Hardness 550hbw steel plate for erosion and delayed cracking resistant dredging pipes and method for producing the same

Abstract

Hardness 550HBW slurry dredging pipe with resistance to delayed cracking and erosion resistant steel plate and its production method, its component weight percentage is: C 0.28~0.32%, Si 0.1~0.3%, Mn 1.2~1.6%, P≤0.015%, S≤0.005%, Al 0.02~0.04%, Cr 1.8~3.6%, Cu 0.15~0.35%, Ni 0.05~0.15%, B 0.001~0.003%, N≤0.005%; contain one or both of Nb 0.01~0.03%, Ti 0.01~0.03%, the rest Fe and inevitable impurities, and need to meet: 6.65N < Nb+Ti≤0.04.Its yield strength≥1400MPa, tensile strength≥1700MPa, elongation≥8%, hardness 550±30HBW, low temperature impact energy value at-40℃ 40≥J, erosion resistance performance reaches 3 times of common carbon steel material such as Q235B; at the same time, cracking time under U-bending 0.1mol / L hydrochloric acid solution immersion test condition is above 500h, which embodies excellent resistance to delayed cracking performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low alloy steel manufacturing, in particular to a hard 550HBW slurry dredging pipe anti-delay cracking wear-resistant steel plate and its production method. BACKGROUND

[0002] In the reclamation, channel dredging, embankment maintenance and other operations, a large amount of solid particles such as silt and gravel in the form of slurry are transported through the dredging pipeline for a long distance. The pipe body is subjected to electrochemical corrosion of the slurry medium and wear and tear of the solid particles and their interaction. In particular, the abrasion caused by weathered rock, coral reefs and medium-coarse sand in seawater slurry is more serious. The existing dredging pipelines are mostly made of ordinary Q235B and Q345B materials, which have a short service life under harsh working conditions, even less than one year. Due to the interaction of corrosion and wear and tear during the failure process, material failure caused by wear and tear is much higher than the sum of pure corrosion and wear and tear. Therefore, the steel for dredging pipes not only requires wear-resistant performance, but also requires corrosion-resistant properties, thereby having good wear-resistant performance. In order to reduce the dredging cost, it is required to use higher strength wear-resistant steel plates to make the dredging pipe to improve the service life of the pipeline. Research shows that high-strength steel plates have a delayed cracking problem in the presence of corrosion in the dredging operation working condition, so the high-strength wear-resistant steel for dredging pipes must solve the problem of delayed cracking.

[0003] In terms of improving the wear resistance of steel materials, there are many related patent technologies disclosed. For example, Chinese patent CN102517509A discloses "HB500 grade wear-resistant steel plate and its preparation method", and Chinese patent CN103397275A discloses "a martensite series wear-resistant steel and its preparation method". Both patents add a large amount of alloy elements such as Mo, Cu and Ni to the C-Mn base in terms of composition design. On the one hand, the alloy cost is high, and at the same time, Cu and Ni are commonly used corrosion-resistant elements in atmospheric corrosion-resistant steel, which promote the formation of protective rust layer on the steel surface, increase the wear and tear loss during wear and tear, and accelerate the wear and tear failure of the material. The two patents involve steel hardness at 500HBW level, which has good wear resistance and is mainly used in the fields of engineering machinery and mining equipment. The hardness is lower than 550HBW, and at the same time, the composition design of the steel does not consider corrosion inhibition, so the wear-resistant performance is poor. In addition, the anti-delay cracking property is not considered, so it cannot meet the use requirements under the working condition of corrosion + wear and tear.

[0004] A large number of patents have been applied for and disclosed abroad in the field of wear resistance, mainly for engineering machinery manufacturing, but not for the field of slurry conveying with abrasion characteristics. For example, Japanese patents JP2007231321A and JP2008169443A disclose "wear resistant steel sheet" and "wear-resistant steel sheet superior in workability and manufacturing method therefor", which disclose a method for improving wear resistance by precipitating Ti and W carbide particles, and contain Cu, Ni, Cr, Mo and other precious alloy elements in the composition. The steel grade has high hardness and wear resistance, but the hardness of the former is basically between 396-431 HBW, and the hardness of the latter is less than 300 HBW, which does not reach the 550 HBW hardness level, and a large number of carbide particles in the matrix play a "cathode" role under the conditions of corrosion and wear, promote the occurrence of electrochemical corrosion, reduce the corrosion resistance, and worsen the abrasion resistance of the material. Moreover, it does not involve the delayed cracking resistance, and it is difficult to meet the requirements of large particle size and high content of slurry abrasion in the slurry dredging environment.

