Stainless Steel Alloy 20
UNS N08020 · EN 2.4660 · also 20Cb-3, Carpenter 20
Alloy 20 (UNS N08020, Carpenter 20Cb-3) is a niobium-stabilized iron–nickel–chromium austenitic alloy with roughly 33 % Ni, 20 % Cr, 3.5 % Cu and 2.5 % Mo, developed for hot sulfuric acid and mixed-acid service.
Values for the Annealed condition
Alloy 20 tempers and conditions
Alloy 20 is supplied in 5 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
925–1010 °C, rapid quench | Full solution treatment for maximum corrosion resistance after heavy cold work or fabrication welding. | 290 | 600 | 45 | 155 HB | — |
hot rolled/forged and annealed bar, plate or seamless pipe | Choose for heavy sections, forgings and large-diameter seamless pipe where scale/tolerance is acceptable. | 300 | 610 | 38 | 170 HB | 1.6 % IACS |
AnnealedDefault mill annealed (ASTM B463/B473/B464 standard supply) | Default stock condition for plate, sheet, bar, pipe and fittings in acid-service equipment. | 310 | 620 | 40 | 160 HB | — |
cold drawn (and stress-relieved) bar/wire | Higher strength and better surface/tolerance for machined shafts, fasteners and pump parts. | 620 | 760 | 22 | 24 HRC | — |
heavily cold-reduced strip, wire or tube | Maximum strength condition for springs, fasteners and thin-wall tubing; ductility and formability are much reduced. | 790 | 930 | 12 | 32 HRC | — |
What is Alloy 20?
Alloy 20 (UNS N08020, Carpenter 20Cb-3) is a niobium-stabilized iron–nickel–chromium austenitic alloy with roughly 33 % Ni, 20 % Cr, 3.5 % Cu and 2.5 % Mo, developed for hot sulfuric acid and mixed-acid service. Copper and molybdenum give good general corrosion resistance in mid-concentration sulfuric and phosphoric acids and in chloride-bearing acids, and the Nb stabilization lets welded parts resist intergranular attack without post-weld solution treatment. Limits are high nickel-driven cost, moderate machinability (about 40 % of B1112) with marked work hardening, pitting resistance below 6Mo superaustenitics, and no use in strongly reducing hydrochloric acid or above ~500 °C. Alloy 20 has a density of 8.08 g/cm³ (0.292 lb/in³), heavier than 99% of stainless steel grades. It melts at 1,370°C (2,498 °F). Alloy 20 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 40% and the elastic modulus is 193 GPa (28 Msi).
What is Alloy 20 used for?
- Sulfuric acid tanks and vessels
- Chemical process pumps and impellers
- Valve bodies for acid service
- Heat exchanger tubing and tubesheets
- Pickling line fixtures and racks
- Mixing tank agitators and shafts
- Piping spools for phosphoric acid
Advantages
- Good corrosion resistance — 80/100, better than 88% of stainless steel grades
- Forms and bends easily — 72/100, better than 84% of stainless steel grades
- Readily welded — 80/100, better than 80% of stainless steel grades
Limitations
- Low electrical conductivity — 1.6 % IACS, worse than 99% of stainless steel grades
- High embodied carbon — 7.5 kg CO₂/kg, worse than 97% of stainless steel grades
- Poor heat conductor — 12 W/m·K (6.93 BTU/hr·ft·°F), worse than 93% of stainless steel grades
Alloy 20 properties
Typical room-temperature values for Alloy 20-Annealed; bars are the position among stainless steel grades.
Physical3
Alloy 20 has a density of 8.08 g/cm³ (0.292 lb/in³), heavier than 99% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical13
Alloy 20 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 40% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
Alloy 20 is rated for continuous service to 500°C (932 °F). It conducts heat at 12 W/m·K (6.93 BTU/hr·ft·°F), worse than 93% of stainless steel grades. Thermal expansion is 14.8 µm/m·K (8.22 µin/in·°F).
Electrical3
Alloy 20 conducts electricity at 1.6 % IACS, worse than 99% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is very good (80/100), better than 88% of stainless steel grades.
Sustainability4
Producing a kilogram of Alloy 20 takes about 100 MJ of energy and emits 7.5 kg of CO₂ — more than 98% of stainless steel grades. Typical recycled content is 45%.
Manufacturability8
Alloy 20's machinability is fair (38/100, better than 63% of stainless steel grades); weldability very good (80/100); formability very good (72/100).
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. Alloy 20 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Alloy 20
Is Alloy 20 easy to machine?
