Alloy 59 vs Hastelloy C-276: Ni-Cr-Mo Selection

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: Alloy 59 or Hastelloy C-276?

Alloy 59 is the better choice in oxidising media - nitric acid, nitric-hydrofluoric pickling liquors, wet chlorine, chlorine dioxide and hypochlorite bleach streams - because it carries about 23 % chromium with very low iron and no tungsten. Hastelloy C-276 remains the workhorse of the family for reducing acids, chloride pitting and general chemical plant, where its tungsten-bearing chemistry and long qualified history suit it.

Key Takeaways

• Chromium is the dividing line, and Alloy 59 has far more of it. Alloy 59 carries 22.0-24.0 % chromium against 14.5-16.5 % in C-276, with iron held to 1.5 % maximum against 4.0-7.0 %, and that difference drives the alloy's advantage in every oxidising environment.
• C-276's tungsten helps in reducing acids. Tungsten at 3.0-4.5 % strengthens the alloy and supports its performance in hydrochloric and sulphuric acid service, which is where C-276 has historically been strongest and where Alloy 59 offers less marginal benefit.
• Thermal stability favours Alloy 59. C-276 is susceptible to secondary-phase precipitation in the region of roughly 600-900 °C during slow cooling or post-weld heat treatment, which is why its fabrication rules restrict those treatments. Alloy 59's low iron and tungsten contents reduce that susceptibility.
• Molybdenum content is high in both, and that is why neither is a nitric acid alloy. Both alloys contain roughly 15-17 % molybdenum, and molybdenum is detrimental in strongly oxidising nitric acid service, so for nitric acid alone a lower-molybdenum grade is generally the correct answer rather than either of these two.
• Neither alloy is the answer for seawater at ambient temperature if a cheaper material will do. Both work in chlorides, but the super-austenitic stainless steels and, where appropriate, the nickel-copper grades offer adequate performance at lower cost for many chloride duties.
• Filler metals are not interchangeable. C-276 is welded with ERNiCrMo-4 and Alloy 59 with ERNiCrMo-13; using the C-276 filler on an Alloy 59 fabrication gives away part of the corrosion margin the alloy was specified to provide.

What Are Alloy 59 and Hastelloy C-276?

Alloy 59 is a nickel-chromium-molybdenum alloy, designated UNS N06059 and W.Nr 2.4605, with approximately 22.0-24.0 % chromium, 15.0-16.5 % molybdenum, iron held to a maximum of 1.5 %, a small deliberate aluminium addition of 0.1-0.4 %, and carbon limited to 0.010 % maximum. It was developed as a member of the Ni-Cr-Mo family with a higher chromium content and a lower iron content than its predecessors, specifically to extend performance in oxidising media while retaining the family's general chemical resistance. It is supplied as plate, sheet, strip, rod, bar, seamless tube, welded tube and pipe, and forgings under the ASTM product standards that govern the low-carbon Ni-Cr-Mo alloys. Our Hastelloy and Ni-Cr-Mo plate & bar page lists the forms and certifications we hold across this family.

Hastelloy C-276 is also a nickel-chromium-molybdenum alloy, designated UNS N10276 and W.Nr 2.4819, with approximately 14.5-16.5 % chromium, 15.0-17.0 % molybdenum, 3.0-4.5 % tungsten, 4.0-7.0 % iron and carbon limited to 0.010 % maximum. It is the most widely used alloy in the family and, for many engineers, the reference material for aggressive chemical service. Its combination of molybdenum and tungsten gives it excellent resistance to reducing acids and to chloride-induced pitting and crevice corrosion, and its very low carbon content limits carbide precipitation at grain boundaries, which is what made it a practical weldable material for chemical plant when it was introduced. It is supplied in the full range of wrought product forms and has by far the longest and broadest service history of any Ni-Cr-Mo alloy.

The two alloys are often treated as interchangeable members of one family, and that treatment is understandable: they are both low-carbon Ni-Cr-Mo alloys, they are both covered by the same ASTM product standard numbers, they are both fabricated and welded in similar ways, and their mechanical properties are close enough that a strength-based comparison will not separate them. They are nevertheless different alloys whose relative performance reverses depending on the chemistry of the medium. In oxidising environments, where the cathodic reaction is fast and the alloy's own chromium content controls whether a protective film can form, Alloy 59's higher chromium and lower iron give it a real and often decisive advantage. In reducing acids, where hydrogen evolution is the cathodic reaction and the alloy does not depend on a passive film, C-276's tungsten and molybdenum combination performs at least as well and often better. This article sets out the chemistry, mechanical and thermal properties, corrosion behaviour by medium, fabrication rules and selection, and closes with explicit recommendations and a decision matrix.

It is worth stating the metallurgical logic at the outset, because it explains both the corrosion behaviour and the fabrication rules. Both alloys are solid-solution strengthened face-centred-cubic nickel alloys, and neither is hardened by precipitation. Their corrosion resistance comes from a molybdenum-rich, chromium-bearing passive film that forms and repairs itself in many environments, and the balance between chromium and molybdenum is what decides which environments the film can survive. Chromium supports passivity in oxidising conditions; molybdenum supports resistance to chloride attack and to reducing acids; and the two compete, in the sense that a very high molybdenum content with a low chromium content performs poorly in strongly oxidising media. Alloy 59 shifts that balance towards chromium, and C-276 towards molybdenum plus tungsten. That single trade-off drives almost every recommendation in this article, and the second consequence - the susceptibility of high-molybdenum, high-iron alloys to secondary-phase precipitation at intermediate temperatures - drives the heat treatment and welding rules that follow.

