In the selection of stainless steel precision castings, CF8 and CF8M are two very common grades. Many purchasing personnel directly interpret CF8 as 304 and CF8M as 316, which is generally correct. However, in engineering applications, it is necessary to make a comprehensive judgment based on casting standards, corrosive environments, subsequent processing, cost budgets, and service life. For industries such as pumps and valves, food machinery, building hardware, and marine engineering, choosing the wrong material is often not just a simple matter of price, but also affects the product's corrosion resistance, sealing reliability, and subsequent maintenance costs.
This article systematically explains the differences between CF8 and CF8M from an engineering material selection perspective, and combines typical applications of 304 and 316 stainless steel castings to help you in stainless steel...Precision castingMake more prudent material choices in the project.
What are CF8 and CF8M?
CF8 and CF8M are common austenitic stainless steel grades used in casting, often for investment casting, silica sol precision casting, and sand casting parts. They typically correspond to material grades in casting stainless steel standards such as ASTM A351, ASTM A743, and ASTM A744.
In practical terms, CF8 typically corresponds to 304 stainless steel castings, while CF8M typically corresponds to 316 stainless steel castings. Both are austenitic stainless steels, possessing good toughness, formability, and corrosion resistance, and are suitable for making stainless steel precision castings with complex structures and high dimensional accuracy requirements.
The most fundamental difference between the two lies in the addition of molybdenum to CF8. Molybdenum significantly improves the material's resistance to pitting corrosion in chloride-containing environments, thus making CF8M more stable in seawater, salt spray, some chemical media, and even more severe corrosive environments.
Comparison of chemical composition between CF8 and CF8M
The material composition determines the basic properties of stainless steel castings. Both CF8 and CF8M use chromium and nickel as the main alloying elements to form a stable austenitic structure; CF8M additionally contains molybdenum, which is the main reason why its corrosion resistance is superior to that of CF8.
| project | CF8 | CF8M | Engineering significance |
|---|---|---|---|
| Corresponding commonly used forging and rolling grades | 304 | 316 | To facilitate procurement and communication of drawings, the casting grade should conform to the standard. |
| Chromium (Cr) | Approximately 18.01 TP3T - 21.01 TP3T | Approximately 18.01 TP3T - 21.01 TP3T | The formation of a passivation film is fundamental to the corrosion resistance of stainless steel. |
| NickelNi | Approximately 8.01 TP3T - 11.01 TP3T | Approximately 9.01 TP3T - 12.01 TP3T | Stabilize the austenitic structure and improve toughness and overall performance. |
| Molybdenum | Adding is usually not required. | Approximately 2.01 TP3T - 3.01 TP3T | Improve resistance to pitting and crevice corrosion |
| Carbon C | Generally not higher than 0.08% | Generally not higher than 0.08% | Carbon content affects intergranular corrosion susceptibility and weldability. |
It is important to note that the composition range of castings is not entirely the same as that of plates and bars. When submitting drawings, requesting quotes, and during acceptance, it is recommended to clearly specify the applicable standards, heat treatment status, whether a material report is required, and whether spectral analysis, tensile testing, or corrosion-related tests are necessary.
Comparison of mechanical properties between CF8 and CF8M
From a mechanical performance perspective, both CF8 and CF8M can meet the requirements of most pump and valve housings, connectors, brackets, and other components.impellerThe strength requirements for mechanical parts are similar to those for conventional mechanical parts. The differences are usually less pronounced than in corrosion resistance. In actual projects, mechanical properties are also affected by casting processes, heat treatment, wall thickness, defect control, and machining allowances.
| Performance items | CF8 | CF8M | Selection Reference |
|---|---|---|---|
| tensile strength | It can typically meet the requirements for conventional austenitic stainless steel castings. | Similar to CF8 | This is generally not the main dividing line between the two selection criteria. |
| Yield strength | Suitable for general structural load-bearing parts | Suitable for general structural load-bearing parts | High load conditions should be combined with structural calculations. |
| elongation | Good toughness | Good toughness | Suitable for complex castings and subsequent machining |
| Processing performance | better | Slightly more difficult than CF8 | CF8M contains molybdenum, so machining tools and parameters need to be optimized appropriately. |
| Welding and repair | Good weldability | Good weldability | For critical components, the welding materials, heat input, and inspection methods need to be controlled. |
If the component primarily bears static loads and the medium is not highly corrosive, CF8 is usually sufficient. If the component is simultaneously exposed to corrosive media, humid salt spray, cleaning agents, or chlorine-containing environments, CF8M offers higher overall reliability.
