Effect of Close-Packed Plane Boundaries in a Bain Zone on the Crack Path in Simulated Coarse-Grained HAZ of Bainitic Steel

The Role of Microstructure Morphology on Fracture Mechanisms of Continuously Cooled Bainitic Steel Designed for Rails Application

“…On the other hand, packet boundaries and other structural constituents influenced local changes in crack propagation (Figure 12d), which is consistent with the other results. [19] A change in the crack path after reaching the grain boundary of the prior austenite was also noticed. In addition, the crack path propagation temporarily changed after exceeding the M/A constituent.…”

“…Based on current investigations and published results, [18][19][20][21] the scheme characterizing the effect of continuous cooling and isothermal heat treatment on the microstructure of bainitic steels was developed (Figure 1). Generally, during the bainitic transformation the prior austenite grain (PAG) may be divided into packets with a similar habit plane with respect to austenite.…”

“…[24,[26][27][28][29][30][31] It was also found that packets are responsible for significant changes in the crack path, while the close-packet boundaries inside the packets and M/A constituents influence the local changes of the crack path. [19] Generally, the packet boundaries are characterized by high-angle misorientation boundaries (HABs) near the 48 and 55 deg, while block boundaries are characterized by the lower misorientation angle. [32] Moreover, refined prior austenite grains enhance the fraction of HABs in the entire microstructure, which results in toughness improvement.…”

Effect of Heat Input on Microstructure and Toughness of Coarse Grained Heat Affected Zone of Q890 Steel

“…Considering the effect of effective grain size on the toughness, it is suggested that both M-A constitutions and effective grain size are the key factors to determine the absorbed energy when t 8/5 is larger than 60 s. However, at high heat input, M-A constitutions plays more dominant role on the toughness than effective grain size owing to severe damage of M-A constitutions on the toughness. 3,[26][27][28][29][30][31] Coarse austenite grain size increases the size of M-A constituents and lowers the CGHAZ impact energy. Li et al 26) have elucidated the role of the fraction, size, shape, distribution of M-A constituents on impact toughness and concluded that the size of M-A constituent was influenced by the prior austenite grain size, consequently, which governed impact energy.…”

Effect of coiling temperature on impact toughness of hot rolled ultra-high-strength multiphase steel strips

“…Considering the role of bainite on ductility and impact toughness of bainitemartensite steels, several conflicting observations have been reported. In general, the presence of granular bainite or upper bainite imposes an adverse effect on the toughness of tempered martensitic steels due to the following reasons: (i) The coarse carbide particles or coarse islands of MA constituents act as cleavage crack initiation sites; (ii) The low-angle boundaries between adjacent bainite laths (or sub-units) are ineffective in retarding (or deviating) cleavage crack propagation; and (iii) Bainite is far less responsive to tempering (or coiling) treatment than martensite [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Due to the finer carbide size as well as finer bainitic-ferrite plate, block, and packet sizes, the impact toughness of lower-bainite is superior to that of granular-and upper bainite [46].…”