YÜKSEK KROMLU BEYAZ DÖKME DEMİRLERDE FAZ DENGESİNİN BENZETİMİ

Yıl 2018, Cilt: 23 Sayı: 3, 179 - 190, 31.12.2018

Öncü Akyıldız , Duygu Candemir , Hakan Yıldırım

https://doi.org/10.17482/uumfd.333701

Cited By: 4

Öz

Bu çalışmada Materials Calculator yazılımı kullanılarak, farklı molibden
içeriğine sahip yüksek kromlu beyaz dökme demirlerin (ağırlıkça ~%19) ikilimsi faz
diyagramları (eşdeğer kesit haritaları) benzetilmiştir.  Hesaplanan faz diyagramlarının doğruluğunu
test etmek amacı ile, diyagramlardan belirli kompozisyonlarda okunan dönüşüm
sıcaklıkları, aynı kompozisyonlarda döküm sonrası yavaşça soğutularak üretilen
numunelerin diferansiyel taramalı kalorimetri (İng.: Differential Scanning
Calorimetry, DSC) analizi ile ölçülen faz dönüşüm sıcaklıkları ile
karşılaştırılmıştır. Yine aynı amaçla, faz diyagramlarından okunan düşük
sıcaklık fazları ve döküm ile üretilen numunelerin içindeki, X-ışını kırınım
yöntemi (İng.: X-Ray Diffraction, XRD) ile belirlenen, kristalin fazlar
karşılaştırılmıştır. Benzetilen diyagramlar, artan molibden içeriği ile ikincil
M₂₃C₆ karbürlerin miktarında bir artış öngörmüştür. Bu
öngörünün geçerliliği döküm ile üretilen numuneler içerisindeki faz dağılımı ve
faz kompozisyonlarını metalografik muayene, taramalı elektron mikroskobu (İng.:
Scanning Electron Microscopy, SEM) – enerji saçınım spektrometresi (İng.:
Energy Dispersive Spectroscopy, EDS) analizleri ile belirleyerek test
edilmiştir. Numunelerin sertlik değerlerine bakıldığında ise, herhangi bir ısıl
işlem yapılmaksızın Mo içeriğindeki %1 'lik bir artış ve buna bağlı ikincil
karbürlerin miktarındaki artış ile sertliğin 44,90'dan 51,05 HRC'ye yükseldiği
görülmüştür. Elde edilen sonuçlar deneysel ölçümler ve teorik tahminlerin
uyumlu olduğunu ve çok bileşenli sistemlerde faz dengesinin tahmin
edilebilmesinin pratik önemini göstermiştir.

Anahtar Kelimeler

Hesaplamalı termodinamik, MatCalc, Alaşım tasarımı, Yüksek kromlu beyaz dökme demir, ikincil karbürler

Simulation of Phase Equilibria in High Chromium White Cast Irons

Öz

In this study, using the Materials Calculator software program, the
pseudo binary phase diagrams (i.e. isoplethal maps) of high chromium white cast
irons (~19% in weight) with different molybdenum contents were simulated. In
order to test the accuracy of the calculated phase diagrams, the transformation
temperatures read from the diagrams at certain compositions were compared with
the phase transformation temperatures measured using Differential Scanning
Calorimetry (DSC) analysis of the samples produced by casting in the same
composition followed by slow cooling. With the same purpose, low temperature
phases read from the phase diagrams were compared with the crystalline phases
determined by X-Ray Diffraction (XRD) of the casted samples. Simulated diagrams
predicted an increase in the amount of secondary M₂₃C₆carbides with increasing molybdenum content. The
validity of this prediction was tested by determining the phase distribution
and phase compositions in the casted samples by means of metallographic
examinations and Scanning Electron Microscopy (SEM) - Energy Dispersive
Spectroscopy (EDS) analyzes. When the hardness values of the samples were taken
into consideration, it was seen that the hardness increased from 44.90 to 51.05
HRC with a 1% increase in Mo content and a corresponding increase in the amount
of secondary carbides without any heat treatments. Results show that
theoretical predictions and experimental measurements are in accord and
estimating phase equilibria in multi-component systems is of practical
importance.

Anahtar Kelimeler

MatCalc, Computational thermodynamics, Alloy design, High chromium white cast iron, Secondary carbides

Kaynakça

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