Steel for agricultural machinery harrow blade and plough blade and manufacturing method thereof

Abstract

The invention relates to the technical field of steel for agricultural machinery, in particular to steel for a harrow blade and a plough blade of the agricultural machinery and a manufacturing method of the steel. According to the invention, Cr, Nb, B and Ca are alloyed, and process parameters such as casting blank heating, rough and finish rolling descaling pressure, rolling temperature, reduction rate, coiling temperature, cooling speed and the like are controlled at the same time, so that the yield strength of the prepared steel hot-rolled plate for the agricultural machinery harrow blade and plough blade is 400-500MPa, the tensile strength is 600-700MPa, and the ductility is greater than 15%; after heat treatment, the yield strength of the harrow blade and plough blade parts of the agricultural machine produced by using the steel is more than 1300MPa, the tensile strength is more than 1800MPa, the ductility is more than or equal to 8%, the impact energy Akv at 20 DEG C is more than or equal to 20J, the hardness is more than 51HRC, and the surface hardness difference is within + / -1HRC.

Description

Technical Field

[0001] The present invention relates to the technical field of steel for agricultural machinery, and in particular, to a steel for agricultural machinery harrow discs and plow discs and a manufacturing method thereof. Background Art

[0002] Agricultural mechanization is the central link of agricultural modernization. Soil-engaging tools such as harrow discs and plow discs are key components of agricultural machinery, directly affecting the operation quality and efficiency of agricultural machinery. The hot-rolled plates of high-carbon materials such as 65Mn originally used for processing and manufacturing soil-engaging tools for harrow discs and plow discs have a yield strength of more than 500 MPa, a tensile strength of more than 800 MPa, oil quenching + tempering in a heating furnace for more than 10 hours, a finished product hardness of 42 - 48 HRC, a strength of 1300 - 1400 MPa, and an impact energy AKv at 20 °C of less than 10 J, with low production efficiency. The hot-rolled plates have a high yield strength, high hardness, great difficulty in processing and forming, large brittleness and poor toughness after heat treatment, are easy to fracture, have low and uneven hardness and poor wear resistance, need to be replaced frequently, and have low operation efficiency, making it difficult to meet the development requirements of large-scale, compound, and high-speed agricultural machinery and the need for continuous and efficient operation, and have become one of the main short boards for the high-quality development of agricultural machinery in China.

[0003] Analysis shows that the brittle fracture problem of agricultural machinery components such as harrow discs and plow discs is mainly related to uneven hardness and insufficient ductility and plasticity. Currently, there is no steel for harrow discs and plow discs with a low hot-rolled strength, a strength of more than 1800 MPa after heat treatment, a surface hardness of more than 51 HRC, a hardness difference of ±1 HRC, an impact toughness Akv ≥ 20 J, and excellent service performance. On the other hand, with the continuous improvement of environmental protection requirements, water quenching and high production efficiency are the development directions of the industry.

[0004] To adapt to the development of the times and meet the demand for the replacement of agricultural machinery components, there is an urgent need to develop a steel for harrow discs and plow discs with a low yield strength of hot-rolled plates, easy to form, a heat treatment strength of more than 1800 MPa, an impact toughness Akv ≥ 20 J, a surface hardness ≥ 51 HRC, a hardness difference within ±1 HRC, and suitable for water quenching. Summary of the Invention

[0005] Aiming at the problems of poor surface hardness uniformity, insufficient wear resistance, poor toughness and easy fracture of the existing steel for agricultural machinery tools such as harrow discs and plow discs, and the heat treatment process being not environmentally friendly, with low efficiency and unable to meet the use requirements of high-end soil-engaging agricultural machinery accessories, the present invention provides a steel for agricultural machinery harrow discs and plow discs and a manufacturing method thereof.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a steel for agricultural machinery harrow discs and plow discs. The chemical composition of the steel is as follows by weight percentage: C 0.25% - 0.40%, Si 0.01% - 0.3%, Mn 0.5% - 1.5%, B 0.0005% - 0.005%, Cr 0.1% - 0.8%, Nb 0.01% - 0.5%, Ti 0.01% - 0.1%, Al 0.01% - 0.1%, N 0.001% - 0.01%, Ca 0.0005% - 0.02%, 0.01% ≤ Ti + Al ≤ 0.15%, 1 ≤ Nb / Ti ≤ 10, P ≤ 0.020%, S ≤ 0.020%, and the balance is Fe and inevitable impurities.

