CT6946 Hastelloy G3 Sheet and Hastelloy G3 Plate

Hastelloy G3 Sheets/Plates Description

Hastelloy G3 sheets/plates present a thermomechanically processed microstructure. The microstructure is characterised by elongated γ‐austenite grains aligned parallel to the rolling direction. Hot‐rolled variants maintain equiaxed grains (ASTM 4–6, 30–50 μm) with limited texture, while cold‐rolled sheets exhibit a pronounced <110>∥RD fibre texture and dislocation densities greater than 1×10¹⁴ m⁻², thereby increasing the yield strength to between 550 and 750 MPa. Uniformity through the thickness is maintained with edge-to-centre hardness variations within 10 HRB.

The corrosion resistance is attributed to a self-repairing passive film composed primarily of Cr₂O₃, MoO₂ and CuO complexes. The film remains stable in reducing acids; for example, tests show a corrosion rate below 0.03 mm/year in 40% H₂SO₄ at 80°C. The alloy sustains a critical pitting temperature above 85°C in 6% FeCl₃ and displays repassivation potentials exceeding +250 mV_SCE in chloride brines. Furthermore, cold‐rolled sheets achieve a surface finish of Ra ≤1.6 μm, thereby reducing the risk of crevice corrosion, while pickled surfaces exhibit chromium depletion confined to a depth of less than 0.1 μm.

The thermomechanical behaviour includes anisotropic thermal expansion: CTE_&∥RD is 13.8 μm/m·°C compared with CTE_&⊥RD of 14.5 μm/m·°C over the temperature range 20–400°C. The material exhibits directional thermal conductivity, recorded as 10.2 W/m·K along the rolling direction and 9.1 W/m·K perpendicular to it at 100°C. The phase remains stable below 650°C, with σ‐phase precipitation requiring more than 50 hours at 760°C to attain 1 vol%. After 10 000 hours at 400°C, cold‐rolled sheets retain over 90% of their yield strength but show a 15–20% reduction in transverse ductility due to carbide coarsening. Passive film rupture is observed in rolling-direction shear bands as a result of slip steps; this is mitigated by repassivation enhanced with molybdenum.

Hastelloy G3 Sheets/Plates Applications

Hastelloy G3 sheets/plates are used in corrosive environments that require maintained structural performance. In chemical processing, they are employed to manufacture reactor vessels and liners that handle concentrated sulphuric acid (up to 93%) and phosphoric acid (up to 85%) at temperatures not exceeding 110°C, with the copper component contributing to a passivation that limits overall thinning to below 0.05 mm/year. In flue gas desulphurisation (FGD), the plates are fabricated into absorber tower shells and mist eliminators; the molybdenum content, exceeding 6.5%, inhibits chloride-induced pitting in acidic brines with pH values from 1.5 to 2.5 at temperatures between 60 and 90°C. In the petrochemical sector, these materials are utilised for sour gas separator vessels exposed to H₂S, CO₂ and chloride-containing environments, with the alloy maintaining resistance to stress corrosion cracking at H₂S partial pressures of 3.5 bar or less.

Thin cold-rolled sheets (0.5–3 mm) are employed as electrolytic cell liners in zinc/copper electrowinning, providing resistance to sulphate electrolytes that contain fluoride impurities. In contrast, thick plates (50–100 mm) are machined into valve bodies and pump casings for geothermal brine systems, where silica-containing flows at 200–300°C require resistance to erosion-corrosion. In nuclear applications, the material is used for waste vitrification furnace liners that resist nitric/nitrate oxidation, while in architectural applications it is utilised for spill containment liners in phosphoric acid storage facilities. The consistent through-thickness properties (hardness variation within 10 HRB) and the cold-rolled surface finish (Ra ≤1.6 μm) ensure leak-tight performance in pressurised vessels, with weld joints maintaining at least 90% of the base metal’s corrosion resistance when matching filler metals are used. The performance has been verified for continuous service at 400°C and under thermal cycling up to 600°C.

Hastelloy G3 Sheets/Plates Packaging

The products are packaged in customised cartons of various sizes, based on material dimensions. Small items are packed in PP boxes, while larger items are placed in customised wooden crates. Packaging customisation and the use of appropriate cushioning materials minimise damage during transportation.

Packaging: Carton, Wooden Box, or Customised.

Kindly review the packaging details provided for your reference.

