CN111471936A

CN111471936A - Improved steel for agricultural machinery cutting tool and production method thereof

Info

Publication number: CN111471936A
Application number: CN202010360149.6A
Authority: CN
Inventors: 左辉; 唐宁; 林鹏; 石可伟; 郑力宁; 肖波
Original assignee: Jiangsu Lihuai Steel Co ltd; Jiangsu Shagang Group Huaigang Special Steel Co Ltd
Current assignee: Jiangsu Lihuai Steel Co ltd; Jiangsu Shagang Group Huaigang Special Steel Co Ltd
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2020-07-31

Abstract

The invention discloses an improved steel for agricultural machinery cutting tools, which comprises the following chemical elements, by mass, 0.33% -0.35% of C, 0.30% -0.40% of Si, 1.30% -1.40% of Mn, 0.50% -0.60% of Cr, 0.002% -0.004% of B, 0.050% -0.065% of Ti, 0.070% -0.090% of Al, less than or equal to 0.015% of P, less than or equal to 0.005% of S, and Fe. as a smelting raw material, wherein the smelting raw material is subjected to KR desulfurization, converter smelting, L F refining, RH vacuum degassing, soft blowing, continuous casting and continuous rolling to obtain flat steel with the thickness of 10mm × and the width of 78 mm.

Description

Improved steel for agricultural machinery cutting tool and production method thereof

Technical Field

The invention belongs to the technical field of alloy steel, relates to tool steel in the steel industry, and particularly relates to improved steel for agricultural machinery cutting tools and a production method thereof.

Background

Agriculture is the foundation of national economy and meets the basic material requirements of people's life. The development of agriculture is related to the prosperity and the stability of the country. The development of modern agriculture can not leave advanced agricultural machinery, and the quality of the agricultural machinery determines the level of the modern development of agriculture. The most common large agricultural machine at present is a harvester, and the most important of the harvester is a cutting tool except power equipment. Agricultural machinery cutting tools are tools for agricultural machinery operation, and the quality of the cutting tools determines the use efficiency of the agricultural machinery. At present, 30MnB5 material is mostly used for forging agricultural machinery cutting tools.

The German technical Condition for delivery of quenched and tempered steels, alloy steels in part 3 (EN 10083-3) specifies the 30MnB5 material as follows: 0.27 to 0.33 percent of C, less than or equal to 0.40 percent of Si, 1.15 to 1.45 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.035 percent of S, B: 0.0008% -0.0050%. The cutting tool is used as a wearing part of agricultural machinery and is often required to be replaced or maintained after being used for a period of time, so that more and more agricultural machinery equipment manufacturers require the cutting tool to have longer service life, namely the cutting tool is required to be more corrosion-resistant, wear-resistant and have higher strength, and the traditional 30MnB5 material cannot meet the requirement, so that the use of the cutting tool is limited.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an improved steel for agricultural machinery cutting tools, which improves the steel grade aiming at the existing 30MnB5 product, improves the strength, wear resistance and corrosion resistance of materials, and finally prolongs the service life of the agricultural machinery cutting tools; the invention also aims to provide a production method of the steel for the agricultural machinery cutting tool.

The invention is realized by the following technical scheme:

the improved steel for the agricultural machinery cutting tool consists of the following chemical elements in percentage by mass: c: 0.33% -0.35%, Si: 0.30% -0.40%, Mn: 1.30% -1.40%, Cr: 0.50% -0.60%, B: 0.002% -0.004%, Ti: 0.050% -0.065%, Al: 0.070-0.090 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S and the balance of Fe.

The invention further improves the scheme as follows:

the method for producing the improved steel for the agricultural machinery cutting tool is characterized by comprising the following steps of preparing smelting raw materials according to the chemical components, and sequentially carrying out KR desulfurization, converter smelting, L F refining, RH vacuum degassing, soft blowing, continuous casting and continuous rolling on the smelting raw materials to obtain the finish rolling flat steel with the thickness of 10mm, × and the width of 78 mm.

The invention has the further improvement scheme that:

when KR is desulfurized, low-sulfur and low-phosphorus molten iron with S less than or equal to 0.05 percent and P less than or equal to 0.12 percent is selected to produce the steel grade of the invention; the molten iron slag is completely removed before desulfurization, a KR desulfurization method is adopted, a self-made desulfurizer is added in the molten iron stirring process for desulfurization, the desulfurized product is removed by removing slag, the content of molten iron S is reduced, and the desulfurized molten iron S is ensured to be less than or equal to 0.005%.

