CN117265432A

CN117265432A - Delayed cracking resistant and abrasion resistant steel for dredging high-hardness slurry and manufacturing method thereof

Info

Publication number: CN117265432A
Application number: CN202210676983.5A
Authority: CN
Inventors: 宋凤明; 温东辉; 陆敏; 华骏山; 张国民
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
Also published as: WO2023241471A1

Abstract

The delayed cracking resistant and abrasion resistant steel for dredging high-hardness slurry and the manufacturing method thereof comprise the following components in percentage by weight: 0.17 to 0.22 percent of C, 0.1 to 0.3 percent of Si, 1.0 to 1.4 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, 0.15 to 0.60 percent of Cu, 0.1 to 0.3 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 meets the following conditions: nb+Ti is more than or equal to 6.65 and less than or equal to 0.04, and Cu/Ni is more than or equal to 2. The yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1300MPa, the elongation is more than or equal to 12%, the hardness is 450+/-30 HBW, the impact power value at minus 40 ℃ is more than or equal to 60J, and the abrasion resistance is 2 times that of a common steel plate; meanwhile, the time for cracking under the condition of a U-shaped bending 0.1mol/L hydrochloric acid solution soaking test is more than 600 hours, the excellent delayed cracking resistance is shown, and the method is suitable for manufacturing dredging pipelines in the fields of inland-sea construction, channel dredging and the like.

Description

Delayed cracking resistant and abrasion resistant steel for dredging high-hardness slurry and manufacturing method thereof

Technical Field

The invention belongs to the field of low alloy steel manufacturing, and particularly relates to delay cracking and abrasion resistant steel for high-hardness slurry dredging and a manufacturing method thereof.

Background

In the operations of 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, and the pipe body simultaneously bears electrochemical corrosion of slurry media and abrasion of the solid particles and interaction of the solid particles, and particularly the abrasion caused to the inner wall of the pipe body is more serious when weathered rock, coral reef and medium coarse sand are contained in seawater slurry. Most of the existing dredging pipelines are made of common Q235B, Q345B materials, and the service life of the existing dredging pipelines is short under severe working conditions, and the existing dredging pipelines are scrapped even less than 1 year. Due to the interaction of corrosion and wear during failure, the material failure caused by abrasion is much higher than the sum of pure corrosion and wear, so that the steel for dredging pipes is required to have not only wear resistance but also corrosion resistance, and thus good wear 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. The wear-resistant steel plate with low crack sensitivity index and high strength and the preparation method thereof are disclosed in Chinese patent CN103397272A, and the wear-resistant steel plate with low alloy and high strength and toughness is disclosed in Chinese patent CN 103103448A. The two patents relate to the steel grade reaching 450HBW grade in hardness, and are mainly used in the fields of engineering machinery, mining equipment and the like, and have good wear resistance. The higher Mo alloy element is added on the basis of C-Mn in component design, and the alloy cost is higher. Meanwhile, the steel contains higher corrosion resistant element Si, which is disadvantageous to toughness. Meanwhile, the patent steel types do not take measures to control corrosion, and the use requirements cannot be met 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. Such as:

U.S. patent No. 5284529a discloses "abscission-resistance steel" which relates to steel grades containing up to 0.05-1.5% Ti, and 0.1-3.0% Mo, with higher alloy costs and hardness up to 420HBW.

Japanese patent No. JP2007231321A, JP2008169443A discloses "wear resistant steel sheet" and "spar-resistant steel sheet superior in workability and manufacturing method therefor" which describe a method for improving wear resistance by carbide precipitated particles of Ti and W, but the former has hardness substantially between 396 and 431HBW, while the latter has hardness less than 300HBW and does not reach the 450HBW hardness scale. The carbide particles in the matrix play a role of cathode in an abrasion environment, so that electrochemical corrosion is promoted, abrasion loss of the material is increased, and the abrasion resistance of the steel plate is poor although the steel plate has good abrasion resistance, and meanwhile, the problem of delayed cracking resistance is not considered.

The corrosion-resistant and wear-resistant steel and the preparation method thereof are disclosed in Chinese patent CN101886225A, which relates to steel with the hardness of more than 52HRC, wherein the matrix is added with 0.4-0.9 percent of C and 14-16 percent of Mn, the content of Mo and Cr is 5-10 percent, and the steel also contains a certain amount of Pr, nd, gd and other rare elements, thus belonging to high alloy steel and having high cost.

