A steel for a self-hardening broken blade for straw returning and a method for manufacturing the same

Abstract

The application provides a kind of straw returning to field with self-hardening broken blade steel and its preparation method, and belongs to the field of steel preparation.The broken blade steel chemical composition includes C, Si, Mn, Cr, Ni, Mo, Nb, Ti, V, B and Fe; wherein, the content of C is 0.30%~0.55%, the content of Si is 0.15%~0.25%, the content of Mn is 0.45%~0.75%, the content of Cr is 0.85%~2.0%, the content of Ni is 3.0%~4.5%, the content of Mo is 0.4%~1.2%, the content of Nb is 0.01%~0.060%, the content of Ti is 0.015%~0.03%, the content of V is 0.3%~0.9%, and the content of B is 0.002%~0.005% by mass fraction.By limiting the addition of C, Si and Mn to improve the tensile strength of steel, adding Ti and Nb elements for fine-grain strengthening and second phase particle precipitation strengthening, adding B and Cr elements to improve the hardenability of steel, adding Ni to improve the toughness of steel, adding Mo element to improve the ability of anti-tempering brittleness, and adding V element to ensure hardenability at local high temperature, the metallographic structure of the steel is obtained in the form of lath martensite, thereby improving the performance of the broken blade.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a self-hardening crushing blade steel for straw return to the field and its preparation method. Background Technology

[0002] In agriculture, straw return to the field is a measure that utilizes straw for soil improvement and yield enhancement, widely valued globally. It eliminates air pollution caused by straw burning while simultaneously increasing soil fertility and yield. Straw return increases soil organic matter, improves soil structure, loosens the soil, increases porosity, reduces volume, and promotes microbial activity and crop root development, resulting in significant fertilization and yield-increasing effects. One method is straw crushing and compaction, which involves mechanically crushing harvested straw and then directly compacting it into the soil during tilling. However, this process may encounter hard sand, gravel, scrap iron, and other impurities. The high-speed rotation and impact can wear down and damage blades and cutting tools.

[0003] Traditional blades and cutting tools are mostly made from medium- to high-carbon steel blanks, manufactured through quenching and low-temperature tempering to achieve high hardness and strength. However, their microstructure is relatively brittle and prone to localized high-temperature tempering softening. Under the intense rotation, impact, compression, and shearing forces during crushing, they often experience wear and chipping, leading to frequent tool replacements, damage to the crushing mechanism, and poor performance. Therefore, improving the strength, toughness, and resistance to tempering softening of straw-returning crushing blades, and obtaining a self-hardening martensitic microstructure to improve the performance of the crushing blades, is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application provides a self-hardening crushing blade steel for straw return to the field and its preparation method. By improving the strength, toughness and resistance to tempering softening of the crushing blade steel, the technical problem of poor performance of traditional blades is solved.

[0005] In a first aspect, this application provides a self-hardening crushing blade steel for straw return to the field, wherein the chemical composition of the crushing blade steel includes: C, Si, Mn, Cr, Ni, Mo, Nb, Ti, V, B, and Fe; wherein, by mass fraction,

[0006] The content of C is 0.30%–0.55%, the content of Si is 0.15%–0.25%, the content of Mn is 0.45%–0.75%, the content of Cr is 0.85%–2.0%, the content of Ni is 3.0%–4.5%, the content of Mo is 0.4%–1.2%, the content of Nb is 0.01%–0.060%, the content of Ti is 0.015%–0.03%, the content of V is 0.3%–0.9%, and the content of B is 0.002%–0.005%.

[0007] Optionally, the metallographic structure of the steel used for the crushing blade is lath martensite.

[0008] Optionally, the steel used for the crushing blades meets at least one of the following properties: hardness of 550HV~650HV, tensile strength ≥1675MPa, toughness ≥50J, and resistance to tempering softening ≥850℃.

[0009] Secondly, this application provides a method for preparing the steel for crushing blades according to any embodiment of the first aspect, characterized in that the method includes:

[0010] The casting blank having the aforementioned chemical composition is sequentially heated, forged, and slowly cooled to obtain a first microstructure matrix blank.

[0011] The first tissue matrix blank is rough-machined to obtain the second tissue matrix blank;

[0012] The second microstructure blank is reheated and finished to obtain steel for crushing blades.

