Wear-resistant steel thick plate having uniform thickness direction microstructure and hardness and method for producing the same

Abstract

The application belongs to the technical field of steel material, and discloses a wear-resistant steel thick plate with uniform microstructure and hardness in thickness direction, and the main chemical components and contents include: C 0.45~0.55wt%, Cr 1.5~2.8wt%, Mo 1.8~2.2wt%, V 1.2~1.6wt%, Ni 0.8~1.2wt%, Si 0.5~1.4wt%, B 0.003~0.005wt%; the Mn content is controlled according to Si / Mn≥3.5, and the Mn content is ≤0.35%; the Ti content is controlled according to Ti / B=2~3; RE is introduced according to (Cr+Mo) / RE=100~170; P≤0.015%, S≤0.015%; the rest is Fe and inevitable impurity elements. The application can realize uniform distribution of full-thickness martensite / bainite composite structure, and has balanced strength and toughness and excellent uniformity; the production cost is low, the cycle is short, and the application is wide.

Description

Technical Field

[0001] This invention belongs to the field of steel materials technology, specifically relating to a wear-resistant steel thick plate with uniform microstructure and hardness in the thickness direction and its production method. Background Technology

[0002] Wear-resistant steel plates typically refer to wear-resistant steel plates with a thickness of ≥50mm. They possess high hardness, high wear resistance, and a certain degree of impact toughness, and are widely used in extreme working conditions involving strong impact, high wear, and heavy loads. They are core structural materials for equipment such as engineering machinery and mining machinery. However, uneven microstructure and properties along the thickness direction (such as segregation, banded structure, and large hardness gradient) can directly degrade their service performance and even lead to safety accidents.

[0003] The core manifestation of non-uniform microstructure in the thickness direction is high surface hardness and low core hardness. The surface layer is martensite / bainite, and the core is ferrite / pearlite, accompanied by obvious banding and segregation. Its harm persists throughout the entire processing, assembly, and service life of the component. Compared with thin plates, thick plates exhibit more pronounced segregation and banding after rolling. The core reason is the poor deformation uniformity during the rolling process of thick plates, making it difficult to effectively break up segregated areas and suppress the formation of banding. Thick wear-resistant steel plates (≥50mm) generally suffer from non-uniform microstructure in the thickness direction and significant hardness reduction. The hardness difference between the surface and the core can reach 30-50 HBW, leading to reduced overall performance and shortened service life, seriously affecting the safety and reliability of use in harsh working conditions such as engineering machinery and mining machinery.

[0004] To address the above problems, existing solutions and improvements include: (1) Composition design; low C + micro Nb + B + RE composite alloying to reduce segregation sensitivity, improve hardenability, and achieve a core hardness of over 95% of the surface hardness; precise C-Mn-Cr-B ratio to form a uniform martensitic structure and suppress banding; high Mn / C ratio + trace Ti to refine austenite grains and improve core hardness uniformity; precise control of Ca / S ratio and carbon content to ensure both strength and hardness while reducing segregation tendency. (2) Segregation control during continuous casting; large reduction technology at the end of solidification in continuous casting; single roll dynamic reduction (SRD) fan-shaped section, large reduction is implemented at the end of solidification; large roll diameter high penetration reduction, through special roll system design, the reduction force penetrates to the center of the billet, eliminating "W-shaped" segregation; heavy reduction at the end of solidification + electromagnetic stirring composite technology, the center segregation is reduced by more than 40%, and the grains are refined at the same time; (3) Improvement of rolling process; two-stage rolling + surface-core temperature difference control, high pressure water descaling before rough rolling, creating a temperature difference of 100~300℃ between the surface and the core, and then immediately large reduction, so that the deformation penetrates to the core, water cooling control of surface temperature during the finishing rolling stage, control of final rolling temperature control, and refinement of austenite grains; gradient temperature control rolling, with heated furnace, gradient heating of the heating section, total heating time ≥360 minutes, solving the problem of uneven rolling deformation caused by uneven heating in traditional process, and improving the uniformity of hardness of the whole cross section by more than 30%. (4) Improved heat treatment: direct air cooling after rolling + low temperature tempering, direct quenching after rolling, no need for reheating, 100% martensite in full thickness, hardness difference ≤15HBW, immediate ultra-fast cooling after rolling, self-tempering with residual heat, avoiding deformation of traditional quenching, core hardness ≥92% of surface hardness.

