CN114480949B

CN114480949B - 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, steel plate and manufacturing method thereof

Info

Publication number: CN114480949B
Application number: CN202011160463.6A
Authority: CN
Inventors: 邹德辉; 战国锋; 李红斌; 董中波; 汪荣; 刘自成; 苗雨川
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2023-01-20
Anticipated expiration: 2040-10-27
Also published as: CN114480949A

Abstract

The invention discloses 690 MPa-grade low-yield-ratio weather-resistant welding structural steel which contains the following chemical elements in percentage by mass besides Fe and inevitable impurity elements: 0.05 to 0.11 percent of C; 0.01 to 0.20 percent of Si; 0.50 to 1.10 percent of Mn; cu:0.20 to 0.50 percent; 0.50 to 1.20 percent of Ni; 0.20 to 0.50 percent of Mo; 0.80 to 1.80 percent of Cr; 0.030 to 0.060 percent of Nb; v is 0.030 to 0.060 percent; 0.008 to 0.020 percent of Ti; 0.015-0.045% of Als; ca:0.0005 to 0.0060 percent; and satisfies [ Mn ] + [ Cr ] = 1.80-2.50%; and the steel does not contain B element. Accordingly, the present invention also discloses a steel sheet made of the corrosion-resistant steel for low-density mobile pressure vessels, which is manufactured by a method comprising the steps of: smelting and casting; (2) heating; (3) rolling in two stages; (4) heat treatment: primary quenching, sub-temperature quenching and tempering; wherein the heat preservation temperature of the primary quenching is 890-940 ℃, the heat preservation time is 5-7min, and the water quenching is carried out to the room temperature; the temperature of the sub-temperature quenching is 810-840 ℃, and the holding time is 7-9min; the tempering temperature is 300-380 ℃, and the heat preservation time is 9-12min.

Description

690 MPa-grade low-yield-ratio weather-resistant welding structural steel, steel plate and manufacturing method thereof

Technical Field

The invention relates to steel, a steel plate and a manufacturing method thereof, in particular to low yield ratio weather-proof welding structural steel, a low yield ratio weather-proof welding structural steel plate and a manufacturing method thereof.

Background

The high-strength welded structure steel is widely applied, and not only can the bearing capacity of the structure be improved, but also the self weight of the structure can be effectively reduced by using the high-strength welded structure steel, and the manufacturing and construction cost of the structure can be reduced.

Generally, as the strength of steel is increased, the yield ratio of steel is also increased, generally to 0.90 or more. For some welding structure projects related to personal safety, such as steel structure bridges and high-rise buildings, certain potential safety hazards still exist when the high-strength structural steel with the high yield ratio is applied. Therefore, in these fields, one of the important reasons why high-strength steels have not been widely used is that the yield ratio of the steel is difficult to stably control at a low level.

A large number of researches and practices show that a main control structure with proper hard and soft phases is obtained in the steel, and a lower yield ratio can be realized. The master control tissue with suitable hard and soft phases is obtained by two production processes: hot rolling or heat treatment.

The hot rolling method is to control the final rolling temperature of the hot rolled steel within a certain range and then rapidly cool the steel, namely, the ferrite and martensite dual-phase structure is obtained by controlling the final deformation temperature and the cooling speed. The hot rolling method for producing the dual-phase steel has become a trend of producing the dual-phase steel due to lower cost and relatively simple process. This production method is well established for thin gauge steel plates, but for thick gauge steel plates, up to 60mm, for example, there are major difficulties in actual production. For thick steel plates, the final rolling temperature is selected in a double-phase region, and the requirement on the rolling force of a rolling mill is high; if a staged cooling process is adopted, the control requirement on a cooling system is higher, and for thick steel plates, the problems of uneven performance and the like caused by large temperature difference between the core part and the surface layer exist.

The heat treatment method is to heat the hot rolled or cold rolled steel to a two-phase region or a complete austenitizing region again, keep the temperature for a certain time, and then carry out controlled cooling, thereby obtaining the required ferrite and martensite dual-phase structure. Controlled cooling is generally divided into two cases: one is that after the two-phase region is insulated, the temperature is directly accelerated and cooled to the martensite transformation temperature or below by a cooling medium, in the phase of the two-phase region insulation, the austenitized structure is transformed into martensite or bainite in the subsequent cooling process, and the structure without austenitization is transformed into ferrite in the subsequent cooling process; secondly, after complete austenitizing (or partial austenitizing), the steel is cooled in stages, the steel is slowly cooled to a certain temperature, a small amount of proeutectoid ferrite is precipitated in the steel, the carbon content of an untransformed austenite structure is continuously enriched in the process of precipitating the ferrite, and then the steel is cooled in an accelerated manner, and the untransformed austenite structure is converted into martensite or ferrite. Wherein, the requirement of the equipment for controlling cooling is lower in the first case, and the requirement of the equipment for accurately controlling the temperature and the speed of slow cooling is higher in the second case.

