304 stainless steel is an extremely common and widely used austenitic stainless steel, also recognized as the quintessential “18-8 stainless steel” (containing approximately 18% chromium and 8% nickel).
📌 Basic Characteristics:
① Excellent Corrosion Resistance: It exhibits excellent corrosion resistance against atmospheric air, common acids, alkalis, salts, and other media, making it a top choice for the food, medical, and chemical industries.
② Good Heat Resistance: It maintains its strength and oxidation resistance at high temperatures and is commonly used in boilers, barbecue grills, and other applications.
③ Low-Temperature Strength: It maintains excellent mechanical properties even in low-temperature environments (such as refrigeration equipment).
④ Excellent Processability: It is easily adaptable to forming processes such as stamping, bending, and stretching.
⑤ Non-Magnetic: It is non-magnetic or weakly magnetic in its solid solution state. Note: After cold working (such as cutting and stamping), some of the microstructure may transform to martensite, exhibiting weak magnetism.
⑥ Attractive Surface: Polishing, frosting, and other treatments can achieve a bright, attractive surface.
📊 Chemical Composition (Typical %)
C: ≤0.08%, Si: ≤1.0%, Mn ≤2.0%, P ≤0.045%, S ≤0.03%, 18.0 ≤ Cr ≤20.0%, 8.0 ≤ Ni ≤11.0
Chromium (Cr) is a key element in forming a passive film and providing corrosion resistance; nickel (Ni) stabilizes the austenitic structure, imparting excellent toughness and workability.
🏭 Main Applications
Due to its comprehensive properties, 304 stainless steel is used in nearly every application:
① Kitchenware and tableware: pots, bowls, ladles, basins, spoons, chopsticks, sinks, etc.
② Food industry: Brewing, milk, food processing equipment, and pipelines.
③ Medical equipment: Surgical instruments and medical utensils.
④ Home building materials: Door and window accessories, handrails, railings, decorative pipes, and curtain walls.
⑤ Chemical industry: Storage tanks, containers, and heat exchangers.
⑥ Automotive accessories: exhaust pipes (parts).
⑦ Consumer goods: thermoses, watch cases, etc.
🔬 Relationship with ER304 welding wire
As we discussed previously, ER304 stainless steel welding wire is specifically designed for welding 304 stainless steel and similar grades of base metal. They share similar chemical compositions, ensuring that the weld metal’s properties match those of the base metal, resulting in strong, corrosion-resistant weld joints.
⚠️ Important Considerations: Intergranular Corrosion
▶Problem: When 304 stainless steel is held in the 450°C-850°C temperature range (such as during welding or slow cooling), carbides precipitate along grain boundaries, resulting in chromium depletion near the grain boundaries and making it susceptible to intergranular corrosion in corrosive media.
▶Solution:
① Choose a low-carbon grade: Use 304L stainless steel (carbon content ≤0.03%) to fundamentally reduce chromium carbide precipitation.
② Solution treatment: After welding, heat the workpiece to 1040°C – 1150°C, then rapidly cool (water quench) to redissolve the precipitated carbides.
③ Control the welding process: Use a low-energy-density, rapid-cooling welding method to minimize dwell time in sensitive temperature zones.
Why use 304 instead of 308
This is a very common and crucial issue in welding practice. A more accurate description of “using 304 instead of 308” is “using ER304 welding wire to weld 304 stainless steel base metal that should be welded with ER308.”
The following is a detailed explanation of the reasons for this substitution and the risks involved:
① Availability and Cost:
▶ As a versatile material, ER304 welding wire is more widely available and easier to find at hardware stores or smaller suppliers.
▶ In some cases, ER304 may be slightly less expensive than ER308.
② Misconception: “Similar composition is sufficient”:
▶ In terms of chemical composition, ER304 and ER308 are very similar, both being “18-8” steel grades. This can easily give the impression that they are similar.
▶ Many people believe that using welding wire with essentially the same composition to weld the same base metal is perfectly reasonable.
③ “Seems OK” in Non-Critical Applications:
▶For some non-structural, non-corrosive, and non-critical decorative welds, welding ER304 with ER308 may not present any immediate issues. This gives some people false confidence that it’s a viable alternative.
⚠️ Why is this not recommended professionally? (Risks of Using ER304 Instead of ER308)
The fundamental reason is: ER308’s composition is specifically optimized for welding 304 stainless steel, while ER304 simply “happens” to share the same composition as the base material.
The core difference between the two lies in a subtle but crucial difference in chemical composition:
ER304: Cr ≈ 18.20%, Ni ≈ 9.58%
ER308: Cr ≈ 20.0%, Ni ≈ 10.0%
See the difference? ER308 has slightly higher chromium and nickel contents than ER304. This isn’t accidental; it stems from a crucial engineering consideration: compensating for alloy burnout during welding.
Alloy burnout: Under the high temperature of the arc, some alloying elements (especially chromium) in the weld pool will oxidize and burn away. If not compensated, the actual composition of the weld metal will be lower than that of the base metal.
▶The design logic of ER308: The chromium and nickel content is intentionally increased so that after weld burnout, the chemical composition of the weld center is stabilized within the “18-8” composition range required for 304 stainless steel, thereby ensuring its corrosion resistance and mechanical properties.
▶Problems with ER304: If ER304 is used for welding, the chromium and nickel content in the weld center after weld burnout may fall below the standard, resulting in reduced performance.
🚨 Specific Risk Consequences
1. Reduced Corrosion Resistance: This is the greatest risk. Rust may first appear in the weld area, especially in environments sensitive to intergranular corrosion (such as chemical, food, and marine environments). The weld can become the “Achilles’ heel” of the entire structure.
2. Inadequate Mechanical Properties: The strength and toughness of the weld may not meet design standards, posing a safety hazard in load-bearing or vibration-prone structures.
3. Non-Compliance with Standards and Regulations: In formal manufacturing, pressure vessel fabrication, piping engineering, and other fields, welding materials must comply with specific standards and regulations (such as AWS). Using incompatible welding wire will result in acceptance failure.
💎 Summary and Recommendations
Core Principle: ER308 is a welding consumable tailored for welding 304 stainless steel, while ER304 is simply another type of 304 stainless steel. To use an analogy: it’s like using ordinary fabric to patch a piece of high-end clothing. While the colors may appear similar, a professional tailor will use specially matched wire and fabric to ensure the patch’s strength, color durability, and overall aesthetic. Substituting ordinary fabric may not be noticeable in the short term, but after a few washes, color differences, shrinkage, or cracking may occur.
Conclusion: While substituting ER304 for ER308 may be acceptable in some minor applications, from a technical and professional perspective, it is strongly recommended to always use ER308 welding wire when welding 304 stainless steel to ensure weld quality, durability, and safety.