[0005] Existing technologies typically address segregation issues through the smelting and continuous casting process. However, in practical applications, problems such as strong reliance on technical equipment, high control difficulty, and instability still exist. Improvements are needed through subsequent rolling and heat treatment processes. The main improvement methods are to ensure consistent internal and external temperatures of the billet, utilize temperature difference rolling to promote core deformation, and ensure phase transformation uniformity. However, there are still deficiencies in deformation uniformity control technology and insufficient precise control technology for the rolling temperature field. Summary of the Invention

[0006] The main objective of this invention is to address the problems of inconsistent microstructure and uneven hardness distribution in the thickness direction caused by inherent component segregation and banded structure in existing wear-resistant steel thick plates (due to the difficulty and instability in controlling the continuous casting process, defects in deformation uniformity control technology, and insufficient precise control technology of rolling temperature field). This invention provides a wear-resistant steel thick plate with uniform microstructure and hardness along the thickness direction and its production method.

[0007] To achieve the above steps, the technical solution adopted by the present invention is as follows: A wear-resistant steel thick plate with uniform microstructure and hardness in the thickness direction is designed with the following composition to achieve uniform microstructure and properties in the thickness direction: C 0.45~0.55wt%, Cr 1.5~2.8wt%, Mo 1.8~2.2wt%, V 1.2~1.6wt%, Ni 0.8~1.2wt%, Si 0.5~1.4wt%, B 0.003~0.005wt%; Mn content is controlled according to Si / Mn≥3.5, and Mn content≤0.35%; Ti content is controlled according to Ti / B=2~3; RE is introduced according to (Cr+Mo) / RE=100~170; P≤0.015%, S≤0.015%; the remainder is Fe and unavoidable impurity elements.

[0008] Furthermore, in the wear-resistant steel thick plate, RE can be selected from one or more of La, Ce, Pr, Nd, etc.

[0009] Furthermore, in the wear-resistant steel thick plate with uniform microstructure and hardness in the thickness direction, the main metallographic structure includes martensite, bainite and dispersed nanoscale carbonitride precipitates, wherein the martensite accounts for 65-82%, the bainite accounts for 18-35%, and the nanoscale carbonitride particles have a size of 3-8 nm.

[0010] Furthermore, the wear-resistant steel plate has a thickness of 60~80mm, and its microstructure (martensite / bainite composite structure + nanoscale carbonitride precipitates) and hardness are uniform along the thickness direction, with a hardness difference of less than 10HBW across the entire cross section.

[0011] According to the above scheme, the wear-resistant steel thick plate has a hardness ≥500HBW, tensile strength ≥1650MPa, elongation A ≥8%, and impact energy at -20℃ ≥85J.

[0012] This invention also provides a method for producing wear-resistant steel thick plates with uniform microstructure and hardness in the thickness direction, which can effectively reduce component segregation and banded structure, and improve the uniformity of microstructure and properties; the core process includes the following: (1) High temperature and high pressure rolling + immediate furnace reheating improves the grain morphology and element segregation of the billet; (2) Rolling in the recrystallization zone of the whole austenite + immediate reheating in the furnace refines the grains and phase transformation products and inhibits the formation of banded structure; (3) Water mist cooling + tempering heat treatment promotes the acquisition of full-thickness martensite / bainite composite structure and diffusely distributed nanoscale carbon and nitrogen compound precipitates.

[0013] The specific implementation steps include the following: 1) After converter smelting, Ar, LF and RH treatments are carried out in sequence, and the final composition is tested to meet the steel composition requirements (except for RE). 2) Continuous casting; Add an appropriate amount of RE (feeding with wire) to the continuous casting mold at (Cr+Mo) / RE=100~170, and continuously cast the billet to a thickness of 260~300mm; 3) Controlled rolling; 3-1) Single rolling: The billet is heated, and the single rolling temperature, deformation rate, pass reduction rate and rolling thickness are controlled to carry out high temperature and high reduction rolling to obtain an intermediate billet; 3-2) Immediate reheating in the furnace: If the furnace temperature is higher than the phase change temperature (Ar3+10~20℃), perform a medium-temperature heating. 3-3) Secondary rolling: Control the secondary rolling temperature to be higher than the recrystallization temperature (Tnr+30~60℃), and adjust the deformation rate and pass reduction rate to roll to the finished thickness; 3-4) Immediate reheating in the heat treatment furnace: The furnace temperature is higher than the phase transformation temperature (Ar3+10~20℃), and a second low-temperature heating is performed; 4) Controlled cooling; after exiting the furnace, water mist cooling to 320~340℃; self-tempering, cooling to room temperature; to obtain the wear-resistant steel thick plate for later use.

