Section 01 — Overview
What Makes 1.2779 Different From Other Tool Steels?
1.2779 is not a conventional hot work tool steel. It is a precipitation-hardenable austenitic steel — a material category that derives exceptional high-temperature strength from intermetallic phase formation within a stable austenite matrix, not from carbide hardening or martensitic transformation.
Engineers most often encounter 1.2779 (X6NiCrTi26-15) when H13 or 316L stainless steel starts failing in service above 600 °C — either softening under sustained thermal load or losing structural yield strength. The grade fills the performance gap between expensive nickel-base superalloys and conventional tool steels, operating reliably at continuous service temperatures up to 750 °C at 30–40% lower material cost than Alloy 625 (UNS N06625).
The alloy achieves its properties through controlled precipitation of Ni₃Ti intermetallic particles uniformly distributed through the austenite matrix during aging heat treatment at 710–730 °C. This mechanism produces consistent mechanical properties across the entire forging cross-section — a result that standard quench-and-temper steels cannot replicate at elevated service temperatures.
Key structural fact: The austenitic matrix of 1.2779 is inherently non-magnetic (μᵣ ≈ 1.003–1.010). For electromagnetic stirring roll applications in continuous casting machines, this is a functional requirement, not a preference — ferritic or martensitic steels disrupt the electromagnetic field and cannot serve this application.
Section 02 — Designations
Names, Standards & Cross-References
The same grade appears under several designations across international standards, supplier documentation, and mill certificates. Confusion between them is a common and preventable procurement error.
| Standard System | Designation | Notes |
|---|---|---|
| DIN EN Material Number | 1.2779 | Primary ordering designation — use on all purchase orders |
| DIN EN Chemical Symbol | X6NiCrTi26-15 | Also written X6NiCrTi26.15 or X6NiCrTi2615 |
| Governing Standard | DIN 17752 | Precipitation-hardenable stainless and heat-resistant steels |
| Nearest ASTM/UNS | S66286 (A-286) | Similar concept; different Mo/Ti/B balance — not interchangeable without engineering review |
| Nearest AMS | AMS 5737 / 5525 | A-286 equivalent — reference only; confirm before substitution |
| British BS | No direct equivalent | — |
| JIS (Japan) | No direct equivalent | — |
| Chinese GB | No direct equivalent | Imported or produced to DIN EN specification |
Procurement rule: Mill Test Certificates must explicitly state "DIN 17752 / X6NiCrTi26-15 / 1.2779". Descriptions like "precipitation-hardenable austenitic steel" without the DIN material number are insufficient for quality-controlled purchasing — they create ambiguity that cannot be resolved after material delivery.
Section 03 — Chemistry
Chemical Composition per DIN 17752
Every element in 1.2779 (X6NiCrTi26-15) serves a specific metallurgical role. Understanding these roles helps engineers evaluate supplier heat analysis certificates and identify substandard or mis-specified material before it enters service.
| Element | DIN EN Range (wt%) | Metallurgical Role |
|---|---|---|
| Carbon (C) | ≤ 0.08 | Kept low to preserve toughness; high C depletes Ti from the Ni₃Ti precipitation reaction |
| Silicon (Si) | ≤ 1.00 | Deoxidation; moderate oxidation resistance |
| Manganese (Mn) | ≤ 2.00 | Austenite stabilization; sulfide inclusion morphology control |
| Phosphorus (P) | ≤ 0.030 | Minimized to prevent grain boundary embrittlement |
| Sulfur (S) | ≤ 0.030 | Controlled for hot ductility and forgeability |
| Chromium (Cr) | 13.5 – 16.0 | Oxidation and corrosion resistance; austenite stabilization |
| Molybdenum (Mo) | 1.00 – 1.50 | Solid solution strengthening; creep resistance enhancement |
| Vanadium (V) | 0.10 – 0.50 | Secondary carbide precipitation; grain refinement during forging |
| Nickel (Ni) | 24.0 – 27.0 | Primary austenite former; provides the stable non-magnetic matrix for precipitation hardening |
| Titanium (Ti) | 1.90 – 2.30 | Principal hardening agent — precipitates coherent Ni₃Ti intermetallic during aging at 710–730 °C |
| Boron (B) | 0.003 – 0.010 | Grain boundary strengthening; improves creep rupture life |
Why Titanium Content Control Is Critical
Titanium directly governs the volume fraction of Ni₃Ti precipitates and therefore peak hardening response. Material at Ti = 1.90% will produce measurably lower aged yield strength than material at Ti = 2.20%, yet both pass the DIN 17752 composition requirement. For critical applications, specify a tighter internal Ti target on the purchase order — for example, Ti: 2.00–2.20%.
