Stellite 6B (UNS R30016 / Cobalt-Base Alloy)

Technical Whitepaper for Extreme Wear & High-Heat Service

Issued by: Shanghai Hangbo Alloy Group — Technical Whitepaper Series Document: HB-TWP-6B-002 | Revision: 1.0 | Date: August 2026 Applicable Specifications: UNS R30016, AMS 5894 (bar & forgings), AMS 5788 (welding wire, Stellite 6 family), manufacturer datasheets (Deloro/Kennametal Stellite)

Abstract. Stellite 6B is a wrought cobalt–chromium–tungsten alloy engineered for the most punishing combinations of sliding wear, abrasion, erosion, galling, and elevated temperature encountered in industrial service. Its hardness is inherent — carried by a dense dispersion of chromium and tungsten carbides in a tough cobalt solid-solution matrix — rather than applied by heat treatment, plating, or nitriding. Stellite 6B retains significant hardness at red heat (recovering full hardness on cooling), resists seizing and galling under unlubricated contact, and has a documented service record exceeding 19 years in steam-turbine erosion shielding. This whitepaper presents the chemistry, mechanical and physical property database, corrosion and oxidation behavior, fabrication guidance, industrial case studies, and a procurement checklist for valve, pump, and wear-component engineers.

1. Introduction: History & Market

The Stellite family traces its origin to Elwood Haynes, who patented cobalt–chromium alloys in the early 1900s and established the Haynes Stellite Company (Kokomo, Indiana) to commercialize them. The "Stellite 6" composition — roughly Co–28Cr–4W–1C — became the most widely used wear alloy in history, specified wherever components must survive metal-to-metal sliding, particle impingement, cavitation, or hot abrasive environments. Stellite 6B is the wrought, extensively hot-worked form of the classic Stellite 6 composition (UNS R30016): the thermomechanical processing refines the carbide network, closes casting porosity, and improves toughness and impact resistance while preserving the same carbide-bearing microstructure that gives the alloy its wear resistance. A sister grade, Stellite 6K, carries 1.4–1.9% carbon for even higher abrasion resistance at the expense of toughness.

The market for cobalt-base wear alloys is anchored by valve manufacturing (seats, disks, and trim for steam, gas, and abrasive process service), power generation (turbine erosion shields, feed-pump sleeves), oil & gas (choke trims, safety valves in sour service), chemical processing (plungers, bushings, doctor blades), cement and mining (screw conveyor flights, crusher wear plates), and aerospace (high-temperature bearing and seal surfaces). Because the wear resistance is a bulk material property, Stellite 6B parts can be machined, ground, welded, and repaired repeatedly without losing performance — a major life-cycle cost advantage over coated or hardened components.

Shanghai Hangbo Alloy Group supplies Stellite 6B in bar, plate, sheet, strip, and forging stock, solution heat-treated per the standard 2250 °F (1232 °C) air-cool practice, with full AMS 5894 chemical certification and hardness verification.

2. Metallurgical Basis of Wear Resistance

Stellite 6B's performance derives from a hypoeutectic Co–Cr–W–C microstructure: a ductile, FCC (with strain-induced HCP transformation) cobalt solid-solution matrix reinforced by a primary and eutectic dispersion of M₇C₃ and M₂₃C₆ chromium carbides, with minor tungsten-rich M₆C carbides. Three mechanisms produce the alloy's signature behavior:

1. Inherent hardness without surface treatment. At 37–43 HRC, hardness comes from the carbide volume fraction (~13 vol%) in a strong matrix. Grinding, lapping, or wear do not consume a coating — they simply expose the same hard microstructure beneath.
2. Red hardness. Cobalt's high melting range and the thermal stability of chromium carbides keep hardness serviceable at temperatures where tool steels soften catastrophically. Data in Section 4.2 show Stellite 6B retains useful hardness at 1600 °F (871 °C) and recovers its original hardness on return to ambient.
3. Low stacking-fault energy. The cobalt matrix deforms by twinning and strain-induced FCC→HCP transformation, which produces rapid work hardening at the contact surface. This is the fundamental reason Stellite 6B resists galling and seizing: contacting asperities work-harden rather than microweld and tear.

The alloy is not hardenable by heat treatment alone — quenching, tempering, and aging cycles (with the exception of a mild 1500 °F/3 h age that raises hardness ~2–4 HRC via carbide precipitation) cannot replace the carbide content. Wear resistance is designed in at melting, which is why specifications control carbon (0.90–1.40%) and tungsten (3.50–5.50%) as tightly as they do.