Further, during converter smelting, smelting is carried out in a top-bottom combined blowing type converter with the weight of more than 100 tons, the temperature of molten iron after desulphurization is controlled to be more than or equal to 1250 ℃, the converter adopts a double-slag method to realize pre-desorption P, the terminal point P of the converter is ensured to be less than or equal to 0.011 percent, aluminum cakes, lime, pre-melted refining slag, carbon powder, high-carbon ferromanganese, high-carbon ferrochromium and silicon-manganese alloy are added into steel tapping to carry out pre-deoxidation and initial component adjustment, a sliding plate slag blocking mechanism is adopted to control slag tapping, and the slag tapping return P is ensured to be less than or equal to 0.

Further, during refining, molten steel is deoxidized, desulfurized and alloyed in an L F furnace with the volume of more than 100 tons to produce refining slag with the alkalinity R of 5-8, lime and premelted refining slag are used for desulfuration, the slag materials are mixed according to the proportion of 2:1, the whole refining process is stirred, the stirring strength of 400-600N L/min is adopted in the early stage of refining, the steel slag reaction is used for strengthening S removal and removing impurities, and the weak stirring of 100-200N L/min is adopted in the later stage of refining, so that the molten steel is not exposed, and the secondary oxidation of the molten steel is prevented.

Further, during vacuum degassing, bottom blowing stirring is continuously kept after L F refining, RH circulation degassing equipment is adopted for vacuum degassing and inclusion removal treatment, the vacuum degassing is kept for more than 20 minutes under high vacuum of less than 100Pa, the vacuum breaking [ H ] is less than or equal to 0.00015%, the vacuum breaking [ O ] is less than or equal to 0.0010%, and all components enter the required internal control range.

Further, during the soft blowing and denaturation treatment, feeding 120-150 m of calcium silicate wires through a wire feeding machine for denaturation treatment before the soft blowing; the soft blowing requires that the slag surface is micro-moved, molten steel is not exposed, the soft blowing time is 20-25 min, and on the premise of ensuring the production rhythm, impurities are fully gathered, grown and floated to be removed.

Furthermore, during continuous casting, 5-flow casting is carried out by adopting a 150mm × 150mm arc square billet continuous casting machine, the residence time of molten steel in a steel ladle is reduced, the superheat degree is controlled to be 15-30 ℃, constant casting speed is carried out by adopting the casting speed of 2.2M/min, the cold water quantity is controlled to be 100-130L/min, a low-silicon tundish covering agent and special crystallizer protecting slag are used, the whole-process full-protection casting is carried out to produce continuous casting billets, and an M-EMS + F-EMS two-section electromagnetic stirring device is adopted, so that the structure is fully and uniformly formed, and the internal quality is improved.

Further, during rolling, the continuous casting billet is subjected to cold charging, the heating time in a heat accumulating type stepping heating furnace is not more than 100min, the air-fuel ratio is controlled to be 0.70-0.85, and oxidation decarburization is reduced; controlling the heating temperature, especially the temperature of a high-temperature section, ensuring the rolling temperature to be 900-950 ℃, and carrying out the finish rolling of the flat steel by adopting an eighteen continuous rolling unit.

Furthermore, during finishing, the steel is finished by manually checking and grinding one by one, so that the size, the appearance and the surface quality of the steel are ensured.

The comparison between the steel for 30MnB5 agricultural machinery cutting tools used in China and the chemical components of the invention is shown in the following table 1.

TABLE 1 chemical composition comparison (wt%)

The invention discloses a reason for limiting the chemical components of steel for improved agricultural machinery cutting tools:

the invention relates to an improved steel for agricultural machinery cutting tools, which is designed based on 30MnB5, wherein the contents of Si and Mn are designed at the upper limit of the existing 30MnB5, so that the strength of the steel can be improved; the content of C is 0.02 percent higher than that of the existing 30MnB5, so that the strength can be improved, and the toughness is prevented from being obviously reduced; the addition of 0.50-0.60% of Cr can improve the hardenability and corrosion resistance of the steel, but does not influence the ductility and toughness of the steel; the B element has obvious influence on the hardenability of the steel, the range of the B element is strictly limited, and the B element mainly stabilizes the performance of the steel after quenching; ti and Al are grain refining elements, and because of the particularity of the elements, the elements are not suitable to be added too high, Ti and Al inclusions are easily formed, and the service life of the steel is influenced, so that the elements are only properly added by 0.050 to 0.065 percent and 0.070 to 0.090 percent.