Our factory practice: Jiangsu Liangyi controls titanium to 2.00–2.20% — narrower than DIN EN's 1.90–2.30% requirement — to ensure consistent Rp0.2 response and batch-to-batch repeatability.
Section 04 — Physical Data
Physical & Thermal Properties of 1.2779
Values measured on solution-annealed and aged material. The low thermal conductivity — roughly one-third that of carbon steel — is the most important property for both component design and the forging process.
| Property | 20 °C | 500 °C | 700 °C | Unit |
|---|---|---|---|---|
| Density | 8.05 | 7.90 | 7.80 | g/cm³ |
| Elastic Modulus (E) | 196 | 178 | 163 | GPa |
| Thermal Conductivity (λ) | 12.5 | 16.8 | 19.2 | W/(m·K) |
| Thermal Expansion (α) | 16.2 (avg 20–500 °C) | 17.8 (avg 20–700 °C) | ×10⁻⁶/K | |
| Specific Heat (cₚ) | 460 | 510 | 540 | J/(kg·K) |
| Electrical Resistivity | ~1.00 | ~1.18 | — | μΩ·m |
| Magnetic Permeability | Non-magnetic — μᵣ ≈ 1.003–1.010 (austenitic) | — | ||
Design implication — low λ: At 12.5 W/(m·K), 1.2779 conducts heat at approximately one-third the rate of carbon steel. For heavy sections (wall thickness >200 mm), this requires extended furnace soaking times and controlled slow cooling after forging — both mandatory, not optional.
Section 05 — Heat Treatment
Heat Treatment Routes for 1.2779 X6NiCrTi26-15
Unlike most tool steels, 1.2779 requires a precisely controlled two-stage thermal cycle to reach its design properties. Omitting or abbreviating either stage has measurable, predictable consequences that may not be visible on standard incoming inspection.
What Happens When Aging Time Is Insufficient
Under-aging leaves Ni₃Ti precipitation incomplete. The Rp0.2 deficit is not visible on a room-temperature hardness test. For load-bearing and creep-critical applications, always request the furnace time-temperature chart and aging hold time record alongside the MTC. A conforming hardness result without aging time documentation is insufficient evidence of adequate heat treatment.
Section 06 — Mechanical Data
Guaranteed Mechanical Properties (Solution Annealed + Aged)
All values refer to the solution-annealed and aged condition, tested on qualification test coupons (QTC). Testing per ASTM A370, ASTM E8, ASTM E23, or ISO 6892-1.
| Property | Value | Test Standard |
|---|---|---|
| 0.2% Proof Strength Rp0.2 (min) | 650 MPa | ASTM E8 / ISO 6892-1 |
| Tensile Strength Rm | 950 – 1,150 MPa | ASTM E8 / ISO 6892-1 |
| Elongation A5 (min) | 15% | ASTM E8 |
| Reduction of Area Z (min) | 30% | ASTM E8 |
| Charpy V-Notch KV (min, long., RT) | 40 J | ASTM E23 |
| Rp0.2 at 600 °C (typical) | 580 – 640 MPa | Elevated-temperature tensile |
| Rp0.2 at 700 °C (typical) | 520 – 580 MPa | Elevated-temperature tensile |
| Rp0.2 at 750 °C (typical) | 480 – 560 MPa | Elevated-temperature tensile |
Section 07 — Material Comparison
1.2779 vs H13 vs Alloy 625 vs 316L Stainless Steel
The value proposition of 1.2779 (X6NiCrTi26-15) is clearest in direct comparison against the materials it is most often asked to replace or compete with.
1.2779 vs H13 — The Definitive Differences
H13 carbide precipitation degrades rapidly above 600 °C. At 750 °C, H13 yield strength drops below 200 MPa — unusable for structural loading. 1.2779 retains 480–560 MPa at the same temperature, translating to a reported up to 35–50% service life extension in continuous-service applications. H13 is also magnetic — a functional disqualifier for electromagnetic stirring roll applications.