[0008] The mechanism of action of each alloying element of the steel for agricultural machinery harrow discs and plow discs of the present invention is elaborated in detail as follows:

[0009] C: C is the main solid solution strengthening element in the steel. In the present invention, sufficient C is required to form carbides with Ca and Nb to inhibit surface oxidation decarburization and improve hardness and hardness uniformity. If the C content is lower than 0.25%, it is difficult to ensure the hardness of the steel plate after heat treatment. On the other hand, if the C content is higher than 0.40%, the strength is too high, deteriorating the toughness and plasticity of the steel after heat treatment and making it prone to fracture. Therefore, the C content should be controlled at 0.25% - 0.40%.

[0010] Mn: Mn is relatively inexpensive and is a good deoxidizer and desulfurizer, and is an essential element to ensure the strength and toughness of the steel. Manganese and iron can form a solid solution infinitely to form a solid solution, improving hardness and strength with relatively little impact on plasticity. Mn combines with S to form MnS, avoiding the thermal cracks formed by FeS at the grain boundaries and affecting the hot formability of the steel. At the same time, Mn is also a good deoxidizer and increases hardenability. If the Mn content in the steel is low, it cannot meet the requirements of high hardness. If the Mn content is too high, segregation is serious, affecting welding performance and formability, and increasing production costs. Therefore, considering factors such as cost and performance requirements, the Mn content should be controlled at 0.50% - 1.5%.

[0011] Si: Si is one of the common elements in the steel. It is used as a reducing agent and deoxidizer in the steelmaking process. Si is a ferrite-forming element and a non-carbide-forming element. Si dissolved in ferrite improves hardenability and tempering resistance, increases strength and hardness, improves wear resistance, significantly increases the elastic limit, yield strength and yield ratio, and improves fatigue strength, extending the service life of the steel. If the Si content exceeds 0.3%, the surface of the steel is decarburized and oxidized, seriously affecting fatigue performance.

[0012] B: Boron dissolved in steel can significantly improve hardenability and quenching penetration. 0.001% - 0.003% of boron is equivalent to 0.6% manganese, 0.7% chromium, 0.5% molybdenum, and 1.5% nickel. Therefore, a very small amount of boron can save a large amount of precious alloying elements. After adding B in the present invention, all martensite structures can be obtained after oil quenching of steel plates with a carbon content lower than 0.4%, significantly improving the hardenability of the steel. On the other hand, by limiting the content relationship of three elements, Nb, Ti, and Al, the present invention effectively controls the content of dissolved B in the steel, avoids boron embrittlement phenomenon, and gives full play to the beneficial effects of boron.

[0013] Cr: Chromium is a medium-strong carbide-forming element. After adding Cr in the present invention, it forms complex carbides with Nb, inhibits microsegregation, and reduces banding. Chromium can also increase the A3 and A1 temperatures, shift the GS line to the upper left, slow down the decomposition of A, improve quenching penetration; improve the oxidation resistance and corrosion resistance of the steel, improve tempering stability, increase hardness, and improve wear resistance.

[0014] Nb: A fine-grain strengthening element, high-temperature solution improves quenching penetration. 1 ≤ Nb / Ti ≤ 10 ensures the formation of fine NbN particles with a dispersion distribution of ≤ 50nm and composite N compounds with Ca in the steel, with high melting points, high hardness, and strongly improves wear resistance. At the same time, adding Nb helps to improve the impact resistance after heat treatment and avoid operation cracking. 1 ≤ Nb / Ti does not form square TiN particles, and Nb / Ti ≤ 10 enables Ti and Al to effectively control the content of dissolved B in the steel, avoids boron embrittlement phenomenon, gives full play to the beneficial effects of boron, inhibits microsegregation, homogenizes the structure, and reduces banding. 1 ≤ Nb / Ti ≤ 10 improves impact resistance and fatigue life.

