What Is 1.7375 (12CrMo9-10) Steel?
1.7375 is the European material number (per EN 10027-2) for the alloy steel designated 12CrMo9-10. It is a ferritic chromium-molybdenum (Cr-Mo) steel containing nominally 2.25% chromium and 1.0% molybdenum, standardized under EN 10028-2 for flat and forged products for pressure purposes. Its ASTM equivalent is ASTM A182 Grade F22. The steel is designed for continuous elevated-temperature service up to approximately 540°C in boilers, pressure vessels, and piping systems.
The 1.7375 material number is assigned by the EN 10027-2 numbering system, where the prefix 1.7xxx identifies heat-treatable steels alloyed with chromium and molybdenum. Its compositional designation, 12CrMo9-10, encodes the chemistry directly: the leading "12" approximates the carbon content in hundredths of a percent (0.12%), "Cr9" indicates approximately 2.25% chromium (9/4 = 2.25), and "10" indicates approximately 1.0% molybdenum. This naming logic allows engineers to decode the approximate alloy chemistry directly from the grade designation without consulting a datasheet.
1.7375 belongs to the ferritic Cr-Mo family of pressure steels, a group that also includes 1.7335 (13CrMo4-5), 1.7380 (10CrMo9-10), and 1.7383 (11CrMo9-10). Among these, 1.7375 occupies the niche defined by the need for service above 480°C and below 560°C — particularly in hydrogen-partial-pressure environments where lower-alloy grades are unsafe per the API 941 Nelson curve.
The 2.25Cr-1Mo composition was developed specifically for applications above 480°C where plain carbon steels lose strength, and above the safe operating boundary of 1Cr-0.5Mo grades for hydrogen service. Chromium provides oxidation resistance and stabilizes fine carbides; molybdenum raises creep rupture strength through solid-solution hardening and by retarding carbide coarsening. The result is a steel capable of continuous duty in conditions that degrade carbon-grade forgings within their intended design life.
Jiangsu Liangyi Co.,Limited manufactures custom 1.7375 forged components — including open die forgings, seamless rolled rings, discs, and machined parts — from 30 kg to 30,000 kg, in EN 10028-2 and ASTM A182 F22 compliance.
12CrMo9-10 Chemical Composition (EN 10028-2)
The chemical composition of 1.7375 (12CrMo9-10) per EN 10028-2 by weight percentage (ladle analysis) is: C 0.10–0.15%, Si ≤0.50%, Mn 0.30–0.60%, P ≤0.025%, S ≤0.010%, Cr 2.00–2.50%, Mo 0.90–1.10%, Ni ≤0.30%, Cu ≤0.20%, Al ≤0.020%.
| Element | Symbol | EN 10028-2 Range (wt%) | Metallurgical Function |
|---|---|---|---|
| Carbon | C | 0.10 – 0.15 | Hardness, carbide formation, creep strength; controlled low for weldability |
| Silicon | Si | ≤ 0.50 | Deoxidizer; minor oxidation resistance improvement |
| Manganese | Mn | 0.30 – 0.60 | Hardenability; sulfide morphology control |
| Phosphorus | P | ≤ 0.025 | Impurity — low limit prevents temper embrittlement |
| Sulfur | S | ≤ 0.010 | Impurity — low limit minimizes MnS inclusion stringers in forgings |
| Chromium | Cr | 2.00 – 2.50 | Oxidation resistance; carbide stabilization; corrosion resistance in H₂ service |
| Molybdenum | Mo | 0.90 – 1.10 | Primary creep strength driver; solid-solution hardening; retards carbide coarsening |
| Nickel | Ni | ≤ 0.30 | Residual; improves low-temperature toughness |
| Copper | Cu | ≤ 0.20 | Residual; controlled to avoid hot-rolling surface cracking |
| Aluminum | Al | ≤ 0.020 | Grain refiner/deoxidizer; excess impairs creep properties |
The Engineering Logic Behind the Carbon Window
The narrow carbon specification of 0.10–0.15% is not arbitrary. Carbon above 0.15% increases hardness after normalizing but reduces ductility and significantly complicates field welding — both unacceptable for large pressure components requiring post-weld heat treatment. Carbon below 0.10% erodes tensile strength from solid-solution effects and reduces the fine carbide precipitation that contributes to creep resistance. The 0.10–0.15% window is the optimized engineering balance between these competing requirements.
