CN104046899B - A 550MPa-grade steel plate that can be welded with large heat input and its manufacturing method - Google Patents

Abstract

A 550MPa-grade steel plate that can be welded with high heat input and its manufacturing method, the composition weight percentages of which are: C0.04-0.08%, Si≤0.10%, Mn1.30-1.60%, P≤0.013%, S≤0.003%, Cu0.05～0.30%, Ni0.25～0.55%, B0.0015～0.0030%, Ti0.008～0.016%, Nb0.015～0.030%, N0.0040～0.0080%, Al≤0.010%, Ca0.001 ~0.004%, the rest is Fe and unavoidable inclusions. The invention uses ultra-low carbon C-ultra-low Si-high Mn-Nb low alloy steel as the basis, reduces Al content in steel, Ti-B microalloying, 0.25≤B/N≤0.4, Ca/S ratio of 1.0～ 3.0 and Ca×S ^0.28 ≤1.0×10 ^-3 , optimize the TMCP process. Steel plate yield strength ≥ 465MPa, tensile strength 550 ~ 650MPa, Charpy impact energy (single value) ≥ 100J at -60°C, high heat input weldability steel plate, high heat input steel plate welding heat affected zone - 40°C Xia Specific impact energy (single value) ≥ 100J.

Description

A 550MPa-grade steel plate that can be welded with large heat input and its manufacturing method

technical field

The present invention relates to low-carbon (high-strength) low-alloy steel and its manufacturing method, in particular to a 550MPa-grade steel plate that can be welded with high heat input and its manufacturing method. The Charpy impact energy (single value) of ℃ ≥ 100J, and the steel plate that can be welded with large heat input, the Charpy impact energy (single value) of the steel plate welding heat affected zone of large heat input -40 ℃ ≥ 100J.

Background technique

As we all know, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, widely used in oil and gas pipelines, offshore platforms, shipbuilding, bridge structures, boiler pressure vessels, building structures, automobile industry, railway transportation and machinery under manufacture. The properties of low-carbon (high-strength) low-alloy steel depend on its chemical composition and the process system of the manufacturing process, among which strength, toughness and weldability are the most important properties of low-carbon (high-strength) low-alloy steel, which are ultimately determined by the finished steel state of the microstructure. With the continuous development of science and technology, people put forward higher requirements for the strength, toughness and weldability of steel, that is, to greatly improve the comprehensive mechanical properties and service performance of steel plates while maintaining low manufacturing costs, so as to reduce the The cost is saved by using the quantity, and the weight, stability and safety of the steel member itself are reduced.

At present, the research climax of developing a new generation of high-performance steel materials has been set off worldwide. Through alloy combination design, innovative controlled rolling/TMCP technology and heat treatment process, better microstructure matching can be obtained, so that the steel plate can obtain better strength, toughness and strength. Plastic matching, seawater corrosion resistance, better weldability and fatigue resistance.

In the prior art, when producing thick steel plates with yield strength ≥ 420MPa and low-temperature impact toughness ≥ 34J at -60°C, a certain amount of Ni or Cu+Ni elements (≥ 0.30%) should generally be added to the steel, such as (TheFirth (1986 )internationalSymposium and Exhibit on Offshore Mechanics and Arctic Engineering, 1986, Tokyo, Japan, 354; "DEVELOPMENTS IN MATERIALS FOR ARCTIC OFFSHORE STRUCTURES"; Newspaper, 1985, No.1 68～72; "Application of Accelerated Cooling For Producing 360MPa Yield Strength Steel plates of up to 150mm in Thickness with Low Carbon Equivalent", Accelerated Cooling Rolled Steel, 1986, 209～219; "High Strength Steel Plates For Ice－ Breaking Vessels Produced by Thermo－Mechanical Control Process", Accelerated Cooling Rolled Steel, 1986, 249～260; "420MPa Yield Strength Steel Plate with Superior Fracture Toughness for Arctic Offshore Structures", Kawasaki steel technical report, 1999, No.40, 56; and500MPa Yield Strength Steel Plate with High HAZtoughness Produced by TMCP for Offshore Structure", Kawasaki steel technical report, 1993, No.29, 54; "Toughne ss Improvement in Bainite Structure by Thermo-Mechanical Control Process” (Japanese) Sumitomo Metal, Vol.50, No.1(1998), 26; 1984, No. 314, 19~43), to ensure that the base steel plate has excellent low-temperature toughness. When welding with a heat input of <50KJ/cm, the toughness of the heat-affected zone HAZ can also reach -60℃Akv≥34J; but When welding with super large heat input (≥100KJ/cm), the low-temperature toughness of the welding heat-affected zone (HAZ) is generally difficult to achieve, and the low-temperature toughness of the heat-affected zone (HAZ) is seriously deteriorated.

