An in-situ microscopy study on nucleation and growth of acicular ferrite in Ti-Ca-Zr deoxidized low-carbon steel

摘要

We describe here an in-situ microscopy study on the nucleation and growth of acicular ferrite in Ti-Ca-Zr deoxidized low-carbon steel as a function of cooling rate. The study indicated the starting transformation temperature of acicular ferrite decreased with increasing cooling rate. Moreover, the average growth rate of acicular ferrite was increased from similar to 2.2 mu m/s to similar to 14.4 mu m/s with the increase of cooling rate from 2 degrees C/s to 15 degrees C/s. In Ti-Ca-Zr deoxidized steel, (Ti, Ca, Zr, Al)-O-Mn-S oxide inclusions effectively promoted the formation of intragranular acicular ferrite. A significantly high proportion of acicular ferrite was characterized by high angle grain boundaries and reduced grain size. When the cooling rate was low at 5 degrees C/s, the proportion of acicular ferrite was high at similar to 85%, with similar to 48% high angle grain boundaries and small average grain size of similar to 2.7 mu m. Additionally, MnS precipitated in the vicinity of (Ti, Ca, Zr, Al)-O-Mn-S oxide particles, which promoted the nucleation of acicular ferrite.