The molybdenum band of 0.90–1.10% similarly reflects decades of service experience: above 1.1%, diminishing creep returns accompany increased susceptibility to embrittlement; below 0.9%, the solid-solution strengthening contribution at service temperatures above 500°C deteriorates meaningfully.
1.7375 Mechanical Properties at Room and Elevated Temperature
The mechanical properties of 1.7375 (12CrMo9-10) in the normalized and tempered (N+T) condition per EN 10028-2, for forged product up to 150mm thickness, are: tensile strength 490–640 MPa, 0.2% proof strength ≥310 MPa, elongation ≥18%, Charpy V impact ≥41 J at +20°C, and Brinell hardness 143–187 HBW.
| Property | Symbol | Value | Test Condition |
|---|---|---|---|
| Tensile Strength | Rm | 490 – 640 MPa | RT, longitudinal |
| 0.2% Proof Strength | Rp0.2 | ≥ 310 MPa | RT, longitudinal |
| Elongation | A | ≥ 18 % | L₀ = 5.65√S₀, longitudinal |
| Reduction of Area | Z | ≥ 45 % | Longitudinal |
| Impact Energy (Charpy V) | KV | ≥ 41 J | +20°C, transverse, average of 3 |
| Brinell Hardness | HBW | 143 – 187 | N+T condition |
Elevated Temperature Proof Strength — Design Values
For pressure equipment design per EN 13445 or ASME VIII, the 0.2% proof strength at operating temperature is the primary design parameter below the creep regime. The following values are representative of 1.7375 in N+T condition:
Creep Rupture Strength
In continuous service above 450°C, the governing design parameter shifts from proof strength to creep rupture strength — the stress producing rupture after 100,000 hours (the standard design life in EN 13445 and ASME power boiler codes). For 1.7375 at 550°C, the 100,000-hour creep rupture strength is approximately 60–80 MPa, representing a decisive advantage over 1.7335 (13CrMo4-5) and the primary justification for specifying this grade in superheater headers and steam manifolds.
12CrMo9-10 in sustained high-temperature service is susceptible to temper embrittlement — a shift in the ductile-to-brittle transition temperature caused by grain boundary segregation of phosphorus, tin, antimony, and arsenic over time. Modern steel practice controls P to ≤0.010% and specifies the Bruscato X-bar factor (X = 10P + 5Sb + 4Sn + As, all in ppm; X ≤15 for critical applications) to mitigate this risk. Specifying a step-cooling embrittlement assessment for continuous high-temperature service is good engineering practice.
Heat Treatment of 1.7375 (12CrMo9-10) Forgings
1.7375 forgings are supplied in the normalized and tempered (N+T) or quenched and tempered (Q+T) condition. Normalizing is performed at 900–960°C followed by air cooling; tempering at 680–750°C, minimum 1 hour per 25mm section (not less than 2 hours). Q+T is preferred for sections exceeding approximately 100mm.
Normalizing — 900–960°C
The forged component is austenitized by heating to 900–960°C and held for a time sufficient to achieve uniform through-section temperature (typically 1 hour per 25mm of ruling section, minimum 2 hours). Air cooling follows, producing a refined ferritic-bainitic microstructure free from as-forged segregation. Normalizing dissolves coarse carbides formed during forging and resets grain structure, directly improving strength uniformity and subsequent tempering response.
