Abstract
Simultaneously improving the toughness and strength of B-microalloyed steel by adding microalloying elements (Nb, V, Ti) has been an extensively usedmethod for researchers. However, coarse Ti(C, N) particle will precipitate during solidification with inappropriate Ti content addition, resulting in poor impact toughness. The effect of the size, number density, and location of Ti(C, N) particle on the impact toughness of B-microalloyed steel with various Ti/N ratios was investigated. Coarse Ti(C, N) particles were investigated to act as the cleavage fracture initiation sites, by using scanning electron microscopy (SEM) analysis. When more coarse Ti(C, N) inclusions were located in ferrite instead of pearlite, the impact toughness of steel with ferrite–pearlite microstructure was lower. Meanwhile, when the size or the number density of Ti(C, N) inclusions was larger, the impact toughness was adversely affected. Normalizing treatment helps to improve the impact property of B-microalloyed steel, owing to the location of Ti(C, N) particles being partly changed from ferrite to pearlite. The formation mechanism of coarse Ti(C, N) particles was calculated by the thermodynamic software Factsage 7.1 and Thermo-Calc. The Ti(C, N) particles formed during the solidification of molten steel, and the N-rich Ti(C, N) phase precipitated first and, then, followed by the C-rich Ti(C, N) phase. Decreasing the Ti and N content is an effective way to inhibit the formation of coarse Ti(C, N) inclusions.
Highlights
It has been widely recognized, for microalloyed steel, that long service life can frequently be accompanied by high toughness and high strength
In the boron-containing steel, Ti element is added to tie up N and C elements to avoid the formation of BN phase [5] and, more available boron would segregate to the austenite grain boundaries to suppress the γ–α transformation, which would dramatically improve the hardenability of boron-containing steel [6]
The impact toughness of microalloyed steel is associated with the Ti content and N content [18], Ti/N ratio [12], number density of TiN particles [19], and the size of TiN particles [20]
Summary
It has been widely recognized, for microalloyed steel, that long service life can frequently be accompanied by high toughness and high strength. Several studies [1,2,3] have been conducted that the addition of microalloying elements, such as niobium, vanadium, titanium, and boron, can observably improve the service performance of steels due to the grain refinement by pinning the austenite grain boundaries (typically the fine TiN particles because of their strong high-temperature stability) [4]. Many researchers [15,16,17] reach an agreement that grain size control is optimized at the Ti/N ratio in molten steel close to 2, resulting in better impact toughness. The impact toughness of microalloyed steel is associated with the Ti content and N content [18], Ti/N ratio [12], number density of TiN particles [19], and the size of TiN particles [20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
