the publication number is CN110791715A
  • the publication date is February 14, 2020
  • the Chinese patent document entitled "A kind of steel for high-strength bolts containing niobium and titanium resistant to atmospheric corrosion 14.9 and its production method" discloses a Niobium-titanium steel for atmospheric corrosion-resistant 14.9 high-strength bolts needs to be added with 0.80-1.00% Mo, and a large amount of V, Nb, Ti, Cr, and Cu elements are also added.
  • the alloy production of this scheme is difficult and costly. The performance stability of processed bolts cannot be guaranteed.
  • the present invention expects to obtain a steel for bolts and a preparation method thereof.
  • the steel for bolts has uniform structure and properties, good performance consistency and stability, low production cost, and It has high strength and good delayed fracture resistance.
  • the steel for bolts can be processed to produce homogeneous high-strength durable bolts, which are conducive to improving the stability of the fastening force of the engine, thereby realizing the miniaturization and high combustion efficiency of the engine, and achieving the goal of energy saving and emission reduction. Purpose, has very good economic benefit and social benefit.
  • One of the objects of the present invention is to provide a steel for bolts.
  • the steel for bolts has a uniform structure and performance, and has good resistance to delayed fracture.
  • the steel for bolts can be used to process and produce homogeneous high-strength durable bolts, and is effective Applied to automotive engines, high-end precision mechanical equipment and other application scenarios that require high tightening force, it can significantly improve engine efficiency and mechanical equipment processing accuracy. It has broad market application prospects and has very good economic and social benefits.
  • the present invention proposes a steel for bolts, except Fe and unavoidable impurities, said steel for bolts also contains the following chemical elements in mass percentage:
  • the steel for bolts of the present invention consists of the following chemical elements in mass percent:
  • the balance is Fe and unavoidable impurities.
  • the element C is the chemical composition necessary to ensure the high strength of the steel for bolts, and the content of element C determines the amount of carbide precipitated in the wire rod and finished bolts after quenching and tempering heat treatment , which greatly affects the hardness and strength of the alloy. Therefore, in order to ensure the quality of steel, in the steel of the present invention, the content of element C must be controlled above 0.37%. However, it should be noted that the content of C element in the steel should not be too high. Excessively high carbon content design will lead to excessive precipitation of carbides in the material, increase in size, reduce the plastic toughness of the material, and lead to deterioration of delayed fracture resistance. Therefore, The C element content needs to be controlled below 0.45%. Based on this, in the steel for bolts according to the present invention, the mass percentage content of element C is controlled between 0.37-0.45%.
  • Si element is often added into the steel as a deoxidizer during the smelting process, and at the same time, Si element solid-dissolved in the ferrite phase will significantly increase the strength of the steel.
  • the Si element content of the steel should not be too high.
  • the content of Si element needs to be controlled below 0.08%.
  • the content of Si element needs to be controlled above 0.01%. Based on this, in the bolt steel according to the present invention, the mass percent content of Si element is controlled between 0.01-0.08%.
  • Mn element In the steel for bolts according to the present invention, Mn element is often added to the steel as a deoxidizer during the steelmaking process. At the same time, the Mn element is easy to combine with the harmful element S in the steel to form MnS, which can reduce the harm of the element S.
  • Mn is also a commonly used strengthening element in steel. It mainly plays the role of solid solution strengthening, and the formed alloy cementite has higher strength. Therefore, it is necessary to control the content of Mn element in the alloy to be more than 0.45%. However, it should be noted that the Mn content should not be too high. When the Mn content in the steel is too high, it will increase the grain coarsening tendency during the heating process of the material and increase the difficulty of controlling the cooling structure.
  • the Mn element is easy to promote the formation of residual elements. Segregation, so it is necessary to control the content of Mn element in the steel to be below 0.80%. Based on this, in the bolt steel according to the present invention, the mass percentage content of Mn element is controlled between 0.45-0.80%.
  • the addition of Cr element is beneficial to improve the hardenability of the alloy, and the quenching and tempering process of the bolt is beneficial to the refinement of the structure, and at the same time, the strength of the cementite is improved, which is beneficial to the strength and plasticity of the material. improve.
  • the Cr element is conducive to improving the corrosion resistance of the material and reducing the susceptibility to hydrogen embrittlement. Therefore, in order to ensure the quality of the steel, it is necessary to control the Cr content in the steel to be more than 0.90%.
  • the content of Cr element in the steel should not be too high, and the content of Cr element should be controlled below 1.30%. Therefore, in the bolt steel according to the present invention, the mass percentage content of Cr element is controlled between 0.90-1.30%.
  • Mo In the bolt steel according to the present invention, the addition of Mo element is beneficial to refine the structure, improve the tempering stability of the material, improve the strength and hardness of the material under high temperature tempering, and help improve the delayed fracture resistance of the material.
  • the content of Mo element in the steel should not be too high. When too much Mo element is added in the steel, it will lead to more difficulty in controlling the material structure, and at the same time, the cost of the alloy will increase. Therefore, in the bolt steel according to the present invention, the mass percentage content of Mo element is controlled between 0.20-0.45%.
  • Ni element is an austenite forming element, which can be dissolved in the ferrite phase and is beneficial to improve the strength of the material. At the same time, the Ni element can also effectively improve the hardenability of the material, improve the uniformity of the structure and refine the structure during the quenching and tempering process of the bolt.
  • the content of Ni element in the steel should not be too high. Excessively high content of Ni will lead to abnormal martensitic structure in the production process of the material, and will also affect the cost of the alloy. Therefore, in the bolt steel according to the present invention, the mass percentage content of Ni element is controlled between 0.10-0.30%.
  • V In the steel for bolts according to the present invention, the V element is very easy to react with the C and N elements in the steel to precipitate carbonitrides, and these nanoscale precipitates are very effective in improving the strong plasticity of the material. At the same time, the carbonitridation of V can be used as a hydrogen trap to combine with free hydrogen in the steel to reduce its harm.
  • the amount and size of carbonitrides of V in the steel By controlling the amount and size of carbonitrides of V in the steel, the delayed fracture resistance of the material will be improved, and the Improve material performance consistency.
  • the content of V element in the design steel is more than 0.15%, but adding excessive V element will cause the size of its carbonitride to increase, and deteriorate the plastic toughness and formability of the material. Therefore, it is also necessary to control the steel
  • the V element content is below 0.30%. Based on this, in the steel for bolts according to the present invention, the mass percent content of V element is controlled between 0.15-0.30%.
  • the Al element is the most effective deoxidizing element in the steelmaking process, and it can play a deoxidizing role.
  • Al is easy to produce Al 2 O 3 particles during the deoxidation process, which has sharp edges and corners.
  • the oxygen content in the steel is too high, it will have a great impact on the fatigue life, durability, and delayed fracture resistance of the finished bolt. Therefore, in order to ensure the performance of high-strength bolts, prevent the generation of large-grained brittle inclusions, and improve the purity of steel, in the steel for bolts according to the present invention, the mass percentage content of Al element can be controlled within 0.015-0.035%. between.
  • the content of impurity elements in terms of mass percentage satisfies: Cu ⁇ 0.05%; P ⁇ 0.01%; S ⁇ 0.010%; O ⁇ 0.001%; N ⁇ 0.005%.
