What's the difference between an H-grade and a stabilised grade?

An H-grade (304H, 316H) simply has carbon kept at the high end of the range for better creep resistance. A stabilised grade (321H, 347H) additionally adds titanium or niobium to pin down that carbon.

Why is chromium carbide precipitation a problem?

Because it locally depletes chromium at grain boundaries, a phenomenon called sensitisation, which sharply reduces intergranular corrosion resistance at that specific spot — often near a weld.

Are these grades more expensive than standard grades?

Slightly, due to tighter composition control and sometimes the addition of titanium or niobium. The premium remains modest compared with duplex or nickel families, and is justified as soon as high-temperature creep comes into play.

My H-grade or stabilised grade isn't listed — what should I do?

This family partly overlaps the austenitic one (321H and 347H also appear there) — other variants exist depending on standard and mill. Send us your exact designation via a quote request.

GRADE FAMILY

H-grades and stabilised grades

H-grades (304H, 316H) have carbon controlled at the high end of the range for better high-temperature creep resistance; stabilised grades (321H, 347H) add titanium or niobium to pin down carbon and prevent intergranular corrosion after welding. Boilers, biomass plants and prolonged creep are their territory.

What is an H-grade or stabilised grade?

H-grades and stabilised grades are variants of austenitic steels optimised for prolonged high temperature rather than aqueous corrosion. H-grades keep carbon at the high end of the range for better creep resistance; stabilised grades add titanium or niobium to prevent chromium from precipitating as carbides at grain boundaries during prolonged exposure to temperature.

When to choose this family — and when not to?

Choose it for boilers, biomass plants and any equipment subject to prolonged high-temperature creep, where a standard grade would risk a progressive loss of mechanical strength. Avoid it for room-temperature or moderate-temperature use: a standard grade (304L, 316L) is sufficient and costs less.

Grades in this family

The grades listed are examples, never a closed catalogue — every grade belongs to one of the nine families, which is what makes this claim reliable.

Examples in the h-grades and stabilised grades family (familles-nuances.json), EN and PREN filled in from nuances-inox.json when the entry exists — not a closed catalogue
Grade (example)	EN	Indicative PREN
304H	—	—
316H	—	—
321H	—	—
347H	no exact equivalent	17–19 †

† PREN is calculable but not the deciding factor for this grade, see the note below.

PREN caveats (†)

347H: ⚠️ PREN is not the deciding factor for this grade. 347H is chosen for creep resistance and stabilisation, not aqueous corrosion — its pitting resistance is at the level of a 304.

Typical applications for this family: Creep resistance · Boilers · Biomass.

My grade isn't listed →

Available forms and dimensions

Welded and seamless tube, heat-exchanger tube, fittings, flanges and bars available depending on grade through our partner mills, for high-temperature fabrication. Precise dimensions are not yet documented in our structured reference data for this family: send us your requirement (diameter, wall thickness, length) via a quote request — we check with our partner mills and confirm within 2 to 3 business days.

Applicable standards

ASTM A312/A312M
ASTM A213/A213M
ASME SA312
ASME SA213
EN 10216-5

Frequently asked questions

What's the difference between an H-grade and a stabilised grade?: An H-grade (304H, 316H) simply has carbon kept at the high end of the range for better creep resistance. A stabilised grade (321H, 347H) additionally adds titanium or niobium to pin down that carbon.
Why is chromium carbide precipitation a problem?: Because it locally depletes chromium at grain boundaries, a phenomenon called sensitisation, which sharply reduces intergranular corrosion resistance at that specific spot — often near a weld.
Are these grades more expensive than standard grades?: Slightly, due to tighter composition control and sometimes the addition of titanium or niobium. The premium remains modest compared with duplex or nickel families, and is justified as soon as high-temperature creep comes into play.
My H-grade or stabilised grade isn't listed — what should I do?: This family partly overlaps the austenitic one (321H and 347H also appear there) — other variants exist depending on standard and mill. Send us your exact designation via a quote request.