20# hot rolled steel sheet

(1) Characteristics 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 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 a pressure of ≤6N/square and a temperature of ≤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 die 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.

The chemical composition of standard JB/T 6057-92 steel (mass fraction, %)

C	Si	Mn	P	S	Ni	Cr	Cu
0.17~0.23	0.17~0.37	0.35~0.65	≤0.035	≤0.035	≤0.30	≤0.25	≤0.25

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 drops to 550~600℃ with the furnace, and the furnace is air cooled.
The hardness before treatment is ≤143HBS, and the hardness after softening is ≤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.
 

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