CN110791702B

CN110791702B - Marine steel plate with good welding performance and low yield ratio and manufacturing method thereof

Info

Publication number: CN110791702B
Application number: CN201910932576.4A
Authority: CN
Inventors: 朱隆浩; 赵坦; 任子平; 周成; 金耀辉; 李家安; 韩鹏; 黄松; 海天; 王东旭
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2019-09-29
Filing date: 2019-09-29
Publication date: 2021-04-02
Anticipated expiration: 2039-09-29
Also published as: CN110791702A

Abstract

The invention belongs to the field of steel material preparation, and particularly relates to a marine steel plate with good welding performance and low yield ratio and a manufacturing method thereof. The paint comprises the following components in percentage by weight: 0.05 to 0.09 percent of C, 0.1 to 0.4 percent of Si, 1.0 to 1.5 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, 0.005 to 0.03 percent of Als, 0 to 0.6 percent of Ni, 0 to 0.3 percent of Cu, 0.008 to 0.05 percent of Nb, 0.005 to 0.03 percent of Ti, 0.002 to 0.01 percent of N, 0.02 to 0.08 percent of V, 0 to 0.3 percent of Mo, and the balance of Fe and inevitable impurities, wherein the yield-strength ratio of the steel plate is less than or equal to 0.80, the carbon equivalent Ceq is less than or equal to 0.41, and Pcm is less than or equal to 0.21. According to the invention, a certain content of N element is added, and the V, Ti element is matched for second phase dispersion and precipitation, so that the large heat input welding performance and the low-temperature impact toughness of the steel plate are improved. The high service safety with yield ratio less than or equal to 0.8 can be obtained by combining chemical components and the processes of high finishing rolling temperature, low water inlet, high red returning temperature and low cooling speed, and a corresponding production process is formed while the high service safety performance steel plate easy for large-line energy welding is obtained.

Description

Marine steel plate with good welding performance and low yield ratio and manufacturing method thereof

Technical Field

The invention belongs to the field of steel material preparation, and particularly relates to a marine steel plate with good welding performance and low yield ratio and a manufacturing method thereof.

Background

With the rapid development of ocean engineering, the development level and production capacity of steel as the main structure of ocean engineering are also continuously improved. The ocean engineering equipment is generally in a severe use environment, so the ocean engineering steel has high comprehensive performance, such as excellent plasticity, low-temperature impact toughness and high heat input weldability. At present, steel for ocean engineering can meet most of requirements of the market in the field of maritime work, but part of high-grade special steel cannot be stably produced, and the ultrahigh-strength steel plate which is resistant to low-temperature impact, efficient, easy to weld and high in service safety is high in difficulty of scientific research problems, strict in production process, high in requirements on equipment, high in development difficulty and at the starting stage. In order to meet the demand of ocean engineering on high-performance ultrahigh-strength steel plates, the development of low-yield-ratio high-quality ultrahigh-strength steel with good welding performance for ocean engineering is urgently needed.

In the process of developing ocean oil and gas resources and building an ocean platform, ultrahigh-strength steel is more and more commonly applied and has higher and higher strength in order to reduce the dead weight of the platform and improve the safety. In the construction of self-elevating platforms and semi-submersible platforms, the use amount of ultrahigh-strength steel is increasing. The common high-strength steel plate is usually increased in thickness in order to achieve the structural design of ocean engineering equipment, so that the welding workload is increased, and the weight of the upper building structure of the ocean engineering equipment is increased, so that the center of gravity is shifted upwards. With the emphasis on the large-scale marine equipment and the ultra-deep water operation safety of the ocean platform, higher requirements are put forward on the light weight of the ocean platform. The most effective mode is to adopt the marine steel sheet of higher intensity level, design more frivolous atress structure, can reduce platform focus like this and promote stability, can increase the payload of important equipment again, improve equipment efficiency. At present, ocean engineering equipment still adopts a large amount of ocean engineering steel plates below 40 kg level, and the main reasons for limiting the development of the ultrahigh-strength steel plates are higher alloy cost, unstable low-temperature impact toughness, low yield, poorer welding performance, overhigh yield ratio and low plate shape control precision due to large internal stress.

