Investment casting materials fall into three main categories: ferrous alloys (including carbon steels, stainless steels, and tool steels), non-ferrous alloys (such as aluminum, copper-based alloys, and titanium), and superalloys designed for extreme temperatures. Each material group offers distinct advantages—ferrous alloys provide strength and cost-effectiveness, non-ferrous alloys deliver properties like light weight and corrosion resistance, while superalloys maintain performance at temperatures exceeding 1,500°F.
Ferrous Alloys
Ferrous alloys, characterized by their iron base, constitute a significant proportion of materials used in investment casting.
Carbon Steels
Carbon steels represent the most economical choice for investment casting when moderate strength and good machinability are required. The carbon content directly influences the material’s hardness, strength, and ductility.
- Low-Carbon Steel (Mild Steel): Contains less than 0.30% carbon and offers excellent weldability with tensile strengths ranging from 50,000 to 70,000 psi.
- Medium-Carbon Steel: With 0.30% to 0.60% carbon content, these steels balance strength and ductility effectively. They achieve tensile strengths between 70,000 and 100,000 psi after heat treatment.
- High-Carbon Steel: Containing 0.60% to 1.4% carbon, these steels deliver exceptional hardness and wear resistance but sacrifice some toughness. After proper heat treatment, they reach hardness levels of 60 HRC or higher.
Low Alloy Steels
Low alloy steels contain less than 8% or 12% total alloying elements beyond iron and carbon. These additions of chromium, molybdenum, nickel, or vanadium enhance specific properties without significantly increasing cost.
Low alloy steels generally exhibit good ductility, with elongation values potentially reaching up to 25%, and as-cast yield strengths typically ranging from 45,000 to 75,000 PSI. These mechanical properties can be significantly enhanced through heat treatment processes. They possess good fluidity and cast well in the investment casting process but have lower corrosion resistance compared to stainless steels.
Stainless Steels
Stainless steels resist corrosion through chromium content exceeding 10.5%, which forms a protective oxide layer on the surface. Investment casting handles these materials exceptionally well, producing smooth surfaces that enhance corrosion resistance.
- Austenitic Stainless Steels: The 300 series steels like 304 and 316 contain 16-26% chromium and 6-22% nickel. They maintain excellent corrosion resistance and remain non-magnetic.
- Martensitic Stainless Steels: Grades like 410 and 440C contain 11.5-18% chromium with higher carbon levels. Heat treatment can harden these steels to 50-60 HRC.
- Ferritic Stainless Steels: With 10.5-27% chromium and minimal nickel, grades like 430 offer good corrosion resistance at lower cost than austenitic types.
- Duplex Stainless Steels: These steels combine austenitic and ferritic structures, typically containing 18-28% chromium and 4.5-8% nickel. They provide twice the strength of austenitic grades with superior stress corrosion cracking resistance.
- Precipitation Hardening (PH) Stainless Steels: 17-4 PH and 15-5 PH are typically martensitic or semi-austenitic in structure and are strengthened by a precipitation hardening heat treatment after casting. They provide an excellent combination of high strength, good corrosion resistance, and good toughness.
Tool Steels
Tool steels represent highly specialized alloys designed for cutting, forming, or shaping other materials. Powder metallurgy tool steels cast through investment methods achieve extremely fine, uniform microstructures that enhance toughness and wear resistance beyond conventional tool steels.
Cast Irons
Cast irons are ferrous alloys with higher carbon content (typically >2%) than steels. While less common in investment casting than other processes, certain cast iron grades work well with the lost-wax method when specific properties are needed.
- Ductile Iron (Nodular Iron): Ductile iron contains magnesium or cerium additions that cause graphite to form as spherical nodules rather than flakes. This microstructure provides tensile strengths from 60,000 to 120,000 psi with elongation values reaching 18%.
- Gray Iron: Gray iron features graphite in flake form, which provides excellent damping capacity and thermal conductivity. It is often a cost-effective alternative to welded fabrications or steel forgings.
Non-Ferrous Alloys
Non-ferrous alloys expand investment casting capabilities into applications requiring specific properties like light weight, electrical conductivity, or extreme corrosion resistance. These materials generally cast at lower temperatures than ferrous alloys, allowing more economical shell systems and reducing energy costs.
Aluminum Alloys
Aluminum alloys combine light weight with good strength and excellent corrosion resistance. The investment casting process captures fine details in aluminum parts while maintaining dimensional accuracy within ±0.003 inches per inch.
Copper-Based Alloys
Copper alloys provide unique combinations of electrical conductivity, thermal properties, and corrosion resistance.
- Bronze: Primarily alloys of copper and tin.
- Brass: Primarily alloys of copper and zinc.
Titanium Alloys
Titanium alloys deliver the highest strength-to-weight ratio among common engineering materials. Investment casting produces near-net-shape titanium components that would prove extremely expensive to machine from solid stock.
Superalloys
Superalloys maintain strength and corrosion resistance at temperatures where conventional alloys fail. Investment casting excels at producing superalloy components with complex cooling passages and thin walls impossible to achieve through other manufacturing methods.
Nickel-Based Superalloys
Nickel-based superalloys are renowned for their outstanding mechanical strength, creep resistance, fatigue life, and resistance to oxidation and corrosion at high temperatures, with some grades capable of service beyond 1500∘C.
Cobalt-Based Superalloys
Cobalt-based superalloys are distinguished by their excellent wear resistance, high-temperature strength, corrosion resistance, and resistance to thermal fatigue. Investment casting is a preferred method for producing near-net-shape components from these alloys.
