CN109055858B - refractory weathering steel with yield strength not less than 620MPa for welding structure and production method thereof - Google Patents

refractory weathering steel with yield strength not less than 620MPa for welding structure and production method thereof Download PDF

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CN109055858B
CN109055858B CN201811015759.1A CN201811015759A CN109055858B CN 109055858 B CN109055858 B CN 109055858B CN 201811015759 A CN201811015759 A CN 201811015759A CN 109055858 B CN109055858 B CN 109055858B
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steel
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CN109055858A (en
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童明伟
卜勇
张开广
范巍
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Wuhan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper

Abstract

The invention relates to fire-resistant weather-resistant steels with yield strength of more than or equal to 620MPa for welding structures and a production method thereof, wherein the fire-resistant weather-resistant steels comprise the following main components, by mass, 0.035-0.075% of C, 0.13-0.24% of Si, 1.56-1.82% of Mn, less than or equal to 0.003% of P, less than or equal to 0.002% of S, 0.12-0.23% of Mo, 0.21-0.40% of W, 0.22-0.48% of Cu, 0.21-0.43% of Ni, 0.048% of Nb, 0.058-0.077% of V, 0.045-0.068% of Ti, 0.0022-0.0052% of Ca and 0.0028-0.0065%.

Description

refractory weathering steel with yield strength not less than 620MPa for welding structure and production method thereof
Technical Field
The invention belongs to the technical field of low-alloy high-strength steel manufacturing, and relates to kinds of fire-resistant weather-resistant steel with yield strength of more than or equal to 620MPa for a welding structure and a production method thereof.
Background
With the continuous development of ferrous metallurgy technology, structural members such as columns and beams of steel structures all provide new requirements for the strength, fire resistance, corrosion resistance, earthquake resistance and other properties of steel plates, while the poor fire resistance, fire resistance and corrosion resistance of common steel structures in the construction industry face severe tests. In recent years, metallurgical workers at home and abroad actively develop researches on fire-resistant, weather-resistant, earthquake-resistant and other series of steels, and the fire-resistant and weather-resistant steels can not only make up the defect of poor fire-resistant, disaster-resistant and corrosion-resistant performances of common steel structures, greatly reduce fire-resistant coatings and weather-resistant coatings, reduce environmental pollution, but also improve the utilization efficiency of resources and energy, and meet the requirements of national policy and administration.
Chinese patent application No. CN1354273A discloses high-performance fire-resistant weather-resistant construction steel and a production method thereof, the construction steel contains C, Si, Mn, P, S, Cr, Mo, Ti, Als, N, O, Cr, Ni, Cu, Ca and B, in addition, or more than of Nb, V and RE, and the balance of Fe, and the steel has high strength, high toughness and excellent fire-resistant and weather-resistant performances after smelting, rolling and heat treatment.
The products of the Chinese invention patents disclosed in the Chinese invention patent application numbers CN201110247615.0, CN200910011963.0, CN200910272414.9, CN200910045146.7 and CN201110080774.6 all have good fire resistance, but have the defect that the products do not have weather resistance; in addition, the products of the invention disclosed in Chinese patent application Nos. CN201010113848.7, CN03804658.X and CN200910056602.8 have good weather resistance, but have the disadvantage of no fire resistance.
Chinese patent application No. CN201110247615.0 discloses fire-resistant and earthquake-resistant steel for construction, which comprises (by weight percent) 0.1-0.18% of C, 0.1-0.50% of Si, 1-1.80% of Mn, less than or equal to 0.025% of P, less than or equal to 0.015% of S, less than or equal to 0.50% of Cr, less than or equal to 0.30% of Mo, less than or equal to 0.04% of Al, less than or equal to 0.007% of N, less than or equal to 0.006% of Ca, less than or equal to 0.050% of Nb, less than or equal to 0.055% of V, less than or equal to 0.035% of Ti, and Nb + V + Ti less than or equal to 0.055%, with the balance being Fe and inevitable impuritiesp0.2(600 ℃ yield Strength)/Rp0.2(room temperature yield strength) is not less than 2/3, and the yield ratio (yield ratio R) is lowp0.2/RmThe steel is limited to steel with the yield strength of 235-460 MPa, the content of P, S in the steel is high, definite influence is caused on the subsequent welding performance, and in addition, the steel does not have good weather resistance.
