CN108531808B - Low-yield-ratio weather-proof bridge structural steel with yield strength of more than or equal to 690MPa and production method thereof - Google Patents
Low-yield-ratio weather-proof bridge structural steel with yield strength of more than or equal to 690MPa and production method thereof Download PDFInfo
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Abstract
The weather-resistant bridge steel with the yield strength not less than 690MPa and the low yield ratio comprises the following components in percentage by weight: 0.04-0.10% of C, 0.01-0.20% of Si, 0.80-1.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.20-0.55% of Cu, 0.40-1.50% of Ni, 0.20-0.80% of Mo, 0.35-0.70% of Cr, 0.030-0.090% of Nb, 0.008-0.030% of Ti, 0.015-0.060% of Als, less than or equal to 0.0080% of N and 0.0010-0.0050% of Ca. The production method comprises the following steps: heating a casting blank; rough rolling; fine rolling; cooling in sections; tempering; naturally cooling to room temperature. The invention ensures that the yield strength of the high-strength steel for the bridge structure is more than or equal to 690MPa, the tensile strength is 810-930 MPa, and KV is at minus 40 DEG C2On the premise of being more than or equal to 150J, the yield ratio is 0.74 ~ 0.85.85, the problem of material selection and material use in the development of bridge engineering towards a large-span and heavy-load direction is solved, the self weight of the structure can be reduced, and the design, manufacture and construction difficulty of the bridge engineering and the like are reduced.
Description
Technical Field
The invention relates to bridge steel and a production method thereof, in particular to low-yield-ratio weather-resistant bridge structural steel with yield strength of more than or equal to 690MPa and a production method thereof, wherein the use thickness of the structural steel is 8 ~ 50 mm.
Background
With the development of steel structure bridges in the direction of large span, heavy load and high driving speed, the technical requirements on steel plates for bridge structures are more and more strict. The use of the high-strength steel plate can theoretically enable the span of the bridge to be larger, the load to be heavier, the self weight of the structure to be reduced, the structural design, manufacturing and construction difficulty to be reduced and the like.
It is known that as the strength of steel increases, the yield ratio of steel generally increases, even to 0.93 or more. The high-strength steel adopts the idea of grain refinement, the strength is improved at the cost of reducing plasticity, and the organization characteristic is mainly single-phase and does not introduce the concept of complex phase. Due to the high yield ratio, once the component is overloaded, the ultimate strength of the steel grade can be quickly reached, and accidents are caused. Therefore, the application of high-strength structural steel in bridge engineering is limited due to the high yield ratio. High strength steel can make the component thinner, and corrosion becomes a problem to be faced, which requires the structural design to take into account the corrosion margin, and increases the self-weatherability of the steel.
In order to reduce the yield ratio of steel without deteriorating other properties of steel, it is necessary to appropriately refine grains and to make the main structure in steel a complex phase structure having appropriate hard and soft phase ratios, morphology and dimensions. When the volume fraction of the soft phase is not large and the distribution is proper, the yield strength of the steel is mainly determined by the yield strength of the soft phase, and the tensile strength of the steel is basically close to that of the hard phase; if the strength difference between the hard phase and the soft phase is large, the yield ratio of the steel can be obviously reduced.
For a high-strength bridge structural steel with the yield strength of 690MPa, the existing production process is generally divided into quenching and tempering and TMCP.
When the steel of the quenching and tempering process of complete austenitizing and quenching is adopted, the yield ratio is generally more than 0.90. When the two-phase zone quenching process of partial austenitization is adopted, a low yield ratio can be generally obtained for thin steel plates, but for thick steel plates for bridges (for example, the plate thickness is greater than 32 mm), because the actual cooling speed difference between the surface layer and the core part is large, stable low yield ratio performance is difficult to obtain, and the low-temperature toughness of the steel plate is unstable, which is also a very outstanding problem. The quenched and tempered steel sheet also has a problem of softening and embrittlement of a welded joint due to its large welding line energy (> 25 kJ/cm). In addition, the two quenched and tempered steels have the defects of long production process flow and high production cost.
