Production method for homogenization of alloy tool steel SAE6150 structure

Abstract

The invention belongs to the technical field of steel rolling, and particularly relates to a controlled cooling method for alloy tool steel SAE6150 structure homogenization, and the production process route comprises the steps of molten iron pretreatment, converter treatment, LF furnace treatment, continuous casting, continuous rolling, billet cleaning, heating, rolling, controlled cooling and finishing. Rolling: the initial rolling temperature is 930-980 DEG C, the temperature of a finish rolling inlet is 880-950 DEG C, the temperature of a reducing and sizing inlet is 850-920 DEG C, and the spinning temperature is 890-930 DEG C; a water bath cooling mode is as follows: the wire rod enters a water tank after spinning, the wire rod is cooled to 600-700 DEG C at the cooling speed of 10-15 DEG C / s and then is discharged out of the water tank, the wire rod enters a heat preservation cover, the heat preservation cover is completely closed, the cover discharging temperature is 450-600 DEG C, and a cooling bed is used for air cooling. The method has the advantages that the cooling technology combining water bath cooling and slow cooling is adopted, the structure obtained after the wire rod is cooled only contains ferrite and pearlite structures, and the performance difference of the same circle of the wire rod is reduced.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling technology, and particularly relates to a production method for homogenizing the microstructure of alloy tool steel SAE6150. Background Technology

[0002] SAE6150 alloy tool steel wire rod is mainly used to manufacture high-precision, high-strength small hexagonal hand tools. The traditional cooling method for wire rod during production is the Stellmore cooling process. This involves cooling the rolled piece to 850-950℃ in a water tank after the final rolling pass, then cooling it with a fan after wire drawing, followed by slow cooling through heat preservation to complete the phase transformation. However, due to uneven cooling at the overlap points and in the middle of the wire rod during fan cooling, the tool steel wire rod contains both bainite and martensite structures, resulting in significant differences in properties within the same coil. This type of wire rod is prone to breakage during subsequent transportation and processing, affecting product quality stability and downstream user experience.

[0003] In the prior art, patent publication number CN107142417A discloses a carbon tool steel wire rod for files and its preparation method. The chemical composition of the wire rod, by weight percentage, is: [C] 1.26-1.32%, [Si] 0.08-0.18%, [Mn] 0.20-0.35%, [Cr] 0.55-0.70%, [V] 0.10-0.25%, [P] ≤0.025%, [S] ≤0.025%, [Al] ≤0.008%, with the remainder being Fe and unavoidable impurities. The rolling process employs high-temperature heating, high-pressure water descaling, low wire drawing, and air cooling. The high-temperature heating is carried out in an oxidizing atmosphere. However, the air cooling method also suffers from uneven cooling.

[0004] Patent publication number: CN111690801A, discloses a production process for hot-rolled alloy tool steel wire rods to obtain a fully bainitic structure. In the billet opening process, the heating temperature of the slab soaking zone is 1200-1250℃; in the heating process, the temperature of the intermediate slab high-temperature zone does not exceed 1100℃; in the rolling process, a finishing mill + MINI mill is used for rolling to achieve high strain rate and large deformation rolling in the non-recrystallization zone and (α+γ) two-phase zone, with a cumulative area reduction rate of 55-85%. The austenitic structure generates a large number of dislocations and deformation bands and other crystal defects during deformation, and the resulting deformation stored energy shortens the phase transformation incubation period and increases the phase transformation driving force; the rolling process adopts high-temperature heating, high-pressure water descaling, low wire drawing, and air cooling processes. In the cooling process, the wire drawing temperature is 750-800℃, and Stellmore controlled cooling is used. This invention effectively prevents the precipitation of martensite and mixtures of martensite, pearlite, and ferrite during the rolling and cooling process, resulting in a fully bainitic microstructure. This avoids brittle fracture caused by the martensitic microstructure, which is beneficial for the processing and use of wire rod and improves its fatigue performance. However, it also suffers from the problem of uneven cooling. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a production method for homogenizing the microstructure of SAE6150 alloy tool steel. By controlling the heating temperature, rolling temperature, and water bath cooling after wire rod coiling, the cooling uniformity of the wire rod is improved, resulting in a more uniform wire rod microstructure, avoiding the generation of bainite and martensite microstructures, and improving the uniformity of performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A production method for homogenizing the microstructure of SAE6150 alloy tool steel, wherein the production process of SAE6150 alloy tool steel is as follows: hot metal pretreatment, converter, LF furnace, continuous casting, continuous rolling, billet cleaning, heating, rolling, controlled cooling, and finishing.