In the prior art, when a heat treatment method is adopted to produce a thick steel plate with high strength and low yield ratio, some steel plates are mainly added with trace element B to improve the hardenability of the steel; some steel contains a high content of the noble alloying element Ni in spite of not adding the B element, so as to improve the hardenability or low-temperature toughness of the steel, or to obtain a certain amount of reversed austenite in the steel to reduce the yield ratio.

The methods for producing the thick steel plate with high strength and low yield ratio adopted in the prior art have certain defects.

For example: chinese patent document with publication No. CN106399840A, publication date of 2017, 2, 15 and titled 'a low-cost low-yield-ratio quenched and tempered Q690E steel plate and production method' discloses a low-cost low-yield-ratio quenched and tempered Q690E steel plate and production method, wherein the thickness of the steel plate is 8-40mm, the yield strength is more than or equal to 690MPa, the tensile strength is 770-940MPa, the elongation A50% is more than or equal to 14%, the yield ratio is less than or equal to 0.90, the longitudinal impact power at-40 ℃ is more than or equal to 34J, and the Ceq is less than or equal to 0.50. The method does not adopt a sub-temperature quenching mode, proper hard and soft phases cannot be obtained, the actual yield ratio of the steel is still higher, the content of C in the steel is higher and is 0.16-0.18%, and the trace element B is added. B is a light element, is not easy to control during steel making, and can influence the low-temperature toughness of a welding joint and the like.

Another example is: the Chinese patent document with the publication number of CN104789892B and the publication number of 2017, 3 and 8 also discloses a low-yield-ratio high-toughness thick steel plate with excellent low-temperature impact toughness and a manufacturing method thereof, wherein the Chinese patent document also discloses the low-yield-ratio high-toughness thick steel plate with excellent low-temperature impact toughness and the manufacturing method thereof, the steel is produced by adopting the processes of two-stage rolling, quenching, cooling after quenching and tempering, the low-yield-ratio high-toughness thick steel plate with excellent low-temperature impact toughness has higher tensile strength, the tensile strength is more than or equal to 1100MPa, the yield strength is more than or equal to 690MPa, the elongation is more than or equal to 14 percent, the yield ratio is lower than 0.65. The thickness specification can reach 5-60 mm. The method reduces the yield ratio of the steel by adding a large amount of Ni element to form a reverse austenite structure in the steel sheet during tempering. Since Ni is a precious alloy, the alloy cost of the steel is significantly increased, and meanwhile, too low yield ratio, for example, less than 0.65, for thick gauge steel plate which does not require deep drawing performance, causes a large waste of resources. The method also requires the addition of Mn with the content of 1.60-2.20%, and the high content of Mn can easily generate obvious center segregation and deteriorate the comprehensive mechanical property of the steel.

For another example: chinese patent publication No. CN109536850A, published as 3/29/2019, entitled "a high toughness and low yield ratio thick steel plate and process for producing the same" discloses a high toughness and low yield ratio thick steel plate and process for producing the same. The heat treatment of the method adopts a secondary quenching process, and after primary quenching, secondary quenching in a two-phase region and tempering, a high-strength and high-toughness low-yield-ratio thick steel plate is obtained, the thickness is 20-80 mm, the microstructure is ferrite and tempered lath martensite, the yield strength is more than or equal to 800MPa, the yield ratio is less than or equal to 0.93, the impact power is more than or equal to 200J at the temperature of minus 50 ℃, the elongation is more than or equal to 18 percent, and the reduction of area is more than or equal to 70 percent. The invention patent does not add trace element B in the aspect of component design, but adds Ni element with the content of 4.0-6.0%, which obviously increases the cost of steel alloy.

Based on the above, in order to overcome the defects of the prior art in producing the high-strength and low-yield-ratio thick steel plate, the invention expects to obtain 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, and the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel not only has high strength and low yield ratio, but also has excellent low-temperature toughness, weldability, weather resistance and cold-hot workability, and meanwhile has better process adaptability, low dependence on steel-making and steel-rolling equipment, and good popularization prospect and application value.