  • Cu, P, S, O and N elements are all impurity elements in steel. If technical conditions permit, in order to obtain steel with better performance and better quality, the impurity elements in steel should be reduced as much as possible. content.
  • the impurity element Cu is likely to cause hot brittleness of high-strength steel, and the uneven distribution of excessive Cu element in the material will lead to an increase in the retained austenite content in the material and a decrease in performance stability. Therefore, in the steel for bolts according to the present invention, it is necessary to control the Cu element content to be Cu ⁇ 0.05%.
  • the N element will also cause the material to increase, and at the same time, the excessively high content of N and C elements will cause the size of the microalloy precipitates in the steel for bolts to increase, reducing the delayed fracture resistance of the material, so in In the steel for bolts described in the present invention, the N element content needs to be controlled to be N ⁇ 0.005%.
  • the content of O element as an impurity element can be controlled so that O ⁇ 0.001%.
  • the content ratio of the elements Al and O in terms of mass percentage satisfies: Al/O>20.
  • controlling Al/O>20 is not only beneficial to reduce the oxygen content in the steel, but also does not produce too many coarse single-grain inclusions, which can ensure that the size of the large-grain inclusions produced is less than 38 ⁇ m, thereby preventing damage The plastic toughness and delayed fracture resistance of the material.
  • the content of the elements V, C and N in terms of mass percentage satisfies: V ⁇ (C+N) ⁇ 1/8.
  • the content of V element, C element and N element can also be controlled to satisfy: V ⁇ (C+N) ⁇ 1/8.
  • the elements are all substituted into the value before the percentage sign of the content in mass percentage corresponding to each element.
  • V ⁇ (C+N) ⁇ 1/8 can be further controlled, and then the content of V element in the steel can be controlled, so that the size of the carbon and nitrogen precipitates of V in the finished bolt is 5-50nm. higher than 90%.
  • the existence of such nanoscale carbides is beneficial to improve the strength and plasticity of the material, and at the same time, it can act as a hydrogen trap to reduce the hydrogen embrittlement tendency of the bolt.
  • the microstructure of the bolt steel according to the present invention includes tempered sorbite.
  • the microstructure of the bolt steel according to the present invention also has carbon and nitrogen precipitates of V, wherein the amount of carbon and nitrogen precipitates of V with a size of 5-50 nm accounts for more than 90%.
  • size with respect to carbon-nitrogen precipitates and inclusions of V refers to the size of a single precipitate or inclusion, specifically the length of the longest line segment passing through the center of the precipitate or inclusion, For example diameter (when spherical or approximately spherical) or major axis (when ellipsoidal or approximately ellipsoidal) or other length (when other shapes).
  • the size of the inclusions in the bolt steel according to the present invention is ⁇ 38 ⁇ m.
  • the properties of the bolt steel according to the present invention meet: tensile strength ⁇ 1200MPa, yield ratio > 0.9, slow tensile strength loss ⁇ 10% after hydrogen charging, bolt tightening and twisting fluctuation ⁇ 8%, bolt fatigue life >75000 times.
  • Yield strength ratio refers to the ratio of yield strength to tensile strength.
  • another object of the present invention is to provide a method for manufacturing bolt steel, which is easy to operate, and the structure and performance of the bolt steel obtained by the manufacturing method are uniform, and its tensile strength is ⁇ 1200MPa, and the yield ratio >0.9, the loss of tensile strength after hydrogen filling is ⁇ 10%, the fluctuation of bolt tightening and twisting is ⁇ 8%, and the fatigue life of bolts is >75,000 times.
  • Application scenarios that require high tightening force have very good economic and social benefits.
  • the present invention proposes a manufacturing method of steel for bolts, said method comprising the following steps:
  • Heat treatment including spheroidizing heat treatment, drawing, and quenching and tempering heat treatment for the wire rod in sequence.
  • the holding temperature of the spheroidizing heat treatment is 760-790°C, and the holding time is 4-12h. After the heat preservation, it is cooled slowly and the cooling speed is low. At 40°C/h, the area reduction rate of the wire rod during drawing is controlled to be 5-30%, the heating temperature of quenching and tempering heat treatment is 850-950°C, and the tempering temperature is 500-600°C.
  • the manufacturing method of the homogeneous high-strength and durable steel for bolts according to the present invention may also include other steps generally performed in the manufacturing process of steel for bolts in the art, such as cold heading after drawing.
  • the wire rod of the steel for bolts described in the present invention having the above-mentioned excellent properties can be effectively produced.
  • the molten steel can be smelted through an electric furnace or a converter, and then refined outside the furnace.
  • LF furnace and VD or RH degassing treatment process can be used; during the smelting process, the composition and addition amount of synthetic slag can be adjusted, the content of impurity elements in steel can be controlled, and the vacuum degassing time can be controlled to >15min.
  • the content of impurity elements P and S in the steel can be controlled to be lower than 0.010%, the vacuum degassing time must be greater than 15 minutes, the O content of the control end point is lower than 0.0010%, the N content is lower than 0.0050%, and the H content is low. at 2ppm.
  • a bloom continuous casting machine can be used to cast a billet during the casting process, which can be protected by argon during the casting process, and the size of the bloom can be controlled to 300 -450mm, the carbon segregation in the core of the billet is controlled to be lower than 1.10 by adjusting the casting speed, cooling and end light reduction parameters during the continuous casting process.
  • core carbon segregation refers to the ratio of the carbon content in the core of the slab to the average carbon content of the slab, where the carbon content can be measured according to the standard GB/T 20123.
  • a two-firing forming process can be used to pre-roll the continuous casting slab at a temperature of 1050-1250° C. to form a 150-250 mm square billet.
  • the billet is subjected to eddy current flaw detection, magnetic particle flaw detection, grinding wheel mold repair, supplementary magnetic particle flaw detection and mold repair, it enters the heating furnace for heating.
  • the heating temperature can be controlled at 960-1150°C, and the holding time can be controlled at 1.5-3.0h .
  • step (4) of the manufacturing method of the present invention during the high-speed wire rolling process, the rolling speed can be controlled to be 8-90 m/s.
  • the inlet temperature of the finishing rolling group in the online temperature is 850-970°C
  • control the inlet temperature of the reducing and sizing group is 800-950°C
  • Control spinning temperature is 750-900 °C.
  • the size specification of the wire rod obtained by rolling can be ⁇ 6-26mm, and in the Steyrmo controlled cooling process in the step (5) of the present invention, it is possible to adjust the temperature of the Steyrmo line fan Air volume, control the change of wire rod structure to optimize the wire rod structure.
  • the prepared wire rod in the heat treatment step, can be subjected to spheroidization heat treatment, wherein the heat preservation temperature of the spheroidization heat treatment can be controlled between 760-790°C,
  • the heat preservation time can be controlled to 4-12 hours. After heat preservation, it can be cooled slowly at a speed lower than 40°C/h.
  • the area reduction rate of the wire rod can be controlled between 5-30%.
  • the heating temperature of quenching and tempering heat treatment can be controlled at 850- 950°C, the tempering temperature can be controlled at 500-600°C.