[0007] LF Refining: The main tasks of LF refining are composition fine-tuning, temperature control, and slag-forming operations. Nitrogen increase in molten steel is controlled by using a slightly positive pressure operation, large slag volume, and limited heating time. Lime and fluorite are used for slag-forming, and the electrode heating time is controlled to 20–30 minutes. Two composition adjustments are performed: during the coarse adjustment, 0.5–0.8 kg / t of aluminum powder is added for deoxidation; during the fine adjustment, the C, Si, Mn, Cr, and V contents in the steel are controlled according to the target.

[0008] Continuous casting: The cross-sectional dimensions of the continuously cast billet are (250~350)mm×(350~450)mm. The superheat of the tundish is controlled at 20~30℃, and the casting speed is constant (the casting speed of the continuously cast billet is controlled at 0.55±0.02m / min); protective casting (low oxidizing and alkaline covering agents are added to the molten steel in the ladle and tundish; protective sleeves are used from the ladle to the tundish and from the tundish to the crystallizer, and argon blowing is used for protection; high-quality protective slag is added to the crystallizer); electromagnetic stirring in the crystallizer: the electromagnetic stirring voltage of the crystallizer is 100~200V, the current intensity is 300~500A, and the frequency is 3~8Hz. Electromagnetic stirring can promote the flotation of non-metallic inclusions in molten steel, reduce the size of inclusion particles in steel, and make inclusions more uniformly distributed; reduce elemental segregation in steel, thereby homogenizing the structure and reducing banded defects in steel; reduce the number and depth of surface defects such as transverse cracks, longitudinal cracks, and corner cracks in steel billets, and provide high-quality raw materials for rolling scratch-free wire rods. Rolling: The initial rolling temperature is 930–980℃, the finishing rolling inlet temperature is 880–950℃, the sizing inlet temperature is 850–920℃, and the wire drawing temperature is 890–930℃. Cooling control: Water bath cooling method: After the wire rod is spun, it enters a water tank. The cooling water temperature in the tank is 80-100℃. The wire rod is cooled to 600-700℃ at a cooling rate of 10-15℃ / s before exiting the water tank and entering an insulation hood. The insulation hood is completely closed, and the cooling rate inside the hood is 0.5-1.0℃ / s. The exit temperature from the hood is 450-600℃. Air cooling is then performed on a cooling bed. Through heating, rolling, and water bath cooling control, a uniform wire rod microstructure dominated by pearlite is obtained, avoiding the formation of bainite and martensite microstructures.

[0009] This invention employs a cooling technology combining water bath cooling and slow cooling. The resulting microstructure of the wire rod after cooling contains only ferrite and pearlite, without bainite or martensite. The performance difference within the same coil of the wire rod is also significantly reduced, providing favorable conditions for subsequent processing.

[0010] The chemical composition of the alloy tool steel SAE6150, by weight percentage, includes: The rationale for the alloy design of this invention is as follows: C: 0.50%–0.60%, Si: 0.20%–0.50%, Mn: 0.60%–1.00%, Cr: 0.90%–1.20%, V: 0.15%–0.30%, with the remainder being Fe and residual elements.

[0011] The alloy tool steel SAE6150 is a tool steel wire rod with a diameter of ø5.5 to ø25 mm.

[0012] The microstructure of the alloy tool steel SAE6150 includes pearlite, ferrite, and trace amounts of bainite. The pearlite content is 92% to 94% by area, with the remainder being ferrite and less than 0.2% bainite.

