MULTIMET^®

Principal Features

MULTIMET^® alloy (UNS R30155, W73155) is recommended for use in applications involving high stress at temperatures up to 1500°F, and moderate stress up to 2000°F. It has excellent oxidation resistance, good ductility, and is readily fabricated. Its high-temperature properties are inherent and are not dependent upon age-hardening. Production and use of the alloys dates back to the late 1940s.

The alloy has been used in a number of aircraft application including tailpipes and tail cones, afterburner parts, exhaust manifolds, combustion chambers, turbine blades, buckets, and nozzles. It also gives excellent service for high-temperature bolts, and has proven to be an economical material of construction for use in heat-treating equipment where strength at high temperatures is essential.

MULTIMET^® alloy has good resistance to corrosion in certain media under both oxidizing and reducing conditions. When solution heat treated, MULTIMET^® alloy has about the same resistance to nitric acid as does stainless steel. It has better resistance than stainless steel to weak solutions of hydrochloric acid. It withstands all concentrations of sulfuric acid at room temperature.

MULTIMET^® alloy can be machined, forged and cold-formed by conventional methods. The alloy can be welded by various arc and resistance-welding processes.

MULTIMET^® alloy is available as sheet, strip, plate, wire, coated electrodes, billet stock and sane and investment castings. It is also available in the form of re-melt stock to a certified chemistry.

Most wrought forms of MULTIMET^® alloy are shipped in the solution heat-treated condition to assure optimum properties. Sheet is given a solution heat-treatment of 2150°F, for a time dependent upon section thickness, followed by a rapid air cool or water quench. Bar stock and plate (1/4 in. and heavier) are usually solution heat treated at 2150°F followed by water quench.

MULTIMET^® alloy suffered from mediocre oxidation resistance, a tendency for heat affected zone cracking during welding, and a relatively wide scatter band of mechanical properties.  HAYNES^® 556^® alloy was developed to address these concerns and as an improvement.

*Please contact our technical support team if you have technical questions about this alloy.

Nominal Composition

*Also known as Columbium

Hardness

HRBW = Hardness Rockwell “B”, Tungsten Indentor.
All samples tested in solution-annealed condition

Tensile Data

Elevated temperature tensile tests for sheet were performed with a strain rate that is no longer standard.  These results were from tests with a strain rate of 0.005 in./in./minute through yield and a crosshead speed of 0.5 in./minute for every inch of reduced test section from yield through failure.  The current standard is to use a strain rate of 0.005 in./in./minute though yield and a crosshead speed of 0.05 in./minute for every inch of reduced test section from yield through failure.

Typical Short-Time Tensile Data, Wrought

RAC- Rapid Air-Cooled
WQ-Water Quenched
*Elongation in 1 in
RT= Room Temperature

Typical Short-Time Tensile Data, Weldments

Impact Strength

All samples were in solution annealed condition.
RT = Room Temperature

Creep and Stress-Rupture Data

MULTIMET^® Sheet, Solution Annealed

Thermal Stability

Room Temperature Tensile Properties after 1200°F (650°C) /16,000 hours

Oxidation Resistance

MULTIMET^® exhibits acceptable oxidation resistance up to around 1800°F.  However, due to concerns with oxidation resistance, MULTIMET^® has been generally replaced by 556^® alloy, which has comparable creep-rupture strength but superior oxidation resistance, particularly at temperatures greater than 1800°F.

Short-term Oxidation
Comparative Oxidation Resistance in Flowing Air, 1008 Hours

Flowing air at a velocity of 7.0 ft/min (213.4 cm/min) past the samples.  Samples cycled to room temperature once per week.

 Dynamic Oxidation Burner Rig

Burner rig oxidation tests were conducted by exposing sampIes 3/8 in. x 2.5 in. x thickness (9 mm x 64 mm x thickness), in a rotating holder, to products of combustion of No. 2 fuel oil burned at a ratio of air to fuel of about 50:1. (Gas velocity was about 0.3 mach). Samples were automatically removed from the gas stream every 30 minutes and fan-cooled to near ambient temperature and then reinserted into the flame tunnel.

Metallographic Technique used for Evaluating Environmental Tests

Hot Corrosion Resistance

Hot Corrosion Burner Rig

Hot Corrosion Resistance at 1650°F (900°C)

Hot corrosion tests were conducted in a low velocity burner rig burning No. 2 Fuel oil with 0.4 percent sulfur. The air:fuel ratio was 30:1. Artificial sea water was injected at a rate equivalent to the salt concentration noted in the table. Tests were run for 1000 hours, with samples cycled out of the gas stream once an hour and cooled to near ambient temperature. Gas velocity was 13 ft./ sec. (4 m/s).

