Stainless Steel HT Aged
Heat-treated state
UNS N08605
Aged = aged / service-exposed
Use these numbers when designing for room-temperature handling loads on parts that have already seen furnace service.
Values for the Aged condition
Other HT tempers and conditions
HT is listed in 4 conditions; see the grade overview at HT.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ASTM A351 low-carbon (0.25–0.35 C) pressure-casting version | Pick when the casting is a pressure-containing part needing better ductility and weld repair tolerance than full-carbon HT. | 240 | 485 | 15 | 170 HB | 1.7 % IACS |
AS-CASTDefault sand/investment cast, no post-cast heat treatment | Standard supply condition for furnace fixtures and trays; used as-cast because service temperature exceeds any heat-treat benefit. | 275 | 485 | 10 | 180 HB | 1.7 % IACS |
HT50, centrifugally cast tube | Choose for radiant tubes and furnace rolls where a dense, directionally solidified centrifugal tube wall is required. | 275 | 500 | 12 | 185 HB | 1.7 % IACS |
AgedThis page Aged / service-exposed | Use these numbers when designing for room-temperature handling loads on parts that have already seen furnace service. | 310 | 515 | 4 | 200 HB | 1.8 % IACS |
What is HT Aged?
HT Aged is HT heat treated to Aged — use these numbers when designing for room-temperature handling loads on parts that have already seen furnace service. HT Aged has a yield strength of 310 MPa (45 ksi) and a tensile strength of 515 MPa (74.7 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 4% and the elastic modulus is 175 GPa (25.4 Msi). HT Aged has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,340°C (2,444 °F). AS-CAST is the default condition FabDigit quotes; Aged 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
Limitations
- Limited ductility — 4%, worse than 100% of stainless steel grades
- Limited formability — 2/100, worse than 100% of stainless steel grades
- Low stiffness — 175 GPa (25.4 Msi), worse than 99% of stainless steel grades
- Difficult to machine — 18/100, worse than 99% of stainless steel grades
- Hard to polish — 40/100, worse than 99% of stainless steel grades
HT Aged properties
Typical room-temperature values for HT Aged; 22 are specific to this condition. Other listed values are HT reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
HT Aged has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,340°C (2,444 °F).
Mechanical14
HT Aged has a yield strength of 310 MPa (45 ksi) and a tensile strength of 515 MPa (74.7 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 4% and the elastic modulus is 175 GPa (25.4 Msi).
Thermal5
HT Aged is rated for continuous service to 1,100°C (2,012 °F). It conducts heat at 13.5 W/m·K (7.8 BTU/hr·ft·°F), worse than 83% of stainless steel grades. Thermal expansion is 14.7 µm/m·K (8.17 µin/in·°F).
Electrical3
HT Aged conducts electricity at 1.8 % IACS, worse than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (45/100), worse than 85% of stainless steel grades.
Sustainability4
Producing a kilogram of HT Aged takes about 78 MJ of energy and emits 5.6 kg of CO₂ — more than 87% of stainless steel grades. Typical recycled content is 60%.
Manufacturability8
HT Aged's machinability is poor (18/100, worse than 99% of stainless steel grades); weldability poor (15/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with HT Aged
Is HT easy to machine?
Difficult — abrasive primary carbides and rapid work hardening; use rigid setups, carbide/ceramic tooling, low speed with heavy positive feed and flood coolant, avoid dwelling.
Can HT be welded?
Weldable with matching HT (35Ni) or Ni-base (ERNiCr-3) filler; preheat 150–260 °C, low heat input, and expect reduced repair weldability on service-exposed (carburized/sigma-embrittled) parts.
Can HT be formed, bent or molded?
Cast-only alloy — no cold forming; design generous fillets, uniform sections and adequate risers because of the wide freezing range and high solidification shrinkage.
What surface finishes work on HT?
Normally supplied shot-blasted and ground at gates; no anodizing/plating — the protective Cr/Ni oxide scale forms in service, so avoid contaminating surfaces with sulfur or zinc-bearing compounds.
HT 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 |
|---|---|---|
| C0.25–0.35 for A351 HT30 | 0.35 – 0.75 | 0.5 |
| Mn | ≤ 2 | 1.2 |
| Sihigh Si aids carburization resistance | ≤ 2.5 | 1.6 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Cr | 15 – 19 | 17 |
| Ni | 33 – 37 | 35 |
| Moresidual, not intentionally added | ≤ 0.5 | — |
| Fe | balance | — |
HT Aged — frequently asked
What is HT Aged used for?
HT Aged is typically used for carburizing furnace fixtures, radiant tubes and heat-treatment retorts. In short: best carburization resistance; 1100 °C cast grade; cast-only, hard to machine.
What is the yield strength of HT Aged?
HT Aged has a typical yield strength of 310 MPa (45 ksi) and a tensile strength of 515 MPa (74.7 ksi) — weaker than 63% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is HT Aged easy to machine?
Not especially — machinability is rated poor (18/100, worse than 99% of stainless steel grades). Difficult — abrasive primary carbides and rapid work hardening; use rigid setups, carbide/ceramic tooling, low speed with heavy positive feed and flood coolant, avoid dwelling.
Can HT Aged be welded?
Not readily — weldability is rated poor (15/100). Weldable with matching HT (35Ni) or Ni-base (ERNiCr-3) filler; preheat 150–260 °C, low heat input, and expect reduced repair weldability on service-exposed (carburized/sigma-embrittled) parts.
What surface finishes work on HT Aged?
Normally supplied shot-blasted and ground at gates; no anodizing/plating — the protective Cr/Ni oxide scale forms in service, so avoid contaminating surfaces with sulfur or zinc-bearing compounds.
Can HT Aged be formed, bent or molded?
Cast-only alloy — no cold forming; design generous fillets, uniform sections and adequate risers because of the wide freezing range and high solidification shrinkage.
What is the maximum service temperature of HT Aged?
HT Aged 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 HT AS-CAST and HT Aged?
AS-CAST is the default condition — standard supply condition for furnace fixtures and trays; used as-cast because service temperature exceeds any heat-treat benefit. Aged: use these numbers when designing for room-temperature handling loads on parts that have already seen furnace service. Yield strength is 275 MPa in AS-CAST versus 310 MPa in Aged.
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 — ASTM International (2018)
- ASTM A608/A608M — Centrifugally Cast Iron-Chromium-Nickel High-Alloy Tubing for Pressure Application at High Temperatures — ASTM International (2018)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Heat-Resistant Castings) — ASM International (1990)
- Steel Castings Handbook, 6th ed. — High Alloy Data Sheets, Heat Series — Steel Founders' Society of America / ASM (1995)
- ASM Handbook Vol.13B — Corrosion: Materials (high-temperature corrosion of cast Fe-Cr-Ni alloys) — ASM International (2005)
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.