Induction annealing method for solving heavy quenching ring crack

Abstract

The present application relates to a kind of inductive annealing method for solving heavy quenching ring crack, annealing is carried out in trolley resistance furnace, reduce quenching hardness, balance quenching and non-quenching tissue, reduce stress and stress mutation;According to hardness detection, mark area value, mark the lowest hardness area, hardness change boundary;Using 50Hz double-frequency induction coil separately to mark area heating, heating range is in the range of 150mm above and below the lowest hardness;Heating back and forth is carried out in 5 times, and heating temperature is controlled at 70-80 degrees each time, and after the last heating, stay 10min, hoist and unload rolling roller, cool room temperature and detect hardness, outer circle is re-grounded, after inductive annealing, roller is installed in 350 DEG preheating furnace and kept warm, and 50Hz / 250Hz double-frequency quenching is carried out again, solve the problem that when Cr3, Cr5 roller body quenching process occurs interruption, ring crack often occurs when surface quenching is carried out again in quenching heating cooling zone and non-heating cooling zone, and workpiece is scrapped.

Description

Technical Field

[0001] This invention relates to an induction annealing method for surface heat treatment of Cr3 and Cr5 rolls. Specifically, it relates to an induction annealing method that solves the problem of ring cracks that often occur when the surface quenching process of Cr3 and Cr5 rolls is interrupted and then re-quenched in the quenching heating and cooling zone and the unheated cooling zone, resulting in scrap. By incorporating induction annealing and furnace preheating into the conventional annealing furnace annealing process, the microstructure is further balanced before normal 50Hz / 250Hz dual-frequency quenching is performed. This solves the problem of ring cracks that occur when the interrupted rolls are re-quenched, thus reducing scrap loss. Background Technology

[0002] Forged steel cold rolling rolls, used as materials for Cr3 and Cr5 rolling mills, are widely used in finishing mill stands both domestically and internationally. They require high resistance to fracture, spalling, thermal shock, accidents, and wear. This type of material is generally produced through electric furnace smelting, ladle refining, electroslag remelting, forging, tempering heat treatment, rough machining, roll body surface quenching, finishing, and external cylindrical grinding. The surface hardness of the finished roll body is generally required to be HSD75-100, with a hardened layer of 15-30mm, and the surface is obtained through dual-frequency induction quenching.

[0003] Due to abnormalities in the electrical components during the quenching process, such as power outages, leakage of the induction coil, and other abnormalities, the quenching process is frequently interrupted. When Cr3 and Cr5 material rolls that have been interrupted during quenching are annealed using traditional methods and then subjected to 50Hz / 250Hz dual-frequency quenching again, ring cracks often occur in both the quenching heating and cooling zones and the unheated cooling zone. The ring cracking rate accounts for 80% to 90% of the interrupted rolls, resulting in significant losses.

[0004] This is how it is achieved using traditional techniques: 1) For Cr3 and Cr5 material rolls where the quenching process is interrupted, annealing is often performed in a trolley resistance furnace. The annealing curve of the roll heating furnace during the interrupted quenching process is shown in the figure below. Figure 1 As shown, this method reduces the hardness of the quenched zone, balances the microstructure of the quenched and non-quenched zones, and reduces stress.

[0005] 2) After conventional annealing, the hardness of the interrupted area of ​​the 50Hz / 250Hz dual-frequency quenched roll was tested using an HS141 roll-specific hardness tester. The hardness distribution of the interrupted area is shown in Table 1. In Table 1, the unheated area of ​​the quenched interrupted roll refers to the area above 100mm above the 50Hz induction coil. Figure 2 Zone A. The overheating / underheating zone of the interrupted quenching rolls refers to the upper 100mm area of ​​the 50Hz induction coil, see [link / reference]. Figure 3Zone B. The quenching interruption heating zone for the interrupted roll quenching refers to the area enclosed by the 50Hz induction coil and the 250Hz wrapping zone. See [link / reference]. Figure 2 Middle C zone. The quenching interruption roll cooling zone refers to the area inside the water spray ring, see... Figure 2 Middle D area.

[0006] Table 1. Hardness distribution of 50Hz / 250Hz dual-frequency re-quenching interrupted rolls after conventional annealing

[0007] Analysis of the hardness data in Table 1 shows that the hardness of the unheated zone of the interrupted quenching roll is the same as the original tempering hardness (see area A in Table 1); the hardness of the transition zone between heating and unheating of the interrupted quenching roll is slightly lower than the original tempering hardness (see areas B and C in Table 1); the hardness of the heated zone of the interrupted quenching roll is significantly lower than the original tempering hardness (see area D in Table 1). The hardness of the cooled zone of the interrupted quenching roll is higher than the original tempering hardness, with a clear boundary and a very sudden change in hardness. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an induction annealing method for re-quenching ring cracks in interrupted rolls by using a 50Hz / 250Hz quenching equipment to balance the microstructure through 50Hz / 250Hz induction annealing and furnace preheating, followed by normal 50Hz / 250Hz dual-frequency quenching. This method addresses the issue of ring cracks during re-quenching of interrupted rolls. Based on traditional annealing processes, this invention adds local induction annealing and furnace preheating on a 50Hz / 250Hz quenching equipment to balance the microstructure of the interrupted heating and unheated zones, followed by normal 50Hz / 250Hz dual-frequency quenching.

