UNS S41500 Forgings ASTM A473 and ASME SA-473 / A182 F6NM / Type 415 / EN 1.4313 X3CrNiMo13-4

ASTM A473 is the forging specification that covers austenitic, austenitic-ferritic, ferritic and martensitic stainless steel forgings for general use and for low- or high-temperature service, which is why S41500 forgings are normally bought against A473 rather than a bar or plate standard. The grade sits in the family the oil and gas industry calls supermartensitic or soft martensitic. It replaced plain 12% Cr steels and CA15 castings in many duties because the low-carbon 13Cr-4Ni structure handles fluids containing CO2 and H2S better than its predecessors.

Because the same alloy is produced both cast and forged, the designation you order against matters. CA6NM is the casting, F6NM is the forging, and the hardness response is close enough that the two are usually discussed together in the literature on hydraulic turbine runners.

Limits for UNS S41500 and F6NM. Iron is the balance. Single values are maximum limits.

Source: Special Quality Alloys F6NM datasheet, cross-checked against the Virgamet 1.4313 comparison table.

Why carbon and nitrogen are worth specifying

On a NACE order, the exact carbon and nitrogen levels inside the allowed band change the result. A 2017 study of industrial 13Cr-4Ni-0.5Mo heats found that two casts of almost identical composition behaved differently under the same tempering cycles. The heat at 0.027% C and 180 ppm N could be brought close to 23 HRC. The heat at 0.030% C and 280 ppm N stayed near 300 HV even with the NACE double temper. A third heat at 0.018% C and 68 ppm N reached 21.4 HRC with 583 MPa yield and 751 MPa tensile. If your order is hardness-critical, state a carbon and nitrogen ceiling rather than relying on the grade limits alone. Melting on site is what lets us aim the heat at that target instead of accepting a purchased billet as delivered.

Two sets of figures are in common use. The ASTM route quotes minima for the hardened and double tempered condition. The European route quotes quenched and tempered strength classes.

Source: Special Quality Alloys F6NM datasheet.

Source: Virgamet 1.4313 / X3CrNiMo13-4 data sheet.

Source: Virgamet. Modulus of elasticity over the same range: 195 GPa at 100 °C, 185 GPa at 200 °C, 175 GPa at 300 °C, 170 GPa at 400 °C.

The spread between these two sets is the most common cause of confusion on enquiries for this grade. A part specified as F6NM to NACE and a part specified as 1.4313 +QT900 are the same alloy in very different conditions, and the second cannot meet 23 HRC. State the condition or the strength class on the order, not just the grade.

Sources: MakeItFrom AISI 415 (S41500) property data; expansion against temperature from Virgamet.

Service temperature is quoted differently by different sources, and the gap is wide enough to matter. MakeItFrom gives a maximum corrosion temperature of 390 degrees Celsius and a maximum mechanical temperature of 780 degrees Celsius. Virgamet describes 1.4313 components as operating up to about 300 degrees Celsius and tabulates proof stress only to 350 or 400 degrees Celsius depending on class. For pressure-retaining parts, use the allowable stresses in the governing design code rather than either figure. Corrosion resistance is described as medium in media with only a low chloride content, so this is not a grade to substitute for a duplex or 6Mo alloy in seawater.

Close equivalents, with the composition differences that affect acceptance.

Source: Virgamet 1.4313 equivalents table. Other designations listed for the same alloy include C39NiH, C39NiL, T 8MoNiCr125, 0Ch12N4ML and UNS S42400.

Note the nickel band. S41500 allows up to 5.5% Ni, EN 1.4313 stops at 4.5%, and EN additionally sets a nitrogen minimum of 0.02%. A heat that passes as S41500 will not automatically certify as 1.4313. If your drawing calls out both, say which one governs.

Source: Virgamet.

The 23 HRC requirement

NACE MR0175 limits 13Cr-4Ni alloys to 23 HRC maximum for sour service and calls for a double temper after quenching: first temper 650 to 690 degrees Celsius, second temper 595 to 620 degrees Celsius. The first cycle recovers the as-quenched martensite and forms reverted austenite. The second recovers any virgin martensite formed when that austenite destabilised on cooling.

Two practical points come out of the published work on this grade. First, the hardness conversion normally used does not apply here. The BS 860 and ASTM E140 tables put 23 HRC at about 253 HV, but researchers working on 13Cr-4Ni-(Mo) treat 23 HRC as roughly 275 HV, and a weld procedure qualification judged on the wrong conversion can fail a heat that is actually compliant. Second, an intermediate cool between the two tempers helps bring hardness down, while a sub-zero treatment at minus 30 degrees Celsius after tempering pushes hardness back up by destabilising retained austenite. That last point is worth remembering for parts that will see low service temperatures.

Welding

Sources disagree, and we would rather say so than pick the convenient one. A mill datasheet for F6NM describes the grade as having a high level of corrosion resistance and weldability. Virgamet states that 1.4313 is not suitable for welding. Both positions reflect the same reality: the alloy can be welded, but only under a qualified procedure with controlled preheat, matched consumables and post-weld heat treatment, and post-weld heat treatment on 13Cr-4Ni is known to be difficult to bring below 23 HRC in the heat affected zone. Tell us at enquiry stage if the forging will be welded, so the melt chemistry can be aimed accordingly.

All of it forged from steel melted on this site. No purchased billet of unknown origin, no castings, no welded fabrications. Single pieces run to 30 tonnes on a 6,300 t press, and rings to 6,000 mm outside diameter on a 6 m radial-axial mill.

Applications

The grade is used for valves and actuators and for subsea and downhole tooling in oil and gas, and for turbine, pump and compressor components in the oil, chemical, metallurgical and power industries, including parts exposed to both high and low temperatures. S41500 and CA6NM are both widely used for the manufacture and repair of hydraulic turbine runners.

Other martensitic and duplex grades we forge, for comparison.

• AISI 431 and 1.4057Higher-carbon martensitic, used where 23 HRC is not a constraint
• UNS S43100The UNS designation for the same 431 family
• AISI 422 and UNS S42200 / SAE 5142212% Cr for elevated-temperature turbine duty
• AISI 440AHardenable martensitic for wear surfaces
• AISI 329, UNS S32900 and 1.4460Duplex, where chloride resistance rules out 13Cr-4Ni
• All stainless and duplex gradesFull grade index

• ASTM A473, Standard Specification for Stainless Steel ForgingsScope: austenitic, austenitic-ferritic, ferritic and martensitic stainless steel forgings
• Special Quality Alloys, F6NM datasheetChemical range, minimum mechanicals, 23 HRC, Charpy 42/34 J at −60 °C
• Virgamet, 1.4313 X3CrNiMo13-4 / F6NM / UNS S41500Equivalents, QT classes, elevated-temperature proof stress, heat treatment temperatures
• MakeItFrom, AISI 415 (S41500) stainless steelPhysical and typical mechanical property data
• De Sanctis M., Lovicu G., Varone A., Richetta M., Buccioni M., Donato A., Metals 7(9):351, 2017Study of 13Cr-4Ni-(Mo) (F6NM) steel grade heat treatment for maximum hardness control in industrial heats. NACE double-temper ranges, 275 HV equivalence, carbon and nitrogen effects
• voestalpine Specialty Metals, F6NMSoft martensitic 4% Ni grade, medium corrosion resistance in low-chloride media

Data on this page is compiled for engineering reference. Material is supplied against the purchase order specification and the EN 10204 3.1 certificate issued for the actual heat. Confirm requirements in writing before ordering.