Breaking Down 347 Stainless Steel Castings: Composition, Properties, and Applications

347 stainless steel castings are stainless steel cast parts and components made through casting methods such as investment casting or sand casting. AISI 347 stainless steel castings are widely used in manufacturing industries due to their superior strength and corrosion resistance. This grade of stainless steel is also known for its stability and durability besides high strength and superior corrosion resistance; therefore, it is frequently used in applications operating in high-temperature environments. As a variation of the basic grade 304, SS347 contains additions of columbium and tantalum, which enhance its ability to withstand intergranular corrosion.

This article dives deep into explaining the intricate aspects of 347 stainless steel castings, including their international equivalents, chemical composition, physical and mechanical properties, casting processes, surface treatments, and a range of industrial applications.

Before we delve into a detailed explanation, I’d like to quickly introduce our company and services. Taiyuan Simis Investment Casting Co., Ltd. is an ISO-accredited investment casting manufacturer in China with over 40 years of metal casting experience. More importantly, we offer custom investment casting services, which means we can tailor dimensions, structures, materials, properties, finishes, logos, and more according to your needs. Simply get in touch with our sales team to discuss your detailed requirements. Now, back to this article.

International Equivalents

The inherent resilience and thermal stability of AISI 347 stainless steel contribute to its widespread industrial use. To facilitate global manufacturing and specification, this grade of stainless steel is cross-referenced with several international standards. You can check below table for a simple, intuitive view of the globally equivalent grades.

Country/Region	Standard	Designation	Notes
United States	AISI/UNS	AISI 347 / S34700	Commonly used in the USA
European Union	EN	X6CrNiNb18-10	European Norm (EN) designation
United Kingdom	BS EN	347S31	British Standard European Norm
Germany	DIN EN	X6CrNiNb18-10	DIN (Deutsches Institut für Normung) EN standard
China	GB	0Cr18Ni11Nb	Guobiao (GB) standards in China
Japan	JIS	SUS 347	Japanese Industrial Standards
India	IS	X04Cr18Ni10Nb	Indian Standard

Please also note that CF8C is the designation for a casting grade of 347 stainless steel, specifically under the ASTM standard from the United States. It corresponds to the cast version of the 347 stainless steel, which is part of the austenitic family of stainless steels.

Chemical Composition

AISI 347 is well-regarded for its excellent resistance to high-temperature oxidation and intergranular corrosion, attributes that are largely due to its specific chemical makeup. This grade is primarily composed of iron, chromium, and nickel.

The addition of columbium (niobium) and tantalum is a distinctive feature of this alloy, which helps in stabilizing the steel and preventing chromium carbide precipitates.

The high chromium and nickel content enhances the corrosion resistance and heat resistance of 347 stainless steel, therefore making it a viable material for high-temperature environments. The addition of columbium allows the alloy to maintain exceptional mechanical properties even after prolonged exposure to high temperatures. See below table for detailed breakdown of its elements and percentages.

Element	Percentage (%)
Chromium (Cr)	17.00% – 19.00%
Nickel (Ni)	9.00% – 13.00%
Columbium + Tantalum (Cb + Ta)	10xC to 1.00%, minimum 0.10%
Carbon (C)	0.08% max
Manganese (Mn)	2.00% max
Silicon (Si)	0.75% max
Phosphorus (P)	0.045% max
Sulfur (S)	0.030% max
Iron (Fe)	Balance

Physical Properties

347 stainless steel is often chosen in various applications due to its excellent physical properties that include good ductility, thermal stability, and resistance to high temperatures. These properties are important data for reference when selecting materials for specific engineering and industrial applications.

Property	Value	Unit
Density	7.96	g/cm³
Melting Point	1398 – 1446	°C (°F)
Thermal Conductivity	16.3 at 100°C	W/m·K
Coefficient of Thermal Expansion	16.6 (20°C to 100°C)	µm/m·°C

• Density: The density of 347 stainless steel is typically about 7.96 g/cm³, which is a standard measure for stainless steels and affects the weight calculations in design and usage.
• Melting Point: This alloy has a melting point range, which typically lies between 1398°C and 1446°C (2550°F to 2635°F). This high melting point makes it suitable for applications involving elevated temperatures.
• Thermal Conductivity: At 100°C, the thermal conductivity of 347 stainless steel is approximately 16.3 W/m·K. This property is essential for evaluating the material’s ability to conduct heat, influencing its performance in heat exchangers and other thermal applications.
• Thermal Expansion: The coefficient of thermal expansion for SS347 is about 16.6 µm/m·°C at temperatures ranging from 20°C to 100°C. This measure is crucial for applications that involve significant temperature changes, helping in the design to accommodate expansion and contraction.

