Metallographic Examination of 20CrMo and 9G6W3Mo2V2 Steels
Metallography is an essential tool for gaining a better understanding of the mechanical and structural behaviour of a metal. As such it is widely used in the study of steels, including the high performance steels 20CrMo and 9G6W3Mo2V2, for both research and industrial applications. This paper examines the microstructure of the two steels through a combination of optical and electron microscopy to detail the effects of processing on the different phases present in the alloy.
The investigation begins with optical microscopy, which allows for the rapid assessment of the microstructure of large specimens. Microscopic examination of a polished and etched 20CrMo sample reveals the presence of a large amount of ferrite, with smaller amounts of pearlite and bainite. The ferrite grains are uniformly distributed, indicating that the steel has a homogeneous structure, while the bainite and the pearlite interphase suggests good strength and ductility.
A comparison of the 20CrMo with the 9G6W3Mo2V2 also shows an increase in the amount of ferrite, which in this case is mixed with bainite and lower amounts of pearlite. It is hypothesised that this structure may have been induced by the higher amounts of molybdenum and vanadium present in the 9G6W3Mo2V2 sample.
Further analysis of the microstructure of both samples was carried out with a scanning electron microscope (SEM). In this case, the sample surfaces were coated with gold to reduce charging effects and then observed to observe the microstructural details more closely. Analysis revealed a significant difference in the amount of ferrite present in the 9G6W3Mo2V2 sample, with a greater proportion of martensite and bainite being present. The martensite, in particular, had a much larger grain size compared to the ferrite, implying that the increased amounts of molybdenum and vanadium impart a greater strength to the sample.
In addition to the optical and electron microscopy analyses, X-ray diffraction analysis was also used to investigate the alloying elements present in the two steels. In both cases the results indicated the presence of iron, carbon, manganese and the specified amounts of molybdenum and vanadium in the samples.
In conclusion, optical, electron and X-ray diffraction analysis have been used to investigate the microstructure of two high performance steels: 20CrMo and 9G6W3Mo2V2. The investigation showed a considerable difference in the microstructures of the two samples, with the 9G6W3Mo2V2 having a greater proportion of ferrite, bainite and martensite compared to the 20CrMo sample. It is believed that the increased amounts of molybdenum and vanadium present in the alloy are largely responsible for these differences.