[0015] Ti: The main role of Ti in the present invention is a deoxidizer, and at the same time, it has precipitation strengthening and improves quenching penetration, increases the strength of the steel, while maintaining good plasticity and toughness.

[0016] Al: Al is used as a deoxidizer during steelmaking, refines grains, inhibits the aging of the steel, improves the toughness of the steel at low temperatures, especially can reduce the brittle transition temperature of the steel; Al is a non-carbide-forming element, can improve the oxidation resistance of the steel, inhibit surface oxidation and decarburization, and improve surface quality.

[0017] 0.01 ≤ Ti + Al ≤ 0.15: The three elements, Nb + Ti + Al, act together to effectively control the content of dissolved B in the steel, avoid boron embrittlement phenomenon, give full play to the beneficial effects of boron, inhibit microsegregation, homogenize the structure, reduce banding, and improve impact and fatigue properties. When Ti + Al is lower than 0.01%, the above effects are not obvious. When Ti + Al is higher than 0.15%, coarse inclusions are formed in the steel, and it is not conducive to the formation of fine and dispersed NbC particles, affecting impact and fatigue properties.

[0018] N: Generally, N is considered a harmful element, and the lower the N content in steel, the better. In the present invention, a composition design containing N is adopted. During refining, N with a content of more than 0.001% is introduced, so that N forms fine carbide particles with Nb and C with a size of ≤50 nm, inhibits microsegregation, homogenizes the structure, and reduces banding. When the N content exceeds 0.01%, it will form a BN phase with B, resulting in boron embrittlement and reducing the toughness and plasticity.

[0019] P, S: Both P and S are inevitable harmful impurities in steel. Their presence will seriously deteriorate the toughness of steel. Therefore, measures should be taken to reduce the P and S contents in steel as much as possible. In the present invention, the P content is limited to P≤0.020%, and the maximum S content is limited to 0.010% to reduce the formation of MnS.

[0020] Ca: As a microalloying element, Ca forms complex carbides with Cr and Nb, etc., inhibits microsegregation, reduces banding, promotes carbide nucleation and spheroidization, and improves impact and fatigue resistance.

[0021] In the above technical solution, further, the yield strength of the steel is 400 - 500 MPa, the tensile strength is 600 - 700 MPa, and the elongation is >15%; after heat treatment, the yield strength is above 1300 MPa, the tensile strength is above 1800 MPa, the elongation is ≥8%, the impact energy Akv at 20 °C is ≥20 J, the surface hardness is above 51 HRC, and the surface hardness difference is within ±1 HRC.

[0022] On the other hand, the present invention provides a manufacturing method for the steel used in the above agricultural machinery harrow blades and plow blades, and the method includes the following steps:

[0023] (1) Smelting and continuous casting: Before tapping from the converter, the C content of the molten steel is 0.2% - 0.3%. The molten steel enters the LF electric furnace for refining. After the sulfur content ≤0.020%, alloying is carried out, and at the same time, N is introduced to adjust the N content of the molten steel to 0.001% - 0.010%, and continuous casting is carried out to obtain a continuous casting billet;

[0024] (2) Billet treatment: The billet is hot delivered and hot charged into a walking beam reheating furnace for heating at a temperature above 500 °C. The temperature of the preheating section is 500 - 600 °C, and the holding time is more than 60 min. The temperature of the first heating section is 900 - 1100 °C, and the holding time is more than 60 min. The temperature of the second heating section is 1200 - 1350 °C, and the total time in the furnace is 3 - 4 h;