C: the invention can effectively improve the strength and hardenability of steel, but in order to prevent quenching deformation and cracking, and considering the requirement of toughness of the material, the invention improves the lower limit and the upper limit of the content of C by 0.08 percent and 0.02 percent on the basis of the existing 30MnB5, and can improve the strength of the steel on the premise of not influencing the ductility and toughness, so the invention controls the content of C between 0.33 percent and 0.35 percent;

si: is a deoxidizer which can be dissolved in ferrite and austenite to improve the strength and hardness of steel; the silicon can also improve the hardenability of the steel in a small amount, and in order to improve the strength, particularly the yield strength of the steel, the Si content of the invention is controlled between 0.30 percent and 0.40 percent of the upper limit of the existing 30MnB 5;

mn can improve the hardness and wear resistance of steel, remarkably improve the hardenability of steel and improve the hot workability of steel. Mn also has the function of solid solution strengthening, can enlarge an austenite region, reduce the transformation temperature from austenite to ferrite, further refine ferrite grains, improve the toughness of steel and compensate the strength loss caused by low carbon. The Mn content is increased as much as possible, but when the Mn content is higher than 1.40%, segregation is easy to generate due to relatively high C content, so that the Mn content is controlled to be 1.30-1.40%;

cr: can obviously improve the strength, hardness, wear resistance and hardenability of the steel, but simultaneously reduces the plasticity and toughness. And a layer of passive film can be formed on the surface of the steel, so that the steel has oxidation resistance and corrosion resistance, and meanwhile, Cr can improve the carbon dioxide corrosion resistance and improve the hardenability of the material. The Cr content is improved as much as possible, but in the consideration of production cost and performance matching, 0.50-0.60% of Cr element is obviously added to further improve the hardenability, wear resistance and corrosion resistance of the steel;

b: the hardenability of the steel can be obviously improved, in order to stably improve the hardenability of the invention, the element B is strictly controlled according to the upper limit of the existing 30MnB5, the overall performance of the steel is improved, and the stability of the performance of the steel can be ensured, so the invention designs B: 0.002% -0.004%.

Ti: the steel is a strong oxidant in steel, so that the steel structure is more compact, the effect of refining crystal grains is obvious, the aging sensitivity and the cold brittleness of the steel can be reduced, and the welding performance of the steel is improved. However, Ti element such as Ti-containing non-metallic inclusion formed by oxidation influences the performance and service life of the steel, so that the Ti element cannot be used too much, and tests prove that the service life is not influenced significantly by adding less than or equal to 0.065 percent of Ti. Therefore, the invention obviously adds 0.050 to 0.065 percent of Ti.

Al: the deoxidizer is a strong deoxidizer in steel, can also refine crystal grains and improve impact toughness; al also has certain oxidation and corrosion resistance. The defects of Al are that the hot workability and the welding performance of the steel are influenced, a large amount of Al is easy to combine with O in the steel to form oxide inclusion containing Al, the fatigue life of the steel is seriously influenced, and the production process is also obviously influenced. However, tests prove that the oxidation resistance and the corrosion resistance of the steel can be obviously improved by adding more than 0.07 percent of Al, so that the Al content is controlled to be 0.070 to 0.090 percent and is far higher than that of the common steel.

P causes cold brittleness of steel, lowers impact toughness of steel, deteriorates weldability of steel, lowers plasticity, and deteriorates cold bending property. Therefore, the P content is controlled to be below 0.015 percent;

s is an easily segregated element and influences the uniformity of steel performance, and S mainly exists in the form of non-metallic inclusions in steel and influences the purity of the steel. Therefore, the S content is strictly controlled and must be less than or equal to 0.005 percent.

The invention has the beneficial effects that:

compared with the traditional steel for 30MnB5 agricultural machinery cutting tools, the invention adds or obviously adds the following components: 0.050% -0.065% of Ti element, 0.070% -0.090% of Al element and 0.50% -0.60% of Cr element, and can improve the hardenability of steel and simultaneously improve the strength and wear resistance of steel. Meanwhile, the ductility and toughness of the steel are not lower than those of the traditional 30MnB5 steel for agricultural machinery cutting tools.

