High performance forged extruder rotor material and heat treatment process

Abstract

This invention relates to a high-performance forged extruder rotor material and heat treatment process. The rotor material is medium-carbon chromium-molybdenum steel, to which 0.04–0.08% vanadium is added by mass percentage. Specifically, the rotor material comprises the following chemical composition by mass percentage: C: 0.37–0.45%; Si: 0.17–0.37%; Mn: 0.60–0.90%; Cr: 1.40–1.70%; Mo: 0.40–0.70%; V: 0.04–0.0%. 8%; P:≤0.010%; S:≤0.005%; Al:0.020~0.040%; balance is iron. The process route is: normalizing after forging + annealing → normalizing + quenching and tempering. This material has a high chromium and molybdenum content, high hardenability, and the high molybdenum content can prevent the agglomeration of impurity elements, effectively reduce temper brittleness, and maintain high tempering stability and high temperature strength. Vanadium plays a role in refining grains and improving the tempering stability of the material. After quenching and tempering, this steel has high strength and high impact performance.

Description

Technical Field

[0001] This invention belongs to the field of extruder rotor material production technology, specifically relating to a high-performance forged extruder rotor material and its heat treatment process. Background Technology

[0002] The rotor is an indispensable and crucial component of extrusion equipment. In recent years, with the advancement of technology and the development of the rubber and plastics industry, extrusion equipment has trended towards larger sizes. Therefore, as a core component, the rotor must adapt to the requirements of larger extrusion machines, placing higher demands on its mechanical properties. The mechanical properties of conventional 38CrMoAl material cannot meet these requirements, making the design of new materials and heat treatment processes an urgent priority. Simultaneously, designing heat treatment processes specifically for new materials to fully exploit their potential can satisfy the design and usage requirements of the rotor. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for obtaining high-performance rotor materials, thereby improving the service life of the rotor and meeting the material and heat treatment process requirements of large-scale extruder rotors.

[0004] The objective of this invention is achieved as follows: A high-performance forged extruder rotor material, characterized in that: the rotor material is medium-carbon chromium-molybdenum steel, to which 0.04-0.08% vanadium is added by mass percentage, specifically comprising the following chemical composition by mass percentage: C: 0.37-0.45%; Si: 0.17-0.37%; Mn: 0.60-0.90%; Cr: 1.40-1.70%; Mo: 0.40-0.70%; V: 0.04-0.08%; P: ≤0.010%; S: ≤0.005%; Al: 0.020-0.040%; the balance being iron.

[0005] A heat treatment process for a high-performance forged extruder rotor material, wherein the rotor material undergoes normalizing + annealing after forging, and normalizing + quenching and tempering after rough machining, specifically carried out according to the following steps: Step 1) Select medium-carbon chromium-molybdenum steel as the material, and add 0.04-0.08% vanadium by mass percentage; the chemical composition by mass percentage includes the following: C: 0.37-0.45%; Si: 0.17-0.37%; Mn: 0.60-0.90%; Cr: 1.40-1.70%; Mo: 0.40-0.70%; V: 0.04-0.08%; P: ≤0.010%; S: ≤0.005%; Al: 0.020-0.040%; the balance is iron; Step 2) The heat treatment process after forging adopts normalizing + annealing: First, after forging, the material is held at 600℃~650℃ for waiting. After holding, it is air-cooled to 350℃~450℃, and the holding time is calculated at 1.2h / 100mm. Then, the temperature is raised to 870℃~890℃ at full power and held for 1.5h / 100mm. It is then air-cooled to 350℃~450℃ and held for 1.2h / 100mm. The temperature is raised to 640℃~660℃ at full power and held for 4h / 100mm. The temperature is then reduced to 400℃ at ≤40℃ / h and then reduced to ≤200℃ at ≤20℃ before being taken out of the furnace and air-cooled. Step 3) Normalizing: After completing Step 2), the forging is rough machined and then put into a normalizing furnace. It is heated to 630-670℃ at full power and held at that temperature. Then it is heated to 870-890℃ at full power and held at that temperature. After holding at that temperature, it is taken out of the furnace and air-cooled to room temperature. Step 4) Quenching: Place the forgings that have completed step 3) into the quenching furnace, heat them to 630-670℃ at full power and hold them, then heat them to the quenching temperature of 860-880℃ at full power and hold them. After holding, remove them from the furnace and quench them for cooling. The quenching medium is water or oil. Step 5) Performance tempering: The forgings from step 4) are placed in a tempering furnace at 590℃~630℃ for performance tempering, held for 3 hours / 100mm and then air-cooled.

