Oxidation behaviour of Super 304H stainless steel in supercritical water

Abstract

Oxidation of Super 304H steel in supercritical water at 600°C and 25 MPa was investigated, for the oxidation time of up to 1000 h. The oxidation kinetics approximately followed a parabolic law. The composition and microstructure of the oxide were investigated using the SEM equipped with EDS, EBSD and XRD. The phase compositions of the oxide evolve with increasing time. Cr 2 O 3 was present at the initial stage and not detected while Fe 2 O 3 appeared at longer time. EBSD indicated that continuous Cr 2 O 3 formed at the interface of oxide and matrix for HR3C at 600°C for 40 h but only scattered Cr 2 O 3 can be observed for 200 h. After the formation of a thin Fe-Cr-Ni oxide film on the Super 304H steel surface, the Fe-rich outer nodular oxide begins to grow and forms a continuous layer after 1000 h. The growth process of Super304H steel in supercritical water was discussed.

Steam Oxidation of Aluminide-Coated and Uncoated TP347HFG Stainless Steel under Atmospheric and Ultra-Supercritical Steam Conditions at 700 °C

“…Indeed, within the shown grain (Figure 11), metallic un-oxidised zones can still be observed inside the grain. Lath preferential oxidation was also observed by Bischoff and coworkers on ferritic steels [31] and similar microstructures were observed by Li [8] Yang [19] and Tepylo [26] and coworkers on 304 H stainless steel and by Zhu et al on TP347HFG stainless steel [32] after steam oxidation. In agreement with Chen and coworkers' findings [11], the formation of Cr-rich layers in this inner oxide leads to Cr depletion and indeed, on the areas surrounding the nodules, Cr depletion can be observed on the element map showed in Figure 9.…”

“…This was also proposed by Yang and coworkers to form on 304H after 1000 h under flowing steam at 650 °C [19], and by Li et al when exposing SS310 to supercritical (29 MPa) steam at 625 °C [6]. The lower Cr content of the outer zone of the scale may be caused by Cr evaporation as proposed by other authors [8]. Under this scale a Cr depletion substrate zone was observed, with only 10.5 wt.% Cr as opposed to 18 wt.% in the bulk alloy.…”

“…Indeed, the oxide scale was significantly thicker with an outer Fe oxide layer and an inner Fe-Cr spinel, whereas at 1 bar very thin pure chromia formed according to the author. Some other studies related to testing austenitic steels under ultra-supercritical steam can be found in the open literature at temperatures ranging from 600-800 • C, and in general, at higher pressure, higher oxidation rates are observed [6][7][8][9][10][11]. At lower temperatures (<700 • C), a thin protective Cr-rich oxide accompanied by the presence of deep and large oxide nodules was observed at relative short.…”

Oxidation Processes and Involved Chemical Reactions of Corrosion-Resistant Alloys in Supercritical Water

“…Although the alloy with a high Cr content tends to form a dense, continuous, and protective Cr 2 O 3 layer than does the alloy with a low Cr content, the optimum Cr content is approximately 20 wt % commonly. , However, Cr 2 O 3 can evaporate in the forms of CrO 3 , CrO 2 (OH), and especially CrO 2 (OH) 2 in SCW with a high oxygen content . More specifically, Cr 2 O 3 and CrO 3 can react with water and oxygen to form an oxide hydroxide (i.e., CrO 2 (OH) 2 (chromium­(VI)) by reactions ,,,,,,,− and . CrO 2 (OH) 2 is an active volatile species and probably formed in the metal wastage process in high-temperature and high-pressure water on the oxide/substrate interface .…”

Microstructural investigation of the nodular corrosion of 304NG stainless steel in supercritical water

“…Therfore, it has been a promising candidate material for fuel cladding in SCWR [3]. Its corrosion behavior in SCW and water vapor has been widely studied [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Previous results showed that 304 stainless steel has good corrosion resistance in SCW under 550 ºC, however, a substantial increase of corrosion rate appeard above this temperature.…”