Quenching surface strengthening method for roll neck of large forged steel supporting roll

Abstract

The invention discloses a roll neck quenching surface strengthening method for a large forged steel supporting roll. The roll neck quenching surface strengthening method comprises the steps of high-temperature normalizing, high-temperature tempering, rough machining, roll neck quenching and tempering after quenching. The heating mode of roller neck quenching is flame heating, the quenching heating temperature is 700-900 DEG C, and water spraying cooling is carried out while quenching heating is carried out. According to the method, conventional post-forging heat treatment is combined with the roller neck quenching and water spraying cooling process, compared with a conventional supporting roller pre-heat treatment process, the problems that pollution is caused when quenching oil serves as a medium for hardening and tempering, physical and psychological health of workers is damaged and the like are solved, and the problems that production efficiency is low and production cost is low when spraying hardening and tempering are conducted are solved. And the product quality is not qualified. Compared with a preheat treatment process in the document CN116970789A, the method has the advantages that the total heat treatment time is greatly shortened, the hardness of the roll neck can reach about 45 HSD, and the treatment effect is better.

Description

Technical Field

[0001] The invention belongs to the technical field of large forged steel support rollers, and in particular relates to a method for strengthening the roll neck quenching surface of a large forged steel support roller. Background Art

[0002] Large forged steel support rolls are important components of modern rolling mills. They often bear large loads and impacts during the rolling process. If the product strength is insufficient, it will lead to roll breakage or other failure problems. Therefore, with the continuous development of my country's current steel industry towards high-end, green and intelligent, the requirements for large forged steel support rolls are also getting higher and higher.

[0003] The conventional heat treatment method for large forged steel support rollers includes three stages: post-forging heat treatment → quenching and tempering heat treatment → final heat treatment. The first two stages are also commonly referred to as preliminary heat treatment.

[0004] Among them, the role of tempering heat treatment is mainly to make the roll neck hardness meet the technical requirements, while ensuring that the roll neck has sufficient mechanical properties. The conventional processes are oil-cooled quenching and spray water-cooled quenching. The former is not only expensive, but also has a large amount of oil fume pollution, which is harmful to the human body and does not meet my country's current green, low-carbon and environmentally friendly production and manufacturing requirements; the latter has a long production cycle, low production efficiency, and unstable quality. It is also prone to problems such as roll neck breakage during use.

[0005] To address the challenges of existing quenching and tempering heat treatments, Chinese patent document CN116970789A discloses a preparatory heat treatment method for large forged steel backup rolls, comprising post-forging residual heat normalizing, high-temperature annealing, high-temperature normalizing, and high-temperature tempering. This method optimizes the post-forging heat treatment, eliminating the quenching step in the quenching and tempering heat treatment, while ensuring that the roll neck hardness and various mechanical properties meet technical requirements.

[0006] However, this method still has the following problems: (1) Although the quenching treatment is omitted, the total heat treatment time is greatly increased; (2) Due to the omission of the quenching treatment, the roll neck hardness is only about 40HSD, and the treatment effect is not good. Summary of the Invention

[0007] The object of the present invention is to solve the above-mentioned problems and to provide a method for quenching and surface strengthening the roll neck of a large forged steel backup roll that can not only solve the problems of high cost, high pollution and low efficiency of the existing tempering heat treatment, but also shorten the total heat treatment time and, in particular, achieve higher roll neck hardness after treatment.

[0008] The technical solution for achieving the purpose of the present invention is: a method for quenching and surface strengthening the roll neck of a large forged steel support roll, comprising high-temperature normalizing → high-temperature tempering → rough machining → roll neck quenching → tempering after quenching; the heating method for the roll neck quenching is flame heating, the quenching heating temperature is 700-900°C, and water spray cooling is performed simultaneously with quenching heating.

[0009] During the roller neck quenching heating process, the heating device is moved between the roller neck end face and the roller body roller neck joint to ensure that the entire bearing stop roller neck is fully heated, and the moving speed is 20 to 60 mm / min.

[0010] The high-temperature normalizing process is as follows: the large forged steel backup roll forging is first kept at a temperature of 250-350°C for 1.0-2.0 min / mm, then heated to 600-800°C at a rate of ≤60°C / h and kept at this temperature for 0.5-1.0 min / mm, then heated to 850-980°C at a rate of ≤60°C / h and kept at this temperature for 1.0-2.0 min / mm, and finally air-cooled to 200-300°C.

