1. The 20 of 20# steel refers to the carbon content, and it is 0.2%, which belongs to low carbon steel. Steel can be divided into low carbon steel, medium carbon steel and high carbon steel. Low carbon steel – carbon content is generally less than 0.25%; medium carbon steel – carbon content is generally between 0.25 and 0.60%; high carbon steel – carbon content is generally greater than 0.60%. In addition to carbon (C) elements and a certain amount of silicon (Si) (generally no more than 0.40%) and manganese (Mn) (generally no more than 0.80%, higher up to 1.20%) alloying elements for deoxidation, steel Does not contain other alloying elements (except residual elements). Second, the higher the carbon content in steel, the worse the toughness, and the higher the carbon content in iron, the better the toughness. 1. Characteristics The steel belongs to high quality low carbon carbon steel, cold extrusion hardened steel. The steel has low strength, good toughness, plasticity and weldability. The tensile strength is 253-500MPa, and the elongation is ≥24%. Normalizing can promote the spheroidization of the steel, refine the bulk pro-eutectoid ferrite, and improve the cutting performance of the blank smaller than 160HBS. The process route of the steel mold parts is: blanking → forging die blanks → annealing → mechanical roughing → cold extrusion molding → recrystallization annealing → mechanical finishing → carburizing → quenching, tempering → grinding and polishing → assembly.
2. Supply state and hardness Unheated state, hardness ≤ 156HBS. 3. 20# steel implements JB/T 6057-92 standard 4. Chemical composition of 20# steel (mass fraction, %) C: 0.17~0.23 Si: 0.17~0.37 Mn 0.35~0.65 P≤0.035 S≤0.035 Ni≤0.30 Cr≤0.15 Cu≤0.25.
Refer to the corresponding steel number The standard steel number of GB/JB in my country is 20, the standard steel number of Taiwan CNS in my country is S20C, the German DIN standard material number is 1.0402, and the German DIN standard steel number is CK22/C22. British BS standard steel number IC22, French AFNOR standard steel number CC20, French NF standard steel number C22, Italian UNI standard steel number C20/C21, Belgium NBN standard steel number C25-1, Sweden SS standard steel number 1450, Spain UNE standard steel No. F.112, American AISI/SAE standard steel No. 1020, Japanese JIS standard steel No. S20C/S22C.
(2.1) Phase transition temperature (approximate value) Ac1=735℃, Ac3=855℃, Ar3=835℃, Ar1=680℃
(2.2) Normalizing specification The temperature is 920~950℃, and the furnace is air-cooled. Hardness 131~156HBS.
(2.3) Specification for softening treatment of cold-pressed blanks The temperature is 700~720°C, the holding time is 8~15h, and then the cooling rate is 50~100°C/h, and the temperature is reduced to ≤550~600°C with the furnace, and the furnace is air-cooled. The hardness before treatment is less than or equal to 143HBS, and the hardness after softening is less than or equal to 131HBS.
(2.4) Quenching specification Temperature 910℃±10℃, 10%NaCl brine cooling.