The Chinese patent CN102776445A, CN108930001A discloses a lower bainite abrasion-resistant steel pipe for slurry transportation and a manufacturing method thereof, and a high-hardness abrasion-resistant steel plate for slurry dredging and a production method thereof, wherein the steel types involved in the lower bainite abrasion-resistant steel pipe are bainite or bainite+acicular ferrite structures, 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 the transportation of ore pulp or crude oil with tiny particles (tens of micrometers), and is not applicable to the transportation field of large-particle and high-density seawater slurry; the latter is an ultra-high strength abrasion-resistant steel plate of 450HBW, and the problem of delayed cracking resistance is not considered in the aspects of component design and performance requirements. When the steel plate is scratched by knocks and hard objects in the dredging operation process, crack initiation is easy to induce, 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 anti-delayed cracking abrasion-resistant steel for high-hardness slurry dredging and a manufacturing method thereof, wherein the yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1300MPa, the elongation is more than or equal to 12%, the hardness is 450+/-30 HBW, the impact power value at minus 40 ℃ is more than or equal to 60J, and the abrasion-resistant performance is 2 times that of the conventional steel plate; meanwhile, the time for cracking under the condition of a U-shaped bending 0.1mol/L hydrochloric acid solution soaking test is more than 600 hours, the excellent delayed cracking resistance is reflected, the method is suitable for manufacturing dredging pipelines in the fields of sea reclamation, channel dredging and the like, and the surface is free from cracking leakage risks when being impacted and scratched in a corrosive environment, so that the dredging efficiency is greatly improved, and the operation cost is reduced.

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

the delayed cracking resistant and abrasion resistant steel for dredging the high-hardness slurry comprises the following components in percentage by weight: c:0.17 to 0.22 percent, si:0.1 to 0.3 percent, mn:1.0 to 1.4 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%, cu:0.15 to 0.60 percent, ni:0.1 to 0.3 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 impurities, and satisfying: nb+Ti is more than or equal to 6.65 and less than or equal to 0.04, and Cu/Ni is more than or equal to 2.

Further, the alloy also contains one or more than one of less than or equal to 2.0 percent of Cr, 0.01 to 0.5 percent of W, 0.01 to 0.5 percent of Mo, 0.01 to 0.2 percent of Sb, 0.01 to 0.2 percent of RE, 0.01 to 0.2 percent of V and 0.001 to 0.01 percent of Ca.

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

c is the cheapest strengthening element in steel, and can significantly improve the strength of the steel plate, but many C are detrimental to the welding, toughness and plasticity of the steel plate. The range is limited to 0.17-0.22% under the condition of meeting the performance requirement;

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. Therefore, the content thereof is limited to 0.1 to 0.3%.

Mn is also a common strengthening element in steel, and improves yield strength through solid solution strengthening, so that elongation is reduced, meanwhile, phase transition temperature of the steel is obviously reduced, microstructure of the steel is thinned, and Mn content is excessive, so that hardenability is increased, weldability and toughness of a welding heat affected zone are deteriorated, and cost is increased. So that the content is controlled to be 1.0-1.4%.

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, and on one hand, more Al reduces the strength of the steel plate, and increases the brittleness of ferrite in the steel to reduce the toughness of the steel, so the content of the ferrite 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;

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 one of elements for improving corrosion resistance, the electrochemical potential is higher than that of Fe, and the addition of a proper amount of Cu is beneficial to improving the self-corrosion potential of the steel plate and reducing the corrosion rate; meanwhile, densification of a rust layer on the surface of the steel and formation of a stable rust layer are promoted, so that corrosion resistance is improved. Along with the improvement of corrosion resistance, the precipitation of hydrogen in the corrosion process is reduced, and the delayed cracking resistance is improved; after copper is added into the steel, the diffusion of hydrogen can be inhibited, 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 0.60%.