3. Chemical Analysis (AMS 5894 / UNS R30016)

Table 1 — Chemical Requirements, wt%

Note: Some legacy manufacturer datasheets list broader residual limits (Si 2.0 max, Mn 2.0 max); purchase orders citing AMS 5894 control the tighter limits shown above. Chromium provides oxidation resistance and hard carbide formers; tungsten strengthens the matrix and raises the recrystallization temperature; carbon controls carbide volume fraction and therefore the hardness/abrasion-resistance balance.

4. Mechanical Properties

4.1 Room-Temperature Properties (Solution Heat-Treated, 2250 °F/1232 °C AC)

Table 2 — Average RT Tensile, Wrought Stellite 6B

*Elongation in 1 in (25.4 mm). Aged condition: 3 h at 1500 °F (816 °C), air cool.

Supporting mechanical data (solution-treated): compressive strength 347 ksi (2392 MPa) at room temperature; modulus of rupture 338 ksi (2360 MPa); modulus of elasticity 30.4–31.1 × 10⁶ psi (210–214 GPa); Izod impact (unnotched) 62 ft·lbf (84 J); Charpy impact (unnotched) 72 ft·lbf (98 J) longitudinal, with notched values ~6–15 ft·lbf reflecting the carbide-sensitive nature of the alloy — designers must avoid severe stress raisers in tension.

4.2 Elevated-Temperature Properties & Red Hardness

Stellite 6B's hot hardness is the property that justifies its use in steam, valve, and hot-gas service. Table 3 gives Brinell hardness measured at temperature (mutual-indentation method).

Table 3 — Hot Hardness of Stellite 6B

Tensile strength retention follows the same pattern (Table 4): the alloy still exhibits ~74 ksi (509 MPa) UTS at 1500 °F (816 °C) and ~56 ksi (385 MPa) at 1600 °F (871 °C), with elongation increasing with temperature — a signature of a stable, non-embrittling matrix.

Table 4 — Elevated-Temperature Tensile, Sheet 0.063 in (1.6 mm), Solution Treated

Stress-rupture data (solution-treated sheet): at 1000 °F (538 °C) under 60 ksi (414 MPa), life exceeds 190 h; at 1200 °F (649 °C)/50 ksi (345 MPa), rupture life is ~360 h; at 1500 °F (816 °C)/25 ksi (172 MPa), ~70 h; at 1800 °F (982 °C)/8 ksi (55 MPa), ~113 h. These numbers define the creep-limited design envelope for hot wear parts such as turbine erosion shields.

5. Physical Properties

Table 5 — Typical Physical Properties, Stellite 6B

The moderate CTE (~13.9 ppm/K) is well matched to austenitic stainless steels and nickel alloys, which simplifies bimetallic valve and pump designs. Thermal conductivity (~15 W/m·K) is low enough that frictional heat concentrates at the surface — acceptable because the hot hardness carries the load — but designers of high-speed journal bearings should budget for heat removal.

6. Corrosion & Oxidation Performance

Stellite 6B couples wear resistance with good, but not universal, corrosion resistance. Its chromium content (27–32%) confers stainless-like passivity in oxidizing media and excellent resistance to atmospheric and elevated-temperature oxidation; the cobalt matrix additionally resists the erosive-corrosive attack of slurries and cavitating fluids far better than austenitic stainless steels. Reported service and laboratory behavior:

• Atmospheric and hot oxidation: highly resistant at ordinary temperatures; good oxidation resistance at elevated temperature. The alloy's dimensional stability under repeated thermal cycling to 1800 °F (982 °C) is one reason it is chosen for hot valve trim and turbine shielding.
• Aqueous media: good resistance in food-handling service, many chemical plant streams, salt water, and mildly acidic/alkaline process fluids; suitable where combined wear + corrosion defeat stainless grades (Type 316 and 304 lose the abrasion and galling battle in slurry service).
• Cavitation-erosion: outstanding. In standardized vibratory cavitation testing, Stellite 6B lost ~42 mg over 100 h, whereas Type 304 stainless lost a comparable mass in only 7 h — an order-of-magnitude advantage in normalized terms.
• Limitations: like all high-chromium cobalt alloys, 6B is attacked by strongly reducing acids (hot HCl, dilute H₂SO₄ at elevated temperature) and by chloride pitting above ~50–60 °C in stagnant brine. Where extraordinary general corrosion resistance is required, the Hastelloy family or a nickel-base alloy with a 6B wear overlay is the recommended composite solution.

Galvanic behavior: 6B is noble relative to carbon steel and most stainless steels; in wet service, couple it thoughtfully (insulating sleeves or compatible trim pairs) to avoid accelerating attack on the less-noble member. In dry gas, steam, and hydrocarbon service — the classic valve applications — galvanic effects are not a concern.

