Incoloy 800H vs Inconel 601 for Furnace Service

By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012

Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360

Quick Answer: Incoloy 800H or Inconel 601 for Furnace Service?

Inconel 601 is the better choice where oxidation resistance at the top of the temperature range dominates, because its 1.0-1.7 % aluminium addition supports a highly protective and spallation-resistant oxide scale. Incoloy 800H is the better choice where the component must carry load at temperature, because its controlled coarse grain structure gives it markedly higher creep and stress-rupture strength above about 700 °C at a lower alloy cost.

Key Takeaways

• 601 wins on oxidation resistance, and it is not close at the top of the range. Inconel 601 carries 21.0-25.0 % chromium with 1.0-1.7 % aluminium, which produces an alumina-supported scale capable of surviving repeated cycling in air at temperatures where a chromia-only scale spalls away.
• 800H wins on creep strength above about 700 °C. Incoloy 800H is specified with a coarse grain size, typically ASTM E112 grain size 5 or coarser, and that coarse structure is what gives it its stress-rupture capability in reformer and cracking furnace service.
• Ordering plain Incoloy 800 instead of 800H fails a creep duty. The two grades differ principally in carbon content and in the coarse-grain requirement; if the drawing or the purchase order does not call up 800H and verify the grain size, the material supplied may not meet the rupture properties the design assumed.
• Carburising atmospheres are a separate question. 800H's higher nickel content gives it useful resistance to carbon ingress in reducing and carburising furnace atmospheres, and where carbon activity is high, neither grade is adequate on its own and a cast heat-resistant alloy or a coating is often the correct answer.
• The cost comparison must be made on life, not on price per kilogram. Inconel 601 costs more per kilogram, but where it survives several thermal cycles that destroy an 800H component the total cost of ownership reverses. Conversely, specifying 601 for a load-carrying support that 800H could carry is wasted alloy cost.
• Both are supplied to well-defined ASTM product standards by form. The governing standards differ between rod, bar, plate, sheet, seamless tube and welded product, and the correct standard for the form must be named on the purchase order.

What Are Incoloy 800H and Inconel 601?

Incoloy 800H is an iron-nickel-chromium heat-resisting alloy, designated UNS N08810 and W.Nr 1.4958, with approximately 30.0-35.0 % nickel, 19.0-23.0 % chromium and iron as the balance, and a controlled carbon range of 0.05-0.10 % together with a specified coarse grain size. It belongs to the family of solid-solution strengthened alloys developed for high-temperature service where neither a fully nickel-based alloy nor a stainless steel is appropriate, and its particular strength is creep and stress-rupture behaviour above about 700 °C in oxidising and carburising furnace atmospheres. It is supplied as seamless tube, welded tube, pipe, rod, bar, plate, sheet and strip under the ASTM product standards, and it is one of the established materials for steam reformer and cracking furnace tubing.

Inconel 601 is a nickel-chromium-iron alloy, designated UNS N06601 and W.Nr 2.4851, with approximately 58.0-63.0 % nickel, 21.0-25.0 % chromium and 1.0-1.7 % aluminium, with iron forming the balance. The aluminium addition is the defining feature of the alloy. Combined with a high chromium level, it produces a mixed chromium-and-aluminium oxide scale that is unusually resistant to spalling under thermal cycling, and this is what allows 601 to be used in air at temperatures where most nickel-chromium alloys fail by repeated scale breakdown. The alloy is supplied in the same range of product forms and is widely used for furnace muffle, radiant tubes, heat-treatment baskets and fixtures, thermocouple protection sheaths, combustion chamber components and annealing and galvanising line hardware.

The two alloys are often specified interchangeably by maintenance engineers and by furnace builders working from a general "heat-resistant alloy" requirement, and the substitution usually appears harmless because both are solid-solution alloys that are easy to fabricate and both are readily available. They are nevertheless quite different materials. One has more nickel and aluminium and wins on surface protection; the other has more iron, less nickel, a deliberately coarse structure and wins on load-carrying capacity at temperature. Treating them as one material produces two distinct failure modes: an 800H component used in a duty that required 601 will scale and lose section until it perforates, while a 601 component used in a duty that required 800H will sag or rupture under its own weight and the imposed load. This article examines composition, mechanical and creep properties, heat treatment and grain-size control, furnace atmosphere behaviour and selection, and closes with explicit rules and a decision matrix.

It is worth stating the underlying metallurgy at the outset, because it explains the recommendations that follow. Neither alloy can be strengthened by a precipitation-hardening treatment of the kind used for Inconel 718, and neither relies on a gamma-prime or gamma-double-prime precipitate for its strength. Their creep resistance comes from two things: a solid-solution matrix that resists deformation at temperature, and, in the case of 800H, a deliberately coarse grain structure that reduces the total grain-boundary area available for the grain-boundary sliding and diffusion processes that cause creep. That second factor is why the grain size specification matters as much as the chemistry, and why a heat of 800H that meets its composition limits but has been processed to a fine grain size will fail a creep duty even though the mill certificate shows a fully compliant chemistry. Hold that fact and the purchasing rules at the end of this article follow directly.

