26NiCrMoV14-5 (EN 1.6957) and 26NiCrMoV11-5 (EN 1.6948) are both low-alloy NiCrMoV steels for turbine rotor forgings, standardised in EN 10222-5 and SEW 555. The decisive difference is nickel content: 1.6957 contains 3.40–3.80% Ni; 1.6948 contains 2.60–3.00% Ni. Higher nickel provides deeper hardenability, enabling full martensitic transformation to the centre of large sections during quenching.
Grade selection rule: Specify 26NiCrMoV14-5 (1.6957) for effective section diameters ≥ 800 mm, cold-climate applications (FATT ≤ −10°C required), and large LP turbine rotor shafts. Specify 26NiCrMoV11-5 (1.6948) for sections below 750 mm — delivering identical surface mechanical properties at 15–25% lower material cost. Both grades have a maximum service temperature of 450°C.
Both grades are manufactured and certified by Jiangsu Liangyi Co., Limited — ISO 9001:2015 certified, founded 1997, Jiangyin, Jiangsu, China — with EN 10204-3.1 standard on every order. EN 10204-3.2 available via buyer-arranged third-party inspection. our 26NiCrMoV14-5 (1.6957) product page
For rotor sections below 800 mm effective diameter, specify 26NiCrMoV11-5 (1.6948) — it meets the same mechanical targets at 15–25% lower material cost. For sections 800 mm and above, the higher nickel content of 26NiCrMoV14-5 (1.6957) is required to achieve full through-hardening and adequate core toughness. Over-specifying 1.6957 on smaller rotors is the single most common — and most avoidable — grade selection error we encounter on customer drawings.
01 Why These Two Grades Exist Side by Side
Both 26NiCrMoV14-5 and 26NiCrMoV11-5 belong to the NiCrMoV family of low-alloy steels engineered for large turbine rotor shafts operating at temperatures up to 450°C. The designation logic is consistent: the number following "Ni" encodes the nominal nickel content multiplied by four — so "14" means approximately 3.4–3.8% Ni, while "11" means approximately 2.6–3.0% Ni.
Nickel is the decisive variable. It is the element most responsible for deep hardenability — the ability to transform austenite to martensite at the center of a large cross-section during quenching. A leaner-nickel grade like 1.6948 hardens fully through sections up to approximately 800 mm. Beyond that threshold, the quench front cannot penetrate to the core fast enough to prevent bainite or pearlite formation. This produces inadequate impact toughness values in the bore region of a turbine rotor — a failure mode that does not appear on a surface hardness report but shows up clearly on a Charpy specimen from the axial core position.
At Jiangsu Liangyi, we have produced over 2,000 NiCrMoV turbine rotor forgings across 25+ years of production. The practical reality of this hardenability boundary is well-established in our data, and it is the foundation of every grade recommendation we make to customers.
02 Chemical Composition: What the Numbers Actually Mean
The table below compares the chemical composition limits of both grades. Nickel and Chromium deserve the closest attention — they drive the most important differences in hardening behavior.
| Element | 26NiCrMoV14-5 (1.6957) | 26NiCrMoV11-5 (1.6948) | Engineering significance |
|---|---|---|---|
| Carbon C (%) | ≤ 0.28 | ≤ 0.28 | Identical — both balance hardness against toughness at same level |
| Nickel Ni (%) | 3.40 – 3.80 | 2.60 – 3.00 |
The critical difference.
Higher Ni in 1.6957 enables full through-hardening in sections above 800 mm.
1.6957 → large sections |
| Chromium Cr (%) | 1.40 – 1.80 | 1.50 – 2.00 | Slightly higher Cr in 1.6948 partially compensates for lower Ni in smaller sections |
| Molybdenum Mo (%) | 0.30 – 0.45 | 0.30 – 0.50 | Near-identical — both suppress temper embrittlement and improve creep strength |
| Vanadium V (%) | ≤ 0.15 | ≤ 0.15 | Identical — grain refinement; both grades perform equivalently Equal |
| Phosphorus P (%) | ≤ 0.010 | ≤ 0.010 | Identical tight limits — both require high-purity VCD melt to prevent temper embrittlement |
| Sulfur S (%) | ≤ 0.010 | ≤ 0.010 | Identical — minimised to prevent MnS stringer inclusions in large forgings |
| Silicon Si (%) | ≤ 0.25 | ≤ 0.25 | Identical — kept low for vacuum degassed quality melt |
03 Mechanical Properties Compared
At room temperature in the quenched-and-tempered condition, both grades are designed to meet essentially equivalent minimum property targets at the surface. The divergence becomes significant only in core properties and large-section performance — which is exactly what matters for a turbine rotor.
