45 steel is a medium carbon steel widely used in industrial production. Its name comes from its average carbon content of about 0.45%. This compositional feature gives it a good balance of strength, hardness and processing performance, making it an important material in many fields.

Chemical Composition Of 45 Steel

Chemical composition is the basis of 45 steel performance. It is mainly composed of iron, accounting for about 97% of the total, and the rest are various alloying elements and impurities.

The carbon content is between 0.42%-0.50%, which is the key factor determining the properties of carbon steel. The silicon content is 0.17%-0.37%, which can improve the strength and hardness of steel composite plates. The manganese content is in the range of 0.50%-0.80%, which helps to enhance the hardenability and strength of steel.

In terms of impurity control, the phosphorus content is required to be less than 0.035%, the sulfur content is less than 0.04%, and the nickel, chromium, and copper contents are all controlled below 0.25% to avoid adverse effects on the performance of carbon steel plates. For high-quality and super-high-quality 45 steel varieties (such as 45A, 45E), the control of phosphorus and sulfur is more stringent, with phosphorus content as low as 0.025% and sulfur content as low as 0.020%.

Mechanical Properties

The mechanical properties of 45 steel reflect its ability to withstand external forces during use. After proper heat treatment, its tensile strength can reach at least 600MPa, ensuring that it is not easy to break when subjected to tension. The yield strength is not less than 355MPa, which means that it can maintain its shape without permanent deformation under a certain load.

In terms of plasticity, the elongation is 16% and the cross-sectional shrinkage is 40%, indicating that 45 steel has a certain deformation ability before breaking, which can avoid sudden brittle fracture. The impact energy is 35J, showing a certain toughness to resist impact loads.

In terms of hardness, the delivery hardness of the hot-rolled state does not exceed 229HB, and the annealed state does not exceed 197HB, which provides favorable conditions for subsequent processing.

Heat Treatment And Processing

Heat treatment is an important means to adjust the properties of 45 steel. Annealing usually heats the steel to 820-840℃ and then slowly cools it, which can reduce the hardness and improve the processing performance. Normalizing is heating to 850-870℃ and then air cooling, which can refine the grain structure and improve strength and toughness.

Quenching and tempering is a common combination process. Quenching heats the steel to 820-860℃ and then water quenches or oil quenches, which can significantly increase the hardness to more than 50HRC. Tempering is carried out by heating to 150-600℃ after quenching. When tempering at 500-560℃, the hardness can be adjusted to 25-33HRC, achieving a good balance of strength, plasticity and toughness.

In terms of processing performance, the cutting performance of 45 steel is good in the unheat-treated state, but the hardness increases after heat treatment, and the cutting difficulty increases. It has good forging performance and is suitable for hot forging. However, the welding performance is poor. It needs to be preheated to 200-300℃ before welding and annealed after welding to avoid cracks in the weld and heat-affected zone.

Comparison With Similar Steels

45 Steel Vs. 40Cr

40Cr is an alloy structural steel containing 0.8%-1.1% chromium, with a tensile strength of 1000MPa and a yield strength of 800MPa, which are significantly higher than 45 steel. 40Cr has better hardenability and comprehensive mechanical properties, and is suitable for parts that bear greater forces, while 45 steel is more economical and is used for general mechanical parts.

45 Steel Vs. 42Crmo

42CrMo contains chromium (0.9%-1.2%) and molybdenum (0.15%-0.25%), with a tensile strength of 1100MPa and a yield strength of 950MPa, and its performance is better than 45 steel. It has better high temperature strength and fatigue resistance, and is suitable for high reliability and heavy load parts, while 45 steel has more cost advantages in ordinary load situations.

45 Steel Vs. Q235

Q235 carbon steel plate is a low-carbon steel with a carbon content of less than 0.20%. The yield strength is 235MPa, which is lower than 45 steel, but has good plasticity and welding properties. Q235 is mainly used for structural parts such as steel pipes and profiles, while 45 steel is more used for mechanical parts that require certain wear resistance and strength due to its higher strength and hardness.

Applications Of 45 Steel

With good comprehensive performance and economy, 45 steel is widely used in machinery manufacturing, construction, tool manufacturing and other fields. In machinery manufacturing, it is used to produce various parts such as shafts, gears, pins, connecting rods, nuts, bolts, etc. These parts can obtain suitable strength and toughness after heat treatment to meet the needs of transmission and connection.

In the field of tools, tools such as knives, gauges, and molds can be made, relying on a certain hardness and wear resistance after heat treatment. In the field of construction, building structural parts and brackets can be manufactured to play a supporting and fixing role. In addition, after surface carburizing and quenching, it can replace carburizing steel to make gears, shafts and other parts that require surface quenching to improve the surface hardness.

Equivalent Grades In Other Standards

45 steel has corresponding equivalent grades in various international standards. The Japanese JIS standard is S45C and S48C; the German DIN standard corresponds to material number 1.0503 and grades such as C45 and Ck45; the British BS standard is IC45 and 080A47; the Italian UNI standard is C45; the Spanish standard is F.114; and the American AISI/SAE standard is 1045.

The International Organization for Standardization (ISO) standard is C45E4. These equivalent grades are similar to 45 steel in chemical composition and mechanical properties, which facilitates international material selection and application.

Advantages And Limitations

The advantages of 45 carbon steel composite plate are significant. It has high strength and hardness, which can meet the use requirements of many mechanical parts. After heat treatment, the performance adjustment range is wide and can adapt to different working conditions. It has good cutting and forging performance and is easy to process and shape. It is relatively cheap and has sufficient material sources, making it an economical engineering material.

However, 45 steel plate also has limitations. It has low toughness and is easy to break under impact load. It has poor welding performance and requires preheating and post-weld heat treatment, which increases the complexity of the welding process. In addition, the hardenability is not ideal, and it is difficult to obtain uniform hardness for large-section parts. After quenching and tempering, the surface hardness is low and not wear-resistant. If necessary, surface quenching and other processes are required to improve the surface performance.

Conclusion

As a commonly used medium carbon steel, 45 steel has been widely used in machinery manufacturing, construction, tool manufacturing and other fields due to its suitable chemical composition, good mechanical properties, various heat treatment methods and economic advantages. Understanding its chemical composition, mechanical properties, heat treatment process and comparison with similar steels can better select 45 steel.

Although there are certain limitations in toughness, welding performance and hardenability, through reasonable process control and performance improvement measures, 45 steel will continue to play an important role in industrial production and provide reliable material support for various engineering projects and mechanical products.