The question we hear most from procurement engineers: "We need a high-performance nickel alloy forging — should we specify Inconel 600, 625, or 718?" These three grades account for the majority of nickel superalloy forging orders at Jiangsu Liangyi — including Inconel 600 forged bars, rings, and discs — yet they serve entirely different roles. Choosing wrong means either over-spending on capabilities you don't need, or under-specifying a part that fails in service. This guide provides real data — not marketing language — so you can make the right call.
Three Grades, Three Engineering Philosophies
Inconel 600, 625, and 718 are all nickel-chromium superalloys, but they reach their performance targets through completely different metallurgical mechanisms. The "right" choice is always application-specific — never simply "the strongest" or "most corrosion-resistant."
ⓘ "Inconel" is a registered trademark of Special Metals Corporation (a PCC company). On this page, Inconel 600, 625, and 718 refer to the alloy compositions designated UNS N06600, UNS N06625, and UNS N07718 per ASTM, ASME, AMS, and DIN standards. Jiangsu Liangyi Co., Limited is not affiliated with or endorsed by Special Metals Corporation.
Solid-solution strengthened. The thermal workhorse. Excellent oxidation resistance to 1,095°C, outstanding chloride SCC resistance, and the most forgiving grade to forge, machine and weld of the three.
Solid-solution + precipitation strengthened by Nb and Mo. Outstanding seawater and acid corrosion resistance (PREN ≈ 48). The primary choice for marine, subsea, and aggressive chemical environments.
Age-hardened precipitation superalloy. The highest room-temperature and cryogenic strength of the three — exceeding 1,100 MPa yield. Dominant in gas turbines, aerospace, and high-pressure rotating equipment.
Why Chemistry Drives Performance
The performance gap between these grades traces directly to elemental composition. Understanding what each alloying element does is the fastest route to understanding which grade you need.
| Element | Inconel 600 (%) | Inconel 625 (%) | Inconel 718 (%) |
|---|---|---|---|
| Nickel (Ni) | ≥ 72.0 | 58.0 min | 50.0 – 55.0 |
| Chromium (Cr) | 14.0 – 17.0 | 20.0 – 23.0 | 17.0 – 21.0 |
| Iron (Fe) | 6.0 – 10.0 | ≤ 5.0 | Balance (~18) |
| Molybdenum (Mo) | — | 8.0 – 10.0 | 2.8 – 3.3 |
| Niobium (Nb) | — | 3.15 – 4.15 | 4.75 – 5.50 |
| Aluminum (Al) | — | ≤ 0.40 | 0.20 – 0.80 |
| Titanium (Ti) | — | ≤ 0.40 | 0.65 – 1.15 |
| Carbon (C) | ≤ 0.15 * | ≤ 0.10 | ≤ 0.08 |
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* For nuclear-grade Inconel 600, Jiangsu Liangyi achieves C ≤ 0.05% via VIM melting to prevent sensitization in weld heat-affected zones between 427°C and 760°C.
Mo + Nb in Inconel 625 provide exceptional pitting resistance (Mo) and solid-solution strengthening from large Nb atoms. In Inconel 718, those same Nb atoms form the γ″ (Ni₃Nb) precipitate phase — the primary strengthening mechanism — delivering yield strength above 1,000 MPa that neither 600 nor 625 can approach in the annealed condition.
