Investigation of microstructures, mechanical properties, wear behavior and machinability of EN-GJS-500-7 (GGG50) grade ductile cast irons having modified chemical composition

Abstract

Ductile cast irons (DI) are promising candidates for forged steels due to their lower density (10-15 %), lower production cost and good specific strength. The mechanical properties of DIs are heavily influenced by matrix (ferrite, pearlite, or ferrite+pearlite), type and concentration of alloying elements (Si, Cu, Sn, Cr and Ni. etc). The pearlite phase, which is stronger and harder than ferrite phase, depends not only on the chemical composition but also the cooling rate of sections having various section thickness. In this situation non-uniform microstructure and mechanical properties occur between the thick and thin sections of the parts. In this manner solid solution strengthened (with Si) ferritic DIs become prominent with more uniform microstructure and mechanical properties. In the present study, the microstructural properties, mechanical properties (tensile properties, hardness, and impact energy), wear resistance and tool life (turning machining operations) of EN-GJS-500-7 grade ductile cast irons, having modified composition (increased amount of Si, decreased amount of C and pearlite former), are studied in detail. The resultant microstructures and mechanical properties are compared with those for having traditional composition. For modified composition, the ferrite (solid solution strengthened with excess Si) amount considerably increases, and so the cast part exhibits uniform hardness distribution among the surface layer and center regions). In addition, the yield strength and the ultimate tensile strength (UTS) of the modified composition is slightly lower than those for traditional composition. In addition, modified composition exhibits better wear resistance (lower wear loss and friction coefficient) and longer tool life compared to those for traditional composition. As a result, an alloy with improved mechanical properties and good machinability has begun to be applied industrially

Keywords

• Ductile cast iron
• Chemical composition
• Microstructure
• Mechanical Properties
• Wear behavior

Geliştirilmiş kimyasal bileşime sahip EN-GJS-500-7 (GGG50) kalite küresel grafitli dökme demirlerin mikroyapısının, mekanik özelliklerinin aşınma davranışının ve işlenebilirliğinin incelenmesi

Abstract

Küresel grafitli dökme demirler (KGDD), düşük yoğunlukları (%10-15), düşük üretim maliyetleri ve iyi özgül mukavemetleri nedeniyle dövme çelikler için aday malzemeler olarak düşünülmektedir. KGDD'lerin mekanik özellikleri matris tipine (ferrit, perlit veya ferrit + perlit), alaşım elementlerinin türü ve konsantrasyonuna (Si, Cu, Sn, Cr ve Ni. vb.) bağlıdır. Ferrit fazına göre daha güçlü ve daha sert olan perlit fazı sadece kimyasal bileşime değil aynı zamanda farklı kesit kalınlığına sahip parçalarda soğuma hızına da bağlıdır. Bu durum parçaların kalın ve ince bölümleri arasında farklı mikroyapıların oluşmasına ve farklı mekanik özelliklerin ortaya çıkmasına sebep olmaktadır. Bu durumda katı çözeltiyle güçlendirilmiş (Si) ferritik KGDD'ler daha homojen mikroyapı ve mekanik özelliklere sahip olarak öne çıkmaktadır. geliştirilmiş bileşime sahip (arttırılmış Si miktarı, azaltılmış C miktarı ve perlit oluşturucu) EN-GJS-500-7 kalite KGDD’lerin mikroyapısal ve mekanik özellikleri (çekme özellikleri, sertlik ve darbe enerjisi), aşınma direnci ve takım ömrü (tornalama sırasında) detaylı biçimde incelenmiştir. Elde edilen mikroyapılar ve mekanik özellikler, geleneksel bileşime sahip KGDD’lerin mikroyapı ve mekanik özellikleri ile karşılaştırılmıştır. Geliştirilmiş bileşim için, ferrit (fazla Si ile güçlendirilmiş katı çözelti) miktarı önemli ölçüde artmakta ve bunun sonucunda döküm parçanın yüzey bölgeleri ile merkez (çekirdek) arasında düzgün bir sertlik dağılımı elde edilmiştir Ek olarak, geliştirilmiş bileşimin akma ve çekme mukavemeti , geleneksel bileşime göre çok az daha düşüktür. Buna ilaveten, geleneksel bileşime kıyasla geliştirilmiş bileşimin daha üstün aşınma direncine (daha düşük aşınma kaybı ve sürtünme katsayısı) sahip olduğu ve talaşlı imalat süreçlerinde uzun takım ömrünü uzattığı tespit edilmiştir. Sonuç olarak, geliştirilmiş mekanik özelliklere ve iyi işlenebilirliğe sahip bir alaşım endüstriyel olarak uygulanmaya başlanmıştır.

Keywords

• Küresel grafitli dökme demir
• Kimyasal bileşim
• Mikroyapı
• Mekanik Özellikler
• Aşınma Davranışı

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