Characterisation comparison of laser and laser-arc hybrid welding of Invar 36 alloy

Laser and laser-arc hybrid welding are employed to join Invar 36 alloy. The microstructure, coefficient of thermal expansion (CTE) and mechanical properties of laser weld (LW) and hybrid weld (HW) are analysed and compared. The tensile test shows both LW and HW fractured in the weld metal, but the HW is stronger than the LW. Especially, the yield strength of HW is 362.8 MPa, 16.2% higher than that of LW. Both the CTE and Curie temperature of LW are almost the same with those of base material. The CTE of HW is higher than that of base material because the Ni content reduces and the content of other alloying elements increases. Moreover, the CTE of HW deviates from the theoretic curves of Fe-Ni alloy apparently. According to the theory of Invar effect, the deviation is attributed to the formation of new phase, FeCr0.29Ni0.16C0.06.