Alloy N50 - UNS S20910

UNS S20910

Typical Inventory

Round Bar, Flat Bar, Hex Bar, LooseCoil, Wire Reel, Plate, Hot Band, Pipe, Fastener, Cut Disk, Forge, Slab, Billet, Ingot

Product Description

HPAlloys N50 (also called Nitronic 50) Stainless Steel provides a combination of corrosion resistance and strength not found in any other commercial material available in its price range. This austenitic stainless steel has corrosion resistance greater than that provided by Types 316, 316L 317 and 317L, plus approximately twice the yield strength at room temperature. In addition, N50 Stainless Steel has very good mechanical properties at both elevated and sub-zero temperatures. And, unlike many austenitic stainless steels, N50 does not become magnetic when cold worked or cooled to sub-zero temperatures. In addtion, High Strength (HS) N50 Stainless Steel has a yield strength about three times that of Type 316 stainless steel.

General Data

  • N50 has the best corrosion resistance of all stainless steels.
  • N50 has exceptionally low magnetic permeability.
  • N50 has a strength that is almost double Type 316.

Applications

  • Seawater pump shafts.
  • Heat exchangers.
  • Pressure vessels.
  • Marine hardware.

Common Specifications

The typical properties listed on page one can be provided in rounds, sheet, strip & plate. We have the equipment to produce small quantities in special sizes to meet our customers’ specific needs.

AMS 5764, ASTM A 193, ASTM A 262, ASTM A 276, ASTM A 276 Condition A, ASTM A 276 Condition S, ASTM A 479, ISO 15156-3, NACE MR0175, UNS S20910

Chemistry

C Mn P S Si Cr Ni Mo Cu N Ti Al B Nb Ta Sn V W
Max % 0.050 5.50 0.040 0.015 0.60 22.00 13.00 2.50 0.75 0.30 0.020 0.020 0.0025 0.20 0.10 0.030 0.30 0.15
Min % 0.030 4.00 0.20 20.50 11.75 2.00 0.24 0.0008 0.12 0.10

Annealing Temperature

HPAlloys N50 Stainless Steel can be supplied annealed at 1950 F to 2050 F (1066 C to 1121 C). For most applications, the 1950 F (1066 C) condition should be selected, as it provides a higher level of mechanical properties along with excellent corrosion resistance. When as-welded material is to be used in strongly corrosive media, the 2050 F (1121 C) condition should be specified in order to minimize the possibility of intergranular attack.

Mechanical Properties

Minimum Properties Acceptable for Material Specification Annealed Bars
Condition Ultimate Tensile ksi (MPa) Yield Strength ksi (MPa) Elong. % in 2 in.
Annealed 1950F (1066C) to 2050F (1121 C) and water quenched (up to 144 in' [9290cm2]) 100.000 (690) 55.000 (379) 35 55
Over 144 in2 (9290 cm2) to 324 in' (2091 cm2) 95.000 (655) 50.000 (345} 30 45

Shear Strength

The shear strength of N50 Stainless Steel in double shear has been determined following Boeing Aircraft Go. 02-2860, Procedures for Mechanical Testing of Aircraft Structural Fasteners.

Galling and Wear Resistance

The galling resistance of HPAloys N50 Stainless Steel is similar to Type 316 or just slightly better. Metal-to-metal wear tests demonstrate the superiority of NITRONIC 50 over alloy K-500 despite the higher hardness of the latter. Comparative wear data are shown. For applications requiring superior galling, wear and cavitation resistance coupled with good corrosion resistance, HPAloys N60 Stainless Steel should be considered.

Physical Properties

Density at 75 F (24 C) 7.88 gm/cm3 .285 Ibs/in3
Electrical Resistivity at 70 F (21 C) 80 microhm-cm

Magnetic Permeability

N50 Stainless Steel exhibits good corrosion resistance to a variety of media. Pitting resistance, as measured by tests in 10% FeCl3 solution, is better than Type 304. In sulfuric acid and hydrochloric acid, N50 is much better than Types 409 and 410 and approaches Type 304 in more dilute solutions. Typical laboratory test data obtained on these alloys are shown in Table 10. Atmospheric corrosion resistance is shown in Figure 5.

