1. Introduction
In the machinery manufacturing industry, gear forgings play a crucial role in power transmission systems. Among them, 30Cr2Ni4MoV steel is widely used due to its excellent mechanical properties. This article focuses on in – depth research into the manufacturing process of 30Cr2Ni4MoV gear forgings, aiming to optimize the process and improve the quality of forgings.
1.1 Background and Significance
The development of modern industry has put forward higher requirements for the performance of mechanical components. Gear forgings, as key parts in power transmission, need to have high strength, good toughness, and wear – resistance. 30Cr2Ni4MoV steel, with its unique chemical composition and heat treatment characteristics, can meet these requirements to a certain extent. By studying its manufacturing process, we can not only improve the performance of gear forgings but also reduce production costs and enhance the competitiveness of products in the market.
1.2 Research Objectives
The main objectives of this research are as follows:
- To optimize the chemical element ratio of 30Cr2Ni4MoV steel ingots to improve the material’s performance.
- To explore the optimal hot – forming method for gear forgings to ensure good internal structure and mechanical properties.
- To determine the appropriate quenching and tempering heat treatment system to enhance the comprehensive mechanical properties of forgings.
- To analyze the microstructure and mechanical properties of forgings after processing to evaluate the effectiveness of the manufacturing process.
2. Overview of 30Cr2Ni4MoV Steel
2.1 Chemical Composition and Classification
30Cr2Ni4MoV is an alloy quenched and tempered steel. Its carbon content is generally in the range of 0.3% – 0.6%, belonging to medium – carbon steel. Table 1 shows its chemical composition requirements and typical analysis results.
| Element | C | Si | Mn | S | P | Cr | Ni | Mo | V |
|---|---|---|---|---|---|---|---|---|---|
| Composition Requirements (wt%) | ≤0.35 | 0.18 – 0.35 | 0.20 – 0.40 | ≤0.020 | ≤0.015 | 1.55 – 2.05 | 3.25 – 3.75 | 0.30 – 0.60 | 0.07 – 0.16 |
| Typical Analysis Results (wt%) | 0.32 | 0.21 | 0.38 | 0.007 | 0.008 | 2.01 | 3.69 | 0.57 | 0.14 |
| This steel contains multiple alloying elements such as Cr, Ni, Mo, and V. These alloying elements play important roles in improving the hardenability, strength, and toughness of the steel. |
2.2 Mechanical Properties and Characteristics
After quenching and tempering treatment, 30Cr2Ni4MoV steel has excellent comprehensive mechanical properties. It has high strength, good plasticity, and toughness. Table 2 shows the mechanical properties of 30Cr2Ni4MoV steel after quenching and tempering.
| Sampling Direction | Rm (MPa) | Rp0.2 (MPa) | A (%) | Z (%) | Akv (J) |
|---|---|---|---|---|---|
| Tangential | 1020 | 960 | 18 | 63 | 97, 98, 98 |
| Transverse Required Value | ≥940 | ≥870 | ≥13 | ≥34 | ≥60 |
| The high hardenability of 30Cr2Ni4MoV steel allows it to obtain a homogeneous microstructure of tempered sorbite after heat treatment, which contributes to its excellent mechanical properties. |
2.3 Application Fields
30Cr2Ni4MoV steel is widely used in various fields. In the power generation industry, it is used to manufacture large – scale turbine rotors and generator shafts. In the heavy – machinery industry, it is applied to produce gears, axles, and other key components that bear high loads. In the automotive industry, it can be used for manufacturing some high – strength and high – performance parts.
3. Manufacturing Process of 30Cr2Ni4MoV Gear Forgings
3.1 Steel Ingot Melting
3.1.1 Selection of Steel Ingot and Refining Method
The gear forgings in this study use 6T VOD – refined steel ingots. The VOD (Vacuum Oxygen Decarburization) refining method can effectively remove harmful impurities and gases in the steel, improving the purity of the steel. Since 30Cr2Ni4MoV steel contains multiple alloying elements with a complex composition, and gear forgings have high requirements for strength and toughness, strict control of the chemical composition during steel ingot melting is necessary.
3.1.2 Optimization of Chemical Composition
During the melting process of steel ingots, the chemical composition needs to be optimized. Considering the high – strength requirements of gear forgings, the content of alloying elements such as Cr and V should be at the upper limit of the specified range. In addition, due to the harsh working environment of gear forgings, the content of Ni and Mo elements is increased to improve the corrosion resistance of the material. Table 3 shows the comparison of chemical compositions before and after optimization.
| Element | Before Optimization (wt%) | After Optimization (wt%) |
|---|---|---|
| C | 0.30 | 0.32 |
| Si | 0.20 | 0.21 |
| Mn | 0.30 | 0.38 |
| S | ≤0.020 | 0.007 |
| P | ≤0.015 | 0.008 |
| Cr | 1.60 | 2.01 |
| Ni | 3.30 | 3.69 |
| Mo | 0.40 | 0.57 |
| V | 0.10 | 0.14 |
| The optimized chemical composition can improve the mechanical properties and service performance of the steel. After the composition optimization, the 6T VOD – refined steel ingot is forged into a billet by a 5000T oil press. The initial forging temperature is controlled in the range of 1185℃ ± 15℃, and after the 3000 – ton oil press forms the billet, it is pre – treated by normalizing at 900℃ × 6H. |
3.2 Forging Process of Forgings
3.2.1 Forging Equipment and Process Control
The gear forgings are forged on a 3000 – ton oil press. Due to the large size of the forgings, strict control of the forging process is required. The initial forging temperature is set at 1185℃, and the final forging temperature is 800℃. The forging ratio of each heating cycle also needs to be controlled. Before forging, the steel ingot is heated to 1185℃ in an electric heating furnace and kept warm for 6 – 7 hours. It is pre – heated appropriately and then heated to a high temperature for forging. Figure 1 shows the heating process of the steel ingot.
