Stainless Steel HI Aged
Heat-treated state
UNS J94003
Aged = 24 h at ~760 °C, air cooled
Use these numbers for design of parts that have seen prolonged 700–900 °C service: strength edges up but ductility and impact toughness collapse from carbide/sigma precipitation.
Values for the Aged condition
Other HI tempers and conditions
HI is listed in 4 conditions; see the grade overview at HI.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution Annealed | Chosen when castings are to be machined or welded before service, or when maximum as-delivered ductility and homogeneity are wanted. | 290 | 530 | 16 | 170 HB | 1.9 % IACS |
AS-CASTDefault no post-cast heat treatment | Standard supply condition for furnace hardware and other components that will be put straight into high-temperature service. | 310 | 550 | 12 | 180 HB | 1.9 % IACS |
Centrifugally Cast (tube/cylinder form), as-cast | Pick for radiant tubes, muffles and rolls where the denser, more directional centrifugal structure raises strength and soundness over static sand casting. | 325 | 580 | 12 | 185 HB | 1.9 % IACS |
AgedThis page 24 h at ~760 °C, air cooled | Use these numbers for design of parts that have seen prolonged 700–900 °C service: strength edges up but ductility and impact toughness collapse from carbide/sigma precipitation. | 345 | 490 | 6 | 200 HB | 1.9 % IACS |
What is HI Aged?
HI Aged is HI heat treated to Aged — use these numbers for design of parts that have seen prolonged 700–900 °C service: strength edges up but ductility and impact toughness collapse from carbide/sigma precipitation. HI Aged has a yield strength of 345 MPa (50 ksi) and a tensile strength of 490 MPa (71.1 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 6% and the elastic modulus is 195 GPa (28.3 Msi). HI Aged has a density of 7.6 g/cm³ (0.275 lb/in³), lighter than 98% of stainless steel grades. It melts at 1,370°C (2,498 °F). AS-CAST is the default condition FabDigit quotes; Aged is available on request or by drawing note.
Advantages
- High service temperature — 1,175°C (2,147 °F), better than 100% of stainless steel grades
Limitations
- Limited formability — 4/100, worse than 100% of stainless steel grades
- Limited ductility — 6%, worse than 99% of stainless steel grades
- Low fracture toughness — 30 MPa·√m (27.3 ksi·√in), worse than 99% of stainless steel grades
- Difficult to machine — 20/100, worse than 98% of stainless steel grades
- Hard to polish — 50/100, worse than 93% of stainless steel grades
HI Aged properties
Typical room-temperature values for HI Aged; 22 are specific to this condition. Other listed values are HI reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
HI Aged has a density of 7.6 g/cm³ (0.275 lb/in³), lighter than 98% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical16
HI Aged has a yield strength of 345 MPa (50 ksi) and a tensile strength of 490 MPa (71.1 ksi) — weaker than 54% of stainless steel grades. Elongation at break is 6% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
HI Aged is rated for continuous service to 1,175°C (2,147 °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
HI Aged conducts electricity at 1.9 % IACS, worse than 84% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (58/100), worse than 62% of stainless steel grades.
Sustainability4
Producing a kilogram of HI Aged takes about 52 MJ of energy and emits 4.2 kg of CO₂ — less than 76% of stainless steel grades. Typical recycled content is 75%.
Manufacturability8
HI Aged's machinability is poor (20/100, worse than 98% of stainless steel grades); weldability poor (25/100); formability not recommended (4/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HI Aged
Is HI easy to machine?
Machine in the as-cast or solution-annealed state with rigid setups, sharp carbide tooling, low speed and heavy positive feed — the massive Cr carbides are abrasive and the matrix work-hardens; grinding is often preferred on aged parts.
Can HI be welded?
Weldable with matched 28-15 or 25-20 (ER310) filler using low heat input and no post-weld quench; welding service-exposed material usually requires a full solution anneal first to redissolve sigma phase and avoid cracking.
Can HI be formed, bent or molded?
Casting-only alloy — good fluidity for sand, investment and centrifugal casting, but design generous fillets and control feeding as solidification shrinkage and hot tearing risk are high.
What surface finishes work on HI?
Normally supplied shot-blasted or pickled/passivated; the self-forming chromium oxide scale is the working surface, so paints and platings are unnecessary and generally not used at temperature.
HI 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 C for creep strength | 0.2 – 0.5 | 0.4 |
| Mn | ≤ 2 | 1 |
| Siaids scaling resistance | ≤ 2 | 1.3 |
| Cr | 26 – 30 | 28 |
| Ni | 14 – 18 | 15.5 |
| Moresidual, not intentionally added | ≤ 0.5 | — |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
HI Aged — frequently asked
What is HI Aged used for?
HI Aged is typically used for furnace fixtures, kiln components and heat-treatment equipment. In short: higher-temperature HH upgrade; scaling resistance to 1175 °C; limited weldability, cast only.
What is the yield strength of HI Aged?
HI Aged has a typical yield strength of 345 MPa (50 ksi) and a tensile strength of 490 MPa (71.1 ksi) — weaker than 54% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is HI Aged easy to machine?
Not especially — machinability is rated poor (20/100, worse than 98% of stainless steel grades). Machine in the as-cast or solution-annealed state with rigid setups, sharp carbide tooling, low speed and heavy positive feed — the massive Cr carbides are abrasive and the matrix work-hardens; grinding is often preferred on aged parts.
Can HI Aged be welded?
Not readily — weldability is rated poor (25/100). Weldable with matched 28-15 or 25-20 (ER310) filler using low heat input and no post-weld quench; welding service-exposed material usually requires a full solution anneal first to redissolve sigma phase and avoid cracking.
What surface finishes work on HI Aged?
Normally supplied shot-blasted or pickled/passivated; the self-forming chromium oxide scale is the working surface, so paints and platings are unnecessary and generally not used at temperature.
Can HI Aged be formed, bent or molded?
Casting-only alloy — good fluidity for sand, investment and centrifugal casting, but design generous fillets and control feeding as solidification shrinkage and hot tearing risk are high.
What is the maximum service temperature of HI Aged?
HI Aged is rated for continuous use to about 1,175°C (2,147 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between HI AS-CAST and HI Aged?
AS-CAST is the default condition — standard supply condition for furnace hardware and other components that will be put straight into high-temperature service. Aged: use these numbers for design of parts that have seen prolonged 700–900 °C service: strength edges up but ductility and impact toughness collapse from carbide/sigma precipitation. Yield strength is 310 MPa in AS-CAST versus 345 MPa in Aged.
Sources
- ASTM A297/A297M — Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant, for General Application — ASTM International (2019)
- ASTM A743/A743M — Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application — ASTM International (2019)
- ASM Specialty Handbook: Heat-Resistant Materials — ASM International (1997)
- Steel Castings Handbook, 6th ed. — Steel Founders' Society of America / ASM (1995)
- UNS J94003 alloy data (SAE/ASTM Metals & Alloys in the Unified Numbering System) — SAE International (2017)
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.