CN115505692B - High-strength bridge steel and heat treatment method thereof - Google Patents

High-strength bridge steel and heat treatment method thereof Download PDF

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CN115505692B
CN115505692B CN202211107808.0A CN202211107808A CN115505692B CN 115505692 B CN115505692 B CN 115505692B CN 202211107808 A CN202211107808 A CN 202211107808A CN 115505692 B CN115505692 B CN 115505692B
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bridge steel
steel
strength bridge
strength
temperature
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CN115505692A (en
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马宏驰
李晓刚
程学群
刘智勇
黄运华
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University of Science and Technology Beijing USTB
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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
    • 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
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    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • 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
    • 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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention provides high-strength bridge steel and a heat treatment method thereof, and belongs to the technical field of steel materials. The heat treatment method comprises the steps of sequentially carrying out two-phase zone heat preservation, water cooling quenching and medium temperature tempering, heating the high-strength bridge steel in the two-phase temperature zone between (Ac 1+20 ℃) and (Ac 3-20 ℃), carrying out water cooling treatment after heat preservation for 20-60 min, and then carrying out medium temperature tempering at 400-500 ℃ for 30-90 min to obtain the high-strength bridge steel containing ferrite and granular bainite dual-phase structure. According to the invention, the double-phase structure containing undissolved ferrite is obtained through heat preservation and air cooling treatment between the two-phase regions, and then the yield ratio of the high-strength bridge steel can be greatly reduced through the coordinated deformation of the soft phase and the hard phase, and the high-strength bridge steel has excellent corrosion fatigue resistance.

Description

High-strength bridge steel and heat treatment method thereof
Technical Field
The invention relates to the technical field of steel materials, in particular to high-strength bridge steel and a heat treatment method thereof.
Background
With the development of bridge construction technology and the rising of large-span bridges, the strength level of bridge steel reaches 690MPa, and is mainly prepared by TMCP (thermo-mechanical control process) +T or thermal refining, and the thermal treatment process often causes that the yield ratio of the high-strength steel is higher, is difficult to reach below 0.85 of national standard requirements of the high-strength bridge steel, is easy to generate brittle fracture under typhoons, earthquakes or other overload conditions, and has higher corrosion fatigue fracture risk in severe marine environments. The high-strength bridge steel or the cross-sea bridge built in the coastal environment is severely corroded by the marine environment due to long-term service in the marine atmospheric environment with high humidity and high salt mist, and simultaneously bears larger dead weight and traffic fatigue load, and has higher risk of corrosion fatigue failure, so that the high-strength bridge steel generally requires lower yield ratio, corrosion resistance, stress corrosion resistance or corrosion fatigue performance besides higher toughness, low-temperature toughness and weldability.
In the steel production and manufacturing process, different performance requirements are generally achieved through different heat treatment systems, and the yield ratio is a very important performance parameter for bridge steel. The traditional thermal process of quenching, low-temperature tempering or quenching and high-temperature tempering can obtain tempered martensite or tempered sorbite high-strength steel, and has good obdurability matching. However, the high strength steel obtained by the two heat treatment processes tends to have a high yield ratio (generally more than 0.9), and the stress corrosion and corrosion fatigue sensitivity are also high.
Disclosure of Invention
The invention aims to provide high-strength bridge steel and a heat treatment method thereof, which can obtain the high-strength bridge steel with high strength, low yield ratio and excellent corrosion fatigue resistance.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a heat treatment method of high-strength bridge steel, which comprises the following steps:
after the high-strength bridge steel is insulated in a two-phase region, carrying out water cooling treatment, and carrying out medium-temperature tempering on the obtained steel;
the heat preservation temperature of the two-phase region is (Ac 1+20 ℃) to (Ac 3-20 ℃) and the heat preservation time is 20-60 min; ac1 is the transformation temperature at which austenite transformation begins to occur when the steel grade is heated; ac3 is the phase transition temperature at which the steel grade undergoes complete austenite transformation;
the temperature of the intermediate tempering is 400-500 ℃ and the time is 30-90 min;
the chemical components of the high-strength bridge steel comprise Nb, V, ti and Cu.