[0025] (3) Rolling: High-pressure water descaling is adopted before both rough rolling and finish rolling. Rough rolling is carried out by continuous rolling in 2 - 3 passes. The reduction rate of the first pass is more than 30%, and the rolling start temperature is 1200 - 1250 °C. The temperature difference along the whole length of the steel strip during rolling is ≤20 °C. Finish rolling is carried out by continuous rolling in 5 - 7 passes. The reduction rate of the first pass is 25% - 40%, and the rolling temperature is 850 - 950 °C. The temperature difference along the whole length of the steel strip during rolling is ≤10 °C;

[0026] (4) Cooling: After the steel plate exits the finishing mill, it enters laminar cooling for cooling, is coiled after being cooled to 600 - 700 °C, and then slowly cooled to below 300 °C, and air-cooled to room temperature.

[0027] In the above technical solution, further, in step (1), the molten steel is cast by a vertical bending arc continuous caster, and the arc radius of the vertical bending continuous caster is not less than 5 m;

[0028] During continuous casting, soft reduction and mold electromagnetic stirring are adopted. The electromagnetic stirring current is 300 - 500 A, the frequency is 2.2 - 2.9 Hz, the dynamic water volume of the mold is 80 - 160 L / min, the mold powder is used for casting, the mold liquid level is 750 - 850 mm, the superheat degree is 20 - 30 °C, the continuous casting speed is 1.0 - 1.5 m / min, and the secondary cooling water volume is 0.25 - 0.35 L / kg;

[0029] The thickness of the continuous casting slab is 170 - 250 mm.

[0030] In the above technical solution, further, in step (3), the high-pressure water pressure is not less than 30 MPa;

[0031] During the finishing process, edge heating devices are adopted on both sides of the steel plate, with a compensation temperature of 30 - 40 °C and a width of 30 - 40 mm.

[0032] In the above technical solution, further, in step (4), the cooling rate of laminar cooling is 25 - 40 °C / s, and the cooling rate difference in the width direction at the same position is ≤ 1 °C / s;

[0033] The cooling rate of slow cooling is 15 - 25 °C / h.

[0034] The present invention also provides a heat treatment method for agricultural machinery harrow blades and plow blades produced using the above steel for agricultural machinery harrow blades and plow blades. The steel for agricultural machinery harrow blades and plow blades is processed into part blanks, induction heated to 900 - 950 °C, hot stamped into shape, quenched rapidly to 180 - 200 °C with a coolant containing 60% - 90% water and held for 5 - 10 min, and then air-cooled to room temperature.

[0035] The present invention uses converter smelting and LF electric furnace refining without RH vacuum treatment. Before tapping from the converter, the molten steel has a C content of 0.2% - 0.3%, ensuring uniform carbon content in the billet after continuous casting of fine steel and no macroscopic segregation. LF electric furnace refining is adopted. After the refined S content is ≤0.020%, alloys are added for alloying. At the same time, nitrogen is introduced to adjust the N content of the molten steel, change the composition, quantity and morphology of non-metallic inclusions, accelerate the flow of the molten steel, promote the full floating of inclusions, improve the steel purity. The non-metallic inclusions in the finished steel do not exceed grade 1.5, and the surface finish of the steel is improved, and the anisotropy of the structure is eliminated. Continuous casting adopts soft reduction and mold electromagnetic stirring. The electromagnetic stirring current is 300A - 500A, and the frequency is 2.2 - 2.9Hz. The dynamic water volume of the mold is 80 - 160L / min. The mold powder is used for casting. The mold liquid level is 750 - 850mm, and the superheat is 20 - 30°C. Inclusions and segregation are controlled. At the same time, the continuous casting speed is 1.0 - 1.5m / min, and the secondary cooling water volume is 0.25 - 0.35L / kg, ensuring that the surface temperature deviation of the billet is not greater than 10°C, the cooling rate of the billet is uniform, the structure is uniform, the strength difference of the coiled strip steel after rolling is ≤20MPa, the hardness difference of the coiled strip is ≤3HRB, and the equiaxed crystal ratio is more than 50%, controlling the liquid micro-segregation of alloys at the end of columnar crystals.