Disclosure of Invention

The invention aims to provide 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, and 690 MPa-grade low-yield-ratio weather-resistant welding structural steel with excellent comprehensive performance can be obtained through reasonable chemical component design. The 690 MPa-grade weather-resistant welding structural steel with the low yield ratio has the advantages of low yield ratio, good toughness matching, good weldability, weather resistance and cold-hot workability, and good popularization prospect and application value.

In order to achieve the aim, the invention provides 690 MPa-grade low-yield-ratio weather-resistant welding structural steel which contains the following chemical elements in percentage by mass in addition to Fe and inevitable impurity elements:

0.05 to 0.11 percent of C; 0.01 to 0.20 percent of Si; 0.50 to 1.10 percent of Mn; cu:0.20 to 0.50 percent; 0.50 to 1.20 percent of Ni; 0.20 to 0.50 percent of Mo; 0.80 to 1.80 percent of Cr; 0.030 to 0.060 percent of Nb; v is 0.030 to 0.060 percent; 0.008 to 0.020 percent of Ti; 0.015-0.045% of Als; ca:0.0005 to 0.0060 percent; and satisfying [ Mn ] + [ Cr ] = 1.80-2.50%, wherein Mn and Cr respectively represent the mass percentage content of each corresponding chemical element in the formula;

and the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel does not contain B element.

Further, in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, the mass percentages of the chemical elements are as follows:

0.05 to 0.11 percent of C; 0.01 to 0.20 percent of Si; 0.50 to 1.10 percent of Mn; cu:0.20 to 0.50 percent; 0.50 to 1.20 percent of Ni; 0.20 to 0.50 percent of Mo; 0.80 to 1.80 percent of Cr; 0.030 to 0.060 percent of Nb; v is 0.030 to 0.060 percent; 0.008 to 0.020 percent of Ti; 0.015-0.045% of Als; ca:0.0005 to 0.006 percent; the balance of Fe and other unavoidable impurities; and satisfying [ Mn ] + [ Cr ] = 1.80-2.50%, wherein Mn and Cr respectively represent the mass percentage content of each corresponding chemical element in the formula;

In the technical scheme of the invention, in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, the design principle of each chemical element is as follows:

c: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, C is an effective element for improving the strength of the steel. The content of C element in steel is not too high, when the content of C element in steel is higher, such as more than 0.11 percent, martensite is easily formed to deteriorate the low-temperature toughness of the steel, the tensile strength is easy to exceed the upper limit, and the influence on the weldability is larger; when the content of C element in the steel is low, for example, less than 0.05%, the strength of the steel sheet is insufficient, the hard phase in the steel is relatively small, and the yield ratio is difficult to control. Therefore, in consideration of the performance of steel, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of the C element is controlled to be 0.05-0.11%.

Of course, in some preferred embodiments, the content of C element may be controlled between 0.06% and 0.1% by mass for better implementation.

Si: in the 690MPa grade low yield ratio weather-resistant welding structural steel of the invention, a certain Si element remains in the steel due to deoxidation, so the lower limit of the Si element in the steel can be set to 0.01%. Accordingly, the content of Si element in steel should not be too high, and too high content of Si will deteriorate the low temperature toughness of HAZ welded to high strength steel, and the upper limit of Si is set to 0.20% in order to ensure the performance of steel. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of the Si element is controlled to be 0.01-0.20%.

Of course, in some preferred embodiments, the content of Si element by mass may be controlled between 0.01 and 0.15% in order to obtain better practical effects.

Mn: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, 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. However, it should be noted that the relatively high Mn content is very likely to cause severe center segregation in the steel, deteriorate the low temperature toughness of the steel, and easily cause cracks in the HAZ of the steel sheet during welding; and too low content of Mn tends to lower the strength of the steel. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of Mn element is controlled to be 0.50-1.10%.

Of course, in some preferred embodiments, the content of Mn element by mass may be controlled between 0.60 and 0.90% for better performance.

Cu: in the 690 MPa-grade weather-resistant welding structural steel with the low yield ratio, cu not only can effectively improve the hardenability of the steel, but also can obviously improve the core strength of a thick steel plate, and is an important element for improving the weather resistance of steel. The Cu element content in the steel is not suitable to be too high, when the Cu element content in the steel is more than 0.50%, the toughness of a welding heat affected zone of the steel plate is reduced, and the network crack is easy to generate in the heating process of the steel billet. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of the Cu element is controlled to be 0.20-0.50%.

