DYNAMIC RECOVERY IN NB-TI IF STEELS DURING HOT AND WARM WORKING

Three ultra low carbon interstitial free steels, containing niobium an d titanium, and a plain carbon steel were prepared to investigate thei r flow behaviour during hot and warm working. When the steels were sub jected to com= at constant strain rates in the austenite region they e xhibited typical work hardening and dynamic restoration behaviour. Whe n they were worked in the ferrite region, they showed unusual and unex pected behaviour, featuring a rapid and quasi-linear increase in flow stress at a low strain value, followed by a decrease with further incr easing strain. Such abnormal flow behaviour was attributed to the pres ence of dissolved Nb atoms. When the niobium precipitated or when the steel was free from Nb, the typical work hardening and dynamic restora tion curves were obtained during deformation in the ferrite region as well.