Understanding the 21CrMoNiV4-7 Designation
21CrMoNiV4-7 — assigned the DIN material number 1.6981 — is a low-alloy, heat-resistant engineering steel developed primarily for gas and steam turbine construction. The designation is self-describing: "21" encodes the nominal carbon content at 0.21 wt%, "Cr" is chromium, "Mo" molybdenum, "Ni" nickel, and "V" vanadium. The trailing numbers "4-7" are multiplication factors for the chromium and nickel content respectively per DIN nomenclature conventions.
The grade is standardised primarily under EN 10269 (steels and nickel alloys for fasteners and bolting at elevated and/or low temperatures) and is also referenced in AD 2000 Merkblatt W7 for pressure-bearing components. It is not a recent development — 1.6981 has been specified in turbine OEM requirements since the early 1970s, and its long track record in service is part of its appeal for engineers procuring replacement forgings.
Naming note: 21CrMoNiV4-7 is also written as 21CrMoNiV4.7 and 21 CrMoNiV 4-7. All three designations refer to the same grade. When sourcing internationally, always confirm using the DIN number 1.6981 — near-equivalent CrMoV grades without the nickel addition are frequently offered as substitutes, and the difference has significant consequences for heavy-section toughness.
The grade belongs to a closely related family that includes 21CrMoV5-7 (1.7709) and 28CrMoNiV4-9 (1.6985). The nickel addition in 1.6981 vs. 1.7709 substantially improves toughness in heavy cross-sections without meaningfully compromising high-temperature creep resistance — making 1.6981 the preferred choice for forgings with ruling sections exceeding 200 mm. For detailed product specifications, shapes, and weight ranges, see the 21CrMoNiV4-7 (1.6981) forged parts page.
Chemical Composition per EN 10269
The table below gives the permissible compositional range for 21CrMoNiV4-7 (1.6981) as specified in EN 10269. All values are mass percentages from the ladle analysis. The tight tolerances on carbon (0.17–0.25%) and vanadium (0.25–0.35%) are particularly important — they control hardenability and carbide precipitation behaviour across production heats.
| Element | Symbol | Min (%) | Max (%) | Nominal (%) | Primary Function |
|---|---|---|---|---|---|
| Carbon | C | 0.17 | 0.25 | 0.21 | Strength matrix |
| Silicon | Si | — | 0.40 | ~0.25 | Deoxidation |
| Manganese | Mn | 0.40 | 0.80 | 0.60 | Hardenability & sulphur scavenging |
| Chromium | Cr | 0.85 | 1.20 | 1.00 | Hardenability, oxidation resistance |
| Molybdenum | Mo | 0.90 | 1.10 | 1.00 | Creep resistance, temper embrittlement |
| Nickel | Ni | 0.60 | 1.00 | 0.70 | Toughness in heavy sections |
| Vanadium | V | 0.25 | 0.35 | 0.28 | Grain refinement, elevated-temp strength |
| Phosphorus | P | — | 0.025 | — | Residual — max. limited |
| Sulphur | S | — | 0.010 | — | Residual — max. limited |
| Aluminium | Al | To be reported — no range specified | Grain boundary control | ||
OEM aluminium limit: EN 10269 does not specify an aluminium maximum, but most turbine OEM technical specifications impose Al ≤ 0.020% to prevent aluminium nitride (AlN) precipitation at grain boundaries, which causes embrittlement during high-temperature service. Always check the project-specific technical specification.
The Role of Each Alloying Element
Every element in 21CrMoNiV4-7 earns its place. The composition window for each was set through decades of plant experience — understanding what each element does explains why grade substitution is risky in turbine service.
Room-Temperature Mechanical Properties (Q+T Condition)
All values below are minimum specification values for forgings in the quenched and tempered condition, tested at room temperature per EN 10002-1. Actual certified results typically exceed these by 5–15% on well-controlled production heats.
For forgings with ruling sections exceeding 250 mm, EN 10269 permits slightly reduced proof stress values (approximately 690 MPa minimum at 300 mm ruling section). For large disc or shaft forgings, buyers must specify whether mechanical property requirements apply to the surface or the core, and agree the coupon location in the technical specification before order placement.
