Several characteristics that should be paid attention to when analyzing the microstructure of materials using a metallographic microscope
The optical metallographic structure of metallographic microscope is lath like, which is Flat noodles martensite. X-ray diffraction phase analysis and transmission analysis show that there is residual austenite in the quenching structure, which mainly exists between martensite Flat noodles. The content of residual austenite is 4.5% by X-ray quantitative test. Low temperature tempering after quenching can improve the stability of retained austenite between martensitic Flat noodles and improve the strength and toughness of the material. In addition, the austenitic film between martensitic Flat noodles is a ductile phase, Metallographic microscopes undergo plastic deformation and phase transformation induced plastic effects under external forces The TRIP effect consumes energy, hinders the propagation or passivation of cracks, and achieves a good combination of strength and toughness. Therefore, the strength after quenching and tempering is higher, while the impact toughness value is also higher, which is related to the residual austenite in the martensitic structure formed after quenching. In practical metallographic analysis and research, it is beneficial to pay appropriate attention to the following characteristics of the material microstructure, especially for the systematic and rigorous design of experimental schemes Sex, as well as reducing the possibility of misunderstandings and unreasonable analysis of apparent microstructure morphology.
1. The multi-scale nature of material microstructure structure: atomic and molecular levels, crystal defect levels such as dislocations, grain microstructure levels, microstructural levels, macroscopic organizational levels, etc;
2. Inhomogeneity in the microstructure of material microscopes: In actual microstructures, there are often geometric and chemical heterogeneity, as well as heterogeneity in microscopic properties such as microhardness and local electrochemical degree;
3. The directionality of material microstructure structure, including anisotropy of grain morphology, directionality of macrostructure, crystallographic preferred orientation, and directionality of material macroscopic properties, should be analyzed and characterized separately;
4. The variability of material microstructure: Changes in chemical composition, external factors, and time can cause phase transitions and structural evolution, which may lead to changes in material microstructure. Therefore, in addition to qualitative and quantitative analysis of static microstructure morphology, attention should be paid to whether there is a need to study the solid-state phase transition process, microstructure evolution kinetics, and evolution mechanism;
5. The fractal characteristics that may exist in the microstructure of materials and the resolution dependent characteristics that may exist in specific metallographic observations: may lead to a strong dependence of the quantitative analysis results of microstructure on image resolution. This should be particularly noted when conducting quantitative analysis of the surface microstructure of material fractures and storing and processing digital image files of microstructure;
6. Limitations of non quantitative research on material microstructure: Although qualitative research on microstructure can meet the needs of material engineering, material science analysis research always requires quantitative measurement of the geometric morphology of microstructure and error analysis of the obtained quantitative analysis results.
