Multi-Response Optimization of Cryogenic Treatment for EN Series Steels using Taguchi Method

Abstract

Deep cryogenic treatment (DCT) has emerged as a supplementary process to conventional heat treatment for enhancing the mechanical and tribological properties of engineering steels. However, its systematic evaluation for commonly used EN series steels remains insufficiently explored. This study presents a comprehensive comparative investigation of the effect of DCT on the hardness and wear resistance of EN08, EN24, and EN31 steels using Taguchi L18 orthogonal array design. The specimens were subjected to conventional hardening and tempering, followed by deep cryogenic treatment at -196°C for 48 hours. Rockwell C hardness testing and Pin-on-Disk wear testing (ASTM G99) were conducted. The results revealed that DCT improved hardness in all three materials: EN08 from 50 to 54 HRC (8.0% improvement), EN24 from 53 to 55 HRC (3.8% improvement), and EN31 from 56 to 59 HRC (5.4% improvement). Wear testing showed mass loss ranging from 0.040 g to 0.100 g across 18 experiments. Taguchi S/N ratio analysis identified EN31 with DCT as the optimal combination for maximizing hardness, while ANOVA revealed Material (72.5%) and Treatment (20.1%) as the most significant factors influencing hardness. The study demonstrates that cryogenic treatment is an effective method for enhancing hardness of EN series steels, with material-dependent response, and provides quantifiable data for industrial adoption.

Introduction

The text presents a study on improving the wear resistance and hardness of EN series steels (EN08, EN24, and EN31) using deep cryogenic treatment (DCT) and optimizing the process parameters through the Taguchi L18 design method. Wear is a major cause of industrial component failure, increasing maintenance costs and reducing machine efficiency. Although conventional heat treatment improves steel properties, retained austenite remains a problem because it can reduce wear resistance and cause dimensional instability.

Deep cryogenic treatment, which involves cooling materials to approximately −196°C using liquid nitrogen, helps convert retained austenite into martensite and promotes the formation of fine secondary carbides. These microstructural changes improve hardness, wear resistance, and dimensional stability. Previous studies have shown significant improvements in wear performance after DCT, but limited research compares different EN steels under identical conditions.

The study uses EN08, EN24, and EN31 steels as test materials. Specimens were prepared according to ASTM G99-17 standards and subjected to conventional heat treatment. They were then divided into two groups: conventional treatment (CT) and deep cryogenic treatment (DCT) followed by tempering. The DCT process used liquid nitrogen cooling at −196°C, with a controlled cooling rate, 48-hour soaking period, and gradual warming.

A Taguchi L18 orthogonal array was applied to optimize experimental conditions by considering three factors:

• Material type (EN08, EN24, EN31)
• Treatment condition (CT or DCT)
• Applied load (2 kg, 3 kg, and 4 kg)

Wear testing was conducted using a Pin-on-Disk apparatus with a HARDOX 500 steel disk, while hardness was measured using a Rockwell C hardness tester. Multiple hardness readings were taken for accuracy.

The objective of the research is to determine how deep cryogenic treatment affects the mechanical properties of different EN steels and to identify the optimum combination of material, treatment condition, and load for achieving maximum hardness and minimum wear rate. The study aims to provide useful guidelines for improving the service life and performance of industrial components.

Conclusion

Based on the experimental results and analysis, the following conclusions are drawn: 1) Deep cryogenic treatment improved hardness in all three materials: EN08 showed an improvement from 50 HRC to 54 HRC (8.0% improvement), EN24 from 53 HRC to 55 HRC (3.8% improvement), and EN31 from 56 HRC to 59 HRC (5.4% improvement). The improvement is attributed to the transformation of retained austenite to martensite and the precipitation of fine carbides during cryogenic treatment [20, 21]. 2) The degree of hardness improvement is material-dependent: EN31 achieved the highest absolute hardness (59 HRC) after DCT, EN08 showed the highest percentage improvement (8.0%), and EN24 showed the least improvement (3.8%). This is consistent with the carbon and alloy content of each steel [22]. 3) Taguchi S/N ratio analysis identified optimal parameters: For hardness, EN31 with DCT was optimal. For wear, EN08 with CT at 4 kg was optimal. For combined performance, EN31 with DCT at 3 kg was the best compromise. 4) ANOVA revealed Material and Treatment as the most significant factors: For hardness, Material contributed 72.5% and Treatment contributed 20.1%. For wear, Material contributed 45.2% and Treatment contributed 35.6%. Load had no significant effect on hardness (0.0%) and a moderate effect on wear (18.8%) [23]. 5) The confirmation test validated the Taguchi model: Hardness prediction showed excellent agreement (0.3% error), while wear prediction showed higher error (16.7%) due to test variability. 6) The HARDOX 500 disk provided a stable counter-face: The disk achieved a hardness of 64 HRC and remained unworn during all tests, ensuring consistent test conditions. 7) The mass loss method proved effective for wear measurement: Mass loss was measurable for all experiments, and the method was simple and accurate.