Tempering — 680–750°C
After returning to ambient temperature, the forging is reheated to 680–750°C and held for minimum 1 hour per 25mm of section (not less than 2 hours). This converts the hard, brittle bainite/martensite formed during normalizing into a tough, tempered microstructure with well-distributed fine carbides. Tempering below 680°C produces insufficient softening and leaves the steel prone to creep embrittlement; above 750°C risks approaching the Ac₁ transformation point, which can partially re-austenitize surface layers and destroy the established microstructure.
Quench & Temper (Q+T) — For Heavy Sections
For sections exceeding ~100mm ruling section, or where enhanced through-thickness property uniformity is required, the forging is austenitized at 900–960°C and water or polymer quenched to increase hardening depth, then immediately tempered at 680–750°C before the component cools below the martensite start temperature (Ms ≈ 350°C). Q+T 1.7375 consistently exceeds minimum impact energy requirements and shows improved Charpy transition temperature compared to normalized equivalents.
Stress Relief (SR) — Post-Machining or Post-Welding
A stress relief anneal at 600–660°C (below the tempering temperature to avoid over-tempering) may be specified after rough machining or as the basis for post-weld heat treatment. This operation minimizes residual stress and distortion in the final machined product.
How 1.7375 (12CrMo9-10) Is Forged
The forging process for 1.7375 is performed between 1,050°C and 1,250°C with a minimum finish forging temperature above 900°C. For pressure-service components, the minimum reduction ratio from ingot is 4:1; for hydrogen or fatigue-critical service, 6:1 or above.
Starting Stock and Melting Practice
For critical pressure-service 1.7375 forgings, starting stock is produced via EAF + LF + VD (electric arc furnace + ladle furnace secondary refining + vacuum degassing). This triple process removes hydrogen (preventing internal cracking in large sections), minimizes oxide inclusions, and controls sulfur to ≤0.010%. For components requiring EN 10228-3 Class 4 ultrasonic testing, ESR (electroslag remelting) of the ingot further reduces macrosegregation and inclusion content.
Open Die Forging vs Seamless Rolled Rings
| Process | Typical Geometry | Weight Range | Primary Advantage |
|---|---|---|---|
| Open Die Forging | Bars, blocks, shafts, discs, custom shapes | 30 kg – 30,000 kg | Maximum shape flexibility; highest reduction ratios; optimum internal soundness |
| Seamless Ring Rolling | Flanges, rings, headers, cylindrical bodies | 30 kg – 15,000 kg | Circumferential grain flow aligned with hoop stress direction; ideal for ring-form pressure components |
Both processes are available for 1.7375 supply. For a full breakdown of geometry ranges, weight limits, and delivery conditions, see the available product forms for 1.7375 (12CrMo9-10) forgings on the product page.
Reduction Ratio and Internal Soundness
The forging reduction ratio (ratio of starting cross-section to final cross-section) governs closure of internal porosity and refinement of the as-cast ingot structure. For 1.7375 pressure components:
NDT Standards for 12CrMo9-10 Forgings
Ultrasonic testing of 1.7375 forgings is performed per EN 10228-3 (or ASTM A388 for ASME-coded equipment). For standard pressure vessel forgings, Quality Class 3 (FBH Ø 4mm) is the baseline. For hydrogen or fatigue-critical components, Quality Class 4 (FBH Ø 2mm) is specified.
| Quality Class | Max Single Indication FBH Ø | Typical Application |
|---|---|---|
| Class 1 | FBH Ø 8 mm | Low-criticality structural components |
| Class 2 | FBH Ø 6 mm | General pressure vessel forgings, lower criticality |
| Class 3 | FBH Ø 4 mm | Standard pressure-boundary 1.7375 forgings in steam and gas service |
| Class 4 | FBH Ø 2 mm | Hydrogen service (hydroprocessing), rotating equipment, safety-critical pressure components |
Surface NDT — Magnetic Particle Testing (MT)
Surface and near-surface discontinuities are detected by magnetic particle testing (MT) per EN 10228-1. For 1.7375, MT is preferred over penetrant testing (PT) due to the ferromagnetic nature of the steel. AC yoke method MT reliably detects linear indications of 1–2mm length at the surface and up to approximately 3mm depth.