Chemical Composition: Chromium, Iron and Tungsten Decide the Behaviour

The composition table below sets out the two chemistries with the governing standard named for each. The three lines that separate the alloys are chromium, iron and tungsten, and those three elements in combination explain both the corrosion response and the fabrication behaviour of each material.

Element (wt %)	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Per standard	Function in the alloy
Nickel	balance	balance	ASTM B575 / ASTM B574	matrix
Chromium	22.0-24.0	14.5-16.5	ASTM B575 / ASTM B574	passivity in oxidising media
Molybdenum	15.0-16.5	15.0-17.0	ASTM B575 / ASTM B574	chloride and reducing-acid resistance
Iron	1.5 max	4.0-7.0	ASTM B575 / ASTM B574	residual; low Fe aids oxidising performance
Tungsten	not specified	3.0-4.5	ASTM B575 / ASTM B574	strengthens and aids reducing-acid resistance
Aluminium	0.1-0.4	not specified	ASTM B575 / -	deoxidation and stability in Alloy 59
Cobalt	0.3 max	2.5 max	ASTM B575 / ASTM B574	residual
Carbon	0.010 max	0.010 max	ASTM B575 / ASTM B574	carbide control
Silicon	0.10 max	0.08 max	ASTM B575 / ASTM B574	residual, tightly controlled
Manganese	0.5 max	1.0 max	ASTM B575 / ASTM B574	deoxidation residual
Copper	0.50 max	0.50 max	ASTM B575 / ASTM B574	residual
Sulphur	0.010 max	0.03 max	ASTM B575 / ASTM B574	residual, controlled
Vanadium	not specified	0.35 max	ASTM B575 / ASTM B574	residual

Table note: Values are the standard composition limits of the governing ASTM product standards (ASTM B575 for plate, sheet and strip, ASTM B574 for rod and bar, and the corresponding pipe and tube standards ASTM B619, B622 and B626), latest editions. Wide variations exist between the product standards of other systems and between historic editions, so the controlling limits are those of the standard named on the purchase order. GB and other cross-system designations for Ni-Cr-Mo alloys are written in their own standard system, and although designations such as the NS-series are commonly cited as equivalents of the C-276 type, they are not interchangeable limits and a GB heat must be re-qualified against the ASTM or ASME specification actually required.

Three observations follow. First, the chromium difference is large - roughly 23 % against roughly 15.5 % - and it is the reason the two alloys behave differently in any environment where the alloy depends on a passive film rather than on resistance to hydrogen evolution. Second, iron is held to 1.5 % maximum in Alloy 59 deliberately; iron is a cheaper element than nickel, and raising it would reduce cost while degrading the alloy's performance in the oxidising media for which it was designed, so an offer of Alloy 59 at an unusually low price deserves a chemistry check. Third, both alloys are low-carbon, and both depend on that low carbon content for weldability: carbon at the levels permitted in the older Ni-Cr-Mo alloys precipitated as carbides at grain boundaries during welding and caused intergranular attack in service, and the 0.010 % maximum in both specifications is what makes them practical for welded chemical plant today.

The practical purchasing consequence is that the two alloys cannot be distinguished by the elements most commonly checked. Nickel, molybdenum and carbon are similar between them, and even chromium differences can be partially masked by certified ranges that overlap at the extremes. Separating them requires the chromium value itself, the iron value and, decisively, the tungsten content, which is present in C-276 and absent from Alloy 59. That is why we recommend verification by optical emission spectrometry to ASTM E1476 or ASTM E572 on any delivery where both grades are stocked, and why the certificate alone is not sufficient evidence when the two materials are interchangeable in a drawing's material list.

Mechanical Properties and the Standard Basis

Both alloys are solid-solution strengthened and are supplied and used in the annealed condition, so neither offers the high strength of a precipitation-hardening alloy such as Inconel 718. They are used for their corrosion resistance, and the mechanical properties that matter are adequate strength, good ductility and toughness in the welded and formed condition. The table below gives typical published values with the standard basis stated; acceptance minima for a specific order come from the governing product specification.

Property (typical)	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Basis
Tensile strength, 20 °C	~690-780 MPa	~750-800 MPa	typical, not a standard minimum
0.2 % yield strength, 20 °C	~340-380 MPa	~355-420 MPa	typical, not a standard minimum
Elongation, 20 °C	~50-55 %	~40-50 %	typical, not a standard minimum
Hardness	~85-95 HRB	~90-100 HRB	typical, not a standard minimum
Impact toughness, welded condition	good	good	typical published data
Strength mechanism	solid solution	solid solution	published metallurgy
Formability	excellent, low work-hardening rate	good	published practice
Structural load-bearing use	not a structural alloy	not a structural alloy	design consideration

Table note: The values shown are typical published annealed 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 B575, B574, B619, B622, B626 and B564 for the forms of both alloys - and the corresponding ASME Code adoption of those standards governs pressure-retaining design. Room-temperature tensile testing follows ASTM E8/E8M, elevated-temperature testing ASTM E21, hardness testing ASTM E10 or E18, and grain size determination ASTM E112. Neither alloy should be selected on the basis of its mechanical properties: both are corrosion-resistant materials with moderate strength, and where high strength is required the correct approach is to change the component design rather than to look for a stronger Ni-Cr-Mo alloy.

