Investigation of the Effect of Nb Alloying Element on the Mechanical Properties of Low Carbon Steel Structures Using EBSD

Year 2025, EARLY VIEW, 1 - 1

Zeynep Erpek , Nil Toplan

https://doi.org/10.2339/politeknik.1648120

Abstract

This work aims to investigate the relationship between grain structure, crystallographic properties, tensile strength, and hardness in low-carbon structural steels both without niobium (Nb) and with Nb additions up to 0.012 wt.%. The microstructure of the samples was examined through optical microscopy, SEM, and EBSD techniques incorporated within the SEM setup. Additionally,chemical composition analysis of the steel samples was conducted via optical emission spectroscopy.The steel samples were produced as slabs through a slab casting process, following the ladle vacuum treatment conducted with an AC type electric arc furnace. Subsequently, the slabs were placed into the hot sheet rolling mill's annealing furnace, heated to rolling temperatures, and processed into coils after the final rolling stage.The rolling parameters of the produced coils were kept constant. Specifically, to assess the impact of niobium on grain refinement in steel, the grain boundary characteristics, texture analysis, and dislocation density distributions were examined using the EBSD. The results show that Nb increases the yield strength by reducing the grain size and improving the steels' mechanical performance. Although Nb-added low-carbon steels have been the subject of various studies, comprehensive EBSD-based microstructural examinations are few. Therefore, this thesis enhances the understanding of Nb-alloyed low-carbon structural steels by presenting a thorough EBSD-focused study of their crystallographic and mechanical performance.

Keywords

Low-carbon steel , Niobium (Nb) alloying , EBSD (Electron backscatter diffraction) , Grain refinement mechanism

Düşük Karbonlu Yapı Çeliklerinde Nb Alaşım Elementinin Mekanik Özelliklere Etkisinin EBSD ile İncelenmesi

Abstract

Çalışma kapsamında; niyobyum katkısız ve maksimum ağ. %0,012 Nb içeriğine sahip çelik numunelerde tane yapısı, kristalografik özellikler, çekme ve sertlik özellikleri arasındaki ilişki incelenmiştir. Numunelerin mikro yapısal özellikleri, optik mikroskop ve yüksek çözünürlüklü taramalı elektron mikroskobu (SEM) ve bu sisteme bağlı EBSD (Elektron Geri Saçılım Difraksiyonu) detektörü kullanılarak gerçekleştirilmiştir. Çeliğin kimyasal bileşimi optik emisyon spektrometresiyle çıkarılmıştır. Çalışmada kullanılan çelikler, alternatif akımlı (AC tip) elektrik ark ocağı ile üretilmiş, pota vakum işlemlerinin ardından slab döküm makinesinde slab haline getirilmiştir. Daha sonra slablar sıcak sac haddehanesinde tav fırınına şarj edilerek hadde sıcaklığına çıkarılmış ve nihai haddeleme sonrası bobin olarak üretilmiştir. Üretilen bobinlerin haddeleme parametreleri sabit tutulmuştur. Özellikle niyobyumun çelikte tane boyutuna etkisi EBSD yöntemi kullanılarak tane sınırı karakterizasyonu, doku analizi ve dislokasyon yoğunluğu dağılımları incelenmiştir. Elde edilen sonuçlar, Nb ilavesinin tane boyutunu küçülterek akma mukavemetini artırdığını ve çeliklerin mekanik performansını iyileştirdiğini göstermektedir. Literatürde Nb içeren düşük karbonlu çelikler üzerine çeşitli çalışmalar bulunsa da EBSD tekniği ile yapılan detaylı incelemelerin sınırlı olması nedeniyle bu çalışma literatüre önemli katkı sunacaktır.

Keywords

Düşük karbonlu çelik , Niyobyum (Nb) alaşımlama , EBSD (Elektron geri saçılım difraksiyonu) , Tane küçültme mekanizması

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