[Insert a picture of the steel ingot heating process here, with temperature on the y – axis and time on the x – axis, showing the pre – heating, heating, and holding stages]
3.2.2 Forging Steps and Shaping
The steel ingot is first forged into a blank on a 3000 – ton oil press, with dimensions of 650 square × 1520 × 2 pieces, as shown in Figure 2. Then, it is formed and finished. After forging, due to the high alloy content of the steel, it needs to be rough – machined before quenching and tempering heat treatment. Figure 3 shows the forging diagram, and Figure 4 shows the rough – turned forging diagram.
[Insert pictures of the blanking diagram, forging diagram, and rough – turned forging diagram here]
3.3 Quenching and Tempering Heat Treatment of Forgings
3.3.1 Heat Treatment Process Parameters
The heat treatment process of forgings is shown in Figure 5. First, the forging is heated to 870℃ – 890℃ at a heating rate of less than 400℃/h, held for 5h + 1h, and then cooled in water. Then, it is reheated to 580℃ – 600℃ at a heating rate of less than 300℃/h, held for 12h + 1h, and finally cooled in the air.
[Insert a picture of the forging quenching and tempering heat treatment process here, with temperature on the y – axis and time on the x – axis, clearly showing the heating, holding, and cooling stages]
3.3.2 Influence of Heat Treatment on Microstructure and Properties
The quenching and tempering heat treatment can significantly affect the microstructure and properties of 30Cr2Ni4MoV gear forgings. After heat treatment, the microstructure of the forging is tempered sorbite, which has high strength and toughness. This microstructure can improve the service performance of gear – type components. The heat treatment process can also refine the grains of the steel, improving its mechanical properties.
4. Physical and Chemical Testing of Forging Products
4.1 Sampling and Testing Methods
After the forging is heat – treated, test rings are cut from the forging. The sampling position is at the outer – circle end face of the disc – shaped forging, as shown in Figure 6. The 金相试样规格采用 15 × 15 × 15, and the tensile test specimens are 10 – mm – diameter test bars with a gauge length of 50 mm. The impact test specimens are Charpy V – notch specimens. A Nikon LV150N microscope is used to observe the material structure, a WDW – 100D mechanical property tensile testing machine is used for tensile tests, and a JB – 300B Charpy impact testing machine is used for impact tests.
[Insert a picture of the forging specimen sampling position here]
4.2 Test Results and Analysis
Figure 7 shows the micro – structure photo of the forging after quenching and tempering heat treatment. It can be clearly seen that the microstructure is tempered sorbite. Table 4 shows the mechanical properties of the gear forging after quenching and tempering. The results show that the room – temperature mechanical tensile and impact toughness of the forging fully meet the product’s technical indicators, and the tensile and impact margins are large, indicating that the material’s basic mechanical properties are uniform and stable.
| Sampling Direction | Rm (MPa) | Rp0.2 (MPa) | A (%) | Z (%) | Akv (J) |
|---|---|---|---|---|---|
| Tangential | 1020 | 960 | 18 | 63 | 97, 98, 98 |
| Transverse Required Value | ≥940 | ≥870 | ≥13 | ≥34 | ≥60 |
| The uniform microstructure and excellent mechanical properties are the results of the optimized manufacturing process, including the optimization of the chemical composition of the steel ingot, the control of the forging process, and the appropriate heat treatment system. |
5. Optimization and Improvement of the Manufacturing Process
5.1 Analysis of Process Defects
During the manufacturing process of 30Cr2Ni4MoV gear forgings, some potential problems may occur. For example, if the forging temperature is not properly controlled, it may lead to uneven grain size, affecting the mechanical properties of the forging. In addition, if the heat treatment process parameters are not accurate, it may cause insufficient hardness or poor toughness.
5.2 Optimization Measures
To solve these problems, the following optimization measures can be taken:
- Further improve the accuracy of temperature control during the forging process. For example, use advanced temperature – measuring equipment and control systems to ensure that the initial and final forging temperatures are within the specified range.
- Optimize the heat treatment process parameters according to the actual situation of the forging. Through more experiments and simulations, determine the best heating rate, holding time, and cooling method to obtain the best microstructure and mechanical properties.
- Strengthen the quality inspection during the manufacturing process. Increase the frequency of sampling and testing to timely detect and correct problems in the manufacturing process.
6. Conclusion
In this study, the manufacturing process of 30Cr2Ni4MoV gear forgings was comprehensively studied. Through the optimization of the chemical element ratio of steel ingots, the improvement of the hot – forming method, and the determination of the appropriate quenching and tempering heat treatment system, the performance of 30Cr2Ni4MoV gear forgings was significantly improved. The optimized manufacturing process can make the forging’s mechanical properties fully meet the technical requirements, and the mechanical strength, plasticity, and impact toughness have large margins. The microstructure of the forging is uniform, which improves the comprehensive mechanical properties of the product, enhances the service safety, and extends the service life. This research also provides technical data and reference for the manufacturing process of similar materials. Future research can focus on further improving the manufacturing process, reducing production costs, and exploring new applications of 30Cr2Ni4MoV steel.
