Is Inconel Stronger Than Stainless Steel?

Inconel alloys are generally stronger than the most commonly used stainless steels — especially when the service requires high tensile/yield strength at elevated temperature, outstanding creep resistance, and sustained performance in oxidizing or carburizing atmospheres. For room-temperature toughness and everyday corrosion resistance in benign media, many stainless steels (e.g., 304/316) are fully adequate and much more economical. When the application pushes temperature, creep life, or extreme corrosive environments, Inconel (and other nickel-base superalloys) typically outperforms stainless steels.

What are Inconel and stainless steels?

Inconel is a registered trade name for several nickel-chromium based alloys (sometimes with Fe, Mo, Nb, Ti, Al depending on grade) engineered for high strength and corrosion resistance at elevated temperatures. Typical Inconel grades encountered in industry include Inconel 600 (a general-purpose Ni-Cr alloy), Inconel 625 (a solid-solution strengthened Ni-Cr-Mo alloy), and Inconel 718 (a precipitation-hardened Ni-Cr-Nb alloy with very high strength). These alloys are classed among nickel-base “superalloys” and are intentionally designed for aggressive, high-temperature environments.

Stainless steels are iron-based alloys with a minimum of ~10.5% chromium that gain corrosion resistance from a passive chromium oxide film. The family is large: ferritic (e.g., 430), austenitic (e.g., 304, 316), martensitic (e.g., 410, 420), and precipitation-hardening stainless steels (e.g., 17-4 PH). Strength and temperature capability vary widely across this family. Austenitic grades offer good corrosion resistance and toughness; martensitic and PH grades can achieve high room-temperature strength but typically lose strength and oxidation resistance at high temperatures.

Chemistry and microstructure: why they behave differently

• Nickel content & matrix: Inconel alloys have high nickel content (often 50%+), which stabilizes a face-centered cubic (fcc) matrix that resists phase changes at high temperature and supports solid-solution and precipitation strengthening strategies. Nickel also slows diffusion and oxidation kinetics, boosting creep life.

• Strengthening mechanisms: Inconel 718 is strengthened primarily by precipitation of γ'' and other Nb/Ti-rich phases; 625 relies on solid-solution and some carbide formation; 600 is a simpler Ni-Cr system with good high-temperature stability. Stainless steels get strength by solution strengthening (austenitics), martensitic transformation (martensitics), or precipitation hardening (e.g., 17-4PH). The mechanisms determine temperature limits and how strength changes with heat.

• Phase stability: Many stainless steels form deleterious phases (sigma, carbides) if exposed to certain temperatures or long times; superalloys are engineered to avoid such embrittling phases in the intended service window.

Direct mechanical comparison (tables)

Below are condensed, representative property ranges for commonly compared grades. Materials data vary with temper, processing, and supplier; values listed are typical annealed/standard temp conditions and are intended for direct, practical comparison.

Table 1 — Typical tensile and yield strength (room temperature, typical heats)

Interpretation: Inconel 718 delivers much higher sustained tensile and yield than common austenitic stainless steels; Inconel 625 also typically exceeds 304/316 in tensile strength. A specialized PH stainless like 17-4PH in certain tempers can rival or exceed some Inconel grades in room-temperature strength, but it lacks the same high-temperature creep/oxidation resistance.

Table 2 — High-temperature capability (qualitative)

Key point: If temperature is a primary driver, Inconel and other nickel-base superalloys were designed for that environment and maintain mechanical integrity where stainless steels soften or oxidize.

Inconel Equivalent Grades

STANDARD	WERKSTOFF NR.	UNS	GOST	AFNOR	JIS	BS	EN	OR
Inconel 600	2.4816	N06600	МНЖМц 28-2,5-1,5	NC15FE11M	NCF 600	NA 13	NiCr15Fe	ЭИ868
Inconel 601	2.4851	N06601	XH60BT	NC23FeA	NCF 601	NA 49	NiCr23Fe	ЭИ868
Inconel 617	2.4663	N06617
Inconel 625	2.4856	N06625	ХН75МБТЮ	NC22DNB4M	NCF 625	NA 21	NiCr22Mo9Nb	ЭИ602
Inconel 690	2.4642	N06690
Inconel 718	2.4668	N07718
Inconel 725	-	N07725
Inconel X-750	2.4669	N07750