The invention of Chinese patent application No. CN200910180490.7 discloses non-quenched and tempered acicular structure high-strength low-yield-ratio weathering steel and a preparation method thereof, the steel comprises the following components and the weight percentages of the basic components are that C is 0.03-0.08%, Si is 0.30-0.60%, Mn is 1.30-1.80%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, Cu is 0.30-0.60%, Ni is 0.20-0.50%, Cr is 0.40-0.80%, Mo is 0.10-0.40%, Nb is 0.030-0.080% and Ti is less than or equal to 0.04%, the optional components are two or more of Als and RE are less than or equal to 0.40kg/t steel or Ca is less than or equal to 0.005%, and the balance of Fe and impurities, the welding cold crack coefficient is low, the corrosion resistance index is high.
The invention Chinese patent application No. CN200910056602.8 discloses high corrosion resistance Cr-containing weathering steel with yield strength of more than 700MPa and excellent toughness and a manufacturing method thereof, wherein the weathering steel comprises, by mass, 0.02-0.10% of C, 0.1-0.4% of Si, 0.3-1.3% of Mn, less than or equal to 0.01% of P, less than or equal to 0.006% of S, 0.2-0.5% of Cu, 2.5-10% of Cr, 0.2-1.0% of Ni, 0.02-0.06% of Nb, 0.01-0.05% of Al, less than or equal to 0.005% of N, 0.02-0.10% of Ti and the balance Fe and inevitable impurities.
In addition, Chinese invention patent application numbers CN103695772A and CN103695773A respectively disclose a fire-resistant weather-resistant earthquake-resistant construction steel with yield strength of 550MPa and a production method thereof, and a fire-resistant weather-resistant earthquake-resistant construction steel with yield strength of 690MPa and a production method thereof, wherein the two pieces of construction steel contain C, Si, Mn, P, S, Nb, Ti, Mo, W, Mg, O, Sb or Zr or a mixture of two of the Sb and Zr in any proportion, and the balance of Fe and inevitable impurities, and the steel is subjected to molten iron desulphurization, converter smelting, vacuum treatment, Mg element addition, conventional continuous casting, heating, sectional rolling, cooling after final rolling and other processes, so that the steel has excellent fire-resistant, weather-resistant and earthquake-resistant properties and excellent comprehensive properties, but the defects of the two kinds of steel are that the welding property and the corrosion resistance are not ideal.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides kinds of fire-resistant weather-resistant steel with yield strength of more than or equal to 620MPa for a welding structure and a production method thereof, optimizes chemical components and a production process, and ensures that the produced product has high strength and toughness, high plasticity, low yield ratio, excellent fire resistance, weather resistance and lamellar tearing resistance, and also has good welding performance and cold processing performance.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
refractory and weather-resistant steels for welding structures with yield strength of more than or equal to 620MPa are provided, and the refractory and weather-resistant steels comprise, by mass, 0.035-0.075% of C, 0.13-0.24% of Si, 1.56-1.82% of Mn, less than or equal to 0.003% of P, less than or equal to 0.002% of S, 0.12-0.23% of Mo, 0.21-0.40% of W, 0.22-0.48% of Cu, 0.21-0.43% of Ni, 0.026-0.048% of Nb, 0.058-0.077% of V, 0.045-0.068% of Ti, 0.0022-0.0052% of Ca, 0.0028-0.0065% of Ta, 0.0022-0.0057% of N, 0.0024-0.0042% of O, and the balance of Fe and inevitable impurities of Ta 56 (Ca + 3)/(3 + 1.65)/(30% of C + 20/30/20) of Cu, 13 + 35/3 + 35% of Mo.
