DOI: 10.52150/2522-9117-2026-40-010
І. І. Alekseenko1, ORCID 0000-0002-2595-1684
V. А. Kostin1,*, D. Sc. (Engin.), Senior Researcher, ORCID 0000-0002-2677-4667
1 E. O. Paton Institute of Electric Welding, NAS of Ukraine
* Corresponding author: valerykostinepwi@gmail.com
FEATURES OF STRUCTURAL TRANSFORMATIONS OF THE HEAT AFFECTED ZONE METAL OF HIGH-HARDNESS STEELS. (REVIEW)
Abstract. A comprehensive metallurgical analysis of alloying of high-hardness (HHA, 450–550 HB) and ultra-high-hardness (UHHA, > 600 HB) armor steels is presented. The main attention is paid to the synergistic and competing effects of the influence of silicon (Si) and aluminum (Al) depending on the thickness of the armor plate, where 20 mm is a critical technological threshold. It is established that for light armor (< 20 mm), under conditions of dominance of the threat of penetration by high-speed shells, the maximum silicon content is a priority to ensure surface hardness. For heavy armor (> 20 mm), the provision of through-hardness and toughness is of paramount importance, which is achieved due to the increased aluminum content to grind austenite grain. The influence of the Al/Si ratio on the balance of hardness, strength, impact toughness and processability, in particular on the stability of the microstructure in the heat-affected zone (HAZ) of the welded joint, is analyzed. The need for a differentiated approach to the choice of the alloying system and optimization of the Al/Si ratio in strict accordance with the thickness of the armor and the expected fracture mechanisms is shown. It is confirmed that silicon Si and aluminum Al critically affect the formation of the structure of the metal of the heat-affected zone (HAZ), and the nature of this influence is determined by the thickness of the armor, providing an optimal balance of mechanical properties at a high level of hardness > 400 HB. The use of silicon Si increases the structural stability of the HAZ metal, while alloying with chromium Cr provides hardness at a level of about 500 HB due to the formation of carbides of the M₇C₃ type. For steels with small armor thicknesses (< 20 mm), the optimal ratio is Al/Si < 0.02. For armor steels with large armor thicknesses (> 20 mm), the optimal ratio of aluminum to silicon shifts towards Al/Si > 0.1. Increasing the aluminum content (up to 0.5 %) is necessary to ensure a fine-grained structure throughout the thickness of the plate.
Key words: high-hardness steels, HHA and UHHA steels, armor thickness, HAZ metal, microstructure.
For citation: Alekseenko, I. I., & Kostin, V. A. (2026). Features of structural transformations of the heat affected zone metal of high-hardness steels. (Review). Fundamental and applied problems of ferrous metallurgy, 40. 166-185. https://doi.org/10.52150/2522-9117-2026-40-010
References
1. Crouch, I. G. (2016). The Science of Armour Materials. Woodhead Publishing.
2. Adeyemi, A. A. (2018). Key Alloying Elements in Steel Design. In Introduction to Physical Metallurgy of Welding (pp. 45-78). Springer
3. Department of Defense. (2008). Detail specification: Armor plate, steel, wrought, high-hardness (MIL-DTL-46100E). US Army Research Laboratory
4. NATO Standardization Office. (2014). STANAG 4569: Protection levels for occupants of logistic and light armored vehicles (Vol. 2). NATO
5. Maweja, K., & Stumpf, W. (2008). The design of advanced armour steels. Materials Science and Technology, 24(9), 1089-1094
6. Bhadeshia, H. K. D. H. (2015). Bainite in Steels: Theory and Practice (3rd ed.). Maney Publishing
7. Slyvinsky, O. A., & Kovtonyuk, M. M. (2025). Ways to increase the bullet resistance of welded joints of high and ultra-high hardness armor steels (Review). Automatic Welding, (6), 51–59. https://doi.org/10.37434/as2025.06.06
8. Garrison, W. M., & Amburgey, A. (2020). Reduced activation ferritic/martensitic steels for armor applications: The role of Silicon. Journal of Alloys and Compounds, 815, 152-160
