Stainless Steel Rounds

Give the grade, the diameter, the length per bar and the number of bars. The two grades are different steels, not two qualities of one steel. 304 is the 18/8 austenitic chromium-nickel grade. 430 is a ferritic chromium grade with no nickel, made for decorative use, with good formability but lower corrosion and temperature resistance.^[2]

Neither grade here is the molybdenum grade, 316, which is the one known as marine grade for its higher resistance to chloride corrosion. If the part will sit in seawater or salt spray, say so on the requisition; the supplier may have to offer 316 bar from outside this group.^[2]

Ask for the inspection document (mill certificate) with the bars. JIS G 4303 refers to JIS G 0415 for steel inspection documents, so a supplier selling to that standard can provide one showing the grade and heat.^[1]

Seawater is a hard service for plain stainless. Atlas Steels’ technical note puts 304 as susceptible to pitting in seawater (about 20,000 mg/l chloride) above roughly 10 °C, with a safe chloride level of about 200 mg/l at warm ambient temperatures. 316 is more resistant but still marginal in seawater, and can be attacked in crevices. Stagnant liquid, deposits and contamination by mild steel make attack more likely.^[3]

A magnet tells the two grades apart. All ferritic grades, 430 among them, are attracted to a magnet. Austenitic grades such as 304 are not in the annealed condition, although 304 can become somewhat magnetic after cold work such as bending or drawing.^[4]