Metal dusting resistance
The service condition alloy 693 was developed for
Metal dusting is a form of high-temperature carburization that breaks metal down into a powder of graphite and fine metal particles. It occurs in strongly carburizing, reducing atmospheres rich in carbon monoxide and hydrogen. Those conditions are present in steam reformers, syngas plants, direct-reduced-iron units, and methanol and ammonia trains.
Attack rates are high. A component can go from sound to perforated within a single campaign, and because the pitting is local, wall-thickness surveys often miss it until leakage begins. Alloy 693 was developed to extend the incubation time for this attack, and it provides the highest metal dusting resistance of the conventional nickel alloys in current production.
High chromium content builds a protective chromia scale. The aluminum addition supplements that scale with alumina, which is less permeable to carbon. Alloy 690 carries the same chromium but no aluminum addition. Alloy 693 is alloy 690 with 3.1% aluminum added, and that addition accounts for the difference in carburization resistance.
Metal dusting attacks exposed surfaces. On a forging that means the faces of tube sheets, reformer outlet headers, thermowells, nozzles and flanges. Machining allowance and surface finish therefore affect service life. A rough, cold-worked or decarburized surface will initiate attack earlier than a clean annealed one. State the service atmosphere when you enquire and we will set the finishing allowance accordingly.
- Resists oxidation and carburization to approximately 1150 °C (2100 °F).
- Good sulfidation resistance in oxidizing and reducing sulfur-bearing atmospheres.
- Performs well against oxide-rich media such as glass frit and fluxing compounds to 1100 °C (2012 °F).
- Retains useful creep-rupture strength at temperature.
Chemical composition of UNS N06693
Weight percent, limits per ASTM B168
The composition limits below are those given for UNS N06693 in ASTM B168. Each heat is supplied with a ladle analysis on the mill certificate. An independent product analysis can be run on request.
| Element | Min | Max | Typical | Function |
|---|---|---|---|---|
| Nickel, Ni | - | - | 60.5 | Balance. Austenitic matrix. |
| Chromium, Cr | 27.0 | 31.0 | 29.0 | Chromia scale. Oxidation and sulfidation resistance. |
| Aluminum, Al | 2.5 | 4.0 | 3.1 | Alumina scale. Metal dusting and carburization resistance. |
| Iron, Fe | 2.5 | 6.0 | 4 | Residual from melt stock. |
| Niobium, Nb | 0.50 | 2.5 | 0.7 | Carbide former. Stabilizes carbon. |
| Titanium, Ti | - | 1.0 | - | Minor addition. |
| Manganese, Mn | - | 1.0 | - | Deoxidizer. |
| Copper, Cu | - | 0.50 | - | Residual. |
| Silicon, Si | - | 0.50 | - | Residual. Held low to protect hot workability. |
| Carbon, C | - | 0.15 | - | Residual. |
| Sulfur, S | - | 0.010 | - | Residual. Low sulfur is required for hot workability. |
Nickel is determined by difference. Typical values describe a representative heat and are not specification limits. Order acceptance is against the minimum and maximum columns.
Physical and mechanical properties
Room-temperature data, annealed condition
Inconel 693 is a single-phase solid-solution alloy. Room-temperature strength comes from solution strengthening rather than precipitation, so the values below apply to material in the annealed condition as normally supplied.
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.77 g/cm3 | 0.281 lb/in3 |
| Melting range | 1317-1367 °C | 2403-2493 °F |
| Crystal structure | Disordered face-centred cubic austenite, single phase | |
| Magnetic response | Non-magnetic in the annealed condition | |
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, Rm | 937 MPa | 136 ksi |
| 0.2% proof stress, Rp0.2 | 530 MPa | 77 ksi |
| Elongation, A | 42% | 42% |
These are typical values for wrought annealed product, published for design guidance. They are not specification minima and should not be used as acceptance criteria. Mechanical properties of a forging vary with section size, reduction ratio and test-piece location. The values that govern an order are those written into the purchase specification and reported on the EN 10204 3.1 or 3.2 certificate.