Chemical Composition: Iron-Base versus Nickel-Base Oxidation Chemistry

The composition table below sets out the two chemistries with the governing standard named for each. The two lines that decide most conversations are aluminium, which is 1.0-1.7 % in 601 and only 0.15-0.60 % in 800H, and carbon, which is deliberately controlled at 0.05-0.10 % in 800H to support the coarse-grain structure and creep behaviour.

Element (wt %)	Incoloy 800H (N08810)	Inconel 601 (N06601)	Per standard	Function in the alloy
Nickel	30.0-35.0	58.0-63.0	ASTM B409 / ASTM B168	matrix; higher Ni aids carburisation resistance
Chromium	19.0-23.0	21.0-25.0	ASTM B409 / ASTM B168	oxidation and corrosion resistance
Aluminium	0.15-0.60	1.0-1.7	ASTM B409 / ASTM B168	alumina scale formation, decisive in 601
Titanium	0.15-0.60	not specified	ASTM B409 / -	stabilising addition in 800H
Carbon	0.05-0.10	0.10 max	ASTM B409 / ASTM B168	supports coarse grain structure in 800H
Iron	39.5 min	balance	ASTM B409 / ASTM B168	matrix component
Manganese	1.5 max	1.0 max	ASTM B409 / ASTM B168	deoxidation residual
Silicon	1.0 max	0.50 max	ASTM B409 / ASTM B168	deoxidation residual
Copper	0.75 max	1.0 max	ASTM B409 / ASTM B168	residual
Sulphur	0.015 max	0.015 max	ASTM B409 / ASTM B168	residual, controlled
Grain size requirement	coarse, typically ASTM E112 grain size 5 or coarser	not specified	ASTM B409 / ASTM B407	creep resistance in 800H

Table note: Values are the standard composition limits of the governing ASTM product standards (ASTM B409 for plate, sheet and strip, ASTM B408 for rod and bar, ASTM B407 for seamless tube, ASTM B514 and B515 for welded pipe and tube, and ASTM B166, B167 and B168 for the Inconel 601 product forms), latest editions. The coarse grain size requirement for 800H is a specification requirement and not a preference: the applicable product standard and the purchase order must call up the grade and the grain size together, and compliance is verified by testing to ASTM E112. GB and other cross-system designations for iron-nickel-chromium heat-resisting alloys are written in their own standard system and must not be substituted line for line for the ASTM limits, nor should a GB designation be assumed to satisfy the coarse-grain requirement of 800H.

Two consequences follow from the table and both have direct purchasing implications. First, aluminium is the element that costs money in 601 and the element that delivers its oxidation performance, and there is no cheaper substitute for it: an alloy with the same chromium level but without the aluminium does not perform like 601 in cyclic oxidation, no matter how similar the datasheet tensile figures are. Second, the grain-size line is unusual in a specification table and it is the line most often missed. A purchase order for furnace tubing or fixtures that names only the grade and the chemistry will be filled with material that meets the chemistry, but unless the order also calls up the coarse grain size and requires verification to ASTM E112, the creep properties cannot be relied upon. In our experience this single omission accounts for a material share of premature furnace component failures, and it is the first thing we check when a customer reports short life in an 800H application.

The cross-system reference deserves the usual caution. Neither alloy has a single widely used Chinese GB designation that can be treated as an exact equivalent. The GB system contains its own iron-nickel-chromium heat-resisting grades and its own nickel-chromium grades, and the designations are written against different composition limits, property minima, test requirements and inspection documents. Where a drawing originates in China and will be manufactured to an ASTM specification, or the reverse, the conversion must be stated explicitly with the source system identified in its own column, and the delivered material must be verified against the specification actually named on the purchase order rather than against the nearest-sounding designation.

Mechanical Properties and Creep Strength

At room temperature the two alloys are close enough that a tensile comparison will not decide the selection, and in fact 601 is generally the stronger of the two at ambient temperature. The distinction appears as the temperature rises. Above roughly 700 °C, and particularly in long-term tests, 800H's coarse grain structure and higher nickel content give it higher stress-rupture strength, which is why reformer and cracking furnace tubing is built in 800H rather than in 601.

Property (typical)	Incoloy 800H	Inconel 601	Basis
Tensile strength, 20 °C	~450-520 MPa	~600-680 MPa	typical, not a standard minimum
0.2 % yield strength, 20 °C	~170-210 MPa	~250-320 MPa	typical, not a standard minimum
Elongation, 20 °C	~45-50 %	~35-45 %	typical, not a standard minimum
Tensile strength, 800 °C	~150-200 MPa	~130-170 MPa	typical, not a standard minimum
Creep-rupture strength, 800-900 °C	higher	lower than 800H	typical published guidance
Load-carrying capability above 700 °C	good, coarse grain	limited by lower creep strength	typical published guidance
Oxidation-limited service in air	~950-1,000 °C	~1,100 °C and above with cycling	typical published guidance
Grain size	coarse, typically ASTM E112 size 5 or coarser	not specified	ASTM B407 / B408 / B409

Table note: The values shown are typical published properties and are explicitly not standard minima. Acceptance minima for a specific product form are fixed by the governing specification named on the purchase order - ASTM B407, B408, B409, B514 and B515 for the 800H forms and ASTM B166, B167, B168, B516 and B517 for the Inconel 601 forms - and the required grain size for 800H must be stated and verified to ASTM E112. Room-temperature tensile testing follows ASTM E8/E8M, elevated-temperature testing ASTM E21, hardness testing ASTM E10 or E18, and stress-rupture testing is performed to the applicable ASTM practice for the product form. The service temperatures quoted are typical published guidance rather than standard limits, and for pressure-retaining design the ASME Code allowable stresses for the specific product form and temperature apply.