[0005] For example, Chinese patent CN101886225A discloses "a kind of corrosion and wear resistant steel and its preparation method", which involves adding up to 0.4-0.9% C, 14-16% Mn, and Mo, Cr content of 5-10%, in addition to a certain amount of Pr, Nd and Gd and other rare elements, and the hardness can reach more than 52HRC, but the addition of a large amount of precious alloy increases the manufacturing cost, and the delayed cracking resistance is not involved.

[0006] Chinese patents CN102776445A and CN108950422A disclose "a kind of slurry conveying lower bainite wear-resistant steel pipe and its manufacturing method" and "hardness 550HB slurry dredging pipe wear-resistant steel plate and its production method", the former is bainite or bainite + acicular ferrite structure, the matrix hardness is not high, and the tensile strength is only 600-800 MPa, mainly applied to the conveying of mineral slurry or crude oil with small particles (tens of μm) and other light wear working conditions, not suitable for large particle and high density seawater slurry conveying field. The latter is a 550 HBW hardness level wear-resistant steel plate, which has certain wear resistance and is suitable for the processing of dredging pipes. However, as a super high strength wear-resistant steel with a hardness of 550 HBW, the composition design and performance requirements do not consider the delayed cracking resistance. When the steel plate is subjected to impact and hard scratching during dredging operation, it is easy to induce crack initiation, especially in the corrosion environment, which is prone to delayed cracking, resulting in pipe leakage or even cracking during dredging, affecting the smooth progress of dredging operation.

[0007] In the dredging operation, the dredging pipeline as an important component faces the corrosion problem inside and outside the pipe body during use, and the outer wall of the pipe body inevitably bears the impact and hard scratching. When the strength of the pipe body steel plate is low, such as Q235B and 3Q345B, the impact energy can be absorbed by the deformation of the low yield strength of the steel plate itself to ensure the safety of the pipe body. However, for high-strength steel plates, especially ultra-high-strength steel plates with a yield strength exceeding 1000 MPa, it is difficult for the damage stress to exceed the yield strength of the steel plate to cause deformation when such damage occurs, thereby causing the initiation and propagation of cracks at the damaged location. In a corrosive environment, the initiation and propagation of cracks promote the permeation and diffusion of hydrogen, and electrochemical corrosion also promotes the precipitation and aggregation of hydrogen. The hydrogen atoms penetrate into the steel lattice, causing the vacancy concentration to increase, thereby forming microporous holes of vacancy clusters, further promoting the initiation of microcracks, and causing the steel plate to crack in a brittle manner, i.e. delayed cracking. This will significantly affect the normal operation of the dredging operation and shorten the service life of the dredging pipeline, increasing the dredging cost. The higher the strength of the steel plate, the more susceptible it is to hydrogen permeation. Therefore, under the dredging working condition, even if the surface of the pipe body is not damaged, there is still a problem of delayed cracking caused by hydrogen. The high-strength steel plate used for the dredging pipeline must consider the resistance to delayed cracking in terms of performance.

[0008] From the existing patents, it can be found that the current wear-resistant steel does not consider corrosion resistance or delayed cracking under high stress, and is not suitable for the manufacture and processing of dredging pipes. SUMMARY

[0009] The purpose of the present application is to provide a hard 550 HBW slurry dredging pipe with anti-delayed cracking and wear-resistant steel plate and its production method, the steel plate has a yield strength of ≥1400 MPa, a tensile strength of ≥1700 MPa, an elongation of ≥8%, a hardness of 550±30 HBW, a low temperature impact energy value of 40≥J at -40℃, and a wear-resistant performance that is 3 times that of existing plain carbon steel materials such as Q235B. At the same time, the cracking time under the condition of U-bending 0.1 mol / L hydrochloric acid solution immersion test is more than 500h, which reflects excellent anti-delayed cracking performance, easy welding and cold bending processing; suitable for the manufacture of dredging pipelines in the fields of land reclamation and channel dredging, etc. There is no risk of cracking and leakage when the surface is subjected to impact and scratching in a corrosive environment, thereby greatly improving the dredging efficiency and reducing the operation cost.

[0010] To achieve the above-mentioned goal, the technical solution of the present application is:

[0011] The hard 550HBW slurry dredging pipe resistant to delayed cracking and abrasion resistant steel plate has the following components by weight percentage: C: 0.28-0.32%, Si: 0.1-0.3%, Mn: 1.2-1.6%, P≤0.015%, S≤0.005%, Al: 0.02-0.04%, Cr: 1.8-3.6%, Cu: 0.15-0.35%, Ni: 0.05-0.15%, B: 0.001-0.003%, N≤0.005%; containing one or both of Nb: 0.01-0.03%, Ti: 0.01-0.03%, and the balance comprising Fe and inevitable impurity elements, and needs to satisfy: 6.65N

[0012] Further, one or more of W 0.01-0.5%, Mo 0.01-0.5%, Sb 0.01-0.2%, RE 0.01-0.2%, V 0.01-0.2% and Ca 0.001-0.01% are further included.