| Property | 26NiCrMoV14-5 (1.6957) | 26NiCrMoV11-5 (1.6948) | Notes |
|---|---|---|---|
| Yield strength Rp0.2 (N/mm²) | ≥ 730 (typ. 780) | ≥ 690 (typ. 750) | Similar in practice; 1.6957 minimum slightly higher |
| Tensile strength Rm (N/mm²) | 830 – 980 | 790 – 950 | Overlapping ranges; section-size dependent |
| Elongation A (%, l₀=5d) | ≥ 15 | ≥ 15 | Equal |
| Reduction of area Z (%) | ≥ 50 | ≥ 50 | Equal |
| Charpy V impact (J, tangential) | ≥ 100 (typ. 135) | ≥ 80 (typ. 110) | 1.6957 requires higher minimum — better low-temperature toughness 1.6957 advantage |
| Axial core FATT (°C) | ≤ −10°C | ≤ 0°C | 1.6957 achieves lower FATT — critical for cold-start turbines and cold climates 1.6957 advantage |
| Barrel radial impact (J) | ≥ 70 | ≥ 55 | 1.6957 superior in radial direction — important for large diameter rotors |
| Hardness after Q+T (HB) | 248 – 302 | 235 – 285 | Comparable; 1.6957 slightly higher range |
| Maximum service temperature (°C) | ≤ 450°C | ≤ 450°C | Equal |
Elevated-temperature strength retention
At 380–450°C operating temperatures, both grades show similar strength retention. Neither holds a meaningful advantage over the other at elevated temperature for the same rotor geometry. The choice between them is driven entirely by section size and core toughness requirements — not high-temperature performance.
Retention figures relative to room-temperature yield strength. Values typical for mid-range Rm, quenched and tempered condition.
04 The Section Size Threshold: The Most Important Factor
The single most important variable in grade selection is the effective cross-section diameter at the location where core mechanical properties are tested. This is not necessarily the maximum outer diameter of the finished rotor — it is the diameter of the critical section through which the quench must penetrate to achieve martensite transformation at the geometric centre.
threshold
Overlap zone ~750–900 mm: either grade may qualify depending on quench parameters, furnace uniformity, and OEM requirements.
Why 800 mm is not a hard line
The 800 mm boundary is a practical engineering guideline, not a sharp physical threshold. Several factors shift it in real production:
Quench method: Rotating spray-ring quenching achieves more uniform surface cooling than static immersion, effectively pushing the hardenability threshold by 50–80 mm compared to a static water quench.
Steel cleanliness: Vacuum degassed (VCD) or electroslag remelted (ESR) heats have fewer non-metallic inclusions acting as transformation nuclei, slightly improving through-hardening behavior for borderline sections.
OEM specification: Some European turbine OEMs mandate 1.6957 for all rotors above 700 mm as a conservative engineering margin, regardless of calculated hardenability. If your purchase order references a drawing with this requirement, the grade is specified — do not deviate without a formal engineering deviation approval.
05 Decision Framework: Which Grade to Specify
- Body diameter below 750 mm
- HP or IP turbine rotors (smaller cross-sections)
- Rotor discs and disc packs under 800 mm
- Cost-sensitive projects without OEM grade override
- Replacement rotors where original drawing shows 1.6948
- Marine applications where section size permits
- Body diameter 800 mm or above
- Large LP turbine rotor shafts
- Cold-climate plants: FATT ≤ −10°C required
- OEM drawing explicitly calls out 1.6957
- Applications requiring EN 10204-3.2 third-party inspection
- Rotors where axial core toughness is formally tested
For complete dimensional tolerances, available bar and ring stock sizes, heat treatment records, and EN 10204‑3.1 certificate samples, see our 26NiCrMoV14‑5 open-die forging and ring-rolling product page.
06 How to Select the Correct Grade — Step by Step
The following five-step process covers every grade selection scenario for 26NiCrMoV14-5 and 26NiCrMoV11-5 turbine rotor forgings, in sequence. Earlier steps can short-circuit the process if a definitive answer is found.
