50Cr-50Ni-Nb castings: composition, properties and uses

50Cr-50Ni-Nb is a cast nickel-chromium alloy of roughly equal parts chromium and nickel with a small niobium addition, specified in ASTM A560 and widely known by the licensed name IN657. It was developed to resist fuel-ash corrosion, and it is used for tube supports, hangers and tube sheets in fired heaters that burn residual or low-grade fuel oil.

Published 17 Oct 2026 · Updated 17 Oct 2026 · Ni-Chrome Alloy Castings

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What is the composition of 50Cr-50Ni-Nb?

It is a nickel-base alloy, not an iron-base stainless. The main limits for grade 50Cr-50Ni-Cb in ASTM A560 are below, in weight percent. "Cb", columbium, is the older American name for niobium.

Element	ASTM A560 50Cr-50Ni-Cb, wt %
Chromium	47 to 52
Niobium (columbium)	1.4 to 1.7
Carbon	0.10 max
Manganese	0.30 max
Silicon	0.50 max
Nickel	Balance

Source: ASTM A560, grade 50Cr-50Ni-Cb, as listed by MetalTek and Total Materia. The edition on your purchase order governs.

The chemistry is the opposite of the H-series grades. Carbon is kept very low instead of high, and chromium is about double. The alloy relies on chromium for its resistance to ash attack.

What are the equivalents of 50Cr-50Ni-Nb?

UNS: R20501.
ASTM: A560, grade 50Cr-50Ni-Cb. The same standard also lists 50Cr-50Ni and 60Cr-40Ni without niobium.
Trade name: IN657 (also written IN-657), originally an Inco alloy and cast by several foundries under licence or to the same chemistry.
Shop names: 50/50 Nb, 50Ni-50Cr-Nb.

There is no common EN number for this grade. Specify it by ASTM A560 grade or by full chemistry.

Where is 50Cr-50Ni-Nb used?

It is used for static castings in the flue gas path of fired heaters and furnaces burning fuels high in vanadium, sodium and sulphur:

tube supports and tube sheets in the convection section;
tube hangers in the radiant section;
support beams and other furnace internals exposed to ash deposits.

Schmidt + Clemens describe it as created for increased resistance to fuel-ash corrosion and used in static castings such as convection-section tube support plates and radiant-section tube hangers. The reformer furnace castings guide shows where supports and hangers sit in a furnace, and the castings page covers the shapes we pour. Ni-Chrome casts furnace internals, supports and fittings in this grade.

How does 50Cr-50Ni-Nb fail in service?

Burning residual fuel oil leaves ash rich in vanadium pentoxide and sodium sulphate. Those compounds melt at furnace temperatures and dissolve the protective oxide on ordinary heat-resistant alloys. High chromium is the defence, and it is why this grade exists. The published work shows where that defence holds and where it stops.

Temperature limit on ash resistance. A 2015 study in Corrosion Engineering (Japan) exposed six heat-resistant cast alloys to actual boiler ash. At 850 °C corrosion was not severe, and 50Cr-50Ni was among the best performers. At 1,050 °C its corrosion weight loss rose sharply. Ash resistance does not extend to the top of the H-series temperature range.
Long-term aging. As with other high-chromium, high-nickel castings, long exposure changes the microstructure. Cracking of a high chromium-nickel cast tube sheet after about three years in a refinery heater has been reported (Mechanika, 2013), though that paper did not establish a single cause.

Practical service limits quoted by producers sit below the A560 scope temperature. MetalTek, for example, gives 950 °C for its version of the grade, while the A560 scope refers to service up to about 1,090 °C. Design to the lower figure where ash is present.

When should you choose 50Cr-50Ni-Nb over HK40 or HP grades?

Choose it when fuel-ash corrosion, not creep, is what limits the life of the part. That usually means:

the heater fires residual oil or other fuel with high vanadium, sodium or sulphur;
existing HK40 or HH supports show wastage, scaling or thinning from ash attack;
the part is a static support, hanger or tube sheet rather than a pressure tube.

Stay with HK40 or HP-Nb where the fuel is clean gas, where the main load is creep at high temperature, or where toughness matters more than corrosion resistance. The 50/50 grade costs more because of its nickel and chromium content, so it pays only where ash attack is the real problem.

Which casting route suits 50Cr-50Ni-Nb?

In general practice this grade is used for static castings, so parts are made in sand moulds to the drawing. Supports and hangers are usually designed as castings from the start, so the shape can follow the load path without welded joints. Machining and welding of high-chromium nickel alloys call for procedures qualified for the grade.

What should an RFQ for 50Cr-50Ni-Nb castings include?

The standard and grade: ASTM A560 50Cr-50Ni-Cb (UNS R20501), or the full IN657-type chemistry you require.
The drawing with tolerances, machining and finished weight if known.
The fuel being burned and, if available, its vanadium, sodium and sulphur content.
Operating temperature of the part and whether it sees thermal cycling or shutdowns.
Testing: chemistry and tensile certificates, radiography or dye penetrant, and any third-party inspection.
Quantity, and any EIL, licensor or end-user approval required.

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50Cr-50Ni-Nb questions

Is 50Cr-50Ni-Nb the same as IN657?

IN657 is the trade name for the same nominal chemistry. ASTM A560 grade 50Cr-50Ni-Cb is the open standard that describes it.

Which other grades does ASTM A560 cover?

Two niobium-free grades: 50Cr-50Ni (UNS R20500) and 60Cr-40Ni (UNS R20600). The niobium-bearing grade is R20501.

Is it suitable above 1,000 °C?

Not where fuel ash is present. Published tests show ash corrosion rising sharply at 1,050 °C, and producers quote service limits near 950 °C.