[0013] In the component design of the abrasion resistant steel plate described in the application:

[0014] C is the cheapest strengthening element in steel, and martensite structure is obtained after heat treatment, which can significantly improve the strength and hardness of the steel plate, but too much C is not conducive to the welding, toughness and plasticity of the steel plate. Under the condition of meeting the performance requirements, the C content is limited to 0.28-0.32%.

[0015] Si is a deoxidizing element and also a solid solution strengthening element, and is also a common corrosion-resistant element in atmospheric corrosion-resistant steel. Si replaces Fe atoms in the steel in a displacement manner, hinders dislocation movement to achieve solid solution strengthening. At the same time, Si can reduce the diffusion coefficient of C in ferrite, increase the activity of carbon, inhibit the formation of carbides, and inhibit the precipitation of coarse carbides at defects to improve toughness. However, too much Si promotes graphitization of C, which is not conducive to toughness; at the same time, it is not conducive to surface quality and welding performance. Therefore, the Si content is limited to 0.1-0.3%.

[0016] Mn is also a common strengthening element in steel, which increases the yield strength through solid solution strengthening, reduces the elongation, and significantly reduces the phase transition temperature of the steel, thereby refining the microstructure of the steel and being an important strengthening and toughening element. However, too much Mn increases the hardenability, thereby causing deterioration of weldability and toughness of the heat-affected zone, so the Mn content is controlled between 1.2-1.6%.

[0017] P is the main corrosion resistant element in traditional atmospheric corrosion resistant steel, which promotes the formation of protective rust layer on the surface and effectively improves the atmospheric corrosion resistance of the steel. However, the formation of the rust layer on the surface during the abrasion process will accelerate the abrasion and weight loss of the material, and reduce the abrasion resistance. In addition, the presence of P will cause segregation, reduce the toughness and plasticity of the steel, and make the steel brittle, thus affecting the toughness. Therefore, the content of P in the steel should be reduced as much as possible, and the content of P in the present application is required to be controlled below 0.015%.

[0018] S can improve the yield strength of the steel, but the presence of S will deteriorate the atmospheric corrosion resistance of the steel and make the steel brittle, thus reducing the low-temperature toughness of the steel. Therefore, the content of S is required to be controlled below 0.005%.

[0019] Al is usually added to the steel as a deoxidizer during the steelmaking process. A small amount of Al is beneficial to the refinement of grains and the improvement of the strength and toughness of the steel. In addition, Al is a ferrite forming element. Too much Al will reduce the strength of the steel and increase the brittleness of ferrite in the steel, thus reducing the toughness of the steel. Therefore, the content of Al is limited to 0.02-0.04%.

[0020] B has good hardenability, which can improve the hardness of the steel plate. However, too high content of B is not conducive to welding. Therefore, the content of B is controlled in the range of 0.001-0.03%.

[0021] Cr has a solid solution strengthening effect. In addition, the addition of Cr can effectively improve the self-corrosion potential of the steel and inhibit the occurrence of corrosion, thus effectively reducing the promoting effect of corrosion on material failure during abrasion and improving the abrasion resistance. In particular, with the improvement of corrosion resistance, the precipitation of hydrogen during corrosion can be reduced, thus improving the resistance to delayed cracking. However, Cr is a precious alloying element. In addition, a high content of Cr promotes the formation of protective rust layer on the surface of the steel. In the abrasion environment, these rust layers quickly detach from the surface, thus promoting the abrasion failure of the material. Therefore, the content of Cr is limited to 1.8-3.6%.

[0022] Cu has solid solution and precipitation strengthening effect. When the content of Cu is high, the steel plate will have secondary hardening effect after tempering at a proper temperature, thus improving the strength. In addition, Cu is one of the elements that can improve the corrosion resistance. The electrochemical potential of Cu is higher than that of Fe, which can promote the densification of the rust layer on the surface of the steel and the formation of stable rust layer. In addition, the addition of Cu to the steel can inhibit the diffusion of hydrogen and reduce the sensitivity to hydrogen-induced cracking. In particular, the combination of Cu and Cr can improve the resistance to delayed cracking. In order to ensure the effect of Cu, the content of Cu should be no less than 0.15%. Too high content of Cu will cause cracks in the billet during heating and hot rolling, which will deteriorate the surface performance. Therefore, the upper limit of the content of Cu is limited to 0.35%.

