The Effects of Martensite Thermomechanical Parameters on the Formation of Nano/Ultrafine Grained Structure in ۲۰۱LN Stainless Steel

In this study, the effects cold rolling and annealing parameters during thermomechanical processing of the AISI ۲۰۱LN stainless steel were investigated. The cast samples were homogenized, hot-rolled and solution-annealed to acquire a suitable microstructure for the subsequent thermomechanical treatment. Unidirectional and transverse multi-pass cold rolling at ۲۵, ۰ and -۱۵ °C was carried out to ۹۰% reduction in thickness, followed by annealing at temperature range of ۷۰۰–۹۰۰ °C for different times of ۱۵–۱۸۰۰ s. Microstructures were characterized by optical and scanning electron microscopy, X-ray diffraction and feritscope measurements. Hardness test was also used for evaluating mechanical properties of the specimens. The results showed that the saturation strain of martensite formation during the cold rolling at ۲۵, ۰ and -۱۵ °C in ۲۰۱LN stainless steel was about ۰.۲۹, ۰.۲۳ And ۰.۱۷, respectively. A nano/ultrafine grained structure was formed by annealing the ۹۰% cold rolled specimen at ۸۰۰ °C for ۶۰ s with a grain size of about ۳۰۰ nm.

Keywords:

Martensite thermomechanical processing , ۲۰۱LN stainless steel , Strain-induced martensite , Nitrogen