Stainless Steel HK-F (As fabricated)
Temper · default condition
UNS J94224
Default supply condition for furnace hardware, tube supports and trays — used as-cast with no post-cast heat treatment.
Values for the F condition
Other HK tempers and conditions
HK is listed in 5 conditions; see the grade overview at HK.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed ~1150 °C, rapid cooled | Occasionally specified for corrosion-service or weld-repaired A743 HK castings to dissolve grain-boundary carbides and restore ductility. | 300 | 490 | 20 | 170 HB | 1.9 % IACS |
A351/A743 HK30, static cast, 0.25–0.35 %C | Lower-carbon HK for pressure-containing castings where ductility and weld repair matter more than creep strength. | 310 | 500 | 15 | 180 HB | 1.9 % IACS |
FDefaultThis page As fabricated | Default supply condition for furnace hardware, tube supports and trays — used as-cast with no post-cast heat treatment. | 345 | 520 | 12 | 190 HB | 1.9 % IACS |
A351/A297 HK40, 0.35–0.45 %C, as-cast | The workhorse high-carbon variant — pick it for maximum creep-rupture strength in reformer/cracking furnace service. | 360 | 540 | 10 | 200 HB | 1.9 % IACS |
Thermally aged / ex-service | Reference condition for remaining-life and repair-weld assessment: carbide coarsening and σ-phase leave the alloy strong but nearly brittle at room temperature. | 380 | 520 | 3 | 17 HRC | 2 % IACS |
What is HK-F?
HK-F is HK in the F temper — default supply condition for furnace hardware, tube supports and trays — used as-cast with no post-cast heat treatment. HK-F has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 185 GPa (26.8 Msi). HK-F has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,340°C (2,444 °F).
Advantages
- High service temperature — 1,150°C (2,102 °F), better than 99% of stainless steel grades
Limitations
- Hard to polish — 45/100, worse than 96% of stainless steel grades
- Limited ductility — 12%, worse than 95% of stainless steel grades
- Limited formability — 10/100, worse than 95% of stainless steel grades
- Poor heat conductor — 13 W/m·K (7.51 BTU/hr·ft·°F), worse than 85% of stainless steel grades
- Low electrical conductivity — 1.9 % IACS, worse than 84% of stainless steel grades
HK-F properties
Typical room-temperature values for HK-F; 21 are specific to this condition. Other listed values are HK reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
HK-F has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,340°C (2,444 °F).
Mechanical15
HK-F has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 185 GPa (26.8 Msi).
Thermal6
HK-F is rated for continuous service to 1,150°C (2,102 °F). It conducts heat at 13 W/m·K (7.51 BTU/hr·ft·°F), worse than 85% of stainless steel grades. Thermal expansion is 15 µm/m·K (8.33 µin/in·°F).
Electrical3
HK-F conducts electricity at 1.9 % IACS, worse than 84% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (62/100), worse than 52% of stainless steel grades.
Sustainability4
Producing a kilogram of HK-F takes about 53 MJ of energy and emits 4.5 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 65%.
Manufacturability8
HK-F's machinability is poor (30/100, worse than 70% of stainless steel grades); weldability fair (50/100); formability not recommended (10/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HK-F
Is HK easy to machine?
Machine with rigid setups, positive-rake carbide or ceramic inserts, low speed and heavy positive feed to cut under the work-hardened skin; interdendritic chromium carbides are abrasive and aged material machines far worse than as-cast.
Can HK be welded?
Weldable by SMAW/GTAW with matching HK or ER310-type filler; preheat 150–260 °C, limit heat input, avoid restraint — service-aged castings need carbide-dissolution anneal or buttering to avoid HAZ cracking.
Can HK be formed, bent or molded?
Cast only (sand, investment or centrifugal); no cold forming — design generous fillets and controlled section changes to limit hot tearing and shrinkage in the wide freezing range.
What surface finishes work on HK?
Normally supplied shot-blasted or as-cast; grind/machine sealing faces, no anodizing or plating needed since the Cr₂O₃ scale is self-protective — avoid halide-bearing cleaners.
HK 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 |
|---|---|---|
| CA297 HK; A351 HK30 = 0.25–0.35, HK40 = 0.35–0.45 | 0.2 – 0.6 | 0.4 |
| Mn | ≤ 2 | 1.2 |
| Si≤1.75 in A351/A608 variants | ≤ 2 | 1.3 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| CrA351 HK30/HK40: 23.0–27.0 | 24 – 28 | 25.5 |
| Ni | 18 – 22 | 20 |
| Moresidual, not intentionally added | ≤ 0.5 | — |
| Fe | balance | — |
HK-F — frequently asked
What is HK-F used for?
HK-F is typically used for reformer/pyrolysis furnace fixtures, radiant tube supports, kiln furniture and heat-treat trays. In short: most-used heat-resistant casting; strength and oxidation to 1150 °C; widest foundry availability.
What is the yield strength of HK-F?
HK-F has a typical yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 54% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is HK-F easy to machine?
Not especially — machinability is rated poor (30/100, worse than 70% of stainless steel grades). Machine with rigid setups, positive-rake carbide or ceramic inserts, low speed and heavy positive feed to cut under the work-hardened skin; interdendritic chromium carbides are abrasive and aged material machines far worse than as-cast.
Can HK-F be welded?
With care — weldability is rated fair (50/100). Weldable by SMAW/GTAW with matching HK or ER310-type filler; preheat 150–260 °C, limit heat input, avoid restraint — service-aged castings need carbide-dissolution anneal or buttering to avoid HAZ cracking.
What surface finishes work on HK-F?
Normally supplied shot-blasted or as-cast; grind/machine sealing faces, no anodizing or plating needed since the Cr₂O₃ scale is self-protective — avoid halide-bearing cleaners.
Can HK-F be formed, bent or molded?
Cast only (sand, investment or centrifugal); no cold forming — design generous fillets and controlled section changes to limit hot tearing and shrinkage in the wide freezing range.
What is the maximum service temperature of HK-F?
HK-F is rated for continuous use to about 1,150°C (2,102 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between HK-F and HK-SA?
F is the default condition — default supply condition for furnace hardware, tube supports and trays — used as-cast with no post-cast heat treatment. SA: occasionally specified for corrosion-service or weld-repaired A743 HK castings to dissolve grain-boundary carbides and restore ductility. Yield strength is 345 MPa in F versus 300 MPa in SA.
Sources
- ASTM A297/A297M — Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant, for General Application — ASTM International (2019)
- ASTM A351/A351M — Castings, Austenitic, for Pressure-Containing Parts (HK30, HK40) — ASTM International (2022)
- ASTM A608/A608M — Centrifugally Cast Iron-Chromium-Nickel High-Alloy Tubing for Pressure Application at High Temperatures — ASTM International (2018)
- ASTM A743/A743M — Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application — ASTM International (2019)
- ASM Specialty Handbook: Heat-Resistant Materials — Heat-Resistant Cast Steels — ASM International (1997)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Steel Castings Handbook, 6th ed. — Steel Founders' Society of America / ASM (1995)
- 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.