CN117265385A

CN117265385A - Delayed cracking resistant and abrasion resistant steel plate for hardness 550HBW slurry dredging pipe and production method thereof

Info

Publication number: CN117265385A
Application number: CN202210677603.XA
Authority: CN
Inventors: 宋凤明; 温东辉; 周庆军; 刘明亮; 唐骜
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-06-15
Filing date: 2022-06-15
Publication date: 2023-12-22

Abstract

The delayed cracking resistant and abrasion resistant steel plate for the hardness 550HBW slurry dredging pipe and the production method thereof comprise the following components in percentage by weight: 0.28 to 0.32 percent of C, 0.1 to 0.3 percent of Si, 1.2 to 1.6 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.02 to 0.04 percent of Al, 1.8 to 3.6 percent of Cr, 0.15 to 0.35 percent of Cu, 0.05 to 0.15 percent of Ni, 0.001 to 0.003 percent of B and less than or equal to 0.005 percent of N; contains one or two of Nb 0.01-0.03% and Ti 0.01-0.03%, and the balance of Fe and unavoidable impurities, and is required to satisfy: nb+Ti is more than 6.65 and less than or equal to 0.04. The yield strength is more than or equal to 1400MPa, the tensile strength is more than or equal to 1700MPa, the elongation is more than or equal to 8%, the hardness is 550+/-30 HBW, the low-temperature impact power value at-40 ℃ is more than or equal to 40J, and the abrasion resistance is 3 times that of plain carbon steel materials such as Q235B; meanwhile, the time for cracking under the condition of a U-shaped bending 0.1mol/L hydrochloric acid solution soaking test is more than 500 hours, and the excellent delayed cracking resistance is reflected.

Description

Delayed cracking resistant and abrasion resistant steel plate for hardness 550HBW slurry dredging pipe and production method thereof

Technical Field

The invention relates to the field of low alloy steel manufacturing, in particular to a delayed cracking resistant and abrasion resistant steel plate for a hardness 550HBW slurry dredging pipe and a production method thereof.

Background

In operations such as land reclamation, channel dredging, bank maintenance and the like, a large amount of solid particles such as silt, sand and the like are conveyed for a long distance through a dredging pipeline in the form of slurry, the pipe body simultaneously bears electrochemical corrosion of slurry media and abrasion of the solid particles, and interaction of the slurry media and the solid particles, particularly abrasion caused to the pipe body when sea water slurry contains weathered rock, coral reefs and medium coarse sand is more serious, the conventional dredging pipeline is made of common Q235B, Q345B materials, and the service life is short under severe working conditions, and is scrapped even less than 1 year. The material failure due to erosion is much higher than the sum of simple erosion and wear due to the interaction of erosion and wear during failure. The steel for dredging pipes is required to have not only wear resistance but also corrosion resistance, and thus good abrasion resistance. To reduce dredging costs, it is desirable to make dredging pipes from higher strength abrasion resistant steel plates to increase pipeline life. Research shows that the high-strength steel plate has the problem of delayed cracking in the corrosive dredging working condition, so that the abrasion-resistant steel for the high-strength dredging pipe has to solve the problem of delayed cracking. .

There are many related patent techniques disclosed in the art for improving the wear resistance of steel materials. "HB500 grade wear-resistant steel plate and preparation method thereof" as disclosed in Chinese patent No. CN102517509A and "a martensite series wear-resistant steel and preparation method thereof" as disclosed in Chinese patent No. CN 103397275A. On the basis of the component design of C-Mn, a large amount of alloying elements such as Mo, cu, ni and the like are added in the two patents, so that on one hand, the alloy cost is high, and meanwhile, cu and Ni are common corrosion-resistant elements in the atmospheric corrosion-resistant steel, so that the formation of a protective rust layer on the steel surface is promoted, the abrasion loss is increased in the abrasion process, and the abrasion failure of the material is accelerated. The two patents relate to the steel grade with the hardness of 500HBW and good wear resistance, and are mainly used in the fields of engineering machinery, mining equipment and the like. The hardness is lower than 550HBW hardness level, and the corrosion resistance is poor and the delayed cracking resistance is not considered because the corrosion inhibition is not considered in the composition design of the steel, so that the steel cannot meet the use requirement under the working conditions of corrosion and abrasion.

