Hydrogen-induced delayed fracture of a martensitic steel with fine prior-austenite grain size

Solutions for Hydrogen-Induced Delayed Fracture in Hot Stamping

“…In addition, many studies show that grain refinement reduces the delayed fracture resistance of steel [9]. Nb, as one of the important alloy additives of high-strength steel, is widely used because of its distinct effect on the grain refinement of metal.…”

Mechanical Property of Ultrafine Elongated Grain Structure Steel Processed by Warm Tempforming and Its Application to Ultra-High-Strength Bolt

“…There are three fundamental guidelines to improving delayed fracture resistance: 1) increasing the intrinsic fracture resistance of the materials, 2) suppressing hydrogen accumulation at crack initiation sites and crack tips (utilizing effective hydrogen trapping sites), and 3) decreasing hydrogen uptake in the service environment. Since delayed fracture in tempered martensitic steel is often observed to occur along the boundaries of prior-austenite grains, the techniques that have be proposed to improve delayed-fracture resistance are: 1) reduction of impurity elements such as P and S, 2) refinement of prior-austenite grain size, [74][75][76][77] 3) elongation of prior-austenite grains, 78) and 4) refinement of filmlike intergranular carbides, 79) and so on. Furthermore, in secondary-hardening steels, delayed fracture resistance was reported to be enhanced through the precipitation of nanosized alloy carbides.…”

Influence of Prior Austenite Grain Structure on Hydrogen-Induced Fracture in As-Quenched Martensitic Steels

“…In many cases, hydrogen-induced cracking initiates and propagates along PAG boundaries in QT martensitic steels [9,[21][22][23][24][25]. The influence of PAG size has been extensively studied aiming to suppress intergranular crack propagation by modifying grain size, grain shape, and grain boundary characteristics with somewhat controversial results [9].…”

“…The influence of PAG size has been extensively studied aiming to suppress intergranular crack propagation by modifying grain size, grain shape, and grain boundary characteristics with somewhat controversial results [9]. Grain refinement of QT steels has proven to improve resistance against delayed fracture [21,26,27]. Smaller grain size increases the grain boundary area, which reduces the concentrations of the grain boundary embrittling impurity elements via enhanced distribution over a larger area [3].…”

“…The challenge in achieving quantitative understanding lies in widely differencing microstructures (retained austenite content, carbides, impurity segregation, grain boundary structure, etc. ), which may form during heat treatments conducted for the grain size modification [9,21].…”