[0036] The billet is hot delivered and hot charged into a walking beam reheating furnace at a temperature above 500°C to save energy and reduce consumption. The reheating furnace adopts a weakly oxidizing atmosphere (air excess coefficient 1.02 - 1.1, air-fuel ratio 2.0 - 2.2). The temperature of the preheating section is 500 - 600°C, and the holding time is more than 60min. The temperature of the first heating section is 900 - 1100°C, and the holding time is more than 60min. The temperature of the second heating section is 1200 - 1350°C, and the total time in the furnace is 3 - 4h, ensuring the surface quality of the billet and avoiding oxidation and decarburization.

[0037] High-pressure water descaling is adopted before rough rolling and finish rolling. The high-pressure water pressure is not less than 30MPa to ensure the surface quality of the steel plate. Rough rolling adopts 2 - 3 passes of continuous rolling. The reduction ratio of the first pass is more than 30%, and the rolling start temperature is 1200 - 1250°C, providing nucleation driving force for the precipitation of various carbides and nitrides. The temperature difference of the steel strip during rolling is ≤20°C, and the structure and properties are uniform. Finish rolling adopts 5 - 7 passes of continuous rolling. The reduction ratio of the first pass is 25% - 40%, and the rolling temperature is 850 - 950°C, which helps to obtain a fine pearlite colony and ferrite mixed structure after subsequent cooling, and the banding does not exceed grade 2.0. Edge heating devices are adopted on both sides of the steel plate, with a compensation temperature of 30 - 40°C and a width of 30 - 40mm. The temperature difference of the steel strip during rolling is ≤10°C, and the structure and properties are uniform. The thickness fluctuation of the strip steel is within ±0.20mm, the convexity is ≤40μm, the tensile strength difference of the coiled strip is ≤20MPa, and the hardness difference of the coiled strip is ≤3HRB.

[0038] After the steel plate exits the finishing mill, it enters laminar cooling. The cooling rate is 25 - 40 °C / s, and the cooling rate difference in the width direction at the same position is ≤ 1 °C / s. Ensure that the volume fraction of ferrite is below 20%, the tissue properties of the same plate are uniform, the strength difference is ≤ 20 MPa, the hardness difference is ≤ 3 HRB, and ensure that the surface hardness difference is within ±1 HRC after heat treatment. Cool to 600 - 700 °C and coil, and cool to below 300 °C at a cooling rate of 15 - 25 °C / h, which helps carbide nucleation and obtains a mixed structure of uniformly fine spheroidized pearlite, lamellar pearlite and ferrite. The diameter of the spheroidized pearlite is below 0.25 μm, the spheroidization rate is above 30%, and the banding does not exceed grade 2.0. If the cooling rate exceeds 25 °C / h, lamellar pearlite is likely to form; if the cooling rate is lower than 15 °C / h, the spheroidized pearlite is likely to grow, and the toughness and plasticity are poor.

[0039] The part blank is induction heated to 900 - 950 °C, hot stamping formed, quenched with a coolant containing 60% - 90% water, held at 180 - 200 °C for 5 - 10 min, and then air cooled to room temperature to obtain a fine lath martensite structure. Excellent service performance can be achieved without tempering treatment. After heat treatment, the yield strength is above 1300 MPa, the tensile strength is above 1800 MPa, the elongation is ≥ 8%, the impact energy Akv at 20 °C is ≥ 20 J, the surface hardness is above 51 HRC, and the surface hardness difference is within ±1 HRC.

[0040] The beneficial effects of the present invention are as follows:

[0041] The present invention uses alloying elements such as Cr, Nb, B, and Ca, and simultaneously controls process parameters such as slab heating, descaling pressure in roughing and finishing rolling, rolling temperature, reduction ratio, coiling temperature, and cooling rate, to obtain a mixed structure of uniformly fine spheroidized pearlite, lamellar pearlite and ferrite. The volume fraction of ferrite is below 20%, the diameter of the spheroidized pearlite is below 0.25 μm, the spheroidization rate is above 30%, the yield strength of the steel is 400 - 500 MPa, the tensile strength is 600 - 700 MPa, the elongation is greater than 15%, and the hardness is 80 - 90 HRB.

