CF3 vs CF3M Stainless Steel Casting: Which Should You Choose?

CF3 vs CF3M has been a topic of debate as to which is a superior material grade, Both are common cast stainless steel alloys (cast versions of 304l and 316l) used for a wide range of industries. They are often compared because both have a low carbon content, which is beneficial for welding. A key difference, however, is the addition of molybdenum in CF3M, which changes its properties.

This guide looks at the specific CF3 and CF3M differences to help you decide on the right material for your project. Knowing these distinctions is important for getting the best performance from your cast parts.

What are CF3 and CF3M

To understand the CF3 vs CF3M comparison, you need to look at their basic composition. The CF3 and CF3M differences come down to the specific elements they contain.

CF3

CF3 is a cast austenitic stainless steel alloy. Its chemical makeup includes chromium and nickel, but it has a low carbon content. This low carbon is a key factor. The composition of CF3 makes it a cast version of 304L stainless steel. The main CF3 and CF3M differences start here, with the specific elements in each alloy’s makeup.

CF3M

The CF3M vs CF3 comparison shows a distinct change in its composition. CF3M is very similar to CF3, but it has one important addition: molybdenum. This element is the primary difference between CF3M and CF3. The addition of molybdenum gives CF3M better corrosion resistance than CF3. Like CF3, CF3M also has a low carbon content. This alloy is the cast equivalent of 316L stainless steel. The CF3 and CF3M differences in composition lead to different properties, which we will look at next.

Material Composition Differences

A main difference between CF3 and CF3M is their chemical makeup. This is the source of many of the CF3 and CF3M differences that matter for performance. Both alloys are low-carbon, but the presence of other elements creates a clear distinction.

• Carbon: The low carbon content is a key feature of both CF3 and CF3M. For both, the carbon content is limited to a maximum of 0.03%. This low level is important for welding, as it helps prevent a type of corrosion that can happen after welding. This low carbon content is a common factor in the CF3 vs CF3M discussion.
• Chromium and Nickel: The chemical composition of both alloys has a high percentage of chromium and nickel. Chromium provides the basic corrosion resistance by forming a protective layer on the surface. Nickel adds stability and toughness to the material.
• Molybdenum: The addition of molybdenum is the primary difference between CF3M and CF3. CF3M contains 2.0% to 3.0% molybdenum, while CF3 does not have this element. Molybdenum provides a strong improvement in corrosion resistance, especially against pitting and crevice corrosion that can happen in environments with chlorides.

This table shows a direct comparison of the typical chemical composition ranges for each alloy, based on ASTM A351 standards.

Element	CF3 (UNS J92500)	CF3M (UNS J92800)
Carbon	0.03% max	0.03% max
Manganese	1.50% max	1.50% max
Silicon	1.50% max	1.50% max
Phosphorus	0.04% max	0.04% max
Sulfur	0.04% max	0.04% max
Chromium	17.0% – 21.0%	17.0% – 21.0%
Nickel	8.0% – 12.0%	9.0% – 13.0%
Molybdenum	None	2.0% – 3.0%

CF3 vs CF3M Corrosion Resistance Comparison

Corrosion resistance is a major point in the CF3 vs CF3M discussion. While both CF3 and CF3M are generally considered good corrosion resistant cast metals because of their high chromium content, the key difference between CF3M and CF3 is how they perform in more aggressive environments.

The main difference between CF3 and CF3M in corrosion performance comes from molybdenum. The presence of molybdenum in CF3M provides superior resistance to pitting and crevice corrosion. Pitting is a localized form of corrosion that can cause small holes to form in the metal, which can compromise the part. This type of corrosion is a risk in environments with high chloride content, such as seawater or chemical processing fluids. The CF3M vs CF3 comparison in these settings shows that CF3M holds up much better.

For this reason, the CF3 and CF3M differences mean that CF3M is often chosen for marine or chemical applications, where its added resistance to chlorides is very useful.

Mechanical Properties Differences

The CF3 and CF3M differences also extend to their mechanical properties. These properties describe how a material behaves under force and are important for the part’s function. The CF3 vs CF3M discussion about mechanical properties focuses on strength, ductility, hardness, and impact resistance.