The practical reading of this table is that the two alloys fail in different ways, and the selection should follow the failure mode the design cannot tolerate. An 800H component in an oxidation-dominated duty will lose section through scale formation and eventually perforate; a 601 component in a load-dominated duty will sag, bow or rupture as it creeps. Furnace engineers recognise both patterns and can usually identify within minutes which one a failed component suffered, which is why the first question we ask about a short-life component is whether the failure was section loss or deformation. The answer usually reveals whether the original material selection was wrong, or whether the material was correct and the grain size or the operating temperature was not what the design assumed.

Two qualifications deserve emphasis. First, creep properties are time-dependent, so a material comparison at 800 °C is meaningless without a time base: 800H's advantage over 601 grows with exposure time, and a component that runs for a few hundred hours between rebuilds may show no difference at all while a component expected to run for years will show a large one. When we quote for a furnace component we ask for the expected service life for exactly this reason. Second, oxidation resistance and creep strength are not traded against one another in a simple way, because the two alloys can experience both mechanisms simultaneously in a hot, load-bearing, cycled furnace component. Where that combination exists, the honest engineering answer is often to change the design - by reducing the metal temperature, by supporting the component differently, or by increasing the section - rather than to look for an alloy that solves both problems at once.

Heat Treatment, Grain Size Control and Fabrication

Incoloy 800H is supplied in a solution-annealed condition with a coarse grain size that is specified and verified, and the grain size requirement is what separates it from plain Incoloy 800 and from the fine-grain product. Inconel 601 is supplied annealed and has no grain-size requirement, because its design driver is surface protection rather than creep resistance. The difference has direct consequences for fabrication: any shop process that alters the grain structure or the surface condition of an 800H component can destroy the property the customer paid for.

Parameter	Incoloy 800H	Inconel 601	Basis
Supplied condition	solution annealed, coarse grain	annealed	ASTM B407 / B409 / B166
Annealing temperature (typical)	~1,100-1,170 °C	~1,100-1,200 °C	typical commercial practice
Grain size requirement	ASTM E112 size 5 or coarser	none specified	ASTM B407 / B408 / B409
Effect of cold work on properties	reduces creep resistance, anneal after forming	acceptable for many duties	published metallurgy
Welding consumable	matching nickel-iron-chromium filler	matching nickel-chromium filler	AWS A5.14
Post-weld heat treatment	normally not required	normally not required	fabrication practice
Heat-affected zone grain structure	refine and may reduce local creep life	not the controlling concern	published metallurgy
Hot forming range (typical)	~1,000-1,150 °C	~1,000-1,200 °C	typical practice
Cleaning requirement	sulphur and lead excluded	sulphur and lead excluded	fabrication requirement

Table note: The temperatures shown are typical commercial practice; the governing specification and the producer's certified heat treatment record govern the delivered material. The grain size requirement for 800H is a specification requirement verified by testing to ASTM E112, and it applies to the material as delivered. Welding consumables are selected under AWS A5.14 to match the base material, and the applicable code or customer specification governs procedure qualification. The requirement to exclude sulphur, lead and other low-melting-point contaminants from marking materials, lubricants and shop dirt is a fabrication discipline rather than a standard limit, but it is not optional for these alloys at elevated temperature.

The single most important fabrication point in this comparison concerns the heat-affected zone of a weld in an 800H component. Welding refines the grain structure locally, and because 800H's creep resistance depends on a coarse grain size, the weld and its heat-affected zone are the weakest regions of a high-temperature component in creep terms. That is not a reason to avoid welding 800H - the material is fabricated by welding every day in reformer and furnace construction - but it is a reason to place welds away from the highest-stress, highest-temperature region wherever the design permits, and to require a qualified procedure with controlled heat input. Where a welded 800H component fails prematurely in service, the crack is very often in or beside the weld rather than in the parent metal, and the investigation should begin there.

Cold work raises a related concern. Because creep resistance depends on the microstructure rather than on a precipitate, any cold forming operation that leaves residual strain in the component will reduce its creep life unless the part is subsequently annealed. For cold-formed 800H parts, the correct route is to form and then anneal before service, and the purchase order should state the final heat treatment so that the supplier's process route and the customer's expectation agree. Inconel 601 is more forgiving in this respect because its performance depends principally on the surface oxide rather than on the grain structure, but it is still good practice to anneal after significant cold forming so that the component enters service in a uniform condition.