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; 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. Ni is also used as an important corrosion-resistant element to be enriched in the rust layer, so that crystal grains of the rust layer are thinned, the formation of nano-phase and superparamagnetic alpha-FeOOH in the inner rust layer is promoted, and the particle size of the formed alpha-FeOOH is smaller than 15nm, so that the compactness of the inner rust layer is increased, chloride ions are difficult to contact with a steel substrate through the rust layer, and the corrosion rate is reduced. In particular, ni can promote the stabilization of rust layers and improve the problem of hot working brittleness caused by Cu. Considering the effect of Cu on improving the potential and the inhibition effect of Cu and Ni on hydrogen diffusion, the invention takes Cu and Ni as important elements for improving the delay cracking resistance. In order to achieve the best matching effect and consider the inhibition of copper embrittlement, the content matching of Cu and Ni is limited, and Cu/Ni is required to be less than or equal to 2.0. But Ni is a noble element, and the content of Ni is limited to 0.1-0.3%.

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. However, more Nb is disadvantageous to welding, and at the same time, it is easy to form brittle metal hydride with hydrogen, and its toughness is greatly different from that of the matrix, and the binding force with the matrix is also poor, resulting in delayed cracking. The recommended content is 0.01-0.03%.

On one hand, 0.01 to 0.03 percent of Ti is added to inhibit the growth of austenite grains in the slab reheating process, and on the other hand, inhibit the growth of ferrite grains in the recrystallization controlled rolling process, 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, too high Ti is detrimental to low temperature impact toughness and it is as prone to forming brittle hydrides with hydrogen as Nb is detrimental to delayed cracking performance.

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, in the present invention, the content of N is controlled to be not more than 0.0050% by controlling N as an impurity element. 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 Cr, W, mo, sb, RE, V and Ca, wherein Cr.ltoreq.2.0%, W0.01.about.0.5%, mo 0.01.about.0.5%, sb 0.01.about.0.2%, RE 0.01.about.0.2%, V0.01.about.0.2% and Ca 0.001.about.0.01% may be optionally added to the components of the abrasion-resistant steel sheet of the present invention for further improvement of the properties.

Cr is an important corrosion-resistant element and 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 valuable alloying element, and the higher Cr content promotes the formation of protective rust layers on the steel surface, which rapidly detach from the surface in abrasive environments, promoting abrasive failure of the material. The upper limit of the content thereof is optionally added and defined to be 2.0%.

Mo has the functions of phase transformation 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 adopting the components has high strength and hardness, and has higher self-corrosion potential, so that the corrosion is inhibited, and the corrosion resistance is improved. After heat treatment, a high-strength martensitic structure is obtained, the yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1300MPa, the elongation is more than or equal to 12%, the hardness is 450+/-30 HBW, and the impact power value at-40 ℃ is more than or equal to 60J. The high-strength dredging pipe manufactured by the high-strength dredging pipe is particularly suitable for the field of large-particle and high-density slurry transportation, and is not easy to crack and leak in the use process.

The invention relates to a manufacturing method of anti-delayed cracking abrasion-resistant steel for high-hardness slurry dredging, which comprises the following steps:

1) Smelting and casting

Smelting and casting into blanks according to the components;

2) Heating of cast blanks

The total heating time of the casting blank in a heating furnace is required to be not less than 2 hours at the heating temperature of 1230 ℃, wherein the heat preservation time of a soaking section is not less than 40 minutes;

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 of the finish rolling is more than or equal to 880 ℃;

4) Cooling

Cooling by laminar cooling to 550-680 ℃ and coiling;

5) Heat treatment of

Quenching and tempering the steel plate, wherein:

the quenching heating temperature is 820-845 ℃, the quenching heat preservation time T1 is counted from the center of the steel plate to the beginning of the temperature, T1= (1.5-2) x H, T 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 200-240 ℃, the tempering heat preservation time T2 is counted from the center of the steel plate to the beginning of the tempering, 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 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 ℃.

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 8-20 mm.

