Preheat treatment method for forged steel cold rolling working roll

Abstract

The invention discloses a preheat treatment method for a forged steel cold rolling working roll. The preheat treatment method comprises high-temperature quenching and high-temperature tempering. The cooling mode after high-temperature quenching is spray cooling and air spraying cooling, and the specific method is as follows: opening all nozzles to uniformly spray and cool the roller body and the roller neck; after the temperature of the small-diameter roll neck is cooled to 200-300 DEG C, closing a water pipe valve of a corresponding nozzle, retaining an air pipe valve, and continuously spraying air for cooling; after the temperature of the large-diameter roll neck is cooled to 200-300 DEG C, closing a water pipe valve of a corresponding nozzle, retaining an air pipe valve, and continuously spraying air for cooling; and when the temperature of the roller body is cooled to 200-300 DEG C, all the valves are closed. According to the preheat treatment method for the forged steel cold-rolling working roll, the cooling mode after high-temperature quenching is spray cooling and air spraying cooling, the cooling mode is low in cost and environmentally friendly, various mechanical properties are not greatly different from those of traditional oil quenching and tempering, and the technical requirements of preheat treatment are met.

Description

Technical Field

[0001] The invention belongs to the technical field of forged steel cold rolling working rolls, and in particular relates to a preparatory heat treatment method for forged steel cold rolling working rolls. Background Art

[0002] The purpose of the preliminary heat treatment (also called quenching and tempering heat treatment) of forged steel cold rolling work rolls is to make the roll neck hardness meet the technical requirements, while ensuring that the mechanical properties of the roll neck meet the technical requirements.

[0003] The preparatory heat treatment methods for forged steel cold rolling work rolls include high temperature quenching + high temperature tempering. According to different cooling methods, high temperature quenching can be divided into the following types: (1) Oil quenching, see reference 1.

[0004] Oil-cooled quenching can ensure that the roll neck hardness meets the technical requirements, and can also ensure that the various mechanical properties meet the technical requirements. However, oil-cooled quenching is not only costly, but also produces a lot of oil fume pollution, which is harmful to the human body and does not meet the current green, low-carbon and environmentally friendly production and manufacturing requirements in my country.

[0005] (2) Blowing cooling, see reference 2.

[0006] Blowing cooling has low cost and is environmentally friendly, but the cooling effect is not good, especially the tissue uniformity is poor and cannot meet the technical requirements.

[0007] (3) Spray water cooling quenching, see reference 3.

[0008] Spray water cooling is also low-cost and environmentally friendly, but the cooling intensity is high and it is easy to cause cracks on the roll surface.

[0009] Document 4 discloses a method for preparatory heat treatment of support rollers, and the cooling method adopted in this document is spray cooling; however, this document is aimed at support rollers, which mainly play a supporting role during service, and therefore, do not have high requirements for mechanical properties; in actual production processes, the spray cooling method disclosed in this document is used to spray cool forged steel cold-rolled working rollers, but the effect is not good, and in particular, it cannot guarantee that various mechanical properties meet the technical requirements.

[0010] Document 1: Chinese patent document CN102400048A, published on April 4, 2012.

[0011] Document 2: Chinese patent document CN104630637A, published on May 20, 2015.

[0012] Reference 3: “Preparatory heat treatment process of MC5 steel after cold rolling and roll forging”, Yang Xinwu et al., “Metal Heat Treatment”, Issue 09, 2013, pp. 55-57.

[0013] Document 4: Chinese patent document CN103572034A, published on February 12, 2014. Summary of the invention

[0014] The purpose of the present invention is to solve the problems of high cost and great environmental pollution caused by oil cooling quenching of existing forged steel cold rolling working rolls, poor uniformity of air blowing cooling structure and easy cracking of the rolling roll surface caused by spray water cooling, and to provide a preparatory heat treatment method for forged steel cold rolling working rolls which is not only low in cost and environmentally friendly, but also has various mechanical properties that can meet the technical requirements.

[0015] The technical solution to achieve the purpose of the present invention is: a preparatory heat treatment method for forged steel cold rolling work rolls, including high-temperature quenching and high-temperature tempering; the cooling method after high-temperature quenching is spray cooling + air jet cooling.

[0016] The specific method of spray cooling + air jet cooling is as follows: In the first stage, all nozzles, water pipe valves and air pipe valves are opened to evenly spray cool the roll body and roll neck of the forged steel cold rolling work roll.

[0017] In the second stage, when the temperature of the small diameter roll neck is cooled to 200-300°C, the water pipe valve of the nozzle corresponding to the small diameter roll neck is closed, the air pipe valve is retained, and the small diameter roll neck is continued to be sprayed with compressed air for cooling.

[0018] In the third stage, when the temperature of the large diameter roll neck is cooled to 200-300°C, the water pipe valve of the nozzle corresponding to the large diameter roll neck is closed, the air pipe valve is retained, and the large diameter roll neck is continued to be sprayed with compressed air for cooling.