Of course, in some preferred embodiments, the content of Cu element may be controlled between 0.25 and 0.45% by mass in order to obtain better practical effects.

Ni: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, the Ni element can effectively improve the hardenability of steel, has a certain strengthening effect, and can also obviously improve the low-temperature toughness of a base metal and a welding HAZ (welding heat affected zone). In addition, ni element can also effectively prevent the network fracture caused by the hot brittleness of Cu. For high-strength steel, when the addition amount of Ni element in the steel is less than 0.50%, the function of improving the low-temperature toughness of Ni is not obvious; when the content of Ni element in steel is too high, the production cost is significantly increased. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of the Ni element is controlled to be 0.50-1.20%.

Of course, in some preferred embodiments, the mass percentage of the Ni element may be controlled between 0.60 and 1.10% in order to achieve better practical effects.

Mo: in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, mo element can precipitate ferrite from austenite, increase the stability of the austenite, have a strong barrier effect on the formation of pearlite and promote bainite structural transformation. 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 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. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of the Mo element is controlled to be 0.20-0.50%.

Of course, in some preferred embodiments, the content of Mo may be controlled between 0.30 and 0.45% by mass in order to achieve better performance.

Cr: in the 690 MPa-level low-yield-ratio weather-resistant welding structural steel, cr element can beForms continuous solid solution with Fe element in steel and forms various carbides, which have great influence on critical point, and a small amount of Cr can make A ₃ The point drops. In addition, cr is also a medium carbide-forming element, and among all the various carbides, cr carbide is the finest one, which can be uniformly distributed in the matrix of the steel, and therefore has high strength, hardness, yield point properties. Because the structure can be thinned and uniformly distributed, the plasticity and the toughness are good. Cr carbide is difficult to dissolve, and can play a role in inhibiting the growth of crystal grains under the condition of short-time heating. Cr element can slow down the decomposition speed of austenite and reduce the critical cooling speed during quenching. However, the content of Cr in steel should not be too high, and when the content of Cr in steel exceeds 1.80%, the welding difficulty is increased, while when the content of Cr in steel is less than 0.80%, the effect of Cr cannot be effectively exerted. Therefore, in the 690 MPa-grade low yield ratio weather-resistant welding structural steel, the mass percentage of the Cr element is controlled to be 0.80-1.80%.

Of course, in some preferred embodiments, the content of Cr element may be controlled between 0.90 and 1.70% by mass for better practical effects.

Nb: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, nb is a strong carbon-nitrogen compound forming element, and can improve the austenite recrystallization temperature of the 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 the content of Nb in the steel is more than 0.060 percent, the effects of refining grains and improving the strength in the low-carbon bainite steel are very obvious, and the yield ratio of the steel is difficult to control; and when the content of the Nb element in the steel is less than 0.030 percent, the grain refining effect of the steel is not obvious, and the strength and the toughness of the steel are influenced. Therefore, in the 690 MPa-grade low yield ratio weather-resistant welding structural steel, the mass percentage of the Nb element is controlled to be between 0.030 and 0.060 percent.

V: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, the appropriate content of the V element can generate a composite strengthening effect with the Nb element, so that the strengthening effect of the steel is improved, the weldability is poor when the content of the V element in the steel is too high, and the beneficial effect cannot be exerted when the content of the V element in the steel is too low. Therefore, in the 690 MPa-grade low yield ratio weather-resistant welding structural steel, the content of the V element is controlled to be between 0.030 and 0.060 percent by mass.

Of course, in some preferred embodiments, the content of V element may be controlled between 0.030 and 0.05% by mass in order to obtain better practical effects.

Ti: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, 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. Therefore, in the 690 MPa-grade low yield ratio weather-resistant welding structural steel, the mass percentage of the Ti element is controlled to be 0.008-0.020%.

And (3) Als: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, als is a main deoxidizing element in the steel. When the content of Als is too high, oxide inclusions of Als are increased, the purity of the steel is reduced, and the toughness of the steel is not facilitated. In addition, the melting point of Als is high, and Als can be used for preventing grain growth in the production process. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the mass percentage of Als is controlled to be 0.015-0.045%.

Ca: in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, proper Ca can spheroidize sulfides, improve the difference of longitudinal and transverse mechanical properties of the 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. Therefore, in the 690 MPa-grade weather-resistant welding structural steel with the low yield ratio, the content of the Ca element in percentage by mass is controlled to be between 0.0005 and 0.006 percent.

