The work-hardening tendency of FE-Cr-Al wire stems from the microscopic mechanism of increased dislocation density and intensified lattice distortion during its cold plastic deformation. When the wire undergoes plastic deformation during processes such as drawing and rolling, dislocation movement is hindered, forming entangled networks. This leads to residual stress within the material, macroscopically manifesting as a significant increase in strength and hardness, while plasticity and toughness decrease simultaneously. This characteristic affects the forming process throughout the entire process, encompassing both direct challenges in process implementation and indirect control of product performance.
The most direct impact of work hardening on the forming process of FE-Cr-Al wire is the increased equipment load and energy consumption. As the degree of deformation deepens, the material's deformation resistance increases exponentially, forcing drawing machines, rolling mills, and other equipment to provide greater traction force or rolling pressure. For example, in multi-pass drawing processes, if intermediate annealing is not performed in a timely manner, slip lines or even breakage may appear on the wire surface, leading to production interruptions. Furthermore, high deformation resistance accelerates die wear, shortens die life, and increases production costs.
Work hardening-induced decrease in plasticity poses a challenge to the continuity of the forming process. In cold working of FE-Cr-Al wire, when the deformation exceeds a critical value, the material loses its ability to deform further due to localized stress concentration, exhibiting a phenomenon known as "work hardening embrittlement." This characteristic is particularly pronounced in the forming of wires with complex cross-sections, such as irregularly shaped cross-sections or fine wires, where edge areas are prone to cracking due to over-hardening. To overcome this problem, process design must strictly control the deformation amount per pass and achieve the target size through the accumulation of small deformations in multiple passes, while simultaneously using lubricants to reduce frictional resistance.
Work hardening places higher demands on the forming accuracy control of FE-Cr-Al wire. The increased elastic recovery of the hardened material exacerbates dimensional springback after forming. For example, in bending processes, the bent portion of the wire may deviate from the design angle due to elastic recovery, requiring compensation by adjusting the bending radius or adding a correction step. Furthermore, the anisotropy caused by hardening can lead to differences in the elongation of the wire in different directions, affecting the shape stability of the formed part, necessitating consideration of directional factors in process parameter settings.
Work hardening also provides a means of controlling the process optimization of FE-Cr-Al wire. By controlling the degree of deformation in conjunction with the annealing process, gradient design of material properties can be achieved. For example, a work-hardened layer can be retained in the surface areas of the wire where high strength is required, while the core is annealed to restore plasticity, forming a composite structure of "hard on the outside and tough on the inside". This strategy is widely used in the production of spring wire, ensuring both the elastic limit and avoiding the risk of brittle fracture.
Work hardening has a profound impact on the subsequent processing performance of FE-Cr-Al wire. Hardened materials are prone to cracking or peeling during secondary processing such as welding and coating. For example, the hardness difference between the hardened layer and the heat-affected zone during welding may lead to joint embrittlement, which needs to be mitigated by pre-weld annealing or adjustment of welding parameters. Furthermore, the high hardness of the hardened layer increases the difficulty of machining, such as accelerated tool wear during cutting, requiring the use of higher hardness tool materials or optimization of cutting parameters.
Controlling the work hardening tendency is a core aspect of the FE-Cr-Al wire forming process. The process design must comprehensively consider the influence of factors such as deformation temperature, deformation rate, and lubrication conditions on the hardening rate. For example, increasing the deformation temperature can reduce dislocation movement resistance and slow down the hardening process; optimizing lubrication conditions can reduce frictional heat generation and inhibit localized hardening. Simultaneously, intermediate annealing can eliminate work hardening, restore material plasticity, and provide conditions for subsequent processing. However, precise control of annealing temperature and time is crucial to avoid grain coarsening leading to performance degradation.
The work hardening tendency of FE-Cr-Al wire has a dual impact on the forming process. It increases the difficulty and cost of process implementation, but also provides opportunities for product optimization through performance control. In actual production, precise control of process parameters and dynamic management of the hardening-softening balance are necessary to achieve the optimal match between material properties and processing efficiency, ultimately meeting the stringent requirements of high-end applications for the comprehensive performance of wires.
