Abstract: Mechanical properties of welding region and phase constitution characteristics of the Fe-Al alloy layer in HAZ of calorised steel pipes are researched by means of metallography,SEM,TEM,X-ray diffractometer and electron diffraction,etc. Experimental results indicate that the Fe-Al alloy layer in HAZ of calorised steel pipe is mainly composed of FeAl,Fe₃Al and α-Fe(Al) solid solution, and has no higher aluminium content phases,such as brittle FeAl₂, Fe₂Al₅ and FeAl₃ phases,The deformation ability and the weldability of the calorised steel pipe are remarkably improved. Microstructure and performance of the welding region on calorised steel pipe can be easily ensured.