[0014] According to the above scheme, the converter smelting control is P≤0.005% and C≤0.09%.

[0015] According to the above scheme, in the Ar-LF-RH treatment process, the temperature is controlled and the composition is finely adjusted until the final composition meets the requirements of the steel.

[0016] According to the above scheme, in step 3-1), the billet heating temperature is 1270~1290℃ and the holding time is 40~55min.

[0017] According to the above scheme, in step 3-1), the primary rolling temperature is 1120~1180℃, and the deformation rate is 4~6s. -1 The reduction rate per pass is 20-25%; the thickness of the intermediate billet is 160-180mm.

[0018] According to the above scheme, the temperature for one medium-temperature heating is 1100~1150℃, and the time is 4~5 hours.

[0019] According to the above scheme, in step 3-3), the deformation rate is 2~4s. -1 The pass reduction rate is 10-20%.

[0020] According to the above scheme, the secondary low-temperature heating temperature is 880~900℃, and the time is 20~40min.

[0021] According to the above scheme, the water mist cooling rate is 3~8℃ / s.

[0022] The principles of this invention include the following: 1) Principles of ingredient design technology: Carbon plays a decisive role in microstructure and properties. Each 0.1% increase can increase hardness by about 4 HRC. When the content is 0.45~0.55%, the entire martensite / bainite microstructure can be obtained and the hardness of the microstructure can be guaranteed at a relatively low cooling rate. Too high a content will reduce toughness and increase the risk of cracking.

[0023] Cr + Mo; Cr is a carbide-forming element that can improve the hardness of wear-resistant steel. Simultaneously, it shifts the C-curve to the right, significantly reducing the austenite transformation rate and improving hardenability. It is a key element in the formation of martensite / bainite at low cooling rates. In steel, it can also form a dense oxide film, improving the corrosion resistance of wear-resistant steel. Mo is one of the strongest hardenability-enhancing elements, superior to Cr. It effectively inhibits the formation of pearlite and ferrite, ensuring the formation of martensite / bainite at low cooling rates. It is also a carbide-forming element, improving the hardness of wear-resistant steel. Excessive addition of Cr or Mo will cause carbide aggregation and coarsening, increasing costs. Therefore, Cr and Mo are added at 1.5~2.8% and 1.8~2.2%, respectively.

[0024] Ni expands the austenite region, improves high-temperature stability, enhances toughness, and reduces cold brittleness. However, Ni is expensive, so from a cost and market perspective, it is appropriate to add 0.8~1.2%.

[0025] Mn + Si; While Mn can improve hardenability and increase strength, its strong affinity with S leads to the formation of numerous strip-shaped MnS inclusions. This not only significantly affects the distribution and segregation of S but also results in severe banded microstructure. The abundant formation of MnS leads to Mn enrichment. In Mn-rich regions, austenite exhibits high stability, and during cooling, proeutectoid ferrite preferentially nucleates in Mn-poor regions, forming banded microstructure along the rolling direction. Furthermore, Mn-P co-segregation at grain boundaries increases the P concentration at grain boundaries, leading to intergranular brittle fracture. This effect is particularly pronounced in medium carbon steel and is a significant cause of temper brittleness. Therefore, in this patent, Mn is a deoxidizing residue, and its upper limit should be controlled to ≤0.35%, with its specific content determined by the Si / Mn ratio. Si plays a role in strengthening the matrix and improving tempering stability. Increased Si content causes the solidification interface growth to shift from dendritic growth to endogenous growth, altering the segregation mode. Adding 0.5-1.4% Si and controlling the Si / Mn ratio to ≥3.5 can effectively improve P segregation and banded structure. However, excessive Si increases the viscosity of molten steel, reduces fluidity, slows down the diffusion of solute elements, and may exacerbate macrosegregation. Therefore, the Si content should not exceed 1.4%.

[0026] Based on medium Si (below 1.4%) and low Mn, this invention further controls the Si / Mn ratio to be ≥3.5. When Si and Mn coexist in the steel, Si preferentially occupies the grain boundary position, effectively blocking the Mn-P co-segregation path. Si is enriched at the grain boundary and has a repulsive effect on P, reducing the P concentration at the grain boundary.

[0027] Adding boron (B) causes trace amounts of B to segregate at austenite grain boundaries, inhibiting the nucleation of non-martensite structures and significantly improving the stability of supercooled austenite. This is because B preferentially accumulates at austenite grain boundaries, and the nucleation of non-martensite structures such as pearlite and bainite occurs precisely at the active sites within these austenite grain boundaries. When B atoms occupy these sites, it effectively "blocks" the nucleation pathways for non-martensite structures, thereby increasing austenite stability, reducing the critical cooling rate, and enabling air-cooled hardening (a cooling rate typically requiring oil or water cooling; this invention achieves the required air cooling).