[0011] The high temperature tempering is to first keep the large forged steel support roll forgings after high temperature normalizing at a temperature of 200-300°C for 0.5-1.0 min / mm, then heat it to 500-650°C at a rate of ≤60°C / h, and keep it at this temperature for 3.0-4.0 min / mm, and finally cool it to 200-300°C in the furnace, take it out of the furnace, and air cool it to room temperature.

[0012] The post-quenching tempering is to first heat the large forged steel support roll forging after roll neck quenching to 100-300°C, and keep it at this temperature for 1-3 hours, then heat it to 560-610°C at a rate of ≤60°C / h, and keep it at this temperature for 1.0-2.0min / mm, and finally cool it to 200-300°C in the furnace, take it out of the furnace, and air-cool it to room temperature.

[0013] The unit of mm in the above-mentioned holding time is the diameter of the support roll.

[0014] The present invention has the following positive effects: the method of the present invention adopts conventional post-forging heat treatment (high-temperature normalizing + high-temperature tempering) combined with roll neck quenching + water spray cooling process. Compared with the conventional support roll preparatory heat treatment process, this method not only reduces the pollution during tempering with quenching oil as the medium and the damage to the physical and mental health of workers, but also reduces the problems of low production efficiency and unqualified product quality during spray tempering; compared with the preparatory heat treatment process of document CN116970789A, this method greatly shortens the total heat treatment time, and can ensure that the roll neck hardness reaches about 45HSD, with better treatment effect. DETAILED DESCRIPTION

[0015] (Example 1) The chemical composition of the large forged steel backup roller of this embodiment is as follows: carbon 0.52%, silicon 0.53%, manganese 0.55%, chromium 5.10%, nickel 0.45%, molybdenum 0.52%, vanadium 0.11%, phosphorus 0.014%, sulfur 0.008%, and the remainder is iron and unavoidable impurities.

[0016] The specifications of the large forged steel support rollers of this embodiment are as follows: Φ1200mm×3880mm.

[0017] The method for quenching and surface strengthening the roll neck of a large forged steel backup roll of this embodiment comprises the following steps: ① High temperature normalizing: The large forged steel support roller forgings are first kept at a temperature of 300±10℃ for 30h, then quickly heated to 700±10℃ and kept at this temperature for 15h, then heated to 900±10℃ at a rate of ≤60℃ / h, kept at this temperature for 30h, and finally air-cooled to 250±10℃.

[0018] ② High temperature tempering: The large forged steel support roller forgings after high temperature normalizing in step ① are first kept at a temperature of 250±10℃ for 15h, then heated to 580±10℃ at a rate of ≤60℃ / h and kept at this temperature for 70h. Finally, the forgings are furnace cooled to 250±10℃, taken out of the furnace, and air cooled to room temperature.

[0019] ③ Rough machining: According to the rough machining requirements of the product, the roll body and roll neck of the large forged steel support roll forging after high-temperature tempering in step ② are machined to the requirements of the drawing. Among them, the outer contour of the bearing roll neck imitates the contour of the finished product and retains a machining allowance of ≤5mm.

[0020] ④ Roller neck quenching: Use flame heating to quench the roll neck of the large forged steel support roll after rough processing in step ③. The quenching heating temperature is 800±10℃, and water spray cooling is performed at the same time.

[0021] During the roller neck quenching heating process, the mobile quenching heating device ensures that the bearing roller neck (between the roller neck end face and the roller body and roller neck junction) is fully heated, and the moving speed is controlled at 40mm / min.

[0022] ⑤ Tempering after quenching: Heat the large forged steel support roll forgings after the roll neck quenching in step ④ to 200±10℃ and keep it at this temperature for 2h, then heat it to 580±10℃ at a rate of ≤60℃ / h and keep it at this temperature for 30h, finally cool it to 250±10℃ in the furnace, take it out of the furnace, and air cool it to room temperature.

[0023] After the roll neck quenching surface strengthening method of this embodiment, the large forged steel backup roll forging can obtain a tempered martensite structure, the roll neck hardness reaches about 45HSD, and the other performance indicators meet the technical requirements, as shown in Table 1.

