RESUMO
A popular issue of recent scientific research is the surface modification induced by plastic deformation, such as ultrasonic shot peening (USP) on workpiece surface. USP is an efficient way to improve the mechanical behavior of specimens by inducing severe plastic deformation on their surface. Nevertheless, this surface treatment induced complex microstructural evolutions, such as grain refinement and phase transformation. In this work, the microstructure and properties of 347 austenite steel samples before and after USP for 5, 10, and 15 min treatments have been investigated. The affected layers show a significant hardness increase (~450 µm in depth) on the USP treated surface, and the 10 min USP treated specimen shows the best corrosion resistance in all tested specimens. The magnetic properties and microstructures of the tested specimens show gradient evolution during deformation.
RESUMO
The retained austenite (RA) in advanced high-strength steels directly affects their plasticity. It is very important for the accurate characterization of their content and types. This paper prepared three specimens with three different Mn contents (1.0%, 1.4%, and 1.7%) that are used to obtain high-strength steel by ultrafast cooling heat treatment. The volume content and distribution of the RA were analysed by an X-ray Debye ring measurement system, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). In addition, the mechanical tensile test provided the tensile properties and elongation of three specimens. It was finally concluded that when the content of Mn increased, the island-type and thin film-type RA both increased, which may effectively improve the plasticity of the martensitic steels.
RESUMO
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.
RESUMO
Plastic deformations, such as those obtained by shot peening on specimen surface, are an efficient way to improve the mechanical behavior of metals. Generally, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) are commonly used to observe the complex microstructural evolutions, such as grain refinement and phase transformation, induced by the surface treatment. In this work, the microstructure of 347 stainless steel, after ultrasonic shot peening (USP) treatments, was investigated. SEM, EBSD, transmission electron microscopy, and X-ray diffraction were used to observe the microstructural evolutions, such as grain refinement and phase transformation. Deformation depth after the USP treatment was about 200 µm. Grain size on the treated surface layer was about 100 nm, with two phases: austenite and α'-martensite. The percentages of the austenite and α'-martensite phases were 54% and 46%, respectively, which constitute an exact expression of the degree of plastic deformation on austenitic stainless steel.