[0019] In the fourth stage, when the roller body temperature cools to 200-300℃, all valves are closed, and the roller is loaded into the furnace for tempering after air cooling.

[0020] The water pressure and wind pressure of each of the above levels are controlled at 30-60 kPa and remain constant.

[0021] The high temperature quenching is firstly kept at a temperature of 350-500°C for 2.5-5h, then heated to 600-750°C at a rate of 30-60°C / s, and kept at this temperature for 5-10h, and finally heated to 850-980°C at a rate of 30-60°C / s, and kept at this temperature for 10-20h.

[0022] The high temperature tempering is firstly kept at a temperature of 300-400°C for 2.5-5h, then heated to 500-650°C at a rate of 30-60°C / s, and kept at this temperature for 15-42h, and finally taken out of the furnace and air-cooled to room temperature.

[0023] The material of the forged steel cold rolling working roll is Cr3, Cr4 or Cr5, preferably Cr5.

[0024] The present invention has the positive effect that the cooling method of the forged steel cold-rolled working roll preparatory heat treatment method after high-temperature quenching is spray cooling + air jet cooling. This cooling method is not only low in cost and environmentally friendly, but also has various mechanical properties that are not much different from traditional oil quenching and tempering, and meets the technical requirements of preparatory heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of spray cooling + air jet cooling of the present invention.

[0026] Figure 2 This is the metallographic structure diagram of the roller body surface of the forged steel cold-rolled work roll after the preliminary heat treatment in Example 1.

[0027] Figure 3 This is a hardness distribution diagram of the forged steel cold-rolled work roll body after the preliminary heat treatment in Example 1; wherein the squares represent the Rockwell hardness HRC, and the circles represent the Shore hardness HSD. DETAILED DESCRIPTION

[0028] (Example 1) The preparatory heat treatment method for forged steel cold rolling work rolls of this embodiment comprises the following steps: ① High temperature quenching: The machined conventional Cr5 forged steel cold-rolled working roll is first kept at 400-450°C for 4 hours, then heated to 650-700°C at a rate of 45°C / s, and kept at this temperature for 8 hours, and finally heated to 900-930°C at a rate of 45°C / s, and kept at this temperature for 15 hours.

[0029] ② Spray cooling + air jet cooling, the specific method is as follows [see Figure 1 】: In the first stage, all nozzles 10, 20, 30 and water pipe valves and air pipe valves are opened to evenly spray cool the roll body and roll neck of the forged steel cold rolling work roll, and the water pressure and air pressure are both 45kPa (the same below).

[0030] In the second stage, when the temperature of the small diameter roll neck 300 is cooled to 200-300°C, the water pipe valve of the nozzle 30 corresponding to the small diameter roll neck 300 is closed, the air pipe valve is retained, and the small diameter roll neck 300 is continued to be sprayed with compressed air.

[0031] In the third stage, when the temperature of the large diameter roll neck 200 is cooled to 200-300°C, the water pipe valve of the nozzle 20 corresponding to the large diameter roll neck 200 is closed, the air pipe valve is retained, and the large diameter roll neck 200 is continued to be sprayed with compressed air for cooling.

[0032] In the fourth stage, when the temperature of the roller body 100 is cooled to 200-300℃, all valves are closed, and after air cooling for 1-4 hours, the roller is loaded into the furnace for tempering.

[0033] ③ High temperature tempering: first keep it at 350℃ for 4h, then heat it to 550-600℃ at a rate of 45℃ / s, and keep it at this temperature for 36h, finally take it out of the furnace and air cool it to room temperature.

[0034] (Test Example 1) The surface structure of the forged steel cold-rolled work roll after the preliminary heat treatment of Example 1 was observed, and the results are shown in Figure 2 .

[0035] Depend on Figure 2 It can be seen that the surface structure of the roller body is uniform tempered troostite.

[0036] (Test Example 2) The hardness of the forged steel cold rolling work roll after the preliminary heat treatment of Example 1 was tested, and the results are shown in Figure 3 .

[0037] Depend on Figure 3 It can be seen that within the depth range of 140mm, the roller body hardness meets the technical requirements of 45-50HSD.

[0038] (Test Example 3) The deformation of the roll body and each roll neck of the forged steel cold rolling work roll after the preliminary heat treatment in Example 1 was measured, and the results showed that the deformation was within 6 mm.

[0039] (Example 2 to Example 3) The preparation methods of the embodiments are basically the same as those of embodiment 1, except for the process parameters of step ① and step ③, as shown in Table 1.

[0040] (Comparative Example 1) The difference from Example 1 is that step ② adopts traditional oil quenching and tempering.