The invention also provides a production method of the refractory weather-resistant steel with the yield strength of more than or equal to 620MPa for the welding structure, which comprises the following process steps of smelting and casting into a casting blank, heating the casting blank, removing phosphorus by high-pressure water, controlling rolling, laminar cooling and the like, and the specific process steps are as follows:
1) smelting and casting into a casting blank: smelting and pouring molten iron to form a casting blank, and controlling Ca: 0.0022-0.0052%, Ta: 0.0028-0.0065%, and the vacuum treatment time is more than or equal to 30 min;
2) heating a casting blank: heating a casting blank to 700-720 ℃ at a heating rate of 6.0-7.0 ℃/s, then heating to 830-890 ℃ at a heating rate of 7.1-8.8 ℃/s, then heating to 1180-1230 ℃ at a heating rate of 9.0-11.5 ℃/s, preserving heat for 32-42 min, controlling the discharging temperature at 1120-1150 ℃, and carrying out high-pressure water dephosphorization treatment;
3) controlling rolling: the method comprises the steps of I-stage rolling, II-stage rolling and III-stage rolling, wherein the rolling start temperature of the I-stage rolling is not lower than 1100 ℃, the final rolling temperature is 1060-1080 ℃, the rolling passes are 3-5, and the total reduction rate of the passes is 50-60%; the rolling initial temperature of the second stage is 1020-1050 ℃, the rolling pass is 3-5, the single pass reduction rate is 15-25%, and the thickness of the plate blank after rolling is (h +40) mm; the rolling start temperature of the stage III is (980-9h/4) +/-5 ℃, the final rolling temperature is (880-7h/8) +/-5 ℃, the rolling passes are 4-6, and the cumulative reduction rate of the last three passes is 30-35%, wherein h is the thickness value of a finished product in mm;
4) laminar cooling: and (3) carrying out relaxation slow cooling on the steel plate rolled in the stage III for 2-8 s, then carrying out laminar cooling, controlling the opening cooling temperature to be (760+3h/4) +/-5 ℃, controlling the cooling speed to be 12-18 ℃/s, controlling the cooling re-reddening temperature to be 400-450 ℃, and finally carrying out air cooling to room temperature to obtain the refractory weathering steel for the welding structure with the yield strength of more than or equal to 620MPa, wherein h is the thickness value of a finished product in mm.
, the ratio of the water feeding amount to the water discharging amount in the laminar cooling in the step 4) is controlled to be 0.79 to 0.92.
The reason for selecting the chemical components of the invention is as follows:
c is an element essential for securing the strength of steel, and enhances the strength mainly by interstitial solid solution strengthening, and has a yield ratio lowering effect, C also forms fine carbide or carbonitride particles in combination with Nb, V, Ti, Mo, W and the like in steel, and has fine grain strengthening and precipitation strengthening effects, thereby further improving the strength, low-temperature impact toughness and weldability3The C and M-A structures increase, which aggravates carbon segregation and a tendency to generate cold cracks during welding, thereby deteriorating low-temperature impact toughness, welding properties, and cold-hot workability. Therefore, the content of C is limited to 0.035-0.075%.
Silicon (Si): the main functions of the Si element are solid solution strengthening and deoxidation, and because the Ca element and the Ta element are added in the invention, the Ca element and the Ta element have stronger binding force with [ O ] and form fine oxides to play a role in deoxidation, and only a small amount of Si is added to play a role in solid solution strengthening in order to balance and ensure that the low-temperature toughness and the welding performance are not damaged. Therefore, the Si content is limited to 0.13-0.24%.
Manganese (Mn): mn is an indispensable element for ensuring the toughness of steel and the low-temperature toughness of a welding heat affected zone, and a proper amount of Mn can eliminate the hot brittleness effect of S, O on the steel, improve the processability and cold brittleness tendency of the steel, and simultaneously has the functions of fine grain strengthening, strength improvement, plasticity improvement and low-temperature toughness. In order to ensure the above functions of Mn, the Mn content is not less than 1.56%, while excessive Mn weakens the bonding force of iron atoms during heating, accelerates the self-diffusion of the iron atoms, promotes the growth of austenite grains, and is not favorable for low-temperature toughness and welding performance. Therefore, the Mn content is limited to 1.56 to 1.82%.