Heat treatment
Anneal and rapid cool
Inconel 693 is annealed at 1010-1066 °C (1850-1950 °F), held for a time appropriate to the section thickness, then cooled rapidly by air blast or water quench.
Hold time is set by the ruling section. Rapid cooling through the intermediate temperature range preserves the single-phase structure and the corrosion resistance associated with it. A slow furnace cool on a heavy forging will not meet the requirement.
Alloy 693 is not a precipitation-hardening grade and is not solution treated and aged. Some material listings describe N06693 as solution treated and aged. That description applies to gamma-prime strengthened grades such as Inconel 718, Inconel 725 and Waspaloy. Alloy 693 is a disordered single-phase solid solution and an ageing cycle will not raise its strength. If a specification issued to you calls for ageing on N06693, query it before releasing the order.
Standards and designations
Specifications that cover UNS N06693
UNS N06693 is listed by name in the ASTM product specifications for bar, pipe and plate. It is often assumed to be covered by ASTM B564, the nickel alloy forging specification. That assumption should be checked before it reaches a purchase order.
| Designation | Covers | N06693 in scope |
|---|---|---|
| UNS N06693 | Unified Numbering System designation | The grade itself |
| ASTM B166 | Rod, bar and wire | Yes |
| ASTM B167 | Seamless pipe and tube | Yes |
| ASTM B168 | Plate, sheet and strip | Yes |
| ASTM B564 | Nickel alloy forgings | No. See note below |
| AWS A5.14 ERNiCrFeAl-1 | Bare welding filler metal | Matching consumable |
| EN 10204 3.1 / 3.2 | Type of inspection certificate | Supplied with every order |
| EN 10228-3, SEP 1921, ASTM A388 | Ultrasonic examination of forgings | Applied to order |
The scope of ASTM B564 names the UNS numbers it covers. Among the nickel-chromium-iron alloys it names N06600, N06603 and N06690. Among the nickel-chromium-iron-aluminum alloys it names N06025. N06693 does not appear. A forging cannot be certified to a specification that does not cover the grade, so an order line reading "Inconel 693 forged flange to ASTM B564" cannot be met as written.
Our practice is to supply forgings to the UNS N06693 chemistry of ASTM B168, with the mechanical property requirements, test-piece location, grain size and NDT acceptance level agreed in writing on the purchase order, or to a customer specification, or to a customer-nominated ASME code case. This is standard practice for grades that have a chemistry specification but no dedicated forging specification. It is stated on the certificate so that the inspection authority can accept the material without a concession.
INCONEL is a registered trademark of Special Metals Corporation, which developed alloy 693. Material manufactured by Special Metals and sold under that brand belongs to that company. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as UNS N06693 or Alloy 693, the same generic chemistry, manufactured independently. We are not affiliated with, sponsored by, or endorsed by Special Metals Corporation.
Forging and fabrication
Hot working range for UNS N06693
Alloy 693 is more difficult to forge than the grade it replaces. The 3.1% aluminum that provides metal dusting resistance also reduces hot workability, so the working temperature range is narrower than for alloy 690 or alloy 600.
Control requirements are correspondingly tighter: soak temperature and uniformity, reduction per pass, interpass reheat discipline, and die and manipulator temperature. Finishing too cold or taking too heavy a reduction can cause edge and surface cracking. The alloy also shows reduced ductility over certain elevated temperature ranges, so a schedule written for a nickel-chromium-iron grade should not be applied unchanged to N06693.
Machining and cold forming characteristics are broadly similar to Inconel 600 and 690. The alloy work-hardens rapidly and requires low speeds, positive feed, rigid setups and sharp tooling, with no dwelling. Welding is carried out in the annealed condition by GTAW or GMAW using a near-matching filler, INCONEL Filler Metal 53MD, classified AWS A5.14 ERNiCrFeAl-1.