AISI 347 Mechanical Properties

347 stainless steel is highly regarded for its mechanical properties, which make it suitable for a variety of engineering and industrial applications, particularly those involving high temperatures. The mechanical properties of this alloy include excellent resistance to creep and stress rupture at high temperatures, as well as good tensile strength.

• Tensile Strength: 347 stainless steel has a tensile strength of approximately 515 MPa (75 ksi), making it robust enough for many applications under both high stress and high temperature conditions.
• Yield Strength: The yield strength of 347 stainless steel is about 205 MPa (30 ksi), indicating the maximum stress that can be applied before it begins to deform permanently.
• Elongation: This material exhibits an elongation of about 40%, which measures its ability to stretch or elongate before breaking, indicating good ductility.
• Hardness: Typically, 347 stainless steel has a Brinell hardness of around 201 HB, which contributes to its wear resistance under various working conditions.

Property	Value	Unit
Tensile Strength	515	MPa (ksi)
Yield Strength	205	MPa (ksi)
Elongation	40	%
Hardness	201	HB (Brinell)

These mechanical properties showcase the strength and durability of 347 stainless steel and explain why it is an excellent choice for parts and components that are exposed to high temperatures and corrosive environments, such as those found in the aerospace and energy sectors.

Casting Processes

Casting is typically the most common method in the manufacturing of 347 stainless steel components, allowing precise control over dimensions and mechanical properties. The versatility of 347 stainless steel makes it suitable for various casting processes, each with its advantages and specific applications. This section explores three common casting techniques: investment casting, sand casting, and lost foam casting.

Investment Casting

The investment casting process begins by creating a wax model, which is then coated with a ceramic material to form a mold. After de-waxing and shell firing, molten 347 stainless steel is poured into the ceramic mold. Following cooling and solidification, we cut the raw 347 stainless steel castings from the tree and proceed with post-processing procedures.

Investment casting is perfect for casting 347 stainless steel components, known for its ability to produce high-precision and complex parts with an excellent surface finish. With the advanced silica sol casting technique, which features an automated system including automated shell building and drying chamber, we can achieve parts starting from CT4 dimensional tolerances. We also utilize ceramic cores to produce 347 parts with complex internal structures. Please visit our stainless steel casting page for more information about our comprehensive stainless steel casting services.

Sand Casting

Sand casting is one of the most traditional casting methods and involves compacting sand around a pattern to form a mold. This method is known for its ability producing large and rugged 347 stainless steel castings. Although the surface finish and dimensional accuracy are not as refined as in investment casting, sand casting is highly economical and adaptable for larger volumes and sizes.

Lost Foam Casting

In lost foam casting, a model made of foam is used, which is vaporized when molten 347 stainless steel is poured over it, forming the cast. This method is similar to investment casting in terms of the ability to produce complex shapes and high-quality surface finishes. Lost foam casting is beneficial when intricate designs and internal passageways are involved, eliminating the need for cores.

Each of these casting processes offers distinct advantages and can be selected based on the specific requirements of the part, such as size, complexity, and cost considerations. Let us know your specific requirements and we can guide you with the most optimal process for your AISI 347 casting project.

Surface Treatments

Surface treatments are essential for enhancing the performance and durability of 347 stainless steel castings. These treatments can improve corrosion resistance, wear resistance, aesthetic appeal, and other functional properties. Common surface treatments for 347 stainless steel include nitriding, powder coating, passivation, and electroplating, each offering unique benefits depending on the application.