[0023] Ni exists in the form of solid solution in the steel and does not form carbide, and is an austenite forming element. The addition of Ni has the effect of grain refinement, and improves the low temperature impact toughness by refining the grain and reducing the stacking fault energy; in particular, Ni can promote the stability of the rust layer and improve the hot working brittleness problem caused by Cu. In high strength steel, nickel can also homogenize the microstructure of the steel, inhibit the diffusion behavior of hydrogen, reduce the content of irreversible hydrogen traps, and thus improve the resistance to delayed cracking. However, Ni is a precious element, and its content is limited to 0.05-0.15%.

[0024] Nb is a strong nitrogen carbide forming element, which can combine with carbon and nitrogen in the steel to form intermediate phases such as NbC, Nb(CN) and NbN, and the fine carbide particles formed can refine the structure and produce precipitation strengthening effect, significantly improving the strength of the steel plate; and Nb can inhibit the expansion of the austenite interface and improve the recrystallization temperature of the steel, and can realize non-recrystallization rolling at a higher temperature, so that the addition of an appropriate amount of Nb in the steel is beneficial to the improvement of the strength. The carbonitride formed by Nb can pin the austenite grain boundary during austenitization, inhibit the abnormal growth of austenite grains, and is beneficial to the improvement of the toughness of the steel plate after quenching. Nb is a precious alloying element, and too much Nb is not conducive to welding, and it is easy to form brittle metal hydride with hydrogen, and the plasticity and toughness are greatly different from the matrix, and the bonding force with the matrix is also poor, leading to delayed cracking. Therefore, the content of Nb is controlled to be 0.01-0.03%.

[0025] The addition of 0.01-0.03% Ti can inhibit the growth of austenite grains during the reheating process of the slab, and can also inhibit the growth of ferrite grains during the recrystallization controlled rolling process, thereby improving the toughness of the steel. In addition, Ti can preferentially combine with N in the steel to reduce the amount of AlN in the steel. However, too high Ti is not conducive to low temperature impact toughness, and it is easy to form brittle metal hydride with hydrogen like Nb, which is not conducive to the resistance to delayed cracking.

[0026] N can form nitrides with Nb, V and Ti in the steel, the fine precipitates have the effect of pinning grain boundaries to refine austenite grains, the precipitated nitrides have the effect of precipitation strengthening at the same time, but higher N in the steel can easily form AlN in combination with Al, thereby significantly increasing the amount of nitrides in the steel. When AlN exists independently as a non-metallic inclusion in the steel, it destroys the continuity of the steel matrix, especially when the Al content is higher, the amount of AlN formed is more, and the degree of harm is more serious when it is aggregated, and at the same time, oxides with poor plasticity are formed; and higher N is easy to enrich at defects, which deteriorates the low temperature impact toughness. At the same time, N is similar to C, easy to segregate at dislocations to form Cottrell atmosphere, leading to strain concentration. Therefore, the content of N must be controlled below 0.0050%. The addition of Ti and Nb makes N form nitrides, reducing the adverse effects of N. In order to maximize the elimination of the adverse effects of N, the contents of the three satisfy the relationship: 6.65N < Nb + Ti < 0.04.

[0027] In addition to the above elements, in order to further improve the performance, one or more of W, Mo, Sb, RE, V and Ca can be selected to be added to the steel. The limited range of each element: W, Mo: 0.01-0.5%, Sb, RE and V: 0.01-0.2%, Ca: 0.001-0.01%.

[0028] Among them, Mo has the effect of phase transformation strengthening and dislocation strengthening, which can improve the tempering stability of the steel, slow down the tempering softening phenomenon, and inhibit high temperature temper brittleness, and improve the low temperature impact toughness of the steel plate; W forms carbides in the steel to produce secondary strengthening and solid solution strengthening effect and suppresses the segregation of impurity atoms and non-metallic inclusions at the grain boundaries in overaging to improve the fracture toughness;

[0029] The addition of RE (rare earth) is beneficial to the improvement of corrosion resistance, which forms RE compounds, RE / Fe intermetallic compounds and solid solution rare earth in the steel, and hydrolyzes in the corrosion thin liquid film, and precipitates at the cathode at a higher pH value, thereby playing a corrosion inhibition effect.

[0030] Sb can combine with Cu in the steel to form a Cu2Sb thin film on the surface, thereby improving the corrosion resistance. V is also a strong carbonitride forming element, which can precipitate during phase transformation, has solid solution strengthening and carbonitride precipitation strengthening effect in the steel, and increases the tempering stability, thereby improving the strength. Ca added to the steel can change the shape of sulfides, inhibit the hot shortness of S, and improve the toughness.