[0028] Ti; Add an appropriate amount of Ti based on a Ti / B ratio of 2~3, because the hardenability effect of B requires a prerequisite: avoiding the combination of B and nitrogen in the steel to form BN. Ti has a much higher affinity for N than B, preferentially forming TiN to fix nitrogen, ensuring boron exists in a solid solution state, thus fully exerting its hardenability-enhancing effect. The proportionally added Ti can also form TiB2 nano-reinforcing phases with B, with dispersed distribution improving strength and thermal stability.

[0029] The combined addition of Ti and V forms stable carbides, preventing austenite grain coarsening, refining the martensite / bainite microstructure, and improving strength and toughness. However, excessive addition of Ti and V increases the risk of coarsening of the composite carbides / nitrides. This invention controls the V addition amount to 1.2~1.6%, and Ti must be added to B in a Ti / B ratio of 2~3.

[0030] Rare earth elements (REs) are typically used to modify MnS inclusions, removing harmful impurities such as low-melting-point elements like Pb, Sn, and As, preventing grain boundary weakening and hot brittleness. REs also segregate at grain boundaries, inhibiting austenite grain coarsening, reducing grain size, and significantly improving strength and toughness. However, excessive REs can form excessive rare earth phases, leading to uneven microstructure, decreased toughness, and increased cost. They are generally added in a RE / S ratio. This invention, due to the addition of significant amounts of carbide-forming elements Cr and Mo, carries the risk of carbide aggregation or the formation of continuous network carbides. Adding an appropriate amount of RE at (Cr+Mo) / RE = 100~170 effectively controls carbide morphology, breaks up continuous network carbides, and promotes their formation into a dispersed spherical distribution, enhancing high-temperature stability and hardness.

[0031] S and P are harmful impurity elements in steel, and the lower the P and S content in steel, the better. When the S content in steel is high, hot rolling is prone to problems such as hot brittleness; while when the P content in steel is high, cold brittleness is likely to occur. In addition, phosphorus is also prone to segregation. In order to reduce production costs and control difficulty, this patent only requires the S and P contents to be controlled at normal levels, that is, below 0.015% each.

[0032] 2) The technological principle is as follows: Adding an appropriate amount of rare earth element (RE) to the continuous casting mold at a ratio of (Cr+Mo) / RE = 100~170 helps ensure stable RE yield, content, and uniform distribution. After addition to the mold, RE rapidly participates in the solid-liquid interface behavior during the initial solidification stage of molten steel. This coincides with the critical stage of inclusion formation and grain growth, allowing for precise intervention in the solidification process. At the solidification front, RE reacts directly with sulfur and oxygen, generating fine rare earth sulfides / oxides that act as heterogeneous nucleation sites, simultaneously inhibiting columnar crystal growth and forming uniformly distributed spherical inclusions. The continuous casting billet thickness is 260~300mm to ensure a rolling compression ratio >3.5 for thick plates.

[0033] The core innovation of the rolling process is to improve segregation and banded structure through a two-step thermomechanical treatment, thereby obtaining a uniform microstructure (martensite / bainite composite structure and dispersed nanoscale carbonitrides) and properties across the entire thickness section. The specific mechanisms of action are as follows: Single rolling: The billet is heated and then subjected to high-temperature, high-reduction rolling. Under high-temperature conditions (1120~1180℃), the plastic deformation capacity of the metal is significantly improved, with large reduction (20~25%) and large deformation rate (4~6s). -1 The deformation penetrates the core, forcefully breaking up the cast dendritic network. Segregated elements (such as C, S, P, and alloying elements) enriched between dendrites are released into the matrix, creating conditions for subsequent homogenization. Defects such as central porosity and shrinkage cavities are compacted under high pressure, improving the material's density. High-temperature, large-scale deformation promotes dynamic recrystallization of austenite, forming fine equiaxed crystals. The newly formed uniform austenite provides a good microstructure basis for subsequent phase transformations and reduces the tendency for banded structures to form.