A number of patents are also filed and disclosed for wear-resistant applications abroad, mainly for engineering machinery manufacture, but not for slurry delivery with abrasive properties. As disclosed in Japanese patent publication Nos. wear resistant steel sheet and resistant steel sheet superior in workability and manufacturing method therefor, japanese patent publication Nos. JP2007231321A, JP2008169443A disclose methods for improving wear resistance by carbide-precipitated particles of Ti and W, in which the components contain noble alloying elements such as Cu, ni, cr, mo. The steel has high hardness and wear resistance, but the hardness of the steel is basically 396-431HBW, the hardness of the steel is less than 300HBW, the steel cannot reach 550HBW hardness level, and a large number of carbide particles in a matrix play a role of a cathode under the condition of corrosive wear, so that electrochemical corrosion is promoted, the corrosion resistance is reduced, the abrasion resistance of the material is deteriorated, the delayed cracking resistance is not related, and the requirements of large particle size and high-content slurry abrasion in a slurry dredging environment are difficult to meet.

The corrosion-resistant and wear-resistant steel and the preparation method thereof are disclosed in Chinese patent CN101886225A, which relates to steel with the content of C up to 0.4-0.9 percent, mn up to 14-16 percent and Mo and Cr of 5-10 percent, and also contains a certain amount of Pr, nd, gd and other rare elements, the hardness can reach more than 52HRC, but the addition of a large amount of noble alloy increases the manufacturing cost, and the characteristics of delayed cracking resistance are not related.

The lower bainite abrasion-resistant steel pipe for slurry transportation and a manufacturing method thereof, and the abrasion-resistant steel plate for slurry dredging pipe with the hardness of 550HB and a manufacturing method thereof are disclosed in Chinese patent CN102776445A, CN108950422A, wherein the lower bainite abrasion-resistant steel pipe is of a bainite or bainite+acicular ferrite structure, the hardness of a matrix is not high, the tensile strength is only 600-800MPa, and the lower bainite abrasion-resistant steel pipe is mainly applied to working condition environments with slight abrasion such as ore pulp with tiny particles (tens of micrometers), crude oil transportation and the like, and is not suitable for the field of large-particle and high-density seawater slurry transportation. The latter is a wear-resistant steel plate with 550HBW hardness level, has certain abrasion resistance, and is suitable for processing dredging pipes. However, as an ultra-high strength abrasion-resistant steel with the hardness reaching 550HBW, the problem of delayed cracking resistance is not considered in the aspects of component design and performance. When the steel plate is knocked and scratched by hard objects in the dredging operation process, cracks are easy to initiate, particularly delayed cracking is easy to occur in a corrosive environment, so that the pipe body leaks and even cracks in the dredging process, and the smooth progress of the dredging operation is influenced.

In dredging operation, the dredging pipeline as an important component is subject to corrosion on one hand in the inside and outside of the pipeline in the use process, and meanwhile, the outer wall of the pipeline inevitably bears collision and hard object scratch. When the strength of the steel plate of the pipe body is lower, such as Q235B and 3Q345B, the impact energy can be absorbed through deformation of the low yield strength of the steel plate, so that the safety of the pipe body is ensured; however, when such a damage is applied to a high-strength steel sheet, particularly an ultra-high-strength steel sheet having a yield of more than 1000MPa, the steel sheet is not easily deformed due to the damage stress applied thereto exceeding the yield strength of the steel sheet, and cracks at the affected part are initiated and spread. Under the corrosive environment, the initiation and the extension of cracks promote the permeation and the diffusion of hydrogen, and particularly the electrochemical corrosion also promotes the precipitation and the aggregation of hydrogen. The hydrogen atoms infiltrate into the inner crystal lattice of the steel to increase the vacancy concentration, so that micropore holes of vacancy clusters are formed, the germination of microcracks is further promoted, and the steel plate is subjected to brittle fracture, namely delayed fracture. This will significantly affect the normal performance of the dredging operation and shorten the life of the dredging line, increasing the dredging costs. The higher the strength of the steel sheet, the more susceptible it is to hydrogen permeation. Therefore, under dredging working conditions, the problem of delayed cracking caused by hydrogen exists even if the surface of the pipe body is not damaged. High strength steel plates for dredging lines must be considered resistant to delayed cracking in performance.

It has been found from the prior art that the current wear-resistant steel is not suitable for the manufacturing process of dredging pipes, either without considering corrosion resistance or without considering the problem of delayed cracking under high stress.

Disclosure of Invention

The invention aims to provide a delayed cracking resistant and abrasion resistant steel plate for a hardness 550HBW slurry dredging pipe and a production method thereof, wherein the yield strength of the steel plate is more than or equal to 1400MPa, the tensile strength is more than or equal to 1700MPa, the elongation is more than or equal to 8%, the hardness is 550+/-30 HBW, the low-temperature impact energy value at-40 ℃ is 40 or more than or equal to J, and the abrasion resistant performance is 3 times that of the existing plain carbon steel material such as Q235B; meanwhile, the cracking time under the condition of the U-shaped bending 0.1mol/L hydrochloric acid solution soaking test is more than 500 hours, so that the excellent delayed cracking resistance is reflected, and the welding and cold bending processing are easy; the method is suitable for manufacturing dredging pipelines in the fields of sea-going land building, channel dredging and the like, and has no risk of cracking and leakage when the surface is impacted and scratched in a corrosive environment, thereby greatly improving the dredging efficiency and reducing the operation cost.

