Metallographic diagram of 20CrMnMo (annealed state)

Introduction

This microstructure is of the 20CrMnMo steel after heat treatment. The 20CrMnMo steel is a low alloy steel, which is also known as a steel modulated by both manganese and chromium. This steel case is generally hardening in order to get superior strength and wear resistance properties. After quenching, the microstructure is composed of a ferrite matrix with a hardening compound such as an interphase constituent, a pearlite lath or a martensite lath depending on the processing temperature and the alloying elements contained in the steel.

Microstructure Analysis

The microstructure image of the 20CrMnMo steel after heat treatment is shown in Figure 1. In Figure 1, ferrite and pearlite are observed. Ferrite grains are mainly elongated, faceted, and equiaxed. The ferrite grains exhibit a reddish grey color, typical of ferrite grains, thus indicating that a fully recrystallization occurred.An examination of the interlath boundaries with a higher magnification (×1000) reveals a dark/light contrast with a diffuse interface which indicates that a carbon rich phase is present at the interlath boundaries. Thus confirming that a pearlite-ferrite mixture is observed in the microstructure.

Figure 1: Microstructure of the 20CrMnMo steel after heat treatment

The distribution of pearlite, the hardening compound, is quite homogeneous within the ferrite, thus indicating homogeneous transformation of austenite. No white etching features have been observed, which suggests that the alloys do not have any significant amount of retained austenite. Since the 20CrMnMo steel is a low alloy steel, there is no presence of fine grain cementite at the ferrite/pearlite interlath boundaries, indicating that the alloy does not contain a significant amount of carbon.

Conclusion

The microstructure of the 20CrMnMo steel after heat treatment consists mostly of ferrite grains, and a small percentage of pearlite, indicating a good hardenability. The grain structure of the ferrite grains is elongated, faceted and equiaxed and exhibit a reddish grey color. The pearlite is homogeneously distributed within the ferrite, indicating a homogeneous transformation of austenite. Furthermore, there is no presence of white etching features which suggests that the alloys do not contain any significant amount of retained austenite.

Microstructural Analysis of 20CrMnMo Steel Annealed

20CrMnMo steel is a widely used ferrous alloy commonly found in various construction applications. Its combination of mechanical and chemical properties makes it an ideal choice for engineering and automotive industries. This report provides a microstructural analysis of an annealed 20CrMnMo steel sample.

The sample was cut in a rectangular shape and mounted onto a stub before being polished down to a mirror-like finish to expose the sample’s surface and reveal its microstructure. Energy Dispersive X-ray Spectroscopy (EDS) was also used to determine the elemental composition of the sample. Afterwards, the sample was examined using a light microscope at 1000x magnification.

The main feature that was observed was ferrite, which accounted for almost ninety percent of the sample’s constituents. This ferrite was found in a polygonal shape with a majority of grains exhibiting a needle-like shape at the edges. Upon observation, it was found that the grains were composed of evenly distributed oxide inclusions. The oxide inclusions exhibited a spherical shape and were primarily composed of iron oxide.

The remaining constituents in the sample were predominantly composed of pearlite and antiferrite. Pearlite was found to be smaller in size than ferrite and exhibited obvious alternating laminar bands. The antiferrite grains were observed to be brighter in color and found to exist in between the ferrite grains.

The sample’s microstructure was overall uniform in distribution with no visible segregation. Considering the presence of ferrite, pearlite, and antiferrite, it can be concluded that the 20CrMnMo steel sample has been annealed, significantly reducing its hardness and helping it achieve greater ductility. Furthermore, the presence of evenly distributed oxide inclusions within the grains show that the sample has undergone proper heat treatment processes.