Physical Properties

RT = Room Temperature

Formability

RAC- Rapid Air-Cooled                   WQ-Water-Quenched

Aged and Cold-reduced Hardness Data

*Special Brinell hot hardness tests were made using a 2000 kg. load and 10mm tungsten carbide ball. Both the ball and specimen were help at temperature for 20 minutes before testing.
†Special Brinell hardness measured at room temperature using a 2000 kg. load and 10mm tungsten carbide ball.
RT=Room Temperature
HRBW = Hardness Rockwell “B”, Tungsten Indentor.
HRC = Hardness Rockwell “C”.
RAC- Rapid Air-Cooled
WQ-Water-Quenched

Welding

MULTIMET^® alloy is readily welded by Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding (GMAW), Shielded Metal Arc Welding (SMAW), and resistance welding techniques. Submerged Arc Welding (SAW) is not recommended as this process is characterized by high heat input to the base metal and slow cooling of the weld.  These factors can increase weld restraint and promote cracking.

Base Metal Preparation

The welding surface and adjacent regions should be thoroughly cleaned with an appropriate solvent prior to any welding operation.   All greases, oils, cutting oils, crayon marks, machining solutions, corrosion products, paint, scale, dye penetrant solutions, and other foreign matter should be completely removed.  It is preferable, but not necessary, that the alloy be in the solution- annealed condition when welded.

Filler Metal Selection

MULTIMET^® filler wire (AMS 5794) is recommended for joining MULTIMET^® alloy by Gas Tungsten Arc or Gas Metal Arc welding.  Coated electrodes of MULTIMET^® alloy (AMS 5795) are also available for Shielded Metal Arc welding.  For dissimilar metal joining of MULTIMET^®  alloy to nickel-, cobalt-, or iron- base materials, MULTIMET^® filler wire, HAYNES 556^® alloy (AWS A5.9 ER3556, AMS 5831), HASTELLOY S alloy (AMS 5838) or HASTELLOY W alloy (AMS 5786, 5787) welding products may all be considered, depending upon the particular case. Please click here or see the Haynes Welding SmartGuide for more information.

Preheating, Interpass Temperatures, and Postweld Heat Treatment

Preheat is not required. Preheat is generally specified as room temperature (typical shop conditions).   Interpass temperature should be maintained below 200°F (93°C). Auxiliary cooling methods may be used between weld passes, as needed, providing that such methods do not introduce contaminants.  Postweld heat treatment is not generally required for MULTIMET^® alloy.  For further information, please consult the click here.

Nominal Welding Parameters

Details for GTAW, GMAW and SMAW welding are given Nominal welding parameters are provided as a guide for performing typical operations and are based upon welding conditions used in our laboratories.

Welded Tensile Data

Heat Treatment and Fabrication

Ingots should be hot-forged, using an initial maximum of 2200°F. If the ingots are heated to higher temperatures, they will rupture at the surfaces and become badly oxidized. The minimum temperature at which MULTIMET^® alloy should be forged is 1700°F. Forging at a lower temperature might have an adverse effect on the high-temperature strength of the alloy, especially if it is to be used at temperatures of 1300°F and above. The ingots should be thoroughly soaked at about 2200°F, after which forging can be conducted at a relatively fast rate. MULTIMET^® alloy does not rupture easily and, in most cases, it is not necessary to use light hammer blows to break up the ingot structure. When reheating is necessary, the forging should be permitted to soak thoroughly to make sure that it reaches the proper temperature.

Forming

Cold-worked is the preferred method for such operation as spinning, drawing, and dishing. As the alloy work-hardens to a considerable extent, solution heat-treating between various stages of forming may be required to soften the material and restore the ductility lost in the cold-working operations.

Heat Treatment

Optimum properties can be developed in MULTIMET^® alloy sheet by a solution heat-treatment at 2150°F for a time depending on the section thickness. This is followed by either a rapid air-cool or a water-quench. Bar stock and plate (1/4 in. and heavier) are generally solution heat treated at 2150°F and then water-quenched. Most wrought products are shipped in the solution heat treated condition.

Stress-relieving the metal after hot-working is advisable to eliminate internal stress. Heavy or intricate forging may warp during machining unless stresses are remove. The recommended stress-relieving procedure is to heat the alloy two to four hours at temperatures corresponding to the maximum service temperature to be encountered. The heat-treatment brings about a mild precipitation hardening effect simultaneously with the removal stresses.

Bars and forgings that have been solution heat-treated may be aged at 1500°F for four hours followed by an air-cool. This increases the Brinell hardness to a range of 192 to 241. Since bar in the aged condition is difficult to straighten and form, it is recommended that the bar be purchased in the solution heat treated condition and then aged after final fabrication.

Specifications

Specifications

Disclaimer

Haynes International makes all reasonable efforts to ensure the accuracy and correctness of the data displayed on this site but makes no representations or warranties as to the data’s accuracy, correctness or reliability. All data are for general information only and not for providing design advice. Alloy properties disclosed here are based on work conducted principally by Haynes International, Inc. and occasionally supplemented by information from the open literature and, as such, are indicative only of the results of such tests and should not be considered guaranteed maximums or minimums.  It is the responsibility of the user to test specific alloys under actual service conditions to determine their suitability for a particular purpose.

For specific concentrations of elements present in a particular product and a discussion of the potential health affects thereof, refer to the Safety Data Sheets supplied by Haynes International, Inc.  All trademarks are owned by Haynes International, Inc., unless otherwise indicated.

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