Grades
17-4 PH
UNS S1740017-4 PH is a martensitic precipitation-hardening stainless steel offering high strength with corrosion resistance similar to 304.
Alloy 316L
UNS S31603Alloy 316L is a low-carbon austenitic stainless steel with molybdenum for improved chloride pitting resistance and easy welding.
Fermonic® 50
UNS S20910Fermonic® 50 is a nitrogen-strengthened austenitic stainless steel with about twice the yield strength of 316.
Fermonic® 60
UNS S21800Fermonic® 60 is a nitrogen-strengthened austenitic stainless steel with outstanding galling and wear resistance.
How the grades compare
At a glance: UNS number, defining property, typical applications and the forms we stock for each stainless steel grade.
| Grade | UNS | Key property | Typical applications | Forms stocked |
|---|---|---|---|---|
| Alloy 316L | S31603 | Molybdenum-bearing austenitic; PREN 25, far better chloride resistance than 304 | Chemical process, marine, oil & gas, heat exchangers | Bar |
| Fermonic® 50 | S20910 (XM-19) | Nitrogen-strengthened austenitic; ~2x the yield strength of 316L, non-magnetic | Downhole, marine, pump/valve, fasteners | Bar |
| Fermonic® 60 | S21800 | Galling- and wear-resistant austenitic; properties retained to 1200°C | Fasteners, pins, bushings, valve trim, wear rings | Bar |
| 17-4 PH | S17400 | Martensitic precipitation-hardening; high strength, moderate corrosion resistance | Shafts, valves, fasteners, pump and aerospace components | Bar |
Why specify austenitic stainless steel?
Our stainless range covers the workhorse austenitic grade plus higher-performance nitrogen-strengthened, wear-resistant and precipitation-hardening options:
- Alloy 316L adds molybdenum for far better pitting and crevice corrosion resistance than 304 (PREN 25 vs 19)
- Fermonic® 50 (Nitronic® 50 / XM-19) gives almost double the yield strength of 304 and 316L while staying non-magnetic
- Fermonic® 60 (Nitronic 60) resists galling and wear, retaining properties to 1200°C
- 17-4 PH is precipitation-hardened for high strength with moderate corrosion resistance
- Excellent ductility and toughness from cryogenic to elevated temperatures
- Grades for chloride, acid, marine and wear-critical service
Material tools
PREN calculator
PREN = %Cr + 3.3 × (%Mo + 0.5 × %W) + 16 × %N. Guidance only; always confirm against the grade's datasheet before specifying.
Pitting & crevice resistance
Pitting & Crevice Resistance
Rank alloys by PREN and get an indicative pitting temperature for a chloride service. Pick a grade and a service temperature to see whether it has margin against pitting, or compare the range in the table below. A first-pass screen for chloride and seawater service.
| Grade | UNS | PREN | Indicative CPT | Relative pitting resistance |
|---|
Indicative screen, not a certified result. PREN ranks pitting resistance; the pitting temperature here is estimated from PREN (CPT ≈ 2.5 × PREN - 50), consistent with Langley's "PREN >40, CPT exceeding 50°C" for super duplex. Real critical pitting/crevice temperature depends on test method, product form, surface finish and service chemistry. Crevice corrosion starts well below the pitting temperature - allow a margin at gaskets, deposits and flange faces. Use certified data for design.
Hardness converter
Hardness Converter
Convert between Brinell, Vickers, Rockwell C and Rockwell B, with the approximate tensile strength. Values follow the ASTM A370 conversion tables for non-austenitic steels; nothing is extrapolated beyond the tabulated range.
Conversions are approximate and material-dependent. Based on ASTM A370 hardness conversion tables for non-austenitic steels (equivalent to ASTM E140). Brinell is not reported above about HRC 65, and each Rockwell scale is only valid over its own range - values outside it show as out of range, never extrapolated. Use as a guide, not a substitute for direct measurement on the actual material.
Applications
How do you machine austenitic stainless steel?
Austenitic grades like 316L and the nitrogen-strengthened Fermonic® alloys are tough and work-hardening, so keep tooling sharp, cuts positive and continuous, speeds moderate and feeds firm, with plenty of coolant. Fermonic® 50 is stronger and rewards rigid set-ups, while Fermonic® 60's galling resistance also helps tool life.
17-4 PH machines best in the solution-annealed (Condition A) state, with final finishing after age-hardening where tolerances are tight. Machinability-enhanced (Sanmac®) 316L is available for higher throughput.
Technical resources
Common questions
What is the difference between 304 and 316?
Alloy 304 is the most widely used austenitic stainless (18% chromium, 8% nickel). Alloy 316 and 316L add molybdenum, which markedly improves resistance to pitting and crevice corrosion, especially in chlorides, so 316L is preferred for marine and more aggressive service.
What is austenitic stainless steel?
Austenitic stainless steels have a face-centred-cubic crystal structure, giving good toughness, corrosion resistance, consistent properties across a wide temperature range, and non-magnetic behaviour. 304 and 316 are the best-known grades.
What is Fermonic® (Nitronic / XM-19)?
Fermonic® is Langley's trademark for nitrogen-strengthened austenitic stainless steels, also known as Nitronic. Fermonic® 50 is XM-19 / UNS S20910; Fermonic® 60 is UNS S21800. Both offer much higher strength than standard austenitic grades while staying non-magnetic.
What is galling, and how does Fermonic® 60 help?
Galling is adhesive wear where two loaded metal surfaces seize. Fermonic® 60 (Nitronic 60) is alloyed with silicon and manganese to resist galling and wear, a cost-effective alternative to cobalt or nickel alloys in wear-critical parts.
What is precipitation hardening (17-4 PH)?
Precipitation hardening (ageing) is a heat treatment that greatly increases strength. 17-4 PH is a martensitic PH stainless that reaches high strength through a low-temperature ageing step, with conditions from H900 to H1150 trading strength against toughness.
What is the difference between austenitic and martensitic stainless steel?
Austenitic grades (304, 316, Fermonic®) are non-magnetic, tough and not hardenable by heat treatment. Martensitic and precipitation-hardening grades such as 17-4 PH can be heat-treated to much higher strength, at some cost to corrosion resistance.
History of austenitic stainless steel
The modern 18/8 stainless steel begins not in Sheffield but in Essen. In 1912, Benno Strauss and Eduard Maurer of Friedrich Krupp in Germany patented a chromium-nickel steel of roughly 18% chromium and 8% nickel. This austenitic alloy, later sold as Nirosta, offered outstanding resistance to acids and corrosion. It is distinct from the hardenable, martensitic cutlery steel that Harry Brearley developed in Sheffield around 1913. Both are milestones, but the austenitic family that dominates industry today traces to the Krupp work.
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Austenitic grades developed quickly. From the early 1930s, molybdenum was added to 18/8 to create the Type 316 family, sharply improving resistance to pitting and crevice corrosion in chloride environments such as seawater. After the war, the low-carbon variant 316L followed, reducing carbide precipitation so that welded fabrications kept their corrosion resistance.
A further leap came mid-century, when Armco developed the nitrogen-strengthened Nitronic alloys. Using nitrogen and manganese instead of extra nickel, these reach around twice the yield strength of standard 304 and 316, with excellent galling and wear resistance. Langley Alloys supplies this lineage today as Alloy 316L and the high-performance grades Fermonic® 50 and Fermonic® 60.
When 304 and 316 aren't enough - extra strength, wear resistance or precipitation hardening, from stock.
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