[0031] The steel designed by the above components obtains high-strength martensite structure after heat treatment, the yield strength is greater than or equal to 1400 MPa, the tensile strength is greater than or equal to 1700 MPa, the elongation is greater than or equal to 8%, the hardness is 550±30 HBW, and the low-temperature impact energy value at-40 DEG C is greater than or equal to 40 J, so that the steel has good wear resistance; meanwhile, the corrosion potential of the matrix is improved by adding a proper amount of corrosion-resistant alloy, the corrosion is effectively slowed down and inhibited, and the corrosion resistance of the material is improved, so that the steel has good wear resistance, and the wear resistance is 3 times that of the existing plain carbon steel material such as Q235B; and the good delayed cracking resistance is obtained by the component design and performance optimization. The high-strength dredging pipe made of the steel is particularly suitable for the field of slurry conveying with large particles and high density, and is not prone to cracking and leakage during use.

[0032] The production method of the steel plate with hardness of 550 HBW for slurry dredging pipe according to the application comprises the following steps:

[0033] 1) smelting and casting

[0034] The slabs are smelted and cast according to the above components;

[0035] 2) heating of the cast slabs

[0036] The heating temperature is higher than 1230 DEG C, and the total heating time in the heating furnace is not less than 2 h, wherein,

[0037] The soaking time is not less than 40 min;

[0038] 3) rolling

[0039] Large reduction is adopted in the rough rolling stage, the pass reduction rate is controlled to be higher than 15% or the pass reduction is higher than 25 mm, the deformation ratio in the rough rolling stage is greater than 80%, and the pass reduction rate in the last pass of the finish rolling is not less than 16%; the finish rolling final rolling temperature is higher than or equal to 830 DEG C, preferably higher than or equal to 850 DEG C;

[0040] 4) cooling

[0041] The laminar flow cooling is adopted, and the steel plate is coiled after being cooled to 550-650 DEG C;

[0042] 5) heat treatment

[0043] The steel plate is quenched and tempered, wherein:

[0044] The quenching heating temperature is 800-825 DEG C, the quenching soaking time T1 is counted from the center of the steel plate to the temperature, T1=(1-2)×H, T is in min, and H is the plate thickness in mm; the steel plate is directly water quenched to room temperature after being discharged from the furnace, and the cooling speed is required to be greater than or equal to 50 DEG C / s;

[0045] The tempering temperature is 150-210℃, and the tempering holding time T2 is counted from the center of the steel plate to the beginning of the tempering, T2=(2-3)×H, T is in min, H is the thickness of the plate in mm, and T2≥12min;

[0046] Finally, the tempered steel plate is subjected to finishing treatment.

[0047] Preferably, in step 1), the cast blank is hot charged into the furnace after the casting is completed, i.e. after the cast blank surface is confirmed to have no quality problems, the cast blank is directly transported from the casting area to the heating furnace via a roller way for heating and holding, so that the energy consumption can be reduced; if hot charging is not possible, the cast blank after casting must be placed in a holding pit for slow cooling, and after the temperature is reduced to below 200℃, the holding pit can be removed for air cooling.

[0048] Preferably, in step 5), the steel coil cooled to room temperature is subjected to uncoiling and straightening, and then the steel plate is subjected to quenching and tempering treatment.

[0049] Preferably, the obtained anti-abrasion steel plate has a thickness of 8-18mm.

[0050] In the production method of the anti-delay cracking anti-abrasion steel plate according to the present application:

[0051] The cast blank is heated and held before rolling, the heating temperature is above 1230℃, and the holding time is 2h, wherein the soaking holding time is not less than 40min. In addition, the cast blank can be hot charged into the furnace after the casting is completed, i.e. after the cast blank surface is confirmed to have no quality problems, the cast blank is directly transported from the casting area to the heating furnace via a roller way for heating and holding, so that the energy consumption can be reduced; if hot charging is not possible, the cast blank after casting must be placed in a holding pit for slow cooling, and after the temperature is reduced to below 200℃, the holding pit can be removed for air cooling.

[0052] The rolling is divided into two stages of rough rolling and finish rolling. In order to obtain fine original austenite grain size, the cast blank is rolled with large reduction in the rough rolling stage, and the pass reduction rate is controlled to be above 15% or the pass reduction amount is above 25mm under the condition that the rolling load of the rolling mill is allowed. In order to obtain fine grain size and good plate shape, the deformation ratio in the rough rolling stage is greater than 80%, and the pass reduction rate in the last pass of the finish rolling is controlled to be not less than 16%.

