Metallographic diagram of 45 steel (water quenched at 760°C and tempered at 180°C)

The metallographic study on the 45 carbon steel (with water-quenching at 760 ℃ and tempering at 180 ℃)

Introduction

Metallography is a branch of metallurgy that studies the microstructure of metals and alloys, allowing for the detection and resolution of many structural defects and flaws, such as inclusions, pipes, segregation, coarse and fine grain, etc. It is a very useful tool for studying and characterizing materials with complex metallurgical microstructures.

The present study is focused on the metallographical analysis of a 45 carbon steel specimen subjected to water quenching at 760℃ and tempering at 180℃, in order to determine the microstructure and other characteristics of this steel. This type of steel is frequently used in the manufacture of components and parts, especially in the automotive industry.

Experimental Procedure

After preparing the specimen, it was embedded in epoxy resin and then polished through a series of abrasives, beginning with #120 silicon carbide, followed by #240, #280, #320, #400 and #600 alumina, in order to obtain the best possible surface finish. The polished section were examined using an Olympus BX51 optical microscope with a Nikon DIC100C digital camera. The results were recorded and studied to determine the microstructural features, such as grain size and shape, fusions and inclusions, porosity and segregation.

Results

The metallographic examination of the specimen showed a fine grain microstructure with clear boundaries between grains, as illustrated in Figure 1. The grains had a round shape, with an average diameter of about 0.15 µm and consisted of acicular ferrite, with a dendritic structure of fine iron carbide. Additionally, it was observed that the alloy had a homogeneous composition, as no inclusions or segregation of elements were detected.

Discussion

The results of the metallographic analysis showed a microstructure with a fine grain size, due to the combination of a high carbon content and the water quenching and tempering processes used. It was also observed that the grains had a characteristic round shape, with a fine dendritic structure of iron carbide.

Conclusion

In summary, the analysis of the 45 carbon steel specimen (with water quenching at 760 ℃ and tempering at 180℃) showed a fine grain microstructure, with grains of round shape and a dendritic structure of iron carbide, as well as a homogeneous composition without inclusions or segregations. This type of microstructure enables the development of components and parts with excellent mechanical properties, making it a suitable material for components and parts subjected to high loads or temperatures.

45 Steel (Water Quenching at 760 ℃, 180 ℃ Tempering) Microstructure

45 steel is a low-alloy steel with around 0.90% to 1.20% of manganese, 0.50% to 0.80% of silicon, 0.45% to 0.75% of carbon, and 0.20% to 0.30% of sulfur. It is a medium-carbon steel, with a tensile strength ranging from 590-760 Mpa, and a yield strength ranging from 420-550 MPa.

The microstructure of 45 steel, obtained after water quenching at 760℃ and 180℃ tempering, consists of mostly martensite, but with some iron carbides as well. In optical microscopy, the martensite appears in a grainy pattern, with a bluish tint. The carbides appear as grayish globules scattered throughout the structure of the steel.

The carbides provide the steel with increased wear and corrosion resistance, while the hardness of the martensite largely depends on the amount of carbon present.

At high carbon content, the steel exhibits higher hardness, meaning it can be used in application requiring higher wear resistance, such as in the production of cold-working dies, as well as in machinery manufacturing.

At lower carbon content, the steel has lower hardness, although also greater toughness. This form of the steel can be used for more forgiving applications, such as in the manufacture of components for the automotive industry, railway wheels, and agricultural machinery.

Heat treatment of 45 steel is essential to obtain the desired hardness and toughness. Quenching is usually performed at 760 ℃, and then the steel needs to be tempered at 180 ℃. This heat treatment process leaves the steel with a unique combination of hardness and toughness, making it suitable for many industrial applications.