References

[1] Rabinowicz, E. (1995). Friction and Wear of Materials (2nd ed.). John Wiley & Sons. [2] Krauss, G. (2015). Steels: Processing, Structure, and Performance (2nd ed.). ASM International. [3] Bhadeshia, H. K. D. H., & Honeycombe, R. W. K. (2017). Steels: Microstructure and Properties (4th ed.). Butterworth-Heinemann. [4] Baldissera, P., & Delprete, C. (2008). Deep cryogenic treatment: A bibliographic review. Open Mechanical Engineering Journal, 2, 1-11. [5] Gill, S. S., Singh, H., Singh, R., & Singh, J. (2010). Cryoprocessing of cutting tool materials—A review. International Journal of Advanced Manufacturing Technology, 48(1-4), 175–192. [6] Molinari, A., Pellizzari, M., Gialanella, S., Straffelini, G., & Stiasny, K. H. (2001). Effect of deep cryogenic treatment on the mechanical properties of tool steels. Journal of Materials Processing Technology, 118(1-3), 350–355. [7] Das, D., Dutta, A. K., & Ray, K. K. (2016). On the enhancement of wear resistance of AISI 52100 steel by deep cryogenic treatment. Philosophical Magazine, 96(29), 2990–3010. [8] Dhokey, N. B., & Nirbhavne, S. (2009). Dry sliding wear of cryotreated AISI D2, D3, and H13 tool steels. Wear, 267(9-10), 1521–1529. [9] Vimal, J., Bensely, A., Lal, D. M., & Srinivasan, K. (2008). Deep cryogenic treatment improves wear resistance of En 31 steel. Materials and Manufacturing Processes, 23(4), 369-376. [10] Mohan Lal, D., Renganarayanan, S., & Kalanidhi, A. (2001). Cryogenic treatment to augment wear resistance of tool and die steels. Cryogenics, 41(3), 149-155. [11] Ross, P. J. (1996). Taguchi Techniques for Quality Engineering (2nd ed.). McGraw-Hill. [12] Roy, R. K. (2010). A Primer on the Taguchi Method (2nd ed.). Society of Manufacturing Engineers. [13] Montgomery, D. C. (2017). Design and Analysis of Experiments (9th ed.). John Wiley & Sons. [14] Huang, J. Y., Zhu, Y. T., Liao, X. Z., & Beyerlein, I. J. (2003). Microstructure of cryogenic treated M2 tool steel. Materials Science and Engineering: A, 339(1-2), 241-244. [15] Podgornik, B., Paulin, I., Zajec, B., Jacobson, S., & Leskovšek, V. (2016). Deep cryogenic treatment of tool steels. Journal of Materials Processing Technology, 229, 398-406. [16] Yun, D., Xia, L., & Zhang, W. (2018). The effect of cryogenic treatment on the microstructure and mechanical properties of AISI D2 steel. Materials Science and Engineering: A, 715, 278–285. [17] ASTM International. (2017). Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus (ASTM G99-17). West Conshohocken, PA. [18] Antony, J. (2014). Design of Experiments for Engineers and Scientists (2nd ed.). Elsevier. [19] Singh, H., & Kumar, P. (2005). Optimizing multi-machining characteristics through Taguchi\'s approach and utility concept. Journal of Manufacturing Technology Management, 16(7), 722-728. [20] Bensely, A., Prabhakaran, A., Lal, D. M., & Nagarajan, G. (2005). Enhancing the wear resistance of case carburized steel (En 353) by cryogenic treatment. Cryogenics, 45(12), 747–754. [21] Stratton, P. F. (2007). Optimising nano-carbide precipitation in tool steels. Materials Science and Engineering: A, 449, 809-812. [22] Li, H., Tong, W., Cui, J., Zhang, H., & Chen, L. (2016). The influence of deep cryogenic treatment on the properties of high-vanadium alloy steel. Materials Science and Engineering: A, 662, 356-362. [23] Sahoo, A. K., & Sahoo, B. (2013). Performance studies of multilayer hard surface coatings (TiN/TiCN/Al2O3/TiN) of indexable carbide inserts in hard machining: Part-II (RSM, grey relational and techno economical approach). Measurement, 46(8), 2868-2884.

Copyright

Copyright © 2026 Mr. Sagar Shivaji Sonawane, Dr. C. S. Padmavat, Dr. Abhay Pawar, Prof. S. B. Janjal, Prof. A. B. Humbe. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.