Study On Hot Deformation Behavior And Strain Induced Precipitation In 2.25Cr-1Mo-0.25V Steel

The 2.25Cr-1Mo-0.25V steel had been widely used in manufacturing hotwall hydrogen reactor for its higher intensity and stronger resistance to the hightemperature creeping, and hydrogen corrosion and brittleness temperedbrittleness. However, the investigations of essential character lag behindpractical manufacture, furthermore, the further optimization of hot workingprocess were firmly retarded.Therefore the hot deformation behaviors and precipitation during holdingprocess in 2.25Cr -1Mo-0.25V steel were investigated by using of Gleeble-3500thermal simulator.The results show that the stress vs. strain curves of this steel can beclassified into two types: dynamic recover and dynamic recrystallization, Hotdeformation activation energy which was calculated based on stress vs. straincurves is 474.82kJ/mol and the hot deformation formation was fitted asfollowing:ε|-= 3 .03e³⁴ [sinh(0 .0329σ)]^1.309exp(-474820/RT)From the microstructure and the map of dynamic recrystallization state withstrain rate of 0.01s-1, we can credibly conclude that the lower strain rate orhigher deformation temperature is, the more easily dynamic recrystallization canoccur. Otherwise, the larger the Z parameter is, i.e. lower deformationtemperature or higher strain rate, the more difficultly dynamic recrystallizationcan occur. Strain induced precipitation took place during holding process after hotdeformation, strain relaxation curves exhibit several short plateaus which arerelated to the inoculation, precipitation and growth process of the second phaseparticles. The inoculation time at 900 ℃ is the shortest, and the PTT(Precipitation-Time-Temperature) curves do not exhibit typical "C" shape. Theshape of the second phase particles transformed from small-scale spherical tolarge-scale quadrate. The short virgulate precipitates were observed in waterquenched samples;The second phase particles did not dissolve duringhomogenized treatment can not retard stress relaxation effectively. The finegrains can be obtained by controlling the holding time.