HAYNES® 556® alloy for Molten Salt Bath Heat Treat Baskets Tech Brief


Salt & Gantry Furnace Heat Treat Baskets End User:
The Boeing Company - Portland, OR Fabricator: Marks Brothers, Inc - Portland, OR

Boeing Aircraft experienced excessive cracking and weld repair maintenance in very short periods of time with their 316 stainless steel salt pot heat treat baskets. The baskets are used to hold a variety of components including critical machined landing gear segments during hardening and tempering cycles. The cracking was believed to be caused by a combination of constant thermal cycling of the heavily welded baskets from 1800°F to 600°F and corrosion from the molten salt.

In their search for an improved material of construction, Boeing was looking for an alloy which would avoid catastrophic basket failure and subsequent loss of expensive machined components, reduce life-cycle cost by reducing extensive weld repair, and increase up-time and resultant capacity through the heat treat operation

Boeing selected HAYNES® 556® alloy and was pleased to note its availability from Haynes’ Service Center Stock.

HAYNES® 556® alloy has nearly twice the strength of 316 alloy at 1600°F. Combined with its excellent ductility, thermal fatigue resistance is improved. Laboratory tests and field experience show 556® alloy to be equal to, or better than, nickel-base HASTELLOY® X alloy regarding resistance to molten chloride salts. In addition, as-welded ductility of 556® alloy is excellent.

Thus far, at comparable operating times, 556® alloy baskets have far outperformed 316 alloy baskets. Maintenance costs are down and reliability is increased. Can you afford not to consider HAYNES 556 alloy?

Nominal Composition

Iron: Balance
Nickel: 20
Cobalt: 18
Chromium: 22
Molybdenum: 3
Tungsten: 2.5
Tantalum: 0.6
Nitrogen: 0.2
Silicon: 0.4
Manganese: 1
Aluminum: 0.2
Carbon: 0.1
Lanthanum: 0.02
Zirconium: 0.02
Resistance to Corrosion in Molten 100%
NaCl for 100 Hours at 1500°F
Alloy Average Metal Affected
556® 2.6
X 3.8
310 4.2
800H 4.3
625 4.4
RA330® 4.6
RA333® 7.5
600 7.7

Typical All-Weld-Metal Tensile Properties*

Typical All-Weld-Metal Tensile Properties* (0.25-inch diameter speciments machined from cruciform weldment)
Test Temperature GTAW Weldments GMAW Weldments
0.2% Yield Strength Ultimate Tensile Strength Elongation 1.25 in. 0.2% Yield Strength Ultimate Tensile Strength Elongation 1.25 in.
°F °C ksi ksi % ksi ksi %
RT RT 67 107 40 77 115 38
1200 650 45 71 39 53 81 39
1400 760 42 55 39 50 66 26
1600 870 29 32 52 37 40 34
1800 980 21 29 126 24 24 30

*Average of two tests for each condition