[0042] Through the controlled rolling and controlled cooling process, the present invention controls the strip thickness fluctuation within ±0.20 mm, the convexity ≤ 40 μm, the tensile strength difference of the same coil ≤ 20 MPa, and the hardness difference of the same coil ≤ 3 HRB.

[0043] The agricultural machinery harrow blades and plow blades produced using the steel of the present invention for agricultural machinery harrow blades and plow blades obtain a uniform fine lath martensite structure after quenching with a coolant containing 60% - 90% water. The longest martensite lath does not exceed 25 μm. No tempering treatment is required. The yield strength is above 1300 MPa, the tensile strength is above 1800 MPa, the elongation is ≥ 8%, the impact energy Akv at 20 °C is ≥ 20 J, the hardness is above 51 HRC, and the surface hardness difference is within ±1 HRC. Description of the Drawings

[0044] Figure 1This is the metallographic structure diagram of the hot-rolled steel plate in Embodiment 1 of the present invention. Detailed implementation manners

[0045] The following embodiments can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0046] The chemical compositions of the steel in Examples 1-15 and Comparative Example 1 are shown in Table 1; the smelting and continuous casting process parameters are shown in Table 2; the billet treatment process parameters are shown in Table 3; the rolling process parameters are shown in Table 4; the cooling process parameters are shown in Table 5; the microstructure and properties of the steel are shown in Table 6; the properties of the parts after heat treatment are shown in Table 7.

[0047] Table 1 Chemical compositions of the steel in Examples 1-15 and Comparative Example 1, %

[0048]

[0049]

[0050] Table 2 Smelting and continuous casting process parameters in Examples 1-15 and Comparative Example 1

[0051]

[0052] Table 3 Billet treatment process parameters in Examples 1-15 and Comparative Example 1

[0053]

[0054]

[0055] Table 4 Rolling process parameters in Examples 1-15 and Comparative Example 1

[0056]

[0057]

[0058] Table 5 Cooling process parameters in Examples 1-15 and Comparative Example 1

[0059] Number Cooling rate of the layer / ℃ / s Cooling rate difference in the bandwidth direction / ℃ / S Cooling rate after coiling / ℃ / h Coiling temperature / ℃ Example 1 25 0.78 19 686 Example 2 38 0.69 23 645 Example 3 39 0.63 18 632 Example 4 32 0.79 24 698 Example 5 36 0.95 16 660 Example 6 39 0.44 23 655 Example 7 29 0.39 18 614 Example 8 38 0.62 21 690 Example 9 25 0.57 23 628 Example 10 26 0.55 21 611 Example 11 35 0.49 16 645 Example 12 28 0.86 23 688 Example 13 26 0.69 22 624 Example 14 31 0.83 20 698 Example 15 39 0.92 19 631 Comparative Example 1 62 25 36 730

[0060] Table 6 Microstructure and properties of the steel in Examples 1-15 and Comparative Example 1

[0061]

[0062] Table 7 Part heat treatment process and properties in Examples 1-15 and Comparative Example 1

[0063]

[0064]

[0065] The above embodiments are only the preferred embodiments of the present invention and do not limit the implementation manners. The protection scope of the present invention shall be subject to the scope defined by the claims. Other different forms of changes or alterations can be made on the basis of the above description. The obvious changes or alterations derived therefrom are still within the protection scope of the present invention.

Claims

1. A steel for agricultural machinery harrow blades and plow blades, characterized in that: The chemical composition of the steel is as follows by weight percentage: C 0.25%-0.40%, Si 0.01%-0.3%, Mn 0.5%-1.5%, B 0.0005%-0.005%, Cr 0.1%-0.8%, Nb 0.01%-0.5%, Ti 0.01%-0.1%, Al 0.01%-0.1%, N0.001%-0.01%, Ca 0.0005%-0.02%, 0.01%≤Ti+Al≤0.15%, 1≤Nb / Ti≤10, P≤0.020%, S≤0.020%, and the balance is Fe and unavoidable impurities.

