What is the Meaning of L and H in 304 Stainless Steel Pipe?

What is the difference between 304, 304H and 304L? They are 304 stainless steel according to the content of chromium and nickel, and the composition contains 18% chromium (Cr) and 8% nickel (Ni), but the main difference is the carbon content.

304L is an ultra-low carbon stainless steel. The carbon content is less than 0.03%, which can avoid corrosion. In theory, the effect of stress corrosion resistance is stronger than 304, but it is not obvious in practical applications. The purpose of reducing carbon and adding titanium is the same, but the smelting cost of titanium-added 321 is higher, the molten steel is thick, and the price is more expensive.

The H in 304H refers to high temperature. High carbon content is the guarantee of high temperature strength. GB150 requires that when austenitic steel is used above 525 degrees, the carbon content should not be less than 0.04%. Carbides are strengthening phases, especially high temperature strength. Better than pure austenite.

The highest carbon content is 304H in them, the lowest carbon content is 304L, and the carbon content of 304 stainless steel is in the middle. The higher the carbon content, the worse the corrosion resistance of stainless steel and the easier to rust. The difference in carbon content causes difference price .