A production method of 50Cr15MoV high-end cutter cold hard steel strip

Abstract

The application discloses a production method of 50Cr15MoV high-end cutter cold hard steel strip, and is characterized in that the following steps are completed: (1) selecting 50Cr15MoV hot-rolled white skin coil; (2) welding the head and tail of the 50Cr15MoV hot-rolled white skin coil through a preparation unit, improving the coiling tension of the steel coil, and obtaining a recoiled white skin coil; (3) rolling the recoiled white skin coil through a 20-roller mill, and obtaining the 50Cr15MoV high-end cutter cold hard steel strip with a hardness greater than 310HV before annealing. The finished product rate of the steel coil is improved to more than 98.7%, the rolling pass is reduced, and the rolling cost is reduced; the thickness precision of the prepared cold hard steel strip is high, the plate shape is flat, the hardness index is stable, and the cold hard steel strip is suitable for manufacturing high-end cutters.

Description

Technical Field

[0001] This invention relates to an improvement on the production method of processing 50Cr15MoV hot-rolled white steel coils into chilled steel strips for cutting tools, specifically a production method of 50Cr15MoV high-end chilled steel strips for cutting tools. Background Technology

[0002] The current criteria for classifying high-end, mid-range, and low-end tool steels are as follows: High-end tool steel: Rust resistance indicators: Salt spray test for more than 60 hours, hardness before annealing > 310HV, longitudinal thickness difference < ±10um, plate convexity index < 20um; hardness of the cutting edge after tempering after machining into a tool > 60HRC; Mid-range tool steel: Rust resistance indicators: Salt spray test for more than 40 hours, hardness before annealing > 285HV, longitudinal thickness difference < ±15um, plate convexity index < 30um; hardness of the cutting edge after tempering after machining into a tool > 55HRC; Low-end tool steel: Rust resistance indicators: Salt spray test for more than 30 hours, hardness before annealing < 285HV, longitudinal thickness difference > ±15um, plate convexity index > 30um; hardness of the cutting edge after tempering after machining into a tool > 52HRC.

[0003] With the continuous development of society, stainless steel products have penetrated into every corner of life. The steel used for knives has continuously improved from 20Cr13 and 30Cr13 to 50Cr15MoV or even higher-end materials. This change in material composition brings about improvements in performance indicators and strength. The specific composition of 30Cr13 stainless steel, calculated by weight percentage, is: C: 0.26-0.35%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.03%; Ni: 0.6%; Cr: 12-14%; balance Fe. 50Cr15MoV stainless steel is a high-carbon martensitic stainless steel, used for making knives. Its specific composition is: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; balance Fe. This stainless steel has good corrosion resistance and high hardness. The addition of Mo and V elements further enhances its hardness, rust resistance, toughness, and wear resistance. Finished knives made from this stainless steel are popular with customers in the market, and more than 20% of them are exported overseas.

