20Cr, alloy structural steel. Uniform digital code: A20202 Standard GB / T 3077-1999 

 Chemical composition 
 (Wt) (%) Carbon C: 0.18 ~ 0.24 Si Si: 0.17 ~ 0.37 Manganese Mn: 0.50 ~ 0.80 Chromium Cr: 0.70 ~ 1.00 S S: to allow the residual phosphorus content ≤ 0.035 P: ≤ 0.035 to allow the residual content of Ni-Ni: allow the residual content ≤ 0.030 Copper Cu: ≤ 0.030 to allow the residual content 

 Mechanical Properties 
 Sample blank size (mm): 15 Heat treatment: first quenching temperature (℃): 880; coolant: water, oil the second quenching temperature (℃): 780 ~ 820; coolant: water, oil tempered heating temperature (℃): 200; coolant: water, air and tensile strength (σb / MPa): ≧ 835 Yield strength (σs / MPa): ≧ 540 Elongation (δ5 /%): ≧ 10 Reduction of (ψ /%): ≧ 40 impact absorbed energy (Aku2 / J): ≧ 47 Brinell hardness (HBS100/3000) (annealing or tempering state): ≦ 179 Delivery status: to heat treatment (normalizing, annealing, or high-temperature tempering) or heat treatment delivery, delivery status should be indicated in the contract. 

 Key Features 
 Compared with the 15Cr steel, higher strength and hardenability, quenching in oil critical diameter 4 ~ 22mm, the critical quenching diameter in water up to 11 ~ 40mm, but the toughness is poor, this was still carburizing steel a tendency to grain growth, direct quenching temperature greater impact on the toughness, so after carburizing secondary hardening required to improve the toughness of the Ministry of parts heart, no temper brittleness; steel cold plastic strain is high, drawing in cold state ; cutting at high temperatures can be normalized or quenched and tempered condition is good, but after annealing poor; good weldability, weld heat treatment is generally not required, but the thickness of the parts is greater than 15mm to be preheated before welding to the 100 ~ 150 ℃. 

 Application examples 
 Most of the steel used to make the heart require a higher intensity of the Department of the surface to withstand wear and tear, cross-section in the shape of 30mm or less complex and less load carburizing parts (oil quenched), such as: machine tool transmission gear, gear shaft, cam , worm, piston pin, a claw clutch, etc.; of heat deformation and high wear resistance of parts after carburizing high-frequency surface hardening, such as modulus in three of the gears, shafts, spline shafts. This steel can also be used in the quenched state, the speed for the manufacture of large and medium withstand shock loading of the parts, this also can be used as a low-carbon martensitic steel hardened steel, to further increase the yield strength of steel and tensile strength (an increase of about 1.5 to 1.7 times)