Microstructure of Coarse-grained Heat Affected Zone of Zr Microalloyed HSLA Steel

Microstructure of simulated coarse grain heat affected zone (CGHAZ) of Zr Microalloyed HSLA Steel are investigated using optical microscopy and transmission electron microscopy.The austenite grain size of simulated CGHAZ increases with the increase of weld heat input.The grain size of simulated CGHAZ without Zr treatments is larger while that of Zr treated are smaller after same heat input welding.The microstructure of simulated CGHAZ consist of bainite mainly after 30kJ/cm heat input weld.The amount of the M-A constituent gets less and ferrite and pearlite appear with the increase of weld heat input.The inclusions are changed from chain shape with acute angle to spherical shape.Those are complex inclusions with the Zr containing inclusions are the nuclei for the inclusions,Al2O3 and / or MnS are located in the surface layer of the inclusions whose size is in the range of 10 to 3.0 μm.