Short answer: heat-resistant (heat-resisting) steel is designed to resist oxidation and scaling in hot gases, up to about 1000–1150 °C, when mechanical loads are low. Creep-resistant steel is designed to carry sustained loads and pressure at high temperature without slowly deforming, typically at 450–650 °C (austenitic creep grades higher). The first is chosen for furnace parts and flue gas systems, the second for boiler tubes, steam lines, pressure vessels and bolts.
Heat-resistant vs creep-resistant steel: key differences
| Feature | Heat-resistant steel | Creep-resistant steel |
|---|---|---|
| Main task | Resist oxidation, scaling and hot-gas corrosion | Keep strength and shape under long-term load at temperature |
| Key alloying elements | High Cr (13–28%), Si, Al; Ni in austenitic grades | Mo, Cr, V, Nb, W; in austenitic grades also Ni and higher carbon |
| Protection mechanism | Dense, adherent Cr₂O₃ (and SiO₂/Al₂O₃) scale | Solid-solution strengthening and stable carbides/nitrides that block dislocation movement |
| Typical temperature | Up to 800–1150 °C, depending on grade | About 450–650 °C (ferritic Cr-Mo), up to about 700 °C and above for austenitic grades |
| Design data | Maximum scaling temperature in air | Creep rupture strength (e.g. 100,000 h) and creep strain limits |
| Main standards | EN 10095, ASTM A240 / A312 (309S, 310S) | EN 10216-2, EN 10028-2, EN 10302, ASTM A335 / A213 |
| Is it stainless? | Yes, all common grades are stainless | Not always: 16Mo3, 13CrMo4-5 and P91 are alloy steels, 304H and 321H are stainless |
| Typical parts | Furnace muffles, grates, radiant tubes, burners, flue ducts, heat shields | Superheater and reheater tubes, steam piping, headers, pressure vessels, turbine casings, high-temperature bolts |
What is heat-resistant steel?
Heat-resistant steel is used where the main threat is hot, oxidizing or sulfur-containing gas. At high temperature, chromium (supported by silicon and aluminum) forms a dense oxide scale that slows further oxidation. The higher the service temperature, the more chromium is needed. Ferritic heat-resistant grades are cheaper and resist sulfur well; austenitic grades with nickel have better strength and ductility at temperature.
Heat-resistant grades still lose strength quickly above about 600 °C. They suit parts that carry little more than their own weight. Read more about applications in Heat-resistant steel: properties and industrial uses.
Common heat-resistant grades and scaling temperatures
| EN number | Designation | AISI / common name | Structure | Max. scaling temperature in air (approx.) |
|---|---|---|---|---|
| 1.4724 | X10CrAlSi13 | – | Ferritic | 850 °C |
| 1.4742 | X10CrAlSi18 | – | Ferritic | 1000 °C |
| 1.4762 | X10CrAlSi25 | – | Ferritic | 1150 °C |
| 1.4749 | X18CrN28 | 446 type, 15X25T equivalent | Ferritic | 1100 °C |
| 1.4828 | X15CrNiSi20-12 | 309 type | Austenitic | 1000 °C |
| 1.4833 | X12CrNi23-13 | 309S | Austenitic | 1000 °C |
| 1.4845 | X8CrNi25-21 | 310S | Austenitic | 1050 °C |
| 1.4841 | X15CrNiSi25-21 | 314 | Austenitic | 1150 °C |
Values are guide figures for clean air; sulfur, carburizing atmospheres, thermal cycling and load reduce the usable limit. More on the ferritic grade 1.4749 in Steel 15X25T as equivalent of 1.4749.
What is creep-resistant steel?
Creep is slow, permanent deformation of a metal under constant stress at high temperature. A tube that is perfectly safe at 20 °C can, at 550 °C and under pressure, stretch a little every hour until it bulges or ruptures years later. Creep-resistant steels are alloyed with molybdenum, chromium, vanadium, niobium and tungsten, which strengthen the matrix and form fine, stable carbides and nitrides that pin dislocations. Design is based on creep rupture strength, for example the stress that causes rupture after 100,000 hours at a given temperature.
Common creep-resistant grades
| Grade (EN) | ASTM / ASME | Type | Typical upper service temperature |
|---|---|---|---|
| 16Mo3 (1.5415) | ~ A335 P1 / A204 | Mo alloy steel, not stainless | about 500–530 °C |
| 13CrMo4-5 (1.7335) | A335 P11 / P12 | Cr-Mo alloy steel | about 550–560 °C |
| 10CrMo9-10 (1.7380) | A335 P22 | Cr-Mo alloy steel | about 580 °C |
| X10CrMoVNb9-1 (1.4903) | A335 P91 | 9% Cr martensitic, CSEF | about 600–620 °C |
| X6CrNi18-10 (1.4948) | 304H | Austenitic stainless | about 600–700 °C |
| X6CrNiTiB18-10 (1.4941) | 321H | Austenitic stainless, Ti-stabilized | about 600–700 °C |
Upper temperatures depend on the stress, the required life and the design code (EN 13480, EN 12952, ASME B31.1). Exceeding the design temperature by even 20–30 °C can cut creep life by a factor of several.
Where the two groups overlap
The split is not absolute. Austenitic heat-resistant grades such as 1.4845 (310S) and 1.4841 also have useful creep strength, and creep-resistant austenitic grades such as 304H and 321H resist oxidation well up to about 800 °C. Alloy 800H (1.4958/1.4959) combines both properties and is used for petrochemical furnace tubes. Above 800–900 °C under load, cast heat-resistant alloys and nickel alloys take over.
How to choose: three practical cases
- Furnace muffle, heat shield or flue duct (900–1100 °C, low load): heat-resistant steel such as 1.4828, 1.4845 or 1.4841; ferritic 1.4762 or 1.4749 where sulfur is present and loads are very low.
- Steam line or superheater tube in a power plant (500–600 °C, high pressure): creep-resistant 13CrMo4-5, 10CrMo9-10 or P91, sized according to creep data.
- Petrochemical or heat-treatment equipment under load at 600–800 °C: austenitic grades with creep data, such as 321H, 304H, 1.4845 or Alloy 800H.
A simple rule: if hot gas is the main enemy and the part carries little load, choose heat-resistant steel; if the part carries pressure or load at temperature and must not deform, choose creep-resistant steel and design with creep rupture values.
What about fire resistance?
Fire is a short-term event, not continuous service, so fire design uses different data. In a fire, austenitic stainless steels such as 304 and 316 retain a higher share of their strength and stiffness than carbon structural steel above about 550 °C; reduction factors are given in EN 1993-1-2. For permanent furnace service, however, use the heat-resistant grades above.
FAQ
Is creep-resistant steel the same as heat-resistant steel?
No. Heat-resistant steel resists oxidation at high temperature; creep-resistant steel keeps its strength under sustained load at high temperature. Some austenitic grades do both reasonably well.
What temperature can creep-resistant steel handle?
It depends on stress and required life: roughly up to 530 °C for 16Mo3, about 560 °C for 13CrMo4-5, 600–620 °C for P91 and higher for austenitic grades such as 304H and 321H.
Is 304 stainless steel heat-resistant?
304 resists scaling in air up to about 870 °C in intermittent and about 925 °C in continuous service, but it is not designed for continuous high-temperature service under load. Use 304H or 321H for creep service and 309S/310S or 1.4841 for high-temperature oxidation.
What is the difference between heat-resisting and heat-resistant steel?
None; both terms describe the same group of steels covered by EN 10095. "Scale-resisting steel" is an older name for the same thing.