What are the heat treatments for stainless steel? Are different types of stainless steel heat treated differently?

1 ferritic stainless steel

The main alloying element is Cr, or a small amount of stable ferrite elements are added, such as Al, Mo, etc., and the structure is ferrite. The strength is not high, and the properties cannot be adjusted by heat treatment. 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

Contains high Cr, generally greater than 18%, and contains about 8% Ni. Some use Mn instead of Ni. In order to further improve corrosion resistance, elements such as Mo, Cu, Si, Ti, Nb, etc. must be added. It does not undergo phase change when heated and cooled, and cannot be strengthened by heat treatment. It has low strength, high plasticity and high toughness. It has strong corrosion resistance to oxidizing media, and after adding Ti and Nb, it has better resistance to intergranular corrosion.

3 martensitic stainless steel

Martensitic stainless steel mainly contains 12~18% Cr, and the amount of C is adjusted as needed, usually 0.1~0.4%. When making tools, C can reach 0.8~1.0%. Some to improve the anti-tempering stability, Add Mo, V, Nb, etc. After heating at high temperature and cooling at a certain speed, the structure is basically martensite. Depending on the difference in C and alloy elements, some may contain a small amount of ferrite, residual austenite or alloy carbides. Phase changes occur upon heating and cooling, so the tissue structure and morphology can be adjusted over a wide range, thereby changing properties. The corrosion resistance is not as good as austenite, ferrite and duplex stainless steel. It has good corrosion resistance in organic acids and poor corrosion resistance in media such as sulfuric acid and hydrochloric acid.

4 Ferritic-Austenitic Duplex Stainless Steel

Generally, the Cr content is 17~30%, and the Ni content is 3~13%. In addition, Mo, Cu, Nb, N, W and other alloying elements are added, and the C content is controlled to be very low. Depending on the proportion of alloying elements, some are ferrite. Mainly, some are mainly austenite, forming duplex stainless steel with two phases existing at the same time. Because it contains ferrite and strengthening elements, after heat treatment, its strength is slightly higher than that of austenitic stainless steel, and its plasticity and toughness are good. Basically, heat treatment cannot be used to adjust its properties. It has high corrosion resistance, especially in Cl-containing media and seawater, and has good resistance to pitting corrosion, crevice corrosion, and stress corrosion.

5 Precipitation hardened stainless steel

The composition is characterized by that in addition to elements such as C, Cr, and Ni, it also contains elements such as Cu, Al, and Ti that can precipitate over time. Mechanical properties can be adjusted through heat treatment, but its strengthening mechanism is different from martensitic stainless steel. Because it relies on precipitation and 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.