Preferably, the high-strength bridge steel comprises the following chemical components in percentage by mass: 0.08 to 0.15 percent of C, 0.15 to 0.30 percent of Si, 1.0 to 1.6 percent of Mn, less than or equal to 0.01 percent of S, less than or equal to 0.01 percent of P, 0.3 to 1.5 percent of Cr, 0.4 to 2.0 percent of Ni, 0.20 to 0.80 percent of Cu, 0.1 to 0.5 percent of Mo, 0.04 to 0.08 percent of Nb, 0.01 to 0.05 percent of V, 0.01 to 0.03 percent of Ti, 0.01 to 0.1 percent of Al, and the balance of Fe and unavoidable impurities.
Preferably, the high-strength bridge steel comprises the following chemical components in percentage by mass: 0.08% of C, 0.25% of Si, 1.55% of Mn, 0.001% of S, 0.009% of P, 0.45% of Cr, 0.49% of Ni, 0.21% of Cu, 0.28% of Mo, 0.04% of Nb, 0.03% of V, 0.016% of Ti, 0.04% of Al, and the balance of Fe and unavoidable impurities.
Preferably, the high-strength bridge steel comprises the following chemical components in percentage by mass: 0.11% of C, 0.20% of Si, 1.00% of Mn, 0.002% of S, 0.006% of P, 0.82% of Cr, 1.20% of Ni, 0.60% of Cu, 0.36% of Mo, 0.06% of Nb, 0.02% of V, 0.01% of Ti, 0.02% of Al, and the balance of Fe and unavoidable impurities.
Preferably, the temperature of the two-phase region is 780-800 ℃, and the temperature keeping time is 40-45 min.
Preferably, the medium temperature tempering temperature is 400-450 ℃ and the time is 30-60 min.
The invention provides the high-strength bridge steel obtained by the heat treatment method, and the microstructure of the high-strength bridge steel is a dual-phase structure of ferrite and granular bainite.
Preferably, the yield strength is more than or equal to 690MPa, and the yield ratio is less than 0.8.
The invention provides a heat treatment method of high-strength bridge steel, which comprises the steps of sequentially performing two-phase zone heat preservation, water cooling quenching and medium-temperature tempering, heating the high-strength bridge steel in a two-phase temperature zone between (Ac 1+20 ℃) and (Ac 3-20 ℃), performing water cooling treatment after heat preservation for 20-60 min, and performing medium-temperature tempering at 400-500 ℃ for 30-90 min to obtain the high-strength bridge steel with a ferrite and granular bainite dual-phase structure. According to the invention, through water cooling treatment after heat preservation between two phase regions, a double-phase structure containing undissolved ferrite is obtained, and then through the coordinated deformation of soft and hard phases, the yield ratio of the high-strength bridge steel can be greatly reduced, and the corrosion fatigue resistance is excellent.
The invention adopts a heat treatment method of two-phase region heat preservation and medium temperature tempering, ensures that the chemical components of the high-strength bridge steel comprise Nb, V, ti and Cu, and ensures that a large amount of dispersed nano precipitated phases (NbC and TiC) are precipitated in the steel through the strengthening effect of carbide precipitated phases of Nb, V and Ti and nano Cu particles on a ferrite matrix so as to prevent austenite grains from growing up when the two-phase region is heated and insulated, form fine austenite grains and subsequent fine-grain bainite, and improve the coordination deformability and tensile strength so as to improve the yield ratio; meanwhile, a (TiNb) C precipitated phase is reserved in the tempering stage, a large amount of nano Cu particle precipitated phase is precipitated, a ferrite matrix is reinforced, the yield strength of the bridge steel is ensured to be higher than 690MPa, and the high-strength bridge steel has high strength and low yield ratio. In addition, the heat treatment method can also greatly improve the corrosion and fatigue resistance of the high-strength steel in the marine environment, and has important reference significance for the production and manufacture of the high-strength bridge steel.