[0034] Immediate reheating in the furnace: The furnace temperature is higher than the phase transformation temperature (Ar3+10~20℃), then heated to 1100~1150℃ and held for 4~5 hours. Rolling deformation introduces high-density dislocations and subgrain boundaries within the grains, forming "short-circuit diffusion channels" with short atomic diffusion distances. Immediately after this, the grains are placed in the furnace and heated to above 1100℃ for 4~5 hours. The high temperature provides sufficient thermal activation energy, enabling atoms to overcome diffusion barriers and migrate from high-concentration areas to low-concentration areas, significantly promoting element homogenization and further eliminating residual slight segregation. The holding time is determined based on the cross-sectional thickness to ensure a sufficiently uniform distribution of carbon atoms and alloying elements. However, the temperature cannot be too high, as deformed grains will grow abnormally at excessively high temperatures, destroying the uniformity of the microstructure and properties. Therefore, the temperature cannot exceed 1150℃.

[0035] Immediate heating after rolling, ensuring the furnace temperature is above the phase transformation temperature (Ar3 + 10~20℃), is to avoid phase transformations from austenite to ferrite / pearlite / bainite. If the phase transformation occurs after cooling immediately after rolling, solute elements will preferentially enrich at the phase transformation interface or new phases (such as ferrite grain boundaries and pearlite lamellae), forming phase transformation-induced segregation. During subsequent reheating for austenitization, the diffusion difficulty of these enriched elements increases significantly, making it difficult to completely eliminate segregation. Immediately heating the furnace after rolling at a temperature above Ar3 completely avoids this phase transformation process, fundamentally breaking the vicious cycle of "deformation segregation → phase transformation amplified segregation," ensuring that segregation only occurs at the deformation segregation stage caused by rolling, and can be rapidly eliminated through high-temperature diffusion. During rolling, austenite grains are elongated along the rolling direction, forming deformation bands, which are the core structural cause of banded structures during subsequent cooling phase transformation. Immediately after rolling, the austenite is placed in a furnace and held at a temperature above Ar3. The elongated deformed austenite undergoes static recrystallization at high temperatures, transforming into equiaxed fine grains without preferred orientation, thus completely eliminating deformation texture and deformation bands. Since no phase transformation occurs, the austenite remains a single phase, preventing the growth of phase transformation products along the deformation direction and inhibiting the formation of banded structures from the source.

[0036] In addition, the billet is put into the furnace immediately after rolling without waiting for it to cool down and then be reheated, which reduces the temperature fluctuation of "cooling-reheating" and significantly shortens the process cycle. At the same time, the residual heat of rolling is used for homogenization, which reduces the energy consumption of additional heating and meets the production requirements of energy saving and consumption reduction.

[0037] Secondary rolling: The rolling temperature is higher than the recrystallization temperature (Tnr+30~60℃), and the deformation rate is 2~4s. -1The reduction rate per pass is 10-20%, rolling to the finished thickness. The core principle of secondary rolling is to use rolling in the full austenitic recrystallization zone. Compared to primary rolling, the deformation temperature, deformation amount, and deformation rate should be relatively smaller at this stage. During rolling in the full austenitic recrystallization zone at lower temperatures, the austenite undergoes dynamic recrystallization after each deformation pass, forming equiaxed fine grains without preferred orientation, leaving no unrecrystallized deformation bands or deformation textures. In rolling in the full austenitic recrystallization zone, the deformation amount (10-20%) and deformation rate (2-4s) per pass are... -1 Matching ensures thorough and uniform recrystallization, ultimately yielding an equiaxed grain structure with a grain size deviation of <10%. Each pass requires a deformation amount >20% and a deformation rate >4s. -1 Abnormal grain growth and banding tendencies can also occur. The high-temperature environment of the fully austenitic recrystallization zone, combined with the rapid migration of grain boundaries during dynamic recrystallization, promotes the diffusion of segregated elements (such as Mn and P), breaks the dendritic segregation network structure, and further makes the composition distribution more uniform. Moreover, this process is highly stable, has low production control difficulty, and is more suitable for rolling large-section, complex-shaped parts. Compared with the traditional two-stage rolling process (in the crystallization zone + non-recrystallization zone), the above-mentioned fully austenitic recrystallization zone rolling process of this invention is more conducive to the uniformity of microstructure and properties in the thickness direction of high-hardness ultra-thick steel plates (non-recrystallization controlled rolling is prone to inducing banding structure, producing uneven mixed structure, and aggravating micro-composition inhomogeneity).

