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What's the difference between 304, 304L and 304H?

Attention:     Issuing time:2019-12-02 09:02

What's the difference between 304, 304L and 304H stainless steel?
 
In fact, the content of chromium and nickel is 304 stainless steel, which contains 18% chromium (CR) and 8% nickel (Ni), but the main difference is the carbon content.
 
 
Chemical composition (%) of 304, 304L and 304H 
stainless steel
 
Type C Mn P S Si Cr Ni N
304 ≤0.08 ≤2.00 ≤0.045 ≤0.030 ≤0.75 18.0-20.0 8.0-10.5 ≤0.10
304L ≤0.03 ≤2.00 ≤0.045 ≤0.030 ≤0.75 18.0-20.0 8.0-12.0 ≤0.10
304H 0.04-0.10 ≤2.00 ≤0.045 ≤0.030 ≤0.75 18.0-20.0 8.0-10.5  
 

304L stainless steel
304L is a kind of 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 better 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 higher, the molten steel is thick and the price is more expensive.
 

304H stainless steel
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%. Carbide is the strengthening phase, especially the high temperature strength is better than pure austenite.
 
Among them, 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. Different carbon content also leads to different prices, or different requirements for different purposes.
 
 
 
Mechanical properties of 304, 304L and 304H 
stainless steel
 
Type Tensile strength Yield strength Elongation Hardness
Brinell hardness Rockwell hardness
304 ≥515 ≥205 ≥40 ≥201 ≥92
304L ≥485 ≥170 ≥40 ≥201 ≥92
304H ≥515 ≥205 ≥40 ≥201 ≥92
 
In addition, it can be judged from these two lists that the view that 304L can be used instead of 304 is wrong. Whether it can be used is related to the use situation. Moreover, according to the regulations of the code, we have no right to carry out "material substitution". Only the original design department can carry out "material substitution". Please remember this.



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