What Material is G3 Hastelloy - Knowledge

1.What Material is G3 Hastelloy?

G3 Hastelloy is a nickel-chromium-molybdenum (Ni-Cr-Mo) alloy with a small addition of copper. It is a type of superalloy designed for excellent corrosion resistance in harsh environments, especially in strong oxidizing, reducing, and mixed acid media.

Its key characteristics make it widely used in industries such as chemical processing, petrochemicals, and flue gas desulfurization systems. It combines the corrosion resistance of nickel-based alloys with good mechanical properties and weldability, making it suitable for applications involving aggressive chemicals like sulfuric acid, hydrochloric acid, and phosphoric acid.

2.What is the chemical composition of G3 Hastelloy?

The chemical composition of G3 Hastelloy follows international standards (e.g., ASTM B625, UNS N06985). The following table lists its typical composition (in weight percentage, wt%):

Element	Content Range	Role
Nickel (Ni)	≥ 48.0	Base element, provides basic corrosion resistance and alloy stability.
Chromium (Cr)	21.0 - 23.5	Enhances oxidation resistance and resistance to oxidizing acids.
Molybdenum (Mo)	6.0 - 8.0	Improves resistance to reducing acids (e.g., hydrochloric acid) and pitting corrosion.
Copper (Cu)	1.5 - 2.5	Enhances resistance to sulfuric acid and hydrochloric acid.
Iron (Fe)	18.0 - 21.0	Improves mechanical strength and weldability.
Tungsten (W)	0.2 - 1.0	Assists molybdenum in enhancing corrosion resistance and wear resistance.
Carbon (C)	≤ 0.015	Low carbon content reduces the risk of carbide precipitation during welding, avoiding intergranular corrosion.
Silicon (Si)	≤ 0.80	Improves casting performance (for cast alloys) but is controlled to avoid brittleness.
Manganese (Mn)	≤ 1.0	Aids in deoxidation during alloy smelting, with minimal impact on corrosion resistance.
Phosphorus (P)	≤ 0.030	Impurity element, strictly controlled to prevent brittleness.
Sulfur (S)	≤ 0.015	Impurity element, controlled to avoid reducing corrosion resistance and weldability.

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3.What is the hardness of G3 Hastelloy?

The hardness of G3 Hastelloy varies depending on its heat treatment state and whether it has undergone cold working. Below are the typical hardness values for common states:

Annealed State

This is the most common state for G3 Hastelloy, as annealing relieves internal stress and optimizes corrosion resistance.

Brinell Hardness (HB): Approximately 180 - 220 HB.

Rockwell Hardness (HRC): Approximately 17 - 25 HRC.

Vickers Hardness (HV): Approximately 190 - 230 HV.

Cold-Worked State

Cold working (e.g., rolling, forging) increases the alloy's hardness and strength but may slightly reduce its ductility.

The hardness can increase by 30% - 50% compared to the annealed state. For example, the Brinell hardness may reach 240 - 300 HB, and the Rockwell hardness may reach 26 - 32 HRC.

Welded Joints

The hardness of welded joints is usually similar to or slightly higher than the base metal in the annealed state. Proper post-weld heat treatment can restore the hardness to the annealed level and prevent intergranular corrosion.