Laser welding and weld hardness analysis of thick section S355 structural steel

Laser welding is becoming increasingly common and has been found to be of particular interest in the welding of various steel structures. A new generation of high power lasers has entered the market during recent years. These lasers have thus far mostly been used for welding of thin sheet. However, with the availability of higher power, such lasers have possible application to thick section welding. This study investigates the performance and potential of deep penetration laser welding of S355 EN 10025 structural steel of 20 and 25 mm thickness with a high power fiber laser at power levels of 12–30 kW. Visual examinations of the macrographs and hardness tests of all welded specimens were made. Quality windows were drawn based on the results of the experiments. Preferable welding parameters are formed based on the experimental study. The results of the hardness test show that surface hardness level of the weld is up to 2.5 times higher than the surface hardness of the base material.

► We welded S355 20 and 25 mm thickness steel plates with 12–30 kW laser power level.
► S355 tend to hardness increase in the HAZ up to 450–500 HV.
► (20 mm thickness) Line energy increasing = reduction of the hardness of the weld.
► (25 mm thickness) Line energy increasing = no significant changes in the weld hardness.