What Is 24NiCrMoV10-10 Steel?
A Complete Guide for Turbine Engineers

24NiCrMoV10-10 — registered under EN material number 1.6961 and standardised in EN 10083-3 — is the benchmark low-alloy martensitic steel for high-pressure and intermediate-pressure steam turbine rotors. Its Nickel–Chromium–Molybdenum–Vanadium chemistry delivers high yield strength from ambient temperature to 500 °C, excellent fatigue resistance under cyclic thermal loading, and impact toughness sufficient for 30–40 years of continuous power-generation service.

1. What Is 24NiCrMoV10-10 Steel?

24NiCrMoV10-10 is a low-alloy, quench-and-tempered engineering steel whose grade name directly encodes its nominal chemistry: "24" indicates approximately 0.24% carbon; "Ni10" signals roughly 2.5% nickel; "Cr" confirms chromium presence; "Mo" molybdenum; and "V10" signals approximately 0.25% vanadium. After quenching from the austenitizing temperature, the steel transforms into a fine tempered martensite — the microstructural state responsible for its exceptional balance of strength and toughness.

What separates 1.6961 from simpler Cr-Mo steels such as 21CrMoV5-7 or 14MoV6-3 is the deliberate combination of nickel and vanadium. Nickel lowers the ductile-to-brittle transition temperature (DBTT), keeping the steel tough after decades of thermal cycling that would otherwise cause grain-boundary embrittlement. Vanadium forms fine, thermally stable carbides that pin grain boundaries, resist creep deformation at elevated temperature, and maintain long-term strength without requiring higher carbon content.

Jiangsu Liangyi Co., Limited manufactures EN 1.6961 as open-die forgings and seamless rolled rings from 30 kg up to 30,000 kg, delivered in the quenched-and-tempered condition with full EN 10204 3.1 material certification and in-house NDT. Engineers looking to source custom components can review the full 24NiCrMoV10-10 forging parts page for product range, available shapes, and RFQ details.

2. Chemical Composition per EN 10083-3

The table below shows the EN 10083-3 specification limits alongside our internal production targets. Every heat is verified by Optical Emission Spectrometry (OES) before forging. Our internal P and S limits are deliberately tighter than the standard to maximise toughness in heavy-section rotor forgings.

★ Our internal limits for P and S are stricter than EN 10083-3 minimums to enhance toughness and resist temper embrittlement in heavy-section turbine rotors.

3. The Role of Each Alloying Element

Carbon (0.20–0.28%)

Carbon is the primary strengthening element. It controls martensite hardness after quenching and through-hardening capability across large sections. The narrow 0.08% window reflects the trade-off: enough C to achieve ≥ 780 MPa yield strength, while limiting C to preserve toughness and weldability. Forgings produced at the upper end of the carbon range require higher preheat temperatures before welding.

Chromium (2.0–2.6%)

Chromium is the creep and oxidation resistance workhorse in this alloy. At 2.0–2.6%, it significantly raises the steel's recrystallization temperature, suppressing creep deformation at 400–500 °C. Chromium also contributes substantially to hardenability — critical for through-hardening large-diameter turbine rotor shafts exceeding 500 mm diameter.

Nickel (2.0–2.8%)

Nickel provides toughness insurance. It lowers the ductile-to-brittle transition temperature (DBTT), so even after 20 years of thermal cycling, the rotor retains adequate impact energy. Nickel at this level also boosts hardenability without degrading weldability as severely as additional carbon would.

Molybdenum (0.50–0.80%)

Molybdenum delivers solid-solution strengthening at high temperature and is the primary barrier against temper embrittlement caused by phosphorus segregation to grain boundaries. Mo forms a P-Mo complex that reduces grain-boundary phosphorus activity — a key reason this grade performs reliably after decades in the embrittlement temperature range.

Vanadium (0.15–0.40%)

Vanadium is the long-term creep stabiliser. Fine VC and VCN precipitates formed during tempering pin grain boundaries, resist dislocation climb at elevated temperature, and maintain yield strength over 100,000+ service hours. ASTM A470 Class 8 does not specify a guaranteed minimum vanadium content — engineers substituting ASTM material must always verify V on the MTR before accepting delivery for turbine rotor service.

4. Room-Temperature Mechanical Properties

All values below apply to the standard Quenched + Tempered (+QT) delivery condition, measured from specimens at the ¼-radius position of the forging cross-section per EN 10250-1 and EN 10228-3.

5. High-Temperature Strength Retention

For turbine rotor design, the critical input is how much yield strength the steel retains at service temperature. The table below shows minimum guaranteed 0.2% proof stress values — these are measured on the same ¼-radius specimens and reported per heat on request.

Even at 500 °C, 24NiCrMoV10-10 retains approximately 70% of its ambient yield strength — a level no simple Cr-Mo steel without vanadium and nickel can match at equivalent carbon content.

6. Heat Treatment Protocol

Heat treatment is the single most influential process step in determining final mechanical properties. The standard production route at Jiangsu Liangyi follows six stages, refined over 25 years of rotor forging.

