Zinc is an increasing threat because increasingly more automotive is being galvanized. In cupola melting, most of the zinc is volatilized, complicating the effluent disposal, but leaving little detriment to the iron. In induction melting, zinc has penetrated the lining and damaged In , troubles have been experienced from graphite deterioration from excessive zinc in the iron. Much is yet to be learned as threats of zinc contamination increase. ALUMINUM - (AI) Aluminum is present in amounts in alloys and is beneficial in inoculants. These do not cause excessive concentration unless supplemented by other inadvertent sources. But, if all cumulative sources of aluminum exceed .04%, graphite nodularity can be damaged. Fig. 46 shows deteriorated graphite from .13% aluminum. Aluminum is present in killed steels, and aluminum metal can be attached to steel scrap. ZIRCONIUM (Zr) Zirconium .01% can distort nodular graphite shape. SELENIUM (Se) similar to sulfur, causes flake graphite and should be below .01%. Combinations of these trace elements can be additive in effect. However, cerium can precipitate out and counteract marginal amounts of these deleterious elements and extend safe concentration levels. However, it is safer to avoid these contaminating elements than to depend on cerium protection. There is yet much to be learned about trace element combinations and their neutralization. UNDESIRABLE CARBIDE FORMERS - (B) Boron is a most powerful carbide former at trace levels of .002% and must be avoided. can be absorbed from new induction furnace linings with borate binder. Other sources can be vitreous enamels, some steels, malleable iron scrap, etc. CHROMIUM - (Cr) Chromium is a very potent carbide and pearlite stabilizer. In ferritic grades, chromium should be kept below .05%. In pearlitic grades, chromium may be tolerated up to .10%. Beyond .10%, chromium increases carbide tendency strongly and retards annealing. For wear and abrasion resistance, chromium is intentionally added to produce some wear resistant carbides in the microstructure.
Zinc is an increasing threat because increasingly more automotive is being galvanized. In cupola melting, most of the zinc is volatilized, complicating the effluent disposal, but leaving little detriment to the iron. In induction melting, zinc has penetrated the lining and damaged In , troubles have been experienced from graphite deterioration from excessive zinc in the iron. Much is yet to be learned as threats of zinc contamination increase. ALUMINUM - (AI) Aluminum is present in amounts in alloys and is beneficial in inoculants. These do not cause excessive concentration unless supplemented by other inadvertent sources. But, if all cumulative sources of aluminum exceed .04%, graphite nodularity can be damaged. Fig. 46 shows deteriorated graphite from .13% aluminum. Aluminum is present in killed steels, and aluminum metal can be attached to steel scrap. ZIRCONIUM (Zr) Zirconium .01% can distort nodular graphite shape. SELENIUM (Se) similar to sulfur, causes flake graphite and should be below .01%. Combinations of these trace elements can be additive in effect. However, cerium can precipitate out and counteract marginal amounts of these deleterious elements and extend safe concentration levels. However, it is safer to avoid these contaminating elements than to depend on cerium protection. There is yet much to be learned about trace element combinations and their neutralization. UNDESIRABLE CARBIDE FORMERS - (B) Boron is a most powerful carbide former at trace levels of .002% and must be avoided. can be absorbed from new induction furnace linings with borate binder. Other sources can be vitreous enamels, some steels, malleable iron scrap, etc. CHROMIUM - (Cr) Chromium is a very potent carbide and pearlite stabilizer. In ferritic grades, chromium should be kept below .05%. In pearlitic grades, chromium may be tolerated up to .10%. Beyond .10%, chromium increases carbide tendency strongly and retards annealing. For wear and abrasion resistance, chromium is intentionally added to produce some wear resistant carbides in the microstructure.
Ductile-Iron-Quality-Assurance-Guide-Apendix-3-to-end.docx