UNS N06333 Forgings

UNS N06333 was developed for furnace and process equipment operating in conditions where stainless steels scale rapidly and standard nickel alloys absorb carbon from the atmosphere.

Three elements in the composition account for its behaviour in service. Chromium at 24 to 27 % forms a Cr₂O₃ scale that reforms continuously at temperature. Silicon at 0.75 to 1.5 % stabilises that scale and is the principal reason the alloy resists carburization and metal dusting better than Alloy 800H or Alloy 601. Molybdenum, cobalt and tungsten strengthen the matrix and maintain that strength over long exposures rather than declining after a few hundred hours.

The grade is normally selected where one of the following governs component life:

• Carbon pickup. Carburizing furnace fixtures, retorts, muffles, conveyor chains and belt pins that embrittle progressively from the surface inward.
• Metal dusting. Catastrophic carburization in CO-rich syngas and reformer service in the range of 450 to 800 °C.
• Thermal shock. Components quenched into oil or water on each production cycle.
• Shutdown corrosion. Dew-point sulfuric acid attack and polythionic acid stress corrosion cracking affecting refinery hardware during outages.
• Hot corrosion. Molten salt and hot-corrosion environments in glass manufacture and waste incineration.

UNS N06333 is a heat- and corrosion-resistant alloy rather than a high-strength one. A precipitation hardened grade such as Inconel 718 is several times stronger at moderate temperature. Applications requiring both high mechanical loading and this level of surface stability generally need a different grade or a design change.

Melting and forging stock

Forging stock is melted by EAF with AOD or VOD refining, with ESR remelting where the application requires improved cleanliness and reduced segregation. Heat chemistry is verified before the billet is released to the forge shop, and heat identity is carried through every subsequent operation.

Open-die forging

UNS N06333 has a narrow hot-working window. Forging is carried out from approximately 1180 °C down to a finishing temperature no lower than approximately 950 °C, with reheats scheduled so that no pass finishes below that temperature. Forging reduction is planned to break down the cast structure and produce grain flow following the part contour.

Testing and certification

Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 to the acceptance class stated on the order. Liquid penetrant testing to ASTM E165 is available for surface examination. Every forging is supplied with an EN 10204 3.1 certificate. EN 10204 3.2 third-party certification through Lloyd's, DNV, BV, TÜV or SGS is available when specified at order stage.

Machining

The machinability rating of UNS N06333 is approximately 12 to 15 % of free-machining B1112 steel. Turning with high-speed-steel tooling is normally carried out at 20 to 25 surface feet per minute. Carbide tooling permits higher speeds. The alloy work hardens rapidly, so rigid setups, positive rake geometry, constant heavy feed and sharp tooling on a fixed change schedule are required. Tools should not be allowed to dwell in the cut. Flood coolant is recommended. Machining allowance should be agreed at order stage so that the forging is supplied with adequate stock in the required locations.

Welding

UNS N06333 is welded with matching bare filler wire, or with matching coated electrodes for SMAW. No preheat is required. Interpass temperature should be kept below 100 °C (212 °F) and reinforced stringer beads used in place of a wide weave. Restraint should be minimised on heavy forged sections. A post-weld solution anneal restores the fully annealed condition where the design permits it.

The applications listed below share a common profile of high temperature combined with a carbon-bearing or corrosive atmosphere, frequently with thermal cycling.

• Heat treatment plant. Muffles, retorts, baskets, grids and fixtures, carburizing furnace conveyor chains and belt pins.
• Refining. Tube hangers and supports in fired heaters and power boilers, flare tips, stack dampers, and hardware exposed to polythionic acid during shutdown.
• Petrochemical and syngas. Reformer and CO-rich service where metal dusting governs, process piping components and forged fittings.
• Radiant tubes and burner hardware. Forged flanges, sleeves and return bends.
• Rotary kilns and calciners. Forged rings, tyres and support components.
• Glass manufacture. Molten glass process equipment, stirrers and forehearth hardware.
• Gas turbines. Combustion chamber components and transition hardware.
• Furnace mechanicals. Fan shafts, hubs and rotors operating inside the hot zone, and refractory anchors.
• Waste incineration. Grate bars, dampers and hardware in hot salt-bearing flue gas.

Forged parts commonly supplied for this service include seamless rolled rings, shaft forgings, tube sheets, flanges, sleeves, bushings, discs and custom forged parts to drawing.

Published by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu Province, China, producing forged rings, seamless rolled rings, bars, discs, flanges and shafts in carbon steel, alloy steel, tool steel, stainless steel and nickel-base superalloys.

Composition and specification data follow ASTM B718 and ASTM B719 for UNS N06333. Mechanical and physical values are typical published values for the solution-annealed condition and are given for comparison and shortlisting. They are not design allowables. All values should be confirmed against the governing specification and the applicable design code before use.

Last reviewed 29 August 2026 by the technical sales department, Jiangyin Jiangnan Metal Co., Ltd.