Behind every aircraft, turbine, and high-load structure is a steel alloy doing the heavy lifting. Advanced high-performance alloys are critical for their function.
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Steel, one of the most popular alloys used today, is optimized for specific engineering applications by adding selected elements that enhance its properties. The article highlights some of the most widely used steel alloys across various engineering fields.
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Steel Alloys & Their Use Cases
| Alloy / Grade |
Type |
Standout properties |
Typical uses |
Best for |
| ASTM A36 |
Mild/carbon structural steel |
Affordable, very weldable, easy to form |
Buildings, bridges, plates, brackets |
General structural fabrication |
| AISI 4140 (Cr–Mo) |
Alloy steel |
High strength, toughness, fatigue + wear resistance |
Shafts, spindles, crankshafts, heavy-duty parts |
Dynamic loading + heat-treated parts |
| 304 Stainless (18/8) |
Austenitic stainless |
Excellent corrosion resistance, ductile, and cryogenic toughness |
Tanks, pressure vessels, railings, furnace sheets |
Corrosion resistance + weldability |
| ASTM A572 Grade 50 |
HSLA structural steel |
Higher strength-to-weight vs mild steel, good weldability |
Buildings, heavy equipment, wind towers, trucks |
Stronger structural members |
| 2205 Duplex (UNS S32205/S31803) |
Duplex stainless |
High strength + strong pitting/stress corrosion resistance |
Oil & gas, marine, chemical processing |
High chloride + high strength needs |
ASTM A36 Mild/Carbon Structural Steel
ASTM A36 Mild carbon structural steel is one of the most used structural hot-rolled steel alloys, which is highly affordable and excellent for welding and fabrication. The yield strength of A36 mild-carbon structural steel makes it possible to bend it easily, making it a preferred choice for a variety of structural steel parts.
As per the ASTM A36/A36M-19 standard, this hot-rolled mild steel contains Carbon, Manganese, Phosphorus, Sulfur, Silicon, and Copper. The maximum percentage of Carbon ranges between 0.25-0.29 % and manganese ranges between 0.85-1.2 for structural plates, while 0.6-0.9 % for steel bars. The maximum percentage for phosphorus, sulfur, and copper is 0.04 %, 0.05 %, and 0.2 %, respectively.
The mechanical attributes make this steel highly preferred for riveted, bolted, or welded constructions for bridges and buildings.1 Furthermore, experts have used A36 mild steel for fabricating bearing plates, forgings, brackets, weldable automotive parts, gears, and landing ramps.
AISI 4140 Steel Alloy
AISI 4140 steel alloy is a preferred choice for manufacturing components with exceptional toughness, superior strength, and high wear resistance under varying dynamic loading conditions. AISI 4140 steel alloy contains about 1.36 % Chromium and 0.215 % Molybdenum, imparting it with exquisite strength, hardness, and fatigue resistance.
AISI 4140 (Cr-Mo) alloy steel is crucial for the aerospace and automotive industry as it can withstand high temperatures exceeding 700 °C. Experts have used heat-treatment techniques such as quenching and tempering to tailor the microstructure of AISI 4140 steel to optimize its properties.2 Apart from the conventional heat treatment techniques, novel unconventional methods like deep cryogenic treatment at -196 °C for 24 hours improved the wear resistance of 4140 steel alloy by 215 %.
Among the various treatment methods, oil quenching is the best one for improving hardness, leading to a gain of 120 %, while annealing leads to the lowest improvement in hardness, while massively boosting the toughness of the steel alloy.
The ability to withstand dynamic loads has encouraged manufacturers to use 4140 alloy steel for rotating automotive parts like cranks, shafts, spindles, connecting rods, and crankshafts, with the agricultural sector utilizing Cr-Mo steel alloy for disc blades, plowshares, and high-strength cultivator teeth.
304 Stainless Steel
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Among austenitic steel grades, 304 stainless steel is undoubtedly the most versatile and widely used material, particularly for its exceptional corrosion resistance, durability, high ductility, and unmatched toughness at cryogenic temperatures.