[0006] In step 4), in order to obtain high performance, the cooling method after quenching is water quenching and oil cooling. The specific quenching cooling method includes the following steps: a) air cooling: ≤100S; b) water cooling: ≥2.5S / mm, where the initial water temperature is ≤30℃; c) oil cooling: ≥9S / mm, where the initial oil temperature is ≤70℃.

[0007] The beneficial effects of this invention are as follows: This invention provides a high-performance forged extruder rotor material and heat treatment process, which achieves a reasonable balance of strength and toughness while ensuring that the forging does not crack, thus meeting the design and usage requirements of the rotor material. The rotor material involved in this invention is medium-carbon chromium-molybdenum steel with 0.04-0.08% vanadium added. This material has a high chromium and molybdenum content, resulting in high hardenability. The high molybdenum content prevents the agglomeration of impurity elements, effectively reducing temper brittleness and maintaining high temper stability and high-temperature strength. The trace amount of vanadium refines the grain size and improves the temper stability of the material. After quenching and tempering, this steel exhibits high strength and high impact resistance, meeting the high-performance requirements of the material design. The chemical composition of the material is: C: 0.37-0.45%; Si: 0.17-0.37%; Mn: 0.60-0.90%; Cr: 1.40-1.70%; Mo: 0.40-0.70%; V: 0.04-0.08%; P: ≤0.010%; S: ≤0.005%; Al: 0.020-0.040%. With appropriate heat treatment design, the design and usage requirements of the rotor material are met.

[0008] The production process route of this invention is designed as follows: normalizing after forging + annealing → normalizing + quenching and tempering; the implementation of the technical solution mainly lies in the control of chemical composition design, post-forging heat treatment and final heat treatment process.

[0009] Design of heat treatment after forging: Due to the large size of the product and the large number of forging heats, the grains are coarse and there are many impurities after forging, which affects the accuracy of ultrasonic testing. Normalizing and annealing are adopted after forging to obtain a balanced structure of ferrite and carbides, refine the grains, improve the internal structure, eliminate forging stress and impurities, and prepare conditions for ultrasonic testing and subsequent quenching and tempering.

[0010] Final heat treatment design: Normalizing followed by quenching and tempering is employed. Normalizing further refines the grains, resulting in a fine and uniform ferrite + pearlite microstructure, preparing a suitable microstructure for the subsequent quenching and tempering process. Strong cooling is used for quenching to reduce retained austenite and increase the hardened layer depth, providing suitable microstructural conditions for high performance. Water and oil are selected as the quenching media, and water-quenching-oil-cooling is used to achieve a high hardened layer depth and low microstructural stress. Through normalizing and quenching and tempering, a fine-grained and uniform tempered sorbite microstructure is obtained.

[0011] Forgings produced using the process of this invention have a yield strength ≥750MPa, tensile strength ≥940MPa, average room temperature U-shaped impact energy greater than 113J, and actual grain size ≥7.5. Attached Figure Description

[0012] Figure 1 This is the post-forging heat treatment process of the present invention.

[0013] Figure 2This is the final heat treatment process of the present invention.

[0014] Figure 3 The metallographic structure and actual grain size of Example 1 are shown.

[0015] Figure 4 The metallographic structure and actual grain size of Example 2 are shown. Detailed Implementation

[0016] Example 1: The rotor material is medium carbon chromium-molybdenum steel with 0.04-0.08% vanadium added. The chemical composition of the material is C: 39%; Si: 0.27%; Mn: 0.79%; Cr: 1.55%; Mo: 0.54%; V: 0.06%; P: 0.009%; S: 0.002%; Al: 0.021%.

[0017] The forging specifications are: small step φ404mm, middle large step φ528mm.

