The difference between various stainless steel

The attractiveness of stainless steel is its corrosion resistance and durability. However, in order to optimize the cost/performance ratio, it is necessary to understand what level of corrosion resistance is required in practical applications.

Therefore, the interval between scrubbing is affected by many factors. The main influencing factors are the requirements for reviewing the metallurgical structure: ferritic (F) stainless steel, martensitic (M) stainless steel, and austenite (A) Type stainless steel, austenitic-ferritic (AF) duplex stainless steel, austenitic-martensitic (AM) duplex stainless steel, and precipitation hardened (PH) stainless steel.
Ferritic stainless steel has an internal microstructure of ferrite with a chromium content of 11.5% to 32.0%. With the increase of chromium content, its acid resistance is also improved. After adding molybdenum (Mo), it can improve acid corrosion resistance and stress corrosion resistance. Such national standards for stainless steel are 00Cr12, 1Cr17, 00Cr17Mo, 00Cr30Mo2 and so on.

Martensitic stainless steel has a microstructure of martensite. The mass fraction of chromium in this kind of steel is 11.5%~18.0%, but the mass fraction of carbon up to 0.6%. The increase in carbon content increases the strength and hardness of the steel. The small amount of nickel added to this type of steel promotes the formation of martensite while increasing its corrosion resistance. This type of steel has poor weldability. Steels listed in national standard grades include 1Cr13, 2Cr13, 3Cr13, and 1Cr17Ni2.

Austenitic stainless steels have austenitic microstructure. It is formed by adding appropriate nickel (nickel mass fraction of 8% to 25%) in high-chromium stainless steel with stainless steel in austenitic structure. Austenitic stainless steels are based on Cr18Ni19 iron-based alloys. Based on this, they develop into the chromium-nickel austenitic stainless steel series shown in Fig. 1-2.

Austenitic stainless steels generally belong to corrosion resistant steels and are the most widely used type of steel. Among them, 18-8 type stainless steels are the most representative. They have good mechanical properties and are convenient for machining, stamping and welding. In the oxidizing environment with excellent corrosion resistance and good heat resistance. However, it is particularly sensitive to the medium containing chlorine ions (CL-) in the solution and is prone to stress corrosion. Type 18-8 stainless steel is divided into three grades according to the carbon content of its chemical composition: general carbon content (Wc ≤ 0.15%) low carbon grade (Wc ≤ 0.08%) and ultra-low carbon grade (Wc ≤ 0.03% ). For example, the three steel plates of 1Cr18Ni9Ti, 0Cr18Ni9, and 00Cr17Ni14M02 in China's national standards belong to the above three grades. Many countries in the world feel that nickel reserves are in short supply. In order to save nickel, as early as in the 40s and 50s, the world began to replace part of nickel in 18-8 stainless steel with manganese and nitrogen. The steel grades developed and included in the national standards include 1Cr17Mn6Ni5N and 0Cr19Ni9N.
The microstructure of austenitic-ferritic stainless steel is austenite plus ferrite. Stainless steel with a volume fraction of ferrite of less than 10% is a steel grade developed on the basis of austenitic steel.

Precipitation-hardening stainless steels can be classified into three types according to their microstructure: precipitation-hardened semi-austenitic, precipitation-hardened martensitic, and precipitation-hardened austenitic stainless steels. Included in our national standard steel grades are 0Cr17Ni7A, 0Cr17Ni4Cu4Nb, and 0Cr15Ni7M02Al, which are precipitation-hardened semi-austenitic stainless steels. The microstructure of the steel is characterized by austenite plus ferrite with a volume fraction of 5% to 20% in the solution or annealed state. This steel undergoes a series of heat treatment or mechanical deformation treatment to transform austenite into martensite, and then it is hardened by aging precipitation to achieve the required high strength. This steel has good forming properties and good weldability, and can be used as an ultra-high strength material in the nuclear industry, aerospace and aerospace industries.

Posted on