Precipitation behavior of V- N microalloyed steel at the normalizing process

Abstract

The precipitation behavior of V-N microalloyed steel at the normalizing process was studied by physicochemical phase analysis and high resolution transmission electron microscopy. The effect of this precipitation behavior on the mechanical properties of the steel was discussed by theoretical calculations. At soaking of the normalizing process,32.9% of V(C,N) precipitations keep undissolved into austenite,and they prevent austenite from growing up. At the subsequent cooling process,the undissolved V(C,N)precipitations induce intra-granular ferrite nucleating,which can refine ferrite grains; besides,the dissolved V(C,N) precipitations re-precipitate and play the role of precipitation strengthening. Compared with the hot-rolled steel,the normalized steel gains a 31 MPa increment in grain-refined strengthening but a 45 MPa decrease in precipitation strengthening.

Keywords

• steel heat treatment
• normalizing
• microalloying
• precipitation
• grain refinement
• strengthening