[0038] Immediate reheating in a heat treatment furnace: The furnace temperature should be higher than the phase transformation temperature (Ar3+10~20℃), heated to 880~900℃, and held for 20~40 minutes. Immediately after the second rolling, the material is placed in a heat treatment furnace, requiring the furnace temperature to be higher than the phase transformation temperature (Ar3+10~20℃). Heating to above 880℃ ensures thorough homogenization of the deformed austenite after rolling, eliminating residual compositional differences. Controlling the heating temperature and time yields uniform and fine austenite grains, providing an ideal microstructure basis for subsequent phase transformation. During subsequent cooling, the homogenized austenite ensures consistent phase transformation conditions in all regions, significantly reducing banded structure formation. Residual stress generated during rolling is eliminated through static recrystallization at high temperatures, preventing stress concentration during subsequent phase transformation. The homogenized austenite provides a stable parent phase for subsequent phase transformation, facilitating the acquisition of uniform phase transformation products. Excessively high heating temperatures can lead to abnormal grain growth; therefore, the heating temperature is controlled at 880~900℃.

[0039] After exiting the furnace, the steel is cooled by water mist at a rate of 3-8°C / s, first to 320-340°C, then subjected to self-tempering and cooled to room temperature. A key objective of this invention's composition design and control is to achieve a transformation to a martensitic / bainitic composite structure under water mist cooling conditions, controlling the final cooling temperature within the bainitic transformation range to promote appropriate bainite formation and optimize the strength-toughness balance. Compared to traditional wear-resistant steel quenching processes, water mist cooling has a relatively slower cooling rate, better cooling uniformity, significantly reduced cross-sectional temperature differences, and simultaneously suppresses the asynchronous transformation between surface martensite and core bainite, achieving consistent microstructure distribution, eliminating the "surface-core" microstructure gradient, and thus obtaining a uniform martensitic / bainitic microstructure across the entire thickness cross-section. The interlacing of martensite laths and bainitic acicular bodies forms a three-dimensional network structure, completely eliminating the basis for banded microstructure formation.

[0040] Self-tempering is used to further promote the formation of high-density, uniformly dispersed nano-precipitates. When water mist cools to 320-340℃, the martensitic / bainitic phase transformation is just completed, and the matrix retains high-energy sites such as high-density dislocations, martensitic lath boundaries, and bainitic acicular interfaces. These sites are preferential nucleation sites for the MX phase. Solute atoms (Cr, Mo, V, etc.) do not need to overcome high nucleation energy barriers and can directly aggregate and nucleate at dislocation lines and interfaces to form nano-precipitates with uniform distribution. With the martensitic / bainitic phase transformation just completed, C / N and alloying elements in the matrix are in a supersaturated solid solution state, providing the strongest driving force for solute atom precipitation and enabling rapid formation of high-density nano-precipitates. Self-tempering utilizes the residual heat of the workpiece itself, allowing solute atoms to only complete short-range diffusion. The precipitates remain at the nanoscale and do not coarsen. Furthermore, as the workpiece naturally cools to room temperature, it further inhibits the growth of the precipitates.

[0041] According to the above scheme, a uniformly distributed martensite / bainite composite structure can be obtained, forming a complementary strengthening and toughening mechanism, achieving high strength and hardness while also obtaining high toughness; it also contains dispersed nanoscale carbonitrides, uniformly distributed within the martensite laths and bainite needles, further providing a strong precipitation strengthening effect without compromising plasticity and toughness; in addition, this invention effectively improves problems such as component segregation and banded structure, and by combining the uniform martensite / bainite composite structure across the entire thickness section with dispersed nanoscale carbonitrides, the uniformity of properties in the thickness direction is improved, effectively solving problems such as "surface-to-center difference" in thick plates.

[0042] Compared with the prior art, the beneficial effects of the present invention include: 1) From a technical perspective, this invention effectively solves the industry pain point of uneven microstructure and properties in the thickness direction of wear-resistant steel thick plates through the synergistic effect of component design and innovative processes; In terms of composition design, the alloy element ratio is optimized, which not only ensures hardenability but also inhibits compositional segregation and banded structure, and promotes the diffuse precipitation of nano-sized carbon and nitrogen compounds. In terms of process improvement, a combination of two-step thermomechanical treatment + instant reheating + water mist cooling self-tempering is adopted to completely break up the cast dendrites and eliminate non-uniform structures such as deformation segregation and texture. Achieving uniform distribution of martensite / bainite composite microstructure across the entire thickness, with balanced strength and toughness and excellent uniformity.

[0043] 2) From an economic perspective, it has significant advantages in production cost and cycle control, leading to industrialization. The process adopts a conventional converter-Ar-LF-RH smelting process, which does not require the addition of special equipment. It utilizes the residual heat of rolling to achieve instant heating and self-tempering, shortening the production cycle and reducing energy consumption. P and S are controlled at conventional levels, reducing the difficulty of smelting control and raw material costs.

