13CrMo4-5
1.7335
Low-alloy chromium-molybdenum steel for pressure equipment and elevated-temperature service · EN 10028-2:2017 — flat products for pressure purposes with specified elevated-temperature properties · EN 10028-1:2017 — general requirements for flat products for pressure purposes
13CrMo4-5, material number 1.7335, is a nominal 1Cr-0.5Mo ferritic pressure-vessel steel used where carbon or simple Mo steels do not provide sufficient elevated-temperature strength. Under EN 10028-2 it is principally a flat-product grade supplied normalized and tempered, with thickness-dependent tensile requirements, specified proof strength up to 500 °C, and informative long-duration creep data. Its successful use depends on controlling welding and post-weld heat treatment, accounting for possible service embrittlement around 400–500 °C, and applying the appropriate pressure-equipment design code rather than treating the material standard as a service-temperature approval.
- 1.7335Material number · The steel name and material number identify the same EN grade.
- Approximately 1% Cr and 0.5% MoNominal alloy concept · Chromium and molybdenum improve elevated-temperature strength; the alloy content is not high enough to make the steel stainless.
- +NTUsual delivery condition · Normalized and tempered; properties must be associated with the specified delivery and test condition.
- 450–600 MPa for t ≤ 60 mmRoom-temperature tensile range · EN 10028-2 transverse requirement; 440–590 MPa applies for 60 < t ≤ 100 mm.
- 31 J minimum at +20 °CCharpy requirement · Transverse KV2 requirement; lower-temperature values require agreement.
- Possible embrittlement at approximately 400–500 °CCritical service consideration · A step-cooling test can be specified when temper-embrittlement susceptibility is important.
Overview
- Designation system
- EN steel name according to EN 10027; numerical designation according to EN 10027-2
- Product forms
- Hot-rolled plate, Sheet and strip within the dimensional scope and availability of EN 10028
- Condition
- +NT — normalized and tempered; usual condition under EN 10028-2, +QT — quenched and tempered, where agreed, Normalized, tempered or untreated delivery only by specific agreement, with testing in the usual condition
Definition and scope of the grade
EN 10028-2 defines 13CrMo4-5 as an alloy special steel for flat products used in pressure equipment with specified elevated-temperature properties. The designation convention indicates approximately 0.13% nominal carbon and chromium-molybdenum alloying at about the 1Cr-0.5Mo level. The grade is commonly selected for boilers, pressure vessels, heat exchangers and process equipment operating at temperatures where creep resistance and retention of proof strength matter.
EN 10028-2 covers flat products. The same steel name and material number also appear in separate standards for seamless tubes, pressure-purpose forgings and hot-rolled bars, but those standards have their own chemistry, heat-treatment, dimensional and mechanical-property provisions. A tube, forging or bar must therefore be ordered to its applicable product standard, not merely as “1.7335.”
Specified chemical composition
| Element | Requirement | Metallurgical or purchasing significance |
|---|---|---|
| C | 0.08–0.18 | Controls strength and hardenability; the permitted range is too wide to infer weldability from the grade name alone. |
| Si | ≤ 0.35 | Deoxidizing and strengthening element. |
| Mn | 0.40–1.00 | Contributes to strength and hardenability. |
| P | ≤ 0.025 | Residual element; lower levels may be desirable where temper embrittlement is a concern. |
| S | ≤ 0.010 | Controlled for cleanliness, toughness and weldability. |
| Al total | Reported | No general numerical range is specified for this grade; the cast value is determined and stated in the inspection document. |
| N | ≤ 0.012 | Maximum nitrogen content. |
| Cr | 0.70–1.15 | Provides oxidation and elevated-temperature strength benefits; a minimum of 0.80% may be agreed when resistance to pressurized hydrogen is important. |
| Cu | ≤ 0.30 | A lower Cu limit or a Cu-plus-Sn restriction may be agreed where hot formability is important. |
| Mo | 0.40–0.60 | Principal contributor to creep strength and resistance to softening at elevated temperature. |
These are cast-analysis requirements. Product analysis is assessed using the permissible deviations in EN 10028-2 and must not be judged directly against the cast limits without applying those tolerances. Elements not listed are not to be intentionally added without purchaser agreement, except as required for finishing the heat.
