Metallographic diagram of 20CrMo (1100℃×20min water quenching)

20CrMo is a ferrous alloy used in a variety of applications. It is composed of a combination of chromium and molybdenum with a specified range of carbon. 20CrMo is typically supplied in the annealed condition and then reheated in order to increase its ductility and machinability. It is also used for a variety of wear-resistant applications and components, often needing to be cold-forged or hot-formed to specific shapes. To ensure optimal properties of the alloy, it is important to heat treat the material to achieve the desired microstructure and mechanical properties.

In this case, the 20CrMo alloy was heat treated in a water quench of 1100°C for 20 minutes. This is a common technique used to harden the alloy, allowing it to be strengthened and made more resistant to impact and wear. This type of heat treatment can also be referred to as a “quench-and-temper treatment” since a tempering process is often used following the quenching. The microstructure will be examined under a metallographic microscope.

The resulting structure of the 20CrMo alloy can be seen in the accompanying micrograph. The steel has a bainitic-ferrite microstructure, which is the desirable end result of the quench-and-temper treatment. The primary constituent is ferrite, comprised of small, lightly colored grains. This is surrounded by a matrix of a more darkly colored bainite. Fine round carbides can also be seen in the microstructure, which are indications of the martensitic transformation occurring during the quenching process.

The quench-and-temper heat treatment of the 20CrMo alloy has resulted in the desired microstructure and mechanical properties. The size and volume fraction of ferrite, bainite, and the round carbides are all within accepted specifications and the hardness has been significantly increased. This makes it well suited for applications that require high strength and wear resistance such as gear blanks, pinions, and gear shafts.

The physical and chemical properties of 20CrMo steel are typically studied through metallographic observation. The main purpose of this laboratory experiment is to understand the microstructure of 20CrMo steel after being treated with water quenching at 1100℃ for 20 minutes. The purpose of quenching is to increase the strength of the steel.

First, a 20CrMo steel sample was cut from the bulk material to create a flat and polished specimen. This sample was then placed in an oven to heat the steel up to 1100℃ for 20 minutes. Afterwards, the sample was immediately transferred to a tank containing warm water for cooling.

Afterwards, a metallographic observation was conducted for the quenched steel sample. It was found that the microstructure of the steel had changed significantly due to the quenching process. At higher magnifications, the grain boundaries were more distinct and the grain size was finer compared to the as-received steel sample.

It was observed that the transformation of austenite to martensite was completed, confirming that the quenching was successful. Furthermore, the etching of the sample revealed the actual size of the martensite crystals. The overall microstructure of the quenched 20CrMo steel sample was composed of plate-like martensite phase with a small amount of pearlite phase throughout.

The microstructure of the quenched 20CrMo steel showed a large number of precipitates embedded in the grain boundaries of the martensite phase. This was an indication of a successful quenching process that achieved the desired properties for the sample material.

In conclusion, the metallographic study of the 20CrMo steel sample revealed a microstructure composed of martensite with a small amount of pearlite phase distributed throughout. The quenching process proved to be a successful treatment in achieving the desired properties for the sample material.