In the method for manufacturing an abrasion-resistant steel sheet according to the present invention:

and heating and preserving heat of the casting blank before rolling, wherein the heating temperature is more than 1230 ℃. The heating and heat preservation of the casting blank in the heating furnace is divided into a preheating section, a heating section and a soaking section, wherein the total heating time of the casting blank in the heating furnace is required to be not less than 2 hours, and the heat preservation time of the soaking section 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 a fine grain size and a good plate shape, it is required that the deformation ratio at the rough rolling stage is more than 80% and the reduction ratio at 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 finish rolling and coiling temperatures are used. From the continuous transition curve of fig. 1, the alpha- & gtgamma transition point of the steel grade is about 780 ℃, so that the finish rolling finishing temperature above 880 ℃ is recommended, thereby ensuring that the rolling in a complete austenite region is realized, further realizing low rolling load and stability of the rolling load, and facilitating the subsequent obtaining of high-quality plates; when the steel sheet is thicker, the finish rolling temperature can be suitably reduced, but not lower than 850 ℃. After the steel coil is rolled, the steel coil is cooled to 550-680 ℃ 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 uncoiling and straightening the steel coil cooled to the room temperature, cutting the steel plate, quenching and tempering the steel plate to obtain high strength and hardness, and ensuring the wear resistance.

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 the matrix to be fully austenitized, a heating temperature of 30-50 ℃ above the Ac3 point is generally adopted. 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 invention particularly adopts a critical zone quenching process to quench the steel plate. 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 between 820 and 845 ℃, so as to obtain better low-temperature toughness. The quenching heat-preserving time T1 is 1.5 to 2 times (min) of the plate thickness H (mm) from the center of the steel plate to the beginning of the 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 plasticity 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 200-240 ℃ for a tempering and heat preserving time T2 from the center of the steel plate to the beginning of temperature, wherein the time is 2-3 times (min) of the thickness H (mm), 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 process can realize the production of the high-hardness abrasion-resistant steel plate with the thickness of 8-20 mm. The yield strength of the steel plate is above 1100MPa, the tensile strength is above 1300MPa, the elongation is more than or equal to 12%, the hardness is 450+/-30 HBW, and the impact power value at minus 40 ℃ is above 60J. The steel plate has good abrasion resistance and delayed cracking resistance by combining with the corrosion resistance design of the steel type. The abrasion resistance in the large-particle and high-density seawater slurry conveying environment can reach more than 2 times of that of a common Q235B pipe.

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 potential of the matrix is improved through corrosion resistance elements such as Cu, ni, cr and the like, the occurrence of corrosion is inhibited, and the corrosion resistance of the steel plate is improved. 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 2 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 has excellent low-temperature toughness and corrosion resistance, obviously improves the delayed cracking resistance of the steel plate, reduces the risk of cracking and leakage of the dredging pipe in the service process, improves the dredging efficiency and reduces the maintenance cost.

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

Aiming at the service condition of a dredging pipeline, the invention provides an abrasion-resistant steel plate with high hardness, the steel plate forms a martensitic structure with high hardness after heat treatment, the yield strength is more than or equal to 1100MPa, the tensile strength is more than or equal to 1300MPa, the elongation is more than or equal to 12%, the hardness is 450+/-30 HBW, and the impact power value at minus 40 ℃ is more than or equal to 60J. The wear resistance is excellent, the corrosion resistance is improved, the wear resistance is 2 times that of the conventional plain carbon steel material, the delayed cracking resistance is good, and the welding and cold bending processing are easy. The high-strength dredging pipe manufactured by the method is particularly suitable for the field of large-particle and high-density slurry conveying, and is not easy to crack and leak in the use process, which is not available in other known patent steel types at present.

Compared with the prior art, the invention relates to steel grades which have obvious differences in composition and performance from the comparative patents:

in terms of components, compared with patent 1 (Chinese patent CN 102776445A), 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, and meanwhile, 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 components of the comparative patent 2 (Chinese patent CN 101886225A) are respectively up to 0.4-0.9%, 14-16% and 5-10%, and various rare elements such as Pr, dy, gd and Nd are required to be added.

The Cr content in the composition of the comparative patent 3 (Chinese patent CN 10893001A) is lower, but the Al content is higher, which is disadvantageous to the toughness. The steel grade of the invention improves the corrosion resistance through Si, cr, cu, ni, and the content of the elements is different from that of the steel grade of the invention in comparison patent 3.

Furthermore, the performance requirements of the steels of the present invention are also different from those of the comparative patents 1 to 3.