A large number of patent documents only explain how to realize the low-temperature toughness of the base steel plate, and explain less about how to obtain excellent low-temperature toughness of the heat-affected zone (HAZ) under welding conditions, especially how to ensure the heat-affected zone (HAZ) when welding with super large heat input. HAZ) has very little low temperature toughness, and in order to ensure the low temperature toughness of the steel plate, a certain amount of Ni or Cu+Ni elements are generally added to the steel, and the low temperature toughness of the heat affected zone (HAZ) of the steel plate with super large heat input welding is rarely able Reach -60°C, such as (Japanese Patent No. 63-93845, No. 63-79921, No. 60-258410, No. 4-285119, No. 4-308035, No. 3-264614, No. 2-250917, No. 4 -143246, US Patent 4855106, US Patent 5183198, US Patent 4137104).

At present, only Nippon Steel Corporation of Japan adopts oxide metallurgy technology (US Patent4629505, WO 01/59167A1) to improve the low temperature toughness of the heat-affected zone (HAZ) of the ultra-large heat input welded steel plate, that is, during the welding process of large heat input, near the fusion line , due to long-term high-temperature action, TiN particles will dissolve and lose their effect. Ti ₂ O ₃ is more stable than TiN, even if it reaches the melting point of steel, it will not dissolve. Ti ₂ O ₃ particles can become the nucleation site of acicular ferrite in the austenite grain, promote the nucleation of acicular ferrite (AF) in the austenite grain, effectively divide the austenite grain, and fine The HAZ structure is formed to form a high-strength and high-toughness acicular ferrite structure.

Contents of the invention

The object of the present invention is to provide a kind of 550MPa grade steel plate that can be welded with large heat input and its manufacturing method. The steel plate that can be welded with large heat input, the Charpy impact energy (single value) of the steel plate welding heat affected zone at -40°C (single value) ≥ 100J.

For achieving the above object, technical scheme of the present invention is:

Steel plates for low-temperature structures that can be welded with high heat input are one of the more difficult types of thick plate products. The reason is that such steel plates not only require ultra-low C, low carbon equivalent Ceq, high strength, excellent low-temperature toughness and fatigue resistance Performance, and the steel plate must be able to withstand large heat input welding, and the low-temperature impact toughness of the welding heat-affected zone is excellent; however, it is difficult to meet these performance requirements at the same time. Ultra-low C, low carbon equivalent Ceq and high strength conflict with each other in composition design and process design, and it is difficult to reconcile, that is, it is difficult to achieve high strength of steel plate while reducing C content and carbon equivalent Ceq; while increasing strength, It is difficult to achieve excellent weldability of steel sheets, especially high heat input weldability. How to balance high strength, low temperature toughness and high heat input weldability is one of the biggest difficulties of the product of the present invention, and it is also a key core technology.

