| Abstract: | The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed that the inclusions in A1 treated steel were mainly aluminum oxides and titanium nitrides which could not promote the formation of acicular ferrite microstructures.Microstructure of coarse-grain HAZ in A1 treated steels consists of heavy grain boundary ferrite and ferrite side plate.The inclusions in Ti treated steel were A1,Ti,Mg,Ca composite oxides with size in the range of 0.5-3μm and titanium nitrides with size less than 0.3μm.Ti composite oxide could promote the formation of acicular ferrite and microstructures of coarse-grain HAZ in Ti treated steel consists of grain boundary ferrite,small amounts of ferrite side plate and large amounts of intragranular acicular ferrite.The size of grain boundaries ferrite was increased and the amount of ferrite side plate was decreased with the increase of soaking time at the peak temperature.The amount of grain boundary ferrite and the size of acicular ferrite were also increased with the increase of cooling rate during ferrite phase formation. |
