What do 20 1, 202, 204, 30 1, 304 in steel mean?

Stainless steel model, precipitation hardening stainless steel:

1, 20 1, 202, 204 belong to 200 series (Cr, Mn, Ni).

2.30 1 and 304 both belong to 300 series: chromium-nickel austenitic stainless steel.

30 1: Good ductility, used for molding products. It can also be rapidly hardened by machining. Good weldability. Wear resistance and fatigue strength are better than 304 stainless steel.

304: universal model; Namely 18/8 stainless steel. Products such as: corrosion resistant containers, tableware, furniture, railings, medical equipment. The standard components are 18% chromium and 8% nickel. It is a non-magnetic stainless steel, and its metallographic structure will not be changed by heat treatment.

Extended data:

Stainless steel is usually divided into martensite steel, ferrite steel, austenite steel, austenite-ferrite (duplex) stainless steel and precipitation hardening stainless steel. In addition, it can also be divided into chromium stainless steel, chromium nickel stainless steel and chromium manganese nitrogen stainless steel. There is also a special stainless steel for pressure vessels, GB245 1 1_2009_ Stainless steel plate and strip for pressure equipment.

The corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, the carbon content of most stainless steels is low, and the maximum carbon content does not exceed 1.2%. The ωc (carbon content) of some steels is even lower than 0.03% (such as 00Cr 12). The main alloying element in stainless steel is chromium. Only when Cr content reaches a certain value can steel have corrosion resistance.

Generally, the Cr content of stainless steel is at least 10.5%. Stainless steel also contains elements such as nickel, titanium, manganese, nitrogen, niobium, molybdenum, silicon and copper.

References:

Baidu encyclopedia-stainless steel