Nickel Aluminium Bronze Investment Casting Grades: C95500 vs C95800, Standards and Procurement Guide

The Bottom Line

• Nickel aluminium bronze investment casting grades aren't interchangeable under one label - C95500 and C95800 are genuinely different ASTM B148 alloys with different aluminium content, different mechanical property targets, and different jobs.

  
  

• C95500 is the higher-aluminium, higher-strength grade used for gears, bushings, and wear components; C95800 is the lower-aluminium grade tuned specifically for seawater dealuminification resistance and is the standard marine propeller alloy. Specifying the wrong one, or treating 'NAB' as a single generic material, is a real procurement risk.

• C95500 runs roughly 10.5-11.5% aluminium and is heat-treatable (TQ50 quench-and-temper) for maximum strength and hardness - the grade to specify for bearings, worm gears, and high-load wear components.

  
  

• C95800 runs a lower 8.5-9.5% aluminium, giving it better resistance to dealuminification and stress corrosion cracking in continuous seawater immersion - the grade behind most ship propellers, pump bodies, and valve trim.

  
  

• Both grades are cast at Pahwa MetalTech via lost-wax investment casting, which holds tighter dimensional tolerance and a cleaner as-cast surface than the sand casting these alloys have traditionally been specified against.

Why "NAB" Isn't One Grade: C95500 vs C95800

Nickel aluminium bronze (NAB) is a family name, not a single alloy - and the two ASTM B148 grades most commonly specified for structural and marine components, C95500 and C95800, are formulated for different priorities. C95500 carries a higher aluminium content, roughly 10.5-11.5%, alongside about 4% each of iron and nickel. That higher aluminium content is what pushes C95500's strength and hardness up - it's the highest-strength standard copper-base casting alloy commonly available, and it can be heat treated for even higher hardness where a job calls for it.

C95800 deliberately runs lower on aluminium, roughly 8.5-9.5%, with iron in the 3.5-4.5% range and nickel plus cobalt in the 4.0-5.0% range. That reduction in aluminium content isn't a cost-cutting move - it's a corrosion-resistance decision. Higher aluminium content in NAB increases susceptibility to dealuminification, a selective corrosion mechanism where aluminium leaches out of the alloy in seawater service, leaving a weakened, porous copper-rich layer behind.

C95800's lower aluminium content and tighter compositional control is specifically what makes it the alloy that's been the marine industry's default propeller and seawater-hardware choice for decades, rather than C95500. ASTM B148 enforces that control directly: for C95800, the standard specifies that iron content shall not exceed nickel content - a compositional constraint C95500 doesn't carry, and one that's easy to miss if a mill certificate is only checked against overall alloy family rather than the specific grade's compositional limits.

The aluminium content difference also drives a real microstructural difference between the two grades. Both alloys solidify with an alpha copper matrix strengthened by iron- and nickel-rich kappa phase precipitates, which is where most of NAB's strength comes from. At C95500's higher aluminium level, the alloy retains more of the harder, more brittle beta phase in the as-cast structure - the source of its higher strength and hardness, but also a phase that's more chemically active and more prone to selective corrosion if left untreated. C95800's lower aluminium content and its foundry-controlled cooling rate are aimed at minimizing retained beta phase, which is the metallurgical reason the grade holds up better under sustained seawater exposure.

This is also why buyers who ask for "NAB" without specifying a grade sometimes receive parts that pass a chemistry certificate but don't perform the way the application actually needs - the certificate confirms the alloy family, not which grade's property and corrosion profile the part was built to.

C95500 vs C95800: Composition and Property Comparison

This NAB casting grades comparison lines up the two grades directly. Property values for C95800 reflect ASTM B148 standard (as-cast, non-heat-treated) minimums; C95500 is reported qualitatively here since its full ASTM B148 property table depends on the specific temper ordered.