The practical reading of the table is that the mechanical differences between the two alloys are small and are unlikely to decide a project. Both have adequate strength for pressure-retaining equipment, both retain ductility after welding, and both have sufficient toughness for the services in which they are used. Where a Ni-Cr-Mo alloy must also carry significant structural load at ambient temperature, the design approach that works is to use a thicker section, not to search for a stronger grade. Where the load is cyclic, fatigue design is governed by the geometry and the surface condition rather than by the alloy choice, and the correct fatigue assessment should be performed on the actual fabricated geometry.

One property difference deserves attention in fabrication planning rather than in design. Alloy 59 has a lower work-hardening rate than C-276, which is a practical advantage in forming operations: cold forming and pressing operations require less force, produce less springback and require fewer intermediate anneals, and the risk of cracking during a severe forming operation is lower. For components with significant cold forming content - dished heads, formed ductwork, complex fabricated assemblies - this can materially reduce fabrication cost and risk, and it is one of the less obvious reasons why an alloy selected on corrosion grounds may also be the better manufacturing choice. Where a fabricator has not worked with Alloy 59 before, the difference is usually noticed on the first job.

Heat Treatment, Thermal Stability and Welding

The most important fabrication difference between the two alloys is thermal stability, and it is a difference that shows up most often in welded construction and in any component that is exposed to intermediate temperatures during fabrication. Both alloys are supplied solution annealed and both are used in the as-welded condition, but their tolerance for being held in, or slowly cooled through, the intermediate temperature range is not the same.

Parameter	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Basis
Solution annealing (typical)	~1,100-1,180 °C, rapid quench	~1,100-1,180 °C, rapid quench	typical commercial practice
Supplied condition	solution annealed	solution annealed	ASTM B575 / B574
Secondary-phase precipitation risk	lower	higher in the ~600-900 °C range	published metallurgy
Post-weld heat treatment	not normally used	not normally used, avoided where possible	fabrication practice
Cooling after annealing	rapid quench required	rapid quench required	specification requirement
Welding consumable	ERNiCrMo-13	ERNiCrMo-4	AWS A5.14
Welding process	GTAW, GMAW, SMAW	GTAW, GMAW, SMAW	published practice
Heat input control	normal good practice	more critical to avoid intermediate-temperature exposure	fabrication practice
Contamination control	sulphur, lead, zinc excluded	sulphur, lead, zinc excluded	fabrication requirement
Weld qualification	per applicable code	per applicable code	code 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. Welding consumables are selected to match the base material under AWS A5.14 and, where an aerospace, ASME or customer specification applies, under that document. Neither alloy normally requires post-weld heat treatment, and post-weld heat treatment of C-276 is generally avoided rather than specified because it risks the precipitation of secondary phases at the grain boundaries within the intermediate temperature range, which reduces corrosion resistance. The requirement to exclude sulphur, lead, zinc and other low-melting-point contaminants is a fabrication discipline and not a standard limit, but it is essential for these alloys at elevated temperature.

The mechanism behind the thermal-stability difference is worth understanding because it explains the rules. In high-molybdenum Ni-Cr-Mo alloys, holding or slowly cooling through an intermediate temperature range allows molybdenum-rich secondary phases, commonly described as mu phase or related intermetallic precipitates, to form preferentially at grain boundaries. Those phases are depleted in molybdenum and chromium relative to the matrix around them, leaving narrow zones that are less corrosion resistant, and the result is a material that looks and tests correctly in a tensile test while corroding preferentially along its grain boundaries in service. C-276 carries more iron and tungsten than Alloy 59 and is more prone to this behaviour; Alloy 59's low iron and absence of tungsten reduce the driving force. In practice, both alloys are solution annealed and rapidly quenched, both are used in the as-welded condition without post-weld heat treatment, and the practical advice for C-276 is to keep heat input and interpass temperature under control and to avoid holding the material at intermediate temperature for extended periods. For components that must be formed and then annealed, Alloy 59 gives the fabricator a wider window before the same concern arises.

Welding practice itself is similar for the two alloys and well established. Both are welded with matching nickel-based fillers - ERNiCrMo-4 for C-276 and ERNiCrMo-13 for Alloy 59 - using GTAW, GMAW or SMAW with clean joint preparation and controlled heat input. Using a C-276 filler on an Alloy 59 fabrication is a common shortcut and a poor one, because the weld metal then has lower chromium than the parent metal and becomes the least corrosion-resistant part of the component in precisely the oxidising medium the alloy was chosen for; in an oxidising chloride or nitric-hydrofluoric service the weld becomes the location of first attack. Two further disciplines apply to both alloys: sulphur and lead must be excluded from marking materials, lubricants and shop dirt, and zinc contamination, which is common in galvanised shop environments, must be avoided because it causes cracking in nickel alloys at temperature. Where a fabrication has been completed and the weld chemistry is uncertain, a PMI check to ASTM E1476 on the weld caps will confirm which filler was used.