In order to achieve the above object, the technical scheme of the invention is as follows:

the delayed cracking resistant and abrasion resistant steel plate for the hardness 550HBW slurry dredging pipe comprises the following components in percentage by weight: c:0.28 to 0.32 percent, si:0.1 to 0.3 percent, mn:1.2 to 1.6 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, al: 0.02-0.04%, cr:1.8 to 3.6 percent, cu:0.15 to 0.35 percent, ni:0.05 to 0.15 percent, B:0.001 to 0.003 percent, and N is less than or equal to 0.005 percent; contains Nb:0.01 to 0.03 percent of Ti:0.01 to 0.03%, the balance comprising Fe and unavoidable impurity elements, and the requirements being: nb+Ti is more than 6.65 and less than or equal to 0.04.

Further, one or more of W0.01-0.5%, mo 0.01-0.5%, sb 0.01-0.2%, RE 0.01-0.2%, V0.01-0.2% and Ca 0.001-0.01% are contained.

In the composition design of the abrasion-resistant steel sheet of the present invention:

c is the cheapest strengthening element in steel, and martensite structure is obtained after heat treatment, so that the strength and hardness of the steel plate can be obviously improved, but more C is unfavorable for welding, toughness and plasticity of the steel plate. The C content is defined to be 0.28-0.32% under conditions meeting performance requirements.

Si is a deoxidizing element, is also a solid solution strengthening element, and is also a common corrosion resistant element in the atmospheric corrosion resistant steel. Si substitutes Fe atoms in the steel in a substitutional manner, impeding dislocation motion and thus achieving solid solution strengthening. Meanwhile, si can reduce the diffusion coefficient of C in ferrite, improve the activity of carbon, inhibit the formation of carbide, inhibit the precipitation of coarse carbide in defect occurrence and improve the toughness. However, too high Si promotes graphitization of C, which is disadvantageous in toughness; while being disadvantageous in terms of surface quality and welding performance. The Si content is limited to 0.1-0.3%.

Mn is also a common strengthening element in steel, improves yield strength through solid solution strengthening, reduces elongation, obviously reduces phase transition temperature of the steel, refines microstructure of the steel, and is an important toughening element, but the Mn content is excessive to increase hardenability, so that weldability and toughness of a welding heat affected zone are deteriorated, and the Mn content is controlled to be 1.2-1.6%.

P is a main corrosion resistant element in the traditional atmospheric corrosion resistant steel, promotes the formation of a surface protective rust layer, and effectively improves the atmospheric corrosion resistant performance of the steel, but the formation of the surface rust layer accelerates the abrasion loss of materials in the abrasion process, reduces the abrasion resistant performance, and meanwhile, the existence of P is easy to generate segregation, reduces the toughness and plasticity of the steel, and makes the steel plate become brittle and influence the toughness, so the content of P in the steel is required to be reduced as much as possible, and the content is required to be controlled below 0.015 percent in the invention.

S can improve the yield strength of steel, but the presence of S deteriorates the atmospheric corrosion resistance of steel and makes the steel sheet brittle, reduces the low temperature toughness of steel, and requires the content to be controlled to 0.005% or less.

Al is usually added into steel as deoxidizer in the steelmaking process, and trace Al is beneficial to grain refinement and improves the toughness of the steel. Meanwhile, al is used as a ferrite forming element, more Al reduces the strength of the steel plate on one hand, and increases the brittleness of ferrite in the steel to reduce the toughness of the steel, so that the content of Al is limited to 0.02-0.04%.

B has good hardenability, so that the hardness of the steel plate is improved, but the too high B content is unfavorable for welding, so that the range of B is controlled to be 0.001-0.03% respectively.

Cr has a solid solution strengthening effect, and meanwhile, the addition of Cr can effectively improve the self-corrosion potential of steel and inhibit corrosion, so that the promotion effect of corrosion on material failure in the abrasion process is effectively reduced, and the abrasion resistance is improved; particularly, with the improvement of corrosion resistance, the precipitation of hydrogen in the corrosion process can be reduced, and the delayed cracking resistance is further improved; however, cr is a noble alloying element, and the higher Cr content promotes the formation of protective rust layers on the steel surface, and under abrasive environments, the rust layers are rapidly separated from the surface, so that the abrasion failure of the material is promoted, and the Cr content is limited to be 1.8-3.6%.

