Stainless Steel S21640
UNS S21640
S21640 is a nitrogen-strengthened Cr-Mn-Ni austenitic stainless related to the XM-17/XM-18 (S21600/S21603) family, supplied for high-strength non-magnetic fastener and structural use.
Reference datasheet — S21640 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the ANN condition
S21640 tempers and conditions
S21640 is supplied in 7 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hot Finished and Annealed bar | Large-diameter hot-rolled/forged bar, annealed and descaled — pick for big machined parts and forgings. | 440 | 710 | 45 | 195 HB | 2 % IACS |
ANNDefault Annealed | Standard stocked condition — maximum corrosion resistance and ductility, yield already ~2× that of 304. | 450 | 725 | 45 | 200 HB | — |
Cold drawn | Light strain-hardening for straightness, close tolerance and better chip control on screw-machine parts. | 620 | 860 | 25 | 24 HRC | — |
Cold Worked, 1/4 Hard | Entry-level high-strength fastener/shaft condition with useful residual ductility. | 690 | 900 | 20 | 26 HRC | 2 % IACS |
Cold Worked, 1/2 Hard | High-strength bolting and pump shafting where ~830 MPa yield is required. | 830 | 1,035 | 15 | 31 HRC | 2 % IACS |
Cold Worked, 3/4 Hard | Near-maximum strength bar/wire for highly loaded fasteners and springs; limited ductility. | 965 | 1,170 | 12 | 35 HRC | 2 % IACS |
Cold Worked, Full Hard | Maximum strength wire/small bar for springs and studs where forming is finished. | 1,100 | 1,275 | 8 | 38 HRC | 2 % IACS |
What is S21640?
S21640 is a nitrogen-strengthened Cr-Mn-Ni austenitic stainless related to the XM-17/XM-18 (S21600/S21603) family, supplied for high-strength non-magnetic fastener and structural use. Annealed values are about 450 MPa yield, 725 MPa tensile, 45% elongation and 200 HB (95 HRB), with cold-worked tempers from 1/4 hard to full hard available in bar and wire. Corrosion resistance rates 72, above the plain 200-series, and service reaches about 815 °C, but the alloy work-hardens rapidly, machines slowly and is a specialty item; S21600 or S21900 are the usual substitutes when stock is unavailable. S21640 has a density of 7.86 g/cm³ (0.284 lb/in³), heavier than 59% of stainless steel grades. It melts at 1,370°C (2,498 °F). S21640 has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 200 GPa (29 Msi).
What is S21640 used for?
- fasteners
- structural hardware
- non-magnetic parts
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- High service temperature — 815°C (1,499 °F), better than 77% of stainless steel grades
- Ductile — tolerates forming and impact — 45%, better than 76% of stainless steel grades
Limitations
- Difficult to machine — 25/100, worse than 88% of stainless steel grades
- High embodied carbon — 5.8 kg CO₂/kg, worse than 86% of stainless steel grades
- Low electrical conductivity — 2 % IACS, worse than 77% of stainless steel grades
S21640 properties
Typical room-temperature values for S21640-ANN; bars are the position among stainless steel grades.
Physical3
S21640 has a density of 7.86 g/cm³ (0.284 lb/in³), heavier than 59% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical15
S21640 has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
S21640 is rated for continuous service to 815°C (1,499 °F). It conducts heat at 15 W/m·K (8.67 BTU/hr·ft·°F), worse than 59% of stainless steel grades. Thermal expansion is 16.2 µm/m·K (9 µin/in·°F).
Electrical3
S21640 conducts electricity at 2 % IACS, worse than 77% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is very good (72/100), better than 73% of stainless steel grades.
Sustainability4
Producing a kilogram of S21640 takes about 56 MJ of energy and emits 5.8 kg of CO₂ — more than 59% of stainless steel grades. Typical recycled content is 60%.