Phosphorus (P): p is a harmful impurity element in steel, and although P can improve corrosion resistance, P is easy to cause segregation, promotes austenite to grow during heating, and seriously damages low-temperature toughness.
S and P element , wherein S is a harmful impurity element in steel, and S and Mn are easy to form coarse MnS inclusions, thereby not only damaging low-temperature toughness and thickness direction performance, but also being easy to become crack sources.
Molybdenum (Mo): the Mo element has the main functions of solid solution strengthening and yield ratio reduction, belongs to the element of reducing the austenite region, promotes the right shift of an austenite transformation curve, promotes the formation of bainite of a high-density dislocation substructure, and obviously improves the strength at room temperature and high temperature. A proper amount of Mo can also form refractory carbide and promote more Nb and V fine carbon and nitrogen compounds to be precipitated, and the compounds can effectively prevent austenite grains from growing during heating, so that the steel at high temperature has higher heat resistance. However, too high Mo tends to obtain coarse martensite during rapid cooling and welding cooling, deteriorating low temperature toughness and welding performance. Therefore, the Mo content is limited to 0.12-0.23%.
Tungsten (W) and Mo , W element mainly plays a role in solid solution strengthening, meanwhile, a proper amount of W can form refractory carbide, and can relieve the aggregation process of carbide and keep higher high-temperature strength during tempering at higher temperature, but the excessively high W is not beneficial to low-temperature toughness and welding performance, and in order to ensure that the steel has excellent high-temperature strength and the low-temperature toughness and the welding performance are not damaged, the W content is limited to 0.21-0.40%.
Copper (Cu): the prominent effect of the Cu element is to improve the atmospheric corrosion resistance of the steel, and has the effects of solid solution and precipitation strengthening (epsilon-Cu), and the proper amount of Cu does not reduce the low-temperature toughness and the welding performance. However, when the Cu content is high, it is not favorable for hot deformation, and copper embrittlement occurs during hot deformation, and is not favorable for low-temperature toughness and weldability. Therefore, the Cu content is limited to 0.22-0.48%.
Ni strengthens ferrite and refines pearlite in the steel, has constant effect on improving strength and improves atmospheric corrosion resistance, and Ni can also improve the resistance of the steel to fatigue, reduce the sensitivity of the steel to notches, reduce the low-temperature brittle transition temperature and obviously improve the low-temperature toughness of the steel, but excessive Ni easily generates a large amount of iron scale on the surface of the steel plate and obviously deteriorates the surface quality, so the content of Ni is limited to 0.21-0.43 percent.
Niobium (Nb): nb element belongs to a strong carbide forming element, has obvious functions of fine grain strengthening and precipitation strengthening, improves the impact toughness and plasticity while improving the strength, and reduces the ductile-brittle transition temperature. Nb is also an element for reducing an austenite phase region, and the austenite recrystallization temperature is increased, so that the steel can be processed and deformed at a higher temperature, and austenite grains are refined through recrystallization. The addition of Mo in proper amount can also promote the precipitation of more Nb fine carbon nitrogen compounds, refine structure grains, improve the strength and the low-temperature impact toughness and ensure the high-temperature performance. However, excessive Nb causes a large amount of M/A island structures to appear in the welding cooling process, and influences the heat influence on the low-temperature toughness. Therefore, the Nb content is limited to 0.026-0.048%.
Vanadium (V): the V element belongs to a strong carbide forming element and has the functions of grain refinement and precipitation strengthening. When Nb and V are added compositely, the occurrence of transverse crack phenomenon can be obviously improved, and the recrystallization temperature is obviously increased. The addition of Mo in proper amount can also promote the precipitation of more V fine carbon nitrogen compounds with better high-temperature stability, thereby improving the fire resistance. In the invention, V also has the functions of solid solution strengthening and yield ratio reduction, so that the content of V is not less than 0.055 percent, and when the content of V is too high, although the strength is improved, the low-temperature toughness and the welding performance are damaged. Therefore, the V content is limited to 0.058 to 0.077%.
