UNS R30021Stellite 21

Hardness & wear

Hardness acceptance criterion Required by the standard

As-cast hardness must not be higher than 34 HRC, or equivalent, determined to ASTM E18.

⚠ This is a MAXIMUM, the opposite direction from Stellite 6 in the same family (a 37 HRC minimum). The reason: exposure to elevated temperature hardens these castings further (about 800 °C for 50 h can take them to 45 HRC). The alloy keeps hardening in service, and holding the as-cast hardness down preserves machinability and a reserve of toughness.

⚠ The 45 HRC figure is only an example, not an acceptance criterion, and must not be used to pass or fail material. The as-cast 34 HRC is the acceptance line.

⚠ The practical consequence: incoming material on the soft side is not necessarily a problem — it is what the specification asks for — and a part measured above 40 HRC after service does not show that the incoming material was out of specification. Any judgement has to separate as-cast from after-service.

⚠ Three cobalt wear alloys in the same family, three different directions of hardness requirement — read the direction before the number:

· R30006 (Stellite 6 castings) — not lower than 37 HRC: a minimum, because the hardness is the function;

· R30021 (Stellite 21 castings) — as-cast not higher than 34 HRC: a maximum, because the alloy age-hardens further in service;

· R30016 (Stellite 6B wrought) — 33 to 43 HRC: a two-sided band.

When you see a cobalt hardness figure, establish first whether it is a floor, a ceiling or a range.

What the standard says about wear service Informative only — not a basis for acceptance

Typical uses: parts such as turbine vanes that need high strength up to 1500 °F (816 °C) and oxidation resistance up to 2000 °F (1095 °C); use is not limited to these.

⚠ Note that the intended use differs from Stellite 6: Stellite 21 is positioned for high strength plus oxidation resistance, with turbine vanes as the example, whereas Stellite 6 is the wear- and erosion-resistant grade. In its own specification, Stellite 21 is not positioned primarily as a wear grade.

⚠ 816 °C and 1095 °C are two different temperatures — the first for strength, the second for oxidation resistance, nearly 280 °C apart, and they must not be used interchangeably. Load-bearing parts belong to the 816 °C figure, and the specification gives no allowable stress at that temperature.

Weld-deposit hardness across the family Informative only — not a basis for acceptance

⚠ These are typical hardness values for multilayer welds in the as-welded condition — not an acceptance range: the body of the standard verifies only the chemical composition of the filler metal or weld metal, never hardness. Using this table to pass or fail a deposit is a misuse of it.

How to read it: the carbide fraction rises A → B → C → G and hardness rises with it, while impact toughness and corrosion resistance fall. E and H take the other route — low carbide, solid-solution strengthened, winning on toughness and work hardening. Choosing a grade means picking a point on that trade-off.

⚠ The bands are wide (ERCoCr-A spans 24 HRC points). As-welded hardness depends on dilution, the number of layers, preheat and interpass temperature; it is not a material constant. A single-layer deposit is diluted by the base metal and reads distinctly softer — A7.2.8 is about MULTILAYER welds.

⚠ This matches the 34 HRC as-cast cap for the castings: ERCoCr-E is also the softest of the family as deposited (20-35 HRC). It is not the grade in this family that wins on hardness.

A7.2.4.1: good strength and ductility to 1150 °C, resistance to thermal shock and to both oxidising and reducing atmospheres, excellent self-mated galling resistance and very high cavitation-erosion resistance, and it work-hardens. Valve trim, hot shear blades and hot extrusion dies choose it for thermal shock and galling, not for hardness.

Condition as supplied and heat treatment Required by the standard

The nominal composition is 62Co-27Cr-2.8Ni-5.5Mo. Compared with Stellite 6 (60Co-29Cr-4.5W) it substitutes molybdenum for tungsten and carries far less carbon, which is why it is softer as cast yet age-hardens in service.

Chemical composition

Nominal: mid-range where both limits are given, the cap where only a maximum is, balance takes the remainder. Exact specified ranges below.

Mechanical minima by form

Guaranteed values differ by form, size and delivery condition; quotations confirm the specification, form, size and condition.

Where this grade is recommended

Matched in 1 service conditions; ranks and scores computed from the condition-scoring matrix.

Designations & equivalents

Cross-references are common near-equivalents for search and shortlisting; substitution across standards requires clause-by-clause verification. All grades in one cross-reference table →

Applicable standards

2 specifications. Name the standard and its edition on the order.

Guaranteed values and required tests differ between specifications — see Mechanical minima by form for the figures per form.

Frequently asked questions

Same series

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Supply & enquiry

Tube & pipeφ1 – 219 × 0.25 – 25 mmPlate4.76 – 80 mmBarφ8 – 300 mmWire & filler metalsφ0.01 – 8 mm