Property	C95500	C95800
Nominal aluminium content	~10.5-11.5%	~8.5-9.5%
Nominal iron / nickel content	~4% Fe / ~4% Ni	~3.5-4.5% Fe / ~4.0-5.0% Ni+Co
Relative strength and hardness	Highest-strength standard copper-base casting alloy; heat-treatable for further hardness	High strength, but formulated below C95500 on aluminium to prioritize corrosion resistance over peak hardness
ASTM B148 as-cast minimums	Chemistry-dependent; consult full B148 table for the ordered temper	Tensile 85 ksi (586 MPa) min | Yield 35 ksi min | Elongation 15% min
Seawater dealuminification resistance	Lower than C95800 due to higher aluminium content	Higher - this is the grade's defining design intent
Typical duty	Gears, worm wheels, bushings, valve stems, high-load bearing and wear components	Ship propellers, pump and valve bodies, sea chest fittings, through-hull hardware

ASTM B148 Compliance for Investment-Cast NAB

ASTM B148 is the governing specification for both C95500 and C95800, defining chemical composition limits and mechanical property minimums by grade and temper. The standard's mechanical property tables were written against sand castings, but the same chemistry and mechanical acceptance criteria apply when either grade is investment cast - a buyer specifying "ASTM B148 C95800" is specifying a chemistry and property floor the part has to meet, not a casting process. Investment casting doesn't change what the standard requires; it changes how consistently the casting meets it, since a controlled lost-wax process produces less part-to-part variation in microstructure than a sand mould rebuilt on every cycle.

For marine and defence-adjacent procurement, ASTM B148 chemistry and mechanical certification is usually the baseline, with non-destructive testing specified on top of it. Dye penetrant inspection per ASTM E1417 or an equivalent standard is common for surface-breaking defect detection, and radiographic or ultrasonic testing gets added for pressure-retaining or safety-critical sections. A procurement spec that only cites "ASTM B148" without also specifying NDT scope and heat treatment condition leaves real room for a foundry to under-deliver on a technically compliant part.

Whether you need C95500 C95800 investment casting for a single prototype component or a multi-year production contract, the ASTM B148 certificate should always be paired with a clearly stated heat treatment condition and NDT scope in the purchase order itself, not left to the foundry's standard practice. That's especially true across multiple production runs over time, where a foundry's default process can drift or change between orders unless the buyer's own specification pins it down explicitly.

Heat Treatment Options: TQ50 and As-Cast

ASTM B148 defines a TQ50 temper - a solution anneal followed by a controlled quench - that's most commonly applied to C95500 to push strength and hardness higher than the as-cast condition delivers. TQ50 also improves microstructural homogeneity, relieves casting residual stress, and increases resistance to stress corrosion cracking, which matters on components that see sustained mechanical load rather than pure corrosion exposure.

C95800 doesn't respond to conventional heat treatment for hardening or strengthening the way C95500 does - TQ50 isn't an option to boost C95800's strength. What C95800 does sometimes get is stress relieving or annealing, applied to relieve casting residual stress or condition the part for aggressive service environments, not to increase tensile or yield strength.

If an application genuinely needs more strength than as-cast C95800 delivers, the answer isn't heat-treating C95800 harder - it's evaluating whether C95500 or a different alloy actually fits the duty cycle better, which is exactly the grade-selection question this article works through below.

Choosing Between C95500 and C95800 for Your Application

The grade choice comes down to which failure mode the part is actually exposed to in service - mechanical wear and load, or continuous seawater corrosion.

• Specify C95500 for gears, worm wheels, bushings, valve stems, and wear plates where mechanical load, friction, and hardness dominate the failure risk, and where the component isn't in continuous direct seawater immersion.

  
  

• Specify C95800 for propellers, pump housings, valve bodies, sea chests, and through-hull fittings where continuous seawater exposure and dealuminification resistance are the primary design driver.

  
  

• For components that see both meaningful mechanical load and continuous seawater immersion - large propeller hubs and some pump internals - the grade decision should be made with the foundry against the specific duty cycle, not defaulted to either alloy.

Common NAB Procurement Mistakes to Avoid

The most common mistake in NAB procurement isn't picking the wrong grade outright - it's not picking a grade at all. A purchase order that says "nickel aluminium bronze casting" without a UNS or ASTM designation leaves the foundry to default to whichever grade it normally stocks or finds easiest to pour, which may not match what the application actually needs. The second most common mistake is treating heat treatment as automatic: assuming a NAB casting will arrive in TQ50 condition, or conversely assuming C95800 will always be left as-cast, without confirming it on the order.