Therefore, in terms of key technical route, composition and process design, the present invention integrates the key factors affecting the high and high strength of the steel plate, excellent low-temperature toughness, and high heat input weldability, etc., and successfully avoids the technology patented by Nippon Steel Corporation Blockade (titanium oxide metallurgy technology and magnesium oxide metallurgy technology), starting from alloy design, using ultra-low carbon C-ultra-low Si-high Mn-Nb low-alloy steel as the basis, reducing the content of Al, Ti- B microalloying, 0.25≤B/N≤0.45, [1.17(%Si)+6.77(%Al)+2.12(%Nb)+0.13(%Mn)]×(%C)≤0.053, Ca treatment and Ca The /S ratio is controlled between 1.0 and 3.0 and Ca×S ^0.28 ≤1.0×10 ^-3 , and the TMCP process is optimized so that the microstructure of the finished steel plate is a small amount of ferrite + diffusely distributed bainite, and the microstructure The average grain size is less than 10 μm. While obtaining uniform and excellent low-temperature toughness of the base metal steel plate, the low-temperature toughness of the HAZ is also excellent during high heat input welding, that is, the base metal steel plate -60°C Akv≥100J, welding simulated heat-affected zone (HAZ)－40℃Akv≥100J, especially suitable for icebreaker hulls, offshore platforms, sea-crossing bridges, offshore wind tower structures, port machinery, etc. in icy sea areas, and can achieve low-cost and stable batch industrial production.

Specifically, the large heat input weldable 550MPa grade steel plate of the present invention has a composition weight percentage of:

C: 0.04% to 0.08%

Si: ≤0.10%

Mn: 1.30% to 1.60%

P: ≤0.013%

S: ≤0.003%

Cu: 0.05% to 0.30%

Ni: 0.25% to 0.55%

B: 0.0015% to 0.0030%

Ti: 0.008% to 0.016%

Nb: 0.015% to 0.030%

N: 0.0040%～0.0080%

Al: ≤0.010%

Ca: 0.001% to 0.004%

The rest are Fe and unavoidable inclusions; and the above elements must satisfy the following relationship at the same time:

0.25≤B/N≤0.45;

[1.17(%Si)+6.77(%Al)+2.12(%Nb)+0.13(%Mn)]×[(%C)+0.033(%Mn)]≤0.053;

Ca treatment, and the Ca/S ratio is controlled between 1.0-3.0 and Ca×S ^0.28 ≤1.0×10 ^-3 .

In the composition system design of the steel plate of the present invention:

In order to obtain uniform and excellent strength, toughness, and strong plasticity matching, and the steel plate can withstand large heat input welding, the chemical composition of the TMCP steel plate of the present invention has the following characteristics:

C has a great influence on the strength, low temperature toughness, elongation and weldability of TMCP steel plate, especially the high heat input weldability. From the perspective of improving the low temperature toughness and high heat input weldability of TMCP steel plate, it is hoped that the content of C in the steel should be controlled low; but From the perspective of steel strength, low temperature toughness, microstructure control and manufacturing cost in the manufacturing process, the C content should not be controlled too low; too low C content will easily lead to high grain boundary mobility, and the base metal steel plate and welded HAZ The grains in the microstructure are coarse, and the low C content in the steel leads to the weakening of the grain boundaries, which seriously deteriorates the low-temperature toughness of the base steel plate and the welded HAZ; therefore, the reasonable range of C content is 0.04% to 0.08%.

As the most important alloying element in the steel, Mn not only increases the strength of the steel plate, but also expands the austenite phase region, reduces the temperature of the Ar ₃ point, and refines the bainite clusters of the TMCP steel plate to improve the low-temperature toughness of the steel plate. The formation of low-temperature phase transformation structure can improve the strength of the steel plate; but Mn is prone to segregation during the solidification process of molten steel, especially when the Mn content is high, it will not only cause difficulty in casting operation, but also easily conjugate with C, P, S and other elements Segregation phenomenon, especially when the C content in the steel is high, will aggravate the segregation and porosity in the central part of the slab. Severe segregation in the central area of the slab will easily form abnormal structures in the subsequent rolling, heat treatment and welding processes, resulting in low temperature toughness of the steel plate. Cracks appear in welded joints; therefore, according to the C content range, it is extremely important to select the appropriate Mn content range for TMCP steel plates, and the suitable Mn content is 1.30% to 1.60%.