Delivery condition and heat-treatment sensitivity
The usual EN 10028-2 condition is +NT, normalized and tempered. +QT may be agreed where the standard permits it. Other delivery conditions, including normalized, tempered or exceptionally untreated material, require explicit agreement; testing is then performed on specimens brought to the usual specified condition. This distinction matters because as-supplied hardness or tensile results from non-standard delivery cannot be assumed to represent the final pressure-equipment condition.
| Operation | Temperature | Status |
|---|---|---|
| Normalizing | 890–950 °C | Guidance from the standard's informative annex, not a universal fabrication cycle. |
| Tempering | 630–730 °C | An appropriate hold is required after the full section reaches temperature. |
Actual furnace cycles depend on thickness, equipment, manufacturing route and required properties. Forming heat treatment and PWHT can change the original +NT properties, so the complete thermal history must be considered during procedure qualification and purchasing.
Mechanical properties of EN 10028-2 flat products
| Nominal thickness t | Minimum yield strength ReH | Tensile strength Rm | Minimum elongation A |
|---|---|---|---|
| t ≤ 16 mm | 300 MPa | 450–600 MPa | 19% |
| 16 < t ≤ 60 mm | 290 MPa | 450–600 MPa | 19% |
| 60 < t ≤ 100 mm | 270 MPa | 440–590 MPa | 19% |
| Test temperature | Minimum KV2 | Qualification |
|---|---|---|
| +20 °C | 31 J | Standard minimum for full-size transverse specimens. |
| 0 °C | By agreement | An additional value can be specified at enquiry and order. |
| −20 °C | By agreement | Not an automatic low-temperature toughness qualification. |
The EN 10028-2 mechanical-property range for this flat-product grade ends at 100 mm nominal thickness. Material outside the stated dimensional scope requires another supported specification or a separately qualified technical agreement; properties must not simply be extrapolated.
Elevated-temperature strength and creep behaviour
The defining advantage of 13CrMo4-5 over ordinary pressure-vessel carbon steel is improved retention of strength at temperature and useful creep resistance. EN 10028-2 specifies minimum 0.2% proof strength at elevated temperature. The following values reproduce the standard basis commonly published for flat product in the indicated thickness groups.
| Proof strength (MPa) | 50 °C | 100 °C | 150 °C | 200 °C | 250 °C | 300 °C | 350 °C | 400 °C | 450 °C | 500 °C |
|---|---|---|---|---|---|---|---|---|---|---|
| Minimum Rp0.2 for t ≤ 16 mm | 294 | 285 | 269 | 252 | 234 | 216 | 200 | 186 | 175 | 164 |
| Proof strength (MPa) | 50 °C | 100 °C | 150 °C | 200 °C | 250 °C | 300 °C | 350 °C | 400 °C | 450 °C | 500 °C |
|---|---|---|---|---|---|---|---|---|---|---|
| Minimum Rp0.2 for t > 16 mm within the applicable product range | 285 | 275 | 260 | 243 | 226 | 209 | 194 | 180 | 169 | 159 |
| Temperature | 1% creep strain, 10,000 h | 1% creep strain, 100,000 h | Creep rupture, 10,000 h | Creep rupture, 100,000 h | Creep rupture, 200,000 h |
|---|---|---|---|---|---|
| 450 °C | 245 MPa | 191 MPa | 370 MPa | 285 MPa | 260 MPa |
| 500 °C | 157 MPa | 98 MPa | 239 MPa | 137 MPa | 115 MPa |
| 550 °C | 76 MPa | 36 MPa | 109 MPa | 49 MPa | 39 MPa |
| 570 °C | 53 MPa | 24 MPa | 76 MPa | 33 MPa | 26 MPa |
The Annex C creep values are informative mean values with a stated scatter band of approximately ±20%; they are not guaranteed minimum properties, allowable stresses or service-temperature limits. Pressure design must use the allowable stresses, time basis and damage rules of the governing construction code. Oxidation, cyclic operation, weldments and accumulated creep damage must also be considered.
Embrittlement, hydrogen and environmental limits
EN 10028-2 warns that Cr-Mo steels may become brittle during service at approximately 400–500 °C. The concern is a shift in the ductile-to-brittle transition behaviour rather than simple loss of room-temperature tensile strength. For equipment with severe long-term exposure, a step-cooling test and agreed acceptance procedure can be specified at the time of enquiry and order.