Room-Temperature and Elevated-Temperature Data
| Property | Inconel 600 Annealed · ASTM B564 |
Inconel 625 Annealed · ASTM B564 |
Inconel 718 Age-hardened · AMS 5663 |
|---|---|---|---|
| Tensile Strength (UTS) | 550 – 690 MPa | 827 – 965 MPa | Best: 1,275 – 1,380 MPa |
| Yield Strength (0.2%) | 240 – 310 MPa | 414 – 517 MPa | Best: 1,034 – 1,103 MPa |
| Elongation | Best: 35 – 45% | 30 – 35% | 12 – 20% |
| Hardness | ≤ 22 HRC | ≤ 30 HRC | Best: 36 – 44 HRC |
| Max Continuous Temp. | Best: 1,095°C (2,000°F) | 980°C (1,800°F) | 704°C (1,300°F) |
| Oxidation Resistance | Best: Excellent | Good | Fair |
| Weldability | Best: Excellent | Very Good | Good (needs PWHT) |
| Forgeability | Best: Excellent | Good | Moderate (tight window) |
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Yield Strength vs. Temperature
Values are representative of published industry literature for forged stock in the stated heat treatment condition. These are reference values only. Always obtain and verify certified material test reports (CMTRs) specific to each heat before use in any engineering or design calculation.
Where Each Grade Excels — and Where It Falls Short
Corrosion behavior is often the decisive factor for chemical processing, oil and gas, and marine applications. The three grades occupy clearly distinct niches.
| Corrosion Environment | Inconel 600 | Inconel 625 | Inconel 718 |
|---|---|---|---|
| Chloride stress corrosion cracking | Best: Excellent | Best: Excellent | Good |
| Seawater pitting & crevice corrosion | Fair | Best: Excellent (PREN ≈ 48) | Good |
| High-temp oxidation (> 800°C) | Best: Excellent | Good | Not for > 704°C |
| Carburization & sulfidation | Best: Excellent | Good | Limited |
| Caustic / alkaline environments | Best: Excellent | Good | Good |
| HCl & H₂SO₄ (dilute acid) | Good | Best: Excellent (Mo effect) | Good |
| Hydrofluoric acid (HF) | Best: Excellent | Good | Not recommended |
| Sour gas (H₂S + Cl⁻) NACE MR0175 | Fair | Best: Excellent | Good (hardness limits apply) |
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Inconel 625 is the only grade that combines both excellent pitting resistance AND chloride SCC resistance. This dual capability — driven by Mo + elevated Cr — is why it dominates subsea and offshore applications where both mechanisms act simultaneously. Inconel 600's strength lies in high-temperature alkaline and oxidizing gas environments, not aggressive aqueous corrosion.
Forging Behavior and Process Considerations
At Jiangsu Liangyi, all three grades are produced daily across our 4,000-ton and 6,000-ton hydraulic presses. The differences in forging behavior are significant and directly affect lead time, scrap rate, and final part cost. If Inconel 600 meets your temperature and corrosion requirements, you can request a custom Inconel 600 forging quotation directly from our product page.
- Forging range: 900°C – 1,200°C
- Widest hot-working window of the three
- Lowest flow stress — most forgiving in complex shapes
- Open die and ring rolling: excellent up to 3,000 mm OD
- No mandatory PWHT for most applications
- Lowest scrap risk; shortest typical lead time
- Forging range: 960°C – 1,175°C
- Mo and Nb increase flow stress vs. 600
- Surface cracking risk if finish-forged too cold
- Ring rolling: excellent up to 6,000 mm OD
- No PWHT usually required; excellent weld overlay capability
- Moderate scrap risk on heavy sections
- Forging range: 950°C – 1,120°C (tightest window)
- Highest flow stress — most demanding on press tonnage
- Overheating causes immediate grain coarsening (rejects)
- Mandatory dual-stage age hardening after forging
- Welding requires preheat and post-weld heat treatment
- Highest scrap risk; premium lead time
- All grades: VIM + ESR + VAR triple melt process
- Eliminates Nb segregation in heavy 625 and 718 forgings
- Critical for γ″ uniformity in large 718 sections
- Single piece weight: 30 kg to 30,000 kg
- Annual capacity: 120,000 metric tons
Which Industries Specify Each Grade
| Industry / Application | Inconel 600 | Inconel 625 | Inconel 718 |
|---|---|---|---|
| Nuclear power (reactor internals, steam generators) | Primary | Used | — |
| Furnace hardware, radiant tubes, retorts | Primary | — | — |
| Gas turbine blades and discs | — | Some | Primary |
| Aerospace fasteners and structural forgings | — | Some | Primary |
| Subsea wellheads and Christmas trees | — | Primary | Used |
| Chemical processing (acid / caustic service) | Good | Primary | — |
| Marine propeller shafts and sea water systems | Fair | Primary | — |
| Pressure vessels and heat exchangers (tube sheets) | Primary | Used | — |
| Cryogenic applications | Good | Good | Best: Excellent |
| Oil and gas wellhead equipment (API 6A) | Limited | Primary | Used |
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Relative Cost Comparison
Nickel alloy pricing fluctuates with LME Ni, Mo, Nb, and energy costs. The relative cost relationship between the three grades is however fairly stable:
Lowest raw material cost. Simplest processing. Shortest typical lead time: 4 – 8 weeks for standard shapes.
