Precipitation, recrystallization and elemental propositions in micro-alloyed steels

Abstract

Aim of microalloyed steel has been solid solution strengthening and precipitation strengthening. Austenitic solid solutions at greater temperature have produced precipitation during cooling. In vanadium carbonitride (V(C, N)) nitrogen has major role in precipitation sequence and kinetics. Vanadium diffusion has been rate controlling in the growth of carbonitride precipitation. Kinetics of static recrystallization critical temperature (SRCT) has studied to be a function of strain, austenite grain size and microalloy content of steel. V(C, N) has stated to improve steel properties by ferrite formation instead bainite. Interphase boundary precipitation of vanadium has related to boundary migration during ferrite transformation from austenite in isothermal phase transformation. Studies on heat-treatment of service exposed rotor steel has showed removal of grain boundary precipitates and regaining life by formation of equi-disperse precipitation over matrix at the expense of grain boundary precipitates. Long term boiler tube applications has stated to be formation of coherent precipitation, which in subsequent period has formed stable Laves phases to control over microstructural stability. Hydrogen embrittlement has reduced by trapping source in steel. Vanadium precipitates has been effective source for trapping. V precipitates act as one type of trap with specific activation energy. Phosphorous segregation has always appeared too dominated through grain boundaries than bulk diffusion.