Metallographic diagram of 45 steel (900℃ water quenching)

Introduction

45 steel is a medium carbon steel commonly used in engineering components, such as gears, shafts and fasteners. It provides good wear resistance and excellent toughness at elevated temperatures. In this experiment, the grain morphology of 45 steel (900℃ water quenched) will be evaluated by an optical and scanning electron microscopy (SEM).

Experimental Procedures

A sample of 45 steel was cut into a reduced section (3 mm thick x 30 mm wide). The sample was then heated in a furnace up to 900℃, and quenched in water. The sample was either polished and etched with a nital etchant (2%) to reveal grain morphology.

The sample was then observed under an optical microscope (Nikon) with a magnification up to 500x. The sample was then placed in the SEM in order to observe the microstructure of the steel at a high magnification.

Results and Discussion

The optical micrograph of the sample (see fig.1) revealed a ferrite-like structure with a matrix of small grains having a mean size of ~ 2 µm. In addition, there were also some larger grains (about 10-20 µm) dispersed throughout.

Figure 2 is the scanning electron microscopy micrograph of the sample. It can be seen that the grain structure of the steel consisted of a matrix of small grains with an average size of 2µm. The larger grains (10-20µm) appeared to be more rounded, indicating a higher temperature treatment of the steel.

Conclusion

The microstructure of the 45 steel revealed by optical and SEM showed the presence of ferrite-like structure with a matrix of small grains with a mean size of ~ 2 µm, and some larger grains (about 10-20 µm) dispersed throughout. This indicates that the steel was water quenched from 900℃, which caused the larger grains to be more rounded.

Steel 45 (900℃ water Tempered) Microstructure Observations

Steel 45 (900℃ water tempered) is a kind of steel with high strength and good cutting performance and high impact strength. The microstructure can be observed under a metallographic microscope. The micrograph of steel 45 (900℃ water tempered) is shown in the Figure 1.

Figure 1 is a metallographic microstructure observation of steel 45 (900℃ water tempered). It can be clearly seen that the microstructure of the steel consists of a uniform Widmanstatten ferrite layer and a number of flat untempered martensite layers embedded in the ferrite. Widmanstatten ferrite layers mainly include ferrite grains, particularly austenite and cementite. Cross-section observation showed that the Widmanstatten ferrite layer was sandwiched between the martensite and bainite layers. The martensite structure of the steel has a very fine cast-structure with a large number of micro-cracks on the surface. It has strong toughness and good cutting performance. The bainite layer is mainly composed of bainite grains, cementite particles and a small amount of intergranular carbides.

The above microscopic observations shows that steel 45 (900℃ water tempered) has a well-balanced microstructure, which is beneficial to obtaining good strength, toughness and cutting performance. In contrast to other steels, this steel has well-balanced microstructures. This property makes it an ideal material for many applications.