Corrosion resistance comparison
The real difference between CF8 and CF8M lies primarily in their corrosion resistance. 304 grade materials are stable in ordinary atmospheres, fresh water, and weakly corrosive environments; 316 grade materials, due to their molybdenum content, are less prone to pitting and crevice corrosion in chloride-containing environments.
Freshwater environment
In ordinary fresh water, municipal tap water, general cooling water, and humid indoor environments, CF8 can usually meet the usage requirements. For example, in conventional water pump components, ordinary valve accessories, indoor hardware, and food machinery components operating in non-high-salt conditions, CF8 can balance performance and cost.
However, if the freshwater contains high levels of chloride ions, disinfectants, cleaning agents, or remains stagnant for extended periods, the passivation film on the material's surface may be damaged. In such cases, while CF8 can still be used, it is necessary to assess water quality, temperature, and maintenance schedules; in such situations, CF8M may be a more reliable choice.
marine environment
The marine environment is more demanding on stainless steel materials, with the core issues being pitting corrosion, crevice corrosion, and salt spray corrosion caused by chloride ions. When used in marine environments with atmospheric conditions, humid salt spray, or seawater contact, the risks are significantly higher for CF8 than for CF8M.
For products such as seaside railing connectors, marine pump and valve components, dock equipment accessories, and seawater pipeline fittings, CF8M or higher grade materials are generally preferred. For components that are submerged in seawater for extended periods, pressure-bearing components, or critical fluid equipment, 316L, duplex 2205, or other corrosion-resistant alloys should be further evaluated.
Chemical media environment
Chemical media environments cannot be simply judged by whether "304 is sufficient" or "316 is definitely sufficient." Acids, alkalis, salts, temperature, concentration, flow rate, and the presence of chloride ions all affect material lifespan. CF8 is suitable for some weakly corrosive media and general industrial environments; CF8M is suitable for a wider range of media containing chlorides, weak acids, and salts.
If the medium is highly corrosive, or if component failure would cause downtime, safety risks, and high maintenance costs, material selection should be based on specific medium parameters, rather than solely on price. If necessary, the medium composition, temperature, pressure, and service life can be provided for joint confirmation of the material selection by the foundry and end-user engineers.
Application Scenarios Analysis of 304 and 316 Castings
In actual procurement, material selection is usually not based on the grade alone, but rather on considerations such as industry, medium, surface treatment, dimensional accuracy, and subsequent processing. The following explains the applicable scenarios for CF8 and CF8M based on common industries.
Pump and valve industry
The pump and valve industry is one of the most concentrated areas of use for CF8 and CF8M valves. Common parts include valve bodies, valve covers, valve discs, pump bodies, impellers, connecting flanges, and pipeline accessories.
- For ordinary water, air, steam, and general industrial fluids, CF8 is preferred.
- For environments containing saline water, seawater, weakly acidic media, or chloride ions, CF8M is recommended as the preferred choice.
- In addition to the material, attention should also be paid to internal defects in castings, pressure testing requirements, and non-destructive testing for critical pressure-bearing components.
- For impeller-type parts, dynamic balance, surface roughness, and machining accuracy should be considered simultaneously.
Food machinery
Food processing machinery commonly uses 304 and 316 stainless steel. For general food contact, dry environments, and routine cleaning conditions, CF8 can meet the needs of most structural and support components. For components handling salty foods, dairy products, condiments, acidic foods, or those frequently cleaned with detergents, CF8M is more suitable.
In addition to material grade, surface quality is also important for food machinery castings. The surface of the casting should have fewer sand holes, shrinkage cavities, inclusions, and hard-to-clean corners. When necessary, CNC finishing, polishing, pickling and passivation, or electropolishing should be used to reduce residue and corrosion risks.
Architectural Hardware
Architectural hardware includes glass clamps, railing fittings, door and window hardware, connectors, decorative parts, and non-standard brackets. For indoor or general outdoor environments, CF8 is generally a good choice as it is relatively easier to control costs. For architectural hardware in coastal cities, around swimming pools, in damp areas of underground garages, or those exposed to salt spray for extended periods, CF8M is recommended.
For exterior components, materials are only the foundation; surface treatment is equally important. Processes such as brushing, mirror finishing, sandblasting, and passivation can affect corrosion resistance and aesthetic consistency. If the product is exposed to the outdoors for extended periods, the design should also avoid structures prone to water accumulation and narrow gaps.
Marine Engineering
In marine engineering environments, CF8 is generally not the preferred option. CF8M is more suitable for salt spray and coastal environments than CF8, but this does not mean that CF8M can be used directly in all marine conditions. For components subjected to long-term immersion, strong erosion, obvious crack structures, or pressure-bearing critical components, 316L, 2205 duplex steel, or higher corrosion-resistant materials should be selected based on the specific operating conditions.
