In stainless steel investment casting, 316 and 316L stainless steel castings are widely used in the fluid control industry, marine engineering, and medical equipment. Although these two grades look very similar, they differ significantly in many ways. Choosing the wrong one can lead to intergranular corrosion and cracking, resulting in higher procurement costs and project delays. This article will explain the differences between 316 and 316L, helping you make better choices for stainless steel materials and reduce unnecessary costs.
Cast Equivalent Grade
316 and 316L have different casting grades under different standards. Understanding the corresponding casting grades will help you specify the correct grade requirements to manufacturers in different countries.
| Standard System | 316 | 316L |
| ASTM | ASTM A351 CF8M | ASTM A351 CF3M |
| EN | 1.4408 | 1.4409 |
| JIS | SCS 14 | SCS 19A |
Chemical Composition
As austenitic stainless steels, 316 and 316L differ primarily in their carbon content. The “L” in 316L stands for “low carbon”; its carbon content must be ≤0.03%, whereas the carbon content in 316 is only required to be ≤0.08%. Aside from this, there is no significant difference in the other alloying elements.
Manufacturing Performance
The difference between 316 and 316L essentially lies in their carbon content. Understanding the specific differences will help you accurately select the appropriate material based on the casting’s requirements and operating environment, thereby avoiding rapid cracking and the need for large-scale recasting caused by an unsuitable material, which would increase costs.
Weldability
This is the crucial difference between 316 and 316L in manufacturing. For 316, when subjected to the sensitization temperature range of 425°C to 860°C during welding, excess carbon in 316 will combine with chromium to form chromium carbides that precipitate along the grain boundaries, resulting in severe chromium-depleted zones at these boundaries. Without post-weld heat treatment, the risk of intergranular corrosion in 316 in corrosive operating environments will significantly increase, leading to a substantial reduction in mechanical strength and causing the system operation to stop.
In contrast, the extremely low internal carbon content of 316L means that no chromium carbides form during welding, resulting in a minimal risk of intergranular corrosion. This allows 316L castings to be put into service without requiring any post-weld heat treatment. Therefore, if your castings require welding and are exposed to corrosive media, selecting 316L investment castings can significantly eliminate the need for expensive post-weld solution annealing, lower post-weld heat-treatment costs, and shorten lead time.
Heat Treatment Specifications
316 and 316L are both austenitic stainless steels; they do not require quenching to increase hardness; they need solution heat treatment and stress-relief annealing. For both grades, the solution treatment process is the same: they must be heated to 1040°C–1150°C and rapidly cooled in water quenching to eliminate precipitated chromium carbides and prevent intergranular corrosion. However, since 316L has an extremely low carbon content and is hardly prone to intergranular corrosion, the post-weld heat treatment can often be omitted for thin-wall castings under 10 mm.
Regarding the stress-relief annealing process, because the 316 castings are highly prone to chromium carbide precipitation within the sensitization range of 425°C–860°C without post-weld heat treatment, this range must be avoided, placing extremely high demands on operators. However, 316L castings do not have a sensitization range, so the temperature requirements for stress-relief annealing are lower, and the selection of annealing temperatures is more flexible.
Machinability
The higher carbon content in 316 stainless steel castings gives them high hardness and mechanical strength. These properties cause chips from 316 castings to break easily during machining, preventing them from sticking to the cutting tool, thereby improving workshop efficiency and reducing lead time.
In contrast, 316L has a lower carbon content, resulting in a softer material with greater toughness. During CNC machining, this characteristic causes chips to adhere easily to the cutting tool. Furthermore, during machining, the internal austenitic structure is more prone to transform into martensite, exhibiting a strong tendency to work-harden. Therefore, machining 316L castings places higher demands on cutting tools. Sharper tools, moderate cutting speeds, and adequate coolant are all required to prevent excessive tool wear and avoid incurring additional tool replacement costs.
Corrosion Resistance
Without welding, the corrosion resistance of 316 and 316L is nearly identical because they have essentially the same elements, except for carbon content. However, 316L castings exhibit significantly higher corrosion resistance than 316 castings after welding. This is because the sensitization temperature range at the weld seam of 316 castings will degrade quickly in a corrosive environment, leading to intergranular corrosion that causes the casting to crack and delays your system. In contrast, the excellent weldability of 316L castings ensures that the casting maintains its integrity, minimizing the risk of cracking.