When the TMCP process is adopted, due to the specific controlled rolling and accelerated cooling processes, generally, although the ratio, distribution, size and the like of hard and soft phases in steel can be effectively adjusted to obtain a lower yield ratio, the defects exist in the aspects of weather resistance, weldability, cold and hot processing stability and the like, and therefore the TMCP process cannot be popularized and applied in bridge engineering.
After retrieval:
the Chinese patent publication No. CN 102851615A provides a low yield ratio structural steel plate with 800 MPa-level tensile strength and a manufacturing method thereof, and the steel plate comprises the following components: c: 0.02% -0.08%, Si: 0.30-0.50%, Mn: 1.50% -1.80%, Nb: 0.02-0.04%, Ti: 0.005% -0.030%, Mo: 0.010-0.19%, Cr: 0.30-0.45%, Cu: 0.10% -0.29%, Ni: 0.10% -0.40%, Als: 0.010-0.070 percent, and the balance of Fe. The method comprises smelting, continuous casting and rolling, wherein the heating temperature of a steel billet before rolling is 1040-1230 ℃; the rolling temperature of the recrystallization zone is more than or equal to 1000 ℃; the rolling temperature of the non-recrystallization zone is 950 ℃ to (Ar3+0 ℃ to 100 ℃), and the accumulated deformation is more than 50%; the cooling speed after rolling is 30-60 ℃/s, and the final cooling temperature is 100-300 ℃. The steel grade has low cost, good welding performance, high strength, high toughness and low yield ratio. The document requires a cooling rate of 30-60 ℃/s after rolling of the steel sheet. For the medium plate with the thickness of 32mm or more for the bridge, the existing cooling equipment has difficulty in achieving the large cooling rate of the steel plate.
The foreign literature with the Chinese patent publication number CN 104583441A discloses a material with the yield strength of 670-2And tensile strength 780-2The steel plate of (1) has a thickness of 25-200 mm. The steel sheet has chemical compositions within a predetermined range, an alpha value of 0.13 to 1.0 mass%, a beta value of 8.45 to 15.2, a yield strength of 670 to 870N/mm2 and a tensile strength of 780 to 940N/mm2, and the steel sheet is characterized by being produced by using a steel sheet produced byThe average crystal grain diameter of the central part of the plate thickness is less than 35 μm, and the plate thickness is 25-200 mm. When the steel sheet is subjected to stress removal annealing, the Charpy absorption energy at-40 ℃ of the portion subjected to the stress removal annealing is 100J or more. Although the toughness of the parent material and the CTOD (thermal shock absorption) characteristic of the welding heat affected zone of the steel are excellent after stress relief annealing, the steel adopts a relatively complex quenching and tempering heat treatment process, and the actual yield ratio of the steel is generally more than 0.85 and can reach 0.93 at most.
The Chinese patent publication No. CN 107312981A provides a low yield ratio high strength and toughness thick steel plate and a manufacturing method thereof, and discloses a low yield ratio high strength and toughness thick steel plate, which comprises the following chemical components in percentage by mass: 0.060-0.080% of C, 5.5-6.0% of Mn, 0.10-0.30% of Si, 0.015-0.040% of Al, 0.15-0.30% of Mo, 0.20-0.40% of Cr, 0.15-0.40% of Ni, 0.01-0.03% of Ti, less than or equal to 0.006% of S, less than or equal to 0.010% of P, and the balance of Fe and inevitable impurity elements; the steel plate has high yield strength, low yield ratio and good low-temperature impact toughness. The invention also discloses a manufacturing method of the steel plate, which comprises the following steps: heating, rolling and heat treatment; the manufacturing method only needs one-time heat treatment, has simple process and is easy to produce and implement. Although the yield strength is more than or equal to 690MPa, the yield ratio is less than or equal to 0.80, the steel plate has good low-temperature impact toughness, the thickness specification of the steel plate reaches 50-100mm, and quenching and tempering treatment is not needed, but the content of Mn reaches 5.5-6.0%, the carbon equivalent CEV of the steel calculated according to the embodiment reaches more than 1.0%, the welding cold crack sensitivity index reaches 0.36-0.41%, and obviously, the weldability is poor, (note: CEV (%) = C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15, Pcm (%) = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+ 5B.)
