In fact, according to the content of chromium and nickel, they are all 304 stainless steel, containing 18% chromium (CR) and 8% nickel (Ni), but the main difference lies in the carbon content.
Chemical composition (%) of 304, 304L and 304H
304L is an ultra-low carbon stainless steel with carbon content below 0.03%, which can avoid intergranular corrosion. In theory, the effect of stress corrosion resistance is stronger than that of 304, but the effect is not obvious in practical application. The purpose of reducing carbon is the same as adding titanium, but the smelting cost of 321 with titanium is high, the molten steel is thick and the price is expensive.
H in 304H refers to high temperature, and high carbon content is the guarantee of high temperature strength. GB150 requires that when austenitic steel is used above 525 ℃, the carbon content shall not be less than 0.04%, and carbides are strengthening phase, especially the high temperature strength is better than that of pure austenite.
Among the three, the highest carbon content is 304H, the lowest is 304L, and the carbon content of 304 stainless steel is between the two. The higher the carbon content, the worse the corrosion resistance of stainless steel, and the easier it is to rust. The difference in carbon content also leads to the difference in the price. In that sentence, the requirements are different for different purposes.
