Development of High Silicon Dual Phase Austempered Ductile Iron

Abstract

This work deals with the feasibility of obtaining Austempered Ductile Iron with Dual Phase structures (DPADI) through heat treatment, starting from different as-cast microstructures. The mechanical properties on these microstructures were evaluated. DPADI microstructures were obtained by adding different tenors of silicon (2.4% to 4.2%) to the melts and keeping the other alloying elements constant. The study focused on the determination of the time required to achieve the percentages of equilibrium phases (ferrite and austenite) at different temperatures in the intercritical temperature interval as a function of the starting as cast microstructure. The results showed that, as the silicon content increases, higher amount of ferrite is present in the as cast structure, and the time required to reach the thermodynamic equilibrium phases in the intercritical temperature interval is markedly reduced. Similarly, for a constant chemical composition, as the intercritical austenitizing temperature increases, the time required to reach the quantities of the equilibrium phases decreases.Regarding mechanical properties, the tests revealed that, as expected, as intercritical austenitising temperature increases so do tensile strength and hardness due to the higher ausferrite content in the DPADI matrix.These results indicate that high silicon Ductile Iron (with Si content higher than 3%) with a mostly ferritic microstructure in as cast conditions yields DPADI microstructures able to dispense with prior annealing heat treatments since the time required to reach the phase equilibrium percentages is compatible with the industrial practice and the mechanical properties are similar as compared to DPADI structures deriving from fully ferritic matrices.

A Novel Step-Up Austenitization and Austempering Heat Treatment Process for Ductile Cast Iron

“…Thus, a combination of high strength and high ductility is not possible to produce in conventionally processed ADI. Therefore, in recent years many researchers [11][12][13][14][15][16][17][18] have used an intercritical austempering process to improve the ductility of ADI.…”

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

“…Çift fazlı küresel grafitli dökme demirlerin (ÇF-KGDD) kontrol edilebilir farklı dayanım ve süneklik seçenekleri sunmaları, son yıllarda araştırmacıların dikkatini çekmiştir [4][5][6][7]. Ötektoid öncesi ferrit+martenzit mikroyapısına sahip ÇF-KGDD'ler Fe-C-Si faz diyagramında Ac1 ve üst kritik sıcaklık arasında kalan γ+α+G bölgesinde [8][9][10] kısmi östenitleme ardından hızlı soğutularak, bu bölgede oluşan östenitin martenzite dönüşümünün sağlanması ile elde edilmektedirler [11,12]. Levye kuralı gereği, ara kritik sıcaklığa bağlı olarak ötektoid öncesi ferrit, östenit hacim oranları ve östenitin karbon içeriği değişime uğramaktadır [13][14][15].…”

Genetic Algorithm-Based Optimization Methodology of Bézier Curves to Generate a DCI Microscale-Model

“…DCIs are ferrous alloys that are comprised of graphite elements within a ferritic matrix, where the graphite elements, usually called graphite nodules, are characterized by a semi-spherical shape [2]. Because of the particular geometry of the graphite nodules, the DCIs have good characteristics, such as excellent mechanical properties, machinability characteristics, superior corrosion, and abrasive resistance [3][4][5][6]. The different DCIs mechanical properties, such as, high values of tensile strength and Young's modulus, among others [7], are some of the reasons that make DCIs very versatile for different engineering fields such as the automotive industry, mining industry, among others [8,9].…”