• Tensile and Yield Strength: Both CF3 and CF3M have similar minimum tensile and yield strength values. Tensile strength is the maximum stress the material can take before breaking, while yield strength is the point at which it begins to deform permanently. The minimal difference between CF3M and CF3 in this area means that both are suitable for many similar pressure-containing applications.
• Ductility and Elongation: Ductility is the ability of a material to deform under tensile stress without fracturing. It is measured by elongation, which is the percentage a material stretches before it breaks. The CF3 vs CF3M comparison shows that CF3 has a slightly higher minimum elongation than CF3M. This small difference between CF3 and CF3M means that CF3 may be slightly more ductile, or have more “give,” before it fails.
• Hardness: Hardness is a measure of a material’s resistance to scratching or indentation. While specific values can vary based on heat treatment and other factors, both alloys have a similar hardness range, typically in the 135-202 Brinell Hardness (BHN) range. This shows they have similar surface durability.
• Toughness and Impact Resistance: Toughness is a material’s ability to absorb energy and plastically deform without fracturing. It is often measured by an impact test, like the Charpy V-notch test. Both CF3 and CF3M have good toughness and impact resistance, which is typical of austenitic stainless steels. The presence of molybdenum in CF3M can slightly enhance its toughness, particularly in certain environments, making it a preferable choice for more demanding applications.

This table shows a direct comparison of the minimum mechanical properties for each alloy, based on ASTM A351 standards. The CF3 and CF3M differences are minor but can be a factor in specific engineering decisions.

Property	CF3 (UNS J92500)	CF3M (UNS J92800)
Tensile Strength, min	70 ksi (485 MPa)	70 ksi (485 MPa)
Yield Strength, min	30 ksi (205 MPa)	30 ksi (205 MPa)
Ductility (Elongation), min	35%	30%
Hardness, Brinell	201 max	201 max
Toughness (Charpy V-notch)	Good	Good (27 J at room temp.)

Note: While both alloys have good toughness, the specific values can vary depending on testing conditions. The value for CF3M is a common typical minimum from specifications.

Castability Comparison

The final point of comparison in the CF3 vs CF3M discussion is how well they can be cast into parts. Both CF3 and CF3M are considered to have good castability, which means they can be used to create complex shapes with high quality. However, there are some subtle differences that can be a factor in manufacturing.

Both alloys are typically made using either sand casting or investment casting processes. Key casting characteristics include fluidity, solidification, and shrinkage.

• Fluidity: Fluidity is the ability of the molten metal to fill the mold cavity, especially thin sections. Molybdenum, the key difference between CF3M and CF3, can slightly lower the melting point and improve the fluidity of the molten metal. This can make CF3M a bit easier to cast into intricate or thin-walled parts compared to CF3.
• Solidification: Both alloys have a similar solidification range, which is the temperature range where the metal changes from a liquid to a solid. A wide solidification range can lead to certain casting defects, such as porosity and hot tearing. Foundries must carefully control the cooling rate to avoid these issues for both CF3 and CF3M.
• Shrinkage: Like all alloys, both CF3 and CF3M will shrink as they cool. This requires foundries to design the mold with enough “risers” to feed molten metal to the part as it solidifies. The shrinkage characteristics are similar for both alloys, and proper mold design is crucial to prevent defects.

Overall, the difference between CF3M and CF3 in terms of castability is minor. Both are well-suited for a variety of casting applications, but the slightly improved fluidity of CF3M may offer a small advantage for complex designs.

Weldability Comparison

Weldability is an important factor for parts that need to be joined to other components or repaired. The good weldability of both CF3 and CF3M is a key advantage, largely due to their low carbon content.

The low carbon content (maximum 0.03%) in both alloys is the most significant factor for their excellent weldability. When welding, the heat can cause chromium carbides to form at the grain boundaries of the steel. This process, known as sensitization, can reduce the corrosion resistance of the material in the heat-affected zone. By keeping the carbon content very low, the formation of these carbides is minimized, which is the main difference between CF3 and CF3M when compared to higher carbon grades like CF8 and CF8M. This means that both CF3 and CF3M can often be welded without needing a post-weld heat treatment to restore corrosion resistance.