Chinese patent publication No. CN 101985725B discloses a 780MPa grade low yield ratio steel plate for construction and a manufacturing method thereof, wherein the steel plate comprises the following chemical components in percentage by weight: 0.05 to 0.07 percent of C, 0.2 to 0.3 percent of Si, 1.8 to 2.0 percent of Mn, less than or equal to 0.005 percent of S, less than or equal to 0.008 percent of P, 0.02 to 0.03 percent of Nb, 0.15 to 0.3 percent of Cr, 0.2 to 0.4 percent of Ni, 0.01 to 0.03 percent of Ti, 0.2 to 0.4 percent of Cu, 0.25 to 0.4 percent of Mo, and the balance of Fe and inevitable impurities. The process system comprises the following steps: heating the blank to 1190-1210 ℃, rolling at the second stage, cooling by using ultra-fast cooling equipment after rolling, and then cooling to room temperature in air. Although the document does not need heat treatment, the Mn content of the steel is 1.8-2.0%, so that the steel is easy to cause serious center segregation, and the cooling rate of the steel after rolling is 30-100 ℃/s, which is too high for equipment, and the yield strength of the steel is low and is only required to be in the 630MPa level.
Chinese patent publication No. CN 102011068B discloses an 800 MPa-grade low yield ratio structural steel plate and a production method thereof. The steel comprises the following chemical components in percentage by weight: 0.045-0.075%, Si: 0.30-0.55%, Mn: 1.55-1.95%, P: less than or equal to 0.01 percent, S: less than or equal to 0.0025 percent, Alt: 0.012-0.035%, Cr:0.15 to 0.25%, Mo:0.15 to 0.3%, Cu:0.2 to 0.4%, Ni:0.2 to 0.4%, Nb: 0.008-0.04%, V: 0.008 to 0.04%, Ti: 0.008-0.03%, B: 0.0008 to 0.0015% of Fe and inevitable impurities. The steel is produced by RH vacuum treatment, LF external refining, full-protection pouring, TMCP process and tempering heat treatment, and has low yield ratio, high strength and high work hardening rate. The steel plate has the thickness specification of 10-40 mm, the yield strength of more than or equal to 550MPa, the tensile strength of more than or equal to 800MPa, the yield ratio of less than 0.70, and excellent low-temperature impact property, cold forming property and welding property. Although the yield ratio is less than 0.70, the strength grade is low, B belongs to light elements and is easy to oxidize due to micro B treatment, and the low-temperature toughness of the welded HAZ of the steel containing B is unstable. The steel is tempered at a temperature of 720-750 ℃ after rolling, wherein the temperature is Ac1The yield ratio of the steel is reduced but the low temperature toughness is deteriorated, and according to the examples, the-20 ℃ impact work after tempering is reduced by 10-20% on average compared with the rolled state, and the-40 ℃ impact work data is not shown. It is clear that this process has certain drawbacks.
Chinese patent No. CN 103352167 provides a steel for a bridge with low yield ratio and high strength and a manufacturing method thereof, and discloses a steel for a bridge with low yield ratio and high strength and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.06-0.10%, Si: 0.20 to 0.45%, Mn: 1.20-1.50%, P: less than or equal to 0.010 percent, S: less than or equal to 0.0020 percent, Ni: 0.30-0.60%, Cu:0.20 to 0.50%, Mo:0.15 to 0.50%, Nb: 0.025 to 0.060%, Ti: less than or equal to 0.035%, Alt: 0.020 to 0.040 percent, and the balance of Fe and inevitable impurities. According to the invention, through smelting and refining, a reasonable rolling and cooling control process and optimized tempering heat treatment production, the tensile strength of the steel plate is 700-780 MPa, the yield strength is 530-600 MPa, the elongation is more than or equal to 18%, the yield ratio is less than or equal to 0.80, the longitudinal impact at the low temperature of minus 40 ℃ is more than or equal to 100J, and the steel plate has good obdurability matching and low yield ratio. But the steel does not take into account corrosion resistance.
