Evolution of magnetic phase at low aging temperature in a heavily cold-drawn stainless steel fiber

The evolution of the magnetic phase upon aging at 300–520 °C in a heavily cold-drawn AISI 316L austenitic stainless steel fiber was studied using thermomagnetic analysis (TMA) and magnetic force microscopy with a heating stage. An increasing trend of magnetization from 50 °C to around 470 °C in the heating curves of TMA in austenitic stainless steels after a cold-drawing process was observed. No significant Ms temperature signal in the TMA curve at cooling indicated an increase in magnetization upon cooling period without significant phase transformation. A series of in situ magnetic force microscopy observations reveal a growth of the magnetic domain structure after aging at 300 °C for 2.5 h. Results show that the ferromagnetic increase during aging at lower annealing temperature resulted from the growth of martensite.

► An increasing magnetization of TMA from 50 °C to ∼470 °C in a cold-drawn 316L fiber was observed.
► The cold-drawing the main factor to generate a peak magnetization in austenitic stainless steels.
► No significant Ms temperature signal in the TMA curves upon cooling.
► In-situ MFM reveals growth in the existing α′-martensite during aging at 300 °C.