The presence of molybdenum in CF3M does not significantly change its welding characteristics compared to CF3. Both alloys can be welded using common processes like shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), and gas metal arc welding (GMAW). The choice of filler metal is important to maintain the properties of the weld joint, with consumables like 308L for CF3 and 316L for CF3M being common choices to match the base material composition and corrosion resistance.

In summary, the CF3 vs CF3M discussion on weldability shows that both are excellent choices. Their low carbon content provides superior resistance to weld-related corrosion, making them highly reliable for applications where welding is required.

High-Temperature Service Comparison

When considering CF3 vs CF3M for high-temperature applications, it’s important to look at their thermal stability and maximum service temperatures. Both are austenitic stainless steels and offer good resistance to high temperatures, but there are some key differences.

• Maximum Service Temperature: The maximum recommended service temperature for CF3M is generally limited to around 800∘F (425∘C). This limitation is primarily due to potential thermal instability and the risk of forming undesirable intermetallic phases with extended exposure to high temperatures. In comparison, CF3 (the cast equivalent of 304L) can be used for moderate thermal service and retains structural integrity up to 800∘C and higher in some applications, though its creep resistance is moderate. It is often recommended for applications below 345∘C.
• Oxidation Resistance: Both alloys have good oxidation resistance, which is their ability to resist corrosion when exposed to high-temperature air or other oxidizing gases. This is due to their high chromium content, which forms a protective passive layer. The presence of molybdenum in CF3M slightly enhances its overall stability, but the difference in oxidation resistance is not as significant as the difference in corrosion resistance at ambient temperatures.
• Thermal Stability: The main concern for high-temperature applications is the risk of sensitization and the formation of sigma phase. The low carbon content in both CF3 and CF3M is crucial, as it helps prevent the formation of chromium carbides, which can lead to intergranular corrosion. This makes both alloys suitable for welded high-temperature applications where post-weld heat treatment is not possible. However, the presence of molybdenum in CF3M can make it more susceptible to sigma phase formation after prolonged exposure to temperatures in the 1000−1650∘F (540−900∘C) range, which can embrittle the material. For this reason, CF3 is sometimes preferred for certain high-temperature services within this range if the added corrosion resistance of CF3M is not required.

For high-temperature service, CF3 and CF3M have different limitations and strengths. CF3 is generally seen as more stable for prolonged high-temperature exposure without the risk of sigma phase embrittlement, while CF3M has a lower recommended maximum service temperature due to its susceptibility to thermal instability. The choice depends on the specific temperature range, duration of exposure, and the corrosive nature of the environment.

Manufacturing and Cost Comparison

The final point in the CF3 vs CF3M discussion is the manufacturing process and the resulting cost. The cost difference between CF3M and CF3 is mainly driven by the material composition, while the manufacturing process, such as investment casting, is very similar for both alloys.

• Investment Casting Process: Both CF3 and CF3M are well-suited for the investment casting process (also known as the “lost wax” process). This method is excellent for producing intricate parts with high dimensional accuracy and a smooth surface finish. The general steps of the investment casting process—creating a wax pattern, building a ceramic shell, melting out the wax, and pouring the molten metal—are identical for both alloys. This means that the core manufacturing labor and equipment costs are comparable.
• Cost of Raw Materials: The primary difference between CF3M and CF3 in terms of cost is the addition of molybdenum in CF3M. Molybdenum is a more expensive alloying element than the other components. Therefore, the raw material cost for CF3M is inherently higher than for CF3. This difference is the most significant factor affecting the final price of the casting.
• Manufacturing Complexity and Yield: While both alloys have good castability, minor differences in their fluidity (as mentioned in the Castability section) can slightly affect manufacturing. However, these small differences do not significantly alter the overall cost of the process. The low carbon content in both alloys simplifies welding, reducing the need for expensive post-weld heat treatments, which is a cost benefit shared by both.
• Cost vs. Performance: The CF3 vs CF3M cost comparison is ultimately a decision based on the required performance. While CF3M is more expensive, its superior corrosion resistance in specific environments can justify the higher cost. A part made of CF3M may have a longer service life and lower maintenance costs in a highly corrosive environment (like one with chlorides) compared to a CF3 part, which could fail prematurely.