Si promotes the deoxidation of molten steel and can improve the strength of the steel plate, but the deoxidation effect of Si is not great when the molten steel is deoxidized by Al. Although Si can improve the strength of the steel plate, Si seriously damages the low temperature toughness, elongation and weldability of the steel plate, especially in large Under heat input welding conditions, Si not only promotes the formation of M-A islands, but also the formed M-A islands are relatively large in size and unevenly distributed, which seriously damages the low-temperature toughness of the welding heat-affected zone (HAZ). Therefore, the Si content in the steel should be controlled as much as possible. Low, considering the economy and operability of the steelmaking process, the Si content is controlled below 0.10%.

As a harmful inclusion in steel, P has a huge damage effect on the mechanical properties of steel, especially low-temperature impact toughness, elongation and weldability (especially high heat input weldability), and the lower the requirement in theory, the better; but considering the possibility of steelmaking Operability and steelmaking costs, for TMCP steel plates that require large heat input welding, -60°C toughness, high strength and high heat input welding, the P content needs to be controlled at ≤0.013%.

S, as a harmful inclusion in steel, has a great detrimental effect on the low temperature toughness of steel. More importantly, S combines with Mn in steel to form MnS inclusions. During hot rolling, the plasticity of MnS makes MnS extend along the rolling direction. , forming a MnS inclusion band along the rolling direction, which seriously damages the low-temperature impact toughness, elongation, Z-direction performance, and weldability of the steel plate (especially the weldability with large heat input), and S is also the main element that produces hot embrittlement during hot rolling. Theoretically, the lower the requirement, the better; but considering the operability of steelmaking, steelmaking cost and the principle of smooth logistics, for TMCP steel plates that require large heat input welding, -60°C toughness, high strength and high heat input welding, S content needs to be controlled at ≤0.003%.

Cu is also an austenite stabilizing element, adding Cu can also reduce the Ar ₃ point temperature, improve the hardenability of the steel plate, the atmospheric corrosion resistance of the steel plate, the strength and low temperature toughness of the steel plate (the effect is obvious under the TMCP process); but the amount of Cu added Too much (higher than 0.30%), the weldability of the steel plate will deteriorate sharply with large heat input; too little Cu addition, less than 0.05%, will have little effect; therefore, the Cu content is controlled between 0.05% and 0.30%; In addition to reducing the copper embrittlement of copper-containing steels and alleviating intergranular cracking in the hot rolling process, the compound addition of Ni and Ni is more important because both Cu and Ni are austenite stabilizing elements, and the compound addition of Cu and Ni can greatly Reduce Ar ₃ , increase the driving force of austenite to ferrite transformation, refine the microstructure, improve the strength and low temperature toughness of the steel plate.

The addition of Ni can not only improve the mobility of dislocations in the ferrite phase, promote the cross-slip of dislocations, and improve the intrinsic toughness of ferrite _; Therefore, Ni has the function of improving the strength and low temperature toughness of TMCP steel plate at the same time. Adding Ni to steel can also reduce the copper embrittlement of copper-containing steel, reduce the intergranular cracking in the hot rolling process, and improve the atmospheric corrosion resistance of the steel plate; theoretically speaking, the higher the Ni content in the steel, the better. However, too high Ni content will harden the heat-affected zone of welding, which is unfavorable to the large heat input weldability of the steel plate; at the same time, Ni is a very precious element. Considering the performance and price ratio, the Ni content is controlled between 0.25% and 0.55%. To ensure the hardenability of the steel plate and the strength and toughness of the steel plate, the level of strong plasticity without damaging the weldability of the steel plate.