[0013] Optionally, the heating temperature is 1000℃~1250℃.

[0014] Optionally, the forging temperature is 900℃~1250℃.

[0015] Optionally, the forging compression ratio of the thickness of the cast blank to the thickness of the first microstructure blank is ≥1.5.

[0016] Optionally, the reheating temperature is 850℃~980℃.

[0017] Optionally, the slow cooling is air cooling to room temperature.

[0018] Optionally, the hardness of the first tissue matrix blank is 220HV to 350HV.

[0019] The technical solutions provided in this application have the following advantages compared with the prior art:

[0020] The self-hardening crushing blade steel for straw return to the field provided in this application improves the tensile strength of the steel by limiting the addition of C, Si, and Mn, then adds Ti and Nb elements for grain refinement and second-phase particle precipitation strengthening, then adds B and Cr elements to improve the hardenability of the steel, adds Ni to achieve solid solution and improve the toughness of the steel, adds Mo elements to improve the resistance to temper brittleness, and adds V elements to ensure hardenability at local high temperatures. This results in a lath martensite microstructure of the steel, giving the crushing blade high hardness, toughness, and resistance to temper softening during operation, thereby improving the performance of the crushing blade. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic flowchart illustrating a method for preparing self-hardening crushing blade steel for straw return to the field, provided in an embodiment of this application;

[0024] Figure 2 The metallographic structure of the steel for the self-hardening crushing blade used for straw return to the field provided in Embodiment 5 of this application is shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0027] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0029] In a first aspect, this application provides a self-hardening crushing blade steel for straw return to the field, wherein the chemical composition of the crushing blade steel includes: C, Si, Mn, Cr, Ni, Mo, Nb, Ti, V, B, and Fe; wherein, by mass fraction,

[0030] The content of C is 0.30%–0.55%, the content of Si is 0.15%–0.25%, the content of Mn is 0.45%–0.75%, the content of Cr is 0.85%–2.0%, the content of Ni is 3.0%–4.5%, the content of Mo is 0.4%–1.2%, the content of Nb is 0.01%–0.060%, the content of Ti is 0.015%–0.03%, the content of V is 0.3%–0.9%, and the content of B is 0.002%–0.005%.

[0031] In some implementations, the positive effect of controlling the carbon content to be between 0.30% and 0.55% is that carbon is a fundamental strengthening element of steel, and its content largely determines the tensile strength level of the steel plate, making it a crucial indicator affecting carbon equivalent. When the mass fraction exceeds the maximum value of this range, the adverse effect is obtaining a high-carbon martensitic structure, resulting in excessively high hardness and increased brittleness, making the steel plate prone to fracture under severe impact during high-speed operation. Conversely, when the mass fraction is below the minimum value of this range, the adverse effect is excessively low hardness and decreased wear resistance. The carbon content can be 0.30%, 0.35%, 0.40%, 0.45%, 0.55%, etc.

[0032] The positive effects of controlling the Si content to 0.15%–0.25% are that, as Si is a solid solution strengthening element in steel, it improves the hardenability of the steel, thereby increasing its strength. However, if the mass fraction exceeds the maximum value of this range, the adverse effect is that the excessive Si content makes the steel plate brittle. Conversely, if the mass fraction is below the minimum value of this range, the adverse effect is that the strength and hardness will not meet the predetermined requirements. The Si content can be 0.15%, 0.20%, 0.22%, 0.25%, etc.

[0033] The positive effect of controlling the Mn content to 0.45%–0.75% is that Mn improves the hardenability of steel, enabling high-hardness martensite to be obtained in steel plates of a certain size under specific heating and cooling conditions, thereby refining the substructure of the strip steel. When the mass fraction exceeds the maximum value of this range, the adverse effect is embrittlement of the microstructure, failing to meet the high toughness requirements of the breaker blade. When the mass fraction is less than the minimum value of this range, the adverse effect is insufficient hardenability, resulting in a difference between surface hardness and core hardness, reducing the wear resistance of the breaker blade. The Mn content can be 0.45%, 0.50%, 0.55%, 0.65%, 0.75%, etc.