The failure costs of marine engineering components are typically high, therefore material selection should be conservative. In addition to the grade, the requirements for casting heat treatment, non-destructive testing, pressure testing, machining dimensions, surface passivation, and packaging protection should also be clearly defined.
Cost difference between CF8 and CF8M
CF8M is generally more expensive than CF8, mainly because it contains molybdenum and typically has a slightly higher nickel content. Both molybdenum and nickel are alloying elements whose prices fluctuate significantly, so the material cost of CF8M will change with market conditions.
From the perspective of the total cost of precision castings, materials are only one part. Mold making, wax model making, shell making, melting, casting, heat treatment, cutting and polishing, CNC machining, inspection, packaging, and logistics all affect the final price. For parts with complex structures, large machining volumes, or high quality requirements, the final price difference between CF8 and CF8M is not necessarily calculated solely based on the proportion of raw materials.
Generally speaking, under the same structure, weight, and manufacturing process, CF8M will be more expensive than CF8. For small-batch orders, the price difference may be offset by furnace start-up, processing, and inspection costs; for large-batch orders, the material differences will be more significant. When purchasing, it is not recommended to only compare unit prices, but also to assess the usage environment and failure costs.
How to select suitable stainless steel precision casting materials
When choosing between CF8 and CF8M, you can use the following approach to determine your choice:
- If the operating conditions are ordinary atmospheric, fresh water, indoor, or general industrial environments, CF8 should be given priority.
- If there is salt spray, a seaside environment, chlorinated water, a weak acid medium, or frequent cleaning, CF8M should be given priority.
- If the part is an exterior component, in addition to the material, the polishing, passivation, and packaging methods must also be confirmed.
- If the part is a pressure-bearing component, the requirements for pressure testing, non-destructive testing, and material reports should be clearly defined.
- If the medium is complex, information such as temperature, pressure, concentration, pH value, and chloride ion content should be provided before determining the materials.
- If CNC finishing is required later, a reasonable machining allowance should be reserved during the casting stage and deformation should be controlled.
For projects requiring customized valve castings, pump body castings, impeller castings, and mechanical parts, it is recommended to provide drawings, 3D models, material requirements, annual usage, surface treatment, and inspection standards before providing a quote. Haijin Stainless Steel can customize products based on customer drawings.Stainless steel precision castingCustomization helps clients strike a balance between materials, processes, and costs.
Summarize
CF8 and CF8M are both commonly used austenitic stainless steel casting grades. Simply put, CF8 corresponds to 304 stainless steel castings, and CF8M corresponds to 316 stainless steel castings. Their mechanical properties are similar; the real difference lies in their corrosion resistance, especially in environments containing chloride ions, salt spray, seawater, and certain chemical media, where CF8M is more reliable than CF8.
If the project is cost-sensitive and the operating environment is mild, CF8 is an economical and practical choice; if the product is used in marine, chemical, food cleaning, saline media, or high-reliability scenarios, CF8M is a better choice. Material selection should not only consider the grade, but also the casting process, machining, surface treatment, testing standards, and the actual operating environment.
Haijin Stainless Steel specializes in stainless steel precision casting, silica sol precision casting, and CNC machining, and can provide customized services for various materials such as 304, 304L, 316, 316L, and 2205 duplex stainless steel.
If you are looking for a reliable supplier of stainless steel precision castings, please contact us for a free quote.
FAQ
1. Is CF8 equal to 304?
In engineering communication, CF8 can generally be understood as 304 stainless steel casting. However, strictly speaking, CF8 is a cast stainless steel grade, while 304 is mostly used for forged and rolled materials. The correspondence between the two is close, and the drawings and applicable standards should be the basis for acceptance.
2. Is CF8M equal to 316?
CF8M is typically used for 316 stainless steel castings. CF8M contains molybdenum, therefore it performs better than CF8 in chloride-containing and some corrosive media.
3. Which is more corrosion resistant, CF8 or CF8M?
Generally speaking, CF8M is more corrosion resistant than CF8, especially in salt spray, seawater, chlorinated water and some chemical media environments.
4. Which materials should be chosen for a seaside environment?
For coastal environments, CF8M is the preferred choice. If the parts are exposed to seawater for extended periods, are subject to pressure, or are critical components, 316L, 2205 duplex stainless steel, or higher-grade corrosion-resistant materials should also be evaluated.
5. How much more expensive is the CF8M compared to the CF8?
CF8M is generally more expensive than CF8, mainly because it contains molybdenum and may have a higher nickel content. The specific price difference will vary depending on the alloy price, casting weight, machining difficulty, order quantity, and inspection requirements. It is recommended to provide a separate quote based on the drawings.
