Dynamic recrystallization behavior and interfacial bonding mechanism of 14Cr ferrite steel during hot deformation bonding

In this study, hot compression bonding was first applied to join 14Cr ferrite steel at temperatures of 950-1200 degrees C and strains of 0.11-0.51 under strain rates of 0.01-30 s(-1). Subsequently, tensile tests were performed on the joints to evaluate the reliability of the joints formed. Detailed microstructural analyses suggest that two different competing dynamic recrystallization (DRX) mechanisms occur during the bonding process depending on the strain rate, and the joints obtained at different strain rate exhibits distinct healing effect. At a low strain rate (0.01 s(-1)), continuous DRX occurs, as expected in high-stackingfault-energy materials, and is characterized by the progressive conversion of the sub-boundaries into larger-angle boundaries, which involves very limited grain boundaries migration. In addition, straininduced precipitation (SIP) is sufficient under this condition, further impeding the healing of bonding interface. Hence, the joints obtained at low strain rate fractured at the bonding interface easily. Whereas discontinuous DRX is activated at high strain rates (10 and 30 s(-1)). Under this condition, the formation of sub-boundaries is severely suppressed, resulting in the piling-up of dislocations and hence the storage of a greater amount of stored energy for nucleation and subsequent nuclei growth via the long-distance grain boundaries migration. Meanwhile, the SIP process is sluggish, making the conditions much more favorable for grain boundaries migration which plays a key role in the healing of the original bonding interface. Thus, the joints can be successfully bonded when a high strain rate is applied, with the joints exhibiting tensile properties similar to that of the base material. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.