Nitronic 50® UNS S20910 (XM-19)Stainless Steel 1.3964

What is Nitronic 50® UNS S20910 (XM-19)1.3964?

XM-19 is a highly alloyed austenitic stainless steel as listed in ASTM A276/A479 as UNS S20190. It is also commonly referred to as Nitronic 50 and Fermonic 50, which are trademarks of AK Steel Inc and Langley Alloys respectively.

Through the combination of chromium content (20.50-23.50%), increased molybdenum content (1.5 – 3.0%) and raised levels of nitrogen (0.20 – 0.40%) its pitting resistance equivalent number (PREN) exceeds 34. This is comparable with that of a duplex stainless steel such as Sanmac 2205 (1.4462). Therefore, it provides good levels of corrosion resistance, way beyond standard 3xx grades where the PREN = 25.

Applications include Oil & Gas industry downhole equipment, marine pumps, valves, masts, tie downs, fixtures and fittings, food processing equipment and pulp and paper Industry valves and fittings. Of all these applications, valve stems are perhaps the most common end use for this application. As an austenitic stainless steel, it has better impact strength across a wider range of temperatures than alternative grades. This is relevant as the stems can be subjected to more of a shock loading when actuating a large valve. The next most common application would be fixtures and fittings for marine applications, due to the relative ease of fabrication without compromising the good corrosion resistance.

XM-19 can be a confusing alloy to work with, as there are three different types of conditions used for numerous applications. The three conditions are annealed, as-rolled and high strength. As-rolled is a term used by the mill to state the fact that it is a “rolled” material. All conditions of XM-19 are first rolled. Both the annealed condition and the as-rolled condition are rolled at the same temperature. To acquire XM-19 annealed, the material would first be rolled, followed by either a mill or local annealing process which lowers the tensile and yield properties resulting in a more workable material. On the other hand, transforming XM-19 into the high strength condition can only be done at the mill after the original rolling process, which is done at a lower temperature than annealed and as-rolled material to further help increase the properties. Then high strength material is rolled a second time and later cold worked, which again increases the physical properties of the material even more

NITRONIC® 50Product Forms

Sheet, Strip, Foil,Round Bar, Flat, Square Bar, wire, plate, forgings.

Applications for NITRONIC® 50 stainless steel

NITRONIC® 50 (XM-19) is widely used in the following sectors:

• Textile
• Marine
• Nuclear
• Medical
• Fertilizer
• Chemical
• Petroleum
• Petrochemical
• Food processing
• Pulp and Paper

Equivalents of gradeNITRONIC® 50

STANDARD	EN	UNS	DIN
Nitronic Alloy 50 / XM-19	1.3964	S20910	X2CrNiMnMoNNb21-16-5-3

Composition ranges for NITRONIC® 50grade of stainless steel

	Carbon (C)	Manganese (Mn)	Phosphorus (P)	Sulpher (S)	Silicon (Si)	Chrome (Cr)	Nickel (Ni)	Nitrogen (N)	Molybdenum (Mo)	Other Elements
Min						20.5	11.5	0.20	1.50	Cb 0.10-0.30, V 0.10-0.30
Max	0.06	4.0-6.0	0.045	0.030	1.00	23.5	13.5	0.40	3.00	Cb 0.10-0.30, V 0.10-0.30

Stainless steel Mechanical Properties

Properties	Metric	Imperial
Tensile strength	690 MPa	100 ksi
Yield strength	380 MPa	55 ksi
Elongation	35%	35%
Hardness	293	293

Stainless steel Physical Properties

Properties	Metric	Imperial
Density	7.89 g/cm3	0.285 lb/in3

NITRONIC® 50 Thermal Properties

Properties	Metric	Imperial
Thermal expansion co-efficient (@25.6-93.3°C/78-200°F)	16.2 µm/m°C	9 µin/in°F

Forging

The alloy is normally forged at 2100/2200ºF (1150/1205ºC) and forgings may be safely rapidly cooled. For optimum corrosion resistance, parts should be annealed after forging.

Corrosion Resistance

UNS S20910/XM-19 stainless steel provides outstanding resistance to general corrosion and is superior in this respect to Types 316/316L and 317/317L in many media. The 1950°F (1066°C) annealed condition provides adequate corrosion resistance for many applications combined with a high strength level. Where the material is to be employed in the as-welded condition or in very corrosive media, the 2050°F (1121°C) annealed condition should be chosen. Material in the high strength cold-worked condition is often specified for bolting and shafting, but there is some small compromise in terms of corrosion resistance in some environments when compared with the annealed condition. The resistance to selective attack such as crevice corrosion for UNS S20910/XM-19 stainless steel (annealed) is superior to that of Type 316/316L. In common with most austenitic stainless steels for example Types 304 and 316, XM-19 steel may suffer stress corrosion cracking in hot chloride ion containing environments.

Heat Treatment

Nitronic 50 stainless steel can be annealed by heating the material to temperatures between 1950-2050°F (1066-1121°C) and cooling/quenching rapidly. If used as in a highly corrosive environment, annealing should be performed at maximum temperature (2050°F) to minimize the risk of intergranular attack.

Cold Working

Due to the high strain hardening, higher forming forces are required. Note the slight increase in permeability!

Machinability

Stainless steel grade Nitronic® 50 has machinability characteristics that are similar to other austenitic stainless steels; however it requires slower speeds, more power, and higher rigidity due to its high work hardening rate. It is recommended that coated carbide tooling be used.

Welding

1.3964 steel is weldable by commonly used methods, recommended filler metals 1.3954 and 1.3984. The max. interpass temperature should remain below 200°C and downstream heat treatment (PWHT) depends on the geometries.