Of course, in some preferred embodiments, the content of Ca element may be controlled between 0.0010 and 0.005% by mass in order to achieve better practical effects.

In addition, in the invention, in addition to the control of the mass percentage of a single chemical element, the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel also needs to control Mn and Cr to satisfy the condition of [ Mn ] + [ Cr ] = 1.80-2.50%, wherein Mn and Cr in the above formula respectively represent the mass percentage of each corresponding chemical element.

In addition, it should be noted that the 690MPa grade low yield ratio weather-resistant welding structural steel does not contain B element, and even if trace B element may exist, the B element also belongs to impurity elements in the steel.

Furthermore, in the 690 MPa-grade weather-resistant welding structural steel with low yield ratio, the welding cold crack sensitivity index Pcm is less than or equal to 0.28 percent; and/or weather resistance index I is more than or equal to 6.0%, wherein Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B;

I＝26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu×Ni-9.10Ni×P-33.39Cu ² 。

in the technical scheme, the welding cold crack sensitivity index Pcm of the 690 MPa-grade weather-proof welding structural steel with low yield ratio can meet Pcm not more than 0.28%; the weather resistance index I can meet the condition that I is more than or equal to 6.0 percent. In the above calculation formulas for the weld cold crack sensitivity index Pcm and the weather resistance index I, each element represents the mass percentage of the corresponding element.

Further, in the 690MPa grade low yield ratio weather-resistant welded structural steel of the present invention, among inevitable impurities: p is less than or equal to 0.010 percent; s is less than or equal to 0.005 percent; n is less than or equal to 0.008 percent.

In the above technical scheme, in the 690 MPa-grade low yield ratio weather-resistant welding structural steel, P, S and N are impurity elements in the steel, and the content of the impurity elements in the steel should be reduced as much as possible in order to obtain a steel with better performance and better quality under the permission of technical conditions.

Among them, when the P element in steel is too high, the weather resistance of steel is remarkably improved, but the weldability of steel is also lowered, the cold brittleness tendency of steel is increased, and relatively serious center segregation occurs. Accordingly, if the content of the S element in the steel is too high, the corrosion resistance, low-temperature toughness, and Z-direction properties of the steel are deteriorated. Therefore, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the P element is controlled to be less than or equal to 0.010 percent, the S element is controlled to be less than or equal to 0.005 percent, and the content of the N element in the steel is controlled to be less than or equal to 0.008 percent.

Furthermore, in the 690 MPa-grade weather-resistant welding structural steel with the low yield ratio, the matrix of the microstructure is ferrite + lath bainite.

Further, in the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the performances of the steel meet the following requirements: the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 810MPa, the yield ratio is less than or equal to 0.85, and the impact power KV at the temperature of minus 40 DEG C ₂ ≥120J。

Correspondingly, the invention also aims to provide a steel plate which has lower yield ratio while ensuring the strength of steel, wherein the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 810MPa, the yield ratio is less than or equal to 0.85, and the impact power KV at minus 40 ℃ is lower than ₂ ≥120J。

In order to achieve the purpose, the invention provides the steel plate which is made of the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel.

Further, the steel sheet of the present invention has a thickness of 16 to 50mm.

In addition, another object of the present invention is to provide a method for manufacturing the steel plate, which has a simple manufacturing process and a low manufacturing cost, and the steel plate obtained by the method has excellent properties, and can be effectively applied to a large-span steel structure bridge, thereby having very important practical significance.

In order to achieve the above object, the present invention provides a method for manufacturing the above steel sheet, comprising the steps of:

(1) Smelting and casting;

(2) Heating;

(3) Rolling in two stages;

(4) And (3) heat treatment: primary quenching, sub-temperature quenching and tempering; wherein the heat preservation temperature of the primary quenching is 890-940 ℃, the heat preservation time is 5-7min, and the water quenching is carried out to the room temperature; the temperature of the sub-temperature quenching is 810-840 ℃, and the holding time is 7-9min; the tempering temperature is 300-380 ℃, and the heat preservation time is 9-12min.

In the technical scheme, the manufacturing method is simple in production process and low in production cost. The manufacturing method of the steel plate adopts a three-stage heat treatment operation method, which comprises 'primary quenching, sub-temperature quenching and tempering', and can manufacture the steel plate with lower yield ratio and good toughness matching by reasonably controlling and optimizing the process parameters in the three-stage heat treatment.