  • the vacuum degassing time is controlled to be >15 minutes during the smelting process.
  • step (2) the carbon segregation at the center of the billet is controlled to be lower than 1.10 during the casting process.
  • step (3) during the blank heating process, the heating temperature is controlled to be 960-1150°C, and the holding time is 1.5-3.0h.
  • step (4) the rolling speed is controlled to be 8-90m/s.
  • the temperature at the inlet of the finishing rolling unit is controlled to be 850-970°C
  • the temperature at the inlet of the reducing and sizing unit is 800-950°C
  • the spinning temperature is 750-950°C. 900°C.
  • Stelmore cooling uses at least 14 fans, wherein the air volume of fans F1-F5 is ⁇ 80%, and the air volume of fans F6-F12 is ⁇ 50%, and the air volume of fans F13-F14 is ⁇ 45%.
  • the "air volume” in % refers to the air volume ratio of each fan, where the air volume of each fan is 200,000 m 3 /h.
  • the air volume of fans F1-F5 ⁇ 80% means that the air volume ratio of each fan in fans F1-F5 is ⁇ 80%, that is, the air volume of each fan in fans F1-F5 is ⁇ 160,000 m 3 /h;
  • the air volume of fans F6-F12 ⁇ 50% means that the air volume ratio of each fan in F6-F12 is ⁇ 50%, that is, the air volume of each fan in F6-F12 is ⁇ 100,000 m 3 /h;
  • “Fan F13- The air volume of F14 ⁇ 45%” means that the air volume of each fan in the fans F13-F14 is ⁇ 45%, that is, the air volume of each fan in the fans F13-F14 is ⁇ 90,000 m 3 /h.
  • At least 14 fans are used to carry out Steyrmor controlled cooling, and the wire rod of steel for bolts obtained after Steyrmor cooling can obtain good plasticity and toughness.
  • the bolt steel of the present invention Compared with the prior art, the bolt steel of the present invention and its preparation method have the following advantages and beneficial effects:
  • the structure and properties of the bolt steel of the invention are uniform, it has good performance consistency and stability, its production cost is low, and it has high strength and good resistance to delayed fracture.
  • the steel for bolts can be processed to produce homogeneous high-strength durable bolts, which can be effectively used in automotive engines, high-end precision mechanical equipment and other application scenarios that require high tightening force, and can significantly improve engine efficiency And the machining accuracy of mechanical equipment, its market application prospect is broad, and it has very good economic and social benefits.
  • the bolt steel according to the invention has a refined tempered sorbite structure after quenching and tempering heat treatment, and its structure and properties are uniform.
  • the number of carbon and nitrogen precipitates with a V size of 5-50 nm accounts for more than 90%, the size of the inclusions is less than 38 ⁇ m, and the tensile strength can reach more than 1200 MPa.
  • the fatigue life and delayed fracture resistance of the finished high-strength bolts processed by the bolt steel of the present invention are more than double those of commonly used materials.
  • the fluctuation of bolt tightening and twisting is ⁇ 8%, which can significantly improve the bolt tightening.
  • the uniformity of power so as to realize the miniaturization and high combustion efficiency of the engine, and achieve the purpose of energy saving and emission reduction.
  • the bolt steel of embodiment 1-10 all adopts following steps to make:
  • melt steel is smelted according to the chemical composition shown in Table 1-1 and Table 1-2: After being smelted in an electric furnace or a converter, it is refined outside the furnace.
  • the refining outside the furnace adopts LF furnace and VD or RH degassing treatment process. Adjust the synthetic slag composition and addition amount during the process, and control the vacuum degassing time>15min during the smelting process.
  • the continuous casting billet is rough-rolled at a temperature of 1100-1250° C. into a 150-250 mm square billet by adopting the second-fire forming process.
  • the billet After the billet is subjected to ultrasonic flaw detection, magnetic particle flaw detection, grinding wheel mold repair, supplementary magnetic particle flaw detection and mold repair, it enters the heating furnace for heating.
  • the heating temperature is controlled at 960-1150°C, and the holding time is 1.5-3.0h.
  • High-speed wire rolling to produce wire rods with a size of ⁇ 6-26mm control the rolling speed to 8-90m/s, the inlet temperature of the finishing rolling unit is 850-970°C, and the inlet temperature of the reducing and sizing unit is 800 -950°C, spinning temperature is 750-900°C.
  • Steyrmo controlled cooling of the wire rod 14 sets of Steyrmo line fans are used to carry out the Steyrmo controlled cooling of the wire rod, among which: the air volume of the fans F1-F5 is ⁇ 80%, and the fans F6-F12 The air volume of the fan is ⁇ 50%, and the air volume of the fans F13-F14 is ⁇ 45%.
  • the air volume of the Stelmore line fan By adjusting the air volume of the Stelmore line fan, the wire rod structure transformation is controlled and the wire rod structure is optimized.
  • Heat treatment including spheroidizing heat treatment, drawing and quenching and tempering heat treatment for the wire rod in sequence, wherein the holding temperature for controlling the spheroidizing heat treatment is 760-790°C, and the holding time is 4-12h. If it is lower than 40°C/h, the drawing area reduction rate of the wire rod is controlled to be 5-30%, the heating temperature of quenching and tempering heat treatment is controlled to be 850-950°C, and the tempering temperature is to be 500-600°C.
  • wire rods of Examples 1-11 of the present invention are all prepared by the above steps, and their chemical composition and related process parameters all meet the control requirements of the design specification of the present invention.
  • comparison wire rod of comparative example 1-4 adopts equally: the technological process of smelting, casting, rough rolling, high-speed wire rod rolling, Stelmo controlled cooling and heat treatment is made, but its chemical composition and relevant process parameter all have unidentified Parameters that can meet the design requirements of the present invention.
  • Table 1 lists the mass percentage distribution of each chemical element in the bolt steels of Examples 1-10 and the comparative steels of Comparative Examples 1-4.
  • Table 1-1 (wt%, the balance is Fe and other unavoidable impurities except Cu, P, S, O and N)
  • Example 1 37.5 0.093
  • Example 2 21.4 0.099
  • Example 3 21.4 0.098
  • Example 4 30.0 0.099
  • Example 5 40.0 0.101
  • Example 6 35.0 0.121
  • Example 7 37.5 0.121
  • Example 8 25.0 0.067
  • Example 9 25.0 0.091
  • Example 10 25.0 0.123 Comparative example 1 14.0 0 Comparative example 2 13.3 0.217 Comparative example 3 6.2 0.042 Comparative example 4 30.0 0.088
  • Table 2-1 and Table 2-2 list the specific process parameters in the above steps for the bolt steels of Examples 1-10 and the comparative steels of Comparative Examples 1-4.
  • the bolt steel of finally made embodiment 1-10 and the comparative steel of comparative example 1-4 were sampled respectively, and the steel samples of each embodiment and comparative example were observed and analyzed, to obtain the results of each embodiment and comparative example. steel tissue. After the observation was completed, mechanical property tests were performed on the steel samples of the examples and comparative examples, and the obtained observation results and mechanical property test results were listed in Table 3 and Table 4, respectively.