The steel of the invention requires that the yield strength is more than 1100MPa, the elongation is more than or equal to 12 percent, the low-temperature impact energy value at minus 40 ℃ is more than or equal to 60J, and the steel has good delayed cracking resistance, which is not possessed by the steel of the comparative patents 1-3. 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 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 of the steel according to the present invention.

Detailed Description

The invention is further illustrated below with reference to examples.

The compositions of the example steels of the present invention are shown in Table 1, the manufacturing process parameters of the example steels are shown in Table 2, and the performance parameters of the example steels are shown in Table 3.

The process route of the embodiment of the invention is as follows: 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 abrasion-resistant steel plate, steelmaking is carried out in a 500kg vacuum induction furnace, the specific chemical composition is shown in table 1, 100kg steel ingots are cast, the heating temperature is 1230 ℃ or higher, the finish rolling finishing temperature is 892 ℃, and the coiling temperature is 680 ℃; cutting the steel coil after straightening, quenching and tempering the steel plate, wherein the quenching temperature of the steel plate is 820 ℃ and the tempering temperature is 210 ℃.

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 delayed 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 plates according to the invention reaches the 450HBW level, and the tensile property also meets the design requirements, so that the steel plates have excellent abrasion resistance. Particularly, the delayed cracking time is generally more than 600 hours, and the excellent delayed cracking resistance is reflected.

The present invention is compared with the current conventional 450HBW grade wear resistant steel as a comparative example.

Comparative examples 1 to 4 were designed using C-Si-Mn composition, wherein Mn content was about 1.6%, cr content was 0.4 to 1.2%, and Cu and Ni were not added. Comparative example 1 uses a finish rolling temperature of 820 ℃, but the impact power value is only 33J at-40 ℃, cracking occurs in 48 hours in a U-shaped bending soaking test, and the low-temperature toughness and the delayed cracking resistance are far lower than those of the steel grade of the invention; the finish rolling temperature of 880-900 ℃ is adopted in comparative examples 2-4, the low-temperature impact power value of minus 40 ℃ is 23-33J, the cracking time of the U-shaped bending soaking test is only 57 hours at most, and the cracking time is far lower than that of the steel grade of the invention. Therefore, the comparative example does not have the delayed cracking resistance required by the dredging working condition and is not suitable for manufacturing dredging pipelines.

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.

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Claims

1. The delayed cracking resistant and abrasion resistant steel for dredging the high-hardness slurry comprises the following components in percentage by weight: c:0.17 to 0.22 percent, si:0.1 to 0.3 percent, mn:1.0 to 1.4 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%, cu:0.15 to 0.60 percent, ni:0.1 to 0.3 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 impurities, and satisfying: nb+Ti is more than or equal to 6.65 and less than or equal to 0.04, and Cu/Ni is more than or equal to 2.

2. The delayed fracture resistant and abrasion resistant steel for dredging of high hardness slurry according to claim 1, further comprising one or more of Cr.ltoreq.2.0%, 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%.

3. The delayed fracture resistant and abrasion resistant steel for dredging of high hardness slurry according to claim 1 or 2, wherein the yield strength of the abrasion resistant steel is not less than 1100MPa, the tensile strength is not less than 1300MPa, the elongation is not less than 12%, the hardness is 450±30HBW, the impact power value at-40 ℃ is not less than 60J, and the abrasion resistance is more than 2 times that of a common steel plate 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 600 hours.

4. A method of manufacturing a delayed fracture resistant and abrasion resistant steel for high hardness slurry dredging as claimed in claim 1 or 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 550-680 ℃ and coiling;

5) Heat treatment of

Quenching and tempering the steel plate, wherein:

and finally, finishing the tempered steel plate.

5. The method for manufacturing the delayed fracture resistant and abrasion resistant steel for dredging of high hardness slurry according to claim 4, wherein in the step 1), a casting blank is hot charged into a furnace after casting is completed, namely, the casting blank is directly transported to a heating furnace from a casting area through a roller way for heating and heat preservation after no quality problem of the surface of the casting blank is confirmed, so that 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 ℃.

6. The method for manufacturing the delayed fracture resistant and abrasion resistant steel for dredging as claimed in 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 manufacturing a delayed fracture resistant and abrasion resistant steel for high hardness slurry dredging as claimed in claim 4, wherein the thickness of the obtained abrasion resistant steel plate is 8-20 mm.