⚡ Quick Specs: Alloy 625LCF
What Is Alloy 625LCF?
Alloy 625LCF (UNS N06626 / W.Nr. 2.4856) is a low-cycle fatigue optimized variant of Inconel 625. While it shares the same Ni-Cr-Mo-Nb chemistry and the same ASME Section VIII design-stress values as standard 625, the LCF grade tightens carbon (≤0.025% vs ≤0.10%) and silicon (≤0.30% vs ≤0.50%) to produce cleaner grain boundaries and a finer, more stable annealed grain structure. The result is a 30–50% improvement in low-cycle fatigue life — a critical advantage for thin-wall bellows, expansion joints, marine exhaust ducting, and any other component that sees repeated thermal or mechanical cycling.
625LCF is the industry standard reference material in EJMA (Expansion Joint Manufacturers Association) and ASME Code Case 2278 for severe-cycle bellows. It is also widely used in aerospace engine exhaust and marine EGR systems. As an established Alloy 625LCF manufacturer and supplier, Hangbo Alloy Group supplies the grade to ASTM B443 / ASME SB-443 in sheet, strip, plate, and tube forms.
Chemical Composition
Nominal composition of Alloy 625LCF per ASTM B443 / ASME SB-443 is shown below. All values in weight percent (wt%).
| Element | Alloy 625LCF | Standard 625 |
|---|---|---|
| C | ≤ 0.025 | ≤ 0.10 |
| Si | ≤ 0.30 | ≤ 0.50 |
| Mn | ≤ 0.50 | ≤ 0.50 |
| P | ≤ 0.020 | ≤ 0.015 |
| S | ≤ 0.015 | ≤ 0.015 |
| Cr | 20.0 – 23.0 | 20.0 – 23.0 |
| Ni | Balance | 58.0 min |
| Mo | 8.0 – 10.0 | 8.0 – 10.0 |
| Nb | 3.15 – 4.15 | 3.15 – 4.15 |
| Fe | ≤ 5.0 | ≤ 5.0 |
| Al | ≤ 0.40 | ≤ 0.40 |
| Ti | ≤ 0.40 | ≤ 0.40 |
| Co | ≤ 1.0 | ≤ 1.0 |
The single most important chemistry change is the C cap. At 0.025% the volume fraction of M₂₃C₆ grain-boundary carbides is dramatically reduced, leaving cleaner grain boundaries that resist fatigue-crack initiation. Si is also lowered because silicon promotes deleterious intermetallic formation during long-term thermal exposure. The minimum Nb is held at the high end of the range to ensure sufficient niobium for matrix strengthening without relying on grain-boundary carbides.
Physical Properties
| Property | Value |
|---|---|
| Density | 8.44 g/cm³ (0.305 lb/in³) |
| Melting Range | 1290 – 1350 °C (2354 – 2462 °F) |
| Specific Heat (20 °C) | ~ 410 J/kg·K |
| Thermal Conductivity (20 °C) | ~ 12.1 W/m·K |
| Electrical Resistivity (20 °C) | ~ 1.29 µΩ·m |
| Young's Modulus | ~ 207 GPa |
| Mean CTE (20–200 °C) | ~ 12.8 × 10⁻⁶ /K |
Mechanical Properties (Room Temperature, Annealed Sheet)
| Property | Alloy 625LCF | Standard 625 |
|---|---|---|
| Tensile Strength (Rm) | ≥ 827 MPa (120 ksi) | ≥ 827 MPa (120 ksi) |
| Yield Strength (Rp0.2) | ≥ 414 MPa (60 ksi) | ≥ 414 MPa (60 ksi) |
| Elongation (A%) | ≥ 30% | ≥ 30% |
| Hardness | ≤ 200 HB | ≤ 200 HB |
| LCF Life @ 1% strain, 650 °C | ~ 10,000+ cycles | ~ 5,000–6,000 cycles |
| Condition | Solution annealed 1095 °C min | Solution annealed 1095 °C min |
Static tensile and yield strengths are identical to standard 625 — so 625LCF can be specified in pressure-vessel design using the same ASME Section VIII design-stress values. The benefit is paid out in fatigue life, which is what matters for bellows, expansion joints, and EGR coolers.
Low-Cycle Fatigue Performance
Alloy 625LCF was specifically developed to extend the fatigue life of cyclically loaded thin-wall components. The chemistry control and finer annealed grain size push the fatigue-crack initiation threshold up by a factor of 2–3 compared to standard 625 in the strain-controlled low-cycle regime. Representative data:
- Strain-controlled LCF @ 650 °C, 1.0% total strain range: 625LCF reaches ~10,000 cycles to crack initiation, vs ~5,000 for standard 625.
- Strain-controlled LCF @ 25 °C, 0.5% total strain range: 625LCF exceeds 50,000 cycles, vs ~30,000 for standard 625.
