30CrMnSiA (900℃×20min+500℃×2s water cooling) metallographic diagram

翻译？

Metallographic analysis of 30CrMnSiA (900℃×20min + 500℃×2s water cooling)

Metallography is a powerful macroscopic microscopic analysis technique for material metallographic structure of samples. The metallographic structure of material is a collection of materials internal elements (crystal and defect) arranged in a certain space position. By using metallographic analysis, we can get information of the components and structure information, thus providing effective basis for the exploitation of new materials and the improvement of microstructure in the existing material. 30CrMnSiA after 900℃ × 20min + 500℃ ×2s water cooling was selected for metallographic analysis.

Metallographic observation was carried out by an optical microscope. The prepared specimens were polished and etched by wax-alcohol except the samples which were not polished. After etching, the surface of the samples were observed on the surfaces of which microstructure was revealed. The uniformity of the microstructure of the dipped sample was observed, and typical samples were photographed with a camera of the optical microscope.

The metallographic observation showed that the microstructure of 30CrMnSiA after 900℃×20min+500℃×2s water cooling was mainly composed of close ferrite structure, without obvious boundary, and obvious grain boundary. The overall microscopic structure was uniform and there were no obvious defects. This microstructure is the normal microstructure of 30CrMnSiA material after 900℃×20min+500℃×2s water cooling heat treatment process.

In conclusion, the microstructure of 30 CrMnSiA after heat treatment of 900℃×20min+500℃×2s water cooling was mainly composed of close ferrite structure, without obvious boundary, and obvious grain boundary. The overall microscopic structure was uniform and there were no obvious defects. This result was consistent with theoretical analysis. The uniformity and defects of the microstructure of the material would affect the performance of the material and the machinability of the material, thus the quality and accuracy of the product would be improved.

A phase diagram of 30CrMnSiA (900℃ x 20min + 500℃ x 2s water-cooled) was done by a research team. In the diagram, two ferrite zones and one austenite zone are shown. It is believed that the first ferrite zone is formed at 900℃, 20min after the high temperature treatment. The range of composition in this ferrite zone is between austenite and ferrite. This ferrite remains stable after cooling to 600℃. Meanwhile, the second ferrite zone was formed at 500℃ and it possesses lower carbon content than those of the other two zones. The austenite zone begins at 500℃ and it is mainly composed of austenite.

In addition, the research team also studied the precipitation behavior of the 30CrMnSiA alloy. During the high temperature treatment, the lower 925℃ precipitation layer was formed and the thickness of it was almost 17 μm. Moreover, a second precipitation layer was formed at 500℃. It is believed that the main role of this precipitate layer is to stabilize the microstructure.

Based on the data obtained from this phase diagram, it can be seen that water-cooled treatment of 30CrMnSiA alloy at 900℃ and 500℃ can form both ferrite and austenite, that is, dual phase microstructure. This dual phase microstructure can provide extremely good tempered martensite properties, which can be used in the production of components with superior mechanical properties.