Effect Of Hot Rolling On Microstructure And Properties Of Nano-Structured12Cr-ODS Steels

Nano-structured oxide dispersion strengthened (ODS) steels are the structural materials candidates for first wall application in future fusion reactors. The ODS steels have excellent radiation tolerance, helium embrittlement resistance and improved high-temperature properties due to ultra high-density of nano-precipitates, high-density of dislocation and fine grain size. In this thesis, a12Cr-ODS steel was prepared by mechanical alloying (MA) and hot isostatic pressing (HIP) method. Hot rolling was applied to optimize the microstructure and mechanical properties of the ODS steels. The microstructures, before and after hot rolling, were characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The mechanical properties before and after hot rolling were measured.The following results were obtained:(1) The matrix of12Cr-ODS steels is ferritic before hot rolling, and is ferritic/martensitic mixture after hot rolling. The relative density of both ODS steels are good.(2) The average grain size of12Cr-ODS steels before hot rolling is1.06μm. The average grain sizes after hot rolling are0.33μm(RD plane),0.36μm(TD plane) and0.56μm (ND plane), respectively. This indicates that hot rolling can refine effectively the grain size.(3) Y-Ti-O-enriched nano-clusters are formed in12Cr-ODS ferritic steels. The density of nano-scale precipitates before hot rolling is2.3X1023/m3with the average size of1.2nm, and the density of precipitates after hot rolling is2.1X1023/m3with the average size of1.2nm.The density and size of nano-scale precipitates almost unchanged before and after hot rolling. The number density of TiCr2O4precipitates increases after hot rolling.(4) The tensile strength decreases and the total elongation increases with the increasing test temperature before600℃.The fracture mechanism is changing from quasi-cleavage fracture to dimple fracture.(5) Hot rolling is a kind of effective thermo-mechanical method, which can refine the grain and improve the properties of12Cr-ODS steel.