Cr12 Steel Metallographic Analysis
Introduction
Cr12 steel is commonly used in production of cutting tools due to its hardness and low cost. The steel is composed of iron and chromium and is often used in applications that require a high degree of wear resistance. This paper examines the microstructure of Cr12 following heat treatments of quenching and tempering with the subsequent gas nitriding process.
Quenching and Tempering
The objective of quenching and tempering is to attain desired fracture toughness and hardness. Quenching is a rapid cooling process that provides a martensitic structure and a high degree of hardness. Excessive quenching can produce a brittle martensitic structure due to lack of sufficient softening.
Tempering is to reduce the brittleness caused by quenching and precipitation of carbides near the martensite/austenite interface. Two stages of heat treatment are employed, with some heat treatment recipes involving a third stage. After the first heat treatment, Cr12 steel is quenched and tempered until the desired properties of toughness and hardness are achieved.
In the second stage of tempering, the austenite and martensite grain sizes are refined, creating a homogenous structure.
Gas Nitriding
Gas nitriding is a process of surface hardening in which nitrogen is released into the surface of the steel. The nitrogen is then diffused into matrix and provides an increase in surface hardness as well as wear and corrosion resistance. Gas nitriding can also increase fatigue strength, tensile strength and toughness of Cr12 steel.
Metallographic Analysis
In order to understand the effect of the quenching and tempering with subsequent gas nitriding process, metallographic analysis was conducted on the sample. Optical microscopy was employed to assess the microstructure after each step of the process. In the metallographic analysis, a microstructure consisting of martensite and austenite grains was observed after the process of quenching and tempering.
The gas nitriding process had little effect on the microstructure as seen in the optical analysis. However, exposure to nitriding did cause refinement of the martensite grains along with the formation of nitrides. This led to an increase in hardness in the surface of the steel.
Conclusion
In conclusion, the results of this study showed that quenching and tempering followed by gas nitriding had a beneficial effect on the microstructure and hardness of Cr12 steel. The martensite grains were refined during quenching and tempering and nitrides were formed during the subsequent gas nitriding process which caused an increase in hardness. These results demonstrate that quenching and tempering with subsequent gas nitriding is a viable approach to hardening Cr12 steel.