  • Table 3 lists the microstructure observation results of the bolt steels of Examples 1-10 and the comparative steels of Comparative Examples 1-4.
  • the microstructure of the steel for bolts in Examples 1-10 includes tempered sorbite.
  • the microstructure also has carbon and nitrogen precipitates of V, wherein the carbon and nitrogen with a size of V between 5-50nm The amount of precipitates accounted for more than 90%.
  • the size of the inclusions in the steel is ⁇ 38 ⁇ m.
  • Table 4 lists the mechanical property test results of the bolt steels of Examples 1-10 and the comparative steels of Comparative Examples 1-4.
  • Table 5 lists the performance test results of bolts processed by using the bolt steels of Examples 1-10 and the comparison steels of Comparative Examples 1-4.
  • the steel for bolts of the present invention can be processed to produce homogeneous high-strength durable bolts, and the prepared homogeneous high-strength durable bolts can be effectively applied to application scenarios requiring high tightening force, such as automobile engines and high-end precision mechanical equipment, which can significantly Improving engine efficiency and machining accuracy of mechanical equipment has broad market application prospects and has very good economic and social benefits.

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Abstract

本发明公开了一种螺栓用钢，其除Fe和不可避免的杂质以外还含有以质量百分比计的下述化学元素：C：0.37-0.45％；Si：0.01-0.08％；Mn：0.45-0.80％；Cr：0.90-1.30％；Mo：0.20-0.45％；Ni：0.10-0.30％；V：0.15-0.30％；Al：0.015-0.035％。此外，本发明还公开了一种螺栓用钢的制造方法，其包括步骤：(1)冶炼；(2)铸造；(3)粗轧；(4)高速线材轧制；(5)斯太尔摩控冷；(6)热处理：其中球化热处理的保温温度为760-790℃，保温时间为4-12h，保温后缓慢冷却，冷却速度低于40℃/h，控制盘条拉拔减面率为5-30％，调质热处理的加热温度为850-950℃，回火温度为500-600℃。本发明所述的螺栓用钢的组织、性能均匀，其生产成本较低，且具有较高的强度和良好的耐延迟断裂性能。

Description

一种螺栓用钢及其制备方法 技术领域
本发明涉及一种金属材料及其制备方法，尤其涉及一种钢种及其制备方法。
背景技术
紧固件是将两个或两个以上的零件(或构件)紧固连接成为一件整体时所采用的一类机械零件的总称，它是国民经济各部门应用范围最广、使用数量最多的机械基础件，素有“工业之米”之称。螺栓紧固件连接具有简单便捷、可以多次拆卸重新装配、标准化程度高、成本低等优点。在各种机械设备、车辆船舶、飞机卫星、铁路桥梁、建筑结构、工具器械、仪器仪表和生活用品等中，都使用了各种各样、数量可观的紧固件。
目前，紧固件主要用于汽车工业、电子工业和建筑及维修工业中。其中，紧固件在汽车工业中的应用最为广泛，汽车紧固件常用材料有钛合金、钢、铜、铝、尼龙和其他金属、非金属等，汽车紧固件用钢按照产品特点可分为以下四类：(1)非热处理型；主要是低碳钢系列，加工的成品等级是3.6-5.8级；(2)调质型：主要是中碳钢、低合金钢、合金钢系列；(3)表面硬化型：以ML18Mn、ML22Mn、ML20Cr为代表，主要加工的成品为自攻螺钉、自攻自钻螺钉和其他要求表面渗碳型的产品；(4)非调质钢：也称为合金非调质钢，紧固件用非调质钢主要是冷作硬化型非调质钢，牌号前常冠以字母“LF”。
目前，市场广泛使用的汽车高强度紧固件共有四个性能等级，分别是8.8、9.8、10.9和12.9级，8.8级以上的高强度螺栓因为需要承受较大的载荷，又因受力状态非常复杂，所以这类螺栓多采用碳素钢或中碳合金钢制造，并需要经过调质处理操作以保证产品具有足够的强度和屈强比。
在汽车发动机中，常用的高强度紧固件通常可以包括：缸盖螺栓、连杆螺栓、飞轮螺栓、轴承盖螺栓、皮带轮螺栓等几大类，这几类同时也是汽车用紧固件中要求最高的产品。在汽车行驶过程中，随着发动机高速运转，发动机紧固螺栓经受拉伸循环应力，容易发生疲劳断裂失效。发动机紧固螺栓属于8.8 级以上的高强度紧固件，近年来随着发动机紧凑型、小型化发展，螺栓强度不断提高，这种高强度螺栓极易发生氢脆延迟断裂，一旦发动机紧固螺栓出现问题，将会影响汽车发动机的正常工作，带来巨大的危害。由此可见，发动机缸盖螺栓等紧固螺栓的均匀性问题，将极大影响发动机可靠性和燃油效率。
因此，为了保证汽车发动机的可靠性和燃油效率，针对汽车发动机螺栓这类高强度螺栓进行抗氢脆延迟断裂性能增强、提升材料均匀性，从而保证螺栓性能一致性，一直都是发动机螺栓研究的重点。
例如：公开号为CN111621714A，公开日为2020年9月4日，名称为“一种耐蚀耐延迟断裂性能优异的螺栓用圆钢及其生产方法”的中国专利文献公开了一种耐蚀耐延迟断裂性能优异的螺栓用圆钢，其碳含量为0.55-0.60％，大量添加Si元素至1.80-2.00％，同时还需添加0.20-0.35％的Cu元素。采用该技术方案，在合金热轧及热处理过程中脱碳控制和开裂控制难度大，加工成型的螺栓性能不佳。
