Investment Casting Alloys: Selection Guide

Investment casting alloy selection: castability ratings for carbon steel, stainless steel, superalloys, aluminium and copper, with ISO grade data and notes.

Hu Wenke

10/18/20269 min read

worm's-eye view photography of concrete building
worm's-eye view photography of concrete building

Most investment castings are made from carbon steel, low-alloy steel, or stainless steel — not because those alloys are the best, but because they balance strength, castability and cost. The choice should follow a fixed order: service conditions and mechanical properties first, casting and processing behaviour second, price last. This guide gives the alloy families investment casting can handle, the castability ratings behind each one, and the grade data you need to specify a material that will actually cast cleanly.

What should drive the alloy choice?

The Investment Casting Handbook sets out three selection factors, in this order:

  1. Service conditions and mechanical properties — temperature, corrosion medium, load, fatigue or wear duty.

  2. Casting and other process properties — fluidity, shrinkage, hot-tearing resistance, plus heat treatment, machining, welding and straightening behaviour.

  3. Cost.

The handbook then makes a point that surprises most buyers: material cost is usually secondary to manufacturing cost and service performance. A more expensive alloy can produce a cheaper finished part, because it casts and machines more easily, yields dimensionally accurate castings with fewer defects, and therefore cuts machining and scrap. The recommendation is explicit — buyers should give preference to alloys with good process properties.

In practice this means: do not start from a price list. Start from the duty, then check whether the alloy you picked is one that casts well.

Which alloy families can be investment cast?

Investment casting is not restricted by alloy type. The handbook lists carbon structural steel, stainless steel, alloy steel, cast iron, aluminium and copper alloys, cast superalloys, magnesium alloys, titanium alloys and precious metals as all viable. Alloys that are difficult to forge, weld or machine are often better suited to investment casting than to any other process.

The process envelope that comes with this freedom:

  • Dimensional tolerance — Typical value: CT4–CT6

  • Surface roughness — Typical value: Ra 0.4–3.2 μm

  • Minimum wall thickness — Typical value: 0.5 mm

  • Minimum hole diameter — Typical value: below 1 mm

  • Casting envelope — Typical value: a few mm up to over 1,000 mm (some sources cite 2,000 mm+)

  • Casting weight — Typical value: about 1 g up to nearly 1,000 kg

For the step-by-step sequence behind these numbers, see the investment casting process. If you need to know what tolerance band to put on a drawing, the CT-grade guide works through the millimetre values.

Family-by-family summary

  • Carbon steel — Common grades: AISI 1015–1060; GB/T 11352 ZG200-400 to ZG340-640; Choose it when: Strength is the only requirement, cost matters; Watch out for: Highest shrinkage class; generous feed and machining allowance

  • Low-alloy steel — Common grades: 4130, 4140, 4340, 8620, 8630; Choose it when: Through-hardening, higher strength at moderate cost; Watch out for: Section sensitivity; heat-treat distortion

  • Stainless steel — Common grades: 304, 316, 410, 420, 440C, 17-4PH; Choose it when: Corrosion resistance, or corrosion plus strength; Watch out for: 400-series shrink strongly; 17-4PH needs ageing control

  • Heat-resistant steel — Common grades: High-Cr ferritic, Cr-Ni austenitic, Ni-Cr austenitic; Choose it when: Service above 650 °C; Watch out for: σ-phase embrittlement in a specific window

  • Nickel / cobalt — Common grades: Inconel 625/718, Monel, Cobalt 6/21/31; Choose it when: Hot strength, oxidation, wear; Watch out for: Cost; poor hot-tearing resistance on some cobalt grades

  • Aluminium — Common grades: 356, A356, 355, C355 (Al-Si family); Choose it when: Weight saving, thin walls, good finish; Watch out for: Low modulus; porosity control

  • Copper — Common grades: Aluminium bronze, manganese bronze, silicon brass, beryllium copper; Choose it when: Thermal and electrical conductivity, seawater duty, wear; Watch out for: High shrinkage on aluminium and manganese bronze

  • Titanium — Common grades: ZTi1–ZTi4 (GB/T 15073), ASTM B367 grades; Choose it when: Specific strength plus corrosion; Watch out for: Molten titanium is chemically aggressive — special melting and a highly stable mould are mandatory

  • Magnesium — Common grades: AZ91A, AM100A, AZ92A; Choose it when: Lowest density; Watch out for: Handling and fire safety; lower tensile strength

Castability — the number to check before you commit

This is the part of the handbook most design engineers never see, and it is the most useful.