Manufacturing Process

1.       Brief Manufacturing Process Flow

2.       Testing Method

(1)    Chemical Composition Analysis is performed using techniques such as GDMS or XRF to confirm that the material meets the defined purity requirements.

(2)    Mechanical Properties Testing comprises tensile, yield strength and elongation tests in order to assess material performance.

(3)    Dimensional Inspection measures the thickness, width and length to ensure adherence to the specified tolerances.

(4)    Surface Quality Inspection involves visual and ultrasonic examinations for the detection of scratches, cracks or inclusions.

(5)    Hardness Testing determines the material hardness to confirm uniform mechanical properties.

Please refer to the testing procedures provided by SAM for detailed information.

Hastelloy G3 Sheets/Plates FAQs

Q1. How does the alloy maintain corrosion resistance in sulphuric acid environments above 60°C, where standard stainless steels fail?

The alloy’s composition, consisting of 22% Cr, 6.5% Mo and 2% Cu, permits the formation of passivating Cr/Mo-rich oxide layers. Consequently, corrosion in sulphuric acid concentrations up to 50% is controlled at temperatures up to 90°C. In contrast, 316L stainless steel experiences thinning of more than 5 mm/year above 60°C owing to the failure of chromium-only passive films.

Q2. What maximum chloride concentration and temperature limit prevent stress corrosion cracking in sour gas service?

SCC resistance is maintained in brines containing up to 150 000 ppm chlorides with H₂S partial pressures of 3.5 bar or less at temperatures not exceeding 150°C. Exceeding these limits may lead to molybdenum depletion at the grain boundaries, which can initiate cracking; a solution anneal at 1120°C is employed to control the microstructure.

Q3. Does cold working impact corrosion performance in welded assemblies?

Cold working that results in a thickness reduction exceeding 15% leads to a 20–30% reduction in the critical pitting temperature in chloride environments due to the induction of passive film defects by dislocations. Subsequently, post-weld solution annealing at 1100°C (±15°C) is applied to restore a uniform microstructure and achieve corrosion performance equivalent to that of the base metal.

Related Information

1.       Common Preparation Methods

Hastelloy G3 sheets/plates are produced using an integrated thermomechanical process. Initially, vacuum induction melting (VIM) is carried out on high-purity raw materials—electrolytic nickel, chromium pellets, molybdenum powder, oxygen-free copper and low-carbon iron—under an argon atmosphere to achieve precise compositional targets. The molten alloy is subsequently processed by vacuum arc remelting (VAR) for secondary refinement, thereby reducing interstitial elements (O ≤30 ppm, N ≤100 ppm) and eliminating macrosegregation. The resulting ingots, typically weighing between 5 and 15 metric tons, are homogenised at 1200–1250°C for 8–12 hours to dissolve eutectic phases. Thereafter, hot forging is performed at 1100±50°C with a minimum reduction ratio of 4:1 to break down the as-cast structure. Hot rolling is then executed within the γ‐austenite stability range (1000–1150°C), progressively reducing the thickness from 300 mm to between 3 and 50 mm using reversing mills, with interpass recrystallisation annealing at 1120°C to maintain a uniform grain size (ASTM 4–6).

For cold-rolled products, the hot-rolled bands are solution annealled at 1120±10°C and water-quenched, followed by pickling in HNO₃/HF to remove scale. Cold rolling achieves a thickness reduction of 30–80% via tandem mills with controlled tension, thereby producing a distinct <110>∥RD texture and dislocation densities exceeding 1×10¹⁴ m⁻². Intermediate soft annealing at 1080°C is applied after a cumulative reduction of 40–50% to restore ductility. Final cold passes attain target thicknesses between 0.5 and 10 mm with a surface finish of Ra ≤1.6 μm, while heavy plates (10–100 mm) are subjected to controlled finish rolling below 900°C to suppress σ‐phase formation. Critical microstructural control is achieved by rapid cooling through 650–900°C, with a dwell time of less than 15 minutes to prevent intermetallic precipitation, and by isothermal holding at 850°C to dissolve Laves phases. Final solution annealing at 1120°C stabilises the γ-matrix, followed by electrochemical polishing or abrasive blasting to ensure surface integrity. Non-destructive validation is conducted using ultrasonic testing for internal flaws exceeding 2 mm, eddy current inspection for surface defects over 100 μm, and corrosion verification in accordance with ASTM G48A (with a critical pitting temperature of at least 85°C).