In order to ensure that a certain amount of solid-solution B atoms in the steel segregate at the austenite grain boundaries, inhibit the formation of grain boundary ferrite, promote the formation of bainite/martensite in the low-temperature phase transformation structure during the TMCP process, and achieve ultra-low carbon, low High strength under the condition of carbon equivalent; secondly, there are enough B atoms in the steel to combine with N atoms to generate a certain number of dispersed BN particles, which promotes the formation of ferrite grains in austenite grains during the welding process of large heat input , split the original coarse austenite grains, refine the microstructure of the heat-affected zone of welding with large heat input, and improve the low-temperature toughness of the heat-affected zone of welding; therefore, the B element content in the steel shall not be less than 0.0015%; but when the B in the steel If the content is too high, a large amount of coarse Fe ₂₃ (CN) ₆ will be precipitated on the original austenite grain boundary, which will seriously embrittle the base metal steel plate and the low-temperature toughness and plasticity of the welding heat-affected zone, resulting in the cold and hot processing characteristics, service bearing and crack resistance of the steel plate. The crack arrest property deteriorates sharply, and the safety of the steel plate cannot be guaranteed during service, so the B content of the steel plate should not exceed 0.0030%.

The affinity between Ti and N is much greater than that between B and N. When a small amount of Ti is added, N preferentially combines with Ti to form dispersed TiN particles, which can inhibit the excessive growth of austenite grains during slab heating and hot rolling. Improve the low-temperature toughness of the steel plate; more importantly, to a certain extent, inhibit the grain growth in the heat-affected zone (farther from the fusion line) during the welding process of large heat input, and improve the toughness of the heat-affected zone; add too little Ti content (0.008% ) has little effect. When the Ti content is added too much (0.016%), the precipitation of BN particles in the steel is inhibited, resulting in a small number of BN particles, which cannot improve the low-temperature toughness of the heat-affected zone of large heat input welding; in addition, the Ti content in the steel is particularly For a long time, most of the N in the steel is combined with Ti, resulting in too high solid solution B content in the steel, which affects the low temperature toughness and high heat input weldability of the steel plate; therefore, the appropriate Ti content range is 0.008% to 0.016%.

The purpose of adding a small amount of Nb element in the steel is to perform non-recrystallized controlled rolling and improve the strength and toughness of the TMCP steel plate. When the Nb addition is less than 0.015%, in addition to the controlled rolling effect that cannot be effectively exerted, the TMCP steel plate can be strengthened. It is not enough; when the Nb addition exceeds 0.030%, the formation of upper bainite (Bu) and the secondary precipitation embrittlement of Nb (C, N) will be induced under the condition of high heat input welding, which will seriously damage the heat affected zone of high heat input welding (HAZ) low-temperature toughness, so the Nb content is controlled between 0.015% and 0.030%, to obtain the best controlled rolling effect, and to achieve the matching of strength and toughness/strong plasticity of TMCP steel plate without compromising the toughness of high heat input welding HAZ .

Ensure that there are enough BN particles in the heat-affected zone of large heat input welding to promote the nucleation of ferrite, split the coarse prior austenite grains in the heat affected zone, refine the microstructure of the heat affected zone of large heat input welding, and improve the large heat input The low-temperature toughness of the welding heat-affected zone, the N content in the steel should not be less than 0.0040%; however, when the N content in the steel is too high, all the B atoms in the steel will combine with the N atoms, and after BN particles are formed, there will be no solid solution B in the steel. atoms, resulting in low strength of ultra-low C and low carbon equivalent steel sheets, which cannot meet the development requirements; in addition, the excessive N content in the steel reaches the increase of solid solution N atoms in the welding heat-affected zone with large heat input, seriously deteriorating the low temperature of the welding heat-affected zone Toughness; therefore the N content in the steel shall not exceed 0.0080%.

In order to ensure the formation of a sufficient amount of BN particles in the steel and suppress the massive generation of AlN particles, the upper limit of the Al content in the steel must be controlled; therefore, the Al content in the steel should not exceed 0.010%.

Ca treatment of steel, on the one hand, can further purify the molten steel, on the other hand, denature the sulfide in the steel to make it into non-deformable, stable and fine spherical sulfide, inhibit the hot brittleness of S, and improve the steel plate Low-temperature toughness, elongation and Z-direction performance, and anisotropy for improving toughness of steel plates. The amount of Ca added depends on the level of S content in the steel. If the amount of Ca added is too low, the treatment effect will not be great; The starting point of fracture cracks reduces the low-temperature toughness and elongation of steel, and at the same time reduces the purity of steel and pollutes molten steel; therefore, the appropriate range of Ca content is 0.0010% to 0.0040%.

