Effect of dual beam laser welding on microstructure-property relationships of hot-rolled complex phase steel sheets

The work addresses microstructure-property relationships of hot-rolled complex phase steel sheets subjected to various conditions of dual beam laser welding. The article also contains a comparison between single-spot and twin-spot laser welding. Test-related joints were made using a Yb:YAG disc laser having a maximum power of 12 kW and a welding head enabling the focusing of a laser beam on two spots. The tests involved investigating the effect of power distribution on the macrostructure, microstructure and mechanical properties of joints. Microscopic investigations revealed the stabilisation of some fraction of retained austenite in the intercritical heat affected zone (ICHAZ) of joints. The application of the second beam resulted in tempering-like effects in the martensite of the fusion zone and in the HAZ, favourably reducing the hardness of the joint. The use of bifocal welding enabled the obtainment of a 10% hardness reduction in the fusion zone as against single-spot laser beam welding.