Because the working range is narrow, reduction ratio alone is not sufficient to specify the job. We will state the intended soak temperature, finishing temperature and reduction per pass on request before the order is placed.
Inconel 693 forgings we produce
Made to drawing at Jiangyin, Jiangsu
Jiangyin Jiangnan Metal Co., Ltd. forges UNS N06693 to customer drawings and to size lists. The forms below are those most often specified for reformer, syngas and petrochemical service.
| Form | Typical use in N06693 | Size envelope |
|---|---|---|
| Seamless rolled rings | Reformer headers, pressure-housing rings, ring blanks | 200-2,500 mm OD |
| Forged flanges | Nozzle and header connections in carburizing gas | To drawing |
| Tube sheets | Reformer and waste-heat exchanger tube sheets | To drawing |
| Discs and blanks | Blind flanges, closure heads, machining blanks | To 1,800 mm dia. |
| Round bar and billet | Thermowells, valve internals, machined fittings | 80 mm dia. and up |
| Shafts and spindles | High-temperature rotating and reciprocating parts | To 8 m length |
| Sleeves and bushings | Burner and nozzle assemblies, liners | To drawing |
| Blocks and hollows | Valve bodies, manifold and header blanks | To drawing |
The envelope above covers the works general open-die and ring-rolling capability across all grades. Achievable size in N06693 is lower than in carbon or alloy steel because of the narrower hot-working range and available billet size. Confirm a part against a drawing rather than against this table.
Manufacturing route
- Melting. Vacuum and refining routes appropriate to a nickel superalloy, VIM plus ESR, or EAF plus VOD followed by ESR, for low sulfur and clean forgeable stock.
- Forging. Open-die hammers from 1 to 9 tonnes and a 5,000 tonne hydraulic press, with 3 m and 6 m seamless ring-rolling mills.
- Heat treatment. Anneal at 1010-1066 °C with rapid cooling, on a charted and calibrated furnace cycle.
- Testing. Chemical analysis, tensile and impact testing, hardness, metallographic examination and grain size.
- Non-destructive examination. Ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388, with dye-penetrant or magnetic-particle inspection where the geometry requires it.
- Certification. EN 10204 3.1 works certificate, or 3.2 with third-party witnessing and countersignature.
Applications
Service conditions that justify the grade
Alloy 693 is specified where a lower-cost grade has failed by carburization or metal dusting, or where the cost of an unplanned outage justifies the material cost.
| Industry | Components | Governing condition |
|---|---|---|
| Hydrogen and syngas | Reformer tube sheets, outlet headers, transfer-line components, thermowells | Metal dusting in CO and H2 atmospheres |
| Ammonia and methanol | Waste-heat boiler parts, nozzles, flanges | Carburization with thermal cycling |
| Petrochemical processing | Reactor internals, catalyst-handling hardware, valve bodies | Combined carburizing and sulfidizing duty |
| Fertiliser production | Process piping components, tube sheets, baffle plates | High-temperature corrosion |
| Waste-to-energy and biomass | Superheater supports, burner nozzles, grate hardware | Chloride, alkali and oxide-rich deposits |
| Thermal processing | Furnace retorts, muffles, fixtures, radiant-tube parts | Cyclic oxidation to 1150 °C |
| Fuel cells | High-temperature reformer hardware | Carbon-bearing reducing gas |
| Glass and ceramics | Contact hardware exposed to frit and fluxes | Oxide-rich media to 1100 °C |
Inconel 693 compared with 690, 601 and 602 CA
Selecting among the high-chromium heat-resisting grades
These four grades compete for the same service. Aluminum content is the main variable. Chromium alone provides oxidation and sulfidation resistance, while restricting carbon ingress requires an alumina-forming addition on top of the chromia scale.