• Not specifying grade explicitly - defaults to whatever the foundry stocks, which may prioritize strength (C95500) when the application actually needs corrosion resistance (C95800), or vice versa.

  
  

• Omitting heat treatment condition - leaves TQ50 vs as-cast to foundry default rather than an engineering decision matched to the duty cycle.

  
  

• Citing ASTM B148 without NDT scope - a chemistry-and-mechanical-property certificate says nothing about internal soundness unless radiography, ultrasonic, or dye penetrant testing is specified separately.

  
  

• Assuming sand-cast tolerance data applies to an investment-cast part - ASTM B148's dimensional guidance is written for sand castings, and a lost-wax investment casting can and should hold tighter tolerance than the standard's baseline allows for.

Nickel Aluminium Bronze Lost Wax Casting: Why Process Matters as Much as Grade

Grade selection only controls half the outcome - the casting process controls the other half, because both C95500 and C95800 are alloys where oxide film entrainment and mould-to-mould consistency directly affect whether a part actually delivers the properties its chemistry promises.

Nickel aluminium bronze lost wax casting builds each part's ceramic shell around a wax pattern from a single reusable tool, producing tighter, more repeatable dimensional tolerance and a cleaner as-cast surface than the sand casting these alloys were traditionally specified against - the full mechanism is covered in marine bronze investment casting vs sand casting. For NAB specifically, that process choice also shows up directly in total landed cost, machining allowance, and NDT rejection rate, covered in nickel aluminium bronze investment castings cost advantage.

A Procurement Checklist for Specifying NAB Castings

Use this checklist when writing a purchase spec for nickel aluminium bronze castings, regardless of which grade the application calls for:

• Grade: state C95500 or C95800 explicitly - never just "NAB" or "nickel aluminium bronze" without the UNS/ASTM designation.

  
  

• Standard and revision: cite ASTM B148 (or the specific standard governing the project, e.g. a defence procurement standard) and its current revision.

  
  

• Heat treatment condition: as-cast, or TQ50 - state it explicitly rather than leaving it to the foundry's default.

  
  

• Mechanical property requirements: tensile strength, yield strength, and elongation minimums, matched to the grade and temper actually ordered.

• NDT scope: dye penetrant, radiographic, or ultrasonic testing requirements, and what percentage of the production run gets sampled versus first-article only.

• Dimensional tolerance class and critical-to-function dimensions, especially for parts with mating or sealing surfaces.

  
  

• Casting process: specify investment (lost wax) casting explicitly if part geometry, tolerance, or surface finish requirements make sand casting unsuitable.

  
  

• Weld and joining method, if applicable: C95800 suits shielded metal arc and gas-shielded arc welding but isn't recommended for oxyacetylene or carbon arc welding - confirm the intended joining method is compatible with the grade before finalizing design.

  
  

• Traceability and certification: material test certificates tied to the specific heat/lot, not a generic alloy datasheet.

Nickel Aluminium Bronze Investment Casting Grades: Related Reading

This grade and standards overview connects to the deeper NAB and marine bronze content on this site. For the NAB-specific investment casting cost case against sand casting, see nickel aluminium bronze investment castings cost advantage. For oxide film inclusion issues that affect mechanical test results on aluminium bronze castings, see why aluminium bronze castings fail mechanical testing. For how C95800 compares against duplex stainless steel for seawater service, see NAB vs duplex stainless steel for seawater service. And for choosing between NAB, aluminium bronze, and silicon bronze for seawater valve bodies specifically, see aluminium bronze vs NAB vs silicon bronze alloy selection guide.

Source ASTM B148-Compliant NAB Castings

As an NAB foundry India OEMs and marine buyers turn to for both grades, Pahwa MetalTech casts C95500 and C95800 nickel aluminium bronze via lost-wax investment casting, with ASTM B148 chemistry and mechanical certification, TQ50 heat treatment where specified, and NDT to the scope your application requires.

This capability sits within our wider copper alloys range, our broader investment casting process capability, and our marine parts and propellers industry focus.

Share your drawing, duty cycle, and grade preference (or let us help you choose between C95500 and C95800) through our contact page, and we'll confirm chemistry, heat treatment, and NDT scope before you commit to a supplier.