Cu has the functions of solid solution and precipitation strengthening, and tempering has the secondary hardening effect at proper temperature when the content is higher, so that the strength is improved. Meanwhile, cu is also one of elements for improving corrosion resistance, electrochemical potential is higher than that of Fe, and densification of a rust layer on the surface of steel and formation of a stable rust layer are promoted; in addition, after copper is added into the steel, the diffusion of hydrogen can be restrained, the sensitivity to hydrogen induced cracking is reduced, and particularly, the delayed cracking resistance is improved together with Cr. In order to ensure the effect of Cu, the content is not less than 0.15%. Too high Cu causes cracking of the slab during heating and hot rolling, deteriorating surface properties, and the upper limit is limited to 0.35%.

Ni exists in steel in a solid solution form, does not form carbides, and is an element for enlarging austenite. The addition of Ni has the grain refining effect, and can improve the low-temperature impact toughness by refining grains and reducing the stacking faults; in particular, ni can promote the stabilization of rust layers and improve the problem of hot working brittleness caused by Cu. Nickel in the high-strength steel can also homogenize the structure of the steel, inhibit the diffusion behavior of hydrogen, reduce the content of irreversible hydrogen traps, and further improve the delayed cracking resistance. But Ni is a noble element, and the content of Ni is limited to 0.05-0.15%.

Nb is a strong nitrogen carbide forming element, can combine with carbon and nitrogen in steel to form intermediate phases such as NbC, nb (CN), nbN and the like, and the formed fine carbide particles can refine the structure and generate precipitation strengthening effect so as to remarkably improve the strength of the steel plate; in addition, nb can inhibit the expansion of an austenite interface, improves the recrystallization temperature of the steel, and can realize rolling in a non-recrystallization zone at a higher temperature, so that the addition of a proper amount of Nb to the steel is beneficial to the improvement of strength. The carbon nitride formed by Nb can spike and roll an austenite grain boundary in the austenitizing process, inhibit abnormal growth of austenite grains, and is beneficial to improving the toughness of the quenched steel plate. Nb is a noble alloy element, more Nb is unfavorable for welding, meanwhile, the Nb is easy to form brittle metal hydride with hydrogen, the toughness and the matrix are relatively large, the binding force with the matrix is also relatively poor, and the delayed cracking is caused, so that the Nb content is controlled to be 0.01-0.03%.

On one hand, 0.01-0.03% of Ti is added to inhibit the growth of austenite grains in the slab reheating process, and on the other hand, the growth of ferrite grains in the recrystallization controlled rolling process is inhibited, so that the toughness of the steel is improved. And Ti can be preferentially combined with N in the steel, so that the amount of AlN in the steel is reduced. However, ti which is too high is disadvantageous in low-temperature impact toughness, and it forms brittle metal hydrides with hydrogen as much as Nb is disadvantageous in resistance to delayed cracking.

N can form nitrides with Nb, V and Ti in steel, fine precipitates have the effect of pinning grain boundaries to refine austenite grains, and the precipitated nitrides have the effect of precipitation strengthening, but higher N is combined with Al in steel to easily form AlN, so that the amount of the nitrides in the steel is obviously increased. When AlN is independently present in steel as a nonmetallic inclusion, the continuity of a steel matrix is damaged, especially when the AlN is formed in a large quantity and in aggregation distribution when the Al content is high, the AlN is more harmful, and meanwhile, oxide with poor plasticity is formed; and the higher N is easy to concentrate at the defect, and the low-temperature impact toughness is deteriorated. Meanwhile, N is similar to C, and is easy to form a Korotkoff's air mass by offset polymerization at a dislocation, so that strain concentration is caused. Therefore, the N content must be controlled to 0.0050% or less. And the addition of Ti and Nb leads N to form nitride, thus reducing the adverse effect of N. In order to eliminate the adverse effect of N to the maximum extent, the contents of the three components are required to meet the relation: nb+Ti is more than 6.65 and less than or equal to 0.04.

In addition to the above elements, one or more of W, mo, sb, RE, V and Ca may be optionally added to the steel for further improvement of the properties. Each element defines a range: w, mo:0.01-0.5%, sb, RE and V:0.01-0.2%, ca:0.001-0.01%.

Wherein Mo has the functions of phase change strengthening and dislocation strengthening, can improve the tempering stability of steel, slow down tempering softening phenomenon, inhibit high-temperature tempering brittleness and improve the low-temperature impact toughness of the steel plate; the W forms carbide in the steel to generate secondary strengthening and solid solution strengthening effects and inhibit segregation of impurity atoms and nonmetallic inclusions in grain boundaries in overaging so as to improve fracture toughness;

the addition of RE is favorable to the improvement of corrosion resistance, RE compound, RE/Fe intermetallic compound, solid solution RE, etc. are formed in steel, hydrolyzed in the corrosive thin liquid film and deposited in cathode with high pH value to inhibit corrosion.

