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Probing True Microstructure-Hardening Relationship in Simulated Heat Affected Zone of P91B Steels

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Abstract

The inducement of this paper was the revelation of true microstructure-hardening relationship in heat affected zones (HAZs) of P91B steels. This work reports erroneous metallographic practices in revealing true microstructure and establishes prior austenite grain (PAG) hardening and softening phenomenon. Different HAZs were simulated having distinguished microstructural features. True microstructure of simulated and post-weld heat treatment (PWHT) samples were revealed completely and discussed with respect to microhardness indicating the degree of hardening. It was revealed that true microstructure features of sub-HAZs were governed by peak temperature, hold time at peak temperature, PAG size, and microhardness. The simulated samples showed different microstructural features on using different reagents/etchants. Rate of revealing microstructural features and degree of keying force influencing PAG size were observed to be dependent on peak temperature and hold time at peak temperature. However, true-microstructural features of furnace simulated and PWHT samples were independent of reagents’ composition. Degree of hardening varied due to the difference in solid solution strengthening and formation of second phases at a given peak temperature and hold time at peak temperature. In simulated samples, PAG softening was observed for coarse-grained HAZ (CGHAZ) after PWHT, while in furnace simulated samples, softening occurred in inter-critical HAZ (furnace simulated ICHAZ). Interpass temperature with second pass led to the formation of mixed PAGs and PAG hardening. This hardening was retained in inter-critically reheated CGHAZ after PWHT, whereas it was absent in super-critically reheated CGHAZ.

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Acknowledgements

Modassir is very much thankful to his M.Tech mentor, Dr. T. Jayakumar, DRDO Chair (Prof. S. Bhagavantam Chair), DMRL, Hyderabad. Authors are thankful to Director, CSIR-NML, Jamshedpur, Dr. I. Chattoraj for allowing to carry out the experimental work like Gleeble simulations, microhardness testing and microscopy techniques. Dr. Saroja Saibaba, Scientist-H, IGCAR Kalpakkam for nice discussions and suggestions; Director, IGCAR Kalpakkam for providing materials. Modassir would like to thank Dr. Sandip Ghosh Chowdhury, Chief Scientist, CSIR-NML, Jamshedpur for providing metallography facility. Modassir is also thankful for Dr. C. Vanitha, Associate Professor, NIT Warangal and Dr. Asit Kumar Khanra, Associate Professor, NIT Warangal for motivation.

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Authors and Affiliations

  1. Department of Metallurgical and Materials Engineering, National Institute of Technology Warangal, Hanamkonda, Telangana, 506004, India

    Modassir Akhtar

  2. Materials Engineering Division, CSIR-National Metallurgical Laboratory, Jamshedpur, 831007, India

    Modassir Akhtar

  3. Department of Mechanical Engineering, Dr. B. R. Ambedkar National Institute of Technology Jalandhar, Jalandhar, Punjab, 144011, India

    Akhil Khajuria

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Akhtar, M., Khajuria, A. Probing True Microstructure-Hardening Relationship in Simulated Heat Affected Zone of P91B Steels. Metallogr. Microstruct. Anal. 8, 656–677 (2019). https://doi.org/10.1007/s13632-019-00573-w

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