Ti, which also belongs to a strong carbonitride forming element, can refine grains and improve welding performance, is added together with Ca and Ta to precipitate ultrafine compound particles containing Ti, the effective size of the ultrafine compound particles is below 1.05 mu m, and the austenite grains can be effectively prevented from growing in the heating and welding processes, the combined addition of Ti, Nb and V can further increase step to improve austenite recrystallization temperature, facilitate high-temperature processing deformation, avoid mixed crystal structure, form Ti, Ca and Ta compound particles with larger sizes when the content of Ti is too high, and is not beneficial to refining the austenite grains in the heating and welding processes, so the content of Ti is limited to 0.045-0.068%.
Calcium (Ca): ca element is an important element of the invention, and proper amount of Ca not only promotes the spheroidization and uniform distribution of the strip-shaped MnS inclusion, but also refines the spherical inclusion to ensure that the equivalent circle diameter is below 2.0 μm, thereby effectively improving the low-temperature toughness, the elongation property, the welding property and the lamellar tearing resistance; more importantly, the smaller the size of the spherical inclusions is, the higher the interface strength of the spherical inclusions and a matrix is, and the spherical inclusions are less prone to becoming core of pore nucleation during cold deformation, so that pore formation is delayed, tensile strength is improved, and yield ratio is reduced. However, excessive Ca will form mixed inclusions with larger Ca sizes, which are not favorable for low-temperature toughness, elongation property, lamellar tearing resistance and yield ratio reduction. Therefore, the content of Ca is limited to 0.0022 to 0.0057%.
Ta element is also an important element in the invention, and is also a carbide forming element with Nb , so that the toughness can be improved, and the corrosion resistance can be obviously improved, in addition, important function of Ta in the invention is that the fine oxide particles formed by combining with [ O ] can be used as MnS and a phase transformation nucleation core, tissue crystal grains can be refined, and the low-temperature toughness and the welding performance can be improved, in order to ensure the above function of Ta, when the content of Ta is not less than 0.0025%, Ta-containing inclusions with larger size can be formed when the content of Ta exceeds 0.0065%, the low-temperature toughness and the high-temperature performance are not improved, and the content of Ta is limited to 0.0028-0.0065%.
Nitrogen (N): the N element forms nitrides or carbonitrides with Nb, Ti, V, C and the like in the steel, and is an important element for refining the structure grains. If [ N ] is less than 0.0022%, the number of nitride particles per unit area is limited, and the effect of refining the structure is weak. When the [ N ] is more than 0.0057%, the solid solution N in the steel is increased, the aging sensitivity is increased, and the surface quality of the steel billet is not favorable. Therefore, the content of N is limited to 0.0022 to 0.0057%.
Oxygen (O), wherein O is a harmful gas in steel, the content of O is strictly limited to a low level in the case of , when [ O ] is less than 0.0024%, the number of Ta and Ca fine oxide particles formed per unit area is small, and in order to avoid a large amount of large-size inclusions, the content of O is not more than 0.0042%, so the content of O is limited to 0.0024-0.0042%.
Meanwhile, ① (Ca +2Ta)/3[ O ] is 1.32-1.65, ② 4(15C + Mo +2W) +3(Mn + Cu) is 11.52-13.61%, ③ Pcm (%) -C + Si/30+ (Mn + Cu)/20+ Ni/60+ Mo/15+ V/10 is less than or equal to 0.20%.
In the steel of the invention, when (Ca +2 Ta)/3O is less than 1.32, the modification effect of Ca spheroidized MnS inclusion is not obvious, meanwhile, the quantity of the Ca and Ta fine oxide particles in unit area is less, when (Ca +2 Ta)/3O is more than 1.65, a large quantity of large-size complex inclusion appears, which is not beneficial to the comprehensive performance; when 4(15C + Mo +2W) +3(Mn + Cu) < 11.52%, excellent overall properties of the steel cannot be ensured, and when 4(15C + Mo +2W) +3(Mn + Cu) > 13.61%, low-temperature toughness and weldability are deteriorated and alloy cost is increased; the invention requires Pcm (%) ═ C + Si/30+ (Mn + Cu)/20+ Ni/60+ Mo/15+ V/10 to be less than or equal to 0.20 percent so as to ensure that the product of the invention has good welding performance.
