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

Tension experiments were performed on mild steel samples predeformed i n rolling or predeformed in rolling and recovered. Particular attentio n was paid to the transient mechanisms produced by a change of the loa ding mode. In the predeformed and unrecovered specimens just after rel oading, there occurs a rapid now localization and gradual evolution to fracture. In the predeformed and recovered specimens, changing the st rain path produces the abrupt occurrence of a short transient domain o f plastic instability, characterized by a serrated flow. Transmission electron microscopy observations showed that the appearance of this do main is connected with the drastic dissolution of the cell walls creat ed 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 conditi ons, leading to a renewed increase in the flow stress.