1.2779 vs Alloy 625 — The Cost-Performance Case
Alloy 625 operates to 980 °C but costs 3.5–5× more and is significantly harder to machine. For applications below 750 °C where corrosion resistance is not the primary driver, 1.2779 delivers comparable mechanical performance at 30–40% lower total cost.
1.2779 vs 316L — Not the Same Material Category
316L has no precipitation-hardening mechanism. Its Rp0.2 drops to 110–160 MPa at 600 °C — less than one-quarter the value 1.2779 delivers. Specifying 316L for structural service above 500 °C means operating well outside the material's strength envelope.
Section 08 — Temperature Capability
Continuous Service Temperature Range Comparison
The 750 °C limit for 1.2779 is defined by the onset of Ni₃Ti precipitate dissolution back into the austenite matrix (overaging). Above this threshold, the precipitation-hardening effect degrades progressively and permanently.
Bars shown proportionally on a 980 °C baseline. 316L oxidation limit is 870 °C; structural strength limit approximately 550 °C.
For applications with continuous service above 750 °C, specify nickel-base superalloys: Alloy 625 (UNS N06625) or Alloy 718 (UNS N07718). Contact our engineering team for substitution guidance.
Section 09 — Industrial Applications
Proven Industrial Applications of 1.2779 Forging Parts
1.2779 (X6NiCrTi26-15) has been in serial industrial production for over 25 years across five well-established application categories. Each application below is chosen specifically because it requires either the non-magnetic austenitic structure, the precipitation-hardened high-temperature strength, or both — properties that no single conventional alternative fully provides. For available forging forms, dimensions, and weight range, see our custom X6NiCrTi26-15 forged rings, bars, and components page.
Non-magnetic structure is a functional requirement. Rolls supplied to steel mills in Germany, Italy, and Southeast Asia. Service life typically up to 40% longer than H13 in continuous casting environments at 600–750 °C.
Dies, die cases, and container liners for copper, brass, aluminum, and magnesium extrusion. Reported improvements in tool replacement frequency and extrusion production efficiency in field applications.
Heavy-duty hot rolling lines operating continuously at 650–750 °C. Stable hardness where conventional hot work steels soften. Used in facilities in Russia, India, and Brazil.
Precision forged valve seats, spindles, and bodies for industrial gas engines and steam turbines in Europe and North America. Long-term creep strength at 600–700 °C at lower cost than nickel-base superalloys.
Extrusion liners, forming dies, forging dies, and high-stress components in the 600–750 °C band. Economical alternative to nickel-base alloys where continuous temperature does not exceed 750 °C.
Section 10 — Procurement
Procurement Guide for Engineering and Purchasing Teams
Specifying 1.2779 (X6NiCrTi26-15) correctly requires more precision than standard tool steel grades. The following covers the critical items for purchase orders, supplier qualification, and incoming inspection.
Purchase order specification checklist
Material designation: Always specify DIN 17752 / X6NiCrTi26-15 / 1.2779 — not just the chemical symbol or a descriptive phrase.
Titanium range: For critical applications, add tighter internal Ti target such as Ti: 2.00–2.20%. Verify against actual heat analysis, not a conformance declaration.
Delivery condition: State explicitly — soft annealed, solution annealed, or solution annealed + aged — with minimum mechanical properties required.
Mill Test Certificate: Specify EN 10204 3.1 as minimum. For critical applications, specify EN 10204 3.2 — buyer arranges a nominated accredited body (BV, SGS, TÜV, Intertek); we accommodate inspector access at our Jiangyin facility.
Smelting route: Specify EAF+LF+VOD for standard, AM/VAR for heavy-section uniformity, or VIM/VAR for aerospace-grade purity.
Process documentation: For safety-critical parts, request furnace charts, pyrometry logs, and press tonnage records in addition to the MTC.
Common Procurement Mistakes
The most frequent error is accepting a certificate describing material as "precipitation-hardenable austenitic steel" without the DIN 17752 material number. The second common error is treating 1.2779 and A-286 (UNS S66286) as interchangeable — different Mo, B, and V balance, governed by different standards. Engineering review is mandatory before substitution.