7. Fabrication Guide

7.1 Heat Treatment

Stellite 6B is supplied solution heat-treated at 2250 °F (1232 °C), air cooled, which dissolves coarse carbides into a homogeneous austenitic cobalt matrix and optimizes toughness. An optional age at 1500 °F (816 °C) for 3 h, air cool, precipitates secondary carbides and raises hardness ~2–4 HRC (to 40–41) at some sacrifice of ductility — useful for abrasion-dominated, impact-free service. Do not quench to harden: the alloy is not martensitic, and rapid cooling of heavy sections risks cracking from thermal stress.

7.2 Machining

6B is machinable but demanding; it is roughly 2–4× harder than stainless and work-hardens rapidly:

• Tools: tungsten carbide only — C-3 carbide for turning/boring, C-2 for drilling/reaming. High-speed steel is not recommended; threads are best produced by EDM or grinding.
• Turning: 50–70 SFPM (0.25–0.35 m/s), feeds 0.008–0.012 in/rev roughing, 0.002–0.005 in/rev finishing; use −5° rake holders and 30–45° lead angles.
• Drilling: 30–35 SFPM with thin-web, carbide-tipped screw-machine drills; reaming: 40–50 SFPM, 45° cutting lead angle.
• Coolant: water-base fluid, 15:1 dilution, flood applied.
• Grinding: the preferred finishing method for close tolerances — 2800–6000 SFPM with aluminum-oxide wheels; never water-quench a ground surface (surface checking). Honing is used for internal diameters.

7.3 Welding

Joining 6B to itself or to steels is routine in valve and wear-part manufacture:

• Preferred processes (in order): gas tungsten-arc (TIG) with argon shielding (~25 CFH), gas metal-arc, shielded metal-arc, then oxy-acetylene (use a 3× reducing flame; the alloy "boils" in an oxidizing flame, causing porosity).
• Preheat and maintain ≥ 1000 °F (538 °C) during welding to prevent cracking; still-air cool afterward — do not use chilled fixturing or quench.
• Filler selection: to join 6B to itself where wear resistance is needed in the weld, use cobalt fillers (Stellite 6 / 6B / 21); for joining to carbon or stainless steel, use Haynes 25 or Hastelloy W for root passes, then overlay with the hard cobalt filler. Shielding the root side of GTAW welds improves penetration.
• Brazing: readily brazed with silver, gold, palladium, or nickel fillers; thin joints (0.001–0.005 in) give strongest bonds; vacuum or dry-hydrogen atmospheres preferred.

7.4 Forming

Hot working at 1900–2250 °F (1040–1232 °C) is the primary route (the alloy is "extensively hot worked" as wrought product); cold work is limited but possible (10–20% reduction increases hardness ~6 HRC). Anneal after any cold reduction.

8. Industry Applications & Case Studies

8.1 Unlubricated Valve Service (Galling Resistance)

Valve trim in gas letdown, steam, oxygen, and abrasive process service frequently operates dry or with degraded lubrication — the exact regime where stainless steel trim seizes and gall. Stellite 6B's low static coefficient of friction (0.119 against itself on 120-grit dry surfaces — far below steel-on-steel) and its strain-induced work hardening let seats and disks slide without metal pickup.

Case Study — High-Pressure Natural-Gas Letdown Valves. A gas processing plant's pressure-reduction valves suffered repeated seat-galling failures on 17-4PH/316 trim, with rebuild intervals of 6–8 weeks. Stellite 6B seat rings and disks (solution-treated, finish-ground) eliminated galling failures entirely; overhaul intervals extended beyond 24 months, and the trim was reconditioned by grinding rather than replacement. The plant also eliminated the lubrication regime that had contaminated downstream gas.

8.2 Steam-Turbine Erosion Shielding

Last-stage steam-turbine blades suffer water-droplet erosion that can shorten blade life to a few years. Stellite 6B shields, brazed or welded to the blade leading edges, are the industry-standard defense.

Case Study — 19-Year Turbine Service. A utility steam turbine fitted with Stellite 6B erosion shields operated for over 19 years of continuous service (documented in the alloy's manufacturer data) before the shields required attention — versus typical 3–5 year lives for unprotected 12Cr blades. The combination of erosion resistance, cavitation resistance, and red hardness meant the shields neither washed out nor cracked under repeated thermal cycles between cold starts and full load.

8.3 Pump & Screw-Conveyor Wear Components

Abrasive slurries (fly ash, cement dust, metal powder, shale, coke) destroy both soft and hardened-steel bushings by three-body abrasion.

Case Study — Ash-Handling Pump Sleeves. In a coal-fired plant's fly-ash slurry pumps, case-hardened 4620 sleeves wore through in ~4 months, contaminating bearings. Stellite 6B sleeves (mill-annealed, ground OD) exhibited a wear volume loss of 8.2 mm³ versus 37.2 mm³ for hardened 1090 steel and 102 mm³ for Type 304 stainless in standardized abrasive-wear testing, and in service lasted 14+ months between overhauls. The same sleeves resisted seizing when the water flush — which had doubled as lubrication — was lost during upsets.

