一.18CrNiMo7-6 is a low alloy high strength steel, especially suitable for the manufacture of transmission gear and shaft components requiring high strength and high wear resistance. This kind of steel is widely used in the manufacture of rail train gears, mainly due to its excellent mechanical properties and processing characteristics. According to EN 10084, 18CrNiMo7-6 has excellent chemical composition and mechanical properties, which makes it an ideal material for the manufacture of rail train gears.
二. chemical composition
The chemical composition of 18CrNiMo7-6 complies with EN 10084, as follows:
1. Carbon (C)
Carbon is one of the most important alloying elements in steel and has a significant impact on the hardness and strength of steel. The carbon content of 18CrNiMo7-6 is in the range of 0.15-0.21%, providing good hardness and strength. An increase in carbon generally increases the hardness of steel, but may also reduce its plasticity. Therefore, in 18CrNiMo7-6, the carbon content is controlled in a balanced range to ensure that good plasticity and toughness are maintained while providing the necessary hardness.
2. Silicon (Si)
The main role of silicon is to remove impurities in the steel, while improving the strength and hardness of the steel. The silicon content of 18CrNiMo7-6 does not exceed 0.4%, which is enough to improve the deoxidation capacity of steel, but does not affect the plasticity and processing properties of the material too much. The presence of silicon contributes to the overall stability of the steel.
3. Manganese (Mn)
Manganese helps to improve the hardness and strength of steel and improve its processability. The manganese content of 18CrNiMo7-6 is 0.5-0.9%, which helps to improve the strength of the steel while making it show good machinability during processing. The presence of manganese is very important for improving the wear resistance of steel and improving its load-bearing capacity.
4. Phosphorus (P) and sulfur (S)
Phosphorus and sulfur are generally considered to be harmful impurities in steel, and excessive phosphorus and sulfur will reduce the toughness and plasticity of steel. The phosphorus and sulfur content of 18CrNiMo7-6 is strictly controlled within a maximum range of 0.035%, ensuring that the toughness and strength of the material are not negatively affected.
5. Chromium (Cr)
Chromium is a key element to improve the wear resistance and hardness of steel. The chromium content of 18CrNiMo7-6 is 1.5-1.8%, which helps to form a hardened layer and improve the oxidation resistance of the steel. The addition of chromium makes 18CrNiMo7-6 exhibit excellent wear resistance in gear manufacturing, maintaining stable performance even under high load and high speed working environments.
6 .molybdenum (Mo)
The role of molybdenum is to further improve the hardness and wear resistance of steel, and improve the hardenability of steel. The molybdenum content in 18CrNiMo7-6 is 0.25-0.35%, and this content helps to form a uniform hardness distribution during the quenching process, ensuring stable performance of the gear under high loads.
7. Nickel (Ni)
The addition of nickel improves the toughness and strength of steel. The nickel content of 18CrNiMo7-6 is 1.4-1.7%, which makes the material exhibit excellent toughness when subjected to impact loads, preventing brittle fracture. Nickel also enhances the wear and impact resistance of the steel. 8. The content of oxygen (O2) and hydrogen (H2) impurities is controlled at a very low level, which helps to maintain the purity of the steel and avoid the performance decline caused by impurities. The content of oxygen and hydrogen has a certain effect on the mechanical properties of steel, and the lower content can reduce the brittleness of steel and improve its reliability.
8. The content of oxygen (O2) and hydrogen (H2)
impurities is controlled at a very low level, which helps to maintain the purity of the steel and avoid the performance decline caused by impurities. The content of oxygen and hydrogen has a certain effect on the mechanical properties of steel, and the lower content can reduce the brittleness of steel and improve its reliability.
三.Mechanical property
According to EN 10084, 18CrNiMo7-6 has the following mechanical properties:
Tensile strength: not less than 1080 MPa. Tensile strength is the maximum stress that a material can withstand in tensile test, and it is an important index to evaluate the strength of a material. For rail train gears, this high strength ensures that the gears can withstand the stresses in high-load operating environments without breaking or deforming.
Yield strength: 785 MPa. The yield strength is the stress value of the material at the beginning of permanent deformation, reflecting the strength limit of the material. The high yield strength indicates that the material can maintain its shape and function under high loads, avoiding degradation due to deformation.
Elongation (A5) : not less than 8%. Elongation is an important index to measure the plasticity of a material, indicating the degree of extension of the material in the tensile test. The higher elongation means that the material can undergo moderate deformation without brittle breakage when subjected to external forces, which is essential for the safety of gear use.
Section shrinkage (Z) : not less than 35%. The section shrinkage reflects the plastic deformation ability of the material, and the higher section shrinkage indicates that the material has good toughness and impact resistance. This is necessary to withstand the impact and vibration generated during the operation of rail trains.
These mechanical properties make 18CrNiMo7-6 exhibit excellent performance in high load and high speed working environments, and can meet the requirements of strength, toughness and wear resistance of rail train gears. Fourth, why choose 18CrNiMo7-6 for rail train gear
四. why choose 18CrNiMo7-6 for rail train gear
1. High strength and wear resistance 18CrNiMo7-6 is widely used in manufacturing gears because of its high strength and wear resistance. Its main alloying elements such as chromium, molybdenum and nickel, through a suitable heat treatment process (such as carburizing treatment), the formation of a hardened layer on the surface of the gear, thus significantly improving the surface hardness and wear resistance of the gear. According to ISO 6336, high hardness gear surfaces can effectively reduce friction and wear and extend the service life of the gear. Specifically, the carburizing treatment can form a hardened layer on the surface of the gear, and the hardness can reach HRC 58-62, while the core part maintains a relatively low hardness to ensure its toughness and load-bearing capacity. This hardened layer can effectively resist wear under high loads and high speeds, reduce gear wear and replacement frequency, and improve operating efficiency.
2. Good hardenability 18CrNiMo7-6 has excellent hardenability, which means that it can maintain a uniform hardness during the quenching process. This characteristic allows the gear to maintain stable performance under high loads. According to ASTM A255 standard, the hardenability test can evaluate the hardness distribution of the material at different depths, for 18CrNiMo7-6, its excellent hardenability ensures that the ideal hardness can be obtained in the thickness range of the entire gear, preventing the failure of the gear caused by local uneven hardness.
3. High toughness High toughness makes 18CrNiMo7-6 able to withstand large impact loads without brittle fracture. According to ISO 148, the toughness test assesses the performance of the material in impact tests. 18CrNiMo7-6 has a high elongation and section shrinkage rate, which means that it can withstand the impact of moderate deformation, without breaking, which is particularly important for rail train gear in actual use to withstand the impact from the track and wheels.
4. Excellent processing performance 18CrNiMo7-6 after quenching, although the hardness is higher, but its processing performance is still good. Especially in the grinding process, the machinability of the material directly affects the manufacturing accuracy and consistency of the gear. Good processing performance can reduce the waste and processing difficulty in the production process, ensure the high precision and stability of the gear, thus improving the production efficiency.
5. Standardization requirements 18CrNiMo7-6 comply with EN
The 10084 standard provides manufacturers with clear benchmarks for quality and performance. Standardization requirements ensure the stability of the production process and help maintain the consistency and reliability of the product. This standardization makes 18CrNiMo7-6 have a high degree of recognition and applicability in the world, and provides a solid guarantee for the safe and stable operation of rail trains.