Inconel vs Stainless Steel: Complete Technical Comparis

For operating conditions that demand exceptional high-temperature strength, creep resistance, and superior resistance to aggressive corrosion (especially chloride, seawater, and oxidizing/high-temperature environments), Inconel (nickel-based superalloys) is the correct choice despite its higher upfront cost; for general structural, architectural, food-grade, and many marine or chemical service cases where cost, formability, and weldability are decisive, stainless steels (iron-chromium-nickel alloys, e.g., 304/316) remain the best value. Choose by matching service temperature, corrosion mechanism, mechanical loads and whole-life cost rather than by brand or instinct.

Metallurgical fundamentals

Core difference

• Inconel is a trademarked family name for nickel-chromium (Ni-Cr) based superalloys, often with additions of Mo, Nb (columbium), Ti, Al and other elements that stabilize a tough, high-temperature microstructure. Common alloys: Inconel 625 (solid-solution strengthened) and Inconel 718 (precipitation-hardenable).

• Stainless steels are iron-based alloys with ≥10.5% chromium (Cr) to form a passive oxide film; many contain nickel (Ni) to stabilize the austenitic phase (e.g., 304, 316). They span ferritic, austenitic, martensitic and duplex families.

Microstructure consequences

• Nickel-base alloys retain strength and toughness at elevated temperatures because the Ni matrix and alloying additions resist diffusion and softening; certain alloys (718) form γ′/γ″ precipitates that dramatically raise yield strength after aging.

• Austenitic stainless steels rely on the face-centered cubic iron matrix stabilized by Ni; they are ductile and corrosion resistant at ambient and moderate temperatures but soften and lose creep strength faster than nickel superalloys at high service temperatures.

Chemical composition snapshots

The table below shows simplified, typical compositions for representative grades. (Use manufacturer datasheets and purchase specs for procurement; compositions vary by specification and producer.)

(Sources: producer technical bulletins and alloy datasheets.)

Mechanical properties and temperature performance

Room-temperature strength and toughness

• Many Inconel alloys have higher tensile and yield strengths than common austenitic stainless steels at room temperature. For example, Inconel 625 and 718 have higher yield/tensile ranges and greater fatigue strength than 304/316.

Elevated-temperature behavior (crucial difference)

• Creep and rupture strength: Inconel alloys (especially precipitation-hardened grades like 718) maintain much higher creep-resistance up to several hundred °C (and in some alloys up to 700–1000 °C) compared with stainless steels, which begin to lose load-bearing capability above ~400–600 °C depending on grade.

• Thermal stability: Nickel base alloys resist grain growth and maintain fatigue life under thermal cycling better than common stainless grades.

Example mechanical properties (simplified)

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 %

Corrosion behavior: which attacks which?

Stainless steel (304, 316) — strengths and weaknesses

• Austenitic stainless steels form a passive chromium oxide film giving general resistance to atmospheric corrosion, many chemicals, and moderate seawater exposure (316 better than 304 because of Mo). However, they are vulnerable to pitting and crevice corrosion in chloride-bearing environments, and certain grades can suffer stress-corrosion cracking under tensile stress and elevated temperatures.

Inconel — broader corrosion envelope

• Many nickel-base alloys have outstanding resistance to pitting, crevice corrosion, chloride stress-corrosion cracking, and high-temperature oxidation and carburization; Inconel 625 is noted for seawater resistance and resistance to chloride-induced cracking, while 718 balances strength and corrosion resistance for severe service. For aggressive media (strong oxidizers, hot chloride environments), Inconel often outperforms stainless steels.

Practical rule

• If the fluid or environment includes chlorides at elevated temperature, acid/chloride mixtures, or oxidizing salts and you need long life, prefer nickel alloys. If economy and formability for ambient/low temp service dominate, stainless steels typically suffice.

Fabrication, welding and machining

Forming and shaping

• Stainless steels (300 series) are readily formed and cold-worked; they're forgiving in sheet and pipe fabrication with common forming processes.

• Inconel alloys are tougher to cold-form and may require higher forces and careful annealing cycles to avoid work hardening.

Welding and joining

• Many Inconel alloys are weldable, but they often require controlled pre- and post-weld heat treatments and matching filler metals (especially precipitation-strengthened grades like 718 to avoid cracking or loss of properties). Stainless steel welding is generally simpler for 304/316, but both may need filler selection to prevent sensitization or hot cracking.

Machining

• Inconel alloys are harder to machine than stainless steels — they work-harden, have low thermal conductivity, and require rigid tooling, coated inserts and slower cutting speeds. This increases manufacturing time and cost. Stainless steel machining is also nontrivial, but conventional practices are more mature and often cheaper.

Standards, grades and procurement notes

Important standards and specs

• For stainless steel plate/sheet/strip: ASTM A240 / A240M (specifies chemical and mechanical requirements for many stainless grades).

• For Inconel / nickel alloys: refer to manufacturer technical bulletins and ASTM specifications relevant to the desired form — for example ASTM B637 covers certain nickel alloy bars/forgings and is commonly referenced for IN718 materials; individual alloys also have AMS, ISO and proprietary specifications.

Traceability & test reports

• For critical applications request mill test certificates (MTC) to EN 10204 3.1 or 3.2 (or equivalent), hardness reports, heat treatment records, and NDT/pressure test records where relevant.

Cost, availability and lifecycle economics

Acquisition price

• Nickel base alloys usually cost substantially more per kg than common stainless steels — often multiple times (varies with market and alloy). The initial cost premium can be 2–5× or more depending on grade, form and market volatility. The Nickel Institute and materials economics reviews emphasize that nickel alloys are more expensive but can save life-cycle costs in corrosive/high-temperature service.