| Grade | UNS | Cr % | Al % | Metal dusting resistance | Selection note |
|---|---|---|---|---|---|
| Alloy 693 | N06693 | 27-31 | 2.5-4.0 | Highest of the conventional nickel alloys | Specify where metal dusting governs the design |
| Alloy 690 | N06690 | 27-31 | - | Moderate | Predecessor grade. Same Cr, easier to work, no Al |
| Alloy 601 | N06601 | 21-25 | 1.0-1.7 | Fair | Lower cost, good cyclic oxidation resistance |
| Alloy 602 CA | N06025 | 24-26 | 1.8-2.4 | Good | High carbon gives strong creep resistance above 1000 °C |
Nominal chemistries, given for grade selection rather than for specification. Alloy 602 CA also carries deliberate carbon at 0.15 to 0.25% with yttrium and zirconium, which gives it higher creep strength above 1000 °C than alloy 693. Where creep governs and metal dusting does not, alloy 602 CA may be the better selection. Where metal dusting governs, alloy 693 is normally specified.
Frequently asked questions about Inconel 693
Answered by the Jiangyin Jiangnan Metal engineering department
What is Inconel 693?
Inconel 693 is a nickel-chromium-aluminum alloy designated UNS N06693, containing nominally 60.5% nickel, 29% chromium and 3.1% aluminum. It was developed by Special Metals Corporation to resist metal dusting, a severe form of high-temperature carburization, and it also resists oxidation, sulfidation and general carburization to about 1150 °C.
Is Inconel 693 a cobalt alloy?
No. Alloy 693 is a nickel-chromium-aluminum alloy and cobalt is not an alloying addition. Some material listings describe it as a nickel and cobalt alloy, which is incorrect. The elements that define the grade are chromium at 27 to 31% and aluminum at 2.5 to 4.0%, with nickel as the balance.
What makes Inconel 693 resistant to metal dusting?
The aluminum addition. High chromium builds a protective chromia scale that handles oxidation and sulfidation, but chromia alone is relatively permeable to carbon. The 3.1% aluminum in alloy 693 supplements it with alumina, which is a more effective barrier to carbon ingress. Alloy 690 has the same chromium content but no aluminum, and does not perform comparably against dusting.
Is Inconel 693 covered by ASTM B564?
No. ASTM B564, the standard specification for nickel alloy forgings, lists the UNS numbers within its scope, and N06693 is not among them. The nickel-chromium-iron alloys it covers are N06600, N06603 and N06690, and the nickel-chromium-iron-aluminum alloy it covers is N06025. UNS N06693 is named in ASTM B166 for rod and bar, ASTM B167 for pipe and tube, and ASTM B168 for plate, sheet and strip. Forgings in this grade are therefore supplied to the ASTM B168 chemistry, with mechanical properties, grain size, test location and NDT acceptance agreed on the purchase order or to a customer specification.
Which ASTM standards cover UNS N06693?
ASTM B166 for rod, bar and wire, ASTM B167 for seamless pipe and tube, and ASTM B168 for plate, sheet and strip. The matching welding consumable is classified AWS A5.14 ERNiCrFeAl-1.
Is Inconel 693 age-hardenable?
No. Alloy 693 is a single-phase, disordered face-centred-cubic solid solution. It is annealed at 1010 to 1066 °C (1850 to 1950 °F) and rapidly cooled. There is no ageing step and an ageing cycle will not increase its strength. Descriptions of N06693 as solution treated and aged confuse it with gamma-prime strengthened grades such as Inconel 718, Inconel 725 and Waspaloy.
Can Inconel 693 be forged, and is it difficult?
It is forged commercially, but it is more demanding than alloy 690 or alloy 600. The aluminum content that provides the corrosion resistance also reduces hot workability, narrowing the temperature range in which the alloy can be worked without cracking. It requires close control of soak temperature, reduction per pass and interpass reheating, and a forging schedule qualified on this grade rather than carried over from a nickel-chromium-iron alloy.
What is the maximum service temperature of Inconel 693?