In addition to these properties, engineering sectors also use 304 stainless steel material owing to its excellent weldability and exceptional fatigue resistance.4
In some documents, AISI 304 austenitic stainless steel is also referred to as 18/8 stainless steel, which is due to its nominal composition comprising 18 % Chromium and 8 % nickel. Apart from these two elements, 304 stainless steel consists of trace amounts of manganese (0.1-2 %), silicon (up to 1 %), phosphorus (up to 0.05 %), sulfur (up to 0.03 %), and nitrogen (up to 0.11 %).
The low-cost, exceptional corrosion and oxidation resistance make 304 austenitic stainless steel the best choice for petrochemical industries, and for the fabrication of critical components of fuel-burning systems, such as the exhaust gas pipes, and furnace sheets.5 Furthermore, 304 stainless steel is the best material for the construction of storage tanks, pressure vessels, and for construction applications like railings.
The exceptional strength, combined with oxidation and corrosion resistance, has arguably made 304 stainless steel the king of austenitic materials.
ASTM A572 High Strength Low Alloy (HSLA) Structural Steel
Among the different types of HSLA steel, ASTM 572, particularly grade 50, has much better strength, weldability, corrosion resistance, and weather resistance than its counterparts. Research studies have found that A572 steel exhibits exceptional strength and can withstand high temperatures, with creep deformation becoming predominant above 550 °C.
Research groups have also observed that cooling down A572 stainless steel after being heated to 600 °C leads to 100 % recovery of the inherent yield strength at room temperature, an exceptional property discovered in any HSLA steel material.6
The ASTM designation specifies the material as A 572 High-Strength Low Alloy Columbium-Vanadium structural steel comprising carbon (0.21 – 0.26 % max.), manganese (1,35 % max.), phosphorus (0.04 % max.), sulfur (0.05 % max.), columbium (0.005 – 0.05 %), and Vanadium (0.01 – 0.15 %).
The ASTM standard sets the maximum rolled Tee thickness for plates, bars, sheets, pilings, and Zees to be 20 mm, while the maximum thickness for structural parts like flanges is around 40mm for grade 50 steel containing Columbium, only when the steel hasn’t been fully deoxidized during manufacturing.7
The high strength-to-load ratio, machinability, and cost-efficiency of A572 have made it popular for building and construction engineering applications, manufacturing of heavy equipment, steel plate fabrication for freight trucks, wind turbine towers, and manufacturing of high-strength mining equipment.
2205 Duplex Stainless Steel (UNS 232205)
Duplex stainless steel is a commonly used steel alloy, often expressed as an improvement over the most common 304 austenitic steel, as it combines attributes of both austenite and ferrite phases. It is highly corrosion and pitting-resistant.8
Duplex stainless steel 2205 offers better weldability than ferrite stainless steel, much higher strength and toughness than austenitic 304 steel, and higher resistance to stress cracking.
The Duplex steel grade 2205 comprises 22 % chromium, 5 % nickel, 3 % molybdenum, and 0.16 % nitrogen. The presence of nitrogen improves the corrosion resistance, and the composition imparts the duplex steel an inherent yield strength that is twice that of conventional austenitic steel, especially for engineering applications involving welded joints.
The increased strength of duplex steel grade 2205 allows for reduced wall thickness in tubular components and welded pipes, making it a popular choice for industrial applications.9
The key attributes have made 2205 a viable choice for oil and gas exploration, storage tanks, chemical processing plant equipment, marine engineering applications, and mechanical components operating in high chloride environments.
High arc energy welding techniques are suitable for welding 2205 stainless steel. Research studies have also shown that duplex steel grade 2205 has higher impact toughness in the operational temperature range of -40 °C to 400 °C, as compared to conventional austenitic steel material.
However, when it comes to machining, conventional austenitic materials are cost-effective and offer better surface finish and lower tool wear.10 Despite these challenges, duplex stainless steel is among the most used steel alloys for high-strength and corrosion-resistant engineering applications.