[0013] The rationale for the alloy design of this invention is as follows: C: C is the element with the most significant solid solution strengthening effect in steel. As the C content increases, the strength and hardness of steel increase, while the plasticity and toughness decrease. For tool steel, the C content should be selected as 0.50-0.60%. Si: Si is a ferrite solid solution strengthening element that can effectively inhibit grain growth, thereby improving the hardness and strength of steel. Si can also promote the formation of fine grains in steel, thus improving its toughness. For tool steel SAE6150, the Si range is set at 0.20%–0.50%. Mn plays a role in solid solution strengthening and grain refinement, and delays the transformation of pearlite and ferrite, thereby improving the strength and work hardening properties of steel; therefore, the range of Mn is 0.60–1.00%. Cr: Cr can improve the strength and toughness of steel and enhance its resistance to atmospheric corrosion. It also effectively improves hardenability, ensuring the strength and hardness of the material after quenching. Therefore, the composition range of Cr is 0.90–1.20%. V: V forms stable carbides in steel, which are finely dispersed and play a role in precipitation strengthening. This improves the red hardness, hardness, and wear resistance of steel. Therefore, V is often added to tool steels, with a composition range of 0.15~0.30%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention involves immersing the wire rod in a water tank for cooling after coiling, followed by slow cooling with heat preservation to complete the phase transformation. Because the wire rod is cooled in water, its microstructure is more uniform than that produced by fan cooling, significantly improving the uniformity of its microstructure and preventing the formation of bainite and martensite. The alloy tool steel SAE6150 produced by this invention has a microstructure composed of a small amount of ferrite and pearlite, avoiding the harmful martensite structure produced by conventional cooling methods. It can be used to produce measuring tools, cutting tools, hand tools, and other tools requiring high strength and toughness. Attached Figure Description

[0015] Figure 1 This is a metallographic diagram of Example 1.

[0016] Figure 2 This is a metallographic diagram with proportions. Detailed Implementation

[0017] The present invention will be described in more detail through embodiments. These embodiments are merely descriptions of the best mode of the invention and do not limit the scope of the invention in any way.

[0018] Example 1: For the production method of homogenizing the microstructure of SAE 6150 alloy tool steel, see [link to relevant documentation]. Figure 1 ,include: LF Refining: The main tasks of LF refining are composition fine-tuning, temperature control, and slag-forming operations. Nitrogen enrichment in molten steel is controlled using a slightly positive pressure operation, large slag volume, and limited heating time. Quicklime and fluorite are used for slag-forming, and the electrode heating time is controlled to 20 minutes. Two composition adjustments are performed: during the coarse adjustment, 0.8 kg / t aluminum powder is added for deoxidation; during the fine adjustment, the C, Si, Mn, Cr, and V contents in the steel are controlled according to the target.

[0019] Continuous casting: The cross-sectional dimensions of the continuously cast billet are 320mm×410mm. The superheat of the tundish is controlled at 25℃, and the casting speed is constant (the casting speed of the billet is controlled at 0.55m / min). Protective casting (low oxidizing and alkaline covering agents are added to the molten steel in the ladle and tundish; protective sleeves are used from the ladle to the tundish and from the tundish to the crystallizer, and argon blowing is used for protection; high-quality protective slag is added to the crystallizer). Electromagnetic stirring of the crystallizer: The electromagnetic stirring voltage of the crystallizer is 120V, the current intensity is 400A, and the frequency is 6Hz. The steel billet is rolled into ø8mm wire rod on a high-speed wire rod mill. The rolling process is as follows: the initial rolling temperature is controlled at 940℃, the finishing rolling inlet temperature is 900℃, the sizing inlet temperature is 890℃, and the wire drawing temperature is 910℃. After wire drawing, the wire enters a water tank and is cooled in 95℃ cooling water at a cooling rate of 13℃ / s. After cooling to 620℃, the wire exits the water tank and enters an insulation hood. The insulation hood is completely closed, and the cooling rate inside the hood is 0.5℃ / s. The wire exit temperature is 485℃. After coiling, the wire is cooled to room temperature.

[0020] Example 2: The production method for homogenizing the microstructure of SAE 6150 alloy tool steel includes: LF Refining: The main tasks of LF refining are composition fine-tuning, temperature control, and slag-forming operations. Nitrogen enrichment in molten steel is controlled using a slightly positive pressure operation, large slag volume, and limited heating time. Quicklime and fluorite are used for slag-forming, and the electrode heating time is controlled at 22 minutes. Two composition adjustments are performed: during the coarse adjustment, 0.7 kg / t aluminum powder is added for deoxidation; during the fine adjustment, the C, Si, Mn, Cr, and V contents in the steel are controlled according to the target.