The magnetic permeability of HPAlloys N50 Stainless Steel remains very low at cryogenic temperatures, but not as low as HPAlloys N30 and N40 Stainless Steels. The magnetic susceptibility data in Table 25 were obtained on mill-annealed sheet samples using the Curie Force Method.

Note that the magnetic susceptibility of HPAHoys NITRONIC 50 Stainless Steel exhibits a cusp at approximately -400 F ( -240 C). This phenomenon, which also occurs with HPAlIoys N3o and N40 Stainless Steels, is dependent on temperature but not on field strength. Unlike the AISI 300 series stainless steels, most HPAlIoys NITRONIC Alloys show no supermagnetism.

Corrosion Resistance

HPAlloys N50 Stainless Steel provides outstanding corrosion resistance -superior to Types 316, 316L, 317 and 317L in many media. For many applications the 1950 F ( 1066 C) annealed condition provides adequate corrosion resistance and a higher strength level. In very corrosive media or where material is to be used in the as-welded condition, the 2050 F (1121 C) annealed condition should be specified. High-Strength (HS) N50 bars are useful for applications such as shafting and bolting, but do not quite exhibit the corrosion resistance of the annealed conditions in all environments.

Typical corrosion rates obtained from laboratory tests on N50 Stainless Steel in its several conditions are shown in Table 29 along with comparable data for Types 316, 316L, 317 and 317L stainless steels.

Seawater Resistance

Here is how N50 High-Strength (HS) shafting and Alloy 400 (Ni-Cu) looked after 18 months exposure in quiet seawater off the coast of North Carolina. The test was conducted without zinc anodes to establish the relative corrosion resistance of N50 High-Strength (HS) shafting. Had zinc anodes been used or a bronze propeller fitted to these bars, no crevice corrosion should have occurred. The photograph was taken after barnacles and other forms of marine life were cleared from the test bars.

Before exposure, all specimens were polished tc 120 grit finish, degreased and passivated. They were then clamped into pepper wood racks and exposed fully immersed in seawater. N50 high-strength (HS) shafting showed no crevice attack under the wooden blocks after the 18 months. One bar of N50 high-strength (HS) shafting remained perfect, while the other showed a few areas of very light crevice attack, < .001 " (0.025 mm) deep under marine attachments. Both samples of Alloy 400 suffered shallow crevice attack .001 "-.003" (0.025-0.076 mm) deep under the area in contact with the wooden rack, and also under numerous attached barnacles.

Type 316 stainless steel tested similarily for nine months suffered random pitting and crevice corrosion under the area in contact with the wooden rack and also under marine attachments, while N50 again remained in perfect condition. These specimens are shown in the photograph.

N50 seawater resistance vs alloy 400 and vs Type 316
N50 seawater resistance vs alloy 400

These two bars are immersed in quiet seawater for nine months. Bright shiny bar at right is HPAlloys N50 stainless steel, and at left is Type 316 stainless steel showing considerable pitting and crevice corrosion.

Weldability

In addition to the improved mechanical properties and corrosion resistance, HPAlloys N50 Stainless Steel can be welded successfully by using any of the conventional welding processes that are normally employed with the austenitic stainless steels.

HPAlloys N50 Stainless is readily arc welded in all forms. As with most austenitic stainless steels, good weld joint properties can be obtained without the necessity of preheat or post-weld annealing. Good shielding of the molten weld puddle is important to prevent any absorption of nitrogen from the atmosphere that could result in porosity.

Autogenous, high-power density joining processes such as electron beam (EB) and laser welding should be used with caution due to the low FN potential of the base metal (FN approximately 2). Field reports also indicate the possibility of severe outgassing during EB welding in a vacuum atmosphere. Under vacuum conditions, this outgassing is to be expected for liquid weld metal containing a high nitrogen level.

Filler Metals

Filler metal, when added to the joint, should be HPAlloys N50W (AWS E/EA 209), a matching filler metal composition that provides comparable strength and corrosion resistance to the base metal. However, sound weld joints may also be obtained using the conventional austenitic stainless steel fillers such as Types 308L and 309. When using these more common filler metal compositions, allowances should be made for the strength and corrosion differences.