[0024] (Example 2-Example 3) The methods for quenching and surface strengthening the roll necks of large forged steel backup rolls in Examples 2 and 3 are substantially the same as those in Example 1, with the difference being the process parameters, as shown in Table 1.

[0025] Table 1 Example 1 Example 2 Example 3 Step ① High temperature normalizing temperature 900±10℃ 930±10℃ 870±10℃ Step ① High temperature normalizing time 30h 27h 33h Step ② High temperature tempering temperature 580±10℃ 620±10℃ 540±10℃ Step ② High temperature tempering time 70h 60h 80h Step ④ Quenching heating temperature 800±10℃ 770±10℃ 830±10℃ Step 5: High temperature tempering temperature 580±10℃ 620±10℃ 540±10℃ Step 5: High temperature tempering time 30h 25h 35h Roll neck hardness / HSD 45 44 46 Yield strength Rp0.2 / MPa 880 887 876 Tensile strength Rm / MPa 990 995 985 Elongation after break / A(%) 15 15 16 Sectional shrinkage / Z(%) 45 46 45 Impact energy AKu / J 21 / 19 / 22 22 / 20 / 23 23 / 21 / 23

[0026] (Example 4-Example 5) The roll neck quenching surface strengthening method of the large forged steel backup rolls in Examples 4 and 5 is the same as that in Example 1, except that the chemical composition of the large forged steel backup rolls is shown in Table 2.

[0027] Table 2 Example 1 Example 4 Example 5 carbon 0.52% 0.49% 0.57% silicon 0.53% 0.50% 0.58% manganese 0.55% 0.52% 0.60% chromium 5.10% 4.92% 5.27% nickel 0.45% 0.48% 0.42% molybdenum 0.52% 0.55% 0.49% vanadium 0.11% 0.13% 0.10% phosphorus 0.014% 0.012% 0.016% sulfur 0.008% 0.006% 0.010% Roll neck hardness / HSD 45 45 46 Yield strength Rp0.2 / MPa 880 882 878 Tensile strength Rm / MPa 990 992 983 Elongation after break / A(%) 15 14 16 Sectional shrinkage / Z(%) 45 44 46 Impact energy AKu / J 21 / 19 / 22 20 / 18 / 21 21 / 18 / 21

Claims

1. A method for quenching and surface strengthening of a large forged steel backup roll neck, characterized in that: The process includes high-temperature normalizing → high-temperature tempering → rough machining → roll neck quenching → tempering after quenching. The roll neck quenching is performed by flame heating at a quenching temperature of 700-900°C, and water spray cooling is performed simultaneously with the quenching heating.

2. The method for quenching and surface strengthening of a large forged steel backup roll neck according to claim 1, characterized in that: During the roller neck quenching heating process, the heating device is moved between the roller neck end face and the roller body roller neck joint to ensure that the entire bearing stop roller neck is fully heated, and the moving speed is 20 to 60 mm / min.

3. The method for quenching and surface strengthening of a large forged steel backup roll neck according to claim 1 or 2, characterized in that: The high-temperature normalizing process is as follows: the large forged steel backup roll forging is first kept at a temperature of 250-350°C for 1.0-2.0 min / mm, then heated to 600-800°C at a rate of ≤60°C / h and kept at this temperature for 0.5-1.0 min / mm, then heated to 850-980°C at a rate of ≤60°C / h and kept at this temperature for 1.0-2.0 min / mm, and finally air-cooled to 200-300°C.

4. The method for quenching and surface strengthening of a large forged steel backup roll neck according to claim 1 or 2, characterized in that: The high temperature tempering is to first keep the large forged steel support roll forgings after high temperature normalizing at a temperature of 200-300°C for 0.5-1.0 min / mm, then heat it to 500-650°C at a rate of ≤60°C / h, and keep it at this temperature for 3.0-4.0 min / mm, and finally cool it to 200-300°C in the furnace, take it out of the furnace, and air cool it to room temperature.

5. The method for quenching and surface strengthening of a large forged steel backup roll neck according to claim 1 or 2, characterized in that: The post-quenching tempering is to first heat the large forged steel support roll forging after roll neck quenching to 100-300°C, and keep it at this temperature for 1-3 hours, then heat it to 560-610°C at a rate of ≤60°C / h, and keep it at this temperature for 1.0-2.0min / mm, and finally cool it to 200-300°C in the furnace, take it out of the furnace, and air-cool it to room temperature.