又例如：公开号为CN108754303A，公开日为2018年11月6日，名称为“一种耐大气腐蚀及耐延迟断裂性能优良的高强度螺栓钢”的中国专利文献公开了一种耐大气腐蚀及耐延迟断裂性能优良的高强度螺栓钢，其不仅需要添加0.30-1.20％的Ni和0.20-0.60％的Cu，同时还需要填加0.005-0.030的Re稀土元素，合金成本很高，同时冶炼控制难度大。
再例如：公开号为CN110791715A，公开日为2020年2月14日，名称为“一种含铌钛耐大气腐蚀14.9级高强度螺栓用钢及其生产方法”的中国专利文献公开了一种含铌钛耐大气腐蚀14.9级高强度螺栓用钢，其需要添0.80-1.00％的Mo，同时还添加了大量V、Nb、Ti、Cr、Cu元素，该方案的合金生产难度大，成本高，加工螺栓性能稳定性无法保证。
由此可见，现有技术中的众多解决方案仍然存在不少缺陷，而近年来随着法律法规对于车辆节能减排效果的要求越来越高，市场和用户对于汽车也提出了更高的要求，其要求汽车在满足轻量化的同时还需要提高发动机的效率。为此，为了确保汽车发动机在满足轻量化、小型化的同时，具有良好的可靠性和燃油效率，亟需一种强度较高，材料均匀性和耐延迟断裂性能优异的均质高强耐久螺栓。
基于此，为了解决上述问题，本发明期望获得一种螺栓用钢及其制备方法， 该螺栓用钢的组织、性能均匀，其具有良好的性能一致性和稳定性，其生产成本较低，且具有较高的强度和良好的耐延迟断裂性能。采用该螺栓用钢可以加工制得均质高强耐久螺栓，制得的均质高强耐久螺栓有利于提高发动机紧固力的稳定性，从而实现发动机的小型化和高燃烧效率，达到节能减排的目的，具有十分良好的经济效益和社会效益。
发明内容
本发明的目的之一在于提供一种螺栓用钢，该螺栓用钢的组织、性能均匀，其具有良好的耐延迟断裂性能，采用该螺栓用钢可以加工制得均质高强耐久螺栓，并有效应用于汽车发动机、高端精密机械设备等对拧紧力要求较高的应用场景，可显著提高发动机效率及机械设备加工精度，其市场应用前景广阔，具有十分良好的经济效益和社会效益。
为了实现上述目的，本发明提出了一种螺栓用钢，除Fe和不可避免的杂质之外，所述螺栓用钢还含有以质量百分比计的如下化学元素：
C：0.37-0.45％；
Si：0.01-0.08％；
Mn：0.45-0.80％；
Cr：0.90-1.30％；
Mo：0.20-0.45％；
Ni：0.10-0.30％；
V：0.15-0.30％；
Al：0.015-0.035％。
优选地，本发明所述的螺栓用钢由以质量百分比计的如下化学元素组成：
C：0.37-0.45％；
Si：0.01-0.08％；
Mn：0.45-0.80％；
Cr：0.90-1.30％；
Mo：0.20-0.45％；
Ni：0.10-0.30％；
V：0.15-0.30％；
Al：0.015-0.035％；
余量为Fe和不可避免的杂质。
在本发明所述的螺栓用钢中，各化学元素的设计原理具体如下所述：
C：在本发明所述的螺栓用钢中，C元素是保证螺栓用钢高强度所必需的化学成分，C元素含量决定了盘条及成品螺栓中经调质热处理后，析出碳化物的数量，极大影响合金硬度和强度。因此，为保证钢的质量，在本发明的钢中，C元素含量需控制在0.37％以上。但需要注意的是，钢种C元素含量不宜过高，过高的碳含量设计将导致材料中碳化物析出数量过多，尺寸长大，降低材料的塑韧性，导致耐延迟断裂性能劣化，因此需控制C元素含量为0.45％以下。基于此，在本发明所述的螺栓用钢中，将C元素的质量百分含量控制在0.37-0.45％之间。
Si：在本发明所述的螺栓用钢中，Si元素在冶炼过程中常作为脱氧剂加入钢中，同时固溶于铁素体相中的Si元素将显著提高钢材的强度。但需要注意的是，钢种Si元素含量不宜过高，当钢中Si元素含量过高时，会降低材料冷镦成型性能，进而对材料耐延迟断裂性能不利。因此，为确保钢材的质量，在本发明的钢中，Si元素含量需控制在0.08％以下。同时为了降低钢中夹杂物熔点、去除大颗粒不可变形夹杂物，需将Si元素含量控制在0.01％以上。基于此，在本发明所述的螺栓用钢中，将Si元素的质量百分含量控制在0.01-0.08％之间。
Mn：在本发明所述的螺栓用钢中，Mn元素在炼钢过程也常作为脱氧剂加入钢中。同时，Mn元素易与钢中的有害元素S结合形成MnS，从而可以降低元素S的危害。此外，Mn也是钢中常用的强化元素，其主要起到固溶强化的作用，形成的合金渗碳体具有更高的强度，因此需要控制合金中Mn元素含量为0.45％以上。但需要注意的是，Mn元素含量不宜过高，当钢中Mn含量过高时，将增大材料加热过程中晶粒粗化倾向，增大控冷组织控制难度，Mn元素易促进残余元素的偏聚，因此需控制钢中Mn元素含量为0.80％以下。基于此，在本发明所述的螺栓用钢中，将Mn元素的质量百分含量控制在0.45-0.80％之间。
Cr：在本发明所述的螺栓用钢中，添加Cr元素有利于提高合金淬透性，螺栓调质处理过程中有利于细化组织，同时提高渗碳体强度，对材料强度和塑性均有改善。同时，Cr元素有利于提高材料耐腐蚀性能，降低氢脆敏感性，因 此，为确保钢材的质量，需控制钢中Cr含量为0.90％以上。此外，为了防止出现马氏体异常组织、降低盘条组织控制难度，钢中Cr元素含量同样也不宜过高，需控制Cr元素含量为1.30％以下。因此，在本发明所述的螺栓用钢中，将Cr元素的质量百分含量控制在0.90-1.30％之间。
Mo：在本发明所述的螺栓用钢中，Mo元素的添加有利于细化组织、提高材料回火稳定性，提高材料高温回火下的强度和硬度，有利于提高材料耐延迟断裂性能。但需要注意的是，钢中Mo元素含量不宜过高，当钢中Mo元素添加过多时，将会导致材料组织控制难度加大，同时合金成本上升。因此，在本发明所述的螺栓用钢中，将Mo元素的质量百分含量控制在0.20-0.45％之间。
Ni：在本发明所述的螺栓用钢中，Ni元素是奥氏体形成元素，其可以固溶于铁素体相中并有利于提高材料强度。同时，Ni元素还可以有效提高材料淬透性，提高螺栓调质处理过程中的组织均匀性、细化组织。但需要注意的是，钢中Ni元素含量同样不宜过高，过高含量的Ni将会导致材料生产过程中易于出现马氏体异常组织，同时也会影响到合金成本。因此，在本发明所述的螺栓用钢中，将Ni元素的质量百分含量控制在0.10-0.30％之间。
V：在本发明所述的螺栓用钢中，V元素极易与钢中的C、N元素反应析出碳氮化物，这些纳米级析出物对材料强塑性提升十分有力。同时，V的碳氮化可以作为氢陷阱，与钢中游离的氢元素结合，降低其危害，通过控制钢中V的碳氮化物数量和尺寸将实现材料耐延迟断裂性能的提升，同时也将改善材料性能一致性。为发挥V元素的有效作用，设计钢中V元素含量为0.15％以上，但添加过量的V元素将会导致其碳氮化物尺寸增大，劣化材料塑韧性和成型性能，因此同时还需要控制钢中V元素含量为0.30％以下。基于此，在本发明所述的螺栓用钢中，将V元素的质量百分含量控制在0.15-0.30％之间。