[0044] 3) The wear-resistant steel thick plate obtained by the present invention can meet the demand for thick wear-resistant steel in heavy-duty and wear-resistant working conditions, broaden the application scenarios, and has good market prospects. Attached Figure Description

[0045] Figure 1 This is a comparison of the microstructure of the wear-resistant steel at the center of its thickness obtained in Example 4 (left) and Comparative Example 2 (right). Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0047] Examples 1-5 The preparation steps of the wear-resistant steel thick plates described in Examples 1-5 are as follows: 1) After smelting in a converter according to the composition requirements in Table 1, Ar-LF-RH treatment is carried out in sequence. The final composition of the test results meets the requirements of Table 1. In the continuous casting crystallizer, an appropriate amount of RE (any two of La, Ce, Pr, Nd) is added at (Cr+Mo) / RE=100~170. The slab is continuously cast into a billet with a thickness of 300mm. 2) Single rolling: The billet is heated to 1270~1290℃ and held at that temperature for 40~55min. The rolling temperature is controlled at 1120~1180℃ and the deformation rate is 4~6s. -1 The reduction rate per pass is 20-25%, and the intermediate billet is rolled to a thickness of 160-180 mm. 3) Immediate reheating in the furnace: The furnace temperature is higher than the phase change temperature (Ar3 + 10~20℃; where the Ar3 values ​​in Examples 1-5 are 685℃, 692℃, 688℃, 695℃, and 692℃ respectively), and the temperature is held at 1100~1150℃ for 4~5 hours. 4) Secondary rolling: The rolling temperature is higher than the recrystallization temperature (Tnr + 30~60℃, where Tnr values ​​in Examples 1-5 are 1055℃, 1028℃, 1018℃, 1015℃, and 1012℃, respectively), and the deformation rate is 2~4s. -1 The reduction rate per pass is 10-20%, and the product is rolled to the finished thickness. 5) Immediate reheating in the heat treatment furnace: The furnace temperature is higher than the phase transformation temperature (Ar3+10~20℃), and the temperature is raised to 880~900℃ and held for 20~40 minutes; 6) After exiting the furnace, use water mist to cool the furnace at a rate of 3-8℃ / s until the temperature reaches 320-340℃. Then, perform self-tempering and cool to room temperature. 7) To be used.

[0048] The specific core process parameters of the embodiments of the present invention are described in detail below: The weight percentage content of the wear-resistant steel components in the examples is shown in Table 1.

[0049] Table 1. Component composition (weight percentage) of the examples and comparative examples.

[0050] Note: Mn, Ti, and RE meet the requirements of the technical solution: "Control the Mn content according to Si / Mn≥3.5 and the total amount ≤0.35%, add an appropriate amount of Ti according to Ti / B=2~3, and add an appropriate amount of RE according to (Cr+Mo) / RE=100~170". Among them, RE is added in the continuous casting crystallizer.

[0051] The core process parameters for rolling-heat treatment in each embodiment and comparative example are shown in Table 2 and Table 3, respectively.

[0052] Table 2. Core process parameters of the single rolling-reheating process in the examples and comparative examples.

[0053] Table 3. Core process parameters of the secondary rolling-heat treatment process in the examples and comparative examples.

[0054] The conventional controlled rolling-quenching + tempering heat treatment process described in Tables 2 and 3 includes the following steps: heating the billet to uniformly austenitize, two-stage controlled rolling (rolling in the austenite recrystallization zone (first stage rolling) and rolling in the austenite non-recrystallization zone (second stage rolling)), controlled cooling after rolling, offline heating to uniformly austenitize, rapid cooling and quenching, and tempering; wherein, the rolling temperature of the first stage is controlled at 1060~1080℃, the rolling temperature of the second stage is controlled at 950~980℃, and the final rolling temperature is controlled at 820~880℃; after rolling, cooling to room temperature at a cooling rate of 8~15℃ / s; the steel plate is reheated (860~880℃) and quenched, and then tempered (tempering temperature is 220~240℃).

[0055] The performance test results of the wear-resistant steels obtained in each embodiment and comparative example are shown in Table 4.

[0056] Table 4 Performance test results of wear-resistant steels obtained in each embodiment and comparative example

[0057] As can be seen from section 4, the wear-resistant steel plate of the present invention has a thickness of 60-80mm, a hardness of ≥500HBW, a tensile strength of ≥1650MPa, an elongation of A of ≥8%, and an impact energy of -20℃ of ≥85J.