In order to reduce the manufacturing cost and improve the construction efficiency, maritime work equipment enterprises generally adopt a welding mode with large heat input, which can cause coarsening of the structure in a heat affected zone, seriously affect the toughness of a coarse-grain heat affected zone and easily cause defects such as welding cold cracks. Several steel enterprises in Japan and Korea successfully develop steel suitable for large heat input welding respectively, the heat input of the steel for ship plates can reach 350-680 kJ/cm, and the heat input of the steel for ocean engineering is about 200 kJ/cm.

The enterprises which are the first enterprises to develop the high-linear-energy ultrahigh-strength maritime work steel internationally have the steel manufacturing institute of Jiefu iron and Steel works, Kabushiki Kaisha and the like. The research and development of the high-heat input ultrahigh-strength marine steel are also carried out by domestic steel factories such as Bao steel, south steel, Xingcheng and the like, but specific research and analysis are not carried out on the ultrahigh-strength marine steel with high heat input welding, low temperature resistance and low yield ratio. The carbon equivalent of the steel plate for high heat input welding disclosed in the patent with the publication number of CN106574316A is 0.38-0.43, the rolling process only limits the accumulated reduction below 850 ℃, and the welding performance and the yield ratio performance of a large-thickness finished steel plate cannot be well guaranteed by the component process. The steel plate with excellent toughness of the welding heat affected part disclosed in the patent publication No. CN104603314A adopts the theoretical design components of oxide metallurgy, and has the defects of great difference with the prior art, high requirements on the shape, size and distribution of the oxide and great production difficulty. The steel plate for TMCP state low-cost large heat input welding disclosed in the patent publication No. CN106756543A improves the welding performance of the steel plate by a peroxide metallurgy mode, the steel-making continuous casting process is complex and is not easy to implement, and the effect of grain refinement in the thermomechanical rolling process can be influenced by giving up the addition of Nb element in the steel plate. The steel for ocean engineering disclosed in the patent publication No. CN106191659A does not fully mix the N element with the elements such as Ti and V, and does not fully utilize the control of the steel plate structure state in the low-temperature rolling stage, and the effect of low yield ratio cannot be achieved.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a marine steel plate with good welding performance and low yield ratio and a manufacturing method thereof. The production method can be used for preparing the steel plate with high service safety performance, which is suitable for the marine engineering field of ships and is easy to weld with large heat input, the mechanical property, the high heat input welding performance and the high service safety performance of the steel plate can reach the service conditions of ships and marine engineering, and a set of specific steel components with large heat input, low yield ratio and ultrahigh strength and a corresponding production process are formed.

In order to achieve the purpose, the invention adopts the following technical scheme:

the marine steel plate with the low yield ratio and the good welding performance comprises the following components in percentage by weight:

0.05 to 0.09 percent of C, 0.1 to 0.4 percent of Si, 1.0 to 1.5 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, 0.005 to 0.03 percent of Als, 0 to 0.6 percent of Ni, 0 to 0.3 percent of Cu, 0.008 to 0.05 percent of Nb, 0.005 to 0.03 percent of Ti, 0.002 to 0.01 percent of N, 0.02 to 0.08 percent of V, 0 to 0.3 percent of Mo, and the balance of Fe and inevitable impurities, wherein the yield-strength ratio of the steel plate is less than or equal to 0.80, the carbon equivalent Ceq is less than or equal to 0.41, and Pcm is less than or equal to 0.21.

The invention carries out optimization design on the chemical components of the steel grade:

(1) c is an essential reinforcing element in steel, and determines the structure of the weld heat affected zone while ensuring strength and hardness. Too high C content will produce a large amount of hardened structure and cause weld cracks, so the C content in the steel should be minimized. The content of C is controlled between 0.05 percent and 0.09 percent.

(2) Si can improve the strength of the steel plate and effectively stabilize a ferrite phase, and simultaneously, Si can be used as a deoxidizer to reduce the content of O, and when the content of Si is more than 0.4%, the structure can be coarsened, and the content of Si in the invention is 0.1-0.4%.