One further point affects both alloys and is frequently overlooked in furnace work: the effect of service exposure on the material that is already installed. A component that has run at 900 °C for several years has a different microstructure and a different remaining life from the same component when new, and repair welding or re-rating a used furnace requires an assessment of the aged material rather than a repeat of the original material certificate. Where an operator is planning a life extension or a temperature increase on an existing furnace, the correct first step is a metallurgical assessment of samples taken from the hottest, most highly stressed locations, not an assumption based on the original specification.

Oxidation, Carburisation and Furnace Atmospheres

Furnace atmospheres are not simply "hot air", and the alloy that performs best in one furnace will not necessarily perform best in the next. The three mechanisms that decide life in industrial furnaces are oxidation under an oxidising or cycling atmosphere, carburisation under a reducing or carbon-bearing atmosphere, and sulphidation where sulphur is present. Inconel 601 is resistance to the first, Incoloy 800H has a useful position in the second, and neither is a good answer to the third.

Furnace atmosphere / duty	Incoloy 800H	Inconel 601	Basis
Air or clean combustion gas, 900-1,000 °C	good	excellent	typical published guidance
Air with frequent thermal cycling, 1,000-1,100 °C	limited, scale spalling risk	excellent	typical published guidance
Intermittent service to ~1,150 °C	not recommended	good	typical published guidance
Carburising atmosphere, 850-1,000 °C	useful resistance from high nickel	moderate	typical published guidance
Strongly carburising or carbon activity high	review, consider cast alloys	review, consider cast alloys	engineering guidance
Nitriding atmosphere	fair, review	fair, review	engineering guidance
Sulphur-bearing reducing atmosphere	limited	limited	engineering guidance
Molten salt or liquid metal contact	review case by case	review case by case	engineering guidance
Steam or hydrogen-rich process gas	good, established in reformer service	moderate	published practice
Thermal shock / rapid cycling	moderate	good	typical published guidance

Table note: The rankings summarise typical published guidance on high-temperature corrosion and furnace atmosphere behaviour and are engineering guidance rather than standard requirements. Actual performance depends on temperature, gas composition, sulphur and alkali content, cycling frequency and stress, and where the atmosphere is strongly carburising, nitriding or sulphur-bearing the correct approach is an assessment of the actual conditions or a test exposure rather than a datasheet comparison. For severely carburising or sulphidising service, cast heat-resistant alloys with higher nickel and silicon contents, or protective coatings, are often the appropriate selection and the wrought alloys discussed here are not.

The practical division between the alloys in furnace work follows the mechanism. Where the hot face sees clean oxidising gas and the temperature climbs above roughly 1,000 °C, or where the component is cycled through the scale-spalling temperature range repeatedly, 601 is the safer material because its alumina-supported scale survives the cycling that destroys a chromia scale. Where the atmosphere is reducing or carbon-bearing and the component carries load, 800H is the more sensible selection because it combines useful carburisation resistance with creep strength that 601 cannot match at temperature. Where sulphur is present in a reducing atmosphere, neither wrought alloy is a reliable long-life answer, and this is the case in which furnace operators most often discover that the material they are replacing was not the only option available.

One further mechanism deserves a mention because it is frequently misdiagnosed as oxidation. In a carburising furnace, the failure appears as a hard, brittle case with a changed volume, followed by cracking under thermal cycling, and the component often looks superficially intact until it is sectioned. Because the damage is internal rather than on the surface, a visual inspection of a carburised component can be misleading, and the correct diagnostic is a metallographic examination of a section taken from the hottest location. This matters for selection because a furnace that is nominally oxidising can develop a carburising or alternating environment at the point where the burner flame impinges or where carbon deposits accumulate, so the atmosphere that governs material life is often local rather than average.

Selection Matrix: Furnace Component by Component

The selection between these two alloys in furnace service reduces to three questions: is the component load-bearing, is the duty oxidising or carburising, and what is the peak temperature? The matrix below maps the common furnace components to a recommendation.

Furnace component / duty	Recommended alloy	Why
Steam reformer and cracking furnace tubes	800H	creep strength under pressure at 850-1,000 °C
Radiant tubes in a load-bearing radiant section	800H	creep strength plus good oxidation resistance
Furnace muffle with high temperature and cycling	601	spallation-resistant oxide scale
Heat-treatment baskets, trays and fixtures	601	cyclic oxidation resistance at the hot face
Annealing and galvanising line hardware	601	oxidation resistance with thermal cycling
Combustion chamber liners and baffles	601	surface protection, limited load
Thermocouple protection sheaths	601	thin section, oxidation-limited, low load
Catalyst support grids and internals	800H	load-bearing at temperature in process gas
Retorts and reaction vessels in process gas	800H	creep strength under pressure
Supports, hangers and spacers in hot zones	either, decide on load and atmosphere	800H if load-bearing, 601 if oxidation-driven
Components cycled to 1,100 °C or above in air	601	800H will spill scale and lose section
Components in a strongly carburising load-bearing duty	review, consider cast alloys	neither wrought grade is the ideal answer

Table note: The recommendations reflect the typical published properties and atmosphere behaviour of the two alloys and are engineering guidance rather than standard requirements. The final selection for a safety-critical or high-value furnace component must consider the actual peak and average metal temperature, the load and support arrangement, the true local atmosphere, the number of thermal cycles and the required campaign length. Where a furnace component has failed prematurely, the failure mechanism should be established metallurgically before the replacement material is chosen, because oxidation, creep, carburisation and thermal fatigue each point to a different remedy.