Mechanical Properties
The differences in the mechanical properties of 316 and 316L primarily stem from the varying degrees of strengthening due to their carbon content. Carbon atoms with a small radius cause lattice distortion within the austenitic structure, which significantly enhances the material’s mechanical strength.
| Mechanical Properties | 316 | 316L | Analysis |
| Yield Strength | ≥205MPa | ≥170MPa | The yield strength of 316 is significantly higher than 316L. This indicates that 316 castings have greater resistance to permanent deformation. |
| Tensile Strength | ≥515MPa | ≥485MPa | The tensile strength of 316 is higher than 316L, indicating that 316 castings have a higher load-bearing capacity. |
| Elongation at Break | ≥40％ | ≥40％ | Both offer excellent ductility. The lower carbon content in 316L gives it higher impact toughness and ductility, making it less susceptible to brittle failure. |
| Hardness | ≤95HRB | ≤95HRB | Both have the same hardness in the unprocessed state, but after processing, 316L exhibits a greater tendency toward work hardening and also has greater surface toughness. |
| Creep Strength | Higher | Lower | The creep strength of 316 is higher than 316L. At temperatures above 500°C, the long-term strength of 316 is significantly greater than that of 316L. |
| Cryogenic Performance | Good（-100℃） | Excellent(-196℃) | The cryogenic performance of 316L is better than that of 316. Because of the low carbon content of 316L, the castings are not prone to brittle transformation even at low temperatures. |
| Wear Resistance | Better | Poor | Both have relatively poor wear resistance, but 316 castings have a higher yield strength, so the wear resistance is slightly better than that of 316L castings. |
Total Cost of Ownership Analysis
Total costs include raw materials, processing, maintenance, and so on. The cost differences between 316 and 316L castings differ at each process. Understanding the different costs of 316 and 316L castings at each step will help you choose the appropriate selection based on your castings and minimize your costs.
Material Cost
In raw materials costs, there is no significant difference. But the cost of 316L is 2%–5% more than 316 due to the low-carbon properties. Although the procurement cost of 316L is higher, this 2%–5% price difference is essentially negligible in total costs.
Manufacturing Cost
In manufacturing costs, because 316 and 316L castings have different properties, costs must be differentiated based on the specific application of each material.
For components that require welding, 316L clearly offers a lower processing cost. This is because 316 requires solution annealing due to chromium depletion during welding, which incurs additional costs. In contrast, 316L can be delivered directly after welding without heat treatment due to its low – carbon content. This not only saves you 15%–20% in secondary processing costs but also significantly shortens the production cycle.
For components requiring only machining, 316 has lower processing costs. Compared to 316 castings, which just cause moderate tool wear, 316L castings are more ductile and softer in texture. These properties make the chips tend to stick easily, and severe work hardening occurs, requiring tool replacement and slower machining speeds. This leads to a 10%–20% increase in tool consumption, thereby raising the total cost.
Maintenance Cost
The difference in maintenance costs is primarily in the welded equipment made of 316 and 316L; the costs of 316L castings are significantly lower than 316 castings. When performing non-destructive testing on 316 welded components, high-frequency ultrasonic and radiographic testing are often required to detect internal defects. However, due to 316L’s lower carbon content, they exhibit greater stability in corrosive environments and does not require the frequent inspection and maintenance that 316 castings do.
Furthermore, if the 316 welded components, such as welded piping, have not undergone a thorough solution treatment to remove precipitated chromium carbides, intergranular corrosion is highly probable to occur at the welds during operation. This can result in leaks, contamination, project delays, and emergency repairs, which incur costs that are often dozens or even hundreds of times higher than material costs.
Service Life
The service life of 316 and 316L determines the replacement frequency. However, the service life of 316 and 316L castings varies with their microstructure and operating environment.
For welded components used in highly corrosive environments, 316L castings have an average service life 2 to 5 times longer than 316 castings that have not undergone solution treatment, resulting in a lower replacement frequency.
However, for non-welded mechanical components used in high-temperature environments, 316 castings possess higher yield strength and creep resistance due to their higher carbon content, resulting in a slightly longer service life than 316L castings.
These differences in service life, combined with manufacturing and maintenance costs, collectively determine the overall cost advantage. For welded components used in corrosive environments, like pump housings or piping, 316L is the more economical choice; the cost savings from eliminating post-weld heat treatment, combined with its longer service life, far outweigh its slightly higher material cost. For non-welded components that require only machining, such as bolts and bearing sleeves, 316 is better because its excellent machinability and higher mechanical strength reduce tool wear and lower replacement frequency.
Typical Application
Due to their different properties, 316 stainless steel castings and 316L stainless steel castings are used in different applications. Knowing the specific applications of each will help you more intuitively select the most suitable material for your castings’ operating environment.
Application of 316 Stainless Steel
The high carbon content of 316 gives it higher yield strength, excellent high-temperature creep resistance, better machinability, and high susceptibility to intergranular corrosion. These characteristics make 316 castings commonly used in non-welded mechanical components.
