Metallographic analysis of steel 65 (1100℃ × 20min + 440℃ × 5s water cool)
Introduction
The study of the microstructure of materials is known as Metallography. Metallography is used to determine the quantity, distribution, and quality of a specimen’s microstructures by taking a sample, sectioning it and then observing the structure’s individual components under magnification. There are many methods used for metallographic analysis, such as optical microscopy, scanning electron microscopy, and X-Ray diffraction. This study was conducted with the use of Optical Microscopy, to investigate the microstructure of steel 65 after it had undergone heating at 1100℃ for 20 minutes and cooling with water at 440℃ for 5 seconds.
Steel 65 is a low alloy steel with a carbon content of 0.64-0.70%. Has a low hardenability and can be fully annealed when needed, achieving a hardness of around 100 Brinell. It is used mainly in structural components and parts, since it can be machined without requiring much heat treatment.
Experimental Procedure
The sample used in this study was heat treated at 1100℃ for 20 minutes, and rapidly cooled with water at 440℃ for 5 seconds. It was then mounted in a low humidity cement, cut and ground to a 500 grind, and polished to a 1μm finish.
A Thin Section was then produced from the sample, and a Metallographic Mount was then prepared for use in the examination.
Metallographic Analysis
An Olympus BX51 optical microscope was used to observe the sample’s microstructures. Using this microscope, the sample’s microstructures can be observed under magnification up to 1500x.
The observation results of the sample revealed that the steel was composed of an array of pearlite and proeutectoid ferrite. A pearlitic microstructure is composed of alternating layers of ferrite and cementite, and is very tough and strong. Proeutector ferrite is a microstructure that results from the slow cooling of steel, and is well suited for applications that require wear resistance.
Conclusion
This study has shown that steel 65 is composed of an array of pearlite and proeutectoid ferrite microstructures. The high proportion of pearlite provides the material with a high strength, toughness and wear resistance, making it suitable for many heavy load applications. The proeutectoid ferrite is capable of providing additional wear resistance, making it even more suitable for wear applications. The results of this study have proven that steel 65 can be both strong and wear resistant after being heated to 1100℃ for 20 minutes, and rapidly cooled with water at 440℃ for 5 seconds.