Inconel Melting Point, Density and Tensile Strength

	Density	Melting Point	Tensile Strength	Yield Strength (0.2%Offset)	Elongation
600	8.47 g/cm3	1413 °C (2580 °F)	Psi – 95,000 , MPa – 655	Psi – 45,000 , MPa – 310	40 %
601	8.1 g/cm3	1411 °C (2571 °F)	Psi – 80,000 , MPa – 550	Psi – 30,000 , MPa – 205	30 %
617	8.3g/cm³	1363°C	≥ 485 MPa	≥ 275 MPa	25 %
625	8.4 g/cm3	1350 °C (2460 °F)	Psi – 135,000 , MPa – 930	Psi – 75,000 , MPa – 517	42.5 %
690	8.3g/cm³	1363°C	≥ 485 MPa	≥ 275 MPa	25 %
718	8.2 g/cm3	1350 °C (2460 °F)	Psi – 135,000 , MPa – 930	Psi – 70,000 , MPa – 482	45 %
725	8.31 g/cm3	1271°C-1343 °C	1137 MPa	827 MPa	20 %
X-750	8.28 g/cm3	1430°C	1267 MPa	868 MPa	25 %

Stainless Steel

Stainless Steel Equivalent Grades

STANDARD	WERKSTOFF NR.	UNS	JIS	BS	GOST	AFNOR	EN
SS 304	1.4301	S30400	SUS 304	304S31	08Х18Н10	Z7CN18‐09	X5CrNi18-10
SS 304L	1.4306/1.4307	S30403	SUS 304L	304S11	03Х18Н11	Z3CN18‐10	X2CrNi18-9 / X2CrNi19-11
SS 310	1.4845	S31000	-	-	-	-	-
SS 310S	1.4845	S31008	SUS310S	-	20Ch23N18	-	X8CrNi25-21
SS 316	1.4401 / 1.4436	S31600	SUS 316	316S31 / 316S33	-	Z7CND17‐11‐02	X5CrNiMo17-12-2 / X3CrNiMo17-13-3
SS 316L	1.4404 / 1.4435	S31603	SUS 316L	316S11 / 316S13	03Ch17N14M3 / 03Ch17N14M2	Z3CND17‐11‐02 / Z3CND18‐14‐032	X2CrNiMo17-12-2 / X2CrNiMo18-14-3
SS 317	1.4449	S31700	SUS 317	-	-	-	X6CrNiMo19-13-4
SS 317L	1.4438	S31703	SUS 317L	-	-	-	X2CrNiMo18154
SS 321	1.4541	S32100	SUS 321	-	08Ch18N10T	-	X6CrNiTi18-10
SS 321H	1.4541	S32109	SUS 321H	-	-	-	X6CrNiTi18-10
SS 347	1.4550	S34700	SUS 347	-	08Ch18N12B	-	X6CrNiNb18-10
SS 347H	1.4961	S34709	SUS 347H	-	-	-	X7CrNiNb18-10
SS 446	1.4762	S44600	-	-	-	-	-

Stainless Steel Composition

Grade	C	Mn	Si	P	S	Cr	Mo	Ni	N
SS 304	0.08 max	2 max	0.75 max	0.040 max	0.030 max	18 – 20	-	8 – 11	-
SS 304L	0.03 max	2 max	0.75 max	0.045 max	0.030 max	18 – 20	-	8 – 12	0.10 max
SS 310	0.25 max	2 max	1.50 max	0.045 max	0.030 max	24 - 26	-	19 - 22	-
SS 310S	0.08 max	2 max	1.50 max	0.045 max	0.030 max	24 - 26	-	19 - 22	-
SS 316	0.08 max	2 max	0.75 max	0.045 max	0.030 max	16 - 18	2 - 3	10 - 14	0.1 max
SS 316L	0.3 max	2 max	0.75 max	0.045 max	0.030 max	16 - 18	2 - 3	10 - 14	0.10 max
SS 317	008 max	2 max	1 max	0.040 max	0.03 max	18 - 20	3 - 4	11 - 14	0.10 max
SS 317L	0.035 max	2 max	1 max	0.040 max	0.03 max	18 - 20	3 - 4	11 - 15	-
SS 321	0.08 max	2 max	0.75 max	0.045 max	0.03 max	17 - 19	5xC min 0.60% max	9 - 12	0.10 max
SS 321H	0.04 - 0.10 max	2 max	0.75 max	0.045 max	0.03 max	17 - 19	4xC min 0.60% max	9 - 12	0.10 max
SS 347	0.08 max	2 max	0.75 max	0.045 max	0.03 max	17 - 20	10xC min 1.00 max	9 - 13	62.74
SS 347H	0.04 – 0.10	2 max	0.75 max	0.045 max	0.03 max	17 - 20	8xC min 1.00 max	9 - 13	62.74
SS 446	0.2 max	1.5 max	0.75 max	0.040 max	0.03 max	23 – 30	0.10 – 0.25	0.50 max	Balance

