CHARACTERIZATION OF AISI O1 TOOL STEEL APPLIED BY DOUBLE QUENCHING TEMPERING AND DEEP CRYOGENIC TREATMENT

• Main Author: FERNANDA (NIM: 12513017), NICKY
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/23473
• Institution: Institut Teknologi Bandung

Conventional heat treatment in tool steels has not changed the austenite phase into martensitic structure to increase the hardness and toughness. Deep Cryogenic Treatment (DCT) has become the easiest and most economical method of reducing the number of retained austenite. However, increasing hardness by DCT will reduce the toughness. Austenite grain refinement can increase the toughness of martensitic steels. This grain refinement can be done through double austenization. In this study, Deep Cryogenic Treatment (DCT) will be combined with the Double Quenching Tempering (DQT) to produce finer grain size of austenite than using conventional heat treatment. Characterization is performed to know the change of microstructure and the phase transformation during heat treatment. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> In this study, heat treatment of AISI O1 Tool Steel specimen are applied in the form of double austenization, DCT, and tempering. The experiments were performed by heating the specimen at temperature of 950°C for 30 minutes followed by oil quenching, followed by the second austenization with temperature variations of 950°C, 900°C, and 850°C for 30 minutes, followed by oil quenching. Then, tempering was carried out at temperature variations of 200°C, 300°C, and 400°C for 2 hours followed by DCT process for 36 hours. The experiments is continued by tempering with temperature variations of 200°C, 300°C, and 400°C for 2 hours. In addition, Conventional Heat Treatment (CHT) and DQT were also conducted as comparison. CHT is performed at austenization temperature of 950°C and tempering temperature of 300°C, while DQT is performed at the first austenization temperature of 950°C, second austenization temperature variations of 950°C, 900°C, and 850°C, and tempering temperature of 300°C. The results were then characterized using optical microscopy, SEM-EDS, XRD, and vickers hardness testing. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> The test results show that the DQT treatment can provide finer austenite grain size, followed by refined martensite structure compared to CHT treatment. DQT was able to improve grain size from 17,9 &#956;m using CHT method to 6,7 &#956;m. Meanwhile, all the retained austenite has been transformed into martensite after DCT was performed. The analysis using SEM-EDS showed smaller carbide particles in DQT and DCT treatment specimens. The highest hardness value of 765,4 HV was obtained on specimen with second austenization temperature of 950°C and tempering temperature of 200°C.