Sb can be combined with Cu in steel to form a Cu2Sb thin film on the surface, thereby improving corrosion resistance. V is also a strong carbon-nitrogen compound forming element, can be precipitated in the phase transformation process, has solid solution strengthening and carbon nitride precipitation strengthening effects in steel, and increases tempering stability, thereby improving strength. Ca can change the shape of sulfide when being added into steel, inhibit the hot shortness of S and improve the toughness.

The steel grade designed by the components is subjected to heat treatment to obtain a high-strength martensitic structure, wherein the yield strength is more than or equal to 1400MPa, the tensile strength is more than or equal to 1700MPa, the elongation is more than or equal to 8%, the hardness is 550+/-30 HBW, and the low-temperature impact energy value at minus 40 ℃ is more than or equal to 40J, so that the steel grade has good wear resistance; meanwhile, by adding a proper amount of corrosion-resistant alloy, the self-corrosion potential of the matrix is improved, the corrosion is effectively slowed down and inhibited, and the corrosion resistance of the material is improved, so that the material has good corrosion resistance, and the corrosion resistance is 3 times that of the conventional plain carbon steel material such as Q235B; and good delayed cracking resistance is obtained through component design and performance optimization. The high-strength dredging pipe manufactured by the method is particularly suitable for the field of large-particle and high-density slurry conveying, and cracking and leakage are not easy to occur in the using process.

The invention relates to a production method of a delayed cracking resistant and abrasion resistant steel plate for a hardness 550HBW slurry dredging pipe, which comprises the following steps:

1) Smelting and casting

Smelting and casting into blanks according to the components;

2) Heating of cast blanks

Heating temperature is above 1230 ℃, and total heating time in a heating furnace is not less than 2 hours, wherein,

soaking and heat preserving time is not less than 40min;

3) Rolling

The rough rolling stage adopts large reduction rolling, the pass reduction rate is controlled to be more than 15% or more than 25mm, meanwhile, the deformation ratio in the rough rolling stage is more than 80%, and the reduction rate of the last pass of finish rolling is controlled to be not less than 16%; the finish rolling temperature is more than or equal to 830 ℃, preferably more than or equal to 850 ℃;

4) Cooling

Cooling by laminar cooling to 550-650 ℃ and coiling;

5) Heat treatment of

Quenching and tempering the steel plate, wherein:

the quenching heating temperature is 800-825 ℃, the quenching heat preservation time T1 is counted from the center of the steel plate to the beginning of the temperature, T1= (1-2) x H, T is unit min, H is the plate thickness, and unit mm; directly water-quenching the steel plate to room temperature after discharging, wherein the cooling speed is more than or equal to 50 ℃/s;

the tempering temperature is 150-210 ℃, the tempering heat preservation time T2 is counted from the center of the steel plate to the beginning of the temperature, T2= (2-3) x H, T is unit min, H is the plate thickness, unit mm, and T2 is more than or equal to 12min;

and finally, finishing the tempered steel plate.

Preferably, in the step 1), the casting blank is hot-charged into a furnace after casting is finished, namely, the casting blank is directly conveyed to a heating furnace from a casting area through a roller way for heating and heat preservation after no quality problem on the surface of the casting blank is confirmed, so that the energy consumption can be reduced; if the casting blank can not be hot-packed, the cast casting blank is put into a heat preservation pit for slow cooling, and the heat preservation pit is removed for air cooling after the temperature is reduced to below 200 DEG C

Preferably, step 5) uncoiling and straightening the steel coil cooled to room temperature, cutting the steel plate, and then quenching and tempering the steel plate.

Preferably, the thickness of the obtained abrasion-resistant steel plate is 8-18 mm.

In the production method of the anti-delayed cracking and anti-abrasion steel plate, provided by the invention, the following steps are adopted:

heating and preserving heat of the casting blank before rolling, wherein the heating temperature is more than 1230 ℃, and the preserving heat time is 2 hours, and the soaking and preserving heat time is not less than 40 minutes. In addition, the casting blank can be hot-charged into the furnace after casting is finished, namely, the casting blank is directly conveyed to the heating furnace from the casting area through the roller way for heating and heat preservation after no quality problem on the surface of the casting blank is confirmed, so that the energy consumption can be reduced; if the casting blank cannot be hot-packed, the casting blank after casting is placed in a heat preservation pit for slow cooling, and the heat preservation pit is removed for air cooling after the temperature is reduced to below 200 ℃.

Rolling is divided into two stages, rough rolling and finish rolling. In order to obtain the fine prior austenite grain size, the casting blank is rolled by adopting large reduction in the rough rolling stage, and the pass reduction rate is controlled to be more than 15% or more than 25mm under the condition of allowing the rolling mill load. In order to obtain fine grain size and good plate shape, the deformation ratio in the rough rolling stage is more than 80%, and the reduction rate in the last pass of finish rolling is controlled to be not less than 16%.