Elevated-Temperature Tensile Properties at 560°C
The defining application requirement for 21CrMoNiV4-7 is its behaviour under sustained load between 450°C and 570°C — the operating range of HP and IP steam turbines in conventional fossil-fuel plant. The minimum values below are per EN 10002-5 testing on forged disc specimens.
| Test Temperature | 0.2% Proof Stress | Tensile Strength | Elongation A | Reduction of Area Z |
|---|---|---|---|---|
| 20°C (room temperature) | ≥ 735 MPa | ≥ 880 MPa | ≥ 14% | ≥ 45% |
| 300°C | ≥ 590 MPa | ≥ 730 MPa | ≥ 14% | ≥ 50% |
| 450°C | ≥ 510 MPa | ≥ 640 MPa | ≥ 16% | ≥ 60% |
| 560°C — turbine design point | ≥ 290 MPa | ≥ 400 MPa | ≥ 18% | ≥ 68% |
Why ductility increases at 560°C: The marked rise in elongation (≥18%) and reduction of area (≥68%) at the design temperature is deliberate. At operating temperature, the material must accommodate limited local plastic flow to redistribute stress concentrations at notches and bore surfaces. Brittle failure in a rotating turbine component would be catastrophic — this is a requirement simpler Cr-Mo grades such as 42CrMo4 cannot reliably meet in large sections.
Creep rupture strength — the stress to produce 1% total strain in 100,000 hours — is approximately 155–170 MPa at 550°C, qualifying 1.6981 for conventional fossil-fuel plant with live steam below 565°C. For ultra-supercritical plant above 600°C, advanced 9–12% Cr martensitic steels such as 1.4913 (X19CrMoNbVN11-1) are typically specified instead.
Heat Treatment Protocol for 1.6981 Forgings
21CrMoNiV4-7 is always supplied in the quenched and tempered (Q+T) condition — this is not optional. The two-stage thermal cycle creates the metastable microstructure required for service performance. Deviating from the temperature windows produces either insufficient strength or unacceptable toughness.
Work the material above 1050°C with a minimum press reduction ratio of 3:1. This closes ingot voids, refines the as-cast dendritic structure, and develops wrought grain flow essential for toughness anisotropy control. Do not continue forging below 950°C — the steel becomes significantly harder and hot surface cracking becomes a risk.
Hold at 900–950°C for approximately 1 hour per 25 mm of ruling section to ensure complete austenitisation and carbide dissolution. Too low: undissolved carbides reduce hardenability. Too high: permanent austenite grain coarsening that irreversibly degrades toughness.
Rapid cooling transforms austenite to martensite. Quench medium is selected by section size. For ruling sections above 300 mm, oil or polymer quench is standard to ensure full martensite transformation in the core. Inadequate quench rate produces bainite or pearlite, reducing strength below specification.
The 680–720°C band is where the grade's service properties are established. Tempering relieves quench stresses and precipitates fine V(C,N) and Mo₂C particles that provide creep resistance. Do not exceed 720°C — over-precipitation produces a coarser, softer microstructure with degraded elevated-temperature properties. This is the most process-sensitive step.
Applied only if the forging is rough-machined before final delivery, to prevent distortion during precision machining. Temperature is set below the tempering window to avoid altering the established microstructure.
Forging Characteristics and Manufacturing Considerations
21CrMoNiV4-7 is a medium-to-high complexity forging alloy. Its hardenability is sufficient for full martensite transformation in sections up to approximately 350 mm on oil quench, but the narrow tempering window and sensitivity to forging temperature control demand process discipline that separates technically capable producers from commodity suppliers.
Forging temperature window: 1050–1200°C. Below 950°C the steel becomes significantly stronger and less ductile — surface cracking risk on complex shapes increases sharply. If a billet cools below the working limit during a heavy reduction step, reheating is required before continuing. This is a non-negotiable rule for surface quality in turbine-grade components.
Hot ductility is adequate for open-die forging of bars, discs, rings, and shafts. The alloy does not suffer from the hot shortness that affects some higher-Ni grades. However, the vanadium content means carbides re-precipitate quickly during slow post-forging cooling — controlled cooling from the forging temperature (in a furnace or sand pit) prevents grain-boundary carbide networks that would complicate subsequent austenitising.
Ingot quality and reduction ratio are particularly critical for turbine-service forgings. For disc and rotor shaft forgings where ultrasonic cleanliness requirements are stringent (typically EN 10228-3 Class 3 or better), electric arc furnace or vacuum induction + vacuum arc remelted (VIM-VAR) ingots are preferred over basic electric arc for consistently low inclusion levels.