[0018] Heat treatment includes the following steps: Step 1) Post-forging heat treatment using normalizing + annealing: After forging, the material is held at 600℃~650℃, then air-cooled to 400℃ and held for 6.5h. Then, the temperature is increased to 880℃ at full power and held for 8h, air-cooled to 390℃ and held for 6.5h, then increased to 650℃ at full power and held for 22h. The temperature is then decreased to 400℃ at 30℃ / h, and then decreased to 190℃ at 15℃ / h before being removed from the furnace and air-cooled. Normalizing + annealing refines the grains, eliminates forging stress, and removes impurities from the forging, preparing a suitable microstructure for subsequent quenching and tempering. Step 2) Normalizing: The forgings that have completed Step 1) are rough machined and then put into a normalizing furnace at a furnace temperature of 480℃ and held at 650℃ for 6.5 hours; then the temperature is raised to the normalizing temperature of 880℃ and held for 8 hours. After the holding period, the parts are taken out of the furnace and air cooled. The grains and microstructure are further refined by normalizing again. Step 3) Quenching: Place the forgings from Step 2) into a quenching furnace at an initial temperature of 450℃ and hold at 650℃ for 6.5 hours. Then raise the temperature to 870℃ and hold for 8 hours. After holding, remove the forgings from the furnace and quench them using water as the quenching medium. The quenching cooling methods are: a) air cooling: 90 seconds; b) water cooling: 22 minutes, with an initial water temperature of 25℃; c) oil cooling: 80 minutes, with an initial oil temperature of 40℃. Step 4) Performance tempering: The forgings from step 3) are placed in a tempering furnace and heated to 615°C. After holding at this temperature for 16 hours, they are removed from the furnace and air-cooled.

[0019] After normalizing to refine the microstructure and quenching for strong cooling, the martensitic transformation and decomposition of retained austenite were completed. Subsequent high-temperature tempering resulted in a fine-grained and uniform tempered sorbite microstructure, with mechanical properties meeting the application requirements. The mechanical properties of Example 1 are shown in the table below:

[0020] Example 2: The rotor material is medium carbon chromium-molybdenum steel with 0.04-0.08% vanadium added. The chemical composition of the material is C: 0.38%; Si: 0.25%; Mn: 0.79%; Cr: 1.57%; Mo: 0.52%; V: 0.07%; P: 0.08%; S: 0.002%; Al: 0.024%.

[0021] The forging specifications are: small step φ404mm, middle large step φ528mm.

[0022] Heat treatment includes the following steps: Step 1) Post-forging heat treatment adopts normalizing + annealing: After forging, the material is held at 600℃~650℃, then air-cooled to 380℃ and held for 6.5h. Then, the temperature is raised to 880℃ at full power and held for 8h. After air-cooling to 410℃ and held for 6.5h, the temperature is raised to 650℃ at full power and held for 22h. The temperature is then lowered to 400℃ at 25℃ / h and then lowered to 180℃ at 10℃ / h before being removed from the furnace and air-cooled. Through normalizing + annealing, the grains are refined, forging stress is eliminated, and impurities in the forging are eliminated, preparing a suitable microstructure for the subsequent quenching and tempering treatment.

[0023] Step 2) Normalizing: The forgings that have completed Step 1) are rough machined and then put into a normalizing furnace at a furnace temperature of 450℃ and held at 640℃ for 6.5 hours; then the temperature is raised to the normalizing temperature of 880℃ and held for 8 hours. After the holding period, the forgings are taken out of the furnace and air cooled. The grains and microstructure are further refined by normalizing again. Step 3) Quenching: Place the forgings from Step 2) into a quenching furnace at an initial temperature of 430℃ and hold at 660℃ for 6.5 hours. Then raise the temperature to quenching temperature of 870℃ and hold for 8 hours. After holding, remove the forgings from the furnace and quench them using water as the quenching medium. The quenching cooling methods are as follows: a) Air cooling: 80 seconds; b) Water cooling: 23 minutes, with an initial water temperature of 26℃; c) Oil cooling: 81 minutes, with an initial oil temperature of 35℃.

