1. Ferritic stainless steel: The main alloying element is Cr, or a small number of stable ferrite elements such as Al, Mo, etc. are added, and the structure is ferrite. The strength is not high, and the performance cannot be adjusted by heat treatment methods. It has a certain plasticity and is relatively brittle. It has good corrosion resistance in oxidizing media (such as nitric acid) and poor corrosion resistance in reducing media.
2. Austenitic stainless steel: It contains a high Cr content, generally greater than 18%, and contains about 8% Ni. Some use Mn instead of Ni. In order to further improve corrosion resistance, Mo, Cu, Si, Ti, Nb, and other elements must be added. No phase change occurs during heating and cooling, and it cannot be strengthened by heat treatment methods. It has low strength, high plasticity, and high toughness. It has strong corrosion resistance to oxidizing media and has good resistance to intergranular corrosion after adding Ti and Nb.
3. Martensitic stainless steel: Martensitic stainless steel mainly contains 12~18% Cr, and the amount of C is adjusted as needed, generally 0.1~0.4%. For tool making, C can reach 0.8~1.0%. Some add Mo, V, Nb, etc. to improve tempering stability. After high-temperature heating and cooling at a certain speed, the structure is basically martensite. Depending on the difference in C and alloying elements, some may contain a small amount of ferrite, residual austenite, or alloy carbide. Phase change occurs during heating and cooling, so the structure and morphology can be adjusted in a wide range, thereby changing the performance. The corrosion resistance is not as good as austenitic, ferritic, and duplex stainless steel. It has better corrosion resistance in organic acids, and poor corrosion resistance in sulfuric acid, hydrochloric acid, and other media.
4. Ferrite-austenite duplex stainless steel: generally contains 17~30% Cr, 3~13% Ni, and alloying elements such as Mo, Cu, Nb, N, and W are added. The C content is controlled at very low. According to the different proportions of alloying elements, some are mainly ferrite, and some are mainly austenite, forming duplex stainless steel with two phases coexisting. Because it contains ferrite and strengthening elements, after heat treatment, the strength is slightly higher than that of austenitic stainless steel, and the plasticity and toughness are good. Basically, the performance cannot be adjusted by heat treatment. It has high corrosion resistance, especially in Cl-containing media and seawater, and has good resistance to pitting, crevice corrosion, and stress corrosion.
5. Precipitation hardening stainless steel: The composition characteristics are that in addition to C, Cr, Ni, and other elements, it also contains Cu, Al, Ti, and other elements that can precipitate precipitates. The mechanical properties can be adjusted by heat treatment, but its strengthening mechanism is different from that of martensitic stainless steel. Since it relies on precipitation phase strengthening, C can be controlled very low, so its corrosion resistance is better than martensitic stainless steel and equivalent to Cr-Ni austenitic stainless steel.
Post time: Feb-06-2025