During cold working, the hardness change of FE-Cr-Al wire is closely related to the amount of deformation. This relationship stems from the evolution of the material's internal microstructure. When the wire undergoes plastic deformation under external force, the crystal lattice structure is distorted due to dislocation movement. The originally regularly arranged atoms gradually deviate from their equilibrium positions, forming numerous dislocation entanglements. As the amount of deformation increases, the dislocation density continues to rise, and the interaction between dislocations intensifies, leading to work hardening within the material. This hardening effect directly manifests as an increase in hardness because the resistance to dislocation movement increases, enhancing the material's ability to resist further deformation.
In the initial stage of cold working, when the deformation is small, the hardness change of the wire is relatively gradual. At this time, although the dislocation density increases somewhat, a dense entanglement network has not yet formed, and some mobile dislocations still exist within the material, capable of coordinating some deformation. Therefore, the increase in hardness is limited, and the material retains a certain degree of plasticity. As the amount of deformation further increases, the dislocation density rises sharply, dislocation entanglement and interaction intensify, forming a complex dislocation network. These dislocation networks act like "pins" to the center, severely hindering dislocation slip and climb, leading to a significant increase in material hardness. At this point, the material's plasticity gradually decreases because the number of movable dislocations reduces, limiting its deformation capacity.
When the deformation reaches a certain level, the increase in wire hardness gradually slows down. This is because a highly dense dislocation structure has already formed inside the material, and further increases in deformation have a weaker effect on increasing dislocation density. Simultaneously, excessive deformation may lead to microcracks or localized stress concentrations within the material; these defects can become the starting point for material failure, potentially reducing the material's effective load-bearing capacity to some extent. However, before reaching the fracture limit, the overall hardness will still increase with increasing deformation, albeit at a slower rate.
During cold working, the hardness change of FE-Cr-Al wire is also affected by material composition and processing technology. Different compositions of FE-Cr-Al alloys exhibit differences in dislocation mobility and work hardening tendency. For example, materials with higher alloy element content have stronger interactions between dislocations and solute atoms, resulting in more significant work hardening and a greater increase in hardness. Furthermore, processing techniques such as deformation rate and temperature also affect the hardness variation. Lower deformation rates and temperatures promote the full multiplication and entanglement of dislocations, thus enhancing work hardening; while high-temperature or high-speed deformation may partially offset the work hardening effect due to dynamic recovery or recrystallization.
It is worth noting that cold-worked FE-Cr-Al wire typically requires annealing to eliminate internal stress and improve plasticity. During annealing, recovery and recrystallization occur within the material, reducing dislocation density, promoting grain nucleation and growth, and consequently decreasing hardness. By controlling the annealing temperature and time, the hardness and plasticity of the material can be adjusted to meet the needs of different applications. For example, for wear-resistant parts requiring high hardness, lower-temperature annealing can be used to retain some work hardening effect; while for molded parts requiring good plasticity, full recrystallization annealing is necessary to restore the material's plasticity.
The influence of cold-working deformation on the hardness of FE-Cr-Al wire reflects the intrinsic relationship between the material's microstructure and macroscopic properties. By rationally controlling the deformation amount and processing technology, the balance between hardness and plasticity can be optimized to meet the needs of different engineering applications.