Al：在本发明所述的螺栓用钢中，Al元素是炼钢过程中最有效的脱氧元素，其可以起到脱氧作用。但Al在脱氧过程中易于生产Al 2O 3颗粒，其具有尖锐的棱角，特别是钢中氧含量过高时，对成品螺栓疲劳寿命、耐久性、耐延迟断裂性能都会产生极大影响。因此，为保证高强度螺栓性能，防止产生大颗粒脆性夹杂物，提升钢质纯洁度，在本发明所述的螺栓用钢中，可以将Al元素的质量百分含量控制在0.015-0.035％之间。
优选地，在本发明所述的螺栓用钢中，杂质元素以质量百分比计的含量满 足：Cu≤0.05％；P≤0.01％；S≤0.010％；O≤0.001％；N≤0.005％。
在上述技术方案中，Cu、P、S、O和N元素均为钢中杂质元素，在技术条件允许情况下，为了获得性能更好、质量更优的钢材，应尽可能降低钢中杂质元素的含量。
需要说明的是，在本发明中，杂质元素Cu易造成高强钢热脆性，同时过高的Cu元素在材料中的不均匀分布将会导致材料中残余奥氏体含量增多，性能稳定性降低，因此在本发明所述的螺栓用钢中，需要将Cu元素含量控制为Cu≤0.05％。
相应地，在本发明中，钢中P、S元素含量过高将增加钢材的脆性，特别是当出现偏析时，因此在本发明所述的螺栓用钢中，需要将P和S元素含量控制为P≤0.01％、S≤0.010％。
此外，在本发明中，N元素同样会导致材料增大，同时过高含量的N、C元素含量将会导致螺栓用钢中微合金析出物尺寸增大，降低材料耐延迟断裂性能，因此在本发明所述的螺栓用钢中，需要将N元素含量控制为N≤0.005％。
另外，在本发明中，可以将作为杂质元素的O元素含量控制为O≤0.001％。
优选地，在本发明所述的螺栓用钢中，元素Al和O以质量百分比计的含量比满足：Al/O＞20。
在本发明所述的技术方案中，为了获得更优的实施效果，得到质量和性能更优的钢材，在控制单一化学元素的含量的同时，还可以优选地控制Al元素和O元素的含量比满足：Al/O＞20。式中元素均代入各元素对应的以质量百分比计的含量。
在本发明中，控制Al/O＞20既有利于降低钢中氧含量，同时又不会产生过多粗大的单颗粒夹杂物，其可以确保产生的大颗粒夹杂物尺寸小于38μm，进而防止损害材料的塑韧性和耐延迟断裂性能。
优选地，在本发明所述的螺栓用钢中，元素V、C和N以质量百分比计的含量满足：V×(C+N)≤1/8。
在本发明所述的技术方案中，在控制单一化学元素的含量的同时，还可以控制V元素、C元素和N元素的含量满足：V×(C+N)≤1/8。式中元素均代入各元素对应的以质量百分比计的含量的百分号之前的数值。
在本发明中，优选地，可以进一步控制V×(C+N)≤1/8，进而控制钢中V 元素含量，以使成品螺栓中V的碳氮析出物尺寸为5-50nm数量占比高于90％。该类纳米级碳化物的存在有利于提高材料强度和塑韧性，同时可作为氢陷阱降低螺栓的氢脆倾向。
优选地，本发明所述的螺栓用钢的微观组织包括回火索氏体。
优选地，本发明所述的螺栓用钢的微观组织还具有V的碳氮析出物，其中尺寸为5-50nm的V的碳氮析出物的数量占比高于90％。
在本文中，就V的碳氮析出物和夹杂物而言的“尺寸”是指单个析出物或夹杂物的尺寸，具体是指穿过析出物或夹杂物的中心的最长线段的长度，例如直径(当为球形或近似球形时)或长轴(当为椭球形或近似椭球形时)或其他长度(当为其他形状时)。
优选地，本发明所述的螺栓用钢中的夹杂物尺寸＜38μm。
优选地，本发明所述的螺栓用钢的性能满足：抗拉强度≥1200MPa，屈强比＞0.9，充氢慢拉伸强度损失≤10％，螺栓拧紧扭住波动≤8％，螺栓疲劳寿命＞75000次。“屈强比”指屈服强度与抗拉强度的比值。
在本文中，钢材的力学性能按照GB/T 228.1-2010《金属材料拉伸试验》进行测定。“螺栓疲劳寿命”是指螺栓发生断裂时的试验次数，根据GBT 13682-1992《螺纹紧固件轴向载荷疲劳试验方法》进行测定。“充氢慢拉伸强度损失”被计算为：(空气条件下抗拉强度-充氢腐蚀条件下抗拉强度)/空气条件下抗拉强度，根据GB/T 15970.7-2017《金属和合金的腐蚀应力腐蚀试验第7部分：慢应变速率试验》进行测定。“螺栓拧紧扭住波动”被计算为：|螺栓拧紧过程中实际加载的扭矩-目标扭矩|/目标扭矩，其中该数值越小，表明材料均匀性越好。
相应地，本发明的另一目的在于提供一种螺栓用钢的制造方法，其操作简便，采用该制造方法制得的螺栓用钢的组织及性能均匀，其抗拉强度≥1200MPa，屈强比＞0.9，充氢慢拉伸强度损失≤10％，螺栓拧紧扭住波动≤8％，螺栓疲劳寿命＞75000次，其可以用于制得螺栓，并有效应用于汽车发动机、高端精密机械设备等对拧紧力要求较高的应用场景，具有十分良好的经济效益和社会效益。
为了实现上述目的，本发明提出了一种螺栓用钢的制造方法，所述方法包括以下步骤：
(1)对钢水进行冶炼；
(2)对经冶炼的钢水进行铸造，制得坯料；
(3)对坯料进行粗轧；
(4)高速线材轧制，制得盘条；
(5)对盘条进行斯太尔摩控冷；
(6)热处理：包括对盘条依次进行球化热处理、拉拔和调质热处理，其中球化热处理的保温温度为760-790℃，保温时间为4-12h，保温后缓慢冷却，冷却速度低于40℃/h，在拉拔中控制盘条拉拔减面率为5-30％，调质热处理加热温度为850-950℃，回火温度为500-600℃。
优选地，在本发明所述的均质高强耐久螺栓用钢的制造方法中，还可以包括本领域螺栓用钢制造过程中通常进行的其他步骤，例如在拉拔之后进行冷镦。
通过本发明所述的螺栓用钢的制造方法，可以有效制得本发明所述的具有上述优异性能的螺栓用钢的盘条。
在本发明所述的技术方案中，在步骤(1)的冶炼过程中，可以经电炉或转炉对钢水进行冶炼，而后再进行炉外精炼。其中，在炉外精炼时，可以采用LF炉以及VD或RH脱气处理工艺；在冶炼过程中调整合成渣的成分和加入量，控制钢中杂质元素含量，控制真空脱气时间＞15min。其中，在冶炼过程中可以控制钢中杂质元素P、S含量均低于0.010％，真空脱气时间需大于15分钟，控制终点O含量低于0.0010％，N含量低于0.0050％，H含量低于2ppm。
相应地，在本发明所述制造方法的步骤(2)中，在铸造过程中可以采用大方坯连铸机浇注方坯，其在浇铸过程中可以采用氩气保护，大方坯尺寸可以控制为300-450mm，通过调整连铸过程中拉速、冷却及末端轻压下参数达到控制坯料心部碳偏析低于1.10。
在本文中，“心部碳偏析”是指铸坯心部碳含量与铸坯平均碳含量的比值，其中碳含量可以根据标准GB/T 20123进行测定。
在本发明所述制造方法步骤(3)的粗轧步骤中，可以采用二火成材工艺，将连铸坯于1050-1250℃温度下初轧开坯为150-250mm方坯料。方坯料经涡流探伤、磁粉探伤、砂轮修模、补充磁粉探伤及修模后，进入加热炉加热，在坯料加热过程中，可以控制加热温度为960-1150℃，控制保温时间为1.5-3.0h。
