A number of features should be considered when analysing the microstructure of materials using a metallographic microscope
Metallographic microscope optical metallographic organisation is lath-like, for the lath martensite organisation, X-ray diffraction physical analysis and transmission analysis shows that there is also residual austenite in the quenched organisation, the residual austenite mainly exists in the martensite between the laths, and the content of the residual austenite is 4.5% when tested by X-ray method quantitatively. The low-temperature tempering treatment after quenching can improve the stability of the residual austenite between the martensite slats and improve the toughness of the material. In addition, the austenite film that exists between the martensite slats, is the toughness phase, metallurgical microscopy in the external force will occur under plastic deformation and phase transition induced plasticity effect (TRIP effect, consume energy, impede the expansion of cracks or cracks ** passivation, to obtain a better strong toughness with. Therefore, after quenching and tempering of higher strength at the same time, the impact toughness value is also higher, which is related to the presence of residual austenite in the martensitic organisation formed after quenching. In the actual metallographic analysis of the study, appropriate attention to the following characteristics of the material microstructure is very beneficial, in particular, to help the systematic and rigorous design of experimental programmes, as well as to reduce the apparent microstructure morphology of the misunderstanding and the possibility of unreasonable analysis.
1, the material microstructure of the multi-scale: atomic and molecular levels, dislocations and other crystal defects level, grain microstructure level, the level of microstructure, macroscopic organisation level, macrostructure level;
2, the material microscopic organisation structure of inhomogeneity: the actual microstructure often exists in the geometric morphology of inhomogeneity, chemical composition of inhomogeneity, micro-properties (such as micro-hardness, local electrochemical potential) inhomogeneity and so on;
3, the directionality of the microstructure of the material: including grain morphology anisotropy, the directionality of the low-fold organization, crystallography choose especially orientation, the directionality of the macroscopic properties of the material and other directionality, should be analysed and characterized separately;
4, the material microstructure variability: chemical composition changes, external factors and time changes caused by phase changes and tissue evolution may lead to changes in the microstructure of the material, thus, in addition to the need for qualitative and quantitative analysis of static microstructure morphology, attention should be paid to whether there is a solid-state phase transition process, microstructure evolution kinetics and the evolution of the mechanism of the need for research;
5, the material microstructure may have a fractal (fractal) characteristics and specific metallographic observations may exist resolution-dependent properties: may lead to quantitative analysis of its microstructure results are strongly dependent on the image resolution, when quantitative analysis of the material fracture surface tissue morphology, as well as the microstructure of digital image files for storage and processing of the more attention should be paid to this point;
6, the limitations of non-quantitative study of the microstructure of materials: although the qualitative study of microstructure can sometimes still meet the needs of materials engineering, but materials science analysis and research is always needed to quantitatively determine the science of microstructure geometry as well as the results of the quantitative analysis of the error analysis.
