Metric carbon steel rods are categorized based on their carbon content and mechanical properties. The primary grades include: 1. **C10 (1.0301)**: Low carbon steel with approximately 0.10% carbon content. It is soft, ductile, and easily machinable, suitable for forming and welding applications. 2. **C15 (1.0401)**: Slightly higher carbon content than C10, around 0.15%. It offers better strength while maintaining good ductility and weldability. 3. **C22 (1.0402)**: Contains about 0.22% carbon. It provides a balance between strength and ductility, often used in general engineering applications. 4. **C35 (1.0501)**: Medium carbon steel with approximately 0.35% carbon. It offers higher strength and hardness, suitable for parts requiring moderate wear resistance. 5. **C45 (1.0503)**: Contains around 0.45% carbon. Known for its good machinability and high strength, it is commonly used in shafts, gears, and bolts. 6. **C60 (1.0601)**: High carbon steel with about 0.60% carbon content. It provides high strength and hardness, used in applications requiring wear resistance, such as springs and cutting tools. 7. **C70 (1.0603)**: Contains approximately 0.70% carbon. It offers excellent hardness and wear resistance, suitable for high-stress applications like knives and blades. These grades are standardized under various international norms, such as DIN, EN, and ISO, ensuring consistency in mechanical properties and chemical composition. The choice of grade depends on the specific requirements of the application, including strength, ductility, machinability, and wear resistance.

The strength levels of metric carbon steel rods vary based on their grade, which is determined by the carbon content and other alloying elements. The most common grades include: 1. **Low Carbon Steel (Grades 4.6, 5.6):** These have a carbon content of up to 0.25%. They are relatively soft and ductile, making them easy to form and weld. The tensile strength ranges from 400 to 500 MPa, and the yield strength is between 240 to 300 MPa. 2. **Medium Carbon Steel (Grades 8.8, 10.9):** With a carbon content between 0.25% and 0.60%, these steels offer a balance of strength and ductility. They are often heat-treated to improve mechanical properties. The tensile strength ranges from 800 to 1000 MPa, and the yield strength is between 640 to 900 MPa. 3. **High Carbon Steel (Grade 12.9):** These contain more than 0.60% carbon, providing high strength and hardness but reduced ductility. They are used in applications requiring high wear resistance. The tensile strength is around 1200 MPa, and the yield strength is approximately 1080 MPa. The strength levels are also influenced by the presence of other elements like manganese, silicon, and chromium, which can enhance hardness and tensile strength. Additionally, the manufacturing process, such as cold working or heat treatment, can further modify the mechanical properties of the steel rods.

To improve the hardness and durability of metric carbon steel rods, several alloying elements are commonly added: 1. **Carbon**: Increasing the carbon content enhances hardness and strength through the formation of iron carbide, but it can reduce ductility. 2. **Manganese**: This element improves hardenability, tensile strength, and wear resistance. It also helps in deoxidizing the steel and counteracts the brittleness caused by sulfur. 3. **Chromium**: Added for increased hardness, wear resistance, and corrosion resistance. It forms stable carbides and contributes to the steel's ability to be heat-treated. 4. **Nickel**: Enhances toughness and impact resistance, especially at low temperatures. It also improves corrosion resistance and strength. 5. **Molybdenum**: Increases hardenability and strength at high temperatures. It also helps in reducing brittleness and improving weldability. 6. **Vanadium**: Contributes to increased strength and wear resistance by refining the grain structure and forming stable carbides. 7. **Silicon**: Acts as a deoxidizer and can improve strength and hardness without significantly affecting ductility. 8. **Tungsten**: Adds to hardness and heat resistance, often used in tool steels. 9. **Boron**: Even in small amounts, it significantly enhances hardenability and strength. 10. **Copper**: Improves corrosion resistance and can increase strength. These elements are carefully balanced to achieve the desired mechanical properties while maintaining workability and other essential characteristics of the steel.

Metric carbon steel rods differ in wear and stress resistance primarily due to their carbon content and the presence of other alloying elements. Higher carbon content generally increases hardness and tensile strength, enhancing wear resistance. However, this also makes the steel more brittle, potentially reducing its ability to withstand stress without fracturing. Low-carbon steel rods (up to 0.3% carbon) are more ductile and less hard, offering better stress resistance due to their ability to deform under load without breaking. They are less wear-resistant compared to higher carbon steels but are more forgiving under stress. Medium-carbon steel rods (0.3% to 0.6% carbon) strike a balance between hardness and ductility, providing moderate wear and stress resistance. They are often used in applications requiring a good combination of strength and toughness. High-carbon steel rods (0.6% to 1.0% carbon) are very hard and wear-resistant, making them suitable for applications where surface wear is a concern. However, their increased brittleness can lead to reduced stress resistance, making them more prone to cracking under high stress. Alloying elements like manganese, chromium, and vanadium can further influence wear and stress resistance. Manganese improves toughness and wear resistance, while chromium enhances hardness and corrosion resistance. Vanadium increases strength and wear resistance by refining the grain structure. Heat treatment processes such as quenching and tempering can also modify the wear and stress resistance of carbon steel rods. Quenching increases hardness and wear resistance, while tempering can restore some ductility, improving stress resistance. In summary, the wear and stress resistance of metric carbon steel rods are determined by their carbon content, alloying elements, and heat treatment, with higher carbon content generally increasing wear resistance at the expense of stress resistance.

Carbon steel rods are available in a variety of standard metric dimensions and specifications, which are typically defined by international standards such as ISO, DIN, and EN. The dimensions and specifications can vary based on the intended application, but generally include the following: 1. **Diameter**: Carbon steel rods are commonly available in diameters ranging from 5 mm to 100 mm. Standard increments are often 1 mm for smaller diameters and 5 mm for larger diameters. 2. **Length**: Standard lengths for carbon steel rods are typically 1 meter, 2 meters, 3 meters, and 6 meters. Custom lengths can be produced based on specific requirements. 3. **Tolerances**: Dimensional tolerances for carbon steel rods are specified in standards such as ISO 286-2, which defines the permissible deviations for different diameter ranges. 4. **Grades**: Carbon steel rods are classified into various grades based on their carbon content and mechanical properties. Common grades include C20, C45, and C60, with higher numbers indicating higher carbon content and strength. 5. **Surface Finish**: The surface finish of carbon steel rods can vary, with options including hot-rolled, cold-drawn, or polished finishes. The choice of finish affects the rod's appearance and suitability for specific applications. 6. **Mechanical Properties**: Specifications often include tensile strength, yield strength, and elongation, which are determined by the carbon content and heat treatment of the steel. 7. **Standards**: Common standards for carbon steel rods include ISO 683-1, DIN 1013, and EN 10083-2, which provide guidelines for chemical composition, mechanical properties, and testing methods. These specifications ensure that carbon steel rods meet the necessary requirements for various industrial applications, including construction, manufacturing, and engineering.