此外，在本发明所述制造方法的步骤(4)中，在高速线材轧制过程中， 可以控制轧制速度为8-90m/s。当然，在一些优选的实施方式中，为了获得更好的实施效果，可以优选地控制在线温度中的精轧机组进口温度为850-970℃，控制减定径机组进口温度为800-950℃，控制吐丝温度为750-900℃。
另外，在本发明中，轧制得到的盘条尺寸规格可以为Ф6-26mm，在本发明所述步骤(5)的斯太尔摩控冷过程中，可以通过调整斯太尔摩线风机的风量，控制盘条组织转变，以优化盘条组织。
相应地，在本发明所述制造方法的步骤(6)中，在热处理步骤中，可以对制得的盘条进行球化热处理，其中球化热处理保温温度可以控制在760-790℃之间，保温时间可以控制为4-12小时，保温后缓慢冷却，速度低于40℃/h，盘条拉拔减面率可以控制在5-30％之间，调质热处理加热温度可以控制为850-950℃，回火温度可以控制为500-600℃。
优选地，在本发明所述的制造方法中，在步骤(1)中，在冶炼过程中控制真空脱气时间＞15min。
优选地，在本发明所述的制造方法中，在步骤(2)中，在铸造过程中控制坯料心部碳偏析低于1.10。
优选地，在本发明所述的制造方法中，在步骤(3)中，在坯料加热过程中，控制加热温度为960-1150℃，保温时间为1.5-3.0h。
优选地，在本发明所述的制造方法中，在步骤(4)中，控制轧制速度为8-90m/s。
优选地，在本发明所述的制造方法中，在步骤(4)中，控制精轧机组进口温度为850-970℃，减定径机组进口温度为800-950℃，吐丝温度为750-900℃。
优选地，在本发明所述的制造方法中，在步骤(5)中，斯太尔摩控冷采用至少14台风机，其中风机F1-F5的风量≤80％，风机F6-F12的风量≤50％，风机F13-F14的风量≤45％。
在本文中，以％为单位的“风量”是指每台风机的风量比例，其中每台风机的风量为20万m 3/h。例如，“风机F1-F5的风量≤80％”是指风机F1-F5中每台风机的风量比例≤80％，即风机F1-F5中每台风机的风量≤16万m 3/h；“风机F6-F12的风量≤50％”是指风机F6-F12中每台风机的风量比例≤50％，即风机F6-F12中每台风机的风量≤10万m 3/h；“风机F13-F14的风量≤45％”是指风机F13-F14中每台风机的风量≤45％，即风机F13-F14中每台风机的风量≤9万m 3/h。
在本发明的上述技术方案中，利用至少14台风机进行斯太尔摩控冷，经斯太尔摩冷却后制得的螺栓用钢的盘条可以获得良好的塑韧性。
本发明所述的螺栓用钢及其制备方法相较于现有技术具有如下所述的优点以及有益效果：
本发明所述的螺栓用钢的组织、性能均匀，其具有良好的性能一致性和稳定性，其生产成本较低，且具有较高的强度和良好的耐延迟断裂性能。采用该螺栓用钢可以加工制得均质高强耐久螺栓，制得的均质高强耐久螺栓能够有效应用于汽车发动机、高端精密机械设备等对拧紧力要求较高的应用场景，可显著提高发动机效率及机械设备加工精度，其市场应用前景广阔，具有十分良好的经济效益和社会效益。
本发明所述的螺栓用钢经调质热处理后具有细化的回火索氏体组织，其组织及性能均匀。在一些优选的实施方式中，V的尺寸为5-50nm的碳氮析出物数量占比高于90％，夹杂物尺寸小于38μm，抗拉强度可达到1200MPa以上。
采用本发明所述的螺栓用钢加工制得的成品高强度螺栓的疲劳寿命、耐延迟断裂性能均较常用材料提高一倍以上，同时螺栓拧紧扭住波动≤8％，可显著提高螺栓紧固力的均匀性，从而实现发动机的小型化和高燃烧效率，达到节能减排的目的。
具体实施方式
下面将结合具体的实施例对本发明所述的螺栓用钢及其制备方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-10以及对比例1-4
实施例1-10的螺栓用钢均采用以下步骤制得：
(1)按照表1-1和表1-2所示的化学成分对钢水进行冶炼：经电炉或转炉冶炼后进行炉外精炼，炉外精炼采用LF炉以及VD或RH脱气处理工艺，冶炼过程中调整合成渣成分和加入量，其中在冶炼过程中控制真空脱气时间＞15min。
(2)对经冶炼的钢水进行铸造，制得坯料：采用大方坯连铸机浇注方坯，在铸造过程中，可以采用氩气保护，大方坯尺寸可以控制为300-450mm，通过调整连铸过程中拉速、冷却及末端轻压下参数达到坯料心部碳偏析低于1.10。
(3)对坯料进行粗轧：采用二火成材工艺，将连铸坯于1100-1250℃温度下初轧开坯为150-250mm方坯料。方坯料经超声波探伤、磁粉探伤、砂轮修模、补充磁粉探伤及修模后，进入加热炉加热，在坯料加热过程中，控制加热温度为960-1150℃，保温时间为1.5-3.0h。
(4)高速线材轧制，制得尺寸规格为Ф6-26mm的盘条：控制轧制速度为8-90m/s，精轧机组进口温度为850-970℃，减定径机组进口温度为800-950℃，吐丝温度为750-900℃。
(5)对盘条进行斯太尔摩控冷：采用14台斯太尔摩线风机对盘条进行斯太尔摩控冷，其中：风机F1-F5的风量≤80％，风机F6-F12的风量≤50％，风机F13-F14的风量≤45％，通过调整斯太尔摩线风机的风量控制盘条组织转变，优化盘条组织。
(6)热处理：包括对盘条依次进行球化热处理、拉拔和调质热处理，其中控制球化热处理的保温温度为760-790℃，保温时间为4-12h，保温后缓慢冷却，冷却速度低于40℃/h，控制盘条拉拔减面率为5-30％，控制调质热处理加热温度为850-950℃，回火温度为500-600℃。
需要说明的是，本发明所述的实施例1-11的盘条均采用以上步骤制得，且其化学成分及相关工艺参数均满足本发明设计规范控制要求。而对比例1-4的对比盘条同样采用：冶炼、铸造、粗轧、高速线材轧制、斯太尔摩控冷和热处理的工艺流程制得，但其化学成分及相关工艺参数均存在未能满足本发明设计要求的参数。
表1列出了实施例1-10的螺栓用钢以及对比例1-4的对比钢的各化学元素的质量百分配比。
表1-1(wt％，余量为Fe和除Cu、P、S、O以及N之外的其他不可避免的杂质)
Figure PCTCN2022094924-appb-000001
表1-2
编号 Al/O V×(C+N)
实施例1 37.5 0.093
实施例2 21.4 0.099
实施例3 21.4 0.098
实施例4 30.0 0.099
实施例5 40.0 0.101
实施例6 35.0 0.121
实施例7 37.5 0.121
实施例8 25.0 0.067
实施例9 25.0 0.091
实施例10 25.0 0.123
对比例1 14.0 0
对比例2 13.3 0.217
对比例3 6.2 0.042
对比例4 30.0 0.088
表2-1和表2-2列出了实施例1-10的螺栓用钢以及对比例1-4的对比钢在上述步骤中的具体工艺参数。
表2-1