(3) The Mn element has similar atomic radius with Fe, can be greatly dissolved in the Fe matrix in a solid manner, is an element for expanding an austenite phase region, improves the stability of austenite, reduces the strength when the Mn content is lower than 1.0 percent, and ensures that the low-temperature toughness of the thick plate core is poorer due to the segregation of the Mn element when the Mn element mass percentage is higher than 1.5 percent, the performance of a welding heat affected zone is reduced, and the Mn content is 1.0 to 1.5 percent.

(4) P, S element has no benefit to the mechanical property and welding property of the steel plate, P should be controlled to be less than or equal to 0.02%, S should be controlled to be less than or equal to 0.02%.

(5) Al is a main deoxidizing element in steel, when the content of Al is too low, the deoxidizing effect is poor, and micro-alloy elements such as Ti and the like cannot achieve the purposes of refining grains and improving welding performance due to oxidation; on the contrary, if the Al element is too high, large inclusions are formed, and the content of Als is 0.005-0.03%.

(6) Ni is effective in improving hot workability and improving toughness. The proper addition can obtain lower ductile-brittle transition temperature, and the Ni content is 0-0.6%.

(7) The addition of Cu can improve the strength of the steel plate by forming a precipitated phase to precipitate in bainite, and the addition of Cu can also improve the hardenability of the steel plate and increase the corrosion resistance of the steel plate under a reducing atmosphere. The Cu content is 0-0.3%.

(8) The Nb element can effectively increase the recrystallization temperature of the steel plate in the rolling process to obtain the effect of refining grains, and can improve the low-temperature toughness of the TMCP steel plate by matching with N, Ti and V, and the Nb content is 0.008-0.05 percent.

(9) Ti element is a key factor of the chemical composition of the invention, elements such as Ti, V/N/Nb and the like can be separated out near a welding pool and a heat affected zone to form a fine and dispersed second phase of an N compound, so that the nucleation of ferrite in crystal can be effectively promoted to be long, the growth of original austenite crystal grains can be effectively controlled, and further, the performance of the welding heat affected zone of the steel plate is obviously improved. The reasonable design of Ti, V and N contents can reduce the content of N dissolved in a matrix and improve the comprehensive performance of the steel plate, so that the Ti/N content is controlled to be 2-3.5, and the Ti content is 0.005-0.03%.

(10) The N element can be matched with the TiV element to form a fine and dispersed N compound precipitated phase, so that the in-grain ferrite nucleation can be effectively promoted to be long, and the growth of original austenite grains can be effectively controlled. The increase of the N content increases TiN in the steel. The N content increases and a large amount of undissolved TiN still remains at the high temperature stage. The nitrogen content is increased, the number of TiN in steel at high welding temperature can be increased, and the inhibiting capability of the material on the austenite grain coarsening tendency in the welding process is improved. However, when the content of dissolved N is too large, the thermoplasticity of the steel material decreases, and the toughness of the steel sheet decreases. Therefore, the N content is 0.002% -0.01%.

(11) The V element can form V (C, N) particles in the matrix, and can obviously improve the welding performance of the steel plate and reduce the yield ratio under the combined action of the V element, the Ti element and the N element. The content of V is 0.02-0.08%.

(12) The Mo element can play a role in improving hardenability in a steel billet, expands an austenite phase region, promotes the main elements formed by the acicular ferrite, plays an important role in controlling a phase change structure, and can effectively improve the strength of the material and improve the welding performance; the phase transition temperature is reduced, the critical cooling rate of bainite transformation is reduced, the bainite transformation is promoted in a wider cooling rate range, and the stability of the toughness in the thickness direction of the steel plate can be effectively improved. The content of Mo is 0-0.3%.

(13) Carbon equivalent Ceq is less than or equal to 0.41, Pcm is less than or equal to 0.21, wherein Ceq is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, and Pcm is C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+ 5B.

A manufacturing method of a marine steel plate with good welding performance and low yield ratio comprises the following steps of molten steel smelting, continuous casting, casting blank heating and rolling:

(1) high cleanliness and alloying smelting; and performing secondary refining on the molten steel through a converter and an LF furnace to further reduce P, S and the content of nonmetallic inclusions.