Nominal compositions and representative mechanical properties are shown for the more common electrode filler rods in Table 36. The weld metal alloys are listed generally in the order of (a) increasing alloy content, (b) increasing strength level, (c) increasing corrosion resistance and (d) increasing cost.

These data show that the highest strength levels with good tensile ductility and alloy elements that impart good corrosion resistance are provided by the HPAlloys N50W Electrode. In some specific applications where the high strength levels or superior corrosion resistance in the weld deposits are not required, other filler metals can be used to advantage because of reduced costs and/or ready availability.

The matching weld filler (N50W, AWS E/EA 209) for HPAloys N50 Stainless Steel is similar to many of the regular austenitic stainless steel filler metals in that a small percentage of the magnetic ferrite phase has been introduced to assure sound weld deposits. The small quantity of the second phase usually produces a magnetic permeability value of approximately 1.2 in shielded metal-arc weld deposits. This corresponds to a ferrite number (FN) of approximately 6.

Highly overalloyed Ni base fillers are suggested for applications requiring high resistance to pitting media or very low as-deposited magnetic permeability.

GTA Weld Joints

Gas tungsten arc weld joints have been fused successfully in several flat-rolled thicknesses of HPAlloys N50 Stainless Steel. Mechanical property values similar to those of the base metal have been obtained in the as welded condition.

The corrosion resistance of GTA welded joints has been evaluated using the standard Huey test (ASTM A 262, Practice C) for detecting intergranular attack in stainless steels. Laboratory test experience shows that welds made using the N50W Stainless Steel filler metal exhibit the same resistance to intergranular attack as the base metal.

Heavy Section Weld Joint Properties

The mechanical properties of welds in 1-1/4" (32.1 mm) thick plate have been determined using two weld processes that are normally employed in heavy section welding, namely, (a) shielded metal arc (SMA) or stick electrode welding and (b) gas metal arc (GMA) or MIG welding wit!l the spray mode. Typical test values that can be expected from tensile samples cut transverse to the weld centerline are shown in Table 37.

Heat input is important in obtaining the most satisfactory weld joint. Narrow stringer beads rather that a wide "weave" technique should be used for highest weld ductility. Good shielding of the molten puddle is important to eliminate additional nitrogen from the atmosphere that could cause porosity. Both stringer beads and adequate shielding are normal factors in good stainless steel welding practice.

Resistance Welding

Although no direct resistance welding experience has been obtained with HPAlloys N50 Stainless Steel, the similarity of the alloy to HPAlloys N40 Stainless Steel suggests a good response to resistance spot welding and cross-wire welding techniques. The welding schedules outlined in the fabricating bulletin, "Welding HPAlloys Stainless Steels", can be used as a guide to produce sound, high-strength joints in both annealed and cold-reduced sheet. Average shear strength data for spot welded joints in HPAlloys N40 Stainless Steel appear in the Product Data Bulletin, "HPAlloys N40 Stainless Steel Sheet and Strip". HPAloys N50 Stainless Steel is expected to perform in a similar manner.

Machinability

HPAlloys N50 Stainless Steel has machining Characteristics similar to other austenitic stainless steels. It is suggested that coated carbides be considered when machining all NITRONIC alloys, since higher cutting rates may be realized. NITRONIC 50 Stainless Steel is more susceptible to cold work hardening than types 304 and 316 stainless steels. Also, the alloy has higher strength. Machining tests show the alloy to machine at approximately 21% of the cutting rate for B1112. This means N50 Stainless Steel can be machined at approximately 1/2 the cutting rate (SFM) used for Type 304 or 316 stainless steels, based on using high-speed tool steels. For that reason, as stated above, coated carbides are recommended for best results. Because of the high strength of N50 Stainless Steel, more rigid tool and work holders than used for Types 304 and 316 stainless steels should be used. Care should be taken not to allow tools to slide over the alloy. Positive cutting action should be initiated as soon as possible. The alloy provides a good surface finish.

Data Sheet

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