Stainless Steel CK20 CPK20
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ASTM CK20 · UNS J94202
CPK20 = 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.
Values for the CPK20 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 |
CPK20This page 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 |
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 CPK20?
CK20 CPK20 is CK20 in the CPK20 condition — choose for high-temperature piping and furnace tubes; the centrifugal structure gives cleaner, denser walls and slightly better strength than static castings. CK20 CPK20 has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 540 MPa (78.3 ksi) — weaker than 84% of stainless steel grades. Elongation at break is 35% and the elastic modulus is 193 GPa (28 Msi). CK20 CPK20 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; CPK20 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
- Tough — resists crack growth — 195 MPa·√m (177.5 ksi·√in), better than 77% of stainless steel grades
Limitations
- Limited formability — 18/100, worse than 89% of stainless steel grades
- Hard to polish — 55/100, worse than 89% of stainless steel grades
- Low strength — 260 MPa (37.7 ksi), worse than 84% of stainless steel grades
- Low electrical conductivity — 2 % IACS, worse than 77% of stainless steel grades
CK20 CPK20 properties
Typical room-temperature values for CK20 CPK20; 22 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 CPK20 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 CPK20 has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 540 MPa (78.3 ksi) — weaker than 84% of stainless steel grades. Elongation at break is 35% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
CK20 CPK20 is rated for continuous service to 1,100°C (2,012 °F). It conducts heat at 14.2 W/m·K (8.2 BTU/hr·ft·°F), worse than 76% of stainless steel grades. Thermal expansion is 15.9 µm/m·K (8.83 µin/in·°F).
Electrical3
CK20 CPK20 conducts electricity at 2 % IACS, worse than 77% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (68/100), better than 63% of stainless steel grades.
Sustainability4
Producing a kilogram of CK20 CPK20 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 CPK20's machinability is poor (27/100, worse than 83% of stainless steel grades); weldability good (60/100); formability poor (18/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with CK20 CPK20
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 CPK20 — frequently asked
What is CK20 CPK20 used for?
CK20 CPK20 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 CPK20?
CK20 CPK20 has a typical yield strength of 260 MPa (37.7 ksi) and a tensile strength of 540 MPa (78.3 ksi) — weaker than 84% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is CK20 CPK20 easy to machine?
Not especially — machinability is rated poor (27/100, worse than 83% 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 CPK20 be welded?
Yes — weldability is rated good (60/100). 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 CPK20?
Grind/blast and passivate or pickle to restore the chromium oxide film; do not anodize, and avoid carbon-steel contamination during cleaning.
Can CK20 CPK20 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 CPK20?
CK20 CPK20 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.