Manufacturability8
S21640's machinability is poor (25/100, worse than 88% of stainless steel grades); weldability very good (70/100); formability good (55/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. S21640 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with S21640
Is S21640 easy to machine?
Treat like Nitronic 50: rigid setup, sharp positive-rake carbide, heavy positive feed to cut under the work-hardened skin, ~30 % of 1212 speeds and flood coolant.
Can S21640 be welded?
Readily welded by GTAW/GMAW/SMAW with no preheat and no PWHT; use over-alloyed N-bearing filler (e.g. 209/Nitronic 50 type) and keep interpass low to protect corrosion resistance.
Can S21640 be formed, bent or molded?
Cold forms well but work-hardens very fast — allow extra press tonnage, generous radii and intermediate solution anneals at 1040–1090 °C followed by rapid cooling; hot work 1150–1230 °C.
S21640 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cper UNS S21600 (XM-17); the low-carbon S21603/XM-18 variant is 0.03 max | ≤ 0.08 | 0.05 |
| Mnaustenite stabiliser replacing part of the Ni | 7.5 – 9 | 8.3 |
| Si | ≤ 1 | 0.5 |
| P | ≤ 0.05 | 0.03 |
| S | ≤ 0.03 | 0.01 |
| Cr | 17.5 – 22 | 20 |
| Ni | 5 – 7 | 6 |
| Mopitting resistance | 2 – 3 | 2.5 |
| Nprimary solid-solution strengthener | 0.25 – 0.5 | 0.35 |
| Fe | balance |
What surface finishes work on S21640?
Not anodizable; passivate to ASTM A967 (nitric or citric) or electropolish after descaling/pickling for the best pitting performance and mirror finish.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel S21640 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- S21600
How much does S21640 cost?
S21640 is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
S21640 — frequently asked
What is S21640 used for?
S21640 is typically used for fasteners, structural hardware and non-magnetic parts. In short: high-strength non-magnetic bar; nitrogen-strengthened Cr-Mn-Ni; weldable without PWHT.
What is the yield strength of S21640?
S21640 has a typical yield strength of 450 MPa (65.3 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 70% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is S21640 easy to machine?
Not especially — machinability is rated poor (25/100, worse than 88% of stainless steel grades). Treat like Nitronic 50: rigid setup, sharp positive-rake carbide, heavy positive feed to cut under the work-hardened skin, ~30 % of 1212 speeds and flood coolant.
Can S21640 be welded?
Yes — weldability is rated very good (70/100). Readily welded by GTAW/GMAW/SMAW with no preheat and no PWHT; use over-alloyed N-bearing filler (e.g. 209/Nitronic 50 type) and keep interpass low to protect corrosion resistance.
What surface finishes work on S21640?
Not anodizable; passivate to ASTM A967 (nitric or citric) or electropolish after descaling/pickling for the best pitting performance and mirror finish.
Can S21640 be formed, bent or molded?
Cold forms well but work-hardens very fast — allow extra press tonnage, generous radii and intermediate solution anneals at 1040–1090 °C followed by rapid cooling; hot work 1150–1230 °C.
What is the maximum service temperature of S21640?
S21640 is rated for continuous use to about 815°C (1,499 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between S21640-ANN and S21640 CW-FH?
ANN is the default condition — standard stocked condition — maximum corrosion resistance and ductility, yield already ~2× that of 304. CW-FH: maximum strength wire/small bar for springs and studs where forming is finished. Yield strength is 450 MPa in ANN versus 1,100 MPa in CW-FH.
How much does S21640 cost?
S21640 is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM International (2023)
- ASTM A479/A479M — Stainless Steel Bars and Shapes for Pressure Vessels — ASTM International (2023)
- SAE/ASTM DS-56 (UNS) Metals & Alloys in the Unified Numbering System — SAE International / ASTM (2017)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 13B — Corrosion: Materials — ASM International (2005)
- Nitrogen-strengthened Cr-Mn austenitic stainless bar datasheets (Nitronic-type) — Electralloy / Universal Stainless (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.