In the manufacturing method of the 690 MPa-level low yield ratio weather-resistant welded structure steel plate, in the smelting and casting in the step (1), molten iron pre-desulfurization, converter top and bottom combined blowing, LF furnace treatment, RH vacuum circulation degassing process and full-process protective pouring can be adopted during smelting of the steel so as to ensure and control chemical element components of the molten steel.

Further, in the manufacturing method of the present invention, in the step (2), the core temperature of the billet in the soaking section of the heating furnace is 1080 to 1180 ℃.

Further, in the manufacturing method of the present invention, in the step (3), the rough rolling temperature is controlled to 1130 to 980 ℃, the intermediate blank temperature-waiting thickness T = T + (25 to 70) mm, wherein T represents the thickness of the finished board; and controlling the finish rolling temperature to be 880-760 ℃, and naturally cooling the steel plate after the rolling of the steel plate is finished.

In the technical scheme of the invention, in the two-stage rolling process of the step (3), the controlled finish rolling temperature is moderate, and the requirement on equipment control is low, so that the method is easy to popularize.

Compared with the prior art, the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel, the steel plate and the manufacturing method thereof have the following advantages and beneficial effects:

in the technical scheme, in the chemical composition design of the 690 MPa-grade weather-resistant welding structural steel with the low yield ratio, the design of low carbon, low manganese and high chromium is adopted, and the final steel plate can obtain a microstructure with a matrix of ferrite and lath bainite by adding suitable weather-resistant elements such as Cu-Cr-Ni and the like and suitable refined grain elements such as Nb-V-Ti and the like and assisting the processes of quenching, sub-temperature quenching and tempering. The 690 MPa-grade low-yield-ratio weather-resistant welding structural steel has the yield strength of 690MPa grade, is low in yield ratio, has excellent low-temperature toughness, weldability, weather resistance, cold and hot workability and the like, has good process adaptability, and is not high in dependence on steel making and rolling equipment.

The steel plate prepared from the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel has lower yield ratio while ensuring the strength of steel, wherein the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 810MPa, and the yield ratio is less than or equal to 0.85 and KV impact power at minus 40 DEG C ₂ Not less than 120J, and has excellent weldability and weather resistance.

Correspondingly, the manufacturing method provided by the invention is simple in production process and low in production cost, and the steel plate obtained by the manufacturing method is quite excellent in performance, can be effectively applied to a large-span steel structure bridge, and has very important practical significance.

Drawings

FIG. 1 is a metallographic structure photograph of a steel sheet according to example 1.

Detailed Description

The 690MPa class low yield ratio weathering welded structural steel, steel plate and method for making the same according to the present invention will be further explained and illustrated with reference to the following specific examples and drawings, but the explanation and illustration should not be construed to unduly limit the technical scope of the present invention.

Examples 1 to 7 and comparative examples 1 to 3

The steel plates of examples 1-7 of the present invention were all prepared by the following steps:

(1) Smelting and casting were carried out according to the chemical compositions shown in tables 1-1 and 1-2.

(2) Heating: the core temperature of the billet steel at the soaking section of the heating furnace is 1080-1180 ℃.

(3) Two-stage rolling: the method comprises rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1130-980 ℃, the thickness T = T + (25-70) mm of the intermediate billet to be heated, and T represents the thickness of a finished product plate; and controlling the finish rolling temperature to be 880-760 ℃, and naturally cooling the steel plate after the rolling of the steel plate is finished.

(4) And (3) heat treatment: primary quenching, sub-temperature quenching and tempering; wherein the heat preservation temperature of the primary quenching is 890-940 ℃, the heat preservation time is 5-7min, and the water quenching is carried out to the room temperature; the heat preservation temperature of the sub-temperature quenching is 810-840 ℃, and the heat preservation time is 7-9min; the tempering temperature is 300-380 ℃, and the heat preservation time is 9-12min.

The chemical element compositions and the related process designs of the steel plates of examples 1-7 described in the present invention all meet the design specification requirements of the present invention.

It should be noted that the steel plates of examples 1 to 7 were all made of 690MPa grade low yield ratio weathering welding structural steel of the present invention; the steel sheets of comparative examples 1 to 3 were example 1 in the patent publication No. CN106399840A, example 1 in the patent publication No. CN109266812A, and example 1 in the patent publication No. CN109536850A, respectively.

