STUDY OF THE EFFECT OF AUSTEMPERING TEMPERATURE ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AISI 4340 STEEL: CRITICAL REVIEW

• Main Author: Arintya Karuni, Anselma
• Format: Final Project
• Language: Indonesia
• Subjects: Metalurgi
• Online Access: https://digilib.itb.ac.id/gdl/view/51414
• Institution: Institut Teknologi Bandung

AISI 4340 steel is a type of medium carbon steel that is commonly used in aircraft and the automotive industry. That utilization makes this steel must have high strength, high wear resistance, and high deformation resistance. One of the methods to improve the mechanical properties of the steel is austempering. Austempering is a steel cooling process that is held at an austempering bath temperature for a certain time to transform austenite into bainite. Compared with conventional hardening and tempering methods, austempering has several advantages for example, it can reduce distortion and the possibility of cracking, provides a good combination of hardness and toughness, and higher fatigue life. In this study, a literature study was carried out regarding one of the austempering parameters, namely the austempering temperature. This was studied to determine the effect of the austempering temperature on the microstructure and mechanical properties of AISI 4340 steel. This study was conducted using a critical review method which begins with formulating the problem, namely the effect of austempering temperature on the microstructure and mechanical properties of AISI 4340 steel. From the formulation of these problems, literature searches were carried out through journals, books and internet pages. The literature obtained is then selected by reviewing the abstract to fit the study topic. Furthermore, the experimental data from the literature were summarized and analyzed. After that, a discussion is carried out by combining the literature data with the theory from the literature review to obtain a conclusion that answers the problem formulation. In this study, the microstructure that will be discussed is the volume fraction of retained austenite and bainitic ferrite, and the structure of bainite (upper bainite and lower bainite). While the mechanical properties that will be discussed are the hardness, strength, and toughness. The results of the review show that the volume fraction of retained austenite increases with increasing austempering temperature from 260oC to 400oC. This is inversely proportional to the volume fraction of bainitic ferrite, in which the bainitic ferrite volume fraction decreases with increasing austempering temperature. It is also known that the formation of upper and lower bainite depends on the decarburation time from saturated bainitic ferrite to austenite. As the austempering temperature increases, the decarburation time will be faster. For the mechanical properties of steel, hardness and strength decrease with increasing austempering temperature from 260oC to 400oC. The toughness of steel first increases to a certain temperature around 325oC to 340oC, then decreases to temperatures below 400oC.