What Are The Characteristics Of Martensitic Stainless Steel Materials?

What are the characteristics of martensitic stainless steel materials?

Martensitic stainless steel is a stainless steel with a martensite structure as its matrix, which is magnetic and whose mechanical properties can be adjusted through heat treatment. There are two main types of martensitic stainless steel: 013 and Cr17. Commonly used martensitic stainless steels include 12Cr13, 20Cr13, 30Cr13, 40Cr13 and 14Cr17Ni2. The role of chromium in steel is multifaceted, such as improving the strength and hardenability of steel, but its main role is to improve the corrosion resistance of steel. The corrosion resistance of steel is closely related to the chromium content in the steel. Only when the chromium content (mass fraction) is greater than 12%, can the electrode potential of the steel matrix be significantly increased, thereby improving the corrosion resistance of steel forgings. Since chromium can significantly improve the hardenability of steel, when this type of steel is heated to an austenite state and air-cooled, even small-section workpieces can obtain a martensitic structure. Moreover, as the carbon content in steel increases, the strength, hardness and wear resistance increase. The main reason is that carbon and chromium form carbides, which reduces the chromium content of the matrix. Martensitic stainless steel has a strong tendency to harden and is prone to cold cracks. In areas where the welded joint is heated above 1150°C, the grain size increases significantly. Too fast or too slow cooling rates may cause embrittlement of the joint and may also cause Embrittlement at 475°C, less tendency to intergranular corrosion.

The characteristics of martensitic stainless steel are obviously different from those of ferritic stainless steel and austenitic stainless steel. Martensitic stainless steel transforms into austenite when heated to high temperature, and austenite transforms into martensite structure after rapid cooling. Martensitic stainless steel forgings have an obvious phase transformation point and can be strengthened by quenching. They have high chromium content and good hardenability. Their hardness, strength and toughness can be adjusted within a wide range during tempering. Moreover, high carbon martensitic stainless steel has higher hardness, so it can be used as both structural steel and tool steel.

Decarburization of forgings during the heating process will promote the formation of ferrite, so decarburization on the surface of forgings should be reduced to a minimum. There are no special requirements for the deformation amount of martensitic stainless steel in the final fire. This type of steel is prone to cracking after forging. The reason is that martensite and carbide structures appear during air cooling after forging, and the internal stress is large. Therefore, cooling must be done slowly after forging, usually in a sand pit at 200°C. Or slow cooling in the slag, isothermal annealing must be carried out in time after taking out the sand pit to prevent cracking. Martensitic stainless steel, especially Cr13 martensitic stainless steel, is low in price, so it is widely used in less corrosive media (such as water vapor) and under conditions that require high mechanical properties.