Carbon Restoration in Investment Casting and Its Technical Benefits for Heat Treating

Investment casting is method of production that allows for creation of parts with complex geometries that require little to no machining for them to be put into service. As the castings cool after pouring decarburization can occur at the part surface. Decarburization, frequently truncated to decarb, can lead to a range of negative consequences spanning from reduced wear to premature failure during service. The most common way to remediate this without the need for additional material removal is to perform a specialized form of heat treatment called carbon restoration.  

The Carbon Restoration Process:

Carbon restoration is a specialized heat treatment designed to return the surface of the material back to its nominal carbon content. Essentially, this method involves carburizing the part such that the surface carbon potential aligns with the base carbon content of the designated material. ThermTech achieves this by exposing the parts to a carbon rich atmosphere at high heat to replenish the carbon content at the surface of our customers parts.

Technical Benefits for Heat Treating:

  • Improved Mechanical Properties: Proper carbon balance contributes to enhanced tensile strength, and toughness, especially after heat treatment.
  • Uniform Microstructure: Ensuring a consistent carbon distribution results in a more uniform microstructure post-heat treatment.
  • Reduced Decarburization Risk: Carbon restoration minimizes the risk of further decarburization during subsequent heat treatments.
  • Enhanced Wear Resistance: Balanced carbon levels can amplify the hardness of the alloy after heat treatment.
  • Minimized Distortion and Internal Stresses: Uniform carbon distribution aids in ensuring consistent heating and cooling during heat treatment, thereby reducing residual stresses and distortion.
  • Improved Corrosion Resistance: Proper carbon balance minimizes the material’s susceptibility to corrosion reactions.
  • Cost-Efficiency: Preventing the need for repeated treatments due to inconsistent carbon levels ensures economic benefits.

Critical Variables in the Carbon Restoration Process:

  • Base Carbon and Chemistry: Key elements to determine are the material’s base carbon and chemistry, as well as the depth of decarburization.
  • Hardening and Carbon Restoration: Depending on the alloy, hardening and carbon restoration can often be achieved simultaneously.
  • Machining Requirements: If machining is needed, an annealed microstructure might be prefferable.
  • Final Properties Consultation: It’s crucial to converse about the end properties required prior to finalizing orders to ensure alignment on the most suitable process or processes.

Expert Recommendations from ThermTech:

  • The carbon restoration process is versatile process achievable for a wide variety of steel alloys.
  • The process parameters can differ substantially depending on the alloy in question and the desired end properties for a component.
  • Paramount aspects of carbon restoration are the precise carbon potential, ensuring effective carbon diffusion into the part’s surface, and an adequate time at the right heat. This guarantees a uniform carbon content from the surface inwards and the complete restoration of the previously low carbon zone.

In summary, carbon restoration is a fundamental step for preparing investment castings for heat treatment, ensuring superior quality, enhanced performance, and cost-effectiveness in the manufacturing process.

ThermTech—Experts in Austempering Stampings, Machined Parts, and Investment Castings

ThermTech, Inc. offers both small and large batch capabilities for austempering steel and iron investment castings. Between our neutral salt bath furnaces and our larger austempering furnaces, we have the capabilities to austemper a wide variety of stamping, machined components, and investment castings. We have run austempering on alloys from 1060 through 4340 to ductile iron machined parts.

Our dedicated team works with you to ensure we meet your specifications. Count on our decades of experience with hardening, tempering, surface heat treatments, vacuum treatments, and annealing. To learn more about our services, please contact us today.

Learn more about austempering and how ThermTech can serve you by watching these videos.

Request a free quote online or call us at 800-752-6917. You can also contact us online for all your austempering and heat treating needs.

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ThermTech’s quality policy is ZERO DEFECTS for all customer products and in all quality management system activities. Through our efforts to continually improve the quality of the work we offer, we’ve been recognized as being able to meet the rigorous quality standards required by several of our major customers. ThermTech is certified for ISO 9001 and AS9100 in both Metal Heat Treat and Metal Finishing.