Burak NALÇACI, Volkan KILIÇLI, Mehmet ERDOĞAN

Çift Fazlı (α + M) Küresel Grafitli Dökme Demirlerde Martenzit Hacim Oranı-Mekanik Özellikler-Dislokasyon Yoğunluğu Arasındaki İlişkilerin İncelenmesi

Bu çalışmada, çift fazlı (α+M) küresel grafitli dökme demirlerde (ÇF-KGDD) martenzit hacim oranı-mekanik özellikler-dislokasyon yoğunluğu arasındaki ilişkiler incelenmiştir. Farklı faz hacim oranlarında martenzit ve ötektoid öncesi ferritten oluşan çift fazlı mikroyapılar 770°C, 775°C ve 780°C ara kritik kısmi östenitleme sıcaklıklarından oda sıcaklığındaki suda soğutularak üretilmiştir. Mikroyapı karakterizasyon çalışmaları optik mikroskop, taramalı elektron mikroskobu (SEM) ve X-Işını kırınım (XRD) analizi teknikleri kullanılarak gerçekleştirilmiştir. Mekanik özelliklerin belirlenmesi için çekme ve sertlik testleri yapılmıştır. Dislokasyon yoğunluğu XRD desenlerinden faydalanılarak Williamson-Hall (W-H) eşitliği ile hesaplanmıştır. Artan arakritik östenitleme sıcaklığıyla martenzit hacim oranı ve dislokasyon yoğunluğunun arttığı belirlenmiştir. Martenzit hacim oranı arttıkça sertlik, akma ve çekme dayanımı arttığı, toplam % uzama azaldığı ve kırılma modunun sünekten-gevreğe geçtiği gözlemlenmiştir.

Anahtar Kelimeler:

Çift fazlı küresel grafitli dökme demir (ÇF-KGDD), arakritik östenitleme sıcaklığı, martenzit hacim oranı, mekanik özellikler, dislokasyon yoğunluğu

Investigation of Correlations among Martensite Volume Fraction-Mechanical Properties-Dislocation Density in Dual Phase (α + M) Ductile Cast Irons

In this study, the correlations among martensite volume fraction-mechanical properties-dislocation density was investigated in dual-phase (α+M) ductile cast irons (DP-DCI). Dual-phase microstructures consisting of martensite and proeutectoid ferrite in different phase volume fractions were produced by cooling in the water at room temperature from 770°C, 775°C, and 780°C intercritical austenitizing temperatures. Microstructure characterization studies were performed using an optical microscope, scanning electron microscope (SEM), and X-ray diffraction (XRD) analysis techniques. Tensile and hardness tests have been conducted to determine the mechanical properties. Dislocation density was calculated via Williamson-Hall (W-H) equation by using XRD patterns. It was determined martensite volume fraction and dislocation density enhanced with increasing intercritical austenitizing temperature. As the martensite volume fraction increased, that the hardness, yield, and tensile strength increased, the total % elongation decreased and the fracture mode changed from ductile to brittle were observed.

Keywords:

Dual phase ductile cast ıron (DP-DCI), intercritical austenization temperature, martensite volume fraction, mechanical properties, dislocation density,

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