1. Different components：

Austenite is generally composed of equiaxed polygonal grains with twinning within the grains.

There are two types of martensitic structures. The medium and low carbon steel is quenched to obtain lath martensite. The Flat noodles martensite is composed of many bundles of thin Flat noodles with roughly the same size and approximately parallel arrangement, and the angle between each bundle of Flat noodles is relatively large; High carbon steel is quenched to obtain needle like martensite, which is in the shape of bamboo leaves or convex lenses. The needle like martensite is generally confined within the original austenite grains and forms an angle of 60 ° or 120 ° with each other.

2. Different physical characteristics:

Austenite has good plasticity, low strength, certain toughness, and no ferromagnetism.

Flat noodles martensite has high strength and hardness, good toughness, and can withstand a certain degree of cold working; Needle like martensite is hard and brittle, with no plastic deformation ability.

3. Different applications:

Martensitic stainless steelThe ability to weld in annealed, hardened, and tempered states, regardless of the original state of the steel, will result in a hardened martensitic zone near the weld bead after welding. The hardness of the heat affected zone mainly depends on the carbon content of the base metal. As the hardness increases, the toughness decreases, and this area becomes more prone to cracking. Preheating and controlling the interlayer temperature are the most effective methods to avoid cracking. To achieve optimal properties, post weld heat treatment is required.

austenitic stainless steelIt is the most common and widely used type of stainless steel, accounting for approximately 65-70% of the total stainless steel production. The most commonly used austenitic stainless steel is Fe Cr Ni alloy (i.e. AISI300 series in the United States); Fe Cr Ni Mn system (i.e. American AISI200 system); There are three types of special austenitic stainless steel.

The three-dimensional structure of martensite usually has plate or plate shape, but in metallographic observation (two-dimensional), it usually shows needle shaped, which is why it is usually described as needle shaped in some places. The crystal structure of martensite is a body centered tetragonal structure (BCT). Accelerated cooling in medium and high carbon steel can usually obtain this structure. High strength and hardness are one of the main characteristics of martensite in steel.

We have accumulated a lot of knowledge about the characteristics of martensitic transformation in steel, and have successively discovered that martensitic transformation also exists in certain pure metals and alloys, such as Ce, Co, Hf, Hg, La, Li, Ti, Tl, Pu, V, Zr, Ag Cd, Ag Zn, Au Cd, Cu Al, Cu Sn, Cu Zn, In Tl, Ti Ni, etc. The phase transformation products with basic characteristics belonging to martensitic phase transformation are widely referred to as martensite (see solid-state phase transformation).

PS:

The representative steel grades of martensitic stainless steel are 12Cr13, 20Cr13, 30Cr13, etc., while the representative steel grades of ferritic stainless steel are 10Cr17, 10Cr17Mo, etc.

The representative steel grade of austenitic stainless steel is 06 Cr19Ni10(304)、022Cr19Ni10(304L)、 06Cr17Ni12Mo2(316)、022Cr17Ni12Mo2(316L)、06Cr18Ni11Ti(321)。