Take the example of the technical route of refining grains by superplastic pre treatment,the
ZrC particle,which density
is the same as liquid steel at 1 650 ℃ in and does not dissolve in steel,were mixed into 20Mn2 steel.It acted as deformation nuclei and the recrystallization nuclei of austenite and deformation induced ferrite during hot rolling.Meanwhile,the effects of deformation
strengthening,phase transformation strengthening,second phase strengthening and grain boundary strengthening were introduced.The results showed that grain size of the tested steels with two different heat treatments was refined to 1~2 μm.Compared with standard 20Mn2 steel,the σ 0.2 and σ b of water quenched steel were increased by 187.0% and 131.8% respectively,and the elongation was increased as well.Both σ 0.2 and σ b of oil quenched steel were increased by 39.9% and 34.2%.The plasticity of oil quenched and low temperature tempered specimens increased by 90% and 111% comparing with 20Mn2 steel.