ithin a heat treating furnacenitridation At stake for the heatand the nuisance of downtime for 20 HEAT TREATING P ID: 261611
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What to Do About Metal Dusting ithin a heat treating furnacenitridation. At stake for the heatand the nuisance of downtime for 20 HEAT TREATING PROGRESS AUGUST 2003 Generic and practical information presentedhere is not intended to replace or supplementfederal, state, and local codes, governmentstandards, insurance requirements, companypolicies and procedures, or common sense. Inaddition, all equipment manufacturers in-structions and operating and maintenancemanuals should always be thoroughly readand followed. Further, personnel trainingshould be provided unequivocally to everyonewho will be associated with operating suchequipment. Fig. 1 (a) Metal dusting is evident on this section of a 150 mm (6 in.) in diameter radiant tube (a) (b) 0803htdr.qxd 7/23/03 10:24 PM Page 2 Photomacrographs of metal dustingalloys composition: 0.350.75 C, 1519Cr, 3337 Ni, bal. Fe.subsequent disintegration of meta-of carbon atoms from the surface intoAs a result, there is a continuousbuildup of carbon within the surface 22 HEAT TREATING PROGRESS AUGUST 2003 THEHEAT TREAT DOCTOR (a) (b) Fig. 2 (a) Surface pit resulting from severe metal dusting and oxidation on the outside diameterof the cast HT alloy radiant tube. Unetched, differential interference contrast (DIC). 100. (b) Thesurface pit at 1000. The austenite matrix underneath the surface oxidation contains a complex net-work of (eutectic) carbide (due to the high carbon content). Note that the larger patches of primarycarbide have a lamellar structure. General precipitation of fine carbide has occurred. Kallings II, DIC.Photomicrographs courtesy Aston Metallurgical Services Co. Inc., Wheeling, Ill. 0803htdr.qxd 7/23/03 10:25 PM Page 4 THEHEAT TREAT DOCTOR Circle 14 or visit www.adinfo.cc point eutectic.Another approach toerally take the form of a chromium-tive, but they are reduced by the fur-the coating, resulting in pitting.is necessary to help the alloy compo-fight this destructive enemy. Wheeling, Ill. presented in this column?Very useful, Circle 270Of general interest,Circle 271Not useful,Circle 272 24 (a) (b) Fig. 3 (a) Surface and subsurface attack on the inside diameter of the cast HT alloy radianttube. Unetched, DIC. 100. Dendritic structure is clearly visible. (b) Image at 1000of the rightside of the specimen. The (eutectic) carbide particles have agglomerated and formed continuousnetworks. Coarsening of secondary carbide has also occurred. Kallings II, DIC. Photomicrographscourtesy Aston Metallurgical Services Co. Inc., Wheeling, Ill. See us at Heat Treat Show Booth 901 0803htdr.qxd 7/23/03 10:26 PM Page 6