Effect of Solutionization Temperature on the Interfacial Microstructure of a Hot Roll Bonded Alloy 690/Carbon Steel Clad Steel Plate

Abstract Fabrication of a Ni-based superalloy Alloy 690 cladded ASTM SA516 GR60 carbon steel (GR60) clad steel plate was carried out through vacuum hot roll bonding at 1323 K for the first time. The as-rolled clad plate showed excellent metallurgical bonding at the joining interface, however, a precipitation zone within the Alloy 690 layer containing Cr 23 C 6 carbides was observed, which is detrimental to the intergranular corrosion resistance. A comprehensive approach integrating thermodynamic calculations and numerical simulations of long-range diffusion of alloying elements was employed to optimize the post rolling solutionization heat treatment temperature. Thermodynamic calculations predicted the possibility of reduction in Cr-carbide amount on solutionization in the temperature range of 1373 K to 1573 K. Guided by these calculations, as-rolled specimen was solutionized at 1373 K for 4 hours, however, the width of the Cr 23 C 6 carbide precipitation zone was found to increase instead of decreasing due to enhanced Cr and C diffusion. On the other hand, solutionization at 1473 K for 4 hours resulted in a substantial reduction in Cr 23 C 6 precipitates on Alloy 690 side. Formation of a thin stabilized γ -FCC ( γ s ) was noticed on the GR60 side after solutionization at 1373 K due to net influx of Ni from Alloy 690 alloy, which separates the original joining interface from the bulk GR60. The width of this γ s region further increased after 1473 K-4 hours solutionization due to enrichment of Ni within GR60 layer. Overall, a higher solutionization temperature (1473 K) was found to be more effective to reduce the Cr-carbide amount in Alloy 690 cladded GR60 plates than that usually employed 1373 K for monolithic Alloy 690 plate.