Stainless Steel CK20 Aged
Heat-treated state
ASTM CK20 · UNS J94202
Aged = service-exposed / thermally aged
Reference condition for assessing parts after long furnace service: carbide and sigma precipitation raise hardness but sharply cut room-temperature toughness.
Values for the Aged condition
Other CK20 tempers and conditions
CK20 is listed in 4 conditions; see the grade overview at CK20.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
HTDefault Solution heat treated | Standard supply condition for ASTM A351 CK20 pressure castings: maximum ductility, toughness and corrosion resistance. | 250 | 520 | 37 | 170 HB | 2 % IACS |
Spheroidize annealed | Used for non-pressure heat-resistant furnace hardware where interdendritic carbides are acceptable; slightly harder, lower ductility and toughness. | 260 | 490 | 22 | 180 HB | 2 % IACS |
Centrifugally cast pipe/tube, heat treated | Choose for high-temperature piping and furnace tubes; the centrifugal structure gives cleaner, denser walls and slightly better strength than static castings. | 260 | 540 | 35 | 175 HB | 2 % IACS |
AgedThis page Service-exposed / thermally aged | Reference condition for assessing parts after long furnace service: carbide and sigma precipitation raise hardness but sharply cut room-temperature toughness. | 300 | 560 | 8 | 14 HRC | 2 % IACS |
What is CK20 Aged?
CK20 Aged is CK20 heat treated to Aged — reference condition for assessing parts after long furnace service: carbide and sigma precipitation raise hardness but sharply cut room-temperature toughness. CK20 Aged has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 68% of stainless steel grades. Elongation at break is 8% and the elastic modulus is 190 GPa (27.6 Msi). CK20 Aged has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,400°C (2,552 °F). HT is the default condition FabDigit quotes; Aged is available on request or by drawing note.
Advantages
- High service temperature — 1,100°C (2,012 °F), better than 96% of stainless steel grades
Limitations
- Limited ductility — 8%, worse than 99% of stainless steel grades
- Limited formability — 8/100, worse than 97% of stainless steel grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 95% of stainless steel grades
- Difficult to machine — 22/100, worse than 95% of stainless steel grades
- Hard to polish — 55/100, worse than 89% of stainless steel grades
CK20 Aged properties
Typical room-temperature values for CK20 Aged; 23 are specific to this condition. Other listed values are CK20 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
CK20 Aged has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
CK20 Aged has a yield strength of 300 MPa (43.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 68% of stainless steel grades. Elongation at break is 8% and the elastic modulus is 190 GPa (27.6 Msi).
Thermal6
CK20 Aged is rated for continuous service to 1,100°C (2,012 °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 15.9 µm/m·K (8.83 µin/in·°F).
Electrical3
CK20 Aged conducts electricity at 2 % IACS, worse than 77% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), worse than 78% of stainless steel grades.
Sustainability4
Producing a kilogram of CK20 Aged takes about 55 MJ of energy and emits 4.5 kg of CO₂ — more than 50% of stainless steel grades. Typical recycled content is 75%.
Manufacturability8
CK20 Aged's machinability is poor (22/100, worse than 95% of stainless steel grades); weldability poor (30/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with CK20 Aged
Is CK20 easy to machine?
Machine with rigid setups, sharp carbide tooling, low speed and heavy positive feed to cut under the work-hardened skin; flood coolant is essential.
Can CK20 be welded?
Weld with 310/ER310 filler using GTAW or SMAW, low heat input and no preheat; interpass temperature control limits hot cracking and sigma formation.
Can CK20 be formed, bent or molded?
Supplied as a casting — design generous risers and fillets for the high solidification shrinkage; no cold forming.
What surface finishes work on CK20?
Grind/blast and passivate or pickle to restore the chromium oxide film; do not anodize, and avoid carbon-steel contamination during cleaning.
CK20 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 |
|---|---|---|
| C0.20 max per ASTM A351/A451 CK20 | ≤ 0.2 | 0.15 |
| Mnsome standards/foundries limit to 1.50 max | ≤ 2 | 1.2 |
| Si | ≤ 1.75 | 1.2 |
| P | ≤ 0.04 | 0.03 |
| S | ≤ 0.04 | 0.02 |
| Cr | 23 – 27 | 25 |
| Ni | 19 – 22 | 20.5 |
| Moresidual, per purchaser agreement | ≤ 0.5 | — |
| Fe | balance | — |
CK20 Aged — frequently asked
What is CK20 Aged used for?
CK20 Aged is typically used for furnace parts, high-temperature process equipment and heat treating baskets and fixtures. In short: cast 310 equivalent; 1100 °C oxidation service; stable fully austenitic structure.
What is the yield strength of CK20 Aged?
CK20 Aged has a typical yield strength of 300 MPa (43.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 68% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is CK20 Aged easy to machine?
Not especially — machinability is rated poor (22/100, worse than 95% of stainless steel grades). Machine with rigid setups, sharp carbide tooling, low speed and heavy positive feed to cut under the work-hardened skin; flood coolant is essential.
Can CK20 Aged be welded?
Not readily — weldability is rated poor (30/100). Weld with 310/ER310 filler using GTAW or SMAW, low heat input and no preheat; interpass temperature control limits hot cracking and sigma formation.
What surface finishes work on CK20 Aged?
Grind/blast and passivate or pickle to restore the chromium oxide film; do not anodize, and avoid carbon-steel contamination during cleaning.
Can CK20 Aged be formed, bent or molded?
Supplied as a casting — design generous risers and fillets for the high solidification shrinkage; no cold forming.
What is the maximum service temperature of CK20 Aged?
CK20 Aged is rated for continuous use to about 1,100°C (2,012 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between CK20-HT and CK20 Aged?
HT is the default condition — standard supply condition for ASTM A351 CK20 pressure castings: maximum ductility, toughness and corrosion resistance. Aged: reference condition for assessing parts after long furnace service: carbide and sigma precipitation raise hardness but sharply cut room-temperature toughness. Yield strength is 250 MPa in HT versus 300 MPa in Aged.
Sources
- ASTM A351/A351M — Castings, Austenitic, for Pressure-Containing Parts — ASTM International (2018)
- ASTM A451/A451M — Centrifugally Cast Austenitic Steel Pipe for High-Temperature Service — ASTM International (2021)
- ASM Handbook Vol. 1: Properties and Selection: Irons, Steels, and High-Performance Alloys (Cast Stainless Steels) — ASM International (1990)
- Steel Castings Handbook — Steel Founders' Society of America / ASM International (1995)
- ASM Handbook Vol. 13B: Corrosion — Materials — ASM International (2005)
- GB/T 8492 (ZG40Cr25Ni20 ) (2014)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.