Clarification of the ferrite formed in the laser welded joint of the Al–Si coated press-hardened steel

Abstract

The clarification of the type of the ferrite formed owing to the melting of the Al–Si coating into the weld metal plays a significant role in the improvement of the mechanical properties of the laser welded joint. The results obtained by optical microscope (OM) and scanning electron microscope (SEM) in the regions near the ferrite before and after thermal simulation clearly demonstrate the negligible change in microstructure morphology, even for the ferrite with the size around 2 μm. In addition, simulated by JMatPro software, it can be found that the content of the α-ferrite decreases with the increase of the cooling rate. Based on the ultra-high cooling rate during laser welding and negligible change in the morphology of the ferrite by decreasing the cooling rate, the type of the ferrite formed in the WM is clarified as the δ-ferrite, without the formation of α-ferrite. The differences in the formation condition between the δ-ferrite and α-ferrite can affect the control of their size, morphology and distribution.

Keywords

• Ferrite clarification
• In-situ observation
• Al–Si coating
• Laser welding
• Press-hardened steel
• Thermal simulation