Aiming at the characteristics and development requirements of the steel grade, the invention improves the contents of C, Si, Mn and B elements to the upper limit of the traditional 30MnB5, fully plays the role of alloy elements and improves the strength and wear resistance of the steel.

The method adopts the following process measures to ensure the purity and uniformity of steel, the steel grade is produced by selecting low-sulfur and low-phosphorus molten iron with S being less than or equal to 0.05 percent and P being less than or equal to 0.12 percent, KR equipment is adopted for deep desulfurization to ensure that the S content after desulfurization is not more than 0.005 percent, a converter is operated by a double-slag method to realize pre-removal of P, the end point P of the converter is ensured to be less than or equal to 0.011 percent, a sliding plate slag blocking device is adopted to control the slag return P to be less than or equal to 0.002 percent, refining slag with alkalinity R of 5-8 is manufactured in the refining process, lime and pre-melting slag are used as slag materials with the ratio of 2:1 in the desulfurization process, the stirring strength of 400-600N L/min is adopted in the early stage of refining, the S removal and inclusion removal are strengthened through steel slag reaction, the inclusion removal is removed, 100-200N L/min is adopted in the later stage of refining, the non-exposure of molten steel is ensured, the secondary oxidation of molten steel is prevented, the vacuum degassing is maintained for more than 20 minutes under the high vacuum of 100Pa, the high vacuum, the air-200N L/min, the continuous casting temperature of the continuous casting machine is ensured to be less than 0.0010.10 mm, the continuous casting process of a continuous casting furnace is adopted to control of an air-cooling process, the continuous casting machine, the continuous casting process of a continuous casting furnace is carried out, the continuous casting process of a continuous casting machine, the continuous casting process of a continuous casting machine with a continuous casting process of an air-cooling process of a.

The invention aims at the requirements of modern agricultural machinery cutting tools on strength, wear resistance and corrosion resistance, and the service life of the hot-rolled flat steel produced by using improved chemical components and processes can be prolonged by 50 percent after forging and processing by users.

The steel for the agricultural machinery cutting tool produced according to the invention has the characteristics of high strength, high wear resistance, corrosion resistance and the like, and the material performance can reach the following level: the tensile strength Rm is more than or equal to 1150Mpa, the yield strength Rel is more than or equal to 950Mpa, the elongation after fracture is more than or equal to 15 percent, and the section shrinkage is more than or equal to 55 percent; the wear resistance is improved by more than 50 percent, and the corrosion and the rust are not easy to occur when the device is operated in a weak acid or weak alkaline environment.

Detailed Description

Examples 1 to 4

The preparation method comprises the following steps:

(1) KR desulfurization: selecting low-sulfur and low-phosphorus molten iron with S less than or equal to 0.05 percent and P less than or equal to 0.12 percent to produce the steel grade of the invention; the molten iron slag is completely removed before desulfurization, a KR desulfurization method is adopted, a self-made desulfurizer is added in the molten iron stirring process for desulfurization, the desulfurized product is removed by removing slag, the content of molten iron S is reduced, and the desulfurized molten iron S is ensured to be less than or equal to 0.005%;

(2) smelting in a converter: smelting in a top-bottom combined blowing type converter with the weight of more than 100 tons, controlling the temperature of molten iron after desulphurization to be more than or equal to 1250 ℃, adopting a double-slag method to operate the converter to realize pre-deoxidation, ensuring that the end point P of the converter is less than or equal to 0.011 percent, adding aluminum cakes, lime, pre-melted refined slag, carbon powder, high-carbon ferromanganese, high-carbon ferrochromium and silicon-manganese alloy into steel tapping to carry out pre-deoxidation and primary component adjustment, adopting a sliding plate slag blocking mechanism to control slag tapping, and ensuring that the slag tapping return P is less than or equal to 0.002 percent;

(3) refining, namely deoxidizing, desulfurizing and alloying the molten steel in an L F furnace of more than 100 tons to produce refining slag with the alkalinity R of 5-8, wherein the desulfurization uses slag materials of lime and premelted refining slag with the ratio of 2:1, the whole refining process is stirred, the stirring strength of 400-600N L/min is adopted in the early stage of refining, the S removal and the inclusion removal are strengthened through the reaction of the steel slag, and the weak stirring of 100-200N L/min is adopted in the later stage of refining to ensure that the molten steel is not exposed and prevent the secondary oxidation of the molten steel;