- Fluid Control Industry
The fluid control industry requires castings that can withstand long-term and high-frequency impacts. Since the yield strength of 316 castings is significantly higher than that of 316L, the pump shafts, valve stems, and valve body castings made from it are less prone to bending or permanent deformation under high torque and friction, ensuring the system’s smooth operation without frequent replacement.
- High-Temperature Industry
The high-temperature creep resistance of 316 castings is far superior to that of 316L castings. This property enables heater support brackets and exhaust system components made from 316 castings to maintain tensile strength at high temperatures up to 500℃. It ensures that the castings do not undergo permanent deformation during long-term operation at high temperatures, thereby safeguarding the integrity of the operating system’s seals and significantly reducing your maintenance costs.
- Heavy-Duty Marine Fasteners
316 castings are commonly used in marine bolts and nuts because these fasteners are machined castings that do not require welding and rely on tensile force. The higher tensile and yield strengths of 316 compared to 316L allow these bolts to achieve greater preload, effectively preventing loosening under severe vibration and wave impact, thereby preventing leaks.
Application of 316L Stainless Steel
Due to its extremely low carbon content, high resistance to intergranular corrosion, and excellent cryogenic performance, 316L is commonly used in welding components and cryogenic environments.
- Pharmaceutical & Food Industry
In this industry, 316L is commonly used in sterile piping for the pharmaceutical industry or CIP piping for the food industry. Its low-carbon composition prevents carbide formation on the casting surface, making the castings extremely easy to electropolish. After polishing, the surface can achieve a mirror-like finish with a surface roughness of Ra < 0.4 μm, effectively preventing bacterial growth and residual media from contaminating the food or pharmaceuticals and reducing the cleaning cycle times.
- Chemical Industry
In the chemical industry, 316L is commonly used in pipelines for transporting strong acids and in welded pressure vessels. This is because chemical pipelines require welding; if 316 castings were used, the heat-affected zone at the welds would rapidly undergo intergranular corrosion due to exposure to corrosive media, leading to media leakage. In contrast, the low-carbon composition of 316L stainless steel castings eliminates the risk of intergranular corrosion at its source, ensuring zero leakage in the piping system.
- Marine Industry
In marine casting, 316L is commonly used in high-pressure pumps, impellers, valves, and pipe fittings for seawater desalination and offshore drilling platforms. With 2-3% molybdenum content and low-carbon composition, it provides long-term, effective resistance to chloride-ion corrosion in seawater and crevice corrosion caused by marine organisms, thereby preventing fluid leaks and ensuring the efficient, smooth operation of pump and valve systems.
- Liquefied Natural Gas Industry
The liquefied natural gas industry requires castings capable of operating at cryogenic temperatures of -196°C. The low carbon content in 316L steel ensures it retains exceptional toughness even in low-temperature environments, preventing cold brittleness. Castings made from this material for ultra-low-temperature valves in LNG receiving terminals and cryogenic transport pipelines can maintain their toughness even under prolonged impact, thereby preventing sudden fracture.
Final Thought
Believe you now understand the differences between 316 and 316L grades and can select the appropriate material for your application. If you’re looking for a reliable stainless steel investment casting manufacturer, please contact us. Pingheng Machinery, with exceptional quality control, rigorous inspections, and one-stop customization service, will provide you with perfect stainless steel castings.
FAQ
Q1. What’s the main difference between 316 and 316L stainless steel?
The main difference is the carbon content. The 0.08% carbon content of 316 gives it higher machine strength, while the 0.03% carbon content of 316L gives it excellent resistance to intergranular corrosion.
Q2. Can I use 316L to replace 316 in most applications?
Yes, 316L can be used as a substitute in most situations, including for welded components, highly corrosive environments, and sanitary-grade castings. However, for non-welded components, high-temperature applications, and castings subject to high stress, 316 is still the first choice, as these applications require 316’s higher yield strength and creep resistance.
Q3. How do you ensure that the elemental content in the 316L stainless steel castings you provide meets the standards?
We have a professional spectrometer machine. Before and after casting, we use this spectrometer to test each 316L casting to verify that the carbon content is ≤0.03%, ensuring that the castings leaving our factory fully meet the standards.
Q4. Can 316 stainless steel casting be welded?
Yes, but after welding, 316 stainless steel casting must undergo high-temperature solution treatment and rapid water quenching to ensure that surface carbides are completely removed, thereby reducing the risk of intergranular corrosion and cracking.
Q5. Are there other grades of stainless steel used in investment casting?
Yes, there are many types of stainless steel. For austenitic stainless steel, there are 304, 304L, 316, and 316L. And there are four other categories of stainless steel by properties: martensitic, duplex, precipitation-hardening, and ferritic. If you want to know more, please click “An Ultimate Guide for Different Types of Stainless Steel”.