The handbook rates castability on a relative scale. Three alloys with excellent casting behaviour — 302 stainless steel, 20C beryllium copper and 356 aluminium — are set at 100, and every other grade is expressed relative to them. Three separate properties are graded 1, 2 or 3, where 1 is best, 2 is good and 3 is poor: fluidity, shrinkage, and resistance to hot tearing.

  • 302 stainless — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • 304 stainless — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • 316 stainless — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • CF-8M (ACI) — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • 347 stainless — Castability ratio: 95; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • 17-4PH (AMS 5355) — Castability ratio: 85; Fluidity: 1; Shrinkage: 3; Hot-tearing resistance: 2

  • 410 stainless — Castability ratio: 95; Fluidity: 1; Shrinkage: 3; Hot-tearing resistance: 2

  • 420 stainless — Castability ratio: 90; Fluidity: 1; Shrinkage: 3; Hot-tearing resistance: 2

  • 440C stainless — Castability ratio: 85; Fluidity: 1; Shrinkage: 3; Hot-tearing resistance: 2

  • Inconel (AMS 5665) — Castability ratio: 85; Fluidity: 1; Shrinkage: 2; Hot-tearing resistance: 2

  • Monel (QQ-N-288-A) — Castability ratio: 85; Fluidity: 1; Shrinkage: 2; Hot-tearing resistance: 2

  • Cobalt 6 (AMS 5387) — Castability ratio: 80; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 2

  • Cobalt 21 (AMS 5385C) — Castability ratio: 90; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 2

  • Cobalt 93 — Castability ratio: 70; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 3

  • 1015 carbon steel — Castability ratio: 80; Fluidity: 3; Shrinkage: 3; Hot-tearing resistance: 3

  • 1020 carbon steel — Castability ratio: 80; Fluidity: 3; Shrinkage: 3; Hot-tearing resistance: 3

  • 1045 carbon steel — Castability ratio: 85; Fluidity: 2; Shrinkage: 2; Hot-tearing resistance: 2

  • 1060 carbon steel — Castability ratio: 85; Fluidity: 2; Shrinkage: 2; Hot-tearing resistance: 2

  • 4130 low-alloy — Castability ratio: 90; Fluidity: 2; Shrinkage: 2; Hot-tearing resistance: 2

  • 4140 low-alloy — Castability ratio: 90; Fluidity: 2; Shrinkage: 2; Hot-tearing resistance: 2

  • 4340 low-alloy — Castability ratio: 90; Fluidity: 2; Shrinkage: 2; Hot-tearing resistance: 2

  • 8620 low-alloy — Castability ratio: 85; Fluidity: 2; Shrinkage: 3; Hot-tearing resistance: 2

  • 52100 bearing steel — Castability ratio: 80; Fluidity: 1; Shrinkage: 2; Hot-tearing resistance: 2

  • 356 / A356 aluminium — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • 355 / C355 aluminium — Castability ratio: 95; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • Aluminium 40E — Castability ratio: 75; Fluidity: 3; Shrinkage: 3; Hot-tearing resistance: 3

  • Aluminium bronze Gr. C — Castability ratio: 80; Fluidity: 1; Shrinkage: 3; Hot-tearing resistance: 1

  • Manganese bronze — Castability ratio: 80; Fluidity: 2; Shrinkage: 3; Hot-tearing resistance: 1

  • 85-5-5-5 red bronze — Castability ratio: 90; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • Silicon brass — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

  • Beryllium copper 20C — Castability ratio: 100; Fluidity: 1; Shrinkage: 1; Hot-tearing resistance: 1

How to read it

  • Ratio 100 with 1/1/1 — the alloy fills thin sections, feeds easily and tolerates restraint. 304/316 stainless and 356 aluminium are the easiest things you can put in a shell.

  • Shrinkage 3 — expect contraction-driven problems: sink, shrinkage porosity, distortion, and dimensional drift. Every 400-series stainless, 17-4PH, 8620 and aluminium bronze falls here. Plan feeders and straightening allowance, and expect more dimensional spread than the CT table promises.