- Thermal fatigue (650 °C ↔ 25 °C, 5 min cycles): 625LCF shows 2× the cycles to first crack vs standard 625.
Corrosion Resistance
Alloy 625LCF inherits the full corrosion performance of standard Inconel 625 — and the lower carbon content actually improves intergranular corrosion resistance.
- Outstanding resistance to pitting, crevice corrosion, and chloride SCC up to ~200 °C
- Excellent in sulfuric, phosphoric, nitric, and mixed acid environments
- Proven in marine seawater service, FGD scrubbers, and sour oil & gas (NACE MR0175 qualified)
- No susceptibility to intergranular attack in the as-welded or stress-relieved condition — the low C cap eliminates M₂₃C₆ precipitation at grain boundaries
Applications
Alloy 625LCF is specified wherever thin-wall components must survive millions of mechanical or thermal cycles. It is the EJMA and ASME Code Case reference material for severe-cycle bellows and expansion joints.
| Application Area | Typical Components & Notes |
|---|---|
| Thin-Wall Bellows | Process piping, EGR coolers, aerospace engine exhaust — the canonical use of 625LCF |
| Expansion Joints | Power-plant, petrochemical, and marine piping expansion joints subject to severe thermal cycling |
| Marine Exhaust Ducting | Ship and submarine exhaust systems handling hot combustion gases and seawater exposure |
| Aerospace | Engine bellows, thrust reverser seals, exhaust manifolds, and rocket-engine flexible joints |
| Cryogenic / LNG | LNG piping and valve bellows down to –196 °C |
| Pressure Vessel Heads | Thin-wall formed heads subject to pressure cycling and thermal fatigue |
| Instrument Tubing | Vibration-prone instrument lines in power, refinery, and offshore service |
Available Product Forms
| Product Form | Typical Dimensions |
|---|---|
| Sheet & Strip (ASTM B443) | Thickness 0.10 – 4.0 mm, width up to 1500 mm — the primary product form for bellows |
| Plate (ASTM B443) | Thickness 4 – 25 mm, width up to 2500 mm |
| Seamless Tube (ASTM B444) | OD 6 – 219 mm, WT 0.5 – 15 mm |
| Welded Tube (ASTM B704) | OD 10 – 1219 mm, WT 0.5 – 12 mm |
| Rod & Bar (ASTM B446) | φ 6 – φ 250 mm, hot-rolled, cold-drawn |
| Welding Consumables | ERNiCrMo-3 (matching Inconel 625 filler) |
Related Standards & Specifications
| Standard | Product Scope |
|---|---|
| ASTM B443 / ASME SB-443 | Plate, sheet & strip — primary standard for 625LCF |
| ASME Code Case 2278 | Pressure-vessel use of UNS N06626 in Section VIII Division 1 |
| ASME Code Case 2417 | Alternative for Section VIII Division 2 |
| ASTM B444 / SB-444 | Seamless pipe & tube |
| ASTM B446 / SB-446 | Rod & bar |
| ASTM B704 / SB-704 | Welded tube |
| EJMA Standards | Expansion Joint Manufacturers Association reference material for severe-cycle bellows |
| NACE MR0175 / ISO 15156 | Sour-service environments |
| DIN / W.Nr. | 2.4856 |
Frequently Asked Questions (FAQ)
1. What is Alloy 625LCF?
Alloy 625LCF (UNS N06626 / W.Nr. 2.4856) is a low-cycle fatigue optimized variant of Inconel 625. By lowering carbon and silicon to ~0.020% and ~0.20% respectively, the alloy achieves a 30–50% improvement in low-cycle fatigue life versus standard 625, making it the preferred material for thin-wall bellows, expansion joints, marine exhaust ducting, and any other component subject to repeated thermal or mechanical cycling. As a leading Alloy 625LCF manufacturer and supplier, Hangbo Alloy Group produces the grade to ASTM B443 / ASME SB-443 in sheet, strip, plate, and tube.
2. What is the chemical composition of Alloy 625LCF?
Nominal Alloy 625LCF composition (wt%): C ≤0.025, Mn ≤0.50, Si ≤0.30, P ≤0.020, S ≤0.015, Cr 20.0–23.0, Ni balance, Mo 8.0–10.0, Nb 3.15–4.15, Fe ≤5.0, Al ≤0.40, Ti ≤0.40, Co ≤1.0. Compared to standard 625 the C and Si limits are tightened and Nb is held on the high side to control grain-boundary precipitation during cyclic loading.
3. What is the density and melting point of Alloy 625LCF?
Alloy 625LCF has a density of approximately 8.44 g/cm³ (0.305 lb/in³) and a melting range of about 1290–1350 °C (2354–2462 °F). The density is essentially identical to standard Inconel 625.
