Stainless Steel HH TYPE-I
Grade
UNS J93503
Choose when higher room- and intermediate-temperature strength is wanted and long holds in the 650–900 °C σ-phase range are avoided.
Values for the TYPE-I condition
Other HH tempers and conditions
HH is listed in 7 conditions; see the grade overview at HH.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Optional treatment to dissolve grain-boundary carbide networks before heavy machining or welding, giving better ductility at slightly lower strength. | 260 | 540 | 25 | 165 HB | 2 % IACS |
fully austenitic (ferrite-free) as-cast HH | Choose for continuous high-temperature service above ~900 °C where stable creep-rupture life and resistance to σ-embrittlement matter more than room-temperature strength. | 275 | 550 | 18 | 178 HB | 1.9 % IACS |
Centrifugally cast tube, 0.30 % C class | Centrifugally cast HH tubing for furnace radiant tubes and reformer-type service where creep-rupture strength is specified at temperature. | 300 | 570 | 14 | 185 HB | 2 % IACS |
FDefault As fabricated | Standard supply condition for HH furnace parts, radiant tubes and grate bars — used directly at temperature without heat treatment. | 310 | 585 | 15 | 185 HB | 2 % IACS |
Centrifugally cast tube, 0.33 % C class | Higher-carbon centrifugal HH tube grade for slightly greater creep-rupture strength at the cost of ductility and weldability. | 315 | 590 | 12 | 192 HB | 2 % IACS |
TYPE-IThis page partially ferritic as-cast HH (A297/A447 Type I) | Choose when higher room- and intermediate-temperature strength is wanted and long holds in the 650–900 °C σ-phase range are avoided. | 345 | 600 | 12 | 192 HB | 2.1 % IACS |
Aged / service-exposed | Use these numbers when assessing residual room-temperature properties of parts that have run in the 650–900 °C range — strength rises but ductility and impact toughness collapse. | 380 | 620 | 5 | 17 HRC | 2.1 % IACS |
What is HH TYPE-I?
HH TYPE-I is HH in the TYPE-I grade — choose when higher room- and intermediate-temperature strength is wanted and long holds in the 650–900 °C σ-phase range are avoided. HH TYPE-I has a yield strength of 345 MPa (50 ksi) and a tensile strength of 600 MPa (87 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 195 GPa (28.3 Msi). HH TYPE-I has a density of 7.72 g/cm³ (0.279 lb/in³), lighter than 72% of stainless steel grades. It melts at 1,400°C (2,552 °F). F is the default condition FabDigit quotes; TYPE-I is available on request or by drawing note.
Advantages
- High service temperature — 1,040°C (1,904 °F), better than 89% of stainless steel grades
Limitations
- Limited formability — 7/100, worse than 97% of stainless steel grades
- Limited ductility — 12%, worse than 95% of stainless steel grades
- Hard to polish — 55/100, worse than 89% of stainless steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 88% of stainless steel grades
- Difficult to weld — 50/100, worse than 77% of stainless steel grades
HH TYPE-I properties
Typical room-temperature values for HH TYPE-I; 23 are specific to this condition. Other listed values are HH reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
HH TYPE-I has a density of 7.72 g/cm³ (0.279 lb/in³), lighter than 72% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
HH TYPE-I has a yield strength of 345 MPa (50 ksi) and a tensile strength of 600 MPa (87 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 12% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
HH TYPE-I is rated for continuous service to 1,040°C (1,904 °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 µm/m·K (8.33 µin/in·°F).
Electrical3
HH TYPE-I conducts electricity at 2.1 % IACS, worse than 73% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (60/100), worse than 58% of stainless steel grades.
Sustainability4
Producing a kilogram of HH TYPE-I takes about 48 MJ of energy and emits 4 kg of CO₂ — less than 85% of stainless steel grades. Typical recycled content is 75%.
Manufacturability7
HH TYPE-I's machinability is poor (29/100, worse than 76% of stainless steel grades); weldability fair (50/100); formability not recommended (7/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HH TYPE-I
Is HH easy to machine?