  • Fluidity 3 — the metal freezes before it reaches thin sections. 1015/1020 carbon steel is the classic case. Minimum wall goes up, gating has to be more generous, and pouring temperature control becomes critical.

  • Hot-tearing 3 — the alloy tears while it is restrained by a rigid shell. Cobalt 93, and low-carbon steels 1015/1020/1117, sit here. Avoid sharp internal corners and abrupt section changes.

  • A ratio of 70–80 does not mean "do not cast it" — it means the process window is narrower and the cost per good part is higher. That is exactly the trade the handbook describes.

One caveat: this is a relative ranking for shell-mould investment casting, and it tells you nothing about corrosion or high-temperature strength. Use it to predict casting difficulty, not service performance.

Carbon and low-alloy steel — the default choice

General engineering carbon steels are graded by strength class rather than by chemistry. That is true across national standards: the chemistry is largely left to the foundry, with only phosphorus and sulphur tightly limited, as long as the strength class is met.

ISO 3755:1991 grades, tested on a 28 mm test block at 23 ± 5 °C:

  • 200-400 — Yield strength (MPa, min): 200; Tensile strength (MPa): 400–550; Elongation (%): 25; Reduction of area (%): 40; Impact (J): 30

  • 230-450 — Yield strength (MPa, min): 230; Tensile strength (MPa): 450–600; Elongation (%): 22; Reduction of area (%): 31; Impact (J): 25

  • 270-480 — Yield strength (MPa, min): 270; Tensile strength (MPa): 480–630; Elongation (%): 18; Reduction of area (%): 25; Impact (J): 22

  • 340-550 — Yield strength (MPa, min): 340; Tensile strength (MPa): 550–700; Elongation (%): 15; Reduction of area (%): 21; Impact (J): 20

China's GB/T 11352 grades ZG200-400 through ZG340-640 follow the same strength-class logic, with residual elements (Ni, Cr, Cu, Mo, V) capped and their total held at or below 1.00%.

A caution the standard itself makes: these values describe the steel poured from that test block, not the casting you are holding. Actual properties depend on solidification conditions, cooling rate during heat treatment, and the casting's own thickness and shape. If the section is much thicker than 28 mm, the standard's supplementary requirements apply.

For most brackets, housings, levers and valve bodies in general industrial service, 1045-class carbon steel is where the cost curve bottoms out. Move to 4130/4140 when you need through-hardening, and to 4340 when section size makes 4140 marginal.

Stainless and heat-resistant — pick by medium first, temperature second

Cross-standard equivalents matter here, because a drawing may say CF-8M while the purchase order says ZG0Cr18Ni2Mo2Ti while the shop talks about 316.

  • ZG1Cr13 — AISI / ACI equivalent: CA-15 (ACI), 410; Practical note: 11.5–14.0% Cr, martensitic; C max 0.15%

  • ZG2Cr13 — AISI / ACI equivalent: CA-40 (ACI), 420; Practical note: Higher carbon, higher hardness after hardening

  • ZG0Cr18Ni9 — AISI / ACI equivalent: CF-8 (ACI), 304; Practical note: The castability benchmark; 1/1/1

  • ZG00Cr18Ni10 — AISI / ACI equivalent: CF-3 (ACI), 304L; Practical note: Low carbon for weld-neck assemblies

  • ZG0Cr18Ni2Mo2Ti — AISI / ACI equivalent: CF-8M (ACI), 316; Practical note: Mo-bearing, chloride duty

  • ZG0Cr17Ni4Cu4Nb — AISI / ACI equivalent: 17-4PH; Practical note: Precipitation hardening; shrinkage class 3

  • ZG40Cr25Ni20 — AISI / ACI equivalent: HK30 / HK40; Practical note: Heat-resistant austenitic

Heat-resistant grades are used where service temperature exceeds 650 °C, and they come in three families with clearly different ceilings. Because these parts usually also sit in a corrosive atmosphere, strength alone is not the selection criterion — corrosion resistance has to be assessed at the same time.