Two hydrogen-related issues should not be confused. For pressurized-hydrogen applications, EN 10028-2 allows agreement of a minimum 0.80% chromium content. For wet H2S or sour environments, a hydrogen-induced cracking test to EN 10229 can be ordered using the acceptance classes in EN 10028-2 Annex D. Neither provision alone establishes suitability for a particular hydrogen or sour-service duty; the applicable equipment and environmental standard remains controlling.
13CrMo4-5 is not a stainless steel. Its chromium content provides only limited oxidation benefit and does not confer general aqueous-corrosion resistance. Corrosion allowance, cladding, lining or another alloy may be needed depending on the process environment.
Welding and post-weld heat treatment
13CrMo4-5 belongs to ISO/TR 20172 material group 5.1, the nominal 1Cr-0.5Mo group. It is weldable using qualified procedures, but its greater hardenability than carbon pressure-vessel steel makes control of hydrogen, heat input, preheat, interpass temperature and cooling rate important. Filler-metal selection must address both room-temperature toughness and elevated-temperature weld-metal performance. Universal preheat or PWHT values should not be assigned solely from the grade designation; thickness, restraint, hydrogen level, process, construction code and service condition all affect the required procedure.
| Parameter | Value | Interpretation |
|---|---|---|
| Critical parameter Pcrit | 18.5 | Excessive PWHT above this parameter can reduce mechanical properties. |
| Illustrative stress relief pair | 650 °C for 1 h | Pair corresponding to the critical parameter; not an automatic recommended cycle. |
| Illustrative stress relief pair | 635 °C for 2 h | Pair corresponding to the critical parameter; not an automatic recommended cycle. |
If the intended fabrication heat treatment exceeds the critical time-temperature parameter, the purchaser should notify the plate manufacturer and consider tests on specimens subjected to the simulated complete thermal cycle. This is particularly important when multiple PWHT cycles, repair welding or long furnace holds are anticipated.
Ordering, inspection and substitution control
| Item | What to state or verify |
|---|---|
| Specification | EN 10028-2 edition together with EN 10028-1. |
| Material identity | 13CrMo4-5 and/or 1.7335. |
| Dimensions | Thickness, width, length, dimensional tolerances and mass basis. |
| Delivery condition | +NT unless another permitted condition is explicitly agreed. |
| Inspection document | Required EN 10204 document type, commonly 3.1 or project-specified 3.2. |
| Toughness | Required test temperature, impact energy and specimen location if the standard +20 °C requirement is insufficient. |
| Fabrication thermal cycle | Expected forming heat treatment, PWHT temperature, duration and number of cycles. |
| Internal soundness and surface quality | Required acceptance standard and class; these should not be assumed from the grade alone. |
| Special environments | HIC class for sour service, step-cooling test, or minimum 0.80% Cr for relevant pressurized-hydrogen duty. |
| Additional options | Any Cu/Sn limitation, 40 J impact requirement, +QT delivery or mid-thickness impact testing. |
Review the inspection certificate against the ordered standard, product form, heat number, dimensions, delivery condition, cast chemistry and thickness-dependent mechanical requirements. Confirmation of the steel name alone is insufficient. Traceability through cutting and fabrication is especially important for pressure equipment.
Do not approve substitution solely from a cross-reference table. Chemistry, tensile class, heat treatment, toughness, creep basis, product-form standard, code allowables and certification must all be reconciled before interchangeability is accepted.
Sources
- DIN EN 10028-2:2017-10 — Flat products made of steels for pressure purposes, Part 2DIN Media
- EN 10028-2:2017 — Standard previewSIST / iTeh Standards
- BS EN 10028-2:2017 — Flat products made of steels for pressure purposesBritish Standards Institution
- ISO/TR 20172:2009 — Welding: Grouping systems for materialsInternational Organization for Standardization
- 13CrMo4-5 heat-resistant pressure-vessel steel, edition 08/2022Salzgitter Flachstahl GmbH
- SIQUAL 7335 technical data sheet, 2023SIJ ACRONI
- EN 10222-2:2017 — Steel forgings for pressure purposes, Part 2SIST / iTeh Standards
- EN 10216-2:2024 — Seamless steel tubes for pressure purposes, Part 2SIST / iTeh Standards
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