Hot cracking in laser welding of Hastelloy X with pulsed Nd:YAG and continuous wave fiber lasers

• Total solidification and liquation cracks remarkably reduced with increasing pulse frequency and pulse duration.
• Increasing the pulse frequency changes the tendency of solidification cracks to connect to liquation cracks inside the HAZ.
• All the hot cracks eliminated when the laser source for welding changed to continuous wave fiber laser.
• A deeper weld penetration obtained with continuous wave fiber laser at low heat inputs.

Hastelloy X is a corrosion and heat resistance solution hardened nickel base super alloy. This alloy having an austenitic microstructure and in this regard is expected to be prone to hot cracking in fusion welding. In this research a 400 W Nd:YAG pulsed laser and 600 W continuous wave fiber laser welding are employed to weld a 2 mm thick Hastelloy X plates. Comparison is made with regard to weld penetration and tendency of occurrence of solidification cracking in the weld metal and liquation cracks in the heat affected zone. It is found that with pulsed laser hot cracks are formed, however, with continuous wave laser hot cracking can be avoided. Increasing the laser pulse frequency and pulse duration resulted in a significant reduction in hot cracking tendency in pulsed laser welding. The reduction in cooling rate and thermal stresses during solidification and backfilling of liquated grain boundaries are proposed to be the factors contributing to the prevention or reduction of hot cracks in laser welding of Hastelloy X. With a 0.2 mm beam diameter fiber laser at 500 W power and 5 mm/s travel speed full penetration weld was achieve with no observation of hot cracks in the weld cross sections.

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