[0004] The current production process of 50Cr15MoV tool chilled steel strip is generally made by the following methods: (1) Selecting 50Cr15MoV hot-rolled white steel coil: The specific composition of the 50Cr15MoV hot-rolled white steel coil, calculated by weight percentage, is: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; the balance is Fe; the convexity of the 50Cr15MoV hot-rolled white steel coil is less than 80 micrometers; (2) Coiling and threading: A 50Cr15MoV hot-rolled white steel coil is transported to the left coiler drum by a coil transport trolley for uncoiling. The strip head passes through the two-roll mill and enters the right coiler jaws to complete 1.5 turns of coiling operation; (3) 1. Reciprocating rolling of steel coils: After the rolling force of the stand is established by the roll pressing down, the tension of the left coiler and the tension of the right coiler are established by the left and right coilers and the two-roll mill respectively. The emulsion spray lubrication is turned on through the control panel. The maximum rolling force is set to 700 tons and the maximum tension is 150KN. Reciprocating rolling is carried out. During the rolling process, the thickness gauge of the two-roll mill and the AGC control system are used to detect and control the rolling thickness. (4) Rolling completion: When the thickness gauge of the two-roll mill shows that the thickness reaches the thickness tolerance range required by the technical requirements, the rolling of this pass is completed. The two-roll mill is stopped through the control panel. The strip is sheared by the hydraulic shear. The coiler selected for coiling the steel coil is determined according to the total reduction and the setting of the rolling pass. One side coiler is responsible for uncoiling the finished steel coil, and the other side coiler is responsible for coiling and uncoiling the tail of the strip to obtain 50Cr15MoV cold hardened steel strip. Testing revealed that the surface color difference stripes of this 50Cr15MoV tool chilled steel strip were quite obvious; the salt spray test lasted 32.5 hours, the plate convexity was 35-36 μm, the longitudinal thickness difference was ±15 μm, and the hardness before annealing was 303 HV; the hardness of the cutting edge after tempering after machining into a tool was 53.2-53.4 HRC.The current shortcomings of this 50Cr15MoV tool cold hardening steel strip production process are: (1) According to index analysis, this 50Cr15MoV tool cold hardening steel strip is only suitable for making medium and low-end tools; (2) During the rolling process of the two-roll mill, due to the large contact area of ​​the roll system diameter > 400mm, the rolling reduction per pass is small, resulting in more rolling passes, which is time-consuming and labor-intensive, and the rolling cost is high; and the more passes, the higher the work hardening of the steel plate and the lower the toughness of the steel plate; (3) Due to the accuracy deviation of the thickness gauge of the two-roll mill, the longitudinal thickness and plate convexity of the product exceed the technical requirements of the product; (4) Due to the small tension of the two-roll mill, the plate shape control only has tilt adjustment and bending roll adjustment, which results in a large wave shape after rolling; (5) Due to the direct entry of the head and tail of the steel coil into the coiler on both sides, the ends of the steel strip cannot be rolled, resulting in a steel coil yield of only 96%; (6) Due to the use of emulsion lubrication, the lubrication capacity is insufficient, resulting in obvious color difference stripes on the surface of the rolled plate. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing 50Cr15MoV high-end tool chilled steel strip using a preparation unit and a 20-roll mill. The resulting chilled steel strip is suitable for manufacturing high-end cutting tools, and has high thickness accuracy, flat shape, stable quality, and low production cost.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for producing 50Cr15MoV high-end tool chilled steel strip, characterized by being completed by the following steps: (1) Select 50Cr15MoV hot-rolled white sheet: The convexity of the 50Cr15MoV hot-rolled white sheet is less than 80 micrometers. (2) The 50Cr15MoV hot-rolled white coil is welded at the head and tail to increase the coiling tension and obtain a re-coiled white coil by the preparation unit: The preparation unit consists of an uncoiler, an argon arc welder, a three-roll tension device and a coiling mechanism; a 50Cr15MoV hot-rolled white coil is installed on the uncoiler for uncoiling, the strip head is welded to the head guide strip by the argon arc welder, and the strip head is controlled to pass through the three-roll tension device and enter the coiling machine for coiling. The three-roll tension device is operated to press down the middle roller of the three-roll tension device. The uncoiling tension is set to 5 tons and the coiling tension is set to 15 tons respectively; the preparation unit is started and operated until the strip tail leaves the coiling machine, and the preparation unit is slowed down and stopped; the strip tail is welded to the tail guide strip by the argon arc welder; the coiling machine is started to coil the strip tail and the tail guide strip onto the coiling machine to obtain a re-coiled white coil. (3) Rolling the re-coiled white paper roll using a 20-roll mill: The 20-roll mill consists of a left coiler, a 20-roll mill stand, and a right coiler; the re-coiled white paper roll is installed on the left coiler for uncoiling, and the tail guide belt is passed through the 20-roll mill stand and then enters the right coiler for winding; the 20-roll mill stand is pressed down to establish the tension of the left coiler and the tension of the right coiler, and the tension of the left coiler is set to 35 tons and the tension of the right coiler is set to 37 tons respectively; after turning on the rolling oil spray, the 20-roll mill is turned on for reciprocating rolling; during the rolling process, the 20-roll mill... The thickness gauge of the mill is used to detect the rolling thickness. When the thickness gauge of the 20-roll mill shows that the thickness meets the requirements, the steel coil is padded with lining paper. After the rolling of this pass is completed, the 20-roll mill is stopped and the rolling oil spray is turned off. The 20-roll mill stand is opened, the winding tension during rewinding is set to 8 tons, and the rewinding operation is carried out. Before rewinding, the head strip and strip head are removed by hydraulic shears. After rewinding, the tail strip and strip tail are removed by hydraulic shears. After rewinding, 50Cr15MoV high-end tool chilled steel strip with a hardness >310HV before annealing is obtained.

