Research On The Effects Of Nanoprecipitates On Hydrogen Embrittlement Of Martensitic Steels

Under the background of peak carbon dioxide emission and carbon neutrality,it is important to be an industrial policy to develop novel high-strength steel and extend their service life.However,hydrogen could be easily adsorbed and trapped into steels during the process of smelting,heat treatment,welding,electroplating,as well as in the duration of storage,transportation and service.A critical shortcoming for the high-strength steel is the catastrophic hydrogen embrittlement(HE),especially in the complex and harsh environment,which is not fully understood for more than a century.Much of research has explored how nanoprecipitates can produce substantial hydrogen traps,indicating that NbC possesses superior hydrogen trapping capacity.Nevertheless,there is still inexplicit comprehension of the exact location of hydrogen trapping sites and HE resistence in NbC due to the lack of providing structural information to correlate with its effective hydrogen detection.Thus,to explore the nature of strengthening and high HE resistence in nanoprecipitates,which acting as high-efficiency hydrogen traps,is beneficial for the development and utilization of resources and energy and national defense security,as well as the development of HE studies.To inhibit the HE of high strength martensitic steels,the concept of highdensity deep hydrogen traps inside the grains is proposed in this study.The correlation between different microstructural components and hydrogen trapping in tempered martensitic steel was quantitatively investigated.The uniformly distributed NbC nanoprecipitates and the high-angle grain boundaries were found to act as irreversible hydrogen traps,with a density of 1020cm^-3.The NbC with deep hydrogen trapping could not only trap hydrogen irreversibly,but also can inhibit the accumulation of hydrogen.The interpretation of hydrogen trapping is significant to enhance the HE resistance of high-strength martensitic steels.Moreover,the role of the semi-coherent interface between NbC and ?-Fe on hydrogen trapping and HE resistance in high-strength tempered martensitic steel was further investigated.High-resolution transmission electron microscopy observations are performed to reveal the atomic-scale crystallographic orientation relationship,atomic arrangements,and associated crystalline defects in the NbC/?Fe semi-coherent interface.The Kurdjumov-Sachs orientation relationship is (111)_NbC//(101)_?-Fe and[011]_NbC//[111]_?-Fe between the NbC and ?-Fe phases.Noticeably,density functional theory-based first-principles calculations revealed that the deep binding energy between the NbC/?-Fe semi-coherent interface and hydrogen is?77kJ/mol,which well matches the hydrogen desorption activation energy determined via thermal desorption spectroscopy experiments.These demonstrate that the nature of the deep hydrogen trapping sites of the NbC/?-Fe semi-coherent interface is the misfit dislocation core.Distinguished HE resistance was obtained and ascribed to the deep hydrogen trapping of uniformly dispersed NbC nanoprecipitates with an average diameter of 10.0±3.3nm.The strategy of deep hydrogen trapping in the NbC/?-Fe semi-coherent interface is beneficial for designing HE-resistant steels.Furthermore,a novel Fe-based high-strength martensitic steel was developed by the trace-element regional supply method during deoxidization to generate insitu nanoparticles with a high number density in the matrix.These Al₂O₃-MnS and Ti₃O₅-Nb(C,N)in-situ nanoparticles could simultaneously improve the strength and toughness.Finally,the critical influence of in-situ nanoparticles on the HE of high-strength steels was studied.The results reveal that the HE susceptibility is substantially mitigated with approximately 30%with in-situ nanoparticles under the conditions of 0.5mA/cm² current density and 5×10^-6s^-1strain rate in deionized water with 0.2mol/L sodium hydroxide and 0.22g/L thiourea.This is attributed to the heterogeneous in-situ nanoparticles and the spherical and soft Al₂O₃-MnS coreshell inclusions that could suppress HE.In-situ nanoparticles generated by the regional trace-element supply have strong potential and provide feasible scientific and technical route for the development of high-strength and hydrogen-resistant martensitic steels.