Material Test Certificate — EN 10204 Types
For pressure equipment compliance under PED 2014/68/EU, EN 13445, or ASME VIII, the appropriate MTC level is:
- EN 10204 Type 3.1: Inspection certificate issued and signed by the manufacturer's authorized inspection representative. This is Jiangsu Liangyi's standard certificate for all forgings.
- EN 10204 Type 3.2: Inspection certificate countersigned by an independent third-party inspector nominated by the buyer (e.g., TÜV, Bureau Veritas, SGS, Intertek). Required for nuclear, offshore, and safety-critical applications. Can be arranged upon request — the buyer typically nominates and engages the inspection body directly.
Welding 1.7375: Preheat, Fillers, and PWHT Requirements
Welding 1.7375 (12CrMo9-10) requires mandatory preheat at 200–250°C and post-weld heat treatment (PWHT) at 690–720°C. PWHT is required by EN 13445, ASME VIII, and PED 2014/68/EU for all pressure-boundary weldments. Filler metals are to AWS A5.5 E9018-B3 (SMAW) or AWS A5.28 ER90S-B3 (GMAW/GTAW), low-hydrogen classification H4 or better.
Preheat Requirements
Preheat of 200–250°C is mandatory for all thicknesses. The preheat temperature must be maintained as the interpass minimum throughout welding. Purpose: (1) slows HAZ cooling rate to prevent hydrogen-induced cold cracking in the martensitic HAZ; (2) reduces thermal gradient and welding residual stress; (3) promotes hydrogen diffusion from the joint before cooling to ambient temperature.
Post-Weld Heat Treatment (PWHT)
PWHT for 1.7375 weldments is performed at 690–720°C, held for minimum 1 hour per 25mm of weld thickness (minimum 2 hours). Functions: tempers hard HAZ microstructure, reduces residual welding stresses to safe levels, and allows hydrogen to diffuse safely from the joint. Failure to PWHT 1.7375 weldments is associated with stress corrosion cracking, hydrogen-assisted cracking, and premature creep damage in the heat-affected zone.
When 1.7375 is joined to austenitic stainless steel (e.g., 316L) in mixed-material systems, the PWHT temperature for the ferritic side must be checked against the sensitization risk for the austenitic side. In practice, an Inconel 82/182 buttering layer or dedicated ferritic-austenitic transition piece is specified to decouple the PWHT requirements of the two base materials.
1.7375 vs. Related Cr-Mo Grades: Selection Guide
1.7375 (12CrMo9-10) is the preferred grade when operating temperature exceeds 480°C or hydrogen partial pressure exceeds the 1Cr-0.5Mo Nelson curve limit. Below 480°C, 1.7335 (13CrMo4-5) is more cost-effective. Above 560°C, P91 or P92 should be evaluated.
ASTM / ASME Cross-Reference for 1.7375
| Standard | Designation | Product Form | Note |
|---|---|---|---|
| EN 10028-2 | 1.7375 / 12CrMo9-10 | Flat products (plate) | Primary European standard |
| ASTM A182 | Grade F22 | Forgings (flanges, fittings) | Closest forging equivalent |
| ASME SA182 | Grade F22 | Forgings (ASME code) | Same as A182; ASME acceptance |
| ASTM A335 | Grade P22 | Seamless pipe | Pipe form; composition equivalent |
| ASTM A387 | Grade 22 | Plate | Plate form; widely used in US vessels |
| DIN 17155 | 12 CrMo 9 10 | All forms | Older German designation; essentially identical composition |
Industry Applications of 1.7375 (12CrMo9-10) Forged Components
1.7375 (12CrMo9-10) forged components are used across power generation, oil refining, petrochemical processing, and pressure vessel fabrication industries wherever operating temperatures exceed 480°C or hydrogen service requirements eliminate lower-alloy alternatives.