[0007] As an improvement, annealing of 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV is performed using a bell-type annealing furnace: 1-4 rolls of 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV are placed in the bell-type annealing furnace, hydrogen is introduced, the temperature is raised to 420℃, held for 2 hours, then raised to 780℃, held for 22 hours, then cooled under a hood to 650℃, and finally rapidly cooled to 230℃ before being removed from the furnace. After removal from the furnace, the strip is allowed to cool naturally to obtain 50Cr15MoV high-end tool chilled steel strip with a post-annealing hardness of 280-300HV.

[0008] The 50Cr15MoV hot-rolled white coil, calculated by weight percentage, contains the following components: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; with the balance being Fe.

[0009] The beneficial effects of this invention are as follows: by using a pre-forming unit to weld the head and tail guide strips, the steel coil rolling yield is increased to over 98.7%; due to the 63mm diameter of the work rolls of the 20-roll mill, the reduction is large, reducing the number of rolling passes, lowering rolling costs, reducing work hardening index, and improving the toughness of the chilled steel strip; the resulting 50Cr15MoV high-end tool chilled steel strip has high thickness accuracy, flat shape, stable hardness index, stable surface quality of the steel coil, uniform brightness, longitudinal thickness difference <±8um, and plate convexity index <18um, making it suitable for manufacturing high-end tools. Detailed Implementation

[0010] Example 1: Fabrication of 50Cr15MoV high-end tool chilled steel strip suitable for laser cutting.

[0011] The production method of a 50Cr15MoV high-end tool chilled steel strip is characterized by the following steps: (1) Select 50Cr15MoV hot-rolled white steel coil: The 50Cr15MoV hot-rolled white steel coil contains the following components by weight percentage: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; the balance is Fe; the convexity of the 50Cr15MoV hot-rolled white steel coil is less than 80 micrometers; (2) The 50Cr15MoV hot-rolled white coil is welded at the head and tail to increase the coiling tension and obtain a re-coiled white coil by the preparation unit: The preparation unit consists of an uncoiler, an argon arc welder, a three-roll tension device and a coiling mechanism; a 50Cr15MoV hot-rolled white coil is installed on the uncoiler for uncoiling, the strip head is welded to the head guide strip by the argon arc welder, and the strip head is controlled to pass through the three-roll tension device and enter the coiling machine for coiling. The three-roll tension device is operated to press down the middle roller of the three-roll tension device. The uncoiling tension is set to 5 tons and the coiling tension is set to 15 tons respectively; the preparation unit is started and operated until the strip tail leaves the coiling machine, and the preparation unit is slowed down and stopped; the strip tail is welded to the tail guide strip by the argon arc welder; the coiling machine is started to coil the strip tail and the tail guide strip onto the coiling machine to obtain a re-coiled white coil. (3) Rolling the re-coiled white paper roll using a 20-roll mill: The 20-roll mill consists of a left coiler, a 20-roll mill stand, and a right coiler; the re-coiled white paper roll is installed on the left coiler for uncoiling, and the tail guide belt is passed through the 20-roll mill stand and then enters the right coiler for winding; the 20-roll mill stand is pressed down to establish the tension of the left coiler and the tension of the right coiler, and the tension of the left coiler is set to 35 tons and the tension of the right coiler is set to 37 tons respectively; after turning on the rolling oil spray, the 20-roll mill is turned on for reciprocating rolling; during the rolling process, the thickness gauge of the 20-roll mill is used to detect the rolling thickness; when the thickness gauge of the 20-roll mill shows that the thickness reaches the specified value... When the required conditions are met, the steel coil is padded with liner paper. After the current rolling pass is completed, the 20-roll mill is stopped and the rolling oil spray is turned off. The 20-roll mill stand is opened, and the winding tension during rewinding is set to 8 tons. The rewinding operation is then carried out, that is, the steel coil is rewinded from one side coiler to the other side coiler. At the same time, the liner paper previously padded into the steel coil is removed, and new liner paper is padded into the steel coil during the winding process of the other side coiler. Before rewinding, the head guide strip and strip head are removed by hydraulic shears. After rewinding, the tail guide strip and strip tail are removed by hydraulic shears. After rewinding is completed, 50Cr15MoV high-end tool chilled steel strip with a hardness >310HV before annealing is obtained.