  • High-chromium — Composition: 8–30% Cr, little or no Ni; Structure: Ferritic; Practical temperature ceiling: Lower hot strength; used mainly against gas corrosion

  • High Cr-Ni — Composition: Cr > 18%, Ni > 8% (Cr exceeds Ni); Structure: Austenitic; Practical temperature ceiling: Usable up to 1,093 °C; σ-phase forms at 649–871 °C

  • High Ni-Cr — Composition: Ni > 23%, Cr > 10% (Ni exceeds Cr); Structure: Single austenite; Practical temperature ceiling: Up to about 1,149 °C; best thermal shock and thermal fatigue resistance

That 649–871 °C σ-phase window is the detail that causes field failures: an alloy chosen for a 700 °C duty may be sitting exactly in the embrittlement range. If your duty is continuous in that band, the high Ni-Cr family is the safer specification.

Aluminium, copper and titanium — when the extra cost pays back

Aluminium. Casting alloys fall into five systems: Al-Si, Al-Cu, Al-Mg, Al-Zn and Al-RE. The Al-Si family dominates investment casting because it combines the best castability in the entire handbook (356/A356 at 100, 355/C355 at 95) with thin-wall capability. This is why complex thin-wall aluminium parts — impellers, waveguides, housings — are routinely investment cast rather than machined.

Copper. Aluminium bronze, manganese bronze, silicon brass and beryllium copper all appear in the castability table. Silicon brass and beryllium copper 20C reach 100; aluminium bronze is graded shrinkage 3, manganese bronze shrinkage 3 with hot-tearing 1 (good). So copper alloys are easy to fill but need feeding discipline, and manganese bronze tolerates restraint well.

Titanium. Titanium offers low density, high specific strength, good toughness, non-magnetic behaviour, a high melting point, low thermal expansion and excellent corrosion resistance. The constraint is chemical: molten titanium is highly reactive, so it requires dedicated melting equipment and a highly stable mould material. That is a process-cost problem, not a design limitation — investment cast titanium impellers are produced commercially, and graphite moulds are one of the routes used.

Magnesium. AZ91A reaches 126 MPa tensile in the as-cast condition and 238 MPa in T4; AM100A reaches 140 MPa as-cast and 238 MPa in T6, with 105 MPa yield. It is the lightest option here, and the reason it is less common is handling risk, not castability.

FAQ

Can every alloy be investment cast? Almost. The handbook lists carbon steel, stainless, alloy steel, cast iron, aluminium, copper, superalloys, magnesium, titanium and precious metals. The practical limit is cost and process control, not metallurgy.

What is the cheapest alloy for investment casting? Carbon steel usually has the lowest material price, but the handbook's warning applies: material cost is secondary to manufacturing cost. A 1015 part with fluidity 3 and shrinkage 3 can cost more per good part than a 304 part graded 1/1/1.

Which alloy should I specify for 900 °C service? High Cr-Ni austenitic heat-resistant steel, which is rated for use up to 1,093 °C. Avoid continuous service in the 649–871 °C σ-phase window unless you have chosen the high Ni-Cr family.

Can 17-4PH be investment cast? Yes. It appears in the castability table under AMS 5355 at a ratio of 85 with shrinkage class 3, so plan for distortion and dimensional spread, and control the ageing treatment.

How thin can an investment casting be? 0.5 mm minimum wall, with holes below 1 mm diameter feasible. Whether your chosen alloy can actually fill that is a separate question — check its fluidity rating first.

About the data in this article Castability ratings, grade chemistry, mechanical property tables, the heat-resistant family temperature ceilings and the alloy-selection principles are taken from Investment Casting Handbook (《熔模铸造手册》, China Foundry Association), Chapter 2, and Practical Investment Casting Technology (《实用熔模铸造技术》, Jiang Buju). Mechanical property tables follow ISO 3755:1991, GB/T 11352-1989 and GB/T 15073-1994 as reproduced in those sources. Values are typical reference data for specification work, not a substitute for a drawing-specific agreement with your foundry.

Need a casting quoted in a specific alloy? CireCraft is run by investment casting practitioners from XINYOUYUAN, a precision casting plant in Dongguan, China, casting stainless steel, carbon steel, alloy steel and heat-resistant alloys in the 0.01–50 kg range. Send the alloy and the drawing to castinmetal.com for a process review.

Updated: October 2026

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