Abstract
Hydrogen embrittlement can easily occur in high strength martensitic steel, manifesting itself as a sudden failure or fracture without warning and greatly threatening the safety of automotive applications. Optimizing the composition of the alloy can be performed by matching heat treatment processing methods and controlling the precipitation amounts to form hydrogen traps. In doing so, the hydrogen embrittlement susceptibility of steel can be effectively delayed, reducing the risk of hydrogen-induced delayed cracking. In this study, four kinds of 1500 MPa strength grade martensitic steel were selected for testing and supplemented with different loadings of Nb and V, respectively. Their grains, phases, and precipitations were compared by optical microscopy (OM), electron backscattered diffraction (ESBD), and transmission electron microscopy (TEM) analyses. After the addition of Nb and V, the microstructure was refined, the residual austenite content increased, and the hydrogen embrittlement resistance was significantly improved.
Highlights
High strength martensitic steels exhibit excellent mechanical properties, which enables them to be extensively applied in the automotive industry [1]
The decrease in the size and quantity of carbides leads to an increase in the diffusion distance of hydrogen in steel, which is known method used to reduce the susceptibility of hydrogen-delayed fracture in high strength steel
Transmission electron microscopy (TEM) analysis was performed on a JEOL 2100F at a working voltage of 200 kV, with energy dispersive X-ray spectrometers (EDS) by Oxford Instruments
Summary
High strength martensitic steels exhibit excellent mechanical properties, which enables them to be extensively applied in the automotive industry [1]. It is well known that adding microalloying elements can reduce hydrogen-induced delayed fracture to improve their residual austenite (RA) and material microstructure and create more hydrogen traps. Controlling the precipitation of C or N nanocompounds to form a benign “hydrogen trap” in high strength martensitic steel can effectively reduce the risk of hydrogen-delayed cracking [17]. A hydrogen trap can be caused by various microstructural defects, such as PAGB, lath boundaries, high-density dislocations, and interfaces between the second phase particles and matrix. The decrease in the size and quantity of carbides leads to an increase in the diffusion distance of hydrogen in steel, which is known method used to reduce the susceptibility of hydrogen-delayed fracture in high strength steel. Nb and V were added to high strength steel, and their grain sizes, boundaries, and RA contents were compared
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