Formation of ferrospinel layer at the corroded interface between Al₂O₃‐spinel refractory and molten steel in RH refining ladle

Abstract

Incorporation of magnesia alumina spinel confers excellent thermal shock/spalling resistance, good slag resistance, high creep resistance and refractoriness, on calcium aluminate cement bonded corundum-magnesia alumina spinel (Al 2 O 3 -MgAl 2 O 4 ) refractory castables. [1][2][3][4] To date, they have been widely applied as lining materials in refining ladles, 1,5,6 Ruhrstahl Heraeus (RH) snorkels, 7-9 purging plug, 10 and slagging gasifiers, 11-12 etc.Their corrosion behaviors in the clean steel refining processes mentioned above have been extensively investigated. [13][14][15][16][17] Zhang and Lee studied the dissolution processes of fused and tabular corundum aggregates in a silicate slag, and observed the formation of calcium hexaaluminate (CA 6 ) and hercynitic spinel layers close to the Al 2 O 3 /slag interfaces, whose continuity and morphology varied, dominating the indirect or direct dissolution processes. 18 Cho et. al. investigated the corrosion behavior of three kinds of spinel clinkers (47, 69, 94 wt% Al 2 O 3 ) in a

A post‐mortem analysis of the used gel‐bonded Al2O3–MgAl2O4 castables in an industrial steelmaking ladle

“…After 169 cycles in the refining ladle trials, the thickness of the tested sample decreased to 140 mm from the initial thickness of 210 mm. According to Equation ( 1), the average corrosion rate of every cycle was .41 mm/cycle, which was the best trial results compared with our previous works [41][42][43][44] :…”

“…Compared with fused alumina aggregates under the same corrosion conditions, the sintered alumina aggregates were degraded by an intergranular corrosion process and controlled by an active corrosion mechanism, but a passive corrosion mechanism for former one. [41][42][43][44] In this case, the fused alumina aggregates presented better slag corrosion and penetration resistance than that of the sintered ones. Moreover, the combination intensity between corundum aggregate and matrix was reduced for the formation of low-melting phase, resulting in the spalling of the aggregates.…”

“…The macro-cracks formation not only reduced the bonding strength between aggregates and matrix, but also provided the permeation pathway for molten steel/slag, and significantly increased the risk of structure spalling of refractory lining's hot side. [41][42][43][44] The corrosion mechanisms of various alumina aggregates in contact with molten slag have been investigated by many researchers. 8,[41][42][43][44] As seen in Figure 10, the typical corroded microstructures of two types of alumina aggregates, such as sintered alumina (tabular alumina) and fused alumina, in the PL were presented, respectively.…”

“…[41][42][43][44] The corrosion mechanisms of various alumina aggregates in contact with molten slag have been investigated by many researchers. 8,[41][42][43][44] As seen in Figure 10, the typical corroded microstructures of two types of alumina aggregates, such as sintered alumina (tabular alumina) and fused alumina, in the PL were presented, respectively. For the former, the tabular corundum aggregate was obviously disintegrated and penetrated by the low melt phase along the grain boundary, and then the CA 6 , CaO-Al 2 O 3 -SiO 2 low-melting phase, and (Fe, Mg)Al 2 O 4 were in situ formed at the interface between the tabular aggregate and the matrix, whereas the remaining alumina grains were also surrounded by CaO-Al 2 O 3 -SiO 2 low-melting phase via the grain boundary, keeping the original aggregate structure (Figure 10A,B and points 1-6 in Table 5).…”

“…6,8,25,[37][38][39][40] On the other hand, their corrosion behaviors in the clean steel refining processes mentioned above have been extensively investigated. As reported in our previous publication, [41][42][43][44] the corroded microstructures of the used Al 2 O 3 -spinel refractory with cement or cement-free were investigated to determine the degradation mechanism by molten steel/slag attacks. Postmortem analyses on the corroded microstructures after service under various conditions were carried out in detail to assist in understanding the degradation processes and corrosion mechanisms.…”