Machines like a tough austenitic: rigid setups, positive-rake sharp carbide, heavy constant feed, low-to-moderate speed and flood coolant to avoid work-hardened glazing; rating ≈ 40% of B1112.
Can Alloy 20 be welded?
Readily welded by GTAW/GMAW/SMAW with matching 20Cb-3 or ENiCrMo-3/ERNiCrMo-3 filler; keep heat input and interpass temperature low, no preheat, PWHT normally unnecessary thanks to Nb stabilization.
Can Alloy 20 be formed, bent or molded?
Good cold formability with high work-hardening — allow extra springback and interstage annealing at 925–1010 °C; hot work at 1040–1180 °C and quench after forming.
Manufacturability
The process limits FabDigit applies to Alloy 20. Every Alloy 20 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair38 / 100 |
|---|---|
| ISO material group | M.1 |
| Cutting speed (rough / finish) | 150 / 180 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better72 / 100 |
|---|---|
| Weldability | Better80 / 100 |
| Bendable | Yes |
Alloy 20 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 |
|---|---|---|
| Niprimary austenite stabilizer, SCC resistance | 32 – 38 | 34 |
| Cr | 19 – 21 | 20 |
| Cukey for sulfuric acid resistance | 3 – 4 | 3.5 |
| Mo | 2 – 3 | 2.5 |
| NbCb (+Ta) ≥ 8×C; stabilization against sensitization | ≤ 1 | 0.5 |
| C | ≤ 0.07 | 0.03 |
| Mn | ≤ 2 | 0.6 |
| Si | ≤ 1 | 0.4 |
| P | ≤ 0.05 | |
| S | ≤ 0.04 | |
| Febalance, approx. 35% | balance |
What surface finishes work on Alloy 20?
Pickle (HNO3-HF) and passivate per ASTM A967 after hot work or welding; electropolishing gives the smoothest acid-service surface; not anodizable, plating rarely used.
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).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel Alloy 20 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- N08020
- EN / DIN / Werkstoff-Nr.
- 2.4660
- Trade names
- 20Cb-3Carpenter 20Carpenter 20Cb-3
- Other
- B462
How much does Alloy 20 cost?
Alloy 20 is a specialty-cost stainless steel ($$$$$), pricier than about 99% 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.
Alloy 20 — frequently asked
What is Alloy 20 used for?
Alloy 20 is typically used for sulfuric acid tanks and vessels, chemical process pumps and impellers, valve bodies for acid service, heat exchanger tubing and tubesheets, pickling line fixtures and racks and mixing tank agitators and shafts. In short: best chemical resistance.
What is the yield strength of Alloy 20?
Alloy 20 has a typical yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is Alloy 20 easy to machine?
Not especially — machinability is rated fair (38/100, better than 63% of stainless steel grades). Machines like a tough austenitic: rigid setups, positive-rake sharp carbide, heavy constant feed, low-to-moderate speed and flood coolant to avoid work-hardened glazing; rating ≈ 40% of B1112.
Can Alloy 20 be welded?
Yes — weldability is rated very good (80/100). Readily welded by GTAW/GMAW/SMAW with matching 20Cb-3 or ENiCrMo-3/ERNiCrMo-3 filler; keep heat input and interpass temperature low, no preheat, PWHT normally unnecessary thanks to Nb stabilization.
What surface finishes work on Alloy 20?
Pickle (HNO3-HF) and passivate per ASTM A967 after hot work or welding; electropolishing gives the smoothest acid-service surface; not anodizable, plating rarely used.
Can Alloy 20 be formed, bent or molded?
Good cold formability with high work-hardening — allow extra springback and interstage annealing at 925–1010 °C; hot work at 1040–1180 °C and quench after forming.
What is the maximum service temperature of Alloy 20?
Alloy 20 is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Alloy 20 cost?
Alloy 20 is a specialty-cost stainless steel ($$$$$), pricier than about 99% 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.
Can FabDigit make parts in Alloy 20?
Yes — Alloy 20 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM B463 — UNS N08020 Plate, Sheet and Strip — ASTM International (2020)
- ASTM B473 — UNS N08020 Bar and Wire — ASTM International (2020)
- ASTM B464/B729 — UNS N08020 Welded and Seamless Pipe/Tube — ASTM International (2020)
- Carpenter 20Cb-3 Stainless Alloy Technical Datasheet — Carpenter Technology (2020)
- Alloy 20 (N08020) Data Sheet — Rolled Alloys / Sandmeyer Steel (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
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.