Stainless Steel Grade 304 vs 304L – Austral Wright Metals
Product Data Sheet – Stainless Steel
Grades 304 vs 304L
Grade 304L is used in welded sections of about 5mm and thicker. When comparing 304 vs 304L stainless steel, the lower carbon content (0.03% maximum) avoids the formation of coarse chromium carbide particles at grain boundaries due to extended times at elevated temperatures during welding. Grade 304 may suffer corrosion at grain boundaries due to sensitisation after welding at these gauges. Grade 304 is usually adequate at lighter gauges. There are several different national & international specifications for grade 304L. This note details some of these differences.
Time – Temperature – Transformation (TTT) Diagram 304 vs 304L
This diagram (for grade 304) shows curves which separate the area to the left, where sensitisation is negligible, from that to the right of the curve, where sensitisation is present. It can be seen that the critical cooling rate to avoid sensitisation depends strongly on the carbon content.
The critical time to avoid sensitisation is slightly different for each grade, but the form of the effect is the same.
Typical Applications For 304 and 304L Stainless Steel
304 stainless steel has a range of applications across different industries. Brewing and dairy equipment, evaporators, drums, barrels, heat exchangers, hospital equipment, refrigeration parts, chemical and food processing, shop fittings, benchtops, kitchens, kitchen utensils, sinks, wash troughs, urinals, handrails, dishwashers, clothes dryers, ovens, heating trays, air conditioning equipment, guttering and rain water goods, counters and display cabinets, hot and cold food bars, commercial oven hoods, beer barrels.
Grade 304 stainless steel contains 18% chromium, which makes it resistant to many corrosive environments. It is austenitic in structure because of the 8% nickel it contains. The very tough and ductile austenitic structure gives grade 304 excellent formability and fabrication characteristics.
In most applications, 304 stainless steel is used where its corrosion resistance gives long-lasting appearance and service life. The ease of cleaning and of maintaining a hygienic surface on the steel make it excellent for many purposes.
The low carbon version, 304L stainless steel, may be required for full corrosion resistance when sections thicker than about 6mm are welded. The version with guaranteed high carbon, 304H stainless steel, may be required for elevated temperature service, such as pressure vessels.
Grade 304 stainless steel has excellent corrosion resistance in many environments. Austral Wright Metals will be pleased to provide advice for specific applications.
304 stainless steel gives good service in atmospheric conditions, resisting most environments except for marine conditions, or where industrial pollution is heavy. Best appearance is maintained where the design allows even rain washing of the surface, or where dirt deposits are occasionally washed off the steel.
It has given excellent service in some situations in potable water. Pitting and crevice corrosion may occur at higher chloride content, and 200 ppm is accepted as the upper limit.
Grade 304 stainless steel is not generally used in seawater, due to the probability of crevice corrosion developing under sediments, precipitation and biofouling.