[0024] Step 4) Performance tempering: The forgings from step 3) are placed in a tempering furnace and heated to 620°C. After holding at this temperature for 16 hours, they are removed from the furnace and air-cooled.

[0025] After normalizing to refine the microstructure and quenching for strong cooling, the martensitic transformation and decomposition of retained austenite were completed. Subsequent high-temperature tempering resulted in a fine-grained and uniform tempered sorbite microstructure, with mechanical properties meeting the application requirements. The mechanical properties of Example 1 are shown in the table below:

[0026] The mechanical properties of conventional 38CrMoAl material and those required by this patent are shown in the table below.

[0027] 38CrMoAl requirements ≥750 ≥920 ≥14 ≥40 The patent requires ≥700 ≥900 ≥14 ≥100

Claims

1. A high-performance forged extruder rotor material, characterized in that: The rotor material is medium-carbon chromium-molybdenum steel, with 0.04-0.08% vanadium added by mass percentage. Specifically, the chemical composition by mass percentage is as follows: C: 0.37-0.45%; Si: 0.17-0.37%; Mn: 0.60-0.90%; Cr: 1.40-1.70%; Mo: 0.40-0.70%; V: 0.04-0.08%; P: ≤0.010%; S: ≤0.005%; Al: 0.020-0.040%; the balance is iron.

2. A heat treatment process for a high-performance forged extruder rotor material, characterized in that: After forging, the rotor material undergoes normalizing and annealing treatment, followed by normalizing and quenching and tempering treatment after rough machining. The specific steps are as follows: Step 1) Select medium-carbon chromium-molybdenum steel as the material, and add 0.04-0.08% vanadium by mass percentage; the chemical composition by mass percentage includes the following: C: 0.37-0.45%; Si: 0.17-0.37%; Mn: 0.60-0.90%; Cr: 1.40-1.70%; Mo: 0.40-0.70%; V: 0.04-0.08%; P: ≤0.010%; S: ≤0.005%; Al: 0.020-0.040%; the balance is iron; Step 2) The heat treatment process after forging adopts normalizing + annealing: First, after forging, the material is held at 600℃~650℃ for waiting. After holding, it is air-cooled to 350℃~450℃, and the holding time is calculated at 1.2h / 100mm. Then, the temperature is raised to 870℃~890℃ at full power and held for 1.5h / 100mm. It is then air-cooled to 350℃~450℃ and held for 1.2h / 100mm. The temperature is raised to 640℃~660℃ at full power and held for 4h / 100mm. The temperature is then reduced to 400℃ at ≤40℃ / h and then reduced to ≤200℃ at ≤20℃ before being taken out of the furnace and air-cooled. Step 3) Normalizing: After completing Step 2), the forging is rough machined. Before normalizing, the forging needs to be kept at a furnace temperature of ≤500℃. Then, it is put into the normalizing furnace and heated to 630~670℃ at full power and held for 1h / 100mm. Then, it is heated to 870℃~890℃ at full power and held for 1.5h / 100mm. After holding, it is taken out of the furnace and air-cooled to room temperature. Step 4) Quenching: Place the forgings that have completed step 3) into the quenching furnace. Before quenching, the forgings need to be kept at the furnace temperature ≤500℃. Then, heat the forgings to 630~670℃ at full power and hold for 1h / 100mm. Then, heat the forgings to quenching temperature 860℃~880℃ at full power and hold for 1.5h / 100mm. After holding, remove the forgings from the furnace and quench them. The quenching medium is water or oil. Step 5) Performance tempering: The forgings from step 4) are placed in a tempering furnace at 590℃~630℃ for performance tempering, held for 3 hours / 100mm and then air-cooled.

3. The heat treatment process for a high-performance forged extruder rotor material as described in claim 2, characterized in that: In step 4), in order to obtain higher strength and high impact performance, the quenching cooling method adopts water quenching and oil cooling. The specific quenching cooling method includes the following steps: a) air cooling: ≤100S; b) water cooling: ≥2.5S / mm, where the initial water temperature is ≤30℃; c) oil cooling: ≥9S / mm, where the initial oil temperature is ≤70℃.

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