Mo and Nb premiums add 50 – 80% over Inconel 600 base cost. Typical lead time: 6 – 12 weeks for forged components.
Premium alloy + mandatory age hardening + tighter process control = highest total cost. Lead time: 8 – 16 weeks including heat treatment cycles.
Do not over-specify. Inconel 718's superior strength is valuable only if your part is genuinely strength-limited at service temperature. For static pressure vessel components operating below 650°C, Inconel 600 or 625 will meet all code requirements at 40 – 60% lower cost. Specify the grade that satisfies the most demanding design requirement — not the one with the highest number on a datasheet.
Applicable Codes and Standards
| Standard / Code | Inconel 600 | Inconel 625 | Inconel 718 |
|---|---|---|---|
| ASTM / ASME Forgings | ASTM B564 / ASME SB-564 | ASTM B564 / ASME SB-564 | ASTM B637 / ASME SB-637 |
| Aerospace (AMS) | AMS 5665 | AMS 5666 | AMS 5663 (AH) / 5664 (Ann) |
| DIN / EN European | W.Nr. 2.4816 | W.Nr. 2.4856 | W.Nr. 2.4668 |
| Oil & Gas | NACE MR0175 (limited) | NACE MR0175 / ISO 15156 / API 6A | NACE MR0175 (hardness limits) |
| Nuclear | ASME Sect. III / RCC-M (primary) | Per project specification | Rare in nuclear pressure boundary |
| NDT (Jiangsu Liangyi) | ASTM A388 / EN 10228-3 | ASTM A388 / API 6A UT | AMS 2154 (UT) / AMS 2175 (FPI) |
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At Jiangsu Liangyi, we produce Inconel 600 forging parts (UNS N06600) in accordance with ASTM B564 / ASME SB-564 and AMS 5665, with full traceability including VIM/ESR/VAR melt records, chemistry certifications, mechanical test reports, and complete NDT documentation. All three grades are available from stock material or custom-melted to tighter chemistry for nuclear and aerospace projects.
How to Choose: A Practical Specification Guide
Work through these criteria in sequence. The first criterion that uniquely qualifies a grade determines your specification:
Common Questions from Engineers and Buyers
Mechanically, Inconel 625 meets or exceeds Inconel 600's properties — so the substitution is conservative from a strength standpoint. However, if the original design is written to a specific code (such as ASME Section III for nuclear service), a material substitution requires formal engineering review and, typically, code-body approval. Never substitute without engineering sign-off, regardless of how conservative the change appears.
At temperatures above approximately 704°C, the γ″ (Ni₃Nb) precipitate phase that gives Inconel 718 its exceptional strength begins to dissolve and transform into the equilibrium δ (delta) phase, which provides no strengthening. The alloy does not simply become "weaker" — its strengthening mechanism literally ceases to function. This is a fundamental metallurgical limit, not a conservative design margin. For applications above this temperature, Inconel 600, 617, or 625 must be evaluated.
ASTM B564 allows up to 0.15% carbon in Inconel 600. However, carbon above 0.08% significantly increases sensitization risk when parts are welded or operate between 427°C and 760°C. For field-welded parts or components in this temperature range, specify a maximum of 0.05% carbon. Jiangsu Liangyi achieves this through controlled VIM melting, and we recommend this limit for all nuclear and critical-service applications.