In particular, the content of the above elements must simultaneously satisfy the following relationship:

0.25≤B/N≤0.45: While ensuring that there are sufficient and dispersed BN precipitation in the large heat input welding heat-affected zone, both the base metal steel plate and the welding heat-affected zone have certain solid-solution B atoms. Realize the following functions: A) Under the condition of ultra-low carbon and low carbon equivalent, through the high hardenability of solid solution B, the balance of high strength, high strength and low temperature toughness of the base steel plate is guaranteed; secondly, solid solution B suppresses high heat The formation of side lath ferrite with coarse austenite grain boundaries in the input welding heat affected zone promotes the formation of austenite intragranular ferrite and improves the low temperature toughness of the heat affected zone of large heat input welding; B) After the steel plate experiences high heat During the input welding process, the diffusely distributed BN in the welding heat-affected zone promotes the nucleation of ferrite in the austenite grain, divides the coarse original austenite grains in the heat-affected zone, refines the microstructure of the heat-affected zone, and improves the large heat-affected zone. Enter the low temperature toughness of the weld heat affected zone.

[1.17(%Si)+6.77(%Al)+2.12(%Nb)+0.13(%Mn)]×[(%C)+0.033(%Mn)]≤0.053: Suppress large heat input welding heat-affected zone M-A Form and reduce the number of heat-affected zone M-A, reduce the size of heat-affected zone M-A, promote the phase transformation of polygonal ferrite in the heat-affected zone and the decomposition of M-A during the welding thermal cycle, and improve the low-temperature toughness and Crack resistance and crack arrest characteristics greatly improve the safety and reliability of welded structures.

Ca treatment and the Ca/S ratio is controlled between 1.0 and 3.0 and Ca×S ^0.28 ≤1.0×10 ^-3 : while ensuring sulphide spheroidization and minimizing the impact of inclusions on low temperature toughness and weldability, Ca(O, S) The particles are uniformly and finely distributed in the steel, which can inhibit the growth of austenite grains in the heat-affected zone of large heat input welding, and improve the low-temperature toughness of the heat-affected zone of welding.

The manufacturing method of the large heat input welding 550MPa grade steel plate of the present invention, it comprises the following steps:

1) Smelting and casting

Smelt and cast slabs according to the above ingredients; then the slabs are heated and the temperature is controlled between 1030°C and 1130°C to ensure that all Nb in the steel is solid-dissolved into the austenite during the slab heating process, and the slabs Austenite grains do not grow abnormally;

2) Rolling, the total compression ratio of the steel plate is the thickness of the slab/thickness of the finished steel plate ≥ 3.6

The first stage is ordinary rolling, using the maximum rolling capacity of the rolling mill for continuous rolling to maximize the production capacity of the rolling line while ensuring recrystallization of the deformed billet and refining austenite grains;

The second stage adopts non-recrystallized controlled rolling, the controlled rolling start temperature is controlled at 780°C-820°C, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥50%, and the final rolling temperature is 760°C-800 ℃;

3) cooling

Accelerated cooling of the steel plate is carried out immediately after the controlled rolling is completed. The steel plate is cooled at a temperature of 750°C to 790°C, the cooling rate is ≥7°C/s, and the cooling stop temperature is 350°C to 550°C. Then the steel plate is naturally air-cooled to 350°C and then slowly cooled. , the slow cooling process is to keep the steel plate for at least 24 hours under the condition that the surface temperature of the steel plate is greater than 300°C.

In the manufacturing process of the present invention:

According to the above content ranges of C, Mn, Nb, B and Ti, the slab heating temperature is controlled between 1030°C and 1130°C to ensure that all Nb in the steel is solid-dissolved into the austenite during the slab heating process, The austenite grains in the slab do not grow abnormally.