[0034] The positive effect of controlling the Cr content within the range of 0.85% to 2.0% is that within this mass fraction range, Cr improves the hardenability of steel, which is beneficial for martensitic transformation after hot working, and also has a certain solid solution strengthening effect. When the mass fraction exceeds the maximum value of this range, the adverse effect is the formation of more carbide particles, reducing the intergranular bonding strength and thus reducing toughness, making the crusher blade prone to brittle fracture. When the mass fraction is less than the minimum value of this range, the adverse effect is that the target strength and hardness indicators cannot be obtained, reducing the wear resistance of the crusher blade. The Cr content can be 0.85%, 1.0%, 1.2%, 1.6%, 2.0%, etc.

[0035] The positive effects of controlling the Ni content to 3.0%–4.5% are that Ni improves the hardenability of steel, acts as a solid solution strengthening element, enhances the low-temperature toughness of steel, and ensures that the steel will not fracture under severe impact. When the mass fraction exceeds the maximum value of this range, the adverse effect is that the hardness value required by this invention is exceeded, and intermetallic compounds are formed with Cr, reducing the grain boundary bonding strength. When the mass fraction is less than the minimum value of this range, the adverse effect is that the target high toughness requirement cannot be achieved, impact resistance decreases, and the cutting tool is prone to breakage. The Ni content can be 3.0%, 3.5%, 4.0%, 4.5%, etc.

[0036] The positive effects of controlling the Mo content to 0.4%–1.2% are due to Mo's ability to improve the hardenability of steel, its role as a solid solution strengthening element, and its enhancement of low-temperature toughness. Simultaneously, Mo resists temper brittleness, hindering the aggregation of carbide particles towards grain boundaries under the influence of localized high temperatures during heat treatment and use of the breaker blade, thus ensuring the stability of toughness. When the mass fraction exceeds the maximum value of this range, the adverse effect is that it exceeds the hardness value required by this invention, which is detrimental to ensuring toughness. When the mass fraction is less than the minimum value of this range, it will lead to fluctuations in toughness. The Mo content can be 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, etc.

[0037] The positive effect of controlling the Nb content to be between 0.01% and 0.060% is that within this mass fraction range, Nb can refine the grain size, providing both grain refinement and precipitation strengthening effects, while also improving the toughness of the steel. When the mass fraction exceeds the maximum value of this range, the adverse effect is the formation of a large amount of Nb carbide, which adsorbs carbon and reduces the hardenability of the steel. When the mass fraction is less than the minimum value of this range, the adverse effect is that during heat treatment, it causes grain coarsening, reducing hardness and toughness. The Nb content can be 0.01%, 0.02%, 0.04%, 0.05%, 0.060%, etc.

[0038] The positive effect of controlling the Ti content to 0.015%–0.03% is that within this mass fraction range, Ti can fix nitrogen and precipitate nano-sized particles, producing a strong precipitation strengthening effect, thereby improving the high-temperature plastic deformation capacity of the steel and making it easier to forge. When the mass fraction exceeds the maximum value of this range, the adverse effect is the formation of micron-sized titanium nitride, resulting in microscopic defects and reduced toughness. When the mass fraction is less than the minimum value of this range, the adverse effect is that the target hardness of the breaker blade cannot be achieved. The Ti content can be 0.015%, 0.020%, 0.025%, 0.030%, etc.

[0039] The positive effects of controlling the V content to 0.3%–0.9% lie in V's status as a strong carbide and nitride forming element. Nitrides can hinder austenite grain growth, thereby increasing the grain coarsening temperature and refining the grains. This facilitates grain refinement during heat treatment and forging, improving strength and toughness. It also ensures hardenability under the localized high temperatures caused by crushing, extrusion, and friction, providing good resistance to tempering softening, thus enhancing the performance of the crusher blade. The V content can be 0.3%, 0.5%, 0.7%, 0.9%, etc.

[0040] The positive effect of controlling the boron content to be between 0.002% and 0.005% is that within this mass fraction range, boron improves the hardenability of the steel, resulting in martensitic structure during the localized heating and rapid cooling process of the breaker blade, thus achieving high local hardness. When the mass fraction exceeds the maximum value at the end of this range, the adverse effect is increased brittleness, making the breaker blade prone to brittle fracture. When the mass fraction is less than the minimum value at the end of this range, the adverse effect is insufficient hardenability, making it impossible to achieve the target hardness of the breaker blade. The boron content can be 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0041] In some embodiments, the metallographic structure of the steel used for the crushing blade is lath martensite.

