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.

Your position:Home > PRODUCT MATERIAL > Special Alloys

PRODUCT

Special Products

BW Pipe Fittings

Forged Pipe Fittings

Steel Pipe Tube

Flanges

Fasteners

Steel Sheet Plate

Round Bar

Welding Wire Electrodes

Prefabrication Pipe Spools

PRODUCT MATERIAL

Special Alloys

Duplex Stainless Steel

HOT PRODUCTS

PRODUCT MATERIAL

Hastelloy C4Download

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.