INTERACTION BETWEEN THERMAL RECOVERY AND THE CHANGE IN STRAIN PATH IN LOW-CARBON STEEL

Tension experiments were performed on mild steel samples predeformed in rolling or predeformed in rolling and recovered. Particular attention was paid to the transient mechanisms produced by a change of the loading mode. In the predeformed and unrecovered specimens just after reloading, there occurs a rapid now localization and gradual evolution to fracture. In the predeformed and recovered specimens, changing the strain path produces the abrupt occurrence of a short transient domain of plastic instability, characterized by a serrated flow. Transmission electron microscopy observations showed that the appearance of this domain is connected with the drastic dissolution of the cell walls created during the prestraining, as the result of bath latent hardening and Bauschinger effects. After this short domain of plastic instability, the dislocations rapidly organize according to the new loading conditions, leading to a renewed increase in the flow stress.