Affect Factors for Toughness of Steel

1. Material Composition: The elements added to steel, such as carbon, manganese, nickel, and chromium, can affect its toughness. For example, higher carbon content can increase hardness but may decrease toughness.

2. Microstructure: The grain structure of steel, which is determined by the heat treatment process, can significantly impact toughness. Fine-grained structures generally exhibit higher toughness than coarse-grained structures.

3. Crystal Defects: Dislocations, loops, and other crystal defects can influence the propagation of cracks, thus affecting toughness.

4. Hardness: While hardness is not directly proportional to toughness, higher hardness can sometimes lead to reduced toughness due to increased brittleness.

5. Contaminants: Impurities in the steel, such as sulfur or phosphorus, can reduce toughness by facilitating the formation and propagation of cracks.

6. Processing History: The way the steel is melted, forged, rolled, drawn, or extruded can affect its toughness. Controlled processing techniques can enhance toughness.

7. Thermal Treatment: The heat treatment process, including annealing, normalizing, quenching, and tempering, plays a critical role in determining the toughness of steel.

8. Strain Rate: The rate at which stress is applied (strain rate) can affect toughness. Faster strain rates often result in less toughness, as there is less time for crack propagation to be hindered.

9. Notch Sensitivity: Steels with high notch sensitivity will have lower toughness, as notches can serve as stress concentrators, initiating crack formation.

10. Ageing: Over time, some steels can undergo ageing processes that affect their microstructure and, consequently, their toughness.

11. Service Conditions: The environment in which the steel will be used, such as temperature, corrosiveness, and presence of impact loading, can also affect toughness.