Tables 1-1 and tables 1-2 show the mass percentage of each chemical element in the 690MPa class low yield ratio weathering welded structural steel used in examples 1-7 and the comparative steel used in comparative examples 1-3.

TABLE 1 (wt%, balance Fe and unavoidable impurities other than P, S, N)

Tables 1-2.

Numbering	Mn+Cr	Pcm	I
				Example 1	1.90	0.24	6.2
Example 2	1.90	0.26	6.4
				Example 3	1.80	0.25	6.9
Example 4	1.90	0.26	7.6
				Example 5	2.00	0.27	8.1
Example 6	2.30	0.28	8.3
				Example 7	2.30	0.25	7.3
Comparative example 1	1.44	0.29	1.1
				Comparative example 2	1.81	0.24	1.0
Comparative example 3	2.10	0.28	-

Note: in the above formula, the weld cold crack sensitivity index Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B; weather resistance index I =26.01Cu +3.88Ni +1.20Cr +1.49Si +17.28P-7.29Cu X Ni-9.10Ni X P-33.39Cu ² (ii) a The elements in the above formula all represent the mass percentage of the corresponding elements.

Table 2 lists the finished plate thicknesses of the steel sheets of examples 1-7 and the comparative steel sheets of comparative examples 1-3 and the specific process parameters in the above process steps.

Table 2.

Note: in the actual operation process, the rough rolling temperature and the finish rolling temperature are not constant values but are variable range values, so that the rough rolling temperature and the finish rolling temperature of each example in table 2 are both range values.

The steel plates of finished examples 1 to 7 and comparative examples 1 to 3 were sampled, respectively, the density of the steel plates was measured, and various mechanical property tests were performed, and the obtained mechanical property test results are listed in table 3.

The specific mechanical property test method is as follows:

(1) And (3) tensile test: the test results are shown in Table 3, which were carried out at room temperature according to the provisions of GB 228 "Metal tensile test methods".

(2) And (3) impact test: according to the provisions of GB/T229 metal Charpy impact test method, the impact energy at a test temperature of-40 ℃ is measured, and the test results in Table 3 are obtained.

Table 3 shows the results of mechanical property tests of the steel sheets of examples 1 to 7 and comparative examples 1 to 3.

Table 3.

As can be seen from tables 1 to 1, the chemical composition of comparative example 1 has a high carbon content of 0.18%, and an excessively high C content inevitably deteriorates the weldability thereof, and the steel does not contain Ni, which increases the low-temperature toughness, and thus makes the low-temperature toughness thereof unstable, and the steel also contains B, which makes the steel-making control difficult and causes the low-temperature impact work in the welding heat affected zone to be unstable. The chemical composition of comparative example 2, with a carbon content of 0.12% still higher, with B added, without Ni addition, had the same effect on performance as comparative example 1. In comparative example 3, the carbon content was low and the trace element B was not added, but a large amount of Ni was added to the alloy to a content of 4.5%, which is a precious alloy, inevitably increasing the manufacturing cost thereof and adversely affecting the weldability. In tables 1 to 2, the weld cold crack sensitivity index Pcm is two important indices for evaluating the weldability of steel, and generally, the higher the value, the worse the weldability. In general, examples 1-7 of the present invention all had lower Pcm values than comparative examples 1 and 3. The value I is a weather resistance index for evaluating the weather resistance of steel, and the higher the general value is, the better the weather resistance is considered, and the I of the examples 1 to 7 of the invention is more than 6.0%, which is much higher than that of the comparative examples 1, 2 and 3, and shows that the weather resistance of steel is better.

As can be seen from Table 2, the heat treatments of examples 1 to 7 of the present invention each employ a three-stage process, which is a slightly longer process, as in comparative example 3. However, comparative examples 1 and 2 employ only two-stage heat treatment, which makes the yield ratio of steel higher and is not a suitable treatment.

As can be seen from Table 3, the steel sheets of examples 1 to 7 of the present invention all had yield strengths of 690MPa or more and tensile strengths of 810MPa or more, which were comparable to those of comparative steel sheets of comparative examples 1 to 3. However, the steel sheets of examples 1 to 7 according to the present invention all had yield ratios of 0.85 or less and much lower than those of comparative examples 1 to 3, compared to comparative examples 1 to 3, and the steel sheets of examples 1 to 7 according to the present invention had very stable low-temperature toughness and had a work-to-impact KV of-40 deg.C ₂ Are all more than or equal to 120J and are far higher than the comparative steel plates of comparative example 1 and comparative example 2.