[0021] Continuous casting: The cross-sectional dimensions of the continuously cast billet are 320mm×410mm. The superheat of the tundish is controlled at 28℃, and the casting speed is constant (the casting speed of the billet is controlled at 0.54m / min). Protective casting (low oxidizing and basic covering agents are added to the molten steel in the ladle and tundish; protective sleeves are used from the ladle to the tundish and from the tundish to the crystallizer, and argon blowing is used for protection; high-quality protective slag is added to the crystallizer); the electromagnetic stirring voltage of the crystallizer is 180V, the current intensity is 350A, and the frequency is 6Hz. The steel billet is rolled into ø10mm wire rod on a high-speed wire rod mill. The rolling process is as follows: the initial rolling temperature is controlled at 970℃, the finishing rolling inlet temperature is 920℃, the sizing inlet temperature is 900℃, and the wire drawing temperature is 900℃. After wire drawing, the wire enters a water tank and is cooled in 96℃ cooling water at a cooling rate of 12.5℃ / s. After cooling to 660℃, the wire exits the water tank and enters an insulation hood. The insulation hood is completely closed, and the cooling rate inside the hood is 0.5℃ / s. The wire exit temperature is 490℃. After coiling, the wire is cooled to room temperature.

[0022] Example 3: The production method for homogenizing the microstructure of SAE 6150 alloy tool steel includes: LF Refining: The main tasks of LF refining are composition fine-tuning, temperature control, and slag-forming operations. Nitrogen enrichment in molten steel is controlled using a slightly positive pressure operation, large slag volume, and limited heating time. Quicklime and fluorite are used for slag-forming, and the electrode heating time is controlled to 25 minutes. Two composition adjustments are performed: during the coarse adjustment, 0.6 kg / t aluminum powder is added for deoxidation; during the fine adjustment, the C, Si, Mn, Cr, and V contents in the steel are controlled according to the target.

[0023] Continuous casting: The cross-sectional dimensions of the continuously cast billet are 320mm×410mm. The superheat of the tundish is controlled at 25℃, and the casting speed is constant (the casting speed of the billet is controlled at 0.55m / min). Protective casting (low oxidizing and alkaline covering agents are added to the molten steel in the ladle and tundish; protective sleeves are used from the ladle to the tundish and from the tundish to the crystallizer, and argon blowing is used for protection; high-quality protective slag is added to the crystallizer). Electromagnetic stirring in the crystallizer: The electromagnetic stirring voltage of the crystallizer is 100V, the current intensity is 400A, and the frequency is 4Hz. The steel billet is rolled into ø9mm wire rod on a high-speed wire rod mill. The rolling process is as follows: the initial rolling temperature is controlled at 940℃, the finishing rolling inlet temperature is 915℃, the sizing inlet temperature is 895℃, and the wire drawing temperature is 910℃. After wire drawing, the wire enters a water tank and is cooled in 95℃ cooling water at a cooling rate of 12.6℃ / s. After cooling to 640℃, the wire exits the water tank and enters an insulation hood. The insulation hood is completely closed, and the cooling rate inside the hood is 0.5℃ / s. The wire exit temperature is 510℃. After coiling, the wire is cooled to room temperature.

[0024] Example 4: The production method for homogenizing the microstructure of SAE 6150 alloy tool steel includes: LF Refining: The main tasks of LF refining are composition fine-tuning, temperature control, and slag-forming operations. Nitrogen enrichment in molten steel is controlled using a slightly positive pressure operation, large slag volume, and limited heating time. Quicklime and fluorite are used for slag-forming, and the electrode heating time is controlled at 23 minutes. Two composition adjustments are performed: during the coarse adjustment, 0.7 kg / t aluminum powder is added for deoxidation; during the fine adjustment, the C, Si, Mn, Cr, and V contents in the steel are controlled according to the target.