The total compression ratio of the steel plate (thickness of the slab/thickness of the finished steel plate) is ≥3.6, which ensures that the rolling deformation penetrates to the core of the steel plate and improves the microstructure and performance of the central part of the steel plate.

The first stage is ordinary rolling, using the maximum rolling capacity of the rolling mill for continuous rolling to maximize the production capacity of the rolling line while ensuring recrystallization of the deformed billet and refining austenite grains;

The second stage adopts non-recrystallization controlled rolling. According to the content range of Nb element in the above steel, in order to ensure the effect of non-recrystallized controlled rolling, the controlled rolling start temperature is controlled at 780℃～820℃, and the reduction rate of rolling pass is ≥ 7%, cumulative rolling reduction ≥ 50%, finish rolling temperature 760℃～800℃.

After the controlled rolling is completed, the steel plate is immediately transported to the ACC equipment at the maximum conveying speed of the roller table, and then the steel plate is accelerated to cool; The temperature is 350°C to 550°C, and then the steel plate is naturally air-cooled to 350°C and then slowly cooled. The slow cooling process is to keep the temperature of the steel plate surface higher than 300°C for at least 24 hours.

The beneficial effects of the present invention are:

The steel plate of the present invention is designed through a simple combination of components and combined with the TMCP manufacturing process, not only can produce TMCP steel plate with excellent comprehensive performance at low cost, but also greatly shorten the manufacturing cycle of the steel plate, creating huge value for the enterprise and realizing Green environmental protection of the manufacturing process. The high performance and high added value of the steel plate are concentrated in the fact that the steel plate has high strength and excellent low-temperature toughness. At the same time, the weldability of the steel plate (especially the high heat input weldability) is also excellent, successfully solving the problem of ultra-low C, low carbon equivalent Under certain conditions, the steel plate obtains high strength and excellent low-temperature toughness, which greatly improves the safety, stability and fatigue resistance of large-scale heavy steel structures; good weldability (especially single-pass welding with large heat input) saves the user's steel component manufacturing The cost has greatly shortened the time for the user's steel component manufacturing, and created huge value for the user.

Description of drawings

Fig. 1 is a photograph of the microstructure (1/4 thickness) of Steel Example 3 of the present invention.

detailed description

The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

Table 1 shows the composition of the steel example of the present invention, and the balance is Fe and unavoidable impurities. Tables 2 to 3 are the manufacturing processes of the steel examples of the present invention, respectively. Table 4 is the performance of the steel of the embodiment of the present invention.

It can be seen from the microstructure of the steel of the embodiment of the present invention shown in Fig. 1 that the microstructure of the steel of the present invention is a small amount of ferrite + dispersedly distributed bainite, and the average grain size of the microstructure is below 10 μm .

With the development of our country's national economy and the requirement of building a conservation-oriented harmonious society, marine development has been placed on the daily agenda. At present, my country's marine engineering construction and its related equipment manufacturing industry are in the ascendant. The key materials for marine engineering construction and its related equipment manufacturing industry— ―The low-temperature structural steel plate capable of large heat input has a broad market prospect; the low-temperature structural steel capable of high heat input welding is still a brand-new steel type in my country.

The steel plate of the invention is mainly used for icebreaker hulls, ocean platforms, sea-crossing bridges, ocean wind tower structures, port machinery, steel structures of Antarctic research stations, etc. in icy sea areas, and can realize low-cost, stable batch industrial production.

To sum up, the steel plate of the present invention is designed through a simple combination of components and combined with the TMCP manufacturing process, not only can produce TMCP steel plate with excellent comprehensive performance at low cost, but also greatly shorten the manufacturing cycle of the steel plate, creating huge benefits for the enterprise. The value of the product realizes the green environmental protection of the manufacturing process. The high performance and high added value of the steel plate are concentrated in the conditions of ultra-low carbon and low carbon equivalent. While the steel plate has excellent strength, toughness, and strong plasticity matching, the weldability of the steel plate (especially the weldability of large heat input) is also excellent, and Successfully solved the problem of uneven performance of TMCP thick steel plate along the thickness direction of the steel plate, greatly improving the safety, stability and fatigue resistance of large heavy steel structures; good weldability saves the cost of steel component manufacturing for users and shortens the time for users The manufacturing time of steel components creates great value for users.