[0009] The technical solution of this invention is implemented as follows: An induction annealing method for solving the problem of ring cracks during re-quenching is characterized by addressing the issue that ring cracks often occur during re-surface quenching in the quenching heating and cooling zones and the unheated cooling zone after the quenching process of Cr3 and Cr5 roll bodies is interrupted, resulting in workpiece scrap. Based on traditional annealing, this method adds local induction annealing on a 50Hz / 250Hz quenching equipment and furnace preheating to balance the microstructure of the interrupted heating and unheated zones before normal 50Hz / 250Hz dual-frequency quenching. The specific steps are as follows: Step 1) Annealing is carried out in a trolley resistance furnace. The rolls after quenching interruption are sent to the heating furnace for annealing. This method reduces the hardness of the quenching section, balances the microstructure of the heating zone and cooling zone of the quenching interruption roll, and reduces stress and stress abrupt changes. Step 2) Based on the hardness test results and the marked area values, mark the area with the lowest hardness and the hardness change boundary; Step 3) Use a 50Hz dual-frequency induction coil to heat the marked area separately, with the heating range being 150mm above and below the point of lowest hardness; the moving speed is 0.6mm / s, and the rotation speed is 40r / min; the heating is performed in 5 round trips. Step 4) During the 5 rounds of heating, the heating temperature should be increased by 70-80 degrees each time, and the final heating temperature should not exceed 700 degrees. Step 5) After the final heating, wait 10 minutes, then lift and unload the roll. After the quenching is interrupted, cool the roll to room temperature of 20-25℃ and test the roll body hardness and hardness uniformity. Step 6) Re-grind the outer circle, and the surface wave flaw detection is qualified; Step 7) Place the induction annealed rolls in a 350℃ preheating furnace and keep them at that temperature for ≥10 hours, then repeat the normal 50Hz / 250Hz dual-frequency quenching.

[0010] The present invention has the following advantages: 1) Utilizing the characteristics of a 50HZ / 250HZ dual-frequency machine tool, induction annealing is performed on the interrupted area of ​​the quenching interrupted roll; 2) According to the testing label, the 50HZ / 250HZ dual-frequency machine tool can accurately anneal the area during induction annealing and achieve 5 reciprocating annealing cycles; 3) The annealing process can precisely control temperature changes and temperature rise gradients, thereby achieving the purpose of annealing and meeting the quality control technical indicators. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the annealing curve of the interrupted roll heating furnace for quenching Cr3 and Cr5 rolls.

[0012] Figure 2 This is a schematic diagram of quenching on a 50Hz / 250Hz quenching machine.

[0013] The diagram is labeled as follows: A - Unheated zone of the quenching interrupted roll; B - Overheated zone of the quenching interrupted roll; C - Heated zone of the quenching interrupted roll; D - Cooling zone of the quenching interrupted roll.

[0014] Figure 3 Schematic diagram of the preheating curve during roll quenching interruption. Detailed Implementation

[0015] Example 1: Verification of process results for the quenching process of Cr5 rolls with Φ450*1450 material.

[0016] Step 1) Annealing is carried out in a trolley resistance furnace. A schematic diagram of the annealing curve for the interrupted quenching of Cr5 material rolls in the roll heating furnace is shown below. Figure 1As shown, this method reduces the hardness of the quenching section, balances the microstructure of the heating zone and cooling zone of the quenching interruption roll, and reduces stress and stress abrupt changes. Step 2) Based on the hardness test results and the marked area values, mark the area with the lowest hardness and the hardness change boundary; Step 3) Use a 50Hz dual-frequency induction coil to heat the marked area separately, with the heating range being 150mm above and below the point of lowest hardness; the moving speed is 0.6mm / s, and the rotation is 40r / min; the heating is performed in 5 round trips. Step 4) Heat back and forth 5 times, with the heating temperature increasing by 70-80 degrees each time, and the final heating temperature not exceeding 700 degrees. Step 5) After the final heating, wait 10 minutes, then lift and unload the roll. After the quenching is interrupted, cool the roll to room temperature of 20-25℃ and test the roll body hardness and hardness uniformity. Step 6) Re-grind the outer circle, and the surface wave flaw detection is qualified; Step 7) Place the induction-annealed rolls in a 350℃ preheating furnace and hold for ≥10 hours, then repeat the normal 50Hz / 250Hz dual-frequency quenching. See the preheating process below. Figure 3 As shown.

Claims

1. An induction annealing method for solving ring cracks during quenching, characterized in that, To address the issue of annular cracks frequently occurring during re-surface quenching in the heating and cooling zones of Cr3 and Cr5 roll bodies after an interruption in the quenching process, leading to workpiece scrap, a solution is added to the traditional annealing process: localized induction annealing on a 50Hz / 250Hz quenching machine and furnace preheating. This balances the microstructure of the interrupted heating and unheated zones before normal 50Hz / 250Hz dual-frequency quenching. The specific steps are as follows: Step 1) Annealing is carried out in a trolley resistance furnace. The rolls after quenching interruption are sent to the heating furnace for annealing. This method reduces the hardness of the quenching section, balances the microstructure of the heating zone and cooling zone of the quenching interruption roll, and reduces stress and stress abrupt changes. Step 2) Based on the hardness test results and the marked area values, mark the area with the lowest hardness and the hardness change boundary; Step 3) Use a 50Hz dual-frequency induction coil to heat the marked area separately, with the heating range being 150mm above and below the point of lowest hardness; the moving speed is 0.6mm / s, and the rotation speed is 40r / min; the heating is performed in 5 round trips. Step 4) During the 5 rounds of heating, the heating temperature should be increased by 70-80 degrees each time, and the final heating temperature should not exceed 700 degrees. Step 5) After the final heating, wait 10 minutes, then lift and unload the roll. After the quenching is interrupted, cool the roll to room temperature of 20-25℃ and test the roll body hardness and hardness uniformity. Step 6) Re-grind the outer circle, and the surface wave flaw detection is qualified; Step 7) Place the induction annealed rolls in a 350℃ preheating furnace and keep them at that temperature for ≥10 hours, then repeat the normal 50Hz / 250Hz dual-frequency quenching.

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