Investigation on Strengthening Mechanism of China Low-Activation Ferrite Steel upon Thermo-Mechanical Treatment

The objective of this study was to investigate the influence of strengthening mechanisms on the high-temperature mechanical properties of China low-activation ferrite(CLF-1)steel,which underwent thermodynamic design and thermo-mechanical treatment(TMT).The microstructure characterization in the normalized and tempered condition and the TMT condition was carried out using optical microscopy,X-ray diffractometer,and scanning electron microscopy with electron backscatter diffraction.High-resolution transmission electron microscopy was employed to determine the crystallographic structures of precipitated phases.The results indicated that the addition of Ti led to an increase in the allocation of C in MC phase and an enhancement in the content of MC phase.Compared to CLF-P steel in the normalized and tempered condition,a 1.5-fold increase in dislocation density and an order of magnitude improvement in MX phase density were achieved after TMT.The formation of high-density nano-scale MC phases during TMT played a significant role in precipitation strengthening due to their favorable coherent relationship with the matrix and low interfacial free energy.The excellent high-temperature mechanical properties observed in CLF-P steel after TMT can be attributed to the combined effects of precipitation strengthening,dislocation strengthening,and lath strengthening.