In fact, all three are 304 stainless steel based on their chromium-nickel content, which comprises 18% chromium (Cr) and 8% nickel (Ni). However, the main difference is in the amount of carbon present.
Chemical composition table (%) of 304, 304L, 304H
| Item | W | Mn | P | s | Yes | Cr | No | N |
| 304 | 0.08 | two | 0.045 | 0.03 | 0.75 | 18-20 | 8-10.5 | 0.1 |
| 304L | 0.03 | two | 0.045 | 0.03 | 0.75 | 18-20 | 8-12 | 0.1 |
| 304H | 0.04-0.1 | two | 0.045 | 0.03 | 0.75 | 18-20 | 8-10.5 |
Note: Unspecified range is less than or equal to.
In reality, all three are 304 stainless steel based on their chromium-nickel composition, which contains 18% chromium (Cr) and 8% nickel (Ni). The distinction is in the amount of carbon present.
304L is an ultra-low carbon stainless steel with carbon content reduced to less than 0.03%, which helps prevent intergranular corrosion and potentially increases resistance to stress corrosion cracking. However, this effect is not always noticeable in practice.
The goal of reducing carbon is similar to adding titanium, but 321 with titanium is more expensive to produce, resulting in thicker, more expensive steel.
The “H” in 304H stands for high temperature. High carbon content improves high temperature resistance, as GB150 requires austenitic steel used at 525°C or higher to have a carbon content of no less than 0.04%, with carbides as a reinforcing phase and improved resistance to high temperatures compared to pure austenitic steel.
Of the three, 304H has the highest carbon content, 304L has the lowest, and 304 falls somewhere in between. The higher the carbon content, the worse the corrosion resistance of stainless steel and the more likely it is to rust.
This difference in carbon content also leads to price differences and varying requirements for different applications.
Table of mechanical properties of 304, 304L, 304H
| Item | Tensile strength | Yield Strength | 50mm elongation | Toughness | Cold bending | |
|---|---|---|---|---|---|---|
| MPa | MPa | Brinell | Rockwell | |||
| 304 | >515 | ≥205 | ≥40 | ≥201 | ≥92 | no requirements |
| 304L | >485 | ≥170 | ≥40 | ≥201 | ≥92 | no requirements |
| 304H | ≥515 | ≥205 | ≥40 | ≥201 | ≥92 | no requirements |
Note: Yield limit refers to the 0.2% yield limit.
It is important to note that the idea that 304L can be used instead of 304 is incorrect. The suitability of the material depends on the application and cannot be determined without considering the relevant rules and regulations. Only the original design department has the authority to make changes, and this must be kept in mind.