Large-section behaviour: For shaft forgings exceeding 500 mm diameter, the slower core cooling rate during quenching means core properties are always lower than surface values. Buyers must specify whether mechanical property requirements apply to the surface or the core, and agree the test coupon location before order placement — surface coupons overstate core properties in very large forgings.
Jiangsu Liangyi manufacturing capability: We produce 1.6981 open-die forgings in all standard shapes — bars, discs, rings, shafts, hollow forgings — from 30 kg to 30 tonnes, and seamless rolled rings up to 6 metres in diameter. Full in-house supply chain: forging → heat treatment → rough and finish machining → NDE. For available dimensions, delivery conditions, and inspection options, visit our 1.6981 steel forging parts product page to request a quotation.
NDE Requirements and Inspection Types per EN 10228-3
For turbine-grade 1.6981 forgings, non-destructive examination (NDE) is a contractual and safety requirement — not optional. The applicable standard is EN 10228-3, with the inspection type determined by forging geometry.
All forgings receive visual inspection and material verification testing as standard. 100% volumetric ultrasonic testing (UT) is performed in the delivery condition — after final heat treatment and rough machining, before precision machining — to the agreed acceptance class. For turbine OEM projects, Class 3 or Class 4 acceptance limits are typical.
Customer-nominated third-party inspectors are welcome at Jiangsu Liangyi's Jiangyin facility. Material certificates are issued to EN 10204-3.1 as standard with every order. EN 10204-3.2 witness certification requires the buyer to arrange their own approved inspection body — please discuss your specific inspection requirements at the enquiry stage.
Where 21CrMoNiV4-7 Is Used in Industry
The grade's combination of high room-temperature strength, adequate toughness, and strong creep and oxidation resistance up to 570°C makes it the material of choice for a defined set of high-stress, high-temperature components in power generation and related heavy industry.
The grade is not appropriate for corrosive or cryogenic service. Its pitting resistance is negligible, and Charpy impact toughness falls below acceptable limits below −20°C. For seawater or sour-gas environments, stainless or nickel alloy forgings such as 1.4418 (X4CrNiMo16-5-1) or 2.4858 (Alloy 825) are appropriate alternatives.
International Grade Equivalents of 21CrMoNiV4-7 (1.6981)
21CrMoNiV4-7 is a DIN/EN designation with no exact equivalents in ASTM, JIS, or Chinese GB standards — a common source of procurement confusion. The table below lists the closest compositional and property matches in other standards systems. These are approximate equivalents only; for critical turbine components, always verify chemistry and mechanical properties independently before any grade substitution.
| Standard System | Grade / Designation | Reference Standard | Key Differences vs. 1.6981 |
|---|---|---|---|
| DIN / EN (primary) | 21CrMoNiV4-7 / 1.6981 | EN 10269, AD 2000 W7 | — Reference grade |
| ASTM / ASME | No exact match | — | Closest: A193 B16 — lower Ni and Cr content |
| British Standard | No current BS equivalent | Withdrawn in favour of EN | Historical 3% CrMoV grades differ in Ni and V |
| JIS (Japan) | No direct equivalent | — | SCM445 is weaker; no Ni or V additions |
| GB / YB (China) | 20Cr1Mo1VNbTiB (approx.) | GB/T 3077 | Nb and Ti additions present; different creep behaviour |
| GOST (Russia) | 20Kh1M1F1TR (approx.) | GOST 20072 | Ti addition present; slightly different Cr range |
Procurement note: When purchasing 1.6981 forgings internationally, always insist on chemistry certified against the EN 10269 composition table. The vanadium content (0.25–0.35%) is the most commonly deviated element in near-equivalent grades — its absence significantly degrades elevated-temperature creep performance and is not detectable without spectrographic analysis of the heat certificate.
21CrMoNiV4-7 (1.6981) — FAQ
Direct answers to the most common technical and procurement questions about this grade, optimised to match how engineers and buyers search for this material.
Need 21CrMoNiV4-7 (1.6981) forgings for your project?
Jiangsu Liangyi Co., Limited supplies open die forgings and seamless rolled rings from 30 kg to 30 tonnes, with full in-house heat treatment, machining, and NDE.
- ISO 9001:2015 certified quality management system
- EN 10204-3.1 material certificate with every order
- Customer-nominated third-party inspection welcome
- Global export — contact us for your country's delivery terms