For forgings, "annealed" and "solution annealed" are typically the same treatment: heating to 1,093°C – 1,177°C followed by rapid cooling, producing a single-phase austenitic matrix with maximum corrosion resistance. If a supplier quotes "annealed" Inconel 625 without specifying the treatment temperature, always confirm a full solution anneal was performed — and verify with a microstructure report. Incomplete annealing can leave secondary carbide phases that reduce corrosion performance.
Yes — though its role has evolved. Inconel 600 was the original material for steam generator tubing in pressurized water reactors (PWRs). Some plants experienced primary-water stress corrosion cracking (PWSCC) in tube-to-tubesheet welds, leading to widespread adoption of Inconel 690 for new steam generators. However, Inconel 600 forgings remain widely used for non-tubular nuclear components — pressure boundary forgings, flanges, nozzles, and valve bodies — where PWSCC is not a governing failure mode.
The Bottom Line
The choice between Inconel 600, 625, and 718 is not about which is "best" — it is about which is right for the specific combination of temperature, environment, mechanical load, code, and budget your application demands.
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Inconel 600 — specify when the primary challenge is high temperature, oxidizing atmospheres, or alkaline corrosion. Best value for furnace, boiler, nuclear, and heat exchanger forgings. Easiest to forge, weld, and inspect.
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Inconel 625 — specify when the primary challenge is aqueous corrosion, pitting, crevice attack, or aggressive chemical media. The dominant choice for subsea, offshore, chemical processing, and marine forgings.
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Inconel 718 — specify when the primary challenge is maximum tensile and yield strength at service temperatures below 704°C. The dominant choice for gas turbines, aerospace rotating parts, and high-pressure structural components.
If you are uncertain which grade is right for your application, our technical team at Jiangsu Liangyi provides a free material grade consultation. Send us your operating temperature, environment, applicable code, and required mechanical properties — we will recommend the correct grade and provide a custom quotation from 30 kg to 30,000 kg per piece.
For full technical specifications, production capability data, chemical composition tables, and available product forms, see our dedicated page for UNS N06600 forging parts manufactured by Jiangsu Liangyi — covering every standard and custom shape from forged bars to seamless rings up to 3,000 mm OD.
For full technical data, production capabilities, and a custom quotation for custom Inconel 600 forging parts (UNS N06600), visit our dedicated product page.
Verified Technical Facts: Inconel 600 vs 625 vs 718
The following table consolidates the most-cited engineering facts about Inconel 600, 625, and 718 forging grades in a single verified reference. All values are consistent with ASTM B564, ASTM B637, AMS 5665, AMS 5666, AMS 5663, and published industry data sheets. "Inconel" is a registered trademark of Special Metals Corporation (a PCC company). Jiangsu Liangyi is an independent manufacturer and is not affiliated with Special Metals Corporation. UNS N06600, UNS N06625, and UNS N07718 are the official material designations used in our production and quality documentation.
