These three materials of stainless steel 304, 304H and 304L are often used in valve industry. Among three, 304 is the most common one, like SS304 ball valve, SS304 gate valve, SS304 globe valve, SS304 check valve we often see.

In fact, according to the content of chromium and nickel, they all belong to stainless steel 304, since they all contains 18% chromium (Cr) and 8% nickel (Ni). The main difference lies in carbon content.

304L is an ultra-low carbon stainless steel. The carbon content is below 0.03%, which can avoid intergranular corrosion. In theory, its ability of stress corrosion resistance is stronger than 304, but it is not that distinct in practical applications. The purpose of reducing carbon and adding titanium is the same, but 321 with titanium added has a higher smelting cost, thicker molten steel, and likewise more expensive.

H in 304H refers to high temperature. High carbon content means the guarantee of high strength in high temperature. GB150 requires austenitic steel to be used above 525 degrees, and the carbon content not less than 0.04%.

Among the three, the highest carbon content is 304H, the lowest carbon content is 304L, and the carbon content of stainless steel 304 is between the two. The higher the carbon content, the worse the corrosion resistance of stainless steel and the more rusty it is.