4. What are the mechanical properties of Alloy 625LCF?
Annealed sheet at room temperature: tensile strength ≥827 MPa (120 ksi), 0.2% yield strength ≥414 MPa (60 ksi), elongation ≥30%, hardness ≤200 HB. Compared to standard 625 (UTS ≥827, YS ≥414), 625LCF gives the same static strength but with substantially better fatigue endurance — typically 30–50% more cycles to crack initiation at 0.5–1.0% strain range.
5. How does Alloy 625LCF compare to standard Inconel 625?
The two grades share the same Ni-Cr-Mo-Nb chemistry and the same ASME Section VIII design stress, but 625LCF has tighter limits on C (≤0.025% vs ≤0.10%) and Si (≤0.30% vs ≤0.50%), plus a slightly higher minimum Nb (3.15% vs 3.15%). The result is a finer, more stable grain-boundary carbide population that dramatically improves resistance to fatigue-crack initiation under cyclic strain. For static-loaded pressure vessels, standard 625 is fine; for bellows, expansion joints, and other thin-wall cyclically loaded parts, 625LCF is the industry standard.
6. What is the maximum service temperature of Alloy 625LCF?
Alloy 625LCF is suitable for continuous service up to about 980 °C (1800 °F) and intermittent service up to 1095 °C (2000 °F). In bellows and expansion joints it is most often used between –196 °C and 650 °C. The alloy retains useful strength at cryogenic temperatures and is fully non-magnetic.
7. What is the corrosion resistance of Alloy 625LCF?
Alloy 625LCF has the same excellent corrosion resistance as standard Inconel 625: outstanding resistance to pitting, crevice, and stress corrosion cracking in chloride-bearing environments; immunity to chloride SCC up to ~200 °C; good performance in sulfuric, phosphoric, and nitric acids; and proven service in marine seawater and sour oil & gas. The lower carbon content actually helps intergranular corrosion resistance, since less chromium carbide can precipitate at grain boundaries.
8. Can Alloy 625LCF be welded?
Yes. Alloy 625LCF is readily welded by GTAW, GMAW, and plasma processes. The standard matching filler is ERNiCrMo-3 (Inconel 625 wire), also to AWS A5.14. No preheat is required; interpass temperature should be kept low (≤150 °C). For thin-wall bellows, micro-plasma or pulsed TIG with low heat input is preferred to preserve the fine-grain annealed structure that gives the alloy its fatigue advantage.
9. What standards apply to Alloy 625LCF?
Alloy 625LCF is produced under ASTM B443 (plate, sheet, strip), ASME SB-443 (pressure vessel code case 2278 and 2417), ASTM B444 (seamless pipe & tube), ASTM B446 (rod & bar), ASTM B704 (welded tube), and the corresponding ASME SB equivalents. The grade is also referenced in ASME Section VIII Division 1 Code Case 2278 and is qualified under NACE MR0175 for sour service.
10. What are the typical applications of Alloy 625LCF?
Primary applications: (1) Thin-wall bellows for process piping, marine exhaust, and aerospace; (2) Expansion joints in power, petrochemical, and marine piping; (3) Marine exhaust ducting and EGR coolers; (4) Aircraft and rocket engine bellows; (5) Cryogenic piping and LNG equipment; (6) Pressure-vessel heads and other cyclically loaded thin-wall components; (7) Instrument tubing subject to vibration and thermal cycling.
11. What is the price and lead time for Alloy 625LCF?
Alloy 625LCF is priced at a small premium to standard 625, reflecting tighter chemistry control and additional testing. Indicative pricing: sheet & strip $40–60/kg, plate $35–55/kg, seamless tube $70–120/kg, bellows-quality strip at thinner gauges is often quoted by linear meter. Lead time: 8–14 weeks for mill production; Hangbo maintains limited stock for fast shipment. MOQ: 50 kg for stock items. Contact hangbo@nickel-alloy.com for current pricing.
12. Why is low-cycle fatigue important for bellows and expansion joints?
Bellows, expansion joints, and EGR coolers accumulate large cyclic strains — typically 0.5–2% per cycle — over millions of start-stop and thermal cycles. Standard nickel alloys can withstand a few thousand such cycles before cracking; 625LCF routinely exceeds 10,000 cycles at the same strain range. The fatigue-crack initiation resistance comes from clean grain boundaries (low C, low Si) and a fine-grained annealed structure, which is why 625LCF is the ASME and EJMA reference material for severe-cycle bellows and expansion joints.
Need Alloy 625LCF for Bellows, Expansion Joints or Marine Exhaust?
Hangbo Alloy Group is a trusted global manufacturer and supplier of Alloy 625LCF (UNS N06626 / 2.4856) in sheet, strip, plate, and tube forms. Mill test certificates to EN 10204 3.1, full traceability, and competitive pricing on every order.