Corrosion Behaviour by Medium and Temperature

The relative performance of the two alloys changes with the chemistry of the medium, and the change follows a consistent rule: where the environment is oxidising, chromium is the controlling element and Alloy 59 is ahead; where the environment is reducing, molybdenum and tungsten are the controlling elements and C-276 is at least as good. The table below summarises the typical position of each alloy by medium family.

Medium / environment	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Practical note
Nitric acid, all concentrations	good, better than C-276	limited, especially when hot or concentrated	a low-molybdenum grade is usually correct for nitric acid alone
Nitric-hydrofluoric pickling liquor	excellent, established selection	usable, shorter life	Alloy 59 is a standard pickling line material
Hydrochloric acid	good	excellent	C-276 is the traditional selection
Sulphuric acid, reducing conditions	good	excellent, including chloride-contaminated acid	C-276 preferred where the acid is reducing
Sulphuric acid, oxidising or aerated	good	limited at higher concentrations	chromium content decides the ranking
Phosphoric acid with chlorides and fluorides	good	good, established in fertiliser plant	both are used, confirm the chloride and fluoride levels
Organic acids, formic and acetic	good	good to excellent	both are widely used in chemical and pharmaceutical plant
Wet chlorine gas and chlorine-bearing liquors	excellent	limited	Alloy 59 is the stronger selection
Chlorine dioxide and hypochlorite bleach streams	excellent	limited in strong oxidising bleach	Alloy 59 preferred in bleach plant
Seawater and chloride pitting	excellent	excellent	super-austenitic stainless may be adequate at lower cost
Chloride stress-corrosion cracking	highly resistant	highly resistant	both are immune in practical terms
Flue gas desulphurisation and scrubber liquors	excellent, especially when oxidising	good	Alloy 59 favours oxidising and chlorinated liquors
Incineration and off-gas with mixed acids	good	good	medium analysis decides the selection
Caustic and alkaline media	acceptable	acceptable	neither is the first choice above moderate concentration

Table note: The rankings summarise typical published corrosion data and long-established service experience for these alloys; they are engineering guidance and not standard requirements. Actual performance depends on concentration, temperature, aeration, chloride and oxidiser content, and on whether the surface is in a passive or active state, and corrosive service should be confirmed by test data for the actual medium - typically ASTM G48 for pitting and crevice resistance and ASTM G28 for intergranular attack - or by an immersion test on the specific liquor. Where a service sits close to a limiting condition, or where temperature and concentration fluctuate, the correct approach is a corrosion assessment on the actual process stream rather than a comparison of datasheets.

The most important point in this table is the qualification on nitric acid. Nitric acid is strongly oxidising, and molybdenum is detrimental in that environment, which means that both alloys, with roughly 15-17 % molybdenum, are compromised in hot concentrated nitric acid even though Alloy 59 is clearly the better of the two. A designer who needs a nitric acid material should generally be looking at a low-molybdenum austenitic stainless steel or a nickel-chromium alloy without molybdenum, and this is one of the cases where the correct answer to "which of these two?" is "neither". Where nitric acid is present as one component of a mixed acid - which is the normal situation in pickling lines, where nitric and hydrofluoric acids are combined - the picture changes completely, because the mixture requires both oxidising resistance and resistance to the fluoride and chloride species, and Alloy 59 is a standard material for exactly that duty. We ask for the full liquor analysis rather than the name of the process whenever a mixed-acid application is quoted.

Three practical observations follow for plant engineers. First, bleach plant and chlorine dioxide service is the clearest case in this comparison: C-276 has historically suffered in strongly oxidising bleach liquors while Alloy 59 was developed with such service in mind, and where a plant has a record of short C-276 life in a chlorine dioxide stage the substitution is a well-established remedy. Second, flue gas desulphurisation and scrubber environments are frequently borderline, and their behaviour is dominated by the oxidation state and the chloride content of the liquor rather than by the nominal acid composition, which is why the same plant can report good life from both alloys in different parts of the same system. Third, wherever an alloy is selected on corrosion grounds for a welded fabrication, the first place to look when unexpected corrosion appears is the weld and the heat-affected zone, because that is where composition and microstructure differ most from the property the design assumed.

Selection Matrix: Which Ni-Cr-Mo Alloy for Which Plant?

The selection between these two alloys reduces to three questions: is the medium oxidising or reducing, is the service welded and exposed to intermediate temperatures during fabrication, and is the alloy actually necessary in the first place?

