What Is The Difference Between 308 And 316 Welding Rod?

308 and 316 welding rods (often labeled ER308 and ER316 under AWS A5.9 standards) are two of the most widely used stainless steel filler metals, but their unique compositions and properties make them suited for distinct applications. Understanding their differences is critical for ensuring weld integrity, corrosion resistance, and long-term performance in various industries.
1. Chemical Composition: The Core Distinction
The primary difference between 308 and 316 welding rods lies in their alloying elements, which directly influence their performance:
• ER308: Based on 304 stainless steel, its composition typically includes 18–20% chromium (Cr) and 8–10.5% nickel (Ni), with trace amounts of carbon (≤0.08%) and manganese (≤2%). It contains no molybdenum-a key element for enhanced corrosion resistance in harsh environments.
• ER316: Derived from 316 stainless steel, it retains similar chromium (16–18%) and nickel (10–14%) levels but adds 2–3% molybdenum (Mo). This molybdenum is a "corrosion fighter," specifically boosting resistance to pitting, crevice corrosion, and attack by chloride-rich fluids. It also has slightly higher silicon (≤0.75%) for improved weld fluidity.
2. Compatible Base Metals
Each rod is designed to match the chemistry of specific stainless steel base metals, ensuring the weld metal performs similarly to the parent material:
• ER308: Ideal for welding 304 and 304L stainless steels-the most common austenitic stainless steels, used in general-purpose applications. It also works for joining 301, 302, or 305 alloys, as its chromium-nickel balance mirrors these grades to prevent carbide precipitation (a cause of intergranular corrosion).
• ER316: Formulated to weld 316 and 316L stainless steels, which are molybdenum-alloyed for harsh environments. It is also suitable for 317 alloys (higher molybdenum) and can be used to join 304 to 316 when corrosion resistance of the weld needs to match the 316 base metal.
3. Corrosion Resistance: A Critical Divide
The presence of molybdenum in 316 rods creates a stark contrast in corrosion performance:
• ER308: Offers good resistance to mild acids, atmospheric corrosion, and freshwater exposure. However, it is vulnerable to pitting and crevice corrosion in chloride-rich environments (e.g., saltwater, road de-icing salts, or industrial chemicals like bleach). It performs well in dry, clean, or low-chloride settings but struggles in "wet" or aggressive conditions.
• ER316: The molybdenum in ER316 forms a protective oxide layer that resists chloride ions, making it far more durable in harsh environments. It withstands seawater, brines, sulfuric acid (dilute concentrations), and industrial solvents-settings where 308 would corrode rapidly. For example, in a 5% NaCl (saltwater) immersion test, 316 welds showed 70% less pitting than 308 welds after 1,000 hours.
4. Mechanical Properties
Both rods produce welds with excellent ductility and toughness, but 316 edges out in certain conditions:
• Tensile Strength: ER308 welds typically have a tensile strength of 80,000–90,000 psi, while ER316 welds range from 85,000–95,000 psi-slightly higher due to molybdenum's strengthening effect.
• High-Temperature Performance: ER316 retains strength better at elevated temperatures (up to 1,500°F/815°C) than ER308, making it suitable for high-heat applications like exhaust systems or industrial furnaces.
• Ductility: Both offer elongation rates of 35–45%, ensuring good weld flexibility and resistance to cracking under stress.
5. Applications: Where to Use Each Rod
Their distinct properties drive divergent use cases:
• ER308: Thrives in general-purpose, low-corrosion environments, such as:
◦ Food processing equipment (e.g., stainless steel tanks, conveyors)
◦ Architectural features (handrails, facades)
◦ Freshwater piping or appliances (dishwashers, refrigerators)
• ER316: Excels in aggressive or high-chloride settings, including:
◦ Marine hardware (boat hulls, offshore platforms)
◦ Chemical processing tanks and pipelines (handling acids, salts)
◦ Medical equipment (sterilization chambers, surgical tools)
◦ Coastal infrastructure (bridges, seawater intake systems)
6. Welding Considerations
While both rods are compatible with TIG (GTAW) and MIG (GMAW) processes, minor differences in handling exist:
• Heat Input: ER316 may require slightly higher heat input than ER308 to ensure full fusion, especially in thick sections, due to its molybdenum content (which slightly increases melting point).
• Protection Gas: Both perform best with pure argon (99.99%) or argon-helium mixes (for thicker material) to prevent oxidation of chromium.
• Post-Weld Treatment: Neither typically requires post-weld annealing for general use, but ER316 may benefit from passivation (with nitric acid) in critical corrosion applications to restore its protective oxide layer.
Conclusion: Choosing the Right Rod
The choice between 308 and 316 welding rods hinges on the environment the weld will face:
• Use ER308 for cost-sensitive, low-corrosion applications with 304-series base metals.
• Use ER316 when chloride exposure, chemical resistance, or high-temperature strength is critical, particularly with 316-series base metals.
Mismatching rods (e.g., using 308 on 316 in marine settings) can lead to premature weld failure, while overspecifying (using 316 where 308 suffices) increases costs unnecessarily. Always align the filler metal with the base metal's chemistry and the application's environmental demands.