[0041] (Comparative Example 2) The difference from Example 1 is that step ② uses the spray cooling process parameters of document 4 for tempering, which are as follows: In the first stage, all nozzles 10, 20, 30 and water pipe valves and air pipe valves are opened to evenly spray cool the roll body and roll neck of the forged steel cold rolling work roll, and the water pressure and air pressure are both 45kPa (the same below).

[0042] In the second stage, when the temperature of the small-diameter roll neck 300 is cooled to 200-300° C., the water pipe valve and the air pipe valve of the nozzle 30 corresponding to the small-diameter roll neck 300 are closed.

[0043] In the third stage, when the temperature of the large-diameter roll neck 200 is cooled to 200-300° C., the water pipe valve and the air pipe valve of the nozzle 20 corresponding to the large-diameter roll neck 200 are closed.

[0044] In the fourth stage, when the temperature of the roller body 100 is cooled to 200-300℃, all valves are closed, and after air cooling for 1-4 hours, the roller is loaded into the furnace for tempering.

[0045] (Test Example 4) The mechanical properties of the large diameter roll neck 200 of the forged steel cold rolling work roll after the preliminary heat treatment of Examples 1 to 3 and Comparative Examples 1 and 2 were tested, and the results are shown in Table 1.

[0046] It can be seen from Table 1 that the mechanical properties of the present application are not much different from those of the traditional oil quenching and tempering, and meet the technical requirements of the preliminary heat treatment.

[0047] Table 1 Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 High temperature quenching first stage 400~450℃ insulation for 4h 360~390℃ insulation for 5h 460~490℃ insulation for 3h 400~450℃ insulation for 4h 400~450℃ insulation for 4h High temperature quenching second stage 650~700℃ insulation for 8h 610~640℃ insulation for 10h 710~740℃ insulation for 6h 650~700℃ insulation for 8h 650~700℃ insulation for 8h High temperature quenching third stage 900~930℃ insulation for 15h 860~890℃ insulation for 18h 940~970℃ insulation for 12h 900~930℃ insulation for 15h 900~930℃ insulation for 15h High temperature tempering first stage 350℃ insulation for 4h 320℃ insulation for 5h 380℃ insulation for 3h 350℃ insulation for 4h 350℃ insulation for 4h High temperature tempering second stage 550~600℃ insulation for 36h 510~540℃ insulation for 40h 610~640℃ insulation for 24h 550~600℃ insulation for 36h 550~600℃ insulation for 36h Yield strength / MPa 958 933 946 960 743 Tensile strength / MPa 1180 1156 1163 1192 948 Elongation after break / % 15% 17% 16% 14% 25% Sectional shrinkage / % 24% 27% 26% 22% 38% Impact absorption energy / J 12 / 16 / 13 14 / 18 / 13 13 / 17 / 14 12 / 15 / 12 23 / 25 / 21

Claims

1. A method for preparatory heat treatment of forged steel cold rolling work rolls, comprising high temperature quenching and high temperature tempering; characterized in that: The cooling method after high temperature quenching is spray cooling + air jet cooling.

2. The method for preparatory heat treatment of forged steel cold rolling work rolls according to claim 1, characterized in that The specific method of spray cooling + air jet cooling is as follows: In the first stage, all nozzles, water pipe valves and air pipe valves are opened to evenly spray cool the roll body and roll neck of the forged steel cold rolling work roll; In the second stage, when the temperature of the small diameter roll neck is cooled to 200-300°C, the water pipe valve of the nozzle corresponding to the small diameter roll neck is closed, the air pipe valve is retained, and the small diameter roll neck is continued to be sprayed with compressed air for cooling; In the third stage, when the temperature of the large diameter roll neck is cooled to 200-300°C, the water pipe valve of the nozzle corresponding to the large diameter roll neck is closed, the air pipe valve is retained, and the large diameter roll neck is continued to be sprayed with compressed air for cooling; In the fourth stage, when the roller body temperature cools to 200-300℃, all valves are closed, and the roller is loaded into the furnace for tempering after air cooling.

3. The method for preliminary heat treatment of forged steel cold rolling work rolls according to claim 2, characterized in that: The water pressure and wind pressure of each of the above levels are controlled at 30~60kPa and remain constant.

4. The method for preparatory heat treatment of forged steel cold rolling work rolls according to any one of claims 1 to 3, characterized in that: The high temperature quenching is firstly kept at a temperature of 350-500°C for 2.5-5h, then heated to 600-750°C at a rate of 30-60°C / s, and kept at this temperature for 5-10h, and finally heated to 850-980°C at a rate of 30-60°C / s, and kept at this temperature for 10-20h.

5. The method for preparatory heat treatment of forged steel cold rolling work rolls according to any one of claims 1 to 3, characterized in that: The high temperature tempering is firstly kept at a temperature of 300-400°C for 2.5-5h, then heated to 500-650°C at a rate of 30-60°C / s, and kept at this temperature for 15-42h, and finally taken out of the furnace and air-cooled to room temperature.

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