The invention adopts off-line heat treatment after rolling the steel, and has no special requirement on the rolling temperature of casting blanks. However, in order to reduce the rolling load, the maximum finishing and coiling temperatures are used. From the continuous transition curve of fig. 1, the alpha- & gtgamma transition point of the steel grade is about 755 ℃, so that a finishing temperature above 850 ℃ is recommended, thereby ensuring that rolling in a complete austenite region is realized, further realizing low rolling load and stability of the rolling load, and facilitating subsequent obtaining of high-quality plate shapes; the finishing temperature can be suitably reduced when the steel sheet is thicker, but not lower than 830 ℃. After the steel coil is rolled, the steel coil is cooled to 550-650 ℃ by laminar cooling and coiled, and if the cooling speed is too high, on the one hand, the steel coil grains are coarse and the coiling machine is not good; when the temperature is too low, a bainite structure is easy to form, the strength of the steel plate is improved, and the subsequent uncoiling and straightening difficulties are increased.

And (3) uncoiling and straightening the steel coil cooled to the room temperature, cutting the steel plate, and quenching and tempering the steel plate. The quenching heating temperature directly influences the granularity of a follow-up martensitic structure, thereby influencing the toughness of the steel plate. In order to ensure sufficient austenitization of the matrix, a heating temperature of 30-50 ℃ above the Ac3 point is generally employed. The austenite grains are easily coarsened due to the over high heating temperature, the martensite structure is coarse after quenching, and the toughness is deteriorated; however, the lower heating temperature results in insufficient austenitization, and after quenching, a complete martensitic structure cannot be obtained and the toughness is not good. The heat preservation time has a similar rule on quenching performance, the grains are easy to be coarse due to overlong time, meanwhile, the energy consumption is increased, the cost is increased, austenitization is insufficient due to overlong time, and the hardness and strength after quenching cannot meet the requirements. In order to obtain outstanding low-temperature toughness, the steel plate is quenched by a critical zone quenching process. The undissolved acicular ferrite exists in the critical zone quenching structure, and the undissolved acicular ferrite can reduce the strength, but reaches the strength limit before martensite under the action of external force, so that cracks first initiate and expand in the undissolved acicular ferrite, absorb energy and improve the toughness. Therefore, the quenching heating temperature is required to be controlled to be between minus 5 ℃ and plus 20 ℃ above Ac3 point, namely 800-825 ℃, so as to obtain better low-temperature toughness. The heat preservation time is 1-2 times (min) of the thickness (mm) of the steel plate, calculated from the center of the steel plate to the beginning of temperature. And (3) directly water quenching the steel plate to room temperature after discharging the steel plate from the furnace, wherein the cooling speed is more than or equal to 50 ℃/s.

The tempering treatment is mainly to slow down and eliminate quenching stress and improve toughness and toughness. The higher tempering temperature easily reduces the strength and hardness of the steel plate too much to meet the design requirements, and meanwhile, the cost is increased. The tempering process parameters of the steel sheet should be limited. In the invention, the steel plate is tempered at 150-210 ℃ for 2-3 times (min) of the plate thickness (mm) from the center of the steel plate to the beginning of temperature, but the minimum time is not less than 12min. And finally, carrying out finishing treatment (straightening and trimming) on the quenched and tempered steel plate, and leaving the factory for release after the performance is qualified.

The invention has the following advantages:

the invention adopts simple and economic C-Mn component design and is supplemented with a small amount of Nb and Ti microalloy elements, thereby realizing the high hardness of the steel grade; meanwhile, the addition of corrosion-resistant elements such as Si, cr, cu, ni improves the potential of the matrix, inhibits the corrosion in the abrasion process, and improves the corrosion resistance of the steel plate. Therefore, the steel has good abrasion resistance under the corrosive wear environment, and particularly the abrasion resistance under the large-particle and high-density seawater slurry conveying condition is more than 3 times of that of a common pipe.

The invention relates to a steel grade with good low-temperature impact toughness and cold bending processability, which meets the requirements of pipe manufacturing processing of a subsequent dredging pipeline and can realize easy pipe manufacturing of a high-hardness steel plate on the basis of the existing equipment.

The steel of the invention obviously improves the delayed cracking resistance of the steel plate through improving the toughness and the corrosion resistance, thereby reducing the cracking leakage risk of the dredging pipe in the use process, improving the dredging efficiency and reducing the maintenance cost.

The invention has simple production process and low content of noble alloy elements, reduces the production difficulty and the production cost, and is beneficial to the large-scale popularization of steel types.

