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What is Cast Stainless Steel?
Cast stainless steel is something you may heard even if you are not familar with it. You may do not really know what this type of metal alloy is produced from, and even do not understand the term “cast”. As a professional cast stainless steel manufacturer and supplier, we will explain everything about cast stainless steel.
Cast stainless steel is a specific alloy that has gone through one of the primary metal forming processes known as casting.
When it comes to corrosion resistance, cast stainless steel is the right way to go. The bright apperance, good corrosion resistance, and high strength all makes cast stainless steel popular in several applications like marine, food machinery, building fittings, medical, etc.
Cast Stainless Steel – Manufacturing Process
A design engine first makes a wax pattern using a metal injection die. The pattern will have all the details for a section or portion of the finished component but with slightly larger dimensions to account for thermal contraction.
Next, the engineer creates the runner and gating system by connecting multiple patterns to form the final component. Molten metal will flow through the runner system as it fills cavities in the mold, creating a well-balanced casting. Gates are the openings between the runner and the cavity that feeds molten metal into the space.
Once the entire pattern is complete, it is dipped into a ceramic slurry and covered with sand stucco. The design engineer repeats the dipping process until the shell achieves the appropriate thickness. At this point, the dried shell’s durability is strong enough to withstand the heat from the molten metal. Also, it will retain its shape during the last step.
The wax melts away under high temperatures, and trace amounts soak into the plaster or ceramic mold. The void left by the melted wax pattern will be filled with an alloy to create a precise cast stainless steel part.
Why Cast Stainless Steel?
Cast stainless steel is usually chosen because it is resistant against corrosion—but it is also chosen because it is steel. Besides corrosion resistance, cast stainless steel also has some other advantages as below:
High Accuracy
Cast stainless steel parts created by investment casting process are extremely accurate and near net shape. Since cast stainless steel components are created by using the same wax patterns, this accuracy can be maintained from part to part.
Custom Design
Cast stainless steel can be used to make any shape you like. It is also a designer’s dream. Logos, product ID’s or numbers, and letters can easily be added to the inside and/or outside of components. Lots of complicated stainless steel parts unavailable from forging or machining could be produced by casting process.
Good Hardness
Compared to other cast alloys, cast stainless steel exhibits superior hardness. Hardness is the ability of cast stainless steel to resist indentation and abrasion. Due to its good hardness, parts made from cast stainless steel can work longer than expected.
Technical Comparison of Investment Casting vs. Sand Casting for Stainless Steel
| Feature | Investment Casting (Lost-Wax Process) | Sand Casting |
| Precision & Tolerances | Dimensional tolerance: ±0.5% to ±1% of part size. High precision, ideal for intricate geometries (e.g., fine internal passages or thin walls). | Dimensional tolerance: ±2% to ±4% of part size. Suitable for parts where precision is less critical. |
| Surface Finish | Ra (Roughness Average): 0.5 to 3.2 µm, depending on mold material. Excellent surface finish with minimal machining required. | Ra (Roughness Average): 3.2 to 12.5 µm. Requires additional post-machining for smoother surfaces. |
| Part Complexity | Can cast very complex geometries with fine details (e.g., aerospace turbine blades, medical implants). | Limited to less complex shapes. More difficult to cast parts with intricate internal features. |
| Material Yield | Material utilization: Up to 95-98% of the material is used (low waste). Ideal for high-cost materials. | Material utilization: Typically around 75-85%, with higher scrap due to rougher molds and gating systems. |
| Production Volume | Low to medium volume production, ideal for batches of 10 to 1,000 parts. Longer lead times due to mold preparation and multiple stages. | High volume production, ideal for 1,000+ parts per run. Faster cycle time, especially for simple parts. |
| Cycle Time | Cycle time: 2-6 hours per part, depending on complexity. Multiple stages (wax pattern, mold creation, casting). | Cycle time: 15 minutes to 1 hour per part, depending on part size and mold complexity. |
| Tooling Costs | High initial tooling cost: $10,000 to $100,000 for mold creation, due to complex mold-making process. | Lower tooling cost: $500 to $10,000 depending on part size and mold complexity. |
| Material Strength | Tensile strength: Typically 550-1,200 MPa (depending on alloy). Excellent for critical, high-stress parts. | Tensile strength: Typically 400-800 MPa (depending on alloy). Suitable for general-purpose parts but may not match investment casting in high-stress applications. |
| Mold Material | Molds made of ceramic or silica, which can withstand extreme temperatures (up to 3,000°F or 1,650°C). | Molds made from sand mixed with binders can withstand temperatures up to 1,800°F (980°C) but are not as heat-resistant as investment casting molds. |
| Casting Materials | Limited to high-performance stainless steel alloys, superalloys, and precious metals. Alloy compositions must flow easily and hold fine detail. | Suitable for a broad material range including stainless steel, iron, aluminum, and bronze. More flexible in material selection. |
| Machining Requirements | Minimal machining is required due to high precision and fine surface finish. However, post-casting processes like heat treatment may still be necessary. | Significant machining is required to achieve the desired finish, especially for complex parts, due to rougher surfaces and tolerances. |
| Heat Treatment & Post-Processing | Requires solution annealing and stress relief for improved strength. Higher uniformity in microstructure due to controlled cooling. | Typically requires additional heat treatment, such as normalizing or tempering, for strength enhancement. Post-casting processes are more labor-intensive. |
| Porosity and Defects | Low porosity and minimal defects due to a controlled environment during casting. Porosity rate: Typically < 1%. | Higher likelihood of porosity and surface defects. Porosity rate: Up to 5-10%, depending on sand and mold preparation. |
| Cost Efficiency | Higher per-part cost due to complex tooling, slower production rate, and precision required. Ideal for small, high-value components. | More cost-effective for high-volume production, especially when precision is not critical. Suitable for large parts and less complex shapes. |
Application
Automotive Parts
Due to the amazing strength and corrosion resistance, it is very popular in the production of automotive parts. For example, exhaust pipe is made with investment cast stainless steel. In addition, other automotive parts such as transmission components, vehicle interior components, are also made from cast stainless steel.
Medical Components
Many medical components are also made from cast stainless steel, not only due to the strength but also due to its easy clean. Some of the more common medical components you may see made from this cast stainless steel is parts for various pumps, surgical tools, components for monitors, and even gearboxes for hospital beds.
Marine Hardwares
Another popular application for cast stainless steel is the production of marine boat hardwares. While many popular firearms may have aluminum components, there are still a number of parts that are created from cast stainless steel. Some of these cast stainless steel marine parts may include boat deck drain, marine boat anchors, hand rail end fitting and much more.
Kitchen hardware
For decades, cast stainless steel has been a vital material in a well-stocked home kitchen. It is dishwasher safe, making for a quick and easy clean up. Typical kitchen hardwares made from cast stainless steel are: cookware handles, meat grinder parts, etc.