Section 11 — Forging Process
Forging Process Requirements for 1.2779
Process parameters for 1.2779 differ significantly from standard carbon and low-alloy steel practice. The high nickel content (24–27%), low thermal conductivity (12.5 W/m·K), and strict finishing temperature sensitivity require process controls that commodity forging suppliers do not apply by default.
| Parameter | 1.2779 Requirement | Why It Matters |
|---|---|---|
| Forging temperature range | 950 – 1,160 °C | Below 1,100 °C: incomplete homogenization. Above 1,180 °C: grain boundary liquation risk |
| Min. finishing temperature | 950 °C — hard limit | Below 950 °C: adiabatic shear band formation and inter-granular cracking — most common root cause of 1.2779 field failures |
| Furnace soaking time | ≥ 1.5 h per 100 mm section | Required for temperature uniformity (±15 °C across section) due to low thermal conductivity |
| Minimum reduction ratio | 3:1 standard · 5:1+ critical | Breaks dendritic structure; ≥5:1 achieves ASTM grain size 5–7 |
| Post-forging cooling | Controlled slow cool to <200 °C | Rapid air cooling of heavy sections causes differential thermal stress cracking |
| Equipment preference | Hydraulic press for >1,000 kg | Controlled stroke limits adiabatic heating in high-Ni matrix |
Quality verification: A forging produced at incorrect finishing temperature or insufficient reduction ratio will pass chemical composition testing but fail in service. For safety-critical components, request furnace charts, pyrometry logs, and press tonnage records. Jiangsu Liangyi provides these on request.
Section 12 — FAQ
Frequently Asked Questions: 1.2779 (X6NiCrTi26-15) Steel
1.2779 (X6NiCrTi26-15) is a precipitation-hardenable austenitic steel per DIN 17752. It contains 24–27% nickel and 13.5–16% chromium, with titanium (1.90–2.30%) as the principal hardening agent. Aging at 710–730 °C precipitates coherent Ni₃Ti intermetallic particles throughout the austenite matrix, delivering minimum Rp0.2 of 650 MPa. Non-magnetic (μᵣ ≈ 1.003–1.010), continuous service to 750 °C.
750 °C continuous service, retaining typical Rp0.2 of 480–560 MPa at this temperature. Above 750 °C, Ni₃Ti precipitates begin to dissolve (overaging), permanently degrading strength. For above 750 °C, specify Alloy 625 (UNS N06625) or Alloy 718 (UNS N07718).
1.2779 retains 480–560 MPa Rp0.2 at 750 °C while H13 drops below 200 MPa — unusable for structural loading. In continuous high-temperature service, 1.2779 delivers reported up to 35–50% service life extension over H13. 1.2779 is also non-magnetic, which is a functional requirement for electromagnetic stirring roll applications where H13 cannot be used.
Two stages: (1) Solution annealing at 980–1,010 °C with rapid quench. (2) Aging at 710–730 °C for minimum 16 hours with controlled furnace cooling. This produces guaranteed minimum Rp0.2 650 MPa and Rm 950–1,150 MPa. A soft annealing step at 970–990 °C can be added before machining to improve machinability.
No. Fully austenitic, μᵣ ≈ 1.003–1.010. This is decisive for electromagnetic stirring roll applications in continuous casting. It also means standard magnetic particle inspection (MT/MPI) cannot be used — liquid penetrant (PT) must be specified instead.
Both are precipitation-hardenable austenitic grades with Ti-based Ni₃Ti hardening, but not interchangeable. Key differences: different Mo, B, and V balance; governed by different standards (DIN 17752 vs ASTM A638/AMS 5525/5737). Engineering review is mandatory before substitution in any qualified or safety-critical application.
EN 10204 3.1 as minimum (manufacturer's authorized inspector). For critical applications (aerospace, nuclear, PED pressure-containing), EN 10204 3.2 via third-party inspection arranged by the buyer through a nominated accredited body (BV, SGS, TÜV, Intertek). Jiangsu Liangyi accommodates inspector access at our Jiangyin facility. Both documents must reference "DIN 17752 / X6NiCrTi26-15 / 1.2779" explicitly.
No fixed MOQ at Jiangsu Liangyi. We accept single-piece orders for engineering qualification and tooling trials, as well as full production runs. Weight range: 30 kg to 30,000 kg per piece.
Ready to Source 1.2779 Forging Parts?
This guide covers the material engineering of 1.2779 (X6NiCrTi26-15). If you are ready to specify or procure, our product page lists all available forging forms, weight range (30 kg–30,000 kg), heat treatment conditions, smelting routes, and NDT options — with a direct quotation form.