[0025] Continuous casting: The cross-sectional dimensions of the continuously cast billet are 320mm × 410mm. The superheat of the tundish is controlled at 27℃, and the casting speed is constant (the casting speed of the billet is controlled at 0.54m / min). Protective casting (low oxidizing and basic covering agents are added to the molten steel in the ladle and tundish; protective sleeves are used from the ladle to the tundish and from the tundish to the crystallizer, and argon blowing is used for protection; high-quality protective slag is added to the crystallizer). Crystallizer electromagnetic stirring: The voltage of the crystallizer electromagnetic stirring is 200V, the current intensity is 500A, and the frequency is 7Hz. The steel billet is rolled into ø8mm wire rod on a high-speed wire rod mill. The rolling process is as follows: the initial rolling temperature is controlled at 940℃, the finishing rolling inlet temperature is 900℃, the sizing inlet temperature is 900℃, and the wire drawing temperature is 900℃. After wire drawing, the wire enters a water tank and is cooled in 96℃ cooling water at a cooling rate of 12.8℃ / s. After cooling to 630℃, the wire exits the water tank and enters an insulation hood. The insulation hood is completely closed, and the cooling rate inside the hood is 0.6℃ / s. The wire exit temperature is 490℃. After coiling, the wire is cooled to room temperature.

[0026] Steelmaking was carried out according to the chemical composition and content designed in this invention. Wire rods were produced through processes such as LF refining, continuous casting, continuous rolling, and wire rod rolling. The measured chemical composition is shown in Table 1.

[0027] Table 1 Chemical composition (wt%) Table 2 Results of wire rod microstructure and properties test The wire rod produced using the above invention can be used to manufacture tools that require high strength and toughness, such as measuring tools, cutting tools, and hand tools.

Claims

1. A method for producing alloy tool steel SAE6150 with homogeneous microstructure, characterized in that, The production process of the alloy tool steel SAE6150 is as follows: hot metal pretreatment, converter, LF furnace, continuous casting, continuous rolling, billet cleaning, heating, rolling, controlled cooling, and finishing. Rolling: The initial rolling temperature is 930–980℃, the finishing rolling inlet temperature is 880–950℃, the sizing inlet temperature is 850–920℃, and the wire drawing temperature is 890–930℃. Cooling control: Water bath cooling method: After the wire rod is spun out, it enters the water tank. The cooling water temperature in the water tank is 80-100℃. The wire rod is cooled to 600-700℃ at a cooling rate of 10-15℃ / s and then exits the water tank into the insulation cover. The insulation cover is completely closed. The cooling rate inside the cover is 0.5-1.0℃ / s. The temperature at the exit of the cover is 450-600℃. The cooling bed is air-cooled.

2. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 1, characterized in that, The continuous casting process includes: tundish superheat control at 20–30°C; constant casting speed of the billet at 0.55 ± 0.02 m / min; protective casting; and electromagnetic stirring in the crystallizer with a voltage of 100–200 V, a current intensity of 300–500 A, and a frequency of 3–8 Hz.

3. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 2, characterized in that, The cross-sectional dimensions of the continuously cast billet are (250~350)mm×(350~450)mm.

4. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 1, characterized in that, The LF refining process involves: using a micro-positive pressure operation, controlling the electrode heating time to 20-30 minutes; and performing two composition adjustments. During the coarse adjustment, 0.5-0.8 kg / t of aluminum powder is added for deoxidation, while during the fine adjustment, the contents of C, Si, Mn, Cr, and V in the steel are controlled according to the target.

5. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 1, characterized in that, The chemical composition of the alloy tool steel SAE6150, by weight percentage, includes: C: 0.50%–0.60%, Si: 0.20%–0.50%, Mn: 0.60%–1.00%, Cr: 0.90%–1.20%, V: 0.15%–0.30%, with the remainder being Fe and residual elements.

6. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 5, characterized in that, The microstructure of the alloy tool steel SAE6150 includes pearlite, ferrite, and trace amounts of bainite. The pearlite content is 92% to 94% by area, with the remainder being ferrite and less than 0.2% bainite.

7. A method for producing alloy tool steel SAE6150 with homogenized microstructure according to claim 1, characterized in that, The alloy tool steel SAE6150 is a tool steel wire rod with a diameter of ø5.5 to ø25 mm.

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