• Nitriding: Nitriding is a heat treating process that enriches the surface layer of the steel with nitrogen. For 347 stainless steel, this process significantly enhances surface hardness and wear resistance without compromising the material’s corrosion resistance. Nitriding involves heating the steel in an ammonia environment at sub-critical temperatures, typically between 500°C and 550°C, which allows nitrogen to diffuse into the surface, forming a hard nitride layer.
• Powder Coating: Powder coating is a dry finishing process that provides a thick, protective coating. This method involves applying a dry powder, typically a thermoplastic or a thermoset polymer, which is then cured under heat to form a ‘skin.’ It offers an attractive finish with excellent durability and resistance to chipping, scratches, and corrosion, and is available in a range of colors and textures.
• Passivation: Passivation is a chemical process that removes free iron from the surface of the stainless steel, enhancing its natural chromium oxide layer, which increases its corrosion resistance. This treatment is crucial for maintaining the long-term integrity and cleanliness of the metal, especially in medical or food-processing applications.
• Electroplating: Electroplating involves coating the stainless steel with a thin layer of another metal, such as nickel, chromium, or zinc, by using an electric current. This method can enhance the aesthetic qualities, corrosion resistance, and surface hardness of the castings. Electroplating is especially useful for applications that require additional resistance to corrosion and wear.
• Mirror Polishing: Mirror polishing is a finishing process that provides a high-gloss, reflective surface on the stainless steel. This is achieved through mechanical polishing using progressively finer abrasives followed by buffing with polishing compounds. Mirror polishing not only enhances the appearance of the steel but also improves its cleanliness and ability to resist bacterial growth, which is particularly important in applications such as pharmaceutical processing, food processing, and other hygienic environments.

Typical Applications of 347 Stainless Steel Castings

347 stainless steel castings are frequently used in various industries primarily due to their superior strength, excellent corrosion resistance, and high-temperature endurance. These properties enable them to meet the rigorous demands of diverse sectors such as marine, railway, automotive, oil and gas, and engineering machinery.

Marine Industry

In the marine sector, 347 stainless steel castings are crucial for manufacturing propeller shafts that must resist saltwater corrosion. They are also used in pump and valve components, which need to withstand harsh marine conditions. Deck fittings made from 347 stainless steel benefit from the material’s durability and resistance to sea air. Additionally, the material is used in the housing for marine instruments to protect sensitive equipment, in engine parts for high-temperature operations, and in exhaust systems, which require corrosion resistance against saltwater and exhaust gases.

Automotive Industry

Various automotive castings could be cast from AISI 347 steel, this material grade can be used for engine components such as pistons, manifolds and turbocharger systems, which operate at high temperatures. Exhaust parts benefit from the material’s ability to resist environmental corrosion and heat. Gear components, suspension parts, fuel injection systems, and valve train components are other applications where the strength, wear resistance, and ability to endure high pressures and temperatures of 347 stainless steel are indispensable.

Oil and Gas Industry

For the oil and gas sector, 347 stainless steel castings are vital in manufacturing valve and pump components that handle high-pressure fluids, pipeline couplings that resist corrosion, and offshore platform fixtures designed to endure harsh sea environments. The material is also used in compressor parts and turbine components, which must reliably perform in extreme conditions, and in instrumentation enclosures to protect critical measurement devices from environmental exposure.

Engineering Machinery

In engineering machinery, 347 stainless steel castings are employed in gearbox components for their high strength and precision, and in hydraulic system parts, which must resist high pressure and wear. Structural components for heavy equipment provide stability and durability, while bearing housings support smooth operation and load-bearing capacity.

Additionally, piston and cylinder heads for high-temperature resistance and cutting and drilling machine components that resist wear during intense operations are also crafted from this robust material. Mechanical seals, crucial for preventing fluid leaks in machinery, also benefit from the durability and corrosion resistance of 347 stainless steel, ensuring reliable sealing performance under various operational conditions.

Conclusion

347 stainless steel castings are indispensable in multiple high-demand industrial sectors due to their outstanding mechanical properties, corrosion resistance, and ability to withstand high temperatures.

From the marine environments where saltwater resistance is crucial to the high-stress demands of the automotive industry, 347 stainless steel proves to be an exceptional material choice. Its versatility is further demonstrated in the oil and gas industry, where robustness against corrosive substances is required, and in engineering machinery, where strength and durability under extreme conditions are paramount.

In conclusion, the comprehensive application of 347 stainless steel across diverse fields underscores its importance and adaptability. Its robust reliability and proven performance enable significant advancements in industrial applications and manufacturing.