[0053] Since the present application involves offline heat treatment of the steel after rolling, there is no special requirement for the rolling temperature of the cast blank. However, in order to reduce the rolling load, the final rolling and coiling temperature is as high as possible. From the Figure 1From the continuous transformation curve of the steel, the α→γ transformation point of the steel is about 755℃, so it is recommended to adopt the finish rolling temperature above 850℃, so as to ensure the realization of the complete austenite zone rolling, and then realize the low rolling load and the stability of the rolling load, which is beneficial to the subsequent obtaining of the high quality plate shape; the finish rolling temperature can be appropriately reduced when the steel plate is thick, but should not be lower than 830℃. The steel coil is rolled to 550-650℃ between the laminar cooling and coiling, and the temperature is too high, on one hand, the cold speed is too low, which leads to the coarse grain of the steel coil, and meanwhile, it is not beneficial to the coiling machine; the temperature is too low, which is easy to form the bainite organization, increases the strength of the steel plate, and increases the difficulty of the subsequent uncoiling and straightening.

[0054] After the steel coil cooled to room temperature is uncoiled and straightened, the steel plate is cut, and the steel plate is quenched and tempered. The quenching heating temperature directly affects the grain size of the subsequent martensite organization, and then affects the toughness of the steel plate. In order to ensure the full austenitization of the matrix, a heating temperature of 30-50℃ above the Ac3 point is generally adopted. If the heating temperature is too high, the austenite grains are easy to be coarsened, the martensite organization after quenching is coarse, and the toughness is deteriorated; and if the heating temperature is too low, the austenitization is not sufficient, and the complete martensite organization after quenching cannot be obtained, which is not conducive to the toughness. The holding time also has similar rules on the quenching performance, and the time is too long, which is easy to make the grains coarse, increases the energy consumption, and increases the cost, and the time is too short, which is not sufficient for the austenitization, 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 using the critical zone quenching process in the present application. There are unsolved acicular ferrite in the critical zone quenching organization, and these unsolved acicular ferrite, although the strength is reduced, but under the action of external force, the strength limit is reached before the martensite, so that the crack is first generated and expanded in the acicular ferrite, and the energy is absorbed, so as to improve the toughness. Therefore, the quenching heating temperature is required to be controlled between-5℃ to +20℃ above the Ac3 point, that is, 800-825℃, so as to obtain better low-temperature toughness. The holding time is 1-2 times (min) of the thickness (mm) of the steel plate from the center of the steel plate to the temperature. The steel plate is directly water quenched to room temperature after being discharged from the furnace, and the cooling speed is required to be greater than or equal to 50℃ / s.

[0055] The tempering treatment is mainly to slow down and eliminate the quenching stress, improve the toughness and the toughness. If the tempering temperature is too high, the strength and hardness of the steel plate are reduced too much, which cannot meet the design requirements, and the cost is increased. Therefore, the tempering process parameters of the steel plate should be limited. In the present application, the steel plate is tempered at 150-210℃, and the tempering holding time is 2-3 times (min) of the thickness (mm) of the steel plate from the center of the steel plate to the temperature, but the minimum time should not be less than 12min. Finally, the quenched and tempered steel plate is subjected to finishing treatment (straightening and edge cutting), and is put into the market after the performance is qualified.

[0056] The present application has the following advantages:

[0057] The application adopts simple and economical C-Mn component design, supplemented with a small amount of Nb and Ti micro-alloy elements, realizes high hardness of the steel grade, and improves the corrosion resistance of the steel plate by adding Si, Cr, Cu, Ni and other corrosion resistance elements to improve the base potential and inhibit the corrosion in the abrasion process.

[0058] The application relates to a steel grade with good low-temperature impact toughness and cold bending performance, which meets the pipe manufacturing requirements of the subsequent dredging pipeline, and can realize easy pipe manufacturing of the high-hardness steel plate on the basis of the existing equipment.

[0059] The steel grade improves the toughness and corrosion resistance, significantly improves the delayed cracking resistance of the steel plate, reduces the cracking and leakage risk of the dredging pipe in the use process, improves the dredging efficiency and reduces the maintenance cost.

[0060] The production process is simple, the content of precious alloy elements is low, the production difficulty and cost are reduced, and the steel grade is conducive to wide promotion.

[0061] The difference between the application and the prior art lies in that:

[0062] The application relates to a steel grade with significant differences in composition and performance from the comparative patents.

[0063] In terms of composition, the comparative patent 1 (Chinese patent CN102776445A "A bainite wear-resistant steel pipe for slurry conveying and a manufacturing method thereof") needs to add 0.01-1.0% of Mo, Ca and RE, and also requires the N content to be 0.01-0.1%, to improve the strength through N, and the Mn content in the composition is relatively high, and the upper limit of the Mn content reaches 5%, close to the composition of medium manganese steel.

[0064] The C, Mn and Cr contents in the comparative patent 2 (Chinese patent CN101886225A "A corrosion-resistant and wear-resistant steel and a preparation method thereof") are as high as 0.4-0.9%, 14-16% and 5-10% respectively, and a plurality of rare elements such as Pr, Dy, Gd and Nd are required to be added.

