Alloy Grade UNS: HH – Higher in Chromium

  • Overview

    Alloy HH (25-12) is higher in chromium than MTEK 20-10 and will resist scaling to 2000° F with applications in the 1600 to 1900° F range. For maximum strength above 1500° F, the composition must be balanced to insure a stable austenitic structure. For applications requiring higher ductility at service temperatures, the composition can be balanced to give some ferrite in the structure. This increase in ductility is accompanied by a considerable loss in creep strength. Specification ASTM A447 designates two classes of the alloy: Type I, with some ferrite in the structure, for maximum ductility, and Type II, completely austenitic for maximum strength.

  • Typical Uses

    Convection furnace components, grate bars, rabble arms, radiant tubes, and refractory support hardware.

  • MetalTek Designation

    MTEK 25-12

  • Poured At:

    Carondelet Division, Sandusky International Division, Wisconsin Centrifugal Division, Wisconsin Investcast Division

Similar Specifications

Cast UNS: J93503

Wrought UNS: S30900

Wrought Grade: 309

Cast Grade: HH

Cast ASTM: A297, A608

Typical Chemical Composition (% by wt.)

Aluminum: n/a

Carbon: 0.20-0.50

Chromium: 24-28

Manganese: 2

Iron: n/a

Copper: n/a

Nickel: 11.0-14.0

Lead: n/a

Tin: n/a

Silicon: 2

Zinc: n/a

Minimum Mechanical Properties

Tensile, ksi

0

Tensile, MPa

0

Calculated PREn (Minimum)

0

Yield, ksi

0

Yield, MPa

0

Elongation

0%

Heat Treatment: Not Heat Treated

Frequently Asked Questions

Heat resistant stainless steel refers to alloys designed to maintain mechanical properties and resist oxidation at elevated temperatures.

Applications include furnace parts, heat exchangers, and components in petrochemical plants.

Heat resistant stainless steels can withstand temperatures up to 1,150°C (2,100°F), depending on the grade and exposure time.

High chromium and nickel contents stabilize the austenitic structure and form a protective oxide layer, resisting scale and oxidation.

Explore Other Alloys

Gears

Non-Ferrous

Non-ferrous alloys are, literally, materials that are not iron-based. While others may provide non-ferrous materials of other materials, the MetalTek family of non-ferrous alloys are copper-based. In general, these materials deliver high strength, and excellent wear and corrosion resistance. They are often found in marine applications and also bushing, bearing, and gear environments.
Stainless Steel Parts

Stainless Steel

Stainless steels owe their ability to resist corrosion primarily to the presence of a passive film on their surface. Chromium is chiefly responsible for formation of the passive film. Iron ceases to rust at approximately 12% chromium content and resistance to oxidizing corrosives increases rapidly with chromium content up to approximately 20%.
Petrochemical Fittings

Specialty Alloys

Specialty Alloys comprise a broad group of materials that deliver properties for more demanding applications, use more exotic or expensive materials, or require special processes to manufacture. Where standard materials may not offer desired performance, specialty alloys (including those that are modified further) may be a sensible selection.