[0042] The metallographic structure of the steel used for crushing blades in this application is lath martensite, which gives the steel for crushing blades high hardness, toughness and resistance to tempering softening during operation, thereby improving the performance of the crushing blades.

[0043] In some embodiments, the steel used for the crushing blades meets at least one of the following properties: hardness of 550HV to 650HV, tensile strength ≥1675MPa, toughness ≥50J, and resistance to tempering softening ≥850℃.

[0044] The steel used for breaker blades possesses high hardness, toughness, and resistance to tempering softening, thereby improving the performance of the breaker blades. The hardness can be 550HV, 580HV, 610HV, 630HV, 650HV, etc.; the tensile strength can be 1675MPa, 1700MPa, 1750MPa, 1850MPa, 1950MPa, etc.; the toughness can be 50J, 60J, 80J, 90J, etc.; and the resistance to tempering softening can be 850℃, 900℃, 950℃, 1000℃, etc.

[0045] Secondly, this application provides a method for preparing the steel for crushing blades according to any embodiment of the first aspect, characterized in that the method includes:

[0046] S1. The casting blank having the chemical composition is sequentially heated, forged, and slowly cooled to obtain the first microstructure matrix blank.

[0047] In some embodiments, the heating temperature is 1000°C to 1250°C.

[0048] The positive effects of controlling the heating temperature to 1000℃~1250℃ are: it ensures sufficient heating of the casting blank, thus facilitating phase transformation and forging; if the temperature is too high, it may lead to excessively coarse grains, affecting the strength of the steel; if the temperature is too low, it may lead to excessive resistance during the forging process, affecting the effectiveness of the forging process. The heating temperature can be 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, etc.

[0049] In some embodiments, the forging temperature is 900°C to 1250°C.

[0050] The positive effects of controlling the forging temperature to 900℃~1250℃ are: good plasticity of the cast blank, which is conducive to multiple and repeated forging, ensuring the control requirements of the forging compression ratio. If the temperature is too high, it may lead to excessively coarse grains, affecting the strength of the steel; if the temperature is too low, it may lead to excessive resistance during the forging process, affecting the forging effect and failing to guarantee the required compression ratio. The forging temperature can be 900℃, 1000℃, 1100℃, 1200℃, 1250℃, etc.

[0051] In some implementations, the slow cooling is air cooling to room temperature.

[0052] In some embodiments, the hardness of the first tissue matrix blank is 220HV to 350HV.

[0053] The hardness of the first tissue matrix blank can be 220HV, 250HV, 280HV, 320HV, 350HV, etc.

[0054] In some embodiments, the forging compression ratio of the thickness of the cast blank to the thickness of the first microstructure blank is ≥1.5.

[0055] The positive effects of controlling the forging compression ratio to ≥1.5 include: eliminating casting defects and obtaining a first microstructure blank with a good match of strength and toughness; if the compression ratio is less than this value, casting defects cannot be eliminated, and the first microstructure blank is brittle. This forging compression ratio can be 1.5, 1.6, 2.0, 2.5, 3.0, 3.5, etc.

[0056] S2. Roughly process the first tissue matrix blank to obtain the second tissue matrix blank;

[0057] S3. The second tissue matrix blank is reheated and finished to obtain steel for crushing blades.

[0058] In some embodiments, the reheating temperature is 850°C to 980°C.

[0059] The positive effects of controlling the reheating temperature to 850℃~980℃ include: sufficient austenitization of the first microstructure matrix blank, adequate diffusion between elements, and obtaining a uniform high-temperature microstructure. The reheating temperature can be 850℃, 880℃, 920℃, 950℃, 980℃, etc.

[0060] The preparation method of the steel for crushing blades is based on the chemical composition of the steel for crushing blades described above. The specific chemical composition of the steel for crushing blades can be referred to in the above embodiments. Since the preparation method of the steel for crushing blades adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0061] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0062] The molten steel of Examples 1 to 6 was prepared and cast into casting blanks. The chemical composition of the casting blanks is shown in Table 1.