(2) Heating the casting blank by adopting a two-stage heating mode; and (3) loading the casting blank into a heating furnace at the furnace temperature of 600-650 ℃, and keeping the temperature for 20-45 min at the low-temperature section of 600-650 ℃ so as to keep the internal and external temperatures of the steel blank consistent at the low-temperature stage and prepare for uniform structure of the high-temperature section. The temperature rise rate of the casting blank is controlled to be 4-6 ℃/min in the subsequent temperature rise process, so that the condition that the interior of the steel blank is heated unevenly due to the fact that the steel blank is heated too fast is avoided. Soaking temperature is 1150-1200 ℃, and heat preservation is carried out for 30-60 min.

(3) A rolling process; a three-stage rolling process is adopted, and the initial rolling temperature of the first stage is controlled to be 1080-1160 ℃; the purpose of the first-stage rolling is to improve the cast structure of a slab, reduce the temperature waiting thickness of a billet and shorten the temperature waiting time of a steel plate. The second-stage initial rolling temperature is 940-990 ℃, the accumulated reduction rate is 25-35%, the single-pass reduction rate is more than or equal to 8%, and austenite tissues can be refined by carrying out recrystallization rolling and relaxation on austenite in a critical temperature interval to prepare for final tissue refinement; the third stage is at the initial rolling temperature of 815-875 ℃, the accumulated reduction rate is 35% -55%, the final rolling temperature is 755-800 ℃, and the deformation amount below the non-recrystallization temperature is increased as much as possible in the final rolling stage so as to increase the strain accumulation of deformed austenite, increase the distortion energy, provide more nucleation sites, obtain uniform and fine final structures and ensure the low-temperature toughness of the steel plate. And the yield ratio can be reduced by properly increasing the finishing rolling temperature.

(4) A controlled-cooling watering process: the starting cooling temperature is 650-750 ℃, and the temperature of red return is 390-510 ℃. The cooling speed is 4-10 ℃/s. The ferrite and bainite dual-phase structure can be obtained by adopting the process of relaxation and controlled cooling. The volume content and the grain size of the ferrite are directly determined by the water inlet temperature, and the ferrite content is increased and the grain size is increased along with the reduction of the water inlet temperature. When the volume content of the ferrite soft phase exceeds 40%, the yield ratio is lower than 0.8. But the increase of the polygonal ferrite content will decrease the strength of the steel sheet. Therefore, in order to achieve the best performance matching, the temperature range of the entering water is 650-750 ℃. Along with the increase of the cooling rate, the proportion of hard phases in the structure is increased, the yield strength and the tensile strength are both increased, the yield ratio is increased, and therefore the cooling rate is 4-10 ℃/s.

The thickness of the finished steel plate is 6-80 mm, the steel plate is suitable for large heat input welding with welding heat input of 100-200 KJ/cm, and the steel contains 40-60% of ferrite and 40-60% of bainite according to volume percentage.

Compared with the prior art, the invention has the beneficial effects that:

(1) a certain content of N element is added and is matched with V, Ti element second phase to be dispersed and separated out, so that the austenite grains of the effective structure in a welding pool and a heat affected zone are grown to be large, the nucleation of acicular ferrite and polygonal ferrite in the grains is promoted, the large heat input of the steel plate is improved, and the heat input of large heat input welding is 100-200 KJ/cm.

(2) By combining the N/V/Ti microalloying and three-stage rolling process, austenite is subjected to recrystallization rolling and relaxation in a critical temperature interval, so that the austenite structure can be refined and preparation is made for final structure refinement. The strain accumulation of the deformed austenite is increased in a low-temperature range, the distortion energy is increased, more nucleation sites are provided, uniform and fine final tissues are obtained, and the low-temperature impact toughness of the steel plate with the Charpy impact energy of-40 ℃ is more than or equal to 100J is ensured.

(3) By combining chemical components and processes of high finishing temperature, low water inlet, high re-reddening temperature and low cooling speed, the microstructure is controlled to be 40-60% of ferrite and 40-60% of bainite, and high service safety with yield ratio not more than 0.8 can be obtained.

Drawings

FIG. 1 is a metallographic structure diagram of example 1 of the present invention.

