YÜKSEK KROMLU BEYAZ DÖKME DEMİRLERDE FAZ DENGESİNİN BENZETİMİ

Abstract

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.

Keywords

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

Simulation of Phase Equilibria in High Chromium White Cast Irons

Abstract

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.

Keywords

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

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