[0012] Testing revealed: no color difference on the surface, uniform brightness; rust resistance indicators: salt spray test result of 61.5 hours, exceeding 60 hours; plate convexity of 13-16µm, <20µm; longitudinal thickness difference of ±6µm, <±10µm; hardness before annealing of 322HV, >310HV; hardness of the cutting edge after tempering after machining into tools of 60.8-61.1HRC, >60HRC. This 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV is suitable for manufacturing high-end tools using laser cutting processes.

[0013] Example 2: Fabrication of 50Cr15MoV high-end tool chilled steel strip suitable for stamping and cutting.

[0014] The production method of a 50Cr15MoV high-end tool chilled steel strip is characterized by the following steps: (1) Select 50Cr15MoV hot-rolled white steel coil: The 50Cr15MoV hot-rolled white steel coil contains the following components by weight percentage: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%; P: 0.04%; S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; the balance is Fe; the convexity of the 50Cr15MoV hot-rolled white steel coil is less than 80 micrometers; (2) The 50Cr15MoV hot-rolled white coil is welded at the head and tail to increase the coiling tension and obtain a re-coiled white coil by the preparation unit: The preparation unit consists of an uncoiler, an argon arc welder, a three-roll tension device and a coiling mechanism; a 50Cr15MoV hot-rolled white coil is installed on the uncoiler for uncoiling, the strip head is welded to the head guide strip by the argon arc welder, and the strip head is controlled to pass through the three-roll tension device and enter the coiling machine for coiling. The three-roll tension device is operated to press down the middle roller of the three-roll tension device. The uncoiling tension is set to 5 tons and the coiling tension is set to 15 tons respectively; the preparation unit is started and operated until the strip tail leaves the coiling machine, and the preparation unit is slowed down and stopped; the strip tail is welded to the tail guide strip by the argon arc welder; the coiling machine is started to coil the strip tail and the tail guide strip onto the coiling machine to obtain a re-coiled white coil. (3) Rolling the re-coiled white paper roll using a 20-roll mill: The 20-roll mill consists of a left coiler, a 20-roll mill stand, and a right coiler; the re-coiled white paper roll is installed on the left coiler for uncoiling, and the tail guide belt is passed through the 20-roll mill stand and then enters the right coiler for winding; the 20-roll mill stand is pressed down to establish the tension of the left coiler and the tension of the right coiler, and the tension of the left coiler is set to 35 tons and the tension of the right coiler is set to 37 tons respectively; after turning on the rolling oil spray, the 20-roll mill is turned on for reciprocating rolling; during the rolling process, the thickness gauge of the 20-roll mill is used to detect the rolling thickness; when the thickness gauge of the 20-roll mill shows that the thickness reaches the specified value... When the required conditions are met, the steel coil is padded with liner paper. After the current rolling pass is completed, the 20-roll mill is stopped and the rolling oil spray is turned off. The 20-roll mill stand is opened, and the winding tension during rewinding is set to 8 tons. The rewinding operation is then performed, i.e., the steel coil is rewinded from one side coiler to the other side coiler. At the same time, the liner paper previously padded into the steel coil is removed, and new liner paper is padded into the steel coil during the winding process of the other side coiler. Before rewinding, the head guide strip and strip head are removed by hydraulic shears. After rewinding, the tail guide strip and strip tail are removed by hydraulic shears. After rewinding is completed, a 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV is obtained. Testing revealed: no color difference on the surface, uniform brightness; rust prevention indicators: salt spray test result was 62.1 hours, exceeding 60 hours; plate convexity was 14-16 μm, <20 μm; longitudinal thickness difference was ±6 μm, <±10 μm; hardness before annealing was 321 HV, >310 HV. (4) Annealing operation of 50Cr15MoV high-end tool chilled steel strip with a hardness >310HV before annealing in a bell-type annealing furnace: 1-4 rolls of 50Cr15MoV high-end tool chilled steel strip with a hardness >310HV before annealing are placed in a bell-type annealing furnace, hydrogen is introduced, the temperature is raised to 420℃, held for 2 hours, then raised to 780℃, held for 22 hours, then cooled to 650℃ with a hood, and finally rapidly cooled to 230℃ before being taken out of the furnace. After being taken out of the furnace, it is naturally cooled to obtain 50Cr15MoV high-end tool chilled steel strip with a hardness of 280-300HV after annealing.