Superheater headers, steam outlet manifolds, economizer headers, and drum nozzles in coal, biomass, and waste-to-energy boilers at 450–540°C.
High-pressure and intermediate-pressure turbine casings, valve chests, nozzle boxes, and steam inlet flanges subjected to thermal cycling with internal pressure.
Hydroprocessing reactor shells, high-pressure flanges, and nozzle forgings in high-temperature hydrogen environments above the 1Cr-0.5Mo Nelson curve.
Forged heads, thick-walled nozzles, and tube sheets for heat exchangers and reactors coded to ASME VIII, EN 13445, or PED 2014/68/EU.
High-temperature, high-pressure weld-neck flanges, fittings, and special-configuration forgings for critical piping per ASME B31.3.
Compressor casings, valve bodies, and heat exchanger shells for natural gas processing where temperature and pressure co-exist.
When to Specify 1.7375 (12CrMo9-10): Engineer's Checklist
Use this checklist to determine whether 12CrMo9-10 is the appropriate material selection for your application.
Conditions Strongly Favoring 1.7375
- Continuous operating temperature exceeds 480°C
- Hydrogen partial pressure exceeds the 1Cr-0.5Mo Nelson curve limit (per API 941) for your operating temperature
- Design life requirement is 100,000 hours or more without component replacement
- Cyclic thermal loading exceeds 500 start/stop cycles over the design life
- Wall thickness of the pressure boundary exceeds 50mm
- Code compliance requires EN 10028-2, ASTM A182 F22, or ASME SA182 F22 certification
Conditions Favoring an Alternative Grade
- Operating temperature below 450°C, no hydrogen service → consider 1.7335 (13CrMo4-5) at lower cost and better weldability
- Operating temperature above 560°C → evaluate P91 (X10CrMoVNb9-1) for superior creep performance
- Weldability is the primary fabrication constraint and preheat capability is restricted → consider 1.7335
- Aqueous corrosion resistance is the primary concern → consider duplex or austenitic stainless steel grades
- Cryogenic service below −20°C → this grade is not suitable; use nickel steel or austenitic alternatives
Frequently Asked Questions About 1.7375 (12CrMo9-10) Steel
1.7375 is the European material number (per EN 10027-2) for the alloy steel 12CrMo9-10, a ferritic chromium-molybdenum steel with 2.00–2.50% Cr and 0.90–1.10% Mo. It is standardized under EN 10028-2 for pressure vessel and boiler applications, with a continuous service temperature limit of approximately 540°C. Its ASTM equivalent is ASTM A182 Grade F22 (2.25Cr-1Mo).
The closest ASTM equivalent of 1.7375 (12CrMo9-10) is ASTM A182 Grade F22 / ASME SA182 F22, which specifies the 2.25Cr-1Mo composition for forged flanges, fittings, and valves in high-temperature service. For pipe, the equivalent is ASTM A335 Grade P22; for plate, ASTM A387 Grade 22. The DIN equivalent designation is 12 CrMo 9 10 per DIN 17155.
The practical maximum continuous operating temperature for 1.7375 (12CrMo9-10) is approximately 540°C. Above this temperature, creep rate accelerates and design becomes governed by creep rupture life rather than proof strength. For service above 560°C, grades such as P91 (X10CrMoVNb9-1) or P92 should be evaluated.
1.7375 forgings are supplied in the normalized and tempered (N+T) or quenched and tempered (Q+T) condition. Normalizing is carried out at 900–960°C followed by air cooling. Tempering is performed at 680–750°C with a hold time of minimum 1 hour per 25mm of section (not less than 2 hours total). For heavy sections above approximately 100mm, Q+T is preferred for improved through-thickness mechanical property uniformity.
