High-Alloy Steel is a specialised category of steel containing more than 10% alloying elements by weight. These alloying elements—such as chromium, nickel, molybdenum, vanadium, tungsten, cobalt, and niobium—are added to dramatically enhance corrosion resistance, oxidation resistance, high-temperature strength, wear resistance, and mechanical reliability.
High-alloy steels are engineered for extreme service conditions including high temperatures, high pressures, aggressive chemical environments, heavy mechanical loads, and severe wear—where carbon and low-alloy steels cannot perform reliably.
Metallurgical Classification
Austenitic High-Alloy Steels
• High chromium and nickel content
• Excellent corrosion resistance and ductility
• Non-magnetic in annealed condition
• Examples: 304, 316, 310
Ferritic & Martensitic High-Alloy Steels
• High chromium, lower nickel
• Magnetic structure
• Good oxidation and wear resistance
• Examples: 410, 420, 430
Tool & Die High-Alloy Steels
• Alloyed with W, Mo, V, Co
• Extreme hardness and wear resistance
• Examples: H13, D2, M2
Heat- & Creep-Resistant Alloys
• High Cr-Ni-Mo content
• Retain strength at elevated temperatures
• Examples: ASTM A297, A335 P91
Typical Chemical Composition
| Element | Typical Range (%) | Primary Function |
|---|---|---|
| Carbon (C) | 0.05 – 1.5 | Hardness & strength |
| Chromium (Cr) | 10 – 30 | Corrosion & oxidation resistance |
| Nickel (Ni) | 8 – 35 | Toughness & thermal stability |
| Molybdenum (Mo) | 0.5 – 10 | Wear & creep resistance |
| Vanadium (V) | 0.1 – 3 | Grain refinement |
| Tungsten (W) | 1 – 18 | Hot hardness |
| Cobalt (Co) | 2 – 12 | High-temperature strength |
| Iron (Fe) | Balance | Base metal |
Mechanical & Physical Properties
| Property | Typical Range |
|---|---|
| Tensile Strength | 500 – 1,200 MPa |
| Yield Strength | 300 – 1,000 MPa |
| Hardness | 180 – 700 HB |
| Elongation | 10 – 40% |
| Impact Toughness | Moderate to Excellent |
| Density | 7.7 – 8.2 g/cm³ |
| Service Temperature | Up to 1,100 °C |
| Creep Resistance | Excellent |
High-Temperature & Corrosion Performance
• Chromium forms a protective oxide layer (Cr₂O₃)
• Nickel stabilizes structure at elevated temperatures
• Mo, W, and Co enhance creep resistance and hot strength
• Suitable for continuous service up to 600–1100 °C
Fabrication & Heat Treatment
• Solution annealing, quenching, tempering, and precipitation hardening used
• Weldability depends on grade (best in austenitic steels)
• Martensitic and tool steels require preheat and PWHT
• Machinability is moderate to difficult due to hardness
Available Forms
✔ Plates & sheets
✔ Coils
✔ Bars & billets
✔ Pipes & tubes (seamless / welded)
✔ Forgings & castings
✔ Wires, fittings, flanges, precision components
Applications
Petrochemical & Energy: Reactors, boilers, turbines, heat exchangers
Automotive & Aerospace: Exhaust systems, engine valves, fasteners
Marine & Offshore: Platforms, pipelines, propeller shafts
Tooling & Machinery: Dies, molds, wear plates, cutting tools
Why Choose High-Alloy Steel
High-alloy steel is selected for environments where reliability, safety, and long service life are critical. Its superior resistance to heat, corrosion, wear, and mechanical stress makes it indispensable in energy, petrochemical, marine, aerospace, tooling, and heavy engineering industries.