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A Cost-Effective Fe-based Medium-entropy Alloy
With the rising demand of steel alloys for engineering applications, experts have recently developed a first-of-its-kind cost-effective Fe62Ni15Cr13Si7Al3 medium entropy alloy using cold-rolling and short-annealing treatment techniques.
Experimental testing revealed its ultimate tensile strength to be around 1.8 GPa, with an exceptional uniform ductility of 45% at 77K. The alloy demonstrated superior cryogenic corrosion resistance due to inherent microstructural stacking faults, B2 nanoprecipitates, and Lomer-Cottrell locks. The excellent strength, cryogenic damage resistance, and high ductility make the novel alloy a possible choice for future engineering applications.
The article highlights the top steel alloys used for engineering applications worldwide. None of the above can be termed as the best choice, as it depends on the application, the cost of the project, and the availability of resources. However, these alloys are used by major engineering experts and manufacturers all over the world.
With advances in materials science and the integration of novel technologies such as Machine Learning (ML), the field of steel alloys is expected to usher in a new era of sustainable, cost-efficient development.
Further Reading
- Astm.org. (2019). Standard Specification for Carbon Structural Steel. [online] Available at: https://store.astm.org/a0036_a0036m-19.html.
- Lee, G.H., Park, M., Noh, S., Kim, B. and Kim, B.J. (2025). Microstructure and Mechanical Properties of Modified AISI 4140 Steel with Addition of Cr and W Elements. Archives of Metallurgy and Materials, [online] pp.1133–1137. Available at: https://doi.org/10.24425/amm.2025.154456.
- Mudda, S., Hegde, A., Sharma, S., Gurumurthy, B.M., Manjunath Shettar and Gowrishankar, M.C. (2025). Effect of various heat treatment methods and optimization of their parameters on mechanical properties of AISI 4140 steel. Scientific Reports, [online] 15(1). Available at: https://doi.org/10.1038/s41598-025-17299-1.
- Kumar, A., Sharma, R., Kumar, S. and Verma, P. (2021). A review on machining performance of AISI 304 steel. Materials Today: Proceedings. Available at: https://doi.org/10.1016/j.matpr.2021.11.003.
- Peeratatsuwan, C., Kanjanangkoonpan, S., Reabroy, R. and Chowwanonthapunya, T. (2023). Corrosion resistant degradation of AISI 304 austenitic stainless steel exposed to simulated carburizing environments. Research on Engineering Structures and Materials. [online]Available at: https://doi.org/10.17515/resm2023.782ma0531tn.
- Lee, S.-H. and Choi, B.-J. (2021). Mechanical Properties of ASTM A572 Grades 50 and 60 Steels at High Temperatures. Applied Sciences, 11(24), p.11833. Available at: https://doi.org/10.3390/app112411833.
- Astm.org. (2017). Standard Specification for High-Strength Low-Alloy Columbium-Vanadium Structural Steel. [online] Available at: https://store.astm.org/a0572_a0572m-12.html.
- Chaudhari, A.N., Dixit, K., Bhatia, G.S., Singh, B., Singhal, P. and Saxena, K.K. (2019). Welding Behaviour of Duplex Stainless Steel AISI 2205: AReview. Materials Today: Proceedings, 18, pp.2731–2737. Available at: https://doi.org/10.1016/j.matpr.2019.07.136.
- Kahar, Dr.S.D. (2017). Duplex Stainless Steels-An overview. International Journal of Engineering Research and Applications, 07(04), pp.27–36. Available at: https://doi.org/10.9790/9622-0704042736.
- Vinoth Jebaraj, A., Ajaykumar, L., Deepak, C.R. and Aditya, K.V.V. (2017). Weldability, machinability and surfacing of commercial duplex stainless steel AISI2205 for marine applications – A recent review. Journal of Advanced Research, [online] 8(3), pp.183–199. Available at: https://doi.org/10.1016/j.jare.2017.01.002.
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