Whole-life cost

• When maintenance, downtime, replacement frequency, and safety margins are tallied, Inconel can be economically justified despite upfront cost for long-service or mission-critical components (e.g., gas turbines, chemical processing, subsea), because it reduces failures and inspection/repair cycles. Stainless steel often wins on first cost and is ideal when operating conditions remain moderate.

Application matrix (recommended use cases)

Design and inspection tips

• Design for inspection: When using stainless steels in chloride waters anticipate periodic crevice/pitting inspections; use suitable design to minimize stagnant zones.

• Avoid dissimilar metal galvanic traps without insulation — a nickel alloy in contact with certain steels can create galvanic couples; account for this in bolted assemblies and sacrificial anodes.

• Specify heat treatment and temper for Inconel 718 to guarantee precipitate structure (solution treatment + aging) and tensile performance.

• Surface finish matters: smoother surfaces reduce pitting susceptibility; specify Ra targets for critical chloride service.

Key comparison tables

Table A — Mechanical & temperature comparison (representative)

Table B — Corrosion resistance (qualitative)

Table C — Fabrication & manufacturing cost impact

Common mistakes and procurement traps

1. Buying “Inconel” generically without specifying grade, heat treatment and form — different Inconel alloys behave radically differently (e.g., 625 vs 718). Always specify UNS number or proprietary designation and required temper.

2. Assuming stainless steel will survive prolonged hot chloride exposure — if chloride SCC or pitting at elevated temps is possible, stainless may fail prematurely.

3. Not accounting for galvanic corrosion when mixing nickel alloys with low-alloy steels in seawater — design insulating layers or use compatible fasteners.

FAQs

1. Q: Is Inconel stronger than stainless steel?
   A: For room temp and especially elevated temperatures, many Inconel alloys (e.g., 718, 625) exhibit higher tensile, yield and creep strength than common stainless steels (304/316).

2. Q: Which is better in seawater, Inconel or 316 stainless?
   A: Although 316 performs well in many marine environments, nickel alloys such as Inconel 625 provide superior resistance to pitting, crevice corrosion and chloride stress-corrosion cracking in aggressive seawater exposures.

3. Q: Can Inconel be welded easily?
   A: Many Inconels are weldable, but some grades (718) require specific welding procedures and post-weld heat treatment to restore age-hardened properties; welding costs and qualification are typically higher than for stainless steels.

4. Q: Are there stainless steels with properties close to Inconel?
   A: Super-austenitic and duplex/super-duplex stainless steels can improve high-temperature and chloride resistance, but they rarely match the combined high-temperature strength and oxidation resistance of nickel-base superalloys. Compare by performance requirement.

5. Q: Which is more expensive, Inconel or stainless?
   A: Inconel and other nickel base alloys are generally considerably more expensive per mass than 304/316 stainless steel — often several times the price depending on market conditions and alloy choice.

6. Q: What Inconel grade is best for high-temperature fasteners?
   A: Inconel 718 and certain precipitation-hardened nickel alloys are common for high-temperature, high-strength fasteners, though selection depends on operating temperature and environment. Request ASTM/AMS spec compliance for fasteners.

7. Q: Can stainless steel be used in cryogenic service?
   A: Some stainless steels (304L, 316L, certain austenitics and duplexes) have good cryogenic toughness; select alloys with proven low-temperature performance. Certain Inconel alloys also have favorable cryogenic properties.

8. Q: What testing should I require when buying Inconel?
   A: Require mill test certificates (3.1/3.2), tensile and hardness tests, heat treatment records, and NDT where required. For critical parts, specify certified chemical composition and traceability.

9. Q: How does thermal expansion compare?
   A: Nickel alloys often have different coefficients of thermal expansion (CTE) than stainless steels — this matters in assemblies exposed to temperature swings. Check datasheets and design allowances.

10. Q: Are there environmental or regulatory upsides to choosing stainless vs nickel?
    A: Environmental impact and recyclability differ by alloy and process. Both stainless and nickel alloys are recyclable, but embodied energy and resource considerations can influence selection in sustainability-driven projects. Consider life-cycle assessment if this is important.

How to pick: quick decision checklist

1. Will service exceed 400–500°C under sustained load? → lean to Inconel/other Ni-base.

2. Is chloride pitting / SCC a credible failure mode? → consider Inconel 625 or high-Ni alloys.

3. Is budget the primary constraint and loads/temps moderate? → stainless 304/316 is likely sufficient.

4. Are fabrication and machining cost/sign-off cycles constrained? → stainless is usually cheaper and easier.

5. For bolting and safety-critical hardware at high temps choose alloys with appropriate ASTM/AMS specs and verified MTCs.

Final summary

Nickel-based alloys (Inconel family) and stainless steels are not interchangeable: each family solves a different engineering problem. Choose nickel alloys when temperature, creep and aggressive corrosion demand it and total cost of ownership justifies the premium; choose stainless steels when economy, manufacturability and good general corrosion resistance at ambient to moderate temperatures are the priorities. Always specify the exact grade, temper, standards and test/inspection requirements in procurement documents to avoid surprises.

Authoritative references

• INCONEL® alloy 625 — Technical Bulletin (Special Metals)
• INCONEL® alloy 718 — Technical Bulletin (Special Metals)
• Nickel Institute — High-Temperature, High-Strength Nickel-Base Alloys (technical review)
• ASTM A240/A240M — Standard Spec. for Chromium & Chromium-Nickel Stainless Steel Plate, Sheet, Strip