9. Procurement Checklist for Engineers

• <input type="checkbox" disabled> Specification: AMS 5894 (bar/forgings); UNS R30016; state whether sheet/plate per manufacturer (Deloro/Kennametal Stellite) or AMS 5773 where applicable.
• <input type="checkbox" disabled> Chemistry certification per heat: C, Cr, W, Ni, Fe, Si, Mn, Mo, P, S within Table 1; Co balance.
• <input type="checkbox" disabled> Condition: solution heat-treated 2250 °F (1232 °C), air cooled, unless aged (1500 °F/3 h) is specified for wear-only applications.
• <input type="checkbox" disabled> Hardness verification: 37–43 HRC (solution-treated); 40–44 HRC (aged) — sample per AMS/ISO 6508.
• <input type="checkbox" disabled> Tensile verification: UTS, 0.2% YS, elongation per Table 2 (minimums per AMS 5894).
• <input type="checkbox" disabled> Ultrasonic examination for bar and plate used in critical valve trim (no cracks, porosity, or inclusions; AMS 2630/AMS 2631 class).
• <input type="checkbox" disabled> Surface finish: lapped/ground seat faces (Ra ≤ 0.4 µm for tight-shutoff trim); edge condition of sheet.
• <input type="checkbox" disabled> Hot hardness data if service exceeds 1000 °F — request manufacturer's temperature-hardness curves.
• <input type="checkbox" disabled> Traceability & docs: mill certificates, COC 3.1, heat/lot traceability, and, for nuclear service, compliance with ASME Section III/NCA-3800 material documentation.
• <input type="checkbox" disabled> Supplier capability: in-house machining/grinding, welding procedure qualification (WPS/PQR per ASME IX) for overlay or repair, and EDM threading capability.

10. FAQ — Stellite 6B

1. Is Stellite 6B hardenable by heat treatment? Not in the martensitic sense — hardness comes from carbides. Only a mild secondary hardening (1500 °F/3 h) is available.
2. What does "red hardness" mean practically? Hardness remains serviceable at 1000–1600 °F (e.g., 226 BHN at 1000 °F) and fully recovers on cooling.
3. Can 6B run against 6B? Yes — its self-mated friction coefficient (~0.12 dry) is low and it resists galling; this is standard for valve trim.
4. 6B vs 6K? 6K has more carbon (1.4–1.9%) — higher abrasion resistance, lower toughness. Choose 6K for pure abrasion, 6B for impact + wear.
5. Is 6B magnetic? Essentially non-magnetic (permeability < 1.2 at 200 Oe).
6. Can it be welded onto stainless steel? Yes, with preheat ≥ 1000 °F and proper filler (Hastelloy W/Haynes 25 root + cobalt overlay).
7. Why is machining so slow? 37–43 HRC carbide-rich microstructure; tungsten-carbide tooling at 50–70 SFPM is the proven envelope.
8. Does 6B resist seawater? Reasonably, and far better in erosion-cavitation; but for static seawater corrosion, consider 6B overlays on a more corrosion-resistant substrate.
9. What temperature limit for continuous service? Oxidation and strength data support use to ~1800 °F (982 °C); above that, stress-rupture life collapses.
10. How does it compare to hardened tool steel for wear? In abrasive tests, 6B loses ~5× less volume than hardened 1090 steel and ~12× less than 304 SS.
11. Is there a cast version? Yes — cast Stellite 6 (UNS R30006) is the founding composition; 6B is the wrought form with finer carbides and better impact toughness.
12. What certifications matter? AMS 5894, hardness certification, chemistry, and NDT; nuclear trim may additionally require ASME material traceability.

11. References

1. SAE AMS 5894, Cobalt-Chromium-Tungsten Alloy, Bars and Forgings (Stellite 6B, UNS R30016).
2. SAE AMS 5788, Cobalt-Chromium-Tungsten Alloy, Welding Wire (Stellite 6 family).
3. Deloro Stellite / Kennametal Stellite, Alloy 6B Product Data (stellite.com).
4. High Temp Metals, 6B Wrought Technical Data (compiled manufacturer test data).
5. Corrosion Materials, Alloy 6B Data Sheet (UNS R30016/AMS 5894).
6. ASM International, ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, cobalt-base wear alloys chapter.
7. Haynes International, Haynes® 25 and Cobalt-Base Alloy Joining Guidelines.

Disclaimer: Data presented are typical values from public manufacturer data sheets and standards; they are indicative only and must be verified against actual mill certifications and application testing. © 2026 Shanghai Hangbo Alloy Group. Stellite is a registered trademark of Kennametal Inc.; all trademarks belong to their respective owners.