Detailed Description

The invention discloses a marine steel plate with good welding performance and low yield ratio and a manufacturing method thereof. Those skilled in the art can modify the process parameters appropriately to achieve the desired results with reference to the disclosure herein. It is expressly intended that all such similar substitutes and modifications which would be obvious to one skilled in the art are deemed to be included in the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of ordinary skill in the art that variations and modifications in the methods and applications described herein, as well as other suitable variations and combinations, may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.

[ examples ] A method for producing a compound

The chemical components of the steels of the embodiments (1-12) of the invention are shown in Table 1; the rolling preparation method of the steel of the embodiment (1-12) of the invention is shown in Table 2; the mechanical properties of the steels of the examples (1-12) of the invention are shown in Table 3; the high heat input weldability of the steels of examples (1-12) of the present invention is shown in Table 4.

TABLE 1 chemical composition wt% of steel of examples of the invention

TABLE 2 Rolling preparation method of steel of the examples of the present invention

TABLE 3 general mechanical properties of steels of examples of the invention

TABLE 4 high heat input weldability of the steels of the examples of the invention

Examples	Welding method	Welding line energy (KJ/cm)	Rm(MPa)	HAZ-40 ℃ average impact energy (J)
					1	Submerged arc welding	200	598	152
2	Submerged arc welding	100	605	149
					3	Submerged arc welding	150	613	165
4	Electro-gas welding	120	619	124
					5	Electro-gas welding	155	630	140
6	Electro-gas welding	140	590	131
					7	Submerged arc welding	200	640	121
8	Submerged arc welding	100	631	113
					9	Submerged arc welding	150	633	143
10	Electro-gas welding	100	669	138
					11	Electro-gas welding	120	679	129
12	Electro-gas welding	130	663	122

The production method can be used for preparing the steel plate with high service safety performance, which is suitable for the marine engineering field of ships and is easy to weld with large heat input, the mechanical property, the high heat input welding performance and the high service safety performance of the steel plate can reach the service conditions of ships and marine engineering, and a set of specific steel components with large heat input, low yield ratio and ultrahigh strength and a corresponding production process are formed.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. A manufacturing method of a marine steel plate with good welding performance and low yield ratio is characterized by mainly comprising the steps of molten steel smelting, continuous casting, casting blank heating and rolling;

the steel plate comprises the following components in percentage by weight:

0.051-0.09% of C, 0.10-0.39% of Si, 1.01-1.19% of Mn, less than or equal to 0.02% of P, less than or equal to 0.02% of S, 0.005-0.03% of Als, 0.33-0.60% of Ni, 0.05-0.29% of Cu, 0.008-0.029% of Nb, 0.011-0.018% of Ti, 0.0065-0.01% of N, 0.051-0.08% of V, 0.07-0.29% of Mo, and the balance of Fe and inevitable impurities, wherein the carbon equivalent Ceq of the steel plate is less than or equal to 0.41, and the Pcm is less than or equal to 0.21, wherein the Ceq = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, and the Pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V + B;

the thickness of the steel plate finished product is 6-80 mm, and the yield ratio of the steel plate is less than or equal to 0.80;

the manufacturing method comprises the following steps:

1) secondary refining is carried out by a converter and an LF furnace, so that the content of P, S and nonmetallic inclusions in molten steel is further reduced;

2) heating a casting blank by adopting a two-stage heating mode, loading the casting blank into a heating furnace at the furnace temperature of 600-650 ℃, keeping the temperature for 20-45 min at the low-temperature section of 600-650 ℃, controlling the temperature rise rate of the casting blank to be 4-6 ℃/min, controlling the soaking temperature to be 1150-1175 ℃, and keeping the temperature for 30-60 min;

3) adopting three-stage rolling and precise controlled cooling watering processes, wherein the initial rolling temperature of the first stage is controlled to be 1120-1160 ℃; the initial rolling temperature of the second stage is controlled to be 940-990 ℃, the accumulated reduction rate is 25% -35%, and the single-pass reduction rate is more than or equal to 8%; the initial rolling temperature of the third stage is 815-848 ℃, the accumulated reduction rate is 35-55%, and the final rolling temperature is 755-800 ℃; the start cooling temperature is 650-750 ℃, the temperature of red returning is 390-510 ℃, and the cooling speed is 4-10 ℃/s.