(4) vacuum degassing, namely continuously keeping bottom blowing stirring after L F refining, performing vacuum degassing and inclusion removal treatment by adopting RH circulating degassing equipment, and keeping the vacuum degassing equipment under high vacuum of 100Pa for more than 20 minutes to ensure that the broken vacuum [ H ] is less than or equal to 0.00015 percent and [ O ] is less than or equal to 0.0010 percent, and all the components enter the required internal control range;

(5) soft blowing and denaturation treatment: before soft blowing, feeding 120m-150m of calcium silicate wire by a wire feeder to perform denaturation treatment; the soft blowing requires that the slag surface is micro-moved, molten steel is not exposed, the soft blowing time is 20-25 min, and on the premise of ensuring the production rhythm, impurities are fully gathered and grown up and float upwards to be removed;

(6) continuous casting, namely adopting a 150mm × 150mm arc square billet continuous casting machine for 5-flow casting, reducing the residence time of molten steel in a steel ladle, controlling the superheat degree to be 15-30 ℃, adopting a drawing speed of 2.2M/min for constant drawing speed casting, controlling the cold water amount to be 100-130L/min, adopting a low-silicon intermediate cladding covering agent and special crystallizer protecting slag to carry out full-protection casting in the whole process to produce continuous casting billets, adopting an M-EMS + F-EMS two-section electromagnetic stirring device to fully and uniformly organize and improve the internal quality.

(7) Rolling: the continuous casting billet is subjected to cold charging, the heating time in a heat accumulating type stepping heating furnace is not more than 100min, the air-fuel ratio is controlled to be 0.70-0.85, and the oxidation and decarburization are reduced; controlling the heating temperature, especially the temperature of a high-temperature section, ensuring the rolling temperature to be 900-950 ℃, and carrying out the finish rolling of the flat steel by adopting an eighteen continuous rolling unit.

(8) And (3) finishing: and finishing is carried out by adopting manual inspection and grinding one by one, so that the size, the appearance and the surface quality of the steel are ensured.

The process conditions not limited in the above preparation method can be referred to the conventional techniques in the art.

The chemical composition of the obtained steel for agricultural machinery cutting tools is shown in table 2.

TABLE 2 Steel composition for agricultural machinery cutting tools (wt%)

The mechanical properties of the steels for agricultural machinery cutting tools prepared in the embodiments 1 to 4 are respectively tested according to GB/T228.1, the test results are shown in Table 3, and the comparison conditions of the nonmetallic inclusions of the steels for agricultural machinery cutting tools prepared in the embodiments 1 to 4 and the prior art are shown in Table 4; the results of atmospheric corrosion resistance are shown in Table 5.

TABLE 3 comparison of the mechanical Properties of the invention with those of the prior art

TABLE 4 comparison of non-metallic inclusions of the invention with the prior art

TABLE 5 comparison of the Corrosion resistance of the invention with the prior art

As shown in Table 5, the products processed by the invention have the atmospheric corrosion resistance test according to TB/T2375, and the relative corrosion rate is reduced by more than 60 percent compared with the common Cr-free 30MnB 5.

TABLE 5 Corrosion resistance

Steel grade	Relative rate of corrosion
		Example 1	38％
Example 2	36％
		Example 3	38％
Example 4	40％
		Existing 30MnB5 steel	100％

As shown in tables 3, 4 and 5, the control level of the non-metallic inclusions in the invention reaches the international advanced level, the tensile strength Rm is more than or equal to 1150MPa, the yield strength Rel is more than or equal to 950MPa, the elongation after fracture is more than or equal to 15 percent, and the reduction of area is more than or equal to 55 percent; the wear resistance is improved by more than 50 percent, and the corrosion and the rust are not easy to occur when the device is operated in a weak acid or weak alkaline environment.

Claims

1. The improved steel for the agricultural machinery cutting tool is characterized by comprising the following chemical elements in percentage by mass: c: 0.33% -0.35%, Si: 0.30% -0.40%, Mn: 1.30% -1.40%, Cr: 0.50% -0.60%, B: 0.002% -0.004%, Ti: 0.050% -0.065%, Al: 0.070-0.090 percent, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S and the balance of Fe.

2. The method for producing the improved steel for the agricultural machinery cutting tool, which is described in claim 1, is characterized by comprising the following steps of preparing a smelting raw material according to the chemical components described in claim 1, and sequentially carrying out KR desulfurization, converter smelting, L F refining, RH vacuum degassing, soft blowing, continuous casting and continuous rolling on the smelting raw material to obtain the finish-rolled flat steel with the thickness of 10mm, × mm and the width of 78 mm.