In the heat treatment method, soft-phase ferrite is partially formed in the heat preservation process of the two-phase region, austenite is formed in the other part, water-cooling quenching is carried out on the austenite to form hard-phase bainite, then nano Cu particles are separated out through medium-temperature tempering to improve the strength of the ferrite, reduce the hardness difference between internal stress and soft and hard phases and improve the toughness of plastic.
The heat treatment method can regulate and control the two-phase volume ratio of ferrite and bainite by controlling the quenching temperature, and further regulate and control the yield strength and the yield ratio of the high-strength bridge steel.
Drawings
FIG. 1 is a microstructure topography of example 1 and comparative examples 1-2, (a) example 1, (b) comparative example 1, (c) comparative example 2;
FIG. 2 is a morphology and composition of precipitated phase TEM of the high-strength bridge steel prepared in example 1;
FIG. 3 is a graph showing stress strain curves of the steels prepared in examples 1 to 2 and comparative examples 1 to 2 in air at room temperature;
FIG. 4 is a graph of corrosion fatigue S-N in a simulated marine environment for the steels prepared in example 1 and comparative examples 1-2;
FIG. 5 is a profile of corrosion fatigue fracture in a simulated marine environment for the steels prepared in example 1 and comparative examples 1-2.
Detailed Description
The invention provides a heat treatment method of high-strength bridge steel, which comprises the following steps:
after the high-strength bridge steel is insulated in a two-phase region, carrying out water cooling treatment, and carrying out medium-temperature tempering on the obtained steel;
the heat preservation temperature of the two-phase region is (Ac 1+20 ℃) to (Ac 3-20 ℃) and the heat preservation time is 20-60 min; ac1 is the transformation temperature at which austenite transformation begins to occur when the steel grade is heated; ac3 is the phase transition temperature at which the steel grade undergoes complete austenite transformation;
the temperature of the intermediate tempering is 400-500 ℃ and the time is 30-90 min;
the chemical components of the high-strength bridge steel comprise Nb, V, ti and Cu.
In the present invention, the desired materials are those of well known origin to those skilled in the art unless specified otherwise.
In the invention, the high-strength bridge steel comprises the following chemical components in percentage by mass: 0.08 to 0.15 percent of C, 0.15 to 0.30 percent of Si, 1.0 to 1.6 percent of Mn, less than or equal to 0.01 percent of S, less than or equal to 0.01 percent of P, 0.3 to 1.5 percent of Cr, 0.4 to 2.0 percent of Ni, 0.20 to 0.80 percent of Cu, 0.1 to 0.5 percent of Mo, 0.04 to 0.08 percent of Nb, 0.01 to 0.05 percent of V, 0.01 to 0.03 percent of Ti, 0.01 to 0.1 percent of Al, and the balance of Fe and unavoidable impurities.
In the present invention, the chemical components of the high-strength bridge steel are more preferably 0.08 to 0.11% by mass, more preferably 0.20 to 0.30% by mass, more preferably 0.4 to 1.0% by mass, and more preferably 0.4 to 1.0% by mass of Cr.
The source or specification of the high-strength bridge steel is not particularly limited, and the high-strength bridge steel with the composition is obtained according to a manner well known in the art.
In the embodiment of the invention, the chemical components of the high-strength bridge steel preferably comprise, in mass percent: 0.08% of C, 0.25% of Si, 1.55% of Mn, 0.001% of S, 0.009% of P, 0.45% of Cr, 0.49% of Ni, 0.21% of Cu, 0.28% of Mo, 0.04% of Nb, 0.03% of V, 0.016% of Ti, 0.04% of Al, and the balance of Fe and unavoidable impurities.
In the embodiment of the invention, the chemical components of the high-strength bridge steel preferably comprise, in mass percent: 0.11% of C, 0.20% of Si, 1.00% of Mn, 0.002% of S, 0.006% of P, 0.82% of Cr, 1.20% of Ni, 0.60% of Cu, 0.36% of Mo, 0.06% of Nb, 0.02% of V, 0.01% of Ti, 0.02% of Al, and the balance of Fe and unavoidable impurities.