Duty / requirement	Recommended alloy	Note
Nitric-hydrofluoric pickling lines	Alloy 59	the standard material for this duty
Chlorine dioxide and hypochlorite bleach stages	Alloy 59	strong oxidising service, where C-276 has a weaker record
Wet chlorine gas handling	Alloy 59	oxidising service
Hydrochloric acid service, all concentrations	C-276	tungsten and molybdenum combination
Sulphuric acid, reducing or chloride-contaminated	C-276	established workhorse duty
Flue gas desulphurisation, oxidising liquors	Alloy 59	oxidative and chlorinated liquors favour higher chromium
Flue gas desulphurisation, reducing liquors	C-276	reducing conditions favour molybdenum and tungsten
Incineration and mixed-acid off-gas	either, decide on medium analysis	oxidation state decides the ranking
Pharmaceutical and fine chemical reactors	either, C-276 more commonly qualified	check solvent and halide compatibility
Severely cold-formed components	Alloy 59	lower work-hardening rate than C-276
Components with restricted annealing windows	Alloy 59	better thermal stability than C-276
Maximum availability and longest service history	C-276	broadest stock and qualification record
Seawater cooling where a stainless will do	neither	review super-austenitic or duplex grades first
Hot concentrated nitric acid alone	neither	a low-molybdenum grade is generally required

Table note: The recommendations reflect typical published corrosion data and established service experience and are engineering guidance rather than standard requirements. Final selection for critical service requires the actual medium analysis, temperature, aeration state and chloride content, the applicable design code, and confirmation of any client or licensor material approval that applies to the plant. Where the process includes more than one environment, or where conditions vary with the process cycle, each condition should be evaluated separately because the ranking of these two alloys can reverse between stages of the same plant.

Three rules are worth stating as rules rather than as rows in a table. First, if the medium is oxidising - nitric acid mixtures, hypochlorite, chlorine dioxide, wet chlorine, aerated acid - the answer is Alloy 59 unless the analysis says otherwise. Second, if the medium is a reducing acid or a chloride-bearing reducing environment, the answer is C-276, which remains the most broadly qualified material of its class. Third, if the requirement is general chloride resistance at ambient temperature in a plant where a super-austenitic stainless steel would be adequate, the honest answer is that neither alloy should be specified, because the stainless will do the job at a fraction of the cost and the decision to use a Ni-Cr-Mo alloy should be justified by a specific condition that the stainless cannot handle.

Product Forms, Standards and Fabrication

Both alloys are supplied in the full range of wrought product forms and are covered by the same family of ASTM product standards, which is convenient for specification but also a reason the two are so often confused. The table below sets out the standard applicable to each form and the welding consumable to use.

Item	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Standard / reference
Plate, sheet and strip	covered	covered	ASTM B575
Rod and bar	covered	covered	ASTM B574
Seamless pipe and tube	covered	covered	ASTM B622
Welded pipe	covered	covered	ASTM B619
Welded tube	covered	covered	ASTM B626
Forgings	covered	covered	ASTM B564
Welding filler metal	ERNiCrMo-13	ERNiCrMo-4	AWS A5.14
ASME adoption	ASME SB-575 / SB-574 / SB-619 / SB-622 / SB-626	ASME SB-575 / SB-574 / SB-619 / SB-622 / SB-626	ASME Section II
PMI verification	ASTM E1476 / E572	ASTM E1476 / E572	test method
Corrosion acceptance testing	ASTM G48 / ASTM G28	ASTM G48 / ASTM G28	test method

Table note: Standards are listed by scope and summarised from the published documents (latest editions). The standard applicable to the specific form and size ordered governs the delivered material, and for pressure-retaining equipment the ASME Code adoption of that standard, together with the Code allowable stresses, governs the design rather than the raw ASTM document. Welding consumables are selected to match the base material under AWS A5.14 and the applicable code. Because both alloys are covered by the same standard numbers, the purchase order must always name the UNS number or the alloy designation and not only the standard, and the material certificate must be checked for the alloy actually supplied rather than for the standard number alone.

The fabrication picture is favourable for both alloys. They are readily formed, machined and welded, they do not require post-weld heat treatment, and they are available in a wide range of standard plate, sheet and tube sizes. Alloy 59 offers the fabricator a modest advantage in cold forming and a wider window in thermal exposure, while C-276 offers the advantage of ubiquity: more fabricators have qualified procedures, more stock is held in more sizes, and more reference experience exists in the industry. Where a project has a tight schedule or an unfamiliar fabricator, availability and familiarity are legitimate reasons to choose C-276 provided that the service conditions do not include the strongly oxidising media in which Alloy 59 is clearly superior. Where the service does include those media, the material choice should be made on corrosion grounds and the fabrication arrangements built around it.

Price Reference (2026, EXW Shanghai)

Both alloys are nickel-based with similar molybdenum contents, so their prices are in the same band, and the difference between them is driven by the substitution of iron and tungsten in C-276 against the higher chromium and lower iron of Alloy 59. In practice, C-276 typically carries a modest price advantage as a result of much larger production volume and wider competition, and Alloy 59 is priced at a small premium.

