Stainless Steel HT
UNS N08605
HT is a high-nickel, moderate-chromium heat-resistant cast steel supplied to ASTM A297/A351/A743 as Grade HT (UNS N08605).
Reference datasheet — HT is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the AS-CAST condition
HT tempers and conditions
HT is supplied in 4 conditions, soft to hard. AS-CAST is the default FabDigit quotes; the values on this page are for it.
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 |
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?
HT is a high-nickel, moderate-chromium heat-resistant cast steel supplied to ASTM A297/A351/A743 as Grade HT (UNS N08605). Engineers specify it for resistance to carburization and thermal cycling in furnace atmospheres up to 1100 °C, and it is available only as castings — sand, investment or centrifugal — in as-cast, aged, HT30 and HT50-centrifugal conditions. Ductility is low (275 MPa yield, 485 MPa tensile, 10 % elongation, 180 HB), primary carbides make machining abrasive, and parts that have seen service weld poorly once carburized or sigma-embrittled. HK (25Cr-20Ni) is the nearest alternative where oxidation strength matters more than carburization resistance. HT 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). HT has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 485 MPa (70.3 ksi) — weaker than 77% of stainless steel grades. Elongation at break is 10% and the elastic modulus is 175 GPa (25.4 Msi).
What is HT used for?
- carburizing furnace fixtures
- radiant tubes
- heat-treatment retorts
Advantages
- High service temperature — 1,100°C (2,012 °F), better than 96% of stainless steel grades
Limitations
- Low stiffness — 175 GPa (25.4 Msi), worse than 99% of stainless steel grades
- Limited formability — 5/100, worse than 99% of stainless steel grades
- Hard to polish — 40/100, worse than 99% of stainless steel grades
- Limited ductility — 10%, worse than 98% of stainless steel grades
- Low electrical conductivity — 1.7 % IACS, worse than 93% of stainless steel grades
HT properties
Typical room-temperature values for HT-AS-CAST; bars are the position among stainless steel grades.
Physical3
HT 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 has a yield strength of 275 MPa (39.9 ksi) and a tensile strength of 485 MPa (70.3 ksi) — weaker than 77% of stainless steel grades. Elongation at break is 10% and the elastic modulus is 175 GPa (25.4 Msi).
Thermal5
HT is rated for continuous service to 1,100°C (2,012 °F). It conducts heat at 12.5 W/m·K (7.22 BTU/hr·ft·°F), worse than 90% of stainless steel grades. Thermal expansion is 14.7 µm/m·K (8.17 µin/in·°F).
Electrical3
HT conducts electricity at 1.7 % IACS, worse than 93% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (55/100), worse than 71% of stainless steel grades.
Sustainability4
Producing a kilogram of HT 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's machinability is poor (25/100, worse than 88% of stainless steel grades); weldability fair (35/100); formability not recommended (5/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. HT is highlighted; hover a dot for its name, or open the interactive family chart.
Working with HT
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.
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 |
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.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel HT in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- N08605
How much does HT cost?
HT is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
HT — frequently asked
What is HT used for?
HT 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?
HT has a typical yield strength of 275 MPa (39.9 ksi) and a tensile strength of 485 MPa (70.3 ksi) — weaker than 77% of stainless steel grades. Strength varies by condition: see the 4 listed tempers.
Is HT easy to machine?
Not especially — machinability is rated poor (25/100, worse than 88% 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 be welded?
With care — weldability is rated fair (35/100). 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?
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 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?
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 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.
How much does HT cost?
HT is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.