In the invention, nb, V and Ti are added to prepare refined grains during the heat treatment of the two-phase region, and the yield strength is improved; cu is convenient for precipitating nano Cu particles to strengthen ferrite in the tempering stage, and tempering softening is avoided.
In the present invention, the high-strength bridge steel is preferably used in the form of a steel plate, and the rolling process of the steel plate and the thickness thereof are not particularly limited, and the steel plate may be rolled according to a process well known in the art and the required thickness may be adjusted according to actual demands. In an embodiment of the present invention, the thickness of the steel plate is specifically 16mm or 20mm.
In the invention, the steel plate of the high-strength bridge steel is preferably TMCP rolled steel plate, and the specific rolling process is preferably as follows: introducing continuous casting blanks of corresponding components of high-strength bridge steel into a heating furnace, soaking at 1200 ℃ for 4 hours, performing rough rolling after high-pressure descaling, wherein the initial rolling temperature and the final rolling temperature are 1150-1180 ℃ and 1020-1050 ℃ respectively, and the rolling reduction is 70%; and then finish rolling to 16-20 mm thick in a non-recrystallization zone, wherein the initial rolling temperature is 800-810 ℃, the final rolling temperature is 780-830 ℃, more preferably 790-800 ℃, then laminar cooling is carried out, the reddening temperature is 350-450 ℃, more preferably 400-410 ℃, and then air cooling is carried out to room temperature, thus obtaining the steel plate. The method for obtaining the continuous casting blank is not particularly limited, and the method is carried out according to a process well known in the art; the thickness of the continuous casting blank is preferably more than or equal to 200mm, more preferably 260mm.
In the present invention, the two-phase region has a heat-retaining temperature of (Ac 1+20℃) to (Ac 3-20 ℃), more preferably 780-800 ℃, and a heat-retaining time of 20-60 minutes, preferably 40-45 minutes; ac1 is the transformation temperature at which austenite transformation begins to occur when the steel grade is heated; ac3 is the transformation temperature at which the steel grade undergoes a complete austenitic transformation.
In the present invention, for specific steel grades of different chemical compositions, the Ac1 and Ac3 temperatures of the steel grades are preferably measured by a thermal expansion method, and the temperature range of the two-phase zone quenching is determined according to the measured Ac1 and Ac3 temperatures. The process of measuring the Ac1 and Ac3 temperatures by the thermal expansion method is not particularly limited, and may be performed according to a process well known in the art.
The invention limits the heat preservation temperature of the two-phase region to (Ac 1+20 ℃) to (Ac 3-20 ℃) so as to ensure that partial austenitization occurs to form fine island austenite, and the two-phase region is subjected to water cooling treatment after heat preservation so as to form a ferrite and granular bainite two-phase structure.
After the two-phase region is insulated, the invention preferably carries out water cooling treatment and then intermediate temperature tempering. The process of the water passing cooling treatment is not particularly limited, and the water passing cooling treatment is carried out to room temperature according to the process well known in the art.
In the present invention, the medium tempering temperature is 400 to 500 ℃, preferably 400 to 450 ℃, for 30 to 90 minutes, more preferably 30 to 60 minutes. The invention limits the medium temperature tempering temperature to 400-500 ℃, on one hand, the internal stress and dislocation density can be effectively reduced, on the other hand, the M/A component in the granular bainite is partially decomposed to form carbide and tiny cementite, the hard and brittle M/A component is prevented from promoting crack initiation, and meanwhile, nano Cu particles can be greatly separated out in the temperature area, the separation strengthening effect is generated on a ferrite matrix, and the strength loss caused by tempering softening is compensated. The invention limits the medium temperature tempering time to 30-90 min, ensures a large amount of precipitated nano Cu particles, simultaneously avoids the remarkable coarsening of the nano Cu particles after more than 90min, reduces the precipitation strengthening effect and wastes energy.