Claims (2)

1. A 550MPa-grade steel plate that can be welded with a large heat input, and its composition weight percentage is: C: 0.04% to 0.08% Si: ≤0.10% Mn: 1.30% to 1.60% P: ≤0.013% S: ≤0.003% Cu: 0.05% to 0.30% Ni: 0.25% to 0.55% B: 0.0015% to 0.0030% Ti: 0.008% to 0.016% Nb: 0.015% to 0.030% N: 0.0040%～0.0080% Al: ≤0.010% Ca: 0.001% to 0.004% The rest are Fe and unavoidable inclusions; and the above elements must satisfy the following relationship at the same time: 0.25≤B/N≤0.45; [1.17(%Si)+6.77(%Al)+2.12(%Nb)+0.13(%Mn)]×[(%C)+0.033(%Mn)]≤0.053; Ca treatment, and the Ca/S ratio is controlled at 1.0-3.0, Ca×S ^0.28 ≤1.0×10 ^-3 ; and obtained by the following method: including the following steps: 1) Smelting and casting According to the composition of claim 1, smelting and casting into a slab; then heating the slab, the temperature is controlled between 1030°C and 1130°C, ensuring that all Nb in the steel is solid-dissolved into the austenite during the heating process of the slab , the slab austenite grain does not grow abnormally; 2) Rolling, the total compression ratio of the steel plate is the thickness of the slab/thickness of the finished steel plate ≥ 3.6 The first stage is ordinary rolling, using the maximum rolling capacity of the rolling mill for continuous rolling to maximize the production capacity of the rolling line while ensuring recrystallization of the deformed billet and refining austenite grains; The second stage adopts non-recrystallized controlled rolling, the controlled rolling start temperature is controlled at 780°C-820°C, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥50%, and the final rolling temperature is 760°C-800 ℃; 3) cooling Accelerated cooling of the steel plate is carried out immediately after the controlled rolling is completed. The steel plate is cooled at a temperature of 750°C to 790°C, the cooling rate is ≥7°C/s, and the cooling stop temperature is 350°C to 550°C. Then the steel plate is naturally air-cooled to 350°C and then slowly cooled. , the slow cooling process is to keep the steel plate for at least 24 hours under the condition that the surface temperature of the steel plate is greater than 300°C. 2. The method for manufacturing a 550MPa grade steel plate that can be welded with large heat input as claimed in claim 1, characterized in that it comprises the following steps: 1) Smelting and casting According to the composition of claim 1, smelting and casting into a slab; then heating the slab, the temperature is controlled between 1030°C and 1130°C, ensuring that all Nb in the steel is solid-dissolved into the austenite during the heating process of the slab , the slab austenite grain does not grow abnormally; 2) Rolling, the total compression ratio of the steel plate is the thickness of the slab/thickness of the finished steel plate ≥ 3.6 The first stage is ordinary rolling, using the maximum rolling capacity of the rolling mill for continuous rolling to maximize the production capacity of the rolling line while ensuring recrystallization of the deformed billet and refining austenite grains; The second stage adopts non-recrystallized controlled rolling, the controlled rolling start temperature is controlled at 780°C-820°C, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥50%, and the final rolling temperature is 760°C-800 ℃; 3) cooling Accelerated cooling of the steel plate is carried out immediately after the controlled rolling is completed. The steel plate is cooled at a temperature of 750°C to 790°C, the cooling rate is ≥7°C/s, and the cooling stop temperature is 350°C to 550°C. Then the steel plate is naturally air-cooled to 350°C and then slowly cooled. , the slow cooling process is to keep the steel plate for at least 24 hours under the condition that the surface temperature of the steel plate is greater than 300°C.