Yes. 1.7375 (12CrMo9-10) is qualified for hydrogen partial pressure service above the 1Cr-0.5Mo Nelson curve limit per API 941. The 2.25Cr-1Mo composition provides resistance to high-temperature hydrogen attack (HTHA) at temperatures and hydrogen partial pressures where 1Cr-0.5Mo and plain carbon steels are not safe. It is widely used in hydroprocessing reactor shells, flanges, and nozzles in petroleum refineries.
Post-weld heat treatment (PWHT) for 1.7375 (12CrMo9-10) weldments is mandatory and is performed at 690–720°C, held for a minimum of 1 hour per 25mm of weld thickness (minimum 2 hours). PWHT is required by EN 13445, ASME VIII Division 1, and PED 2014/68/EU for all pressure-boundary weldments in this grade.
For standard boiler and pressure vessel forgings in steam or gas service, EN 10228-3 Quality Class 3 (maximum indication equivalent to FBH Ø 4mm) is the baseline specification. For components in hydrogen-rich hydroprocessing service, fatigue-critical applications, or rotating equipment, Quality Class 4 (FBH Ø 2mm) should be specified. Always confirm with the equipment designer and the applicable pressure vessel design code.
Per EN 10028-2, the chemical composition of 12CrMo9-10 (1.7375) by weight percentage is: C 0.10–0.15%, Si ≤0.50%, Mn 0.30–0.60%, P ≤0.025%, S ≤0.010%, Cr 2.00–2.50%, Mo 0.90–1.10%, Ni ≤0.30%, Cu ≤0.20%, Al ≤0.020%.
Sourcing 12CrMo9-10 Forged Parts from a Qualified Manufacturer
The quality of a 1.7375 forging is entirely a function of its manufacturing chain: melting practice, forging process, heat treatment furnace calibration, NDT equipment, operator qualification, and certification rigor. A material certificate with correct numbers can be issued for non-conforming product — the only reliable protection is a supplier with a demonstrably controlled, independently audited quality system and a proven track record in the grade.
Jiangsu Liangyi Co.,Limited is an ISO 9001:2015 certified Chinese forging manufacturer established in 1997, with over 25 years of experience producing open die forgings and seamless rolled rings in 1.7375 (12CrMo9-10) and the full range of related Cr-Mo pressure alloy steels. All forgings are produced with complete mill test certificates (MTC) per EN 10204 Type 3.1 as standard; EN 10204 Type 3.2 certificates countersigned by independent third-party inspectors (such as TÜV, Bureau Veritas, or Lloyd's Register) can be arranged at the customer's request and cost. Annual forging capacity exceeds 120,000 tons across all grades, serving customers in Europe, the Middle East, Southeast Asia, and the Americas.
Include the following in your RFQ or purchase order to ensure compliance and avoid misunderstandings:
- Melting practice requirement (EAF+LF+VD minimum; ESR if Class 4 UT is needed)
- Heat treatment condition (N+T or Q+T) and minimum tempering temperature
- Mechanical test requirements: tensile, 0.2% proof, elongation, impact energy, and Charpy test temperature
- NDT class under EN 10228-3 or ASTM A388 (Class 3 or Class 4)
- MTC type required: EN 10204 Type 3.1 (standard) or Type 3.2 (if third-party inspector countersignature is required — buyer nominates the inspection body)
- Additional compliance requirements: NACE MR0175 (if sour service), AD 2000-Merkblatt W0, or other applicable standards
- Dimensional tolerances, surface finish, and marking requirements
To discuss your 1.7375 forging requirement — including alloy selection advice, forging feasibility for complex geometries, or third-party inspection coordination — contact the Jiangsu Liangyi engineering team directly:
sales@jnmtforgedparts.com
+86-135-8506-7993
www.jnmtforgedparts.com
Chengchang Industry Park, Jiangyin City, Jiangsu Province, China
To review full product specifications, available sizes, and lead times, or to request a quote for 12CrMo9-10 forged components, visit the product page directly.