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Stellite 21 Round Bars Supplier in Mumbai, India – UNS R30021
Nicorex Alloys is an ISO 9001 / ISO 14001 certified supplier, stockist, and trading company based in Mumbai, India. We supply batch-tested Stellite 21 round bars with full compliance to AWS, AMS, and ISO standards.
Stellite 21, also known as Cobalt Alloy 21 (UNS R30021, AWS A5.21 ERCoCr-E), is a cobalt-chromium-molybdenum (CoCrMo) alloy. Stellite 21 uses molybdenum as the ternary element. Low carbon (<0.35%) produces only ~4% carbide volume fraction, so the CoCrMo matrix dominates wear and corrosion properties. Originally developed in as a biocompatible hip implant and denture alloy, it remains a close analogue of ASTM F75. Stelliye 21 exhibits a hardness of HRC 27–40 (290–430 HV), and it can work harden up to 550 HV (48 HRC). It consists of cobalt balance, approximately 27% chromium, ~5.5% molybdenum, and 0.35% carbon max. It is a CoCrMo alloy that provides excellent resistance to corrosion in reducing acids (H₂SO₄, HCl, H₂S). It provides oxidation resistance up to 1150°C (21000F). Alloy 21 is weakly ferromagnetic to paramagnetic depending on the condition, with a density of 8.33 g/cm³ (lightest Stellite).
Diameters of Stellite 21 round bars span from 5 mm to 300 mm. Lengths range from 300–3000 mm. We stock UNS R30021 round bars in forms like cast, HIPed, P/M, ground, centreless-ground, welding rod, powder. We also supply Stellite alloy grade 21 plates. Key applications include valve trim for sour gas service, forging and hot stamping die build-up, medical implants, and high-temperature components.
Cobalt Alloy UNS R30021 Bar Specifications
Specifications of Stellite 21 (UNS R30021) round bar, including standards, dimensions, conditions, tolerances, and other key details, are covered in the table below:
| Designation | Stellite 21 / Cobalt Alloy 21 |
|---|---|
| AWS | A5.21 ERCoCr-E (rod), ERCCoCr-E (wire); A5.13 ECoCr-E (electrode) |
| AMS | AMS 5385 (castings); AMS 5819 (rod, wire) |
| Alloy System | Cobalt-Chromium-Molybdenum (CoCrMo) |
| Carbide Type | (Cr, Mo, Co)₂₃C₆ (NOT M7C3 like CoCrW Stellites) |
| Diameter | 5 mm to 300 mm |
| Length | 300 mm to 3000 mm (custom available) |
| Manufacturing | Casting (investment, centrifugal, sand), HIP, Powder Metallurgy |
| Conditions | As-Cast, Solution Heat-Treated, HIPed, Ground, Centreless Ground |
| Heat Treatment | Solution 1200–1240°C, quench; age 700–1150°C |
| Tolerances | Standard or h6/h7 (ground bars) |
| Testing | PMI, Hardness (HRC), Chemical Analysis, UT, Dimensional |
| Certification | MTC per EN 10204 – 3.1 / 3.2 |
Chemical Composition of Stellite 21 Alloy
The chemical composition of Stellite 21 alloy and its key alloying elements are mentioned in the table below:
| Element | Cobalt (Co) | Chromium (Cr) | Molybdenum (Mo) | Carbon (C) | Nickel (Ni) | Iron (Fe) | Silicon (Si) | Manganese (Mn) |
|---|---|---|---|---|---|---|---|---|
| Min (%) | Balance | 26.0 | 4.5 | – | – | – | – | – |
| Max (%) | Balance | 29.0 | 6.0 | 0.35 | 3.0 | Balance | Balance | Balance |
Chromium (26–29%) forms M23C6-type carbides and builds a Cr₂O₃ passive layer for corrosion protection. Molybdenum (4.5–6.0%) replaces tungsten, providing solid-solution strengthening and superior resistance to reducing acids (H₂SO₄, HCl) and sour gas (H2S). Carbon below 0.35% produces only ~4% carbide volume, so the CoCrMo matrix dominates, giving 9%+ elongation but limited abrasion resistance. Cobalt’s FCC matrix provides galling resistance and biocompatibility.
Mechanical Properties of Stellite 21 Bar and Rod
The mechanical properties of Stellite 21 bar and rod, including tensile and yield strength, hardness, elongation, and more, are provided in the table below :
| Property | Hardness (as-cast) | Work-Hardened Surface | UTS (typical) | Yield, 0.2% (min) | Elongation (min) | Elastic Modulus |
|---|---|---|---|---|---|---|
| Value | HRC 27–40 (290–430 HV) | Up to 550 HV (48 HRC) | 710–724 MPa (103–105 ksi) | ≥565 MPa (82 ksi) | ≥9% | ~250 GPa |
Work hardening is the defining feature. Surface hardness can double from HRC 27 to HRC 48 during service. Elongation of 9%+ is dramatically higher than any CoCrW Stellite (Grade 6: 1–3%, Grade 1: <1%), giving exceptional impact and thermal shock tolerance.
Physical Properties of Cobalt Alloy 21
Physical properties of Stellite 21 (UNS R30021), including density, melting point, thermal expansion and conductivity, and other key properties are mentioned below:
| Property | Density | Melting Range | Thermal Expansion (20–100°C) | Thermal Conductivity (25°C) | Oxidation Resistance | Magnetic Behaviour |
|---|---|---|---|---|---|---|
| Value | 8.33 g/cm³ (0.301 lb/in³) | 1295–1435°C (2360–2615°F) | ~14.0 µm/m·°C | ~14.8 W/m·K | Up to 1150°C (2100°F) | weakly ferromagnetic to paramagnetic depending on the condition |
Lightest common Stellite (8.33 vs 8.44 for Grade 6, 8.69 for Grade 1) because Mo is lighter than W. Highest melting range due to the absence of tungsten.