3. The production method of the improved steel for the agricultural machinery cutting tool according to the claim 2, characterized in that: when KR is desulfurized, low-sulfur and low-phosphorus molten iron with S less than or equal to 0.05 percent and P less than or equal to 0.12 percent is selected to produce the steel grade of the invention; the molten iron slag is completely removed before desulfurization, a KR desulfurization method is adopted, a self-made desulfurizer is added in the molten iron stirring process for desulfurization, the desulfurization product is removed by removing slag, the content of molten iron S is reduced, and the desulfurized molten iron S is ensured to be less than or equal to 0.005%.

4. The production method of the improved steel for the agricultural machinery cutting tool according to the claim 2, characterized in that: when the converter is smelted, smelting is carried out in a top-bottom combined blowing type converter of more than 100 tons, the temperature of molten iron after desulphurization is controlled to be more than or equal to 1250 ℃, the converter adopts a double-slag method to operate to realize pre-deoxidation, the terminal point P of the converter is ensured to be less than or equal to 0.011 percent, aluminum cakes, lime, pre-melted refining slag, carbon powder, high-carbon ferromanganese, high-carbon ferrochrome and silicon-manganese alloy are added into steel tapping to carry out pre-deoxidation and component primary adjustment, a sliding plate slag blocking mechanism is adopted to control slag tapping, and the slag tapping return P is ensured to be less than.

5. The production method of the improved steel for the agricultural machinery cutting tool as claimed in claim 2, wherein during refining, molten steel is deoxidized, desulfurized and alloyed in an L F furnace of more than 100 tons, refining slag with the alkalinity R of 5-8 is produced, slag materials with the proportion of lime and premelted refining slag being 2:1 are used for desulfurization, the whole refining process is stirred, the stirring strength of 400-600N L/min is adopted in the early stage of refining, the steel slag reaction is used for strengthening S removal and impurity removal, and the weak stirring of 100-200N L/min is adopted in the later stage of refining, so that the molten steel is not exposed, and secondary oxidation of the molten steel is prevented.

6. The production method of the improved steel for the agricultural machinery cutting tool as claimed in claim 2, wherein during the vacuum degassing, bottom blowing stirring is continuously kept after L F refining, RH circulation degassing equipment is adopted for vacuum degassing and inclusion removal treatment, the vacuum degassing and inclusion removal treatment are kept for more than 20 minutes under high vacuum of <100Pa, the broken vacuum [ H ] is less than or equal to 0.00015%, the broken vacuum [ O ] is less than or equal to 0.0010%, and all components enter the required internal control range.

7. The production method of the improved steel for the agricultural machinery cutting tool according to the claim 2, characterized in that: during the soft blowing and denaturation treatment, before the soft blowing, 120-150 m of calcium silicate wire is fed by a wire feeding machine for denaturation treatment; the soft blowing requires that the slag surface is micro-moved, molten steel is not exposed, the soft blowing time is 20-25 min, and on the premise of ensuring the production rhythm, impurities are fully gathered, grown and floated to be removed.

8. The production method of the improved steel for the agricultural machinery cutting tool as claimed in claim 2, wherein during continuous casting, a 150mm × 150mm arc-shaped billet continuous casting machine is adopted for 5-flow casting, the residence time of molten steel in a steel ladle is reduced, the superheat degree is controlled to be 15-30 ℃, constant casting at a casting speed of 2.2M/min is adopted, the cooling water amount is controlled to be 100-130L/min, a low-silicon intermediate coating covering agent and special crystallizer protecting slag are used for producing a continuous casting billet through whole-process full-protection casting, and an M-EMS + F-EMS two-stage electromagnetic stirring device is adopted, so that the structure is fully uniform, and the internal quality is improved.

9. The production method of the improved steel for the agricultural machinery cutting tool according to the claim 2, characterized in that: during rolling, cold charging is adopted for the continuous casting billet, the heating time in a heat accumulating type stepping heating furnace is not more than 100min, the air-fuel ratio is controlled to be 0.70-0.85, and oxidation and decarburization are reduced; and controlling the heating temperature, particularly the temperature of a high-temperature section, ensuring the initial rolling temperature to be 900-950 ℃, and performing finish rolling on the flat steel by adopting an eighteen continuous rolling unit.