Humans have a long history of application and research in steel, but until the invention of the Bayesian steelmaking process in the 19th century, steel production was a costly and inefficient job. Today, steel is one of the most used materials in the world for its low price and reliable performance. It is also an indispensable component of the construction industry, manufacturing industry and people’s daily lives. It can be said that steel is the material basis of modern society. We commonly use four types of steel.Now we will discuss the four types of steel.
Steel I（carbon steel）： Q235、20#、20g、20R、L210、S205、HP265.
Carbon containing less than 1.35% (0.1%-1.2%), except for iron, carbon and limited impurities such as silicon, manganese, phosphorus, sulfur, etc., does not contain other alloying elements. The performance of carbon steel depends mainly on the carbon content.
As the carbon content increases, the strength and hardness of the steel increase, and the ductility, weldability and weldability decrease. Compared with other steels, carbon steel is the earliest use, low cost, wide performance range and maximum dosage. Applicable to medium, such as water, steam, air, hydrogen, ammonia, nitrogen and petroleum products, with nominal pressure PN≤32.0MPa and temperature -30-425°C. Commonly used grades are WC1, WCB, ZG25 and high quality steel 20, 25, 30 and low alloy structural steel 16Mn.
Steel II (low-alloy steel):16MnR、12Cr1MoV、20MnMoD、S240、L245、HP295.
Low alloy steel is relative to carbon steel. On the basis of carbon steel, in order to improve one or several properties of steel, one or several alloying elements are intentionally added to the steel. The amount of alloy added exceeds. When the normal content of the normal production method of carbon steel is used, the steel is referred to as an alloy steel.
Standard martensitic stainless steels are: 403, 410, 414, 416, 416 (Se), 420, 431, 440A, 440B, and 440C, which are magnetic. The corrosion resistance of these steels comes from “chromium”, which ranges from 11.5 to 18%. The higher the chromium content, the higher the carbon content of the steel. To ensure the formation of martensite during heat treatment, we rarely consider the applications of 440 stainless steels. And the melt filler metal of the 440 type component is not easy to obtain.
Ferritic stainless steel (400 series) contains 15% to 30% chromium and has a body-centered cubic crystal structure. These steels generally do not contain nickel, and sometimes contain a small amount of elements such as Mo, Ti, Nb, etc. These steels have the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent resistance to stress corrosion, etc. Parts that are corroded by water vapor, water, and oxidizing acids.
The price of ferritic stainless steel is not only relatively low and stable, but also has many unique features and advantages. Ferritic stainless steel is an excellent alternative to many applications where austenitic stainless steels (300 series) were originally considered to be used. Ferritic stainless steel does not contain nickel, the main element is chromium (>10%) and iron, which is a particularly corrosion-resistant element of stainless steel, and its price is relatively stable.
Austenitic stainless steel refers to stainless steel having an austenite structure at normal temperature. When the steel contains about 18% Cr, 8%-10% Ni, and 0.1% C, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes 18Cr-8Ni steel and Cr-Ni, Cr ,Ni Mo, Cu, Si, Nb and Ti.
Duplex Stainless Steel refers to about 50% of ferrite and austenite, and generally requires less than 30% of stainless steel. With lower C content, the Cr content is 18% to 28%, and the Ni content is 3% to10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N.
Compared with austenitic stainless steel, it has high strength and resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting resistance and is also a nickel-saving stainless steel.