Influence of boron content on the fracture toughness and fatigue crack propagation kinetics of bainitic steels

Abstract

The relatively good combination of high strength and ductility makes bainitic steels a candidate to replace many other steels in industrial applications. However, in service, ductility and strength are not up to standard requirements. In many industrial components, toughness and fatigue performance are also very relevant. In the present study, bainitic steels with varying content of boron were fabricated, with the aim of analyzing the fracture toughness and changes in the fatigue life. The results show that a relatively small change in the boron content can cause a notable variation in the fracture toughness of bainitic steels. The maximum value obtained in fracture toughness was for the steel with the highest boron content. It was observed that the amount of interlath martensite constituents decreases in steels with the addition of boron, leading to the promotion of the presence of void coalescence and a remarkable rise in the toughness of bainitic steels. An increase on the fatigue life of the bainitic steels with an increase in the boron content was also observed, through analysis by means of Paris’ law. A comprehensive micrographic study was carried out in order to examine the mechanics of fatigue crack growth in the bainitic steels, revealing small longitudinal cracks in bainitic steels that lack boron. These cracks tend to disappear in bainitic steels that contain boron. To elucidate this behavior, micrographs of the surfaces generated by the crack growth process were taken, showing that several nano-cracks appeared between the bainite laths. It is finally argued that this high-energy consumption process of nano-crack nucleation and growth is the reason for the improved toughness and fatigue life observed in bainitic steels.Peer ReviewedPostprint (author's final draft

Comparative Fatigue Performance of Decarburized Surfaces in Railway Rails

“…Severe plastic deformation induces substantial changes in the steel, affecting the initiation, spreading, and combination of cracks. The numerous cracks, along with the impact of severe plastic deformation, leads to the formation of crushed material within the crack [61]. Table 2 provides a comprehensive insight into the size statistics of fatigue cracks for two significant rail materials, R260 and U71Mn: decarburization and non-decarburization.…”

Effects of Boron Content on the Microstructure and Impact Toughness of 12Cr1MoVR Low-Alloy Heat-Resistant Steel Weld Metals

“…Hu et al [ 10 ] showed that the IGF nucleation on particles in austenite refined the microstructure of steels. Rodríguez-Galeano et al [ 11 ] indicated that with the increase in B content from 0 ppm to 60 ppm, the grain size of hard phases, such as the martensite phase or M-A constituents, decreased, which induced higher toughness. Klimenkov et al [ 12 ] reported that B content also affected the density and composition of M 23 C 6 and MX precipitates, the appearance of BN, and affected the microstructure.…”

Wheel Rail Interaction and a Finite Element Analysis on Fatigue Failure Resistance of Pearlitic and Bainitic Steels

“…İlk olarak demiryollarında tüm makas bölgesini kapsayan ve uygulama alanı bulan beynitik mikroyapıdaki çeliklerin tüm hat boyunca kullanımına yönelik araştırma geliştirme ve saha deneme çalışmaları halen devam etmektedir. Bu kapsamda kimyasal kompozisyon ve ısıl işlem rejimlerinin etkilerini inceleyen farklı çalışmalar literatürde yer almaktadır [6]. Amerika ve Japonya'da yer alan beynitik yapıdaki çelik kompozisyonları ve sertlik değerleri Tablo 2 ve Tablo 3'de yer almaktadır [6,7].…”

“…Bu kapsamda kimyasal kompozisyon ve ısıl işlem rejimlerinin etkilerini inceleyen farklı çalışmalar literatürde yer almaktadır [6]. Amerika ve Japonya'da yer alan beynitik yapıdaki çelik kompozisyonları ve sertlik değerleri Tablo 2 ve Tablo 3'de yer almaktadır [6,7]. [19], rayların aşınma değerleri ve yuvarlanma temas yorulmasında iyileştirmeler için yeni beynitik rayların geliştirilmesi konularında çalışmalar yapılmıştır [20].…”