| Fact / Specification | Inconel 600 (N06600) | Inconel 625 (N06625) | Inconel 718 (N07718) |
|---|---|---|---|
| Also known as | Alloy 600, NiCr15Fe, W.Nr. 2.4816 | Alloy 625, NiCr22Mo9Nb, W.Nr. 2.4856 | Alloy 718, NiCr19Fe19Nb5Mo3, W.Nr. 2.4668 |
| Primary standard (forgings) | ASTM B564 / ASME SB-564 | ASTM B564 / ASME SB-564 | ASTM B637 / ASME SB-637 |
| Aerospace standard | AMS 5665 | AMS 5666 | AMS 5663 (AH) / AMS 5664 (Ann) |
| Nickel content | ≥ 72.0% | 58.0% min | 50.0 – 55.0% |
| Chromium content | 14.0 – 17.0% | 20.0 – 23.0% | 17.0 – 21.0% |
| Strengthening mechanism | Solid solution | Solid solution + Nb/Mo precipitation | γ″ (Ni₃Nb) precipitation hardening |
| UTS (room temp, std condition) | 550 – 690 MPa (annealed) | 827 – 965 MPa (annealed) | 1,275 – 1,380 MPa (age-hardened) |
| Yield strength (room temp) | 240 – 310 MPa (annealed) | 414 – 517 MPa (annealed) | 1,034 – 1,103 MPa (age-hardened) |
| Max continuous service temp | 1,095°C (2,000°F) | 980°C (1,800°F) | 704°C (1,300°F) |
| Pitting resistance (PREN) | ~20 | ~48 | ~32 |
| Primary corrosion resistance | Oxidation, caustic, HF, Cl⁻ SCC | Seawater pitting, crevice, sour gas, acids | Moderate — not for aggressive aqueous |
| Forging temperature range | 900 – 1,200°C | 960 – 1,175°C | 950 – 1,120°C |
| Post-weld heat treatment | Not required (most applications) | Not required (most applications) | Required (dual-stage age hardening) |
| Primary industries | Nuclear, furnace, heat exchanger, chemical | Subsea, offshore, marine, chemical processing | Aerospace, gas turbine, cryogenic |
| Relative cost index | 1.0× (baseline) | 1.5 – 1.8× | 1.8 – 2.5× |
| Carbon limit (nuclear/weld service) | ≤ 0.05% (VIM controlled) | ≤ 0.10% standard | ≤ 0.08% standard |
| NACE MR0175 compliance | Limited | Full compliance | Conditional (hardness limit HRC ≤ 40) |
| Max ring OD (Jiangsu Liangyi) | 3,000 mm | 6,000 mm | 3,000 mm |
| Part weight range | 30 kg – 30,000 kg | 30 kg – 30,000 kg | 30 kg – 30,000 kg |
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All data in this table represents values achievable from Jiangsu Liangyi's VIM + ESR + VAR triple-melt forging process. Certified material test reports (EN 10204 3.1 or 3.2) are supplied with every order. For design calculations, always verify against your applicable code and request lot-specific certified test reports from your forging supplier.
Additional FAQ
Both Inconel 600 (UNS N06600, 72%+ Ni, 14–17% Cr) and Incoloy 800 (UNS N08800, 30–35% Ni, 19–23% Cr) are nickel-chromium alloys for high-temperature service. Inconel 600 has significantly higher nickel content, giving it superior resistance to chloride SCC, caustic attack, and reduction in environments containing HCl and HF. Incoloy 800 is more economical due to lower nickel content and is preferred for carburization and high-temperature oxidation service in the 600°C–900°C range when the extreme corrosion resistance of Inconel 600 is not required.
Jiangsu Liangyi manufactures custom forgings in Inconel 600 (UNS N06600), Inconel 625 (UNS N06625), Inconel 718 (UNS N07718), and over 10 additional Inconel and Incoloy grades including 601, 617, 625, 690, X-750, and 783. Minimum order weight is one piece from 30 kg. Maximum single-piece weight is 30,000 kg. There is no minimum order quantity for custom forgings — single-piece prototypes are accepted. Free technical consultation and quotation are provided within 24 hours.
At Jiangsu Liangyi, all nickel superalloy forgings receive 100% ultrasonic testing (UT) per ASTM A388 and EN 10228-3 as standard. For aerospace and nuclear applications, additional liquid penetrant inspection (LPI/FPI) per AMS 2175 and magnetic particle inspection (where applicable) are performed. For Inconel 718 forgings per AMS 5663/5664, UT acceptance criteria are performed to the requirements of AMS 2154 class A or B per customer specification. All test records are included in the EN 10204 3.1 or 3.2 material documentation package. Note: AMS and API designations referenced throughout this page are material and process standards, not certifications held by Jiangsu Liangyi. Our only quality management system certification is ISO 9001:2015.