Hot corrosion behaviour of constant and pulsed current welded Hastelloy X in Na2SO4, V2O5, and NaCl salt mixture at 900 °C

Abstract

The high-temperature corrosion behavior of constant current gas tungsten arc (GTA) and pulsed current gas tungsten arc (PCGTA) welded Hastelloy X with different filler wires (C263 and ERNiCr-3) are studied for 50 cycles at 900 °C. Molten salt I (MS I) (75% Na _2 SO _4 + 25% V _2 O _5 ) and molten salt II (MS II) (75% Na _2 SO _4 + 20% V _2 O _5 + 5% NaCl) were coated on the welded specimens. MS II coated substrate shows the highest weight gain than MS I with a parabolic constant for GTA ERNiCr-3 as 21.440 × 10 ^–6 mg ^2 /(cm ^4 .s). Whereas PCGTA C263 welded sample with MS I, revealed parabolic constant (lowest) of 0.008 × 10 ^–6 mg ^2 / (cm ^4 .s). Based on the results, an increasing pattern of hot corrosion resistance of substrates is arranged as GTA ERNiCr-3 < GTA C263 < PCGTA C263 < PCGTA ERNiCr-3. PCGTA shows more refined grains, higher grain boundary volume, better corrosion resistance, and more protective phases like Cr _2 O _3 , NiO, NiCr _2 O _4 , CoCr _2 O _4 , Al _2 O _3 , NiFe _2 O _4 , NbO than GTA weldment. But phases such as Fe _2 O _3 , MoO _3 , and Cr _2 S _3 (non-protective phases) decrease corrosion resistance due to acid fluxing of alloying elements that promote the oxide scale exfoliation, spallation, chipping, and cracking. This study observed that PCGTA with C263 filler in MS I and MS II environment provides good corrosion resistance at high temperatures.

Keywords

• hastelloy X
• C263
• ERNiCr-3 fillers
• pulsed current
• parabolic constant
• spallation and cracking