Integrated laser based pre‐tempering at laser welding of AISI 1045 steel by using 3D‐scanner optics

Abstract

AbstractLaser‐based pre‐heating of laser beam welding with a 3D scanning optics, applied to AISI 1045 steel, is studied. Laser beam welding of heat‐treatable steel is challenging due to martensitic hardening in combination with defects. Pre‐tempering aims the reduction of the cooling rates and martensitic microstructure within the weld seam. An oscillating defocused laser beam was guided over the surface for pre‐heating by means of a 3D scanner optics. During pre‐heating, the laser power, the scanning speed and the number of cycles were varied. Welding with 4000 W and 2 m/min with a focused laser beam was executed. Thus the resulting temperature profile behind the ongoing laser beam and cooling time T8|5 between 800 °C–500 °C was significantly extended. Two parameter combinations (15 cycles|600 W|50 mm/s(2) and 10 cycles|800 W|50 mm/s2) succeeded in a microstructure of bainite and martensite. By extending the cooling time T8|5 to 3.11 s(2) and 4.17 s2. Thus, average hardness for laser based pre‐tempering of 487 HV 0.5(2) and 455 HV 0.52 was achieved. As a reference, global pre‐heating at 400 °C using a heating plate can reduce the average hardness of the weld zone from 729 HV 0.5 at room temperature to 304 HV 0.5 at a cooling time T8|5 of 5.63 s.