The Chinese patent publication No. CN 105950849A discloses a production process of a high-strength steel plate with a low yield ratio of 690MPa, the steel plate is designed by adopting Cu-Ni-Mo-Cr microalloy composite components, and the steel plate comprises the following main chemical components in percentage by weight: cr: 0.40-0.60%, Mo: 0.40-0.60%, Cu:0.20 to 0.35%, Ni: 0.7-1.0%, the steel plate structure is tempered B + F, and the yield ratio is less than or equal to 0.85. According to the invention, the high-strength steel plate with good mechanical properties is obtained by optimally designing the Cu-Ni-Mo-Cr series microalloy elements and strictly controlling the rolling and cooling processes. Although the steel does not need a quenching and tempering process, the thickness of the steel plate is 40-70mm, the second-stage rolling temperature is required to be less than or equal to 750 ℃, equipment is required to provide larger rolling force for thick steel plates, the steel is difficult to implement on site, the weldability of the steel is poor, and the welding cold crack sensitivity index Pcm value calculated according to the embodiment of the steel reaches 0.25-0.29%.
The applicant starts from the market development trend and urgent need of bridge steel at present and in a certain period in future, and combines the actual conditions of the existing production technical equipment, such as the capability of cooling equipment (even if the existing new technology is improved or adopted, the cooling speed cannot reach more than 35 ℃/s for steel plates with the thickness of more than 32 mm), and proposes that the performance of the bridge structural steel is represented by a technical performance index with a low yield ratio (0.74 ~ 0.85.85) on the premise of ensuring the service performance of the bridge structural high-strength steel, so that the large span, the larger load, the reduction of the self weight of the structure, the reduction of the structural design, the manufacture, the construction difficulty and the like are realized.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for ensuring that the yield strength of the high-strength steel of the bridge structure is more than or equal to 690MPa, the tensile strength is 810-930 MPa, and the KV is at-40 DEG C2On the premise of being more than or equal to 150J, the yield ratio is 0.74 ~ 0.85.85, so that the problem of material selection and material use in the development of bridge engineering towards a large-span and heavy-load direction is solved, the self weight of the structure is reduced, the difficulty in designing, manufacturing and constructing the bridge engineering is reduced, and the yield strength of the structural steel for the low-yield-ratio weather-resistant bridge is more than or equal to 690MPa, and the production method thereof.
The measures for realizing the aim are as follows:
the weather-resistant bridge steel with the yield strength not less than 690MPa and the low yield ratio comprises the following components in percentage by weight: 0.04-0.10% of C, 0.01-0.20% of Si, 0.80-1.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.20-0.55% of Cu, 0.40-1.50% of Ni, 0.20-0.80% of Mo, 0.35-0.70% of Cr, 0.030-0.090% of Nb, 0.008-0.030% of Ti, 0.015-0.060% of Als, less than or equal to 0.0080% of N, 0.0010-0.0050% of Ca, and the balance of Fe and inevitable impurities, wherein the weight ratio of C to Nb is as follows: 0.11-0.15%; simultaneously, the following requirements are met: carbon equivalent CEV = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 ≤ 0.65%, weld cold crack sensitivity index Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B ≤ 0.25%, and weather resistance index I (%) =26.01Cu +3.88Ni +1.20Cr +1.49Si +17.28P-7.29Cu × Ni-9.10Ni × P-33.39Cu2More than or equal to 6.0 percent, the yield strength of the mechanical property is more than or equal to 690MPa, the tensile strength is 810-930 MPa, the yield ratio is 0.74 ~ 0.85.85, and the KV at minus 40 ℃ is2More than or equal to 155J; the metallographic structure is bainite and ferrite, wherein the volume ratio of the ferrite is not less than 20%.
Preferably: the weight percentage of the following components is as follows: c: 0.044-0.89%, Si: 0.022-0.187%, Mn: 0.92-1.65%, Ni: 0.47-1.35%, 0.28-0.72% of Mo, 0.38-0.63% of Cr, 0.042-0.083% of Nb, C + Nb: 0.115-0.142%.
