Corrosion Metals and alloys containing vanadium or exposed to vanadium oxide are subject to rapid oxidation In@ M a r n 4;. lirNItana
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the past 2 years, great interest developed rapid oxidation phenomenon first described in the literature in this column for June 1948 and in the Proceedings of the Pittsburgh International Conference on Surface Reactions, June 1948. Extremely rapid attack occurs, under certain conditions, when the alloy contains molybdenum, vanadium, tungsten, or several other elements, or a metal or alloy is in contact with the oxides or vapors of the oxides of the.% elements. This rapid oxidation is also called accelerated oxidation and catastrophic oxidation. The interest in this connection concerns mainly jet engine applications requiring high strength alloys, and the use of vanadium-containing fuel oils, such as oil from Venezuela. In June 1948 it was pointed out that vanadium pentoxide produced the mast spectacular oxidation. Numerous inquiries have been received by the writer concerning this phenomenon and many actual occurrences in service were described. It seems worth while to report on additional work on vanadium-hearing steels and metals in contact with vanadium oxide. One purpose of the study was to determine whether or not a slagging effect would occur when steel is in contact with molten vanadium oxide. Rapid attack OCCUIS in steel boiler tuhes as a result of a deposit of vanadium oxide on the tuhes when vanadiumhearing fuel oil is used. This work was carried out by Richard M. Berry as an undergraduate metallurgical investigation a t The Ohio State University. The metals used in this study were ordinary 1020 ~i~~~ 1. ~ o ~ ~ i i .Rapid ed w b o n steel, Type 410 Ox%ktion of 8% Chw(12% chromium) stainles mium-2qo Vanadium Steel steel, and a chromiumvanadium steel containing 7.89% chromium, 2.06% vanadium, 0.13% carbon, 0.387, silicon, O.llyoaluminum, and O . o O l ~ onitrogen. The specimens were placed in partially covered crucibles in the furnace to obtain an almost completely stagnant atmosphere. Previous work showed that slight movement of air in the furnace prevented rapid oxidation and a more normal type of corrosion occurred. The chromium-vanadium steel showed the rapid oxidation effect, in thst a very heavy oxide scale developed in a few hours a t 1600° F. In most cases the UKINQ III the
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bulk oxide forms more or less over the entire surface of the specimen, hut sometimes the effect is somewhat localized and a growth or knob ocours. This latter effect is shown in Figure 1, where the oxide growth is on one corner of the specimen. A series of tests was run with the carbon steel, the Type 410 stainless steel, and the chromium-vanadium deet in separate isolated crucibles, and also with the carhon steel in contact with the chromium-vanadium steel in oue crucible and the 410 stainless steel with the chromium-vanadium steel in another crucible. These tests were run at 1650" F. for 29 hours. The attack on the carbon steel and the 410 stainless steel was much greater when they weie in contact with the chromium-vanadium steel than when they sere 1)v themselves. A thin flat specimen of chromiumvanadium steel increased in weight 43%, about 1.5% per hour. The rate of oxidation of the chromiumvanadium steel was about ten times greater than ordinary carbon steel. The former contains about 8% chromium and is actually a stainless steel. The deleterious effect of the vanadium in this alloy is obvious.
Figure 2. Oxidstion of Carbon S t a l (Top Rew), Type 410 Stainless Steel (Middle Row), and 8% Chromium-2% Vanadium Steel (Bottom Row) s t 1650°F. with Variable Time
Another series of tests was run on isolated spec' 'imena a t 1650' F. for various times (Figure 2). Going from left to right the specimens were exposed for 0, 7, 15, 19, and 29 hours. The rapid oxidation of the chromiumvanadium steel is apparent. The attack on this steel is much greater than that on the plain carbon steel. The second phase of this investigation included exposure of ordinary carbon steel specimens to molten vanadium pentoxide. Regular (CmUinuud rm page 66 A )
Corrosion steel specimens and ateel with an oxide coating formed prior to exposure to the vanadium oxide were u.%d. The specimens were placed in crucibles containing the molten oxide. The temperature waa maintained at, 1320" F. or not far ahovo the melting point of the oxide. The specimens were poaitioned at ahout a 45" angle and were about one half submerged. The angle between the underside of the specimen and the liquid l i e served as a sort of pocket for trapping vapors of t,he vanadium oxide.
1, Rapid Corn?,*i',,B uc Sled b, ,Woltn, Vanadium I'entoxidr s t Liyeid Line n
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b.
Vi& most With E-SIOP
ol - r e d e m
p a l u e b a mmeral p d u e t m intlet
Severe 1ot:aliu.d currosioii ocwrred uii the steel at the liquid line. The attack oil the underneat,h portion of the steel WRJ much greater than on the upper face of the sperimen. Figure 3 illustrates the grooving or localized attack observed. Figure 3 , a, ahows a specimen expoved for 14 hours and with mast of the corrmion products removed. Figure 3, 6, is a steel spe~' .men as removed from the furnace with the eorrmion produck in place This specimen was rxposed for 3.5 houn. The greatly increased attack on the underside of the specimen indicates the acceleration of corrmion hy stagnail t vanadium pentoxide vapor and corresponds t,o the rapid oxidation by molyhdmum oxide (Mool) lJl>SeNed in previous work. No appreciable differences in corrosion were observed between clean specimens and preoxidized specimens. This xtudy of a vanadium-hearing alloy and vanadium oxide shows rapid oxidation similar to khat obtained in molybdenum-bearing alloys and molybdenum oxide. The mechanism is essentially the same. Incidentally, a recent publication by Brasunas and Grant l h n Age, 166, 85-90 (Aug. 17, 1950)) of the Massachu.&ts Institute of Tcehnology indicatea that some of our earlier work on the rapid oxidation of 16 25-6 (Cr, Ni, Mo) alloy was duplicated and reprcdooed. @A