Machine with rigid setups, positive-rake carbide and heavy feeds to cut under the work-hardened skin; the interdendritic carbide network is abrasive, so keep speeds low (~30–60 m/min) and flood-cool.
Can HH be welded?
Weldable with matching 25-12 (AWS ER309/E309) filler using low heat input and interpass control; preheat/postweld solution treatment reduces hot-cracking and carbide-network cracking in aged castings.
Can HH be formed, bent or molded?
Foundry grade only — sand or centrifugal cast with generous fillets and directional solidification; no cold forming, and hot straightening should be done above 1050 °C.
What surface finishes work on HH?
Shot-blast and pickle/passivate to remove casting scale; no anodizing — surfaces self-protect by forming a chromia scale in service, and machined faces can be ground/polished to a moderate finish.
HH 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 |
|---|---|---|
| Chigh carbon gives carbide strengthening | 0.2 – 0.5 | 0.35 |
| Cr | 24 – 28 | 26 |
| Ni | 11 – 14 | 12 |
| Siimproves fluidity and scaling resistance | ≤ 2 | 1.5 |
| Mn | ≤ 2 | 1 |
| Moresidual, not intentionally added | ≤ 0.5 | — |
| Npromotes austenite (Type II) | ≤ 0.2 | — |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
HH TYPE-I — frequently asked
What is HH TYPE-I used for?
HH TYPE-I is typically used for furnace rollers, radiant tubes, heat-treatment baskets and kiln furniture. In short: baseline heat-resistant casting; oxidation resistance to 1090 °C; cast-only furnace alloy.
What is the yield strength of HH TYPE-I?
HH TYPE-I has a typical yield strength of 345 MPa (50 ksi) and a tensile strength of 600 MPa (87 ksi) — weaker than 54% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is HH TYPE-I easy to machine?
Not especially — machinability is rated poor (29/100, worse than 76% of stainless steel grades). Machine with rigid setups, positive-rake carbide and heavy feeds to cut under the work-hardened skin; the interdendritic carbide network is abrasive, so keep speeds low (~30–60 m/min) and flood-cool.
Can HH TYPE-I be welded?
With care — weldability is rated fair (50/100). Weldable with matching 25-12 (AWS ER309/E309) filler using low heat input and interpass control; preheat/postweld solution treatment reduces hot-cracking and carbide-network cracking in aged castings.
What surface finishes work on HH TYPE-I?
Shot-blast and pickle/passivate to remove casting scale; no anodizing — surfaces self-protect by forming a chromia scale in service, and machined faces can be ground/polished to a moderate finish.
Can HH TYPE-I be formed, bent or molded?
Foundry grade only — sand or centrifugal cast with generous fillets and directional solidification; no cold forming, and hot straightening should be done above 1050 °C.
What is the maximum service temperature of HH TYPE-I?
HH TYPE-I is rated for continuous use to about 1,040°C (1,904 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between HH-F and HH Aged?
F is the default condition — standard supply condition for HH furnace parts, radiant tubes and grate bars — used directly at temperature without heat treatment. Aged: use these numbers when assessing residual room-temperature properties of parts that have run in the 650–900 °C range — strength rises but ductility and impact toughness collapse. Yield strength is 310 MPa in F versus 380 MPa in Aged.
Sources
- ASTM A297/A297M — Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant, for General Application — ASTM International (2019)
- ASTM A447/A447M — Steel Castings, Chromium-Nickel-Iron Alloy (25-12 Class), for High-Temperature Service — ASTM International (2019)
- ASTM A608/A608M — Centrifugally Cast Iron-Chromium-Nickel High-Alloy Tubing for Pressure Application at High Temperatures — ASTM International (2018)
- ASM Specialty Handbook: Heat-Resistant Materials — ASM International (1997)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Heat-Resistant Castings) — ASM International (1990)
- Steel Castings Handbook, 6th ed. — Steel Founders' Society of America / ASM (1995)
- GB/T 8492 — (ZG40Cr25Ni12) — SAC (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.