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Introduction to the Stainless Steel Investment Casting Process

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Introduction to the Stainless Steel Investment Casting Process

The investment casting process enables the production of intricate shapes which maintain high dimensional accuracy and high surface quality. Stainless steel is often chosen for the material because of its strength and exceptional corrosion-resistant properties. This benefits combination makes stainless steel an ideal choice to create castings for use in a diverse array of industries, including automotive, aerospace, marine, medical, and food processing.

What is the Process of Stainless Steel Investment Casting?

The metal forming process of investment casting involves the creation of a wax pattern, which is then surrounded by a ceramic shell to form a ceramic mold. The wax is melted out, leaving the ceramic shell as a mold. Molten stainless steel is then poured into the mold to form a casting component. After the metal solidifies and the mold is removed, some investment castings may require a secondary machining process.

What Materials are Used in Stainless Steel Investment Casting?

Stainless steel is a form of low-carbon steel. It includes a minimum of 10% chromium, which leads to the formation of a chromium-oxide film. This film gives stainless steel its unique corrosion-resistant properties, and the ability to heal when in the presence of oxygen. The metal is highly-formable, resulting in the capability of producing components with accurate dimensions, complex structures, and a good surface finish. Stainless steels are classified by their crystalline structure into five main types:

  • Martensitic Stainless Steel: Martensitic stainless steel alloys contain chromium, a small amount of carbon, and other elements in different grades. This stainless steel alloy lends itself well to hardening and tempering processes to improve the casting’s mechanical properties. This alloy is appropriate when corrosion- and oxidation-resistance are needed, as well as either creep resistance at high temperatures or high strength at low temperatures.
  • Ferritic Stainless Steel: This alloy contains over 12% chromium and very low carbon content. It differs from other forms of stainless steel in molecular grain structure and chemical composition. It is not hardenable by heat treatment.
  • Austenitic Stainless Steel: The most frequently used stainless steel alloys, the 300 series consists of a nonmagnetic, chromium-nickel alloy. Alloys in this series exhibit high levels of corrosion-resistance, but do not gain strength through heat treatment. The 304 alloy is known for its high standards of cleanliness. The 304-L and 316-L alloys are low carbon, resulting in a softer but more corrosion-resistant material that can withstand high-temperature finishing processes.
  • Duplex Stainless Steel: Duplex stainless steel combines characteristics from both the ferritic and austenitic alloys. These alloys are often used in environments where pitting and corrosion are of concern, especially in a cold working environment. Benefits include improved strength, high toughness, good ductility, and high corrosion resistance.
  • Precipitation Hardening Stainless Steel: This process uses a heat application to make the alloy very tough. Precipitation hardening produces the strongest alloy of the stainless steel family, and is used for parts that cannot bend.

What are the Benefits of Stainless Steel Investment Casting?

Stainless steel investment castings of various alloys can provide a wide variety of end-user benefits, including:

  • High levels of corrosion resistance
  • Heat resistance
  • Precision tolerances
  • High level of detail
  • Superior surface finish
  • Ability to produce complicated shapes
  • Tight tolerance levels
  • Requires minimal surface finishing after casting
  • Size flexibility

What are Common Applications for Stainless Steel Investment Castings?

With their highly desirable qualities of corrosion resistance, high strength, and low maintenance, stainless steel investment castings have a wide variety of applications:

  • Food processing: With their corrosion-resistant capabilities, stainless steel investment castings are widely used in the food processing industry. Typical components might include food storage, coffee machine components and metal grinder components.
  • Marine applications: Stainless steel is highly resistant to corrosion, heat and abrasion, making it highly suitable for marine applications.
  • Automotive: Typical automotive components include grill, trim, converters and exhaust parts.
  • Medical Equipment: Medical equipment often requires tight tolerances and high levels of dimensional precision. Stainless steel investment casting components include dental and surgical tools, operating room equipment, implantable components, MRI machinery, X-ray equipment, stretchers, and wheelchairs.
  • Pipe Fittings: Typical stainless steel investment casting applications for pipe fittings include elbow, nipple, tee, and bushing.
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