The application of ultrahigh‐strength martensitic steel in automotive key parts can achieve automotive lightweight. However, the hydrogen embrittlement sensitivity of ultrahigh‐strength martensitic steel is widely concerned by the industry. This article compares the microstructure and the hydrogen brittleness resistance of two 1500 MPa martensitic steels. The grain boundary, the grain size, the martensitic lath, and the precipitate phase in martensitic steel are analyzed by electron backscatter diffraction and transmission electron microscope. The hydrogen desorption curves of the two steels are measured by thermal desorption analysis, and the phenomenon of hydrogen trapping in the materials is analyzed. A U‐bend test is used to compare the hydrogen embrittlement of these two samples. The results demonstrate that the thickness of the martensitic lath and the dislocation are directly related to the diffuse hydrogen concentration in the material. In addition, the Cu‐rich nanoparticles show a better hydrogen trapping effect, which is beneficial in improving the hydrogen embrittlement resistance of the material.

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.

Ultrahigh-strength steel (2000 MPa) is a key material widely used in national defense, aerospace, and various other sectors. This kind of steel is more likely to break as its strength increases. To improve its toughness, it is crucial to fully understand the strengthening and toughening mechanisms, microstructural evolution characteristics, and heat-treatment parameters of ultrahigh-strength steel. Herein, an improved 40CrNi 2 Si 2 MoV test steel is designed based on the composition of the 40CrNi 2 Si 2 MoV ultrahigh-strength martensitic steel and is subjected to quenching at 860/900/930/1050/1150 °C. The effects of microstructural changes on the test materials are analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, transmission electron microscopy, and other characterization methods. The results show that at a quenching temperature of 1050 °C, the material exhibits an elongation of 8.2% and a strength as high as 2200 MPa owing to the coupled effects of complex multicomponent laths, substructures, dislocations, and nano-precipitates.

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