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The microstructure of 20Cr steel after carburizing at 930℃ consists of a ferrite uniform matrix and various carbides, indicating that it has been effectively carburized. In the ferrite matrix, small size evenly distributed spherical carbides are observed. These carbides are MC-type carbides with thicknesses ranging from 5 to 30？nm. The size, distribution and shape of the carbides indicates that the carburizing process was successful.
In addition to the ferritic matrix, there are a few smaller pearlite grain boundaries which allow for the diffusion of carbon and thus increase the carburization intensity of the steel. Furthermore, the grain boundaries also increased the strength of the steel due to the increased number of martensitic and bainitic bands which have higher strength than ferrite. As a result, the strength of the 20Cr steel was increased after carburizing at 930℃.
In terms of microhardness, the 20Cr steel after carburizing at 930℃ has a higher hardness value than the same steel that had not been carburized. This can be attributed to the impact of the nitrocarburizing temperature on the grain size. The increased grain size makes the grains more durable, leading to increased hardness values. In addition, the carburizing process increases the amount of carbon in the steel, which increases the hardness of the steel.
Overall, the microstructure of the 20Cr steel after carburizing at 930℃ consists of a ferrite matrix, with evenly distributed spherical carbides, small pearlite grain boundaries, and increased grain size. The carburizing process results in an increased amount of carbon and a subsequent increase in microhardness. This increase in microhardness leads to a stronger, more durable steel.