[0015] Testing revealed the following: The hardness of the annealed product was 291-292 HV, falling within the 280-300 HV range; the hardness of the cutting edge after tempering in cutting tools was 60.5-60.7 HRC, exceeding 60 HRC. This 50Cr15MoV high-end tool chilled steel strip, with an annealed hardness of 280-300 HV, is suitable for manufacturing high-end tools using stamping and cutting processes.

Claims

1. A method for producing 50Cr15MoV high-end tool chilled steel strip, characterized in that: This can be accomplished by following these steps: (1) Select 50Cr15MoV hot-rolled white sheet: The convexity of the 50Cr15MoV hot-rolled white sheet is less than 80 micrometers. The 50Cr15MoV hot-rolled white steel coil, by weight percentage, contains the following components: C: 0.45-0.55%; Si: 1.0%; Mn: 1.0%. P：0.04%； S: 0.015%; Cr: 14-15%; Mo: 0.5-0.8%; V: 0.1-0.2%; balance Fe; (2) The 50Cr15MoV hot-rolled white coil is welded at the head and tail to increase the coiling tension and obtain a re-coiled white coil by the preparation unit: The preparation unit consists of an uncoiler, an argon arc welder, a three-roll tension device and a coiling mechanism; a 50Cr15MoV hot-rolled white coil is installed on the uncoiler for uncoiling, the strip head is welded to the head guide strip by the argon arc welder, and the strip head is controlled to pass through the three-roll tension device and enter the coiling machine for coiling. The three-roll tension device is operated to press down the middle roller of the three-roll tension device. The uncoiling tension is set to 5 tons and the coiling tension is set to 15 tons respectively; the preparation unit is started and operated until the strip tail leaves the coiling machine, and the preparation unit is slowed down and stopped; the strip tail is welded to the tail guide strip by the argon arc welder; the coiling machine is started to coil the strip tail and the tail guide strip onto the coiling machine to obtain a re-coiled white coil. (3) Rolling the re-coiled white paper rolls using a 20-roll mill: The 20-roll mill consists of a left coiler, a 20-roll mill frame, and a right coiler. The working roll diameter of the 20-roll mill is 63mm. The re-coiled white paper rolls are installed on the left coiler for uncoiling. After the tail guide is passed through the 20-roll mill frame, it enters the right coiler for winding. The 20-roll mill frame is pressed down to establish the tension of the left coiler and the tension of the right coiler. The tension of the left coiler is set to 35 tons and the tension of the right coiler is set to 37 tons. After the rolling oil spray is turned on, the 20-roll mill is turned on for reciprocating rolling. During the rolling process, the thickness gauge of the 20-roll mill is used to detect the rolling thickness. When the thickness gauge of the 20-roll mill shows that the thickness meets the requirements, the steel coil is padded with lining paper. After the rolling of this pass is completed, the 20-roll mill is stopped and the rolling oil spray is turned off. Open the 20-roll mill stand, set the winding tension to 8 tons, and carry out the rewinding operation; before rewinding, the head guide and belt head are removed by hydraulic shears, and after rewinding, the tail guide and belt tail are removed by hydraulic shears. After rewinding, a 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV is obtained. The longitudinal thickness difference of the 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV is <±8um, and the plate convexity index is <18um.

2. The method for producing a 50Cr15MoV high-end tool chilled steel strip according to claim 1, characterized in that: Annealing of 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV was performed using a bell-type annealing furnace: 1-4 rolls of 50Cr15MoV high-end tool chilled steel strip with a pre-annealing hardness >310HV were placed in the bell-type annealing furnace, hydrogen was introduced, the temperature was raised to 420℃, held for 2 hours, then raised to 780℃, held for 22 hours, then cooled under a hood to 650℃, and finally rapidly cooled to 230℃ before being removed from the furnace. After being removed from the furnace, it was allowed to cool naturally to obtain 50Cr15MoV high-end tool chilled steel strip with a post-annealing hardness of 280-300HV.