The method for producing the weather-resistant bridge steel with the yield strength of more than or equal to 690MPa and the low yield ratio comprises the following steps:
1) heating the casting blank, and controlling the temperature of the casting blank core at a soaking section to be 1080-1180 ℃;
2) carrying out rough rolling, controlling the rough rolling temperature to be 1130-980 ℃, and controlling the thickness of the intermediate blank according to the thickness t + (25-60) mm of a finished product;
3) performing finish rolling, and controlling the start rolling temperature of the finish rolling to be 930-830 ℃ (the specific temperature is related to the thickness of a finished product, the thinner the thickness of the finished product is, the higher the start rolling temperature is), and the finish rolling temperature to be 750-820 ℃;
4) carrying out sectional cooling: the first stage is as follows: the cooling rate is 1-2 ℃/s, and the volume ratio of ferrite of the section of steel plate is controlled to be 20-40%; and a second stage: the cooling starting temperature is 730-800 ℃, and the cooling is carried out to 100-350 ℃ at the cooling rate of 10-30 ℃/s; and a third stage: naturally cooling to room temperature;
5) tempering is carried out, the tempering temperature is 180-380 ℃, the temperature is kept for 20 ~ 40min, and the temperature keeping time is in positive correlation with the thickness of a finished product;
6) naturally cooling to room temperature.
Preferably: the start rolling temperature of finish rolling is 920-820 ℃, and the finish rolling temperature is 760-810 ℃.
Preferably: the cooling starting temperature of the second stage is 740-790 ℃, and the cooling rate is 12-30 ℃/s.
Preferably, the tempering temperature is 200-350 ℃, and the temperature is kept for 25 ~ 32 min.
Effect of elements of the invention
The content of C in the invention is selected to be 0.04-0.10%. C is an effective element for improving the strength of steel, and when the carbon content is high, for example, more than 0.12%, martensite is easily formed to deteriorate the low-temperature toughness of steel, and the tensile strength easily exceeds the upper limit, and the influence on weldability is large. When the carbon content is low, for example, less than 0.04%, the strength of the steel sheet becomes insufficient, the hard phase in the steel becomes small, and the yield ratio control becomes difficult. The content of C is preferably 0.044-0.89%.
The Si content of the present invention is 0.01 to 0.20%, and an excessively high content of Si deteriorates the low-temperature toughness of the HAZ welded to the high-strength steel, and the upper limit of Si is set to 0.20%, and the lower limit of Si is set to 0.01% because a certain amount of Si remains in the steel due to deoxidation. The Si content is preferably 0.022 to 0.187%.
The Mn content of the invention is 0.80-1.70, and Mn is an important toughening element and an austenite stabilizing element, and can expand an austenite region in an iron-carbon phase diagram and promote medium-temperature structure transformation. The high Mn content is liable to cause severe center segregation in the steel, deteriorates the low temperature toughness of the steel, and tends to cause cracking of the HAZ steel sheet during welding, which is not necessary for obtaining the mechanical properties of the steel of the present invention, while too low Mn content tends to lower the strength of the steel. The preferable Mn content is 0.92 to 1.65%.
The P content is less than or equal to 0.010 percent, and the higher content of P can obviously improve the weather resistance of steel, but also can reduce the weldability of steel, increase the cold brittleness tendency of steel and generate more serious center segregation.
The S content of the steel is less than or equal to 0.005 percent, and the higher content of S can reduce the corrosion resistance, the low-temperature toughness and the Z-direction performance of the steel.
The Cu content of the steel plate is 0.20-0.55%, the Cu can improve the hardenability of steel, the core strength of the steel plate can be obviously improved, and the steel plate is also an important element for improving the weather resistance, when the addition of the Cu is more than 0.50%, the toughness of a welding heat affected zone of the steel plate is reduced, and the net crack is easily generated in the heating process of a steel billet. The preferable Cu content is 0.25 to 0.45%.
The Ni content of the invention is 0.40-1.50, the Ni can improve hardenability, has a certain strengthening effect, and can also obviously improve the low-temperature toughness of the base material and the welding HAZ. Ni is also effective in preventing network cracking caused by the hot embrittlement of Cu. For high-strength steel, if the addition amount is less than 0.40%, the effect of improving the low-temperature toughness of Ni is not obvious, but if the content is too high, the production cost is increased. The Ni content is preferably 0.47 to 1.35%.