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Available Types of Stellite Grade 12 Round Bar
Nicorex Alloys stocks Stellite 21 round bars in these forms:
Stellite 21 Cast Round Bar
UNS R30021 Centreless-Ground Bar
Cobalt Alloy 21 Ground Bar
Stellite 21 Alloy Rod
Wear Resistance & Corrosion Behaviour of Stellite Alloy 21
Stellite 21 provides excellent cavitation, galling, and metal-to-metal sliding wear resistance. The CoCrMo matrix dominates wear properties due to low carbide volume (~4%). Work hardening progressively increases surface hardness from HRC 27–40 up to 48 HRC (550 HV).
Corrosion resistance is superior to CoCrW Stellites in reducing environments. Mo replaces W, giving higher resistance to H₂SO₄, HCl, and sour gas (H₂S). Electrode potential in seawater: ~–0.3 V (SCE). Oxidation-resistant up to 1150°C.
Excellent impact and thermal shock resistance. 9%+ elongation gives ductility that CoCrW Stellites cannot match. Used for building up forging and hot stamping dies.
Work hardening is both an advantage (progressive surface hardening) and a machining challenge. Positive-rake carbide inserts with adequate feed rates cut below any hardened layer.
Limitations: Not recommended for severe hard-particle abrasion. Low carbide content means poor sand/grit erosion resistance. For abrasion, Stellites 1, 12, or 6 are superior.
Industries & Applications of Stellite 21 Round Bar
Stellite 21 round bar is specified for 6 key applications where superior corrosion resistance, impact toughness, and thermal shock resistance are required:
- Valve seats, plugs, and stems in sour gas (H₂S) environments. Pump components where cavitation resistance is critical.
- Valve trim for steam and gas turbines. One of the first heat-resistant alloys trialled for jet engines.
- Forging die and hot stamping die build-up. 9%+ elongation absorbs repeated loads without cracking.
- Originally, a biocompatible hip implant and denture alloy from the 1930s. Close analogue of ASTM F75 (UNS R30075).
- Superior to CoCrW Stellites in reducing acid service. Mo provides resistance to chloride and sulphide attack that tungsten cannot match.
- Used for hot-section wear components. AMS 5385 (castings) and AMS 5819 (rod/wire) provide aerospace qualification.
How to Order Stellite 21 Round Bar from Nicorex Alloys
Provide the following 10 documents to place an order for Stellite 21 round bars:
- Product Form — Hot Rolled / Cold Drawn / Forged / Cast Round Bar
- Size — Diameter: 6mm to 300mm — specify diameter and length
- Condition — Solution Annealed / As-Cast / Forged & Annealed
- Surface Finish — Black (as-rolled) / Turned & Polished / Centreless Ground
- Material Grade — Stellite 21 / UNS R30021 / AMS 5385 (castings) / AMS 5819 (rods) ISO / Co-Cr-Mo Alloy
- Quantity — Total weight in kg or MT (specify pieces and length)
- Standard — AMS 5385 (castings) / AMS 5819 (rods & wire) Deutsche-nickel, ASTM F75, ASME Section IX
- Additional Requirements — Co-Cr-Mo composition confirmation (Cr: 26–29%, Mo: 4.5–6.0%) ISO, PMI, heat/lot traceability
- Documentation — MTC 3.1/3.2, PMI Report, Mechanical Properties Report, Hardness Certificate, TPI Certificate
- Delivery — Domestic / International (specify destination)
Frequently Asked Questions
What is the Price of Stellite 21 Round Bar in India?
The price of Stellite 21 round bar depends on diameter, condition, heat treatment, and cobalt market rates. HIPed and solution heat-treated bars have a premium price range. Contact Nicorex Alloys for current pricing.
What is the Hardness of Cobalt 21 Alloy Round Bar?
HRC 27–40 (290–430 HV) as-cast. Surface can work harden to 550 HV (48 HRC) during wear or machining, providing progressively increasing wear resistance.
Can Stellite Grade 21 Be Machined?
Yes, but with caveats. Stellite 21 work hardens considerably. Use fresh carbide inserts, positive rake, and adequate feed to cut below any hardened layer.
Is Stellite 21 Suitable for Sour Gas Service?
Yes. Mo replaces W, giving higher resistance to reducing environments, including H2S sour gas, H₂SO₄, and HCl, than CoCrW grades. Preferred for valve trim in sour gas applications.
What is the Maximum Service Temperature for Stellite Grade 21?
Oxidation-resistant up to 1150°C (2100°F) in oxidising and reducing atmospheres. Solution treatment at 1200–1240°C with ageing at 700–1150°C gives optimum high-temperature strength.
Is Stellite 21 Magnetic?
Stellite 21 is weakly ferromagnetic to paramagnetic depending on the condition. Cr and Mo alloying suppresses cobalt’s natural ferromagnetism.
What Welding Processes Work with Stellite 21?
GTAW, GMAW, SMAW, PTA, HVOF, and laser cladding work with Stellite 21. Filler metals like AWS A5.21 ERCoCr-E (rod), A5.13 ECoCr-E (electrode) can be used. OAW (oxy-acetylene welding) is NOT recommended, unlike Stellites 1, 6, and 12.
Is Stellite 21 Used in Medical Implants?
Yes. It was developed in the 1930s as a biocompatible hip implant and denture alloy. Close analogue of ASTM F75 (CoCrMo surgical standard). Many modern medical implants use variants of the Stellite 21 composition.