[0058] The microstructure along the thickness direction is a martensitic / bainitic composite structure (see...). Figure 1 The central part is also a martensitic / bainitic composite structure and a diffusely distributed nano-sized carbonitridium compound precipitate phase, with a hardness difference of less than 10 HBW across the entire cross section.

[0059] The embodiments described above are merely illustrative of the core concept of the present invention and do not constitute a limitation on the technical solutions of the present invention. Those skilled in the art can make various changes or optimizations to its form, parameters, or process steps without departing from the basic design concept of the present invention, and such changes, optimizations, or equivalent substitutions should all fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A wear-resistant steel thick plate with uniform microstructure and hardness in the thickness direction, characterized in that, The main chemical components and their content requirements include: C 0.45~0.55wt%, Cr 1.5~2.8wt%, Mo 1.8~2.2wt%, V 1.2~1.6wt%, Ni 0.8~1.2wt%, Si 0.5~1.4wt%, B 0.003~0.005wt%; Mn content is controlled according to Si / Mn≥3.5, and Mn content≤0.35%; Ti content is controlled according to Ti / B=2~3; RE is introduced according to (Cr+Mo) / RE=100~170; P≤0.015%, S≤0.015%; the remainder is Fe and unavoidable impurity elements.

2. The wear-resistant steel thick plate according to claim 1, characterized in that, In the wear-resistant steel thick plate, RE is one or more of La, Ce, Pr, and Nd.

3. The wear-resistant steel thick plate according to claim 1, characterized in that, The main metallographic structure includes martensite, bainite, and dispersed nanoscale carbonitride precipitates, of which martensite accounts for 65-82%, bainite accounts for 18-35%, and the nanoscale carbonitride particles have a diameter of 3-8 nm.

4. The wear-resistant steel thick plate according to claim 1, characterized in that, The thickness is 60~80mm, and the microstructure and hardness are uniform along the thickness direction, with a hardness difference of less than 10HBW across the entire cross section.

5. The wear-resistant steel thick plate according to claim 1, characterized in that, Its hardness is ≥500HBW, tensile strength is ≥1650MPa, elongation A is ≥8%, and impact energy at -20℃ is ≥85J.

6. A method for producing a wear-resistant steel thick plate with uniform microstructure and hardness in the thickness direction as described in any one of claims 1 to 5, characterized in that, The key control requirements for processes including converter smelting, continuous casting, controlled rolling, and controlled cooling are as follows: 1) After converter smelting, Ar, LF and RH treatments are carried out in sequence, and the final composition is tested to ensure that it meets the requirements of steel composition. 2) Continuous casting; RE is added in the continuous casting mold at (Cr+Mo) / RE=100~170, and the billet is continuously cast. 3) Controlled rolling; 3-1) Single rolling: The billet is heated, and the single rolling temperature, deformation rate, pass reduction rate and rolling thickness are controlled to carry out high temperature and high reduction rolling to obtain an intermediate billet; 3-2) Immediate reheating in the furnace: If the furnace temperature is higher than the phase change temperature, perform a medium-temperature heating. 3-3) Secondary rolling: Control the secondary rolling temperature to be higher than the recrystallization temperature, and adjust the deformation rate and pass reduction rate to roll to the finished thickness; 3-4) Immediate reheating in the heat treatment furnace: The furnace temperature is higher than the phase change temperature, and a second low-temperature heating is performed; 4) Controlled cooling; after exiting the furnace, water mist cooling to 320~340℃; self-tempering, cooling to room temperature; to obtain the wear-resistant steel thick plate for later use.

7. The production method according to claim 6, characterized in that, In 3-2), the furnace temperature is controlled at Ar3+10~20℃; in 3-3), the secondary rolling temperature is controlled at Tnr+30~60℃; in 3-4), the furnace temperature is controlled at Ar3+10~20℃.

8. The production method according to claim 6, characterized in that, In step 3-1), the billet heating temperature is 1270~1290℃, and the holding time is 40~55min; the primary rolling temperature is 1120~1180℃, and the deformation rate is 4~6s. -1 The pass reduction rate is 20-25%; the intermediate billet thickness is 160-180mm; the first medium-temperature heating temperature is 1100-1150℃, and the time is 4-5h.

9. The production method according to claim 6, characterized in that, In step 3-3), the deformation rate is 2~4s. -1 The reduction rate per pass is 10-20%; the secondary low-temperature heating temperature is 880-900℃, and the time is 20-40 minutes.

10. The production method according to claim 6, characterized in that, The water mist cooling rate is 3~8℃ / s.

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