Mo: 0.28～0.72%，Cr: 0.38～0.63%%，Nb: 0.042～0.083%， C+Nb：0.115～0.142%。
The content of Mo is 0.20-0.80, the Mo can precipitate ferrite from austenite, increase the stability of the austenite, have a strong inhibiting effect on the formation of pearlite and promote the transformation of bainite structure. Mo has a low diffusion speed, so that the thermal stability of the microalloy carbonitride can be improved, and the Mo is particularly important for the high-strength medium plate bridge steel. Because the bridge member can be deformed due to uneven heating in the welding process, in order to ensure the dimensional accuracy of the member, only a flame mode can be adopted for correction, the common bridge structure thick steel plate can be obviously weakened in strength and deteriorated in toughness after flame correction, and the influence can be effectively reduced by proper Mo. The proper amount of Mo also improves the problem of uneven structure due to uneven cooling rate in the thickness direction. However, Mo is a precious element, and excessive Mo will increase the alloy cost of steel and significantly deteriorate the low-temperature toughness of steel plates and welded joints. The preferable Mo content is 0.28 to 0.72%.
The content of Cr in the steel is 0.35-0.70%, the proper Cr can improve the strength of the steel and obviously improve the weather resistance of the steel, but the content is too high, if the content is more than 0.80%, the welding difficulty is easy to increase, and if the content is less than 0.35%, the effect cannot be effectively played. The preferable Cr content is 0.38-0.63%.
The Nb content of the present invention is 0.030 to 0.090%, preferably 0.042 to 0.083%. Nb is a strong carbonitride forming element and increases the austenite recrystallization temperature of steel, and austenite can be rolled at a higher rolling temperature. In addition, the Nb has precipitation strengthening effect in the continuous cooling process of rolling control, and austenite grains can be fixed through strain-induced precipitation of Nb carbonitride, so that the austenite grains are refined, and the strength and the low-temperature toughness are improved. When Nb is more than 0.090%, the effect of refining grains in low-carbon bainite steel to improve strength is very obvious, the yield ratio is difficult to control, and when Nb is less than 0.030%, the effect of refining the grains of the steel is not very obvious, and the strength and the toughness of the steel are influenced.
The content of Ti is 0.008-0.030, Ti is a strong nitride forming element, and the nitride of Ti can effectively pin austenite crystal boundaries, so that the growth of austenite crystal grains is controlled.
The content of Als in the steel is controlled to be less than or equal to 0.060, and Al is a main deoxidizing element in the steel. When the content of Al is too high, the content of Al oxide inclusions is increased, the purity of steel is reduced, and the toughness of the steel is not facilitated. The melting point of Al is high, and Al can be used for preventing grains from growing in production.
The invention has limitation on the content of N, the requirement is less than or equal to 0.0080%, and the aging performance of the steel is influenced by excessively high content of N.
In the invention, the content of Ca is controlled to be 0.0005-0.0060%, proper Ca can spheroidize sulfides, improve the longitudinal and transverse mechanical property difference of steel and improve the weather resistance of the steel, but the excessive content of Ca increases the risk of inclusions and deteriorates the steel quality.
In addition, in order to ensure proper toughness, C and Nb must also satisfy C + Nb = 0.11-0.15%, preferably 0.115-0.142%. Lowering the C content increases the solid solubility of niobium carbide, which allows higher Nb contents to be added to improve the strengthening effect of the steel. Therefore, when the carbon content is high, it is impossible to sufficiently exert the intended reinforcing effect by adding a high content of Nb to the steel. In the present invention, for the sake of simplicity, the contents of C and Nb are suitably limited, i.e., C + Nb =0.115 to 0.142%.
The invention controls the initial rolling temperature of finish rolling to be 930-830 ℃, and the final rolling temperature to be 750-820 ℃; preferably, the finish rolling initial rolling temperature is 920-820 ℃, the finish rolling temperature is 760-810 ℃, because too high initial rolling temperature is easy to cause mixed crystal, too low initial rolling temperature cannot ensure effective finish rolling temperature, when the finish rolling temperature is too high or too low, the required hard and soft complex phase structure is not easy to generate, and the toughness of the steel can be influenced.
