Orta manganlı bir çeliğin mikroyapısı ve mekanik özellikleri üzerinde Cr ilavesinin ve kritik tavlama koşullarının etkisi

Abstract

İleri yüksek mukavemetli çelikler, yüksek mukavemetleri ve iyi şekillendirilebilirlik özellikleri sayesinde hem hafiflik hem de güvenlik sunan malzemeler olarak otomotiv endüstrisinin ilgisini çekmektedir. Bu çelik grubu içinde, orta manganlı çelikler, dönüşüm kaynaklı plastisite etkisi sayesinde mükemmel bir mukavemet-süneklik dengesi sunarak yeni nesil mühendislik uygulamalarında öne çıkmaktadır. Bu çalışmada, Cr ilavesi ve kritik ara tavlama koşullarının orta manganlı çeliklerin mikro yapı ve mekanik özellikleri üzerindeki etkileri incelenmiştir. %0, %0,4, %0,8 ve %1,2 ağırlık oranlarında Cr ilavesi içeren 45 mm kalınlığındaki orta Mn çelik levhalar (0,16C-5,5Mn) döküm yöntemiyle üretilmiş ve ardından sıcak presleme ve sıcak dövme yöntemleriyle 5 mm kalınlığa indirilmiştir. Numuneler kritik ara bölgede (650 °C) tavlanmış ve ardından havada veya suda soğutma ile soğutulmuştur. Mikroyapısal karakterizasyon optik ve taramalı elektron mikroskobu kullanılarak gerçekleştirilmiştir. Kalan ostenitin faz bileşimi ve hacim oranı, X-ışını kırınımı ve enerji dağılımlı spektroskopisi ile belirlenmiştir. Sonuçlar, kalan ostenit fazının hacim oranının hızlı soğuma ve Cr içeriğiyle arttığını göstermiştir. Çekme testlerinde, çelik bileşimindeki Cr'un çekme dayanımı-toplam uzama kombinasyonunu iyileştirdiği gözlemlenmiştir. En iyi kombinasyon, kritikler arası tavlama sonrası suda söndürme ile %1,2 Cr ilave edilen numunede elde edilmiştir.

Keywords

• Çekme davranışı
• Gelişmiş yüksek mukavemetli çelikler
• Orta manganlı çelikler
• Kritik tavlama
• Cr ilavesi
• Kalıntı östenit

Effect of Cr Addition and Intercritical Annealing Conditions on Microstructure and Mechanical Properties of A Medium Manganese Steel

Abstract

Advanced high-strength steels are attracting the attention of the automotive industry as materials that offer both lightness and safety due to their high strength and good formability properties. Within this group of steels, medium-manganese steels stand out in new-generation engineering applications by offering an excellent balance of strength-ductility thanks to the transformation-induced plasticity effect. In this study, the effects of Cr addition and intercritical annealing conditions on microstructure and mechanical properties of medium manganese steels were investigated. 45 mm thick medium Mn steel plates (0.16C-5.5Mn) with 0, 0.4, 0.8, 1.2 wt.% Cr additions were manufactured by casting and then reduced to 5 mm thickness by hot pressing and hot forging. The samples were annealed in the intercritical region (650 °C) and then cooled either in air or by water quenching. Microstructural characterization was performed using optical and scanning electron microscopy. The phase composition and volume fraction of retained austenite were determined through X-ray diffraction and energy-dispersive spectroscopy. The results showed that the volume fraction of the retained austenite phase increased with rapid cooling and Cr content. In the tensile tests, it was observed that the Cr in the steel composition improved the tensile strength-total elongation combination. The best combination (32 GPa.%) was obtained in the 1.2% Cr added sample by water quenching after intercritical annealing.

Keywords

• Advanced high-strength steels
• Medium manganese steels
• Intercritical annealing
• Cr addition
• Retained austenite
• Tensile behavior

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