Effect of Process Parameters on the Metallurgical Properties of a Boron-Added Cast Austenitic Steel Designed for Special Purposes

Year 2024, Volume: 16 Issue: 1, 93 - 105, 31.01.2024

Ersel Aydın , Fikri Erdem Şeşen , Selim Coşkun Cevat Fahir Arısoy

https://doi.org/10.29137/umagd.1359083

Abstract

A new kind of boron-added cast austenitic steel which also contained chromium, molybdenum and manganese was manufactured via vacuum induction melting followed by casting procedure. Solution annealing heat treatment was performed at three different temperatures for three different times to dissolve eutectic M2C carbides in austenitic matrix. All of the samples were rapid-cooled in oil medium after the solution annealing heat treatment. Aging treatments were carried out after solution annealing heat treatment performed at 1250 °C for 24 hours. Hardness value was decreased after solution annealing performed at 1250 °C for 24 hours. Transformation of M2C carbide with a hexagonal lattice into Fe-rich M6C carbide with a face-centered cubic lattice and formation of precipitates occurred as a result of aging performed at 700 and 800 °C. Sub-micron sized Cr23C6 carbides and Mo2BC precipitates were formed and hardness value was increased after aging performed at 700 °C. Nano-sized Cr23C6 carbides, Mo2B borides and Cr7BC4 precipitates were formed and hardness value was higher after aging performed at 800 °C. An optical light microscope was utilized to characterize solution annealing treatments and to perform grain size measurements. A scanning electron microscope was used to identify carbide types and carbide transformation during aging.

Keywords

Vacuum induction melting, Cast austenitic steel, Heat treatment, Precipitation hardening, Carbide and boride precipitate, Carbide transformation

Ethical Statement

This manuscript has been originated from the MSc thesis of the first author.

Supporting Institution

This work was financially supported by Scientific Research and Project Unit of Istanbul Technical University.

Özel Amaçlara Yönelik Tasarlanmış Bor Katkılı bir Dökme Ostenitli Çeliğin Metalurjik Özelliklerine İşlem Parametrelerinin Etkisi

Abstract

Yeni bir tür bor katkılı, aynı zamanda krom, molibden ve manganez içeren, dökme ostenitli çelik vakum indüksiyon ergitmenin ardından döküm yoluyla üretilmiştir. Ötektik M2C karbürlerini ostenitli matriks içerisinde çözündürmek amacıyla üç farklı sıcaklıkta üç farklı süreyle çözeltiye alma ısıl işlemi uygulanmıştır. Çözeltiye alma ısıl işleminin ardından numunelerin tümü yağ ortamında hızlı soğutulmuştur. 1250 °C sıcaklıkta 24 saat süreyle uygulanmış çözeltiye alma ısıl işleminin ardından yaşlandırma işlemleri yapılmıştır. 1250 °C sıcaklıkta 24 saat süreyle uygulanmış çözeltiye alma işlemi sonucu sertlik değeri düşmüştür. 700 ve 800 °C sıcaklıklarda uygulanan yaşlandırma işlemleri sonucu hegzagonal kafes yapısındaki M2C karbürünün yüzey merkezli kübik kafes yapısındaki demirce zengin M6C karbürüne dönüşümü ve çökelti oluşumu meydana gelmiştir. 700 °C sıcaklıkta yapılan yaşlandırma işlemi sonucunda mikron altı boyutta Cr23C6 karbürleri ve Mo2BC çökeltileri oluşmuş ve sertlik değeri yükselmiştir. 800 °C sıcaklıkta yapılan yaşlandırma işlemi sonucunda da nano boyutta Cr23C6 karbürleri, Mo2B borürleri ve Cr7BC4 çökeltileri oluşmuş ve sertlik değeri daha fazla yükselmiştir. Çözeltiye alma işlemlerinin karakterize edilmesi ve tane sınırı ölçümlerinin yapılması amacıyla bir ışık mikroskobu kullanılmıştır. Karbür tiplerinin ve yaşlandırma sırasında meydana gelen karbür dönüşümünün tanımlanması amacıyla da bir taramalı elektron mikroskobu çalıştırılmıştır.

Keywords

Vakum indüksiyon ergitme, Dökme ostenitli çelik, Isıl işlem, Çökelme sertleşmesi, Karbür ve borür çökelmesi, Karbür dönüşümü

Ethical Statement

Bu metin, birinci yazarın Yüksek Lisans tez çalışmasından üretilmiştir.

Supporting Institution

İstanbul Teknik Üniversitesi Bilimsel Araştırmalar ve Proje Birimi tarafından maddi olarak desteklenmiştir.

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