Effects of High Magnetic Field on Microstructure and Mechanical Property of Medium Mn Steels Tempered at Low-Temperature after Deep Cryogenic Treatment

The effects of high magnetic field (HMF) on microstructure and mechanical properties of Fe-0.3C-10Mn-3Al medium Mn steels tempered at low-temperature after deep cryogenic treatment (DCT) have been studied. The results show that the experimental steel has a high strength and a relative low elongation due to the presence of a large amount of martensite phases after the DCT. During the low temperature tempering process under the HMF, the martensite phases transform into ferrite gradually with the increase of magnetic flux density (MFD) as a result of a significant increase in elongation with a negligible decrease in tensile strength and maintaining a high work hardening capacity. With the MFD increases from 0 T to 10 T, the yield strength gradually decreases from about 1 GPa to 545 MPa with almost a constant strength more than 1.2 GPa. The uniform elongation has been improved for about 4.5 times and the product of strength and elongation has been improved for about 4 times. Besides, the volume fraction of austenite increases from 21.6% to 61.2% and the average grain size of austenite increases from 0.7 μm to 1.1 μm. This study provides new insights into the role of HMF in modulating the microstructure and mechanical properties of medium Mn steel.