Effect of Intercritical Annealing on the Properties of Dual Phase Steel via Finite Element Method

Abstract

Dual phase (DP) steels are rapidly becoming more and more popular for automotive applications. They offer a weight reduction with a combination of energy absorption for crash zones. Rails, reinforcements, back panels, cross members, and pillars can be given as application examples. DP steels microstructure consists of a soft ferrite matrix with hard martensite islands. The hard martensite islands provide strength while the ductile ferrite provides formability. The strength level of DP steel is related to the amount of martensite in the microstructure, and the martensite amount can be arranged via intercritical annealing. In this work, thermodynamic analysis of St52 steel was carried out with Thermo-Calc software. A1 and A3 temperatures were determined by calculating the temperature-dependent phase fractions. Intercritical annealing temperatures were determined according to the calculated critical temperatures (A1 and A3). The intercritical annealing process was modelled by using Simheat NxT software. In this modelling and simulation work, the effect of intercritical annealing temperature on the final microstructure and hardness of DP steel was investigated.

Keywords

• Automotive
• DP Steel
• Simheat NxT
• Thermo-Calc
• Finite Element Method

Sonlu Elemanlar Metodu ile Kritikler Arası Tavlamanın Çift Fazlı Çeliğin Özelliklerine Etkisi

Abstract

Çift fazlı (DP) çelikler, AHSS kaliteleri arasında otomotiv endüstrisinde yaygın olarak kullanılan bir çelik grubudur. Çarpışma bölgeleri için enerji emilimi ve ağırlık azaltma sunarlar. Günümüzde jantlarda, ön ve arka panellerde kullanılır. DP çeliklerinin mikroyapısı, ferrit ve martenzit fazlarının kombinasyonundan oluşur. Sert martenzit adaları mukavemet sağlarken, sünek ferrit fazı şekillendirilebilirliği sağlar. DP çeliğinin mukavemet seviyesi, mikroyapıdaki martenzit miktarı ile ilgilidir. Martenzit miktarı, kritikler arası tavlama işlemiyle düzenlenebilir. Bu çalışmada Thermo-Calc yazılımı ile St52 çeliğinin termodinamik analizi yapılmıştır. A1 ve A3 sıcaklıkları, sıcaklığa bağlı faz fraksiyonları hesaplanarak belirlenmiştir. Hesaplanan kritik sıcaklıklara (A1 ve A3) göre kritikler arası tavlama işlemi Simheat NxT yazılımı kullanılarak modellenmiştir. Bu modelleme ve simülasyon çalışmasında, kritikler arası tavlama sıcaklığının DP çeliğinin nihai mikroyapısı ve sertliği üzerindeki etkisi araştırılmıştır.

Keywords

• Otomotiv
• DP Çeliği
• Simheat NxT
• Thermo-Calc
• Sonlu Elemanlar Metodu

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