Three rules are worth stating as rules rather than as rows in a table. First, if the component carries load at temperature above roughly 700 °C, the answer is 800H, and the purchase order must require the coarse grain size to be verified. Second, if the peak temperature exceeds roughly 1,000 °C in an oxidising atmosphere, or if the component is cycled through the scale-spalling range, the answer is 601, and the correct fixation method must be chosen so that the component is not constrained against thermal expansion. Third, if the atmosphere is strongly carburising or contains sulphur in a reducing condition, neither of these wrought grades should be selected without an assessment, because the failure mechanism is different from the one either alloy was designed to resist.

Availability, Product Forms and Standards

Both alloys are produced in a full range of wrought product forms, and both are covered by defined ASTM product standards that differ by form, so the correct standard must be named on the purchase order. Availability is broader for standard tube and plate sizes than for large forgings, and lead time is often the deciding commercial factor in furnace rebuild schedules.

Product form	Incoloy 800H standard	Inconel 601 standard	ASME equivalent
Rod and bar	ASTM B408	ASTM B166	ASME SB-408 / SB-166
Plate, sheet and strip	ASTM B409	ASTM B168	ASME SB-409 / SB-168
Seamless tube	ASTM B407	ASTM B167	ASME SB-407 / SB-167
Welded tube	ASTM B515	ASTM B516	ASME SB-515 / SB-516
Welded pipe	ASTM B514	ASTM B517	ASME SB-514 / SB-517
Forgings	ASTM B564	ASTM B564	ASME SB-564
Grain size verification	ASTM E112, coarse grain required	not applicable	-

Table note: Standards are listed by scope and are summarised from the published documents (latest editions). The standard applicable to the specific form and size ordered is the one that governs the delivered material, and for pressure-retaining applications the ASME Code adoption of that standard, together with the Code allowable stresses, governs the design rather than the raw ASTM document. The coarse grain size requirement is part of the 800H specification and must be stated on the order and verified to ASTM E112. Where a customer's drawing names a standard that does not cover the form being ordered - for example calling up a plate standard for tube - the discrepancy must be resolved before the order is placed rather than at inspection.

The availability picture is worth understanding before scheduling a furnace rebuild. Seamless and welded tube in 800H is a well-established product supplied against the standard reformer and furnace sizes, and plate and sheet in 601 is similarly well established, so these forms carry shorter lead times and more competitive pricing than large or unusual items. Large forged or thick-wall components in either alloy are less standard and should be ordered with realistic lead times. Where a rebuild schedule is tight, the practical approach is to identify the long-lead items early and to keep the balance of the order in standard forms, rather than to attempt to compress the whole scope at once.

Price Reference (2026, EXW Shanghai)

Inconel 601 costs more per kilogram than Incoloy 800H because it contains roughly twice as much nickel and a deliberate aluminium addition, while 800H is diluted with a substantial iron content. That relationship is stable enough to plan around, but the correct comparison in furnace service is not price per kilogram at all: it is the total cost of the component over the campaign, which depends on which alloy survives the duty.

Product form	Incoloy 800H	Inconel 601	Note
Round bar	USD 25-40/kg	USD 38-58/kg	601 carries a nickel premium
Plate and sheet	USD 28-45/kg	USD 42-65/kg	thickness and width affect yield
Seamless tube	USD 40-65/kg	USD 55-85/kg	size and wall thickness dominate
Welded tube and pipe	USD 32-55/kg	USD 48-75/kg	weld and test regime matter
Fabricated fixtures and baskets	quote by drawing	quote by drawing	fabrication dominates cost
Forgings	quote by drawing	quote by drawing	size and complexity dominate

Table note: Reference range only, 2026, EXW Shanghai, USD/kg. These figures float with the LME nickel price and are not a quotation. The bands are wide because price depends strongly on quantity, product form, size, wall thickness and the testing and certification regime required; a furnace tube order with full third-party inspection and dimensional verification sits at the top of a range while a standard commercial certificate order sits lower. For fabricated components, the cost of fabrication, welding and any required heat treatment frequently exceeds the cost of the material, which is a further reason to decide the alloy on technical grounds before comparing quotes.

The commercial conclusion requires discipline, because it is easy to justify either alloy on a price comparison alone. Specify 800H for load-bearing components above roughly 700 °C, and require the coarse grain size to be verified, because this is the cheapest way to obtain creep strength in a furnace. Specify 601 where oxidation at the top of the temperature range and thermal cycling dominate, and accept the higher unit price, because a component that survives three campaigns is cheaper than one that is replaced every campaign even if the second is cheaper per kilogram. Where the two alloys are genuinely close, the deciding question is which failure mode the furnace can least tolerate: section loss in a load-bearing part, or deformation in a precision part.

