Both martensite and Austenite are a kind of microstructure of steel during heat treatment. The code name of Austenite is gamma, face-centered cubic structure, the gap solid solution of carbon in γ-Fe, and the maximum dissolved carbon content is 2.11% (1148 °C). The Austenite with eutectic composition is rapidly (the cooling rate is greater than the critical cooling rate of quenching) to the martensite transformation zone, and the martensite transformation occurs. In the process of martensite transformation, only the lattice reconstruction of iron occurs, and the iron and carbon atoms do not spread. There is no change in concentration, only from face-centered cubic lattice to body-centered cubic lattice, so martensite and Austenite have the same chemical composition. However, because martensite is a supersatured solid solution of carbon in α-Fe, its strength and hardness are very high. Martensite can be a kind of microstructure of steel at normal room temperature, but Austenite is only a kind of microstructure in the process of heating. Different microstructure can be obtained by cooling down at different rates, and not just one kind of martensite. Martensite has hardness, while Austenite has no hardness because it is hot.
Austenite is basically Austenite structure in metallography, and the general grade begins with three words for Austenite structure, such as 304316, which has good plastic corrosion resistance, and martensite is the main metallographic structure. Generally begins with 4 words such as 410 (except 430, for Ferrite tissue). The properties of maraging stainless steel can be changed by heat treatment, such as hardness, generally used as cutting tool, products with high hardness requirements, corrosion resistance is not as good as Austenite, duplex stainless steel refers to the two kinds of metallographic structure in metallographic phase. The properties have two kinds of microstructure characteristics, corrosion resistance, high temperature resistance and so on. When the two kinds of metallography reach 50% each by heat treatment, the performance is the best.