After the medium temperature tempering is finished, the method is preferably air-cooled to room temperature to obtain the high-strength bridge steel.
The invention provides the high-strength bridge steel obtained by the heat treatment method, and the microstructure of the high-strength bridge steel is a dual-phase structure of ferrite and granular bainite.
In the invention, the yield strength of the high-strength bridge steel is more than or equal to 690MPa, and the yield ratio is less than 0.8.
The technical solutions of the present invention will be clearly and completely described in the following in connection with the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The high-strength bridge steel comprises the following chemical components in percentage by mass: c:0.08%, si:0.25%, mn:1.55%, S:0.001%, P:0.009%, cr:0.45%, ni:0.49%, cu:0.21%, mo:0.28%, nb:0.04%, V:0.03%, ti:0.016%, al:0.04% of Fe and the balance of unavoidable impurities;
rolling the continuous casting billet corresponding to the chemical components into a steel plate with the thickness of 16mm by adopting a TMCP process: introducing a continuous casting billet with the thickness of 260mm into a heating furnace, soaking for 4 hours at 1200 ℃, performing rough rolling after high-pressure descaling, wherein the initial rolling temperature and the final rolling temperature are 1150 ℃ and 1020 ℃ respectively, and the rolling reduction is 70%; then finish rolling in a non-recrystallization zone until the thickness is 16mm, wherein the initial rolling temperature is 800 ℃, the final rolling temperature is 790 ℃, then laminar cooling is carried out, the reddening temperature is 410 ℃, and then air cooling is carried out until the room temperature, thus obtaining the steel plate with the thickness of 16 mm;
quenching the steel plate in a two-phase zone: the Ac1 and Ac3 temperatures of the chemical component steel are 740 ℃ and 880 ℃ respectively measured by a thermal expansion instrument, the steel plate with the thickness of 16mm is put into a heating furnace, heated to 800 ℃, kept warm for 40min, cooled to room temperature through water, and a quenched steel plate containing ferrite and granular bainite dual-phase structures is obtained;
and carrying out medium temperature tempering on the quenched steel plate: and (3) introducing the quenched steel plate into a tempering furnace, tempering at 400 ℃ for 60min, and air-cooling to room temperature to obtain the high-strength bridge steel.
Example 2
The high-strength bridge steel comprises the following chemical components in percentage by mass: c:0.11%, si:0.20%, mn:1.00%, S:0.002%, P:0.006%, cr:0.82%, ni:1.20%, cu:0.60%, mo:0.36%, nb:0.06%, V:0.02%, ti:0.01%, al:0.02% of Fe and the balance of unavoidable impurities;
rolling the continuous casting billet corresponding to the chemical components into a steel plate with the thickness of 20mm by adopting a TMCP process: introducing a continuous casting blank with the thickness of 260mm into a heating furnace, soaking for 4 hours at 1200 ℃, performing rough rolling after high-pressure descaling, wherein the initial rolling temperature and the final rolling temperature are 1180 ℃ and 1050 ℃, and the reduction rate is 70%; then finish rolling in a non-recrystallization zone until the thickness is 20mm, wherein the initial rolling temperature is 810 ℃, the final rolling temperature is 800 ℃, then laminar cooling is carried out, the reddening temperature is 400 ℃, and then air cooling is carried out until the room temperature, thus obtaining the steel plate with the thickness of 20 mm;
quenching the steel plate in a two-phase zone: measuring the Ac1 and Ac3 temperatures of the chemical component steel by a thermal expansion instrument to be 728 ℃ and 860 ℃, loading the steel plate with the thickness of 20mm into a heating furnace, heating to 780 ℃, preserving heat for 45min, and cooling to room temperature by passing through water to obtain a quenched steel plate with a ferrite and granular bainite dual-phase structure;
and carrying out medium temperature tempering on the quenched steel plate: and (3) introducing the quenched steel plate into a tempering furnace, tempering at 450 ℃ for 60min, and air-cooling to room temperature to obtain the high-strength bridge steel. The mechanical property test at room temperature of the high-strength bridge steel obtained in the example 2 shows that the high-strength bridge steel has higher toughness and lower yield ratio (0.75).
