When should I choose Hastelloy C-4 over C-276?

Choose C-4 when you have thick-section multi-pass welding, intermediate temperature exposure (650–1040°C), a requirement for intergranular corrosion resistance as-welded, or nuclear applications requiring low Co content (≤2.0% minimizes cobalt-60 activation).

What is the key metallurgical difference between C-4 and C-276?

Fe content is limited to ≤3.0% in C-4 (versus 4–7% in C-276), tungsten is eliminated entirely, and titanium is added at ≤0.70% to stabilize carbon as TiC, preventing chromium carbide precipitation at grain boundaries.

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Hastelloy C-4Download

Ni-Cr-Mo Solid Solution N06455 UTS ≥ 690 MPa ~1040°C 8.64 g/cm³

Hastelloy C-4

Q: Does Hastelloy C-4 require post-weld heat treatment?

No — this is C-4's defining advantage. It is designed to pass ASTM G28 intergranular corrosion testing in the as-welded condition without PWHT.

Q: Is Hastelloy C-4 still in production?

Yes. C-4 continues to be produced for niche applications where phase stability is the primary requirement, particularly in nuclear and thick-section chemical equipment.

Q: Is Hastelloy C-4 suitable for seawater applications?

C-4 resists seawater but is not the first choice. For seawater and marine environments, Hastelloy C-22 is preferred due to its superior pitting and crevice corrosion resistance.

High-Stability Ni-Cr-Mo Alloy — Eliminates Intergranular Corrosion After Welding | ASTM B574/B575 | Special Alloys

Overview

Hastelloy C-4 was developed to solve intergranular attack after welding that affected earlier C alloys. By reducing Fe to ≤3.0% and eliminating W, C-4 achieves exceptional metallurgical stability through 650–1040°C.

The trade-off: modestly lower corrosion resistance than C-276 in oxidizing chloride environments.

Chemical Composition (wt%)

Element	Ni	Mo ☆	Cr	Fe ☆	Co	Ti ☆	Mn	Si	C
Content	Bal	14.0–17.0	14.0–18.0	≤3.0	≤2.0	≤0.70	≤1.0	≤0.08	≤0.015

☆ Key elements: Mo for corrosion resistance, Fe deliberately minimized (≤3.0%) for phase stability, Ti stabilizes carbon as TiC.

Mechanical Properties

Ultimate Tensile Strength

≥ 690

MPa

Yield Strength

≥ 280

MPa

Elongation

≥ 40

Hardness

≤ 100

HRB

Elastic Modulus

E = 211 GPa

Shear Modulus

G = 81 GPa

Poisson's Ratio

ν = 0.30

Physical Properties

Property	Value	Unit
Density	8.64	g/cm³
Melting Range	1330–1380	°C
Thermal Conductivity	10.0	W/m·K
Specific Heat	410	J/kg·K
Electrical Resistivity	1.30	μΩ·m
CTE (20–100°C)	11.4	μm/m·°C
CTE (20–500°C)	13.3	μm/m·°C

Heat Treatment

Solution Anneal

1065°C + Water Quench (WQ)

Stress Relief

400–450°C

As-Welded Acceptable

C-4's primary advantage — designed to pass IGC testing without PWHT.

⚠ Max Service: Stable to approximately 1040°C, but prolonged exposure above 650°C should be evaluated. For critical high-temperature service, consult HT PIPE.

Corrosion Resistance

General Corrosion

Good performance across a wide range of oxidizing and reducing media. Narrower passivity range than C-276.

Pitting Resistance

Good pitting resistance with PREN ≈ 60–74.

Intergranular Corrosion ☆

Passes ASTM G28 as-welded — THE key differentiator from C-276. No PWHT required.

Stress Corrosion Cracking

Immune to chloride stress corrosion cracking.

Grade Selection Matrix

Alloy	Corrosion	IGC As-Welded	Phase Stability	Thick Weld	Cost
C-4	★★★	★★★★	★★★★★	★★★★★	$$$$

Best for: Thick-section weldments requiring IGC immunity as-welded.

Typical Applications

Chemical Processing

Thick-section welded vessels and reactors operating in corrosive environments.

Nuclear Fuel Reprocessing

Low Co content (≤2.0%) minimizes cobalt-60 activation, critical for nuclear environments.

FGD Components

Flue gas desulfurization systems requiring as-welded corrosion resistance.

Industry Standards

ASTM B574 ASTM B575 ASTM B619 ASTM B622 ASTM B626 ASTM B366

Project Case Study

4.1 Tons C-4 Plate — Nuclear Waste Evaporator

ASTM G28 as-welded corrosion test passed with corrosion rate < 0.2 mm/yr. Demonstrated C-4's unique capability for thick-section welded components in nuclear service requiring as-welded intergranular corrosion immunity.

Frequently Asked Questions

Q1: When should I choose C-4 over C-276?

Choose C-4 when you have thick-section multi-pass welding, intermediate temperature exposure (650–1040°C), a requirement for IGC resistance as-welded, or nuclear applications requiring low Co content (≤2.0% minimizes cobalt-60 activation).

Q2: Does C-4 require post-weld heat treatment (PWHT)?

No — this is C-4's defining advantage. It is designed to pass ASTM G28 intergranular corrosion testing in the as-welded condition without PWHT.

Q3: What is the key metallurgical difference versus C-276?

Fe content is limited to ≤3.0% (versus 4–7% in C-276), tungsten (W) is eliminated entirely, and titanium (Ti) is added at ≤0.70% to stabilize carbon as TiC, preventing chromium carbide precipitation at grain boundaries.

Q4: Is Hastelloy C-4 still in production?

Yes. C-4 continues to be produced for niche applications where phase stability is the primary requirement, particularly in nuclear and thick-section chemical equipment.

Q5: Is C-4 suitable for seawater applications?

C-4 resists seawater but is not the first choice. For seawater and marine environments, Hastelloy C-22 is preferred due to its superior pitting and crevice corrosion resistance.