Standard Index

Standard	Title / scope	Covers	Form
ASTM B407	Nickel-iron-chromium alloy (UNS N08800, N08810, N08811) seamless tube	composition + mechanical + grain size	seamless tube
ASTM B408	Nickel-iron-chromium alloy (UNS N08800, N08810, N08811) rod and bar	composition + mechanical + grain size	rod, bar
ASTM B409	Nickel-iron-chromium alloy (UNS N08800, N08810, N08811) plate, sheet and strip	composition + mechanical + grain size	plate, sheet, strip
ASTM B514 / B515	Nickel-iron-chromium alloy welded pipe (B514) and welded tube (B515)	composition + mechanical	welded pipe, tube
ASTM B166	Nickel-chromium-iron alloy (UNS N06601 and others) rod, bar and wire	composition + mechanical	rod, bar, wire
ASTM B167	Nickel-chromium-iron alloy (UNS N06601 and others) seamless pipe and tube	composition + mechanical	pipe, tube
ASTM B168	Nickel-chromium-iron alloy (UNS N06601 and others) plate, sheet and strip	composition + mechanical	plate, sheet, strip
ASTM B516 / B517	Nickel-chromium-iron alloy welded tube (B516) and welded pipe (B517)	composition + mechanical	welded tube, pipe
ASTM B564	Nickel alloy forgings	composition + mechanical	forgings
ASTM E112	Determining average grain size	test method	-
ASTM E8 / E8M	Tension testing of metallic materials	test method	-
ASTM E21	Elevated-temperature tension testing of metallic materials	test method	-
ASTM E10 / E18	Brinell and Rockwell hardness testing	test method	-
ASTM E1476 / E572	Metals identification by PMI and by X-ray spectrometry	test method	-
AWS A5.14	Nickel and nickel-alloy bare welding electrodes and rods	consumable selection	filler wire
ASME SB-407 / SB-408 / SB-409 / SB-166 / SB-167 / SB-168	ASME Code adoption of the above	Code allowable basis	all forms

Table note: Standards are listed by number and scope; where an edition year is not quoted, the latest edition applies and the controlling edition is the one named on the purchase order. The ASTM standard applicable to a given product form is the one that governs the delivered material, and the ASME adoption of that standard, together with the Code allowable stresses, governs pressure-retaining design. The coarse grain size requirement for UNS N08810 is set out in the applicable product standard and verified by testing to ASTM E112; it must be stated on the order because a chemistry-compliant heat that does not meet the grain size requirement does not meet the material specification.

FAQ

Q1: What is the difference between Incoloy 800H and Inconel 601?

The difference is one of design intent: Incoloy 800H is built to carry load at temperature, and Inconel 601 is built to resist the atmosphere. Incoloy 800H is an iron-nickel-chromium alloy with 30.0-35.0 % nickel, 19.0-23.0 % chromium and a controlled carbon content of 0.05-0.10 %, supplied with a coarse grain size that gives it good creep and stress-rupture strength above about 700 °C. Inconel 601 is a nickel-chromium-iron alloy with 58.0-63.0 % nickel, 21.0-25.0 % chromium and a deliberate 1.0-1.7 % aluminium addition, which forms a highly protective and spallation-resistant oxide scale that survives thermal cycling at temperatures up to about 1,100 °C and above. In practice, 800H is specified for reformer and cracking furnace tubes and other load-bearing hot components, while 601 is specified for muffle, baskets, fixtures, sheaths and other components whose life is limited by oxidation rather than by load. They are not interchangeable in either direction.

Q2: Which alloy should I use for reformer or cracking furnace tubes?

Incoloy 800H is the correct material for steam reformer and cracking furnace tubes, and the reason is that these components operate under internal pressure at 850-1,000 °C for years, which makes creep and stress-rupture strength the controlling properties. Inconel 601 has higher room-temperature strength but does not match 800H's long-term creep performance at these temperatures, so a 601 tube would deform and eventually rupture in a duty that 800H carries routinely. The critical purchasing point is that the order must call up UNS N08810 with the coarse grain size verified to ASTM E112, because a heat of the chemically similar but finer-grained plain 800 grade will pass a chemistry check and fail in creep service. Weld placement also matters: welding refines the grain structure locally, so the weld and its heat-affected zone are the weakest regions in creep terms and should be positioned away from the hottest, most highly stressed sections wherever the design allows.

Q3: Which alloy is better for a furnace muffle or heat-treatment basket?

Inconel 601 is usually the better choice for muffle, baskets, trays and fixtures, because those components are thin-section, lightly loaded and exposed to repeated thermal cycling, which makes oxidation resistance the controlling property rather than creep strength. The aluminium addition in 601 produces an alumina-supported scale that resists spalling through repeated heating and cooling, while a chromia-only scale on a comparable alloy progressively breaks down and allows section loss to accelerate. There is an important qualification: a heat-treatment basket that carries a heavy static load at temperature for long periods is a load-bearing component as well as an oxidising one, and in that case the selection should be reviewed, because neither alloy is designed to combine heavy load carrying with the most severe cyclic oxidation. Our Incoloy heat-resisting alloy range and our Inconel high-temperature range cover the product forms used in these applications, and we will review the load and cycle before recommending.