Comparative example 1
The same batch of TMCP rolled steel plates as in example 1 are adopted, the rolled steel plates are subjected to direct tempering heat treatment, the tempering temperature is 400 ℃, the tempering time is 100min, and the steel plates are subjected to air cooling to room temperature after tempering, so that the high-strength steel with the lath and granular bainite mixed structure is obtained.
Comparative example 2
The same steel sheet (same composition) as in example 2 was subjected to tempering heat treatment in the following steps: water cooling quenching and high temperature tempering, wherein the quenching temperature is 910 ℃, the heat preservation time is 40min, water quenching is carried out to room temperature, and then the high temperature tempering treatment is carried out for 60min at 650 ℃ to obtain 690 MPa-grade quenched and tempered high-strength steel.
Characterization and performance testing
1) FIG. 1 is a microstructure topography of example 1 and comparative examples 1-2, (a) example 1, (b) comparative example 1, (c) comparative example 2; as shown in fig. 1, the bridge steel obtained in example 1 had a ferrite+fine island-like granular bainite dual-phase structure, the high-strength steel of comparative example 1 had a mixed structure of laths and granular bainite, and the tempered high-strength steel of comparative example 2 had an equiaxed tempered sorbite structure.
2) Fig. 2 shows the morphology and composition of the precipitated phase TEM of the high-strength bridge steel prepared in example 1, and as can be seen from fig. 2, the nano precipitated phase precipitated in the ferrite matrix is mainly a (NbTi) C precipitated phase with a size of 30-50 nm and a large number of epsilon-Cu particles dispersed and distributed about 10nm, and these nano precipitated phases greatly improve the toughness of the bridge steel.
3) The mechanical properties of the steel grades prepared in examples 1-2 and comparative examples 1-2 were tested, and the stress-strain curves of the four steels obtained according to the national standard GB/T228-09 test are shown in FIG. 3, and the mechanical properties obtained are shown in Table 1.
As can be seen from FIG. 3 and Table 1, the high-strength bridge steel obtained by the heat treatment method has the yield strength of more than 700MPa, the tensile strength of approximately 1000MPa, higher elongation and surface shrinkage, higher strain hardening capacity, obviously lower yield ratio (below 0.8) and excellent toughness matching. The yield ratio of the tempered high-strength steel of comparative example 1 and that of the tempered high-strength steel of comparative example 2 are both high (0.9 or more).
TABLE 1 mechanical property data of the grades obtained in examples 1 to 2 and comparative examples 1 to 2
4) The steel grades prepared in example 1 and comparative examples 1 to 2 were subjected to a simulated marine environment corrosion fatigue test, and according to ASTM E466-2007, a test apparatus was referred to in patent No. CN212693564U, and the fatigue test specimens were polished longitudinally to 2000# by sandpaper, then washed with alcohol and blow-dried, packaged in an organic glass box, and mounted on a fatigue tester, and a humidifier spray apparatus was used to continuously introduce a salt spray into the test box, wherein the simulated solution in the humidifier was 3.5wt% NaCl+0.1wt% NaHSO 3 Simulating the severe marine atmospheric environment of industrial pollution. The stress amplitude of the fatigue test was set to 0.5 and the frequency was 1Hz, and the corrosion fatigue test of three steels (example 1 and comparative examples 1 to 2) was performed under different stress level conditions, resulting in corrosion fatigue S-N curves of the three steels as shown in FIG. 4.
As can be seen from fig. 4, the high-strength bridge steel prepared in example 1 has excellent corrosion fatigue resistance, and compared with comparative example 2, the corrosion fatigue resistance in the marine environment is greatly improved, and the high stress concentration is not easy to generate due to the coordinated deformation of the two-phase structure. The corrosion fatigue performance of comparative example 1 is also excellent, and the high density grain boundary and bainite lath can effectively block the propagation of fatigue cracks due to the fine grain size generated by TMCP rolling, but the yield ratio of comparative example 1 is too high, the toughness is poor, and a large number of M/a components exist, so that the initiation of corrosion fatigue cracks is easy to be induced, and the surface of the sample after corrosion fatigue fracture is obvious from fig. 5 (b).
