TKD/EBSD and TEM analysis of microstructural changes ongoing in AISI 304L steel exposed to the cyclic loading

The study deals with microstructural evolution of the 304L steel exposed to the low cycle straining. The two states of material were studied, the as-received and solution annealed state. Solution annealing caused grain growth from 29 & PLUSMN; 10 & mu;m to 48 & PLUSMN; 30 & mu;m, reduction of chemical heterogeneity and decrease of overall dislocation density. Cyclic hardening/softening curves were measured and three stages of fatigue life were distinguished. Initial cyclic hardening was followed by cyclic softening. The pronounced secondary hardening was measured in the last stage of fatigue life. Advanced techniques of electron microscopy were used to enlighten origin of the material behavior in particular stages. The material response in individual stages is thoroughly discussed in terms of microstructure evolution. Electron channeling contrast imaging visualized the fine microstructural features and revealed structure evolution, however was not able to identify the features. Transmission electron microscopy is useful for individual structural features characterization, however, it is quite complicated to be performed. Transmission Kikuchi diffraction provided similar results to transmission electron microscopy while characterization of evolved microstructural features revealed the deformation mechanism acting under loading at lower time and relatively smaller effort. Particular damage mechanisms operating in material are linked to the mechanical data.

Automated summary

This study investigates the microstructural evolution of 304L steel exposed to low cycle straining. The as-received and solution annealed states were studied, with the latter causing grain growth, reduction of chemical heterogeneity, and overall dislocation density. Cyclic hardening and softening were observed, with a pronounced secondary hardening in the final stage of fatigue life. Advanced electron microscopy techniques were used to explore the material behavior in different stages. The techniques were able to visualize fine microstructural features and reveal structure evolution.