ARAKRİTİK SICAKLIKLARDAN ÖSTEMPERLENMİŞ FERRİTİK KÜRESEL GRAFİTLİ DÖKME DEMİRDE YENİ FERRİT OLUŞUMU

Öz

Bu çalışmada, ferritik küresel grafitli dökme demirlerde, arakritik sıcaklıklardan östemperleme sırasında oluşanmikroyapılar incelenmiştir. Bu amaçla ferritik küresel grafitli dökme demir, farklı arakritik sıcaklıklardatavlanmış (kismi östenitlenmiş) ve ardından 365 °C’deki tuz banyosunda farklı sürelerde östemperlenmiştir.Farklı arakritik sıcaklıklardan östemperlemenin ardından, östemperleme süresine bağlı olarak östenittendönüşüm ürünlerinin miktarlarındaki farklılık, mikroyapı değişim grafikleri ile kantitatif olarak gösterilmiştir.Metalografik ölçümler, özellikle belirli bir arakritik tavlama sıcaklığında oluşan orijinal östenitten östemperlemesırasında dönüşen fazların toplam hacim oranının yaklaşık olarak bütün östemperleme süreleri için orijinalöstenitin hacim oranına eşit olduğunu göstermiştir. Arakritik tavlama sıcaklıklarından östemperlenmişnumunelerin her birinde ötektoid öncesi ferrit ve beynitik ferrite ilaveten yeni ferrit (epitaksiyel ferrit) açığaçıkmıştır. Artan arakritik sıcaklığı ile yeni ferrit hacim oranıda artmıştır. Ancak, yeni ferritin arakritiköstenitleme sıcaklığındaki orijinal östenitten dönüşüm yüzdesi, azalan arakritik östenitleme sıcaklığı ile artmıştır.Östemperleme süresindeki artış yeni ferrit, beynitik ferrit ve yüksek karbonlu östenitin martensitle yerdeğişimine neden olmuştur. Numunelerin bazıları karşılaştırma amacıyla 900°C’ den geleneksel olaraköstemperlenmiştir. Geleneksel östemperlenmiş numunelerde yeni ferritin varlığına rastlanmamıştır.

Anahtar Kelimeler

• Çift fazlı matris yapı (ÇFMY), kısmi östenitleme, ösferrit hacim oranı, östemperlenmiş küresel grafitli dökme demir (ÖKGDD), yeni ferrit hacim oranı.

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