Product form	Alloy 59 (N06059)	Hastelloy C-276 (N10276)	Note
Round bar	USD 38-60/kg	USD 34-55/kg	availability favours C-276
Plate and sheet	USD 42-68/kg	USD 38-62/kg	thickness and width affect yield
Seamless tube and pipe	USD 58-95/kg	USD 52-88/kg	size and wall thickness dominate
Welded pipe and tube	USD 46-78/kg	USD 42-72/kg	weld and test regime matter
Forgings	quote by drawing	quote by drawing	complexity and quantity dominate
Filler wire (ERNiCrMo-13 / ERNiCrMo-4)	quote by size	quote by size	priced separately from base metal

Table note: Reference range only, 2026, EXW Shanghai, USD/kg. These figures float with the LME nickel price and with the molybdenum and tungsten markets and are not a quotation. The bands are wide because price depends strongly on quantity, product form, size and the certification and testing regime required; a bleach plant order with full third-party inspection and corrosion testing sits at the top of a range, while a standard commercial certificate order sits lower. Where the two alloys are within a few percent of each other on price, the decision should be made on corrosion grounds, and where the service is strongly oxidising the Alloy 59 premium is small relative to the cost of a premature failure in a bleach or pickling line.

Standard Index

Standard	Title / scope	Covers	Form
ASTM B575	Low-carbon nickel-chromium-molybdenum alloy plate, sheet and strip	composition + mechanical	plate, sheet, strip
ASTM B574	Low-carbon nickel-chromium-molybdenum alloy rod and bar	composition + mechanical	rod, bar
ASTM B622	Nickel-chromium-molybdenum alloy seamless pipe and tube	composition + mechanical	seamless pipe, tube
ASTM B619	Nickel-chromium-molybdenum alloy welded pipe	composition + mechanical	welded pipe
ASTM B626	Nickel-chromium-molybdenum alloy welded tube	composition + mechanical	welded tube
ASTM B564	Nickel alloy forgings	composition + mechanical	forgings
ASME SB-575 / SB-574 / SB-619 / SB-622 / SB-626 / SB-564	ASME Code adoption of the above	Code allowable basis	all forms
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 E112	Determining average grain size	test method	-
ASTM E1476	Standard guide for metals identification, sorting and examination (PMI)	test method	-
ASTM E572	Analysis of stainless steel and nickel alloys by X-ray spectrometry	test method	-
ASTM G48	Pitting and crevice corrosion resistance in ferric chloride	test method	-
ASTM G28	Detecting susceptibility to intergranular corrosion	test method	-
ASTM G31	Laboratory immersion corrosion testing of metals	test method	-
AWS A5.14	Nickel and nickel-alloy bare welding electrodes and rods	consumable selection	filler wire

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. Both alloys are covered by the same product standard numbers for each form, so the purchase order must name the UNS number as well as the standard and the certificate must be checked for the alloy actually supplied. Cross-system designations for the Ni-Cr-Mo family, including the NS-series designations used in the Chinese standard system, are written against different limits and must not be substituted for the ASTM or ASME requirements on an order.

FAQ

Q1: What is the difference between Alloy 59 and Hastelloy C-276?

The difference is the balance between chromium and the molybdenum-tungsten combination. Alloy 59, UNS N06059, contains 22.0-24.0 % chromium with iron held to 1.5 % maximum and no tungsten, while Hastelloy C-276, UNS N10276, contains 14.5-16.5 % chromium with 4.0-7.0 % iron and 3.0-4.5 % tungsten. Both contain roughly 15-17 % molybdenum and both are low-carbon, solution-annealed alloys with similar mechanical properties. That chemistry difference produces a consistent reversal in service: Alloy 59 performs better in oxidising media such as nitric-hydrofluoric pickling liquor, wet chlorine, chlorine dioxide and hypochlorite, because it can sustain a passive film under oxidising conditions, while C-276 performs at least as well in reducing acids such as hydrochloric and reducing sulphuric acid, where the molybdenum and tungsten combination is the controlling factor. Alloy 59 also has the better thermal stability, with a lower tendency to form secondary phases at grain boundaries when exposed to intermediate temperatures during fabrication.

Q2: Which alloy is better for nitric-hydrofluoric pickling liquor?

Alloy 59 is the correct and well-established material for nitric-hydrofluoric pickling lines, and it is one of the clearest cases in the Ni-Cr-Mo family. Pickling liquor combines nitric acid, which is strongly oxidising, with hydrofluoric acid, which is aggressive to the passive film and to many alloys, and the mixture therefore demands both oxidising resistance and resistance to the fluoride species. C-276 can be used but has a shorter life in the same duty, because its lower chromium content restricts its ability to maintain passivity under the oxidising influence of the nitric component. Alloy 59's higher chromium, in combination with low iron and the absence of tungsten, gives it the margin that pickling line operators require, and the alloy is a standard selection for tanks, immersion hardware, heating coils, ducting and associated pipework in stainless steel pickling installations. Where a plant has a history of C-276 component replacement in a pickling line, the substitution to Alloy 59 is a routine remedy, and it should be accompanied by a matching change of welding consumable to ERNiCrMo-13.

Q3: Which alloy should I use in a bleach plant or chlorine dioxide stage?

Alloy 59 is the stronger selection in chlorine dioxide and hypochlorite bleach stages, and this is essentially the same oxidising-service argument as for pickling lines. Chlorine dioxide and hypochlorite are strong oxidisers, and in their presence an alloy must be able to maintain a chromium-rich passive film to survive; C-276, with roughly 15.5 % chromium and a significant molybdenum content, has a much narrower margin in these liquors and has a long record of accelerated attack in bleach plant service. Alloy 59 was developed for exactly this class of duty, and it is used for bleach stage washers, vats, piping, and the internals of chlorine dioxide generators and associated equipment. The practical qualification is that bleach plant chemistry varies widely between installations and between stages, and the correct engineering approach is to obtain the liquor analysis for the specific stage - including pH, temperature, chloride and oxidiser content - and to confirm the material against it rather than to apply a single answer across the whole bleach line.

