Creep Properties and Corrosion Behavior of TP347H Stainless Steel with Al in Molten Carbonate Salt

Molten carbonate salts are a promising candidate for next-generation concentrated solar power technology owing to their excellent heat storage and heat transfer properties. This represents overcoming several problems that structural materials exhibit, including severe corrosion and high-temperature creep. Alloys with an aluminum element are alternatives in this regard as they are highly resistant to corrosive environments. In this paper, the corrosion behavior in molten carbonates (Li2CO3-Na2CO3-K2CO3) and creep properties of TP347H with different aluminum contents at 650 °C were studied. The results demonstrated that the alloy corrosion rate was reduced via Al addition. The alloy with 2.5 wt.% Al exhibited the lowest corrosion rate: ~25% lower than that without Al after 1000 h of corrosion. With increasing Al content, the inner corrosion layer of the alloys transformed from a Cr-containing oxide layer to a Cr–Al-containing composite oxide layer. The addition of Al promoted the formation of a layer of continuous and dense LiFeO2 product on the alloy surface during early corrosion stages, which prevented the carbonate from coming into direct contact with the substrate. After 1000 h of corrosion, the surface of the alloy is mainly composed of LiFeO2 and LiCrO2. Compared to TP347H, the added Al element enhanced the strength and elongation of TP347H at 650 °C. The TP347H containing 2 wt.% Al exhibited the best high-temperature tensile properties. When the stress was 110 MPa, the lowest steady-state creep rate of the alloy containing 2 wt.% Al was 3.61 × 10−6, and the true stress index was 5.791. This indicates that the creep mechanism was a dislocation climb assisted by lattice diffusion.