Stainless Steel Melting Point, Density and Tensile Strength

Grade	Density	Melting Point	Tensile Strength	Yield Strength (0.2%Offset)	Elongation
SS 304	8.0 g/cm3	1400 °C (2550 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 304L	8.0 g/cm3	1400 °C (2550 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	40 %
SS 310	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 310S	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 316	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 316L	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	40 %
SS 317	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 317L	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 321	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 321H	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	35 %
SS 347	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	40 %
SS 347H	8.0 g/cm3	1454 °C (2650 °F)	Psi – 75000 , MPa – 515	Psi – 30000 , MPa – 205	40 %
SS 446	7.5 g/cm3	1510 °C (2750 °F)	Psi – 75,000 , MPa – 485	Psi – 40,000 , MPa – 275	20 %

Elevated temperature behavior: where Inconel pulls ahead

• Strength retention: Many Inconel grades maintain a much higher fraction of their room-temperature strength at elevated temperatures compared with stainless steels. For example, Inconel 718 retains high tensile and creep strength up to ~650°C due to its precipitation-hardened microstructure.

• Creep and rupture life: Creep — time-dependent deformation under load — is a critical failure mode for hot components. Nickel-base alloys have slower diffusion rates and engineered precipitates to resist creep; this results in substantially longer creep life at a given stress and temperature than most stainless steels. The Nickel Institute practical guides and ASM data describe classifying alloys by creep strength and intended service.

• Thermal stability & phase control: Superalloys resist microstructural transformations that embrittle or soften alloys at certain temperature ranges. Many stainless grades can form sigma or carbides that weaken the matrix after long exposure at intermediate temperatures — a problem rarely seen in purpose-designed nickel superalloys.

Practical implication: For gas-turbine discs, hot section fasteners, high-temperature exhaust hardware, and chemical plant components operating at elevated temperature, nickel superalloys are the accepted solution; stainless steels are not usually suitable for long-term strength at those temperatures.

Corrosion and oxidation resistance

• General corrosion in aqueous environments: Austenitic stainless steels (304/316) are excellent for many water, food, and low-chloride environments because of their chromium-rich passive film. Inconel alloys (e.g., 625) have exceptional resistance to many aggressive media (pitting, crevice, reducing acids, sea water) because of high nickel, molybdenum, and chromium levels. Which is “better” depends heavily on environment chemistry.

• Pitting and crevice corrosion: In chloride-rich environments (seawater, brines), 316 will pit sooner than Inconel 625, which was specifically designed for resistance to localized attack.

• Oxidation at high temperature: Inconel alloys form stable chromia and alumina scales and resist rapid scaling/oxidation compared to most stainless steels, enabling longer service in oxidizing high-temperature atmospheres.

Bottom line: Corrosion performance is application specific. Inconel often provides superior performance in aggressive and high-temperature corrosion regimes; stainless steels do well for many less severe aqueous environments and are more economical.

Fabrication, welding, and heat treatment considerations

• Forming and machining: Stainless steels (especially austenitics like 304/316) are generally easier and cheaper to form and cut than nickel superalloys. Superalloys can work-harden quickly and are abrasive on tooling; machining strategies and carbide tooling are common.

• Welding: Both families can be welded but with different concerns. Inconel alloys (618/625/718) can be welded with compatible filler metals and maintain strength after appropriate heat treatment; some Inconel grades do require specific procedures to avoid cracking. Stainless steels are well understood for welding in industry but may need post-weld heat treatment (PWHT) for martensitics or care to avoid sensitization of austenitics.

• Heat treatment: Many Inconel alloys are age-hardened (e.g., 718) and require controlled solution + aging cycles to reach peak properties. PH stainless steels (17-4PH) also need specific aging cycles to develop high strength. Improper heat treatment reduces performance.

Cost, availability, and manufacturing scale

• Raw material cost: Nickel and certain alloying elements (Nb, Mo) make Inconel markedly more expensive than common stainless steel grades. Cost differential can be multiple-times depending on market. Stainless steel remains the economical choice when performance requirements permit.

• Lead time & availability: Stainless steels are widely stocked worldwide in many sizes and tempers. Some Inconel grades are stocked, but special tempers, large sections, or exotic fabrication steps add lead time.

• Lifecycle cost: For high-temperature or highly corrosive services, the higher alloy cost can be offset by longer life, fewer shutdowns, and lower maintenance. A life-cycle cost analysis is essential for engineering selection.

Standards, specifications, and authoritative references

When specifying materials for engineering, reference recognized standards (ASTM, AMS, EN, UNS) and supplier datasheets. Examples:

• Inconel 718: UNS N07718 / AMS 5662 / ASTM B637 etc. (refer to Special Metals technical bulletins for behavior and recommended practices).