Q4: Is Alloy 59 suitable for hydrochloric and sulphuric acid service?

Alloy 59 performs well in hydrochloric acid and in sulphuric acid across much of the practical range, and it is used in both. The honest qualification is that C-276 is the traditional and more broadly qualified selection for reducing acid service, particularly for hydrochloric acid at higher concentrations and for sulphuric acid containing chlorides, because its molybdenum and tungsten combination is optimised for exactly that situation. Alloy 59 gives up a small amount of margin in strongly reducing conditions in exchange for its much stronger position in oxidising conditions. The practical consequence is that a plant using C-276 successfully in a reducing acid duty has no corrosion reason to change, and a plant selecting a material for a new reducing-acid application may reasonably stay with C-276 on the strength of its longer service record and wider availability. Where the duty involves a mixture of reducing and oxidising conditions, which is common in chemical plant, the balance shifts and the medium should be assessed in full rather than by acid name.

Q5: Why is post-weld heat treatment avoided for C-276?

Post-weld heat treatment is avoided for C-276 because holding the alloy in the intermediate temperature range, roughly 600-900 °C, allows molybdenum-rich secondary phases to precipitate preferentially at the grain boundaries. The zones immediately around those precipitates become depleted in chromium and molybdenum, and although the material's tensile properties and its chemistry certificate remain perfectly acceptable, the depleted boundaries corrode preferentially in service, producing a localised intergranular attack that looks nothing like general wastage. The same concern applies, to a lesser degree, to any slow cooling through that range after solution annealing, which is why both alloys require rapid quenching after annealing. Alloy 59 is more tolerant because its low iron and absence of tungsten reduce the driving force for that precipitation, which gives a fabricator a wider processing window. In practice, neither alloy normally requires post-weld heat treatment, and where a heat treatment is proposed for another reason on a C-276 fabrication, the procedure should be reviewed before it is applied.

Q6: Can these alloys be replaced by super-austenitic stainless steel?

In many chloride duties, yes, and the substitution is worth considering on cost grounds before a Ni-Cr-Mo alloy is specified. The super-austenitic stainless steels, including the high-molybdenum grades such as 904L, 254SMO and the 6 % molybdenum alloys, provide substantial resistance to chloride pitting and crevice corrosion and to many acid environments at a fraction of the price of a nickel-based alloy, and for ambient-temperature seawater, chloride-bearing cooling water and moderate acid service they are frequently adequate. They fall short in strongly reducing acids, in hot concentrated acids, in the presence of strong oxidisers combined with chlorides, and where stress or thermal cycling is significant. For any proposed substitution, the correct basis is a comparison of the actual corrosion data for the specific medium at the actual temperature, and our super-austenitic and duplex stainless range covers the grades we supply for those duties. Where the medium demands a Ni-Cr-Mo alloy, we will say so rather than accept an order that will fail.

Q7: Which welding filler metal should be used for each alloy?

Use ERNiCrMo-13 for Alloy 59 and ERNiCrMo-4 for Hastelloy C-276, both selected under AWS A5.14. The distinction matters more than it appears. Using a C-276 filler on an Alloy 59 fabrication is a common procurement shortcut, and it produces a weld whose chromium content is materially lower than that of the parent metal; in the oxidising medium for which Alloy 59 was selected - a pickling liquor, a bleach stream, wet chlorine - the weld then becomes the least corrosion-resistant part of the component and the location of first attack. The converse substitution, using ERNiCrMo-13 on a C-276 component, is less harmful from a corrosion standpoint but leaves a weld whose properties were not qualified with the base material. Both alloys are welded with the usual attention to joint preparation, controlled heat input and interpass temperature, and both require sulphur, lead and zinc contamination to be excluded from marking materials, lubricants and shop dirt. Our corrosion and materials articles cover the wider selection and testing questions in more detail.

Q8: How do I verify that Alloy 59 was supplied and not C-276?

Verify by chemistry, because the two alloys share the same ASTM product standards and the same product forms, and the certificate alone does not prove what was supplied. The decisive elements are chromium, iron and tungsten: Alloy 59 contains 22.0-24.0 % chromium with 1.5 % maximum iron and no tungsten, while C-276 contains 14.5-16.5 % chromium, 4.0-7.0 % iron and 3.0-4.5 % tungsten. Portable optical emission spectrometry to ASTM E1476 or ASTM E572 will separate the two materials in the field, and laboratory analysis to ASTM E572 provides the documented result for a claim. Copper, nickel and molybdenum are similar between the two and will not distinguish them. Alongside the chemistry check, confirm that the certificate names the UNS number specified on the order, reconcile the heat number on the material with the certificate, and confirm the producing mill is named. Because the standard numbers are identical for both alloys, a certificate that quotes only a standard number and a grade family name is not adequate evidence.

Q9: Which alloy is better for flue gas desulphurisation?