2. The steel for agricultural machinery harrow blades and plow blades according to claim 1, characterized in that: The steel has a yield strength of 400-500MPa, a tensile strength of 600-700MPa, and an elongation of >15%; after heat treatment, the yield strength is above 1300MPa, the tensile strength is above 1800MPa, the elongation is ≥8%, the impact energy Akv at 20°C is ≥20J, the surface hardness is above 51HRC, and the surface hardness difference is within ±1HRC.

3. A method for manufacturing steel for agricultural machinery harrow blades and plow blades according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: (1) Smelting and continuous casting: The C content of the molten steel before tapping the converter is 0.2% to 0.3%. The molten steel enters the LF electric furnace for refining. After the sulfur content is ≤ 0.020%, alloying is performed. At the same time, N is introduced to adjust the N content of the molten steel to 0.001% to 0.010%, and continuous casting is performed to obtain a continuous casting billet. (2) Ingot treatment: the ingot is heated at 500℃ or above and then put into a heating furnace for heating. The preheating section is 500-600℃ with a holding time of more than 60min. The first heating section is 900-1100℃ with a holding time of more than 60min. The second heating section is 1200-1350℃ with a total time in the furnace of 3-4h. (3) Rolling: High-pressure water descaling is used before rough and finish rolling. Rough rolling adopts 2-3 continuous rolling, with the first pass reduction rate of more than 30%, the starting rolling temperature of 1200-1250°C, and the temperature difference of the whole length of the steel strip is ≤20°C. Finishing rolling adopts 5-7 continuous rolling, with the first pass reduction rate of 25%-40%, the rolling temperature of 850-950°C, and the temperature difference of the whole length of the steel strip is ≤10°C. (4) Cooling: After leaving the finishing mill, the steel plate enters the layer cooling, cools to 600-700℃ for coiling, then slowly cools to below 300℃ and air cools to room temperature.

4. The manufacturing method according to claim 3, characterized in that: In step (1), the molten steel is cast by a vertical bending arc continuous casting machine, and the arc radius of the vertical bending continuous casting machine is not less than 5m; Continuous casting adopts light pressure and crystallizer electromagnetic stirring, the electromagnetic stirring current is 300-500A, the frequency is 2.2-2.9Hz, the dynamic water volume of the crystallizer is 80-160L / min, the crystallizer protection slag is used for casting, the crystallizer liquid level is 750-850mm, the superheat is 20-30℃, the continuous casting speed is 1.0-1.5m / min, and the secondary cooling water volume is 0.25-0.35L / kg; The thickness of the continuous casting billet is 170-250 mm.

5. The manufacturing method according to claim 3, characterized in that: In step (3), the high-pressure water pressure is not less than 30 MPa; During the finishing rolling process, edge heating devices are used on both sides of the steel plate, with a compensation temperature of 30 to 40°C and a width of 30 to 40 mm.

6. The manufacturing method according to claim 3, characterized in that: In step (4), the cooling rate of the layer cooling is 25-40°C / s, and the cooling rate difference in the bandwidth direction at the same position is ≤1°C / s; The slow cooling rate is 15-25℃ / h.

7. A method for heat treatment of agricultural machinery harrow blades and plow blades produced using the agricultural machinery harrow blade and plow blade steel according to any one of claims 1 to 2 or the agricultural machinery harrow blade and plow blade steel produced by the manufacturing method according to any one of claims 3 to 6, characterized in that: The agricultural machinery harrow blade and plow blade steel are processed into part blanks, induction heated to 900-950° C., hot stamped, rapidly cooled to 180-200° C. with a coolant containing 60%-90% water for 5-10 minutes, and then air cooled to room temperature.

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