Synergistic strengthening of 30Cr2Ni3Mo3V steel by nanoscale MC carbides and dynamic dislocation networks at high temperatures
摘要
The mechanisms governing the high-temperature strengthening of the novel medium-alloy steel 30Cr2Ni3Mo3V are investigated, and tensile tests are conducted in the temperature range of 500–700 °C. Comprehensive characterization was carried out using scanning electron microscopy, high-temperature X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Results indicate a progressive decrease in tensile strength with rising temperatures. Notably, at 600 °C, rapid material softening is observed, where the grain boundary strength drops below the intragranular strength, resulting exclusively in transgranular fracture. The degradation of mechanical properties at elevated temperatures is primarily attributed to the dynamic recovery of tempered martensite, recrystallization phenomena, and a reduction in dislocation density. Within the steel matrix, spherical MC carbides are uniformly dispersed, while fine, rod-shaped M23C6 carbides anchor the lath boundaries, effectively retarding grain boundary migration and subsequent grain coarsening. Upon tensile deformation at 700 °C, finer-sized (approximately 3–5 nm) thermally stable MC precipitates form, further contributing to high-temperature strength. Both theoretical analysis and transmission electron microscopy characterization confirm that the dispersion of nanoscale MC carbides and dislocation strengthening synergistically improve the elevated-temperature strength of 30Cr2Ni3Mo3V steel.