The steel of the present invention contains the above chemical components, and the balance of Fe and inevitable impurities.
The process parameters of the steel are selected for the following reasons:
in order to accurately control the content of Ca and Ta and ensure that the Ca and Ta can play an important role, the invention selects to add Ca and Ta alloy in an RH furnace, and simultaneously, the vacuum treatment time is not less than 30min in order to ensure the properties of steel purity, low-temperature toughness, lamellar tearing resistance and the like.
In order to prevent the billet from generating internal cracks due to the excessively high heating speed and take the problems of energy consumption, production rhythm and the like into consideration, the heating speed is controlled within different temperature ranges of the billet; the temperature is kept at 1180-1230 ℃ for 32-42 min, so that the alloy such as W, Mo is promoted to be fully dissolved in austenite, the component segregation is prevented, the temperature of each part of the billet is fully uniform, and the formation of Ta-containing fine oxide particles is promoted to fully play the role of inhibiting the growth of austenite grains.
According to the invention, three-stage rolling is adopted, the pass, the initial rolling temperature and the final rolling temperature of each rolling stage are strictly controlled, and proper relaxation slow cooling, laminar flow fast cooling, upper-lower water ratio and other process parameter limitations are assisted, especially the limitation of laminar flow cooling starting temperature and cooling speed can ensure that the product can obtain bainite and a (quasi) polygonal ferrite two-phase structure with the volume percentage of 15-30%, a proper amount of (quasi) polygonal ferrite can continuously yield during cold deformation, the yield strength is reduced, and the bainite can ensure that the product has higher tensile strength, so that the product has a lower yield ratio; more importantly, under the cooling process parameters, a fine M/A island structure with the equivalent size of less than 0.25 mu M and uniform distribution can be obtained, and as the smaller the equivalent size of the M/A island is, the higher the strength of the interface between the M/A island and the substrate is, the micropore formation can be effectively delayed during cold deformation, and the separation (fracture) of the M/A island and the substrate is delayed, so that the excellent plastic property (elongation) of the product is ensured.
The invention has the beneficial effects that: 1. the fire-resistant weather-resistant steel for the welding structure has high strength and toughness, high plasticity, low yield ratio, excellent fire resistance, weather resistance and lamellar tearing resistance, and also has excellent welding performance, preheating is not needed before welding, heat treatment is not needed after welding, and the steel has good cold and hot processing performance and large deformation resistance; 2. the production method provided by the invention has simple manufacturing process, is easy for large-scale production, and can be implemented in various metallurgical enterprises.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the present invention is further described in with reference to the following examples.
Examples 1 to 9
The refractory and weather-resistant steels for the welding structure with the yield strength of more than or equal to 620MPa are prepared in the embodiment of the invention, and the refractory and weather-resistant steels comprise, by mass, 0.035-0.075% of C, 0.13-0.24% of Si, 1.56-1.82% of Mn, less than or equal to 0.003% of P, less than or equal to 0.002% of S, 0.12-0.23% of Mo, 0.21-0.40% of W, 0.22-0.48% of Cu, 0.21-0.43% of Ni, 0.026-0.048% of Nb, 0.058-0.077% of V, 0.045-0.068% of Ti, 0.0022-0.0052% of Ca, 0.0028-0.0065% of Ta, 0.0022-0.0057% of N, 0.0024-0.0042% of O, ①% of Ta, 3 + 3% of Ca + 7% of Mo, 3 + 5% of Mo, 0.7% of Cu, 3 + ③% of Mo, 3 + 35% of C + 3/30 + Mn and 35% of Mo.
