Metallographic diagram of 20CrMnMo (normalized at 870°C)

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The 20CrMnMo is a ferrous alloy with a wide variety of uses, most commonly used for fasteners and/or components requiring high-strength and hardness, such as gear parts and splines. This article will examine the microstructure of the 20CrMnMo ferrous alloy after undergoing a normalizing heat treatment at 870℃.

A normalizing heat treatment is a thermal process used to refine the structure of some alloys, usually those that are composed mainly of iron and steel, to improve their mechanical properties. This process involves heating a ferrous alloy to a temperature above the upper critical temperature of the alloy for a certain duration of time, holding the temperature for a period of time, and then cooling it back down. In the case of the 20CrMnMo alloy, the upper critical temperature is 870℃, so it was heated to 870℃ and then held at that temperature for a period of time in order to complete the normalizing process.

Once the normalizing heat treatment was complete, the microstructure of the 20CrMnMo alloy was then evaluated in order to assess changes induced by the heat treatment. Microstructural analysis of the alloy was performed using optical microscopy, which revealed that the alloy underwent a transformation from ferritic to austenitic. The primary components of the microstructure after normalizing were austenite grains, a small quantity of ferrite grains, plus some carbide particles in the ferritic regions.

The overall microstructure of the 20CrMnMo alloy was also increased in terms of grain size as a result of the normalizing heat treatment. The grain size after heat treatment was found to be exponentially larger than it was initially, which is apt given that the grain size is largely dependent on the upper critical temperature of the alloy. Furthermore, a finer grain size of the microstructure serves to improve the mechanical properties of the alloy, such as tensile strength and fatigue resistance, making it more capable of withstanding stress in arduous environments.

In conclusion, normalizing heat treatment of 20CrMnMo ferrous alloy at a temperature of 870℃ exhibited a number of beneficial effects including the mostly austenitic microstructural transformation, an increase in grain size, and improved mechanical properties such as tensile strength and fatigue resistance. These results demonstrate that the normalizing heat treatment at 870℃ was effective in refining the microstructure of the 20CrMnMo alloy and making it more suitable for use in difficult situations.

Metallographic examination of 20CrMnMo (890℃ normalizing)

Metallographic examination is a process of visually inspecting the structure of a material. It is performed by mounting, cutting and polishing thin samples of the material, staining the surface and finally studying the microstructural features of the sample through a microscope. This article describes the metallographic examination of 20CrMnMo (890℃ normalizing).

The sample was first prepared using the standard metallographic preparation sequence. This included mounting it in a phenolic resin and grinding and polishing the surface to a mirror-like finish. It was then examined with a metallographic microscope.

The 20CrMnMo sample had an ferritic-pearlitic microstructure. The microstructure consists of ferrite grains and pearlite. Ferrite is a solid solution of iron, carbon and other trace elements. It has a body-centered-cubic structure. Pearite is a compound of ferrite and cementite, a joint compound between carbon and iron. It has an interpenetrating phase structure.

The average grain size of the ferrite grains was found to be about 25 microns, with some finer grains at the 15 micron mark. A significant amount of pearlite was also visible, often around the ferrite boundaries. The pearlite lamellae were particularly well developed at the grain boundaries.

Overall, the metallographic examination of the 20CrMnMo (890℃ normalizing) showed a typical ferritic-pearlitic microstructure, with satisfactory grain size and a large amount of pearlite. The microstructure is expected to be stable due to the normalizing process, which will have improved the structure by relieving some of the stress present in the ferrite grains.