The difference between the invention and the prior art is that:

the present invention relates to steel grades which differ significantly in composition and properties from the comparative patents.

In terms of components, compared with patent 1 (Chinese patent CN102776445A 'a bainite abrasion resistant steel pipe for slurry conveying and a manufacturing method thereof'), 0.01-1.0% of Mo, ca and RE are required to be added, meanwhile, the content of N is required to be 0.01-0.1%, the strength is improved through N, meanwhile, the content of Mn in the components is higher, and the upper limit of the content of Mn reaches 5%, which is close to the components of medium manganese steel.

The contents of C, mn and Cr in the comparative patent 2 (Chinese patent CN101886225A, a corrosion-resistant and wear-resistant steel and a preparation method thereof) are respectively as high as 0.4 to 0.9 percent, 14 to 16 percent and 5 to 10 percent, and various rare elements such as Pr, dy, gd, nd and the like are required to be added.

Compared with patent 3 (Chinese patent CN108950422A 'hardness 550HB slurry dredging pipe abrasion-resistant steel plate and production method thereof'), the Al content is higher, which is unfavorable for low-temperature impact toughness and has no delayed cracking resistance, and meanwhile, the invention also adds higher Cr, cu and Ni content to ensure the corrosion resistance.

In addition, the mechanical properties of the steel according to the invention are also different from those of the comparative steel. The steel of the invention requires that the yield strength is more than 1400MPa, the elongation is more than or equal to 8 percent, the low-temperature impact energy value at minus 40 ℃ is more than or equal to 40J, and the steel has good delayed cracking resistance, which is not possessed by the steel of the comparative patents 1 to 3. The yield strength range of the comparative patent 1 is wider, namely 300MPa to 2500MPa, and the high strength can be realized, but the plasticity is sacrificed, the elongation can not be ensured, and the cold working application range is limited; although the hardness of the alloy can exceed 50HRC through the high-content strengthening elements in the comparative patent 2, the cost is too high, and the problem that the extensibility cannot be ensured affects the processing performance; and the steel types of the comparative patent 1 and the comparative patent 2 do not have good low-temperature impact toughness.

Drawings

Fig. 1 is a CCT curve (calculation) of the present invention relating to steel grades.

Detailed Description

The invention is further illustrated below with reference to examples.

The chemical compositions of the weathering steel examples of the invention are shown in Table 1, the production process parameters are shown in Table 2, and the mechanical properties and corrosion resistance of the weathering steel of the invention are shown in Table 3.

The production process of the embodiment of the abrasion-resistant steel plate comprises the following steps:

deep S removal (ensuring low S content in steel), converter top-bottom combined converting (controlling C content), external refining, continuous casting (machine cleaning), slab reheating, controlled rolling, controlled cooling, coiling, uncoiling, straightening, cutting, heat treatment (quenching and tempering), finishing and delivery.

Example 1

According to the chemical composition requirements of the steel, steel is made in a 500kg vacuum induction furnace, chemical compositions are shown in table 1, 100kg steel ingots are cast, the heating temperature is 1230 ℃ or higher, the finishing temperature is 874 ℃, and the coiling temperature is 648 ℃. The quenching temperature of the steel plate is 812 ℃ and the tempering temperature is 160 ℃.

Example 2

According to the chemical composition requirements of the abrasion-resistant steel plate, steel plates with different thickness specifications are prepared. The chemical compositions are shown in Table 2, the heating temperature of the billet is 1230 ℃, the finish rolling temperature is 876 ℃, and the billet is cooled to 635 ℃ after rolling and coiled.

And evaluating the delayed cracking resistance of the steel plate by adopting a U-shaped bending soaking test. The sample plate was 2 x 20 x 90mm in size, the sample was bent into a U-shape with a radius of 10mm, the sample was loaded on both sides of the sample in parallel using a jig, and then immersed in 0.1mol/L hydrochloric acid solution, and the solution was replaced every 24 hours. And (3) observing for 2 times a day in the test process, confirming the specific cracking time of the sample according to video playback, and recording the cracking time of the sample. The shorter the sample cracking time, the poorer the delayed cracking resistance and the higher the risk of cracking under corrosive conditions. It is generally considered that if it exceeds 300 hours, the cracking resistance is good.

As can be seen from Table 3, the hardness of the steel plate reaches 550HBW hardness level, the tensile property also meets the design requirement, and the steel plate has good wear resistance; meanwhile, the corrosion resistance is improved by adding corrosion resistant elements such as Si, cr, cu, ni, so that the steel grade has excellent corrosion resistance. Particularly, the delayed cracking time is more than 500 hours, and the extremely excellent delayed cracking resistance is embodied.