- Step 1 — Determine the effective section diameter. Identify the diameter of the cross-section at which core mechanical properties will be tested — typically the rotor body at mid-length. This is the controlling dimension, not the maximum flange or journal OD.
- Step 2 — Check for OEM or contractual grade requirements. Review the purchase order, customer drawing, and project specification for any explicit material designation (1.6957 or 1.6948). If specified, that requirement governs — a formal written engineering deviation is required before any substitution.
- Step 3 — Apply the 800 mm threshold rule. Below 750 mm: specify 26NiCrMoV11-5 (1.6948). Above 800 mm: specify 26NiCrMoV14-5 (1.6957). In the 750–900 mm overlap zone: perform a Grossmann DI hardenability calculation with the agreed chemistry range, site quench method, and OEM requirements.
- Step 4 — Confirm FATT requirement. If the project specification requires axial core FATT ≤ −10°C — required for cold-climate installations, Northern Europe, North America, or high-altitude sites — specify 26NiCrMoV14-5 (1.6957) regardless of section size.
- Step 5 — Issue RFQ with full technical details. Include: effective section diameter, operating temperature, required FATT, applicable standards (EN, ASTM, or dual), third-party inspection body if required (e.g. EN 10204-3.2 third-party), and MTC type required (EN 10204-3.1 or 3.2).
06 Real-World Scenarios from Our Order Book
The following cases illustrate how grade selection decisions play out in production. Details have been anonymised but the engineering facts are drawn directly from orders we have processed.
07 Cost Implications of Grade Selection
The price difference between 26NiCrMoV14-5 and 26NiCrMoV11-5 forgings is driven primarily by the nickel content differential — approximately 0.7–1.0% additional nickel in 1.6957. Given nickel's market premium over the base steel price, this compositional difference typically translates to a 15–25% increase in raw forging cost when comparing equivalent geometries.
For a 10-tonne LP turbine rotor, this can represent a significant procurement cost difference. The calculation must, however, be weighed against the cost of misspecification in the other direction: an under-specified core in a large LP rotor that fails in service carries costs — turbine replacement, plant downtime, engineering investigation, and liability — that dwarf the upfront material differential many times over.
08 Standards and Certification Differences
| Standard / Document | 26NiCrMoV14-5 (1.6957) | 26NiCrMoV11-5 (1.6948) |
|---|---|---|
| Primary EN standard | EN 10222-5, VdTÜV WB 397 | EN 10222-5, VdTÜV WB 395 |
| ASTM equivalent (approx.) | A470 Class 8 / A471 Class 10 | A470 Class 7 / A471 Class 8 |
| MTC type — standard | EN 10204-3.1 | EN 10204-3.1 |
| MTC type — critical applications | EN 10204-3.2 (via third-party inspection) | EN 10204-3.2 (via third-party inspection) |
| Third-party inspection bodies | major international inspection bodies — all supported | major international inspection bodies — all supported |
| Core impact specimen requirement | Tangential + axial core — FATT ≤ −10°C | Tangential + axial core — FATT ≤ 0°C |
| Dual EN + ASTM certification | Available on request | Available on request |
From a documentation standpoint, both grades follow the same inspection and testing protocol at Jiangsu Liangyi. The key distinction on the mill test certificate is the material designation, chemical composition values, and the FATT acceptance criterion on the axial core Charpy specimen — which is 10°C more stringent for 1.6957.
09 Frequently Asked Questions
Can 26NiCrMoV11-5 (1.6948) be used as a direct substitute for 26NiCrMoV14-5 (1.6957)?
Is 26NiCrMoV14-5 always the better steel grade?
What is FATT and why does the 10°C difference between 1.6957 and 1.6948 matter?
What section diameter threshold determines whether to use 1.6957 or 1.6948?
What is the nickel content difference between 26NiCrMoV14-5 and 26NiCrMoV11-5?
What is the maximum service temperature for 26NiCrMoV14-5 and 26NiCrMoV11-5?
Can Jiangsu Liangyi provide dual EN 26NiCrMoV14-5 and ASTM A470 Class 8 certification?
What are the typical lead times for 26NiCrMoV14-5 and 26NiCrMoV11-5 forgings?
Get a Free Grade Assessment and Quotation
Send us your rotor dimensions and application details. Our metallurgical engineering team will confirm the correct grade and deliver a detailed quotation within 24 hours.