Carbide Dissolution Kinetics during Partial and Full Austenitization in 100Cr6 Steel

Öz

In this work, cementite dissolution kinetics was studied in 100Cr6 steel during partial and full austenitization. The change in cementite volume fraction and size was determined from samples heat treated for different durations at 840 °C and 1050 °C. The SEM micrographs were analyzed by using ImageJ software to count size and volume fraction of carbides. The obtained statistical data were used to draw the dissolution curves with a nonlinear curve fitting method. It was found that the cementite dissolution rate is fast at the beginning of partial and full austenitization. A model was established and carbide dissolution was calculated using DICTRA software. The dissolution curves were obtained and compared with the DICTRA simulations. The calculation results are in good agreement with the dissolution curves from statistical results of SEM micrographs. According to the calculation results, the fast carbide dissolution is due to dissolution under non-partitioning local equilibrium (NPLE) mode controlled by diffusion of C atoms and neglecting diffusion of Cr. 

Anahtar Kelimeler

• Austenitization,kinetic simulations,dissolution kinetics,image analysis,imageJ

100Cr6 Çeliğinde Kısmi ve Tam Östenitlemede Karbür Çözünmesi Kinetiği

Öz

Bu çalışmada, 100Cr6 çeliğinde kısmi ve tam östenitleme koşullarında sementit çözünme kinetiği incelenmiştir. 840 °C ve 1050 °C sıcaklıkta farklı sürelerde ısıl işleme tabi tutulan numunelerde sementit hacim oranındaki ve boyutundaki değişim belirlenmiştir. ImageJ yazılımı ile SEM mikrografları analiz edilerek karbürlerin boyutu ve hacim oranları belirlenmiştir. Elde edilen istatistiksel veriler “lineer olmayan eğri uydurma” yöntemi kullanılarak çözünme eğrilerine dönüştürülmüştür. Tam ve kısmi östenitleme işlemlerinin başlangıcında sementit çözünme hazının yüksek olduğu belirlenmiştir. Bir model kurularak DICTRA yazılımında karbür çözünmesi hesaplanmıştır. Elde edilen çözünme eğrileri DICTRA sonuçları ile karşılaştırılmıştır. SEM mikrograflarından elde edilen istatistikler ile DICTRA hesaplamalarının uyumlu olduğu görülmüştür. Elde edilen hesaplama sonuçlarına göre başlangıçtaki hızlı karbür çözünmesinin nedeni, C atomları difüzyonu ile kontrol edilen ve Cr difüzyonunun ihmal edildiği “ihmal edilebilir yerel denge” modunda çözünmenin gerçekleşmesidir.

Anahtar Kelimeler

• Östenitleme,kinetik simülasyon,çözünme kinetiği,görüntü analizi,ımageJ

Kaynakça

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