FIG. 1 is a photograph of a metallographic structure of a steel plate according to example 1.

As shown in fig. 1, in the embodiment of example 1, the 690MPa class low yield ratio weathering resistant welded structural steel of the present invention was observed and analyzed, and the microstructure matrix was ferrite + lath bainite.

Therefore, the steel plate obtained by the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel has a lower yield ratio while ensuring that the yield strength of the steel is 690MPa grade, wherein the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 810MPa, and the yield ratio is less than or equal to 0.85 KV work of impact energy at-40 DEG C ₂ The high-strength steel plate has the advantages of high low-temperature toughness, high weldability, high weather resistance and high cold and hot workability, can be effectively applied to large-span steel structure bridges, and has very important practical significance.

It should be noted that the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradicted by each other.

It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention.

Claims

1. The 690 MPa-grade weather-resistant welding structural steel with the low yield ratio is characterized by comprising the following chemical elements in percentage by mass:

0.05 to 0.11 percent of C; 0.01 to 0.20 percent of Si; 0.50 to 1.10 percent of Mn; cu:0.20 to 0.50 percent; 0.50 to 1.20 percent of Ni; 0.20 to 0.50 percent of Mo; 0.80 to 1.80 percent of Cr; 0.030 to 0.060 percent of Nb; v is 0.030 to 0.060 percent; 0.008 to 0.020 percent of Ti; 0.015 to 0.045 percent of Als; ca:0.0005 to 0.0060 percent; the balance being Fe and other unavoidable impurities; and satisfies [ Mn ] + [ Cr ] = 1.80-2.50%;

the 690 MPa-grade low-yield-ratio weather-resistant welding structural steel does not contain B element;

the matrix of the microstructure is ferrite + lath bainite; the performance of the material meets the following requirements: the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 810MPa, the yield ratio is less than or equal to 0.79, and the impact energy KV at the temperature of minus 40 DEG C ₂ ≥120J；

The 690 MPa-level weather-resistant welding structural steel with low yield ratio adopts primary quenching, sub-temperature quenching and tempering in the heat treatment step; wherein the heat preservation temperature of the primary quenching is 890-940 ℃, the heat preservation time is 5-7min, and the water quenching is carried out to the room temperature; the temperature of the sub-temperature quenching is 810-840 ℃, and the holding time is 7-9min; the tempering temperature is 300-380 ℃, and the heat preservation time is 9-12min.

2. The 690MPa grade low yield ratio weathering weld structural steel of claim 1, characterized in that its chemical elements satisfy at least one of the following in mass percent:

C：0.06～0.1％；

Si：0.01～0.15％；

Mn：0.60～0.90％；

Cu：0.25～0.45％；

Ni：0.60～1.10％；

Mo：0.30～0.45％；

Cr：0.90～1.70％；

V：0.030～0.05％。

3. the 690MPa grade low yield ratio weathering resistant welded structural steel of claim 1, having a weld cold crack susceptibility index Pcm of 0.28% or less; and/or weather resistance index I is more than or equal to 6.0%, wherein Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B; i =26.01Cu +3.88Ni +1.20Cr +1.49Si +17.28P-7.29Cu X Ni-9.10Ni X P-33.39Cu ² 。

4. The 690MPa grade low yield ratio weathering weld structural steel of claim 1, wherein, among unavoidable impurities: p is less than or equal to 0.010 percent; s is less than or equal to 0.005 percent; n is less than or equal to 0.008 percent.

5. A steel sheet, characterized in that it is made of the 690MPa grade low yield ratio weather-resistant welded structural steel according to any one of claims 1 to 4.

6. A steel sheet according to claim 5, wherein the thickness is 16 to 50mm.

7. A method of manufacturing a steel sheet according to claim 5 or 6, characterized by comprising the steps of:

(1) Smelting and casting;

(2) Heating;

(3) Rolling in two stages;

8. The manufacturing method according to claim 7, wherein in the step (2), the core temperature of the billet at the soaking section of the heating furnace is 1080-1180 ℃.

9. The manufacturing method according to claim 8, wherein in the step (3), the rough rolling temperature is controlled to be 1130 to 980 ℃, the intermediate slab temperature-waiting thickness T = T + (25 to 70) mm, wherein T represents the thickness of the finished board; and controlling the finish rolling temperature to be 880-760 ℃, and naturally cooling the steel plate after the rolling of the steel plate is finished.