The production method comprises the process steps of smelting and casting into a casting blank, heating the casting blank, removing phosphorus by high-pressure water, controlling rolling, carrying out laminar cooling and the like, and comprises the following specific process steps:
1) smelting and casting into a casting blank: smelting and pouring molten iron to form a casting blank, and controlling Ca: 0.0022-0.0052%, Ta: 0.0028-0.0065%, and the vacuum treatment time is more than or equal to 30 min;
2) heating a casting blank: heating a casting blank to 700-720 ℃ at a heating rate of 6.0-7.0 ℃/s, then heating to 830-890 ℃ at a heating rate of 7.1-8.8 ℃/s, then heating to 1180-1230 ℃ at a heating rate of 9.0-11.5 ℃/s, preserving heat for 32-42 min, controlling the discharging temperature at 1120-1150 ℃, and carrying out high-pressure water dephosphorization treatment;
3) controlling rolling: the method comprises the steps of I-stage rolling, II-stage rolling and III-stage rolling, wherein the rolling start temperature of the I-stage rolling is not lower than 1100 ℃, the final rolling temperature is 1060-1080 ℃, the rolling passes are 3-5, and the total reduction rate of the passes is 50-60%; the rolling initial temperature of the second stage is 1020-1050 ℃, the rolling pass is 3-5, the single pass reduction rate is 15-25%, and the thickness of the plate blank after rolling is (h +40) mm; the rolling start temperature of the stage III is (980-9h/4) +/-5 ℃, the final rolling temperature is (880-7h/8) +/-5 ℃, the rolling passes are 4-6, and the cumulative reduction rate of the last three passes is 30-35%, wherein h is the thickness value of a finished product in mm;
4) laminar cooling: and (3) carrying out relaxation slow cooling on the steel plate rolled in the stage III for 2-8 s, then carrying out laminar cooling, controlling the ratio of the water feeding amount to the water discharging amount to be 0.79-0.92 during laminar cooling, controlling the starting cooling temperature to be (760+3h/4) +/-5 ℃, controlling the cooling speed to be 12-18 ℃/s, controlling the cooling re-reddening temperature to be 400-450 ℃, and finally carrying out air cooling to room temperature to obtain the refractory weathering steel for the welding structure with the yield strength being more than or equal to 620MPa, wherein h is the finished product thickness value in mm.
According to the chemical components and the requirements of the production process of the steel, 9 batches of the steel are smelted and rolled, and batches of the weathering steel are prepared according to the traditional process conditions and are respectively marked as examples 1-9 and comparative examples, wherein the thickness of the products in examples 1-3 is 24mm, the thickness of the products in examples 4-6 is 48mm, the thickness of the products in examples 7-9 is 72mm, and the thickness of the products in the comparative examples is 48mm, the components and the mass percentage content of the steel products in examples 1-9 and comparative examples are shown in a table 1, the value of the main process parameters of each example is shown in a table 2, and the mechanical property test results of each example and comparative example are shown in a table 3.
As can be seen from Table 3, the room temperature elongation property and Z-direction of the steel sheet of the present invention were evaluatedTensile property, longitudinal impact energy at-40 ℃ and-60 ℃, high-temperature property at 600 ℃ and 264h week immersion corrosion rate test, and the results show that: the invention has the following physical properties: r is more than or equal to 662MPaeL≤679MPa，868MPa≤Rm≤889MPa，0.745≤ReL/RmNot more than 0.772 percent, not less than 30.5 percent and not more than A not more than 33.5 percent, not less than 70 percent and not more than 77 percent Zz, and R is not less than 516MPa and not more than 600 ℃ atP0.2≤530MPa，331J≤-40℃KV2≤346J，273J≤-60℃KV2300J or less, the corrosion rate of 264h immersion is lower than 0.305g/m2H, the yield strength of the comparative example is at the same level as that of the example , but the tensile strength is obviously lower than that of the example, so that the yield ratio of the comparative steel is higher than 0.80, and the Z-direction tensile property, -40 ℃ and-60 ℃ longitudinal impact energy and 600 ℃ high-temperature property of the comparative example are both greatly lower than those of the example, but the 264h cycle immersion corrosion rate is obviously higher than that of the example, which shows that the corrosion resistance of the steel product produced by the comparative example is poorer than that of the product produced by the examples 1-9 of the invention.