9. Yuroka, N., & Suzuki, H. (1990). Hydrogen assisted cracking in C-Mn and low alloy steel weldments. International Materials Reviews, 35(1), 217-249
10. Jena, P. K., Mishra, B., & Bhat, T. B. (2010). Effect of tempering on the ballistic behavior of a high strength armour steel. Journal of Applied Research and Technology, 8(3), 303-310
11. Ryan, H. J., & Rvidya, P. (2021). Adiabatic shear bands in high-hardness armor steels: Mechanisms of formation. Acta Materialia, 205, 116-128
12. Zhao, J., Jiang, Z., & Lee, W. (2017). Synergistic effects of Al and Si on the retained austenite stability in TRIP-aided steels. ISIJ International, 57(3), 543-551
13. Msolli, S., Baïlon, J. P., & Martineau, D. (2015). Influence of silicon content on the mechanical properties and fracture toughness of ultra-high strength steels. Engineering Fracture Mechanics, 135, 1-15
14. Lutsenko, V. A., Parusov, E. V., Golubenko, T. N., & Lutsenko, O. V. (2019). Energy effective mode of softening heat treatment of silicon-manganese steel. Chernye Metally, (11), 31–35
15. Reddy, G. M., & Mohandas, T. (2012). Ballistic performance of high-strength low-alloy steel weldments. Journal of Materials Processing Technology, 212(11), 2267-2275
16. Robineau A., & Lefebvre, D. (2019). Evolution of French Armour Steels: From Mars 190 to Mars 650. 30th International Symposium on Ballistics, Long Beach, CA.
17. Kostin, V. А., Poznyakov, V. D., Berdnikova, O. М., Alekseyenko, T. O., & Alekseyenko, I. I. (2021). Influence of Structural Transformations on the Mechanical Properties of Welded Joints of Armor Steels. Materials Science, 56(4), 472–480. https://doi.org/10.1007/s11003-021-00453-1
18. SSAB. (2020). Armox 500T: Data sheet. SSAB Oxelösund AB
19. ArcelorMittal. (2025). Mars® 600: Ultra-high-hardness protection steel. Industeel
20. Kostin, V. A., Grigorenko, G. M., Poznyakov, V. D. et al. (2020). Structural Transformations of the Metal of Heat-Affected Zone of Welded Joints of High-Strength Armor Steels. Materials Science, 55(6), 863-869. https://doi.org/10.1007/s11003-020-00380-7
21. Bassim, M. N., & Odeshi, A. G. (2016). Impact behavior of high hardness armor steels. Journal of Materials Engineering and Performance, 25(1), 321-329
22. Easterling, K. (2013). Introduction to the Physical Metallurgy of Welding. Butterworth-Heinemann
23. Zhang, L., & Thomas, B. G. (2023). Segregation of Phosphorus and Silicon in Continuous Casting of Steel. Metallurgical and Materials Transactions B, 54, 120-135
24. National Research Council. (2018). Opportunitiesin Protection Materials Science and Technology for Future Army Applications. National Academies Press.
25. Gram, A., & Manne, T. (2021). Weldability of modern ultra-high strength structural steels. Welding in the World, 65, 1245-1258
26. Nikitin, N. Yu., & Stepashkin, A. А. (2025). Classification of tensile test results of unidirectional carbon fiber-polysulfone composite material based on random forest, KNN and CNN methods. Results in Materials, 28, 100788, https://doi.org/10.1016/j.rinma.2025.100788
27. Mohandas, T., Reddy, G. M., & Kumar, B. S. (1999). Heat affected zone softening in high strength low alloy steels. Journal of Materials Processing Technology, 88(1-3), 284–294
28. Vander Voort, G. F. (2004). Metallography of steels for armor applications. In ASM Handbook, Vol. 9: Metallography and Microstructures. ASM International.
29. Kushnarova, O., Berdnikova, O., Alekseenko, T. et al. Structure features and their effect on the physical and mechanical properties of the special steel welded joints. International conference “Mechanical Technologies and Structural Materials 2024” Split, Croatia, 19-20 September 2024, 235-243.
Рукопис надійшов до редакції / Received 12.03.2026
Рекомендовано до друку / Accepted 28.05.2026
Опубліковано / Published 30.05.2026