Q4: Why does Incoloy 800H need a coarse grain size?

Incoloy 800H needs a coarse grain size because creep in these alloys occurs largely by grain-boundary sliding and by diffusion along grain boundaries, and a coarse structure reduces the total grain-boundary area available for those mechanisms. The specification for UNS N08810 therefore includes a grain size requirement, typically of the order of ASTM E112 grain size 5 or coarser, and compliance is verified by testing to ASTM E112. The consequence is that 800H cannot be treated as a simple chemistry upgrade of plain Incoloy 800: the two grades differ in carbon range and in the required grain structure, and only 800H carries the creep properties that reformer and cracking furnace designs assume. This matters in procurement because a purchase order that names only the grade family or the chemistry can be filled with material that satisfies the analysis but not the grain size. Where the duty is creep-critical, the order should name UNS N08810, quote the governing product standard and require the grain size test result on the certificate.

Q5: Can Inconel 601 be used above 1,100 °C?

Inconel 601 is one of the wrought nickel-chromium alloys that can be used in air at around 1,100 °C and above, particularly for intermittent or cycled service where its alumina-supported oxide scale is more resistant to spalling than a plain chromia scale. That capability is a surface-protection property, not a strength property, and it applies to components that are lightly loaded. A heavily loaded 601 component at that temperature would creep unacceptably, and the practical applications at the top of the alloy's range are therefore muffle, liners, sheaths, baffles, supports and similar parts rather than pressure-retaining or load-carrying components. The other limiting factor is the atmosphere: the excellent behaviour applies in clean oxidising gas, and where the gas contains sulphur, alkali or a high carbon activity, the failure mechanisms change and the allowable temperature falls accordingly. Any duty above about 1,050 °C should be reviewed against the actual gas composition rather than specified from a general maximum temperature figure, because published ceilings assume a favourable atmosphere.

Q6: Which alloy performs better in a carburising atmosphere?

Incoloy 800H has the more useful carburisation resistance of the two because its higher iron content is balanced by 30.0-35.0 % nickel, and nickel reduces the rate at which carbon diffuses into the alloy compared with a lower-nickel material. Inconel 601 performs acceptably at moderate carbon activity but is not the specialist choice for a strongly carburising duty. In practice, however, the correct answer for a strongly carburising furnace is often neither wrought alloy. Where carbon activity is high, the damage mechanism is the inward diffusion of carbon producing a hard, brittle case, a volume change and cracking under thermal cycling, and cast heat-resistant alloys with higher nickel and silicon contents, or protective coatings, frequently give better life than any wrought product. This is one of the cases where the honest recommendation is to change the material class rather than to choose between the two options on the table, and we say so when a customer's furnace data shows high carbon activity.

Q7: How do the two alloys compare in cost and life?

Inconel 601 costs more per kilogram than Incoloy 800H because it contains roughly twice as much nickel and a deliberate aluminium addition; in 2026 EXW Shanghai reference terms the difference is of the order of 40-60 % for the same product form. The comparison that matters in furnace service, however, is cost per campaign rather than cost per kilogram. Where a component's life is limited by oxidation and thermal cycling, 601 will outlast a comparable 800H component by a margin that frequently exceeds the price difference, so the cheaper material costs more per year of service. Where the component is load-bearing at temperature, the comparison reverses: 800H provides the creep strength at a lower price and specifying 601 is simply paying a premium for a surface property the duty does not require. The judgement should be made on the failure mechanism actually observed, which is why we ask for a failed component or a description of the failure when helping a customer select a replacement material.

Q8: How do I verify that I received 800H and not plain 800?

Verify the grade from the certificate and verify the grain size from the test result, because the chemistry difference between 800H and plain 800 is small and is not by itself conclusive. The distinguishing features are the controlled carbon range of 0.05-0.10 % for UNS N08810 and the coarse grain size requirement verified to ASTM E112; plain Incoloy 800, UNS N08800, permits a wider carbon range and carries no coarse-grain requirement. Confirm that the mill certificate names UNS N08810, that it reports the carbon content within the specified range, and that it reports the grain size test result to ASTM E112 with a value at or coarser than the limit in the applicable product standard. Reconcile the heat number on the material with the certificate and confirm the producing mill is named. A portable chemistry check to ASTM E1476 is a useful confirmation of the alloy family but will not by itself distinguish 800H from 800. Our technical knowledge centre sets out the reconciliation steps we apply to incoming material.

Q9: Is post-weld heat treatment required for either alloy?

Neither Incoloy 800H nor Inconel 601 normally requires post-weld heat treatment, and both are widely used in the as-welded condition in furnace construction. The engineering effort therefore goes into procedure qualification, heat input control, joint preparation and cleanliness rather than into a furnace cycle after welding. Two disciplines are essential rather than optional: sulphur, lead and other low-melting-point contaminants must be excluded from marking materials, lubricants, cutting fluids and shop dirt around the joint because they embrittle these alloys at elevated temperature, and the welding procedure should be qualified for the specific combination of material, thickness and position. For 800H there is one additional consideration: because the alloy's creep resistance depends on a coarse grain structure, the weld and its heat-affected zone are locally weaker in creep terms than the parent metal, and the design should place welds away from the hottest and most highly stressed regions wherever that is practical.