[0063] Table 1 shows the chemical composition (wt%) of the cast blank, with the remainder being Fe and unavoidable impurities.

[0064] Group C Si Mn Cr Ni Mo Nb Ti V B Example 1 0.30 0.25 0.45 2.0 3.0 0.4 0.02 0.015 0.3 0.005 Example 2 0.35 0.22 0.65 1.5 3.5 0.5 0.01 0.018 0.5 0.003 Example 3 0.40 0.18 0.75 1.2 4.0 0.6 0.06 0.02 0.6 0.005 Example 4 0.45 0.16 0.70 1.0 3.8 1.2 0.04 0.03 0.9 0.004 Example 5 0.50 0.20 0.65 1.44 3.9 0.8 0.03 0.03 0.5 0.003 Example 6 0.55 0.15 0.45 0.85 4.2 1.0 0.04 0.02 0.7 0.002

[0065] Based on the chemical composition of the above-mentioned casting blank, this application provides a method for preparing steel for crusher blades, the method comprising the following steps:

[0066] S11. Obtain a casting blank having the aforementioned chemical composition;

[0067] S21. The casting blank is sequentially heated, forged and slowly cooled to obtain a first microstructure blank.

[0068] S31. The first tissue matrix blank is rough-machined to obtain the second tissue matrix blank;

[0069] S41. The second substrate blank is reheated and finished to obtain steel for crushing blades. The main process parameters are shown in Table 2.

[0070]

[0071]

[0072] The mechanical properties of the steel used for crushing blades obtained in Examples 1-6 were tested, and the specific results are shown in Table 3.

[0073] Table 3. Mechanical properties of steel used for breaker blades

[0074]

[0075] Appendix Figure 2 Detailed explanation: Figure 2 The image shows the metallographic structure of the steel for the crushing blade provided in Embodiment 5 of this application. It has a lath martensite structure with obvious forging flow lines.

[0076] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A type of steel for self-hardening crushing blades used in straw returning to the field, characterized in that, The chemical composition of the steel used for the crushing blade includes: C, Si, Mn, Cr, Ni, Mo, Nb, Ti, V, B, and the balance being Fe; wherein, by mass fraction, The content of C is 0.30%~0.55%, the content of Si is 0.15%~0.25%, the content of Mn is 0.45%~0.75%, the content of Cr is 0.85%~2.0%, the content of Ni is 3.0%~4.5%, the content of Mo is 0.4%~1.2%, the content of Nb is 0.01%~0.060%, the content of Ti is 0.015%~0.03%, the content of V is 0.3%~0.9%, and the content of B is 0.002%~0.005%. The method for preparing the steel for the crushing blade includes: A casting blank having the aforementioned chemical composition is obtained; The casting blank is sequentially heated, forged, and slowly cooled to obtain a first microstructure blank. The first tissue matrix blank is rough-machined to obtain the second tissue matrix blank; The second microstructure matrix blank is reheated and finished to obtain steel for crushing blades; The forging temperature is 900℃~1250℃, the forging compression ratio of the thickness of the cast blank to the thickness of the first microstructure blank is ≥1.5, and the reheating temperature is 850℃~980℃.

2. The steel for crushing blades according to claim 1, characterized in that, The metallographic structure of the steel used for the crushing blade is lath martensite.

3. The steel for crushing blades according to claim 1, characterized in that, The steel used for the crushing blades meets at least one of the following properties: hardness of 550HV~650HV, tensile strength ≥1675MPa, toughness ≥50J, and resistance to tempering softening ≥850℃.

4. A method for preparing the steel for crushing blades according to any one of claims 1-3, characterized in that, The method includes: A casting blank having the aforementioned chemical composition is obtained; The casting blank is sequentially heated, forged, and slowly cooled to obtain a first microstructure blank. The first tissue matrix blank is rough-machined to obtain the second tissue matrix blank; The second microstructure blank is reheated and finished to obtain steel for crushing blades.

5. The method according to claim 4, characterized in that, The heating temperature is 1000℃~1250℃.

6. The method according to claim 4, characterized in that, The slow cooling refers to air cooling to room temperature.

7. The method according to claim 4, characterized in that, The hardness of the first tissue matrix blank is 220HV~350HV.

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