The first stage is controlled to have cooling rate of 1-2 ℃/s and the ferrite volume ratio of the steel plate of the section of the steel plate of 20-30%, and the second stage is controlled to have cooling starting temperature of 730-800 ℃, cooling speed of 10-30 ℃/s to 100-350 ℃, preferably cooling starting temperature of 730-790 ℃ in the second stage and cooling speed of 12-30 ℃/s, because in the first stage, a proper ferrite structure needs to be obtained in the steel, and in the second stage, a larger cooling speed is needed to complete the transformation of a hard phase structure, the tempering temperature is controlled to be 180-380 ℃, and the temperature is kept for 20 ~ 40min, preferably 187-365 ℃, and is kept for 25 ~ 32min, so that the residual stress of the steel plate can be reduced, and the tempering yield ratio is not too high.
Compared with the prior art, the invention ensures high strength for bridge structuresThe yield strength of the steel is more than or equal to 690MPa, the tensile strength is 810-930 MPa, and KV is at-40 DEG C2On the premise of being more than or equal to 150J, the yield ratio is 0.74 ~ 0.85.85, the problem of material selection and material use in the development of bridge engineering towards a large-span and heavy-load direction is solved, the self weight of the structure can be reduced, and the design, manufacture and construction difficulty of the bridge engineering and the like are reduced.
Description of the drawings
FIG. 1 is a metallographic structure diagram of the present invention.
Detailed Description
The present invention is described in detail below:
table 1 is a list of values for each example and comparative example of the present invention;
table 2 list of main process parameters of each example of the present invention and comparative example;
table 3 is a table of the performance test of each example and comparative example of the present invention.
The preparation method comprises the following steps:
1) heating the casting blank, and controlling the temperature of the casting blank core at a soaking section to be 1080-1180 ℃;
2) carrying out rough rolling, controlling the rough rolling temperature to be 1130-980 ℃, and controlling the thickness of the intermediate blank according to the thickness t + (25-60) mm of a finished product;
3) performing finish rolling, and controlling the start rolling temperature of the finish rolling to be 930-830 ℃ and the finish rolling temperature to be 750-820 ℃;
4) carrying out sectional cooling: the first stage is as follows: the cooling rate is 1-2 ℃/s, and the ferrite volume ratio of the section of steel plate is controlled to reach 20%; and a second stage: the cooling starting temperature is 730-800 ℃, and the cooling is carried out to 100-350 ℃ at the cooling rate of 10-30 ℃/s; and a third stage: naturally cooling to room temperature;
5) tempering is carried out, the tempering temperature is 180-380 ℃, the temperature is kept for 20 ~ 40min, and the temperature keeping time is in positive correlation with the thickness of a finished product;
6) naturally cooling to room temperature.
TABLE 1 list of chemical compositions (wt%) of inventive and comparative examples
Note that ① in examples 1-9 were all treated with Ca in an amount of not more than 0.0060%.
② comparative example 2 has an Al content of total Al.
③ comparative example 1 is example 1 in CN 102851615A, comparative example 2 is example 3 in CN 101985725B, and comparative example 3 is case 1 in CN 102011068B, the same shall apply.
TABLE 2 List of the main process parameters of the examples of the invention and the comparative examples
TABLE 3 comparative list of mechanical and corrosion resistance properties of inventive and comparative examples
Note ① that the impact specimen of example 1 used an auxiliary specimen size of 10X 7.5X 55mm, and examples 2-9 used a standard impact specimen size of 10X 55 mm;
② comparative example 1 is reported as ReL。
As can be seen from table 1, comparative example 1 does not pay attention to the detrimental effect on the base metal and weld HAZ low temperature toughness when the Si content is too high, and the Ni content of the steel grade is too low to maintain stable low temperature impact toughness of such high strength steel, and does not consider the beneficial ratio of C and Nb in the steel. Comparative example 2 in addition to having all the disadvantageous characteristics of comparative example 1, the steel has a high Mn content and is very susceptible to strong center segregation. Comparative example 3 also has a high Si content and also contains B element, which is very easily oxidized. As can be seen from the corrosion resistance index I in Table 1, the corrosion resistance of the inventive steels is significantly better or equal to that of the comparative examples since the inventive examples are generally 6.3 to 7.6% and significantly higher than the comparative examples 6.1 to 6.3%.
