On the Construction of Analytical Cooling Curves from ASTM D6200 Data Using Multi-Variable Gradient Descent Method

• Published in: Journal of materials engineering and performance 2024-05, Vol.33 (9), p.4234-4252
• Main Authors: Jan, James, MacKenzie, D. Scott
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Materials Science; Original Research Article; Quality Control; Reliability; Safety and Risk; Tribology
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-023-09104-9

ASTM D6200 is a standard test method published by ASTM International for evaluating the cooling characteristics of quench oils. The results obtained through this standard can serve as a guide for quench oil selection and for comparing quench severities among different quench oils, whether they are new or used. The standard provides six parameters representing the cooling characteristics of the reference quench oil: three time-based scales (time to cool to 600, 400, and 200 °C), two cooling rates (maximum cooling rate and cooling rate at 300 °C), and one temperature scale (at the maximum cooling rate). ASTM D6200 is widely used in production plants to monitor the quality of the quench oil so that parts can be produced with consistent properties, such as hardness, and dimensions. However, it is important to note that the current ASTM D6200 standard only references one specific quench oil, and its usages are limited to characterizing quench severity in physical prototyping or production in the plants. The aim of this research is to explore the possibility of extending the application of the standard to more quenchants in addition to one specific quench oil and expanding the support of the standard beyond physical testing to include virtual engineering by simulations. This research comprises two main portions. The first one involves developing a systematic method for identifying the characteristic points of a time series of thermocouple data. The second one involves constructing an analytical cooling curve based on these characteristic points. This analytical cooling curve is a closed-form mathematical function that relates temperature to time, providing temperature value at any given time during the quenching process. Furthermore, this curve is second-order differentiable, allowing users to derive cooling rate information at any specific time.