[0065] The Al content in the comparative patent 3 (Chinese patent CN108950422A "A wear-resistant and corrosion-resistant steel plate with a hardness of 550HB for slurry dredging pipe and a production method thereof") is relatively high, which is not conducive to low-temperature impact toughness, and does not have the anti-delayed cracking performance, and higher contents of Cr, Cu and Ni are also added in the application to ensure the corrosion resistance.

[0066] In addition, the mechanical property requirements of the steel of the present application are also different from those of the comparative steels. The steel of the present application requires a yield strength of 1400 MPa or higher, an elongation of 8% or greater, a low-temperature impact energy value of 40 J or greater at -40 DEG C, and has good resistance to delayed cracking, which is not possessed by the steels of the comparative patents 1-3. The yield strength range of the comparative patent 1 is relatively wide, from 300 MPa to 2500 MPa, and although a very high strength can be achieved, the plasticity is sacrificed, the elongation cannot be guaranteed, and the cold working application range is limited; the comparative patent 2 can achieve a hardness of more than 50 HRC through a high content of strengthening elements, but this results in a high cost and the problem of the elongation not being guaranteed, which affects the processing performance; and the steels of the comparative patents 1 and 2 do not have good low-temperature impact toughness. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 The CCT curve (calculation) of the steel of the present application is shown in the following table. DETAILED DESCRIPTION

[0068] The present application is further described below in conjunction with examples.

[0069] The chemical composition of the weathering steel of the present application is 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 present application are shown in Table 3.

[0070] The production process of the abrasion-resistant steel plate of the present application is as follows:

[0071] Deep S removal of molten iron (to ensure a low S content in the steel) → top and bottom combined blowing in a converter (to control the C content) → secondary refining outside the furnace → continuous casting (machine cleaning) → slab reheating → controlled rolling → controlled cooling → coiling → uncoiling → straightening → cutting → heat treatment (quenching + tempering) → finishing → delivery.

[0072] Example 1

[0073] According to the chemical composition requirements of the steel of the present application, the steel was smelted in a 500 kg vacuum induction furnace, and the chemical composition shown in Table 1 was obtained. The steel ingot was cast in a 100 kg ingot, the heating temperature was 1230 DEG C or higher, the finish rolling temperature was 874 DEG C, and the coiling temperature was 648 DEG C. The steel plate quenching temperature was 812 DEG C, and the tempering temperature was 160 DEG C.

[0074] Example 2

[0075] According to the chemical composition requirements of the abrasion-resistant steel plate related to the present application, steel plates of different thickness specifications were prepared. The chemical composition is shown in Table 2, the billet heating temperature was 1230 DEG C, the finish rolling temperature was 876 DEG C, and the water cooling after rolling was coiled at 635 DEG C.

[0076] The U-bend immersion test is used to evaluate the resistance to delayed cracking of the steel plate. The sample size is 2*20*90mm, the sample is bent into a U shape with a radius of 10mm, the sample is loaded to the two sides of the sample in parallel using a clamp, and then placed in a 0.1mol / L hydrochloric acid solution, and the solution is replaced every 24h. During the test, it is observed twice a day, and the specific cracking time of the sample is confirmed according to the video playback, and the cracking time of the sample is recorded. The shorter the cracking time of the sample, the worse the resistance to delayed cracking, and the higher the risk of cracking under the corrosion working condition. It is generally considered that the resistance to delayed cracking is good if it does not crack for more than 300h.

[0077] As shown in Table 3, the hardness of the steel plate involved in the application reaches the 550HBW hardness level, the tensile properties also meet the design requirements, and has good wear resistance; at the same time, the corrosion resistance is improved by adding corrosion-resistant elements such as Si, Cr, Cu and Ni, so that the application steel has excellent wear and corrosion resistance. In particular, the delayed cracking time is more than 500h, which reflects excellent resistance to delayed cracking.

[0078] The existing 550HBW grade wear-resistant steel material is used as a comparative example. Comparative examples 1-4 use C-Si-Mn design, with Cr content of 0.54-1.18%, supplemented with a small amount of Nb and Ti to further refine the structure and improve the strength; no Cu or Ni is added in the composition. The quenching temperature of the comparative example is 860℃, which is higher than the quenching temperature of 800-825℃ of the application. As can be seen from the results, although the steel plates of comparative examples 1-4 have comparable strength and hardness to the application, the impact energy value is significantly lower, only 21-33J at-40℃. Poor impact toughness will lead to brittle cracking of the steel plate when subjected to external impact or collision; moreover, the cracking time of comparative examples 1-4 in the U-bend immersion test is not more than 50h, which is much lower than that of the steel of the application, and the resistance to delayed cracking is poor, and there is a significant risk of cracking and leakage under the dredging working condition. It is shown that the steel plates of comparative examples 1-4 are not suitable for the manufacture of dredging pipelines.