FIG. 5 shows the side profile of corrosion fatigue fracture in simulated marine environment for the steels prepared in example 1 and comparative examples 1-2, (a) example 1, (b) comparative example 1, (c) comparative example 2; as can be seen from fig. 5 (a), the steel surface prepared in example 1 has less fatigue cracks; whereas the steel surfaces prepared in comparative example 1 and comparative example 2 both produced a large number of microcracks. As shown in fig. 5 (b), the steel of comparative example 1 was liable to develop a large number of dense microcracks on the surface, and to interconnect to form a stepped macrocrack, and as shown in fig. 5 (c), comparative example 2 was liable to develop corrosion fatigue microcracks along the prior austenite grain boundaries, resulting in a lower corrosion fatigue life.
As can be seen from the above examples and comparative examples, the high-strength bridge steel obtained by the heat treatment method of the present invention has significant overall performance advantages over the comparative examples, not only has good toughness matching, in particular, has a lower yield ratio (as low as 0.75), but also has excellent corrosion fatigue cracking resistance in severe marine atmospheric environments.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims (7)

1. The heat treatment method of the high-strength bridge steel is characterized by comprising the following steps of:
after the high-strength bridge steel is insulated in a two-phase region, carrying out water cooling treatment, and carrying out medium-temperature tempering on the obtained steel;
the heat preservation temperature of the two-phase region is (Ac 1+20 ℃) to (Ac 3-20 ℃) and the heat preservation time is 40-45 min; ac1 is the transformation temperature at which austenite transformation begins to occur when the steel grade is heated; ac3 is the phase transition temperature at which the steel grade undergoes complete austenite transformation;
the temperature of the intermediate tempering is 400-500 ℃ and the time is 30-90 min;
the high-strength bridge steel comprises the following chemical components: 0.08-0.15% of C, 0.15-0.30% of Si, 1.0-1.6% of Mn, less than or equal to 0.01% of S, less than or equal to 0.01% of P, 0.3-1.5% of Cr, 0.4-2.0% of Ni, 0.20-0.80% of Cu, 0.1-0.5% of Mo, 0.04-0.08% of Nb, 0.01-0.05% of V, 0.01-0.03% of Ti, 0.01-0.1% of Al, and the balance of Fe and unavoidable impurities.
2. The heat treatment method according to claim 1, wherein the high-strength bridge steel comprises the chemical components in mass percent: 0.08% of C, 0.25% of Si, 1.55% of Mn, 0.001% of S, 0.009% of P, 0.45% of Cr, 0.49% of Ni, 0.21% of Cu, 0.28% of Mo, 0.04% of Nb, 0.03% of V, 0.016% of Ti, 0.04% of Al, and the balance of Fe and unavoidable impurities.
3. The heat treatment method according to claim 1, wherein the high-strength bridge steel comprises the chemical components in mass percent: 0.11% of C, 0.20% of Si, 1.00% of Mn, 0.002% of S, 0.006% of P, 0.82% of Cr, 1.20% of Ni, 0.60% of Cu, 0.36% of Mo, 0.06% of Nb, 0.02% of V, 0.01% of Ti, 0.02% of Al, and the balance of Fe and unavoidable impurities.
4. The heat treatment method according to claim 1, wherein the two-phase region has a holding temperature of 780-800 ℃.
5. The heat treatment method according to claim 1, wherein the medium tempering temperature is 400-450 ℃ and the time is 30-60 min.
6. The high-strength bridge steel obtained by the heat treatment method according to any one of claims 1 to 5, wherein the microstructure of the high-strength bridge steel is a ferrite+granular bainite dual-phase structure.
7. The high-strength bridge steel according to claim 6, wherein the yield strength is equal to or greater than 690MPa and the yield ratio is < 0.8.
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