Figure BDA0001786041100000111
Figure BDA0001786041100000121

Claims (3)

  1. refractory and weather-resistant steels for welding structures with yield strength of more than or equal to 620MPa are characterized by comprising, by mass, 0.035-0.075% of C, 0.13-0.24% of Si, 1.56-1.82% of Mn, less than or equal to 0.003% of P, less than or equal to 0.002% of S, 0.12-0.23% of Mo, 0.21-0.40% of W, 0.22-0.48% of Cu, 0.21-0.43% of Ni, 0.026-0.048% of Nb, 0.058-0.077% of V, 0.045-0.068% of Ti, 0.0022-0.0052% of Ca, 0.0028-0.0065% of Ta, 0.0022-0.0057% of N, 0.0024-0.0042% of O, Ta and inevitable impurities of Fe and ① +3 + 35% of Ca +3 + 3.30 + 5% of Mo, 0.7% of C +3 + 20/20% of Cu, and the balance of Mo + ③ +3 + 20+ 3/20% of C + 3/20;
    the microstructure of the refractory weathering steel for the welding structure with the yield strength of more than or equal to 620MPa is a bainite and quasi-polygonal ferrite two-phase structure with the volume percentage of 15-30% and a fine M/A island structure with the equivalent size of less than 0.25 mu M and uniform distribution.
  2. 2, A production method of the fire-resistant weather-resistant steel with yield strength not less than 620MPa for the welding structure according to claim 1, which comprises the following process steps of smelting and casting into a casting blank, heating the casting blank, descaling with high pressure water, controlled rolling, laminar cooling and the like, and is characterized in that the specific process steps are as follows:
    1) smelting and casting into a casting blank: smelting and pouring molten iron to form a casting blank, and controlling Ca: 0.0022-0.0052%, Ta: 0.0028-0.0065%, and the vacuum treatment time is more than or equal to 30 min;
    2) heating a casting blank: heating a casting blank to 700-720 ℃ at a heating rate of 6.0-7.0 ℃/s, then heating to 830-890 ℃ at a heating rate of 7.1-8.8 ℃/s, then heating to 1180-1230 ℃ at a heating rate of 9.0-11.5 ℃/s, preserving heat for 32-42 min, controlling the discharging temperature at 1120-1150 ℃, and carrying out high-pressure water descaling treatment;
    3) controlling rolling: the method comprises the steps of I-stage rolling, II-stage rolling and III-stage rolling, wherein the rolling start temperature of the I-stage rolling is not lower than 1100 ℃, the final rolling temperature is 1060-1080 ℃, the rolling passes are 3-5, and the total reduction rate of the passes is 50-60%; the rolling initial temperature of the second stage is 1020-1050 ℃, the rolling pass is 3-5, the single pass reduction rate is 15-25%, and the thickness of the plate blank after rolling is (h +40) mm; the rolling start temperature of the stage III is (980-9h/4) +/-5 ℃, the final rolling temperature is (880-7h/8) +/-5 ℃, the rolling passes are 4-6, and the cumulative reduction rate of the last three passes is 30-35%, wherein h is the thickness value of a finished product in mm;
    4) laminar cooling: and (3) carrying out relaxation slow cooling on the steel plate rolled in the stage III for 2-8 s, then carrying out laminar cooling, controlling the opening cooling temperature to be (760+3h/4) +/-5 ℃, controlling the cooling speed to be 12-18 ℃/s, controlling the cooling re-reddening temperature to be 400-450 ℃, and finally carrying out air cooling to room temperature to obtain the refractory weathering steel for the welding structure with the yield strength of more than or equal to 620MPa, wherein h is the thickness value of a finished product in mm.
  3. 3. The method for producing the fire-resistant and weather-resistant steel with yield strength not less than 620MPa for the welded structure according to claim 2, wherein the ratio of the water feeding amount to the water discharging amount in the laminar cooling in the step 4) is controlled to be 0.79-0.92.
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