Figure PCTCN2022094924-appb-000002
表2-2
Figure PCTCN2022094924-appb-000003
将最终制得的实施例1-10的螺栓用钢以及对比例1-4的对比钢分别取样，并对各实施例和对比例的钢样本进行观察分析，以得到各实施例和对比例的钢的组织。观察完成后对各实施例和对比例的钢样本分别进行力学性能测试，将所得的观察结果和力学性能测试结果分别列于表3和表4中。
相关力学性能测试方法，如下所述：
拉伸试验：在室温条件下，按照GB/T 228.1-2010《金属材料拉伸试验》进行检测。
表3列出了实施例1-10的螺栓用钢以及对比例1-4的对比钢的组织观察结果。
表3
Figure PCTCN2022094924-appb-000004
如表3所示，需要说明的是，本发明中，在实施例1-10的螺栓用钢的微观组织包括回火索氏体。
此外，需要说明的是，在本发明所述的实施例1-10的螺栓用钢中，其微观组织还具有V的碳氮析出物，其中，V的尺寸在5-50nm之间的碳氮析出物的数量占比高于90％。
另外，在本发明所述的实施例1-10的螺栓用钢中，钢中的夹杂物尺寸＜38μm。
表4列出了实施例1-10的螺栓用钢以及对比例1-4的对比钢的力学性能测试结果。
表4
Figure PCTCN2022094924-appb-000005
需要说明的是，上述取样的实施例1-10的螺栓用钢以及对比例1-4的对比钢在加工生产后，可以获得对应的螺栓。对得到的实施例1-10和对比例1-4的螺栓进行相关各项性能的测试，将所得的性能测试结果列于表5之中。
表5列出了采用实施例1-10的螺栓用钢以及对比例1-4的对比钢加工制得的螺栓的性能测试结果。
表5
Figure PCTCN2022094924-appb-000006
结合表4和表5可以看出，对比例1-4的对比螺栓在性能上均明显逊色于实施例1-10的螺栓。在本发明中，实施例1-10的螺栓用钢均具有良好的性能，其抗拉强度≥1200MPa，屈强比＞0.9，充氢慢拉伸强度损失≤10％，螺栓拧紧扭住波动≤8％，螺栓疲劳寿命＞75000次。
采用本发明的该螺栓用钢可以加工制得均质高强耐久螺栓，制得的均质高强耐久螺栓能够有效应用于汽车发动机、高端精密机械设备等对拧紧力要求较高的应用场景，可显著提高发动机效率及机械设备加工精度，其市场应用前景广阔，具有十分良好的经济效益和社会效益。
此外，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或具体实施例中所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
需要注意，以上所列举的实施例仅为本发明的具体实施例。显然本发明不局限于以上实施例，随之做出的类似变化或变形是本领域技术人员能从本发明公开的内容直接得出或者很容易便联想到的，均应属于本发明的保护范围。

Claims (16)

  1. 一种螺栓用钢，其特征在于，除Fe和不可避免的杂质之外，所述螺栓用钢还含有以质量百分比计的如下化学元素：
    C：0.37-0.45％；
    Si：0.01-0.08％；
    Mn：0.45-0.80％；
    Cr：0.90-1.30％；
    Mo：0.20-0.45％；
    Ni：0.10-0.30％；
    V：0.15-0.30％；
    Al：0.015-0.035％。
  2. 如权利要求1所述的螺栓用钢，其特征在于，所述螺栓用钢由以质量百分比计的如下化学元素组成：
    C：0.37-0.45％；
    Si：0.01-0.08％；
    Mn：0.45-0.80％；
    Cr：0.90-1.30％；
    Mo：0.20-0.45％；
    Ni：0.10-0.30％；
    V：0.15-0.30％；
    Al：0.015-0.035％；
    余量为Fe和不可避免的杂质。
  3. 如权利要求2所述的螺栓用钢，其特征在于，杂质元素以质量百分比计的含量满足：Cu≤0.05％；P≤0.01％；S≤0.010％；O≤0.001％；N≤0.005％。
  4. 如权利要求3所述的螺栓用钢，其特征在于，元素Al和O以质量百分比计的含量比满足：Al/O＞20。
  5. 如权利要求3所述的螺栓用钢，其特征在于，元素V、C和N以质量百分比计的含量满足：V×(C+N)≤1/8。
  6. 如权利要求1或2所述的螺栓用钢，其特征在于，所述螺栓用钢的微观组 织包括回火索氏体。
  7. 如权利要求6所述的螺栓用钢，其特征在于，所述微观组织还具有V的碳氮析出物，其中尺寸为5-50nm的V的碳氮析出物的数量占比高于90％。
  8. 如权利要求1或2所述的螺栓用钢，其特征在于，所述螺栓用钢中夹杂物尺寸＜38μm。
  9. 如权利要求1或2所述的螺栓用钢，其特征在于，所述螺栓用钢的性能满足：抗拉强度≥1200MPa，屈强比＞0.9，充氢慢拉伸强度损失≤10％，螺栓拧紧扭住波动≤8％，螺栓疲劳寿命＞75000次。
  10. 如权利要求1-9中任意一项所述的螺栓用钢的制造方法，其特征在于，所述方法包括以下步骤：
    (1)对钢水进行冶炼；
    (2)对经冶炼的钢水进行铸造，制得坯料；
    (3)对坯料进行粗轧；
    (4)高速线材轧制，制得盘条；
    (5)对盘条进行斯太尔摩控冷；
    (6)热处理：包括对盘条依次进行球化热处理、拉拔和调质热处理，其中球化热处理的保温温度为760-790℃，保温时间为4-12h，保温后缓慢冷却，冷却速度低于40℃/h，在拉拔中控制盘条拉拔减面率为5-30％，调质热处理的加热温度为850-950℃，回火温度为500-600℃。
  11. 如权利要求10所述的制造方法，其特征在于，在步骤(1)中，在冶炼过程中控制真空脱气时间＞15min。
  12. 如权利要求10所述的制造方法，其特征在于，在步骤(2)中，在铸造过程中控制坯料心部碳偏析低于1.10。
  13. 如权利要求10所述的制造方法，其特征在于，在步骤(3)中，粗轧包括在初轧后对坯料进行加热，在坯料加热过程中，控制加热温度为960-1150℃，保温时间为1.5-3.0h。
  14. 如权利要求10所述的制造方法，其特征在于，在步骤(4)中，控制轧制速度为8-90m/s。
  15. 如权利要求14所述的制造方法，其特征在于，在步骤(4)中，控制精轧机组进口温度为850-970℃，减定径机组进口温度为800-950℃，吐丝温 度为750-900℃。
  16. 如权利要求10所述的制造方法，其特征在于，在步骤(5)中，斯太尔摩控冷采用至少14台风机，其中风机F1-F5的风量≤80％，风机F6-F12的风量≤50％，风机F13-F14的风量≤45％。
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