Fe-Cr-Al wire, a high-temperature alloy material with an iron matrix and additions of chromium and aluminum, can be characterized by the influence of cold working deformation on its mechanical properties through the combined effects of work hardening mechanisms, microstructure evolution, and residual stress distribution.
Increasing cold working deformation significantly improves the strength and hardness of Fe-Cr-Al wire. This phenomenon stems from the work hardening effect. When the material undergoes plastic deformation, the dislocation density within the grains increases dramatically, and the interactions between dislocations intensify, forming an entangled network that increases the resistance to dislocation movement. Simultaneously, the grains are elongated or flattened during deformation, forming a fibrous structure with blurred grain boundaries and more uniform orientation. This structural change creates a greater barrier to dislocation movement under load, resulting in increased yield strength and tensile strength. For example, in cold-rolled Fe-Cr-Al wire strip, the high density of dislocation entanglements significantly hinders plastic deformation. If not eliminated through subsequent heat treatment, the material exhibits significant brittle characteristics.
With increasing deformation, the plasticity and toughness of Fe-Cr-Al wire gradually decrease. This trend is closely related to the formation of a dislocation cellular structure: when the deformation exceeds a critical value, the dislocation density reaches saturation, and subgrain boundaries begin to form within the grains, dividing the original grains into multiple cellular regions with lower dislocation density. While this structure can partially alleviate stress concentration, it still reduces the material's overall uniform deformation capacity. Furthermore, residual internal stresses generated during cold working further weaken the material's toughness. Residual stresses arise from deformation inhomogeneity. When local stresses exceed the material's yield strength, they trigger microcrack initiation, which then expands into macrofractures under subsequent stress.
The influence of deformation on the mechanical properties of Fe-Cr-Al wire is also reflected in its anisotropic characteristics. The convergence of grain orientation caused by cold working creates a texture structure, resulting in differences in mechanical properties in different directions. For example, the tensile strength along the rolling direction is generally higher than that perpendicular to the rolling direction, while the elongation shows an opposite trend. This anisotropy requires special attention in complex forming processes such as deep drawing and stretching. If the texture strength is too high, it can lead to defects such as earing and cracking.
It's worth noting that the mechanical properties of Fe-Cr-Al wires exhibit a critical threshold in their response to deformation. When deformation is low, work hardening dominates, and strength increases approximately linearly with increasing deformation. However, when deformation exceeds a certain limit, dislocation density approaches saturation, and grain fragmentation intensifies. At this point, internal defects (such as microcracks and voids) begin to dominate property changes, leading to a slowdown or even decrease in strength growth and a continuous increase in plasticity loss. Furthermore, the sensitivity of alloy composition to deformation also influences the ultimate properties. For example, after cold working, Fe-Cr-Al wires with a chromium content exceeding 15% experience a decrease in strength gain due to a weakening of the solid solution strengthening effect, while elongation may remain relatively stable due to the plasticity-regulating effect of chromium.
To optimize the mechanical properties of Fe-Cr-Al wires, heat treatment is required to adjust the relationship between deformation and microstructure. Annealing can eliminate residual stresses, promote recrystallization to form equiaxed grains, and thus restore the material's plasticity. For example, when bright annealing cold-rolled strip, the annealing temperature, holding time and atmosphere selection need to be controlled in coordination with the deformation amount to avoid performance degradation caused by grain coarsening or hydrogen embrittlement.