[0079] The wear-resistant steel plate involved in the application can be used for the manufacture of slurry dredging pipes, and is widely used in land reclamation, channel dredging, river dredging and ore slurry transportation fields, replacing the current Q235 and Q345 grade ordinary dredging pipelines, thereby improving the production efficiency and reducing the operation cost.

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Claims

1. A delay-fracture-resistant and abrasion-resistant steel plate for a slurry dredging pipe with a hardness of 550 HBW, comprising, by weight percentage, C: 0.28-0.32%, Si: 0.1-0.3%, Mn: 1.2-1.6%, P≤0.015%, S≤0.005%, Al: 0.02-0.04%, Cr: 1.8-3.6%, Cu: 0.15-0.35%, Ni: 0.05-0.15%, B: 0.001-0.003%, N≤0.005%, one or both of Nb: 0.01-0.03% and Ti: 0.01-0.03%, and the balance of Fe and other inevitable impurities, and satisfying 6.65N<Nb+Ti≤0.04; the steel plate has a yield strength of≥1400 MPa, a tensile strength of≥1700 MPa, an elongation of≥8%, a hardness of 550±30 HBW, a low-temperature impact energy value of 40≥J at-40℃, and an abrasion resistance that is 3 times that of a conventional carbon steel material Q235B; and the steel plate cracks after being soaked in a U-shaped bending 0.1 mol / L hydrochloric acid solution for more than 500 h. It further comprises one or more of W 0.01-0.5%, Mo 0.01-0.5%, Sb 0.01-0.2%, RE 0.01-0.2%, V 0.01-0.2%, and Ca 0.001-0.01%.

2. A hardbanding sheet for a 550 HBW slurry pipe for dredging, according to claim 1, characterized in that, The method comprises the following steps:

3. The method of producing a hardbanding sheet for a 550 HBW slurry pipe according to claim 1 or 2, characterized in that, 1) smelting and casting The steel plate is smelted and cast into a slab according to the composition of claim 1 or 2; 2) slab heating The heating temperature is higher than 1230℃, and the total heating time in the heating furnace is not less than 2h, wherein the soaking time is not less than 40min; 3) rolling Large reduction is adopted in the rough rolling stage, and the pass reduction rate is controlled to be higher than 15% or the pass reduction amount is higher than 25mm, while the deformation ratio in the rough rolling stage is greater than 80%, and the pass reduction rate in the last pass of the finish rolling is not less than 16%; and the finish rolling final pass temperature is≥830℃; 4) cooling The laminar flow cooling is adopted, and the steel plate is coiled after being cooled to 550-650℃; 5) heat treatment The steel plate is quenched and tempered, wherein: The quenching heating temperature is 800-825℃, and the quenching holding time T1 is counted from the temperature reaching the center of the steel plate, and T1=(1-2)×H, T is in min, and H is the thickness of the steel plate in mm; and the steel plate is directly water quenched to room temperature after being discharged from the furnace, and the cooling rate is required to be≥50℃ / s; The tempering temperature is 150-210℃, and the tempering holding time T2 is counted from the temperature reaching the center of the steel plate, and T2=(2-3)×H, T is in min, and H is the thickness of the steel plate in mm, and T2≥12min; Finally, the tempered steel plate is subjected to finishing treatment. In step 1), the cast slab is hot charged into the furnace after the casting is completed, that is, the cast slab is directly transported from the casting area to the heating furnace for heating and holding after confirming that the surface of the cast slab has no quality problems, so that the energy consumption can be reduced; if the cast slab cannot be hot charged, the cast slab after the casting must be removed from the holding pit for slow cooling, and can be removed from the holding pit for slow cooling after the temperature is reduced to below 200℃. ​ 4. The method of producing a hardbanding sheet for a 550 HBW pulp dredge pipe according to claim 3, characterized by, ​ 5. The method of producing a hardbanding sheet for a slurry pipeline according to claim 3, wherein the steel sheet has a tensile strength of 550 HBW. Step 5) After the steel coil is opened and straightened at room temperature, the steel plate is cut, and then the steel plate is quenched and tempered.

6. The method of producing a hardbanding sheet for a slurry pipe with a hardness of 550 HBW according to claim 3, characterized by, The obtained abrasion-resistant steel plate has a thickness of 8-18 mm.

7. The method of producing a hardbanding sheet for a slurry pipe according to claim 3, wherein the steel sheet has a hardness of 550 HBW, and the steel sheet is subjected to a heat treatment after the surface treatment. In step 3), the finish rolling temperature is greater than or equal to 850 DEG C.

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