Resistance to oxidation and carburization extends to approximately 1150 °C (2100 °F). Against oxide-rich media such as glass frit and fluxing compounds it performs well to about 1100 °C (2012 °F). The allowable design temperature for a given part is lower and is set by the stress, the code and the required life, not by the corrosion limit alone.
What is the density and melting range of Inconel 693?
Density is 7.77 g/cm3 (0.281 lb/in3) and the melting range is 1317 to 1367 °C (2403 to 2493 °F).
What filler metal is used to weld Inconel 693?
A near-matching composition filler, INCONEL Filler Metal 53MD, classified AWS A5.14 ERNiCrFeAl-1, with a nominal 59 nickel, 29 chromium, 4 iron, 3 aluminum composition. Welding is performed in the annealed condition, normally by gas tungsten arc welding or gas metal arc welding.
What is the difference between Inconel 693 and Inconel 690?
Alloy 693 is alloy 690 with an aluminum addition. Both carry 27 to 31% chromium, so both resist oxidation and sulfidation well. Alloy 693 adds 2.5 to 4.0% aluminum, which gives it markedly better resistance to carburization and metal dusting. The trade-off is workability. Alloy 690 is easier to forge, form and machine, so 693 is specified when the service atmosphere is carburizing enough to justify the added difficulty and cost.
Who supplies Inconel 693 forged rings, flanges and discs?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, that forges UNS N06693 to customer drawings, including seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings and tube sheets. Parts are supplied annealed, ultrasonically examined and certified to EN 10204 3.1 or 3.2. For a quotation, send a drawing or size list to sales@steelforgepieces.com or call 0086-189-2135-9659.
What information do you need to quote?
Grade and specification, meaning UNS N06693 plus any customer or code requirement, the drawing or finished dimensions with machining allowance, quantity, delivery condition, the NDT standard and acceptance level required, and the certificate type, EN 10204 3.1 or 3.2. If the part is a replacement, the service atmosphere and the failure mode of the part it replaces will usually improve the recommendation.
Manufacturer
Open-die forging works, Jiangyin, Jiangsu
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, established in 2008 and operating a quality system certified to ISO 9001:2015. The works forges nickel alloys, stainless, tool, alloy and carbon steels into seamless rolled rings, flanges, bars, discs, shafts, sleeves and tube sheets, supplied with EN 10204 3.1 or 3.2 certification.
- Company
- Jiangyin Jiangnan Metal Co., Ltd.
- Role
- Open-die forging manufacturer
- Address
- No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Telephone
- 0086-189-2135-9659
- sales@steelforgepieces.com
- Website
- www.steelforgepieces.com
- Established
- 2008
- Quality system
- ISO 9001:2015
- Certification
- EN 10204 3.1 and 3.2
- Forging plant
- 1 t, 3 t, 5 t and 9 t open-die hammers, 5,000 t hydraulic press
- Ring rolling
- 3 m and 6 m seamless ring-rolling mills
- Inspection
- Ultrasonic, magnetic particle, universal tensile, impact, hardness, metallographic microscopy
- Serves
- Worldwide
Data sources
- ASTM B168, Standard Specification for Nickel-Chromium-Aluminum Alloys (UNS N06699), Nickel-Chromium-Iron Alloys (UNS N06600, N06601, N06603, N06690, N06693, N06025, N06045 and N06696) Plate, Sheet, and Strip. Chemistry limits for N06693.
- ASTM B166 and ASTM B167. Rod, bar and wire, and seamless pipe and tube for N06693.
- ASTM B564, Standard Specification for Nickel Alloy Forgings. Scope reviewed, N06693 is not listed.
- Special Metals Corporation, INCONEL alloy 693 technical bulletin. Nominal composition, metal dusting behaviour, annealing practice and filler metal.
- Distributor datasheet data for UNS N06693. Density, melting range and typical room-temperature tensile properties.
- AWS A5.14, classification ERNiCrFeAl-1. Matching welding consumable.