• 01
  Sections > 400 mm Only

  Pre-heat to 300–400 °C

  Slow heat at ≤ 60 °C/hour to equalise temperature through the heavy section. Eliminates thermal gradient stresses before austenitizing and reduces risk of thermal shock cracking in large forgings.
• 02
  All Sections

  Austenitizing — 880 to 920 °C

  Hold: minimum 1 hour per 100 mm maximum section thickness; minimum 2 hours total. Furnace temperature uniformity: ±10 °C. Slightly reducing atmosphere prevents surface decarburization.
• 03
  Quench Medium by Section

  Quenching — Oil or PAG Polymer

  Transfer to quench tank within 30 seconds of furnace exit. Oil or PAG polymer solution for sections above 200 mm; forced water for sections below 150 mm. Minimum surface cooling rate: 15 °C/s for sections up to 300 mm diameter.
• 04
  Large Hollow Forgings ≥ 600 mm — Optional

  Intermediate Temper — 200–250 °C

  Hold 2–4 hours. Reduces quench cracking risk in very large forgings and promotes hydrogen outgassing from the section before final high-temperature tempering.
• 05
  All Sections — Critical Step

  Final Tempering — 580 to 680 °C

  Hold: minimum 2 hours per 100 mm section; minimum 4 hours total. Furnace-cool to 150 °C before air cooling. Standard turbine rotor target 620–650 °C achieves 248–268 HBW with ≥ 70 J KV at +20 °C. Never temper below 580 °C — this risks hardness exceeding 280 HBW and brittle failure.
• 06
  ESR Grade / Large Hollow Forgings

  Hydrogen Diffusion Anneal — 200–300 °C, 24–48 hours

  Post-temper treatment to ensure dissolved hydrogen < 1.5 ppm in the finished part, eliminating hydrogen flaking risk in heavy cross-sections. Required for all ESR-grade rotor shaft orders.

7. Weldability

With a carbon equivalent (IIW formula) of approximately:

This CE value does not mean 1.6961 cannot be welded. It means welding requires a controlled procedure to prevent hydrogen-induced cracking and post-weld temper embrittlement:

• Preheat: 200–250 °C minimum, maintained throughout the entire welding sequence
• Interpass temperature: 200–300 °C — do not allow the weld to cool between passes
• Filler metal: Low-hydrogen electrode ≤ 4 ml H₂/100 g (e.g., AWS E9018-B3, or NiCrMoV matching type)
• PWHT: 620–660 °C, minimum 1 hour per 25 mm weld throat thickness (minimum 2 hours total); heat and cool at ≤ 100 °C/hour through 300 °C

8. ASTM and International Equivalent Grades

The table below lists the closest international equivalents. "Equivalent" indicates similar chemistry and application intent — it does not confirm identical composition or interchangeable specification compliance.

9. Grade Comparison: How Does 1.6961 Stack Up?

The cards below compare 24NiCrMoV10-10 against the three most commonly evaluated alternatives in turbine material selection.

10. Industrial Applications

HP and IP Steam Turbine Rotor Shafts

The primary application. Monolithic rotor shafts in custom dimensions, produced from a single heat-poured ingot. Delivered in +QT condition with EN 10228-3 Class 3 or Class 4 UT, Charpy testing at −10 °C, and high-temperature tensile testing at 450 °C per customer specification. Suitable for coal-fired, gas-fired, and biomass steam turbine applications.

Gas Turbine Compressor Discs

Precision disc forgings for the compressor stages of industrial gas turbines, where bore diameter requires Class 4 UT tolerance and 100% surface magnetic particle testing. The grade's creep strength at 400–450 °C compressor outlet temperatures and its machinability at 240–280 HBW suit bore-critical disc geometries.

Seamless Rolled Rings — Labyrinth Seals and Casing Flanges

Large-diameter seamless rings from 300 mm to 6,000 mm OD produced by radial-axial ring rolling. Circumferential grain flow from rolling gives superior mechanical property uniformity compared to flame-cut plate rings. Applications include labyrinth seal assemblies, turbine casing flanges, and generator stator rings.

High-Pressure Valve Spindles and Bodies

Custom valve spindle forgings for upstream oil and gas processing and power station turbine bypass valves. When sour-service hardness limits (≤ 248 HBW) are specified by the customer, this is achievable through controlled tempering at 660 °C while maintaining full mechanical property certification — please state this requirement in your RFQ. EN 10204 3.1 material test reports are supplied as standard. Third-party EN 10204 3.2 inspection can be arranged upon customer request — please specify the preferred inspection agency in your purchase order.

11. NDT and Inspection

Every EN 1.6961 forging undergoes a structured inspection sequence before dispatch, based on EN 10228-3 (volumetric UT) and EN 10228-1 (surface MT) as the baseline.

All accessible surfaces receive wet fluorescent magnetic particle testing (WFMT) per EN 10228-1. Final inspection includes a full Brinell hardness survey, dimensional check against the customer drawing, and visual inspection per EN 10228-4. The complete documentation package — EN 10204 3.1 MTR, heat treatment time–temperature charts, dimensional inspection report, and NDT report — ships with every order.

12. Frequently Asked Questions