Hot deformation behavior of a novel V–N microalloyed high-strength steel: Microstructure evolution, constitutive equation, and processing MAP

The variation in flow stress, microstructural evolution, and Zener-Hollomon parameter of a novel V-N microalloyed high-strength steel, with deformation temperatures ranging from 850 to 1050 °C and strain rates from 10 -2 to 10 s -1 , was analyzed using a hot deformation experimental system. The deformation temperature and strain rate have an impact on the sensitivity of flow stress. Experimental results reveal a significant rise in the flow stress of the studied steel as the deformation temperature decreases and the strain rate increases. The stress exponent ( n ) and activation energy ( Q ) are determined to be 8.629 and 468.499 kJ·mol -1 , respectively. Through processing map analysis, two distinct instability domains harmful to workability are identified: 850–940 °C (strain rates: 10 -2 –10 s -1 ) and 985–1020 °C (strain rates: 0.043–1.21 s -1 ). These hot deformation conditions should be avoided in the production. TEM observations revealed two phenomena: the continuous dynamic recrystallization (CDRX) characterized by grain boundary protrusions toward regions with high a dislocation density, and the strain-induced grain boundary migration (SIBM) occurring at the triple junctions of grain boundaries. At the same time, the precipitates in the experimental steel have an important influence on the hot deformation behavior of the material.