Grade 20# steel
The 20# steel refers to a carbon content of 0.2%, which is a low-carbon steel. Steel can be divided into low carbon steel, medium carbon steel and high carbon steel.

Carbon content: low carbon steel is generally less than 0.25%; medium carbon steel is generally between 0.25 and 0.60%; high carbon steel is generally greater than 0.60%.
In addition to the carbon (C) element and a certain amount of silicon (Si) (generally no more than 0.40%) and manganese (Mn) (generally no more than 0.80%, up to 1.20%) alloy elements in steel for deoxidation, No other alloying elements (except residual elements).
Usually called wrought iron with a carbon content of less than 0.02%, pig iron with a carbon content of more than 2.11% to 4.3%, and steel in the middle.
Chinese name No. 20 steel standard GB/T 699-2015 carbon content 0.2% category low carbon steel
contents

characteristic
(1) Features The steel belongs to high-quality low-carbon carbon steel, cold-extruded, carburized and hardened steel. The steel has low strength, good toughness, plasticity and weldability. The tensile strength is 253-500MPa, and the elongation is ≥24%.
The properties of 20 are basically similar to those of 15 steel, but the strength is slightly higher. Uses: suitable for the manufacture of small and medium-sized carburizing and carbonitriding parts that are not important for the construction of automobiles, tractors and general machinery manufacturing, such as handbrake shoes, lever shafts, gearbox speed forks, transmission passive gears and Camshafts on tractors, suspension equalizer shafts, equalizer inner and outer bushings, etc.; used to manufacture various mechanical parts that are not stressed but require high toughness under hot-rolled or normalized conditions; in heavy and medium-sized machinery manufacturing Medium, such as forged or pressed tie rods, shackles, levers, sleeves, clamps, etc. In the steam turbine and boiler manufacturing industry, it is mostly used for pipes, flanges, headers and various fasteners working in non-corrosive media with pressure ≤ 6N/square and temperature ≤ 450 ℃; used to make crosses on railways, locomotives and vehicles Castings such as heads and pistons.
Normalizing can promote the spheroidization of the steel, refine the massive proeutectoid ferrite, and improve the cutting performance of the blank less than 160HBS.
The process route of the steel mold parts is: blanking→forging die blank→annealing→mechanical rough machining→cold extrusion molding→recrystallization annealing→mechanical finishing→carburizing→quenching, tempering→grinding and polishing→assembly.
(2) Delivery state and hardness Unheated state, hardness ≤156HBS.
chemical composition
(3) The chemical composition of standard JB/T 6057-92 steel (mass fraction, %)

(4) Refer to the corresponding steel grade. The standard steel grade of my country’s GB/JB is 20, my country’s Taiwan CNS standard steel grade S20C, German DIN standard material number 1.0402, German DIN standard steel number CK22/C22, British BS standard steel number IC22, France 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 number F.112, American AISI/ SAE standard steel number 1020, Japanese JIS standard steel number S20C/S22C.
Mechanical properties
(5) Phase transition temperature (approximate value) Ac1=735℃, Ac3=855℃, Ar3=835℃, Ar1=680℃
(6) Normalizing specification The temperature is 920~950℃, and the furnace is air-cooled. The hardness is 131~156HBS.
(7) Specification for softening treatment of cold-pressed blanks The temperature is 700~720℃, the holding time is 8~15h, and the cooling rate is 50~100℃/h, and the temperature is lowered to 550~600℃ 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.
(8) Quenching specification Temperature 910℃±10℃, cooling with 10% NaCl brine.
(9) Measured yield strength fy=245Mpa, elastic modulus E=206Gpa, Poisson’s ratio ν=0.3.
(10) The shear strength is 275~392MPa, the tensile strength is 253~500MPa, the yield strength is 275MPa, and the elongation is 25%.
(11) The annealing temperature is only 600-650 degrees, and the holding time is 1-2h.

Allowable stress of No. 20 steel at 225℃: (16-36mm) between 111-124MPa; (6-16mm) between 117-131MPa
Allowable stress of No. 20 steel at 100°C: at 150°C, the allowable stress of No. 20 steel pipe is 130 MPa, and that of No. 20 steel forgings is 108 MPa

Both steels are low-carbon steels. From the data point of view, the carbon content of No. 20 steel is slightly higher, and the metallographic structure of both is pearlite + ferrite. The performance reflected in the performance is that the tensile strength and impact toughness of the 20 steel are slightly higher, and basically there is no big difference between the two steels. Both steels cannot be quenched, and the heat treatment process is relatively simple. Usually the blank is directly cut or forged and normalized, used for unimportant structural parts, connecting parts or stamping parts, or used as carburizing steel. No. 15 steel seems to be found on the market, and it can be replaced with 20 steel.