• Inconel 625: UNS N06625 / ASTM B443 / AMS 5666 etc. (Special Metals datasheet outlines applications and limits).

• Stainless steels: AISI/ASTM specifications for 304/316, and AMS/ASTM documents for PH or martensitic stainless. Use supplier material certifications (mill test reports) for traceability.

How to choose: practical selection checklist

Use this quick checklist to decide between Inconel and stainless steel:

1. Operating temperature > 400–500°C? If yes, prioritize Inconel or high-temp stainless (e.g., 309/310) — Inconel preferred for sustained load/creep.

2. Creep or rupture life required? Inconel likely necessary.

3. Chloride, acidic brines, or oxidizing high-temp atmosphere? Consider Inconel 625/718 or other nickel alloys.

4. Is cost the primary driver and conditions are moderate? Stainless steel (304/316) is usually adequate.

5. Is very high room-temperature static strength needed but temperature low? PH stainless (17-4PH) could be cost-effective vs. Inconel.

Decision matrix (simplified)

Representative applications and short case notes

• Inconel 718: turbine disks, cryogenic fasteners (also used at low temp), rocket motor components, high-temp bolts and shafts. High strength and toughness across a broad temperature span makes it a go-to superalloy for aerospace and power generation.

• Inconel 625: chemical process piping, heat exchangers in corrosive media, marine components, subsea connectors — chosen for localized corrosion resistance plus high strength.

• 304/316 stainless: kitchenware, food processing, architectural components, many chemical plant internals where temperatures and stresses are moderate.

• 17-4 PH: shafts, fasteners, components where high static strength and good corrosion resistance at ambient temp are required (often used in aerospace, petrochemical).

Frequently asked questions

1. Is Inconel always “better” than stainless steel?
No. “Better” depends on application. For high temperature and extreme corrosion stress, Inconel often outperforms; for routine, low-stress, cost-sensitive uses, stainless steels are superior economically and fully capable.

2. Can a stainless steel ever match Inconel’s strength?
Some PH stainless steels (e.g., 17-4PH in certain tempers) can approach or match the room-temperature strength of some nickel alloys, but they typically fail to match high-temperature creep/oxidation performance.

3. Does Inconel corrode in seawater?
Certain Inconel grades (notably 625) have excellent seawater resistance, including pitting and crevice resistance. However, selection must account for temperature, dissolved oxygen, and crevice geometry.

4. Why is Inconel so expensive?
High nickel content and alloying with costly elements (Nb, Mo, Ti) plus more difficult machining and processing increase raw and manufacturing costs.

5. Are Inconel and “Hastelloy” the same?
No — both are nickel-base families, but different trademarks and chemistries. Hastelloy (Haynes) and Inconel (Special Metals) designations refer to different proprietary compositions and performance envelopes.

6. Which alloys are standard for gas-turbine hot sections?
Nickel-base superalloys (Inconel family and similarly engineered alloys) dominate due to exceptional creep/oxidation resistance; stainless steels are not suitable for the hottest sections.

7. Can you weld Inconel to stainless steel?
Yes, but you must select compatible filler metals and manage dilution/thermal cycles. Welding dissimilar metals needs engineering control to avoid galvanic issues and maintain needed mechanical properties.

8. Which material is lighter?
Density of nickel alloys (~8.4–8.5 g/cm³) is generally similar to stainless steels (about 7.7–8.0 g/cm³). So weight differences are modest; selection will be driven by properties rather than mass savings.

9. Does Inconel require special heat treatment?
Many Inconel alloys, notably 718, require specified solution and aging cycles to develop designed strength; follow supplier heat-treatment schedules.

10. How to specify between them in procurement?
Define service temperature, stresses, environment (corrosives), life target, and budget; request mill certificates, and ask suppliers for recommended grades and traceability. For critical parts specify relevant ASTM/AMS/EN standards.

Short wrap-up

If your primary design constraints are sustained mechanical load at high temperature, long creep life, oxidation resistance at elevated temperature or aggressive localized corrosion, Inconel (and other nickel superalloys) will usually provide superior performance — at a higher material and processing cost. For everyday corrosion resistance, formability, and lower cost, stainless steel is the practical choice. Select the alloy that matches the service envelope (temperature, mechanical load, environment, allowable life and budget), and use supplier datasheets, standards, and mill test reports for firm specifications and design inputs.

Authoritative references

• INCONEL® alloy 718 — Special Metals technical bulletin (PDF)
• INCONEL® alloy 625 — Special Metals technical bulletin (PDF)
• MatWeb / ASM: INCONEL® alloy 718 material data
• MatWeb / ASM: AISI Type 304 stainless steel material data
• Nickel Institute — Practical Guide to High-Temperature Alloys (PDF)