Stainless Steel CK20-HT (Solution heat treated)
Heat-treated state · default condition
ASTM CK20 · UNS J94202
Standard supply condition for ASTM A351 CK20 pressure castings: maximum ductility, toughness and corrosion resistance.
Values for the HT 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 |
|---|---|---|---|---|---|---|
HTDefaultThis page 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 |
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-HT?
CK20-HT is CK20 heat treated to HT — standard supply condition for ASTM A351 CK20 pressure castings: maximum ductility, toughness and corrosion resistance. CK20-HT has a yield strength of 250 MPa (36.3 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 91% of stainless steel grades. Elongation at break is 37% and the elastic modulus is 193 GPa (28 Msi). CK20-HT 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).
Advantages
- High service temperature — 1,100°C (2,012 °F), better than 96% of stainless steel grades
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
Limitations
- Low strength — 250 MPa (36.3 ksi), worse than 91% of stainless steel grades
- Hard to polish — 55/100, worse than 89% of stainless steel grades
- Limited formability — 20/100, worse than 86% of stainless steel grades
- Low electrical conductivity — 2 % IACS, worse than 77% of stainless steel grades
CK20-HT properties
Typical room-temperature values for CK20-HT; 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-HT 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-HT has a yield strength of 250 MPa (36.3 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 91% of stainless steel grades. Elongation at break is 37% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
CK20-HT 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-HT 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-HT 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-HT's machinability is poor (28/100, worse than 79% of stainless steel grades); weldability good (60/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with CK20-HT
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-HT — frequently asked
What is CK20-HT used for?
CK20-HT 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-HT?
CK20-HT has a typical yield strength of 250 MPa (36.3 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 91% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is CK20-HT easy to machine?
Not especially — machinability is rated poor (28/100, worse than 79% 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-HT 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-HT?
Grind/blast and passivate or pickle to restore the chromium oxide film; do not anodize, and avoid carbon-steel contamination during cleaning.
Can CK20-HT 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-HT?
CK20-HT 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.