Q10: Can these alloys be used for galvanising and annealing line hardware?

Inconel 601 is a well-established material for annealing line hardware and for parts of galvanising equipment exposed to high-temperature oxidising conditions, because its cyclic oxidation resistance is the property those components need. The qualification is important: galvanising involves molten zinc, and molten zinc attacks nickel-based alloys aggressively in the same way that it attacks steels, so no nickel alloy should be selected for direct contact with molten zinc without a specific review of the immersion conditions. Where the component is a roller, a support or a fixture that operates in the furnace atmosphere above the zinc bath, 601 is a sensible selection; where it is immersed in or splashed by molten zinc, the material choice is a specialist question and the answer frequently involves a different material class or a protective arrangement. For annealing line furnaces operating in clean oxidising gas, 601 is a conventional and reliable choice, and 800H is used where the hardware carries load at temperature.

Q11: What are the alternatives if neither alloy is suitable?

The right alternative depends on which requirement fails. Where the temperature is below roughly 700 °C and the load is moderate, heat-resisting stainless steels such as the higher-chromium austenitic grades offer useful oxidation resistance at a fraction of the cost, and our heat-resisting and PH stainless range covers those grades. Where the temperature is higher but the load is modest, the higher-nickel and higher-chromium wrought alloys extend the oxidation-limited ceiling further, and the cobalt-bearing solid-solution alloys are used for combustion hardware. Where the atmosphere is strongly carburising or sulphidising, the answer is usually a cast heat-resistant alloy with higher nickel and silicon contents, or a protective coating, rather than a wrought product. Where the load at temperature is extreme, the gamma-prime strengthened alloys are used, though at a much higher cost. The honest position is that each of these alternatives is correct for a definable set of conditions, which is why we ask for the temperature, load, atmosphere and cycle before recommending.

Q12: What information should I provide for a furnace material recommendation?

Five pieces of information resolve most furnace material questions: the peak metal temperature and the normal operating temperature, the load the component carries and how it is supported, the actual local gas composition including whether carbon activity or sulphur is present, the number of thermal cycles expected per year and the severity of those cycles, and the required campaign length between rebuilds. It also helps to know the product form and size, the governing standard, and whether the component has an existing approved material, because a change from an approved material may require re-approval. Where a component has already failed, a sample or a photograph of the failure is more useful than any of these, because the failure mechanism tells us immediately whether the original selection was wrong or whether the operating conditions differed from those assumed. Send your requirement through our contact page and we will return a material recommendation with the governing standard citations, and if the answer is that neither alloy is right for the duty we will say so. Our other furnace and high-temperature articles cover related selection problems in more detail.

Conclusion and Selection Rules

The selection rules for these two alloys are short and they resolve almost every furnace case. Use Incoloy 800H when the component carries load at temperature above roughly 700 °C - reformer and cracking furnace tubes, radiant tubes, retorts, catalyst support grids and process internals - and always specify UNS N08810 with the coarse grain size verified to ASTM E112. Use Inconel 601 when the component's life is limited by oxidation and thermal cycling rather than by load - muffle, heat-treatment baskets and trays, fixtures, thermocouple sheaths, combustion liners and annealing line hardware - and accept the higher unit price as the cost of a scale that survives repeated cycling.

Two of the rules are constraints rather than preferences. A load-bearing component above roughly 700 °C should not be specified in 601, because its creep strength will not carry the duty that 800H carries. A component cycled to the top of the temperature range in air should not be specified in 800H, because the scale will spall and the component will lose section until it fails. Everything else is a trade between alloy cost and campaign life, and where the atmosphere is strongly carburising or contains sulphur, the decision moves outside these two alloys altogether.

Shanghai Hangbo Alloy Group Co., Ltd. supplies Incoloy 800H and Inconel 601 as seamless tube, welded tube and pipe, rod, bar, plate, sheet and strip, with mill test certification including grain size verification to ASTM E112 for 800H, PMI to ASTM E1476 or E572 where required, and third-party inspection by SGS, BV or TUV on request. We supply furnace builders and operators directly and hold material in the standard furnace sizes, and we will review your temperature, load, atmosphere and cycle before quoting so that the alloy and the product standard are matched to the duty. Send your requirement through our contact page and we will return a material recommendation with the governing standard citations and a costed quotation. For related furnace and high-temperature selection questions, see our other technical articles.

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Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier

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Ni: NI200-N6 | Monel: 400-502, K-500, R-405 | Inconel: 600-740H, X-750, 725 | Incoloy: 800-27-7MO | Hastelloy: C-276-HYBRID-BC1, N | Super Austenitic: 904L-AL-6XN | Chromium-Rich: Alloy 33 | High-Strength Stainless: Nitronic 50/60, PH13-8Mo | Chlorination: Alloy 45 | Nimonic: 75-263 | Haynes: 25-HR-160 | RA: 330/333 | Precision: 1J22-4J45 | High-Strength: 18Ni250-AerMet100 | Heating: Cr20Ni80/60 | Specialty: Alloy 20-602CA

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