The existing 550HBW grade wear-resistant steel material is used as a comparison example for comparison. The comparative examples 1-4 adopt C-Si-Mn design, the Cr content is 0.54-1.18%, and a small amount of Nb and Ti are added to further refine the structure and improve the strength; the components have no Cu and Ni added. The comparative example used a quench temperature of 860 ℃ which was higher than 800-825 ℃ according to the invention. From the results, although the steel sheets of comparative examples 1 to 4 had strength and hardness comparable to those of the present invention, the impact energy value was significantly lower, and was only 21 to 33J at-40 ℃. The poor impact toughness can cause brittle fracture of the steel plate when the steel plate is subjected to external impact and collision; and the time for cracking in the U-shaped bending soaking test of comparative examples 1-4 is not more than 50 hours, which is far lower than that of the steel grade of the invention, the delayed cracking resistance is poor, and obvious cracking leakage risks exist under the dredging working condition. The steel plates of comparative examples 1-4 are shown to be unsuitable for use in the fabrication of dredging lines.

The abrasion-resistant steel plate can be used for manufacturing slurry dredging pipes, is widely applied to the fields of inland-sea land making, channel dredging, inland dredging, ore pulp conveying and the like, and replaces the conventional Q235 and Q345 level common dredging pipelines, so that the production efficiency is improved, and the operation cost is reduced.

Claims

1. The delayed cracking resistant and abrasion resistant steel plate for the hardness 550HBW slurry dredging pipe comprises the following components in percentage by weight: c:0.28 to 0.32 percent, si:0.1 to 0.3 percent, mn:1.2 to 1.6 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.005 percent, al: 0.02-0.04%, cr:1.8 to 3.6 percent, cu:0.15 to 0.35 percent, ni:0.05 to 0.15 percent, B:0.001 to 0.003 percent, and N is less than or equal to 0.005 percent; contains Nb:0.01 to 0.03 percent of Ti:0.01 to 0.03%, the balance comprising Fe and other unavoidable impurity elements, and the requirements being: nb+Ti is more than 6.65 and less than or equal to 0.04.

2. The delayed fracture resistant and abrasion resistant steel sheet for a 550HBW slurry dredging pipe according to claim 1, further comprising one or more of W0.01 to 0.5%, mo 0.01 to 0.5%, sb 0.01 to 0.2%, RE0.01 to 0.2%, V0.01 to 0.2% and Ca 0.001 to 0.01%.

3. The delayed cracking resistant and abrasion resistant steel plate for a 550HBW slurry dredging pipe according to claim 1 or 2, wherein the yield strength of the abrasion resistant steel plate is equal to or more than 1400MPa, the tensile strength is equal to or more than 1700MPa, the elongation is equal to or more than 8%, the hardness is 550±30HBW, the low-temperature impact power value at-40 ℃ is 40 or more than J, and the abrasion resistance is 3 times that of the existing plain carbon steel material such as Q235B; and meanwhile, the cracking time under the condition of the U-shaped bending 0.1mol/L hydrochloric acid solution soaking test is more than 500 hours.

4. A method for producing a delayed fracture resistant and abrasion resistant steel sheet for a 550HBW slurry dredging pipe according to claim 1, 2 or 3, comprising the steps of:

1) Smelting and casting

Smelting and casting into billets according to claim 1 or 2;

2) Heating of cast blanks

Heating temperature is 1230 ℃ or higher, and total heating time in a heating furnace is not less than 2 hours, wherein soaking and heat preserving time is not less than 40 minutes;

3) Rolling

4) Cooling

Cooling by laminar cooling to 550-650 ℃ and coiling;

5) Heat treatment of

Quenching and tempering the steel plate, wherein:

and finally, finishing the tempered steel plate.

5. The method for producing a delayed cracking resistant and abrasion resistant steel plate for a hardness 550HBW slurry dredging pipe according to claim 4, wherein in step 1), a cast blank is hot charged into a furnace after casting is completed, i.e., the cast blank is directly transported from a casting area to a heating furnace through a roller way for heating and heat preservation after confirming no quality problem on the surface of the cast blank, thereby being capable of reducing energy consumption; if the casting blank cannot be hot-packed, the casting blank after casting is placed in a heat preservation pit for slow cooling, and the heat preservation pit is removed for air cooling after the temperature is reduced to below 200 ℃.

6. The method for producing a delayed cracking resistant and abrasion resistant steel plate for a hardness 550HBW slurry dredging pipe according to claim 4, wherein step 5) is to cut a steel coil cooled to room temperature after uncoiling and straightening, and then to quench and temper the steel plate.

7. The method for producing a delayed fracture resistant and abrasion resistant steel sheet for a 550HBW slurry dredging pipe as claimed in claim 4, wherein the thickness of the obtained abrasion resistant steel sheet is 8-18 mm.