As can be seen from Table 2, comparative example 1 is directed to the post-rolling cooling rateToo high a cooling rate of 59.2 ℃/s is required, and for thick steel plates (e.g.. gtoreq.25 mm), it is obvious that conventional equipment cannot meet the requirements. The steel sheet of 40mm thickness in comparative example 2 requires a cooling rate of 31 ℃/s, and is apparently high. The cooling rate of comparative example 3 was moderate, but the steel sheet was tempered at 720 ℃ because this temperature was close to the critical point A of the steelc1Although the yield ratio can be secured, the low-temperature toughness of the steel is deteriorated. The invention requires the cooling speed of the rolled steel to be 10-30 ℃/s, and common equipment can meet the requirements.
As can be seen from Table 3, the low temperature toughness of comparative example 1 is low. The yield strength of comparative example 2 is low. Comparative example 3 has a very low yield ratio of only 0.65, and it is clear that too low a yield ratio would also result in a certain waste of resources, due to too low a yield strength and also to a low temperature toughness of the steel, as only-20 ℃ impact test performance is demonstrated.
The present embodiments are merely preferred examples, and are not intended to limit the scope of the present invention.
Claims (4)
1. The weather-resistant bridge steel with the yield strength not less than 690MPa and the low yield ratio comprises the following components in percentage by weight: 0.09-0.10% of C, 0.01-0.08% of Si, 0.80-1.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.20-0.55% of Cu, 0.60-1.50% of Ni, 0.50-0.80% of Mo, 0.35-0.70% of Cr, 0.030-0.090% of Nb, 0.008-0.030% of Ti, 0.015-0.060% of Als, less than or equal to 0.0080% of N, and the balance of Fe and inevitable impurities, wherein the weight ratio of C to Nb: 0.11-0.15%; simultaneously, the following requirements are met: carbon equivalent CEV = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 ≤ 0.65%, weld cold crack sensitivity index Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B ≤ 0.25%, and weather resistance index I (%) =26.01Cu +3.88Ni +1.20Cr +1.49Si +17.28P-7.29Cu × Ni-9.10Ni × P-33.39Cu2More than or equal to 6.0 percent, the yield strength of the mechanical property is more than or equal to 690MPa, the tensile strength is 810-930 MPa, the yield ratio is 0.74 ~ 0.85.85, and the KV at minus 40 ℃ is2More than or equal to 155J; the metallographic structure is bainite and ferrite, wherein the volume ratio of the ferrite is not less than 20%.
2. The method for producing the low yield ratio weather-resistant bridge steel with yield strength of more than or equal to 690MPa according to claim 1 comprises the following steps:
1) heating the casting blank, and controlling the temperature of the casting blank core at a soaking section to be 1080-1160 ℃;
2) carrying out rough rolling, controlling the rough rolling temperature to be 1130-980 ℃, and controlling the thickness of the intermediate blank according to the thickness t + (25-60) mm of a finished product;
3) performing finish rolling, and controlling the start rolling temperature of the finish rolling to be 930-830 ℃, wherein the specific temperature is related to the thickness of a finished product, the thinner the thickness of the finished product is, the higher the start rolling temperature is, and the final rolling temperature is 750-820 ℃;
4) carrying out sectional cooling: the first stage is as follows: the cooling rate is 1-2 ℃/s, and the volume ratio of ferrite of the section of steel plate is controlled to be 20-40%; and a second stage: the cooling starting temperature is 770-800 ℃, and the temperature is cooled to 100-350 ℃ at a cooling rate of 22-30 ℃/s; and a third stage: naturally cooling to room temperature;
5) tempering is carried out, the tempering temperature is 180-380 ℃, the temperature is kept for 20 ~ 40min, and the temperature keeping time is in positive correlation with the thickness of a finished product;
6) naturally cooling to room temperature.
3. The production method of the weather-resistant bridge steel with the yield strength of more than or equal to 690MPa and the low yield ratio as claimed in claim 2, characterized in that: the start rolling temperature of finish rolling is 920-820 ℃, and the finish rolling temperature is 760-810 ℃.
4. The production method of the weather-resistant bridge steel with the yield strength of more than or equal to 690MPa as claimed in claim 2, wherein the tempering temperature is 200-350 ℃, and the temperature is kept for 25 ~ 32 min.
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| CN117248167B (en) * | 2023-11-20 | 2024-01-30 | 江苏省沙钢钢铁研究院有限公司 | Corrosion-resistant I-steel and production method thereof |
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