The manufacturing process for both CF3 and CF3M is very similar, particularly with investment casting. The main difference between CF3M and CF3 in terms of cost is the higher price of the raw materials for CF3M due to the presence of molybdenum. The decision between the two should be a balance of upfront cost and the long-term performance and durability requirements of the application.

Applications Comparison

The choice between CF3 and CF3M is highly dependent on the application’s specific environment. While both alloys are used for pressure-containing parts like pumps and valves, the key difference between CF3M and CF3 in corrosion resistance guides their use in different settings.

Typical CF3 Applications

Since CF3 is the cast equivalent of 304L stainless steel, it is suitable for general-purpose applications where good corrosion resistance is needed but the environment is not highly aggressive. Its key applications include:

• Food and Pharmaceutical Processing: CF3 is used for equipment and components that require cleanliness and good general corrosion resistance, such as those in contact with food products or non-aggressive chemical fluids.
• General Industrial Use: It is a cost-effective choice for pump and valve components, heat exchangers, and other industrial machinery parts in environments without significant chloride content.
• Weld-intensive Structures: Due to its excellent weldability from the low carbon content, CF3 is a preferred choice for large assemblies or applications where post-weld heat treatment is not possible.

Typical CF3M Applications

The addition of molybdenum in CF3M provides superior resistance to pitting and crevice corrosion, making it the better choice for harsh environments, particularly those with chlorides. Its applications include:

• Marine and Offshore: CF3M is the ideal choice for marine casting parts exposed to saltwater and marine environments, such as offshore platforms, shipbuilding components, and subsea equipment. Its resistance to chloride corrosion is essential here.
• Chemical Processing: This alloy is widely used for pump and valve components, impellers, and fittings that handle aggressive chemicals, acids, and solutions with high chloride content. Its enhanced corrosion resistance ensures a longer service life and better reliability.
• Hydroelectric Power Industry: This alloy is used for components that handle high-velocity water, such as Pelton turbines, due to its excellent resistance to cavitation and erosion.
• Pulp and Paper Industry: CF3M is used for equipment in paper mills that are exposed to corrosive chemicals used in the processing of pulp and paper.
• Petrochemical and Oil & Gas: It is a common material for components in the oil and gas industry where equipment must withstand corrosive media and high pressures.

In the CF3 vs CF3M discussion on applications, the deciding factor is often the presence of chlorides. If the environment is aggressive, particularly with salt or other chloride-containing fluids, the higher cost of CF3M is a necessary investment for long-term performance and safety. For more benign environments, the cost-effectiveness and good performance of CF3 make it an excellent choice.

Before You Make the Decision

Both CF3 and CF3M are commonly used casting materials, due to their low carbon content, which provides excellent weldability and resistance to weld decay. The CF8 and CF8M grades, while also very common, have a higher carbon content (0.08% max). This higher carbon level makes CF8 and CF8M more susceptible to sensitization and intergranular corrosion after welding, often requiring post-weld heat treatment to restore corrosion resistance.

Therefore, when a project requires extensive welding and a post-weld heat treatment is not feasible or desired, CF3 and CF3M are the superior choice. For a deeper dive into these other grades, be sure to read our detailed comparison article: What to Know About CF8 vs CF8M Stainless Steel Casting.

Conclusion

In summary, the decision between CF3 and CF3M hinges on a careful evaluation of the application’s environment and performance requirements. CF3 is a robust and cost-effective choice for general industrial use, providing good weldability and mechanical properties. However, for more demanding environments with a high risk of chloride corrosion, the added molybdenum in CF3M provides a superior defense against pitting and crevice corrosion, justifying its higher cost.

SIMIS Investment Casting Co., Ltd. offers a full range of customized casting services. As a professional investment casting foundry, we specialize in a process dedicated to producing both CF3 and CF3M stainless steel castings, and have extensive experience manufacturing a variety of high-quality stainless steel parts for a wide range of industries.

We are equipped not only with cutting-edge casting equipment and facilities, but also with a comprehensive suite of testing and inspection. All of our castings undergo a strict quality control process, which allows us to supply defect-free castings to all our customers. Contact us now to begin your stainless steel casting projects.