It depends on the oxidation state of the liquor, and this is one of the clearest examples of why the process data matters more than the alloy name. In oxidising FGD liquors - which are typically aerated, contain chlorides and may carry residual oxidiser - Alloy 59's higher chromium content gives it the better margin, and it is the preferred selection for the more aggressive absorber internals, ducting and mist eliminator components. In reducing liquors, C-276 has the advantage for the same reasons it leads in other reducing environments. Many plants contain both conditions in different parts of the system, which is why the same operator can report good life from both alloys in different locations. The practical approach for a new or refurbished scrubber is to obtain the liquor chemistry and oxidation state at each critical location, including the chloride level and any transient excursions during start-up and upset conditions, and to select per location rather than applying a single alloy across the whole system.

Q10: Can these alloys be used in seawater service?

Both alloys perform well in seawater and both resist chloride pitting and crevice corrosion and chloride stress-corrosion cracking, but for most seawater duties a Ni-Cr-Mo alloy is an expensive answer. Ambient-temperature seawater, chloride-bearing cooling water and similar duties are usually served adequately by the super-austenitic stainless steels or, in some cases, by the nickel-copper grades, and the decision to specify a Ni-Cr-Mo alloy should be justified by a specific condition - elevated temperature, chlorination, high flow velocity with entrained solids, or a combination of chlorides with acid or oxidiser. Where such conditions exist, both Alloy 59 and C-276 are suitable, and the selection follows the same oxidising-versus-reducing logic as elsewhere: Alloy 59 where chlorination or oxidiser injection creates oxidising conditions, and C-276 for reducing or oxygen-depleted conditions with high chloride levels.

Q11: What are the alternatives for hot nitric acid service?

For hot concentrated nitric acid alone, neither of these two alloys is the right answer, and a low-molybdenum material is generally required. Molybdenum is detrimental in strongly oxidising nitric acid, and both Alloy 59 and C-276 contain roughly 15-17 % of it, so although Alloy 59 outperforms C-276 in nitric acid it remains a compromise. The correct materials are the low-molybdenum austenitic stainless steels for moderate conditions and the higher-chromium, molybdenum-free nickel alloys for more severe ones, and the selection depends on concentration, temperature and the presence of other species. Where the nitric acid is part of a mixed acid, however, the conclusion reverses: nitric-hydrofluoric pickling liquor requires both oxidising resistance and resistance to fluoride attack, and Alloy 59 is a standard material for that duty. Our Inconel high-temperature range and our Ni-Cr-Mo plate and bar range together cover the alternatives, and we will review the medium rather than simply quote the alloy requested.

Q12: What information should I provide to get a corrosion material recommendation?

Provide the full medium analysis rather than the process name: the chemical species present with concentrations, the normal and maximum operating temperature, the pH, whether the conditions are aerated or oxidising, the chloride and fluoride levels including any transient excursions during start-up, shutdown or upset, the flow velocity and whether solids are entrained, and any welding or fabrication exposure the component will see. For a mixed-acid duty, the ratio between the components matters as much as the individual concentrations, because the balance between oxidising and reducing behaviour decides whether a chromium-rich or a molybdenum-rich alloy is the correct answer. It is also useful to know whether an existing material has failed and how it failed, because the failure mode - uniform wastage, pitting, crevice attack, weld attack or intergranular penetration - narrows the selection considerably. Send your process data through our contact page and we will return a material recommendation with the governing standard citations and, where the margin is genuinely uncertain, a recommendation for corrosion testing on the actual liquor. Our other corrosion and materials selection articles cover related cases.

Conclusion and Selection Rules

The selection rules for these two alloys are short and they resolve most chemical plant cases. Use Alloy 59 where the medium is oxidising - nitric-hydrofluoric pickling liquor, chlorine dioxide and hypochlorite bleach streams, wet chlorine, oxidising flue gas desulphurisation liquors, aerated chlorinated chloride service - and where the fabrication involves severe cold forming or a restricted thermal window. Use Hastelloy C-276 where the medium is reducing - hydrochloric acid, reducing and chloride-bearing sulphuric acid, reducing scrubber liquors - and where maximum availability, the broadest qualified service history and the widest fabrication familiarity are worth more than a marginal corrosion advantage.

Two of the rules are constraints rather than preferences. Neither alloy is the correct selection for hot concentrated nitric acid alone, because their molybdenum content works against them and a low-molybdenum material should be used instead. Neither alloy should be specified for a chloride duty that a super-austenitic stainless steel would handle, because the cost difference is large and the stainless will usually suffice at ambient temperature. Everything else is a judgement about the oxidation state of the medium, and that judgement should be made from the actual process data rather than from the process name.

Shanghai Hangbo Alloy Group Co., Ltd. supplies Alloy 59 and Hastelloy C-276 as plate, sheet, strip, rod, bar, seamless tube, welded tube, welded pipe and forgings, with mill test certification, PMI to ASTM E1476 or E572 where required, corrosion testing to ASTM G48 or G28 on request, and third-party inspection by SGS, BV or TUV. We supply chemical plant, pickling line and bleach plant operators directly and hold material in the standard plate and tube sizes. Send your medium analysis and operating conditions through our contact page and we will return a material recommendation with the governing standard citations and a costed quotation. For related corrosion and 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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